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Accepted papers to appear in an upcoming issue

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Coherent states of Laguerre-Gauss modes

Maria del Pilar Morales Rodriguez, Omar Magana Loaiza, Benjamin Perez-Garcia, Luis Miguel Nieto Calzada, Francisco Marroquin Gutierrez, and Blas Rodriguez-Lara

DOI: 10.1364/OL.511439 Received 10 Nov 2023; Accepted 21 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: Complex interactions within large quantum photonic systems offer the potential to perform computations beyond classical capabilities. Despite their potential, preparing these quantum systems remains a significant challenge. We explore an alternative approach to studying multiparticle dynamics by utilizing spatial modes of light. Our operational approach facilitates the mapping of the excitation mode of the electromagnetic field to physical properties of spatial Laguerre-Gauss modes, enabling us to leverage various symmetries to construct coherent states for Laguerre-Gauss modes. Interestingly, our work establishes a direct link between the excitation number dynamics of multiparticle systems and the evolution of transverse and longitudinal properties of Laguerre-Gauss modes. This connection highlights the potential of the transverse spatial degree of freedom of the photon as a versatile platform for testing fundamental properties of quantum multiparticle systems in a relatively simple manner.

Interference induced generation of chirp-free short isolated attosecond pulse in the water window region with multi-color laser fields

Jinxu Du, Guoli Wang, XUAN-HONG Gao, Xiaoyong Li, Zhi-Hong Jiao, Song-Feng Zhao, and Xiaoxin Zhou

DOI: 10.1364/OL.515677 Received 13 Dec 2023; Accepted 21 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: Compensating for the intrinsic attosecond chirp (atto-chirp) of wide-band high-order harmonics in the water window region is a significant challenge, in order to obtain isolated attosecond pulses (IAP) with width of tens of attoseconds (as). Here, we propose to realize the generation of IAP with duration as short as 20 as, central energy of 365 eV, and bandwidth exceeding 150 eV from chirp-free high harmonics generated by a four-color driving laser, without the necessity for atto-chirp compensation with natural materials. Unlike any other gating methods that an IAP arises from only one electron ionization event, we take advantage of the interference between harmonic radiation produced by multiple ionizing events. We further demonstrate that such chirp-free short IAP survives after taking account of the macroscopic propagation effects. Given that the synthesized multi-color laser field can also effectively increase the harmonic flux, this work provides a practical way for experiments to generate the broad bandwidth chirp-free IAPs in the water window region.

Multiple Hyperbolic Waves

Zixun Ge, shan zhu, Wen Xiao, and Huanyang Chen

DOI: 10.1364/OL.513530 Received 29 Nov 2023; Accepted 21 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: This study presents a conceptual design for a hyperbolic material utilizing transformation optics. This material is designed to produce multiple hyperbolic wave fields or polaritons excited by a point source. The design dictates key parameters including branch number, propagation range, and overall propagation direction of deflection. Through this approach, the hyperbolic material demonstrates new effects compared to traditional hyperbolic materials. These advancements offer possibilities for the design and applications of photonic devices in other degree of freedoms.

Tunability-selective lithium niobate light modulators via high-Q resonant metasurface

Xiaoshan Liu, Guolan Fu, Shimei Song, Yikun Huang, Mulin Liu, Guiqiang Liu, and Zhengqi Liu

DOI: 10.1364/OL.513631 Received 22 Nov 2023; Accepted 21 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: Herein, we propose and demonstrate an efficient light modulator by intercalating the nonlinear thin film into the optical resonator cavities, which introduce the ultra-sharp resonances and simultaneously lead to the spatially overlapped strong optical field between the nonlinear material and the resonators. Differential field intensity distributions in the geometrical perturbation assisted optical resonator make the high quality-factor resonant modes and strong field confinement. Multiple channels light modulation is achieved in such layered system, which enables the capability for tunability-selective modulation. The maximal modulation tunability is up to 1.968 nm/V and the figure of merit (FOM) reaches 65.6 V-1, showing orders of magnitude larger than that of the previous state-of-art modulators. The electrical switch voltage down to 0.015 V, the maximal switching ratio of 833% and the extinction ratio up to 9.70 dB, confirms the realization of high-performance modulation. The findings provide potential for applications in switches, communication and information, augmented and virtual reality, etc.

Bifurcation of bound states in the continuum inperiodic structures

Nan Zhang and Ya Yan Lu

DOI: 10.1364/OL.514532 Received 29 Nov 2023; Accepted 21 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: In lossless dielectric structures with a single periodic direction,a bound state in the continuum (BIC) is a special resonant mode with an infinite quality factor ($Q$ factor).The $Q$ factor of a resonant mode near a typical BIC satisfies $Q\sim 1/({\beta}-{\beta}_*)^{2}$, where $\beta$ and $\beta_*$ are Bloch wavenumbers of the resonant mode and the BIC, respectively.However, for some special BICs with $\beta_*=0$ (referred to as {\em super}-BICs by some authors), the $Q$ factor satisfies $Q\sim1/\beta^6$. Although {\em super}-BICs are usually obtained by merging a few BICs through tuning a structural parameter,they can be precisely characterized by a mathematical condition.In this letter, we consider arbitrary perturbations to structures supporting a {\em super}-BIC.The perturbation is given by $\delta F({\bf r})$, where $\delta$ is the amplitude and $F({\bf r})$ is the perturbation profile.We show that for a typical $F({\bf r})$, the BICs in the perturbed structure exhibit a pitchfork bifurcation around the {\em super}-BIC.The number of BICs changes from one to three as $\delta$ passes through zero.However, for some special profiles $F({\bf r})$, there is no bifurcation, i.e., there is only a single BIC for $\delta$ around zero.In that case, the {\em super}-BIC cannot be associated with a merging process.

Selective excitation of high-order modes in 2D cavity resonator integrated grating filters (CRIGFs)

Antoine Rouxel, Olivier Gauthier-Lafaye, Antoine Monmayrant, and Stephane Calvez

DOI: 10.1364/OL.519472 Received 18 Jan 2024; Accepted 21 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: The selective spatial mode excitation of a bi-dimensional grating-coupled micro-cavity called a Cavity Resonator Integrated Grating Filter (CRIGF) is reported using an incident beam shaped to reproduce the theoretical emission profiles of the device in one- and subsequently two-dimensions.In both cases, the selective excitation of modes up to order 10 (per direction) is confirmed by responses exhibiting one (respectively two) spectrally narrow-band resonance(s) with a good extinction of the other modes, the latter being shown to depend on the parity and order(s) of the involved modes.These results paves the way towards the demonstration of multi-wavelength spatially-selective reflectors or fibre-to-waveguide couplers.Also, subject to an appropriate choice of the materials constituting the CRIGF, this work can be extended to obtain mode-selectable laser emission or nonlinear frequency conversion.

Loading-effect-based 3-D microfabrication empowers on-chip Brillouin optomechanics

Peng Lei, Mingyu Xu, Yunhui Bai, Zhangyuan Chen, and Xiaopeng Xie

DOI: 10.1364/OL.519929 Received 25 Jan 2024; Accepted 20 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: The acousto-optic interaction known as stimulated Brillouin scattering (SBS) has emerged as fundamental principles for realizing crucial components and functionalities in integrated photonics. However, the main challenge of integrated Brillouin devices is how to effective confinement of both optical and acoustic waves. Apart from that, the manufacturing processes for these devices need to be compatible with standard fabrication platforms, and streamlined to facilitate their large-scale integration. Here, we demonstrate a novel suspended nanowire structure that can tightly confine photons and phonons. Furthermore, tailored for this structure, we introduce a loading-effect-based three-dimensional microfabrication technique, compatible with complementary metal-oxide-semiconductor (CMOS) technology. This innovative technique allows for the fabrication of the entire structure using a single-step lithography exposure, significantly streamlining the fabrication process. Leveraging this structure and fabrication scheme, we have achieved a Brillouin gain coefficient of 1100 1/(W·m) on the silicon-on-insulator platform within a compact footprint. It can support a Brillouin net gain over 4.1 dB with modest pump powers. We believe that this structure can significantly advance the development of SBS on chip, unlocking new opportunities for the large-scale integration of Brillouin-based photonic devices.

Optimized pilot structure for PS-PDM ultra-high order QAM coherent optical transmission

Xin Shi, Mingyi Gao, xuejing huang, Jiamin Fan, Xinbang Han, Xiaodi You, and Gangxiang Shen

DOI: 10.1364/OL.519424 Received 23 Jan 2024; Accepted 20 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: We proposed and experimentally demonstrated a general pilot structure for probabilistic shaped (PS) polarization division multiplexing (PDM) M-ary quadrature amplitude modulation (MQAM) coherent optical transmission, where a portion of PS-MQAM symbols are exploited as the pilot symbols with the same information entropy as the transmitted signal. The pilot symbols are simultaneously used in the entire digital signal processing (DSP) modules for polarization de-multiplexing, frequency offset estimation, carrier phase recovery, nonlinear equalization, and linear equalization. Compared to the conventional quadrature phase shift keying (QPSK) pilot structure, the proposed MQAM pilot structure can yield the nonlinear properties of the overall signal so that nonlinear equalization can effectively improve the performance of normalized generalized mutual information. The remarkable performance has been achieved at the shaping parameters of 3.65 and 4.35 for 1024QAM and 4096QAM signals based on the proposed pilot scheme, which corresponds to the raw spectral efficiency of 17.714bit/s/Hz and 20.381bit/s/Hz, respectively. The pilot ratio is optimized to 5% for higher achievable information rates (AIR).

Zeptojoule detection of terahertz pulses by parametric frequency upconversion

Défi Jubgang Fandio, Aswin Vishnu Radhan, Eeswar Yalavarthi, Wei Cui, Nicolas Couture, Angela Gamouras, and Jean-Michel Menard

DOI: 10.1364/OL.517916 Received 05 Jan 2024; Accepted 20 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: We combine parametric frequency upconversion with single-photon counting technology to achieve terahertz (THz) detection sensitivity down to the zeptojoule (zJ) pulse energy level. Our detection scheme employs a near-infrared ultrafast source, a GaP nonlinear crystal, optical filters, and a single photon avalanche diode. This configuration is able to resolve a 1.4 zJ THz pulse energy, corresponding to 1.5 photons per pulse, when the signal is averaged within only 1 s (or 50,000 pulses). A single THz pulse can also be detected when its energy is above 1185 zJ. These numbers correspond to noise-equivalent power and THz-to-NIR photon detection efficiency of 0.13 fW/Hz⁰·⁵ and 0.058 %, respectively. To test our scheme, we perform spectroscopy of water vapor between 1 and 3.7 THz and obtain results in agreement with those acquired with a standard electro-optic sampling (EOS) method. Our technique provides a 0.2 THz spectral resolution offering a fast alternative to EOS THz detection for monitoring specific spectral components in spectroscopy, imaging, and communication applications.

Observation of quantum correlated twin beams in cascaded nonlinear interactions

Salvatore Castrignano, Iolanda Ricciardi, Pasquale Maddaloni, Paolo De Natale, Stefan Wabnitz, and Maurizio De Rosa

DOI: 10.1364/OL.514976 Received 11 Dec 2023; Accepted 20 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: We report on the generation of twin beams through a cascaded process of optical parametric oscillation in a doubly resonant second-harmonic generation system. These bright beams exhibit strong quantum correlation, enabling the observation of up to 5 dB of noise reduction in their intensity difference below the standard quantum limit.

Interplay of gain and loss in arrays of nonlinear plasmonic nanoparticles: toward parametric downconversion and amplification

Syed Shah, Michael Clark, Joseph Zyss, Maxim Sukharev, and Andrei Piryatinski

DOI: 10.1364/OL.515621 Received 11 Dec 2023; Accepted 20 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: With the help of a theoretical model and finite-difference-time-domain simulations based on the hydrodynamic-Maxwell model, we examine the effect of difference frequency generation in an array of L-shaped metal nano-particles characterized by intrinsic plasmonic nonlinearity. The outcomes of the calculations reveal the spectral interplay of the gain and loss in the vicinity of the fundamental frequency of the localized surface-plasmon resonances. Subsequently, we identify different array depths and pumping regimes facilitating parametric amplification and parametric down-conversion. Our results suggest that the parametric amplificationregime becomes feasible on a scale of hundreds of nanometers and parametric downconversion on the scale of tens of nanometers, opening up new exciting opportunities for developing building blocks of photonic metasurfaces.

A Novel Pre-equalization Scheme for Visible Light Communications with Trial-and-Error Learning

Shupeng Li, Yi Zou, Fangming Liu, and Jian Song

DOI: 10.1364/OL.516235 Received 21 Dec 2023; Accepted 20 Feb 2024; Posted 20 Feb 2024  View: PDF

Abstract: In this Letter, we propose a novel neural network pre-equalizer based on the trial-and-error (TE) mechanism for visible light communication. This approach, unlike indirect learning (IL) architecture, does not require an additional auxiliary post-equalizer. Instead, it allows the pre-equalizer to be trained directly from the transmitter side through continuous interaction with the actual system. In a 1.95-Gbps 64-QAM carrier-less amplitude phase free space optical transmission platform, the proposed scheme demonstrates superior nonlinear approximation capabilities and noise resilience. Specifically, the TE-RNN based pre-equalizer exhibits signal-to-noise ratio gains of 0.8 dB and 1.8 dB over the IL-RNN based and IL-Volterra based pre-equalizers, respectively. To the best of our knowledge, this is the first application of trial-and-error learning for training pre-equalizer in visible light communications.

Polarization-resolved super-resolution second-harmonic generation imaging based on multifocal structured illumination microscopy

Yong Zhang, Chenshuang Zhang, Renlong zhang, Rong Xu, Bin Yu, Danying Lin, and Junle Qu

DOI: 10.1364/OL.514724 Received 29 Nov 2023; Accepted 19 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: Polarization-resolved second harmonic generation (PSHG) microscopy is widely used in investigating the structural and morphological alterations of collagen. However, the resolution of PSHG imaging remains constrained by optical diffraction to approximately 250 nm, rendering visualization of the ultrastructure of collagen fibrils unattainable. In this study, multifocal structured illumination microscopy (MSIM) was combined with PSHG to achieve polarization-resolved super-resolution imaging of second harmonic generation signals. Notably, imaging of zinc oxide (ZnO) nanoparticles revealed an average full width at half maximum of 145 nm. Additionally, for the first time, periodic structures with an average pitch of 277 nm were observed in mouse tail tendons using optical microscopy, and the orientation angle of fibrils within each period was found to exhibit an alternating arrangement along the axis in a regular pattern.

Multispectral Stealth Multilayer Etched Film Structure Based on Ultrathin Silver

He yan Wang, Yingzheng Ren, Wenjing Geng, Lin Han, Yilei Zhang, Danni Zheng, Lu Zhengang, and Jiubin Tan

DOI: 10.1364/OL.519362 Received 24 Jan 2024; Accepted 19 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: Spontaneous infrared radiation dissipation is a critical factor in facilitating object cooling, which influences the thermal stability and stealth efficacy of infrared stealth devices. Furthermore, the compatibility between efficient visible, infrared and radar stealth is challenging due to different camouflage principles in different bands. This study presents a five-layer etched film structure to achieve multispectral stealth, and the utilization of the high-quality ultrathin silver films enables highly efficient infrared selective emission. This etched film structure with few layers demonstrates potential applications in diverse domains, including multi-band anti-detection and multispectral manipulation.

Visible-NIR surface plasmon resonance sensing technology for high precision refractive index detection

zhiyong yin and Xi Jing

DOI: 10.1364/OL.520025 Received 25 Jan 2024; Accepted 19 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: Molybdenum disulfide (MoS2), as a representative transition metal disulfide material, has contributed significantly to the development of plasmonic technology towards the near-infrared (NIR). In this paper, the physical mechanism of MoS2 excitation of surface plasmon resonance (SPR) in the NIR is investigated, and it is shown that the MoS2 film can induce the resonance dip to move toward NIR and demonstrate a sensitivity higher than that in the visible band. A dual-channel SPR sensor capable of operating in the visible and NIR bands for refractive index (RI) detection was also prepared using the cascade method. The simulated and experimental results of the sensor show consistency. The experimental results show that the maximum sensitivity of the NIR detection channel is 14600 nm/RIU in the RI range of 1.333-1.420, which is 37% higher than the sensitivity of the visible channel. However, the visible channel has the advantage of a narrow FWHM. Therefore, the proposed cascaded dual-channel RI sensor combines high-sensitivity and narrow FWHM. This dual-channel construction method improves the detection level of RI, promotes the development of SPR sensing technology to the NIR band, and significantly improves the narrow-band problem existing in the previous multi-channel sensing.

High-Efficiency Radiation-Balanced Yb-Doped Silica Fiber Laser With 200-mW Output

Enkeleda Balliu, Bailey Meehan, Mary Ann Cahoon, Thomas Hawkins, John Ballato, Peter Dragic, Tommy Boilard, Lauris Talbot, Martin Bernier, and Michel Digonnet

DOI: 10.1364/OL.517568 Received 02 Jan 2024; Accepted 18 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: The focus of this study was the development of a second generation of fiber lasers internally cooled by anti-Stokes fluorescence. The laser consisted of a length of single-mode fiber spliced to fiber Bragg gratings to form the optical resonator. The fiber was single-moded at the pump (1040 nm) and signal (1064 nm) wavelengths. Its core was heavily doped with Yb, in the initial form of CaF2 nanoparticles, and co-doped with Al to reduce quenching and improve the cooling efficiency. After optimizing the fiber length (4.1 m) and output-coupler reflectivity (3.3%), the fiber laser exhibited a threshold of 160 mW, an optical efficiency of 56.8%, and a radiation-balanced output power (no net heat generation) of 192 mW. On all three metrics, this performance is significantly better than the only previously reported radiation-balanced fiber laser, which is even more meaningful given that the small size of the single-mode fiber core (7.8-µm diameter). At the maximum output power (~2 W), the average fiber temperature was still barely above room temperature (470 mK). This work demonstrates that with anti-Stokes pumping, it is possible to induce significant gain and energy storage in a small-core Yb-doped fiber while keeping the fiber cool.

Improvement of light extraction efficiency in AlGaInP-based vertical miniaturized-LEDs via surface texturing

Siyuan Cui, Lang Shi, Leonard Jin, Qianxi Zhou, Yuechang Sun, Conglong Jin, jiahui Hu, Kuosheng Wen, Zhou Xu, and Shengjun Zhou

DOI: 10.1364/OL.519723 Received 24 Jan 2024; Accepted 18 Feb 2024; Posted 20 Feb 2024  View: PDF

Abstract: AlGaInP-based light emitting diodes (LEDs) suffer from a low external quantum efficiency (EQE), which is mainly restrained by the poor light extraction efficiency. Here, we demonstrate AlGaInP-based vertical miniaturized-LEDs (mini-LEDs) with a porous n-AlGaInP surface using a wet etching process to boost light extraction. We investigated the effects of etching time on the surface morphology of porous n-AlGaInP surface. We find that as the etching time prolonged, the density of pores increases initially and decreases subsequently. In comparison with vertical mini-LED with a smooth n-AlGaInP surface, the vertical mini-LEDs with the porous n-AlGaInP surface reveal improvement in light output power and EQE, meanwhile, without the deterioration of electrical performance. The highest improvement of 38.9% in EQE measured at 20 mA is observed from the vertical mini-LED with maximum density of pores. Utilizing a three-dimensional finite-difference time-domain method, we reveal the underlying mechanisms of improved performance, which are associated with suppressed total internal reflection and efficient light scattering effect of the pores.

Adaptive layer-based (ALB) computer-generated holograms

Yongwei Yao, Yaping Zhang, Qingyang Fu, jilu duan, BING ZHANG, Liangcai Cao, and Ting-Chung Poon

DOI: 10.1364/OL.509961 Received 24 Oct 2023; Accepted 18 Feb 2024; Posted 20 Feb 2024  View: PDF

Abstract: We propose a novel and fast adaptive layer-based (ALB) method for generating a computer-generated hologram (CGH) with accurate depth information. A complex three-dimensional (3D) object is adaptively divided into layers along the depth direction according to its own non-uniformly distributed depth coordinates, which reduces the depth error caused by conventional layer-based method. Each adaptive layer generates a single-layer hologram using the angular spectrum method for diffraction, and the final hologram of a complex three-dimensional object is obtained by superimposing all the adaptive-layer holograms. A hologram derived with the proposed method is referred to as an adaptive layer-based hologram (ALBH). Our demonstration shows that the desired reconstruction can be achieved with 52 adaptive layers in 8.7 seconds, whereas the conventional method requires 397 layers and 74.9 seconds.

Composite membrane of graphene oxide and gold nanoparticles functionalized S fiber taper aptasensor for highly sensitive bisphenol A detection

Wanmei Guo, Yong-Sen Yu, Chao Xin, and guang yong jin

DOI: 10.1364/OL.515264 Received 05 Dec 2023; Accepted 18 Feb 2024; Posted 20 Feb 2024  View: PDF

Abstract: The S fiber taper (SFT) aptasensor with a composite sensitive membrane of graphene oxide and gold nanoparticles was proposed for the rapid and highly sensitive detection of bisphenol A. The SFT was obtained using a fusion splicer; subsequently, the composite film was deposited on its surface, and the specific aptamer was covalently bonded to the surface of gold nanoparticles. The detection mechanism relies on monitoring changes in external refractive index induced by the specific binding of BPA to the aptamer. The developed SFT aptasensor exhibited a remarkable sensitivity of 15.5 nm/nM and a limit of detection as low as 0.01 nM for bisphenol A. These findings highlight the aptasensor's potential for diverse monitoring applications.

Computer-generated holography with ordinary display

Otoya Shigematsu, Makoto Naruse, and Ryoichi Horisaki

DOI: 10.1364/OL.516005 Received 19 Dec 2023; Accepted 18 Feb 2024; Posted 20 Feb 2024  View: PDF

Abstract: We propose a method of computer-generated holography (CGH) using incoherent light emitted from a mobile phone screen. In this method, we suppose a cascade of holograms in which the first hologram is a color image displayed on the mobile phone screen. The hologram cascade is synthesized by solving an inverse problem with respect to the propagation of incoherent light. We demonstrate three-dimensional color image reproduction using a two-layered hologram cascade composed of an iPhone and a spatial light modulator.

Net-432-Gb/s/λ PS-PAM transmission based on Advanced DSP and single DAC for 400G/λ IM/DD Links

An yan, Guoqiang Li, Sizhe Xing, Wangwei Shen, Yongzhu Hu, Aolong Sun, Jianyang Shi, Ziwei Li, Chao Shen, Nan Chi, and Junwen Zhang

DOI: 10.1364/OL.517152 Received 28 Dec 2023; Accepted 18 Feb 2024; Posted 20 Feb 2024  View: PDF

Abstract: The escalating surge in datacenter traffic a pressing demand for augmenting the capacity of cost-effective intensity modulation and direct detection (IM/DD) systems. In this letter, we report the demonstration of single-lane 128-GBaud probabilistically shaped (PS)-PAM-20 IM/DD transmission using only a single digital-to-analog converter (DAC) for net 400G/λ system. Based on advanced digital signal processing (DSP), we achieve net bitrates of up to 437 Gb/s for optical back-to-back and 432 Gb/s after 0.5-km SSMF transmission in the C-band with 128-Gbaud PS-PAM-20 signals. This work is the latest demonstration on ultrahigh-order PS-PAM signals achieving net bitrates exceeding 400 Gb/s despite symbol rate limitations. Notably, to the best of our knowledge, the realized net information rate ([net bitrate]/ [symbol rate]) of 3.37 marks a new achievement within the domain of 400G/λ IM/DD systems, with promising implications for enhancing bandwidth efficiency in the upcoming 1.6-Tb Ethernet scenario.

Designing High Thermally Stable Deep Red Phosphors based on Low Thermal Expansion Coefficient for Optical Applications

Jianqiang Sun, Mochen Jia, Wei Xu, Mingli Wang, and Zhen Sun

DOI: 10.1364/OL.519126 Received 17 Jan 2024; Accepted 17 Feb 2024; Posted 20 Feb 2024  View: PDF

Abstract: Mn4+-activated oxide phosphors with low cost and unique luminescent properties have been considered as promising candidate for various optical applications, while the search for high thermal stable red-emitting phosphors is still a huge challenge. In our work, we find and unveil the relationship between luminescence thermal quenching behavior and thermal expansion coefficients (α/10-6 K-1) based on double-perovskite niobate phosphors Ca2LnNbO6: Mn4+ (Ln3+=Y3+, Gd3+, La3+ or Lu3+). It can be concluded that the phosphors with low thermal expansion coefficients contribute to get high thermal stability. Subsequently, the Ca2LuNbO6: Mn4+ accomplishes accurate temperature testing and high-CRI white light-emitting diodes. Thus, thermal expansion coefficients strategy is a new guide to select appropriate substrate with high thermal stability for Mn4+-activated emitter.

Robust Self-Injection Locking to a NonconfocalMonolithic Fabry-Perot Cavity.

Anatoliy Savchenkov, wei zhang, Vladimir Ilchenko, and Andrey Matsko

DOI: 10.1364/OL.516371 Received 21 Dec 2023; Accepted 17 Feb 2024; Posted 20 Feb 2024  View: PDF

Abstract: We demonstrate an efficient simultaneous self-injectionlocking of two semiconductor lasers to high-ordermodes of a stand-alone monolithic non-confocal Fabry-Perot cavity. The lasers are used to generate a low noisemicrowave signal on a fast photodiode. The overall im-provement of the laser spectral purity exceeds 80 dB.The observed single-sideband phase noise of X- to Ka-band signals is at the -110 dBc/Hz level and is limitedby the fundamental thermorefractive noise of the cav-ity. The demonstrated cavity-laser configuration canbe tightly packaged and is promising for generation ofhigh frequency RF signals as well as for referencing op-tical frequency combs.

Hyperspectral digital holography realized by using electro-optic frequency comb via injection locking

Ziwen Long, Zhengchao Yuan, Xinyu Fan, and Zuyuan He

DOI: 10.1364/OL.516131 Received 14 Dec 2023; Accepted 17 Feb 2024; Posted 20 Feb 2024  View: PDF

Abstract: Hyperspectral digital holography (HSDH) is a versatile holographic imaging technique that offers a large unambiguous depth range and spectroscopic information. In this letter, we propose a novel HSDH system that is realized by using an electro-optical frequency comb (EOFC) via injection locking. In comparison with conventional dual-comb HSDH, the proposed system only requires one EOFC and few other devices, which not only simplifies the system structure and reduces the cost, but also improves the imaging speed. We validated the system using an EOFC with 20 optical frequencies spaced at 18 GHz intervals. In a total measurement time of 0.5 seconds, we successfully captured images of two targets that were 0.74 millimeters apart without phase ambiguity, and obtained the transmission spectrum of an absorbing gas simultaneously. This work provides valuable insights for HSDH systems relying on optical frequency comb.

High quality Holographic 3D display with enhanced focus cues based on multiple directional light reconstruction

Wang Zi, Li liang, Tao Chen, Guoqiang Lv, Qibin Feng, Anting Wang, and Hai Ming

DOI: 10.1364/OL.516202 Received 15 Dec 2023; Accepted 14 Feb 2024; Posted 20 Feb 2024  View: PDF

Abstract: Holographic display faces the trade-off between image quality and focus cues, resulting from the specific choice of phase distribution. In this letter, we propose a speckle-free holographic display with enhanced focus cues by multiple directional light reconstruction. The uniform phase hologram is first generated by the gradient descent optimization algorithm. The blazed grating phase is used to steer the object light to a specific direction. Multiple sub-holograms with different blazed gratings are refreshed fast to reconstruct the images from different directions. Thus, the defocus blur is improved due to the separation of multiple spots on the defocus plane. The multi-plane reconstruction is also realized by pre-processing the depth images to eliminate image separation. The proposed method provides apparent focus cues while maintaining high image qualities, which is expected to realize comfortable holographic near-eye display in the near future.

Laser nanoprocessing via enhanced longitudinal electric field of a radially polarized beam

Yukine Tsuru, Yuichi Kozawa, Yuuki Uesugi, and Shunichi Sato

DOI: 10.1364/OL.517382 Received 02 Jan 2024; Accepted 14 Feb 2024; Posted 14 Feb 2024  View: PDF

Abstract: Single-shot laser ablation is performed on the surface of a transparent glass material using a radially polarized femtosecond beam. Theoretical and experimental investigation revealed the significant role of the material interface under high-numerical-aperture conditions. The longitudinal electric field at the focus was remarkably enhanced due to total reflection on the interface when a radially polarized beam was focused on the back surface of the glass from the inside using an immersion lens. This focusing condition enabled the fabrication of a small ablation hole sized 67 nm. This study offers a novel approach to realizing laser nanoprocessing with radially polarized beams.

Multiplicative-noise-multiplexing holography with ultrahigh capacity and low crosstalk

Wenhao Tang, Huan Yuan, Zheqiang Zhong, and Bin Zhang

DOI: 10.1364/OL.514569 Received 29 Nov 2023; Accepted 14 Feb 2024; Posted 15 Feb 2024  View: PDF

Abstract: Optical multiplexing technologies by utilizing various dimension of light can effectively expand the information capacity and density for holography, but may also lead to multiplexing crosstalk. Here, we propose and demonstrate a novel multiplicative-noise-multiplexing holography, by utilizing the orthogonality between multiplicative noise as a multiplexing dimension. The results prove that this holography can provide a new multiplexing dimension, significantly enhancing information capacity and effectively lowering crosstalk. This promising scheme for ultrahigh capacity holography has the potential to address the limitations of traditional holographic multiplexing technologies.

Loss free shaping of few-cycle terawatt laser pulses

Lucas Railing, Manh Le, Carlo Maria Lazzarini, and Howard Milchberg

DOI: 10.1364/OL.516590 Received 21 Dec 2023; Accepted 13 Feb 2024; Posted 15 Feb 2024  View: PDF

Abstract: We demonstrate loss-free generation of 3 mJ, 1 kHz, few-cycle (5 fs at 750 nm central wavelength) double pulses with separation from 10 fs to 100 fs, using a helium filled hollow core fiber and chirped mirror compressor. Crucial to our scheme are simulation-based modifications to the spectral phase and amplitude of the oscillator seed pulse to eliminate the deleterious effects of self-focusing and nonlinear phase pickup in the chirped pulse amplifier.

Magnetic-field-assisted optical fiber quantum temperature sensor with enhanced sensitivity

Jiayao Chen, Yunhan Luo, jiajia luo, huang huanhuan, Hongda Cheng, Guishi Liu, Lei Chen, Zhe Chen, and Yaofei Chen

DOI: 10.1364/OL.511061 Received 03 Nov 2023; Accepted 13 Feb 2024; Posted 14 Feb 2024  View: PDF

Abstract: In recent years, utilizing nitrogen-vacancy color centers in diamond for temperature sensing has drawn great attentions. However, increasing the sensitivity has encountered challenges due to the intrinsic temperature-dependent energy level shift being limited to -74 kHz/K. In this letter, we take advantage of magnetic field to regulate the energy level to enhance temperature sensitivity. The sensor is formed by adhering a micron-sized diamond on end face of an optical fiber, and a small magnet is mounted to a certain distance with diamond exploiting a cured Polydimethylsiloxane block as bridge. Temperature change leads to the variation of distance between diamond and magnet, thus affecting the magnetic strength felt by diamond. This finally contributes an additional temperature-induced energy level shift, giving rise to an enhanced sensitivity. Experiment results demonstrated the proposed scheme, and achieved a 4.2-fold improvement in the temperature responsivity and a 2.1-fold enhancement in sensitivity. Moreover, the diamond and fiber-optic integrated structure improves the portability of the sensor.

Manipulating Random Lasing Correlations in Doped Liquid Crystals

Yiyang Zhi, Giuseppe Strangi, and Andrew Lininger

DOI: 10.1364/OL.516290 Received 18 Dec 2023; Accepted 13 Feb 2024; Posted 14 Feb 2024  View: PDF

Abstract: Random lasers are highly configurable light sources that are promising for imaging and photonic integration. In this study, random lasing action was generated by optically pumping N-(4-Methoxybenzylidene)-4-butylaniline (MBBA) liquid crystals infiltrated with gold nanoparticles and laser dye (pyrromethene 597). By varying the pump energy near lasing threshold, we show that it is possible to control the intensity correlations between the random lasing modes. The correlations in the system were phenomenologically characterized using the Levy statistics of the emission spectra survival function. We also find that correlations and persistence of lasing action are correlated. These results demonstrate the possibility to dynamically control a key physical feature of random lasers, which may find applications in biomedical settings and network communications.

Beam-shaped femtosecond laser printing of quasi-capsule-shaped holographic terahertz metasurfaces

Dan Rao, Jing Qian, Xiao-Han Yu, Le Liu, Guande Wang, Yiwen Zhou, Teng Zhang, and Quan-Zhong Zhao

DOI: 10.1364/OL.516068 Received 14 Dec 2023; Accepted 13 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: Terahertz (THz) metasurfaces have opened up a new avenue for the THz wavefronts modulation. However, high-efficient and low-cost fabrication of THz meta-surfaces remains a great challenge today. Here, quasi-capsule-shaped polarization-multiplexed holographic THz metasurfaces were printed by a beam-shaped femtosecond laser. The laser beam was spatially modulated by holograms of optimized cylindrical lens loaded on spatial light modulator (SLM). And the size of quasi-capsule apertures can be exquisitely and flexibly controlled by adjusting focal length in holograms, pulse energy and pulse number. Based on near-field diffraction and Burch encoding, an array of 100×100 basic unit apertures were initially designed and a polarization-multiplexed THz metasurface was finally printed with a dimension of 8 mm × 8 mm. The function of polarization multiplexing was demonstrated, which two kinds of images were reconstructed in response to X and Y-polarization THz waves, respectively. The present work highlights a great leap in fabrication method for THz metasurfaces and hopefully stimulates the development of miniaturized and integrated THz systems.

Dynamic beam steering for wireless optical power transfer in IoT applications

NGOC-LUU NGUYEN, Khanh-Hung Nguyen, Nadeem Javed, and Jinyong Ha

DOI: 10.1364/OL.518243 Received 12 Jan 2024; Accepted 13 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: The alignment of a receiver with pencil beam in a wireless optical power transfer (WOPT) system employing resonance beam charging (RBC) technology limits the establishment of a resonance cavity. Accurate tracking necessitates precise and dependable monitoring, which requires the exact placement of transmitting and receiving devices. Herein, we present a concept of a two-dimensional (2D) beam steering mechanism for RBC-based WOPT systems utilizing dispersed laser beams. The proposed approach allows significant improvement, including reduction of scanning times and minimization of errors, in relation to conventional pencil-beam-based systems. Experimental results reveal an improvement of 121.01% in the efficiency of acquisition time, a reduction of 81.09% in pointing errors, and 75.4% increase in tracking performance. These results establish the prerequisites for the implementation of dispersed beam steering in the RBC-based WOPT system. This capability empowers the system to charge movable devices and Internet of Things devices consistently in smart factories.

High-performance multi-junction cascade 1.3 μm quantum dot vertical cavity surface emitting laser

Ping Song, Yubo Xue, Hailiang Dong, Zhigang Jia, wei jia, Jian Liang, Zhiyong Wang, and bingshe xu

DOI: 10.1364/OL.516880 Received 28 Dec 2023; Accepted 13 Feb 2024; Posted 13 Feb 2024  View: PDF

Abstract: A high-performance 5-junction cascade quantum dot (QD) vertical cavity surface emitting laser (VCSEL) with 1.3 μm wavelength was designed. The characteristics of QD as active regions and tunnel junctions are combined to effectively increase output power. The photoelectric characteristics of single-junction, 3-junction cascade, and 5-junction cascade QD VCSELs are compared at continuous-wave conditions. Results indicate that threshold current gradually decreases, output power and slope efficiency exponential increase with the increase of the number of active regions. The peak power conversion efficiency of 58.4% is achieved for 5-junction cascade individual QD VCSEL emitter with 10 μm oxide aperture. And the maximum slope efficiency of the device is 6.27 W/A, which is approximately six times than that of single-junction QD VCSEL. The output power of 5-junction cascade QD VCSEL reaches 188.13 mW at injection current 30 mA. High-performance multi-junction cascade 1.3-μm QD VCSEL provides data and theoretical support for the preparation of epitaxial materials.

Elliptical spiral zone plate fabrication using direct laser writing for generating an elliptical perfect vortex beam

Minglong Li, Haodong Zhu, Yi Huang, Ruiqi Yin, Zhen Yu Yang, and Ming Zhao

DOI: 10.1364/OL.518123 Received 15 Jan 2024; Accepted 12 Feb 2024; Posted 13 Feb 2024  View: PDF

Abstract: We report and fabricate a novel vortex beam generator called elliptical spiral zone plate (ESZP) using direct laser writing (DLW), which can generate the elliptical perfect vortex beam (EPVB). It is shown that the radius of the EPVB can be adjusted by tuning the control parameters of the ESZP. It is verified through interference experiment and the Hermitian-Gaussian light field that the orbital angular momentum (OAM) carried by the EPVB is consistent with the designed topological charge. In addition, we integrate ESZP at the tip of the single-mode fiber. Our work may set the scene for applications in fiber optical tweezers, optical communications and integrated optics.

Sub-gigahertz bandwidth photonic differentiator with high energy efficiency based on a micro-ring resonator

Liao Ye, zhaoyang zhang, Haoran Ma, hui Yu, Yuehai Wang, and Jianyi Yang

DOI: 10.1364/OL.510770 Received 10 Nov 2023; Accepted 12 Feb 2024; Posted 12 Feb 2024  View: PDF

Abstract: We propose and demonstrate a tunable fractional-order photonic differentiator (DIFF) that can process input pulses with sub-gigahertz bandwidth. Our scheme utilizes the self-induced optical modulation effect observed in a silicon-on-insulator micro-ring resonator. Gaussian-like pulses with varying pulse widths between 7.5 ns and 20 ns are employed for differentiation, achieving an energy efficiency over 45%, to the best of our knowledge, which surpasses all previously reported schemes for input pulses with sub-gigahertz bandwidth. We simulate the temporal dynamics of pulses to gain insight into the physical mechanisms underlying the differentiated outputs and provide a method for differentiation order adjustment, which is experimentally realized using an all-optical pump-probe technique.

Formation of electromagnetic pulses with nonzeroelectrical area by media with ferromagnetism

Nikolay Rosanov

DOI: 10.1364/OL.512437 Received 15 Nov 2023; Accepted 12 Feb 2024; Posted 12 Feb 2024  View: PDF

Abstract: The known rule of conservation of the electrical area of pulses, which plays a decisive role in the effectiveness of the action of extremely short pulses on microobjects, is valid for a wide class of media, including all non-magnetic ones. We show how this rule changes in magnetically ordered media, where pulses can induce magnetization variation. We found that such variations serve as another, additional to the movement of charges, source of pulse electrical area.

Slotted surface gratings fabricated by selective area growth of p-InP cladding layer for BH lasers

Jing Guo, huan li, xinkai xiong, daibing zhou, Ling-Juan Zhao, and Song Liang

DOI: 10.1364/OL.517585 Received 05 Jan 2024; Accepted 12 Feb 2024; Posted 12 Feb 2024  View: PDF

Abstract: In this paper, we present a novel method for the fabrication of slotted surface gratings for buried heterostructure (BH) lasers. In the device fabrication process, SiO2 strips needed for InP current blocking layer growth are reused for the formation of slot grating pattern masks. In the following growth of p-InP cladding layer, because the slot areas are covered by SiO2, the InP material is grown selectively in only the ares out side the slot areas, forming slots of the surface gratings in the p-InP layer at the same time of cladding layer growth. Single longitude mode BH lasers having slotted surface gratings have been fabricated successfully and the spectra show higher than 40 dB side mode suppression ratio (SMSR). The adoption of the method helps to simply the device fabrication and thus lower the device fabrication cost notably.

Guided wave resonance-based digital holographic microscopy for high-sensitivity monitoring of refractive index

Chunyu Wang, Jingyu Mi, Hua Lu, Shouhao Shi, Jianxu Zhao, Dikun Li, Jiwei Zhang, Jiadeng Zheng, and Jianlin Zhao

DOI: 10.1364/OL.510562 Received 31 Oct 2023; Accepted 12 Feb 2024; Posted 14 Feb 2024  View: PDF

Abstract: Surface plasmon resonance holographic microscopy (SPRHM) has been employed to measure the refractive index, but whose performance is generally limited by the metallic intrinsic loss. Herein, we to our knowledge first utilize the guided wave resonance (GWR) with low loss to realize the monitoring of refractive index by integrating with digital holographic microscopy (DHM). By depositing a dielectric layer on a silver nanofilm, we observe a typical GWR in the dielectric layer with stronger field enhancement and higher sensitivity to surrounding refractive index compared with silver film-supported SPR, which agrees well with calculations. The innovative combination of the GWR and DHM contributes to the highly sensitive dynamic monitoring of surrounding refractive index variation. Through the measurement with DHM, we find that the GWR presents an excellent sensitivity, which is 2.6 times higher than SPR on silver film. The results will pave a new pathway for digital holographic interferometry and its applications in the environmental and biological detections.

Long-lived Nitric Oxide Molecular Tagging Velocimetry with Two-Photon Excitation

Naibo Jiang, Paul Hsu, Sukesh Roy, Jincheng Wang, Hui Hu, Neil Rodrigues, and Paul Danehy

DOI: 10.1364/OL.514912 Received 01 Dec 2023; Accepted 11 Feb 2024; Posted 13 Feb 2024  View: PDF

Abstract: The successful demonstration of long-lived nitric oxide (NO) fluorescence for Molecular Tagging Velocimetry (MTV) measurements is described in this Letter. Using two-photon excitation of NO at a resonant wavelength near 226 nm, targeting the overlapping Q1(7) and Q21(7) lines of the A-X (0, 0) electronic system, the lifetime of the NO MTV signal was observed to be approximately 8.6 µs within a 100-torr cell containing 2% NO in nitrogen. This is in stark contrast to the commonly reported single photon NO fluorescence, which has a much shorter calculated lifetime of approximately 43 ns at this pressure and NO volume fraction. While the shorter lifetime fluorescence can be useful for molecular tagging velocimetry with single-laser excitation within very high-speed flows at some thermodynamic conditions, the longer lived two-photon fluorescence shows potential for an order of magnitude more accurate and precise velocimetry, particularly within lower-speed regions of hypersonic flowfields such as wakes and boundary layers. The physical mechanism responsible for generation of this long-lived signal is detailed. Furthermore, the effectiveness of this technique is showcased in a high-speed jet flow, where it is employed for precise flow velocity measurements.

Gradient-metasurface directional photodetectors

Jianing Liu and Roberto Paiella

DOI: 10.1364/OL.509642 Received 18 Oct 2023; Accepted 11 Feb 2024; Posted 14 Feb 2024  View: PDF

Abstract: Angle-sensitive photodetectors are a promising device technology for many advanced imaging functionalities, including lensless compound-eye vision, lightfield sensing, optical spatial filtering, and phase imaging. Here we demonstrate the use of plasmonic gradient metasurfaces to tailor the angular response of generic planar photodetectors. The resulting devices rely on the phase-matched coupling of light incident at select geometrically tunable angles into guided plasmonic modes, which are then scattered and absorbed in the underlying photodetector active layer. This approach naturally introduces sharp peaks in the angular response, with smaller footprint and reduced guided-mode radiative losses (and therefore improved spatial resolution and sensitivity) compared to analogous devices based on diffractive coupling. More broadly, these results highlight a promising new application space of flat optics, where gradient metasurfaces are integrated within image sensors to enable unconventional capabilities with enhanced system miniaturization and design flexibility.

A wearable strain sensor by integrating the mechanoluminescent fiber with a flexible printed circuit

Qinchuan Jiang, Xifa Liang, zhenshi chen, Yang Zou, Shuyan Zhu, Rui Min, Quandong Huang, zhiqiang yang, Zhaohui Li, and Qingming Chen

DOI: 10.1364/OL.516883 Received 28 Dec 2023; Accepted 11 Feb 2024; Posted 13 Feb 2024  View: PDF

Abstract: This paper reports an optical strain sensor that integrates a self-powered mechanoluminescent (ML) elastic fiber with a flexible circuit. The inclusion alumina nanoparticle as additive results in seven-fold enhancement of ML intensity while maintaining exceptional flexibility, reaching up to 120% strain. The sensor facilitates the detection of strain and stretching speed. It attains a sensitivity of 0.0022 lx/(1% strain) and the resolution of 0.2% strain, respectively. We have successfully applied this sensor in the strain measurement during bending motions in the finger, wrist, and elbow of a human being. This wearable strain sensor holds promise for diverse applications in wearable technology.

GeSn lateral PIN detector on Insulator Prepared by Rapid Melting Growth Method

Qinxing Huang, Jun Zheng, Yupeng Zhu, Xiangquan Liu, Zhipeng Liu, Yazhou Yang, Jinlai Cui, Liu Zhi, Yuhua Zuo, and Buwen Cheng

DOI: 10.1364/OL.516928 Received 27 Dec 2023; Accepted 11 Feb 2024; Posted 12 Feb 2024  View: PDF

Abstract: In this work, GeSn lateral p-i-n photodetectors (PDs) on insulator were fabricated with active GeSn layer grown by rapid melting growth (RMG) method. Taking advantages of the defect-free GeSn strips, GeSn PDs with 5.3% Sn content have low dark current and high responsivities, which are about 0.48A/W, 0.47A/W and 0.24 A/W for wavelength 1550 nm, 1630 nm and 2000 nm, respectively. The radio frequency of lateral GeSn PDs was also studied and 3dB bandwidth about 3.8 GHz was achieved. These results indicate that GeSn grown by rapid melting growth method is capable of fabricating high-performance Si based optoelectronic devices.

Heterogeneous Integration of on-chip Nd:YAG WGM laser with LNOI platform

Huiqi Li, Zhaocong WANG, Qingming Lu, Lei Wang, Yang Tan, and Feng Chen

DOI: 10.1364/OL.515441 Received 07 Dec 2023; Accepted 10 Feb 2024; Posted 12 Feb 2024  View: PDF

Abstract: The integration of heterogeneous optical components onto the optical platform is crucial for the advancement of photonic chips. To achieve this, efficient coupling of optical signals between components and the platform is essential, overcoming the challenge of refractive index mismatch caused by different materials. Here, we have successfully integrated a Nd:YAG microdisk laser with a lithium niobite on insulators (LNOI) photonic platform by modulating propagation modes of LNOI. Ridged waveguides are fabricated on the LNOI by carefully adjusting the cross-sectional dimensions to enable the propagation of higher-order transmission modes. This ridged waveguide ensures that the effective refractive index of the higher-order mode closely matches that of the fundamental mode of Nd:YAG microdisk, ensuring efficient waveguide-microdisk coupling. This on-chip laser, consisting of an Nd:YAG microdisk and LNOI integration, achieves a maximum output power of μW, and a mode suppression ratio of 53.6 dB. This research presents an efficient approach for constructing highly functional heterogeneous integrated optical chips.

Coherent Multi-Band MIMO Radar: Robustness Analysis to SSMF-based RF Signal Delivery

GAURAV PANDEY, Mirco Scaffardi, Salvatore Maresca, Malik Muhammad Haris Amir, Antonella Bogoni, and Antonio Malacarne

DOI: 10.1364/OL.510328 Received 25 Oct 2023; Accepted 09 Feb 2024; Posted 13 Feb 2024  View: PDF

Abstract: A numerical evaluation is conducted to assess the impact of distributing radiofrequency (RF) signals through optical fiber links on the performance of a coherent multi-band multiple-input multiple-output (MIMO) radar system. The analysis focuses on scenarios where the antennas are widely separated in comparison to the employed signal wavelengths. The development of a model to quantify the phase noise (PN) induced on each RF band due to the signal transmission through optical fiber links between the centralized base station and each radar peripheral, is described. Monte Carlo simulation results are collected to estimate the key performance indicators (KPIs) for varying standard single-mode fiber (SSMF) length and different PN contributions. The main contributors to the PN are revealed to be chromatic dispersion (CD), double Rayleigh scattering (DRS) and mechanical vibrations. In a shipborne scenario, a significant performance degradation only occurs when the length of the fiber links reaches approximately 20 km. Further, PN impact has also been studied in shipborne scenario to analyze the robustness of the system for worse phase noise level assumptions. The results reveal an excellent robustness of the proposed centralized acquisition and processing approach in presence of both very long fiber links and economic employed RF oscillators.

Low in-band spurious arbitrary waveform generator based on 1-bit time-wavelength interleaved photonic digital-to-analog conversion

Jinghan Yu, Shangyuan Li, Zhuoya Bai, Weichen Hou, Xiaoxiao Xue, Xiaoping Zheng, and Bingkun Zhou

DOI: 10.1364/OL.515301 Received 05 Dec 2023; Accepted 09 Feb 2024; Posted 12 Feb 2024  View: PDF

Abstract: We proposed an arbitrary waveform generator based on a 1-bit photonic digital-to-analog converter (PDAC). The system is based on the principle of photonic pulse sampling and time interleaving. High-speed optical pulses are generated and modulated by digital signals, then synthesized in one path. The analog signals are obtained by optical-to-electrical conversion of the time-interleaved pulses. Due to the 1-bit structure, there are no spurious components in principle. In the experiment, a 1-bit PDAC of 50 GSa/s is realized, and the X-band linear frequency modulated (LFM) waveform with a bandwidth of 4GHz is generated, the signal-to-spur-rejection ratio is as high as 50dB, and the millimeter-wave 64QAM signal is generated, with an EVM of 4.27%.

Dynamic monitoring of oxygen partial pressure in photodynamic therapy using pump-probe-based photoacoustic tomography

jiaying Xiao, XIAO HE, Zhuojun Xie, and Bo Wang

DOI: 10.1364/OL.517135 Received 27 Dec 2023; Accepted 09 Feb 2024; Posted 09 Feb 2024  View: PDF

Abstract: Pump-probe-based photoacoustic tomography (PP-PAT) is an innovative and promising molecular imaging technique. In this study, we utilized PP-PAT for the first time to monitor the dynamics of oxygen partial pressure (pO2) within murine tumors during photodynamic therapy (PDT) with methylene blue (MB). We developed a novel two-step fitting method to simultaneously map both the pO2 and the MB concentrations, and implemented it with mexCuda to accelerate the pixel-wise-based calculation. The results demonstrated a penetration depth of up to 5 mm, and revealed a significant decrease in pO2 during the PDT process, consistent with existing research findings. This study suggests that PP-PAT has the potential to become a valuable tool for intraoperative monitoring of PDT, thereby enhancing therapeutic efficacy.

Optimizing numerical k-sampling for swept-source optical coherence tomography angiography

Naixing Huang, Tristan Hormel, GUANGRU LIANG, Xiang Wei, Yukun Guo, Siyu Chen, and Yali Jia

DOI: 10.1364/OL.518720 Received 11 Jan 2024; Accepted 09 Feb 2024; Posted 09 Feb 2024  View: PDF

Abstract: High-quality swept-source optical coherence tomography (SS-OCT) requires accurate k-sampling, equally vital for optical coherence tomography angiography (OCTA). Most SS-OCT systems are equipped with hardware-driven k-sampling. However, this conventional approach raises concerns over system cost, optical alignment, imaging depth, and stability in the clocking circuit. This work introduces an optimized numerical k-sampling method to replace additional k-clock hardware. Using this method, we can realize high axial resolution (4.9 μm full-width-half-maximum, in air) and low roll-off (2.3 dB loss) over 4 mm imaging depth. The high axial resolution and sensitivity achieved by this simple numerical method can reveal anatomic and microvascular structures with structural OCT and OCTA in both macular and deeper tissues, including lamina cribrosa, suggesting its usefulness in imaging retinopathy and optic neuropathy.

On-chip Multi-trap Optical Tweezers Based on Guided Wave–Driven Metalens

Gang Yu, Jiaqi Guo, Jianwei Shi, Xu Mao, Hongsheng Ding, Houzhi Zheng, and Chao Shen

DOI: 10.1364/OL.517932 Received 09 Jan 2024; Accepted 08 Feb 2024; Posted 12 Feb 2024  View: PDF

Abstract: Optical tweezer arrays (OTAs) have emerged as a powerful tool for quantum simulation, quantum computation and quantum many-body physics. Conventional OTAs require bulky and costly optical components to generate multiple optical traps, such as spatial light modulators (SLMs). An integrated way to achieve on-chip OTAs is a sought-after goal for compact optical manipulation. In this letter, we have numerically demonstrated a new class of on-chip multi-trap optical tweezers based on guided wave–driven metalens. The presented on-chip optical tweezers are capable of capturing multiple polystyrene nanospheres in parallel. Moreover, we proposed an analytical design method to generate customized focal points from the integrated photonics chip into free space. Different trapping patterns are demonstrated to validate our proposed off-chip emission scheme. Our approach offers a promising solution to realize on-chip optical tweezers and provides a prospective way to realize elaborate emission control of guided waves into free-space beams.

Aplanatic solar concentrators for tubular absorbers

Leonardo Souza, Naum Fraidenraich, and Jeffrey Gordon

DOI: 10.1364/OL.517874 Received 16 Jan 2024; Accepted 08 Feb 2024; Posted 08 Feb 2024  View: PDF

Abstract: A fundamentally new class of linear (2D) dual-mirror aplanats tailored to tubular absorbers is developed, for the types of solar concentrators used for thermal power. It is shown that the prior investigation establishing this concept possesses unrecognized additional designs, as well as having missed high-performance configurations. It is shown that our line-focus solar concentrators can attain intercept factors exceeding 0.9 at concentration values as high as 55, with practical mirror contours and assemblies. Designed expressly for tubular absorbers, they represent improvements upon previous aplanatic concentrators that were tailored to flat one-sided absorbers but applied to tubular absorbers (as well as to conventional parabolic troughs).

Ultra-broadband frequency shifting of laser pulses in a square multicore chalcogenide fiber

Alexey Balakin, Sergey Skobelev, Alexey Andrianov, Elena Anashkina, and A Litvak

DOI: 10.1364/OL.514070 Received 23 Nov 2023; Accepted 08 Feb 2024; Posted 08 Feb 2024  View: PDF

Abstract: The process of Raman frequency shifting of out-of-phase laser pulses in fibers with a square configuration of weakly coupled cores having two or more zero dispersion wavelengths has been studied. The use of out-of-phase distributions in multicore fibers makes it possible to increase pulse energies by orders of magnitude in comparison with the case of single-core fibers. Conditions for the stability of out-of-phase laser pulses are determined and confirmed by numerical simulations. A configuration of chalcogenide multicore fiber with three zero dispersion wavelengths is proposed, allowing ultra-broadband frequency shifting of laser pulses up to 6.2 μm with an energy efficiency of more than 25%.

Low-noise co-arm differential sensor for optical frequency comb sampling E-field test system

zixian Guo, Yang Yan, Yumo Tian, Shenda Zhang, Yuanyuan Li, and shuguo xie

DOI: 10.1364/OL.510956 Received 01 Nov 2023; Accepted 08 Feb 2024; Posted 09 Feb 2024  View: PDF

Abstract: Optical frequency comb (OFC) technology can realize the rapid measurement of electric fields (E-fields) with large bandwidth. However, this technology suffers from the problem of high intensity noise, resulting in low sensitivity and blind frequency region. In order to solve the above problems, a dual-path optical E-field sensor with a common reference arm based on lithium niobate optical waveguide is proposed. The introduction of the reference arm improves the balance of optical paths and the degree of integration. A segmented electrode is also designed to ensure the generation of reverse electrical signals on two Mach-Zehnder interferometers (MZIs). After exiting from the differential photodetector (PD), the intensity noise can be removed, and the sensitivity of the sensor can be improved. After testing, the intensity noise can be reduced by 25dB, the signal response can be increased by about 6dB, and the blind frequency region can be eliminated with the co-arm differential optical E-field (CDOE) sensor in the process of measuring the signal. This sensor can be used in the 1MHz-12GHz bandwidth with a sensitivity better than 10mV/m•√Hz.

Miniaturized guided-mode resonance laser based on a one-dimensional finite heterostructure cavity

Lin Yong Qian, xin zhang, Zhengweiyi Yang, shuozhe xu, Yun Qiu, and wang kangni

DOI: 10.1364/OL.516509 Received 21 Dec 2023; Accepted 07 Feb 2024; Posted 08 Feb 2024  View: PDF

Abstract: Lasers based on the resonant nanostructures have attracted much attention due to their low threshold and compact dimensions. Guided-mode resonance (GMR) structures have been studied in lasing configurations because of their optical field enhancement and convenient free space excitation. However, the GMR inherently requires a larger footprint and is not suitable for high-density packaging. Here, we present numerical evidence of a miniaturized laser implemented in a one-dimensional finite heterostructure cavity (FHC). A GMR resonator and distributed Bragg reflectors are integrated to create the FHC, which enables the efficient coupling and localization of the electric field. Numerical findings indicate that the threshold is approximately 22.5 μJ/cm2, while the emission region is confined within a length of 5.4 µm. In addition, by adjusting the coupling strength, it is capable to achieve controllable lasing emission. The proposed structure provides a compact source for photonic integrated device, with applications in high-capacity optical communications, sensing, and quantum information processing.

Multistability, Relaxation Oscillations and Chaosin Time-Delayed Optoelectronic Oscillatorswith Direct Laser Modulation

Jimmi Hervé Talla Mbé, Michael Chiajeu Njidjou, Alain Francis Talla, Paul Woafo, and Yanne Chembo

DOI: 10.1364/OL.516965 Received 22 Dec 2023; Accepted 07 Feb 2024; Posted 07 Feb 2024  View: PDF

Abstract: We investigate the \textcolor[rgb]{0,0,0}{nonlinear dynamics of an optoelectronic oscillator} that is implemented with a laser-diode with time-delayed feedback. In this system, the electrical-to-optical conversion is implemented using the direct modulation of the laser-diode itself, instead of an electrooptical modulator as in conventional architectures. Moreover, we consider the cubic nonlinear saturation of the characteristic laser power-intensity (P-I) transfer function far above the threshold, instead of its simplified piece-wise linear counterpart. We perform the stability analysis of the oscillator and we show that it displays a rich dynamics that includes quasi-harmonic, relaxation oscillations and chaos. We also show that the oscillator is strongly hysteretic and displays a wide variety of multistable behaviors, including the rare case of bistability between chaotic attractors. Our analytical and numerical results are found to be in good agreement with the experimental measurements.

A technique for enhancing the accuracy of the Rayleigh-Sommerfeld convolutional diffraction through the utilizationof independent spatial sampling

Wanli Zhao, Lu Jing, Jun Ma, Caojin Yuan, Chenliang Chang, and Rihong Zhu

DOI: 10.1364/OL.509688 Received 19 Oct 2023; Accepted 07 Feb 2024; Posted 12 Feb 2024  View: PDF

Abstract: The Rayleigh-Sommerfeld diffraction integral (RSD) is a rigorous solution that precisely satisfies both Maxwell's equations and Helmholtz's equations. It seamlessly integrates Huygens' principle, providing an accurate description of the coherent light propagation within the entire diffraction field. Therefore, the rapid and precise computation of the RSD is crucial for light transport simulation and optical technology applications based on it. However, the current FFT-based Rayleigh-Sommerfeld integral convolution algorithm (CRSD) exhibits poor performance in the near field, thereby limiting its applicability and impeding further development across various fields. The present study proposes a novel approach to enhance the accuracy of the Rayleigh-Sommerfeld convolution algorithm by employing independent sampling techniques in both spatial and frequency domains. The crux of this methodology involves segregating the spatial and frequency domains, followed by autonomous sampling within each domain. The proposed method significantly enhances the accuracy of RSD during the short distance while ensuring computational efficiency.

A qudit-based high-dimensional controlled-not gate

Fang-Fang Du, Xue-Mei Ren, Ming Ma, and Gang Fan

DOI: 10.1364/OL.518336 Received 15 Jan 2024; Accepted 06 Feb 2024; Posted 07 Feb 2024  View: PDF

Abstract: High-dimensional quantum systems expand quantum channel capacity and information storage space. By implementing high-dimensional quantum logic gates, the speed of quantum computing can be practically enhanced. We propose a deterministic $4\times4$-dimensionalcontrolled-not (CNOT) gate for a hybrid system without ancillary qudits required, where the spatial and polarization states of a single photon serve as four control qudits, whereas two electron-spin states in nitrogen-vacancy centers act as four target qudits. As the control qudit are easilyoperated employing simple optical elements and the target qudit are available for storage, the CNOT gate works in a deterministicway and it can be flexibly extended to $n\times n$-dimensional ($n>4$) quantum gates for other hybrid system or different photonic degrees of freedoms. The efficiency and fidelity of the CNOT gate are analyzedaligning with current technological capabilities, finding that they have satisfactory performances.

Governance of Friedrich-Wintgen bound states in the continuum by tuning internal coupling of meta-atoms

Peiliang Liu, Zhenyu ZHAO, Yonghui Xue, xuelian zhang, Chunping Jiang, Rajour Ako, Hua Qin, and Sharath Sriram

DOI: 10.1364/OL.515072 Received 05 Dec 2023; Accepted 06 Feb 2024; Posted 08 Feb 2024  View: PDF

Abstract: Bound state in the continuum (BIC) is a phenomenon that describes perfect confinement of electromagnetic waves despite their resonant frequencies lying in the continuous radiative spectrum. BICs can be realized by introducing destructive interference between distinct modes, referred to as Friedrich-Wintgen BICs (FW-BICs). Herein, we demonstrate that a dual band FW-BICs can be derived from the coupled modes of individual split-ring resonators (SRR) in the terahertz band. The simulation results manifest that the dual band FW-BICs are in the center of the far-field polarization vortexes. One of the dual band quasi-FW-BICs keeps ultra-high-quality factor (Q factor) in a broad momentum range along Γ – X direction. Our results can facilitate the design of devices with high-Q factors, with extreme robustness against the incident angle.

Experimental comparison of E-band BDFA and Raman amplifier performance over 50 km G.652.D fiber using 30 GBaud DP-16-QAM and DP-64-QAM signals

Aleksandr Donodin, Pratim Hazarika, Mingming Tan, Dini Pratiwi, Shabnam Noor, Ian Phillips, Paul Harper, and Wladek Forysiak

DOI: 10.1364/OL.515331 Received 08 Dec 2023; Accepted 06 Feb 2024; Posted 06 Feb 2024  View: PDF

Abstract: We compare the performance of three optical amplifiers in the E-band: a bismuth-doped fiber amplifier, a distributed Raman amplifier, and a discrete Raman amplifier. Data transmission performance of 30 GBaud DP-16-QAM and DP-64-QAM signals transmitted over 50 km of G.652.D fiber is compared in terms of gain, noise figure, and achieved SNR. Due to the impact of nonlinear penalties at high input signal powers in distributed and discrete Raman amplifiers, the bismuth-doped fiber amplifier exhibited the best overall performance.

Nonreciprocal toroidal dipole resonance and one-way quasi-bound state in the continuum

Junqing Li, ZHIXU WU, DANDAN ZHANG, yong sun, Wenxing Liu, and Tian Yu

DOI: 10.1364/OL.516427 Received 20 Dec 2023; Accepted 06 Feb 2024; Posted 06 Feb 2024  View: PDF

Abstract: Bound states in the continuum (BICs) provides an alternative way of trapping light at nanoscale. Although last ten years have witnessed tremendous progress on BICs from fundamentals to applications, nonreciprocal BICs and their potential applications have not been fully exploited yet. In this study, we demonstrated one-way quasi-BIC by leveraging all-dielectric magneto-opticla metasurfaces. We show that the key point for achieving one-way quasi-BIC is to excite a magnetization-induced leaky resonance. Here we adopt the toroidal dipole (TD) resonance characterized by a vortex distribution of head-to-tail magnetic dipoles. We show that, by breaking the time-reversal symmetry, at oblique incidence the TD resonance can be enhanced in the forward channel and perfectly canceled in the time reversed channel, resulting in one-way quasi-BIC. The demonstrated phenomena hold significant promise for practical applications such as magnetic field optical sensing, nonreciprocal optical switching, isolation and modulation.

Co-processed heterogeneous near-infrared lasers on thin film lithium niobate

Theodore Morin, Jon Peters, Mingxiao Li, Joel Guo, Yating Wan, Chao Xiang, and John Bowers

DOI: 10.1364/OL.516486 Received 21 Dec 2023; Accepted 06 Feb 2024; Posted 06 Feb 2024  View: PDF

Abstract: Thin-film lithium niobate (TFLN) is an attractive platform for photonics applications on account of its widebandgap, its large electro-optic coefficient and its large nonlinearity. Since these characteristics are used in systems which require a coherent light source, size, weight, power and cost can be reduced and reliability enhanced by combining TFLN processing and heterogeneous laser fabrication. Here, we report the fabrication of laser devices on a TFLN wafer, and also the co-processing of five different GaAs-based III-V epitaxial structures, including InGaAs quantum wells and InAs quantum dots. Lasing is observed at wavelengths near 930, 1030 and 1180 nm, which, if frequency-doubled using TFLN, would produce blue, green and orange visible light. Single-sided power over 25 mW is measured with an integrating sphere.

Frequency selective surface filters with ultra-high quality factors based on Fano resonance

Dongzhi Shan, Jinsong Gao, Naitao Song, Nianxi Xu, yi zhao, hai liu, and Yang Tang

DOI: 10.1364/OL.517008 Received 26 Dec 2023; Accepted 06 Feb 2024; Posted 06 Feb 2024  View: PDF

Abstract: In this work, we propose a design method of the narrow pass-band filters with a high Q-factor based on Fano resonance. A single-layer metallic FSS with simple structure is first designed according to this idea, but the result is not satisfying since the filter transmittance will significantly decrease with the increase with the Q-factor due to the presence of inherent ohmic damping. Furtherly to improve the design, a ceramic-based FSS filter based on the similar mechanism is proposed, and the requirements of the ultra-high Q-factors can be met owing to the high permittivity and low loss tangent of microwave ceramics. The design strategy proposed in this paper may have a promising potential in modern wireless communication and related fields.

Anomalous far-field polarization around bound states in the continuum in non-Bravais lattices

Mengyao Wang, Chang-Yin Ji, Liangsheng Li, and Ning Zheng

DOI: 10.1364/OL.516016 Received 14 Dec 2023; Accepted 06 Feb 2024; Posted 07 Feb 2024  View: PDF

Abstract: It is generally believed that at-Γ bound states in the continuum (BICs) are enclosed by linearly polarized vortex in the momentum space when the structures have both mirror (σz) symmetry, in-plane inversion (I) symmetry and time reversal symmetry (T). Here, we reveal an anomalous situation that at-Γ BICs can be enclosed by linearly and elliptically polarized far-field even the σz, I and T symmetries are all maintained in non-Bravais lattices, which is radically different from the previous cognition. The asymmetric diatomic structures are designed to elaborate this intriguing phenomenon. By controlling the geometric parameters or refractive indexes of the two meta-atoms, the far-field polarization around the at-Γ BICs gradually deviates from linear polarization and approaches circular polarization. Our findings reveal that the non-Bravais lattices can provide a novel platform to manipulate the far-field polarization, showing important applications in quantum entanglement, structured light and radiation modulating.

Reconfigurable Integrated Photonic Filters for Optical Signal Processing using a Silicon Photonics Platform

Ranjan Das, Keru Chen, Yanran Xie, and Andy Knights

DOI: 10.1364/OL.514230 Received 23 Nov 2023; Accepted 06 Feb 2024; Posted 08 Feb 2024  View: PDF

Abstract: We present a systematic photonic filter design approach by deploying pole-zero optimization. The filter transfer function is derived from its specifications by formulating closed-form optimization objective functions and subsequently translating them into optical design parameters. Two distinct filter examples, namely Chebyshev and elliptic filters are considered for design and validation. A compact reconfigurable three-pole photonic filter is fabricated on a silicon photonics platform to illustrate the proposed design technique including transmission tunability. Integrated thermal phase shifters coupled with micro-ring resonators are used to reconfigure filter responses. A well-matched experimental demonstration is presented to validate the proposed tuning method. We achieved a sharp out-of-band rejection of at least 20 dB and 40 dB for the elliptic and Chebyshev filter respectively.

Increasing contrast in water embedded particles via time-gated mid-infrared photothermal microscopy

Panagis Samolis and Michelle Sander

DOI: 10.1364/OL.513742 Received 12 Dec 2023; Accepted 06 Feb 2024; Posted 08 Feb 2024  View: PDF

Abstract: The transient dynamics of photothermal signals can provide interesting insights into material properties and heat diffusion. In a mid-infrared photothermal microscope, the imaging contrast in standard amplitude imaging can vary for PMMA particles of different sizes when embedded in an absorbing medium of H2O water. Using time-resolved boxcar detection, a detailed analysis of the associated transient thermal dynamics at the bead-water interface is presented and the time decay parameters for 500 nm and 100 nm beads are determined. Enhanced imaging contrast is observed for less heat exchange between the water and bead, as in the case for the 100 nm bead. For the 500 nm bead, boxcar imaging at specific times during the diffusion process leads to an increase of the imaging contrast up to a factor of 1.8.

Fiber-optics spectrum monitoring of WDM telecommunication signals with MHz update rates

Afsaneh Shoeib, Manuel Fernández, Connor Rowe, Reza Maram, Pasquale Ricciardi, and Jose Azana

DOI: 10.1364/OL.509441 Received 18 Oct 2023; Accepted 06 Feb 2024; Posted 06 Feb 2024  View: PDF

Abstract: We propose a novel and simple real-time optical monitoring (RTOM) system for dynamic spectral analysis of telecommunication signals, involving electro-optic temporal sampling followed by dispersion-induced frequency-to-time mapping and high-speed photodetection. This system is shown to enable tracking of the presence and relative intensity of multiple wavelength-division-multiplexed (WDM) data streams that span over a broad frequency band with high resolution, accuracy, and fast measurement update rates. We derive the design conditions and trade-offs of the proposed scheme, and report proof-of-concept experiments that demonstrate successful spectral monitoring of dense-WDM signals with different modulation formats and bit rates, over the full C-band, with the needed resolution to discern channels separated by a few tens of GHz, and with an unprecedented fast measurement update rate in the MHz range.

Optical path optimization of chromatic line confocal displacement sensor for high resolution and wide range

Shuai Wang, Kuan Diao, xiaojun liu, and Chuqiao Gong

DOI: 10.1364/OL.518595 Received 10 Jan 2024; Accepted 05 Feb 2024; Posted 05 Feb 2024  View: PDF

Abstract: This study introduces the optical path-optimized dual grating chromatic line confocal imaging (DG-LCI) technique for high-resolution and wide-range surface topography measurements. Chromatic Line Confocal Imaging (LCI) finds extensive applications in high-speed 3D imaging of surface morphology, roughness analysis in industrial production and quality inspection. A key advantage of LCI is its ability to achieve a large depth of focus, enabling the imaging system to measure a wide range in the Z-direction. However, the challenge lies in the trade-off between measurement range and resolution. Increasing the measurement range reduces the resolution, making it unsuitable for precise measurements required in industrial processing. Conversely, enhancing the resolution limits the measurement range, thereby sacrificing the advantage of LCI systems’ broad measurement capabilities. Addressing this limitation, we propose a dual optical path dual grating structure using a simplified and ingenious optical-path optimization design. This design overcomes the challenge of sacrificing millimeter-level measurement range while simultaneously improving resolution. Rigorous simulations and experiments validate the effective-ness and validity of our proposed method.

Configurable SNAP microresonators induced by axial prestrain-assisted CO2 laser exposure

Yu Qi, Zhenxiang Xu, Zuowei Xu, Yulong Wang, Hongtao Li, Qi Miao, H Li, Xuewen Shu, and liang lu

DOI: 10.1364/OL.516550 Received 21 Dec 2023; Accepted 05 Feb 2024; Posted 09 Feb 2024  View: PDF

Abstract: Flexible engineering of the complex shapes of the surface nanoscale axial photonics (SNAP) bottle microresonators (SBMs) is challenging for future nanophotonic technology applications. Here, for the first time to the best of our knowledge, we experimentally propose a powerful approach for the one-step fabrication of SBMs with simultaneous negative and positive radius variations, exhibiting a distinctive “bump-well-bump” profile. It is executed by utilizing two focused and symmetrical CO2 laser beams exposed on the fiber surface for only several hundred milliseconds. The spectral characteristics of different eigenmodes are analyzed, providing deep insights into the complex physical processes during CO2 laser exposure. The shapes of the SBMs can be flexibly adjusted by the exposure time, laser power, and applied pre-strains. As a proof of this technique, the developed approach enables the efficient production of a bat SBM, ensuring a uniform field amplitude of the bat mode over the length exceeding 120 µm with 7% deviation. Our proposed technique provides a powerful technique for the efficient fabrication of SBMs with predetermined shapes, laying the groundwork for its applications on microscale optical signal processing, quantum computing, and so on.

Sensitivity-enhanced strain sensor based on a shape-modulated multimode fiber

Zhiyuan Zhao, Xinruo Li, Shi Hao YAN, Ke Tian, Xin Wang, Haiyan Zhao, Elfed Lewis, Gerald Farrell, and Pengfei Wang

DOI: 10.1364/OL.519450 Received 18 Jan 2024; Accepted 05 Feb 2024; Posted 06 Feb 2024  View: PDF

Abstract: In this letter, we demonstrate a sensitivity-enhanced strain sensor based on a shape-modulated multimode fiber (MMF). In contrast to conventional singlemode-multimode-singlemode (SMS) fiber structures, which typically contain a single cylindrical homogeneous MMF section, the shape of the MMF section in this investigation is modulated by lateral offset splicing of multiple MMF segments. Simulation results show that the designed shape-modulated MMF has a higher peak mechanical strain than that of a cylindrical MMF. Experimental results demonstrate that the strain sensitivity achieved by the shaped-modulated MMF formed SMS fiber structure is as high as -55.63 pm/με, which is 33 times higher than that for a cylindrical MMF formed conventional SMS fiber structure at -1.65 pm/με. This high sensitivity and low- fabrication cost SMS fiber sensor has the potential to be a promising candidate in precise strain measurement applications.

Phase matching-free ultrashort laser pulse characterization from transient plasma lens.

Rishabh Kumar BHALAVI, Pierre Bejot, adrien leblanc, Antoine Dubrouil, Franck Billard, Olivier Faucher, and edouard hertz

DOI: 10.1364/OL.516584 Received 04 Jan 2024; Accepted 05 Feb 2024; Posted 06 Feb 2024  View: PDF

Abstract: A phase-matching free ultrashort pulse retrieval based on the defocusing of a laser-induced plasma is presented. In this technique, a pump pulse ionizes a rare gas providing a plasma lens whose creation time is ultrafast. A probe pulse propagating through this gas lens experiences a switch of its divergence. The spectrum of the diverging part, isolated by a coronograph, is measured as a function of the pump-probe delay providing a spectrogram that allows for a comprehensive characterization of the temporal properties of the probe pulse. The method, called PI-FROSt for ``Plasma-Induced Frequency resolved Optical Switching'', is simple, free of phase matching constraints, and can operate in both self- and cross-referenced configurations at ultra-high repetition rate in the whole transparency range of the gas. The assessment of the method demonstrates laser pulse reconstructions of high reliability in both near-infrared and ultraviolet spectral ranges.

Optimal parameter selection for THz-CCS system based on incoherent light source

Cong Cheng, Fan Huang, Zoulong Li, Donglin Sun, Xunyuan Jin, Jianqiang Gu, Jiaguang Han, and Weili Zhang

DOI: 10.1364/OL.514869 Received 04 Dec 2023; Accepted 04 Feb 2024; Posted 07 Feb 2024  View: PDF

Abstract: Terahertz cross-correlation spectroscopy (THz-CCS) systems using broadband incoherent light as the pumping source have received increasing attention from researchers in recent years. However, a comprehensive and in-depth understanding of THz- CCS is still needed to obtain a detailed optimization scheme. Here we systematically investigate the influences of the pump source, propagation process, and detection parameters on the CCS signals. The impacts of the filter slopes and time constants in lock-in detection are revealed for optimizing the signal-to-noise ratio and bandwidth of the THz signal. By varying the optical fiber length and using a dispersion-compensating fiber, the dispersion insensitivity of THz-CCS was experimentally demonstrated. The comparison of different pump sources (SLD and ASE) shows that the over-wide and non-flat pump spectrum may attenuate the CCS signal because of the energy waste brought by the photomixing process under the limited bandwidth of the transmitter. Our research may lead to a deeper understanding and further optimization of the THz-CCS system, which will promote the development and widespread application of this new technique.

Harmonic active mode-locking optoelectronic oscillator with suppressed supermode noise based on pulse intensity feedback

Bo Yang, bo bai, Hao Chi, shuna yang, Yiran Gao, and hongxia he

DOI: 10.1364/OL.514349 Received 27 Nov 2023; Accepted 04 Feb 2024; Posted 06 Feb 2024  View: PDF

Abstract: A harmonic active mode-locking optoelectronic oscillator (HAML-OEO) with pulse intensity feedback is proposed and experimentally demonstrated. It is capable of generating microwave pulses characterized by suppressed supermode noise, uniform intensity, and tunable repetition rates. Unlike traditional HAML-OEOs, active mode-locking and pulse intensity feedback are simultaneously achieved through the use of a dual-drive Mach-Zehnder modulator (DDMZM). By synchronously feeding back the generated microwave pulses to the DDMZM, each pulse undergoes a loss proportional to its intensity, facilitating pulse intensity equalization and supermode noise suppression. In the experiment, intensity-equalized microwave pulse trains with repetition rates of 499 kHz and 998 kHz are generated by 5th and 10th-order HAML-OEOs, respectively, with the measured supermode noise suppression ratios exceeding 40 dB.

Broadband ASE source-enabled self-homodyne DA-RoF fronthaul using cascaded SOAs and multicore fiber

Jingjing Lin, Chenbo Zhang, Yixiao Zhu, Xu Liu, Weisheng Hu, Zhangyuan Chen, Weiwei Hu, and Xiaopeng Xie

DOI: 10.1364/OL.515939 Received 14 Dec 2023; Accepted 04 Feb 2024; Posted 05 Feb 2024  View: PDF

Abstract: Broadband amplified spontaneous emission (ASE) light sources are recognized for their cost-effective generation. However, their inherent high-intensity noise and the stringent requirement for time delay matching limits their widespread application in coherent optical telecommunication. Here we propose a broadband ASE source-enabled digital-analog radio-over-fiber (DA-RoF) mobile fronthaul architecture, leveraging semiconductor optical amplifiers (SOAs) and multicore fiber in tandem. Our proposed system uses SOAs to suppress the intensity noise of the ASE carrier and transmits the DA-RoF signal alongside an unmodulated carrier through distinct cores of an 8-core, 1-km fiber. This setup significantly enhances the signal-to-noise ratio (SNR) by 19.4 dB, boosts capacity and enables self-homodyne detection at the receiver end. We achieve an aggregated bandwidth of 35 GHz (7 cores × 5 GHz), supporting a 2.05-Tb/s CPRI-equivalent data rate with 1024-ary quadrature-amplitude-modulated (1024-QAM) signals. Additionally, we analyze the impact of chromatic dispersion on signal-to-noise ratio for broadband source coherent detection systems. This innovative scheme offers a pragmatic solution for integrating low-cost broadband sources into cost-sensitive fronthaul systems, providing both high capacity and fidelity in massive deployment scenarios.

High-performance Ge-on-insulator lateral p-i-n waveguide photodetectors for electronic–photonic integrated circuits at telecommunication wavelengths

TZU-YANG HUANG, RADHIKA BANSAL, Soumava Ghosh, Kwang Hong Lee, Qimiao Chen, Chuan Seng Tan, and Guo-En Chang

DOI: 10.1364/OL.517863 Received 05 Jan 2024; Accepted 04 Feb 2024; Posted 05 Feb 2024  View: PDF

Abstract: We report high-performance germanium-on-insulator (GeOI) waveguide photodetectors (WGPDs) for electronic–photonic integrated circuits (EPICs) operating at telecommunication wavelengths. The GeOI samples were fabricated using layer transfer and wafer-bonding techniques, and high-quality Ge active layer was achieved. Planar lateral p-i-n WGPDs were fabricated and characterized, and they exhibited a minimal leakage current of 0.1 μA. Strain-induced alterations in the optical properties were observed, resulting in an extended photodetection range up to λ= 1638 nm. This range encompasses crucial telecommunication bands. The WGPDs exhibited a high responsivity of 0.56 A/W and a high detectivity of D*=1.87x10^9 cmHz^1/2W^-1 at 1550 nm. Frequency response analysis revealed bandwidth enhancement with the application of bias voltage. This study offers a comprehensive understanding of GeOI WGPDs, fostering high-performance EPICs with implications for telecommunications and beyond.

Observing thermal lensing with quantum light

Marco Barbieri, Iole Venditti, Chiara Battocchio, Vincenzo Berardi, Fabio bruni, and Ilaria Gianani

DOI: 10.1364/OL.513656 Received 16 Nov 2023; Accepted 04 Feb 2024; Posted 05 Feb 2024  View: PDF

Abstract: The introduction of quantum methods in spectroscopy can provide enhanced performance and technical advantages in the management of noise. We investigate the application of quantum illumination in a pump and probe experiment. Thermal lensing in a suspension of gold nanorods is explored using a classical beam as the pump and the emission from parametric downconversion as the probe. We obtain an insightful description of the behaviour of the suspension under pumping with a method known to provide good noise rejection. Our findings are a further step towards investigating effects of quantum light in complex plasmonic media.

Tunable double notch filter on thin-film lithiumniobate platform

Songyan Hou, Hao Hu, Zhihong Liu, Weichuan Xing, Jincheng Zhang, and Yue Hao

DOI: 10.1364/OL.505362 Received 08 Sep 2023; Accepted 04 Feb 2024; Posted 20 Feb 2024  View: PDF

Abstract: Tunable optical filter at the chip scale plays a crucial role in fulfilling the need for the reconfigurability in channel routing,optical switching, and wavelength division multiplexing systems. In this letter, we propose a tunable double notch filteron thin-film lithium niobate using dual micro-ring architecture. This unique integrated filter is essential for complexphotonic integrated circuits, along with multiple channels and various frequency spacing. With only one loaded voltage,the device demonstrates a wide frequency spacing tunability from 16.1 GHz to 89.9 GHz by reversely tunning theresonances of the two micro-rings while the center wavelength between the two resonances remains unaltered. Moreover,by utilizing the pronounced electro-optic properties of lithium niobate, associated with the tight light confinementnanophotonic waveguides, the device demonstrates a spacing tunability of 0.82 GHz/V and a contrast of 10~16 dB. Inaddition, the device has an ultracompact footprint of 0.0248 mm2.

Terahertz super-resolution imaging based on metamaterial waveguide

Xinyu Li, Zhengxin Wang, Jiang Huiqi, Minghui Deng, Lesiqi Yin, Cheng Gong, and Weiwei Liu

DOI: 10.1364/OL.513859 Received 21 Nov 2023; Accepted 03 Feb 2024; Posted 05 Feb 2024  View: PDF

Abstract: A terahertz metamaterial waveguide (meta-waveguide) and the meta-waveguide-based lens-free imaging systems are presented. The meta-waveguide not only inherits the low-loss transmission performance of waveguide, but also achieves sub-wavelength focusing under the action of the metamaterial resonant field, thereby realizing super-resolution imaging. For verification, a metal ring-based meta-waveguide was designed and fabricated by a 3D printing and metal coating technology. Then, a transmission scanning imaging system working at 0.1THz was built. High quality terahertz images with a resolution of 1/3 of the wave-length were obtained by performing two-dimensional scanning. The imaging distance is far greater than the Rayleigh length, thus enabling far-field imaging. Meanwhile, high-resolution three-dimensional tomography can also be achieved on biological tissues (such as artificial blood vessels) using the meta-waveguide through Radon scanning. Finally, the focusing and transmission of terahertz wave in the meta-waveguide were simulated and analyzed.

Polarized Emission of Cs3Cu2I5 Nanowires Embedded in Nanopores of Anodic Aluminum Oxide Template

Min Wang, Chen Kunlin, lingling xie, Yafeng Wu, Xiyao Chen, Ning Lv, Fang Zhang, Yongtian Wang, and Bingkun Chen

DOI: 10.1364/OL.515767 Received 18 Dec 2023; Accepted 03 Feb 2024; Posted 06 Feb 2024  View: PDF

Abstract: Due to the intrinsic polarized emission property, polarized emissive materials with anisotropic nanostructures are expected to be potential substitutes for polarizers. Herein, by the template-assisted strategy, well-aligned lead-free metal halide Cs3Cu2I5 nanowire (NW) arrays are fabricated by evaporating the precursor ink in the anodic aluminum oxide (AAO) for polarized emission. The Cs3Cu2I5/AAO composite film emits highly polarized light with a degree of polarization (DOP) of 0.50. Furthermore, by changing the molar ratio of CsI/CuI, the stability of Cs3Cu2I5 precursor inks is improved. Finally, an ultraviolet (UV) light-emitting diode (LED) is adopted to pump the composite film to achieve a blue LED device. The reported Cs3Cu2I5/AAO composite film with highly polarized light emissions will have great potential for polarized emissions applications such as liquid crystal display backlights, waveguides, and lasers.

Robust Anderson transition in non-Hermitian photonic quasicrystals

Stefano Longhi

DOI: 10.1364/OL.517182 Received 28 Dec 2023; Accepted 02 Feb 2024; Posted 05 Feb 2024  View: PDF

Abstract: Anderson localization, i.e. the suppression of diffusion in lattices with random or incommensurate disorder, is a fragile interference phenomenon which is spoiled out in the presence of dephasing effects or fluctuating disorder. As a consequence, Anderson localization-delocalization phase transitions observed in Hermitian systems, such as in one-dimensional quasicrystals when the amplitude of the incommensurate potential is increased above a threshold, are washed out when dephasing effects are included. Here we consider localization-delocalization spectral phase transitions occurring in non-Hermitian quasicrystals with local incommensurate gain and loss, and show that, contrary to the Hermitian case, the non-Hermitian phase transition is robust against dephasing effects. The results are illustrated by considering synthetic quasicrystals in photonic mesh lattices.

Improving temperature characteristic of GaN-based ultraviolet laser diodes by using InGaN/AlGaN quantum well

Jing Yang, Yujie Huang, Zong Liu, yuheng zhang, Feng liang, and De Zhao

DOI: 10.1364/OL.515502 Received 11 Dec 2023; Accepted 02 Feb 2024; Posted 05 Feb 2024  View: PDF

Abstract: Temperature characteristics of GaN-based laser diodes are investigated. It is noted that the characteristic temperature of threshold current (T0) decrease with decreasing lasing wavelength for GaN-based LDs. The performance deteriorates seriously for UV LDs at high temperature. It is ascribed to the increase of carriers escaping from quantum wells due to the lower potential barrier height. In this paper, AlGaN is used as barrier layer in UV LDs instead of GaN to improve the temperature characteristic of threshold current and slope efficiency by increasing the potential barrier height of quantum wells and forming more uniform distribution of In content in InGaN quantum wells. Based on this structure, a high output power of 4.6 W is obtained at injection current of 3.8 A, the lasing wavelength is 386.8 nm.

Performance Enhancement via XPM Suppression in a Linear all-PM Mode-locked Fiber Oscillator

Marvin Edelmann, Yi Hua, Mikhail Pergament, and Franz Kaertner

DOI: 10.1364/OL.515953 Received 14 Dec 2023; Accepted 02 Feb 2024; Posted 02 Feb 2024  View: PDF

Abstract: We demonstrate strong performance enhancement of an all polarization-maintaining fiber oscillator mode-locked using a linear self-stabilized fiber interferometer via suppression of cross-phase modulation (XPM). Numerical simulations reveal that XPM significantly affects the saturable absorber dynamics resulting in strong distortions of the mode-locked steady-states and output pulse quality. For experimental verification, we construct an oscillator with XPM suppression, employing an intra-cavity YVO4 crystal to obtain a differential walk-off effect, and compare its characteristics with a reference oscillator in standard configuration. It is shown, that XPM suppression not only lowers the mode-locking threshold by more than 45%, but further results in improved pulse quality at the output ports and reduced nonlinear loss in the artificial saturable absorber.

Recovery of polarization entanglement in partially coherent photonic qubits

Sakshi Rao, PREETI SHARMA, and bashkar kanseri

DOI: 10.1364/OL.518329 Received 09 Jan 2024; Accepted 02 Feb 2024; Posted 05 Feb 2024  View: PDF

Abstract: Partially coherent photonic qubits, owing to their robustness in propagation through random media compared to fully coherent qubits, find applications in free-space communication, quantum imaging and quantum sensing. However, the reduction of spatial coherence degrades the entanglement in qubits, adversely affecting the entanglement-based applications. We report the recovery of entanglement in the partially coherent photonic qubits generated using spontaneous parametric down-conversion process despite retaining their multimode nature. This study utilizes an electron multiplying charge-coupled device (EMCCD) to perform coincidence measurements, eliminating the need for raster scanning of single-pixel detectors, which simplifies the optical alignment, enhances precision, and reduces the time consumption. We demonstrate that the size of the apertures used to select the biphotons substantially impacts the visibility and S-parameter of polarization entangled partially coherent qubits. The entanglement is recovered with partial spatial coherence properties by choosing small sizes of aperture in the captured image plane. This study could help in the advancement of free-space quantum communication, quantum imaging and quantum metrology.

Highly birefringent side-hole fiber Bragg grating for high-temperature pressure sensing

Baijie Xu, Guanfeng Chen, Xizhen Xu, Shen Liu, Changrui Liao, xiaoyu weng, Liwei Liu, Junle Qu, Yiping Wang, and Jun He

DOI: 10.1364/OL.509522 Received 18 Oct 2023; Accepted 01 Feb 2024; Posted 01 Feb 2024  View: PDF

Abstract: We demonstrate a novel high-temperature pressure sensor based on a highly birefringent fiber Bragg grating (Hi-Bi FBG) fabricated in a dual side-hole fiber (DSHF). The Hi-Bi FBG is generated by a femtosecond laser directly-written sawtooth structure in the DSHF cladding along the fiber core through the slow axis (i.e., the direction perpendicular to the dual-hole axis). The sawtooth structure serves both as an in-fiber stressor and also generates Bragg resonance due to its periodicity. The DSHF was etched by hydrofluoric acid to increase its pressure sensitivity and the diameter of two air-holes was enlarged from 38.2 to 49.6 µm. A Hi-Bi FBG with a birefringence of up to 1.9 × 10-3 was successfully created in the etched DSHF. Two distinct reflection peaks could be observed by using a commercial FBG interrogator. Moreover, pressure measurement from 0 to 3 MPa at a high temperature of 700 ºC was conducted by monitoring the birefringence-induced peak splits and achieved a high pressure sensitivity of -22.4 pm/MPa. The discrimination of temperature and pressure could be realized by simultaneously measuring the Bragg wavelength shifts and peak splits. Furthermore, a wavelength-division-multiplexed (WDM) Hi-Bi FBGs array was also constructed in DSHF and was used for quasi-distributed high-pressure sensing up to 2.5 MPa. As such, the proposed femtosecond laser-inscribed Hi-Bi FBG is a promising tool for high-temperature pressure sensing in harsh environments, such as aerospace vehicles, nuclear reactors, and petrochemical industries.

Turbulence Mitigation of 4 Mode-Division-Multiplexed QPSK Channels in a Pilot-Assisted Self-Coherent Free-Space Optical Link Using a PD Array and DSP-Based Channel Demultiplexing

Huibin Zhou, Hao Song, Xinzhou Su, Yuxiang Duan, Kaiheng Zou, Runzhou Zhang, Moshe Tur, and Alan Willner

DOI: 10.1364/OL.511797 Received 09 Nov 2023; Accepted 31 Jan 2024; Posted 01 Feb 2024  View: PDF

Abstract: Mode-division multiplexed (MDM) free-space optical (FSO) links can increase the aggregate data rate by simultaneously transmitting multiple orthogonal data-carrying beams. Moreover, there are various performance advantages when using temporal phase-based data encoding (e.g., quadrature-phase-shift-keying (QPSK)) in FSO links. A typical approach to recovering phase-encoded data is to use a coherent receiver such that the data beam is mixed with a single-mode local oscillator (LO). However, atmospheric turbulence can cause power coupling from the transmitted spatial mode to many other modes, resulting in significant LO-data mixing loss and inter-channel crosstalk in MDM FSO coherent links. Here, we demonstrate turbulence mitigation of 4 MDM QPSK channels in a pilot-assisted self-coherent FSO link using a photodetector (PD) array and electrical digital signal processing (DSP)-based channel demultiplexing. A Gaussian pilot beam is co-transmitted with four 1-Gbaud QPSK channels, each carried on one of four different orbital angular momentum (OAM) modes. The pilot beam experiences similar turbulence-induced wavefront distortion as the data beams. At the receiver, the turbulence distortion is mitigated by its conjugate during the mixing of the pilot and data beams in a PD array. Subsequently, we demultiplex the 4 channels by applying a fixed DSP matrix on the detected “mixing” signals. Results show that our approach has <3-dB turbulence-induced power penalty at a 7% forward error correction (FEC) limit under a turbulence strength of 2w₀/r₀=~4.4, whereas the same turbulence strength can cause >18-dB penalties for a LO-based coherent MDM system.

A wearable photoacoustic watch for human

Ting Zhang, Heng Guo, Weizhi Qi, and Lei Xi

DOI: 10.1364/OL.514238 Received 30 Nov 2023; Accepted 31 Jan 2024; Posted 01 Feb 2024  View: PDF

Abstract: Longitudinal detection of hemodynamic changes based on wearable devices is imperative for monitoring human healthcare. Photoacoustic effect is extremely sensitive to variations in hemoglobin. Therefore, wearable photoacoustic devices are apt to monitor human healthcare via the observation of hemodynamics. However, the bulky system and difficulties in miniaturizing and optimizing the imaging interface restrict the development of wearable photoacoustic devices for human use. In this study, we developed a wearable photoacoustic watch with a fully integrated system in a backpack that has a size of 450 mm × 300 mm × 200 mm and an affordable weight of 7 kg for an adult to wear. The watch has a size of 43 mm × 30 mm × 24 mm, weights 40 g, and features a lateral resolution of 8.7 µm, a field of view (FOV) of 3 mm in diameter, and a motorized adjustable focus for optimizing the imaging plane for different individuals. We recruited volunteers to wear the watch and the backpack, and performed in vivo imaging of the vasculatures inside human wrists under the conditions of walking and human cuff occlusion to observe hemodynamic variations during different physiological states. The results suggest that the focus shifting capability of the watch makes it suitable for different individuals and the compact and stable design of the entire system allows free movements of humans.

Matched dielectric slot waveguide as all-dielectric terahertz magnetic dipole

Daniel Headland, Ashish Kumar, Harrison Lees, Withawat Withayachumnankul, and Guillermo Carpintero

DOI: 10.1364/OL.516561 Received 20 Dec 2023; Accepted 31 Jan 2024; Posted 01 Feb 2024  View: PDF

Abstract: We observe that the modal field distribution of a dielectric slot waveguide closely resembles a magnetic dipole antenna. Such an aperture distribution traditionally demands metals, making it ill-suited to high frequencies due to excessive Ohmic loss. By terminating a dielectric slot waveguide with a matched free-space interface, a compact all-dielectric radiating magnetic dipole is realized. In this way, we introduce general-purpose dipole antennas, which have long been a mainstay of the RF and microwave ranges, into the realm of lightwave photonic integrated circuits. The existence of the desired magnetic dipole aperture distribution is experimentally confirmed in the terahertz range, at ∼275 GHz, and good matching is evident in the ∼−25 dB reflection level. This is the electrically-smallest radiator to ever be incorporated into an all-dielectric waveguiding platform.

Light sheet fluorescence microscopy with active optical manipulation

Jun Yin, Ruijing Liang, Haoyi Hou, Yan Miao, and Lingyao Yu

DOI: 10.1364/OL.515280 Received 08 Dec 2023; Accepted 31 Jan 2024; Posted 31 Jan 2024  View: PDF

Abstract: We present a light sheet fluorescence microscopy (LSFM) with active optical manipulation by using the linear optical tweezers (LOTs). In this method, two co-axially transmitting laser beams of different wavelengths are shaped using cylindrical lenses to form a linear optical trapping perpendicular to the optical axis and an excitation light sheet (LS) parallel to the optical axis, respectively. Multiple large-sized polystyrene fluorescent microspheres are stably captured by LOTs, and their rotation angles around specific rotation axes are precisely controlled. During sample rotation, the stationary excitation LS scans in sample to obtain fluorescence sectioning images of the sample at different angles.

Large-range two-dimensional sub-nano misalignment sensing for lithography with a piecewise frequency regression network

Nan Wang, YI LI, Wei Jiang, Zhen Qin, and Jun Liu

DOI: 10.1364/OL.511013 Received 02 Nov 2023; Accepted 31 Jan 2024; Posted 13 Feb 2024  View: PDF

Abstract: Circular gratings have been traditionally used as coarse alignment markers rather than fine ones for carrying out two-dimensional (2D) large-range misalignment measurements. This is primarily due to the complex phase distribution inherent to circular gratings, which renders the extraction of information from high-precision alignment challenging using the conventional frequency filtering methods. Along these lines, in this work, a novel convolutional regression filter capable of achieving 2D misalignment measurement with an impressive accuracy of 0.82 nm across a 3 mm range was introduced. Importantly, the proposed approach exhibited robustness against system errors and noise. It is anticipated that this strategy will provide an effective solution for similar misalignment sensing applications and hold promise for addressing future challenges in these fields.

Heterogeneous Optical Network and Power Allocation Scheme for Inter-CubeSat Communication

Xuan Huang, Peng Chen, and Xu Xia

DOI: 10.1364/OL.514198 Received 20 Dec 2023; Accepted 30 Jan 2024; Posted 31 Jan 2024  View: PDF

Abstract: In this letter, the problems of achieving inter-CubeSat communication through radio frequency (RF) and Lasers is first elaborated, and the feasibility of using visible light communication to replace RF and Lasers is investigated. On this basis, a novel heterogeneous optical network with high flexibility is proposed, in which CubeSats are divided into clusters in pairs. CubeSats in each cluster utilize different optical modulation methods to achieve a compromise between optical power efficiency and spectral efficiency, as well as avoid inter-CubeSat interference. Furthermore, under the maximum power and minimum capacity constraints, a closed-form optical power allocation solution minimizing overall bit error rate (BER) is investigated. Simulation results show that our proposed scheme is more preferred in practical systems and can achieve 3.8 dB gains compared to the conventional power allocation scheme at a BER of 10^{-4}.

Dual vector millimeter-wave signal generation basedon optical carrier suppression modulation and directdetection with one photodetector

Jiahao Bi, tangyao Xie, Dong Guo, Xinying Li, Xiaolong Pan, Hengxin Yan, Jie Hou, zhipei li, Chenchen Wang, Qi Zhang, Ran Gao, Ze Dong, and Xiangjun Xin

DOI: 10.1364/OL.511238 Received 07 Nov 2023; Accepted 29 Jan 2024; Posted 31 Jan 2024  View: PDF

Abstract: We propose a novel scheme for the dual vector millimeter-wave (mm-wave) signal generation and transmission, based on optical carrier suppression (OCS) modulation, precoding, and direct detection by a single-ended photodiode (PD). At the transmitter side, two independent vector radio-frequency (RF) signals with precoding, generated via digital signal processing (DSP), are used to drive an in-phase/quadrature (I/Q) modulator operating at optical OCS modulation mode, to simultaneously generate two independent frequency-doubling optical vector mm-wave signals, which can reduce the bandwidth requirement of transmitter’s components and enhance the spectral efficiency. With the aid of a single-ended PD and subsequent DSP at the receiver side, two independent frequency-doubling vector mm-wave signals can be separated and demodulated without data error. Based on our proposed scheme, we experimentally demonstrate the generation, transmission, and detection of 2-Gbaud 30-GHz quadrature-phase-shift-keying (QPSK) and 2-Gbaud 46-GHz QPSK signals over 10-km single-mode fiber-28 (SMF-28) and 1-m wireless transmission. The results indicate that the bit-error ratio (BER) of the dual vector mm-wave signals can both reach the hard-decision forward-error-correction (HD-FEC) threshold of 3.8×10-3.

Experimental demonstration of a novel digitization method for a photonic analog-to-digital converter with phase-shifted optical quantization

Bowen Zhang, Jifang Qiu, Qiuyan Li, YiJun He, Ran Tao, Yan Li, and Jian Wu

DOI: 10.1364/OL.507144 Received 02 Oct 2023; Accepted 28 Jan 2024; Posted 29 Jan 2024  View: PDF

Abstract: This letter proposes a novel matrix digitization method for a photonic analog-to-digital converter with phase-shifted optical quantization (PSOQ-ADC). This method overcomes the issues of excessive bit width of output code and the generation of invalid codes encountered by the traditional direct digitization method. The PSOQ-ADC, which uses a 5-channel multimode interference coupler (MMI) as an optical quantizer, combined with 2-bit electronic ADCs (EADCs), quantifies the analog voltage into 30 digital values. When a direct digitization method is used, it requires 10 bits output codes to represent these values, while our proposed matrix digitization method only needs 5 bits. At last, the PSOQ-ADC was fabricated on a commercial lithium niobate on insulator (LNOI) platform, and was used to experimentally demonstrate a photonic analog-to-digital conversion with 50GS/s of optical sampling rate and 1/2/5 GHz of radio frequency (RF) signals. Experimental results showed that the matrix digitization method reduced the bit width of output code from 10 bits to 5 bits. Besides, during the digitization process of RF signals, the direct digitization method encountered invalid codes, while the matrix digitization method successfully finished signal digitization.

Difference frequency generation enhancement from a waveguide-coupled plasmonic metasurface

Tsafrir Abir, Symeon Sideris, and Tal Ellenbogen

DOI: 10.1364/OL.507953 Received 16 Oct 2023; Accepted 28 Jan 2024; Posted 05 Feb 2024  View: PDF

Abstract: Metasurfaces, typically constructed from spatial arrangements of localized building blocks, can enhance light-matter interactions through local field enhancement or by coherent coupling to extended photonic modes. It was recently shown that extended photonic modes also emerge from the coupling of a nonlinear plasmonic metasurface to a guided-mode resonance. Here we investigate the impact these modes have on difference frequency generation in the waveguide-coupled metasurface. We show that a conventional design of gold split-ring resonators on high-index TiO₂ waveguide results in a modest enhancement of the nonlinear conversion process. By introducing extrinsic chirality stemming from broken mirror symmetry of the localized modes and the guided-modes propagation, we demonstrate higher quality modes leading to a 70-fold enhancement of the difference frequency generation process. The capacity to manipulate the nonlocal modes through the design offers broader control over the interaction and new avenues to tailor the nonlinear processes. These findings suggest an encouraging path for the realization of integrated nonlinear plasmonic devices.

Saturable absorption properties and ultrafast photonics applications of HfS3

Lu Li, Ze Xue, Li Pang, Xusheng Xiao, Huiran Yang, Jinniu Zhang, Yaming Zhang, Qiyi Zhao, and Wen Liu

DOI: 10.1364/OL.513573 Received 17 Nov 2023; Accepted 27 Jan 2024; Posted 29 Jan 2024  View: PDF

Abstract: In this study, we focused on investigating the ultrafast photonics applications of two-layer HfS3 nanosheets. We prepared two-layer HfS3 nanosheets and carried out experiments to study their nonlinear saturable absorption properties. The results showed that the two-layer HfS3-based saturable absorber (SA) exhibited a modulation depth of 16.8%. Additionally, we conducted theoretical calculations using first principles to estimate the structural and electronic band properties of the two-layer HfS3 material. Furthermore, we utilized the two-layer HfS3 materials as SAs in an erbium-doped fiber (EDF) cavity to generate mode-locked laser pulses. For the mode-locked operation, we measured a repetition frequency of 8.74 MHz, a pulse duration of 540 fs, and a signal-to-noise ratio (SNR) of 77 dB. Overall, our findings demonstrate that the two-layer HfS3 material can serve as a reliable saturable absorber, possessing properties comparable to currently used two-dimensional materials. This expands the application fields of HfS3 materials and highlights their potential for advanced optoelectronic devices.

Ultra-thin sub-diffraction metalens with a wide field of view for UV focusing

Lianhong Dong, Weijie Kong, fei zhang, Ling Liu, Mingbo Pu, Changtao Wang, xiong li, Xiaoliang Ma, and Xiangang Luo

DOI: 10.1364/OL.514291 Received 24 Nov 2023; Accepted 25 Jan 2024; Posted 31 Jan 2024  View: PDF

Abstract: In recent years, the wide-field-of-view imaging technology based on metasurface has been widely applied. However, reported sub-diffraction metalens with a wide field-of-view works indicate that the multiple structures are essential to effectively eliminate aberrations, which results in a heavy device thickness and weakens the advantage of ultra-thin metasurface. To solve this problem, according to super-oscillation theory and the translational symmetry of quadratic phase, as well as the principle of virtual aperture diaphragm based on wave vector filter, this Letter demonstrates a sub-diffraction metalens combined with single quadratic metalens and a wave vector filter. Our design not only realizes the super-resolution effects of 0.74 times to 0.75 times the diffraction limit in the wide field-of-view of nearly 180° for the first time, but also compresses the device thickness to the subwavelength order in principle. The proposed ultra-thin sub-diffraction metalens with a wide field-of-view is expected to be applied in the fields of super-resolution fast scanning imaging, information detection, small target recognition, and so on.

OAM-mode Coupling by Segmented Helical-Ring-Core Waveguides Inscribed with Femtosecond Laser Beam

Vladislav Likhov, Sergei Vasiliev, Grigory Alagashev, and Andrey Okhrimchuk

DOI: 10.1364/OL.515710 Received 12 Dec 2023; Accepted 25 Jan 2024; Posted 26 Jan 2024  View: PDF

Abstract: Azimuthally segmented helical-ring-core waveguides (HRCW) were fabricated in silica glass by direct laser writing. Triple-segmented waveguides provided single-mode or few-mode light guidance depending on the core diameter. Bragg resonance reflection of light carrying Orbital Angular Momentum (OAM) was registered confirming the generalized angular phase matching condition, which considers azimuthally segmented structure of the waveguides.

OFDR shape sensor based on femtosecond-laser-inscribed weak fiber Bragg grating array in multicore fiber

Cailing Fu, Shuai Xiao, Yiping Wang, Rongyi Shan, Wenfa Liang, huajian zhong, Changrui Liao, Yanjie Meng, and Xiaoyu Yin

DOI: 10.1364/OL.516067 Received 15 Dec 2023; Accepted 25 Jan 2024; Posted 25 Jan 2024  View: PDF

Abstract: A OFDR shape sensor was demonstrated based on femtosecond-laser-inscribed weak fiber Bragg grating (WFBG) array in multicore fiber (MCF). A WFBG array consisting of 60 identical WFBGs was successfully inscribed in each core along a 60 cm long MCF using femtosecond-laser point-by-point technology, where the length and space of each WFBG were 2 and 8 mm, respectively. The strain distribution of each core in two-dimensional (2D) and three-dimensional (3D) shape sensing was successfully demodulated using traditional cross-correlation algorithm, attributing to the accurate localization of each WFBG. The minimum reconstruction error per unit length of the 2D and 3D shape sensor was been improved to 1.08% and 1.07%, respectively, using apparent curvature vector method based on Bishop frame.

A high-frequency surface-micromachined optical ultrasound transducer (HF-SMOUT) array for 3D micro photoacoustic computed tomography (µPACT)

Zhiyu Yan and Jun Zou

DOI: 10.1364/OL.505676 Received 13 Sep 2023; Accepted 24 Jan 2024; Posted 25 Jan 2024  View: PDF

Abstract: This letter reports a 2D high-frequency surface-micromachined optical ultrasound transducer (HF-SMOUT) array for micro-PACT (µPACT) applications. A 11 mm by 11 mm HF-SMOUT array with 220 by 220 elements (35 µm in diameter) is designed, fabricated and characterized. The center frequency and bandwidth of the HF-SMOUT elements are ~15 MHz and ~20 MHz (133%), respectively. The noise equivalent pressure (NEP) is 156 Pa (or 19 mPa/√Hz) within a measurement bandwidth of 5-75 MHz. PACT experiments are conducted to evaluate the imaging performances of the SMOUT array. Spatial resolution is estimated as 90 µm (axial) and 250-750 µm (lateral) within a 10 × 10 mm^2 FOV (field of view) and the imaging depth up to 16 mm. 3D PA image of a knotted human hair target is also successfully acquired. These results show the feasibility of using the HF-SMOUT array for µPACT applications.

FPGA and deep neural network-accelerated spatial-spectral interferometry for rapid optical dispersion analysis

Xin-Li Lee, Jui-Chi Chang, Xiang-Yu Ye, and Chia-Yuan Chang

DOI: 10.1364/OL.510618 Received 31 Oct 2023; Accepted 24 Jan 2024; Posted 25 Jan 2024  View: PDF

Abstract: Spatial-spectral interferometry (SSI) is a technique used to reconstruct the electrical field of an ultrafast laser. By analyzing the spectral phase distribution, SSI provides valuable information about the optical dispersion of the laser beam, which is related to the energy concentration of the laser pulses. SSI is a single-shot measurement process and has a low laser power requirement. However, the reconstruction algorithm involves numerous Fourier transform and filtering operations, which limits the applicability of SSI for real-time dispersion analysis. To address this issue, this letter proposes an FPGA-based deep neural network to accelerate the spectral phase reconstruction and dispersion estimation process. The results show that the analysis time is improved from 124 ms to 9.27ms, which represents a 13.4-fold improvement on the standard Fourier transform-based reconstruction algorithm.

High-Efficiency Narrow-Bandwidth KTP Optical Parametric Oscillator for kHz–MHz Planar Laser Induced Fluorescence

Austin Webb, Christopher Crabtree, Venkat Athmanathan, Terrence Meyer, Sean Kearney, and Mikhail Slipchenko

DOI: 10.1364/OL.510334 Received 29 Nov 2023; Accepted 23 Jan 2024; Posted 29 Jan 2024  View: PDF

Abstract: The electronic excitation of key combustion species or flow tagging of molecules requires a narrowband tunable UV source. In this work, a potassium titanyl phosphate (KTP) burst-mode optical parametric oscillator (OPO) pumped by a 532 nm laser is developed to generate a spectrally narrow signal and idler output with 1.48 ± 0.19 cm¯¹ bandwidth without the need for injection seeding. The idler (1410–1550 nm range) is further mixed with 355 nm or 266 nm to generate 284 nm or 226 nm for OH or NO planar laser induced fluorescence (PLIF), respectively, with up to 1.9% conversion efficiency from 1064 nm to the UV. MHz-rate burst profiles are reported, and OH and NO PLIF are demonstrated in a rotating detonation combustor at rates up to 200 kHz.

Speed enhanced scattering compensation method with sub-Nyquist sampling

Zhenghan Li, Jiazhu Zhu, Wei Gong, and Ke Si

DOI: 10.1364/OL.515325 Received 05 Dec 2023; Accepted 22 Jan 2024; Posted 24 Jan 2024  View: PDF

Abstract: A rapid feedback-based scattering compensation method is particularly important for guiding light precisely within turbid tissues, especially dynamic tissues. However, the huge number of measurements which comes from the underutilization of the signal frequency channel greatly limits the modulation speed. This paper introduces a rapid compensation method with sub-Nyquist sampling which improves the channel utilization and the speed of wavefront shaping. The number of measurements is reduced to ~ 1500 with 32×32 freedom, and the PBR of the focus reaches ~ 200. The system performances are demonstrated by focusing light through brain slices of different thicknesses.

Dynamic structured illumination for confocal microscopy

Guillaume Noetinger, Fabrice Lemoult, and Sebastien Popoff

DOI: 10.1364/OL.500524 Received 06 Sep 2023; Accepted 16 Jan 2024; Posted 25 Jan 2024  View: PDF

Abstract: Structured illumination typically enables the tailoring of an imaging device's optical transfer function to enhance resolution. We propose the incorporation of temporal periodic modulation, specifically a rotating mask, to encode multiple transfer functions simultaneously in the temporal domain. This approach is demonstrated using a confocal microscope configuration. At each scanning position, a temporal periodic signal is recorded, superseding the usual approach consisting in measuring average intensity at each spatial location. By filtering around each harmonic of the rotation frequency, multiple images of the same object can be constructed. The image associated with the averaged intensity signal is similar to the confocal image. Meanwhile, the image carried by the $n{\mathrm{th}}$ harmonic corresponds to an image that is equivalent to a convolution of the object with a phase vortex of topological charge $n$, similar to the outcome when using a vortex phase plate for illumination. This technique enables the selective collection of chosen high spatial frequencies from the sample, thereby enhancing the spatial resolution of the confocal microscope.

Hybrid spherical array for combined volumetric optoacoustic and B-mode ultrasound imaging

Hsiao-Chun Amy Lin, XOSÉ LUÍS DEÁN-BEN, Ali Ozbek, Yi-Hsuan Shao, Berkan Lafci, and Daniel Razansky

DOI: 10.1364/OL.503118 Received 01 Sep 2023; Accepted 14 Jan 2024; Posted 12 Feb 2024  View: PDF

Abstract: Optoacoustic (OA) imaging has achieved tremendous progress with state-of-the-art systems providing excellent functional and molecular contrast, centimeter scale penetration into living tissues, and ultrafast imaging performance, making it highly suitable for handheld imaging in the clinics. OA can greatly benefit from efficient integration with ultrasound (US) imaging, which remains the routine method in bedside clinical diagnostics. However, such integration has not been straightforward since the two modalities typically involve different image acquisition strategies. Here, we present a new hybrid optoacoustic ultrasound (OPUS) imaging approach employing a spherical array with dedicated segments for each modality to attain volumetric OA data complemented by conventional B-mode US imaging. The system performance is subsequently showcased in healthy human subjects. The new OPUS approach hence represents an important step towards establishing OA in point-of-care diagnostic settings.

Wavelength Conversion Through Stimulated RamanScattering in Oxygen Filled Fiber for Multi-Band LiDAR

Micah Raab, Daniel Leaird, Trevor Courtney, Christian Keyser, and Rodrigo Amezcua Correa

DOI: 10.1364/OL.513743 Received 22 Nov 2023; Accepted 14 Jan 2024; Posted 14 Feb 2024  View: PDF

Abstract: Wavelength conversion afforded by stimulated Ramanscattering within hollow core fiber is potientially use-ful for multispectral LiDAR. Herein, we make use ofthe ideal 1550 cm−1 vibrational Raman shift of an an-tiresonant fiber filled with gaseous oxygen so that thefirst and second Raman orders as well as the transmittedpump are all located in separate atmospheric transmis-sion windows. To the best of our knowledge, this is thefirst report of stimulated Raman scattering in an oxygenfilled fiber. The host of closely spaced rotational SRSlines (12 cm−1) accompanying the transmitted pumpand vibrational Raman orders form continuum bandsallowing for much greater spectral coverage of the atmo-spheric transmission windows. The temporal profiles ofthe Raman orders can be separated without the use of agrating to potentially achieve multi-band LiDAR

GHz repetition rate, sub-100-fs Ho:CALGO laser at 2.1 µm with watt-level average power

Weichao Yao, Mohsen Khalili Kelaki, Yicheng Wang, Martin Saraceno, Marcel Delden, Thomas Musch, and Clara Saraceno

DOI: 10.1364/OL.507459 Received 23 Oct 2023; Accepted 07 Jan 2024; Posted 18 Jan 2024  View: PDF

Abstract: We report on a GHz fundamental repetition rate Kerr-lens mode-locked Ho:CALGO laser emitting at 2.1 µm. The laser employs a ring-cavity to increase the fundamental repetition rate to 1.179 GHz and can be made to oscillate in both directions stably with nearly identical performance: for counterclockwise oscillation, it generates 93-fs pulses at 1.68 W of average power, whereas 92 fs and 1.69 W were measured for clockwise operation. Our current results represent the highest average power from a 2-µm GHz oscillator and the first sub-100-fs pulse duration from a Ho-based oscillator.

Surface recoil force on dielectric nano--particles enhancement via graphene acoustic surface plasmons excitation: non--local effects consideration

Mauro Cuevas, Hernán Ferrari, and Julieta Olivo

DOI: 10.1364/OL.511071 Received 03 Nov 2023; Accepted 04 Jan 2024; Posted 25 Jan 2024  View: PDF

Abstract: Controlling opto--mechanical interactions at sub--wavelength levels is of great importance in academic science and nano--particle manipulation technologies. This letter focuses on the improvement of the recoil force on nano--particles placed close to a graphene--dielectric--metal structure. The momentum conservation involving the non--symmetric excitation of acoustic surface plasmons (ASPs), via near field circularly polarized dipolar scattering, implies the occurrence of a huge momentum kick on the nano--particle. Owing to the high wave--vector values entailed in the near field scattering process, it has been necessary to consider the non--locality of the graphene electrical conductivity to explore the influence of the scattering loss on this large--wave--vector region, which is neglected by the semi--classical model. Surprisingly, the contribution of ASPs to the recoil force is negligibly modified when the non--local effects are incorporated through the graphene conductivity. On the contrary, our results show that the contribution of the non--local scattering loss to this force becomes dominant when the particle is placed very close to the graphene sheet and that it is mostly independent of the dielectric thickness layer. Our work can be helpful for designing new and better performing large--plasmon momentum opto--mechanical structures using scattering highly dependent of the polarization for moving dielectric nano--particles.

Off-plane quartz-enhanced photoacoustic spectroscopy

Huijian Luo, Junming Li, Haohua Lv, Jiabao Xie, Chenglong Wang, Haoyang Lin, Ruobin Zhuang, Wenguo Zhu, Yongchun Zhong, Ruifeng Kan, JianHui Yu, and Huadan Zheng

DOI: 10.1364/OL.506650 Received 25 Sep 2023; Accepted 01 Jan 2024; Posted 31 Jan 2024  View: PDF

Abstract: In this work, we developed off-plane quartz-enhanced photoacoustic spectroscopy (OP-QEPAS). In the OP-QEPAS the light beam neither went through the prong spacing of the quartz tuning fork (QTF), nor in the QTF plane. The light beam is in parallel with the QTF with an optimal distance, resulting in low background noise. A radial-cavity (RC) resonator was coupled with the QTF to enhance the photoacoustic signal by radial resonance mode. By offsetting both the QTF and the laser position from the central axis, we enhance the effect of acoustic radial resonance and prevent the noise generated by direct laser irradiation of the QTF. Compared to IP-QEPAS based on a bare QTF, the developed OP-QEPAS with a RC resonator showed a >10× signal-to-noise ratio (SNR) enhancement. The OP-QEPAS system has great advantages in the use of light emitting devices (LEDs), long-wavelength laser sources such as mid-infrared quantum cascade lasers, and terahertz sources. When employing a LED as excitation source, the noise level was suppressed by ~2 orders of magnitude. Furthermore, the radial and longitudinal resonance modes can be combined to further improve the sensor performance.

Extreme-value statistics in nonlinear optics

Aleksei Zheltikov

DOI: 10.1364/OL.510419 Received 26 Oct 2023; Accepted 27 Dec 2023; Posted 13 Feb 2024  View: PDF

Abstract: We show that, although nonlinear optics may give rise to a vast multitude of statistics, all these statistics converge, in their extreme-value limit, to one of a few universal extreme-value statistics. Specifically, in the class of polynomial nonlinearities, such as those found in the Kerr effect, weak-field harmonic generation, and multiphoton ionization, the statistics of the nonlinear-optical output converges, in the extreme-value limit, to the exponentially tailed, Gumbel distribution. Exponentially growing nonlinear signals, on the other hand, such as those induced by parametric instabilities and stimulated scattering, are shown to reach their extreme-value limits in the class of the Fréchet statistics, giving rise to extreme-value distributions with heavy, manifestly nonexponential tails, thus favoring extreme-event outcomes and rogue-wave buildup.

A highly efficient single-layer graphene electro-absorption modulator

Hao Zhang, zhuang ma, Lutong Cai, and Lin Zhang

DOI: 10.1364/OL.509620 Received 31 Oct 2023; Accepted 26 Dec 2023; Posted 25 Jan 2024  View: PDF

Abstract: We propose a single-layer graphene electro-absorption modulator with an angled waveguide sidewall. By utilizing the hybridization of the TM0 mode and the TE1 mode in the waveguide, the light-graphene interaction is enhanced. A modulation depth of 0.098 dB/𝛍m and a figure of merit up to 35 are obtained at 1550 nm. Moreover, we show that the longitudinal electric field plays a significant role in making the optical absorption efficient, which indicates that modulation depth can be increased by enhancing the longitudinal electric field in modulators. This provides a promising solution for the future design of graphene optical modulators.

Space-time domain equalization algorithm based on complex-valued neural network in a long-haul photonic-aided MIMO THz system

Sicong Xu, Wen Zhou, Weiping Li, Yumeng Gou, Bohan Sang, Rahim Uddin, and lingchuan zeng

DOI: 10.1364/OL.512416 Received 15 Nov 2023; Accepted 20 Dec 2023; Posted 04 Jan 2024  View: PDF

Abstract: The urgent demand for high-bandwidth wireless services in enhanced mobile broadband networks needs innovative solutions for mobile front-haul systems. The terahertz (THz) band offers a promising candidate for ultra-high-capacity data transmission. This study investigates the integration of photonics-aided THz signal generation with MIMO and PDM technologies. We proposed a novel space-time domain equalization algorithm based on MIMO-Complex-Valued Neural Networks (CVNN), which can preserve the signal phase and the relation between X- and Y-polarization. We experimentally demonstrate the transmission of 60-GBaud PDM-QPSK and 30-GBaud PDM-16QAM signals over a 100-meter 2×2 wireless MIMO link at 320-GHz, with BER below 3.8×10-3 and 1.56×10-2 for QPSK and 16QAM signals, respectively. Compared with MIMO-Volterra, our MIMO-CVNN has an advantage in terms of calculation complexity and decision accuracy due to its effective handling of phase information and inter-polarization relationships simultaneously.