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Accepted papers to appear in an upcoming issue

Optica Publishing Group posts prepublication articles as soon as they are accepted and cleared for production. See the FAQ for additional information.

Chiral Zener tunneling in non-Hermitian frequency lattices

Lingzhi Zheng, Bing Wang, Chengzhi Qin, Lange Zhao, Shuyue Chen, Weiwei Liu, and Peixiang Lu

DOI: 10.1364/OL.470880 Received 19 Jul 2022; Accepted 17 Aug 2022; Posted 18 Aug 2022  View: PDF

Abstract: A waveguide doublet under both phase and intensity modulation is proposed to generate a non-Hermitian Su-Schrieffer-Heeger lattice in frequency dimension. By varying the modulation period and phase, we can manipulate the on-site potential of the lattice and realize anisotropic coupling of the supermodes in the waveguides. The artificial electric field associated with the modulation phase can also be introduced simultaneously. The Zener tunneling is demonstrated in the non-Hermitian system and manifests an irreversibly unidirectional conversion between the odd and even supermodes. The conversion efficiency can be optimized by varying the on-site potential of the waveguides. The study provides a versatile platform to explore non-Hermitian multiband physics in synthetic dimensions, which may find great application in chiral mode converters and couplers.

Epsilon-near-zero Substrate Enabled Strong Coupling between Molecular Vibrations and Mid-infrared Plasmons

Penghua Ma, Kaizhen Liu, Guangyan Huang, Youyi Ding, Wei Du, and Tao Wang

DOI: 10.1364/OL.469491 Received 04 Jul 2022; Accepted 16 Aug 2022; Posted 18 Aug 2022  View: PDF

Abstract: As the strong light-matter interaction between molecular vibrations and mid-infrared optical resonant modes, vibrational strong coupling (VSC) has the potential to modify the intrinsic chemistry of molecules, leading to the control of ground-state chemical reactions. Here, by using quartz as an epsilon-near-zero (ENZ) substrate, we have realized VSC between organic molecular vibrations and mid-infrared plasmons on metallic antennas. The ENZ substrate enables sharp mid-infrared plasmonic resonances (Q factor ~ 50) which efficiently couple to the molecular vibrations of polymethyl methacrylate (PMMA) molecules with prominent mode splitting. The coupling strength is proportional to the square root of the thickness of the PMMA layer and reaches the VSC regime with a thickness ~300 nm. The coupling strength also depends on the polarization of the incident light, illustrating an additional way to control the molecule-plasmon coupling. Our findings provide new possibility to realize VSC with metallic antennas and pave the way to promote the sensitivity of molecular vibrational spectroscopy.

Photonic Fock states generation using superradiance

Qihang Liu and Jung-Tsung Shen

DOI: 10.1364/OL.468481 Received 24 Jun 2022; Accepted 16 Aug 2022; Posted 17 Aug 2022  View: PDF

Abstract: Photonic Fock states are the most basic quantum states of a radiation field, but arbitrary number states are still difficult to produce. Here we propose to use superradiant atoms in a chiral waveguide to generate multi-photon Fock states deterministically. We calculate the explicit forms of the output quantum photonic states and their correlation functions. We further establish the conditions for the output optical fields to approach the Fock states asymptotically.

Topological edge states of long-range surface plasmon polariton at the telecommunication wavelength

Ran Gladstein Gladstone, Sukrith Dev, Jeffery Allen, Monica Allen, and Gennady Shvets

DOI: 10.1364/OL.471442 Received 25 Jul 2022; Accepted 16 Aug 2022; Posted 17 Aug 2022  View: PDF

Abstract: Confining light by plasmonic waveguides is promising for miniaturizing optical components, while topological photonics has been explored for robust light localization. Here we propose combining the two approaches into a simple periodically-perforated plasmonic waveguide (PPW) design exhibiting robust localization of long-range surface plasmon polaritons. We predict the existence of a topological edge state originating from a quantized topological invariant, and numerically demonstrate the viability of its excitation at telecommunication wavelength using near-field and waveguide-based approaches. Strong modification of the radiative lifetime of dipole emitters by the edge state, and its robustness to disorder, are demonstrated.

Fast non-line-of-sight imaging based on product-convolution expansions

Weihao Xu, Songmao Chen, Xiuqin Su, Yuyuan Tian, and Dingjie Wang

DOI: 10.1364/OL.469719 Received 21 Jul 2022; Accepted 16 Aug 2022; Posted 16 Aug 2022  View: PDF

Abstract: Non-line-of-sight (NLoS) imaging reveals hidden scene from indirect diffuse reflections. A common choice for analyzing the time-of-flight (ToF) data from non-confocal system is ellipsoid model whose operator is high-dimensional, leading to a computationally arduous task. In this letter, the product-convolution expansions method is utilized to formulate the operator and its adjoint based on the observation of shift-variant point spread function (PSF) in ToF data. The operator and its adjoint are locally approximated as a convolution, which allows the forward and backward procedure computed efficiently through fast Fourier transform (FFT). Moreover, the low-rank approximation of the operator is obtained by matrix decompositions, further improving the computational efficiency. The proposed method is validated on the publicly accessible datasets.

The spontaneous Raman spectra analysis and efficient nanosecond pulse Raman laser of a novel crystal BaTeW₂O₉

Feifei Guo, Pingzhang Yu, Zeliang Gao, zhengping wang, and Xutang Tao

DOI: 10.1364/OL.470067 Received 08 Jul 2022; Accepted 16 Aug 2022; Posted 16 Aug 2022  View: PDF

Abstract: In this paper, the spontaneous Raman spectra of a novel crystal α-BaTeW₂O₉ (α-BTW) have been characterized and analyzed. The relative Raman gain coefficient of the α-BTW crystal was calculated to be 0.84 times as that of YVO₄. With a length of 35 mm crystal, the first order Raman laser of α-BTW operating at 1178 nm was realized. The Raman laser exhibits a threshold of 14.7 MW/cm². In our experiments, a maximum pulse energy of 21.5 mJ was obtained with an optical-to-optical conversion efficiency and slope efficiency of 43.6%, 57.9%, respectively. Due to its high laser damage threshold, relative high Raman gain coefficient, and excellent thermal properties, the α-BTW crystal would be a potential Raman material.

Cooling neutral atoms into maximal entanglement in the Rydberg blockade regime

Wei-Lin Mu, Xiao-Xuan Li, and xq shao

DOI: 10.1364/OL.471591 Received 25 Jul 2022; Accepted 16 Aug 2022; Posted 16 Aug 2022  View: PDF

Abstract: We propose a cooling scheme to prepare stationary entanglement of neutral atoms in theRydberg blockade regime by combination of periodically collective laser pumping and dissipation. In each cycle, the controlled unitary dynamics process can selectively pump atoms away from the non-target state while maintaining the target state unchanged. The subsequent dissipative process redistributes the populations of ground states through the engineered spontaneous emission. After a number of cycles, the system will be eventually stabilized into the desired steady state independent of the initial state. This protocol does not rely on coherent addressing of individual neutral atoms or fine control of Rydberg interaction intensity, which can in principle greatly improve the feasibility of experiments in related fields.

Step-like beam scanning in slow-light grating beam scanner for FMCW LiDAR

Toshihiko Baba, Jun Gondo, Takemasa Tamanuki, Ryo Tetsuya, Mikiya Kamata, and Hiroyuki Ito

DOI: 10.1364/OL.461112 Received 13 Apr 2022; Accepted 16 Aug 2022; Posted 17 Aug 2022  View: PDF

Abstract: We have developed a nonmechanical beam scanner equipped with a Si photonics slow-light grating toward an on-chip frequency-modulated continuous-wave light detection and ranging (FMCW LiDAR) device. An optical beam is scanned thermo-optically, but it is also shifted sensitively to the frequency modulation, which is inconvenient for FMCW LiDAR. In this study, we canceled this shift and obtained step-like beam scanning with synchronized thermo-optic signals, which was confirmed in space-time-domain beam observations. The step-like scanning allows for finer angular resolution of the range profile.

Ultrafast photoluminescence at telecom wavelengths from wafer-scale monolayer graphene enabled by Fabry-Perot interferences

Kunze Lu, Yadong Wang, Manlin Luo, Bongkwon Son, Yi Yu, and Donguk Nam

DOI: 10.1364/OL.463073 Received 11 May 2022; Accepted 16 Aug 2022; Posted 17 Aug 2022  View: PDF

Abstract: Ultrafast photoluminescence from monolayer graphene shows attractive potential for developing integrated light sources for next-generation graphene-based electronic-photonic integrated circuits. In particular, graphene light sources operating at the telecom wavelengths are highly desired for the implementation of graphene-based ultra-high-speed optical communication. Currently, most of the studies on ultrafast photoluminescence from graphene lie in the visible spectrum, while studies on ultrafast photoluminescence at the telecom wavelengths remain scarce. Here, we present experimental observations of strong ultrafast photoluminescence at telecom wavelengths from wafer-scale monolayer graphene. Our results show that the emission spectra can be strongly modified by the presence of the cavity effect to produce an enhanced emission at telecom wavelengths. We corroborate our experimental results with simulations and show that by designing a suitable cavity thickness, one can easily tune the emission profile from visible to telecom wavelength regardless of the pump power. In addition, we demonstrate that the insertion of a monolayer hexagonal boron nitride between graphene and the substrate helps improve the thermal stability of graphene, thereby providing five times enhancement of the ultrafast photoluminescence. Our results provide a potential solution for stable on-chip nanoscale light sources with ultrahigh speed modulation.

Simple Amplifier Configuration Algorithm for Dynamic C+L-Band Systems in Presence of Stimulated Raman Scattering

yuchen song, qirui Fan, Chao Lu, Danshi Wang, and Alan Pak Tao Lau

DOI: 10.1364/OL.465942 Received 06 Jun 2022; Accepted 15 Aug 2022; Posted 16 Aug 2022  View: PDF

Abstract: We propose a simple two-step amplifier configuration algorithm based on signal power across different channels to improve the generalized signal-to-noise ratio (GSNR) performance of dynamic C+L-band links in presence of amplifier spontaneous emission (ASE) noise, Kerr nonlinearity and stimulated Raman scattering (SRS) using erbium-doped fiber amplifiers (EDFA). In step 1, ASE noise and Kerr nonlinearity are taken into account to derive sub-optimal signal power profiles at the beginning of each span using the local optimization global optimization (LOGO) strategy. The effect of SRS is compensated through amplifier gain pre-tilt in step 2. Simulations for homogeneous-/heterogeneous-span links, static full channel loading, and dynamic loading due to gradual channel additions shows that the proposed algorithm can achieve similar GSNR performance but require much less execution time compared to other iterative methods that directly optimize the GSNR profile across the C+L-band, thus making it a fast and efficient GSNR management strategy for future dynamic C+L-band networks.

Tunable kilohertz microwave photonic bandpass filter based on backscattering in a microresonator

Linhao Ren, Shixing Yuan, Song Zhu, Lei Shi, and Xinliang Zhang

DOI: 10.1364/OL.468442 Received 22 Jun 2022; Accepted 15 Aug 2022; Posted 16 Aug 2022  View: PDF

Abstract: A tunable microwave photonic bandpass filter (MPBPF) with a kilohertz bandwidth based on the backscattering mode of a silica microsphere resonator is proposed and experimentally demonstrated. In this work, an ultrahigh-quality-factor microsphere resonator is utilized to generate a radio frequency bandpass response with a bandwidth of 600 kHz. Meanwhile, scattering induced coupling between the clockwise mode and the counterclockwise mode is introduced to reduce the number of resonance modes, and a single backscattering mode which has a high extinction ratio is obtained. Therefore, a MPBPF with a tuning range of 40 GHz and a rejection ratio of 16.9 dB is realized. This MPBPF possesses advantages such as ultranarrow bandwidth, large tuning range and compactness, which shows great potential for microwave photonic applications.

Magnetometry based on laser-induced plasmas effect in a sodium-containing environment

Ning Ding, Guoguo Kang, XiaoXu Zhang, YiXin Guo, ZongYu Guo, Luo Zhao, Weiqi Jin, Huiqi Zheng, Qiongying Ren, and Hua Zhao

DOI: 10.1364/OL.468358 Received 24 Jun 2022; Accepted 15 Aug 2022; Posted 15 Aug 2022  View: PDF

Abstract: Magnetic-optic resonance response of sodium plasma generated by a high-energy solid-state pulse Nd: YAG laser is studied in different external magnetic field. We investigated resonance fluorescence signal of sodium atom in simulated sea fog environment based on laser-induced plasmas (LIP) effect. By ionizing NaCl solution spray to generate sodium plasma in a sodium-free environment, we built a Bell-Bloom magneto-optical resonance system under laboratory condition. With the help of laser-induced breakdown spectroscopy (LIBS) and transmission absorption spectrum we obtained sodium plasma with a lifetime of 250 μs. A narrow-band tunable continuous-wave (CW) 589 nm laser tuned at D2 line with modulation frequency around Larmor frequency was utilized as pump beam to polarize sodium plasma in test magnetic field. We found the magneto-optic resonance signal vary with different external magnetic field and the position of resonance signal was consistent with theoretical value. An enhanced magnetic field sensitivity up to 85 pT/√Hz was achieved at D2 line of sodium atoms.

Optical Single Sideband Modulation for Coherent Doppler LiDAR

Sze Set, Sean Wolfe, Takuma Shirahata, and Shinji Yamashita

DOI: 10.1364/OL.469026 Received 06 Jul 2022; Accepted 15 Aug 2022; Posted 15 Aug 2022  View: PDF

Abstract: The first implementation of optical single sideband modulation (OSSBM) in coherent Doppler LiDAR (CDL), for use with short pulse widths. It is shown that by mitigating the interference that comes from spectrum broadening with shorter pulses, the OSSBM CDL provides better accuracy at shorter pulse widths than a traditional CDL. Ultimately, a 4 ns pulse width with a 1 GHz intermediate frequency is achieved without degradation of velocimetry accuracy, which represents a multi-fold improvement over conventional fiber based CDL implementations.

Random color filters based on all-dielectric metasurface for compact hyperspectral imaging

Zhipeng Wu, zhiqing zhang, yijing xu, Yusheng Zhai, Canran Zhang, bozhi wang, and Qilong Wang

DOI: 10.1364/OL.469097 Received 30 Jun 2022; Accepted 14 Aug 2022; Posted 15 Aug 2022  View: PDF

Abstract: Metasurface filters are a compact, lightweight, and inexpensive solution for the miniaturized hyperspectral imaging system. However, the emerging applicability of these filters is limited by the tradeoff between spatial and spectral resolutions. In this study, we established and experimentally demonstrated a compact hyperspectral photodetection method using random all-dielectric metasurface filters that were directly integrated on the detectors. Based on compressive sensing algorithms, the compact photodetectors can accurately reconstruct the incident spectrum in the visible range. The minimum full width at half maximum (FWHM) of the spectrum reconstructed was 4.8 nm, which fully satisfied the requirements of hyperspectral imaging. The proposed method may be applied in the design, development, and measurement of the compact hyperspectral imaging systems.

Data transmission under high scattering based on OAM-basis transmission matrix

zeqi liu, Hengkang Zhang, Kaige Liu, Bin Zhang, Xing Fu, and Qiang Liu

DOI: 10.1364/OL.469688 Received 11 Jul 2022; Accepted 14 Aug 2022; Posted 15 Aug 2022  View: PDF

Abstract: Multiplexing of orbital angular momentum(OAM) channels is an important method to increase optical communication capacity at present, but the multiple scattering and distortion of long-distance optical communication greatly limit its application. Here, a data transmission method based on OAM-basis transmission matrix (TM) under high scattering is proposed. In this method, OAM modes are directly encoded by OAM-basis TM, and the incident power spectral distribution of OAM modes can be directly acquired by the intensity profile of the speckle field on the camera. This method can realize the multiplexing of large number of OAM channels and is easy to operate. Experimentally, we have achieved a maximum of 800 OAM modes multiplexed, and a bit error rate of 0.01% in the data transmission of color images.

Dynamic intelligent measurement of multiple chirped signals based on optical computing STFT and YOLOv3 neutral network

Yitang Dai, Huang Can, Xie Xiangzhi, and Kun Xu

DOI: 10.1364/OL.470700 Received 18 Jul 2022; Accepted 14 Aug 2022; Posted 15 Aug 2022  View: PDF

Abstract: We demonstrate a dynamic intelligent measurement system of multiple chirped signals based on optical computing short-time Fourier transform (STFT) and You Only Look Once (YOLOv3) video detection neutral network, where the dynamic spectrum of the broadband non-stationary signals can be measured with high frequency resolution and the analytical expressions can be obtained directly with short time consuming. Experimentally, the dynamic observation bandwidth can reach 1.98GHz and frequency resolution can reach 60MHz. In the proof-to-accuracy experiment, the mean IoU of 87.78% and mean Accuracy Precision (mAP) of 84.52% in 895 samples are simultaneously achieved. In the meanwhile, every loop of acquisition and detection takes approximately 29ms. Factors affecting the performance of the measurement system, such as the quantity of the signal and the number of the category, are discussed.

Tunable acousto-optic optical frequency combs

Sergey Mantsevich and Andrey Voloshin

DOI: 10.1364/OL.464394 Received 23 May 2022; Accepted 14 Aug 2022; Posted 15 Aug 2022  View: PDF

Abstract: Examination of various issues related to the generation and application of optical frequency combs (OFCs) is an important brunch of modern optoelectronics. Some of proposed OFCs generation methods apply acousto-optic (AO) devices. The AO devices are used either as the element devoted to the OFC phase stabilization, or they play the role of optical radiation frequency shifting element in the frequency-shifting loop (FSL) scheme. The results of two experiments related to the application of AO cells in the FSL scheme are represented in this paper. The first experiment confirms the previously proposed effect of AO mismatch influence on all the OFC characteristics. The second experiment shows the possibility of tunable AO dual-comb down-conversion applying single AO device.

Design High-Q Cavity of Dark Hollow Beam Based on one-dimension topological photonic crystal

Wei Caiyang, Ping Jiang, miaofang zhou, Yan Qin, Junyi He, Jing Yang, Jingxin Deng, Lizhong Hu, Yang Huajun, and Guangjun Wen

DOI: 10.1364/OL.468005 Received 16 Jun 2022; Accepted 14 Aug 2022; Posted 17 Aug 2022  View: PDF

Abstract: Dark hollow beam(DHB) possesses great prospects in material processing, holography and vortex beam, thus designing high-Q DHB cavity is significant for these applications. In this letter, based on one-dimension topological photonic crystal, a method of designing and the optimizing a high-Q DHB cavity is proposed. Besides, how the structural parameters control the performance of the cavity is analyzed with the help of finite-element-method(FEM) simulation. According to the simulation results, the Q-factor of the designed cavity can achieve the order of 10⁵ with only 19 periods of layers. It is critical to mention that, although increasing the layers can improve the average Q of the cavity, it will cause serious fluctuation of both the Q factor and the divergence angle of the output beam. The designing method proposed in this letter may not only give a hint to designers of DHB laser but also promote the applications of DHB in various fields.

Sum rules for energy deposition eigenchannels in scattering systems

Alexey Yamilov, Nicholas Bender, and Hui Cao

DOI: 10.1364/OL.468697 Received 04 Jul 2022; Accepted 12 Aug 2022; Posted 12 Aug 2022  View: PDF

Abstract: In a random-scattering system, the deposition matrix maps the incident wavefront to the internal field distribution across a target volume. The corresponding eigenchannels have been used to enhance the wave energy delivered to the target. Here we find the sum rules for the eigenvalues and eigenchannels of the deposition matrix in any system geometry: including two and three-dimensional scattering systems, as well as narrow waveguides and wide slabs.We derive a number of constraints on the eigenchannel intensity distributions inside the system as well as the corresponding eigenvalues. Our results are general and applicable to random systems of arbitrary scattering strength as well as different types of waves including electromagnetic waves, acoustic waves, and matter waves.

Boosting Topological Zero Modes Using Elastomer Waveguide Arrays

Angelina Frank, Daniel Leykam, Daria Smirnova, Dimitris Angelakis, and Alexander Ling

DOI: 10.1364/OL.469657 Received 05 Jul 2022; Accepted 12 Aug 2022; Posted 12 Aug 2022  View: PDF

Abstract: We employ the Su-Schrieffer-Heeger model in elastic polymer waveguide arrays to design and realize travelling topologically protected modes. The observed delocalization of the optical field for superluminal defect velocities agrees well with theoretical descriptions. We apply mechanical strain to modulate the lattices' coupling coefficient. This work demonstrates a novel platform for rapid prototyping of topological photonic devices and establishes strain-tuning as a viable design parameter for topological waveguide arrays.

Super-resolution stimulated Raman scattering microscopy with phase-shifted spatial frequency modulation

Zhiwei Huang, Xiaobo Lv, Li Gong, Shulang Lin, and Peng Jin

DOI: 10.1364/OL.463087 Received 04 May 2022; Accepted 12 Aug 2022; Posted 15 Aug 2022  View: PDF

Abstract: We present a unique super-resolution stimulated Raman scattering (SRS) microscopy technique based on phase-shifted spatial frequency modulation (PSFM) under wide-field illumination, permitting super-resolution chemical imaging with single-pixel detection. Through projecting a series of the pump and Stokes laser patterns with varying spatial frequencies onto the sample and combining with the proposed 𝜋-phase shift, the higher spatial information can be rapidly retrieved by implementing the fast inverse Fourier-transform on the spatial frequency-encoded SRS data. We have derived the theory of the PSFM-SRS technique for super-resolution imaging. Our further modeling results confirm that PSFM-SRS microscopy provides ~2.2-fold improvement in spatial resolution but with a much reduced laser excitation power density required as compared to conventional point-scan SRS microscopy, suggesting its potential for label-free super-resolution chemical imaging in cells and tissue.

Hyperfine coupling constants of the cesium 7D5/2 state measured up to the octupole term

Bubai Rahaman and Sourav Dutta

DOI: 10.1364/OL.469086 Received 29 Jun 2022; Accepted 11 Aug 2022; Posted 12 Aug 2022  View: PDF

Abstract: We report the measurement of the hyperfine splitting in the 7D5/2 state of 133Cs using high resolution Doppler-free two-photon spectroscopy enabled by precise frequency scans using an acousto-optic modulator. All the six hyperfine levels are resolved in our spectra. We determine the hyperfine coupling constants A = -1.70867(62) MHz and B = 0.050(14) MHz which represent over 20-times improvement in the precision of both A and B. Moreover, our measurement is sufficiently precise to put bounds on the value of the magnetic octupole coupling constant C = 0.4(1.4) kHz for the 7D5/2 state. We additionally report the measurement of ac Stark shift [-46±4 Hz/(W/cm2)], collisional shift and pressure broadening which are important for optical frequency standards based on the 6S1/2 - 7D5/2 two-photon transition.

Reconstruction design method of aspherical recording optical system for varied line-space grating

xinyu wang, yanxiu jiang, Zhong-Ming Zheng, Wei Wang, zhendong chi, and Wenhao Li

DOI: 10.1364/OL.469523 Received 05 Jul 2022; Accepted 11 Aug 2022; Posted 11 Aug 2022  View: PDF

Abstract: A reconstruction design method for an aspherical recording system for varied line-space gratings is introduced. This method converts the recording system design from achieving specific groove distribution coefficients within the expansion model into reconstruction of the auxiliary mirror surface via the ray-tracing method. The effects of advanced expansion terms in the expansion model are investigated and more accurate design of the varied line-space grating recording structure is achieved. By varying the surface reconstruction target, this method can be used to design aspherical recording structures with any auxiliary mirror surface shapes.

A system to eliminate graininess of integral imaging 3D display by using a transmissive mirror device

Han-Le Zhang, XIAO-LI MA, Xing-Yu Lin, Yan Xing, and Qiong-Hua Wang

DOI: 10.1364/OL.470442 Received 14 Jul 2022; Accepted 11 Aug 2022; Posted 11 Aug 2022  View: PDF

Abstract: We propose a system to eliminate the graininess of integral imaging 3D display by using a transmissive mirror device (TMD). The proposed system consists of a 2D display, a micro-lens array (MLA), and a TMD. The TMD is composed of square apertures with mirror-reflective inner wall. The light rays pass through the square aperture to form a diffraction spot, and the diffraction light intensity has a Sinc function distribution. Therefore, the TMD can be used as an optical low-pass filter. In a certain imaging range, the main-lobe of the Sinc function distribution is almost unchanged. The TMD has the property of a volumetric optical low-pass filter. It can interpolate the interval between discrete 3D pixels. Therefore, the TMD can be used to eliminate the graininess. The resolution of 3D image is improved by 2.12 times. The experimental results verify the feasibility of the proposed system.

Tm:Sc₂SiO₅-based diode-pumped eye-safe ultrafast laser

Qianqian Hao, Qingguo Wang, Lihe Zheng, Luyang Tong, lina zhao, Jie Liu, Liangbi Su, and Jun Xu

DOI: 10.1364/OL.472091 Received 01 Aug 2022; Accepted 11 Aug 2022; Posted 11 Aug 2022  View: PDF

Abstract: We report a diode-pumped passively mode-locked Tm:Sc₂SiO₅ laser for the first time, to the best of our knowledge. The stable continuous-wave mode-locking is achieved with a semiconductor saturable absorber mirror. Operating at the eye-safe wavelength of 1967.7 nm, the pulsed laser delivers a pulse duration of 16.5 ps with an average output power of 207 mW. At a fundamental repetition frequency of 81 MHz, the signal-to-noise ratio is as high as 70 dB. These results demonstrate the great potential of Tm:Sc₂SiO₅ crystal for ultrashort pulse generation.

Efficient mode converters and filters using asymmetrical directional couplers with subwavelength gratings

Xuefeng Chen, Xiaodong Shi, pengfei qiu, ZiJie Dai, Yu Yu, HAITING ZHANG, Mingyang Chen, Yunxia Ye, XIAOXIAN SONG, Xudong Ren, and JingJing Zhang

DOI: 10.1364/OL.466344 Received 08 Jun 2022; Accepted 11 Aug 2022; Posted 11 Aug 2022  View: PDF

Abstract: Mode-division multiplexing (MDM) is a promising solution to improve the data transmission capacity for the future optical interconnect networks.Mode converters and mode filters play a key role in on-chip MDM systems.Here, we propose and experimentally demonstrate a device, enabling mode conversion and filtering simultaneously, which is composed of asymmetrical directional couplers with subwavelength gratings, in a small footprint of 14.7 $\mu$m $\times$ 1.42 $\mu$m.The device can realize optical mode conversion between the first-order transverse-electric (TE) mode and the fundamental TE mode, and can also filter the fundamental TE mode efficiently.The conversion efficiency is over 95$\%$, with a broad 1-dB bandwidth over 80 nm and a high mode extinction ratio of $>$ 29 dB.As a mode filter, strong mode elimination of $>$ 30 dB is achieved.

Full-duplex visible light communication system using a single channel

Kang Fu, Xumin Gao, QingXi Yin, JiaBing yan, xiangyang ji, and yongjin wang

DOI: 10.1364/OL.470796 Received 18 Jul 2022; Accepted 11 Aug 2022; Posted 11 Aug 2022  View: PDF

Abstract: Multiple quantum well (MQW) III-nitride diodes can emit light and detect light at the same time. In particular, given the overlapping region between the emission spectrum and the detection spectrum of the III-nitride diode, the III-nitride diode can absorb photons of shorter wavelengths generated from another III-nitride diode with the same MQW structure. In this study, a wireless visible light communication system was established using four identical III-nitride diodes with different wavelengths. In this system, two green light diode chips were used to transmit and receive green light signals on both sides. Researchers added two blue light chips with optical filtering in the middle of the optical link to carry out blue light communication, with one end transmitting and one end receiving. Simultaneously, green light was allowed to pass through two blue light chips for optical communication. Combined with a distributed Bragg reflection (DBR) coating, we proposed using four chips in one optical path to carry out optical communication between chips with the same wavelength and used the coating principle to gate the optical wavelength to filter the clutter of green light chips on both sides to make the channel purer and the symbols easier to demodulate. Based on this multifunctional equipment, advanced single-optical path, III-nitride, full-duplex optical communication links can be developed for the deployment of the Internet of Things.

Ultra-high-dynamic range wavefront sensor based on absolute double-slit interferometry

Peyman Soltani, Saifollah Rasouli, and ALI MOHAMMAD KHAZAEI

DOI: 10.1364/OL.469009 Received 28 Jun 2022; Accepted 10 Aug 2022; Posted 11 Aug 2022  View: PDF

Abstract: This Letter reports a new technique for quality testing of steep optical samples by introducing an absolute interferometry method based on a double-slit interference experiment. We determine the quality of the sample with an ultra-high-dynamic range wavefront sensor by determining deformation of central fringe of the double-silt interferometer recorded in two different separations of the slits. The transmission function of the double-slit is implemented on an amplitude spatial light modulator. Therefore the slits' location can be easily displaced over the entire area of the sample's wavefront. We applied the proposed method on two samples; a microscope slide and a conventional ophthalmic lens, and maximum absolute phase variations of 0.33 and 26.7 rad were measured, respectively. Our estimation shows that an absolute phase variation of about 700 rad can be measured with this method.

Fully-connected aperture array design of the segmented planar imaging system

gang liu, Desheng Wen, Wen-Hui Fan, zongxi song, and Zhonghan sun

DOI: 10.1364/OL.465133 Received 31 May 2022; Accepted 10 Aug 2022; Posted 11 Aug 2022  View: PDF

Abstract: Compared to the traditional imaging systems, segmented planar imaging technology has the advantages of low mess, small size and low power in the same resolution situation. To obtain relatively complete frequency domain coverage, the lenslet array requires a large number of lenslets, and the photonic integrated circuit board requires a large number of optical devices, which limits the application and development of the segmented planar imaging technology. In this paper, we introduce a novel design of the photonic integrated circuit to ensure that each lenslet in the lenslet array can form a baseline with any other lenslets. This breaks the barrier between segmented planar imaging technology and the traditional synthetic aperture, giving segmented planar imaging technology a sufficient number of frequency domain samples and a concise photonic integrated circuit structure.

Integrated polarization mode interferometer in 220 nm silicon-on-insulator technology

Christian Schweikert, Anastasia Tsianaka, Niklas Hoppe, Rouven Klenk, Raik Elster, Markus Greul, Mathias Kaschel, Alexander Southan, Wolfgang Vogel, and Manfred Berroth

DOI: 10.1364/OL.463911 Received 17 May 2022; Accepted 10 Aug 2022; Posted 11 Aug 2022  View: PDF

Abstract: A compact integrated and high-efficient polarization mode interferometer in the 220 nm silicon-on-insulator platform is presented. Due to the operation with two polarization modes in a single waveguide, low propagation losses and high sensitivities combined with a small footprint are achieved. The designed and fabricated system with 5 mm long sensing region shows a measured excess loss of only 1.5 dB with an extinction ratio up to 30 dB, while its simulated homogeneous bulk sensitivity can excess 8000 rad/RIU. The combination with a 90° hybrid readout system offers single wavelength operation with unambiguousness for phase shifts up to 2π and constant sensitivity.

Using the generation of Brunel harmonics by elliptically polarized laser pulses for high-resolved detecting lower frequency radiation

Alexander Silaev, Alexander Romanov, and Nikolay Vvedenskii

DOI: 10.1364/OL.462916 Received 02 May 2022; Accepted 09 Aug 2022; Posted 10 Aug 2022  View: PDF

Abstract: We propose to use the generation of even Brunel harmonics (BHs) by optical laser pulses for high-resolved sampling detection of lower-frequency radiation. BHs originate from the acceleration of free electrons produced during tunneling ionization, and BHs pulses durations are much shorter than the laser pulse duration. The latter makes it possible to significantly increase the temporal resolution of detection compared to the second harmonic generated due to the cubic nonlinear response of bound electrons. However, as we show by solving time-dependent Schrödinger equation for the He atom, for linearly-polarized intense laser pulse, the atomic response contains a broadband noise signal that interferes with BHs and allows the detection of very high electric fields only. We show that the nature of this noise is related to the population of the Rydberg states of the atom, which can be effectively suppressed by using elliptical polarization of the gating pulse.

Dark-field spin-Hall effect of light

Nirmal Viswanathan, Upasana Baishya, and Nitish Kumar

DOI: 10.1364/OL.468088 Received 16 Jun 2022; Accepted 09 Aug 2022; Posted 09 Aug 2022  View: PDF

Abstract: While an optical system’s symmetry ensures that the spin-Hall effect of light (SHEL) vanishes at normal incidence, the question of how close to the normal incidence can one reliably measure the SHEL remains open.Here we report simulation and experimental results on the measurement of SHEL at ∼ 0.12^o away from normal incidence in the Fourier plane of a weakly-focused beam of light, reflected at an air-glass interface. Measurement of transverse spin-shift due to < 0.05^o polarizationvariation in the beam cross-section along X- and Y- direction is achieved in the dark-field region of the reflected beam. Our ability to measure the SHEL at near normal incidence with no moving optical – optomechanicalparts and significantly improved sensitivity to phase-polarization variations are expected to enable several applications in the retro-reflection geometry including material characterization with significant advantages.

A phase unwrapping algorithm for segmented phase based on iterative pseudo-phase inpainting

nianfeng wang, Jun Ma, Hui Ding, Cong Wei, Xinyu Miao, Zhonghao Shen, and Caojin Yuan

DOI: 10.1364/OL.469264 Received 30 Jun 2022; Accepted 09 Aug 2022; Posted 10 Aug 2022  View: PDF

Abstract: Segmented phase unwrapping is an intractable problem in phase-shifting technique. To solve the problem, this letter presents an iterative pseudo-phase inpainting algorithm (IPPI). By means of image inpainting, the IPPI can be used to realize the pseudo-phase connecting each other among these phase islands. For the error points existing in the pseudo-phase, with the reference pseudo-phase obtained by introducing the numerical carrier frequency and using the 2-D Fourier transform, the amount of them can be decreased through multiple iterations of phase inpainting. Compared with other methods, the proposed algorithm does not have to do any processing on the effective area of the wrapped phase, which ensures the authenticity of the final result. The simulated and experimental verifications show that the proposed method not only possesses high precision, but also can be applied to the segmented phase with severe noise.

Total absorption and coherent perfect absorption in metal-dielectric-metal resonators integrated into a slab waveguide

Evgeni Bezus, Dmitry Bykov, and Leonid Doskolovich

DOI: 10.1364/OL.470962 Received 22 Jul 2022; Accepted 09 Aug 2022; Posted 10 Aug 2022  View: PDF

Abstract: We propose and investigate integrated metal-dielectric-metal (MDM) resonators operating with semi-guided waves (guided modes of dielectric slab waveguides). The MDM resonators are constituted by two metal strips ``buried'' in the waveguide core layer and separated by a dielectric waveguide segment. We theoretically prove and numerically demonstrate that by a proper choice of the mode incidence geometry, the widths of the metal strips, and the distance between them, it is possible to achieve either total absorption of the incident wave, or coherent perfect absorption (in the case of symmetric incidence of two modes on the structure). The proposed planar MDM resonators may find application as absorbers or filters in integrated optical circuits.

Phase space quantum Wiener-Khintchine theorem

Alfredo Luis and Ainara Alvarez-Marcos

DOI: 10.1364/OL.467687 Received 15 Jun 2022; Accepted 09 Aug 2022; Posted 11 Aug 2022  View: PDF

Abstract: We derive a quantum version of the classical-optics Wiener-Khintchine theorem within the framework of detection of phase-space displacements with a suitably designed quantum ruler. We find that the mutual coherence function is the auto correlation of the Wigner function of the probe and ruler. We obtain an universal equality linking resolution with coherence. Also, we find that the mutual coherence function may coincide with the statistics. This is illustrated with the case of Gaussian states and number states.

Optical Pulling and Pushing Forces via Bloch Surface Waves

Nataliia Kostina, Mihail Petrov, Vjaceslavs Bobrovs, and Alexander Shalin

DOI: 10.1364/OL.464037 Received 18 May 2022; Accepted 08 Aug 2022; Posted 08 Aug 2022  View: PDF

Abstract: Versatile manipulation of nano- and microobjects underlies the optomechanics and a variety of its applications in biology, medicine, and lab-on-a-chip platforms. For flexible tailoring optical forces, as well as for extraordinary optomechanical effects, additional degrees of freedom should be introduced into the system. Here, we demonstrate that photonic crystals are a flexible platform for optical manipulation due to both Bloch surface waves (BSWs) and the complex character of the reflection coefficient paving a way for controlled optomechanical interactions. We demonstrate enhanced pulling and pushing transversal optical forces acting on a single dipolar bead above a one-dimensional photonic crystal due to directional excitation of BSW. Our results demonstrate angle or wavelength assisted switching between BSW-induced optical pulling and pushing forces. Easy-to-fabricate for any desired spectral range photonic crystals are shown to be prospective for precise optical sorting of nanoparticles, which are difficult to sort with conventional optomechanical methods. Our approach opens opportunities for novel optical manipulation schemes and platforms, and enhanced light-matter interaction in optical trapping setups.

Design of a Frequency-multiplexed metasurface with asymmetric transmission

Guanyu Shang, Chunsheng Guan, Kuang Zhang, Qun Wu, Jian Liu, Xuemei Ding, Haoyu Li, Shah Nawaz Burokur, and XUMIN DING

DOI: 10.1364/OL.464854 Received 24 May 2022; Accepted 08 Aug 2022; Posted 09 Aug 2022  View: PDF

Abstract: Metasurfaces presenting diversified functionalities have broadened the prospect of manipulating the phase, amplitude and polarization from the optical to microwave fields. Although the frequency-multiplexing strategy is one of the intuitive and effective approaches to expand the number of channels, demonstrations reported on the combination between directional asymmetric transmission and frequency-multiplexing via an ultrathin flat device are limited. In this study, a novel strategy is proposed to generate four independent holographic images under opposite illumination directions at two operating frequencies, utilizing a single metasurface composed of two types of metallic resonators and one grating layer. Specifically, each scattering channel with independent information makes full use of the whole metasurface. Simulation and experimental results show good agreement, highlighting the attractive capabilities of the multi-functional metasurface platform, which provides more freedom for the manipulation of electromagnetic waves.

Multimode Nonlinear Dynamics in Anomalous Dispersion Spatiotemporal Mode-locked Lasers

Yuhang Wu, Demetrios Christodoulides, and Frank Wise

DOI: 10.1364/OL.471457 Received 25 Jul 2022; Accepted 08 Aug 2022; Posted 09 Aug 2022  View: PDF

Abstract: Spatiotemporal mode-locking in a laser with anomalous dispersion is investigated. Mode-locked states with varying modal content can be observed, but we find it difficult to observe highly multimode states. We describe the properties of these mode-locked states and compare them to the results of numerical simulations. Prospects for the generation of highly-multimode states and lasers based on multimode soliton formation are discussed.

Vortex beam assisted energy up-scaling for multiple-plate compression with a single spiral phase plate

Bo-Han Chen, Hsing-Wei Huang, Ren-Siang Ye, Chih-Hsuan Lu, Kai Chen, and Shang-da Yang

DOI: 10.1364/OL.465661 Received 02 Jun 2022; Accepted 08 Aug 2022; Posted 10 Aug 2022  View: PDF

Abstract: Vortex beam (Laguerre-Gaussian, LG10 mode) is employed to alleviate crystal damage in multiple-plate continuum generation. We successfully compressed 190-fs, 1030-nm pulses to 42 fs with 590 μJ input pulse energy, which is 5.5 times higher than that obtained by a Gaussian beam setup of the same footprint. High throughput (86%) and high intensity-weighted beam homogeneity (>98%) have also been achieved. This experiment confirms the great potential of beam shaping in energy upscaling of nonlinear pulse compression.

Anti-reflection metallic anode enhanced the performance of organic solar cells via across coupling between Fabry-Perot cavity modes and microcavity modes

Yu Jin, ZhongShen Huang, JingXian Jiang, z j wu, Xiaoyan Li, DongMei Gong, and Chunping Xiang

DOI: 10.1364/OL.470114 Received 19 Jul 2022; Accepted 08 Aug 2022; Posted 08 Aug 2022  View: PDF

Abstract: An effective anti-reflection metallic anode with the structure of glass/dielectric2 /Ag (D1D2M) is demonstrated both in small-molecule (SM) and conjugated polymer (CP) organic solar cells (OSCs). The anti-reflection mechanism is investigated by Finite-difference time-domain numerical calculation method and experimental method. By tuning the refractive index and the thickness of D2 layer, the reflection light is confined into the Fabry-Perot (F-P) cavity modes, which effectively enhances the transmittance of D1D2M anode in the wavelength range of 420 nm-800 nm. Compared with the conventional glass/Ag (D1M) anode, the experimental transmittance of D1D2M anode is enhanced by 33.24% at wavelength of 550 nm. By replacing the D1M anode by the D1D2M anode in the OSCs, the F-P cavity modes cross couple with the microcavity modes in the active layers. As a result, the absorption intensity is obviously increasing in a wide angle range (0°≤ θ≤ 85°) in the wavelength range of 475 nm-650 nm and 540 nm-720 nm for the SM and CP OSCs, respectively. The short circuit current and power conversion efficiency of the SM OSC is increased by 25.07% and 27. %, respectively.

Modeling and comparison of bulk and thin-film luminescent solar concentrators based on colloidal perovskite quantum dots

Zida Zheng, Yi Zhang, Xiudong Cao, Gangwei Gu, Ye Tian, and Xiaowei Zhang

DOI: 10.1364/OL.467704 Received 28 Jun 2022; Accepted 08 Aug 2022; Posted 08 Aug 2022  View: PDF

Abstract: Photovoltaic integrated luminescent solar concentrators (LSCs) can be embedded in modern buildings and serve as power-generation units. In this letter, we demonstrate and develop a Monte Carlo ray-tracing model and a numerical description for the performance and loss evaluation of LSCs based on colloidal quantum dots. The performance differences between bulk and thin-film LSCs are systematically analyzed at different sizes and concentrations. It is found that large-area thin-film LSCs generally perform better, which is attributed to the suppression of scattering and the retention of quantum yield by this structure with twice the performance of bulk LSCs.

Telecom-wavelength spectra of a Rydberg state in a hot vapor

wenhui Li, Jinjin Du, Mark Lam, and Wenfang Li

DOI: 10.1364/OL.469443 Received 05 Jul 2022; Accepted 08 Aug 2022; Posted 08 Aug 2022  View: PDF

Abstract: We study telecom-wavelength spectra of a Rydberg state in an atomic vapor with a three-photon excitation scheme. Two lasers of 780 nm and 776 nm are used to pump Rubidium-85 atoms in a vapor cell to the $5D_{5/2}$ state, from which a probe beam of 1292 nm in the O-band telecommunication wavelength drives a transition to the $21F_{7/2}$ Rydberg state. We investigate the probe spectra over the power of pump lasers. The simulation based on a 4-level theoretical model captures the main features of the experimental results. This spectroscopic study paves the way for future experiments of making a direct link between fiber optics and radio transmission via Rydberg atoms.

Perturbing period-one laser dynamics for frequency-modulated microwave generation with external locking

Luan Zhang and Sze-Chun Chan

DOI: 10.1364/OL.469061 Received 28 Jun 2022; Accepted 07 Aug 2022; Posted 08 Aug 2022  View: PDF

Abstract: Period-one (P1) dynamics of two lasers under a common injection are perturbed for externally locked frequency-modulated continuous-wave (FMCW) generation. The first laser is injected into P1 dynamics at microwave frequency f₀, where the dynamics is then perturbed using a slow modulation to induce adiabatic sweeping for FMCW generation and a fast modulation to seed the whole frequency comb for external locking. The second laser is injected into a faster P1 dynamics at 3f₀ that is then perturbed for harmonic locking. The central frequency is boosted to 4f₀ by coherently combining the lasers. FMCW generation with external locking is demonstrated with a sweep range of 6 GHz, comb contrast enhancement to 42 dB, and 4f₀ reaching 80 GHz. Inherent competition between external locking and frequency modulation is unveiled, although an optimal strength is identified for locking the whole comb. Wide tuning of the boosted central frequency is also supported by the P1 dynamics.

Nanovibration detection based on a microsphere

Chunlei Jiang, WEICHENG WANG, Bing Yan, peng chen, Kaichuan Xu, yu sun, zhicheng cong, Taiji Dong, yekun zhou, and Zengbo Wang

DOI: 10.1364/OL.464848 Received 26 May 2022; Accepted 07 Aug 2022; Posted 11 Aug 2022  View: PDF

Abstract: We propose a novel sensor for nanovibration detection based on a microsphere. The sensor consists of a stretched single-mode fiber and a 2 μm microsphere. The light from the optical fiber passes through the microsphere, forming a photonic nanojet (PNJ) phenomenon at the front of the microsphere. The evanescent field in PNJ enhances the reflected light from the measured object to the single-mode fiber microsphere probe (SMFMP). The experiment results show that the system can detect arbitrary nanovibration waveforms in real time, the detection resolution of SMFMP is 1 nm. The voltage signal received and the vibration amplitude shows a good linear relationship within the range of 0–100 nm. The sensor is expected to have potential applications in the field of cell nanovibration detection.

An in-fiber duplex optical antenna and its programmable spectral filter application

Qingguo Song, Yuze Dai, Xiangpeng Xiao, Chen Liu, Haoshuo Chen, Qizhen Sun, Lin Zhang, and Zhijun Yan

DOI: 10.1364/OL.468940 Received 27 Jun 2022; Accepted 07 Aug 2022; Posted 09 Aug 2022  View: PDF

Abstract: In this letter, we have proposed an in-fiber duplex optical antenna based on 45 ° radiated titled fiber grating (RTFG), in which the 45 ° RTFG not only radiates the light from the fiber core to the free space, but also harvests the light from the free space back into the fiber core. Using the finite difference time domain (FDTD) method, we have theoretically analyzed the light recoupling efficiency of RTFG. The simulated results have shown that the RTFG-based optical antennas have a maximum coupling efficiency of 10%. The recoupling wavelength and efficiency are related to the grating period and horizontal incidence angle. Furthermore, we demonstrate a programmable spectral filtering system based on the 45 ° RTFG antennas, which could achieve the filtering with arbitrary spectral shapes. The spectral resolution is 0.08 nm and the insertion loss is around 20dB. The proposed programmable spectral filtering system has a compact structure compared with the traditional filter.

Spatiotemporal chaos induces extreme events in a three-element laterally coupled laser array

YU HUANG, Shuangquan Gu, YAO ZENG, Pei Zhou, and Nianqiang Li

DOI: 10.1364/OL.470524 Received 14 Jul 2022; Accepted 07 Aug 2022; Posted 09 Aug 2022  View: PDF

Abstract: Extreme events (EEs) are predicted for the first time, to the best of our knowledge, in the spatiotemporal chaos dynamics of a three-element laterally coupled laser array. With the help of the statistical and dynamical analyses, we confirm that spatiotemporal chaos induces extreme pulses that are high enough to be identified as EEs. Instead, EEs cannot be found in synchronization chaos. Interestingly, our results show that EEs always preferentially appear in the middle laser as the laser separation ratio is decreased, i.e., increasing the coupling strength, which is followed by the two outer lasers. This thus reveals the importance of the middle laser in the transition between synchronization chaos and spatiotemporal chaos states. Additionally, we show the evolution of EEs in the plane of the pump level and laser separation ratio by calculating the proportion of EEs. Our results build a relation between EEs and the spatiotemporal dynamics, which makes it easy to understand the formation mechanism of EEs.

Color dynamic holographic display based on complex amplitude modulation with bandwidth constraint strategy

Dapu Pi, Jie Wang, Juan Liu, jingnan li, Yutong Sun, Yan Yang, Weirui Zhao, and Yongtian Wang

DOI: 10.1364/OL.469463 Received 07 Jul 2022; Accepted 06 Aug 2022; Posted 08 Aug 2022  View: PDF

Abstract: In this letter, we introduce an encoding method with bandwidth constraint strategy to realize color dynamic holographic display based on complex amplitude modulation. In recording process, red, green, and blue holograms are synthesized into a double-phase color-multiplexing hologram based on double-phase method after the band-limited function is used to extract the local spectrums. In reconstruction process, red, green, and blue lights are combined together to illuminate the double-phase color-multiplexing hologram and 4f system with a filter is introduced to extract the desired spectrums and realize color holographic display. Our proposal is simple, fast, and the display system is compact. It is expected that proposed method could be widely used in holographic field in the future.

Self-starting spatiotemporal mode-locking using Mamyshev regenerators

Changxi Yang, Bo Cao, Xiaosheng Xiao, Chenxin Gao, Chengying Bao, and Yihang Ding

DOI: 10.1364/OL.469291 Received 30 Jun 2022; Accepted 06 Aug 2022; Posted 08 Aug 2022  View: PDF

Abstract: Bridging multi-mode fibers and Mamyshev regenerators holds promises for pulse energy scaling in fiber lasers. However, initialization of a multi-mode Mamyshev oscillator remains a practical challenge. Here we report self-starting spatiotemporal mode-locking (STML) in a multi-mode Mamyshev oscillator without active assistance. The first initialized mode-locking was unstable and stable STML can be attained by increasing the filter separation. Simulations verified the capability of reaching self-starting STML using Mamyshev regenerators and unveiled the impact of filter separation on the self-starting ability.

Design and fabrication of As2S3-based non-quarterwave multi-cavity Fabry-Perot filters with laser-adjustable central wavelength

Antoine Bourgade, Frederic Lemarquis, Antonin MOREAU, Thomas Begou, and Julien Lumeau

DOI: 10.1364/OL.471421 Received 25 Jul 2022; Accepted 05 Aug 2022; Posted 08 Aug 2022  View: PDF

Abstract: We present a thorough study of the use of As2S3 thin films for the fabrication of high performance multi-cavity bandpass filters. We show that such layers can be used inside a non-quarterwave multi-cavity Fabry-Perot structure to produce a local change of the central wavelength of the filter, thanks to the photosensitive properties of this material. In particular, we study the impact of these (refractive index) changes on the spectral performances of the filters and show how to adapt the design of the Fabry-Perot structures to produce a spectral shift without degrading the bandpass profile. Double and three-cavity Fabry-Perot filters are theoretically and experimentally studied.

Gallium Nitride-based Resonant Cavity Light Emitting Diode with Single-longitudinal-mode Emission

Shuyu Zhao, Binbin Xu, Zhenyu Zhao, Dandan Gu, yan zhang, Lv Wenlong, and Xueqin Lv

DOI: 10.1364/OL.469233 Received 30 Jun 2022; Accepted 05 Aug 2022; Posted 08 Aug 2022  View: PDF

Abstract: A novel gallium nitride (GaN)-based resonant cavity light-emitting diode (RCLED) with single-longitudinal-mode light emission was demonstrated. A Ta2O5/SiO2 dielectric distributed Bragg reflector (DBR) with a filter-film structure was adopted as the top mirror. In contrast to the flat-topped reflectivity spectrum of the conventional high-reflective-structure DBR, for this filter-film-structure DBR, there is a light-transmitting concave band on the reflectivity spectrum. Owing to the modulation effect of this band on the output light, a single-peak-mode light emission with a full width at half maximum as low as 0.63 nm was realized. Furthermore, the novel RCLED exhibited better wavelength stability. With an increase in the injection current from 50 to 500 mA, the redshift of the emission peak was only 0.2 nm. The novel RCLED with ultra-narrow-band emission has a high potential for application in optical communication systems and optical fiber sensing applications.

Time-domain Hong-Ou-Mandel interference of quasi-thermal fields and its application in linear optical circuit characterization

Anna Romanova, Konstantin Katamadze, Ivan Dyakonov, Nikolay Skryabin, Alexander Kalinkin, Grant Avosopiants, Yurii Bogdanov, Sergei Kulik, and Leon Biguaa

DOI: 10.1364/OL.464120 Received 19 May 2022; Accepted 05 Aug 2022; Posted 08 Aug 2022  View: PDF

Abstract: We study temporal correlations of interfering quasi-thermal fields, obtained by scattering laser radiation on a rotating ground glass disk. We show that the Doppler effect causes oscillations in temporal cross-correlation function. Furthermore, we propose how to use Hong-Ou-Mandel interference of quasi-thermal fields in the time domain to characterize linear optical circuits.

Optical vortex fields with arbitrary orbital angular momentum orientation

Xindong Meng, Yaodan Hu, Chenhao Wan, and Qiwen Zhan

DOI: 10.1364/OL.468360 Received 22 Jun 2022; Accepted 05 Aug 2022; Posted 05 Aug 2022  View: PDF

Abstract: Optical vortex fields with a tilted phase singularity line are associated with a tilted orbital angular momentum (OAM). In this paper, we propose a method to generate optical vortex fields with arbitrary OAM orientation based on the time-reversal method, the vectorial diffraction theory, and the 4Pi optical configuration. The ability to control the 3D OAM orientation may find applications in optical tweezing, light-matter interaction, and spin-orbital coupling.

Visible-to-ultraviolet-C upconverted photon for multifunction via Ca2SiO4:Pr3+

Pinshu Lv, li leipeng, Zhiqian Yin, Chunzheng wang, and Yanmin Yang

DOI: 10.1364/OL.469090 Received 28 Jun 2022; Accepted 05 Aug 2022; Posted 05 Aug 2022  View: PDF

Abstract: The ultraviolet C (UVC) photon plays a key role in a broad spectrum of fields. With the implementation of the Minamata Convention, searching for a new way to achieve the UVC light is highly desired. Here we develop a material of Ca2SiO4:Pr3+ that can emit the UVC light upon excitation of a 450 nm laser or even a very cheap 450 nm LED. It has been further demonstrated by using a solar blind camera to capture the UVC emission from Ca2SiO4:Pr3+. In addition, the smart anti-counterfeiting and inactivation of Bacillus subtilis applications via Ca2SiO4:Pr3+ are also confirmed.

High-performance waveguide-coupled lateral Ge/Si avalanche photodetector

Yaqing Pang, zhi Liu, Yupeng Zhu, Xiangquan Liu, Diandian Zhang, Chaoqun Niu, Mingming Li, Jun Zheng, Yuhua Zuo, and Buwen Cheng

DOI: 10.1364/OL.466206 Received 07 Jun 2022; Accepted 05 Aug 2022; Posted 05 Aug 2022  View: PDF

Abstract: A high-performance waveguide-coupled lateral APD is experimentally demonstrated without silicon epitaxy and charge layer ion implantation. At the wavelength of 1550 nm, it shows a high responsivity of 48 A/W and a gain-bandwidth product (GBP) of 360 GHz. 25 Gbps wide-open eye diagrams can be observed at various avalanche gains. These outstanding performances indicate the proposed APD with great potential in highspeed optical transceivers for optical links.

Measurement of the coherence-orbital angular momentum matrix of a partially coherent beam

haohui yang, Haiyun Wang, Yahong Chen, Fei Wang, Gregory Gbur, Olga Korotkova, and Yangjian Cai

DOI: 10.1364/OL.467452 Received 09 Jun 2022; Accepted 05 Aug 2022; Posted 05 Aug 2022  View: PDF

Abstract: The recently introduced Coherence-Orbital Angular Momentum (COAM) matrix of a partially coherent beam [Phys. Rev. A 103, 0 529 (2021)] is experimentally measured for the first time. The new methodology based on the Young’s interference experiment with a pair of ring-shaped slits with embedded spiral phases is thoroughly described. By introducing the phase shift of 0 and π / 2 between two ring slits, the real and imaginary parts of the elements of the COAM matrix are obtained by measuring the on-axis spectral density in the far field of the double ring-slit, respectively. We validate our protocol through measuring the COAM matrix of an elliptical Gaussian Schell-model beam which reveals the existence of non-trivial correlations between modes with different topological indices. The experimental results agree reasonably well with the theoretical predictions.

Actively Q-switched radially polarized Ho:YAG laser with an intra-cavity laser-written S-waveplate

Matthew Barber, Peter Shardlow, Yuhao Lei, Peter Kazansky, and W. Clarkson

DOI: 10.1364/OL.467960 Received 15 Jun 2022; Accepted 05 Aug 2022; Posted 05 Aug 2022  View: PDF

Abstract: Nanosecond Q-switched pulses and radial polarization are established standalone techniques for enhanced laser materials processing applications, but are generally challenging to achieve simultaneously at high average power levels. Here, we demonstrate a 20.6 W radially polarized Ho:YAG rod laser which has been actively Q-switched in order to generate 515 μJ, 210 ns pulses at 2097 nm. By utilizing an ultra-low-loss spatially-variant birefringent waveplate (S-waveplate) inside the laser cavity, the linearly polarized fundamental mode has been converted to a radially polarized donut-shaped beam with very high conversion efficiency.

Quantum reflection of single photons in a cold Rydberg atomic gas

Guoxiang Huang, Yao Ou, and Qi Zhang

DOI: 10.1364/OL.469347 Received 04 Jul 2022; Accepted 05 Aug 2022; Posted 05 Aug 2022  View: PDF

Abstract: We propose and analyze a scheme for realizing the quantum reflection of single photons in a cold Rydberg atomic gas via electromagnetically induced transparency, by which a deep and tunable attractive potential well can be prepared by using stored gate photons. Such a scheme is promising for designing dispersion-type single-photon switches, and may be taken as a quantum device for observing the wave and particle natures of photons simultaneously.

Decision Region Partition Aided MLSE for O-Band 65GBaud PAM-4 System over 40km transmission with Severe Bandwidth Constraint

Fan Li, Weihao Ni, Mingzhu Yin, Zhiwei Chen, Wei Wang, Dongdong Zou, Yi Cai, and Zhaohui Li

DOI: 10.1364/OL.469838 Received 06 Jul 2022; Accepted 04 Aug 2022; Posted 05 Aug 2022  View: PDF

Abstract: Maximum likelihood sequence estimation (MLSE) is an optimal solution to realize sequence detection in short reach O-band intensity modulation/direct detection (IM/DD) systems with bandwidth limitation. However, traditional MLSE cannot meet the requirement of low computational complexity digital signal processing (DSP) algorithms in short reach optical interconnect. Although the computational complexity of single-symbol sequence detection is quite low, the capability of combating with the inter symbol interference (ISI) is inadequate. To combine the low computational complexity of single-symbol sequence detection with the high reliability of multi-symbol sequence detection in MLSE, the decision region partition aided MLSE (DRP-MLSE) is proposed in this letter. The performance of the DRP-MLSE has been verified over 40km single mode fiber (SMF) transmission with the baud rate of 60 Gbaud and 65 Gbaud PAM-4 signal. The results show that the DRP-MLSE can realize similar performance to conventional MLSE with negligible penalty but reduce the computational complexity significantly, which indicates the scheme is effective for bandwidth-limited short reach optical interconnection.

Generating Multi-Mode Vortex Beam based on Spoof Surface Plasmon Polaritons

Juan-Feng Zhu, Du Chao-Hai, Zi-Wen Zhang, and Fan-Hong Li

DOI: 10.1364/OL.465695 Received 01 Jun 2022; Accepted 04 Aug 2022; Posted 04 Aug 2022  View: PDF

Abstract: The vortex beam provides a promising alternative for next-generation wireless communication, but it is a long-standing challenge to generate a multi-mode and robust vortex beam. A multi-mode vortex beam emitter with a broad bandwidth is introduced and experimentally verified based on spoof surface plasmon polaritons (SSPP) in this Letter. The SSPP on the helical grating carries multi-mode orbital angular momentum mode and can be converted into high-purity vortex beams via the diffraction of a ring array. The operation frequency and topological charge are determined by that of the SSPP. This emitter can achieve the function of beam-scanning in each radiation band. The beam-scanning and vortex characteristics are experimentally verified. The designed emitter is compact and robust, and we are confident that this work will have great application prospects in the communication systems.

Significant performance enhancement of UV-Vis self-powered CsPbBr₃ quantum dots photodetectors induced by ligand modification and P3HT embedding

Meng Wang, Dehai Liang, Wen Ma, Qionghua Mo, Zhigang Zang, Qingkai Qian, and wensi cai

DOI: 10.1364/OL.468847 Received 24 Jun 2022; Accepted 04 Aug 2022; Posted 04 Aug 2022  View: PDF

Abstract: In this work, we report a novel strategy in improving the performance of UV-Vis self-powered CsPbBr₃ quantum dots (QDs) photodetectors (PDs) by ligand modification and P3HT embedding. Compared with those based on pure QDs, modified PDs show a shorten of response time by nearly 10 times, and an increase of maximum responsivity and specific detectivity for nearly 45 and 97 times, respectively. Such PDs also show a high stability with 90% of the initial photocurrent being maintained even after the storage in ambient air without any encapsulation for 30 days.

A parity-time-symmetric optoelectronic oscillator based on higher order optical modulation

Yu Qiao, Yu Zhang, Ruiqi Zheng, Erwin Chan, Xudong Wang, Xinhuan Feng, Bai-Ou Guan, and Jianping Yao

DOI: 10.1364/OL.469634 Received 04 Jul 2022; Accepted 03 Aug 2022; Posted 04 Aug 2022  View: PDF

Abstract: An optoelectronic oscillator (OEO) for single-frequency microwave generation enabled by broken parity time (PT) symmetry based on higher order modulation using a Mach-Zehnder modulator is proposed and demonstrated. Instead of using two physically separated mutually coupled loops with balanced gain and loss, the PT symmetry is realized using a single physical loop to implement two equivalent loops with the gain loop formed by the beating between the optical carrier and the ±1st order sidebands and the loss loop formed by the beating between the ±1st order sidebands and the ±2nd order sidebands at a photodetector. The gain and loss coefficients are made identical in magnitude by controlling the incident light power to the modulator and the modulator bias voltage. Once the gain/loss coefficient is greater than the coupling coefficient, the PT symmetry is broken and a single-frequency oscillation without using an ultra-narrow passband filter is achieved. The approach is evaluated experimentally. For an OEO with a loop length of 10.1 km, a single-frequency microwave signal at 9.997 GHz with a 55 dB sidemode suppression ratio and -142 dBc/Hz phase noise at a 10 kHz offset frequency is generated. No mode hopping is observed during a 5-hour measurement period.

Sub-1-nm misalignment sensing for lithography with structured illumination

Nan Wang, YI LI, FENG SHA, and YU HE

DOI: 10.1364/OL.468177 Received 20 Jun 2022; Accepted 03 Aug 2022; Posted 05 Aug 2022  View: PDF

Abstract: Lithography for the next generation of integrated-circuit manufacturing at the 3 nm node requires sub-1-nm misalignment measurement accuracy, which is almost impossible for existing systems due to the optical diffraction limit. Herein, we propose a misalignment sensing strategy based on structured illumination. By virtue of the distinctive modulation effect of a Talbot diffractive illuminated field on moiré fringes, the measurement signals can pass unhindered through the optical system and be used for sensing. Experiments are used to demonstrate that the proposed method can implement real-time-lapse (100 Hz) misalignment sensing with an accuracy of sub-1-nm (0.31 nm @ 3σ), making it suitable for various lithography techniques (e.g., proximity, X-ray, projective, and nanoimprint lithography) and fields requiring advanced precision measurement (e.g., quantum measurement, gravitational wave detection, and molecular biology).

Heterogeneously integrated III-V-on-Lithium Niobate broadband light sources and photodetectors

xian zhang, Xiaoyue Liu, Rui Ma, Zichao Chen, Zhuohui Yang, Ya Han, Bing Wang, Siyuan Yu, Ruijun Wang, and Xinlun Cai

DOI: 10.1364/OL.468008 Received 21 Jun 2022; Accepted 03 Aug 2022; Posted 03 Aug 2022  View: PDF

Abstract: Heterogeneous integration of III-V active devices on lithium niobate-on-insulator (LNOI) photonic circuits enable fully integrated transceivers. Here we present the co-integration of InP-based light emitting diodes (LEDs) and photodetectors on LNOI photonics platform. Both devices are realized based on the same III-V epitaxial layers stack adhesively bonded on a LNOI waveguide circuit. The light is evanescently coupled between the LNOI and III-V waveguide via a multiple-section adiabatic taper. The waveguide-coupled LEDs have a 3 dB bandwidth of 40 nm. The photodetector features a responsivity of 0.37 A/W in the 1550 nm wavelength range and a dark current of 9 nA at -0.5 V at room temperature.

Background-penalty-free waveguide enhancement of CARS signal in air-filled anti-resonance hollow-core fiber

Aysan Bahari, Kyle Sower, Kai Wang, Zehua Han, James Florence, Yingying Wang, Shoufei Gao, Ho Wai Howard Lee, Aleksei Zheltikov, Marlan Scully, and Alexei Sokolov

DOI: 10.1364/OL.461614 Received 02 May 2022; Accepted 03 Aug 2022; Posted 03 Aug 2022  View: PDF

Abstract: We study coherent anti-Stokes Raman spectroscopy in air-filled anti-resonance hollow-core photonic crystal fiber, otherwise known as ‘revolver’ fiber. We compare the vibrational coherent anti-Stokes Raman signal of N2, at ∼ 31 cm−1, generated in ambient air (no fiber present), with the one generated in a 2.96 cm of revolver fiber. We show a ∼ 170 times enhancement for the signal produced in the fiber, due to an increased interaction path. Remarkably, the N2 signal obtained in the revolver fiber shows near-zero non-resonant background, due to near-zero overlap between the laser field and the fiber cladding. Through our study, we find that the revolver fiber properties make it an ideal candidate for the coherent Raman spectroscopy signal enhancement.

Quadraxial metamaterial

Denis Sakhno, Eugene Koreshin, and Pavel Belov

DOI: 10.1364/OL.461657 Received 27 Apr 2022; Accepted 03 Aug 2022; Posted 03 Aug 2022  View: PDF

Abstract: We study the dispersion of electromagnetic waves in a spatially dispersive metamaterial with Lorentz-like dependence of principal permittivity tensor components on the respective components of the wave vector performing the analysis of isofrequency contours. The considered permittivity tensor describes triple non-connected wire medium. It is demonstrated that the metamaterial has four optic axes in the frequency range below artificial plasma frequency. The directions of the optical axes do not depend on frequency and coincide with the diagonals of quadrants. The conical refraction effect is observed for all four optic axes.

Encoding information in the mutual coherence of spatially separated light beams

Alfonso Nardi, Shawn Divitt, Massimiliano Rossi, Felix Tebbenjohanns, Andrei Militaru, Martin Frimmer, and Lukas Novotny

DOI: 10.1364/OL.463813 Received 24 May 2022; Accepted 02 Aug 2022; Posted 03 Aug 2022  View: PDF

Abstract: Coherence has been used as a resource for optical communications since its earliest days. It is widely used for multiplexing of data, but not for encoding of data. Here we introduce a coding scheme, which we call ``mutual coherence coding", to encode information in the mutual coherence of spatially separated light beams. We describe its implementation and analyze its performance by deriving the relevant figures of merit (signal-to-noise ratio, maximum bit-rate, and spectral efficiency) with respect to the number of transmitted beams. Mutual coherence coding yields a quadratic scaling of the number of transmitted signals with the number of employed light beams, which might have benefits for cryptography and data security.

Compact cyclic fiber three-mode converter based on mechanical fiber grating

Hangming Fan, Ziheng Zhang, Mengfan Cheng, Qi Yang, Ming Tang, Deming Liu, and Lei Deng

DOI: 10.1364/OL.465641 Received 31 May 2022; Accepted 02 Aug 2022; Posted 03 Aug 2022  View: PDF

Abstract: In this paper, a novel compact cyclic mode converter (CMC) based on mechanical fiber grating is proposed and fabricated to eliminate differential mode group delay and mode-dependent loss in the mode division multiplexing (MDM) transmission system. The proposed CMC can realize cyclical interchange of any input mode among the LP01/LP11a/LP11b modes, which requires only one mechanical grating. The mode conversion is evaluated by observing the mode field patterns of the fiber output. The experimental results prove that the introduction of CMC does not significantly degrade the transmission performance of the photonic lanterns back-to-back system. The insertion loss and the average crosstalk of the whole system are lower than 5dB and -11.3dB. The proposed CMC provides a new method for reducing link damage in the MDM transmission system.

Time-multiplexed method for view density enhancement in integral imaging-based light field displays

Hong Hua and Xuan Wang

DOI: 10.1364/OL.467856 Received 14 Jun 2022; Accepted 02 Aug 2022; Posted 03 Aug 2022  View: PDF

Abstract: Conventional light field display systems based on integral imaging (InI) suffer from a major tradeoff between the view density and spatial resolution. In this letter, a new time-multiplexed method is proposed and demonstrated to enhance the view density of InI-based light field displays. By utilizing a digitally switchable shutter array, the view density and elemental view numbers can be improved multiple times without sacrificing spatial resolution. A four-phase time multiplexed InI-based display prototype was built and demonstrated with a total of 4x4 views over a 6mm by 6mm eyebox (or equivalently a view density of 0.69mm-2 ) and angular resolution of 2 arcmins.

Directional Dependent Magnetooptical Effect and Photonic Spin Hall Effect in Magnetic Weyl Semimetals based Photonic Crystal

xia da, Qi Song, and Huapeng Ye

DOI: 10.1364/OL.470205 Received 25 Jul 2022; Accepted 02 Aug 2022; Posted 03 Aug 2022  View: PDF

Abstract: The ability to generate and manipulate the directional dependent magnetooptical effect and photonic spin Hall effect is essential towards the realistic unidirectional optoelectronic devices, but its exploration remains very scarce. Here we theoretically identify that the multilayer structure whose unit cell is composed of the new emergent magnetic Weyl semimetal layer and two anisotropic dielectric layers has the capability of creating the propagation direction dependent magnetooptical effect and photonic spin Hall effect simultaneously due to its intrinsic lack of space inversion and time reversal symmetries. Specifically, we also realize the continuous manipulation of magnetooptical effect and photonic spin Hall effect in this structure under two opposite directions by the electrical means, which is contributed by the control of the optical properties in magnetic Weyl semimetals by Fermi energy. Our work enables the alternative strategy to achieve the directional dependent optical as well as magnetooptical effects simultaneously, which opens up new perspectives in the fresh field of unidirectional optoelectronics and spin photonics.

Square wave generation in vertical external-cavity Kerr-Gires-Tournois interferometers

Elias Koch, Thomas Seidel, Svetlana Gurevich, and Julien Javaloyes

DOI: 10.1364/OL.468236 Received 21 Jun 2022; Accepted 02 Aug 2022; Posted 02 Aug 2022  View: PDF

Abstract: We study theoretically the mechanisms of square-wave (SW) formation in vertical external-cavity Kerr-Gires-Tournois interferometers in presence of anti-resonant injection. We provide simple analytical approximations for their plateau intensities and for the conditions of their emergence. We demonstrate that SWs may appear via a homoclinic snaking scenario, leading to the formation of complex-shaped multistable SW solutions. The resulting SWs can host localized structures and robust bound-states.

Highly reflective Ru/Sr multilayer mirrors for wavelengths 9–12 nm

Roman Shaposhnikov, Vladimir Polkovnikov, Nikolay Salashchenko, Nikolay Chkhalo, and Sergey Zuev

DOI: 10.1364/OL.469260 Received 04 Jul 2022; Accepted 02 Aug 2022; Posted 02 Aug 2022  View: PDF

Abstract: The results of investigations of new Ru/Sr multilayer coatings optimized for the spectral range 9–12 nm are presented in the paper. Such mirrors are promising optical elements for solar astronomy and for the development of BEUV lithography. A near-normal incidence reflectivity of up to 62.3% (λ = 11.4 nm) right after the synthesis was measured. The reflection coefficient decrease to 56.8% after 5 days of storage in the air with a subsequent stabilization of its value was observed. At a wavelength of λ = 9.34 nm the reflection coefficient was 48.6% after 2 months of storage in air. To date, this is the highest reflectivity measured in this spectral range. The possibility of further increasing the reflectivity is discussed.

Group IV THz Large Area Emitter based on GeSn Alloy

WANG-CHIEN CHEN, Chia-Wei Chang, and Shang Hua Yang

DOI: 10.1364/OL.464541 Received 20 May 2022; Accepted 31 Jul 2022; Posted 05 Aug 2022  View: PDF

Abstract: THz photoconductive emitters based on III-V materials have demonstrated excellent THz radiation properties enabling many unique applications. However, the incompatibility with the complementary-metal-oxide-semiconductor (CMOS) foundry fabrication process and the challenging growth condition hampers THz photoconductive emitter from large-scale productization. To address this limitation, we proposed GeSn alloy as the photoconductive material candidate through the CMOS-compatible epitaxy instrument. The GeSn photoconductor features a 518 cm²/V-s mobility and a 7187 cm¯¹ absorption coefficient at the wavelength of 1560nm, resulting in sufficient ultrafast photocurrent generation for THz radiation. As a result, the GeSn THz emitter provides over a bandwidth of 2 THz and a 40 dB signal-to-noise ratio, which shows its potential in realizing mass-producible, cost-effective THz integrated systems with CMOS technology.

Over-20-octaves-bandwidth ultra-low-intensity-noise 1064 nm single-frequency fiber laser based on a comprehensive all-optical technique

Yuxin Sun, Qilai Zhao, Chun Zeng, Changsheng Yang, Zhouming Feng, Changhe Wang, Wei Lin, Qinyuan Zhang, Zhongmin Yang, and Shanhui Xu

DOI: 10.1364/OL.468045 Received 16 Jun 2022; Accepted 30 Jul 2022; Posted 03 Aug 2022  View: PDF

Abstract: An over-20-octaves-bandwidth ultra-low-intensity-noise 1064 nm single-frequency fiber laser (SFFL) is demonstrated based on a comprehensive all-optical technique. With a joint action of booster optical amplifier (BOA) and reflective Yb-doped fiber amplifier (RYDFA), twofold optical gain saturation effects, respectively occurred in the media of semiconductor and fiber, have been synthetically leveraged. Benefitting from the gain dynamics in complementary time scales, i.e., nanosecond-order carrier lifetime in BOA and millisecond-order upper-level lifetime in RYDFA, the relative intensity noise (RIN) is reduced to -150 dB/Hz from 0.2 kHz to 350 MHz, which exceeds 20-octaves bandwidth. Remarkably, a maximum suppressing ratio of >54 dB is obtained, and the RIN in the range of 0.09~10 GHz reaches -161 dB/Hz which is only 2.3 dB above the shot-noise limit. This broad-bandwidth ultra-low-intensity-noise SFFL can serve as an important building block for squeezed light generation, space laser communication, space gravitational wave detection, etc.

Fluorescence saturation imaging microscopy: molecular fingerprinting in live cells using two-photon absorption cross-section as a contrast: supplemental document

Boris Yakimov, ALEXEY GAYER, Eugene Maksimov, Anton Maydykovskiy, Evgeniy Mamonov, Tatyana Murzina, Victor Fadeev, and Eugeniy Shirshin

DOI: 10.1364/OL.465605 Received 31 May 2022; Accepted 30 Jul 2022; Posted 05 Aug 2022  View: PDF

Abstract: Imaging of molecular-specific photophysical parameters such as fluorescence intensity, emission band shape or fluorescence decay parameters are widely used in biophysics. Here we propose the method for quantitative mapping of another molecular-specific parameter in living cells, two-photon absorption cross-section, based on the fluorescence saturation effect. Using model dye solutions and cell culture, we show that the analysis of the fluorescence signal dependencies on the intensity of two-photon excitation within the range typical for routine two-photon microscopy experiments allows one to reconstruct two-photon absorption cross-section maps across the sample. We believe the absorption cross-section contrast visualized by proposed fluorescence saturation imaging microscopy (FSIM) could be a new tool for studying processes in living cells and tissues.

Temperature-insensitive optical sensors based on two cascaded identical microring resonators

Guoshuai Su, Mingyu Li, Zhiping Yang, Jiayi Xie, Yuxia Song, and Jian-Jun He

DOI: 10.1364/OL.463589 Received 11 May 2022; Accepted 29 Jul 2022; Posted 01 Aug 2022  View: PDF

Abstract: We demonstrate a novel temperature-insensitive optical sensor based on two cascaded identical microring resonators (CIMRR) in this paper. The structural parameters of the reference ring and sensing ring are designed to be identical. The upper cladding in the sensing windows of two rings is removed. With different microfluidic channels, the reference ring and sensing ring are exposed to the reference solution and reagent sample, respectively. For the wavelength interrogation experiments in the transmission spectrum contrast ratio and the low-cost intensity interrogation experiments, the sensitivities of the refractive index (RI) sensing are 3402.4 dB/RIU and 1087.3 dB/RIU, respectively, while the temperature sensitivities are as low as 0.0 dB/K and 0.0124 dB/K, respectively.

High bandwidth thermo-optic phase-shifters for lithium niobate-on-insulator photonic integrated circuits

Andreas Maeder, Fabian Kaufmann, David Pohl, Jost Kellner, and Rachel Grange

DOI: 10.1364/OL.469358 Received 11 Jul 2022; Accepted 29 Jul 2022; Posted 01 Aug 2022  View: PDF

Abstract: Phase-shifters are key components of large scale photonic integrated circuits. For lithium niobate-on-insulator (LNOI), thermo-optic phase-shifters (TOPS) have emerged as a more stable and compact alternative to the common electro-optic phase-shifters (EOPS), which are prone to anomalous behaviour and drifting at low frequencies. Here, we model and experimentally characterize the influence of geometry on the performance of metal strip TOPS. Compared to EOPS, a 10-fold reduction of the voltage-length product is measured and bandwidths beyond 100 kHz are demonstrated, while keeping the footprint as low as 0.04 mm². This shows the potential of TOPS as small-scale building blocks for stable tuning and switching in LNOI photonic circuits.

120-fs single-pulse generation from stretched-pulse fiber Kerr resonators

Xue Dong, Zhiqiang Wang, and William Renninger

DOI: 10.1364/OL.454498 Received 24 Jan 2022; Accepted 28 Jul 2022; Posted 02 Aug 2022  View: PDF

Abstract: Fiber Kerr resonators are simple driven resonators with desirable wavelength and repetition rate flexibility for generating ultrashort pulses for applications including telecommunications, biomedicine, and materials processing. However, fiber Kerr resonators to date often generate longer pulses and require more complicated techniques for generating single pulses than would be desirable for applications. Here we address these limits by demonstrating robust single-pulse performance with 120-fs pulse durations in fiber Kerr resonators based on stretched-pulse solitons. Through matching numerical and experimental studies, stretched-pulse soliton performance is found to strongly depend on the total cavity length, and the optimum length is found to depend on the drive, Raman scattering, and the total pulse stretching. By designing the cavity for this optimum with the described setup, stable stretched-pulse solitons with 120-fs duration are experimentally observed. In addition, soliton trapping is demonstrated with a pulsed drive source despite large intracavity breathing and single-pulse performance is observed. Robust with high performance single-pulse generation is a critical step toward useful femtosecond pulse generation.

Advanced laser heterodyne spectroradiometer utilizing optical amplification for high-resolution sensitive measurements of atmospheric CO2 column absorption

Hao Deng, Renshi Li, Hao Liu, Yabai He, Chenguang Yang, Li xiang, Zhenyu Xu, and Ruifeng Kan

DOI: 10.1364/OL.468198 Received 17 Jun 2022; Accepted 28 Jul 2022; Posted 03 Aug 2022  View: PDF

Abstract: A novel performance-enhanced laser heterodyne spectroradiometer has been developed by utilizing a semiconductor optical amplifier to amplify the collected weak solar radiation in an optical fiber. High-resolution measurements of atmospheric carbon dioxide column absorption are used to validate the technique and performance of the developed instrument. The implementation of optical amplification has achieved a 7.7-times improvement in sensitivity for atmospheric greenhouse gas sensing measurements.

Light bullets in moiré lattices

Yaroslav Kartashov

DOI: 10.1364/OL.471022 Received 20 Jul 2022; Accepted 27 Jul 2022; Posted 11 Aug 2022  View: PDF

Abstract: We predict that photonic moiré lattices produced by two mutually twisted periodic sublattices in the medium with Kerr nonlinearity can support stable three-dimensional light bullets localized in both space and time. Stability of light bullets and their properties near propagation constant cutoff are tightly connected with the properties of linear spatial eigenmodes supported by moiré lattice. These modes undergo localization-delocalization transition (LDT) upon increase of the depth of one of the sublattices forming moiré lattice, but only for twist angles corresponding to incommensurate, aperiodic moiré structures. Above LDT threshold such incommensurate moiré lattices support stable light bullets without energy threshold, that remain spatially well-localized and extend only in time, when their propagation constant approaches the cutoff. In contrast, commensurate, or periodic, moiré lattices arising at Pythagorean twist angles, whose eigenmodes are delocalized Bloch waves, can support stable light bullets only above certain energy threshold. Light bullets near the cutoff in commensurate lattices become extended in both space and time. The difference in energy thresholds for the formation of stable light bullets in commensurate and incommensurate lattices is most pronounced near LDT threshold. Moiré lattices below LDT threshold cannot support stable light bullets for our parameters. Our results illustrate that periodicity/aperiodicity of the underlying lattice is a crucial factor determining stability properties of the nonlinear three-dimensional states.

Ultrafast 3D histological imaging based on minutes-timescale tissue clearing and multidirectional selective plane illumination microscopy

Jiajia Chen, Zhenhong Du, Chenhao Xu, Xiao Xiao, Wei Gong, and Ke Si

DOI: 10.1364/OL.463705 Received 13 May 2022; Accepted 27 Jul 2022; Posted 27 Jul 2022  View: PDF

Abstract: Conventional histopathological examinations are time-consuming, labor-intensive, and insufficient to depict 3D pathological features due to finite imaging depth and throughput. Here we report an ultrafast 3D histological imaging scheme based on an optimized selective plane illumination microscopy (mSPIM), a minutes-timescale clearing method (FOCM) and deep learning-based image enhancement algorithm (SRACNet) to realize histological examination of kidney tissues. Our scheme enables 1-minute clearing and imaging (up to 900 mm2/min) at micron-level resolution for 200-μm thick mouse kidney sections. With H&E analog, we demonstrated the detailed 3D morphological connections between glomeruli and their surrounding kidney tubules, which was difficult to be identified in conventional 2D histological images. This study will facilitate clinical histological preparation and disease diagnosis, while promoting the high-throughput 3D digital pathology.

Single-shot and noninvasive imaging through scattering medium and around corners beyond 3D memory effect

YingJie Shi, Enlai Guo, Lianfa Bai, and Jing Han

DOI: 10.1364/OL.470222 Received 12 Jul 2022; Accepted 27 Jul 2022; Posted 28 Jul 2022  View: PDF

Abstract: The three-dimensional(3D) memory effect(ME) has been shown to exist in a variety of scattering scenes. Limited by the scope of ME, speckle correlation technology only can be applied in a small imaging field of view(FOV) with a small depth of view(DOF). In this letter, an untrained neural network is constructed used as an optimization tool to restore the targets beyond the 3D ME range. The autocorrelation consistency relationship and the generative adversarial strategy are combined. Only single frame speckle and unaligned real targets are needed for online optimization, therefore, the neural network does not need to train in advance. Furthermore, the proposed method does not need to conduct additional modulation for the system. This method can reconstruct not only hidden targets behind the scattering medium but also targets around corners.The combination strategy of the generative adversarial framework with physical priors used to decouple the aliasing information and reconstruct the target will provide inspiration for the field of computational imaging.

All-polarization maintaining and high-energy fiber optical parametric chirped-pulse amplification system using a solid core photonic hybrid fiber

LAFARGUE Léa, Florent Scol, Emmanuel Hugonnot, Geraud Bouwmans, Olivier Vanvincq, and Etienne Poeydebat

DOI: 10.1364/OL.468791 Received 24 Jun 2022; Accepted 27 Jul 2022; Posted 01 Aug 2022  View: PDF

Abstract: We present an all-fiber optical parametric chirped-pulse amplification integrated system delivering a single mode polarized beam. The system makes use of a specifically designed solid-core photonic hybrid fiber (i.e. combining Modified Total Internal Reflection and Photonic BandGap mechanisms) that ensures sufficient birefringence to maintain the signal polarization. Moreover, the fiber combines a large mode area to handle energetic pump pulses (without generating damage neither unwanted non-linear effects) and weak dispersion to generate parametric gain bands broad enough to amplify ultrashort pulses. Efficient parametric process allows obtaining a very high gain (> 45 dB) with an output pulse energy reaching µJ range at 1053 nm by using a single 5 m hybrid fiber amplifier.

Clamp-type quartz tuning fork enhanced photoacoustic spectroscopy

Qian Wu, Haohua Lv, leqing Lin, Hongpeng Wu, Marilena Giglio, Wenguo Zhu, Yongchun Zhong, Angelo Sampaolo, Pietro Patimisco, Lei Dong, Vincenzo Spagnolo, JianHui Yu, and Huadan Zheng

DOI: 10.1364/OL.464334 Received 20 May 2022; Accepted 26 Jul 2022; Posted 05 Aug 2022  View: PDF

Abstract: In this letter, clamp-type quartz tuning fork enhanced photoacoustic spectroscopy (Clamp-type QEPAS) was proposed and realized through the design, realization, and test of clamp-type quartz tuning forks (QTFs) for photoacoustic gas sensing. The clamp-type QTF provides a wavefront shaped aperture with a diameter up to 1 mm, while keeping Q factors > 104. This novel design results in a more than ten times increase of the area available for laser beam focusing for the QEPAS technique with respect to a standard QTF. The wavefront-shaped clamp-type prongs effectively improve the acoustic wave coupling efficiency. The achieved results open the way to the exploitation of clamp-type QTFs with light sources characterized by poor beam qualities such as high-power LEDs or THz QCLs sources. The possibility to implement a micro-resonator system for clamp-type QTF was also investigated. A ~30 times signal-to-noise enhancement has been obtained with a single-tube acoustic micro resonator length of 8 mm, ~20% shorter than the dual-tube micro-resonator employed in conventional QEPAS system.

The performance and complexity analysis using a sparse deep learning method for indoor terahertz transmission

govind sharan yadav, pouya torkaman, XUAN-WEI MIAO, Kai-Ming Feng, and Shang Hua Yang

DOI: 10.1364/OL.468331 Received 21 Jun 2022; Accepted 24 Jul 2022; Posted 01 Aug 2022  View: PDF

Abstract: In this letter, we propose and experimentally validate a sparse deep learning method (SDLM) for terahertz indoor wireless over-fiber by transmitting a 16-QAM OFDM signal over 15-km single-mode fiber (SMF) and a wireless link distance of 60-cm at 135-GHz through a cost-effective intensity-modulated direct detection (IM-DD) communications systems. The proposed SDLM utilizes the L1-regularized mechanism to the cost function, which not only improves performance but also reduces complexity when compared with traditional Volterra nonlinear equalizer (VNLE), sparse VNLE, and conventional DLM. Our experimental findings show that the proposed SDLM provides viable options for successfully mitigating nonlinear distortions and outperforms conventional VNLE, conventional DLM and SVNLE by 76%, 72% and 61% complexity reduction for 8-QAM without losing signal integrity.

Higher order Exceptional Points in optical lattices

Dimitrios Kaltsas, Ioannis Komis, and Konstantinos Makris

DOI: 10.1364/OL.459398 Received 29 Mar 2022; Accepted 23 Jul 2022; Posted 25 Jul 2022  View: PDF

Abstract: One of the hallmarks of non-Hermitian photonics is theexistence of unique degeneracies, the so called higherorder exceptional points (HEPs). So far HEPs have beenexamined only in finite coupled systems. In this paperwe present a systematic way to construct infinite opticalwaveguide lattices that exhibit higher order exceptionalpoints of any order. The spectral properties and thesensitivity of these lattices around such points are inves-tigated by employing the method of pseudospectra.

Fourier spatial transform-based method ofsuppressing motion noises in OCTA

Yue Zhang, Wanrong Gao, and Chenxia Xie

DOI: 10.1364/OL.464501 Received 24 May 2022; Accepted 22 Jul 2022; Posted 22 Jul 2022  View: PDF

Abstract: A large amount of lateral noise will be generated in blood flow imaging with the optical coherence tomography angiography (OCTA) due to the presence of muscle shaking, heartbeat, and respiration, resulting in the deterioration of images. In this paper, to the best of our knowledge, for the first time, the spatial frequency information of the motion noise in the blood flow signal region is used to remove the motion noise and false connections in the blood flow signal region. The effectiveness of the proposed adaptive denoising algorithm is verified by the imaging of finger blood flow. It is found that the OCTA with different projection methods have improved signal-to-noise ratio and contrast-to-noise ratio after applying our algorithm. It is also found that the visual effect of the original blood flow image based on standard deviation projection is better, but the mean projection is the most sensitive to the algorithm, and the average signal-to-noise ratio and contrast-to-noise ratio are improved by 5.7dB and 8.9dB, respectively.

High efficiency second harmonic generation in coupled nano Fabry-Perot thin resonators

Tomasz Matthia, Baptiste Fix, Lena Soun, Christophe Dupuis, Nathalie Bardou, and Patrick Bouchon

DOI: 10.1364/OL.465602 Received 01 Jun 2022; Accepted 17 Jul 2022; Posted 19 Jul 2022  View: PDF

Abstract: In this paper we experimentally demonstrate SHG enhancement in thin 1D periodic plasmonic nanostructures on GaAs in the infrared spectral range. Due to the properly designed coupling of horizontal Fabry-Perot nanoresonators that occur inside these structures, the obtained conversion efficiencies go up to the 10¯⁷ W¯¹ range. Moreover, we demonstrate that the engineering of the plasmonic nanoantennas dimensions on the same GaAs layer can lead to SHG enhancement for pump wavelength ranging from 2.8 µm to 3.3 µm.

Giant terahertz pulling force within an evanescent field propelled by wave coupling into radiation and bound modes

Mauro Cuevas, Hernán Ferrari, and Carlos Zapata-Rodriguez

DOI: 10.1364/OL.460202 Received 07 Apr 2022; Accepted 06 Jul 2022; Posted 11 Jul 2022  View: PDF

Abstract: Manipulation of subwavelength objects by engineering the electromagnetic waves in the environment medium is pivotal for several particle handling techniques. In this letter, we theoretically demonstrate the possibility of engineering a compact and tunable plasmon-based terahertz tweezer using a graphene monolayer that is deposited on a high-index substrate. Under total-internal-reflection illumination, such device is shown to be capable of inducing an enhanced rotating polarizability thus enabling directional near-field coupling into the graphene plasmon mode and radiation modes in the substrate. As a result of the total momentum conservation, the net force exerted on the particle points in a direction opposite to the pushing force of the exciting evanescent field. Our results can contribute to novel realizations of photonic devices based on polarization dependent interactions between nanoparticles and electromagnetic mode fields.

High dynamic range electro-optic dual-comb interrogation of optomechanical sensors

David Long, Benjamin Reschovsky, Thomas LeBrun, Jason Gorman, Joseph Hodges, David Plusquellic, and Jasper Stroud

DOI: 10.1364/OL.460028 Received 05 Apr 2022; Accepted 09 Jun 2022; Posted 14 Jun 2022  View: PDF

Abstract: An interleaved, chirped electro-optic dual comb system is demonstrated for rapid, high dynamic range measurements of cavity optomechanical sensors. This approach allows for the cavity displacements to be interrogated at measurement times as fast as 10 µs over ranges far larger than can be achieved with alternative methods. While the performance of this novel readout approach is evaluated with an optomechanical accelerometer, this method is applicable to a wide range of applications including temperature, pressure, and humidity sensing as well as acoustics and molecular spectroscopy.

Complex-valued decision feedback equalizer for optical IMDD signals with adaptive manipulations in time and amplitude domains

Lin Sun, Jiawang Xiao, Yi Cai, Gangxiang Shen, Ning Liu, and Chao Lu

DOI: 10.1364/OL.462524 Received 03 May 2022; Accepted 05 Jun 2022; Posted 06 Jun 2022  View: PDF

Abstract: In this work, we innovatively equalize optical intensity-modulated and directly-detected (IMDD) PAM-4 signals using a complex-valued decision feedback equalizer (CDFE). Through mapping the adjacent symbols of PAM-4 signals onto the complex domain, the influence of strongest inter-symbol interference (ISI) can be alleviated during the decision process in DFE, which effectively alleviate the burst-error propagation when signals are noisy. Moreover, signal-adaptive manipulations of DFE parameters on both time- and amplitude-domain are performed by using an ultra-stable timing recovery and level-adaptive decision. Performance evaluations are made on VCSEL-modulated and MMF-transmitted 100-Gbps optical PAM-4 signals. Based on experimental results of the short-reach optical communication, the proposed DFE outperforms the traditional DFE with 0.5-dB system power budget gain at the 7%OH-FEC BER threshold.