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Accepted papers to appear in an upcoming issue

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Free-space beam shaping and steering based on a silicon optical phased array

Wenbo Ren, Qingqing Liang, Jijun Feng, Haipeng Liu, Jianhua Hu, Shuo Yuan, Xincheng Xia, Wei Jiang, Qiwen Zhan, and Heping Zeng

DOI: 10.1364/PRJ.494546 Received 02 May 2023; Accepted 30 Sep 2023; Posted 02 Oct 2023  View: PDF

Abstract: In this study, we present a method for free-space beam shaping and steering based on a silicon optical phased array, which addresses the theoretical limitations of traditional bulk optics. We analyze the theoretical beam propagation properties with modulation of the applied phase. Different beam profiles can be shaped by varying the phase combination, and a quasi-Bessel beam can be generated with a cubic change to the phase modulation. The simulated results are further validated by experimental realization, which coincide well with each other. Beam steering can be achieved with a field of view as large as 140°, which has potential benefits for practical applications. The presented method is expected to have broad prospects for applications in optical communications, free-space optical interconnects, and light detection and ranging.

Spiking information processing in a single fabricated photonic spiking neuron with double integrated electronic dendrites

YAHUI ZHANG, Shuiying Xiang, Xingxing Guo, Yanan Han, Yuechun Shi, Xiangfei Chen, Genquan Han, and Yue Hao

DOI: 10.1364/PRJ.499767 Received 05 Jul 2023; Accepted 29 Sep 2023; Posted 02 Oct 2023  View: PDF

Abstract: Dendrites, as branches of neurons, play a vital role in spiking information processing. However, the investigation of dendritic computations and the fabrication of dendritic devices in photonic spiking neural networks (SNNs) remain open problems. Here, we fabricate and integrate two dendrites and one soma in a single Fabry–Pérot laser with an embedded saturable absorber (FP-SA) neuron. Note that, the two intrinsic electrodes of gain section and saturable absorber section in the FP-SA neuron are defined as two dendrites for two ports of information reception, with one electronic dendrite receiving excitatory stimuli and the other receiving inhibitory stimuli. The information receipted by two electronic dendrites is integrated nonlinearly in FP-SA neuron, generating spikes for photonic SNNs. The properties of frequency encoding and spatiotemporal encoding are investigated experimentally on the FP-SA neuron with two electronic dendrites. For SNNs equipped with FP-SA neurons, the range of weights between presynaptic neurons and postsynaptic neurons is from negative to positive values because of the ability of integrating excitatory and inhibitory stimuli in FP-SA neurons. Compared with SNN with all-positive weights due to the only connection to gain section of photonic neurons, the recognition accuracy of Iris flower data is improved numerically in SNN consisting of FP-SA neurons. The results in the paper valuable insights into the development of photonic SNNs and the potential applications in multi-functional integrated photonic SNN chips, pattern classification.

High-speed Adaptive Photoacoustic Microscopy

Linyang Li, Wei Qin, Tingting Li, Junning Zhang, Baochen Li, and Lei Xi

DOI: 10.1364/PRJ.499598 Received 03 Jul 2023; Accepted 28 Sep 2023; Posted 28 Sep 2023  View: PDF

Abstract: Optical-resolution photoacoustic microscopy (OR-PAM) is capable of observing the distribution of optical absorbers inside bio-tissues with a high spatial resolution of micrometers. Unfortunately, due to the employment of a tight optical focus, it suffers from a limited depth of field (DOF), making it challenging to achieve high-resolution imaging of targets with arbitrary surfaces. Here, we propose a high spatiotemporal adaptive photoacoustic focusing mechanism through integrating a high-speed optical focuser, a time-of-flight contour deriving algorithm and the rotary-scanning photoacoustic microscopy. The developed system, named high-speed adaptive photoacoustic microscopy (HA-PAM), features an ultrashort focus-shifting time of 5 ms, and an enlarged DOF of up to 5 mm. With the assistance of the proposed mechanism, we can achieve a homogeneous lateral resolution of 6 μm over a 10-mm circular imaging domain within 5 seconds. We demonstrate the advantages of HA-PAM through imaging phantoms with curved surfaces, subcutaneous tumor-bearing mice, resected rabbit kidneys and pulsating mouse brains. The imaging results suggest that this approach provides a high and consistent spatial resolution for imaging bio-tissues with arbitrary surfaces without sacrificing the imaging speed, and has the potential to extend the fundamental and clinical applications of OR-PAM.

Pulse packages and self-chaotic operation in a circular-sided square microcavity laser

Jian-Cheng Li, Jin-Long Xiao, Yue-De Yang, Youling Chen, and Yong-Zhen Huang

DOI: 10.1364/PRJ.489371 Received 07 Mar 2023; Accepted 28 Sep 2023; Posted 29 Sep 2023  View: PDF

Abstract: Self-chaotic dual-mode and tri-mode microcavity lasers have been proposed and demonstrated for high-speed random number generation recently. Here, we report the characteristics of pulse packages and self-chaos operation for a dual-mode circular-sided square microcavity laser. In addition to the mode interaction between the fundamental and first order transverse modes, we observed pulse packages due to the mode beating of degenerated modes for the first time. Moreover, a successive route from periodic-one, periodic-three states to chaos is first experimentally illustrated by increasing injection current. The chaotic state is observed over a current range of 10 mA, and the maximum chaos effective bandwidth of 22.4 GHz is realized with a flatness of ± 4 dB. Chaotic characteristics are also investigated for different longitudinal modes, which indicates that the self-chaotic microlaser can provide robust parallel chaotic outputs for practical application.

A super-simplified fiber scanner for cellular-resolution endoscopic imaging

Lu He, Xijie Li, Jie Yang, Longjie Jiang, Qian Liu, and Ling Fu

DOI: 10.1364/PRJ.499747 Received 05 Jul 2023; Accepted 26 Sep 2023; Posted 27 Sep 2023  View: PDF

Abstract: Fiber scanners are portable and miniaturized laser scanning devices for a wide range of applications, such as endoscopic probes for biomedical imaging. However, in order to achieve different resonant frequencies for 2D actuation, existing fiber scanners have complex actuation mechanisms and structures, resulting in an obstacle for endoscopic imaging. By exploiting the intrinsic difference in bending stiffness of non-symmetrical fibers, we present the most simplified fiber scanner to date, containing only a single piezoelectric bimorph and a single non-symmetrical fiber with a 1D actuator for 2D laser scanning. 5-fps Lissajous scan is achieved with a scanning range of >300 μm and a driving voltage of ≤10 Vpp. The ultra simplified structure of the fiber scanner enables a miniaturized optical probe with a diameter of 1.9 mm, and image quality comparable to that of commercial microscopes. Taking advantage of its ease of manufacture and low cost, the fiber scanner offers a transformative way forward for disposable endoscopic probes that avoid the risk of cross-infection during endoscopic inspections.

Universal dynamics and deterministic motion control of de-coherently seeded temporal dissipative solitons via spectral filtering effect

ZILONG LI, Huanhuan Liu, zimin zha, Lei Su, Perry Shum, and Hairun Guo

DOI: 10.1364/PRJ.500126 Received 26 Jul 2023; Accepted 26 Sep 2023; Posted 27 Sep 2023  View: PDF

Abstract: Temporal dissipative solitons generated from optical systems exist in various soliton states, showing great potential in optical encoding and sensing fields. Motion control of such temporal dissipative solitons have been achieved in both coherently and de-coherently seeded systems. Most previous reports have demonstrated passive control and records of some fixed switching moments. However, active motion control of temporal dissipative solitons remains an outstanding challenge. Here, we report a universal dynamics and deterministic motion active control of temporal dissipative solitons in mode-locked fiber laser by introducing the spectral filtering effect. We investigate single switching dynamics of soliton disassembly as well as complex switching dynamics of soliton assembly. Moreover, we demonstrate completed switching dynamics of soliton molecules by filter scanning and spot a significant hysteresis between red-shift and blue-shift. The actively soliton motion control enabled by filter scanning highlights the potential prospects of encoding and sensing using soliton molecules.

On-chip sorting of orbital angular momentum beams using Bloch surface wave structures

Nannan LI, Qi Zou, Yizhi Lan, Yaqi Wang, Jun Zhang, Xiaocong Yuan, Michael Somekh, Changjun Min, and Fu Feng

DOI: 10.1364/PRJ.502760 Received 10 Aug 2023; Accepted 21 Sep 2023; Posted 22 Sep 2023  View: PDF

Abstract: Owing to their unique optical properties and new degrees of freedom, orbital angular momentum (OAM) beams have been applied in various fields. Detection of the topological charges (TCs) of OAM beams is the key step for their applications. However, on-chip sorting of OAM beams with large TCs still remains a challenge. In this paper, Bloch surface wave (BSW) structures with five semi-ring shaped nanoslits are modelled. A spatial separation of 135 nm on the chip is obtained between two neighboring OAM states. OAM beams with TCs up to 35 can be successfully sorted by the BSW structures, which is much larger than that using metallic structures (only 7). BSW structures exhibit superior OAM sorting performances than metallic structures. We systematically show how the lower attenuation of BSW structures leads to far superior separation ability compared to surface plasmons propagating on metallic structures. In addition, sorting of two OAM beams with different TCs simultaneously can be achieved in this way. Our results reveal that BSW structures should be an excellent solution for OAM sorting with large TCs, which is beneficial for applications in integrated on-chip devices and optical communications.

Long distance all-optical logic operations through a single multimode fiber empowered by wavefront shaping

Zhipeng Yu, Tianting Zhong, huanhuan Li, Haoran Li, Chi Man Woo, shengfu cheng, Shuming Jiao, Honglin Liu, Chao Lu, and Puxiang Lai

DOI: 10.1364/PRJ.499523 Received 05 Jul 2023; Accepted 20 Sep 2023; Posted 22 Sep 2023  View: PDF

Abstract: Multimode fibers (MMFs) are a promising solution for high-throughput signal transmission in the time domain. However, crosstalk among different optical modes within the MMF scrambles input information and creates seemingly random speckle patterns at the output. To characterize this process, a transmission matrix (TM) can be used to relate input and output fields. Recent innovations use TMs to manipulate the output field by shaping the input wavefront for exciting advances in deep-brain imaging, neuron stimulation, quantum networks, and analog operators. However, these approaches consider input/output segments as independent, limiting their use for separate signal processing, such as logic operations. Our proposed method which makes input/output segments as interdependent adjusts the phase of corresponding output fields using phase bias maps superimposed on input segments. Coherent superposition enables signal logic operations through a 15-meter-long MMF. In experiments, a single optical logic gate containing three basic logic functions and cascading multiple logic gates to handle binary operands is demonstrated. Bitwise operations are performed for multi-bit logic operations, and multiple optical logic gates are reconstructed simultaneously in a single logic gate with polarization multiplexing. The proposed method may open new avenues for long-range logic signal processing and transmission via multimode fibers.

Photonic Crystal Slabs with Maximal Chiroptical Response Empowered by Bound States in the Continuum

Qilin Duan, Yali Zeng, Yuhang Yin, jinying xu, Zhining Chen, Zhanlei Hao, Huanyang Chen, and Yi Liu

DOI: 10.1364/PRJ.497954 Received 14 Jun 2023; Accepted 18 Sep 2023; Posted 19 Sep 2023  View: PDF

Abstract: To enhance the strength of chiral light-matter interaction for practical applications, the chirality and quality factors (Q-factors) of current methods need to be strengthened simultaneously. Here, we propose a design of photonic crystal slabs (PhCs) supporting chiral bound states in the continuum (BIC) of transverse electric (TE) and transverse magnetic (TM) mode, exhibiting maximal chiroptical responses with high Q-factors and near-unity circular dichroism (CD = 0.98). Different from the past, the PhCs we employed only have reduced in-plane symmetry and can support simultaneously chiral quasi-BICs (q-BICs) of TE and TM mode with two-dimensional ultra-strong external and internal chirality. Based on the temporal coupled-mode theory, two analytical expressions of CD of chiral q-BICs response are revealed, which are consistent with the simulation results. Furthermore, we elucidate these results within the charge-current multipole expansion framework and demonstrate that the co-excitation of higher-order multipole electric/magnetic modes is responsible for near-perfect CD. Our results may provide more flexible opportunities for various applications requiring high Q-factors and chirality control, such as chiral lasing, chiral sensing, and enantiomer separation.

Characterizing Bubble Interaction Effects in Synchronous-Double-Pulse Laser Ablation for Enhanced Nanoparticle

Farbod Riahi, Alexander Bussmann, Carlos Doñate Buendía, Stefan adami, Nikolaus Adams, Stephan Barcikowski, and Bilal Gökce

DOI: 10.1364/PRJ.498204 Received 15 Jun 2023; Accepted 17 Sep 2023; Posted 18 Sep 2023  View: PDF

Abstract: To further advance nanomaterial applications and reduce waste production during synthesis, greener and sustainable production methods are necessary. Pulsed laser ablation in liquids (PLAL) is a green technique that enables the synthesis of nanoparticles. However, there is a discrepancy between practical PLAL scenarios where dozens of cavitation bubbles are simultaneously interacting, but research is mainly looking at isolated cavitation bubbles. To address this challenge, this study uses synchronous-double-pulse-PLAL to understand bubble interaction effects on the nanoparticle size. By adjusting the lateral separation of the pulses relative to the maximum bubble size, an inter-pulse separation is identified where nanoparticle size fourfold. The cavitation bubble pair interaction is recorded using a unique co-axial diffuse shadowgraphy system. This system allows to record the bubble pair interaction from top and side, enabling the identification of the bubble´s morphology, lifetime, volumetric, and displacement velocity. It is found that the collision and collapse of the bubbles generated at a certain inter-pulse separation results in a larger nanoparticle size. The experimentally observed trends are confirmed by high-resolution numerical simulations. This study serves as a starting point to bridge the gap between upscaled multi-bubble practices and fundamental knowledge concerning the determinants that define the final nanoparticle size.

Gate voltage control of helicity-dependent photocurrent and polarization detection in (Bi1-xSbx)2Te3 topological insulator thin films

Chen Shenzhong, jinling Yu, Hong Xiyu, Kejing Zhu, Y. H. Chen, Shuying Cheng, Yunfeng Lai, Ke He, and Qikun Xue

DOI: 10.1364/PRJ.494932 Received 11 May 2023; Accepted 14 Sep 2023; Posted 18 Sep 2023  View: PDF

Abstract: Optical helicity provides us with an effective means of controlling the helicity-dependent photocurrent in the spin-momentum-locked surface states of topological insulators (TIs). Also, the TIs show the potential in polarization detection as an intrinsic solid-state optical chirality detector for easier integration and fabrication. However, the complex photoresponses with both circular photogalvanic effect, linear photogalvanic effect and photon drag effect in the TIs prevent it from direct chirality detection of the elliptical polarized light. Here, by fitting with the theoretical models to the measured photocurrents, the microscopic origin of different components of the helicity-dependent photocurrent has been demonstrated. We show a comprehensive study of the helicity-dependent photocurrent in (Bi1-xSbx)2Te3 thin films of different thicknesses as a function of the light incident angle and the gate-tuned chemical potential. The observation of the light incident angle dependence of the helicity-dependent photocurrent provides us with a polarization detection strategy using a TI thin film without the use of any additional optical elements, and the detection accuracy can be enhanced by gate tuning. Additionally, the Stokes parameters can be extracted by arithmetic operation of photocurrents measured with different incident angles and gating voltages for complete characterization of the polarization states of a light beam. By this means, we realize the polarization detection and the Stokes parameters analysis using a single device. Our work provides an alternative solution for developing miniaturized intrinsic polarization-sensitive photodetectors.

Time reversal of the optical branched flow on the curved surface

Weifeng Ding, Zhaoying Wang, and Chaokai Yang

DOI: 10.1364/PRJ.502521 Received 03 Aug 2023; Accepted 12 Sep 2023; Posted 12 Sep 2023  View: PDF

Abstract: The phenomenon of branched flow has attracted researchers since its inception, with recent observations of the light branching on soap bubbles. However, previous studies have predominantly focused on the flat space-time, overlooking the effect of surface curvature on branched flows. In this paper, we explore the branched flow phenomenon of light on a rough curved surface called constant Gaussian curvature surfaces (CGCSs). Compared with flat space, it demonstrates that the first branching point advances due to the focusing effect of positive curvature of the surface. Furthermore, unlike on flat space, optical branches on curved surfaces do not consistently become chaotic during its transmission in a random potential field. On the contrary, the "entropy" decreases at specific positions, which reveals a sink flow phenomenon following the generation of branched flows. This result highlights the time inversion characteristics of CGCS. At last, it is also demonstrated that the anomalous entropy reduction is related to the transverse and longitudinal coherence transformations of light. We suppose, these efforts would fuel the further investigation of the thermodynamic evolution and spatiotemporal inversion of random caustics, as well as their future application in information transmission of random potentials in curved space-time.

High-speed 2D beam steering with Large Field of View based on Thin-Film Lithium Niobate Optical Phased Array

Wenlei Li, Xu Zhao, Jianghao He, Hao Yan, Bingcheng Pan, Zichen Guo, Xiang E Han, Jingye Chen, Daoxin Dai, and Yaocheng Shi

DOI: 10.1364/PRJ.502439 Received 02 Aug 2023; Accepted 10 Sep 2023; Posted 12 Sep 2023  View: PDF

Abstract: On-chip optical phased array (OPA) is considered as a promising solution for next generation solid-state beam steering. However, most of the reported OPAs suffer from low operating bandwidth, making them limited in many applications. We propose and demonstrate a high-speed 2D scanning OPA based on thin-film lithium niobate phase modulators with traveling-wave electrodes. The measured modulation bandwidth is up to 2.5 GHz. Moreover, aperiodic array combined with a slab grating antenna is also used to suppress the grating lobes of far-field beam, which enables large field of view (FOV) as well as small beam width. A 16-channel OPA demonstrate an FOV of 50° × 8.6° and a beam width of 0.73° × 2.8° in the phase tuning direction and the wavelength scanning direction, respectively.

Large-area ultracompact pixelated aluminium wire-grid-based metamaterials for Vis-NIR full-Stokes polarization imaging

Yuanyi Fan, Jinkui Chu, Ran Zhang, Chuanlong Guan, and jianying liu

DOI: 10.1364/PRJ.494728 Received 04 May 2023; Accepted 07 Sep 2023; Posted 12 Sep 2023  View: PDF

Abstract: The study of pixelated metamaterials that integrate both the functions of linear and circular polarization filters is rapidly growing due to the need for full-Stokes polarization imaging. However, there is a lack of large-area, ultracompact pixelated full-Stokes metamaterials with excellent performance, especially circular polarization filters with high extinction ratio, broad operating bandwidth, and a low-cost, high-quality, efficient manufacturing process, which limits the practical applications of pixelated full-Stokes metamaterials. In this study, we propose a universal design and fabrication scheme for large-area, ultracompact pixelated aluminum wire-grid-based metamaterials used in Vis-NIR full-Stokes polarization imaging. The aluminum wire-grid is designed as a linear polarization filter with an average linear polarization extinction ratio of 36000 and a circular polarization filter with an average circular polarization extinction ratio of 110 in Vis-NIR. A large-area, ultracompact 320×320 pixelated aluminum wire-grid-based full-Stokes metamaterial is fabricated using nano imprint lithography and nano transfer printing with the advantages of low cost and high efficiency. This metamaterial is used to achieve full-Stokes polarization imaging with errors within 8.77%, 12.58%, 14.04%, and 25.96% for Stokes parameters S0, S1, S2, and S3, respectively. The inversion errors of the compensated Stokes parameters can be reduced to 0.21%, 0.21%, 0.42%, and 1.96%, respectively.

Intracavity dynamics-based optical phase amplifier with over tenfold amplification

Yidong Tan and Mingwang Tian

DOI: 10.1364/PRJ.494882 Received 08 May 2023; Accepted 06 Sep 2023; Posted 06 Sep 2023  View: PDF

Abstract: The relative phase change between two light fields can be used as a fundamental parameter to measure the physical quantity causing this change. Therefore, amplifying the relative phase change becomes attractive to improve the measurement resolution. Phase amplification using many-body entangled state (NOON state) is a well-known method, nevertheless, the preparation process for high-number NOON state is difficult and sensitive to optical loss. Here, we propose and experimentally verify a concise phase amplification method with a tolerance of about 5 orders of magnitude for optical loss. The method is based on the optical feedback-induced intracavity harmonics generation effect to amplify the phase change by 11 times, which reaches the highest level of about 10 experimentally reached in NOON states. Furthermore, the 20th intracavity harmonic is generated when the reinjected photon number increases, indicating that 20 times phase amplification is attainable. The proposed method is prospect in the precision measurement applications.

Significant enhancement of multiple resonant sidebands in a soliton fiber laser

Tianqi Zhang, Fanchao Meng, Qi Yan, Chuanze Zhang, Zhixu Jia, WP Qin, Guanshi Qin, and Huailiang Xu

DOI: 10.1364/PRJ.496302 Received 29 May 2023; Accepted 05 Sep 2023; Posted 05 Sep 2023  View: PDF

Abstract: Resonant sidebands in soliton fiber lasers have garnered substantial interest in recent years due to their crucial role in understanding soliton propagation and interaction dynamics. However, most previous studies and applications are restricted to focusing on only the first few low-order resonant sidebands because higher-order sidebands usually decay exponentially as their wavelengths shift far away from the soliton center and are negligibly weak. Here we report numerically and experimentally significant enhancement of multiple resonant sidebands in a soliton fiber laser mode-locked by nonlinear polarization evolution mechanism. The birefringence and the gain profile of the laser cavity were shown to be critical for this novel phenomenon. Multiple intense resonant sidebands were generated whose maximum intensity was more than 30 dB higher than that of the soliton, which is the highest yet reported. To accurately predict the wavelengths of all high-order resonant sidebands, an explicit formula was derived by taking the third-order dispersion effect into account. The temporal features of multiple orders of resonant sidebands were characterized, which all exhibit exponentially decaying leading edges. This study provides new insight into understanding the properties of high-order resonant sidebands in a soliton laser and opens new possibilities for constructing multi-wavelength laser sources.

Experimental demonstration of phase sensitive multimode continuous variable quantum key distribution with improved secure key rate

Zikang su, jintao wang, Dajian Cai, Xiaojie Guo, Dawei Wang, and Zhaohui Li

DOI: 10.1364/PRJ.485654 Received 16 Jan 2023; Accepted 04 Sep 2023; Posted 05 Sep 2023  View: PDF

Abstract: We develop and experimentally demonstrate a phase-sensitive continuous variable quantum key distribution (CVQKD) system with improved secure key rate. This is achieved by using multimode coherent states with phase-conjugated subcarrier (PCS) modulation and phase sensitive detection. The local oscillator (LO) for detection is regenerated from a polarization-multiplexed carrier wave via optical injection locking. The LO is phase locked to the signal by active feedback. The proposed scheme has a higher classical information capacity at a given number of received photons and exhibits a higher secure key rate when applying the security analysis of the GG02 protocol. We perform the experimental implementation of the proposed scheme and the results confirm the higher secret key rate and better excess noise tolerance of the new scheme compared to the other existing schemes.

Detection of per- and polyfluoroalkyl water contaminants with multiplexed 4D microcavities sensor

Anton Saetchnikov, Elina Tcherniavskaia, Vladimir Saetchnikov, and Andreas Ostendorf

DOI: 10.1364/PRJ.496737 Received 01 Jun 2023; Accepted 01 Sep 2023; Posted 05 Sep 2023  View: PDF

Abstract: The per- and polyfluoroalkyl substances (PFAS) constitute a group of organofluorine chemicals treated as the emerging pollutants and currently are of particularly acute concern. These compounds have been employed intensively as surfactants over multiple decades and are already to be found in surface and ground waters at amounts sufficient to have an effect on the human health and ecosystems. Because of the carbon-fluorine bonds the PFAS have an extreme environmental persistence and their negative impact accumulates with further production and penetration into the environment. In Germany alone, more than thousands sites have been identified to be contaminated with PFAS and thus timely detection of PFAS residues is becoming a high-priority task. In this paper we report on the high performance optical detection method based on whispering gallery modes microcavities applied for the first time for detection of the PFAS contaminants in aqueous solutions. A self-sensing boosted 4D microcavity fabricated with two-photon polymerization is employed as an individual sensing unit. On example of the multiplexed imaging sensor with multiple hundreds of simultaneously interrogated microcavities we demonstrate the possibility to detect the PFAS chemicals representatives at the level of down to 1 ppb.

The design strategy of a high-performance multispectral stealth material based on the 3D meta-atom

PINGPING MIN, ZICHENG SONG, TIANYU WANG, Victor Ralchenko, Yurong He, and Jiaqi Zhu

DOI: 10.1364/PRJ.498640 Received 04 Jul 2023; Accepted 01 Sep 2023; Posted 05 Sep 2023  View: PDF

Abstract: In this paper, a 3D meta-atom-based structure is constructed for the multifunctional compatible design of visible, infrared, and microwave. To achieve high-performance, a novel dispersion tailoring strategy is proposed. Through the incorporation of multiple controllable losses within the 3D meta-atom, the dispersion characteristics are tailored to the desired target region. The effectiveness of the strategy is verified with an error rate of less than 5%. A proof-of-concept prototype is designed and fabricated, exhibiting high visible transparency, low infrared emission of 0.28, and microwave ultra-broadband absorption with a fractional bandwidth of 150% under 2.7 GHz to 18.7 GHz. This work contributes a novel design strategy for the development of high-performance multispectral stealth materials with wide applications.

Broadband Infinite-Q Plasmons Enable Intense Smith-Purcell Radiation

Zi-Wen Zhang, Du Chao-Hai, Yu-Lu Lei, Juan-Feng Zhu, and Pu-Kun Liu

DOI: 10.1364/PRJ.499770 Received 05 Jul 2023; Accepted 01 Sep 2023; Posted 05 Sep 2023  View: PDF

Abstract: With the rapid development of nanophotonics for enhancing free electron radiation, bound states in the continuum (BICs) have emerged as a promising approach for emitting intense Smith-Purcell radiation (SPR) with enhanced intensity. However, current BIC-based methods are limited to single-frequency operation, thereby restricting their applications requiring spectral and angular tunability, such as particle detectors and light sources. To overcome this limitation, this work proposes a novel approach for constructing plasmonic BICs over a broad spectral range in symmetry-broken systems. By leveraging the high-Q resonances near the BICs, we achieve intense SPR with broadband tunability, potentially improving the radiation intensity by six orders compared to traditional methods. Experimentally, we validate the construction of BIC using plasmonic antennas and achieve broadband demonstration. Our proposed concept can be extended to other plasmonic or guided-wave systems, paving the way toward compact and efficient free-electron sources in hard-to-reach frequency regimes.

Arbitrary terahertz chirality construction and flexible manipulation enabled by anisotropic liquid crystal coupled chiral metasurfaces

Xin Jiang, Yun-Yun Ji, Fei Fan, Song-Lin Jiang, Zhi-Yu Tan, Hunjun Zhao, Jie -Rong Cheng, and Shengjiang Chang

DOI: 10.1364/PRJ.501047 Received 20 Jul 2023; Accepted 01 Sep 2023; Posted 05 Sep 2023  View: PDF

Abstract: Chiral metasurfaces integrated with active materials can dynamically control the chiral response of electromagnetic waves, making them highly significant in physics, chemistry, and biology. Herein, we theoretically proposed a general and feasible design scheme to develop a chiral metadevice based on bilayer anisotropic metasurface composite monolayer liquid crystal (LC) that can construct and flexibly manipulate arbitrary terahertz (THz) chirality. When the twist angle between the anisotropic axes of two metasurfaces θ is not 0°, the spatial mirror symmetry of the chiral metadevice is severely broken, resulting in a strong THz chiral response. In addition, the introduction of anisotropic LCs not only enhances the chiral response of the metadevice, but also induces the inversion regulation and frequency tunability of the chirality. More importantly, by optimizing the twist angle θ, we can flexibly design the arbitrary chiral response and operating frequency, thereby promoting the emergence of various chiral manipulation devices. The experimental results also show that the maximum circular dichroism can reach −33 dB at 0.94 THz and flip to 28 dB at 0.69 THz by rotating LC optical axis from the x-axis to the y-axis, with the maximum operating frequency tunable range of ~120 GHz. We expect this design strategy can create new possibilities for the advancement of active THz chiral devices and their applications, including chiral spectroscopy, molecular recognition, biosensing, and fingerprint detection.

Multi-mode microcavity frequency engineering through a shifted grating in a photonic crystal ring

Xiyuan Lu, Yi Sun, Ashish Chanana, Usman Javid, Marcelo Davanco, and Kartik Srinivasan

DOI: 10.1364/PRJ.500375 Received 21 Jul 2023; Accepted 30 Aug 2023; Posted 31 Aug 2023  View: PDF

Abstract: Frequency engineering of whispering-gallery resonances is essential in microcavity nonlinear optics. The key is to control the frequencies of the cavity modes involved in the underlying nonlinear optical process to satisfy its energy conservation criterion. Compared to the conventional method that tailors dispersion by the cross-sectional geometry, thereby impacting all cavity mode frequencies, grating-assisted microring cavities, often termed as photonic crystal microrings, provide more enabling capabilities through mode-selective frequency control. For example, a simple single period grating added to a microring has been used for single-frequency engineering in Kerr optical parametric oscillation (OPO) and frequency combs. Recently, this approach has been extended to multi-frequency engineering by using multi-period grating functions, but at the cost of increasingly complex grating profiles that require challenging fabrication. Here, we demonstrate a simple approach, which we term as shifted grating multiple mode splitting (SGMMS), where spatial displacement of a single period grating imprinted on the inner boundary of the microring creates a rotational asymmetry that frequency splits multiple adjacent cavity modes. This approach is easy to implement and presents no additional fabrication challenges than an un-shifted grating, and yet is very powerful in providing multi-frequency engineering functionality for nonlinear optics. We showcase an example where SGMMS enables OPO generation across a wide range of pump wavelengths in a normal-dispersion device that otherwise would not support OPO.

Experimental demonstration of microring resonator based on Germanium-on-insulator platform at mid-infrared range

Jinha Lim, Joonsup Shim, Inki Kim, and SangHyeon Kim

DOI: 10.1364/PRJ.495076 Received 09 May 2023; Accepted 28 Aug 2023; Posted 28 Aug 2023  View: PDF

Abstract: We first demonstrate a microring resonator (MRR) based on a Germanium-on-insulator (Ge-OI) at the mid-infrared (mid-IR) range. The ring resonator was numerically designed to have a high-quality factor at 4.18 μm to 4.22 μm wavelength in the fundamental TE mode. According to our design, the Ge-OI ring resonator was fabricated by the direct wafer-bonding technology with a yttria (Y₂O₃) buried oxide layer, which is transparent at the mid-IR region, for the bonding interface and the electron beam lithography. The experimental resonant characteristic was obtained by using our fiber-based mid-IR measurement setup. As a result, the extinction ratio and insertion loss of the Ge-OI MRR was 22.77 dB and 1.204 dB, respectively. Furthermore, the free-spectral range of the device was 5.29 nm, and the loaded quality (Q) factor of 94,528 (176,158 of intrinsic Q factor) was extracted by the nonlinear least square method. We believe that the first demonstration of our Ge-OI MRR suggests a valuable opportunity to implement multi-purpose devices such as an optical sensor, switch, and filter in the mid-infrared range.

Biophotonic rogue waves in red blood cell suspensions

Yuxuan Ren, Joshua Lamstein, Chensong Zhang, Claudio Conti, Demetrios Christodoulides, and Zhigang Chen

DOI: 10.1364/PRJ.496013 Received 23 May 2023; Accepted 26 Aug 2023; Posted 28 Aug 2023  View: PDF

Abstract: Rogue waves are ubiquitous in nature, appearing in a variety of physical systems ranging from acoustics, microwave cavities, optical fibers and resonators, to plasmas, superfluids and Bose-Einstein condensates. Unlike nonlinear solitons, rogue waves are extreme events that can happen even without nonlinearity, for example by spontaneous synchronization of waves with different spatial frequencies in a linear system. Here, we report the observation of rogue-wave-like events in human disc-like red blood cell (RBC) suspensions, characterized by an abnormal L-shaped probability distribution. The biophotonic extreme events occur without requiring optical nonlinearity, but rather from the constructive interference of Mie-scattered waves from healthy RBCs, whose biconcave shape and mutable orientation give rise to a time-dependent random phase modulation to an incident laser beam. We numerically simulate the beam propagation through the colloidal system with added disorder in both spatial and temporal domains to mimic the random scattering due to Brownian motion. In addition, at high power levels, nonlinear beam self-focusing is also observed, leading to a dual-exponential probability distribution associated with the formation of multiple soliton-like spots. Such rogue wave events may also be observed in environments with cells of other species such as swimming bacteria, and the understanding of underlying physics may lead to unexpected biophotonic applications.

Whispering-gallery optical microprobe for photoacoustic imaging

Jialve Sun, Shuijing Tang, Jiawei Meng, and Changhui Li

DOI: 10.1364/PRJ.495267 Received 12 May 2023; Accepted 23 Aug 2023; Posted 24 Aug 2023  View: PDF

Abstract: Optical ultrasonic probes, exemplified by Fabry–Pérot cavities on optical fibers, have small sizes, high sensitivity, and pure optical characteristics, making them highly attractive in high-resolution ultrasonic/photoacoustic imaging especially in near-field or endoscopic scenarios. Taking a different approach, we demonstrate an ultrasensitive and broadband ultrasound microprobe formed by an optical whispering-gallery-mode polymer microcavity coupled to a U-shaped microfiber. With the high-quality factors (>10^6), the noise equivalent pressure of the ultrasound microprobe reaches 1.07 mPa/√Hz with a record broadband response to 150 MHz and a large detection angle of 180 degrees. Our results show that this optical microprobe can overcome the strong decay resulting from ultrasound diverging and medium absorption through short working distances. And we further demonstrate high-quality in-vivo whole-body photoacoustic imaging of a zebrafish larva. Our implementation provides a new strategy to develop miniature ultrasound detectors and holds great potential for broad applications.

Resonance cavity-enhanced all-optical switching in a GdCo alloy absorber

Yunqing Jiang, Zhang Xiaoqiang, Houyi cheng, Huan Liu, Yong Xu, Anting Wang, Cong Wang, Stéphane Mangin, and weisheng zhao

DOI: 10.1364/PRJ.497939 Received 13 Jun 2023; Accepted 23 Aug 2023; Posted 24 Aug 2023  View: PDF

Abstract: In spintronic applications, there is a constant demand for lower power consumption, high densities, and fast writing speed of data storage. All-optical switching (AOS) is a technique that uses laser pulses to switch the magnetic state of a recording medium without any external devices, offering unsurpassed recording rates and a simple structure. Despite extensive research on the mechanism of AOS, low energy consumption and fast magnetization reversing remain challenging engineering questions. In this paper, we propose a newly designed cavity-enhanced AOS in GdCo alloy, which promotes optical absorption by 2-fold, leading to a 50% reduction in energy consumption. Additionally, the time-resolved measurement shows that the time of reversing magnetization reduces at the same time. This new approach makes AOS an ideal solution for extremely energy-effective and fast magnetic recording, paving the way for future developments in high-speed, low-power-consumption data recording devices.

Multiple conical odd harmonics from filament-inscribed nanogratings

Robertas Grigutis, Vytautas Jukna, Gintaras Tamosauskas, and Audrius Dubietis

DOI: 10.1364/PRJ.494150 Received 26 Apr 2023; Accepted 21 Aug 2023; Posted 23 Aug 2023  View: PDF

Abstract: We report on the observation of conical third, fifth, seventh and ninth harmonics that gradually emerge during the supercontinuum generation by filamentation of femtosecond mid-infrared pulses in lithium strontium hexafluoroaluminate (LiSAF) crystal. We show that the generation of conical odd harmonics is an optical signature of light-driven material reorganization in the form of volume nanogratings at the site irradiated by repetitive femtosecond filaments. The angle-resolved spectral measurements demonstrate remarkably broad spectra of individual odd harmonics, benefiting from spectrally broadened pump pulse (supercontinuum) and reveal that filament-inscribed nanogratings represent photonic structures that are able to provide ultrabroad phase matching bandwidths covering the wavelength range from the ultraviolet to the near infrared. We propose the scenario which interprets the generation of conical fifth, seventh and ninth harmonics as nanograting-phase-matched cascaded non-collinear four-wave mixing processes.

High robust spatio-temporal wavefront prediction with mixed graph neural network in adaptive optics

Ju Tang, Ji Wu, jiawei zhang, Mengmeng Zhang, Zhenbo Ren, Jianglei Di, liuseng hu, Guodong Liu, and Jianlin Zhao

DOI: 10.1364/PRJ.497909 Received 13 Jun 2023; Accepted 19 Aug 2023; Posted 21 Aug 2023  View: PDF

Abstract: Time-delay problem, which is introduced by the response time of hardware for correction, is a critical and non-ignorable problem of adaptive optics (AO) systems. It will result in significant wavefront correction errors while turbulence changes severely or system responses slowly. Predictive AO is proposed to alleviate the time-delay problem for more accurate and stable corrections in the real time-varying atmosphere. However, the existing prediction approaches either lack the ability to extract non-linear temporal features, or overlook the authenticity of spatial features during prediction, leading to poor performance in generalization. Here, we propose a mixed graph neural network (MGNN) for spatio-temporal wavefront prediction. MGNN introduces the Zernike polynomial for model enhancement and takes the inherent covariance matrix as physical constraints. It takes advantage of convolutional and graph convolutional layers for temporal feature catch and spatial feature analysis, respectively. Especially, the graph constraints from covariance matrix and the weight learning of transformation matrix promote the establishment of a realistic internal spatial pattern from limited data. Furthermore, its prediction accuracy and robustness to varying unfamiliar turbulences, including the generalization from simulation to experiment, are all discussed and verified. By comparing with two conventional methods, the outperformance of proposed method is demonstrated by root mean square error (RMS). With the prediction of MGNN, the mean and standard deviation values of RMS in conventional AO are reduced by 54.2% and 58.6% at most, respectively. The stable prediction performance makes it suitable for wavefront predictive correction in astronomical observation, laser communication, and microscopic imaging.

Have different kinds of photon-pair sources the same indistinguishability in quantum silicon photonics?

Jong-Moo Lee, Alessio Baldazzi, Matteo Sanna, Stefano Azzini, Joon Tae Ahn, Myung-Lae Lee, Youngik Sohn, and Lorenzo Pavesi

DOI: 10.1364/PRJ.489869 Received 16 Mar 2023; Accepted 18 Aug 2023; Posted 21 Aug 2023  View: PDF

Abstract: In the same silicon photonic integrated circuit, we compare two types of integrated degenerate photon-pair sources (microring resonators or waveguides) by means of Hong-Ou-Mandel (HOM) interference experiments. Two nominally identical microring resonators are coupled to two nominally identical waveguides which form the arms of a Mach-Zehnder interferometer. This is pumped by two lasers at two different wavelengths to generate by spontaneous four-wave mixing degenerate photon pairs. In particular, the microring resonators can be thermally tuned in or out of resonance with the pump wavelengths, thus choosing either the microring resonators or the waveguides as photon-pair sources, respectively. In this way, an on-chip HOM visibility of 94\% with microring resonators and 99\% with straight waveguides is measured. We compare our experimental results with theoretical simulations of the joint spectral intensity and the purity of the degenerate photon pairs. We verify that the visibility is connected to the sources' indistinguishability, which can be quantified by the overlap between the joint spectral amplitudes (JSA) of the photon pairs generated by the two sources. We estimate a JSA overlap of 98\% with waveguides and 89\% with microring resonators.

High speed silicon photonic electro-optic Kerr modulation

Jonathan peltier, Weiwei Zhang, Leopold Virot, Christian Lafforgue, Lucas Deniel, Delphine Marris-Morini, GUY AUBIN, Farah Amar, Denh Tran, Xingzhao Yan, Callum Littlejohns, Carlos Alonso Ramos, David Thomson, Graham Reed, and Laurent Vivien

DOI: 10.1364/PRJ.488867 Received 28 Feb 2023; Accepted 07 Aug 2023; Posted 08 Aug 2023  View: PDF

Abstract: Silicon-based electro-optic modulators contribute to ease the integration of high-speed and low-power consumption circuits for classical optical communications and data computations.Beyond the plasma dispersion modulation, an alternative solution in silicon is to exploit the DC Kerr effect, which generates an equivalent linear electro-optical effect enabled by applying a large d.c. electric field.Although some theoretical and experimental studies have shown its existence in silicon, limited contribution relative to plasma dispersion have been achieved in high speed modulation so far.This paper presents high-speed optical modulation based on the DC Kerr effect in silicon PIN waveguide.The contributions of both plasma dispersion and Kerr effects have been analyzed in diferent waveguide configurations and we demonstrated that the Kerr induced modulation is dominant when a high external DC electric field is applied in PIN waveguide.High-speed optical modulation response is analyzed and eye diagrams up to 80 Gbits/s in NRZ format are obtained under a d.c. voltage of 30 V.This work paves the way to exploit Kerr effect to generate high speed Pockels-like optical modulation.

Submicron optical frequency combs based on surface plasmon polaritons metallic multi-ring resonator

Zhitao Huang, Fangyuan Ma, Keqian Dong, Shizhong Yue, Chao Li, Yulin Wu, Junhui Huang, Xu Han, Jiaqian Shun, Zhaofeng Li, Kong Liu, Zhijie Wang, Yong Lei, Shengchun Qu, and Zhanguo Wang

DOI: 10.1364/PRJ.488160 Received 20 Feb 2023; Accepted 03 Jul 2023; Posted 14 Aug 2023  View: PDF

Abstract: Optical frequency combs (OFCs) have great potential in communications, especially in dense wavelength division multiplexing. However, the size of traditional OFCs based on conventional optical microcavities or dispersion fibers is at least tens of microns, far larger than that of nanoscale electronic chips. Therefore, reducing the size of OFCs to match electronic chips is of necessity. Here, for the first time, we introduce surface plasmon polaritons (SPPs) to the construction of OFCs to realize a miniature device. The thickness of our device is reduced below 1 μm. Though the presence of SPPs may induce ohmic and scattering loss, the threshold of the device is obtained as 9 μW, comparable to the conventional device. Interestingly, the response time is 13.2 ps, much faster than the optical counterparts. This work provides a feasible strategy for the miniaturization of OFCs.