Michelson interferometer-based coherent demodulation for joint time and frequency transfer

qingwei liu, Hao Gao, Jiameng Dong, Zhaohui Wang, Rui Zhang, Guohua Wu, Song Yu, and Bin Luo

DOI: 10.1364/OL.547452 Received 08 Nov 2024; Accepted 06 Mar 2025; Posted 06 Mar 2025  View: PDF

Abstract: A high-precision joint time and radio frequency (RF) transfer scheme based on coherent demodulation is demonstrated. A one-pulse-per-second (1 PPS) time signal and an RF signal, transmitted at the same wavelength over a fiber link, are coherently demodulated at the receiver. Coherent demodulation is then achieved using a Michelson interferometer, with balanced detection employed to enhance the signal-to-noise ratio (SNR) of the demodulated signals. An interferometer differential delay of 1042 ps is precisely designed through microwave phase discrimination techniques, enabling simultaneous demodulation of both time and RF signals. A joint time and frequency transfer experiment is then performed over a 560 km fiber link. The time stability (TDEV), measured as time deviation, of 1 PPS reached 31.1 ps at 1 s and 3.9 ps at 10,000 s. The frequency stability, in terms of Allan deviation (ADEV), for a 2.4 GHz signal reached 3.9E-14 at 1 s and 6.2E-17 at 10,000 s. This proposed technique could help to improve the integration of time and frequency synchronization networks using existing optical fibers.

Measuring choriocapillaris blood flow with laser Doppler optical coherence tomography

Léo Puyo, Jonas Franke, Lisa Kutzner, Clara Pfaeffle, Hendrik Spahr, and Gereon Hüttmann

DOI: 10.1364/OL.551061 Received 05 Dec 2024; Accepted 06 Mar 2025; Posted 06 Mar 2025  View: PDF

Abstract: We report on using a laser Doppler processing of Fourier-domain optical coherence tomography (OCT) data for the assessment of pulsatile blood flow in the choriocapillaris. Signal fluctuations in B-scans recorded at a few kHz were analyzed by Fourier transform to extract blood flow information. The spectral broadening of light backscattered by the choriocapillaris was used to derive a choriocapillaris flow velocity index in physical units, with sufficient temporal resolution to capture heartbeat-induced variations. Furthermore, the asymmetry in the spectral broadening enabled us to determine the axial direction of blood flow with high sensitivity, allowing for the detection of flow orientation in retinal capillaries. This approach is promising as it can be directly implemented on widely available fast-scanning Fourier-domain OCT instruments.

Polarization-recycling phase tuning in an integrated ring resonator

Yunhao Zhang, Qingzhong Deng, Bitao Shen, Jianyang Cai, Haoren Wang, Liyuan Yao, Lei Wang, Xingjun Wang, and Haowen Shu

DOI: 10.1364/OL.551961 Received 13 Dec 2024; Accepted 06 Mar 2025; Posted 06 Mar 2025  View: PDF

Abstract: The necessity for efficient optical phase tuning has long been critical and is increasingly urgent in light of system scaling and growing demands of data transmission. In an integrated ring resonator, the design freedom for high efficiency is even more constrained due to its ultra-compact footprint and low cross-talk requirements for large scale operation. In this letter, we demonstrated a polarization multiplexed microring resonator for efficient phase tuning. Experimental results indicate 55%/177% enhancement in phase tuning efficiency compared with traditional devices operated in pure TE/TM mode. With zero-change in fabrication process, the proposed structure provides a versatile design methodology for efficiency enhancement in the realm of data communications and optical computing.

A layered ternary message passing decoder of LDPC codes for 50G-PON

Ming Jiang, Qiushi Xu, and Chunming Zhao

DOI: 10.1364/OL.557079 Received 11 Feb 2025; Accepted 06 Mar 2025; Posted 06 Mar 2025  View: PDF

Abstract: This letter presents a layered ternary message passing (LTMP) decoder for the low-density parity-check (LDPC) code tailored for 50G passive optical networks (50G-PON). The proposed decoder adopts a layered architecture and a corresponding density evolution analysis that enhance error correction performance is introduced. Additionally, we propose an optimization method for parameter combinations, which effectively achieves stronger performance. Results indicate that the LTMP decoder achieves exceptional error correction capabilities for the LDPC code in 50G-PON, even in low-precision input conditions.

High-speed femtosecond UV laser writing of low-loss waveguides in fused silica

Lisa Ackermann, Benedikt Hermann, Daniel Echarri, Ernesto Gribaudo, and Yves Bellouard

DOI: 10.1364/OL.557978 Received 06 Feb 2025; Accepted 06 Mar 2025; Posted 06 Mar 2025  View: PDF

Abstract: We demonstrate ultra-low loss femtosecond laser waveguide writing in fused silica using 450 fs ultraviolet pulses from a frequency-tripled Ytterbium laser. This favourable regime only appears at a low pulse density, enabling a three orders of magnitude faster processing speed compared to current practice. The refractive index contrast is comparable to the values reported for infrared-written waveguides and the propagation losses, below 0.1 dB/cm, are to date among the lowest values reported for fused silica.

On-chip wavelength beam combined DFB quantum cascade laser arrays

Tushar Sanjay Karnik, Laurent Diehl, Qingyang Du, Jia Xu Brian Sia, Christian Pfluegl, Daryoosh Vakhshoori, and Juejun Hu

DOI: 10.1364/OL.558575 Received 04 Feb 2025; Accepted 06 Mar 2025; Posted 06 Mar 2025  View: PDF

Abstract: Quantum cascade lasers (QCLs) are essential for a wide range of mid-infrared applications. Achieving wavelength beam combining (WBC) of QCLs on a chip scale is highly desirable for power scaling and/or broadband emission multi-wavelength output while maintaining a single output beam. We propose a straightforward architecture that monolithically integrates five distributed feedback (DFB) QCLs with an arrayed waveguide grating (AWG), using III-V semiconductor waveguides. The AWG channels wavelengths are carefully designed to align with the corresponding DFB emissions. An amplifier is also incorporated at the output to boost the total power. After the deposition of anti-reflection coatings on the output facet, the best-performing laser element achieved a peak power of 3 W under pulsed operation, with at least 1.75 W from the other channels. These results mark a significant step toward the realization of on-chip high-power WBC QCLs.

On-chip broadband power splitters via non-Hermitian subspaces

Xiaohong Li, Zhiqiang Qi, Hongyu Tan, Yang Liu, Lu Ding, and Shaolin Ke

DOI: 10.1364/OL.559011 Received 07 Feb 2025; Accepted 06 Mar 2025; Posted 06 Mar 2025  View: PDF

Abstract: We propose and demonstrate a broadband 3-dB power splitter based on a non-Hermitian triplet waveguide fabricated on a silicon on insulator (SOI) platform. By exploiting mirror symmetry, we show that the triplet can be decoupled into two virtual subspaces: a Hermitian subspace featuring a lossless zero mode, and another non-Hermitian subspace supporting lossy modes. The zero mode, with its intensity equally distributed between the outer two waveguides, plays a crucial role in achieving broadband performance, effectively suppressing mode competition and maintaining stable splitting against dimensional errors. Experimentally, the 1-dB operational bandwidth of the splitter is confirmed to exceed 70 nm, ranging from 1480 nm to 1550 nm. Furthermore, this approach can be directly extended to any 1×n power splitter, providing a scalable and robust solution for photonic integration.

Ring-focused light-fields generated through a liquid-crystal module assisted by embedded aluminum concentric-cylinders driven electrically

Zhe Wang, Kewei Liu, Mao Ye, Liu Taige, Zongtao Chen, Jiashuo Shi, Haiwei Wang, and Zhang Xinyu

DOI: 10.1364/OL.554520 Received 30 Dec 2024; Accepted 05 Mar 2025; Posted 05 Mar 2025  View: PDF

Abstract: A new liquid-crystal (LC) module based on an electrically driven and inducted formation of the spatial electric-fields in the LC micro-cavity for re-orienting LC molecules sealed, leading to a wavelike refractive index profile equivalent to traditional convex or concave ring-lenses, is proposed. The typical features of the LC module are a fine manipulation of lightwave converging or diverging and a switching performance for regulating incident lightwaves according to the beam converging or diverging mode co-driven by a set of signal voltage applied over the top and bottom indium tin oxide (ITO) electrodes, and also the aluminum concentric-cylinders (ACCs) embedded between the adjacent top circular ITO-electrodes. The beam-diverging mode can be roughly simulated by an intermediate LC structure without any ACC. The electric-fields generated in the LC micro-cavity can be obviously concentrated by the charged ACC through inducted net positive or negative charges over both ends or only one end immersed in the LC film. This work has laid a solid foundation for developing a new type of dual-mode LC ring-lenses driven electrically.

Diode-pumped few-optical-cycle laser based on ytterbium-doped disordered strontium yttrium borate crystal

huangjun zeng, Zhanglang Lin, Shijia Sun, Pavel Loiko, Haifeng Lin, Ge Zhang, zhoubin lin, Chengbo Mou, Xavier Mateos, Valentin Petrov, and Weidong Chen

DOI: 10.1364/OL.559850 Received 18 Feb 2025; Accepted 05 Mar 2025; Posted 05 Mar 2025  View: PDF

Abstract: The generation of sub-20 fs pulses from all-solid-state mode-locked ytterbium lasers have been traditionally plagued constrained by low laser efficiency and limited average output power, typically restricted to only a few milliwatts. In this work, we present a power-scalable, diode-pumped sub-20 fs mode-locked laser based on a multisite ytterbium-doped strontium yttrium borate crystal, Yb:Sr3Y2(BO3)4 exhibiting broadband spectral gain. Pumping with a low-power, spatially single-mode fiber-coupled laser diode at 976 nm, the Yb:Sr3Y2(BO3)4 laser produces soliton pulses as short as 19 fs at 1073.1 nm via soft aperture Kerr-lens mode locking. The record-high average output power of 131 mW for such pulse durations represents a sixfold increase compared to previous work. It corresponds to a laser efficiency of 12.6%. The peak power calculated from the pulse repetition rate of ~74.1 MHz amounts to ⁓82 kW. Peak pulse powers as high as ⁓140 kW were achieved increasing the average output power to 328 mW at 1070.5 nm for a slightly longer pulse duration of 28 fs. This corresponds to an impressive laser efficiency of 30%. The results highlight the potential of diode-pumped ytterbium lasers operating in the few-optical-cycle regime for achieving simultaneously high average output power and laser efficiency.

Compressive motionless optical scanning holography

Qingyang Fu, Jiasong Sun, Yaping Zhang, Ting-Chung Poon, Yao Fan, and Chao Zuo

DOI: 10.1364/OL.555692 Received 13 Jan 2025; Accepted 05 Mar 2025; Posted 06 Mar 2025  View: PDF

Abstract: Optical scanning holography (OSH) is a powerful computational imaging technique that encodes three dimensional (3D) information of an incoherently illuminated or self-luminous object into 2D holograms using Fresnel zone patterns (FZPs) as structured illumination. However, conventional OSH methods require complex setups with mechanical scanning or multi-frame phase shifting devices, limiting their imaging efficiency and system stability. In this Letter, we propose compressivemotionless optical scanning holography (CMOSH), a novel framework that eliminates phase-shifting and mechanical scanning for 3D incoherent holography. The unique combination of compressive holography and motionless OSH enables single-scan, twin-image-freeholographic reconstructions, significantly improving the system stability and imaging throughput. It also provides true 3D depth-resolved imaging, accurately resolving multi-layer samples while eliminating defocused information. The effectiveness of CMOSH is demonstrated through numerical simulations and experimentaldemonstrations, highlighting its potential for robust and efficient 3D holographic imaging across diverse applications.

Deployed quantum link characterization via Bayesian ancilla-assisted process tomography.

Arefur Rahman, Noah Wasserbeck, Zachary Goisman, Rhea Fernandes, Brian Kirby, Muneer Alshowkan, Chris Kurtz, and Joseph Lukens

DOI: 10.1364/OL.545625 Received 24 Oct 2024; Accepted 05 Mar 2025; Posted 05 Mar 2025  View: PDF

Abstract: The development of large-scale quantum networks requires reliable quantum channels, the quality of which can be quantified by the framework of quantum process tomography. In this work, we leverage ancilla-assisted process tomography (AAPT) and Bayesian inference to probe a 1.6 km deployed fiber-optic link. We send one of two polarization-entangled photons from Alice in one building to Bob in another, exploiting the local qubit as an ancilla system to characterize the corresponding quantum channel. Monitoring over a 24 h period returns a steady process fidelity of 97.6(1)%, while controllable spectral filtering with passbands from 0.025--4.38 THz finds fidelities that first increase, then level off with bandwidth, suggesting both stable operation with time and minimal polarization mode dispersion. To our knowledge, these results represent the first AAPT of a deployed quantum link, revealing a valuable tool for "in situ" analysis of entanglement-based quantum networks.

Atomic coherence-assisted wide tunable range laser frequency offset locking using four-wave mixing

Jun Guo, Zheng Tan, Kexiang Mou, Li Wang, Yinan Hu, Xianping SUN, and Xin ZHOU

DOI: 10.1364/OL.543109 Received 08 Oct 2024; Accepted 04 Mar 2025; Posted 04 Mar 2025  View: PDF

Abstract: In this letter, we present a wide tunable range laser frequency offset locking technique based on four-wave mixing. The Raman amplified probe light and the newly generated conjugate light have considerable signal amplitude and ultra-narrow spectral characteristics, benefiting robust laser frequency stabilization. The laser frequency can be selectively locked to Stokes or anti-Stokes frequency of four-wave mixing spectrum, which has a fixed frequency difference relative to the pump light, corresponding to the atomic ground state hyperfine splitting. By changing the detuning of the pump light frequency, a large tunable range of several GHz can be obtained. Compared to the frequency modulation spectroscopy method, an atomic coherence enhanced error signal with larger peak-to-peak amplitude and steeper zero-crossing gradient is obtained by the modulation transfer technique in a double-lambda atomic system, resulting in much better performance of laser frequency stabilization. The present method could be used to improve the measurement sensitivity of atomic sensors such as enhancing the stability of the Raman light for an atomic interferometer, and the laser stability for a highly sensitive atomic magnetometer.

Turbulence effects in Frozen Waves: experimental generation and analysis via holographic techniques

George Brian dos Reis and Marcos Gesualdi

DOI: 10.1364/OL.547691 Received 11 Nov 2024; Accepted 04 Mar 2025; Posted 04 Mar 2025  View: PDF

Abstract: In this letter, we present the characterization of the effect of atmospheric turbulence on Frozen Waves using holographic techniques. Frozen Waves are diffraction-resistant optical beams obtained by superposing co-propagating Bessel beams, achieving efficient shaping of their shape. Based on this, we developed a holographic optical system for the generation and characterization of Frozen Waves under conditions of turbulence effects. Using this setup we demonstrate how these Frozen Waves propagate longitudinally, the transverse intensity profiles and phase map, without and with turbulence. These results indicate that Frozen Waves are promising for optical communication systems and characterization of turbulent media, due to its non-diffractive properties and the control of its longitudinal propagation and transverse profile properties.

Dual-band achromatic wavefront control of spintronic terahertz via cascaded metasurfaces

Zhang Xiaoqiang, Ruimin Li, Yunqing Jiang, Jiawei Ji, Yong Xu, Qiwen Zhan, and weisheng zhao

DOI: 10.1364/OL.554430 Received 30 Dec 2024; Accepted 04 Mar 2025; Posted 04 Mar 2025  View: PDF

Abstract: In the past decades, terahertz (THz) technology has made significant progress. However, multifunctional THz devices are still lacking, particularly low-cost and convenient ones. Recently, ultrathin spintronic THz emitters (STEs) have demonstrated remarkable advantages for a wide range of applications, thanks to their cost-effectiveness and high performance. Integrating STEs with multifunctional metasurfaces is a fascinating topic. However, most metasurfaces exhibit certain limitations, with chromatic aberration being a key issue that has garnered significant attention. Conventional achromatic metasurfaces are typically designed to operate exclusively in either reflection or transmission mode. In this letter, we combine a multifunctional metasurface with the unique forward and backward emission characteristics of THz waves from a thin STE, carefully designing two types of dual-band achromatic metasurfaces (DBAMs). In these two DBAMs, THz waves at 0.85 THz and 1 THz generated by the STE are focused on the same focal point. More importantly, one of the THz waves features a conventional focused wavefront, while the other exhibits a focused helical wavefront. Our design significantly expands the capabilities of metasurfaces and greatly advances the development of state-of-the-art multifunctional THz devices.

Topological invariant of non-Hermitian space-time modulated photonic crystals

Xiaoke Gao, Xiaoyu Zhao, Jiawei Wang, Xikui Ma, and Tianyu Dong

DOI: 10.1364/OL.555293 Received 09 Jan 2025; Accepted 04 Mar 2025; Posted 05 Mar 2025  View: PDF

Abstract: We propose a medium transformation approach to formulate the adjoint system of space-time modulated photonic crystals (STMPCs), essential for the bi-orthogonal Berry connection when calculating the topological invariant. We show that the non-Abelian Zak phase of STMPCs comprising stacked photonic time crystals and dielectrics is quantized to 0 or 1 for both the entangled and isolated bands. We find that the eigenmodes at the center and edge of the Brillouin zone differ in symmetry for the band with non-trivial Zak phases, while they share the same symmetry for the trivial Zak phases. In addition, topological phase transitions owing to band inversion are observed. Moreover, a generalized Brillouin zone of the non-Hermitian STMPCs is established, which is identical to the Hermitian counterpart, implicating that the non-Bloch band theory is not required in this regard. The proposed medium transformation method may serve as an alternative approach to exploring more intricate topological phenomena in non-Hermitian systems when incorporating non-Bloch band theory.

Absorbing molecules as optical clearing agents improve the resolution and sensitivity of photoacoustic microscopy

tianxiang Zuo, Chao Tao, and XiaoJun Liu

DOI: 10.1364/OL.555723 Received 15 Jan 2025; Accepted 04 Mar 2025; Posted 05 Mar 2025  View: PDF

Abstract: Photoacoustic microscopy (PAM) offers high resolution and 100% sensitivity to optical absorption, making it promising for biomedicine. However, strong light scattering in tissues limits its imaging depth, intensity, and resolution. Optical clearing agents (OCA) can reduce light scattering. However, traditional methods often use toxic substances or damage tissue components, restricting their application in living tissues. Recently, tartrazine, a common food pigment, has been shown to significantly improve tissue optical transparency while maintaining good biosafety. However, since this type of OCA is an absorbing molecular, it remains unclear whether tartrazine can effectively enhance PAM, which relies on optical absorption and ultrasound detection. In this study, we show that tartrazine, despite its strong light absorption, can significantly enhance the performance of PAM, when used at the appropriate concentration. Our ex vivo experiments demonstrate tartrazine solution enables PAM to achieve an optical resolution of 21 μm even through the skin. A 0.6M tartrazine solution improves resolution by 3.5 times and the imaging intensity by 4.5 times. Finally, in vivo brain imaging of a mouse with an intact scalp reveals that tartrazine not only increases the imaging intensity by about 4 times, but also allows PAM achieve an optical resolution of brain through the scalp and skull, revealing much more details of the microvascular in brain.

High accuracy calibration method for 3D curve reconstruction based on twisted multicore fiber

Keyuan Yang, Changjian Ke, Zikang Xv, Zhihao Wang, and Deming Liu

DOI: 10.1364/OL.555220 Received 09 Jan 2025; Accepted 03 Mar 2025; Posted 04 Mar 2025  View: PDF

Abstract: A high accuracy calibration method for three-dimensional (3D) curve reconstruction based on twisted multicore fiber (MCF) is proposed and experimentally investigated. The core spacing, core azimuth and twist bias of the twisted MCF are decoupled and calibrated according to the amplitude, phase and period information derived from the strain curves. A 3D curve reconstruction experimental system based on twisted MCF and optical frequency domain reflectometry (OFDR) is established, and the curve reconstruction performance is evaluated before and after calibration. The results show that, with a reconstruction length of 25cm, the average tip position error is reduced from 28.12mm to 2.50mm.

1060 nm interferometric near-infrared spectroscopy

Dibbyan Mazumder, Santosh Aparanji, Oybek Kholiqov, Drew Hamilton, Rabisankar Samanta, and Vivek Srinivasan

DOI: 10.1364/OL.558899 Received 07 Feb 2025; Accepted 03 Mar 2025; Posted 04 Mar 2025  View: PDF

Abstract: Recently, interferometric near-infrared spectroscopy (iNIRS) has emerged to measure diffuse light field fluctuations with time-of-flight (TOF) resolution. Yet, current iNIRS implementations suffer from low signal-to-noise ratio (SNR). Longer wavelengths, with lower photon energy, lower reduced scattering, and higher permissible exposures, have the potential to increase SNR. Here, we investigate iNIRS at 1060 nm. Across various forehead locations, we find that the autocorrelation SNR is improved 3.7-9.3 times compared to 855 nm and 6.0-33.5 times compared to 773 nm at TOFs of 800-1000 picoseconds. Physical system parameters account for much of this improvement, but the tissue response may also play a role. We conclude that wavelengths near 1060 nm can potentially improve iNIRS measurements of TOF-resolved speckle fluctuations.

Four-channel silicon nitride wavelength beam combiners for multi-gas absorption spectroscopy

Qing Gao, Xiangeng Wang, Kan Huang, Jincheng Wei, Yanwei Huang, Yanfeng Zhang, Ruijun Wang, and Siyuan Yu

DOI: 10.1364/OL.558983 Received 07 Feb 2025; Accepted 03 Mar 2025; Posted 04 Mar 2025  View: PDF

Abstract: The detection and measurement of multiple trace gases based on laser absorption spectroscopy technique requires laser sources with wavelength tunability in multiple wavebands. In this letter, we present an on-chip wavelength beam combiner based on silicon nitride Mach–Zehnder interferometers (MZIs) and a modified multi-mode interferometer (MMI) structure to multiplex light with different wavelength spacing. A MZI composed by a standard 1×2 MMI and 2×2 MMI is employed to digitally multiplex two wavelengths within ~one hundred nanometer spacing. The two wavebands with a spacing of a few hundred of nanometers are multiplexed by a compact modified MMI structure. The measured insertion losses of all four channels are around 2.5 dB from the 1650 nm waveband to the 2050 nm waveband. A tunable diode laser absorption spectroscopy (TDLAS) measurement of multi-gas is demonstrated using the device as the wavelength beam combiner.

Multicolor 4Pi single molecule localization based on differences in interference patterns

Jianwei Chen, HAOYU WANG, Zhaojun Lin, and Yiming Li

DOI: 10.1364/OL.553445 Received 18 Dec 2024; Accepted 03 Mar 2025; Posted 03 Mar 2025  View: PDF

Abstract: 4Pi single-molecule localization microscopy (4Pi-SMLM) achieves sub-10 nm isotropic three-dimensional resolution, representing a significant advancement in super-resolution imaging. However, traditional multicolor imaging techniques generally require additional modifications to the optical path, which complicates the system and leads to photon loss. In this study, we introduce a new multicolor imaging method that leverages the differences in 4Pi-PSF size and interference fringe spacing caused by wavelength variations, enabling multi color 4Pi-SMLM imaging without hardware modifications. This method captures color information directly from the raw data by utilizing the wavelength-dependent point spread functions (PSFs). By globally fitting the data within multiple interference channels, we could achieve both high localization accuracy and color separation accuracy for single molecules of different colors.

Precision Analysis of ToF LiDAR in Atmospheric Turbulence Channels

Tianzhu Zhang, Zhongji Yan, Anning Pang, and Anhong Dang

DOI: 10.1364/OL.554208 Received 29 Dec 2024; Accepted 03 Mar 2025; Posted 03 Mar 2025  View: PDF

Abstract: This paper derives and verifies the ranging precision of time-of-flight (ToF) light detection and ranging (LiDAR) in atmospheric turbulence channels. Double-passage atmospheric turbulence channels satisfying the Gamma-Gamma distribution are simulated in laboratory using a random phase screen, and the derived Cramer-Rao lower bounds (CRLBs) for LiDAR ranging in Gamma-Gamma channels are verified by Monte Carlo simulation and experiment. The CRLBs demonstrate that the precision values at a Rytov variance of 0.25, 0.5, and 0.75 are 1.45, 2.07, and 2.91 times those at a Rytov variance of zero for the ToF LiDAR, respectively. Consequently, this paper provides a theoretical foundation for the deployment of high-precision LiDAR applications in turbulent channels.

Effect of the doping concentration on the performance of 2.8 µm Er:CaF2 lasers

Venkatesan Jambunathan, Simone Normani, Pavel Loiko, Karel Veselsky, liza Basyrova, Abdelmjid Benayad, Patrice Camy, Ammar Hideur, and Alain BRAUD

DOI: 10.1364/OL.555586 Received 14 Jan 2025; Accepted 03 Mar 2025; Posted 03 Mar 2025  View: PDF

Abstract: The effect of the rare-earth doping on the spectroscopy and mid-infrared laser performance of Er3+:CaF2 crystals was investigated. The optimum doping level of 3 to 5 at.% was identified owing to the ion clustering. Pumped by a high-brightness Yb-fiber laser at 976 nm, the continuous-wave 5at.% Er3+:CaF2 laser generated 1.22 W at 2798 nm with a slope efficiency of 38.3% exceeding the Stokes limit, and the laser wavelength was continuously tunable across 2690-2830 nm (tuning range: 140 nm). The ratio of energy-transfer upconversion rates from the 4I11/2 and 4I13/2 states was quantified relating to the energy recycling process.

Ultra-Low Return Loss LPFGs Fabricated via Femtosecond Laser Direct Writing of Ultrashort TFBGs

li xingyong, Tian xin Duan, Ruohui Wang, chen fengyi, and Xueguang Qiao

DOI: 10.1364/OL.555175 Received 08 Jan 2025; Accepted 03 Mar 2025; Posted 03 Mar 2025  View: PDF

Abstract: In this study, we propose for the first time the use of femtosecond laser direct writing to fabricate ultrashort tilted fiber Bragg gratings (TFBGs) for the development of long-period fiber gratings (LPFGs) with ultra-low return loss. A series of spectral transmission characteristics of the TFBG-LPFGs, constructed from ultrashort TFBGs, were systematically investigated, focusing on the effects of tilt angles and grating periods. As the tilt angle of the ultrashort gratings increases (from 0° to 10°), the return loss of the LPFGs decreases to -56.31 dB, representing a reduction of approximately 39.42 dB compared to the LPFG with a 0° tilt angle. The TFBG-LPFGs exhibited a resonance mode transmission depth of 38.34 dB, demonstrating enhanced resolution for refractive index (RI) measurements. Notably, the TFBG-LPFGs, composed of multiple 100 μm ultrashort TFBGs, were fabricated using femtosecond laser direct writing technology, reducing the fabrication time for a single TFBG-LPFG to approximately 30 seconds, thereby significantly shortening the overall manufacturing time for LPFGs. High-quality LPFGs with ultra-low return loss demonstrate promising applications across areas such as fiber lasers, optical communications, biosensing, chemical detection, and structural health monitoring.

Thorium doped strontium fluoride crystal: a unique candidate for solid nuclear optical clock material

Qiaorui Gong, Lin Li, Shanming Li, shulong zhang, Siliang Tao, Guoliang Deng, Peixiong Zhang, Chengchun Zhao, Yin Hang, Shining Zhu, and Long-Sheng Ma

DOI: 10.1364/OL.558637 Received 05 Feb 2025; Accepted 03 Mar 2025; Posted 03 Mar 2025  View: PDF

Abstract: Thorium-doped vacuum ultraviolet transparent crystals are attracted widespread attention to be used in the solid-state nuclear optical clock because of the advantages with frequency stability, miniaturization and spaceborne ability. However, the doping efficiency, doping loss, and doping uniformity of these existing crystals are still not ideal. Herein, a candidate with unique advantages in the cultivation of solid-state nuclear clock material, Th: SrF2 crystal is introduced for the first time. It not only has a segregation coefficient close to 1, which can achieve highly efficient and uniform doping of Th, but also ensures a high transmittance (~69% at 149 nm) while achieving extremely high doping concentration ( 2Th>6×1020 cm-3). In addition, Th:SrF2 crystal would not be irradiated-colored under strong α radiation, which is expected to ensure its transmission performance in nuclear transition band not be severely affected by 229Th radiation damage. The discovery of this crystal would greatly promote the development of solid-state nuclear clock materials.

Tunable topological edge states based on anomalous scattering

Chengxi Yang, Jianfei Li, Jialin Liu, Jingfeng Yao, Ying Wang, Zhongxiang Zhou, and Chengxun Yuan

DOI: 10.1364/OL.555560 Received 10 Jan 2025; Accepted 02 Mar 2025; Posted 03 Mar 2025  View: PDF

Abstract: The present work combines traditional dielectric materials with metal foils to form composite scatterers and constructs a two-dimensional square lattice photonic crystal, from which its band topology is achieved. The photonic band gap (PBG) is caused by local Mie scattering resonances between adjacent structures, where the Mie scattering resonance can be analogized to the role of the atomic energy levels in the crystal. The energy levels of the composite scatterers can be controlled by rotation, thus manipulating the PBG and topological properties. The topological phase transition is realized by altering the rotation angle of the composite scatterers in the unit cell. A programmable topological insulator with Single-chip Control System (SCCS) is developed to verify the numerical results. This design not only achieves tunable topological edge states (TES), but it can also realize arbitrary coding.

Fiber Bragg grating sensors demodulated by a speckle silicon chip

Zihao Ye, Haole Kong, Zhiming Zhang, Zhihang Lin, Yanghui Li, Juan Kang, Le Wang, and Yi Li

DOI: 10.1364/OL.549969 Received 26 Nov 2024; Accepted 02 Mar 2025; Posted 03 Mar 2025  View: PDF

Abstract: Fiber Bragg Gratings (FBGs) have been widely adopted as sensors for measuring various physical parameters, such as temperature, strain, and vibration. However, existing FBG demodulation methods face significant challenges related to stability, size, and cost. In this study, we proposed a silicon on insulator (SOI) chip to demodulate FBGs based on random speckles. A 20 mm long coiled multimode silicon waveguide was designed to generate the speckle pattern, which was then compressed into eight singlemode outputs. The architecture similarity between the convolutional neural network (CNN) and the proposed SOI chip was discussed. And a multilayer perceptron (MLP) network was applied to regress the speckle data for prediction. The demonstrated experiments indicated that a standard deviation of 0.0414°C was achieved in the single FBG demodulation. Furthermore, we also explored the capability of demodulating multiple FBGs. This speckle based SOI chip provides a highly stable, compact and lightweight solution in FBG sensing system.

Implementing photonic-crystal resonator frequency combs in a photonics foundry

Haixin Liu, Ivan Dickson, Alin Antohe, Lewis Carpenter, Jizhao Zang, Alexa Carollo, ATASI DAN, Jennifer Black, and Scott Papp

DOI: 10.1364/OL.553980 Received 26 Dec 2024; Accepted 02 Mar 2025; Posted 03 Mar 2025  View: PDF

Abstract: We explore an AIM Photonics silicon-nitride platform to fabricate photonic-crystal resonators for generating optical parametric oscillators (OPO) and soliton microcombs. Our approach leverages the scalability and fine feature size of silicon-nitride processing on large-scale silicon wafers to achieve low-loss, high-Q microresonators, functionalized by nano-scale photonic-crystal structures. We demonstrate intrinsic microresonator quality factor up to 1.2 × 10^7 with complete foundry fabrication on 300 mm silicon, a 700 nm thick silicon nitride device layer, and inclusion of complex nanophotonics. These features enable a host of nonlinear nanophotonics sources on the platform, including OPOs, microcombs, parametric amplifiers, squeezed-light generators, and single-photon sources. By fine-tuning the photonic-crystal design parameters, we achieve broad tunability in the frequency of the OPO output, spanning a significant portion of the near-infrared. Additionally, we observe the formation of soliton frequency combs, enabled by the precise dispersion engineering of the microresonators. These results highlight the potential of silicon-nitride photonics to enable wide access to and complex integration of frequency-comb sources, with applications in spectroscopy, metrology, and communications.

Regenerative vectorial breathers in a delay-coupled excitable microlaser with integrated saturable absorber

Stefan Ruschel, Anirudh Pammi, Rémy BRAIVE, Isabelle Sagnes, Grégoire Beaudoin, Neil Broderick, Bernd Krauskopf, and Sylvain Barbay

DOI: 10.1364/OL.550201 Received 25 Nov 2024; Accepted 02 Mar 2025; Posted 05 Mar 2025  View: PDF

Abstract: We report on the polarization dynamics of regenerative light pulses in a micropillar laser with integrated saturable absorber coupled to an external feedback mirror. The delayed self-coupled microlaser is operated in the excitable regime, where it regenerates incident pulses with a supra-threshold intensity --- resulting in a pulse train with inter-pulse period approximately given by the feedback delay time, in analogy with a self-coupled biological neuron. We report the experimental observation of vectorial breathers in polarization angle, manifesting themselves as a modulation of the linear polarized intensity components without significant modulation of the total intensity.%Numerical analysis of a suitable model reveals that the observed polarization mode competition is a consequence of symmetry-breaking bifurcations induced by polarization anisotropy. Our model reproduces well the observed experimental results and predicts different regimes as a function of the polarization anisotropy parameters and the pump parameter. We believe that these findings are relevant for the fabrication of flexible sources of polarized pulses with controlled properties, as well as for neuroinspired on-chip computing applications, where the polarization may be used to encode or process information in novel ways.

High temporal contrast 1053 nm femtosecond pulses via spectral broadening and filtering in an air-filled multi-pass cell using a Yb:CALGO amplifier

liya shen, Jiaming Jiang, Jiajun Song, Yujie Peng, Yinfei Liu, guanguang gao, Junze Zhu, tianze xu, Xiaoming Lu, and Yuxin Leng

DOI: 10.1364/OL.556024 Received 27 Jan 2025; Accepted 01 Mar 2025; Posted 04 Mar 2025  View: PDF

Abstract: Temporal contrast is crucial for the interaction of ultra intense, ultrashort pulse lasers with matter. Seed laser sources that offer high temporal contrast are essential for enhancing overall temporal contrast. In this study, we demonstrate the generation of a high temporal contrast seed laser by spectral broadening and filtering of a Yb: CALGO femtosecond amplifier in an air-filled multi-pass cell. The temporal contrast exceeds 109 within 100 ps prior to the main pulse, with a pulse energy of 227 µJ and a duration of 118 fs. Given its excellent beam quality and stability, this laser source is well-suited as a high-quality seed for Nd: glass-based ultra intense laser facilities. This work achieves a remarkable internal efficiency of over 70% in generating a clean seed pulse for ultra intense lasers.

On the theory of bi-chromatic pulsed ring lasers with synchronised transient Raman amplification

Sergei Turitsyn

DOI: 10.1364/OL.553521 Received 27 Dec 2024; Accepted 01 Mar 2025; Posted 06 Mar 2025  View: PDF

Abstract: Analytical theory is presented for a simplified model of dual wavelength pulsed Raman laser with synchronous pumping. The lasing regime features trains of M pump and M - N Stokes optical pulses coexisting in the resonator and shifting relative to each other by N periods after every round trip. The considered shift register mechanism enables generation of bi-chromatic pulses with a common repetition rate that is inversely proportional to the differential delay between pumping and tokes waves.

A high-sensitivity miniature fiber optic temperature probe based on cholesteric liquid crystal laser emission

Dong Zhou, Ziqi Zhou, Xu Li, Lishuang Yao, Wenzhu Cao, and yongjun liu

DOI: 10.1364/OL.555545 Received 10 Jan 2025; Accepted 01 Mar 2025; Posted 06 Mar 2025  View: PDF

Abstract: This paper presents the method for cholesteric liquid crystal (CLC)-filled miniature optical fiber liquid crystal probes to achieve highly sensitive temperature detection. Due to the periodic structure of CLC, it can function as a resonant microcavity and generate laser light under the gain of the dye, with the laser wavelength shifting with temperature. The temperature response characteristics of several CLCs were studied by observing the variation of CLC laser wavelength with temperature. In order to further improve the temperature sensitivity, this paper used a method of linear superimposing the sensitivity of two liquid crystals. Finally, the sensitivity of the fiber optic temperature sensing probe produced in this paper reached 7.41nm/℃. The probe has a good temperature response, small size and easy to make, so it can be used in temperature sensing and medical monitoring.

Green laser pumped watt-level femtosecond OPO with high spectra and power stability based on side-of-fringe locking technique

heng jing, Shang Wang, zhenhua cong, Zhaojun Liu, and Zhigang Zhao

DOI: 10.1364/OL.554484 Received 07 Jan 2025; Accepted 01 Mar 2025; Posted 03 Mar 2025  View: PDF

Abstract: A green laser pumped 100-MHz LBO-based femtosecond optical parametric oscillator (fs-OPO) with high spectra and power stability is presented, which is enabled by side-of-fringe locking technique and whose signal wavelength can be tuned from 650 nm to 980 nm. The average powers are higher than 1 W within the nearly whole wavelength range (700-980 nm). Especially, the average power goes up to 1.8 W at 800 nm, with a conversion efficiency of 27.3%. To demonstrate the universality, three wavelengths of 740 nm, 800 nm, and 920 nm, which are called for by biophotonics, are advisedly chosen to verify the capability of the side-of-fringe locking technique for both spectra and power stabilizations. As a result, the power fluctuations (in RMS) of 1.6%, 0.5%, and 1.6%, and the central wavelength drift (in SD) of 0.44 nm, 0.13 nm, and 0.19 nm, are obtained for those three wavelengths, respectively. In addition, the pulse durations are measured to be 630 fs, 139 fs, and 182 fs. Those combined performances leave the possibility for long time data acquirement in imaging experiments.

Direct Gaussian to high-order Laguerre-Gauss beam shaping in GRIN multimode fiber

Wasyhun Gemechu, Mario Ferraro, Stefan Wabnitz, Fabrizio Frezza, and Fabio Mangini

DOI: 10.1364/OL.550610 Received 29 Nov 2024; Accepted 28 Feb 2025; Posted 28 Feb 2025  View: PDF

Abstract: We report our observation of direct transformation of a Gaussian-like laser beam, initially injected into the cladding of a graded-index multimode fiber, into a high-order Laguerre-Gauss mode within the fiber core.

Optical edge detection with adjustable resolution using planar liquid crystal Alvarez lens

Lin Liu, Qun Hao, Cancan Yao, Haoyue Xing, and Yang Cheng

DOI: 10.1364/OL.557550 Received 21 Jan 2025; Accepted 28 Feb 2025; Posted 03 Mar 2025  View: PDF

Abstract: In this Letter, we proposed an optical edge detection method with adjustable resolution using a planar liquid crystal Alvarez lens. A planar liquid crystal Alvarez lens was fabricated by laser direct writing. When the focal length liquid crystal Alvarez lens changes and linearly polarized light passes through the liquid crystal Alvarez lens, the angle between the emitted left-handed circularly polarized light and right-handed circularly polarized light can be controlled, enabling adjustable resolution edge detection. The lens can adjust edge width from 32.5 μm to 73.7 μm without requiring any rotation or axial displacement. Moreover, it can accomplish comprehensive edge detection across a broadband spectral range. This edge detection method could offer potential application value for compact optical devices such as high-contrast microscopes and smart cameras.

Coherence shaping for optical vortices: a coherence shift keying scheme enabled by deep learning for optical communication

Yanghong Li, JingHuan Huang, WeiQing Lin, Shengdi Lian, Haoyu Huang, Qingying Quan, Wen Chenyu, Wu Zitong, Yu Xiao, and Dongmei Deng

DOI: 10.1364/OL.549356 Received 25 Nov 2024; Accepted 28 Feb 2025; Posted 03 Mar 2025  View: PDF

Abstract: To meet the rapidly growing communication demands, researchers have focused on structured light-based shift keying techniques. However, higher-order modes are prone to large diffraction divergence and are easily perturbed. In this study, we experimentally demonstrate a novel coherence shaping method for petal-like structures of optical vortices, enabling the generation of non-diffraction interference states between completely coherent and incoherent states. In addition, we propose a coherence shift keying scheme enabled by deep learning and achieve a high recognition accuracy ( > 0.93) of interference states under practical conditions, including complex environments. This study provides a new, as far as we know, platform for low-order structured light mode-based high-capacity and encrypted shift keying communication systems.

Inverse-designed multi-directional remote cloak

Qingze Tan, Chao Qian, Zheng Zhen, Xiaojun Xie, Xihua Zou, and Lianshan Yan

DOI: 10.1364/OL.559384 Received 13 Feb 2025; Accepted 27 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: Invisibility as a superior self-protection tactic has long captivated the popular interest in both academia and industry. However, state-of-the-art invisibility cloaks typically need to completely wrap or shield a hidden object, leading to the hidden object cannot interact with the environment outside. This study develops a precise and efficient de-homogenization optimized-architecture to produce high-performance, simple-parameters and fabricable remote cloak without constrains on geometry. As proof of concept, we demonstrate that an open cloak composed by four separate parts of metamaterial can remotely hide arbitrarily shaped object located at a certain distance for four mutually orthogonal directions of incident waves. Additionally, we extend this concept to a remote illusive device with the capability of transforming any arbitrary object into another one. Our work provides the available strategies of remote devices closer to a widespread range of in situ practical-oriented applications.

Ultra-Thin Si-PD Design with Enhanced Lateral Mode Resonance through Metagrating Deflectors

Weinan Feng, Jiangtao Ma, and Makoto Tsubokawa

DOI: 10.1364/OL.551902 Received 13 Dec 2024; Accepted 27 Feb 2025; Posted 28 Feb 2025  View: PDF

Abstract: We propose a new surface-illuminated Si photodetector (PD) structure with deflecting metagrating that solves issues of the low sensitivity to near-infrared (NIR) light and the trade-off between the absorption layer thickness and high-speed response. The metagrating, composed of tilted Si and SiO₂ arrays, efficiently deflects normally incident photons. When coupled with the lateral quasi-propagating mode in the absorption layer with a circular resonator shape, the photon lifetime is dramatically extended, resulting in increased absorption of NIR photons. Simulations have confirmed that even an absorption layer as thin as 300 nm can achieve an extremely high absorption of 29.2% at a wavelength of 1012 nm. We believe that this innovative design can play a crucial role in the design of thin and high-speed PDs.

Wideband chaos generation based on integrated mutual coupling laser

Yuanyuan Guo, yuanye zhang, Hua Gao, Longsheng Wang, Pengfa Chang, Hong Han, Zhiwei Jia, Anbang Wang, and Yuncai Wang

DOI: 10.1364/OL.558091 Received 24 Jan 2025; Accepted 27 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: To further enhancing the bandwidth of integrated chaotic semiconductor laser, a structure of integrated mutual coupling laser is proposed. The laser integrates two distributed feedback lasers and two semiconductor optical amplifiers in the middle of the lasers. The dynamics state of the integrated laser undergoes complex changes with the variation of the bias currents of the DFB lasers and SOAs. We find that the bias currents have an influence on the enhancement of chaotic signal bandwidth. The proposed structure can generate over 30 GHz ultra-wide chaotic laser when the DFB and SOA regions are under proper bias current conditions.

Shaped vector beams generated with a phase-only modulation – retarder optical configuration

Ignacio Moreno, Jeffrey Davis, Maria del Mar Sanchez-Lopez, and Don Cottrell

DOI: 10.1364/OL.546144 Received 05 Nov 2024; Accepted 26 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: This work presents a new optical configuration to generate vector beams, with shaped intensity and polarization distributions, based on two liquid-crystal spatial light modulators (SLM). The first device is used in a scalar mode to shape an input linearly polarized beam with a phase-only computer-generated hologram. Then, the Fourier transform is imaged onto the second SLM, which operates as a pixelated retarder to spatially modify the state of polarization. The proposed optical architecture allows shaping the amplitude profile, while easily generating the cylindrically polarized vector beam pattern. Experimental results demonstrate the versatility and advantages of the approach.

Direct vibration waveform extraction based on synthetic wavelength amplitude modulation in SMI system

Hanqiao Chen, Jiaxin Chen, Shuang Zhang, Desheng Zhu, Xiulin Wang, zhipeng dong, and Wencai Huang

DOI: 10.1364/OL.550355 Received 29 Dec 2024; Accepted 26 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: This paper proposes an amplitude modulation method based on synthetic wavelength to directly acquire the vibration waveform of targets in self-mixing interferometry (SMI) system. The vibration waveform of the target is directly extracted from the envelope of the amplitude-modulated SMI signal, which arises from the synthetic differential wavelength. Experimentally, targets with different vibration frequencies were measured, demonstrating an average frequency measurement error of 0.6% and an average coefficient of determination of 0.9938 for waveform agreement. To the best of our knowledge, this is the first time in the SMI field to extract vibration waveform by using amplitude modulation generated by lasers with different wavelengths. This method provides a simple and accurate approach for measuring target vibration waveforms, significantly simplifying the demodulation process of SMI signals.

Tunable Multi-wavelength Generation of Integrated Self-Injection Locking Laser based on Vernier Effect

Dongwei Zhuang, Quanxin Na, Qijie Xie, li wang, Baisong Chen, Chunyang Ma, Lanxuan Zhang, Lei Wang, Qin li, and Junfeng Song

DOI: 10.1364/OL.550686 Received 29 Nov 2024; Accepted 26 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: A narrow-linewidth laser based on self-injection locking has witnessed wide applications such as wavelength division multiplexing, sensing and LiDAR detection. Although multi-wavelength operation can be supported by self-injection locking, conventional implementations have typically been bulky and constrained by limited wavelength spacing. In this paper, we have demonstrated an integrated multi-wavelength self-injection locking (MWSIL) laser to generate multiple narrow-linewidth lights with tunable spacing. The multi-wavelength operation is based on the Vernier effect that occurred in the injection locking of a single distributed feedback laser (DFB) to a Si3N4-based micro-resonator (MRR). In the experimental demonstration, the wavelength spacing of the laser can be tuned from 1.155 nm to 9.24 nm by adjusting the phase of the cavity. The intrinsic linewidths of the multi-wavelength laser (MWSIL) are all below 1.6 kHz, with the optimal wavelength linewidth being 125 Hz, representing up to a 703-fold improvement compared to the laser operating in a free-running state. Additionally, the laser also exhibits mode-hop-free frequency tuning over 2.6 GHz. The MWSIL offers an effective on-chip solution to generate a tunable multi-wavelength optical source with ultra-narrow linewidth.

Transient chirp reconstruction of ultrafast electron beam via tightly focused chirped laser pulse

Zhijun Zhang, Shiyi Zhou, and Jiansheng Liu

DOI: 10.1364/OL.552063 Received 20 Dec 2024; Accepted 26 Feb 2025; Posted 28 Feb 2025  View: PDF

Abstract: Controlling the phase space of particle beams is critical for producing high-quality, ultrashort electron beams in plasma-based accelerators. Diagnosing the transient energy chirp, which evolves rapidly during the early stages of acceleration, remains a significant challenge. Here, we present a novel method to reconstruct the transient energy chirp of ultrashort electron beams using tightly focused and chirped laser pulses. The conditions for enhancing electron beam divergence modulation are analyzed, and the chirp reconstruction is demonstrated by leveraging the intrinsic phase correlation of modulated divergence projected onto specific phase-space coordinates. Furthermore, the temporal delay between the laser and electron beam is determined via a Fourier transform of the reconstructed divergence modulation in the frequency domain. This method offers a promising tool for optimizing accelerator performance and probing timing jitter in ultrafast electron diffraction experiments with attosecond-level precision.

Embedding Matrices in Programmable Photonic Networks with Flexible Depth and Width

Matthew Markowitz, Kevin Zelaya, and Mohammad-Ali Miri

DOI: 10.1364/OL.553436 Received 18 Dec 2024; Accepted 26 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: We show that programmable photonic circuit architectures composed of alternating mixing layers and active layers offer a high degree of flexibility. This alternating configuration enables the systematic tailoring of both the network's depth (number of layers) and width (size of each layer) without compromising computational capabilities. From a mathematical perspective, our approach can be viewed as embedding an arbitrary target matrix into a higher-dimensional matrix, which can then be represented with fewer layers and larger active elements. We drive a general relation for the width and depth of a network that guarantees representing all N×N complex matrix operations. Remarkably, we show that just two such active layers—interleaved with passive mixing layers—are sufficient to universally implement arbitrary matrix transformations. This result promises a more adaptable and scalable route to photonic matrix processors.

Hyperboloidal mirror reflection for super-wide viewing zones in computer-generated holography

Yusuke Sando, Satoh Kazuo, Makoto Kawamura, Yutaro Goto, Daisuke Barada, and Toyohiko Yatagai

DOI: 10.1364/OL.553901 Received 02 Jan 2025; Accepted 26 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: A hyperboloidal mirror can widen the spreading angle of an incident spherical wave by reflecting the spherical wave outside the hyperboloidal mirror. We propose using this geometrical reflection property to widen the viewing zone in computer-generated holography. A hyperboloidal mirror was placed after wavefront modulation by a hologram, and it reflected the wavefront radially with a wide spreading angle. Viewers can observe a 3D object as a virtual image anywhere around the hyperboloidal mirror. A hologram calculation algorithm that considers the hyperboloidal mirror reflection was theoretically derived. The optical experiment successfully demonstrated super-wide viewing zones of 360° and 75° in the azimuthal and elevation directions, respectively.

Flipable multitask diffractive neural networks based on double-sided metasurfaces

He Ren, Shuai Zhou, Yuxiang Feng, Di Wang, Xu Yang, and Shouqian Chen

DOI: 10.1364/OL.555533 Received 14 Jan 2025; Accepted 26 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: Diffractive neural networks (DNN) have garnered significant attention in recent years as a physical computing framework, combining high computational speed, parallelism, and low power consumption. However, the non-reconfigurability of cascaded diffraction layers limits the ability of DNNs to perform multitasking, and methods such as replacing diffraction layers or light sources, while theoretically feasible, are difficult to implement in practice. This Letter introduces the flipable diffractive neural network (F-DNN), in which the diffraction layer is an integrated structure processed on both sides of the substrate. This design allows rapid task switching by flipping diffraction layers and overcomes alignment challenges that arise when replacing layers. Classification-based experimental results demonstrate that F-DNN addresses the limitations of traditional multitask DNN architectures, offering both superior performance and scalability, which provides a new approach for realizing high-speed, low-power, and multitask artificial intelligence systems.

High-efficiency De-scattering 3D Measurement with a Single Exposure based on Polarization Angle Shifting

Mingke Lei, Qican Zhang, and Yajun Wang

DOI: 10.1364/OL.555543 Received 14 Jan 2025; Accepted 26 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: The issue of scattering effect is common in imaging and optical 3D measurements, which introduces global illumination into the classical geometrical optics model. Separating the interested information from complex global-direct illumination often poses significant challenges. However, to suppress the global illumination, the conventional polarized modulated method generally requires manual adjustment to obtain multiple signals, which strictly limits the real-time detection and adaptability. To solve this problem, based on our analysis for the intensity distribution of four-channels of the polarization camera from Malus's Law, we establish a Polarization Angle Shifting (PAS) model and further propose a separation strategy to efficiently achieve global-direct light transmission components pixel-by-pixel separation with a single exposure. And the proposed method eliminates the limitation of the linear polarization of the light source. With the proposed method, we could obtain contamination-free phase of scattering interface and global information imaging. Experimental results in a structured light measurement system confirm the effectiveness of the method for separation imaging, and the final de-scattering 3D phase results are also shown.

Resolution-enhanced multifocal structured illumination microscopy using fluorescence fluctuations and Fourier ptychography scheme

Bin Yu, Mengjiao Nie, Zizhen Jiang, Danying Lin, Junle Qu, and Huiqun Cao

DOI: 10.1364/OL.555763 Received 14 Jan 2025; Accepted 26 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: Multifocal structured illumination microscopy (MSIM) provides a twofold resolution enhancement beyond the optical diffraction limit at sample depths of up to 50 μm. This is achieved through sparse multifocal excitation patterns and digital image postprocessing, rendering MSIM a highly advantageous technique for the three-dimensional super-resolution (SR) imaging of thick specimens. However, the spatial resolution of MSIM is inherently constrained by its underlying imaging principle. This paper presents a novel method that integrates SR optical fluctuation imaging based on Fourier ptychography and deconvolution (SFPD) with MSIM, termed SFPD-MSIM. Using photoblinking InP/ZnSe/ZnS core-shell quantum dot fluorescent probes for sample labelling, we demonstrate that, compared to widefield imaging microscopy, SFPD-MSIM achieves a fourfold resolution improvement. Additionally, it substantially reduces the image-acquisition time while preserving the structural integrity of the original samples. This advancement marks a major step forward in MSIM technology, providing a powerful tool for detailed structural analysis of complex and thick biological specimens.

An All-Optical Implementation of an Optoelectronic Oscillator Reservoir Computer with an Integrated Spatial Photonic Processor

tang fei, en liang, Hai Zhao, and Ziwei Li

DOI: 10.1364/OL.557054 Received 16 Jan 2025; Accepted 26 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: Abstract—Reservoir computing (RC), inspired by neural networks, has gained significant attention for tackling complex tasks such as recognition and classification. Most RC implementations are limited to software, which restricts both processing speed and energy efficiency, as reservoir outputs are often processed through slow, digital offline post-processing in previous work. To address these constraints, we propose a solution that combines a nonlinear time-delayed optoelectronic oscillator (OEO) with an integrated spatial photonic processor (ISPP) for online reservoir output processing. This approach leverages both temporal multiplexing and spatial processing, enabling high-speed, energy-efficient, and parallel hardware implementation. We achieve enhanced performance in modulation format recognition (MFR) for visible light communication (VLC) signals using a photonic reservoir with 64 nodes. Tests on 16 widely-used modulation formats at a 2 Gbps data rate over a 1.2 m VLC transmission link demonstrate that this spatiotemporal multiplexing technique can accurately classify all formats, achieving a state-of-the-art overall accuracy of 99.5%.

Forward polarization sensing triggered area-focus DAS over bidirectional coherent network

Jingchuan WANG, Maoqi LIU, Junwei Zhang, Liwang lu, Alan Pak Tao Lau, and Chao Lu

DOI: 10.1364/OL.554903 Received 07 Jan 2025; Accepted 25 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: Empowering optical communication networks with sensing capabilities is an emerging trend. In this letter, we propose a method to preliminarily detect perturbations in a bidirectional coherent network by utilizing forward polarization information. This information acts as a trigger and provides prior knowledge to backscattering-based distributed acoustic sensing (DAS), enabling more detailed event recovery. Consequently, the need to keep DAS continuously active is eliminated, making it highly practical for long-haul, high-resolution DAS sensing networks. Once activated, DAS can focus on a preliminary area of interest, significantly reducing its data processing workload. Experimentally, we employ a commercial 200-kHz laser to simultaneously achieve bidirectional 60-GBaud 16-QAM transmission and forward polarization sensing. The forward sensing information, extracted through equalization taps, triggers area-focused DAS, enabling fine-grained and ultra-low complexity sensing. This seamless integration of communication and sensing functions enhances efficiency and reduces complexity, paving the way for advanced network applications and more effective network surveillance capabilities.

Compact underwater single-photon imaging lidar

Mingjia Shangguan, Ye Li, Yican Mo, Jun Wang, and Tao Huang

DOI: 10.1364/OL.557195 Received 04 Feb 2025; Accepted 25 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: Underwater target imaging is important for marine resource exploration, underwater archaeology, and related fields. Lidar, with its high angular resolution, excellent depth resolution, and long-range 3D imaging capabilities, has become an essential tool for target imaging. However, the strong absorption and scattering properties of water, along with the constraints of lidar power consumption and system size, present significant challenges for high-performance lidar systems that are deployable in underwater and even deep-sea environments. To address these challenges, this work proposes and demonstrates a compact, all-fiber underwater imaging lidar. This lidar incorporates highly sensitive single-photon detection technology and features a cylindrical design with a diameter of 0.18 m and a length of 0.68 m. To achieve miniaturization, time-division multiplexing based on fiber arrays is employed, enabling the imaging of small underwater targets using two single-pixel detectors and a two-channel acquisition card. Additionally, an algorithm is introduced to effectively extract and subtract scattering signals from suspended particles in the water column. Tank experiments confirm that the system achieves imaging distances exceeding 10 times the optical attenuation length, and its distance and lateral resolutions are validated using step and stripe targets. With its outstanding performance and broad application potential, this compact lidar system is poised to complement imaging sonar and play a key role in underwater target monitoring and search operations.

Light Tunneling and Anomalous Reflection from the Diffraction of Complex Annuli: Modeling the Forward Light Scattering by Spherical Particles

Lilian Chabrol and Fabrice Onofri

DOI: 10.1364/OL.557822 Received 23 Jan 2025; Accepted 25 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: Anomalous reflection and tunneling contributions of the high-frequency forward light scattering by transparent spheres are modeled by the scalar diffraction of two complex annuli - one for TM and TE polarizations. Their complex radii, which depend on the refractive indices and particle size, are derived from the complex angular momentum (CAM) method, thus suggesting possible extensions to non-electromagnetic scattering. Coupled with the diffraction of a disk, and a geometrical optics approximation (GOA) for the refractive contributions, we propose an accurate hybrid model that requires one to two orders of magnitude less computational time than the Lorenz-Mie theory (LMT) in the near-field, a crucial improvement for e.g. inverse methods.

Three-dimensional polarization states generated from random paraxial light

Mengwen Guo, Dao Zhao, Jose Gil, Ari Tapio Friberg, Tero Setälä, and Andreas Norrman

DOI: 10.1364/OL.557844 Received 22 Jan 2025; Accepted 25 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: We investigate the polarimetric structure of three-dimensional (3D) light fields generated by an optical system from a random two-dimensional (paraxial) wave. In particular, we show that some central 3D polarimetric properties, e.g., the overall structure of the characteristic decomposition of the polarization matrix and whether the field is in a regular or nonregular polarization state, are determined by the geometry alone. The results areapplied to tightly focused fields.

Active breathing pulses induced by the periodic loss in a passive mode-locked laser

Jialong Feng, Zhenzhu Zhang, Jiajun Wei, Du Yueqing, Chao Zeng, Dong Mao, and Jianlin Zhao

DOI: 10.1364/OL.554512 Received 09 Jan 2025; Accepted 25 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: The breather is an important emerging topic in nonlinear optics. In fiber lasers, the breather is generally achieved by tuning the loss of the laser system to search for the proper Hopf-bifurcation route. Here, we propose a simple and reliable method to generate breathers, i.e., to introduce a controlled periodic transmittance, i.e., a periodic loss, within the laser that drives the mode-locked pulses to produce a synchronous periodic evolution. Therefore, we name this type of pulses as active breathers. Experimental results show that the characteristic parameters of the active breather, e.g., the breathing ratio and breathing frequency, can be accurately controlled by the modulation depth and modulation frequency of the periodic transmittance introduced by the electro-optical modulator. Numerical simulations can reproduce the experimental phenomena. Our work not only gives a new approach to modulate the characteristics of the breather but is also promising for the discovery of novel Hopf-bifurcation phenomena and soliton patterns in a periodically varying system.

High-power-seed femtosecond longwave infrared difference frequency generators

Songyin Yu, y zy, Mengke Qin, peining li, and Zhaowei Zhang

DOI: 10.1364/OL.557109 Received 15 Jan 2025; Accepted 25 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: We present a high-power-seed difference frequency generator (DFG) system using two signal pulse trains with the same power level from two optical parametric oscillators (OPOs). Compared to the conventional signal-idler DFG system, our scheme can avoid the efficiency drop of the longwave infrared pulses at longer wavelengths due to the power drop of the OPO at near degeneracy wavelength. Moreover, neither the pump nor the seed waves of our DFG would be affected by the atmospheric absorption. Experimentally, femtosecond pulses tunable over 5-20 μm, with up to 62 mW power and % quantum conversion efficiency (QCE) are obtained at the repetition rate of ~82 MHz. Over 20 mW power and nearly 20% QCE can be obtained at the central wavelength of 13 μm. This represents the highest value at such high repetition rate. To the best of our knowledge, our scheme represents the first experimental demonstration of high-repetition-rate DFG systems with the seed and pump waves having the same power level.

Solar Module as a High Speed Data Receiver with Ambient Light Suppression in an Outdoor Scenario

Rahul RAHUL, Abhijit Mitra, Anand Srivastava, Vivek Bohara, and Deepak Solanki

DOI: 10.1364/OL.545006 Received 21 Oct 2024; Accepted 24 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: Cost-effective, energy-efficient, and high-speed data transmissions are important requirements for future networks. Light communication using light-emitting diodes can fulfill these requirements owing to the huge unlicensed light spectrum. Optical sources are highly directional with low co-channel interference and interference with the radio frequency devices. On the receiver side, positive-intrinsic-negative photodiodesand avalanche photodiodes are used due to their ability to providehigh-speed linear photodetection. However, the impact of ambient light and misalignment issues due to smaller receiver areas is the biggest challenge for the outdoor operation of light communication.This paper presents a hardware implementation of analog circuitry to suppress the impact of ambient light along with bandwidth enhancement of a solar module as a data receiver. Solar modules having bigger receiver areas can also mitigate misalignment issues along with the speed of data transmission. This work presents a 99 % ambient light suppression tested in an outdoor environment with a peak intensity of 93500 lux over a solar module. A maximum transmission distance of 3.5 m is achieved using an infrared light source with a data rate of 5.5 Mbps.

Azimuth-Dependent Chiroptical Response in Dielectric Achiral Metasurfaces

nai jiang, Jianwei Shi, Chao Shen, and Jiaqi Guo

DOI: 10.1364/OL.551331 Received 20 Dec 2024; Accepted 24 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: Dielectric chiral metasurfaces have attracted tremendous attention for their potential applications on the next-generation planar photonic and biophotonic devices. However, most chiral metasurfaces are generally composed of complex chiral meta-atom structures and few design schemes are developed to dynamically tune the chiroptical response. Here, we experimentally demonstrated a new strategy to design achiral metasurfaces based on the extrinsic chirality of all-dielectric nanodisks arranged in square array. We found there exists two characteristic lattice modes corresponding to the coupling of nanodisk meta-atoms, and the azimuth induced asymmetric distribution of electromagnetic fields leads to an obvious CD signal. Intriguingly, the azimuth-dependent CD signals exhibit 4-fold rotational symmetry that is strongly dependent on the lattice symmetry. Meanwhile, the CD response can be modulated by simply changing azimuth of the nanodisks without fabricating two opposite chiral structures. Our work provides a simple design strategy for chiral metasurfaces based on the geometrically simplest 2D planar achiral meta-atoms and highlights the generation mechanism as well as adjustable ability of the chirality, which may promise various practical applications on on-chip azimuth and horizontal sensors.

Ultra-compact multimode waveguide bend based on central width controllable dual Bezier structure

Shenghang Zhou, Xing Yu, Qun Yuan, and Xiubao Sui

DOI: 10.1364/OL.553371 Received 17 Dec 2024; Accepted 24 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: Multimode waveguide bend (MWB) with compactness and high performance is essential for modern mode-division multiplexing (MDM) systems. Here we present a MWB with dual Bezier curves, allow for direct optimize of the bend's central width, enabling precise control of the MWB’s overall curvature variation and preventing overly narrowing of the waveguide width to suppress radiation loss. The realized bending effective radius is 10μm, equivalent to the most compact work to date, but based on a simpler method using mathematical curves. The calculated excess losses demonstrate very low rates of (0.0114, 0.0111, 0.0047, 0.0310) dB for the former four TE modes at 1550 nm, offers the best transmission efficiency. Notably, there is a significant improvement in the performance of high-order mode, which was previously considered challenging at such small size.

Fast and Accurate Waveform Modeling Based on Sequence-to-Sequence Framework for Multi-channel and High-rate Optical Fiber Transmission

Minghui Shi, Zekun Niu, Hang Yang, Junzhe Xiao, Chuyan Zeng, Yunfan Zhang, Zhixiong Zheng, Weisheng Hu, and Lilin Yi

DOI: 10.1364/OL.555880 Received 16 Jan 2025; Accepted 24 Feb 2025; Posted 25 Feb 2025  View: PDF

Abstract: We propose a sequence-to-sequence (Seq2Seq) framework integrated with a feature decouple distributed (FDD) method for fast and accurate channel waveform modeling in multi-channel, high-rate wavelength-division multiplexing (WDM) optical fiber transmission. This framework enables simultaneous prediction of multiple output symbols in a single inference, dramatically reducing the repeated calculation of adjacent padding symbols and achieving a significant reduction in time complexity compared to the traditional split-step Fourier method (SSFM). Additionally, transfer learning is leveraged to streamline the training processing and improve the accuracy of the Seq2Seq architecture. In a 40-channel, 140 GBaud WDM system, Seq2Seq-FDD reduces computation time to a mere 0.22% of that required by the variable step size SSFM. In a 5-channel configuration, Seq2Seq-FDD achieves an 85.5% improvement in NMSE over simplified FDD-Co-LSTM and a 99.88% reduction in computation time compared to vanilla-FDD. This framework provides a highly efficient solution for waveform modeling in multi-channel, high-rate WDM systems.

Enhancing pixel density in augmented reality displays via multi-channel interleaved imaging with metalens-coupled micro-LED islands

Sheng-Hui Li, Yu-Hsiang Hsieh, BO-HUEI FUNG, Yi-Syuan Huang, YEN-HSIANG FANG, WEI-HUNG KUO, Ming-Hsien Wu, and Guo-Dung Su

DOI: 10.1364/OL.558515 Received 30 Jan 2025; Accepted 24 Feb 2025; Posted 25 Feb 2025  View: PDF

Abstract: With continuous advancements in technology, augmented reality (AR) is emerging as a next-generation display solution, seamlessly integrating real and virtual environments. This study presents a direct near-eye AR system based on the integration of blue micro light-emitting diode (LED) islands and a metalens array. Each channel employs a transmissive metalens to collimate divergent light from micro-LEDs into parallel rays, which are directed to the eye to form an augmented image. Additionally, precisely designed optical axis offsets control the light paths across multiple channels, facilitating pixel interleaving to minimize pixel spacing and enhance pixel density. This approach resolves micro-LED pixels measuring 5 × 5 µm² with a 12 µm pitch into a target image with the same pixel size but an effective pitch of 6 µm. The demonstrated multi-channel system leverages optical interleaving to bypass pixel pitch limitations in lateral micro-LED structure, paving the way for ultra-thin, high-efficiency AR systems.

High-sensitivity measurement of low frequency vibration signal based on an optoelectronic oscillator with an intra-loop Michelson interferometer

Jun Hu, Wenrui Wang, Xueqian Bai, Biying Zhou, Ruoqi Wang, Haojie Wu, Lingyun Ye, and Kaichen Song

DOI: 10.1364/OL.549737 Received 21 Nov 2024; Accepted 24 Feb 2025; Posted 25 Feb 2025  View: PDF

Abstract: A high-sensitivity demodulation method for the vibration-induced frequency shift of an optoelectronic oscillator (OEO) using an acousto-optic modulator (AOM) has been proposed and experimentally demonstrated. This is achieved by separating the optical carrier (OC) and the first-order sideband, directing them into the reference and sensing arms of a Michelson interferometer (MI), respectively. Additionally, since the system sensitivity depends on the optical frequency rather than the oscillating frequency, high-sensitivity vibration sensing can be achieved at OEO oscillating frequencies as low as 80 MHz. By reducing the OEO system's oscillating frequency and using only single mode fiber components, system complexity and cost are greatly reduced.Experimental results indicate that for low-frequency vibration signals in the range of 200-800 Hz, the system achieves an vibration amplitude sensitivity up to 1.77 GHz/cm and a minimum detectable vibration amplitude of 5.1 pm, representing the best result within our current knowledge for low-frequency vibration demodulation using OEO.

Up to 182GBd PAM-4 optical interconnects eliminating receiver-side DSP

Lingjun Zhou, Xiansong Fang, Yixiao Zhu, Junbo Zhu, Yunchen Li, Zhen chen, Xiaomin Nie, Chuanchuan Yang, Xian Zhou, Zhixue He, Lei Wang, Ke LI, and Fan Zhang

DOI: 10.1364/OL.555167 Received 10 Jan 2025; Accepted 24 Feb 2025; Posted 25 Feb 2025  View: PDF

Abstract: The rapid development of artificial intelligent clusters and computing networks demands solutions with minimized power consumption and latency to scale effectively. Traditionally, high-speed intensity modulation with direct detection (IMDD) optical interconnects rely heavily on digital signal processing (DSP), leading to substantial power consumption and high latency. In this work, we utilize a broadband thin-film lithium niobate (TFLN) Mach-Zehnder modulator (MZM) chip to compare the performance differences between linear receive optics (LRO) and fully DSP-based solutions. We achieve up to 196 GBd OOK and 182 GBd PAM4 transmission eliminating receiver-side DSP while maintaining a bit-error rate below the 20% soft-decision forward error correction (SD-FEC) threshold. Furthermore, with feed-forward equalizer (FFE) only, we successfully transmit up to 210 GBd OOK signals. LRO addresses these challenges by removing the DSP from the receiver side, drastically reducing both power consumption and latency. Leveraging high-bandwidth devices, it retains performance to a significant extent while ensuring general interoperability.

Frequency conversion of 100-fs Ti:Sapphire laser pulse into the mid-IR range in a single HgGa₂S₄ nonlinear crystal with quantum efficiency of 30%

Igor Kinyaevskiy, Andrew Koribut, Yakov Grudtsin, and Maxim Ionin

DOI: 10.1364/OL.555407 Received 14 Jan 2025; Accepted 24 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: Difference frequency generation setup for frequency conversion of a femtosecond Ti:sapphire laser pulse into the long wavelength mid-IR range with a single HgGa₂S₄ nonlinear crystal was launched and demonstrated to be the best combination of simplicity and efficiency, to the best of our knowledge. In this setup the signal wave was formed by spectrum broadening of the aforementioned laser pulse under its filamentation in a CO₂ gas cell. The spectrum tuning of a mid-IR laser pulse within wavelength interval of 6-10.5 μm was demonstrated. The maximum energy of 0.24 ps laser pulse at 8 μm wavelength reached up to 35 μJ at internal quantum conversion efficiency of 30%.

Generation of subfemtosecond ultraviolet pulses by three-color near-infrared ionizing fields

Ivan Laryushin, Alexander Romanov, and Nikolay Vvedenskii

DOI: 10.1364/OL.545132 Received 18 Oct 2024; Accepted 24 Feb 2025; Posted 24 Feb 2025  View: PDF

Abstract: We propose a method for generating extremely short (few- and even sub-cycle) ultraviolet (UV) pulses with the use of three-color ionizing fields. We demonstrate that low-order combination frequencies can form supercontinuum up to the 5th harmonic of the fundamental field. This effect is achieved by using three-color fields with two weak components detuned from the half of the frequency of the intense fundamental field, which can be obtained from an optical parametric generator. Ourcalculations based on the solution of the time-dependent Schrödinger equation for the helium atom show that using a three-color near-infrared ionizing field with a duration of 25 fs, can result in generating an extremelyshort UV pulse with a central wavelength of about 300 nm and a duration of about 0.9 fs.

Spectral stripe based large range chromatic confocal displacement system with nanometer uncertainty

Yuehua Li, Ziheng Zhang, Tiejun Li, Wei Bian, Zhi Niu, Xiaohong Liu, and Jingbo Zhou

DOI: 10.1364/OL.553869 Received 21 Jan 2025; Accepted 24 Feb 2025; Posted 24 Feb 2025  View: PDF

Abstract: We present a novel design of chromatic confocal displacement system (CCDS) based on spectral stripe. In this system, confocal light collected by dispersive lens is shaped by Powell lens, and then diffracted onto the detector in the form of a thin straight stripe. The displacement variant is converted into the change of stripe positions on detector. Unlike the spectral profile or the diffractive spot, the spectral stripe significantly increases the pixel number for analysis and effectively suppresses random noises. Simulation and experiment results show that the positional uncertainty of spectral stripe is dramatically reduced and reach less than 1‰ pixel. Measurement uncertainty is less than 14.3 nm within the whole measuring range of 4 mm. It provides a new way for developing large range CCDS with nanometer uncertainty.

Titanium dioxide-assisted metal focusing grating couplers for thin-film lithium niobate waveguides

Jungwoo Lee and Min-Suk Kwon

DOI: 10.1364/OL.555001 Received 07 Jan 2025; Accepted 24 Feb 2025; Posted 24 Feb 2025  View: PDF

Abstract: Thin-film lithium niobate (TFLN)-based photonic integrated circuits (PICs) demand efficient, compact, and simply realizable grating couplers for optimal performance. This work introduces titanium dioxide (TiO₂)-assisted metal focusing grating couplers (TMFGCs) as a promising solution. The TMFGCs leverage a simplified fabrication process based on metal gratings. Moreover, they achieve a smaller footprint compared to previous one-dimensional metal grating couplers. Theoretical simulations predict a 1.3 dB enhancement in coupling efficiency due to the integrated TiO₂ structure. Experimental results demonstrate a maximum coupling efficiency of -4.88 dB, with the potential to reach -4.07 dB through refined fabrication techniques. The TMFGCs offer a simple yet effective approach to efficient light coupling in TFLN-based PICs.

Single-layer metasurface enables compact rotational speed detection system

jintao liang, siqi li, Lifei Li, Guoxi Wang, xiaofang wang, Yan Kang, and Zhang Tong-Yi

DOI: 10.1364/OL.554478 Received 02 Jan 2025; Accepted 23 Feb 2025; Posted 24 Feb 2025  View: PDF

Abstract: The detection of rotational speed based on the rotational Doppler effect (RDE) has gained notable attention due to its quick response, wide measurement range, and non-contact operation. However, previous methods for generating conjugate topological vortex beams in the rotational speed detection process rely on a series of bulky optical elements, such as the spatial light modulator (SLM) or digital micromirror device (DMD), making the system complex and difficult to integrate.In this letter, we propose a method to generate conjugate topological vortex beams via a single-layer metasurface, thereby realizing, to the best of our knowledge, the first compact version of an RDE–based rotational speed detection system. By analyzing the adjacent frequency peak gaps in echo light signals, the rotational speed of a rotating target can be accurately measured, with the maximum measurement error for each experiment being 0.812%. This method paves the way for development of miniature and compact RDE–based metrology devices, which are particularly suitable for applications with limited volume and payload, thereby enhancing the practical implementation of RDE-based metrology

Anisotropic magnetic response of opto-mechanical resonance in a high Q microbubble optical resonator filled with magnetic fluids

Yuxing Zhang, Sheng Liu, Lei Xu, and Liying Liu

DOI: 10.1364/OL.554788 Received 03 Jan 2025; Accepted 23 Feb 2025; Posted 24 Feb 2025  View: PDF

Abstract: We reported opposite change of the resonant frequency of mechanical modes in magnetic fluids filled optical microbubble resonators (MF-filled MBRs) under magnetic field. Such change was found to come from the anisotropic responses of the acoustic wave to the aligned MF. The acoustic wave in wineglass mechanical mode propagates along azimuthally and that of the breathing mechanical mode propagates axially, therefore the acoustic wave of the two modes interacts with the aligned magnetic particle chain differently, leading to the opposite change of resonant frequency. The anisotropy also results in opposite change of resonant frequency of the same mechanical mode when the magnetic field is applied in orthogonal directions. Our work provides a novel optomechanical system with rich resonance manipulation capabilities.

Compact all-PM fiber gain-managed nonlinear amplification system based on a stretched-pulse oscillator

Kun Chen, Jinlong Zheng, Qi Xu, Zhou Li, Xinyi Yan, Leyan Yang, Jing Li, Mingtao Peng, Yuxin Leng, and Jiahui Peng

DOI: 10.1364/OL.554814 Received 06 Jan 2025; Accepted 22 Feb 2025; Posted 24 Feb 2025  View: PDF

Abstract: The high-performance gain-managed nonlinear amplification (GMNA) system benefits from the dynamic interaction between seeding pulses and the evolving gain spectrum, making it ideal for high-power, sub-50 fs fiber laser systems. In this work, we demonstrate a compact all-polarization-maintaining fiber GMNA system based on a stretched-pulse oscillator (SPO). The SPO directly generates high-energy, chirp-optimized pulses for subsequent GMNA, eliminating the need for additional pre-compressors and pre-amplifiers. By jointly optimizing both the seeding and amplification stages, this monolithic SPO-GMNA laser system enables efficient energy extraction and spectral broadening exceeding 100 nm, delivering 106.8 nJ and 31.8 fs pulses. This robust, high-peak-power femtosecond fiber laser holds significant potential for applications in biomedicine and advanced manufacturing.

All-optical diode based on asymmetric nonlinear optical absorption in ternary transition metal chalcogenides

Lei Yan, Dechao Shen, Qinyong He, Anping Ge, Guohong ma, Ye Dai, Liaoxin Sun, and Saifeng Zhang

DOI: 10.1364/OL.553268 Received 19 Dec 2024; Accepted 21 Feb 2025; Posted 24 Feb 2025  View: PDF

Abstract: As the typical representative of ternary transition metal chalcogenides, CrPS4 and MnPS3 exhibit unique light-matter interactions, demonstrating great potential in photonic devices. In this work, we systematically studied the nonlinear optical (NLO) responses of CrPS4 and MnPS3 flakes by the I-scan technique. CrPS4 and MnPS3 flakes show saturable absorption and reverse saturation absorption excited by fs laser at wavelengths of 600 nm, respectively. Furthermore, utilizing the non-degenerate transient absorption technology, we observed the fast and slow carrier relaxation times of CrPS4 at different probe wavelengths were components with constants of about 1.4 – 3 ps and 490 – 1420 ps, respectively. The excellent ultrafast NLO properties of them imply that they can be applied in photoelectronic fields for advanced and functional devices. Here, we designed and demonstrated the all-optical diode based on a CrPS4/MnPS3 tandem structure by breaking the time-reversal symmetry. And, it achieved nonreciprocal transmission of light similar to that of p-n electron diode. This work describes fundamental NLO responses of CrPS4 and MnPS3 and facilitates the applications of them in versatile optoelectronic devices.

Pulsed cascaded Raman fiber laser widely tunable in the second near-infrared and visible window for hyperspectral photoacoustic imaging

Abhigyan Goswami, Swathi Padmanabhan, Sarthak Dash, Jaya Prakash, and V R Supradeepa

DOI: 10.1364/OL.553618 Received 19 Dec 2024; Accepted 21 Feb 2025; Posted 21 Feb 2025  View: PDF

Abstract: Pulsed laser sources with nanosecond pulse duration are widely used in numerous non-invasive biomedical imaging applications, notably photoacoustic imaging (PAI), an in-vivo imaging modality. Multiple laser sources are required to target the absorption features of multiple endogenous chromophores (optical absorbers inside tissue). We demonstrate a widely tunable pulsed cascaded Raman fiber laser continuously tunable in the second near-infrared window (NIR-II, 1060 nm-1600 nm) and through harmonic conversion in the visible window (530 nm-600 nm, limited by crystal availability in-house) for PAI in multiple wavelength bands. The laser generates pulse energy ~10 uJ in the NIR-II window and ~0.1 uJ in the visible window with a high repetition rate tunable from 20 kHz to 80 kHz, pulse duration tunable from 40 ns to 200 ns. The source is then used for PAI, demonstrating photoacoustic spectroscopy of lipids in the second resonance of C-H bonds (1145-1257 nm).

Eye-safe 1.5 µm Passively Q-switched solid-state Raman laser

Hongbo Zhang, NiHui Zhang, Di Xin, hongkun he, Jianghao Xu, Xuyan Zhou, Wan-hua Zheng, and Hong Zhang

DOI: 10.1364/OL.555069 Received 08 Jan 2025; Accepted 21 Feb 2025; Posted 21 Feb 2025  View: PDF

Abstract: Due to the high Raman threshold and the complex structure of actively Q-switched devices, a challenge is to achieve efficient stimulated Raman generation via passively Q-switched strategy. In this paper, first-order Raman laser at 1525 nm was successfully demonstrated through a passively Q-switched Nd:YVO₄/V:YAG excitation with compact and easily integrable structure. The pulse energy at 1525 nm could be up to 17.6 µJ at 1 kHz repetition rate with pulse duration of 6.2 ns. The corresponding optical efficiency was 21% and the measured beam quality factor M² < 1.3. Raman lasers operating at 1.5 µm have important applications in fields such as optical communication, laser scanning, distance measure-ment, remote sensing, and spectral analysis.

Megawatt peak-power, single-mode, mid-infrared femtosecond pulse delivery at 5-6 μm via silica-based anti-resonant hollow core fiber

ANG DENG, Linzhen He, Yuxi Wang, Trivikramarao Gavara, Liangliang Lu, Wonkeun Chang, Hongyu Luo, Jianfeng Li, and Houkun Liang

DOI: 10.1364/OL.555306 Received 08 Jan 2025; Accepted 21 Feb 2025; Posted 21 Feb 2025  View: PDF

Abstract: We demonstrate the first delivery of megawatt peak power, single-mode mid-infrared (MIR) femtosecond pulses at 5-6 μm using a silica-based anti-resonant hollow core fiber (AR-HCF). Benefiting from the light confinement inside the hollow core, the AR-HCF exhibits high damage thresholds, reliable power stability, efficient spatial beam self-cleaning, and pulse shape preservation. Pumped by a homemade LGS-based two-stage optical parametric amplifier generating high power ~200 fs pulses, the fiber achieves a maximum delivered peak power of 4 MW at 5.1 μm and 5 MW at 6.1 μm, with peak intensities reaching 100 GW/cm2, despite fiber losses exceeding 2 dB/m. This flexible, meter-scale delivery system demonstrates exceptional potential for addressing the challenges of high peak power MIR laser delivery in precise, minimally invasive interventional ablation, particularly at resonant peaks like amide-I (6.1 μm) and cholesterol esters (5.75 μm).

0.5 GHz femtosecond Yb:YAG thin-disk oscillator

Tingting Yang, Heyan Liu, qingzhe cui, xudong wei, Guichun Xia, Kunjian Dai, Qing Wang, and Jinwei Zhang

DOI: 10.1364/OL.557650 Received 21 Jan 2025; Accepted 20 Feb 2025; Posted 21 Feb 2025  View: PDF

Abstract: Thin-disk oscillators have made significant progress in high power and pulse energy generation, but their ability to achieve high repetition rates is limited, primarily due to the structure of the multi-pass pumping cavity and the requirement for large beam spot sizes within the cavity. In this letter, we employed asymmetric cavity structure and used the thin-disk crystal as an end mirror, successfully achieving repetition rates of 432 MHz and 520 MHz in Kerr-lens mode-locked Yb:YAG thin-disk oscillators, with corresponding output powers of 33 W and 36 W, and pulse durations of 253 fs and 276 fs, respectively. These results represent the highest repetition rates reported for mode-locked thin-disk oscillators to date. Achieving a repetition rate of 1 GHz appears feasible by integrating custom components within the disk pumping module

4.5 W Er-doped ZBLAN fiber laser at 3.78 μm

lu Zhang, Shijie Fu, Quan Sheng, Xuewen Luo, junxiang zhang, chunpeng shi, Wei Shi, and Jian-Quan Yao

DOI: 10.1364/OL.554676 Received 03 Jan 2025; Accepted 20 Feb 2025; Posted 21 Feb 2025  View: PDF

Abstract: In this work, we demonstrate an efficient long-wavelength operation of Er-doped ZBLAN fiber laser in the 3.5 μm band with 4F9/2→4I9/2 transition. A high-transmission band-pass filter is employed to the laser cavity to select the specific lasing wavelength around 3.78 μm. The fiber laser yields a maximum output power of 4.5 W at 3781.6 nm, with a slope efficiency (with respect to absorbed 1990 nm pump power) of 17.1% and a spectral linewidth of 0.17 nm. To the best of our knowledge, this work represents the highest output power ever achieved in fiber lasers beyond 3.7 μm. Wavelength tuning from 3770 nm to 3782 nm, without laser power degradation, is also achieved by rotating the filter.

In-amplifier soliton self-frequency shift optimization by pre-chirping – Experimental demonstration

Robi Kormokar, Md Faysal Nayan, and Martin Rochette

DOI: 10.1364/OL.551176 Received 04 Dec 2024; Accepted 20 Feb 2025; Posted 21 Feb 2025  View: PDF

Abstract: Soliton self-frequency shift (SSFS) is a fundamental mechanism of optical wavelength conversion and supercontinuum generation. Often, it is desirable to use a nonlinear propagation design that provides a large amount of SSFS, leading to wavelength conversion with a large frequency offset, or leading to a broad supercontinuum generation. The most effective approach to enhance SSFS is using an amplifying medium. In this context, it was theoretically predicted that a pre-amplified seed pulse should be chirped to maximize the extent of SSFS. Here, we make the experimental verification of this claim. For this purpose, a chirped seed pulse at a wavelength of 1880 nm is amplified and experiences SSFS in a Tm3+-doped fiber amplifier. The resulting soliton reaches a final wavelength that is tuned by adjusting the energy and chirp of the pre-amplified seed pulse. The experiment demonstrates that SSFS and energy conversion efficiency are maximized when the pre-amplified seed pulse is chirped at C0 ≈ 0.65gLD, where gLD is the total gain over one dispersion length. This research provides fundamental conclusion for the optimization of SSFS processes using any amplifying medium and finds application for large offset wavelength conversion and broadband supercontinuum generation.

Low-Loss, Low-Background Aluminum Oxide Waveguide Platform for Broad-Spectrum On-Chip Microscopy

Firehun Dullo, Nikhil Jyakumar, MICHEAL GETZ, AINA K. HERBJONROD, Christopher Dirdal, Daniel Wright, FRØYDIS S. SKOTTVOLL, SIRAWIT BOONSIT, Ganapathy Senthil Murugan, and Balpreet Ahluwalia

DOI: 10.1364/OL.551736 Received 26 Dec 2024; Accepted 20 Feb 2025; Posted 21 Feb 2025  View: PDF

Abstract: A versatile wide-spectrum photonic integrated circuit (PIC) platform, spanning from ultraviolet (UV) to infrared (IR) wavelengths, is essential for advancing on-chip optical microscopy and spectroscopy applications. The key desirable requirements for PICs are low loss, low autofluorescence background signals and high-refractive index contrast (HIC) to enable compact designs. Here, we present low-loss, low-autofluorescence aluminum oxide (Al2O3) waveguide platform developed using atomic layer deposition (ALD). At 405 nm, the Al2O3 strip waveguide exhibits an autofluorescence background approximately 200 times lower than the silicon nitride (Si3N4) and a propagation loss of less than 0.5 dB/cm. We demonstrate the suitability of the Al2O3 platform for multicolor on-chip total internal reflection fluorescence (TIRF) and super-resolution optical microscopy. The proposed Al2O3 platform offers a promising solution for highly sensitive on-chip bio-imaging and spectroscopy applications.

Integrated high-Q cascaded Fabry-Perot resonators based on lithium niobate Sagnac loop reflectors

Qian Qiao, Jintian Lin, Renhong Gao, Jianglin Guan, Chuntao Li, Guanghui Zhao, Xinzhi Zheng, Minghui Li, QIFENG HOU, Xiaochao Luo, Yingnuo Qiu, Lingling Qiao, Min Wang, and Ya Cheng

DOI: 10.1364/OL.553883 Received 26 Dec 2024; Accepted 20 Feb 2025; Posted 24 Feb 2025  View: PDF

Abstract: We demonstrated an integrated high-Q cascaded Fabry Perot (FP) resonator on lithium niobate on insulator (LNOI) implemented by multi-Sagnac-loop-reflectors, which was fabricated by femtosecond laser photolithography assisted chemo-mechanical polishing. Compared with the resonator comprised of only two Sagnac loop reflectors (SLRs), there is a significant Q factor enhancement in the cascaded resonator formed by multi-SLRs. The loaded Q factor of the cascaded resonator was measured to 1.16×10⁶, a five-fold improvement compared to the state of the art on the same material platform.

Independent measurement and dynamic observation of scalar and tensor coefficients in polarization holography

Zhengyu Li, Yi Yang, Yiping Liu, JinYu Wang, Xianmiao Xu, Zheng Shujun, Xinyi Yuan, and Xiaodi Tan

DOI: 10.1364/OL.558178 Received 27 Jan 2025; Accepted 20 Feb 2025; Posted 24 Feb 2025  View: PDF

Abstract: Polarization holography offers a distinctive advantage by enabling simultaneous control over light waves' amplitude, polarization, and phase. Within the tensor polarization holography theory framework, coefficients A and B, representing the scalar and tensor components of photoinduced changes in the dielectric tensor, respectively, play a pivotal role in manipulating the reconstruction wave. Accurate measurement and control of A/B are essential for achieving specific functionalities. In this Letter, we present a straightforward and effective method for measuring coefficients A and B, enabling independent observation of their variations while determining A/B. Unlike previous methods, this approach eliminates the influence of the interference angle, simplifies the experimental process, and accommodates the arbitrary polarization state of the recorded hologram. It provides a powerful means of precisely controlling A/B through exposure adjustment, facilitating the fabrication of advanced optical devices for diverse applications.

Chiral Flatband in Refractive Index Modulated Metasurfaces

Yidan Hu, Qilin Duan, Jiangbin Li, Shan Zhu, Yuhang Yin, and Huanyang Chen

DOI: 10.1364/OL.555234 Received 09 Jan 2025; Accepted 19 Feb 2025; Posted 19 Feb 2025  View: PDF

Abstract: Flatband exhibits unique properties, such as slow light effects and a high density of states, incorporating these properties into chiral metasurfaces can significantly enhance chiroptical responses across a range of incident angles. In this study, we establish a theoretical framework to analyze circular dichroism in the presence of broken mirror symmetry along the z-direction. Building on this framework, we implement strategies to modify the refractive index and utilize selective etching techniques, which lead to a metasurface with a pronounced flatband with chiroptical response. This metasurface holds significant potential for applications in chiral light source emission and detectors, chiral sensing, and enantioseparation, particularly at wide incidence angles.

Polarization-multiplexing metafiber for dual-mode bright-field and dark-field microscopy

Zilei Liu, Yingbo Li, xiaoyi zhang, siqi li, Guoxi Wang, and Wenfu Zhang

DOI: 10.1364/OL.551939 Received 27 Dec 2024; Accepted 19 Feb 2025; Posted 20 Feb 2025  View: PDF

Abstract: Bright-field and dark-field microscopy are typically used together as complementary techniques to provide comprehensive information about biological specimens with different optical absorption properties. However, switching between these two modes usually involves replacing several bulk optical components, which inevitably increases system complexity, introduces alignment challenges, and results in longer switching times. Herein, we propose a new polarization-multiplexing metafiber device for dual-mode bright-field and dark-field microscopy. Utilizing the polarization-multiplexing metalens, two tailored beams (i.e. Gaussian and OAM beam) can be generated, respectively, with simply changing the handedness of the incident circularly polarized light. By integrating such metalens onto the tip of a large-mode-area photonic crystal fiber, we experimentally demonstrated this compact and flexible metafiber can realize the dual-mode bright-field and dark-field microscopy using raspberry trichomes and pine stem, without the need to replace any optical components. The ultra-compact and flexibility features of the proposed metafiber-based dual-mode microscopy paves the way for promising applications in portable and in vivo biological imaging.

Polymer-based O-band waveguide amplifier using NaLuF4: Yb, Pr–PMMA nanocomposite as gain medium

Yu Yang, Siliang Tao, Zixuan Jiang, Fei Wang, Guanshi Qin, Zhixu Jia, Fanchao Meng, Dan Zhao, and Weiping Qin

DOI: 10.1364/OL.555941 Received 16 Jan 2025; Accepted 19 Feb 2025; Posted 20 Feb 2025  View: PDF

Abstract: Nanoparticles doped polymer waveguide devices have attracted increasing interest in some rapidly developing areas of broadband communications because they are easy to integrate on chip. As an important part of the gain medium of waveguide amplifiers, lanthanide doped nanoparticles have been widely studied to improve the amplification performance of devices. However, current research work is almost limited to erbium-doped nanoparticles and amplifiers operating in the C-band. Implementing O-band optical amplification technology remains a challenge. Here, we report a method for preparing O-band waveguide amplifiers using Yb3+ and Pr3+ co-doped nanoparticles-PMMA composite as gain media, recording for the first time a maximum optical gain of 19.4 dB/cm at 1300 nm in a polymer based waveguide amplifier. Our results provide a valuable insight into the development of O-band polymer waveguide amplifiers with high gain. By combining with erbium-doped waveguide amplifiers and thulium-doped waveguide amplifiers, amplification of the (O+S+C) band is expected to be achieved.

Slow Light Waveguides based on Bound States in the Continuum

Yuta Tanimura, Yuki Ishii, Kenta Takata, Takahiro Uemura, Masaya Notomi, Satoshi Iwamoto, and Yasutomo Ota

DOI: 10.1364/OL.558273 Received 28 Jan 2025; Accepted 18 Feb 2025; Posted 19 Feb 2025  View: PDF

Abstract: The concept of bound states in the continuum (BIC) has been advancing light confinement technology in leaky environments. In this letter, we propose and numerically demonstrate a slow light waveguide based on a BIC mode. We considered a waveguide with a polymer core loaded on a plane slab, which supports a leaky guided mode coupled to the radiation continuum in the slab. We found that periodic modulation of the polymer core along the propagation direction can result in a high group index mode with a low propagation loss due to BIC confinement. The introduction of one-dimensional photonic crystals into the BIC waveguides will largely expand its functionality and applications in integrated photonics.

Ink-Sprayed Transparent Ceramic Multilayer Planar Waveguides for Ribbon Lasers

Ross Osborne, Nerine Cherepy, Romain Gaume, Joseph Boro, and Stephen Payne

DOI: 10.1364/OL.554532 Received 02 Jan 2025; Accepted 18 Feb 2025; Posted 18 Feb 2025  View: PDF

Abstract: Multilayer transparent ceramic planar waveguides were fabricated using a newly developed particle-loaded ink spraying method, characterized, and lased. Waveguides with five Yb:YAG gain regions and four Lu:YAG index-matched regions were produced for application as a “ribbon laser”, as well as a homogeneous Yb:YAG waveguide. Elemental mapping revealed that the waveguide thicknesses varied from 40 to 69 μm, comprised of layers of less than 10 µm. The Yb concentration profiles were fit to a diffusion profile. The homogeneous and multilayer waveguides were tested in a laser cavity and produced similar slope efficiencies, with a maximum of 31% achieved. Their beam profiles provided evidence of the ribbon structure affecting the preferred mode.

Rapid measurements of Rayleigh-Brillouin scattering in gases at low temperature and low pressure using a VIPA-based spectrometer

Sihao Pi, Tao Wu, Xinxin Feng, hongda yan, Chenwen Ye, and Xing Dao He

DOI: 10.1364/OL.551346 Received 09 Dec 2024; Accepted 18 Feb 2025; Posted 19 Feb 2025  View: PDF

Abstract: We report on a novel method for rapid measurements of Rayleigh–Brillouin scattering (RBS) profiles in air at low temperatures and low pressures, using a spectrometer based on a virtually imaged phased array (VIPA). RBS profiles were measured over a temperature range of 213–293 K and a pressure range of 343–996 mbar. The Tenti S6 model was used to fit profiles and retrieve gas temperatures. The calculated root-mean-square error (RMSE) for the spectral fitting curve was less than 3. %, while the absolute error of retrieved temperatures was less than 2.44 K with an acquisition time of 2 s per profile. These results confirm the viability of using a VIPA-based spectrometer for rapid RBS profile measurements at low temperature and low pressure, with potential application to atmospheric measurements.

Laser Mpemba effect

Stefano Longhi

DOI: 10.1364/OL.550728 Received 29 Nov 2024; Accepted 17 Feb 2025; Posted 19 Feb 2025  View: PDF

Abstract: This work explores the emergence of Mpemba-like effects within the quantum theory of lasers. By examining the temporal dynamics of photon number statistics in a single-mode laser above threshold, we reveal the curious and counterintuitive possibility that a laser system, starting with photon statistics far from equilibrium, may reach its stationary nearly-Poissonian distribution faster than a system initially closer to equilibrium. Drawing parallels to both classical and quantum Mpemba effects, we suggest that this behavior results from the unique relaxation dynamics of photon states, which is described by a non-integrable birth-death process. Our findings offer new insights into the foundational aspects of quantum laser light and contribute to the expanding body of research on non-equilibrium phenomena in quantum systems.

Estimation of refractive index profile of a GeO₂-SiO₂ graded-index fiber from the elemental composition

Yongsop Hwang

DOI: 10.1364/OL.553553 Received 23 Dec 2024; Accepted 17 Feb 2025; Posted 18 Feb 2025  View: PDF

Abstract: We propose methods for the estimation of the refractive index profile of a GeO₂-SiO₂ graded-index fiber (GIF) from its elemental composition. We measured the mole fraction of GeO₂ as a function of radial position in a commercially available GIF, Thorlabs GIF625, using energy dispersive spectroscopy (EDS) and electron probe microanalysis (EPMA). Its refractive index profiles were also measured at multiple wavelengths.We found that the GeO₂ mole fractions estimated from the measured refractive index profiles show a discrepancy with the elemental composition obtained from the EDS/EPMA measurement. Two empirical approaches are proposed to bridge the elemental composition and the index profiles over the discrepancy: (1) Effective mole fraction approach and (2) density parameter approach. Using these approaches, we provide index profile parameters at important wavelengths from visible to infrared near 2.0 μm so that the index profile can be generated for applications of the GIF. The proposed approaches can be applied to other binary glass system GIFs.

Ultraviolet narrowband all-dielectric metasurface absorber with ultra-thin absorption layer

Fuming Yang, Zhong Liang, xiaoyan shi, Jinhuan Li, siyu guo, zhe wu, Wenwen Sun, xiangtao chen, Xintong Wei, Dai Rui, and junying liu

DOI: 10.1364/OL.554792 Received 03 Jan 2025; Accepted 17 Feb 2025; Posted 18 Feb 2025  View: PDF

Abstract: Ultraviolet (UV, 200~400 nm) detection with high efficiency and excellent spectral resolution is essential in spectral analysis. This letter proposes a UV narrowband all-dielectric metasurface absorber with an ultra-thin absorption layer. The design incorporates lossless Al2O3 resonators placed on a thin (20 nm) lossy Ga2O3 film, which enhances the absorption intensity at a specific wavelength. The near-perfect narrowband absorption enhancement results from the spectral overlap of the magnetic dipole (MD) and the electric dipole (ED) absorption modes by surface lattice resonance (SLR). The proposed absorber exhibits high-efficiency and high-quality (Q) absorption performance (A>95%, Q~ 1) and allows for flexible control over the absorption wavelength through simple parameter adjustments. These features make it ideal for narrowband emission, spectrum detection, and multispectral sensing.

Heavy metal-free white light-emitting diodes based on multinary copper chalcogenide nanocrystals

Peiwen Lv, Kai Wang, Danxing Hou, Shengli Wu, Jintao Guan, Zhe Yin, and Aiwei Tang

DOI: 10.1364/OL.555369 Received 17 Jan 2025; Accepted 17 Feb 2025; Posted 18 Feb 2025  View: PDF

Abstract: Quantum dot (QD) white light-emitting diodes (WLEDs) aimed at improving high-color gamut displays and solid-state lighting, yet faced scrutiny due to the toxicity of Cd. We have successfully fabricated WLED with a high color rendering index of 93 via heavy metal-free multinary copper chalcogenide nanocrystals. The devices demonstrate a maximum luminance of 1062 cd/m2 and a peak external quantum efficiency (EQE) of 1.15%. Notably, these devices exhibit minimal efficiency roll-off, maintaining an EQE of 1.09% even at elevated luminance levels (500 cd/m2). This investigation presents a compelling methodology for fabricating WLEDs and holds significant promise for potential applications.

DMD-Based Reflective Compressive Spectral Imaging System Coupled with Transformer-Based Reconstruction Method

Xinyu Liu, Chang Wang, Yang Zhang, Qiangbo Zhang, Qiuyu Yue, Zhenrong Zheng, and Liangcai Cao

DOI: 10.1364/OL.555832 Received 14 Jan 2025; Accepted 16 Feb 2025; Posted 18 Feb 2025  View: PDF

Abstract: Compressive spectral imaging (CSI) enables rapid acquisition of encoded measurements, followed by spectral image reconstruction using compressive sensing algorithms. However, existing CSI systems lack compact, effective encoding designs coupled with fast, high-quality decoding methods. This paper presents a CSI system with a compact reflective optical path design based on a Digital Micromirror Device (DMD), which facilitates additional independent compressive measurements by switching DMD patterns, thereby improving reconstruction accuracy. The system also establishes a direct one-to-one mapping between object points and image points, simplifying the design of the patch-based reconstruction algorithm. Leveraging this feature, a Transformer-based reconstruction method is proposed, which divides measurements into patches and employs a Transformer network to capture long-range dependencies and inter-patch similarities, reconstructing coefficients under a spatial-spectral dictionary for each patch. The proposed system and method achieve efficient acquisition and reconstruction of 256×256×22 spectral image data cubes across the 465–675 nm wavelength range.

Vector atom interferometry in a blue-detuned guiding optical potential

Changwen Liang, Qufei Wang, huankai Zhang, Bokun Liu, Jun Yang, Shuhua Yan, xiaoxiao ma, and Lingxiao Zhu

DOI: 10.1364/OL.551889 Received 13 Dec 2024; Accepted 16 Feb 2025; Posted 18 Feb 2025  View: PDF

Abstract: We propose and demonstrate a novel scheme for vector atom interferometry, using slender light pulses that nests around a blue-detuned guiding optical potential (BDGOP). The cold atoms could be uniformly transported through guiding optical potential and interacted coherently by slender light pulses. We analyze the coherence of cold atoms in BDGOP using Ramsey interference. In comparison to free-falling atom interferometry, the rapid exponential decay of fringe contrast is changed to slower linear decay when subjected to a tilting angle. The contrast could be enhanced approximately fourfold by BDGOP. Our work paves the way for multi-axis inertial vector measurements based on BDGOP.

Wavelength tunable blue light generation based on frequency tripling of a random Raman fiber laser

Wei Deng, Lu Chen, Zunwang Bo, Mengqiu Fan, Zhitao Leng, Houkun Liang, Bo Hu, and Han Wu

DOI: 10.1364/OL.553695 Received 20 Dec 2024; Accepted 16 Feb 2025; Posted 18 Feb 2025  View: PDF

Abstract: Nonlinear frequency up-conversion of random fiber lasers can generate wavelength flexible visible light with low temporal coherence. In this work, we demonstrate wavelength tunable blue light generation based on frequency tripling of a random Raman fiber laser (RRFL) in two cascaded periodically poled lithium niobate (PPLN) crystals. The RRFL can deliver watt-level and narrowband lasing in the spectral range of 1412-1435.5 nm, and by using a combination of a second-harmonic generation (SHG) followed by a sum frequency generation (SFG) in two cascaded PPLN crystals, blue light with a spectral tuning range from 470.6 to 478.7 nm is experimentally achieved, which is the first demonstration of visible light below 500 nm from frequency conversion of random fiber lasers. Moreover, we confirmed that the temporal intensity fluctuations of the generated blue light are uncorrelated, making such a blue light source suitable for chaotic Lidar and temporal ghost imaging applications. We believe the proposed frequency tripling of high power and tunable RRFL can provide a new platform for generating wavelength flexible and temporal chaotic blue light, which can have promising applications in underwater Lidar, display, and sensing applications.

Block-based single-pixel imaging by means of the Talbot effect

Erick Fabian Ipus Bados, Armin Lenz, Vicente Duran, Lluís Martinez, Jesus Lancis, and Enrique Tajahuerce

DOI: 10.1364/OL.550906 Received 02 Dec 2024; Accepted 16 Feb 2025; Posted 27 Feb 2025  View: PDF

Abstract: Block-based single-pixel imaging systems use multiple detectors of a focal plane array to implement highly parallel extensions of the single-pixel camera. This letter presents a new approach for parallel single-pixel imaging based on the Talbot effect. The method involves scanning an object with a short sequence of periodic light patterns, which are encoded on a digital micromirror device (DMD) and projected using the Talbot effect. The small unit cell of each pattern is a function of the Walsh-Hadamard basis. To collect the light from each unit cell, we implement an array of bucket detectors by using multiple pixels of a conventional camera. The image is recovered by applying single-pixel imaging algorithms in parallel. In addition to improving the spatial resolution of 2D sensor arrays and speeding up the frame rate of typical single-pixel cameras, our system provides a way to avoid optical elements between the DMD and the object. Both simulations and experiments with two optical setups are presented.

Second harmonic and sum frequency generation in silicon nitride microring on thin-film lithium niobate

Jianguo Wang, Binbin WANG, Junling Qu, Yanyan Zhang, chenyang Zhao, Jie Wang, Fang Liang, Jianlin Zhao, and Xuetao Gan

DOI: 10.1364/OL.555906 Received 16 Jan 2025; Accepted 15 Feb 2025; Posted 19 Feb 2025  View: PDF

Abstract: We demonstrate significant second harmonic generation (SHG) and sum frequency generation (SFG) on the thin-film lithium niobate (TFLN) platform by loading a silicon nitride (SiN) microring resonator, which avoids the dry etching of lithium niobate. By optimizing the SiN-loaded TFLN waveguide geometry, the phase-matching conditions between the fundamental pump laser and the SHG/SFG signals are designed. Combining with the enhancement by the microring resonator, remarkable SHG and SFG signals with conversion efficiencies of 16.43 %/W and 5.90 %/W are realized, respectively. Compared to traditional TFLN photonic platform, this CMOS-compatible strategy offers an opportunity for achieving large-scale on-chip nonlinear photonic devices based on TFLN.

Collective Transport of Particles and Cells Enabled by Wavelength Division Multiplexing in Microcavity Cascade Optical Tweezers

Jianguo Jiang, Qizan Shi, Weida Chen, Xu Liu, Linzhi Yao, Zhaoqi Ji, Minghui Zhang, xiufang wang, peng chen, Taiji Dong, and Chunlei Jiang

DOI: 10.1364/OL.553192 Received 17 Dec 2024; Accepted 15 Feb 2025; Posted 20 Feb 2025  View: PDF

Abstract: This study introduces an innovative microcavity cascade optical tweezers (MCOTs) system with wavelength-division multiplexing technology for collective transport of particles and cells in biomedical applications. The MCOTs system efficiently traps and transports yeast cells (5 μm diameter) and silica microspheres using 980 nm and 1550 nm lasers, achieving a maximum transport capacity of six particles. Under 980 nm laser irradiation, capillary forces surpass optical forces to stably trap multiple particles within the microcavity. At 1550 nm, significant heat absorption excites thermophoretic forces, which, combined with optical forces, enhance particle transport out of the MCOTs. Experimental results align closely with numerical simulations, confirming the system's feasibility for efficient collective transport of particles and cells, particularly in drug and cell delivery applications.

High-power single-cycle THz emission from large-area photoconductive emitters at 400 kHz

Mohsen Khalili, Yicheng Wang, Stephan Winnerl, and Clara Saraceno

DOI: 10.1364/OL.555079 Received 05 Dec 2024; Accepted 14 Feb 2025; Posted 18 Feb 2025  View: PDF

Abstract: We report high average power THz emission from a GaAs-based large-area photoconductive emitter, excited by a commercial Yb-laser amplifier without any compression schemes, doubled to the green. The LAE is pumped at 11.4 W of green average power (515 nm) and 310 fs pulse duration at 400-kHz repetition rate. We obtain a maximum THz power of 6.7 mW with a spectrum extended up to 3 THz. Using electro-optic sampling (EOS) for detection, we measure a high dynamic range of 107 dB in a measurement time of 70 s. To the best of our knowledge, this is the highest power THz source so far demonstrated with photoconductive emitters, based on a simple and robust, commercially available Yb-laser.

Hollow Optical Pin-Like Beams based Cassegrain System Performance Enhancement under Atmospheric Turbulence

Jinhao Wang, YUYANG TAN, LI HUI, LI MING, Han xida, wu xianlin, and LIN XUDONG

DOI: 10.1364/OL.557379 Received 23 Jan 2025; Accepted 13 Feb 2025; Posted 18 Feb 2025  View: PDF

Abstract: Cassegrain system, widely used in laser ranging system, faces emission efficiency challenges due to central obstruction. Current methods utilizing hollow beams based on orbital angular momentum (OAM) aim to mitigate these effects. However, such beams maintain the hollow structure, leading to the ineffective target illumination. Far-field center-healing hollow beams, such as hollow Gaussian beams (HGB), can effectively address these problems to ensure the proper target illumination, but are distorted by atmospheric turbulence, resulting in reduced echo intensity. In this study, to the best of our knowledge, hollow optical pin-like beams (HOPBs) are experimentally demonstrated for the first time, with superior turbulence resistance. Based on hollow beams, the emission efficiency of the central obstruction system increases from 72.45\% to around 90\%. The minimal echo decline of HOPBs is only 15\% under moderate turbulence, significantly outperforming HGBs, which experience reductions exceeding 31\%. Even under strong turbulence, HOPBs maintain the minimal echo reduction (41.19\%). This study highlights the advantages of HOPBs in addressing limitations from both central obstruction and atmospheric turbulence, offering a promising solution for improving the performance of laser ranging systems.

Statistical evaluation for enhancing robustness of optical PUF-based authentication systems

KUN CHEN, FENG HUANG, PIDONG WANG, and YAO YAO

DOI: 10.1364/OL.554001 Received 02 Jan 2025; Accepted 13 Feb 2025; Posted 19 Feb 2025  View: PDF

Abstract: Optical physical unclonable functions (PUFs) based authentication systems are gaining significant attention in the field of hardware security. However, its susceptibility to external factors (especially PUF misalignment) leads to a relatively low robustness, which severely hinders its practical applications. To address this, we propose a highly robust authentication scheme by integrating the strengths of multiple speckle-comparison methods. The speckle recognition performance of conventional metrics and newly introduced KAZE method is extensively analyzed and quantitatively assessed, utilizing a wide range of statistical measures, including False Rejection Rate (FRR), False Acceptance Rate (FAR), and Receiver Operating Characteristic (ROC) curve. Notably, even when traditional methods underperform, our solution still achieves ultra-high robustness with a FRR as low as 10^(-320) on the premise of ensuring security. Our results provide a comprehensive and in-depth understanding for optical PUF-based authentication systems, advancing their practical application in the field of hardware security.

A high-efficiency rectangular transverse air-gap metalens for visible light based on dual-coupled PB phase

Kaiwei Zhang, Haifei Lu, min li, Xiaoyan Wen, Mingyu Li, Shuo Deng, Sisi Liu, and Hong-Yun Gao

DOI: 10.1364/OL.549532 Received 19 Nov 2024; Accepted 13 Feb 2025; Posted 14 Feb 2025  View: PDF

Abstract: Pancharatnam-Berry (PB) phase modulation leverages the precise linear correspondence between output phase and nanopillar rotation angle, enabling wide application in modulating focal spherical waves. However, the intrinsic material absorption of waveguide structure inevitably brings energy loss within the visible light spectral range, severely limiting focusing efficiency over broad bandwidths under general models of nanopillars. Here, we introduce a dual-coupled metalens composed of air slot etched rectangular TiO2 nanopillar, and the extremely narrow air gap along its long axis of nanopillar can be regarded as a high-aspect-ratio rectangular waveguide for strictly confining the incident light. In the visible spectrum of 440~670 nm, the optical performance of the dual-coupled metalens is tested at the numerical apertures (NAs) of 0.35, 0.44, 0.6 and 0.82. Simulation results indicate that the structure not only meets the basic requirements of PB phase control, but also exhibits ultra-low loss and ultra-high focusing efficiency. The novel structure proposed in this work provides new design inspiration for general phase modulations and efficient micro-optical devices including wide-spectral metalens.

Bistable soliton optical frequency combs in a second harmonic generation Kerr cavity

Francesco Rinaldo Talenti, Stefan Wabnitz, Yifan SUN, Tobias Hansson, Luca Lovisolo, Andrea Gerini, Giuseppe Leo, Laurent Vivien, Christian Koos, Huanfa Peng, and Pedro Parra-Rivas

DOI: 10.1364/OL.551383 Received 12 Dec 2024; Accepted 13 Feb 2025; Posted 14 Feb 2025  View: PDF

Abstract: We study the dynamics and stability of soliton optical frequency comb generation in a dissipative, coherently pumped cavity with both second and third-order nonlinearity. Cavity sweep simulations and linear stability analysis based on path continuation reveal the existence of bistable solitons. These families of solutions represent a continuous transition between a purely quadratic and a Kerr cavity soliton frequency comb. Perspective demonstrations of these novel optical sources is an ongoing relevant subject within the frequency comb community.

An Optical Axis Calibration Method Using a 4-DOFM System for Long-travel Linear Guide Detection

Shao-Hua Ma, Ruijun Li, Kai Jiang, Zhen-Ying Cheng, and Jie Li

DOI: 10.1364/OL.551205 Received 05 Dec 2024; Accepted 12 Feb 2025; Posted 12 Feb 2025  View: PDF

Abstract: In laser measurement, geometric motion errors detection in long-travel linear guides is challenging because of air disturbances. This letter proposes an optical axis calibration method for long-travel linear guide detection using a 4-degree-of-freedom measurement (4-DOFM) system. The 4-DOFM system, which is based on laser collimation and autocollimation, can measure two straightness errors and two angular errors (pitch and yaw). The measured long-travel guide rail is detected in several sections. The difference in each optical axis can be measured solely through the 4-DOFM system without any additional equipment. The optical axis calibration algorithm is derived to achieve the synthesis of different optical axis measurement results. A series of experiments was conducted on the linear guide with a 2 m travel to verify the effectiveness of the proposed method. The proposed method can provide practical significance for laser detection of long-travel guide rails.

Single-pixel complex-field imaging through scattering media

Yining HAO and Wen Chen

DOI: 10.1364/OL.551397 Received 09 Dec 2024; Accepted 12 Feb 2025; Posted 12 Feb 2025  View: PDF

Abstract: Much research in optics was conducted to retrieve phase of the light field, e.g., via a reference wave (such as holography) or single-path optical diffraction. However, it is well recognized that a complete application of complex-field imaging (i.e., amplitude and phase) is still restricted by the existence of scattering media. In this Letter, we report high-resolution complex-field imaging with single-pixel detection which can effectively suppress scattering effect. Complex fields are retrieved by using a series of collected single-pixel light intensities with an alternating projection (AP) method. A momentum and the denoising engine are integrated into the iterative process to increase convergence speed and reduce sampling ratios with quality enhancement of the retrieved complex fields. A series of optical experiments are designed and conducted, and it is experimentally demonstrated that the retrieved complex fields related to the object are of high quality. The proposed method could open an avenue for a wide range of applications related to complex-field imaging through scattering media.

Smartphone Based Bimodal Device (SBBD) for Oral Precancer Diagnosis and Biopsy Guidance in Clinical Settings

Nemichand Nemichand, Shivam Shukla, BHASWATI DEO, Amar Sah, Subrata Mishra, Rachna Rath, and Asima Pradhan

DOI: 10.1364/OL.555254 Received 09 Jan 2025; Accepted 12 Feb 2025; Posted 12 Feb 2025  View: PDF

Abstract: We present a smartphone-based bimodal device (SBBD)combining fluorescence imaging and spectroscopy fornon-invasive, portable, cost-effective, and real-time diagnosisof oral precancer. The device utilizes a 405 nmlaser excitation to collect native fluorescence from intrinsicbiomarkers such as flavin adenine dinucleotide(FAD) and porphyrin in 136 subjects with both normaland abnormal oral cavities. The fluorescence imagingmodule identifies regions of interest (ROI) based on thered-to-green band ratio, while the spectroscopy moduleconfirms findings through multiple point measurements.A 2D convolutional neural network (CNN) classifiesnormal tissue, oral potentially malignant disorders(OPMD), and oral squamous cell carcinoma (OSCC)with 97.04% accuracy, 96.13% sensitivity, and 97.73%specificity. Fluorescence spectroscopy, enhanced by anartificial neural network (ANN), achieves 97.44% accuracy,95.24% sensitivity, and 97.44% specificity. Thisintegrated approach shows strong potential for earlyoral cancer detection and biopsy

Pupil wobble in point-scanning retinal optical coherence tomography systems

Amit Narawane, Pablo Ortiz, Mark Draelos, Ryan McNabb, Anthony Kuo, and Joseph Izatt

DOI: 10.1364/OL.547035 Received 05 Nov 2024; Accepted 12 Feb 2025; Posted 12 Feb 2025  View: PDF

Abstract: Optical coherence tomography (OCT) systems utilize 2D scanning methods to acquire reflectance-based volumetric images of samples, such as the human retina, with micrometer-scale depth resolution. A common method for performing this scanning at high speeds is to use a pair of sequential, single-axis galvanometer scanners. An undesired effect of using separated scanners is the variation in beam position at the pupil plane, a phenomenon known as beam wander or pupil wobble. This can lead to loss of signal and vignetting artifacts in the resulting images. To overcome these limitations, we propose a method to deterministically analyze the pupil wobble in a given retinal OCT system, and to correct for the deviation using pupil tracking OCT with a 2D scanning mirror is placed anti-conjugate to the pupil plane. We demonstrate that we can model the pattern of pupil wobble present in any OCT system both theoretically and empirically, and then use a pupil tracking system to correct for the deviation of the beam to acquire OCT images without the imposed artifacts.

Near-IR Photoluminescence at the Photon Level in Silica Fiber Patch Cable

Alexander Greenwood, Abhay Verma, Jackson Russett, Andi Shahaj, and Li Qian

DOI: 10.1364/OL.549799 Received 21 Nov 2024; Accepted 12 Feb 2025; Posted 21 Feb 2025  View: PDF

Abstract: We measure the spectral fluorescence emitted by commercial pure-silica core and germanium-doped core fibers in the range of 760 - 860 nm and find that the broadband fluorescence that exists in Ge-doped fiber can be avoided by adopting pure-silica core fiber. Most importantly, we present a narrowband (~1 nm FWHM) emission line characteristic of the zirconia ferrules used in both commercial Ge-doped and pure-silica core fiber patch cables. The results of this work are significant to many applications in the fields of quantum optics and fluorescence spectroscopy, where strong pump light co-propagates with signals at the photon level.

Inverse Design Fiber-to-Chip Couplers for the O- and C-Bands

Julian Pita Ruiz, Paulo Dainese, Jr., and Michael Menard

DOI: 10.1364/OL.550095 Received 25 Nov 2024; Accepted 11 Feb 2025; Posted 11 Feb 2025  View: PDF

Abstract: High-efficiency fiber-to-chip couplers are critical for achieving high-performance optical interconnects. In this letter, we experimentally demonstrate two inversedesigned silicon-on-insulator (SOI) couplers tailored for single-mode fibers (SMFs) in the C and O telecommunication bands. These couplers are robust against fabrication variations and are implemented with a single layer of silicon, with the O-band coupler being the first experimental demonstration of a topology-optimized coupler for this band. Operating at an 8° angle, they are optimized for the TE polarization and have a minimum feature size of 120 nm. The C-band coupler achieves acoupling efficiency of −3.3 dB with a 3-dB bandwidth of 64 nm, whereas the O-band coupler achieves a −3.4 dB coupling efficiency over a 3-dB bandwidth spanning from 1292 nm to 1355 nm. Measuring 12 µm by 12 µm,these devices are the most compact couplers implemented with a single silicon layer reported to date, and they achieve efficiencies comparable to those of much larger high-performance grating couplers. Their compact size can increase integration density and contribute to reduce fabrication costs. Additionally, these couplers could be suitable for spatial division multiplexing (SDM) interconnects using multicore fibers, where the mode field diameter is compatible with single-mode fibers. They could also be used with multimode fibers configurations, where multiple couplers could be combinedto generate higher-order modes.

THz-Driven Electron Manipulation via Non-Velocity-Matched Interaction in Dielectric-Loaded Waveguides

Xie He, Jiaqi Zheng, Kunlei Li, Dace Su, and Dongfang Zhang

DOI: 10.1364/OL.547993 Received 19 Nov 2024; Accepted 11 Feb 2025; Posted 13 Feb 2025  View: PDF

Abstract: Multi-cycle THz-driven electron compression and focusing in dielectric-loaded waveguides (DLWs) offer a compact solution for precise ultrafast electron beam control. However, practical implementation often suffers from dephasing effects due to fabrication tolerances. In this study, we investigate the dynamics of electron beam control in the context of non-velocity-matched interactions between non-relativistic electron beams and THz waves within the DLWs, revealing the relationship between velocity mismatch and the THz energy required for effective electron manipulation. Moreover, we propose a method for achieving cascaded electron compression and focusing within a single DLW by matching the electron beam to different phase components of the THz wave during their interaction. This adaptable strategy could significantly broaden the applications of THz-driven devices in generating high-quality ultrafast electron sources.

A two photon lensless endoscope with a double-clad tapered multi-core fiber

Luca Genchi, Matthias Hofer, Adrien Carron, Fatima El Moussawi, aymeric pastre, Remy Bernand, Damien LABAT, Andy Cassez, Rosa Cossart, Olivier Vanvincq, Geraud Bouwmans, Siddharth Sivankutty, Herve Rigneault, and Esben Andresen

DOI: 10.1364/OL.550709 Received 10 Dec 2024; Accepted 11 Feb 2025; Posted 12 Feb 2025  View: PDF

Abstract: We present an implementation of a multi-core fiber-based lensless micro-endoscope combining several novelties, Fermat’s golden spiral core layout, low-index polymer cladding, and longitudinally-varying diameter. We haracterize the resulting impacts on the various performance metrics, Strehl ratio, field-of-view, and memory effect, and demonstrate its application on biological cellular samples.

Theory of multicolor soliton microcombs

Carlo Silvestri, Justin Widjaja, Austin Lin, C. Martijn de Sterke, and Antoine Runge

DOI: 10.1364/OL.551523 Received 11 Dec 2024; Accepted 10 Feb 2025; Posted 11 Feb 2025  View: PDF

Abstract: We present a general theory of multicolor soliton microcombs. These frequency combs require specially engineered dispersion and have an optical spectrum consisting of multiple spectral windows, centered at distinct frequencies. Our theory is based on a multiple-scale approach applied to the Lugiato-Lefever equation, and provides a framework to investigate different pumping configurations. For multi-frequency pumping, we predict a progressively lower pumping threshold as the number of spectral windows increases due to an enhancement of the effective nonlinear parameter. However, multi-frequency pumping is not a prerequisite for the formation of these combs and can emerge even with a single driving field. Our theoretical predictions are in excellent agreement with numerical simulations.

Non-dispersive short pulses supported by quasiperiodic spatiotemporal gratings.

Vladimir Konotop

DOI: 10.1364/OL.547115 Received 05 Nov 2024; Accepted 10 Feb 2025; Posted 12 Feb 2025  View: PDF

Abstract: It is shown that a quasiperiodic spatiotemporal grating formed in a dispersive medium enables the propagation of linear localized pulses of the probe field without dispersive spreading. Increasing the lattice amplitude or modulation depth of the grating allows for the accommodation of a larger number of probe pulses. In the case of a formally infinite grating, these pulses propagate without distortion at the velocity of the spatiotemporal lattice. When the grating has finite spatial and temporal extents, input probe Gaussian pulses propagate over long distances with suppressed dispersion.

Multichannel High-Saturation Photodetection Technology for Femtosecond Pulse Optical Measurement System

Yaru Yang, Yifeng Li, Yumo Tian, MEILING YANG, Shenda Zhang, shuguo xie, and Yang Yan

DOI: 10.1364/OL.550545 Received 29 Nov 2024; Accepted 10 Feb 2025; Posted 19 Feb 2025  View: PDF

Abstract: The femtosecond pulse optical sampling downconverts broadband electromagnetic signals to the hundreds of MHz range, enabling fast measurement and enhancing electromagnetic monitoring efficiency. However, due to the high peak power of the optical pulses, the received power of the detector is severely limited, and thus the sensitivity of the system is reduced. To address this problematic issue, this paper presents a multichannel parallel high-saturation optical power balanced photodetection technique that uses parallel reception to enhance detector received power thereby improving the signal-to-noise ratio (SNR) and system sensitivity. To achieve the synthesis of multiple received signals, a miniature power divider filter is suitably designed, which achieves high amplitude and phase consistency through a slow wave transmission structure loaded with interdigital capacitors and serpentine inductors. The operating frequency of this structure ranges from 105 MHz to 210 MHz with amplitude imbalance less than 0.01 dB and phase difference less than 0.04°. Compared to similar designs, the area is reduced by 92.3%. The designed high-saturation photodetector allows an input saturation light power of 15 dB, and the detection system achieves a sensitivity of better than 4 mV/m. In the frequency range of 3 to 12 GHz, the sensitivity remains above 0.3 mV/m, representing a 14 dB improvement over commercial detectors.

Enhanced Fourier single-pixel imaging via positive-negative dithering

Haiyu Fan, Shijian Li, Chongwu Shao, Yinran Shen, Xu-Ri Yao, and Qing Zhao

DOI: 10.1364/OL.551685 Received 11 Dec 2024; Accepted 08 Feb 2025; Posted 20 Feb 2025  View: PDF

Abstract: Fourier single-pixel imaging (FSI) takes full advantage of the high modulation speed of digital micromirror devices by applying upsampling and spatial dithering to binarize grayscale Fourier patterns, thereby achieving efficient imaging. However, upsampling process of patterns sacrifices spatial resolution. Here we propose a binarization method for FSI that enhances reconstructed image quality without the need for upsampling. The key of the proposed method is directly applying spatial dithering on the positive-negative Fourier patterns before generating binary patterns. This method reduces quantization errors during the acquisition of Fourier coefficients. Both simulation and experimental results demonstrate that the method significantly improves imaging quality. It can also be applied to other types of single-pixel imaging that use positive-negative grayscale patterns.

Real-time calculation of Fresnel holograms using the split-Lohmann method

Antoine Lagrange, Antonin Gilles, Kevin Heggarty, Bruno FRACASSO, Patrick Gioia, and Vincent Savaux

DOI: 10.1364/OL.554228 Received 27 Dec 2024; Accepted 08 Feb 2025; Posted 05 Mar 2025  View: PDF

Abstract: Holography is often considered as the most promising technology to enable high fidelity 3D perception in augmented and virtual reality applications. However, the computation of holograms in real-time is still a challenging process especially for 3D scene with a complex geometry. To overcome this limitation, we propose a one-step technique to compute the Fresnel diffraction integral for several propagation distances. Our approach is based on the split-Lohmann method which consists of successive operations in both space and frequency domains. We demonstrate that our technique can compute Fresnel holograms of complex geometry scenes in real-time with a GPU implementation up to 18.1 times faster than layer-based approaches. Optical experiments are also conducted on a 4K full-color holographic display to show the high fidelity 3D perception provided by Fresnel split-Lohmann holograms.

Single-exposure X-ray dark-field imaging via a dual-energy propagation-based setup

Jannis Ahlers, Konstantin Pavlov, Marcus Kitchen, Stephanie Harker, Emily Pryor, James Pollock, Michelle Croughan, Ying Ying How, Marie-Christine Zdora, Lucy Costello, Dylan O'Connell, Chris Hall, and Kaye Morgan

DOI: 10.1364/OL.553310 Received 18 Dec 2024; Accepted 07 Feb 2025; Posted 07 Feb 2025  View: PDF

Abstract: X-ray dark-field imaging visualises scattering from sample microstructure, and has found application in medical and security contexts. While most X-ray dark-field imaging techniques rely on masks, gratings, or crystals, recent work on the Fokker--Planck model of diffusive imaging has enabled dark-field imaging in the propagation-based geometry. Images captured at multiple propagation distances or X-ray energies can be used to reconstruct dark-field from propagation-based images but have previously required multiple exposures. Here, we show single-exposure dark-field imaging by exploiting the harmonic content in a monochromatised synchrotron beam and utilising an energy-discriminating photon-counting detector to capture dual-energy propagation-based images. This work opens the way for low-dose and dynamic dark-field X-ray imaging without the need for a high-stability set-up and precision optics.

Dynamical simulations of single-mode lasing in large-area all-semiconductor PCSELs

Mindaugas Radziunas, Hans Wenzel, Ben King, Paul Crump, and Eduard Kuhn

DOI: 10.1364/OL.553405 Received 19 Dec 2024; Accepted 06 Feb 2025; Posted 07 Feb 2025  View: PDF

Abstract: We perform modeling and dynamic simulations of all-semiconductor photonic crystal surface-emitting lasers (PCSELs). A two-dimensional photonic crystal consists of a GaAs layer with InGaP features, repeating periodically in both lateral directions. In our dynamic simulations, we demonstrate for the first time that photonic crystals with large isosceles triangular features, having a base angle close to 71.5º, enable suppression of higher-order modes and achieve single-mode, high-quality lasing in large-area all-semiconductor PCSELs under moderate and even high pump levels.

From broadband biphotons to frequency combs via spectral compression with time-varying cavities

Karthik Myilswamy, Jordan Gaines, Jason McKinney, Joseph Lukens, and Andrew Weiner

DOI: 10.1364/OL.546633 Received 06 Nov 2024; Accepted 05 Feb 2025; Posted 21 Feb 2025  View: PDF

Abstract: Biphoton frequency combs are promising resources for quantum networking due in large part to their compatibility with the telecommunication infrastructure. In this work, we propose a method to periodically compress broadband frequency-entangled photons into biphoton frequency combs by utilizing time-varying linear cavities. Our approach hinges on rapid modulation of the input cavity coupling, yielding high spectral purity in each output comb line similar to that achieved with narrowband filters, but without the associated loss in flux. We examine the dependence of spectral purity and compression on coupling strength, cavity loss, and switching speed, finding realistic regimes supporting purities in excess of 0.999 and peak enhancement factors of 100× and beyond.

Non-reciprocal ponderomotive laser lens

Johan Ribbing, Giovanni Perosa, and Vitaliy Goryashko

DOI: 10.1364/OL.546892 Received 08 Nov 2024; Accepted 16 Jan 2025; Posted 21 Jan 2025  View: PDF

Abstract: When charged particles interact with laser fields, they are usually thought to be pushed out from the regions of higher laser intensity via the mechanism known as the ponderomotive force (PMF). In contrast to the existing theories, we show that there exist several regimes in which charged particles are drawn into the regions of strongly focused laser fields. We derive a simple, covariant and relativistically correct expression for the ponderomotive laser force that holds for arbitrary strength of field focusing, and for all particle velocities.We predict three new physical effects: (1) non-relativistic reversal of PMF,(2) focusing-dependent reversal of PMF, and (3) non-reciprocity of PMF for weakly-relativistic particle velocities.

ROLLING PHASE MODULATION REGIME FOR DYNAMIC FULL FIELD OCT

Tual Monfort, Kate Grieve, and Olivier Thouvenin

DOI: 10.1364/OL.543474 Received 02 Oct 2024; Accepted 14 Jan 2025; Posted 16 Jan 2025  View: PDF

Abstract: Dynamic full-field optical coherence tomography (DFFOCT) has recently emerged as an invaluable label-free microscopy technique, owing to its sensitivity to cell activity, as well as speed and sectioning ability. However, the quality of DFFOCT images are often degraded due to phase noise and fringe artifacts. In this work, we present a new implementation named Rolling-Phase (RP) DFFOCT, in which the reference arm is slowly scanned over magnitudes exceeding 2π. We demonstrate mathematically and experimentally that it shows superior image quality while enabling to extract both static and dynamic contrast simultaneously. We showcase RP DFFOCT on monkey retinal explant, and demonstrate its ability to better resolve subcellular structures, including intranuclear activity.