Early Posting

Accepted papers to appear in an upcoming issue

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

Radiation of Optical Angular Momentum by a Dipole Source inside a Magneto-optical Environment

Bart Van Tiggelen

DOI: 10.1364/OL.468802 Received 31 Aug 2022; Accepted 22 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: Radiation of electromagnetic energy by electric or magnetic multipole sources can be modified by their local environment. In this work we demonstrate that a magneto-optical environmentof an unpolarized dipole source induces the radiation of angular momentum into space. This effect is enhanced by local resonances.

Improving diameter measurement from Fraunhofer diffraction with fringe segment splicing

Bin Wu, Yingpeng Zhao, Zekuan Yang, Dianrong Li, Kaijun Zhang, Xiaochao Cao, Qiang Lin, and Zhenghui Hu

DOI: 10.1364/OL.476848 Received 30 Sep 2022; Accepted 22 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: Fraunhofer diffraction is known to provide an easy but powerful method for measuring the diameter of a thin filament.In practice, however, the diffraction pattern attainable is always subject to limits imposed by various imperfections in real systems, such as small angle approximation and sensor threshold, thus degrading measurement resolution. In this paper, we proposed a method of fringe segment splicing for improving diameter measurement from Fraunhofer diffraction. The fringe segment is chosen from a real diffraction pattern and is utilized to reproduce an ideal diffraction fringe, where the theoretical estimates get the best approximation to the observations. The problem of diameter measurement is solved in the spatial frequency-domain with an ideal diffraction fringe. Our results show that the relative error in this method is less than 0.1% and is much superior to that of previous methods.

Coherence induced depolarization effects inpolarization singular beams

Saba Khan, Stuti Joshi, and Paramasivam Senthilkumaran

DOI: 10.1364/OL.477229 Received 05 Oct 2022; Accepted 22 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: We demonstrate theoretically and experimentally coherence-induced depolarization effects in generic and higher index polarization singular beams endowed with C-point (or V-point) polarization singularity. Theirradiance profiles and degree of polarization (DoP) distributions were found to be governed by spatial coherence length, polarization singularity index and the orbital angular momentum (OAM) of the superposition states of the beam. On reducing the coherence length, the DoP distribution in the V-point deteriorates uniformly. On the contrary, C-point beams resist de-polarization exhibiting anti-depolarization around the central core of the beam due to the non-zero net OAM of the beam. Interestingly, the polarization vortex structure remains preserved on reducing the spatialcoherence length.

Transverse mode switchable fiber laser with a multimodal interference-based beam shaper

WENTAN FANG, Xiaohui Ma, Zhou Yong, Zhang Wei, Xiaolin Chen, Song Huang, Meisong Liao, Yasutake Ohishi, and Weiqing Gao

DOI: 10.1364/OL.478033 Received 11 Oct 2022; Accepted 22 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: We proposed an Yb-doped fiber laser with all-fiber beam shaper based on a single-mode-graded index multimode-few-mode fiber (SMF-GIMF-FMF) structure. The excitation coefficients of mode can be adjusted continuously by changing the GIMF length. Numerical simulations are performed to investigate beam shaping dynamics in the fiber structure. Through adding the simple device geometry in the laser cavity, the switchable output between the fundamental transverse (LP01) mode and the second order transverse (LP11) mode can be obtained. Cylindrical vector beams with high mode purity are also showed by removing the degeneracy of the LP11 mode.

3 TW single-cycle pulses enabled by thin plate post-compression

Szabolcs Tóth, Roland Nagymihály, Imre Seres, Levente Lehotai, Janos Csontos, László Tóth, Prabhash GEETHA, Tamas Somoskoi, Barna Kajla, Dániel Abt, Viktor Pajer, Arnold Farkas, Árpád Mohácsi, Adam Borzsonyi, and Karoly Osvay

DOI: 10.1364/OL.478253 Received 13 Oct 2022; Accepted 22 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: Post-compression of 12 fs laser pulses with multi-TW peak power from an Optical Parametric Chirped Pulse Amplification (OPCPA) system was performed by using a single thin fused silica plate in vacuum. By optimizing the input pulses in both spatial and temporal domains, after compression with customized chirped mirrors we achieved pulses as short as 3.87 fs, in combination with 12 mJ energy. Spatio-spectral quality of the post-compressed pulses was thoroughly analyzed. The generated 1.4-cycle pulses pave the way for next generation attosecond and particle acceleration experiments.

Gain switched Ho:YAG laser with 3.35 ns pulse duration.

Yechiel Bach, rotem nahear, and Salman Noach

DOI: 10.1364/OL.479205 Received 24 Oct 2022; Accepted 22 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: This paper presents a gain-switched Ho:YAG laser at2090 nm, pumped by a passively Q- switched Tm:YLF.Pulse duration of 3.35 ns was achieved with pulse en-ergy of 0.7 mJ at 1.3 kHz repetition rate correspondingto 209 kW peak power. The pump energy was 2.8 mJcorresponding to 25% conversion efficiency with 37%slope efficiency. This laser performance with its com-pact design can be implemented in applications thatrequire short pulse durations, that have not been ad-dressed to date.

Birefringent, low loss and broadband semi-tube anti-resonant hollow-core fiber

Yifeng Hong, Anqing Jia, Shoufei Gao, Xiaosong lu, Zhi Liang, Zhe Zhang, Wei Ding, Yingying Wang, and Yulin Sheng

DOI: 10.1364/OL.476126 Received 20 Sep 2022; Accepted 22 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: We report on the design, fabrication and characterization of a low-loss birefringent semi-tube anti-resonant hollow-core fiber (AR-HCF). By optimizing the structure design and the stack-and-draw fabrication technique, a transmission loss of 4.8 dB/km at 1522 nm, a < 10 dB/km bandwidth of 154 nm and a phase birefringence of 1.8×10−5 is demonstrated. This achieved loss is more than one order of magnitude lower than the previously reported birefringent AR-HCF and the bandwidth is one order of magnitude broader than the reported birefringent photonic bandgap hollow core fiber (PBG-HCF) with the same loss level. The polarization extinction ratio (PER) reaches ~20 dB level after 90 m-long fiber under >25 cm bending radius. Combining with the single mode and low dispersion feature, the developed semi-tube AR-HCF may find a variety of applications in frequency metrology, interferometric fiber gyroscope, and long-baseline stellar interferometry.

Thin-Film Dynamics Unveils Interplay Between LightMomentum and Fluid Mechanics

Gopal Verma, Gyanendra Yadav, and Wei Li

DOI: 10.1364/OL.479860 Received 03 Nov 2022; Accepted 22 Nov 2022; Posted 23 Nov 2022  View: PDF

Abstract: We quantitatively measure the nanomechanical dynamics of the water surface excited by the radiation pressure of a Gaussian/annular laser beam near-total internal reflection incident (TIR). Notable, radiation pressure near TIR allowed us to induce the pushing force (Abraham's momentum of light) for a wide annular Gaussian beam excitation of the thin-film regime of water, that has never been observed with nanometric precision previously. Our finding suggests that the observation of either/both Abraham and Minkowski's theories can be witnessed by the interplay between optics and fluid mechanics. Furthermore, we demonstrate the first simultaneous measurement of Abraham and Minkowski's momenta emerging in a single setup with a single laser shot. Our experimental results are strongly backed by the numerical simulations performed with realistic experimental parameters and offer broad range of light applications in optofluidics and light-actuated micro-mechanics.

In-line mode-dependent loss equalizer with femtosecond laser induced refractive index modification

Cong Zhang, senyu zhang, Yuwen Qin, and Songnian Fu

DOI: 10.1364/OL.480200 Received 03 Nov 2022; Accepted 22 Nov 2022; Posted 23 Nov 2022  View: PDF

Abstract: We demonstrate an in-line all-fiber mode-dependent loss (MDL) equalizer with femtosecond laser induced refractive index (RI) modification. By inscribing a RI-modified structure into the core of few-mode fiber (FMF), a differential mode attenuation (DMA) can be achieved for LP01 and LP11 modes. The DMA can serve as an in-line MDL equalizer for the long-haul mode-division multiplexing transmission system. Through numerical simulations, we identify that LP01 mode has a larger attenuation than that of higher-order modes, where the sign of DMA is contrary to that of the conventional FMF links and devices. Finally, a proof-of-concept experiment is implemented by inscribing a RI modified region with a width of 4 μm, a height of 13 μm, and a length of 200 μm into the FMF core. An average additional attenuation of 8.4 dB and 3 dB can be applied to LP01 and LP11 modes over the C-band, respectively, leading to an MDL equalization range of 5.4 dB. Meanwhile, the average polarization dependent loss (PDL) of LP01 and LP11 mode is less than 0.3 dB over the C-band. Power matrix measurement indicates that the in-line MDL equalizer has a negligible mode coupling. The proposed in-line MDL equalizer with a wider range and low insertion loss is feasible by precise manipulation of femtosecond laser inscription.

A gate-tunable bolometer based on strongly-coupled graphene mechanical resonators

Hui Chen, Zi-Fan Zhao, Wei-Jie Li, Ze-di Cheng, Jiao-Jiao Suo, Bo-Lin Li, Meng-Lin Guo, Boyu Fan, Qiang Zhou, You WANG, Hai-Zhi Song, Xiaobin Niu, Xiao-Yu Li, Konstantin Arutyunov, Guang-Can Guo, and Guangwei Deng

DOI: 10.1364/OL.476010 Received 26 Sep 2022; Accepted 21 Nov 2022; Posted 23 Nov 2022  View: PDF

Abstract: Bolometers based on graphene have demonstrated outstanding performance with high sensitivity and short response time. In-situ adjustment of bolometers is very important in various applications, but it is still difficult to implement in many systems. Here we propose a gate-tunable bolometer based on two strongly-coupled graphene nanomechanical resonators. Both resonators are exposed to the same light field, and we can measure the properties of one bolometer by directly tracking the resonance frequency shifts, and indirectly measure the other bolometer through the mechanical coupling. We find that the sensitivity and the response bandwidth of both bolometers can be independently adjusted by tuning corresponding gate voltages. Moreover, the properties of the indirectly measured bolometer show a dependence on the coupling between the two resonators, with other parameters being fixed. Our method has the potential to optimize the design of large-scale bolometer arrays, and open new horizons in infrared / terahertz astronomy and communication systems.

Micro-cone arrays enhance outcoupling efficiency in horticulture luminescent solar concentrators

Zhijie Xu, Mark PORTNOI, and Ioannis Papakonstantinou

DOI: 10.1364/OL.478206 Received 13 Oct 2022; Accepted 21 Nov 2022; Posted 23 Nov 2022  View: PDF

Abstract: Luminescent solar concentrators (LSCs) have shown the ability to realize spectral conversion, which could tailor solar spectrum to better match photosynthesis requirements. However, conventional LSCs are designed to trap, rather than extract, spectrally converted light. Here, we propose an effective method for improving outcoupling efficiency, based on protruded and extruded micro-cone arrays patterned on the bottom surface of LSCs. Using Monte-Carlo ray tracing, we estimate a maximum external quantum efficiency (EQE) of 37.73% for our Horticulture-LSC (HLSC), corresponding to 53.78% improvement relatively to conventional, planar LSCs. Additionally, structured HLSCs provide diffuse light, beneficial for plant growth. Our micro-patterned surfaces provide a solution to light trapping in LSCs and a foundation for practical application of HLSC.

Electromagnetic induction for reinforced concrete blasting: Principles, simulations, experiments, and applications

Min Wang, Zhan Wang, Zhaojun Chen, Xiaopeng Wang, and Ruichan Lv

DOI: 10.1364/OL.477472 Received 10 Oct 2022; Accepted 21 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: Reinforced concrete structures are widely used in the field of architecture. With the rapid development of highway construction all over the world, the structure of some buildings has various problems and needs to be demolished. However, various traditional dismantling methods are either time-consuming and labor-intensive, or cause pollution and have certain safety hazards. In this research, Comsol simulation and experimental verification on various schemes of electromagnetic heating blasting reinforced concrete were carried out. Also, the conducted blasting experiments using electromagnetic wave including microwave were further processed to verify the infeasibility. Finally, we proposed a feasible electromagnetic heating device for blasting reinforced concrete. Compared with the traditional blasting technology, the device has the advantages of high efficiency, environmental protection, safety and convenience, and has high social value and practical value.

A simple and fast calibration method for phase-only spatial light modulators

Minchol Lee, Donghoon Koo, and Jeongmin Kim

DOI: 10.1364/OL.473703 Received 22 Aug 2022; Accepted 21 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: Phase-only spatial light modulators (SLMs) are widely used to engineer the phase of light in various applications. However, liquid-crystal-on-silicon SLMs have undesirable spatial variations in phase response and optical flatness across the SLM panel, which must be compensated for accurate phase control. Here, we present a simple and fast way to calibrate these non-uniformities of the SLM at single pixel resolution. Using Twyman-Green interferometry without a piezoelectric transducer, our method only needs to collect 18 interferograms for constant gray-level SLM patterns and, to our knowledge, has the shortest measurement time of ~4.5 s. This is fast enough that there is no concern for environmental disturbances during interferometry. We detail the calibration procedure, discuss the performance of calibrated local pixel response, and verify the flatness calibration with SLM-based phase shift interferometry.

Silicon photonic receiver for satellite laser communication terminals

Jeong Hwan Song, Tangla Kongnyuy, Mathias Prost, Hakimeh Mohammadhosseini, and Roelof Jansen

DOI: 10.1364/OL.475063 Received 06 Sep 2022; Accepted 20 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: We report the optical performance of the photonic lantern receiver for laser communication applications. The receiver is composed of 14 × 12 customized grating coupler arrays. The photonic lantern receiver is designed for 20µm to 30µm mode field diameter (MFD) input sources. To maximize the fill factor of the 200µm×200µm light-receiving area per, a design strategy has been proposed. 1) Grating couplers are customized such as having a 5µm-long taper for compactness. 2) Periods of grating couplers are designed to work as end- and back-fire grating couplers for the same incident angle of the input laser source. 3) Different widths of routing waveguides are used to minimize cross-talks. The received optical signal power will be combined electrically via germanium photodiodes. The optical evaluation of the photonic lantern receiver is implemented with a 10µm-MFD source. As a result of the evaluation, the fulfillment of the specification of minimum efficiency of -10.5dB will be 95% when illuminating a 20-30µm-MFD laser source.

Predictive correction method based on deep learning for phase compensation system with frozen flow turbulence

Jingjing Meng, Jianguo He, Min Huang, Yang Li, ZHU Baoyu, Xinxin Kong, Zhe Han, Xin Li, and Yang Liu

DOI: 10.1364/OL.479359 Received 25 Oct 2022; Accepted 20 Nov 2022; Posted 21 Nov 2022  View: PDF

Abstract: We propose a deep learning method that includes convolution neural network (CNN) and convolutional long short-term memory (ConvLSTM) models to realize atmospheric turbulence compensation and correction of distorted beams. The trained CNN model can automatically obtain the equivalent turbulent compensation phase screen based on the Gaussian beams affected by turbulence and without turbulence. To solve the time delay problem, we use the ConvLSTM model to predict the atmospheric turbulence evolution and acquire a more accurate compensation phase under the Taylor frozen hypothesis. The experimental results show that the distorted Gaussian and vortex beams are effectively and accurately compensated.

Neuronal integration mechanisms with a quantum dot laser neuron

Michael Dillane, Evgeny Viktorov, and Bryan Kelleher

DOI: 10.1364/OL.475805 Received 02 Oct 2022; Accepted 20 Nov 2022; Posted 21 Nov 2022  View: PDF

Abstract: Neuromorphic computing has garnered a lot of attention in recent years. Excitable photonic systems in particular demonstrate great potential for ultrafast, controllable spike processing. Optically injected quantum dot lasers display several distinct excitable regimes. We demonstrate here that optically injected dual state quantum dot lasers can display the classic leaky integrate and fire mechanism where the integration of several sub-threshold perturbations can yield an effective supra-threshold perturbation. Intriguingly, a contrasting integrate and inhibit mechanism is demonstrated in this work where the integration of two supra-threshold perturbations yields an effective sub-threshold perturbation similar to the pre-pulse inhibition mechanism of biological neurons. This is the first such mechanism in neuromorphic photonics to the best of our knowledge.

Snapshot multi-frames parallel hyperspectral holographic microscopy based on reconfigurable optical comb

Yanqi Chen, Fangjian Xing, wei li, yuhang Sheng, Yunsong Di, Zhixing Gan, and Cihui Liu

DOI: 10.1364/OL.479993 Received 02 Nov 2022; Accepted 20 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: We present a snapshot multi-frames parallel holographic microscopic system through a reconfigurable optical comb source, which consists of a digital micromirror device (DMD) based spectrum filter system and a spectroscopic Michelson interferometric system. The proposed system allows arbitrarily tuning comb spacing and comb number, and capturing multi-frames images without overlaps in one exposure. As a result, high-quality hyperspectral holograms can be obtained with less acquisition time. Performance of the system is detailed in the experiment and 45-wavelengths holographic imaging for perovskite micro-platelets is conducted, which proves the system has ability to realize high-performance four dimensional (4D) imaging.

Spatially modulated light harvesting with plasmonic crescent metasurface

Jing-Wen Wu, Rong Cong, Su Xu, and Yue-Feng Liu

DOI: 10.1364/OL.478778 Received 23 Oct 2022; Accepted 19 Nov 2022; Posted 21 Nov 2022  View: PDF

Abstract: Harvesting light by metallic structures with sharp corners, or the so-called photonic singularities, has exhibit their potential in nanophotonics, sensing and biomedical applications. The high-quality light confinement of the light energy mainly relies on the precise preparation of nano-scale photonic singularities. However, the realization of massive photonic singularities still meets the challenges on integration and low-cost mask multiplexing. Here, we show an angle-dependent elevated nanosphere lithography to achieve massive photonic singularities for spatially modulated light harvesting at near-infrared regime. The photonic geometrical singularity is constructed by the gold crescent array of plasmonic materials. The numerical simulation shows that the light can be localized at the spatially distributed singularities. This phenomenon is verified experimentally through the infrared spectral measurement. Our work provides the possibility to produce integrated light-harvesting devices for numerous optical applications in illumination, display and enhanced nonlinear excitation.

Research Article Optics Letters 1Efficient single-scattering look-up table for lidar andpolarimeter water cloud studies

Eduard Chemyakin, Snorre Stamnes, Johnathan Hair, Sharon Burton, Adam Bell, Chris Hostetler, Richard Ferrare, Jacek Chowdhary, Richard Moore, Luke Ziemba, Ewan Crosbie, Claire Robinson, Michael Shook, Kenneth Thornhill, Edward Winstead, Yongxiang Hu, Bastiaan van Diedenhoven, and Brian Cairns

DOI: 10.1364/OL.474282 Received 01 Sep 2022; Accepted 18 Nov 2022; Posted 21 Nov 2022  View: PDF

Abstract: Combined lidar and polarimeter retrievals of aerosol, cloud and ocean microphysical properties involve single-scattering cloud calculations that are time consuming. We create a look-up table to speed up these calculations for water droplets in the atmosphere. In our new Lorenz-Mie look-up table we tabulate the light scattering by an ensemble of homogeneous isotropic spheres at wavelengths starting from 0.35 µm. The look-up table covers liquid water cloud particles with radii in the range of 0.001-500 µm while gaining an increase of up to 10^4 in computational speed. The covered complex refractive indices range from 1.25 to 1.36 for the real part and from 0 to 0.001 for the imaginary part. We show that we can precisely compute inherent optical properties for the particle size distributions ranging up to 100 µm for the effective radius and up to 0.6 for the effective variance. We test wavelengths from 0.35 to 2.3 µm and find that the elements of the normalized scattering matrix as well as the asymmetry parameter, the absorption, backscatter, extinction, and scattering coefficients are precise to within 1% for 96.7-100% of cases depending on the inherent optical property. We also provide an example of using the look-up table with in situ measurements to determine agreement with remote sensing. The table together with C++, Fortran, Matlab, and Python codes to interpolate the complex refractive index and apply different particle size distributions are freely available online.

Digital image correlation based on pre-deformation assist strategy and optimized checkerboard-like speckle pattern for large deformation measurement

Jingchen Ye, Xiaochuan Zhang, Hongwei Ji, and yujiang liu

DOI: 10.1364/OL.479603 Received 28 Oct 2022; Accepted 18 Nov 2022; Posted 21 Nov 2022  View: PDF

Abstract: Large deformation measurement is one of the main issues faced by digital image correlation method, and the specially designed speckle pattern offers a promising solution. This letter suggests an extremely simple to fabricate optimized speckle pattern for large deformation problems. It demonstrates a more effective large deformation initial estimation capability and measurement accuracy when combined with the pre-deformation assist strategy. A series of simulated and real experiments are used to test the effectiveness of the proposed method, and the results reveal that it performs significantly better than the traditional method in large deformation problems.

Multi-task photonic time-delay reservoir computing based on polarization modulation

Long Huang and Jianping Yao

DOI: 10.1364/OL.479472 Received 26 Oct 2022; Accepted 17 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: We propose and experimentally demonstrate a multi-task photonic time-delay reservoir computing (RC) system based on polarization modulation. The key component in the system is a polarization modulator (PolM) which functions, jointly with a polarization controller (PC) and a polarizer, as an equivalent Mach-Zehnder modulator (MZM), to perform electrical to optical conversion and to provide nonlinear operation. By adjusting the bias of the equivalent MZM, the nonlinear function can be optimized for different tasks to achieve the best multi-task performance. In this paper, the task-independent information processing capacity (IPC) of the time-delay RC system is evaluated. The results show that the readout bias of the equivalent MZM leads to different IPC which can be optimized for different tasks. Two benchmark tasks (NARMA10 and IPIX radar signal prediction) are performed experimentally. The readout bias is adjusted independently for each of the two tasks to give a minimum normalized mean square error (NMSE), which are 0.2103 and 0.0031 for the NARMA10 and IPIX radar signal prediction tasks, respectively.

3D microfabrication by applying the laser-induced bubble (microFLIB) method to the thermoset polymer PDMS using a conventional nanosecond laser

Yoichi Toba and Yasutaka Hanada

DOI: 10.1364/OL.477649 Received 11 Oct 2022; Accepted 17 Nov 2022; Posted 21 Nov 2022  View: PDF

Abstract: We recently developed a microfabrication technique (microfabrication using laser-induced bubble (microFLIB)) and applied it to polydimethylsiloxane (PDMS), a thermoset polymer. The technique enabled the rapid fabrication of a microchannel on a PDMS substrate and selective metallization of the channel via subsequent plating; however, the technique was limited to surface microfabrication. Therefore, we here explored the feasibility of three-dimensional (3D) microFLIB of PDMS using a nanosecond laser. In the experiment, a laser beam was focused inside pre-curing liquid PDMS and was scanned both perpendicular and parallel to the laser-beam axis to generate a 3D line of laser-induced bubbles. In the microFLIB processing, the shape of the created bubbles was retained in the pre-curing PDMS for more than 24 h; thus, the line of bubbles generated by the perpendicular laser scanning successfully produced a 3D hollow transverse microchannel inside the PDMS substrate after subsequent thermal curing. In addition, a through-hole with an aspect ratio greater than ~200 was easily fabricated in the PDMS substrate by parallel laser scanning. The fabrication of a 3D microfluidic device comprising two open reservoirs in a PDMS substrate was also demonstrated for biochip applications.

Light-driven transport of microparticles with phase-gradient metasurfaces

Mohammad Mahdi Shanei, Einstom Engay, and Mikael Käll

DOI: 10.1364/OL.478179 Received 18 Oct 2022; Accepted 17 Nov 2022; Posted 21 Nov 2022  View: PDF

Abstract: Optical tweezers have opened numerous possibilities for precise control of microscopic particles for applications in life science and soft matter research and technology. However, traditional optical tweezers employ bulky conventional optics that prevents construction of compact optical manipulation systems. As an alternative, we present an ultrathin silicon-based metasurface that enables simultaneous confinement and propulsion of microparticles based on a combination of intensity and phase gradient optical forces. The metasurface is constructed as a water-immersion line-focusing element that enables trapping and transport of 2-μm particles over a wide area within a thin liquid cell. We envisagethat the type of multifunctional metasurfaces reported herein will play a central role in miniaturized optical sensing, driving and sorting of microscopic objects, such as cells or other biological entities.

Optical Two-dimensional Coherent Spectroscopy of Cold Atoms

Danfu Liang, Lexter Savio, haitao zhou, Yifu Zhu, and Hebin Li

DOI: 10.1364/OL.478793 Received 18 Oct 2022; Accepted 17 Nov 2022; Posted 21 Nov 2022  View: PDF

Abstract: We report an experimental demonstration of optical 2DCS in cold atoms. The experiment integrates a collinear 2DCS setup with a magneto-optical trap (MOT), in which cold rubidium (Rb) atoms are prepared at a temperature of about 200 μK and a number density of 10¹⁰ cm¯³. With a sequence of femtosecond laser pulses, we first obtained one-dimensional second- and fourth-order nonlinear signals and then acquired both one-quantum and zero-quantum 2D spectra of cold Rb atoms. The capability of performing optical 2DCS in cold atoms is an important step toward optical 2DCS study of many-body physics in cold atoms and ultimately in atom arrays and trapped ions. Optical 2DCS in cold atoms/molecules can also be a new avenue to probe chemical reaction dynamics in cold molecules.

Focused vortex beam generator suitable for optical fiber spanners in complex liquid environment

Zhiyong Bai, Luping Wu, rui liu, Jian Yu, Dingbang Ma, Zikan Chen, RANJIANJUN RAN, Yiping Wang, Changrui Liao, and Ying Wang

DOI: 10.1364/OL.465949 Received 06 Jun 2022; Accepted 17 Nov 2022; Posted 17 Nov 2022  View: PDF

Abstract: We experimentally demonstrated an all-fiber focused vortex beam (FVB) generator which was prepared by milling a spiral zone plate (SZP) on the Au-coated end face of a hybrid fiber by Focused Ion Beam. In this generator, the fundamental modes propagating in the hybrid fiber are focused while being modulated into high-order orbital angular momentum mode by SZP at the end face. The focus length, and topological charge were designed, and then were both theoretically and experimentally verified. The results show that, the obtained characteristics of the FVB agree with the designed ones. The measured diameters of focal spots are 2.2μm, 4.4μm and 5.2μm for the FVB with the topological charge of 0, 1 and 2, respectively. The simulated results show that the proposed FVB generators can maintain good focusing characteristics in different liquid, so it is a good candidate for optical fiber spanner using in complex liquid environment. Moreover, the processing efficiency of the proposed FVB generators is nearly 10 times higher than that of the previously reported ones due to the Au-coated film.

Segmented mirror fine phasing using model-based wavefront sensorless adaptive optics and Chebyshev segmented piston-tip-tilt modes

Hongxi Ren, Bing Dong, and Zexia Zhang

DOI: 10.1364/OL.470209 Received 12 Jul 2022; Accepted 16 Nov 2022; Posted 17 Nov 2022  View: PDF

Abstract: On-orbit cophasing is essential for high-resolution imaging of space telescopes with a segmented primary mirror. An efficient and precise fine phasing method based on model-based wavefront sensorless adaptive optics (WFSless AO) is proposed and demonstrated by experiment. In our method, the tip-tilt error is related to the second moment of spot intensity and the piston error is related to the Strehl ratio. Chebyshev segmented piston-tip-tilt (CSPTT) modes are proposed to represent the cophasing error to suppress the effect of imaging noises. The CSPTT modal coefficients are estimated by the “2N+1” algorithm that introduces bidirectional biases for each mode. The proposed method can work well in the presence of image noises and figure errors.

Frequency Conversion in High-Pressure Hydrogen

Alireza Aghababaei, Christoph Biesek, Frank Vewinger, and Simon Stellmer

DOI: 10.1364/OL.475703 Received 15 Sep 2022; Accepted 16 Nov 2022; Posted 16 Nov 2022  View: PDF

Abstract: State-preserving frequency conversion in the opticaldomain is a necessary component in many configura-tions of quantum information processing and commu-nication. Thus far, nonlinear crystals are used for thispurpose. Here, we report on a new approach based on co-herent anti-Stokes Raman scattering (CARS) in a densemolecular hydrogen gas. This four-wave mixing processsidesteps the limitations imposed by crystal properties,it is intrinsically broadband and does not generate anundesired background. We demonstrate this method byconverting photons from 434 nm to 370 nm and showthat their polarization is preserved.

Realization of Optical Fiber Regenerated Gratings by Rapid Cooling and Split Annealing

Somnath Bandyopadhyay, Palas Biswas, John Canning, and Sayantani Bhattacharya

DOI: 10.1364/OL.476471 Received 26 Sep 2022; Accepted 16 Nov 2022; Posted 21 Nov 2022  View: PDF

Abstract: Rapid cooling, or quenching, during regeneration of seed gratings in single mode silica optical fiber is explored. It is shown that regeneration can be broken up into stages in time. The novel method of “split annealing” offers a unique tool for optimising regeneration and studying fundamental glass science within a one-dimensional bimaterial system. We demonstrate regeneration at temperatures as high as T = 1200 °C for the first time as well as opening up an approach suited to batch processing of regenerated gratings

Multiband topological states in the Penrose-Triangle photonic crystals

Qingxi Xu, Yuchen Peng, Bei Yan, Aoqian Shi, Peng Peng, Jianlan Xie, and Jianjun Liu

DOI: 10.1364/OL.477077 Received 06 Oct 2022; Accepted 16 Nov 2022; Posted 21 Nov 2022  View: PDF

Abstract: The topological edge state (TES) and topological corner state (TCS) in photonic crystals (PCs) provide effective ways to manipulate the propagation of light. In order to improve the performance and integration of topological photonic devices, the realization of multiband topological states by PCs combined with quasi-periodic structure needs to be urgently explored. In this Letter, a Penrose-Triangle (P-T) PC, which arranges the basic structural unit of a 12-fold Penrose-type photonic quasi-crystal (PQC) in a triangular lattice, is proposed. The TES and TCS at low and high frequency bands can be generated in the same structure. This will provide a new structure for the generation of TESs and TCSs in PCs, and will provide a new way to improve the performance and integration of topological photonic devices.

Enhancement of calculation accuracy of the integrated photonic tensor flow processer by global optical power allocation

Sicheng Yi, Shaofu Xu, Jing Wang, and Weiwen Zou

DOI: 10.1364/OL.477426 Received 05 Oct 2022; Accepted 16 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: We present a global optical power allocation architecture, which can enhance the calculation accuracy of the integrated photonic tensor flow processer (PTFP). By adjusting the optical power splitting ratio according to the weight value and loss of each calculating unit, this architecture can efficiently utilize optical power so that signal-to-noise ratio of the PTFP is enhanced. In the case of considering the on-chip optical delay line and spectral loss, the calculation accuracy measured in the experiment is enhanced by more than 1 bit compared with the fixed optical power allocation architecture.

Passive Mode-Locked Cesium Diode Pumped Alkali Laser

Matthew Rotondaro, Boris Zhdanov, Michael Shaffer, Zachary Eyler, and Randall Knize

DOI: 10.1364/OL.478871 Received 03 Nov 2022; Accepted 15 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: A first demonstration of passive mode-locking in Diode Pumped Alkali Laser (DPAL) is reported in this paper. An intracavity cesium vapor cell, buffered by atmospheric pressure methane, was used to passively mode lock a continuously pumped cesium DPAL with a static gain medium. A train of short pulses with duration less than 460 ps was observed using a 2.0 GHz bandwidth detector that limited the real time duration measurements. The calculated minimum duration for these pulses is 57 ps.

Polarization-insensitive multimode antisymmetric waveguide Bragg grating filter based on SiN-Si dual layer stack

nannan ning, hui Yu, Qiang Zhang, Qikai Huang, Zhilei Fu, Penghui Xia, Zhujun Wei, Xiaofei Wang, Yuehai Wang, and Jianyi Yang

DOI: 10.1364/OL.478452 Received 18 Oct 2022; Accepted 15 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: A polarization-insensitive multimode antisymmetric waveguide Bragg grating filter based on the SiN-Si dual-layer stack is demonstrated. Carefully optimized grating corrugations patterned on the sidewall of silicon waveguide and the SiN overlay are used to perturbate TE and TM modes, respectively. Furthermore, the lateral-shift apodization technique is utilized to improve the side-lobe suppression ratio (SLSR). A good overlap between the passbands measured in TE and TM polarization states is obtained. Insertion losses, SLSRs, and 3-dB bandwidths of measured passbands in TE/TM polarizations are 1/1.72 dB, 18.5/19.1 dB, and 5.1/3.5 nm.

Seeing the strong suppression of higher order modes in single trench fiber through S² technique

Yi An, Huan Yang, Xiao Chen, Liangjin Huang, Zhiping Yan, Zhiyong Pan, Zefeng Wang, Jiang Zongfu, and Pu Zhou

DOI: 10.1364/OL.478287 Received 13 Oct 2022; Accepted 15 Nov 2022; Posted 16 Nov 2022  View: PDF

Abstract: Single trench fiber (STF) is a promising fiber design for mode area scaling and higher order mode (HOM) suppression. In this paper, we experimentally demonstrate the strong HOM-suppression in a homemade STF using the spatially and spectrally resolved imaging(S²) technique. This STF has a 20 μm core and its performance is compared to a conventional step-index fiber with almost the same parameter. Results show that the bending loss of HOM in STF is 8 times larger than conventional fiber at a bend radius of 7 cm. In addition, when severe coupling mismatch is introduced at the input end of fiber, STF can keep the fundamental-mode output while the conventional fiber cannot. To the best of our knowledge, this is the first time to experimentally analyze the HOM content in STF and compare its performance with conventional fiber. Our results indicate the great potential of the STF for filtering HOM in fiber laser applications.

Fiber-integrated catenary ring-array metasurfaces for beam shaping

Zhongyue Luo, Wentao Zhang, Niannian Song, Dawei Chen, Shijie Deng, Hongchang Deng, Ming Chen, Libo Yuan, and Houquan Liu

DOI: 10.1364/OL.476289 Received 26 Sep 2022; Accepted 15 Nov 2022; Posted 21 Nov 2022  View: PDF

Abstract: Catenary is referred to as "the real mathematical and mechanical form" in the architectural field. Because of the unique phase control characteristic of the catenary, it has excellent ability in optical manipulation. Here, we proposed an optical waveform conversion device based on optical fiber-integrated catenary ring-array metasurfaces. The device consists of a cascade structure of a single-mode fiber and a graded-index fiber (GIF). At the GIF end, two kinds of catenary ring-array metasurface are introduced to realize beam shaping from Gaussian beam to Bessel beam. The device can selectively generate a focused or non-diffracting Bessel beam by changing the circular polarization state of the incident light. It is worth noting that under some parameters of the device, the output Bessel beam can break through the diffraction limit, which has potential application in the fields of optical imaging, optical communication, and optical trapping.

Design of an achromatic zoom metalens doublet in the visible

Tie Hu, feng xing, Yunxuan Wei, Shengqi Wang, Yuhong Wei, Zhen Yu Yang, and Ming Zhao

DOI: 10.1364/OL.473597 Received 19 Aug 2022; Accepted 15 Nov 2022; Posted 21 Nov 2022  View: PDF

Abstract: Zoom metalens doublets, featuring ultra-compactness, strong zoom capability and CMOS compatibility, exhibit unprecedented advantages over the traditional refractive zoom lens. However, the huge chromatic aberration narrows the working bandwidth, which limits their potential applications in broadband systems. Here, by globally optimizing the phase profiles in the visible, we designed and numerically demonstrated a Moire lens based zoom metalens doublet that can achromatically work in the band of 440-640 nm. Such a doublet can achieve a continuous zoom range from 1× to 10×, while also maintaining high focusing efficiency up to 86.5% and polarization insensitivity.

Monolithic multi-wavelength lasing from multi-sized microdisk lasers

Wai Yuen Fu, Yuk Cheung, and H. Choi

DOI: 10.1364/OL.479375 Received 26 Oct 2022; Accepted 15 Nov 2022; Posted 15 Nov 2022  View: PDF

Abstract: This paper demonstrates monolithic multi-wavelength lasing through fabrication of multi-sized microdisks on a green-emitting thin film sample. The different dimensions of the microdisks incur different extent of strain relaxation, thus changing the emission/gain spectra due to the reduction of the Quantum Confined Stark Effect. Under room-temperature optical pumping, lasing thresholds of 15.1 mJ/cm², 2.9 mJ/cm² and 5.3 mJ/cm² with Q factors of 70, 2060 and 4308 are realized, respectively, for fabricatedmicrodisks with diameters of 950 nm, 6 μm and 10 μm. By exciting the microdisks with a pump laser spot diameter of 2 mm, simultaneous multi-wavelength lasing action is thus observed. The strain relaxation effect is confirmed by the shift of the E₂(high) Raman peak from 563.2 cm-1 to 561.5cm-1 as the diameter of the fabricated microdisk reduces.

Broadband polarization-entangled source for C+L-band flex-grid quantum networks

Muneer Alshowkan, Joseph Lukens, Hsuan-Hao Lu, Brian Kirby, Brian Williams, Warren Grice, and Nicholas Peters

DOI: 10.1364/OL.471363 Received 25 Jul 2022; Accepted 15 Nov 2022; Posted 16 Nov 2022  View: PDF

Abstract: The rising demand for transmission capacity in optical networks has motivated steady interest in expansion beyond the standard C-band (1530-1565 nm) into the adjacent L-band (1565-1625 nm), for an approximate doubling of capacity in a single stroke. However, in the context of quantum networking, the ability to leverage the L-band will require advanced tools for characterization and management of entanglement resources which have so far been lagging. In this work, we demonstrate an ultrabroadband two-photon source integrating both C- and L-band wavelength-selective switches for complete control of spectral routing and allocation across 7.5 THz in a single setup. Polarization state tomography of all 150 pairs of 25 GHz-wide channels reveals an average fidelity of 0.98 and total distillable entanglement greater than 181 kebits/s. This source is explicitly designed for flex-grid optical networks and can facilitate optimal utilization of entanglement resources across the full C+L-band.

Analog wavelet-like transform based on stimulated Brillouin scattering

Pengcheng Zuo, Dong Ma, and Yang Chen

DOI: 10.1364/OL.477007 Received 02 Oct 2022; Accepted 14 Nov 2022; Posted 16 Nov 2022  View: PDF

Abstract: A photonics-enabled analog wavelet-like transform system, characterized by multiscale time-frequency analysis (TFA), is proposed based on a typical stimulated Brillouin scattering (SBS) pump-probe setup using an optical nonlinear frequency-sweep signal. The periodic SBS-based frequency-to-time mapping (FTTM) is implemented by using a periodic nonlinear frequency-sweep optical signal with a time-varying chirp rate. The frequency-domain information of the signal under test (SUT) in different periods is mapped to the time domain via the FTTM in the form of low-speed electrical pulses, which is then spliced to analyze the time-frequency relationship of the SUT in real-time. The time-varying chirp rate in each sweep period makes the signals with different frequencies have different frequency resolutions in the FTTM process, which is very similar to the characteristics of the wavelet transform, so we call it wavelet-like transform. An experiment is carried out. Multiscale TFA of a variety of RF signals is carried out in a 4-GHz bandwidth limited only by the equipment.

Unidirectional spintronic terahertz emitters with high efficiency

Zhang Xiaoqiang, Yunqing Jiang, Yong Xu, Fengguang Liu, Guanghao Rui, Anting Wang, and weisheng zhao

DOI: 10.1364/OL.476809 Received 30 Sep 2022; Accepted 14 Nov 2022; Posted 15 Nov 2022  View: PDF

Abstract: Due to the high performance and low cost, spintronic terahertz emitters (STEs) have been a hot spot in the field of terahertz sources. However, most of the research focus on the THz generation process and little attention has been paid to the control and modulation of the THz waves generated by the STE. In this paper, a unidirectional spintronic terahertz emitter (USTE) integrated a common STE with a metal grating is proposed to manipulate the THz emission process. The dyadic Green’s function method and finite element method are adopted to survey the characteristics of the USTE. Simulations show that the metal grating not only has a transmission larger than 97% in the optical band, but also has a higher reflectivity larger than 99% in the THz band. As a result, the USTE has a unidirectional THz emission along the direction of the pump beam with a larger than 4-fold enhancement in intensity. Moreover, the USTE has the capability of tuning the central frequency and THz wave steering by adjusting the distance and angle between the STE and the metal grating. We believe that this USTE can be used in THz wireless communications and holographic imaging, especially in the field of THz bio-sensing, which needs some resonance frequencies to sense.

Determination of Raman shift laser power coefficient based on cross-correlation

Nicholas Hunter, Mahya Rahbar, Ridong Wang, masoud Samani, and Xinwei Wang

DOI: 10.1364/OL.475008 Received 06 Sep 2022; Accepted 14 Nov 2022; Posted 15 Nov 2022  View: PDF

Abstract: This work presents a novel cross-correlation technique for determining the laser heating-induced Raman shift laser power coefficient psi required for energy transport state-resolved Raman (ET-Raman) methods. The cross-correlation method determines the measure of similarity between the experimental intensity data and a varying test Gaussian signal. By circumventing the errors inherent in any curve fittings, the cross-correlation method quickly and accurately determines the location where the test Gaussian signal peak is most like the Raman peak, thereby revealing the peak location and ultimately the value of psi. This method also avoids reliance on any specific Raman signal features such as peak intensity and linewidth. Rather the global experimental data of the Raman spectrum provides sufficient information for determining the precise peak lo-cation. This method improves the reliability of optothermal Raman-based methods for micro/nanoscale thermal meas-urements and offers a robust approach to data processing through a global treatment of Raman spectra.

Smoothing of inter-layer edge artifacts in depth-map computer generated holograms

SungJae Park, Jonghyun Lee, wonwoo choi, Shinwoong Park, and Hwi Kim

DOI: 10.1364/OL.475282 Received 08 Sep 2022; Accepted 14 Nov 2022; Posted 17 Nov 2022  View: PDF

Abstract: In the depth-map computer-generated hologram (CGH), inter-layer edge artifacts are observed in the discontinuous edges of section-wise depth-map objects. CGH synthesis utilizing the hybrid smoothing method of silhouette masking and edge-apodization alleviates unwanted inter-layer edge artifacts. The proposed method achieves improved de-artifact filtering that generates holographic images closer to the ground-truth image of the depth-map object unattainable by the conventional CGH synthesis method.

Adding/dropping polarization multiplexed cylindrical vector beams with local polarization matched plasmonic metasurface

Yanliang He, Zebin Huang, Canming Li, Bo Yang, Zhiqiang Xie, Haisheng Wu, Peipei Wang, Ying Li, Yatao Yang, Dianyuan Fan, and Shuqing Chen

DOI: 10.1364/OL.477849 Received 10 Oct 2022; Accepted 14 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: Here we proposed a polarization-dependent gradient phase modulation strategy and fabricated a local polarization matched metasurface to add/drop polarization multiplexed cylindrical vector beams (CVBs). The two orthogonal linear polarization states in CVB multiplexing will represent as radial- and azimuthal-polarized CVBs, which means that we must introduce independent wave vectors to them for adding/dropping the polarization channels. By designing the rotation angle and geometric sizes of meta-atom, a local polarization matched propagation phase plasmonic metasurface was constructed, and the polarization-dependent gradient phases were loaded to perform this operation. As a proof of concept, the polarization multiplexed CVBs, carrying 150 Gbit/s quadrature phase shift keying signals, were successfully added and dropped, and the bit-error-rates approach 1×10-6. Besides representing a route for adding/dropping polarization multiplexed CVBs, it is expected for other functional phase modulation of arbitrary orthogonal linear polarization bases, which might find potential applications in polarization encryption imaging, spatial polarization shaping, etc.

Mosaic-free compound eye camera based on multidirectional photodetectors and single-pixel imaging

Zhong Ji, Yujin Liu, and Xueli Chen

DOI: 10.1364/OL.478591 Received 19 Oct 2022; Accepted 14 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: Compound-eye wide field-of-view (FOV) imaging generally faces the disadvantages of complex system, low resolution, and complicated image mosaic. Single-pixel imaging has proven to be a great advantage in building high resolution and simple wide-FOV camera, but its ability to overcome image mosaic has yet to be demonstrated. We in this paper propose a new kind of artificial compound eye based on multidirectional photodetectors (PDs). We theoretically and experimentally prove that mosaics are not necessary in multidirectional PDs based single-pixel imaging. In addition, we experimentally find that only nine multidirectional PDs are needed to obtain wide-angle images in a hemispherical sphere to realize wide-FOV mosaic-free imaging. This work greatly simplifies the compound eye camera and is very enlightening for detector design in wide-FOV single-pixel imaging, may lead to the development of single-pixel endoscopic imaging.

Continuously-tunable Photonic True Time Delay Device for mmWave Beamforming

Banaful Paul, Kubilay Sertel, and Niru Nahar

DOI: 10.1364/OL.476962 Received 04 Oct 2022; Accepted 13 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: We present a novel CMOS compatible plasma dispersionmodulation scheme, for slow wave photonic truetime delay structure harnessing the frozen-mode to enableapplications in mmWave beamforming. LeveragingSoref and Bennett’s model for electro-refractive effectin Silicon plasma dispersion, continuous tunabilityof about 7.5 ps/V with a peak delay of about 11.4 psis achieved for a low threshold voltage of 0.9 V. Thisplasma dispersion will enable fast and sophisticatedmodulation and beamforming in 5G mmWave and 6GTerahertz communications.

Optical Neural Ordinary Differential Equations

Yun Zhao, Hang Chen, Min Lin, Haiou Zhang, Tao Yan, Xing Lin, Ruqi Huang, and Qionghai Dai

DOI: 10.1364/OL.477713 Received 10 Oct 2022; Accepted 13 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: Increasing the layer number of on-chip photonic neural networks (PNNs) is essential to improve its model performance. However, the successively cascading of network hidden layers results in larger integrated photonic chip areas. To address this issue, we propose the optical neural ordinary differential equations (ON-ODE) architecture that parameterizes the continuous dynamics of hidden layers with optical ODE solvers. The ON-ODE comprises the PNNs followed by the photonic integrator and optical feedback loop, which can be configured to represent residual neural networks (ResNet) and recurrent neural networks with effectively reduced chip area occupancy. For the interference-based optoelectronic nonlinear hidden layer, the numerical experiments demonstrate that the single hidden layer ON-ODE can achieve approximately the same accuracy as the two-layer optical ResNet in image classification tasks. Besides, the ON-ODE improves the model classification accuracy for the diffraction-based all-optical linear hidden layer. The time-dependent dynamics property of ON-ODE is further applied for trajectory prediction with high accuracy.

Yellow Pumped Pr3+-doped ZBLAN fiber laser at 1015-nm

Bo Xiao, Chenyao Shen, Shuaihao Ji, Zhongyu Wang, Zhengdong Dai, Weihang Cao, Yuchen Xue, Huiying XU, and Zhiping Cai

DOI: 10.1364/OL.477015 Received 11 Oct 2022; Accepted 12 Nov 2022; Posted 17 Nov 2022  View: PDF

Abstract: To date, lasers in visible to near-infrared wavelengths have been studied in praseodymium-doped fluoride fibers with the upper energy level of 3P0. In this paper, a fiber laser operating at 1015 nm has been realized for the first time, which confirms a new mechanism that 1D2 can be the upper energy level. A maximum output power of 241 mW, with a slope efficiency of 30% was achieved by using a 150-cm long active fiber pumped at a maximum pump power of 8 mW. Furthermore, the broad emission spectra of Pr3+-doped fibers in the near-infrared band have been exploited as new spectral sources.

Electrically controllable self-assembly of gold nanorods into plasmonic nanostructure for highly efficiency SERS

Jun Dong, Jiaxin Yuan, yi cao, yizhen zhao, Qingyan Han, wei gao, Tuo Li, Lipeng Zhu, and Jianxia Qi

DOI: 10.1364/OL.477507 Received 06 Oct 2022; Accepted 12 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: In this letter, a method for the rapid and efficient preparation of ultrasensitive detection substrates by assembling gold nanorod suspensions by applying an alternating electric field (AC) was proposed, and it was found that frequency and voltage are the effective means of regulation. Sandwich structure (parallel SiO2 plate) not only effectively slows down the evaporation rate, but also visually observes the changes in the assembly process. Under the optimal assembly conditions, the sensitivity and uniformity of the substrate to different probe molecules were tested respectively. The Raman detection results show that the detection limits of Rhodamine 6G (Rh6G), crystal violet (CV) and Aspartame (APM) molecular solutions are 10-14M, 10-10M and 62.5mg/L was experimental obtained, respectively, and the mixed dye molecular solutions can also be effectively distinguished. Furthermore, Rh6G and CV characteristic peaks were randomly selected at the positions of 1647cm-1 and 1619cm-1, and their relative standard deviations (RSD) were 5.63% and 8.45%, respectively, indicating that the substrate has good uniformity. The effective regulation of the self-assembly results of nanoparticles will further enhance the practical application effect of surface-enhanced Raman technology and expand the application prospects of this technology.

Non-Hermitian Bloch-Zener phase transition

Stefano Longhi

DOI: 10.1364/OL.478059 Received 11 Oct 2022; Accepted 12 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: Bloch-Zener oscillations (BZO), i.e. the interplay between Bloch oscillations and Zener tunneling in two-band lattices under an external dc force, are ubiquitous in different areas of wave physics, including photonics. While in Hermitian systems such oscillations are rather generally aperiodic and only accidentally periodic, in non-Hermitian (NH) lattices BZO can be rather generally either periodic or aperiodic. Remarkably, a phase transition, from periodic to aperiodic BZOs, can be observed as a NH parameter in the system is varied. This behavior is illustrated by considering a discrete-time photonic quantum walk on a synthetic lattice, which provides a discrete-time version of the NH Rice-Mele model.

Phase space topology of four-wave mixing reconstructed by a neural network

Anastasiia Sheveleva, Pierre Colman, John Dudley, and Christophe Finot

DOI: 10.1364/OL.472039 Received 01 Aug 2022; Accepted 12 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: The dynamics of ideal four-wave mixing in optical fiber is reconstructed by taking advantage of the combination of experimental measurements with supervised machine learning strategies. The training data consist of power-dependent spectral phase and amplitude recorded at the output of a short segment of fiber. The neural network is able to accurately predict the nonlinear dynamics over tens of kilometers, and to retrieve the main features of the phase space topology including multiple Fermi-Pasta-Ulam recurrence cycles and the system separatrix boundary.

Dissipative Kerr solitons, breathers and chimera states in coherently driven passive cavities with parabolic potential

Yifan SUN, Pedro Parra-Rivas, Mario Ferraro, Fabio Mangini, Mario Zitelli, Raphaël Jauberteau, Francesco Rinaldo Talenti, and Stefan Wabnitz

DOI: 10.1364/OL.472900 Received 17 Aug 2022; Accepted 12 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: We analyze the stability and dynamics of dissipative Kerr solitons in the presence of a parabolic potential. This potential stabilizes oscillatory and chaotic regimes, favoring the generation of static DKSs. Furthermore, the potential induces the emergence of new dissipative structures, such as asymmetric breathers and chimera-like states. Based on a mode decomposition of these states, we unveil the underlying modal interactions.

Time delay interferometry with transfer oscillator

Hanzhong Wu, mingyang xu, Panpan Wang, Zhenqi Zhang, pengcheng fang, Yujie Tan, Jie Zhang, Qunfeng Chen, Zehuang Lu, and Chenggang Shao

DOI: 10.1364/OL.473812 Received 23 Aug 2022; Accepted 11 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: In this work, we experimentally perform the time delay interferometry by using a transfer oscillator, which is capable of reducing the laser frequency noise and the clock noise simultaneously in the post processing. The Iodine frequency reference is coherently down converted to the microwave frequency using a laser frequency comb. The residual noise of the down conversion network is 5E-6 Hz/rtHz at 0.7 mHz, and 4E-6 Hz/rtHz at 0.1 Hz, indicating high homology between the optical frequency and the microwave frequency. We carry out time delay interferometry with the aid of the electrical delay module, which can introduce large time delays. The results show that the laser frequency noise and the clock noise can be reduced simultaneously by 10 and 3 orders of magnitude respectively in the frequency band from 0.1 mHz to 0.1 Hz. The performance of the noise reduction can reach 6E-8 Hz/rtHz at 0.1 mHz, and 7E-7 Hz/rtHz at 1 mHz, meeting the requirements of the space-borne gravitational wave detection. Our work will be able to offer an alternative method for the frequency comb-based time delay interferometry in the future space-borne gravitational wave detectors.

Design of ultracompact broadband focusing spectrometers based on deep diffractive neural networks

Luca Dal Negro, Yuyao Chen, and Yilin Zhu

DOI: 10.1364/OL.475375 Received 09 Sep 2022; Accepted 11 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: We propose the inverse design of ultracompact, broadbandfocusing spectrometers based on adaptive deepdiffractive neural networks (a-D2NNs). Specifically, weintroduce and characterize two-layer diffractive deviceswith engineered angular dispersion that focus and steerbroadband incident radiation along predefined focal trajectorieswith desired bandwidth and nanometer spectralresolution. Moreover, we systematically study thefocusing efficiency of two-layer devices with side lengthL = 100 μm and focal length f = 300 μm across thevisible spectrum and demonstrate accurate reconstructionof the emission spectrum from a commercial superluminescentdiode. The proposed a-D2NNs designmethod extends the capabilities of efficient multi-focaldiffractive optical devices to include single-shot focusingspectrometers with customized focal trajectories forapplications to ultracompact multispectral imaging andlensless microscopy.

Photonics Millimeter Wave Bidirectional Full-duplex Communication based on Polarization Multiplexing

Weiping Li, Jianjun Yu, Feng Wang, Xiaoxue Ji, Yang Xiongwei, Tianqi Zheng, Qihang Wang, Wen Zhou, Jianguo Yu, and Feng Zhao

DOI: 10.1364/OL.478619 Received 18 Oct 2022; Accepted 11 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: We have proposed and experimentally implemented a photonics-aided large-capacity long-distance mm-wave bidirectional full-duplex fiber-wireless-integration communication system at the W-band based on polarization multiplexing. Uplink and downlink share the same Radio Frequency (RF) carrier resource. We use a pair of Orthomode Transducers (OMTs) as H/V diplexers for communication links to separate the dual orthogonally polarized channels. To achieve the maximum spectrum efficiency and throughput, 10 Gbaud probabilistically shaped 256-level quadrature-amplitude-modulation (PS-256QAM) signals whose entropy is 7.07 bit/symbol/Hz are transmitted in Ch. H and Ch. V. The system can support the bidirectional transmission with 103 Gbps data rate over the fusion link of 20 km single-mode fiber (SMF) and 4600 m RF wireless. For all we know, based on a photonics-aided bidirectional full-duplex system, this is the first time to realize a record-breaking rate-distance product at the W-band, i.e., 103 Gbps × 4.6 km = 473.8 Gbps•km.

Broadband saturable absorption of indium tin oxide nanocrystals towards mid-infrared regime

Jing Huang, dongyang Liu, Longlong Chen, Ning Li, Lili Miao, and Chujun Zhao

DOI: 10.1364/OL.478536 Received 17 Oct 2022; Accepted 11 Nov 2022; Posted 16 Nov 2022  View: PDF

Abstract: We demonstrate the ultrabroadband optical nonlinearity of the indium tin oxide nanocrystals (ITO NCs) in the mid-infrared regime experimentally. Especially, the ITO NCs show considerable saturation absorption behavior with large modulation depth covering the spectral range from 2 μm to 10 μm wavelength. We also demonstrate the application of the optical nonlinearity to modulate the erbium-doped fluoride fiber laser to deliver nanosecond pulse with signal-to-noise ratio over 43 dB at 2.8 μm wavelength successfully. The results provide a promising platform for the development of ITO-based broadband and robust optoelectronic devices towards the deep mid-infrared spectral range.

Adjustment-free two-sided 3D direct laser writing for aligned micro optics on both substrate sides

Michael Schmid, Simon Thiele, Alois Herkommer, and Harald Giessen

DOI: 10.1364/OL.476448 Received 26 Sep 2022; Accepted 11 Nov 2022; Posted 15 Nov 2022  View: PDF

Abstract: 3D direct laser writing is a powerful and widely used tool to create complex micro optics. The fabrication method offers two different writing modes. During dip-in mode the objective is in direct contact with the photoresist and the structure is fabricated on the substrate side facing the objective. Alternatively, when using an immersion medium between the objective and the substrate the photoresist is exposed on the backside of the substrate. In this paper, we demonstrate the combination of dip-in and photoresist immersion printing, by using the photoresist itself as immersion medium. This way, two parts of a doublet objective can be fabricated on the front and back side of a substrate, using it as a spacer with a lateral registration below 1 µm and without the need of additional alignment. This approach also enables the alignment free combination of different photoresists on the back and front side. We utilize this benefit by printing a black aperture on the back of the substrate, while the objective lens is printed on the front.

Diffuse optical properties of Fresnel lens sunlight concentrator

Maxim Shvarts, Dmitry Malevskiy, Maria Nakhimovich, Pavel Pokrovskiy, Nikolay Sadchikov, and Andrey Soluyanov

DOI: 10.1364/OL.475800 Received 21 Sep 2022; Accepted 10 Nov 2022; Posted 15 Nov 2022  View: PDF

Abstract: A combined module jointing concentrator and planar photovoltaic circuits provides energy conversion of both parts of global terrestrial radiation: direct sunlight by concentrator solar cells and scattered (diffuse) one by planar (non-concentrator) photoconverters. The decrease in Fresnel lens concentrating ability is usually associated with imperfectness in optical refractive surfaces, where some part of the direct light, which comes along the normal to the surface of the Fresnel lens and intended to be concentrated, is getting scattered and directing off a highly efficient concentrator solar cell. The diffuse light flux generated propagates inside the volume of the combined photovoltaic module. This flux undergoes multiple reflections from the structural elements, partially absorbed and ultimately reaches the photoconverters of the planar circuit. Thus, two types of diffuse light impinge the planar circuit: “external” from the atmosphere and “internal” produced by the Fresnel lens from direct light. This paper proposes a method for determining the diffuse properties of sunlight concentrators such as Fresnel lens.

Optimized computer-generated hologram for enhancing depth cue based on complex amplitude modulation

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

DOI: 10.1364/OL.476443 Received 22 Sep 2022; Accepted 10 Nov 2022; Posted 16 Nov 2022  View: PDF

Abstract: In this letter, we introduce a computer-generated hologram optimization method with enhanced depth cue based on complex amplitude modulation. Firstly, a modified iteration algorithm is utilized to generate the optimized random phase which can be used as the initial phase of arbitrary target image according to the size of the target image and the required bandwidth condition. Subsequently, the hologram based on complex amplitude modulation can be calculated directly according to the target complex amplitude and analytical formula. Our proposal can achieve fast generation of the hologram and a suitable balance between the reconstruction quality and the depth cue. It is expected that the proposed method could be widely used in holographic field in the future. © 2022 Optical Society of America

High-power continuous-wave self-frequency-doubled monolithic laser

Jinheng Du, Xiufang Chen, Haohai Yu, and Huaijin Zhang

DOI: 10.1364/OL.478823 Received 20 Oct 2022; Accepted 10 Nov 2022; Posted 10 Nov 2022  View: PDF

Abstract: We report a high-power self-frequency-doubled (SFD) Yb:YCa₄O(BO₃)₃ (Yb:YCOB) laser by employing a simply and high-integration monolithic configuration with the oscillator length of 6 mm. By reducing the reabsorption and increasing the quantum efficiency, the continuous-wave output power of 21.62 W was obtained with an optical conversion efficiency of 19.0% and beam quality of Mx²=1.73, My²=1.67 at the wavelength of about 510 nm. To our knowledge, the results represent the highest output power of SFD laser. We believe that the high-power SFD laser with highly compact structure will have broad and promising application prospects in laser display, medical treatment, spectral analysis, scientific research and other fields.

Control of the VCSEL spectrum by dual microwave frequency modulation

Alexander Bogatov, Alexander Drakin, Mariya Vaskovskaya, Dmitriy Chuchelov, Kirill Sabakar, Eugene Tsygankov, Vitaliy Vassiliev, Vladimir Velichansky, and Sergey Zibrov

DOI: 10.1364/OL.476838 Received 29 Sep 2022; Accepted 10 Nov 2022; Posted 10 Nov 2022  View: PDF

Abstract: We propose and investigate a method for controlling spectrum of the vertical-cavity surface-emitting laser by simultaneous modulation of the injection current at single and doubled frequencies. We experimentally demonstrate the ability to control the power asymmetry of the first-order sidebands and to suppress the carrier by the proposed method. These possibilities are beneficial to improve frequency stability of atomic clocks based on the effect of coherent population trapping.

Tapered tip optical fibers for measuring ultra-small refractive index changes with record-high sensitivity

Chunyu Lu, Hamed Nikbakht, Mert Yusuf Erdolu, Bob van Someren, and Imran Akca

DOI: 10.1364/OL.477288 Received 04 Oct 2022; Accepted 09 Nov 2022; Posted 10 Nov 2022  View: PDF

Abstract: Here we demonstrate an inexpensive, simple, and ultra-sensitive refractive index sensor based on a tapered tip optical fiber combined with a straightforward image analysis method. The output profile of this fiber exhibits circular fringe patterns, whose intensity distribution dramatically changes even with ultra-small refractive index variations in the surrounding medium. The sensitivity of the fiber sensor is measured using different concentrations of saline solutions with a transmission setup consisting of a single wavelength light source, a cuvette, an objective lens, and a camera. By analyzing the areal changes in the center of the fringe patterns for each saline solution, we obtain an unprecedented sensitivity value of 24160 dB/RIU (refractive index unit), which is the highest value reported so far among intensity modulated fiber refractometers. The resolution of the sensor is calculated to be 6.9 ×10-9. Moreover, we measure the sensitivity of the fiber tip in the back reflection mode using salt-water solutions and obtained a sensitivity value of 480 dB/RIU. This sensor is ultra-sensitive, simple, easy to fabricate, and low-cost, which makes it a promising tool for on-site measurements and point-of-care applications.

One-joule 500 Hz cryogenic Yb:YAG laser driver of composite thin-disk design

Luis Zapata, Mikhail Pergament, Matthias Schust, Simon Reuter, Jelto Thesinga, Collette Zapata, Martin Kellert, Umit Demirbas, Anne-Laure Calendron, Yizhou Liu, and Franz Kaertner

DOI: 10.1364/OL.476964 Received 05 Oct 2022; Accepted 09 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: We present results on development of a cryogenic Yb:YAG multi-pass laser amplifier based on a composite thin-disk design and demonstrate one-joule, diffraction limited, chirped 4 ps pulses with 50% optical-to-optical efficiency. High beam quality was obtained for repetition rates up to 400 Hz. The hardware was disassembled and thoroughly inspected after accumulating 80 hours of use at repetition rates from 100 to 500 Hz and exhibited no signs of damage. This laser driver is now commissioned to a dedicated laboratory where a grating compressor is producing 5.2 ps pulses used in the development of a compact x-ray source based on inverse Compton scattering

Antenna-based reduced IR absorbers for high performance microbolometers

S Jagan Mohan Rao, Dai-Sik Kim, Seon Namgung, and Dukhyung Lee

DOI: 10.1364/OL.474768 Received 06 Sep 2022; Accepted 09 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: Absorbers for long-wavelength infrared (LWIR) were designed to have a reduced geometry fitted to a gold cross antenna and numerically studied. Compared to the square membrane geometry widely used in conventional microbolometers, the reduced geometry provides smaller thermal capacities of vanadium dioxide (VO2) and silicon nitride (Si3N4) layers. On the other hand, near-field focusing by the cross antenna enables a high LWIR absorption. The calculation results show that, temperature change per incident energy increases with decreasing arm width, and the reduced absorber surpasses the square geometry for all incident angles and polarizations. The antenna-based reduced absorber studied here could serve as an alternative geometry for high performance microbolometers.

Generation of vector vortex beams by axially-symmetric sheared polymer network liquid crystals

Ting-Hua Lu, Yu-Jen Wang, Yu-Fang Chen, and Yi-Hsin Lin

DOI: 10.1364/OL.476307 Received 27 Sep 2022; Accepted 09 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: Liquid crystals have been widely used in optoelectronic devices because of their fast response and excellent electro-optic properties. Featuring unique ability to manipulate light, they are also proposed as a good candidate in topological photonics for further applications. In this study, an axially-symmetric sheared polymer network liquid crystals (ASPNLC) was fabricated to demonstrate vector vortex beams. Linearly and circularly polarized light are utilized to illuminate the sample, and the output vector vortex beams generated from the ASPNLC indicate that the polarization states of the output beams are dependent on the polarization of incident light. The measured phenomena were modeled on the basis of phase retardation and Jones calculus to eventually calculate the polarization-resolved intensity profiles accordingly. Hence, our experimental study provides a holistic understanding of the method for generating vector vortex beams by ASPNLC, which is expected to enhance the knowledge of optical mechanisms for liquid crystal applications.

Full-resolution, full-field-of-view, and high-quality fast Fourier single-pixel imaging

jiaxiang Li, Kai Cheng, shaoting qi, Zibang Zhang, Guoan Zheng, and Jingang Zhong

DOI: 10.1364/OL.475956 Received 21 Sep 2022; Accepted 09 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: Fourier single-pixel imaging (FSI) uses Fourier basis patterns for spatial light modulation to acquire the Fourier spectrum of the object image. The object image can be reconstructed via an inverse Fourier transform. However, the Fourier basis patterns are inherently grayscale, which results in the difficulty that the patterns can hardly be generated in a high speed by using a commonly used spatial light modulator--digital micromirrors device. To tackle this problem, fast FSI, which uses upsampled and dithered Fourier basis patterns to approximate the grayscale patterns, has been reported, but the achievable spatial resolution has to be sacrificed in the pattern upsampling process. Here we propose method that can achieve not only full-resolution but also full-field-of-view and high-quality FSI. The key to the proposed method is to use a new error diffusion dithering algorithm combined with two different scanning strategies to generate two sets of binarized Fourier basis patterns for FSI. As a result, two reconstructed images with a sub-pixel shift from each other are derived. Synthesizing the two images results in the final high-quality reconstruction. We experimentally demonstrate the method can produce a high-quality 1024×768-pixel image with a digital micro-mirror device with 1024×768 micromirrors.

Formation of monodomain polymer-stabilized blue phase liquid crystals using surface acoustic waves

Risti Suryantari, Yi-Hong Shih, Yu-Han Shih, Hui-Yu Chen, Cen-Shawn Wu, and Chia-Yi Huang

DOI: 10.1364/OL.475938 Received 19 Sep 2022; Accepted 09 Nov 2022; Posted 23 Nov 2022  View: PDF

Abstract: This work uses surface acoustic waves (SAWs) that are generated by a piezoelectric substrate containing an interdigital transducer (IDT) applied with a low voltage of 1 mV with a frequency of 1 KHz to fabricate a polymer-stabilized blue phase liquid crystal (PS-BPLC) layer. The PS-BPLC layer has a more uniform optical microscope (OM) image at a voltage of 1 mV than at zero voltage, and its reflective spectrum exhibits a smaller full width at half maximum (FWHM) at the former than at the latter. The uniform OM image and small FWHM reveal that the lattices in the PS-BPLC layer have monodomain structure. The monodomain PS-BPLC layer is formed because the SAWs cause the longitudinal and transverse vibrations of the PS-BPLC lattices in the vertical plane along their traveling direction. The proposed method for fabricating the monodomain PS-BPLC layer using the SAWs has potential for developing reflective optical devices that consume low power during their fabrication.

Multidetection scheme for Transient-Grating-based spectroscopy

Marta Brioschi, Pietro Carrara, Vincent Polewczyk, Dagur Deepak, Giovanni Vinai, Pietro Parisse, Simone Dal Zilio, Giancarlo Panaccione, Giorgio Rossi, and Riccardo Cucini

DOI: 10.1364/OL.476958 Received 13 Oct 2022; Accepted 08 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: Time-resolved optical spectroscopy represents an effective non-invasive approach to investigate the interplay of different degrees of freedom, which plays a key role in the development of novel functional materials. Here, we present magneto-acoustic data on Ni thin films on SiO2 as obtained by a versatile pump-probe setup that combines transient grating spectroscopy with time-resolved magnetic polarimetry. The possibility to easily switch from pulsed to continuous-wave probe allows probing of acoustic and magnetization dynamics on a broad timescale, in both transmission and reflection geometry.

Simultaneous distributed acoustic sensing and communication over a two-mode fiber

Juan Marin Mosquera, Islam Ashry, Omar Alkhazragi, Abderrahmen Trichili, Tien Khee Ng, and Boon Ooi

DOI: 10.1364/OL.473502 Received 22 Aug 2022; Accepted 08 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: We designed and tested a distributed acoustic sensing (DAS) that co-exists with optical communication over a two-mode fiber (TMF). In particular, we excited both LP01 and LP11a modes using a photonic lantern for simultaneous information signal transmission while collecting the backscattered Rayleigh light at the near end of the fiber to detect vibrations from a predetermined source. While transmitting data using on-off keying (OOK) or orthogonal frequency-division multiplexing (OFDM) modulation schemes, the optical fiber DAS offers high signal-to-noise ratio (SNR) values that are always larger than the minimum acceptable 2-dB SNR. Additionally, as a proof-of-concept experiment, we report parallel sensing and OFDM transmission achieving a data rate of up to 4.2 Gb/s with a bit error rate (BER) of 3.2 ×10−3.

Correcting sampling bias in speckle contrast imaging

Shuqi Zheng and Jerome Mertz

DOI: 10.1364/OL.474604 Received 31 Aug 2022; Accepted 08 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: When performing spatial or temporal laser speckle contrast imaging (LSCI), contrast is generally estimated from localized windows containing limited numbers of independent speckle samples $N_S$. This leads to a systematic bias in the estimated speckle contrast. We describe an approach to determine $N_S$ and largely correct for this bias, enabling a more accurate estimation of the speckle decorrelation time without recourse to numerical fitting of data. Validation experiments are presented where measurements are ergodic or non-ergodic, including in-vivo imaging of mouse brain.

Architecture for Integrated RF Photonic Downconversion of Electronic Signals

Nathan O'Malley, Keith McKinzie, Mohammed Al Alshaykh, Junqiu Liu, Daniel Leaird, Tobias Kippenberg, Jason McKinney, and Andrew Weiner

DOI: 10.1364/OL.474710 Received 01 Sep 2022; Accepted 08 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: Electronic analog to digital converters (ADCs) are running up against the well-known bit depth vs bandwidth tradeoff. Towards this end, RF photonic-enhanced ADCs have been the subject of interest for some time. Optical frequency comb technology has been used as a workhorse underlying many of these architectures. Unfortunately, such designs must generally grapple with SWaP concerns, as well as frequency ambiguity issues which threaten to obscure critical spectral information of detected RF signals. In this work, we address these concerns via an RF photonic downconverter with potential for easy integration and field deployment by leveraging a novel hybrid microcomb / electro-optic comb design.

Self-consistent soliton evolution in single-two mode fiber lasers

Lingxiao Liu, Zhiwen He, Qun Gao, Du Yueqing, Chao Zeng, and Dong Mao

DOI: 10.1364/OL.475837 Received 16 Sep 2022; Accepted 08 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: Ultrafast few-mode fiber lasers have received increasing attention from basic research to practical applications due to their unique pulse performance and intriguing nonlinear dynamics. Here, we experimentally and numerically revealed the formation and evolution behaviors of soliton in a mode-locked fiber laser composed of two-mode and single-mode fibers. The LP11 pulse walks away from the LP01 pulse in the two-mode fiber due to modal dispersion and then transforms into an auxiliary LP01 pulse after entering the single-mode fiber. After re-entering the two-mode fiber, the LP01 pulse excites the LP11 pulse via mode coupling, therefore the LP11 pulse also consists of dominant and auxiliary pulses. Such soliton fiber laser converges to an asymptotic steady state with unlocked spatial modes arising from the interplay between the strong modal dispersion and weak mode coupling.

Accurate MTF determination in X-ray image restoration

Xin Liu, Rongze Chen, Yaohu Lei, Huang Jianheng, and Xiaoli Liu

DOI: 10.1364/OL.476041 Received 20 Sep 2022; Accepted 08 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: An X-ray image can be significantly improved by a deconvolution algorithm with the modulation transfer function(MTF) when the source's focal spot is known. Utilizing X-ray speckle imaging, we propose a simple method to measure the MTF for image restoration. In this method, the MTF is reconstructed with intensity and total variation (TV) constraints from a single X-ray speckle of an ordinary scatter. Compared with the traditional time-consuming measurement with a pinhole camera, the speckle imaging method is fast, and easy to be carried out. When the MTF is available, we use a deconvolution algorithm to reconstruct the sample's radiography image, and the result provides more structural details than the original images.

Ultra-wideband discrete Raman amplifier optimisation for single-span S-C-L-band coherent transmission systems

Pratim Hazarika, Mingming Tan, Aleksandr Donodin, Mohammed Patel, Ian Phillips, Paul Harper, and Wladek Forysiak

DOI: 10.1364/OL.475246 Received 12 Sep 2022; Accepted 08 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: We experimentally compare the performance of two key ultra-wideband discrete Raman amplifier structures, a cascaded dual-stage structure and an in-parallel dual-band structure, in fully loaded S-C-L band coherent transmission systems over 70km of single mode fiber. Our results show that dual-band discrete Raman amplifier with minimized back reflections can effectively avoid unstable random distributed feedback lasing, reduce unwanted pump-to-pump interactions, and therefore improve the transmission performance for signals at shorter wavelengths, versus the cascaded dual-stage structure. The average noise figure for S-band signals is 6.8dB and 7.2dB for the dual-band structure and cascaded dual-stage structure, respectively, while the average S-band Q2 factor is similarly improved by 0.6dB. Moreover, the cascaded dual-stage discrete Raman amplifier requires guard bands around the 1485nm and 1508nm pumps as the signal and pump wavelengths overlap, which results in a bandwidth loss of ~10nm and reduces the potential net data throughput to 28.6Tb/s for 30GBaud DP-16QAM signals. However, dual-band structure can utilize the bandwidth more effectively, which leads to a higher estimated net data throughput of 31.2Tb/s.

Inter-mode soliton linear-wave scattering in a Kerr microresonator

Yiqing Xu, shuang Liu, Pierce Qureshi, Miro Erkintalo, Stephane Coen, Huilian Ma, and Stuart Murdoch

DOI: 10.1364/OL.475540 Received 15 Sep 2022; Accepted 08 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: Soliton microresonator frequency combs (microcombs) have recently emerged as an attractive new of type optical comb source with a wide range applications proposed and demonstrated. To extend the optical bandwidth of these microresonator sources, several previous studies have proposed and studied the injection of an additional optical probe wave into the resonator. In this case, nonlinear scattering between the injected probe and the original soliton enables the formation of new comb frequencies through a phasematched cascade of four-wave mixing process. In this work, we expand the relevant analyses to consider soliton-linear wave interactions when the soliton and the probe fields propagate in different mode families. We obtain an expression for the phasematched idler locations as a function of the dispersion of the resonator and the phase detuning of the injected probe. We confirm our theoretical predictions in experiments performed in a silica waveguide ring microresonator.

Laser pulse cutoff at nonlinear reflection due to Raman backscattering in plasma

Alexey Balakin, Sergey Skobelev, and A Litvak

DOI: 10.1364/OL.477494 Received 06 Oct 2022; Accepted 08 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: A method for generating subrelativistic laser pulses with a sharp leading edge is proposed, which is based on Raman backscattering of an intense short pump pulse by a counter-propagating long low-frequency pulse propagating in a thin plasma layer. A thin plasma layer serves both to attenuate parasitic effects and to effectively reflect the central part of the pump pulse when the field amplitude exceeds the threshold value. A prepulse with a lower field amplitude passes through the plasma almost without scattering. This method works for subrelativistic laser pulses with durations up to 100 fs. The contrast of the leading edge of the laser pulse is determined by the seed pulse amplitude.

Compact diode-pumped continuous-wave and passively Q-switched Tm:YAG laser at 2.33 µm

Fangyuan Zha, Xiaoxu Yu, Hongwei Chu, Zhongben Pan, Shengzhi Zhao, Pavel Loiko, Han Pan, and Dechun Li

DOI: 10.1364/OL.478341 Received 16 Oct 2022; Accepted 08 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: Compact diode-pumped continuous-wave (CW) and passively Q-switched Tm:YAG lasers operating on the 3H4 → 3H5 transition are demonstrated. Using a 3.5at. % Tm:YAG crystal, a maximum CW output power of 1.49 W was achieved at 30 nm with a slope efficiency of 10.1%. The first Q-switched operation of the mid-infrared Tm:YAG laser was realized with a few-atomic-layer MoS2 saturable absorber. Pulses as short as 150 ns were generated at a repetition rate of 190 kHz, corresponding to a pulse energy of 1.07 µJ. Tm:YAG is an attractive material for diode-pumped CW and pulsed mid-infrared lasers emitting around 2.3 µm.

Luminescence Efficiency Improvement of Small-size Micro Light-emitting Diodes by Digital Etching Technology

Yi-Kai Jin, HUNG-YI Chiang, Kuan-Heng Lin, Chia-An Lee, and JianJang Huang

DOI: 10.1364/OL.476967 Received 03 Oct 2022; Accepted 07 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: The decrease of light output efficiency with the shrink of LED (light-emitting diode) die size is one of the challenges of micro-LED displays. Here we propose a digital etching technology that employs multi-step etching and treatment to mitigate sidewall defects exposed after mesa dry etching. In this study, by two-step etching and N2 treatment, the electrical properties of the diodes show an increase of forward current and a decrease in reverse leakage due to suppressed sidewall defects. An increase of light output power by 92.6 % is observed for 10 × 10 μm2 mesa size with digital etching, as compared with that with only one step etching and no treatment. We also demonstrated only 1.1 % decrease in output power density for a 10 × 10 μm2 LED as compared with a 100×100 μm2 device without performing digital etching.

Submillimeter-spatial-resolution φ-OFDR strain sensor using femtosecond laser induced permanent scatters

Yanjie Meng, Cailing Fu, Lin Chen, Chao Du, Huajian Zhong, Yiping Wang, Jun He, and Weijia Bao

DOI: 10.1364/OL.476349 Received 22 Sep 2022; Accepted 07 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: A φ-OFDR strain sensor with a submillimeter-spatial-resolution of 3 μm, was demonstrated by using the femtosecond laser induced permanent scatters (PSs) in standard single mode fiber (SMF). The PSs-inscribed SMF, i.e., strain sensor, with an interval of 3 μm exhibited a Rayleigh backscattering intensity (RBS) enhancement of 26 dB and insertion loss of 0.6 dB, respectively. A novel method, i.e., PSs-assisted φ-OFDR, was proposed to demodulate the strain distribution based on the extracted phase difference of P- and S-polarized RBS signal. The maximum measurable strain was up to 1400 μm at a spatial resolution of 3 μm.

Observation of Strong Terahertz Field-Induced Second Harmonic Generation in Plasma Filaments

Kareem Garriga Francis, Mervin Lim Pac Chong, Yiwen E, and Xi-Cheng Zhang

DOI: 10.1364/OL.477508 Received 06 Oct 2022; Accepted 06 Nov 2022; Posted 07 Nov 2022  View: PDF

Abstract: We report the observation of Terahertz Field-Induced Second Harmonic (TFISH) Generation produced by directly mixing an optical probe beam onto femtosecond plasma filaments. The produced TFISH signal is spatially separated from the laser-induced supercontinuum by impinging on the plasma at a noncollinear angle. The conversion efficiency of the fundamental probe beam to its second harmonic beam is greater than 0.02%, which represents a record in optical probe to TFISH conversion efficiency that is nearly five orders of magnitude larger than previous experiments. We also present the terahertz spectral buildup of the source along the plasma filament and retrieve coherent terahertz signal measurements. This method of analysis has the potential to provide local electric field strength measurements inside of the filament.

Ultrafast laser writing of arbitrary long low loss waveguides in optical fibers

Léo Colliard, Guillaume Bilodeau, Tommy Boilard, Jerome Lapointe, Real Vallee, Martin Bernier, and matthieu bellec

DOI: 10.1364/OL.478386 Received 14 Oct 2022; Accepted 06 Nov 2022; Posted 07 Nov 2022  View: PDF

Abstract: We propose an innovative femtosecond laser writing approach, based on a reel-to-reel configuration, allowing the fabrication of arbitrary long optical waveguides in coreless optical fibers, directly through the coating. We report few meters long waveguides operating in the near-IR with propagation losses as low as 0.055 ± 0.004 dB/cm at 700 nm. The refractive index distribution is shown to be homogeneous with a quasi-circular cross section, its contrast being controllable via the writing velocity. Our work paves the way to the direct fabrication of complex arrangements of cores in standard and exotic optical fibers.

Ratiometric optical thermometry based on upconversion luminescence with different multi-photon processes in CaWO4: Tm3+/Yb3+ phosphor

Lixin Peng, wang wen, li leipeng, feng qin, and Zhiguo Zhang

DOI: 10.1364/OL.478285 Received 13 Oct 2022; Accepted 05 Nov 2022; Posted 07 Nov 2022  View: PDF

Abstract: Ratiometric optical thermometry based on the upconversion (UC) emissions with different multi-photon processes in CaWO4: Tm3+, Yb3+ phosphor was developed. A new FIR thermometry, utilizing the ratio of cube of 3F2,3 emission to the square of 1G4 emission of Tm3+ and remaining the feature of anti-interference of excitation light source fluctuations, is proposed. Under the hypotheses of the UC terms are neglected in the rate equations and the ratio of the cube of 3H4 emission to the square of 1G4 emission of Tm3+ is a constant in a relative narrow temperature range, the new FIR thermometry is valid. The correctness of all hypotheses was confirmed by testing and analyzing the power dependent emission spectra at different temperatures and the temperature dependent emission spectra of CaWO4: Tm3+, Yb3+ phosphor. The results prove that the new ratiometric thermometry based on UC luminescence with different multi-photon processes is feasible through optical signal processing, and maximum relative sensitivity (Sr) of thermometry is 6.61% K-1 at 303 K. This study provides guidance in selecting the UC emissions with different multi-photon processes to construct the ratiometric optical thermometers with anti-interference of excitation light source fluctuation.

Complete characterization of picosecond optical pulses by offset frequency intensity modulation

Kenichi Oguchi, Sho Nitanai, and Yasuyuki Ozeki

DOI: 10.1364/OL.475647 Received 21 Sep 2022; Accepted 04 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: We present a method of characterizing the intensity waveform, spectrum, frequency chirp, and spectral phase of picosecond pulses at a moderate repetition rate of ~100 MHz. The proposed method exploits the intensity modulation at ~10 GHz, which is slightly offset from the integer multiple of the repetition rate of the pulses. The modulated pulses are split into two, and one is measured by an optical spectrum analyzer, whose output is detected by a lock-in amplifier, while the other is directly detected by a photodiode and its output is used as a reference signal of the lock-in amplifier. In the experiment, we demonstrate the measurement of picosecond Ti:sapphire laser pulses to investigate frequency chirp induced by self-phase modulation. We anticipate that the proposed method will be useful for the characterization of various types of picosecond pulses.

DFB laser array based on four phase-shifted sampled Bragg grating with precise wavelength control

Yiming Sun, Bocheng Yuan, xiao sun, Song Liang, Yongguang Huang, Ruikang Zhang, Shengwei Ye, Yizhe FAN, Weiqing cheng, John Marsh, and Lianping Hou

DOI: 10.1364/OL.475909 Received 16 Sep 2022; Accepted 04 Nov 2022; Posted 04 Nov 2022  View: PDF

Abstract: A four-laser array based on sampled Bragg grating DFB lasers in which each sampled period contains four phase-shift sections is proposed, fabricated, and experimentally demonstrated. The wavelength spacing between adjacent lasers is accurately controlled to 0.8 nm ± 0.026 nm and the lasers have single mode suppression ratios larger than 50 dB. Using an integrated semiconductor optical amplifier, the output power can reach 33 mW and the optical linewidth of the DFB lasers can be as narrow as 64 kHz. This laser array uses a ridge waveguide with sidewall gratings and needs only one metalorganic vapor-phase epitaxy (MOVPE) step and one III-V material etching process, simplifying the whole device fabrication process, and meeting the requirements of dense wavelength division multiplexing systems.

Frequency locking and alternation of topological indices of vortex laser solitons

Nikolay Rosanov, Nikolay Veretenov, and Sergey Fedorov

DOI: 10.1364/OL.477217 Received 03 Oct 2022; Accepted 03 Nov 2022; Posted 03 Nov 2022  View: PDF

Abstract: We analyze the effect of frequency locking for polarization components of a semiconductor laser with a fast saturating absorber and weak anisotropy. A mode of alternation of topological indices when leaving the locking area was found.

Mechanoluminescence ratiometric thermometry via MgF2:Tb3+

Chongyang Cai, Yanmin Yang, Pei Li, Tao Li, Dengfeng Peng, and li leipeng

DOI: 10.1364/OL.476530 Received 26 Sep 2022; Accepted 03 Nov 2022; Posted 03 Nov 2022  View: PDF

Abstract: Mechanoluminescent (ML) materials have attracted considerable attention over the past two decades due to the ability of converting external mechanical stimuli into useful photons. Here we present a new type of ML material, i.e., MgF2:Tb3+. In addition to the demonstration of traditional application such as stress sensing, we show the possibility of ratiometric thermometry via this ML material. Under stimulation of external force rather than the conventional photoexcitation, the luminescence ratio of 5D3-7F6 to 5D4-7F5 emission lines of Tb3+ is confirmed to be a good indicator of temperature. Our work not only expands the family of ML materials, but also provides a new and energy-saving route for temperature sensing.

Anomalous soliton trapping in net-normal dispersion lasers

Du Yueqing, Zhiwen He, Chao Zeng, Dong Mao, and Jianlin Zhao

DOI: 10.1364/OL.477826 Received 10 Oct 2022; Accepted 03 Nov 2022; Posted 03 Nov 2022  View: PDF

Abstract: In the nonlinear optical system with birefringence e.g. fiber lasers, the soliton trapping can be achieved when the fast (slow) component experiences blue (red)-shift at normal-dispersion for compensating the polarization-mode dispersion. In this letter, we demonstrate an anomalous vector soliton whose fast (slow) component shifts to the red (blue) sides, which is opposite to the traditional soliton trapping. It is found that the repulsion between two components is induced by the net-normal-dispersion and polarization-mode dispersion, while the attraction is ascribed to the linear mode-coupling and saturable absorption. The equilibrium of attraction and repulsion permits the self-consistent evolution of vector soliton circulating in the cavity. Our results indicate that the stability and dynamics of vector solitons are worth revisiting and studying in-depth especially in lasers with complex configurations, despite it is already a well-known object in nonlinear optics.

Spatially multiplexed dielectric tensor tomography

Juheon Lee, Seungwoo Shin, Herve Hugonnet, and YongKeun Park

DOI: 10.1364/OL.474969 Received 06 Sep 2022; Accepted 03 Nov 2022; Posted 04 Nov 2022  View: PDF

Abstract: Dielectric tensor tomography (DTT) enables the reconstruction of three-dimensional (3D) dielectric tensors, which provides a physical measure of 3D optical anisotropy. Herein, we present a cost-effective and robust method for DTT measurement using a multiplexing approach. By exploiting two orthogonally polarized reference beams with different angles in an off-axis interferometer, two polarization-sensitive interferograms were overlapped and recorded using a single camera. Then, the two multiplexed interferograms were separated in the Fourier domain, enabling the reconstruction of polarization-sensitive fields. Finally, by measuring the polarization-sensitive fields for various illumination angles, 3D dielectric tensor tomograms were reconstructed. The proposed method was experimentally demonstrated by reconstructing the 3D dielectric tensors of various liquid crystal particles with radial and bipolar orientational configurations.

Ultra-high level enhancement on nonlinear optical susceptibility of cubic quantum dot achieved by THz laser and electric field

Keyin Li, Lijun Wei, Hao Yin, Zhen Li, Shi-Bo Dai, and Zhenqiang Chen

DOI: 10.1364/OL.475271 Received 08 Sep 2022; Accepted 02 Nov 2022; Posted 04 Nov 2022  View: PDF

Abstract: Multi-physics coupling, composed of intense THz laser and electric field, serves as a new approach to realize the utra-high level enhancement on third-harmonic generations (THG) of cubic quantum dot (CQD). The exchange of quantum states caused by anticrossing of intersubbands is demonstrated by the Floquet method and finite difference method with the increasing laser-dressed parameter and electric field. The results show that the rearrangement of the quantum states excites the THG coefficient of CQD four orders of magnitude higher than that of single physical field. The optimal polarization direction of incident light that maximizes the THG exhibits strong stability along the Z axis at high laser-dressed parameter and electric field.

Ultra high-Q WGM microspheres from ZBLAN for the mid-IR band

Tatiana Tebeneva, Artem Shitikov, Oleg Benderov, Valery Lobanov, Igor Bilenko, and Alexander Rodin

DOI: 10.1364/OL.475259 Received 08 Sep 2022; Accepted 02 Nov 2022; Posted 03 Nov 2022  View: PDF

Abstract: The advantages of high-quality-factor whispering gallery mode microresonators can be applied to develop novel photonic devices for the mid-IR range. ZBLAN (glass based on heavy metal fluorides) is one of the most promising materials to be used for this purpose due to low optical losses in the mid-IR. We developed original fabrication method based on melting of commercially available ZBLAN-based optical fiber to produce high-Q ZBLAN microspheres with the diameters of 250 to 350 μm. We effectively excited whispering gallery modes in these microspheres and demonstrated high quality factor both at 1.55 µm and 2.64 µm. Intrinsic quality factor at telecom wavelength was shown (5.4±0.4)·10⁸ which is defined by the material losses in ZBLAN. In the mid-IR at 2.64 μm we demonstrated record quality factor in ZBLAN exceeding 10⁸ which is comparable to the highest values of the Q-factor among all materials in the mid-IR.

Maximisation or levelling: The characterisation of the trade-offs for the transmission throughput in ultrawideband optical transmission

Anastasiia Vasylchenkova, Eric Sillekens, Robert Killey, and Polina Bayvel

DOI: 10.1364/OL.470105 Received 11 Jul 2022; Accepted 02 Nov 2022; Posted 02 Nov 2022  View: PDF

Abstract: In ultrawideband transmission, the overall noise comes from the amplification, fibre properties at different wavelengths and stimulated Raman scattering, and its impact on channels across transmission bands is different. This requires a range of methods to mitigate the noise impact. Performing channel-wise power pre-emphasis and constellation shaping, one can compensate for the noise tilt and attain maximum throughput. In this work, we study the trade-off between the goals of maximising the total throughput and levelling the transmission quality for different channels. We use an analytical model for multi-variable optimisation and identify the penalty from constraining the mutual information variation.

Stern–Gerlach effect of vector light bullets in a nonlocal Rydberg medium

Guoxiang Huang and Yue Mu

DOI: 10.1364/OL.475924 Received 16 Sep 2022; Accepted 02 Nov 2022; Posted 02 Nov 2022  View: PDF

Abstract: We show that stable (3+1)-dimensional vector light bullets with ultraslow propagating velocity and extreme low generation power can be realized in a cold Rydberg atomic gas. They can also be actively controlled by using a nonuniform magnetic field; especially, trajectories of their polarization components can have significant Stern–Gerlach deflections. The results obtained are useful for revealing the nonlocal nonlinear optical property of Rydberg media and for measuring weak magnetic fields.

Cold-atom shaping with MEMS scanning mirrors

Alan Bregazzi, Paul Janin, James McGilligan, Oliver Burrow, Erling Riis, Deepak Uttamchandani, Ralf Bauer, Paul Griffin, and Sean Dyer

DOI: 10.1364/OL.475353 Received 09 Sep 2022; Accepted 02 Nov 2022; Posted 17 Nov 2022  View: PDF

Abstract: We demonstrate the integration of micro-electro-mechanical-systems (MEMS) scanning mirrors as active elements for the local optical pumping of ultra-cold atoms in a magneto-optical trap. A pair of MEMS mirrors steer a focused resonant beam through a cloud of trapped atoms shelved in the \textit{F}=1 ground-state of \textsuperscript{87}Rb for spatially-selective fluorescence of the atom cloud. Two-dimensional control is demonstrated by forming geometrical patterns along the imaging axis of the cold atom ensemble. Such control of the atomic ensemble with a microfabricated mirror pair could find applications in single atom selection, local optical pumping and arbitrary cloud shaping. This approach has significant potential for miniaturisation and in creating portable control systems for quantum optic experiments.

Net 400 Gbps/λ IMDD Transmission Using Single-DAC DSP-free Transmitter and Thin-Film Lithium Niobate MZM

Essam Berikaa, Md Samiul Alam, and David Plant

DOI: 10.1364/OL.476399 Received 22 Sep 2022; Accepted 01 Nov 2022; Posted 02 Nov 2022  View: PDF

Abstract: The insatiable growth of datacenter traffic mandates increasing the capacity of cost-effective intensity modulation direct detection (IMDD) systems to meet the foreseen demand. This letter demonstrates the first single-DAC IMDD system achieving a net 400 Gbps transmission using a TFLN MZM. Employing a driver-less DAC channel (128 GSa/s, 800 mVpp) with neither pulse-shaping nor pre-emphasis filtering, we transmit (1) 128 Gbaud PAM16 below the 25% overhead SD-FEC BER threshold and (2) 128 Gbaud PS-PAM16 under the 20% overhead SD-FEC threshold, which respectively corresponds to record net rates of 410 and 400 Gbps for single-DAC operation. Our results highlight the promise of operating 400 Gbps IMDD links with reduced DSP complexity and driving swing requirements

Scattering correcting wavefront shaping for three-photon microscopy

Bernhard Rauer, Hilton de Aguiar, Laurent Bourdieu, and Sylvain Gigan

DOI: 10.1364/OL.468834 Received 27 Jun 2022; Accepted 01 Nov 2022; Posted 03 Nov 2022  View: PDF

Abstract: Three-photon (3P) microscopy is getting traction due to its superior performance in deep tissues. Yet, aberrations and light scattering still pose one of the main limitations in the attainable depth ranges for high-resolution imaging. Here, we show scattering correcting wavefront shaping with a simple continuous optimization algorithm, guided by the integrated 3P fluorescence signal. We demonstrate focusing and imaging behind scattering layers and investigate convergence trajectories for different sample geometries and feedback non-linearities. Furthermore, we show imaging through a mouse skull and demonstrate a novel fast phase estimation scheme that substantially increases the speed at which the optimal correction can be found.

A silicon source of frequency-bin entangled photons

Federico Sabattoli, Linda Gianini, Angelica Simbula, Marco Clementi, Antonio Fincato, Frederic Boeuf, Marco Liscidini, Matteo Galli, and Daniele Bajoni

DOI: 10.1364/OL.471241 Received 22 Jul 2022; Accepted 01 Nov 2022; Posted 01 Nov 2022  View: PDF

Abstract: We demonstrate an integrated source of frequency-entangled photon pairs on a silicon photonics chip. The emitter has a signal to noise ratio improved by two orders of magnitude with respect to the state of the art. We prove entanglement by showing two-photon frequency interference with a visibility of 94.6% ± 1.1%. This result was obtained without background subtraction, a necessary condition for the use of frequency-bin entangled photons in quantum information protocols.

Temporal coherence of optical fields in the presence of entanglement

yunxiao zhang, Nan Huo, Liang Cui, Xueshi Guo, Xiaoying Li, and Zheyu Ou

DOI: 10.1364/OL.470115 Received 11 Jul 2022; Accepted 31 Oct 2022; Posted 09 Nov 2022  View: PDF

Abstract: In classical coherence theory, coherence time is typically related to the bandwidth of the optical field. Narrowing the bandwidth will result in the lengthening of the coherence time. This will erase temporal distinguishability of photons due to time delay in pulsed photon interference. However, this is changed in an SU(1,1)-type quantum interferometer where quantum entanglement is involved. In this paper, we investigate how the temporal coherence of the fields in a pulse-pumped SU(1,1) interferometer changes with the bandwidth of optical filtering. We find that, because of the quantum entanglement, the coherence of the fields does not improve when optical filtering is applied, in contrary to the classical coherence theory, and quantum entanglement plays a crucial role in quantum interference in addition to distinguishability.

Intensity self-compensation method against multi-factors for polarization-based Fabry-Perot interrogation system

Zhiyuan Li, Shuang Wang, Junfeng Jiang, Haokun Yang, peng zhang, Xiaoshuang Dai, Xueping Li, and T. Liu

DOI: 10.1364/OL.476154 Received 20 Sep 2022; Accepted 31 Oct 2022; Posted 10 Nov 2022  View: PDF

Abstract: Phase interrogation methods for Fiber-optic Fabry-Perot (F-P) sensors may inevitably fail in field due to the influence of irrelevant factors on signal intensity. To address this severe problem, this letter proposes an intensity self-compensation method (ISCM) to eliminate the consecutive signal fluctuations of polarization-based F-P interrogation system caused by multiple factors. By only providing the initial intensities of the reference signals, this attempt realizes the real-time intensity compensation of the output signal without affecting their quadrature-relationship. Consecutive intensity fluctuations caused by variation of light source power, fiber loss, and polarization state are reduced to 2 % - 3 % by ISCM. Furthermore, the method performs ideally under dynamic modulation of the sensor. Owning to the high efficiency, real-time ability and no moving parts advantage, the proposed method provides an excellent candidate for improving the accuracy and stability of the F-P interrogation systems.

Anomalously enhanced transverse optical torque on a dipolar plasmonic nanoparticle in two-wave interference

Lv Feng, jiangnan Ma, Wanli Lu, Huajin Chen, and Hongxia Zheng

DOI: 10.1364/OL.476994 Received 30 Sep 2022; Accepted 30 Oct 2022; Posted 01 Nov 2022  View: PDF

Abstract: Based on the multipole expansion theory, we show that a transverse optical torque acting on a dipolar plasmonic spherical nanoparticle can be anomalously enhanced in two plane waves with linear polarization. Compared to a homogeneous Au nanoparticle, the transverse optical torque acting on an Au-Ag core-shell nanoparticle with an ultra-thin shell thickness can be dramatically enhanced by more than two orders of magnitude. Such enhanced transverse optical torque is dominated by the interaction between the incident optical field and the electric quadrupole excited in the dipolar core-shell nanoparticle. It is thus noted that the torque expression based on the dipole approximation usually used for dipolar particles is not available even in our dipolar case. These findings deepen the physical understanding of the OT and may have applications in optically driven rotation of plasmonic microparticles.

Harvesting Planck radiation for free-space optical communications in the LWIR band

Haley Weinstein, Zhi Cai, Jonathan Habif, and Stephen Cronin

DOI: 10.1364/OL.476394 Received 22 Sep 2022; Accepted 28 Oct 2022; Posted 31 Oct 2022  View: PDF

Abstract: We demonstrate a free-space optical communication link with an optical transmitter that harvests naturally occurring Planck radiation from a warm body and modulates the emitted intensity. The transmitter exploits an electro-thermo-optic effect in a multi-layer graphene device that electrically controls the surface emissivity of the device resulting in control of the intensity of the emitted Planck radiation. We design an amplitude-modulated optical communication scheme and provide a link budget for communications data rate and range based on our experimental electro-optic characterization of the transmitter. Finally, we present an experimental demonstration achieving error-free communications at 100 bits per second over laboratory scales.

Experimental demonstration of tomography-basedquantum key distribution

Min Wei, Chunhui Zhang, Jian Li, JiaLi Zhu, and Qin Wang

DOI: 10.1364/OL.478199 Received 13 Oct 2022; Accepted 26 Oct 2022; Posted 31 Oct 2022  View: PDF

Abstract: Tomography is a very beneficial and fundamental technique in the fields of quantum information and quantum optics, which can be applied to infer information about quantum states or quantum processes. Inthe quantum key distribution (QKD), tomography hasbeen proposed to improve the secure key rate by takingfull advantage of the data from both matched and mismatched measurement outcomes to characterize quantum channels accurately. However, up to date, no experimental work has been achieved on it. In this work, wedo a systematic study on tomography-based QKD (TBQKD), and for the first time, carry out proof-of-principleexperimental demonstrations by implementing sagnacinterferometers to simulate different transmission channels. Furthermore, we compare it with the referenceframe-independent QKD (RFI-QKD) and demonstratethat TB-QKD can significantly outperform RFI-QKDunder certain circumstances, e.g., when passing throughamplitude damping channels or probabilistic rotationchannels.

Directly diode-pumped femtosecond Cr:ZnS amplifier with ultra-low intensity noise

Alexander Weigel, Shizhen Qu, Arun Paudel, Aleksandar Sebesta, Philipp Steinleitner, Nathalie Nagl, Markus Poetzlberger, Vladimir Pervak, and KaFai Mak

DOI: 10.1364/OL.475438 Received 12 Sep 2022; Accepted 21 Oct 2022; Posted 26 Oct 2022  View: PDF

Abstract: Diode-pumped Cr:ZnS oscillators have emerged as precursors for single-cycle infrared pulse generation with excellent noise performance. Here we demonstrate a Cr:ZnS amplifier with direct diode-pumping to boost the output of an ultrafast Cr:ZnS oscillator with minimum added intensity noise. Seeded with a 0.66 W pulse train at 50 MHz repetition rate and 2.4 μm center wavelength, the amplifier provides over 2.2 W of average power with a pulse duration of 35 fs. Due to the low-noise performance of the laser pump diodes in the relevant frequency range, the amplifier output achieves a root-mean-square intensity noise level of only 0.03 % in the 10 Hz – 1 MHz frequency range and a long-term power stability of 0.13 % RMS over one hour. The diode-pumped amplifier reported here is a promising driving source for nonlinear compression to the single- or sub-cycle regime, as well as for the generation of bright, multi-octave-spanning mid-infrared pulses for ultra-sensitive vibrational spectroscopy.

Effect of AlN strain compensation layer on InGaN quantum well red light emitting diodes beyond epitaxy

Zhiyuan Liu, Mingtao Nong, Yi Lu, Haicheng Cao, Saravanan Yuvaraja, Na Xiao, ZAHRAH ALNAKHLI, Raul Aguileta Vázquez, and Xiaohang Li

DOI: 10.1364/OL.476727 Received 28 Sep 2022; Accepted 21 Oct 2022; Posted 26 Oct 2022  View: PDF

Abstract: An atomically thick AlN layer is typically used as the strain compensation layer (SCL) for InGaN-based red light-emitting diodes (LEDs). However, its impacts beyond strain control have not been reported despite its drastically different electronic properties. In this letter, we fabricated and characterized InGaN-based red LEDs with a wavelength of 628 nm. A 1-nm AlN layer was inserted between the InGaN quantum well (QW) and the GaN quantum barrier (QB) as the SCL. The output power of the fabricated red LED is greater than 1 mW at 100 mA current and its peak on-wafer wall plug efficiency (WPE) is approximately 0.3%. Based on the fabricated device, we then used numerical simulation to systematically study the effect of the AlN SCL on the LED emission wavelength and operation voltage. The results show that the AlN SCL enhances the quantum confinement and modulates the polarization charges, modifying the device band bending and the subband energy level in the InGaN QW. Thus, the insertion of the SCL considerably affects the emission wavelength; and the effect on the emission wavelength varies with different SCL thicknesses and the Ga content introduced into the SCL. In addition, the AlN SCL in this work reduces the LED operation voltage by modulating the polarization electric field and energy band, facilitating carrier transport. This implies that heterojunction polarization and band engineering is an approach that can be extended to optimize the LED operation voltage. We believe our study better identifies the role of the AlN SCL in InGaN-based red LEDs, promoting their development and commercialization.

Demonstration of 4096QAM THz MIMO Wireless Delivery Employing One bit Delta-Sigma Modulation

Feng Zhao, Yang Xiongwei, Li Zhao, yi wei, and Jianjun Yu

DOI: 10.1364/OL.477155 Received 03 Oct 2022; Accepted 20 Oct 2022; Posted 15 Nov 2022  View: PDF

Abstract: We experimentally demonstrate 2G baud 4096-ary quadrature amplitude modulation (4096QAM) signal transmission over 2m wireless distance at 370 GHz in a photonics-aided terahertz (THz)-wave communication system. By using one-bit quantized Delta-sigma Modulation (DSM) and photonics-aided technology, we have successfully achieved the transmission of high-order QAM signals over THz MIMO links. After 2 meters of free space transmission, its bit error rate (BER) is below 20% soft-decision forward error correction (20% SD-FEC) threshold 2.4×10−2. To the best of our current knowledge, it is the first time to apply DSM technology in a THz MIMO link transmission.