The 100 most-cited articles in Optics Express, 2024

Many applications involve the phenomenon of a material absorbing electromagnetic radiation. By exploiting wave interference, the efficiency of absorption can be significantly enhanced. Here, we propose Friedrich-Wintgen bound states in the continuum (F-W BICs) based on borophene metamaterials to realize coherent perfect absorption with a dual-band absorption peak in commercially important communication bands. Metamaterials consist of borophene gratings and a borophene sheet that can simultaneously support a Fabry-Perot plasmon resonance and a guided plasmon mode. The formation and dynamic modulation of the F-W BIC can be achieved by adjusting the width or carrier density of the borophene grating, while the strong coupling leads to the anti-crossover behavior of the absorption spectrum. Due to the weak angular dispersion originating from the intrinsic flat-band characteristic of the deep sub-wavelength periodic structure, the proposed plasmonic system exhibits almost no change in wavelength and absorption at large incident angles (within 70 degrees). In addition, we employ the…

High-speed 3D measurement is receiving increasing attention. However, simultaneously achieving high computational efficiency, algorithmic robustness, and reconstructing ratio is challenging. Therefore, a dynamic phase-differencing profilometry (DPDP) is proposed. By capturing the minimum three phase-shifting sinusoidal deformed patterns and establishing a brand-new model, the phase difference between the object on the reference plane and the reference plane is directly resolved to effectively improve computational efficiency. Although it is wrapped, by using only two auxiliary complementary gratings with a purposely designed lower frequency, a DPDP-based number-theoretical temporal phase unwrapping (NT-TPU) algorithm is also proposed to unwrap the wrapped phase difference rather than the phase itself with high robustness. Furthermore, compared to existing PSP-based NT-TPU, the proposed NT-TPU can normally work under more relaxed restrictions. In order to accomplish a high reconstructing ratio, a pentabasic interleaved projection (PIP) strategy based on time division multiplexing is…

With the increasing demands for protecting privacy, multispectral camouflage devices using metasurface design in combination with mature detection technologies has become an effective way. However, this early design exposures challenging while implementing the multispectral camouflage on single metasurface with limited modes. For this reason, this paper proposes a dynamically tunable metasurface. The metasurface consists of Au (gold), Sb2Se3 (antimony selenide) and Al (aluminum) that enables radiative cooling, LiDAR (light detection and ranging) and infrared camouflage. In amorphous phase of Sb2Se3, the thermal radiation reduction rate of MWIR (mid wave infrared) is up to 98.2%. The echo signal reduction rate for 1064 nm LiDAR can reach 96.3%. In crystalline phase of Sb2Se3, the highest cooling power is 65.5 Wm-2. Moreover, the cooled metasurface can further reduce the surface temperature and achieve efficient infrared camouflage. This designed metasurface provides a new strategy for the device to be compatible with multispectral camouflage and radiative cooling.

In this paper, a kind of plasma metastructures-photonic crystals (PMPC) structure is proposed to investigate the absorption and transmission properties of electromagnetic waves (EWs) incident from opposite directions. The results show that the PMPC can achieve a dual-channel asymmetric absorption-transmission (AAT) phenomenon. At an operating bandwidth (OB) of 2.15∼2.85 GHz, EWs are absorbed in the forward incidence and transmitted in the backward case, and a relative bandwidth (RB) with forward absorption above 0.9 is 28.0%. On the contrary, at an OB of 7.07∼7.67 GHz, EWs can be transmitted in the forward propagation and absorbed in the backward case with a RB of 8.1%. Moreover, the effects of parameters such as applied magnetic field, incident angle, and tilt angle on AAT performance are investigated separately. The proposed dual-channel tunable AAT will further extend the application of asymmetric devices in the fields of optical communication and optical transmission.

Unmanned aerial vehicle (UAV) assisted wireless communications have been expected to play a vital role in the next generation of wireless networks. UAVs can serve as either repeaters or data collectors within the communication link, thereby potentially augmenting the efficacy of communication systems. Despite their promise, the channel analysis and modeling specific to terahertz (THz) wireless channels leveraging UAVs remain under-explored. This work delves into a ground-to-UAV channel at 140 GHz, with a specific focus on the influence of UAV hovering behavior on channel performance. Employing experimental measurements through an unmodulated channel setup and a geometry-based stochastic model (GBSM) that integrates three-dimensional positional coordinates and beamwidth, this work evaluates the impact of UAV dynamic movements and antenna orientation on channel performance. Our findings highlight the minimal impact of UAV orientation adjustments on channel performance and underscore the diminishing necessity for precise alignment between UAVs and ground stations as beamwidth increases.

This paper presents a simultaneous measurement light-induced thermoelectric spectroscopy (LITES) sensor with high sensitivity for detecting methane (CH 4 ), carbon monoxide (CO) and acetylene (C 2 H 2 ). It employs a multi-pass cell (MPC) with an overlapped spots pattern and low resonant frequency circle-head quartz tuning forks (QTFs) for the first time. The fiber-coupled MPC with an optical length (OPL) of 40 m was combined with a thin-film filter (TFF) to improve the laser absorption and enable light spots multiplexing on mirrors. Three self-designed circle-head QTFs with low resonant frequencies of less than 10 kHz and a quality factor of ∼ 11500 were adopted to improve the detection ability. The LITES sensor detected multi-gas signals based on their unique absorption spectrum, enabling real-simultaneous measurement of CH 4 , CO, and C 2 H 2 . After optimization, the minimum detection limits (MDLs) of 0.5 ppm, 126.9 ppm and 0.4 ppm for these gases were obtained, respectively. With integration times of 300 s for CH 4 and 200 s each for CO and C 2 H 2 , the MDLs could be further…

An optical pumping scheme is proposed for reducing the gradient of electron spin polarization and suppressing light source noise in a spin-exchange relaxation-free magnetometer. This is achieved by modulating only the phase of a narrow-linewidth pump light field with external Gaussian noise. Compared to the absence of phase modulation, the uniformity of electron spin polarization was improved by over 40%, and the light-frequency noise suppression ratio of the magnetometer was enhanced by 4.3 times. Additionally, the response of the magnetometer was increased by 54%, resulting in a sensitivity of 0.34 fT/Hz 1/2 at 30 Hz. The applicability of this scheme can extend to other optical pumping experiments involving large atom ensembles requiring uniform electron spin polarization distribution, which is beneficial for developing ultra-high sensitivity and high stability magnetometers essential for magneto-cardiography and magneto-encephalography research applications.

Fringe projection profilometry plays an important role for quality control in production line. However, it is facing challenges in the measurement of objects with intricate structures and high dynamic range that involved in precision manufacturing and semiconductor packaging. In this paper, a multi-view fringe projection profilometry system, which deploys a vertical telecentric projector and four oblique tilt-shift cameras, is presented to address the “blind spots” caused by shadowing, occlusion and local specular reflection. A flexible and accurate system calibration method is proposed, in which the corrected pinhole imaging model is used to calibrate the telecentric projection, and the unified calibration is performed by bundle adjustment. Experimental results show that the 3D repeated measurement error and standard deviation are no more than 10 μ m within a measurable volume of 70 × 40 × 20 mm 3 . Furthermore, a group of experiments prove that the developed system can achieve complete and accurate 3D measurement for high dynamic range surfaces with complex structures.

This paper introduces an adjustable metamaterial absorber in terahertz spectrum which has exclusive properties such as resistance to polarization variation. Although this absorber can operate in various applications like chemical and environmental industries, its captivating features in different refractive index (RI) make it a good choice to use in sensing and biomedical applications like cancer early detection, blood glucose, and detecting malaria mosquito bites. The structure originally includes of four different layers that from top to bottom follows: graphene/ SiO2/Si/Au, Respectively, and the finite integration technique has been used in simulation. In terms of absorbing parameters the proposed structure shows an excellent absorption of 98.32% at 4.3 THz and 98.49% at 7.35 THz with an average Q-factor of 8.92 by following simple absorption rules, simulation and electrical field distribution of the suggested structure is illustrated through diagrams to take various parameters such as frequency, sensitivity and physical mechanism into consideration.

Deep learning has been widely used in phase unwrapping. However, owing to the noise of the wrapped phase, errors in wrap count prediction and phase calculation can occur, making it challenging to achieve high measurement accuracy under high-noise conditions. To address this issue, a three-stage multi-task phase unwrapping method was proposed. The phase retrieval was divided into three training stages: wrapped phase denoising, wrap count prediction, and unwrapped phase error compensation. In the first stage, a noise preprocessing module was trained to reduce noise interference, thereby improving the accuracy of the wrap count prediction and phase calculation. The second stage involved training the wrap count prediction module. A residual compensation module was added to correct the errors from the denoising results generated in the first stage. Finally, in the third stage, the phase error compensation module was trained to correct errors in the unwrapped phase calculated in the second stage. Additionally, a convolution-based multi-scale spatial attention module was proposed, which…

The challenges presented by the directly reflected field in optical feedback cavity-enhanced spectroscopy systems serve as substantial obstacles, introducing additional complexity to existing systems and compromising their sensitivity, as the underlying mechanisms of its adverse effects remain not fully understood. This study aims to address this issue by introducing a comprehensive analytical model. Additionally, frequency locking can be achieved by decreasing the feedback rate, the laser’s linewidth enhancement factor, and the directly reflected field, and by increasing the refractive index of the gain medium, the length of the laser’s resonant cavity, the electric field reflectivity of the laser’s output facet, and the resonant field. These parameters can affect the feedback coupling rate pre-factor, and for a resonant cavity with a length of 0.394 m, optical feedback can only be established when the feedback coupling rate pre-factor is less than 1.05 × 10 9 . Through experimental validation, we successfully confirm the effectiveness of the proposed solution in eliminating the…

A surface plasmon resonance (SPR) sensor composed of photonic crystal fibers (PCFs) is designed for the detection of low-concentration liquids. The excellent sensing properties are attributed to the sensitivity enhancement at the dispersion turning point (DTP) of the surface plasmon polariton (SPP) modes. The sensor consists of two identical and structurally simple D-shaped PCFs together with a plasmonic thin film coated on the polished surface in direct contact with the analyte. Changes in the refractive index (RI) result in the splitting of the degenerate plasma peaks, thus allowing the monitoring of the analyte concentration variations by measuring the peak separation. In the RI range between 1.328 RIU and 1.33 RIU, the sensor exhibits an ultra-high sensitivity of 129,800 nm/RIU, which is 37.22 times higher than that of the unsensitized single D-shaped structure. Compared to fiber grating sensors operating in the vicinity of the cladding mode DTP, the spliced dual D-shaped PCF still has a predictably high mechanical strength. In addition, the RI detection range of the sensor can…

Near-eye displays are widely recognized as a groundbreaking technological advancement with the potential to significantly impact daily life. Within the realm of near-eye displays, micro-LEDs have emerged as a highly promising technology owing to their exceptional optical performance, compact form factor, and low power consumption. However, a notable challenge in integrating micro-LEDs into near-eye displays is the efficient light collimation across a wide spectrum range. In this paper, we propose what we believe to be a novel design of a broadband beam collimation metasurface for full-color micro-LEDs by harnessing wavefront phase modulation based on Huygens' principle. Our results demonstrate a substantial reduction in the full width at half maximum (FWHM) angles, achieving a reduction to 1/10, 1/10, and 1/20 for red, green, and blue micro-LEDs compared to those without the metasurface, which is the best collimation result as far as we know. The central light intensity increases by 24.60, 36.49, and 42.15 times. Furthermore, the significant enhancement in the light energy within…

The discovery of bound states in the continuum (BIC) of optical nanostructures has garnered significant research interest and found widespread application in the field of optics, leading to an attractive approach to achieve high-Q (Quality factor) Fano resonance. Herein, an all-dielectric metasurface consisting of four gallium phosphide (Gap) cylinders on the MgF 2 substrate is designed and analyzed by the finite element method (FEM). By breaking the symmetry of the plane, specifically by moving the two cylinders to one side, it is possible to achieve a transition from the symmetry-protected BIC to quasi-BIC. This transition enables the excitation of sharp dual-band Fano resonance at wavelengths of 1,045.4 nm and 1,139.6 nm, with the maximum Q factors reaching 1.47 × 10 4 and 1.28 × 10 4 , respectively. The multipole decomposition and near-field distributions show that these two QBICs are dominated by the electric quadrupole (EQ) and magnetic quadrupole (MQ). Furthermore, bidirectional optical switching can be accomplished by changing the polarization direction of the incident…

We demonstrate telecommunication-wavelength Pockels electro-optic modulators in thin-film lithium tantalate (TFLT) with superior DC stability compared to equivalent thin-film lithium niobate (TFLN) modulators. Less than 1 dB output power fluctuation for quadrature-biased TFLT is measured compared to 5 dB with TFLN over 46 hours with 12.1 dBm input power. Our TFLT modulators maintain properties similar to those in TFLN: 3.4 Vcm half-wave voltage length product, 39 dB extinction ratio, flat RF electro-optic response from 3-50 GHz, and 0.35 dB on-chip loss. We also show low error-rate data modulation over 0-70°C with TFLT modulators and optical loss of 9 dB/m.

Underwater wireless optical communication (UWOC) has demonstrated high-speed and low-latency properties in clear and coastal ocean water because of the relatively low attenuation 'window' for blue-green wavelengths from 450 nm to 550 nm. However, there are different attenuation coefficients for transmission in ocean water at different wavelengths, and the light transmission more seriously deteriorates with fluctuations in the water turbidity. Therefore, traditional UWOC using a single wavelength or coarse blue-green wavelengths has difficulty tolerating variations in water turbidity. Dense wavelength division multiplexing (WDM) technology provides sufficient communication channels with a narrow wavelength spacing and minimal channel crosstalk. Here, we improve the UWOC in clear and coastal ocean water using dense blue-green WDM. A cost-effective WDM emitter is proposed with directly modulated blue-green laser diodes. Dense wavelength beam combination and collimation are demonstrated in a 20-metre underwater channel from 490 nm to 520 nm. Demultiplexing with a minimum channel spacing…

This study introduces what we believe to be a novel photonic crystal fiber sensor utilizing surface plasmon resonance (SPR), incorporating four gold nanowires to enhance sensing capabilities. The research employs machine learning, specifically artificial neural networks (ANN), to predict confinement loss and sensitivity, achieving high accuracy without needing the imaginary part of the effective refractive index. The machine learning technique is applied in three different scenarios, resulting in mean squared errors of 0.084, 0.002, and 0.003, highlighting the reliability of the ANN models in predicting sensor outputs. Additionally, the sensor demonstrates impressive wavelength sensitivities of 2000-18000 nm/RIU (nanometers per refractive index unit) for refractive indices of 1.31-1.4 within the 720-1280 nm wavelength range, and a notable maximum amplitude sensitivity of 889.89 RIU -1 . This integration of SPR, photonic crystal fiber, and machine learning not only optimizes sensor performance but also offers an efficient methodology for prediction, showcasing the potential of…

-nonlinear WGM resonator, by directionally quantum squeezing one of two coupled resonator modes. The directional quantum squeezing results in a chiral photon interaction between the resonators and a frequency shift of the squeezed resonator mode with respect to the unsqueezed bare mode. We show that the directional quantum squeezing can modify the effective optomechanical coupling in the optomechanical resonator, and analyze the impacts of driving direction and squeezing extent on the phonon laser action in detail. Our analytical and numerical results indicate that the controllable nonreciprocal phonon laser action can be effectively realized in this system. The proposed scheme uses an all-optical and chip-compatible approach without spinning resonators, which may be more beneficial for integrating and packaging of the system on a chip. Our proposal may provide a new route to realize integratable phonon devices for on-chip nonreciprocal phonon manipulations, which may be used in chiral quantum acoustics, topological phononics, and acoustical information processing.

Low kerf-loss and high surface quality silicon carbide (SiC) wafer slicing is key to reducing cost, improving productivity, and extending industrial applications. In this paper, a novel all-laser processing approach is proposed by combining laser micro-cracks generation and growth manipulation. The first high fluence pulsed laser is applied to generate micro-cracks inside SiC, which increases its laser energy absorption. The second low fluence pulsed laser achieves the manipulation of micro-cracks growth and interconnection to separate SiC wafer. The optimal laser processing parameters are obtained to separate a 4H-SiC substrate at a thickness of 500 µm. The sliced surface is clean with average surface roughness (Sa) of 186 nm, standard deviation of 0.037, and kerf-loss of 915 nm. This laser slicing approach can be applied for high-hardness transparent material separation.

In this paper, complex-variable sine-Gaussian cross-phase (CVSGCP) beams are proposed, and the transmission dynamics properties of the CVSGCP beams in strongly nonlocal nonlinear media are investigated. CVSGCP beams can produce a variety of mode transformation characteristics during transmission. The roles of parameters in the sine and cross-phase terms of the initial light field expression in the evolution of light intensity modes, phase, and beam width are analyzed in detail, and it is proved that the effect of cross phase is to cause the beams to rotate. The control of different modes can be achieved by selecting suitable parameters, which have certain advantages in the practical application of CVSGCP beams. CVSGCP beams can be regarded as generalized high-order breathers because light intensity modes and beam width show periodic oscillation distribution during transmission. The typical evolution characteristics of the CVSGCP beams are verified by numerical simulation. Strongly nonlocal nonlinear optical media can be mathematically equivalent to a variety of optical systems, such…

A Fabry-Pérot interferometer (FPI) with an asymmetric tapered structure and air microbubble with an ultrathin wall is designed for high-sensitivity strain measurement. The sensor contains an air microbubble formed by two single-mode fibers (SMF) prepared by fusion splicer arc discharge, and a taper is applied to one side of the air microbubble with a wall thickness of 3.6 µm. In this unique asymmetric structure, the microbubble is more easily deformed under stress, and the strain sensitivity of the sensor is up to 15.89 pm/µɛ as evidenced by experiments.The temperature sensitivity and cross-sensitivity of the sensor are 1.09 pm/°C and 0.069 µɛ/°C in the temperature range of 25-200°C, respectively, thus reducing the measurement error arising from temperature variations. The sensor has notable virtues such as high strain sensitivity, low-temperature sensitivity, low-temperature cross-sensitivity, simple and safe process preparation, and low cost. Experiments confirm that the sensor has good stability and repeatability, and it has high commercial potential, especially strain…

Tabletop three-dimensional light field display is a kind of compelling display technology that can simultaneously provide stereoscopic vision for multiple viewers surrounding the lateral side of the device. However, if the flat panel light field display device is simply placed horizontally and displayed directly above, the visual frustum will be tilted and the 3D content outside the display panel will be invisible, the large oblique viewing angle will also lead to serious aberrations. In this paper, we demonstrate what we believe to be a new vertical spliced light field cave display system with an extended depth content. A separate optimization of different compound lens array attenuates the aberration from different oblique viewing angles, and a local heating fitting method is implemented to ensure the accuracy of fabrication process. The image coding method and the correction of the multiple viewpoints realize the correct construction of spliced voxels. In the experiment, a high-definition and precisely spliced 3D city terrain scene is demonstrated on the prototype with a correct…

Directional energy weapons such as high-power microwaves and high-energy lasers pose a huge threat to optoelectronic detection systems. With that in mind, we designed an infrared optical window that has a nonlinear optical response to high-energy lasers and electromagnetic shielding to microwaves. By constructing a periodic metal circular hole array structure at the subwavelength scale, surface plasmons resonance is excited and its local field enhanced characteristics are utilized to form information transmission compatibility in the infrared band. At the same time, after laser etching off the subwavelength structure, the remaining metal forms a continuous conductive structure, forming an ultra-wideband shielding layer to achieve ultra-high and wide protection in the microwave band. Moreover, a layer of Ge2Sb2Te5 thin film was deposited between the transparent substrate and the metal film. Utilizing its nonlinear optical properties of high-temperature phase transition to reduce damage of directed energy weapons to the photoelectric detection system and equipment. Thus, when the…

We demonstrate reactively sputtered Al2O3:Er3+ waveguide amplifiers with an erbium concentration of 3.9 × 1020 ions/cm3, capable of achieving over 30 dB small signal net gain at 1532 nm using bidirectional pumping at 1480 nm. We observe on chip output powers of 10.2 13.6 dBm of amplified signal power at 1532 nm for a 12.9 cm waveguide amplifier considering -25.4 dB of lumped coupling losses per facet. Annealing and waveguide facet polishing were carried out to improve the performance of the devices, which were patterned using electron beam lithography and reactive ion etching. This result, to our knowledge, represents record breaking on-chip internal net gain for Al2O3:Er3+ waveguide amplifiers, which show promise over other technologies due to wafer scalability and promise of easy monolithic integration with other material platforms to support a wide variety of applications.

In order to broaden the sensing bandwidth of surface plasmon resonance (SPR) sensors, we propose and demonstrate a dual-channel SPR fiber optic sensor with wide bandwidth. The sensor is fabricated using no-core fiber (NCF), in which the film consists of a silver film and a ZnO film. The sensing characteristics are investigated by simulation and experiment. The resonance wavelength range of the SPR sensor can be significantly tuned by varying the thickness of the ZnO film. In the experiments, a dual-channel SPR sensor that can be used for simultaneous detection of temperature and refractive index was realized by cascading ZnO/Ag film with Ag film. The experimental results show that the two sensing channels are independent without crosstalk. The sensitivity of this sensor is 3512 nm/RIU in the range of 1.333 ∼ 1.385 and 4.6 nm/°C in the range of 0 ∼ 60 °C, which is better than most of the current dual-channel SPR sensors. In addition, the experimental results show that this sensor has good stability in use. The sensor proposed in this work has the advantages of a wide operating…

At present, pesticides are widely used in the cultivation of crops. Glyphosate is widely used in many pesticides. Glyphosate ingestion can cause a series of health problems. Therefore, this paper proposes to use localized surface plasmon resonance (LSPR) technology to develop a WaveFlex biosensor (plasma wave-based optical fiber sensor) to detect glyphosate concentration in pesticides. The evanescent field is improved by using the fusion of seven-core fiber and single-mode fiber and the tapering of the sensing area to improve the sensing performance. The gold nanoparticles (AuNPs) are used to excite the LSPR effect. Multi-walled carbon nanotubes (MWCNTs) and cerium oxide nanorods (CeO 2 -NRs) are used to increase the surface area and promote the adhesion of the enzyme. The sensitivity of the sensor is 137.7 pm/µM in the range of 0-60 µM glyphosate concentration, and the limit of detection (LoD) is 1.94 µM, which has good performance in compared to the existing biosensors. Subsequently, the sensor was tested for reusability, reproducibility, selectivity, stability, and excellent…

This work presents a bulk refractive index sensor based on quasi-bound states in the continuum (BICs) induced by broken symmetries in metasurfaces. The symmetry is broken by detuning the size and position of silicon particles periodically arranged in an array, resulting in multiple quasi-BIC resonances. We investigate the sensing characteristics of each of the resonances by measuring the spectral shift in response to changes in the refractive index of the surrounding medium. In addition, we reveal the sensing range of the different resonances through simulations involving a layer of deviating refractive index of increasing thickness. Interestingly, the resonances show very different responses, which we describe via the analysis of the near-field. This work contributes to the development of highly sensitive and selective BIC-based sensors that can be used for a wide range of applications.

Chiral metasurfaces with strong chirality and high quality factors (Q-factors) have become essential components for achieving strong light-matter interactions and have a wide range of applications in chiral lasers, detectors, etc. However, current schemes primarily focus on enhancing the chiral response and Q-factor, with limited consideration of their modulability and flexibility. In this paper, we present a chiral a-Si metasurface that can support multiple symmetry-protected bound states in the continuum (BIC). The perfect extrinsic and intrinsic chiral responses (circular dichroism exceeding 0.99), with ultra-high Q-factors, are achieved by utilizing quasi-BICs induced by illumination symmetry and in-plane symmetry breaking. The circular dichroism value and the transmittance of the two circular polarization states can be arbitrarily controlled by adjusting the structural parameters. Furthermore, the feasibility of achieving dynamic modulation of chiral response is demonstrated based on the a-Si-graphene hybrid metasurface. Our research offers an approach to the design of…

In this paper, a terahertz (THz) dual-band bandpass filter based on spoof surface plasmon polaritons (SSPPs) with wide upper stopband suppression is proposed. The filter utilizes two types of SSPP unit cells loaded on a double-sided quasi-SSPPs transmission line to achieve dual-band filtering responses and wide upper stopband suppression simultaneously. The performance and bandwidth of the filter's passbands can be adjusted by modifying the SSPP unit cells within the dual-band filtering part. The detailed design method is provided to enhance understanding of the operating principle of the presented filter. The simulation results of the designed THz filter demonstrate its excellent dual-band filtering performance. It features a wide stopband spanning from 0.91 to 1.45 THz with | S 21 | < -35 dB. To validate the proposed approach, a microwave filter with a similar design is implemented. Finally, the simulated and measured S-parameter responses of the filter are provided for comparison and evaluation.

We demonstrate the design, fabrication, and experimental characterization of a single transverse mode adiabatic microring resonator (MRR) implemented using the silicon-on- insulator (SOI) platform using local oxidation of silicon (LOCOS) approach. Following its fabrication, the device was characterized experimentally and an ultrahigh intrinsic Q-factor of ∼2 million with a free spectral range (FSR) of 2 nm was achieved, giving rise to a finesse of ∼1100, the highest demonstrated so far in SOI platform at the telecom band. We have further studied our device to analyze the source of losses that occur in the MRR and to understand the limits of the achievable Q-factor. The surface roughness was quantified using AFM scans and the root mean square roughness was found to be ∼ 0.32±0.03 nm. The nonlinear losses were further examined by coupling different optical power levels into the MRR. Indeed, we could observe that the nonlinear losses become more pronounced at power levels in the range of hundreds of microwatts. The demonstrated approach for constructing high-Q and high finesse MRRs can…

We report on a free-space-coupled superconducting nanowire single-photon detector array developed for NASA's Deep Space Optical Communications project (DSOC). The array serves as the downlink detector for DSOC's primary ground receiver terminal located at Palomar Observatory's 200-inch Hale Telescope. The 64-pixel WSi array comprises four quadrants of 16 co-wound pixels covering a 320-µm diameter active area and embedded in an optical stack. The detector system also includes cryogenic optics for filtering and focusing the downlink signal and electronics for biasing the array and amplifying the output pulses. The detector system exhibits a peak system detection efficiency of 76% at 1550 nm, a background-limited false count rate as low as 3.7 kcps across the array, a timing jitter less than 120 ps FWHM, and a maximum count rate of ∼1 Gcps.

In many cases, optical metasurfaces are studied in the single-resonant regime. However, a multiresonant behavior can enable multiband devices with reduced footprint, and is desired for applications such as display pixels, multispectral imaging and sensing. Multiresonances are typically achieved by engineering the array lattice (e.g., to obtain several surface lattice resonances), or by adopting a unit cell hosting one (or more than one) nanostructure with some optimized geometry to support multiple resonances. Here, we present a study on how to achieve multiresonant metasurfaces in the visible spectral range by exploiting high-order multipoles in dielectric (e.g., diamond or titanium dioxide) nanostructures. We show that in a simple metasurface (for a fixed particle and lattice geometry) one can achieve triple resonance occurring nearly at RGB (red, green, and blue) wavelengths. Based on analytical and numerical analysis, we demonstrate that the physical mechanism enabling the multiresonance behavior is the lattice induced coupling (energy exchange) between high-order Mie-type…

An innovative ultra-sensitive, dual-functional sensor employing a D-shaped microchannel photonic crystal fiber (PCF) for refractive index (RI) and temperature measurements is proposed and comprehensively investigated. Its high-sensitivity is achieved through the incorporation of gold (Au) and magnesium fluoride (MgF 2 ) as plasmonic materials in the micro-rectangular channel. This configuration significantly enhances the interaction between the surface plasmon polaritons (SPPs) field and y-polarized evanescent field on external surfaces. Additionally, the integration of a temperature-sensitive fluid within the sensor allows for precise detection of temperature changes. Our simulations demonstrate a broad detection spectrum, covering RI values from 1.27 to 1.43 and temperatures ranging from 45°C to 100°C. The sensor achieves peak sensitivities of 31800nm/RIU for RI and 49 nm/°C for temperature. Besides, the sensor only has a cladding consisting of three air holes to enhance coupling and reduce the difficulty of preparation. Importantly, the sensor's performance remains robust against…

We proposed multilayered graphene (Gr)-based surface plasmon resonance-induced high-performance terahertz (THz) modulators with tunable resonance frequencies. Previously reported Gr metamaterials-based THz plasmonic modulators had small group delay, low extinction ratio (ER), and difficult-to-tune resonant frequency without changing structural parameters in the THz range. A comprehensive investigation employing the finite-difference time-domain (FDTD) simulation technique revealed high group delay, broad tunability independent of structural parameters, and large ER for our proposed quadband and pentaband plasmonic modulators. We obtained tunable group delays with a maximum of 1.02 ps and 1.41 ps for our proposed quadband and pentaband plasmonic modulators, respectively, which are substantially greater compared to previously reported Gr-based metamaterial structures. The maximum ER of 22.3 dB was obtained, which was substantially high compared to previous reports. Our proposed modulators were sensitive to the polarization angle of incident light; therefore, the transmittance at…

Metamaterials offer exciting opportunities for developing multispectral stealth due to their unique electromagnetic properties. However, currently transparent radar-infrared-visible compatible stealth metamaterials typically involve complex hierarchical designs, leading to thickness and transparency limitations. Here, we propose an integrated metamaterial for multispectral stealth with high transparency. Our design features an ITO/dielectric/ITO sandwich structure, with the upper-layer ITO acting as a resonator for broadband microwave absorption while maintaining a high filling ratio to suppress infrared (IR) radiation. Experimental results demonstrate excellent performance, with over 90% microwave absorption in 8-18 GHz, an IR emissivity of approximately 0.36 in 3-14 µm, an average optical transmittance of 74.1% in 380-800 nm, and a thickness of only 2.4 mm. With its multispectral compatibility, the proposed metamaterial has potential applications in stealth and camouflage fields.

This paper introduces an innovative, compact, and high-gain metasurface antenna, covering both the 24 GHz millimeter wave (mmWave) radar band and the 5 G n257 and n258 bands. The proposed metasurface antenna consists of a wideband stacked patch antenna and a dual-layer metasurface to focus its radiation beams for multiple mmWave bands. The operating frequency can be slightly shifted by altering the distance between the feeder and the metasurface. The distribution of the metasurface unit cells is designed based on a simplified phase compensation formula. The dimension of the fabricated feeder is 6 mm × 6 mm, and the metasurface occupies a 65 mm × 65 mm radome area. Experimental results demonstrate a wide bandwidth from 23.5 GHz to 29.1 GHz for the feeder, and impressive maximum gains of 19.7 dBi and 19.5 dBi for the lower band and higher band of the metasurface antenna are achieved simultaneously. The frequency reconfiguration ability was characterized by a 750 MHz frequency shift with every 1 mm distance adjustment. The compact size and high gain performance of the proposed design…

We report a dual-polarization radio frequency (RF) channelizer based on microcombs. Two high-Q micro-ring resonators (MRRs) with slightly different free spectral ranges (FSRs) are used: one MRR is pumped to yield soliton crystal microcombs ("active"), and the other MRR is used as a "passive" periodic optical filter supporting dual-polarization operation to slice the RF spectrum. With the tailored mismatch between the FSRs of the active and passive MRRs, wideband RF spectra can be channelized into multiple segments featuring digital-compatible bandwidths via the Vernier effect. Due to the use of dual-polarization states, the number of channelized spectral segments, and thus the RF instantaneous bandwidth (with a certain spectral resolution), can be doubled. In our experiments, we used 20 microcomb lines with ∼ 49 GHz FSR to achieve 20 channels for each polarization, with high RF spectra slicing resolutions at 144 MHz (TE) and 163 MHz (TM), respectively; achieving an instantaneous RF operation bandwidth of 3.1 GHz (TE) and 2.2 GHz (TM). Our approach paves the path towards…

In this paper, we improve the learned digital back propagation (LDBP) and propose a novel joint intra and inter-channel nonlinearity compensation scheme for polarization division multiplexing wavelength-division multiplexed (PDM-WDM) systems. From the perspective of interpretable neural network, the scheme realizes the alternating compensation of chromatic dispersion (CD) and nonlinearity based on physical models. The chromatic dispersion compensation (CDC) adopts one-dimensional convolution operation in the time domain. Moreover, the pulse-broadening effect is introduced into the overlap-and-save method. For nonlinear compensation, the improved joint model is applied, and the impact of the intra-channel pulse broadening and the walk-off effect between different channels caused by CD on the nonlinear effect is considered. To validate the effectiveness of the proposed scheme, we construct an 11-channel simulation system of 36 GBaud PDM uniform 16 quadrature amplitude modulation (PDM-16QAM) 1600 km and 64 GBaud PDM-64QAM 400 km, as well as a 5-channel experimental system of 28 GBaud…

Polarization is a fundamental characteristic of electromagnetic (EM) waves, and accurately determining the polarization state is crucial for spectral imaging and information processing. However, implementing broadband polarization detection in the terahertz (THz) range poses significant challenges when employing conventional optics. This paper proposes and experimentally evaluates a broadband polarization detection strategy using all-dielectric metasurfaces. By employing the technique of circular polarization multiplexing, the proposed approach allows for the generation of a focus that contains the incident polarization information at a predetermined plane. When a fully polarized THz beam interacts with the proposed design, its two orthogonal circularly polarized components weighted equally and simultaneously converge at designed spatial coordinates. Subsequently, by capturing the complex amplitude at the target pixel, the full-Stokes parameters and equations of the polarization ellipse corresponding to the incident polarization state can be extracted in real time. Further…

We present a procedure for the design of multilevel metalenses and their fabrication with multiphoton-based direct laser writing. This work pushes this fast and versatile fabrication technique to its limits in terms of achievable feature size dimensions for the creation of compact high-numerical aperture metalenses on flat substrates and optical fiber tips. We demonstrate the design of metalenses with various numerical apertures up to 0.96, and optimize the fabrication process towards nanostructure shape reproducibility. We perform optical characterization of the metalenses towards spot size, focusing efficiency, and optical functionality with a fiber beam collimation design, and compare their performance with refractive and diffractive counterparts fabricated with the same technology.

On-chip microring resonators (MRRs) have been proposed to construct time-delayed reservoir computing (RC) systems, which offer promising configurations available for computation with high scalability, high-density computing, and easy fabrication. A single MRR, however, is inadequate to provide enough memory for the computation task with diverse memory requirements. Large memory requirements are satisfied by the RC system based on the MRR with optical feedback, but at the expense of its ultralong feedback waveguide. In this paper, a time-delayed RC is proposed by utilizing a silicon-based nonlinear MRR in conjunction with an array of linear MRRs. These linear MRRs possess a high quality factor, providing enough memory capacity for the RC system. We quantitatively analyze and assess the proposed RC structure's performance on three classical tasks with diverse memory requirements, i.e., the Narma 10, Mackey-Glass, and Santa Fe chaotic timeseries prediction tasks. The proposed system exhibits comparable performance to the system based on the MRR with optical feedback, when it comes to…

The three-dimensional (3D) light field display (LFD) with dense views can provide smooth motion parallax for the human eye. Increasing the number of views will widen the lens pitch, however, resulting in a decrease in view resolution. In this paper, an approach to smooth motion parallax based on optimizing the divergence angle of the light beam (DALB) for 3D LFD with narrow pitch is proposed. DALB is controlled by lens design. A views-fitting optimization algorithm is established based on a mathematical model between DALB and view distribution. Subsequently, the lens is reversely designed based on the optimization results. A co-designed convolutional neural network (CNN) is used to implement the algorithm. The optical experiment shows that a smooth motion parallax 3D image is achievable through the proposed method.

A tri-layer chiral metasurface with multi-functions of asymmetric transmission (AT), polarization conversion (PC) and circular dichroism (CD) is proposed in the terahertz (THz) range. Simulation results show that the metasurface is able to realize AT with more than 90% efficiency and PC fractional bandwidth of 80% over a frequency range of 0.15 to 0.35 THz. At 0.33 THz, it showcases the utmost CD of 58%. Through experimental measurements, the fabricated device demonstrate that the AT parameters exceed 35% in the frequency range of 0.24-0.33 THz. This broad frequency range represents a PC fractional bandwidth of 69% and reveals a prominent peak at 0.28 THz, wherein the transmission attains a value of 0.62. The proposed configuration exhibits CD, achieving 14% at 0.24 THz. Furthermore, the functionalities of AT, PC and CD are stable for changes in incident angle up to 60° for both linearly polarized and circularly polarized incident waves. Moreover, the experimental and measured results demonstrate that the proposed multilayer chiral metamaterial achieves multifunctionality for THz…

In response to the rapid advancements in radar detection technology and the widespread deployment of infrared sensors, single-function stealth materials are increasingly challenged to meet the sophisticated demands of concealment within complex electromagnetic environments. As a result, there is a pressing need for research into metamaterial structures that can simultaneously deliver ultra-wideband radar stealth and controllable infrared invisibility. Here, a novel metamaterial structure was proposed and realized, comprising vertically integrated infrared stealth and radar stealth layers, with the aim of accomplishing both ultra-wideband radar stealth and controlled infrared invisibility. Coded units were designed based on the geometric phase modulation mechanism and then arrayed through a random matrix strategy optimized by a genetic algorithm, yielding a radar stealth layer characterized by outstanding properties such as ultra-wideband radar stealth and insensitivity to polarization states. A temperature-adaptive infrared stealth switching function was successfully achieved by…

Phase unwrapping is a crucial step in obtaining the final physical information in the field of optical metrology. Although good at dealing with phase with discontinuity and noise, most deep learning-based spatial phase unwrapping methods suffer from the complex model and unsatisfactory performance, partially due to simple noise type for training datasets and limited interpretability. This paper proposes a highly efficient and robust spatial phase unwrapping method based on an improved SegFormer network, SFNet. The SFNet structure uses a hierarchical encoder without positional encoding and a decoder based on a lightweight fully connected multilayer perceptron. The proposed method utilizes the self-attention mechanism of the Transformer to better capture the global relationship of phase changes and reduce errors in the phase unwrapping process. It has a lower parameter count, speeding up the phase unwrapping. The network is trained on a simulated dataset containing various types of noise and phase discontinuity. This paper compares the proposed method with several state-of-the-art…

Fourier ptychography (FP) imaging, drawing on the idea of synthetic aperture, has been demonstrated as a potential approach for remote sub-diffraction-limited imaging. Nevertheless, the farthest imaging distance is still limited to around 10 m, even though there has been a significant improvement in macroscopic FP. The most severe issue in increasing the imaging distance is the field of view (FoV) limitation caused by far-field conditions for diffraction. Here, we propose to modify the Fourier far-field condition for rough reflective objects, aiming to overcome the small FoV limitation by using a divergent beam to illuminate objects. A joint optimization of pupil function and target image is utilized to attain the aberration-free image while estimating the pupil function simultaneously. Benefiting from the optimized reconstruction algorithm, which effectively expands the camera’s effective aperture, we experimentally implement several FP systems suited for imaging distances of 12 m, 65 m, and 120 m with the maximum synthetic aperture of 200 mm. The maximum synthetic aperture is thus…

Over the last two decades, spatial light modulators (SLMs) have revolutionized our ability to shape optical fields. They grant independent dynamic control over thousands of degrees-of-freedom within a single light beam. In this work we test a new type of SLM, known as a phase-only light modulator (PLM), that blends the high efficiency of liquid crystal SLMs with the fast switching rates of binary digital micro-mirror devices (DMDs). A PLM has a 2D mega-pixel array of micro-mirrors. The vertical height of each micro-mirror can be independently adjusted with 4-bit precision. Here we provide a concise tutorial on the operation and calibration of a PLM. We demonstrate arbitrary pattern projection, aberration correction, and control of light transport through complex media. We show high-speed wavefront shaping through a multimode optical fiber – scanning over 2000 points at 1.44 kHz. We make available our custom high-speed PLM control software library developed in C++. As PLMs are based upon micro-electromechanical system (MEMS) technology, they are polarization agnostic, and possess…

We report a trace gas sensing technique of cavity-enhanced light-induced thermoelastic spectroscopy (CE-LITES) with a Fabry–Pérot (F-P) optical cavity and a high-quality-factor resonant quartz tuning fork (QTF). Pound-Drever-Hall (PDH) locking method is used to lock the laser to the optical cavity. With only a short 9-cm optical cavity (finesse, ∼1283) and a tiny commercially available standard QTF ( Q -factor, ∼38910), a CE-LITES sensor for acetylene detection was developed to demonstrate this technique, achieving a minimum detection limit (MDL) of 7.5 parts-per-billion (ppb) for a 216-s integration time and a normalized noise equivalent absorption (NNEA) coefficient of as low as 1.91 × 10 −10 cm −1 ·W·Hz −1/2 . The developed technique bears promising potential for sensitive and accurate measurement that is needed for studying trace gas-phase analyte.

Quantum computing in high-dimensional spaces holds promise for a plethora of applications, i.e., handling more intricate information and executing wider quantum operations, in complex quantum information technologies (QITs). In the paper, we set up an error-heralded, resource-saving, circuit-simplified, and 4×4-dimensional controlled-not (CNOT) gate, where the polarized and spatial state of the flying photon (i.e., the control qudit) can effectively control the collective spin wave state of two atomic ensembles (i.e., the target qudit) in two double-sided cavities. Moreover, through meticulous analysis, the feasibility of the high-dimensional gate using existing technology boasts the exceptional performance including a near-unity fidelity and high efficiency exceeding 0.95, in principle, as the undesired performances originated from the little side leakage and the finite coupling strength, and the imperfect atom-ensemble-cavity interactions are heralded by single-photon detectors. Besides, auxiliary photons or atomic ensembles are unnecessary. Therefore, our protocol stands out for…

We report on the high-efficiency storage and retrieval of weak coherent optical pulses and photonic qubits in a cavity-enhanced solid-state quantum memory. By using an atomic frequency comb (AFC) memory in a Pr 3+ :Y 2 SiO 5 crystal embedded in an impedance-matched cavity, we stored weak coherent pulses at the single photon level with up to 62% efficiency for a pre-determined storage time of 2 µs. We also confirmed that the impedance-matched cavity enhances the efficiency for longer storage times up to 70 µs. Harnessing the temporal multimodality of the AFC scheme, we stored weak coherent time-bin qubits with a record (51 ± 2%) efficiency and a fidelity over (94.8 ± 1.4)%, limited by imperfections in the qubits creation and measurement.

An all-sapphire fiber-optic extrinsic Fabry-Perot interferometric (EFPI) sensor for the simultaneous measurement of ultra-high temperature and high pressure is proposed and experimentally demonstrated. The sensor is fabricated based on all-sapphire, including a sapphire fiber, a sapphire capillary and a sapphire wafer. A femtosecond (fs) laser is employed to drill a through hole at the side wall of the sapphire capillary to allow gas flow. The sapphire fiber is inserted from one side of the sapphire capillary. The sapphire wafer is fixed at the other side of the sapphire capillary. The first Fabry-Perot (FP) cavity, composed of the end face of the sapphire fiber and the front surface of the sapphire wafer, is used for measuring pressure, while the second FP cavity, composed of the two surfaces of the sapphire wafer, is used for measuring temperature. Experimental results show that the sensor can simultaneously measure ultra-high temperature and gas pressure within the temperature range of 20 - 1400 °C and the pressure range of 0 - 5 MPa. The temperature sensitivity is 0.0033 µm/°C,…

In contrast to the passive remote sensing of global CO2 column concentrations (XCO2), active remote sensing with a lidar enables continuous XCO2 measurements throughout the entire atmosphere in daytime and nighttime. The lidar could penetrate most cirrus and is almost unaffected by aerosols. Atmospheric environment monitoring satellite (AEMS, also named DQ-1) aerosol and carbon dioxide detection Lidar (ACDL) is a novel spaceborne lidar that implements a 1572 nm integrated path differential absorption (IPDA) method to measure the global XCO2 for the first time. In this study, special methods have been developed for ACDL data processing and XCO2 retrieval. The CO2 measurement data products of ACDL, including the differential absorption optical depth between the online and offline wavelengths, the integral weighting function, and XCO2, are presented. The results of XCO2 measurements over the period from 1st June 2022 to 30th June 2022 (first month data of ACDL) are analyzed to demonstrate the measurement capabilities of the spaceborne ACDL system.

Pure-quartic solitons (PQSs) have recently received increasing attention due to their energy-width scaling over the traditional soliton, which has expanded our understanding of soliton dynamics with high-order dispersion in nonlinear systems. Here, we numerically reveal the asynchronization and synchronization processes of the sub-pulse within the vector PQS molecule in a mode-locked fiber laser by solving the coupled Ginzburg-Landau equations. During the establishment of a vector PQS molecule, the repulsion, attraction, and finally stabilization processes have been observed. Specifically, sub-pulse disappearance, regeneration, and finally synchronization with the other pulses are also investigated. Our analysis of the pulse energy, time interval, and relative phase evolution dynamics with the round trip indicates that the asynchronization and synchronization within the vector PQS molecule associate tightly with the gain competition and the cross-phase modulation. Our findings provide insights into the internal mutual dynamics within the vector soliton molecule and offer guidance…

This paper proposes a covert chaotic encryption (CCE) scheme based on compressive sensing (CS). The chaotic sequences used are generated by a six-dimensional hyper-chaotic D-system, where the y sequence is utilized for a chaotic index sparse block (CISB), the x sequence is used for generating the CS measurement matrix effectively, the w , s , and u sequences are employed for variable-parameter iterative Arnold transformations, and the z sequence is used for dual-random least significant bit (LSB) scrambling and embedding. The combination of these technologies enabled the scheme to achieve multi-domain, multi-dimensional, ultra-high-security encryption for multimedia image data. The scheme allows for the 4 Gb/s W-band orthogonal frequency division multiplexing (OFDM) signal transmission over 10 m in a radio-over-fiber (RoF) system. When the input optical power (IOP) exceeds 1 dBm, the bit error rate (BER) of the system is lower than the forward error correction (FEC) threshold of 3.8×10 −3 . When the IOP is 6 dBm, the mean structural similarity index (MSSIM) between the decrypted and…

In this paper, a wideband optically transparent absorber based on multilayer indium tin oxide (ITO) films is designed, fabricated, and measured. The structure uses polyethylene terephthalate (PET) and ITO films to replace the dielectric substrate and metal pattern of the traditional absorber to achieve optical transparency characteristics. The absorption of the proposed absorber is above 90% from 4.92 to 24.55 GHz and exceeding 95% in the range of 5.74 ∼ 21.85 GHz, respectively, under normal transverse electric (TE) and transverse magnetic (TM) polarized incidences. Moreover, it shows outstanding stability with various incident angles over a wide range. A prototype of the proposed absorber is fabricated and experimentally verified, with good measurement results. The optical transparency and great absorption performance make the absorber a promising candidate for transparent electromagnetic compatibility.

Integrating quantum key distribution (QKD) with classical optical communication is a deployment-friendly and cost-effective approach to advancing QKD network implementation. However, the noise introduced by intense classical signals into the quantum channel severely impacts the performance of the QKD system, presenting challenges for long-distance coexistence transmission. In this paper, we successfully demonstrate the simultaneous propagation of QKD and optical transport network (OTN) in the C-band over distances exceeding 100 km. We establish a coexistence transmission system based on a commercial OTN equipment and QKD device equipped with the Fabry-Perot filters, demonstrating the feasibility of combining QKD with 11 Tbps (110×100 Gbps) classical data over a 101.86 km fiber. To investigate longer transmission distances, we employ an optimized wavelength allocation method and conduct the co-propagation of QKD and 1 Tbps classical data over a 152.34 km fiber. To the best of our knowledge, these results are the first time that report the integration of QKD and large-capacity…

This study presents a numerical study of a highly sensitive photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor capable of detecting five types of cancer and bacterial contamination in water. By precisely arranging only two air holes in a single channel of an elliptical-shaped PCF, the sensor maximizes interaction between core-guided modes and surface plasmon polaritons (SPP) along the fiber. Evaluation using COMSOL Multiphysics simulation software, based on finite element method (FEM), demonstrates outstanding sensor performance across a wide refractive index (RI) range (1.33 to 1.43). With a maximum wavelength sensitivity (WS) of 188,000 nm/RIU and amplitude sensitivity (AS) of -22,377.99 RIU −1 , the sensor achieveStructural Design and Methodologys a sensor resolution (SR) of 5.3191 × 10 −7 RIU and figure of merit (FOM) of 854.55 RIU −1 . Notably, it exhibits AS and WS values tailored for specific cancer cell types and water contamination. These results endorse the sensor’s potential in diverse biological and molecular analyte RI detection applications within the…

This study proposes a solid-state two-dimensional beam-steering device based on an electro-optical phased array (EOPA) in thin-film lithium niobate (TFLN) and silicon nitride (SiN) hybrid platforms, thereby eliminating the requirement for the direct etching of TFLN. Electro-optic (EO) phase modulator array comprises cascaded multimode interference couplers with an SiN strip-loaded TFLN configuration, which is designed and fabricated via i-line photolithography. Each EO modulator element with an interaction region length of 1.56 cm consumed a minimum power of 3.2 pJ/π under a half-wave voltage of 3.64 V and had an estimated modulation speed of 1.2 GHz. Subsequently, an SiN dispersive antenna with a waveguide grating was tethered to the modulator array to form an EOPA, facilitating the out-of-plane radiation of highly defined near-infrared beams. A prepared EOPA utilized EO phase control and wavelength tuning near 1550 nm to achieve a field-of-view of 22° × 5° in the horizontal and vertical directions. The proposed hybrid integrated platform can potentially facilitate low-power and…

In this paper, a novel laser spot tracking algorithm that incorporates the Kalman filter with the continuously adaptive Meanshift algorithm (Cam-Kalm) is proposed and employed in an underwater optical wireless communication (UOWC) system. Since the Kalman filter has the advantage of predicting the state information of the target spot based on its spatial motion features, the proposed algorithm can improve the accuracy and stability of the moving laser spot tracking. A 2 m optical wireless communication experimental system with auto-tracking based on a green laser diode (LD) is built to evaluate the tracking performance of different algorithms. Experimental results verify that the proposed algorithm outperforms conventional tracking algorithms in aspects of tracking accuracy, interference resistance, and response time. With the proposed Cam-Kalm algorithm, the experimental system can establish an effective communication link, while the maximum tracking speed is 20 mm/s given the forward-error-correction (FEC) threshold.

High-Q resonances excited by bound states in a continuum (BIC) in metamaterial have sparked increasing research interests for its prospective applications in sensing, lasing, and nonlinear optical devices. This paper introduces a quasi-BIC supported flexible terahertz (THz) metamaterial sensor for curvature measurement. The symmetry-protected BICs based on metallic rectangle structures on a thin flexible polyimide substrate are designed. After introducing defect perturbations along the x and y directions into the metallic rectangle, two observable quasi-BICs would be excited by x and y-polarized THz waves, respectively. Moreover, an experimental demonstration of the curvature sensing performance is conducted by monitoring spectral evolution in response to the bending BIC metallic metamaterial. The measured results indicate that the resonant transmission amplitude is sensitive to variations in the applied curvatures. The flexible, easy manufacturing, and highly-sensitive quasi-BIC micro structured metamaterial sensor paves a new way toward developing sensitive and wearable…

To address challenges in enhancing color uniformity and ambient contrast ratio (ACR) in RGB light-emitting diodes (LEDs) without losing efficiency, we developed a scattering-enhanced magnetic manipulation (SEMM) bilayer structure. The effect of the TiO 2 scattering layer on improving the LED’s angular intensity non-uniformity (AIN) was studied by ray-tracing simulations and optimized by varying the particle concentration. The magnetic manipulation technique formed the microcolumns and magnetic chains of the Fe 3 O 4 anti-reflective layer, which was optimized by adjusting Fe 3 O 4 particle size, magnetic field strength, and Fe 3 O 4 concentration. The resulting bilayered device significantly increased the ACR by 11.38 times and reduced AIN by 63% compared to conventional graphite-based LEDs, while maintaining high brightness and consistent color quality across angles. This marks a pioneering application of magnetic manipulation in enhancing LED display quality.

A scheme for high-efficiency transfer of optical vortices is proposed by an inelastic two-wave mixing (ITWM) process in an inverted-Y four-level atomic medium, which is originally prepared in a coherent superposition of two ground states. The orbital angular momentum (OAM) information in the incident vortex probe field can be transferred to the generated signal field through the ITWM process. Choosing reasonable experimentally realizable parameters, we find that the presence of the off-resonance control field can greatly improve the conversion efficiency of optical vortices, rather than in the absence of a control field. This is caused by the broken of the destructive interference between two one-photon excitation pathways. Furthermore, we also extend our model to an inelastic multi-wave mixing process and demonstrate that the transfer efficiency between multiple optical vortices strongly depends on the superposition of the ground states. Finally, we explore the composite vortex beam generated by collinear superposition of the incident vortex probe and signal fields. It is obvious…

An ultra-high sensitivity weak magnetic field detecting magnetic fluid surface plasmon resonance (SPR) sensor based on a single-hole fiber (SHF) is proposed for detecting weak magnetic fields. The sensor is constructed with a single-hole fiber in which an exclusive air hole in the cladding is embedded with a metal wire and filled with a magnetic fluid (MF) to enhance the magnetic field sensitivity. The effects of the structural parameters, embedded metals, and refractive index difference between the core and cladding on the magnetic field sensitivity and peak loss are investigated and optimized. The sensitivity, resolution, figure of merit (FOM), and other characteristics of the sensor are analyzed systematically. The numerical results reveal a maximum magnetic field sensitivity of 451,000 pm/mT and FOM of 15.03 mT -1 . The ultra-high magnetic field sensitivity renders the sensor capable of detecting weak magnetic fields at the pT level for the first time, in addition to a detection range from 3.5 mT to 17 mT. The SHF-SPR magnetic field sensor featuring high accuracy, simple…

We report on stable, long-term operation of a diode-pumped solid-state laser (DPSSL) amplifying 15 ns pulses at 1029.5 nm wavelength to 10 J energy at 100 Hz pulse rate, corresponding to 1 kW average power, with 25.4% optical-to-optical efficiency. The laser was operated at this level for over 45 minutes (∼3 · 10 5 shots) in two separate runs with a rms energy stability of 1%. The laser was also operated at 7 J, 100 Hz for 4 hours (1.44 · 10 6 shots) with a rms long-term energy stability of 1% and no need for user intervention. To the best of our knowledge, this is the first time that long-term reliable amplification of a kW-class high energy nanosecond pulsed DPSSL at 100 Hz has been demonstrated.

Multi-pass cell (MPC) compressors have proven to be the method of choice for compression of high average power long-pulse Yb lasers. Yet, generating sub-30 fs pulses at high pulse energy with compact and simple components remains a challenge. This work demonstrates an efficient and cost-effective approach for nonlinear pulse compression at high pulse energy using a hybrid air-bulk MPC. By carefully balancing the relative nonlinear contributions of ambient air and fused silica, we achieve strong spectral broadening without dispersion engineering or pressure-control inside the cell at 400-µJ pulse energy. In this way, we compress pulses from 220 fs to 27 fs at 40.3 W of average power (100 kHz repetition rate), enhancing the peak power from 1.6 GW to 10.2 GW while maintaining 78% of the energy within the main pulse. Our approach combines the strengths of gas-filled and bulk compression schemes and exhibits excellent overall optical transmission (91%) and spectral uniformity. Moreover, we utilize the INSIGHT technique to investigate spatio-temporal couplings and geometrical aberrations…

Independently tunable biaxial color pixels, composed of isolated nanosquare dimers, are demonstrated in this study. These pixels are capable of displaying a full range of colors under a linear-polarization dependent reflection mode. The metasurface is constructed by arranging LiNbO 3 nanodimers on a PDMS substrate. By exciting a strong magnetic dipole (MD) resonance and effectively suppressing other multipolar resonances using surface lattice resonances, the researchers achieved a single reflection peak with a bandwidth of less than 9 nm and a reflective efficiency of up to 99%. Additionally, the stretchability of the PDMS substrate allows for active and continuous tuning of the metasurface by up to 40% strain, covering almost 150 nm of the visible light spectrum and enabling changes in reflection color. This metasurface holds potential applications in various fields, such as color displays, data storage, and anti-counterfeiting technologies.

Matrix effect is one of the obstacles that hinders the rapid development of laser-induced breakdown spectroscopy (LIBS), and it is currently a hot, challenging, and focal point in research. To eliminate the matrix effect, this study proposed a plasma parameters correction method based on plasma image-spectrum fusion (PPC-PISF). This method corrects the total number density, plasma temperature, and electron number density variations caused by matrix effect using effective features in plasma images and spectra. To verify the feasibility of this method, experiments were conducted on pressed and metal samples, and the results were compared with those corrected by image-assisted LIBS (IA-LIBS). For the pressed samples, after correction by PPC-PISF, the R 2 of the calibration curves all improved to above 0.993, the average root-mean-square error (RMSE) decreased by 41.05%, and the average relative error (ARE) decreased by 59.35% evenly in comparison to IA-LIBS. For the metal samples, after correction by PPC-PISF, the R 2 of the calibration curves all increased to above 0.997.…

We propose a large viewing angle integral imaging 3D display system based on a symmetrical compound lens array (SCLA). The display system comprises a high-resolution 2D display panel, an SCLA, and a light shaping diffuser. The high-resolution 2D display panel presents an elemental image array, the SCLA modulates the light rays emitted from the 2D display panel to form 3D images in space, and the light shaping diffuser eliminates the gaps between 3D pixels of the 3D images. We find that the lateral aberration is a crucial factor that affects the resolution of the reconstructed 3D image. The symmetrical structure of the SCLA enables a reduced focal length and the elimination of lateral aberration, improving the viewing angle and the 3D image resolution simultaneously. The experimental results confirm that the proposed display system increases the viewing angle to 68.6°, achieving a comparable resolution of the full field of view while maintaining a simple structure.

The resolution of optical imaging is limited by diffraction as well as detector noise. However, thermal imaging exhibits an additional unique phenomenon of ghosting which results in blurry and low-texture images. Here, we provide a detailed view of thermal physics-driven texture and explain why it vanishes in thermal images capturing heat radiation. We show that spectral resolution in thermal imagery can help recover this texture, and we provide algorithms to recover texture close to the ground truth. We develop a simulator for complex 3D scenes and discuss the interplay of geometric textures and non-uniform temperatures which is common in real-world thermal imaging. We demonstrate the failure of traditional thermal imaging to recover ground truth in multiple scenarios while our thermal perception approach successfully recovers geometric textures. Finally, we put forth an experimentally feasible infrared Bayer-filter approach to achieve thermal perception in pitch darkness as vivid as optical imagery in broad daylight.

We propose an alternative data-free deep learning method using a physics-informed neural network (PINN) to enable more efficient computation of light diffraction from 3D optical metasurfaces, modeling of corresponding polarization effects, and wavefront manipulation. Our model learns only from the governing physics represented by vector Maxwell's equations, Floquet-Bloch boundary conditions, and perfectly matched layers (PML). PINN accurately simulates near-field and far-field responses, and the impact of polarization, meta-atom geometry, and illumination settings on the transmitted light. Once trained, the PINN-based electromagnetic field (EMF) solver simulates light scattering response for multiple inputs within a single inference pass of several milliseconds. This approach offers a significant speed-up compared to traditional numerical solvers, along with improved accuracy and data independence over data-driven networks.

The remarkable ability of polarization imaging to suppress the backscattered light makes it a highly attractive solution for various underwater applications. In recent years, emerging learning-based polarization technologies have shown significant potential for application and achieved great success. However, the majority of learning-based studies primarily employ data-driven approaches, which lack interpretability and generalizability. To address this problem, we propose a polarization de-scattering method in which the combination of an active polarization imaging model with deep learning is well executed. Firstly, the network can focus more attention on specific polarization information by applying a well-designed polarization feature-refined block. Secondly, the network directly predicts the polarization-related parameters of the active polarization imaging model, eliminating the need for prior parameters and manual estimation during its operation. Lastly, the network generates clear de-scattered images under the guidance of the model. Additionally, we design efficient loss…

Multi-core fiber (MCF) has attracted increasing attention for application in distributed fiber sensing owing to its unique properties of independent light transmission in multiple spatial channels. Here, we report a distributed acoustic sensing (DAS) system integrated MCF to suppress coherent fading, which overcomes an inevitable challenge in DAS systems. Because the parallel spatial cores in MCF allow the use of space-division multiplexed (SDM) technology, we propose that fading can be effectively suppressed by merging different signals with the spatial rotated-vector-average (SRVA) method. We theoretically analyze the principle of SRVA in fading suppression, and identify that it can effectively reduce phase noise with preventing phase unwrapping failures. In our experiment, a DAS system with 2.58-km length MCF have been investigated, the fading rate of Rayleigh backscattered signals is effectively reduced by three orders of magnitude and the amplitude fluctuation range is decreased by 21.9 dB. Compared with the conventional spectrum extraction and remix method (SERM), SRVA reduces…

A vector magnetic field sensor based on a ferrofluid-encapsulated coreless D-shaped fiber is proposed and demonstrated. The core of the singlemode fiber (SMF) is completely removed by fiber polishing technology, and the remaining part transformed into a multimode interference (MMI) waveguide. The exposed side-polishing plane enable the evanescent field to interact with surrounding magnetic fluid (MF). Relying on the non-circularly symmetric geometry of the coreless D-shaped fiber and the MF refractive index modulation by the orientation and intensity of the applied magnetic field, vector magnetic field sensing is achieved. The magnetic field response characteristics of the coreless D-shaped fibers with different residual thicknesses (RTs) are investigated. The experimental results show that a reduced RT yields enhanced sensitivity, and the magnetic field intensity sensitivity reaches -0.231 nm/mT and -0.483 dB/mT at a RT of 42.7 µm. The developed coreless D-shaped fiber sensor exclusively utilizes SMF, thereby offering a cost-effective scheme for the fabrication of vector magnetic…

Conventional radar jamming and deception systems typically necessitate the custom design of complex circuits and algorithms to transmit an additional radio signal toward a detector. Consequently, they are often cumbersome, energy-intensive, and difficult to operate in broadband electromagnetic environment. With the ongoing trend of miniaturization of various devices and the improvement of radar system performance, traditional techniques no longer meet the requirements for broadband, seamless integration, and energy efficiency. Time-varying metasurfaces, capable of manipulating electromagnetic parameters in both temporal and spatial domains, have thus inspired many contemporary research studies to revisit established fields. In this paper, we introduce a time-varying metasurface driven radar jamming and deception system (TVM-RJD), which can perfectly overcome the aforementioned intrinsic challenges. Leveraging a programmable bias voltage, the TVM-RJD can alter the spectrum distribution of incident waves, thereby deceiving radar into making erroneous judgments about the target's…

Orthogonal frequency-division multiplexing (OFDM) waveform is highly preferred as a dual-function candidate for integrated sensing and communication (ISAC) systems. However, the sensitivity to both carrier frequency offset (CFO) and phase noise greatly impedes its applications in millimeter-wave ISAC systems. Here, we propose and experimentally demonstrate a photonic millimeter-wave ISAC system employing the virtual-carrier-aided self-coherent OFDM technique, wherein a digitally-generated local oscillator is transmitted along with the OFDM signal. Then, a compact CFO-immune and phase noise-immune envelope detection method is implemented for down-converting millimeter-wave communication and radar echo signals. In experiments, a V-band ISAC system is successfully implemented with a simplified remote radio unit, using the remote photonic millimeter-wave heterodyning up-conversion for downlink and the envelope detection-assisted down-conversion for uplink (or radar echoes). In the converged transmission link with a 5-km fiber link and 2-m space link, the Kramers-Kronig (KK) receiver…

The generation of a specific laser beam profile on the work surface is key to various laser beam shaping tasks, relying heavily on diffractive optical elements (DOEs). Most beam-shaping DOEs are designed using iterative Fourier transform algorithms (IFTAs), which generally have slow convergence and prone to stagnate at local minima. Moreover, the microreliefs generated by IFTAs tend to be irregular, complicating manufacturing and causing uncontrolled scattering of light. We propose a differentiable DOE design method that applies a phase-smoothness constraint using multi-level B-splines. A multi-scale gradient-descent optimization strategy, naturally linked with the multi-level B-splines, is employed to robustly determine the optimized phase distribution that is fully continuous. This, in turn, can lead to more regular DOE microreliefs, which can simplify the fabrication process and be less sensitive to changes in wavelength and working distance. Furthermore, our method can also design a fully continuous freeform lens, distinguished from most freeform lens design approaches by its…

The benefits of higher data transmission rates, extensive communication frequency bandwidths, reduced power consumption, and enhanced anti-interference capabilities make inter-satellite optical communication (ISOC) a promising technology for the future. However, during orbital motion, satellites are subjected to external perturbation forces, which affect the performance of the ISOC system. This paper establishes an ISOC system consisting of two co-orbital satellites orbiting the Earth under the influence of perturbations. For what we believe to be the first time, the probability density function (PDF) of the radial displacement caused by perturbations is introduced. Subsequently, a PDF detailing the inter-satellite pointing errors, while accounting for the effects of perturbations and platform vibrations, is presented. Moreover, pointing errors and plasma absorption are considered in the PDF derivation process for the end-to-end ISOC system. The closed-form expression for the average bit-error rate (BER) of the proposed system is derived using Meijer's G function. Simulation results…

Outdoor long-range terahertz (THz) communications often come at the expense of transmission rate. Moreover, the practicability of the single polarization optical/THz link, which is commonly used in the previous long-range THz demonstrations based on photonics, is extremely limited by the following two fatal defects. One is relying on active polarization control, and the other is not supporting the transparent bridging of optical polarization division multiplexed (PDM) signals for mature coherent optical communication networks. In this work, a large-capacity photonics-aided THz wireless communication system based on the outdoor long-range 2 × 2 multiple-input multiple-output (MIMO) links has been successfully demonstrated. We first build the 200-m 2 × 2 MIMO THz wireless links at the 300 GHz band. The cascaded linear and nonlinear equalizers are proposed which can significantly improve the transmission performance of 100- and 200-Gb/s PDM quadrature phase shift keying (QPSK) signals. Then an interesting 2 × 2 MIMO structure which can provide certain diversity reception gain under…

An ultra-high sensitive dual-parameter sensor based on double-hole fiber (DHF) is proposed for simultaneous detection of magnetic fields and temperatures. The sensor utilizes the DHF containing a Ge-doped core with two large air holes symmetrically arranged at its two sides. To enhance the sensitivity to both a magnetic field and temperature, Al wires with different diameters are embedded on the inner walls of the air holes in the DHF, creating a magnetic field sensing channel filled with magnetic fluid and a temperature sensing channel filled with thermo-sensitive liquid. Structural parameters and metal materials of the sensor are optimized by using the finite element method. Numerical results demonstrate that this DHF-based dual-parameter sensor can detect magnetic fields ranging from 40 Oe to 130 Oe and temperatures ranging from 24.3 °C to 49.3 °C simultaneously. The maximum magnetic field sensitivity reaches up to 64000 pm/mT, while the maximum temperature sensitivity is approximately 44.6 nm/°C, both exceeding current reports by more than one order of magnitude for simultaneous…

Optical chirality is highly demanded for biochemical sensing, spectral detection, and advanced imaging, however, conventional design schemes for chiral metamaterials require highly computational cost due to the trial-and-error strategy, and it is crucial to accelerate the design process particularly in comparably simple planar chiral metamaterials. Herein, we construct a bidirectional deep learning (BDL) network consists of spectra predicting network (SPN) and design predicting network (DPN) to accelerate the prediction of spectra and inverse design of chiroptical response of planar chiral metamaterials. It is shown that the proposed BDL network can accelerate the design process and exhibit high prediction accuracy. The average process of prediction only takes ∼15 ms, which is 1 in 40000 compared to finite-difference time-domain (FDTD). The mean-square error (MSE) loss of forward and inverse prediction reaches 0.0085 after 100 epochs. Over 95.2% of training samples have MSE ≤ 0.0042 and MSE ≤ 0.0044 for SPN and DPN, respectively; indicating that the BDL network is robust in the…

Metasurfaces hold great promise for terahertz (THz) chiral-optical devices. Here, we proposed a chiral THz metasurface with quasi-bound state in the continuum (BIC) for maximum chirality. By exploiting structural perturbations of the dipole displacement and the diverging angle for the THz metasurface, the symmetry-protected BIC transforms into quasi-BIC. The critical coupling condition is satisfied by the introduction of graphene, enabling the theoretical maximum absorption of the quasi-BIC. Subsequently, the perturbations are balanced to obtain maximum chirality. The numerical simulations show that the THz metasurface exhibits strong linear chirality with the circular dichroism (CD) of 0.99 at the quasi-BIC. Additionally, the chiral third harmonic generation (THG) is achieved, characterized by high efficiency up to 19% and strong THG-CD as high as 0.99. It is expected that the THz metasurfaces has great potential for applications in chiral sensing and imaging.

A compound resonant cavity-type single longitudinal mode erbium-doped fiber laser is proposed and verified in this paper. We use a compound four-cavity to expand the longitudinal mode spacing of the laser and a homemade grating F-P filter and a saturable absorber to narrow the gain spectral bandwidth, enabling the laser to operate in a single-frequency state. Through theoretical analysis and experimental verification of the important roles of the main constructed fiber laser parts, the center wavelength of the laser output of 1550.06 nm is obtained, and the optical signal-to-noise ratio is 65 dB. In a 50 minute period, the wavelength fluctuation is exhibited along with the maximum power fluctuation of 0.28 dB. The value of the laser output linewidth is ∼250 Hz, measured by using the delayed self-heterodyne method.

Antiresonant hollow-core fiber (AR-HCF) exhibits unprecedented optical performance in low transmission attenuation, broad transmission bandwidth, and single spatial mode quality. However, due to its lower numerical aperture, when utilizing the Fiber-Enhanced Raman Spectroscopy (FERS) principle for gas detection, the efficiency of AR-HCF in collecting Raman signals per unit length is significantly lower than that of hollow-core photonic crystal fiber. Nonetheless, AR-HCF effectively suppresses higher-order modes and offers bandwidth in hundreds of nanometers. By increasing the length of AR-HCF, its advantages can be effectively harnessed, leading to a considerable enhancement in the system's ability for low-concentration gas detection. We combine the nodeless antiresonant hollow-core fiber and Raman spectroscopy for enhanced Raman gas sensing in a forward scattering measurement configuration to investigate the attenuation behavior of the silica background signals. The silica background attenuation behavior enables the low baseline of the gas Raman spectroscopy and extends the…

Deep learning has become an attractive tool for addressing the limitations of traditional digital image correlation (DIC). However, extending learning-based DIC methods to three-dimensional (3D-DIC) measurements is challenging due to the limited displacement estimation range, which cannot handle the large displacements caused by stereo-matching disparities. Besides, most of the existing learning-based DIC architectures lack prior information to guide displacement estimation, resulting in insufficient accuracy. To solve these problems, we proposed a learning-based 3D-DIC (i.e., Deep 3D-DIC) using a coarse-to-fine network called G-RAFT for large and accurate image displacement estimation. Specifically, the large displacement estimation network GMA is adopted to calculate the large coarse displacement field, which is further warped on the deformed image to eliminate the main displacement component. The residual small deformation between the reference image and the warped image is further extracted using the recently proposed RAFT-DIC with high accuracy. By subtracting small…

In this study, a (400) crystal-oriented β-Ga2O3 thin film with a thickness of approximately 400 nm was grown on a c-plane sapphire substrate using atomic layer deposition. Schottky contact-type metal-semiconductor-metal solar-blind ultraviolet detectors with an Au/Ni/Ga2O3/Ni/Au structure were fabricated on the epitaxial thin films. The Schottky barrier height is about 1.1 eV. The device exhibited a high responsivity of up to 800 A/W, and a detectivity of 6 × 1014 Jones while maintaining a relatively fast response speed with a rise time of 4 ms and a fall time of 12 ms. The photo-to-dark current ratio was greater than 103, and the external quantum efficiency exceeded 103, indicating a significant gain in the device. Through the analysis of TCAD simulation and experimental results, it is determined that the impact ionization at the edge of the MSM electrode and channel contact is the main source of gain. Barrier tunneling effects and the photoconductive effect due to different carrier mobilities were not the primary reasons for the gain.

The minimalist optical system has a simple structure, small size, and lightweight, but the low optical complexity will produce optical aberration. Addressing the significant aberration degradation in minimalist systems, we propose a high-quality computational optical framework. This framework integrates a global point spread function (PSF) change imaging model with a transformer-based U-Net deep learning algorithm to achieve high-quality imaging in minimalist systems. Additionally, we introduce an imaging performance evaluation method based on the modulation transfer degree of resolution (MTR). We addressed severe chromatic and spherical aberrations in single-lens systems, a typical example of minimalist optical systems, by simulating the degradation process and reconstructing the imaging effects. This approach demonstrated significant improvements, thus validating the feasibility of our method. Specifically, our technique calculated the MTR values in real images captured with the GCL010109 single lens at 0.8085, and with the GCL010110 single lens at 0.8055. Our method enhanced the…

This study utilizes spectral analysis to quantify water pollutants by analyzing the images of biological oxygen demand (BOD). In this study, a total of 2545 images depicting water quality pollution were generated due to the absence of a standardized water pollution detection method. A novel snap-shot hyperspectral imaging (HSI) conversion algorithm has been developed to conduct spectral analysis on traditional RGB images. In order to demonstrate the effectiveness of the developed HSI algorithm, two distinct three-dimensional convolution neural networks (3D-CNN) are employed to train two separate datasets. One dataset is based on the HSI conversion algorithm (HSI-3DCNN), while the other dataset is the traditional RGB dataset (RGB-3DCNN). The images depicting water quality pollution were categorized into three distinct groups: Good, Normal, and Severe, based on the extent of pollution severity. A comparison was conducted between the HSI and RGB models, focusing on precision, recall, F1-score, and accuracy. The water pollution model's accuracy improved from 76% to 80% when the…

Novel evanescently coupled waveguide modified uni-traveling carrier photodiodes (MUTC-PDs) employing a thick multi-layer coupling waveguide are reported. To improve the optical-to-electrical (O/E) conversion efficiency, a thick multi-layer coupling waveguide with a gradually increased refractive index from the bottom layer to the absorption layer is utilized. The refractive index profile facilitates the upward transmission of incident light into the absorption region, thereby enhancing the evanescent coupling efficiency. Meanwhile, the coupling waveguide, with a total thickness of 1.75 µm, expands the mode field diameter, thereby reducing the input coupling loss. Additionally, the top layer of the coupling waveguide also serves as the drift layer. This configuration facilitates efficient light absorption within a short PD length, thus ensuring ultrawide bandwidth and high O/E conversion efficiency simultaneously. Without an additional spot size coupler or anti-reflection coating, the measured responsivity is as high as 0.38 A/W for the PD with an active area of 5 × 6 µm 2 .…

Photonic topological insulators with topologically protected edge states featuring one-way, robustness and backscattering-immunity possess extraordinary abilities to steer and manipulate light. In this work, we construct a topological heterostructure (TH) consisting of a domain of nontrivial pseudospin-type topological photonic crystals (PCs) sandwiched between two domains of trivial PCs based on two-dimensional all-dielectric core-shell PCs in triangle lattice. We consider three THs with different number of layers in the middle nontrivial domain (i.e., one-layer, two-layer, three-layer) and demonstrate that the projected band diagrams of the three THs host interesting topological waveguide states (TWSs) with properties of one-way, large-area, broad-bandwidth and robustness due to coupling effect of the helical edge states associated with the two domain-wall interfaces. Moreover, taking advantage of the tunable bandgap between the TWSs by the layer number of the middle domain due to the coupling effect, a topological Y-splitter with functionality of wavelength division multiplexing…

We report a Ta 2 O 5 photonic platform with a propagation loss of 0.49 dB/cm at 1550 nm, of 0.86 dB/cm at 780 nm, and of 3.76 dB/cm at 2000 nm. The thermal bistability measurement is conducted in the entire C-band for the first time to reveal the absorption loss of Ta 2 O 5 waveguides, offering guidelines for further reduction of the waveguide loss. We also characterize the Ta 2 O 5 waveguide temperature response, which shows favorable thermal stability. The fabrication process temperature is below 350°C, which is friendly to integration with active optoelectronic components.

Self-powered deep ultraviolet photodetectors (DUV PDs) are essential in environmental monitoring, flame detection, missile guidance, aerospace, and other fields. A heterojunction photodetector based on p-CuI/n-ZnGa 2 O 4 has been fabricated by pulsed laser deposition combined with vacuum thermal evaporation. Under 260 nm DUV light irradiation, the photodetector exhibits apparent self-powered performance with a maximum responsivity and specific detectivity of 2.75 mA/W and 1.10 × 10 11 Jones at 0 V. The photodetector exhibits high repeatability and stability under 260 nm periodic illumination. The response and recovery time are 205 ms and 133 ms, respectively. This work provides an effective strategy for fabricating high-performance self-powered DUV photodetectors.

Silicon microring resonators serve as critical components in integrated photonic neural network implementations, owing to their compact footprint, compatibility with CMOS technology, and passive nonlinear dynamics. Recent advancements have leveraged their filtering properties as weighting functions, and their nonlinear dynamics as activation functions with spiking capabilities. In this work, we investigate experimentally the linear and nonlinear dynamics of microring resonators for time delay reservoir computing, by introducing an external optical feedback loop. After effectively mitigating the impact of environmental noise on the fiber-based feedback phase dependencies, we evaluate the computational capacity of this system by assessing its performance across various benchmark tasks at a bit rate of few Mbps. We show that the additional memory provided by the optical feedback is necessary to achieve error-free operation in delayed-boolean tasks that require up to 3 bits of memory. In this case the microring was operated in the linear regime and the photodetection was the nonlinear…

Laser-induced fluorescence (LIF) technology has been widely applied in remote sensing of aquatic phytoplankton. However, due to the weak fluorescence signal induced by laser excitation and the significant attenuation of laser in water, profiling detection becomes challenging. Moreover, it remains difficult to simultaneously retrieve the attenuation coefficient ( K l i d a r m f ) and the fluorescence volume scattering function at 180° ( β f ) through a single fluorescence lidar. To address these issues, a novel all-fiber fluorescence oceanic lidar is proposed, characterized by: 1) obtaining subsurface fluorescence profiles using single-photon detection technology, and 2) introducing the Klett inversion method for fluorescence lidar to simultaneously retrieve K l i d a r m f and β f . According to theoretical analysis, the maximum relative error of β f for the chlorophyll concentration ranging from 0.01 mg/m 3 to 10 mg/m 3 within a water depth of 10 m is less than 20%, while the maximum relative error of K l i d a r m f is less than 10%. Finally, the shipborne single-photon…

Digital holographic microscopy (DHM) is a powerful quantitative phase imaging (QPI) technique that is capable of recording sample's phase information to enhance image contrast. In off-axis DHM, high-quality QPI images can be generated within a single recorded hologram, and the system stability can be enhanced by common-path configuration. Diffraction gratings are widely used components in common-path DHM systems; however, the presence of multiple diffraction beams leads to system power loss. Here, we propose and demonstrate implementation of a volume holographic grating (VHG) in common-path DHM, which provides single diffraction order. VHG in common-path DHM (i.e., VHG-DHM) helps in improving signal-to-noise ratio as compared to the conventional DHM. In addition, VHG, with inherently high angular selectivity, reduces image noise caused by stray light. With a simple fabrication process, it is convenient to utilize VHG to control the beam separation angle of DHM. Further, by using Bragg-matched wavelength degeneracy to avoid potential cell damaging effect in blue light, the VHG is…

Recent advancements in deep learning, particularly generative networks capable of producing high-freedom structures, have significantly enhanced the precise generation of meta-atoms. However, these methodologies typically rely on an abundance of high-performance data, which remains scarce in many practical design scenarios. To bridge this gap, our study introduces what we believe to be a novel approach that synergistically combines multi-objective optimization algorithms with an enhanced diffusion model featuring an attention mechanism, termed MetaDiffusion-Att. Using the complex design task of dual-polarized, wide-angle incidence, and broadband low-emissivity electromagnetic glass as an application example, we demonstrate the effectiveness of our method through qualitative and quantitative experiments. The introduced multi-objective optimization method significantly captures more high-performance samples while ensuring high degrees of freedom, compared to currently widely used generic dataset construction methods. The MetaDiffusion-Att model, improved by the introduced attention…

Chiral metasurfaces with high quality factors (Q-factors) and strong circular dichroism (CD) are excellent platforms for studying chiral optical response. Here, a design is proposed of an intrinsic chiral silicon metasurface driven by bound states in the continuum (BIC), with ultra-high Q-factor (Q = 3722) and chirality response close to the unit CD (CD > 0.99). By breaking the in-plane and out-of-plane symmetry of the structure, the intrinsic chirality based on BIC can be precisely controlled. In addition to studying intrinsic chirality, we have also achieved extrinsic chirality by obliquely incident circularly polarized light without introducing out-of-plane asymmetry. Moreover, we introduce graphene into the intrinsically chiral metasurface to form a graphene-Si hybridized metasurface. Selective absorption of intensity-controlled right-handed/left-handed circularly polarized light (RCP/LCP) was achieved by actively tuning the Fermi level and out-of-plane tilt angle of the graphene structure based on coupled-mode theory. Our research provides another insight into the application…

The security and confidentiality of information are crucial in contemporary communication systems. In this work, we propose a physical layer security-enhanced optical communication scheme based on dual-level protection with chaos masking (CMS) and chaotic hardware encryption. The integration of CMS and chaotic hardware encryption contributes to enhancing the security of the system. Different uncorrelated chaos generated from a single Fabry-Perot (FP) laser are employed to independently mask and encrypt the confidential signals for multiple channels in a wavelength division multiplexing (WDM) system. Thanks to the CMS and temporal intensity scrambling, the signals are encrypted into a noise-like signal to against direct demasking or decryption attacks. Compared to individual CMS or encrypting the signals using stand-alone dispersion components, numerical results demonstrate that the proposed scheme significantly enhances communication security. The decrypted bit error rate (BER) for 10 Gb/s data in each channel at the legitimate receiver is lower than the hard decision forward error…

We present hybrid-integrated extended cavity diode lasers tunable around 637 nm, with a gain-wide spectral coverage of 8 nm. This tuning range addresses the zero-phonon line of nitrogen-vacancy centers and includes the wavelength of HeNe lasers (633 nm). Best performance shows wide mode-hop free tuning up to 97 GHz and a narrow intrinsic linewidth down to 10 kHz. Also, the maximum output power is 2.5 mW in a single-mode fiber, corresponding to an on-chip power of 4.0 mW. Full integration and packaging in standard housing with fiber pigtails provide high intrinsic stability and enable integration into complex optical systems.

Infections caused by Vibrio parahaemolyticus ( V. parahaemolyticus ) can be highly fatal, making rapid and sensitive detection of them is essential. A new optical fiber biosensor based on localized surface plasmon resonance (LSPR) phenomenon is developed in this paper. A tapered-in-tapered fiber structure based on MFM is constructed by using four-core fiber (FCF) and multi-mode fiber (MMF) to qualitatively detect different concentrations of V. parahaemolyticus . The sensor successfully excites the LSPR phenomenon and increases the attachment point of biomolecules on the probe surface by fixing gold nanoparticles (AuNPs), molybdenum disulfide nanoparticles (MoS 2 -NPs) and cerium dioxide nanorods (CeO 2 -NRs). The functionalization of polyclonal antibodies on the probe surface can improve the specificity of the sensor. The linear detection range of the developed sensor was 1 × 10 0 -1 × 10 7 CFU/mL, the sensitivity was 1.61 nm/[CFU/mL], and the detection limit was 0.14 CFU/mL. In addition, the reusability, reproducibility, stability, and selectivity of the sensor probe are also…

We show a thermally stable self-injection DFB laser lock to a microring resonator system, increasing the range of temperature for which a laser stays within 100 MHz of the target frequency by a factor of 100. By including amplification in the feedback loop, the per-laser power dedicated to this locking was reduced. We further added a 2.2 km fiber spool to explore the remote locking performance of the system.