OE lists the reviewers who served the journal in 2023.

Microplastics impose a major threat to the environment and biota. Reported release of secondary microplastics from tea bags while brewing tea results in their direct ingestion into the human body. The results reported here indicate the presence of variety of plastic materials and point to further need for investigations on the presence of micro- and nanoplastics from plastic packaging materials. In this work, the presence of microplastics from tea bags diffused into boiled water is explored using a multimodal approach comprising of digital holographic microscopy (DHM) and micro-Raman spectroscopy. The leachates derived from the tea bag into water while brewing was analyzed using DHM and micro-Raman spectroscopy, which helped in the detection, characterization, and identification of the detected microplastics. A systematic analysis of 11 teabag samples indicates the presence of plastic materials such as polyethylene, polyvinyl chloride, nylon, etc. in a variety of shapes within micrometer sizes. The morphology, size, concentration, and chemical structure of the microparticles are characterized using nondestructive techniques with minimum sample preparation. The imaging results are complemented and validated using scanning electron microscopy. DHM and micro-Raman spectroscopy are sufficient for the detection and identification of secondary microplastics demanding only a very small volume of samples.

Optical diffractive neural networks (ODNNs) implement a deep learning framework using passive diffractive layers. Although ODNNs offer unique advantages for light-speed, parallel processing, and low power consumption, their accuracy of image reconstruction still needs to be further improved. Here, we extend ODNNs to deep optics in lensless optics by proposing an optical-electronic neural network (OENN) for multi-modality encoder design, and high-accurate image reconstruction. The OENN includes an ODNN in which a pixel-level learnable diffractive layer is included for lensless camera design and an electrical convolutional neural network for image reconstruction. And the performance of OENN is relatively comparable. For speckle reconstruction using phase information, Pearson correlation coefficient (PCC) and peak signal-to-noise ratio (PSNR) can reach to 0.929 and 19.313 dB, respectively. For speckle reconstruction using intensity information, PCC and PSNR can reach to 0.955 and 19.779 dB, respectively. For lens imaging with phase information, PCC and PSNR can reach above 0.989 and 29.930 dB, respectively. For lens imaging with intensity information, PCC and PSNR can reach above 0.990 and 30.287 dB, respectively. In the future, the proposed optoelectronics artificial intelligent framework can be further applied for “end-to-end” optics design and imaging process of lensless or computational imaging modalities.

The viewing zones in the conventional dual-viewing-zone three-dimensional (3D) display are still narrow. We propose a dual-viewing-zone 3D display that consists of a display panel, a parallax barrier, and a barrier array. The adjacent slits are separated by the barrier. Two adjacent elemental images that are respectively obtained from two 3D scenes are located between two adjacent slits. The light rays from two adjacent elemental images that are alternatively arranged in the horizontal direction are only integrated by a slit. The light rays from the left elemental images are propagated into the left viewing zone, whereas those from the right elemental images are propagated into the right one. Different 3D images are reconstructed in the left and right viewing zones. The experimental results prove that two viewing zones are both enlarged in the proposed dual-viewing-zone 3D display.

The sensitivity of active targeting systems in the shortwave infrared band is currently limited by high read noise associated with conventional readout integrated circuitry. This limit imposes a barrier to leveraging other performance trades, such as source power, illumination wavelength, and temporal coherence. Introducing gain in the charge domain prior to signal readout can reduce the impact of read noise, to the point that it no longer limits performance. In preparation for a series of planned active-imaging field tests, we demonstrate improved system performance on a modeling basis with two different charge-domain gain cameras: the electron bombarded active pixel sensor (EBAPS) and the mercury cadmium telluride avalanche photodiode sensor. We find that both solutions mitigate read noise to make either one suitable for laser range gating, but the high dark current associated with EBAPS may make it unsuitable for continuous-wave imaging in some scenarios. These results aid in our understanding of expected performance in field testing of charge-domain gain systems.

With the aim of handling the characteristics of infrared images, including their high dynamic range (HDR), low contrast, and blurry edges, this paper proposes an approach for displaying infrared images with gradient domain guided image filter (GIF). First, the original image is decomposed into base layer and detail layer by gradient domain GIF and Gaussian filter. Second, the adaptive double plateau histogram equalization method is used to compress the dynamic range and enhance the overall brightness of the base layer. Third, a detail gain factor is constructed to gain the detail layer, and then a display method for the detail layer is designed by considering the “3σ” rule in Gaussian distributions. Finally, the processed base layer and detail layer are linearly fused to obtain the result image. The proposed method and five mainstream infrared image display methods are used to process infrared images collected in four different scenes. Subjective and objective evaluation methods are used to demonstrate that the proposed method is capable of compressing the dynamic range, improving the overall brightness and enhancing the local details, as well as displaying HDR infrared images with a high degree of fidelity.

A spatial phase unwrapping algorithm based on multi-anchors bidirectional location and suppression (SPUA-MBLS) is proposed. Spatial phase unwrapping algorithms (SPUAs) can play an important role in three-dimensional (3-D) measurement due to their phase unwrapping without any additional auxiliary pattern. SPUAs based on line scanning can achieve much faster phase unwrapping line-by-line than the traditional SPUA based on reliability sort, such as the quality-guided SPUA. But they are prone to suffer from residual error propagation caused by noise. The proposed algorithm first binarizes the wrapped phase to generate a crude fringe order map with multi-anchors and then cross-validates this map forward-backward to locate and suppress those multi-anchors as much as possible. Thus, a more perfect fringe order map can be segmented to achieve spatial phase unwrapping with a more effective improvement of residual error propagation. The experimental results show the feasibility and validity of the proposed algorithm. The proposed algorithm is proved to have higher measurement accuracy, and it has also shown higher robustness in anti-noise performance while inheriting the high-speed phase unwrapping feature.

An adaptive confocal photothermal microscope was developed to perform thermal diffusivity measurements on irregular surfaces at the micrometer scale. The developed equipment automatically aligns an optical system having precise control of the position and angle of the beams on the sample. Several studies on samples with various surfaces are presented and the alignment algorithms are described.

Space gravitational wave detection is one of the most critical techniques that maintain high stability of the laser link to reduce the coupling of ranging noise. We model and simulate the laser pointing jitter noise of the laser link between two satellites and build an experimental system for testing. We adopt an FFT-based method for Monte Carlo generation of a random noise time-series signal with a prescribed power spectral density. This experimental system with noise inputs can be simulated in a way that is more consistent with the actual operation of the satellite in space. The experimental results show that laser pointing jitter noise mainly comes from the jitter of the satellite platform. In the 1 mHz to 1 Hz band, laser pointing jitter noise is an order of magnitude higher in the space environment than in the laboratory environment. However, the pointing system can still suppress the laser pointing jitter noise to the noise floor.

The growth rate of GaN on the GaAs (110) substrate as deduced from reflectivity measurements exhibits a peculiar behavior. A transient regime with a relatively high initial growth rate progressively decreases to a limit value during the early stage of high temperature GaN growth. An optical model, incorporating time-dependent profiles of the growth rate and surface roughness, was used to simulate the corresponding in situ reflectivity recorded during the growth of GaN layers on the GaAs (110) substrate. The growth rate transient, characterized by a time constant (τ) and a diffusion length (L), is proposed to originate from Ga self-diffusion in the GaN layer. Both the time constant (τ) and the diffusion length (L) increase with the rising growth temperature. This allows for the estimation of the Ga self-diffusion coefficient in GaN, which, in the growth temperature range of 750°C to 900°C, was found to be equal to D=1.35 10−11 exp(−(0.28∓0.04)/kBT) cm2 s−1.

To accurately and promptly obtain the conventional lifetime of light-emitting diode (LED) lights, accelerated degradation tests of LED lights under four groups of accelerated stresses were designed and carried out. Three-parameter Weibull function and the right approximation method were used to fit the average luminance degradation test data at each constant accelerated current stress. Combined with the failure criteria, the service lifetime of the samples under each accelerated stress condition was calculated. Then, four groups of accelerated degradation data points were extrapolated by power function and exponential function respectively, and the average lifetime of LED lights was calculated, thereby achieving the estimation of conventional lifetime. The results show that the luminance degradation rate of LED lights is initially fast, then slow, which accurately represents the basic rule of luminance decay. The model established by the Weibull right approximation method exhibits high fitted accuracy for the luminance degradation data of LED lights. By comparing the determination coefficients and the mean absolute percentage errors of extrapolation, it can be found that the conventional lifetime extrapolated by power function has superior accuracy, satisfying the actual project requirements. The relevant research results can provide technical support for the life prediction of LED lights.

The precision polishing of optoelectronic materials, such as silicon carbide (SiC) and niobate, poses significant challenges due to their hardness and brittleness. Conventional polishing techniques, including the use of traditional diamond slurries, often result in surface defects, such as scratches and dig marks, compromising the quality and integrity of the materials. In this study, we introduce a nano/sub-micro diamond slurry technology designed to enhance the precision polishing of optoelectronic materials. The developed surface-engineered diamond slurries exhibit improved particle dispersion and controlled size distribution, minimizing particle aggregation and elongation. Polishing experiments conducted on SiC and lithium niobate substrates demonstrate the superior performance of the surface-engineered diamond slurries in terms of material removal rate (MRR) and surface roughness. The MRR achieved with the developed slurries is significantly higher compared to traditional slurries, while the resulting surfaces exhibit reduced dig marks and scratches. Furthermore, the developed slurry technology enables stable and reproducible polishing processes, contributing to reliable and predictable outcomes. This study presents a promising approach for the precision polishing of optoelectronic materials, addressing the limitations of conventional techniques and facilitating the manufacturing of high-quality optoelectronic devices and wafers.

An underwater microbubbles detection and identification method based on dark field imaging is presented, focusing on measurement of the characteristics of microbubbles with high-resolution image capture. The target microbubbles in sampling volume of interest are illuminated by a laser sheet, which is matched with the depth of field. Images are captured in-focus under an observation angle of 90 deg to implement dark field detection, which suppresses the influence of interferential light, such as backlighting, scattering light, and blur caused by defocus. In this configuration, we propose to measure bubble size based on the distance of peak values of two glare points formed by the diffraction and reflection lights. The modified Resnet18 is employed to recognize the bubble images, and the number of bubbles with different diameters in bubble images is counted by template matching. Experimental results show that this dark field configuration allows high resolution imaging and evaluation of the diameter scale of the microbubbles. The precision of bubble recognition and quantification of bubbles within a certain range achieves more than 90%.

Experimental Shack–Hartmann wavefront sensor (SHWFS) measurements were collected for a laser beam that propagated through a weakly compressible shear layer. Complementary computational fluid dynamics (CFD) was also conducted to match the experiment. The path-integrated CFD results were then applied to a SHWFS model such that the experimental and CFD results could be compared. Using both the experimental and CFD wavefront results, it was found that, although the CFD results slightly overestimated the resultant wavefront error, the CFD and experimental results revealed extremely similar wavefront topology. In order to further examine the aberrations imposed onto the laser beam in both datasets, the SHWFS image-plane irradiance patterns and circulation of phase gradients were studied. Similar to the overall wavefront topology, these data reduction approaches revealed similar phenomena in both the experimental and CFD-modeled results. Specifically, appreciable circulation and beam spread of the SHWFS image-plane irradiance patterns were exhibited throughout the shear layer’s braid region. Both of these findings suggest that sharp phase gradients exist in the weakly compressible shear layer and both (1) the SHWFS resolution and (2) the continuous nature of the phase estimate obtained using SHWFS data in a least-squares reconstruction algorithm make these phase gradients challenging to resolve. The findings presented here inform efforts looking to experimentally or computationally study aero-optical environments.

Optical waves can induce collective oscillations of free electrons on a metal surface and propagate on the surface under specific conditions. These waves are known as surface plasmon polaritons (SPPs). SPPs are implemented in sensors because their excitation is affected by the refractive index of the surface medium. When SPPs are excited on a metal film in a Kretschmann configuration, they are indirectly detected through the difference between the incident and reflected light because SPPs are non-radiative surface waves. We scattered SPPs to directly observe them using a rough surface. Accordingly, we discussed the corresponding resolution characteristics and influence of roughness on the SPP excitation. Our method allows to quickly take two-dimensional images of samples because scattered waves from the surface can be observed using conventional imaging optics.

The fixed denture supported by multiple implants can effectively improve the retention and stability of traditional complete dentures, and greatly improve the masticatory ability and life quality of patients, which has been proven to be a reliable treatment method. However, how to accurately obtain the position and posture of multiple implants while the patient feels comfortable is still one of the main clinical difficulties. We design a four-camera system and propose its corresponding method, which accurately measures the position and posture of stereo probes (note that the stereo probes are finely screwed on the implants, i.e., the coordinate systems of the implants are transferred to the stereo probes). In the calibration, a ChArUco calibration board is introduced and the calibration parameters are derived utilizing the proposed three-stage calibration strategy. In the measurement, the stereo probes are screwed on the implants and captured by the four-camera system. Through Canny/Devernay method, the gauge points on the surface of the stereo probe can be solved. Subsequently, the decoding of the gauge points and stereo probes is achieved by the implementation of the proposed matching and decoding strategy. In addition, to achieve higher accuracy, a refinement approach under multiview for the position and posture of stereo probes is established. The result of the experiments verifies that our system and method have higher accuracy and effectiveness (note that the distance error between the two stereo probes is about 19 μm), which is entirely satisfactory for the application of digital implant impressions.

In the tensor polarization holography theory, parameters A and B represent the scalar and tensor coefficients of the photo-induced change in the dielectric tensor, respectively. A/B is called the exposure response coefficient, a key factor for manipulating the polarization state of the reconstructed wave in polarization holography. We measure the initial exposure response coefficient of the polarization-sensitive material, phenanthrenequinone-doped polymethyl methacrylate (PQ/PMMA), and analyze the effect of the interference angle and the polarization states of the signal and reference waves on the coefficient in linear polarization holography. To better understand the linear polarization holography, we develop a formula to describe the law of the initial exposure response coefficient.

In a GPS-denied environment, distinct structures, such as cell towers and transmission towers, are useful as an aid to vision-based navigation. Cell towers are surveyed such that their locations are well known, and the imagery of these towers can be compared to imagery databases to assist in navigation. In this research, imagery of the cell towers was taken in the visible (VIS), short-wave infrared (SWIR), and long-wave infrared (LWIR) bands with both clear sky and portions of the ground in the background. The contrast of the cell towers in the two reflective bands (VIS and SWIR) was determined against the sky and the ground in terms of equivalent reflectivity. The contrast of the cell towers was also determined in the LWIR in terms of equivalent blackbody temperature. The analysis of contrast, the results, and recommendations on band use are provided for use in three-dimensional map image comparisons.

The traditional numerical analysis in waveguide design can be time-consuming and inefficient. This is even more prominent in the THz region and with complex shapes and materials. As an alternative to overcome these drawbacks, we propose a machine learning (ML) approach to design porous-core photonic crystal fibers (PCFs) for the THz band. This method is based on an artificial neural network (ANN) model trained to predict key parameters such as the effective refractive index, effective area, dispersion, and loss values with accuracy and speed. In that sense, the network was trained to perform multiple-output regression of the above parameters. The training data for this model comes from numerical calculations that use the finite element method (FEM) to simulate and evaluate analytical expressions. Our results demonstrate the ML model’s ability to capture the complex and nonlinear relationships between the input and output parameters and accurately predict the behavior of the THz PCF. Moreover, the proposed model has an inference time of ∼0.03584 s for a batch of 32 data sets, which substantially outperforms typical calculation times needed in FEM simulations for THz waveguide design. These results show that this approach is efficient and effective and has the potential to significantly accelerate the design process of PCFs for THz applications.

This research focuses primarily on investigating the optical scattering characteristics of a structured aluminum surface with periodic circular hollow cavities. The influence of cavity parameters on the scattering characteristics is examined through numerical computation and experimentation. The numerical computations reveal that the reflectance characteristics are primarily determined by the depth and radius of the cavities, as well as the angle of incidence. The samples with periodic microstructures were fabricated, and their bidirectional reflectance distribution function (BRDF) was measured. The measurement results demonstrate good agreement with the numerical computations, indicating that BRDF accurately describes the spectral scattering of the structured surface. This study highlights the significance of comprehensively investigating the scattering properties of microstructures to better understand their reflection properties and evaluate their optical control effects.

Musical instruments are complex multimodal interfaces combining audiovisual information and motivating researchers to design intuitive and creative ways of communication between the user and the digital system. We demonstrated a musical interface based on an optical fiber specklegram sensor (FSS) for one octave of C major scale. The setup comprises a laser source and a camera connected by a multimode optical fiber cable with foam pads marking the notes. The software recovers the pressed key by computing the cross-correlation coefficient between the immediate speckle pattern and the reference images from prior calibration, estimating their similarity, and taking the closest option as the output. Simultaneously, the software plays the identified key with a sound synthesizer. The experiments validated the proposed interface to play the calibrated notes, independent of the input sequence, with a response delay within 0.5 s, for a single fiber cable and further discuss the possibility of playing chords. With the musical interface processing the positional information of external stimuli, it simplifies the hardware configuration and allows different techniques of musical expression.

A tunable and switchable multi-wavelength random fiber laser (MW-RFL) is proposed and experimentally demonstrated in this work, which consists of a random distributed feedback mechanism, an improved Lyot filter, and a nonlinear optical loop mirror (NOLM). The theoretical derivation and simulation analysis of the improved Lyot filter are carried out by using the transfer matrix theory. The results show that by adjusting the polarization controller (PC) in the filter, not only the channel interval can be switched between 0.9 and 0.45 nm, but also the extinction ratio (ER) of the transmission spectrum can be adjusted and the wave peak position can be moved. The feedback mechanism of the proposed laser is provided by the randomly distributed backward Rayleigh scattering generated in the single-mode fiber. By changing the pump laser power, the number of output laser channels will be linearly increased. When the channel interval is kept constant, the wavelength can be tuned within a certain range by carefully adjusting the PC3 in the NOLM. When the channel interval of the spectrum is 0.9 nm, the wavelength tuning ranges of the three and four laser channels are 3.6 and 3.5 nm, respectively. When the channel interval of the spectrum is 0.45 nm, the wavelength tuning ranges of the three and four laser channels are 2.8 and 2.77 nm, respectively. Then the variations of the output spectrum when using 25 km single-mode fiber (SMF) are studied. It is observed that the linewidth and side mode suppression ratio (SMSR) of the laser channel are significantly increased. Finally, the stability of the random laser is discussed, and the maximum central wavelength drift and peak power fluctuation measured at room temperature are 0.05 nm and 0.34 dB, respectively. The average peak power and SMSR are maintained at −4.47 dBm and 34.6 dB, respectively, which confirms that the laser has good stability.

The Er3+/Bi+/Ag nanoparticles (NPs) triple-doped oxyfluoride tellurite glasses were prepared by melt-quenching method, showing an intense 3.1 μm mid-infrared fluorescence emission under 980 nm laser diode pumping. The as-prepared tellurite glass samples exhibit good thermal stability and resistance to crystallization based on X-ray diffraction and differential scanning calorimetry measurements. After an introduction of AgNPs into the tellurite glass matrix, a broadband fluorescence emission at 3.1 μm is detected, in which the full width at half maximum (FWHM) is 181 nm. Moreover, the 3.1 μm fluorescence intensity in this Er3+/Bi+/AgNPs triple-doped glass is enhanced by 42%, compared with a pristine sample, and the corresponding fluorescence lifetime is obtained with a value of 0.53 ms. It is reasonable that there is strong absorption of the incident photons due to the vibration frequency matching between AgNPs and incident photons, it can promote the localized surface plasmon resonance and energy transfer between AgNPs and Er3+ ions, and in turn lead to an enhancement of fluorescence intensity. The above results demonstrate that the as-prepared Er3+/Bi+/AgNPs triple-doped oxyfluoride tellurite glasses possess excellent fluorescence properties and may be a good carrier for mid-infrared fibers and laser gain materials.

Fiber optic current sensors (FOCSs) are prone to environmental disturbances and have to be calibrated before going into service. A commonly adopted scheme is the single dimensional calibration method based on temperature. In this work, we propose a multi-dimensional FOCS calibration method based on the extreme gradient boosting (XGBoost) algorithm. Six operating parameters of the FOCS are chosen as the input of the calibration model, including the drive current of the light source, the average optical power of the photo detector (PD), the second harmonic of the PD output, the drive voltage of the piezoelectric transducer, the measured current, and the ambient temperature. The ratio error is acquired as the output. Temperature cycling experiments on three finished sensors in an environment of −40°C to 72°C are conducted. The experimental results show that the max absolute ratio error after multi-dimensional calibration based on XGBoost is 0.031% and the mean absolute ratio error is 0.003%, both of which are much lower than the single-dimensional calibration method based on temperature. It can be concluded that the proposed multi-dimensional calibration method based on XGBoost can effectively improve the accuracy and stableness of FOCSs.

A multichannel laser self-mixing interferometry (SMI) is proposed based on a combination of linear injection current modulation and carrier frequency division multiplexing (FDM) technique. The laser output is split into several beams with each beam directed toward a specific target for measurement. The reflected beams then return to the laser cavity, where self-mixing interference takes place. Since the external cavity length of each measurement channel is different, the SMI signal contains multiple carriers due to the injection current modulation. An algorithm based on FDM is developed for displacement sensing of multiple targets from a single SMI signal. Experimental results show that the relative error of multichannel displacement measurement is <1.4%. This work demonstrates an attractive multichannel SMI for displacement sensing featuring compact configuration and high resolution.

For practical engineering applications, Brillouin optical time domain reflectometry (BOTDR)’s double-peak Brillouin gain spectrum (BGS) can be measured when the strain is not uniform within spatial resolution. This double-peak BGS will affect the extraction accuracy of Brillouin frequency shift (BFS) and the following disaster monitoring. A detection method based on artificial neural network (ANN) is proposed for the double-peak BFS extraction. The ANN model is trained to deal with multi-parameters cases, including different frequency ranges, signal-to-noise-ratios, spectral widths, etc. The retraining of ANN model for different single-mode optical-fibers is not necessary. After training, the ANN model successfully detects the double-peak BFS from both the simulated and experimental data. The ANN model based BOTDR system is applied to the urban safety monitoring of underground pipe gallery. Under 5 m spatial resolution, 20 cm strained fiber can be detected, and the standard deviation of BFS can be as low as 1 MHz in experiment.

We characterize the behavior of modes propagating along a hollow elliptical waveguide with lossy metamaterial cladding. The proposed metamaterial-dielectric elliptical waveguide supports surface-plasmon polariton (SPP) and hybrid ordinary-SPP modes in the operating frequency ranges. Previous studies on metamaterial-dielectric elliptical waveguides either ignore the effect of energy loss on the modes characteristics or employ approximate approaches to characterize modes behavior. Although some previous works include energy loss, they do not specify SPPs propagation versus hybrid-ordinary SPPs propagation in the operating frequency ranges. Here, we consider energy loss in the waveguide to eliminate errors resulting from neglecting the loss. Our waveguide structure facilitates SPP and hybrid ordinary-SPP modes propagation along the waveguide, has better energy confinement, and higher propagation length than previous results in the literature. In the elliptical waveguide, the propagation coefficient changes by changing the waveguide eccentricity; therefore, the elliptical nature of the studied waveguide facilitates its applications in pressure optical sensors.

An ion implanter was used to irradiate protons with a dose of 8×1016 ions/cm2 and an energy of 400 keV into a Ce³⁺:GGG crystal. To our knowledge, this is the first time that ion implantation was applied to a Ce³⁺:GGG crystal. The penetration depth was determined by the stopping and range of ions in matter simulation. The prism coupling method was utilized to evaluate the propagation modes in the H⁺-implanted waveguide. The end-face coupling method and the finite-difference beam propagation were employed for the analysis of the waveguide performance. The refractive index distribution was reconstructed by the reflectivity calculation method. The main significance of the investigation is to confirm the potential of the ion-irradiated Ce³⁺:GGG crystals for fabricating waveguide structures and devices.

Corrosion-resistant antireflective (AR) coatings on ZnS were developed for IR outer window applications. The AR coating was based on a multilayer design using physical vapor deposited (PVD) Si and SiO2 as high (H) and low (L) refractive index coating materials for a spectral range of short-wavelength to mid-wavelength IR (SWIR-MWIR). The coating material selection and process tuning led to a coating that can pass durability tests in severe conditions including fluid, ozone, bacteria, and enhanced humidity exposure. No optical or mechanical degradation was observed after SO2 salt-fog test for 168 h (7 days) and H2SO4+salt-fog solution test for 672 h (28 days). Transmission improvement after corrosion tests was attributed to a reduced surface roughness. The reduction of RMS roughness was confirmed by atomic force microscope measurement. Time-of-flight secondary ion mass spectrometry was further employed to confirm that no compositional change was observed after SO2 salt fog corrosive testing for 168 h. The results suggest that the enhanced durability of multilayer AR coating can be realized by (1) selecting chemically inert materials, such as silicon and silicon dioxide, (2) ensuring good layer density, (3) reducing defects, and (4) balancing coating stress. A patent was issued for the novelty of layer stack design, material system, processing conditions, optical performance, and particularly the corrosion resistance.

A low-loss and compact TM-pass polarizer is demonstrated based on improved hybrid plasmonic grating (HPG) on a Z-cut lithium-niobate-on-insulator (LNOI) platform. In this work, we introduced the silica partition structures surrounding an LN (LiNbO₃) ridge waveguide to support two parallel metal gratings, achieving the optimal coupling coefficient for HPG. Compared with the traditional HPG structure, the transverse electric (TE) mode suffers a higher confinement and the transverse magnetic (TM) mode transmission loss exhibits a significant reduction in the improved HPG structure. The simulation shows that the polarizer achieves a broad bandwidth of 150 nm (1500 to 1650 nm) with an extinction ratio (ER) over 20 dB and an insertion loss varying from 0.18 to 0.3 dB, including a maximum ER of 36 dB at the wavelength 1550 nm. In addition, the length of the demonstrated polarizer is only 10 μm, making it compact for integration. The proposed polarizer shows a good application prospect for integrated photonics in LNOI.

In this paper, we present the results of simulating heat propagation processes in the thermoelectric detection pixel after absorbing single photons of UV radiation with energies ranging from 7.1 to 124 eV. The detection pixels, with an operating temperature of 1 K, consist of an absorber (W), a thermoelectric sensor (La0.99Ce0.01B6), a heat sink (W), and a substrate (Al2O3). The heat transfer processes in the detection pixels with different layer thicknesses and surface areas were modeled and simulated using the three-dimensional matrix method for differential equations based on the equation of heat propagation from a limited volume. The temporal dependencies of the temperature at various points in the detection pixels and the average temperature of the layers’ surfaces were calculated. The main signal parameters, such as the maximum value, time to the peak value, decay time, full width at half maximum, and signal power, were determined. In addition, the phonon noise, Johnson noise, and the total noise equivalent power of the detection pixels were calculated. The data obtained show how the signal-to-noise ratio (SNR) depends on the energy of the absorbed photon, the geometry of the detection pixel, and the bandwidth of the signal measurement. Moreover, it was observed that the SNR exceeds unity multiple times for the absorption of photons of all considered energies in the detection pixel with a surface area of 1μm2.

In this work, a transverse magnetic (TM)-pass polarizer based on subwavelength grating (SWG) on the emerging potential hybrid silicon-LNOI platform is proposed. By integrating silicon material onto the LNOI platform, the optical power of TE0 and TM0 modes is judiciously distributed to distinct regions. This design not only effectively blocks the TE0 mode but also enables low-loss transmission of the TM0 mode, thereby achieving a balanced manipulation of both polarizations. Due to the strong reflection of TE0 mode by SWG, a polarizer is realized with a high polarization extinction ratio (PER) and low insertion loss (73 dB and 0.37 dB respectively at 1550 nm) in a compact size (device length is 23.38 μm). Moreover, the PER is beyond 50 dB and the insertion loss is under 0.46 dB in a broad wavelength range of 1525 to 1585 nm.

In the existing binocular fringe projection methods, the continuous phase is commonly employed for performing 3D scene reconstruction. However, this method has phase ambiguity issues that require the addition of patterns or the utilization of embedded signals to be solved. However, this approach not only leads to the introduction of cumbersome steps but also fails to accurately reconstruct objects without obvious features. To effectively overcome these challenges, an active stereo 3D measurement method was proposed that eliminated the need for phase unwrapping. More specifically, the proposed method first applied binary processing to the wrapped phase map, followed by extracting phase order lines, and assigning symbolic labels to the phase intervals between them, accomplishing thus rough matching. Finally, based on the region block matching, the phase values were used to refine the disparity map. The proposed method was evaluated using a standard sphere with a diameter of 60 mm, and the root-mean-square error of the proposed method is 0.053 mm.

The adder is a highly fundamental part of the central processing unit. The carry lookahead adder (CLA) has become the fastest adder used in digital circuits. For high-speed operations, optical computing has become an essential research field. In this manuscript, a microring resonator (MRR)-based all-optical (AO) CLA is proposed and analyzed. The MRR-based AO design is capable of getting a higher operational speed to fulfill the demands of end users. The Z domain’s mathematical model of the CLA is developed using the unit delay signal processing method. The numerical simulations validate the proposed circuit’s operational speed of close to 260 Gbps. The parameters for this design are chosen optimally to enable it to be effectively implemented for optical computations.

We present an inter-satellite coherent laser communication prototype system, highlighting a low complexity receiver with a simplified two independent real-valued (TIR) equalizer suitable for space laser communication scenarios. An extensive comparison of classical single complex-valued equalizer, 2×2 real-valued equalizer, TIR, and two dependent real-valued (TDR) equalizer is presented on the basis of equalization principles, algorithm performance, and computational complexity. The analysis results show that TIR equalizer has the advantages of low logic resource consumption in implemented on field programmable gate array (FPGA) and zero sensitivity penalty to combat I/Q gain imbalance and I/Q skew caused by device aging. The constant modulus algorithm-based TIR equalizer fits binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), or higher-order QAM modulation format, while the traditional complex-valued equalizer needs to customize the tap coefficient updating algorithm for different modulation formats. In addition, to show the feasibility of the proposed TIR equalizer-based coherent laser receiver as a promising candidate for forthcoming inter-satellite networks, we demonstrate single polarization (SP) on-line 2.5 GBaud data rate, QPSK and BPSK coherent transmissions using an FPGA-based transmitter and receiver prototype. Thanks to our proposed equalizer, the number of hardened multipliers is reduced by 47%, while no receiver sensitivity penalty is observed both in numerical simulation and in real-time FPGA experiment.

We study the communication capabilities of a bi-directional real-time communication system that employs superconducting nanowire single-photon detectors (SNSPDs) under ultra low received optical power conditions. Furthermore, we analyze the influence of received optical power jitter on the system’s communication performance. To accomplish this, we construct a bi-directional real-time fiber optic communication system based on SNSPDs using the pulse position modulation. We successfully achieve bi-directional real-time video communication even under very low received optical power conditions, maintaining an average received optical power level of −75 dBm. The bit error rates for the uplink and downlink are measured at 2.56×10−5 and 3.08×10−5, respectively. Additionally, our investigation reveals that the SNSPD can tolerate a jitter range of up to 5 dB in received optical power while ensuring uninterrupted communication. This paper delves into the practical engineering application of a high-sensitivity optical communication system based on SNSPDs, offering novel insights for optimizing their future use in free space optical communication systems.

A scheme for generating a width-tunable optical pulse is proposed and experimentally demonstrated, which is based on the Mach–Zehnder modulator’s traveling wave modulation characteristics in the Sagnac loop. In the proposed scheme, the clockwise light is modulated, and the counterclockwise light remains unmodulated and acts as a continuous-wave light. By adjusting the polarization controller and the bias voltage of the modulator, the generation of tunable-width pulses can be achieved. Experimental results show that the full-width at half-maximum of pulses (20 GHz) can be tuned continuously from 10.97 to 25.06 ps, with corresponding duty cycles of 21.94% and 50.12%, which is consistent with the simulated results. An 80 to 10 Gbit/s optical time division multiplexing (OTDM) signal after 100 km transmission demultiplexing experiment has also been demonstrated with the time window provided by the proposed scheme. The experimental results demonstrate the applicability of this scheme for high-speed OTDM signal demultiplexing after long-distance transmission. Furthermore, by adding an additional photodetector and an electric bandpass filter to the proposed scheme, both demultiplexing and clock extraction can be achieved simultaneously.