Since the proposal of bonnet polishing technology, it has been widely used in the surface polishing of various high-precision curved components. Because of its unique polishing tools and polishing method, it has the characteristics of high polishing efficiency and high polishing accuracy. Therefore, bonnet polishing technology is particularly important in engineering applications. We mainly review the research progress of bonnet polishing technology in the past 10 years, including the introduction of bonnet polishing technology applied to important engineering projects such as the European Extremely Large Telescope, the main mirror of Japan’s next-generation space telescope, the Shenguang-III mainframe unit, and the artificial skeleton. We summarize the key technologies of bonnet polishing technology such as removal mechanism, removal function, motion control, process control, and software development according to the typical applications of bonnet polishing technology. Finally, the current limitations are summarized according to the characteristics of bonnet polishing technology, and the development trend of bonnet polishing technology is also foreseen, hoping to provide a reference for the subsequent in-depth research of bonnet polishing technology.

We proposed a polarized bidirectional reflectance distribution function (PBRDF) modeling method based on the Monte Carlo method to study the light reflection polarization characteristics of the coating surface. First, the Fourier transform was used to complete the three-dimensional reconstruction of the coating-substrate bilayer rough surface. Then, the random process of reflection and refraction on a single facet was solved according to the microfacet theory and the Fresnel equations. Finally, the statistical summation of the polarized light scattering process of the reconstructed surface was made using the polarization ray tracing technique and the Monte Carlo method to obtain the PBRDF of the coating surface. The simulation and experimental results show that the PBRDF established by the method in this paper is correct and has higher precision than the existing models. The rules of the effect of incidence angle, incident light wavelength, surface roughness, and substrate material on the light reflection polarization characteristics of the coating surface were analyzed, providing a theoretical basis for the target detection and measurement of the coating surface.

Fourier ptychographic microscopy (FPM) is a novel technique for coherent imaging with the advantages of high-resolution, wide field-of-view, quantitative phase contrast, and label-free imaging. However, the light source of most FPM systems is light-emitting diode (LED) arrays, which are not an ideal coherent point source and lead to deviations between theory and experiment. In this paper, the temporal and spatial coherence of the LED light source used in the FPM is reanalyzed by the Gaussian-Schell model, and a new spatial spectrum constraint is proposed, which is called Gaussian coherent transfer function (CTF). Through theoretical calculation, numerical simulation, and experimental reconstruction, the imaging recovery quality of FPM is improved by introducing the Gaussian CTF constraint. The proposed Gaussian CTF is applicable to other coherent imaging techniques based on LED light sources.

We analyze a novel modified hexagonal porous core photonic crystal fiber (MHPC-PCF) whose design parameters are optimized to maximize terahertz (THz) wave transmission efficiency. The core structure of the modified hexagonal PCF has four-ring hexagonal pores in the middle of the core. The dispersion at 1 THz is −0.004453 ps/THz/cm, the confinement loss is 1×10−12 dB/cm, and the practical material loss is 0.001158 cm−1. Remarkably, the bending losses are much minimized and measured at 1.141×10−28 and 1.454×10−59 dB/cm for a bend radius of 1 and 2 cm, respectively. These implicit results open great potential for exploiting our proposed fiber in THz applications such as communication, sensors, and imaging. Our work contributes to resolving the major issues, including losses due to propagation and sensitivity to bending, in making great strides toward the creation of practical, high-performance THz photonic systems to be used in a variety of photonics applications.

In this exploration, we present a compact and easy-to-set imaging system to analyze the quantitative phase information of macroscopic and microscopic transparent phase samples using a radial shearing interferometric design. The proposed setup introduces a wire-grid polarizer as a beam-splitting optical element in a triangular cyclic configuration to render the two counter-propagating beams linearly polarized in orthogonal directions. These beams are made to pass through the samples in a counter direction. The focusing lens to image the sample is aligned in such a way that either the p-polarized beam illuminates the phase sample in a focused position concerning the imaging lens position and the remaining s-polarized beam is far apart from its focal length or vice versa. Hence, polarization phase shifting is implemented to generate a three-dimensional phase pattern, which is digitally captured in a charge-coupled device camera to yield the sample phase. The proposed setup is robust and sufficiently tolerant to ambient vibrations and shows encouraging experimental results using the minimum optics.

Prism coupling refractometry, a versatile and well-characterized technique, is a valuable tool for measuring the refractive index of transparent media in film or bulk forms. It offers distinct advantages over other refractometry methods as it does not require the same level of fabrication or user modeling of optical response. Our method, presented in combination with an infrared prism coupler, further enhances this technique. It not only allows for the measurement of optical constants but also significantly reduces the standard deviation previously found in this measurement. Furthermore, it enables the refractive index of these materials to be certified to the third decimal point or more, demonstrating the value and potential of this technique.

The current light field occlusion removal methods are generally computationally demanding and have insufficient effect on the global receptive field. To address these issues, we introduce SwinSccNet, an occlusion removal network based on the Swin-Unet encoder–decoder system. We employ Scconv to compress redundant features in the shallow convolutional neural network (CNN), and the Swin transformer is used to improve the global receptive field of the deep Swin-Unet encoder–decoder. The experimental results show that our technique not only minimizes computational costs and complexity but also achieves state-of-the-art performance on publicly accessible datasets.

To improve the frequency domain resolution of Doppler frequency of the optical frequency difference in the beat frequency–based laser Doppler velocimetry based on self-mixing interference and heterodyne interference, an ultra-low frequency measurement method with long short-term memory (LSTM) is presented. LSTM can predict the signal for the next period based on the characteristics of the original Doppler signal. The characteristics of the predicted signal remain basically consistent with the previous signal, with almost no change in frequency components. This is very beneficial for directly extracting the frequency information of ultra-low frequency Doppler signals with insufficient signal length. Experimentally, LSTM was utilized to measure Doppler signals generated at different velocities, achieving a resolution of more than 10−4 Hz. Compared with other signal extension methods such as zero padding, LSTM can truly enhance the resolution of Doppler frequency measurement without introducing direct current components and uncorrelated components. This method improves the velocity measurement accuracy while simplifying the signal processing for frequency measurement, demonstrating potential application value.

We present a phase demodulation technique for fringe analysis in fringe projection profilometry, based on digital moiré and the co-phase technique. The approach involves the use of stereo illumination and the simultaneous projection and acquisition of two π-shifted sinusoidal patterns from each projector. By taking advantage of color multiplexing, we code the sinusoidal patterns in the red and blue channels of the color images, so we need to project and acquire one image for each digital light projector. The phase demodulation involves three steps: first, digitally generating the moiré pattern for each colored fringe pattern using the synchronous detection method; second, computing the analytic signals for the two moiré patterns via a third-order low-pass Butterworth filter in the frequency domain; and third, calculating the final phase by merging the two analytic signals with the co-phasing technique.

Modulation transfer functions (MTFs) describe how a sensor system transfers spatial frequencies of a scene through an imaging system. For infrared systems, lab measurements are performed in a laboratory setting with a collimated source and a tilted edge target. This method is the standard way to measure a sensor’s performance metric. When these sensors are used for practical applications in the field, factors such as focus, atmospheric turbulence, and path radiance limit the performance of the system. These environmentally induced blurs need to be considered when designing sensor systems to ensure the required performance is met. The effects of these factors on the sensor’s performance can be quantified by measuring an MTF while in the field. By matching laboratory and static field MTFs, the effects of other blurs can be isolated, such as platform dynamics, vibration, and atmospheric turbulence, which will affect the performance of the system. To obtain a field MTF that matches one measured in the laboratory, the variable field conditions need to be well controlled. The effects of MTF target nonuniformity, tilt angle, illumination spectra, integration time, dynamic range, and number of pixels on target were explored as possible environmental factors affecting the quality of field MTF measurements.

To solve the problem of large filtering error of the fundamental frequency in the composite Fourier transform profilometry and shorten the measurement time needed in the phase shifting profilometry, a symmetrical transformation method (STM) for measuring the three-dimensional (3D) contour of objects is proposed. Only one composite grating is projected on the object in the STM. The grating is composed of overlapping two orthogonal sinusoidal fringe patterns with a π/2 phase difference and different frequencies. The two sinusoidal deformed patterns with a π/2 phase difference are demodulated from the deformed composite pattern reflected on the surface of an object. The other two patterns can be obtained through a symmetric transformation with sub-pixel precision. Based on the captured and calculated fringe patterns, the fast reconstruction of the 3D shape of the objects could be achieved. The STM has broad application prospects in the real-time 3D measurement field due to its single-shot feature.

We present a closed-form equation to design a generator lens. Using our procedure, the lens shape can be obtained to focus on a single image point given an arbitrary input wavefront. Several scenarios have been tested, and the results are as expected.

Solid attenuators are crucial instruments used at X-ray free electron laser experimental endstations for rapidly attenuating light intensity. With high-repetition-rate free electron lasers, the absorption plates accumulate heat as the repetition frequency increases, which will limit the use of solid attenuators. We designed a solid attenuator suitable for the FEL-I experimental endstation of Shanghai high-repetition-rate X-ray free-electron laser and extreme (SHINE) light facility, including the physics design, mechanical design, and thermal analysis under the high repetition rate. Through a combination of absorption plates, the precise light intensity across the 3 to 15 keV range was attenuated by 10 grades, and the mechanical design of the solid attenuation was developed with the corresponding cooling solutions. The solid attenuator design is proven to fulfill the high repetition rate of up to 10 kHz through the numerical results at different repetition frequencies and meet the operational requirements planned for SHINE.

A high-speed receiver optical subassembly (ROSA) based on silica hybrid-integrated technology for 400 G Ethernet applications is designed and manufactured. It consists of an eight-channel-arrayed waveguide grating (AWG) with a 2% refractive index difference, two 4-channel InP-based waveguide photodetector (PD) array chips, eight lenses for enhancing the coupling between AWG and PDs, two 4-channel trans-impedance amplifier array chips, and an eight-channel high-frequency flexible printed circuit. All the channels of the ROSA have achieved 3 dB bandwidths of above 27.05 GHz, and receiver sensitivities of below −8.5 dBm, supporting a receiving rate of 8×53 Gbps.

We delve into applying the “Urdhva Tiryagbhyam” Vedic mathematics sutra, or “Vertically and Crosswise,” to develop a 2-bit multiplier tailored for binary integers. Originating from ancient Indian mathematical traditions, this sutra historically expedited the multiplication of decimal numbers. To implement our proposed circuit, we employ four microring modulators designed by the electroabsorption method and scrutinize the impact of various variables on its on–off logic. The study emphasizes the significance of Vedic mathematics sutras in optimizing binary multiplication operations within the optical domain. To substantiate the optical output results, we have measured the extinction ratio, which consistently exceeds at least 2.9 dB for each operation. By integrating traditional mathematical principles with contemporary technologies, we aim to streamline and accelerate binary multiplication processes, contributing to advancements in digital circuit design and computation.

Beams carrying spin angular momentum (SAM) and orbital angular momentum (OAM) have created many application opportunities in optical communication, micromanipulation, quantum optics, and other fields. Beam arrays carrying multiple different angular momentum (AM) have attracted widespread attention due to their application prospects in high-dimensional information storage and high-security information encryption. Traditional optical devices have complex structures and large systems and are not conducive to integration. We proposed a method of using a quarter-wave plate (QWP) metasurface to regulate photon AM to generate a vortex beam array with two kinds of circularly polarized light at the wavelength 1550 nm. Different from the traditional method of using a half-wave plate to generate a vortex beam array, the use of transmission phase and geometric phase through QWP metasurface can not only realize the flexible modulation of SAM and OAM but also play a role in the optimization of partial circularly polarized light phase by geometric phase, which facilitates the generation of high-quality vortex beam arrays. Compared with traditional QWP metasurfaces that rely solely on the transmission phase, the introduction of a geometric phase can increase the number of channels without losing the quality of vortex beams. The simulation results verify the feasibility and advantages of the theory. Finally, a manufacturing tolerance analysis was conducted on the designed metasurface, verifying the feasibility of using the designed metasurface to regulate AM. We first attempt to generate circularly polarized vortex beam arrays using QWP metasurface and provide an effective idea for the regulation of optical AM.

We designed and implemented a compact silicon nitride mode-spot converter that is non-linear and stepwise segmented. The mode-spot converter with a length of 20 μm and a simulated transmission efficiency of 95.7% was obtained using the three-dimensional finite-difference time-domain method and particle swarm optimization algorithm. This device can connect a 10-μm wide waveguide with a 1-μm wide single-mode waveguide for O-band operation. Compared with a linear taper with equivalent transmission efficiency, this device reduces the footprint by 80%. The mode-spot converter was fabricated on a silicon nitride platform using electron-beam lithography and inductively coupled plasma etching processes. The fabricated device exhibits a measured average insertion loss of 0.30 dB in the O-band and 1 dB bandwidth of more than 100 nm.

A well-established method for 3D nanoparticle tracking is the double-helix point spread function (DH-PSF) engineering, which uses additional optical elements to make the PSF exhibit different rotation angles with varying depths of nanoparticles. Splicing the symmetric spiral phases together using the phase splicing method can generate the modulated phase mask of 2π-DH-PSF. The 2π-DH-PSF has a linear rotation rate at each axial position and has a larger rotation angle, showing a more accurate rotation angle and depth translation. Experiments with a phase-only spatial light modulator demonstrate the potential of the 2π-DH-PSF. Finally, we successfully conducted 3D nanoparticle tracking experiments at 8-μm depth with a numerical aperture of 1.4, showing its great potential.

The growing use of photonic integrated circuits in light detection and ranging (LiDAR) sensors has made the speckle and phase distribution of the reflected light relevant for coupling into the guided modes of these systems. We adopt the use of a simplified diffuse surface model to show the average coupling efficiency of reflected speckle into guided modes can be predicted from the optical intensity at the target. For the first time, we provide experimental results to show that this relationship is valid for predicting free-space loss as a function of range. We intend to aid optics design for integrated photonic LiDAR systems, providing a simple and accurate model to predict the free-space loss from a representative target at all distances.

An optical fiber Fabry-Perot (FP) interferometric humidity sensor based on multimode fiber (MMF)-black phosphorus quantum dot (BPQD)-polyvinyl alcohol (PVA) is proposed and experimentally verified. The sensor is made by splicing a brief MMF to single-mode fiber and coating BPQD-PVA film on the end face of the MMF. BPQD-PVA adsorbs water molecules in the air with the increase of humidity, which changes the length of the FP cavity as well as the refractive index of the BPQD-PVA, resulting in a spectral redshift. The effect of coating thicknesses on the humidity response characteristics is experimentally investigated. Experimental results show that the sensor has a sensitivity of 0.2609 nm/%RH in the humidity range of 32 to 40 %RH, 0.8208 nm/%RH in the humidity range of 40 to 48 %RH, and 6.5072 nm/%RH in the humidity range of 48 to 53 %RH, whereas the instability error is 0.008 %RH. The proposed sensor is a prospective solution with high sensitivity that can be applied in the fields of highly accurate humidity monitoring.

We report on an all–fiber polarization maintained (PM) erbium-based figure-9 structured nonlinear amplifying loop mirror mode-locked laser where a stable carrier-envelope offset frequency (fCEO) signal was detected via a fiber-packaged f-2f interferometer. At the pump power of 145 mW at 976 nm, the oscillator delivers an average output power of 6.13 mW with a repetition of 88.6 MHz and a signal-to-noise ratio of 79 dB. The spectrum of 3 dB bandwidth was measured to be 54.3 nm. Furthermore, an average power of 270 mW was obtained by a two-stage cascaded amplifier, corresponding to a single pulse energy of 3.05 nJ. Then, the lasing was injected into a 40-cm-long PM highly nonlinear fiber after optimizing the length of dispersion compensated PM single-mode fiber. At last, an fCEO beat note signal exceeding 34 dB was obtained, which implies the system can be potentially used in all–fiber optical frequency comb.

We propose a method for the measurement of laser linewidth by delayed self-heterodyne interferometry with ultra-short optical fiber. This method can measure the laser linewidth by the signal-to-noise ratio characteristics of the self-heterodyne power spectrum and the frequency spacing of the coherent envelope peaks. It can measure the laser linewidth at the kHz level using several meters of fiber. The feasibility and accuracy of this method are proved by theoretical derivation and experimental verification. In contrast to the conventional linewidth measurement method, the proposed method is simpler to implement, does not necessitate a rigorous experimental environment, and has a broad application range, which can be used as a new scheme for measuring laser linewidth.

We explore the spatiotemporal evolution of dispersion-induced pulse broadening in water. The Lorentz–Lorenz function is utilized to establish the relationship between the refractive index and the wavelength of the incident laser. Therefore, the dispersion coefficients are derived. Using the Schrödinger equation, we model the propagation of laser pulses over a 1-m optical length in water. Subsequently, the spatiotemporal evolution is obtained by the relationship between the spatial and temporal components of the light field. The results indicate that lasers with shorter central wavelengths and shorter pulse durations experience greater pulse broadening and significant bandwidth reduction. This methodology demonstrates the potential for enhancing underwater optical communication, representing a noteworthy advancement in both scientific research and practical applications.

We demonstrate a hybrid fiber laser system utilizing an angled fiber coupler and high-Q magnesium fluoride (MgF2) whispering gallery mode resonator (WGMR). The angled fiber coupler, with two polished facets, serves as both a coupling mechanism to the WGMR and a partial reflector, enabling lasing even without the WGMR. By integrating a 340 μm diameter MgF2 microcavity, we create a hybrid fiber cavity nested with a WGMR. This configuration results in dual-wavelength lasing, indicating the unique capabilities of our hybrid system. Our findings highlight the potential of angled fiber coupler-WGMR systems for enhancing spectral control in fiber lasers, opening new avenues for multi-wavelength laser sources.

The response frequency of a uniform sampling phase-sensitive optical time-domain reflectometry vibration sensing system is constrained by the sensing distance, for which non-uniform sub-Nyquist sampling can be employed to extend the detectable frequency range. However, sub-sampling corresponds to a low sampling rate, and when conventional signal recognition algorithms such as moving average and moving differential (MA-MD) are used, the achieved signal-to-noise ratio (SNR) is often not satisfactory. To address this issue, we propose a weighted MA-MD algorithm, in which the signal with more energy can be amplified more than the noise. For additive random sampling, the effectiveness of the proposed algorithm is evaluated through experiments conducted at various frequencies over a 6-km sensing distance. Compared with the conventional MA-MD and image edge detection methods, a significant SNR enhancement was achieved, and 109-kHz vibration was successfully retrieved with maximum and average sampling rates of 16.67 and 4.04 kHz, respectively.

To investigate the discharge parameters of the prism laser gyro under high-frequency excitation, a finite element simulation model is developed using a prism gyro structure with an optical length of 0.28 m. The optimal high-frequency excitation parameters were determined by simulating the effects of high-frequency discharge, voltage, size of the electrode plates, and horizontal displacement of the electrode plates on the gas discharge: high-frequency voltage is 6.5 to 7.5 V, frequency is 130±5 MHz, flat electrode discharge structure is used, and upper and lower electrode plates are 16×5×2 mm3 and 12×5×2 mm3, respectively. It is preferable that the center positions of both upper and lower plates be as symmetrical as possible. Finally, the experimental results validate the accuracy of the finite element analysis.

The gain degradation behavior of erbium-doped fiber amplifiers (EDFA) in a master oscillator power amplifier (MOPA) configuration was characterized using the fibers irradiated with varying irradiation dosages from our in-house Co60-ray source. The results indicate that power degradation and photo-anneal recovery processes simultaneously exist for erbium-doped fibers with relatively low concentrations of the co-dopants cerium and germanium added. For fibers with relatively high concentrations of germanium and comparable levels of cerium co-dopants, highly effective radiation hard behavior is exhibited, which is attributed to germanium alone. A fiber optimized for efficiency also provides a radiation-hard EDFA where after a 100-kRad (1000 Gy) exposure, the degradation in signal gain was 5 dB at a MOPA pump power of 315 mW.

The 1×1 multi-mode interference (MMI) coupler structure has a large multi-mode waveguide, which can increase the gain area of active photoelectronic devices such as laser diodes and superlight-emitting diodes and realize the improvement of output power. Most of the traditional 1×1 MMI regions are designed as rectangles, and the large symmetric optical mode interference density increases the sensitivity of the output light intensity to the MMI structural parameters. To solve this problem, we design a 1×1 double trapezoid MMI (DT-MMI) structure and use the mode propagation theory to model the DT-MMI structure. The analysis results show that DT-MMI weakens the influence of structural parameters on the number of interference points and reduces the sensitivity of output light intensity of the DT-MMI structure to structural parameters. The experimental results show that, when the injection current is 1.4 A and the base width and waist width are changed by 0.5 μm simultaneously, the output power of the laser with a rectangular MMI structure decreases to 86% of the device with unchanged base width and waist width, whereas that of the laser with DT-MMI decreases to 89%, which proves that the DT-MMI structure can reduce the parameter sensitivity of the device.

Ge has become a focus in the development of optoelectronic devices integrated into silicon platforms due to its compatibility with standard complementary metal-oxide-semiconductor (CMOS) technology. To reduce the bandgap of Ge, thereby enhancing its optical properties and accelerating the development of CMOS-compatible silicon-based germanium light sources, we propose a strained Ge LED with a microbridge structure. By etching two isosceles triangles with opposite apexes on the Ge layer and utilizing the edge stress concentration, the ideal tensile strain is achieved at the edge of the microbridge. Simulation results show that the Ge LED exhibits a peak wavelength of 1960 nm and a maximum electrical-to-optical conversion efficiency of 1.6%. Finally, this single structure is expanded into a ring-shaped array to increase the area of stress concentration. Simulation results show that the Ge LED array exhibits a peak wavelength of 1790 nm and a maximum electrical-to-optical conversion efficiency of 1.45%.

Modifying germanium to achieve efficient light emission holds great potential in the field of silicon-based light sources. We propose a method of introducing stress by repeatedly etching trenches and filling them with silicon nitride (SiN). By combining germanium tin (GeSn) alloys with an external stress layer of SiN, efficient modification of germanium is achieved. We performed process and device simulations on the structure, and the results showed that ∼0.8 GPa of biaxial tensile stress was introduced into the active region of the light-emitting diode, with a peak wavelength of 2200 nm and a maximum photoelectric conversion efficiency of about 5%. The device structure we proposed provides an effective solution for realizing silicon-based integrated light sources.

Plasmonic structures can localize incident light at sub-wavelength scales, improving the quantum efficiency and integration of detection devices with broad applications in civilian and military fields. However, metallic materials face several challenges in the middle and long infrared wavelengths, such as difficult excitement of plasmons, poor localization performance, and incompatibility with fabrication processes, which greatly limit their applications. An all-semiconductor plasmonic type-II superlattice (T2SL) infrared detector with dual-band absorption enhancement is proposed and analyzed by simulations in this paper. The detector is composed of a plasmonic cavity and cross-shaped hollow ellipses with heavily doped InA layers instead of traditional metals, which has better-fabricating compatibility. Simultaneous absorption enhancements in mid-wave and long-wave infrared (MW/LWIR) wavelengths can be realized because of the excitation of surface plasmons and localized plasmons at the interface of heavily doped InAs/T2SLs. The top ellipse arrays are utilized for better impedance matching and reducing the reflectance of incident light on the detector surface. The influences of the film thickness and angle dependence of the designed structures are discussed by COMSOL simulations. The results show that the structure can realize significant enhancement of infrared detection in both MWIR and LWIR spectrum and the absorption is increased from 40% to 90% compared with a reference device without heavily doped micro-structures. This approach provides a new way to design more effective all-semiconductor plasmonic T2SL detectors and promote the development of multi-color infrared detectors.

In visible light imaging positioning systems, the design of light-emitting diode identification (LED-ID) plays a crucial role in enhancing the system access capacity. The frequency feature based on frequency division multiplexing (FDM) is widely used for distinguishing LED-ID owing to its simplicity of deployment. Appropriately assigning frequency bands to each LED and designing effective recognition algorithms can support more available addresses. We derived a formula for the influencing factors of LED imaging stripes in the FDM scenario. The formula indicates that, if the LED-ID is distinguished by stripe width, the driving frequency interval of LEDs should be inversely proportional to the distribution of the driving frequency. On this basis, we derive the upper and lower bounds and the minimum resolution of frequency and give the theoretical maximum number of LED access and the corresponding optimal LED-driven frequency distribution. To ensure a high recognition accuracy when the number of LEDs in the system reaches the theoretical limit, two corresponding image processing algorithms are proposed: a local binarization method based on the Lambertian model and an improved stripe width recognition algorithm. Results show that the proposed method reduces the system recognition error rate to 1.1% within the applicable frequency range. The feasibility of the proposed scheme is introduced through hardware implementation.

The transmission characteristics of vortex beams in layered media are of great significance in the fields of optical thin film technology, optical devices, and optical communications. We studied the reflection and transmission characteristics of higher-order vortex beams in layered media, and the theoretical derivation is carried out according to the plane wave angular spectrum expansion method and matrix transmission theory. The expressions of the electric field of the reflection and transmission of the vortex beam in the layered medium are obtained, and the influence of the medium on the light intensity and phase is analyzed. The results show that the reflected and transmitted light intensity distributions of the homogeneous medium basically remain circular. With the increase of topological charge, the attenuation of the reflected and transmitted light intensity of the uniform medium decreases and then increases, whereas the attenuation of the reflected and transmitted light intensity of the multilayer medium gradually increases. This indicates that the reflected and transmitted light intensities produced by vortex beam incident on different media are significantly different and that various angles of incidence cause the initial position of the phase center to change. The results lay a theoretical foundation for the transmission of vortex light in layered media.

A simplified dual-output and filter-free photonic-assisted single sideband mixer is proposed, which uses a 2×2 optical coupler (OC) instead of a 2×4 optical hybrid to process optical modulation signals. Using two dual-parallel Mach–Zehnder modulators (DPMZMs) in parallel to achieve carrier-suppressed single-sideband modulation of the radio frequency (RF) signal and carrier-suppressed double-sideband (CS-DSB) modulation of the local oscillator (LO) signal at DPMZM1 and CS-DSB modulation of the LO signal only at DPMZM2, with a 2×2 OC coupling, the down- and up-converted RF signals can be obtained simultaneously and output separately. Because the −1st-order or +1st-order optical sidebands of the LO signal can be canceled out via a 2×2 OC instead of a 2×4 optical hybrid or an optical filter in previous reports, the proposed mixer has a simplified structure and a large bandwidth. Simulation results show that the proposed mixer has mixing spurs suppression of over 30 dB, frequency tunability, and spurious-free dynamic range of over 101.55 dB·Hz2/3. In addition, to evaluate the mixer performance for the broadband signal, 16-quadrature amplitude modulation RF vector signals with tunable center frequency are applied to the mixer, and the measured error vector magnitudes of the down- and up-converted vector signals are <1.53%.

We investigate the performance of a free-space optical (FSO) coherent communication system in imprecise atmospheric composite channels, taking into account the combined effects of Malaga atmospheric turbulence, channel estimation errors, nonzero boresight pointing errors, and path loss. The probability density function (PDF) of the instantaneous signal-to-noise ratio of FSO systems using heterodyne detection technology in imprecise channels is derived. Based on this PDF, Meijer’s G functions are used to derive analytical expressions for the outage probability, average bit error rate, and average channel capacity of the quaternary phase-shift keying modulation system, to quantify the performance of the considered system. Through numerical simulation, the performance of FSO communication under imprecise and precise channels is compared and analyzed, and the effects of turbulence intensity, channel estimation errors, boresight error, spot jitter, beam divergence angle, and link distance on FSO coherent communication systems are evaluated. Finally, we validate the accuracy of both the simulation results and the analytical results through Monte Carlo methods.

A broadband tunable channelized microwave instantaneous multi-frequency measurement system based on interleaving dual-optical frequency combs (OFC) is proposed. In the first branch, the unknown signals are input into a dual-parallel Mach–Zehnder modulator for carrier-suppressed single-sideband modulation. In the second branch, the frequency-shifted signal which is related to the reference signal is input into the OFC generator. The generated 25-line OFC is split into two paths. One path is frequency-shifted so that the two OFCs are interleaved distribution. The two OFCs are input into the photonic I/Q receivers to mix with the unknown signals for intermediate frequency reception. By adjusting the reference signal frequency f0≥24.5Δf, a measurement range of f0−24.5Δf to f0+25.5Δf GHz can be achieved. Simulation experiments demonstrate that the system can measure frequencies in the range of 0 to 70 GHz, with a measurement error of <8 MHz. Moreover, the system achieves an image rejection ratio of >14 dB, with passband power fluctuation less than 0.2 dB.

The significance of artificial neural networks (ANNs) in complex algorithm design and analysis is undeniable. We have made a design using an electro-optic Mach-Zehnder interferometer (EOMZI), driven by a photodiode (PD). Therefore, the proposed EOMZI is optically driven. Depending on the input optical intensity to the PD, the optical output power of the EOMZI varies. The output signals are taken from the bar and cross ports of the EOMZI. Using the ANN model, variations of different parameters have been observed. From this model, the output signals of both ports have been successfully analyzed. In terms of the PD input light intensity, we have also analyzed the dynamic responsiveness of our proposed system.