Infrared (IR) imaging can highlight thermal radiation objects even under poor lighting or severe sheltering but suffers from low resolution, contrast, and signal-to-noise ratio. While visible (VIS) light imaging can guarantee abundant texture details of targets, it is invalid in low lighting or sheltering conditions. Therefore, IR and VIS image fusion has more extensive applications, but it is a still challenging work because conventional methods cannot balance dynamic range, edge enhancement, and lightness constancy during fusion. To overcome these drawbacks, we propose a self-supervised dataset-free method for adaptive IR and VIS image fusion named deep Retinex fusion (DRF). The key idea of DRF is first generating component priors that are disentangled from a physical model using generative networks; then combining these priors, which are captured by networks via adaptive fusion loss functions based on Retinex theory; and finally reconstructing the IR and VIS fusion results. Furthermore, to verify the effectiveness of our reported physics driven DRF, qualitative and quantitative experiments via comparing with other state-of-the-art methods are performed using public datasets and in practical applications. These results prove that DRF can provide distinctions between day and night scenes and preserve abundant texture details and high-contrast IR information. Additionally, DRF can adaptively balance IR and VIS information and has good noise immunity. Therefore, compared to large dataset trained methods, DRF, which works without any dataset, achieves the best fusion performance.

The color quality and sharpness of the dual-band color fusion images have the greatest impact on the audience’s understanding of the scene content. Traditional image quality assessment (IQA) methods focus on the luminance contrast of image and attach limited attention to pixel-wise relationship. As a result, these methods perform poorly on color-related distortions. An objective assessment model for the comprehensive quality of fusion images is proposed. According to the correlation between the gray level co-occurrence matrix (GLCM) and the image color, the model extracts the homogeneity, angular second moment, and contrast of the GLCM as the image color quality features. Gradient-weighted class activation mapping is used to calculate the heat map, reflecting the visual saliency of each region. We use the visual saliency weight of each region to weight the rotation and uniform invariant local binary pattern histograms of the corresponding regions to obtain sharpness features. The experimental results show that the performance of the proposed method is better than the existing eight no-reference IQA models.

In electronic holography, a light source that can control coherence steplessly is desired to adjust the balance between speckle noise and the resolution of reconstructed images. We propose a high-brightness light source that can control speckle by adjusting the bandwidth. In general, narrowing the bandwidth of the light source results in a decrease in brightness. To compensate for this, the proposed system contains a yellow phosphor light source in the projector as a high-intensity light source. The results of experiments show that bandwidth of the proposed device can be adjusted as intended, and it is brighter than high brightness light emitting diode. Therefore, it is confirmed that the proposed device is useful as a reconstruction light source for electro-holography with evaluating the quality of reconstructed images.

A neural network-based system designed for automated detection of concealed items using a postal terahertz scanner is presented, with system optimization provided. A dataset of objects scanned by a THz scanner is introduced. A convolutional neural network is trained on this dataset of terahertz images to classify and detect whether an image contains a prohibited item or not. The system is tested using real-world samples, achieving an accuracy of 95.5% mAP@0.5. The results demonstrate the effectiveness of employing a neural network in postal terahertz scanners and its potential for use in security and surveillance applications.

We propose a taper thread compensation algorithm that considers the taper thread tilt state and tooth distortion to address the problem of low accuracy of taper thread inspection by machine vision. The analysis of the taper thread inspection process reveals the reason for the low accuracy of taper thread inspection, and the mathematical modeling of the taper thread is established according to the spatial geometric relationship. The experiment shows that the compensation rate of the algorithm is 80% of the base median, 70% of the thread half-angle, and 85% of the bottom width of the thread compared with that before the compensation, and it has less influence on the large diameter and pitch.

We investigated the scanning differential heterodyne microscope response for a plasmonic metasurface-dielectric film system. Superresolution effect for microscope phase response with 6.5 superresolution coefficient in the vicinity of π optical phase increment was observed. Use of an additional dielectric film allowed local adjustment of the optical phase increment over a wide range (0 deg to 100 deg). The ability to adjust the width of the phase response function by changing the microscope heterodyne frequency has been demonstrated experimentally.

To accurately characterize the geometric form of key components in industrial products, many profile measuring instruments have been developed to date. However, there are some special components, such as the hemispherical resonators featuring thin curved transparent surfaces, which are difficult to be measured using general instruments. The chromatic confocal technology was introduced in this paper to conduct the bilateral form characterization of this type of surfaces. Based on the assumption of tilted plate approximation, a modified ray tracing model was presented to correct the errors produced by the curved surfaces. The experiment of measurement on tilted, fused silica plates was conducted to demonstrate the effectiveness of the proposed model. Results show that the developed model improves the measurement accuracy of plates with large tilt angle. A three-axis motion stage was built with self-developed chromatic confocal sensor to obtain the bilateral profiles of the resonator. By fitting the spheres with the scanning profiles, the form error between the measurement points and the fitted spheres can be calculated. Partial form errors along the circumferential and axial directions of the resonator are evaluated, and an intuitive assessment of its thickness variation along the circumferential direction was made.

Montel mirror coated by laterally graded multilayer is a key two-dimensional collimating optics for x-ray analysis instrument. To provide guidance for the fabrication, the collimation property of a W/Si multilayer Montel mirror with parabolic shape is simulated systematically by a ray-tracing program. The influence of different source sizes, multilayer reflection bandwidth, mirror-detector distance, figure errors, and the assembly errors on the collimation performance is simulated. The mechanism for the change of divergence angle, collimation efficiency, beam uniformity, and so on is analyzed. Based on the results, the optimum mirror structure and the tolerance for fabrication and assembly errors were estimated for a high-performance x-ray Montel mirror.

In the field of augmented reality/virtual reality head-mounted displays or eyeglasses, electro-optical tunable lenses have great potential to resolve the issue of accommodation-convergence conflicts and to correct vision problems. A high-quality tunable lens with a large field of view is highly desired for these near-to-eye applications. Recently, gradient refractive index tunable liquid crystal lenses with a concentric ring electrode design and segmented phase profile have received attention due to their compactness, low-voltage requirement, and ability to provide a large aperture size while maintaining a fast-switching speed. However, this design can result in degradation of optical quality, causing haze from the phase reset boundaries and electrode discontinuity. We analyze the cause of haze and presents solutions to reduce these effects, and we experimentally validate them.

Holography is the ultimate three-dimensional (3D) imaging technology, and research is actively being conducted on generating at high-speed holograms with enormous amounts of information and improving image quality. Because computer holography is based on wave optics algorithms, reconstructing the texture of 3D images is difficult. On the other hand, in principle, reconstructing texture in integral photography based on geometric optics is easy and the method is well established. We developed a high-performance special-purpose computer, called holographic reconstruction for ultra-realistic imaging, dedicated to the ray-wavefront conversion method. The design and implementation of the circuit for the hologram generation were performed using field-programmable gate array technology. Parallelization was performed at each step for increasing the speed of the calculation process. Furthermore, by sending output data directly to a displaying device in the high-definition multimedia interface, the communication between the host personal computer (PC) and special-purpose computer was controlled in one direction, which significantly reduced communication time. The system was ∼7.7 times faster than a PC alone and succeeded in the holographic reproduction of a textured 3D image in real time at 30 frames per second for a 1024 × 1024-pixel hologram.

Photovoltaic (PV) conversion is highly wavelength-dependent. The efficiency of a PV system is maximum when converting photons of energy close to the bandgap energy of solar cells. In a spectral-splitting solar cell system, an appropriately designed holographic lens provides wavelength-selective performance to disperse and concentrate a specific spectral region of solar radiation with appreciable diffraction efficiency. However, for holographic lenses, the angular range over that diffraction efficiency remains appreciable is limited. To overcome the difficulties associated with the limited acceptance angle (angular selectivity) of a single holographic lens, an investigation on the design aspect of a multiplexed off-axis holographic lens has been made for the collection and concentration of sunlight effectively over a wide angular range with appreciable diffraction efficiency. Processing parameters for a typical thick-phase holographic lens have been optimized to get the maximum value of the acceptance angle. Based on the theoretical design, a multiplexed hologram consisting of four angularly multiplexed holographic lenses of equal fringe spacing has been recorded. Experimental curves for the variation of diffraction efficiency with the angle of reconstruction have been presented to show the effectiveness of such multiplexed lens for solar tracking. Simulation results for the multiplexed holographic lens are also presented, which shows a good agreement with the experimental results. Results show that such off-axis multiplexed holographic lenses can advantageously be used for wavelength-selective performance with appreciable diffraction efficiency over a wide angular range.

Simulation of Gaussian laser beam propagation has many practical applications in teaching optics behavior and in laser design engineering. For the case of laser resonator cavity studies, most current techniques use the widely taught self-consistency round trip method to analyze the beam radius envelope through the cavity. We present a simpler method for simulating a confined Gaussian beam by modeling the real components of a complex ray. The procedure relies heavily on the classic multi-lens ABCD formulations for ray tracing optical cavities developed by Kogelnik, though it avoids the use of the q-parameter and its ABCD transfer law traditionally carried within the matrix optics transfer computations. Arnaud’s pioneering complex ray formulation and the Delano y-ybar ray theory provide the essential framework. The result is an easy computer simulation technique, which only requires a single calculation of the one-way complete traverse optical matrix. We present multiple detailed examples of our procedure for representative laser resonator beam simulations. The complex ray method significantly improved the efficiency of Gaussian beam ray tracing in cavities compared to the conventional q-parameter method. The optical elements considered only include end mirrors and intracavity thin lenses.

Generating high uniformity Bessel beam is an interesting target in laser processing. An axicon with a high-order curved surface is proposed to generate Gaussian–Bessel beams with high uniformity and high energy utilization. The original phase function of the standard axicon is replaced by multiple polynomials, which are optimized by a combined algorithm employing the genetic algorithm and the unconstrained nonlinear minimization algorithm. Simulation and experiment results demonstrate that the combined algorithm not only significantly reduces the time complexity of the algorithm greatly but also achieves high uniform intensity distribution at the focal segment. By compensating and optimizing the fifth-order surface axicon, the energy utilization is 17.734%, and the uniformity can reach 93.86%. The processing experiment results confirmed that the presented method can extend the processing depth and obtain high quality.

An optical-based pressure sensor for a 150 × 150 mm surface was designed and fabricated. The sensor utilizes a fiber Bragg grating (FBG) attached to a 30 × 30 × 30 mm actuator as the pressure sensing mechanism. The middle section of the actuator, which is circular, can bend into an elliptical form and, in the process, pull the FBGP via both ends when force or pressure is applied, thus converting the pressure applied to its surface into a wavelength shift. In laboratory testing, a sensitivity of 0.152 nm / kPa was obtained. Subsequently, the pressure sensor was tested in the field by burying it 20 cm underground to measure soil pressure, while another FBG was spliced in series to the FBGP to compensate for temperature variations. Testing shows that the proposed design can realize a compact optical-based pressure sensor with enhanced soil monitoring applications such as dynamic soil pressure caused by soil movement.

We present and experimentally verify a deep learning approach to synchronously measure the multi-beam pointing error for coherent beam combining systems. This approach uses only one detector by acquiring the far-field interference focal spot, which can greatly reduce the complexity in coherent beam combining systems with high accuracy. The amplitude modulation is utilized to eliminate the confusion of the label values in symmetric system. The position assist camera is used to acquire accurate label value, which solves the mismatch between sample and label value caused by ambient vibration in long-term data acquisition. In simulation and experiment, the RMS accuracy is about 0.3 and 0.5 μrad, respectively, which can greatly meet the pointing measurement requirement in coherent beam combining systems. The result shows that this approach can be well applied to multi-beam coherent combination for high-power laser systems.

We report the first implementation of an advanced waveguide structure, consisting of GaSb separate confinement layers, n-doped InAs/AlSb superlattice intermediate cladding layers, and n ⁺ -doped InAs_0.91Sb_0.09 plasmon-enhanced cladding layers for GaSb-based interband cascade lasers (ICLs) with lasing wavelengths in the 3 to 4 μm wavelength region. This advanced waveguide configuration for ICLs can have improved thermal dissipation and enhanced optical confinement. Although the grown ICL wafers had significant layer thickness deviations from the designed values, devices made from them exhibited room temperature (RT) threshold current densities as low as 148 A / cm² and high voltage efficiencies (e.g., 69%), implying a considerable potential of the advanced waveguide configuration for further improved device performance. A comparative study among the devices revealed how the structural variations could affect the carrier transport and threshold voltage, providing useful guidance for future research. Additionally, the ICLs tested here had characteristic temperatures of nearly 60 K, which are the highest among RT ICLs with similar lasing wavelengths, supporting the further development of the advanced waveguide in GaSb-based ICLs operating in this wavelength range.

We present the design of a compact channel drop filter based on 2D photonic crystals on silicon-on-insulator platform. The proposed device consists of three channel sections with line defect waveguides as the bus and drop waveguides and L3 cavity as the resonator. The input and output ends of the bus waveguide are connected to silicon strip waveguides through tapered waveguide regions for efficient mode transmission. Each L3 cavity filters one resonant wavelength, which will be coupled to the drop waveguide. The effect of the size and position of the structural parameters on the proper selection of resonant wavelengths and drop efficiencies is studied. The device performance has been numerically analyzed, and thermal stability is studied using the 3D finite-difference time-domain method. The proposed device can filter three wavelengths in the C-band with minimum channel spacing of 3.03 nm. With the tapered-coupled bus waveguide, drop efficiency has been improved from 77% to 91%, and the quality factor and linewidth are found as 5042 and 0.31 nm, respectively. The footprint of the filter is 116 μm² per channel section. The proposed device is suitable for practical wavelength division multiplexing applications in optical communication systems.

Metalenses have drawn a lot of interest for use in near-infrared (NIR) bioimaging due to their benefits, such as flexible design, light weight, and simple integration. However, chromatic aberration is inevitable in optical systems, which substantially reduces their imaging quality. A broadband achromatic metalens for linearly polarized light in the range 1200 to 1550 nm is constructed to address this challenge. The phase and dispersion of the incident light are modulated by altering the ratio between the long and short axes of the elliptical nanopillars. Through the application of the particle swarm optimization algorithm, appropriate compensating phases can be added to the phase profiles at various wavelengths to align the real phase with the target phase of the broadband achromatic metalens. The structure of the nanopillar at any position in the metalens can be found from a relative phase library. Our numerical experimental results demonstrate that the proposed metalens has relatively consistent focusing characteristics and robustness in the 1200 to 1550 nm band, with an average focusing efficiency of 83.14%. The proposed high-efficiency robust NIR achromatic metalens can increase the quality of NIR biological imaging and the efficiency of a detector.

We examine the use of foundry process optical waveguide couplers in making 1 × 2 optical switches. The concept involves a post-foundry process to provide a moveable dielectric load over one of the waveguides in the coupler, such that the dielectric load changes the propagation constant of the affected waveguide depending on its proximity to the waveguide. Coupled mode theory is employed to explain the operation of the switch and identify key requirements of the dielectric load. Finite difference time domain simulations are employed to verify that the concept is viable for two standard photonic integrated circuit platforms. The concept ensures that the optical signals are always constrained within the high-quality foundry process waveguides while also allowing the material and lithography requirements for the layer in which the movable load is realized to be relaxed. Results show that a contrast between the switch ports of >20 dB is possible with relaxed tolerances for the dielectric load layer, at an operating wavelength of 1550 nm. We envision that the dielectric load would be moved by a micro-electromechanical systems actuator. Having the optical signals always within the foundry waveguides will permit fabrication of high-performance mechanically switched optical systems by a wide range of facilities.

Germanium and chalcogenide glasses are used as infrared lens materials, but there is no one that combines both excellent optical properties and mass production. Against this background, we worked on the development of a new infrared lens material, and a novel infrared lens material named FI-02 has been developed. FI-02’s most useful feature is its infrared transmission property. It can transmit up to 20-μm-wavelength infrared light and has a vast transmittance spectrum in the infrared region compared to germanium and conventional chalcogenide glass. In addition, FI-02 has a high refractive index of 3.47 (at a wavelength of 10 μm). This enables the fabrication of thin and high-performance infrared lenses. Furthermore, FI-02 can be processed through press molding. This enables making of high-performance lenses with high productivity. In an infrared lens unit using FI-02, infrared images are captured with better contrast as compared to those captured using the germanium or conventional chalcogenide glass lenses. This could be attributed to the good infrared transmission property of FI-02. In addition, we confirmed that using FI-02 with a high refractive index as an aspheric lens, it is possible to design a lens unit with unprecedented characteristics, such as a low-distortion ultra-wide-angle lens.

Mode phase matching (MPM) is a widely used phase-matching technique in χ⁽²⁾ nonlinear thin film lithium niobate waveguides for efficient wavelength conversion. Unfortunately, the conversion efficiency is limited by the reduction in the spatial overlap of the three interacting waves due to the intrinsic mode mismatch of spatial symmetry. However, changing the χ⁽²⁾ distribution of the waveguide can greatly increase the mode overlap factor, resulting in high second-harmonic conversion efficiency. In this work, we have optimized the structure of the semi-nonlinear photonic waveguide to greatly attenuate the shift of the central wavelength due to the fine structure of the waveguide while ensuring a similar conversion efficiency. This designed waveguide is more suitable for devices with high wavelength range requirements. Then, we propose a MPM scheme, which can achieve a large mode overlap factor of 0.8019 and a theoretical normalized SHG conversion efficiency of up to 10,872 % W ^{− 1} cm ^{− 2} by modifying the χ⁽²⁾ distribution of the waveguide. The proposed working principle is also applicable to other quadratic nonlinear platforms and has great potential for applications in nonlinear optics.

A photodetector that utilizes the phase-changing material Ge₂Sb₂Te₅ (GST) integrated with a silicon on insulator (SOI) waveguide is designed and analyzed in the wavelength (λ) range of 1500 to 1600 nm for telecommunication and optical fiber communication. The analysis of simulated structure reveal that GST is a promising material for photodetection applications due to phase-change property on a nanoscale, excellent absorption (with an absorption coefficient of ∼10⁶ cm ^{− 1}), lower bandgap of 0.63 eV in the amorphous phase, and 0.53 eV in the crystalline phase, tunability, and high phase stability. The photodetector structure consists of an SOI substrate, silicon waveguide, GST layer as phase changing material, and gold (Au) to make contacts. The photodetector’s optical and electrical parameters, such as electric field distribution of carrier generation rate (G), absorbed power (P_abs), dark current (I_dark), photocurrent (I_ph), and responsivity (R), are analyzed for both the amorphous (a-GST) and crystalline (c-GST) phases. The results demonstrate the potential of GST material to design high-performance photodetectors for various applications. The highest resistivity of 2.29 A / W is achieved for a-GST at λ = 1550 nm, with a bias voltage range of 0.5 to 2.5 V. The maximum absorption is observed in the amorphous phase as compared to the crystalline phase of GST. The calculated values of I_ph and I_dark are 0.24 mA and 78.54 μA for a-GST and 0.12 mA and 15.71 μA for c-GST, respectively. The optoelectrical behavior of GST-based photodetector on SOI waveguide demonstrates their potential application in photonic integrated circuits. Our work proposes an approach for using GST in photodetectors and analyzes both phases of GST that have not been explored before. Therefore, for the viability of the reported work, a detailed comparison is also presented with other simulated structures and found that the proposed device provided excellent results with low bias voltage.

Electromagnetic-induced transparency (EIT) is a transparent window phenomenon with high transmittance in atomic systems, which has a broad application in the sensing field. We propose a compact graphene metamaterial sensor and analyze its mechanism of EIT-like effect. The unit cell is composed of an octagonal star graphene ring and a rectangular graphene ring and excites EIT-like effect through the strong coupling of the light mode and the dark mode. The compact graphene structure design improves the area utilization rate and contributes to the miniaturization of devices, and the EIT window is actively tunable by the change of the Fermi level of graphene to improve the applicable range of the sensor. The numerical simulation demonstrates that the refractive index sensitivity can reach 2.828 THz/RIU, meaning that the transmission curves of the sensor shift 2.828 THz per unit change of refractive index of the surrounding medium and its figure of merit can reach 5.34. The proposed structure can be applied to the high-sensitivity refractive index sensing in the terahertz band and has great application potential in the biological and chemical sensing field.

Multipartite quantum steering has crucial applications in the field of asymmetric secure quantum networks. In the actual quantum communication transmission process, the inevitable loss and noise in the channels will lead to reduction or even disappearance of quantum steering, which is extremely unfavorable to the transmission of information, so it has important practical significance for research of the revival of quantum steering. We theoretically studied the influence of noise on steering and investigated the revival of quantum steering by correlated noisy channels. The results show that excessive noise can cause sudden death of steering, whereas the disappeared steering can be revived by introducing correlated noise. Simultaneously, we also confirmed that the steerability and direction of steering can be manipulated by changing the transmissivity of the revived beam splitter. Our work provides a feasible reference for secure quantum communication in real noisy environment.