Early studies of laser beam propagating in turbulence indicated that the log-amplitude variance of the received intensity would grow without bound as the refractive index structure parameter and range increase. This was an ominous observation. It suggests that the laser communications and remote sensing systems would not be useful during the hot daytime conditions. Fortunately, it does not increase without limit. We describe the various scintillation indices that predict this type of performance. Specifically, we will develop the scintillation indices for satellite communications (SATCOM) downlink, SATCOM uplink, and atmospheric slant path and horizontal communications link geometries, which also include tracking, untracked, and aperture averaging receiver effects. The focusing and saturation regimes in the turbulent channel will be defined. An example analysis will be provided using this information. The importance of log-amplitude variance is that the scintillation indices will have peak values for some refractive index structure parameters and range values.

The most common configuration of liquid crystal devices incorporated within spectral imaging systems is using liquid crystal tunable filters. Usually, these filters suffer from low light throughput or slow response times which may not meet the growing demands of industry and research. However, in most applications, multispectral imaging is adequate, and there is no need for hyperspectral imaging. We implemented a discrete tunable Lyot-based filter in such systems to obtain spectral images more efficiently. The Lyot filter consists of three liquid crystal cells combined with nine narrow bands of passive filter covering the visible-infrared spectroscopy and near-infrared spectroscopy, which makes it a potential candidate for various applications. A system with a smaller number of bands designed for oximetry imaging is even faster and shows higher light throughput. Experimental results show that our approach yields a relatively faster response with high light throughput while providing reliable spectral information for food quality assessment and remote sensing applications.

Continuous-wave (CW) and laser range-gate (LRG) imaging are two effective imaging modes for long-range target acquisition and object discrimination. Continuous wave time-of-flight (CWToF) and LRG with range resolve (LRGRR) are modulated versions of CW and LRG that produce 3D imagery of the target. In this study, the sensitivity and range resolution benefits of these four systems are quantified. A performance model is developed and used to compare trade-offs between range resolution and sensitivity for the four active imaging techniques presented. It is found that the LRG-based systems deliver increased performance over the CW-based systems due to higher sensitivity in nighttime circumstances and in degraded visual environments. The results will enable systems engineers to discern whether the added complexity associated with CWToF and LRGRR imaging is worth implementing over traditional approaches such as CW and LRG.

Compared with traditional optical microscopes, lensless holographic imaging technology can provide large field-of-view cell images without the need for any lenses. Therefore, lensless holographic imaging can be widely used in biological detection and diagnosis. Based on the theory of physical optics, this article designs a lensless holographic imaging experimental device. Combining the designed experimental device with a method of determining the reconstruction distance by calculating the phase distribution, it can complete the construction of reconstruction images of animal and plant cells with diameters ranging from 5 to 40 μm, with an imaging range >20 mm2. This method can statistically analyze various characteristics of cells, with an accuracy rate of ∼92% for quantity and over 90% for diameter and area. It has great potential in medical detection.

Phase-only holograms (POHs) are often generated by the Gerchberg–Saxton (GS) algorithm. Nevertheless, low-quality reconstruction and iterative divergence plague the traditional GS method, reducing the quality of holographic display. Noise still affects adaptive weighted GS (AWGS) algorithms, despite their ability to ensure convergence through the addition of planned feedback. We propose an optimized AWGS algorithm, named optimized adaptive weighting constraints (OAWGS), for the generation of POHs for high-quality holographic display. The contrast and intensity of the signal domain are enhanced by adding a weighting factor to the AWGS feedback. By introducing non-signal regions and applying an optimized random phase as the initial phase, the OAWGS algorithm substantially improves the quality of holographic reconstruction. Compared with the AWGS algorithm, the proposed method can improve the peak signal-to-noise ratio by 5.45 dB and converge. It could reach convergence after 20 iterations. Both simulation and experiment results verify the effectiveness of the proposed method.

Telescopes employing linear detector arrays in a push-broom configuration enable the reconstruction of two-dimensional images of the Earth by recombining successive one-dimensional captures. This configuration, which typically features a wide field of view in the across-track direction but a narrow one in the along-track direction, often suffers from stray light, which degrades optical quality by introducing artifacts into the images. With increasingly stringent performance requirements, there is a critical need to implement effective stray light (SL) correction algorithms in addition to control by design. We describe the development of such an algorithm, using the cloud imager (CLIM) linear detector array instrument as a case study. Our approach involves calibrating SL kernels obtained by illuminating the instrument with a point-like source from various angles. In the along-track direction, we interpolate the SL kernel for any field angle without initial assumptions about SL behavior. For the across-track direction, we employ a local shift variant assumption. When applied to images of a checkerboard scene, which includes transitions between bright and dark areas, our algorithm successfully reduces SL by two orders of magnitude, demonstrating its efficacy and potential for broader application in telescopes with linear detector array.

It is generally assumed that using a retro-reflective surface as the target of an interferometric measurement, an accurate alignment to the illumination beam is not really necessary. On the contrary, we show that even a few degrees of angular misalignment can corrupt the interferometric signal with the onset of a large artifact, which is also misleading because it is similar to the waveform of the high-level feedback regime. We first provide the experimental evidence of the artifact in a self-mixing interferometer, showing that the artifact is canceled after an alignment to <0.2 deg error, and then provide a theoretical evaluation, in good agreement with the observations.

Structured light 3D reconstruction point clouds are highly susceptible to camera distortion, which hinders their ability to meet the requirements of high-precision measurements. We propose a point cloud distortion correction method based on the Hippopotamus Optimization algorithm optimized Back Propagation neural network (HO-BP). The method involves performing a least squares (LS) plane fitting on the actual point cloud corrected by OpenCV to obtain the Z coordinates on the same plane. Using the pinhole model, the X and Y coordinates of the fitted plane are then recovered, resulting in the target plane point cloud. The HO-BP model establishes a mapping relationship between the actual point cloud and the target point cloud, thereby achieving distortion correction. The correction was applied to standard sphere point clouds at multiple different positions. Compared with the original point clouds, the mean absolute error (MAE) and root mean square error (RMSE) of the LS radius of the sphere point clouds corrected by HO-BP decreased by 72.42% and 62.62%, respectively. This demonstrates that the corrected target point clouds are closer to the ideal point clouds. Compared with existing algorithms, HO-BP also showed superior performance in terms of MAE and RMSE.

Color fringe projection profilometry (FPP) has high measurement efficiency because multiple fringe patterns can be extracted from a single color image. However, a key problem, lateral chromatic aberration (LCA), is introduced due to the use of colored fringe patterns, which modify the fringe order and further reduce the measurement accuracy of three-dimensional (3D) data. We propose the use of the relationship among depth information, pixel deviation, and imaging position to correct the LCA among three color channels. Compared with existing LCA correction methods using polynomial fitting, the method takes into account the effect of imaging position on LCA distribution, thus removing the time-consuming operation of polynomial fitting for each pixel. Sufficient experiments are performed to prove that the proposed LCA correction method is able to effectively decrease the influence of the LCA and attain accurate 3D shape measurement in color FPP.

Laser displays commonly utilize spatial light modulators (SLM) as imaging devices, but the contrast ratio is limited by uniform illumination and the diffraction properties of SLM, which hinder the realization of high dynamic range (HDR) within a single frame. We investigate the fundamental diffraction properties of a phase light modulator (PLM) using the blazed grating model, explore its capability to steer beams, and evaluate its uniformity as a light field modulator. By employing PLM to modulate various light field distributions and conducting contrast ratio tests in laser display systems, we examine the illumination characteristics of PLM. We specifically select a representative light field distribution to assess the contrast ratio and analyze how altering the light field distribution through PLM affects it. Our findings reveal that reducing the proportion of individual spot size relative to the entire image area enhances the contrast ratio when there is a single spot area present in the modulated light field; conversely, increasing their number decreases the contrast ratio when multiple spots are present in the modulated image. By integrating PLM with a digital micromirror device (DMD), we have validated the feasibility of manipulating light field illumination in display systems, resulting in a remarkable improvement of over 300 times in contrast ratio and achieving HDR of projected images. Through utilization of the central light spot image to confirm its smaller proportion within the entire image, we can enhance the contrast ratio by more than 100 times and peak brightness by over 70 times. These findings demonstrate the viability of employing this approach to achieve HDR in laser displays.

We introduce an innovative optical phase shifter that utilizes a microelectromechanical system (MEMS) tuning mechanism, providing low power consumption, fast tuning, small dimensions, and high performance. In this approach, a rotating MEMS actuator is presented, enabling bi-directional actuation, which allows for both an increase and decrease in the effective mode index and phase shift. This provides lower operating voltage and shorter response time compared with other existing MEMS actuators. The proposed device exhibits impressive functional characteristics, including an overall dimension of 1920 μm2, an effective phase shifting length of 30 μm, an insertion loss of 0.033 dB, an operating voltage of 10 V, a tuning time of 2.5 μs, and a phase shift of more than 3π at a wavelength of 1550 nm. With such advantages, this device is well-suited for use in large photonic integrated circuits, enabling complex applications such as artificial intelligence applications including machine learning, neural networks, and neuromorphic computing.

Stimulated emission on the ultraviolet and blue transitions in Cs has been achieved by pumping via two-photon absorption and four-wave mixing for the pump transition 62S12→82D32,52. The emission performance of the optically pumped cesium vapor laser operating in ultraviolet and blue has been extended to 650 nJ/pulse for 387 nm, 1 to 3 μJ/pulse for 388 nm, 200 nJ/pulse for 455 nm, and 500 nJ/pulse for 459 nm. Emission performance improves dramatically as the cesium vapor density is increased, and no scaling limitations associated with energy pooling or ionization kinetics have been observed.

The photonic hook (PH) generated by a partially illuminated high-index dielectric particle hemi-immersed in the dielectric film is investigated. A tunable PH is generated from a cylinder deposited on a dielectric film, and the cylinder is partially illuminated by the placement of a thin, flat aluminum mask in front of it. The effects of film type, mask width, and height of dielectric film are mainly discussed. The results provide a novel design method for PHs, which have potential applications in optical manipulation and high-resolution imaging.

The integrated optical gyroscope is a highly possible way to achieve chip-level gyroscopes. We proposed and simulated a three-dimensional Si3N4 optical interconnect platform. It transforms the waveguide coil from a single-layer structure to a multi-layer structure, which can increase the sensing area of the coil under the same footprint. The proposed platform with low interlayer transition loss and crossing loss can reduce the overall loss in the coil and improve the theoretical angular random walk (ARW). A quadruple-layer sensing coil with a maximum radius of 30 mm and a total length of 2.08 m is derived, which can attain an ARW of 0.15 deg/√h and an insertion loss of 3.15 dB in theory.

We present a quadrature phase-shift keying (QPSK) signal demodulator that combines the graphene photodetector with symmetrical electrodes and an optical hybrid based on standing wave interference to demodulate the QPSK signal. Compared with a conventional QPSK demodulator, which contains a hybrid based on multimode interference couplers and two pairs of balanced detectors, the proposed demodulator can greatly decrease the complexity and size. The simulation with the finite-difference time-domain method demonstrates that the demodulator can achieve QPSK signal extraction. We further discuss the effective responsivity, bandwidth, and error vector magnitude of the QPSK constellation diagram. The scheme will provide a feasible approach for realizing high-speed compact QPSK coherent receivers theoretically.

Visible light communication (VLC) is considered an effective complementary solution for indoor wireless communication to achieve high-speed and secure data transmission. In the random access process of VLC, the collision problem caused by hidden terminals is prominent. The multiple packet reception (MPR) technique can effectively mitigate the multi-terminal collision in VLC and improve the performance and reliability of the system. We proposed, considering the MPR-capable uplink VLC system, a quality of service (QoS)-constrained admission control scheme based on the improved coati optimization algorithm (COA) to guarantee delay requirement. First, we adopt the ALOHA mechanism as the basis of the service, and the arrival stream consists of a primary arrival stream and a background arrival stream. Then, we evaluate the delay performance using the large deviation theory, and the optimization problem with the objective of maximizing the arrival rate is constructed. Finally, we incorporate a cat chaotic map, Lévy flight strategy, and t-distribution mutation strategy to improve COA, which makes solving the optimization problem more efficient. Simulation results show that the proposed algorithm is dependable and can improve the system resource utilization.

When utilizing the tunable diode laser absorption spectroscopy technique for gas concentration measurement, the second harmonic signal is significantly affected by noise, leading to a decrease in measurement accuracy. We proposed a noise reduction algorithm to address this issue. It combines a multi-resolution singular value decomposition (MRSVD) and an improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) algorithm optimized by the improved crested porcupine optimizer (ICPO) algorithm. First, the MRSVD algorithm is utilized to denoise the signal, followed by optimizing the ICEEMDAN parameters using the ICPO algorithm. Subsequently, the signal is decomposed by ICEEMDAN and reconstructed based on the correlation coefficients of intrinsic mode functions to obtain a final denoised signal. In the experiment, the proposed algorithm achieved a signal-to-noise ratio of 116.8707 dB, and the linearity between the gas concentration and the maximum value of the second harmonic signal improved from 0.9893 to 0.9984. Moreover, the average relative error of the gas concentration decreased by 3.12%. The proposed algorithm exhibits superior denoising efficiency compared with traditional methods and proves effective for denoising open optical range signals.

We investigate and analyze the transmission performance of free-space optical (FSO) communication systems at three different working wavelengths, 1.55, 4, and 9 μm, under the combined effects of weather conditions (rain, snow, fog, and haze) and atmospheric turbulence, which is modeled by the gamma-gamma turbulence model. The simulation system of FSO communication based on quadrature phase-shift keying (QPSK) modulation format with a data transmission rate of 10 Gbps is built using OptiSystem software. The results show that the working wavelength has less influence on the transmission performance of the FSO communication system under rainy weather and turbulence conditions. In snowy and turbulent conditions, the short-wavelength laser has a stronger transmission advantage. In fog and turbulence situations, the transmission performance of the FSO communication system is significantly improved with the increase of wavelength. Under the combined influence conditions of haze and medium turbulence, the transmission distance of 9-μm laser is 2.67 and 1.56 times that of 1.55- and 4-μm lasers, respectively, when the bit error rate is 10−9. The results can provide an important reference for the design and optimization of practical FSO communication systems.