Editor-in-Chief Adam Wax announces two new senior editors.

Optical Engineering lists the reviewers who served the journal in 2021.

The imaging quality of astronomical targets observed by ground-based telescopes is affected by atmospheric turbulence and the image resolution is seriously reduced. A deep attention generative adversarial network is proposed to restore the astronomical image and to learn the end-to-end imaging law between the blurred image and the ground truth image from image dataset directly. The attention mechanism module is designed to improve the performance of the network. Based on the conventional theory of atmospheric imaging of telescopes and combining optical system parameters, a series of astronomical images are simulated to establish a dataset for training networks. The proposed method is verified by simulated test image and real astronomical image. The experimental results show that the proposed method can effectively eliminate the influence of atmospheric turbulence and improve the resolution of astronomical images. We demonstrate the possible and good prospects for future applications of deep learning to high-resolution imaging of astronomical images.

A metalens is a planar optical device that can accurately control the phase, polarization, and amplitude of light. Aiming at the application requirements of polarization imaging equipment for miniaturization, integration, and common field of view, we designed and fabricated two kinds of orthogonally polarized metalenses based on amorphous silicon and fused quartz. These metalenses can achieve orthogonal linear or circular polarization light imaging with a common field of view. The samples with a 2-mm diameter and 20-mm focal length were fabricated by electron beam exposure. The test results show that these metalenses can realize the imaging of orthogonal linearly or circularly polarized light simultaneously; the focusing efficiency is more than 50%, and the polarization contrast is >22  dB.

We propose an integral three-dimensional (3D) display system with a wide viewing zone and depth range using a time-division display and eye-tracking technology. In the proposed system, the optical viewing zone (OVZ) is narrowed to a size that only covers an eye to increase the light ray density using a lens array with a long focal length. In addition, a system with low crosstalk with respect to the viewer’s movement is constructed by forming a combined OVZ (COVZ) that covers both eyes through a time-division display. Further, an eye-tracking directional backlight is used to dynamically control the COVZ and realize a wide system viewing zone (SVZ). The luminance unevenness is reduced by partially overlapping two OVZs. The combination of OVZs formed a COVZ with an angle that is ∼1.6 times larger than that of the OVZ, and an SVZ of 81.4 deg and 47.6 deg for the horizontal and vertical directions, respectively, was achieved using the eye-tracking technology. The comparison results of the three types of display systems (i.e., the conventional system, our previously developed system, and our currently proposed system) confirmed that the depth range of the 3D images in the proposed system is wider than that of the other systems.

Infrared (IR) dim small target detection in heavy noise has always been a challenging research task. Detection methods based on energy accumulation have achieved effective detection results. However, the general inaccuracy of the target energy distribution model for subpixel motion weakens the performance of these detection methods. The discretization process of a target is described in detail, and the effect of two-dimensional (2D) subpixel motion on the energy spatial distribution of the target is introduced. Based on the analysis of target energy distribution for subpixel motion, a novel energy spatial distribution model of the target for 2D subpixel motion (NESDSM) is proposed. The NESDSM model well describes the energy spatial distribution variation of a subpixel moving target. Furthermore, to verify the accuracy of the model, a target detection method based on energy compensation accumulation (ECA) is proposed. The ECA synchronously enhances the signal noise ratio and suppresses noise effectively. Finally, experimental results show that ECA has better detection performance in comparison with traditional energy accumulation methods. Moreover, by analyzing the performance of ECA in a quantitative manner, ECA shows an average 10.5% improvement in the output SNR in comparison with energy accumulation methods.

Aero-optical beam control relies on the development of low-latency forecasting techniques to quickly predict wavefronts aberrated by the turbulent boundary layer around an airborne optical system, and its study applies to a multidomain need from astronomy to microscopy for high-fidelity laser propagation. We leverage the forecasting capabilities of the dynamic mode decomposition (DMD) — an equation-free, data-driven method for identifying coherent flow structures and their associated spatiotemporal dynamics — to estimate future state wavefront phase aberrations to feed into an adaptive optic control loop. We specifically leverage the optimized DMD (opt-DMD) algorithm on a subset of the Airborne Aero-Optics Laboratory-Transonic experimental dataset, characterizing aberrated wavefront dynamics for 23 beam propagation directions via the spatiotemporal decomposition underlying DMD. Critically, we show that opt-DMD produces an optimally debiased eigenvalue spectrum with imaginary eigenvalues, allowing for arbitrarily long forecasting to produce a robust future state prediction, while exact DMD loses structural information due to modal decay rates.

Accurate 3D perception is vital for the localization of mobile robots and autonomous vehicles. Sparse 3D LIDAR scanners and 3D vision sensors (stereo and RGB-D cameras) are commonly used environment perception sensors. The former could provide accurate but sparse-range data, while the latter is dense but full of uncertainty. Since the acquired depth map by each sensor alone could not accurately perceive complex surrounding environment, an innovative probabilistic fusion model based on Bayesian Kriging (BK) is proposed for dense high-precision depth map estimation, to fully utilize the complementary characteristics of the two distinct sensors. Combing the geometric piece-wise planar hypotheses of the scene, the noisy disparity map from the 3D vision sensor is segmented into multiple small planes. In each segmented plane, the BK-based fusion estimator is founded to predict depth for each pixel with sparse scattered LIDAR points. In particular, we focus on analyzing the spatial variation prior and correlation between these two types of data, based on regionalized variable theory. Experiments on various scenes of KITTI stereo datasets are carried out to demonstrate the effectiveness of our algorithm, and validate the superiority compared with existing fusion methods.

The continuous-variable quantum key distribution experimental system requires the randomness and speed of a Gaussian modulator. We present the hardware design for a Gaussian random number (GRN) generator based on the Box–Muller method, which can be implemented on a field-programmable gate array (FPGA). An external high-speed true random number generator application-specific integrated circuit (ASIC) is used to this end. The ASIC operates faster and more independently compared with other Gaussian algorithms based on a linear feedback shift register. The trigonometric and logarithmic functions are calculated using the nonuniform piecewise linear approximation. The calculation of the Gaussian random modulus and phase value is realized using this hardware. Compared with an arbitrary waveform generator, the GRN can be uploaded to a computer to estimate the security key rate. Furthermore, the GRN generator accurately provides a Gaussian probability density function that passes the Jarque–Bera inspection and Lilliefors tests. The proposed FPGA-based system is demonstrated to convert eight-channel 320-Mbps uniform random numbers to 40-MHz 16-bit GRN in real time. Finally, the control of the optical module and Gaussian modulation is realized via the FPGA-based outputs of four dual-channel, 16-bit, 1-giga samples per second digital-to-analog converters.

An accurate large-scale positioning system is a high-precision distributed large-scale dimensional metrology system that is widely used in smart manufacturing and assembly applications. The system comprises multiple transmitters with locations and orientations that are typically calibrated based on auxiliary measurement equipment. However, the calibration method is complicated and time consuming. We propose a rapid and flexible calibration method based on the highly precise three-dimensional coordinate control network established by a calibration bar with an accuracy of   ±  0.005  mm, including both estimation and optimization algorithms. Exploratory experiments were performed to validate the feasibility of the proposed calibration method. The results demonstrate that the proposed calibration method enables the repeated measurement errors to be maintained at <0.05  mm in X and Y and <0.04  mm in Z. The standard deviation after calibration was 0.18 mm in comparison with the laser tracker.

A self-injection locking method for resonant micro-optical gyroscope (RMOG) is proposed. The resonator is used as the sensitive element of the gyroscope and the device of light compression locking. The fiber and waveguide ring resonator (WRR) are designed and fabricated, consecutively. Both of the resonators can narrow the linewidth by three orders of magnitude, and the phase noise and the relative intensity noise can be reduced to −120 and −150  dBc  /  Hz, respectively. By evaluating the locking effect, WRR is more suitable for optical locking of a resonant micro-optical gyroscope (RMOG) light source, and its theoretical locking accuracy can reach 6.02 deg/s.

We present the design and performance verification of a fiber-fed Fourier transform spectrograph (FTS) for spectroscopy in the optical band with the ability to reach a maximum optical path difference of 15 mm and allowing for an adjustable spectral resolution (λ  /  Δλ) between 1 and 15,000. The designed FTS system was successfully constructed using only off-the-shelf optical components. The technique for correction of the phase distortion in the FTS using a metrology interferogram and cubic spline interpolation was investigated and discussed. The contrast performance and the instrument line shape of the FTS were measured and analyzed. To further verify the performance of the developed system, the absorption spectrum of the sunlight was measured and compared with a synthetic model with identified telluric and absorption lines. The result shows that the developed FTS can detect the absorption lines with a spectral resolution close to 15,000.

The optical method of photon correlation for the measurement of the free-field acoustic pressure has meaningful applications, such as forming a traceability chain based on the absolute measurement for various types of acoustic sensors. The optical method based on photon correlation has been considered to be a potentially new primary standard that overcomes the limitations of existing acoustic standards based on microphones. The key issue is accurately obtaining the spacing of the interference fringes or equivalently the crossing angle between two laser beams. Usually, the trigonometry method is used to calculate the crossing angle, which imposes limitations on the accuracy of the measurement. Optical microscopic imaging is introduced to directly measure the spacing of the interference fringes in the acoustic pressure measurement based on photon correlation method for the first time. We propose directly measuring the spacing of the fringes where the standard resolution target is placed in the interference region to produce the superimposed image with the fringes and recording the results by the CCD. Both the calibration of magnification and the measurement of the fringe spacing are performed through the same single-shot image. The uniformity of the interference fringes is analyzed by numerical simulation, and the optical configuration is optimized according to the influence of the crossing angle of the two Gaussian beams. The experimental system is built based on the photon correlation method. The experimental results show that this method improves the accuracy of the acoustic pressure measurement by 0.03 to 0.82 dB in the frequency range of 0.5 to 4 kHz in free-field conditions.

Based on the spatial phase delay of beams, a displacement measurement method is proposed for homodyne interferometers. In this method, two detectors are arranged in the interference spot to collect signals. Based on the algorithm of least squares fitting the parameters of the ellipse equation, the relative phase of the signals is solved to calculate the displacement. The proposed method uses optical fiber bundles for beam reception, which is more compact in structure than the traditional quadrature phase calculation method, and eliminates polarization mixing. The spatial delay phase in the method can be any unknown constant, which makes it more applicable in practice. The feasibility of this method is verified by ZEMAX simulations and experiments. The experimental results show that the 3σ of errors without the effect of power noise and vibration is 7.2 nm.

For optical measurement of high-temperature components, it is a challenge to analyze the measurement error caused by light refraction due to the inhomogeneous distribution of the air refractive index. Aiming at the problem of line laser measurement under the high-temperature environment, a method for analysis of line laser measurement error on high-temperature surfaces combined with backward ray tracing technology is proposed. The temperature field of the air is simulated based on the heat conduction theory, and the air refractive index is obtained according to the classical empirical formula. Combining with the refraction law of light and the laser triangulation method, the deviation of the spatial position corresponding to each point on the charged-coupled device is calculated. The imaging principle of backward ray tracing is applied to obtain the actual imaging point, and the measurement error of the sensor is calculated. The experiment results prove that the proposed method can effectively evaluate the line laser measurement error under the high-temperature environment. We analyze the system error of the laser sensor under high-temperature conditions and promote the development of high-temperature components on-machine measurement.

Exact ray tracing is the fundamental tool of geometric optics, it constitutes the foundation on which aberration theory and, therefore, optical design is based. We present the KrakenOS, a Python library focused on the accuracy of ray tracing and the generation of systems composed by optical surfaces with arbitrary shapes and orientations, as well as a compendium of practical examples for the use of our library. We describe a series of quality tests to compare the results obtained from ray tracing with KrakenOS with respect to those obtained with the commercial software Zemax. Among the performance computations, we include the final intersection coordinates with optical surfaces, the resulting director cosines, the calculation of surface-to-surface length of the optical path, the energy of the transmitted and reflected resulting rays, Zernike standard coefficients from wavefront fitting, and a comparison of the resulting intersection coordinates with a larger optical system. The difference between our results and those of Zemax is of the order of 9.0  ×  ^{10  −  8} mm, demonstrating that KrakenOS can be used in industrial or scientific work with high precision requirements for simple and very complex optical configurations.

The process of laser cladding can be described as the rapid melting and deposition of metal powder on the dieface by high-energy laser beam, and the deposited layer possesses specific properties which meet dieface requirements. It is of great significance to study the influence of process parameters on the geometry of cladding layers. To better control the geometric characteristics of laser cladding layer, a modified mathematical model is proposed to predict the height and width of cladding layers in accordance with process parameters (namely laser power, scanning speed, powder feeding speed, and overlapping rate). Then, a comparison of predictive results with experimental results shows that the proposed model can accurately predict the height and width of cladding layers. Meanwhile, this model is in good agreement with experimental height and width of cladding layers for single- and double-track. So, the model can guide the monitoring and controlling of laser cladding process, especially the control of cladding layer height and width.

A microphone was used to study the characteristics of acoustic emission for millisecond laser-induced damage of BK7 glass. Different temporal and spectral distributions were obtained for the front and rear surface damage processes. The front surface damage was associated with the strong thermal melting process, and the size of the conical molten pit was strongly linked to the intense oscillating period of the acoustic signal. The effects of the detection distance and angle on the spectrum below 5 kHz, which were induced during the front surface damage process, were found to be associated with the distribution of the ejection expelled out of the molten pit. The results indicate that the detection of acoustic emission can be used as a real-time online method to obtain information on the millisecond laser-induced damage.

We present a tunable, general-purpose, light-emitting diode-based spectrally tunable light source that achieves high-precision fitting of chlorophyll b absorption spectra from 400 to 700 nm using 11 LEDs with different peak wavelengths. The target spectrum is divided into gentle and steep segments, and the optimal number of LEDs to be used at different wavelengths is determined by the segment fitting method. Then, the results were further optimized by fitting experiments, and finally the best combination consisting of 11 different peak wavelength LEDs was obtained. The results showed that the correlation coefficient R² reached 0.9664. The precise control of each LED current by means of the pulse width modulation signal output from the microcontroller, and the output spectrum of the system was measured using a spectrometer. The results show that the correlation coefficient R² reaches 0.9315.

In chip-integrated optical circuits, the polarization beam splitter (PBS) is one of the core elements that separates TE/TM modes and transmits them to different ports. We designed an ultracompact Si-based PBS with a footprint of 2  μm  ×  2  μm by an intelligent inverse design method. This method combines the method of moving asymptotes algorithm and the finite element method, and it has a high polarization extinction ratio (PER) and large splitting bandwidth from 850 to 1450 nm. The transmission of the TE and TM modes reaches 93% and 73%, respectively, and the average PER is 21 and 20 dB, respectively. Moreover, we developed other PBSs with different materials and different directional output ports that have wonderful splitting performance in different wavebands.

We present a method of hyperspectral snapshot imaging that is based on diffraction in an intermediate image plane. In this intermediate image, plane diffracting microstructures are used to deflect light toward an iris that performs spectral filtering. The method is related to imaging spectrometry with a reduced spectral resolution. However, the spectral shifts of the signal are detected very accurately at a potentially low cost. Our prototype system is capable of detecting a spectral shift of 0.5 nm, and the spectral operating range reaches from 510 to 700 nm. Application-specific arrays of microgratings are lithographically manufactured and lead to custom spatial and spectral sampling of an (intermediate) image. Compared with filter-based hyperspectral snapshot imaging, this approach avoids the difficult manufacturing of the mosaic filter array, but the spatial and spectral resolutions will become coupled. This leads to an uncertainty product for spatial and spectral resolutions. We explain the basic principle and show an experimental verification based on a first laboratory prototype.

The saturable absorption properties of Co^2  +  :  MgAl₂O₄ crystals in three different cutting directions were studied experimentally. The characteristic of the transmission of polarized incidence light through the [100], [110], and [111]-cut Co^2  +  :  MgAl₂O₄ single crystal was investigated. The [110]-cut crystal had the maximum transmittance observed. We conclude that using a [110]-cut Co^2  +  :  MgAl₂O₄ crystal to form a Co^2  +  :  MgAl₂O₄  /  Er,Yb:glass passive Q-switched microchip laser can improve the output characteristics of the laser, such as pulse energy and extinction ratio without changing any other parameters.

In recent years, quantum communication technology has gradually entered the practical stage. Multiple quantum key distribution (QKD) networks have been built and tested all over the world. However, quantum communication networking mode always evolves from a point-to-point network to a many-to-many network. The major challenges in quantum communication are secret key rate, distance, cost, and size of QKD devices. We proposed a low-cost, lightweight-client, twin-field QKD network with wavelength division multiplexing (WDM). The proposed implementation adopts polarization multiplexing, time-division multiplexing, and WDM technology to solve all these major challenges and implement a many-to-many dynamic communications network. Furthermore, our scheme can effectively reduce the cost to less than half of that of current QKD networks and has reference significance for large-scale deployment of QKD networks.

We studied the structural and elemental evolutions during the femtosecond laser percussion drilling of high-aspect-ratio diamond microholes. Microholes 225-μm-deep having an aspect ratio of 15 were drilled with an exposure time of 100 s and a laser power of 60 mW. It is found that when the specimen was machined by femtosecond laser at low power and short exposure time, the laser-affected zone (LAZ) may be still solid in the interior rather being void, even it reached the bottom of the diamond. A clear crack appeared between the solid portion and pristine diamond. Elemental analysis revealed that oxygen was incorporated into the solid portion of the LAZs, and its atomic percentage reached 6.5% for a laser power of 10 mW at initial position and decreased as the depth increased in the solid portion. The wall of the void contained nearly no oxygen. Furthermore, nanoripples were observed on the sidewall surface of the hole.

Global positioning system uses satellite signals to infer position. In buildings, however, these signals are attenuated and scattered by walls and other objects, making it impossible to measure an exact position inside them. Using the location information supplied by the lighting infrastructure, we propose an indoor navigation system based on visible light communication (VLC). The application presented relates the use of robotic solutions in a modern, efficient warehouse. As warehouses and distribution centers compete for a competitive advantage, automated guided vehicles (AGVs) are becoming increasingly popular. Our work reports a VLC-based geolocalization and navigation system to address automated logistics control. The proposed system includes VLC links and a space layout connecting RGB lamps and AGVs. The controlling flowchart, methods, and the data frame content required to support bidirectional communication between the infrastructure and AGVs are also discussed. The communication network is supported by VLC emitters using trichromatic RGB white LEDs and dedicated receivers based on a-SiC:H/a-Si:H photodiodes with selective spectral sensitivity. The downlink channel establishes the infrastructure-to-vehicle link and transmits information through the modulation of the red and blue emitters of the white RGB LEDs. The decoding strategy is based on accurate calibration of the output signal. Synchronization of the transmitted frames is used to ensure the identification of the start and end of each message. The uplink channel is used for the communication from the vehicle-to-infrastructure. This link is established using a single optical signal. The communication flowchart model was defined to establish the different communication modes and types of messages transmitted by each of the system entities. We present basic system requirements, give details on the network topology, define the communication flowchart model, and discuss the methodology used to decode the multiplexed signal transmitted by simultaneous emitters.

The effects of temperature on the dispersion properties of a square lattice photonic crystal fiber (PCF) have been studied. Holes in the cladding part of PCF are packed with a semiconducting material, InSb, whose characteristics depend upon temperature in the terahertz optical frequency. The effective index of PCF is calculated with the help of a semivectorial finite difference technique. Using the effective index values, computation of chromatic dispersion parameters is done, which are plotted against wavelength. Four temperatures have been considered in our work from 290 to 335 K in equal steps. The results depict that as the temperature rises, the values of effective indexes of PCF decrease while dispersion of the fiber increases. In places where temperature is not constant and keeps varying, this type of PCF can be installed for multiple optical channel dispersion compensating applications. It has also been observed that with the change in surrounding temperatures, mode carrying capacity of the fiber remains unaffected, which makes this fiber suitable for special applications, such as distributed perimeter sensing of chemical plants.

A photonic crystal fiber is designed with chalcogenide glass As₂Se₃ as the base material. As₂Se₃ has a high refractive index and a high nonlinear refractive index; as a result, it has a desired application for strengthening birefringence and nonlinearity. The outer layer of the fiber is a regular decagonal structure composed of four layers of circular air holes, and the inner cladding area is composed of four elliptical air holes arranged in a diamond pattern. The influence of the size of the circular air holes in the fiber cladding, the thickness between each layer, and the size and position of the elliptical air holes in the inner cladding area on the birefringence is analyzed and studied using the full vector finite element method. The results show that the birefringence value of the fundamental mode of the fibers is 0.108 at a wavelength of 1.55  μm, and at the same time, the nonlinear coefficients of the X and Y polarization states are 240 and 197  m^−  1  ·  W^−  1, respectively.

We demonstrated a simultaneous residual chromatic dispersion (CD) and optical signal-to-noise ratio (OSNR) monitoring method for non-return-to-zero on-off keying signals by employing the delay-tap sampling and image processing techniques. Delay-tap sampling scatter plots reflect the signal pulse shape change and image processing can extract the contour of the scatter plots. Numerical simulation shows that the OSNR monitoring range is from 12 to 32 dB with <0.5  dB error and the CD monitoring range is from 0 to 1360 ps/nm. In the experiment, the OSNR monitoring range is from 14 to 30 dB and the CD monitoring range can go up to 1275 ps/nm.

In a high-speed free-space optical communication system, a far-field space laser is usually coupled with a single-mode fiber via the optical antenna and then transmitted to a detector by an optical fiber. However, atmospheric turbulence will affect the coupling effect of the optical fiber. A fuzzy fraction-order stochastic parallel gradient descent (SPGD) is proposed based on the traditional SPGD algorithm to achieve efficient fiber coupling. In this algorithm, the fraction-order differential is integrated into the SPGD for the purpose of improving the speed of the fiber coupling. Furthermore, the fuzzy control method is combined with the fraction-order SPGD approach, and fuzzy rules are designed for the gradient. The fractional order and learning rate are adjusted adaptively in each iteration. In the simulation, the fuzzy fraction-order SPGD can converge to the extreme point quickly and has excellent robustness.

A hybrid Kretschmann configuration-based surface plasmon resonance biosensor is investigated to detect formalin in water was proposed. The modification is done in the conventional sensor by adding the indium phosphide (InP) and black phosphorus (BP) material layer. The silver (Ag) metal thickness is 45 nm, the optimized thickness of the metal for the proposed design. The thickness of the InP and BP materials 2 and 0.34 nm are considered. For three InP layers and one BP layer, the maximum sensitivity of 250.2  deg  /  RIU is achieved. The BP layer is used to improve the biorecognition ability of the sensor. The performance of the sensor is analyzed using the angular interrogation method. The proposed sensor is investigated for the aqueous sensing medium. The InP is an air-stable semiconductor material and has applications in chemical, medical, and biological fields.

A high-sensitivity optical sensor based on a Fabry–Pérot interferometer (FPI) has been demonstrated. The cavity of the FPI is formed by two parallel half-reflective film-coated glass substrates with a distance of 1 mm and works as the sensing area. The interaction between the propagating wave and the analyte gives the sensing signal. High sensitivity of 1149  nm  /  RIU has been achieved for the wavelength interrogation. The Fabry–Pérot sensor can be made into a large array with multiple microfluidic channels to detect the different types of analytes. It has great potential in biochemical sensing.

To study the influence of laser intensity and temperature on the performance of laser power converters (LPCs), a two-dimensional model of an In_0.3Ga_0.7As LPC by the finite element method was established. The validity of the model was verified by comparing the theoretical value with the experimental results. The factors that influence the performance of LPCs were analyzed from the perspective of recombination. Results indicate that the existence of grids at the front surface improves the collection of carriers efficiently, and the influence of temperature and laser intensity on carriers recombination is quite different at 0 and V_m (voltage at maximum power point) bias voltages. The research of this paper provides a reference for the optimization of LPCs.

The design and development of a multiband ceramic material-based optical antenna are discussed. A square-shaped aperture is utilized to excite the silicon-based dielectric resonator. This type of excitation system provides the capability to create a triple hybrid mode (HEM_11δ, HEM_12δ, and HEM_{11δ  +  2}) inside the cylindrical-shaped ceramic material. Due to this feature, the proposed aerial is operating over diverse frequency bands, i.e., 117.5 to 140 THz, 158 to 165.5 THz, and 175.2 to 190.5 THz, respectively. Stable radiation characteristics as well as the good value of gain (about 4.0 dBi) make the proposed nanoradiator applicable for hyperspectral imaging system (125 THz) and VLC for wireless LAN (160  /  180  THz).