Traditional star image identification methods use adjacent stellar angular distances to form identification features. The missed detection of high-magnitude stars due to noise interference affects their identification accuracy. We propose a star image identification method based on perceptual hash features. The multiple Gaussian distribution superposition constructed by stars within a certain range around the center star forms the unique standard identification image of that star, in which the brightness distribution is determined by stellar magnitudes. The perceptual hash feature of the standard identification image is then used as a standard identification feature. The observation feature is extracted from the identification image as-constructed by the star points extracted from the star image. Finally, the observation feature is matched with the standard feature to identify the star image. Simulation results indicate that the proposed method can efficiently identify star images and effectively prevent missed stars from influencing the matching results.

We proposed an incoherent self-interference digital holography imaging system based on the Michelson interferometer. The proposed system records holograms of USAF1951 resolution target, herbaceous stem crosscut, and osteocyte. The reconstruction of the captured hologram using a three-step generalized phase shift can effectively eliminate bias and a twin image and obtain a clear reconstructed image. Element 3 in group 9 on the USAF1951 resolution target can be clearly seen, and the resolution achieves 645  lp  /  mm. Results indicate that the diffraction distance can influence the reconstructed image quality, which was confirmed by analyzing their relationship. In addition, the hair hologram was reconstructed, thereby demonstrating that the proposed system can record a 3D image of the object.

A compound eye optical system design allows us to construct a compact image scanner with a large field of view and a large depth of field, both of which are beneficial for use in a copier’s flatbed scanner. Our prototypes are constructed of 32 or 28 imaging units, which are ommatidia, and the representations from the imaging units are electrically combined. Since the arrangement of the imaging units is a key factor in combining the images correctly without any loss at the boundaries, we discuss two types of arrangements along with results of their prototypes: a one-line arrangement of varying magnification imaging units and a two-line staggered arrangement of telecentric imaging units. We also discuss the effectiveness of wavefront coding (WFC) in suppressing chromatic aberration, which is caused using cheap refractive imaging units, along with experimental results of applying both cubic- and quartic-phase-modulated WFC.

New hydrodynamic improvements have been developed in order to enable pulsed polishing with the HyDRa system. The operational parameters of the tool are not affected by these modifications, i.e., tool bias and the tool’s floating capability are not lost, and a linear erosion function is produced. The minimum removal is no longer ruled by maximum computer numerical control speed, allowing for high-precision removal that can be taken from zero to the maximum attainable of the tool, in minimum increments of 3.5  nm  /  ms. This modification also improves the convergence rate of the polishing process toward the desired surface. This development guarantees a high-speed, pulsed operation that enables the tool to be used in a variety of polishing modes, ranging from discrete pixel to continuous pulse width modulation (PWM) polishing. This new capability opens a wide range of applications that can now be tackled with the system, such as zonal and tessellated polishing. PWM capability also allows for simultaneous, multi-head polishing of large optical surfaces.

When the optical homogeneity of parallel plates is measured using wavelength phase shifting interferometers, the nonlinearity of phase shifts caused by nonlinear wavelength tuning results in spectrum aliasing, and thus the optical homogeneity cannot be obtained accurately. We propose a nonuniform fast Fourier transform algorithm based on low-rank approximation and Taylor expansion (LRTE-NUFFT) to solve the problem. The principle of the LRTE-NUFFT method is introduced and compared with the FFT method and the nonuniform fast Fourier transform algorithm based on fast Gauss gridding (FGG-NUFFT) method proposed earlier through simulations and experiments. The results show that LRTE-NUFFT can improve the accuracy of the optical homogeneity measurement of parallel plates compared with the FFT method, and it can also improve the computational efficiency compared with the FGG-NUFFT method.

Mo/Be multilayers are promising optical elements for extreme ultraviolet (EUV) lithography and space optics. Experimentally derived optical constants are necessary for accurate and reliable design of beryllium-containing optical coatings. We report optical constants of beryllium derived from synchrotron radiation-based reflectivity data of Mo/Be multilayers. Results are in good agreement with available data in the literature obtained from the well-known absorption measurements of beryllium thin films or foils. We demonstrate synchrotron based at-wavelength reflectometry as an accurate and non-destructive technique for deriving EUV optical constants for materials that are difficult or unstable to make thin foils for absorption measurements.

An adaptive telescope was developed to perform measurements using the confocal photothermal microscopy technique. The telescope automatically aligns to reinject the reflected probe beam as the measurement scans over irregular surfaces. The system uses DVD lenses that adapt to surfaces through controlled movements. Alignment algorithms are presented along with measurements on complex surfaces.

Reed woodwind instruments pose great challenges in modeling because their functioning is based on a combination of hydrodynamics, acoustics, and mechanics. Reproducible measurements therefore remain crucial for further development of reeds and instrument mouthpieces. We present a method to measure reed behavior and acoustic response under realistic, well-defined playing conditions. A measurement setup based on constant phase stroboscopic digital imaging correlation (DIC) is proposed. A computer-controlled timer delay triggering system combined with high-power LEDs allows one to obtain clear images at different phases of the vibrational period. From these high-quality images, digital image correlation DIC allows one to analyze both displacement and strain over the full visible surface of the reed. The presented technique can also be applied to other nonfrequency-imposed vibrating structures. The method is demonstrated on a saxophone reed, and we show how it can be used to determine playability range of a mouthpiece and vibrational behavior of the reed.

Speed range is an important specification of coherent Doppler wind lidar (CDWL). However, it is difficult to identify the lower speed bound of CDWL, because the Doppler signal is often overlapped or covered by relative intensity noise (RIN) at the low-frequency end of the spectrum. Therefore, how to distinguish the Doppler signal and the RIN at the low frequency is always an important issue. In the optical information processing, Rayleigh criterion specifies the spatial resolution limit, which is the minimum distance between the two distinguishable Airy disks. Due to the rigorous one-to-one correspondence between optical signals and electrical signals in photoelectric conversion, Rayleigh criterion can be extended to the electrical signal processing. We mapped the Doppler signal and RIN into the Airy disk profile and used the generalized Rayleigh criterion to study the signal resolution limit to define the lower speed bound of the system. The comparative experiments were carried out and the results were consistent with the generalized Rayleigh criterion. It shows that the generalized Rayleigh criterion is available and effective and can be used as a new method for the signal resolution on coherent Doppler wind measurements.

Chalcogenide glasses are amorphous solid materials formed from chalcogen elements bonding with metals to form typically in binary or tertiary compounds. One family of chalcogenide glasses, based on gallium and lanthanum sulphides, possesses properties important for the infrared (IR) window transmissions and IR applications; these include thermal stability, high solubility of rare earth ions, low phonon energy and high laser damage threshold. Efforts have been made to produce new chalcogenide glasses that can extend the IR transmission window further into the IR. Work has led to the successful melting of a selenium-modified gallium lanthanum sulphide (GLS-Se) glass that can transmit up to 15  μm, however these glasses have, to date, only been demonstrated in bulk glass form. We aim to develop processes for the fabrication of chalcogenide optical fiber to exploit the properties of chalcogenide glasses. Several potential applications include sensing for the civil, medical, and military areas, as these materials offer transmission over much of the molecular fingerprint region (2 to 25  μm). The aim of our work is to understand and control the thermal properties and stability of GLS-Se glasses without compromising their optical properties, in order to produce transparent glass rods and demonstrate the feasibility in fabrication for structured optical preforms by extrusion, as the first step to achieve optical fiber from GLS-Se glass.

We investigated a high-precision grating interferometer displacement measurement system that can be applied to high-end immersion lithography machines and explained its composition and measurement algorithm. By analyzing the optical path variation caused by the installation error of the grating interferometer, we calculated the influence of the installation error on the displacement measurement. A displacement measurement model of a grating interferometer using three read heads was established, and the influence of the model coefficients on the displacement measurement model was analyzed. The simulation results show that, under the condition that the error of the measurement model in the X direction and the Y direction is <0.1  nm, the translation error of the read head should be within ±100  μm, and the relative rotation deviation between the two read heads or two gratings placed along the diagonal should be within ±50  μrad. The methods and results of studying the influence of grating interferometer installation error on the displacement measurement provide a theoretical basis for the application of a grating interferometer displacement measurement system in immersive high-end lithography scanners.

A photonic crystal fiber (PCF) sensor based on surface plasmon resonance with a gold film coating is designed and investigated for detecting the analytes with a low refractive index (RI). The critical geometry parameter is optimized by the finite element method to increase the sensitivity of the sensor. An open-ring structure with a 70-nm-thickness gold film coated on the inner surface is located on the left and right sides of the PCF sensor, and its angle is equal to or greater than 90 deg. The spectral and amplitude sensitivities are numerically calculated to evaluate the sensing performance of the proposed sensor. The simulation results indicate that the maximum and average sensitivities are 68,000 and 9583  nm  /  RIU, respectively. The resolution is a critical parameter for assessing the sensing performance of the sensor with a maximum value of 1.47  ×  10^−  6  RIU. The simulation results show that the RI of analytes that the sensor can detect ranges from 1.20 to 1.31. Therefore, the sensor possesses wide application prospects in the field of biosensors.

Phase-change materials, such as vanadium dioxide (VO₂), exhibit high contrast in their optical properties upon transitions between their insulator and metallic phases, providing an interesting tool to design active devices. A cavity structure consisting of a VO₂ ring within a nanodisk is proposed to control the propagation of light through a metal–insulator–metal plasmonic waveguide. Numerical simulations indicate that the transmission of the designed structure is higher than 0.56 in the wavelength range of 1500 to 1600 nm in the insulating phase of the VO₂ rings. However, transition of the VO₂ rings to the metallic phase considerably increases their absorption coefficient. Then the transmission of the structure falls to lower than 0.0034 in the 1500- to 1600-nm wavelength range. Therefore, the achieved extinction ratio is higher than 22.1 dB in this wavelength range. We demonstrate that the central wavelength of the transmission band of the structure can be tuned by changing the geometrical parameters of the VO₂ ring. The influence of partial phase transition on the transmission level is also studied by effective medium theory.

This paper proposes a high-precision and robust visible-light dynamic imaging positioning system based on improved kernelized correlation filters (IKCF) and fast-weighted Levenberg–Marquardt (FWLM) algorithm. First, using IKCF, we propose a novel LED-ID dynamic recognition algorithm, which can achieve fast LED-region of interest detection, and an adaptive model update mechanism is used to reduce the interference of occlusion. Second, an FWLM positioning algorithm is designed. The direct linear transformation is used to obtain the initial estimate of the pose quickly, and LM is employed to optimize the pose iteratively by minimizing the reprojection error. An adaptive weighting matrix is used to reduce the impact of LEDs with low detection reliability on positioning accuracy. Finally, an experimental platform is set up to verify the effectiveness of the proposed dynamic positioning algorithm. The experimental results show that the average positioning time is 4.08 ms, the average positioning accuracy is 1.9830 cm without occlusion, and the average positioning accuracy is 4.4024 cm with occlusion.

Based on the birefraction of crystals and phase retardation of wave plate, a 2  ×  4 90-deg crystal spatial optical hybrid is designed. It is comprised of three birefringent optical plates, λ  /  4 wave plate and two λ  /  2 wave plates. By splitting and recombining the signal beam and local oscillator beam, four mixed beams with phase shift of 90 deg are obtained. The mathematical model of the mixer is established by Jones matrices. The results show that the hybrid has low insertion loss, and by rotating the wave plate, the phase difference and split ratio between in-phase and quadrature-phase can be changed. It proved that the crystal hybrid design method we proposed has good performance; the phase compensation and splitting ratio adjustment scheme is simple, effective, and feasible; and it can be applied to free-space coherent optical communication system well.

A precisely tunable heterodyne-injection-locked dual-loop optoelectronic oscillator (HIL-DL OEO) is analyzed and experimentally demonstrated. The primary loop, utilizing a narrow bandpass filter, generates a frequency-fixed signal, and the secondary loop, incorporating a yttrium iron garnet filter, outputs the tunable signal. The oscillating signal in each loop experiences frequency translation at an external frequency translation module (FTM) and is then fed to the other loop. The frequency translation at the FTM, which is composed of two mixers and a power splitter, is realized with the help of a tunable low-frequency signal. Thanks to the low-frequency signal, the oscillation frequency in the secondary loop would vary accordingly under injection locking.

A dual-function beam separation grating with double structure periodic ridges is proposed. The parameters of the grating structure and characteristics of the incident light are all optimized by the finite-element method and rigorous coupled-wave analysis, so the grating can display the polarization-selective characteristic. At the parameter values that will be discussed in Sec. 2, the diffraction efficiency of the zeroth order, first order, and second order for transverse electric (TE) polarization is 32.30%, 32.34% and 32.30%, respectively, and the uniformity is calculated to be 99.88%. For transverse magnetic (TM) polarization, the reflectivity of the zeroth order and second order is 47.23% and 47.24%, respectively, and the uniformity of two ports is 99.97%. Compared with most previously reported polarization-selective beam splitters that achieve single-port output for TE polarization and dual-port output for TM polarization, the grating realizes TE-three/TM-two output with a decent diffraction efficiency uniformity.

Cylindrical vector-polarized vortex pulses from a passively Q-switched laser are demonstrated. Pump radiation reshaped into a size-controlled annular profile via circular Dammann grating produces an efficient excitation of the LG01 mode. The YAG  /  Nd  :  YAG  /  Cr^4  +  :  YAG composite crystal structure is found to reduce the Q-switching threshold and significantly suppress thermal damage, thus allowing ability to obtain a passively Q-switched pulse. The threshold pumping power is found to be 4.35 W, with a slope efficiency of 23.1%. A maximum peak power of 3.24 kW, maximum pulse energy of 53.46  μJ, pulse width of 17.5 ns, and repetition rate of 2.695 kHz are obtained. Furthermore, a radially polarized output with a polarization degree of 88.9% is confirmed. Finally, mode and polarization tuning are also discussed.

Coherent Doppler lidar (CDL) has been considered a powerful and reliable tool for horizontal wind shear monitoring since the 1990s. However, radial observations obtained by Doppler lidar are limited in determining sophisticated variations in horizontal wind field and thus the wind shear. In our work, this problem is solved by applying a statistical interpolation technique to a CDL system, which is implemented at Lanzhou Zhongchuan Airport (103°E, 36°03′N) since August 2019, for routine observation of the horizontal shear along the pathway of the aircraft. By means of that, the horizontal wind vectors are retrieved in real time and the wind shear is also obtained simultaneously. Compared with radial observations, the accuracy of real-time horizontal wind vectors is indicated with the root mean squared error of 0.504  m  ·  s^−  1. During the field campaign, a typical wind shear induced by wind gust is obtained by the CDL system, which moves from south to north with the maximum up to 9.6  m  ·  s^−  1   ·  km^−  1. Also, five cases resulting in flights going around are described in detail and compared with the reports from the airport terminal control office. The results reveal that the CDL system is quite suitable for wind shear forewarning for demonstrating the time, position, and intensity of wind shear with acceptable accuracy.

High-quality gold nanospheres (Au NPs) were transferred to a sapphire substrate. The balanced twin-detector measurement technique was used to study the saturable absorption properties of the Au NPs. With the as-prepared Au NPs as a saturable absorber (SA), an efficient passively Q-switched laser was realized at 1.93  μm. Under an absorbed pump power of 4.5 W, a maximum output power of 400 mW was obtained with the shortest pulse width of 410 ns and repetition rate of 126 kHz. The results indicate that Au NPs are promising candidates as SAs for mid-infrared laser pulse generation.

Line structured light scanning technology is extensively applied in three-dimensional (3D) reconstruction due to its advantages of having high precision and being non-contact. To quickly and accurately obtain the feature information of the light stripe center, a method of extraction and adaptive segmentation of the light stripe center is proposed for 3D measurement of structured light. First, a subpixel extraction method is presented to extract the light strip center; it quickly determines the normal direction of the light stripe and accurately extracts the light stripe center in the normal direction by employing the improved gray gravity method. Second, an adaptive contour segmentation method based on slope difference and dynamic neighborhood optimization is presented. Finally, the proposed method is adopted to measure the geometric size of the complex manufactured parts. The experimental results demonstrate that the maximum measurement error is 0.15 mm and the accuracy is <1  %  , indicating that the method is accurate enough to be applied to various kinds of measurements.

Dense wavelength-division multiplexing is conceived as an appropriate solution for the 5G fronthaul system to cope with the rapidly increasing demand for bandwidth. While the cross-phase modulation (XPM) would appear when the signals are transmitted simultaneously in the single-mode fiber. The XPM effect on the 5G fronthaul wavelengths is investigated through both simulation and experimental campaigns. Simulation results show that the electrical spectrum crosstalk will occur with the wavelengths transmitting synchronously, when the channel spacing is 100 GHz and the speed is 25  Gbit  /  s per channel in the 10-km link. Also, the intensity of the electrical spectrum crosstalk becomes stronger when the launch power increases from 10 until 14 dBm. While comparing with the results obtained from the positive-intrinsic-negative (PIN) detector, the XPM-induced sensitivity penalty can be alleviated by 0.3 dB in use of avalanche photodiode (APD), which can provide higher signal-to-noise ratio. Consistent with the simulation results, the electrical spectrum crosstalk also appears in the experimental campaign under the same conditions. Furthermore, a sensitivity improvement of 0.5 dB is obtained using 25-GHz APD receiver, compared with the adoption of 35-GHz PIN receiver case.

We provide a numerical model to investigate the performance of a visible light communication-based vehicle-to-vehicle (V2V) communication system that incorporates organic light emitting diode (OLED) transmitters and discrete multitone modulation to overcome the bandwidth limitations of the organic devices. Different application scenarios using vehicle’s headlights and taillights as optical transmitters are considered. The results indicate the potential of using OLEDs for cooperative intelligent transportation system applications to achieve transmission of low-to-moderate data rates, providing evidence that the proposed OLED-based V2V system can achieve data communication of several Mbps. In the scenario that involves transmitting data to the leading car using the OLED headlights as transmitters, we show that the data rate can exceed 5 Mbps, despite the low modulation bandwidth of the OLED. When transmitting data to the trailing car using the taillights, we show that the transmission rate can reach 2 Mbps. We also discuss the trade-off between vehicle distance and communication performance and show that, even for distances up to 40 m, data rates on the order of several hundred kbps can be supported.

We investigate fiber optical parametric amplification (FOPA) in a structure of an As₂S₃ core and TeO₂ cladding photonic crystal fiber (PCF). Various amplification features such as wavelength area, parametric gain value, and bandwidth are investigated. In order to design the FOPA system with optimal features, effects of different structural parameters variation on optical features of the PCF and parametric gain subsequently are also investigated numerically based on the finite-difference time domain numerical method. Using 15 cm of this fiber and a continuous wave pump laser of 1.1 W, we attain a gain spectrum of 350 nm with a maximum value of 37 dB around 1550 and 1310 nm, which are favored wavelengths in optical telecommunication systems. In fact, our structure ends in a wideband amplifier in an absolutely compact size, which is optimized exactly for optical telecommunication applications.

We experimentally demonstrate a wavelength-switchable noise-like pulse (NLP) with modulation sidebands in an erbium-doped mode-locked fiber laser. The central wavelength of NLPs can be switched from 1530.2 to 1558.8 nm due to the birefringence filtering effect based on nonlinear polarization rotation. The corresponding pulse durations are 656 and 613 fs, respectively. As the total pump power increases to 700 mW, the modulation sidebands of NLPs can be observed by adjusting the polarization controller appropriately. The formation of modulation sidebands is caused by cross-phase modulation-induced modulation instability.

This paper reports the numerical demonstration of a silicon (Si)-compatible continuous wave laser based on the erbium-doped lithium niobate-on-insulator rib waveguide, emitting around 1531 nm by optical pumping at 980 nm. The model involves a full vector finite-element-method-based modal analysis of the proposed device with the solution of laser rate equations and propagation equations using in-house developed computer codes. Optimization of the laser cavity, which maximizes the laser output, is investigated for different values of background loss along with a set of realistic input parameters. For 0.027-dB  /  cm loss, a maximum laser output of 79.64 mW with a threshold of 10 mW is computed when 200-mW pump power is coupled to the cavity and the cavity length is optimized to 13.54 cm. For a 6.04-cm long optimized cavity, the laser threshold is reduced to 5 mW with a computed output power of 43.59 mW. The computed slope efficiencies at 20 mW of the coupled pump are 37.72% and 43.79%, respectively, for 13.54- and 6.04-cm long laser cavities. These results indicate the possibility of realizing an efficient hybrid Si laser operating at the third telecommunication window, which may find potential application in Si photonics.

The purpose of our study is to investigate the behavior and performance of photonic crystal fibers with two different structures in the cladding region. The same shape is chosen for the core of both fibers, but the structure of the cladding region is embedded in triangular and square shapes. The finite element method is used for numerical examinations. The results indicated that the relative sensitivity of the triangular and square structures is 41.77% and 35.47% at the wavelength of 1.33  μm, respectively. The simulation results showed that the structure of the triangular cladding has a higher ability to trap light in the core, for which the confinement loss of the triangular and square structures is 2.2 and 6.1  dB  /  m at the 1.33-μm wavelength. The variation in diameters of both cladding and core regions is investigated for both structures. The results indicated that the optical behavior of square fiber has a high resistance to changes in the dimensions of the core and cladding. Therefore, square cladding is more reliable than triangular cladding for fabrication purposes. The birefringence and effective area of the two structures were computed, revealing that the triangular cladding gives the highest birefringence and effective area at the wavelength of 1.33  μm.

A silicon nanowire embedded dual-core pentagonal photonic crystal fiber (PCF)-based polarization-independent wavelength splitter is proposed. The proposed PCF structure is analyzed using the finite element method. The wavelength splitting behavior of the PCF is investigated using the coupled-mode theory. The structural parameters of the PCF are optimized to achieve a coupling length ratio of 2. For the proposed PCF of length 102  μm, the cross-talk (CT) of −48.27 and −61.54  dB and CT bandwidth of 29.3 and 37.7 nm at 1.3 and 1.55  μm for X-polarization mode is achieved. However, the proposed PCF of length 115.5  μm attained the CT of −42.83 and −46.74  dB and CT bandwidth of 27.6 and 34.5 nm at 1.3 and 1.55  μm, respectively for Y-polarization mode. The polarization-independent wavelength splitter is achieved with the proposed PCF of length 108.75  μm. The proposed PCF-based wavelength splitter will be an inevitable candidate for integrated optical systems.

A simple method has been proposed to use four-wave mixing to design and simulate the all-optical AND logic gate in a photonic crystal semiconductor optical amplifier (PC-SOA) that is integrated with an ideal optical bandpass filter. The preferred logical function could be carried out in the proposed scheme with no use of a continuous-wave signal. Nonlinearities including carrier depletion, carrier heating, and spectral hole burning have been considered in the presented simulations. Furthermore, for improvement of the AND logic gate performance, the impacts of the pattern effect of the signals propagating in the PC-SOA medium, the input signal bit rate effects, and gain recovery have been extensively investigated. The findings demonstrated that the optimal output signal featuring 3-fJ energy and 2-mA injection current could be achieved at a bit rate of 50 Gbps.

Gratings with low diffracted wavefront errors are crucial in many applications. Existing methods to reduce the diffracted wavefront errors of holographically produced gratings mainly address misalignment errors during exposure system adjustment, leaving the inevitable residual errors of collimation lenses uncorrected. The broad-beam scanning exposure method was recently proposed to fabricate gratings with large size and low stray light. We explore its ability to reduce the diffracted wavefront errors caused by both system misalignment and lens errors. During the exposure, the substrate translates in the direction perpendicular to the grating lines to pass through the exposure area, so the aberrations over different parts of the interference field along the scanning path are averaged. We prove the validity of this method by a theoretical analysis and numerical simulations. The averaging effect on different aberrations and with different scanning lengths is discussed. The peak-valley values of diffracted wavefront errors of gratings fabricated with an exposure field of defocus aberration and a more complicated aberration were reduced by 42.5% and 50%, respectively.

A C-shaped split ring resonator-based metamaterial (MTM) structure placed on a patch antenna is proposed. An artificial neural network (ANN) is applied to design and determine dimensions of an MTM structure that is similar to those used in wireless communication systems, such as Wi-Fi and WiMax, as well as in military vehicles and space stations. The proposed microstrip antenna interacts with the MTM-based structures to improve the reflection coefficient (S₁₁) and quality factor. The design of the proposed structure is optimized for this purpose in accordance with the ANN studies in the related literature. Both simulation and experimental studies show that ANN calculated MTM antennas improved the quality factor, which is calculated as 230 at 5.18 GHz. The simulated S₁₁ is verified by experiment to show the integrity of the proposed work.

This erratum corrects the units in parts (a) and (b) of Fig. 56.