Images taken under low light or dim backlight conditions usually have insufficient brightness, low contrast, and poor visual quality of the image, which leads to increased difficulty in computer vision and human recognition of images. Therefore, low illumination enhancement is very important in computer vision applications. We mainly provide an overview of existing deep learning enhancement algorithms in the low-light field. First, a brief overview of the traditional enhancement algorithms used in early low-light images is given. Then, according to the neural network structure used in deep learning and its learning algorithm, the enhancement methods are introduced. In addition, the datasets and common performance indicators used in the deep learning enhancement technology are introduced. Finally, the problems and future development of the deep learning enhancement method for low-light images are described.

Focused on small celestial body deflection missions using a kinetic impactor spacecraft, we propose a method for estimating the center of small objects with unknown shape and small size, which relaxes the requirement for prior information of the object shape model and lowers the risk of missing the target. The impact center is inferred using the visible part of the object in a single image. In the first step, the illuminated part of the object’s true contour is segmented from the whole contour extracted from the image based on the prior information of the illumination direction. In the second step, the concave–convex characteristic of the illuminated contour is identified. In the third step, one of two modes, moment estimation or skeleton center estimation, is chosen based on the concave–convex characteristic to calculate the impact center. The proposed algorithm was verified by a simulation study under various conditions. Due to the problems of the unknown model shapes of small objects and complex illumination conditions in kinetic impact missions, the proposed centroiding algorithm will play an important role.

An optimization-based algorithm is introduced to achieve the subpixel resolution in x-ray imaging. In this approach, the image captured by a detector is to be considered as a degradation of a high-resolution image. The inverse problem of the degradation is formulated as an optimization program. Through solving the cost function with Chambolle–Pock (CP) algorithm, we can reconstruct the subpixel image from multiple images shifted with subpixel precision. Numerical studies indicate that the iterative algorithm can numerically accurately invert the degradation. A set of x-ray imaging experiments were performed, and some structural information can be found in the reconstruction of the high-resolution image but not existing in the original image data. It would have potential applications in x-ray high-resolution imaging and industrial detection.

We propose a robust steganography scheme for large-capacity lossless images based on visual cryptography and ptychography. The introduction of the quick response code as a container for information hiding can realize the lossless extraction of information and performs well in robustness when subjected to compression, noise, and tailoring attacks. The security of the proposed system is provided by the Arnold scrambling algorithm, the visual cryptographic scheme, and the structural parameters of ptychography. The proposed method is verified with optical experiments. In the experiments, a spatial light modulator is used to complete specific experiments through nonmechanical moving ptychography, which greatly reduces the error of traditional ptychography experiments and improves the quality of reconstruction. The results demonstrate that the method can achieve satisfactory robustness performance with high repeatability and excellent information fidelity.

Spectral and polarization imaging (SPI) is an emerging sensing method that permits the analysis of both spectral and polarization information of a scene. The existing acquisition systems are limited by several factors, such as the space requirement, the inability to capture quickly the information, and the high cost. We propose an SPI acquisition system with a high spatial resolution that combines six spectral channels and four polarization channels. The optical setup employs two color-polarization filter array cameras and a pair of bandpass filters. We define the processing pipeline, consisting of preprocessing, geometric calibration, spectral calibration, and data transformation. We show that, around specular highlights, the spectral reconstruction can be improved by filtering the polarized intensity. We provide a database of 28 spectropolarimetric scenes with different materials for future simulation and analysis by the research community.

Many image processing applications require a quantitative estimation of the underlying correspondence (of the relative position in space) between two or more images. Here, we propose a unique, less numerically intensive method, which we refer to as the subtraction method (SM), to measure in-plane object motion with subpixel accuracy. This method can be usefully employed in conjunction with the correlation method (CM) to provide fine motion information very quickly (∼100 times faster). We first review the CM, then, demonstrate, explain, and examine the proposed SM using analytic functions, standard digital images, and using both simulated and experimental data. Specifically, subpixel motion results for Gaussian functions, four different standard images, and speckle images are examined. Performance is compared to that of the CM. Experimentally, images are captured using both optical and THz imaging systems. A high-resolution megapixel camera is used in the optical system and a low-resolution camera with 16  ×  16  pixels is used to perform the THz measurements. One-dimensional subpixel motion in both x and y is examined and analyzed. The results demonstrate that the method can be flexibly used in different areas.

Since the laser linewidth is an important performance-metric for devices that use laser light, determining the precise value of linewidth is an essential prerequisite for evaluating the overall performance of laser-based devices. However, due to the influence of various kinds of noises, current laser linewidth detection methods are unable to measure the laser linewidth accurately. Accordingly, we propose a simple laser linewidth detection method, which uses the coherent envelope power spectrum to characterize laser linewidth based on the short delay self-homodyne system. Relying on theoretical derivation, simulations, and experiments, the feasibility and accuracy of proposed method are verified. This new approach is expected to enable the realization of a compact and precise laser linewidth measurement method.

Due to the instability of motor speeds, asynchrony in trigger systems, and mechanical factors, the use of continuous dual-rotating compensator (DRC)-Mueller matrix ellipsometer (MME) is limited. And the stepping one is more often used on an extremely wide spectrum measuring range. However, its long measuring time limits its use. To solve this problem, we propose a weighed factor to judge the stability and robustness of this ellipsometer. This factor describes the performance of ellipsometers better than the condition number. We use this factor as the merit function to optimize the configuration of a 16-point measurement system with an improved genetic algorithm (IGA). Repeated measurement experiments on SiO₂ films revealed that the optimal configuration considerably increased the measurement speed, without a notable decrease in measurement precision. The findings are not only aimed at the optimization of stepping DRC-MMEs; the IGA can also be used for other multiparameter optimization issues, and the weighed factor can be applied for the parameter optimization of other MMEs.

A curtain-type phase unwrapping algorithm is proposed. First, the 2  ×  2 closed curve method is used to find out the residual point of the wrapped phase to form the residual template, and the Otsu threshold method is used to binary the modulation of the deformed pattern to form the shadow template. Second, the effective phases of up-down symmetrical points about the starting point are simultaneously unwrapped in turn until all the points in the column are completed. Third, the starting point is taken as the center of left-right symmetry, the effective phases of the nearest symmetric points are simultaneously unwrapped, and the corresponding columns are unwrapped in the same way as above. Fourth, in this way, the effective phases in the corresponding symmetric columns are successively unwrapped in the form of curtain opening until the whole phases are completely unwrapped. In the previous procedure, the shadow template and residual template guide the curtain-type phase unwrapping to avoid error diffusion. Finally, the 8-neighborhood mean algorithm and the cubic b-spline algorithm are employed to unwrap the phase values of residual points and shadow areas, respectively. The proposed method realizes the whole phase unwrapping without phase error diffusion. Experimental results show that the efficiency of the proposed method is 26% higher than that of the diamond algorithm, and its accuracy is significantly improved.

We use wave-optics simulations to investigate branch-point density (i.e., the number of branch points within the pupil-phase function) in terms of the grid sampling. The goal for these wave-optics simulations is to model plane-wave propagation through homogeneous turbulence, both with and without the effects of a finite inner scale modeled using a Hill spectrum. In practice, the grid sampling provides a gauge for the amount of branch-point resolution within the wave-optics simulations, whereas the Rytov number, Fried coherence diameter, and isoplanatic angle provide parameters to setup and explore the associated deep-turbulence conditions. Via Monte Carlo averaging, the results show that without the effects of a finite inner scale, the branch-point density grows without bound with adequate grid sampling. However, the results also show that as the inner-scale size increases, this unbounded growth (1) significantly decreases as the Rytov number, Fried coherence diameter, and isoplanatic angle increase in strength and (2) saturates with adequate grid sampling. These findings imply that future developments need to include the effects of a finite inner scale to accurately model the multifaceted nature of the branch-point problem in adaptive optics.

A single-shot N-step phase measurement profilometry (single-shot N-PMP) is proposed. In the traditional N-step PMP, N (N  >  2) frames of phase-shifting sinusoidal gratings are needed to be projected onto the measured object. The corresponding N frames of phase-shifting deformed patterns modulated by the object are needed to be captured. And the larger the N is, the higher the measuring accuracy will be. In the proposed method, only one sinusoidal grating is needed to be projected and only one corresponding deformed pattern is captured. The proposed method can efficiently avoid direct filtering in the spectrum of the deformed pattern because of the secondary modulation in computer. The proposed method is an innovative single-shot, three-dimensional (3D) measurement with the highest accuracy among the single-shot 3D measurements so far for inheriting of the traditional optional N-step PMP. And the optional larger N can result in higher accuracy while the single-shot feature can be always guaranteed both the static and real-time 3D measurements. Furthermore, the mathematical model of the proposed method is more concise compared with the traditional PMP for the phase just modulated by the measured object itself can be directly solved without two phase resolutions and two phase unwrappings for both the reference plane and the measured object. The simulations and experimental results show the feasibility and validity of the proposed method.

The widespread applications of thin films in optronics demand innovative techniques for its characterizations. The work reported here proposes electronic speckle pattern interferometry and fractal-based methods for assessing the quality of thin films taking the industrially relevant molybdenum oxide (MoO₃) incorporated niobium oxide (Nb₂O₅) films. The films with different levels of MoO₃ incorporation (1, 2, 3, 5, and 10 wt. %) are prepared by radio frequency sputtering. The study reveals the structure modifications of Nb₂O₅ from the orthorhombic to monoclinic phases with an associated morphological variation revealed through atomic force microscopy and field-emission scanning electron microscopy analyses. The films’ specklegrams are recorded under thermal stress; the inertia moment (IM) and fractal analyses are computed and compared with the root-mean-square surface roughness of the films. The lacunarity analysis of the AFM films agrees well with the specklegrams. Thus, the lower IM and lacunarity values of the specklegrams can be regarded as indicators of the good quality of thin films.

We propose a visible light positioning system based on four-quadrant photodetector and improved genetic algorithm, where single light-emitting diode lamp and four-quadrant photodetector are adopted as light source transmitter and receiver. The improved genetic algorithm and the illuminance values received by the light source receiver are employed to accurately locate the position of measured points. The improved genetic algorithm has a better performance in accuracy and convergence speed. The experimental results indicate that the average positioning error of the proposed scheme is 4.0230 cm. Compared with the indoor visible light positioning system using standard genetic algorithm, the proposed scheme can obtain higher positioning accuracy and robustness under the condition of shorter average positioning time.

In this study, a polarization-maintaining fiber optical gyro (PMFOG) with orthogonal-polarization states is constructed, and the non-reciprocity error induced by varying temperatures has been studied. Compared with the traditional optical gyro system based on single-polarization, theory and experiments have shown that the non-reciprocity error induced by varying temperatures is more evident in the PMFOG with orthogonal-polarization states. It is approximately five times larger than that of the traditional PMFOG. To decrease the non-reciprocity error induced by varying temperatures, we proposed an innovative structure in this study, which enhances the symmetry of the light path without the addition of redundant optical devices. The clockwise and counterclockwise light beams experience the same change of refractive index along the fast and slow axes of the fiber, and the non-reciprocity error induced by varying temperatures can be reduced to zero when the whole gyro is heated up nearly uniformly. This research, which overcomes a design limitation in PMFOGs with orthogonal-polarization states, is significant for the miniaturization and optimization of the environmental adaptability of fiber optic gyroscopes.

A unique high-performance digital to analog conversion (DAC) approach based on dual-electrode Mach–Zehnder modulators (DEMZMs) is proposed and experimentally demonstrated. According to the modulation transfer characteristics of DEMZM, the output waveform can be edited in-line by properly adjusting the input digital signals. In our design, a 2-bit photonic DAC module can be realized by using only one DEMZM, which is biased at the minimum transmission point. The scheme is extendable, i.e., a 4-bit DAC system can be achieved by using two parallel DEMZMs, and an 8-bit system can be obtained with four DEMZMs. As few modulators are employed and the system configuration is simplified, the proposed approach can greatly improve the bit resolution with less complexity. A proof-of-concept experiment of a 4-bit DAC system is successfully carried out, which fully verifies the feasibility of the proposed approach. Moreover, the system performance in terms of integral nonlinearity and differential nonlinearity is also discussed. The proposed scheme provides a potential solution for high-bandwidth and high-resolution photonic DAC.

With the growing need for high specification requirements for the latest manufacturing processes and optical designs of glass lenses, the technical requirements for lens polishing have increased. The manufacturing parameters must be adjusted in a timely manner to meet the required specifications. We use a Fizeau interferometer to classify and analyze interference fringes measured in the actual polishing process of glass lenses. Given the low incidence of interference fringes in practice, the training dataset contained a disproportionate ratio of data for each data type. To reduce the manufacturing cost and data collection time, this study focused on three common types of interference fringes in the manufacturing processes and integrated a deep convolutional generative adversarial network with convolutional neural networks (CNNs) for fringe type classification. The deep convolutional generative adversarial network was used to establish a data augmentation generator, and Jensen–Shannon divergence was employed to identify the epoch number that yielded distributions of interference fringe numbers closest to the real distributions; this approach could achieve the diversity of interference fringes in the generated images. Finally, the generated data were used to train the CNN models, and the accuracy of image recognition reached above 86%.

Imaging technology at various scales of spatial resolution is crucial for understanding the physiological and morphological complexity of living organisms. The existing imaging technologies fail to facilitate images of a sample at different magnification levels at a given instant of time. We report the detailed design and instrumentation of an optical imaging system, namely, simultaneous multiple-level magnification selective plane illumination microscopy (with an acronym being given as sMx-SPIM), which addresses one of the technological challenges of imaging biological specimens at different magnification levels simultaneously. The simultaneous magnified views assist in perceiving biological activities occurring over a short period, especially in developmental biology, where the time scales (fraction of seconds) are critical. The proposed imaging system comprises one illumination arm and two detection arms, each of which uses a different magnification to attain multiple magnification levels simultaneously and overcomes the time consumption for changing the objective lens. The system is automated for image acquisition using a custom-built assembly of motion stages and external hardware. Experimental studies are carried out using biological specimens such as Daniorerio and Alliumcepa to validate the home-built sMx-SPIM imaging system at an obtainable spatial (axial) resolution of   ∼  3 to 5  μm.

In the field of precision optical manufacturing, the manufacturing method using industrial robots as the carrier has highlighted its advantages of being more economical and efficient than existing methods. The application of different end-effectors has expanded the scenarios and processing limits of optical polishing. However, concise and simplified polishing technologies remain challenging. To improve the versatility of industrial robots in different processes and reduce the number of polishing iterations, pre-polishing with uniform removal is introduced and optimized, providing an excellent basic surface for polishing and finishing. Combined with the performance of an industrial robot, we adopt a swing composite path, to which the motion parameters are adjusted and optimized to minimize the fluctuation of the overall overlap rate (within 5%). The optimal path is based on the uniform B-spline curve characterization, which improves the consistency of the dwelling time and reduces the complexity of pre-polishing, laying a theoretical foundation for efficient and high-quality optical manufacturing.

Scaling to a higher-power green laser with good beam quality is a challenge for meeting the requirements of different industrial applications. An acousto-optic Q-switched TEM₀₀ mode Nd:YLF laser using the master oscillator power amplifier (MOPA) technology is presented and demonstrated. Output power of 17.2 W and TEM₀₀ mode laser of 527 nm at 1.5 kHz with a pulse energy of 11.5 mJ is achieved. The output green laser had a Gaussian spatial profile with beam quality factors of Mx2=1.07 and My2=1.15. Z-type end-pumping structures are used for the MOPA system to ensure laser power stability. The green laser power fluctuation is <0.3  %   based on 4 h measurement data.

Vortex optical communication is a method to improve the spectral efficiency of underwater wireless optical communication. However, facing the complex marine environment, the turbulence effect in the offshore area is a big challenge to vortex optical communication. Oceanic turbulence will influence the transmission performance of the vortex beam. After turbulent transmission, crosstalk will inevitably occur between different topological modes. This paper studies the degree of crosstalk of Hankel–Bessel (HB) vortex light in different oceanic turbulences. By establishing a mathematical model of anisotropic oceanic turbulence, the main focus is on average temperature dissipation rate, turbulent energy dissipation rate, and temperature-salinity balance parameters. The influence of different turbulence parameters on the propagation of HB vortex light is discussed, and the degree of influence of the above parameters on the channel capacity of the orbital angular momentum HB (OAM-HB) optical communication system is studied. Simulation experiments show that anisotropic oceanic turbulence will cause energy migration in different topological models and cause significant decreases in channel capacity. We observed the capacity of HB vortex beams and compared the communication effects of Laguerre–Gaussian and HB vortex beams in anisotropic ocean turbulence. The communication performance of OAM-HB light in anisotropic turbulent is better than that in an isotropic one. The research results of the transmission characteristics of the vortex HB light underwater show that the OAM-HB underwater communication is worthy of further study.

A high-power external cavity diode laser (ECDL) system at 445 nm is proposed that has narrow-band linewidth emission and adjustable polarization state and can be used for nonlinear frequency conversion in deep ultraviolet spectrum. By introducing a half-wave plate to control the polarization state of the laser source, the first-order diffraction (R_1st) efficiency is changed. The relationship between the linewidth and the first-order diffraction efficiency is discussed through simulation and experiment. In addition, the tunable ranges of the ECDL are measured. Finally, a continuous-wave output with the spectral width of 72 pm at 445 nm and a maximum optical output power of 1.52 W can be obtained when R_1st is 25%, of which the tunable range has a minimum of 2.3 nm.

We demonstrated the efficient generation of a linearly polarized Ho:YAG laser pumped by a thulium fiber laser. Independent of the pumping power and without utilizing any dispersive optical element, the output radiation remained stable with a high degree of linear polarization. The output with 2044 nm wavelength and 0.12 nm bandwidth was measured. In the free-running generation, with respect to the incident pump power, we recorded more than 9 W of output power with 59% slope efficiency. In addition, in the pulsed generation, we obtained more than 2.2 mJ pulses with 50 ns time duration, and 44 kW peak power.

Frictional resistance significantly reduces the energy efficiency of aircraft. The ridge surface has a drag reduction effect, and its processing has become one of the important ways for improving the energy efficiency of aircraft. The micro-ridge and microgroove are the basic units of the ridge surface. A nanosecond laser can prepare them. However, numerous parameters and complex laser etching mechanisms make it difficult to determine their molding conditions, the forming quality of which is difficult to guarantee. This problem restricts the high-precision preparation of the ridge surface, which inevitably affects its drag reduction performance. Therefore, it is crucial to determine the high-quality molding conditions of the microgroove and micro-ridge to ensure the drag reduction effect of the ridge surface. Here, we focus on aviation titanium alloy TC4. Through an etching experiment of the straight section, the influence of parameters on the feature size of its cross-section profile is systematically studied. The recast layer scale, symmetry, and smoothness of the cross-section profile are used to evaluate the molding quality of microgrooves. The symmetry of the cross-section profile assesses the molding quality of micro-ridges. The forming parameter range and high-quality forming condition of microgrooves and the high-quality forming parameter range of micro-ridges are determined. Finally, the morphology evolution rule and mechanism of the nanosecond laser etching TC4 is revealed based on this research. The direct molding rules and parameter range of micro-ridges on the TC4 surface are reported and show a broadening of the nanosecond laser micromachining range. Moreover, this study will provide a process window for optimizing nanosecond laser processing for microgrooves and micro-ridges on the TC4 surface.

Visible light communication (VLC) has gained attention due to its ability to provide a high data rate in underwater communication. We consider an underwater VLC (UWVLC) system and vertical propagation through the column of water with L layers (channels) and M relays between the transmitter and the receiver. We consider the real-time adverse effects of depth-dependent weak turbulence and path loss. We model each of the L channels with a log-normal distribution, where its statistical parameters mean and variance are functions of the parameters representing the adverse effects of the turbulence. For this concatenated L layered UWVLC, using Gauss–Hermite integral technique, we derive closed-form expressions of outage probability and average symbol error probability taking square quadrature amplitude modulation and rectangular quadrature amplitude modulation modulations with different configurations and assuming imperfect channel state information available at the receiver for detection. We have observed that there is a drastic degradation in the performance as the depth (distance between the transmitter and the receiver) is increased. However, the severity can be alleviated by installing multiple relays between the transmitter and the receiver.

Laser cladding is usually used for remanufacturing plate and shaft parts. Because the laser cladding process belongs to the energy loading process, it is inevitable to produce stress and plastic deformation, which will cause the parts to lose the original shape precision after the cladding. To reduce the deformation of the parts after laser cladding and reduce the workload of the processing parts, the influence of different laser scanning sequence methods on the deformation of the substrate is studied at this angle. Due to the very uneven distribution of the temperature field of the substrate during the laser irradiation, the uneven distribution of the temperature field will eventually cause the deformation of the cladding parts. To reduce the deformations of the parts after the cladding, we should make the temperature field distributed more evenly in the parts of the cladding process. Based on this theory, laser cladding of a stainless-steel plate for three different laser scanning sequence methods is studied. The results show that the scanning path significantly influences the temperature field and deformation of the part. The study’s main objective was to reduce the temperature variance and thermal deformation of a flat plate stainless steel clamped substrate using different laser scanning sequences. During the investigation, it was found that the same direction and different side cladding can better balance the relationship between heat accumulation and heat dissipation on the substrate and molten pool, making the temperature field more uniform and decreasing the deformation of the parts. This study is helpful in improving the quality of the laser cladding parts. Finally, optimized process parameters have been used to further minimize the temperature variance and substrate deformation.

In a high-power Pr:YLF solid-state laser, the thermal effect of gain medium is one of the prime limiting factors, and its thermal damage has become the major concern. The thermal effect of Pr:YLF crystal was analyzed theoretically, and the distribution of temperature, thermal stress, thermal focal length, and pump polarization effects of the Pr:YLF crystal were simulated. The thermal effect investigation indicates that under reasonable pumping power density, crystal length, and beam waist size and location, the temperature rise and nonuniformity of thermal distortion are not intensified under high-power operation. Additionally, the relationship between Gauss or Super-Gaussian pump mode and thermal focal length of Pr:YLF crystal was simulated. To the best of our knowledge, this analysis is the first to examine the thermal effect of Pr:YLF crystal for power scaling, and this thermal effect investigation of Pr:YLF crystal provides first-hand data for a high-power, visible, solid-state laser that could be helpful for high-power Pr:YLF solid-state laser design.

To stabilize the frequency-difference of the two-cavity dual-frequency Nd:YAG laser at 1064 nm, a quadrature-demodulated Pound–Drever–Hall (QD-PDH) frequency-difference stabilizing system has been designed, which is composed of two sets of QD-PDH frequency stabilizing subsystems sharing the same Fabry–Perot cavity as the frequency reference. Both phase modulators are driven by the signals with the same frequency of 10 MHz generated by a single direct digital synthesizer (DDS), and the DDS also outputs the other two orthogonal signals as the demodulation reference signals of both frequency stabilizing subsystems. A QD-PDH frequency-difference stabilizing system for a two-cavity dual-frequency Nd:YAG laser with a frequency-difference of ∼24  GHz at 1064 nm has been established and investigated experimentally. The experimental results have indicated that during a period of 1 h, the laser frequency stabilities of the linear and right-angle cavities are estimated by Allan variance to be better than 2.3  ×  ^{10  −  11} and 2.7  ×  ^{10  −  11}, respectively, corresponding to frequency-difference stability of better than 4.2  ×  ^{10  −  7}. Such a frequency-difference-stabilized two-cavity dual-frequency Nd:YAG laser can be used as an ideal light source for the synthetic-wave absolute-distance interferometric system.

To obtain the dual-frequency laser output with large and tunable frequency difference, a design scheme of dual-frequency Nd:YAG laser with two standing-wave cavities sharing the common gain medium has been proposed, which is based on the principles of polarization splitting and single longitudinal mode selection of intracavity Fabry–Perot etalon. With each of the cavities containing a piece of Fabry–Perot etalon, the p- and s-polarized components of the laser at 1064 nm will be forced to oscillate simultaneously in single longitudinal mode in the linear and right-angle cavities, respectively. As a result, the orthogonally and linearly polarized dual-frequency laser at 1064 nm can be obtained. The principle of single longitudinal mode selection by use of the Fabry–Perot etalon has been analyzed, and the Fabry–Perot etalons have been designed. An experimental system of the two-cavity dual-frequency Nd:YAG laser at 1064 nm has been established, and the characteristics of single longitudinal mode oscillation of the two cavities have been investigated experimentally. The orthogonally and linearly polarized dual-frequency laser output at 1064 nm has been obtained; the main characteristics of the oscillating threshold and output power, the polarization state as well as the laser beam quality have been tested experimentally. The frequency difference of the dual-frequency laser has been tuned in turn to 16, 24, 37, and 76 GHz, by slightly adjusting the tilt angles of the intracavity Fabry–Perot etalons. Such a two-cavity dual-frequency Nd:YAG laser will be widely used in the synthetic-wave absolute-distance interferometry and other fields.

The conventional logic circuits dissipate energy into the environment due to the loss of information; hence these are termed irreversible logic circuits. The reversible logic (RL) circuits are capable of minimizing the power dissemination, quantum cost, and garbage outputs. The RL circuits based on all-optical technology have been adopted by many researchers in recent. The Fredkin gate is a significant RL gate. A modified Fredkin gate (MFG) made of a silicon all-optical microring resonator is realized in MATLAB. The MFG is capable of designing 16-Boolean functions with very small complexity. The figure of merit of the proposed MFG is achieved through numerical simulation. The parameters are selected from the determined specifications, and this could provide a practicable implementation of the proposed design.

A specially designed tri-tunable pixelated metamaterial was investigated emphasizing the transmission characteristics. The top metasurface (of metamaterial) was comprised of squared pixels of SrTiO₃ and graphene mediums deposited over an indium antimonide nanolayer; the SiO₂ dielectric medium constitutes the bottom substrate. The transmission characteristics of metamaterial, along with the electrical and magnetic tuning, were artificially controlled, and therefore, the effects due to altering external stimuli, such as thermal ambience, graphene chemical potential, and magnetostatic bias, were studied. The results yielded high sensitivity resonance transmission in the THz frequency range. The ON/OFF switching states of metamaterial, as illustrated in the form of transmission spectra, supported very high (∼98  %  ) or almost vanishing transmission in the 1 to 6 THz frequency range along with the polarization-insensitive property. In addition, the response to the incidence obliquity also remained fairly stable. The results reveal the potentials of the reported metamaterial in optical sensing due to its capabilities under the thermal, electrical, and magnetic stimulations.

The sealing state of the watertight door (SSWD) is important information for the safe operation of a ship. A monitoring method for the SSWD based on fiber Bragg grating (FBG) sensor is designed, which can monitor the opening and closing state of the watertight door in real-time. A highly sensitive and temperature-independent sensor is installed under the rubber of the watertight door, the relationship between the displacement of the door panel and the wavelength shift of FBG is linearly fitted with the sensitivity of about 314.511  pm  /  mm, and the error percentage with the finite element analysis is 6.22%. The watertight door is opened and closed many times, the results show that the sensor has good stability and reliability, and the opening state, closing state, and the degree of opening and closing can be accurately judged by the wavelength shift of FBG. At the same time, the sensor can also identify the foreign body within a certain range on the rubber surface.

The slow crack growth rate and inert strength of multispectral zinc sulfide were measured for use in aircraft window lifetime analysis. Dynamic fatigue data for uncoated multispectral zinc sulfide were fit to a power law by linear regression and to an exponential law by computer-aided numerical integration to obtain best-fit slow crack growth rate parameters. For the power law slow crack growth equation, crack velocity   (  v  )    =  A^*(KI/KIc)ⁿ, we find A^*  =  0.00769  m  /  s and n  =  14.65, where K_I is the stress intensity factor, K_Ic  =  0.72  MPam is the critical stress intensity factor, and we assign the value of the geometric factor to be Y  =  2  /  π. Parameters for the exponential law slow crack growth equation, crack velocity   (  v  )    =  v_o exp  (  βK_I  )   are v_o  =  3.02  ×  10^−  14  m  /  s and β  =  43.64  (MPam)^−  1. There were only small differences in the crack growth rate between uncoated and antireflection-coated material. The crack growth rate that we observe is 10 to 200 times faster than previously reported for a stress intensity factor K_I  =  0.25  MPam, which is a representative value of K_I for an aircraft window in service. The faster crack growth rate predicts a correspondingly shorter window lifetime. The inert strength of uncoated biaxial flexure disks (38.1 mm diameter with 15.88 mm load diameter and 31.75 mm support diameter) measured in dry nitrogen exhibited a 50% Weibull failure probability at 115 MPa with an unbiased ASTM C1239 Weibull modulus of 4.68. Antireflection-coated material had a 50% Weibull failure probability at 100 MPa with a Weibull modulus of 5.25.

We report on the fabrication of active optical waveguide splitters with circular cladding geometry in Nd:KGW crystals using direct femtosecond laser writing. Y-branch waveguides capable of one to two beam splits were fabricated with a single 60-μm-diameter straight waveguide as the input end and two 30-μm-diameter output ends. The full branching angle between the two output arms changed from 1.0 deg to 2.4 deg. Confocal micro-Raman and microphotoluminescence spectra were used to investigate the Y-branch waveguides. Under the action of an optical pump at 806 nm, simultaneous continuous-wave laser oscillation at a wavelength of 1067 nm in both arms of the Y-branch waveguides was achieved. The laser output was spatially multimodal with a power-splitting ratio of 49.7:50.3 between the arms. A maximum laser output power of 106 mW and slope efficiency of 27.3% were achieved in the active Y-branch waveguide splitter with a splitting angle of 1.0 deg.

Digital coded metasurface has greatly simplified the method for electromagnetic wave regulation. However, the traditional metasurface usually focuses on the half-space beam modulation, such as transmissive or reflective direction regulation, which hinders the application of the metasurface-based device. We proposed a full-space terahertz regulation metasurface, which can realize the functions of beam splitting, vortex beam convolution, and focusing for both transmissive and reflective modes. Furthermore, the transmission and reflection modes can be easily switched by changing the external temperature of vanadium dioxide. The presented structure shows excellent performance of full-space terahertz regulation. This method provides a new idea for multifunctional terahertz devices and can be exploited in applications where active manipulation of terahertz transmission direction is required.