This editorial outlines the editor’s annual report on the journal.

The goal of our paper is to show the design of a Smith–Purcell (SP) terahertz (THz) emitter with two circular and elliptical groove grating structures and its simulations. The SP source is a vacuum-state electronic device that is suitable for generating THz radiation. As a prerequisite for the main goal of the paper, a prebunched electron gun with Gaussian type has been used. Based on the design and simulations, the emitter can radiate THz waves with the frequency of f  =  0.8  THz. Radiation frequency changes by filling grooves of gratings with different glasses. Also, the radiation frequency of emitted waves can be tuned by the types of groove structures and the energy of electrons emitted from electron gun. For simulating the emitter, 3-D particle-in-cell codes and eigenmode solver have been utilized.

The attitude parameter is an important state parameter for a long axisymmetric target. The plane intersection (PI) method is a commonly used method for attitude estimation. However, this method only uses planes’ information in the object space under a multiple camera system (more than two cameras simultaneously observing a target). We propose two methods to address the aforementioned issue. One method involves minimizing the square of the object-space angle residual (OAR) and the other method involves minimizing the square of the image-space angle residual (IAR). The linear optimization method is used for the above minimizing problems. The simulation results demonstrate that the IAR method has higher accuracy than the PI and OAR methods under multiple and dual camera systems because it incorporates information of a pair of corresponding image points. Furthermore, our experiments have shown that the linear method is generally faster, and it has an equivalent accuracy compared to the iterative method.

The illumination variation exerts a significant influence on the accuracy and efficiency of digital image correlation (DIC) technology. However, the existing intensity change models assume that all the pixels in the reference subset have the same gray-level intensity change parameters, which cannot accurately reflect the effect of illumination variations. We pay attention to the position effect on intensity variations and propose a position-based intensity change model to study the illumination variation in DIC. The proposed model combines the gray-level intensities, the illumination variation, and the position parameters of a reference subset. The forward additive Gauss–Newton algorithm with a first-order shape function is applied to evaluate the feasibility and effectiveness. Simulation and experimental results verify that the proposed model has higher accuracy in different illumination conditions as compared with the existing second-order intensity change model.

In traditional phase measurement deflectometry (PMD), a number of sinusoidal fringe patterns are displayed on the screen in two orthogonal directions, which is time-consuming and not suitable for dynamic measurements. A phase-extraction algorithm based on the spatial-carrier phase-shifting technology for a single-shot spatial-carrier orthogonal fringe pattern is proposed. The phase increment of each pixel in two orthogonal directions is obtained by the least squares method and then the amount of spatial phase shift of all pixels relative to the probe pixel in the rectangular neighborhood centered on the probe pixel can be obtained. The number of fringe patterns required for the PMD is reduced to one by displaying a spatial-carrier orthogonal fringe pattern. Finally, the feasibility of the algorithm is verified by simulation and experiment.

Reducing the number of structured patterns for three-dimensional (3-D) reconstruction is of great importance for high-speed 3-D shape measurement. We present a method that reconstructs absolute 3-D shape using three projected binary patterns: one direct current (DC), one low-frequency, and one high-frequency fringe pattern. The procedures are (1) take the difference between the sinusoidal fringe patterns and the DC pattern; (2) apply Hilbert transform to the difference images to generate two phase maps; (3) employ the geometric-constraint-based phase unwrapping method to unwrap the low-frequency phase map; (4) unwrap the high-frequency phase map using the unwrapped low-frequency phase map; and (5) reconstruct 3-D shape. We developed a prototype system that can capture two-dimensional images at 6000 Hz, achieving 2000 Hz 3-D shape measurement speed.

Conventional cytology is a rapid chair-side method for diagnosis, but it relies on laborious fixing and staining protocols. As cytology specimens are transparent, it is very hard to visualize them under a bright-field microscope without staining. Quantitative phase imaging techniques have opened up an interesting and potential diagnostic method for volumetric three-dimensional (3-D) visualization of the transparent specimens without any need for sample preparations. We explore the use of digital holographic microscopy in clinical application of oral cytology for the 3-D visualization of buccal cells with high contrast without any additional sample preparations. We also propose nuclear to cytoplasmic (N  /  C) volumes as a much more accurate parameter for identification of multinucleate and actively dividing cells. We quantify the cellular volumes, and N  /  C ratios for 203 buccal cells taken from five healthy volunteers to clinically validate the technique and compare them with the traditional N  /  C area ratios as well as the histology standards. The mean N  /  C area and volume ratios are found to be 0.0322  ±  0.0149 and 0.0648  ±  0.0286, respectively. Our approach highlights the dawn of a new method for a label-free/nondestructive volumetric oral cytology evaluation, with high potential for exploration of suspicious oral lesions, in subjects with chronic habits such as alcoholism and tobacco use.

In the application of the grating, it is necessary to quickly obtain the measurement results of the structural parameters, and the parameters of the measured grating are usually reversed by means of scatterometry. We propose a neural network-based grating parameter optimization model. By inversely calculating the diffraction efficiency measurement results, the structural parameters of the grating can be quickly obtained. Applying the model in the experiment, the relative error of the groove depth of the transmission grating is 0.23%, the relative error of the duty ratio is 0.92%, the relative error of the groove depth of the reflection grating is 0.91%, and the relative error of the duty ratio is 2.15%. Using the neural network tool to measure the grating structure parameters, the measurement results can be obtained quickly and accurately.

Fringe projection technique has been widely used for three-dimensional (3D) shape measurement. However, it remains challenging to achieve high-speed measurement. A two-wavelength phase-shifting profilometry method with only four patterns is presented. Specifically, all these four patterns contain two wavelength components. The short wavelength component was used to compute the wrapped phase map, while the long one was used to unwrap the wrapped phase map. The performance of the proposed method was validated by both simulation study and experimental results.

Ferroelectric materials are of great interest because of their rich applications. Several techniques have been used to understand their behaviors. Two-beam coupling configuration using LiNbO₃ crystal as a recording mediums has been extensively used for real-time in-plane displacement of a transparent rough object. Low-power He–Ne laser was used to create the index grating of the speckle pattern inside the crystal and to read the grating to give the Young’s fringes. In this technique, for the in-plane displacement measurement, the image of the transmitted object is formed in the crystal. The aim of our work is to extend the applicability of the two-beam coupling configuration using LiNbO₃ as a recording medium for the evaluation of in-plane displacement of a transparent rough object using speckle photography method; measurement uncertainty of in-plane displacement was studied on a wide range of displacements using experimental and new theoretical formula for displacement measurement.

We present a simple fiber-optics probe system that could be used in any lab for convenient determination of optical properties of liquid phantoms based on diffuse reflectance and transmittance measurements in the visible/near-infrared region. We employed Monte Carlo simulations to determine the optimal system setup and to test the inverse algorithm employed to extract the optical properties from measured reflectance and transmittance. The inverse algorithm involved obtaining the fit merit function for values within the optical property range and determining the minimum. The performance of the method was tested by predictive error and validated using similar matrix of milk–ink phantoms on reflectance and transmittance. In the range of optical properties of phantoms with optical properties of 0 to 0.5  cm^−  1 for μ_a and 20 to 140  cm^−  1 for μ_s, the median prediction error for the test phantoms at 630 nm was 1.51% for μ_s and 8.82% for μ_a. The median difference in predicted values versus expected values was 1.15  cm^−  1 for μ_s and 0.01  cm^−  1 for μ_a. In comparison with other techniques, our method was a simple, fast, and convenient way to determine optical properties of liquid phantoms.

We report on the design, development, and field deployment of a 10-mW, 4320-nm distributed-feedback quantum cascade laser-based tunable diode laser spectroscopy (TDLS) system in India for in situ measurement of atmospheric CO₂. The portable system was deployed at Mount Abu (24.5926° N, 72.7156° E), a hill station in western India, to carry out week-long measurements of background atmospheric CO₂ using direct detection. The mean mole fraction was estimated to be 396  ±  8  ppm. The system was then deployed in Gandhinagar (23.2156° N, 72.6369° E), the capital of the state of Gujarat, to make foreground measurements over the next week. The mean mole fraction at this location was 503  ±  27  ppm. The difference between the background levels in Mount Abu and foreground levels in Gandhinagar is evident. The detection limit of the system, as measured from an Allan variance analysis, was determined to be 260 ppb for an integration time of 58 s and a path length of 20 cm, which is sufficient for such measurements. Another compact and light-weight TDLS system was also deployed for water vapor measurement. It consisted of a 1392.54-nm distributed feedback laser driven by custom electronics and a digital signal processor to carry out waveform generation, data acquisition, and postprocessing tasks.

Polarimeters have broad applications in remote sensing, astronomy, and biomedical imaging to measure a scene’s polarization state. An intrinsic coincident (IC) full-Stokes polarimeter was previously demonstrated and optimized to achieve high temporal and spatial resolution. We optimized the IC polarimeter by introducing additional waveplates or measurement channels and compared it with existing polarimeter architectures under signal-independent Gaussian noise and signal-dependent Poisson noise. The quantitative comparison of noise variances showed that the IC and division-of-amplitude polarimeters have the lowest noise variances due to their higher signal collection ability. Both polarimeters have a factor of 2 and 2 improved signal-to-noise ratio, in the S₀ component, for Gaussian and Poisson noises, respectively, as compared to division of time, division of focal plane, and division of aperture polarimeters. While the division of amplitude and IC polarimeters outperforms other approaches, the IC polarimeter has a significantly simpler design, potentially allowing for cost-effective, high-performance polarimetric imaging.

A telephoto structure-based laser autocollimation with common-path compensation method is proposed to compensate laser beam drift of laser autocollimator. According to the analysis, the measurement beam and the reference beam propagate alongside nearly the same path with approximately identical amounts of drift. Moreover, the ellipses fitting algorithm based on least square approach ensures the accuracy of extracting centroid of the beam while the only photodetector (CCD) with the telephoto objective and several reflectors guarantees the compaction and effectiveness of the system. Simulations and experiments demonstrate a significant beam drift compensation result up to 86.5%. In other words, the stability of the laser beam in the process of measurement is improved.

The purpose of this study was to compare the optical properties of different astigmatic optical surfaces by direct physical measurement of their surface shapes. The back-surface heights of different astigmatic optical lenses were measured with a freeform measuring machine (FMM). In order to calculate the function of the part point cloud fitting surface for the dispersed data points of the astigmatic lenses, the measured shape data were modeled through surface fitting of a bicubic spline. The principal curvatures of each point on the surface were calculated, and the optical properties of each surface and their combinations were generated as contour plots using custom MATLAB routines. The fitting surface of the actual measurement points was compared with the design surface to determine the surface error. Analyses showed that this nonoptical method using an FMM can be used to effectively evaluate a cylindrical lens by surface height measurements alone. Compared to the optical measurement method, the optical properties derived directly from the surface shape can provide information not accessible by other methods. Therefore, this approach is potentially useful to clinicians who want to better understand the design of astigmatic optical lenses for making better recommendations to their clients.

Conventional double-grating monochromators used in pure rotational Raman (PRR) temperature LIDAR usually adopt the Littrow configuration to separate backscattered PRR lines. A mirror is added to this configuration, thereby producing the Littman configuration. The dispersion of the modified configuration is greater than thrice that of the Littrow configuration for incident angles larger than 60 deg. A spectroscopy system with a linear dispersion better than 0.9  mm  /  nm is designed for the 532-nm excitation laser wavelength, and the selected N₂ PRR lines are effectively separated. The overall system is simulated using only off-the-shelf optical components, and the results show that the volume is smaller than 240  ×  200  ×  80  mm³.

Stray light represents a major performance limitation for optical instruments. Analyses are done with ray-tracing software to evaluate the stray light performances of a design and, if necessary, improve it before manufacturing. Accurate simulations, however, require sending a sufficient number of rays. Hence, the process can be very time-consuming. We introduce the concept of stray light entrance pupil (SLEP) and demonstrate how it can be an efficient tool for simulating stray light for point sources. The SLEP defines a pupil over which light entering the optical system generates stray light reaching the detector. When that pupil is smaller than the first lens of the system, rays can be sent only through that pupil instead of the full lens aperture. Therefore, the time required to perform the simulation is reduced. Moreover, the efficiency can be further improved by defining a source with nonuniform ray density. The SLEP method is demonstrated on a wide-angle Earth observation camera and a time reduction up to about 20 is obtained. The SLEP concept can also be used to facilitate experimental characterization.

Our study contains performance and design of a spectral amplitude code-optical code division multiple access (SAC-OCDMA) system using proposed modified new diagonal (MND) code. The proposed MND code has advantages as very low cross-correlation value compared to other code sequences. Also the code has a short length for the higher code weight value. Furthermore, due to its enormous code property, it also introduces very low multiple access interference. Thus the MND code-based SAC-OCDMA system permits a higher number of users. The MND code construction method is also explained, which is very easy using diagonal matrices. Based on the theoretical analysis, bit error rate (BER) performance of MND code AND-subtraction scheme compare with conventional codes is better than random diagonal code, Pascal’s triangle matrix code (PTMC), and multidiagonal (MD) code, which makes it spectral efficient. It provides 5 dB lower BER compared to MD code and PTMC for 90 users. Simulation of the MND code-based system for four users with 2 Gbps data rate has been successfully demonstrated using the AND-subtraction scheme and the direct detection scheme.

A compact optical zoom camera module with Alvarez freeform elements is reported. A 3  ×   magnification in the optical zoom system was achieved by means of lateral shifting two pairs of Alvarez lenses. The optical design performances, profiles of the freeform surfaces, tolerance analysis results, and Monte Carlo yield simulation for mass production of the optical zoom system are presented. The optomechanical structures of the whole camera module including the barrels, actuators, and the slide-guiding systems are also described. The Alvarez elements and aspheric lenses were fabricated by precise injection molding and the movable elements are actuated by voice coil motors with a stroke of 3 mm. A camera module was developed with a size of 25 mm (width) × 25 mm (length) × 6 mm (height). The zooming and imaging capabilities of this Alvarez zoom lens were demonstrated experimentally.

We present a general optical design survey of two-mirror unobstructed plane-symmetric freeform (FF) telescopes to provide a standardized framework and reference for further developments in the field of FF optics. We find that there are fundamentally two main design forms: those that use a positive tilt of the secondary and those that employ a negative rotation to achieve the unobstructed condition. Utilizing this survey, results can be categorized into simple groups of two-mirror unobstructed FF telescopes, analogous to the distinction between a Gregorian-type telescope and Cassegrain-type telescope. Allowing FF surfaces in optical design can enable more compact telescopes while potentially improving the image quality and allowing wider fields of view (FOVs). We define a FF optic as a nonrotationally symmetric mirror or lens, typically with large departures from a best-fit spherical surface (many microns or even millimeters). New manufacturing and testing methods have enabled the production of these types of surfaces. The telescopes we present maintain a 4  ∶  1 aspect ratio of the FOV and utilize X–Y polynomials for mirror surface description. We impose a plane symmetric constraint on the system and an accessible entrance pupil. We generate charts documenting the relationship between FOV and F  /  # for the presented optical design forms. We also compare our results to a baseline rotationally symmetric system. These results provide a general method of evaluating baseline designs for two-mirror unobstructed FF telescopes.

A Q-switched fiber laser at the C + L band using an organic solution saturable absorber (SA) of dimethyl sulfoxide (DMSO) is proposed and demonstrated. The modulation depth of the DMSO-SA is measured to be 5.09%. The Q-switched operation in the laser was achieved using DMSO-SA. This Q-switched fiber laser shows an average output power of 7.9 mW with a pulse repetition rate of 21.74 kHz, a pulse width of 9  μs, and single pulse energy reaches 458.2 nJ with power set to 140 mW. Varying wavelength from 1561 to 1594 nm resulted in a stable Q-switched pulse output. The novel Q-switched laser exhibits self-starting, good stability, and high pulse energy characteristics.

The free-space optical communication based on 8-ary orbital angular momentum shift keying (8OAM-SK), where information can be encoded as the OAM state of light, is studied. We implement a numerical simulation using a phase screen model for atmospheric turbulence, which is based on the Fourier transformation method, to analyze the influence of atmospheric turbulence. The bit error rate performance of the 8OAM-SK system is investigated in several different conditions. The numerical simulations demonstrate that higher received power is required in stronger turbulence to achieve acceptable signal quality. It is also revealed that lower data rate shows better tolerance to the turbulence strength.

A hybrid technique for terrestrial free space optic (FSO) system has been proposed in this paper. The hybrid technique is a combination of 8  ×  40  Gbps dense wavelength-division multiplexing and a multicarrier transmission (MCT) scheme such as coherent optical orthogonal frequency-division multiplexing (CO-OFDM). The prime design objective is to minimize the issues related to the terrestrial FSO-based system for atmospheric turbulence, bandwidth management, and receiver sensitivity. The cyclic prefix bits have been added with the data symbols of CO-OFDM, which minimizes the effect of nonlinearity due to atmosphere and reduces intersymbol interference. The dual-polarized quadrature phase-shift keying (DP-QPSK) sequence is used to modulate the subcarriers of the MCT system. DP-QPSK is very well known for its optical signal-to-noise ratio tolerance. It has been found that, by the incorporation of a hybrid scheme in the FSO system, a propagation range of 2.2 km in atmospheric turbulence regime for the targeted bit error rate (BER) of 3.8  ×  10^−  3 or log of BER of −2.42 is achieved. A contrast performance comparison has also been carried out for the proposed hybrid system with different advanced modulation schemes such as differential quaternary phase-shift keying and four-level quadrature amplitude modulation. The Gamma-Gamma-type distribution function is considered for estimating the turbulence effect of the free space channel. Mathematical modeling related to the proposed system has also been incorporated for better analysis. This type of hybrid technique for the FSO system with the incorporation of DP-QPSK modulation format will give more technical feasibility to the modern communication system.

A single-longitudinal-mode pulsed Ho:YLF laser was demonstrated and studied experimentally at 2065.68 nm via injecting a unidirectional seed laser with double corner cubes to a Q-switched Ho:YLF power-oscillator. Up to 733-mW single-longitudinal-mode Ho:YLF laser with a structure of double corner cubes cavity is employed as seed laser with the advantages of narrow linewidth and high antimisalignment sensitivity. For single-longitudinal-mode injection-seeded Q-switched Ho:YLF laser, the output energy of 4.41 mJ is obtained with the repetitive frequency of 100 Hz, pulse width of 136 ns, and slope efficiency of 19.3%. The experimental results show that this method is a potential way to realize single-longitudinal-mode injection-seeded Q-switched Ho:YLF laser with narrow linewidth and high antimaladjustment sensitivity.

As a common air pollutant, incense has caused certain harm to the atmospheric environment and human health. The spectra of the incense ash smoke were analyzed online in situ to identify the main elements such as Ca, K, N, and H by laser-induced breakdown spectroscopy (LIBS) technology. Additionally, molecular bands of CN were also recognized in the spectrum of smoke and the vibrational and rotational temperatures of CN molecule were calculated. Moreover, the incense was dipped into the solutions containing Pb to simulate heavy metal pollution in the atmosphere for offline quantitative analysis and online detection. The internal standard calibration method was applied for the quantitative analysis of Pb/Fe and the linear correlation coefficients (R²) obtained is 0.99709. Furthermore, a home-built single-particle aerosol mass spectrometer was utilized in combination with LIBS technology for online analysis of Pb isotopes in smoke. Finally, the detection limit of Pb in the incense ash is calculated to 46.6  mg  /  kg.

We report the simulation and modeling of a passively Q-switched dual-cavity fiber-laser-doped Yb–Yb. To the best of our knowledge, this is the first time that the traveling-wave model has been applied to the study of the dynamics and to the optimization of the two laser signals produced by the two-cavity laser. An excellent agreement between our simulation results and the experimental measurements published by other researchers is obtained. In addition, we show that the density of the saturable absorber (SA) is a crucial parameter for the optimization of the two laser signals. An increase in the peak power of the two laser signals by an order of magnitude is obtained by increasing the density of the SA.

A two-color visible frequency comb system based on a 1.5-μm all-polarization-maintaining (PM) fiber femtosecond laser was developed. This configuration relies on the implementation of three amplifiers, seeded by a single master oscillator. With the repetition rate (f_r) of the oscillator locked to a reference frequency of 200 MHz, the output of the first amplifier was used to generate the feedback signal and achieve simultaneous phase lock of the carrier envelop offset frequency (f_ceo). The remaining two independently configurable amplifiers followed by highly nonlinear fibers and MgO-doped periodically poled lithium niobite crystals were used to produce visible comb lights at 543 and 633 nm (in air), respectively. By referencing to a hydrogen maser, the Allan deviations of f_r and f_ceo at a gate time of 1 s are 438  μHz and 63 mHz, respectively. The spectral bandwidths of the 543- and 633-nm comb lights are 0.157 and 0.174 nm, respectively, and the single-mode powers of these comb lights are higher than 1  μW. The multiple-branch all-PM fiber-based visible frequency comb system exhibiting a narrow spectrum and a high single-mode power will facilitate the development of optical clocks and wavelength standard calibrations.

Channel estimation is a key digital signal processing algorithm in optical discrete multitone (DMT) transmission systems. The least-square (LS)-based channel estimation is a simple method, but it is very sensitive to various noises and other interference. The estimation accuracy can be improved using the LS-based intrasymbol frequency-domain averaging (ISFA) channel estimation method. However, there exists inaccurate channel estimation for the edge data subcarriers caused by chromatic dispersion and nonsymmetric averaging windows. We propose a hybrid channel estimation method with LS-based intersymbol frequency-domain averaging and modified ISFA to improve the estimation accuracy of edge data subcarriers and the stability of the bit error rate (BER) performance. The proposed hybrid channel estimation method is experimentally investigated in a short-reach 16-ary quadrature amplitude modulation-encoded DMT transmission system. After 20-km standard single-mode fiber transmission, with the help of the proposed hybrid channel estimation and at a BER of 3.8  ×  10^−  3, the receiver sensitivity in terms of the received optical power can be improved by about 1.8 dB compared to that of the conventional ISFA. Furthermore, the proposed hybrid channel estimation has better BER stability.

The 2.5-terahertz quantum cascade lasers (THz QCLs) based on first-order distributed feedback (DFB) Bragg grating are reported. The loss and threshold gain within different grating duty cycles are calculated according to the mode-coupling theory. The laser output power reaches up to record values of 34.1 mW in pulse mode and 23.4 mW in continuous wave mode at 15 K. The threshold current density is as low as 125  A  /  cm². The single-mode emission is achieved, and the side-mode suppression ratio is 12 dB. In addition, the device is bonded together with the other two DFB THz QCLs (2.9 and 3.0 THz) on a copper chip. The simultaneous different wavelength emissions with single mode are successfully realized.

We propose and demonstrate an approach to generating a frequency-hopping (FH) microwave signal using an optoelectronic oscillator (OEO) based on stimulated Brillouin scattering (SBS). An SBS-based OEO is utilized to generate pure microwave signals as local frequency signal, and a dual-drive Mach–Zehnder modulator is employed to generate the FH signal. During the experiment, the local frequency generated by the OEO is 9.2 GHz with a power of 0 dBm and the FH signal hopping between 9.2 and 18.4 GHz is generated with FH speed up to 2 GHz.

A high-temperature fiber sensor based on two paralleled fiber-optic Fabry–Perot interferometers (FPIs) with ultrahigh sensitivity is proposed and experimentally demonstrated. Unlike the structures of the traditional Vernier effect composed of the cascaded components, the proposed fiber sensor is made up of two paralleled FPIs for high-temperature sensing with advantages of simple fabrication, high sensitivity, and low noise. One FPI for sensing is obtained by fusing a short section of polarization-maintaining photonic crystal fiber into the lead-in single-mode fiber (SMF). The other for reference is obtained by fusing a short section of hollow core silica tube between two SMFs. The two FPIs have similar free spectral range, with the spectral envelope of the paralleled sensor shifting much more than the single-sensing FPI. Experimental results indicate that the proposed sensor possesses considerable temperature sensitivities of −45 and −92  pm  /    °  C, respectively, in the measurements of 100°C to 300°C and 300°C to 800°C.

A laser-tuned whispering gallery mode (WGM) microbottle resonator based on ethyl-orange (EO)-doped polyvinyl alcohol (PVA) film is proposed. Due to the photo-induced isomerization feature of the azobenzene material, the WGM resonance wavelength could be tuned by controlling the power density of the lateral pumping laser at 473 nm. Experimental results indicate that the resonance wavelength tunability would generally get strengthened with the increment of the thickness of the PVA film, while it almost remains unchanged under different microresonator diameters. The proposed laser-tuned microcavity integrated with EO is anticipated to find potential applications in tunable optical filtering, optical sensing, and future all-optical network systems.

Currently, reversible logic has gained a lot of interest, and it is a reliable solution in optical computing, low-power CMOS, quantum computing, and nanotechnology. Being reversible logic, one-to-one mapping between input and output causes minimal loss of information. In fact, optical Feynman gate (FG), one among many reversible logic gates, is a potential candidate for the realization of low-power photonic computational circuits. We propose and design a reversible optical FG using four titanium indiffused lithium niobate (Ti  :  LiNbO₃) directional couplers. The elaborate design and analysis of uniform Δβ electrodes configuration of directional coupler has been presented preceded by in-depth design details and analysis of single-mode waveguides, fabrication tolerance, and S-type bend waveguides at 1.55-μm transmitting wavelength, using effective-index-based matrix method. Switching voltage of directional coupler, considering z-cut substrate, for a 134-nm-thick SiO₂ buffer layer, is obtained as 24 V. The chip dimension of optical Feynman gate is of 23.8 mm length and 0.63 mm width.

To analyze the mechanism of damage threshold enhancement after laser conditioning, the fluorescent and stimulated Raman scattering properties of unconditioned and laser-conditioned KD₂PO₄ crystals are compared in detail. It is revealed that the intensity of fluorescence decreases significantly, especially fluorescence <400  nm, after nanosecond laser conditioning, and the change of the stimulated Raman scattering peak at 921  cm^−  1 is very weak. Moreover, the intensity of fluorescence further decreases after subnanosecond laser conditioning. A sharp decrease in the fluorescence intensity <400  nm reflects a change in energy levels of the electron defects in a crystal. The Raman scattering proves very weak change of the PO₄ vibrational modes. Furthermore, a laser-conditioning mechanism is discussed in combination with electronic transition and thermal processes.

Ultracompact simultaneous XOR and XNOR logic gates are proposed and analyzed. The suggested design is based on two-dimensional Si photonic crystal (PhC) with a central hole infiltrated by nematic liquid crystal (NLC) of type E7. The plane wave expansion method is used to obtain the photonic bandgap for both transverse electric mode and transverse magnetic mode. Further, the transmission through the proposed logic gates is calculated by the full vectorial finite element method. The numerical results show that the reported XOR and XNOR logic gates can be operated around wavelength of 1500 nm. In addition, the operation of the designed logic gates can be switched on/off by controlling the NLC biasing state. Such PhC logic gates have a compact size of 47  μm² and can achieve a large contrast ratio of 26 dB. Therefore, the suggested design has advantages in terms of tunability, low power consumption, compact size, simplicity, and compatibility with nowadays fabrication technology, which will be suitable for photonic integrated circuits.

Celestial navigation has remarkable performance in autonomous navigation without error accumulation. For supplying orientation information to a portable vehicle in real time, a compact polarization sensor with high precision and strong robustness was constructed in this study based on the mechanism of insect polarization-opponent neurons structure. The sensor, composed of polarization-dependent module and microcontroller unit, could supply heading angle for real-time navigation. To enhance the robustness of sensor in a complex environment, a self-adaptive algorithm based on information entropy theory was proposed. The algorithm could eliminate the effect of random obstacles in the sensor field under constantly changing light conditions. The laboratory and outdoor tests indicated that the sensor, with ±0.1  deg measured error and ±0.4  deg fluctuation under natural obstacle, had potential application prospects in polarization navigation.

We designed all-optical AND, OR, NOT, and XOR logic gates based on photonic crystals configuration. This configuration consists of a bend waveguide with single embedded rod and a T-branch waveguide. The proposed structure does not consist of nonlinear rods. The constructive and destructive interferences between incident and reflected waves have caused to switch the output of gate. The gate contains a two-dimensional square lattice made of dielectric rods embedded in the air. It operates at communication wavelength of 1550 nm when the lattice constant of structure is 500 nm. Simplicity of the proposed logic gates provides the possibility of application in practical logic gate and large-scale optical integration.

We design and demonstrate a temperature sensor based on an ethanol-sealed double helix microfiber coupler (DHMC). The sensor consists of two intertwined microfibers with a minimum waist diameter of up to 3.4  μm. The temperature sensitivity of the DHMC can reach up to −2.03  nm  /    °  C in the range of 25°C to 55°C due to the thermo-optic effect of ethanol and the thermal expansions of the sealant and sealed liquid. Effects of different mechanisms on the temperature sensitivity are also investigated theoretically and experimentally. By encapsulating the coupler in a capillary, the mechanical strength and environmental anti-interference of the sensor are greatly improved. Moreover, the device with easy fabrication, compact size, and low cost is suitable for temperature measurement in most environments.