OE lists the reviewers who served the journal in 2022.

The idea of photonic crystal came to be when E. Yablonovitch and S. John recommended a structure in 1987 having periodic alteration of refractive index in one or multiple directions. Photonic crystals have the potential to manipulate and tailor the flow of light across the crystal, which gives advantage to invent many photonic devices on the microscopic scale having very small footprints. In recent years several articles have been published on the advances of photonic crystal-based structures. This review article mainly focuses on the several fabrication techniques of photonic crystals and their applications in different fields. Several photonic crystal-based structures such as logic gates, optical sensors, polarization beam splitters, and absorbers for solar cells are reviewed in this paper to show recent advancements on this trending topic. Also, a brief review of the different steps of fabrication of photonic crystals and different fabrication methods proposed by researchers is articulated in this paper.

Fiber Bragg grating (FBG) pressure sensors have the potential to replace conventional voltage sensors due to their compact size, resistance to electromagnetic interference, excellent safety, distributed sensing, and numerous other intrinsic benefits. It is frequently employed in the domains of civil engineering, aerospace, and medicine. Our work examines two types of sensitized FBG pressure sensors, namely FBG pressure sensors with innately improved sensitivity and FBG pressure sensors with extrinsically increased sensitivity. Our work examines microstructured fiber Bragg grating pressure sensors and polymer fiber Bragg grating pressure sensors for FBG pressure sensors with innately heightened sensitivity. Our research examines metal-mechanical FBG pressure sensors and polymer-mechanical FBG pressure sensors for extrinsically sensitized FBG pressure sensors. This report also summarizes the benefits and drawbacks of various FBG pressure sensors and temperature compensation techniques. Finally, the future of FBG pressure sensors is examined.

A method of the zero-order-removal off-axis digital holographic reconstruction by recording three holograms with different beam ratios is presented. The zero-order-removal hologram can be constituted using two fitting coefficients in the combination of three holograms, in which the three off-axis holograms with different intensity ratios of the object and reference beams are recorded via arbitrarily turning a half-wave plate. The validity of the zero-order removal of the resultant hologram is proved by expression. The filtering region for the zero-order-removal hologram can extend to the center of its spatial-frequency spectrum domain, which makes higher spatial frequencies on the positive first-order intercepted. In the experiments, the reconstructed amplitude and phase images demonstrate the effectiveness of this zero-order-removal approach and the improvement on imaging resolution.

Dictionary methods have proved very useful in compressive sensing. Herein we show that, for dictionaries to represent the point spread functions (PSFs) of image formation in atmospheric turbulence, it is possible to construct dictionaries computationally. Computationally created dictionaries make unnecessary the exhaustive collection of PSF data, for arbitrarily large numbers of conditions of turbulence and optical image formation systems, while also reducing the overall number of dictionaries that need to be created and stored.

The high dynamic range image obtained by multi-exposure image fusion (MEF) contains more detailed information, which has broad application prospects and crucial practical significance in many fields. However, due to the introduction of the ghosting artifacts caused by object movement and camera shake, MEF in the dynamic scenes has always been a challenge. To address this problem, we designed a deghosting method for MEF. The over- and under-exposed images are corrected by intensity mapping and consistency detection to obtain the aligned latent images. Then the high- and low-frequency components of the latent images are generated using weighted least squares filtering. The blending weights are calculated based on the image luminance and the exposedness function. These frequency components are integrated into the final deghosted image with more texture details and vivid color. A comprehensive evaluation experiment is carried out, proving that the proposed method has a better visual effect and stable performance than the state-of-the-art deghosting MEF methods.

In this work, we present a method to generate vector beams with a 4f polarization Fourier filtering system that combines a spatial light modulator (SLM) at the input plane and a polarization diffraction grating (PDG) at the output plane. In the Fourier plane, two quarter-wave plates are employed to transform the +1 and −1 diffraction orders onto circular right (RCP) and left (LCP) polarizations, respectively. The PDG at the output plane recombines the two beams producing the colinear superposition of RCP and LCP beams. The application of a random encoding technique to multiplex diffractive elements on the SLM allows the independent encoding of different patterns on the final beam, thus arbitrary vector beams can be generated at the output. Experimental results are included that demonstrate the capability for this approach to encode a variety of polarization vector beams with different topological charges.

We present an iterative procedure to retrieve the wavefront using a Shack–Hartmann sensor. Traditionally, a uniform array of microlens is used as a domain to reconstruct the wavefront under test; however, this properly works if the wavefront differs slightly from a plane. But generally in optical tests, astronomy, and ophthalmology the wavefronts under test can have appreciable deviations with respect to a plane wavefront. The proposed method considers the reconstruction of the wavefront deformations with respect to a known reference wavefront. At each iteration, the wavefront deformation is used to find a reference wavefront closer to the wavefront under test and a domain closer to the actual domain. When the values of the wavefront deformations are small enough, we can take the reference as the wavefront under test. In addition, we simulate the centroid positions of the spot pattern used to retrieve the wavefront under test using the proposed method. We compare our results with those obtained by three other different approaching methods described in the literature (Modal, Trapezoidal Rule, and Southwell). For the simulations used in this work, our method retrieves wavefronts closer to the real wavefront than the other methods. Also, we apply the proposed method to an experimental case to reconstruct the wavefront under test using a Shack–Hartmann sensor.

We summarize our development of a low-cost instrument for the detection of fabrication errors in diffraction gratings. Our instrument applies a low-cost digital camera and high dynamic range (HDR) imaging in the focal plane of a lens to analyze light reflected by a diffraction grating. A dynamic range close to 10¹⁰ is achieved for a spatial frequency range that is relevant for types of errors that occur in the lithographic fabrication of gratings. We also describe a modification of the instrument in which a spatial filter is used to block the large fraction of light that does not carry information on fabrication errors. This “coronagraph” modification reduces measurement times by about an order of magnitude. A unique pseudologarithmic transformation is described for the visualization of wide range data that include zero or negative values, such as HDR images.

Foucault knife-edge method is an irreplaceable qualitative testing method in the early stage of optical processing, but it needs to accurately place the knife-edge at the focus of the mirror surface to be measured for testing. In view of the complex and difficult calibration process of the knife-edge instrument and the inability to perform quantitative testing efficiently, here the Foucault knife-edge testing method is improved by digitizing and automating it. The knife-edge instrument is first placed on the motorized precision translation stage for two programmed cutting movement perpendicular to the optical axis with controlled axial spacing. And the normal vector of each point on the mirror surface to be measured is solved through the knife-edge transverse position relationship for the bright and dark transition of the corresponding point on a series of knife-edge shadow grams obtained by two cuts. Then the automation and quantification of knife-edge method can be realized. The experimental results of this method are compared with the interferometer testing results, which have good consistency and high accuracy. This method does not require high calibration accuracy for the knife-edge instrument and can perform rapid and efficient testing. It provides a testing method with good performance for automatic and quantitative testing in the early stage of optical processing.

We present both experimental measurements and Monte-Carlo-based simulations of transmission polarization to analyze the concentration variation effects of the water fog particles. Simulations based on Monte Carlo program have been conducted for tracking photon transmission process with the radius and refractive index of water fog samples under different optical thicknesses. Correspondingly, experiments with an environment modulation system show that by controlling the water fog concentration, the Mueller matrix and the depolarization characteristic change in a regular way. Both the simulation and the experimental results show a good distinction of Mueller matrix among the light, moderate, and thick fog samples, and the depolarization property of thick fog environment is more prominent. Moreover, circular polarization persists better than linear polarization in more serious fog. These works can provide a tool to examine different media concentrations by the polarization patterns and broaden the application range of polarization.

Quantum key distribution (QKD) can provide an unconditionally secure communication encryption method. Continuous-variable QKD (CVQKD) requires extracting the key from the noisy channel, leading to higher requirements for the error-correcting codes used in multidimensional reconciliation. We extend the quasi-cyclic low-density parity-check of the radio design for the global 5G mobile communication technology standard to achieve error correction under lower signal-to-noise ratio on integrated hardware. A field programmable gate array (FPGA) chip is used to realize the approximate lower triangular matrix encoding algorithm, and the core module only has the circular shift register, which reduces the encoding complexity, improves the encoding efficiency, and reduces the hardware resource consumption. For extended super-long code words, the decoding algorithm requires additional hardware resources to implement, which the previous algorithm cannot meet. Therefore, we present a hardware implementation of offset minimum sum algorithm (OMSA), which can avoid operations of complex mathematical formula. The offset factor of OMSA reduce the error caused by the low accuracy of calculation on the hardware. The update of the decoding information is layered in a partially parallel way in the matrix to achieve the cross processing of node information. It speeds up the transmission of information between different nodes and the convergence of decoding algorithm of low-complexity parallel structure. Simulation results show that the maximum theoretical coordination efficiency is 85% when the code with block length is 69632 at a bit rate of 22/68 and the signal-to-noise ratio asymptotic threshold is 0.7. Using an FPGA, ∼0.1 frame error rate was achieved, but with a zero-bit error rate, the optimal achievable secret key rate is about 200 Kbps at 30-km distance theoretically. For a 200-MHz system clock on the successfully decoded block, 125 Gbps encoding throughput and 472 Kbps decoding throughput was achieved, better than the theoretical key rate of prototype of CVQKD.

A self-built laser projection system for optical transverse strain measurements in tensile testing is presented. The setup based on laser diode modules, charge-coupled device array detectors, and standard optomechanical components is proposed to be a low-cost system for testing polymer samples. The optical setup is mobile and can easily be mounted on a tensile test machine. Circular cross-sectional changes in polymer diameter were detected with 10-μm resolution and stress-strain curves obtained by a tensile test machine. The article describes signal processing using the open-source programming language R, and the transverse deformation of the polymer sample is evaluated in two perpendicular planes. The results obtained by the optical system may be used to accurately describe the models of energy-based mechanical properties of polymers for complex load conditions.

We present a fringe order correction method for various absolute phase retrieval algorithms. In fringe projection profilometry based on absolute phase retrieval (FPP-APR), the mismatches tend to be easily generated around the 2π discontinuities or edges of the wrapped phase due to the defocus and noise of the system. In this paper, a staggered wrapped phase with a phase shift of 2π / N segments the calculated wrapped phase into a left-wrapped phase and a right-wrapped phase. Then, a statistical method independently determines the fringe order of each closed-wrapped phase without the 2π discontinuities. The experiments demonstrate that the proposed fringe order correction has the generality and simplicity for the existing absolute phase retrieval and performs high robustness to measure the colorfully complex objects of daily life.

A configuration for the measurement of thickness changes in materials through one-shot digital speckle pattern interferometry (DSPI) was developed. The phase maps calculation was made by adding carrier fringes by the multiple aperture principle and Fourier Transform Method (FTM). With this setup, interferometry configurations verified that the simultaneous and instantaneous visualization of two opposite faces of a surface is possible. In addition, the combination of the simultaneous results obtained from both sides of the material makes it possible to determine displacements with greater sensitivity or to identify changes in their thickness. The validation and demonstrative tests were carried out with a 1-mm-thick aluminum plate with a 5-mm diameter through hole coated. Thickness changes to 2 μm were measured.

Conventional temporal pulse shaping (TPS) for radio frequency (RF) arbitrary waveform generation (RF AWG) based on the Fourier transform relation between the input–output waveform pair requires the electronic AWG to generate RF input signal, which greatly limits the output waveform diversity due to the relative low sampling rate and bit resolution of electronic AWG, i.e., high-fidelity square waveforms are hard to be achieved since high-resolution broadband Sinc input signals are difficult to be generated by current commercial electronic AWGs. The approaches based on TPS with phase modulation incorporating with iterative algorithms can relatively improve the waveform diversity by applying the optimal phase information. However, time-consuming iterative algorithms significantly restrict the waveform reconfigurability, i.e., desired RF waveforms cannot be generated in real-time. We propose a novel high-stable and reconfigurable RF AWG scheme with multi-tone inputs, which aims to improve the output waveform diversity with simple manipulation and high stability. In our design, any desired RF waveform can be achieved in real-time by simply adjusting the power values of multi-tone inputs. A proof-of-concept experiment was implemented, which fully verified the feasibility of the approach. The system performance in terms of output waveform stability was investigated in detail. As no electronic AWG is employed and no iterative algorithms are required, the proposed design provides a promising solution for high-performance reconfigurable photonic-based RF arbitrary waveforms generation.

A composite process of laser cladding and laser shocking is proposed to prepare the Ti-6Al-4V alloy coating. The structure before laser shocking is flake β phase and acicular martensite α ^′ phase precipitated at the grain boundary of the flake β phase. The staggered distribution of acicular martensite α ^′ forms a basket structure. After laser shocking, the flake β phase is refined, and the basket structure orientation becomes more complex. In addition, the structure is more uniform and denser. The laser shocking influence depth is about 1.7 mm, the microhardness is increased to 470 to 530 HV_0.2, the friction coefficient is decreased to 0.35, the wear amount is decreased by 26%, and the wear form changes from the comprehensive role of abrasive and adhesive wear to abrasive wear.

The additive manufacture of polymer optical elements has the promise of reducing component weight, providing new design capabilities, and enhanced performance for a wide variety of military and commercial optical systems. We review progress in the development of three-dimensional (3D)-printed gradient index (GRIN) lenses and optical phase masks. The 3D printing process uses a modified commercial inkjet printer and ultraviolet curable polymers that have specific nanoparticles added to them to modulate the index of refraction. Complex optical phase masks for the generation of Airy laser beams and polymer GRIN lenses to replace conventional glass lenses used in a telescope or riflescope are created. The generation and propagation of Airy beams using these polymer-generated optical phase masks have been investigated and analyzed through experimentation, simulations, and comparison with recent theoretical predictions. Airy beams have been generated using the conventional approach with a spatial light modulator and compared to the 3D printed optical phase masks. The maximum nondiffracting propagation distance of an aperture truncated Airy beam was experimentally measured. The results show that the maximum nondiffracting propagation distance of a laboratory generated Airy beam is proportional to x02, the Airy beam waist size squared. The size of the Gaussian envelope beam has a weaker effect on the Airy beam propagation distance. The experimental results were compared with current theoretical models. A set of 1-inch-diameter 100-mm focal length polymer GRIN lenses have been made using 3D printing. Transmission and modulation transfer function results for the lenses are reported.

A Doppler asymmetric spatial heterodyne (DASH) interferometer was designed to measure atmospheric winds at a height of 60 to 80 km by observing the airglow emission line of molecular oxygen at 867 nm. The designed monolithic DASH interferometer exhibited decent thermal stability. The phase thermal drift of the fabricated interferometer obtained from thermal performance measurements was 0.376 rad / ° C. To accurately model and minimize the thermal drift performance of an interferometer in the design phase, it is necessary to include the influence of thermal distortion of the monolithic interferometer components. Therefore, an optical–structural–thermal integrated analysis method based on Zernike polynomials was proposed to accurately calculate the phase thermal drift of the interferometer. The optical model modified by the finite-element method calculated the phase thermal drift to be 0.420 rad / ° C, which agreed with the experimental result within 11.7%. This analysis method can accurately calculate and optimize thermal stability during the design of a DASH interferometer.

Optical switches are critical components for optical communication devices, and currently, they are now bottlenecking the development of optical telecommunications. In this study, we propose an innovative all-optical Kerr switch based on the Brewster angle effect, which exhibits a graphene/SiO₂/graphene/SiO₂ structure and an insertion loss (IL) that can be minimized by tuning the Fermi level of the graphene layers. A novel Brewster’s angle effect is achieved, resulting in a change in the incidence angle under nonlinear conditions as well as on–off switching of the phase change. The proposed switch has perfect absorption at an incident angle of 63 deg, where the phase of the reflected light is shifted from − π to 0. Furthermore, the Brewster angle of the switch was successfully shifted from 63 deg to 80 deg with an incident frequency of 0.8 THz. It was observed that an increase in Fermi level continuously shrank the nonlinear region of the switch. The minimum IL of the proposed optical switch was only 2 dB, which is indicative of excellent energy efficiency. The results of this study can aid in the development of key devices for broadband communications and electromagnetic sensing.

A macrolens with fully covered nanopillars in large area was fabricated by a combination of air-assisted deformation and nanoimprinting. The planar nanopillars were transformed into macrocurved distribution by air-assisted deformation. We tested the nonwetting and antireflectance performance of the fabricated structures and both performances improved by the addition of nanopillars relative to the planar surface. The nanopillars and the curved architecture increased the contact angle by 27 deg and 13 deg, respectively. In addition, the height and diameter of the macrolens could be controlled precisely by the change of the mold size and adjustment of applied negative pressure. Furthermore, the surface reflection was reduced by 1% to 2% over a wavelength range of 500 to 2200 nm by the introduction of gradual index variation. The proposed method is simple, controllable, and has high fabrication efficiency. The macrolens with nanopillars have wide potential applications, such as in optical devices for harsh environments.

Computational design and analyses of nanoantennas obtained via surface shape optimization are presented. Starting with a kernel geometry, free deformations are applied on selected surfaces to reach optimal designs that can provide improved power enhancement capabilities at desired frequencies. An in-house implementation of genetic algorithms is efficiently combined with the multilevel fast multipole algorithm developed for accurate solutions of plasmonic problems to construct the effective optimization environment. The geometries obtained via optimization do not only represent optimal shapes within the allowed deformation limits but also reveal certain types of modifications on kernel geometries to improve their performances.

In aims to enhance the electric-field confinement capability of Bloch surface wave (BSW) with low propagation loss, here, we develop a high-performance hybrid BSW waveguide that incorporates a high-index nano-ridge loaded photonic crystal slab with a silicon dielectric nanowire. Leveraging the mode hybridization, a subwavelength mode confinement in conjunction with long-range waveguiding is achievable. Its robust properties against the possible fabrication imperfection for practical implementations and comparisons with similar hybrid waveguide configurations are also discussed to indicate the improved guiding performance of our proposed waveguide. These remarkable optical properties render such waveguide to hold the promise of building numerous high-performance nanophotonic devices.

We propose a novel family of two-dimensional multi-methods with two codes keying (2D MM with TCK) in spectral amplitude coding optical code division multiple access (OCDMA) networks. The idea transfers one code keying (OCK) of one-dimensional (1D) MM codes into two code keying (TCK) of 2D MM codes. The rationale has OCK transferred into TCK, 2D matrix formulations using the 2D MM codes, and modified cross-correlation. The research solution resolves the first item using two OCKs of 2D MM codes to become TCK of 2D MM codes to call 2D MM codes with TCK, the second item using two sets of 1D MM codes to produce 2D matrix formulations using 2D MM codes, and the third item using the cross-correlation to transfer into a modified cross-correlation. The modified cross-correlation eliminates multiuser interference. The proposed analysis utilizes a modified photocurrent to suppress phase-induced intensity noise. In the numerical results, the number of simultaneous users, data transmission rate, and effective source power using 2D MM codes with TCK are 294, 4.72 Gbps, and − 12 dBm, respectively.

Mode-locked erbium-doped fiber lasers (EDFL) with the low repetition rate and high pulse energy play an important role in many fields, such as micromechanical processing, ophthalmic surgery, biological sample detection, and LiDAR detection. However, in the 1550 nm band, due to the anomalous dispersion and nonlinear effects of erbium-doped fiber lasers (EDFLs), it is difficult to achieve mode-locked pulses especially in long cavities, which brings many difficulties to engineering applications. We analyze and simulate the pulse formation and evolution process in a mode-locked EDFL at a low repetition rate of sub-megahertz. The results show that by decreasing the gain or increasing modulation depth/saturation light intensity of saturable absorber in a specific range, a stable single-pulse mode-locked state can be achieved. Then a multipulse mode-locked state can be achieved by gradually increasing the gain or decreasing the saturation light intensity. In addition, the pulse width can be compressed by adjusting the second-order dispersion coefficient. The numerical simulation results are instructive for the design and development of EDFL at a low repetition rate of sub-megahertz.

Optical systems that emit radiation between the visible and near-infrared wavelength region pose a potential hazard to human vision as the radiation is imaged on the retina. The radiation interacts with the retinal tissue in a photomechanical, photothermal, and photochemical manner that can result in irreversible injuries. To ensure an eye safe system, it is important to correctly apply the laser safety standard IEC 60825-1:2014 or the lamp safety standard IEC 62471:2006. We aim to provide a general calculation procedure for both coherent and incoherent sources, which are compliant with the respective safety standards. An air-equivalent eye model generates retinal images. Two software-based calculation methods are introduced, which are referred to as image analysis. The first method calculates the angular subtense of the apparent source needed for photomechanical and photothermal limits. The second method applies to photochemical limits. Using exemplary optical systems, the image analysis is investigated. The proposed image analysis gives guidance for missing aspects in the standards and reduces ambiguity and complexity. The proposed method can be used for eye safety evaluations since it follows the concept of the safety standards with conservative approaches.

An intracavity, second-harmonic generation, tunable, dual-frequency, passively Q-switched Nd:YAG laser based on a T-resonator configuration with polarization splitting is proposed, whose frequency difference could be doubled in comparison with fundamental lasing. The Nd:YAG, Cr^{4 +} : YAG, and potassium titanyl phosphate (KTP) crystals were set at the shared arm, which could considerably reduce thermal fluctuation and pulse timing jitter between dual-frequency lasers. One birefringent filter consisting of a polarized beam splitter and a half-wave plate (HWP) is placed in each divided arm to select their single longitudinal mode. As a result, the p-polarized and s-polarized passively Q-switched components of 532 nm are simultaneously operated, whose power easily reaches to same and frequency is beneficial to tune theoretically throughout the whole gain bandwidth. The main characteristics of the power, longitudinal mode selection, and the pulse have been tested experimentally. Moreover, the frequency difference of the dual-frequency laser at 532 nm has been widely tuned from 9.6 to 117 GHz, by slightly adjusting the tilt angles of the HWPs. We offer a simple and widely tunable source with potential for portable frequency reference applications in absolute-distance interferometry, terahertz-wave generation, and other fields.

To study the joint effects of turbulence and fog on free-space optical (FSO) communication, a joint fog-turbulence-pointing error probability model for FSO is derived based on the random fog channel, Malaga turbulence model, and pointing error model. The closed-form expressions for the average signal to noise ratio (SNR), outage probability, average bit error rate (BER), ergodic channel capacity, and moment generating function in FSO communication under intensity modulation/direct detection are derived based on the joint model. Based on the unmanned aerial vehicle (UAV) working scenario, applying these expressions, the performance analysis of the inter-UAVs optical wave communication is implemented under the conditions for different beam widths, turbulence intensity and fog density and the pointing error caused by position, orientation, and jitter deviations. The calculated results are in good agreement with the Monte Carlo simulations. The analytical results for the average BER and outage probability show that the increase in beam width can significantly degrade the BER and outage probability, for the UAVs optical communication link. The analysis for the ergodic channel capacity shows that it increases with the increase of average transmission power; however, it increases slowly with the increase of beam width. And the increase in turbulence intensity, fog density, and drone jitter will degrade the communication performance of the system. Our study lays an important theoretical foundation for the development of FSO communication and UAV communication performance improvement in joint fog and turbulent environment.

In this paper, a ring cavity of Er:YAG laser with a single corner cube prism is investigated. Due to the depolarization effect of the corner cube, the tunable output coupling ratio was 0.25% to 72.67% by changing the angle of the λ / 4 plate according to the calculation results of Jones matrix. An experiment for checking the anti-detuning performances of the single corner cube cavity was also carried out. The results indicated that the output power was stable at the rotating angles of <3.06 deg and 1.637 deg along the vertical and horizontal directions, respectively. Under continuous wave operation, a 5.4 W vertically-polarized laser of 1645.1 nm was acquired through double polarizers with the beam quality factors (M²) of 1.17 in the x direction and 1.42 in the y direction, and the slope efficiency was 45.47%. Additionally, under the condition of a pulse-repetition-frequency (PRF) of 200 Hz, the pump power of 29.04 W, a maximum pulse energy of 2.2 mJ was realized, and the minimum pulse width was 86 ns, leading to a peak power of 25.58 KW.

Much progress has been made in the power and energy scaling of mid-infrared lasers based on transition metal ions, such as Cr^{2 +} , Co^{2 +} , and Fe^{2 +} , in zinc and cadmium chalcogenides. Still, the exploration of the physics of these devices is incomplete. In this work, we analyze absorption spectra collected from Fe^{2 +} ions in several binary, ternary, and quaternary host crystals at temperatures from a few degrees Kelvin to room temperature. We use the zero-phonon lines of the low-temperature spectra to calculate the value of the crystal field energy of Fe^{2 +} ions in these hosts. We plot these crystal field energies with respect to the anion–cation distance of the host crystal and show that their crystal field strengths deviate somewhat from the trend predicted by crystal field theory. We use a model which we previously developed to describe the upper state lifetime of Fe^{2 +} ions to predict the steady-state radiative efficiency of Fe:II–VI materials with respect to temperature. The impact of relative crystalline disorder on the output characteristics of lasers based on Cr:ZnS, Cr:ZnSe, Fe:ZnSe, and Fe:CdMnTe is explored. The effect of decreased long-range order of the host crystal is observed in the broadening of the absorption spectra of Fe^{2 +} -doped ternary and quaternary alloys, the broadening of the spectral linewidth of continuous-wave Fe:II–VI lasers, and a reduction in the portion of the Cr:ZnSe emission spectrum accessible for modelocked lasing. This survey provides a richer picture of the tradespaces that can be leveraged when producing laser devices based on transition metal chalcogenides.

Zinc oxide (ZnO) nanofilms were synthesized by electrochemical deposition from a simple aqueous zinc chloride onto indium tin oxide (ITO) substrate. Chronoamperometry experiments were performed to deposit nanofilms at the cathodic potential −1.0 V and time 5000 s at 70°C. Diffraction measurements of x-ray showed the hexagonal wurtzite structure of the as-grown nanofilms and the preferred orientation was along the (002) axis. A well-defined ZnO morphology was generated under −1.0 V for 1000 s on ITO glass. Atomic force microscopy observations explored the effect of electrode coating technique on the microscale ZnO nanofilms. The optical constants and thickness of nanofilms were determined with high precision using spectroscopic ellipsometry. The measurements of photoluminescence demonstrated two emission peaks; the first of which was related to excitonic emissions at about 392 nm, referring to the band gap of ZnO, and the second was related to oxygen vacancies ionized singly at about 490 nm.

A dynamically tunable terahertz metamaterial structure, comprising a split ring resonator made of lossy metal and a graphene formed square ring resonator, is designed and proposed. Subsequently, the influence of geometrical parameters of the proposed metamaterial structure and electromagnetic properties of graphene on the tunable terahertz spectral characteristics are investigated in detail. Meanwhile, the use of the equivalent model can provide numerical alternative methods and theoretical support for the design, optimization, simulation, and verification of metamaterial devices. The performances of the unit cell and the metamaterial are studied by a coupled oscillator model and a semi-analytical transmission line model; the analytic results agree excellently with our numerical results using full-wave simulations. The dynamical adjustment capacity of terahertz transmission spectra depends on the tunable terahertz metal-graphene hybrid metamaterial, which allows for designing an efficient device for a wide range of specific tasks including applications in sensing and switching. Furthermore, a comprehensive analytical approach based on these models constructs a theoretical basis for the design of metamaterial structures in a wider range and supports the mutual verification of the fitting results.

Cholesterol plays an important role in biological systems, and the quantity of cholesterol in the human body serves as a diagnostic marker for a range of disorders. This article presents a localized surface plasmon resonance (LSPR) sensor based on dual-tapered optical fiber (DTOF) that can detect cholesterol levels in the human body. To stimulate the LSPR effect and increase the sensitivity of the sensing probe, gold nanoparticles were fixed on the DTOF’s surface. In this study, the reaction between cholesterol and cholesterol oxidase altered the refractive index near the sensing probe, and the related spectrum was obtained. In addition, the sensor’s performance, including linear range, repeatability, reusability, stability, and selectivity, was examined. The experimental results indicate that the proposed DTOF-based LSPR sensor is capable of reliably measuring cholesterol levels and has promising biomedical applications.

Compact surface plasmon resonance (SPR) sensors are highly demanded due to their small size, low cost, and wide application scenarios compared with benchtop sensors. To realize high-precision spectral or angular analysis, most compact SPR sensors need spectrometers or rotation stages, which increase the cost of the device. We demonstrate a low-cost and compact SPR sensor by utilizing a single grating as a coupler and a disperser. The polychromatic light emitted from a light-emitting diode was coupled to surface plasmon modes by a grating made from a digital versatile disc-recordable disc. The light was dispersed by the same grating and collected by a linear charge-coupled device. The real-time detection of the SPR spectra and the resonant wavelengths was realized by homemade software based on the laboratory virtual instrument engineering workbench. By measuring different concentrations of glucose solution and sodium chloride solution, we obtain a high refractive index (RI) resolution of 5.52 × ^{10 − 5} RI unit. This compact SPR sensor can be applied in the areas of food safety, environmental monitoring, medical diagnosis, and so on.

III-nitride ultraviolet light-emitting diodes (UV LEDs) face low carrier confinement and poor p-doping. In this study, we propose a thin AlInN electron-blocking layer (EBL) in UV LEDs instead of conventional AlGaN EBL. Numerical results demonstrate that UV LED with thin AlInN enhances the optoelectronic performance. The results also reveal that AlGaN EBL is more sensitive to p-doping as compared to AlInN EBL. Thin AlInN layer facilitates hole transportation through intra-band tunneling. Moreover, AlInN has a high conduction band offset that suppresses the electron leakage effectively. Hence, the carrier radiative recombination rate considerably enhances with thin AlInN EBL. The efficiency droop in the proposed LED is also alleviated.

The quasi-two-dimensional (quasi-2D) perovskite possesses good film coverage and high photoluminescence quantum efficiency, and exhibits a characteristic of high-level radiation recombination. However, the charge transferring from quasi-2D perovskites is not comparable to that of three-dimensional perovskites due to the insulating nature of large organic cations, thus limits the brightness of quasi-2D perovskite light-emitting diodes (PLEDs). In this work, phenylethylammonium bromide (PEABr) and formamidine hydrobromide (FABr) were strategically introduced as two spacer cations to form quasi-2D perovskite phase, thus weakened the van der Waals gap between individual perovskite layers. The enhanced coupling strength between each layer promoted the energy transfer efficiency and led to an increasing radiative recombination rate of the perovskite films. Meanwhile, an optimized molar ratio of PEABr: FABr: PbBr₂ improved perovskite film morphology and passivated its defects, which reduced the nonradiative recombination loss of quasi-2D PLEDs. As a result, a maximum brightness of 32,368 cd m ^{− 2} can be obtained for this kind of devices.

To meet the anticipated future demand for optical wireless high data rates, our study proposed a deep learning model-based adaptive digital pre-equalization scheme for visible light communication (VLC) channels is proposed to increase the data rate. We established the deep learning model to predict pre-equalization parameter (PEP) which is adaptive for various VLC channels. The proposed system is flexible and adaptive for commercial light emitting diode with different channel conditions. It improves the bandwidth of different VLC channels up to 125 MHz and has been validated on a 250-Mbps testbed. Based on the experimental results, the PEP update time is at most 5.1 s, and the bit error ratio is always <1 × 10 ^{− 6} while using the PEP in the deep learning network. Meanwhile, the predicted and optimal values of the PEP correspond at 250 Mbps, and the maximum error between the predicted and optimal values of the PEP are only 7 for various channel conditions, including optical power, data rate, send distance, and send angle. The adaptive pre-equalization capability of the proposed system would be a universal digital solution for high-speed access in 6G scenarios combined with the VLC spectrum.