A graphene-sandwich metasurface for electrically controlled operation as a frequency shifter, a reciprocal switch, and a bidirectional isolator in the terahertz spectral regime was simulated using CST Microwave Studio™ 2019 software. The metasurface is a biperiodic array of identical meta-atoms, each of which comprises a silicon layer with a graphene patch on each of its two faces. The polarization-insensitive metasurface has ∼15  dB isolation loss as well as ∼15  dB extinction ratio and can be controlled to function over a wide frequency range.

Color conversion matrices and chromatic adaptation transforms (CATs) are of central importance when converting a scene captured by a digital camera in the camera raw space into a color image suitable for display using an output-referred color space. In this article, the nature of a typical camera raw space is investigated, including its gamut and reference white. Various color conversion strategies that are used in practice are subsequently derived and examined. The strategy used by internal image-processing engines of traditional digital cameras is shown to be based upon color rotation matrices accompanied by raw channel multipliers, in contrast to the approach used by smartphones and commercial raw converters, which is typically based upon characterization matrices accompanied by conventional CATs. Several advantages of the approach used by traditional digital cameras are discussed. The connections with the color conversion methods of the DCRaw open-source raw converter and the Adobe digital negative converter are also examined, along with the nature of the Adobe color and forward matrices.

Internet-based communication has become a major field, with a user base that is expanding day-by-day. The needs have overloaded the available bandwidth, and higher speed has become a mandatory requirement to satisfy the user demands and increased use of the internet. Therefore, there is a need for high-performance computers due to increasing dependence on computing technology. Optics is emerging as the best possible solution over electronics because it is capable of providing parallel data processing with fewer expenses and greater speed of more than 10,000 times faster than electronic computers. The main building block of optical computing is the all-optical logic gates, which are designed using different techniques. Different types of photonic crystal-based all-optical logic gates have been reviewed in detail by discussing the key characteristics and demonstrating the advantages over the previously available technologies (semiconductor optical amplifier and nonlinear waveguide) that are used to build all-optical logic gates.

This guest editorial introduces the Special Section on Advances in Gradient Index Optics Technology.

Optical materials capable of advanced functionality in the infrared will enable optical designs that can offer lightweight or small footprint solutions in both planar and bulk optical systems. The University of Central Florida’s Glass Processing and Characterization Laboratory, together with our collaborators, have been evaluating compositional design and processing protocols for both bulk and film strategies employing multicomponent chalcogenide glasses (ChGs). These materials can be processed with broad compositional flexibility that allows tailoring of their transmission window, physical and optical properties, which allows them to be engineered for compatibility with other homogeneous amorphous or crystalline optical components. We review progress in forming ChG-based gradient refractive index (GRIN) materials from diverse processing methodologies, including solution-derived ChG layers, poled ChGs with gradient compositional and surface reactivity behavior, nanocomposite bulk ChGs and glass ceramics, and metalens structures realized through multiphoton lithography. We discussed current design and metrology tools that lend critical information to material design efforts to realize next-generation IR GRIN media for bulk or film applications.

The Raman spectra of polymethylmethacrylate (PMMA)/SAN17 nanolayered composite material are used to retrieve the volumetric refractive index of a manufactured gradient index (GRIN) lens. A series of five PMMA/SAN17 nanolayered composite sheets with varying PMMA to SAN17 filling fraction ratios of 0/100, 25/75, 50/50, 75/25, and 100/0 were constructed to calibrate the 785-nm Raman measurement. An additive model was then used to extrapolate the volumetric refractive index profile of the fabricated GRIN lens based on PMMA/SAN17 filling fraction. A good overall agreement between the calculated and modeled GRIN profiles can be observed with an error of ±0.003.

New moldable, infrared (IR) transmitting glasses and diffusion-based gradient index (GRIN) optical glasses enable simultaneous imaging across multiple wavebands including short-wave infrared, midwave infrared, and long-wave infrared, and offer potential for both weight savings and increased performance in optical sensors. Lens designs show potential for significant reduction in size and weight and improved performance using these materials in homogeneous and GRIN lens elements in multiband sensors. An IR-GRIN lens with Δn  =  0.2 is demonstrated.

Scanning confocal Raman microscopy is proposed to measure a gradient index (GRIN) profile at an optical surface. The Raman microscope is calibrated to index of refraction for a binary copolymer GRIN material, and then the index of refraction is mapped on the plano surface of a GRIN polymer lens. The measurement deduces axial shift of 680  μm and identifies lateral tilt or decenter with respect to the nominal position of the GRIN profile. Results suggest that the mapping method is a nondestructive way to measure the GRIN profile of a GRIN lens and its positioning within the lens geometry, to within the sampling precision of the Raman microscope.

In the last few years, interest in research and development into new ways of creating gradient index optics has increased dramatically. One approach revisited was to employ diffusion, governed by Fick’s law, to generate both axial and radial index gradients. However, Fick’s law of diffusion tends to yield index gradients that are mathematically uncommon in optical engineering and lens design. The impact of these new gradients on lens aberrations and image quality are not well understood. We will examine index gradients that can be described by (makeable by) solving Fick’s diffusion laws but limited by the assumptions made to simplify the mathematics, the most significant of these being a diffusion coefficient of 1 on both sides of the boundary (implying a concentration change only) and that the change in concentration yields a one-to-one change in refractive index.

Both intensity and phase information of images have been the most important similarity measures in solving the general stereo matching problem. Intensity contains most of the imaging information of the scene/object, yet the phase information could reflect the local structure of images, which is more robust than the grayscale value. Plenty of work has been done in intensity-based or phase-based stereo matching methods. However, neither of them could work well enough when process images were taken under varied illuminations. A robust depth recovery method by making use of both intensity and phase information of stereo images properly is proposed. Firstly, 2D signal analysis is conducted by using the multiscale monogenic wavelet transform, from which local phase and intensity amplitude information are extracted into different scales. Secondly, disparity maps are estimated in different scales based on the intensity information. Thirdly, the optimal disparity is obtained by weighted-combining the disparity maps in different scales. The weighted coefficients are computed by making use of the phase information. Extensive experimental evaluation demonstrates the benefits of the proposed method.

High-resolution imaging with large ground-based telescopes is limited by atmospheric turbulence. The observed images are usually blurred with unknown point spread functions (PSFs) defined in terms of the wavefront distortions of light. To effectively remove the blur, numerical postprocessing with a good approximation of the wavefront is required. The gradient measurements of the wavefront recorded by Shack–Hartmann wavefront sensor (WFS) can be used to estimate the wavefront. A gradients measurement model for Shack–Hartmann WFS is built. This model is based on the frozen flow hypothesis and uses a least-squares-fit of tip and tilt across the subaperture in the WFS to genarate the averaged gradient measurements. Then a high-resolution wavefront reconstruction method using multiframe Shack–Hartmann WFS measurements is presented. The method uses high cadence WFS data in a Bayesian framework and takes into account the available a priori information of the wavefront phase. Numerical results show that the method can effectively improve the spatial resolution and accuracy of the reconstructed wavefront in different seeing conditions.

To quantitatively analyze the influence of vehicle platform vibration on the vehicle laser radar (LIDAR) measurement accuracy, the modal, harmonic response, and random vibration are analyzed using finite-element software. On this basis, combined with the optical path structure of LIDAR, the deformation of mirror caused by vibration is analyzed. The results show that the maximum deflection of the laser output angle resulting from the mirror deformation is about 0.0001 deg, which is much less than the 0.00573 deg (0.1 mrad) that is required by the performance of the vehicle LIDAR.

Two-dimensional digital image correlation (2D-DIC) has the advantages of high computation efficiency and simple experimental setup compared to three-dimensional DIC (3D-DIC). However, 2D-DIC is sensitive to out-of-plane motion, which leads to rather poor strain results. Recently, optical extensometers realized by dual-reflector imaging have been proposed, which can self-compensate the strain errors introduced by out-of-plane motion of the specimen. We will extend strain measurement from an extensometer to full-field deformation measurement. To this end, first, two corresponding areas of interest (AOIs) are created based on the symmetrical axis of the reference image. Second, the displacement and strain fields of these AOIs are computed with a common 2D-DIC algorithm, respectively. Subsequently, high-accuracy deformation results are obtained by taking the average of the deformation of the corresponding calculation points in two AOIs. Two types of uniaxial tensile tests that correspond to uniform and nonuniform strain fields were conducted to validate the feasibility of the proposed self-compensation method. The first experiment indicates that the strain results obtained using the proposed method are in good agreement with those with strain gauges and that the proposed method can achieve higher strain accuracy than 3D-DIC with a small stereo-angle. The results of the second experiment are basically in agreement with those of the ANSYS numerical simulation, which demonstrates the feasibility of the proposed method for the measurement of nonuniform strain fields. Both of the experiments demonstrate that rigid out-of-plane motion will lead to a global strain field error for common 2D-DIC. With no external compensation device, the proposed self-compensation method has the potential in 2D-DIC for accurate strain measurement due to its high level of accuracy.

In the beam control system, the correction of optical axis is an essential process of the optical system. Adjusting the installation angle of the relay mirror is an effective way to change the optical axis direction. However, due to the forced deviation of the installation angle from the theoretical design value, the supporting structure will produce greater stress, which will affect the surface accuracy of the mirror. Therefore, we present an optimization method that can reduce the sensitivity of mirror surface. First, the surface sensitivity is introduced to measure the surface accuracy under the forced deflection angle. Second, the external response function of surface sensitivity is realized by combining dynamic link library and MATLAB. At last, the topological structure is optimized with the sum of the sensitivity weights of two cases as the objective function and the dynamic resonance frequency as the constraint. The optimized structure shows that the surface sensitivity around the x axis decreases from 2.58  nm  /    ±  1^″ to 0.32  nm  /    ±  1^″, and the surface sensitivity around the y axis decreases from 3.75  nm  /    ±  1^″ to 0.09  nm  /    ±  1^″.

Coherent diffractive ptychographic imaging via a modified multi-state ptychographic algorithm can be used to simultaneously detect double orbital angular momentum (OAM) modes in monochromatic bi-OAM-mode multiplexing. The wavefronts for individual vortex beams modulated by two-dimensional amplitude and temporal pulses and mixed together can be reconstructed independently. In contrast to most other OAM detection methods, this approach solves for the OAM detection in a monochromatic dynamic multi-OAM beam and can be applied as an early step in OAM mode demultiplexing.

Aiming to minimize the surface distortion of large-aperture laser transport mirrors in high-power laser facilities, an assembly design and mounting method are proposed for the mirror. First, a theoretical model on the mirror surface deformation is established. With a new assembly design, the mirror is fastened on its neutral plane and its optical surface distortion can be precisely compensated through several adjustable forces on the sides, which will generate bending moments on the mirror body. Furthermore, a dynamic kinematic joint is designed, in which a corresponding relationship between spring compression and screw rotation ensures the accurate control of the magnitude of mirror preload. Finally, the performance of the presented method has been validated through field experiments and numerical simulations. This transport mirror assembly and mounting design have obvious technical advantages on simple mechanical structure, high operational efficiency, and precise preload control. The results show that the assembly design and optimized mounting strategy can keep the total surface distortion of the mirror within 350 nm (peak-valley).

For two decades, extraordinary optical transmission has amplified exploration into subwavelength systems. Researchers have previously suggested exploiting the spectrally selective electromagnetic field confinement of subwavelength slits for multispectral detectors. Utilizing the finite-difference frequency-domain method, we examine electromagnetic field confinement in both two-dimensional and three-dimensional scenarios from 2.5 to 6  μm, i.e., midwave infrared. We explore the trade space of deep subwavelength slits and its impact on resonant enhancement of the electromagnetic field. This builds a fundamental understanding of the coupling mechanisms, allowing for prediction of resonant spectral behavior based on slit geometry and material properties.

This paper presents a beam reconfigurable graphene-based Yagi–Uda antenna consisting of five iterations of the driven elements. These iterations are aligned with each other at different angles. Each iteration of the antenna can be individually biased for controlling the chemical potential. Thus, chemical potential can be effectively controlled using the external biasing to use a single iteration at a time, and the others are maintained at zero potential. The antenna provides the resonant frequency at 7.83 THz for each iteration due to similar aspect ratio. However, the radiation pattern of the antenna can be reconfigured depending upon the alignment at particular angle. This provides the beam reconfiguration in the antenna with the deflection ranging from −65  °   to 65° using different iterations. The antenna with the proposed dimensions excites the higher-order TM₁₄ mode inside the driven element. In addition, the resonant frequency of the antenna can be tuned by varying the physical parameters of driven elements.

Optical hierarchical sorting has attracted significant attention in recent years. The existing approaches use either complex numerical calculation or computer-aided experimental tools for optical hierarchical sorting. We proposed a method to perform hierarchical sorting, which is computationally simple and does not need computer aid. In particular, we employed a focused optical vortices array (FOVA), which is generated and focused by a spiral phase plate array (SPPA) and a microlens array, respectively. We designed different heights for the spiral phase plate in different columns of the SPPA. This enabled different columns of the FOVA to carry different topological charges and consequently possess different capture capabilities. To realize hierarchical sorting, we exploited the properties of FOVA by deploying it in a microfluidic chamber containing particles of various sizes. The four columns of the FOVA formed four corresponding capture regions in the flow area of the particles. From our theoretical analysis and numerical results, we observed that particle sizes in the range of 1 to 582 nm could be sorted. Our approach provides a theoretical framework that can be readily employed in experiments for optical hierarchical sorting.

The performance of free-space optical (FSO) communication systems based on avalanche photodiodes (APDs) is investigated over the aggregated double generalized gamma (double GG) fading channels. The approximate average bit error rate (ABER) expression is theoretically derived in terms of the double GG distributions under moderate and strong turbulent atmospheric conditions considering thermal noise and shot noise. The union bound and Hermite polynomials are then used to estimate the ABER performance of M-ary pulse-position modulation (PPM)-based systems and orthogonal frequency division multiplexing scheme (OFDM)-based systems. The ABER performance is studied with different receiver noise temperatures, modulation orders, turbulence strengths, and average photon counts assuming plane wave and spherical wave propagations. The results show that adopting an optimal average APD gain affected by the receiver temperature minimizes the ABER value for both wave propagations. In addition, the present APD-based system offers better ABER performance than that of a PIN-based FSO system over the double GG fading channels at two receiver noise temperatures of 200 and 400 K for both the PPM and OFDM schemes. We provide a reference for FSO system design.

The differential phase-shift keying-based dual-hop underwater wireless optical communication-free-space optics (UWOC-FSO) convergent system is proposed for UOWSNs and Internet of Underwater Things (IoUT) applications. In the proposed system, the collected sensor data are transmitted to a decode-and-forward relay using underwater optical wireless communication links modeled as gamma–gamma distribution. The relay transmits the signal to the terrestrial destination using free-space optical link modeled as Malaga distribution. The end-to-end performance of the system (novel expression for asymptotic bit error rate) is derived and analyzed over combined channel model (including the effects of attenuation, turbulence, and pointing errors for both FSO and UWOC channels). The in-depth study is carried out for different weather conditions of FSO (attenuation—very clear, haze, rain, and fog; turbulence—weak and strong; and pointing error—weak and strong based on the g values 1, 2, and 6) and UWOC (attenuation—clear, coastal ocean, and turbid harbor; turbulence—weak, moderate, and strong; and pointing error—weak and strong based on the g values 1, 2, and 6), respectively. The proposed system is highly useful in coastal environments, where the climate is changing adequately as clear, rain, haze, and fog.

Rapidly space-division multiplexing (SDM) techniques have drawn attention because the traditional available physical dimensions to orthogonally multiplex data have been almost exhausted. Few-mode fiber becomes a viable option to realize a high-density SDM system. Thus, we propose an air-hole assisted elliptical ring fiber. Four air-holes are introduced surrounding the elliptical ring fiber, and one air-hole is in the core, which can prevent higher-order modes to be cutoff and improve the degeneracy between modes to achieve multiple-input multiple-output-free data transmission. This fiber can support 14 modes in a wide wavelength range from 1.52 to 1.58  μm (h  =  5.0  μm, d_x  =  0.3  μm, and d_y  =  1.1  μm), and the effective index difference of its adjacent modes is larger than 1.25  ×  ^{10  −  4}. The fiber we designed would be a strong candidate for SDM to improve optical transmission capacity.

By using the orthogonality of the orbital angular momentum (OAM) beam and the characteristics of its annular intensity distribution, a method for separating the OAM beam from the Gaussian beam is proposed. This method uses a dual-area mirror in an OAM multiplexed data link. Experiments show that the topological charge of the multiplexed OAM beams can be reconfigured with the aid of a dual-area mirror. Compared with previous separation methods, this method is low cost, easy to implement, easy to integrate, and can freely control the direction of the separated beam. Furthermore, it can considerably reduce the optical power loss and is expected to reduce the bit error rate in the optical communication link.

We proposed an adaptive two-stage nonlinear feedforward equalizer and decision feedback equalizer to minimize the negative influence of nonlinear distortions. A data rate of 960 Mbit/s is experimentally achieved on the guided visible-light transparent transmission over a 100-m ultra-large effective area pure silica fiber. The experimental results verified the effectiveness and improvement of the proposed method compared with the traditional feedforward post-equalizers.

A high-capacity spectral-efficient dual-polarization quadrature phase-shift keying (DP-QPSK)-polarization shift-keying (PolSK) hybrid modulation scheme for terrestrial free-space optics (FSO) transmission link is proposed and investigated. A DP-QPSK signal modulated at 300 Gbps and a PolSK signal modulated at 40 Gbps are simultaneously transmitted using a single optical carrier over the FSO link. The proposed link performance is investigated under different weather conditions, where the bit error rate metric is used to evaluate the performance of the PolSK modulated signal and the error vector magnitude parameter is used for the DP-QPSK signal. The FSO link range and the required received power are carefully explored. The conducted numerical simulations of the proposed system showed reliable 340-Gbps data transmission over link ranges varying from 1.6125 to 50 km depending on the weather conditions. The impact of the channel scintillation due to atmospheric turbulence is also investigated. The proposed high-speed FSO transmission system offers a promising solution for high-bandwidth hungry systems used for the internet of things, 5G, and smart cities. It can also be used in developing fronthaul/backhaul links for future wireless networks and optical access networks. The performance of the proposed transmission system is compared with recently published work in the literature.

The dissipative soliton resonance (DSR) pulses are demonstrated experimentally in an all polarization-maintaining (PM) thulium-doped mode-locked fiber laser. The mode-locked operation is achieved using of the nonlinear amplifying loop mirror mechanism (NALM). Each loop of the apparatus includes an independently controlled amplifier and a section of gain fiber. The experiment is carried out at a central wavelength of 1969.8 nm and 3.5 ns as the maximum output pulse width. The time domain and spectrum characteristics of output pulse are analyzed with different positions of PM-1950 fiber in the NALM loop. In addition, the DSR pulse properties are experimentally verified by changing the length of the PM-1950 fiber spliced into the NALM loop. We have achieved environmentally stable mode-locked pulses at 3, 2.1, and 1.62 MHz corresponding to the maximum pulse energies of 6.8, 20, and 29.1 nJ. The output pulse is stable and robust at different ambient temperatures.

Our study describes the development of coherent beam combining of an array of nine fiber lasers using an all-optical ring cavity feedback loop based on a diffractive optical element to achieve a single-aperture output. Nine 300-mW Yb-doped fiber amplifier beams arranged in a 1  ×  9 end-cap array were combined to achieve a single-aperture beam with a power of 739 mW and a beam quality (M²) of 1.18 with 21.5% combining efficiency. The optical spectra, far-field distributions, and time-domain characteristics of the combined beams were investigated under open- and closed-loop conditions. Under open-loop conditions, the far-field coherent visibility changed constantly from 72.1% to 90.9% and the fluctuation intensity was strong. Under closed-loop conditions, the system achieved a steady state with a visibility of 98.6% and an average feedback intensity of 0.4 V, indicating the occurrence of phase locking. Furthermore, mode hopping was observed when there were more than four channels in a combination. However, the system interference pattern remained stable. Comprehensive research on the relevant literature indicated that novel filled-aperture CBC was achieved using an all-optical ring cavity feedback loop based on a DOE.

A scheme for detecting the phase of an incoming optical signal is systematically optimized and demonstrated experimentally. It makes use of four-wave mixing in a highly nonlinear fiber but differs from a phase-sensitive amplifier by its focus on phase detection, rather than on phase-dependent noise reduction. This experimental setup combines the signal with its phase-conjugated idler at the same frequency, before sending the combination to a photodetector. Experimental results show that the ratio of maximum and minimum currents can exceed 1000 even at a relatively low pump power of 10 mW. The proposed scheme may be useful for detecting the signal phase in coherent communication systems without the need of heterodyne detection.

Ultraviolet (UV) 266-nm nanosecond (ns) laser was obtained through fourth-harmonic-generation by using new nonlinear optical crystals of NaSr₃Be₃B₃O₉F₄ (NSBBF) with different lengths. Since NSBBF crystals are prone to crack during laser experiments, we added a water-cooling device under NSBBF crystal in the experiment, and compared the experimental results under conditions of water cooling and no water cooling. Moreover, different laser focusing effects were explored to optimize the experimental conditions. The maximum optical conversion efficiency from 532 to 266 nm was 4.8% with the pump power of 2.8 W. The maximum average output power of the 266-nm UV laser was 420 mW when the 532-nm pump power was 23.82 W. The study provides research ideas and experimental basis for NSBBF crystal to realize higher-power 266-nm ns laser output.

An all-optical fiber curvature sensor is proposed, which is composed of a polydimethylsiloxane elastic material encapsulated all-optical fiber Mach–Zehnder interferometer, and its bending characteristics are demonstrated. Our experimental results show that the output spectrum of the sensor is sensitive to the curvature of the bend angle with a result of interferent dip wavelength drift with it. The curvature sensitivity of the sensor presents 205.36  nm/cm^−  1 with 98.27% linearity in the curvature range from 0.03 to 0.08  cm^−  1. The temperature sensitivity is 0.1235  nm  /    °  C in 35°C to 105°C range. This sensor structure also has the advantages of small size, low cost, and easy fabrication, which means it has potential applications in robots, artificial intelligence, aerospace, and so on.

We report a systematic study of cuprous oxide (Cu₂O) films prepared on glass substrates via radio frequency reactive magnetron sputtering at room temperature. We consider the effects of the target power and film thickness on film structures, morphologies, and optical properties. X-ray diffraction indicates significant changes from an amorphous film to a paramelaconite film and then to a cuprite film as the sputtering power increases. Increasing the sputtering power also contributes to variation in the surface roughness of the film. The optical transmittances and bandgaps of the films change with the crystalline structure. The film with a cuprite structure obtained using 60 W of sputtering power exhibits the preferred cuprite orientation (111) with an average roughness of 2.6 nm. This corresponds to an average transmittance of 73% in the 500-1000 nm range and a bandgap of 2.48 eV. The optimized Cu₂O thin film exhibits excellent UV- and blue-light shielding capabilities and high optical transparency in the visible-light region. This suggests possible applications in radiation-proof windows and glasses.

In this study, a one-way electromagnetic waveguide consisting of magneto-optical (MO) and parity-time (PT)-symmetric materials was constructed. Due to the composite boundary conditions, this waveguide simultaneously has two unidirectional dispersive curves and two different unidirectional mechanisms. One unidirectional mechanism is breaking the time-reversal symmetry of MO materials, and the other unidirectional mechanism is asymmetric complex eigenvalues in the local PT symmetrical configuration. The designed structure provides an effective approach to control the directions of electromagnetic waves.

A hybrid plasmon waveguide (HPWG) consisting of a gold layer, a 100-nm high nanogap, and a SiN layer with a high refractive index on a SiO₂  /  Si substrate was designed by simulation and was applied in a Mach–Zehnder interferometer biosensor. For the incidence of a transverse magnetic (TM) mode light, a strongly enhanced electric field in the nanogap region caused by the modified surface plasmon enabled highly sensitive detection at the metal/solution interface. In contrast, the transverse electric (TE) mode enabled a high bulk-sensitivity due to the evanescent field in the nanogap. The HPWG structure was formed by electron beam lithography and electrochemical sacrificial layer etching. The output intensity of the fabricated device oscillated upon the replacement of the medium in the nanogap for both TE and TM mode excitations, which agreed with the obtained simulation results. Furthermore, the hybridization of DNA on the gold surface was detected, demonstrating that the HPWG structure is applicable to use in biosensing.

In order to obtain reconfigurable topological photonic waveguides, we design a two-dimensional photonic crystal with compound triangular lattice. Through rotating the dielectric rods, we change the topological phase of the lattice and achieve the topological edge states. Through the rotation of rods, we divide the two-dimensional structure space into “0” and “1” blocks made of the topologically trivial and nontrivial lattices, respectively. Through programming the codes of “0” and “1,” we can realize diverse transport pathways of light flow. The controllable light pathways will play important role in the optical circuit. The programmable design results have been demonstrated through the simulations of electromagnetic wave transport.

Detection of high-energy laser strikes is key to the survivability of military assets in future warfare. The introduction of laser weapon systems demands the capability to quickly detect these strikes without disrupting the stealth capability of military craft with active sensing technologies. We explored the use of thermoelectric generators (TEGs) as self-powered passive sensors to detect such strikes. Experiments were conducted using lasers of various power ratings, wavelengths, and beam sizes to strike 2  ×  2  cm² commercially available TEGs arranged in different configurations. Open-circuit voltage and short-circuit current responses of TEGs struck with 808-, 1070-, and 1980-nm lasers at irradiance levels between 8.5 and 509.3  W  /  cm² and spot sizes between 2 and 8 mm are compared. TEG surface temperatures indicate that the sensor can survive temperatures nearing 400°C. TEG open-circuit voltage magnitudes correlate more strongly with net incident laser power than with specific irradiance levels, and linearity is limited by Seebeck coefficient variation with temperature. Open-circuit voltage responses are characterized by 10% to 90% rise times of ∼2 to 10 s despite surface temperatures not reaching equilibrium. With open-circuit voltage as the sensing parameter, detection thresholds three times above the standard deviation noise level can be exceeded within 300 ms of the start of a laser strike with irradiance levels of ∼200  W  /  cm². Potential harvested power levels as high as 16 mW are estimated based on measured electrical responses. A multiphysics finite-element model corresponding to the experiments was developed to further optimization of a lightweight, low-profile TEG sensor for detection of high-energy laser strikes.

Negative refractive index is introduced in metamaterials whereby the Poynting vector of the electromagnetic (EM) wave is in opposition to the group velocity, or alternatively, when the group and phase velocities in the medium are in opposition. In recent years, considerable research has been carried out relative to the EM propagation and refraction characteristics in metamaterials with emphasis on the origins of negative refractive index. The latter phenomenon has been extensively investigated in the literature, including recent work involving chiral metamaterials with material dispersion up to the first and second orders. An EM propagation in a chiral, dispersive material up to the first order is examined for possible emergence of negative refractive index under non-conductive losses. Three loss scenarios are considered, viz., dielectric losses (complex permittivity), magnetic losses (complex permeability), and a combination of both types of losses. A spectral approach combined with a slowly time-varying phasor analysis is applied, leading to the analytic derivation of EM phase and group velocities and corresponding indices. The velocities and indices are examined by selecting arbitrary dispersion parameters based on published practical values. The results indicate the emergence of negative index within specific radio frequency modulation bands. The resulting polarization states of the fields are examined under loss conditions. Finally, a method is suggested whereby the effects of dielectric and magnetic losses may be combined via appropriate Taylor coefficients such that the effective attenuation constant may be driven to zero via induced gain mechanisms arising from the dielectric and magnetic loss models.

Terahertz (THz) antennas can be used for high-speed indoor wireless communications. The antennas must have a wide bandwidth, high gain, and low loss. In this study, a dielectric resonator antenna fed by the photonic crystal (PC) waveguide based on a newly developed silicon-on-glass technology is proposed and analyzed. The PC waveguide is designed by float-zone silicon that can help propagation guided modes with low loss. Coupling matching between waveguide and antenna, and also between the antenna and free space can be analyzed by coupling mode theory. The reflection loss at the interface between the components is minimized using three matching air holes. The proposed compact antenna operates at 325 GHz with about 5.2% bandwidth. The end-fire antenna is introduced with a high gain of about 12 dBi, low loss, and sidelobe levels of −11 and −8.8  dB in the E- and H-planes. The high efficiency of over 97% in the entire antenna operational bandwidth is achieved. The platform is used for THz communications at the high data rate.

Our study proposes a technique to enhance light extraction efficiency of light emitting diodes (LEDs) by incorporating various micro-/nanolens arrays (MNLAs) on the substrate layer, which in turn increases the external quantum efficiency (EQE) of the LEDs. To simulate the LEDs, we utilized the finite difference time domain method. To achieve a white LED, we inserted a thin layer of NiO at the interface between the n-type ZnO and the p-type GaN. The basic n-ZnO/NiO/p-GaN heterojunction-based LED exhibited an EQE of 10.99% where the effective refractive index of the LED structure was 1.48. The EQE was further increased by engraving various planoconvex or planoconcave MNLA on the top surface of the substrate layer. A maximum EQE of 12.4% was achieved for convex-1 type (lens height of 0.5  μm and radius of 0.4  μm) elliptical lens engraved LED where the effective refractive index was 1.4. In addition, the peak electroluminescence (EL) light intensity of convex-1 lens-based LED was twice than the light intensity observed in basic LED. Because of excellent EL spectrum and significant amount of light throughout the visible spectrum, the proposed convex-1 structure-based LED can be considered as a prospective candidate for white LED.

Our paper is focused on an extremely efficient structure for photonic crossbar switch using a fundamental building element, a semiconductor optical amplifier (SOA) in a Mach–Zehnder interferometer configuration. The switch is designed with a 10 Gbps rate and a high Q-factor of 30; a bit error rate ranging between ∼e^−  122 and ∼e^−  184 is achieved. In addition, the designed photonic switch model is reliable in terms of having an extinction ratio of 16 dB on average. High optical signal-to-noise ratio values, ranging between 101 and 104 dB, provide the low interference of noise in the required signals. It is observed that the proposed configuration is fast enough to provide a switching time ranging between 0.146 and 0.227 ns and is feasible in scaling the ports with an increase in the number of users to maintain a good quality factor. Hence, the proposed architecture can be taken as a solution for challenges in future datacenter network switching.