Guest Editors Vitaly Gruzdev and Claude Phipps summarize the Special Section on High Power Laser Ablation II.

Illumination of hafnium dioxide (HfO₂) thin films with a nanosecond pulsed laser reaching peak intensities of 180  GW  /  cm² has been shown to trigger a laterally expanding plasma wave prior to ablation that reaches speeds of up to 100  km  /  s. The phenomenon has recently been described as a defect-initiated laser-driven detonation (LDD) wave propagating in the electron–hole subspace, but the electron/hole effective masses that would be required for quantitative agreement were found to be at least 100 times heavier than band structure calculations predicted for HfO₂. The results are re-examined in the context of a more general description of LDD that accounts for a change in the electron effective mass between the pre- and post-detonation states. Reasonable agreement between theory and experiment is found under the assumption that the electron’s effective mass decreases by a factor of 20 and approaches the free electron mass in the final state.

A density-dependent two-temperature model is applied to describe laser excitation and the following relaxation processes of silicon in an external electric field. Two approaches on how to describe the effects of the external electric field are presented. The first approach avoids the buildup of internal electric fields due to charge separation by assuming ambipolar diffusion and adds an additional carrier-pair current. In the second approach, electrons and holes are treated separately to account for charge separation and the resulting shielding of the external electric field inside the material. The two approaches are compared to experimental results. Both the first approach and the experimental results show similar tendencies for optimization of laser ablation in the external electric field.

In a recent report, the National Academies of Science, Engineering, and Medicine (NASEM) recommends that “the United States should start a national program of accompanying research and technology leading to the construction of a compact pilot plant that produces electricity from fusion at the lowest possible capital cost.” It is generally acknowledged that a decarbonization of the world’s energy system is unavoidable to combat climate change. While an exothermic chemical reaction such as the combustion of fossil fuels produces an energy of <1  eV per molecule, a nuclear fusion reaction is an attractive alternative as it releases 10 million times more energy. To date, considerable effort has been devoted to research involving the fusion between the nuclei of the two heavy isotopes of hydrogen: deuterium (D) and tritium (T). However, the main roadblock for the adoption of this technology is the need to heat the fuel to temperatures in the order of 50 million Kelvin and to keep it stable under extreme pressure conditions. Recent results show that this difficulty can be overcome by utilizing the nonthermal radiation pressure that can be generated via chirped-pulse amplifier laser systems and can trigger the fusion of hydrogen and boron-11 nuclei, producing clean energy in the form of kinetic alpha particles, thus sidestepping nuclear radiation problems due to the aneutronic nature of the process.

Ice disaster has always been a threat to the stable operation of electrical power systems, and it is a challenge to melt ice online for high-voltage composite insulator. Here, we proposed a safe and efficient method to deice a high-voltage composite insulator using high-power mid-infrared (mid-IR) laser. The laser source is a Tm-doped fiber laser, delivering a continuous-wave (CW) output power of 75 W at 1940 nm. Due to the strong vibration absorption of H₂O molecule at 1940 nm, the mid-IR laser could be absorbed efficiently by ice/water with an absorption coefficient as high as 135  cm^−  1. Indoor deicing experiment demonstrated that an 8-mm-diameter ice pillar could be cut off within 28 s under an incident optical intensity of 25  W/cm². Due to the small penetration depth of 148  μm, the residual water film could prevent the laser from damaging the composite insulator. Our research results show that high-power mid-IR Tm-doped fiber laser is a potential scheme for online deicing high-voltage composite insulator.

Modeling of laser-induced photoionization is a key component in simulations of ultrafast laser ablation of transparent solids. Available analytical and phenomenological models consider the ionization by promoting valence band electrons to a conduction band via simultaneous absorption of several laser photons of the same energy defined at central wavelength of laser-pulse spectrum. That assumption corresponds to nearly zero spectrum bandwidth and is not true for ultrashort few-cycle pulses. Treatment of the few-cycle-pulse photoionization by numerical methods, e.g., time-dependent density-functional theory, meets substantial difficulties when modeling of ionization-rate scaling with multiple laser-pulse and material parameters. To address those gaps, we report an analytical approach to evaluation of the photoionization rate by a few-cycle laser pulse with nonnegligible spectral bandwidth. We assume that the pulse spectrum supports the few-cycle pulse duration, but is narrow enough to prevent quantum interference between multiphoton transitions of different orders. We outline the calculation procedure, report examples of simulations with the proposed model, and discuss some novel physics of the photoionization. Our model includes dependence of the photoionization rate on carrier-envelope phase and delivers significantly higher rates compared with the Keldysh model. We interpret those results in terms of laser-driven variations of effective band gap, opening of extra channels of the multiphoton absorption, and involvement of a continuous range of electron states determined by pulse spectrum width. Based on the reported model, we discuss new options to control threshold of ultrafast laser ablation via carrier-envelope and pulse-shape scaling of the photoionization rate.

To improve the quality of reconstructed images of single-bit quanta image sensors, a self-adaptive threshold optimization method is proposed. The method can adaptively adjust the quantization threshold according to different light intensities, making the quality of the reconstructed image improved. First, the bitstream data from the quantization of real images are obtained by sensor model. Second, the optimal threshold value of each row is determined by calculating the bit-density, followed by the threshold value updated according to the deviation value between the bit-density of a single-pixel and 0.5. Finally, the optimal threshold matrix obtained by this method is used to reconstruct the image to improve imaging quality. Four identical test images were processed by the proposed method, the traditional method, and Elgendy’s variable threshold method, respectively. The results show that the proposed method can improve the peak signal-to-noise ratio of the reconstructed image in comparison with the traditional uniform threshold method. Compared with Elgendy’s method, the proposed method can effectively reduce the number of iterations under the same parameter conditions. These experiments prove that the proposed method can effectively improve the quality of reconstructed images with fewer iterations.

Computer-generated hologram (CGH) has a problem in that the calculation time is huge, we use a graphics processing unit (GPU) to enable fast calculation for CGH. Optimization of GPU calculation is studied to bring out the best performance of the GPU. We propose an autotuning method for GPU code that can be applied when the scene or calculation environment changes in CGH for practical use. We created a system that finds the optimal parameters by presenting three parameters for tuning in CGH. We applied autotuning to multiple objects and different GPUs and found optimal parameters for each. In addition, it was confirmed that the calculation time was 1.1 to 1.7 times faster by the autotuning.

With the development of unmanned aerial vehicles (UAVs) and computer vision, target detection methods based on UAVs have been increasingly applied in military and civilian fields. Considering the adaptability requirements of low illumination environments such as rain, fog, and night, visible and infrared (IR) sensors are often installed on UAVs to perform in all-weather and all-day conditions. To improve the near-surface detection performance of UAVs in low illumination environments, a pedestrian detection method using image fusion and deep learning is proposed. Visible and IR pedestrian images are collected by the UAV. The corresponding aerial images are registered and annotated. These two different types of aerial images are aligned at the time sequence and matched using the scale invariant feature transform. A U-type generative adversarial network (GAN) is first developed to fuse visible and IR images. A convolutional block attention module is introduced to strengthen the pedestrian target information in the GAN. The spatial domain and channel domain attention mechanisms are proposed to generate color fusion images with rich details and solve the problems of feature extraction as well as fusion rules designed manually in the existing image fusion methods. Then, You Only Look Once Version 3 (YOLOv3)-spatial pyramid pooling combined with transfer learning is adopted using the fused images to train the model on our aerial dataset to verify the pedestrian detection performance. In addition, comparison experiments are carried out. The experimental results demonstrate that the YOLOv3 model is successfully transferred to the target dataset. The performance of the proposed detection model using the fused images for transfer training is the best among the different methods. Finally, the accuracy P, recall R, mean average precision, and F₁ score reach 0.804, 0.923, 0.928, and 0.859, respectively.

Geometric calibration is a major step in computed tomography (CT) where it provides values for geometrical parameters that later define the system matrix in reconstructing CT images. A standard calibration process usually involves the illumination of an accurate calibration phantom with known coordinates of ball markers using the imaging system, followed by calculation of geometrical parameters by minimizing the errors between reprojected projection of ball markers and its acquired projection image. Although many attempts have been made to estimate the geometrical parameters, little attention has been paid to the optimal structure of calibration phantom. Inspired by the assumption that the larger the regularity of ball markers in the calibration phantom is, the more the stable is, and the better accuracy of estimated geometric parameters is, we propose a method to design phantom that maximize the accuracy of calibration process and mitigate the contribution of errors in indicating the ball centers. The method aims to maximize the regularity of ball markers in the calibration phantom and also in its projection image. The proposed method is applied to different phantom designs with the standard cylindrical holder and is proven to provide more accurate results than the traditional designs. The method can be applied to design scanner-dependent calibration phantoms and potentially free manufacturers and practitioners from manually searching work.

We propose and investigate an N-layered diffusion model with piecewise constant coefficients for approximating the exact solution of the diffusion equation with depth-dependent material coefficients in the spatial frequency domain. It is shown that this numerical approach, which is quite easy in view of the implementation, exhibits a convergence rate of O  (  N^−  2  )   in the discrete L^∞-norm and hence provides an interesting alternative to frequently used numerical approaches such as finite element or finite difference methods. For comparison purposes, we take into account the classical finite element approach under the use of continuous linear basis functions as well as a recently reported nonconforming finite element discretization - the weak Gakerkin method - that employs discontinuous functions in form of locally defined polynomials.

An innovative combined optical fiber transducer (COFT) based on the optical fiber bending loss characteristic has been developed for landslide monitoring. To better understand the working principle and improve the monitoring performance of the transducer, the capability of the COFT for exploring subsurface properties of slopes (sliding direction, magnitude, and rate of slope movement) and the deformation compatibility between the COFT and surrounding geo-materials were explained semi-empirically and semi-theoretically, which was also verified by the laboratory shear experiments of the COFTs constructed with two kinds of host materials (expanded polystyrene and polyvinyl chloride) and three kinds ratios of cement mortars (sand to cement 1:4, 1:5, and 1:6) and the related numerical simulation. In the following, model monitoring tests of an artificial slope and field monitoring application of the proposed COFTs in a field slope were carried out and the progressive slope movements were effectively determined, which validated the performance of the proposed COFT in landslide monitoring.

To solve the small-optical aperture and stroke problem of existing fast steering mirror (FSM), we focus on the design of FSM driven by piezoelectric ceramics in space laser communication and lidar systems. The structure design of the FSM and the theoretical analysis of the piezoelectric actuators are carried out. The special structure and installation process of the mirror assembly are designed to ensure the accuracy of the mirror surface. Theoretical calculation and simulation analysis are conducted to evaluate the mirror’s output angle. The dynamic model of the FSM is established to analyze the stiffness. The operating principle and characteristic analysis results of FSM are verified by experimental tests. The results show that the FSM can provide a mechanical excursion angle of ±2.35  mrad, the closed-loop linearity of X axis and Y axis are 0.71% and 0.67%, respectively, and the closed-loop bandwidth of the FSM is 28 Hz. The surface shape accuracy of the mirror after installation can reach 1  /  50λ.

Airborne light detection and ranging (LiDAR) is frequently influenced by multiple positioning errors when converting laser echo signals into three-dimensional geospatial data. We focus on the error factor of airborne platform vibration, and analysis of the influence of platform instability on the output point cloud data by simulation, so as to correct it in the subsequent work. First, the influence of LiDAR attitude change on the formation of point cloud was analyzed from the airborne LiDAR geo-location equation. Then, the fluid characteristics of airborne platform in hovering state were obtained by simulation, and the vibration transfer relationship between airborne platform and LiDAR and the vibration model of LiDAR system were obtained based on the dynamic model, which was built on the flexible connection between airborne platform and LiDAR. Finally, we coupled the above vibration model with the airborne LiDAR geo-location equation and conducted a simulation to evaluate its effect on point cloud generation in a LiDAR system. The simulation results show that in the 100-m hovering state, the point cloud error caused by unmanned aerospace vehicle vibration can reach 200 and 400 mm in the horizontal and vertical directions, respectively. Moreover, due to the high vibration frequency, this error factor will also lead to the distortion of point cloud image, which will affect the subsequent point cloud data recognition.

A small, portable, high-flux correlated photon-pair source has been designed and constructed from simple opto-mechanical parts. Unique to this device is its straightforward alignment process, together with the direct coupling of signal and idler photons into polarization-maintaining single-mode optical fibers. Spontaneous parametric down-conversion is used to produce photon pairs in β-barium borate (BBO) at a center wavelength of 810 nm. Owing to the applied type-I phase-matching, coincident photons have identical polarization. The estimated fiber-coupling efficiency is 51%, the measured photon and coincidence flux are 636 and 130 kHz/mW, respectively, normalized to pump power (44 mW). The source has an extremely wide wavelength spectrum of 202-nm FWHM, measured at the fiber output, which limits the actual heralding ratio to 20%.

Silicon carbide (SiC) has been widely used in optical components due to its excellent physical and electronic properties. However, it is very difficult to process the SiC owing to hardness and chemical stability. The robot bonnet polishing method was proposed to solve the problems existing in current polishing SiC optical elements methods, which have a low material removal rate and are expensive. First, according to Preston equation, Hertz contact theory and velocity analysis, the removal function model was established, the bonnet polishing head device was designed and put through simulation analysis. Next, aiming at the problem that the workpiece surface is prone to ripple errors during the traditional periodic polishing path trajectory processing, a pseudo-random polishing path based on the traveling salesman problem (TSP) is proposed. The path has the characteristics of multi-direction, high randomness, flatness and continuity, and compared with the raster path and random disturbance path, it is verified that the improved TSP polishing path has the ability to suppress the spatial intermediate frequency error. Then, single-point and multi-point polishing experiments are implemented to verify the accuracy and stability of the removal function. Finally, the application verification polishing processing of the SiC optical element is implemented by rough and fine polishing. The experimental results show that the bonnet polishing method and the improved TSP polishing path can effectively achieve the polishing of SiC optical elements and better suppress the intermediate frequency error of the optical processing surface. After three cycles of rough polishing and four cycles of fine polishing, the surface profile convergence rate is 72.3% and 50.8%, respectively, and the convergence rate is faster and the machining accuracy is higher.

We theoretically demonstrate a high-resolution fluorescence imaging scheme with configurations of oblique right angle optical path and ring-shaped excitation and fluorescent beams. The oblique right angle optical path configuration with two orthogonally aligned objective lenses over the specimen. It has strong abilities to eliminate the imaging stacking process in depth direction, to enhance the fluorescent collection efficiency, to improve the resolution, and to simplify the architecture of the fast fluorescent imaging system. Based on the Fourier domain model simulation, it is verified that the ring-shaped beams can further improve the imaging depth and resolution. The axial resolution can be optimized to 472 nm, the lateral resolution can be improved to 275 nm; meanwhile, the system can have an imaging depth of 398  μm.

Metasurfaces have the characteristics of ultra-thin volume, light weight, and planar structure, which can also effectively control the polarization state of electromagnetic waves. We propose single-layer all-dielectric quarter-wave plate (QWP) and half-wave plate (HWP) metasurfaces that work in the visible light region in transmission mode. The designed QWP can convert y-linearly polarized (YLP) light into left-handed circularly polarized light, whereas the HWP can convert YLP light into x-linearly polarized light. Moreover, the designed wave plates have a certain wide band working ability. When the incident angle is <30  deg for the QWP and <28  deg for the HWP, the polarization conversion performance shows strong robustness. The effects of fabrication tolerance, the height of elliptic-shaped pillar, and lattice constant on the polarization conversion performance are analyzed. In addition, the physical mechanism of polarization conversion is revealed by simulating the distribution of magnetic field and electric field inside unit structures. The results indicate that nanostructures of different sizes will excite different magnetic dipole resonance modes so as to realize the function of different polarization state conversions. It is believed that all-dielectric wave plate metasurfaces will become a good alternative for controlling the polarization state of electromagnetic waves.

We propose a supermartingale-based resource matching algorithm to guarantee delay quality of service (QoS) for the visible light communication uplink system. A network queuing model with multiple bursty arrivals is established, and multipacket reception technology is considered to alleviate terminal collisions. We introduce the supermartingale theory to evaluate the delay QoS performance, and a tighter delay-violation probability bound is derived. Relying on the supermartingale analysis, we design a search algorithm to achieve resource matching under a delay QoS constraint. The simulation results prove that the proposed algorithm guarantees delay QoS and saves service resources.

The space environment is becoming increasingly complicated; therefore, precise detection and identification of space targets are critical to preserving space security. Compared to optical and radar imaging, obtaining space target information using laser echo waveform is more efficient for detection. Based on the skew-normal distribution decomposition, the connection between sub-echoes and target scale following the decomposition of the space target pulse laser echo waveform is explored, and an inversion approach is suggested to identify the scale information of the solar panel utilizing the intersection of skewness and kurtosis contours in the coordinate system of the variables to be solved, based on the high-order moment characteristics of waveforms such as skewness and kurtosis. Using the proposed method, we realized the scale inversion of a 60-cm solar panel of a cube satellite inclined at 45 deg, with the turntable and the detection system placed 80 m apart. The results show that the skewness and kurtosis of the decomposed echo can represent the target size information, and the approach used here can successfully extract the solar panel scale information of a typical satellite, providing methods and data support for space target detection and classification.

Conventional adaptive optics algorithms are studied through calibration or closed-loop control point of view. A Hadamard matrix algorithm was used to calculate the interaction matrix from the wavefront slope to the deformable mirror voltage. A fuzzy proportional integral differential (PID) control algorithm was used to adjust the control parameters to complete the closed-loop control of the adaptive optics. The simulation shows that when the atmospheric turbulence intensities D  /  r₀ are 1, 10, and 20, respectively, the mean wavefront peak to valley (PV) values are are 0.38, 0.93, and 3.53  μm, respectively, after wavefront correction by Hadamard + PID algorithm; the wavefront PV mean values are 0.38, 0.93, and 3.48  μm, after wavefront correction by PushPull + FuzzyPID algorithm; and the wavefront PV mean values are 0.36, 0.92, and 3.30  μm after wavefront correction by Hadamard + FuzzyPID algorithm. The experimental results show that: the wavefront PV mean values are 3.84, 3.56, and 3.36  μm for Hadamard + PID algorithm, PushPull + FuzzyPID algorithm, and Hadamard + FuzzyPID algorithm, respectively. The Hadamard algorithm significantly improves the interaction matrix measurement accuracy, and the FuzzyPID control algorithm improves the adaptive ability under strong turbulence conditions. The wavefront correction using two advanced algorithms is better than that of the combination of advanced and conventional algorithms.

Modulation alphabets using sets of simple superposed and multiplexed superposed orbital angular momentum in a Laguerre–Gauss laser beam over free-space turbulence channel are tested for shift keying demodulation using a convolutional neural network. Simulation results show similar performance in both cases. Moreover, the results suggest a criterion of alphabet formation and bit mapping, leading to a lower topological charge strategy to jointly increase alphabet cardinality and control beam diameter for transmission.

A frequency-doubling optoelectronic oscillator with wideband frequency tunability implemented using a polarization modulator (PolM) and a phase-shifted fiber Bragg grating (PS-FBG) is proposed and experimentally demonstrated. In the proposed structure, the output from the PolM is divided into two branches by an optical coupler. In the lower branch, an optoelectronic feedback loop is formed in which a tunable microwave photonic filter (MPF) is constructed by the joint operation of the PolM, the PS-FBG, a tunable laser source (TLS), a polarization controller (PC), and a polarizer, the MPF serves as an oscillation mode selector that its central frequency is a function of the frequency difference between the TLS and the notch of the PS-FBG. In the upper branch, an equivalent Mach–Zehnder modulator (MZM) is performed by the joint use of the PolM, a second PC, and a second polarizer, the second PC is adjusted to let the bias point of the MZM located at the minimum transmission point (MITP), which generates an optical signal with two sidebands at the ±first orders. By beating the two sidebands at a second photodetector (PD), a frequency-doubled microwave signal is generated. By simply adjusting the wavelength of the TLS, the central frequency of the MPF is shifted, and the fundamental oscillation and its frequency-doubled signals can be tuned. The detailed theoretical study is achieved, and a verified experiment is established. A fundamental oscillation signal with a frequency tuning range from 9.39 to 15.4 GHz is generated in the OEO loop, which is multiplied to generate a tunable frequency-doubled signal. Their overall performances are also investigated.

We demonstrated an improved-beam-quality improved Er:YSGG laser emitting at wavelength of 2.79  μm by applying the Innoslab hybrid stable–unstable resonator and composite crystal with undoped YSGG section bonded to the pump side. With a space-combined, high peak power 976-nm quasicontinuous laser-diode stack and optimized coupling system, we obtained the maximum average output power of 10.2 W at 100 Hz repetition frequency and 500  μs pulse width, corresponding to the slope efficiency of 16.6%. The beam quality factors of M² were measured to be 3.3 and 2.6 in the fast and slow axis directions, respectively. To the best of our knowledge, this is the first mid-infrared laser designed with Innoslab hybrid stable–unstable resonator ever reported.

Considering the low loss transmission and commercialization of hollow core fiber, negative curvature hollow core fiber (NC-HCF) has become a research hotspot in recent years. We report an innovative NC-HCF with an antiresonant layer inside the cladding tubes based on semi-ellipse and semi-circle structures. Based on the COMSOL simulation, it exhibits an ultralow loss from 0.6 to 1.6μm transmission band. On the one hand, as for semi-ellipse and semi-circle with antiresonant layer structure, the fiber lowest confinement loss (CL) of LP₀₁ mode reaches a lowest value of 7.608  ×  10^−  4  dB  /  km at 0.78  μm, and the high-order mode suppression ratio (HOMER) value can reach 4069. On the other hand, the semi-circle and semi-ellipse with antiresonant layer fiber structure shows the lowest CL of 1.675  ×  10^−  4  dB  /  km at 0.79  μm, and the value of HOMER is 1776. Moreover, based on the fabrication tolerance analysis, the hollow core fibers proposed indicate better performance.

We study the optical limiting (OL) property of a newly emerged MXene material, niobium carbide (Nb₂CT_x) nanosheets, using nanosecond laser Z-scan measurement. The nanosheets exhibited excellent OL property, and the OL thresholds are estimated to be about 0.35 and 0.44  J  /  cm² for 532 and 1064 nm, respectively. Compared with the traditional OL material, reduced graphene oxide, Nb₂CT_x nanosheets show a better OL property. The nonlinear scattering (NLS) measurements indicate that the excellent OL behavior of the nanosheets originates mainly from the strong NLS effect due to the good photothermal property of the material.

We numerically investigated an all-optical high-bit-rate 2R-regenerator based on similariton-induced spectral broadening of the optical signal spectrum. The proposed configuration incorporates two cascaded regeneration stages. Active and passive generation of similariton pulses in a highly nonlinear photonic crystal fiber and a comb-like dispersion decreasing fiber are used for the first and the second stages, respectively. The study of the static behavior of the regenerator linking the design to their nonlinear power transfer functions reveals the operating conditions under which the regenerator is able to reduce amplitude noise and improve the signal extinction ratio. Furthermore, the potential of the proposed configuration is evaluated to regenerate an optical signal at 40  Gbit  /  s, and the 2R-regenerator is then assessed in a long recirculating fiber loop to investigate its cascadibility. The ability of the 2R-regenerator to enable operating at high-bit rates up to 160  Gbit  /  s is also investigated. The results demonstrate the high potential of similariton pulses for all-optical 2R-regeneration in future high-speed and long-haul transmission systems.

The propagation and interaction of the optical radiations are analyzed using the theory of a highly multimodal nonlinear guided wave methodology instead of plane wave optics for explaining the optical rotation quasi-phase-matching technique based on total-internal-reflection. Thereby, the yielding second harmonic from a yttrium oxide-coated rectangular slab of magnesium oxide-doped lithium niobate crystal shows very high efficiency. The conversion efficiency of 2.7% has been observed by performing the computer-aided simulation and corresponds to a second harmonic wavelength of 532 nm after considering the surface roughness and absorption.

A photonic crystal fiber (PCF) with an SSK2 dense crown glass ring is designed and analyzed. After optimization of the radius of the central air hole and thickness of the annular region, 394 orbital angular momentum (OAM) modes in the range of 1.48 to 1.62  μm can be transmitted stably. The effective refractive index, effective index difference, dispersion, effective mode area, nonlinear coefficient, numerical aperture (NA), mode quality, and confinement loss are analyzed numerically by the finite element method. The results show that the effective index difference of all the OAM modes is greater than 1  ×  10^−  4 and they can propagate stably in the PCF. Besides, the fiber shows flat dispersion with a minimum variation of 8.55  ps  /    (  km  ·  nm  )  , very small nonlinear coefficient of less than 0.232  W^−  1  ·  km^−  1, as well as high mode quality bigger than 94.57%. This high-performance PCF has immense application potential in optical fiber communication.

Infrared lasers may provide faster and more precise sealing of blood vessels and with lower device jaw temperatures than ultrasonic and electrosurgical devices during surgery. Our study explores three beam shaping methods using optical fibers for transformation of a circular laser beam into a linear beam, necessary for integration into a standard 5-mm-diameter laparoscopic device, and for uniform irradiation perpendicular to the vessel length. In the first design, a servo motor connected to a side-firing, 550-μm-core fiber, provided linear translation of a 2.0-mm-diameter circular beam, back, and forth, over either 5 or 11 mm scan lengths for sealing of small or large vessels. The second design used external beam splitters to divide laser power equally into three side-firing fibers, stacked side-by-side, producing a linear beam of 4  ×  2  mm. The third design used external beam splitters with three forward-firing fibers and a slanted jaw surface, to produce a linear beam of 5  ×  1.5  mm. Laser seals were performed, ex vivo, on 41 porcine renal arteries of 1- to 6-mm diameter (n  ≥  10 samples for each design). Each vessel was compressed to a fixed 0.4-mm-thickness, matching the optical penetration depth at 1470 nm. Vessels were irradiated with fluences of 636 to 800  J/cm², which, based on previous studies, is sufficient for sealing, but not cutting. A burst pressure setup was used to evaluate vessel seal strength. Reciprocating fiber and fiber bundles produced mean burst pressures of 554  ±  142, 524  ±  132, 429  ±  99, and 390  ±  140  mmHg, respectively. All designs consistently sealed blood vessels, with burst pressures above hypertensive (180 mmHg) blood pressures. The reciprocating fiber produced the most uniform linear beam profile and aspect ratio but will require integration of the servo motor into a handpiece. Fiber bundle designs produced shorter, less uniform beams, but enable optical components to be assembled outside the handpiece.

We address the features channel characterization and performance evaluation for wireless body-area networks (WBANs) in medical applications during a walk scenario using optical wireless transmission. More specifically, we focus on optical extra-WBAN uplink communication between a central coordinator node (CN) placed on the patient’s body and an access point (AP) in a typical hospital room. To characterize the optical wireless channel, we use a Monte Carlo ray tracing-based method and take into account the effects of body shadowing and mobility based on realistic models, in contrast to the previous simplistic models considered in the literature. Using this approach, we derive the dynamic behavior of the channel DC gain for different configurations of the CNs and APs. Furthermore, based on the obtained results, we develop a statistical channel model based on kernel density estimation, which we use to investigate the impact of CN and AP placement on the communication link parameters. Also, based on the outage probability criterion, we discuss the link performance and further analyze the improvement in performance achieved through spatial diversity, i.e., by using multiple APs in the room, for different photodetector types, under different background noise conditions. The presented results show that CN placement and user’s local and global mobility significantly impact the performance of extra-WBAN links, which can nevertheless be reduced using spatial diversity. Finally, the presented performance analysis shows that a single AP equipped with an avalanche photodiode photodetector allows an acceptable link performance for low-to-moderate background noise conditions, whereas multiple APs equipped with PIN photodetectors should be used in the case of moderate-to-strong background noise.

Metal–insulator–metal (MIM) structures have been proposed for infrared photodetectors, optical rectennas, and alternative choices to conventional solar cells. Generally, if two dissimilar electrodes are separated by a sufficiently thin insulator, electrons can travel through the insulating gap region due to the quantum tunneling effect. This tunneling through the insulating gap can be driven by an electromagnetic field or an external bias voltage. In our work, we incorporate the contributions of the Poole–Frenkel (PF) effect on the energy barrier of the MIM junction and the effect of Coulomb interaction between the electron charge and its virtual image charges. Using this modified PF-Coulombic barrier, we perform quantum calculations for electron tunneling using the transfer matrix method and Wentzel–Kramers–Brillouin approximations. This, along with the density of states, the Fermi occupation probability, and the quantum confinement effect is used to derive the dark current density for the MIM diode. To test the theory, MIM Au-TiO₂-Ti diodes are designed and fabricated in-house using photolithography, along with electron beam evaporation and sputter depositions. The dark current–voltage (I  −  V) characteristics of the fabricated MIM photodiodes are measured and show good agreement with theoretical predictions.

The lasing mode and internal optical absorption loss profiles of III-nitride edge-emitting laser diode (LD) designs operating at 440 nm were modeled using the transfer matrix method. These models indicate absorption losses are minimized in LDs utilizing tunnel junction (TJ) contacts that (1) optimize the TJ to be as close to fully depleted as possible; (2) spatially separate the metal contact from the lasing mode using lightly doped n-GaN located above the TJ; (3) in designs with optimized TJs, minimize the total thickness of p-type material. These features reduce absorption losses in the model, relative to comparable LD models with an unoptimized TJ contact or with a transparent conducting oxide p-contact, by up to 15.3% and 12.5%, respectively, while at the same time eliminating most or nearly all p-type material.

Nonreciprocal waveguides play a key role in optical communication devices due to their robustness in unidirectional transmission along the edge. We proposed a unidirectional air guide waveguide structure based on eightfold sunflower quasiperiodic magnetic photonic crystal (PC) that has a large working bandwidth, high transmission efficiency, and strong stability. A cross-waveguide is constructed in the sunflower-type eightfold quasiperiodic magnetic PC structure. It can be used as a single-pole double-throw switch by changing the external bias magnetic field direction, in which the isolation is over 28 dB in the microwave band from 4.21 to 4.5 GHz and insertion loss is close to 0.001 dB. It can also achieve 1  ×  2 or 1  ×  3 equal ratio beam splitting, with a total transmission rate of close to 100% and transmission loss of 0.001 dB. The cross-waveguide is simple in structure and easy to integrate and manufacture, and it has a wide range of functions that have tremendous potential applications in optical communication systems.

We propose a gelatin-coated long period fiber grating humidity sensor which has temperature compensation for low-error humidity detection. The output spectrum shows three resonance dips. The dip caused by gelatin-coated grating has humidity sensitivity of 0.09 nm/%RH and temperature sensitivity of 0.15 nm/°C. Another two dips caused by PDMS-coated grating have almost no response to humidity, which can be used for temperature compensation under low temperature and high temperature range, respectively. We come up with a coefficient matrix and experimentally obtain the humidity and temperature sensitivity of both resonance dips, thus temperature and humidity can be demodulated.