Image sensing has entered a new era with advancements in quantum mechanics. The infrared (IR) absorbers are the heart of this new era of image sensing. Within the IR spectra, the shortwave to mid-wave (MWIR) radiations are absorbed by IR photodetectors, whereas the MWIR to very-long wave spectrum is absorbed by IR thermal detectors. Both of these categories of image sensing cover the complete IR spectrum utilized by the applications ranging from biosensing in healthcare sector to autonomous vehicle navigation in military and space purposes. Despite having high-cost semiconductor technology with group-II–VI (mercury–cadmium–telluride) and group-III–V (indium–gallium–arsenide) dominating this IR absorbance industry for many decades, the need to have a cost-effective solution has led to an explosion in the exploration of potential materials. Two-dimensional (graphene, dichalcogenides of transition metals, and black-phosphorous) antimonite-based and group-IV/IV alloys have been found to show unprecedented absorption yield and detector properties comparable to traditional dominators with flexible fabrication methods. At the same time, the photon upconversion phenomenon that upconverts low-energy light to high-energy light has emerged as an exceptionally rich area of research in image sensing. The principle behind this concept lies in different energy transfer mechanisms (two photon absorption, triplet–triplet annihilation, cooperative energy pooling, etc.). The advancements that took place most recently in the development of IR absorbers have been reviewed in a concise way. Furthermore, the advancements in upconversion-based detection focusing on how this is evolving as a low-cost alternative for image sensing have been reviewed. Further discussion on how to anticipate a low-power, cost-effective, and light-weight image sensing system has been presented while mentioning some recent research as a proof-of-concept. We finally suggest a possible approach that could come up by synergizing the two simultaneous technologies to foresee the realization of an all-optical, low-power, and light-weight broad-range IR absorber for various applications.

The guest editors introduce the Special Section on Solid-state Lighting and LED Optics.

We introduce a current development in optical design for vehicle forward lighting based on solid-state lighting, in particular, phosphor-converted white LEDs. The vehicles include bicycles, bikes, and automobiles. Although the requirements regulating different vehicles are different, the low beam always requires a high-contrast cutoff line. Three optical design approaches are discussed; these include a projection lens incorporated with a baffle or beam shaper, multisegment reflectors, and complex lenses. A new design approach called light field management technology for the multisegment reflector is introduced. In addition, the possible related manufacturing errors and the robustness of different optical approaches are analyzed. Finally, we introduce three approaches to adaptive forward lighting that provide a driver with brighter and clearer vision without inducing glare to people on the roadway. The application of video projection technology to roadway illumination could be a trend of vehicle forward lighting based on solid-state lighting.

A programmable ultraviolet light-emitting diode (UVLED) array with a transfer lens forms an adjustable intensity distribution upon a mask, whether for the uniform distribution or variable distribution for compensate wavefront error introduced by the lithographic lens, so as to fabricate an aberration-free pattern on a wafer. The collimating and aligning all rays in one aperture lens with a N  ×  N two-dimensional UVLED array is designed and fabricated by integrating with lithographic lens to form aberration-free smallest linewidth in integrated circuit wafer. Our work provides a transfer lens for the UVLED array to manipulate the intensity distribution fitted for the aligner in the soft- and near-contact mode and steppers.

With the rapid advancement of light-emitting diodes (LEDs), front fog lamps using LEDs have become a main emphasis for vehicle lighting. For vehicle lighting, the front fog lamps should provide a bar-shaped beam of light with a sharp cutoff at the top and are designed to increase the illumination directed toward ground at a sharp angle. In this study, an innovative lens design based on a freeform surface responding to the requirements of the vehicle lighting is proposed. The design of the two-axis asymmetric freeform lens for LED front fog lamp can meet ECE R19 class F3 regulation without any other lens or reflector.

An optical design model of dual-elliptical mirrors near-infrared absorption spectroscopy (NIRAS) for detection of diabetes is proposed. This design model improves the optical efficiency of the conventional NIRAS system without the use of optical components. We used the Henyey–Greenstein scattering skin model in the simulation to calculate the light scattering phenomena. Based on the virtual skin model, the dual-elliptical mirrors NIRAS system can focus the light-emitting diode (LED) light into deeper depths of the human skin and collect more backscattered light. The dual-elliptical mirrors NIRAS system can enhance the light collection efficiency by 1.6 times that of the conventional NIRAS system and 66 times that of the dual-elliptical lens NIRAS system. In terms of assembly tolerance, the normalized light collection efficiency (LCE) of LED and photodiode can be maintained above 0.9 and 0.68, respectively, at a 0.2-mm displacement. The LCEs of the φ and θ rotations are at least 0.95 with a 5-deg tilt error of the chips.

A design scheme for an aspherical lens including two step processes is proposed and demonstrated to direct appropriate flux to the expected target illumination. The first-step design is based on a point source and the surface geometry is determined. The flux deviation between the design and target illumination becomes the factor in the optimization process, and the angular flux compensation is done to adjust the light pattern. Finally, the experimental result shows that high similarity between the target and the measurement is observed and full width at half maximum angle error is within 3%, which are both better than those in the aspherical lens design based a point source and a real light-emitting diode without optimization by flux compensation.

Based on Mie scattering and Monte Carlo ray tracing method, the spectral transmission behavior of visible light in the seawater is estimated. Its optical model is constructed for the fast and accurate prediction of light quality changes of phosphor-based white LED underwater illumination with distance. Because of this, we propose to add a dual-wavelength LED to the original white LED, which would perform spectrum compensation at each illumination distance to restore its good light quality. The result shows that such a dynamic light source can successfully maintain correlated color temperature at 6000 K and color rendering index above 80 under different underwater illumination distances.

In retinal optical coherence tomography (OCT), it is significant to focus the scan beam on the retina layers of the human eye fast to acquire high-quality OCT images. The refractive errors of the human eye are usually compensated by shifting the optical lens in the sample arm manually or electrically. Otherwise, refractive errors of the human eye will cause axial focal shift of the scanning beam and blur the OCT images. We propose a fast automatic focus method using the interference fringes magnitudes of the whole retinal layers to determine the best refractive correction position of motor-driven optical compensation lens without the aid of optical fundus imaging or OCT B-scan imaging. Also, the optical path difference between the sample arm and reference arm is adjusted in the spectral-domain OCT (SD-OCT) to reduce the effects of sensitivity roll-off. The experiments in the lab-built SD-OCT show that the average running time of the method is 15.2 s and the mean absolute deviation of each imaging is within 1 mm. The method is independent of extra optical setup and requires less computational consumption, which is suitable for low-cost and automatic retinal OCT devices.

Due to light being absorbed by water and scattered by suspended particles, color distortion, low image contrast, and detail loss are the common problems found in underwater images. We present an underwater image processing method, which based on an underwater imaging model, makes initial image restoration with the improved red channel prior combining transmission reduction, background light correction, and color compensation to acquire clearer underwater images, and then combines multiscale retinex (MSR) enhancement and hue saturation value to enhance image color contrast and saturation. Results indicate that, compared with the original images, the method proposed in this paper is capable of significantly enhancing image definition, saturation, contrast, and luminance. In comparison with dark channel prior, single-scale retinex (SSR), MSR, and multiscale retinex with color restoration (MSRCR), this method greatly improved the average gradient of images while keeping the information entropy of images unchanged. The average gradient calculated with the proposed method increased by 239%, 199%, 200%, and 220% for the three given images, respectively, compared with the other methods above.

An enzymatic glucose sensor was fabricated and integrated into a heterodyne refractometer. A heterodyne light source was incident into the sensor which the circular birefringence refractive index of sample was changed as the chemical reaction between glucose oxidase and glucose progressed. Therefore, the phase difference before and after chemical reaction could be measured by a lock-in amplifier with phase-lock technology. The optical configuration and measurement procedures indicated that the alignment of the measurement system was straightforward and that it reduced the misalignment effect. The phase stability of the proposed system was superior to 0.04 deg within 1 min. The glucose sensor can be reused 100 times while retaining favorable performance. The results indicated that the resolutions of the proposed method were ∼1.5 and 1.29  mg  /  dl for the glucose solution and serum-based sample (SRM 965b), respectively. The calibration curve revealed high linearity within the dynamic range of 0 to 300  mg  /  dl. Based on these findings, the proposed method has a potential to measure the whole blood glucose concentration for daily monitoring.

We investigate transmission through falling snow using a 3D imaging lidar at 1.56-μm wavelength. The lidar is based on the time-correlated single-photon counting technique. Experimental transmission data are compared with Mie theory transmission calculations based on snow particle size distribution simultaneously measured with a laser disdrometer. The calculations were performed in two ways, using the Beer–Lambert approach where all radiation interacting with a hydrometeor is considered extinct and an approach that includes effects of the forward scattering. Comparison of these two methods shows that inclusion of the contribution from forward scattering gives better agreement between experiment and calculations than using extinction only. When comparing the results using scattering calculations with a curve fit approach based on precipitation rate, it is evident that both the Beer–Lambert approach and the forward scattering approach give a much better correlation between experiment and calculations than relying on precipitation rate, as measured with the disdrometer, only.

Accurate bidirectional reflectance distribution function (BRDF) models are essential for computer graphics and remote sensing performance. The popular microfacet class of BRDF models is geometric-optics-based and computationally inexpensive. Fitting microfacet models to scatterometry measurements is a common yet challenging requirement that can result in a model being fit as one of several unique local minima. Final model fit accuracy is therefore largely based on the quality of the initial parameter estimate. This makes for widely varying material parameter estimates and causes inconsistent performance comparisons across microfacet models, as will be shown with synthetic data. We proposed a recursive optimization method for accurate parameter determination. This method establishes an array of local minima best fits by initializing a fixed number of parameter conditions that span the parameter space. The identified solution associated with the best fit quality is extracted from the local array and stored as the relative global best fit. This method is first applied successfully to synthetic data, then it is applied to several materials and several illumination wavelengths. This method proves to reduce manual parameter adjustments, is equally weighted across incident angles, helps define parameter stability within a model, and consistently improves fit quality over the high-error local minimum best fit from lsqcurvefit by an average of 71%.

A two-step phase-shifting method is proposed. The method realized the rapid measurement of the three-dimensional (3D) contour of some objects using mean envelope denoising based on the striped structured light. First, Butterworth low-pass pre-filtering in the frequency domain was performed on the two deformed fringe images containing the height information of the objects. It reduced the influence of higher harmonics. Then the peak and valley values of fringes with sub-pixel accuracy were obtained through numerical interpolation and point-by-point comparison. Furthermore, the mean envelope was accurately obtained and removed. After removing the mean envelope, the rectangular low-pass filtering was used to thoroughly filter out the remaining background signal. Finally, the fast reconstructions of the 3D contour of the objects were realized. The 3D contour reconstructions of the objects were simulated and experimentally measured using the method proposed. The calculation speed and accuracy were compared with the traditional four-step phase-shifting method and other two-step phase-shifting methods. The method has the advantages of fast calculation speed and high calculation accuracy. It is a valuable method for quickly measuring the 3D contour of some objects.

Motivated by the low efficiency and poor accuracy of the existing techniques for measuring the depth of a pavement structure, we examine the characteristics of laser speckle and speckle measurement methods in relation to the depth of a pavement structure and propose a set of methods for the 3D measurement of such structures based on laser speckle and digital image processing. First, we analyze the relevant characteristics of laser speckle measurement, and then based on the relevant region and temporal sequence correlation, a faster digital speckle correlation method is used to establish a mathematical relationship between the 3D image and the structural depth. The erosion and dilation technique and mean optimization algorithm are proposed to eliminate the noise and burr of primeval 3D reconstruction. After this, a 3D point cloud of information on the depth of the pavement structure is obtained. Finally, through fitting, a good linear relationship was found between the texture depth obtained by the sand paving method and the system. From measurements using a laboratory calibration platform, it was found that the accuracy of measurement of our method can reach the subpixel level, and the running speed is high, meaning that it can be used for highly efficient and accurate detection of the depth of a road structure.

We demonstrate time-, space-, and weight-based calibration techniques for pressure monitoring in the low-cost plastic optical fiber (POF) sensor carpet. It is found that the POF-based pressure sensing platform has several limitations, such as output voltage variations and difference in the sensor response for horizontal and vertical fibers due to convex and concave shapes of bend. To surpass the these limitations, we have developed time-based calibration using time windowing technique to reduce the standard deviation of photodiode output voltage variations by 98%. We have also described space and weight calibration techniques based on the convex and concave shapes of fiber bend. These techniques help in improving the Landweber image reconstruction algorithm to obtain significant clarity and improvement in object pressure images. We also report an artificial intelligence-based algorithm to determine the accuracy of positioning of the load. Experimental results demonstrate that this algorithm gives a mean square error of 0.875 cm in position detection on the carpet. We discuss the potential for a compact and cost-effective pressure sensor carpet, which integrates with the living environment and the outside world.

The chromatic confocal technology (CCT) has ultra-high distance measurement resolution and the characteristics of multi-surface tomography. Based on the principle of optical dispersion and confocal, the technology achieves accurate axial position or micro-displacement measurement. The radial gradient index (GRIN) lens is a typical important inhomogeneous material. Its refractive index gradually decreases from the center to the edge along the radial direction. We propose to measure the thickness of the radial GRIN lens based on CCT. The thickness measurement model is established by the ray-tracing method, the optical Lagrange function, and the ray arc differential in the Cartesian coordinate system. The refractive index distribution makes the eccentric tilt of the lens change the propagation of the probe light and affects the extraction of the peak of the spectral response causing the thickness measurement error. The influence of eccentricity and tilt of the radial GRIN lens on its thickness measurement is studied. The precision shift table drives the radial GRIN lens movement to simulate the eccentric tilt state of the lens under the dispersion probe. According to the comparative analysis between the experimental and simulation results, it is concluded that the greater the eccentric distance and inclination degree of the radial GRIN lens is, the greater the influence on the thickness measurement is. The larger the lens thickness is, the greater the measurement error is. For the radial GRIN lens with a thickness of 2.36 mm, the measurement error is about 20  μm when the eccentricity is 0.1 mm and the tilt is 6 deg. The research results have significance for optimizing the system structure and further improving the system performance for the application of the CCT in measuring non-homogeneous materials or optical thin film. And the research will encourage the development of GRIN lens instrument preparation and application technology by improving the thickness measurement accuracy and precision of the GRIN lens.

The bidirectional reflectance distribution function (BRDF) is used to describe reflectances of materials by calculating the ratio of the reflected radiance to the incident irradiance. While it was found that the isotropic models maintained symmetry about ϕ_s  =  π, such symmetry was not maintained about the θ_s  =  θ_i axis, except for close to the specular peak. This led to the development of a data-driven metric for how isotropic a BRDF measurement is. Research efforts centered around developing an algorithm that could determine material anisotropy without having to fit to models. This algorithm was tested using high fidelity data (containing off-axis BRDFs), which was collected via a modified Complete Angle Scatter Instrument (CASI^®) with a CCD array detector. The algorithm accurately characterized the degree of isotropy for four out of five materials and worked for cases where the BRDF is higher than 100  sr^−  1. This algorithm is intended to improve BRDF characterization, and the applications of light curve analysis, scene generation, and remote sensing.

We studied the dependent factors for improving spectral resolution and signal-to-noise ratio (SNR) in a spatially modulated Fourier transform spectrometer comprised of a Wollaston prism. The obtainable spectral resolution was investigated for the factors such as the ratio of overlapped to nonoverlapped sectors in a focal plane, SNR, and the maximum optical path difference. The accurate application of signal padding for the interferogram was effective in obtaining better spectral resolution and SNR in the spatially modulated Fourier transform spectrometer based on the Wollaston prism, for which it is difficult to have adequate optical path difference. We investigated the change of spectral resolution and shape for the measured and signal padded interferograms of the 6382  cm^−  1 center wavenumber light source. The best obtainable spectral resolution was drastically improved to 27  cm^−  1, whereas the SNR was improved up to 12 times compared to that of the not signal padded.

Ultra-fine powder extinguishing agent (UPEA) concentration measurement is essential for evaluating the validity of aircraft nacelle fire extinguishing system. Based on Beer-Lambert law, the influence of powder contamination, ambient light, and other factors on the measurement signal during high-concentration measurement by the extinction method has been analyzed. We proposed a correction model of the relationship between transmittance and high mass concentration of powder. An optical fiber UPEA concentration measurement device based on the extinction method has been developed. Meanwhile the calibration test platform for the occurrence of stable and uniform concentration powder has been built. The mass concentration of sodium bicarbonate UPEA that is promising halon replacement agent in aircraft nacelle is analyzed by developed device. The results show the modified relational model function fits the test data well, and the device measures concentrations up to 128.8  g  /  m³ with an indication error of 11.7%. The present work provides a new concentration measurement method for high-concentration powder measurement, especially the real-time measurement of UPEA concentration.

The multilayer Laue lens (MLL) is a promising optical element with large numerical aperture and aspect ratio in synchrotron radiation facility to focus hard x-ray to 1 nm with ideal structure. We use a new method of combining actual film thickness and the coupled wave theory to calculate focusing performance. Here, a 17.2-μm-MLL with a focal spot size of 17 nm at 10 keV is designed and fabricated by dynamical diffraction theory and direct current magnetron sputtering technology. Based on a new rate calibration and symbol layer insertion method, we calculate d-spacing of multilayer instead of individual layer thickness and change the order of two layers as a symbol so as not to damage zone plate law. The scanning electron microscope image is smoothed and binary transformed to measure the actual thickness of each layer. The full-width at half-maximum of focus spot is 18 nm, which is close to the theoretical result of 17 nm.

Futuristic mobile data networks are expected to reach higher data rates per user to accommodate the specifications of emerging services, such as triple play and mobile applications. Researchers are carrying out their works to tackle the drawbacks of traditional orthogonal frequency-division multiplexing by designing new waveforms with high spectral efficiency and low out-of-band emissions. Among many others, filter bank multicarrier (FBMC) is an appealing candidate for beyond 5G that fulfills these constraints. Consequently, it is worth to shed light on the performance of FBMC in multichannel transmission system. The main contribution of our paper is to compensate fiber nonlinearity including self-phase modulation and cross-phase modulation effects using adaptive Volterra equalizer in longhaul FBMC system based on a 6  ×  20  Gb  /  s in wavelength-division multiplexing scheme over 100  km  ×  30 spans of single-mode fiber (SMF). The impacts of channel spacing, bit rate, and fiber types on system performance are addressed. For a target of bit error rate  =  10^−  3, the simulations show that this performance can be reached at −12  dBm of launch power when 5-taps third-order Volterra (TOV) equalizer is used for 12.5 GHz of channel spacing and an improvement of approximately 1 dB is obtained for 7 taps compared with the same equalizer with 3 taps. To further enhance the system performance, standard-SMF is replaced by a new class fiber called pure-silica-core fiber with large effective area, which exhibits a gain of almost 1.3 and 1 dB for 3 and 5 taps, respectively. The complexity burden of the TOV filter is also discussed.

In this work, we designed a reconfigurable 2  ×  1 temporal multiplexer (MUX) using a 1  ×  1 microring modulator (MRM) configured in silicon on insulator (SOI) platform. To evaluate the performance of the MUX, logical operations such as NOT, OR, AND, NOR, and NAND are demonstrated. The numerical functionality of the device is assessed using the finite-difference beam propagation method (FD-BPM). The 1  ×  1 MRM has a ring radius of 6  μm having a free spectral range (FSR) of 18 to 19 nm. The transmission characteristics and coupling factors of the all-pass and add-drop configuration are analyzed, especially for switching and logical circuit applications. The voltage tuning across the P-i-N junction is achieved by varying the carrier concentration across the intrinsic region, which corresponds to the change in refractive index. Various design parameters are tuned for this configuration, which offers a switching voltage of 0.79 V with modulation speed of 139 GHz. Further, the logical operations of OR, AND, NOR, and NAND with an extinction ratio of 10.25, 11.40, 18.83, and 16.06 dB is reported.

Light-field and plenoptic cameras are widely available today. Compared with monocular cameras, these cameras capture not only the intensity but also the direction of the light rays. Due to this specificity, light-field cameras allow for image refocusing and depth estimation using a single image. However, most of the existing depth estimation methods using light-field cameras require a prior complex calibration phase and raw data preprocessing before the desired algorithm is applied. We propose a homography-based method with plenoptic camera parameters calibration and optimization, dedicated to our homography-based micro-images matching algorithm. The proposed method works on debayerred raw images with vignetting correction. The proposed approach directly links the disparity estimation in the 2D image plane to the depth estimation in the 3D object plane, allowing for direct extraction of the real depth without any intermediate virtual depth estimation phase. Also, calibration parameters used in the depth estimation algorithm are directly estimated, and hence no prior complex calibration is needed. Results are illustrated by performing depth estimation with a focused light-field camera over a large distance range up to 4 m.

New graphical methods using the Delano y-ybar diagram are shown to yield simple alternative derivations of the M² beam quality factor for Gaussian-like laser beams. Using M² as a scaler for the Lagrange optical invariant, powerful methods of interpreting and calculating the beam factor become apparent. Elegant methods of determining M² using strategic beam sample locations are also developed, taking advantage of the property that a freely propagating beam trace in the Gaussian beam y-ybar plane is a straight line. Application to non-Gaussian beams is explored.

Positive-intrinsic-negative diode (PIN), avalanche photodiode (APD), and single photon avalanche diode (SPAD) are commonly used optoelectronic receivers with different characteristics in practical visible light communication system. To determine the most appropriate candidate, different signal and ambient light strength in the communication scenarios should be taken into account. APD and SPAD receivers have higher sensitivities than PIN, but there are still some defects that restrain their operation performance. APD receiver may generate excessive shot noise, whereas SPAD is limited by the dead time, afterpulsing, and smaller detection area. We initially analyze the noise characteristics of PIN, APD, and SPAD receivers. SNR models are established, and the main factors affecting the performance of APD and SPAD receivers are concluded. Then, the comparison experiments of three kinds of receivers in various transmission distances are conducted, respectively. Finally, the experimental results show that: short and mid distance conditions, PIN and APD are better choices, whereas SPAD performs better in long-distance communication. In addition, if a certain intensity of ambient light is introduced, APD is still better than SPAD even in long distance.

A parabolic pulse generator based on non-reciprocal nonlinear optical fiber loop mirror is proposed. When an incident triangular optical pulse is split into two branches of the loop mirror, two coherent light fields with linear intensity profile are counter-propagated in the interferometer and suffer different nonlinear phase shift caused by self-phase modulation. Because the intensity of interference field is determined by the amplitudes and phase relationship between two coherent lights, the interference result gives parabolic pulse. This concept is verified by theoretical analysis and simulation. In the experiment, tunable bright and dark parabolic pulses with repetition frequencies of 8, 9, and 10 GHz are simultaneously generated, which agree with the theoretical expectation well and exhibit large operation bandwidth.

A method of fine pointing of laser beams using laser arrays has been developed. The telescope system combines a lens system and a vertical cavity surface emitting laser/photodetector array. It does not use moving parts. In computer simulations, it is applied to CubeSats satellites that use body pointing. Body pointing was used by the Aerospace Corporation for CubeSats in LEO at 450 km in NASA’s Optical Communications and Sensors Demonstration (OCSD) program. Computer simulations of this fine pointing capability have been applied previously to CubeSats in the OCSD program. Computer simulations of this laser pointing are applied to CubeSats in LLO at 100 km. With more accurate pointing, a laser beam with smaller divergence can be used. For the case of the AeroCube-7B vehicle that was used in the OCSD program, computer simulations show, for example, that the divergence of the output beam can be reduced from ∼0.06  deg to 0.014 deg. For the proposed electro-optical system, reaction times to pointing changes and vibrations are on a nanosecond time scale, much faster than those for fine pointing systems that use moving parts, such as fast steering mirrors or that use quad-cell photodetectors to improve the body pointing of the CubeSat.

We present a wavelength division multiplexing-passive optical network (WDM-PON) that uses a graphene-based ultrashort pulsed fiber laser (USPL) as multi-wavelength source. The performance of this WDM-PON system is analyzed in two stages: at first, the USPL was designed, implemented, and characterized experimentally. Then experimental data from the USPL spectrum were then introduced into a simulated network using the software VPItransmissionMaker™, for testing the WDM-PON system performance. The results show that it is possible to achieve an error-free transmission (BER  <  10^−  9) for distances up to 30 km using a non-return to zero modulation format with a bit rate of 10 Gbps and 18 dB optical signal-to-noise ratio (OSNR). In comparison with an externally modulated distributed-feedback laser, a distance and OSNR penalties   <  5  km and 0.4 dB, respectively, were achieved. Furthermore, this USPL exhibited a 3-dB bandwidth close to 22 nm, which means more than 100 optical channels could be obtained when considering a 12.5 GHz standard grid. Thus due to the number of generated channels, a remarkable cost reduction could be achieved in comparison with conventional WDM-PON systems.

The exposure lens is a useful tool for fast and convenient chirpiness detection. An exposure lens is proposed by adopting square-root space mapping within the framework of transformation optics, thereby exposing a portion of the optical axis within the body of a conventional graded index lens at the lens surface, while compressing the input facet. This compression enables the proposed lens to detect higher chirpiness than conventional lenses. The results of numerical simulations verify the enhanced chirpiness detection. The family of exposure lenses provides a complete kit for investigating a wide chirpiness range, which has potential for optics signal processing.

The modified Frantz–Nodvik equation considering the pulse repetition rate (PRR) for continuous-wave end-pumped picosecond laser amplifier is theoretically developed for the first time by analogizing Q-switch theory and solving rate equations. Based on the modified Frantz–Nodvik equation, a simple finite-element slice model is established to simulate the output characteristics of the end-pumped high-repetition-rate picosecond amplifier. Moreover, the validity of the theory and model is well verified by the experimental results of a two-staged diode-end-pumped Nd  :  YVO₄ amplifiers using a picosecond fiber laser with adjustable PRRs as the seed source. The agreement between the experimental and theoretical results illustrates that the as-developed pulse amplification theory and model are a powerful tool for designing and optimizing adjustable-high-repetition-rate solid-state picosecond laser amplifiers.

A free-space optical access network with multiple ground stations (GSs) connected by a high-altitude platform (HAP) is proposed. The HAP plays a role of a two-way relay node that supports all-optical amplify-and-forward and half-duplex transmission. In the network, optical code-division multiple-access is utilized to enable asynchronous and simultaneous data transmission among GSs. In further steps of the study, the mathematical expressions of two system metrics including bit-error rate (BER) and network throughput are derived. They consider many physical layer impairments, such as power loss, atmospheric turbulence, pointing error, multiple-access interference, and receiver noise. Eventually, numerical results of the system performance under consideration of the number of GSs, the bit rate, and the received power confirm the feasibility of the proposed system as well as provide useful information for network design.

The damage process of (001) silicon wafer subjected to millisecond Gaussian laser irradiation is investigated. The laser pulse width is 1 ms, and the laser energy density ranges from 18 to 32  J  /  cm². The damage mechanism is discussed by combining real-time experimental observation with numerical analysis based on a dislocation model. The first damage is dislocation multiplication, which is induced by the long irradiation time of a millisecond laser. The subsequent melting process begins at slip lines, not the spot center as is usually assumed. Fracture also occurs outside the spot center. Precise temperature in the cooling period cannot be obtained by simulation due to complicated dependence of thermal conductivity on dislocation, which may be the most urgent problem in further studies.

Three different designs of plasmonic photonic crystal filters (two-channel, three-channel, and four-channel) are proposed and considered. The photonic crystal structures consist of standing rods made of Ag and GaAs, whereby introducing different simple or ring-shaped defects, two-, three-, or four-port filters are realized. Optical fluid is used instead of air as the background material, owing to its versatile benefits. By utilizing different combinations of optical fluids and plasmonic materials, multichannel filters are obtained which can function better by improving the structural parameters such as the rod’s radius. Considering the four-port filter, its applications as the power splitter are also investigated. For tuning the filter properties such as the resonance peak’s value and wavelength, impacts of Ag and GaAs rod radius on the transmission spectrum are examined. The following resonance peak’s value and FWHM are obtained for the proposed structures: two-channel filter (0.9, 4 nm), three-channel filter (0.8, 2 nm), four-channel filter (0.5, 10 nm). The proposed designed filters can be utilized in the photonic integrated circuits as well as the nanophotonics devices for medical and industrial applications.

The fabrication and modeling of bow-tie antenna integrated uni-traveling carrier photodiodes (UTC-PD) are presented. The experimental results show that a −10.68  dBm RF power can be obtained from the 4  ×  50  μm² area UTC-PD at 100 GHz. The device is modeled by high frequency simulation software. The trend of variation of the measured terahertz (THz) power with frequency matches well with the simulation results. Based on the model, the effects of the shape and the contact pads of the antenna on the THz power emission properties of the device are studied numerically, which helps to further optimize the device design.

A generalized surface morphology model is presented and validated to more effectively simulate the effects of surface variations (e.g., surface roughness and local thickness variations) on integrated Si photonic waveguides. To demonstrate the validity of this approach, a variety of surface roughness morphologies generated using this model are incorporated within a commercial finite-difference-time domain (FDTD) modeling package to simulate waveguide loss in Si strip optical waveguide geometries typically encountered in Si-based photonic integrated circuits. The FDTD simulation results are in very good agreement with the Payne and Lacey theoretical model for radiation-mode scattering loss based on surface correlation functions for RMS roughness values exceeding 2 to 3 nm where such scattering dominates. This agreement validates the efficacy of the generalized surface morphology model and its use for investigating the effects of irregular surface variations on photonic device performance.