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The local color display technology utilizes a high refresh rate LCD open‐cell without a color filter and enables color adjustment through independent RGB backlight zones isolated by an anti‐scatter grid (ASG). Synchronized calibration between the open‐cell and the backlight zones is achieved by aligning the backlight controller with the vertical clock pulse (CPV)/vertical start pulse (STV) signals in the open‐cell gate driver, thereby determining the open‐cell scan line position. Once synchronous calibration is completed, the backlight controller refreshes the corresponding RGB backlight zones whenever the open‐cell scan line passes through them. The local color display technology can reduce the cost of open‐cell by 20%, improve resolution by three times, enhance brightness by eight times, expand the color gamut to BT2020, and improve grayscale to 32‐bits. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach for generating structured light using a diffractive beam‐shaping element that can generate multiple beams with distinct spatial structures in the focal plane. The element is constructed by restructuring a spiral zone plate with fork gratings, providing a tunable and controllable means for generating structured light. The element can create linear and 2D arrays of various structured beams, including vortices with adjustable charge and vorticity, petallike beams, and ring‐lattice structures. To control the generation of these beams, it introduces several parameters of the fork gratings, enabling tailoring of the beam properties to specific applications. The proposed approach involves significant mathematical analysis, including the derivation of complex equations and expressions to understand the behavior of the proposed element and its impact on the generated beams. It conducts simulations and experiments to validate the mathematical analysis and demonstrate the feasibility of the proposed approach. [ABSTRACT FROM AUTHOR]

Acoustic radiation force optical coherence elastography (ARF-OCE) has been successfully implemented to characterize the biomechanical properties of soft tissues, such as the cornea and the retina, with high resolution using single-element ultrasonic transducers for ARF excitation. Most currently proposed OCE techniques, such as air puff and ARF, have less capability to control the spatiotemporal information of the induced region of deformation, resulting in limited accuracy and low temporal resolution of the shear wave elasticity imaging. In this study, we propose a new method called 2-D ultrasonic array-based OCE imaging, which combines the advantages of 3-D dynamic electronic steering of the 2-D ultrasonic array and high-resolution optical coherence tomography (OCT). The 3-D steering capability of the 2-D array was first validated using a hydrophone. Then, the combined 2-D ultrasonic array OCE system was calibrated using a homogenous phantom, followed by an experiment on ex vivo rabbit corneal tissue. The results demonstrate that our newly developed 2-D ultrasonic array-based OCE system has the capability to map tissue biomechanical properties accurately, and therefore, has the potential to be a vital diagnostic tool in ophthalmology.

Tensor models have been used extensively in signal processing applications to design different types of communication systems. This paper proposes, for the first time, the use of tensor models for optical communications. The signals of an optical dual-core coupler network are modeled as a multiway array (tensor), which satisfies a generalized Tucker train decomposition. This tensor model is then used to develop an estimation algorithm that enables the network parameters to be estimated from the input and output signals. The performance of this algorithm was evaluated by means of computer simulations, in terms of NMSE of the estimated parameters and convergence speed. For the tested configurations, good levels of NMSE with fast convergence were obtained, demonstrating the effectiveness of the proposed method as a promising tool for studying and designing optical devices, with a wide range of applications in the context of lightwave systems.

Accurate measurement of the spatial angle is key for plane flatness and guide rail straightness detection. This paper presents a lens-array-based optical system and an analytical model for micro-spatial angle measurements. In this system, a collimated light beam passes through four-array lenses arranged in a pyramid shape and forms regular array spots on a charge-coupled device sensor. The angles with respect to the $X$ and $Y$ axes are calculated by analyzing the distance of these spots on the CCD, the distance between adjacent apertures on the lens array, and the inclination angle between the lens array and the CCD. Using the coordinate value of the array spots on the CCD, the angle around the Z-axis can also be calculated simultaneously. Finally, the accuracy of the proposed method was verified by comparing the measured results with those of the autocollimator, and it was shown that the proposed approach enabled the achievement of RMS $\le 0.1''$ . Additionally, this measurement system which is consists of a laser source, lens arrays and CCD, compared with other methods, is smaller in volume and more convenient to carry.

The Laguerre-Gaussian (LG) and Hermite-Gaussian (HG) modes can be interconverted with an astigmatism phase. In this paper, based on the single beam, the interconversion of LG and HG beams array with the astigmatism phase is analyzed theoretically and the spatial mapping relationship is derived. In the experiment, 1 × 3, 2 × 2, 3 × 3 LG beams arrays are generated and converted into HG beams array via employing a spatial light modulator loaded with 0°, 90°, 45°, −45° astigmatism phases. The experimental results are in great agreement with the theoretical analyses. Moreover, from the number and direction of the dark fringe of converted HG beams array, the orbital angular momentum information of LG beams array can be obtained. This work theoretically perfects the theoretical model of the interconversion between LG and HG beams based on an astigmatism phase, and also provides a theoretical support for measuring the LG beams array. [ABSTRACT FROM AUTHOR]

Uniform electron emission (EE) from on-chip micro-emitter arrays based on SiOx tunneling diodes (STDs) in electroformed SiOx is reported. EE from STDs is found to be accompanied with visible light emission, which enables us to resolve the spatial distribution of EE from the micro-emitter arrays and emitter-to-emitter uniformity at the microscale resolution via optical imaging. Up to 99% micro-emitters in a 15 $\times15$ array is observed to work simultaneously with good emitter-to-emitter uniformity, showing an emission current of 0.56 mA and an emission density of 626 mA/cm2. The good uniformity is attributed to the insensitivity of EE from STDs to the microfabricated structures of micro-emitters. [ABSTRACT FROM AUTHOR]

Oriented to the point-to-multipoint free space optical communication (FSO) scenarios, this paper analyzes the micro-mirror array and phased array-type optical intelligent reflecting surface (OIRS) in terms of control mode, power efficiency, and beam splitting. We build the physical models of the two types of OIRSs. Based on the models, the closed form solution of OIRSs’ output power density distribution and power efficiency, along with their control algorithms have been derived. Then we propose the algorithms of beam splitting and multi-beam power allocation for two types of OIRSs. The channel fading in FSO system and the comparison of two types of OIRSs in actual systems are discussed according to the analytical results. Simulations and experiments are both presented to verify the feasibility of models and algorithms. [ABSTRACT FROM AUTHOR]

We report the theory and experimental verification of a method to reduce beam divergence from coherently-coupled ring arrays of photonic crystal vertical cavity surface emitting lasers (VCSELs). The photonic crystal etched into the top distributed Bragg reflector defines the optically coupled array elements, each of which has independent current injection and thus independent gain. Using a 2-dimensional complex waveguide model we simulate the supermodes of a 6-element ring array of VCSELs. The influence of the photonic crystal, free carrier loss, laser gain, and carrier-induced index suppression arising from the spatially defined gain regions are included in our analysis. Our simulations show the latter enables preferred anti-guided supermodes with reduced beam divergence. Optical characterization of the spectral and beam characteristics of 6-ring photonic crystal implanted VCSEL arrays shows that when the arrays are current-tuned to quasi-single mode operation, we find the beam divergence angle approaches 2° consistent with our simulations. This method of reduced beam divergence may have advantages for high-brightness applications. [ABSTRACT FROM AUTHOR]

Optical synchronization of large-span arrays offers significant benefits over electrical methods in terms of the weight, cost, power dissipation, and complexity of the clock distribution network. This work presents the analysis and design of the first phased array transmitter synchronized using a fully monolithic CMOS optical receiver. We demonstrate a bulk CMOS, 8-element, 28-GHz phased array building block with an on-chip photodiode (PD) that receives and processes the optical clock and uses an integrated PLL to generate eight independent phase-programmable RF outputs. The system demonstrates beam steering, data transmission, and remote synchronization of array elements at 28 GHz with fiber lengths up to 25 m, in order to show the scaling benefits of our approach. The provision of small footprint and cost-effective CMOS transceivers with integrated optoelectronic receivers enables exciting opportunities for low-cost and ultralight array systems. [ABSTRACT FROM AUTHOR]

We demonstrate the broadband operation and beam calibration over 70nm tuning range of an optical phased array (OPA) fabricated in a generic InP photonic integration platform, which enables multi-wavelength OPA operation. The broadband performance was demonstrated on an 8-channel OPA, whose calibration and phase modulator characterization were executed through near-field and far-field measurements. The architecture reported here is scalable, and the results are promising for reducing the complexity of calibration and control of large-scale OPAs for their use at multiple wavelengths, for example, for spectral imaging or 2D beam steering through dispersive gratings. [ABSTRACT FROM AUTHOR]

Optical cryptosystems mostly use spatial distributions of amplitude, phase, and polarization of light to encrypt two-dimensional data/image. In this letter, we demonstrate the use of light carrying an array of optical vortices for image encryption. Spatially concatenated orthogonal states of optical vortices allow high-dimensional encoding and minimize the quality degradation during practical implementation. These features offer an efficient way to design an optical cryptosystem. [ABSTRACT FROM AUTHOR]

Abstract An all‐optical half adder based on two‐dimensional photonic crystals is proposed. The proposed structure is composed of a triangular array of dielectric rods made of non‐linear optical material in air. The structure consists of four waveguides and one ring resonator which are formed by removing a number of dielectric rods. The structure has been simulated and analysed by the plane wave expansion method and the finite‐difference time‐domain method. The size of the proposed structure is small with dimensions of 17 μm × 14.8 μm, and the material of the rods and lattice constant are uniform across the structure. The proposed half adder has a minimum contrast ratio of 13.51 dB in the steady state, with a maximum time delay of 2 ps.

For photonic-based continuous THz-wave generation for a wireless communication, a fiber-based configuration has been used. Without the fiber-optics, THz-wave generation system could be minimized by monolithic integration. Thus, based on the monolithic integration, a THz-wave generator consisting of arrayed light sources and arrayed photomixers was proposed. Arrayed light sources that can be operated at 600 GHz were designed and fabricated. Experimental results showed that the light sources have a practically uniform optical output. And then, 600-GHz power combining and directional gain were obtained in combination with arrayed photomixers. [ABSTRACT FROM AUTHOR]

An opto-electronic readout of the memory state in spin transfer torque random access memory (STT-RAM) cells is proposed. A single optical beam illuminating an array of STT-RAM cells creates electrical potential along each STT-RAM cell due to optical rectification that can be further enhanced through plasmon drag effect (PLDE). Then, the photo-induced voltage is assumed to be measured by conventional electronics. Here, a theoretical modeling is performed, where the results provide an estimate of the photo-induced voltage in each memory cell and its variation with respect to the changes in state of the memory cell (parallel vs anti-parallel). Our study shows that the plasmonic enhancement facilitates ${\sim }$ 20 times enhancement in the voltage change due to state change of the each memory cell, compared to the case of out-of-resonance excitation. This enhancement potentially improves the memory readout rate if a proper supporting electronic circuit is available. [ABSTRACT FROM AUTHOR]

Objective: With the growth of interest in different medical study on biological function, non-invasive photoacoustic imaging of biological tissue attracts the interests for researchers. To eliminate the limited angle effect of photoacoustic imaging based on ultrasound linear array, spatially distributed ultrasound sensor array is applied. The accurate sensor array position determines the quality of the imaging results. In this study, we proposed three methods based on photoacoustic and ultrasound signals to enhance the imaging quality using a 256-element full-ring array. Methods: Groups of photoacoustic and ultrasound signals are used to regress the position of each element sensor. Result: In phantom study and mouse brain study, photoacoustic imaging results can both yield details clearly with average error rate of less than 1% (50 $\mu \text{m}$). Conclusion: The performance of our three methods have proved that they can be potentially applied to other ultrasound-based medical imaging studies with unknown distributed positions of sensor array to enhance the imaging quality. Significance: The proposed methods can contribute to precise biomedical imaging with unknown distributed positions of sensor array in different application scenarios. [ABSTRACT FROM AUTHOR]

This work develops a new optical photodiode array sensor for flow pattern identification of gas-liquid two-phase flow in minichannel. The array sensor is developed by the following steps to acquire comprehensive information of the flow and maintain a simple structure: 1) optical signals of the flow are acquired by a matrix array sensor with 60 sensing elements; 2) the signals are preprocessed and divided into 5 clusters by hierarchical clustering; 3) one typical sensing element from each cluster is selected; 4) the selected elements of four typical flow patterns are combined and the final sensor structure with 7 elements is determined. Experiments of flow pattern identification based on support vector machine (SVM) is carried out to verify the feasibility of the developed sensor in a 4.04 mm diameter channel. In addition, three types of feature vectors are built, including mean value, standard deviation and frequency, and their performance on the identification is investigated. The flowrate of liquid and gas phase range from 55~332 mm/s and 8~41468 mm/s, respectively. The investigated flow patterns include bubble flow, slug flow, stratified flow and annular flow. Results verifies the feasibility of the optical sensor. Among the three types of feature vectors, the standard deviation has the best performance, while the frequency has the worst. Meanwhile, the results also demonstrate that the combination of some specific feature vectors is an effective way to improve the identification performance. [ABSTRACT FROM AUTHOR]

We present a tightly coupled array antenna excited by high-power photodiodes for millimeter wave transmit operation. The design includes thinned photodiode substrates for improved bandwidth performance at high frequency combined with the inherently lightweight, low-loss, and direct feeding architecture afforded by the photonic approach. Circuit and full wave simulations are conducted for array design and compared against the traditional electronic arrays in the literature. A prototype 1 × 3 photonic array is developed and characterized to validate the design which achieves a 3 dB (VSWR < 1.4) radiated power bandwidth of 4.6:1 across 13–60 GHz and maintains a 3 dB bandwidth near 4:1 across scan angles up to 30°. The fabricated array exhibits a 3 dB radiated power bandwidth of 1.8:1 across 30–55 GHz and a maximum measured effective isotropic radiated power of 19.4 dBm at 40 GHz. [ABSTRACT FROM AUTHOR]

The feasibility of using InGaN/GaN multiple-quantum-well light-emitting diode arrays (LED arrays) as photodiodes (PDs) is investigated experimentally in addition to their light emitting function. Two discrete LED arrays are produced from one 4 × 4 LED array with a parallel-connected pixel configuration. Such compact designs are useful for light emission or detection at the transmitting/receiving terminals of optical wireless communication systems. Despite 4 × 2 LED arrays achieving a light output power of 67.4 mW at 250 mA, they exhibit an optical responsivity (detectivity) of 0.183 A/W (1.61 × 1012 cm Hz1/2W−1) under ultraviolet light illumination (λ = 380 nm) at zero bias. For 4 × 2 LED arrays, the presence of an appreciable ultraviolet light response, together with a high 3-dB bandwidth (∼8 MHz) for modulated light detection, allowed us to build a 15 Mbit/s directed optical link with these LEDs functioning as both the optical transmitter and the receiver. Finally, the unitary LED array-based optical link is capable of real-time transmission of digital audio signals (data rate = 6 Mbit/s) at a propagation distance of 100 cm in free space even though some of the constituent pixels are inactive for light detection. [ABSTRACT FROM AUTHOR]

In this article, we propose a novel type of a wideband 2-D array of cold-electron bolometers (CEBs) sensitive to both polarizations of the incoming optical signal. This array was developed for osservatorio per il lontano infrarosso e le microonde su pallone orientabile (OLIMPO) balloon telescope with a requirement on bandwidth more than 10%. Sensitivity to both polarization components was achieved by a special meander-type arrangement of orthogonal L/2 dipoles. We present theoretical estimations for the optimal arrangement of 2-D arrays of CEBs, which allows achieving maximum efficiency in a wide band with the lowest noise equivalent power (NEP). A pixel layout with an optimal density of CEBs, sensitive to dual polarizations, and having more than 10% FWHM bandwidth at around 350 GHz was proposed and numerically analyzed. The layout consists of a periodic sparse array of orthogonal dipoles sensitive to both polarization components of the incoming signal. The numerical analysis confirmed that the sparse array is the most promising for a combination of high absorbing efficiency and low noise of the system and satisfying the 10% bandwidth requirements for the OLIMPO instrument. Different combinations of series and parallel connections of bolometers were considered for better noise properties to achieve the photon noise-limited level. [ABSTRACT FROM AUTHOR]

This article proposed a novel design for the monolithic micro-LED array, directly integrated with a sapphire microreflector. Its resolution was 300 dpi. Theoretically, each micro-LED pixel owns an individual sapphire microreflector which can directly concentrate rays from an emitting source. Therefore, this study proposed that the optical crosstalk between neighboring micro-LED pixels could be suppressed and the contrast of the micro-LED array improved; as this would be especially beneficial for display. The simulation results showed that the increased thickness of the sapphire microreflector could further improve the optical performance of the micro-LED array. For the fabrication process, the key technology was an integrated process involving the inductively coupled plasma (ICP) etching technology for sapphire and micro-LED fabrication, which was used to fulfill the proposed and reference micro-LED arrays. The measurement results showed that the sapphire microreflector could effectively concentrate the emitting rays and increase the contrast of the micro-LED array. In addition, it also indicated that the inclination angle of the microreflector could further improve optical performance. Therefore, this approach was verified to be capable of improving the performance of the micro-LED display. [ABSTRACT FROM AUTHOR]

In this article, we investigate the performance of the newly designed 4 × 4 optical wireless multiple-input-multiple-output (MIMO-OWC) system based on a linearly-shaped arrangement of transmitters and receivers, to achieve long-distance and high data rate transmission. To highlight the importance of selecting an appropriate arrangement for the optical elements, we carried on a comparative study, considering both the conventional square and the proposed horizontal linear constellation of optical modems. The performance of the bit error rate (BER) is experimentally evaluated at distances up to 65 m, using two important metrics inherent to the MIMO transmission channel matrix, i.e., the Frobenius norm and the condition number. The results show that the channel matrix shape characterized by the condition number dominates the BER if the Frobenius norm is smaller than 1. Furthermore, the proposed MIMO-OWC system employing a linearly-shaped arrangement of transmitters and receivers, shows to be more immune to the calibration error rather than the conventional square constellation optical modems. Moreover, the transmission of 100 Mbps data-rate and a BER lower than $10^{-4}$ could be successfully achieved at a 65 m communication range. [ABSTRACT FROM AUTHOR]

This article presents a digital ultraviolet (UV) beam lithography system for fabricating microstructures of arbitrary patterns on a roller mold. This roller mold can then be used in roller imprinting for fast and large-area replication of microstructures on substrates. This digital optomechanical system consists of a UV light source, a digital micromirror device (DMD) and its electronic controller, a high-precision image lens, a fiber array integrated with microlenses on both ends, and a two-axis (x–θ ) servo-controlled motion stage. It exposes a photoresist (PR) layer coated on the cylindrical surface of a roller with a linear array of 192 small UV spots focused by a microlens/fiber array. On the other end of the fibers, UV light is fed by DMD's micromirrors so that the UV light can be dynamically modulated. Finally, by synchronizing the electronics of DMD chip and the mechanical movement (rotation and translation) of the roller, one can achieve arbitrary UV patterning on the roller's PR layer in a digital and maskless manner. This system can successfully achieve UV patterning with a smallest linewidth of 8 μm, a pattern resolution of 2.5 μm, and a total patterning width of 192 mm on a roller with a diameter of 100 mm. [ABSTRACT FROM AUTHOR]

Light detection and ranging (LiDAR) scene generator is an important device in the LiDAR guidance hardware-in-the-loop (HWIL) simulation system. It generates simulated optical LiDAR scenes under laboratory conditions. A simulated LiDAR scene consists of an array of laser return signals with different intensities and time delays. The intensity of a return signal is determined by the target albedo and the target distance. The time delay of a return signal is determined by the target distance. A time delay array system is crucial for the LiDAR scene generation. In this paper, a programmable all-optical delay array system using an optical true-time-delay (OTTD) method is proposed. It can generate laser return signals with large-signal array size, long delay range, and high delay resolution. The signal array size of the generated LiDAR scene is 32 × 32. The depth of field (DOF) of the LiDAR scene is 19.2 m, which can be placed at different distances from 5.1 to 2481.6 m. The distance resolution is 0.3 m. The all-optical delay array system can also be extended to support tests of the LiDAR guidance systems with larger sensor arrays.

Nano-photonic antennas are one of the key components in integrated photonic transmitter and receiver systems. Conventionally, grating couplers, designed to couple into an optical fiber, suffering from limitations such as large footprint and small field-of-view (FOV) have been used as on-chip antennas. The challenge of the antenna design is more pronounced for the receiver systems, where both the collected power by the antenna and its FOV often need to be maximized. While some novel solutions have been demonstrated recently, identifying fundamental limits and trade-offs in nano-photonic antenna design is essential for devising compact antenna structures with improved performance. In this paper, the fundamental electromagnetic limits, as well as fabrication imposed constraints on improving antenna effective aperture and FOV are studied, and approximated performance upper limits are derived and quantified. By deviating from the conventional assumptions leading to these limits, high-performance multi-mode antenna structures with performance characteristics beyond the conventional perceived limits are demonstrated. Finally, the application of a pillar multi-mode antenna in a dense array is discussed, an antenna array with more than 95% collection efficiency and 170 $^\circ$ FOV is demonstrated, and a coherent receiving system utilizing such an aperture is presented. [ABSTRACT FROM AUTHOR]

Here, the authors propose a new approach for realising wideband and polarisation‐independent antireflection coating, based on a metamaterial composed of a subwavelength array of metallic pillars with a square cross‐section. The effective impedance of the array can be duly adjusted by the size and distance of the pillars. As such, the authors design the effective impedance of the antireflection coating to be the geometrical mean of the impedance of upper and lower media and choose its height to be quarter of operating wavelength. Doing so, the reflection vanishes at the desired frequency and fractional bandwidth of 56% is achieved with a criterion of 10% reflectance (the refractive index of the substrate is assumed to be 4). Importantly, the proposed structure is symmetric in both directions. Thus, in contrast to prior arts, it is not sensitive to the polarisation of the incident wave at normal incidence. In addition to that, it is designed based on a multilayer Chebyshev matching transformer of transmission line theory, which potentially increases the bandwidth of the antireflection up to 107%, albeit at the expense of pass‐band ripples. This structure can be used from very low frequencies up to the infrared regime by appropriate scaling. [ABSTRACT FROM AUTHOR]

Various methods have been developed and used for monitoring marine benthic habitats, such as coral reefs and seagrass meadows. However, the efficiency of general survey methods [e.g., line intercept transects and autonomous underwater vehicles (AUVs)] still is not high. In this article, we propose a practical coral-coverage estimation method combining an effective survey system [Speedy Sea Scanner (SSS)] and a deep-learning-based estimation method. The SSS is a towed-type system with six cameras arrayed on the platform. The depth rating of the system in our trial was 50 m. The length of the array baseline was 4.4 m, and six cameras were placed on the platform with equal spacing. The sea trial was conducted at Kujuku-Shima, Japan, on September 30, 2017. We successfully generated 3-D models and high-quality orthophotos of the seafloor with high resolution of about 1.5 mm/pixel. The survey efficiency of the SSS was about 7000 m2/h. In addition, the experimental results of coral-coverage estimation showed that the corals can be distinguished with accuracy of about 80% in places with relatively high transparency, and the error of coverage estimation was 10% or less. The proposed coral-coverage estimation method is more efficient than other survey techniques and costs less than AUV surveying; therefore, it is expected to become a promising tool for marine environmental surveying. [ABSTRACT FROM AUTHOR]

The chip-on-board light-emitting diodes (COB-LEDs) present low light efficiency due to the total internal reflection (TIR) at the flat encapsulant–air interface. In this study, a simple method based on complementary printing was proposed to realize the millilens array on the flat encapsulant layer to diminish the TIR effect, and thereby improve the light efficiency of the COB-LEDs. Experiments and optical simulation based on the Monte Carlo ray-tracing method were conducted to investigate the effect of the lens curvature θ, lens radius R, and lens spacing D on the light efficiency of the COB-LEDs. The results show that the light efficiency of the COB-LEDs increases with R and decreases with D, and COB-LEDs with hemispherical lens arrays (θ = 90°) have the highest light efficiency when R and D are fixed. Compared with the conventional COB-LEDs with a flat encapsulant, closely arranged hemispherical lens arrays with an R of 0.5, 1, and 1.5 mm enhance the light efficiency of the blue COB-LEDs by 87.56%, 90.62%, and 95.73% and enhance the light efficiency of ~6000-K white COB-LEDs by 17.24%, 18.86%, and 20.33%, respectively. [ABSTRACT FROM AUTHOR]

In this paper the photon counting characteristics, the information rate and the bit error performance of single-photon avalanche diode (SPAD) arrays are investigated. It is shown that for sufficiently large arrays, the photocount distribution is well approximated by a Gaussian distribution with dead-time-dependent mean and variance. Because of dead time, the SPAD array channel is subject to counting losses, part of which are due to inter-slot interference (ISI) distortions. Consequently, this channel has memory. The information rate of this channel is assessed. Two auxiliary discrete memoryless channels (DMCs) are proposed which provide upper and lower bounds on the SPAD array information rate. It is shown that in sufficiently large arrays, ISI is negligible and the bounds are tight. Under such conditions, the SPAD array channel is precisely modelled as a memoryless channel. A discrete-time Gaussian channel with input-dependent mean and variance is adopted and the properties of the capacity-achieving input distributions are studied. Using a numerical algorithm, the information rate and the capacity-achieving input distributions, subject to peak and average power constraints are obtained. Furthermore, the bit error performance of a SPAD-based system with on-off keying (OOK) is evaluated for various array sizes, dead times and background count levels. [ABSTRACT FROM AUTHOR]

Over the last 3 decades, a large portion of coral cover has been lost around the globe. This significant decline necessitates a rapid assessment of coral reef health to enable more effective management. In this paper, we propose an efficient method for coral cover estimation and demonstrate its viability. A large-scale 3-D structure model, with resolutions in the x, y and z planes of 0.01 m, was successfully generated by means of a towed optical camera array system (Speedy Sea Scanner). The survey efficiency attained was 12,146 m2/h. In addition, we propose a segmentation method utilizing U-Net architecture and estimate coral coverage using a large-scale 2-D image. The U-Net-based segmentation method has shown higher accuracy than pixelwise CNN modeling. Moreover, the computational cost of a U-Net-based method is much lower than that of a pixelwise CNN-based one. We believe that an array of these survey tools can contribute to the rapid assessment of coral reefs. [ABSTRACT FROM AUTHOR]

Electrically parallel and optically uncoupled triple and septuple oxide confined vertical-cavity surface-emitting laser (VCSEL) arrays emitting at about 980 nm where each VCSEL has an oxide aperture diameter (φ) of ∼7.5 μm transmit data at 40 Gbps at room temperature (RT) in a back-to-back test configuration using standard two-level non-return-to-zero pulse amplitude modulation at bias current densities (J) of 17.4 and 10.3 kA/cm2, respectively. Reference single VCSELs processed with the VCSEL arrays on the same wafer pieces with φ ∼7.5, 13.5, and 19.5 μm transmit data at up to 45, 40, and 35 Gbps at RT at J of 20.4, 13.3, and 10.7 kA/cm2, respectively, where the latter two single VCSELs have total emitting areas nearly equal to the total additive emitting areas of the triple and septuple VCSEL arrays, respectively. The RT optical output power at J ∼10 and 15 kA/cm2 is 11.4 and 17.2 mW for the triple arrays and 31.1 and 45.9 mW for the septuple arrays, respectively. By increasing the number of emitters in an array for a fixed φ per VCSEL from 3 to 7 we increase the total optical output power and simultaneously we decrease the J required for error free digital data transmission at 40 Gbps. [ABSTRACT FROM AUTHOR]

Signal buffering services such as contention resolution and congestion avoidance are essential in optical packet switching networks. In this paper, an optical memory scheme based on spectral amplitude coding (SAC) and complementary code keying (CCK) is proposed to increase the buffer capacity. CCK is applied to packet buffering by selecting an available code set and encoding the payload bits with either an SAC signal or its complementarity. The capacity constraint is effectively released, as the usable codes for queuing packets are twice those for the conventional code-domain buffers. To minimize system costs by reducing the codec number, a shared structure based on an arrayed waveguide grating (AWG), which is capable of processing both the typical and complimentary coded signals simultaneously, is also investigated. [ABSTRACT FROM AUTHOR]

Photon counting detector arrays are commonly used for free-space optical communications in deep space. Such detector arrays—by virtue of their size—help in the collection of the optical signal even when there is some misalignment between the transmitter and receiver systems. In this paper, we argue that, for the common Gaussian beam profile, a detector array receiver is more useful for minimizing the probability of error than a single detector receiver of the same dimensions. Furthermore, the improvement in the error probability is more pronounced for low signal-to-noise ratio conditions, and the probability of error decreases monotonically as a function of the number of detectors in the array. However, communication with detector arrays results in a larger computational and hardware complexity at the receiver. [ABSTRACT FROM AUTHOR]

Short reach communication systems, such as datacenters and access networks, exhibit steep capacity growth and require opto-electronic technologies with small size, low complexity, and low power consumption. Here, we demonstrate large-scale arrays of reflective surface normal electroabsorption modulators (SNEAMs). With very small active volumes, SNEAMs enable ultra-wide electro-optic bandwidth (>>65 GHz). We show modulation at 25 Gbit/s with 1 Vpp drive voltage on packaged SNEAMs and ultra-high bit-rate modulation at 107 Gbit/s with bare chips. These modulators are polarization-independent and have very low total input/output coupling loss of 0.7 dB to single-mode-fibers. We package SNEAM arrays with arrayed waveguide gratings into wavelength division multiplexing transmitters. Due to their broad wavelength range of modulation, SNEAMs do not need power hungry wavelength tuning or locking systems. Future co-integration of SNEAM arrays with low-power electronic driver arrays will enable high-capacity, low-power electro-optic engines. [ABSTRACT FROM AUTHOR]

This paper showcases a novel composite diffractive element that can be finely tuned to generate a myriad of stunning beam patterns and structures. Specifically, we have redesigned the spiral zone plate by incorporating a complex sinusoidal grating into its structure, which has considerably expanded the range of effective parameters available to engineer various shapes and structures of light beams. Furthermore, this element functions as a multi-focusing component, enabling the creation of optical arrays of diverse forms, ranging from basic spots and grids to intricate and innovative beam shapes. Our research involves extensive mathematical analysis and associated simulations, as well as experimental validation of the mathematical findings. • We present a groundbreaking tunable complex composite diffractive element. • Our research involves extensive mathematical studies and related simulations. • The element can multi-focusing and produce any desired array of optical beams. • It produces an array of optical beams ranging from spot to innovative, shaped beams. • It creates novel optical lattices both in single and array form. [ABSTRACT FROM AUTHOR]

In this communication an efficient method of moments (MoM) code is used for the analysis of the extraordinary transmission (EOT) through a periodic array of rectangular slots in a conducting screen, in the case where the number of slots is finite in one direction and infinite in the orthogonal direction. The slots can be arbitrarily rotated within the periodic unit cell. Once the magnetic current density on the slots is obtained by means of MoM, both the transmission coefficient and the far-field radiated by the array of slots are computed. The onset of EOT turns out to be strongly dependent on the orientation of the slots with respect to the direction in which the array is infinite. If the slots are perpendicular to this direction, EOT appears for a single infinite chain of slots. However, tens of parallel chains of slots are required to reproduce the EOT response when the slots are aligned along the parallel chains direction. The obtained radiation patterns show the excitation of grating lobes as the number of slots grow in the direction where the arrays are finite. [ABSTRACT FROM AUTHOR]

Neuromorphic computing has received considerable attention as promising alternatives to classical von Neumann computing architectures. An attractive concept in this field is reservoir computing which is based on coupled non-linear elements to enable for instance ultra-fast pattern recognition. We focus on the development of microlasers in a dense regular array for the implementation of photonic reservoir computing based on the diffractive coupling. The coupling relies on injection locking of microlasers and sets stringent requirements on the spectral homogeneity of the array, which needs to be on the order of the achievable locking range. We realize GaAs/AlGaAs micropillar arrays with InGaAs quantum dots as active medium. To achieve the high spectral homogeneity on the order of 100 μeV, as determined by injection locking experiments, the emission energy of each individual micropillar is adjusted to compensate for local inhomogeneities of order ∼1.3 meV in the underlying microcavity structure. The realized micropillar arrays have a spectral inhomogeneity as low as 190 μeV for an 8 × 8 array and down to 118 μeV for a 5 × 5 sub-array. The arrays have high potential to enable the implementation of powerful photonic reservoir computing, which can be extended to a reservoir of hundreds of microlasers in the future. [ABSTRACT FROM AUTHOR]

Two‐dimensional (2D) metasurface integrated with strip waveguide in silicon‐on‐insulator (SOI) has been designed to achieve high coupling efficiency for 3.8 μm wavelength. The optimisation in period and radius has been achieved using 3D finite‐difference time‐domain (FDTD). The calculated coupling efficiency in the in‐plane waveguide for the out‐of‐plane surface illumination is over 90% with a bandwidth of 1 μm. The design is consistent with the available lithography using 400 nm thick SOI for mid‐IR applications. Finally, monolithic integration can be achieved using standard multi‐project wafer run. [ABSTRACT FROM AUTHOR]

Single-emitter vertical-cavity surface-emitting lasers (VCSELs) and multiple-emitter VCSEL arrays designed for emission at 980 nm, and with large oxide aperture diameters (φ) from ∼10.5 to 33.5 μm and with φ of ∼7.5 μm that are configured in three-emitter and seven-emitter electrically parallel triangular and hexagonal arrays, respectively, have record bandwidths and optical output powers for VCSELs with such large cumulative emitting areas. We demonstrate room temperature (RT) maximum small-signal modulation bandwidths (f3dBmax) of 26.6 to 18.6 GHz with corresponding continuous wave (CW) optical output powers (L) of 16.2 and 47 mW for VCSELs with φ ∼13.5 and 33.5 μm, respectively. For parallel 980 nm triple and septuple arrays with φ ∼7.5 μm for each VCSEL, we demonstrate RT f3dBmax of 25.5 and 24.8 GHz with corresponding CW L of 22.7 and 50.1 mW, respectively. We perform a comparative analysis of the RT results, which consist of standard static light output power–current–voltage (LIV) characteristics to determine the typical VCSEL figures-of-merit including wall plug efficiency (WPE), LI slope efficiency, spectral emission versus current (I), and small-signal frequency response curves. We examine the tradeoffs in optical output power, small-signal modulation bandwidth, and WPE for the various VCSEL designs, and find that while the combination of f3dBmax and L are record values for single VCSELs and VCSEL arrays, these parameters fall off as the cumulative VCSEL array area increases to emit higher overall optical power. [ABSTRACT FROM AUTHOR]

We present high-performance integrated optical phased arrays along with first-of-their-kind light detection and ranging (LiDAR) and free-space data communication demonstrators. First, record-performance optical phased array components are shown with low-power phase shifters and high-directionality waveguide grating antennas. Then, one-dimensional (1-D) 512-element optical phased arrays are demonstrated with record low-power operation ($< $ 1 mW total), large steering ranges, and high-speed two-dimensional (2-D) beam steering ($< $ 30 $\mu$ s phase shifter time constant). Next, by utilizing optical phased arrays, we show coherent 2-D solid-state LiDAR on diffusive targets with simultaneous velocity extraction at a range of nearly 200 m. In addition, the first demonstration of 3-D coherent LiDAR with optical phased arrays is presented with raster-scanning arrays. Finally, lens-free chip-to-chip free-space optical communication links up to 50 m are shown, including a demonstration of a steerable transmitter to multiple optical phased array receivers at a 1 Gb/s data rate. This paper shows the most advanced silicon photonics solid-state beam steering to date with relevant demonstrators in practical applications. [ABSTRACT FROM AUTHOR]

A general ${N}$ -by- ${N}$ coupling matrix that provides lossless uniform feedback to all laser array elements is demonstrated in the analysis of a passive coherent beam combining resonator. The resonator contains a spatial filter that sends rejected optical power from the combining optic back into the cavity. This recycling of otherwise unused power yields an increase in the average laser output power that scales with array size ${N}$ , even in the absence of passive phase effects that depend on the gain, intensity, and wavelength of the laser mode. To achieve this improvement, tailored path lengths and mirror reflectivities are required in the feedback arms, where the phase may be fixed, whereas in the gain arms, the path lengths vary randomly. [ABSTRACT FROM AUTHOR]

Silicon photonics has become a promising technology for fabrication of compact, highly integrated systems. When dealing with phase sensitive silicon photonic components, however, temperature control and in particular, reduction of temperature gradients across phase sensitive components becomes crucial. Solid-state optical beam steering using optical phased arrays (OPAs), is an exemplary system, which could be miniaturized by using silicon photonics and where temperature control is of utmost importance. In order to reduce the system cost and size as well as to increase the steering velocity, it is desired to replace mechanical beam steering systems by solid-state steering systems. Due to their compatibility with CMOS fabrication processes, silicon photonics based OPAs are promising candidates to become the next generation beam steering solution. However, due to the large thermo-optic coefficient of silicon, these phased arrays are extremely sensitive to temperature. Thermal management of silicon-photonic based OPAs requires not only heat dissipation of integrated active components, but also reduction of temperature gradients across the phased array. Here a novel concept for thermal management of silicon photonic OPAs is proposed and analyzed using finite-element simulations. The proposed concepts show a formidable efficiency in improving the heat dissipation as well as in reducing temperature gradients across the array. [ABSTRACT FROM AUTHOR]

In this letter, we demonstrate $1 \times 8$ linear metal–semiconductor–metal arrays of UV-C photodetectors based on optical-float-zone grown bulk (100)-oriented $\beta $ -Ga2O3. The as-grown polished bulk samples exhibited an RMS roughness of 1.4 nm and the full-width at half-maxima of 0.19°. The average peak responsivity (257 nm), dark current, photo-to-dark current ratio, and UV-to-visible rejection ratio of the devices in the array were measured to be 4 AW $^{-1}$ , 0.23 nA, $\sim 10^{2}$ , and $\sim 10^{3}$ , respectively, at a bias of 40 V. The uniformity as well as the variability of the detector parameters across the devices in the array was investigated before and after wire bonding. [ABSTRACT FROM AUTHOR]

Integrated optical phased arrays (OPAs) capable of adaptive beamforming and beam steering enable a wide range of applications. For many of these applications, a large scale 2-D OPA with full phase control for each radiating element is essential to achieve a functional low-cost solution. However, the scalability of such OPAs has been hampered by the optical feed distribution difficulties in a planar photonics process, as well as the high power consumption associated with having a large number of phase control units. In this paper, we present a two-chip solution low-power scalable OPA with a nonuniform sparse aperture, providing radiation pattern adjustment and feed distribution feasibility in a CMOS compatible silicon photonics process. The demonstrated OPA with a 128-element aperture achieves the highest reported grating-lobe-free field-of-view (FOV)-to-beamwidth ratio of 16°/0.8°, which is equivalent to a 484-element uniform array. This translates to at least 400 resolvable spots, 30 times more than the state-of-the-art 2-D OPAs. Moreover, by utilizing compact phase shifters in a row–column power delivery grid, we reduce the number of required drivers from 144 to 37. A high-swing pulsewidth modulation (PWM) driving circuit featuring breakdown voltage multipliers and soft turn-on activation significantly reduces the power consumption of the system. The electronic driver chip and the integrated photonic chip are fabricated on a 65-nm CMOS process and a thick silicon-on-insulator (SOI) silicon photonics process, occupying 1.7 mm2 and 2.08 mm2 of active area, respectively. [ABSTRACT FROM AUTHOR]

Remote detection by surface plasmon resonance (SPR) is demonstrated through microstructured optical arrays of conical nanotips or micropillars. Both geometries were fabricated by controlled wet chemical etching of bundles comprising several thousands of individual optical fibers. Their surface was coated by a thin gold layer in order to confer SPR properties. The sensitivity and resolution of both shapes were evaluated as a function of global optical index changes in remote detection mode performed by imaging through the etched optical fiber bundle itself. With optimized geometry of micropillar arrays, resolution was increased up to 10−4 refractive index units. The gold-coated micropillar arrays were functionalized with DNA and were able to monitor remotely the kinetics of DNA hybridization with complementary strands. We demonstrate for the first time highly parallel remote SPR detection of DNA via microstructured optical arrays. The obtained SPR sensitivity combined with the remote intrinsic properties of the optical fiber bundles should find promising applications in biosensing, remote SPR imaging, a lab-on-fiber platform dedicated to biomolecular analysis, and in vivo endoscopic diagnosis. Graphical abstract We present a single fabrication step to structure simultaneously all the individual cores of an optical fiber bundle composed of thousands of fibers. The resulting sensor is optimized for reflection mode (compatible with in vivo applications) and is used to perform for the first time highly parallel remote SPR detection of DNA via several thousands of individual optical fiber SPR sensors paving the way for multiplexed biological detection. [ABSTRACT FROM AUTHOR]

A new plasmonic transmitter solution offering 0.8 Tbit/s on an ultra-compact 90 µm × 5.5 µm footprint is introduced. It comprises a densely arranged four-channel plasmonic phase modulator array that directly interconnects an optical fiber array. Each plasmonic modulator features high-index grating couplers—for direct and efficient conversion from a fiber mode to a plasmonic slot mode and vice versa—and a plasmonic waveguide—for efficient high-speed modulation. The individual devices achieve data rates of 200 Gbit/s with a symbol rate of 100 GBd. Electrical and optical crosstalk between neighboring modulators were found to have no significant influence on the data modulation experiment. The modulator array has been tested in a 100 GBd experiment with signals at a single wavelength (mimicking a space division multiplexing scheme) and at different wavelengths (mimicking a wavelength division multiplexing experiment). [ABSTRACT FROM AUTHOR]

Visible light communication (VLC) using III-nitride light-emitting diodes (LEDs) offers many advantages such as license-free operation, high spatial diversity and innate security. In particular, micro-LEDs ($\mu$ LEDs) are strong candidates for VLC due to their high modulation bandwidths. However, the low optical power of a single $\mu$ LED is a key factor limiting VLC performance. In this paper, we report an optimized series-biased $\mu$ LED array to achieve higher optical power while retaining high modulation bandwidth for high-speed VLC. An example array consisting of 3 × 3 40  $\mu$ m-in-diameter $\mu$ LED elements is presented here. At a current density of 3200 A/cm $^2$ in direct-current operation, the optical power and small signal 6-dB electrical modulation bandwidth of a blue-emitting series-biased $\mu$ LED array are over 18.0 mW and 285 MHz, respectively. The data transmission capabilities of this $\mu$ LED array are demonstrated by using on–off keying, pulse-amplitude modulation, and orthogonal frequency division multiplexing modulation formats over free space with the error-free data transmission rates of 1.95, 2.37, and 4.81 Gb/s, respectively. [ABSTRACT FROM AUTHOR]