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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]

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]

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]

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.

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]

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]

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]

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.

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]

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]

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]

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]

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]

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]

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]

In this Letter, high-uniformity 1 × 64 linear arrays of 4H-SiC avalanche photodiode (APD) are reported for ultraviolet detection. Multi-cycle inductively coupled plasma dry etching was adopted for the bevelled mesa formation, during which the wafers were rotated with a small angle for each cycle to suppress the process variation. As a result, a high pixel yield of 100% and a high-uniformity breakdown voltage with a fluctuation of smaller than 0.5 V are achieved for the fabricated 1 × 64 4H-SiC APD linear arrays, which is a great improvement for 4H-SiC APD arrays. Moreover, the dark currents at 95% of breakdown voltage are below 1 nA for all the 64 pixels. Besides, the pixels in the array show a multiplication gain of larger than 106 and a peak responsivity of 0.12 A/W at 285 nm (corresponding to a maximum quantum efficiency of 52%) at room temperature. [ABSTRACT FROM AUTHOR]

The authors demonstrate integrated 1D optical phased arrays (OPAs) for wide‐angle 2D beam‐steering. The 2D OPA consists of 16 1D transversal steering OPAs whose radiators have different grating periods, to assign different longitudinal angles. The transversal steering of each OPA is performed by the phase control of the p‐i‐n electro‐optic phase shifter array. The 1D transversal steering OPAs operate serially, changing the longitudinal radiation angle. The grating radiators were designed with an array pitch of 2 μm, and a varying period in the range of 610–710 nm. The entire 16 × (1 × 16) OPAs were integrated into a small area of 26.5 mm2. The obtained transversal/longitudinal beam‐steering range was 46°/44°, respectively, with a wavelength of 1560 nm, which enables wide 2D beam‐steering. [ABSTRACT FROM AUTHOR]

In-situ observations from research aircraft and instrumented ground sites are important contributions to developing our collective understanding of clouds, and are used to inform and validate numerical weather and climate models. Unfortunately, biases in these datasets may be present, which can limit their value. In this paper, we discuss artefacts which may bias data from a widely used family of instrumentation in the field of cloud physics, Optical Array Probes (OAPs). Using laboratory and synthetic datasets, we demonstrate how greyscale analysis can be used to filter data, constraining the sample volume of the OAP, and improving data quality particularly at small sizes where OAP data are considered unreliable. We apply the new methodology to ambient data from two contrasting case studies: one warm cloud and one cirrus cloud. In both cases the new methodology reduces the concentration of small particles (< 60 μm) by approximately an order of magnitude. This significantly improves agreement with a Mie scattering spectrometer for the liquid case and with a holographic imaging probe for the cirrus case. Based on these results, we make specific recommendations to instrument manufacturers, instrument operators, and data processors about the optimal use of greyscale OAP's. We also raise the issue of bias in OAP's which have no greyscale capability. [ABSTRACT FROM AUTHOR]

Optical array probes (OAPs) are classical instrumental means to derive shape, size, and number concentration of cloud and precipitation particles from 2D images. However, recorded 2D images are subject to distortion based on the diffraction of light when particles are imaged out of the object plane of the optical device. This phenomenon highly affects retrievals of microphysical properties of cloud particles. Previous studies of this effect mainly focused on spherical droplets. In this study we propose a theoretical method to compute diffraction pattern of all kind of cloud particle shapes in order to simulate the response recorded by an OAP. To check the validity of this method, a series of experimental measurements have been performed with a 2D-S probe mounted on a test bench. Measurements are performed using spinning glass discs with imprinted non-circular opaque particle shapes. [ABSTRACT FROM AUTHOR]

A color crosstalk model for an area image sensor with a color filter (CF) array is proposed, which quantifies the crosstalk in a physically intuitive manner by introducing “inter-CF optical crosstalk (inter-CF crosstalk).” The model separates the structural design originated crosstalk from the CF material itself, revealing the sole characteristics of microstructures on a photodiode. A constrained nonlinear estimation is used to solve the model equation of system matrices with an objective function focusing on matching between the modeled quantum efficiency spectra and measured ones at both the peak and crosstalk regions. The model is applied to 1.1- $\mu \text{m}$ backside-illuminated CMOS image sensors having four different kinds of optical structures on the photodiode of the same design, and successfully provides the ground of comparison with excellent matching between the models and the measurement results. [ABSTRACT FROM AUTHOR]

Dependence of beam quality on optical intensity asymmetry among elements in in-phase coherently coupled vertical cavity surface emitting lasers array is analyzed using the finite-difference time domain solutions software. The analysis results reveal that the coupling efficiency of in-phased array decreases and the divergence increases as the level of optical intensity asymmetry increases. Furthermore, an addressable separated-contact three-element triangular in-phased array is fabricated and measured to verify the analysis. The array exhibits a relatively high of coupling efficiency of 24% and a near-diffraction-limit divergence of 3.2° (1.12 times of the diffraction limit, D.L.) when the optical intensity of each element is adjusted to be uniform. By degrading the optical intensity symmetry, the coupling efficiency decreases to 17.07% and the divergence increases to 4.03° ( $1.37\times \text {D.L}$.). After that, a much larger $10\times 10$ array exhibiting in-phase characteristics is produced and its beam quality and optical uniformity are measured and discussed. Analysis and experiment results demonstrate that symmetric optical intensity among elements is essential for in-phased array to achieve high beam quality. Employing separate contacts in the array is proved an effective way to obtain uniform optical intensity and achieve high beam quality. [ABSTRACT FROM AUTHOR]

The focused transmit beam is a standard tool for clinical ultrasound scanning, concentrating energy from a number of array elements toward an imaging target. However, above and below the transmit focus, much of the energy in the beam is spread in a broadened main lobe and long off-axis tails that are ignored by conventional beamforming methods. This paper proposes a method to decompose a set of focused transmit beams into their constituent components—diverging waves from individual array elements. The recovery of this complete data set enables synthetic transmit focusing at all points in the field of view without beam shape or focal depth artifacts commonly associated with virtual source synthetic aperture beamforming. An efficient frequency-domain linear decoding implementation is introduced. The principles of the method are demonstrated both in transmit field simulations and experimental imaging. At depth, up to a 9.6-dB improvement in electronic signal-to-noise ratio and 8.9-dB improvement in contrast were observed in comparison with conventional dynamic receive beamforming. The proposed method is broadly applicable to existing scan sequences and requires only channel data for processing. [ABSTRACT FROM PUBLISHER]

We present a new geometry for on-chip optical circulators based on waveguide arrays. The optical array is engineered to mimic the Fock space representation of a noninteracting two-site Bose-Hubbard Hamiltonian. By introducing a carefully tailored magneto-optic nonreciprocity to these structures, the array operates in the perfect transfer and surface Bloch oscillation modes in the forward and backward propagation directions, respectively. We show that an array made of (2N + 1) waveguide channels can function as N 4-port optical circulators with very large isolation ratios and low forward losses. Numerical analysis using beam propagation method indicates a large bandwidth of operation.

An optimized double-reflector antenna concept for a wideband focal plane array (FPA) configuration is presented for Ka-band applications with a limited scan range, e.g., ground terminals for satellite communication. The proposed reflector configuration allows maximizing the number of active array elements and minimizing the actual array size during scanning. In addition, the FPA configuration has been optimized for wideband optical true-time-delay beamforming, resulting in wideband operation from 20 to 40 GHz. Based on a minimum required 80% aperture efficiency at 30 GHz, the double-reflector concept allows expanding the illuminated region of the array by a factor of 60 compared to traditional prime-focus configurations. The proposed configuration also decreases the magnification factor M by a factor of 2.5 compared to the double-parabolic configuration for a ±1.5° scan range. [ABSTRACT FROM PUBLISHER]

We have fiber-coupled an array of n-i-pn-i-p superlattice photomixers using a fiber array of same pitch of 145 \mu \textm . We experimentally investigate the effect of the finite size of the implemented silicon lens on the interference between the array elements in the far field. We compare the results from a geometry optimized for a collimated terahertz (THz) beam to theory and simulations. Further, beam steering is demonstrated by controlling the optical phase of the individual photomixers. Due to broadband antennas attached to each array element, the array is frequency tunable. It is exemplarily characterized at 165 and 310 GHz. Such arrays can overcome power limitations of individual photomixers. In contrast to bulky individually packaged free space solutions, this array can be packaged to a compact terahertz source, limited in size only by the size of the silicon lens. The investigated $2 \times 2$ array features a spot diameter (full-width at half-maximum) of 12.1 mm at a distance of 19 cm at 310 GHz with a silicon lens of only 20-mm diameter. [ABSTRACT FROM AUTHOR]

The "planispheric optic array" is a full-horizon Mercator projection of the optic array. Such pictures of the environment are coming in common use with the availability of cheap full-view cameras of reasonable quality. This introduces the question of whether the public will actually profit from such pictorial information in terms of an understanding of the spatial layout of the depicted scene. Test images include four persons located at the corners of a square centered at the camera. The persons point at each other in various combinations. Participants in the experiment judge who is pointing at whom in a number of such photographs. It is found that certain very systematic and huge errors are the rule, indicating that naïve viewers are quite unable to parse such planispheric representations. [ABSTRACT FROM AUTHOR]

The theory and method for motion-extended array synthesis (MXAS) are described by Kendra. The concept describes how MXAS, for a one- or two-dimensional synthetic array, is realized specifically without recourse to a reference waveform. The essential idea is that the relative motion between (a minimum of) two collection platforms with different velocity vectors can be exploited to create a virtual array, with the size of the virtual array being equivalent to the space swept out by the relative motion of the collectors. This paper describes a multistage experimental validation for MXAS, progressing from a “closed” (nonfree space) RF-domain test bed, to a highly controlled indoor free-space prototype system, and finally to an outdoor, vehicle-based prototype system. Key imaging principles validated include resolution performance relative to theoretical prediction; capability across a range of scenarios, including extreme near field, multipath, and ultralow power; retention of array degrees of freedom for steering nulls; and satisfaction of system requirements for synchronization and precision using consumer off-the-shelf components. [ABSTRACT FROM PUBLISHER]

Engine and air data probe manufacturers, as well as aviation agencies, are interested in better characterization of high ice water content (HIWC) areas close to thunderstorms, since HIWC conditions are suspected to cause in-service engine power loss and air data events on commercial aircraft. In this context, a collaborative field campaign has been conducted by high-altitude ice crystals (HAIC) and HIWC projects in order to provide ice water content and median mass diameter (MMD) of ice crystals in the HIWC environment. The computation of MMD from in situ measurements relies mainly on the definition of the crystal dimension D and on the relationship, which is used to convert number into mass distributions. The first part of this study shows that MMD can significantly deviate when using different mass-size relationships from the literature. Sensitivity tests demonstrate that MMD is significantly impacted by the choice of β. However, the larger contributor to MMD differences seems to be the choice of the size definition D itself. Since MMDs are quite sensitive to β, this study suggests a generic method for deducing β solely from optical array probes (OAPs) image data for various size definitions. The method is based on simulations of 3D crystal objects projected onto a 2D plane, thereby relating crystal mass to 2D area (projection) and perimeter. The MMD values calculated for different size definitions are quite similar, at least much closer than MMDs derived from different m( D) relationships in the literature. [ABSTRACT FROM AUTHOR]

Particle concentration measurements with underwing probes on aircraft are impacted by air compression upstream of the instrument body as a function of flight velocity. In particular, for fast-flying aircraft the necessity arises to account for compression of the air sample volume. Hence, a correction procedure is needed to invert measured particle number concentrations to ambient conditions that is commonly applicable to different instruments to gain comparable results. In the compression region where the detection of particles occurs (i.e. under factual measurement conditions), pressure and temperature of the air sample are increased compared to ambient (undisturbed) conditions in certain distance away from the aircraft. Conventional procedures for scaling the measured number densities to ambient conditions presume that the air volume probed per time interval is determined by the aircraft speed (true air speed, TAS). However, particle imaging instruments equipped with pitot tubes measuring the probe air speed (PAS) of each underwing probe reveal PAS values systematically below those of the TAS. We conclude that the deviation between PAS and TAS is mainly caused by the compression of the probed air sample. From measurements during two missions in 2014 with the German Gulfstream G-550 (HALO - High Altitude LOng range) research aircraft we develop a procedure to correct the measured particle concentration to ambient conditions using a thermodynamic approach. With the provided equation, the corresponding concentration correction factor ξ is applicable to the high-frequency measurements of the underwing probes, each of which is equipped with its own air speed sensor (e.g. a pitot tube). ξ values of 1 to 0.85 are calculated for air speeds (i.e. TAS) between 60 and 250 m s-1. For different instruments at individual wing position the calculated ξ values exhibit strong consistency, which allows for a parameterisation of ξ as a function of TAS for the current HALO underwing probe configuration. The ability of cloud particles to adopt changes of air speed between ambient and measurement conditions depends on the cloud particles' inertia as a function of particle size (diameter Dp). The suggested inertia correction factor μ (Dp) for liquid cloud drops ranges between 1 (for Dp < 70 µm) and 0.8 (for 100 µm < Dp < 225 µm) but it needs to be applied carefully with respect to the particles' phase and nature. The correction of measured concentration by both factors, ξ and μ (Dp), yields higher ambient particle concentration by about 10-25 % compared to conventional procedures - an improvement which can be considered as significant for many research applications. The calculated ξ values are specifically related to the considered HALO underwing probe arrangement and may differ for other aircraft. Moreover, suggested corrections may not cover all impacts originating from high flight velocities and from interferences between the instruments and e.g. the aircraft wings and/or fuselage. Consequently, it is important that PAS (as a function of TAS) is individually measured by each probe deployed underneath the wings of a fast-flying aircraft. [ABSTRACT FROM AUTHOR]

This paper proposes an optical beamforming network for a 2-D array antenna in a broad direction range with subarray antenna partitioning capability. With reasonable cost and volume, this optical true time delay beamformer offers multiple beams that are independently steered from each other, while radio-frequency (RF) broadband operation is guaranteed. Radiation patterns of an 8 $\times$8 array antenna are calculated and compared with those obtained from the experimental setup. The definition of different subarrays allows presentation of up to four spatially multiplexed beams orientated to different directions according to the concrete application. [ABSTRACT FROM PUBLISHER]

Electrostatically actuated microshutter arrays consisting of rotational microshutters (shutters that rotate about a torsion bar) were designed and fabricated through the use of models and experiments. Design iterations focused on minimizing the torsional stiffness of the microshutters while maintaining their structural integrity. Mechanical and electromechanical test systems were constructed to measure the static and dynamic behavior of the microshutters. The torsional stiffness was reduced by a factor of four over initial designs without sacrificing durability. The analysis of the resonant behavior of the microshutters demonstrates that the first resonant mode is a torsional mode occurring around 3000 Hz. At low vacuum pressures, this resonant mode can be used to significantly reduce the drive voltage necessary for actuation requiring as little as 25 V. The 2-D electrostatic latching and addressing was demonstrated using both a resonant and a pulsed addressing scheme. [2015–0172] [ABSTRACT FROM PUBLISHER]

The Elliott’s procedure for the design of planar waveguide arrays of longitudinal slots has been extended to the cylindrical conformal case. The presented procedure has been devised to deal with the most general case of a cylindrical conformal substrate integrated waveguide (SIW) longitudinal slot array with a dielectric cover. Both external and internal mutual coupling have been accurately and effectively taken into account. The results of the synthesis procedure have been validated using both Ansys HFSS simulations and experimental results, showing a good agreement with the design specifications. [ABSTRACT FROM AUTHOR]

Hexagonal nanoarrays of Au particles were deposited on nanoporous anodic alumina membrane (NAAM) utilizing r.f. magnetron sputtering. The thickness of the NAAMs is adjusted by changing the second anodization time from 5 min to 20 min. The surface morphology, composition, and optical properties are characterized by using SEM, EDX, and spectrophotometer, respectively. The effects of the NAAM thickness and state of polarization on the morphological changes and on the optical properties of the fabricated nanoarrays were addressed. According to the measured optical spectra, the rate of decrease of NAAMs refractive index was found to be 3.825 × 10−4 nm−1. Using the modified Kubelka-Munk radiative transfer model, the energy gap of NAAMs was calculated from diffused reflectance and was decreased from 1.682 to 1.376 as the anodization time increased from 5 to 20 min. Also, the saturation of interference fringes is substantially enhanced, and field enhancement can be achieved due to the excitation and constructive interference of surface plasmon waves by coating NAAMs with the hexagonal nanoarrays of Au. Based on the advantages of the fabrication approach and the enhanced and controlled properties, this new generation of samples can be used as promising building blocks for nanophotonic and nanoelectronics devices. [ABSTRACT FROM AUTHOR]

Vertical-cavity surface-emitting laser arrays can be designed to operate in a coherently coupled mode, however, high yield has been challenging in past efforts. We discuss microcavity laser arrays that are designed to be optically coupled but with independent bias current injection into each array element. We demonstrate that these arrays can be electronically tuned to coherently coupled operation and at bias conditions not previously realized. Control of injection bias conditions to individual array elements allows resonance tuning of each element with the result that the phase relation and coherence of the array can be engineered. This control enables increased output power in either in-phase or out-of-phase coherent operation from a single array, and ensures coherent operation from nearly all arrays. This ability to tune into coherence will enhance the performance of phased vertical cavity laser arrays as well as improve their fabrication yield. [ABSTRACT FROM PUBLISHER]