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A three-dimensional (3D) particle image velocimetry (PIV) system typically consists of multiple cameras. However, micro-PIV systems for measuring microscale velocity fields lack sufficient space to accommodate them. In this work we propose an alternative approach based on computational imaging, enabling monocular micro-PIV systems to perform 3D flow field measurements without additional hardware or complex structure. The microscopic objective is designed to satisfy the required parameters, and the point spread function (PSF) responses of the system to different depths of the object surface are obtained. Additionally, a particle dataset generation method based on the PSFs of the optical system is proposed, and a deep-learning network is constructed for training. To validate the feasibility, particle images are captured in experiments and inputted into the network to reconstruct depth images and build three-dimensional flow fields. Simulation and experimental results demonstrate that the measurement deviation is within 13.2%, indicating the practicality of the proposed model.

In this paper, a novel design of the illumination optical system for a laser target simulator is investigated to determine the optimal relationship between the uniformity of the illumination system and the energy utilization in a laser target simulator. First, the optimal size of the fly-eye lens unit is calculated from the parameters of the DMD to improve the energy utilization of the system; second, the optimal parameters of the TIR prism group are calculated based on the size of the illuminating beam and the optimal deflection angle of the TIR prism group is analyzed, which results in the compact overall structure of the system and improves the uniformity under the premise of ensuring that there is not much change in the energy utilization; and finally, the optimal design of the illumination optics system for laser target simulators is investigated based on the Finally, based on the Scheimpflug principle, the uniformity of the illumination system is further improved by solving the deformation of the image plane caused by the insertion of the TIR prism group. The results show that the simulation results of the system's uniformity reach 96.93%, the simulation results of the energy utilization are 60.05%, and the structure is compact, and the system designed by this method can provide a good design solution to obtain high energy utilization and uniformity.

Commissioned in 2017 by the Italian Space Agency (ASI), the Sardinia Deep Space Antenna (SDSA) is currently able to operate in the X-band, supporting deep space and near Earth telemetry missions and scientific experiments. While sharing its infrastructure with the Sardinia Radio Telescope (SRT), the SDSA boasts its own dedicated control center and specific equipment. This paper outlines a new optical design and the radio frequency upgrades to enhance the SDSA’s capabilities for current and future tracking of deep space and near Earth missions. The proposed design aims to establish the SDSA as a state-of-the-art antenna in the field of space activities by capitalizing on its exceptional versatility. This includes its ability to accommodate new equipment and leverage the inherent characteristics of the SRT antenna, such as its active surface and frequency agility. A collaborative effort with ESA has resulted in a newly designed optical configuration enabling reception and transmission in the X, K, and Ka frequency bands. Specifically, the X and K frequency bands are allocated to near Earth radio communication (within a 2 million kilometer range). Additionally, the X- and Ka- bands configurations are designed for deep space operations, including the well-known triple-link technique for radio science missions beyond 2 million kilometers. To characterize the performance of the upgraded antenna, we present the electromagnetic simulations of the new optical design. We analyze the antenna radiation pattern across various downlink and uplink frequency bands and evaluate key parameters like gain-to-noise system temperature ( $G/T_{sys}$ ) and effective isotropic radiated power (EIRP). The simulations were conducted using the dedicated commercial software GRASP and CHAMP 3D by TICRA. The results of this study provide valuable information on the capability of the upgraded SDSA to enable a wide range of space communication and space science applications, making the SRT in its SDSA configuration one of the most equipped and technologically advanced ground segment facility.

State-of-the-art optical see-through head-mounted displays (OST-HMD) for augmented reality applications lack the ability to correctly render light blocking behavior between digital and physical objects, known as mutual occlusion capability. In this article, we present a novel optical architecture for enabling a high performance, occlusion-capable optical see-through head-mounted display (OCOST-HMD). The design utilizes a single-layer, double-pass architecture, creating a compact OCOST-HMD that is capable of rendering per-pixel mutual occlusion, correctly pupil-matched viewing perspective between virtual and real scenes, and a wide see-through field of view (FOV). Based on this architecture, we present a design embodiment and a compact prototype implementation. The prototype demonstrates a virtual display with an FOV of 34° by 22°, an angular resolution of 1.06 arc minutes per pixel, and an average image contrast greater than 40 percent at the Nyquist frequency of 53 cycles/mm. Furthermore, the device achieves a see-through FOV of 90° by 50°, within which about 40° diagonally is occlusion-enabled, and has an angular resolution of 1.0 arc minutes (comparable to a 20/20 vision) and a dynamic range greater than 100:1. We conclude the paper with a quantitative comparison of the key optical performance such as modulation transfer function, image contrast, and color rendering accuracy of our OCOST-HMD system with and without occlusion enabled for various lighting environments. [ABSTRACT FROM AUTHOR]

This article develops a new sensor that can detect projectiles in all-weather with high sensitivity and a large field of view. Two high-power line lasers are used to design an active photoelectric detection sensor with a fan-shaped detection plane. The size of the designed fan-shaped photoelectric detection receiving plane is the same as the luminous fan-shaped plane light source to make the two fan-shaped planes coincide with each other, forming an active detection screen. Based on the principle of active photoelectric detection sensor, a linear array photoelectric detector is selected, in which multiple unit p-i-n detectors are spliced together, and an amplifier processing circuit with low noise and high sensitivity is designed. Combined with the geometric structural features of the active detection screen, the radiation characteristics calculation model of the projectile in a fan-shaped detection plane is developed using a five-parameters bidirectional reflectance distribution function (BRDF). Finally, the total radiation intensity calculation function of the projectile’s surface is derived considering the influence of environmental factors and the output signal and signal-to-noise ratio (SNR) model of the active photoelectric detection sensor is set up. Comparative experiments under different environmental illuminations verify that the detection ability has been significantly improved in active photoelectric detection sensors. [ABSTRACT FROM AUTHOR]

In this article, we show that desktop speakers' internal (electrical circuitry) and external (reflective diaphragm) design may expose users to confidential information leakage. We demonstrate that these flaws are present in billions of devices produced by global manufacturers and discuss countermeasures. [ABSTRACT FROM AUTHOR]

With the widespread deployment of data centers, Internet service providers are expecting more efficient design strategies to build long-haul data center interconnect (DCI) networks. In this paper, we propose a heuristic-based optimization framework to design these networks. Through this framework, network designers can obtain a site-type design scheme that arranges customized site types such as in-line amplifiers, dynamic gain equalizers, optical terminal multiplexers, and electrical regenerators, and three strategies are provided for reference. Taking the quality of transmission as the main metric, and the overall cost of the network as the ancillary measurement, we compare the schemes obtained by the proposed framework against the baseline scheme obtained by a traditional periodic design strategy. Simulations are conducted on a topology of the Tencent DCI network. Under the condition that all schemes ensure that the minimum general signal-to-noise ratio (GSNR) remains above the given GSNR threshold, the schemes designed by our framework can achieve overall cost savings up to 25.73%. [ABSTRACT FROM AUTHOR]

We propose an off-axis flight vision display system design with a free-form surface using machine learning to simulate the visual distance variation during take-off and landing training for pilots. This design is realized by ray tracing using ZEMAX software, where we build and optimize a series of initial systems that meet the corresponding optical specifications. A deep neural network is used to train the regression model, which is specifically designed to predict the fitted polynomial model for the free-form surface of the system. Our results demonstrate that the design of a flight visual display system can be transformed into a machine learning problem and further optimized by training and learning with abundant data, providing an avenue to design more powerful and complex imaging optical systems.

Near-eye display (NED) systems have various structures, including the freeform prism, off-axis synthesizer, and holographic optical waveguide structures. In this study, the three types of structures of NED systems were analyzed in terms of their advantages and disadvantages. Hence, an optical-digital integrated design method was proposed for the NED imaging system. In particular, a point spread function model with aberration information was developed based on the analysis of optical system aberration. Algorithm preprocessing was conducted on the image-end, and the processed image was transformed into a sharp image by the optical system and sent to the pupil. A NED optical system with a $45^{\circ } \times32$ ° field of view, 10-mm exit pupil diameter, and 30-mm exit pupil distance was developed using the proposed method. This system can meet the NED requirements using three aspherical reflectors instead of a free-form and lens-correction group.

The Y field of view of an off-axis optical system is generally less than 1°. Scholars usually use a freeform surface to achieve a rectangular field of view imaging. However, it adds to the difficulty of processing, testing, assembling, and adjusting, and at the same time has the drawbacks of high manufacturing costs and long processing cycles. In view of the above problems, this paper presents a computational imaging design method for expanding the Y field of view of an off-axis optical system. This method analyzes the aberration characteristics of the optical system, creates a point spread function model based on the wavefront aberration theory and Zernike polynomials, and processes images using a spatial variation deconvolution algorithm. In this paper, we used this method to simulate an off-axis three-mirror optical system with a focal length of 260 mm, the f-number of 2.5, and a field of view of 8° × 1° and compare the images before and after processing. The results show that the processed images have a clear outline, the overall image quality is improved, the field of view is improved to 8° × 6°, and the modulation transfer function of the entire field of view is above 0.4. The off-axis optical system rectangular field of view imaging is realized without using a freeform surface.

This work presents a stable and reliable turnkey continuous-wave laser system for a Yb/Ba multispecies trapped-ion quantum computer. The compact and rack-mountable optics system exhibits high robustness, operating over a year without realignment, regardless of temperature changes in the laboratory. The overall optical system is divided into a few isolated modules interconnected by optical fibers for easy maintenance. The light sources are frequency-stabilized by comparing their frequencies with two complementary references: 1) a commercial Fizeau wavelength meter and 2) a high-finesse optical cavity. This scheme enables automatic frequency stabilization for days with a sub-MHz precision.

Multiple-input-multiple-output (MIMO) optical wireless communication systems are potential candidates for high-speed data transmission in indoor environments. In this work, we present an experimental evaluation of two different MIMO systems, i.e., conventional-MIMO (c-MIMO) and imaging-MIMO (i-MIMO) in terms of design considerations. Both systems use the same transmitter configuration featuring a one-dimensional (light-emitting diode) LED transmitting array. On the receiver side, the c-MIMO system employs a similar one-dimensional receiving avalanche photodetector (APD)-based array, whereas the i-MIMO system uses a customized imaging camera-based receiver design. To assess the performance of the two systems, the channel matrix and the bit-error rate are calculated based on the experimental data. At distances shorter than 50 m, the proposed c-MIMO system demonstrates a good transmission performance, particularly when the maximum likelihood detection (MLD) technique is applied. Whereas, at long distances ranging from 40 m to 65 m, the proposed i-MIMO system can ensure an error-free transmission due to the efficient spatial separation between the emitted optical beams. Furthermore, the experimental results confirm that our systems have the potential for high data rates over longer distances in indoor environments. [ABSTRACT FROM AUTHOR]

Due to the all-weather and all-time imaging capability of synthetic aperture radar (SAR), SAR remote sensing analysis has attracted much attention recently. However, compared with the optical images, SAR images are more difficult to be interpreted. If an SAR image could be translated into its corresponding optical image, then the generated optical image would be helpful for assisting the interpretation. Addressing this issue, we investigate how to translate SAR images into optical ones in this work and propose a parallel generative adversarial model for SAR-to-optical image translation, called parallel generative adversarial network (Parallel-GAN), consisting of a backbone image translation subnetwork and an adjoint optical image reconstruction subnetwork. Under the proposed model, the backbone image translation subnetwork is designed to translate SAR images into optical ones, and simultaneously some of its intermediate layers are required to output similar latent features to those from the corresponding layers of the adjoint image reconstruction subnetwork. Thanks to the imposed hierarchical latent optical features, the proposed Parallel-GAN could achieve the SAR-to-optical image translation effectively. Extensive experimental results on three public datasets demonstrate that the proposed method outperforms ten state-of-the-art methods for SAR-to-optical image translation. [ABSTRACT FROM AUTHOR]

In this paper, vertical cavity surface emitting laser (VCSEL) array is used to establish gigabits/second (Gbps) optical uplink, device-to-device (D2D), and Internet-of-thing (IoT) links, as a supplementary for visible light communication (VLC) and ultra-low latency near-field communication in a typical indoor scenario. The mathematical model based on a modified Monte-Carlo ray-tracing (MMCR) algorithm for VCSEL-based optical wireless communication (OWC) is presented, which takes into account both accuracy and time complexity for the calculation of the channel characteristics including power distribution, impulse response, error analysis, and signal-to-noise ratio (SNR). Simulation firstly takes a global approach to the optical uplink lens design method, compared between Lambertian and Gaussian sources, and then extended six typical line-of-sight (LOS) or non-line-of-sight (NLOS) VCSEL-based OWC models. For demonstration, we adopted a 940-nm VCSEL array and 850-nm single-pixel VCSEL to establish LOS and NLOS systems after measuring the optics-electronics and bandwidth characteristics, respectively. Furthermore, multiple multi-carrier schemes are adopted to improve the OWC performance system based on a 940-nm VCSEL array including uniform-loading orthogonal frequency division multiplexing (OFDM), channel-coded OFDM, bit-loading/ power-allocation OFDM, and OFDM access (OFDMA). Results show that OFDM can effectively decrease the inter-symbol interference (ISI) of the indoor channel and increase the data rate, and the bit/ power-loading method achieves the highest 7.2 Gbps transmission with the bit error rate (BER) within the forward error correction (FEC). All the theoretical and experimental results, for the first time, provide a comprehensive design and optimizing process of VCSEL-based indoor high-capacity OWC systems for future optical uplink, D2D, and IoT applications. [ABSTRACT FROM AUTHOR]

The wavelength-routed optical network on chip (WRONoC) is a promising solution for signal transmission in modern System-on-Chip (SoC) designs. Previous works do not simultaneously handle all the following four main issues for WRONoCs: 1) correlations between the topological structure and physical layout; 2) tradeoffs between the maximum insertion loss and the number of wavelengths; 3) runtime scalability of wavelength assignment scheme; and 4) a fully automated flow to generate predictable designs. As a result, their insertion loss estimation is inaccurate, their wavelength assignment is inefficient, and thus, only suboptimal results are obtained. To remedy these disadvantages, we present a fully automated topological structure and a physical layout co-design flow with improved wavelength assignment schemes to minimize the maximum insertion loss and the laser power simultaneously with a significant speedup. The experimental results show that our co-design flow significantly outperforms state-of-the-art works in the maximum insertion loss, laser power, and runtimes. [ABSTRACT FROM AUTHOR]

Orbital angular momentum (OAM) multiplexing technology is expected as one of the prospective candidates for sustaining the further increment of data-transmission capacity in the optical communication systems. Advanced multiplexing technology of combining OAM-based mode division multiplexing (MDM) in the multicore fiber (MCF) with wavelength division multiplexing (WDM) can further improve the transmission rate and spectrum efficiency in the communication systems. In this paper, a multi-ring-air-core fiber (MRACF) supporting thousands of OAM modes is designed and analyzed. The tradeoffs between ring number/density and their corresponding system performance parameters in this fiber are systematically investigated. Based on the analytical results, MRACF with 37 rings can support a record high 4440 radially fundamental OAM modes at 1550 nm, featuring <−53 dB inter-ring crosstalk and >5.67 × 10−4 intra-ring modal effective refractive index difference. Furthermore, a record-high 4144 radially fundamental OAM modes with <−40 dB inter-ring crosstalk can be supported across C and L bands from 1530 nm to 1625 nm, which is one order of magnitude larger than the number of linearly polarized (LP) modes or supermodes ever reported within one single fiber. [ABSTRACT FROM AUTHOR]

Optical computation, especially the optical neural network, has gained great attention recently due to their high computation throughput and low energy consumption. The 2×2 optical processor, as a building block of high-order matrix multiplication circuit, can be an essential part for optical neural networks. For the first time, we demonstrate a compact and general optical processor on silicon-on-isolator platform with a footprint of 1.68×3.6 μm². The transfer matrix of an optical processor is determined by its nanostructured pattern, which has 2420 possible combinations. To accelerate the design process of arbitrary optical processors, a two-step trained tandem model consisting of a forward model and an inverse model based on deep convolutional neural networks is proposed. After training, the forward model is able to predict the transfer matrix for a given optical processor with prediction accuracy of 98.8%, while the calculation speed is more than one thousand times faster than the electromagnetic simulation. The inverse model can predict the geometry of an optical processor for a target transfer matrix with prediction accuracy of 96.5% and its prediction time is also within a second. This two-step trained tandem model paves a new way for optical processors design. [ABSTRACT FROM AUTHOR]

In order to expand the field of view and improve the resolution, a method of optical butting was proposed for two plane array sensors using beam splitter prism in this paper. The principle of optical butting, the optical design, calibration and focusing technology, and alignment method were presented and analyzed. In addition, the gray image stitch and point cloud data registration were also realized. To prove the concept of the optical butting method, we built a prototype system for experiment. The splicing of two $320\times240$ sensors of plane array laser imaging detection and ranging (PA-LiDAR) was implemented. After optical butting, the total effective pixel number was $320\times480$ , the total effective area was $6.4\times4.8$ mm, and the field of view was $22\,\,^{\circ }\times 15\,\,^{\circ }$ . Compared with the conventional laser radar system, the optical butting system can improve the field of view and resolution by a factor about $2\times 1$ . This method had the advantages of simple constitution, easy accomplishment, small space and high assembly precision which guaranteed the operating requirement of the PA-LIDAR sensor.

We demonstrate a novel tempo-spatial mixed-modulation Fourier-transform infrared imaging spectrometer. The static interference channel based on a stepped micro-mirror contributes a compact system with high stability. The instrument functions in two spectral bands ranging between 3.7– $4.8~\mu \text{m}$ and 7.7–9.3 $\mu \text{m}$ , and the spectral resolution of the dual-interference channels achieves 51.5 and 4.1 cm−1, respectively. The instantaneous field of view is 0.15 mrad, and the working F/1.93 enables high optical throughput. The optical design and tolerance are presented with experimental investigation results, showing attractive potential in remote sensing application.

In this study, a novel high-reliability liquid leakage sensor with a V-shaped defect coupling structure (VDCS) is proposed and experimentally demonstrated using polymer optical fibers (POFs) based on a light-emitting diode (LED) side-coupled light source. Liquid leakage detection is achieved with changes in the refractive index as the coupling medium transforms from air to liquid. The LED lamp both provides a light source and assists positioning. The coupling efficiency of the POF liquid leakage sensor varies with the depth and angle of the VDCS. Experimental results show that the coupling efficiency of the POF leakage sensor is high when the VDCS depth is 0.5 mm and the inclination angle is 60°. Compared to an existing leakage sensor with a hole-shape defect coupling structure (HDCS), the VDCS has a faster response time and higher reversibility. The average reliability of the liquid leakage sensor is increased to 5.92 μW/mL. This research provides a powerful structural reference for POF side-coupling leak measurement and can also be applied to the fields of gas and humidity sensing.

Optical access networks (OANs) with passive optical network technology have been globally deployed on a massive scale, serving as the fundamental information infrastructure of teleCommunication networks. Some telecom service providers are re-architecting their networks based on cloud central office with software-defined networking and network functions virtualization capabilities to provide service agility, intelligence, and scalability. In this article, we present a synthesized analysis of the inherent value and practical use cases of access network (AN) slicing in the context of software-defined OANs. A novel hierarchical abstraction model and a workflow of end-to-end network slicing are presented to illustrate the support of multi-service and multi-tenancy applications over a converged OAN platform by enabling automatic life cycle management of AN slicing. Two successful trials utilizing the model and the workflow are also demonstrated. [ABSTRACT FROM AUTHOR]

Wireless traffic will significantly increase in next-generation networks. Therefore, there is a need for novel optical network front-/mid-/backhaul (x-haul) architectures that can deliver ultra-high bandwidth and ultra-low-latency services to wireless and edge cloud systems, as well as support various cloud radio access network (C-RAN) architectures. Designing and evaluating such architectures requires large-scale experimental platforms. In this article, we present the design and implementation of a unique, remotely accessible, disaggregated, and programmable optical network as the key component of the city-scale PAWR COSMOS advanced wireless testbed. We discuss the design and implementation of a dedicated multi-functional Ryu software-defined networking (SDN) controller for the testbed's optical network wavelength channel assignment and topology reconfiguration. We present an example use of the SDN controller for monitoring and automated measurement of the wavelength-dependent amplifier gain in deployed reconfigurable optical add/drop mul-tiplexer (ROADM) units. We also demonstrate a pilot experiment focusing on a wireless handover scheme for C-RAN architectures in the COSMOS testbed, where high traffic volume can be supported by dynamic wavelength allocation via optical switching in the fronthaul. The field-deployed testbed and SDN controller can be used by the research community to push the envelope in the area of optical networks for beyond 5G and 6G. [ABSTRACT FROM AUTHOR]

The design of optical buffers for packet contention resolution has been recognized as a key issue in all-optical packet switching. One of the most general buffering schemes is priority queues, which includes first-in first-out (FIFO) queues and last-in first-out (LIFO) queues as special cases. In a priority queue, each packet is associated with a unique priority upon its arrival, the packet with the highest priority is sent out from the queue whenever there is a departure request and there are packets in the queue, and the packet with the lowest priority is dumped from the queue whenever there is a buffer overflow. In this paper, we consider the constructions of optical priority queues by using a feedback system consisting of an optical (bufferless) crossbar switch and multiple optical FIFO multiplexers with delay one (FM1’s) in the feedback path for buffering packets and feeding packets back to the switch. Such a feedback system is a generalization of that used in one of the authors’ earlier attempt for the constructions of optical priority queues in Tang et al. (2020). We fix the no-buffering problem in Tang et al. (2020) by using optical FM1’s to replace the optical FIFO multiplexers (FM’s) in Tang et al. (2020), which enables us to successfully achieve an exact emulation of a priority queue. We improve the utilization of buffering capacity over that in Tang et al. (2020) by routing packets to the optical FM1’s according to their buffering tags instead of their tags as used in Tang et al. (2020). We also extend and generalize the construction in Tang et al. (2020) and obtain a much larger class of constructions of optical priority queues. Our constructions are made possible by showing that the highest-priority (resp., lowest-priority) packet is always available at the input links of the switch whenever it needs to be routed to the departure (resp., loss) link, and by showing that there is no collision and there is no buffer overflow at any FM1 at any time so that there is no internal packet loss at any time. Our complexity analysis shows that by using a feedback system consisting of an optical $(M+2) \times (M+2)$ (bufferless) crossbar switch and $M$ fiber delay lines, we can achieve a buffer size of $2^{O(\sqrt {\alpha M})}$ , where $\alpha $ is a constant that depends on the parameters used in our constructions. Furthermore, we show that the best buffer size that we can achieve is $2^{O(\sqrt {4M/15})}$. Our result (exponential in $\sqrt {M}$) substantially improves on the best known result (polynomial in $M$) in the literature. Our numerical results show that the construction complexity of our constructions is lower than that of the construction in Tang et al. (2020), and the actual saving, in terms of the number of $2\times 2$ switches needed, by our constructions could be quite significant even in the tiny-buffer and small-buffer regimes. [ABSTRACT FROM AUTHOR]

This article presents an extra-large (25 × 50 mm2) flexible printed circuit board (FPCB) mirror to cover both the emitting and receiving lenses of a single-point LiDAR to form a biaxial scanning LiDAR with a compact structure and long measurement distance and low cost. The FPCB mirror is fabricated using the low cost and commercially available FPCB fabrication process. In addition, a widely available single–point LiDAR is used as the measurement unit. This article's novelty lies in the following two points: 1) integrating a large aperture scanning mirror and a single-point LiDAR (low cost and widely available) to construct a biaxial scanning LiDAR; 2) proposed a large aperture FPCB mirror using long existing FPCB process such as to achieve low cost. The scanning LiDAR is designed for applications in factory for robots and automated guided vehicles; navigation. The FPCB mirror consists of a mirror plate, two permanent magnets, and a FPCB structure, which includes two torsion beams, a middle seat, and a Flame retardant 4 (FR4) stiffener frame. Four-layer copper coils are embedded in the FPCB structure, which is fabricated using the low cost commercially available FPCB fabrication process. The mirror plate is diced from a thin silicon mirror plate with gold coating and then attached on top of the middle seat of the FPCB structure. With such large aperture FPCB scanning mirror, and a long measurement distance single-point LiDAR, a compact biaxial scanning LiDAR is constructed. The scanning LiDAR based on the FPCB mirror is constructed and tested. Achieved performances are: the field of view of 60°, measurement distance of 50 m, refresh rate of 20 Hz, 500 points for each scanning frame. [ABSTRACT FROM AUTHOR]

As implantable optical systems recently enabled new approaches to study the brain with optical radiations, tapered optical fibers emerged as promising implantable waveguides to deliver and collect light from sub-cortical structures of the mouse brain.They rely on a specific feature of multimodal fiber optics: as the waveguide narrows, the number of guided modes decreases and the radiation can gradually couple with the environment. This happens along a taper segment whose length can be tailored to match with the depth of functional structures of the mouse brain, and can extend for a few millimeters. This anatomical requirement results in optical systems which have an active area that is very long compared to the wavelength of the light they guide and their behavior is typically estimated by ray tracing simulations, because finite element methods are too computationally demanding. Here we present a computational technique that exploits the beam-envelope method and the cylindrical symmetry of the fibers to provide an efficient and exact calculation of the electric field along the fibers, which may enable the design of neural interfaces optimized to meet different goals. [ABSTRACT FROM AUTHOR]

Deep reinforcement learning (DRL) enables autonomic optical networking by allowing the network control and management systems to self-learn successful networking policies from operational experiences. This paper proposes a transfer learning approach for effective and scalable DRL in optical networks. We first present a modular DRL agent design to facilitate retrieving and transferring relevant knowledge between tasks requiring different dimensions of network state data. In particular, we partition network state data into common states, which contain generic information critical to multiple tasks (e.g., the spectrum utilization on fiber links), and task-specific states that are only used by a specific task (e.g., the utilization of virtual network functions). Separate neural network blocks are employed to process different state data. Based on the modular agent design, a multi-task learning (MTL) aided knowledge transferring scheme is proposed. The proposed scheme trains an MTL agent that can master multiple tasks simultaneously and thus enables to learn and transfer better-generalized knowledge across tasks. We perform case studies on the proposed transfer DRL approach considering two scenarios, namely, knowledge transferring between routing, modulation and spectrum assignment (RMSA) tasks for different networks and knowledge transferring from RMSA tasks to anycast service provisioning tasks. The DRL designs for RMSA and anycast service provisioning, including the state, action, and reward formulations and the training mechanisms, are also elaborated. Performance evaluations under both scenarios show that the proposed approach can effectively expedite the training processes of the target tasks and improve the ultimate service throughput. [ABSTRACT FROM AUTHOR]

Planar optical device with continuous phase shifting (CPS) has raised widespread interest recently. Formed by subwavelength micro/nano structures, planar optics are able to control wavefront in multi aspects including phase and polarization. Most phase shifters for CPS devices are individual structures such as cylinders or cuboids. In this study, we specifically discuss grating based continuous phase shifting lenses comparing with aforementioned counterparts, in terms of differences of design mechanism and polarization responses. In addition we found that grating based metalens has outstanding potential in generating emerging artificial focus pattern. A grating based CPS lens with ‘U’ shaped focus was fabricated and characterized for prove of concept. Planar optics with artificial focus pattern has great potential for future applications including micro beam shaping and maskless nano lithography. [ABSTRACT FROM AUTHOR]

Small form-factor sensors are widely used in minimally invasive intravascular diagnostic procedures. Manufacturing complexities associated with miniaturizing current fiber-optic probes, particularly for multi-parameter sensing, severely constrain their adoption outside of niche fields. It is especially challenging to rapidly prototype and iterate upon sensor designs to optimize performance for medical devices. In this work, a novel technique to construct a microscale extrinsic fiber-optic sensor with a confined air cavity and sub-micron geometric resolution is presented. The confined air cavity is enclosed between a 3 μm thick pressure-sensitive distal diaphragm and a proximal temperature-sensitive plano-convex microlens segment unresponsive to changes in external pressure. Simultaneous pressure and temperature measurements are possible through optical interrogation via phase-resolved low-coherence interferometry (LCI). Upon characterization in a simulated intravascular environment, we find these sensors capable of detecting pressure changes down to 0.11 mmHg (in the range of 760 to 1060 mmHg) and temperature changes of 0.036 °C (in the range 34 to 50 °C). By virtue of these sensitivity values suited to intravascular physiological monitoring, and the scope of design flexibility enabled by the precision-fabricated photoresist microstructure, it is envisaged that this technique will enable construction of a wide range of fiber-optic sensors for guiding minimally invasive medical procedures. [ABSTRACT FROM AUTHOR]

A single mode condition (SMC) for silica-titania rib waveguides on glass is the subject of this work. There are two mechanisms leading to the single mode propagation of a lightwave in rib waveguides. Considering waveguides whose rib width is greater than a thickness of a parent-slab waveguide, the one that would be created by extending the rib in the horizontal direction, the first mechanism is related to the leaking of HE01 and EH01 modes to slab waveguides on either side of the rib. The second mechanism is related to cut-off of those modes. Presented condition is expressed by two criterion functions. The first function, corresponding with the first mechanism, was introduced in our previous work describing the SMC for shallow rib waveguides. The second one, allowing to predict when the first order modes are cut-off is presented in this work. As a result, the complete SMC is formulated. It allows to predict a range of morphological parameters in which propagation is single mode, not only in shallow but also in deep rib waveguides. Moreover, considering the leaking of the HE01 mode, it is shown that the prediction is accurate by using coefficients of criterion functions obtained by the linear interpolation. [ABSTRACT FROM AUTHOR]

We develop a ‘perfect’ design for PAM4 Segmented Mach-Zehnder Modulators (SEMZM), featuring a fully linear (uniform) optical DAC (oDAC) staircase (i.e., having equi-spaced PAM4 levels) and no intrinsic modulation loss (the qualifier ‘perfect’ pertains to ideal conditions, barring optical excess losses and other impairments). This is achieved by leveraging our recently introduced maximin optimization strategy, enabling to locate the hitherto unknown optimal operating point in the serial oDAC parameters space, gaining ~7 dB relative to conventional PAM4 designs (typically based on a pair of segment electrodes in 2:1 lengths ratio and using 3 dB modulation backoff in order to compensate for degradation in oDAC linearity). The same photonic design may be reused to generate DAC-free coherent PAM4 (bipolar symmetric field-domain equi-spaced max-full-scale constellations), for efficient I/Q tributaries of 16QAM. [ABSTRACT FROM AUTHOR]

This letter reports proof-of-principle demonstration of 3-D printable, low-cost, and compact terahertz (THz) spectral splitters based on diffractive optical elements (DOEs) designed to disperse incident collimated broadband THz radiation (0.5–0.7 THz) at a prespecified distance. Via inverse design, we show that it is possible to design a diffractive optic that can split broadband incident spectrum in any desired fashion, as is evidenced from both finite-difference time domain (FDTD) simulations and measured intensity profiles using a 500–750-GHz vector network analyzer (VNA). Due to its straightforward as well as simple construction without the usage of movable parts, our approach, in principle, can have various applications such as in portable, low-cost spectroscopy as well as in wireless THz communication systems as a THz demultiplexer. [ABSTRACT FROM AUTHOR]

We propose a new thin and flat virtual reality (VR) display design using a Fresnel lenslet array, a Fresnel lens, and a polarization-based optical folding technique. The proposed optical system has a wide field of view (FOV) of 102°x102°, a wide eye-box of 8.8 mm, and an ergonomic eye-relief of 20 mm. Simultaneously, only 3.3 mm of physical distance is required between the display panel and the lens, so that the integrated VR display can have a compact form factor like sunglasses. Moreover, since all lenslet of the lenslet array is designed to operate under on-axis condition with low aberration, the discontinuous pupil swim distortion between the lenslets is hardly observed. In addition, all on-axis lenslets can be designed identically, reducing production cost, and even off-the-shelf Fresnel optics can be used. In this paper, we introduce how we design system parameters and analyze system performance. Finally, we demonstrate two prototypes and experimentally verify that the proposed VR display system has the expected performance while having a glasses-like form factor. [ABSTRACT FROM AUTHOR]

Network virtualization (NV) is considered to be a promising solution to address the ossification of the current Internet infrastructure. With the recent advancements in optical virtualization, network virtualization can be further extended to virtualization-enabled optical substrate networks that supply connectivity-as-a-service. This integration of NV and optical virtualization is referred to as optical-based network virtualization in this work, which warrants a future-proof Internet that is not only technology-friendly (i.e, due to the service and hardware decoupling in NV) but also bandwidth-abundant (i.e., with optical networking). In optical-based network virtualization, it remains to resolve the classic virtual network embedding (VNE) problem (i.e., a NP-Complete problem) with the extra dimension of complexity from physical characteristics of the specific type of optical network (e.g., WDM or SLICE). In this work, we study this variant of the VNE problem, namely Optical Virtual Network Embedding (OVNE), in SLICE-based network virtualization. We avoid addressing the OVNE problem with simple add-on constraints to VNE but address it with two strategies: first, exploring the OVNE problem structure at different granular of network elements (e.g., path-channel and channel graph) to mitigate the complexity; second, designing a path growing process that solves the OVNE model with substantially reduced variables. The proposed approach is evaluated and compared to other representative path-based schemes with demonstrated improvements. The proposed approach can also obtain near-optimal solution to the OVNE problem with guaranteed closeness to the optimal solution. [ABSTRACT FROM AUTHOR]

A kind of double-layer curved compound eye (DLCCE) inspired by natural compound eye was developed and fabricated in two-photon polymerization (TPP) technology to solve the existing problems, such as defocus at the edge, hard to miniaturize, assemble and detect. For each ommatidium, a corresponding modified microlens was designed to refract and focus the incident rays on the photoelectric detector. The diameter of the complete compound eye is 47.9 μm. It is integrated by 33 ommatidia with a diameter of 3.9 μm and possesses a theoretical FOV angle of 85°. What’s more, extra supports and through-holes were designed to promote to develop the unpolymerized photoresist within the fabricated structure. An imaging experiment was conducted to demonstrate the validity of developed compound eye comparing with the single-layer one. This work was expected to promote compound eyes to be applied in more imaging and sensing fields of microvision for their miniaturization, integration and optimization of optical system. [ABSTRACT FROM AUTHOR]

In this work we evaluated the imaging properties of the Diffractive Corneal Inlay (DCI), a novel type of corneal implant working by diffraction that we proposed for the treatment of presbyopia. ZEMAX OpticStudio software was employed for the numerical assessment, with simulations performed in a human-based eye model. In the ray tracing analysis, we used the Modulation Transfer Function (MTF), the Area under the MTF (AMTF), and the Point Spread Function (PSF). The theoretical performance of the DCI under different situations was evaluated in comparison with a commercially available pinhole based corneal inlay. Finally, real images were obtained experimentally in vitro in a model eye with inlays prototypes. The obtained results allow to state that the DCI exhibits a very high light throughput, improved imaging capabilities for far and near objects, and robustness against decentrations.

In this article, we have designed a surgical light lens especially for oral surgical illumination. It provides a uniform and wide field of view for illumination during oral surgery. The support system, a set of LEDs and a double free-form surface constituted the lighting system. The double free-form surface is composed of traditional free-form surface, designed total internal reflection lens and diffuse transmission plate, which improves the optical performance of the LED. When the light keeps dispersing the pupil constriction, it eventually causes our eyes to fatigue. The purpose of increasing diffuse transmission is to make the emitted light softer, thus making peoples' eyes feel more comfortable. Based on the problems mentioned above, a numerical method is proposed as the basis for designing the double free-form surface. First, establishing a mathematical model based on the characteristics of the transmissive surface and the property of the LED. Henceforth, the nonlinear equations for the illumination distribution of the outside surface can be deduced. By solving the equation, the contour of the free-form surface is obtained. Later, we imported the contour into the 3D modeling software Solidworks to rotate so as to get the corresponding model. Finally, the simulation results suggest that the optical uniformity of the double free-form surface is able to reach as much as 86.18%.

Electrically-pumped AlGaN-based edge-emitting laser diodes with a buried tunnel junction (TJ) for sub-300 nm emission are designed in this paper. Hole injection is one of the major concerns for the design of ultraviolet (UV) lasers based on this material system. The use of a low-resistive TJ as an intracavity contact within the devices will offer an opportunity to replace highly resistive p-type AlGaN-based cladding and contact layers by their n-doped counterparts. This advanced polarization-engineered interband TJs will lead to improved hole injection and a significantly reduced threshold voltage. The thermal properties of the tunnel-injected devices are thoroughly studied theoretically. For the demonstration of continuous-wave operating lasers, possible improvements in terms of better thermal management of the device are also discussed. Our improved design allows CW-operating AlGaN lasers with a threshold current density of <8 kA/cm2 and maximum optical output power of > 220 mW, yielding a wall-plug efficiency of > 2.8%. [ABSTRACT FROM AUTHOR]

Obtaining a high-precision 3-D burden surface (BS) shape of a blast furnace (BF) is of significance for improving energy efficiency in the ironmaking process, and for stabilizing the operation of the BF. However, existing methods used for detecting the BS cannot provide precise data to guide the burden distribution operation of the BF effectively, because they cannot overcome the harsh environment inside the BF. Therefore, to obtain a reliable BS shape under a high-temperature, high-pressure, high-dust, and low-light environment, a 3-D high-temperature industrial endoscope with a large depth of field and wide field of view is proposed in this article. First, image-forming optical system indices are obtained by analyzing the environmental factors and geometry of the BF. Based on these indices, an optical system with a large depth of field, wide field of view, and low-light imaging capacity is designed. Next, a 3-D depth calculation method based on a virtual and real twin binocular optical system is used to obtain 3-D depth of feature points on the burden distribution ring. Furthermore, a functional relationship model between the image defocusing degree and depth of the BS is established, based on the 3-D depth. Finally, a monocular vision 3-D reconstruction method based on the depth from defocus parameter is used to realize the 3-D reconstruction of the BS. Experimental industrial applications of the proposed device demonstrate that it can provide data support for the BF burden distribution operation and has a significant industrial application value. [ABSTRACT FROM AUTHOR]

Optical Network-on-Chip (ONoC) outperforms the traditional electrical NoC with higher bandwidth density, lower power consumption, and better scalability. It has emerged as a promising candidate for future on-chip interconnects. In this article, we propose a universal method for designing microring resonator (MR)-based non-blocking optical router, namely LACE, that can be easily integrated into the ONoC with different network requirements. By embracing the Wavelength Division Multiplexing (WDM) technique, LACE can implement non-blocking interconnection between different ports. The experimental results show that LACE has lower area cost and lower insertion loss compared with other alternatives. The four-port LACE composed of six MRs is also be demonstrated. [ABSTRACT FROM AUTHOR]

Most very-large-scale integration (VLSI) designs of the global optical flow method focus on reducing external memory accesses due to global and iterative processes for low-power operation in mobile systems. However, to achieve this goal, considerable amounts of resources are used and the throughput is decreased. To address these issues, we propose a multirow-based propagation approach and an efficient VLSI architecture. This approach divides an image into multiple small subimages. The flow of each subimage is then estimated sequentially using a small amount of internal memory without accessing any external memory. To avoid discontinuity artifacts stemming from the boundaries of the subimages, boundary conditions are imposed based on the smoothness of the optical flow. In addition, the main equations of the global optical flow method are simplified to boost the processing speed. The experimental results demonstrate that the external memory bandwidth is reduced by 96.7% with negligible accuracy degradation. Furthermore, the proposed design uses 63.4%–98% less internal memory and achieves $1.9\times $ – $18.8\times $ higher throughput-per-watt compared to state-of-the-art designs of the global optical flow method. [ABSTRACT FROM AUTHOR]

We report on the design, fabrication and characterization of a wafer level packaged, vacuum sealed, fully integrated and cell-phone compatible tunable micromachined Fabry-Pérot filter ($\mu $ FPF), operating within the visual and near-infrared (VIS-NIR) optical range. Implementation of a normally closed architecture combined with the electrostatic actuation enlarging, rather than closing, the optical cavity allows to achieve enhanced tunability of the optical gap. To evaluate the design and operational parameters, an electro-opto-mechanical model of the device was built and the resulting system of equations, coupling the structural, squeeze film, electrostatic and electric circuit domains, was solved numerically. The devices with an optical aperture of 1.85 mm and with robust elastic suspensions made of single crystal Si were fabricated and, consistently with the model prediction, the filter tunability within the range between 100 nm and 500 nm was demonstrated in the experiments. Vertically integrated design resulted in a small, 1 mm, thickness of a fully assembled device. Due to its compact size, manufacturability and short response time within the millisecond range, our tunable filter can be directly integrated into mobile phone camera modules, portable hyperspectral imagers, and remote sensors. [ABSTRACT FROM AUTHOR]

This paper presents a photointerrupter based force sensing mechanism to implement a low-cost, high accuracy, and reliable sensor with a miniaturized design. In previous literature, photointerrupter based force sensors have demonstrated a reasonable performance in a cost-effective manner, but have a narrow range of linear output and are significantly susceptible to external disturbances. This makes it difficult to use these sensors in precision force measurement and feedback control. In this work, we present a nonlinear optical model that utilizes a lambertian distribution for the photointerrupter, which is used for optimizing the design parameters of the sensor. The optimized geometry of the screen and a novel dual-screen arrangement are proposed to increase the linear range of the sensor output. A dual-photointerrupter signal acquisition is introduced to compensate the external disturbances and provides robust sensor output. A prototype of the sensor is fabricated in a miniaturized form factor with the ability to measure forces up to 21 N, having 1.08 % nonlinearity, 0.83% hysteresis, and 99.58 % accuracy. The proposed model and sensing mechanisms are experimentally validated. [ABSTRACT FROM AUTHOR]

The telescope design of a very high-resolution earth observation satellite is a challenging task, due to several constraints, including the size, mass, performance, tolerance, assembly, integrating, and environmental aspects. However, the demand for very high-resolution satellite imageries has increased day by day due to the numerous commercial and military applications. In this paper, two different optical configurations with ground sampling distance of 25 cm are investigated according to a definite mission statement. The first configuration represents an on-axis Korsch scheme, whereas the second design is based on the arrangement of the off-axis three-mirror anastigmatic configuration. Both designs have the advantage of small conic mirror constants without higher order parameters. Tolerance analysis of both designs utilizing a Monte Carlo algorithm is performed. The suggested baffling arrangements are simulated and tested according to a series of point sources with different off-axis angles. Finally, a comparison between the performance of the proposed designs and a recent study given by the French space agency is presented. The results show that the proposed designs can be implemented by the existing technologies and launched into space by the available launch vehicles. [ABSTRACT FROM AUTHOR]

We report on the development of a compact (volume ≈ 100 cm3), multimode diffraction-limited Raman spectrograph and probe designed to be compact as possible. The spectrograph uses ‘off the shelf’ optics, a custom 3D-printed two-part housing and harnesses a multi-core fibre (MCF) photonic lantern (multimode to few-mode converter), which slices a large 40 μm multimode input into a near-diffraction-limited 6 μm aperture. Our unique design utilises the hexagonal geometry of our MCF, permitting high multimode collection efficiency with near-diffraction-limited performance in a compact design. Our approach does not require a complex reformatter or mask and thus preserves spectral information and throughput when forming the entrance slit of the spectrograph. We demonstrate the technology over the interval 800 nm to 940 nm (200 cm−1 to 2000 cm−1) with a resolution of 0.3nm (4 cm−1), but other spectral regions and resolutions from the UV to the near infrared are also possible. We demonstrate the performance of our system by recording the Raman spectra of several compounds, including the pharmaceuticals paracetamol and ibuprofen. [ABSTRACT FROM AUTHOR]

Metalens as one of the most popular applications of emerging optical metasurfaces has raised widespread interest recently. With nano structures fully controlling phase, polarization and transmission, metalens has achieved comparable performance of commercial objective lenses. While recent studies seeking for the accomplishment of traditional focusing behaviors through metalens are successful, in this work, we have discovered that instead of focusing light to a point, metasurface further enables shaping the focus into flexibly designed patterns, with more promises and potentials. New mechanism and generalizations of conventional point-focused metalens guiding principles have been proposed with metalens concentrating light to artificial focus pattern. As proving examples, the metalens with ‘M’ shaped focus are fabricated and characterized. It is fabricated with a single layer of silicon-based material through CMOS compatible nano fabrication process. The mechanism to generate artificial focus pattern can be applied to a plethora of future on-chip optical devices with applications ranging from beam engineering to next generation nano lithography. [ABSTRACT FROM AUTHOR]

In this letter, we report a method of designing the optical sensor directivity without using an optical lens. The directivity is realized by attaching the designed through-hole array chip on an optical sensor surface. The through-hole array chip can be formed by a conventional semiconductor manufacturing technique. The directivity can be designed by adjusting the through-hole size and the chip thickness. Its performance is evaluated using the manufactured test chip. For visible light, when the through hole width is $25~\mu \text{m}$ and the partition wall thickness between them is $10~\mu \text{m}$ , the directivity is about 4 ° and the light transmittance is about 31%. Although directivity is slightly broad for near-infrared light, it can be designed utilizing the trade-off between directivity and transmittance. The proposed method enables us to reduce the sensor size to one-tenth or less of that using optical lenses. [ABSTRACT FROM AUTHOR]

The aerial camera lens largely determines the performance of the camera. It is necessary to further optimize the lens to satisfy the requirements of small-scale and lightweight aircraft camera systems. The optical system design is the primary prerequisite. Therefore, considering the image quality and working environment of the aerial camera, an aspherical aerial camera optical system is developed by studying the aerial camera optical system. The work presented in this paper decreases the overall weight of the aerial camera by using an aspherical lens instead of a spherical lens, which reduces the number of lenses and improves the image quality. The athermalization of the optical system ensures that the camera has good temperature adaptability in the temperature range of −60 °C∼60 °C. The definition of the aspherical surface shape is detected by a ZYGO digital interferometer. The root mean square (RMS) of the system is 0.0403λ(λ = 632 nm), and the peak value (PV) is 0.354λ, which ensures the image quality of the camera. The research results verify that the aspherical lens can be well applied to the camera optical system, improving the image quality of the system and reducing the weight of the camera. [ABSTRACT FROM AUTHOR]

Optical see-through augmented reality (AR) systems are a next-generation computing platform that offer unprecedented user experiences by seamlessly combining physical and digital content. Many of the traditional challenges of these displays have been significantly improved over the last few years, but AR experiences offered by today's systems are far from seamless and perceptually realistic. Mutually consistent occlusions between physical and digital objects are typically not supported. When mutual occlusion is supported, it is only supported for a fixed depth. We propose a new optical see-through AR display system that renders mutual occlusion in a depth-dependent, perceptually realistic manner. To this end, we introduce varifocal occlusion displays based on focus-tunable optics, which comprise a varifocal lens system and spatial light modulators that enable depth-corrected hard-edge occlusions for AR experiences. We derive formal optimization methods and closed-form solutions for driving this tunable lens system and demonstrate a monocular varifocal occlusion-capable optical see-through AR display capable of perceptually realistic occlusion across a large depth range. [ABSTRACT FROM AUTHOR]

Lithography simulation is one of the key steps in physical verification, enabled by the substantial optical and resist models. A resist model bridges the aerial image simulation to printed patterns. While the effectiveness of learning-based solutions for resist modeling has been demonstrated, they are considerably data-demanding. Meanwhile, a set of manufactured data for a specific lithography configuration is only valid for the training of one single model, indicating low data efficiency. Due to the complexity of the manufacturing process, obtaining enough data for acceptable accuracy becomes very expensive in terms of both time and cost, especially during the evolution of technology generations when the design space is intensively explored. In this paper, we propose a new resist modeling framework for contact layers, utilizing existing data from old technology nodes and active selection of data in a target technology node, to reduce the amount of data required from the target lithography configuration. Our framework based on transfer learning and active learning techniques is effective within a competitive range of accuracy, i.e., $3 \times -10 \times $ reduction on the amount of training data with comparable accuracy to the state-of-the-art learning approach. [ABSTRACT FROM AUTHOR]