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Fiber pump lasers are widely used in a variety of fields, such as optical fiber communication, national defense, and medical beauty due to their high beam quality and intense laser energy. However, the alignment errors of optical parameters can influence the beam quality in the packaging of the fiber pump lasers. It is necessary to analyze the reflector, focusing lens, fiber, and the laser diode on the coupling influence between for guiding the fiber pump laser packaging. Firstly, we establish the optical path between the laser diode, focusing lens and reflector based on the physical ray-tracing method. On the other hand, the high coupling efficiency of whole system is achieved by optimize the parameters of each optical element. The simulation result shows that the highest coupling efficiency is 98.6% based on optimizing the parameters of the optical path while the experimental result of coupling efficiency is 90.36%. Also, the effects of refractive index, wavelength and fiber diameter on coupling efficiency are further investigated. The experimental results show that the radial displacement has the greatest influence on the coupling efficiency. The simulation results show that increasing the fiber core diameter can effectively improve the coupling efficiency. The results of rigorous analysis will provide an effective reference for manufacturing compact, high coupling efficiency fiber pumped laser. [ABSTRACT FROM AUTHOR]

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Multi-core fibers (MCF) and multichannel optical waveguides have garnered significant attention as viable technologies for enhancing transmission capacity. However, the assembly of multichannel optical components encounters certain challenges, particularly in terms of alignment and takt time. To address these issues, this study proposed and demonstrated an optical coupling method using near-infrared (NIR) light-induced self-written (LISW) optical waveguide technology to simultaneously connect 4-core MCFs. All-solid LISW optical self-coupling between 4-core MCFs was achieved by employing an advanced selective polymerization process using light at 1310 nm wavelength. The resin used was characterized by the presence of an NIR dye in the monomer. The LISW optical waveguide core formation time was approximately 10 s, and the simultaneous 4-core formation was achieved within a short time. The average insertion loss (IL) of the all-solid LISW optical waveguide was 0.2 dB, and both the average IL of each channel and IL variation per channel were reduced compared with those of the butt joint. Thus, the LISW optical self-coupling compensated for the misalignment that occurred in the butt joint. Therefore, the LISW optical waveguide can also be used for the simultaneous optical self-coupling of multiple channels and is an effective method for reducing the fabrication time.

This article presents the optical analysis on how the light coupling performance between optical channel waveguides and gold periodic nanoarrays in the visible spectrum can be improved using an indium tin oxide (ITO) thin film as buffer layer. Coupling efficiency, out-of-plane scattering and far-field projected beam focus and diffraction angle are evaluated using Finite-Difference Time-Domain (FDTD) method and scattering theory for different nanogratings and nanocylinders array patterns. The implementation of ITO enables up to a 12 fold increase in coupling efficiency, a 6.4 fold enhancement of light scattered out of the array plane and consequent improvements in the diffracted beam radiation intensity peaks, without compromising the beam's focus or altering its deflection angle. This configuration provides a cheap and simple solution to increase the device performance without changing the array features, for integrated biosensing and scattering-related applications.

The optical output of a semiconductor laser can fluctuate chaotically by modulating its direct current in limited conditions of the modulated current signal parameters in terms of modulation frequency and modulation index. In this work, single, double, and chaotic pulses of an InGaAsP laser with direct current modulation, are numerically presented through a bifurcation diagram. Numerically, the unidirectional optical coupling system realizes chaotic synchronization between two identical InGaAsP lasers with direct current modulation, as the transmitter/receiver configuration. The transmission time for transmitting light from the transmitted laser to the received laser is essential for controlling the quality of chaos synchronization. The transmission time applies on the order of nanoseconds. Chaos synchronization quality is estimated by a correlation plot and calculated by the cross-correlation coefficient. This study observed the best synchronization quality (complete chaos synchronization) when the two lasers are identical. On the other hand, the chaotic synchronization between two non-identical InGaAsP lasers was investigated. In this case, complete chaos synchronization is not found, and the quality of chaotic synchronization was observed to decrease as the mismatch between the parameters of the two lasers increased.

Subwavelength nanostructures with tunable compositions and geometries show favorable optical functionalities for the implementation of nanophotonic systems. Precise and versatile control of structural configurations on solid substrates is essential for their applications in on-chip devices. Here, we report all-solid-phase reconfigurable chiral nanostructures with silicon nanoparticles and nanowires as the building blocks in which the configuration and chiroptical response can be tailored on-demand by dynamic manipulation of the silicon nanoparticle. We reveal that the optical chirality originates from the handedness-dependent coupling between optical resonances of the silicon nanoparticle and the silicon nanowire via numerical simulations and coupled-mode theory analysis. Furthermore, the coexisting electric and magnetic resonances support strong enhancement of optical near-field chirality, which enables label-free enantiodiscrimination of biomolecules in single nanostructures. Our results not only provide insight into the design of functional high-index materials but also bring new strategies to develop adaptive devices for photonic and electronic applications.

The high sensitivity requirements set by future cosmic microwave background instruments are pushing the current technologies to produce highly performant focal plane arrays with thousands of detectors. The coupling of the detectors to the telescope optics is a challenging task. Current implemented solutions include phased-array antenna-coupled detectors, platelet horn arrays, and lenslet-coupled planar antennas. There are also recent developments of flat graded-index lenses based on etched silicon. However, there are strong requirements in terms of electromagnetic performance, such as coupling efficiency and bandwidth, as well as requirements in terms of easy manufacturing and scalability, and it is very challenging to meet all these requirements with one of the above solutions. Here, we present a novel approach for producing flat metal-mesh lenslet arrays based on devices previously realized using the mesh-filter technology. We have now adapted the polypropylene-based mesh lens design to silicon substrates, thus providing a good mechanical match to the silicon-based detector arrays. The measured performance of prototype pixels operating at millimeter wavelengths is presented.

Optical system consisting of single-mode optical fiber and p-i-n photodiode semiconductor chip with InGaAs active layer was investigated. Considered photodetector module has responsivity in 1.3–1.6 μm. The problem of optical power loss due to inaccurate matching between the optical fiber and the active medium of photodiode in photodetector modules is investigated; resolving the power loss problem will lead to an increase in the spectral photosensitivity and external quantum efficiency of the photodetector module. Optimization of optical fiber coupling with semiconductor chip was implemented in Zemax® software with built-in Levenberg–Marquardt algorithm. Also, numerical calculations of the influence of the transverse and longitudinal displacement on optical coupling efficiency in the photodetector module were carried out. The optical system of photodetector module based on standard metal can package was built in Zemax® software. Optimal distances between elements of the photodetector module were calculated, and maximum efficiency of 93.1 % optical coupling between single-mode fiber and photodiode aperture was achieved. The necessary sensitivity of linear micro translators used during the assembly of photodetector modules was determined to ensure the alignment of optical elements with coupling efficiency more than 90 %. The results of this work can be used in the design of photodetector modules. The proposed solutions can be relatively easily modified to create photodetector modules of other spectral ranges.

The development of novel nanophotonic devices and circuits necessitates studies of optical phenomena in nanoscale structures. Catalyzed semiconductor nanowires are known for their unique properties including high crystallinity and silicon compatibility making them the perfect platform for optoelectronics and nanophotonics. In this work, we explore numerically optical properties of gallium phosphide nanowires governed by their dimensions and study waveguiding, coupling between the two wires and resonant field confinement to unveil nanoscale phenomena paving the way for the fabrication of the integrated optical circuits. Photonic coupling between the two adjacent nanowires is studied in detail to demonstrate good tolerance of the coupling to the distance between the two aligned wires providing losses not exceeding 30% for the gap of 100 nm. The dependence of this coupling is investigated with the wires placed nearby varying their relative position. It is found that due to the resonant properties of a nanowire acting as a Fabry–Perot cavity, two coupled wires represent an attractive system for control over the optical signal processing governed by the signal interference. We explore size-dependent plasmonic behaviors of the metallic Ga nanoparticle enabling GaP nanowire as an antenna-waveguide hybrid system. We demonstrate numerically that variation of the structure dimensions allows the nearfield tailoring. As such, we explore GaP NWs as a versatile platform for integrated photonic circuits. [ABSTRACT FROM AUTHOR]

A localized surface plasmon (LSP) coupling nanorod $\mu $ LED using graphene as a transparent conductive electrode structure was demonstrated. The optical performance of the $\mu $ LED with LSP coupling is enhanced by about 36% in external quantum efficiency and 84% in photoluminescence measurements as compared with the LSP-free sample. This LSP coupling enhancement relies on the very large sidewall area provided by the nanorod structure and the zero distance contact between the nanoparticles and nanorods. This work provides a broad prospect for the application of LSP in the $\mu $ LED field. [ABSTRACT FROM AUTHOR]

In the rapidly evolving field of photovoltaic technology, monolithic perovskite/crystalline silicon tandem solar cells (PSK/c-Si TSCs) have emerged as promising contenders, combining the advantageous properties of PSK with the recognized power conversion efficiency (PCE) of c-Si. Available studies have shown that in the field of PSK/c-Si TSCs, c-Si substrates can be categorized into: flat and pyramidal-textured structures. The limitation of flat structure lies in optical reflection losses, and the commercialization of large-scale pyramid structure is challenging to be compatible with conventional planar PSK solution processes. This study presents a novel quasi-conformal structure with dimensions between flat and pyramidal structures, which facilitates its seamless integration into PSK and c-Si production. Thermally evaporated bis(trifluoromethane)sulfonimide (TFSI)-doping 2,2′,7,7′-tetrakis(N,N-di- p -methoxyphenyl-amine)-9,9′-spirobifluorene (spiro-OMeTAD) has better conformal and electrical properties. The in-situ cesium-based PSK recrystallized-arrays (CPRA) growth scheme achieves current density matching of the two sub-cells by band-edge modulation of the wide-bandgap components. The champion PCE of CPRA-modified PSK/c-Si TSC is 28.53 %. The stability is enhanced due to the protective effect of the inorganic CPRA interface. This research exhibits the successful integration of novel structural elements and light management strategies, which are expected to have wider applications in solar energy harvesting. [Display omitted] • A quasi-conformal structure compatible with perovskite solution processing is proposed. • The thermal evaporation doping method can enhance carrier extraction. • Light management achieves current density matching between the two sub-cells. • Photovoltaic performance and long-term stability of tandem devices are enhanced. [ABSTRACT FROM AUTHOR]

We propose a spot-size converter (SSC) by exploiting the high-efficiency mode conversion capability that a long-period grating (LPG) possesses. Our proof-of-concept LPG-based SSC, fabricated with optical polymer material on silicon nitride (Si3N4) platform, has a length of ∼700 μm, can improve the coupling efficiency between the LPx01 mode of an ultra-high numerical aperture fiber and the Ex11 mode of the Si3N4 waveguide from ∼24% to ∼33% at 1548 nm wavelength, corresponding to 1.4-dB reduction in insertion loss. Therein, the LPG achieves a maximum mode conversion efficiency of 90% between the two Ex11 modes of the polymer cladding and the Si3N4 core. Our proposed SSC provides a new path to achieve low-loss fiber-to-chip coupling.

Space-division multiplexing (SDM) technology is a promising candidate to achieve massive parallelism in optical fiber cables and overcome the capacity limitation of the conventional single-mode fiber (SMF). Among the several kinds of SDM fiber, a weakly coupled multicore fiber (MCF) is advantageous in that it can be easily upgraded for use in existing equipment and requires no complex signal processing for optical multi-input multi-output (MIMO). In this article, we discuss the progress and standardization activity of MCF technologies from the viewpoint of accelerating the practical application of SDM technology. We first describe the possible application areas of SDM fibers and then show the recent progress of the essential technologies to construct the MCF link: the MCF itself, its splicing and connectorization, and the input/output techniques. We also discuss the availability and deployability of MCF as a large-capacity transmission medium and detail the progress on establishing a new international standard for SDM technology, which includes both historical progress and more recent endeavors on the standardization of optical fiber cables and SDM technology in International Telecommunication Union Telecommunication Standardization Sector (ITU-T) and International Electrotechnical Commission (IEC). We close with a summary of MCF technology and its standardization activity with an eye to next-generation transmission systems and the long-term development of ultralarge capacity SDM transmission technology. [ABSTRACT FROM AUTHOR]

We simulate the optical coupling between $2.3\ {\boldsymbol{\mu m}}$ GaSb-based diode lasers (DLs) epitaxially grown on on-axis silicon (001) and passive waveguides in the butt-coupling geometry. 3D FDTD simulations reveal how the optical coupling is affected by the air gap between the laser cavity and the waveguide that arises from the laser etched-facet definition. We also model alternative approaches consisting in filling the gap with higher-refractive index materials transparent in the mid-infrared window. Finally, because of their fabrication flexibility, we propose to implement polymeric waveguides in order to achieve improved coupling performances. [ABSTRACT FROM AUTHOR]

A system for simultaneous measurement of micro-wave Doppler frequency shift (DFS) and angle of arrival (AOA) is proposed based on a silicon integrated chip. In the chip, two dual-drive Mach–Zehnder modulators (DDMZMs) with a microring resonator (MRR) inserted between them are integrated. When an external laser is coupled into the chip, it is first modulated by two echo signals via the first DDMZM and then goes through the MRR to introduce an optical phase shift to one of the first-order sidebands that falls into the resonance of the MRR. After being remodulated by the transmitted signal at the other DDMZM, the lightwave is coupled out from the chip and separated into two channels by an optical coupler. In each channel, a bandpass filter (BPF) is employed to select the upper and lower sidebands. By measuring and comparing the powers, frequencies, and phases of the beat signals in the two channels, the DFS (without direction ambiguity) and AOA can be acquired. Based on the proposed method, DFS within ±100 kHz at 10, 15, and 20 GHz is successfully estimated with a maximum error of ±0.028 Hz, and AOA measurement from 0° to 75° with errors less than ±1.53° is also realized. [ABSTRACT FROM AUTHOR]

We previously proposed a new package substrate called active optical package (AOP) substrate to realize co-packaged optics. An optical redistribution technology on silicon photonics dies was developed to fabricate the AOP substrate. It is composed of a polymer waveguide, with a mirror-based optical coupling between the polymer and silicon waveguides. The fabricated optical redistribution loss was characterized in this study. An average loss of approximately 4 dB and wavelength dependent loss of ±1 dB were observed for the wavelength range of 1460–1600 nm. It was shown that the low wavelength-dependent optical redistribution was available owing to the broadband characteristics of mirror-based optical coupling and polymer waveguide. [ABSTRACT FROM AUTHOR]

Backscattering and back-reflection are one of the main factors restricting the improvement of resonant fiber optic gyroscope accuracy. At present, most researches focus on backscattering. Due to the dependence on narrow linewidth laser, the interference of back-reflection light and the main light produces fluctuations in light intensity, which deteriorates the angle random walk of the resonant fiber optic gyroscope. This paper focuses on the back-reflection light outside the fiber ring resonator, taking the reflection on the end face of the photoelectric detector as an example, and simulates the influence on the detection noise of resonant fiber optic gyroscope. According to the frequency spectrum of intensity noise caused by back-reflection, a suppression method including length matching and frequency separation is proposed. The simulation and experimental results show that this method can effectively reduce the influence of back-reflection, and the angle random walk is improved by 6.06 dB with this method. [ABSTRACT FROM AUTHOR]

An easy-to-fabricate and efficient fiber-to-waveguide adiabatic coupling on a high-index-contrast (HIC) InGaAs/InP quantum well (QW) waveguide platform has been theoretically analyzed and experimentally demonstrated through a 3D spot-size converter (3D-SSC). The 3D-SSC has three monolithically integrated sections: a HIC and a fiber-matched section, coupled using a 3D-adiabatic mode converter (AMC). Vertical tapering of 3D-AMC is achieved by $\text{ZrO}_{2}$ based selective area impurity-free QW intermixing (IFQWI) on the photo-lithographically delineated horizontally tapered region. The 3D-AMC has a compact length of 30 $\mu$ m and adiabatically coupled the expanded mode size to a compressed mode size from input to the output of 3D-SSC. A better than 7 dB improvement in the coupling loss is obtained for the vertical tapered waveguide over a non-tapered waveguide of 4 $\mu$ m rib width. An additional $\sim$ 1 dB improvement in coupling loss is obtained for the vertical and horizontal taper for a bare fiber input. These finding matches very well with the simulated analysis. The fabricated 3D-SSC reduces the insertion loss by 6 dB from that of the non-SSC waveguide for a bare fiber coupling, with a facet coupling loss of 3.33 dB and a large misalignment tolerance. A low coupling loss of 1.85 dB is measured for a lensed fiber. The total propagation loss for a 100 $\mu$ m integrated device is as low as $\sim$ 0.1 dB, making it very suitable for monolithic integration with other optical devices. [ABSTRACT FROM AUTHOR]

Background: Significant interest has been recently shown for using monolithic scintillation crystals in molecular imaging systems, such as positron emission tomography (PET) scanners. Monolithic‐based PET scanners result in a lower cost and higher sensitivity, in contrast to systems based on the more conventional pixellated configuration. The monolithic design allows one to retrieve depth‐of‐interaction information of the impinging 511 keV photons without the need for additional hardware materials or complex positioning algorithms. However, the so‐called edge‐effect inherent to monolithic‐based approaches worsens the detector performance toward the crystal borders due to the truncation of the light distribution, thus decreasing positioning accuracy. Purpose: The main goal of this work is to experimentally demonstrate the detector performance improvement when machine‐learning artificial neural‐network (NN) techniques are applied for positioning estimation in multiple monolithic scintillators optically coupled side‐by‐side. Methods: In this work, we show the performance evaluation of two LYSO crystals of 33 × 25.4 × 10 mm3 optically coupled by means of a high refractive index adhesive compound (Meltmount, refractive index n = 1.70). A 12 × 12 silicon photomultiplier array has been used as photosensor. For comparison, the same detector configuration was tested for two additional coupling cases: (1) optical grease (n = 1.46) in between crystals, and (2) isolated crystals using black paint with an air gap at the interface (named standard configuration). Regarding 2D photon positioning (XY plane), we have tested two different methods: (1) a machine‐learning artificial NN algorithm and (2) a squared‐charge (SC) centroid technique. Results: At the interface region of the detector, the SC method achieved spatial resolutions of 1.7 ± 0.3, 2.4 ± 0.3, and 2.6 ± 0.4 mm full‐width at half‐maximum (FWHM) for the Meltmount, grease, and standard configurations, respectively. These values improve to 1.0 ± 0.2, 1.2 ± 0.2, and 1.2 ± 0.3 mm FWHM when the NN algorithm was employed. Regarding energy performance, resolutions of 18 ± 2%, 20 ± 2%, and 23 ± 3% were obtained at the interface region of the detector for Meltmount, grease, and standard configurations, respectively. Conclusions: The results suggest that optically coupling together scintillators with a high refractive index adhesive, in combination with an NN algorithm, reduces edge‐effects and makes it possible to build scanners with almost no gaps in between detectors. [ABSTRACT FROM AUTHOR]

The optical coupling between dual elements of photonic crystal vertical cavity surface emitting laser arrays is characterized. The optically coupled microcavity lasers have independent bias injection currents. Output power and beam analysis measurements are used to quantify the effects of optical coherence in nominally 850 nm emitting arrays. Modelling and experiment show how the optical coupling is influenced by photonic crystal lattice period and the independent current injection into the elements. [ABSTRACT FROM AUTHOR]

Optical coupling plays a pivotal role in nanophotonic systems, which can be divided into weak, intermediate, and strong‐coupling regimes. Monitoring optical coupling strength is, therefore, the key to understanding light–matter interactions. State‐of‐the‐art approaches based on spectral measurements offer the power to quantify and characterize optical coupling strength at a single cavity level. However, it remains challenging to dynamically characterize coupling strength during the transition from strong‐ to weak‐coupling regimes for many systems simultaneously. Here, a far‐field imaging technique is reported that can directly monitor optical coupling dynamics in plasmon–exciton systems, allowing multiple nanocavity emissions to be characterized from weak‐ to strong‐coupling regimes. Light‐harvesting biomolecules—chlorophyll‐a—is employed to study dynamic light–matter interactions in strongly coupled plasmonic nanocavities. Identification of coupling strength is achieved by extracting red, green, and blue (RGB) values from dark‐field images and an enhancement factor from fluorescence images. Lastly, the ability to monitor subtle changes of coupling dynamics in bioplasmonic nanocavity is demonstrated. These findings may deepen the understanding in light–matter interactions, paving new avenues toward applications in quantum‐based biosensing and imaging. [ABSTRACT FROM AUTHOR]

The increase in capacity provided by coupled space division multiplexing (SDM) systems is fundamentally limited by mode-dependent gain (MDG) and amplified spontaneous emission (ASE) noise. Therefore, monitoring MDG and optical signal-to-noise ratio (SNR) is essential for accurate performance evaluation and troubleshooting. Recent works show that the conventional MDG estimation method based on the transfer matrix of multiple-input multiple-output (MIMO) equalizers optimizing the minimum mean square error (MMSE) underestimates the actual value at low SNRs. Besides, estimating the optical SNR itself is not a trivial task in SDM systems, as MDG strongly influences the electrical SNR after the equalizer. In a recent work we propose an MDG and SNR estimation method using artificial neural networks (ANNs). The proposed ANN-based method processes features extracted at the receiver after digital signal processing (DSP). In this paper, we discuss the ANN-based method in detail, and validate it in an experimental 73-km 3-mode transmission link with controlled MDG and SNR. After validation, we apply the method in a case study consisting of an experimental long-haul 6-mode link. The results show that the ANN estimates both MDG and SNR with high accuracy, outperforming conventional methods. [ABSTRACT FROM AUTHOR]

Large-scale photonic switches are essential components for telecommunications and interconnects, incorporating many cascaded 2 × 2 optical switches. To keep the excess loss of the entire switch low, it is crucial to develop ultralow-loss 2 × 2 optical switches by introducing new coupler designs. In this paper, a low-loss calibration-free 2 × 2 Mach-Zehnder switch (MZS) designed with varied-width multimode-interference (MMI) couplers is proposed and fabricated. In this design, the MMI coupler has a varied-width MMI region and two multimode output waveguides. The MMI coupler optimized by the particle swarm optimization (PSO) algorithm has an ultralow excess loss < 0.053 dB and a suppressed higher-order mode excitation < −26 dB across the C-band (1530–1565 nm). Such a varied-width MMI coupler with two multimode output waveguides can be used compatibly for the MZS with widened phase shifters, so that the random phase imbalance between the two MZS arms can be suppressed effectively, which thus is promising for calibration-free operation. For the present MZS fabricated with standard 180-nm silicon photonic foundry processes, the excess loss is ∼0.5 dB across the C-band and the extinction ratio is ∼25 dB without calibration. [ABSTRACT FROM AUTHOR]

The adiabatically tapered subwavelength-scale optical fiber tapers (OFTs) have been of interest for many photonic applications. We demonstrate chemical etching-based adiabatic OFTs and their relaxed adiabaticity conditions over broad operation wavelength ranges. The etched OFTs show adiabatically-varying tapering angles as small as 1° and mechanical flexibility. When compared to the conventional methods, the proposed OFTs and their fabrication techniques may allow reproducible batch production routes for adiabatic OFTs with enhanced uniformity, enabling a variety of applications in subwavelength-scale light-matter interactions and efficient light coupling between waveguides. [ABSTRACT FROM AUTHOR]

The integration density and the system complexity of photonic integrated circuits are scaling significantly, especially for optical computing, signal processing, and other emerging applications. As is such, the quest for information multiplexing is becoming increasingly important. On-chip mode division multiplexing (MDM) is considered to be a promising solution which is capable of processing a large amount of data via intrinsic parallelism. Various device structures have been proposed for on-chip mode multiplexing while most of which either lack the scalability or occupy too much chip area. Here, a scalable and compact silicon photonic mode (de)multiplexer is proposed and experimentally demonstrated based on tilt waveguide junctions assisted with shallow-etched subwavelength slots. The number of channels can be easily scaled by cascading multiple junctions. Compared with conventional cascaded structures, the proposed shallow etched slots enable a new mode evolution scheme which significantly shrinks the device length. For a proof-of-concept demonstration, four-mode (de)multiplexer for TE0–TE3 modes is designed, fabricated, and characterized. The measured insertion losses for all four modes are below 1.29 dB, while the crosstalks are all below −14.4 dB. [ABSTRACT FROM AUTHOR]

The optically segmented single volume scatter camera (OS-SVSC) aims to image neutron sources for nuclear nonproliferation applications using the kinematic reconstruction of elastic double-scatter events. We report on the design, construction, and calibration of one module of a new prototype. The module includes 16 EJ-204 organic plastic scintillating bars individually wrapped in Teflon tape, each measuring $0.5 {\mathrm {cm}}\times 0.5 {\mathrm {cm}}\times 20 {\mathrm {cm}}$. The scintillator array is coupled to two custom silicon photomultiplier (SiPM) boards consisting of a $2\times 8$ array of SensL J-Series-60035 SiPMs, which are read out by a custom 16 channel DRS4 based digitizer board. The electrical crosstalk between SiPMs within the electronics chain is measured as $0.76\% \,\pm \,0.11\%$ among all 16 channels. We report the detector response of one module including interaction position, time, and energy, using two different optical coupling materials: EJ-560 silicone rubber optical coupling pads and EJ-550 optical coupling grease. We present results in terms of the overall mean and standard deviation of the $z$ -position reconstruction and interaction time resolutions for all 16 bars in the module. We observed the $1\sigma z$ -position resolution for gamma interactions in the 0.3–0.4 MeVee range to be 2.24 cm ± 1.10 cm and 1.45 cm ± 0.19 cm for silicone optical coupling pad and optical grease, respectively. The observed $1\sigma $ interaction time resolution is 265 ps ± 29 ps and 235 ps ± 10 ps for silicone optical coupling pad and optical grease, respectively. [ABSTRACT FROM AUTHOR]

Oak Ridge National Laboratory is developing a portable, pixelated fast-neutron imaging panel for associated particle imaging (API). The panel consists of new and commercially available hardware. Unlike the current generation of API-based neutron imaging systems, this panel is intended to be field deployable. A $30\times30$ array of optically isolated 1 cm $\times$ 1 cm $\times$ 5 cm pulse shape discriminating (PSD) plastic scintillator pixels are optically coupled to a $6\times6$ array of position-sensitive photomultiplier tubes (PMTs) allowing each pixel to be resolved. Each quadrant of $3\times3$ PMTs recombines the 576 PMT anodes using a resistive charge division network to achieve four-corner readout that preserves the average position of the detected light. The design of the panel and initial testing of the light collection and position encoding electronics is presented herein. [ABSTRACT FROM AUTHOR]

Many improvements are required to bring quantum key distribution (QKD) from the laboratory to the commercial market, such as simplifying structure and enhancing stability. In this letter, a QKD module based on planar lightwave circuit (PLC) has been proposed. The chip inside module is based on silica-silicon material and composed of various optical splitter, asymmetric Mach–Zehnder interferometer and directional coupler. The module can allow users adjust temperature stably. The interference visibility can be high to 96% merely by controlling and stabilizing temperature and voltage of the module through self-interfering method which showed its potential in practical application. [ABSTRACT FROM AUTHOR]

The emergence of soliton in plasmonic graphene waveguide is investigated in the presence of optical and microwave fields. The considered configuration encompasses a monolayer graphene waveguide placed between parallel plate capacitor. The optical fields are launched as surface plasmon polariton modes, while the microwave field is applied to the capacitor. The governing nonlinear-Schrödinger equations of the propagating optical fields have been derived. It is shown that electronically controlled coupled optical solitons can be achieved by altering the corresponding self- (and cross-) modulation terms with proper electrical biasing and doping concentration. This present work paves the way towards soliton formation in the field of quantum technology. [ABSTRACT FROM AUTHOR]

Optical interconnects outperforms the traditional electrical interconnects with lower power consumption, higher bandwidth density and scalability. We propose a scalable optical interconnect for on- chip core-to-memory communication. The key part of the optical interconnect is scalable optical switching blocks, which use less microring resonators with different wavelengths to provide higher parallelism for the memory access communication. We demonstrate the 4-port switching block with six microring resonators. The experimental results show the average insertion loss of 4-port optical switching block is 6.956 dB. [ABSTRACT FROM AUTHOR]

In order to stabilize the lateral far-field profile of a broad area laser diode at high pump currents, the design of an asymmetric InGaAs/AlGaAs/GaAs laser heterostructure was developed. Lasers with an aperture formed by ten optically uncoupled ridge waveguides (each 6.5 μm wide) were developed on its basis. To maintain the single-mode operation of each ridge waveguide without coupling between emitters, a High Dense Microstripe Array (HDMSA, the pitch is 13.5 μm) and a Low Dense Microstripe Array (LDMSA, the pitch is 40 μm) were fabricated with a coupling parameter between adjacent lateral waveguides of 2·10−5 and 3·10−19, respectively. The maximum optical output power was 5 W (HDMSA) in CW mode and 25 W (HDMSA) and 26 W (LDMSA) in pulsed mode (130ns/1kHz). It is shown that in both CW and pulsed modes, lasers of both designs provide a stable Gaussian-like distribution in the lateral far field (LFF) with a FWHM of 8–11 degrees for HDMSA and 6.5–10 degrees for LDMSA. It was found that the LFF broadens with a pump current in the range of low currents and stabilizes in the range of high currents for both designs. Studies of the near field in both operating modes at any pump currents showed no array modes and the uncoupling mode is maintained for ridge waveguide arrays. [ABSTRACT FROM AUTHOR]

This paper describes the characteristics of graded-index (GI) core Y-branched polymer optical waveguides as optical couplers for multimode fibers (MMFs) in coarse wavelength division multiplexing links with a restricted mode launch function. In this paper, we compare two GI-core Y-branched waveguides fabricated using different methods: the Mosquito method and the imprint method. Error free transmission is confirmed when transmitting a 25.6125-Gbps NRZ optical signal (PRBS31) at 850-nm wavelength through a 100-m long OM3 fiber using the waveguide as an optical coupler. We also discuss the function of a restricted mode launch exciter for a 1-km long MMF. From the effective modal bandwidth analysis, realizing higher bandwidth-distance product in long MMFs should be possible by reducing the core size of the waveguide coupler. [ABSTRACT FROM AUTHOR]

Optical couplant greases based on polydimethylsiloxane (PDMS) may be employed in devices such as scintillator-based radiation detectors that operate in extreme environmental conditions. The optical transmission of Dow Corning DOWSIL Q2-3067 optical couplant grease was measured at room temperature as a function of wavelength (200–800 nm) and grease thickness (0.13–1 mm). Across the spectral range, transmission decreased with increasing thickness, and the increase was more pronounced at wavelengths < 400 nm. An effective ultraviolet (UV) cutoff wavelength of ~270 nm was found, independent of grease thickness, although a weak transmission feature was observed below this cutoff at 233 nm. The optical transmission spectra exhibited a dependence on temperature, increasing with increasing temperature to 50 °C and decreasing with decreasing temperature to −10 °C. This temperature dependence was more pronounced at wavelengths < 400 nm and for thicker grease layers. Below −10 °C, transmission decreased sharply for all wavelengths. This decrease was correlated with a sharp increase in viscosity, indicating that the grease undergoes a thermal transition at −11 °C ± 1 °C. This thermal transition occurs more slowly with decreasing temperature for thinner layers of grease, but all measured grease thicknesses were reasonably opaque at temperatures below −20 °C. These results will aid in predicting the optical and mechanical performance of optical systems such as radiation detectors exposed to extreme outdoor environmental conditions. [ABSTRACT FROM AUTHOR]

A system of two mutually coupled quantum dot lasers, each with corresponding longitudinal modes, has been studied in this article. Using multimode rate equation model, we demonstrate how this model in conjunction with coupled-mode theory lead to a set of effective Hamiltonians with characteristics inarguably akin to those Hamiltonians associated to the conventional PT-symmetric systems. A fixed frequency detuning has been introduced by a minute difference in cavity lengths in the current system and the strength of optical coupling plays a decisive role in the emergence of the exceptional points at which the so- called non-conventional PT-symmetry breaks. It has also been shown that the predictions about amplification or attenuation of supermodes associated to the longitudinal modes based on effective Hamiltonians, happen to be supported by the multimode rate equation model, yet in the presence of weak coupling. Eventually, the overall output spectrum is potent to be manipulated and in particular exhibit a single longitudinal mode behavior in the vicinity of the exceptional point through the interplay between the frequency detuning and the coupling coefficient. Owing to the inhomogeneous broadening of the optical spectrum, a considerable rise in the number of photons for the single amplified supermode is witnessed within time having the attenuated modes out of the picture via proper mode selection in the present non-conventional PT-symmetric system. [ABSTRACT FROM AUTHOR]

We experimentally demonstrated a long-haul wavelength-division multiplexed (WDM) and space-division multiplexed (SDM) transmission of 32-Gbaud polarization-division multiplexed quadrature phase-shift keying signals over 52-km coupled-4-core fiber spans with amplification by coupled-4-core erbium-doped fiber amplifiers (EDFAs). Error-free performance after forward error correction was achieved up to 2700 km. From converged multi-input multi-output filter coefficients, we estimated the mode dependent loss (MDL) that occurred in this experiment. The MDL was frequency-dependent within a WDM channel and the root-mean square MDL was 1.0 dB per loop. To assess the effect of MDL on SDM transmission performance, we also estimated the outage probability through Monte-Carlo simulations with a Gaussian noise model. The estimated outage probability under MDL showed similar performance to that obtained in the transmission experiment. This suggests that the MDL of coupled-multi-core EDFAs was one of the major limiting factors of the transmission performance and that the rms MDL per span should be below 0.4 dB for further long-haul transmission distance over 6000 km. [ABSTRACT FROM AUTHOR]

We analyze the coupling between an adjacent field ring and a coupling ring of the 2-D optical resonator array to obtain a topological edge state. Using the finite-difference time-domain method, the energy band structure, light field distribution, and transmission spectrum are simulated to investigate the optimized coupling parameters under the topological boundary state. When the coupling coefficient is approximately 0.775, the system can form a topological state in the wavelength of 1.55– $1.56~\mu \text{m}$ , while output can maintain a flat spectral response with normalized power above 0.9. The research in this article provides a basis for the potential application of topological edge states of 2-D coupled resonant optical waveguide in the field of photonic communication. [ABSTRACT FROM AUTHOR]

Optical delay lines are vital for the development of all optical telecommunications, optical computers and for many nonlinear and quantum optics processes. Periodic structures such as coupled resonator optical waveguides (CROW) achieve high delays in a compact manner and with a large bandwidth. Wedge disk resonators have demonstrated high quality factors compared to rectangular disks and rings while remaining integrable on chip. Vertical coupling is needed since the optical mode is pushed toward the disk center by the wedge. We propose an optical delay line made of wedge disks arranged in two overlapping layers. Disks are made of silicon dioxide on silicon pillars. Numerical calculations of the device performance and an experimental proof of concept are presented. A maximum delay of 85 ps for eleven disks is achieved with a loss per cavity of 3.91 dB. This is a first proof of concept of a CROW structure made of wedge disk coupled vertically. [ABSTRACT FROM AUTHOR]

We report on the development of a two-channel digital coherent optics (DCO) module, based on a monolithic InP photonic integrated circuit (PIC) transceiver and SiGe application-specific integrated circuit (ASIC), paired with a real-time 7 nm digital signal processing (DSP) ASIC. The high-performance coherent optical engine, which utilizes digital Nyquist subcarriers and probabilistic constellation shaping (PCS) techniques, enables long-haul and ultra-long-haul transmission distances over mixed fiber and amplifier types. This work discusses the performance of a DCO unit operating at multiple data rates over three practical real-world-like network distances. 800 Gb/s data transmission over a 1,000 km standard single mode fiber link was achieved using a 96 GBd, PCS-64QAM modulation format. Results of extended reaches of over 2,400 km and 5,000 km are also presented with data rates of 600 Gb/s and 400 Gb/s, respectively. [ABSTRACT FROM AUTHOR]

Controllable strong interactions between a nanocavity and a single emitter is important to manipulating optical emission in a nanophotonic system but challenging to achieve. Herein a three-dimensional DNA origami, named as DNA rack (DR) is proposed and demonstrated to deterministically and precisely assemble single emitters within ultra-small plasmonic nanocavities formed by closely coupled gold nanorods (AuNRs). Uniquely, the DR is in a saddle shape, with two tubular grooves that geometrically allow a snug fit and linearly align two AuNRs with a bending angle < 10°. It also includes a spacer at the saddle point to maintain the gap between AuNRs as small as 2–3 nm, forming a nanocavity estimated to be 20 nm3 and an experimentally measured Q factor of 7.3. A DNA docking strand is designed at the spacer to position a single fluorescent emitter at nanometer accuracy within the cavity. Using Cy5 as a model emitter, a ∼ 30-fold fluorescence enhancement and a significantly reduced emission lifetime (from 1.6 ns to 670 ps) were experimentally verified, confirming significant emitter-cavity interactions. This DR-templated assembly method is capable of fitting AuNRs of variable length-to-width aspect ratios to form anisotropic nanocavities and deterministically incorporate different single emitters, thus enabling flexible design of both cavity resonance and emission wavelengths to tailor light-matter interactions at nanometer scale. [ABSTRACT FROM AUTHOR]

Two unique wavelengths (critical and cross-over) observed in the transmission spectra of fiber optic directional couplers exhibit a common (conjugate) characteristic feature, that the nature of spectral shifts flip around them. To free the transmission spectra from the opposite spectral shifts we demonstrate a judicious overlap of these wavelengths using optimized coupler parameters and dispersion management. Theoretical analysis explaining the optimization steps, dispersion management and the influence of these on the transmission and sensing properties of the considered directional coupler are presented. An ultra-high experimental refractive-index sensitivity ($\sim$ 20,550 nm/RIU) has been demonstrated by operating the directional coupler close to the critical wavelength (nearest to it largest spectral shifts are observed). This study should find applications in designing ultra sensitive refractometers which are free from critical wavelength referencing. [ABSTRACT FROM AUTHOR]

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

We propose a general and exact analytical model forintensity modulation and direct detection (IM/DD) fiber optic links using dual-output dual-drive Mach-Zehnder modulator (DO-MZM). This model extends previously published results relying on the small-signal approximation and infinite extinction ratio at the modulator outputs. In our treatment the output optical powers are calculated through analytical expressions taking into account the modulator electronic driver and directional coupler characteristics. Closed-form expressions, explicitly displaying the dependence of the link output power on the directional coupler transmission coefficients, optical modulation depth, and bias point, are obtained for output optical power, frequency chirp, extinction ratio and static characteristic MZM curves. We also propose an equivalent interferometric representation of each DO-MZM output in terms of virtual dual-drive Mach-Zehnder modulators (DD-MZMs) and show that each modulator output has distinct characteristic curves. The model is applied to a photonic-assisted instantaneous frequency measurement (IFM) based on frequency-to-power mapping, in which an amplitude comparison function (ACF) is generated by the power fading functions. We have obtained a generalized ACF through which both the frequency and amplitude of the input RF signal can be determined by a search procedure. [ABSTRACT FROM AUTHOR]

Microwave photonic applications such as beamforming and filtering entail the photonic summation of optically-carried RF signals. The most commonly used components to perform these functions are fiber-optic couplers, arrayed waveguide gratings and optical concentrators, whose common characteristic is to gather these optical signals on a single output before converting them into an RF signal with a photodiode. The spatial superposition of several optical fields causes photonic interference leading to the emergence of noise in the RF domain. This paper focuses on an experimental study of the impact of optical interference and phase decorrelation between delayed optical fields in an optical fiber interferometer, considering two different combining technologies. When a fiber coupler is employed, the full overlap of the spatial fields induces a high-level noise on the electrical signal generated after the photodiode. To solve this problem, the use of a microwave photonic summation device based on an optical power concentrator and a high-speed planar photodiode permits a strong mitigation of the optical interference. The results of the experiments presented reveal that the proposed approach can reduce phase noise effects on the resulting electrical sum signal by a factor of 40 dB. [ABSTRACT FROM AUTHOR]

The terahertz current generated by a photoconductive device (PCD) saturates as the power of the input optical pump is increased. This behavior is induced by various screening effects that stem from the interactions between electromagnetic (EM) fields and semiconductor carriers. In this work, these screening effects are numerically analyzed for the first time using a fully-coupled multiphysics approach. Unlike the previously developed simulation frameworks, this approach rigorously models the nonlinear coupling between the EM fields and the carriers and therefore is capable of accounting for the screening effects. It is demonstrated that the results obtained using this multiphysics approach and actual experiments are in excellent agreement. The optical- and radiation-field screening effects are identified in the simulation results and the optical-field screening is found to play a more dominant role in the saturation of the PCD output under high optical pump power levels. [ABSTRACT FROM AUTHOR]

Distributed optical fiber acoustic sensing (DAS) is a new and rapid-developing detection technology in seismic exploration. Unfortunately, due to the weak energy of scattered optical signals and the inferior coupling between DAS cable and receiving interface, the seismic data received by DAS are often characterized by low signal-to-noise ratio (SNR); this low SNR is likely to affect some subsequent analysis, such as inversion, imaging, and interpretation. In addition, the noise caused by the inferior coupling is a new kind of noise not presented on conventional seismic data. To enhance the SNR of DAS seismic data and suppress the DAS noise effectively, we propose a convolutional adversarial denoising network (CADN) based on the basic strategy of generative adversarial network (GAN) and the usage of a denoiser to replace the original generator in GAN. In CADN, the performance of denoiser is significantly strengthened via its own mean square error (MSE) loss and the adversarial loss between it and the discriminator. To balance the two losses and thus ensure the optimization of denoiser, we construct a novel loss function, where the optimal ratio of MSE and adversarial losses is determined by quantifying the denoising performance. Both real and synthetic examples are included to testify the denoising performance of CADN. Experimental results have demonstrated that CADN can suppress most of the DAS noise and enhance the SNR of DAS seismic data; also, it can recover the effective signals completely, even the extremely weak effective signals reflected by deep layers. [ABSTRACT FROM AUTHOR]

3D hybrid integration based on III-V/Si waveguides by selective undercut wet etching (SUWE) of the lower Si layer has been demonstrated on a silicon-on-insulator (SOI) template. The process was performed on an adhesive-bonding material structure, defined by the upper InP/InAlGaAs (InAlGaAs quantum well) p-i-n heterostructure and the lower 220 nm SOI. After the top p-i-n III-V tapered waveguide was first fabricated and covered by Si3N4, KOH was then used for SUWE of Si layer from SiO2 and Si3N4, forming the bottom SOI single-mode waveguide. In comparison to monolithic III-V waveguide structure (InP based material), the simulated confinement factor of active region shows an enhancement from 10.3% to 16.7%. SOA/EAM devices were also processed and integrated in III-V layer, showing 7.2 dB optical gain at 70 mA injection current in SOA and 21.7 dB extinction ratio within 0~−2 V swing voltage in EAM. The strong quantum confined Stark effect (QCSE) in MQW confirms the improved confinement factor. It suggests a vertical self-alignment scheme could be used for realizing compact and submicron scale heterogeneous integration in a Si photonics template. [ABSTRACT FROM AUTHOR]

An improved linearized analog microwave photonic link (AMPL) with significant multioctave bandwidth performance is experimentally presented. The proposed AMPL configuration is based on a double dual-parallel Mach–Zehnder modulator and a differential balanced photodetector (BPD). Explicitly, a gallium arsenide (GaAs)-based modulators are used as opposed to the commonly known lithium niobate (LiNbO3) modulators, due to its robustness in the harsh environment. The system configuration is designed to process a carrier suppressed double-sideband signal through the link, and then at the receiver, a carrier suppressed double-sideband signal is combined with an unmodulated optical carrier, which is transmitted through a polarization maintained (PM) optical fiber. In our experiment, only PM-based optical components are used for better system stability. The developed theoretical model of the proposed system illustrates the elimination of even-order distortions and a high suppression to the third-order intermodulation distortions at the BPD. Consequently, the fundamental signal to interference ratio of 60 dB was experimentally achieved. Furthermore, experimental results, simultaneously, demonstrate a significant increase of second-order spurious-free dynamic range and third-order spurious-free dynamic range by 19.5 and 3.1 dB, respectively, compared to the previously reported AMPL performances based on polarization multiplexing dual-parallel Mach–Zehnder modulator. To the best of our knowledge, this is the highest dynamic range AMPL system performance deploying GaAs electro-optic modulator which has most significant capabilities in managing RF signals and exhibits excessive performance in harsh operating environment in terms of thermal stability, power-handling, radiation resistance and longevity for aerospace, defense, and satellite-to-ground downlink communication system applications. [ABSTRACT FROM AUTHOR]