Optical Interface Research Articles

Environmental Effects on the Performance of Quantum Dot Luminescent Solar Concentrators.

Luminescent solar concentrators (LSCs) are all-photonic, semitransparent solar devices with great potential in the emerging fields of building-integrated photovoltaics and agrivoltaics. Over the past decade, particularly with the advent of quantum dot (QD) LSCs, tremendous progress has been made in terms of photovoltaic efficiency and device size by increasing solar spectral coverage and suppressing reabsorption losses. Despite these advances in LSC design, the effects of environmental conditions such as rain, dust, and dirt deposits, which are ubiquitous in both urban and agricultural environments, on LSC performance have been largely overlooked. Here, we address these issues by systematically investigating the environmental effects on the solar harvesting and waveguiding capability of state-of-the-art QD-LSCs, namely, the presence of airborne pollutants (dust), water droplets, and dried deposits. Our results show that dust is unexpectedly insignificant for the waveguiding of the concentrated luminescence and only reduces the LSC efficiency through a shadowing effect when deposited on the outer surface, while dust accumulation on the inner LSC side increases the output power due to backscattering of transmitted sunlight. Water droplets, on the other hand, do not dim the incident sunlight, but are detrimental to waveguiding by forming an optical interface with the LSC. Finally, dried deposits, which mimic the evaporation residues of heavy rain or humidity, have the worst effect of all, combining shading and waveguide losses. These results are relevant for the design of application-specific surface functionalization/protection strategies real LSC modules.

Coherent optical two-photon resonance tomographic imaging in three dimensions

Magnetic resonance imaging is a three-dimensional imaging technique, where a gradient of the magnetic field is used to interrogate spin resonances with spatial resolution. The application of this technique to probe the coherence of atoms with good three-dimensional resolution is a challenging application. We propose and demonstrate an optical method to probe spin resonances via a two-photon Raman transition, reconstructing the 3D-structure of an atomic ensemble’s coherence, which is itself subject to external fields. Our method relies on a single time-and-space resolved heterodyne measurement, allowing the reconstruction of a complex 3D coherence profile. Owing to the optical interface, we reach a tomographic image resolution of 14 × 14 × 36 μm3. The technique allows to probe any transparent medium with a resonance structure and provides a robust diagnostic tool for atom-based quantum information protocols. As such, it is a viable technique for application to magnetometry, electrometry, and imaging of electromagnetic fields.

Investigation of Peak-to-Valley Current Ratio of GaN/AlN Resonant Tunneling Diodes

Peak-to-valley current ratios (PVCRs) achie-ved in GaN/AlN resonant tunneling diodes (RTDs) are less than 2, significantly less than their counterparts, such as InGaAs/AlAs RTDs (e.g., PVCR <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 12). This has hindered their high-speed applications because the maximum self-oscillation frequency and minimum switching time generally increase and decrease with PVCR. In this article, we investigate the problem of low PVCR in GaN/AlN RTDs with both modeling and experiments. Firstly, we developed a Schrödinger equation-based solver for RTD simulations. While the solver gives reasonable agreement with the experimental current–voltage ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> – <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> ) characteristics, such as the positions of resonant peaks, it predicts a much higher PVCR. Then, we conducted temperature dependence studies on GaN/AlN RTDs and compared them with InGaAs/AlAs RTDs. The similarities observed suggest that sequential tunneling with phase randomization, resulting from scattering processes such as optical phonon and interface roughness scattering, is responsible for the large valley currents in GaN/AlN RTDs.

Reflective Spin–Orbit Geometric Phase from Planar Isotropic Interface

AbstractManipulating angular momentum of light relies on the change of geometric phase in anisotropic nanostructures or optical interface phenomena. Spin–orbit interactions demonstrated in normal incidence at a planar isotropic interface are conditioned by Brewster reflection, limited to the light beam with a single radial frequency in the k‐space. This study demonstrates a geometric (Pancharatnam–Berry) phase that overcomes Brewster angle limitations providing high variability in the modulation of light reflected from a planar isotropic interface. The examined geometric phase stems from the reflection anisotropy imitating the structural anisotropy of photoaligned liquid crystals and photonic metasurfaces. Using a geometric‐phase modulation of tightly focused light reflected from a glass slab, three modes of spin to orbital angular momentum conversion are demonstrated. The discovered reflective spin–orbit interaction allows for design of a double‐helix focusing sensor to be used in microscopy imaging for precise depth measurements (accuracy 109 nm and precision 7 nm in the range of 8 µm). Experiments with a focused astigmatic beam prove that a glass plate can perform very complex modulation of the geometric phase using illumination structuring. The results thus provide the foundation for the design of low‐cost geometric‐phase systems relying on the space‐variant reflection anisotropy.

Label-free, ultra-low detection limit DNA biosensor using high quality optical microcavity functionalized by DNA tetrahedral nanostructure probes

Abstract This study proposes and demonstrates a novel label-free DNA biosensor using high quality optical microcavity functionalized by 3D DNA nanostructure probes. To achieve ultra-low limit DNA biosensing, optical sensing interface of the hollow-core, thin wall-thickness microcavity was functionalized by self-assembled DNA tetrahedral nanostructure (DTN) probes with size of 17 bp and length of ∼5.8 nm. High efficiency binding of the DTN probes with the optical sensor interface and the target ssDNA are achieved. Whispering gallery mode (WGM) spectra with high-Q factor of &gt;107 are excited and traced for DNA detection inside the microfluidic channel of the microcavity, with a small sample volume of nL. Incorporation of nanoscale DTN probes onto surface of the optical microcavity makes it an effective way for increasing efficient probe density and eliminating entanglement between DNA probes, thus ∼1000 times lower detection limit is achieved as compared to using 1D ssDNA probes. Due to its desirable merits of label-free, ultra-low LoD, real time and compact size, the proposed DNA biosensor has broad application prospects in bioengineering and medical diagnosis.

Entanglement generation using cryogenic integrated four-wave mixing

Cryogenic integrated nonlinear photonics can provide fundamental building blocks for scalable photonic quantum computing and optical interfacing among different platforms. Here, we investigate the spontaneous four-wave mixing effect in an integrated silicon waveguide with cryogenic operating conditions (4 K) and employ the system to generate the entangled photon-pair source, one of the key elements of photonic quantum information applications. We experimentally prove that even at cryogenic temperatures, the four-wave mixing effect in silicon waveguides is still an effective method to generate quantum photonic sources. The cryogenic photon-pair source is verified over multiple frequency channels within a bandwidth of ∼2THz. Furthermore, the source is used to generate high-quality frequency-multiplexed energy–time entangled states. Our results will advance the development of cryogenic nonlinear photonics and scalable integrated photonics for quantum information processing.

Strong coupling of multiple optical interface modes with ultra-narrow linewidth in one-dimensional topological photonic heterostructures.

Coherent coupling of optical modes with a high Q-factor underpins realization of efficient light-matter interaction with multi-channels in resonant nanostructures. Here we theoretically studied the strong longitudinal coupling of three topological photonic states (TPSs) in a one-dimensional topological photonic crystal heterostructure embedded with a graphene monolayer in the visible frequencies. It is found that the three TPSs can strongly interplay with one another in the longitudinal direction, enabling a large Rabi splitting (∼ 48 meV) in spectral response. The triple-band perfect absorption and selective longitudinal field confinement have been demonstrated, where the linewidth of hybrid modes can reach 0.2 nm with Q-factor up to 2.6 × 103. Mode hybridization of dual- and triple-TPSs were investigated by calculation of the field profiles and Hopfield coefficients of the hybrid modes. Moreover, simulation results further show that resonant frequencies of the three hybrid TPSs can be actively controlled by simply changing the incident angle or structural parameters, which are nearly polarization independent in this strong coupling system. With the multichannel, narrow-band light trapping and selectively strong field localization in this simple multilayer regime, one can envision new possibilities for developing the practical topological photonic devices for on-chip optical detection, sensing, filtering, and light-emitting.

Electrical and optical parameters optimization and interface engineering for efficiency improvement of double CIGS absorber based solar cell

In this paper, we present a numerical simulation of double CIGS absorber based solar cell to enhance solar cell performance. The performance characteristics such as open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF) and power conversion efficiency (PCE) were quantitatively analyzed using SCAPS-1D software. Ultrathin WSSe is used as buffer layer due to low reflectance and high bandgap which are favorable for photon transmission from front side to CIGS absorber layer. Optimization of energy bandgap of both CIGS absorbers layer has been done by varying the gallium content in Cu(In1-xGax)Se2 structure. The output characteristics measured here consist of the recombination velocity (S) at the WSSe/ Cu(In0.6Ga0.4)Se2 interface and doping concentration of the buffer and absorber layer. The PCE of double CIGS absorber based solar cell with gallium (Ga) content x=0.4 of Cu(In0.6Ga0.4)Se2 layer along with Ga content x=0.7 of Cu(In0.3Ga0.7)Se2 layer represents the record efficiency of 29 %. The results reveal that, it is possible to achieve PCE to 29 % and beyond and provide a promising solution towards the fabrication of highly efficient thin film CIGS photovoltaic cell.

Spectral Voltage Contour Plots of Optical Constants and Interface Parameters of the Active Layer of a Multilayer Structure Suspended Particle Device Smart Window from Clear on to Dark off States

Smart windows based on suspended particle devices (SPDs) are able to switch optically from dark to clear visual appearance when applying an AC electrical signal. This effect is due to light absorbing nanoparticles that get aligned by the applied voltage. The sandwich structure of an SPD consists of several layers and includes two outer glass substrates, each one covered on its inwards-facing side with a transparent conducting thin layer surrounding the centrally positioned SPD active layer. A knowledge of the optical constants of each layer—i.e., the complex refractive index, including its real and imaginary (absorption) parts—is a key in the design of the visual appearance of the SPD window and is a useful tool to determine the optimum thickness of the active layer.

Improvement of Classification Accuracy of Four-Class Voluntary-Imagery fNIRS Signals using Convolutional Neural Networks

Multiclass functional Near-Infrared Spectroscopy (fNIRS) signal classification has become a convenient way for optical brain-computer interface. fNIRS signal classification with high accuracy is a challenging assignment while the signals are produced by means of voluntary and imagery movements of the same limb. Since the activation in time and space of voluntary and imagery movement show a similar pattern, the classification accuracy by the conventional shallow classifiers cannot reach an acceptable range. This paper proposes an accuracy improvement approach with the use of Convolutional Neural Networks (CNNs). In this work, voluntary and imagery hand movements (left hand and right hand) were performed by several participants. These four-class signals were acquired utilizing fNIRS devices. The signals were separated based on the tasks and filtered. With manual feature extraction, the signals were classified by support vector machine and linear discriminant analysis. The automatic feature extraction and classification mechanism of the CNN were applied to the fNIRS signals. From the results, it was found that CNN improves the classification accuracy to an acceptable range, which has not been achieved by any convolutional network.

MP37-18 A PROSPECTIVE COHORT STUDY DEMONSTRATING EXERCISE EFFECTS FROM HOME BASED PELVIC FLOOR MUSCLE TRAINING TO REHABILITATE NEUROGENIC LOWER URINARY TRACT DYSFUNCTION; 3D REGIONAL EFFECTS

You have accessJournal of UrologyCME1 Apr 2023MP37-18 A PROSPECTIVE COHORT STUDY DEMONSTRATING EXERCISE EFFECTS FROM HOME BASED PELVIC FLOOR MUSCLE TRAINING TO REHABILITATE NEUROGENIC LOWER URINARY TRACT DYSFUNCTION; 3D REGIONAL EFFECTS Lynn Stothers, Andrew Macnab, Naser Hakimi, W. N. J. M. Colier, M. Maresse, and P. Pourabbassi Lynn StothersLynn Stothers More articles by this author , Andrew MacnabAndrew Macnab More articles by this author , Naser HakimiNaser Hakimi More articles by this author , W. N. J. M. ColierW. N. J. M. Colier More articles by this author , M. MaresseM. Maresse More articles by this author , and P. PourabbassiP. Pourabbassi More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003275.18AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Women with neurogenic lower urinary tract dysfunction (NLUTD) rely on pelvic floor muscle rehabilitation therapy (PFMT) to aid continence. However, in NLUTD including spinal cord injury (SCI) PFM function is known to be affected regionally/asymmetrically which is not detected through exam or manometry. Objective: Report clinical translation of a optical PFM system, patient informed design to provide a 3D measures of PFM contractions quantifiable by reoxygenation recovery following sustained maximal voluntary contractions (SMVC) employed in PFMT. METHODS: An optical transvaginal interface was engineered using a circumferential grid of 6 light emitting diodes (LED’s) (wavelengths 750 & 860nm) & 4 photodiode detectors. Engineering design met preferences for size, shape, weight & ergometric features from a prior end user survey (Figure 1) Sampling at 50Hz, changes in oxy and deoxy-hemoglobin concentration (O2Hb/HHb) during PFM contractions monitored in real time, multiple point, from which HbDiff (O2Hb-HHb) is derived. All completed pre/post Qualiveen, were evaluated via NIRS during a standardized sequence of maximum & sustained PFM contractions, engaged in 12 weeks home based PFMT then repeat optical-derived measures of reoxygenation recovery. RESULTS: N=14 women (5 controls 7 NLUTD) 25–82 yrs. Baseline Qualiveen scores range: 0 (controls)-0.7 (NLUTD). Figure 1: output showing post PFMT composite graphics with NIRS data from channels monitoring the right & left sides of both the anterior & posterior segments of the PFM during 3 SMVC’s. All subjects were monitored successfully pre/post PFMT demonstrating 3D detailed functional ability of small segments of the pelvic floor & documenting effects of training. CONCLUSIONS: Optical detection of a validated quantifiable parameter of muscle reoxygenation in the PFM is feasible using this transvaginal optical interface designed based on women with NLUTD end user feedback. The multipoint design allows small regional variations in PFM functionality to be quantified & improvements from PFMT training effects to be measured in NLUTD/SCI to enhance rehabilitation of women living with NLUTD known to impact negatively on quality of life. Source of Funding: Craig H Neilsen Foundation © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e521 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Lynn Stothers More articles by this author Andrew Macnab More articles by this author Naser Hakimi More articles by this author W. N. J. M. Colier More articles by this author M. Maresse More articles by this author P. Pourabbassi More articles by this author Expand All Advertisement PDF downloadLoading ...

Monolithically Integrated Active Passive Waveguide Array Fabricated on Thin Film Lithium Niobate Using a Single Continuous Photolithography Process (Laser Photonics Rev. 17(4)/2023)

High Performance Multifunctional Photonic Chip In article number 2200686, Zhiwei Fang, Ya Cheng, and colleagues demonstrate a robust low-loss optical interface by tiling undoped TFLN and rare earth ions doped TFLN substrates for monolithic integration of passive/active lithium niobate photonics. The interface loss is 0.26 dB; this robust low-loss optical interface for passive/active photonic integration will facilitate large-scale high performance multifunctional photonic chip.

Integrated silicon photonic MEMS

Silicon photonics has emerged as a mature technology that is expected to play a key role in critical emerging applications, including very high data rate optical communications, distance sensing for autonomous vehicles, photonic-accelerated computing, and quantum information processing. The success of silicon photonics has been enabled by the unique combination of performance, high yield, and high-volume capacity that can only be achieved by standardizing manufacturing technology. Today, standardized silicon photonics technology platforms implemented by foundries provide access to optimized library components, including low-loss optical routing, fast modulation, continuous tuning, high-speed germanium photodiodes, and high-efficiency optical and electrical interfaces. However, silicon’s relatively weak electro-optic effects result in modulators with a significant footprint and thermo-optic tuning devices that require high power consumption, which are substantial impediments for very large-scale integration in silicon photonics. Microelectromechanical systems (MEMS) technology can enhance silicon photonics with building blocks that are compact, low-loss, broadband, fast and require very low power consumption. Here, we introduce a silicon photonic MEMS platform consisting of high-performance nano-opto-electromechanical devices fully integrated alongside standard silicon photonics foundry components, with wafer-level sealing for long-term reliability, flip-chip bonding to redistribution interposers, and fibre-array attachment for high port count optical and electrical interfacing. Our experimental demonstration of fundamental silicon photonic MEMS circuit elements, including power couplers, phase shifters and wavelength-division multiplexing devices using standardized technology lifts previous impediments to enable scaling to very large photonic integrated circuits for applications in telecommunications, neuromorphic computing, sensing, programmable photonics, and quantum computing.

Enabling Perovskite Solar Cell Omnidirectional Light Utilizing Via Trapping Technology

AbstractPromising optoelectronic properties of perovskites make it a research hotspot for the scientific community. Previously many groups are working on optical optimization, interface modification, material screening, and energy level matching of perovskite solar cells (PSCs). Herein, PSCs compatible with nano‐structure and photonic crystal (NSPC) are designed theoretically by using the numerical simulation technology that gives better light trapping capability to the PSC devices. The physical model is composed of perovskite spheres based on TiO2 and PDMS with the nanostructure. The size parameters of the photovoltaic devices are optimized and the wide‐angle absorption characteristics of PSCs with NSPC structure are investigated. Simulation results verify the superior optical performance of the new PSCs with a maximum photocurrent of 25.77 mA cm−2, which is 2.17 mA cm−2 higher than that of the conventional flat structured PSCs (23.60 mA cm−2). The results of the wide‐angle study demonstrate that the novel PSCs have omnidirectional absorption of photons. To elucidate the light‐trapping mechanism of the novel PSCs, the electric and magnetic field distributions of different structural PSCs are analyzed. The physical model the authors establish provides a solid theoretical basis for the research and development of PSCs with ultra‐low surface reflection loss and ultra‐high performance.

One-dimensional grating coupler on lithium-niobate-on-insulator for high-efficiency and polarization-independent coupling.

A metal-based one-dimensional grating coupler on an x-cut lithium-niobate-on-insulator wafer structure for a polarization-independent fiber interface is designed and demonstrated. By using a metal-based plasmonic mode, the diffractive angle for the two polarized modes in the lithium niobate ridge waveguide can be tuned to be the same. The polarization dependence of the grating coupler therefore can be effectively reduced. The fabricated device exhibits -3.56-dB and -4.08-dB peak coupling losses per coupler at 1573 nm for the TE and TM modes, respectively. The polarization-dependent losses are less than 0.69 dB in a 44-nm wavelength range. The demonstrated grating coupler can serve as a polarization-independent optical fiber interface on lithium-niobate-on-insulator and facilitate on-chip polarization diversity applications.

Optical Protective Window Design and Material Selection Issues in the Multi-Sensor Electro-Optical Surveillance Systems.

Multi-sensor imaging systems have a very important role and wide applications in surveillance and security systems. In many applications, it is necessary to use an optical protective window as an optical interface connecting the imaging sensor and object of interest's space; meanwhile an imaging sensor is mounted in a protective enclosure, providing separation from environmental conditions. Optical windows are often used in various optical and electro-optical systems, fulfilling different sometimes very unusual tasks. There are lots of examples in the literature that define optical window design for targeted applications. Through analysis of the various effects that follow optical window application in connection with imaging systems, we have suggested a simplified methodology and practical recommendation for how to define optical protective window specifications in multi-sensor imaging systems, using a system engineering approach. In addition, we have provided initial set of data and simplified calculation tools that can be used in initial analysis to provide proper window material selection and definition of the specifications of optical protective windows in multi-sensor systems. It is shown that although the optical window design seems as a simple task, it requires serious multidisciplinary approach.

Laser Cooling of Nuclear Magnons.

The initialization of nuclear spin to its ground state is challenging due to its small energy scale compared with thermal energy, even at cryogenic temperature. In this Letter, we propose an optonuclear quadrupolar effect, whereby two-color optical photons can efficiently interact with nuclear spins. Leveraging such an optical interface, we demonstrate that nuclear magnons, the collective excitations of nuclear spin ensemble, can be cooled down optically. Under feasible experimental conditions, laser cooling can suppress the population and entropy of nuclear magnons by more than 2 orders of magnitude, which could facilitate the application of nuclear spins in quantum information science.

A novel multi-anode MCP-PMT with Cherenkov radiator window

With the proposal of the road map of Time-of-Flight positron emission tomography (TOF-PET) with a Coincidence Time Resolution (CTR) of 10 ps by Paul Lecoq et al. in 2020, the technology based on TOF puts forward higher requirements on the performance of its core optical devices. In this manuscript, we developed a kind of Multi-Anode micro channel plate photomultiplier tube (MCP-PMT) based on Cherenkov radiator window. By using the Cherenkov radiator as the optical window of Multi-Anode MCP-PMT directly, the optical interface between the scintillator and the PMT window in conventional TOF-PET is eliminated, reducing light loss and further improve the time resolution of TOF-PET. The anode of this MCP-PMT can be split into a finely spaced array of collecting electrodes to achieve good positional sensitivity. In this paper, the single photon detection capability and time resolution of this kind of MCP-PMT are evaluated. The transit time spread (TTS) at single photon mode can reach 42.9 ps, and the TTS at multi photon mode is less than 10 ps. The CTR based on this kind of MCP-PMT is 156.7 ± 10.6 ps FWHM, which is equivalent to a position resolution of 23.5 ± 1.6 mm along a line of response (LOR). The performance uniformity of this kind MCP-PMT has also been calibrated.

Monolithically Integrated Active Passive Waveguide Array Fabricated on Thin Film Lithium Niobate Using a Single Continuous Photolithography Process

AbstractThis work demonstrates a robust low‐loss optical interface by tiling passive (i.e., without doping of active ions) thin film lithium niobate (TFLN) and active (i.e., doped with rare earth ions) TFLN substrates for monolithic integration of passive/active lithium niobate photonics. The tiled substrates composed of both active and passive areas allow for patterning the mask of the integrated active passive photonic device at once using a single continuous photolithography process. The interface loss of tiled substrate is measured as low as 0.26 dB. Thanks to the stability provided by this approach, a four‐channel waveguide amplifier is realized in a straightforward manner, which shows a net gain of 5 dB at a 1550‐nm wavelength and 8 dB at a 1530‐nm wavelength for each channel. The robust low‐loss optical interface for passive/active photonic integration will facilitate large‐scale high performance photonic devices that require on‐chip light sources and amplifiers.

Velocity-field characteristics of MgxZn1−xO/ZnO heterostructures

In this work, electron transport in MgxZn1−xO/ZnO heterostructures at room temperature is simulated by the ensemble Monte Carlo (EMC) method. Electron scattering mechanisms including acoustic deformation potential, piezoelectric acoustic phonon, polar optical phonon (POP), interface roughness (IFR), dislocation, electron escape (ESC) and capture (CPR) by optical phonons, and random alloy are considered in EMC. The electron drift velocity in MgxZn1−xO/ZnO heterostructures is calculated for various Mg mole fractions x (0.1–0.3) at electric fields up to 25 kV/cm. We find that no obvious velocity saturation occurs in the range of the electric field considered. The results show that ESC scattering is one of the main physical mechanisms limiting the drift velocity. On the other hand, the competition between IFR and intersubband POP scattering is found to play an important role in the change in electron drift velocity with the increasing Mg mole fractions.