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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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13 pages, 18109 KiB  
Article
Propagation of a Modified Complex Lorentz–Gaussian-Correlated Beam in a Marine Atmosphere
by Baoyin Sun, Han Lü, Dan Wu, Fei Wang and Yangjian Cai
Photonics 2021, 8(3), 82; https://doi.org/10.3390/photonics8030082 - 19 Mar 2021
Cited by 8 | Viewed by 2305
Abstract
In this paper, we study the second-order statistics of a modified complex Lorentz–Gaussian-correlated (MCLGC) beam, which is a new type of partially coherent beam capable of producing an Airy-like intensity pattern in the far field, propagation through marine atmospheric turbulence. The propagation formula [...] Read more.
In this paper, we study the second-order statistics of a modified complex Lorentz–Gaussian-correlated (MCLGC) beam, which is a new type of partially coherent beam capable of producing an Airy-like intensity pattern in the far field, propagation through marine atmospheric turbulence. The propagation formula of spectral density is derived by the extended Huygens–Fresnel integral, which could explicitly indicate the interaction of turbulence on the beams’ spectral density under propagation. The influences of the structure constant of the turbulence, initial coherence width and wavelength on the spectral density are investigated in detail through numerical examples. In addition, analytical expressions for the r.m.s beam width, divergence angle and M2 factor of the MCLGC beam in the marine turbulence are also derived with the help of the Wigner distribution function. The results reveal that the beam spreads much faster, and the M2 factor deteriorates severely with the increase of the structure constant and the decrease of the inner scale size, whereas the outer scale size has little effect on these two quantities. Full article
(This article belongs to the Special Issue Structured Light Coherence)
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14 pages, 1744 KiB  
Article
Optical Machine Learning Using Time-Lens Deep Neural NetWorks
by Luhe Zhang, Caiyun Li, Jiangyong He, Yange Liu, Jian Zhao, Huiyi Guo, Longfei Zhu, Mengjie Zhou, Kaiyan Zhu, Congcong Liu and Zhi Wang
Photonics 2021, 8(3), 78; https://doi.org/10.3390/photonics8030078 - 15 Mar 2021
Cited by 6 | Viewed by 5097
Abstract
As a high-throughput data analysis technique, photon time stretching (PTS) is widely used in the monitoring of rare events such as cancer cells, rough waves, and the study of electronic and optical transient dynamics. The PTS technology relies on high-speed data collection, and [...] Read more.
As a high-throughput data analysis technique, photon time stretching (PTS) is widely used in the monitoring of rare events such as cancer cells, rough waves, and the study of electronic and optical transient dynamics. The PTS technology relies on high-speed data collection, and the large amount of data generated poses a challenge to data storage and real-time processing. Therefore, how to use compatible optical methods to filter and process data in advance is particularly important. The time-lens proposed, based on the duality of time and space as an important data processing method derived from PTS, achieves imaging of time signals by controlling the phase information of the timing signals. In this paper, an optical neural network based on the time-lens (TL-ONN) is proposed, which applies the time-lens to the layer algorithm of the neural network to realize the forward transmission of one-dimensional data. The recognition function of this optical neural network for speech information is verified by simulation, and the test recognition accuracy reaches 95.35%. This architecture can be applied to feature extraction and classification, and is expected to be a breakthrough in detecting rare events such as cancer cell identification and screening. Full article
(This article belongs to the Special Issue Advanced Technique and Future Perspective for Next Generation Optical Fiber Communications)
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16 pages, 2849 KiB  
Article
Engineering of TiO2 or ZnO—Graphene Oxide Nanoheterojunctions for Hybrid Solar Cells Devices
by Duarte Carreira, Paulo A. Ribeiro, Maria Raposo and Susana Sério
Photonics 2021, 8(3), 75; https://doi.org/10.3390/photonics8030075 - 12 Mar 2021
Cited by 7 | Viewed by 3246
Abstract
It is currently of huge importance to find alternatives to fossil fuels to produce clean energy and to ensure the energy demands of modern society. In the present work, two types of hybrid solar cell devices were developed and characterized. The photoactive layers [...] Read more.
It is currently of huge importance to find alternatives to fossil fuels to produce clean energy and to ensure the energy demands of modern society. In the present work, two types of hybrid solar cell devices were developed and characterized. The photoactive layers of the hybrid heterojunctions comprise poly (allylamine chloride) (PAH) and graphene oxide (GO) and TiO2 or ZnO films, which were deposited using the layer-by-layer technique and DC-reactive magnetron sputtering, respectively, onto fluorine-doped tin oxide (FTO)-coated glass substrates. Scanning electron microscopy evidenced a homogeneous inorganic layer, the surface morphology of which was dependent on the number of organic bilayers. The electrical characterization pointed out that FTO/(PAH/GO)50/TiO2/Al, FTO/(PAH/GO)30/ZnO/Al, and FTO/(PAH/GO)50/ZnO/Al architectures were the only ones to exhibit a diode behavior, and the last one experienced a decrease in current in a low-humidity environment. The (PAH/GO)20 impedance spectroscopy study further revealed the typical impedance of a parallel RC circuit for a dry environment, whereas in a humid environment, it approached the impedance of a series of three parallel RC circuits, indicating that water and oxygen contribute to other conduction processes. Finally, the achieved devices should be encapsulated to work successfully as solar cells. Full article
(This article belongs to the Special Issue Photonics, Optics and Laser Technology)
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6 pages, 1061 KiB  
Article
Computational Modeling and Simulation to Increase Laser Shooting Accuracy of Autonomous LEO Trackers
by Jose M. Gambi, Maria L. Garcia del Pino, Jonathan Mosser and Ewa B. Weinmüller
Photonics 2021, 8(2), 55; https://doi.org/10.3390/photonics8020055 - 18 Feb 2021
Cited by 4 | Viewed by 2101
Abstract
In this paper, we introduce a computational procedure that enables autonomous LEO laser trackers endowed with INSs to increase the current accuracy when shooting at middle distant medium-size LEO debris targets. The code is designed for the trackers to throw the targets into [...] Read more.
In this paper, we introduce a computational procedure that enables autonomous LEO laser trackers endowed with INSs to increase the current accuracy when shooting at middle distant medium-size LEO debris targets. The code is designed for the trackers to throw the targets into the atmosphere by means of ablations. In case that the targets are eclipsed to the trackers by the Earth, the motions of the trackers and targets are modeled by equations that contain post-Newtonian terms accounting for the curvature of space. Otherwise, when the approaching targets become visible for the trackers, we additionally use more accurate equations, which allow to account for the local bending of the laser beams aimed at the targets. We observe that under certain circumstances the correct shooting configurations that allow to safely and efficiently shoot down the targets, differ from the current estimations by distances that may be larger than the size of many targets. In short, this procedure enables to estimate the optimal shooting instants for any middle distant medium-size LEO debris target. Full article
(This article belongs to the Special Issue Laser Interaction with Materials)
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14 pages, 4887 KiB  
Article
Mie Resonance Engineering in Two Disks
by Evgeny Bulgakov, Konstantin Pichugin and Almas Sadreev
Photonics 2021, 8(2), 49; https://doi.org/10.3390/photonics8020049 - 13 Feb 2021
Cited by 13 | Viewed by 3401
Abstract
Recently the recipes to achieve the high-Q subwavelength resonances in an isolated dielectric disk have been reported based on avoided crossing (anticrossing) of the TE resonances under variation of the aspect ratio of the disk. In a silicon disk that recipe gives an [...] Read more.
Recently the recipes to achieve the high-Q subwavelength resonances in an isolated dielectric disk have been reported based on avoided crossing (anticrossing) of the TE resonances under variation of the aspect ratio of the disk. In a silicon disk that recipe gives an enhancement of the Q factor by one order of magnitude. In the present paper we present the approach based on engineering of the spherical Mie resonances with high orbital index in two coaxial disks by two-fold avoided crossing of the resonant modes of the disks. At the first step we select the resonant modes of single disk which are degenerate because of the opposite symmetry. Approaching of the second disk removes this degeneracy because of interaction between the disks. As a result at certain distances we realize the hybridized anti-bonding resonant modes whose morphology becomes close to the spherical Mie resonant mode with high orbital index. Respectively the Q factor of the anti-bonding resonant mode can be enhanced by three orders of magnitude compared to the case of single disk. Full article
(This article belongs to the Section Optoelectronics and Optical Materials)
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48 pages, 3859 KiB  
Article
Accurate Power-Efficient Format-Scalable Multi-Parallel Optical Digital-to-Analogue Conversion
by Moshe Nazarathy and Ioannis Tomkos
Photonics 2021, 8(2), 38; https://doi.org/10.3390/photonics8020038 - 04 Feb 2021
Cited by 8 | Viewed by 3508
Abstract
In optical transmitters generating multi-level constellations, optical modulators are preceded by Electronic Digital-to-Analog-Converters (eDAC). It is advantageous to use eDAC-free Optical Analog to Digital Converters (oDAC) to directly convert digital bitstreams into multilevel PAM/QAM optical signals. State-of-the-art oDACs are based on Segmented Mach-Zehnder-Modulators [...] Read more.
In optical transmitters generating multi-level constellations, optical modulators are preceded by Electronic Digital-to-Analog-Converters (eDAC). It is advantageous to use eDAC-free Optical Analog to Digital Converters (oDAC) to directly convert digital bitstreams into multilevel PAM/QAM optical signals. State-of-the-art oDACs are based on Segmented Mach-Zehnder-Modulators (SEMZM) using multiple modulation segments strung along the MZM waveguides to serially accumulate binary-modulated optical phases. Here we aim to assess performance limits of the Serial oDACs (SEMZM) and introduce an alternative improved Multi-Parallel oDAC (MPoDAC) architecture, in particular based on arraying multiple binary-driven MZMs in parallel: Multi-parallel MZM (MPMZM) oDAC. We develop generic methodologies of oDAC specification and optimization encompassing both SEMZM and MPMZM options in Direct-Detection (DD) and Coherent-Detection (COH) implementations. We quantify and compare intrinsic performance limits of the various serial/parallel DD/COH subclasses for general constellation orders, comparing with the scant prior-work on the multi-parallel option. A key finding: COH-MPMZM is the only class synthesizing ‘perfect’ (equi-spaced max-full-scale) constellations while maximizing energy-efficiency-SEMZM/MPMZM for DD are less accurate when maximal energy-efficiency is required. In particular, we introduce multiple variants of PAM4|8 DD and QAM16|64 COH MPMZMs, working out their accuracy vs. energy-efficiency-and-complexity tradeoffs, establishing their format-reconfigurability (format-flexible switching of constellation order and/or DD/COH). Full article
(This article belongs to the Special Issue Reconfigurable Photonic Interconnects)
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9 pages, 3087 KiB  
Review
Inverted p-down Design for High-Speed Photodetectors
by Masahiro Nada, Fumito Nakajima, Toshihide Yoshimatsu, Yasuhiko Nakanishi, Atsushi Kanda, Takahiko Shindo, Shoko Tatsumi, Hideaki Matsuzaki and Kimikazu Sano
Photonics 2021, 8(2), 39; https://doi.org/10.3390/photonics8020039 - 04 Feb 2021
Cited by 12 | Viewed by 3373
Abstract
We discuss the structural consideration of high-speed photodetectors used for optical communications, focusing on vertical illumination photodetectors suitable for device fabrication and optical coupling. We fabricate an avalanche photodiode that can handle 100-Gbit/s four-level pulse-amplitude modulation (50 Gbaud) signals, and pin photodiodes for [...] Read more.
We discuss the structural consideration of high-speed photodetectors used for optical communications, focusing on vertical illumination photodetectors suitable for device fabrication and optical coupling. We fabricate an avalanche photodiode that can handle 100-Gbit/s four-level pulse-amplitude modulation (50 Gbaud) signals, and pin photodiodes for 100-Gbaud operation; both are fabricated with our unique inverted p-side down (p-down) design. Full article
(This article belongs to the Special Issue Advanced Ultra High Speed Optoelectronic Devices)
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14 pages, 24671 KiB  
Article
Topological-Insulator-Based Gap-Surface Plasmon Metasurfaces
by Andreas Aigner, Stefan A. Maier and Haoran Ren
Photonics 2021, 8(2), 40; https://doi.org/10.3390/photonics8020040 - 04 Feb 2021
Cited by 3 | Viewed by 5219
Abstract
Topological insulators (TIs) have unique highly conducting symmetry-protected surface states while the bulk is insulating, making them attractive for various applications in condensed matter physics. Recently, topological insulator materials have been tentatively applied for both near- and far-field wavefront manipulation of electromagnetic waves, [...] Read more.
Topological insulators (TIs) have unique highly conducting symmetry-protected surface states while the bulk is insulating, making them attractive for various applications in condensed matter physics. Recently, topological insulator materials have been tentatively applied for both near- and far-field wavefront manipulation of electromagnetic waves, yielding superior plasmonic properties in the ultraviolet (UV)-to-visible wavelength range. However, previous reports have only demonstrated inefficient wavefront control based on binary metasurfaces that were digitalized on a TI thin film or non-directional surface plasmon polariton (SPP) excitation. Here, we numerically demonstrated the plasmonic capabilities of the TI Bi2Te3 as a material for gap–surface plasmon (GSP) metasurfaces. By employing the principle of the geometric phase, a far-field beam-steering metasurface was designed for the visible spectrum, yielding a cross-polarization efficiency of 34% at 500 nm while suppressing the co-polarization to 0.08%. Furthermore, a birefringent GSP metasurface design was studied and found to be capable of directionally exciting SPPs depending on the incident polarization. Our work forms the basis for accurately controlling the far- and near-field responses of TI-based GSP metasurfaces in the visible spectral range. Full article
(This article belongs to the Special Issue Plasmonic Metasurfaces)
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14 pages, 5322 KiB  
Article
Proposal of Highly Efficient Quantum Well Microring Resonator-Loaded Optical Phase Modulator Integrated with Antenna-Coupled Electrodes for Radio-over-Fiber
by Hiro Kamada and Taro Arakawa
Photonics 2021, 8(2), 37; https://doi.org/10.3390/photonics8020037 - 03 Feb 2021
Cited by 3 | Viewed by 3894
Abstract
Radio-over-fiber (RoF) technology for low-loss, high-speed millimeter-wave transmission using optical fibers has been attracting attention. We propose a highly efficient microring resonator (MRR)-loaded InGaAs/InAlAs multiple-quantum-well (MQW) phase modulator with an antenna coupled electrode (ACE) for 60 GHz RoF systems, and its modulation characteristics [...] Read more.
Radio-over-fiber (RoF) technology for low-loss, high-speed millimeter-wave transmission using optical fibers has been attracting attention. We propose a highly efficient microring resonator (MRR)-loaded InGaAs/InAlAs multiple-quantum-well (MQW) phase modulator with an antenna coupled electrode (ACE) for 60 GHz RoF systems, and its modulation characteristics are theoretically discussed. This modulator is able to directly convert wireless millimeter-wave (MMW) signals into optical signals without an external power supply. The MRR used in the waveguide structure increases the optical phase change obtained by the unique quantum confinement Stark effect in the MQW through phase enhancement effects, while the ACE based on a coupled microstrip resonant electrode applies a strong standing wave electric field to the waveguide. The proposed modulator is expected to provide tens of times higher phase modulation efficiency than a conventional gap-embedded planar antenna-integrated modulator. Full article
(This article belongs to the Special Issue Radio over Fiber)
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6 pages, 3875 KiB  
Communication
Effect of Si Doping on the Performance of GaN Schottky Barrier Ultraviolet Photodetector Grown on Si Substrate
by Fangzhou Liang, Wen Chen, Meixin Feng, Yingnan Huang, Jianxun Liu, Xiujian Sun, Xiaoning Zhan, Qian Sun, Qibao Wu and Hui Yang
Photonics 2021, 8(2), 28; https://doi.org/10.3390/photonics8020028 - 23 Jan 2021
Cited by 8 | Viewed by 2791
Abstract
GaN Schottky barrier ultraviolet photodetectors with unintentionally doped GaN and lightly Si-doped n−-GaN absorption layers were successfully fabricated, respectively. The high-quality GaN films on the Si substrate both have a fairly low dislocation density and point defect concentration. More importantly, the [...] Read more.
GaN Schottky barrier ultraviolet photodetectors with unintentionally doped GaN and lightly Si-doped n−-GaN absorption layers were successfully fabricated, respectively. The high-quality GaN films on the Si substrate both have a fairly low dislocation density and point defect concentration. More importantly, the effect of Si doping on the performance of the GaN-on-Si Schottky barrier ultraviolet photodetector was studied. It was found that light Si doping in the absorption layer can significantly increase the responsivity under reverse bias, which might be attributed to the persistent photoconductivity that originates from the lowering of the Schottky barrier height. In addition, the devices with unintentionally doped GaN demonstrated a relatively high-speed photo response. We briefly studied the mechanism of changes in Schottky barrier, dark current and the characteristic of response time. Full article
(This article belongs to the Special Issue Wide Bandgap Semiconductor Photonic Devices)
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21 pages, 6504 KiB  
Article
Image Deconvolution with Hybrid Reweighted Adaptive Total Variation (HRATV) for Optoacoustic Tomography
by Chen Yang, Yang Jiao, Xiaohua Jian and Yaoyao Cui
Photonics 2021, 8(2), 25; https://doi.org/10.3390/photonics8020025 - 20 Jan 2021
Cited by 4 | Viewed by 2634
Abstract
Optoacoustic tomography (OAT) is a hybrid biomedical imaging modality that usually employs a transducer array to detect laser-generated ultrasonic signals. The reconstructed image suffers low contrast and degraded resolution due to the limited bandwidth and the spatial directivity of the transducer element. Here, [...] Read more.
Optoacoustic tomography (OAT) is a hybrid biomedical imaging modality that usually employs a transducer array to detect laser-generated ultrasonic signals. The reconstructed image suffers low contrast and degraded resolution due to the limited bandwidth and the spatial directivity of the transducer element. Here, we introduce a modified image deconvolution method with a hybrid reweighted adaptive total variation tailored to improve the image quality of OAT. The effectiveness and the parameter dependency of the proposed method are verified on standard test images. The performance of the proposed method in OAT is then characterized on both simulated phantoms and in vivo mice experiments, which demonstrates that the modified deconvolution algorithm is able to restore the sharp edges and fine details in OAT simultaneously. The signal-to-noise ratios (SNRs) of the target structures in mouse liver and brain were improved by 4.90 and 12.69 dB, respectively. We also investigated the feasibility of using Fourier ring correlation (FRC) as an indicator of the image quality to monitor the deconvolution progress in OAT. Based on the experimental results, a practical guide for image deconvolution in OAT was summarized. We anticipate that the proposed method will be a promising post-processing tool to enhance the visualization of micro-structures in OAT. Full article
(This article belongs to the Section Biophotonics and Biomedical Optics)
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20 pages, 92392 KiB  
Article
Spiral Caustics of Vortex Beams
by Viktor A. Soifer, Sergey I. Kharitonov, Svetlana N. Khonina, Yurii S. Strelkov and Alexey P. Porfirev
Photonics 2021, 8(1), 24; https://doi.org/10.3390/photonics8010024 - 19 Jan 2021
Cited by 18 | Viewed by 3810
Abstract
We discuss the nonparaxial focusing of laser light into a three-dimensional (3D) spiral distribution. For calculating the tangential and normal components of the electromagnetic field on a preset curved surface we propose an asymptotic method, using which we derive equations for calculating stationary [...] Read more.
We discuss the nonparaxial focusing of laser light into a three-dimensional (3D) spiral distribution. For calculating the tangential and normal components of the electromagnetic field on a preset curved surface we propose an asymptotic method, using which we derive equations for calculating stationary points and asymptotic relations for the electromagnetic field components in the form of one-dimensional (1D) integrals over a radial component. The results obtained through the asymptotic approach and the direct calculation of the Kirchhoff integral are identical. For a particular case of focusing into a ring, an analytical relation for stationary points is derived. Based on the electromagnetic theory, we design and numerically model the performance of diffractive optical elements (DOEs) to generate field distributions shaped as two-dimensional (2D) and 3D light spirals with the variable angular momentum. We reveal that under certain conditions, there is an effect of splitting the longitudinal electromagnetic field component. Experimental results obtained with the use of a spatial light modulator are in good agreement with the modeling results. Full article
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30 pages, 8836 KiB  
Review
Diagnosis of Glioma Molecular Markers by Terahertz Technologies
by Olga Cherkasova, Yan Peng, Maria Konnikova, Yuri Kistenev, Chenjun Shi, Denis Vrazhnov, Oleg Shevelev, Evgeny Zavjalov, Sergei Kuznetsov and Alexander Shkurinov
Photonics 2021, 8(1), 22; https://doi.org/10.3390/photonics8010022 - 16 Jan 2021
Cited by 25 | Viewed by 6243
Abstract
This review considers glioma molecular markers in brain tissues and body fluids, shows the pathways of their formation, and describes traditional methods of analysis. The most important optical properties of glioma markers in the terahertz (THz) frequency range are also presented. New metamaterial-based [...] Read more.
This review considers glioma molecular markers in brain tissues and body fluids, shows the pathways of their formation, and describes traditional methods of analysis. The most important optical properties of glioma markers in the terahertz (THz) frequency range are also presented. New metamaterial-based technologies for molecular marker detection at THz frequencies are discussed. A variety of machine learning methods, which allow the marker detection sensitivity and differentiation of healthy and tumor tissues to be improved with the aid of THz tools, are considered. The actual results on the application of THz techniques in the intraoperative diagnosis of brain gliomas are shown. THz technologies’ potential in molecular marker detection and defining the boundaries of the glioma’s tissue is discussed. Full article
(This article belongs to the Special Issue Terahertz Biophotonics)
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15 pages, 3866 KiB  
Article
Neural Network DPD for Aggrandizing SM-VCSEL-SSMF-Based Radio over Fiber Link Performance
by Muhammad Usman Hadi, Muhammad Awais, Mohsin Raza, Kiran Khurshid and Hyun Jung
Photonics 2021, 8(1), 19; https://doi.org/10.3390/photonics8010019 - 14 Jan 2021
Cited by 26 | Viewed by 5160
Abstract
This paper demonstrates an unprecedented novel neural network (NN)-based digital predistortion (DPD) solution to overcome the signal impairments and nonlinearities in Analog Optical fronthauls using radio over fiber (RoF) systems. DPD is realized with Volterra-based procedures that utilize indirect learning architecture (ILA) and [...] Read more.
This paper demonstrates an unprecedented novel neural network (NN)-based digital predistortion (DPD) solution to overcome the signal impairments and nonlinearities in Analog Optical fronthauls using radio over fiber (RoF) systems. DPD is realized with Volterra-based procedures that utilize indirect learning architecture (ILA) and direct learning architecture (DLA) that becomes quite complex. The proposed method using NNs evades issues associated with ILA and utilizes an NN to first model the RoF link and then trains an NN-based predistorter by backpropagating through the RoF NN model. Furthermore, the experimental evaluation is carried out for Long Term Evolution 20 MHz 256 quadraturre amplitude modulation (QAM) modulation signal using an 850 nm Single Mode VCSEL and Standard Single Mode Fiber to establish a comparison between the NN-based RoF link and Volterra-based Memory Polynomial and Generalized Memory Polynomial using ILA. The efficacy of the DPD is examined by reporting the Adjacent Channel Power Ratio and Error Vector Magnitude. The experimental findings imply that NN-DPD convincingly learns the RoF nonlinearities which may not suit a Volterra-based model, and hence may offer a favorable trade-off in terms of computational overhead and DPD performance. Full article
(This article belongs to the Special Issue Radio over Fiber)
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9 pages, 2006 KiB  
Communication
InP-Components for 100 GBaud Optical Data Center Communication
by Patrick Runge, Tobias Beckerwerth, Ute Troppenz, Marko Gruner, Hendrik Boerma, Martin Möhrle and Martin Schell
Photonics 2021, 8(1), 18; https://doi.org/10.3390/photonics8010018 - 13 Jan 2021
Cited by 8 | Viewed by 4606
Abstract
Externally modulated DFB lasers (EML) and vertically illuminated photodetectors are presented. Because of their excellent high-speed behavior and operation wavelength of 1310 nm, the devices are of interest for intra-data center communication. Since the EML and the photodetector chips are compatible with current [...] Read more.
Externally modulated DFB lasers (EML) and vertically illuminated photodetectors are presented. Because of their excellent high-speed behavior and operation wavelength of 1310 nm, the devices are of interest for intra-data center communication. Since the EML and the photodetector chips are compatible with current systems, these devices are candidates for upgrading existing transceivers to higher baud rates. Therefore, a proof of concept for 100 GBaud data transmission with the presented components is demonstrated. Even without predistortion, the experiments show clearly open eye diagrams. Full article
(This article belongs to the Special Issue Advanced Ultra High Speed Optoelectronic Devices)
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8 pages, 3504 KiB  
Article
Study of Phase Transition in MOCVD Grown Ga2O3 from κ to β Phase by Ex Situ and In Situ Annealing
by Junhee Lee, Honghyuk Kim, Lakshay Gautam, Kun He, Xiaobing Hu, Vinayak P. Dravid and Manijeh Razeghi
Photonics 2021, 8(1), 17; https://doi.org/10.3390/photonics8010017 - 13 Jan 2021
Cited by 19 | Viewed by 4583
Abstract
We report the post-growth thermal annealing and the subsequent phase transition of Ga2O3 grown on c-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD). We demonstrated the post-growth thermal annealing at temperatures higher than 900 °C under N2 [...] Read more.
We report the post-growth thermal annealing and the subsequent phase transition of Ga2O3 grown on c-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD). We demonstrated the post-growth thermal annealing at temperatures higher than 900 °C under N2 ambience, by either in situ or ex situ thermal annealing, can induce phase transition from nominally metastable κ- to thermodynamically stable β-phase. This was analyzed by structural characterizations such as high-resolution scanning transmission electron microscopy and x-ray diffraction. The highly resistive as-grown Ga2O3 epitaxial layer becomes conductive after annealing at 1000 °C. Furthermore, we demonstrate that in situ annealing can lead to a crack-free β-Ga2O3. Full article
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19 pages, 3253 KiB  
Review
Recent Advances in High Speed Photodetectors for eSWIR/MWIR/LWIR Applications
by Baile Chen, Yaojiang Chen and Zhuo Deng
Photonics 2021, 8(1), 14; https://doi.org/10.3390/photonics8010014 - 11 Jan 2021
Cited by 27 | Viewed by 6582
Abstract
High speed photodetectors operating at a telecommunication band (from 1260 to 1625 nm) have been well studied with the development of an optical fiber communication system. Recent innovations of photonic systems have raised new requirements on the bandwidth of photodetectors with cutoff wavelengths [...] Read more.
High speed photodetectors operating at a telecommunication band (from 1260 to 1625 nm) have been well studied with the development of an optical fiber communication system. Recent innovations of photonic systems have raised new requirements on the bandwidth of photodetectors with cutoff wavelengths from extended short wavelength infrared (eSWIR) to long wavelength infrared (LWIR). However, the frequency response performance of photodetectors in these longer wavelength bands is less studied, and the performances of the current high-speed photodetectors in these bands are still not comparable with those in the telecommunication band. In this paper, technical routes to achieve high response speed performance of photodetectors in the extended short wavelength infrared/mid wavelength infrared/long wavelength infrared (eSWIR/MWIR/LWIR) band are discussed, and the state-of-the-art performances are reviewed. Full article
(This article belongs to the Special Issue Advanced Ultra High Speed Optoelectronic Devices)
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14 pages, 11793 KiB  
Article
Function of Porous Carbon Electrode during the Fabrication of Multiporous-Layered-Electrode Perovskite Solar Cells
by Ryuki Tsuji, Dmitry Bogachuk, David Martineau, Lukas Wagner, Eiji Kobayashi, Ryoto Funayama, Yoshiaki Matsuo, Simone Mastroianni, Andreas Hinsch and Seigo Ito
Photonics 2020, 7(4), 133; https://doi.org/10.3390/photonics7040133 - 18 Dec 2020
Cited by 10 | Viewed by 3796
Abstract
We demonstrate the effect of sheet conductivity and infiltration using the example of two graphite types, showing that, in general, the graphite type is very important. Amorphous and pyrolytic graphite were applied to carbon electrodes in fully printable carbon-based multiporous-layered-electrode perovskite solar cells [...] Read more.
We demonstrate the effect of sheet conductivity and infiltration using the example of two graphite types, showing that, in general, the graphite type is very important. Amorphous and pyrolytic graphite were applied to carbon electrodes in fully printable carbon-based multiporous-layered-electrode perovskite solar cells (MPLE-PSCs): <glass/F-doped SnO2/compact-TiO2/porous-TiO2+perovskite/porous-ZrO2+perovskite/porous-carbon+perovskite>. The power conversion efficiency (PCE) using amorphous graphite-based carbon (AGC) electrode was only 5.97% due to the low short-circuit photocurrent density (Jsc) value, which was due to the low incident photon-to-current efficiency (IPCE) in the short wavelength region caused by the poor perovskite filling into the porous TiO2-ZrO2 layers. Conversely, using pyrolytic graphite-based carbon (PGC) electrode, Jsc, open-circuit photovoltage (Voc), fill factors (FF), and PCE values of 21.09 mA cm−2, 0.952 V, 0.670, and 13.45%, respectively, were achieved in the champion device. PGC had poorer wettability and a small specific surface area as compared with AGC, but it had better permeability of the perovskite precursor solution into the porous TiO2/ZrO2 layers, and therefore a denser filling and crystallization of the perovskite within the porous TiO2/ZrO2 layers than AGC. It is confirmed that the permeability of the precursor solution depends on the morphology and structure of the graphite employed in the carbon electrode. Full article
(This article belongs to the Special Issue Photovoltaic Materials and Devices)
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11 pages, 3519 KiB  
Article
Electromagnetic Scattering Analysis of SHDB Objects Using Surface Integral Equation Method
by Beibei Kong, Pasi Ylä-Oijala and Ari Sihvola
Photonics 2020, 7(4), 134; https://doi.org/10.3390/photonics7040134 - 18 Dec 2020
Cited by 1 | Viewed by 2547
Abstract
A surface integral equation (SIE) method is applied in order to analyze electromagnetic scattering by bounded arbitrarily shaped three-dimensional objects with the SHDB boundary condition. SHDB is a generalization of SH (Soft-and-Hard) and DB boundary conditions (at the DB boundary, the normal components [...] Read more.
A surface integral equation (SIE) method is applied in order to analyze electromagnetic scattering by bounded arbitrarily shaped three-dimensional objects with the SHDB boundary condition. SHDB is a generalization of SH (Soft-and-Hard) and DB boundary conditions (at the DB boundary, the normal components of the D and B flux densities vanish). The SHDB boundary condition is a general linear boundary condition that contains two scalar equations that involve both the tangential and normal components of the electromagnetic fields. The multiplication of these scalar equations with two orthogonal vectors transforms them into a vector form that can be combined with the tangential field integral equations. The resulting equations are discretized and converted to a matrix equation with standard method of moments (MoM). As an example of use of the method, we investigate scattering by an SHDB circular disk and demonstrate that the SHDB boundary allows for an efficient way to control the polarization of the wave that is reflected from the surface. We also discuss perspectives into different levels of materialization and realization of SHDB boundaries. Full article
(This article belongs to the Special Issue Advances in Complex Media Electromagnetics)
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13 pages, 2735 KiB  
Article
Wavelength-Dependent Features of Photoelectron Spectra from Nanotip Photoemission
by Xiao-Yuan Wu, Hao Liang, Marcelo F. Ciappina and Liang-You Peng
Photonics 2020, 7(4), 129; https://doi.org/10.3390/photonics7040129 - 11 Dec 2020
Cited by 5 | Viewed by 3937
Abstract
If a metal nanotip is irradiated with the light of a wavelength much larger than the nanotip’s radius of curvature, optical near-fields become excited. These fields are responsible for distinct strong-field electron dynamics, due to both the field enhancement and spatial localization. By [...] Read more.
If a metal nanotip is irradiated with the light of a wavelength much larger than the nanotip’s radius of curvature, optical near-fields become excited. These fields are responsible for distinct strong-field electron dynamics, due to both the field enhancement and spatial localization. By classical trajectory, Monte Carlo (CTMC) simulation, and the integration of the time-dependent Schrödinger equation (TDSE), we find that the photoelectron spectra for nanotip strong-field photoemission, irradiated by mid-infrared laser pulses, present distinctive wavelength-dependent features, especially in the mid- to high-electron energy regions, which are different from the well known ones. By extracting the electron trajectories from the CTMC simulation, we investigate these particular wavelength-dependent features. Our theoretical results contribute to understanding the photoemission and electron dynamics at nanostructures, and pave new pathways for designing high-energy nanometer-sized ultrafast electron sources. Full article
(This article belongs to the Special Issue Strong Light Fields Coupled with Plasmonic Nano-Structures)
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18 pages, 6403 KiB  
Article
Scaling of Beam Collective Effects with Bunch Charge in the CompactLight Free-Electron Laser
by Simone Di Mitri, Andrea Latina, Marcus Aicheler, Avni Aksoy, David Alesini, Graeme Burt, Alejandro Castilla, Jim Clarke, Hector Mauricio Castañeda Cortés, Michele Croia, Gerardo D’Auria, Marco Diomede, David Dunning, Massimo Ferrario, Alessandro Gallo, Anna Giribono, Vitaliy Goryashko, Andrea Mostacci, Federico Nguyen, Regina Rochow, Jessica Scifo, Bruno Spataro, Neil Thompson, Cristina Vaccarezza, Alessandro Vannozzi, Xiaowei Wu and Walter Wuenschadd Show full author list remove Hide full author list
Photonics 2020, 7(4), 125; https://doi.org/10.3390/photonics7040125 - 04 Dec 2020
Cited by 4 | Viewed by 3440
Abstract
The CompactLight European consortium is designing a state-of-the-art X-ray free-electron laser driven by radiofrequency X-band technology. Rooted in experimental data on photo-injector performance in the recent literature, this study estimates analytically and numerically the performance of the CompactLight delivery system for bunch charges [...] Read more.
The CompactLight European consortium is designing a state-of-the-art X-ray free-electron laser driven by radiofrequency X-band technology. Rooted in experimental data on photo-injector performance in the recent literature, this study estimates analytically and numerically the performance of the CompactLight delivery system for bunch charges in the range 75–300 pC. Space-charge forces in the injector, linac transverse wakefield, and coherent synchrotron radiation in bunch compressors are all taken into account. The study confirms efficient lasing in the soft X-rays regime with pulse energies up to hundreds of microjoules at repetition rates as high as 1 kHz. Full article
(This article belongs to the Special Issue Photonics, Optics and Laser Technology)
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17 pages, 11347 KiB  
Article
Coherent Beam Combining Using an Internally Sensed Optical Phased Array of Frequency-Offset Phase Locked Lasers
by Lyle E. Roberts, Robert L. Ward, Craig Smith and Daniel A. Shaddock
Photonics 2020, 7(4), 118; https://doi.org/10.3390/photonics7040118 - 28 Nov 2020
Cited by 8 | Viewed by 3719
Abstract
Coherent beam combining can be used to scale optical power and enable mechanism-free beam steering using an optical phased array. Coherently combining multiple free-running lasers in a leader-follower laser configuration is challenging due to the need to measure and stabilize large and highly [...] Read more.
Coherent beam combining can be used to scale optical power and enable mechanism-free beam steering using an optical phased array. Coherently combining multiple free-running lasers in a leader-follower laser configuration is challenging due to the need to measure and stabilize large and highly dynamic phase differences between them. We present a scalable technique based on frequency-offset phase locking and digitally enhanced interferometry to clone the coherence of multiple lasers without the use of external sampling optics, which has the potential to support both coherent and spectral beam combining, and alleviates issues of voltage wrapping associated with actuating feedback control using electro-optic modulators. This technique was demonstrated experimentally using a tiled-aperture optical phased array in which the relative output phase of three free-running lasers was stabilized with an RMS output phase stability of λ/104. Full article
(This article belongs to the Special Issue Photonics, Optics and Laser Technology)
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10 pages, 334 KiB  
Article
Multiwavelength Frequency Modulated CW Ladar: The Effect of Refractive Index
by Mariano Barbieri, Deborah Katia Pallotti, Mario Siciliani de Cumis and Luigi Santamaria Amato
Photonics 2020, 7(4), 90; https://doi.org/10.3390/photonics7040090 - 08 Oct 2020
Cited by 3 | Viewed by 4784
Abstract
Frequency modulated continuous wave (FMCW) laser detection and ranging is a technique for absolute distance measurements with high performances in terms of resolution, non-ambiguity range, accuracy and fast detection. It is based on a simple experimental setup, thus resulting in cost restraint with [...] Read more.
Frequency modulated continuous wave (FMCW) laser detection and ranging is a technique for absolute distance measurements with high performances in terms of resolution, non-ambiguity range, accuracy and fast detection. It is based on a simple experimental setup, thus resulting in cost restraint with potential wide spread, not only limited to research institutions. The technique has been widely studied and improved both in terms of experimental setup by absolute reference or active stabilization and in terms of data analysis. Very recently a multi-wavelength approach has been exploited, demonstrating high precision and non ambiguity range. The variability of refractive index along the path was not taken into account with consequent degradation of range accuracy. In this work we developed a simple model able to take into account refractive index effect in multi-wavelength FMCW measurement. We performed a numerical simulation in different atmospheric conditions of temperature, pressure, humidity and CO2 concentration showing a net improvement of range accuracy when refractive index modeling is used. Full article
(This article belongs to the Special Issue Spectroscopy, Metrology and Quantum Technology for Space Science and Astrophysics)
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22 pages, 1693 KiB  
Article
A Metamaterial-Inspired Approach to Mitigating Radio Frequency Blackout When a Plasma Forms Around a Reentry Vehicle
by Bruce A. Webb and Richard W. Ziolkowski
Photonics 2020, 7(4), 88; https://doi.org/10.3390/photonics7040088 - 06 Oct 2020
Cited by 8 | Viewed by 3091
Abstract
Radio frequency (RF) blackout and attenuation have been observed during atmospheric reentry since the advent of space exploration. The effects range from severe attenuation to complete loss of communications and can last from 90 s to 10 min depending on the vehicle’s trajectory. [...] Read more.
Radio frequency (RF) blackout and attenuation have been observed during atmospheric reentry since the advent of space exploration. The effects range from severe attenuation to complete loss of communications and can last from 90 s to 10 min depending on the vehicle’s trajectory. This paper examines a way of using a metasurface to improve the performance of communications during reentry. The technique is viable at low plasma densities and matches a split-ring resonator (SRR)-based mu-negative (MNG) sheet to the epsilon-negative (ENG) plasma region. Considering the MNG metasurface as a window to the exterior of a reentry vehicle, its matched design yields high transmission of an electromagnetic plane wave through the resulting MNG-ENG metastructure into the region beyond it. A varactor-based SRR design facilitates tuning the MNG layer to ENG layers with different plasma densities. Both simple and Huygens dipole antennas beneath a matched metastructure are then employed to demonstrate the consequent realization of significant signal transmission through it into free space beyond the exterior ENG plasma layer. Full article
(This article belongs to the Special Issue Advances in Complex Media Electromagnetics)
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10 pages, 734 KiB  
Article
Tunable THz Pulses Generation in Non-Equilibrium Magnetized Plasma: The Role of Plasma Kinetics
by Anna V. Bogatskaya, Nelli E. Gnezdovskaia and Alexander M. Popov
Photonics 2020, 7(4), 82; https://doi.org/10.3390/photonics7040082 - 24 Sep 2020
Cited by 1 | Viewed by 2552
Abstract
In this paper the theoretical model to consider the influence of kinetic properties of nonequilibrium two-color plasma during the THz pulses generation in the presence of static magnetic field is developed. It is shown that applying a static magnetic field on a gas [...] Read more.
In this paper the theoretical model to consider the influence of kinetic properties of nonequilibrium two-color plasma during the THz pulses generation in the presence of static magnetic field is developed. It is shown that applying a static magnetic field on a gas along the direction of propagation of an ionizing two-color laser pulse allows one to produce two-frequency emissions in THz range with tunable central frequency and bandwidth, which are strongly dependent on electron velocity distribution function (EVDF) formed in the plasma as well as relations between collisional, plasma and cyclotron frequencies. Full article
(This article belongs to the Special Issue Photonics, Optics and Laser Technology)
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17 pages, 10058 KiB  
Article
Near- and Far-Field Excitation of Topological Plasmonic Metasurfaces
by Matthew Proctor, Xiaofei Xiao, Richard V. Craster, Stefan A. Maier, Vincenzo Giannini and Paloma Arroyo Huidobro
Photonics 2020, 7(4), 81; https://doi.org/10.3390/photonics7040081 - 24 Sep 2020
Cited by 9 | Viewed by 3641
Abstract
The breathing honeycomb lattice hosts a topologically non-trivial bulk phase due to the crystalline-symmetry of the system. Pseudospin-dependent edge states, which emerge at the interface between trivial and non-trivial regions, can be used for the directional propagation of energy. Using the plasmonic metasurface [...] Read more.
The breathing honeycomb lattice hosts a topologically non-trivial bulk phase due to the crystalline-symmetry of the system. Pseudospin-dependent edge states, which emerge at the interface between trivial and non-trivial regions, can be used for the directional propagation of energy. Using the plasmonic metasurface as an example system, we probe these states in the near- and far-field using a semi-analytical model. We provide the conditions under which directionality was observed and show that it is source position dependent. By probing with circularly-polarised magnetic dipoles out of the plane, we first characterise modes along the interface in terms of the enhancement of source emissions due to the metasurface. We then excite from the far-field with non-zero orbital angular momentum beams. The position-dependent directionality holds true for all classical wave systems with a breathing honeycomb lattice. Our results show that a metasurface in combination with a chiral two-dimensional material, could be used to guide light effectively on the nanoscale. Full article
(This article belongs to the Special Issue Plasmonic Metasurfaces)
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14 pages, 5446 KiB  
Article
Structural, Optical and Electrical Characterizations of Midwave Infrared Ga-Free Type-II InAs/InAsSb Superlattice Barrier Photodetector
by U. Zavala-Moran, M. Bouschet, J. P. Perez, R. Alchaar, S. Bernhardt, I. Ribet-Mohamed, F. de Anda-Salazar and P. Christol
Photonics 2020, 7(3), 76; https://doi.org/10.3390/photonics7030076 - 18 Sep 2020
Cited by 14 | Viewed by 4054
Abstract
In this paper, a full set of structural, optical and electrical characterizations performed on midwave infrared barrier detectors based on a Ga-free InAs/InAsSb type-II superlattice, grown by molecular beam epitaxy (MBE) on a GaSb substrate, are reported and analyzed. a Minority carrier lifetime [...] Read more.
In this paper, a full set of structural, optical and electrical characterizations performed on midwave infrared barrier detectors based on a Ga-free InAs/InAsSb type-II superlattice, grown by molecular beam epitaxy (MBE) on a GaSb substrate, are reported and analyzed. a Minority carrier lifetime value equal to 1 µs at 80 K, carried out on dedicated structure showing photoluminescence peak position at 4.9 µm, is extracted from a time resolved photoluminescence measurement. Dark current density as low as 3.2 × 10−5 A/cm2 at 150 K is reported on the corresponding device exhibiting a 50% cut-off wavelength around 5 µm. A performance analysis through normalized spectral response and dark current density-voltage characteristics was performed to determine both the operating bias and the different dark current regimes. Full article
(This article belongs to the Special Issue Photonics, Optics and Laser Technology)
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58 pages, 8781 KiB  
Review
The Interband Cascade Laser
by Jerry R. Meyer, William W. Bewley, Chadwick L. Canedy, Chul Soo Kim, Mijin Kim, Charles D. Merritt and Igor Vurgaftman
Photonics 2020, 7(3), 75; https://doi.org/10.3390/photonics7030075 - 15 Sep 2020
Cited by 84 | Viewed by 11293
Abstract
We review the history, development, design principles, experimental operating characteristics, and specialized architectures of interband cascade lasers for the mid-wave infrared spectral region. We discuss the present understanding of the mechanisms limiting the ICL performance and provide a perspective on the potential for [...] Read more.
We review the history, development, design principles, experimental operating characteristics, and specialized architectures of interband cascade lasers for the mid-wave infrared spectral region. We discuss the present understanding of the mechanisms limiting the ICL performance and provide a perspective on the potential for future improvements. Such device properties as the threshold current and power densities, continuous-wave output power, and wall-plug efficiency are compared with those of the quantum cascade laser. Newer device classes such as ICL frequency combs, interband cascade vertical-cavity surface-emitting lasers, interband cascade LEDs, interband cascade detectors, and integrated ICLs are reviewed for the first time. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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8 pages, 2409 KiB  
Letter
Demonstration of Planar Type-II Superlattice-Based Photodetectors Using Silicon Ion-Implantation
by Arash Dehzangi, Donghai Wu, Ryan McClintock, Jiakai Li, Alexander Jaud and Manijeh Razeghi
Photonics 2020, 7(3), 68; https://doi.org/10.3390/photonics7030068 - 03 Sep 2020
Cited by 7 | Viewed by 3387
Abstract
In this letter, we report the demonstration of a pBn planar mid-wavelength infrared photodetectors based on type-II InAs/InAs1−xSbx superlattices, using silicon ion-implantation to isolate the devices. At 77 K the photodetectors exhibited peak responsivity of 0.76 A/W at 3.8 µm, [...] Read more.
In this letter, we report the demonstration of a pBn planar mid-wavelength infrared photodetectors based on type-II InAs/InAs1−xSbx superlattices, using silicon ion-implantation to isolate the devices. At 77 K the photodetectors exhibited peak responsivity of 0.76 A/W at 3.8 µm, corresponding to a quantum efficiency, without anti-reflection coating, of 21.5% under an applied bias of +40 mV with a 100% cut-off wavelength of 4.6 µm. With a dark current density of 5.21 × 10−6 A/cm2, under +40 mV applied bias and at 77 K, the photodetector exhibited a specific detectivity of 4.95 × 1011 cm·Hz1/2/W. Full article
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9 pages, 2191 KiB  
Communication
Wide-Angle Beam-Steering Using an Optical Phased Array with Non-Uniform-Width Waveguide Radiators
by Youngin Kim, Hyeonho Yoon, Jong-Bum You, Minchul Kim and Hyo-Hoon Park
Photonics 2020, 7(3), 56; https://doi.org/10.3390/photonics7030056 - 03 Aug 2020
Cited by 9 | Viewed by 3996
Abstract
We demonstrate wide-angle beam-steering using an optical phased array (OPA) with waveguide radiators designed with non-uniform widths to reduce the crosstalk between waveguides. The OPA consists of a silicon based 1 × 16 array of electro-optic phase shifters and end-fire radiators. The 16 [...] Read more.
We demonstrate wide-angle beam-steering using an optical phased array (OPA) with waveguide radiators designed with non-uniform widths to reduce the crosstalk between waveguides. The OPA consists of a silicon based 1 × 16 array of electro-optic phase shifters and end-fire radiators. The 16 radiators were configured with four different widths and a half-wavelength spacing, which can remove the higher-order diffraction patterns in free space. The waveguides showed a low crosstalk of −10.2 dB at a wavelength of 1540 nm. With phase control, the OPA achieved wide beam-steering of over ±80° with a side-lobe suppression of 7.4 dB. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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14 pages, 3258 KiB  
Article
Characterization and Direct Modulation of a Multi-Section PIC Suited for Short Reach Optical Communication Systems
by Mohab N. Hammad, Aleksandra Kaszubowska-Anandarajah, M. Deseada Gutierrez Pascual, Pascal Landais, Prajwal D. Lakshmijayasimha, Gaurav Jain and Prince M. Anandarajah
Photonics 2020, 7(3), 55; https://doi.org/10.3390/photonics7030055 - 31 Jul 2020
Cited by 3 | Viewed by 3760
Abstract
A multi-section active photonic integrated circuit (PIC) is characterized in detail to gauge its suitability as a transmitter for short reach applications. The PIC is 1.5 mm long and consists of two lasers integrated in a master-slave configuration, which enables optical injection locking [...] Read more.
A multi-section active photonic integrated circuit (PIC) is characterized in detail to gauge its suitability as a transmitter for short reach applications. The PIC is 1.5 mm long and consists of two lasers integrated in a master-slave configuration, which enables optical injection locking (OIL) of the slave laser. The beneficial impact of the injection is characterized by static and dynamic measurements. The results show a reduction of the optical linewidth from 8 MHz to 2 MHz, a relative intensity noise (RIN) value as low as −154.3 dB/Hz and a 45% improvement of the slave laser modulation bandwidth from 9.5 GHz to 14 GHz. This frequency response enhancement allows the direct modulation of the slave gain section at a data rate of 10.7 Gb/s and an error-free transmission over 25 km of standard single-mode fiber (SSMF). Transmission performance of the injected case shows a 2 dB improvement in the minimum optical power required to achieve a bit error rate of 3.8×10−3 (hard decision forward error correction limit). These results demonstrate that the multi-section PIC can serve as an attractive cost-efficient transmitter in a wide variety of low-cost short-reach data communication applications. Full article
(This article belongs to the Section Optical Communication and Network)
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17 pages, 3872 KiB  
Review
Nanoplasmonics in High Pressure Environment
by Grégory Barbillon
Photonics 2020, 7(3), 53; https://doi.org/10.3390/photonics7030053 - 28 Jul 2020
Cited by 6 | Viewed by 3763
Abstract
An explosion in the interest for nanoplasmonics has occurred in order to realize optical devices, biosensors, and photovoltaic devices. The plasmonic nanostructures are used for enhancing and confining the electric field. In the specific case of biosensing, this electric field confinement can induce [...] Read more.
An explosion in the interest for nanoplasmonics has occurred in order to realize optical devices, biosensors, and photovoltaic devices. The plasmonic nanostructures are used for enhancing and confining the electric field. In the specific case of biosensing, this electric field confinement can induce the enhancement of the Raman signal of different molecules, or the localized surface plasmon resonance shift after the detection of analytes on plasmonic nanostructures. A major part of studies concerning to plasmonic modes and their application to sensing of analytes is realized in ambient environment. However, over the past decade, an emerging subject of nanoplasmonics has appeared, which is nanoplasmonics in high pressure environment. In last five years (2015–2020), the latest advances in this emerging field and its application to sensing were carried out. This short review is focused on the pressure effect on localized surface plasmon resonance of gold nanosystems, the supercrystal formation of plasmonic nanoparticles stimulated by high pressure, and the detection of molecules and phase transitions with plasmonic nanostructures in high pressure environment. Full article
(This article belongs to the Special Issue Latest Advances in Nanoplasmonics and Use of New Tools for Plasmonic Characterization)
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12 pages, 586 KiB  
Article
Cloaking Using the Anisotropic Multilayer Sphere
by Sidra Batool, Mehwish Nisar, Fabrizio Frezza and Fabio Mangini
Photonics 2020, 7(3), 52; https://doi.org/10.3390/photonics7030052 - 26 Jul 2020
Cited by 11 | Viewed by 3297
Abstract
We studied a Spherically Radially Anisotropic (SRA) multilayer sphere with an arbitrary number of layers. Within each layer permittivity components are different from each other in radial and tangential directions. Under the quasi-static approximation, we developed a more generalized mathematical model that can [...] Read more.
We studied a Spherically Radially Anisotropic (SRA) multilayer sphere with an arbitrary number of layers. Within each layer permittivity components are different from each other in radial and tangential directions. Under the quasi-static approximation, we developed a more generalized mathematical model that can be used to calculate polarizability of the SRA multilayer sphere with any arbitrary number of layers. Moreover, the functionality of the SRA multilayer sphere as a cloak has been investigated. It has been shown that by choosing a suitable contrast between components of the permittivity, the SRA multilayer sphere can achieve threshold required for invisibility cloaking. Full article
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11 pages, 6410 KiB  
Article
Coupled Cavity Mid-IR Quantum Cascade Lasers Fabricated by Dry Etching
by Kamil Pierściński, Dorota Pierścińska, Aleksandr Kuźmicz, Grzegorz Sobczak, Maciej Bugajski, Piotr Gutowski and Krzysztof Chmielewski
Photonics 2020, 7(3), 45; https://doi.org/10.3390/photonics7030045 - 03 Jul 2020
Cited by 4 | Viewed by 3267
Abstract
In this work, two-section, coupled cavity, mid-IR quantum cascade lasers (QCLs) were characterized in terms of their tuning range and emission stability under operation towards potential application in detection systems. Devices were processed by inductively coupled plasma reactive ion etching (ICP-RIE) from InP-based [...] Read more.
In this work, two-section, coupled cavity, mid-IR quantum cascade lasers (QCLs) were characterized in terms of their tuning range and emission stability under operation towards potential application in detection systems. Devices were processed by inductively coupled plasma reactive ion etching (ICP-RIE) from InP-based heterostructure, designed for emission in the 9.x micrometer range. Single mode devices were demonstrated with a better than 20 dB side mode suppression ratio (SMRS). The fabrication method resulted in improved yield, as well as high repeatability of individual devices. Continuous, mode-hop-free tuning of emission wavelength was observed across ~4.5 cm−1 for the range of temperatures of the heat sink from 15 °C to 70 °C. Using the thermal perturbation in the lasing cavity, in conjunction with controlled hopping between coupled-cavity (CC) modes, we were able to accomplish tuning over the range of up to ~20 cm−1. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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15 pages, 3875 KiB  
Review
Scattering Properties of PT-Symmetric Chiral Metamaterials
by Ioannis Katsantonis, Sotiris Droulias, Costas M. Soukoulis, Eleftherios N. Economou and Maria Kafesaki
Photonics 2020, 7(2), 43; https://doi.org/10.3390/photonics7020043 - 17 Jun 2020
Cited by 7 | Viewed by 4022
Abstract
The combination of gain and loss in optical systems that respect parity–time (PT)-symmetry has pointed recently to a variety of novel optical phenomena and possibilities. Many of them can be realized by combining the PT-symmetry concepts with metamaterials. Here we investigate the case [...] Read more.
The combination of gain and loss in optical systems that respect parity–time (PT)-symmetry has pointed recently to a variety of novel optical phenomena and possibilities. Many of them can be realized by combining the PT-symmetry concepts with metamaterials. Here we investigate the case of chiral metamaterials, showing that combination of chiral metamaterials with PT-symmetric gain–loss enables a very rich variety of phenomena and functionalities. Examining a simple one-dimensional chiral PT-symmetric system, we show that, with normally incident waves, the PT-symmetric and the chirality-related characteristics can be tuned independently and superimposed almost at will. On the other hand, under oblique incidence, chirality affects all the PT-related characteristics, leading also to novel and uncommon wave propagation features, such as asymmetric transmission and asymmetric optical activity and ellipticity. All these features are highly controllable both by chirality and by the angle of incidence, making PT-symmetric chiral metamaterials valuable in a large range of polarization-control-targeting applications. Full article
(This article belongs to the Special Issue Metamaterials for Advanced Photonic and Plasmonic Applications – Selected Papers from Metamaterials’2019)
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8 pages, 1566 KiB  
Letter
Free Electron Laser Measurement of Liquid Carbon Reflectivity in the Extreme Ultraviolet
by Sumana L. Raj, Shane W. Devlin, Riccardo Mincigrucci, Craig P. Schwartz, Emiliano Principi, Filippo Bencivenga, Laura Foglia, Alessandro Gessini, Alberto Simoncig, Gabor Kurdi, Claudio Masciovecchio and Richard J. Saykally
Photonics 2020, 7(2), 35; https://doi.org/10.3390/photonics7020035 - 23 May 2020
Viewed by 2604
Abstract
Ultrafast time-resolved extreme ultraviolet (EUV) reflectivity measurements of optically pumped amorphous carbon (a-C) have been performed with the FERMI free electron laser (FEL). This work extends the energy range used in previous reflectivity studies and adds polarization dependence. The EUV probe is known [...] Read more.
Ultrafast time-resolved extreme ultraviolet (EUV) reflectivity measurements of optically pumped amorphous carbon (a-C) have been performed with the FERMI free electron laser (FEL). This work extends the energy range used in previous reflectivity studies and adds polarization dependence. The EUV probe is known to be sensitive to lattice dynamics, since in this range the reflectivity is essentially unaffected by the photo-excited surface plasma. The exploitation of both s- and p-polarized EUV radiation permits variation of the penetration depth of the probe; a significant increase in the characteristic time is observed upon increasing the probing depth (1 vs. 5 ps) due to hydrodynamic expansion and consequent destruction of the excited region, implying that there is only a short window during which the probed region is in the isochoric regime. A weak wavelength dependence of the reflectivity is found, consistent with previous measurements and implying a maximum electronic temperature of 0.8 eV ± 0.4. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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10 pages, 4017 KiB  
Article
Wave Front Tuning of Coupled Hyperbolic Surface Waves on Anisotropic Interfaces
by Taavi Repän, Osamu Takayama and Andrei V. Lavrinenko
Photonics 2020, 7(2), 34; https://doi.org/10.3390/photonics7020034 - 20 May 2020
Cited by 4 | Viewed by 3470
Abstract
A photonic surface wave, a propagating optical mode localized at the interface of two media, can play a significant role in controlling the flow of light at nanoscale. Among various types of such waves, surface waves with hyperbolic dispersion or simply hyperbolic surface [...] Read more.
A photonic surface wave, a propagating optical mode localized at the interface of two media, can play a significant role in controlling the flow of light at nanoscale. Among various types of such waves, surface waves with hyperbolic dispersion or simply hyperbolic surface waves supported on anisotropic metal interfaces can be exploited to effectively control the propagation of lightwaves. We used semi-analytical and numerical methods to study the nature of surface waves on several configurations of three-layers metal–dielectric–metal systems including isotropic and anisotropic cases where the metal cladding layers were assumed to have infinite thickness. We used semi-analytical and numerical approaches to study the phenomena. We showed that the propagation of surface wave can be tuned from diverging to converging in the plane of the interface by the combination of metals with different anisotropic properties. Full article
(This article belongs to the Special Issue Topological Photonics)
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7 pages, 1512 KiB  
Letter
Nonreciprocal Wavefront Manipulation in Synthetically Moving Metagratings
by Younes Ra’di and Andrea Alù
Photonics 2020, 7(2), 28; https://doi.org/10.3390/photonics7020028 - 18 Apr 2020
Cited by 16 | Viewed by 4929
Abstract
We introduce a metasurface platform for nonreciprocal wave manipulation. We study metagratings composed of nonreciprocal bianisotropic particles supporting synthetic motion, which enable nonreciprocal energy transfer between tailored Floquet channels with unitary efficiency. Based on this framework, we derive the required electromagnetic polarizabilities to [...] Read more.
We introduce a metasurface platform for nonreciprocal wave manipulation. We study metagratings composed of nonreciprocal bianisotropic particles supporting synthetic motion, which enable nonreciprocal energy transfer between tailored Floquet channels with unitary efficiency. Based on this framework, we derive the required electromagnetic polarizabilities to realize a metagrating supporting space wave circulation with unitary efficiency for free-space radiation and design a microwave metagrating supporting this functionality. The proposed concept opens new research venues to control free-space radiation with high efficiency beyond the limits dictated by Lorentz reciprocity. Full article
(This article belongs to the Special Issue Metamaterials for Advanced Photonic and Plasmonic Applications – Selected Papers from Metamaterials’2019)
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8 pages, 3285 KiB  
Article
Generation of over 1000 Diffraction Spots from 2D Graded Photonic Super-Crystals
by Safaa Hassan, Yan Jiang, Khadijah Alnasser, Noah Hurley, Hualiang Zhang, Usha Philipose and Yuankun Lin
Photonics 2020, 7(2), 27; https://doi.org/10.3390/photonics7020027 - 10 Apr 2020
Cited by 4 | Viewed by 2860
Abstract
For the first time, we are able to generate over 1000 diffraction spots from a graded photonic super-crystal with a unit super-cell size of 12a × 12a where a is the lattice constant and hole radii are gradually changed in dual directions. The [...] Read more.
For the first time, we are able to generate over 1000 diffraction spots from a graded photonic super-crystal with a unit super-cell size of 12a × 12a where a is the lattice constant and hole radii are gradually changed in dual directions. The diffraction pattern from the graded photonic super-crystal reveals unique diffraction properties. The first order diffractions of (±1,0) or (0,±1) disappear. Fractional diffraction orders are observed in the diffraction pattern inside a square with vertices of (1,1), (1,−1), (−1,−1) and (−1,−1). The fractional diffraction can be understood from lattices with a period of a. However, a dual-lattice model is considered in order to explain higher-order diffractions. E-field intensity simulations show a coupling and re-distribution among fractional orders of Bloch waves. There are a total of 12 × 12 spots in E-field intensity in the unit supercell corresponding to 12 × 12 fractional diffraction orders in the diffraction pattern and 12 × 12 fractional orders of momentum in the first Brillouin zone in k-space. Full article
(This article belongs to the Special Issue Advanced Optical Materials and Devices)
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11 pages, 8376 KiB  
Article
Topological Protection and Control of Quantum Markovianity
by Gian Luca Giorgi, Salvatore Lorenzo and Stefano Longhi
Photonics 2020, 7(1), 18; https://doi.org/10.3390/photonics7010018 - 08 Feb 2020
Cited by 9 | Viewed by 4012
Abstract
Under the Born–Markov approximation, a qubit system, such as a two-level atom, is known to undergo a memoryless decay of quantum coherence or excitation when weakly coupled to a featureless environment. Recently, it has been shown that unavoidable disorder in the environment is [...] Read more.
Under the Born–Markov approximation, a qubit system, such as a two-level atom, is known to undergo a memoryless decay of quantum coherence or excitation when weakly coupled to a featureless environment. Recently, it has been shown that unavoidable disorder in the environment is responsible for non-Markovian effects and information backflow from the environment into the system owing to Anderson localization. This turns disorder into a resource for enhancing non-Markovianity in the system–environment dynamics, which could be of relevance in cavity quantum electrodynamics. Here we consider the decoherence dynamics of a qubit weakly coupled to a two-dimensional bath with a nontrivial topological phase, such as a two-level atom embedded in a two-dimensional coupled-cavity array with a synthetic gauge field realizing a quantum-Hall bath, and show that Markovianity is protected against moderate disorder owing to the robustness of chiral edge modes in the quantum-Hall bath. Interestingly, switching off the gauge field, i.e., flipping the bath into a topological trivial phase, allows one to re-introduce non-Markovian effects. Such a result indicates that changing the topological phase of a bath by a tunable synthetic gauge field can be harnessed to control non-Markovian effects and quantum information backflow in a qubit-environment system. Full article
(This article belongs to the Special Issue Topological Photonics)
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17 pages, 5514 KiB  
Review
Ultrahigh-Resolution Optical Vector Analyzers
by Oleg Morozov, Ilnur Nureev, Airat Sakhabutdinov, Artem Kuznetsov, Gennady Morozov, German Il’in, Samvel Papazyan, Alexander Ivanov and Roman Ponomarev
Photonics 2020, 7(1), 14; https://doi.org/10.3390/photonics7010014 - 20 Jan 2020
Cited by 25 | Viewed by 5097
Abstract
The optical vector analyzer is a device used to measure the magnitude, phase responses, and other parameters of optical devices. There have been increasingly higher demands placed on optical vector analyzers during the development of optical technologies, which are satisfied by the creation [...] Read more.
The optical vector analyzer is a device used to measure the magnitude, phase responses, and other parameters of optical devices. There have been increasingly higher demands placed on optical vector analyzers during the development of optical technologies, which are satisfied by the creation of new devices and their operating principles. For further development in this area, it is necessary to generalize the experience gained during the development of optical vector analyzers. Thus, in this report, we provide an overview of all the basic types of approaches used for the realization of optical vector analyzers, including the advanced ones with the best performances. The principles of their working, as well as their associated advantages, disadvantages, and existing solutions to the identified problems, are examined in detail. The presented approaches could be of value and interest to those working in the field of laser dynamics and optical devices, as we propose one use of the optical vector analyzer as being the characterization of Fano resonance structures. Full article
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10 pages, 1373 KiB  
Article
Equivalent Circuit Model of High-Performance VCSELs
by Marwan Bou Sanayeh, Wissam Hamad and Werner Hofmann
Photonics 2020, 7(1), 13; https://doi.org/10.3390/photonics7010013 - 18 Jan 2020
Cited by 4 | Viewed by 5567
Abstract
In this work, a general equivalent circuit model based on the carrier reservoir splitting approach in high-performance multi-mode vertical-cavity surface-emitting lasers (VCSELs) is presented. This model accurately describes the intrinsic dynamic behavior of these VCSELs for the case where the lasing modes do [...] Read more.
In this work, a general equivalent circuit model based on the carrier reservoir splitting approach in high-performance multi-mode vertical-cavity surface-emitting lasers (VCSELs) is presented. This model accurately describes the intrinsic dynamic behavior of these VCSELs for the case where the lasing modes do not share a common carrier reservoir. Moreover, this circuit model is derived from advanced multi-mode rate equations that take into account the effect of spatial hole-burning, gain compression, and inhomogeneity in the carrier distribution between the lasing mode ensembles. The validity of the model is confirmed through simulation of the intrinsic modulation response of these lasers. Full article
(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)
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8 pages, 2790 KiB  
Article
RF Injection of THz QCL Combs at 80 K Emitting over 700 GHz Spectral Bandwidth
by Andres Forrer, Lorenzo Bosco, Mattias Beck, Jérôme Faist and Giacomo Scalari
Photonics 2020, 7(1), 9; https://doi.org/10.3390/photonics7010009 - 16 Jan 2020
Cited by 14 | Viewed by 4536
Abstract
We report about RF injection locking of an homogeneous THz quantum cascade laser operating at 3 THz central frequency. The extremely diagonal nature of the optical transition, combined with low-loss copper-based double-metal waveguides, allow CW operation up to 105 K and CW power [...] Read more.
We report about RF injection locking of an homogeneous THz quantum cascade laser operating at 3 THz central frequency. The extremely diagonal nature of the optical transition, combined with low-loss copper-based double-metal waveguides, allow CW operation up to 105 K and CW power in excess of 5.6 mW measured at 80 K. Terahertz emission spanning up to 600 GHz, together with a narrow beatnote, indicate comb operation at 80 K, and strong RF injection clearly modifies the laser spectrum up to 700 GHz spectral bandwidth making these devices ideal candidates for an on-chip dual comb spectrometer. Full article
(This article belongs to the Special Issue Selected papers from “International Quantum Cascade Laser School and Workshop 2018”)
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33 pages, 11871 KiB  
Review
Hybrid Integrated Semiconductor Lasers with Silicon Nitride Feedback Circuits
by Klaus-J. Boller, Albert van Rees, Youwen Fan, Jesse Mak, Rob E. M. Lammerink, Cornelis A. A. Franken, Peter J. M. van der Slot, David A. I. Marpaung, Carsten Fallnich, Jörn P. Epping, Ruud M. Oldenbeuving, Dimitri Geskus, Ronald Dekker, Ilka Visscher, Robert Grootjans, Chris G. H. Roeloffzen, Marcel Hoekman, Edwin J. Klein, Arne Leinse and René G. Heideman
Photonics 2020, 7(1), 4; https://doi.org/10.3390/photonics7010004 - 21 Dec 2019
Cited by 83 | Viewed by 16168
Abstract
Hybrid integrated semiconductor laser sources offering extremely narrow spectral linewidth, as well as compatibility for embedding into integrated photonic circuits, are of high importance for a wide range of applications. We present an overview on our recently developed hybrid-integrated diode lasers with feedback [...] Read more.
Hybrid integrated semiconductor laser sources offering extremely narrow spectral linewidth, as well as compatibility for embedding into integrated photonic circuits, are of high importance for a wide range of applications. We present an overview on our recently developed hybrid-integrated diode lasers with feedback from low-loss silicon nitride (Si 3 N 4 in SiO 2 ) circuits, to provide sub-100-Hz-level intrinsic linewidths, up to 120 nm spectral coverage around a 1.55 μ m wavelength, and an output power above 100 mW. We show dual-wavelength operation, dual-gain operation, laser frequency comb generation, and present work towards realizing a visible-light hybrid integrated diode laser. Full article
(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)
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14 pages, 791 KiB  
Article
Synchronization of Mutually Delay-Coupled Quantum Cascade Lasers with Distinct Pump Strengths
by Thomas Erneux and Daan Lenstra
Photonics 2019, 6(4), 125; https://doi.org/10.3390/photonics6040125 - 10 Dec 2019
Cited by 14 | Viewed by 2702
Abstract
The rate equations for two delay-coupled quantum cascade lasers are investigated analytically in the limit of weak coupling and small frequency detuning. We mathematically derive two coupled Adler delay differential equations for the phases of the two electrical fields and show that these [...] Read more.
The rate equations for two delay-coupled quantum cascade lasers are investigated analytically in the limit of weak coupling and small frequency detuning. We mathematically derive two coupled Adler delay differential equations for the phases of the two electrical fields and show that these equations are no longer valid if the ratio of the two pump parameters is below a critical power of the coupling constant. We analyze this particular case and derive new equations for a single optically injected laser where the delay is no longer present in the arguments of the dependent variables. Our analysis is motivated by the observations of Bogris et al. (IEEE J. Sel. Top. Quant. El. 23, 1500107 (2017)), who found better sensing performance using two coupled quantum cascade lasers when one laser was operating close to the threshold. Full article
(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)
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11 pages, 943 KiB  
Article
Task-Independent Computational Abilities of Semiconductor Lasers with Delayed Optical Feedback for Reservoir Computing
by Krishan Harkhoe and Guy Van der Sande
Photonics 2019, 6(4), 124; https://doi.org/10.3390/photonics6040124 - 02 Dec 2019
Cited by 22 | Viewed by 3625
Abstract
Reservoir computing has rekindled neuromorphic computing in photonics. One of the simplest technological implementations of reservoir computing consists of a semiconductor laser with delayed optical feedback. In this delay-based scheme, virtual nodes are distributed in time with a certain node distance and form [...] Read more.
Reservoir computing has rekindled neuromorphic computing in photonics. One of the simplest technological implementations of reservoir computing consists of a semiconductor laser with delayed optical feedback. In this delay-based scheme, virtual nodes are distributed in time with a certain node distance and form a time-multiplexed network. The information processing performance of a semiconductor laser-based reservoir computing (RC) system is usually analysed by way of testing the laser-based reservoir computer on specific benchmark tasks. In this work, we will illustrate the optimal performance of the system on a chaotic time-series prediction benchmark. However, the goal is to analyse the reservoir’s performance in a task-independent way. This is done by calculating the computational capacity, a measure for the total number of independent calculations that the system can handle. We focus on the dependence of the computational capacity on the specifics of the masking procedure. We find that the computational capacity depends strongly on the virtual node distance with an optimal node spacing of 30 ps. In addition, we show that the computational capacity can be further increased by allowing for a well chosen mismatch between delay and input data sample time. Full article
(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)
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10 pages, 2320 KiB  
Article
Biofunctionalized Polyelectrolyte Microcapsules Encoded with Fluorescent Semiconductor Nanocrystals for Highly Specific Targeting and Imaging of Cancer Cells
by Galina Nifontova, Daria Kalenichenko, Maria Baryshnikova, Fernanda Ramos Gomes, Frauke Alves, Alexander Karaulov, Igor Nabiev and Alyona Sukhanova
Photonics 2019, 6(4), 117; https://doi.org/10.3390/photonics6040117 - 08 Nov 2019
Cited by 8 | Viewed by 3632
Abstract
Fluorescent semiconductor nanocrystals or quantum dots (QDs) are characterized by unique optical properties, including a high photostability, wide absorption spectrum, and narrow, symmetric fluorescence spectrum. This makes them attractive fluorescent nanolabels for the optical encoding of microcarriers intended for targeted drug delivery, diagnosis, [...] Read more.
Fluorescent semiconductor nanocrystals or quantum dots (QDs) are characterized by unique optical properties, including a high photostability, wide absorption spectrum, and narrow, symmetric fluorescence spectrum. This makes them attractive fluorescent nanolabels for the optical encoding of microcarriers intended for targeted drug delivery, diagnosis, and imaging of transport processes on the body, cellular, and subcellular levels. Incorporation of QDs into carriers in the form of polyelectrolyte microcapsules through layer-by-layer adsorption of oppositely charged polyelectrolyte polymers yields microcapsules with a bright fluorescence signal and adaptable size, structure, and surface characteristics without using organic solvents. The easily modifiable surface of the microcapsules allows for its subsequent functionalization with capture molecules, such as antibodies, which ensures specific and selective interaction with cells, including tumor cells, with the use of the bioconjugation technique developed here. We obtained stable water-soluble nanolabels based on QDs whose surface was modified with polyethylene glycol (PEG) derivatives and determined their colloidal and optical characteristics. The obtained nanocrystals were used to encode polyelectrolyte microcapsules optically. The microcapsule surface was modified with humanized monoclonal antibodies (Abs) recognizing a cancer marker, epidermal growth factor receptor (EGFR). The possibility of effective, specific, and selective delivery of the microcapsules to tumor cells expressing EGFR has been demonstrated. The results show that the QD-encoded polyelectrolyte microcapsules functionalized with monoclonal Abs against EGFR can be used for targeted imaging and diagnosis. Full article
(This article belongs to the Special Issue Advances on Applications of Optics and Photonics – Selected Papers from the 4th International Conference on Applications of Optics and Photonics, AOP2019)
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16 pages, 1034 KiB  
Article
Pupil Function in Pseudophakia: Proximal Miosis Behavior and Optical Influence
by Elsa Fonseca, Paulo Fiadeiro, Renato Gomes, Angel Sanchez Trancon, António Baptista and Pedro Serra
Photonics 2019, 6(4), 114; https://doi.org/10.3390/photonics6040114 - 06 Nov 2019
Cited by 2 | Viewed by 4753
Abstract
The pseudophakic eye lacks the ability to produce a refractive change in response to object proximity. Thus, individual anatomical features such as the pupil size play an important role in achieving functional vision levels. In this work, the range of pupil sizes at [...] Read more.
The pseudophakic eye lacks the ability to produce a refractive change in response to object proximity. Thus, individual anatomical features such as the pupil size play an important role in achieving functional vision levels. In this work, the range of pupil sizes at varying object distance was measured in pseudophakic participants. Furthermore, the impact of the measured values on eye optical quality was investigated using a computer simulation model. A binocular eye-tracker was used to measure the participants’ pupil sizes at six object distances, ranging from 0.33 m (i.e., vergence of 3.00 D) to 3.00 m (i.e., vergence of 0.33 D), while observing a Maltese cross with a constant angular size of 1 ∘ . In total, 58 pseudophakic participants were enrolled in this study (age mean ± standard deviation: 70.5 ± 11.3 years). The effects of object distance and age on pupil size variation were investigated using linear mixed effects regression models. Age was found to have a small contribution to individual variability. The mean infinite distance pupil size (intercept) was 4.45 ( 95 % CI: 2.74, 6.17) mm and the mean proximal miosis (slope) was − 0.23 ( 95 % CI: −0.53, 0.08) mm/D. The visual acuity (VA) estimation for a distant object ranged from − 0.1 logMAR (smallest pupil) to 0.04 logMAR (largest pupil) and the near VA ( 0.33 m) when mean proximal miosis was considered ranged from 0.28 logMAR (smallest pupil) to 0.42 logMAR (largest pupil). When mean distance pupil was considered, proximal miosis individual variability produced a variation of 0.04 logMAR for the near object and negligible variation for the distant object. These results support the importance of distance pupil size measurement for the prediction of visual performance in pseudophakia, while suggesting that proximal miosis has a negligible impact in VA variability. Full article
(This article belongs to the Special Issue Advances on Applications of Optics and Photonics – Selected Papers from the 4th International Conference on Applications of Optics and Photonics, AOP2019)
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14 pages, 5918 KiB  
Article
A Comparison between off and On-Chip Injection Locking in a Photonic Integrated Circuit
by Alison H. Perrott, Ludovic Caro, Mohamad Dernaika and Frank H. Peters
Photonics 2019, 6(4), 103; https://doi.org/10.3390/photonics6040103 - 01 Oct 2019
Cited by 7 | Viewed by 3337
Abstract
The mutual and injection locking characteristics of two integrated lasers are compared, both on and off-chip. In this study, two integrated single facet slotted Fabry–Pérot lasers are utilised to develop the measurement technique used to examine the different operational regimes arising from optically [...] Read more.
The mutual and injection locking characteristics of two integrated lasers are compared, both on and off-chip. In this study, two integrated single facet slotted Fabry–Pérot lasers are utilised to develop the measurement technique used to examine the different operational regimes arising from optically locking a semiconductor diode laser. The technique employed used an optical spectrum analyser (OSA), an electrical spectrum analyser (ESA) and a high speed oscilloscope (HSO). The wavelengths of the lasers are measured on the OSA and the selected optical mode for locking is identified. The region of injection locking and various other regions of dynamical behaviour between the lasers are observed on the ESA. The time trace information of the system is obtained from the HSO and performing the FFT (Fast Fourier Transform) of the time traces returns the power spectra. Using these tools, the similarities and differences between off-chip injection locking with an isolator, and on-chip mutual locking are examined. Full article
(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)
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13 pages, 7165 KiB  
Article
Flowline Optical Simulation to Refractive/Reflective 3D Systems: Optical Path Length Correction
by Angel García-Botella, Lun Jiang and Roland Winston
Photonics 2019, 6(4), 101; https://doi.org/10.3390/photonics6040101 - 28 Sep 2019
Cited by 6 | Viewed by 2811
Abstract
Nonimaging optics is focused on the study of techniques to design optical systems for the purpose of energy transfer instead of image forming. The flowline optical design method, based on the definition of the geometrical flux vector J, is one of these [...] Read more.
Nonimaging optics is focused on the study of techniques to design optical systems for the purpose of energy transfer instead of image forming. The flowline optical design method, based on the definition of the geometrical flux vector J, is one of these techniques. The main advantage of the flowline method is its capability to visualize and estimate how radiant energy is transferred by the optical systems using the concepts of vector field theory, such as field line or flux tube, which overcomes traditional raytrace methods. The main objective this paper is to extend the flowline method to analyze and design real 3D concentration and illumination systems by the development of new simulation techniques. In this paper, analyzed real 3D refractive and reflective systems using the flowline vector potential method. A new constant term of optical path length is introduced, similar and comparable to the gauge invariant, which produces a correction to enable the agreement between raytrace- and flowline-based computations. This new optical simulation methodology provides traditional raytrace results, such as irradiance maps, but opens new perspectives to obtaining higher precision with lower computation time. It can also provide new information for the vector field maps of 3D refractive/reflective systems. Full article
(This article belongs to the Special Issue Nonimaging Optics in Solar Energy)
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