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Photonics
Volume 9
Issue 11
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Photonics, Volume 9, Issue 11 (November 2022) – 100 articles

Cover Story (view full-size image): The addition of EABr and KI induced (100)-oriented perovskite crystals, which resulted in an improvement in short-circuit current densities and conversion efficiencies of perovskite solar cells. The structure models and electron density distributions by first-principles calculations for the MA0.625EA0.25K0.125PbI2.5Br0.5 perovskite crystal are shown in the figure. The electron density is higher in the vicinity of Br relative to that for I. An electron distribution is observed near EA, while it was low and delocalized around K. The calculated band structure and density of states are also shown in the figure. The EA addition reduced the total energy and stabilized the perovskite crystal, which suppressed MA desorption. The density of states revealed that Br was dominant in the valence band, which improved the current density. View this paper
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16 pages, 3287 KiB  
Article
Research on Spectral Restoration and Gas Concentration Inversion Accuracy Based on Quasi-Trapezoidal Window
by Yusheng Qin, Xiangxian Li, Xin Han, Jingjing Tong and Minguang Gao
Photonics 2022, 9(11), 885; https://doi.org/10.3390/photonics9110885 - 21 Nov 2022
Cited by 2 | Viewed by 1805
Abstract
The Fourier transform is a popular method for analyzing and processing interference data in which spectrum leakage occurs. Generally, window function (also called apodization function) weighting is employed to limit spectrum leakage. A rectangular window with optimal main-lobe performance and the Rife-Vincent (R-V) [...] Read more.
The Fourier transform is a popular method for analyzing and processing interference data in which spectrum leakage occurs. Generally, window function (also called apodization function) weighting is employed to limit spectrum leakage. A rectangular window with optimal main-lobe performance and the Rife-Vincent (R-V) window were introduced to improve the window function performance, resulting in the establishment of a quasi-trapezoidal window function. Based on the experimental interference data, the quasi-trapezoidal window function was used in the spectral restoration process. The experimental results show that when the apodization degree of the quasi-trapezoidal window was 1.06, the spectral resolution was improved by 17.46% compared with that of the Hanning window; when the apodization degree was 2.71, the spectral signal-to-noise ratio (SNR) was improved by 130.09% compared with that of the Blackman-Harris window function. In the propane (C3H8) and ethylene (C2H4) gas concentration inversion experiment, when the apodization degree was increased from 1.06 to 2.58, the inversion precision was increased by 6.94% for C3H8 gas and 23.93% for C2H4 gas. Through the parameter adjustment, the quasi-trapezoidal window may achieve a high SNR or high-resolution spectral restoration, which can improve the accuracy of gas concentration inversion to some extent. Full article
(This article belongs to the Topic Optical and Optoelectronic Materials and Applications)
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14 pages, 6218 KiB  
Article
Synchronous Clock Recovery of Photon-Counting Underwater Optical Wireless Communication Based on Deep Learning
by Haodong Yang, Qiurong Yan, Ming Wang, Yuhao Wang, Peng Li and Wei Wang
Photonics 2022, 9(11), 884; https://doi.org/10.3390/photonics9110884 - 21 Nov 2022
Cited by 7 | Viewed by 1924
Abstract
In photon-counting underwater optical wireless communication (UOWC), the recovery of the time slot synchronous clock is extremely important, and it is the basis of symbol synchronization and frame synchronization. We have previously proposed a time slot synchronous clock extraction method based on single [...] Read more.
In photon-counting underwater optical wireless communication (UOWC), the recovery of the time slot synchronous clock is extremely important, and it is the basis of symbol synchronization and frame synchronization. We have previously proposed a time slot synchronous clock extraction method based on single photon pulse counting, but the accuracy needs to be further improved. Deep learning is very effective for feature extraction; synchronous information is already implicit in the discrete single photon pulse signal output by single photon avalanche diode (SPAD), which is used as a communication receiver. Aiming at this characteristic, a method of time slot synchronous clock recovery for photon-counting UOWC based on deep learning is proposed in this paper. Based on the establishment of the underwater channel model and SPAD receiver model, the Monte Carlo method is used to generate discrete single photon pulse sequences carrying synchronous information, which are used as training data. Two neural network models based on regression problem and classification problem are designed to predict the phase value of the time slot synchronous clock. Experimental results show that when the average number of photons per time slot is eight, photon-counting UOWC with a data rate of 1Mbps and a bit error rate (BER) of 5.35 × 10−4 can be achieved. Full article
(This article belongs to the Special Issue Advances in Visible Light Communication)
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8 pages, 3788 KiB  
Communication
Experimental Detection of Initial System–Environment Entanglement in Open Systems
by Gaoyan Zhu, Dengke Qu, Lei Xiao and Peng Xue
Photonics 2022, 9(11), 883; https://doi.org/10.3390/photonics9110883 - 21 Nov 2022
Cited by 1 | Viewed by 2007
Abstract
We experimentally investigate how initial entanglement between the system and environment can be detected in an open system by using some prior knowledge of the joint evolutions. The protocol we employed requires classical optimization on the results after performing measurements on the system [...] Read more.
We experimentally investigate how initial entanglement between the system and environment can be detected in an open system by using some prior knowledge of the joint evolutions. The protocol we employed requires classical optimization on the results after performing measurements on the system state. Such an approach does not require a full 2-qubit QST, and works in scenarios where one has access to the system only. We demonstrate the protocol on both pure entangled states and mixed entangled states. The obtained results show the experimental accessibility and validity of the protocol. Compared with the previous methods, which also assume access only to the system, this protocol is less demanding in terms of measurement and state preparation. The experimental results also show that, using the knowledge of the interaction, we can fine-tune the protocol, thus showing the potential of the protocol for developing experimentally feasible and practical entanglement detection methods. Full article
(This article belongs to the Section Quantum Photonics and Technologies)
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10 pages, 4945 KiB  
Communication
Optically Powered and Controlled Drones Using Optical Fibers for Airborne Base Stations
by Natsuki Shindo, Taiki Kobatake, Denis Masson, Simon Fafard and Motoharu Matsuura
Photonics 2022, 9(11), 882; https://doi.org/10.3390/photonics9110882 - 21 Nov 2022
Cited by 9 | Viewed by 4056
Abstract
Mobile communication services are crucial during emergency disasters and temporary events, and future mobile communication systems should be able to provide such services. Airborne base stations using drones are highly effective as stand-in base stations in areas where the ground base stations are [...] Read more.
Mobile communication services are crucial during emergency disasters and temporary events, and future mobile communication systems should be able to provide such services. Airborne base stations using drones are highly effective as stand-in base stations in areas where the ground base stations are inoperable or at temporary event sites. However, it is difficult for conventional drones to provide mobile communication services without interruption due to flight time limitations caused by their limited battery capacity. Thus, a drone drive with a non-interrupted power supply is urgently needed. In this study, we developed an airborne base station that enables drones to be driven and maneuvered by optical fibers. We simultaneously transmitted radio frequency (RF) data signals for the airborne base station and control signals for the drone and evaluated the transmission performances of the RF signals and the controllability of the drone. Furthermore, we conducted a flight experiment on a medium-sized drone powered by optical fibers. Full article
(This article belongs to the Special Issue Latest Papers Related to OWPT 2019-22 on the Topics of Photovoltaic Components, Devices and Systems)
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12 pages, 3395 KiB  
Article
Light-Induced Self-Oscillations and Spoiling of the Bragg Resonance Due to Nonlinear Optical Propagation in Heliconical Cholesteric Liquid Crystals
by Ashot H. Gevorgyan and Francesco Simoni
Photonics 2022, 9(11), 881; https://doi.org/10.3390/photonics9110881 - 21 Nov 2022
Cited by 2 | Viewed by 2110
Abstract
In a recent paper, we have reported the results of a study of the nonlinear light propagation of a beam traveling along the helix direction of a heliconical cholesteric liquid crystal, showing that optical reorientation leads to instabilities in the optical transmission when [...] Read more.
In a recent paper, we have reported the results of a study of the nonlinear light propagation of a beam traveling along the helix direction of a heliconical cholesteric liquid crystal, showing that optical reorientation leads to instabilities in the optical transmission when the light wavelength is close to the Bragg resonance. Here we report a detailed study of this phenomenon, using Ambartsumian’s layer addition modified method to take into account the continuous modification of the wave field during propagation. We show that the whole transmission spectrum is modified by increasing the light intensity and point out that self-induced oscillations take place at lower intensities on the red side edge of the Bragg resonance while stable values of transmittivity are still observed on the blue side edge. A further increase in the intensity leads to oscillations of lower amplitude on the blue side while an irregular behavior of the transmission is achieved on the red side. At higher intensities, the Bragg resonance disappears and transmission becomes unstable for any light wavelength. A simple phenomenological model is proposed to account for the onset of the oscillations and the asymmetry of the behavior at the opposite side of the Bragg resonance. We also point out that the static electric field is a driving parameter to switch from stable to oscillatory to irregular behavior in the transmittivity at a given light wavelength. Full article
(This article belongs to the Topic Liquid Crystal Photonics)
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8 pages, 456 KiB  
Communication
Bound States in the Continuum versus Fano Resonances: Topological Argument
by Denis V. Novitsky and Andrey V. Novitsky
Photonics 2022, 9(11), 880; https://doi.org/10.3390/photonics9110880 - 20 Nov 2022
Viewed by 2687
Abstract
There is a recent surge of interest to the bound states in the continuum (BICs) due to their ability to provide high-quality resonances in open photonic systems. They are usually observed in perturbed systems possessing Fano resonances in their spectra. We argue that, [...] Read more.
There is a recent surge of interest to the bound states in the continuum (BICs) due to their ability to provide high-quality resonances in open photonic systems. They are usually observed in perturbed systems possessing Fano resonances in their spectra. We argue that, generally speaking, the Fano resonances should not be considered as a proxy for BICs (as it is often done) due to their fundamentally different topological properties. This difference is illustrated with the non-Hermitian layered structure supporting both topologically nontrivial quasi-BIC and topologically trivial Fano resonances. Non-Hermiticity can also be a source of additional topological features of these resonant responses. Moreover, the lasing mode associated with BIC in this structure also possesses nonzero topological charge that can be useful for producing unconventional states of light. This paper contributes to the discussion of BIC physics and raises new questions concerning topological properties of non-Hermitian systems. Full article
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16 pages, 943 KiB  
Article
Singlemode-Multimode-Singlemode Fiber-Optic Interferometer Signal Demodulation Using MUSIC Algorithm and Machine Learning
by Nikolai Ushakov, Aleksandr Markvart and Leonid Liokumovich
Photonics 2022, 9(11), 879; https://doi.org/10.3390/photonics9110879 - 20 Nov 2022
Cited by 7 | Viewed by 2042
Abstract
The paper is aimed at improving the efficiency of signal processing for intermode fiber-optic interferometers. To do so, we propose to use the MUSIC algorithm. It is shown that the use of traditional methods for estimating the number of signal components leads to [...] Read more.
The paper is aimed at improving the efficiency of signal processing for intermode fiber-optic interferometers. To do so, we propose to use the MUSIC algorithm. It is shown that the use of traditional methods for estimating the number of signal components leads to poor operation of the MUSIC algorithm when applied to intermode interference signals. The possibility of using machine learning to estimate the number of signal components was investigated. The advantage of the proposed signal processing for demodulating the signals of an intermode interferometer over the Fourier transform has been experimentally demonstrated on the examples of simultaneous strain and curvature measurement, as well as pulse-wave sensing. The results can be also applied for processing signals of other optical-fiber sensors and multi-component signals of a different nature, for example, optical coherence tomography and radar signals. Full article
(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)
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8 pages, 4252 KiB  
Communication
Resolving Intrinsic Modulation Spectral Lines from Electro-Optic Modulation Spectra Based on Boosted Iterative Deconvolution
by Jian Li, Ying Xu, Xinhai Zou, Junfeng Zhu, Zhongtao Ruan, Yali Zhang, Zhiyao Zhang, Shangjian Zhang and Yong Liu
Photonics 2022, 9(11), 878; https://doi.org/10.3390/photonics9110878 - 20 Nov 2022
Viewed by 1677
Abstract
Optical spectrum analysis is the most direct and effective method for characterizing electro-optic modulation spectra. According to the Rayleigh criterion, the best resolution of an optical spectrum analysis is limited by the point spread function of an optical spectrum analyzer (OSA) and the [...] Read more.
Optical spectrum analysis is the most direct and effective method for characterizing electro-optic modulation spectra. According to the Rayleigh criterion, the best resolution of an optical spectrum analysis is limited by the point spread function of an optical spectrum analyzer (OSA) and the relative intensity of closely spaced spectral lines. In this paper, we propose a boosted iterative deconvolution (BID) method to resolve the intrinsic modulation of spectral lines from the measured optical carrier and modulation spectra. In our scheme, the electro-optic modulation spectrum is considered the convolution of the optical carrier spectrum and the intrinsic δ-function modulation spectrum, and the BID method enables fast and accurate extraction of the δ-function spectral lines from the measured modulation spectrum. The proof-of-concept experiment demonstrates that our method can improve the resolution of OSA by 10–30 p.m. at different relative intensities, with a best resolution of 10 p.m. in the iso-intensity case and wavelength errors of less than 2 p.m., which largely improves the measurement resolution and accuracy of the modulation spectrum. Full article
(This article belongs to the Special Issue Advanced Photonic Sensing and Measurement)
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19 pages, 7490 KiB  
Article
Utilizing Dynamic Scattering for Learning Radar Cross-Section of a Flapping-Wing Aircraft
by Zeyang Zhou and Jun Huang
Photonics 2022, 9(11), 877; https://doi.org/10.3390/photonics9110877 - 19 Nov 2022
Viewed by 1597
Abstract
To study the radar cross-section (RCS) of a flapping-wing aircraft, a method of flapping-wing dynamic scattering is presented. The aircraft has two rigid wings and a fuselage similar to a bird’s body, where the plane shape of the wing is U-type. The aircraft [...] Read more.
To study the radar cross-section (RCS) of a flapping-wing aircraft, a method of flapping-wing dynamic scattering is presented. The aircraft has two rigid wings and a fuselage similar to a bird’s body, where the plane shape of the wing is U-type. The aircraft model is established and the pitching and flapping actions of the wing are simulated. The electromagnetic scattering characteristics of aircraft under two flight modes, different radar wave frequencies and observation angles are investigated. The results show that in the given gliding mode, the fuselage provides the main contribution to the lateral peak value. For the given forward azimuth range in the flapping mode, increasing the azimuth can reduce the mean and peak of the aircraft dynamic RCS curve, while increasing the elevation angle will increase the peak and mean of the aircraft dynamic RCS curve. In the flapping mode, the mean RCS of the aircraft in the lateral backward azimuth is significantly lower than that in the lateral forward azimuth. For the given tail azimuth range, the increase of azimuth will increase the mean and peak level of aircraft dynamic RCS curve. The presented method is effective to study the dynamic RCS characteristics of the flapping-wing aircraft. Full article
(This article belongs to the Section Optical Communication and Network)
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14 pages, 3371 KiB  
Article
Joint Pre- and Post-Equalization with Higher-Order Modulation Formats in SDM-Based Optical MIMO Systems
by Jasmeet Singh, Andreas Ahrens and Steffen Lochmann
Photonics 2022, 9(11), 876; https://doi.org/10.3390/photonics9110876 - 19 Nov 2022
Cited by 3 | Viewed by 1871
Abstract
The multiple-input and multiple-output (MIMO) technology is a promising area of research to cope up with the demands of higher data rates and capacity. In the optical communication domain, the combination of space-division multiplexing (SDM) with higher-order modulation (HOM) formats over an optical [...] Read more.
The multiple-input and multiple-output (MIMO) technology is a promising area of research to cope up with the demands of higher data rates and capacity. In the optical communication domain, the combination of space-division multiplexing (SDM) with higher-order modulation (HOM) formats over an optical MIMO system actively addresses these challenges. By allowing multi-level signaling with limited increment in the transmitter’s complexity, a jointly designed pre- and post-equalization (PPE) for an optical MIMO system with a multi-mode fiber (MMF) link is proposed. Cost-effectiveness of the system is incorporated by utilizing intensity modulation/direct detection (IM/DD) with HOM formats such as pulse-amplitude modulation (PAM) schemes. With the aid of a numerical optimization algorithm, the proposed joint-PPE filter coefficients are optimized with respect to the MMF channel and the transmit power constraint. In contrast to existing research on the single-mode fiber (SMF) based optical systems, the effectiveness of the proposed joint-PPE filter is analyzed on an MMF link, which is considerably degraded by the modal dispersion. In the analyzed experimental scenario, the proposed joint-PPE scheme confirms to be beneficial as compared to the post-equalization only (PE-only) in terms of bit-error rate (BER) performance. Furthermore, the required average received optical power to reach a BER 10−4 by the joint-PPE scheme is improved by 2 dB with comparison to the minimum mean-squared error (MMSE) PE-only. Full article
(This article belongs to the Special Issue Optical Fiber Communication Systems)
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12 pages, 372 KiB  
Article
Quantum Speed Limit for a Moving Qubit inside a Leaky Cavity
by Maryam Hadipour, Soroush Haseli, Hazhir Dolatkhah, Saeed Haddadi and Artur Czerwinski
Photonics 2022, 9(11), 875; https://doi.org/10.3390/photonics9110875 - 18 Nov 2022
Cited by 7 | Viewed by 2956
Abstract
The quantum speed limit (QSL) is a theoretical lower bound of the time required for a quantum system to evolve from an arbitrary initial state to its orthogonal counterpart. This figure can be used to characterize the dynamics of open quantum systems, including [...] Read more.
The quantum speed limit (QSL) is a theoretical lower bound of the time required for a quantum system to evolve from an arbitrary initial state to its orthogonal counterpart. This figure can be used to characterize the dynamics of open quantum systems, including non-Markovian maps. In this paper, we investigate the QSL time for a model that consists of a single qubit moving inside a leaky cavity. Notably, we show that for both weak and strong coupling regimes, the QSL time increases while we boost the velocity of the qubit inside the leaky cavity. Moreover, it is observed that by increasing the qubit velocity, the speed of the evolution tends to a constant value, and the system becomes more stable. The results provide a better understanding of the dynamics of atom-photon couplings and can be used to enhance the controllability of quantum systems. Full article
(This article belongs to the Special Issue Photonic State Tomography: Methods and Applications)
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11 pages, 3433 KiB  
Article
Design and Application of Phase-Only Diffractive Optical Element Based on Non-Iterative Method
by Kuo Shi and Gongjian Zhang
Photonics 2022, 9(11), 874; https://doi.org/10.3390/photonics9110874 - 18 Nov 2022
Cited by 2 | Viewed by 2441
Abstract
In this study, we devised a method for the design of continuous phase-only holographic masks that map laser light to arbitrary target illumination patterns, which have a wide range of applications. In this method, the discrete gradient of a holographic mask is obtained [...] Read more.
In this study, we devised a method for the design of continuous phase-only holographic masks that map laser light to arbitrary target illumination patterns, which have a wide range of applications. In this method, the discrete gradient of a holographic mask is obtained by combining geometric optics and the linear assignment problem (LAP) methods, and then the entire problem is transformed into an integral problem with a discrete gradient. Finally, the least squares method is used to solve the gradient integral to complete the construction of a phase holographic mask. Due to its good continuity, this mask design method can also be applied to the production of diffractive optical elements. We discussed the effectiveness of this method by constructing two holographic masks with uniform illumination. At the same time, we successfully constructed an Einstein face holographic mask with non-uniform illumination using the LAP method for the first time. It is believed that this method can be widely used in illumination mode, ion capture and other directions. Full article
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19 pages, 742 KiB  
Article
Systematic Performance Analysis of Hybrid FSO/RF System over Generalized Fading Channels with Pointing Errors
by Yan Wu, Mengwan Jiang, Gang Li and Dejin Kong
Photonics 2022, 9(11), 873; https://doi.org/10.3390/photonics9110873 - 18 Nov 2022
Cited by 7 | Viewed by 2167
Abstract
Hybrid free space optical (FSO)/radio frequency (RF) system has attracted extensive attention because of its advantages of both the FSO and RF links. From the viewpoint of overall system performance, this paper presents a systematic analysis method of communication performance and security performance [...] Read more.
Hybrid free space optical (FSO)/radio frequency (RF) system has attracted extensive attention because of its advantages of both the FSO and RF links. From the viewpoint of overall system performance, this paper presents a systematic analysis method of communication performance and security performance of the hybrid FSO/RF system with the Málaga turbulence channel and the α−μ fading channel. The hybrid FSO/RF system adopts the diversity method of maximum ratio combining (MRC) to receive signals. The new expressions of communication performance parameters (i.e., the bit error rate, the outage probability, the ergodic channel capacity) of the only FSO system and the hybrid system are obtained. Then, the new expressions of the security performance parameters (i.e., the security outage probability and the strictly positive secrecy capacity) of the hybrid system with the FSO or RF links eavesdropping are derived, respectively. Our derived analytical expressions present an efficient tool to investigate the impact of system parameters on the overall performance of the hybrid system, namely modulation scheme, turbulence intensity, pointing errors, target rate, and eavesdropper output signal-to-noise ratio. The simulation results show that compared with the only FSO system, the hybrid system can significantly improve the communication performance of the system; the communication performance of the hybrid system using coherent binary phase shift keying (CBPSK) modulation is obviously better than the other two modulation technologies; with the deterioration of atmospheric environment (increasing turbulence intensity and pointing errors), the communication performance and security performance of the hybrid system will decline; both RF link eavesdropping and FSO link eavesdropping have a greater impact on the security performance of the hybrid systems; whether it is FSO link eavesdropping or RF link eavesdropping, the reduction of target rate and output signal-to-noise ratio of the eavesdropper can improve the security performance of the hybrid system. Full article
(This article belongs to the Special Issue Advances in Free Space Optical Communications and Optical Turbulence Modeling)
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8 pages, 2968 KiB  
Article
Wavefront Correction in Vacuum of SULF-1PW Laser Beamline
by Fenxiang Wu, Ende Li, Yi Xu, Jiayi Qian, Jiacheng Zhu, Jiabing Hu, Yang Zhao, Peile Bai, Zongxin Zhang, Yuxin Leng and Zeping Yang
Photonics 2022, 9(11), 872; https://doi.org/10.3390/photonics9110872 - 18 Nov 2022
Cited by 2 | Viewed by 1706
Abstract
The focusing quality of high peak power lasers plays a crucial role in laser wakefield electron acceleration investigations. We report here an improvement in the focusing quality of the SULF-1PW laser beamline, planning to drive and generate 5~10 GeV electron beams. After the [...] Read more.
The focusing quality of high peak power lasers plays a crucial role in laser wakefield electron acceleration investigations. We report here an improvement in the focusing quality of the SULF-1PW laser beamline, planning to drive and generate 5~10 GeV electron beams. After the wavefront correction in vacuum with an adaptive optical system and the focusing with an f/56 off-axis parabolic mirror, near-diffraction-limited focal spots with a size of 52 × 54 μm2 at full width at half maximum are achieved, and the enclosed energy inside this size is ~36.6%. Consequently, the focused intensity of ~1.66 × 1019 W/cm2 can be achieved at 1 PW peak power. Moreover, we also examine the wavefront stability in air and vacuum, respectively. From the statistical analysis of 1900 shots of successive laser pulses at 1 Hz, we identify the wavefront fluctuation resulting from air turbulence and the better correction capacity in vacuum. This work demonstrates the importance and necessity of wavefront correction in vacuum for high peak power lasers. Full article
(This article belongs to the Special Issue Ultrashort Ultra-Intense (Petawatt) Laser)
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11 pages, 2510 KiB  
Article
Stimulated Emission in Vertically Aligned Hexagonal ZnO Microcrystals Synthesized by Magnetron Sputtering Method
by Andrey P. Tarasov, Arsen E. Muslimov and Vladimir M. Kanevsky
Photonics 2022, 9(11), 871; https://doi.org/10.3390/photonics9110871 - 17 Nov 2022
Cited by 6 | Viewed by 1308
Abstract
This study is devoted to the luminescence and stimulated emission properties of the ZnO hybrid structure, which is vertically aligned microcrystals with the [0001] crystallographic orientation and a pronounced hexagonal shape formed on a continuous layer of micron thickness. These microcrystals are up [...] Read more.
This study is devoted to the luminescence and stimulated emission properties of the ZnO hybrid structure, which is vertically aligned microcrystals with the [0001] crystallographic orientation and a pronounced hexagonal shape formed on a continuous layer of micron thickness. These microcrystals are up to 10 µm high and up to 8 µm in diameter and form the main part of the structure’s thickness. The structure was synthesized on the M(101¯0) plane of sapphire using the magnetron sputtering method. Luminescence of the structure, represented only by conventional near-UV and green components under low-intensity continuous photoexcitation, confirms its high structural and optical quality. Under pulsed photoexcitation with relatively high intensity, stimulated emission (SE) was observed from the structure in the near-UV region at room temperature. The threshold power density for SE was 0.1–0.2 MW/cm2. Exceeding the threshold leads to a significant increase in the emission intensity compared to the control film without [0001] microcrystals, also grown on M(101¯0) sapphire. It was assumed that the optical gain is provided by the whispering gallery modes of individual [0001] microcrystals as a result of inelastic exciton–electron scattering, at least at near-threshold excitation intensities. Full article
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15 pages, 5543 KiB  
Article
Proposal for a Calculation Model of Perceived Luminance in Road Tunnel Interior Environment: A Case Study of a Tunnel in China
by Li Qin, Shiyong He, Deshan Yang and Arturo S. Leon
Photonics 2022, 9(11), 870; https://doi.org/10.3390/photonics9110870 - 17 Nov 2022
Cited by 7 | Viewed by 1825
Abstract
This study describes applying the visual target color and spectra of light sources to calculate the perceived luminance in a tunnel interior lighting environment. The proposed approach aims to identify the combined effects of the light source, target surface color, and human eye [...] Read more.
This study describes applying the visual target color and spectra of light sources to calculate the perceived luminance in a tunnel interior lighting environment. The proposed approach aims to identify the combined effects of the light source, target surface color, and human eye on the perception of luminance in a tunnel interior lighting environment. The new method was tested in DIALux software using three light-emitting diodes (LEDs) with correlated color temperatures (CCTs) of 3000 K, 4000 K, and 6000 K, as well as four observed targets with red, yellow, blue, and green colors. Overall findings demonstrated that the yellow surface target’s mesopic luminance for the specified light source is greater than that of the other three-color surface targets. Additionally, it can be concluded that the mesopic luminance under a low CCT LED is greater than under a high CCT LED in the case of the specific color surface target. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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9 pages, 1654 KiB  
Article
Utilizing a Tunable Delay Line Interferometer to Improve the Sensing Accuracy of an FBG Sensor System
by Erfan Dejband, Cheng-Kai Yao, Yibeltal Chanie Manie, Po-Yang Huang, Hao-Kuan Lee, Tan-Hsu Tan and Peng-Chun Peng
Photonics 2022, 9(11), 869; https://doi.org/10.3390/photonics9110869 - 17 Nov 2022
Cited by 2 | Viewed by 2442
Abstract
This paper proposes a novel sensing system based on a tunable delay line interferometer. The tunable delay line interferometer has been used to interpret strain, bringing us high accuracy as well as tunability. The shifted wavelength of the fiber Bragg grating (FBG) sensor [...] Read more.
This paper proposes a novel sensing system based on a tunable delay line interferometer. The tunable delay line interferometer has been used to interpret strain, bringing us high accuracy as well as tunability. The shifted wavelength of the fiber Bragg grating (FBG) sensor caused by the applied strain can be visualized by an optical power meter (OPM) instead of an optical spectrum analyzer (OSA) by converting it to a power change using a tunable delay line interferometer (TDI). Different free spectral ranges (FSRs) are assigned to the TDI to investigate the accuracy and operation range of the proposed system. Thus, we achieve high accuracy and sensitivity by adjusting the FSR to 0.47 nm. Experimental results show that the maximum output power variation corresponding to a strain of 10 με is about 0.9 dB when the FSR is set to 0.47 nm. The proposed system is also cost-effective regarding the equipment utilized for interrogation: a tunable delay line interferometer and an optical power meter. Full article
(This article belongs to the Special Issue Advancements in Fiber Bragg Grating Research II)
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7 pages, 1819 KiB  
Communication
Improving the Performance of Optical Phased Array by Reducing Relative Intensity Noise of Optically Injection-Locked Laser Array
by Anh-Hang Nguyen and Hyuk-Kee Sung
Photonics 2022, 9(11), 868; https://doi.org/10.3390/photonics9110868 - 17 Nov 2022
Viewed by 1656
Abstract
Relative intensity noise (RIN) is an important factor that determines the performance of optical phased arrays (OPA) that are configured using semiconductor lasers as light emission sources. This study proposes a method of improving the optical signal-to-noise ratio (OSNR) of an OPA by [...] Read more.
Relative intensity noise (RIN) is an important factor that determines the performance of optical phased arrays (OPA) that are configured using semiconductor lasers as light emission sources. This study proposes a method of improving the optical signal-to-noise ratio (OSNR) of an OPA by reducing the RIN and using high coherence of optically injection-locked (OIL) laser arrays. We numerically demonstrated a laser RIN reduction of 22.7 dB by the OIL laser compared to a free-running laser. We achieved an OPA RIN reduction of 13.2 dB by combining the coherent outputs with the uncorrelated noise of 21 OIL lasers, compared to a single OIL laser RIN. Consequently, we demonstrated an OPA OSNR increase of approximately 13.8 dB based on the OIL-based OPA compared to that of the conventional noise-correlated OPA configuration. Additionally, we confirmed the maintenance of OPA OSNR improvement during OPA operations. Full article
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9 pages, 2291 KiB  
Article
Photodetector Based on Twisted Bilayer Graphene/Silicon Hybrid Slot Waveguide with High Responsivity and Large Bandwidth
by Siqi Yan, Ze Zhang, Weiqin Wang, Ziwen Zhou, Wenyi Peng, Yifan Zeng, Yuqin Yuan, Siting Huang, Xuchen Peng, Xiaolong Zhu, Ming Tang and Yunhong Ding
Photonics 2022, 9(11), 867; https://doi.org/10.3390/photonics9110867 - 17 Nov 2022
Cited by 5 | Viewed by 2218
Abstract
Graphene/silicon hybrid photodetector operating at communication wavelength has attracted enormous attention recently due to its potential to realize bandwidth larger than 100 GHz. However, the responsivity is intrinsically limited by the low absorption from the atomic-thick graphene monolayer, which imposes significant obstacles towards [...] Read more.
Graphene/silicon hybrid photodetector operating at communication wavelength has attracted enormous attention recently due to its potential to realize bandwidth larger than 100 GHz. However, the responsivity is intrinsically limited by the low absorption from the atomic-thick graphene monolayer, which imposes significant obstacles towards its practical application. Although plasmonic structures has been widely applied to enhance the responsivity, it may induce the metallic absorption thus limit the responsivity lower than 0.6 A/W. Twisted bilayer graphene (TBG) has been reported to hold the ability to dramatically enhance the optical absorption due to the unique twist-angle-dependent van Hove singularities. In this article, we present a design of a silicon/TBG hybrid photodetector with a responsivity higher than 1 A/W and bandwidth exceeding 100 GHz. The enhanced responsivity is achieved by tuning the twisted angle of TBG to increase the absorption within the 1550 nm as well as utilizing the silicon slot waveguide to boost the mode overlap with TBG. The fabrication process of proposed design is also discussed demonstrating the advantages of low fabrication complexity. The proposed silicon/TBG photodetector could not only exhibit superior performance compared to previously reported silicon/monolayer graphene photodetector, but also pave the way for the practical application of graphene-based silicon optoelectronic devices. Full article
(This article belongs to the Special Issue Emerging Frontiers in Silicon Photonics)
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6 pages, 2674 KiB  
Article
Frequency Pulling and the Linewidth Enhancement Factor in Optically Injected Semiconductor Laser
by Najm M. Al-Hosiny
Photonics 2022, 9(11), 866; https://doi.org/10.3390/photonics9110866 - 17 Nov 2022
Cited by 2 | Viewed by 1682
Abstract
The effect of the linewidth enhancement factor (LEF) on the frequency pulling behavior in optically injected lasers is theoretically investigated. The frequency pulling is found to be exponentially dependent on the LEF. This dependence is systematically revealed and explained. Full article
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24 pages, 6980 KiB  
Article
TSC-1 Optical Payload Hyperspectral Imager Preliminary Design and Performance Estimation
by Weerapot Wanajaroen, Christophe Buisset, Thierry Lépine, Pearachad Chartsiriwattana, Merisa Kosiyakul, Apirat Prasit, Phongsatorn Saisutjarit, Suwicha Wannawichian, Wiphu Rujopakarn, Saran Poshyachinda and Boonrucksar Soonthornthum
Photonics 2022, 9(11), 865; https://doi.org/10.3390/photonics9110865 - 16 Nov 2022
Cited by 5 | Viewed by 2777
Abstract
The Thai Space Consortium aims at building capacities in space technologies and industries with the objective to develop satellites in Thailand. In this framework, the first Earth Observation satellite that will be developed by this consortium is called TSC-1. This satellite comprises a [...] Read more.
The Thai Space Consortium aims at building capacities in space technologies and industries with the objective to develop satellites in Thailand. In this framework, the first Earth Observation satellite that will be developed by this consortium is called TSC-1. This satellite comprises a hyperspectral imager orbiting in a Sun-Synchronous Low-Earth Orbit at the altitude equal to 630 km. The optical payload is specified to provide data cubes with a Ground Sample Distance equal to 30 m, a swath equal to 30 km, a spectral resolution equal to 10 nm over the spectral domain from 400 nm to 1000 nm with a Signal-to-Noise Ratio (SNR) higher than 100. Firstly, we present the trade-off performed to select the design of the Front Telescope and the Spectrometer. Secondly, we describe the payload design and present the image quality, Modulation Transfer Function and distortion. Next, we establish the tolerance budget to estimate the performance of the optical system including manufacturing errors, assembly errors and stability of the mechanical structure. After that, we calculate the instrument’s spatial and spectral response functions and the contamination of the adjacent pixels due to the straylight. Finally, we estimate radiometric performance in both nadir pointing mode and forward motion compensation mode. Full article
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18 pages, 7049 KiB  
Article
Modeling Effect of Bubbles on Time-Dependent Radiation Transfer of Microalgae in a Photobioreactor for Carbon Dioxide Fixation
by Tianhao Fei, Li Lin, Xingcan Li, Jia-Yue Yang, Junming Zhao and Linhua Liu
Photonics 2022, 9(11), 864; https://doi.org/10.3390/photonics9110864 - 16 Nov 2022
Cited by 3 | Viewed by 1881
Abstract
Microalgae are considered one of the most efficient and environmentally friendly ways for carbon dioxide fixation. The bubbles play an important role in analyzing the radiation transfer in photobioreactors during microalgae growth. Herein, Chlorella sp. and Scenedesmus obliquus were cultured in the airlift [...] Read more.
Microalgae are considered one of the most efficient and environmentally friendly ways for carbon dioxide fixation. The bubbles play an important role in analyzing the radiation transfer in photobioreactors during microalgae growth. Herein, Chlorella sp. and Scenedesmus obliquus were cultured in the airlift flat plate photobioreactor and evaluated for the temporal evolution of radiation characteristics. A one-dimensional model of bubbles on time-dependent radiation transfer in a photobioreactor was proposed, and it was well verified with the experimental result. The results indicated that with the increase of bubble volume fraction or the decrease of bubble radius, the local irradiance increased at the illuminated surface of the microalgal culture and was attenuated more rapidly along with the radiation transfer. The average specific growth rate of microalgae decreases as bubble volume fraction increases or bubble radius decreases. The volume fraction of 0.003 and a radius of 3.5 mm are the optimal operating conditions in this study for microalgae growth and carbon dioxide fixation. The presented analysis would facilitate the design and optimization of the optical and aeration configurations of photobioreactors for carbon dioxide fixation. Full article
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14 pages, 7110 KiB  
Article
Terahertz Generation by Optical Rectification of 780 nm Laser Pulses in Pure and Sc-Doped ZnGeP2 Crystals
by Vladimir Voevodin, Svetlana Bereznaya, Yury S. Sarkisov, Nikolay N. Yudin and Sergey Yu. Sarkisov
Photonics 2022, 9(11), 863; https://doi.org/10.3390/photonics9110863 - 16 Nov 2022
Cited by 4 | Viewed by 1940
Abstract
Terahertz wave generation through the optical rectification of 780 nm femtosecond laser pulses in ZnGeP2 crystals has been studied. All of the possible interactions of types I and II were analyzed by modeling and experimentally. We demonstrate the possibility of broadband “low-frequency” [...] Read more.
Terahertz wave generation through the optical rectification of 780 nm femtosecond laser pulses in ZnGeP2 crystals has been studied. All of the possible interactions of types I and II were analyzed by modeling and experimentally. We demonstrate the possibility of broadband “low-frequency” terahertz generation by an ee–e interaction (with two pumping waves and a generated terahertz wave; all of these had extraordinary polarization in the crystal) and “high-frequency” terahertz generation by an oe–e interaction. The arising possibility of achieving the narrowing of the terahertz generation bandwidth at the oe–e interaction using thicker ZnGeP2 crystals is experimentally confirmed. It has been found that the thermal annealing of as-grown ZnGeP2 crystals and their doping with a 0.01 mass % of Sc reduces the absorption in the “anomalous absorption” region (λ = 0.62–3 μm). The terahertz generation by the oo–e interaction in (110) ZnGeP2:Sc and the as-grown ZnGeP2 crystals of equal thicknesses was compared. It has been found that ZnGeP2:Sc is more efficient for 780 nm femtosecond laser pulses optical rectification. Full article
(This article belongs to the Topic Optical and Optoelectronic Materials and Applications)
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12 pages, 9905 KiB  
Review
Prospects of Relativistic Flying Mirrors for Ultra-High-Field Science
by Masaki Kando, Alexander S. Pirozhkov, James K. Koga, Timur Zh. Esirkepov and Sergei V. Bulanov
Photonics 2022, 9(11), 862; https://doi.org/10.3390/photonics9110862 - 15 Nov 2022
Cited by 2 | Viewed by 2977
Abstract
Recent progress of high-peak-power lasers makes researchers envisage ultra-high-field science; however, the current or near future facilities will not be strong enough to reach the vacuum breakdown intensity, i.e., the Schwinger field. To address this difficulty, a relativistic flying mirror (RFM) technology is [...] Read more.
Recent progress of high-peak-power lasers makes researchers envisage ultra-high-field science; however, the current or near future facilities will not be strong enough to reach the vacuum breakdown intensity, i.e., the Schwinger field. To address this difficulty, a relativistic flying mirror (RFM) technology is proposed to boost the focused intensity by double the Doppler effect of an incoming laser pulse. We review the principle, theoretical, and experimental progress of the RFM, as well as its prospects. Full article
(This article belongs to the Special Issue Progress in Laser Accelerator and Future Prospects)
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23 pages, 5638 KiB  
Article
Preliminary Characterization of Robust Detection Method of Solar Cell Array for Optical Wireless Power Transmission with Differential Absorption Image Sensing
by Kaoru Asaba, Kenta Moriyama and Tomoyuki Miyamoto
Photonics 2022, 9(11), 861; https://doi.org/10.3390/photonics9110861 - 15 Nov 2022
Cited by 7 | Viewed by 1698
Abstract
In an optical wireless power transmission (OWPT) system, position and size of the photovoltaic device (PV) should be accurately determined from the light source position. Even though the detection of PV for OWPT has been studied and reported in some literature, the methods [...] Read more.
In an optical wireless power transmission (OWPT) system, position and size of the photovoltaic device (PV) should be accurately determined from the light source position. Even though the detection of PV for OWPT has been studied and reported in some literature, the methods reported thus far are not so robust against varying background illumination. This study aims to solve such problems utilizing an image sensor which generates a differential absorption image from two wavelength images. Unnecessary background illumination presented in the two images is subtracted in the differential image. The differential image of the Si substrate target, which simulates PV, was detected by this sensor from a 104.5 cm distance. Signal illumination intensity was less than 1 μW/cm2 on the target, and detection accuracy was 3.1% for the diameter of the substrate and about 6.3% for the area. The system level requirement is derived, and they were verified by these results. The detection range of this sensor is shown to be expandable at the cost of, for example, increasing the receiver diameter of the image sensor or controlling the transmitter beam’s divergence. With the simple experiment apparatus, preliminary results of performance assessment were obtained and issues for performance improvement and potential of this image sensor were recognized. Full article
(This article belongs to the Special Issue Latest Papers Related to OWPT 2019-22 on the Topics of Photovoltaic Components, Devices and Systems)
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13 pages, 3112 KiB  
Article
First-Passage-Time Analysis of the Pulse-Timing Statistics in a Two-Section Semiconductor Laser under Excitable and Noisy Conditions
by Daan Lenstra, Lukas Puts and Weiming Yao
Photonics 2022, 9(11), 860; https://doi.org/10.3390/photonics9110860 - 14 Nov 2022
Cited by 2 | Viewed by 1657
Abstract
A two-section semiconductor laser can exhibit excitability for certain parameter settings. When used as a photonic spiking neuron, it is relevant to investigate its sensitivity to noise due to, e.g., spontaneous emission. Under excitable conditions, the system emits irregularly timed noise-triggered pulses. Their [...] Read more.
A two-section semiconductor laser can exhibit excitability for certain parameter settings. When used as a photonic spiking neuron, it is relevant to investigate its sensitivity to noise due to, e.g., spontaneous emission. Under excitable conditions, the system emits irregularly timed noise-triggered pulses. Their statistics is analyzed in terms of a first-passage time distribution for the fluctuating intensity to reach the threshold for excitable response. Two analytic approximations valid for short and long times, respectively, are derived which very well explain measured and simulated pulse-repetition time distributions. This provides physical insight into the noise-triggered spiking mechanism. Full article
(This article belongs to the Special Issue Advancements in Semiconductor Lasers)
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17 pages, 8175 KiB  
Article
Dynamics Simulation of Self-Mode-Locking in a Semiconductor Disk Laser Using Delay Differential Equations
by Tao Wang, Renjiang Zhu, Cunzhu Tong, Yunjie Liu and Peng Zhang
Photonics 2022, 9(11), 859; https://doi.org/10.3390/photonics9110859 - 13 Nov 2022
Cited by 2 | Viewed by 1763
Abstract
Self-mode-locked semiconductor disk lasers possess compact resonant cavity and stable construction. These devices have a wide application prospect because of their picosecond to sub-picosecond pulse width, excellent beam quality and tailorable emission wavelength. In this paper, dynamics simulations of self-mode-locking in a semiconductor [...] Read more.
Self-mode-locked semiconductor disk lasers possess compact resonant cavity and stable construction. These devices have a wide application prospect because of their picosecond to sub-picosecond pulse width, excellent beam quality and tailorable emission wavelength. In this paper, dynamics simulations of self-mode-locking in a semiconductor disk laser are performed by using delay differential equations for the first time. The corresponding conditions of different modality of mode-locking, including Q-switched mode-locking, continuous-wave mode-locking and harmonic mode-locking are calculated, and their dynamics evolution processes are presented. We also analyze the characteristics of the three different mode-locking modalities and summarize their overall dynamics evolution tendency. This kind of numerical simulation and analysis provides an understanding of the dynamics process of self-mode-locking, and may be referenced for related experiments. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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21 pages, 8536 KiB  
Article
A Novel Metaheuristic Approach for Solar Photovoltaic Parameter Extraction Using Manufacturer Data
by Salwan Tajjour, Shyam Singh Chandel, Hasmat Malik, Majed A. Alotaibi and Taha Selim Ustun
Photonics 2022, 9(11), 858; https://doi.org/10.3390/photonics9110858 - 13 Nov 2022
Cited by 10 | Viewed by 2153
Abstract
Solar photovoltaic (PV) panel parameter estimation is vital to manage solar-based microgrid operations, for which several techniques have been developed. Solar cell modeling using metaheuristic algorithms is found to be one of the accurate techniques. However, it requires experimental datasets, which may not [...] Read more.
Solar photovoltaic (PV) panel parameter estimation is vital to manage solar-based microgrid operations, for which several techniques have been developed. Solar cell modeling using metaheuristic algorithms is found to be one of the accurate techniques. However, it requires experimental datasets, which may not be available for most of the industrial modules. Therefore, this study proposed a new model to estimate the solar parameters for two types of PV panels using manufacturer datasheets only. In addition, two optimization techniques called particle swarm optimization (PSO) and genetic algorithm (GA) were also investigated for solving this problem. The predicted results showed that GA is more accurate than PSO, but PSO is faster. The new model was tested under different solar radiation conditions and found to be accurate under all conditions, with an error which varied between 7.6212 × 10−4 under standard testing conditions and 0.0032 at 200 W/m2 solar radiation. Further comparison of the proposed method with other methods in the literature showed its capability to compete with other models despite not using experimental datasets. The study is of significance for the sustainable energy management of newly established commercial PV micro grids. Full article
(This article belongs to the Special Issue Nanomaterials for Solar Applications)
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14 pages, 381 KiB  
Article
Reconstructed Hybrid Optical OFDM-NOMA for Multiuser VLC Systems
by Baolong Li, Jianfeng Shi and Simeng Feng
Photonics 2022, 9(11), 857; https://doi.org/10.3390/photonics9110857 - 13 Nov 2022
Cited by 4 | Viewed by 1882
Abstract
Non-orthogonal multiple access (NOMA) is deemed to be a prospective multiple access technology of the next generation. However, in visible light communication (VLC), when advanced hybrid optical orthogonal frequency division multiplexing (O-OFDM), such as hybrid asymmetrically clipped O-OFDM (HACO-OFDM), is combined with NOMA, [...] Read more.
Non-orthogonal multiple access (NOMA) is deemed to be a prospective multiple access technology of the next generation. However, in visible light communication (VLC), when advanced hybrid optical orthogonal frequency division multiplexing (O-OFDM), such as hybrid asymmetrically clipped O-OFDM (HACO-OFDM), is combined with NOMA, error propagation is induced, which degrades the system performance. Therefore, a novel reconstructed hybrid O-OFDM-NOMA (RHO-OFDM-NOMA) scheme is conceived in this paper. In order to eliminate the error propagation, the users in RHO-OFDM-NOMA opt for the ACO-OFDM or clipping-free O-OFDM signals according to their channel qualities, which are subsequently superimposed on pulse-amplitude-modulated discrete multitone (PAM-DMT) to yield the spectrum-efficient hybrid O-OFDM signal. Furthermore, a reconstruction process is designed to ensure the non-negativity. Compared with HACO-OFDM, the proposed RHO-OFDM can retain the error propagation in NOMA-VLC, whilst maintaining the superiorities of high spectral and power efficiency. It is demonstrated by simulation results that RHO-OFDM-NOMA can support a notably higher data rate than the NOMA schemes using conventional O-OFDM. Full article
(This article belongs to the Special Issue Advances in Visible Light Communication)
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9 pages, 4011 KiB  
Communication
Ultra-Wideband Polarization Insensitive Angle Filter Based on ENZ Characteristics and Dynamic Antireflection Structures
by Baofei Wan, Haining Ye and Haifeng Zhang
Photonics 2022, 9(11), 854; https://doi.org/10.3390/photonics9110854 - 12 Nov 2022
Cited by 4 | Viewed by 1948
Abstract
Bandwidth expansion has always been an important dimension in investigating angle filters (AFs) and is critical for optical communication and radar detection. In this paper, the AF with strong selectivity is realized by using the epsilon-near-zero (ENZ) jump characteristic of YaBa2Cu [...] Read more.
Bandwidth expansion has always been an important dimension in investigating angle filters (AFs) and is critical for optical communication and radar detection. In this paper, the AF with strong selectivity is realized by using the epsilon-near-zero (ENZ) jump characteristic of YaBa2Cu3O7 material. At the same time, for both the TE and the TM waves in the range of 237~1000 THz, the transmissivity of the AF is stronger than 0.9 by using dynamic antireflection structures (AFSs). The transfer matrix method is suitable for theoretical calculation, and the impedance matching theory is introduced to analyze the features of the AF. The increment of the thickness of superconductor material can effectively enhance the selectivity of the AF structure, and the consequence is the attenuation of transmission performances. If the temperature is covered from 0 K to 85 K, the filtering performance higher than 0.9 can still be maintained for two polarization waves. For these explicit performances, the proposed design may provide a new idea for widening the frequency bandwidth of the AF. Full article
(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)
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