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An optical wireless communication system deploying active high-pass pre-emphasis circuit for high speed application
摘要： This article presents a high-speed optical wireless communication link with a newly proposed pre-emphasis circuit to increase transmission performance at higher data rates. The effectiveness of the pre-emphasis circuit has been verified through testing on an optical wireless link implemented with existing laser communications components in our laboratory operating at 1550 nm. When the proposed pre-emphasis circuit is included in the optical wireless link, we achieved bit-error-rate (BER) power penalty improvements of 1.6, 2.2, and 1.0 dB at 155 Mbps, 622 Mbps, and 1.244 Gbps, respectively at the BER of 2 × 10?3 compared with the optical wireless communication links without pre-emphasis circuit. For the lower BER of 10?9, BER power penalty improvements of 2.2, 3.7, 0.7 dB at 155 Mbps, 622 Mbps, and 1.244 Gbps are observed, which show the effectiveness of our proposed pre-emphasis circuit in optical wireless communications link.
关键词： pre-emphasis,optical communications,optical wireless communications,free space optical communications,optical wireless link
更新于2025-09-23 15:22:29
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[IEEE GLOBECOM 2019 - 2019 IEEE Global Communications Conference - Waikoloa, HI, USA (2019.12.9-2019.12.13)] 2019 IEEE Global Communications Conference (GLOBECOM) - Intelligent Reflecting Surfaces for Free Space Optical Communications
摘要： In this paper, we investigate the use of intelligent reflecting surfaces (IRSs) (i.e., smart mirrors) to relax the line-of-sight requirement of free space optical (FSO) systems. We characterize the impact of the physical parameters of the IRS, such as its size, position, and orientation, on the quality of the end-to-end FSO channel. In addition, we develop a statistical channel model for the geometric and the misalignment losses which accounts for the random movements of the IRS, transmitter, and receiver due to building sway. This model can be used for performance analysis of IRS-based FSO systems. Our analytical results shows that depending on the angle between the beam direction and the IRS plane, building sway for the IRS has either a smaller or larger impact on the quality of the end-to-end FSO channel than building sway for the transmitter and receiver. Furthermore, our simulation results validate the accuracy of the developed channel model and offer insight for system design.
关键词： Smart mirrors,Channel model,Free space optical communications,Intelligent reflecting surfaces,Building sway
更新于2025-09-23 15:21:01
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[IEEE 2018 Asia Communications and Photonics Conference (ACP) - Hangzhou, China (2018.10.26-2018.10.29)] 2018 Asia Communications and Photonics Conference (ACP) - Dispersion-engineered Optical Phased Array for Aliasing-free Beam-steering with a Plateau Envelope
摘要： We design and fabricate a chip-scale optical phased array (OPA) with a uniform emitting structure composed of bent waveguides. This silicon-on-insulator based device demonstrates aliasing-free beam-steering over the entire field-of-view available (-34°~34°), with a far-field addressability of 6.71°. In addition, the steering process exhibits a plateau envelope, with an intensity fluctuation of less than 0.45 dB from -30°~30°.
关键词： free space optical communications,photonic integrated circuits,integrated optics,LiDAR
更新于2025-09-19 17:15:36
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Historical perspective of free space optical communications: from the early dates to today's developments
摘要： This survey article discusses the revolutions of wireless communication technologies right from the prehistoric man's fire signals to today's space optical communications. A brief description of evaluations of communication technologies from the ancient Greece to today's mature telecommunication fields is discussed in this review paper. Principle, significance, demonstration and development of free space optical (FSO) communication technology over different decades are discussed. Major FSO channel limitations, temporal and spatial challenges of FSO communication system and their state-of-art mitigation techniques are presented. Classical quantitative analysis of reliability of FSO communication, developments on radio over FSO (RoFSO) and hybrid FSO/RF systems are also explained. Advanced developments of FSO communication techniques such as optical free space wavelength division multiplexing (WDM), sub-carrier multiplexing (SCM), worldwide interoperability for microwave access (WiMAX), visible light communications (VLC) and vehicular visible light communications (VVLC) are reported. Deep space optical communication systems and next generation FSO wireless terrestrial/global network architecture are summarised. Research challenges of FSO systems for internet of things/everything (IoT/IoE), 5G communication, mobile-network, terahertz spectrum, quantum communication and underwater optical applications are presented. Based on the review, we outlined the challenges that need to be addressed in near-future researches to realize full potential FSO communication systems.
关键词： quantum communication,RoFSO,SCM,FSO,IoT/IoE,5G,WDM,underwater optical applications,VVLC,free space optical communications,VLC,WiMAX
更新于2025-09-19 17:13:59
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Fiber coupling characteristics of holographic optical element for free-space optical communications
摘要： The use of a holographic optical element (HOE) is proposed as a substitute for the fine-pointing mechanism (FPM) in free-space optical communications. A HOE possessing a function to transform the propagation angle of the received beam to a designed direction is fabricated. The coupling characteristics of the received beam to a single-mode fiber are experimentally evaluated. The results confirm the potential of the proposed method and show the advantages over the FPM.
关键词： holographic optical element,free-space optical communications,fine-pointing mechanism,fiber coupling
更新于2025-09-19 17:13:59
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Free-Space Optical Communications with Detector Arrays: A Mathematical Analysis
摘要： Photon counting detector arrays are commonly used for free-space optical communications in deep space. Such detector arrays—by virtue of their size—help in the collection of the optical signal even when there is some misalignment between the transmitter and receiver systems. In this paper, we argue that, for the common Gaussian beam pro?le, a detector array receiver is more useful for minimizing the probability of error than a single detector receiver of the same dimensions. Furthermore, the improvement in the error probability is more pronounced for low signal-to-noise ratio conditions, and the probability of error decreases monotonically as a function of the number of detectors in the array. However, communication with detector arrays results in a larger computational and hardware complexity at the receiver.
关键词： Free-space optical communications,photon counting detector arrays,error probability,Gaussian beam
更新于2025-09-16 10:30:52
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Differential pulse-amplitude modulation signalling for free-space optical communications
摘要： To improve the bandwidth efficiency of free-space optical systems and at the same time to reduce the impact of the background noise, a differential M-ary pulse-amplitude modulation (M-PAM) signalling scheme that uses two laser transmitters is proposed. The authors first consider the condition that the receiver perfectly knows the instantaneous channel coefficient and compare the performance of the proposed differential PAM with the conventional PAM signalling and show the improved performance when the background noise level is relatively high. Second, the practical situation where the receiver has to estimate the channel for signal detection is considered. The authors propose an estimation scheme based on the characteristics of the differential PAM signalling while requiring no pilot symbol transmission. The proposed data-aided channel estimation is performed on a sequence of received PAM symbols. The authors also show that for a sufficiently large observation window, the proposed estimation method allows achieving a performance close to the perfect channel knowledge.
关键词： bandwidth efficiency,channel estimation,background noise,free-space optical communications,differential M-ary pulse-amplitude modulation
更新于2025-09-11 14:15:04
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[IEEE 2018 11th International Symposium on Communication Systems, Networks and Digital Signal Processing (CSNDSP) - Budapest (2018.7.18-2018.7.20)] 2018 11th International Symposium on Communication Systems, Networks & Digital Signal Processing (CSNDSP) - FSO Communication for High Speed Trains: Blind Data Detection and Channel Estimation
摘要： We consider an free-space optical (FSO) system for high-speed trains where the sampling clock offset is randomly changing and the receiver does not have any information on the instantaneous channel fading coef?cient. Based on the use of multiple samplers at the receiver, we propose a novel sequence blind detection method, thus without requiring any pilot symbol. Furthermore, using the detected data, we propose a channel estimation scheme for the considered system.
关键词： Free-space optical communications,atmospheric turbulence,time synchronization,data detection
更新于2025-09-10 09:29:36
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Pointing errors effect on fiber coupling efficiency for Gaussian-beam wave through atmospheric turbulence channel in FSO links
摘要： In this paper, we theoretically study the pointing errors effect on fiber coupling efficiency for Gaussian-beam wave with consideration of atmospheric turbulence. A numerical expression of the average fiber coupling efficiency is derived based on mutual coherence function of Gaussian-beam wave and effective transmitter parameters. Numerical results show that the coupling efficiency can be evidently degraded by the pointing errors and pointing errors effect also changes optimum design parameter. And other factors, such as path length and the refractive index structure constant, are also analyzed. It is anticipated that this work is helpful to investigate pointing errors effect on optical wave propagation in the atmospheric turbulence.
关键词： Optical communications,Pointing errors,Free-space optical communications,Fiber coupling
更新于2025-09-09 09:28:46
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Atmospheric turbulence mitigation using spatial mode multiplexing and modified pulse position modulation in hybrid RF/FSO orbital-angular-momentum multiplexed based on MIMO wireless communications system
摘要： In this paper, the capacity of a free-space optical (FSO) communication over radio frequency (RF) could potentially be increased by the simultaneous transmission of multiple orbital angular momentum (OAM) based on spatial mode multiplexing (SMM) as an additional effective degree of freedom (EDOF) and quadrature amplitude modulation (QAM). This paper describes using hybrid RF/FSO-OAM based on multiple-input multiple-output (MIMO)/SMM using M-ary modified pulse position modulation (MPPM) and spatial PPM (SPPM) for potentially enhancing capacity in wireless communication systems. We present an analytical system design concerning OAM multiplexing and MIMO/SMM processing in free space communications channel under atmospheric turbulence (AT). Here, we assume a new architecture that closes the gap in speeds between millimeter-wave (mm-wave) wireless and optical links. In this study, we highlight recent advances in the use of OAM multiplexing for high-capacity FSO and mm-wave communications. We have developed the MPPM in FSO communication over RF using the source Gaussian model and SMM by proposing a new version of hybrid SPPM and MPPM. The novelty approach presents performance enhancement of the acquisition, pointing, tracking position and AT mitigation of link. We propose to use SMM combined with OAM-QAM based MIMO communications system to mitigate both weak and strong turbulence distortions. Simulation results show that the capacity of OAM-based MIMO system outperforms the capacity of the conventional MIMO system when the propagation distance is larger than a specific threshold. The use of transmitter lenses could enhance the OAM beams with a larger mode spacing (MS) of 2 (OAM l +1, l +3, l +5, l +7 transmitted) shows a lower power penalty (PP) when the inter-channel crosstalk overwhelms a larger lateral displacement of about 2 mm. Using the lenses at the transmitter to focus OAM beams could reduce power loss and PP in OAM-based FSO links and that this improvement might be more significant for higher-order OAM beams and provide high power-efficiency. With a larger of the transmitter and receiver 8 cm, 10 cm aperture size respectively, the system with mode spacing of 2 (OAM l +1, l +3, l +5, l +7 transmitted) and mode spacing of 3 (OAM l +1, l +4, l +7, l +10 transmitted) of OAM beams based on MIMO should fulfill lower-power penalty of 2.2 dB, 3.4 dB, as respectively and could enhance system robustness under angular error but degrade tolerance of lateral displacement. The proposed system provides an excellent signal-to-noise ratio (SNR) for the capacity in the regime of strong atmospheric turbulence. In this way, the maximization of FSO communication and RF wide, the data capacity enhancement, and it is considered a massive solution in the bandwidth provision for future access networks. This work could be beneficial to the practical implementation of OAM-MIMO/SMM multiplexed RF/FSO links.
关键词： Multiple-input multiple-output,Spatial mode multiplexing,Orbital angular momentum,Free space optical communications,Millimeter-wave communications,Modified pulse position modulation
更新于2025-09-04 15:30:14