Performance Of Optical Communication Systems Research Articles

Investigating performance of optical communication system with FSO/OWC channel

Abstract In recent years, the evolution of optical wireless communication (OWC) system has emerged as a viable alternative to radio frequency communication. These technologies provide an effective solution for addressing the need for point-to-point communication, offering benefits such as higher bandwidth, faster data rates, no licensing requirements, low power usage, quick and simple installation, enhanced security, and resistance to electromagnetic interference. In this article, we analyze two wireless optical communication systems: one using an FSO channel and the other using an OWC channel. The analysis focuses on range and quality factor as performance metrics. We examine the performance of one-to-many Tx/Rx FSO/OWC channel under three different atmospheric conditions: clear weather, haze, and fog, using eye diagrams. The system analysis includes mathematical models for the received optical power and the pointing error. Additionally, we investigate the impact of spatial diversity on the performance of FSO/OWC channel with configurations of 1 × 1, 2 × 2, 4 × 4, and 8 × 8. Our findings indicate that the 8 × 8 FSO/OWC configurations yield better results compared to other configurations and the OWC channel performs well over long distances up to 110 km, while the FSO channel is more suitable for short range communication up to 37 km.

BER and outage throughput analysis of DPIM/DHPIM coded QPSK-OFDM based outdoor optical wireless communications

With the growing demand for fast and reliable communication systems, particularly in outdoor environments, it is essential to investigate advanced encoding techniques. Digital Pulse Interval Modulation (DPIM) and Dual Header Pulse Interval Modulation (DHPIM) emerge as promising alternatives to traditional line coding methods, providing enhanced spectral efficiency and resistance to signal disruptions. This paper presents the performance of a Quadrature Phase-Shift Keying (QPSK) Orthogonal Frequency Division Multiplexing (OFDM)-based Optical Wireless Communication (OWC) system using these advanced encoding schemes. The analysis includes simulation results on QPSK-OFDM-based transmitter design, free space optical channel modeling based on Gaussian and log-normal distribution atmospheric turbulence, and recovery of input digital stream using the mentioned line coding techniques. The results demonstrate optimal bit error rate (BER) values for the QPSK-OFDM-based OWC system. The primary innovation of this research lies in the encoding schemes and their performance in outdoor optical wireless communication systems under turbulent conditions. Through extensive simulations and analysis, detailed insights into the bit error rate and outage throughput characteristics of DPIM/DHPIM coded QPSK-OFDM are provided, offering a unique perspective on the performance of these schemes in real-world scenarios. The findings not only highlight the optimal BER values achievable with the QPSK-OFDM-based OWC system but also offer insights into the system's ability to overcome transmission challenges under various atmospheric conditions.

Vortex inverted pin beams: mitigation of scintillations in strong atmospheric turbulence.

We recently introduced a new class of optical beams with a Bessel-like transverse profile and increasing beam width during propagation, akin to an "inverted pin." Owing to their specially engineered distribution, these beams have shown remarkable performance in atmospheric turbulence. Specifically, inverted pin beams (PBs) were found to have a reduced scintillation index as compared to collimated or focused Gaussian beams as well as other types of pin beams especially in moderate to strong turbulence. In this work, we demonstrate that inverted pin beams carrying orbital angular momentum (OAM) can further suppress intensity scintillations in moderate to strong irradiance fluctuation conditions. Our results can be useful in improving the performance and link availability of free-space optical communication systems.

Robust phase extraction from complex signals/fringe patterns for optical communications in 5G and beyond through continuous wavelet ridge technique

AbstractThe rapid progress in high‐precision optical instruments necessitates sophisticated image processing techniques for extracting vital information from generated images. Most of these instruments output images comprising RGB pixels. Deciphering these pixel values into phase information poses a significant challenge, especially in the presence of background noise. This study focuses on utilizing Two‐Dimensional Continuous Wavelet Transforms (2‐D CWT) for analyzing fringe patterns with varying noise levels and fringe alignments, crucial for high‐precision optical systems pivotal in enhancing the performance and reliability of optical communication systems in advanced 5G networks. The simulation results demonstrate that 2‐D CWT efficiently extracts phase information from complex and highly noisy fringes while requiring less computational time. Furthermore, the algorithm effectively handles noise disturbances with a commendable degree of accuracy, ensuring robust performance in 5G‐enabled optical systems critical for supporting ultra‐high‐speed data transmission and low‐latency communication requirements. This research contributes to optimizing image analysis techniques for 5G optical systems, facilitating their integration into next‐generation communication networks.

Simulative analysis of carrier suppressed return to zero based symmetrical compensated optical link

Abstract Optical communication systems provide high data rates to fulfil users’ demands. In addition, the modulation format is essential to the system’s transmission quality and spectral efficiency. Furthermore, the effects of chromatic dispersion, which impair the performance and quality of transmitted signals, are mitigated using dispersion compensation techniques. In optical communication systems, dispersion compensation techniques are essential for preserving signal quality, increasing transmission distances, improving system performance, and offering network designers flexibility. These methods seek to improve signal quality and enable transmission at longer distances by reducing or eliminating the distortion brought on by dispersion. This paper uses a symmetrical compensation technique to analyze the performance of the CSRZ modulation format-based optical communication system. The research is conducted within a communication range of 150–350 km. The system is evaluated in terms of input power, filter order, and filter depth. The results indicate that the proposed system performed better at an input power of 4 dBm using a third-order filter and 60 dB filter depth.

On the performance of a hybrid optical communication system: MGDM–FSO for challenging environments

On the performance of a hybrid optical communication system: MGDM–FSO for challenging environments

Atmospheric turbulence recognition with deep learning models for sinusoidal hyperbolic hollow Gaussian beams-based free-space optical communication links

The integration of artificial intelligence technology to improve the performance of free-space optical communication (FSO) systems has received increasing interest. This study aims to propose a novel approach based on deep learning techniques for detecting turbulence-induced distortion levels in FSO communication links. The deep learning-based models improved and fine-tuned in this work are trained using a dataset containing the intensity profiles of Sinusoidal hyperbolic hollow Gaussian beams (ShHGBs). The intensity profiles included in the dataset are the ones of ShHGBs propagating for 6 km under the influence of six different atmospheric turbulence strengths. This study presents deep learning-based Resnet-50, EfficientNet, MobileNetV2, DenseNet121 and Improved+MobileNetV2 approaches for turbulence-induced disturbance detection and experimental evaluation results. In order to compare the experimental results, an evaluation is made by considering the accuracy, precision, recall, and f1-score criteria. As a result of the experimental evaluation, the average values for accuracy, precision, recall and F-score with the best performance of the improved method are given; average accuracy 0.8919, average precision 0.8933, average recall 0.8955 and average F-score 0.8944. The obtained results have immense potential to address the challenges associated with the turbulence effects on the performance of FSO systems.

Performance evaluation and investigation of diffraction optical elements effect on bit error rate of free space optics and performance investigation of space uplink wireless optical communication under varying atmospheric turbulence conditions

AbstractSeveral other optical antenna topologies have been developed and implemented throughout the years. These topologies include a variety of optical components, including the axicon optical element, dual‐secondary mirror, cone reflecting mirror, prism beam slier, and beam‐splitter/beam combiner. In contrast, the secondary reflecting mirror causes an obscuration loss that must be compensated for by reducing the transmission power in an optical antenna design. In order to address this issue in space optical communication, the present research helps to develop an enhanced two diffractive optical elements (DOEs) technology however the data presented therein only shows that DOEs may boost transmission power efficiency, which is insufficient for system designers. Though On‐Off Keying (OOK) is widely used in optical communication systems at the moment, the proposed research include DOEs into an OOK space uplink optical. The proposed research uses numerical simulation to explore how much a space uplink OOK system's bit error rate (BER) may be improved by using DOEs and adjusting fundamental parameters. The proposed BER model takes environmental factors like wind and detector noise into account. Using this theoretical model, the present work helps to investigate the effect of DOEs on the BER versus fundamental parameter characteristic curves in space uplink optical communication. Based on the findings, the DOEs structure has the potential to significantly enhance the BER performance of space uplink optical communication systems, especially at high obscuration ratios. When the obscuration ratio is 0.25, 0.167, or 0.125 and the transmission power is 1 W, for instance, the DOEs may improve the BER by a factor of two or one order of magnitude or less when the parameters are changed to the typical parameter values as specified. Results increase by a factor of six, three, and two orders of magnitude, respectively, when transmitting at 5 W. The results show that DOEs can significantly enhance the BER performance, especially at high obscuration ratios. The findings suggest that integrating DOEs into the optical subsystem is a straightforward approach to improving the performance of space uplink optical communication systems.

Investigation of IEEE 802.16e LDPC Code Application in PM-DQPSK System

With the development of the Internet and information technology, optical fiber communication systems need to meet people’s information demand for large capacity and high speed. High-order phase modulation and channel multiplexing can improve the capacity and data rate of optical fiber communication systems, but they also bring the problem of bit error. To improve the transmission quality and reliability of optical fiber communication systems, forward error correction (FEC) coding techniques are commonly used, which serve as the fundamental approach to enhance the quality and reliability of fiber optic communication systems, ensuring that the received data remain accurate and reliable. The FEC in optical fiber communication systems is divided into three generations. The first generation FEC is mainly hard decision codewords, represented as RS code. The second generation FEC is mainly cascaded code, which stands for interleaved cascaded code. The third generation of FEC mainly refers to soft decision codes, which are represented as low-density parity-check (LDPC) codes. As a kind of FEC, LDPC codes stand out as pivotal contributors in the field of optical communication and have gained remarkable attention due to exceptional error correction performance and low decoding complexity. Based on IEEE802.16e standard, LDPC code with specific code length and rate is compiled and simulated in MATLAB and VPItransmissionMaker 10.1 and successfully incorporated into polarization multiplexed differential quadrature phase shift keying (PM-DQPSK) coherent optical transmission system. The simulation results indicate that the bit error rate (BER) can be reduced to 10−3 when the optical signal-to-noise ratio (OSNR) reaches 14.2 dB, and the BER experiences a reduction by nearly three orders of magnitude when the OSNR is 17.2 dB. These findings underscore the efficacy of LDPC codes in significantly improving the performance of optical communication systems, particularly in scenarios demanding robust error correction capabilities. This study provides valuable, significant results regarding the potential of LDPC codes for enhancing the reliability of optical transmission in real-world applications.

Design and Implementation of DSLMS Algorithm Based Photoelectric Detection of Weak Signals

Accurately extracting weak signals is extremely important for overall performance and application in optoelectronic imaging and optical communication systems. While weak signals are susceptible to noise, adaptive filtering is a commonly used noise removal method. Still, its convergence speed is slow, the steady-state error is large, and the anti-interference ability is weak. To solve the above problems, this paper proposes a new type of variable-step-length adaptive filtering algorithm (DSLMS) based on the minutiae function, which effectively reduces the noise component in error through its combination with the pair cancelation system, utilizing the low correlation property of the noise signal, to improve the anti-noise interference ability of the adaptive filter. Using FPGA and Matlab (2018b) for experimental verification, the results show that this algorithm shows significant advantages in noise suppression, accelerated algorithm convergence, and low steady-state error, and it has effectiveness and application potential for the optoelectronic detection of weak signal processing.

Modulation effect of focusing mirror on beam propagation through anisotropic turbulence

In this study, we modulated the Bessel-Gaussian (BG) beam using a focusing mirror to enhance the performance of wireless optical communication (WOC) while considering the angles between turbulence cells and the transmitted direction when beams propagate through anisotropic atmospheric turbulence along a slant path. Numerical results reveal that when the BG beam is modulated by a focusing mirror with a focusing length of 1 km, the detection probability of orbital angular momentum (OAM) is increased by 9.06% compared with the unmodulated BG beam when the OAM quantum number is 1. Simultaneously, this modulation method effectively reduces the bit error rate and enhances the channel capacity in OAM-based WOC. Furthermore, we observed that the smaller the OAM number, the better the effect of the modulation. Through our analysis, we identified that the most significant distortions in OAM mode propagation occur at the exponential parameter approximately 3.1 in the modified von Karman spectrum. Moreover, we demonstrated that the effects of the anisotropic tilt angle can not be negligible for beams through a slant path. Therefore, the modulation of the focusing mirror, in combination with a well-designed propagation direction that takes appropriate angles into account, can significantly improve the overall quality and performance of optical communication systems.

Phase screen prediction using deep phase network for FSO links.

Due to the presence of air turbulence in free-space optical (FSO) links, random fluctuations in wavefront phase and amplitude of the optical signal are reduced after it propagates through the air channel, which degrades the performance of free-space optical communication (FSOC) systems. Phase screen reflects the phase distortions resulting from air turbulence. Accordingly, accurate prediction with respect to phase screen is of significance for the FSOC. In this paper, we propose a phase screen prediction method based on the deep phase network (DPN). The advantages of the proposed method include strong robustness against air turbulence, low model depth, and fewer parameters as well as low complexity. The results reveal that our DPN enables desired inference accuracy and faster inference speed compared with the existing models, by combining the mean square deviation loss function with the pixel penalty terms. More concretely, the accuracy of phase screen prediction can reach up to 95%; further, the average time consumed to predict the phase screen is in the order of milliseconds only under various turbulence conditions. Also, our DPN outperforms the traditional Gerchberg-Saxton algorithm in convergence speed.

Utilizing Joukowsky transformation in the design of optical fiber for elliptical-to-circular mode conversion.

This study addresses the challenge of enhancing coupling efficiency between optical fibers and elliptical Gaussian beams emitted by semiconductor lasers, particularly in fiber communication systems. We introduce a method for fiber design utilizing the Joukowsky transformation to facilitate efficient mode transformation from elliptical to circular, thereby augmenting the coupling efficiency with both single-mode and multimode fibers. Theoretical analysis and numerical simulations demonstrate that the fiber with a structurally transitional core maintains high-efficiency mode transformation across various lengths, and its structure has been optimized accordingly. Additionally, our investigation reveals the designed fiber's ability to preserve polarization states, which could have significant implications in precision optical applications. The proposed design offers an approach to improving performance in optical communication systems, especially in wavelength-division multiplexing (WDM) transmission systems and fiber lasers.

Phase fluctuations-induced bit error ratio of deep-space optical communication systems during superior solar conjunction

Deep-space optical communication has garnered increasing attention for its high data transfer rate, wide bandwidth, and high transmission speed. However, coronal plasma turbulence severely degrades optical signals during superior solar conjunction. In this study, we introduce the models for plasma density and generalized non-Kolmogorov turbulence power spectrum. Based on these models, we derive the variance of the phase fluctuations with the assistance of the Rytov theory in the weak turbulence regime involving various variables, such as turbulence outer scale, spectral index, relative fluctuation factor, and wavelength. Subsequently, we evaluate the bit error ratio (BER) performance of the deep-space optical communication system, considering phase fluctuations and intensity scintillations, under binary phase shift keying modulation. Numerical calculations reveal that small heliocentric distance, large relative fluctuation factor and spectral index, could induce severe phase fluctuations and high BER. Fortunately, the effects of the plasma irregularities on the BER performance can be mitigated by short optical wavelength under large outer scale.

Performance investigation of 1.5 Tb/s optical hybrid 2D-OCDMA/OFDM system using direct spectral detection based on successive weight encoding algorithm

In order to raise the performance of optical communication systems, it is imperative mainly to increase the number of available users while decreasing the bit error rate (BER) in the required spectral width. This can be challenging in optical multiplexing systems including incoherent optical code division multiplexing (OCDMA). In this respect, an interesting two-dimensional hybrid spectral/spatial OCDMA system using orthogonal frequency division multiplexing (OFDM) technology based on successive weight (SW) coding has been investigated. Using the zero cross-correlation (ZCC) feature, the novel approach declined the effect of phase-induced intensity noise (PIIN), and multi-user interference (MUI) at the receiver has been fully eradicated. When compared to systems with Modified Double Weight (MDW), Flexible Cross Correlation (FCC), and two-dimensional hybrid Flexible Cross-Correlation - Modified Double Weight 2D-MDW/FCC codes, numerical findings demonstrate that our proposed system is more efficient, increasing the number of simultaneous users to 350, and achieving a higher overall transfer rate towards 1.5 Tb/s under the required optical communication conditions.

Performance of Orbital Angular Momentum Communication for a Non-Uniformly Correlated High-Order Bessel–Gaussian Beam in a Turbulent Atmosphere

We derived the formula for the detection probability, signal-to-noise ratio (SNR), and average bit error rate (BER) for the signal orbital angular momentum (OAM) state carried via non-uniformly correlated high-order Bessel–Gaussian beam propagation in a turbulent atmosphere. The wavelength, receiver aperture, beam width, strength of the turbulent atmosphere, and topological charge effect on detection probability, SNR, and average BER of the signal OAM state were demonstrated numerically. The results show that the signal OAM state with low topological charge, a small receiver aperture, a narrow beam width, and a long wavelength can improve the performance of optical communications systems under conditions of weak atmospheric turbulence. Our results will be useful in long-distance free space optical (FSO) communications.

Performance analysis of FSO communications over a generalized turbulence fading channel with pointing error

SummaryQuantitatively assessing the performance of free space optical (FSO) communication systems requires an accurate description of turbulence induced fading. However, it is well known that common irradiance distributions inaccurately model intensity tail regions. Recently, a general fading model as the product of arbitrary number of Gamma with inverse Gamma was proposed and shown to accurately predict measurements, besides containing many well‐known models as special cases. This paper is concerned with analyzing the effect of discrepancies among different fading distributions on optical system performance in terms of bit error rates and capacity. Based on the general fading model a unified analysis of the channel structure effects on FSO communications in the presence of turbulence and pointing error is presented. The outage probability is investigated for both homodyne and direct detection schemes. Closed form expressions for the average probability of bit error for intensity modulation, phase shift keying and polarization shift keying, single‐input‐single‐output systems are given and verified by Monte‐Carlo simulations. Spatial diversity is also studied through single‐input‐multiple‐output systems. Also, the ergodic capacity is derived. Comparisons between the proposed distributions and other widely used distributions are carried out and show significant differences among existing fading models. This suggests possible improvements in the spectral efficiency and error performance design of optical wireless communication systems.

Performance analysis of OSSK-UWOC systems considering pointing errors and channel estimation errors.

In this paper, we present the bit error rate (BER) performance of the underwater wireless optical communication (UWOC) systems using the optical space shift keying (OSSK) on the gamma-gamma turbulent fading channel, which also considers pointing errors and channel estimation errors. Firstly, we develop the new expressions for the probability density function (PDF) based on the Gamma-Gamma distribution with error factors. Subsequently, we analyze the statistical characteristic of the difference in attenuation coefficients between two channels in the OSSK system, by which we provide analytical results for evaluating the average BER performance. The results show that the effective improvement of spectral efficiency (SE) and BER performance is achieved by rationally allocating the number of lasers and detectors in the system. The OSSK-UWOC system performs better when a narrow beam waist is used. Furthermore, the presence of channel estimation error brings the BER performance advantage to the system, and the system with a high channel estimation error (ρ = 0.7) shows a 4 dB improvement in signal-to-noise ratio (SNR) gain compared to the system with a low channel estimation error (ρ = 0.95). The findings in this paper can be used for the UWOC system design.

Influence of atmospheric turbulence on coherent detection performance of space coherent optical communication

Space coherent optical communication technology is considered to be an important way to overcome the bottleneck in current high-speed space communication. However, atmospheric turbulence seriously limits its realization. Based on the Huygens-Fresnel principle and the low-frequency compensation power spectrum inversion method, this work first investigates the random distribution characteristics of the amplitude and phase of a Gaussian beam after it has been transmitted through atmospheric turbulence. Then, using the coherent mixing efficiency and communication bit error rate model, the influence of atmospheric turbulence on the performance of spatial coherent optical communication systems is obtained. Finally, a laser heterodyne detection experimental system is built to quantitatively study the influence of atmospheric turbulence on the coherent detection performance of spatial coherent optical communication. The conclusions drawn from this study are as follows. 1) The spatial phase distortion caused by the weak turbulence channel is relatively small and will hardly affect the light intensity distribution characteristics of the Gaussian beam. In the case of weak turbulence, the influence of weak turbulence on the performance of coherent optical communication system is almost negligible. The communication bit error rate will decrease rapidly with the increase of the number of single bit data photons. The communication signal-to-noise ratio can be better than 10<sup>–5</sup> when the number of single-bit photons is greater than 10. 2) Moderate turbulence will change the intensity distribution characteristics of the Gaussian beam, but will not cause a serious shift in the center of the spot. Under moderate turbulence conditions, the coherent mixing efficiency decreases rapidly as the turbulence intensity continues to increase, but the communication bit error rate still decreases rapidly with the increase of the number of single bit data photons. At this time, increasing the number of single-bit photons can suppress the negative influence of moderate intensity turbulence on the performance of coherent optical communication systems. 3) Strong turbulence will cause severe spatial phase distortion of the beam, destroy the consistency of the light intensity distribution, and cause a serious shift in the center of the spot. Under strong turbulence conditions, the coherent mixing efficiency of coherent optical communication systems approaches zero, and increasing the number of single bit data photons cannot significantly reduce the bit error rate, seriously affecting the quality of coherent optical communication. Atmospheric turbulence is an important limiting factor for developing space coherent optical communication. This study can provide useful references for evaluating the performance of space coherent optical communication systems.

Adaptive-optics-based turbulence mitigation in a 400 Gbit/s free-space optical link by multiplexing Laguerre–Gaussian modes varying both radial and azimuthal spatial indices

In general, atmospheric turbulence can degrade the performance of free-space optical (FSO) communication systems by coupling light from one spatial mode to other modes. In this Letter, we experimentally demonstrate a 400 Gbit/s quadrature-phase-shift-keyed (QPSK) FSO mode-division-multiplexing (MDM) coherent communication link through emulated turbulence using four Laguerre Gaussian (LG) modes with different radial and azimuthal indices (LG10, LG11, LG−10, and LG−11). To mitigate turbulence-induced channel cross talk and power loss, we implement an adaptive optics (AO) system at the receiver end. A Gaussian beam at a slightly different wavelength is co-propagated with the data beams as the probe beam. We use a wavefront sensor (WFS) to measure the wavefront distortion of this probe beam, and this information is used to tune a spatial light modulator (SLM) to adaptively correct the four distorted data-beam wavefronts. Using this adaptive-optics approach, the power loss and cross talk are reduced by ∼10 and ∼18 dB, respectively. © 2023 Optical Society of America