Performance Of Optical Communication Systems Research Articles

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

Modelling and numerical analysis of combined dual impact of SRS and FWM on the performance of upstream and downstream channels of a novel UDWDM/DWDM-PON

Wavelength division multiplexing (WDM) is an important method in modern optical communication systems for both long-haul and access networks. Particularly, after being standardized by Telecommunication Standardization Sector of International Telecommunication Union (ITU-T), WDM passive optical network (WDM-PON) becomes a considerable choice for fronthaul implementations of 5G networks. Stimulated Raman scattering (SRS) and four-wave mixing (FWM) are crucial nonlinear impacts that significantly limit the performance of WDM-based optical fiber communication systems. In this paper, an ultra-dense/dense WDM-PON (UDWDM/DWDM-PON) architecture has been proposed and combined dual impact of SRS and FWM on performances of upstream channels (USCs) and downstream channels (DSCs) of the proposed UDWDM/DWDM-PON has been numerically analyzed. USCs have been assumed to operate in 1310 nm region while operating wavelength region of DSCs has been taken as 1550 nm. Simulations have been performed on both UDWDM-PON architectures with 3.125 GHz and 6.25 GHz channel spacings and DWDM-PON architectures with channel spacings between 12.5 GHz and 100 GHz. 2x15-channel and 2x63-channel system structures have been considered in simulations. Signal-to-crosstalk ratio (SXR) has been chosen as performance parameter and its variation with channel input powers, channel spacings and channel lengths have been simulated for both USCs and DSCs of 2x15- and 2x63-channel UDWDM/DWDM-PONs. Results show that the proposed UDWDM/DWDM-PONs using single G.652 fiber can exhibit a reliable communication with minimum 23 dB SXR performance under combined dual impact of SRS and FWM unless some highlights about input powers and channel lengths mentioned in the paper are neglected.

Study on performance of a relay-assisted UWOC system based on adaptive optics

To improve the performance of underwater wireless optical communication (UWOC) systems, we propose a relay-assisted UWOC system model based on adaptive optics (AO). The closed expressions of the scintillation index, composite channel probability density function, and outage probability of the Gaussian beam before and after AO compensation are derived using the extended Rytov theory and Meijer G-function. The performance variation of an UWOC system with different parameters is analyzed by simulation. The results show that AO correction can compensate for the distorted wavefront and significantly reduce the intensity fluctuation at the receiving end. The proposed system can efficiently alleviate channel fading, improving the outage probability performance of the UWOC system.

Near-noiseless and small-footprint phase sensitive optical parametric amplifier using AlGaAs-on-insulator waveguides.

Phase sensitive amplifiers (PSAs) based on optical parametric amplification feature near noiseless amplification, which is of considerable benefit for improving the performance of optical communication systems. Currently, the majority of research on PSAs is carried out on the basis of highly nonlinear fibers or periodically poled lithium niobite waveguides, with the impediments of being susceptible to environmental interference and requiring complex temperature control systems to maintain quasi-phase matching conditions, respectively. Here, a near-noiseless and small-footprint PSA based on dispersion-engineered AlGaAs-on-insulator (AlGaAsOI) waveguides is proposed and demonstrated theoretically. The phase-dependent gain and the phase-to-phase transfer function of the PSA are calculated to analyze its characteristics. Furthermore, we investigate in detail the effects of linear loss, nonlinear coefficient, and pump power on the PSA gain and noise figure (NF) in AlGaAsOI waveguides. The results show that a PSA based on an AlGaAsOI waveguide is feasible with a maximum phase sensitive gain of 33dB, achieving an NF of less than 1dB over a gain bandwidth of 245nm with a gain of >15d B, which completely covers the S+C+L band. This investigation is worthwhile for noiseless PSAs on photonic integrated chips, which are promising for low-noise optical amplification, multifunctional photonic integrated chips, quantum communication, and spectroscopy, and as a reference for low-noise PSAs depending on the third-order nonlinearity, χ (3), of the waveguide material.

Design and analysis of performance for wider field of view of concentrator

A novel wider field of view of concentrators, which is composed of an optical fisheye lens with wider field of view and a traditional compound parabolic concentrator (CPC), is proposed in this paper. In this novel concentrator, exits of rays of meniscus fisheye lens and entrances of rays of CPC is fitted tightly on the basis of principles of ray trace, so that the proposed concentrator can be used to concentrate higher optical power than traditional CPC. In this paper, based on the geometry construction model of the new wide-field concentrator is established, the optics simulation software of TracePro is employed to model and design the structure of the concentrator, and analyses of performances for the concentrator is also carried out. The results show that this new wide-field concentrator can significantly increase the light energy received by the concentrator compared with a conventional concentrator without a wide-field fisheye lens, and can significantly improve the performance of LED wireless optical communication systems if used in the receiving optical antenna of LED wireless optical communication systems.

Underwater Channel Characteristics and Wireless Optical Communications Using a Blue Mode- Locked Semiconductor Disk Laser

An advanced light source at blue-green waveband is the key to improve the link-distance and communication performance of an underwater wireless optical communication (UWOC) system. This work presents the underwater channel characteristics and UWOC system using a blue semiconductor disk laser that passively mode-locked by a semiconductor saturable absorb mirror for the first time. The attenuation coefficients of the continuous-wave and mode-locked lasers under different concentrations of Maalox solution are studied, and the results indicate that the attenuation coefficients of the mode-locked laser are obviously lower than that of the continuous-wave laser. Then an UWOC system based on an acousto-optic modulator are constructed, and the water tank communication experiments are carried out by using quasi-cyclic low-density-parity-check coding and 64-pulse-position-modulation. Experimental results show that the bit error rates of the mode-locked laser are significantly lower than that of continuous-wave laser under the same Maalox solution concentration and same signal-noise-ratio. These results provide an attractive light source for practical long-distance UWOC.

Analysis on the performance of reconfigurable intelligent surface-aided free-space optical link under atmospheric turbulence and pointing errors

<span lang="EN-US">Free-space optical (FSO) communication can provide the cost-efficient, secure, high data-rate communication links required for applications. For example, it provides broadband internet access and backhauling for the fifth-generation (5G) and the sixth-generation (6G) communication networks. However, previous solutions to deal with signal loss caused by obstructions and atmospheric turbulence. In these solutions, reconfigurable intelligent surfaces (RISs) are considered hardware technology to improve the performance of optical wireless communication systems. This study investigates the pointing error effects for RIS-aided FSO links under atmospheric turbulence channels. We analyze the performance of RIS-aided FSO links influenced by pointing errors, atmospheric attenuation, and turbulence for the subcarrier quadrature amplitude modulation (SC-QAM) technique. Atmospheric turbulence is modeled using log-normal distribution for weak atmospheric turbulence. Several numerical outcomes obtained for different transmitter beam waist radius and pointing error displacement standard deviation are shown to quantitatively illustrate the average symbol error rate (ASER).</span>

Analysis on the performance of pointing error effects for RIS-aided FSO link over gamma-gamma channels

In this study, we analysis on the performance of pointing error effects for reconfigurable intelligent surfeces (RISs) aided free-space optical (FSO) communication link over moderate to strong atmospheric turbulence channels. Among these solutions, RISs are considered as hardware technology to improve performance of optical wireless communication systems. Performance evaluation of systems is affected by atmospheric attenuation, pointing errors and moderate to strong atmospheric turbulence channels for quadrature amplitude modulation (QAM) technique. Atmospheric turbulence channel from moderate to strong is modeled using gamma-gamma distribution. Several numerical results obtained the average symbol error rate (ASER) performance versus beam waist radius and signal to noise ratio for three value of pointing error displacement standard deviation. From the results, it is show that with RIS assisted can effectively improve the performance and link distance of the wireless communication systems.