Optical Fiber Communication Systems Research Articles

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.

Full C- and L-band covered second-order OAM mode generator based on a thinned helical long-period fiber grating

A full C- and L-band covered second-order orbital-angular-momentum (OAM) mode generator has been proposed and experimentally demonstrated, which is realized by using a helical long-period fiber grating (HLPG) but inscribed in a thinned four-mode fiber. By optimizing the design of grating period and fiber diameter of the proposed HLPG, an ultra-broadband rejection filter with a depth of ∼23 dB, a bandwidth of ∼156 nm @-10 dB (ranging from 1522 nm to 1678 nm) and a bandwidth of ∼58 nm @-20 dB (ranging from 1574 nm to 1632 nm), has been successfully obtained as a typical sample. To the best of our knowledge, this is the first demonstration of such ultra-broadband second-order OAM mode generator by using only one fiber component, i.e., the thinned HLPG. In addition, the proposed generator is less polarization-dependent and less temperature-sensitive than those of the conventional HLPGs, which is believed to be considerably helpful to find potential applications of the device itself in wavelength division multiplexing (WDM) and OAM mode division multiplexing (MDM) optical fiber communication systems.

Extra-cavity modulation of a chirped Gaussian bisoliton

Optical solitons can find important applications in optical fiber communication systems. Here, we simulate extra-cavity modulation of a chirped Gaussian bisoliton in a 1 μm wavelength band. Several different soliton parameters are varied (including the amplitude ratio and time delay of orthogonal components, the projection angle, phase difference, pulse chirps and propagation distances), to effectively change the optical spectra and pulse shapes of the initial input chirped Gaussian bisoliton. For example, when the two branches in the optical fiber modulation system have the same or different fiber lengths, the modulated chirped Gaussian bisoliton will show obviously different properties in the time domain for orthogonally polarized components, while the corresponding optical spectra have no obvious differences. The simulation results reveal the effects of extra-cavity modulation of the chirped Gaussian bisoliton, which further explores the field of soliton shaping out of a fiber laser cavity.

Empowering high-dimensional optical fiber communications with integrated photonic processors

Mode-division multiplexing (MDM) in optical fibers enables multichannel capabilities for various applications, including data transmission, quantum networks, imaging, and sensing. However, high-dimensional optical fiber systems, usually necessity bulk-optics approaches for launching different orthogonal fiber modes into the optical fiber, and multiple-input multiple-output digital electronic signal processing at the receiver to undo the arbitrary mode scrambling introduced by coupling and transmission in a multi-mode fiber. Here we show that a high-dimensional optical fiber communication system can be implemented by a reconfigurable integrated photonic processor, featuring kernels of multichannel mode multiplexing transmitter and all-optical descrambling receiver. Effective mode management can be achieved through the configuration of the integrated optical mesh. Inter-chip MDM optical communications involving six spatial- and polarization modes was realized, despite the presence of unknown mode mixing and polarization rotation in the circular-core optical fiber. The proposed photonic integration approach holds promising prospects for future space-division multiplexing applications.

Performance analysis of different dispersion compensation techniques in optical fiber communications system

Performance analysis of different dispersion compensation techniques in optical fiber communications system

Grating-assisted hot-electron photodetectors for S- and C-band telecommunication

Although outstanding detectivities, InGaAs photodetectors for optic fiber communication are often costly due to the need for cooling. Therefore, cryogen-free and cost-effective alternatives working in telecommunication bands are highly desired. Here, we present a design of hot-electron photodetectors (HE PDs) with attributes of room-temperature operation and strong optical absorption over S and C bands (from 1460 to 1565 nm). The designed HE PD consists of a metal–semiconductor–metal hot-electron stack integrated with a front grating. Optical simulations reveal that mode hybridizations between Fabry–Pérot resonance and grating-induced surface plasmon excitation lead to high absorption efficiencies (≥0.9) covering S and C bands. Probability-based electrical calculations clarify that device responsivity is mainly determined by working wavelength on the premise of broadband strong absorption. Moreover, through comparison studies between the grating-assisted HE PD and purely planar microcavity system that serves as a reference, we highlight the design superiorities in average absorption and average responsivity with optimized values of 0.97 and 0.73 mA W−1, respectively. The upgraded peformances of the designed device are promising for efficient photoelectric conversion in optic fiber communication systems.

High-order tunable multi-wavelength random Raman fiber laser based on few-mode fiber filter

In recent years, multi-wavelength fiber lasers have become one of the research hotspots and have been extensively applied in optical fiber communication systems. However, the presented multi-wavelength fiber lasers mainly operate in the 1.5 μm band. In this paper, a few-mode fiber filter-based cascaded high-order tunable multi-wavelength random Raman fiber laser (MWRRFL) is demonstrated, for the first time, in which a tuning range covers the 1.1–1.5 μm band. In the half-open MWRRFL, a few-mode fiber-based intermodal interferometer filter is inserted in the point reflector as a wavelength selector. The synergetic effect including high Raman gain and Rayleigh backscattering intensity in the hybrid of dispersion-shifted fiber and standard single-mode fiber is employed. It presents the capability for flat multi-wavelength random lasing stimulation. As a result, the wavelength channel number of the 6th-order random lasing is 6, with a maximum power variation of 4.66 dB and good temporal stability. The proposed cascaded tunable MWRRFL could provide a versatile source for optical fiber communication, optical fiber sensing, spectrum analysis, etc.

ExtraTrees-hidden Markov model based equalizer for mode division multiplexing ring-core fiber communication with non-orthogonal MultiCAP modulation

This paper presents an orbital angular momentum mode division multiplexing (OAM-MDM) ring-core fiber transmission method based on non-orthogonal multiband carrierless amplitude and phase (NMCAP) modulation with an extremely randomized trees-hidden Markov model (ExtraTrees-HMM)-based equalizer. The ExtraTrees-HMM equalizer uses the statistical characteristics of the received distorted signals to model the nonlinear channel of the system to classify these distorted signals into corresponding constellation classes. Experiments were conducted using a 216 Gbit/s OAM-MDM NMCAP modulation optical fiber communication system with 2 km ring-core fiber transmission and the results show that compared with a conventional Volterra nonlinear equalizer (VNE), the proposed ExtraTrees-HMM equalizer could improve the receiver sensitivity by 1 dB for OAM mode l = + 2, and 0.6 dB for OAM mode l = + 3. In addition, the computational complexity of the proposed equalizer was reduced by 43.94% compared with the VNE. In brief, the ExtraTrees-HMM is a promising equalization candidate for ultra-high-capacity inter-data-center interconnections.

Low-loss C-band all-fiber FIFO device by novel bridge fiber

Multi-core fibers (MCF) technology is the feasible path to extend the capacity of optical fiber communication systems. However, there is a lack of low-loss and low-crosstalk multi-core fan-in and fan-out (FIFO) devices for MCF communication in the C-band. In this paper, we proposed all-fiber FIFO devices with seven trench-assisted bridge fibers (TABFs). The special structure of the TABFs could facilitate the matching of single-core fiber with MCF during the tapering progress. By using the TABFs, the average taper loss was less than 0.06 dB. The novel method can reduce the insertion loss of FIFO devices. The experiments indicated that the fabricated FIFO devices exhibited lower than 0.50 dB insertion loss and less than −55.2 dB crosstalk in the C-band. This work provides novel TABFs and an efficient way to fabricate low-loss low-crosstalk FIFO devices for MCF communication systems.

Optical Fiber Communication System Based on Intelligent Joint Source-Channel Coded Modulation

Optical Fiber Communication System Based on Intelligent Joint Source-Channel Coded Modulation

Anion Hybridization for Enhanced Broadband Optical Response in Bi‐Doped Photonic Glass and Fiber

AbstractGiven the ever‐increasing demand for transmission capacity in optical fiber communication systems, there is a growing focus on developing active fibers and devices with an optical response across a wider spectrum. Bismuth (Bi)‐doped photonic glasses have attracted significant interest for their exceptional ultra‐broadband optical response, particularly within telecommunication bands. However, developing advanced Bi‐activated materials with robust optical response, high compatibility with commercial transmission systems, and low processing temperature remains a huge challenge. Herein, an anion hybridization strategy is proposed to overcome the aforementioned limitations. The anion hybridization significantly enhances the broadband optical response (≈10 times) of the Bi center following the introduction of fluorine ions, and reduces the transition temperature of the photonic glass (≈200 °C). Moreover, the near‐infrared optical response bandwidth experiences significant broadening, a result attributed to the larger inhomogeneous broadening. Furthermore, successful fabrication of the anion‐hybridized Bi‐activated glass fiber is achieved, demonstrating excellent compatibility with commercial transmission fibers. Additionally, the fabricated fiber exhibits an amplified spontaneous emission and on‐off gain across a broad waveband, further validating its efficacy. These results indicate that anion hybridization offers an effective strategy to optimize the optical and thermal properties of photonic materials to develop novel advanced photonic devices.

Soliton solutions of the improved perturbed nonlinear Schrödinger equation having parabolic law with non-local nonlinearity in the presence of chromatic and spatio-temporal dispersion terms

This paper was organized to examine the analytical solutions of the improved perturbed parabolic-law nonlinear Schrodinger equation including non-local nonlinearity in the presence of chromatic and spatio-temporal dispersion. This model mostly makes use of studying the propagation of optical pulses in fiber optic communication systems. We performed the Sinh-Gordon equation expansion method so that we produce the analytical solutions of the model under consideration. It was confirmed that the acquired solutions satisfy the main model. Therefore, bright and dark soliton solutions were retrieved; besides, various 3D and 2D graphical illustrations of the solitons were demonstrated via appropriate values of the parameters. Furthermore, this manuscript focused on the parameters’ effect on the acquired solitons behavior.

FrFT-based estimation of linear and nonlinear impairments using Vision Transformer

To comprehensively assess the conditions of an optical fiber communication system, it is essential to implement joint estimation of the following four critical impairments: nonlinear signal-to-noise ratio (SNRNL), optical signal-to-noise ratio (OSNR), chromatic dispersion (CD), and differential group delay (DGD). However, current studies only achieve identifying a limited number of impairments within a narrow range, due to a lack of high-performance computing algorithms and a unified representation of impairments. To address these challenges, we adopt time-frequency signal processing based on the fractional Fourier transform (FrFT) to achieve the unified representation of impairments, while employing a Transformer-based neural network (NN) to break through network performance limitations. To verify the effectiveness of the proposed estimation method, numerical simulations were conducted on a five-channel polarization-division-multiplexed quadrature phase shift keying (PDM-QPSK) long haul optical transmission system with the symbol rate of 50 GBaud per channel. The mean absolute error (MAE) for SNRNL, OSNR, CD, and DGD estimation is 0.091 dB, 0.058 dB, 117 ps/nm, and 0.38 ps, and the monitoring window ranges from 0−20dB, 10−30dB, 1700−51,000ps/nm, and 0−100ps, respectively. Our proposed method achieves accurate estimation of linear and nonlinear impairments over a broad range, representing a significant advancement in the field of optical performance monitoring (OPM).

DACNN-aided nonlinear equalizer for a probabilistic shaping coherent optical communication system.

The probabilistic shaping (PS) technique is a key technology for fiber optic communication systems to further approach the Shannon limit. To solve the problem that nonlinear equalizers are ineffective for probabilistic shaping optical communication systems with non-uniform distribution, a distribution alignment convolutional neural network (DACNN)-aided nonlinear equalizer is proposed. The approach calibrates the equalizer using the probabilistic shaping prior distribution, which reduces the training complexity and improves the performance of the equalizer simultaneously. Experimental results show nonlinear equalization of 120Gb/s PS 64QAM signals in a 375km transmission scenario. The proposed DACNN equalizer improves the receiver sensitivity by 2.6dB and 1.1dB over the Volterra equalizer and convolutional neural network (CNN) equalizer, respectively. Meanwhile, DACNN converges with fewer training epochs than CNN, which provides great potential for mitigating the nonlinear distortion of PS signals in fiber optic communication systems.

Improving orbital angular momentum mode transmission with imperfect ring–core fiber

Orbital angular momentum (OAM), inherent to light beams characterized by helical phase fronts, represents an alternative spatial degree of freedom for photons. In recent years, OAM-based communication has gained significant attention as a potential solution to increase the capacity and spectral efficiency of optical fiber communication systems. In optical fibers, OAM modes can be generated and manipulated by utilizing specialized optical components and techniques. One approach involves using specially designed optical fibers, such as ring–core fibers, which have the capability to support multiple OAM modes. In the manufacturing process, the ring fiber is hardly made perfectly, especially the doped-cores. The introduced defect breaks the symmetry of the ring–core, which has a serious impact on OAM mode transmission. Using a material with a slightly higher refractive index than the cladding to wrap the ring–core is effective in reducing impairment of defects. After numerical simulation, the proposed method improves the walk-off length by a factor of 2–40.

Recent advances of rare earth iron garnet magneto-optical single crystals

R3Fe5O12 (RIG) crystals are the most desirable elements for magneto-optical isolators in the near-infrared (NIR) to mid-infrared (MIR) region, with ever-growing demands for optical fiber communication and high-power laser system. Now, this system is the only commercialized Faraday rotator for optical isolators in 5G wireless communications. However, the growth of high-quality bulk RIG single crystals has been a big challenge for a long time, due to the typical incongruent melting characteristic and complex phase relationships. This work comprehensively summarizes the recent advances for the growth of RIG single crystals, including the proper choice of flux and innovative strategies on several growth techniques, like the flux-Bridgman, edge-defined film-fed growth (EFG) and top seeded solution growth (TSSG), etc. Effective modulation on the optical and magneto-optical performance is highlighted. Some ongoing perspectives are also proposed and discussed. It is anticipated that this work will provide deeper insight into the exploration of high-performance magneto-optical crystals for potential applications in NIR-MIR wavelength.

Transmission challenges in metropolitan area optical networks

Abstract For implementing wide/metropolitan area network in optical fiber communication system the key technology that can be utilized is wavelength division multiplexing (WDM). We discuss the use of WDM in metropolitan networks along with its special feature of using optical add drop multiplexers and also design issues in implementing these systems. The issue of nonlinear crosstalk induced in metropolitan networks is considered in terms of power penalty. Also, the effect of dispersion induced in optical fibers is considered by using two types of transmission systems. One is considering the non-zero dispersion shifted fiber (NZDSF) in dispersion effected environment and second is, implementing dispersion compensation after normal single mode fiber (SMF + DCF). The effect of nonlinear cross talk which can limit transmission performance is discussed in both cases in context with different parameters like power penalty, frequency difference between signal & crosstalk and transmission distance etc.

Coherent all-optical reservoir computing for nonlinear equalization in long-haul optical fiber communication systems

Photonic reservoir computing (RC), as a promising paradigm of optical signal processing, has attracted a great deal of attention in fiber nonlinearity equalization recently. For real long-haul transmission scenarios, we propose an all-optical RC operated in a coherent scheme to mitigate the nonlinear distortion of high-speed signals. Compared with the direct decision architecture, the proposed RC can dramatically improve the Q2 factor by 2.6 dB for a single-wavelength system and 1.9 dB for a 7-channel wavelength-division multiplexing (WDM) system over 3960-km fiber transmission. Furthermore, the robustness of the coherent all-optical RC is also verified by conducting studies on different training sequences. The coherent all-optical RC shows great potential in real-time nonlinearity mitigation for long-haul fiber transmissions.

Performance investigation of geometric constellation shaping-based coherent WDM optical fiber communication system supported by deep-learning autoencoder

Geometric constellation shaping (GCS) has been proposed to enhance the performance of wavelength-division multiplexing (WDM) coherent optical fiber communication (OFC) systems. This paper presents a comprehensive simulation platform to design and simulate these systems' performance using an advanced autoencoder (AE) technique. The design of the AE is based on end-to-end deep learning and takes into account the system parameters, especially those related to the OFC channel. The system design uses identical AEs, one in each WDM channel, and only the AE of the central channel is trained to achieve the required performance target. The developed AE simulation platform is capable of assessing the bit error rate characteristics, signal-to-noise ratio, and mutual information for long-haul coherent OFC-WDM systems operating with various modulation formats. The simulation results indicate that using a multilayer perceptron neural network to design AE requires four hidden layers, sixteen nodes per hidden layer, and a “16x modulation order” batch size to achieve optimum system performance. The AE's behaviour is investigated to identify the allowed ranges of the optimal launch power using two different procedures that achieve better system performance for 2D and 4D constellations.

Fiber Optics Communication: Evolution of Guided Media

Abstract: Fiber Optic Communication system is a key element in modern day telecommunication network used all around the globe. Larger bandwidth signal transmission where data received with lowest possible delay serves as a big edge to both, the telecommunication industry and consumer. Recently, optical fiber communication technology has made great progress, where constantly exploring new technologies has greatly enhanced communications capabilities in the traditional sense. This paper gives an overview of fiber optic communication systems including their key technologies, and also discusses their technological trend towards the next generation. The recent developments in the area of fiber optic communication as well as the advances in different Fiber types, their properties, optical sources, detectors, system limitations and applications are also discussed in the paper.