Optical Fiber Transmission Link Research Articles

Modified failproof physics-informed neural network framework for fast and accurate optical fiber transmission link modeling

Physics-informed neural networks (PINNs) have recently emerged as an important and ground-breaking technique in scientific machine learning for numerous applications including in optical fiber communications. However, the vanilla/baseline version of PINNs is prone to fail under certain conditions because of the nature of the physics-based regularization term in its loss function. The use of this unique regularization technique results in a highly complex non-convex loss landscape when visualized. This leads to failure modes in PINN-based modeling. The baseline PINN works very well as an optical fiber model with relatively simple fiber parameters and for uncomplicated transmission tasks. Yet, it struggles when the modeling task becomes relatively complex, reaching very high error, for example, numerous modeling tasks/scenarios in soliton communication and soliton pulse development in special fibers such as erbium-doped dispersion compensating fibers. We implement two methods to circumvent the limitations caused by the physics-based regularization term to solve this problem, namely, the so-called scaffolding technique for PINN modeling and the progressive block learning PINN modeling strategy to solve the nonlinear Schrödinger equation (NLSE), which models pulse propagation in an optical fiber. This helps PINN learn more accurately the dynamics of pulse evolution and increases accuracy by two to three orders of magnitude. We show in addition that this error is not due to the depth or architecture of the neural network but a fundamental issue inherent to PINN by design. The results achieved indicate a considerable reduction in PINN error for complex modeling problems, with accuracy increasing by up to two orders of magnitude.

113Gbps rainbow visible light laser communication system based on 10λ laser WDM emitting module in fiber-free space-fiber link.

With the advent of the sixth-generation mobile communication standard (6 G), the visible light communication (VLC) technology based on wavelength division multiplexing (WDM) technology can effectively solve the problem of shortage of spectrum resources and insufficient channel capacity. This paper introduces one of our technical achievements, namely the construction of a near-real-time visible light laser communication (VLLC) system based on WDM, which includes a self-designed 10-λ fully-packaged visible light laser emission module, 1 m multimode fiber - 0.175 m free space - 1 m multimode fiber optical transmission link, and receiver array. In the transmitter system, we adopt adaptive discrete multitone (DMT) modulation technique combined with Quadrature Amplitude Modulation (QAM) modulation scheme to obtain maximum spectral efficiency (SE). In the receiving system, we utilize the sparse-structured reservoir computing post-equalization algorithm to achieve superior equalization performance on the basis of the traditional post-equalization algorithm. The experimental results indicate that this quasi-real-time communication system has achieved a signal transmission rate of 113.175Gbps. To the best of our knowledge, this work has set a record in the field of high-speed visible light laser communication. Therefore, the laser communication system constructed by this work, with its flexibility in deployment and high-speed performance, demonstrates the significant potential application of visible light laser communication in data center interconnection and high-speed indoor access networks.

Investigation of crosstalk and BER in multicore fiber optic transmission link for Space Division Multiplexing

The explosive growth of optical communication (i.e., 6G or beyond 5G) will transform the way of communication. Advanced modulation schemes, guided media, high data rate, minimum dispersion, low transmission noise, and signal processing techniques are available to enrich optical networks. The multicore fiber (MCF) will play a significant role in spatial division multiplexing. The major bottleneck of the MCF is the crosstalk in different cores. This article analyzed the crosstalk in multicore fiber (i.e., 2, 3, 4, and five core) as a transmission length function and compared the Q factor, bit error rate, and output power by considering all nonlinearities of the fiber. Maximum BER obtained for 5, 4, 3, and 2 core MCF is 10-14, whereas minimum BER for 5, 4,3, and 2 core MCF are 10–248, 10–248, 10–281, and 10–242, respectively. Maximum crosstalk occurs for 5 core MCF i.e.3166.32 dBm and minimum for 2 core MCF i.e. −44.083dBm. The highest Q factor is obtained at 35.8 for 3 core 10 km, and the minimum Q factor is ∼ 7.351 for 5 core MCF.

Modeling and simulation of fiber optic transmission links

The main aim of the paper is modeling and simulation of fiber optic transmission. It also deals with ways to increase the capacity of fiber optic transmission links by using WDM (Wavelength Division Multiplexing) system. The parameters of the fiber optic transmission link were measured on a real optical transmission links and a model for simulation was set up. A simulation of increasing the capacity of a fiber optic transmission link was made in two ways. The first one is to increase the transmission speeds of the individual channels of the WDM system, and the second one is to increase the number of WDM system channels with lower individual speeds. The simulation results showed that the second method provides better quality of WDM service. The additional experiment was done on an existing ITU T G.655 optical fiber intended for WDM systems whose parameters were measured. Bit error rate and Q parameter for WDM system of 4 and 16 channel was used to check quality of proposed solution.

Long Distance Broadband Fiber Optical Beamforming Over 120 km

With the development of the space exploration and satellite communications, the data transmission at broadband and long distance are in increasing demand. To enhance the signal transmission capability from the satellite to the earth over deep space, multiple radars from distributed ground stations at cooperative mode might be a promising solution. Broadband beamforming with high efficiency over long distance fiber optic transmission links is investigated in the paper. To achieve phase stable transmission for broadband signal, fast active optical compensation is adopted by phase locking each fiber optic link with a separate wavelength to discriminate the time jitter induced phase variation. By matching the time delays between the different channels, the signal-noise ratio (SNR) of the beamformed broadband signal is improved significantly. In the experiment, a root mean square (RMS) of time delay variations of 0.86 ps and Allan deviation of $1.74\times 10 ^{-13}$ for the carrier transmission in the phase locked fiber link over 120 km is achieved, and broadband fiber optical beamforming with data rate over 2 Gbit/s is successfully demonstrated.

Joint OSNR and CD monitoring in digital coherent receiver using long short-term memory neural network.

To enable the high quality-of-service of reliable and dynamic optical networks, it is essential to implement optical performance monitoring (OPM) for fiber optical transmission link. Being directly related to the quality of optical signal, optical signal-to-noise ratio (OSNR) and chromatic dispersion (CD) have become the most vital parameters to be monitored during OPM implementation. However, most existing simultaneous OSNR and CD monitoring schemes still suffer from high implementation complexity and low accuracy. Here, we demonstrate a joint OSNR and CD monitoring scheme for the digital coherent receiver, enabled by the long short-term memory neural network (LSTM-NN). LSTM-NN is able to identify the mapping from the received data to corresponding OSNR and CD values simultaneously, without manual feature pre-engineering. We carry out an experimental verification for optical signals with variable modulation formats and baud-rates. The mean absolute errors (MAEs) of simultaneous OSNR and CD monitoring are below 0.12 dB and 1.09 ps/nm, respectively, when both OSNR and CD are at the range from 15 to 30 dB and 1360 to 2040 ps/nm for 5/10 Gbaud PDM-16QAM/64QAM optical signals.

Design of Wideband GHz Electric Field Sensor Integrated with Optical Fiber Transmission Link for Electromagnetic Pulse Signal Measurement.

The detection of high frequency overvoltage and partial discharge is of great significance in evaluating the insulation condition of high-voltage power equipment. A wideband GHz electric field (E-field) sensor for electromagnetic pulse (EMP) signal measurement was proposed in this paper. An optical fiber transmission link was adopted in the design in order to implement high-voltage isolation and reduce electromagnetic interference during transmission. The designed sensor was mainly made up of a differential electric field (D-dot) antenna, transmitter, and receiver. The D-dot antenna was designed to detect high frequency E-field strength and generate a corresponding voltage signal, which was converted into an optical signal by the transmitter. The optical signal could be transmitted a large distance through an optical fiber without electromagnetic interference and changed back to a voltage signal again by a receiver. The design process of the sensor was introduced in detail, and experiments were performed using a gigahertz transverse electromagnetic (GTEM) cell and an EMP simulator to verify it. The results indicated that the designed sensor had a good performance besides an expectable delay due to the optional amplifier.

On the Impact of Fixed Point Hardware for Optical Fiber Nonlinearity Compensation Algorithms

Nonlinearity mitigation using digital signal processing has been shown to increase the achievable data rates of optical fiber transmission links. One especially effective technique is digital back propagation (DBP), an algorithm capable of simultaneously compensating for linear and nonlinear channel distortions. The most significant barrier to implementing this technique, however, is its high computational complexity. In recent years, there have been several proposed alternatives to DBP with reduced computational complexity, although such techniques have not demonstrated performance benefits commensurate with the complexity of implementation. In order to fully characterize the computational requirements of DBP, there is a need to model the algorithm behavior when constrained to the logic used in a digital coherent receiver. Such a model allows for the analysis of any signal recovery algorithm in terms of true hardware complexity which, crucially, includes the bit-depth of the multiplication operation. With a limited bit depth, there is quantization noise, introduced with each arithmetic operation, and it can no longer be assumed that the conventional DBP algorithm will outperform its low complexity alternatives. In this work, DBP and a single nonlinear step DBP implementation, the \textit{Enhanced Split Step Fourier} method (ESSFM), were compared with linear equalization using a generic software model of fixed point hardware. The requirements of bit depth and fast Fourier transform (FFT) size are discussed to examine the optimal operating regimes for these two schemes of digital nonlinearity compensation. For a 1000 km transmission system, it was found that (assuming an optimized FFT size), in terms of SNR, the ESSFM algorithm outperformed the conventional DBP for all hardware resolutions up to 13 bits.

Signal Transmission Links for the Electron Cyclotron Resonance Heating System on J-TEXT

Electron cyclotron resonance heating (ECRH) is an important auxiliary heating method which is widely used in magnetic confinement fusion. For the ECRH system on J-TEXT, signals should be transmitted to the control system for monitoring and protection and also to the data acquisition system. Considering the high-voltage and harsh electromagnetic interference environment, reliable fiber-optic transmission links are applied. Transmitted by fiber-optic modules, the response time of digital signals can be less than $1~\mu \text{s}$ . According to the ECRH system requirements, two practical analog fiber-optic transmission links based on the voltage-to-frequency and frequency-to-voltage conversion technology have been designed and developed. With IC AD650, the delay time of most analog signals is less than $100~\mu \text{s}$ , and with IC VFC110, critical signal transmission delay can be shortened to $5~\mu \text{s}$ . The test results indicate that the designed signal transmission links for ECRH system on J-TEXT are stable and reliable.

All-Silicon Waveguide Photodetection for Low-Bias Power Monitoring and 20-km 28-Gb/s NRZ-OOK Signal Transmission

We investigate the detection characteristics of a vertical p-n junction embedded waveguide in the low-gain region and strong avalanche gain region. Due to the “L” shape p-n junction and relatively high doping concentration, the photon absorption is enhanced and the working bias is reduced. The detection has linear response to input power in a wide dynamic range and continuous response to wavelength throughout C+L bands. We obtain a responsivity of 0.54 A/W, a 3-dB OE bandwidth of 26 GHz and a gain-bandwidth product of 28 THz at the bias of –9 V in the proposed device. Up to 28-Gb/s NRZ-OOK signal is successfully modulated and detected in an all-silicon scheme in up to 20-km optical fiber transmission link. We believe the proposed device has the potential for applications in integrated power monitors and all-silicon transceivers.

On the limits of digital back-propagation in the presence of transceiver noise.

This paper investigates the impact of transceiver noise on the performance of digital back-propagation (DBP). A generalized expression to estimate the signal-to-noise ratio (SNR) obtained using DBP in the presence of transceiver noise is described. This new expression correctly accounts for the nonlinear beating between the transceiver noise and the signal in the optical fiber transmission link. The transceiver noise-signal nonlinear beating has been identified as the main reason for the discrepancy between predicted and practical performance of DBP; which has not been previously suggested. This nonlinear beating has been included in the GN model, allowing DBP gains in practical systems to be predicted analytically. Experiments and split-step simulations with and without polarization-mode dispersion (PMD) in the transmission link have been performed. The results show that the impact of transceiver noise greatly outweighs that of PMD, and the analytical expressions are confirmed by the numerical simulations.

Transmission performances of solitons in optical wired link

Chaotic signal generation from microring resonators (MRRs) is presented. Two 1.5μm Gaussians with spectral profile having powers of 600mW are input into the system of MRRs. Using nonlinear conditions, the chaotic signals can be generated and propagated within the ring medium. Results show that the chaotic signals can be controlled and manipulated by using additional Gaussian input into the add port of the MRRs. A balance should be achieved between dispersion and nonlinear lengths when the propagating pulse is soliton. Chaotic output signals from the ring resonator can be converted to logic codes then inserted into an optical fiber transmission link which has a length of 180km in order to perform the transmission performance. The transmitted signals in the form of spatial and temporal solitons can be detected at the end of the transmission link.

Space-Time Coding Schemes for MDL-Impaired Mode-Multiplexed Fiber Transmission Systems

Spatial division multiplexing (SDM) holds out the prospects of increasing the capacities of optical fiber transmission links, especially with the recent achievements in the design of few-mode fibers and few-mode optical amplifiers. However, these systems are impaired by the capacity-limiting mode dependent loss (MDL) arising from imperfections in the optical fiber and inline components. Optical solutions were suggested to reduce, yet not completely remove, the accumulated MDL in the link through the use of strong coupling fibers and mode scramblers. Inspired by our previous study on mitigating polarization dependent loss (PDL), we present space-time (ST) coding schemes to mitigate MDL in mode-multiplexed optical transmission systems. We show, for the first time, that the combination of redundancy-free ST coding solutions with inline mode scrambling and optimal maximum-likelihood (ML) detection can completely absorb the SNR penalties induced by the MDL. The performance was assessed through simulations of three- and six-mode multiplexed systems where MDL levels up to 10 dB were observed. However, given the increased computational complexity of the suggested ML-decoded ST schemes, we present two reduced-complexity ST solutions offering a near-optimal performance. The first one consists in using a sub-optimal decoder and the second is a multiblock ST coding approach that can be scaled up for larger SDM systems.

Nanometer Bandwidth Soliton Generation and Experimental Transmission Within Nonlinear Fiber Optics Using an Add-Drop Filter System

An optical add-drop filter system is used to generate ultra-short nanometer (nm) bandwidth soliton pulses to be transmitted along the nano communication nonlinear fiber optics. In order to reduce the loss during the transmission, ultra-short soliton pulses are recommended. The theoretical part of this study uses the Z-transform method to present the characteristic transmission of the optical add-drop filter system. The nonlinear refractive index of the fiber optic transmission link is 2.6×10-20 m2/W. The Wavelength Division Multiplexing (WDM) can be performed to enhance the capacity of the system. This occurs when the bigger size of the ring resonator is used. Here, soliton pulses with bandwidths of 2.1 and 0.42 nm are generated and transmitted over the fiber optic length, where signals with a bandwidth of 55 and 200 ps are successfully detected at the end of the transmission link.

Lengthwise Measurement of Chromatic Dispersion along an Optical Fiber Transmission Link with Enhanced Correction Factor

AbstractIn recent years optical time domain reflectometer (OTDR)-based techniques have become a known practice for measuring chromatic dispersion (CD) distribution along an optical fiber transmission link. In this paper, a measurement technique which uses a four-wavelength bidirectional OTDR to evaluate the CD distribution along the length of an optical fiber transmission system has been presented. A novel formulation has been developed for this nondestructive technique to improve the correction factor, which leads to an improvement in the CD and mode field diameter (MFD) measurement. The obtained experimental outcomes are in good agreement with those obtained by the interferometric technique.

Transmission Performance Investigation of IR-UWB Signals over Existing optical fiber Transmission link

Recently there is increasing interest in using optical fiber links to distribute impulse radio-ultrawideband (IR-UWB) signals in order to increase the coverage area. This paper investigates the transmission performance of these signals over existing fiber links and addresses the possibility of increasing the coverage area beyond 30 km.The transmission link consists of a single- mode fiber, dispersion compensating fiber (DCF) and, optical amplifiers. Simulation results are presented using Optisystem (version 13.0) software package for both Gaussian monocycle and 5th-order derivative Gaussian systems, each operating with ON-OFF keying (OOK) and biphase modulation (BPM) formats. The results reveal that extending the coverage area for 625 Mb/s UWB signal toward 100 km is possible for the UWB signals and modulation formats adopted in this study.

Fiber-Optics Data Transmission for a Gyro Stabilized Platform

An optical fiber based data transmission link for a four-axis gyro stabilized inertial reference system is presented. The operation and configuration of the gyro stabilized platform is introduced to explain the requirement of data transmission. Four passive fiber optic rotary joints (FORJs) instead of traditional electrical sliprings are used to transmit optical signals between these relatively rotating gimbals. The hardware and software design of this optical fiber communication system operated at an updating rate of 1kHz are described to achieve high-speed, real-time, reliable data transmission. The experimental results show that the fiber optic rotary joint-based data transmission link is real-time and reliable. The use of FORJs as fiber optic sliprings will also result in an extremely low friction torque by comparing to electrical slipring assemblies. This allows the system designer to optimize the servo control performance for such high-precision gyro stabilized inertial reference systems.

Higher Spectral Efficiency Coherent Optical OFDM Transmission With Iterative Polar Modulation

Achieving high spectral efficiency in optical transmissions has recently attracted much attention, aiming to satisfy the ever increasing demand for high data rates in optical fiber communications. Therefore, strong Forward Error Correction (FEC) coding in combination with multilevel modulation schemes is mandatory to approach the channel capacity of the transmission link. In this paper we give design rules on the joint optimization of coding and signal constellations. We propose a novel coded modulation scheme based on 512-IPM for a fiber optical transmission link of 800km.The spectral efficiency achieved was 10% greater i.e,12.1 b/s/Hz at a post FEC BER of <10 -15 by using coded optimized constellation. In detail, the Turbo Principle to BICM-ID is adapted and combine it with a high-rate outer algebraic code to obtain a post-FEC BER <10 -15 , which is a typical demand in optical transponders. Furthermore we give simple design principles for the design of BICM-ID based on the extrinsic information transfer (EXIT) chart analysis.

Longitudinal measurement of chromatic dispersion along an optical fiber transmission system with a new correction factor

At present existence OTDR based techniques have become a standard practice for measuring chromatic dispersion distribution along an optical fiber transmission link. A constructive measurement technique has been offered in this paper, in which a four wavelength bidirectional optical time domain reflectometer (OTDR) has been used to compute the chromatic dispersion allocation beside an optical fiber transmission system. To improve the correction factor a novel formulation has been developed, which leads to an enhanced and defined measurement. The investigational outcomes obtained are in good harmony.

Optical generation of microwave passband signals

We investigate generation of microwave passband signals with a tunable central frequency using optical up-conversion. We consider systems without and with optical fiber transmission links. The technique performs photodetection of optically filtered gain switched laser pulses. Using appropriate electrical filters, we demonstrate up-conversion centered at 25, 35, and 45 GHz. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:656–660, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27392