Fiber Span Research Articles

ETUDE DE PERFORMANCE DUN NOUVEL ALGORITHME DE LOFDM ADAPTATIF POUR LA MONTEE EN DEBIT DANS LES RESEAUX DACCES OPTIQUES

Orthogonal Frequency Division Multiplexing (OFDM) has demonstrated its effectiveness as a modulation technique in optical communication systems, where data is transmitted and received through optical channels. This paper proposes and implements a novel adaptive OFDM method, called Minimization E-Tighted (MET), aimed at enhancing the data rate in low-cost optical access network links. The implementation was carried out for a Time Division Multiplexing Passive Optical Network (TDM-PON) link, co-simulated using VPIphotonics™ and MATLAB. Simulation results showed that for the simulated target BER values (10⁻³ and 10⁻⁴), the data rates achieved with the MET method are nearly identical to those obtained using the Levin-Campello method, which is commonly employed for rate enhancement. With the simulated parameters at a target BER of 2.23×10⁻⁴, it is demonstrated that 12 Gb/s data rate are achievable on a TDM-PON link with the MET method, supporting 64 users over a 60 km fiber span. Moreover, the MET method proved its capability to optimize the data rate for any given target BER value. Finally, the study revealed that employing high-resolution DAC/ADC converters can further increase the links data rate when the MET algorithm is used.

Range-scalable distributed acoustic sensing with EDFA repeaters demonstrated over 2227 km

We demonstrate a new, to the best of our knowledge, range-scalable repeatered distributed acoustic sensing (DAS) solution sharing technology with existing long-haul subsea telecom networks capable of low noise and high spatial and temporal resolution. Single ended DAS interrogation through a 2227 km line comprising 39 repeatered fiber spans is demonstrated with a 10 m spatial resolution, a 1.78 kHz sampling rate, and a strain resolution of 35 pε/√Hz for the outermost span. The technique allows for many DAS channels to be wavelength multiplexed on a single fiber pair. Addressing of spans with add/drop (A/D) multiplexers (MUX) is demonstrated with <−60 dB cross talk between spans.

Machine learning model based on the time domain regular perturbation-based theory for performance estimation in arbitrary heterogeneous optical links

To meet the required high demands for the capacity of optical networks, there are several efforts in recent years to further reduce the system margin. To achieve this goal, a fast and reliable QoT estimation tool is needed. The key module of such QoT tool is the nonlinear interference variance estimation. This paper presents a novel machine learning tool to speed up the exact model by six orders of magnitude without scarifying the accuracy and the scalability of this semi-analytical model. Moreover, to further enhance the scalability of the model, we used the cross-correlation functions to re-write the equations. The proposed ML-based framework KerrNet, based on a bank of small ANNs, can handle any arbitrary heterogeneous link up to ten thousand km composed of different fiber span. The transmitting C-band WDM channels in both fully loaded and sparsely occupied configurations are evaluated. The crucial steps for the machine learning algorithm to converge, which are the data preparation and the choice of training data, are presented in detail.

Digital-twin-based active input refinement for insertion loss estimation and QoT optimization in C and C + L networks

Quality of transmission (QoT) prediction is a fundamental function in optical networks. It is typically embedded within a digital twin and used for operational tasks, including service establishment, service rerouting, and (per-channel or per-amplifier) power management to optimize the working point of services and hence to maximize their capacity. Inaccuracy in QoT prediction results in additional, unwanted design margins. A key contributor to QoT inaccuracy is the uncertain knowledge of fiber insertion loss, e.g., the attenuation due to connector losses at the beginning or at the end of each fiber span, as such loss cannot be directly monitored. Indeed, insertion losses drive the choice of the launch power in fiber spans, which in turn drive key physical effects, including the Kerr and stimulated Raman scattering (SRS) effects, which affect services’ QoT. It is thus important to estimate (and detect possibly anomalous) fiber insertion losses at each span. We thereby propose a novel active input refinement (AIR) technique using active probing to estimate insertion losses in C and C + L systems. Here, active probing consists of adjusting amplifier gains span by span to slightly alter SRS. The amount of adjustment must be sufficient to be measurable (such that insertion losses can be inferred from the measures) but small enough to have a negligible impact on running services in a live network. The method is validated by simulations on a European network with 30 optical multiplex sections (OMSs) in C and C + L configurations and by lab experiments on a C-band network, demonstrating that AIR significantly improves insertion loss estimation, network QoT optimization, and QoT prediction compared with other state-of-the-art monitoring techniques. This work underscores the critical role of accurate estimation of QoT inputs in enhancing optical network performance.

Comparing the Performance of Optical Communication Links using G.652 and G.655 Fiber in Python Packages

This study investigates and compares the performance of a 10 Gbps optical communication link utilizing two prevalent single-mode fibers: G.652 and G.655. The analysis employs both theoretical calculations and Python-based simulations to assess the effectiveness of each fiber type in this high-speed transmission scenario. With the ever-growing demand for bandwidth in communication networks, 10 Gbps transmission systems are becoming increasingly commonplace. Single-mode fibers like G.652 and G.655 play a vital role in these systems, offering low signal attenuation for long-distance data transmission. However, each fiber type exhibits distinct dispersion characteristics, which can impact signal integrity over extended distances. This investigation adopts a two method for performance evaluation. Firstly, link power budget calculations are performed to determine the optical signal power before and after propagating through a 50-kilometer fiber span. The received power serves as the foundation for subsequent Q-factor and Bit Error Rate (BER) analysis. These calculations establish the theoretical limitations of the system based on well-defined formulas. Secondly, Python-based simulations are conducted to corroborate the theoretical findings and provide a more comprehensive performance assessment. This approach leverages the capabilities of two prominent Python packages: Opticomlib and OpticommPy. Opticomlib excels at analyzing the behavior of individual optical pulses within the system, enabling an understanding of the signal propagation. On the other hand, OpticommPy specializes in parameter sweep analysis, allowing for the investigation of how critical parameters like received power influence the Q-factor. By combining these functionalities, the simulations provide a detailed picture of the system's performance under various conditions. The calculated BER and Q-factor values for both G.652 and G.655 fiber links surpass the industry-accepted performance standards. These results demonstrate the effectiveness of using Python-based tools for comprehensive performance analysis of optical communication systems. However, it's important to note that slight discrepancies exist between the calculated and simulated results.

A multi-mode free-space delay interferometer with no refractive compensation elements for phase-encoded QKD protocols

We demonstrate a compensation-free approach to the realization of multi-mode delay interferometers, mainly for use in phase-encoded quantum key distribution (QKD). High interference visibility of spatially multi-mode beams in unbalanced Michelson or Mach–Zehnder interferometers with a relatively wide range of delays is achieved by the appropriate choice of the transverse size of the beam. We provide a simple theoretical model that gives a direct connection between the visibility of interference, the delay and the beam parameters. The performed experimental study confirms our theoretical findings and demonstrates measured visibility of up to 0.95 for a delay of 2 ns. Our approach’s simplicity and robust performance make it a practical choice for the implementation of QKD systems, where a quantum signal is received over a multi-mode fiber. The important application of such a configuration is an intermodal QKD system, where the free-space atmospheric communication channel is coupled into a span of the multi-mode fiber, delivering the spatially distorted beam to the remote receiver with minimal coupling loss.

Co-LSTM-based fiber link modeling with ASE noise tracking for long-haul coherent optical transmission.

In this Letter, a novel, to the best of our knowledge, channel modeling scheme based on cascading chromatic dispersion-nonlinearity feature decoupling modules is proposed with the center-oriented long short-term memory (Co-LSTM) network structure adopted for modeling nonlinearity of each optical fiber span. By tracking the amplified spontaneous emission (ASE) noise at the output of each fiber span, the Co-LSTM-based channel modeling scheme achieves high waveform accuracy for long-haul coherent optical transmission compared with the conventional split-step Fourier transform method (SSFM) while saving calculation time by almost one order of magnitude.

Digital-twin-assisted meta learning for soft-failure localization in ROADM-based optical networks

Reconfigurable optical add/drop multiplexer (ROADM) nodes are evolving towards high-degree architectures to support growing traffic and enable flexible network connectivity. Due to the complex composition of high-degree ROADMs, soft failures may occur between both inter- and intra-node components, like wavelength selective switches and fiber spans. The intricate ROADM structure significantly contributes to the challenge of localizing inter-/intra-node soft failures in ROADM-based optical networks. Machine learning (ML) has shown to be a promising solution to the problem of soft-failure localization, enabling network operators to take accurate and swift measures to overcome such challenges. However, data scarcity is a main hindrance when using ML for soft-failure localization, especially in the complex scenario of inter- and intra-node soft failures. In this work, we propose a digital-twin-assisted meta-learning framework to localize inter-/intra-node soft failures with limited samples. In our proposed framework, we construct several mirror models using a digital twin of the physical optical network and then generate multiple training tasks. These training tasks serve as pretraining data for the meta learner. Then, we use real data for fine-tuning and testing of the meta learner. The proposed framework is compared with the rule-based reasoning method, transfer-learning-based method, and artificial-neural-network-based method with no pretraining. Experimental results indicate that the proposed framework improves localization accuracy by over 15%, 33%, and 54%, on average, compared to benchmark approaches, respectively.

High spectral efficiency modulation scheme based on joint interaction of orthogonal compressed chirp division multiplexing and power superimposed code.

In this paper, we propose a high spectral efficiency modulation scheme based on joint interaction of orthogonal compressed chirp division multiplexing (OCCDM) and power superimposed code (PSC) under the intensity modulation and direct detection (IM/DD) system. OCCDM is a novel orthogonal chirp division multiplexing technology featuring spectral compression through the implementation of processing similar to a discrete Fourier transform, enhancing the spectral efficiency (SE) through bandwidth savings without loss of orthogonality of each chirp. Meanwhile, PSC technology enables multiple code words being transmitted superimposed on the same chirp. This technique involves allocating varying power levels to different users, thereby distinguishing them, increasing the transmission's net bit rate and substantially boosting the SE. The transmission has been performed experimentally using a 2 km 7-core fiber span. The impact of the above-mentioned technologies on the bit error rate (BER) performance is assessed in the power, frequency, and joint domain. The BER and enhancements in the SE can be balanced when the spectral bandwidth compression factor (α) and power distribution ratio are equal to 0.9 and 4, respectively. The observed outcome leads to the transmission's SE increase to more than double the baseline value, at 2.22 times. Based on the above analysis, we believe this structure is expected to become a potential for developing next-generation PON.

Compensation of the Distorted WDM Signals by Symmetric Dispersion Map with Nonuniform Zero-Crossing Place of Accumulated Dispersion in Midway-OPC System

The nonlinear Kerr effect and chromatic dispersion are the fundamental causes of optical signal degradation in single-mode fiber (SMF) and erbium-doped fiber-amplification (EDFA)-based wavelength division multiplexing (WDM) transmission. Dispersion management combined with a midway optical phase conjugator among the technologies for compensating for such optical signal distortion is known to not be limited by the modulation format and multiplexing technology. Optimization of the dispersion map can partially alleviate the capacity and maximum transmission distance limitations of the SMF and EDFA system. In this paper, we propose various types of symmetric dispersion maps in which the position of zero-crossing place of the cumulative dispersion is not constant, and analyze the effect of each dispersion map configuration on 40 Gb/s × 24-channel WDM signal distortion compensation. When designed with the residual dispersion per span (RDPS) around 400 ps/nm, it is confirmed that most of the proposed dispersion maps are more effective in compensating the distorted WDM signal than conventional dispersion map. In particular, we confirm that, among the proposed dispersion maps, the dispersion map in which the RDPS is designed uniformly for all fiber spans can increase the power margin of WDM channel and expand the range of the total residual dispersion in the dispersion-managed link.

Hybrid amplifier placement in mesh DWDM networks using integer linear programming models

Hybrid erbium-doped fiber (EDF)/Raman amplifiers (HFAs) can be utilized to improve the performance of specific fiber spans in dense wavelength division multiplexing (DWDM) networks, aiming to extend the reach and/or increase the capacity of optical channels, thereby reducing the total number of line interfaces required to satisfy a given set of traffic demands. However, HFAs are costlier than simpler EDF amplifiers (EDFAs) since they include Raman pumps in addition to an EDFA. Consequently, it is paramount to place them only at selected fiber spans of the network so as to maximize their impact while keeping their number limited. It has been shown that HFA placement can be a complex task in mesh DWDM networks in view of optical channel diversity, with each fiber span traversed by multiple channels with different source and destination nodes. Building on the approximation that noise adds up incoherently along the transmission path, this paper proposes optimal methods to solve the problem of placing hybrid amplifiers in mesh networks. Particularly, it describes two integer linear programming models, one to determine the minimum number and location of HFAs required to reach a target set of feasible optical channels (i.e., without intermediate 3R regenerators) and another to maximize the number of feasible optical channels given a limited number of HFAs to be deployed. A comprehensive set of network simulations using three reference optical network topologies is reported, providing insight into the effectiveness of the proposed models when compared to existing approaches.

Flexible optical fiber channel modeling based on a neural network module.

Optical fiber channel modeling, which is essential in optical transmission system simulations and designs, is usually based on the split-step Fourier method (SSFM), making the simulation quite time-consuming owing to the iteration steps. Here, we train a neural network module termed NNSpan to learn the transfer function of a single fiber (G652 or G655) span with a length of 80 km and successfully emulate long-haul optical transmission systems by cascading multiple NNSpans, which gives remarkable prediction accuracy, even over a transmission distance of 1000 km. Even when trained without erbium-doped fiber amplifier (EDFA) noise, NNSpan performs quite well when emulating the systems affected by EDFA noise. An optical bandpass filter can optionally be added after EDFA, making the simulation more flexible. Comparison with the SSFM shows that NNSpan has a distinct computational advantage, with the computation time reduced by a factor of 12. This method based on NNSpan could be a supplementary option for optical transmission system simulations, thus contributing to system designs as well.

116.66-Tb/s WDM transmission over 16 Km field deployed 7-core fiber based on sub-constellations overlap constellation shaping.

Constellation shaping (CS) has always been a popular research hotspot in optical communication. Recently, most researchers have focussed on using constellation-shaping technology to improve the system's performance, ignoring the additional penalty it brings to the coherent system. This paper proposes a method of constellation truncation using sub-constellation overlap to perform CS on quadrature amplitude modulation (QAM). The experimental results show that compared with the traditional probabilistic shaping 16QAM, the proposed scheme can effectively avoid the extra penalty brought by CS and achieve a gain from 0.5 to 1.5 dB in optical signal-to-noise ratio. To practically verify the proposed scheme's performance, 7-core 16 km fiber span is deployed in the field to experimentally perform space division multiplexed coherent transmission. The wavelength division multiplexing (WDM) of 93 carriers was used to achieve coherent transmission at a net rate of 116.66-Tb/s.

One kilometer balanced analog photonic link based on a single multicore fiber

A one kilometer balanced microwave photonic link based on a single four core multicore optical fiber is demonstrated for the first time, to the best of our knowledge. The radio frequency gains and differential phase stabilities over temperature were measured and compared to a conventional balanced link based on two spans of single mode fiber. Both the multicore fiber link and the single mode fiber balanced link exhibited differential phase fluctuations of |Δφ|≤13° at 25 GHz (corresponding to a differential delay or skew, |Δt|, of ≤1.4ps) under identical periodic temperature oscillations of ±13°C over a 60 min period. In contrast, previous studies have shown that two single mode fiber spans should have exhibited up to an order of magnitude greater Δφs compared to the multicore fiber. Our different results can be attributed to how the fibers are arranged; the previous works kept the two single mode fiber spans separate, on different spools, whereas in this work the two single mode fiber spans were co-located as close as possible together by spooling them ‘side-by-side’ onto a single mandrel, more representative of a balanced link in application. In addition, the radio-frequency crosstalk between the multicore fiber’s cores were measured, exhibiting acceptable levels at least 60 dB below the signal for all core combinations. The crosstalk is shown to be dominated by occurrences at localized points, e.g. at the multiplexers (fan-in/fan-outs) and splices, rather than during propagation. Regardless of the single mode fiber link’s performance, the measurements here demonstrate that multicore fiber-based balanced links are a viable single fiber alternative to conventional dual single mode fiber-based balanced links.

The Shear Capacity Estimation of Reinforced Concrete Short Beams with Steel Fiber by Digital Image Correlation Approach

This research aimed to estimate the shear capacity of reinforced concrete short beams with steel fiber (RSF short beams) using DIC (digital image correlation). Four-point bending tests of RSF short beams with shear span ratio (a/d) of 1.0, 1.5, and 2.0 were conducted. 0.5% or 1.0% volume fraction of steel fiber was used. The distribution of minimum principal strain (Ɛ2) was obtained from DIC then the width of compressive strut was evaluated. The effects of volume fraction of steel fiber and shear span ratio were investigated. Finally, the shear capacity of RSF short beams was estimated with the help of DIC.

A Closed-Form Expression for the Gaussian Noise Model in the Presence of Inter-Channel Stimulated Raman Scattering Extended for Arbitrary Loss and Fibre Length

A closed-form formula for the nonlinear interference (NLI) estimation using the Gaussian noise (GN) model in the presence of inter-channel stimulated Raman scattering (ISRS) is derived. The formula enables accurate estimation of the NLI evolution along any portion of the fibre span together with arbitrary values of optical fibre losses. The formula also accounts for wavelength-dependent fibre parameters, variable modulation formats and launch power profiles. The formula is suitable for ultra-wideband (UWB) optical transmission systems and its accuracy is assessed for a system with 20 THz optical bandwidth over the entire S-, C-, and L- band through comparison with numerical integration of the ISRS GN model and split-step Fourier method (SSFM) simulations in point-to-point transmission and inline NLI estimation scenarios.

Chaos synchronization of semiconductor lasers over 1040-km fiber relay transmission with hybrid amplification

Optical chaos communication and key distribution have been extensively demonstrated with high-speed advantage but only within the metropolitan-area network range of which the transmission distance is restricted to around 300 km. For secure-transmission requirement of the backbone fiber link, the critical threshold is to realize long-reach chaos synchronization. Here, we propose and demonstrate a scheme of long-reach chaos synchronization using fiber relay transmission with hybrid amplification of an erbium-doped fiber amplifier (EDFA) and a distributed fiber Raman amplifier (DFRA). Experiments and simulations show that the hybrid amplification extends the chaos-fidelity transmission distance thanks to that the low-noise DFRA suppresses the amplified spontaneous emission noise and self-phase modulation. Optimizations of the hybrid-relay conditions are studied, including launching power, gain ratio of DFRA to EDFA, single-span fiber length, and number of fiber span. A 1040-km chaos synchronization with a synchronization coefficient beyond 0.90 is experimentally achieved, which underlies the backbone network-oriented optical chaos communication and key distribution.

Spatiotemporal mode decomposition of ultrashort pulses in linear and nonlinear graded-index multimode fibers

We develop a spatiotemporal mode decomposition technique to study the spatial and temporal mode power distribution of ultrashort pulses in long spans of graded-index multimode fiber, for different input laser conditions. We find that the beam mode power content in the dispersive pulse propagation regime can be described by the Bose–Einstein law, as a result of the process of power diffusion from linear and nonlinear mode coupling among nondegenerate mode groups. In the soliton regime, the output mode power distribution approaches the Rayleigh–Jeans law.

Time-Limited Waveforms With Minimum Time Broadening for the Nonlinear Schrödinger Channel

Simple fiber optic communication systems can be implemented using energy modulation of isolated time-limited pulses. Fundamental solitons are one possible solution for such pulses which offer a fundamental advantage: they preserve their shape along the channel. Furthermore, a simple energy detector can be used at the receiver to detect the transmitted information. However, systems based on energy modulation of solitons are not competitive in terms of data rates. This is partly due to the fact that the effective time duration of a soliton depends on its chosen amplitude. In this paper, we propose to replace fundamental solitons by new time-limited waveforms that can be detected using an energy detector, and that are immune to fiber distortions. Our proposed solution relies on the prolate spheroidal wave functions and a numerical optimization routine. Time-limited waveforms that undergo minimum time broadening along an optical fiber are obtained and shown to outperform fundamental solitons. In the case of binary transmission and a single span of fiber, we report rate increases of 33.8% and 12% over lossy and lossless fibers, respectively. Furthermore, we show that the transmission rate of the proposed system increases as the number of used energy levels increases, which is not the case for fundamental solitons due to their effective time-amplitude constraint. For example, rate increases of 164% and 70% over lossy and lossless fibers respectively are reported when using four energy levels.

Ultralong Single‐Ended Random Fiber Laser and Sensor

AbstractRandom fiber laser (RFL) utilizing stimulated Raman scattering and distributed random Rayleigh backscattering in fiber as optical gain and feedback mechanisms, respectively, has been developed rapidly in the past decade. Here, it is found, for the first time, that the combination of a high‐order pump and new transmission fiberthat has lower transmission loss, Rayleigh backscattering coefficient, and Raman gain coefficient than standard single‐mode fibercan break the length limits of both random fiber lasing and sensing. With a higher‐order pump and ultralow loss fiber (ULLF), the position of maximum intracavity lasing power can be shifted toward the far end of the fiber span resulting in more remote pump power for the erbium‐doped fiber (EDF) inserted in the fiber span, which plays a dominant role of cavity length extension in RFL. A 200 km ultralong single‐ended RFL and sensor are experimentally demonstrated, which are the longest single‐ended RFL and sensor with functional remote reflectors reported to date. It is believed that the proposed combination of high‐order random lasing and ULLF with EDF can become a general method to extend the working distance of various fiber sensing systems for safety monitoring of ultralong infrastructures, such as power transmission lines and oil/gas pipelines.