High-capacity Optical Networks Research Articles

Orbital Angular Momentum Multiplexing Architecture for OAM/SDM Passive Optical Networks

Optical Angular Momentum multiplexing (OAM) is a technology of communication systems that enables high-capacity optical communication networks. One of the most important determinants of this technology is the channel capacity, loss of power, and BER that accompany the transmission. This article proposed an OAM/SDM G-PON architecture for a MIMO-type communication system that supports (OAM/SDM G-PON)Technology. The proposed architecture is used to multiplex the downstream OAM channels and the upstream SDM channels, and an OAM multiplexer/demultiplexer (OAM-MUX/DEMUX) is used to multiplex and demultiplex the OAM channels. In the OAM/SDM G-PON system, the signal will propagate through three different mediums, each one having its own nature in influencing the power of the signal that passes through that medium. The experimental study has bidirectional transmissions with the DS/US data rate of 2.4 Gbps and Binary Phase Shift Keying (BPSK) downstream and 1.2 Gbps upstream. The observed results showed that the bit-error rate (BER) is a function of coupling angles and increases with the increasing in the OAM ring size

Scheme for a WDM-PON with colorless optical network units based on a flat optical frequency comb.

A new, to the best of our knowledge, scheme for a wavelength division multiplexing passive optical network (WDM-PON) based on a flat optical frequency comb (OFC) is proposed. Using an OFC as the optical source of the system can realize the colorlessness of optical network units (ONUs), and the direct detection of the downlink data further simplifies the ONU structure. The coherent demodulation of the uplink data improves the system performance due to the coherence of the comb lines. In this research, the proposed system is studied for its performance and power budgeting. The results show the flexibility, effectiveness, and practicability of the proposed scheme, which can be applied to future high-capacity optical access networks.

Power-aware high-capacity elastic optical networks

The power consumption of telecommunication equipment has been identified as a relevant contributor to global energy consumption. In fact, new-generation optical transponders employ power-intensive electronic application-specific integrated circuits (ASICs) for digital signal processing (DSP). DSP design has traditionally prioritized meeting transmission requirements over power consumption optimization. In general, the evolutions of transmission techniques and network design have always been mainly driven by traffic increase; in this context, in order to operate network resources more efficiently, margin reduction has been investigated in the past few years. Indeed, traditionally, high physical layer margins are used to ensure reliability over an extended period, resulting in overprovisioning the optical connections for both physical layer conditions and capacity. On the other hand, super-channels have emerged as a suitable solution for accommodating the continuous traffic growth. However, power consumption has not been deeply considered in the optimization of super-channel transmission. This paper first investigates the power efficiency of super-channels operated with designed and reduced margins. Low-margin operation is enabled by adapting sub-carrier spacing and filter bandwidth. Power-aware super-channel optimization is then experimentally demonstrated leveraging a 600 Gbit/s transponder in the SDN-controlled elastic optical network (EON). The results have identified a trade-off between power consumption and spectrum efficiency. Furthermore, the ongoing bandwidth demand has motivated the investigation of multi-band (MB) transmission for scaling the capacity of the existing infrastructures. However, novel networking devices (e.g., optical amplifiers operating beyond the C- and L-bands) will affect the overall power consumption. In this context, experimental power analysis of a thulium doped fiber amplifier (TDFA) is performed based on the traffic load and corresponding configuration. The results show that TDFA power consumption varies with configuration and increases with output power.

A High-Capacity Optical Metro Access Network: Efficiently Recovering Fiber Failures with Robust Switching and Centralized Optical Line Terminal.

This study proposes and presents a new central office (CO) for the optical metro access network (OMAN) with an affordable and distinctive switching system. The CO's foundation is built upon a novel optical multicarrier (OMC) generation technique. This technique provides numerous frequency carriers that are characterized by a high tone-to-noise ratio (TNR) of 40 dB and minimal amplitude excursions. The purpose is to accommodate multiple users at the optical network unit side in the optical metropolitan area network (OMAN). The OMC generation is achieved through a cascaded configuration involving a single phase and two Mach Zehnder modulators without incorporating optical or electrical amplifiers or filters. The proposed OMC is installed in the CO of the OMAN to support the 1.2 Tbps downlink and 600 Gbps uplink transmission, with practical bit error rate (BER) ranges from 10-3 to 10-13 for the downlink and 10-6 to 10-14 for the uplink transmission. Furthermore, in the OMAN's context, optical fiber failure is a main issue. Therefore, we have proposed a possible solution for ensuring uninterrupted communication without any disturbance in various scenarios of main optical fiber failures. This demonstrates how this novel CO can rapidly recover transmission failures through robust switching a and centralized OLT. The proposed system is intended to provide users with a reliable and affordable service while maintaining high-quality transmission rates.

Simplified colorless characterization scheme for coherent receivers in DWDM scenarios using a single interferer

Intradyne coherent receivers, capable of detecting an individual wavelength-division multiplexed channel just by tuning the local oscillator frequency, is of great interest for the development of high-capacity flexible optical networks. Nevertheless, the unavoidable amplitude imbalances inherent to any realistic coherent receiver induce an interference contribution from the self-beating of the coincident channels present at its input. The characterization of this degraded colorless reception operation is of fundamental importance, but it usually requires the use of rather complex experimental setups, especially when the effects of tens of interference channels should be evaluated. In this work we propose a novel experimental setup that only requires the use of a single intense interferer to emulate those coincident channels, thus drastically simplifying the characterization process. In addition, we develop a general expression for the signal-to-noise ratio of the system that theoretically justifies the intended setup and demonstrate by massive numerical simulations its accuracy in different scenarios. We believe that the proposed approach may contribute to facilitate the experimental characterization of high-performance colorless coherent receivers.

High-Capacity Free Space Optics-Based Passive Optical Network for 5G Front-Haul Deployment

With the expansion of Information and Communication Technology, it is important to develop a communication network that can provide high-capacity ubiquitous connectivity. This work proposes an energy-efficient passive optical network (PON) using orthogonal frequency division multiple access (OFDMA) and wavelength division multiplexing (WDM) to facilitate the dense deployment of radio units (RUs) in a beyond 5G (B5G) communication network. High-speed connectivity is ensured by employing a hybrid PON architecture that includes a combination of free space optics (FSO) links and optical fiber (OF) media to carry OFDM and WDM multiplexed traffic. Furthermore, an optical frequency comb generator (OFCG) is utilized at the transmitter module to generate and leverage the spectrum for transmitting information from baseband units (BBUs) to the RUs situated near the end users. The proposed system is analyzed through (i) simulation analysis using Optisystem for transmission capacity computations and (ii) mathematical analysis to determine the total savings in energy. The simulation analysis shows that the given architecture can carry data across 3 km of FSO medium using 512 subcarriers per BBU transmitting at 10 Gbps of data with QPSK-modulated bit sequence. Additionally, energy efficiency shows that the use of an OFCG cuts the total energy usage by 22% at the transmitter module without negatively impacting the system’s high cardinality and transmission capacity.

Distinguished Contributions to Global Long-Distance, High-Capacity Optical Fiber Network Through the Development of Semiconductor Laser Pumped Optical Amplifier

Distinguished Contributions to Global Long-Distance, High-Capacity Optical Fiber Network Through the Development of Semiconductor Laser Pumped Optical Amplifier

Multi-wavelength transponders for high-capacity optical networks: a physical-layer-aware network planning study

Continued cost- and power-efficient capacity scaling in optical networks is imperative to keep pace with ever-increasing traffic demands. In this paper, we investigate multi-wavelength transponders as a potential way forward. Suitable system architectures and realistic specifications of multi-wavelength transponders are identified and analyzed in terms of transmit optical signal-to-noise ratio penalties and spectral constraints. We investigate the performance for different specifications as compared to single-wavelength transponders in a network planning study on two network topologies, developing guidelines for multi-wavelength transponder specifications and their potential benefits. The studies show a reduction in the number of required lasers of up to 83% at the expense of a slight increase in the number of lightpaths, demonstrating the potential for significant cost savings and efficiency improvements.

Memetic evolutionary algorithms to design optical networks with a local search that improves diversity

The last few years have seen an increasing demand for high-capacity Internet services, and this need has intensified in the years 2020 and 2021. In 2020 and 2021, Internet usage grew by 50% in several European countries, mainly due to home office, video streaming, hybrid teaching, and others. High-capacity optical networks usually meet this growing demand for Internet services. Thus, investigations that can improve the quality of optical networks are highly relevant in the current context. One of the research problems in this area is related to the physical topology design (PTD) of optical networks, which is classified as NP-hard. Several studies on PTD consider the application of meta-heuristics that obtain suboptimal solutions in a time compatible with engineering applications. However, meta-heuristics and local search techniques have been combined in several other optimization problems, which is not typical for the PTD problem. This paper proposes a solution to the PTD problem that combines a known multipurpose optimization algorithm, the NSGA-III, with operators considering the domain-specific knowledge of the problem to provide superior-quality networks. According to our results, the new proposal presents quality up to 8% higher than previous proposals concerning the hypervolume metrics (HV), maintaining a similar computational cost.

400-Gbps/80-km Rate-Flexible PCS-64-QAM WDM-CPON With Pseudo-m-QAM Chaotic Physical Layer Encryption

For next-generation high-capacity, rate-flexible, and secure 400-G passive optical network (PON), a scheme joint wavelength division-multiplexed (WDM), entropy-regulated probabilistic constellation shaping-64-quadrature amplitude modulation (PCS-64-QAM) and chaotic encryption mapping, is proposed and demonstrated. For the first time, chaotic encryption is realized over the PCS-based PON with the architecture from one optical line terminal (OLT) to multiple optical network units (ONUs). Chaotic encryption with an initial-value-sensitive feature can generate a large amount of parallel encrypted sequences which provide a key pair corresponding with every possible entropy/rate. A novel mapping from PCS-64-QAM with various entropies to pseudo- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> -QAM is designed, which erases the entropy information of the link and encrypted the original information of the sequence. The encryption transmission is demonstrated over a real-time dual-polarized coherent optical platform with an 80-km link and typically one-to-many PON configuration, and a net 211.80∼348.12-Gb/s rate result within the hard-decision forward error correction (FEC) threshold is achieved for 6λ × 2 ONUs group. The rate of each polarization state can be tuned in a minimum 3.408-Gbps step in the demonstration. Expanding from the basis of the original WDM-CPON, this work prepares an adapted chaotic encryption scheme for large-scale access. Overall, our proposed scheme can provide an abundant system loss budget, a large rate tunable range, and basic physical layer security for next-generation rate-flexible coherent PON (FLCS-CPON).

A Bidirectional WDM-PON Free Space Optical (FSO) System for Fronthaul 5 G C-RAN Networks

High-speed cellular technologies require low-latency and high-capacity optical networks. The Centralized Radio Access Network (C-RAN) architecture offers a cost-effective solution for mobile network deployment. To maximize flexibility and minimize deployment costs of fronthaul networks, we propose a hybrid bidirectional fronthaul C-RAN topology based on Wavelength Division Multiplexing (WDM) passive optical networks (PONs) and free space optical communication (FSO). The wavelength reuse scheme utilized here relies on reflective semiconductor optical amplifiers (RSOAs) to reduce cost and increase capacity. The system was demonstrated for 20 Gbps 16 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> quadrature amplitude modulation (16-QAM) intensity-modulated orthogonal frequency-division multiplexing (OFDM) downstream signals and 5 Gbps On-off keying (OOK) upstream signals, respectively. A Gamma-Gamma channel model is used to demonstrate optical signal transmission over an FSO link. The bit error rate (BER) results indicate that the hybrid WDM-PON-FSO based fronthaul architecture could achieve 320 Gbps over 20 km of single-mode fiber (SMF) and 700 m free space transmission.

High Capacity Innovations Enabling Scalable Optical Transmission Networks

We review and introduce key optical innovations that enable scalable and efficient high capacity optical networks, such as advanced modulation formats, flexible grid, optical superchannel, 400GE and emerging 400G ZR/ZR+. We show results from recent industry leading technology trial of real-time 2 × 200G Probabilistic Constellation Shaping (PCS) DP-16QAM superchannel transporting 400GE over a live long haul flexible grid link, achieving long term error free performance with a high spectral efficiency of 5.33 bit/s/Hz and significantly enhanced performance over conventional 200G DP-16QAM. We also present results from successful demonstration of emerging 400G ZR/ZR+ technologies and IP over WDM applications, where different network scenarios and use cases are investigated including single span WDM link of 125 km and multi-span WDM link of 252 km as well as unamplified 40 km fiber link. 400G ZR/ZR+ IP over WDM wavelengths have shown robust performance with good optical margin for practical network applications as well as potential for longer optical reach. In comparison, 400G ZR+ has enhanced performance over 400G ZR with additional margin of ∼3 dB. We have also demonstrated streaming telemetry, a new network monitoring approach, for monitoring of 400G ZR/ZR+ IP over WDM wavelengths giving more performance insights. These industry leading trials and demonstration give network operators critical understandings of the performance, maturity and operational viability of emerging optical technologies which will allow them to scale their networks gracefully to meet continuing bandwidth growth.

The effects of optical fiber impairments on communication systems

In this paper, the influence of physical layer impairments on fiber optic channels was evaluated using analytical modeling, and the findings were verified through simulation results. Light propagation inside standard single mode fiber (SSMF) is affected by both linear and nonlinear effects, which must be taken into account in order to develop an appropriate fiber channel model. The use of nonlinear fiber optics in the implementation of highcapacity optical networks is crucial. The "Optisystem 17.0" software package was used to simulate the suggested systems. It can be observed that increased input power tends to increase the effect of cross-phase modulation (XPM) and four wave mixing (FWM) in the nonlinear dispersive fibers. The impact of pulse broadening due to chromatic dispersion (CD), self-phase modulation (SPM), and cross-phase modulation (XPM) was investigated using Gaussian pulses as input signals.

Self-healing of multipartite entanglement in optical quantum networks

Multipartite entanglement serves as an essential resource for constructing quantum networks and makes it possible to realize multi-user quantum information protocols outperforming their classical counterparts. Unfortunately, multipartite entanglement is fragile when distributed in complex environments. Therefore, it is urgent to address the issue of multipartite entanglement decoherence caused by complex environments. Here we demonstrate the self-healing of multipartite continuous-variable (CV) entanglement after an obstruction. In our experiment, the tripartite entanglement destroyed by the obstruction-introduced noise and loss can self-heal after free-space propagation of a certain distance due to the self-healing property of a Bessel–Gaussian (BG) beam. We show that the BG beam provides a more robust mode basis for free-space CV quantum entanglement distribution than the widely used fundamental Gaussian beam under similar conditions. In addition, we also demonstrate the self-healing of five sets of tripartite entanglement and 10 sets of bipartite entanglement in orbital-angular-momentum-multiplexed optical quantum networks. Our results pave the way for constructing obstruction-tolerant high-capacity CV optical quantum networks.

Training strategies to minimize interchannel interference effects using supervised learning in gridless Nyquist-WDM systems.

The dynamism envisioned in future high-capacity gridless optical networks requires facing several challenges in distortion mitigation, such as the mitigation of interchannel interference (ICI) effects in any optical channel without information of their adjacent channels. Machine learning (ML)-based techniques have been proposed in recent works to estimate and mitigate different optical impairments with promising results. We propose and evaluate two training strategies for supervised learning algorithms with the aim to minimize ICI effects in a gridless 3×16-Gbaud 16-quadrature amplitude modulation (QAM) Nyquist-wavelength-division multiplexing (WDM) system. One strategy, called updating strategy, is based on symbol training sequence, and the other one, called characterization strategy, is based on an offline training using a previous system characterization. Artificial neural networks (ANN), support vector machine (SVM), K-nearest neighbors (KNN), and extreme learning machine (ELM) algorithms are explored for both training strategies. Experimental results showed a bit error rate (BER) improvement at low training lengths for both training strategies, for instance, gains up to ∼4dB in terms of optical signal-to-noise ratio were achieved in a back-to-back scenario. Besides, the KNN and ELM algorithms showed significant BER reduction in transmission over 250 km optical fiber. Additionally, we carried out a brief computational complexity analysis where ELM presented only 1.9% of ANN processing time. Hence, the use of ML-based techniques could enhance the optical gridless networks performance and consequently fulfill future traffic demands.

Multi-channel multi-task optical performance monitoring based multi-input multi-output deep learning and transfer learning for SDM

We propose a transfer learning (TL) simplified multi-input multi-output multi-task convolutional neural network (MIMO MT-CNN) to realize the optical performance monitoring (OPM) for space division multiplexing (SDM) fiber transmission systems. TL simplified MIMO MT-CNN is used for NRZ, RZ and PAM4 signal joint monitoring including modulation format identification (MFI) and optical signal-to-noise ratio (OSNR) estimation. Thanks to the TL technologies, the parameters used in single mode fiber transmission is transferred to SDM to reduce the required training data and epochs. The experiment has been demonstrated with MIMO MT-CNN for seven cores fiber systems. The results show that the accuracy of MFI can reach 100% for all signals. For NRZ, RZ, and PAM4, the root-mean-square errors (RMSE) of OSNR estimation are less than 0.6 dB, respectively. In addition, by implementing TL from simulation to experiment, the required training samples and epochs are reduced by 48% and 50%, respectively. Due to its low cost and being easy to implement, the proposed OPM solution has the potential for next-generation SDM fiber transmission systems. The model can realize short training time and multi-task multi-channel OPM for high-capacity SDM elastic optical networks, simultaneously.

Core Function Prepositioning for Point-to-Point Service Slicing in Large-Scale Optical Networks

To accommodate three typical 5G services with satisfied performance requirements, spectrum slicing has been adopted and widely studied in the wireless transmission part. For the wired transmission part, the high-capacity and large-scale optical network is widely used for transferring 5G traffics. To improve the spectrum efficiency and reduce the time delay while accommodating 5G services, optical networks need to adapt to the wireless spectrum slicing. Traditionally, all spectrum resources in optical networks form a resource pool which is equally allocated to applications bit by bit until it is all used up. Although this pattern reduces the resource maintenance complexity, it has a high operation complexity for 5G services. If some important network functions are realized in advance, a 5G service can be easily deployed with simplified operations and satisfied performance requirements. In this letter, a novel framework of core function prepositioning is proposed to efficiently accommodate 5G services in optical networks. It adopts the centralized control model and two network functions of fast connection establishment and disaster-resilient survivability are realized in planned spectrum areas in advance. This framework adapts to the wireless spectrum slicing and has a significant performance boost while accommodating 5G services.

Programmable disaggregated multi-dimensional S-BVT as an enabler for high capacity optical metro networks

To meet the requirements of 5G high capacity optical metro networks, a programmable disaggregated multi-dimensional sliceable bandwidth/bitrate variable transceiver (S-BVT) is proposed. Specifically, transceiver multi-dimensionality is presented exploiting spatial, polarization, and spectral information as a solution to support network capacity and bandwidth scaling 5G requirements. Space division multiplexing is implemented by considering a 19-core multicore fiber enabling capacity scaling with the number of cores, whereas polarization division multiplexing is assessed enabling 50% spectral saving by considering two orthogonal polarization components. Finally, by the implementation of multi-band transmission systems, the optical bandwidth can be increased by a factor of 10, compared to a conventional C-band system. In these last two cases, the existing spectrum and network infrastructure can be reused, bringing new capabilities. In particular, in this work, multi-band transmission is assessed by exploiting the C-band and L-band. Additionally, disaggregation is also addressed at the transceiver level to enhance network flexibility, avoiding vendor lock-in while achieving efficiency and cost reduction. Disaggregation enables assembling open components, devices, and sub-systems into optical infrastructures and networks. On the other hand, the adoption of the software defined networking paradigm enables system/network programmability and reconfigurability, promoting an efficient use of the multi-dimensional network resources. Therefore, in this work, we analyze and experimentally demonstrate different S-BVT advanced functionalities suitable to support the stringent network requirements of 5G. These capabilities include rate/distance adaptability, programmability/configurability, disaggregation, and multi-dimensionality. Different network scenarios have been considered to assess the S-BVT functionalities, enabling Tb/s optical transmission.

Assessment of cross-train machine learning techniques for QoT-estimation in agnostic optical networks

With the evolution of 5G technology, high definition video, virtual reality, and the internet of things (IoT), the demand for high capacity optical networks has been increasing dramatically. To support the capacity demand, low-margin optical networks engage operator interest. To engross this techno-economic interest, planning tools with higher accuracy and accurate models for the quality of transmission estimation (QoT-E) are needed. However, considering the state-of-the-art optical network’s heterogeneity, it is challenging to develop such an accurate planning tool and low-margin QoT-E models using the traditional analytical approach. Fortunately, data-driven machine-learning (ML) cognition provides a promising path. This paper reports the use of cross-trained ML-based learning methods to predict the QoT of an un-established lightpath (LP) in an agnostic network based on the retrieved data from already established LPs of an in-service network. This advanced prediction of the QoT of un-established LP in an agnostic network is a key enabler not only for the optimal planning of this network but it also provides the opportunity to automatically deploy the LPs with a minimum margin in a reliable manner. The QoT metric of the LPs are defined by the generalized signal-to-noise ratio (GSNR), which includes the effect of both amplified spontaneous emission (ASE) noise and non-linear interference (NLI) accumulation. The real field data is mimicked by using a well reliable and tested network simulation tool GNPy. Using the generated synthetic data set, supervised ML techniques such as wide deep neural network, deep neural network, multi-layer perceptron regressor, boasted tree regressor, decision tree regressor, and random forest regressor are applied, demonstrating the GSNR prediction of an un-established LP in an agnostic network with a maximum error of 0.40 dB.

Comprehensive investigation of coherent optical OFDM-RoF employing 16QAM external modulation for long-haul optical communication system

Given the growing need for long haul transmission that requires a high rate of data, the orthogonal frequency division multiplexing scheme (OFDM), is regarded as a technique with high potentials for high-capacity optical networks. OFDM transmits over both optical and wireless channels, with the data distributed over a huge amount of the subcarrier, and the data is distributed over a huge number of subcarriers. OFDM achieves RF signal for a long-haul transmitting by utilizing Radio over Fiber (RoF) system, which is known to produce higher orthogonality of the OFDM modulated signal designed for the wireless network. RoF systems comprise of heterogeneous networks designed through the use of wireless and optical links. The aim of this paper is to carry out an investigation of the performance of the external modulation in RoF links, while analyzing the shortcomings caused by the various elements of the optical system. The Mach–Zehnder modulator (MZM) can be applied in external modulation, and exhibits a more robust performance when implemented with the OFDM modulation technique.