Deployment Of Optical Networks Research Articles

Enhanced Coexistence of Quantum Key Distribution and Classical Communication over Hollow-Core and Multi-Core Fibers

In this paper, we investigate the impact of classical optical communications in quantum key distribution (QKD) over hollow-core fiber (HCF), multi-core fiber (MCF) and single-core fiber (SCF) and propose wavelength allocation schemes to enhance QKD performance. Firstly, we theoretically analyze noise interference in QKD over HCF, MCF and SCF, such as spontaneous Raman scattering (SpRS) and four-wave mixing (FWM). To mitigate these noise types and optimize QKD performance, we propose a joint noise suppression wavelength allocation (JSWA) scheme. FWM noise suppression wavelength allocation and Raman noise suppression wavelength allocation are also proposed for comparison. The JSWA scheme indicates a significant enhancement in extending the simultaneous transmission distance of classical signals and QKD, reaching approximately 100 km in HCF and 165 km in MCF under a classical power per channel of 10 dBm. Therefore, MCF offers a longer secure transmission distance compared with HCF when classical signals and QKD coexist in the C-band. However, when classical signals are in the C-band and QKD operates in the O-band, the performance of QKD in HCF surpasses that in MCF. This research establishes technical foundations for the design and deployment of QKD optical networks.

Ultra-Low Loss Fiber Deployment in Elastic Optical Networks With Fixed and Variable Topologies

Ultra-Low Loss Fiber Deployment in Elastic Optical Networks With Fixed and Variable Topologies

Evolutionary neuron-level transfer learning for QoT estimation in optical networks

To ensure the reliability and efficiency of lightpath transmission in optical networks, it is essential to predict the quality of transmission (QoT) of the candidate lightpaths before their deployment. An artificial neural network (ANN) becomes a promising solution for QoT estimation of lightpaths, owing to its powerful data fitting capability and scalability. As a supervised learning model, an ANN requires a large set of training samples from lightpaths’ observations to ensure its accuracy. Unfortunately, the acquisition of the training samples is hindered by practical limitations, such as the shortage of monitorable lightpaths in the early stage of optical network deployment or/and the absence of optical performance monitors at partial network nodes. Therefore, how to obtain a high-precision QoT estimator with small-sized datasets is challenging. In this paper, we propose an evolutionary neuron-level transfer learning (ENTL) scheme for QoT estimation to improve the accuracy of the ANN model with small-sized datasets. In the ENTL-based QoT estimator, the minimal unit of knowledge transfer is the neuron of the ANN model, and the particle swarm optimization (PSO) algorithm is introduced to determine the trainable neurons and the frozen neurons, where the testing dataset generated by data augmentation assists the PSO algorithm to evaluate the feasible solutions. Simulation results show that the ENTL-based QoT estimator achieves higher accuracy than the traditional layer-level transfer learning (LTL)-based QoT estimator. And, when the ENTL-based QoT estimator is applied to optical network planning, it improves the reliability and throughput of optical networks compared with the LTL-based QoT estimator.

Energy-Efficient Graph Reinforced vNFC Deployment in Elastic Optical Inter-DC Networks

Energy-Efficient Graph Reinforced vNFC Deployment in Elastic Optical Inter-DC Networks

A Single–Multi-Path Combinatorial RMSA Algorithm with Least Resource Consumption in Semi-Filterless Optical Networks

Filterless optical networks (FONs) have become a cost-effective solution for optical network deployment due to their low-cost characteristics. However, eliminating active switching elements causes signals to propagate over unintended links, wasting spectral resources. Therefore, semi-filterless optical networks (Semi-FONs) have become a more cost-effective solution. This paper mainly studies the routing, modulation, and spectrum assignment (RMSA) problem in semi-filterless optical networks. It proposes a single–multi-path combination (LR-SMPC) RMSA algorithm with the least resource consumption. The algorithm first obtains the K shortest paths that satisfy the conditions according to the K short path (KSP) algorithm and re-orders the paths according to the resource consumption path re-ordering strategy, selecting the three paths that consume the least resources as the set of candidate paths. Then, based on the single–multi-path combination scheme of the set of candidate paths, the resource consumption of each scheme and the maximum number of available spectrum blocks for each path is calculated, from which the single path or multi-path with the least resource consumption is selected to serve the request. We perform simulation experiments on two network topologies using Poisson traffic models and compare them with existing single-path algorithms (S-P), fixed spectrum assignment granularity algorithms (g = 1), and adaptation spectrum assignment algorithms (g adaptation) to evaluate the performance of the proposed algorithm. The simulation results show that the proposed algorithm exhibits better performance in terms of both blocking rate and spectrum utilization.

Design and deployment of optical x-haul for 5G, 6G, and beyond: progress and challenges [Invited

Sixth generation (6G) wireless technology, which is the next giant leap in the evolution of wireless communication, has been gaining great interest from academia, industry, and the general public due to its capabilities and the applications that are expected to be supported. Optical x-haul is becoming increasingly important as a key element of the 6G ecosystem due to the increasing demand for high data rates and low latency with the emergence of new 6G applications and use cases. The ability of optical x-haul to support high data rates and low latency along with its scalability and high-reliability performance makes it an essential transport technology for future wireless networks of 6G and beyond. However, optical and wireless technologies operate in different domains and with different standards. Therefore, integration of optical x-haul and 6G needs careful consideration with emphasis on bringing network intelligence softwarization. This is particularly important in supporting the quality of service requirements of emerging applications in the most cost-effective and sustainable manner. To this end, this paper reviews the research that has been carried out in the investigation of the optical x-haul network in a hybrid fiber–wireless system to cater to the next generation of wireless networks. Especially, we review the research carried out in open radio access network architecture, coordination functionalities in radio-over-fiber networks, optimization frameworks that can be used to jointly optimize wireless and optical network deployments, and reconfigurable optical x-haul. We conclude the paper by providing insights into research challenges that we need to overcome in integrating optical x-haul in the 6G ecosystem to support emerging applications.

Optical telecommunications-band clock based on neutral titanium atoms

We propose an optical clock based on narrow, spin-forbidden M1 and E2 transitions in laser-cooled neutral titanium. These transitions exhibit much smaller black body radiation shifts than those in alkaline earth atoms, small quadratic Zeeman shifts, and have wavelengths in the S, C, and L-bands of fiber-optic telecommunication standards, allowing for integration with robust laser technology. We calculate lifetimes; transition matrix elements; dynamic scalar, vector, and tensor polarizabilities; and black body radiation shifts of the clock transitions using a high-precision relativistic hybrid method that combines a configuration interaction and coupled cluster approaches. We also calculate the line strengths and branching ratios of the transitions used for laser cooling. To identify magic trapping wavelengths, we have completed the largest-to-date direct dynamical polarizability calculations. Finally, we identify new challenges that arise in precision measurements due to magnetic dipole-dipole interactions and describe an approach to overcome them. Direct access to a telecommunications-band atomic frequency standard will aid the deployment of optical clock networks and clock comparisons over long distances.

Deep-learning-based path computation without routing convergence in optical satellite networks

Low Earth orbit (LEO) satellite networks, which are composed of multiple inter-connected satellites, have become important infrastructure for future communications. Benefiting from the high bandwidth and anti-interference of satellite laser communication, optical satellite networks, in which satellite links are lasers, can provide global Internet services and have become a research trend. The orbit at a lower altitude has advantages such as low latency, low cost, and easy deployment in LEO optical satellite networks. Meanwhile, the movement of satellites is fast and thus will result in frequent changes for ground–satellite links. The conventional static routing strategy cannot perceive the network state; therefore, the static routing is inapplicable in the case of link failure or congestion. Dynamic routing can ensure the accuracy of the network connection by routing convergence. However, the routing table needs to be updated frequently because of the highly dynamic topology, resulting in the increase in signaling overhead. To compute routing paths accurately while reducing the update frequency of the routing table, this paper proposes a path computation model based on deep learning. By learning the mapping relation of previous services and the routing paths, the model can directly output the routing path according to the current service request. Using this method, the path computation tasks depend less on the frequently updated routing table. The simulation results show that the paths computed by the proposed method are almost the same as the paths computed by Dijkstra’s algorithm, the average accuracy rate is above 90%, and the highest accuracy rate can reach 98.8%. Compared with traditional path computation, the proposed method needs to collect a large amount of previous data for training, and the training time is about several hours.

Deep Neural Network-Based QoT Estimation for SMF and FMF Links

Quality of transmission (QoT) estimation tools for fiber links are the enabler for the deployment of reconfigurable optical networks. To dynamically set up lightpaths based on traffic request, a centralized controller must base decisions on reliable performance predictions. QoT estimation methods can be categorised in three classes: exact analytical models which provide accurate results with heavy computations, approximate formulas that require less computations but deliver a reduced accuracy, and machine learning (ML)-based methods which potentially have high accuracy with low complexity. To operate an optical network in real-time, beside accurate QoT estimation, the speed in delivering results is a strict requirement. Based on this, only the last two categories are candidates for this application. In this paper, we present a deep neural network (DNN) structure for QoT estimation considering both regular single-mode fiber (SMF) and future few-mode fiber (FMF) proposed to increase the overall network capacity. We comprehensively explore ML-based regression methods for estimating generalized signal-to-noise ratio (GSNR) in partial-load SMF and FMF links. Synthetic datasets have been generated using the enhanced Gaussian noise (EGN) model. Results indicate that the proposed DNN-based regressor can provide better accuracy along with less computation complexity, compared with other state-of-the-art ML methods as well as closed-form-EGN and closed-form-GN models.

Digital Subcarrier Multiplexing: Enabling Software-Configurable Optical Networks

The various topologies, traffic patterns and cost targets of optical networks have prevented the deployment of end-to-end solutions across multi-domains, and the optimization of the network as a whole. The consequent limitations in flexibility, scalability, and adaptability of optical networks will become increasingly important with new applications, such as 5G/6G. Coherent transceivers based on digital subcarrier multiplexing (DSCM) are proposed to address these current constraints. In particular, DSCM allows (i) the design of high-capacity point-to-point (P2P) and -multipoint (P2MP) optical networks; (ii) simplified aggregation with passive optics; and (iii) connections between low- and high-speed transceivers. Furthermore, DSCM-based networks reduce the number of opto-electro-opto stages, halve the number of bookended transceivers, and provide a better match for existing hub-and-spoke (H&S) traffic patterns in fast-growing and dynamic access/metro segments. A DSCM-based transceiver will pave the way for the deployment of next-generation flexible, adaptable, and scalable software-configurable optical networks. Key steps and elements to realize this solution are laid out, and promising applications outlined. The first real-time experimental results of coherent P2MP transceivers are presented.

Dynamic Joint Functional Split and Resource Allocation Optimization in Elastic Optical Fronthaul

Dynamic reconfigurability in optical and mobile networks can facilitate heterogeneous service provisioning while utilizing minimal resources. This allows cost-efficient service delivery resulting in high revenues for network operators. Deployment of elastic mobile and optical networks is a key driver for enabling reconfigurability in modern networks. Elastic optical networks can be exploited as the fronthaul portion of new generation of mobile networks. Such elastic optical fronthaul networks facilitate joint reconfiguration of flexible radio and optical elements and provide considerable performance improvements. In this paper, we focus on the joint dynamic selection of functional splits and configuration of optical transponders and illustrate that designing a converged network with optical and radio elements improves network power efficiency. A time-averaged stochastic optimization problem is formulated and its solution is derived using a modified version of the Lyapunov drift technique. Simulation results demonstrate that the proposed scheme can reduce the average power consumption by up to 70% compared to a cloud radio access network with a traditional optical fronthaul. Further, the results show that the modified Lyapunov technique can afford stringent fronthaul delays below 250 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> . We also discuss how future technology upgrades such as increasing the number of radio antenna ports and decreasing the granularity of fiber spectrum grid may influence the results.

SNR Re-Verification-Based Routing, Band, Modulation, and Spectrum Assignment in Hybrid C-C+L Optical Networks

Band division multiplexing technology is a promising medium-term transitional solution to deal with the traffic flood, by leveraging the existing optical fiber transmission infrastructure. Additionally, the deployment of multi-band optical networks requires updating and upgrading key components, such as multi-band amplifiers and multi-band optical cross-connects. From cost view, it would be a promising way for operators to expand transmission capacity on some of the links with high priority, which are used heavily. Therefore, the application scenario of this paper is positioned in the C-C+L hybrid optical networks. In this scenario, the introduction of the L-band brings additional inter-band stimulated Raman scattering (ISRS) which is a non-negligible nonlinear effect, leading new constraint for service provisioning. This paper proposes an ISRS-aware routing, band, modulation, and spectrum assignment (RBMSA) scheme, considering the impact of ISRS generated by new requests on existing requests. By implementing the SNR re-verification, not only the transmission quality of the current request can be realized, but also the service quality of the existing requests will not be seriously degraded to be unacceptable. A two-dimensional model of request bandwidth and duration is established for band selection. Priority is provided for arranging the requests in the L-band when it is available. For each single request, when the least number of slots required by adopting different modulation formats is the same, lower-order modulation is preferred to improve its SNR tolerance of this request under the ISRS impact. Simulation results indicate that the proposed scheme can effectively decrease the blocking probability, and improve the channel SNR for the successfully established requests.

Strategies for training optical neural networks

Optical neural networks have great potential to process information efficiently with the speed of light. Compared with electronic competitors, multiple tasks have been successfully demonstrated in such computing systems with several orders of magnitude improvement in energy consumption. However, current training strategies, as a critical step for bringing optical neural networks into reality, are still at an early stage. The high complexity and long training time fail to meet the requirement for training optical neural networks massively and efficiently. Therefore, appropriate training strategies are still in great demand for future deployment of large scale optical neural networks. In this paper, we investigate current training approaches and the possible paths which could make optical neural networks highly expressive and realistic are also discussed.

Cost-optimal architecture design for adaptive multi-stage TWDM-PON with PtP WDM overlay

Toward greenfield time and wavelength division multiplexed passive optical network (TWDM-PON) deployment in access segment, optimal network planning, and resource provisioning need to be explored in the planning phase to reduce capital expenditure (CapEx) and operational expenditure (OpEx). To address the issue, we propose an integer linear programming (ILP)-based optimization framework to design cost-efficient adaptive multi-stage TWDM-PON architecture, where an optimal number of cascaded splitting stages are used to minimize the combined expenditure comprising the CapEx and OpEx. Point-to-point WDM overlay over TWDM-PON is incorporated, wherein we reserve some wavelengths per optical line terminal (OLT) port to equip the heavily loaded (congested) optical network units (ONUs) with dedicated wavelengths. The ILP model offers the complete interconnection details from OLT to all ONUs providing the minimum combined expenditure, and selects the optimal number and locations of remote nodes (RNs) among the candidate RN locations for passive device placement, the types (either arrayed waveguide grating or power splitter) and splitting ratios of passive devices, and the number of splitting stages. Network constraints, such as the minimum guaranteed traffic rate to each ONU, the maximum number of ONUs with dedicated wavelengths per OLT port, and the maximum number of users per OLT port are taken into consideration. We compare the performance of the proposed TWDM-PON design model with the existing studies on greenfield PON design in terms of the cost savings, methodology features, and limitations. The proposed ILP model is further extended to design cost-optimal single-stage and adaptive multi-stage time division multiplexed PONs (TDM-PONs), and the expenditure for all models are estimated. We also investigate the variation in signal-to-noise ratio due to variation in the number of cascade stages. The models provide globally optimal solutions within a reasonable time bound with all constituent sub-problems and constraints jointly taken into consideration.

Integrated Silicon-on-Insulator Optical Comb Demultiplexer for Elastic Optical Networks

Practical deployment of elastic optical networks requires key enabling technologies supporting the miniaturization of flexible optical transponders for provisioning large-bandwidth services at low-cost per users. A silicon photonics (SiP) reconfigurable optical frequency comb (OFC) demultiplexer based on passive optical filtering exhibiting a minimum spurious tone rejection (STR) of nearly 30dB at 12.5GHz tone spacing is here reported. Low power penalty due to inter-channel crosstalk (IXT) originated by finite STR is observed. Improved filter designs for reduced IXT and/or operation at 6.25GHz comb spacing are experimentally and numerically verified. By monolithic integration with SiP OFC sources and I-Q modulators the scheme has potentials for realizing ultra-compact multiple-flow optical transmitters with adaptive bandwidth and channel spacing.

The advantage of blown fiber technology for out site plan network deployment than conventional cabled optical fiber system in Depok apartment project

The current deployment of optical fiber networks in several major cities in Indonesia is intensive. Development of fiber as the backbone or last mile for special services and almost all of us have encountered. Maybe one of them is a network deployment studio in one of the Apartment Projects in Depok City. The population of Depok reaches 4% per year higher than the national growth, the number of students and students who reach more than 80 thousand who live in Depok from only 2 campuses namely the University of Indonesia and Gunadarma University make the residential business growth both in the form of residential horizontal (boarding rooms) ) or vertical residential (Apartment). Developers are competing to build Apartments which, of course, are potential new revenue and new markets for Internet & Pay-TV Providers. The problem of the length of time the deployment of network infrastructure, traffic is not taken into account and still prioritizes the quality and cost that remains efficient become an issue of concern to the Provider. Blown Fiber is a new technology with four main components namely products, blowing devices, optical fiber bundles, and terminating/connecting hardware. This technology results in more cost-efficient, more flexible designs, better work costs in installation, termination and cheaper testing compared to conventional optical fiber deployment technology. The implementation of Blown Fiber in a deploying studio in one of the Apartments in Depok specifically on the Out Site Plan (OSP) turned out to provide convenience and acceleration in terms of network deployment.

Enabling fully programmable transponder white boxes [Invited

There is great interest in the disaggregation of hardware and software components in the networking community. The reason is that such a strategy enables flexible solutions and achieves efficiency and cost reductions within many network scenarios. Network operators have paid attention to disaggregation because it can help maintain a profit margin as revenues decrease. Optical network deployments historically have been based on end-to-end solutions that offer little interoperability in optical components. Disaggregation enables operators to mix solutions from different vendors to create a complete design that can address the requirements of the intended network scenario. While disaggregation enables the deployment of ad hoc solutions, it worsens system complexity. The definition of software-defined network (SDN) solutions enables a standard view of the network elements so that network operators can have an end-to-end design. The Telecom Infra Project (TIP) is focused on defining solutions for the telecom industry that can speed up network deployment. Within the TIP project, there are two main activities: the definition of white boxes for transport networks and an initiative called Transport Abstraction Interface (TAI). A white box is a hardware design that allows the user to install any software for network operation. On the other hand, TAI facilitates the connectivity of optical components with packet/optical platforms by providing an abstracted view of the optical components. This approach reduces the development time to integrate the components in open packet/optical systems. This paper presents different disaggregation models and their SDN architectures for providing end-to-end designs. Similarly, we present the capabilities of TAI. Finally, this work defines and demonstrates, for what we believe is the first time, a fully programmable optical white-box solution. Thus, we demonstrate how network operators can program a packet/optical white box and optical components using open solutions. This demonstration shows how open ecosystems speed up network innovation and reduce time to market.

A modulator-free quantum key distribution transmitter chip

Quantum key distribution (QKD) has convincingly been proven compatible with real life applications. Its wide-scale deployment in optical networks will benefit from an optical platform that allows miniature devices capable of encoding the necessarily complex signals at high rates and with low power consumption. While photonic integration is the ideal route toward miniaturisation, an efficient route to high-speed encoding of the quantum phase states on chip is still missing. Consequently, current devices rely on bulky and high power demanding phase modulation elements which hinder the sought-after scalability and energy efficiency. Here we exploit a novel approach to high-speed phase encoding and demonstrate a compact, scalable and power efficient integrated quantum transmitter. We encode cryptographic keys on-demand in high repetition rate pulse streams using injection-locking with deterministic phase control at the seed laser. We demonstrate record secure-key-rates under multi-protocol operation. Our modulator-free transmitters enable the development of high-bit rate quantum communications devices, which will be essential for the practical integration of quantum key distribution in high connectivity networks.

Enhancing Performance of Hybrid FSO/Fiber Optic Communication Link Utilizing Multi-Channel Configuration

Abstract Optical wireless is the alternative approach to complete the deployment of optical cable networks in case of failure in implementation. In optical wave the attenuation due to atmospheric turbulence conditions causes a performance degradation of a free space optical (FSO) system. Thus, it will lead to the deterioration of the signal power in the optical cable. To overcome these challenges, multi-channel FSO transmitter and erbium doped fiber in optical link was adopted with high transmission power. In this paper, a hybrid FSO/fiber optic (FSO/FO) link is simulated and investigated under different weather conditions. The proposed hybrid link is evaluated in terms of BER and Q-factor. The proposed system shows a closely performance as compared with the conventional FSO for whole investigation range from 200 m to 2000 m. While the communication distance with the hybrid link is increased by 40 km as compared to conventional FSO. The results show good agreement with Kim model, especially at high input power of 160 mW.

Realization of a Long-haul Optical Link with Erbium Doped Fiber Amplifier

AbstractThe need for high capacity and bandwidth in broadband communication systems increased rapidly in a few past years. Optical fiber is now the major transmission medium for fast and reliable communication replacing the old copper-based connections. However, with the deployment of optical networks, number of problems arise. The main problem of optical networks is the amplification in the long-distance transmission. Erbium doped fiber amplifier (EDFA) is the leading technology in the field of optical amplifiers. It uses erbium doped fiber to amplify optical signal. The importance of amplification in optical domain is relevant in long-haul and high-speed transmission systems. In this paper the study of the EDFA is presented. Based on an analytical study, the simulation model of the EDFA is created. The main aim is to determine the optimal parameters of the EDFA for a long-haul 16-channel DWDM (Dense Wavelength Division Multiplexing) system. The performance of the proposed DWDM system is mathematically analyzed using BER (Bit Error Rate) and Q factor.