Optical Distribution Network Research Articles

Fault monitoring in passive optical network through the integration of machine learning and fiber sensors

SummaryAs the deployment of fiber‐based broadband networks continues to accelerate, the number of network facilities too is increasing exponentially. The network of optical fiber cables keeps growing as the number of passive optical network (PON) customers increases, eventually leading to unforeseen faults. Several solutions are offered for monitoring the optical link in PON with the optical time‐domain reflectometer (OTDR) as the most common for point‐to‐point optical link characterization. However, the OTDR approach has been found to be inadequate for point to multipoint network fault characterizations due to numerous back‐reflected signals converging at the power splitter that cannot be identified simultaneously by the OTDR detector. Several machine learning (ML) methods have recently been introduced for successful monitoring of optical communication links, but much of the ML technique depends on data from network transceivers to train ML algorithms to identify and detect faults. However, the use of data information for monitoring purposes can have an impact on the consistency of the services offered. In this article, we consider the deployment of the fiber Bragg grating sensor to acquire the monitoring data samples used to train the ML technique for effective link characterization. The proposed solution has the advantage of having a separate monitoring source that is independent of the data transmission signal and guarantees transparent transmission of information. The proposed ML‐based technique shows up to 99% precision for the identification of fiber defect in the PON optical distribution network.

Physical Layer Components Security Risks in Optical Fiber Infrastructures.

Optical fiber communications are essential for all types of long- and short-distance transmissions. The aim of this paper is to analyze the previously presented security risks and, based on measurements, provide the risk level evaluation. The major risk is the possibility of inserting a splitter into the optical distribution network and capturing a portion of the entire spectrum, i.e., all channels in the optical fiber. Another significant security risk is crosstalk on multiplexers in networks with wavelength division multiplexing. The paper covers the macrobend attenuation evaluation of fiber and back-reflection measurements. Based on the measurements, risks were evaluated for both point-to-point and point-to-multipoint networks and, lastly, the paper covers crosstalk measurements of an optomechanical switch. Finally, all individual risks are evaluated according to the severity, and a proposal for risk minimization is provided.

Remote Pumping in Point to Multi-point Networks

A remotely pumped Erbium-doped system for the amplification of an optical signal for long-reach (LR) next-generation passive optical networks (NG-PONs) is presented in this paper. The next-generation networks will be deployed with/over the current point to multi-point technology with/without backward compatibility. Remote pumping allows extending the reach of the optical distribution networks and the magnification of the splitting ratio as well, which is most important for increasing the number of end users in the PON network. In our laboratory, we have successfully verified the functionality of the unidirectional and bidirectional remote pumping system based on an Erbium-doped fiber inserted into the route and remote pumping from a central office. Our measurement results prove that it is possible to extend the total reaching point to the multi-point system without the difficult incidence in the optical distribution network. Based on the results, the proposed amplifying passive optical network approach is capable of being used in passive optical networks in C band for extending the total reach of system or increasing the split ratio.

The architecture of hybrid mm-wave ARoF Super-PON system for 5G implementation

Fifth-generation mobile communications are delivering higher data rates and low latency services for costumer by utilizing the benefits of optical fiber. In this paper, we propose the architecture of a hybrid millimeter-wave (mm-wave) analog radio-over-fiber (ARoF) Super-PON optical network for future broadband service and the latest fifth-generation 5G/5G + cellular mobile communications. Our proposed infrastructure shows the trade-off between technology and costs where the optical access network architecture is technologically transformed to transport intermediate frequencies (IF) through the existing fiber optical distribution network (ODN) by integrating baseband units (BBUs) into optical line terminals (OLTs) and the remote radio units (RU) into optical network terminals (ONTs), leaving the traditional broadband architecture unchanged. Performance of investigated mm-wave ARoF Super-PON transmission systems in the C-band downlink scenario for both broadband and mobile service is shown. With the proposed hybrid architecture, it is possible to provide cost-effective deployment of future 5G/5G+ networks as 5G key performance indicators (KPIs) are met and increase PON’s utilization for multiple services by sharing frequency bands and infrastructure. Several intermediate frequencies in Ka-band (26.5 – 40 GHz) are addressed to evaluate the performance of our investigated ARoF Super-PON transmission system for each corresponding frequency in different scenarios of up to 50 km over standard single-mode optical fiber (SMF) link.

An Effective Evaluation of Wavelength Scheduling for Various WDM-PON Network Designs with Traffic Protection Provision

Recently, metropolitan and access communication networks have markedly developed by utilizing a variety of technologies. Their bearer communication infrastructures will be mostly exploiting the optical transmission medium where wavelength division multiplexing techniques will play an important role. This contribution discusses the symmetric sharing of common optical network resources in wavelength and time domains. Wavelength-Division Multiplexed Passive Optical Networks (WDM-PON) attract considerable attention regarding the next generation of optical metropolitan and access networks. The main purpose of this contribution is presented by the analysis of possible scheduling of wavelengths for our novel hybrid network topologies considered for WDM-PON networks. This contribution briefly deploys adequate Dynamic Wavelength Allocation (DWA) algorithms for selected WDM-PON network designs with the provision of traffic protection when only passive optical components in remote nodes are utilized. The main part of this study is focused on the use of wavelength scheduling methods for selected WDM-PON network designs. For evaluation of offline and online wavelength scheduling for novel hybrid network topologies, a simulation model realized in the Matlab programming environment allows to analyze interactions between various metropolitan and access parts in the Optical Distribution Network (ODN) related to advanced WDM-PON network designs. Finally, wavelength scheduling methods are compared from a viewpoint of utilization in advanced WDM-PON networks designs.

FLCS-PON – A 100 Gbit/s Flexible Passive Optical Network: Concepts and Field Trial

We demonstrate concepts and results of a field trial for a flexible-rate passive optical network (FLCS-PON), which delivers bitrates up to 100 Gbit/s and allows for adaptations in the transmission method to match the users' channel conditions and optimize throughput. FLCS-PON builds on top of the hardware ecosystem that will be developed for ITU-T 50 Gbit/s PON and employs three new ingredients: optical network unit (ONU) grouping, flexible modulation format, and flexible forward error correction (FEC) code rate. Together, these techniques take advantage of the optical distribution network (ODN) statistics to realize a system capable of more than twofold throughput increase compared to the upcoming 50 Gbit/s PON, but still able to support a full array of deployed fiber edge cases, which are problematic for legacy PONs. In this paper we explain the concepts behind enabling techniques of FLCS-PON. We then report on a field trial over a deployed fiber infrastructure, using a system consisting of one FLCS-PON OLT and two ONUs. We report both pre- and post-forward-error-correction (post-FEC) performance of our system, demonstrating achievable net bitrate over an operator's fiber infrastructure. We realize a downlink transmission at double the speed of ITU-T 50 Gbit/s PON for ONUs exhibiting lower optical path loss (OPL), while simultaneously continue to support ONUs at high OPLs. We additionally realize a record-high 31.5 dB loss budget for 100 Gbit/s transmission using a direct-detection ONU with an optical preamplifier.

Modeling and comparative analysis of all-class converged-coexistence NG-PON2 network for 5G-IoT-FTTX-services and application

Abstract We presented a concept of converged coexistence (CC) access network and generate, and test model is demonstrated for optimization of channel launch power PTODN in the distribution network which subsequently confirm power budget class of NG-PON2 in this paper. Multiplexing of wavelength and time (TWDM) technology is incorporated for multichannel NG-PON2 configurations for 5G, internet-of-things (IoT) applications, and fiber-to-the-x (FTTX) services. CC NG-PON2 symmetric configuration supporting 2.5 and 10 Gbps channels are analyzed and compared in the sight of channel nonlinear impairments includes Kerr-effect (γ) spanning from self phase modulation (SPM) and cross-phase modulation (CPM), chromatic dispersion (CD), and four wave mixing (FWM) in worst-case scenario. Intensity modulation (IM) technique incorporated before multiplexing the D/S channels by coexisting element (CEx) and coupled to wavelength routed (WR) optical distribution network (ODN). U/S channels are routed using wavelength select (WS) ODN. ODN is implemented using G.652 non zero dispersion shift (NZ-DSF) single-mode (SM) fiber. Multi-channel spectrum envelope propagating in either direction is optimized to PTODN = 3/5/7/9 dBm and 4 dBm, respectively. The theoretical modeling and simulative results confirms the proposed network configuration supports incremental receiver sensitivity (Rxs) as −42.19/−42/−39.75/−37.97 dBm and −35.45/−35.38/−33.45/0.38/−42 dBm for λ1 2.5 Gbps and λ8 10 Gbps TWDM and PtP WDM channels, respectively, for all-class networks supporting splitter configuration ratio of 640 at 50 km mitigating effect of channel nonlinearities like CD, SPM, cross-phase modulation (XPM), and FWM for λ8 10 Gbps channel.

All optical metropolitan quantum key distribution network with post-quantum cryptography authentication.

Quantum key distribution (QKD) provides information theoretically secure key exchange requiring authentication of the classic data processing channel via pre-sharing of symmetric private keys to kick-start the process. In previous studies, the lattice-based post-quantum digital signature algorithm Aigis-Sig, combined with public-key infrastructure (PKI), was used to achieve high-efficiency quantum security authentication of QKD, and we have demonstrated its advantages in simplifying the MAN network structure and new user entry. This experiment further integrates the PQC algorithm into the commercial QKD system, the Jinan field metropolitan QKD network comprised of 14 user nodes and 5 optical switching nodes, and verifies the feasibility, effectiveness and stability of the post-quantum cryptography (PQC) algorithm and advantages of replacing trusted relays with optical switching brought by PQC authentication large-scale metropolitan area QKD network. QKD with PQC authentication has potential in quantum-secure communications, specifically in metropolitan QKD networks.

Design and investigation of N1-class next-generation passive optical network-2 (NG-PON2) coexistence architecture in the presence of Kerr effect and four-wave mixing (FWM) for fiber to the home (FTTX) access networks

Abstract In this paper, we investigated N1-class Time and Wavelength Division Multiplexing (TWDM) Next-Generation Passive Optical Network-2 (NG-PON2) supporting symmetric and coexistence configuration in a worst-case scenario. The network is optimized in the presence of linear and nonlinear impairments such as chromatic dispersion (CD), self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM). On-off key (OOK) modulation technique incorporating hybrid optical distribution network (ODN) i.e., wavelength select (WS) and wavelength-routed (WR) ODN is used to connect downstream (D/S) and upstream (U/S) channels supporting symmetric 80 Gbps data rate operating at 2.5/2.5 and 10/10 Gbps, respectively. G.652 single-mode (SM) fiber channel is modeled for fiber launch power PTODN = 3 dBm and 4 dBm for D/S and U/S channels to implement N1-class network. The D/S and U/S receiver sensitivity (Rxs) demonstrated are −44.23/−37.46 dBm and −28.46/−35.32 dBm and inter-channel crosstalk (Cc) is −31.97/−31.39 dB accommodating 640 splitter configuration at 50 km in the presence of impairments at 10E-7 bit error rate (BER) and Quality (Q)-factor of 5 for 10 Gbps channel.

Real-time high-bandwidth mm-wave 5G NR signal transmission with analog radio-over-fiber fronthaul over multi-core fiber

This article presents an experimental demonstration of a high-capacity millimeter-wave 5G NR signal transmission with analog radio-over-fiber (ARoF) fronthaul over multi-core fiber and full real-time processing. The demonstration validates the core of the blueSPACE fronthaul architecture which combines ARoF fronthaul with space division multiplexing in the optical distribution network to alleviate the fronthaul capacity bottleneck and maintain a centralized radio access network with fully centralized signal processing. The introduction of optical beamforming in the blueSPACE architecture brings true multi-beam transmission and enables full spatial control over the RF signal. The proposed ARoF architecture features a transmitter that generates the ARoF signal and an optical signal carrying a reference local oscillator employed for downconversion at the remote unit from a single RF reference at the central office. A space division multiplexing based radio access network with multi-core fibre allows parallel transport of the uplink ARoF signal and reference local oscillator at the same wavelength over separate cores. A complete description of the real-time signal processing and experimental setup is provided and system performance is evaluated. Transmission of an 800 MHz wide extended 5G NR fronthaul signal over a 7-core fibre is shown with full real-time signal processing, achieving 1.4 Gbit/s with a bit error rate <3.8times 10^{-3} and thus below the limit for hard-decision forward error correction with 7% overhead.

Retraction Note to: Power Budget Analysis of an Ultra-Dense Coherent MB-OFDM WDM Metro-Access Networks

The power budget (PB) of an ultra-dense wavelength division multiplexing virtual-carrier helped coherent-detection multi-band orthogonal frequency division which multiplexes metro-access network with 10.7 Gb/s per client and per band, with groups divided by 3.125 GHz, is surveyed numerically, for channel spacings of 12.5 GHz and 25 GHz. In the light of the findings, the PB ranges between 14.8 and 20.5 dB. It was found that the minimum PB, on one hand, enables an optical distribution network (ODN) splitting ratio of 16 with standard single mode fiber (SSMF) reach of 13 km. The maximum PB, on the other hand, enables an ODN splitting ratio of 64 with SSMF reach of 12 km.

An ultra-dense spacing-based PON by incorporating dual drive Mach–Zehnder modulator for comb generation

Abstract Wavelength division multiplexed passive optical is promising technique to achieve a high data rate and large number of user. The notable advantages of WDM PON is the combination of reliability, cheap in cost, accessible bandwidth, high security, large optical reach and it can support large number of ONU. There are multiple approaches to achieve high-speed WDN PON using different transmission techniques. In WDM, multiple lasers are required which increase the cost of the system. To reduce cost, an optical multicarrier generation system is proposed. An economical multiple carrier generation with the incorporation of sine generator and Mach–Zehndar modulator is demonstrated. Utmost work of sine generator and dual drive modulator was to attain low cost functioning of passive optical networks. Multicarrier generation was done and replacement of laser carriers with optical multicarrier generator. Carriers were generated with the frequency spacing of 20 GHz and these carriers were used in the passive optical networks with the tone-to-noise ratio of 40 dB, amplitude difference of 1.4 dB. For the transmission of downstream in the PON, differential phase shift keying was employed at 10 Gbps data speed. Transmission distance achieved was 30 km using single-mode fiber and this was a part of optical distribution network. Optical network unit was next part after ODN and signals were received with balanced receiver. Moreover, half signal was given to intensity modulator for the signal re-modulation. Bit error rate of 10–9 was achieved at all channels in the downstream. An upstream of 10 Gbps was accomplished in the passive optical network.

Design and analysis of hybrid optical distribution network for worst-case scenario of E2-class symmetric coexistence 80 Gbps TWDM NG-PON2 architecture for FTTX access networks

In this paper, we investigated the cost-effective design and validation of E2-class coexistence 80 Gbps symmetric 8 × 8 Time and Wavelength Division Multiplexing (TWDM) NG-PON2 optical access network considering worst-case scenario for the deployment of Fiber-to-the-X (FTTX) access network using hybrid optical distribution network (ODN). Full-service access network (FASN) unanimously agreed and ITU-T G.989.2 described recommendations for TWDM PON NG-PON2 technology to cater to the need of ever-increasing demand for higher bandwidth and data speed beyond 10 Gbps per user through access networks. Wavelength select (WS) and wavelength-routed (WR) ODN for downstream (D/S) and upstream (U/S) channels symmetric coexistence functionality supporting 80 Gbps accommodating GPON and XGS-PON legacy channels i.e.4-TWDM and 4 point-to-point (PtP) WDM channels operating at 1.25/2.5/10 Gbps respectively in D/S and U/S direction with error free higher splitter configuration of 2304 at 20 km, 640 at 40 km, 576 at 60 km. Precise calculations are done to ensure 11 dBm and 9 dBm ODN launch power (PTODN) to implement worst-case scenario for symmetric E2-class TWDM NG-PON2 network. Calculated inter-channel cross-talk (Cc) is -33.57 dB/-34.74 dB and corresponding cross-talk power penalty (Pc) is 0 dB for D/s and U/S channels respectively. Simulation results demonstrated and verified with the recommendations made in ITU-T G.989.2 confirmed that the proposed network configuration supports extended to reach upto 60 km in D/S and 80 km in U/S direction delivering incremental receiver sensitivity (Rxs) as -34.40/-34.40/42.21 dBm and -34.11/-37.25/-33.37 dBm, ODN path loss 29.40 dB.

100+ Gbps/λ 50 km C-Band Downstream PON Using CD Digital Pre-Compensation and Direct-Detection ONU Receiver

We experimentally demonstrate a single-wavelength 100 Gbps downstream PON transmission aided by chromatic dispersion digital pre-compensation (CD-DPC) using simple digital signal processing (DSP) finite impulse response (FIR) filters in combination with an IQ Mach–Zehnder modulator (IQ-MZM) at the transmitter side and direct-detection receiver at the optical network unit (ONU). A reach of 50 km over standard single-mode fiber in C-band and an optical distribution network (ODN) loss of 28.5 dB are achieved. Transmission of 50 and 125 Gbps over 50 km of fiber is also tested, achieving 32 dB and 24 dB of ODN loss, respectively. The complexity of the filters, the optimization of the main design parameters, and the tolerance of the CD-DPC to the uncertainty of the exact accumulated link dispersion are analyzed in detail.

Fifth‐generation new radio fiber‐wireless system for long‐reach and enhanced mobile broadband scenarios

AbstractThis work reports the implementation of a fifth‐generation (5G) new radio (NR) fiber‐wireless (FiWi) system for long‐reach and enhanced mobile broadband scenarios. The proposed 5G NR FiWi system includes a 12.5 km optical distribution network based on radio over fiber technology, a 7.5 km supercell in a rural area using the 700 MHz band, digital pre‐distortion (DPD), equalization and a Gbit/s indoor femtocell operating in the 26 GHz band. The 5G NR standard has been applied and DPD and equalization have been efficiently employed to enhance the system performance in mm‐waves. Furthermore, experimental results demonstrate successful implementations of a femtocell with 4 Gbit/s throughput and only 4.6% error vector magnitude, as well as a large cell with 33 Mbit/s throughput and 7.51‐km reach.

Lasers in Passive Optical Networks and the Activation Process of an End Unit: A Tutorial

It is 21 years since the first passive optical network (PON) was standardized as an asynchronous transfer mode passive optical network (APON) with same optical distribution network scheme as we know in current networks. A lot of PON networks were standardized in the following years and became an important part of telecommunication. The general principles of these PON networks are described in many papers and books, but only a little information about used lasers is available. The aim of this tutorial is to describe lasers used in PON networks and principles of their operation. The paper describes the principles of single longitudinal mode (SLM), multi longitudinal mode (MLM), distributed-feedback (DFB), and Fabry–Pérot (FP) lasers. Furthermore, the lasers are compared by their usage in optical line termination (OLT) for passive optical networks. The second part of this tutorial deals with activation process of optical network unit. The described principle is the same for connection of a new customer or blackout scenario. The end unit is not able to communicate until reach the operational state; each state is defined with physical layer operation and administration and maintenance (PLOAM) messages sequence and their processing.

Low-complexity probabilistic shaping based on bit-weighted distribution matching in DMT-WDM-PON.

We introduce a novel probabilistic shaping (PS) scheme based on bit-weighted distribution matching (BWDM) into a discrete multi-tone wavelength division multiplexing passive optical network (DMT-WDM-PON) employing low-density parity-check-coded 16-ary quadrature amplitude modulation (16QAM). Unlike the prevailing arithmetic coding-class PS schemes with target symbol probability, such as arithmetic distribution matching and constant composition distribution matching, the proposed one realizes Gaussian-like symbol probability distribution emulation merely based on simple bit-class processing, having the advantage of much lower computational complexity. As the key operation in BWDM, the bit weight intervention is implemented in the process of PS-16QAM generation for elevated transmission probability of binary data '0' by cascaded operations of weight bit labelling and bit reconstruction. The experimental results show that, compared with uniformly-distributed signal with the same net rate, significantly-improved receiver power sensitivity and system tolerance to optical fiber nonlinear effect can be obtained in the DMT-WDM-PON system. The proposed PS scheme can be considered as one of promising practical solutions for more available optical network units due to enlarged system power loss budget for the optical distribution network.

Towards a Scaleable 5G Fronthaul: Analog Radio-over-Fiber and Space Division Multiplexing

The introduction of millimeter wave (mm-wave) frequency bands for cellular communications with significantly larger bandwidths compared to their sub-6 GHz counterparts, the resulting densification of network deployments and the introduction of antenna arrays with beamforming result in major increases in fronthaul capacity required for 5G networks. As a result, a radical re-design of the radio access network is required since traditional fronthaul technologies are not scaleable. In this article the use of analog radio-over-fiber (ARoF) is proposed and demonstrated as a viable alternative which, combined with space division multiplexing in the optical distribution network as well as photonic integration of the required transceivers, shows a path to a scaleable fronthaul solution for 5G. The trade-off between digitized and analog fronthaul is discussed and the ARoF architecture proposed by blueSPACE is introduced. Two options for the generation of ARoF two-tone signals for mm-wave generation via optical heterodyning are discussed in detail, including designs for the implementation in photonic integrated circuits as well as measurements of their phase noise performance. The proposed photonic integrated circuit designs include the use of both InP and SiN platforms for ARoF signal generation and optical beamforming respectively, proposing a joint design that allows for true multi-beam transmission from a single antenna array. Phase noise measurements based on laboratory implementations of ARoF generation based on a Mach–Zehnder modulator with suppressed carrier and with an optical phase-locked loop are presented and the suitability of these transmitters is evaluated though phase noise simulations. Finally, the viability of the proposed ARoF fronthaul architecture for the transport of high-bandwidth mm-wave 5G signals is proven with the successful implementation of a real-time transmission link based on an ARoF baseband unit with full real-time processing of extended 5G new radio signals with 800 MHz bandwidth, achieving transmission over 10 km of 7-core single-mode multi-core fiber and 9 m mm-wave wireless at 25.5 GHz with bit error rates below the limit for a 7% overhead hard decision forward error correction.

Super-PON: an evolution for access networks [Invited

Passive optical networks (PONs) have been widely used in access networks and are today the access technology of choice for operators, especially when they need to build new infrastructure. Significant effort has been put in place across the years to scale the speed of passive optical networks. The super-PON concept has also been proposed in order to scale reach and customer aggregation of PONs. However, it did not produce any standardization efforts nor significant commercial deployments. In November 2018, the IEEE 802.3 Working Group formed the P802.3cs “Super-PON” Task Force to standardize a flavor of super-PON able to support an increased optical reach of up to 50 km and an expanded customer coverage of up to 1024 customers per fiber over a passive optical distribution network. A project with near identical objectives was later started in ITU-T Q2/SG15. This paper presents the latest updates from these industry standardization efforts, with special attention to the activity of the IEEE P802.3cs Task Force, and the technical reasoning behind some of the key decisions that have been made.

Ring based latency-aware and energy-efficient Hybrid WDM TDM-PON with ODN interconnection capability for smart cities

Abstract In the current scenario, there is a huge advancement in Information and Communication Technology (ICT), and almost most of the devices used in a smart city are the Internet of Things (IoT) based smart devices. To support high-speed IoT devices, wavelength division multiplexed passive optical networks (WDM-PON) is one of the most promising and most commonly used technology in optical distribution network (ODN). With the exponential growth of WDM-PON and its applications, energy consumption, operational expenditure (OPEX), communication latency between different users, reliability of service etc. are becoming the most challenging issues to implement the WDM-PON networks in the smart cities. In this paper, we propose a ring based latency aware and energy efficient PON architecture which is capable of providing point to point downstream, upstream, inter-ODN, intra-ODN and inter-ODN broadcasting transmission. Proposed architecture reduces the significant amount of transmission latency, energy consumption, operational expenditure and reduces the emission of Green House Gases (GHGs). The architecture also reduces the downstream and upstream bandwidth consumption by avoiding the transmission of the inter-ODN signal to optical line terminal (OLT) and back to destined ODN. The architecture seems appropriate for supporting various real-time high-speed ICT and IoT applications of a smart city.