Optical Distribution Network Research Articles

Multi-user low-upstream-loss multi-mode passive optical network with compact optical distribution network using multi-plane light conversion

Multi-user low-upstream-loss multi-mode passive optical network with compact optical distribution network using multi-plane light conversion

Benefits of flexibility in current and future IM-DD based TDM-PON [Invited

Due to continuously emerging high bandwidth applications, research and standardization of time division multiplexed passive optical networks (TDM-PONs) have focused on increasing the peak bitrate. However, increasing the bitrate while supporting the stringent optical power budget of a PON becomes increasingly challenging because of the larger chromatic dispersion penalties as well as reduced receiver sensitivity when the bitrate of the intensity modulation with direct-detection (IM-DD) based PON is increased. Also, increasing bitrate generally causes higher power consumption, which leads to more challenging thermal designs and misalignment with environmental targets. In this paper we give an overview of flexible concepts that can help achieve the required optical power budget and support reduced power consumption of a future IM-DD based TDM-PON. We demonstrate that a flexible PON can provide an increased overall throughput or an extended reach and power budget with the use of flexible modulation formats, probabilistic and geometric shaping, and flexible rate forward error correction (FEC). Another dimension of flexibility in the form of a configurable optical distribution network (ODN) is described and its merits and challenges are discussed. Flexible concepts based on interleaving of FEC codewords can align signal processing like FEC decoding and the protocol processing closer to the user-rate of an optical network unit (ONU), which leads to reduced power consumption. Flexibility based on multiple channels based on wavelength multiplexing or spatial multiplexing enables optimization of the power consumption to the amount of traffic on the PON. Several flexible concepts have already been adopted in the PON standards. We highlight flexible gain FEC for upstream 50G PON, the transmitter dispersion eye closure (TDEC) metric, and the flexible split-ratio ODN for power saving. Flexible modulation has not been adopted yet in PON standards, but it is expected that flexibility is more and more needed to support the performance, cost effectiveness, and power conservation of future optical access systems.

Performance and energy efficiency enhancement of existing optical communication systems by incorporating resource allocation on demand technique in FiWi networks

Abstract Fiber-wireless (FiWi) networks have begun to be fully integrated into contemporary optical access network systems as a result of utilizing the combined advantages of wired and wireless techniques. Passive optical networks (PON) are heavy energy consumers and one of the main contributors to greenhouse gas emissions (GHG) that are a result of climate change. These systems also present economic challenges. In this work, three different FiWi systems are presented such as (i) even/odd active transmitters with only free space optical (FSO) based optical network units (ONUs)/with dual channel option such as distribution fiber (DF)/FSO supported ONUs, (ii) a novel resource allocation on demand (RAoD) incorporated bidirectional FiWi system supporting DF/FSO based ONUs and four wave mixing (FWM) generated upstream wavelengths and (iii) transmitter diversity enabled 5G supported FiWi system supporting bidirectional communication. It is observed that the energy efficiency of 26.04 % is obtained in even/odd active transmitter and only FSO supported ONUs and under the harsh weather conditions, by adopting DF channel instead of FSO, 30 % energy efficiency further added. However, in novel RAoD technique, energy efficiencies for optical distribution networks (ODN1), ODN2, ODN3, and ODN4 are 48.52 %, 46.4 %, 36.96 %, and 44.31 %. Further, DF option in channel selection improve 30 % more energy saving. In performance enhanced transmitter diversity employed system, at 60 km reduction in bit error rate (BER) are 25 % for ODN1, 5.88 % for ODN2, 20 % for ODN3, and 12.5 % for ODN3.

ML approaches for OTDR diagnoses in passive optical networks—event detection and classification: ways for ODN branch assignment

An ML-supported diagnostics concept is introduced and demonstrated to detect and classify events on OTDR traces for application on a PON optical distribution network. We can also associate events with ODN branches by using deployment data of the PON. We analyze an ensemble classifier and neural networks, the usage of synthetic OTDR-like traces, and measured data for training. In our proof-of-concept, we show a precision of 98% and recall of 95% using an ensemble classifier on measured OTDR traces and a successful mapping to ODN branches or groups of branches. For emulated data, we achieve an average precision of 70% and an average recall of 91%.

Coexistence in future optical access networks from an operator’s perspective [Invited

In this paper, we address the challenges related to the simultaneous operation of legacy and future network technologies in passive optical networks (PONs) and point-to-point topologies. We explore the coexistence issues for various user categories, including residential, enterprise, factories, and mobile users. The future access networks will need to accommodate multiple technologies concurrently. Our paper demonstrates how G-PON, XGS-PON, and 50G-PON can coexist on the same optical distribution network using triple coexistence multi-PON modules. However, there are certain limitations that need to be considered, such as achieving a high optical budget and the associated costs, both in terms of monetary investment and CO2 emissions for technology deployment by operators. Additionally, we emphasize the significance of optical line terminals (OLTs) as crucial network components in the future. OLTs play a central role in supporting the traffic evolution with optimal efficiency in terms of throughput, latency, jitter, and adherence to CO2 emission constraints. Finally, we experimentally demonstrate the first assessment, to our knowledge, of a 50G-PON prototype with optical budget reaching 23.9 dB limited by the downstream (DS). Furthermore, we evaluate the potential limitations regarding coexistence by examining the effects of stimulated Raman scattering between the DS of 50G-PON and the upstream of XGS-PON for the first time with real PON systems.

Cascaded subarray design and control method for power efficient, thermal crosstalk optimized optical phased array.

Thermo-optic phase shifters (TOPSs) are commonly used in large-scale silicon photonic integrated optical phased arrays (OPAs). However, fast-response TOPSs consume relatively high power; the elevated temperature floor in the dense region of the TOPSs introduces thermal crosstalk between optical paths, which undermines the control accuracy. We propose a combined method that involves subarray design in the optical power distribution network and array control method to predict, optimize, and redistribute the phase shifts and mitigates thermal crosstalk. Thermal simulations and an array control method for generic OPA models are discussed. A silicon photonic chip prototype of a 4 × 4 OPA with three-level cascaded subarrays is fabricated to demonstrate the proposed method. The experimental and statistical results show that the method effectively reduces the average total power consumption by 31%, the maximum local temperature by 18.4%, and the thermal crosstalk within the OPA.

A novel smooth PON evolution based on signal cancellation

A novel smooth evolution from current PONs to next generation PON is proposed. The new PON link is added into the deployed optical distribution network to reuse the existing infrastructure. Pre-cancellation is applied to eliminate the crosstalk from the new PON signal to the legacy PON signal. In the optical line terminator (OLT), the legacy PON signal is added with an inverse new PON signal before optical modulation. The optical signal from the legacy PON transmitter is the sum of the legacy PON signal and the inverse new PON signal. Such optical signal will be received together with new PON optical signal in the existing optical network units (ONUs). The added inverse new PON signal cancels the received new PON signal, with the legacy PON signal left. Compared with the previous coding based smooth evolution, the effective bit rate of the new PON signal is higher as the code efficiency is 100% and the operation complexity is lower as coding and decoding are not required. The signal cancellation based smooth evolution from 1.25 Gb/s, 2.5 Gb/s, and 10 Gb/s legacy PON to 10 Gb/s new generation PON is demonstrated. The tested results show the feasibility of the proposed smooth evolution.

Analysis of a photonic integrated circuit for passive optical network for 5G NR.

This work presents the performance analysis of a passive optical network (PON) proposal with photonic integrated circuits (PIC). The PON architecture was simulated on MATLAB, focusing on the main functionalities of the optical line terminal, distribution network, and network unity regarded its effects on the physical layer. We show a simulated PIC, implemented on MATLAB through its analytic transfer function equation, used to implement orthogonal frequency division multiplexing in the optical domain to enhance the current optical networks for the 5G New-Radio (NR) scenario. We analyzed the OOK and optical PAM4 compared with phase modulation formats such as the DPSK and DQPSK. All modulation formats can be directly detected for the case in the study, simplifying the reception. Consequently, this work achieved a maximum symmetric transmission capacity of 1.2Tbps over 90km of standard single-mode fiber with 128 carriers, 64 carriers for downstream and 64 for upstream, obtained from an optical frequency comb with 0.3dB flatness. We concluded that phase modulation formats associated with PIC could increase PON capability and push further our current scenario to the 5G new era.

Optical Distribution Network Design Using PSO

Fiber To The Home (FTTH) network based on the Gigabit Passive Optical Network (GPON) technology is considered a technology option capable of spreading high-speed Internet. However, the high project cost may make its deployment unfeasible. Given this challenge, we use Particle Swarm Optimization (PSO) to propose an Optical Distribution Network (ODN) design in FTTH network. The ODN is a region that links the Central Office (CO) and the User Network (UN), that is, a strategic region that needs additional attention. In the literature so far is rare to find a technical-economic analysis of the ODN problem. Therefore, the novelty of this letter is to adapt the PSO, an efficient and fast strategy to be applied to multivariable functions, within an ODN design with technical and economic criteria. Using system-level simulations, we attest that the proposed algorithm achieves 12% cost reduction from the conventional way.

Analysis and experiments on C band 200G coherent PON based on Alamouti polarization-insensitive receivers.

Passive optical network (PON) based on coherent detection has attracted a great deal of attention in recent years as a future solution for 100+ Gbps per wavelength. Particularly for 200G-PON, one of the most attractive options would be to switch to QAM transmission and coherent detection, due to its well know advantages compared to the Direct-Detection approaches used so far in PON. However, coherent technology, extensively used in core networks, has costs that are still perceived as too high for the access ecosystem. In order to perform cost reduction, some groups have studied the option of coherent polarization-independent (PI) detection, since it halves the number of optoelectronic components in the receiver front end. In this paper, we thus present a detailed simulative and experimental investigation of polarization-independent receivers to achieve 200 Gbps transmission in C band using the Alamouti polarization time block coding (PTBC). Our goal is to show what would be the system requirements in terms of optoelectronic bandwidths, laser phase noise and ultimate power budget limitations. We study two different modulation formats: quadrature phase-shift keying (QPSK) and 16 quadrature amplitude modulation (16QAM). We also compare heterodyne and homodyne/intradyne solutions through simulations. As a summarizing result, we experimentally show that 200G PON based on 50 Gbaud-16QAM single-polarization Alamouti coded signals would be possible with today state-of-the-art coherent technologies, demonstrating an Optical Distribution Network loss above 33 dB with 25 km fiber length, a very promising result that is compliant with the PON power budget E1 class.

A novel smooth evolution to TWDM PON based on wavelength complement coding

A novel smooth evolution from current PONs to TWDM PON based on wavelength complement coding is proposed. The TWDM PON is added into the existing infrastructure to share the deployed optical distribution network with the legacy PON. One wavelength of TWDM PON is used to carry a complement signal. The complement signal is the inverse sum of the other TWDM PON signals, so the combination of the TWDM PON signals (including the complement signal) is of constant amplitude, inducing little crosstalk to the coexisting legacy PON signal. No retrofitting is required and no code efficiency loss is induced in the evolution. The wavelength complement coding based smooth evolution from 1.25 Gb/s and 2.5 Gb/s legacy PON to 10 Gb/s/λ NGPON is demonstrated. The tested results show the feasibility of the proposed smooth evolution.

Integrated optical frequency comb for 5G NR Xhauls

We experimentally demonstrate the use of optical frequency combs (OFCs), generated by a photonic integrated circuit (PIC), in a flexible optical distribution network based on fiber-optics and free-space optics (FSOs) links, aimed at the fifth generation of mobile network (5G) Xhauls. The Indium Phosphide (InP) monolithically integrated OFC is based on cascaded optical modulators and is broadly tunable in terms of operating wavelength and frequency spacing. Particularly, our approach relies on applying the PIC in a centralized radio access network (C-RAN) architecture, with the purpose of optically generating two low-phase noise mm-waves signals for simultaneously enabling a 12.5-km of single-mode fiber (SMF) fronthaul and a 12.5-km SMF midhaul, followed by a 10-m long FSO fronthaul link. Moreover, the demonstrator contemplates two 10-m reach 5G wireless access networks operating in the 26 GHz band, i.e. over the frequency range 2 (FR2) from the 5G NR standard. The proposed integrated OFC-based 5G system performance is in accordance to the 3rd Generation Partnership Project (3GPP) Release 15 requirements, achieving a total wireless throughput of 900 Mbit/s.

Unequally spaced PAM-4 signaling enabled sensitivity enhancement of a simplified coherent receiver applied in a UDWDM-PON.

We experimentally demonstrate a 4 × 10 Gb/s cost-effective coherent ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON) by the use of unequally-spaced 4-level pulse-amplitude modulation (UES-PAM-4) signaling. Because of the advantages of simple architecture and low cost, the simplified coherent receiver (SCR) based on the transmitted signal diversity (TS-D) has been reported, but its receiver sensitivity is constrained by the severe noise arising in the higher level of conventional PAM-4 signals. Here, we first experimentally demonstrate the UES-PAM-4 signaling for the SCR based on the TS-D, by altering the PAM-4 level spacing and the decision threshold through the gradient descent algorithm (GDA). Consequently, we can experimentally achieve -30.1 dBm RS for single wavelength at the bit-error ratio (BER) of 3.8 × 10-3. Compared with the conventional equally-spaced PAM-4 (ES-PAM-4) signaling, 1.3 dB RS enhancement can be secured after the 20-km standard single-mode fiber (SSMF) transmission. Meanwhile, the UES-PAM-4 signaling is experimentally verified for 4 × 10 Gb/s UDWDM-PON. An average RS of -29.6 dBm and 32.6 dB power budget are obtained after the 20-km SSMF transmission. The proposed UES-PAM-4 signaling with the RS enhancement is a promising candidate for the UDWDM-PON by utilizing the existing optical distribution network (ODN).

Flexible energy-efficient and direct intra-ODN/OPN communication capable TWDM PON architecture with centralized OLT sharing among multiple optical networks

Nowadays, service reliability, operation cost, transmission latency of optical access networks are the major challenging issues that need to be addressed while planning and developing the next-generation passive optical networks (NG-PONs). This paper proposes a flexible, energy-efficient, time and wavelength division multiplexed (TWDM) PON architecture that has the capability of centralized optical line terminal (OLT) resource sharing with multiple optical networks. The architecture has the point-to-point direct inter-optical networking unit (dedicated inter-ONU) transmission capability among the various ONUs located within the same optical distribution network (ODN). Such transmission may also be referred to as direct intra-ODN communication. The architecture also has the potential of transmitting an inter-ONU signal to the ONUs residing in the different ODNs (inter-ODN) belonging to the same optical network (OPN). Such transmission may be referred as the direct inter-ODN or intra-OPN transmission. The architecture reduces the normalized energy consumption of approximately 2.21875 Wh per hour, normalized transmission latency of approximately 148 µs for the direct inter-ONU transmission. This is achieved by diverting the inter-ONU signal from the remote nodes (RNs) itself towards the intended ONUs. The percentage energy saving of the proposed architecture is approximately 74 % as compared to the conventional architecture. The proposed architecture is suitable for strengthening the existing information and communication technology (ICT) infrastructures and can be implemented in next-generation flexible, energy-efficient, latency-aware, and reliable optical networks for developing smart rural and urban communities.

Optical phase-locked loop phase noise in 5G mm-wave OFDM ARoF systems

The use of millimeter-wave (mm-wave) frequencies is required in order to support the increasing number of connected devices expected from the fifth generation (5G) of mobile communications. Subsequently, the generation of radio-frequency (RF) carriers ranging from 10GHz to 300GHz and their transport through optical distribution network (ODN) is a key element of the future 5G fronthaul. Optically assisted RF carrier generation is one of the most promising solutions to tackle this issue, allowing a wide use of analog radio-over-fiber (ARoF) architectures. However the main limitation of these optical methods is related to the finite coherence of lasers sources, which can dramatically degrade data transmission in analog formats. To mitigate its impact, the use of orthogonal frequency-division multiplexing (OFDM) as the 5G standard allows employing efficient phase noise compensation algorithms. Therefore, in this study, we present an experimental demonstration of a mm-wave generation technique based on an optical phase-locked loop (OPLL) that fulfills the frequency specifications for 5G. Then, an algorithm is introduced that improves data recovery at reception and reduces the impact of a possible high phase noise carrier. Finally, a back-to-back data transmission experiment is performed, demonstrating the efficiency of the algorithm to reach the 5G requirements. These results emphasize the use of OPLLs as a viable solution to generate mm-wave carriers for 5G and beyond.

Performance Investigation of Back-Compatible Integrated TWDM/GPON System Using MDM And Pulse Shapes

Optical access networks are the prominent and promising cutting edge technology to provide high speed, and cost effective operation for meeting the requirements of ever-increasing demands of users. Multiple access techniques such as Wavelength and time division in passive optical networks are important innovations to provide high capacity. A mode division multiplexed back compatible integrated next generation PON2 (TWDM PON) and GPON is demonstrated with triple play supportability in this work. Proposed system offer pay as you grow feature and also provide enhanced performance by suppressing the inter-channel interference in TWDM-PON2. System successfully works on same optical distribution network unit for both PON standards without extra arrangements and has potential to support 62.5 Gbps in full duplex mode (Symmetrical downlink/uplink). Moreover, demonstrated back compatible system is analyzed by incorporating diverse modulations such as NRZ-DPSK, RZ-DPSK, RZ-DQPSK, NRZ-DPSK and linecodings NRZ, RZ. Received power, Optical signal to noise ratio (OSNR), BER and Q factor are noted at diverse link lengths and it is noteworthy that LP modes with NRZ in TWDM PON provide outstanding results.

Analysis of GPON capacity by hybrid splitting-ratio base on customer segmentation for Indonesian market during the Covid-19 pandemic

During the Covid-19 pandemic, the impact on internet demand is very high throughout the world. In Indonesia, through a survey conducted, broadband users recorded 175 million people or equivalent to 64 % of the population. Based on field observations, the Passive Optical Network (PON) port utility in the Optical Line Terminal (OLT) is presently below 75 %, as opposed to the initial value, which was more than 95 % [1]. Furthermore, it was also found that more than 80 % of IndiHome customers use a maximum bandwidth of 20 Mbps with majority using 10 Mbps, which is very ineffective, especially related to network capacity. Generally, passive Optical Distribution Network (ODN) devices are not optimally used, therefore this research aims to determine the optimization level of the FTTH network by maximizing the available infrastructure capacity. This process was carried out by increasing the associate ratio of 1:32 to 1:64 while taking into account the Optical Line Terminal (OLT) capacity factor and the standard link budget with schemas A, B and C used to obtain adequate efficiency. Scheme A consists of a 1:2 passive splitter in the Optical Distribution Cabinet (ODC) & 1:32 at the Optical Distribution Point (ODP). Scheme B consists of a 1:4 (ODC) & 1:16 (ODP) passive splitter, while scheme C consists of a 1:8 (ODC) & 1:8 (ODP) passive splitter intended for the use of different customer area types. The result showed an increase in network capacity from 32 to 64 per PON port while taking into account the technical quality of the Link Budget. In conclusion, to ensure this solution functions properly, both simulation and direct measurement tests are carried out using the existing network

Coherent EML+TIA Detector for DSP-Free 1 Gb/s/λ Reception Over Extended Budget

The continuing drive towards broadband access necessitates cost-effective optical access and mobile fronthaul solutions. While the fixed-mobile convergence motivates high-speeds for the antenna remoting through broadband digitized radio-over-fiber, the access segment still uses time division multiplexed access equipment. Although the steadily increasing line rates call for 50 Gb/s solutions, the unshared per-user rate remains in the 1-Gb/s range. It is a question whether such data rate can be facilitated without high-speed components, at the same time supporting higher passive splits for the optical distribution networks. We experimentally demonstrate a simplified receiver based on an electro-absorption modulated laser, co-integrated on a die-level with a transimpedance amplifier. We investigate its sensitivity for the phase-agnostic coherent heterodyne downstream detection of data signals in a passive optical network scenario. We will show that despite the omission of a high-performance local oscillator, balanced detection and digital signal processing, the proposed receiver accomplishes reception of 1 Gb/s phase-modulated signals over a link reach of 57 km and an optical budget of 48 dB, thus enabling high passive splits of 1:128. We study the implications raised by this single-ended coherent receiver architecture under multi-channel transmission and investigate the susceptibility of its integrated local oscillator to optical feedback.

A comprehensive study on radio over fiber systems: present evaluations and future challenges

Abstract In order to serve the explosive demands of triple play services or multimedia services with high quality of data transmission in Fifth Generation (5G) communication systems which has availability of large spectrum unlike Fourth Generation (4G), low latency, improved transmission, and increased reliability, an access networks with optical fiber distribution network and wireless enabled technology is urgently needed and therefore, a prominent technology known as Radio over Fiber (RoF) is suggested by researcher/Scientists due to a perfect blend of flexible fiber technology and wireless mobility. RoF technology is helping the data transmission systems from last thirty years with great success and has numerous advantages such as scalability, transparency, antenna site complexity reduction, low installation cost, accessibility of radio carrier by diverse antenna sites dynamically. Millimeter waves (Mm waves) integration in 5G wireless RoF systems comes out to be an encouraging candidate to cater the bandwidth hungry current as well as future generation internet application such as high definition TV (HDTV), online games, video conferencing, and voice over IP (VoIP) etc. For the prolonged reach, economical installations, and improved performance, optimal Mm wave generation methods should be incorporated in 5G such as employing multi carrier generation technique (MCG). Deployment of single mode fiber (SMF) in 5G offers high speed, large capacity, improved security, etc., but also has a prominent limitation of nonlinear effects and it is unwanted phenomenon which degrade the system performance by introducing intermodulation distortion, distortion of signal phase, harmonic distortion, and interference in the neighbouring channels. Minimum modifications of architecture and minimum cost should be spent on the compensation of nonlinear effects or Kerr’s effects in RoF systems and recently mode division multiplexing has emerged as an ultimate solution. In this review article, detailed discussion of an evolutionary technology, i.e., RoF is presented with a literature review, present evaluations, and future challenges. Our utmost goal is to enrich the young researchers with precious aspects for RoF technology on single platform and also encourage them to conduct the technology advancement research works in various fields such as nonlinear compensation, Mm wave generation, dispersion compensation, cost reduction, complexity reduction, and security enhancements for 5G RoF systems.

FLCS-PON—an opportunistic 100 Gbit/s flexible PON prototype with probabilistic shaping and soft-input FEC: operator trial and ODN case studies

FLCS-PON is a concept of a flexible passive optical network (PON), where the modulation and coding parameters of the downstream signal, consisting of modulation order, code rate, and probabilistic shaping entropy, can be adjusted on a timeslot basis to opportunistically achieve mean net bitrate increase. The system harnesses unused margins of transceivers and optical distribution networks. In this work we describe the architecture of FLCS-PON, which is designed to leverage the 50G-PON ecosystem. We provide updated and accurate performance metrics for FLCS-PON low-density parity check (LDPC) forward error correction (FEC) codes. We then report on the operator trial of a FLCS-PON system prototype carried out jointly with Vodafone and demonstrate maximum achievable net bitrates as a function of the optical path loss for five different transmitter configurations (non-return-to-zero, PAM-4, and probabilistically shaped PAM-4 with three different entropy values). On the receiver side we test four different configurations: F F E 23 + D F E 5 or F F E 16 + D F E 1 equalizers, each followed by either a hard- or a soft-input LDPC decoder. Finally, we consider two study cases on mean bitrates achievable with FLCS-PON over deployed optical distribution networks (ODNs). We map net bitrates obtained during the operator trial to Vodafone’s actual ODN optical path loss probability distribution or an ensemble of simulated ODNs. We show that in the majority of cases, FLCS-PON can provide a significant improvement of mean net bitrate. Further, FLCS-PON also enables extension of nominal power budget classes, beyond guaranteed conventional ODN loss, making it possible to provision links that might otherwise be unsupported by conventional PON.