Overview of High-Speed TDM-PON beyond 50 Gbps per Wavelength using Digital Signal Processing [Invited/Tutorial] PABLOTORRES-FERRERA1,2,*,FRANKEFFENBERGER3,MDSAIFUDDINFARUK1,SEB J.SAVORY1,ROBERTOGAUDINO2 1Electrical Engineering Division, Department of Engineering, University of Cambridge, Cambridge CB3 0FA, United Kingdom. 2Department of Electronics and Telecommunications, Politecnico di Torino, 10129 Turin, Italy. 3Futurewei Technologies, Inc., Plano, TX 75024, United States of America. *Corresponding author: pt449@cam.ac.uk Received XX Month XXXX; revised XX Month, XXXX; accepted XX Month XXXX; posted XX Month XXXX (Doc. ID XXXXX); published XX Month XXXX The recent evolution of Passive Optical Network (PON) standards and related research activities for physical layer solutions achieving bit rates well above 10 Gbps per wavelength ()is discussed. We show that the advancement toward 50, 100 and 200 Gbps/will for sure require a strong introduction of advanced digital signal processing (DSP) technologies for linear, and maybe nonlinear, equalization, and for forward-error correction (FEC). We start by reviewing in detail the current standardization activities in the International Telecommunication Union (ITU)-T and the Institute of Electrical and Electronics Engineers (IEEE), and then we present a comparison of the DSP approaches for traditional Direct-Detection (DD) solutions and for future Coherent Detection approaches. http://dx.doi.org/10.1364/JOCN.99.099999 1. Introduction In this paper, we review the recent research and standardization steps towards thedevelopmentof higher-speedPON physical layer,following the evolution for bit rates well above 10 Gbps/. The paper is organized as follows. We begin with a section (Section 2) that provides an in-depth overview on the evolution of PON market and standardization. Within this overview section there is a specific focus on bit rate standardization for 25 and 50 Gbps/, showing the resultingprogressiveintroductioninthesestandardsofDSP functionalities. The following section (Section 3), details DSP-based solutions that have been proposed recently at the research level for 100 Gbps/direct-detection (DD) PON. This is then contrasted in the next section (Section 4) with approaches for 100 Gbps/and beyond based on Coherent PON, including means of simplifying coherent receivers with a view of reducing cost and DSP power consumption. We then conclude in Section 5 witha final discussion on the ongoing PON trends. 2. Overview of PON standardization A. Overview of market status and deployment The deployment progress of PON is remarkable. Since its initial mass deployments began circa 2004, the technology has grown to approach a billion users worldwide by 2021. It now surpasses digital subscriber line services in number of users, and this will only increase as more networks are upgraded worldwide by their operators. Through this development, system standards have been very important, due to the special practical and commercial characteristicsof broadbandaccess.In short, access networks are a huge investment, and are composed of millions of cables and associated equipment distributed over a wide area. This makes low cost, high volume, and supply-chain reliability key aspectsforPON systems.Bystandardizing the system,multiplevendors can build compliant products that multiple operators can use in an interoperable way. Over time, this has been shown to reduce costs through efficiencies of scale and free market economics. It makes the business more stable since there are multiple vendors and operators, and therefore no single entity is critical. Over the last 20 years, ITU-T and IEEE have been very active in this field. In particular, the ITU-T study group SG-15 (question Q2) has standardizedmanyPONsystems[1].Theearlysystemslike asynchronous transfer mode (ATM)-PON were almost experimental and never reached significant volume. The first system that had over 1 million users was broadband PON (B-PON, ITU-T G.983 series), due to its deployment in Japan and the United States [2]. However, B-PON was quickly overtaken by Gigabit PON (G-PON ITU-T G.984 series), and G- PON is the systemthathas taken PON to the billion level now [3].G-PON delivers 2.5 Gbps downstream and 1.25 Gbps upstream. Its widespread adoption caused the industry to realize that the optical distribution network (ODN) is a huge investment that is intended to work for many decades. This directly led to the consideration of PON coexistence,
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