> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 1 Abstract—This paper discusses novel approaches to improve energy efficiency of different optical access technologies, including time division multiplexing passive optical network (TDM-PON), time and wavelength division multiplexing PON (TWDM-PON), point-to-point (PTP) access network, wavelength division multiplexing PON (WDM-PON), and orthogonal frequency division multiple access PON (OFDMA-PON). These approaches include cyclic sleep mode, energy-efficient bit interleaving protocol, power reduction at component level, or frequency band selection. Depending on the target optical access technology, one or a combination of different approaches can be applied. Index Terms—Broadband communication, Optical fiber subscriber loops, Energy efficiency I. INTRODUCTION NERGY consumption has become a major performance metric of communication systems in recent years. In response, several “green-networking” initiatives have been created. Typically they are calling for a near-term energy- efficiency improvement target of tens of percent.(e.g., EU Code of Conduct [1]). GreenTouch, an international research consortium of operators, vendors, and academia, started in 2010 and aims at a more aggressive and longer-term target [2]. The present study was conducted in the context of the Wireline Access Working Group of GreenTouch. It is commonly agreed that the access network accounts for more than 80% of the total power consumption of a wireline network [1][3] and hence an important area of research on energy efficient networking. Fiber access systems are more efficient in terms of energy per transferred bit than other legacy technologies, such as their copper counterparts, because they feature a lower transmission loss and higher bandwidth. Previous papers in this magazine discussed how different fiber access Manuscript received August 10, 2012. P. Vetter, D. Suvakovic, H. Chow, P. Anthapadmanabhan are with Bell Labs, Alcatel-Lucent, Murray Hill, NJ 07974, USA. (e-Mail of corresponding author: peter.vetter@ alcatel-lucent.com). K. Kanonakis is with AIT, Athens, Greece. K.-L. Lee is with the Centre for Energy-Efficient Telecommunications (CEET), The University of Melbourne, Victoria, Australia. F. Saliou is with Orange Labs, Lannion, France. Xin Yin is with IMEC – Ghent University, Ghent, Belgium. B. Lannoo is with Ghent University - IBBT, Ghent, Belgium. This research was performed in the GreenTouch consortium. technologies exhibit different power consumption levels. Reference [4] reports an analysis of wavelength division multiplexing (WDM) passive optical network (PON) systems, while [5] provides a comprehensive survey of the power consumption by several candidate technologies for the next- generation passive optical network (NG-PON2) standard. This paper examines several potential approaches, applicable to different fiber access technologies, for the purpose of lowering the power consumption at both near-term and long-term. Section II summarizes various optical access technologies and qualitatively discusses their energy efficiency. Section III gives an overview of the proposed power-saving approaches. While an approach may be suitable for a particular access technology, they can also be combined to obtain a better improvement. Section IV describes the model used to quantitatively compare different optical access technologies and analyzes the energy savings of the proposed approaches. Section V concludes the paper with a summary. II. OPTICAL ACCESS TECHNOLOGIES A. TDM-PON In a traditional TDM-PON, an optical line termination (OLT) in the central office is connected to a number of optical network units (ONU) via a point-to-multipoint optical distribution network (ODN). In this architecture, the optical couplers are transparent and broad-spectrum power-splitters, usually simply referred to as “splitters.” Gigabit-capable PON (ITU-T Recommendation series G.984) and Ethernet PON (IEEE Specification 802.3ah) are the most widely deployed fiber-to-the-home (FTTH) technologies today. They employ broadcast-and-select in the downstream and time division multiple access (TDMA) in the upstream direction. As an OLT interface is shared by multiple ONUs, TDM-PON represents the most energy-efficient optical-access solution currently deployed [3]. B. Point-to-Point access Point-to-point (PTP) optical access systems currently deployed consume more power per subscriber than a TDM- PON system, because every subscriber requires its own transceiver port at the OLT in the central office. However, in principle, PTP fiber should be the most energy-efficient in a wireline access network for the following two reasons: (1) subscribers are connected with the central office with a low Energy-Efficiency Improvements for Optical Access Peter Vetter, Dusan Suvakovic, Hungkei Chow, Prasanth Anthapadmanabhan, Konstantinos Kanonakis, Ka-Lun Lee, Fabienne Saliou, Xin Yin, and Bart Lannoo E