1104 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 32, NO. 6, MARCH15, 2014 QPAR: A Quasi-Passive Reconfigurable Green Node for Dynamic Resource Management in Optical Access Networks Yingying Bi, Jing Jin, Ahmad R. Dhaini, Member, IEEE, and Leonid G. Kazovsky, Fellow, OSA Abstract—Passive optical networks (PONs) are regarded as a promising solution for the broadband bandwidth bottleneck prob- lem. However, due to their passive nature, legacy TDM-PONs are limited by their inflexible power distribution, while future WDM- PONs are restricted by their static wavelength allocation. To mit- igate these limitations, we propose QPAR, a Quasi-Passive Re- configurable node, which provides flexible power and bandwidth allocation, and enables a graceful upgrade from TDM-PON to WDM-PON. Due to its quasi-passive nature, QPAR only consumes power during reconfiguration. Simulation results show that QPAR can increase the number of users, extend the reach, and balance the traffic load in the network compared with legacy PONs. QPAR can be implemented using either discrete or integrated components. We demonstrate an experimental QPAR using two different op- tical latching switches based on micro-electro-mechanical systems and magneto-optic materials. Lastly, we experimentally investigate QPAR performances. Index Terms—Energy efficiency, optical access networks, optical latching switch, PON, quasi-passive, reconfigurable. I. INTRODUCTION A CCESS networks connect subscribers to their service providers. They are currently regarded as the bottle- neck for high-speed broadband services encompassing Inter- net access, high-definition video streams, and cloud computing services. Passive optical networks (PONs) have been consid- ered as a promising class of optical access solutions to offer high bandwidth to end-users, including time-division multiplex- ing PON (TDM-PON) and wavelength division multiplexing PON (WDM-PON). PON has a point-to-multipoint topology as shown in Fig. 1. The feeder fiber is connected from the optical line terminal (OLT) residing at the central office, to the re- mote node (RN) from which the distribution fiber is connected to the optical network units (ONUs) located at the customers’ premises. In TDM-PONs, a passive power splitter is deployed at Manuscript received May 8, 2013; revised August 1, 2013 and October 2, 2013; accepted November 25, 2013. Date of publication December 22, 2013; date of current version January 29, 2014. This work was supported by the Center for Integrated Systems (CIS) at Stanford University. The work of A. R. Dhaini was sponsored by the Natural Sciences and Engineering Research Council of Canada (NSERC) and NSF. Few parts of this paper appeared in [7] and [18]. The authors are with the Photonics and Networking Research Lab- oratory, Electrical Engineering Department, Stanford University, CA 94305 USA (e-mail: yybi@stanford.edu; jingjin@stanford.edu; adhaini@ stanford.edu; l.kazovsky@stanford.edu). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JLT.2013.2296052 Fig. 1. PON topology. the RN to distribute power equally among the end-users. TDM- PON has the advantages of low deployment and maintenance costs and high reliability [1]. In WDM-PONs, each ONU can be assigned a dedicated wavelength via a passive WDM cou- pler in the RN (e.g., arrayed waveguide gratings, AWGs). Unlike TDM-PON, WDM-PON does not share the wavelength(s) in the time domain among the users; therefore it is seen as an unavoid- able step to meet the ever-rising bandwidth demands. However, due to the use of rigid passive components, current PON sys- tems are facing several challenges. On one hand, TDM-PON is constrained by its inflexible power distribution and limited bandwidth per user. The ONUs can only be distributed close to the RN such that the variation in the distance from the RN to the ONU is as small as possible. On the other hand, WDM- PON does not fully exploit the available bandwidth because of the static wavelength allocation. Furthermore, it requires ex- pensive and temperature sensitive components with high power consumption [2]. Next-generation optical access networks should have suf- ficient intelligence and re-configurability to manage different power and bandwidth requirements without sacrificing energy efficiency. In addition, although the increasing bandwidth de- mand will motivate an upgrade from legacy TDM-PON to fu- ture WDM-PON, one user may not fully utilize the bandwidth of one dedicated wavelength with most present multimedia ap- plications. Thus, for economical reasons, a graceful upgrade is required. Currently, most branching devices can only accom- modate either TDM or WDM networks, but not both. Sev- eral hybrid TDM/WDM-PON (also known as TWDM-PON) proposals have emerged; however, most would have limited wavelength re-configurability, require a local power supply [3], or need complex scheduling algorithms [4]. The TWDM-PON 0733-8724 © 2013 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information.