2974 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 23, NO. 10, OCTOBER 2005 Novel Schemes for Local Area Network Emulation in Passive Optical Networks With RF Subcarrier Multiplexed Customer Traffic Nishaanthan Nadarajah, Student Member, IEEE, Manik Attygalle, Member, IEEE, Elaine Wong, Member, IEEE, and Ampalavanapillai Nirmalathas, Senior Member, IEEE Abstract—This paper proposes two novel optical layer schemes for intercommunication between customers in a passive optical network (PON). The proposed schemes use radio frequency (RF) subcarrier multiplexed transmission for intercommunication be- tween customers in conjunction with upstream access to the cen- tral office (CO) at baseband. One scheme employs a narrowband fiber Bragg grating (FBG) placed close to the star coupler in the feeder fiber of the PON, while the other uses an additional short- length distribution fiber from the star coupler to each customer unit for the redirection of customer traffic. In both schemes, only one optical transmitter is required at each optical network unit (ONU) for the transmission of customer traffic and upstream access traffic. Moreover, downstream bandwidth is not consumed by customer traffic unlike in previously reported techniques. The authors experimentally verify the feasibility of both schemes with 1.25 Gb/s upstream baseband transmission to the CO and 155 Mb/s customer data transmission on the RF carrier. The experimental results obtained from both schemes are compared, and the power budgets are calculated to analyze the scalability of each scheme. Further, the proposed schemes were discussed in terms of upgradability of the transmission bit rates for the upstream access traffic, bandwidth requirements at the customer premises, dispersion tolerance, and stability issues for the practical implementations of the network. Index Terms—Fiber Bragg grating, local area network (LAN) intercommunication, passive optical network, subcarrier multi- plexing, time division multiple access. I. I NTRODUCTION T HE PASSIVE optical network (PON) technology has been recognized as an efficient solution to facilitate high- bandwidth, low-cost, and fault-tolerant next-generation broad- band access networks [1], [2]. A typical PON architecture employs either a wavelength-insensitive passive power splitter such as star coupler (SC) or a wavelength-sensitive device such as arrayed waveguide grating (AWG) as a branching device to allow communication between the central office (CO) and the optical network units (ONUs) that are located at the customer premises. The former architecture is referred to as power splitting PON (PS-PON) while the latter architecture is referred to as wavelength division multiplexed PON (WDM- PON) [3]. Customers of a PON may require private communi- Manuscript received December 1, 2004; revised July 15, 2005. The authors are with the National ICT Australia, Victoria Research Labora- tory, Department of Electrical and Electronic Engineering, The University of Melbourne, VIC 3010, Australia (e-mail: nnad@ee.unimelb.edu.au). Digital Object Identifier 10.1109/JLT.2005.856300 cation links between themselves for various computer applica- tions and telecommunication services such as distributed data processing, broadcast information systems, teleconferencing, and interactive video games. For a PS-PON in which customers share the same upstream wavelength, such intercommunication between customers may be realized by overlaying a separate network in which each ONU is connected to all other ONUs via a point-to-point optical link. This is neither cost effec- tive nor practical. Consequently, there have been increasing interests in deploying point-to-point customer communication links via local area network (LAN) emulation over an existing PON infrastructure. Reuse of the PON infrastructure to facili- tate intercommunication links between customers of the same PON can greatly reduce the cost and management issues of the network. The IEEE 802.3ah Ethernet in the First Mile task force has considered many techniques for LAN emulation in an Ethernet PON [4], [5]. These techniques are mainly focused on higher- layer protocols in which ONUs are assigned PON tags to es- tablish point-to-point connections with each other. LAN traffic, defined in this paper as the customer traffic originating from one customer to be delivered to all or some customers within the same PON, is carried on the upstream wavelength along with the upstream access traffic to the CO. At the CO, the received upstream packets from each customer are routed back to the ONUs in the downstream direction. At the CO, bridges and/or routers are employed to separate the LAN traffic from the up- stream access traffic to CO [4], [5]. These bridges and/or routers must be capable of supporting higher-layer protocols, thereby potentially increasing the cost and complexity of the network. Further, the effective downstream bandwidth is reduced as the LAN traffic is routed back to the ONUs on the downstream wavelength. Moreover, the redirected LAN traffic needs to be separated from the downstream traffic using complex filtering mechanisms that are employed at the ONUs. By comparison, emulating point-to-point links among customers directly on the optical layer in the PON can effectively overcome several drawbacks [6]–[8]. Optical layer LAN emulation techniques have previously been proposed whereby an additional wave- length is used for customer intercommunication [7], [8]. A fiber Bragg grating (FBG) is placed along the feeder fiber close to the star coupler so that the LAN emulation wavelength can be reflected back to all customers. Nonetheless, this necessi- tates an additional optical transceiver capable of transmitting 0733-8724/$20.00 © 2005 IEEE Authorized licensed use limited to: City College of New York. Downloaded on April 14,2010 at 07:25:54 UTC from IEEE Xplore. Restrictions apply.