World’s First Demonstration of Pluggable Optical Transceiver Modules for Flexible TWDM PONs

Optical transceivers are demonstrated with error-free performance in TWDM PONs. Integrated OLT transceiver in CFP-module transmits 10dBm power and achieves -36dBm sensitivity. Low-cost tunable SFP+ ONU transceiver can be tuned over 4 channels with 4dBm transmitted power and -26dBm sensitivity. Introduction Rapid growth of internet traffic, driven by the proliferation of video services, continues to push broadband optical access networks for higher data rates and better quality of services. Currently GPON and EPON are widely deployed and 10G PONs (e.g. XG-PON and 10G EPON) are expected in next few years [1]. Beyond 10G PONs, TWDM PON has been demonstrated as a viable solution for future broadband services [2]. Such TWDM PON systems use a combination of time and wavelength division multiple access, providing an aggregated capacity of at least 40Gb/s. A new set of standards on TWDM PON will be released by ITU-T in next year, paving the way for future deployment. However, before large scale deployment, technology development and engineering solutions of TWDM PON systems and optical transceiver modules must be made commercially viable for manufactuerability and cost effectiveness. Recently, a flexible TWDM PON system was demonstrated which can support desirable features such as pay-as-you-grow, load balancing, channel protection and power saving [3]. In such a system, OLT (optical line terminal) equips with 4 channel transceivers while ONU (optical network unit) integrates a tunable laser and a tunable receiver. However, discrete transceivers were used in this flexible TWDM PON system. To the authors’ knowledge, integrated transceiver modules have not been reported, and it remains a very challenging task to develop TWDM PON optical transceivers with good performance, small footprint and low power consumption. In this paper, we demonstrate, for the first time, integrated OLT transceiver module and tunable ONU transceiver module for flexible TWDM PONs. The OLT transceiver consists of 4x10Gb/s transmitters, 4x2.5Gb/s burst mode optical receivers, optical mux/demux and integrated optical amplifiers in an enhance CFP (C Form Factor Pluggable) module. The low-cost ONU transceiver includes a tunable laser and a tunable receiver in SFP+ (Small Form Factor Pluggable) package. The average transmitted power of the OLT module is larger than 10dBm and its receiver sensitivity is better than -36dBm, while the tunable ONU achieves more than 4dBm average transmitted power and -26dBm sensitivity. With these pluggable transceiver modules, a flexible TWDM PON system is demonstrated with errorfree performance and over 36dB power budget. Optical Transceiver Module Design For OLT transceiver module in TWDM PONs, performance and footprint is very important, so the integration of both electronics and optics is a primary task. Fig. 1 illustrates the architecture of the 4-channel OLT transceiver module. For the transmitter, there are 4 EMLs (electroabsorption modulated lasers), each modulated by a 10Gb/s data stream. The outputs of EMLs at different wavelengths are then multiplexed by a low-loss multiplexer and amplified by an L-band EDFA. At the receiver side, optical signals from ONUs in 4 different wavelength channels are first amplified by a C-band EDFA and then separated by a demux before being detected by burst-mode APD ROSAs (receiver optical subassembly). Limiting amplifiers (LA) following the ROSA further boosts the received signals. To achieve bidirectional transmission on a single fiber, a WDM (wavelength division multiplexing) filter combines/separates the upstream and downstream wavelengths. A microprocessor is also included in the transceiver module for control and monitoring purpose. It sets Fig. 1: OLT transceiver architecture. EML1