Use of downstream inverse-RZ signal for upstream data re-modulation in a WDM passive optical network Guo-Wei Lu, Ning Deng, Chun-Kit Chan, Lian-Kuan Chen Department of Information Engineering, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR. Tel: + 852-2609-8479, Fax: +852-2603-5032, Email: gwlu1@ie.cuhk.edu.hk Abstract: We propose and experimentally investigate a novel WDM-PON architecture using inverse-RZ modulated centralized light sources. The finite optical power in each bit of the downstream IRZ signal can greatly facilitate the upstream data re-modulation. ©2005 Optical Society of America OCIS codes: (060.4510) Optical communications; (060.40800) Modulation Introduction The wavelength-division multiplexing passive optical network (WDM-PON) is a promising access network technology to meet the ever-increasing bandwidth demand from enterprises and households. Recently, the WDM-PON architecture with centralized light sources (CLS) at the optical line terminal (OLT) has emerged as an attractive solution for low-cost implementation. With this architecture, the downstream wavelength received at the optical network unit (ONU) is reused as the upstream data carrier, thus easing the wavelength management and network maintenance at the ONU side. Recently, several schemes [1,2] have been proposed to reuse the downstream on-off keying (OOK) modulated optical carrier at the ONU. However, reduced extinction ratio of the downstream OOK signal or an additional stage of data erasure was needed. Although advanced modulation formats such as optical differential phase shift keying (DPSK) and optical frequency shift keying (FSK) could be exploited for the downstream signal to tackle this problem [3,4], the corresponding transmitters and receivers were evidently more uneconomical and less controllable than those of the OOK format. In this paper, we propose to use a special line coding of the OOK format, namely inverse-return-to-zero (IRZ) [5,6], as the downstream signal format to facilitate the upstream data re-modulation. An IRZ signal is formed by inverting the intensity level of a conventional return-to-zero (RZ) signal, thus it carries optical power at both the mark levels and the space levels in each bit period. Therefore, the downstream optical power received at the ONU can be directly re-modulated by the upstream OOK data. This can eliminate the process of erasing the downstream data from the received optical carrier and can maintain high extinction ratio of the downstream data. Meanwhile, the downstream IRZ signal does not require any demodulation circuit, except a simple inverting post-amplifier after the photodiode. We have experimentally demonstrated a CLS PON structure with downstream 2.5-Gbit/s IRZ signal. 2.5-Gbit/s and 1-Gbit/s upstream data re-modulation on the downstream IRZ signal was also successfully achieved. Proposed WDM-PON architecture with downstream IRZ signal Optical Output Power 1 0 Driving Voltage Electrical Input Optical Output } } } } t t } } 0 1 1 0 1 01100 200ps/div RF Clock NRZ RF Signal RZ Signal LD MZ-MOD IRZ LD IM RZ-Shaping Circuit Downstream Data Upstream Data Rx TX-N TX-2 TX-1 … AWG OLT λ 1 λ 2 λ Ν … λ 1 ,λ 2 ,... ...λ Ν λ 1 λ 2 … … … Downstream Data Upstream Data Rx IM RN ONU-N λ Ν ONU-2 ONU-1 AWG Fig. 2: Proposed PON architecture using downstream IRZ signal and upstream OOK signal. Fig. 1: Operation principle of optical IRZ transmitter. OFI8