Symmetric 10-Gb/s WDM-PON Using Directly Modulated Lasers for Downlink and RSOAs for Uplink

We demonstrate a cost-effective, 10-Gb/s full-duplex wavelength-division-multiplexed passive optical network over 20 km single-feeder fiber using a single light source per optical network unit (ONU). We exploit a directly modulated laser (DML) and a reflective semiconductor optical amplifier (RSOA) for downlink and uplink, respectively. In this system, a nonreturn-to-zero (NRZ) downstream signal is first frequency up-converted to around 20 GHz before being fed to a DML for downstream transmission. After transmission over the feeder fiber, a portion of the downstream signal is detected at the ONU and the other portion is fed to the RSOA as seed light. The RSOA is directly modulated by a 10-Gb/s NRZ signal for upstream transmission. To overcome the bandwidth limitation of the directly modulated RSOA, we employ an optical delay interferometer at the upstream receiver. The passive optical device acts as an optical equalizer and enables the 10-Gb/s upstream signal to be accommodated with a 1.3-GHz-bandwith RSOA. We investigate through experiment the crosstalk between the downstream and upstream signals as a function of the downstream subcarrier frequency. Also investigated in this paper is the nonlinear frequency mixing of the downstream and upstream signals in the RSOA.