Enabling In-Band Bidirectional OFDM-Uplink and OOK-Downlink Transmission in Long-Reach RSOA-Based WDM-PON Systems

We present a simple, straightforward technique to enable bidirectional transmission of analog and digital signals in single-fiber wavelength division multiplexing passive optical network systems employing reflective semiconductor optical amplifiers (RSOA). An On-Off-Keying (OOK-DL) downlink modulation is effectively erased in a saturated RSOA, reflecting a carrier for retransmitting on the same fiber an in-band analog WiFi orthogonal frequency division multiplexing uplink signal (OFDM-UL). We investigate the operating conditions and the optimization procedure to attain required signal quality for both the uplink and downlink. We demonstrate experimentally the maximum distance and the best attainable performances for different lengths of standard single mode fiber (transmission). Bit error rate below the forward error correction threshold is obtained for WiFi OFDM-UL signal over 40 km and up to 80 km of SSMF using 64QAM and QPSK modulation modes, respectively. In all cases, we achieve error-free operation for the OOK-DL signal at 1 Gb/s.