Downstream modulation index tuning to enable full-duplex OOK-DL/OFDM-UL transmission in RSOA-based Radio-over-Fiber system

In this paper, we investigate the possibility of transmitting full-duplex digital and analog signal in a carrier reused, re-modulating Radio-over-Fiber (RoF) system based on reflective semiconductor optical amplifier (RSOA). We study the effect of tuning the modulation index of the On-Off-Keying Downlink (OOK-DL) signal on its reception performance and the amplitude modulation erasing in RSOA. By properly selecting operating conditions, downlink residual modulation on the reflected optical carrier can be minimized to allow the transmission of a WiFi Orthogonal Frequency Division Multiplexing Uplink (OFDM-UL) signal. We experimentally demonstrate bidirectional transmission over 20km of standard single mode fiber (SSMF) and show an operational region where we can achieve error-free for a 1Gb/s OOK-DL signal while we remain below forward error correction (FEC) threshold for WiFi OFDM-UL using QPSK, 16QAM, and 64QAM modulation modes.