A WDM-PON compatible wavelength-reused bidirectional in-band full-duplex radio-over-fiber system

A bidirectional in-band full-duplex radio-over-fiber system for the WDM-PON architecture is proposed and experimentally demonstrated. To deploy a simplified and low-cost optical network unit (ONU), the downlink optical carrier at the ONU is reused for uplink connection by employing a polarization modulator (PolM) as the transmitter at the center office (CO). Meanwhile, at the CO the wideband optical self-interference cancellation (SIC) is implemented while coping the output of the PolM as the reference signal, to harvest the in-band full-duplex communication and further facilitate a compact ONU. Also, a simple digital SIC algorithm based on the least mean square (LMS) method is introduced to compensate for the delay and amplitude fluctuations arising from fiber transmission. In experiments, simultaneous transmissions of 3.6 Gb/s 16-QAM OFDM downstream and 1.8 Gb/s 16-QAM OFDM upstream signals over the 6.15-km down and up fiber links are successfully demonstrated, wherein both downlink and uplink signals are centered at the same frequency from 3 to 8 GHz. The uplink transmission demonstration is accompanied by the emulated self-interference signal from the 3.6 Gb/s downstream signal. With the existence of 6.15-km fiber transmission, over 20.1-dB cancellation depth for the 1-GHz wideband SIC is experimentally achieved. The error-vector magnitude (EVM) performance of the uplink transmission thereby is improved from over 45.8% to below 9.9%.