RF Self-Interference Cancellation for Radio-Over-Fiber Link Based on Dual Phase Modulation in Sagnac Loop

The in-band full-duplex (IBFD) systems can send and receive data simultaneously in the same frequency band. Although the electromagnetic interference among RF channels can be released using radio over fiber (RoF) links, the receiving antenna is susceptible to the signal leakage from adjacent transmitting antennas. Due to the electronic bottlenecks, traditional RF self-interference cancellation (SIC) systems have some problems, such as low operating frequency, narrow transmission bandwidth, and electromagnetic interference, which seriously reduces the communication performance. In this paper, a photonic RF SIC system based on dual-phase modulation in a Sagnac loop is proposed to further increase the resistance to electromagnetic interference of the IBFD systems. Based on the principle of polarization multiplexing, the damaged received signal and local interference signal are modulated on two beams of a light wave with orthogonal polarization states. The received interference signal can be canceled by polarization adjustment. In the experiment, a single- frequency interference cancelation depth of 45 dB is achieved in the proposed photonic SIC system over the operating frequency range of 5-20 GHz. Also, a demonstration of cancellation for modulated interference with a center frequency of 10 GHz and bandwidths of 20, 30, and 50 MHz is carried out.