All-optical self-interference cancellation method with efficient delay down-conversion

The joint co-frequency co-time full duplex (CCFD)- phased array technology offers high spectral efficiency, large communication capacity, low system latency, strong reliability, and low complexity. It holds broad application prospects in wireless communication, military communication, unmanned aerial vehicles, and satellite communication. Aiming at the self-interference cancellation (SIC) and delay requirements in CCFD-phased array systems, an all-optical SIC method with delay down-conversion is proposed in this paper. Through a Sagnac loop-based optical delay structure and polarization control, delay/amplitude matching and phase inversion are performed, and SIC is implemented in the optical domain. Simultaneously, the desired intermediate frequency (IF) signal is time-delayed using a dispersion medium (DM) and a tunable laser wavelength. Moreover, through appropriate DC bias control, the periodic power fading induced by DM can also be eliminated, and the output signal power can be regulated. Experimental and simulation results indicate that the single-frequency SIC depth exceeds 40 dB, while the broadband SIC depth exceeds 26 dB over sweep bandwidths of 500 MHz and 1 GHz. Additionally, the link gain remains relatively flat during 11 km optical fiber transmission. When the laser wavelength is adjusted from 1544 to 1556 nm, the delay of the IF signal can vary from -1120 to 1120 ps. Finally, the requirements for system gain optimization and image rejection down-conversion are discussed in detail, with preliminary results provided and potential application scenarios analyzed.