Multifunctional microwave photonic processor with multichannel self-interference cancellation

A photonic-assisted multifunctional microwave signal processor for in-band full-duplex system is proposed. It is based on dual-polarization dual-parallel Mach-Zehnder modulator (DPol-DPMZM) and can simultaneously realize multichannel self-interference cancellation (SIC), frequency downconversion and image rejection. The two-channel SIC can be simultaneously achieved in X-DPMZM and Y-DPMZM of the DPol-DPMZM in optical domain when the two DPMZM are biased at the minimum transmission point. After SIC, the two groups of optical orthogonal carrier-suppressed double-sideband signals generated from the two DPMZMs are sent into a fiber Bragg grating to obtain the single-sideband signal, overcoming the dispersion-induced power fading. Subsequently, the orthogonally combined optical signals are separated into two branches and detected by two photodetectors. Two quadrature IF outputs are generated through mixing a pair of quadrature local oscillator signals with the received signals. After combination using a 90° hybrid coupler, the frequency downconversion with image rejection is achieved. Both theoretical and experimental investigations are performed. The results show that the single-frequency SIC depth up to 49.1 dB and the image-rejection ratio (IRR) of 30.4 dB are independently achieved. The frequency downconversion with a broadband SIC depth of 18.8 dB within 150 MHz and an IRR of 21 dB for signal of interest at 6.4 GHz are simultaneously achieved.