High Isolation Multichannel Microwave Photonic Mixer With Linearity Enhancement and Phase Tunability

A high local oscillator (LO) isolation multichannel microwave photonic mixer with linearity enhancement and phase tunability is proposed and experimentally demonstrated. The leakage of LO signal caused by the residual optical carrier of the carrier-suppressed modulation severely impacts the communication quality of the microwave photonic multichannel upconversion system. In the proposed mixer, the LO signal and the intermediate frequency (IF) signal are individually modulated in the form of carrier-suppressed single sideband (CS-SSB) with orthogonal polarization. By aligning the polarization direction of the two CS-SSB signals with the polarizer, their residual optical carriers cancel with each other, thereby facilitating the high LO isolation. Furthermore, the polarization control can introduce a tunable phase difference between the two polarized beams, enabling phase tunability of upconverted signal after photodetection. Owing to the CS-SSB modulation form, the LO and IF sidebands can be amplified efficiently in the optical domain, which results in the linearity enhancement of upconversion. A proof-of-concept experiment is carried out with results showing that a carrier-to-sideband ratio (CSR) of −45.1 dB and an upconversion isolation of 50.4 dB are realized. The spurious-free dynamic range (SFDR) of subchannel is enhanced by 15.1 dB. A three-channel upconversion of the IF signals with the same frequency without interchannel crosstalk and the capability of phase shifting for subchannel are demonstrated.