Microwave Photonic Sub-harmonic Downconverter with Image Rejection Capability

A microwave photonic downconverter with the capability of simultaneously realize sub-harmonic frequency downconversion and intermediate frequency (IF) signal image rejection is presented. Radio frequency (RF) carrier-suppressed double-sideband (CS-DSB) modulation and local oscillator (LO) double-sideband (DSB) modulation can be generated by the two sub Mach-Zehnder modulators (MZMs) in an integrated dual-parallel MZM (DPMZM). Then RF and LO signal upper sidebands and lower sidebands can be separated and selected using a two-channel wavelength division multiplexer (WDM). After photodetector (PD) two downconverted signals with same frequency of $\omega_{RF}-2\omega_{LO}$ and opposite phase are obtained respectively. As can be seen from the simulation results, upper and lower channel suppression of spur is 22.2 dB and 22.37 dB, respectively. System phase deviation is less than 2°. Benefiting from the all-optical and phase-cancellation, excellent image rejection exceeding 45 dB over 20–30 GHz working band is demonstrated.