A Silicon Optical Single Sideband Modulator With Ultra-High Sideband Suppression Ratio

Optical single sideband (OSSB) modulation is widely used in radio-over-fiber (RoF) system, nanophotonic phase noise filter, frequency-modulated continuous wave (FMCW) lidar and so on. We demonstrate a silicon dual-parallel Mach-Zehnder modulator (DP-MZM) with tunable optical power splitting ratio to generate OSSB signal with ultra-high sideband suppression ratio (SSR). To mitigate the SSR deterioration caused by the limited extinction ratios (ER) of the two sub-MZMs due to the process tolerance and the imbalance in their RF driving powers in practical RF links, we adjust the distribution of the incident optical power between the two sub-MZMs with a $1\times 2$ switch. With this technique, the SSR measured at 20 GHz is better than 39.1 dB. A theoretical analysis is also provided to explain how the unwanted sideband is suppressed by adjusting the optical power splitting ratio.