Optical frequency shifting using silicon photonic MZMs for LiDAR signal generation

Abstract

Signal generation for LiDAR using silicon photonic Mach-Zehnder modulators (MZM) has been presented in this work which makes use of optical single sideband (SSB) modulation. Four different techniques have been summarized and the most favorable one has been presented at the end which uses silicon dual-parallel dual-drive Mach-Zehnder modulators (DP-DD-MZMs) to demonstrate frequency shifting by optical single sideband suppressed carrier (SSB-SC) modulation. Frequency modulated continuous wave (FMCW) LiDAR needs a linearly changing optical frequency chirp signal to be transmitted. Shifting optical frequency of a carrier wave is a complicated task, for which, SSB modulation presents a solution as it is a process which can change optical frequency of the output wave electronically by changing the RF modulation frequency. The proposed technique using DP-DD-MZMs uses 4 RF signals for modulation and the generated output signal has significant carrier, sideband and higher order sideband suppression ratios. Simulation results show a 44.92 dB carrier suppression, 30.12 dB lower sideband suppression and a 6 dB increase in the desired upper sideband at modulation frequency of 5 GHz. Experimental results also validate the simulation results. Lumped component design of quadrature and 180 hybrid couplers has also been presented at the end. This work paves way for the signal generation for a LiDAR on silicon-based chips.