Non-mechanical Lidar beamforming enabled by combined wavelength-division- and time-division-multiplexing

We propose and demonstrate a Lidar beam-forming scheme without moving parts, enabled by the combination of wavelength-division-multiplexing (WDM) and time-division-multiplexing (TDM). The lights of different wavelength are demultiplexed into N different waveguides to form N WDM channels; each of them is further switched into M waveguides to form M TDM channels with their exiting ends placed in the focal plane of a lens. The lights exiting from the N × M array at different positions in the focal plane of the lens are collimated into different beams pointing to different directions. Two-dimensional beam-forming of N × M beams is realized in the space-wavelength domain (the WDM channels) and space-time domain (the TDM channels), in which the N WDM beams can be simultaneously directed into different direction by the TDM switches sequentially. The scheme has been successfully demonstrated with the off-the-shelf discrete fiber optic components using 4 WDM channels and 1 × 4 optical fiber switches for beam forming, together with the time-of-flight (ToF) technique for distance measurement for obtaining the three dimensional (3D) point cloud data. In particular, we have experimentally realized four different beam scanning modes using different configurations of the time- and wavelength-channels. The addition of the TDM channels helps to reduce the required number of wavelength channels in the pure wavelength-multiplexed scheme, and vice versa, to overcome the technical limitations on the number of WDM or TDM channels. Furthermore, adding the WDM channels helps to relax the speed requirement of the switches and related electronics of the TDM channels. We believe our Lidar beam-forming scheme combining both TDM and WDM may provide an attractive alternative to the MEMS and optical phased array based beam scanning, as well as the pure WDM beam-forming schemes.