In recent years, high-performance environment perception sensors are increasingly expected to realize autonomous driving systems. Light detection and ranging (LiDAR) is one of the most promising sensors due to its high angular resolution and range accuracy. Recently we've developed two types of cost-effective MEMS-LiDAR systems which consist of a single-pair of an emitter, a photodetector and a two-axis MEMS scanner in coaxial optics. The front-facing type takes advantage of telescopic optics to enlarge effective aperture for long range detection. The wide-view type utilizes omni-directional optics to achieve 360-degree panoramic scanning. In this study, we've investigated catadioptric devices and unique scanning MEMS mirrors for compact omni-directional LiDARs. The concept has been experimentally confirmed on a test bench. Here we report on the recent progress and describe the challenges and the prospects for MEMS-LiDAR systems.