Expanding range of pulsed range sensors with active projection from spatial light modulators

LIDAR-based systems measure the time-of-flight of a laser source onto the scene and back to the sensor, building a wide field of view 3D raster image, but as a scanning process, there are problems associated with motion inside the scene over the duration of the scan. By illuminating the entire scene simultaneously using a broad laser pulse, a 2D camera equipped with a high speed shutter can measure the time-of-flight over the entire field of view (FOV), thereby, recording an instantaneous snap-shot of the entire scene. However, spreading the laser reduces the range. So what is required is a programmable system that can track multiple regions of interest by varying the field of regard to (1) a single direction, (2) the entire FOV, or (3) intermediate views of interest as required by the evolving scene environment. In this project, the investigators intend to add this variable illumination capability to existing instantaneous ranging hardware by using a liquid crystal spatial light modulator (SLM) beam steering system that adaptively varies the (single or multi) beam intensity profiles and pointing directions. For autonomous satellite rendezvous, docking, and inspection, the system can perform long-range sensing with a narrow FOV while being able to expand the FOV as the target object approaches the sensor. To this end in a previous paper, we analyzed the performance of a commercially available TOF sensor (3DVSystems' Zmini) in terms of the depth sensitivity versus target range and albedo. In this paper, we will analyze the laser system specifications versus range of field-of-view when beam steering is performed by means of a Boulder Nonlinear Systems' phase-only liquid crystal SLM. Experimental results show that the adjustable laser beam FOV extensively compensate the reflected image grayscale from objects at long range, and prove the feasibility of expanding range with the projection from the SLM.