A common non-mechanical method for generating wide-angle, high-resolution 3D images is to use two multi-megapixel cameras to capture wide field of view (FOV) stereoscopic images. Such images, when viewed by a human, provide detailed 3D information that can easily be used to plot a course or avoid an obstacle. For a robot or autonomous vehicle, however, it takes considerable computation to convert the imagery into data that can be used for navigation and control. This processing demand can be an issue for small platforms needing real-time 3D data in a dynamic operating environment. With 3D time-of-flight (TOF) sensors (indirect TOF cameras and lidars), depth information can be acquired with minor processing, but high resolution over a large angle is not readily and inexpensively achieved without steering the illumination source, or receiver, or both. Mechanical beam steering systems (including MEMS) have been the answer to this problem for many years, but a truly no-moving-parts solution, using polarization gratings (PGs) combined with liquid crystal (LC) switches,1 offers some unique features while reducing costs when scaled to large volume manufacturing. This paper discusses the advancement and demonstration of wide-angle, large-aperture PG-based scanners incorporated into TOF sensors to improve resolution and range.
Driven by the demands for speed and field of view in the holographic photostimulation community, we designed, built, and tested a liquid crystal on silicon (LCoS) spatial light modulator (SLM) with a 1536x1536 square pixel array and high-voltage LC drive. We discuss some of the engineering work that made the MacroSLM possible, including the custom FPGA board for handling huge data rates, the large pixel size for minimizing rolloff and crosstalk, and the temperature control to handle heating effects from the high-voltage controls and high-power laser illumination. We also designed an FPGA implementation of the overdrive method for increasing liquid crystal switching speed, allowing us to overcome the significant data bottlenecks that limit frame rates for large arrays. We demonstrate 500 Hz hologram-tohologram speed at 1064 nm operating wavelength, and discuss the new science that these speeds and array sizes have enabled.
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