Active pattern projection for increasing range of pulsed range sensors

Phase-only spatial light modulators provide active pattern projection. Unlike incoherent techniques, the pattern energy is inversely proportional to the total pattern area. If the patterns consist of spots or regions of light energy, it is possible to achieve a high signal-to-noise ratio within these regions. A 3DV Systems' Zmini range finder works with fast switching of the illumination source to form the "light wall" and fast gating of the reflected image entering the camera. Zmini operates by using a high speed shutter to temporally clip the energy field going to one camera chip while allowing the full pulsed energy to go to a second camera chip. The second chip captures the albedo which is effectively pixelwise divided out of the shuttered chip, leaving values that are proportional to depth. Thus, video rate time of flight depth information is attained. By combining these two technologies, we can extend the operating range of the Zmini shuttered depth finder significantly. In this paper, we present a feasibility report on the range property of the Zmini. The spatial light modulator under investigation is a 512 × 512 element, phase-only, liquid crystal device recently produced by Boulder Non-linear Systems Incorporated.