Time-of-flight imaging based on resonant photoelastic modulation

A time-of-flight imaging system is proposed and its working principle demonstrated. To realize this system, a new device, a free-space optical mixer, is designed and fabricated. A scene is illuminated (flashed) with a megahertz-level amplitude-modulated light source, and the reflected light from the scene is collected by a receiver. The receiver consists of the free-space optical mixer, comprising a photoelastic modulator sandwiched between polarizers, placed in front of a standard complementary metal-oxide-semiconductor (CMOS) image sensor. This free-space optical mixer downconverts the megahertz-level amplitude modulation frequencies into the temporal bandwidth of the image sensor. A full-scale extension of the demonstrated system will be able to measure phases and Doppler shifts for the beat tones and use signal processing techniques to estimate the distance and velocity of each point in the illuminated scene with high accuracy.