  A time-of-flight (ToF) 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 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.
