Rethinking Machine Vision Time of Flight With GHz Heterodyning

Time-of-flight (ToF) 3-D cameras like the Microsoft Kinect, are prevalent in computer vision and computer graphics. In such devices, the power of an integrated laser is amplitude modulated at megahertz frequencies and demodulated using a specialized imaging sensor to obtain subcentimeter range precision. To use a similar architecture and obtain micrometer range precision, this paper incorporates beat notes. To bring telecommunications ideas to correlation ToF imaging, we study a form of “cascaded Time of Flight”which uses a hertz-scale intermediate frequency to encode high-frequency pathlength information. We show synthetically and experimentally that a bulk implementation of opto-electronic mixers offers: 1) robustness to environmental vibrations; 2) programmability; and 3) stability in frequency tones. A fiberoptic prototype is constructed, which demonstrates 3-μm range precision over a range of 2 m. A key contribution of this paper is to study and evaluate the proposed architecture for use in machine vision.