# A Time-of-Flight Imaging System Based on Resonant Photoelastic Modulation

## TL;DR

This paper introduces a novel time-of-flight imaging system utilizing a resonant photoelastic modulation device to measure distances and velocities in a scene with high accuracy, based on a new free-space optical mixer design.

## Contribution

The paper presents a new free-space optical mixer device using photoelastic modulation for ToF imaging, enabling high-precision distance and velocity measurements.

## Key findings

- Designed and fabricated a photoelastic modulator-based optical mixer.
- Demonstrated the system's ability to downconvert megahertz modulation frequencies.
- Proposed extension for high-accuracy phase and Doppler shift measurements.

## Abstract

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.