Passive Micron-scale Time-of-Flight with Sunlight Interferometry

TL;DR

This paper presents a passive, sunlight-based interferometric technique for micrometer-resolution time-of-flight imaging and depth sensing, capable of operating outdoors and in challenging environments without active illumination.

Contribution

It introduces a novel sunlight-interferometry method that achieves passive, high-resolution depth sensing and imaging under real-world outdoor conditions.

Findings

Achieved micrometer-scale depth resolution using sunlight interferometry.

Demonstrated robustness to indirect illumination effects like interreflections.

Enabled passive imaging through diffusers and in adverse environments.

Abstract

We introduce an interferometric technique for passive time-of-flight imaging and depth sensing at micrometer axial resolutions. Our technique uses a full-field Michelson interferometer, modified to use sunlight as the only light source. The large spectral bandwidth of sunlight makes it possible to acquire micrometer-resolution time-resolved scene responses, through a simple axial scanning operation. Additionally, the angular bandwidth of sunlight makes it possible to capture time-of-flight measurements insensitive to indirect illumination effects, such as interreflections and subsurface scattering. We build an experimental prototype that we operate outdoors, under direct sunlight, and in adverse environment conditions such as machine vibrations and vehicle traffic. We use this prototype to demonstrate, for the first time, passive imaging capabilities such as micrometer-scale depth sensing robust to indirect illumination, direct-only imaging, and imaging through diffusers.