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

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 environmental conditions such as mechanical 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

Computational Interferometric Imaging

Imaging systems typically accumulate photons that, as they travel from a light source to a camera, follow multiple different paths and interact with several scene objects. This multi-path accumulation process confounds the information that is available in captured images about the scene, and makes using these images to infer properties of scene objects, such as their shape and material, challenging.  Computational light transport techniques help overcome this multi-path confounding problem, by enabling imaging systems to selectively accumulate only photons that are informative for any given imaging task. Unfortunately, and despite a proliferation of such techniques in the last two decades, they are constrained to operate only under macroscopic settings. This places them out of reach for critical applications requiring microscopic resolutions, such as medical imaging and industrial fabrication.  In this thesis, we change this state of affairs by introducing a new class of techniques that we call computational interferometric imaging: These techniques realize computational light transport capabilities using optical interferometry, a technology well-suited for micron-scale applications. We achieve this by either manipulating the properties of illumination used in interferometry setups, or using naturally-available illumination with such properties. To this end, we develop a theory of interferometry with illumination of general spatial and temporal coherence, unifying concepts across incoherent and coherent imaging. We invent and implement a hardware system that realizes such illumination in a programmable and light efficient manner. We then specialize our hardware system to enable two exciting capabilities: (a) fast and robust 3D sensing at micrometer axial and lateral resolutions; and (b) passive, outdoor time-of-flight imaging with sunlight, robust to wind, vibrations and ambient light, factors traditionally considered destructive to interferometry signal. Finally, we provide concrete directions for building faster and more robust extensions of our setups that can be easily deployed in existing interferometry systems in applications ranging from industrial fabrication and inspection, to retinal and cancer imaging.  We hope that this thesis will have a three-fold impact on modern imaging research: (a) providing inspiration for the theoretical investigation of interferometric and coherent imaging, to demonstrate never-before-seen capabilities; (b) inventing interferometric systems for application areas where interferometry has never been applied; and (c) translating research inspired by this thesis, combined with the development of novel reconstruction techniques, to critical applications in industrial fabrication and biomedical imaging. </p

Swept-Angle Synthetic Wavelength Interferometry

We present a new imaging technique, swept-angle synthetic wavelength interferometry, for full-field micron-scale 3D sensing. As in conventional synthetic wavelength interferometry, our technique uses light consisting of two optical wavelengths, resulting in per-pixel interferometric measurements whose phase encodes scene depth. Our technique additionally uses a new type of light source that, by emulating spatially-incoherent illumination, makes interferometric measurements insensitive to global illumination effects that confound depth information. The resulting technique combines the speed of full-field interferometric setups with the robustness to global illumination of scanning interferometric setups. Overall, our technique can recover full-frame depth at a spatial and axial resolution of a few micrometers using as few as 16 measurements, resulting in fast acquisition at frame rates of 10 Hz. We build an experimental prototype and use it to demonstrate these capabilities, by scanning a variety of scenes that contain challenging light transport effects such as interreflections, subsurface scattering, and specularities. We validate the accuracy of our measurements by showing that they closely match reference measurements from a full-field optical coherence tomography system, despite being captured at orders of magnitude faster acquisition times and while operating under strong ambient light