High Flux Passive Imaging With Single-Photon Sensors

Abstract

Single-photon avalanche diodes (SPADs) are an emerging technology with a unique capability of capturing individual photons with high timing precision. SPADs are being used in several active imaging systems (e.g., fluorescence lifetime microscopy and LiDAR), albeit mostly limited to low photon flux settings. We propose passive free-running SPAD (PF-SPAD) imaging, an imaging modality that uses SPADs for capturing 2D intensity images with unprecedented dynamic range under ambient lighting, without any active light source.Our key observation is that the precise inter-photon timing measured by a SPAD can be used for estimating scene brightness under ambient lighting conditions, even for very bright scenes. We develop a theoretical model for PF-SPAD imaging, and derive a scene brightness estimator based on the average time of darkness between successive photons detected by a PF-SPAD pixel. Our key insight is that due to the stochastic nature of photon arrivals, this estimator does not suffer from a hard saturation limit. Coupled with high sensitivity at low flux, this enables a PF-SPAD pixel to measure a wide range of scene brightnesses, from very low to very high, thereby achieving extreme dynamic range. We demonstrate an improvement of over 2 orders of magnitude over conventional sensors by imaging scenes spanning a dynamic range of 10 6 : 1.

Counting Statistics of Actively Quenched SPADs Under Continuous Illumination

“…Our results also offer more accurate mean-rate corrections that are important for everyday rate estimation. Among applications that rely on predictable detector response are transmission measurements [38], single-photon imaging [39], or verification of Born's rule [40]. The counting model improves the current treatments of SPAD counting statistics and its applications, such as estimating afterpulsing from a variance-to-mean ratio [29].…”

Asynchronous Single-Photon 3D Imaging

“…However, so far, SPADs are considered specialized devices suitable only for photonstarved (dark) scenarios, and thus, restricted to a limited set of niche applications. This raises the following questions: Can SPADs operate not just in low-light, but across the entire gamut of imaging conditions, including high-flux scenes [15]? In general, is it possible to leverage the exciting capabilities of SPADs for a broader set of mainstream computer vision applications ( Fig.…”

Low-cost SPAD sensing for non-line-of-sight tracking, material classification and depth imaging

“…SPADs are single-photon sensitive devices [Zappa et al 2007] that can be fabricated in CMOS technology [Charbon 2008] and, when combined with precise time-tagging, provide time-resolved images at picosecond resolution [Gariepy et al 2015]. As direct time-of-flight sensors, SPADs have become the workhorse for a wide range of emerging fields [Altmann et al 2018;Richardson et al 2009], such as pulsed light detection and ranging (lidar) in autonomous vehicles [Schwarz 2010], non-line-of-sight (NLOS) sensing [Chen et al 2020;Heide et al 2019;Liu et al 2019], as well as fluorescence lifetime imaging microscopy (FLIM) [Henderson et al 2018] and extremely high dynamic range imaging [Ingle et al 2019]. The sensors employed in all these works are custom-made research-grade devices that need to be combined with an ultrafast laser source, which is bulky and expensive (at least tens of thousands of US Dollars in total) and therefore out of reach for most real-life applications.…”