Acquisition of Multiple Events in Direct Time-of-Flight LiDAR using Single-Photon Avalanche Diodes

Single-Photon Avalanche Diode (SPAD)-based 'Light Detection And Ranging' (LiDAR) systems often use the first photon measurement principle to acquire ranging information. While those systems provide accurate distance measurements, they can easily saturate in high background scenarios. Recent improvements in SPAD quenching circuit technology open up the opportunity for SPAD LiDAR systems to detect multiple photons while measuring with a single laser pulse, partially circumventing this challenge. The theoretical framework for the distribution of higher order single photon detections is presented and discussed how the sensor's typical quenching times influence it. Measurements with a SPAD circuitry capable of detecting multiple events in a single measurement are presented. Differences to first-photon and continuous detection implementations are discussed and advantages in high background light scenarios are shown.

I. Introduction

The term LiDAR describes methods in which photons are used to measure the distance between a sensor and objects in space. Besides LiDAR systems based on highly sensitive avalanche photodiodes (APDs), which are used in many commercially available systems, single-photon avalanche diode (SPAD) LiDAR systems provide comparably high sensitivities while also being scalable to large sensor arrays [1]. In contrast to APDs, SPADs show digital behaviour. The SPAD is an APD operated in Geiger mode which means that a high reverse bias voltage is applied to it, enabling a single photon to trigger a breakdown, resulting in a macroscopic current. This can be used to trigger a time-to-digital converter (TDC) circuit to determine the photons time of arrival t_ToF. This mode of operation is called time-correlated single photon counting (TCSPC) and is presented in Section II.