An Optical Interference Suppression Scheme for TCSPC Flash LiDAR Imagers

Abstract

This paper describes an optical interference suppression scheme that allows flash light detection and ranging (LiDAR) imagers to run safely and reliably in uncontrolled environments where multiple LiDARs are expected to operate concurrently. The issue of optical interference is a potential show-stopper for the adoption of flash LiDAR as a technology of choice in multi-user application fields such as automotive sensing and autonomous vehicle navigation. The relatively large emission angle and field of view of flash LiDAR imagers make them especially vulnerable to optical interference. This work illustrates how a time-correlated single-photon counting LiDAR can control the timing of its laser emission to reduce its statistical correlation to other modulated or pulsed light sources. This method is based on a variable random delay applied to the laser pulse generated by LiDAR and to the internal circuitry measuring the time-of-flight. The statistical properties of the pseudorandom sequence of delays determines the effectiveness of LiDAR resilience against unintentional and intentional optical interference. For basic multi-camera operation, a linear feedback shift register (LFSR) was used as a random delay generator, and the performance of the interference suppression was evaluated as a function of sequence length and integration time. Direct interference from an identical LiDAR emitter pointed at the same object was reduced up to 50 dB. Changing integration time between 10 ms and 100 ms showed a marginal impact on the performance of the suppression (less than 3 dB deviation). LiDAR signal integrity was characterized during suppression, obtaining a maximum relative deviation of the measured time-of-flight of 0.1%, and a maximum deviation of measurements spread (full-width half-maximum) of 3%. The LiDAR signal presented an expected worst-case reduction in intensity of 25%.

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A Probabilistic Approach to Estimating Allowed SNR Values for Automotive LiDARs in “Smart Cities” under Various External Influences

“…A similar approach to considering the LIDAR interference (both unintentional and intentional) has been proposed by Carrara and Fiergolski [59] in the SPAD-based LiDAR structure by introducing time-correlated discrete random delays in the formation of laser pulse of the target LiDAR. Despite the obvious efficiency and simplicity of the proposed approach, the problem of considering the case when all other "adverse" LiDARs work with the same random time-shift scheme remains unsolved.…”

An Overview of Lidar Imaging Systems for Autonomous Vehicles

“…In practice, retro-reflectors flood the SPAD detector with photons, saturating it, and blinding the entire sensor for some frames, rendering it useless. Some schemes based on interference have been proposed to avoid such problems [79]. Issues related to mutual interference of adjacent lidars, where one lidar detects the illumination pattern of the other, are also expected to be a hard problem to solve in flash imagers.…”