title: Holographic single photon LIDAR for adaptive 3d imaging
Creators: name: Bantounos, Konstantinos
Publisher: name: The University of Edinburgh
Year: 2024
Subjects: subject: Photon Counting
subject: 3D
subject: CMOS
subject: SPAD
subject: Single Photon Avalanche Diode
subject: Time of Flight
subject: ToF
subject: Spatial Light Modulator
subject: SLM
subject: Liquid Crystal
subject: LCoS
subject: LIDAR
subject: RADAR
subject: Holography
subject: Holographic Illumination
subject: Structured illumination
subject: Structured Light
subject: Adaptive
subject: Closed Loop

description: Three Dimensional (3D) imaging based on Light Detection And Ranging (LIDAR) is finding its way into an ever-increasing range of applications. For instance, it is a key part of sensory systems of many autonomous vehicles. The "ideal" LIDAR would be able to make precise and accurate measurements in potentially demanding conditions. There currently exists a variety of architectures, each with its own set of advantages and disadvantages, which meet the requirements of different applications to a greater or lesser extent. A common constraint of conventional LIDAR is that many optical system parameters are fixed at the design stage, meaning they cannot be adjusted in-situ. This work reports a programmable on-the-fly, adaptive LIDAR architecture that enables a wide range of configuration possibilities. It comprises photon-efficient sub-systems for structured-illumination by phase-only holographic projection and sensing of the return by single-photon detection. Phase-only holographic projection by Liquid Crystal on Silicon (LCoS) Spatial Light Modulators (SLMs) has been successfully applied to commercial display systems, such as automotive Head-Up Displays (HUDs), Augmented / Virtual Reality (AR / VR) systems and 3D display systems. Single Photon Avalanche Diode (SPAD) sensing, based on the Time of Flight (ToF) method, has already demonstrated great promise for LIDAR. The proposed LIDAR architecture uses a LCoS SLM and a SPAD image sensor for holographic ToF 3D imaging. It supports efficient closed-loop operation, in which the SPAD image sensor collects the return, for algorithmic analysis to inform the next pattern sent to the SLM, which redistributes the light to improve subsequent measurements. A Proof of Concept (PoC) system is demonstrated, based on Commercial Off-The-Shelf (COTS) components. It can mimic a wide variety of existing systems, thus allowing a direct comparison between conventional and adaptive operation. The PoC system is used to evaluate the performance of the architecture and pave the way towards future optimised integrated designs. A system model is developed for simulation-based analysis and is verified by experimental measurements. Two closed-loop techniques are proposed for adaptive operation. The former equalises photon-return by redirecting light from targets with a higher return towards those with a lower one. The latter uses a photon-count threshold to iteratively redirect light from targets whose measurement has exceeded the threshold towards the remaining ones. The PoC system is operated firstly in open-loop, where it demonstrates superior precision and photon-efficiency. It is then operated in closed-loop, which adds superior speed and resilience to ambient noise, offering a path to practical implementations.