One of the goals of IRIS is to develop long-range LiDARs for autonomous vehicles. The core and disruptive technology of the company is the conception of germanium-tin (GeSn) single photon avalanche diodes (SPADs) for short-wavelength infrared (SWIR) sensing. The advantages of the GeSn lie in its high quantum efficiency at wavelengths between 1.5 and 1.6 um (best eye safety conditions) and its layer fabrication allowing to achieve a low cost and scalable solution.

The present idea is to demonstrate the feasibility of 1’550 nm photon detection at mid-range (up to ~80 m) with the GeSn detector in a time-of-flight (ToF) LiDAR configuration. The device will consist of a GeSn SPAD array as receiver and a VCSEL (Vertical-Cavity Surface-Emitting Laser) array as transmitter. The system will be a SWIR solid state flash LiDAR, the first of its kind.

This study aims at demonstrating that the IRIS’ GeSn detector is efficient in remote sensing configuration with VCSELs as 1’550 nm pulsed laser source. Tests will be performed at different distances with target objects with various albedo (reflective power). The optimization of the following points will be addressed to ensure the conception of an effective, compact, light and low cost LiDAR system: (1) optical system for the transmitter and the receiver for perfect matching of respective field of views (micro-optics, lenses, beam shaping, diffusors…) (2) VCSELs operation in pulsed mode (3) 1’550 nm detection with optimal quenching and the coincidence method (4) data acquisition and processing speed (5) overall SNR optimization (6) test range resolution with various detection bins.

The GeSn SPAD array is being developed at the EPFL. Test VCSEL arrays are provided by one of our partners. The whole LiDAR system will be set up in the HE-Arc laboratory/corridor. A preliminary optical system has already been designed and set up for a different LiDAR application, acquisition and post-processing algorithms have been developed and the electronic board for SPAD control and signal retrieval is ready to be tested. Long distance optical alignment will be performed in the corridor illuminating targets at various distances and with different albedo. However, the VCSEL arrays have been designed for continuous wave (CW) operation whereas a LiDAR in direct time-of-flight (dToF) configuration works in pulsed mode. Suitable drivers will have to be identified and study of the VCSELs behaviour in pulsed mode will be carried out. Of course, the eye-safety conditions will be verified from the very beginning and throughout the whole experiment.