An upgradable testing platform designed to characterize and test optical components of FMCW LiDARs, particularly optical phased arrays

Abstract

CEA aims at developing a compact 1550 nm Frequency Modulated Continuous Wave (FMCW) LiDAR on chip. In this paper, individual demonstrators, corresponding to three main components of a LiDAR (Light Distance And Ranging) system, are combined in a test bench: a FMCW laser source, an emission and reception Optical Phased Array (OPA) and an optical heterodyne detection module. Each component has been individually tested, but also evaluated in order to derive the system performance of a complete LiDAR. A test platform has been developed to calibrate an OPA fabricated at CEA platform, either in emission or in reception mode [1]. The tested OPA includes 256 channels based on grating antennae, with 1.5 m pitch and 256 thermo-optic phase shifters. More recently, this platform has been completed with a FMCW interferometer, where the FMCW LiDAR detection can be evaluated through a mixed propagation setup, composed of optical fibers and free space. Then, the OPA may be inserted into this setup. Therefore, the optical fiber FMCW interferometer has been optimized to detect the lowest signal (typically less than one hundred fW) and to estimate the signal-to-noise ratio (up to almost 30 dB) with low noise photodiodes. Performance has been compared to theoretical predictions. Then, our custom OPA is included inside this experimental setup in a free space propagation environment. The performance measurements extracted from the spectral analysis are in agreement with the expectations.

Heterodyne detection for optical FMCW LiDAR: tests, analysis, and experimental comparisons between photodetectors and configurations

“…Our objective is to compare the electrical power measured inside the time domain and inside the frequency domain thanks to the Parseval's theorem (1). v(t) is the signal voltage, including the noises.…”

“…In considering the photonic aspect, a such LiDAR consists of three main parts: a FMCW laser around 1550 nm, an Optical Phased Arrays (OPA) component, which combines two OPA, one in emission (Tx) and the other in reception (Rx) and finally an heterodyne receiver around 1550 nm. Until now, CEA-LETI has already associated a FMCW laser, an OPA component and a photodetector on a large optical test bench to show the possibility to measure a distance with such system [1], [2]. CEA-LETI achieves the OPA module and the photodetector on two different chips.…”