Long-wave infrared (LWIR) wavelengths are expected to provide a better robustness against meteorological perturbations as well as an increased covertness for hard target FMCW LiDAR. However, the implementation and modulation of LWIR sources and detectors constitutes an important challenge. With a custom quantum cascade detector, we demonstrate for the first time a QCL-based FMCW ranging system up to 50 m on an outdoor static target, with a < 2 % relative precision. It relies on the linear optical frequency modulation of the QCL, up to 8.4 GHz in 65 µs with 0.03 % of nonlinearities. Furthermore, through a novel method of self-mixing interferometry, we exploit the laser perturbations caused by optical feedback to perform FMCW ranging with fewer components. Similar results are obtained with both architectures, opening the way to low-complexity LWIR FMCW systems, where the low maturity of optical isolators and components makes it a critical asset.
Martin et al. (Thu,) studied this question.