Frequency-Modulated QCL-Based Mid-Infrared Ranging Systems

Through an efficient linearization of the optical frequency chirps of a quantum cascade laser (QCL), we demonstrate and compare two methods of coherent ranging in the long-wave infrared (LWIR) window. The first method is based on the coherent detection of the light reflected by the target on an external quantum cascade detector (QCD). The second method relies on the measurement of disturbances of the laser properties caused by the reinjection of the collected light inside the laser cavity. Both of the methods are compared in terms of precision and accuracy through the ranging of an outdoor static target up to 54 m. Via a linear optical frequency modulation with a bandwidth of about 8 GHz in a period of 65 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu s$</tex-math></inline-formula> and thanks to linearity errors as low as 0.03%, measurements with a relative precision below 1% of the absolute distance are achieved, paving the way to high-speed and precise mid-infrared ranging systems.