Nonlinear frequency mixing in QCL-based interferometry: Beyond the intrinsic resolution

We demonstrate superresolution in position tracking sensing based on feedback interferometry in quantum cascade lasers (QCLs). QCLs with optical feedback make highly compact sensors since they work as mixer oscillator and detector of infrared radiation. Additionally, QCL continuous-wave emission remains stable at steady state in strong feedback regimes, permitting to gain control on the nonlinearity of the QCL active medium. Here, nonlinear frequency mixing in a QCL-based common-path interferometer is exploited to unveil object's position with nanometer-scale resolution, far beyond the intrinsic limit of half-wavelength. Experimental results are in excellent agreement with simulations based on Lang-Kobayashi model encompassing multiple-target dynamics.