Mid-Infrared Power Limiters and Saturable-Absorber Mirrors Based on $\chi^{(3)}$ GaAsSb/InGaAs Intersubband Polaritonic Metasurfaces

Saturable-absorber mirrors and optical power limiters with fast third-order nonlinear optical responses are crucial elements for the operation of pulsed lasers, protection of sensitive optical equipment, and the implementation of all-optical switches for signal processing and computation. Devices with these functionalities and different levels of technological maturity are now available in the visible and near-infrared spectral regions; however, in the mid-infrared spectral range (mid-IR, wavelengths in the range 3-15 microns), such optical elements are not readily available. We have recently demonstrated that saturable-absorber mirrors and optical power limiters can be constructed in the mid-IR spectral range using the concept of intersubband polaritonic metasurfaces - devices in which transitions between electron subbands in a semiconductor heterostructure are strongly coupled with optical modes in metal or dielectric nanoresonators [1]. Our approach allows one to tailor the position and the strength of the nonlinear response by quantum engineering of intersubband transitions and electromagnetic engineering of the optical nanoresonators.