  Nonlinear intersubband polaritonic metasurfaces support one of the strongest
known ultrafast nonlinear responses in the mid-infrared frequency range across
all condensed matter systems. Beyond harmonic generation and frequency mixing,
these nonlinearities can be leveraged for ultrafast optical switching and power
limiting, based on tailored transitions from strong to weak polaritonic
coupling. Here, we demonstrate synergistic optimization of materials and
photonic nanostructures to achieve large reflection contrast in ultrafast
polaritonic metasurface limiters. The devices are based on optimized
semiconductor heterostructure materials that minimize the intersubband
transition linewidth and reduce absorption in optically saturated
nanoresonators, achieving a record-high reflection contrast of 54%
experimentally. We also discuss opportunities to further boost the metrics of
performance of this class of ultrafast limiters, showing that reflection
contrast as high as 94% may be realistically achieved using all-dielectric
intersubband polaritonic metasurfaces.
