We unraveled a novel optical bistable state in amorphous silicon nanocuboids, featuring an abrupt super-linear jump of scattering intensity during hysteretic switching. The effective intensity dependency reaches 19th power, leading to an nonlinear index n2 as large as 5 ฮผm2/mW, 7-order larger than the bulk value and well explained through coupled electromagnetic and photothermal simulation. Combining the ultralarge super-linear response with dark-field laser scanning microscopy, 3.5-times resolution enhancement was achieved, without any need of temporal/spatial excitation modulation. This hysteresis scattering not only sets a benchmark in optical super-resolution technique, but also suggests further optical signal processing potentials.
In this study, we found giant photothermal nonlinearity with ๐2 = 10-1๐๐2/๐๐ in ~100๐๐ silicon nanoblocks, based on Mie-resonance enhanced absorption and efficient temperature increase via thermal insulation. Through a continuouswave pump-probe setup, we demonstrated an ultrasmall high-contrast all-optical switch with 90% modulation depth. Due to the 0.001๐๐3 small geometrical size, thermal dissipation is as fast as nanosecond, leading to modulation speed at GHz, which is much faster than other thermal optic switches. The large and fast all-optical switching could open the possibility toward high-density integrated photonic nanocircuits based entirely on silicon.
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