Through the combination of nanoscale Mie-resonance and photothermal/thermo-optical effect, the nonlinear index n2 of both plasmonic and metal nanostructure can be enhanced by more than three orders of magnitude. We discovered various types of nonlinearity that include saturation, suppression, and reverse saturation in nanostructures. Through a similar mechanism, we also achieved optical bistability in a nanoscale resonator with a record-low Q-factor (<10) and observed large nonlinearity with hysteretic behavior. These tunable optical nonlinearities with low requirements on sample size and shape open new possibilities for the design of photonic devices and metal/semiconductor super-resolution.
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 μm2/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.
Through the combination of nanoscale Mie-resonance and photothermal/thermo-optical effect, plus a nanosecond excitation source that matches the thermal relaxation time of a silicon nanostructure, we demonstrated an ultra-large nonlinear index n2 = 1 um^2/mW, six-orders larger than the value in bulk. Under a confocal laser scanning scheme, unexpected sharp transition of scattering intensity is unveiled, suggesting a rapid temperature transient. The super-continuum wavelength tunability offers high-efficiency excitation among nano-silicon with various sizes. This robust and ultra-large nonlinearity shall be useful in optical switching and super-resolution mapping of semiconductor nanophotonic structures.
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