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.
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.
We study the scattering behavior of silicon nanoblocks in various displacements with respect to the optical axis of a tightly focused linearly polarized Gaussian beam. Experimentally, the laser scanning image of a single nanoblock deviates significantly from coherent image convolution. Theoretically, with exact Cartesian multipole decomposition, the results are explained through generation of high-order multipoles at large focus displacement and multipole interference. Surprisingly, due to the high-order multipoles, the efficiency of photothermal nonlinearity and Raman scattering are better with displaced focus. Our result extends Mie theory with displaced tight focus, opening up new opportunities in nanoscale light-matter interactions.
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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