All-Optical Steering of Light Upconversion by Nonlinear Metasurfaces Through Coherent Control

Frequency upconversion of near-infrared photons to the visible range is strategical for information technology, as it can provide an alternative for the read out of telecom signals using efficient silicon-based detectors. Light upconversion is a nonlinear process mediated by matter that consists in the interaction of either energy-degenerate photons, such as in second-harmonic and third-harmonic generation (THG), or photons with different energies, such as in sum frequency generation (SFG). We recently investigated frequency upconversion in both plasmonic and dielectric nanoantennas [1], [2]. Thanks to the adopted dual-beam pump scheme, where an ultrashort pulse ($\omega$) at telecom wavelength ($\lambda=1551\ \text{nm}$) impinges on the sample along with its frequency-doubled replica ($2 \omega$), THG and SFG are degenerate in energy. This, along with coherence, enables the interference between the processes. Yet, we found that in individual nanoantennas symmetry plays a major role in enhancing/suppressing the interference between SFG and THG. By tuning the relative phase between the two impinging pulses, we performed all-optical switching of upconverted light with efficiency > 50% in asymmetric plasmonic antennas [2].