0_4641 Recently, a strong drive towards the miniaturization of nonlinear optics has been motivated by the functionalities it could empower in integrated devices. For instance, near-infrared-to-visible upconversion of telecom photons is fundamental for optical communication and night vision, taking advantage of efficient silicon-based detection. Moreover, all-optical control of light can enable ultrafast optical information encoding. In this sense, optical metasurfaces are emerging as suitable platforms to multiplex such functionalities. In past works we devised metasurfaces for nonlinear light generation and polarization-based steering [1]. Here we propose a dual-beam scheme whereby a pulse at the telecom frequency ω (1550 nm wavelength) is mixed with its frequency-doubled replica at 2ω. Recently, we combined these pulses on individual dielectric and plasmonic nanostructures [2,3], exciting two coherent frequency-tripling pathways: third-harmonic generation (THG, ω+ω+ω) and sum-frequency generation (SFG, ω+2ω). Their coherent superposition at 3ω produces interference, which is allowed/suppressed depending on the symmetry of the system. Here we exploit a nonlinear, all-dielectric metasurface to lift symmetry constraints through diffraction, which steers radiation 3ω among different directions. Moreover, interference modulates the power within each diffraction order, depending on the relative phase between the two pumps. Therefore, by exploiting the phase as a tuning knob, the upconverted signal can be switched between opposite pairs of diffraction orders, e.g. (0,±1), with an efficiency >90%. Notably, the phase shift necessary to have a complete switching corresponds to a delay Δt = 1.3 fs between the pumps. The steering can be also reconfigured by changing the polarization state of the pumps. The proposed approach can be envisioned as an all-optical method to reroute upconverted telecom photons in different k-space directions. The instantaneous timescale of the nonlinear interactions involved could enable the ultrafast reconfigurability of the metasurface, paving the way to GHz speed modulation of the optical signal.[1] L. Carletti et al., ACS Photonics, 8, 731-737 (2021)
[2] A. Zilli et al., ACS Photonics, 8, 1175-1182 (2021)
[3] A. Di Francescantonio et al., Adv. Opt. Mat., 2022, 2200757 (2022)