Opto-thermally controlled beam steering in nonlinear all-dielectric metasurfaces

Metasurfaces have recently enabled a further miniaturization of many optical components which are typically bulky and made of different materials. Notably, nonlinear optics in dielectric metasurfaces has been investigated achieving significant Second Harmonic (SH) generation efficiency in χ (2) materials [1] , [2]. In this work, we use a symmetry broken meta-atom shaped as an AlGaAs nano-chair, obtained by removing one quarter of the volume from a nanocylinder with elliptic base, see Fig. 1(a). The proposed geometry is promising for technological applications, because capable of emitting the SH light along the vertical direction ( z axis) [3]. We thus propose to use such structures in a metasurface that is concurrently excited by a Fundamental Frequency (FF) pump in the infrared region (1.55m) and by a Continuous Wave (CW) beam in the visible (550 nm). By varying the CW intensity, it is possible to control the temperature inside the meta-atom. The temperature increasing is responsible for a modification in the AlGaAs refractive index. Thus, by varying the CW light intensity, I 0 , we can optimize the temperature profile so as to change the refractive index of the meta-atom, achieving in such manner the tuning of the linear resonant response and consequently obtaining a detectable variation in the SH light. In Fig. 1(b) we elucidate that is possible to create a look-up table for the emitted SH magnitude and phase coming from the meta-atom as a function of I 0. We verify that for the studied CW intensity range, the SH emission pattern preserves a main lobe ( y -polarized) towards the vertical direction with small amplitude alterations.