Tensorial phase control in nonlinear meta-optics

Nonlinear metasurfaces have recently brought harmonic generation to subwavelength level, with spectral and polarization control unachievable in bulk crystals. Not only does nonlinear meta-optics enable the investigation of nonlinear physics at the nanoscale, but it also opens promising technological perspectives. To date, however, no full-phase control has been demonstrated on a harmonic field generated with a sufficient efficiency for most practical purposes. In this work, based on the chi((2)) fully tensorial features of AlGaAs metasurfaces, we propose a robust method to generate 0 - 2 pi phase-encoded second harmonic light for nonlinear wavefront shaping, experimentally demonstrating nonlinear beam steering and all-dielectric metalenses that generate and focus second harmonic beams to sub-wavelength spot sizes. Nonlinear generation with record efficiency and phase control are achieved in nanostructured arrays that are fully compatible with mature III-V semiconductor technology. This breakthrough paves the way for the development of ultrathin, free-space photonic devices for nonlinear imaging, including night vision. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement