Tensorial phase control in nonlinear meta-optics

Abstract

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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msup> <mml:mi>χ</mml:mi> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo stretchy="false">(</mml:mo> <mml:mn>2</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> fully tensorial features of AlGaAs metasurfaces, we propose a robust method to generate <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>0</mml:mn> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> <mml:mi>π</mml:mi> </mml:math> 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.