Nonlinear Phase Control and Anomalous Phase Matching in Plasmonic Metasurfaces

TL;DR

This paper introduces nonlinear phase control in plasmonic metasurfaces, revealing a new anomalous phase matching condition that enables flat nonlinear optical elements like lenses for frequency conversion.

Contribution

It presents the first demonstration of full nonlinear phase control and a novel nonlinear phase matching condition in plasmonic metasurfaces, expanding their functional capabilities.

Findings

Established nonlinear phase control over plasmonic metasurfaces.

Discovered a new anomalous nonlinear phase matching condition.

Demonstrated flat nonlinear optical elements such as lenses.

Abstract

Metasurfaces, and in particular those containing plasmonic-based metallic elements, constitute a particularly attractive set of materials. By means of modern nanolithographic fabrication techniques, flat, ultrathin optical elements may be constructed. However, in spite of their strong optical nonlinearities, plasmonic metasurfaces have so far been investigated mostly in the linear regime. Here we introduce full nonlinear phase control over plasmonic elements in metasurfaces. We show that for nonlinear interactions in a phase-gradient nonlinear metasurface a new anomalous nonlinear phase matching condition prevails, which is the nonlinear analog of the generalized Snell law demonstrated for linear metasurfaces. This phase matching condition is very different from the other known phase matching schemes. The subwavelength phase control of optical nonlinearities provides a foundation for the design of flat nonlinear optical elements based on metasurfaces. Our demonstrated flat nonlinear elements (i.e. lenses) act as generators and manipulators of the frequency-converted signal.