Wavelength-selective nonlinear wavefront control in resonant thin-film lithium niobate metasurfaces

TL;DR

This paper presents a thin-film lithium niobate metasurface capable of spectrally selective second-harmonic generation, enabling simultaneous frequency conversion and wavefront shaping for advanced nonlinear optical applications.

Contribution

It introduces a resonance-engineered phase control method in metasurfaces for wavelength-selective nonlinear wavefront shaping, overcoming static limitations of previous geometric phase approaches.

Findings

Achieved spectral tuning of Mie-type resonances for phase control

Demonstrated simultaneous frequency conversion and mode shaping

Converted Gaussian pump into Hermite-Gaussian mode at doubled frequency

Abstract

Nonlinear metasurfaces offer compact control over frequency conversion and wavefront shaping. However, existing approaches, often based on geometric phase, lack wavelength selectivity, resulting in static nonlinear responses. Here, we demonstrate a thin-film lithium niobate metasurface that enables spectrally selective shaping of second-harmonic generation through resonance-engineered phase control. The structure consists of two regions with distinct phase responses, realized via spectral tuning of Mie-type resonances. This design enables simultaneous frequency conversion and spatial mode shaping, transforming a Gaussian pump near 1100 nm into a first-order Hermite-Gaussian mode at 550 nm, while maintaining the pump profile. The demonstrated approach offers a pathway toward ultracompact and tunable components for nonlinear holography and related applications.