Photoinduced giant modulation of terahertz nonlinearity from metasurfaces

TL;DR

This paper demonstrates a method to actively control and significantly modulate terahertz nonlinearity in semiconductor metasurfaces using optical stimuli, enabling ultrafast and efficient nonlinear optical functionalities.

Contribution

The study introduces a novel approach to modulate THz nonlinearity via valley degree of freedom manipulation in semiconductor metasurfaces with low optical energy.

Findings

Achieved over 20000% modulation depth in third harmonic generation

Enabled on-off switching of THz nonlinear effects with picojoule optical energy

Demonstrated effective tunability of nonlinear behaviors in a single metasurface

Abstract

Active control of optical nonlinearity is essential for advancing next-generation electronics and photonics, including high-speed wireless communications, optical information processing, and nonlinear signal manipulation. However, achieving tunable nonlinearity at terahertz (THz) frequencies faces significant challenges due to the lack of materials that combine high nonlinear responses with strong sensitivity to external stimuli in this spectral regime. Here, we show giant modulation of THz nonlinearity by optically tailoring the valley degree of freedom in semiconductor-based metasurfaces. Mediated by the resonant behaviors of metasurfaces, photoexcited electrons transition into different valleys in the conduction band in response to the driving THz field, with the transition rate controlled by light intensity. Since THz nonlinearities vary significantly with electron dynamics in different valleys, various nonlinear effects-such as nonlinear transmission and generation-can be efficiently enhanced and modulated within a single metasurface using weak optical pumping. With optical energy as low as a few picojoules, we achieve on-off switching of THz third harmonic generation with a modulation depth exceeding 20000%, along with effective tunability of its nonperturbative behaviors. Our approach breaks new ground in active THz devices fully compatible with semiconductor industry standards, indicating a promising building block for ultrafast THz signal processing, all-optical computing, and nonlinear optical elements.