Thermo-optical bistability enabled by bound states in the continuum in silicon metasurfaces

TL;DR

This paper demonstrates thermo-optical bistability in silicon metasurfaces with bound states in the continuum, enabling tunable optical switching and modulation with low power and high control.

Contribution

It introduces a novel mechanism of nonlinear critical coupling in BIC-supporting metasurfaces, enhancing bistability control and switching efficiency.

Findings

Enhanced thermo-optical nonlinearity observed in BIC metasurfaces

Ability to tune bistability parameters via incidence angle

Proposal of nonlinear critical coupling for optimal hysteresis

Abstract

The control of light through all-optical means is a fundamental challenge in nanophotonics and a key effect in optical switching and logic. The optical bistability effect enables this control and can be observed in various planar photonic systems such as microdisk and photonic crystal cavities and waveguides. However, the recent advancements in flat optics with wavelength-thin optical elements require nonlinear elements based on metastructures and metasurfaces. The performance of these systems can be enhanced with high-Q bound states in the continuum (BIC), which leads to intense harmonic generation, improved light-matter coupling, and pushes forward sensing limits. In this study, we report on the enhanced thermo-optical nonlinearity and the observation of optical bistability in an all-dielectric metasurface membrane with BICs. Unlike many other nanophotonic platforms, metasurfaces allow for fine control of the quality factor of the BIC resonance by managing the radiative losses. This provides an opportunity to control the parameters of the observed hysteresis loop and even switch from bistability to optical discrimination by varying the angle of incidence. Additionally, we propose a mechanism of nonlinear critical coupling that establishes the conditions for maximal hysteresis width and minimal switching power, which has not been reported before. Our work suggests that all-dielectric metasurfaces supporting BICs can serve as a flat-optics platform for optical switching and modulation based on strong thermo-optical nonlinearity.