Electrically Switchable Broadband Photonic Bound States in the Continuum

TL;DR

This paper introduces a novel method to electrically switch broadband photonic bound states in the continuum (BICs) using symmetric substrate waves, enabling broad spectral control with minimal refractive index changes.

Contribution

It demonstrates a new approach to achieve electrically switchable broadband BICs in symmetric periodic waveguides, overcoming previous narrow spectral limitations.

Findings

Achieved high switching contrast at visible wavelengths

Demonstrated broad spectral range of switchability

Validated concept through experimental verification

Abstract

The question of how to continuously manipulate a photonic system between a radiating state and a bound state is an important challenge in photonics, as its solution promises broad technological relevance for optical sensors, modulators, switches and displays. Existing approaches utilise the inherent wave-nature of electromagnetic fields to their advantage, and are commonly identified as bound states in the continuum (BICs), as they resemble singular bound states embedded in a band of radiating states. Although quasi-BICs have been demonstrated for numerous symmetric periodic photonic crystals, their existence so far has been limited to narrow spectral ranges, and their application in switches or modulators needs large changes of the refractive index. Here, we show that the incidence of two guided symmetric substrate waves of opposite phase onto a symmetric periodic film waveguide enables the excitation of self-stabilising BICs which are electrically switchable in a broad optical range, with small changes of the refractive index. An experimental verification of the concept shows a switching contrast C=700 at a wavelength of 532 nm and C=1000 at a wavelength of 632.8 nm.