Excitation of Symmetry Protected Modes in a Lithium Niobate Membrane Photonic Crystal for Sensing Applications

TL;DR

This theoretical study proposes a lithium niobate photonic crystal sensor exploiting symmetry protected modes to achieve ultra-sensitive, tunable Fano-like resonances with high quality factors, significantly enhancing electro-optic detection capabilities.

Contribution

It introduces a novel method to excite symmetry protected modes in lithium niobate photonic crystals for highly sensitive sensing applications.

Findings

Achieved high quality factors up to 10^5 in telecom range

Enhanced electro-optic Pockels effect by up to 4x10^5

Demonstrated ultra-sensitive, tunable Fano-like resonances

Abstract

Our theoretical study reveals the opportunity to develop an electric field sensor basedon the exploitation of Symmetry Protected Mode (SPM) that we excite within an electro-opticalmaterial, namely lithium niobate (LN). The SPM consists of a dark Fano-like resonance thatresults from the combination of a discrete Bloch mode of a Photonic Crystal (PhC) with acontinuum mode of a membrane, both of them made in LN. The dark character is linked tothe structure geometry having a high degree of symmetry. The SPM excitation is then madepossible thanks to an illumination under small oblique incidence which breaks the symmetry ofthe configuration. This results in several ultra-sensitive and tunable Fano-like resonances withhigh quality factors up to 10^5 in the telecoms spectral range. Some of these resonances providemodes with a highly confined electric field inside LN. This confinement allows the enhancementof the electro-optic Pockels effect by a factor up to 4x10^5, thus exacerbating the detectionsensitivity of the designed sensor.