Simultaneous photonic and phononic bandgaps in a hexagonal lattice geometry with gradually transforming circular-to-triangular air gap holes

TL;DR

This study designs a hexagonal silicon lattice with air-gap holes that gradually change shape from circular to triangular, enabling tunable photonic and phononic bandgaps for advanced optomechanical devices.

Contribution

It introduces a method to geometrically tune both photonic and phononic bandgaps in a scalable silicon lattice by smoothly transforming air-gap hole shapes.

Findings

Photonic bandgaps tunable up to 49.7%.

Phononic bandgaps tunable up to 24.8%.

Demonstrates geometric control of wave suppression.

Abstract

The integration of photonic and phononic bandgaps within a single scalable architecture promises transformative advances in optomechanical and acousto-optic devices. Here, we design and simulate a two-dimensional hexagonal lattice in silicon with air-gap holes that transition smoothly from circular to triangular via tuneable geometrical parameters including air-gap hole radius (R) and tether length (l). By independently varying these two parameters, we systematically explore diverse honeycomb lattice geometries and their bandgap properties. This transformation from circular to triangular air-gap holes enables suppression of both electromagnetic and elastic wave modes through Bragg scattering and symmetry modulation. We demonstrate that systematic variation of R and l allows tuning of photonic and phononic bandgaps upto 49.7% and 24.8% respectively. This possibility of geometrically tuning bandgaps provide a strong foundation for applications in Bragg filters, sensors etc. without the need for complex defects or exotic materials.