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

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.