Polarization mode hybridization and conversion in phononic wire waveguides

TL;DR

This paper investigates how phononic wire waveguides made from GaN-on-sapphire can hybridize and convert polarization modes due to anisotropic elasticity, enabling advanced on-chip phononic circuit functionalities.

Contribution

It experimentally demonstrates orientation-dependent polarization hybridization and conversion in phononic waveguides, facilitating efficient actuation and polarization control of phononic modes.

Findings

Mode hybridization depends on crystallographic orientation.

Hybridization enables actuation of otherwise inactive modes.

On-chip polarization conversion between transverse modes is achieved.

Abstract

Phononic wire waveguides of subwavelength cross-section support two orthogonal polarization modes: the out-of-plane motion dominated Rayleigh-like and the in-plane motion dominated Love-like modes, analogous to transverse-electric and transverse-magnetic modes in photonic waveguides. Due to the anisotropic elasticity of the substrate material, the polarization states of phonons propagating along certain crystallographic orientations can strongly hybridize. Here we experimentally investigate the orientation-dependent mode hybridization in phononic wire waveguides patterned from GaN-on-sapphire thin films. Such mode hybridization allows efficient actuation of piezoelectrically inactive Love-like modes using common interdigital electrodes designed for Rayleigh-like modes, and further enables on-chip polarization conversion between guided transverse modes. Both are important for on-chip implementation of complex phononic circuits.