Controlling spectral and power flow behavior in rotated hyperbolic resonators

Abstract Calcite is a classic example of a birefringent material, possessing different optical properties along its crystal axes. This anisotropy becomes extreme in the infrared, resulting in hyperbolic behavior that can support resonances – known as volume-confined hyperbolic phonon polaritons (vHPhPs) – that manipulate and enhance light-matter interactions at the nanoscale. Through a combination of experimental and modeling approaches, here we demonstrate how the relative orientation between calcite resonators and the crystal axes can be exploited to manipulate the spectrum, polarization, and propagation of infrared light confined by hyperbolic materials. This behavior is understood within a simple analytical framework that predicts the spectral behavior without relying on electromagnetic simulations. These general results establish how vHPhPs supported by materials with in-plane anisotropy can be exploited to control light and its propagation at the nanoscale and identify the fundamental mechanism that enables resonances to be spectrally tuned via resonator-crystal alignment in materials with in-plane hyperbolic anisotropy.