Anisotropy and Modal Hybridization in Infrared Nanophotonics Using Low-Symmetry Materials

Anisotropy has been a key property employed in the design of optical components for hundreds of years. However, in recent years there has been growing interest in polaritons supported within anisotropic (low crystal symmetry) materials for their ability to compress light to smaller, deeply subwavelength dimensions. While historically the first anisotropic polaritons probed were hyperbolic modes, research into anisotropic materials has recently turned toward hybrid materials and optical modes, employing phenomena such as phonon confinement, polaritonic strong coupling, and Moiré structures to design the optical properties. In this Perspective, we will briefly introduce the physics and theories of polariton anisotropy, review recently investigated anisotropic and two-dimensional materials, and then move on to a discussion of approaches toward realizing hybrid modes and identifying new materials. Based on the results from the past few years, we extend these discussions to highlight outstanding challenges and outline what we perceive as promising paths to further explore the potential for polariton anisotropy and hybrid systems in future nanophotonic optical devices.