Lithography-free IR polarization converters via orthogonal in-plane phonons in α-MoO3 flakes
Sina Abedini Dereshgi, Thomas G. Folland, Akshay A. Murthy, Xianglian Song, Ibrahim Tanriover, Vinayak P. Dravid, Joshua D. Caldwell, Koray Aydin
Abstract
Abstract Exploiting polaritons in natural vdW materials has been successful in achieving extreme light confinement and low-loss optical devices and enabling simplified device integration. Recently, α-MoO 3 has been reported as a semiconducting biaxial vdW material capable of sustaining naturally orthogonal in-plane phonon polariton modes in IR. In this study, we investigate the polarization-dependent optical characteristics of cavities formed using α-MoO 3 to extend the degrees of freedom in the design of IR photonic components exploiting the in-plane anisotropy of this material. Polarization-dependent absorption over 80% in a multilayer Fabry-Perot structure with α-MoO 3 is reported without the need for nanoscale fabrication on the α-MoO 3 . We observe coupling between the α-MoO 3 optical phonons and the Fabry-Perot cavity resonances. Using cross-polarized reflectance spectroscopy we show that the strong birefringence results in 15% of the total power converted into the orthogonal polarization with respect to incident wave. These findings can open new avenues in the quest for polarization filters and low-loss, integrated planar IR photonics and in dictating polarization control.