Deeply subwavelength mid-infrared phase retardation with α-MoO3 flakes
Michael T. Enders, Mitradeep Sarkar, Maxime Giteau, Aleksandra Deeva, Hanan Herzig Sheinfux, Mehrdad Shokooh‐Saremi, Frank H. L. Koppens, Georgia T. Papadakis
Abstract
Abstract Phase retardation is a cornerstone of modern optics, yet, at mid-infrared (mid-IR) frequencies, it remains a major challenge due to the scarcity of simultaneously transparent and birefringent crystals. Most materials resonantly absorb due to lattice vibrations occurring at mid-IR frequencies, and natural birefringence is weak, calling for hundreds of microns to millimeters-thick phase retarders for sufficient polarization rotation. Here, we demonstrate mid-IR phase retardation with flakes of α -MoO 3 that are more than ten times thinner than the operational wavelength, achieving 90 degrees polarization rotation within one micrometer of material. We report conversion ratios above 50% in reflection or transmission mode, and wavelength tunability by several micrometers. Our results showcase that exfoliated flakes of low-dimensional crystals can serve as a platform for mid-IR miniaturized integrated low-loss polarization control.