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-MoO3 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-MoO3 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-MoO3 is reported without the need for nanoscale fabrication on the α-MoO3. We observe coupling between the α-MoO3 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.
Highlights
Exploiting polaritons in natural van der Waals (vdW) materials has been successful in achieving extreme light confinement and low-loss optical devices and enabling simplified device integration
Hexagonal boron nitride is the most widely investigated of this class, featuring two Reststrahlen (RS) bands where hyperbolic phonon polaritons (PhP) can be supported[28,29]
In this work we have demonstrated the polarization-dependent optical responses of α-MoO3 FP cavities numerically and experimentally. α-MoO3 is a vdW semiconductor with strong longitudinal and transverse optical phonon resonances that give rise to high-quality absorption peaks in all the three orthogonal directions distinctly
Summary
Since OPhs dominate the optical characteristics of α-MoO3 in the mid-infrared, the complex permittivity can be described by phenomenological Lorentz function. Εj:^j; εj 1⁄4 ε1;j j1⁄4x;y;z ω2LO;j À ω2 À iωΓj ω2TO;j À ω2 À iωΓj ð1Þ where ε∞,j and Γj, respectively, stand for the high frequency permittivity and phonon damping
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