In‐Plane Anisotropic Phonon Polaritonic Resonances with α‐MoO₃ Microdisks

Phonon polaritons (PhPs) in 2D van der Waals (vdW) crystals exhibit strong spatial confinement and long polariton lifetimes, making them promising for developing novel nanophotonic devices at midinfrared frequencies. Here, using α‐phase molybdenum trioxide (α‐MoO₃) microdisks, in‐plane anisotropic PhP resonances with degree of polarization (DoP) of almost 100% from far‐field observation are demonstrated. Such in‐plane polarization‐dependent PhP resonances, originating from the anisotropic crystal structure of α‐MoO₃, are readily tuned by the disk length and fit well to numerical simulations. Findings show new possibility for engineering in‐plane polarizers based on vdW crystals and may promote the development of functional polarization‐sensitive optoelectronic devices at midinfrared frequencies.