Phonon Polaritons Assisted Extraordinary Transmission in α-MoO-Silver Grating and Its Application in Switching

Sub-wavelength metal grating structures exhibit extraordinary transmission (EOT) due to constructive interference of surface plasmon polaritons (SPPs) tunneling. Phonon polaritons (PhPs) having several advantages over metal-supported plasmons, such as zero ohmic loss and larger propagation lengths, can further enhance the transmission. We propose the design of silver gratings filled with anisotropic Molybdenum Trioxide (α - MoO₃) to exhibit EOT by utilizing PhPs. We also numerically demonstrate the tunability (amplitude) of EOT by introducing a layer of graphene nanoribbon in the proposed device and show its application as a mid-infrared switch with bandwidth of 650 nm. α-MoO₃/silver grating produces normalized transmission as high as ∼5.5 for [100] and ∼6 for [001] crystalline directions. This extraordinary effect is attributed to the formation of (i) hybrid modes, specifically cavity modes coupled with SPPs outside the reststrahlen band (RB) and (ii) cavity modes coupled with PhPs inside the RB. The reported work can be employed in diverse applications including molecular sensing, space communications, remote controlling and, imaging.