Coupled surface plasmon–phonon polariton nanocavity arrays for enhanced mid‐infrared absorption
Satya R. Kachiraju, Ivan Nekrashevich, Imtiaz Ahmad, Hira Farooq, Long Chang, Sangsik Kim, Myoung-Hwan Kim
Abstract
Abstract Resonant optical cavities are essential components in mid‐infrared applications. However, typical film‐type cavities require multilayer stacks with a micron‐thick spacer due to mid‐infrared wavelengths, and their performance is limited by narrow frequency tunability and angular sensitivity. We propose and experimentally demonstrate the subwavelength‐scale (≈ λ 0 /150) resonant nanocavity arrays that enhance the absorption spectrum of the device in the mid‐infrared (10–12 microns) via excitation of coupled surface plasmon–phonon polaritons. The proposed metal–insulator–polar dielectric (gold–silicon–silicon carbide) structure supports a guided mode of the coupled surface polaritons in the lateral direction while vertically confining the mid‐infrared wave within the 80 nm thick dielectric spacer. In particular, the subwavelength‐scale (≈ λ 0 /10) gratings are imposed to form Fabry–Pérot cavity arrays displaying angle‐insensitive and frequency‐tunable absorption of up to 80% of the optical power in the mid‐infrared. Our work should benefit diverse mid‐infrared applications and novel designs of polariton‐based photonic devices.