Waveguide-coupled surface phonon resonance sensors with super-resolution in the mid-infrared region.

A waveguide-coupled surface phonon resonance (SPhR) sensor with super-resolution based on Fano resonance (FR) by using a multilayer system within the Kretschmann configuration in the mid-infrared wavelength region is proposed. Due to the coherent interference of the waveguide and the surface phonon polariton modes, the calculated reflectivity spectrum possesses sharp asymmetric FR dips. An ultra-small linewidth is formed because of the Fano coupling, and the physical features contribute to a highly efficient nano-sensor for refractive index sensing. The bulk and surface sensitivity by intensities are greatly enhanced relative to those of conventional SPhR sensors.