Fano Resonance Based on Long Range Surface Phonon Resonance in the Mid-Infrared Region

Surface plasmon polaritons with noble metals lack the capability to restrain an optical field in the long wavelength region, while surface phonon polaritons with polar dielectric crystals have been regarded as a potential low-loss alternative. In this paper, long range surface phonon resonance (LRSPhR) is designed to operate in the mid-infrared (MIR) wavelength regime with a narrow resonance dip. Furthermore, by coupling a photonic waveguide with the LRSPhR, strong coupling between waveguide mode and long-range surface phonon polariton has been realized to form high Q Fano resonance. By employing such structure as the index sensor, it is shown that the bulk sensitivity and surface sensitivity can reach ~9000 and 266.9 RIU -1 , respectively, which shows a great enhancement comparing with the one based on merely LRSPhR. The proposed configuration can be a promising platform for MIR biochemical sensing.