Integrated optical bio-sensor based on pure surface plasmon-polariton excited by a waveguide grating

In this paper, we present a theoretical model and the characteristics of a refractive index sensor based on pure surface plasmon-polariton (SPP) excited by a properly designed waveguide Bragg gratings (WBG) or long period gratings (LPG). The gratings are imprinted in a waveguide layer and we propose the potential of a buried waveguide fabricated by a novel method for SPP bio-sensing using a continues-wave (CW) CO2 laser. The pure SPP is propagating in an optimized 5-layer structure which has a metal thickness of 20 nm and separated from the waveguide layer by a dielectric cladding which has thickness of 0.5 µm. As a result, LPG based sensor is more sensitive to changes in the sensed medium refractive index and requires much shorter gratings length for a given sensitivity than the WBG based one. The proposed sensor is highly sensitive and free from any moving parts and can be used as bio/chemical sensor.