A novel dual resonance long period waveguide grating based highly sensitive refractive index sensor with reduced temperature sensitivity

Abstract

In this paper, we are proposing a novel structure to reduce the temperature cross sensitivity of a refractive index (RI) sensor based on dual resonance long period waveguide grating in a metal clad ridge waveguide, operating near the dispersion turning point. The core of the waveguide is considered to be made of two parts having opposite thermo-optic coefficients with grating written in one part only. Considering the coupling between the fundamental TE mode and a higher order TE mode, we have shown that by adjusting the thickness of the two parts of the core, it is possible to achieve blueshifts for both the resonance wavelengths with the increase in temperature unlike the case of a conventional dual resonance spectrum where two resonance wavelengths show opposite shifts. As a result, an extremely low temperature cross sensitivity ∼0.006 nm/0C has been achieved, whereas the dual resonance spectrum holds its conventional behavior with the change in ambient RI, showing an extremely high RI sensitivity ∼57,260 nm/RIU near water RI 1.33. Further, it has been observed that as we approach the dispersion turning point, temperature sensitivity decreases gradually whereas RI sensitivity increases, leading to a more accurate ambient RI measurement