Highly sensitive temperature sensor based on a long period grating inscribed metal clad ridge waveguide with PDMS surrounding

Abstract

A highly sensitive temperature sensor based on a long period grating (LPG) written metal clad ridge waveguide (MCRW) with poly-dimethylsiloxane (PDMS) surrounding is proposed and theoretically analyzed. We have exploited the coupling between the fundamental and a higher order quasi-TE mode via the long period grating written in the core of the MCRW. It is shown that owing to the differential enhancement of the two participating modes' evanescent fields in the PDMS surroundings due to the metal under cladding and the high thermo-optic coefficient of PDMS, the thermal dependence of the higher order mode is significantly enhanced as compared to the fundamental mode. In addition, a dispersion turn around behavior in the phase matching graph of the LPG is observed due to the metal under cladding. As a result, a temperature sensitivity as high as ∼100 nm/°C can be achieved by using the dual resonance near the dispersion turning point. Further, due to the highly lossy nature of the quasi-TM modes, no inline polarizer is required to be used with the proposed structure.