Mode transition induced enhanced temperature sensitivity in long period waveguide gratings near dispersion turning point

Abstract

We propose a highly sensitive temperature sensor based on long period grating inscribed high index coated ridge waveguide in which the unique feature of mode transition (MT) phenomenon combined with the high thermo optic coefficient (TOC) polymer ambient elevates the differential thermal dependence between the participating modes. Using the dual resonance behavior, the temperature sensitivity is found to be ∼100 nm/°C near the dispersion turning point (DTP) at around room temperature with good tolerances with respect to waveguide’s width and grating period. A judicious grating design has also been formulated to operate the proposed structure near the DTP for temperatures other than room temperature including human body temperature, making the device an excellent choice for different bio and chemical applications. A comparative study of temperature sensitivity near the DTP with a conventional ridge waveguide is used to show the importance of the MT in obtaining high sensitivity near the turning point.