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Temperature-insensitive refractometer based on a thermo-optically optimized long-period waveguide grating

We report numerically analyzed results on various parameters of planar-type long period waveguide gratings (LPWGs) for potential temperature-insensitive refractive index sensor applications. The LPWGs based on polymer materials can be low cost mass-produceable devices because they can be fabricated in a wafer-level process with a typical imprinting technology and can be integrated with other multi-functional photonic devices of planar type such as optical printed circuit board (O-PCB). We have designed a temperature insensitive long-period waveguide grating by using a 4-layer waveguide structure which consists of a silica substrate, polymer core and clad layers, and the upper clad layer for materials or analytes to be tested. Our numerical calculation show that there are optimized conditions on the thermo-optic coefficients of the core polymer materials for a temperature-independent LPWGs with given core and clad polymer materials as well as with the given waveguide dimensions. The maximum temperature range and the refractive index sensitivity of the temperature-independent LPWGs have been also calculated for several conditions of the waveguide parameters.