Embossable grating couplers for planar evanescent wave sensors

The paper presents input grating couplers to be applied in planar evanescent wave sensors. Waveguide films SiO₂:TiO₂ were obtained using the sol-gel method, and grating couplers with a groove density of 1000 g/mm and 2400 g/mm were produced using the method of master grating embossing in sol film. The influence of refractive index of the cover on incoupling angles was presented. Basing on the experimental results, detection limits involving the changes of effective indexes and refractive indexes of the cover for the investigated planar structures were determined. Sensor structures with the couplers having a groove density of 1000 g/mm enable to detect minimum changes of the effective index below 3.3×10^-7 and to detect minimum changes of refractive index of the cover below 2.3×10^-6. Detection limits for the structures with couplers having the groove density of 2400 g/mm are over twofold higher.