Ridge-waveguide-based polarization insensitive Bragg grating refractometer

A highly sensitive waveguide Bragg grating (WBG) sensor for measuring small changes of the refractive index of the surrounding liquid is presented. By using an open top ridge waveguide with a small core, the evanescent field interaction of the guided mode with the liquid analyte on the top of the waveguide is enhanced. The sensitivity measured via a shift in the resonance wavelength of the Bragg grating as high as 1 pm of wavelength shift for a change of 4 X 10-5 in the refractive index around 1.402 is realized. With a polarization insensitive Bragg grating, the polarization dependence of the sensor is improved. A theoretical analysis for the sensitivity of ridge waveguide sensors is given. The experimental results are in good agreement with the theoretical analysis.