Sensitivity Enhanced and Polarization Independent Evanescent Field Planar Ridge Waveguide Bragg Grating Refractometer

摘要

Optical Bragg grating sensors based on side polished or etched waveguides have been demonstrated for the measurement of refractive index. However, these devices typically exhibit polarization dependent behavior for index values around 1.3. In this report, a ridge waveguide Bragg grating (WBG) sensor with high sensitivity for refractive index measurement in liquids is presented. The device is based on a small core size silica open top ridge waveguide and polarization independent Bragg gratings (PIBG) written and optimized using UV light. The WBG is surrounded by a liquid analyte and is accessed via evanescent field interaction of the guided waveguide mode with the liquid layer. In the theoretical analysis, enhancement of sensitivity by optimizing waveguide structures is proposed. In the experiment, a Bragg grating is induced in the open top ridge waveguide using a phase mask and excimer laser radiation at 193 nm. A series of refractive index matching liquids are used to test the device. Results indicate the sensitivity is as high as 50 pm of wavelength shift for a change of the index 3 x 10~(-4). This technology can offer many advantages over previously proposed waveguide sensors, including enhanced sensitivity, better polarization stability, and simpler fabrication process.