Refractometric Sensor Based on a Birefringent Silica Waveguide Using a Tapered Cladding

An integrated photonic refractometric sensor was proposed and accomplished based on a birefringent silica rib waveguide incorporating a tapered cladding, which is overlaid with a uniform high-index film. A sensing region is free of the cladding so that the modification of the birefringence incurred by an analyte could be maximized, whereas input/output sections are not subject to it. And a shadow mask was taken advantage of to produce the tapered upper cladding in the light propagation direction. The variation in the refractive index of the analyte was in situ monitored via a polarimetric interference scheme by observing the accumulated phase difference between the transverse-electric (TE) and transverse-magnetic (TM) mode. The fabricated sensor provided a phase difference of 4814 degrees for a variation of 0.015 in the refractive index of the analyte, which is equivalent to an interference count of 13.3 times, and its sensitivity was accordingly 5.2 x 10(-6) refractive index unit (RIU) per degree. Finally, the resolution was estimated to be 0.73 x 10(-6) RIU for a phase measurement resolution of 0.14 degrees. (C) 2011 The Japan Society of Applied Physics