Characterization and chemical/biosensing application of a high-sensitivity integrated optical polarimetric interferometer

Abstract

A tapered thin film of Ta2O5 is sputtered on a single-mode slab glass waveguide to form a composite optical waveguide (COWG) for serving as a prism-coupled integrated optical polarimetric interferometer. The relationship between the refractive-index sensitivity (SRI) of the interferometer and the equivalent thickness (Teq) for the tapered layer of Ta2O5 is theoretically analyzed based on a four-layer homogeneous waveguide model. A comparison of the measured SRI with the simulated data leads to Teq 33.021 nm for the COWG used. The sensitivity of the interferometer to thickness of the protein adlayer is determined to be Sab (2.412 2)/nm. The acetic-acid concentration of a commercial Chinese vinegar is investigated, for the first time, by use of the interferometer combined with the Lorentz-Lorenz effective-medium theory. Water and methanol adulterations of a commercial Chinese liquor are detected with the interferometer. The results indicate that the refractive-index change induced by the adulteration is a quasi-linear function of the adulteration amount. Both the dynamic adsorption process of butyrylcholinesterase and the self-assembly process of cytochrome c/PSS multilayer film are monitored in real time with the sensor. The protein surface coverage is obtained from the combination of the measured phase-difference change and the adlayer-thickness sensitivity.