A new polarimetric interferometer has been developed on the basis of the phase difference between transverse electric (TE)0 and transverse magnetic (TM)0 modes in a composite optical waveguide (OWG). The composite OWG consists of a single-mode potassium ion-exchanged planar waveguide overlaid with a high-index thin film that has two tapered ends and supports only the TE0 mode. Applying tapered velocity coupling theory, we found that the TE0 and TM0 modes coexisting in the potassium ion-exchanged layer were separated in the thin film region of the composite OWG: the TE0 mode was coupled into the thin film while the TM0 mode was confined in the potassium ion-exchanged layer. Interference occurs between TE-and TM-polarized output components when a single output beam is passed through a 45-polarized analyzer. The phase difference between both orthogonal output components is very sensitive to the superstrate index nc in the thin film region. Our experimental results indicate that a slight change of nc = 3.71 10-6 results in the phase-difference variation of = 1 for a 5-mm-long TiO2/K+ composite OWG with a 34-nm-thick TiO 2 film. Such a simple polarimetric interferometer can be applied to chemical or biological sensors by modifying the upper film surface of the composite OWG with a chemically or biologically active substance.
Zhi-Mei Qi, Kiminori Itoh, Masayuki Murabayashi, and Hiroyuki Yanagi, "A Composite Optical Waveguide-Based Polarimetric Interferometer for Chemical and Biological Sensing Applications," J. Lightwave Technol. 18, 1106- (2000)