A composite optical waveguide-based polarimetric interferometer for chemical and biological sensing applications

• Published in: Journal of lightwave technology Vol. 18; no. 8; pp. 1106 - 1110
• Main Authors: Zhi-Mei Qi, Itoh, K., Murabayashi, M., Yanagi, H.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.08.2000; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Biological; Biomedical optical imaging; Chemical and biological sensors; Exact sciences and technology; General equipment and techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Interferometers; Magnetic separation; Optical films; Optical interferometry; Optical sensors; Optical waveguide theory; Optical waveguides; Phase shift; Physics; Potassium; Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing; Surface chemistry; Tellurium; Thin films; Titanium dioxide; Transistors; Velocity coupling; Chemical sensors; Refractive index; Planar waveguides; TM mode; TE mode; Optical waveguides; Interferometers; Thin films; Single mode waveguide; Composite materials; Mode splitter; Coupling; Polarimetry; Ion exchange
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/50.857756

A new polarimetric interferometer has been developed on the basis of the phase difference between transverse electric (TE)/sub 0/ and transverse magnetic (TM)/sub 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 TE/sub 0/ mode. Applying tapered velocity coupling theory, we found that the TE/sub 0/ and TM/sub 0/ modes coexisting in the potassium ion-exchanged layer were separated in the thin film region of the composite OWG: the TE/sub 0/ mode was coupled into the thin film while the TM/sub 0/ 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/spl deg/-polarized analyzer. The phase difference /spl phi/ between both orthogonal output components is very sensitive to the superstrate index n/sub c/ in the thin film region. Our experimental results indicate that a slight change of /spl Delta/n/sub c/=3.71/spl times/10/sup -6/ results in the phase-difference variation of /spl Delta//spl phi/=1/spl deg/ for a 5-mm-long TiO/sub 2//K/sup +/ composite OWG with a 34-nm-thick TiO/sub 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.