Fabrication of low-loss planar waveguides and development of integrated optical chemical sensors

Abstract

Applications of planar integrated optical waveguide (IOW) technology to problems in surface spectroscopy and optical chemical sensing have been partly limited by the difficulty of producing high quality glass IOWs is. The fabrication of IOWs by the sol-gel method from methyltriethoxysilane and titanium tetrabutoxide precursors has therefore been developed. The physical, chemical, and optical properties of the films were studied using a variety of analytical techniques. The results show that the catalyst used to accelerate the sol-gel reaction strongly influenced the optical quality of the IOW. A novel optical sensing platform was subsequently developed using a sol-gel derived, laminate planar IOW structure. The sensing element is fabricated by coating a sol-gel IOW with a second, porous sol-gel layer in which optical indicator molecules are physically entrapped, yet remain sterically accessible to analytes that diffuse into the pore network. Formation of a complex between the analyte and entrapped indicator is detected via attenuated total reflection (ATR) of light guided in the IOW. Feasibility was evaluated by constructing IOW-ATR sensors for Pb2+ and pH, based on entrapped xylenol orange and bromocresol purple respectively. The response of both sensors was sensitive and rapid. This work was further extended to the development of a new class of gaseous iodine sensors. The sensing principle is based on the detection of a charge transfer complex formed between iodine and phenyl groups that have been incorporated into a porous, methylated glass film. The sol-gel iodine sensor exhibits a linear response to gaseous I2 in the range of 100 ppb to 15 ppm with response and recovery times less than 15 sec. Langmuir-Blodgett (LB) films have also been deposited on a sol-gel IOW from zinc 1,4,8,11,15,18,22,25-octabutoxy-phthalocyanine (ZnPc). Planar waveguide linear dichroism was used to determine molecular orientation in a ZnPc LB monolayer. The IOW-supported ZnPc monolayer was found to exhibit a sensitive spectral response to gaseous I2. The overall optical sensing approach described in this dissertation is technically simple, inexpensive, and applicable to a wide variety of chemical sensing problems.