29 November 2000 Polymer-based optical single-arm waveguide interferometer as a chemical sensor
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We report on a single-arm double-mode waveguide interferometer being used as a chemical sensor for detection of presence of ammonia and other pollutants in ambient air. The sensor is based on thin films of polymers such as poly(methyl methacrylate) and polymide doped with various indicator dyes such as bromocresol purple. These dye-doped polymer materials significantly increase their optical absorbance in the presence of the pollutants. The absorbance change is accompanied by the change of the refractive index of the materials in the region of optical transmittance. The change of the refractive index can be converted into a change of the light intensity in the single arm interferometer. The sensor employs interference between two propagating modes of the same polarization. Single-arm configuration makes it rigid but yet sensitive enough to detect concentrations of ammonia of the order of 10 ppm and less. The device also exhibits high sensitivity to ambient temperature change (of the order of 1 degree(s)C per 2(pi) -phase shift). We analyze effects of various factors such as polymer composition, light wavelength, ambient humidity and atmospheric pressure on the performance of the sensor. Various design and fabrication issues are also discussed. The problem of particular interest is coupling the sensor to the optical fiber transmission line, reduction of losses and sensitivity improvement.
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Darnell E. Diggs, Darnell E. Diggs, Sergey S. Sarkisov, Sergey S. Sarkisov, Michael J. Curley, Michael J. Curley, Grigory Adamovsky, Grigory Adamovsky, } "Polymer-based optical single-arm waveguide interferometer as a chemical sensor", Proc. SPIE 4106, Linear, Nonlinear, and Power-Limiting Organics, (29 November 2000); doi: 10.1117/12.408527; https://doi.org/10.1117/12.408527


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