Development of an extended-range fiber optic pH sensor using evanescent wave absorption of sol-gel-entrapped pH indicators

Thomas M. Butler; Brian D. MacCraith; Colette M. McDonagh

doi:10.1117/12.221730

29 September 1995 Development of an extended-range fiber optic pH sensor using evanescent wave absorption of sol-gel-entrapped pH indicators

Thomas M. Butler, Brian D. MacCraith, Colette M. McDonagh

Author Affiliations +

Proceedings Volume 2508, Chemical, Biochemical, and Environmental Fiber Sensors VII; (1995) https://doi.org/10.1117/12.221730
Event: European Symposium on Optics for Environmental and Public Safety, 1995, Munich, Germany

Abstract

The sol-gel process has been used to entrap pH indicators in porous glass coatings for sensor applications. This sensor is based on evanescent wave absorption using an unclad optical fiber dipcoated with the pH sensitive coating. The entrapped pH indicators show a broadening of the pH range with respect to the behavior in solution giving accurate measurement over three pH units when one indicator is used (bromophenol blue) and over six pH units (pH 3-9) when two indicators are used (bromophenol blue and bromocresol purple). The response of the pH sensor was monitored by measuring absorption at 590 nm referenced against a nonabsorbing region of the spectrum. This enabled the use of LED sources together with low cost photodiodes. The sensor displayed short response time and good repeatability. The thickness and stability of the pH sensitive coatings can be influenced by modifying the composition of the starting sol mixture. The evanescent absorption, and hence the sensitivity of the sensor, can be increased by selectively launching higher order modes in the fiber. These issues together with a full sensor characterization will be reported.

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Thomas M. Butler, Brian D. MacCraith, and Colette M. McDonagh "Development of an extended-range fiber optic pH sensor using evanescent wave absorption of sol-gel-entrapped pH indicators", Proc. SPIE 2508, Chemical, Biochemical, and Environmental Fiber Sensors VII, (29 September 1995); https://doi.org/10.1117/12.221730

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