[OPTICAL REVIEW Vol. 4, No. 1A (1997) 111-113]

A Multipoint Quasi-Distributed Optical Fiber pH Sensor

Michael CAMPBELL, Yatao YANG, Peter A. WALLACE and A. Sheila HOLMES-SMITH

Department of Physical Sciences, Glasgow Caledonian University, Cowcaddens Road, Glasgow G4 OBA, United Kingdom

(Received July 2, 1996; Accepted September 12, 1996)

This paper reports the development and characterisation of a multipoint quasi-distributed optical fiber sensor for pH measurement. The system is based on a 170 m length of 200 μm core diameter plastic cladding silica fiber where sections of cladding have been removed and replaced with dye immobilised sol-gel glass to form sensing points. Evanescent wave excitation of a dye, immobilised within 2 mm long sections of cladding, enables the pH value of any spillage material to be determined by optical time domain reflectometry along the length of the fiber. The results suggest a spatial resolution of better than 2.5 meters for this fiber system and indicate that this arrangement could form the basis of a practical sensor/actuator system for chemical spillage, provided that suitable dye/analyte combinations are available.

Key words : distributed sensor, optical fiber, pH measurement, optical time domain reflectometry (OTDR), fluorescence