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Proceedings Paper

Improvement of thermal sensitivity of FBG sensors by combined cladding etching and polymer coating
Author(s): Jinu Paul; Liping Zhao; Bryan Kok Ann Ngoi; Zhong Ping Fang
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Paper Abstract

Bragg grating devices are widely used in the field of optical sensing and communication. Thermally tunable devices utilize the effect of temperature on the wavelength response characteristics of the fiber Bragg grating. But the low sensitivity of a Bragg grating device to temperature limits its usage to many applications. The wavelength sensitivity of a bare FBG is only 1.3 nm for a temperature change of 100°C. In order to enhance the temperature sensitivity of a fiber Bragg grating, we propose modification of the cladding of the FBG through etching and put another coating layer outside the cladding. The cladding is etched to a certain depth around the grating and the etched portion is coated with a suitable polymer. Theoretical analysis has been done to find the relationship between the wavelength shifts and the etching depths and coating thickness of the polymer. A finite element model of the cladding etched FBG coated with polymer has also been developed and the wavelength shift due to thermal expansion is analyzed under various etching depths and coating thickness. The high thermal expansion coefficient of the polymer enables to enhance the thermal sensitivity by improving the wavelength shift due to thermal expansion. Also the polymer coating on the etched fiber reduces the susceptibility of fracture and improves the reliability. It is found that that temperature sensitivity increases with increase in etching depth. But there is maximum limit to which the cladding can be etched without affecting the performance. Also it is found that increasing the coating thickness of the polymer increases the wavelength shift due to temperature change.

Paper Details

Date Published: 8 March 2004
PDF: 7 pages
Proc. SPIE 5272, Industrial and Highway Sensors Technology, (8 March 2004); doi: 10.1117/12.516079
Show Author Affiliations
Jinu Paul, Nanyang Technological Univ. (Singapore)
Liping Zhao, Singapore Institute of Manufacturing Technology (Singapore)
Bryan Kok Ann Ngoi, Nanyang Technological Univ. (Singapore)
Zhong Ping Fang, Singapore Institute of Manufacturing Technology (Singapore)


Published in SPIE Proceedings Vol. 5272:
Industrial and Highway Sensors Technology
Brian Culshaw; Samuel David Crossley; Helmut E. Knee; Michael A. Marcus; John P. Dakin, Editor(s)

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