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Effects of Coating and Diametric Load on Fiber Bragg Gratings as Cryogenic Temperature SensorsCryogenic temperature sensing was demonstrated using pressurized fiber Bragg gratings (PFBGs) with polymer coating of various thicknesses. The PFBG was obtained by applying a small diametric load to a regular fiber Bragg grating (FBG). The Bragg wavelengths of FBGs and PFBG were measured at temperatures from 295 K to 4.2 K. The temperature sensitivities of the FBGs were increased by the polymer coating. A physical model was developed to relate the Bragg wavelength shifts to the thermal expansion coefficients, Young's moduli, and thicknesses of the coating polymers. When a diametric load of no more than 15 N was applied to a FBG, a pressure-induced transition occurred at 200 K during the cooling cycle. The pressure induced transition yielded PFBG temperature sensitivities three times greater than conventional FBGs for temperatures ranging from 80 to 200 K, and ten times greater than conventional fibers for temperatures below 80 K. PFBGs were found to produce an increased Bragg wavelength shift of 2.2 nm compared to conventional FBGs over the temperature range of 4.2 to 300 K. This effect was independent of coating thickness and attributed to the change of the fiber thermo-optic coefficient.
Document ID
20080014178
Acquisition Source
Langley Research Center
Document Type
Conference Paper
Authors
Wu, meng-Chou
(NASA Langley Research Center Hampton, VA, United States)
Pater, Ruth H.
(NASA Langley Research Center Hampton, VA, United States)
DeHaven, Stanton L.
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
August 24, 2013
Publication Date
March 9, 2008
Subject Category
Optics
Report/Patent Number
Paper-6933-3
Meeting Information
Meeting: SPIE Smart Structures and Materials and Nondestructive Evaluation and Health Monitoring
Location: San Diego, CA
Country: United States
Start Date: March 9, 2008
End Date: March 13, 2008
Sponsors: International Society for Optical Engineering
Funding Number(s)
WBS: WBS 645846.02.07.07.02
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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