title: Multipoint temperature-independent fiber-Bragg-grating strain-sensing system employing an optical-power-detection scheme.
abstract: A temperature-independent fiber-Bragg-grating strains-sensing system, based on a novel optical-power-detection scheme, is developed and analyzed. In this system a pair of fiber Bragg gratings with reflection spectra either partially or substantially overlapping is placed side by side to form a temperature-independent strain-sensor unit. Conventional wavelength-interrogation techniques are not used here, and instead an optical-power-detection scheme is proposed to directly calibrate the measurand, i.e., the strain. Unlike the conventional approach in a multiplexed sensing system, the presented power-detection-based interrogation method does not need the fiber-Bragg-grating sensors to be spectrally separate. The only requirement is that the spectra of the two fiber Bragg gratings of each sensor unit in a multiplexed system be identical or slightly separate (slightly overlapping spectra would also work in the sensing scheme) and the source's optical power be sufficient for sensitive measurement. Based on a three-sensor-unit system, we demonstrate simple strain measurements of high linearity (+/- 0.4%), good sensitivity [2 microstrains (microS)], high thermal stability (+/- 0.8%), and zero cross talk. The effects of light source spectral flatness and fiber bending loss on measurement accuracy are also discussed.
authors.affiliation: Department of Electrical Engineering, National Tsing Hua University, Hsinchu, Taiwan 300.
authors.forename: Yan-Ju
authors.initials: YJ
authors.lastname: Chiang
authors.forename: Likarn
authors.initials: L
authors.lastname: Wang
authors.forename: Horng-Shyang
authors.initials: HS
authors.lastname: Chen
authors.forename: Chih-Chung
authors.initials: CC
authors.lastname: Yang
authors.forename: Wen-Fung
authors.initials: WF
authors.lastname: Liu