22 Nov 2007
Australian researchers have developed a spectrally-overlapped chirped-fiber Bragg grating sensor system for simultaneous two-parameter sensing.
One of the advantages of fibre-optic sensors is the ability to perform quasi-distributed (multipoint) sensing through the use of multiplexing. The most widely used scheme for fiber Bragg gratings (FBG) is wavelength division multiplexing (WDM), but for chirped FBGs the number of gratings that can be multiplexed using WDM is limited because of the large spectral bandwidth each chirped FBG occupies within the light source spectrum.
Researchers at the University of New South Wales, Australia, tackled this issue by introducing a sensor system that exploits amplitude-modulated chirped FBGs. These chirped FBGs are amplitude-modulated in such a way that they can be spectrally overlapped with similar spectral characteristics, namely the centre Bragg wavelength and bandwidth (Meas. Sci. Technol. 18 3825).
When used in conjunction with WDM, these unique amplitude modulations significantly increase the number of gratings that can be multiplexed by making use of the so-called spectral-overlap multiplexing scheme.
The researchers exploited the new sensor system to measure two parameters –the strain and temperature of a metal alloy plate – at the same time.
The team found the maximum “self-crosstalk” of the system to be about 16 µ. Such a small amount of crosstalk implies that the undesired effects of spectral shadowing and partial overlapping have very little influence on the overlapped amplitude-modulated grating when using this spectral-overlap multiplexing technique.