This paper describes two different schemes of fiber Bragg Grating-based techniques for simultaneous measurement of temperature and strain. In the first scheme, a single grating is fabricated at the splicing joint of the different type of photosensitive fibers resulting in a dual grating property with similar strain coefficients and dissimilar temperature coefficients. The conventional matrix inversion technique is used in this case to discriminate the parameters. In order to widen the range of measurement, in the second scheme, the measurement is demonstrated by writing a grating with very high reflectivity in a 10 cm long specially fabricated Sb-Er-Ge doped silica fiber. The scheme exploits the grating sensitivity to both strain and temperature in association with the temperature-dependent peak power ratio of the two fluorescence peaks around 1535 nm and 1552 nm of the amplified spontaneous emission due to 4I13/2® 4I15/2 transition arising from the presence of Erbium ions in the fiber core, using a 980 nm laser diode as a pumping source. The sensor can be used for the simultaneous measurement of strain and temperature over the wide ranges of 0-2000me and 20-600 oC, with root mean square errors of 36me and 2.8 oC, respectively.

Fiber Bragg Gratings (FBGs) have generated considerable interest in recent years because of their potential for use in sensor applications such as structural integrity, oil well monitoring and aerospace engineering, in addition to the conventional and well known communications applications . Reliable, accurate, and simultaneous measurement of strain and temperature, and both strain-independent temperature measurements and temperature-independent strain measurements, by using FBGs are of significant interest for various applications for the above-mentioned industries. Improved measurements of these parameters are very important for such industrial uses to achieve enhanced safety and reliability, and lower cost. However, for the measurement of parameters such as strain or temperature, both measurands produce a convoluted shift of the Bragg wavelength due to the inherent property of the FBGs, thus creating a possible error or ambiguity in any measurement of each of these parameters individually. This results in an unwanted cross-sensitivity, which creates several complications in grating-based sensing schemes for the measurement of both parameters simultaneously.

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