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Differential double Bragg grating sensor for temperature-insensitive strain measurement

A novel differential double Bragg grating sensor for temperature-insensitive strain measurement is presented. The sensor consists of two identical weak measuring and reference gratings separated by some distance. The reference grating is placed inside the silica capillary that made it almost strain insensitive. The basic idea in differential double Bragg grating sensor is to measure the energy of the oscillating term in reflection spectrum of double Bragg grating structure. The normalized energy of the interference term depends on the pitch difference of two gratings and does not change when pitch variations of both gratings are equal with temperature variation. Therefore the normalized energy of the interference term can be used for the temperature-insensitive strain measurement.