Distributed measurement of static strain in an optical fiber with multiple Bragg gratings at nominally equal wavelengths

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Abstract
The Fourier transform relationship between the reflected light from a Bragg grating and the complex spatial modulation of the Bragg grating is used to produce a distributed strain sensing system. A tunable external cavity diode laser along with a reference reflector in an optical fiber are used to produce a measurement of the phase and amplitude of the reflected light from the modulated Bragg grating as a function of wavelength. The system is demonstrated with 22 Bragg gratings in a single fiber on a cantilever beam and compared with foil strain gauge readings.