High-spatial-resolution distributed strain measurement in optical fiber with Rayleigh scatter

A method of measuring strain over 30-cm intervals to an accuracy of 10 microstrain in unaltered low-loss communications-grade single-mode optical fiber is presented. The method uses a tunable external cavity diode laser to measure the reflected intensity of a reflector-fiber system as a function of wavelength. This measurement is performed with no strain applied to the fiber to produce a reference and then again after a strain has been induced. Cross correlation of the Rayleigh scatter spectra from a selected section of fiber in the strained and unstrained states determines the spectral shift resulting from the applied strain.