INTERFEROMETRIC FIBEROPTIC SENSING BASED ON THE MODULATION OF GROUP DELAY AND FIRST-ORDER DISPERSION - APPLICATION TO STRAIN-TEMPERATURE MEASURAND

We describe an extension of low coherence interferometry which uses the complete interferogram rather than just the interferogram envelope, We measure the phase across the entire source spectrum using dispersive Fourier transform spectroscopy, and obtain group delay and dispersion from the phase curve. We apply the technique to a simultaneous quasi-static strain-temperature measurand in which strain and temperature are recovered from the modulation of group delay and first-order dispersion, We show these parameters have a negligible crossterm, yield a particularly robust transformation to strain and temperature, are immune to 2 pi phase ambiguity and insensitive to fiber geometry, With an ultra broadband thermal source we achieved simultaneous resolution of strain and temperature to accuracies of 5 mu strain.m and 0.35 K over strain and temperature ranges of 1200 mu strain.m and 22 K, We present detail of a diffraction grating-coupled multiple SELED source and its operation in optical fiber DFTS, With this source we achieved resolutions of < 1 mu strain in single parameter measurement of strain and a temperature insensitive measurement of strain to within 15 mu strain.m over a strain range of 1200 mu strain.m in the presence of a temperature fluctuation of 20 K.