A phase extraction technique based on data dependent system (DDS) method in higher order modal interference (LP<sub>01</sub> and
LP<sub>02</sub>) within the birefringent optical fiber is presented. A frequency modulated optical signal from a laser diode was
launched into the fiber and the higher modes were excited. The interference patterns recorded at the output end of the
fiber was digitized and characterized by means of autoregressive model. Self coherence function of an interferogram was
obtained from the autoregressive parameters and this would provide the phase change due to the measurand. The
modulation of group delay was obtained from the phase curve through unwrapping. An application has been made for
measurement of strain in an array of simply supported beam and cantilever beam at different locations under different
loading conditions. Results have been compared with those obtained using Fourier transform method and parametric
method for different applied strain (200-2000 μstrain).
The use of low coherence broad band optical source in Mach- Zehnder type optical fiber interferometric sensor is presented. The cross-sensitivity effect has been studied for simultaneous measurement of temperature strain. The DFTS technique has been used to retrieve the phase modulation from the interferogram.