A method for the phase detection of straight and equidistant fringes is applied to an optical sensor using a highly birefringent fiber. A birefringent wedge introduces a linear phase difference between orthogonally polarized light which emanates from the fiber, and Young’s fringes are formed on an image sensor. The phase difference between two orthogonal retardations of the fiber is proportional to the phase of Young’s fringes. The phase of Young’s fringes is calculated from Fourier cosine and sine integrals of the fringe profile. The experimental results of a fiber extension induced by a PZT expansion are presented with error estimations. The accuracy of a 2-m long fiber sensor is estimated to be higher than λ/200. A technique to extend the measurement range of the fiber sensor is also presented using two laser wavelengths, in which a new method for calculating the difference between two phases is used. The experimental results are presented with error estimations.
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