Absolute phase birefringence dispersion in polarization-maintaining fiber or birefringent crystal retrieved from a channeled spectrum

We report on a simple method for retrieving the wavelength dependence of the phase birefringence in a polarization-maintaining fiber or a birefringent crystal from a channeled spectrum. The method utilizes interference of polarized modes or waves resolved as the channeled spectrum and its processing by a windowed Fourier transform to reconstruct precisely the phase as a function of wavelength. The ambiguity of the phase is removed provided that we know both the approximative function for the birefringence dispersion and the length of the fiber or the thickness of the crystal. The method is used in measuring the wavelength dependence of the phase birefringence in an elliptical-core fiber or in a quartz crystal in a range from 500 to 900 nm. The dependences are compared with those resulting from the available data, and very good agreement is confirmed.