If multiple pulses, either higher-order or polarization modes, simultaneously travel in a fiber, they might overlap in the time domain, hindering dispersion retrieval of the modes in question using conventional evaluation techniques. In this work, a high-resolution windowed Fourier-ridges (WFR) algorithm is developed for evaluation of spectrally resolved interferograms produced by light pulses that are overlapping in time. The sufficiency of one spectral interferogram to retrieve the differential group dispersion and the polarization dependent chromatic dispersion directly with high accuracy is demonstrated on a meter-long HC-800-02 photonic crystal fiber. Results are in accordance with previously published data.

We present a novel polarization alignment technique based on windowed Fouriertransform (WFT) spectral interferometry to determine the wavelength-dependent orientation of the principal polarization axes of photonic crystal fibers (PCFs). To test the technique, a commercially available, 82.5-cm-long HC-800-02 type hollow-core PCF was measured. The angles belonging to the fast and the slow principal axes of the fiber were determined from the peak intensity values of the ridges in the WFT map at different wavelengths. We demonstrate that the orientation of the principal polarization axes of the tested PCF is wavelength-dependent. The precision of the angle measurement was better than 0.3°.

Dispersion measurements on a birefringent hollow-core (HC-800-02) and a solid-core (LMA-PM-5) photonic crystal fiber (PCF) are presented using a windowed Fourier-transform (WFT) spectral interferometric method. We investigate the optimal value of the spectral window function of the WFT method to reach the highest accuracy in the dispersion measurement. This requires the knowledge of the precise position of the polarization axes of the fibers. In order to determine the position of the polarization axes we have developed a method based on analyzing the WFT signals, which were obtained from a series of interferograms at different excitation ratios of the polarization modes of the PCFs.

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