RESUMEN
We present a novel polarization alignment technique based on windowed Fourier-transform (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°.
RESUMEN
Applications based on photonic crystal fibers depend strongly on their dispersion properties that might differ from the desired specifications due to deficiencies in the manufacturing process. Since dispersion characteristics might also be affected by the placement of the fiber, in this paper the effect of various placements on the chromatic dispersion properties of a commercially available HC-800-02 photonic crystal fiber was investigated between 760 and 870 nm with Fourier-transform spectral interferometry. To test the scaling of dispersion with fiber length, samples of different lengths ranging from 10 to 97 cm were used in the measurements. It was found that the dispersion properties of the orthogonal directions were different. The dispersion parameter showed small dependence on the placement and fiber length. The polarization-mode dispersion (PMD) of the fiber was measured using an indirect and a direct technique. To retrieve the PMD directly in the case of the shorter fibers where the fringes were too sparse for the Fourier method, the so-called minima-maxima method was employed. The precision was comparable with both techniques; however, the direct approach proved to be more accurate when longer samples were measured, and the indirect method seemed to be more reliable in the case of shorter fibers.
RESUMEN
Spectral interferometric measurements are presented that show how wave propagation affects the carrier-envelope phase (CEP) of an ultrashort pulse in the focal region and results in variations that are different from the Gouy phase shift. Wavelength-dependent properties of the input beam are investigated and are seen to influence how the CEP is altered. The measured CEP changes show characteristics similar to the variations predicted by theory.