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Spectral dependence of principal axes in anti-resonant hollow-core fibers with different numbers of capillaries.

We report on measurements highlighting the spectral dependence of the principal axes' angular orientation that is present within three hollow-core fibers samples of various geometries. Hollow-core anti-resonant fibers (ARFs) with six, five, and four capillaries are investigated in several transmission windows. It is shown that the six-capillary fiber structure demonstrates a much smaller shift in the principal axes' orientation, in comparison with five- and four-capillary structures. The four-capillary structure has a 90° shift of its principal axes' orientation inside even- and odd-numbered transmission windows. These results corroborate the suggestion that the six-capillary ARF structure is a great candidate for polarization-maintaining operation over a wide spectral bandwidth.