A new technique is presented for the measurement of the differential group delay (DGD) between principal states of polarization of an optical device, with a demonstrated accuracy and resolution of roughly 50 attoseconds (50 × 10−18 s). Accuracy was directly assessed by measurement of a crystal-quartz DGD Standard. This permits what is to the author's knowledge the first complete measurement of the polarization mode dispersion (PMD) of straight, submeter lengths of optical fiber. PMD can be reliably measured only when the fiber is straight, since spooling of the fiber changes its PMD by introducing additional mode coupling. Measurement of four fiber samples revealed correlation between DGD and fiber core ovality.
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