Apparatus for measuring polarization mode dispersion (PMD) of a device, e.g. a waveguide, comprises a broadband light source (10,12) for passing polarized broadband light through the device (14), an interferometer (20) for dividing and recombining light that has passed through the device to form interferograms, a polarization separator (30) for receiving the light from the interferometer and separating such received light along first and second orthogonal Feb. 25, 2003 Feb. 25, 2003 polarization states, detectors (32.sub.x,32.sub.y) for converting the first and second orthogonal polarization states, respectively, into corresponding first and second electrical signals (P.sub.x(.tau.),P.sub.y(.tau.)), and a processor (36) for computing the modulus of the difference and such, respectively, of the first and second electrical signals to produce a cross-correlation envelope (E.sub.C(.tau.)) and an auto-correlation envelope (E.sub.c(.tau.)), and determining the polarization mode dispersion according to the expression PMD=where and .tau. is the delay difference between the paths of the interferometer.