Polarisation mode dispersion measurement using modulation phase shift method

Polarisation mode dispersion (PMD) remains important for optical communications, despite the impending deployment of PMD compensation methods. These methods depend on a full understanding of the PMD phenomenon in fibers and components. in particular, the compensation of first order as well as second order PMD require a detailed verification of that behaviour within DWDM channels or in components and devices that have very narrow transmission bands. Some, but not all, of the traditional PMD measurement techniques developed for fibers will operate over narrow wavelength bands and/or give full PSP information. Included in these is the long-established modulation phase shift (MPS) method, which is a direct time domain measurement of differential group delay (DGD). It effectively uses so little optical bandwidth that it may be considered as a "spot" measurement of DGD. The DGD can be determined without any form of polarisation differentiation with respect to wavelength and second order PMD with only one stage of differentiation. PMD in fiber Bragg gratings with regions of high ripple have been studied using MPS, where the narrow-band nature of the technique is particularly advantageous