PMD measurement techniques-a consistent comparison

Several different techniques are now widely used for measurement of polarization-mode dispersion (PMD), which can limit the transmission bandwidth of both analog and digital fiber-optic transmission systems. The wavelength scanning technique relies on measurement of the spectral transmission through a polarizer-fiber-polarizer concatenation. The transmission spectrum is analyzed either by the counting of extrema, or by application of a Fourier transform. The interferometric technique uses a similar polarized optical source, but relies on measurement of the mutual coherence between different polarizations at the fiber output. In the Jones matrix technique the polarization response to three input polarizations is measured as a function of wavelength to allow calculation of the wavelength-dependent polarization dispersion vector. Ideally, all techniques would be rigorously linked by theory, which in turn would be confirmed by measurement. As we progress toward this level of understanding, a skeptical review of the theoretical relations between the physics of the various measurement techniques can help establish foundations upon which to build.