PMD measurement techniques and how to avoid the pitfalls

Since polarization-mode dispersion (PMD) can often be so confusing, it is easy to see how its measurement can be complicated as well. Many different techniques for PMD measurement are available, and often many user-selectable parameters are associated with each measurement. Provided here is it description of the various measurement techniques available along with a discussion of the "best practices" for PMD measurement using these described techniques. Section I gives some definitions and lists the parameters that must be measured to fully characterize PMD and introduces the statistical uncertainty inherent in polarization-mode coupled devices. Section 2 describes the various measurement techniques, classifying them as either frequency-domain or time-domain techniques. Section 3 lists several useful practices to reduce measurement errors when measuring PMD. Section 4 discusses the concept of spectral efficiency as a useful figure of merit for describing measurement uncertainty normalized to spectral bandwidth. Finally, Section 5 describes the tradeoffs, associated with wavelength step size (for frequency-domain techniques) and provides some "rules-of-thumb" for choosing appropriate wavelength steps in these measurements.