POLARIZATION-MODE DISPERSION MEASUREMENTS BASED ON TRANSMISSION SPECTRA THROUGH A POLARIZER

Routine characterization of polarization-mode dispersion (PMD) in sing le-mode fiber, both at the manufacturing stage and in installed system s, requires an easy-to-implement measurement technique. One method tha t is particularly simple to implement involves counting the number of extrema (i.e., maxima and minima) per unit wavelength interval in the transmission spectrum measured through a polarizer (analyzer) placed a t the output of a test fiber. In this paper, we establish accurate equ ations relating both the extrema density and mean-level crossing densi ties in such spectra to the expected value of PMD. These equations are used to measure several fiber samples, and are compared to measured v alues obtained with a commercially available test set. It is shown tha t measuring both mean-level crossings and extrema densities provides a simple means for establishing whether a fiber is scaling as square-ro ot L (long-length regime) or L (short-length regime). Using Monte Carl o simulations, the accuracy of the fixed-analyzer measurements is exam ined as a function of the width of the wavelength interval over which measurements are made. In addition, the simulations indicate that fixe d-analyzer measurements are quite robust with respect to the presence of polarization-dependent loss (PDL) in the span, an important conside ration for measurements in amplified systems.