HOW ACCURATELY CAN ONE MEASURE A STATISTICAL QUANTITY LIKE POLARIZATION-MODE DISPERSION

The differential group delay (DGD) due to varying local birefringence and random polarization mode coupling is a statistical quantity. Its v alue at any wavelength fluctuates in time. At any given moment it is w avelength sensitive. Hence, polarization-mode dispersion can only be d efined as a mean or rms value of the DGD. All measurements of polariza tion-mode dispersion involve thus an averaging over a finite sample se t. Consequently, all measurements are intrinsically of limited accurac y. We present analytical formulae and numerical data characterizing th is intrinsic limitation common to all measurement techniques.