Polarization-Dependent Loss: New Definition and Measurement Techniques

We formulate the concatenation properties of polarization-dependent loss (PDL) based on extinction rather than linear units. The advantage of this is that corresponding PDL vectors, defined with length proportional to extinction, can be added with much better accuracy than the traditional linear ones, in particular when PDL is of nonnegligible quantity. We also describe either two concatenated PDL elements or a general constant optical element as a combined PDL element and a retarder, thereby obtaining not only input- but also output-referred PDL vectors. We then propose to model a general optical transmission medium by the concatenation of many differential group delay (DGD) and PDL sections and retarders. An inverse scattering algorithm is provided which allows this physical structure to be obtained from the Jones matrix impulse response. Experimentally, we obtain the latter from the Mueller matrices measured in the optical frequency domain. The finally resulting distributed device structure is displayed in DGD and PDL profiles. The covariance matrix of the normalized Stokes vectors of scrambled polarizations equals 1/3 times the identity matrix. Based on this, we present yet another PDL measurement technique, the sqrt(3) scrambling method. It needs no polarimeter and determines low PDL values with better accuracy than the gradient search-based extinction method.