Recently I have been working on how Mueller matrices handle reciprocal and nonreciprocal optical effects. Mueller matrices are truly informativative about reciprocity, but one needs to know how the information is “stored”.  A series of two papers are going to be published in Optics Letters about the topic.  For the moment they can be accessed in early view.

Mueller matrix description of homogeneous depolarizing media. I. Number of independent parameters

Mueller matrix description of homogeneous depolarizing media. II. Differential decomposition