Book excerpt: I have written this book to ?ll a void between theory and practice, a void that Iperceivedwhileconductingmyownresearchanddevelopmentofcomponents and instruments over the last ?ve years. In the chapters that follow I have pulled materials from the technical and patent literature that are relevant to the understanding and practice of polarization optics in telecommuni- tions, material that is often known by the respective experts in industry and academia but is rarely if ever found in one place. By bringing this material intoonemonograph,andbyapplyingasingleformalismthroughout,Ihopeto create a “base level” upon which future research and development can grow. Polarization optics in telecommunications is an ever-evolving ?eld. Each yearsigni?cantadvancementsaremade,punctuatedbyimportantdiscoveries. The references upon which this book is based are only a snap-shot in time. Areasthatremainunresolvedatthetimeofpublicationmayverywellbecl- i?ed in the years to come. Moreover, the focus of the ?eld changes in time: for instance, there have been few passive nonreciprocal component advancements reported in the last few years, but PMD and PDL advancement continues with only modest abatement.