This course introduces the basic theories and technology behind fundamental components for WDM architectures. These include the circulator, WDM elements like mux/demux, and interleavers. In addition to the inner working of these components, the various technology choices for WDM are compared and it is shown where each best fits into the different applications. Concepts include polarization, birefringence, thin films, planar waveguides, and fiber Bragg gratings, with an emphasis on the thin film technology. Novel experiments using the disruptive technology of the interleaver are described.