US Patent 7262904 Tunable optical add/drop device

Improved designs of optical devices for processing optical signals with one or more specified wavelengths are disclosed. According to embodiment, a filter mirror assembly appears an “L” shape and provides a filtering function as well as a reflecting function. The filter mirror assembly is so mounted that a rotation thereof will not alter the optical path the beam positions of signals resulted from a rotation of the filter mirror assembly. To cancel or minimize a lateral shift introduced to a light beam going through an optical filter, an optical compensator is introduced and rotates oppositely whenever the optical filter rotates.