Architecture of high-order all-fiber birefringent filters by the use of the Sagnac interferometer

Several high-order all-fiber birefringent filters were built by using of Sagnac interferometer. These filters included the narrow bandpass filter, the narrow bandstop filter, the rectangular filter, and the triangular filter. All these filters can be changed into each other by adjusting only the wave plates inside the Sagnac loop. The corresponding architecture theory for these kinds of filters is proposed and verified in experiments.