Polarization-based optical fiber wavelength filters

Polarization-based in-line wavelength filters have been designed and evaluated. These are compact devices fabricated from single-mode optical fiber possessing high linear birefringence. A minimum passband width of 10 nm has been demonstrated at a passband separation of 60 nm. Both bandpass and bandstop devices can be produced. The filters are constructed from a single strand of fiber, less than 1 m in length, positioned between a pair of polarizers. Rotation of the polarization azimuth at appropriate intervals from the fiber input is achieved by twisting portions of the fiber to induce circular birefringence. Passband widths and separations are selected by choice of the number of twisted sections in the filter, and the lengths and twist angles of such sections