NARROW-BAND SPECTRAL FILTER MADE OF W-INDEX AND STEP-INDEX FIBERS

An all-fiber spectral filter constructed with a W-index fiber, supporting a dominant mode with nonzero cutoff frequency, and a step-index single-clad fiber is proposed and analyzed. The proposed filter offers a spectral width on the order of one nanometer, considerably narrower than that provided by a filter made of two single-clad fibers having the same transmission wavelength. The narrow spectral width is achieved by exploiting a relatively large slope difference between the dispersion characteristics of the W-index and step-index fibers constituting the filter. For an example case, transmission characteristic of the proposed filter with peak transmission at 1300 nm is calculated and compared with that of a corresponding filter made of two single-clad fibers.