A Novel Nonpolarizing Tunable Thin-film Filter for Optical Network

The bandwidth of the S-polarization and the P-polarization modes will separate while the narrowband thin-film filter is in oblique incidence, which will cause serious polarization dependent loss and limit its tunable range. The phenomenon of the polarization bandwidth separation and its relationship to the mirror layers of the thin-film filter are analyzed. One novel method about eliminating the polarization bandwidth separation by optimizing the stack of the filter is presented. According to the stack, a novel nonpolarizing 100GHz DWDM four-cavities angle-tuned narrowband filter is designed. The simulation and the experiment results show that it can eliminate the phenomenon of the polarization bandwidth separation and enlarge the tunable range to cover the whole C-band.