A highly efficient channel drop filter. The filter employs a coupling element including a resonator-system between two waveguides, which contains at least two resonant modes. The resonator-system includes one or more interacting resonant cavities which in addition to being coupled to the waveguides,...http://www.google.de/patents/US6130969?utm_source=gb-gplus-sharePatent US6130969 - High efficiency channel drop filter
