Distributed Feedback Channel Dropping Filters

摘要

Passive, Quarter-Wave Shifted Distributed Feed-Back (QWS-DFB) resonators can actas transmission filters either singly, or in cascade. Equivalent circuits can be developed which predict the filter characteristics near the center of the stopband. The performance of recently fabricated filters is described. QWS-DFB resonators side coupled to a signal waveguide, can couple out one channel, without disturbing other channels within the bandgap of the DFB structure. Cascades of such filters have potential application to Wavelength Division Multiplex theory of such structures, their equivalent circuits and predicted responses are presented. Side coupled active Gain Distributed Feedback resonators have desirable properties in that they enhance the responses at chosen resonances in comparison with the undesirable ones. They provide another means for channel dropping. Their performance is compared with that of QWS-DFB resonators.