Narrow-band optical channel-dropping filter

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Abstract
Waveguide couplers are combined with lambda /4 shifted distributed feedback (DFB) resonators to produce narrowband channel dropping filters. The bandwidth of the filter can be made much narrower than the stopband of the grating. It is possible to remove the spurious responses of the grating filter by appropriate dispersion characteristics for the coupled waveguides. However, in some practical applications it may not be necessary to do this, if all channels can be accommodated within half the grating bandwidth of the filters.