An analysis for contradirectional-coupler-type optical grating filters

Characteristics of coupler-type optical-grating filters are analyzed with respect to output efficiency, transmission, crosstalk, and reflections, it is confirmed that the couplers should be asymmetrical in order to obtain high output and transmission efficiency, and that the grating should be fabricated only on the output waveguide of the coupler in order to reduce crosstalk and reflections due to undesired coupling. Calculation examples are given for silica and InP-embedded channel waveguides, which confirm the efficacy of this coupler-type optical grating filter.