Design considerations in optical add/drop multiplexers based on grating-assisted null couplers

The performance of a fully optimized optical add/drop multiplexer (OADM), based on null couplers and tilted Bragg gratings, is studied in detail. It is shown that maximization of the device performance involves three main optimization steps. First, the waveguide asymmetry (V₂ /V₁ ratio) should be optimized in order to minimize the extinction ratio of the unwanted mode at the null coupler waist. Second, the coupler taper shape should he optimized in order to further minimize the aforementioned extinction ratio. Third, the grating tilt angle and relative width can be also optimized to give negligible backreflections at the input port and minimize radiation losses. The results show that the proposed high-performance OADM configuration can meet stringent telecom specifications