Return loss reduction of integrated grating-assisted optical add/drop multiplexer by control of the reflective spectrum

Return loss, a key characteristic of the optical add/drop multiplexer (OADM), has become an urgent and challenging problem in the development of the integrated grating-assisted OADM. In this paper, a novel design approach to achieve low-return-loss integrated grating-assisted OADMs is proposed. The reflective spectrum is properly controlled to ensure the backreflection peaks can fall outside the wavelength channel, so that the return loss can be kept low. Meanwhile, it can also be found that the tolerance in fabrication process is enlarged. Simulation on the null-coupler OADM shows that, by employing the proposed method, the return loss at both input- and add-port can drop to lower than -53 dB from -38 and 0 dB, respectively, and be kept below -53 dB even with a tilt angle ranging from 3.2/spl deg/ to 3.5/spl deg/. The application of this method on the design of the symmetric-coupler OADM is also presented.