Design of an integrated optical add-drop multiplexer with low cross-talk and low back-reflection

Abstract

The design of an integrated optical add-drop multiplexer (OADM), using an adiabatic transition and a symmetric coupler with a superimposed slanted grating, is presented. Through optimization of the shape function of the adiabatic transition, extinction ratio is kept high at both the symmetric coupler and the end of the adiabatic transition. By increasing the separation between the two waveguides of the symmetric coupler, the resultant similarity of the square distributions of the two eigenmodes ensures that the two self-coupling coefficients can reach zero simultaneously with the cross-coupling coefficient being near maximum. Therefore, the design has low cross-talk and low back-reflection at the input and add ports. The simulations show that the back-reflection at both ports can be kept below −43 dB and the cross-talk below −33 dB, and the process tolerances are acceptable, which are critical to mass production.