Design of pair grating in a vertical coupler filter for sidelobe suppression

We propose and test a novel concept for the improvement of sidelobe suppres sion in a grating-assisted codirectional coupler (GACC) optical filter by t he use of pair gratings (PG). This concept adopts a pail-grating unit with an easily controllable variable, s(n), which is the distance between the ed ges of the grating elements. The period of the PG is set to 2 Lambda. The d istance between grating elements controls the coupling strength between the input and the output waveguides as the light signal propagates along the c oupling region. The application of this technique is expected to provide a simple and convenient method to test various types of weighted coupling wit hout the complex side effects due to variation of the effective index or th e propagation constant along the coupling region.