Optimal design method of a low-loss broadband Y branch with a multimode waveguide section.

An optimal design method for a low broadband silica-on-silicon Y branc is considered. A multimode waveguide section, which was used earlier to reduce the excess loss, is designed optimally when the light distribution at the end of the multimode waveguide section is matched to the profile of the symmetric supermode for the structure of the two branching waveguides. An optimization method that combines the genetic algorithm and a gradient-based search method is used to obtain the optimal geometrical parameters for the multimode waveguide section as well as the widths for the input and branching waveguides.