AN IMPROVED SINGLE-MODE Y-BRANCH DESIGN FOR CASCADED 1 2-SPLITTERS/

The power splitting ratio of Y-branches based on step index waveguides has been calculated using three-dimensional (3-D) finite-difference b eam propagation method (FD-BPM). Due to interference of the guided mod e with quasiguided modes generated at distortions of the waveguide the splitting ratio depends on the wavelength and design parameters of th e Y-branch. The simulations show how variations of the splitting ratio can be minimized using a mode-filter in the input section without sig nificant increase of losses or component size.