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 beam propagation method (FD-BPM). Due to interference of the guided mode with quasiguided modes generated at distortions of the waveguide the splitting ratio depends on the wavelength and design parameters of the Y-branch. The simulations show how variations of the splitting ratio can be minimized using a mode-filter in the input section without significant increase of losses or component size.