Y-branch waveguide structures are fundamental elements of integrated optics devices such as power or optical splitters, power or optical combiners, integrated-optic gyroscopes, Mach-Zehnder modulators/interferometers etc. Beam propagation method can be used to simulate the behavior of the optical beam in say a nonlinear crystal. I would like to design the geometry of Y-junction using comsol multiphysics 4.3 (does not contain any in model library) or define the waveguide and S-shape using matlab. I will appreciate any advise on either of the approaches, links or codes.