Annealed proton-exchanged (APE) LiNbO_3 optical waveguides are currently used in many integrated optic devices. Using the wide angle finite difference beam propagation method (FD-BPM), the influences of waveguides parameters, such as the transition length, the variation of the refractive index and the width of mask opening, on the bend loss of the Y-branch optical waveguides with a cosine-generated S-curve fabricated by APE technology is analyzed and compared with the cosine-generated S bend waveguides. The...