ABSTRACT
When a three-dimensional optical waveguide branches into two, or two optical waveguides are merged into one, loss and mode conversion occurs according to certain laws. The analytical method for the merging and branching of optical waveguides differs for the multimode waveguides and the single-mode waveguides. If an optical waveguide bends in its propagation direction, bending loss and a change in the propagation constant will occur. In the guided mode of the optical waveguide except for optical fibers that have the axial symmetry, there are two polarization modes of which electric field is nearly parallel and nearly perpendicular to the substrate surface and their propagation constants are different. In an optical waveguide, the electromagnetic field distribution of the Transverse electric (TE) mode and the Transverse magnetic (TM) mode polarizations slightly differs, so for simplicity, the polarization in a plane wave will be discussed first.
