Single-mode optical waveguides and directional couplers with rectangular cross section: a simple and accurate method of analysis

A new method for obtaining the propagation characteristics of single-mode optical waveguides with rectangular cross section is presented. The method is based on the scalar variational principle using the cosine-exponential trial field. This form of trial field leads to the definition of equivalent guiding structures consisting of homogeneous slab waveguides, which are then used to obtain, in a very simple way, the vector modes of a rectangular waveguide and the coupling characteristics of directional couplers consisting of two rectangular waveguides. The authors have also included the results of some representative calculations along with the results obtained using other approximate methods and the exact numerical method. A comparison shows that the method is much more accurate than the existing approximate methods, particularly in the region of single-mode operation