Improved techniques for the design of planar multimode lightwave circuits

Planar multimode waveguide devices have been widely used in communication applications as they often have advantages over earlier fibre devices in terms of size, ease of fabrication and robustness The design of planar guided wave devices usually starts with the solution of Maxwell´s equations via finite element or finite difference numerical techniques. Numerous commercial software packages are available that can analyse a range of planar waveguide geometries. However by their nature, such programs may conceal from the user the full design space in which the object parameters may be refined. Designers usually resort to repeated numerical simulations in their search of the design space. This approach is usually computationally intensive, time consuming and may miss global minima. This paper outlines a different approach based on a survey of alternative device designs using analytical approximation for weakly guided multimode waveguides. Such analytical approximations provide deeper insight and can lead to useful design formulae and efficient designs.