PLANAR WAVE-GUIDE ANALYSIS BY THE SPECTRAL INDEX METHOD .2. MULTIPLE LAYERS, OPTICAL GAIN AND LOSS

The most general form of the spectral index method is presented for the analysis of multiple-layered rib and related semiconductor waveguide structures where the ribs have vertical sidewalls and are surrounded by air. The model allows for the presence of loss or gain in any layer and the generalization of the method to such complex problems is described. A detailed account is provided on how to set up the transcendental equation to solve problems for single ribs, and both symmetric and asymmetric couplers. Finally, a polarization filter in the form of an asymmetric coupler with one of its ribs capped with metal is analysed numerically to illustrate the technique for a realistic design problem.