IMPROVED COUPLED-MODE THEORY FOR PARALLEL ELECTRON WAVE-GUIDES

A coupled-mode theory for parallel electron waveguide structures is developed and presented. This theory takes the nonorthogonality between the modes belonging to different electron waveguides, which is neglected in the first-order theory, into consideration and reflects this fact by including the modal overlap integral terms in the resultant coupled-mode equations. Various numerical examples are presented, using this improved theory and the first-order theory, and are compared with those of the exact calculations. It is shown that the improved theory can give more accurate results than the conventional first-order theory. Therefore, it is very useful for analyzing the quantum field-effect directional couplers and similar quantum interference devices.