Junction problem and loading effects in grating-assisted couplers

Power transfer in grating-assisted couplers is governed by the excitation of the Floquet modes. This excitation not only is determined by the grating period but is also related to the amplitudes and phases of the uniform normal modes incident upon the grating as well as to the initial phase angle of the corrugation. The details of the junction are thus essential to the description of power flow. Under many practical circumstances it will be necessary to detune the grating period away the from the conventional phase-matching value to maximize coupled power. Higher-order effects that modify the uniform propagation constants, known as loading, are also considered. Coupled-mode theory is used to predict these features, including a simple expression for the detuning that maximizes power transfer.