Optical switching in a directional coupler with the aid of a nonlinear phase shift in second harmonic generation

An analytic investigation is made of a nonlinear directional coupler based on second harmonic generation from constant-intensity fundamental-frequency radiation. The parameters of the coupler are found and the intensity of light needed to induce a nonlinear shift of π is calculated. Single-frequency output of a directional coupler favours its use in optical data processing systems.