A waveguide directional coupler with a nonlinear coupling medium

An all-optical switch using a waveguide directional coupler with a nonlinear coupling medium is shown. At low input power, it performs as a linear directional coupler; but at higher input powers, the coupling length increases, thus reducing coupling. For coupling lengths near multiples of the linear coupling length, switching can occur from a crossed-over state at low power to a straight-through condition at higher input power. A theoretical analysis which describes the behavior is developed. A nonlinear coupler was fabricated which exhibited switching at 45.6 meV below the exciton resonance with a critical intensity of 3*10/sup 4/ W/cm/sup 2/. Modeling of the device shows that n/sub 2/=1.88*10/sup -8/ cm/sup 2//W and alpha =12.9 cm/sup -1/.>