A method for optical switching using an optical directional coupler. In a first step, excitation light is supplied to an interaction region of the coupler having input and output ports. The interaction region is doped with an active ion having the capability for optical amplification. In a second step, signal light is inputted to one of the input ports and amplified in the interaction region. In a third step, the signal light is outputted from one of the output ports depending on whether saturation of optical gain takes place or not.