Directional coupler switches with optical gain

We discuss the design and characteristics of directional coupler switches in semiconductor materials (GaAs/GaAlAs) which exhibit optical gain by laser action. Equal gain in the bar and cross states is achieved by carrier-induced changes in the real as the well as the imaginary parts of the refractive index in directional coupler structures. Conditions for equal gain and crosstalk, design tradeoffs, and saturation characteristics in terms of amplified spontaneous emission in relation to saturation power are briefly discussed.