Image Number 5 for United States Patent #5105232.
A quantum field-effect directional coupler is described comprised of two quantum waveguides closely spaced apart with an adjacent gate electrode over the space between waveguides. The coupling of electron probability density between waveguides is controlled by the voltage applied to the gate electrode. The coupler implements a voltage-controlled current switch. Several couplers can be connected to perform multiplex/demultiplexing functions.