Control of unidirectional operation in semiconductor ring lasers

We have measured unidirectional laser operation in a semiconductor ring laser, controlled through the biasing of a coupled waveguide cavity. The devices fabricated consist of a circular ridge waveguide 2 /spl mu/m wide formed on InGaAs/InGaAsP and GaAs/AlGaAs material systems. The direction of the dominant mode switches as the laser current is increased, and can also be switched by altering the bias of the coupled guide. The subordinate mode is completely suppressed, spectral measurements indicating that any output is purely spontaneous emission.