Optically monostable operation of a monolithic semiconductor ring laser using external optical injections

The semiconductor ring laser (SRL) is attracting more and more interest as a potential all-optical logic device. Whilst previous operations used electrical modulation to induce switching, for all-optical applications such as all optical switching, regeneration, and optical memory it is necessary to switch using an external optical signal. When operated as a monostable way at 110 mA (just above the threshold of 80 mA) where the device operates in the bidirectional regime, SRL should also be dynamically forced to work in clockwise (CW) and anticlockwise (CCW) directions depending on the external injection directions. In this paper the response characteristics of SRL to external optical pulse injection which fed into SRL by CCW direction and continue-wave injection which fed into SRL by CW direction are investigated. The continue-wave light is used to lock SRL in CW direction and the direction is then changed to CCW by the injection of optical pulse signal. Finally the SRL comes back to CW direction with no external optical pulse signal. Both output directions have highly nonlinear relationship with injection signal power and their responses are highly digital. This operation is also simulated in both directions and the agreement with experiment is very good apart from the injection power scale. This confirms that the SRL power is constant above a certain injection power level in both on and off directions, which can be further verified by future devices with 2 couplers.