All-Optical Directional Switching of Bistable Semiconductor Ring Lasers

All-optical directional switching of bistable semiconductor ring lasers is studied by numerical simulations of a traveling-wave model. We discuss how the reversal depends on the bias current applied to the laser as well as on the energy, duration, and wavelength of the trigger pulses. For pulse durations longer than the cavity roundtrip time, the reversal occurs smoothly with a transient that exhibits relaxation oscillations, otherwise, the transient is composed of large long-lived spikes that reveal its multimode character. In the former case, the switching speed can be defined like in electronics systems, but not in the latter, which requires an operational definition of the maximum speed based on, e.g., bit-error rate measurements. Our model includes the light extraction sections present in real devices, which allows us to discuss the experimental problems posed by the differences existing between intracavity fields and output fields.