All-optical two-mode switching in semiconductor ring lasers

We have theoretically investigated the bifurcation scenario that leads to the emergence of a bistable regime in a two-mode model for a Semiconductor Ring Laser. The bistability takes place between two quasi-unidirectional solutions for the electric field, which are selected as stable solutions via gain-crossaturation, for well-above threshold operating conditions. Furthermore, we analyzed the switching properties of a single Semiconductor Ring Laser (SRL) operating in the bistable regime, under coherent optical pulse injection, in view of the possible implementation of a single SRL an optically adressable memory element. The result is that the response time and the minimum switching energy respectively attain values the order of a few tenth of ps, and 1 fJ. Those values are espected to scale down with the device radius, due to the consequent decreasing of the cavity flight time. We have observed that the fast switching dynamic is due to an energy redistribution process between the two counterpropagating modes, that does not involve the (slow) carrier density through field-medium energy exchange processes. This allows to attain time scales much faster than the typical limit represented by the inverse of relaxation oscillation frequency.