Hysteresis and high quantum efficiency have been observed in the light-output/injection-current characteristics of a twin-diode external cavity ring laser. The diodes are GaAs/GaAlAs double heterostructure, 20 µm oxide stripe devices, AR coated and symmetrically placed in the ring. Under certain conditions the output in the bistable region became unstable, and slow, regular oscillations were observed. With increasing drive, this oscillatory behaviour became more irregular and eventually degenerated to chaos. We propose nonlinear effective self-focusing by the mutual action of the counterpropagating beams, in the ring laser as a possible mechanism to explain the effects observed.
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Mclnerney et al. (1985) studied this question.