Operating regimes and optical bistability in InGaAs/InGaAsP and GaAs/AlGaAs ring lasers

It has recently been found that the coexistence of the two counterpropagating modes in the laser cavity may affect the optical stability and lead to a large variety of operating regimes. In this work we report on the ring cavity mode behaviour in ridge-waveguide semiconductor lasers fabricated on GaAs/AlGaAs and InGaAs/InGaAsP material systems. Investigation on the unidirectional operating regime has shown a drastic improvement in the device performance and frequency stability with respect to bidirectional operation. In addition, we found that a semiconductor ring laser (SRL) operating in the unidirectional regime behaves as an optical bistable device between the two counterpropagating modes.