Operating regimes of gaas-algaas semiconductor ring lasers: experiment and model

Abstract

Theory and experiments of single-mode ridge waveguide GaAs-AlGaAs semiconductor ring lasers are presented. The lasers are found to operate bidirectionally up to twice the threshold, where unidirectional operation starts. Bidirectional operation reveals that just above threshold, the lasers operate in a regime where the two counterpropagating modes are continuous wave. As the injected current is increased, a new regime appears where the intensities of the two counterpropagating modes undergo alternate sinusoidal oscillations with frequency in the tens of megahertz range. The regime with alternate oscillations was previously observed in ring lasers of the gas and dye type, and it is here reported and investigated in semiconductor ring lasers. A theoretical model based on a mean field approach for the two counterpropagating modes is proposed to study the semiconductor ring laser dynamics. Numerical results are in agreement with the regime sequence experimentally observed when the injected current is increased (i.e., bidirectional continuous-wave, bidirectional with alternate oscillations, unidirectional). The boundaries of the different regimes are studied as a function of the relevant parameters, which turn out to be the pump current and the conservative and dissipative scattering coefficients, responsible for an explicit linear coupling between the two counterpropagating field modes. By a fitting procedure, we obtain good numerical agreement between experiment and theory, and also an estimation for the otherwise unknown scattering parameters.

Optical injection in semiconductor ring lasers: backfire dynamics

“…Therefore, longitudinal variations of the carrier density will be washed out by the diffusion. As a result, the dynamics of such a carrier grating can be neglected [2,11,12]. However, a linear coupling between the two counter-propagating modes does exist.…”

“…Semiconductor Ring Lasers (SRLs) are currently the subject of many experimental and theoretical investigations, ranging from fundamental studies of its nonlinear dynamical behavior to multiple practical applications [1,2,3,4,5]. In particular, SRLs attract a lot of attention due to their bistability, providing the possibility of operation in either of the two counter-propagating directions.…”

“…In particular, SRLs attract a lot of attention due to their bistability, providing the possibility of operation in either of the two counter-propagating directions. Bistability has been demonstrated [1,2,3], and recently exploited for the realisation of all-optical flip-flops [5].…”

Semiconductor snail lasers

“…Moreover, the LI curves show no evidence of the directional switching that occurs in SRLs ͑see inset for a comparison͒. 4 Directional switching could be observed only for the 40% coupled snail laser for reverse bias Ͻ−2 V on the tail contact, suggesting that as r 3 → r 2 , the laser is no longer forced to operate unidirectionally in the CCW direction.…”

“…The symmetric nature of the coupling in SRLs can produce bidirectional or ͑fluctuating͒ bistable directional lasing of the device. 4 Bistable unidirectionality relies on minimizing reflections within the laser cavity, which, by coupling energy between counter-propagating modes leads to bidirectional emission. So, the necessity for high output coupling for increased quantum efficiency of SRLs also results in increased feedback into the laser cavity and hence, bidirectional lasing.…”