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Register a new userDynamics at Threshold in Mesoscale Class-B Lasers
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The threshold properties of very small lasers (down to the nanoscale) are a topic of active research in light of continuous progress in nanofabrication. With the help of a simple rate equation model we analyze the intrinsic, macroscopic dynamics of threshold crossing for Class B lasers. We use the deterministic aspects of the basic rate equations to extract some fundamental time constants from an approximate analysis of laser dynamics in the threshold region. Approximate solutions for the population inversion and for the field intensity, up to the point where the latter reaches macroscopic levels, are found and discussed. The resulting timescales characterize the lasers ability to respond to perturbations (external modulation or intrinsic fluctuations in the lasing transition region). Numerical verifications test the accuracy of these solutions and confirm their validity. The predictions are used to interpret experimental results obtained in mesoscale lasers and to speculated about their extension to nanolasers.
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In this article we review recent theoretical and experimental developments on multilongitudinal-mode emission in ring cavity lasers, paying special attention to class B lasers. We consider both homogeneously and inhomogeneously broadened amplifying media as well as the limits of small and large cavity losses (i.e., we treat cases within and outside the uniform field limit approximation). In particular we discuss up to what extent the experimental observations of self-mode locking in erbium-doped fiber lasers carried out in recent years are a manifestation of the Risken-Nummedal-Graham-Haken instability.
With the help of a simple rate equation model, we analyze the intrinsic dynamics of threshold crossing for Class B lasers. A thorough discussion of the characteristics and the limitations of this very commonly employed model, which provides excellent qualitative predictions on the laser behaviour, is offered. Approximate solutions for the population inversion and for the field intensity, up to the point where the latter reaches macroscopic levels, are found and discussed, together with the associated characteristic times. Numerical verifications test the accuracy of these solutions and confirm their validity. A discussion of the implications on threshold dynamics is presented, together with the motivation for focussing on this -- nowadays most common -- class of lasers.
The threshold properties of photonic crystal quantum dot lasers operating in the slow-light regime are investigated experimentally and theoretically. Measurements show that, in contrast to conventional lasers, the threshold gain attains a minimum value for a specific cavity length. The experimental results are explained by an analytical theory for the laser threshold that takes into account the effects of slow-light and random disorder due to unavoidable fabrication imperfections. Longer lasers are found to operate deeper into the slow-light region, leading to a trade-off between slow-light induced reduction of the mirror loss and slow-light enhancement of disorder-induced losses.
Chaos in semiconductor lasers or other optical systems have been intensively studied in past two decades. However, the route from period doubling to chaos is still not sufficiently visible, in particular, in gain-modulated semiconductor lasers. In this article we perform a careful investigation of the route to chaos exhibited by directly modulated semiconductor lasers near the threshold region with various values of modulation frequency and amplitude. Gain nonlinearity is included in the simulation of pulse train generation through gain switching, and a new form of phase space representation is introduced to distinctly display period doubling, tripling, quadrupling and chaos. The irregular behaviour is examined at various modulation frequencies and amplitudes, highlighting the possible route to chaos for very large amplitude modulation in the near-threshold region. The existence of deterministic trajectories below the laser threshold is rendered possible by the presence of the (average component of the) spontaneous emission, a point which has not often been explicitly considered. Furthermore, we report on the existence of a transition between similar attractors characterized by a temporal transient which depends on the amplitude of the modulation driving the pump.
We study laser generation in 1D distributed feedback lasers with amplifying and lossy layers. We show that when the lasing frequency differs from the transition frequencies of the amplifying medium, loss induced lasing may occur due to the broadening of the resonator mode with increasing loss in the absorbing layers. This broadening leads to a shift in the lasing frequency towards the transition frequency. As a result, the cavity mode interaction with the amplifying medium is enhanced, and the lasing threshold is lowered.
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