Abstract
We theoretically study topological laser operation in a bosonic Harper-Hofstadter model featuring a saturable optical gain. Crucial consequences of the chirality of the lasing edge modes are highlighted, such as a sharp dependence of the lasing threshold on the geometrical shape of the amplifying region and the possibility of ultraslow relaxation times and of convectively unstable regimes. The different unstable regimes are characterized in terms of spatio-temporal structures sustained by noise and a strong amplification of a propagating probe beam is anticipated to occur in between the convective and the absolute (lasing) thresholds. The robustness of topological laser operation against static disorder is assessed.
Highlights
Starting with the pioneering observation of topologically protected chiral edge modes around a time-reversal-breaking two-dimensional photonic crystal [1,2], the last decade has witnessed the explosion of the field of topological photonics
We have reported a theoretical study of a topological laser device based on a bosonic Harper-Hofstadter lattice model with optical gain
Striking consequences of the chirality of the lasing mode have been highlighted: when gain is distributed around the whole edge, lasing can occur in a number of closely spaced modes and relaxation towards the steady-state occurs on a very slow timescale; when gain is restricted to a finite strip, relaxation is fast but the distinction between convective and absolute instabilities causes an increase of the threshold and introduces new amplification regimes
Summary
Starting with the pioneering observation of topologically protected chiral edge modes around a time-reversal-breaking two-dimensional photonic crystal [1,2], the last decade has witnessed the explosion of the field of topological photonics. Soon afterwards, lasing into the one-dimensional chiral edge states of a two-dimensional topological lattice was experimentally realized in suitably designed semiconductor laser devices [30,31] Such topological lasers appear promising to solve a long-standing technological problem in optoelectronics, namely, the realization of large-area devices offering highpower coherent emission [32]: a pioneering theoretical work [33] has pointed out that the topological protection against fabrication defects should make laser operation into topological edge states to remain single mode and to have a high slope efficiency even well above the laser threshold.
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