Abstract
Combining topologically protected chiral light transport and laser amplification gives rise to topological lasers, whose operation is immune to fabrication imperfections and defects, uncovering the role of topology in a novel nonlinear non-Hermitian regime. We study a topological laser based on the photonic Haldane model with selective pumping of chiral edge modes described by saturable gain. We investigate elementary excitations around the mean-field steady state and their consequences for the coherence properties. In particular, we show that the hybridization of chiral edge modes gives rise to long-lived elementary excitations, leading to large phase fluctuations in the emitted light field and a decrease in light coherence. In contrast to topologically trivial lasers, the lifetime of elementary excitations is robust against disorder in topological lasers. However, the lifetime depends strongly on the edge-mode dispersion around the lasing frequency. As a result, the lifetime can be reduced by orders of magnitude for lasing of different edge modes, leading to a suppression of phase fluctuations and larger coherence of the emitted light. On the other hand, amplitude fluctuations and the second-order autocorrelation function are moderately increased at the same time.
Highlights
Topological photonics has made rapid strides in the past years [1], investigating effects of gain and loss on the topology of photonic energy bands [2,3,4], topology in synthetic dimensions [5,6,7,8], as well as the interplay of topology and nonlinear optics phenomena [9]
We show that the hybridization of edge modes gives rise to long-lived elementary excitations, which lead to large phase fluctuations and a decreased coherence of the emitted light field
We have demonstrated that long-lived elementary excitations, which emerge due to the hybridization of topological edge modes, lead to large phase fluctuations and a decrease in the coherence of the emitted light field
Summary
Topological photonics has made rapid strides in the past years [1], investigating effects of gain and loss on the topology of photonic energy bands [2,3,4], topology in synthetic dimensions [5,6,7,8], as well as the interplay of topology and nonlinear optics phenomena [9]. The single-mode laser operation is robust against on-site disorder in contrast to topologically trivial laser arrays [17]. We show that the hybridization of edge modes gives rise to long-lived elementary excitations, which lead to large phase fluctuations and a decreased coherence of the emitted light field. For lasing at frequencies that do not lie in the middle of the passive-system band gap, the deviation from a linear dispersion is sufficient to reduce the lifetime of elementary excitations by at least one order of magnitude. This leads to a large suppression of phase fluctuations and an increase in light coherence. Frequencies of the chiral edge modes lie in the topological band gap
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