Abstract
We present a theoretical study of the temporal and spatial coherence properties of a topological laser device built by including saturable gain on the edge sites of a Harper-Hofstadter lattice for photons. For small enough lattices, the Bogoliubov analysis applies, and the coherence time is almost determined by the total number of photons in the device in agreement with the standard Schawlow-Townes phase diffusion. In larger lattices, looking at the lasing edge mode in the comoving frame of its chiral motion, the spatiotemporal correlations of long-wavelength fluctuations display a Kardar-Parisi-Zhang (KPZ) scaling. Still, at very long times, when the finite size of the device starts to matter, the functional form of the temporal decay of coherence changes from the KPZ stretched exponential to a Schawlow-Townes-like exponential, while the nonlinear dynamics of KPZ fluctuations remains visible as a broadened linewidth as compared to the Bogoliubov-Schawlow-Townes prediction. While we establish the above behaviors also for nontopological 1D laser arrays, the crucial role of topology in protecting the coherence from static disorder is finally highlighted: Our numerical calculations suggest the dramatically reinforced coherence properties of topological lasers compared to corresponding nontopological devices. These results open exciting possibilities for both fundamental studies of nonequilibrium statistical mechanics and concrete applications to laser devices.
2 More- Received 28 February 2020
- Revised 26 August 2020
- Accepted 22 October 2020
DOI:https://doi.org/10.1103/PhysRevX.10.041060
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Lasers are a fundamental tool in modern science that are getting a boost from the burgeoning field of topological photonics, which aims to develop light-carrying materials that are largely impervious to structural imperfections. Recently, researchers developed a topological laser device with promising power efficiency and robustness to fabrication faults. Here, for the first time, we theoretically study the coherence properties of this class of devices and show that the new laser’s coherence can compete with traditional ones and that the device displays improved resilience to the defects of the optical lattice.
In particular, we consider a 2D photonic lattice with a synthetic magnetic field. Lasing is given by the competition of gains and losses along the edge of the system; topology ensures that the lasing mode stays localized on the boundary of the system and propagates in one direction. This propagation suggests mapping the 2D system to a 1D laser, for which phase fluctuations display universal behavior. Using this mapping, we study in detail the ultimate limits to the spectral width of the laser emission, identifying a crossover between the linear and nonlinear regimes in the phase diffusion.
The next steps will entail characterization of topological lasing when the dynamics of the amplifying medium cannot be neglected, as well as the possibility of simulating other theoretical physics models.