Boosting the output power of lasers by breaking their symmetry
Nov. 11, 2021
More uniform light intensity profiles are possible in large-aperture semiconductor lasers if the optical aperture is intentionally deformed. An international team from Łodz University of Technology, Institute of Microelectronics and Photonics in Warsaw, Technical University of Berlin, and IFISC (UIB-CSIC) present these findings in Optica [1]. Moreover, the research has been highlighted in the ‘News and Views’ section in the November issue of the prestigious journal Nature Photonics [2].
Since lasers were invented, there have been continual efforts to increase their emitted optical power. In general, such efforts have been focused on increasing the size of the region in which stimulated emission occurs or increasing the efficiency of photon generation in that region. Here, the researchers show that intentionally deformed optical apertures induce a spatially more uniform light intensity distribution of broad-area vertical-cavity surface-enhanced lasers (VCSEL) and a higher density of optical states. This, in turn, enhances the stimulated emission of photons as predicted by quantum electrodynamics theory.
To demonstrate this, they first proposed four classes of VCSEL, each with different oxide apertures of symmetry-broken shapes that slightly increase the aperture area. They named the shapes according to the resemblance of the resulting beam profiles with racket shapes used in sports: ball, ping-pong, padel, squash, and tennis, each one with differing side deformations. These deformations break the symmetry of the circular shape aperture leaving only one mirror symmetry.
As a consequence, the light density is more uniformly distributed, and the optical modes experience less gain competition, increasing the probability of stimulated emission and, because of that, the number of electrons recombining per unit of time is also increased. This overall process reduces the heating of the lasers, and a higher maximal emitted optical power is obtained. Although the aperture area was only 6% larger, the team achieved an increase in output power up to 60% and in quantum efficiency of 10%. To cite the authors from the paper: “Our asymmetric ‘ugly ducklings’ become ‘beautiful swans’ shining much more brightly.”
The researchers claim that the possibility of boosting the emitted power by symmetry breaking may apply to other high-power lasers in which circular apertures are commonly used, such as broad-area edge-emitting lasers, solid-state lasers, multimode-fiber lasers, and amplifiers. Future works will focus on determining the optimal oxide aperture shapes expected to enhance the emitted power by design.
[1] A. Brejnak, M. Gębski, A. K. Sokół, M. Marciniak, M. Wasiak, J. Muszalski, J. A. Lott, I. Fischer, and T. Czyszanowski, "Boosting the output power of large-aperture lasers by breaking their circular symmetry," Optica 8, 1167-1175 (2021). https://doi.org/10.1364/OPTICA.421753
[2] O. Graydon, “Asymmetry brings power boost,” Nature Photon. 15, 795 (2021). https://doi.org/10.1038/s41566-021-00899-4
