en.Wedoany.com Reported - A Russian research team has developed a computer model that demonstrates the operating mechanism of multicore fiber lasers and reveals how to achieve a narrower, more stable spectrum. The calculations show that when optical waveguides are closely packed and light flows freely between them, multiple spectral lines merge into one, with the linewidth narrowing nearly tenfold compared to when the waveguides are separated.
Fiber lasers consist of thin glass fibers with cores through which light propagates. Such devices are commonly used for metal cutting and welding, medical instruments, and data transmission systems. To increase power, it is usually necessary to raise the pump power and enlarge the core, but this approach can cause undesirable effects such as beam filamentation and self-focusing, potentially leading to fiber damage.
Multicore fibers, composed of multiple optical waveguides, can achieve higher power. Each core contains a Bragg grating that reflects light at a specific wavelength and enhances its intensity. However, due to slight differences between the gratings, these waveguides operate inconsistently, resulting in a broadened and unstable spectrum that is difficult to focus.
Previously, researchers from the Institute of Automation and Electrometry SB RAS and Novosibirsk State University discovered the spectral "collapse" effect: when cores are closely packed, light begins to transfer between them, and multiple spectral lines become a single narrow line. However, a model explaining and controlling this process was lacking.
In the new study, the scientists constructed a model that accounts for fiber inhomogeneities, noise, nonlinear effects, and Bragg grating parameters. The researchers compared two scenarios: in the first, the optical waveguides were spaced 28 micrometers apart, with weak coupling and no light transfer between cores; in the second, the spacing was reduced to 17 micrometers, enhancing coupling.
In the first scenario, the model showed seven independent spectral lines with a total spectral width between 0.3 and 0.7 nanometers. In the second scenario, the lines merged into one, with a width of approximately 0.07 nanometers. These data are consistent with experimental results. The effect arises from the free transfer of light when cores are closely packed, causing all optical waveguides to emit at the same wavelength; the more cores, the stronger the coupling, and the narrower and more stable the spectrum.
Project leader Sergey Babin, Doctor of Physical and Mathematical Sciences, Academician of the Russian Academy of Sciences, and Director of the Institute of Automation and Electrometry SB RAS, noted that such lasers could be used for precision material processing, fiber-optic communications, medicine, and spectroscopy. According to Sergey Babin, increasing the number of cores to 19 could yield an even narrower spectral line. He stated that future plans include new calculations and experiments, as well as discussions with industrial partners on applications. The research was supported by the Russian Science Foundation, and the results were published in the journal High Power Laser Science & Engineering.
