Spectral correlations in the random fibre laser

The following article appeared in the news section of the AIPT homepage.

Random fibre lasers were first demonstrated by AIPT researchers in 2010. The feedback mechanism in these lasers had been insofar deemed incoherent. Now, in a work appearing in Nature Communications, researchers from AIPT, Aston University and Novosibirsk State University, Russia, have revealed the existence of long-lived narrowband components and correlations in the random fibre laser’s spectrum.

Experimental configuration for real-time spectral measurement; b. Real-time single-scan random fibre laser spectra; c. Real-time spectral evolution of random fibre laser spectra showing the existence of long-living narrowband spectral components (inset); d. Non-vanishing Mutual Information confirming the existence of nonlinear correlations across the generation spectrum.


The random fibre laser is a relatively new lasing modality pioneered by AIPT researchers, which relies on Rayleigh scattering off randomly distributed refractive index inhomogeneities to derive the laser feedback. The fibre platform provides highly directional and stable lasing, with demonstrated efficiencies comparable to conventional fibre lasers. Since its first demonstration in 2011, the technology of random fibre lasers is now a field of its own standing, helping in the understanding of fundamental nonlinear physics, and also in the realization of real-world applications.

While significant progress has been made in the understanding of the underlying physics of random fibre lasers, there still remains a conundrum. It is known that in conventional random lasers based on strongly scattering systems, multiple scattering events can result in generation of closed loops within the medium that can sustain a coherent feedback. These in turn result in pronounced narrowband spectral peaks in the generation. However, the optical spectra of random fibre lasers have been conventionally reported to be of a smooth nature, a feature that has been commonly attributed to the weak nature of the Rayleigh feedback, and an underlying incoherent feedback mechanism.

Now, in their work appearing in the premier cross-disciplinary journal Nature Communications, Dr. Srikanth Sugavanam and Dr. Mariia Sorokina of AIPT, Aston University, and Dr. Dmitry Churkin from Novosibirsk State University, Russia, have shown the existence of narrowband spectral components in a random fibre laser. Employing a real-time spectral measurement technique based on a scanning Fabry Perot interferometer, they have shown the existence of long-living narrowband spectral components in the random fibre laser spectrum. Furthermore, using advanced nonlinear time series analysis originally developed for optical communication, they further confirm the existence of correlations between the different spectral components generated by the laser.

The existence of such narrowband spectral components, together with their observed correlations, establishes a long-missing parallel between the fields of random fibre lasers and conventional random lasers. The results show the potential of realizing narrowband lasing using only intrinsic characteristics of the fibre, doing away the need for specialized spectral filtering elements. The occurrence of such narrowband components also calls in for the re-examination of the underlying nature of generation in the random fibre laser. Furthermore, the simple experimental techniques developed in this work complement existing real-time spectral measurement methodologies, and can be used beyond lasers for a wide variety of light sources.

A better understanding of the nature of underlying correlations, facilitated using real-time methodologies as above, can have profound implications in the intelligent design of random fibre lasers geared towards applications, increasing their versatility even further.

Read more at – http://rdcu.be/s2uz