When one thinks of a laser, the picture that comes to mind is one of an optical resonator encapsulating a gain medium. The optical resonator forms an important part of the laser, which provides the spectrally filtered feedback necessary for the onset of lasing, and often employs active stabilization procedures for optimal operation. In contrast, in a random laser1, the feedback is generated via multiple scatterers interdispersed with gain media, distributed randomly over space and/or time. The relative simplicity of the realization of such lasers holds tremendous potential for practical applications, particularly if the disorder is of natural origin (e.g., one arising from a self-organization process), and does not need to be prefabricated.
The random fibre laser2 is an addition to this growing family. Randomly distributed refractive index inhomogeneities throughout the length of the fiber give rise to scattering, whence a fraction of the scattered light is recaptured and amplified, giving rise to the necessary feedback process. Conventional optical fiber is used as a transport medium, while the gain is established via stimulated Raman scattering (SRS). Such a system intrinsically provides directionality, thus making it a viable solution for commonplace laser applications. The science and technology of long-cavity random fibre lasers are both developing at a very fast rate since the concept was introduced in 2010, resulting in a range of practically important devices, ranging from distributed sensing to optical communications3. Despite rather nontrivial science underlying its operation, a random DFB fiber laser is not a complex and sophisticated engineering system—just the opposite. The combination of relative simplicity of implementation with very good laser performance is the key to the popularity of such devices and the growing number of applications.