  Anderson localization is a regime in which diffusion is inhibited and waves
(also electromagnetic waves) get localized. Here we exploit adaptive optics to
achieve focusing in disordered optical fibers in the Anderson regime. By
wavefront shaping and optimization, we observe the generation of a propagation
invariant beam, where light is trapped transversally by disorder, and show that
Anderson localizations can be also excited by extended speckled beams. We
demonstrate that disordered fibers allow a more efficient focusing action with
respect to standard fibers in a way independent of their length, because of the
propagation invariant features and cooperative action of transverse
localizations.
