Transverse localization of light in laser written designed disorder

Transverse Anderson localization provides the lateral confinement of electromagnetic waves in disordered systems that are invariant along the propagation direction. Here, we demonstrate a disorder induced confinement in glass microstructures where disorder is fabricated ad hoc by the femtosecond direct laser writing technique. By employing a high numerical aperture objective, we are able to write parallel arrays of tiny tubes with a refractive index higher than the surrounding glass and to arrange them in a disordered fashion in the transversal plane. We demonstrate that these paraxial scatterers are supporting transverse localization and that the confinement strength depends on the disorder properties. The proposed approach, which relies on a user-controlled positioning of individual scatterers, allows us to finely tune the structural design, maximizing the transversal confinement.