Multiplexing Vortex Beams using Miniaturized 3D-printed Optical Phase Elements

Optical vortex beams are characterized by a helical wavefront. Their azimuthal phase dependence is exp(ilf), where l, the topological charge, is an integer and f is the transverse azimuthal angle. These beams can carry orbital angular momentum (OAM) of lħ per photon, where ħ is the reduced Planck constant. Optical vortex beams can be used as carriers of information in optical communication and quantum optics applications. Owing to their spatial orthogonality, these beams can be multiplexed and demultiplexed on the same physical channel thereby increasing information capacity of an optical communication channel. However, up till now, OAM demultiplexing was primarily achieved by bulky and large devices such as spatial light modulators and diamond turned-mode convertors. Moreover, it is difficult to integrate these bulky devices directly into optical systems, e.g. at the tip of the optical fiber, or at the exit facets of lasers, lenses, or nonlinear optical crystals. Recently, we have demonstrated a new approach to fabricate miniature vortex mode-sorters, based on three-dimensional laser printing, thereby enabling direct integration into optical systems. These devices can handle both pure and mixed vortex beams with various topological charges. Hence, it is very advantageous to try integrating such mode sorters directly on optical fibers. Single mode fibers are insufficient, and standard few mode fibers do not support OAM states. In light of this, we demonstrate a further extent and development of the capabilities for multiplexing vortex beams in specially designed vortex fibers that support various OAM states. This research may lead into new and exciting optical OAM based communication systems.