Multilevel Spiral Axicon for High-Order Bessel–Gauss Beams Generation

This paper presents an efficient method to generate high-order Bessel–Gauss beams carrying orbital angular momentum (OAM) by using a thin and compact optical element such as a multilevel spiral axicon. This approach represents an excellent alternative for diffraction-free OAM beam generation instead of complex methods based on a doublet formed by a physical spiral phase plate and zero-order axicon, phase holograms loaded on spatial light modulators (SLMs), or the interferometric method. Here, we present the fabrication process for axicons with 16 and 32 levels, characterized by high mode conversion efficiency and good transmission for visible light (λ = 633 nm wavelength). The Bessel vortex states generated with the proposed diffractive optical elements (DOEs) can be exploited as a very useful resource for optical and quantum communication in free-space channels or in optical fibers

Quantum communication networks with optical vortices

Quantum communications introduce a paradigm change in internet security by using quantum resources to establish secure keys between parties. Present-day quantum communication networks are mainly point to point and use trusted nodes and key management systems to relay the keys. Future quantum networks, including the quantum internet, will have complex topologies in which groups of users are connected and communicate with each other. Here we investigate several architectures for quantum communication networks. We show that photonic orbital angular momentum (OAM) can be used to route quantum information between different nodes. Starting from a simple point-to-point network, we will gradually develop more complex architectures: point-to-multipoint, fully connected, and entanglement-distribution networks. As a particularly important result, we show that an n-node fully connected network can be constructed with a single OAM sorter and n-1 OAM values. Our results pave the way to construct complex quantum communication networks with minimal resources.</p