Demonstration of optical vortex propagation in on-chip rectangular dielectric waveguides

Summary form only given. Orbital angular momentum (OAM) of light provides an additional degree of freedom for multiplexing the data streams in optical communications, increasing further the channel capacity [1]. Applications of OAM for both classical data transmission [2] and quantum information [3] have been demonstrated. The key step towards robust, suitable for massive production, and cost-efficient OAM-assisted communications is the development of compact, on-chip integrable optical components.In this work we demonstrate propagation of vortex modes, carrying OAM, in rectangular dielectric waveguides, which can be produced with standard photolithography process. We show by numerical simulation that the specific superposition of waveguide eigenmodes form the quasi-degenerate modes carrying light with high purity states of OAM. Fig. 1(a-f) shows the amplitude and phase distributions of the dominant field component of quasi-TE vortex modes with topological charges ℓ = 1, 2 and 3, propagating in the few-mode waveguide with 10μmκ10μm PMMA core (n1 = 1.4794) and pure silica substrate (n2 = 1.444, n3 = 1). Numerical modelling has been performed using Matlab with full vector finite difference modesolver [4] for waveguide eigenmodes determination. We also demonstrate experimentally the propagation of the 1st order OAM mode in a polymer rectangular waveguide (4.5 μm × 4.1 μm core made of Ormosil with n1 = 1.50 at 1550 nm is deposited on silica substrate).