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.

We present a method to find the optimum distribution of scatterers in an edge-lit lightguide plate (LGP) for rendering a uniform distribution of the outcoupled light. We propose a simple mathematical model describing the light propagation in a waveguide with a distribution of scattering elements located on the lower surface of the waveguide. We have found a differential equation giving the distribution of scattering elements leading to a uniform irradiance along the LGP, and we propose a method to determine the value of the outcoupling coefficient of an individual scattering element from the irradiance (or radiance) measurements. We have verified the validity of this model by performing ray tracing simulations on an LGP with the scattering elements distributed according to the solution of the proposed differential equation, and we have found a quantitative agreement between the analytical results and the simulated ones. Also this model has been used to directly calculate the output power of a given embossed LGP.

In this work, the generation of optical vortices in an optical integrated circuit is numerically demonstrated. The optical vortices with topological charge m = ±1 are obtained by the coherent superposition of the first order modes present in a waveguide with a rectangular cross section, where the phase delay between these two propagating modes is Δ = ±π/2. The optical integrated circuit consists of an input waveguide continued with a y-splitter. The left and the right arms of the splitter form two coupling regions K₁ and K₂ with a multimode output waveguide. In each coupling region, the fundamental modes present in the arms of the splitter are selectively coupled into the output waveguide horizontal and vertical first order modes, respectively. We showed by employing the beam propagation method simulations that the fine tuning of the geometrical parameters of the optical circuit makes possible the generation of optical vortices in both transverse electric (TE) and transverse magnetic (TM) modes. Also, we demonstrated that by placing a thermo-optical element on one of the y-splitter arms, it is possible to switch the topological charge of the generated vortex from m = 1 to m = −1.