Abstract
Harnessing the orbital angular momentum (OAM) of light is an appealing approach to developing photonic technologies for future applications in optical communications and high-dimensional quantum key distribution (QKD) systems. An outstanding challenge to the widespread uptake of the OAM resource is its efficient generation. In this work we design a new device that can directly emit an OAM-carrying light beam from a low-cost semiconductor laser. By fabricating micro-scale spiral phase plates within the aperture of a vertical-cavity surface-emitting laser (VCSEL), the linearly polarized Gaussian beam emitted by the VCSEL is converted into a beam carrying specific OAM modes and their superposition states, with high efficiency and high beam quality. This new approach to OAM generation may be particularly useful in the field of OAM-based optical and quantum communications, especially for short-reach data interconnects and QKD.
Highlights
Optical beams with phase singularities, known as optical vortices, were first discussed by Nye and Berry in 1974 [1], who identified singularities within randomly scattered fields
The fabricated SPPs in the aperture of the vertical-cavity surface-emitting laser (VCSEL) with various orbital angular momentum (OAM) mode orders are pictured in Figs. 2(a1), 2(b1), 2(c1), and 2(d1)
We included this modification to demonstrate that the addition of a dielectric layer on top of the VCSEL had no adverse effect on its operation
Summary
Optical beams with phase singularities, known as optical vortices, were first discussed by Nye and Berry in 1974 [1], who identified singularities within randomly scattered fields. Beams with a well-defined state of OAM have a complex field characterized by exp il φ, where φ is the azimuthal around the optical axis, and l is the topological charge, an integer describing the number of 2π phase changes around the beam axis. Such beams can be created by imposing an azimuthally dependent phase structure onto the beam. Several silicon photonics integrated OAM emitters, which convert planar waveguide modes into free-space OAM modes [10,11,12], have been reported as potential candidates for future communication systems These are significantly more compact and robust than their bulk optics counterparts. Photonic components can be produced, which are highly suitable for OAMbased optical communications systems, and for quantum systems [17,18]
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