Abstract
Vortex beams carrying orbital angular momentum have important applications in high dimensional optical information processing, manipulations of tiny particles, super-resolution imaging and so on. Among various optical components, metasurface represents an ideal platform for realizing vortex beams with multiple optical functionalities due to its strong ability in manipulating the phase, polarization and amplitude of light. A metasurface combing the functions of a lens and a vortex beam generator can greatly shrink the size of many optical systems. Here, we alternatively propose a new metasurface design based on the concept of a Fresnel zone plate to generate, focus the vortex beams, and perform on-axis interference between different vortex beams. These functions are experimentally demonstrated through encoding the spiral phase profiles into the odd and even zones of a dielectric metasurface. The proposed vortex beam generation strategy employs the advantages of both the Fresnel zone plate and the metasurface, and may open new routes for high-dimensional optical information processing.
Highlights
In 1992, Allen et al proposed that a Laguerre-Gaussian beam with a helical phasefront exp(il θ) carries orbital angular momentum (OAM) of lħ per photon [1], where l is the topological charge which determines how fast the phase changes along the azimuthal angle θ, ħ is the reduced Planck’s constant
According to the Huygens-Fresnel principle, a typical Fresnel zone plate for focusing qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi light wave consists of concentric rings with radii of rn 1⁄4
The spiral phase zone plate for generating Vortex beam (VB) with specific OAM value can be obtained by introducing extra spiral phase profiles into the even- and odd-numbered zones respectively
Summary
In 1992, Allen et al proposed that a Laguerre-Gaussian beam with a helical phasefront exp(il θ) carries orbital angular momentum (OAM) of lħ per photon [1], where l is the topological charge which determines how fast the phase changes along the azimuthal angle θ, ħ is the reduced Planck’s constant. Conventional devices including spiral phase plates [9], spatial light modulators [10] and so on have been widely used to generate optical VBs, they are usually bulky and limit the miniaturization of corresponding optical systems. To some extent, this constraint can be circumvented by using metasurfaces which are composed of spatially variant subwavelength meta-atoms [11]. Metasurface chips for quantum entanglement states generation and reconstruction [37,38,39], cold atoms generation [40], high dimensional quantum source [41] were experimentally demonstrated
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