Abstract
In this paper, one spin-selected vortex metalens composed of silicon nanobricks is designed and numerically investigated at the mid-infrared band, which can produce vortex beams with different topological charges and achieve different spin lights simultaneously. Another type of spin-independent vortex metalens is also designed, which can focus the vortex beams with the same topological charge at the same position for different spin lights, respectively. Both of the two vortex metalenses can achieve high-efficiency focusing for different spin lights. In addition, the spin-to-orbital angular momentum conversion through the vortex metalens is also discussed in detail. Our work facilitates the establishment of high-efficiency spin-related integrated devices, which is significant for the development of vortex optics and spin optics.
Highlights
Metasurfaces are made up of subwavelength scatterers and possess great potential for developing ultrathin optics [1,2,3,4,5,6,7,8]
Different from plane waves, vortex beams possess helical phase fronts characterized by exp(il φ) and orbital angular momentum (OAM) of l }, where l is the topological charge, φ is the azimuthal angle and } is the reduced Planck’s constant
Through multiplexing two opposite polarity vortex metalenses based on the PB phase, the focusing vortex beam with arbitrary topological charge can be produced for two opposite spin lights [44,48]
Summary
Metasurfaces are made up of subwavelength scatterers and possess great potential for developing ultrathin optics [1,2,3,4,5,6,7,8]. Through multiplexing two opposite polarity vortex metalenses based on the PB phase, the focusing vortex beam with arbitrary topological charge can be produced for two opposite spin lights [44,48]. We propose two high-efficiency broadband spin-related vortex metalenses based on silicon nanobricks with high transmission efficiency, the design of which is based on both propagation and geometric phases, whereby each unit plays a positive role under LCP or RCP light incidence. We designed one spin-independent vortex metalens, in which the vortex beams can possess the same topological charge and the same focusing plane for different spin lights. The spin-to-orbital angular momentum conversion through the vortex metalens is discussed These spin-related optical vortex metalenses are significant for communication systems and spin-controlled photonics
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