Abstract
Vortex beam is believed to be an effective way to extend communication capacity, but available efforts suffer from the issues of complex configurations, fixed operation mode as well as low efficiency. Here, we propose a general strategy to design dual-modes vortex beam generator by using metasurfaces with polarization-dependent transmission and reflection properties. Combining the focusing and vortex functionalities, we design/fabricate a type of compact dual-modes vortex beam generator operating at both reflection/transmission sides of the system. Experimental results demonstrate that the designed metadevice can switch freely and independently between the reflective vortex with topological charge m1 = 2 and transmissive vortex with m2 = 1. Moreover, the metadevice exhibits very high efficiencies of 91% and 85% for the reflective and transmissive case respectively. Our findings open a door for multifunctional metadevices with high performances, which indicate wide applications in modern integration-optics and wireless communication systems.
Highlights
Orbital angular momentum (OAM) vortex beam is very essential in modern science and technology, since it is an effective way to extend the communication capacity without increasing the bandwidth[1,2,3]
Vortex beams has been generated by spiral phase plates[12,13], holograms[14], spiral reflectors as well as antenna arrays[15,16]
These devices suffer from complex configurations, large structure size, single functionality and low efficiency
Summary
The proposed meta-atom is very suitable to achieve bifunctional metadevices working at both reflection and transmission sides of the metasurfaces. Referring to the measured Re(Ex) and phase distributions at xoy plane (30 cm behind the sample) shown in Fig. 4(c) and (d), we can see clearly that pure vortex beams with m1 = 2 are generated by integrating x-polarized waves reflected by meta-atoms at different positions. Compared with the reported multi-modes vortex beam generators[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16], our design exhibits very high working efficiencies since the interferences among different modes are reduced based on the polarization-dependent property of the metadevice.
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