Novel Designs Of Orbital Angular Momentum Generation Based On Metasurfaces

In this rapidly developing modern society,the wide application of wireless communication apparatus has tremendously enlarged the demands for high-capacity communication,which the limited resources of spectrum cannot meet.Studies have discovered that vortex beams with different orbital angular momentum(OAM)mode numbers are orthogonal to each other.Thus,vortex beams could simultaneously transmit multiple signals at the same carrier frequencies.Vortex beams with OAM are capable to enhance the capacity of communication systems and deal with the problem of channel resources in the field of wireless communication.Since the concept of metasurfaces is proposed,it has become a novel method to manipulate electromagnetic waves.Metasurfaces have advantages,such as low profiles,high gain,conformal designs and low cost,which make metasurfaces easier to be integrated into optical systems rather than traditional devices.In this work,metasurfaces are employed to realize high-efficiency OAM generation.Three different prototypes are proposed for ultra-wideband,multi-mode and multi-frequency applications,respectively.The work of this dissertation is listed as follows:1.An ultra-wideband high-efficiency electromagnetic metasurface is designed.Metasurfaces proposed for orbital angular momentum generation are generally difficult to achieve a good balance between ultra-wideband and high efficiency.However,the fractal design concept is used in this work to design a metasurface that can generate orbital angular momentum for circularly polarized incident waves.The fractional working bandwidth of the metasurface reaches 107%,and the working efficiency can be maintained above 0.9.In this work,a one-dimensional deflector array,a dual-focus orbital angular momentum generating array with the number of modes 1 and-1,and a circularly polarized orbital angular momentum generating array with the number of modes 1 are proposed.These arrays were verified by numerical simulation.Among them,the circularly polarized orbital angular momentum generation array with the mode number of 1 has been processed and experimented.2.A broadband high-efficiency electromagnetic metasurface that can be used for polarization multiplexing is designed.The fractional working bandwidth of the metasurface can reach 86.37%,and the working efficiency can be maintained above0.8.The main feature of the metasurface unitcell is that different polarization manipulation can be achieved for left-hand circularly polarized(LHCP)electromagnetic waves and right-hand circularly polarized(RHCP)electromagnetic waves.Based on the meta-atom,a dual-mode OAM array was constructed and verified by both simulation and experiment.3.A high-efficiency electromagnetic metasurface with dual-frequency operation is designed.The metasurface unit can realize independent phase compensation and regulation at two frequency points of 6.5 GHz and 12 GHz,and the working efficiency can exceed 0.85.Based on the meta-atom,this paper designs a dual-frequency OAM array.Python numerical calculation and full-wave simulation verification are both carried out.