宽带电磁涡旋的设计和实现
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摘要
提出了基于反射型电介质超表面的宽带电磁涡旋波束发生器,它工作在53～70 GHz频段范围内,相对带宽达到了27.6%。本设计采用折射率较高的电介质元件位于低折射率基板上。超表面能够引起反射波和入射波之间的偏振转换。通过调整高折射率电介质元件的尺寸,可以在反射波与入射波之间获得从0到2π的相移。电介质元件尺寸的进一步适当调整可以使得不同元件之间的相位差在53～70 GHz的带宽内基本不变,从而提供产生宽带毫米波电磁涡旋的能力。应用偏振转换效率和模式频谱等品质因数来定量评估生成的电磁涡旋波束的质量。还研究了更高阶的电磁涡旋波束发生器。实验结果证明了该结构的有效性。
Generation of broadband electromagnetic vortex beams operating from 53 to 70 GHz,leading to a fractional bandwidth of 27.6%,based on a reflection-type dielectric metasurface is proposed.Resonant dielectric elements with high refractive index located on a substrate with low refractive index are adopted in this design. The metasurface is able to induce polarization conversion between reflected and incident waves. By tuning dimensions of the high-refractive-index dielectric elements,phase shift from 0 to 2π can be obtained between reflected and incident waves. Further appropriate adjustment of the dielectric elements dimensions can render the phase difference between different elements largely unchanged in a broad bandwidth from 53 to 70 GHz,offering the ability of producing broadband millimeter wave electromagnetic vortex. Figure of merit such as polarization conversion efficiency and mode spectrum are applied to quantitatively evaluate the quality of the generated electromagnetic vortex beams. Higher-order electromagnetic vortex beam generators are also investigated. Simulation and experiment results demonstrate the validity of the proposed structure.
Generation of broadband electromagnetic vortex beams operating from 53 to 70 GHz,leading to a fractional bandwidth of 27.6%,based on a reflection-type dielectric metasurface is proposed.Resonant dielectric elements with high refractive index located on a substrate with low refractive index are adopted in this design. The metasurface is able to induce polarization conversion between reflected and incident waves. By tuning dimensions of the high-refractive-index dielectric elements,phase shift from 0 to 2π can be obtained between reflected and incident waves. Further appropriate adjustment of the dielectric elements dimensions can render the phase difference between different elements largely unchanged in a broad bandwidth from 53 to 70 GHz,offering the ability of producing broadband millimeter wave electromagnetic vortex. Figure of merit such as polarization conversion efficiency and mode spectrum are applied to quantitatively evaluate the quality of the generated electromagnetic vortex beams. Higher-order electromagnetic vortex beam generators are also investigated. Simulation and experiment results demonstrate the validity of the proposed structure.
引文
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[2] Yao Y,Liang X,Zhu W,et al. Phase mode analy-sis of radio beams carrying orbital angular momen-tum[J]. IEEE Antennas and Wireless PropagationLetters,2017(16):1127-1130.
[3] Liu B,Cui Y,Li R. A broadband dual-polarizeddual-OAM-mode antenna array for OAM commu-nication[J]. IEEE Antennas and Wireless Propaga-tion Letters,2017(16):744-747.
[4] Devlin R C,Ambrosio A,Rubin N A,et al. Arbi-trary spin-to-orbital angular momentum conver-sion of light[J]. Science,2017,358(6365):896-901.
[5] Yu Y F,Zhu A Y,Paniagua-Domínguez R,et al.High-transmission dielectric metasurface with 2πphase control at visible wavelengths[J].Laser&Photonics Reviews,2015,9(4):412-418.
[6] Chang Z,You B,Wu L S,et al. A reconfigurablegraphene reflectarray for generation of vortex THzwaves[J]. IEEE Antennas and Wireless PropagationLetters,2016(15):1537-1540.
[7] Cheng L,Hong W,Hao Z C. Generation of electro-magnetic waves with arbitrary orbital angular mo-mentum modes[J]. Scientific reports,2014(4):4814-4818.
[8] Liu K,Liu H,Qin Y,et al. Generation of OAMbeams using phased array in the microwave band[J]. IEEE Transactions on Antennas and Propaga-tion,2016,64(9):3850-3857.
[9] Yuan T,Cheng Y,Wang H Q,et al. Generation ofOAM radio beams with modified uniform circulararray antenna[J]. Electronics Letters,2016,52(11):896-898.
[10]Yang H,Cao X,Yang F,et al. A programmablemetasurface with dynamic polarization,scatteringand focusing control[J]. Scientific reports,2016(6):35692-35696.
[11]Spektor G,Kilbane D,Mahro A K,et al. Reveal-ing the subfemtosecond dynamics of orbital angular momentum in nanoplasmonic vortices[J]. Science,2017,355(6330):1187-1191.
[12]Hui X,Zheng S,Hu Y,et al. Ultralow reflectivityspiral phase plate for generation of millimeter-wave OAM beam[J]. IEEE Antennas and WirelessPropagation Letters,2015(14):966-969.
[13]Chen Y,Zheng S,Li Y,et al. A flat-lensed spiralphase plate based on phase-shifting surface forgeneration of millimeter-wave OAM beam[J]. IEEEAntennas and Wireless Propagation Letters,2016(15):1156-1158.
[14]Bai X,Jin R,Liu L,et al. Generation of OAMradio waves with three polarizations using circularhorn antenna array[J]. International Journal ofAntennas and Propagation,2015(2015).
[15]Guo Z G,Yang G M. Radial uniform circularantenna array for dual-mode OAM communication[J]. IEEE Antennas and Wireless PropagationLetters,2017(16):404-407.
[16]Yang Y,Wang W,Moitra P,et al. Dielectric me-ta-reflectarray for broadband linear polarizationconversion and optical vortex generation[J]. Nanoletters,2014,14(3):1394-1399.