Based on the optical fiber mode theory and employing the expertized software COMSOL,we study the effect of ellipticity and misalignment on the effective refractive indices,walk-off and intensity distribution of the ev...Based on the optical fiber mode theory and employing the expertized software COMSOL,we study the effect of ellipticity and misalignment on the effective refractive indices,walk-off and intensity distribution of the even and odd eigenmodes that form the basis of the orbital angular momentum(OAM)modes in a ring fiber.Our results show that the effective refractive index difference and the walk-off increase with the ellipticity and misalignment,thus reducing the stability of the OAM modes.We find that the misalignment has a greater impact on the OAM modes than the ellipticity,and both the misalignment and ellipticity affect the lower-order OAM modes more significantly,suggesting that the higher-order OAM modes are more stable during propagation.展开更多
A systematic study of the aperture efficiency and mode constituent for orbital angular momentum(OAM) vortex beam generated by digital metasurface is presented. The aperture efficiency and OAM spectrum are computed for...A systematic study of the aperture efficiency and mode constituent for orbital angular momentum(OAM) vortex beam generated by digital metasurface is presented. The aperture efficiency and OAM spectrum are computed for different bit numbers. It is found that the aperture efficiency declines for digital metasurface due to the phase quantization error,especially for 1-bit device. Fortunately, the OAM spectrum is barely affected by phase quantization and the designated main mode keeps dominant for different bit numbers, indicating that high purity OAM vortex beam can be generated by digital metasurface. Besides, the influence of topological charge l is also investigated. For a fixed metasurface, the radiation performance deteriorates sharply with the growing of l and the parasitic OAM mode becomes dominant at certain angle.At last, a prototype of 1-bit metasurface was simulated, fabricated and measured in anechoic chamber. The simulation and experiment results verify the correctness of the numerical analysis.展开更多
Orbital Angular Momentum(OAM)waves are characterized by helical wave fronts and orthogonality between different modes.Therefore,OAM waves have huge potential in improving wireless communications'channel capacity a...Orbital Angular Momentum(OAM)waves are characterized by helical wave fronts and orthogonality between different modes.Therefore,OAM waves have huge potential in improving wireless communications'channel capacity and radar imaging's resolution.Consequently,the generation and application of OAM waves have attracted a lot of attention.And many methods are proposed to generate OAM waves.Although antenna array is the most popular method of generating OAM waves,OAM waves generated by antenna array have redundant modes.However,all advantages of OAM waves are closely related to infinite OAM modes.Thus,to better apply OAM waves to wireless communications and radar,it is very important to reduce unnecessary OAM modes and improve the OAM mode purity.In order to improve the OAM mode purity,two combined antenna arrays composed of X direction antenna and Y direction antenna array are proposed in this paper.The X direction antenna array and the Y direction antenna array are supplied by the excitations with the same amplitude and fixed phase shift.The overall phase shift of the X direction antenna array isπ/2 more or less than that of the Y direction antenna array.The results of formulas and antenna models in CST show that the combined antenna arrays can generate OAM waves with less redundant modes in x component,y component and z component.Besides,the z component carries pure OAM modes.展开更多
The analytic formulae of probability distribution of spiral plane modes for the Whittaker-Gaussian （WG） beams with orbital angular momentum （OAM） in strong turbulence regime are modeled based on the modified Rytov...The analytic formulae of probability distribution of spiral plane modes for the Whittaker-Gaussian （WG） beams with orbital angular momentum （OAM） in strong turbulence regime are modeled based on the modified Rytov approximation. Numerical results show that the erosstalk range of OAM modes in the vicinity of signal mode increases with the increasing refractive-index construction parameter. However, effects of change of the width of the Gaussian envelope and the parameter Wo of WG beams on normalization energy weight of signal mode can be ignored. We find theoretically that signal spiral plane mode of WG beams at each OAM level approximatively has the same normalization energy weight, implying that the channels with WG （pseudo non-diffraction） beam have higher channel capacity than the channels with the Laguerre-Gaussian beam.展开更多
基金supported by the National Natural Science Foundation of China(No.61501214)
文摘Based on the optical fiber mode theory and employing the expertized software COMSOL,we study the effect of ellipticity and misalignment on the effective refractive indices,walk-off and intensity distribution of the even and odd eigenmodes that form the basis of the orbital angular momentum(OAM)modes in a ring fiber.Our results show that the effective refractive index difference and the walk-off increase with the ellipticity and misalignment,thus reducing the stability of the OAM modes.We find that the misalignment has a greater impact on the OAM modes than the ellipticity,and both the misalignment and ellipticity affect the lower-order OAM modes more significantly,suggesting that the higher-order OAM modes are more stable during propagation.
文摘A systematic study of the aperture efficiency and mode constituent for orbital angular momentum(OAM) vortex beam generated by digital metasurface is presented. The aperture efficiency and OAM spectrum are computed for different bit numbers. It is found that the aperture efficiency declines for digital metasurface due to the phase quantization error,especially for 1-bit device. Fortunately, the OAM spectrum is barely affected by phase quantization and the designated main mode keeps dominant for different bit numbers, indicating that high purity OAM vortex beam can be generated by digital metasurface. Besides, the influence of topological charge l is also investigated. For a fixed metasurface, the radiation performance deteriorates sharply with the growing of l and the parasitic OAM mode becomes dominant at certain angle.At last, a prototype of 1-bit metasurface was simulated, fabricated and measured in anechoic chamber. The simulation and experiment results verify the correctness of the numerical analysis.
基金supported by the National Science Foundation of China(NSFC 62073334).
文摘Orbital Angular Momentum(OAM)waves are characterized by helical wave fronts and orthogonality between different modes.Therefore,OAM waves have huge potential in improving wireless communications'channel capacity and radar imaging's resolution.Consequently,the generation and application of OAM waves have attracted a lot of attention.And many methods are proposed to generate OAM waves.Although antenna array is the most popular method of generating OAM waves,OAM waves generated by antenna array have redundant modes.However,all advantages of OAM waves are closely related to infinite OAM modes.Thus,to better apply OAM waves to wireless communications and radar,it is very important to reduce unnecessary OAM modes and improve the OAM mode purity.In order to improve the OAM mode purity,two combined antenna arrays composed of X direction antenna and Y direction antenna array are proposed in this paper.The X direction antenna array and the Y direction antenna array are supplied by the excitations with the same amplitude and fixed phase shift.The overall phase shift of the X direction antenna array isπ/2 more or less than that of the Y direction antenna array.The results of formulas and antenna models in CST show that the combined antenna arrays can generate OAM waves with less redundant modes in x component,y component and z component.Besides,the z component carries pure OAM modes.
基金Supported by the Fundamental Research Funds for the Central Universities under Grant No JUSRP51517the Graduate Student Research Innovation Project of Jiangsu-Province General University under Grant No KYLX15_1187
文摘The analytic formulae of probability distribution of spiral plane modes for the Whittaker-Gaussian （WG） beams with orbital angular momentum （OAM） in strong turbulence regime are modeled based on the modified Rytov approximation. Numerical results show that the erosstalk range of OAM modes in the vicinity of signal mode increases with the increasing refractive-index construction parameter. However, effects of change of the width of the Gaussian envelope and the parameter Wo of WG beams on normalization energy weight of signal mode can be ignored. We find theoretically that signal spiral plane mode of WG beams at each OAM level approximatively has the same normalization energy weight, implying that the channels with WG （pseudo non-diffraction） beam have higher channel capacity than the channels with the Laguerre-Gaussian beam.
