All‐Dielectric Metasurface for Manipulating the Superpositions of Orbital Angular Momentum via Spin‐Decoupling

Abstract

Vortex beam has attracted much attention for carrying orbital angular momentum (OAM). It has a helical phase structure described by exp (ilθ) and an annular intensity distribution, where l is the topological charge corresponding to the OAM of each photon, and θ is the azimuth angle. [1] Vortex beam is widely used in OAM communications, [2,3] optical tweezers, [4] and quantum information coding. [5,6] In particular, the superposition of OAM states is very significant in metrology, [7,8] quantum science, [6,9] and OAM communications. The superposition of high-order OAM modes can be used for ultra-sensitive angle measurement. [8] In Bose-Einstein condensate, multiple OAM states can also be used to generate arbitrary superpositions of atomic rotation states. [10] Vortex beam carrying OAM has shown promising prospects in increasing the data capacity of communication systems, because multiple orthogonal modes can be transmitted at the same frequency in a single communication channel simultaneously.As we all know, photons carry two different kinds of angular momentums, namely spin angular momentum (SAM) and OAM. [11] The SAM represents the polarization state of light, and the OAM is related to the spatial distribution of light. [1,12] Although mode conversion, [13] holograms, [14] spiral phase plates, [15] and spiral zone plates [16][17][18] can be used to generate vortex beam, they usually do not involve the interaction between SAM and OAM. [19] Different from the above, the geometric phase elements can establish a connection between SAM and OAM, but only two conjugate vortex states can be output. Devlin presented a method realizing arbitrary spin-to-OAM conversion, overcoming this limitation mentioned above. [20] In addition, when the paraxial beam is tightly focused, a strong longitudinal component will be generated in the focal area. [21] It is demonstrated that, in a highly focused system, a circularly polarized beam partly transfers its incident SAM to OAM and a helical phase in the longitudinal component of the electric field can be generated. [22] Due to their potential breakthroughs in optical manipulation, metasurfaces have attracted widespread attention in the scientific community. [23,24] Metasurfaces have been widely used in many applications, such as lenses, [25,26] spin Hall effect, [27] holograms, [28] and vortex generators. [29][30][31][32][33] In order to further Vortex beams, carrying orbital angular momentum (OAM), have plenty of applications ranging from particle manipulation to high-capacity data transmissions. In particular, the superpositions of OAM patterns are significant in classical physics and quantum science. The flexible control of spin angular momentum (SAM) to OAM can provide more freedom for the design of multifunctional devices. Here, a kind of dielectric metasurface is proposed that generates polarization-controllable superpositions of OAM patterns in the terahertz (THz) band, which is achieved by the interleaving of anisotropic and isotropic meta-atoms. The conversions of arbitrary S...

Theoretical Study on Generation of Multidimensional Focused and Vector Vortex Beams via All-Dielectric Spin-Multiplexed Metasurface

“…This novel method greatly expands the application scope of metasurface polarization optics and paves an innovative way to generate high-efficiency, multichannel, and multidimensional FOVs and vector vortex beams. Using a kind of dielectric metasurface composed of staggered arrangements of anisotropic and isotropic meta-atoms, Zheng et al experimentally demonstrated polarization-controllable superpositions of OAM states in the terahertz band by combining the propagation phase and PB phase [40]. Xu et al produced two types of polarization-dependent metasurfaces and successfully presented the terahertz cylinder vector beam and vector Bessel beam [41].…”

Manipulation of polarization conversion and multiplexing via all-silicon phase-modulated metasurfaces

“…Compared with conventional optical devices dependent on phase accumulation, metasurfaces can obtain abrupt phase change within subwavelength thickness by appropriately changing specific parameters, thereby generating various functions [4,5] . Specifically, metasurfaces can generate spatial phase discontinuities over the entire 2π range of a specific frequency, which have manifested that they can be utilized in a flat wave plate [6,7] , hologram imaging [8][9][10] , beam deflectors [11,12] , achromatic focusing lenses [13,14] , spin-orbital angular momentum manipulation [15][16][17][18] , and other fields.…”

“…However, the output waves of PB phase metasurfaces under orthogonal CP waves have inherent correlation. To break this restriction, spin-decoupled metasurfaces combining PB phase with dynamic phase were designed to independently manipulate the output waves under left-handed CP (LCP) and right-handed CP (RCP) incidences [12,18,21,22] . Spin-decoupled metasurfaces have many applications in holography [21] , focusing [18] , and polarization multiplexing [22] .…”

Compact Terahertz Dielectric Folded Metasurface

“…and high-refractive-index dielectric materials have been recently developed to replace plasmonic metasurfaces to remove conductor loss. [27][28][29][30][31][32][33][34][35][36][37] Various optical dielectric metasurface devices have been demonstrated, such as metalenses, [27,28] beam splitters, [29][30][31] polarization converters, [32][33][34] and vortex beam generators. [35][36][37] However, limited progress has been achieved in dielectric metasurfaces in the THz band due to the challenging fabrication processes.…”

“…[27][28][29][30][31][32][33][34][35][36][37] Various optical dielectric metasurface devices have been demonstrated, such as metalenses, [27,28] beam splitters, [29][30][31] polarization converters, [32][33][34] and vortex beam generators. [35][36][37] However, limited progress has been achieved in dielectric metasurfaces in the THz band due to the challenging fabrication processes. Conventional integrated circuits lithography and reactive ion etching (RIE) technologies are typically applied to process thin films a few micrometers thick.…”