Huang Hui-Fen, Wang Jian-Yuan
Opt Express. 2023 Oct 9;31(21):34855-34870. doi: 10.1364/OE.503106.
In this study, switchable terahertz (THz) multi-orbital angular momentum (OAM) Bessel beams (BBs) were developed based on a spin-decoupled reflective multifunctional metasurface (MTS). Switchability was achieved by switching the feed between left-hand circular polarization (LCP), right-hand circular polarization (RCP), and linear polarization (LP) incidences. A switchable physical model was established for calculating the beam direction, OAM mode, polarization, and non-diffractive distance of the outgoing BBs. As an example, a spin-decoupled MTS was designed to generate dual BBs under LCP incidence, which was subsequently switched to RCP or LP for switchability. The outgoing BBs could be switched among three types of beams: Type-1 under LCP incidence (LCP, θL = 40°, φL = 0°, lL = 1, dL = 18 cm) and (RCP, θR = -40°, φR = 0°, lR = -1, dR = 20 cm); Type-2 under RCP incidence (RCP, θR = 40°, φR = 0°, lR = 1, dR = 18 cm) and (LCP, θL = -19°, φL = 0°, lL = 3, dL = 16.4 cm); and Type-3 under LP incidence (LP, θ = 40°, φ = 0°, l = 1, d = 18 cm), (RCP, θR = -40°, φR = 0°, lR = -1, dR = 20 cm) and (LCP, θL = -19°, φL = 0°, lL = 3, dL = 16.4 cm). Compared with previous MTSs, the proposed spin-decoupled MTS has the advantages of switchability among BBs, high non-diffractive distance/aperture size ratio of 15, large beam deflection angle of up to 40°, and high BB conversion efficiency of up to 96%. The simulated results were consistent with those calculated using the physical model, thus validating the physical model. The designed switchable BBs have potential THz near-field applications, such as high-capacity near-field wireless communications, wireless power transfer, high-resolution imaging, non-destructive testing, and speed detection of high-speed rotating objects.
在本研究中，基于自旋解耦反射多功能超表面（MTS）开发了可切换太赫兹（THz）多轨道角动量（OAM）贝塞尔光束（BBs）。通过在左旋圆偏振（LCP）、右旋圆偏振（RCP）和线偏振（LP）入射之间切换馈源来实现可切换性。建立了一个可切换物理模型，用于计算出射BBs的光束方向、OAM模式、偏振和无衍射距离。例如，设计了一种自旋解耦MTS，在LCP入射下产生双BBs，随后切换到RCP或LP以实现可切换性。出射BBs可以在三种类型的光束之间切换：LCP入射下的类型1（LCP，θL = 40°，φL = 0°，lL = 1，dL = 18 cm）和（RCP，θR = -40°，φR = 0°，lR = -1，dR = 20 cm）；RCP入射下的类型2（RCP，θR = 40°，φR = 0°，lR = 1，dR = 18 cm）和（LCP，θL = -19°，φL = 0°，lL = 3，dL = 16.4 cm）；以及LP入射下的类型3（LP，θ = 40°，φ = 0°，l = 1，d = 18 cm），（RCP，θR = -40°，φR = 0°，lR = -1，dR = 20 cm）和（LCP，θL = -19°，φL = 0°，lL = 3，dL = 16.4 cm）。与先前的MTS相比，所提出的自旋解耦MTS具有在BBs之间可切换、无衍射距离/孔径尺寸比高达15、光束偏转角高达40°以及BB转换效率高达96%等优点。模拟结果与使用物理模型计算的结果一致，从而验证了物理模型。所设计的可切换BBs在太赫兹近场应用中具有潜力，如高容量近场无线通信、无线功率传输、高分辨率成像、无损检测以及高速旋转物体的速度检测。
