Geometric metasurface for polarization synthesis and multidimensional multiplexing of terahertz converged vortices

Abstract

The investigation of converged twisted beams with a helical phase structure has a remarkable impact on both fundamental physics and practical applications. Geometric metasurfaces consisting of individually orientated metal/dielectric meta-atoms provide an ultracompact platform for generating converged vortices. However, it is still challenging to simultaneously focus left-handed and right-handed circularly polarized incident beams with pure geometric phase modulation, which hinders the independent operation on topological charges between these two helical components. Here we propose and experimentally demonstrate an approach to design terahertz geometric metasurfaces that can generate helicity-independent converged vortices with homogeneous polarization states by the superposition of two orthogonal helical vortices with identical topological charges. Furthermore, the multiplexing of polarization-rotatable multiple vortices in multiple dimensions, i.e., in both longitudinal and transverse directions, and a vortex with an extended focal depth is confirmed by embedding polarization modulation into the geometric metasurfaces. The demonstrated approach provides a new way to simultaneously manipulate orthogonal helical components and expand the design dimension, enabling new applications of geometric metasurface devices in polarization optics, twisted-beam related image and edge detection, high capacity optical communication, and quantum information processing, to name a few.

On-demand multiplexed vortex beams for terahertz polarization detection based on metasurfaces

“…The accumulation of the propagation phase, on the other hand, is determined by the height h and the transverse dimensions of the silicon columns, which can be described using its effective refractive index ( n eff ) in the waveguide mode as Φ prop = 2π n eff h / λ . It is worth mentioning that the employment of the basic building block with a high AR causes a variation in the fundamental resonance mechanism, 54 i.e. , the high transmission efficiency arises from the Fabry–Perot resonance effect (see ESI part 5†).…”

Multimaterial Additively Manufactured Transmissive Spin‐Decoupled Polarization‐Maintaining Metasurfaces

“…[ 26,29 ] Unlike the strategy of the joint modulation of the geometric phase and dynamic phase, the pure geometric phase was also demonstrated to design meta‐lens with spin‐decoupled imaging, [ 38 ] vortex beams, [ 27 ] and intensity‐tunable focusing. [ 39 ] Nevertheless, because of the inherent nature of the P–B phase, the spin always flips after transmitting through these MSs. In practical scenarios such as satellite communications, spin states must be maintained at transmitting and receiving ends when transmitting and receiving data.…”

All‐Silicon Diatomic Terahertz Metasurface with Tailorable Linear Polarization States

“…[ 7,8 ] Conventional phase modulation principles include the propagation phase and geometric phase, the former can act on the circularly polarized and linearly polarized channel, respectively, while the latter is merely for circularly polarized light with conjugate locking distribution. [ 9 ] However, traditional optical polarizers based on natural materials, such as half‐wave plates (HWPs), quarter‐wave plates (QWPs), and beam splitters, are generally bulky and far from the goal of advanced integration and miniaturization. Therefore, an efficient replacement element is urgently needed for the current compact optical systems.…”

“…[7,8] Conventional phase modulation principles include the propagation phase and geometric phase, the former can act on the circularly polarized and linearly polarized channel, respectively, while the latter is merely for circularly polarized light with conjugate locking distribution. [9] However, traditional optical polarizers based on natural materials, such as half-wave plates (HWPs), quarter-wave plates (QWPs), and beam splitters, are generally bulky and far from the goal of advanced integration and Polarization plays a key role in fundamental science, and the improvement in miniaturization and practicability of polarization conversion devices could provide more degrees of freedom for light-matter interactions. Metasurfaces that can manipulate arbitrary polarization states at subwavelength scales can significantly reduce the complexity of meta-optical systems.…”