Dynamic vortex beam generation from metasurface devices with minimum tunable units

Metasurfaces that can produce high-purity vortex beams hold tremendous promise for developing next generation telecommunication systems with unprecedented speed and compactness. The on-demand tuning of the vortex modes, however, is challenging in compact metasurface devices because of the difficulty in realizing dynamic meta-units but important for enhancing data transmission capability, increasing system flexibility, and adapting to various application requirements environments. To tackle such challenges, we establish a cascaded-metasurface-based system that enables dynamic switching between high-quality vortex beams by tuning a very limited number of units. In particularly, the switching between LG_0,4 mode (92.45% overall purity) and LG_0,6 mode (88.85% overall purity) is realized by adjusting only 2 × 2 of coarse pixels, each with a size of 60 × 60 μm², which can be readily realized by existing liquid crystals (LC) devices or phase-change materials. To provide a practical design for device construction, we also demonstrate that the multi-layer design is robust against misalignments between the layers and the addition of gaps between the tunable units, which are often unavoidable for realistic tunable systems. Furthermore, by slightly increasing the tunable units to 30 × 30 pixels, our tunable metasurface device can produce up to 20 completely different high-purity LG_0,l modes (l = −10, −9, …, −1, 1, …, 9, 10) within a single device, significantly increasing the system's transmission capacity and meeting future communication demands. The proposed reconfigurable vortex light generator, with the ability to achieve multiple high-purity LG modes using only a minimal number of pixels, will significantly reduce the complexity of vortex light source system, expand its prospects across various applications such as optical communications, quantum entanglement, and micro-mechanical measurements.