Broadband Orbital Angular Momentum Generation via C2-Symmetric Silicon Nanorod Metasurfaces for High-Capacity Optical Communications

Vortex beams, characterized by their helical phase fronts and annular intensity profiles, have emerged as a transformative tool in optical communications due to their capacity to carry orbital angular momentum (OAM). However, conventional vortex beam generators, such as spiral phase plates and spatial light modulators, suffer from narrow operational bandwidths (<200 nm), limiting their applicability in multi-wavelength systems.To address this challenge, we present a metasurface-based approach leveraging the geometric phase (Pancharatnam-Berry phase) principle to achieve broadband OAM generation. We propose a C2-symmetric silicon nanorod metasurface optimized for the near-infrared (1390–1500 nm) regime, demonstrating 84%–96% polarization conversion efficiency for right-circularly polarized (RCP) light. Through systematic parameter sweeps and finite-difference time-domain (FDTD) simulations, we identify an optimal nanorod geometry (major axis = 320 nm, minor axis = 250 nm, height = 923 nm) that enables full 0–2π phase modulation while maintaining wavelength-independent topological charge stability. The metasurface array, arranged in four quadrant-discrete phase sectors, generates high-purity OAM modes with annular intensity distributions and helical wavefronts across the entire bandwidth. Key innovations include the unification of polarization conversion and geometric phase control in a single nanostructure, eliminating the need for cascaded optical elements. This work advances the state-of-the-art in OAM multiplexing by enabling low-crosstalk, dispersionfree vortex beams for next-generation optical networks, free-space communications, and 6G systems. The design’s compatibility with standard semiconductor fabrication techniques further underscores its potential for scalable integration in photonic circuits.