image: Figure 1 | Principle of generating desired VOFs distributions by SW metasurface and characterization of the PB meta-atoms and plasmonic metal. a, The amplitude and phase of two orthogonal polarization states (LCP and RCP) for generating the desired VOFs. b, The design strategy of the on-chip composite MS constructed by the PB meta-atoms with individual rotation angle distributions for achieving the complex fields shown in (a). c-d, Schematic illustration and sample image of the designed meta-atom. e-g, Calculated and measured reflection phase, reflection amplitude and polarization conversion ratio (PCR) spectra of the periodic PB meta-atoms illuminated by the terahertz light linearly polarized along the two principal axes, i.e., u and v axes. h, Calculated dispersion relation of the eigen SW modes supported by the designed plasmonic metal (see the inset).
Credit: Shulin Sun et al.
With the rapid advancement of integrated photonics, there is an increasing demand for high-compact and multi-functional devices capable of flexibly manipulating light. While metasurfaces have emerged as powerful tools for wavefront engineering, most existing implementations rely on propagating-wave excitation and phase-only modulation, fundamentally limiting their capability to generate complex VOFs with spatially tailored wavefront profiles and polarization distributions.
To address this challenge, a research team led by Professors Shulin Sun and Lei Zhou at Fudan University has developed a surface-wave-excited complex-amplitude metasurface platform for generating VOFs, opening a new avenue toward highly integrated and intelligent photonic systems. By utilizing composite meta-atoms consisting of 2×2 resonators, the present device enables independent and precise control over the amplitude, phase and polarization of radiation fields (see Fig. 1).
The researchers first experimentally demonstrated an on-chip THz metasurface for generating two directional free-space beams with orthogonal polarizations under surface-wave excitation. Both the radiation directions and intensity ratios of these beams can be flexibly designed and precisely controlled. Subsequently, they further realized the second on-chip metasurface capable of producing dual-focus far-field beams with independently controlled focal positions, field intensities, and polarization states. These results showcase the exceptional capabilities of the proposed platform in multifunctional beam shaping and complex wavefront engineering.
By developing an optimized complex-amplitude Gerchberg–Saxton algorithm, the team further constructed the on-chip metasurfaces that can generate high-quality vectorial holographic images (see Fig. 2). Compared to conventional phase-only holography, the proposed approach exhibits the novel advantages such as higher image fidelity, improved field uniformity and polarization programmability.
“Our work establishes a universal on-chip platform for generating complex VOFs with unprecedented flexibility,” said the researchers. “This strategy opens up exciting opportunities for numerous applications such as encrypted holography, augmented reality and intelligent photonic chips.”
Journal
Light: Science & Applications
Article Title
Generating vectorial optical fields via surface-wave-excited complex-amplitude metasurfaces