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.”
Light: Science & Applications
Generating vectorial optical fields via surface-wave-excited complex-amplitude metasurfaces