Metasurfaces have transformed the way scientists manipulate light, but most existing devices still operate under a fundamental constraint: they primarily control the phase of propagating waves. This makes it difficult to create optical fields whose intensity, phase and polarization vary independently across space. A team led by Professors Shulin Sun and Lei Zhou at Fudan University has now developed an on-chip photonic platform designed to overcome that limitation. Their surface-wave-excited complex-amplitude metasurfaces can generate vectorial optical fields (VOFs) with carefully engineered amplitude, phase and polarization distributions, potentially bringing advanced holography and beam shaping into compact optical systems.
The work, published in Light: Science & Applications, uses a metasurface excited by electromagnetic energy travelling along a surface rather than propagating directly through free space. Surface waves can confine optical energy near an interface and guide it across a device, creating a compact route for feeding many nanoscale optical elements. In the Fudan University platform, these waves interact with composite meta-atoms—carefully arranged groups of resonant structures that scatter light into the far field. By tailoring the response of each element, the researchers can determine not only where light travels, but also how intense it is and which polarization state it carries.
This capability is important because vectorial optical fields contain more information than ordinary scalar beams. A scalar beam can be described largely through its intensity and phase, whereas a vectorial field also includes the orientation and spatial evolution of its electric-field polarization. Such fields can contain intricate combinations of polarization textures, focused regions and structured wavefronts. They are being explored for optical communications, microscopy, particle manipulation, quantum technologies and information security. Producing them on a small chip, however, requires simultaneous control of multiple optical parameters—a task that conventional phase-only metasurfaces cannot easily accomplish.
The researchers addressed this challenge with composite meta-atoms built from 2×2 resonators. These structures were designed using Pancharatnam–Berry, or PB, phase principles, in which rotating anisotropic elements changes the phase of converted light. The individual resonators can therefore be assigned different rotation angles, while their collective arrangement provides additional control over the amplitude and polarization of the emitted field. The resulting composite metasurface acts as a compact optical processor: it converts the incoming surface wave into a prescribed free-space field with a spatially tailored complex amplitude, meaning that both the strength and phase of the radiation are controlled.
The team first demonstrated an on-chip terahertz device capable of producing two free-space beams travelling in different directions and carrying orthogonal polarization states. The direction of each beam and the intensity ratio between them could be designed in advance. This is more than a simple beam-steering function. Independent control of the two channels allows the device to distribute optical energy between polarization and angular states, creating a flexible platform for multiplexing information or directing different signals to separate locations. Because the excitation occurs through a surface wave, the architecture also offers a route toward integrating the source, guiding structure and radiation interface on a single photonic chip.
In a second demonstration, the metasurface generated two focused far-field beams. Their focal positions, relative intensities and polarization states were independently controlled, showing that the platform can perform several optical operations simultaneously. Conventional lenses generally focus light according to a fixed geometry, while phase-only holographic elements often require compromises between focusing efficiency, field uniformity and polarization control. The new approach instead treats the desired output as a complex vector field and designs the surface-wave scattering process to reproduce it. This makes it possible to create multiple focal points with distinct optical identities within the same device.
The researchers then expanded the concept to vectorial holography. They developed an optimized complex-amplitude Gerchberg–Saxton algorithm, a computational method widely used to calculate the phase patterns needed for holographic reconstruction. In its conventional form, the algorithm commonly works with phase-only modulation. The optimized version used in this study incorporates complex amplitude and polarization constraints, allowing the metasurface design to account for the full vectorial nature of the target image. The resulting holographic fields showed improved image fidelity and more uniform illumination than comparable phase-only approaches, while also allowing polarization to be programmed across the reconstructed image.
The underlying physics was supported by characterization of the devices’ resonant response. The researchers calculated and measured reflection phase, reflection amplitude and polarization conversion ratio for the periodic PB meta-atoms under terahertz illumination along their principal axes. These measurements helped establish how efficiently the resonators converted the incident polarization and how accurately they produced the intended phase response. The team also calculated the dispersion relation of the supported surface-wave modes in the plasmonic metal, providing a picture of how electromagnetic energy propagates through the structure before being scattered into free space. Together, these results connect the nanoscale properties of individual meta-atoms with the macroscopic behavior of the complete optical platform.
The study points toward a future in which complex light fields are generated directly by intelligent, chip-scale optical systems rather than by bulky assemblies of lenses, spatial light modulators and polarization components. Potential applications include encrypted holography, where information can be encoded simultaneously in intensity, phase and polarization; augmented-reality displays, which require precise control of light in compact form; and programmable photonic chips capable of routing and processing optical information. By combining surface-wave excitation, PB meta-atoms and complex-amplitude computation, the Fudan University team has created a versatile framework for generating structured light. The researchers describe the platform as a universal strategy for producing complex vectorial optical fields, offering a new path toward multifunctional photonics in which a single metasurface can shape where light goes, how bright it is and how its electric field is oriented.
Subject of Research: Surface-wave-excited complex-amplitude metasurfaces for generating vectorial optical fields, structured beams and holographic images.
Article Title: Generating vectorial optical fields via surface-wave-excited complex-amplitude metasurfaces
Web References: https://doi.org/10.1038/s41377-026-02334-1
References: Light: Science & Applications, DOI: 10.1038/s41377-026-02334-1
Image Credits: Shulin Sun et al.
Keywords
Metasurfaces, vectorial optical fields, surface waves, complex-amplitude modulation, terahertz photonics, PB meta-atoms, polarization control, holography, structured light, integrated photonics
