Generalized lattice metasurface enables independent control of stokes polarization

Controlling both the state and degree of polarization of light is a long-standing challenge in optics. While metasurfaces offer compact, high-resolution control over wavefronts, most existing designs struggle to independently tune the full set of Stokes parameters due to strong coupling between structure and optical response.

 

A research team led by Prof. Changyuan Yu at The Hong Kong Polytechnic University tackles this issue by introducing a generalized lattice metasurface. This approach adds a new design degree of freedom: the quantity ratio of different nanostructures. By adjusting size, orientation, and especially the ratio of nanostructures, the team establishes a direct mapping between physical parameters and polarization states, enabling intuitive forward design.

 

The key difference lies in how polarization modulation is achieved. Traditional isotropic metasurfaces transmit orthogonal polarizations equally, making DoP control impossible (Figure 1). Diatomic metasurfaces introduce some asymmetry via interference, but their design remains complex due to coupled parameters. The generalized lattice, however, uses a disordered yet locally balanced distribution of nanostructures (Figure 2), allowing precise, independent control of each polarization component. This structure reduces diffraction and simplifies the overall transmission matrix to a weighted sum of Jones matrices, streamlining analysis and design.

 

Crucially, the method is scalable. By adding a third nanostructure type, the metasurface can achieve arbitrary polarization transformations (Figure 3), covering any target on the Poincaré sphere. The team fabricated 16 metasurface samples to demonstrate this, each targeting specific Stokes parameters. Experiments confirmed accurate tuning of azimuth, elevation, and polarization degree, with results closely matching theoretical predictions.

 

This work establishes a new paradigm in metasurface design, moving from rigid periodicity to versatile, ratio-based architectures. It opens promising paths toward customizable polarization devices for applications in imaging, sensing, and optical communications.

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