A study published in Optics and Lasers in Engineering by researchers from the Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, demonstrated a new method to significantly improve the polarization-maintaining performance of optical systems. They achieved this by integrating specially designed metasurfaces, reducing key polarization aberrations by more than 90%.

Polarization aberrations, which degrade the polarization state of light as it passes through optical components, are a critical issue in high-precision applications like laser communication and polarization imaging. These aberrations, quantified as diattenuation and retardance, can severely impair performance by misaligning the polarization states required for efficient operation. Traditional suppression techniques often involved complex mirror alignments or coatings, but their effectiveness was limited and not universally applicable.

To address this, the team proposed a hybrid design that combines conventional refractive optics with a metasurface—a thin surface engineered with subwavelength nanostructures. The research process involved a systematic four-step workflow. First, they designed and optimized an off-axis laser beam expander to meet stringent wavefront quality criteria. Next, they conducted a full-aperture polarization ray tracing analysis to map the diattenuation and retardance across the system's exit pupil.

The core of the suppression strategy utilized anisotropic metasurface unit cells, made from silicon nanopillars on an alumina substrate, which responded differently to orthogonal polarization states. By strategically selecting and arranging these cells, they counteracted the system's inherent polarization errors. The team formulated a multi-objective suppression function and iteratively adjusted a weighting factor to balance the reduction of diattenuation and retardance. After suppression, a second metasurface composed of isotropic unit cells corrected any induced wavefront errors to restore high image quality.

Simulation results for an 850 nm laser communication system showed that this hybrid design reduced the average diattenuation by 91.8% and the average retardance by 95.0%. The system's wavefront quality, including metrics like Strehl Ratio, remained excellent, meeting the diffraction limit. The researchers also analyzed the design's robustness across different fields of view and conducted a fabrication feasibility study, confirming that the double-sided metasurface could be manufactured with current nanofabrication techniques like electron beam lithography.

This refractive-metasurface hybrid approach offers a highly effective and flexible solution for minimizing polarization aberrations. Its modular nature allows it to be incorporated into existing optical systems without structural redesigns. The method holds promise for enhancing the performance of laser communication, high-resolution imaging, and other polarization-sensitive technologies.