Meta-grating integrated high-ellipticity and wide-band linear-to-circular polarization converter for visible light.

Circularly polarized light is crucial for applications across diverse fields. Comparing with the traditional methods for linear-to-circular polarization conversion, metamaterials offer promising solutions for miniaturizing optical elements. However, developing wide-band polarization converters with high ellipticity remains challenging, especially in the visible range, concerning the difficulty associated with fabricating sub-wavelength structures. To address this, we designed and fabricated a metallic meta-grating by employing a patterned GaN substrate through a cost-effective and mass-productive method, laser interference lithography. These meta-grating converters achieve high ellipticities (ɛ) exceeding 0.995 in the range of 420 nm- 490 nm, 490 nm-590 nm, and 570 nm-680 nm. Our work paves the way for further polarization control and on-chip integration with GaN devices, while also demonstrating a scalable and portable meta-grating fabrication method, enabling multi-functional applications in detection, displays, communication, and medicine.