Highly-efficient and angle-independent zero-order half waveplate at broad visible wavelength based on Au nanofin...

A Au nanofin array embedded in SiO₂ was designed and fabricated to achieve an achromatic half waveplate with high transmittance at visible wavelengths. On the basis of the waveguide theory of nanogaps and the Fresnel reflection theory, nanofin array is calculated to have ideal properties for an achromatic half-waveplate in the visible band from 560 to 660 nm with the transmittance of around 50%. A Au nanofin array with a height of 830 nm and a period of 400 nm was fabricated through a sidewall-deposition process and overcoating with spin on glass. The polarization microscopy results showed that both transmittance greater than 50% and retardation of 165° at broadband wavelengths ranging from 600 to 800 nm were simultaneously achieved. It was also demonstrated that retardation had little dependence on the incident angle.