Half-wave plate based on a birefringent metamaterial in the visible range

In the present paper, a half-wave plate (HWP) based on a birefringent metamaterial is numerically designed to operate in the visible range. The proposed structure consists of an array of double-pattern perpendicular rectangular aperture (RAA) engraved into opaque silver film deposited on a glass substrate. One of the apertures is glass filled. The operating principle of this plate is based on the excitation and the propagation of one guided mode inside each aperture but with different effective index. At the output side, a phase difference is obtained whose value mainly depends on the metal thickness. We have investigated the most simplest configurations using a homemade code based on the finite difference time domain method to design a half-plate with optimized efficiency resulting in transmission coefficient of more than $60\%$ together with a birefringence of $2.1$ at an operation wavelength of 737 nm. This kind of anisotropic metasurface promises a wide range of applications in integrated photonics.