designing a high performance phase gradient metasurface using optical patch antennas with different patch thicknesses

Patch-based metasurfaces as generic structures of the reflective flat optical devices, such as flat mirrors, waveplates, polarizer, and holograms, should fulfill two basic requirements of covering 0 to 2π phase shift range and providing a sufficiently high reflection amplitude. under the current design paradigm, the design process has been based only on the width and length of the patch elements of the metasurfaces. the present study will exploit the potentials of the thickness of the patch elements as a design parameter. while for a metasurface based on patch elements with thickness of 50 nm, a phase shift coverage near 270°, corresponding to 90° phase steps, and reflection amplitude of 0.8 in the wavelength 775 nm are achievable, using just one additional value of 30 nm for thicknesses of the patches will increase the phase shift coverage to 320°, corresponding to 40° phase steps, with reflection amplitude higher than 0.85 in the same wavelength. in this way, the phase steps could be much smaller which means more closely approximating a targeted phase pattern. this would be evidently a remarkable performance improvement, which in the case of a polarization beam splitter, as shown, means reflecting more amount of energy in the desired angles.