Effect of grating mirrors size on focusing reflectors based on two-dimensional high-contrast sub-wavelength gratings

We present an approach to design focusing reflectors using two-dimensional sub-wavelength gratings (2D SWGs). The effect of the grating reflecting mirrors size on the reflection focusing performance is investigated. The performance parameters considered mainly include focal length, phase change, numerical aperture. Using COMSOL software, the simulation results show that the focal length are affected by the grating reflecting mirrors size. The larger grating mirror (at least the total phase change of 3% angle) has better focusing behavior, this conclusion provides some suggestions for our design and fabrication of reflective convergence grating.