| Popis: |
Sub-wavelength focusing of cylindrical vector beams has attracted much attention because of its special properties. On this basis, an all-dielectric concave grating lens with negative refractive index is proposed in this paper. Through discussing the influence of equivalent negative refractive index (neff) and preset focal length on the focusing properties, the parameters of the structure is optimized. The results show that when neff is -1, the focal size is the smallest. A smaller preset focal length results in a smaller the transverse focal size. Furthermore, the effect of higher order diffracted light is also studied. It is found that, sub-focusing can be suppressed effectively by removing the structural part that supports the higher order diffraction. Finally, not only the focusing property is improved, but also the structure is simplified. This work provides a flexible and feasible method for the design of negative-index lens, and offers a reference for manipulating the focus of CVBs. Therefore, it provides a scheme for focusing artificial microstructure. |
