Binary Fresnel zone plates (FZP) are among the most commonly used focusing elements of 2D-planar optical circuits in micro- and nano-photonics. When the diameter and focal distance of a FZP are reduced to the wavelength dimensions, the parameters of the focal area experience strong influence by FZP constructive design (material, thickness, depth of zone relief). By means of the numerical simulations, the near-field diffraction of monochromatic optical wave on a wavelength-scale binary phase plate is investigated. We found a range of optimal depths of zone plate grooves etching as well as substrate thicknesses providing the best focusing of the incident circularly polarized optical wave in terms of maximum field intensity and minimum size of the focal spot. A certain improvement of these focus parameters can be achieved by filling the zone grooves with a dielectric having a specific refractive index contrast against the FZP substrate. Additionally, the concept of a super-focus binary phase plate with a solid immersion layer (SIL) in the form of a truncated cone made of the ZP substrate material is proposed. Similar to conventional SIL device, this flat SIL-FZP can focus a circularly polarized optical radiation into a subdiffraction spot with a full-width of the order λ/2n (n is FZP refraction index).

二元菲涅耳波带片 (FZP) 是微和纳米光子学中二维平面光路中最常用的聚焦元件之一。当 FZP 的直径和焦距减小到波长维度时，FZP 结构设计（材料、厚度、区域浮雕深度）会强烈影响焦区参数。通过数值模拟，研究了单色光波在波长尺度二元相位板上的近场衍射。我们发现波带片凹槽蚀刻的最佳深度范围以及基板厚度在最大场强和最小焦斑尺寸方面提供入射圆偏振光波的最佳聚焦。通过用与 FZP 衬底具有特定折射率对比的电介质填充区域凹槽，可以实现这些聚焦参数的某种改进。此外，还提出了具有由 ZP 衬底材料制成的截锥形式的固体浸没层 (SIL) 的超聚焦二元相位板的概念。与传统的 SIL 设备类似，这种平面 SIL-FZP 可以将圆偏振光辐射聚焦到一个全宽度为λ /2 n（n是 FZP 折射率）。