应用于微型成像的氮化镓超透镜设计

为了实现可见光入射时亚波长尺度内的聚焦,设计了以氮化镓(GaN)纳米柱为基本晶胞的超透镜,该透镜能够改进传统成像系统的笨重低效,可应用于微型成像系统。超透镜表面由宽度渐变高度不变的GaN纳米柱阵列构成,分析GaN在亚波长尺度内对相位的调控能力和机理,并基于时域有限差分法模拟仿真了在蓝光波长为460nm入射时透射场的高效率聚焦,对比超透镜尺寸为3.75μm×3.75μm、6.75μm×6.75μm、8.75μm×8.75μm、10.75μm×10.75μm时超透镜的聚焦能力,得出聚焦后透射场焦点处的半峰全宽分别为1,0.8,0.5,0.3μm,给出了强度分布、聚焦光斑等仿真模拟结果,发现实际焦距与设计值存在偏差,且随超透镜尺寸的变化而变化。文中所设计的超透镜能够在微米级别实现聚焦,有效降低了传统成像系统的复杂度。

GaN based metalens for micro imaging

A metalens consisting of GaN nanopillars as basic cells was designed for subwavelength focusing at visible wavelengths, which provided an improvement over bulky and low-efficiency conventional imaging systems, and the possibility of its application to micro imaging. The metalens is composed of a GaN nanopillar array, which maintains the same height but gradually varying width. An analysis of the capacity and reasons for GaN nanopillars controlling the phase of incoming light was performed. In addition, based on FDTD methods, a simulation of 460 nm wavelength focusing in the transmission mode was performed. Subsequently, full width at half maximum (FWHM) are shown when the sizes of metalens are 3.75 μm×3.75 m, 6.75 μm×6.75 m, 8.75 μm×8.75 m, and 10.75 μm×10.75 m, and the results are 1, 0.8, 0.5, and 0.3 m, respectively. The other focusing results, such as intensity distribution and focus spots, were also discussed. As a result, there are differences between designed focal length and simulated focal length, which changes under the different sizes of metalens. In conclusion, the designed GaN based metalens can focus in micron dimension effectively, which reduces the complexity of traditional imaging systems.