“水窗”波段等直径单模小孔波导光子筛的聚焦分析

Focusing Analysis of Single-Mode Photon Sieve with Equal-Diameter Pinholes Working in"Water Window"Band

随着加工技术的成熟和对空间分辨率要求的不断提高,光子筛小孔越来越小。对于光子筛上不同大小的圆孔,均匀平面波入射时会激发一个或多个波导模,进而导致模间色散和相位差的出现。即使小孔中只有单模传输,基模的有效折射率也与小孔的大小有关,从而会导致不同直径的小孔在出射端面处具有不同的相位。为了消除这些相位差,提出等直径小孔单模光子筛。研究了“水窗”波段中等直径小孔单模光子筛的聚焦效应,并建立了相应的高斯远场衍射模型。基于有限元软件的数值模拟确认了高斯模场的分布,并基于菲涅耳衍射积分的计算进一步确认了远场解析模型的有效性。

As processing technologies become mature,and the requirement for spatial resolution increases,pinholes on the photon sieve get smaller and smaller.For pinholes with different sizes on the photon sieve,the incident uniform plane wave can excite one or more waveguide modes,which results in the inter-modal dispersion and phase difference.Even if there is only single-mode transmission in the pinholes,the effective refractive index of the fundamental mode is related to the size of the pinhole,which leads to different phases of pinholes with different diameters at the exit.To eliminate these phase differences,the single-mode photon sieve with equal-diameter pinholes is proposed.The focusing effect of the photon sieve in the"water window"band is studied,and the corresponding Gaussian far-field diffraction model is established.In addition,the distribution of the Gaussian mode field is confirmed based on the numerical simulation through the finite element software,and the effectiveness of the far-field model is verified by calculating the Fresnel diffraction integral.