Julian Matthew N, MacDonnell David G, Gupta Mool C
Appl Opt. 2019 Jan 1;58(1):109-114. doi: 10.1364/AO.58.000109.
Over the past several decades, the need for high-resolution, high-efficiency, lightweight, high-contrast focusing optics has continued to increase due to their applications in fields such as astronomy, spectroscopy, free-space optical communications, defense, and remote sensing. In recent years, photon sieve planar diffractive optics, which are essentially Fresnel zone plates with the rings broken into individual "pinhole" apertures, have been developed on flexible, lightweight polyimide substrates. However, transmission efficiencies have continuously been very low (∼1%-11%) until this work, thus impeding the widespread use of photon sieves in practical applications. Here, we present flexible, lightweight, four- and eight-level phase photon sieves with 25.7% and 49.7% transmission efficiency, respectively, up to five times greater than that of any other photon sieve reported thus far. Additionally, these sieves were fabricated via a single step pulsed laser ablation method. The total time to fabricate a ∼3 cm photon sieve via the single-step fabrication was tens of seconds, giving the technique a significant advantage over traditional photolithography used to generate multilevel structures. Analytical analysis of the photon sieve was carried out via the finite-difference time-domain (FDTD) method and was in very good agreement with experimental results. We have also calculated via FDTD modeling the behavior of higher-level photon sieves for further enhanced efficiencies, and analytically show an estimated upper bound on photon sieve efficiency of 70% within the first focal plane null in the limit of increasing step number, and the data presented herein provide a relationship between efficiency and step number. Additionally, this process of multilevel diffractive lens fabrication can be extended to multilevel Fresnel zone plates, which have not previously been demonstrated by this process. The results presented in this work represent a new step in high-resolution diffractive optics, showing efficiencies suitable for widespread applications in addition to drastically reducing the cost and complexity of fabricating multilevel focusing elements.
在过去几十年中，由于其在天文学、光谱学、自由空间光通信、国防和遥感等领域的应用，对高分辨率、高效率、轻量化、高对比度聚焦光学器件的需求持续增长。近年来，光子筛平面衍射光学器件已在柔性、轻质的聚酰亚胺基板上得到开发，它本质上是菲涅耳波带片，其环被分解为单个“针孔”孔径。然而，直到这项工作开展之前，传输效率一直非常低（约1%-11%），因此阻碍了光子筛在实际应用中的广泛使用。在此，我们展示了柔性、轻质的四级和八级相位光子筛，其传输效率分别为25.7%和49.7%，比迄今为止报道的任何其他光子筛高出多达五倍。此外，这些筛是通过单步脉冲激光烧蚀法制造的。通过单步制造法制造一个约3厘米的光子筛的总时间为几十秒，这使得该技术相对于用于生成多级结构的传统光刻技术具有显著优势。通过时域有限差分（FDTD）方法对光子筛进行了分析，结果与实验结果非常吻合。我们还通过FDTD建模计算了更高级光子筛的行为以进一步提高效率，并通过分析表明在步数增加的极限情况下，第一焦平面零位内光子筛效率的估计上限为70%，本文所呈现的数据提供了效率与步数之间的关系。此外，这种多级衍射透镜的制造工艺可以扩展到多级菲涅耳波带片，而此前尚未通过该工艺实现。这项工作所呈现的结果代表了高分辨率衍射光学的新进展，除了大幅降低制造多级聚焦元件的成本和复杂性外，还展示了适用于广泛应用的效率。
