Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX1 3PJ, UK.
Department of Physics, Tsinghua University, 100084, Beijing, China.
Nat Commun. 2019 Sep 19;10(1):4264. doi: 10.1038/s41467-019-12286-3.
Graded index (GRIN) lenses are commonly used for compact imaging systems. It is not widely appreciated that the ion-exchange process that creates the rotationally symmetric GRIN lens index profile also causes a symmetric birefringence variation. This property is usually considered a nuisance, such that manufacturing processes are optimized to keep it to a minimum. Here, rather than avoiding this birefringence, we understand and harness it by using GRIN lenses in cascade with other optical components to enable extra functionality in commonplace GRIN lens systems. We show how birefringence in the GRIN cascades can generate vector vortex beams and foci, and how it can be used advantageously to improve axial resolution. Through using the birefringence for analysis, we show that the GRIN cascades form the basis of a new single-shot Müller matrix polarimeter with potential for endoscopic label-free cancer diagnostics. The versatility of these cascades opens up new technological directions.
梯度折射率（GRIN）透镜常用于紧凑型成像系统。人们尚未广泛认识到，形成旋转对称 GRIN 透镜折射率分布的离子交换过程也会导致对称双折射变化。该特性通常被视为一种干扰，因此制造过程会被优化以将其最小化。在这里，我们不是避免这种双折射，而是通过使用 GRIN 透镜与其他光学组件级联来理解并利用它，从而在常见的 GRIN 透镜系统中实现额外的功能。我们展示了 GRIN 级联中的双折射如何产生矢量涡旋光束和焦点，以及如何利用它来有利地提高轴向分辨率。通过利用双折射进行分析，我们表明 GRIN 级联构成了一种新的单次拍摄穆勒矩阵偏振计的基础，该偏振计具有用于内窥镜无标记癌症诊断的潜力。这些级联的多功能性开辟了新的技术方向。
