State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou, 310027, China.
Intelligent Optics and Photonics Research Center, Jiaxing Research Institute, Zhejiang University, Jiaxing, 314000, China.
Sci Rep. 2022 Nov 28;12(1):20476. doi: 10.1038/s41598-022-24785-3.
Optical fiber bundle-based microendoscope, which is significant in clinical diagnosis and industrial detection, calls for miniaturization of the probe and high-resolution observation. Here, we propose a double-layer metasurface array borrowing the structures of insect compound eyes to meet both requirements instead of traditional optical components. Each unit in the array aims for an incident field of view, focusing light at the center of the fiber end face with no chromatic aberration at the wavelengths of 470 nm, 530 nm and 630 nm. The metasurface array is composed of a series of isotropic TiO nanopillars which are special selected after considering resonance mode and angular dispersion characteristics, etched on both sides of a silica substrate, with the individual functions of deflecting and focusing. In image space, numerical aperture (NA) is 0.287 and the particular layout of two layers achieve zero telecentricity theoretically, which meet the requirements of optical fiber bundle coupling. A unit for incident angle of 20° is shown to validate our design approach numerically, which obtains a focused spot close to the diffraction limit. The compact and ultrathin metasurface could greatly reduce the size of the probe in optical fiber bundle based microendoscope while ensuring the imaging quality.
光纤束微内窥镜在临床诊断和工业检测中具有重要意义，需要将探头微型化并实现高分辨率观察。为此，我们提出了一种双层超表面阵列，借鉴昆虫复眼的结构来满足这两个要求，而不是采用传统的光学元件。该阵列中的每个单元都有一个入射视场，在光纤端面的中心聚焦光线，在 470nm、530nm 和 630nm 波长下没有色差。超表面阵列由一系列各向同性 TiO 纳米柱组成，这些纳米柱是在考虑共振模式和角度色散特性后特别选择的，刻蚀在二氧化硅基底的两侧，具有偏折和聚焦的单独功能。在像空间中，数值孔径（NA）为 0.287，两层的特殊布局在理论上实现了零远心度，满足光纤束耦合的要求。数值验证了我们对 20°入射角的单元设计方法，得到了接近衍射极限的聚焦光斑。这种紧凑、超薄的超表面可以大大减小光纤束微内窥镜探头的尺寸，同时保证成像质量。
