Fiber-optical microendoscopy has made significant improvements to in vivo neural imaging, minimally invasive diagnostics, and microsurgery. However, high resolution, miniaturization, and low complexity cannot be simultaneously achieved together in the lens system for fiber-optical microendoscopy because current lens systems are in shape and dimensions restricted by limitations of manufacturing. Recently, two-photon direct laser writing (DLW) has been implemented in the fabrication of low-resolution micro-optics structures. Here, we demonstrate a high-resolution miniaturized singlet aspherical microlens fabricated on the fiber facet using DLW. The microlens has a high numerical aperture (NA), of 0.9, in air with only one aspherical surface, and is 10–20 times smaller in diameter than a typical gradient refractive index (GRIN) microlens. The designs of aspherical microlenses with NAs of 0.3, 0.6, and 0.9 in air are aberration-free at three wavelengths (561, 590, and 630 nm). The full width at half maximum of the effective intensity point spread function of a 0.9 NA aspherical microlens is 0.85 μm. We demonstrate fiber-optical microendoscopy imaging with a 0.6 NA aspherical microlens. The proposed aspherical microlens can potentially be applied to the development of a high-resolution, extremely miniaturized fiber-optical microendoscope.

中文翻译：

---

用于光纤显微内窥镜的双光子直接激光写入实现的非球面微透镜

光纤显微内窥镜在体内神经成像、微创诊断和显微外科手术方面取得了重大进展。然而，在用于光纤显微内窥镜的透镜系统中不能同时实现高分辨率、小型化和低复杂性，因为当前透镜系统在形状和尺寸上受到制造限制的限制。最近，双光子直接激光写入 (DLW) 已用于制造低分辨率微光学结构。在这里，我们展示了使用 DLW 在光纤面上制造的高分辨率微型单线态非球面微透镜。该微透镜在只有一个非球面表面的空气中具有 0.9 的高数值孔径 (NA)，其直径比典型的梯度折射率 (GRIN) 微透镜小 10-20 倍。空气中 NA 为 0.3、0.6 和 0.9 的非球面微透镜的设计在三个波长（561、590 和 630 nm）下均无像差。0.9 NA 非球面微透镜的有效强度点扩散函数的半高全宽为 0.85 μm。我们展示了使用 0.6 NA 非球面微透镜的光纤显微内窥镜成像。所提出的非球面微透镜有可能用于开发高分辨率、极小型化的光纤微内窥镜。