Aspherical Microlenses Enabled By Two-Photon Direct Laser Writing For Fiber-Optical Microendoscopy

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 mu m. 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. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement