Interfacing high numerical aperture metalenses with thermally expanded core fibers via 3D nanoprinting for advanced meta-fiber operation

This study introduces a novel meta-fiber design that combines single-mode fibers with thermally expanded cores and nano-printed high numerical aperture metalenses. These advanced meta-fibers feature enlarged mode field diameters, offering improved mechanical stability, reduced environmental sensitivity and simplified metalens design by minimizing wavefront curvature. The concept's validity is confirmed through high numerical aperture metalenses, nanoprinted onto thermally expanded core fibers, demonstrating diffraction-limited focusing up to a numerical aperture of 0.9 in air and water. This innovative approach has potential applications in optical trapping, life science imaging, environmental sensing, and fiber-chip coupling in integrated photonics.