Femtosecond laser polymerization of hybrid/integrated micro-optical elements and their characterization

TLDR

The study aimed to improve 3D laser polymerization efficiency by forming lenses via outer‑shell scanning and UV exposure of the interior. Femtosecond laser multi‑photon polymerization of a zirconium–silicon sol–gel photopolymer was used to fabricate micro‑optical elements—including convex, Fresnel, and solid immersion lenses and gratings—on glass slides and fiber tips, with polymer caps of 10–90 µm radii and refractive‑index‑matched composite glass‑resist structures acting as single lenses. The fabricated solid immersion lenses exhibited measured magnifications matching theoretical predictions, surface roughness below ~30 nm, and successful integration onto optical fiber tips, confirming their optical performance.

Abstract

The femtosecond laser-induced multi-photon polymerization of a zirconium–silicon based sol–gel photopolymer was employed for the fabrication of a series of micro-optical elements with single and combined optical functions: convex and Fresnel lenses, gratings, solid immersion lenses on a glass slide and on the tip of an optical fiber. The microlenses were produced as polymer caps of varying radii from 10 to 90  µm. The matching of refractive indices between the polymer and substrate was exploited for the creation of composite glass-resist structures which functioned as single lenses. Using this principle, solid immersion lenses were fabricated and their performance demonstrated. The magnification of the composite solid immersion lenses corresponded to the calculated values. The surface roughness of the lenses was below ~ 30 nm, acceptable for optical applications in the visible range. In addition, the integration of micro-optical elements onto the tip of an optical fiber was demonstrated. To increase the efficiency of the 3D laser polymerization, the lenses were formed by scanning only the outer shell and polymerizing the interior by exposure to UV light.