Zernike-guided correction of phase errors in two-photon polymerization over extended printing areas

Abstract

Two-photon polymerization (TPP) has emerged as a powerful technique, widely used across various fields for high-precision 2D and 3D microfabrication. One of its promising applications lies in the fabrication of purely phase-based transparent structures, which proved to be helpful in micro-optics, optical metrology, nanophotonics, novel microscopy techniques, and many more, via testing, calibrating, or enhancing these modern developing areas. However, achieving an accurate control over the phase properties of written structures, especially across extended printing areas still remains a challenge. In this study, we introduce a feedback-loop correction methodology that is compatible with any TPP fabrication system. Our approach relies firstly on an interferometric measurement of the phase map of printed test-component, performed in ex-situ microscopic system. Then, translating its inverse into the designed phase-influencing features of the fabricated body (refractive index and axial thickness) to further compensate the acknowledged artifacts. By using a Zernike polynomial-based analysis of the measured phase map, we unlock a precise error study and allow an accurate correction of each separated component. Such methodology reduces phase errors by up to a factor of 6, lowering the standard deviation from 5.40 rad to 0.83 rad over a 400 μm diameter area, at a wavelength of 635 nm. This marks a significant advancement in phase control over larger area. To validate the effectiveness of our correction, we fabricate a customized set of phase structures spanning the system's maximum printing area, demonstrating their potential practical applications. This work paves the way for more refined phase control in TPP, opening new possibilities for microfabrication in optics, biology, and beyond.