All‑optical fabrication of microlens arrays with multi‑foci capabilities

Introduction

Microlenses play a central role in modern imaging, sensing, and micro‑optical systems by enabling precise light focusing in compact architectures. Conventional fabrication approaches, however, often require costly, multi‑step, and mask‑based processes. Azopolymer‑based holographic lithography has recently emerged as a cost‑effective, maskless, and fully optical strategy for surface micro‑fabrication. In this work, we demonstrate a one‑step, all‑optical method for fabricating microlens on azopolymer films using computer‑generated holography (CGH).

Methods

Azopolymer films were deposited on glass substrates using spin coating. A CGH‑generated intensity pattern served as the illumination source, providing a maskless and digitally controlled illumination strategy. To induce microlens formation, we designed an illumination pattern consisting of dark circular apertures inside a bright background. The intensity gradients triggered light‑driven mass migration within the azopolymer, producing microlens‑like structures at the locations of the dark apertures. Microlens morphology was characterized using atomic force microscopy. Optical performance, including 3D point‑spread functions and focal properties, was evaluated using a custom imaging setup and motorized scanning stage.

Results

A single illumination step successfully produced microlenses at the designed dark‑aperture positions. Exposure time primarily governed microlens growth: longer illumination yielded structures with smaller curvature radii and increased spherical‑cap volume. Minor deviations from ideal spherical profiles were consistently observed, reflecting the intrinsic dynamics of light‑induced mass migration. Optical measurements showed that focal length decreased with increasing exposure time. Conversely, varying the dark‑aperture diameter at fixed exposure time controlled the final microlens aperture, with larger apertures producing longer focal lengths. Using these parameters, we fabricated spatially complex microlens arrays with multiple focal lengths in a single optical step.

Conclusions

Azopolymer‑based holographic lithography enables rapid, maskless, and fully optical fabrication of microlens arrays with tunable spatial and axial focusing properties. This approach offers a promising alternative to conventional microlens manufacturing techniques.