Design, fabrication, and optical imaging performance comparison of precision microlens arrays for application in plenoptic microscopy systems

This study focuses on analyzing the characteristics of a microlens array produced by 3D diffusion lithography and the characteristics of the optical system based on the arrangement of the lenses. The microlens array, with an 85 μm pitch, 2.1 mm focal length, and 1 μm sag, was designed to match the numerical aperture of a 10×, 0.25 NA objective lens. Photoresist, aluminum, and photoresist layers were deposited onto a silicon substrate. After patterning with a photomask, the aluminum layer was etched to form a metal mask for subsequent diffusion lithography. The use of a metal mask improved the uniformity of the mold of the microlens array. A microlens array was replicated using polydimethylsiloxane, and the characteristics of this lens were very close to the design values, with an average pitch of 86.02 μm, sag of 1.078 μm, and substrate thickness of 1.067 mm. In addition, the Strehl ratio had a median value of 0.975, indicating excellent performance. The microlens array was integrated into two configurations: plenoptic camera module 1, in which the microlens array was directly attached to the sensor, and plenoptic camera module 2, in which it was mounted separately. A comparative analysis of the spatial resolution and depth of field of both modules revealed that both configurations achieved the same spatial resolution of 7.8 μm. However, plenoptic camera module 2 provided a wider depth of field than plenoptic camera module 1, allowing for clear imaging over a broader depth range.