Microlens arrays enable variable-focus imaging

Microlens array (MLA) is a key part of optical element for biomedical inspection, lab-on-a-chip device, and light-field cameras. However, conventional MLAs always have only one focal plane, which makes them difficult to capture targets at different positions. To solve this problem, a planar multi-focus MLA (MF-MLA) was prepared on a polydimethylsiloxane (PDMS) substrate by a combination of femtosecond laser wet etching (FLWE) and soft lithography techniques. The modulation transfer function (MTF) values of the microlenses all exceeded 0.2 when the spatial frequency was less than 200 lp/mm, indicating the high imaging ability of the lenses. The reported MF-MLA had three different focal lengths, so that targets at different positions could be easily imaged on a single image sensor. In addition, MLAs with more focal points could be fabricated by selecting appropriate processing parameters. It is anticipated that the as-fabricated MF-MLA will become a promising device to improve the performance of the optical system, especially in optical remote sensing, biomedical imaging, and machine vision.