The Fabrication of Out of Plane Aspherical Microlens Arrays

MOEMS (Micro-Opto-Elecro-Mechanical Systems) has brought new inspirations to the traditional optics design and manufacturing, due to their advantages such as micro sizes, low cost, good performance, easy to integrate, and mass production. From the microfabrication technology perspective, microlens is among the most difficult components to make, and it is also the most important component of all free space micro-optic components. In recent years, the aspherical lens with controllable curvature has become one of the most popular research subjects since it is helpful in eliminating aberration. In this paper, we report a new method of fabricating and replicating aspherical microlens array with primary optic axis in parallel with the substrate surface. The technology was based on ultra-violet (UV) lithography of SU-8 thick resist. A novel water bath oblique lithography technique was adopted. Diameter of the prototype microlenses fabricated is about 200 mu m. By changing the pattern of mask and other process parameters, aspherical microlenses with different sizes and surface curvatures can be obtained. The microlens made using this technique has its main optical axis in parallel with the substrate, this makes it much easier to be integrated with other components into on-chip optical platforms such as optical switch and the imaging systems. This kind of micro-lens arrays will also be incorporated to microfluidic systems such as micro flow cytometry for fluorescence detections.