Polymer microlens with independent control of radius and focal length for an imaging fiber

Abstract

Fabrication of microlens array using polymer reflow is beginning to be a mainstream process, whether the polymer is directly used or whether the spherical profile is transferred by plasma etching to a glass substrate as, for example, in some handphone cameras. The focus so far has been on uniformity and obtaining lenses with equal radius and equal focal length. Actually it is easy to show using a phenomenological model that the focal length is depending on the lens radius, and not much on the contact angle, an effect that can be traced to the line tension force. For a biomedical application we need to terminate a 600um diameter imaging fiber with a group of lenses of different diameters - but with similar focal length. We have devised a microfabrication process on a silicon wafer to produce the lens with variable diameter and identical focal length, while etching the silicon wafer has helped us producing a sheath to insert the optical fiber and mount the lenses on the optical fiber.