An Experimental Study of PTFE Surface Roughness Effect on Microlens Fabricated by Thermal Reflow

摘要

The geometrical profile of a lens directly affect on its optical performance. The lens sag and diameter are the most important geometrical parameters. This paper presented the investigation on the effect of surface roughness on sag and diameter of microlens, fabricated by thermal reflow technique on PTFE substrate. Experiments using various surface roghnesses of PTFE substrates for microlens array production in thermal reflow are designed and conducted. A photomask with aperture diameter 40μm pattern array and photoresist AZ4620 were used to pattern lens structures by the lithography process followed by a thermal reflow process. The experimental results showed that high surface roughness resulted in a large sag-to-diameter ratio of microlens, corresponding to high numerical aperture (NA). By this method, the profile of fabricated microlens is close to hemisphere. Its sag-to-diameter ratio can be improved from 0.29, corresponding to NA 0.32, to 0.46, equivalent to NA 0.44.