Another technique we have developed is mass production of microlens arrays. One example is shown below, in which one of our clients needed a microlens array to be used as beam homogenizer in a high power LED light engine. We designed this hexagonal lens array structure:
The lens arrays had to be produced by polymer injection molding to keep down the price, so a challenge was to make a double-sided mold, that within an Ø65mm diameter contained 2 X 2000 lenslet shapes in optical surface quality. Our solution was the following.
A regular CNC tool was used to fabricate the concave microlens shapes in the two steel parts forming the mold cavity. Subsequently, to fill out the milling roughnesses, we spray coated the mold parts with SU8 photoresist from Microchem:
The microlens arrays were produced in 500+ pieces without any sign of wear in the coating. A few of them are shown here:
The two laser light pictures clearly show that the CNC roughnesses disappears after spray coating the molds.