Design and fabrication of a freeform microlens array for uniform beam shaping

Freeform optics has become a practical solution to solving number of problems in modern optical design. In this paper, we proposed a fabrication method using the combination of ultraprecision diamond machining and microinjection molding to achieve high volume and low cost freeform microlens manufacturing. The freeform microlens array discussed in this research is capable of redistributing a collimated light into a pre determined, in this case, a uniform pattern. The optical design, slow tool servo diamond machining, microinjection molding process and optical measurement were discussed. The simple optical design provided a platform for freeform microlens calculation. Slow tool servo diamond broaching was selected to fabricate the mold insert. After the mold insert was fabricated, microinjection molding machine was utilized to replicate the optical geometry into plastic substrates. The freeform microlens array that was fabricated in this research could achieve light re-distribution at the target with approximately 80% uniformity. The research conducted in this paper can be readily implemented in optical industry.