Replication of optical microlens array using photoresist coated molds

Area of Science:

• Materials Science
• Optical Engineering
• Manufacturing Processes

Background:

• Injection molding tools for optical microlens arrays often involve high production costs.
• Achieving high optical quality and specific performance metrics like acceptance angle is crucial for applications such as LED light engines.

Purpose of the Study:

• To develop and demonstrate a cost-reduced method for producing injection molding tools for optical microlens arrays.
• To optimize the tool and process for fabricating a beam homogenizer for a color mixing LED light engine.

Main Methods:

• Utilized a standard computer-numerical-control (CNC) milling machine to create a rough steel mold.
• Applied a spray coating of photoresist to the steel mold for surface smoothing and improved optical quality.
• Fabricated polymer microlens arrays using both rough and coated molds.

Main Results:

• Surface roughness (Ra) was improved by approximately a factor of two after the photoresist coating process.
• Light scattering was reduced, enabling the use of the molded microlens array in color mixing applications.
• The measured acceptance angle of the microlens array was 40°, consistent with simulations.

Conclusions:

• The developed cost-reduced method effectively produces high-quality optical microlens arrays suitable for LED light engines.
• Surface treatment of CNC-milled molds is a viable technique for enhancing optical performance and reducing manufacturing costs.