Variable focus convex microlens array on K9 glass substrate based on femtosecond laser processing and hot embossing lithography.

We propose a high-precision method for the fabrication of variable focus convex microlens arrays on K9 glass substrate by combining femtosecond laser direct writing and hot embossing lithography. A sapphire master mold with a blind cylindrical hole array was prepared first by femtosecond laser ablation. The profile control of microlenses dependent on the temperature and the diameter of the blind hole in the sapphire mold was investigated. The curvature radius of the microlens decreased with temperature and increased with diameter. Uniform convex microlens arrays were fabricated with good imaging performance. Further, variable focus convex microlens arrays were fabricated by changing the diameter of the blind hole in sapphire, which produced the image at variable z planes. This method provides a highly precise fabrication of convex microlens arrays and is well suited for batch production of micro-optical elements.