Fabrication method of self positioned and focal length tuned microlens

We report a solid microlens with self-positioning and tuned focal length using hydrophobic effects and electrowetting. We propose a novel fabrication method aligning the centers of electrodes and hydrophobic pattern simultaneously using one photomask. The proposed fabrication method offers a solid microlens by using a UV curable polymer. The focal length of the liquid microlens can be tuned to the targeted value by applying voltage to the electrodes before UV exposure solidification. Experiments showed that tuning range of focal length by using electrowetting is 0.43 mm. It covers the initial focal length deviation 0.21 mm of the microlens. Seven samples showed the initial distribution from 1.78 to 1.58 mm in focal length. Their focal lengths are controlled by applying voltages from 1.77 to 1.82 mm. Volume contraction and following focal length change were evaluated, and optical losses are measured to be 0.92 and 0.49 dB in red and green, respectively. The measured surface roughness is 4nm, which is applicable to optical micro-systems.