Variable aperture controlled by microelectrofluidic iris

This Letter presents an adaptive liquid iris based on microelectrofluidic technology with experimental results. In the microelectrofluidic iris (MEFI), the electrostatic force generated by electrowetting in a surface channel unbalances the Laplace pressure acting on two fluidic interfaces between air and a light-absorbing liquid in two connected surface channels in a chamber. Then, the changed net pressure makes the iris aperture of the liquid diaphragm adjustable. The present MEFI was designed to have a tunable range from 4.2 to 0.85 mm in diameter and a tuning ratio of 80%. The MEFI was fabricated with a transparent electrode patterned on three glass plates and two channel spacers. Concerning the optical and interfacial properties of the MEFI for its operation, an aqueous near-infrared dye used in optical coherence tomography (OCT) was forced into a ring shape as the driving liquid in the hydrophobic chamber. By switching the segmented concentric control electrodes in steps, digital operation of the MEFI was successfully observed with clear aperture stops. The measured turnaround speed was 80 mm/s, which is significantly higher than that for other comparable adaptive liquid irises. Due to a scalable aperture range with fast response, the concept of MEFI is expected to be widely applied in various optical systems that require high-quality imaging, as well as in real-time diagnostic OCT.