Closed-loop wavefront calibration of a multi-electrode electrowetting-based tunable microlens

Tunable liquid micro-optical lenses and phase shifters based on multi-electrode electrowetting actuation are often subject to wavefront errors due to processing irregularities or surface defects. To enable the correction of these anomalies, we present here a method that allows calibration and compensation for wavefront errors, thereby leading to the best possible optimization of the tunable optical surface. The approach relies on a measurement of the transmitted wavefront using a Shack–Hartmann sensor and subsequent determination of the actual surface shape. The deviation between this and the target surface shape is calculated, and the electrode voltages are iteratively adjusted. A decentralized control algorithm is implemented which treats the meniscus height at each electrode as a variable with independent feedback; an adaptive update condition determines which electrodes should be adjusted in each cycle. Experimentally obtained calibration curves for a 32-electrode device demonstrate the power and utility of the method.