A study was conducted to investigate electrowetting reversibility associated with repeated voltage actuations for an aqueous droplet situated on a silicon dioxide insulator coated with an amorphous fluoropolymer film ranging in thickness from 20 to 80 nm. The experimental results indicate that irreversible trapped charge may occur at the aqueous-solid interface, giving rise to contact angle relaxation. The accumulation of trapped charge was found to be related to the applied electric field intensity and the breakdown strength of the fluoropolymer. On the basis of the data, an empirical model was developed to estimate the amount of trapped charge in the fluoropolymer as well as the voltage threshold for the onset of irreversible electrowetting.

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We have previously shown through simulation that an optical beam deflector based on the Pancharatnam (geometric) phase can provide high efficiency with up to 80° deflection using a dual-twist structure for polarization-state control [Appl. Opt.54, 10035 (2015)]. In this report, we demonstrate that its optical performance is as predicted and far beyond what could be expected for a conventional diffractive optical device. We provide details about construction and characterization of a ± 40° beam-steering device with 90% diffraction efficiency based on our dual-twist design at a 633nm wavelength.