Liquid lens, as a novel type of adaptive zoom optical element, is widely used in fields such as biomedical detection and 3D display, offering an advanced approach to achieving large depth of field, wide viewing angle, high speed, and high-quality imaging in zoom optical systems. As one of the most popular types of liquid lens, electrowetting liquid lens has advantages such as small size, easy integration, low power consumption, large zoom range, and fast response speed, being well-suited for compact and high-speed zoom optical imaging systems. However, electrowetting liquid lens is prone to dielectric failure under high voltage, and with increasing aperture, the failure probability will be higher and occur within wider voltage range. This reliability issue severely limits the application of large-aperture electrowetting liquid lens in various optical scenarios.
To address the issue of dielectric failure in large-aperture electrowetting liquid lens, we develop unique electrowetting liquid materials based on the theory of dielectric failure suppression. These materials are successfully applied to centimeter-level large-aperture electrowetting liquid lens, achieving ideal imaging results, as shown in Fig. 1. Using standard coating processes and thicknesses for the dielectric and hydrophobic layers, we fabricate a centimeter-level electrowetting liquid lens that operates without dielectric failure under a high voltage of 200V. This lens features an optical power variation range of -11.98m-1 to 12.93m-1, with clear and high-quality imaging function, which can enlarge the field of view and depth adjustment range of holographic reconstructions while maintaining excellent edge clarity of the reconstructed images.
Figure 1 Concept diagram and sample of the proposed centimeter-level large-aperture non‑aqueous electrowetting lens.
In this work, we first apply the transport properties of electrolyte solutions in physical chemistry and the impact of electrochemical reaction rates to reveal the mechanism of dielectric failure. Consequently, a method to suppress dielectric failure is derived from this analysis, as shown in Fig. 2. We reveal the criteria for selecting the conductive liquid for the electrowetting lens: removing reactants involved in electrochemical reactions and controlling the conductivity of the liquid. We screen the electrolyte ions and solvent molecules contained in the electrowetting conductive liquid materials. We select more stable, less prone to electrolysis, non-aqueous polar solvents, supplemented with a small number of organic salt ions to ensure that the solution has a certain conductivity, with a short characteristic relaxation time, resulting in an overall Ohmic response of the solution. Based on this theory, we develop a series of non-aqueous organic solutions to suppress high-voltage dielectric failure. We identify the optimal formulation for comprehensive optical performance and fabricate a centimeter-level large-aperture electrowetting liquid lens.
Figure 2 Principle of preparation of conductive liquid to suppress dielectric failure .
The schematic structure of the proposed 10mm-aperture electrowetting liquid lens is illustrated in Fig. 3. The lens comprises an upper electrode, a lower electrode, a shim, an upper window glass, the conductive liquid, and the insulating liquid. The lens has an aperture of 10mm and a thickness of only 6mm, resulting in an aperture-thickness ratio of 1.67. This lens exhibits excellent optical performance, with a maximum focal power change of 24.91m-1, a rise time of 174ms, and a fall time of 45ms, producing clear and high-quality imaging function.
Figure 3 Structure of the centimeter-level large-aperture non‑aqueous electrowetting lens .
To sum up, our study pioneers the application of electrolyte solution transport properties and electrochemical reaction rates from physical chemistry to reveal the mechanisms of dielectric failure. The non-aqueous electrowetting liquids introduced in this work achieve outstanding dielectric failure suppression, breaking through the fabrication barriers of a centimeter-level large-aperture lens. This advancement holds the potential to revolutionize fields such as 3D display and reconstruction, biomedical observation, and more, offering unprecedented capabilities and new possibilities.