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Lenses with tunable focal lengths play important roles in nature as well as modern technologies. In recent years, the demand for electrically tunable lenses and lens arrays has grown, driven by the increasing interest in augmented and virtual reality, as well as sensing applications. In this paper, we present a novel type of electrically tunable microlens utilizing polymer-stabilized chiral ferroelectric nematic liquid crystal. The lens offers a fast response time (5ms) and the focal length can be tuned by applying an in-plane electric field. The electrically induced change in the lens shape, facilitated by the remarkable sensitivity of the chiral ferroelectric nematic to electric fields, enables the tunable focal length capability. The achieved performance of this lens represents a significant advancement compared to electrowetting-based liquid lenses and opens exciting prospects in various fields, including biomimetic optics, security printing, solar energy concentration, and AR/VR devices. 

The isotropic to ferroelectric nematic liquid transition was theoretically studied over one hundred years ago, but its experimental studies are rare. Here we present experimental results and theoretical considerations of novel electromechanical effects of ferroelectric nematic liquid crystal droplets coexisting with the isotropic melt. We find that the droplets have flat pancake-like shapes that are thinner than the sample thickness as long as there is room to increase the lateral droplet size. In the center of the droplets a wing-shaped defect with low birefringence is present that moves perpendicular to a weak in-plane electric field, and then extends and splits in two at higher fields. Parallel to the defect motion and extension, the entire droplet drifts along the electric field with a speed that is independent of the size of the droplet and is proportional to the amplitude of the electric field. After the field is increased above 1 mV μm −1 the entire droplet gets deformed and oscillates with the field. These observations led us to determine the polarization field and revealed the presence of a pair of positive and negative bound electric charges due to divergences of polarization around the defect volume. 

Abstract Tunable optical lenses are in great demand in modern technologies ranging from augmented and virtual reality to sensing and detection. In this work, electrically tunable microlenses based on a polymer‐stabilized chiral ferroelectric nematic liquid crystal are described. The power of the lens can be quickly (within 5 ms) varied by ≈500 diopters by ramping an in‐plane electric field from 0 to 2.5 V µm⁻¹. Importantly, within this relatively low‐amplitude field range, the lens is optically isotropic; thus, its focal length is independent of the polarization of incoming light. This remarkable performance combines the advantages of electrically tuned isotropic lenses and the field‐controlled shape of the lens, which are unique properties of chiral ferroelectric nematic liquid crystals and have no counterpart in other liquid crystals. The achieved lens performance represents a significant step forward as compared to liquid lenses controlled by electrowetting and opens new possibilities in various applications such as biomimetic optics, security printing, and solar energy concentration.