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Tunable liquid lenses with controllable focal length attract much attention from many researchers due to the unique advantages of strong adjustability, low power consumption, fast response time, and easy integration. In the last two decades, tunable liquid lenses have already been applied in machine vision, code scanner cameras, cellphone cameras, webcams, microscopes, mini projectors, AR/VR displays, 3D displays, and so on. There is no doubt that the tunable liquid lenses play an increasingly more important role in the field of optical technology. In this review, the research background and significance of the tunable liquid lenses are introduced. Tunable liquid lenses are systematically qualified according to the driving mechanism, and their current status and latest progress are presented in detail. The existing problems, directions for future research, and current and potential applications of the tunable liquid lenses are also discussed. [ABSTRACT FROM AUTHOR]

We demonstrate a multi-curved liquid lens with movable liquid–liquid(L–L)​ interface, which has a wide range of focal length. Due to movable L–L interface, the proposed lens can also be used as a single lens to achieve zoom function. The movement of the L–L interface can be achieved by controlling the flow of the liquid, which in turn changes the object distance and image distance to achieve the desired magnification. We fabricated a prototype based on this concept. The experimental result shows that when the movement distance of the L–L interface is ∼ 10 mm, the shortest positive and negative focal lengths of the lens are 9.3 mm and −8 mm, respectively, and the zoom ratio is 1.3 ×. The proposed multi-curved variable-focus lens simplifies the zoom imaging system, and its widespread applications in imaging systems are predictable. [ABSTRACT FROM AUTHOR]

• The first annular variable focus Fresnel lens driven by electrowetting. • Each annular region can be independently controlled, and achieve multiple functions. • Suitable for applications as an optical collection device and for achieving uniform beam illumination. Traditional Fresnel lenses can achieve volume diminution by reducing lens material cost, thereby achieving further integration in optical systems. However, the solid Fresnel lenses in being are fixed once they are fabricated due to the limitation of materials, so their optical parameters, like focal length, cannot change. In this paper, we propose a ring-shaped tunable optofluidic Fresnel lens (OFL) based on the electrowetting effect for the first time. Each annular region of the OFL can be independently controlled. By changing the tilt angle of the liquid-liquid interface of each annular region to control the deflection of the beam, the OFL can achieve axial zoom and multi-focus, as well as off-axis zoom. We analyze and establish a theoretical model, provide calculation formulas for the focusing position, and explain the design principle of an annular Fresnel lens driven by electrowetting. A three-annular-regions OFL is fabricated, and we test the focal length of each ring band through experiments to prove the correctness and feasibility of our proposed theory. The OFL can achieve a maximum zoom range of -254 mm to 223 mm. At the same time, we also demonstrate the different working modes of the OFL for applications such as light collection and uniformity. The OFL has a variety of functions, with a lightweight and thin thickness, which meets the expectations of a more and more compact liquid photonic device in the future. We expect this innovative OFL will have extensive applications in various fields, such as optical imaging, lighting engineering, motion tracking, infrared tracking, solar energy collection, and so on. [ABSTRACT FROM AUTHOR]

The conventional electrowetting lens usually has one tunable liquid-liquid (L-L) interface. The shape of L-L interface is deformed to get variable focal length due to electrowetting effect. However, contact angle saturation of the L-L interface is an unavoidable problem which prevents focal length from further changing. Here, we demonstrate an optofluidic lens based on electrowetting liquid piston. The proposed lens has two connected chambers, the piston chamber and the lens chamber to form a closed-loop fluidic system. The electrowetting liquid piston can generate clockwise and counter-clockwise liquid flows, which can make the L-L interface convex and concave. To prove the concept, we fabricate an optofluidic device whose shortest negative and positive focal lengths are ~−17.9 mm and ~18 mm with 5 mm aperture, respectively. The proposed optofluidic lens has large tunable focal length range. Widespread application of such an adaptive lens is foreseeable. [ABSTRACT FROM AUTHOR]

In this paper, we propose and experimentally demonstrate a tunable liquid lens integrated with an aspherical surface for spherical aberration and distortion compensation. Through optimizing the aspherical surface's morphology, the spherical aberration and distortion can be significantly reduced. The root mean square spot size at focus is distinctly reduced from 55. 7 μ m to 2. 095 μ m after performing optimum optimization. The tunable liquid lens is integrated with the aspheric surface with 6 mm clear aperture and 19.2 mm minimum focal length and demonstrate the improvement in optical performance over the conventional lens without an aspheric surface over a focal length range. Its applications in microscope system and tunable-focus eyeglasses are foreseeable. [ABSTRACT FROM AUTHOR]