Tunable optofluidic Fresnel lens with ring-shaped electrodes

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.