Water droplets offer route to versatile liquid lenses

28 Apr 2025

Ateneo de Manila University method may be a simple way to make dynamic focusing components.

A project group including Ateneo de Manila University and Caraga State University has developed a simple way to create adjustable liquid lenses for multiple potential applications.

The new method is based on using water as the lens fluid, building on the multiple studies of that liquid as a potential focusing material.

Most existing water-based liquid lenses operate by changing the curvature of water at the refractive interface, noted the Manila team. By altering the morphology of the interface, the refraction direction of the beam changes and the focal length of the lens can be altered.

The new project took a modified approach, investigating the feasibility of a static water droplet acting as variable liquid lens. The results were published in Results in Optics.

"This was inspired by the natural shape of a water droplet on a flat surface, which resembles a plano-convex lens," wrote the team in its published paper. "We vary the size and curvature of the droplets by changing the droplet volume, resulting in a variable focusing effect."

The project used a glass slide as a substrate, but enhanced the surface's hydrophobic nature by coating it with a polyvinyl chloride (PVC) plastic. By then adding or removing water from the droplet on the slide, the magnifying power of the liquid lens could be changed and controlled.

New liquid lenses for commercial products

"Various surface modification techniques have enabled commendable performance in dynamic liquid lenses, but these approaches often suffer from complexity and high cost," noted the project. "These limitations highlight the need for simpler and more cost-effective solutions for dynamic liquid lens fabrication."

The key surface treatment in the Manila approach is carried out through electrospinning, in which PVC is melted in an electric field before being stretched out and deposited onto the glass slide as fine microfibers. Varying the deposition time alters the extent and distribution of the microfibers, influencing the degree of hydrophobia shown by the treated surface.

With the modified surface sustaining a droplet's coherence, changes to the droplet volume can then control lens behavior: larger droplets act like lenses with longer focal lengths when laser light was passed through them, while smaller droplets behaved like close-up lenses with the laser maintaining a clean and undistorted beam.

"Because it is low cost, simple to make and easy to use, this discovery has multiple potential practical applications," said the researchers. "It could be used in science classrooms to teach optics, particularly in schools with limited lab equipment; in remote or low-resource areas, it could help build basic optical tools for experiments or diagnostics; and even in research labs, it offers a quick way to adjust laser beams."

The project also expects this research to lay the groundwork for more advanced liquid lenses as commercial products, potentially used in cameras, microscopes, and even wearable tech. With further development, it might also be employed in portable diagnostic devices, or small projection and lighting systems.