Magnetic control of liquid interfaces for tunable optofluidic lenses

Liquid lenses offer a versatile route to adaptive optics, but most existing implementations rely on mechanical deformation or high-voltage actuation, which limits scalability and long-term stability. Here, we demonstrate tunable liquid lenses based on magnetic body forces acting on optically transparent paramagnetic fluids. Spatial gradients of the magnetic field generate volumetric forces that reshape liquid interfaces in a controllable and reversible manner. Using a permanent ring magnet combined with a low-power electromagnet, we realize both concave lenses formed by a single paramagnetic liquid-air interface and compound convex lenses formed by a paramagnetic liquid coupled to an immiscible, nonmagnetic, higher-index liquid. We demonstrate experimentally, with good agreement with simulations, tunability of both types of liquid lenses and characterize their dynamic response and resolution limit. Because the actuation acts on the entire fluid volume, this approach is mechanically passive, electrically simple, and readily scalable, providing a promising platform for magnetically controlled adaptive liquid optics.