Simulating the functioning of variable focus length liquid-filled lenses using the finite element method (FEM)

A variable focal length liquid-filled lens (VFLLFL) is a lens that changes its focal length by modifying the amount of water contained on it. Recent studies show that the use of VFLLFL in micro-optical devices makes them light, simple and compact. The VFLLFL under study is composed of a cylindrical metal mount with a compartment for two elastic membranes and a liquid medium between them. Unlike previous studies that have focused on developing micro-lenses filled with liquid and with thin flat membranes, this paper presents the design, simulation, and analysis of the opto-mechanical behavior of the VFLLFL formed with thick membranes of different profiles and 2 cm diameter. The study considered three lenses with membranes of different profiles. To do so, a preliminary optical design was done of the lenses to reduce the spherical aberration; next, the study describes the modeling, simulation, and analysis of the mechanical behavior of the VFLLFL using FEM. Then a Genetic Algorithm application was developed to obtain the geometrical parameters of the lens when the shape changes due to pressure applied by the liquid medium on the internal surfaces of the membranes. Finally, with the initial geometrical parameters which the lens begins to adjust due to changes of pressure, an analysis and simulation were done of the optical behavior of the lenses using the OSLO commercial ray-trace program. The results obtained are shown.