Optical imaging systems and cameras with autofocus and zooming functions typically require the physical shifting of lens elements to change the overall magnification of the optical system. This is usually realized by means of a bulky mechanical positioning unit. The large physical dimension of such focusing or zooming systems makes it difficult to place such functions onto miniaturized optical systems and cameras.
The scientists at the Fraunhofer IPMS developed a variable focus micro-lens with a compact and scalable design that could be implemented in a variety of miniaturized optical imaging systems. In the liquid-filled micro-lens, the radius of curvature of a lens membrane – and consequently the focal length of the lens – is adjusted by exerting a hydraulic pressure on the membrane. This pressure originates from the mechanical displacement of a liquid inside a silicon micro-fluidic chamber by means of a voltage-driven electroactive polymer actuator of large deformation. The micro-lens is manufactured using wafer level technology, which provides highly precise processing of structures and accurate alignment of optical elements.
The fluidic variable focus micro-lens features a compact design, optical apertures of a few millimeters and voltage adjustable focus range of up to tens of diopters. It can be integrated in miniaturized autofocus or zoom objectives – for instance for a cell phone camera – or in optoelectronics, photonics or image processing components and systems.
On the left side images of two objects 5 cm apart are presented as seen through a lens system including the tunable micro-lens.