In endoscopy there is a need for cameras with adjustable focus. In flexible and capsule endoscopes conventional focus
systems are not suitable, because of restrictions in diameter and lens displacement range. In this paper it is shown that
electrowetting-based variable-focus liquid lenses can provide a solution. A theoretical comparison is made between
displacing and deforming lenses, and a demonstrator was built to prove the optical feasibility of focusing with liquid
lenses in endoscopes.
A 1.7× VGA zoom camera was designed based on two variable-focus liquid lenses and three plastic lenses. The strongly
varying curvature of the liquid/liquid interface in the lens makes an achromatic design complicated. Special liquids with
a rare combination of refractive index and Abbe number are required to prevent chromatic aberrations for all zoom levels
and object positions. A set of acceptable liquids was obtained and used in a prototype that was constructed according to
our design. First photos taken with the prototype show a proof of principle.
The design, manufacturing and application of variable liquid lenses are discussed. The interface between the two immiscible liquids that forms the lens can be altered with a voltage. Results are presented of applying this lens in miniature autofocus and zoom cameras, in optical recording and in illumination systems.
Electrowetting is electrostatic manipulation of liquids. It can be used to displace and deform volumes of polar liquids. A very promising application area is optics. The surface of a volume of liquid can be used as a tunable lens and displacement of the liquid can change the refraction, diffraction or transmission of light when passing through the liquid. In this paper we describe a selection of various tunable optical components that make use of electrowetting, ranging from refractive and diffractive lenses to diaphragms and displays.
The meniscus between two immiscible liquids can be used as an optical lens. A change in curvature of this meniscus by electrowetting leads to a change in focal distance. We demonstrate that two liquids in a tube form a self-centered tunable lens of high optical quality. Several properties were studied, such as optical performance, electrical characteristics and dynamic behavior. We designed and constructed a miniature camera module based on this tunable lens and show that it is very well suited for use in portable applications.