There is an ever increasing demand for low cost, high volume solutions for lens assemblies with adjustable focal length. Modern mobile phones, for example, are now equipped with miniature digital camera modules and the quality and cost demands for lenses and lens assemblies are increasing. More and more miniature cameras used in for example mobile phones and laptop computers comes with auto focus functionality. The design of lens systems for such applications requires fulfilment of a number of requirements, such as ease of operation when fitting the lens on top of a camera module, by providing as few operational steps as possible, etc. These challenges are even greater when the lens arrangement comprises tuneable parameters, such as encountered in auto focus lenses, wherein the focal length must be adjusted to fit the distance from the lens to the object to be photographed, for example. Such lenses are usually complex designs comprising movable parts which can make it difficult to assemble the lens in a simple manner. A further challenge with such designs is the ever increasing requirement to provide as thin lens assemblies as possible. Thin and lightweight mobile phones and cameras are a must in the marketplace.
There exist a number of feasible solutions for making compact auto focus lens elements. For example, liquid filled lens elements based on the principle of electro wetting is disclosed in WO2006136613. Another example is disclosed in the article “Design, fabrication and testing of a micro machines integrated tuneable micro lens”, by Weisong et. Al., Journal of Micromechanics and Microengineering, 9 May, 2006, wherein a lens assembly containing a liquid in a cavity may be compressed or elongated to achieve an adjustment of focal length of the lens.
Both these two examples of prior art lenses comprise one or more liquids. Filling and confining a liquid to a cavity may impose problems during both production and use, as known to a person skilled in the art.
Another principle for a tuneable lens assembly is described in U.S. Pat. No. 4,802,746, wherein a plurality of elastic members is superposed in the optical axial direction. By applying a force on a side of the lens element, a deformation creates a curvature that results in variable focal properties, depending on the magnitude of the applied force.
JP 02178602 disclose a lens with an adjustable focal length comprising a transparent fluid 4 bounded by two transparent surfaces 1d, 2 and an elastic sealing material 3. The curvature of one of the transparent surfaces (1d) is adjusted by applying voltages onto a transparent piezo electric film 1c disposed onto the transparent surface.
JP 01140118 disclose a lens with an adjustable focal length comprising two transparent surfaces 1,3 with a fluid 2 in between bounded by a wall 10. The fluid 2 can be a gel or polymer. One of the transparent surfaces is a transparent piezo electric polymer, wherein the curvature of this surface is controlled by applied voltages onto the two electrodes 4, 5.
US 2002/0048096 disclose how to control deformations of a mirror 1. Piezo electric actuators 3 are arranged in a pattern on the backside of the mirror, and the deformation is controlled based on signals received from sensors attached to the mirror.
The Norwegian patent application No. 20065237 disclose a lens assembly comprising a floating glass cover on top of a gel or elastomer disposed on a transparent support. Piezoelectric actuators on top of the floating glass cover located in the periphery of the floating glass cover provides bending of the floating glass cover when activated that results in a change of the surface curvature of the gel or elastomer. However, the range of focal length adjustments is limited due to the limited range of bending of the floating glass cover. If the actuating force is to high, the edge of the floating glass cover may cut the gel or elastomer located directly under the edge of the floating glass cover thereby damaging the lens body, and hence the range of focal length adjustments are limited by this possibility of damaging the lens body.
Therefore there is a need to provide a lens assembly that provides the principal benefits of a lens assembly as disclosed in the Norwegian patent application No. 20065337, and that at the same time provides an increased range of focal length adjustments without changing properties of the lens assembly when adjustments are performed, and that protect the lens body against any form of damage when adjustment is performed in the whole range of adjustments, and that protect the lens body from damage or interference during manufacturing, when making interconnections, etc. of other optical and electronic components used together with the lens assembly according to the present invention. This property of the lens assembly according to the present invention also protects the lens assembly when using the lens assembly in an application.