Abstract:
A large, thin, variable focus lens that would be practical in a variety of applications, such as eyeglasses. An example of the present invention is a surface that can be deformed to a desirable shape in a simple, controllable fashion. In particular, a surface shape with desirable optical properties is achievable. The surface has the ability to produce a reflective or refractive surface with a variable optical power.

Description:
PRIORITY CLAIM 
   This application claims the benefit of U.S. Provisional Application Ser. No. 60/803,701 filed Jun. 1, 2006, which is hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   An imaging system generally needs the capability to adjust the focus to compensate for varying object distances. There are number of available techniques for performing this function. These techniques will primarily be described in terms of refractive imaging systems using lenses; however, equivalent reflective elements can often be substituted. 
   A first, and probably the most common, technique is to simply mechanically move the lens elements along the optical axis. The focus adjustments on a camera, microscope, or telescope are typical examples. There are numerous variations on mechanical focusing. The primary drawback of this technique is bulk. Large variation in lens position is required in order to accommodate large variations in object distance. 
   A second technique uses segmented optics with individual actuators on the segments. This approach is primarily seen in reflective optical systems such as large telescope mirrors. Segmented optical systems are primarily used in adaptive optics systems to compensate for variable distortions caused by effects such as atmospheric turbulence. Some limited focusing can be achieved with this technique. Clearly, the mechanical and control aspects of a segmented optic is very complex. 
   A third technique uses a liquid filled, elastic lens in which mechanical pressure is used to deform the curvature of the lens. This technique is exemplified by U.S. Pat. No. 7,142,369. Basically, the technique seeks to mimic the focus mechanism used in the eye. The main difficulties with this approach are that the lens quality is highly dependent on the elastic uniformity of the lens material and that the curvature achieved is not optimal for imaging. As with the eye, image quality is only good for objects near the center of the field of vision and non-uniform imaging, e.g. astigmatism, can occur. For larger lenses, gravity or acceleration can significantly affect the imaging quality by causing the lens to sag. 
   A fourth technique also uses a liquid lens approach. In this technique, two, non-mixing liquids are used, e.g. oil and water. An interface is formed between the liquids that can be deformed by applying an electric field. A small lens with a roughly one-to-one diameter to thickness ratio can be formed in this fashion. Large thin lenses are impractical with this approach due to fabrication constraints and gravity or acceleration effects. 
   A fifth technique utilized the ability to change the refractive index of some material by applying an electric field. This approach is exemplified in U.S. Pat. No. 7,215,480. Only small changes in refractive index can be obtained by this technique, which means only small changes in focus can be achieved. 
   SUMMARY OF THE INVENTION 
   The present invention provides a large diameter, thin, variable focus lens that would be practical in a variety of applications, such as eyeglasses. The present invention provides a surface that can be deformed to a desirable shape in a simple, controllable fashion. In particular, a surface shape with desirable optical properties is achievable. The surface has the ability to produce a reflective or refractive surface with a variable optical power. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings: 
       FIGS. 1A  and B shows a top view and cross section view of the invention, 
       FIGS. 2A  and B show the geometry and method by which the surface is controllably deformed, and 
       FIG. 3  illustrates a geometric relationship between components, and 
       FIGS. 4A-C  show an example surface deformation. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The current invention is shown as an optical device  8  in the top view and cross section shown in  FIGS. 1A  and B.  FIGS. 1A  and B shows a specific configuration that is of particular interest as an optical surface. Other configurations are clearly possible. 
   The device  8  includes a first material layer  10  and a second material layer  20 . The first material layer  10  is flexible. The second material layer  20  may or may not be flexible depending on the specific design properties desired. An array of rods  14  connects between layers  10  and  20 . The rods  14  may be round, hexagonal, square—the specific shape is not critical. For this configuration, the rods  14  should be mechanically stiff. 
   The connection between the rods  14  and the material layers  10  and  20  is via flex joints  24 . The flex joints  24  allow the angle between the rods  14  and the material layers  10  and  20  to rotate in both non-axial directions with respect to the material layers  10  and  20 . A ball and socket joint would be one implementation of the flex joint  24  with the ball being fabricated into the end of the rod  14  and the socket being fabricated into the material layers  10  and  20 . 
   A central rod  12  connects to the material layers  10  and  20 . A pair of rotational joints  22  connects the rod  12  to the layers  10  and  20 . The rotation joints  22  allow the material layers  10  and  20  to rotate with respect to each other around the axis defined by the center axis of central rod  12 . Unlike the flex joints  24 , the rotational joints  22  do not allow flexure in the non-axial angles. 
   This arrangement of rods  14 , flex joints  24 , central rod  12 , and rotational joints  22  allows the two material layers  10  and  20  to rotate with respect to each other, but not translate. 
   When the flexible material layer  10  is rotated about the axis of the central rod  12 , the effect for an individual rod  14  is shown in  FIGS. 2A  and B. As rotation occurs, the position of the flex joints  24  connected to each of the rods  14  is translated or shifted with respect to the initial alignment (initial vertically aligned). For a given shift (A) the spacing (t) between the two material layers  10  and  20  must decrease by an amount given by
 
 t =√{square root over ( D   2   −A   e )}  (1)
 
where D is the length of the rod  14 .
 
     FIG. 3  shows how the displacement (A) of an individual rod  14  is further connected to the rotation angle θ and the radial distance r between the central rod  12  and the individual rod  14 . The result is a quadratic relationship in the spacing between the two material lasers  10  and  20  and the radial distance from the rotation axis.
   t =√{square root over ( D   2   −r   2 θ 2 )}  (2) 
   With a stiff second material layer  20 , the first material layer  10  takes on a parabolic shape. This example is shown in  FIGS. 4A , B and C with  FIG. 4A  showing a cross section before rotation and  FIG. 4B  showing the same cross section after rotation. Note that the tilting of the rods  14  is in the plane perpendicular to the cross section, so cannot be seen in this view.  FIG. 4C  is supplied as a top view to clarify the varying tilt of the rods  14  with radius. If both material layers  10  and  20  are flexible, the spacing between the layers  10  and  20  will be parabolic with the relative curvature of each layer  10  and  20  being determined by the relative stiffness of the two layers. This curvature effect is illustrated in  FIG. 4 . 
   A parabolic surface is of particular interest in optics for imaging purposes. As demonstrated above, the imaging power or focal length of the surface is controlled very simply via the rotation angle, θ. A reflective surface is obtained by coating the first material layer  10  with a suitable metal or dielectric reflector. 
   A refractive element can be obtained by fabricating all of the components of a transparent material and then filling the empty space between the layers  10  and  20  with a liquid or gel (Fluid  26 ) with index of refraction that matches the other components. The matching index of refractions will cause all of the mechanical (solid) components to optically ‘disappear’. A thin, variable focus lens is thereby obtained.  FIGS. 1A  and B shows the use of a seal  16  is attached around the edge of material layers  10  and  20  to contain the fluid  26  within the assembly. For example, the seal  16  could be a rubber gasket 
   The above example is illustrative of a basic mechanical configuration which can take on a multitude of variations. For example:
         Clearly, transparent materials such as plastic with a liquid or gel of matching refractive index must be utilized when making a lens. For a mirror, other material such as metals or ceramics could be utilized.   The length of the rods  14  does not have to be equal. A ‘pre-biased’ shape can be formed into the two material layers  10  and  20  by using rods  14  of varying length, e.g. the shape can be initially concave with all rods  14  vertically aligned and become flat when rotated.   The pattern of rods  14  need not be a grid or even regular.   The rods  14  and flex joints  24  need not be individual components, but could be a structured ‘compound’ (monolithic) material that has similar mechanical sheer properties. In this case the material layers  10  and  20  may become an integral part of the structured compound.   The rods  14  are designed to bend if they are directly connected to the surfaces  10  and/or  20  (no flex joints  24 ).   A stiff outer collar used to control the position of the rotation axis.   Lateral shifts between the two material layers  10  and  20  can be used to affect the average spacing between the surfaces. A lateral shift will not affect the surface shape.       

   The central aspect of the current invention is the use of and array of rods  14  with flex joints  24  (or flexible rods) connecting two material layers  10  and  20 , the layers  10  and  20  being stiff along their surface plane and flexible in their transverse axis such that a relative motion of the two layers can be used to produce a relative shape change. Of specific interest is a rotational motion used to produce a parabolic surface of variable curvature. 
   While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.