Abstract:
A liquid crystal lens cell set includes a plurality of liquid crystal lenses overlapping to each other. Each of the liquid crystal lenses is supported between a pair of flat layers. One of the layers supports a planar electrode made of ITO. The other electrode, also formed of ITO, is supported in the center of the opposing substrate and projects toward the center of the liquid crystal layer. A power supply creates a potential difference between the electrodes and imposes a non-uniform electric field on the liquid crystal modules which aligns them in which a way as to act as a lens. By varying voltage between the electrodes the focal length of the lens may be controlled. A central electrode may be in the form of a beam or of a pointed tip. An electrode having a central hole may be associated with the central electrode or the planar electrode.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation in part of U.S. application Ser. No. 12/396,613 filed on Mar. 3, 2009, which claims the benefit of U.S. Provisional application Ser. No. 61/033,050 filed on Mar. 3, 2008, both of which are incorporated herein entirely by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to liquid crystal cells sandwiched between electrodes which exert a non-uniform field on the liquid crystals so as to cause them to act as lenses, and more particularly to such a cell in which the voltage between the electrodes may be varied to control the focal length of the lens and a liquid crystal lens set including a plurality of the cells stacked each other. 
     2. Description of the Prior Art 
     Electrically tunable liquid crystal lenses potentially provide important advantages of size and cost over mechanical zoom lenses. They might be used in cameras, binoculars and other opto-electronic devices. 
     Broadly, these devices employ a pair of electrodes sandwiching a liquid crystal cell. The electrodes are such as to align the liquid crystal molecules to provide a gradient refractive index profile on the lens, transverse to the light path. By use of a variable power supply to adjust the voltage between the electrodes, the focal lengths of the lenses can be varied between a very short focal length and to near infinity, One method proposed to generate a nonhomogeneous electric field within the LC layer is to provide one of the electrodes in spherical shape. Another proposal is to place a central hole in one of the electrodes so as to impose a nonhomogeneous across the LC element. 
     SUMMARY OF THE INVENTION 
     The present invention comprises an electrically tunable LC lens set including a plurality of liquid crystal lenses overlapping to each other along a vertical projective direction. Each of the liquid crystal lenses embodies an LC layer sandwiched between two planar nonconductive layers. One of the nonconductive layers is coated with an ITO (indium tin oxide) layer which acts as a transparent electrode. The other nonconductive layer is formed with a central electrode that projects toward the LC layer and the other electrode. The LC layer, the central electrode, and the other electrode are stacked along the vertical projective direction. The central electrode may take the form of a thin rod with its axis aligned normally to the LC layer or an electrode with a pointed tip terminating close to the LC layer. Either form of electrode may be connected to a power supply at the other end by either a conductive transparent ITO coating extending over an insulation layer or a single transparent conductor formed on the side of the insulation layer opposite to the LC layer. The insulation layer separates this conductive layer from the electrode tip so that the electric field imposed on the LC layer is primarily a function of the voltage between the central tip and the electrode layer on the opposite side of the LC layer. 
     The resulting nonhomogeneous field aligns the LC molecules so as to produce a refractive index gradient over the LC layer which causes it to act as a lens. By varying the voltage between the tipped electrode and the opposed flat electrode, the focal length of the resulting lens may be controlled. 
     This unique electrode structure can be combined with an ITO layer having a central hole which is substantially larger than the tip electrode diameter. This electrode could be formed on the opposite side of the insulation layer from which the tip electrode projects or it could constitute the opposing electrode on the opposite side of the LC layer. A high resistance material layer may be formed in the central hole. 
     The birefringency problem caused by liquid crystal material can be resolved either by use of two layers of liquid crystal aligned in orthogonal directions or through the use of a tin layer of polarizer film attached on top of the LC layer. 
     In the electrically tunable LC lens set of the present invention, two adjacent liquid crystal lenses may constitute identical or opposite lens effects for forming a required optical performance of the LC lens set. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, advantages and applications of the present invention will be made apparent by the following detailed description of preferred embodiments of the invention. The description makes reference to the accompanying drawings in which: 
         FIG. 1  is a schematic diagram of a conventional electrically tunable liquid crystal cell structure representing the prior art; 
         FIG. 2  is a schematic diagram of an electrically tunable liquid crystal cell structure forming a first embodiment of the invention; 
         FIG. 3  is a plot of the interference fringes resulting from passing light through an electrically tunable liquid crystal structure formed in accordance with the present invention; 
         FIG. 4  is an illustration of an alternative embodiment of the tip electrode for use in an LC electrically tunable lens structure; 
         FIG. 5  is a top view of an LC lens structure using the lip electrode, illustrating an alternative of the method of connecting the central electrode to a power supply; 
         FIG. 6  is a schematic view of a layer for an LC electrically tunable lens employing a tip electrode in connection with an electrode having a central hole; 
         FIG. 7  is a schematic diagram of an LC electrically tunable lens structure employing a tip electrode on one side of the LC layer and an electrode with a central hole on the other layer; 
         FIG. 8  is a schematic diagram of an electrically tunable liquid crystal cell structure according to a second embodiment of the invention; 
         FIG. 9  is a schematic diagram of an electrically tunable liquid crystal lens set according to a third embodiment of the invention; 
         FIG. 10  is a schematic diagram of an electrically tunable liquid crystal lens set according to a fourth embodiment of the invention; 
         FIG. 11  is a schematic diagram of an electrically tunable liquid crystal lens set according to a fifth embodiment of the invention, 
         FIG. 12  is a schematic diagram of an electrically tunable liquid crystal lens set according to a sixth embodiment of the invention, and 
         FIG. 13  is a schematic diagram of an electrically tunable liquid crystal lens set according to a seventh embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings,  FIG. 1  illustrates a prior art, electrically tunable liquid crystal cell, generally indicated at  10 . The cell employs a planar liquid crystal layer  12  sandwiched between a pair of glass substrates  14 . The opposed surfaces of the glass layers  14  are each coated with a thin ITO electrode  16 . The surfaces of the ITO layer proximate the liquid crystal layer  12  are coated with alignment layers  18  which are preferably polyimide, SiO 2 , or SiOx. 
     The two ITO layers are connected to a variable voltage power supply  20 . By varying the voltage on the two ITO electrodes, a field is imposed on the LC layer which causes the LC molecules to align and produce a lens-like refraction of light passing through the cell. By adjusting the strength of the field the alignment may be varied to modify the focal length of the lens. 
       FIG. 2  illustrates a preferred embodiment of our invention with the same numerals applied to the parts that are equivalent to the parts of the prior art device of  FIG. 1 . The preferred embodiment of the invention differs from the prior art in the structure of one of the ITO layers  22  and in the provision of an insulation layer  24 . The ITO layer  22  is formed on the side of one of the glass layers  14  that opposes the liquid crystal layer  12 . The electrode comprises a thin ITO layer  24  and a central tip  26  that projects from the surface of the layer  24  toward the LC layer  12 . An alignment layer  18  is formed beyond the edge of the tip  26  so as to be proximate to the LC layer  12 . The space between the section  24  of the ITO layer and the alignment layer  18  is coated with an insulation layer  28 . The insulation layer must be electrically insulating and transparent. Preferably SiO 2  or SiOx may be employed. Since this insulation layer is adjacent to the alignment layer  18 , they can be formed integrally. However, the surface of the alignment layer adjacent to the LC layer  12  must have some kind of grooves or rough formation so that the liquid crystal modules will fall into the layer, forming an angle typically referred to as the pre-tilting angle. If the alignment layer is SiO 2 , or SiOx, then a sputtering or evaporating process may be used to form that layer as well as the insulation material. The thickness of the insulation layer could vary from several microns to several hundred microns. The alignment layer thickness is usually less than one micron. If the insulation layer and the alignment layer use the same inorganic material, then the insulation layer can serve as a base material and would be deposited vertically, while the alignment will be deposited obliquely. If the alignment layer uses an organic material such as polyimide, then a rubbing process will be used to create the pretilt angle. 
     The central projecting tip  26  of the ITO layer  24  results in a more intense field being opposed in the center of the LC layer, compared to its edges, so as to give a lens-like curvature to the refractive index of the LC layer. This produces a lens-like effect when incident light passes through the cell. 
       FIG. 3  is a diagram of the interference fringes produced when light passes through the structure of  FIG. 1 . The tip electrode  26  produces a fringe pattern of the highest frequency at the center and lowering in the direction of the edges. 
       FIG. 4  illustrates an alternative form of the tip electrode which may be used with a structure of the type shown in  FIGS. 1 and 2 . The insulation layer  28  supports an ITO layer  32  which overlies the side of the insulation layer opposite to the LC layer and includes a central, pointed tip  34  which terminates in a pointed end  36  adjacent to the alignment layer. The pointed tip  36  produces a more extreme electric field gradient on the LC layer and allows even shorter focal distances to be achieved by the lens. Focal lengths in the order of seven centimeters have been achieved in prototype devices. 
       FIG. 5  is a top view of an alternative form of insulation layer and ITO layer. Rather than the ITO layer covering the entire surface of the insulation layer as illustrated in  FIGS. 2 and 4 , a central ITO tip in the form of the tips  26  of  FIG. 2  or  34  of  FIG. 4 , indicated in  FIG. 5  as  40 , may be connected to a power supply by an ITO conductor  42  which connects the tip  40  to the edge of the insulation layer so that it can be connected to a power supply. This structure allows the use of thinner insulation layers  28  because the electric field imposed by the conductor  42  is so minimal as to not affect the performance of the device. 
       FIG. 6  illustrates an alternative structure for a tip electrode cell. A tip electrode  50  of the type illustrated in  FIG. 2  is sandwiched between a glass substrate  52  and an insulating layer  54 . A second ITO electrode  58  having a central hole  60  is formed surrounding the tip of the ITO layer  50 . An alignment layer  62  completes the structure. A first variable voltage power supply  64  connects to the tip electrode  50 . A second variable voltage power supply  66  is connected between the terminal of the power supply  64  that connects to the tip ITO layer  50  and the ITO layer  58  with the central hole  60 . The other terminal of the power supply  64  connects to the planar ITO layer  68  supported on the opposite side of the liquid crystal layer  56 . By varying the voltages imposed by the power supply  64  and  66 , the focal length (and other optical parameters such as a spherical effects) of the resulting lens can be carefully controlled between a focus at near infinity and a focus within a few centimeters of the cell. 
     In another embodiment of the invention illustrated in  FIG. 7 , an ITO in the form of a tip electrode  70  is supported on one side of an LC layer  72  and an ITO electrode  74  with a large central hole  76  is supported on the opposite side of the LC layer  72 . Varying an applied voltage between these two layers will allow control of the focal length (and other optical parameters) of the resulting lens over a wide range. 
       FIG. 8  is a schematic diagram of an electrically tunable liquid crystal cell structure according to a second embodiment of the invention. As shown in  FIG. 8 , an electrically tunable liquid crystal lens set  100  is provided. The electrically tunable liquid crystal lens set  100  may also be referred as a liquid crystal cell constituting electrically controllable focal length lenses. The electrically tunable liquid crystal lens set  100  includes a plurality of liquid crystal lenses  110 . Each of the liquid crystal lenses  110  includes a planar liquid crystal layer  112 , a first planar electrode  116 , a second transparent conductive electrode  124 , and a variable voltage power supply  120 . The planar liquid crystal layer  112  is supported between an opposed pair of transparent, insulating, alignment layers  118 . The alignment layers  118  in this embodiment include a first alignment layer  118 A and a second alignment layer  118 B, but not limited thereto. The first planar electrode  116  is formed of a transparent conductive material and supported adjacent to one of the alignment layers  118 , for example the first alignment layer  118 A, on the opposite side of the liquid crystal layer  112 . The second transparent conductive electrode  124  is disposed on the second alignment layer  118 B on the side opposite to the liquid crystal layer  112 , and the second electrode  124  comprises only one central tip electrode  126 . The liquid crystal layer  112 , the first electrode  116 , and the second electrode  124  are stacked along the vertical projective direction Z. The variable voltage power supply  120  is connected to the first electrode  116  and the second electrode  124  so as to impose a nonhomogeneous electric field on the liquid crystal layer  112 . The field has a maximum intensity at a center of the electrodes and decreasing toward the edges of the electrodes, so that the refractive index of the liquid crystal layer  112  is adjusted in a nonhomogeneous manner to provide a lens effect to light passing through the liquid crystal lens  110 . The focal length of the lens may preferably be a function of the applied voltage between the first electrode  116  and the second electrode  124 . 
     It is worth noting that the liquid crystal lenses  110  overlap to each other along the vertical projective direction Z. In this embodiment, the electrically tunable liquid crystal lens set  100  includes a liquid crystal lens  110 A and a liquid crystal lens  110 B. The liquid crystal lens  110 A overlaps the liquid crystal lens  110 B along the vertical projective direction Z. The lens effect of the liquid crystal lens  110 A may be identical or opposite to the lens effect of the liquid crystal lens  110 B. For example, the liquid crystal lens  110 A and the liquid crystal lens  110 B may respectively institute a convex lens effect or a concave lens effect, but the present invention is not limited thereto. Each of the liquid crystal lenses may be used to form other appropriate lens effects and the electrically tunable liquid crystal lens set  100  may include more than two liquid crystal lenses  110  for other design considerations. 
     In this embodiment, the electrically tunable liquid crystal lens set  100  may further include a plurality of glass substrates  114  stacked along the vertical projective direction Z. Two adjacent glass substrates  114  are disposed in contact with the first electrode  116  and the second electrode  124  on the sides of the first electrode  116  and the second electrode  124  opposed to the liquid crystal layer  112 . In this embodiment, the second electrode  124  of the liquid crystal lens  110 A may be disposed on one of the glass substrate  114  on the side opposite to the second electrode  124  of the liquid crystal lens  110 B for forming specific optical effects, but not limited thereto. 
     Additionally, each of the liquid crystal lenses  110  in this preferred embodiment of the invention differs from the prior art in the structure of one of the ITO layers  122  and in the provision of an insulation layer  128 . The ITO layer  122  is formed on the side of one of the glass substrates  114  that opposes the liquid crystal layer  112 . The second electrode  124  comprises the ITO layer  122  and the central tip electrode  126  that projects from the surface of the ITO layer  122  toward the LC layer  112 . In other words, the ITO layer  122  may be regarded as a layer extending over the entire liquid crystal layer  112  and the central tip electrode  126  may be regarded as an extension section supported at a center of the second electrode  124 . The second alignment layer  118 B is formed beyond the edge of the central tip electrode  126  so as to be proximate to the LC layer  112 . The space between the ITO layer  122  and the second alignment layer  118 B is coated with the insulation layer  128 . The insulation layer  128  must be electrically insulating and transparent. Preferably SiO 2  or SiOx may be employed. The insulation layer  128  may surround a central section in abutment to the second alignment layer  118 B. In addition, the central tip electrode  126  in the liquid crystal lens  110  may preferably extend in a direction opposite to the neighbor liquid crystal lens  110 . As shown in  FIG. 8 , a central tip electrode  126  of a liquid crystal lens  110 A may extend in a direction opposite to a liquid crystal lens  110 B which is adjacent to the liquid crystal lens  110 A, and a central tip electrode  126  of the liquid crystal lens  110 B may extend in a direction toward the liquid crystal lens  110 A. In other words, the central tip electrode  126  of the upper liquid crystal lens  110 A may project upwardly to the liquid crystal layer  112 , and the central tip electrode  126  of the lower liquid crystal lens  110 B may project downwardly to the liquid crystal layer  112 , so as to generate a specific optical effect. 
     The central tip electrode  126  of the second electrode  124  results in a more intense field being opposed in the center of the LC layer  112 , compared to its edges, so as to give a lens-like curvature to the refractive index of the LC layer  112 . This produces a lens-like effect when incident light passes through the cell. The fringe pattern produced by the central tip electrode  126  in this embodiment is similar to the fringe pattern shown in  FIG. 3 . The central tip electrode  126  produces a fringe pattern of the highest frequency at the center and lowering in the direction of the edges or a fringe pattern of the lowest frequency at the center and increasing in the direction of the edges. An alternative form of the central tip electrode in this embodiment may be referred to  FIG. 4  and the related descriptions detailed above. In other words, the central tip electrode in the alternative form may vary in width from a small tip at an end nearest to the liquid crystal layer to a larger diameter at an opposite end. 
     An alternative form of insulation layer and ITO layer in this embodiment may also be referred to  FIG. 5  and the related descriptions detailed above. Rather than the ITO layer covering the entire surface of the insulation layer as illustrated in  FIGS. 8 and 4 , a central ITO tip in the form of the central tip electrode  126  of  FIG. 8  or  34  of  FIG. 4 , indicated in  FIG. 5  as  40 , may be connected to a power supply by an ITO conductor  42  which connects the tip  40  to the edge of the insulation layer so that it can be connected to a power supply. In other words, the tip  40  may be regarded as a central extension section, and the conductor  42  may be regarded as a transparent conductive element connecting the central extension section to one terminal of the power supply. 
       FIG. 9  is a schematic diagram of an electrically tunable liquid crystal lens set according to a third embodiment of the invention. As shown in  FIG. 9 , an electrically tunable liquid crystal lens set  200  includes a plurality of liquid crystal lenses  210 . The difference between the liquid crystal lenses  210  of this embodiment and the liquid crystal lenses  110  of the second embodiment is that the liquid crystal lens  210  further includes a third electrode  258 , a first variable voltage power supply  264 , and a second variable voltage power supply  266 . The third electrode  258  has a central hole  260  therein and disposed between the second alignment layer  118 B and the glass substrate  114  which supports the second electrode  124 , with the only one central tip electrode  126  extending centrally through the central hole  260  in the third electrode  258 . The third electrode  258  may also be made of ITO. In other words, the third ITO electrode  258  having the central hole  260  is formed surrounding the tip of the ITO layer  122 . The first variable voltage power supply  264  connects to the central tip electrode  126 . The second variable voltage power supply  266  is connected between the terminal of the first variable voltage power supply  264  that connects to the central tip electrode  126  and the third electrode  258  with the central hole  260 . The other terminal of the first variable voltage power supply  264  connects to the first electrode  116  supported on the opposite side of the liquid crystal layer  112 . By varying the voltages imposed by the power supply  264  and  266 , the focal length (and other optical parameters such as a spherical effects) of the resulting lens can be carefully controlled between a focus at near infinity and a focus within a few centimeters of the cell. In other words, the second variable voltage power supply  266  may be regarded as a separate variable voltage power supply operative to vary the voltage between the third electrode  258  and the first electrode  116 . The third electrode  258  may be used to form a horizontal field on the liquid crystal layer  112  and the third electrode  258  may be used as an accelerator of the response time of the liquid crystal molecules in the liquid crystal layer  112 . In this embodiment, a lens effect of a liquid crystal lens  210 A may be identical or opposite to a lens effect of a liquid crystal lens  210 B. The second electrode  124  of the liquid crystal lens  210 A may be disposed on one of the glass substrate  114  on the side opposite to the second electrode  124  of the liquid crystal lens  210 B for forming specific optical effects, but not limited thereto. 
       FIG. 10  is a schematic diagram of an electrically tunable liquid crystal lens set according to a fourth embodiment of the invention. As shown in  FIG. 10 , an electrically tunable liquid crystal lens set  300  includes a plurality of liquid crystal lenses  310 . The difference between the liquid crystal lenses  310  of this embodiment and the liquid crystal lenses  210  of the third embodiment is that the liquid crystal lens  310  further includes a high resistance material layer  370  disposed in the central hole  260  of the third electrode  258 . The high resistance material layer  370  may be used to optimize the electrical field between the first electrode  116 , the second electrode  124 , and the third electrode  258 . In this embodiment, a lens effect of a liquid crystal lens  310 A may be identical or opposite to a lens effect of a liquid crystal lens  310 B. The second electrode  124  of the liquid crystal lens  310 A may be disposed on one of the glass substrate  114  on the side opposite to the second electrode  124  of the liquid crystal lens  310 B for forming specific optical effects, but not limited thereto. 
       FIG. 11  is a schematic diagram of an electrically tunable liquid crystal lens set according to a fifth embodiment of the invention. As shown in  FIG. 11 , an electrically tunable liquid crystal lens set  400  includes a plurality of liquid crystal lenses  410 . The difference between the liquid crystal lenses  410  of this embodiment and the liquid crystal lenses  110  of the first preferred embodiment is that the second electrode  124  including the central tip electrode  126  is supported on one side of the LC layer  112  and a first electrode  416  with a large central hole  460  is supported on the opposite side of the LC layer  112 . Varying an applied voltage between the first electrode  416  and the second electrode  124  will allow control of the focal length (and other optical parameters) of the resulting lens over a wide range. In this embodiment, a lens effect of a liquid crystal lens  410 A may be identical or opposite to a lens effect of a liquid crystal lens  410 B. The second electrode  124  of the liquid crystal lens  410 A may be disposed on one of the glass substrate  114  on the side opposite to the second electrode  124  of the liquid crystal lens  410 B for forming specific optical effects, but not limited thereto. 
       FIG. 12  is a schematic diagram of an electrically tunable liquid crystal lens set according to a sixth embodiment of the invention. As shown in  FIG. 12 , an electrically tunable liquid crystal lens set  500  includes a plurality of liquid crystal lenses  510 . The difference between the liquid crystal lenses  510  of this embodiment and the liquid crystal lenses  310  of the fourth preferred embodiment is that the central tip electrode  126  extends in a direction toward the neighbor liquid crystal lens  510 . As shown in  FIG. 12 , a central tip electrode  126  of a liquid crystal lens  510 A may extend in a direction toward a liquid crystal lens  510 B which is adjacent to the liquid crystal lens  510 A, and a central tip electrode  126  of the liquid crystal lens  510 B may extend in a direction toward the liquid crystal lens  510 A. In other words, the central tip electrode  126  of the upper liquid crystal lens  510 A may project downwardly to the liquid crystal layer  112 , and the central tip electrode  126  of the lower liquid crystal lens  510 B may project upwardly to the liquid crystal layer  112 , so as to generate a specific optical effect. 
       FIG. 13  is a schematic diagram of an electrically tunable liquid crystal lens set according to a seventh embodiment of the invention. As shown in  FIG. 13 , an electrically tunable liquid crystal lens set  600  includes a plurality of liquid crystal lenses  610 . The difference between the liquid crystal lenses  610  of this embodiment and the liquid crystal lenses  510  of the fifth preferred embodiment is that in a lower liquid crystal lens  610 B, one of the glass substrates  114  is disposed between the first electrode  116  and the liquid crystal layer  112  of the liquid crystal lens  610 B. In other words, an upper liquid crystal lens  610 A and the lower liquid crystal lens  610 B in the electrically tunable liquid crystal lens set  600  share one first electrode  116 . The structure of the electrically tunable liquid crystal lens set  600  may be simplified accordingly. 
     To summarize the above descriptions, in the electrically tunable liquid crystal lens set of the present invention, the central tip electrode in each liquid crystal lens is used to impose a nonhomogeneous electric field on the liquid crystal layer. The liquid crystal lenses are disposed in a stacked configuration and two adjacent liquid crystal lenses may constitute identical or opposite lens effects for generating different optical effects. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.