Abstract:
An electrowetting lens which can move its optical axis using a multiple electrode structure includes: a substrate; a dielectric barrier wall formed on the substrate; polar and non-polar solutions fluidly contained inside the dielectric barrier wall; first and second lower electrodes inserted through lower portions of the dielectric barrier wall in contact with the polar solution, the first and second lower electrodes facing each other; and first and second multiple electrodes respectively disposed in mutually facing first and second legs defining the dielectric barrier wall, each of the first and second multiple electrodes being divided into a plurality of vertically arranged electrode cells.

Description:
[0001]    This application claims priority to Korean Patent Application No. 10-2006-0104693, filed on Oct. 26, 2006, and all the benefits accruing therefrom under 35 U.S.C. §199, the contents of which in its entirety is herein incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an electrowetting lens, and more particularly, to an electrowetting lens which can change an optical axis thereof using a multiple electrode structure. 
         [0004]    2. Description of the Related Art 
         [0005]    Various liquid lenses using electrowetting effect are well known.  FIGS. 1A and 1B  are schematic cross-sectional views illustrating a conventional electrowetting lens  10 . Referring to  FIG. 1A , the conventional electrowetting lens  10  includes a substrate  11 , a dielectric barrier wall  12  vertically formed on the substrate  11 , and polar and non-polar solutions  13  and  14 , respectively, filled in the dielectric barrier wall  12 . For example, the polar solution  13  may be water, and the non-polar solution  14  may be oil. In this case, since the water is heavier than the oil, the polar solution  13  is placed under the non-polar solution  14 , as shown in  FIG. 1A . First electrodes  15  are horizontally disposed on the substrate  11 . In more detail, the first electrodes  15  are inserted through lower portions of the dielectric barrier wall  12  and make contact with the polar solution  13 . Second electrodes  16  are vertically disposed in legs of the dielectric barrier wall  12 . 
         [0006]    Although not shown in  FIG. 1A , inner surfaces  12   a  of the dielectric barrier wall  12  are coated with a hydrophobic material. Therefore, the polar solution  13  tends to reduce contact area with the inner surfaces  12   a  of the dielectric barrier wall  12 , and the non-polar solution  14  tends to increase contact area with the inner surfaces  12   a . As a result, as shown in  FIG. 1A , the polar solution  13  has a convex top surface. In this case, the electrowetting lens  10  functions as a convex lens when the polar solution  13  has a refractive index larger than a refractive index of the non-polar solution  14 . 
         [0007]    When a voltage is applied to the first and second electrodes  15  and  16  using a power supply  17 , the dielectric barrier wall  12  is electrically charged as shown in  FIG. 1B . Then, the inner surfaces  12   a  of the dielectric barrier wall  12  changes from hydrophobic to hydrophilic. Therefore, unlike in  FIG. 1A , the polar solution  13  tends to increase contact area with the inner surfaces  12   a,  and the non-polar solution  14  tends to decrease contact area with the inner surfaces  12   a.  As a result, as shown in  FIG. 1B , the top surface of the polar solution  13  is concaved. 
         [0008]      FIGS. 2A and 2B  are schematic cross-sectional views illustrating another conventional electrowetting lens  20  providing zooming and focusing functions. Referring to  FIG. 2A , the conventional electrowetting lens  20  includes a polar solution  21  filled in a tub, a non-polar solution  22  located in the middle of the polar solution  21 , first electrodes  23  contacting the polar solution  21 , second electrodes  24 , third electrodes  25 , fourth electrodes  26 , fifth electrodes  26 ′, sixth electrodes  25 ′, and seventh electrodes  24 ′. The second through seventh electrodes  24 ,  25 ,  26 ,  26 ′,  25 ′, and  24 ′ are disposed around the tub. Initially, symmetric voltages are applied to the second to seventh electrodes  24 ,  25 ,  26 ,  26 ′,  25 ′, and  24 ′ so as to keep the non-polar solution  22  in a convex state. That is, the same voltages are respectively applied to the second and seventh electrodes  24  and  24 ′, the third and sixth electrodes  25  and  25 ′, and the fourth and fifth electrodes  26  and  26 ′. 
         [0009]    Referring to  FIG. 2B , a right portion of the polar solution  21  is moved to the left using a pump  28  and a conduit  27 . Then, the convex non-polar solution  22  is moved to the right as indicated by the arrow indicating a moving direction of the non-polar solution  22  in  FIG. 2A . Here, voltages to electrodes located in the moving direction of the non-polar solution  22  are increased, and voltages to electrodes located in the opposite direction to the moving direction of the non-polar solution  22  are decreased. In this manner, the non-polar solution  22  can be moved back and forth for zooming and focusing. However, the optical axis of the conventional electrowetting lenses cannot be adjusted for controlling an optical path. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    The present invention provides an electrowetting lens which can change its optical axis and surface curvature. 
         [0011]    According to an exemplary embodiment of the present invention, there is provided an electrowetting lens including: a substrate; a dielectric barrier wall formed on the substrate; polar and non-polar solutions fluidly contained inside the dielectric barrier wall; first and second lower electrodes inserted through lower portions of the dielectric barrier wall in contact with the polar solution, the first and second lower electrodes facing each other; and first and second multiple electrodes respectively disposed in mutually facing first and second legs defining the dielectric barrier wall, each of the first and second multiple electrodes being divided into a plurality of vertically arranged electrode cells. 
         [0012]    The dielectric barrier wall may have a circular or polygonal box shape. 
         [0013]    The substrate may be transparent. 
         [0014]    Both the first lower electrode and the first multiple electrode may be disposed at the first leg of the dielectric barrier wall, and both the second lower electrode and the second multiple electrode may be disposed at the second leg of the dielectric barrier wall. 
         [0015]    When the dielectric barrier wall has a circular box shape, at least one pair of a first lower electrode and a first multiple electrode and at least one pair of a second lower electrode and a second multiple electrode may be arranged along a circumference of the dielectric barrier wall, and the pairs may face each other. 
         [0016]    When the dielectric barrier wall has a polygonal shape, at least one pair of a first lower electrode and a first multiple electrode and at least one pair of a second lower electrode and a second multiple electrode may be respectively disposed at the mutually facing first and second legs of the dielectric barrier wall. 
         [0017]    The electrode cells of the first and second multiple electrodes may each individually receive a voltage. 
         [0018]    An interface between the polar and non-polar solutions may be sloped by making a height of charged electrode cells of the first multiple electrode different from a height of charged electrode cells of the second multiple electrode. 
         [0019]    A voltage may be applied to only some of the electrode cells located at an interface between the polar and non-polar solutions. 
         [0020]    A voltage applied to some of the electrode cells located at an interface between the polar and non-polar solutions may be different from a voltage applied to the other electrode cells. 
         [0021]    A voltage may be applied to only some of the electrode cells facing the polar solution. 
         [0022]    A voltage applied to some of the electrode cells facing the polar solution may be different from a voltage applied to the other electrode cells. 
         [0023]    The polar solution may be an aqueous solution, and the non-polar solution may be an oil solution. 
         [0024]    The aqueous solution and the oil solution may have different refractive indexes. 
         [0025]    According to another exemplary embodiment of the present invention, there provided a microlens array including a plurality of two-dimensionally arranged electrowetting lenses, each of the electrowetting lenses including the same elements as the electrowetting lens described above. 
         [0026]    According to another aspect of the present invention, there is provided a lenticular lens sheet including a plurality of electrowetting lenses arranged side by side, each of the electrowetting lenses including the same elements as the electrowetting lens described above. 
         [0027]    According to another aspect of the present invention, there is provided a three-dimensional image display device including: a display panel; and a lenticular lens sheet disposed in front of the display panel, the lenticular lens sheet being formed by arranging a plurality of electrowetting lenses each including the same elements as the electrowetting lens described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    The above and other aspects, features and advantages of the present invention will become more apparent by describing in further detail exemplary embodiments thereof with reference to the attached drawings, in which: 
           [0029]      FIGS. 1A and 1B  are schematic cross-sectional views illustrating a conventional electrowetting lens; 
           [0030]      FIGS. 2A and 2B  are schematic cross-sectional views illustrating another conventional electrowetting lens; 
           [0031]      FIG. 3  is a vertical cross-sectional view schematically illustrating an electrowetting lens according to an exemplary embodiment of the present invention; 
           [0032]      FIGS. 4A through 4D  are horizontal cross-sectional views illustrating exemplary structures of an electrowetting lens according to exemplary embodiments of the present invention; 
           [0033]      FIGS. 5A and 5B  are vertical cross-sectional views of the exemplary electrowetting lens of  FIG. 3  for explaining an operation thereof according to an exemplary embodiment of the present invention; 
           [0034]      FIGS. 6A through 7B  are vertical cross-sectional views of an exemplary electrowetting lens for explaining an operation thereof according to another exemplary embodiment of the present invention; 
           [0035]      FIGS. 8 through 11  illustrate a three-dimensional image display device with electrowetting lenses according to exemplary embodiments of the present invention; and 
           [0036]      FIGS. 12A through 12C  are vertical cross-sectional views of exemplary electrowetting lens illustrating optic path controlling operations according to exemplary embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout. 
         [0038]    It will be understood that when an element is referred to as being “on” another element, it can be directly on the other element or intervening elements may be present therebetween. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
         [0039]    It will be understood that although the terms “first,” “second,” “third” etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention. 
         [0040]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including,” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components and/or groups thereof. 
         [0041]    Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top” may be used herein to describe one element&#39;s relationship to other elements as illustrated in the Figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in one of the figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on the “upper” side of the other elements. The exemplary term “lower” can, therefore, encompass both an orientation of “lower” and “upper,” depending upon the particular orientation of the figure. Similarly, if the device in one of the figures were turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below. 
         [0042]    Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning which is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
         [0043]    Exemplary embodiments of the present invention are described herein with reference to cross section illustrations which are schematic illustrations of idealized embodiments of the present invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the present invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes which result, for example, from manufacturing. For example, a region illustrated or described as flat may, typically, have rough and/or nonlinear features. Moreover, sharp angles which are illustrated may be rounded. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region and are not intended to limit the scope of the present invention. 
         [0044]    Hereinafter, an electrowetting lens which can change an optical axis thereof using a multiple electrode structure according to an exemplary embodiment of the present invention will be described in further detail with reference to the accompanying drawings. 
         [0045]      FIG. 3  is a vertical cross-sectional view schematically illustrating an electrowetting lens  30  according to an exemplary embodiment of the present invention. Referring to  FIG. 3 , the electrowetting lens  30  includes a substrate  31 , a dielectric barrier wall  34  formed on the substrate  31 , a polar solution  38  and a non-polar solution  39  filled inside the dielectric barrier wall  34 , first and second lower electrodes  32  and  33  contacting the polar solution  38  through a lower portion of the dielectric barrier wall  34 , and first and second multiple electrodes  36  and  37  respectively disposed in mutually facing legs  34   a  and  34   b  of the dielectric barrier wall  34 . 
         [0046]    The substrate  31  is formed of a transparent material (e.g., a light-transmitting material) such as glass. The dielectric barrier wall  34  can be formed of BaTiO 3 . The polar solution  38  can be an aqueous solution having water as a solvent. The non-polar solution  39  may be an oil solution having oil as a solvent. Here, the refractive index of the polar solution  38  is different from a refractive index of the non-polar solution  39 . The refractive indexes of the polar and non-polar solutions  38  and  39  can be adjusted to desired values by varying solutes of the polar and non-polar solutions  38  and  39 . This feature of adjusting the refractive indexes of the polar and non-polar solutions will not be described in further detail since it is well known to those of ordinary skill in the related art. 
         [0047]    Although not shown in  FIG. 3 , hydrophobic layers are formed on inner surfaces  34   a ′ and  34   b ′ of the legs  34   a  and  34   b  of the dielectric barrier wall  34  like in the conventional electrowetting lens of  FIGS. 1A and 1B . The hydrophobic layers may be formed of a fluoropolymer. Since the inner surfaces  34   a ′ and  34   b ′ of the dielectric barrier wall  34  are coated with the hydrophobic layers, the polar solution  38  tends to reduce contact area with the inner surfaces  34   a ′ and  34   b ′ of the dielectric barrier wall  34 . On the other hand, the non-polar solution  39  tends to increase contact area with the inner surfaces  34   a ′ and  34   b ′ of the dielectric barrier wall  34 . For this reason, the polar solution  38  has a convex top surface in an initial state as shown in  FIG. 3 . 
         [0048]    In the current exemplary embodiment, the first and second lower electrodes  32  and  33  pass through lower portions of the mutually facing legs  34   a  and  34   b  of the dielectric barrier wall  34  and face each other. The first and second multiple electrodes  36  and  37  are respectively disposed in the mutually facing legs  34   a  and  34   b  and are opposite each other. The first lower electrode  32  and the first multiple electrode  36  may be located at the same leg  34   a  of the dielectric barrier wall  34 , and the second lower electrode  33  and the second multiple electrode  37  may be located at the same leg  34   b  of the dielectric barrier wall  34 . As shown in  FIG. 3 , the first multiple electrode  36  includes a plurality of electrode cells  36   1 ,  36   2 , through  36   n , and the second multiple electrodes  37  includes a plurality of electrode cells  37   1 ,  37   2 , through  37   n . In the current exemplary embodiment of the present invention, a voltage can be applied to each of the electrode cells  36   1 , through  36   n  and  37   1  through  36   n  in an individual manner. For example, a voltage can be applied to only some of the electrode cells  36   1  through  36   n  and to only some of the electrode cells  37   1  through  36   n . Further, different voltages can be individually applied to the electrode cells  36   1  through  36   n  and  37   1  through  36   n . 
         [0049]      FIGS. 4A through 4D  are horizontal cross-sectional views illustrating exemplary structures of the electrowetting lens  30  according to exemplary embodiments of the present invention. 
         [0050]    Referring to  FIGS. 4A and 4B , the electrowetting lens  30  includes a dielectric barrier wall  34  having a rectangular shape when viewed from the top. Although the dielectric barrier wall  34  has a rectangular box shape in  FIGS. 4A and 4B , the dielectric barrier wall  34  can have different shapes as well in alternative exemplary embodiments. For example, the dielectric barrier wall  34  can have a hexagonal box shape or the dielectric barrier wall  34  can have a polygonal or square box shape. 
         [0051]    In the exemplary embodiment illustrated in  FIG. 4A , first and second multiple electrodes  36  and  37  are respectively disposed in mutually facing legs  34   a  and  34   b  of the dielectric barrier wall  34 . Although not shown in  FIG. 4A , first and second lower electrodes  32  and  33  pass through lower portions of the mutually facing legs  34   a  and  34   b  of the dielectric barrier wall  34 . In the exemplary embodiment illustrated in  FIG. 4B , two first multiple electrodes  36  and  36 ′ are respectively disposed in two legs  34   a  and  34   c  of the dielectric barrier wall  34 . The two first multiple electrodes  36  and  36 ′ face two second multiple electrodes  37  and  37 ′ that are respectively disposed in the other two legs  34   b  and  34   d  of the dielectric barrier wall  34 . When the dielectric barrier wall  34  has a polygonal box shape, at least one pair of first lower and multiple electrodes  32  and  36  and at least one pair of second lower and multiple electrodes  33  and  37  can be disposed at mutually facing legs of the dielectric barrier wall  34 . 
         [0052]      FIGS. 4C and 4D  illustrate circular dielectric barrier walls  34  according to alternative exemplary embodiments of the present invention. Referring to  FIG. 4C , a first multiple electrode  36  and a second multiple electrode  37  can be disposed along the circumference of the circular dielectric barrier wall  34  at mutually facing arcs  34   a  and  34   b.  Although not shown in  FIG. 4C , first and second lower electrodes  32  and  33  can be disposed at the mutually facing arcs  34   a  and  34   b,  respectively, corresponding with the first and second multiple electrodes  36  and  37 . Alternatively, a plurality of first lower electrodes  32  and first multiple electrodes  36  and a plurality of second lower electrodes  33  and second multiple electrodes  37  can be disposed along the circumference of the circular dielectric barrier wall  34  in a mutually facing manner. Referring to  FIG. 4D , two first multiple electrodes  36  and  36 ′ and two second multiple electrodes  37  and  37 ′ are disposed along the circumference of a circular dielectric barrier wall  34  according to an alternative exemplary embodiment of the present invention. In the embodiment of  FIG. 4D , the four multiple electrodes  36 ,  36 ′,  37 , and  37 ′ are respectively disposed at four 90-degree arcs of the circular dielectric barrier wall  34 . However, five or more multiple electrodes can be respectively disposed at smaller arcs of the circular dielectric barrier wall  34  in further alternative exemplary embodiments, as will be recognized by those of ordinary skill in the related art. 
         [0053]      FIGS. 5A and 5B  are vertical cross-sectional views of the exemplary electrowetting lens  30  of  FIG. 3  for explaining an operation thereof to an exemplary embodiment of the present invention. 
         [0054]    When the electrowetting lens  30  is in an initial state as shown in  FIG. 3 , a voltage is applied to the first lower electrode  32 , the first multiple electrode  36 , the second lower electrode  33  and the second multiple electrode  37 . Then, as described above, the inner surfaces  34   a ′ and  34   b ′ of the dielectric barrier wall  34  are electrically charged, and thus the hydrophobic layers formed on the inner surfaces  34   a ′ and  34   b ′ of the dielectric barrier wall  34  are changed from hydrophobic to hydrophilic. Here, the hydrophobic layers can be changed to a desired hydrophilic level by adjusting the voltage applied to the lower electrodes  32  and  33  and the multiple electrodes  36  and  37 . Meanwhile, the polarity of the applied voltage does not affect the change of the hydrophobic layers. As the applied voltage increases from a lower level to a critical level, the convex top surface of the polar solution  38  (as in  FIG. 3 ) is gradually flattened. When the applied voltage reaches the critical level, the interface between the polar solution  38  and the non-polar solution is completely flattened as shown in  FIG. 5A . When the applied voltage increases above the critical level, the interface between the polar and non-polar solutions  38  and  39  is curved toward the polar solution  38 , and as a result, the top surface of the polar solution  38  is concaved. Here, the critical level of the applied voltage may vary depending on the kinds of polar solution  38  and non-polar solution  39 , the material of the dielectric barrier wall  34  and the material of the hydrophobic layers. 
         [0055]    According to the present invention, the first and second multiple electrodes  36  and  37  include a plurality of electrode cells  36   1  through  36   n  and  37   1  through  37   n . Therefore, it is not necessary to apply a voltage to all of the electrode cells  36   1 , through  36   n  and  37   1  through  37   n  to obtain the effect described above. That is, as shown in  FIGS. 5A and 5B , a voltage can be applied to only some of the electrode cells  36   1  through  36   n  and to only some of the electrode cells  37   1  through  37   n  which face the polar solution  38 . Furthermore, a voltage can be applied to only a much smaller number of electrode cells. That is, a voltage can be applied to only the electrode cells located near the interface between the polar and non-polar solutions  38  and  39 . In this manner, the effect shown in  FIGS. 5A and 5B  can be obtained with less power consumption. Moreover, if necessary, a voltage applied to the electrode cells facing the polar solution  38  can be different from a voltage applied to the other electrode cells not facing the polar solution  38 . Similarly, a voltage applied to the electrode cells located near the interface between the polar and non-polar solutions  38  and  39  can be different from a voltage applied to the other electrode cells located away from the interface. 
         [0056]    In another exemplary embodiment of the present invention, it is possible to make the interface between the polar and non-polar solutions  38  and  39  be inclined by applying a voltage to differently located electrode cells of the first and second multiple electrodes  36  and  37 . For example, from the state where a voltage is applied to some of the electrode cells of the first and second multiple electrodes  36  and  37  so as to make the top surface of the polar solution  38  concave as shown in  FIG. 5B , the voltage supply is adjusted so as to decrease the height of the charged electrode cells of the first multiple electrode  36  and increase the height of the charged electrode cells of the second multiple electrode  37 . Then, as shown in  FIG. 6A , the interface between the polar and non-polar solutions  38  and  39  slopes down from the left to the right, and thus an optical axis X of the electrowetting lens  30  inclines to the right. On the other hand, when the voltage supply is adjusted from the state shown in  FIG. 5B  so as to increase the height of the charged electrode cells of the first multiple electrode  36  and decrease the height of the charged electrode cells of the second multiple electrode  37 , an optical axis X′ of the electrowetting lens  30  inclines to the left as shown in  FIG. 6B . In this manner, the focusing direction (angle) of the electrowetting lens  30  can be changed. Meanwhile, when four multiple electrodes are included in the electrowetting lens  30  as shown in  FIG. 4B  or  4 D, the optical axis of the electrowetting lens  30  can be adjusted in front, back, left and right directions by making the heights of charged electrode cells of mutually facing multiple electrodes different from each other. 
         [0057]    When a voltage lower than the critical level is applied to the first and second multiple electrodes  36  and  37  in such a manner that the height of charged electrode cells of the first multiple electrode  36  is different from the height of charged electrode cells of the second multiple electrode  37 , the interface between the polar and non-polar solutions  38  and  39  is shaped as shown in  FIG. 7A  or  7 B. That is, when a voltage lower than the critical level is applied to the first and second multiple electrodes  36  and  37  in such a manner that the height of charged electrode cells of the first multiple electrode  36  is lower than the height of charged electrode cells of the second multiple electrode  37 , the top surface of the polar solution  38  is convex and sloped down from the left to the right as shown in  FIG. 7A . Further, when a voltage lower than the critical level is applied to the first and second multiple electrodes  36  and  37  in such a manner that the height of charged electrode cells of the first multiple electrode  36  is larger than the height of charged electrode cells of the second multiple electrode  37 , the top surface of the polar solution  38  is convex and sloped down from the right to the left as shown in  FIG. 7B . 
         [0058]    The electrowetting lens  30  of the present invention can be applied to various fields, and particularly, to three-dimensional image display devices capable of displaying both two- and three-dimensional images. A commonly used three-dimensional image display device includes a microlens array or a lenticular lens sheet so as to separate left- and right-eye images (e.g., an image for a left eye and another image for a right eye) displayed on a display panel and direct the left-eye image toward the left eye of a viewer and the right-eye image toward the right eye of the viewer. According to the present invention, a microlens array can be fabricated by two-dimensionally arranging a plurality of electrowetting lenses  30  as in the above described structure on a single transparent substrate. Further, a lenticular lens sheet can be fabricated by arranging a plurality of electrowetting lenses  30  having an elongated rectangular shape and attaching them side by side. 
         [0059]      FIG. 8  illustrates a three-dimensional image display device displaying a two-dimensional image using electrowetting lenses  30  according to an exemplary embodiment of the present invention. Referring to  FIG. 8 , the electrowetting lenses  30  are arranged above a display panel  40 . When a two-dimensional image is displayed on the display panel  40 , a voltage having a critical level is applied to electrode cells of first and second multiple electrodes  36  and  37  (see  FIGS. 3-7B ) of the electrowetting lenses  30 . Then, the interface between polar and non-polar solutions  38  and  39  inside the electrowetting lenses  30  is flattened (e.g., neither convex nor concave). As a result, light is transmitted through the electrowetting lenses  30  without refraction. Therefore, the two-dimensional image displayed on all pixels of the display panel  40  can be incident onto both eyes of a viewer. 
         [0060]    Meanwhile, when the refractive index of the polar solution  38  is larger than that of the non-polar solution  39 , and a voltage lower than the critical level or no voltage is applied to the electrode cells of the first and second multiple electrodes  36  and  37 , the electrowetting lenses  30  function as convex lenses. On the contrary, when the refractive index of the non-polar solution  39  is larger than that of the polar solution  38 , the electrowetting lenses  30  can function as convex lenses by applying a voltage higher than the critical level to the electrode cells of the electrowetting electrodes  36  and  37 . In this state, when the display panel  40  displays left-eye and right-eye images alternately per each pixel of the display panel  40 , the electrowetting lenses  30  function as convex lenses to separate the left-eye and right-eye images and direct the separated left-eye and right-eye images respectively to left and right eyes of a viewer as shown in  FIG. 9 . Therefore, the viewer can view a three-dimensional image. 
         [0061]    Generally, when a viewer is at a predetermined location away from a three-dimensional image display device, the viewer can enjoy an exact three-dimensional image. Thus, when the viewer moves away from the predetermined location, the viewer cannot view an exact three-dimensional image. As described above, according to the present invention, the optical axis of the electrowetting lens  30  can be changed by making the height of charged electrode cells of the first multiple electrode  36  different from the height of charged electrode cells of the second multiple electrode  37 . Referring to  FIG. 10 , although the viewer moves to one side of the three-dimensional image display device, the three-dimensional image display device can provide an exact three-dimensional image by inclining the optical axes of the electrowetting lenses  30  toward the viewer. 
         [0062]    Furthermore, although the optical axes of all of the electrowetting lenses  30  are inclined in the same direction in  FIG. 10  (e.g., all inclined to the right), the optical axes of the electrowetting lenses  30  can be inclined in different directions as shown in  FIG. 11  (e.g., one inclined to the right, an opposite one inclined to the left and an intermediate one having no incline). In this case, different images can be provided depending on the location of the viewer relative to the three-dimensional image display device. 
         [0063]    Meanwhile, as shown in  FIG. 5A , after the interface between the polar and non-polar solutions  38  and  39  is flattened by applying a voltage having the critical level to the first and second multiple electrodes  36  and  37 , the interface can be inclined. For example,  FIG. 12A  shows the case where the height of charged electrode cells of the first multiple electrode  36  is the same as the height of the charged electrode cells of the second multiple electrode  37 . In this case, the electrowetting lens  30  transmits light without refraction. Referring to  FIG. 12B , the height of charged electrode cells of the first multiple electrode  36  is adjusted to a higher level as compared with the height of the charged electrode cells of the second multiple electrode  37 , so that the flat interface between the polar and non-polar solutions  38  and  39  can be sloped down from the right to the left. In this case, light is refracted to the left while passing through the electrowetting lens  30 . On the contrary, referring to  FIG. 12C , the height of charged electrode cells of the first multiple electrode  36  is adjusted to a lower level as compared with the height of the charged electrode cells of the second multiple electrode  37 . Thus, the flat contact surface between the polar and non-polar solutions  38  and  39  is sloped down from the left to the right. In this case, light is refracted to the right while passing through the electrowetting lens  30 . Therefore, the electrowetting lens  30  of the present invention can be used for dynamic optical path control devices. 
         [0064]    As described above, according to the present invention, the optical axis of the electrowetting lens can be easily moved to a desired direction by adjusting the height of charged electrode cells of one multiple electrode different from the height of charged electrode cells of the other multiple electrode. The electrowetting lens of the present invention can be used for dynamic optical path control devices. Particularly, when the electrowetting lens of the present invention is used in a three-dimensional image display device, an exact three-dimensional image can be provided to a viewer regardless of the location of the viewer since the optical axis or the electrowetting lens can be controlled depending on the location of the viewer. 
         [0065]    While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.