Abstract:
The present invention relates to a variable focus lens including a fluid chamber containing first and second fluids which are non-miscible and have different refractive indices, the fluid chamber having a plurality of protrusions formed along a circumference of one open end thereof. The variable focus lens also includes a transparent plate attached to the open end of the chamber via a sealing with a predetermined interval from the protrusions. The variable focus lens further includes a first electrode disposed inside the chamber to act on the first fluid and a second electrode disposed inside the chamber and is insulated from the first fluid. The invention allows an easy manufacturing process without bubble formation, and eliminates entry and formation of bubbles due to external changes such as in temperature and pressure, thereby allowing good performance of the lens regardless of external environmental changes.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims the benefit of Korean Patent Application No. 2005-133804 filed on Dec. 29, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a variable focus lens, and more particularly, to a variable focus lens which has a plurality of protrusions formed at one end of a chamber to prevent bubble formation and absorbs volume change of fluid due to changes in external environment such as temperature and pressure to eliminate entry or formation of bubbles, thereby functioning well as a lens regardless of external changes. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, a camera is equipped with a plurality of lenses and is configured to adjust optical focus distance by driving the lenses respectively to vary the relative distances thereof. Due to the miniaturization of optical devices such as a camera with a lens mounted therein, the miniaturization of the lens is increasingly required in turn. 
         [0006]    In order to meet the needs for miniaturization, a variable focus lens has been disclosed in PCT WO 03/069380. 
         [0007]      FIG. 1  is a schematic cross-sectional view of the variable focus lens suggested in an embodiment of WO 03/069380. 
         [0008]    As shown in  FIG. 1 , the variable focus lens includes a fluid chamber  5  with a cylindrical wall, containing first fluid A and second fluid B therein which are non-miscible and have different refractive indices. The first and second fluids A and B are in contact over a meniscus  14  in between. The variable focus lens also includes a fluid contact layer  10  disposed on an inner side of the cylindrical wall of the fluid chamber  5 , a first electrode  2  separated from the first fluid A and the second fluid B by the fluid contact layer  10  and a second electrode  12  acting on the second fluid B. 
         [0009]    The first electrode  2  has a cylindrical shape and is coated by an insulating layer  8  with metallic material. The second electrode  12  is disposed at one end of the fluid chamber  5 . 
         [0010]    In addition, the fluid chamber  5  is covered by transparent front and back elements  4  and  6  to house the fluids A and B. 
         [0011]    In addition, a sealing (shown in  FIG. 4  and denoted by reference numeral  16 ) is provided to bond the front element  4  with the fluid contact layer  10 . 
         [0012]    The operation of the variable focus lens with the above described configuration is as explained hereunder. 
         [0013]    When no voltage is applied between the first electrode  2  and the second electrode  12 , the fluid contact layer  10  has a higher wettability with respect to the first fluid A than the second fluid B. 
         [0014]    Due to electrowetting, wettability by the second fluid B varies under the application of voltage between the first and second electrodes, which changes the contact angle Q 1 , Q 2  and Q 3  of the meniscus  14  as shown. 
         [0015]    Therefore, the shape of the meniscus is variable in response to the voltage applied, thereby adjusting the focus of the lens. 
         [0016]    That is, as shown in  FIGS. 1 to 3 , in accordance with the magnitude of the voltage applied, the angle of the meniscus  14  and the fluid contact layer  10  measured in the side of the first fluid B changes from an obtuse angle to an acute angle, for example, in the order of 140°, 100°, 60°, etc. 
         [0017]    Herein,  FIG. 1  shows a lens configuration with high negative power,  FIG. 2  shows a lens configuration with low negative power and  FIG. 3  shows a lens configuration with positive power. 
         [0018]    The variable focus lens using the fluid as described above has an advantage for miniaturization over the conventional method of adjusting focal distance by mechanically operating the lenses. 
         [0019]    However, the conventional variable focus lens has drawbacks as shown in  FIG. 4 . That is, as the variable focus lens contains fluids, if the fluids are not properly sealed, bubbles  18  may be formed inside the chamber  5  as shown in  FIG. 4 . 
         [0020]    The drawbacks of the conventional variable focus lens will now be explained in greater detail with reference to  FIGS. 5 and 6 . 
         [0021]    First, as shown in  FIG. 5 , the fluids A and B are filled between the space between the chamber walls  30 , forming a convex surface, but not to the degree of flowing over an upper end  32  of the chamber wall. At this state, an upper transparent plate  40  is moved downward in the direction indicated by the arrow C, the fluid A contacts the undersurface of the upper transparent plate  40  and spreads along the undersurface of the upper transparent plate. Thus, when the upper transparent plate  40  is completely attached to the chamber wall  30 , a bubble V is formed in the middle of the fluid A as shown in  FIG. 6 . The fluid lens is not usable if such a bubble is formed. This is an example of the problem described with reference to  FIG. 4 . 
         [0022]    To prevent such a problem, the lens can be assembled inside the liquid, which however does not completely suppress the formation of the bubbles, diminishes productivity and hinders mass production of lens. 
       SUMMARY OF THE INVENTION 
       [0023]    The present invention has been made to solve the foregoing problems of the prior art and therefore an object of certain embodiments of the present invention is to provide a variable focus lens which has a plurality of protrusions formed on one end of a chamber to prevent formation of bubbles. 
         [0024]    Another object of certain embodiments of the invention is to provide a variable focus lens which has a plurality of protrusions formed at one end of a chamber to absorb volume change of fluid due to changes in external environment such as temperature and pressure, eliminating bubble entry or formation due to the volume change of the fluid, thereby allowing good performance of the lens regardless of external changes. 
         [0025]    According to an aspect of the invention for realizing the object, there is provided a variable focus lens including: a fluid chamber containing first and second fluids which are non-miscible and have different refractive indices, the fluid chamber having a plurality of protrusions formed along a circumference of one open end thereof; a transparent plate attached to the open end of the chamber via a sealing with a predetermined interval from the protrusions; a first electrode disposed inside the chamber to affect the first fluid; and a second electrode disposed inside the chamber and is insulated from the first fluid. 
         [0026]    According to certain embodiments of the present invention, the chamber is made of a transparent material, and has a closed end with a predetermined thickness opposing to the open end. 
         [0027]    According to certain embodiments of the present invention, the first fluid is conductive and the second fluid is non-conductive. 
         [0028]    According to certain embodiments of the present invention, each of the protrusions has a sectional shape of one selected from a group consisting of a triangle, a rectangle and a trapezoid. 
         [0029]    According to certain embodiments of the present invention, the variable focus lens according to claim  1 , further includes a second transparent plate attached to the other end of the chamber. 
         [0030]    According to certain embodiments of the present invention, an innermost one and a next one of the plurality of protrusions form a space with a dimension corresponding to 1% of a total volume of the first and second fluids. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0032]      FIGS. 1 to 3  are sectional views illustrating structure and operations of a variable focus lens according to the prior art; 
           [0033]      FIG. 4  is a sectional view illustrating the problems with the variable focus lens according to the prior art; 
           [0034]      FIGS. 5 and 6  are sectional views illustrating the shape and effects of meniscus of the variable focus lens according to the prior art; 
           [0035]      FIG. 7  is a sectional view illustrating a configuration of a variable focus lens according to an embodiment of the present invention; 
           [0036]      FIG. 8  is a plan view illustrating a fluid region of the variable focus lens shown in  FIG. 7 ; 
           [0037]      FIG. 9  is a sectional view illustrating a configuration of a variable focus lens according to another embodiment of the present invention; 
           [0038]      FIG. 10  is a sectional view illustrating a variable focus lens according to further another embodiment of the present invention; 
           [0039]      FIGS. 11 to 13  are sectional views illustrating the shape and effects of meniscus of the variable focus lens shown in  FIG. 10 ; 
           [0040]      FIGS. 14   a  to  15  are sectional views illustrating variations of a plurality of protrusions of the variable focus lens shown in  FIG. 10 ; and 
           [0041]      FIGS. 16 and 17  are sectional views illustrating two types of electrodes formed in the variable focus lens shown in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0042]    Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
         [0043]    First,  FIG. 7  illustrates a configuration of a variable focus lens  100  according to an embodiment of the present invention. 
         [0044]    The variable focus lens  100  includes a chamber wall  110  forming a cylindrical inner space with a first bump or protrusion  112 , a second protrusion  114  and two third protrusions  115  formed on one end thereof, an upper transparent plate  120  attached to an upper end  110 A of the chamber wall  110  with a predetermined interval G in between and a lower transparent plate  130  attached to a lower end  110 B of the chamber wall  110 . 
         [0045]    Here, the first protrusion  112  has a rectangular section and each of the second and third protrusions  114  and  115  has an inverted triangular section. Thus, three grooves are formed by the first protrusion  112 , the second protrusion  114  and the third protrusion  115 . 
         [0046]    At this time, the upper transparent plate  120  and the chamber wall  110  are hermetically attached to each other via a sealing  122 , and the lower transparent plate  130  and the chamber wall  110  are bonded with each other by a bonding layer (not shown). The bonding can be done for example by frit bonding. Alternatively, the lower transparent plate  130  can be formed integrally with the chamber wall  110 . For example, a groove can be machined as the chamber in a transparent plate to form a lens body having the lower transparent plate integrated with the chamber wall. 
         [0047]    In the meantime, non-miscible first and second fluids A and B are filled in the inner space of the chamber formed by the chamber wall  110  and upper and lower transparent plates  120  and  130 . The first and second fluids A and B are provided in substantially the same proportions but have different refractive indices. In addition, one is a conductive fluid while the other one is non-conductive fluid. In this embodiment of the present invention, the fluid A is conductive while the fluid B is non-conductive. 
         [0048]    Examining a part denoted by reference sign A in  FIG. 7 , a portion of the fluid A fills a space between the first protrusion  112  and the second protrusion  114  and forms a bulging surface A 1  between the tip of the second protrusion  114  and the upper transparent plate  120 . And the fluid A is in complete contact with the upper transparent plate  120  in the area from the tip of the protrusion  112  to the inner space of the chamber. Also, as described later with reference to  FIG. 12 , if the amount of fluid A is too much, a portion may drip and stay in the form of droplet D 1  in a bubble region or a void V between the protrusion  114  and the upper transparent plate  120 . As a result, a bubble exists in an outward area from the protrusion  114 , i.e., in the void V between the protrusion  114  and the sealing  122  but not in the inward area of the protrusion  114  inside of the chamber. Such a bulging surface A 1  is formed in a circle along the area between the protrusion  114  and the upper transparent plate  120 . This circular fluid region seen from above is illustrated in  FIG. 8(   a ). 
         [0049]    With fluid A filled in the space between the first and second protrusions  112  and  114 , when the volume of the fluids A and B change according to the temperature change, the surplus portion of the first fluid A forming the bulging surface A 1  moves toward the chamber. As a result, bubbles are not formed in the inward area of the first protrusion  112 . 
         [0050]    Also, as shown in the part denoted by reference sign B in  FIG. 7  and in  FIG. 8(   b ), the bulging surface A 2  of the fluid A may be formed along the area between the first protrusion  112  and the upper transparent plate  120 . 
         [0051]    Moreover, as shown in  FIG. 8(   c ), a portion of fluid A may form the bulging surface A 2  along the area between the first protrusion  112  and the upper transparent plate  120 , and another portion of fluid A may form the bulging surface A 1  along the area between the second protrusion  114  and the upper transparent plate  120 . 
         [0052]    Such a bulging surface A 1 , A 2  is determined by the amount or volume change of fluid A. 
         [0053]      FIG. 9  illustrates a configuration of a variable focus lens  100 A according to another embodiment of the present invention. 
         [0054]    In the variable focus lens  100 A in  FIG. 9 , the chamber wall  110  has an inner surface  116  sloped inward toward the bottom thereof. Therefore, the chamber wall  110  has an inner diameter decreasing from an upper end  110 A to a lower end  110 B. Such a sloped construction is applied to optimize the initial conditions of the first and second fluids A and B, and the angle of the slope is configured to vary according to the contact angles of the fluids A and B. According to this configuration, the first protrusion  112   a  has a trapezoidal section. 
         [0055]    Except for this sloped configuration, the variable focus lens  100 A has substantially the same configuration with that of  FIG. 7 , and thus additional explanation is omitted. 
         [0056]      FIG. 10  illustrates a configuration of a variable focus lens  100 B according to further another embodiment of the present invention. 
         [0057]    Except for the sharp tip of the first protrusion  112   b , the variable focus lens  100 B in  FIG. 10  has substantially the same configuration with that of  FIG. 9 . Of course, the first protrusion  112   b  with the sharp tip can also be adopted in the configuration of  FIG. 7 . 
         [0058]      FIGS. 11 to 13  are sectional views illustrating shapes and effects of menisci of the variable focus lens shown in  FIG. 10 . For the sake of convenience, the explanation is based on the structure of  FIG. 10 , but the same can be applied to the structures of  FIGS. 7 and 9 . 
         [0059]    When the fluid B and then the fluid A are precisely injected, the fluid A on the top is bulged upward beyond the level of the protrusion  112   b . This shape is exaggerated for convenience in explanation, and since the actual injection amount of the fluid A is precisely regulated, the size of the portion of the fluid A bulging upward beyond the protrusion  112   b  is insignificant. 
         [0060]    In this state, when the upper transparent plate  120  is vertically attached to the chamber wall  110 , the bulging portion of the fluid A first comes into contact with an undersurface of the transparent plate  120  and pressed by the transparent plate  120  to be spread outward, i.e., toward the first protrusion  112   b . As a result, the fluid A forms and stays in a bulging shape between the protrusion  114  and the transparent plate  120  as shown in  FIG. 12 . 
         [0061]    In other words, as the fluid A comes into contact with an undersurface of the upper transparent plate  120 , it spreads along the undersurface of the upper transparent plate  120 . At this time, the fluid A fills in the space between the first protrusion  112   b  and the second protrusion  114 , and forms and maintains the bulging surface A 1  between the second protrusion  114  and the upper transparent plate  120 . This is because the force (or surface tension) of the fluid A and the tip of the second protrusion  114  and is greater than the force by which the fluid A spreads along the undersurface of the upper transparent plate  120 , thus capturing fluid A between the second protrusion  114  and the upper transparent plate  120 . This can be understood by the similar example of water drop forming a bulging shape on a planar surface. 
         [0062]    In the meantime, if the amount of the fluid A is too much so that there is a surplus after filling in the inward area of the protrusion  112   b , the surplus of the fluid A overpowers the force working between the protrusion  112   b  and the upper transparent plate  120  and falls from the tip of the second protrusion  114  in a droplet. This surplus fluid forms a droplet D 1  in a groove between the second protrusion  114  and the third protrusion  115  as shown in  FIG. 12 . In the meantime, if the amount of the surplus fluid or droplet is greater than what can be accommodated by the groove between the second protrusion  114  and the third protrusion  115 , this excess amount forms a droplet in a groove between the third protrusions  115 . 
         [0063]    The above described configuration can solve the problem of the prior art depicted in  FIGS. 4 to 6 . 
         [0064]    That is, if the fluid A reaches the tip of the second protrusion  114 , rather than spreading as illustrated in  FIG. 6 , the fluid A stays between the protrusion  114  and the undersurface of the upper transparent plate  120  due to the force working with the protrusion  114 . This allows preventing bubble formation depicted in  FIGS. 4 to 6 . Therefore, the variable focus lens according to the present invention can be easily manufactured in the air, thereby significantly improving productivity. 
         [0065]    The above described condition is not limited to the time of mounting the upper transparent plate  120 . That is, also when the volume of the fluids A and B is increased due to the increase in temperature, etc., a portion of the fluid A corresponding to the increased volume moves into the groove between the second and third protrusions  114  and  115  and form a droplet D 1  as shown in  FIG. 12 . 
         [0066]    Conversely, as shown in  FIG. 13 , when the volume of the fluids A and B is decreased due to the decrease in temperature, etc., the bulging surface A 1  of the fluid A moves in the direction indicated by the arrow C to form the bulging surface A 2 , supplementing the decreased volume of the fluid in the inward area of the first protrusion  112   b . At this time, the bulging surface A 2  is formed along the entire or a part of the first protrusion  112   b  as shown in  FIGS. 8(   b ) and  8 ( c ). That is, when the decrease in the volume is large, the bulging surface A 2  can be formed as shown in  FIG. 8(   b ), and when the decrease in the volume is small, both of the bulging surfaces A 1  and A 2  can be formed. 
         [0067]    In consideration of the above described characteristics, the plurality of protrusions in the present invention not only have a function of preventing bubble formation inside the chamber but also a function of absorbing the stress, due to the volume change of the fluids A and B, affecting a fluid lens body. 
         [0068]    To allow these effects, the first and second protrusions  112   b  and  114  are formed in such an interval and width, although there may be variations depending on the characteristics of the fluid A, that bubble formation is prevented during the assembly and the sealed state is maintained while the fluid lens is operating, 
         [0069]    Back to the structure of protrusions in  FIG. 10 , although the interval G between the protrusions  112   b ,  114  and  115  and the upper transparent plate  120  is adjustable by the injection amount of the fluid, it is preferably up to 20 μm. The interval G may be adjusted by a stopper, which may be provided as a sealing  122  or other physical means. 
         [0070]    Preferably, the interval P 1  between the first protrusion  112   b  and the second protrusion  114  and the interval P 2  between the second protrusion  114  and the third protrusion  115  is about 300 μm. In addition, it is preferable that the depth of the spaces between the first, second and third protrusions  112   b ,  114  and  115 , i.e., the height h of these protrusions  112   b ,  114  and  115  is about 400 μm. 
         [0071]    In the meantime, based on the configurations of  FIGS. 7 and 9 , it is preferable that the first protrusion  112 ,  112   a  has a width of up to 300 μm. 
         [0072]    Such numbers are determined in the range that can accommodate the volume change of fluids A and B, and the volume change can typically amount to 1% at maximum due to the temperature change, etc. Specifically, when a fluid lens is fabricated in a total volume of about 20 μl, the diameter of this lens is about 5 mm, and thus the first protrusion and the second protrusion can be formed in a width of 300 μm and a height of 400 μm around the lens, which will sufficiently absorb the volume change. Of course, if the volume of the fluid lens is less than 20 μl, the protrusions are adjusted to be formed in smaller values. In order for a stable performance, there may be provided one or more third protrusions. 
         [0073]    Now, variations of the plurality of protrusions of the variable focus lens of  FIG. 9  will be examined with reference to  FIGS. 14   a  to  14   c  and  15 . 
         [0074]    In the variation shown in  FIG. 14   a , the second and third protrusions  114   a  and  115   a  have a rectangular section. In the variations in  FIGS. 14   b  and  14   c , the second and third protrusions  114   b ,  114   c ,  115   b  and  115   c  have a right-triangular section. The shape of the protrusions in  FIG. 14   b  is symmetrical to that in  FIG. 14   c.    
         [0075]    In the variation shown in  FIG. 15 , the second protrusion  114  is formed at a pre-set interval P 1  from the first protrusion  112   b . The third protrusion  115  is formed at a pre-set interval P 2  from the second protrusion  114 . 
         [0076]    At this time, it is preferable that the interval P 1  and P 2  is up to 750 μm. This is because if the interval P 1  and P 2  exceeds 750 μm, too large a distance between the protrusions  112   b ,  114  and  115  can hinder the effects expected from forming the second and third protrusions  114  and  115 . 
         [0077]      FIG. 16  illustrates the variable focus lens  100 A of  FIG. 9  with electrodes  140  and  142  formed therein. 
         [0078]    The variable focus lens of  FIG. 16  additionally includes a first electrode  140  formed on an undersurface of the upper transparent plate  120 , a second electrode  142  formed on an inner surface  116  of the chamber wall  110  and an insulation layer  146  formed on a surface of the second electrode  142  for electric insulation between the first electrode  140  and the second electrode  142 . In addition, a conductor  144  is formed on an interface between a lower end  110 A of the chamber wall  110  and the lower transparent plate  130  to connect the second electrode  142  with an external power source  150 . 
         [0079]    Here, the first fluid A is conductive while the second fluid B is non-conductive. The chamber wall  110  is made of insulation material such as glass and ceramics. 
         [0080]    Moreover, the power source  150  and an electric wire are provided so that the first electrode  140  is electrically connected to the power source  150  through the electric wire, and the second electrode  142  is electrically connected to the power source  150  through the conductor  144  and the electric wire. 
         [0081]    With this configuration, the voltage of the power source  150  can be varied to modify the meniscus M between the first and second fluids A and B, thereby adjusting the focal distance of the variable focus lens. 
         [0082]    At this time, to prevent the conductive first fluid A from contacting the second electrode  142  due to the change of the meniscus M, the insulation layer  146  should be formed in an area large enough to cover the second electrode  142 . 
         [0083]    In the meantime, it is preferable that the first and second electrodes  140  and  142  are formed by a deposition method such as sputtering or electron beam deposition. 
         [0084]    This configuration allows a surplus of fluid to form a droplet D 1  in the groove between the first and second protrusions  112   a  and  114 . 
         [0085]      FIG. 17  is a sectional view illustrating the variable focus lens  100 A of  FIG. 9  with another configuration of electrodes formed therein. 
         [0086]    The variable focus lens of  FIG. 17  additionally includes a first electrode  140  formed on an upper end  110 A of the chamber wall  110  as well as on the protrusions  112   a ,  114  and  115  opposed to the upper transparent plate  120 , a second electrode  142  formed on an inner surface  116  of the chamber wall  110  and an insulation layer  146  formed on a surface of the second electrode  142  for electric insulation between the first electrode  140  and the second electrode  142 . 
         [0087]    Except for the configuration of the first electrode  140 , the rest of the configuration of the variable focus lens is identical to that of  FIG. 16 , and thus additional explanation is omitted. 
         [0088]    According to the present invention as set forth above, the variable focus lens has a plurality of protrusions formed on one end of a chamber to prevent degradation of performance thereof due to bubble formation. In addition, the variable focus lens according to the present invention can be manufactured in the air. Therefore, the variable focus lens has enhanced stability and is easily manufactured to significantly improve productivity. Further, the plurality of protrusions absorb volume change of fluid due to temperature change, etc., thereby eliminating the stress, due to the volume change of the fluid, affecting a lens body. 
         [0089]    While the present invention has been shown and described in connection with the preferred embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.