Abstract:
A variable liquid lens system is provided. The variable liquid lens system includes a lens barrel comprising a wall and first and second ends, wherein the first and second ends are substantially transparent, at least one liquid lens disposed in the lens barrel and contacting the wall, the at least one liquid lens comprising a droplet, and a plurality of spaces containing fluid positioned on opposite sides of the at least one liquid lens inside the lens barrel. A plurality of first holes are provided in the wall at a position corresponding to the plurality of spaces. The at least one liquid lens is configured so that a position of the at least one liquid lens within the lens barrel is adjustable by adjusting amounts of the fluid contained in the plurality of spaces via the plurality of first holes.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority from Korean Patent Application No. 10-2013-0136541, filed on Nov. 11, 2013 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    One or more exemplary embodiments relate to a lens system, and more particularly, to a variable liquid lens system having a focal length adjusting function or a zooming function. 
         [0004]    2. Description of the Related Art 
         [0005]    In the field of medical imaging, there is increasing demand for information on the surface of tissue (human body tissue or skin tissue) and a technique for precisely capturing sectional images underneath these surfaces. In particular, most cancers occur under epithelial cells and then spread into dermal cells where blood vessels are present, and thus early detection of cancer may remarkably reduce damage due to the cancer. Internal tomograms may be obtained through the skin by using an existing imaging technique, such as magnetic resonance imaging (MRI), x-ray computed tomography (CT), ultrasonic imaging, or similar. However, due to the low resolution of the tomograms, early detection of cancer, which is small in size, is difficult. On the other hand, a recently introduced optical coherence tomography (OCT) technique uses light, unlike existing techniques of the related art. Thus, the OCT technique is expected to be useful in detecting early cancer with a size of about 50 μm to about 100 μm because the OCT technique has a resolution approximately ten times greater than that of the ultrasonic imaging technique even though its penetration into the skin is as low as about 2 mm to about 3 mm. 
         [0006]    In the OCT technique, as well as in various fields where optical devices are used, there is demand for adjusting a position on which light is focused or the size of an irradiated light spot, and for miniaturizing such optical devices. 
         [0007]    To accommodate such demand for the focal length adjusting function or the zooming function and miniaturization, a liquid lens is provided. A liquid lens does not involve any mechanical movement, and the focus and magnification thereof may be adjusted. 
         [0008]    A liquid lens involves a liquid dispensing process. Due to recent advances in microfluidic technology, a technique for dispensing liquid at a picoliter (pL) level is under development together with various liquid-based devices. 
       SUMMARY 
       [0009]    One or more exemplary embodiments provide a variable liquid lens system whose focal length may be adjusted or which has a zooming function, and which may be miniaturized by reducing an area occupied by a driving device as much as possible. 
         [0010]    According to an aspect of an exemplary embodiment, there is provided a variable liquid lens system including a lens barrel which has a wall and two ends, of which at least the two ends are transparent so that light passes therethrough, at least one liquid lens disposed inside the lens barrel and contacting the wall, the at least one liquid lens comprises of a droplet, and a plurality of spaces which are positioned on opposite sides of the at least one liquid lens inside the lens barrel. A plurality of first holes are provided in the wall at positions corresponding to the plurality of spaces. The at least one liquid lens is configured so that a position of the at least one liquid lens within the lens barrel is adjustable by adjusting amounts of the fluid contained in the plurality of spaces via the plurality of first holes. 
         [0011]    The at least one liquid lens may include first and second liquid lenses positioned apart from each other, the plurality of spaces may include first to third spaces positioned on one side of the first liquid lens, between the first and second liquid lenses, and on another side of the second liquid lens, and the first and second liquid lenses are configured so that positions of the first and second liquid lenses relative to each other are adjustable by adjusting amounts of the fluid contained in the first, second and third spaces. 
         [0012]    During the adjustment of the positions of the first and second liquid lenses, the sum of variances in the amount of the fluid contained in the first to third spaces may be controlled to be zero. 
         [0013]    During the adjustment of the positions of the first and second liquid lenses, the sum of variances in the volumes of the first to third spaces may be controlled to be zero. 
         [0014]    The first and second liquid lenses may be formed of different types of liquid. 
         [0015]    The first and second liquid lenses may include a different type of fluid than the fluid filling the first to third spaces. 
         [0016]    The variable liquid lens system may further include an electrode at a portion of the wall corresponding to at least one of the first and second liquid lenses, and a curvature of the at least one liquid lens may be changed according to an electrowetting principle. 
         [0017]    The wall may have a non-parallel wall area so that a curvature of at least one of the first and second liquid lenses is changed during the position adjustment. 
         [0018]    A second hole may be provided in the wall at a position corresponding to the at least one of the first and second liquid lenses, and a distance between two lens surfaces of the at least one liquid lens may be adjusted by adding or subtracting the liquid to or from the at least one liquid lens. 
         [0019]    The at least one liquid lens may consist of a different type of fluid than the fluid filling the spaces. 
         [0020]    The wall may have a parallel-wall structure 
         [0021]    The lens barrel may have a cylindrical shape. 
         [0022]    The lens barrel may have a cylindrical shape, a truncated cone shape, or a combined shape of two or more truncated cones. 
         [0023]    The variable liquid lens system may further include an electrode provided at a portion of the wall corresponding to the at least one liquid lens, and the curvature of the at least one liquid lens may be changed according to the electrowetting principle. 
         [0024]    The wall may have a non-parallel wall area so that the curvature of the at least one liquid lens is changed during the adjustment of the position of the at least one liquid lens. 
         [0025]    A second hole may be provided in the wall so that liquid flows to the at least one liquid lens, and the distance between two lens surfaces of the at least one liquid lens may be adjusted by adding or subtracting the liquid to or from the at least one liquid lens. 
         [0026]    According to an aspect of another exemplary embodiment, there is provided a variable liquid lens system including a lens barrel including a wall and first and second ends, wherein the first and a second end are substantially transparent; at least one liquid lens disposed in the lens barrel and contacting the wall, the at least one liquid lens comprising a droplet; and a plurality of spaces positioned on opposite sides of the at least one liquid lens inside the lens barrel, wherein at least one first hole is provided in the wall at a position corresponding to the at least one liquid lens, and the at least one liquid lens is configured so that a distance between two lens surfaces of the at least one liquid lens is adjustable by adding or subtracting liquid to or from the at least one liquid lens via the at least one first hole. 
         [0027]    According to an aspect of another exemplary embodiment, there is provided a variable liquid lens system including a lens barrel comprising first and second ends; a liquid lens inside the lens barrel and comprising a droplet; a plurality of spaces positioned between the liquid lens the first and second ends of the lens barrel; and at least one first hole provided in the wall corresponding to at least one first space among the plurality of spaces, wherein hydraulic pressure or air pressure of the at least one first space is configured to be adjusted by adjusting an amount of fluid contained in the first space using the at least one first hole, and the liquid lens is configured so that a position of the liquid lens is adjustable based on the adjustment of the hydraulic pressure or air pressure of the first space. 
         [0028]    The liquid lens may further comprise a lens frame. 
         [0029]    According to an aspect of another exemplary embodiment, there is provided a variable liquid lens system including a lens barrel comprising first and second ends; a liquid lens inside the lens barrel and comprising a droplet; a plurality of spaces positioned between the liquid lens the first and second ends of the lens barrel; and at least one first hole provided in the wall corresponding to the liquid lens, wherein at least one of a size and a shape of the liquid lens is configured to be adjusted by adding or subtracting liquid to or from the at least one liquid lens using the at least one first hole. 
         [0030]    The liquid lens may further comprise a lens frame. 
         [0031]    Here, the at least one liquid lens may include first and second liquid lenses positioned apart from each other, and a distance between two lens surfaces of at least one of the first and second liquid lenses may be adjusted by adding or subtracting the liquid to or from the at least one liquid lens. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    The above and/or other aspects will become apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings in which: 
           [0033]      FIG. 1  schematically shows a variable liquid lens system according to an exemplary embodiment; 
           [0034]      FIG. 2  illustrates the operation of adjusting the distance between first and second liquid lenses in the variable liquid system of  FIG. 1  by adjusting the amounts of fluid contained in first to third spaces; 
           [0035]      FIGS. 3 to 5  schematically show variable liquid lens systems according to other exemplary embodiments; 
           [0036]      FIG. 6  schematically shows a variable liquid lens system according to another exemplary embodiment; 
           [0037]      FIG. 7  shows changes in the volumes of first and second liquid lenses when liquid is subtracted from the first liquid lens and added to the second liquid lens in the variable liquid lens system of  FIG. 6 ; and 
           [0038]      FIGS. 8 to 13  schematically show variable liquid lens systems according to other exemplary embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    Reference will now be made in detail to exemplary embodiments taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, exemplary embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the exemplary embodiments described below, by referring to the figures, are merely provided as examples. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
         [0040]    A variable liquid lens system according to an exemplary embodiment includes at least one liquid lens which consists of a droplet having a contact angle with respect to a wall inside a lens barrel, and a plurality of spaces which are positioned on one side and another side of the at least one liquid lens. In the variable liquid lens system, by adjusting hydraulic or air pressures of the respective spaces, a position of the at least one liquid lens may be adjusted to change a focus. By adding or subtracting liquid to or from the at least one liquid lens, the distance between two lens surfaces of the at least one liquid lens may be adjusted to change the focus. When a plurality of liquid lenses are positioned apart from each other in the lens barrel, the variable liquid lens system may perform the zooming function as well as the variable focus function through adjustment of distances between the plurality of liquid lenses. 
         [0041]    Such a variable liquid lens system according to an exemplary embodiment may perform the variable focus function and the zooming function. Therefore, when the variable liquid lens system is applied to an image scanning apparatus, it is possible to scan for a focus in the depth direction and perform the zooming function. 
         [0042]    Such a variable liquid lens system according to an exemplary embodiment may be applied to various optical apparatuses, such as an optical coherence tomography (OCT) system, a lens auto-focusing apparatus, a lens-zooming apparatus, and so on. 
         [0043]      FIG. 1  schematically shows a variable liquid lens system  1  according to an exemplary embodiment. 
         [0044]    Referring to  FIG. 1 , the variable liquid lens system  1  includes a lens barrel  10 , at least one liquid lens (e.g.,  20  and  30 ) which consists of a droplet having a contact angle with respect to a wall  11  inside the lens barrel  10 , and a plurality of spaces (e.g.,  51 ,  53 , and  55 ) positioned on one side and another side of the liquid lens inside the lens barrel  10 . The variable liquid lens system  1  may be prepared so that hydraulic pressures or air pressures of the respective spaces are adjusted by adjusting amounts of fluid contained in the plurality of spaces, and thus the position of the at least one liquid lens is adjusted to change a focus. Although the liquid lenses have been described as contacting the wall  11 , this is just an example, and the at least one liquid lenses may comprise a lens frame (not shown). In this case, the lens frame may contact the wall  11  inside the lens barrel  10 , and the droplet may contact the lens frame. 
         [0045]    The lens barrel  10  has the wall  11  and two ends  13  and  15 . Both ends  13  and  15  of the lens barrel  10  may be substantially transparent so that light may be input and output therethrough. The entirety of the lens barrel  10  may be formed of a transparent material, or only both ends  13  and  15  may be formed of a transparent material. 
         [0046]    The lens barrel  10  may be formed so that the wall  11  has a parallel-wall structure. In other words, the lens barrel  10  may be formed so that the size of an internal cross-section thereof is uniform and does not vary in a lengthwise direction. Also, the internal cross-section of the lens barrel  10  may be formed to have, for example, a circular shape. As an example, the lens barrel  10  may have a cylindrical shape. In this case, the wall  11  of the lens barrel  10  has a parallel structure. When the wall  11  of the lens barrel  10  has such a parallel structure, a curvature of the at least one liquid lens may be kept uniform during the position adjustment. 
         [0047]    As will be described later with reference to  FIGS. 9 and 10 , the lens barrel  10  may be formed so that the wall  11  has a non-parallel wall area. In other words, the lens barrel  10  may be formed so that the size of an internal cross-section varies in the lengthwise direction. Even in this case, the cross-section of the lens barrel  10  may be formed to have, for example, a circular shape. For example, the lens barrel  10  may have a truncated cone shape, or a combined shape of two or more truncated cones. In this case, the wall  11  of the lens barrel  10  has a non-parallel wall area. When the wall  11  of the lens barrel  10  has such a non-parallel wall area, the curvature of the at least one liquid lens moving through the non-parallel wall area may vary during the position adjustment. 
         [0048]    A plurality of first holes  40  may be formed in the wall  11  of the lens barrel  10  so that the fluid flows to the plurality of spaces. As will be described later, at least one second hole (e.g.,  70  of  FIG. 6 ) may be further formed in the wall  11  of the lens barrel  10  so that the liquid may flow into the at least one liquid lens. By adding or subtracting the liquid to or from the at least one liquid lens through such a second hole, the distance between the two lens surfaces of the at least one liquid lens may be adjusted. 
         [0049]    The at least one liquid lens comes in contact with the wall  11  inside the lens barrel  10 . The at least one liquid lens may consist of a droplet which has a contact angle with respect to the wall  11 . The at least one liquid lens and the spaces may be filled with different types of fluid. 
         [0050]    As shown in  FIG. 1 , the at least one liquid lens may include first and second liquid lenses  20  and  30  which are positioned apart from each other. In this case, the plurality of spaces may include first to third spaces  51 ,  53 , and  55  which are positioned on one side of the first liquid lens  20 , between the first and second liquid lenses  20  and  30 , and on the other side of the second liquid lens  30 , respectively. The first space  51  on the one side of the first liquid lens  20  may be positioned between the first end  13  of the lens barrel  10  and the first liquid lens  20 . The third space  53  on the other side of the second liquid lens  30  may be positioned between the second end  15  of the lens barrel  10  and the second liquid lens  30 . 
         [0051]    When the at least one liquid lens includes the first and second liquid lenses  20  and  30 , and the plurality of spaces include the first to third spaces  51 ,  53 , and  55  as shown in  FIG. 1 , the first holes  40  may be respectively formed at portions of the wall  11  corresponding to the first to third spaces  51 ,  53 , and  55 . One or a plurality of the first holes  40  may be formed at each of the portions of the wall  11  corresponding to the first to third spaces  51 ,  53 , and  55 .  FIG. 1  shows an example of a case where the first holes  40  are formed at the portions of the wall  11  corresponding to the first to third spaces  51 ,  53 , and  55  in a one-to-one fashion. In addition to the plurality of first holes  40  respectively formed at the portions of the wall  11  corresponding to the first to third spaces  51 ,  53 , and  55 , a second hole may be formed in the wall  11  so that the liquid flows to at least one of the first and second liquid lenses  20  and  30 . (See, e.g., second hole  70  of  FIG. 6 ) By forming the second hole, the variable liquid lens system  1  may be prepared so that the distance between the two lens surfaces of a liquid lens is adjusted by adding or subtracting the liquid to or from the liquid lens. Although a plurality of first holes  40  may correspond to the plurality of spaces  51 ,  53 , and  55 , this is only an example, and a single first hole or a plurality of first holes  40  may correspond to fewer than all of the plurality of spaces  51 ,  53 , and  55 . 
         [0052]    The first liquid lens  20  may have a contact angle of, for example, θ1 with respect to the wall  11 , and the second liquid lens  30  may have a contact angle of, for example, θ2 with respect to the wall  11 .  FIG. 1  shows an example in which the first liquid lens  20  has two lens surfaces  21  and  25  and is formed as a convex lens, and the second liquid lens  30  has two lens surfaces  31  and  35  and is formed as a concave lens. Although the first and second liquid lenses  20  and  30  are formed as a convex lens and a concave lens, respectively, this is only an example, and first and second liquid lenses may be formed as various types. The contact angle of the first liquid lens  20  and that of the second liquid lens  30  may vary according to the type of liquid used or the type or level of an impurity added to the liquid. To determine the contact angle of the first liquid lens  20  and that of the second liquid lens  30 , the wall  11  inside the lens barrel  10  may be subjected to surface treatment. 
         [0053]    Positions of the first and second liquid lenses  20  and  30  relative to each other may be adjusted by adjusting the amounts of the fluid contained in the first to third spaces  51 ,  53 , and  55 . Here, the fluid may include gas or liquid. When the fluid is gas, by adjusting the amounts of the fluid contained in the first to third spaces  51 ,  53 , and  55 , the air pressures of the first to third spaces  51 ,  53 , and  55  are adjusted, and the positions of the first and second liquid lenses  20  and  30  are adjusted so that a focus may be changed, and the zooming function may be performed. When the fluid is liquid, by adjusting the amounts of the fluid contained in the first to third spaces  51 ,  53 , and  55 , the hydraulic pressures of the first to third spaces  51 ,  53 , and  55  are adjusted, and the positions of the first and second liquid lenses  20  and  30  are adjusted so that the focus may be changed, and the zooming function may be performed as occasion demands. 
         [0054]    When the wall  11  of the lens barrel  10  has a parallel-wall structure as shown in  FIG. 1 , the curvatures of the respective first and second liquid lenses  20  and  30  may be kept uniform during the position adjustment. When the wall  11  of the lens barrel  10  has a non-parallel wall area in the structure in which the at least one liquid lens includes the first and second lenses  20  and  30  apart from each other, at least one of the first and second liquid lenses  20  and  30  may vary in curvature during the position adjustment. 
         [0055]    The liquid of the first and second liquid lenses  20  and  30  may be of the same type or different types. Also, the first and second liquid lenses  20  and  30  may consist of a different type of fluid than that which fills the first to third spaces  51 ,  53 , and  55 . 
         [0056]    A case where the at least one liquid lens includes the first and second liquid lenses  20  and  30 , and the plurality of spaces include the first to third spaces  51 ,  53 , and  55  has been described above with reference to  FIG. 1 . However, this is merely an example, and exemplary embodiments are not limited thereto. For example, the number of liquid lenses may be three or more, and the number of spaces may increase accordingly. 
         [0057]      FIG. 2  illustrates the operation of adjusting the distance between the first and second liquid lenses  20  and  30  in the variable liquid system  1  of  FIG. 1  by adjusting the amounts of fluid contained in the first to third spaces  51 ,  53 , and  55 . 
         [0058]    It is assumed that, before position adjustment, the width of the first space  51  is dA, the width of the second space  53  is dB, and the width of the third space  55  is dC. For example, when the amounts of fluid in the first and third spaces  51  and  55  are increased, and the amount of the fluid in the second space  53  is reduced, the width of the first space  51  is increased to dA′, the width of the second space  53  is reduced to dB′, and the width of the third space  55  is increased to dC′. In other words, the first liquid lens  20  moves toward the second liquid lens  30 , and the second liquid lens  30  moves toward the first liquid lens  20 , and the distance between the first and second liquid lenses  20  and  30  is reduced from dB to dB′. At this time, a space L1 between the two surface lenses  21  and  25  of the first liquid lens  20  and a space L2 between the two surface lenses  31  and  35  of the second liquid lens  30  may be each kept uniform as exemplified in  FIGS. 1 and 2 . 
         [0059]    During the position adjustment, the sum of variances in the volumes of the fluid contained in the first to third spaces  51 ,  53 , and  55  may be controlled to be zero. In other words, when the flow quantities of the fluid in the first to third spaces  51 ,  53 , and  55  through the first holes  40  formed in the wall  11  are Q A , Q B , and Q C  respectively, the variable liquid lens system  1  may be controlled so that Q A *t+Q B *t+Q C *t=0 (where t is time) is satisfied. 
         [0060]    In addition, during the position adjustment, the sum of variances in the volumes of the first to third spaces  51 ,  53 , and  55  may be controlled to be zero. In other words, when variances in the volumes of the first to third spaces  51 ,  53 , and  55  are ΔV A , ΔV B , and ΔV C  respectively, the variable liquid lens system  1  may be controlled so that ΔV A +ΔV B +ΔV C =0 is satisfied. In this case, when the wall  11  has a parallel-wall structure as shown in  FIGS. 1 and 2 , ΔdA+ΔdB+ΔdC=0 may be satisfied. Here, ΔdA=dA′−dA, ΔdB=dB′−dB, and ΔdC=dC′−dC. 
         [0061]    Various exemplary embodiments of a variable liquid lens system will be described below. 
         [0062]      FIG. 3  shows a variable liquid lens system  100  according to another exemplary embodiment. In the example of  FIG. 3 , the second liquid lens  30  is a convex lens having a contact angle of θ3 with respect to the wall  11 , unlike the variable liquid lens system  1  of  FIG. 1 . As shown in  FIG. 3 , the first and second liquid lenses  20  and  30  may be convex lenses. 
         [0063]      FIG. 4  shows a variable liquid lens system  200  according to another exemplary embodiment. Compared to the variable liquid lens system  1  of  FIG. 1 , the variable liquid lens system  200  further includes an electrode  60  at a portion of the wall  11  corresponding to at least one of the first and second liquid lenses  20  and  30  so that the curvature of the liquid lens is changed according to an electrowetting principle.  FIG. 4  shows an example in which electrodes  60  are formed at portions of the wall  11  respectively corresponding to the first and second liquid lenses  20  and  30  so that the curvatures of the respective first and second liquid lenses  20  and  30  are changed according to the electrowetting principle. Alternatively, an electrode  60  may be prepared to change the curvature of only one of the first and second liquid lenses  20  and  30  according to the electrowetting principle. In  FIG. 4 , solid lines indicate the two lens surfaces  21  and  25  of the first liquid lens  20  before a change in curvature, and dotted lines indicate the two lens surfaces  21  and  25  of the first liquid lens  20  after the curvature is changed due to the operation of the electrodes  60  according to the electrowetting principle. Also, in  FIG. 4 , solid lines indicate the two lens surfaces  31  and  35  of the second liquid lens  30  before the change in curvature, and dotted lines indicate those after the curvature is changed due to the operation of the electrodes  60  according to the electrowetting principle. 
         [0064]    When the electrodes  60  are prepared to change the curvatures of liquid lenses according to the electrowetting principle as in  FIG. 4  and other exemplary embodiments which will be described later, the first and second liquid lenses  20  and  30  may consist of, for example, polar liquid, and the contact angles of the first and second liquid lenses  20  and  30  may be changed by an electric field formed by the electrodes  60  so that the curvatures are changed. The electrodes  60  may have a structure which is fabricated by forming an electrode pattern on the wall  11  inside the lens barrel  10  and coating the electrode pattern with an insulating material. 
         [0065]      FIG. 5  shows a variable liquid lens system  300  according to another exemplary embodiment. The variable liquid lens system  300  has a structure in which the variable liquid lens system  100  of  FIG. 3  and the variable liquid lens system  200  of  FIG. 4  are combined. The second liquid lens  30  may be a convex lens having a contact angle with respect to the wall  11 , and an electrode  60  may be further prepared at a portion of the wall  11  corresponding to at least one of the first and second liquid lenses  20  and  30 , so that the curvature of the liquid lens may be changed according to the electrowetting principle.  FIG. 5  shows an example in which electrodes  60  are formed at portions of the wall  11  corresponding to the respective first and second liquid lenses  20  and  30  so that the curvatures of the respective first and second liquid lenses  20  and  30  are changed according to the electrowetting principle. Alternatively, an electrode  60  may be prepared to change the curvature of only one of the first and second liquid lenses  20  and  30  according to the electrowetting principle. 
         [0066]      FIG. 6  shows a variable liquid lens system  400  according to another exemplary embodiment. The variable liquid lens system  400  is different from the variable liquid lens system  1  of  FIG. 1  in that a second hole  70  is further formed in the wall  11  of the lens barrel  10  so that fluid may flow to at least one of the first and second liquid lenses  20  and  30 .  FIG. 6  shows an example in which second holes  70  have been respectively formed at portions of the wall  11  corresponding to the first and second liquid lenses  20  and  30  so that the liquid may be added to or subtracted from the respective first and second liquid lenses  20  and  30 . Alternatively, a second hole  70  may be formed to add or subtract the liquid to or from only one of the first and second liquid lenses  20  and  30 . 
         [0067]    When the liquid is added to or subtracted from, for example, the first and second liquid lenses  20  and  30  through the second holes  70 , the distance between the two lens surfaces  21  and  25  of the first liquid lens  20  may be adjusted, and the distance between the two lens surfaces  31  and  35  of the second liquid lens  30  may be adjusted. 
         [0068]    In other words, when the volume of at least one of the first and second liquid lenses  20  and  30  is changed by adding or subtracting the liquid to or from the liquid lens, the focus of the variable liquid lens system  400  may be changed, and the zooming function may be performed. While the liquid is added or subtracted, the curvatures of the two lens surfaces of the liquid lens may be kept uniform. For example, in a case where the liquid is allowed to be added to or subtracted from each of the first and second liquid lenses  20  and  30 , while the liquid is added or subtracted, the curvatures of the two lens surfaces  21  and  25  of the first liquid lens  20  may be kept uniform, and the curvatures of the two lens surfaces  31  and  35  of the second liquid lens  30  may also be kept uniform. 
         [0069]      FIG. 7  shows variances in the volumes of the first and second liquid lenses  20  and  30  in the variable liquid lens system  400  of  FIG. 6  when the liquid is subtracted from the first liquid lens  20  and added to the second liquid lens  30 .  FIG. 7  shows an operational state when the amounts of fluid contained in the first to third spaces  51 ,  53 , and  55  are adjusted to adjust the distance between the first and second liquid lenses  20  and  30  and also change the volumes of the first and second liquid lenses  20  and  30 . In other words,  FIG. 7  shows an example of an operational state in which the volumes of the first and second liquid lenses  20  and  30  are additionally changed, further to the operational state of  FIG. 2 . 
         [0070]    As illustrated in  FIGS. 6 and 7 , by adjusting the position of at least one of the first and second liquid lenses  20  and  30  and also the distance between the two lens surfaces of at least one of the first and second liquid lenses  20  and  30 , the focal length adjusting function or the zooming function of the variable liquid lens system  400  may be performed. 
         [0071]      FIG. 8  schematically shows a variable liquid lens system  500  according to another exemplary embodiment. The variable liquid lens system  500  is different from the variable liquid lens system  1  of  FIG. 1  and the variable liquid lens system  400  of  FIG. 6  in that only a second hole  70  is prepared in the wall  11  of the lens barrel  10  without the first holes  40  so that the liquid is added to or subtracted from at least one of the first and second liquid lenses  20  and  30 . As an example,  FIG. 8  shows a case where second holes  70  have been respectively formed at portions of the wall  11  corresponding to the first and second liquid lenses  20  and  30  so that the liquid may be added to or subtracted from the respective first and second liquid lenses  20  and  30 . 
         [0072]    Even when only the second holes  70  are prepared as in  FIG. 8 , the distance between two lens surfaces may be adjusted by adding or subtracting the liquid to or from the first and second liquid lenses  20  and  30 . At the same time, according to such an adjustment of the distance between the two lens surfaces, it is possible to adjust the distance between the first end  13  of the lens barrel  10  and the first liquid lens  20 , the distance between the second end  15  of the lens barrel  10  and the second liquid lens  30 , the distance between the first and second liquid lenses  20  and  30 , and so on. The position adjustment ranges of the first and second liquid lenses  20  and  30  may be smaller than those of  FIG. 6  where the positions of the first and second liquid lenses  20  and  30  are adjusted by adjusting the amounts of the fluid in the first to third spaces  51 ,  53 , and  55  and adding or subtracting the liquid to or from the first and second liquid lenses  20  and  30 . 
         [0073]      FIG. 9  schematically shows a variable liquid lens system  600  according to another exemplary embodiment. The variable liquid lens system  600  is different from the variable liquid lens system  100  of  FIG. 3  in that the wall  11  of the lens barrel  10  has a non-parallel wall area to change the curvature of at least one of the first and second liquid lenses  20  and  30  during position adjustment. 
         [0074]    In other words, as exemplified in  FIG. 9 , the wall  11  may be formed so that the size of a cross-section varies in the length direction. In this case also, the internal cross-section of the lens barrel  10  may be formed to have, for example, a circular shape. As a non-limiting example, the lens barrel  10  may have a truncated cone shape, or a combined shape of two or more truncated cones. In this case, the wall  11  of the lens barrel  10  has a non-parallel wall area. When the wall  11  of the lens barrel  10  has such a non-parallel wall area, the curvature of a liquid lens moving through the non-parallel wall area may vary during position adjustment. 
         [0075]      FIG. 9  shows an example of the lens barrel  10  having, for example, a combined structure of two truncated cones in which the size of an internal cross-section of the lens barrel  10  decreases toward a middle portion between the first and second liquid lenses  20  and  30 . In the example shown in  FIG. 9 , the first and second liquid lenses  20  and  30  are convex lenses, but any one of the first and second liquid lenses  20  and  30  may be a concave lens. 
         [0076]    As exemplified in  FIG. 9 , when each of the first and second liquid lenses  20  and  30  comes in contact with the non-parallel wall area, the position of the first or second liquid lens  20  or  30  is moved by adjusting the amounts of the fluid in the first to third spaces  51 ,  53 , and  55 , and during such a position adjustment, the curvature of at least one of the first and second liquid lenses  20  and  30  is changed due to the non-parallel structure of the wall  11 . 
         [0077]      FIG. 10  schematically shows a variable liquid lens system  700  according to another exemplary embodiment. Compared to the variable liquid lens system  600  of  FIG. 9 , the variable liquid lens system  700  further includes an electrode  60  at a portion of the wall  11  corresponding to at least one of the first and second liquid lenses  20  and  30  so that the curvature of the liquid lens may be changed according to the electrowetting principle as well as the non-parallel structure of the wall  11 .  FIG. 10  shows an example in which electrodes  60  are formed at portions of the wall  11  respectively corresponding to the first and second liquid lenses  20  and  30  so that the curvatures of the respective first and second liquid lenses  20  and  30  may be changed according to the electrowetting principle as well as position movement of the first and second liquid lenses  20  and  30 . Alternatively, an electrode  60  may be prepared to change the curvature of only one of the first and second liquid lenses  20  and  30  according to the electrowetting principle. 
         [0078]    The variable liquid lens systems  600  and  700 , in which the wall  11  of the lens barrel  10  is formed into the non-parallel structure to change the curvature of a liquid lens as described with reference to  FIGS. 9 and 10 , may further include at least one second hole  70  in the wall  11  so that the distance between the two lens surfaces of at least one of the first and second liquid lenses  20  and  30  is adjusted by adding or subtracting the liquid to or from the liquid lens. The variable liquid lens systems  600  and  700  in which the wall  11  of the lens barrel  10  is formed into the non-parallel structure to change the curvature of a liquid lens may only include a second hole  70  in the wall  11  without the first holes  40  so that the distance between the two lens surfaces of at least one of the first and second liquid lenses  20  and  30  is adjusted by adding or subtracting the liquid to or from the liquid lens, and thus the position of the liquid lens may be adjusted. 
         [0079]    Cases where the variable liquid lens systems  1 ,  100 ,  200 ,  300 ,  400 ,  500 ,  600 , and  700  according to the various exemplary embodiments include a plurality of liquid lenses apart from each other, for example, the first and second liquid lenses  20  and  30  have been described and illustrated above with reference to  FIGS. 1 to 10 . However, a variable liquid lens system according to an exemplary embodiment is not limited to the variable liquid lens systems  1 ,  100 ,  200 ,  300 ,  400 ,  500 ,  600 , and  700  including a plurality of liquid lenses apart from each other, and may include a single liquid lens. 
         [0080]    For example, as shown in  FIGS. 11 to 13 , one liquid lens  20 ′ may be prepared in the lens barrel  10 .  FIGS. 11 to 13  show cases of the liquid lens  20 ′ being a convex lens according to various exemplary embodiments. However, this is merely an example, and the liquid lens  20 ′ may have various other lens shapes, such as a concave lens. 
         [0081]    A variable liquid lens system  800  of  FIG. 11  has a constitution corresponding to the variable liquid lens system  1  of  FIG. 1 .  FIG. 11  shows an example in which first holes  40  are formed in the lens barrel  10  so that the amounts of the fluid in a space  51 ′ between one lens surface  21 ′ of the single liquid lens  20 ′ and the first end  13  of the lens barrel  10  and a space  55 ′ between the other lens surface  25 ′ of the single liquid lens  20 ′ and the second end  15  of the lens barrel  10  are adjusted, and the position of the liquid lens  20 ′ is adjusted accordingly. 
         [0082]    Compared to the variable liquid lens system  800  of  FIG. 11 , a variable liquid lens system  900  of  FIG. 12  is an example in which not only the first holes  40  but also a second hole  70  are formed in the lens barrel  10  so that the position of the liquid lens  20 ′ may be adjusted by adjusting the amounts of the fluid in the spaces  51 ′ and  55 ′, and also the distance between the two lens surfaces  21 ′ and  25 ′ may be adjusted by adding or subtracting the liquid to or from the liquid lens  20 ′. 
         [0083]    Compared to the variable liquid lens system  900  of  FIG. 12 , a variable liquid lens system  1000  of  FIG. 13  is an example in which only the second hole  70  is formed in the lens barrel  10  without the first holes  40  so that the distance between the two lens surfaces  21 ′ and  25 ′ may be adjusted by adding or subtracting the liquid to or from the liquid lens  20 ′. As in  FIGS. 11 to 13 , when the single liquid lens  20 ′ is prepared, and the position of the liquid lens  20 ′ and/or the distance between the two lens surfaces  21 ′ and  25 ′ of the liquid lens  20 ′ is adjusted, the focuses of the variable liquid lens systems  800 ,  900 , and  1000  may vary accordingly. Here, the structures of  FIGS. 11 to 13  may further include the aforementioned electrode  60  on the wall  11  of the lens barrel  10  so that the curvature of the liquid lens  20 ′ is changed according to the electrowetting principle. Also,  FIGS. 11 to 13  show cases where the wall  11  of the lens barrel  10  has a parallel structure. However, even in a structure including the one liquid lens  20 ′, the wall  11  of the lens barrel  10  may be formed into the aforementioned non-parallel structure to change the curvature of the liquid lens  20 ′, and/or the electrode  60  may be further prepared on the wall  11  of the lens barrel  10  to change the curvature of the liquid lens  20 ′ according to the electrowetting principle. 
         [0084]    Variable liquid lens systems according to the various exemplary embodiments have been described above with reference to  FIGS. 1 to 13 , but a variable liquid lens system according to an exemplary embodiment may be modified in various other ways. 
         [0085]    In the variable liquid lens systems according to one or more exemplary embodiments, the wall  11  inside the lens barrel  10  may be appropriately subjected to surface treatment so that a contact angle between the wall  11  inside the lens barrel  10  and a droplet may be determined and a liquid lens having the desired contact angle may be formed. When an electrode is further included, the contact angle between the droplet and the wall  11  may be changed according to the electrowetting principle by applying a voltage between the liquid lens consisting of the droplet and the electrode pattern. In addition, when the size of an internal cross-section of the lens barrel  10  is caused to vary in the length direction, the curvature of the liquid lens may be changed by moving the liquid lens. 
         [0086]    When there are two or more droplets, that is, two or more liquid lenses apart from each other, inside the lens barrel  10 , through channels which are open to the outside of the lens barrel  10 , that is, first holes, may be present between the liquid lenses and in front of and/or behind a liquid lens, and the positions and relative positions of the liquid lenses may be changed by the flow of gas, such as air, or liquid which has not been mixed with the liquid of the liquid lenses through the through channels. 
         [0087]    In this way, a liquid lens may be driven by air pressure or hydraulic pressure, and the air pressure or hydraulic pressure may be controlled by a motor pump connected through the outer wall of the lens barrel  10 . 
         [0088]    For a variable liquid lens system according to an exemplary embodiment, a flow path may be formed by the outer wall of the lens barrel  10 , the flow path space of the fluid, and the outer wall of a structure in which the lens barrel  10  is installed. Here, the outer wall of the lens barrel  10  may involve processing for the flow path through which pneumatic air (gas) and hydraulic liquid (e.g., water pressure) flow. 
         [0089]    As described above, according to the one or more exemplary embodiments, a liquid lens consisting of a droplet is formed in a lens barrel of a variable liquid lens system, and thus a plurality of liquid lens groups may be manufactured at the same time. Also, there is no need to use a material, such as a variable membrane, and thus the characteristic of light transmission may be improved. However, this is only an example, an a material, such as a variable membrane may be used. 
         [0090]    Furthermore, since the variable focus or zooming function may be performed by using as little fluid or liquid as possible, the size of a fluid or liquid storage may be reduced as much as possible. Therefore, a portion occupied by a driving device may be reduced as much as possible, and the variable liquid lens system may be manufactured to have a small size. In other words, since there is no need to place the fluid or liquid storage in a cross-sectional area of the variable liquid lens system, a channel with the smallest cross-section may be established in a vertical direction, and electrode wires may be excluded when no electrowetting method is applied. In addition, there is no need for a mechanical structure for adjusting the distance between liquid lenses. 
         [0091]    A variable liquid lens system according to an exemplary embodiment has at least one liquid lens consisting of a droplet in a lens barrel. Therefore, by adjusting the hydraulic pressures or air pressures of respective spaces, the position of the at least one liquid lens may be adjusted to change a focus, or by adding or subtracting liquid to or from the liquid lens, the distance between the two lens surfaces of the liquid lens may be adjusted to change the focus. When a plurality of liquid lenses are positioned apart from each other in the lens barrel, the variable liquid lens system according to one or more exemplary embodiments may perform the zooming function as well as the variable focus function through adjustment of the distance between the plurality of liquid lenses. In addition, the variable liquid lens system may be miniaturized by reducing an area occupied by a driving device as much as possible. 
         [0092]    It should be understood that the exemplary embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each exemplary embodiment should typically be considered as available for other similar features or aspects in other exemplary embodiments. 
         [0093]    While one or more exemplary embodiments have been described with reference to the figures, 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 as defined by the following claims.