Abstract:
A variable focus liquid lens is formed using two substrates with at least two through holes in at least one of the substrates. One end of each through hole is covered with a distensible membrane, one on the exterior surface of the substrate and the other on the interior surface. The substrates are sealed about the periphery to form a chamber and the chamber is filled with a liquid material. When pressure is applied to the membrane the liquid in the chamber is redistributed to form the lens. The variable focus liquid-filled lens is formed by providing a first and second substrate, forming at least two through holes in at least one of the first and second substrate, sealing one end of each of the at least two holes with a flexible transparent membrane, and sandwiching a liquid in a chamber formed between the first and second substrate.

Description:
This invention relates to optical focusing, in particular devices, methods, systems and apparatus for a liquid-based lens and associated zoom lens, wherein the focal length of the lens is variable. 
   BACKGROUND AND PRIOR ART 
   Adaptive-focus liquid lens has been used over the years for eyeglasses, cameras, projectors, cell phone as well as other machine vision applications. Based on the operating mechanisms and device structures, liquid lenses can be classified into three types. The first type is the liquid lens having a fixed volume of clear liquid which is sandwiched between a rigid lens (or a planar substrate) and a thin transparent elastic membrane, as described in U.S. Pat. Nos. 5,138,494, 5,999,328 and 6,040,947 issued to Kurtin et al. and U.S. Pat. No. 5,526,067 issued to Cronin et al. By moving the periphery of the elastic membrane, the liquid inside the lens assembly is redistributed such that the curvature of the film is changed. The changed curvature of the liquid lens surface bounded by the elastic membrane can vary the optical power, also known as diopter, of the lens. The shortcoming of this kind of liquid lenses is the difficulty keeping the periphery of the elastic membrane parallel to that of the rigid lens or planar substrate during the distance change. Moreover, the operating system for tuning the focus is complicated. 
   The second type of liquid lens requires to pump liquid in and out the lens chamber in order to change the curvature of the elastic membrane surface. Such an operating mechanism is described in U.S. Pat. Nos. 5,684,637 and 6,715,876 issued to Floyd. These lenses operate by injecting or pumping liquid into the body of the lens, a complicated control system is usually needed; thus such lenses are bulky, expensive and sensitive to vibration. 
   The third type of lens focuses light based on the electrowetting mechanism; an applied voltage can change the curvature of the liquid lens, see for example, U.S. Pat. No. 6,369,954 to Berge et al and U.S. Pat. No. 6,665,127 to Bao et al. By applying an external voltage to the liquid, the surface profile of the liquid is tuned because of the contact angle change. As a result, the focal length of the liquid lens is varied. Usually the applied voltage is high and the lens system is complicated and expensive. Another drawback of the electrowetting lens is that it is accompanied by liquid evaporation. 
   In the present invention, a tunable-focus liquid lens is demonstrated based on the pressure induced liquid redistribution. The liquid lens is composed of a flat cell and a liquid. The rigid flat cell has two through holes but these two holes are not overlapped. For example, one is on the top substrate and the other is on the bottom. The two holes are sealed with elastic membranes. One membrane is adhered on the outer surface of a substrate and the other is adhered on the inner surface of another substrate. For the convenience of discussion, hereinafter we call the former hole as the reservoir hole and the latter as the lens hole. The liquid is fully filled in the cell chamber and sealed using glue in order to prevent any leakage. Initially the two membranes are flat, so no focusing effect takes place. Squeezing the outside membrane inward by an actuator or other electro-mechanical means will redistribute the liquid rapidly, thus the inside membrane will swell outward. Because of this membrane shape change, focusing effect occurs. 
   To overcome these problems, what is needed is a lens with large aperture, large focusing power, polarization independence, wide spectral range (form visible to infrared), high resolution, and relatively fast response time for real-time imaging. The lens aperture size, in principle, has no constraint, depending on the applications. For instances, it can be made in micron sizes for microlens array, millimeter for call phone zoom lens, to several centimeters for eyeglasses. 
   SUMMARY OF THE INVENTION 
   A primary objective of the invention is to provide new methods, systems, apparatus and devices for a variable-focus liquid lens based on pressure induced liquid redistribution that can deform an elastic membrane with a spherical or other desired aspherical curvature during deformation. 
   A secondary objective of the invention is to provide new methods, systems, apparatus and devices for a variable-focus lens with large aperture, large focusing power, polarization independence, wide spectral range (form visible to infrared). 
   A third objective of the invention is to provide new methods, systems, apparatus and devices for a variable-focus lens that provides a unique and simple method for changing the curvature of the liquid-filled lens to vary its focal length. 
   A fourth objective of the invention is to provide new methods, systems, apparatus and devices for a variable-focus lens with high resolution, and relatively fast response time for real-time imaging. 
   A fifth objective of the invention is to provide new methods, systems, apparatus and devices for a variable-focus lens that exhibits attractive features including large focusing power, wide range of tunable focal length, large aperture, polarization independence, wide spectral range (limited by the transmittance of the employed components), high resolution, fast response time, and simple fabrication. 
   A sixth objective of the invention is to provide new methods, systems, apparatus and devices for a variable-focus lens for use in applications in real-time satellite imaging, surveillance, cellular phone zoom lens, etc. 
   According to the present invention, the variable focus liquid lens is composed of a flat cell chamber with a self-contained liquid. The cell chamber has at least two through holes. The holes are sealed with elastic membranes. One distensible membrane is adhered to the outer side of a substrate surface, referred to as the reservoir hole and the substrate is the top substrate. Another distensible membrane is used to seal the bottom hole, referred to as a lens hole from the inner side of the bottom substrate surface. The liquid is filled in the chamber and sealed with glue in order to prevent leakage. Depending on the amount of the liquid in the chamber, the initial curvature of the elastic membrane may be flat, convex, or concave. 
   In the variable-focus liquid lens, the distensible membrane of the reservoir hole can be squeezed inward and because the liquid is not constringent, the membrane of the lens hole is forced to swell outward and a lens character occurs. By squeezing the outer membrane with different pressure, the inner membrane is inflated with a different convex profile. Thus a variable focal length can be obtained and based on this operation mechanism, several different devices can be designed. 
   Another embodiment provides a method for producing a variable focus liquid-filled lens comprising the steps of providing a first and second substrate, forming at least two through holes in at least one of the first and second substrate, sealing one end of each of the at least two holes with a flexible transparent membrane, and sandwiching a liquid in a chamber formed between the first and second substrate. 
   The through holes include a first through hole in the first substrate, the first through holes sealed on the exterior surface of the first substrate and a second through hole is formed in the second substrates and is sealed on an interior surface of the second substrate. In an embodiment, the first substrate includes a concave or convex lens formed in one side of the first substrate and it is aligned with one of the through holes. The sandwiching steps is accomplished by sealing a periphery edge of the first and second substrate to form the chamber with an opening for the liquid, filling the chamber with the liquid, and sealing the opening to prevent the liquid from leaking. 
   These and other objects, feathers and advantages of this invention will be apparent from the following detailed description of the preferred embodiment that is illustrated schematically in the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1   a  is a perspective view of the two layers each with a hole formed there through. 
       FIG. 1   b  is a perspective view of the two layers with one end of each hole sealed with an elastic membrane. 
       FIG. 1   c  is a perspective view of two layers adhered together with an adhesive material. 
       FIG. 1   d  is a side view of a structure of the lens cell with a clear liquid sealed inside a chamber between the two layers. 
       FIG. 2  is a side view of a lens showing the focus state of the lens cell with an inward pressure applied to an outer membrane. 
       FIG. 3  is a side view of a structure of the lens cell with two holes in one layer according to an embodiment of the present invention. 
       FIG. 4  is a side view of a structure of the lens cell with an initial positive focus. 
       FIG. 5  is a side view of a structure of the lens cell with an initial negative focus. 
       FIG. 6  is a side view of a structure of the lens cell with two lens holes overlapped in the top to bottom and bottom layers. 
       FIG. 7   a  is a perspective view of a substrate with an array of through holes according to an embodiment of the present invention. 
       FIG. 7   b  is a side view of the structure of a liquid lens array with the substrate shown in  FIG. 7   a.    
       FIG. 8   a  shows the focal image of a lens cell with two holes in a non-focusing state. 
       FIG. 8   b  shows the focal image of a lens cell with two holes in a focusing state. 
       FIG. 9  is a graph showing the response time during focus change. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Before explaining the disclosed embodiments of the present invention in detail it is to be understood that the invention is not limited in its application to the details of the particular arrangement shown since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation. 
   The following is a list of reference numerals used in the figures and throughout the description to identify elements of the present invention. 
   
     
       
             
             
           
         
             
                 
             
           
           
             
               10 
               top layer 
             
             
               11 
               reservoir hole 
             
             
               12 
               bottom layer 
             
             
               13 
               lens hole 
             
             
               14 
               top hole membrane cover 
             
             
               15 
               bottom hole membrane cover 
             
             
               16 
               adhesive 
             
             
               17 
               gap hole 
             
             
               18 
               cell chamber 
             
             
               25 20 
               top layer 
             
             
               21 
               bottom layer 
             
             
               22 
               top membrane cover 
             
             
               23 
               bottom membrane cover 
             
             
               24 
               liquid 
             
             
               25 
               ball-headed lever 
             
             
               30 
               top layer 
             
             
               31 
               bottom layer 
             
             
               32 
               right hole 
             
             
               33 
               right membrane cover 
             
             
               34 
               left hole 
             
             
               35 
               left membrane cover 
             
             
               36 
               liquid 
             
             
               40 
               upper layer 
             
             
               41 
               lens hole 
             
             
               42 
               convex lens 
             
             
               50 
               upper layer 
             
             
               15 51 
               lens hole 
             
             
               52 
               concave lens 
             
             
               60 
               top layer 
             
             
               61 
               bottom layer 
             
             
               62 
               right reservoir hole 
             
             
               20 63 
               lens hole 
             
             
               64 
               left reservoir hole 
             
             
               70 
               bottom layer 
             
             
               71 
               lens hole array 
             
             
               72 
               top layer 
             
             
               25 73 
               bottom membrane cover 
             
             
               74 
               top membrane cover 
             
             
               75 
               liquid filled cell chamber 
             
             
                 
             
           
        
       
     
   
   The present invention provides devices, methods, systems and apparatus for a liquid lens with a variable focal length.  FIG. 1   a  shows a pair of layers, the top layer  10  has a reservoir hole  11  there though and the bottom layer  12  has a lens through hole  11 . The material of the top and bottom layers  10  and  12  for the lens cell should be rigid, such as polycarbonate, glass, transparent crystal plate, rigid polymer, plastic, metal or other material that is obvious to those skilled in the art. In a preferred embodiment, the top layer  10  is a clear material while the bottom layer  12  is rigid it is not necessarily clear. The reservoir and lens holes  11  and  13  in the top and bottom layers  10  and  12  can be made by drilling, rubbing, patterning or other process that is commonly known to those skilled in the art. While the top and bottom layers are show as circular layer it is for illustration only, alternative geometric structure of the layers can be designed with disk-shape, square, rectangular or other special shape, depending on the applications. 
   The reservoir hole  11  and lens hole  13  are sealed with an elastic membrane  13  and  14  as shown in  FIG. 1   b . In this example, the reservoir hole  11  is sealed on the outer surface of the top layer  10  with an elastic membrane  14  and the lens hole  13  in the bottom layer  12  is sealed with elastic membrane  15  on the outer top surface of the bottom layer  12 . In the embodiment shown, the elastic membranes  14  and  15  are attached to the surface of the top and bottom layers  10  and  12 . The elastic membrane is preferably a flexible, optically transparent, water impermeable material, such as Saran (polyvinylidene chloride resins or films) rubber, polydimethyl-silioxane (PDMS) membrane, or an elastic polymer. The elastic membrane may be adhered on the layers or may be wedged using a circular ring. 
   In the preferred embodiment, the variable-focus liquid lens is fabricated with a fluid filled in the cell chamber  18 . A cell chamber  18  is formed between the top layer  10  and the bottom layer  12  as shown in  FIG. 1   c  by leaving a thin gap between the top and bottom layers when adhering the periphery edges of the top and bottom layers  10  and  12  with an adhesive  16  material. In an embodiment, the size of the gap is controlled using polymer or glass strips when the periphery edge between the top and bottom layers  10  and  12  is sealed with the adhesive  16 . In a preferred embodiment, the adhesive used for sealing the various structures is preferably cyanoacrylate, commonly known as “super glue,” or alternatively an epoxy adhesive, or ultraviolet monomer can be substituted. 
   An opening  17  is left in the adhesive  16  for injecting liquid into the cell chamber  18  formed by the gap.  FIG. 1   d  is a side view of the variable-focus liquid lens structure of the cell with liquid filled in the cell chamber  18 . After the cell chamber  18  is filled with liquid, the opening  17  is sealed tightly with glue. The volume of liquid injected into the chamber  18  is controlled so that the top membrane  14  and bottom membrane  15  are flat. 
   The liquid encapsulated in the cell chamber  18  is preferably colorless, but can also be tinted, depending on the application of the variable-focus lens. For example, when the intended application is for sunglasses, the fluid is preferably tinted. Fluids having an appropriate index of refraction and viscosity suitable for use in the lens cell include but are not limited to liquids such as degassed water, mineral oil, glycerin and silicone products. 
   In this example, the cell chamber  18  has two holes but the holes are not overlapped as shown in  FIGS. 1   a  through  1   d . As described above, the lens hole  13  is sealed on the inner surface of the bottom layer using clear elastic membrane  15  and the reservoir hole  11  is sealed with elastic membrane  14  on the outer surface of the top layer. The periphery of the cell chamber  18 , the space between the top and the bottom layer, is sealed to form the cell chamber which is filled with liquid prior to completing the seal to prevent liquid leakage. 
   While materials useful in the fabrication of the liquid lens of the present invention have been described, alternative material may be substituted without deviating from the scope of the present invention since those skilled in the art could easily select alternative materials that perform the desired function. 
   When the elastic membrane  14  covering the reservoir hole  11  is pressed inward as shown in  FIG. 2 , liquid in the cell chamber  18  is redistributed, forcing the elastic membrane  15  covering the lens hole  13  to inflate outward. In the example shown in  FIG. 2 , the focusing effect of the cell chamber  24  as the membrane  22  on the top layer  20  is depressed inward using a ball-headed lever  25 . The pressure propagates through liquid  24  and because the liquid  24  is not constringent, the pressure forces the distensible lower layer membrane  23  on the bottom layer  21  to swell outward. The extended membrane  23  acts as a spherical or aspherical profile, causing the outgoing light to focus. 
     FIG. 3  shows another kind of cell where the top layer  30  is clear with no any hole and the bottom layer  31  has two holes at the same side. The hole  32  is sealed by an elastic membrane  33  from outside. The hole  34  is adhered with an elastic membrane  35  from inside. Pressing the elastic membrane  33  inward of the cell can result in liquid in the chamber  36  to be redistributed. Thus, the elastic membrane  35  inflates outward. 
   The tunable focus lens configuration shown in  FIG. 4  is similar to the configuration shown in  FIG. 1   d  except the upper layer  40  has a convex lens  42  formed directly above the lens hole in the bottom substrate so that the center of the convex lens  42  is located at the center of lens hole  41 . Similarly, the configuration shown in  FIG. 5  is similar to  FIG. 4  except the top layer  50  has a concave lens  52  centered directly above the center of lens hole  51 . 
     FIG. 6  shows yet another example of a variable-focus lens cell structure. In this example, the top layer  60  has two separated reservoir holes  62  and  64  and the bottom layer  61  has one lens hole  63 . The left reservoir hole  63  and bottom lens holes  64  overlap and are sealed with elastic membrane respectively on the inside surface of the top layer and inside surface of the bottom layer. Alternatively, the holes can be sealed on the outer surface of the top and bottom layers. The hole  63  and the hole  64  should have the same aperture. The other reservoir hole  62  in the top layer  60  is sealed with an elastic membrane on the outer surface of the top layer. 
     FIG. 7   a  shows the single layer  70  that has an array of holes  71 .  FIG. 7   b  shows the side view of a variable-focus cell structure with the layer  70  shown in  FIG. 7   a  as the bottom layer  70  forming a cell chamber  75  between the top layer  72  and bottom layer  70 . The array of lens holes  71  in the bottom layer are sealed with an elastic membrane  73  adhered to the inner surface of the bottom substrate adjacent to the liquid in the cell chamber  75 . The single reservoir hole in the top substrate is sealed using an elastic membrane  74  on the outer surface of the top layer  72 . As previously described, a liquid  75  is sealed in the cell chamber of the lens. 
     FIG. 8   a  shows an experimentally demonstrated image in the non-focusing state of the lens structure shown in  FIG. 1   d , the incoming light is an ambient white light.  FIG. 8   b  shows an experimentally demonstrated image in the focusing state of the lens structure shown in  FIG. 2 , as with the previous example, the incoming light is an ambient white light. In comparison with the image shown in  FIG. 8   a , the image in  FIG. 8   b  is enlarged significantly. The variable-focus lens according to the present invention is polarization independent and has a resolution of approximately 30 line pairs per millimeter. 
   An experimentally measured response time during focus change is shown in the graph of  FIG. 9 . Response time is an important parameter for active imaging devices because it determines the data acquisition rate. The response time of a variable-focus liquid lens according to the present invention was measured by probing the lens activation using a He—Ne laser beam. Initially the lens has no focus, so the received beam intensity is weak. When the PDMS membrane is deformed to form a convex shape, the beam is converged increasing the light received by the photo-detector. As a result, a transmission peak is obtained. The rise time of the transmission depends on the impulse of the pressure. When the pressure is removed, the lens returns to its original state. As shown in  FIG. 9 , the lens recovery time is approximately 30 ms in this example. The lens response time is affected by the following factors: viscosity of the filled liquid, lens aperture, PDMS thickness, and the cell gap of the cell chamber. Selecting the appropriate liquid having a high index and low viscosity and by reducing the cell gap, the response time of the liquid lens is improved to achieve video rate response time for real time active imaging applications. 
   According to the above device structure and the device performance, the present invention provides a unique and simple method for changing the curvature of the liquid-filled lens to vary its focal length. The size of the reservoir and lens holes can varied so that the aperture of the liquid lens can be made in the millimeter to centimeter range. A single lens or lens array can be fabricated easily. The invented self-contained liquid lens exhibit following attractive features: polarization independence, large focusing power and wide focus-tuning range, high resolution, broad spectral bandwidth, fast response time, and simple fabrication process which leads to low cost. 
   While the invention has been described, disclosed, illustrated and shown in various terms of certain embodiments or modifications which it has presumed in practice, the scope of the invention is not intended to be, nor should it be deemed to be, limited thereby and such other modifications or embodiments as may be suggested by the teachings herein are particularly reserved especially as they fall within the breadth and scope of the claims here appended.