Variable-focus liquid lens

[0001] 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.

[0002] 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.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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).

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0032] 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.

[0033] The following is a list of reference numerals used in the figures and throughout the description to identify elements of the present invention.

[0034]

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

[0035] The present invention provides devices, methods, systems and apparatus for a liquid lens with a variable focal length. FIG. 1a 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.

[0036] The reservoir hole 11 and lens hole 13 are sealed with an elastic membrane 13 and 14 as shown in FIG. 1b. 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.

[0037] 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. 1c 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.

[0038] An opening 17 is left in the adhesive 16 for injecting liquid into the cell chamber 18 formed by the gap. FIG. 1d 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.

[0039] 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.

[0040] In this example, the cell chamber 18 has two holes but the holes are not overlapped as shown in FIGS. 1a through 1d. 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] The tunable focus lens configuration shown in FIG. 4 is similar to the configuration shown in FIG. 1d 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.

[0045] 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.

[0046] FIG. 7a shows the single layer 70 that has an array of holes 71. FIG. 7b shows the side view of a variable-focus cell structure with the layer 70 shown in FIG. 7a 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.

[0047] FIG. 8a shows an experimentally demonstrated image in the non-focusing state of the lens structure shown in FIG. 1d, the incoming light is an ambient white light. FIG. 8b 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. 8a, the image in FIG. 8b 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.

[0048] 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.

[0049] 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.

[0050] 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.