Electrowetting liquid lens and manufacturing method thereof

Abstract

The invention discloses an electrowetting liquid lens and a manufacturing method thereof. The electrowetting liquid lens comprises a lens barrel, a lens body, two transparent cover plates and two electrodes. The lens barrel is provided with a light inlet end and an imaging end which are located at the two ends in the axial direction, the lens barrel is arranged in a gradually-expanding mode from the light inlet end to the imaging end, and the light inlet end and the imaging end are arranged in an open mode. The two transparent cover plates cover the light inlet end and the imaging end respectively; the lens body comprises insulating liquid and conductive liquid, the insulating liquid and the conductive liquid are arranged in an inner cavity of the lens barrel and are sequentially arranged in the direction from the light incident end to the imaging end, and an interface is formed between the insulating liquid and the conductive liquid; the two electrodes are arranged on the side wall of the lens cone and the transparent cover plate located at the imaging end respectively. According to the scheme, the electrowetting liquid lens can have large out-of-focus and focusing state changes in a small voltage adjusting interval, the driving voltage needed by the electrowetting liquid lens for converting the negative focal length into the positive focal length is reduced, the focal length adjusting range is expanded, and the electrowetting liquid lens has the excellent electric control focusing capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of electrowetting liquid lenses, and in particular to an electrowetting liquid lens and a manufacturing method thereof. Background Art

[0002] Since the 20th century, people have been increasingly demanding low-cost, fast-response, small-volume zoom systems that can be used to quickly acquire focal stack image sequences, and a series of new adaptive optical elements that do not rely on mechanical displacement structures have emerged. Among them, liquid lenses based on the dielectric wetting effect have developed particularly rapidly in recent years.

[0003] For example, patent CN113495355A discloses an electrowetting liquid lens based on a wetting surface composite dielectric layer and a manufacturing method, which includes a matrix with a cavity, a polar liquid and a non-polar liquid. The inner wall of the matrix is ​​covered with a wetting surface composite dielectric layer in direct contact with the polar liquid. The wetting surface composite dielectric layer includes a porous insulating layer and a super-lubricating liquid film layer formed on the surface of the porous insulating layer, so as to eliminate the contact line pinning effect on the liquid-liquid surface and accelerate the viscous energy dissipation of the lens.

[0004] However, the cavity of the matrix in this patent is a cylinder, and its interface has a small curvature in the undriven state with an external voltage of 0, resulting in a relatively large driving voltage required for the lens to jump from a negative focal length to a positive focal length. Summary of the invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies and to provide an electrowetting liquid lens to solve the technical problem in the prior art that the driving voltage required for the electrowetting liquid lens to change from a negative focal length to a positive focal length is relatively large.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions: In a first aspect, the present invention provides an electrowetting liquid lens, comprising: The lens barrel has a light incident end and an imaging end located at two ends in the axial direction, and is gradually expanded from the light incident end to the imaging end, and the light incident end and the imaging end are open; Two transparent cover plates, respectively covering the light incident end and the imaging end; A mirror body, comprising an insulating liquid and a conductive liquid, wherein the insulating liquid and the conductive liquid are placed in the inner cavity of the mirror barrel and are arranged in sequence along the direction from the light incident end to the imaging end, and an interface is formed between the two; and Two electrodes are respectively arranged on the side wall of the lens barrel and the transparent cover plate located at the imaging end, and are used to connect a power source, and when the two poles of the power source are connected, the interface can be driven to be concave toward the imaging end.

[0007] In some embodiments, the lens barrel is made of conductive metal, and its side wall constitutes a side wall electrode, the transparent cover plate located at the imaging end is conductive glass, and an indium tin oxide film layer is deposited on a side of the conductive glass close to the lens barrel; Wherein, the side wall electrode and the conductive glass constitute two electrodes.

[0008] In some embodiments, the electrowetting liquid lens further includes an insulating gasket disposed between the lens barrel and the indium tin oxide film layer.

[0009] In some embodiments, the electrowetting liquid lens further includes an insulating film layer, and the insulating film layer is disposed on the inner surface of the sidewall electrode.

[0010] In some embodiments, the electrowetting liquid lens further includes a hydrophobic film layer, and the hydrophobic film layer is disposed on a side of the insulating film layer away from the sidewall electrode.

[0011] In some embodiments, the lens barrel is made of copper, the insulating film layer is a parylene film layer deposited on the inner surface of the sidewall electrode, and the hydrophobic film layer is made of Teflon.

[0012] In some embodiments, a surfactant is added to the conductive liquid.

[0013] In some embodiments, the conductive liquid is an aqueous solution of sodium dodecyl sulfate; The insulating liquid is dimethyl silicone oil.

[0014] In a second aspect, the present invention further provides a method for manufacturing an electrowetting liquid lens, which is used for the electrowetting liquid lens as described above, and the method for manufacturing the electrowetting liquid lens comprises: Processing the conductive metal material into the lens barrel by a numerically controlled machine tool, and performing sandblasting and polishing on the inner wall of the lens barrel; The polished lens barrel is placed in acetone solution, anhydrous ethanol and deionized water in turn for ultrasonic cleaning; Forming the insulating film layer on the inner side wall of the lens barrel by chemical vapor deposition, and then immersing the lens barrel with the insulating film layer deposited in a hydrophobic material solution and then taking it out to dry; The conductive glass deposited with an indium tin oxide film layer is bonded to the imaging end by ultraviolet curing glue, and then the conductive liquid and the insulating liquid are sequentially injected into the inner cavity of the lens barrel from the light incident end, and finally the transparent cover plate located at the light incident end is bonded to the light incident end by ultraviolet curing glue.

[0015] In some embodiments, the steps of bonding the conductive glass deposited with an indium tin oxide film layer to the imaging end through a UV curing adhesive, injecting the conductive liquid and the insulating liquid into the inner cavity of the lens barrel from the light incident end in sequence, and finally bonding the transparent cover plate located at the light incident end to the light incident end through a UV curing adhesive include: Injecting the configured conductive liquid into the inner cavity of the lens barrel from the light incident end until the liquid level of the conductive liquid reaches half the inner cavity height of the lens barrel; Then, injecting the insulating liquid into the inner cavity of the lens barrel from the light incident end until the liquid level of the insulating liquid is slightly higher than the inner cavity of the lens barrel; The insulating liquid is scraped off from the inner cavity of the lens barrel, and the residual liquid at the connection of the light input end is cleaned, and then UV curing glue is applied to the connection of the light input end, and the transparent cover plate located at the light input end is covered.

[0016] Compared with the prior art, in the electrowetting liquid lens provided by the present invention, the lens barrel is arranged to be gradually expanded from the light incident end to the imaging end, that is, the side wall of the lens barrel is radially inclined outward from the light incident end to the imaging end. The side wall of the lens barrel with the above-mentioned inclination angle makes the interface between the insulating liquid and the conductive liquid still have a large curvature in the undriven state where the external voltage is zero, thereby reducing the driving voltage of the electrowetting liquid lens, so that the electrowetting liquid lens can have a large defocus and focus state change within a smaller voltage adjustment range, reducing the driving voltage required for the electrowetting liquid lens to change from a negative focal length to a positive focal length, expanding the focal length adjustment range, and making the electrowetting liquid lens have excellent electrically controlled focusing capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a cross-sectional view of an electrowetting liquid lens provided by an embodiment of the present invention; Figure 2 yes Figure 1 Schematic diagram of the CEC wetting liquid lens in beam divergence mode; Figure 3 yes Figure 2 Schematic diagram of the electrowetting liquid lens in a phase-delay state; Figure 4 yes Figure 2 Schematic diagram of the electro-wetting liquid lens when the light beam is converging; Figure 5 yes Figure 1 A magnified schematic diagram of center A.

[0018] Description of reference numerals: 1. Lens barrel; 11. Light incident end; 12. Imaging end; 13. Side wall electrode; 2. Transparent cover; 21. Conductive glass; 3. Insulating liquid; 4. Conductive liquid; 41. Interface; 5. Power supply; 6. Insulating gasket; 7. Insulating film layer; 8. Hydrophobic film layer. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0020] In order to solve the technical problem in the prior art that the driving voltage required for the electrowetting liquid lens to transition from a negative focal length to a positive focal length is relatively large, the present invention provides an electrowetting liquid lens and a method for manufacturing the same, which can reduce the driving voltage required for the electrowetting liquid lens to transition from a negative focal length to a positive focal length, thereby facilitating the expansion of the focal length adjustment range.

[0021] See also Figure 1 , Figure 1 1 is a schematic diagram of the structure of an electrowetting liquid lens in an embodiment of the present invention, wherein the electrowetting liquid lens comprises a lens barrel 1, a lens body, two transparent cover plates 2 and two electrodes; the lens barrel 1 has a light incident end 11 and an imaging end 12 located at two ends in the axial direction, and is gradually expanded from the light incident end 11 to the imaging end 12, and the light incident end 11 and the imaging end 12 are openly arranged; the two transparent cover plates 2 are respectively covered on the light incident end 11 and the imaging end 12; the lens body comprises an insulating liquid 3 and a conductive liquid 4, the insulating liquid 3 and the conductive liquid 4 are placed in the inner cavity of the lens barrel 1, and are sequentially arranged from the light incident end 11 to the imaging end 12, and a boundary surface 41 is formed between the two; the two electrodes are respectively arranged on the side wall of the lens barrel 1 and the transparent cover plate 2 located at the imaging end 12, and are used to connect a power source 5, and can drive the boundary surface 41 to be recessed toward the imaging end 12 when the two poles of the power source 5 are connected.

[0022] In the electrowetting liquid lens provided by the present invention, the lens barrel 1 is set to be gradually expanded from the light incident end 11 to the imaging end 12, that is, the side wall of the lens barrel 1 is radially inclined outward from the light incident end 11 to the imaging end 12. The side wall of the lens barrel 1 with the above-mentioned inclination angle makes the interface 41 between the insulating liquid 3 and the conductive liquid 4 still have a large curvature in the undriven state where the external voltage is zero, thereby reducing the driving voltage of the electrowetting liquid lens, so that the electrowetting liquid lens can have a large defocus and focus state change within a small voltage adjustment range, reducing the driving voltage required for the electrowetting liquid lens to change from a negative focal length to a positive focal length, expanding the focal length adjustment range, and making the electrowetting liquid lens have excellent electrically controlled focusing ability.

[0023] It should be noted that, as the driving voltage V of the external power supply 5 gradually increases, the contact angle between the interface 41 and the side wall of the lens barrel 1 is continuously reduced, and the interface 41 between the conductive liquid 4 and the insulating liquid 3 changes from protruding toward the light incident end 11 to a plane, and then changes to being concave toward the imaging end 12. Since the refractive indexes of the conductive liquid 4 and the insulating liquid 3 are different, and the refractive index of the insulating liquid 3 is greater than the refractive index of the conductive liquid 4, the liquid lens under different driving voltages can be equivalent to a double glued lens. When the driving voltage V is low, the liquid-liquid interface protrudes from the conductive liquid 4 side to the insulating liquid 3 side. At this time, the liquid lens is equivalent to a concave lens, which has a divergent effect on the light beam. As the driving voltage V increases, within a small voltage interval, the liquid-liquid interface is approximately flat. At this time, the lens is equivalent to two parallel glass plates with different refractive indices that fit closely together. The refractive power of the lens is 0, which has neither a converging effect nor a divergent effect on the light beam. At this time, the liquid lens is in a phase delay state, which has the effect of extending the optical path. As the driving voltage V continues to increase, the liquid-liquid interface sinks from the insulating liquid 3 side to the conductive liquid 4 side. At this time, the liquid lens is equivalent to a convex lens, which converges the light beam. Figures 2 to 4 In the figure, V1<V2<V3, which are the beam divergence mode, phase delay state and beam convergence mode respectively.

[0024] In summary, by adjusting the driving voltage, the liquid lens can be made to work in the beam divergence mode, phase delay state and beam convergence mode respectively. There is a one-to-one correspondence between the contact angle θ and the driving voltage V, which means that the liquid lens has a focal length electrical addressing characteristic. According to the driving voltage V of the liquid lens, the effective focal length of the liquid lens can be quickly calculated, and further the object space depth information such as the object distance and depth of field can be calculated.

[0025] In one embodiment, the lens barrel 1 is made of conductive metal, and its side wall constitutes a side wall electrode 13. The transparent cover plate 2 located at the imaging end 12 is a conductive glass 21, and an indium tin oxide film layer is deposited on the side of the conductive glass 21 close to the lens barrel 1; wherein the side wall electrode 13 and the conductive glass 21 constitute two electrodes.

[0026] In this embodiment, a CNC machine tool (CNC) is used to cut copper and other metals to prepare a sidewall metal electrode with a specific structure. Based on CNC machining, a sidewall electrode 13 with a more complex structure can be prepared, and the cost is lower and it is easy to mass produce. At the same time, an indium tin oxide film layer (ITO film layer) is deposited on the conductive glass 21, so that the conductive glass 21 has good visible light wave transmittance and excellent conductivity. The conductive glass 21 deposited with a 200-nanometer-thick ITO film layer has good performance, and its square resistance is as low as 10Ω / sq. In the visible light band, ITO has a good pass rate. And the ITO conductive electrode with glass as the substrate can be formed into a specific geometric shape structure by laser cutting.

[0027] In one embodiment, the electrowetting liquid lens further includes an insulating spacer 6 , which is placed between the lens barrel 1 and the indium tin oxide film layer.

[0028] In this embodiment, in order to avoid short circuit between the side wall electrode 13 and the bottom ITO film layer, an insulating gasket 6 made of insulating materials such as polycarbonate and silicone is used to effectively isolate the side wall electrode 13 and the ITO film layer.

[0029] In one embodiment, the electrowetting liquid lens further includes an insulating film layer 7 , which is disposed on the inner surface of the sidewall electrode 13 .

[0030] In this embodiment, in order to prevent the conductive liquid 4 from being electrolyzed, an insulating film layer 7 is further provided on the inner surface of the side wall electrode 13 . The insulating film layer 7 is generally made of a material with a relatively large dielectric constant, such as Parylene-C.

[0031] In one embodiment, see Figure 5 The electrowetting liquid lens further includes a hydrophobic film layer 8 , which is disposed on a side of the insulating film layer 7 away from the sidewall electrode 13 .

[0032] In this embodiment, the hydrophobic film layer 8 is generally made of a material with good water vapor insulation, such as Teflon, which can effectively protect the side wall electrode 13 from corrosion and improve the service life of the electrowetting liquid lens. In addition, the hydrophobic film layer 8 can make the conductive liquid 4 have a larger contact angle when not driven, effectively expand the range of contact angle variation, and thus make the liquid lens have a larger focal length variation range. The insulating film layer 7 and the hydrophobic film layer 8 also effectively isolate the direct contact between the side wall electrode 13 and the conductive liquid 4, avoiding the electrolysis of the conductive liquid 4 and extending the service life of the lens.

[0033] In one embodiment, a surfactant is added to the conductive liquid 4. Specifically, the conductive liquid 4 is a sodium dodecyl sulfate aqueous solution; and the insulating liquid 3 is dimethyl silicone oil.

[0034] In this embodiment, in order to ensure that the liquid-liquid interface in the liquid lens working in different spatial postures is still spherical or approximately spherical, the insulating liquid 3 and the conductive liquid 4 in the liquid lens should be selected from two liquids with similar density and immiscible with each other. At the same time, in order to make the liquid lens still have a strong light beam converging ability under the same driving voltage, the refractive index of the insulating liquid 3 and the conductive liquid 4 should be as different as possible.

[0035] For the insulating liquid 3 material, dimethyl silicone oil (Demethicone) is colorless, odorless, non-toxic, and has stable chemical properties at room temperature, and is not easy to react chemically with other substances. It can also remain stable at higher temperatures, and can exist stably for a long time at a temperature of 200 ° C in an environment isolated from air or inert gas. Dimethyl silicone oil can still remain in liquid form at low temperatures of -50 ° C. Dimethyl silicone oil is not easy to volatilize and decompose, so that the liquid lens using it as the insulating liquid 3 has a relatively stable service life. Dimethyl silicone oil has a relatively large relative dielectric constant, and its breakdown voltage strength is 13.7~17.7 kV / m, thereby reducing the risk of the insulating film layer 7 being broken down by the driving voltage during the operation of the liquid lens. Dimethyl silicone oil has good transmittance in the visible light band. Common dimethyl silicone oil has a dynamic viscosity of 50 cSt, 100 cSt, 350 cSt, 500 cSt, etc., while the dynamic viscosity of the conductive liquid 4 is mostly close to the dynamic viscosity of deionized water, that is, 1 cSt. According to the simulation results, when the dynamic viscosities of the insulating liquid 3 and the conductive liquid 4 are 50 cSt and 1 cSt respectively, the dynamic response curve of the center height of the liquid-liquid interface is closer to the critical damping state.

[0036] In summary, dimethyl silicone oil with a dynamic viscosity of 50 cSt can be used as the insulating liquid 3 material. According to the simulation results, adding a surfactant to the conductive liquid 4 can effectively reduce the liquid-liquid interfacial tension, thereby reducing the driving voltage of the liquid lens. Therefore, deionized water with 0.1% sodium dodecyl sulfate (SDS) is selected as the conductive liquid 4, and its density is approximately the density of deionized water, and is therefore closer to the density of dimethyl silicone oil.

[0037] It should be noted that, in one implementation, for the geometrical structural parameters of the lens barrel 1, the structural and material parameters of the liquid lens are designed based on the influence of the liquid dynamic viscosity, interfacial tension and lens geometrical dimensions on the steady-state and dynamic performances of the liquid lens obtained through simulation analysis.

[0038] When the side wall electrode 13 has a certain tilt angle, the driving voltage required for the liquid lens to change from a negative focal length to a positive focal length can be effectively reduced, and the focal length adjustment range can be effectively expanded. It can be seen from the simulation results that the smaller the radial size of the liquid lens, the shorter its dynamic response time. And because of the capillary phenomenon of the liquid, the narrower the lens cavity, the smaller the liquid-liquid interface distortion caused by the gravity of the lens. However, too small a through aperture will reduce the luminous flux of the lens and cause the image field to be unable to completely cover the CMOS image sensor. Taking into account the simulation results and the size of the existing CMOS image sensor in the laboratory, the geometric structure parameters of the liquid lens are designed as follows: the inner diameter of the upper aperture of the lens is 5mm, the inner diameter of the lower aperture of the lens is 10mm, the outer diameter of the lens is 12mm, the height of the lens is 5mm, the thickness of the insulating film layer 7 is 2μm, and the thickness of the hydrophobic film layer 8 is 0.5μm.

[0039] As for the driving electrode, in previous work, plasma enhanced chemical vapor deposition or magnetron sputtering is usually used to sputter and grow metal films such as copper or silver on the inner wall of a transparent glass tube to prepare the side wall electrode 13. The liquid lens prepared based on this processing method can directly observe the change of the liquid-liquid interface with the driving voltage through a transparent glass tube. However, the cost of preparing the side wall electrode 13 film by this method is high. And due to the limitation of the adhesion of the metal to the inner wall of the glass, the quality and thickness of the insulating layer are also difficult to control. Another commonly used preparation method is to adhere a flexible indium tin oxide (ITO) film to the inner wall of a conductive glass 21 tube, but as the working time of the liquid lens increases, the oily insulating liquid 3 may penetrate into the gap between the ITO film and the glass tube wall. And for conical side wall metal electrodes with a certain inclination angle, the processing difficulty and cost of the above two methods will increase further.

[0040] In summary, for the sidewall metal electrodes of the liquid lens, CNC (Computer numerical control) machine tools can be used to directly perform mechanical cutting on metals such as copper to obtain sidewall metal electrodes with specific structures. CNC machining can be used to produce sidewall electrodes with more complex structures13, with lower costs and easy mass production.

[0041] The conductive glass 21 in direct contact with the conductive liquid 4 should have good transmittance in the visible light band and excellent conductivity. The conductive glass 21 deposited with a 200nm thick ITO film layer has good conductivity, and its square resistance is as low as 10Ω / sq. In the visible light band, ITO has a good pass rate. And the ITO conductive electrode with glass as the substrate can be formed into a specific geometric shape structure by laser cutting. In summary, it is very suitable to use ITO conductive glass 21 as the bottom electrode material.

[0042] For the insulating film layer 7 and the hydrophobic film layer 8, the insulating film layer 7 material can be Parylene-C. Parylene-C is a high molecular polymer formed by the polymerization of monochloroparaphenylene dimethyl monomer. Parylene-C can be completely deposited on the surface of the copper electrode under normal temperature and vacuum conditions to form a transparent insulating coating with uniform thickness, smoothness and density. Due to its high relative dielectric constant, it can effectively prevent the conductive liquid 4 from being electrolyzed after being wrapped on the surface of the sidewall metal copper electrode. At the same time, due to the low permeability of Parylene-C, it effectively isolates water vapor and prevents the sidewall metal electrode from being corroded, thereby ensuring the service life of the liquid lens. When the insulating film layer 7 is too thick, it will lead to an increase in the driving voltage, but when the thickness of the insulating film layer 7 is too thin, it will cause the liquid lens to be easily broken down by the driving voltage. Therefore, Parylene-C with a thickness of 2μm is deposited on the surface of the sidewall metal electrode as the insulating film layer 7.

[0043] The hydrophobic film layer 8 can be made of Teflon AF 1601s optical resin. Teflon optical resin has excellent transparency and mechanical properties, which allows it to maintain corrosion resistance, electrical properties and hydrophobic properties over a wide temperature range. A transparent hydrophobic film layer 8 with a micron-level thickness can be formed on the surface of the metal electrode by dip coating.

[0044] For the insulating gasket 6, in order to prevent the ITO conductive glass 21 electrode and the side wall conical metal electrode from contacting each other, resulting in short circuit breakdown and electrolysis of the conductive liquid 4, in addition to depositing an insulating film layer 7 and a hydrophobic film layer 8 on the surface of the side wall metal electrode, an insulating material is also required to make an insulating gasket to isolate the side wall electrode 13 and the transparent electrode. Polycarbonate has high transparency, strong toughness and low cost, so a 0.5 mm thick polycarbonate (PC) film is selected as the insulating gasket material, and is made into an insulating gasket 6 of suitable shape and size by laser cutting.

[0045] In addition, the present invention also provides a method for manufacturing an electrowetting liquid lens, which is used for the electrowetting liquid lens as described above. A first embodiment of the method for manufacturing the electrowetting liquid lens includes: The conductive metal material is processed into a lens barrel 1 by a numerically controlled machine tool, and the inner wall of the lens barrel 1 is subjected to sandblasting and polishing. The polished lens barrel 1 is placed in acetone solution, anhydrous ethanol and deionized water in turn for ultrasonic cleaning; An insulating film layer 7 is formed on the inner wall of the lens barrel 1 by chemical vapor deposition, and then the lens barrel 1 with the insulating film layer 7 deposited thereon is immersed in a hydrophobic material solution and then taken out for drying; The conductive glass 21 deposited with an indium tin oxide film is bonded to the imaging end 12 by UV curing adhesive, and then the conductive liquid 4 and the insulating liquid 3 are injected into the inner cavity of the lens barrel 1 from the light incident end 11 in sequence, and finally the transparent cover plate 2 located at the light incident end 11 is bonded to the light incident end 11 by UV curing adhesive.

[0046] In this embodiment, the preparation of the liquid lens mainly includes the following steps: (1) Electrode machining: The inner diameter of the upper surface aperture of the side wall electrode 13 is 5 mm, the inner diameter of the lower surface aperture is 10 mm, the height is 5 mm, and the electrode wall thickness is 1 mm. The side wall metal electrode of the corresponding structure is obtained by CNC machining. In order to ensure that the liquid-liquid surface of the liquid lens is approximately spherical and to improve the subsequent deposition quality of the insulating film layer 7, the inner wall of the lens barrel 1 should be as smooth and flat as possible. The side wall metal electrode is sandblasted and polished. The surface finish of the inner wall of the side wall copper metal electrode is measured to be Ra3.2. The ITO conductive glass 21 is processed into a specific electrode shape by laser cutting.

[0047] (2) Cleaning of driving electrodes: After the tapered sidewall metal electrode is prepared by CNC machining, in order to ensure that a dense, uniform and smooth parylene-C insulating film layer 7 is subsequently grown on the surface of the sidewall electrode 13 by chemical vapor deposition, the sidewall electrode 13 needs to be effectively cleaned to remove surface dust and oil stains. First, use an ultrasonic cleaner to place the sidewall tapered metal electrode in an acetone solution for 3 minutes of ultrasonic rinsing to remove dust and oil stains on its surface. Then place it in anhydrous ethanol for 3 minutes of ultrasonic rinsing to remove residual acetone. Finally, place it in deionized water for 3 minutes of ultrasonic rinsing to remove residual ethanol. The cleaned sidewall metal electrode is then placed on a 100 °C constant temperature hot plate for drying. The above steps are also used to clean the ITO conductive glass 21 electrode with a specific bottom shape prepared by laser cutting.

[0048] (3) Deposition of insulating film layer 7: The formation of insulating film layer 7 by chemical vapor deposition is mainly divided into three steps: raw material sublimation, high temperature cracking and condensation polymerization. The vacuum coating used for chemical vapor deposition is mainly composed of a sublimation chamber, a cracking furnace, a deposition chamber, a vacuum pump, a cold trap and a CNC panel. Weigh 50 g of parylene-C powder and place it in the raw material box, and turn on the vacuum pump to reduce the pressure in the sublimation chamber to 5 Pa. In the sublimation chamber with a vacuum environment of 5 Pa, the parylene C powder will sublimate at about 112 ° C and turn into a gaseous state. Then turn on the cracking furnace power 5 and set the cracking temperature to 680 ° C. The gaseous parylene-C will undergo thermal cracking at about 680 ° C. The two methylene bonds in the monochloro-p-phenylene dimethyl dimer are broken and an intermediate monomer with free radicals is generated. It enters the deposition chamber at room temperature in a gaseous state. The free radical intermediates that are close to each other come into contact and polymerize in a cross-linking growth mode and form a dense and effective transparent wrapping on the surface of the sidewall metal electrode. At the above evaporation temperature and cracking temperature, the deposition rate of parylene-C is 3 μm / h, so setting the deposition time to 40 minutes can form an insulating film layer 7 with a thickness of about 2 μm on the surface of the sidewall metal electrode.

[0049] (4) Dip-coating the hydrophobic film layer 8: The sidewall conical metal electrode deposited with the insulating film layer 7 is completely immersed in a Teflon solution (Teflon AF1601s) and it is proposed that the thickness of the formed Teflon hydrophobic film layer 8 can be controlled by controlling the speed of pulling from the solution. Subsequently, the sidewall conical metal electrode is suspended on a hot plate and the hot plate temperature is set to 110 °C and dried for 5 minutes to form a Teflon hydrophobic film layer 8 with a submicron thickness on the surface of the conical electrode. The Teflon hydrophobic film layer 8 can effectively increase the initial contact angle of the conductive liquid 4 on its surface and expand the focal length variation range of the liquid lens. In addition, the hydrophobic property of Teflon effectively prevents the conductive liquid 4 from penetrating into the gap between the copper electrode and the ITO metal electrode to cause a short circuit, avoids the electrolysis of the conductive liquid, and improves the service life and stability of the liquid lens.

[0050] (5) Liquid injection: Use UV curing glue to bond the side wall metal electrode, PC insulating gasket 6 and bottom ITO conductive glass 21 electrode covered with insulating film layer 7 and hydrophobic film layer 8 in sequence and cure them through UV light to form a semi-enclosed cavity. Sodium dodecyl sulfate is dissolved in deionized water to form an electrolyte solution as the conductive liquid 4, and its density is approximately the density of deionized water, which is slightly greater than the density of the selected insulating liquid 3 dimethyl silicone oil. The configured conductive liquid 4 is injected into the semi-enclosed cavity of the lens barrel 1. Then dimethyl silicone oil is injected into the semi-enclosed cavity of the lens barrel 1 and covers the transparent cover plate 2 located at the light input end 11.

[0051] (6) UV curing packaging: Use UV curing glue to apply to the bonding point of the liquid lens filled with two liquids and use UV light to cure it to form a completely enclosed structure. Use 3D printing to prepare a black nylon metal shell to seal and protect the entire liquid lens. The packaging is completed to obtain the liquid lens.

[0052] In a second embodiment of the method for manufacturing an electrowetting liquid lens, the steps of bonding the conductive glass 21 deposited with an indium tin oxide film layer to the imaging end 12 by means of a UV curing adhesive, then sequentially injecting the conductive liquid 4 and the insulating liquid 3 into the inner cavity of the lens barrel 1 from the light incident end 11, and finally bonding the transparent cover plate 2 located at the light incident end 11 to the light incident end 11 by means of a UV curing adhesive include: The prepared conductive liquid 4 is injected into the inner cavity of the lens barrel 1 from the light input end 11 until the liquid level of the conductive liquid 4 reaches half the inner cavity height of the lens barrel 1; Then, the insulating liquid 3 is injected into the inner cavity of the lens barrel 1 from the light input end 11 until the liquid level of the insulating liquid 3 is slightly higher than the inner cavity of the lens barrel 1; Scrape off the insulating liquid 3 that is higher than the inner cavity of the lens barrel 1, clean the residual liquid at the connection of the light input end 11, apply UV curing glue at the connection of the light input end 11, and cover the transparent cover plate 2 located at the light input end 11.

[0053] In this embodiment, sodium dodecyl sulfate is dissolved in deionized water to form an electrolyte solution as the conductive liquid 4, and its density is approximately the density of deionized water, and the density is slightly greater than the density of the selected insulating liquid 3 dimethyl silicone oil. The configured conductive liquid 4 is injected into the semi-enclosed cavity of the lens barrel 1 and the liquid level reaches half of the cavity height, that is, 2.5 mm. Then, dimethyl silicone oil is injected into the semi-enclosed cavity of the lens barrel 1 and the liquid level is slightly higher than the entire cavity to ensure that there are no bubbles in the entire cavity after sealing. Then scrape off the part above the cavity and use an alcohol cotton swab to carefully wipe off the residual liquid at the connection and apply a thin layer of ultraviolet curing glue, and cover the transparent cover plate 2 located at the light input end 11.

[0054] In order to better understand the present invention, the following Figures 1 to 5 The technical solution of the present invention is described in detail: (1) When the side wall electrode 13 has a certain tilt angle, the driving voltage required for the liquid lens to change from a negative focal length to a positive focal length can be effectively reduced, and the focal length adjustment range can be effectively expanded.

[0055] (2) Through the effective selection of the conductive liquid 4 and the insulating liquid 3 of the liquid lens, the lens has good stability and impact resistance. The two-dimensional and three-dimensional point spread functions (PSF) measured by the beam quality analyzer well illustrate that under different spatial positions, the liquid-liquid interface is approximately spherical, with good stability and imaging quality. The simplification of the structure reduces the difficulty of the manufacturing process, increases the light transmission rate, and increases the utilization rate of the beam energy.

[0056] (3) By rationally selecting the influence of the preparation materials and structural parameters of the liquid lens on its dynamic response time, the liquid lens has good dynamic performance. The prepared liquid lens can achieve a "jump-type" focal length adjustment from 0 to 80V about 12 times per second. At present, the focal stack depth estimation algorithm based on deep learning generally requires 2-10 frames of focal stack images to obtain a high estimation accuracy. Therefore, the prepared liquid lens is sufficient to achieve the acquisition of focal stack image sequences within one second. It further adapts to the real-time and rapid requirements of the current focal stack technology for image sequence acquisition tasks.

[0057] (4) The liquid lens can be defocused and focused within a relatively small voltage adjustment range. Therefore, the prepared liquid lens has excellent electronically controlled focusing capability.

[0058] (5) The prepared liquid lens can capture a focal stack image sequence with a large depth of field range within a large operating voltage range, which helps to expand the depth of field of the imaging system. In addition, the prepared liquid lens is still sensitive to small changes in driving voltage, so it can achieve dense sampling of spatial scenes, which helps to synthesize fully focused images with richer texture details.

[0059] In addition, the testing process of the electrowetting liquid lens according to the embodiment of the present invention is described in detail below.

[0060] In order to ensure that the designed and prepared liquid lens can meet the real-time and fast acquisition tasks of focal stacking, it is necessary to build different experimental platforms and design corresponding experimental methods to test and evaluate its optical properties such as electronically controlled focusing performance, two-dimensional and three-dimensional point spread functions, electronically controlled focusing range and dynamic response time.

[0061] The electric focusing performance of the liquid lens determines whether the focal stack image acquisition sensor with it as the core zoom element can achieve focal length focusing without mechanical parts. The two-dimensional and three-dimensional point spread functions of the liquid lens can be used to characterize the light field adjustment characteristics of the liquid lens. In addition, the two-dimensional point spread function of the liquid lens under different spatial postures reflects to a certain extent whether the liquid-liquid interface surface is spherical or approximately spherical. If the two-dimensional point spread function is approximately axisymmetric, it means that the liquid-liquid interface of the lens is less affected by gravity. Otherwise, it means that gravity causes the liquid-liquid interface to be distorted. As an important parameter indicator reflecting the zoom speed of the liquid lens, the dynamic response time directly determines the image sequence acquisition frame rate of the optical imaging system with the liquid lens as the core zoom element.

[0062] 1. Liquid lens electronically controlled focusing performance test: The experimental platform for testing and evaluating the electronically controlled focusing performance of the liquid lens is mainly composed of a laser light source, an optical beam expander, a liquid lens, a beam quality analyzer, a DC regulated power supply 5 and a computer for running various driver software. The liquid lens is driven by a bias voltage signal, and the DC regulated voltage source used can output a DC regulated signal of 0 to 200 V. The laser light source used in the experiment is a red laser light source in the 635 to 671 nm band. After being emitted by the laser light source, the red laser beam is expanded by an optical beam expander (HB-20XAR) to form a parallel beam with uniform energy distribution in the space in front of the liquid lens. After the parallel beam is refracted by the liquid lens, the energy distribution of the light field in the space behind the lens will change, and will show different spatial distribution characteristics according to the driving voltage. Finally, a beam quality analyzer (4M-11-045) is placed at a certain distance behind the liquid lens. The beam quality analyzer captures the light beam modulated by the liquid lens and outputs two-dimensional and three-dimensional point spread functions reflecting the spatial light intensity distribution. Point Spread Function (PSF) describes the response of an imaging system to light emitted by a light source (object), reflects the diffusion and blur of the light beam, and can be used to describe the spatial light intensity distribution. Therefore, the light control characteristics of the liquid lens under different voltages can be analyzed based on the two-dimensional and three-dimensional PSF images captured by the beam quality analyzer.

[0063] Through experiments, it can be obtained that the designed liquid lens has multiple light control modes, and can quickly switch between multiple light control modes by adjusting the driving voltage. When the driving voltage is low, the liquid lens works in the beam divergence mode with a negative focal length; when the driving voltage is high, the liquid lens works in the beam convergence mode with a positive focal length; and there is a small driving voltage interval that makes the liquid-liquid interface approximately flat, and the refractive power is approximately 0, at this time the lens works in a phase delay state. When the driving voltage is 62 V and 68 V, the spatial light energy distribution in the circular area in the two-dimensional PSF is symmetrical on the left and right. Affected by gravity, the spatial light energy distribution is slightly asymmetric up and down, but the two-dimensional PSF is still basically a perfect circle. This shows that the liquid-liquid interface in the vertically placed liquid lens is approximately spherical. In addition, the experimentally measured full width at half maxima (FWHM) further shows that the liquid lens can be defocused and focus state changes can be made within a small voltage adjustment interval. Therefore, the prepared liquid lens has excellent electronically controlled focusing ability.

[0064] (II) Liquid lens focal length change test: The focal length variation range determines the object distance range within which the prepared liquid lens can collect point stack image sequences. The focal length of the lens is still measured based on the above-mentioned experimental platform. However, unlike the above-mentioned method of fixing the beam quality analyzer behind the lens, when the driving voltage of the liquid lens is changed, in order to measure the effective focal length of the liquid lens, it is necessary to finely adjust the distance between the liquid lens and the beam quality analyzer through the sliding guide of the optical experimental platform. When the beam quality analyzer captures the sharpest three-dimensional PSF, the distance between the liquid lens and the beam quality analyzer photosensitive chip is the effective focal length of the liquid lens under this driving voltage.

[0065] The driving voltage of the liquid lens was gradually adjusted from 0 V to 110 V, and a series of two-dimensional and three-dimensional PSFs were collected. When the driving voltage was greater than 57 V, the liquid lens had a positive focal length. At this time, the distance between the liquid lens and the beam quality analyzer was adjusted to make the captured two-dimensional and three-dimensional PSF peaks sharpest (the FWHM of the two-dimensional PSF was less than 150 μm). At this time, this distance was approximately the effective focal length (EFL) of the lens. Through multiple experimental measurements, when the driving voltage reached between 115 and 130 V, the liquid lens began to electrolyze to varying degrees, and small bubbles began to appear at the contact between the lens cavity side wall electrode 13 and the polycarbonate gasket, that is, the insulating film layer 7 and the hydrophobic film layer 8 were broken down by the driving voltage, and the conductive liquid 4 was electrolyzed. The breakdown and electrolysis of the liquid lens at around 115 V may be due to the small thickness of the insulating film layer 7 generated by chemical vapor deposition, which is only 2 μm. In multiple measurements, bubbles and electrolysis first appeared at the gluing point of the insulating gasket 6. This is because when the UV curing glue is used for packaging, the glue undergoes a cross-linking chemical reaction after being irradiated by ultraviolet light and turns into a solid state, which causes a certain degree of damage to the insulating film layer 7, making the thickness of the insulating film layer 7 slightly thinner. When the driving voltage is greater than 100 V, the simulated and measured values ​​of the effective focal length both decrease slowly, which may be due to the contact angle saturation phenomenon. Therefore, the operating voltage range of the prepared liquid lens is 0 to 110 V.

[0066] When the driving voltage is low, the liquid lens is in the beam divergence mode and has a negative focal length. The focal length cannot be measured by the beam quality analyzer, but can be tested by the imaging magnification method. In the negative focal length section, there is a certain deviation between the simulated focal length of the liquid lens and the measured data, but the curve change trend is basically the same. This error may be due to the error between the measured value and the actual value of the spacing between the components when the imaging magnification method is used for measurement. In the undriven state, the measured focal length of the liquid lens is -128.6 mm. In summary, the prepared liquid lens can achieve continuous focal length adjustment of (-∞, -128.6 mm) ∪ (48.6 mm, +∞) within the operating voltage range of 0 to 110 V, and has a large focal length variation range.

[0067] (III) Liquid lens dynamic response performance test: In previous research work, high-speed cameras were mostly used to capture the changes in the liquid-liquid interface during the entire zoom process. By analyzing the changes in the contact angle and the height of the liquid-liquid interface frame by frame, the transient response process of the liquid lens under the action of a DC step electrical signal can be studied intuitively. However, the measurement accuracy of this method is limited by the image acquisition frame rate of the high-speed camera, and high-speed cameras with high frame rates are generally expensive. And because the changes in the liquid-liquid interface need to be studied frame by frame, digital image processing operations such as gradient calculation and edge extraction are often required for more than a thousand frames of images, which has a high computational cost.

[0068] After being refracted by the liquid lens, the parallel light beam converges at the focal point of the lens. At this time, the light intensity at the focal point is the strongest in the space below the lens. After the focal length of the liquid lens is changed by adjusting the driving voltage, the focal length changes, and the energy distribution of the light field below the lens also changes. Based on the above principle, a liquid lens dynamic performance experimental test platform is built. The experimental platform mainly consists of a laser light source, an optical beam expander, a liquid lens, an optical power meter, an oscilloscope, an ultrafast signal generator, and a computer for running various driver software. The light source used in the experimental platform is a red laser light source in the 635-671 nm band. After being emitted by the laser light source, the red laser beam is expanded by an optical beam expander (HB-20XAR) to form a parallel beam with uniform light field energy distribution in the space in front of the lens. After beam expansion, the beam converges at the focal point after passing through the dielectric wetting liquid lens. The optical power meter (PM-400) and the photoelectric probe (OPHIR, 7Z02637-0.19-20μm) are placed at the focal point, and a light is placed in front of the optical power meter probe for light limiting. To avoid interference from stray light, the entire experiment was carried out in a dark environment.

[0069] The experimental results show that the prepared dielectric wetting liquid lens has a dynamic response time of about 83 ms under the action of an 80 V DC step telecommunication signal, which is close to the dynamic response time of 30-60 ms of the A-39N0 series 3.9 mm aperture liquid lens of Corning Varioptic, and has a larger aperture and a wider operating voltage range. The prepared liquid lens can achieve a "jump-type" focal length adjustment from 0 to 80 V about 12 times per second. At present, the focal stack depth estimation algorithm based on deep learning generally requires 2-10 frames of focal stack images to obtain a higher estimation accuracy. For example, the differential focus volume (DFV) network architecture in the prior art requires 2-5 frames of input images to achieve a relatively accurate depth estimation. Therefore, the liquid lens prepared in this chapter is sufficient to achieve the acquisition of a focal stack image sequence within one second.

[0070] And because the driving voltage is continuously, sequentially, and incrementally increased in small amplitudes when acquiring the focal stack image sequence, rather than a "jump-type" adjustment voltage of 0-80 V. When the driving voltage adjustment amplitude decreases, the dynamic response time of the lens will also decrease. When the driving voltage is 57 V, the photovoltage output by the optical power meter is about 0.0291 V, and the time required for the photovoltage curve to reach 0.0291 V on the rising edge is about 32 ms. Therefore, it can be reasonably inferred that the prepared liquid lens has a dynamic response time of about 83 ms for the small amplitude driving voltage change of 0-3 V. That is, the liquid lens can achieve dense sampling of about 30 frames per second for the object space scene. In summary, the multi-mode electrically controlled conversion and fast focusing electrowetting liquid lens of the present invention has multiple light control modes, and can quickly switch between beam divergence mode, beam convergence mode and phase delay state according to the driving voltage. The liquid lens can realize continuous adjustment of the focal length within the range of (-∞, -128.6 mm) ∪ (48.6 mm, +∞) within the working voltage range of 0 to 110 V. The two-dimensional and three-dimensional PSFs measured by the beam quality analyzer well illustrate that the liquid-liquid interface is approximately spherical under different spatial positions, and has good stability and imaging quality. The prepared liquid lens has a millisecond zoom speed and can collect about 30 frames of focus stack images per second, which is basically matched with the imaging frame rate of commercial CMOS image sensors at this stage. The liquid lens is still sensitive to small changes in driving voltage and has good imaging quality. It can perform jump interval sampling and dense sampling of the object space scene, and is very suitable for collecting focus stack image sequences with obvious focusing and defocusing characteristics.

[0071] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. An electrowetting liquid lens, characterized in that: include: The lens barrel has a light incident end and an imaging end located at two ends in the axial direction, and is gradually expanded from the light incident end to the imaging end, and the light incident end and the imaging end are open; Two transparent cover plates, respectively covering the light incident end and the imaging end; The lens body comprises an insulating liquid and a conductive liquid, wherein the insulating liquid and the conductive liquid are placed in the inner cavity of the lens barrel and are arranged in sequence along the direction from the light incident end to the imaging end, and an interface is formed between the two; and Two electrodes are respectively arranged on the side wall of the lens barrel and the transparent cover plate located at the imaging end, and are used to connect a power source, and when the two poles of the power source are connected, the interface can be driven to be concave toward the imaging end.

2. The electrowetting liquid lens according to claim 1, characterized in that: The lens barrel is made of conductive metal, and its side wall constitutes a side wall electrode. The transparent cover plate located at the imaging end is conductive glass, and an indium tin oxide film layer is deposited on a side of the conductive glass close to the lens barrel. Wherein, the side wall electrode and the conductive glass constitute two electrodes.

3. The electrowetting liquid lens according to claim 2, characterized in that: The electrowetting liquid lens further includes an insulating gasket, which is placed between the lens barrel and the indium tin oxide film layer.

4. The electrowetting liquid lens according to claim 2 or 3, characterized in that: The electrowetting liquid lens further comprises an insulating film layer, and the insulating film layer is arranged on the inner surface of the sidewall electrode.

5. The electrowetting liquid lens according to claim 4, characterized in that: The electrowetting liquid lens further comprises a hydrophobic film layer, and the hydrophobic film layer is arranged on a side of the insulating film layer away from the sidewall electrode.

6. The electrowetting liquid lens according to claim 5, characterized in that: The lens barrel is made of copper, the insulating film layer is a parylene film layer deposited on the inner surface of the side wall electrode, and the hydrophobic film layer is made of Teflon.

7. The electrowetting liquid lens according to claim 1, characterized in that: A surfactant is added into the conductive liquid.

8. The electrowetting liquid lens according to claim 7, characterized in that: The conductive liquid is an aqueous solution of sodium dodecyl sulfate; The insulating liquid is dimethyl silicone oil.

9. A method for manufacturing an electrowetting liquid lens, used for the electrowetting liquid lens as claimed in claim 5 or 6, characterized in that: The method for manufacturing the electrowetting liquid lens comprises: Processing the conductive metal material into the lens barrel by a numerically controlled machine tool, and performing sandblasting and polishing on the inner wall of the lens barrel; The polished lens barrel is placed in acetone solution, anhydrous ethanol and deionized water in turn for ultrasonic cleaning; Forming the insulating film layer on the inner side wall of the lens barrel by chemical vapor deposition, and then immersing the lens barrel with the insulating film layer deposited in a hydrophobic material solution and then taking it out to dry; The conductive glass deposited with an indium tin oxide film layer is bonded to the imaging end by ultraviolet curing glue, and then the conductive liquid and the insulating liquid are sequentially injected into the inner cavity of the lens barrel from the light incident end, and finally the transparent cover plate located at the light incident end is bonded to the light incident end by ultraviolet curing glue.

10. The method for manufacturing an electrowetting liquid lens according to claim 9, characterized in that: The steps of bonding the conductive glass with the indium tin oxide film layer deposited thereon to the imaging end by means of ultraviolet curing adhesive, injecting the conductive liquid and the insulating liquid into the inner cavity of the lens barrel from the light incident end in sequence, and finally bonding the transparent cover plate located at the light incident end to the light incident end by means of ultraviolet curing adhesive include: Injecting the configured conductive liquid into the inner cavity of the lens barrel from the light incident end until the liquid level of the conductive liquid reaches half the inner cavity height of the lens barrel; Then, injecting the insulating liquid into the inner cavity of the lens barrel from the light incident end until the liquid level of the insulating liquid is slightly higher than the inner cavity of the lens barrel; The insulating liquid is scraped off from the inner cavity of the lens barrel, and the residual liquid at the connection of the light input end is cleaned, and then UV curing glue is applied to the connection of the light input end, and the transparent cover plate located at the light input end is covered.

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