Multi-compartment fluid-lens with two or more membranes

Abstract

The invention relates to a fluid lens (1) with an optical axis (100) comprising at least the following components: - a container (2) with a transparent bottom portion (3), wherein the container (2) comprises a lens volume (VL) comprising: a first compartment (V1) comprising a first fluid, a second compartment (V2) comprising a second fluid, a third compartment (V3) comprising a third fluid, wherein the first, the second and the third compartment (V1, V2, V3) are arranged adjacent to each other on the optical axis (100), - a first, a second, and a third elastically deformable film component (10, 20, 30), - wherein the first and the second compartment (V1, V2) are separated from each other by the second film component (20), - wherein the second and the third compartment (V2, V3) are separated from each other by the third film component (30).

Description

[0001] Multi-Compartment Fluid-Lens with Two or More Membranes

[0002] Specification

[0003] The invention relates to a fluid lens with three compartments each comprising a fluid. The lens according to the inventio allows to compensate for acceleration-dependent aberration, such as gravity-induced aberrations, such as a gravity induced coma, while offering a wide range of fluids and separating deformable films to be used as conventional two-compartment fluid lenses.

[0004] In the art, coma-compensating liquid lenses are known that compensate gravity induced coma. These lenses take advantage of two compartments arranged on the optical axis of the lens, that are filled with liquids exhibiting a differing refractive index and a differing mass density. Depending on the differences in refractive indices and densities of the two liquids, a membrane thickness needs to be selected accordingly to arrive at the desired coma compensating effect. The liquids in turn may have to be selected from a limited range of liquids dictated by technical requirements and potential health concerns in case the lens is to be used close to a person, e.g. in goggles, mobile phones or VR / AR goggle-devices.

[0005] The membrane thickness in turn translates in a membrane stiffness. High stiffness membranes however, are comparably inert, and might require high actuation forces and thus increase energy consumption and speed of the liquid lens.

[0006] It is an object of the current invention to overcome these limitations, so that a wider variety of liquids may be used.

[0007] The object is achieved by the device having the features of claim 1.

[0008] Advantageous embodiments are described in the dependent claims.

[0009] According to claim 1 a fluid lens with an optical axis comprises at least the following components: a container with a transparent bottom portion, wherein the container comprises a lens volume comprising: o a first compartment comprising, particularly filled with a first transparent fluid; o a second compartment comprising, particularly filled with a second transparent fluid, o a third compartment comprising, particularly filled with a third transparent fluid, particularly wherein at least one of the three fluids, particularly the second fluid, differs from the other two fluids, wherein the first, the second and the third compartment are arranged adjacent to each other on the optical axis, a first, a second, and a third elastically deformable transparent film component,

[0010] - wherein the first and the second compartment are separated from each other by the second film component,

[0011] - wherein the second and the third compartment are separated from each other by the third deformable film component.

[0012] The lens according to the invention allows for acceleration-dependent aberrations compensation. Acceleration-dependent aberrations may be gravity-induced aberrations, such gravity-induced coma. Advantageously, this lens allows using a wide variety of fluids which in turn allows a more favorable selection of the elastically deformable film components, in particular a stiffness may be selected from a range of stiffnesses that is neither too thin nor too thick. This allows on the one hand facile manufacturing, durability, non-permeability and robustness of the film components, which becomes increasingly difficult the thinner the film components have to be and on the other hand actuation energies for deforming any of these film components may be selected such that actuators with lower actuation power can be used - the thicker a film component has to be, the higher the actuation forces. Further, actuation speed and reaction time of the lens can be kept comparably high if the films are to too thick. The film component are massive elements of the lens and are not a liquid interface only. The film components may otherwise be referred to as membranes.

[0013] The container may comprise a container wall. The container wall may radially enclose the lens volume. The bottom portion and the container wall, or at least a part of each, may be fixed relative to one another, e.g., attached or attachable to one another.

[0014] According to another embodiment of the invention, the first fluid is a liquid.

[0015] According to another embodiment of the invention, the second fluid is a liquid.

[0016] According to another embodiment of the invention, the third fluid is a liquid.

[0017] The lens may comprise three liquids instead of the three fluids. It may be that only the first and third fluids are liquids.

[0018] In particular, the third compartment is located closest to the bottom portion of the lens, wherein the second compartment is arranged between the third and the first compartment.

[0019] In particular, the first compartment is adjacent to the second compartment which is adjacent to the third compartment along the optical axis.

[0020] The first, the second and the third fluid differ in at least a property of the refractive index and / or the density from each other.

[0021] Particularly, the first, the second and the third fluid are fluids that all differ from each other with regard to the refractive index and or the density.

[0022] According to another embodiment of the invention, only two fluids of the first, the seconds and the third fluid differ from each other in terms of the refractive index and / or the density.

[0023] According to another embodiment of the invention, the first film component separates the first compartment from a gas-filled space.

[0024] This embodiment allows that the first film may form an outermost elastic surface of the lens. The first film component may form an adjustable lens surface of the lens. The gas-filled space may be surrounding air, or a space covered by a protective in particular rigid cover element, such as a cover glass, a spectral filter element or another element that would protect the film component from external damaging or contamination. The space may be filled with a protective gas, such as Nitrogen, Argon or Helium.

[0025] According to another embodiment of the invention, the first film component forms a lens surface, in particular an outermost lens surface, that conveys a refractive in particular focusing power to the lens (as opposed to planar optical element that may not possess refractive power).

[0026] The lens may comprise an annular lens shaper. The annular lens shaper may be arranged on a side of one of the film components. The annular lens shaper may be arranged on a side of one of the film components that faces away from the bottom portion. The annular lens shaper may be arranged on the first, second or third film components. The annular lens shaper may be movable and / or tiltable. The annular lens shaper may be movable and / or tiltable relative to the container wall. The annular lens shaper may be movable and / or tiltable relative to the bottom portion.

[0027] The lens may comprise a gap between the annular lens shaper and the container wall. The lens may comprise an annular membrane portion covering the gap. The annular membrane portion may be of the respective film component on which the lens shaper is arrange. The annular membrane portion may be bent when the lens shaper moves.

[0028] According to another embodiment of the invention, the first film component separates the first compartment from a space with a pressure below atmospheric pressure, for example a vacuum space or near-vacuum space.

[0029] According to another embodiment of the invention, the first film component is a distensible membrane or a self-supporting film component.

[0030] This embodiment distinguishes between two different forms of the elastically deformable first film component.

[0031] Particularly, in the context of the current specification, an elastically deformable film component is considered to be a membrane in case its nondimensional tension parameter t is smaller than 5. The nondimensional tension parameter t is defined as where No is an initial in-plane radial tension load, a a the radius of the film component and D is the bending stiffness. It is defined as Eh3

[0032] D~ 12(1 - v2) where E is the modulus of elasticity, h is a film component’s thickness and v is the Poisson’s ratio (cf. Sheploak, M., & Dugundji, J. (1998)). “Large deflections of clamped circular plates under initial tension and transitions to membrane behavior.” Journal of Applied Mechanics, 65(1), 107-115)

[0033] In turn, the film component is considered a self-supporting film component in case nondimensional tension parameter t is greater than 5.

[0034] This definition may be applied to all film component of this specification.

[0035] Employing a self-supporting film component in the lens allows for active aberration compensation in the lens, as such self-supporting film component may not be deformed significantly under the influence gravitational forces. Therefore, active actuation may be necessary to compensate for gravitational aberration in case the second and third film components are membranes. This embodiment allows for thinner second and third film components, which in tur provides the option to select fluids from a wider variety of fluids / liquids.

[0036] According to another embodiment of the invention, the second film component is a distensible membrane or a self-supporting film component.

[0037] According to another embodiment of the invention, the third film component is a distensible membrane, or a self-supporting film component.

[0038] Both these embodiments may confer the same advantages as elaborated the for the first film component.

[0039] Selecting a self-supporting film component allows for a greater design flexibility of the fluids and remaining film components.

[0040] Particularly, only one or two film component(s) of the three film components is / are formed as a self-supporting film component.

[0041] According to another embodiment of the invention, the first, the second and the third film component are distensible membranes.

[0042] According to another embodiment of the invention, the lens comprises one or more intermediate compartments that are arranged on the optical axis, wherein each intermediate compartment comprises a transparent fluid or in particular a liquid, particularly wherein the intermediate compartments are arranged on the optical axis between the third compartment and the transparent bottom portion of the container. This embodiment allows for lens with even more compartments. This allows an even greater flexibility of fluid selection in terms of refractive index, density and other aspects such as fluid durability, stability, transparency, spectral property, boiling point, volatility, chemical composition etc...

[0043] According to another embodiment of the invention, each intermediate compartment is separated from an adjacent compartment, i.e. the third compartment or an adjacent intermediate compartment, of the lens by an intermediate elastically deformable film component, such as a membrane or a self-supporting film component.

[0044] This embodiment allows for an increased flexibility of the film components of the lens, in terms of stiffness, composition and other manufacturing parameters, such as durability, permeability, inertness, transparency, spectral property etc...

[0045] According to another embodiment of the invention, the transparent bottom portion comprises is a rigid window element arranged on the optical axis delimiting the third or an intermediate compartment from a gas-filled space or an adjacent lens component.

[0046] The rigid bottom element may be a rigid lens or a planar window element.

[0047] According to another embodiment of the invention, the first and the second fluid comprise a different refractive index and / or a different density, particularly wherein the first and the second fluid differ from each other by at least 3%, particularly by at least 5%, more particularly, by at least 7% in density and / or refractive index.

[0048] According to another embodiment of the invention, the third and the second fluid comprise a different refractive index and / or a different density, particularly wherein the third and the second fluid differ from each other by at least 3%, particularly by at least 5%, more particularly, by at least 7% in density and / or refractive index.

[0049] These embodiments define useful ranges and differences of the fluids.

[0050] It may be that the first and the third fluid are identical in terms of refractive index and density, but differ from the second liquid.

[0051] It is advantageous to have fluids of differing refractive index and density in adjacent compartments.

[0052] According to another embodiment of the invention, the first film component has a first stiffness, kl tthe second film component has a second stiffness, k2, the third film component has a third stiffness, k3.

[0053] In particular the term “stiffness” may be understood as defined in the art, e.g. in https: / / en.wikipedia.org / wiki / Stiffness . According to another embodiment of the invention, the first and the second stiffnesses differ from each other, particularly wherein the first and the second stiffnesses differ from each other by a factor in the range between 1.5 to 15, particularly in the range between 2 to 12, particularly in the range between 2.5 to 7.5 or 1.5 to 4.5.

[0054] This embodiment specifies exemplary stiffness ratios, in advantageous ranges.

[0055] According to another embodiment of the invention, the first fluid comprises a first density, p , and a first refractive index, nl twherein the second fluid comprises a second density, p2, and a second refractive index, n2, wherein the third fluid comprises a third density, p3, and a third refractive index, n3.

[0056] According to another embodiment of the invention, the first, the second and the third fluid as well as the second and the third stiffness are selected such that the following relation holds true:

[0057] This embodiment allows for aberration correction of the lens. It can be seen that a wide range of refractive indices, densities may be selected to obtain an aberration corrected lens. This relation allows for a more relaxed selection of liquids and film component as the one which may be used for two-compartment lenses in the art:

[0058] — =n2~ni P1~P2that leaves little space for variation. fc2n2-l p2

[0059] According to another embodiment of the invention, the first fluid and the first stiffness are selected such that the following relation holds true: (n1-l)(p1) g fci

[0060] According to another embodiment of the invention, the first, the second and the third fluid as well as the first, the second and the third stiffness are selected such that the following relation holds true: wherein MinVal is in the range of -10 to 0, particularly in the range of -5 to 0, more particularly in the range of -0.5 to 0, and / or wherein MaxVal is in the range of 0 to 10, particularly in the range of 0 to 5, more particularly in the range of 0 to 0.5.

[0061] This relation provides for lenses that offer a wide range of selection fluids and film components. In particular, in case MinVal and MinVal are 0, the lens may be considered to be perfectly aberration compensated. According to another embodiment of the invention, the second and the third membrane have the same stiffness. In particular, the second and the third membrane have the same thickness.

[0062] According to another embodiment of the invention, the first fluid is the same fluid as the third fluid, while the second fluid differs from the first and the third fluid.

[0063] According to another embodiment of the invention, the first membrane is thicker than the second and / or the third membrane.

[0064] Exemplary Embodiments

[0065] Particularly, exemplary embodiments are described below in conjunction with the Figures. The Figures are appended to the claims and are accompanied by text explaining individual features of the shown embodiments and aspects of the present invention. Each individual feature shown in the Figures and / or mentioned in said text of the Figures may be incorporated (also in an isolated fashion) into a claim relating to the device according to the present invention.

[0066] Fig. 1 shows a first embodiment of the lens according to the invention;

[0067] Fig. 2 shows a second embodiment of the lens according to the invention;

[0068] Fig. 3 shows a third embodiment of the lens according to the invention;

[0069] Fig. 4 shows a comparison of liquid combinations and a resulting film component stiffness, for two-compartment lenses and the lens according to the invention;

[0070] Fig. 5 shows another embodiment of the lens according to the invention.

[0071] In Fig. 1 a first exemplary embodiment of a lens 1 according to the invention is schematically depicted. Fig. 1 shows a cross-section along a plane comprising the optical axis 100 (z-axis) of the lens 1 and a direction orthogonal to it, e.g. along an x- axis of the lens 1.

[0072] The lens in Fig. 1 is oriented with respect to gravity (or any other force) 200 such that the optical axis 100 extends orthogonally to said force 200, wherein the force points in a direction along the x-axis as indicated by arrow 200.

[0073] The lens 1 comprises a container 2 with a transparent rigid bottom portion 3 that seals off the lens 1 on a first side of the lens 1. The container 2 comprises a container wall 6 that radially encloses a lens volume 22. In this example the container wall 6 and the rigid bottom portion 3 are attached to one another in a fixed relationship. The rigid bottom portion 3 may comprise a transparent window element that is fit to the container 2.

[0074] On a second side of the lens 1 facing in the opposite direction than the first side of the lens 1 , the lens volume VL is sealed off by three elastically deformable film components 10, 20, 30, namely a first film component 10 in form of a first membrane, a second film component 20 in form of a second membrane, and a third film component 30 in form of a third membrane. Therefore, in the exemplary embodiment shown in Fig. 1 , each film component 10, 20, 30, is a distensible membrane. A membrane in the context of the current specification is not self-supporting, but elastically deformable upon force exposure.

[0075] The third membrane 30 is attached to the container wall 6 and covers a third compartment V3 extending between the bottom portion 3 and the third membrane 30. The third compartment V3 is completely sealed by the third membrane 30, the container wall 6 and the bottom portion 3. The third compartment V3 is completely filled with a third fluid, in this case it may be a liquid.

[0076] The lens 1 comprises an annular lens shaper 4 that is arranged on a side of the third membrane 30 that faces away from the bottom portion 3. The lens shaper 4 is centered around the optical axis 100. The lens shaper 4 forms a gap 5 between the container wall 6 and the lens shaper 4 along the radial direction, e.g. x- and y- direction. The third membrane 30 extends into the gap 5. The gap 5 renders the lens shaper 4 movable in all directions and also tiltable around any axis, relative to the container 2, wherein an annular portion 31 of the third membrane 30 covering the gap 5 may be bent or relaxed depending on the position and orientation of the lens shaper 4 relative to the bottom portion 3. By moving the lens shaper 4 toward the bottom portion 3 along the optical axis 100, a fluid pressure in the third compartment V3 may be adjusted. The pressure will lead to a corresponding deformation of the third membrane 30 within the aperture 40 formed by the annular lens shaper 4 that allows adjusting of an optical power of the lens 1 and also an adjusting for various aberrations, such as cylinder and others. It will be appreciated that the movement described above is relative movement of the lens shaper 4 and the container 2. In practice, either of the lens shaper 4 and the container 2 may remain stationary relative to another structure and the other of the lens shaper 4 and the container 2 may be moved relative to said other structure. In examples, the container wall 6 may be deformable, for example elastically deformable, such that the rigid bottom portion 3 and / or the lens shaper 4 and / or at least a part of the container wall 6 are movable relative to one another. It will be appreciated that the principals underlying these is that the lens volume VL changes by said relative movement, such that a pressure inside the lens volume VL is changed by the relative movement.

[0077] The lens 1 furthermore comprises a first compartment V1 filled with a first fluid, such as a transparent liquid and a second compartment V2 filled with a second fluid, such as a second transparent liquid. The second compartment V2 is arranged between the first and the third compartment V1, V3 along the optical axis 100. Within the aperture 40 of the lens shaper 4, the first, second and the third compartment V1 , V2, V3 completely overlap radially. That is, the three compartments V1, V2, V3 form a stack of compartments along the optical axis 100.

[0078] The second membrane 20 separates the second compartment V2 from the first compartment V1. The third membrane 30 separates the third compartment V3 from the second compartment V2. The first membrane 10 separates the first compartment V1 from a gas-filled space S. Said space S may be surrounding air. In other words, the first membrane 10 forms an outer lens surface of the lens 1 , wherein said surface is configured to adjust an optical power or an aberration of the lens 1. Therefore, it is possible that the lens 1 comprises a protective cover element (not shown), a filter glass (not shown), or any other element (not shown) that covers the gas-filled space S.

[0079] The first membrane 10 is circumferentially connected to the lens shaper 4 on side of the lens shaper 4 that faces toward the optical axis 100, i.e. on the side limiting the aperture 40. Therefore, the first membrane 10 covers the complete aperture 40 of the lens shaper 4. On the side of the lens shaper facing away from the bottom portion an actuator may be attached (not shown).

[0080] Similarly, the second membrane 20 is circumferentially attached to the lens shaper 4 on the side of the lens shaper facing toward the optical axis 100 as well. The three membranes 10, 20, 30 are spaced apart at the lens shaper 4 along the optical axis 100, so that the membranes do not touch each other.

[0081] It is conceivable that the lens shaper 4 comprises several lens shaper portions (cf

[0082] Fig. 5; annular spacer element 7) that are stacked along the optical axis. For attaching the first membrane to the lens shaper, it may be useful to interject the first membrane 10 between two adjacent lens shaper portions, wherein for attaching the second membrane 20 to the lens shaper 4, the second membrane 20 may be interjected in the same fashion between two adjacent lens shaper portions as well. The third membrane 30 contacts the lens shaper 4 with the side facing away from the bottom portion, i.e. the third membrane 30 contacts the lens shaper on a side of the lens shaper 4 that faces toward the bottom portion 3. One may say that the lens shaper “sits” on the third membrane 30. Therefore, the third membrane 30 may experience a deforming force when the lens shaper 4 is moved along the optical axis 100. In contrast, due to the attachment to the lens shaper 4 on the side facing toward the optical axis 100, the first and the second membrane 10, 20 are not bent by the lens shaper 4, but react to an adjusted pressure conveyed by the third compartment V3. In the context of the current specification these membranes are considered as passive membranes - these membranes are not “directly” bent by a lens shaper motion but solely react to an adjusted pressure in adjacent compartments.

[0083] It may be conceivable that the membranes are attached to the lens shaper at the same portion (not shown) and thus touch each other at the lens shaper.

[0084] As is schematically hinted in Fig. 1 , the force 200 causes all of the membranes 10, 20, 30 to sag to some extent in or opposite the direction of the force, i.e. the membrane deformations along the optical axis are not symmetric to the optical axis 100.

[0085] In a liquid lens having only a single liquid filled compartment this leads to force- induced (and thus acceleration-induced) aberrations, such as gravity coma, in case the force is gravity.

[0086] In the art it has been found that the use of two compartments and two membranes such aberrations may be compensated to a large extent, by selecting the refractive indices, densities and the membrane stiffnesses (e.g. the membrane thicknesses) accordingly. However, the parameter space offered by such lenses may require specific liquids that fulfill the needs for a specific density and refractive index, and also may require membrane thicknesses, that are either too thin or too thick. Some liquids may be hazardous, or may have disadvantageous properties with respect to durability, chemical stability, volatility or other aspects. Other liquid combinations may require the membranes to be very thick, so that actuation and responsiveness of the lens becomes slow and energy-consuming. It may also be that the membrane thickness may become too thin, such that the membrane becomes slightly permeable, allowing liquids to evaporate affecting long term durability of the lens.

[0087] The lens 1 according to the invention allows compensating these force-induced aberrations e.g. by means of at least three fluids or liquids and three membranes and three compartments. Suitable selection of the fluid properties and the membrane stiffnesses allows for compensating such aberrations, while at the same time membrane stiffnesses may be selected within a moderate range of stiffnesses and thus thicknesses and the optical properties of the liquids do not need to be drastically different. Lenses with more than three compartments (and more than three film components and more than three liquids) are conceivable, which would relax the parameter space even more, but at the cost of increased architectural complexity of the lens.

[0088] In the following identical reference numerals indicate the same feature of the lens 1 and may not be elaborated again. However, properties, location and / or function may be the same as elaborated in the context of Fig. 1 and are applicable to the following examples if not indicated or logically mandatory otherwise.

[0089] In Fig. 2 another embodiment of the lens 1 according the invention is schematically depicted. A focus is put on the differences to the lens depicted in Fig. 1.

[0090] In this example, the third membrane 30 is attached to the container wall 6 and not to the lens shaper 4. Therefore, this membrane 30 is not movable at its circumferential attachment portion. When considering the third fluid incompressible and the third compartment V3 completely sealed, the membrane shape of the third membrane 30 is in essence dictated by force components, such as gravity, the densities of the fluids in the lens and the membranes stiffnesses. It can be considered a passive membrane. The third compartment V3 is comprised as in the previous embodiment between the third membrane 30 and the bottom portion 3. The container wall 6 comprises an annular attachment portion 61 that forms an aperture in the lens volume VL. The third membrane 30 is attached to the attachment portion 61 which allows facile attachment and manufacturing of the third membrane 30 and the third compartment V3.

[0091] The second membrane 20 is arranged similarly to the third membrane in Fig. 1. That is, the lens shaper 4 is arranged on a side of the second membrane 20 that faces away from the bottom portion 3, and forms a gap 5 between the second membrane 20 and the container wall 6. The gap 5 is covered by an annular membrane portion

[0092] 21 of the second membrane 20 that is bent when the lens shaper 4 moves.

[0093] The second membrane 20 contacts the lens shaper 4 with the side facing away from the bottom portion 3, i.e. the second membrane 20 contacts the lens shaper 4 on a side of the lens shaper 4 that faces toward the bottom portion 3. One may say that the lens shaper 4 “sits” on the second membrane 20. Therefore, the second membrane 20 may experience a deforming force, when the lens shaper 4 is moved along the optical axis 100. In contrast, due to the attachment to the lens shaper 4 on the side facing toward the optical axis 100, the first membrane 10 is not bent by a movement of the lens shaper 4, but reacts to an adjusted pressure conveyed by the second compartment V2, i.e. the first membrane 10 is a passive membrane, like the third membrane 30.

[0094] T urning to Fig. 3, another embodiment of the lens 1 according to the invention is depicted. In this embodiment, the lens shaper 4 is arranged on a side of the first membrane 10 that faces away from the bottom portion 3, and forms a gap 5 between the first membrane 10 and the container wall 6. The gap 5 is covered by an annular membrane portion 11 of the first membrane 10 that is bent when the lens shaper 4 moves.

[0095] The first membrane 10 contacts the lens shaper 4 with the side facing away from the bottom portion 3, i.e. the first membrane 10 contacts the lens shaper 4 on a side of the lens shaper 4 that faces toward the bottom portion 3. One may say that the lens shaper 4 “sits” on the first membrane 10. Therefore, the first membrane 10 may experience a deforming force, when the lens shaper 4 is moved along the optical axis 100.

[0096] In contrast to the other embodiments of Fig.1 and 2, the lens shaper 4 in the embodiment of Fig. 3 is not in contact with the first, second or third fluid, but may be positioned in the gas-filled space S. This embodiment allows a facile manufacturing, as no additional membranes (except the first member) need to be connected to the lens shaper 4.

[0097] The second and the third membrane 20, 30 are attached to the container wall 6 and not to the lens shaper 4. Therefore, these membranes are not movable at their circumferential attachment portion 61. When considering the second and the third fluid incompressible and the second as well as the third compartment V2, V3 completely sealed, the membrane shapes of the second and the third membranes 20, 30 are in essence dictated by force components, such as gravity, the densities of the fluids in the lens and the membrane stiffnesses. The second and the third membrane 20, 30 can be considered passive membranes. The third compartment V3 is comprised as in the previous embodiments between the third membrane 30 and the bottom portion 3. The container wall 6 comprises an annular attachment portion 61 that forms an aperture in the lens volume VL. The third membrane 30 is attached to the attachment portion 61 which allows facile attachment and manufacturing of the third membrane 301 third compartment V3. Spaced apart from the third membrane 30, the second membrane 20 is also attached to the attachment portion 61 of the container wall 6. Thus, the second compartment V2 is comprised between the third membrane 30, the container wall 6, in particular the attachment portion 61 , and the second membrane 20.

[0098] The lens 1 according to the invention in essence opens the parameter space and relaxes the requirements for the optical properties of the liquids as well as the stiffness of the membranes, because the compensation for gravity-induced aberrations may be facilitated by means of several membrane interfaces. This is elaborated in the following.

[0099] For a perfect acceleration-induced aberration compensation the following equation needs to hold true (for three membranes and three liquids in three compartments): wherein p is the density of the first fluid in the first compartment V1. is the refractive index of the first fluid; wherein p2is the density of the second fluid in the second compartment V2. n2is the refractive index of the second fluid; wherein p3is the density of the third fluid in the third compartment V3. n3is the refractive index of the third fluid. k is the stiffness of the first membrane, k2is the stiffness of the second membrane, k3is the stiffness of the third membrane.

[0100] This equation may be relaxed so that a certain tolerance may be incorporated, e.g. wherein MinVal may be in the range of -10 to 0, particularly in the range of -5 to 0, and / or wherein MaxVal may be in the range of 0 to 10, particularly in the range of 0 to 5.

[0101] For a two-compartment lens with only two membranes and two liquid, the following relation should be fulfilled: wherein the variable names refer to the first and the second liquid refractive index nnn2and density p ,p2as well as to the membrane stiffnesses, k ,k2.

[0102] Here the ratio between the membrane stiffnesses may quickly exceed 15 or 20 which renders manufacturing and suitability for practical applications.

[0103] This situation is depicted in Fig. 4A, which shows a discrete diagram for a lens with two compartments, with two liquids (First Liquid and Second Liquid) and two membranes with stiffness k and k2, respectively. The color-coding I gray-scale coding of the diagram indicates the ratio of the stiffness of the first membrane over the second membrane (see color bar I grayscale bar on the right-hand-side of Fig. 4A). It is noted, that in the two-compartment lens, the first membrane is a membrane that forms an outer lens surface, and thus an interface to the gas-filled space, wherein the second membrane separates the two compartments from each other. In essence, the two-compartment lens corresponds to a three-compartment lens without the third compartment and without the third membrane.

[0104] The liquids are numbered from #1 to #12. The same number refers to the same liquid. Thicker black lines (associated to liquid #3, #5 and #6) in the diagram mark liquids that may be problematic in terms of use for some national health regulations.

[0105] The liquids #1 to #12 have different densities and differing refractive indices. Any combination of a specific first and second liquid requires a certain membrane stiffness ratio, as elaborated in Eq. (3). As can be seen, liquids that may not be associated with a potential health hazard typically require stiffness ratios greater than 12. Only very few combinations of liquids allow for lower membrane stiffness ratios. This means that one membrane has to be about 12 times thicker than the other membrane. This in turn requires manufacturing a very thin membrane to have the twelve-times thicker membrane still be deformable with reasonable actuation forces. These extreme ratios are challenging to meet.

[0106] For aiding understanding, in Fig. 4A the following specific stiffness ratio data points are indicated as follows:

[0107] • D411 : approximately 20.0:

[0108] • D412: approximately 2.5;

[0109] • D413: approximately 7.5;

[0110] • D414: approximately 17.5; and

[0111] • D415: approximately 12.5.

[0112] In Fig. 4B, a diagram for the same liquids is shown for a lens according to the invention. In order to render the diagram of Fig. 4A and 4B comparable, the third membrane has the same stiffness as the second membrane and the third liquid is the same as the first liquid. That is, the identical diagram could be obtained for the membrane stiffness ratio of the first membrane and the third membrane.

[0113] As can be seen in Fig. 4B, the stiffness ratios of the first and the second membrane is in general lower and lies around between 2 and 7 - in essence twice lower than the stiffness ratios for the two-compartment case in Fig. 4A -, which allows using membranes deviating only by a factor two to three in thickness, so that the membrane thicknesses may be tuned to be non-permeable, not too thin and neither too thick, as elaborated in previous paragraphs.

[0114] For aiding understanding, in Fig. 4B the following specific stiffness ratio data points are indicated as follows:

[0115] • D421 : approximately 20.0:

[0116] • D422: approximately 2.5;

[0117] • D423: approximately 7.5; and

[0118] • D424: approximately 12.5.

[0119] Also, as can be seen a great variety of liquids that are not associated with a potential health hazard allow for low membrane thickness ratios. Fig. 5 shows another embodiment of the lens according to the invention. This lens is similar to the lens of Fig. 1. The lens shaper 4, however, is arranged on a side of the first membrane that faces away from the bottom portion. On the side of the first membrane facing the bottom portion an annular spacer element is arranged at the same position as the lens shaper, centred around the optical axis.

[0120] On a side of the annular spacer element facing away from the bottom portion and thus facing to the first membrane, the second membrane is attached to the spacer element, wherein on the opposite side of the spacer element, i.e the side facing toward the bottom portion, the third membrane is attached to the spacer element. The second membrane may be attached to the first membrane at the spacer element / lens shaper. The second and the third membrane are passive membranes.

[0121] This way, the second compartment is formed by the second, third membrane and the spacer element. This embodiment allows pre-manufacturing of the second compartment. It may be advantageous, when the second and the third membrane are made the same material and have the same thickness. The third liquid may be the same liquid as the first liquid, the second liquid may be a different liquid.

[0122] The lens according to the invention allows for durable, tunable liquid lenses with gravity compensation having relaxed requirements with regard to liquid densities and refractive indices as well as to membrane thickness, in particular membrane thickness ratios.

[0123] It will be appreciated that, whilst in the embodiments the first membrane 10 separates the first compartment V1 from a gas-filled space S, in other embodiments the first membrane 10 may separate the first compartment V1 from a space which has a pressure below atmospheric pressure (below 1 bar), or the space could be a vacuum space or a near-vacuum space.

[0124] Reference numerals

[0125] 1 lens

[0126] 2 container

[0127] 3 bottom portion

[0128] 4 lens shaper

[0129] 5 gap

[0130] 6 container wall

[0131] 7 annular spacer element I lens shaper portion

[0132] 10 first film component

[0133] 11 annular portion of the first film component

[0134] 20 second film component

[0135] 21 annular portion of the film component

[0136] 30 third film component

[0137] 31 annular portion of the third film component

[0138] 40 lens shaper aperture

[0139] 100 optical axis

[0140] 200 gravity / acceleration

[0141] S gas-filled space

[0142] V1 first compartment

[0143] V2 second compartment

[0144] V3 third compartment

[0145] VL lens volume x, z Cartesian directions

[0146] *****

Claims

1. Claims1. A fluid lens (1) with an optical axis (100) comprising at least the following components: a container (2) with a transparent bottom portion (3), wherein the container(2) comprises a lens volume (VL) comprising: o a first compartment (V1) comprising a first fluid, o a second compartment (V2) comprising a second fluid, o a third compartment (V3) comprising a third fluid, wherein the first, the second and the third compartment (V1, V2, V3) are arranged adjacent to each other on the optical axis (100), a first, a second, and a third elastically deformable film component (10, 20, 30),- wherein the first and the second compartment (V1 , V2) are separated from each other by the second film component (20),- wherein the second and the third compartment (V2, V3) are separated from each other by the third film component (30).

2. The lens (1) according to claim 1 , wherein the first film component (10) separates the first compartment (V1) from a gas-filled space (S).

3. The lens (1) according to one of the claims 1 or 2, wherein the first film component (10) forms an adjustable lens surface of the lens (1).

4. The lens (1) of any preceding claim, wherein the container (2) comprises a container wall (6) which radially encloses the lens volume (VL).

5. The lens (1) of any preceding claim, comprising an annular lens shaper (4) which is arranged on a side of one of the film components (10, 20, 30).

6. The lens (1) of claim 5, wherein the lens shaper (4) is movable and / or tiltable relative to the or a container wall (6).

7. The lens (1) of claim 5 or claim 6, comprising a gap (5) between the annular lens shaper (4) and the or a container wall (6) and comprising an annular membrane portion (11 , 21, 31) covering the gap (5).

8. The lens (1) according to one of the preceding claims, wherein the first film component (10) is a distensible membrane or a self-supporting film component.

9. The lens (1) according to one of the preceding claims, wherein the second film component (20) is a distensible membrane or a self-supporting film component.

10. The lens (1) according to one of the preceding claims, wherein the third film component (30) is a distensible membrane, or a self-supporting film component.

11. The lens (1) according to one of the preceding claims, wherein the lens (1) comprises one or more intermediate compartments that are arranged on the optical axis, wherein each intermediate compartment comprises a fluid.

12. The lens (1) according to claim 11 , wherein each intermediate compartment is separated from an adjacent compartment of the lens (1) by an intermediate elastically deformable film component, such as a membrane or a self- supporting film component.

13. The lens (1) according to one of the preceding claims, wherein the transparent bottom portion (3) comprises is a rigid window element arranged on the optical axis (100) delimiting the third or an intermediate compartment (V3) from a gas- filled space or an adjacent lens component.

14. The lens (1) according to one of the preceding claims, wherein the first and the second fluid comprise a different refractive index and / or a different density.

15. The lens (1) according to one of the preceding claims, wherein the third and the second fluid comprise a different refractive index and / or a different density.

16. The lens (1) according to one of the preceding claims, wherein the first film component (10) has a first stiffness, kl tthe second film component (20) has a second stiffness, k2, the third film component (30) has a third stiffness, k3.

17. The lens (1) according to claim 15, wherein the first and the second stiffnesses differ from each other.

18. The lens (1) according to one of the preceding claims, wherein the first fluid comprises a first density, p , and a first refractive index, nltwherein the second fluid comprises a second density, p2, and a second refractive index, n2, wherein the third fluid comprises a third density, p3, and a third refractive index, n3-19. The lens (1) according to at least claim 16 and 18, wherein the first, the second and the third fluid as well as the second and the third stiffness are selected such that the following relation holds true:

20. The lens (1) according to at least claims 16 and 18, wherein the first fluid and the first stiffness are selected such that the following relation holds true: (n1-l)(p1) g fcl21. The lens (1) according to at least claim 16 and 18, wherein the first, the second and the third fluid as well as the first, the second and the third stiffness are selected such that the following relation holds true:wherein MinVal is in the range of -10 to 0, particularly in the range of -5 to 0, more particularly in the range of -0.5 to 0, and / or wherein MaxVal is in the range of 0 to 10, particularly in the range of 0 to 5, more particularly in the range of 0 to 0.5.*****

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