WO2026002959A1

WO2026002959A1 - Quasi-stiff gravity coma compensation element

Info

Publication number: WO2026002959A1
Application number: PCT/EP2025/067699
Authority: WO
Inventors: Manuel Aschwanden; Hagen Schray; David Andreas NIEDERER; Roman Patscheider
Original assignee: Optotune Switzerland AG
Current assignee: Optotune Switzerland AG
Priority date: 2024-06-24
Filing date: 2025-06-24
Publication date: 2026-01-02
Anticipated expiration: 2026-12-24

Abstract

The present invention relates to a tunable lens, comprising: a container (10) enclosing an internal space filled with a transparent fluid (F1), a transparent and flexurally rigid thin element (11) configured to perform gravity coma compensation, wherein the thin element is configured to be elastically deformed from a first state to a second state, wherein the thin element (11) forms a wall of the container (10) and contacts the fluid (F1), a support structure (12) configured to support a circumferential boundary region (11a) of the thin element (11), and at least one actuator (13) configured to operatively interact with the thin element (11) to deform the thin element (11) from the first state to the second state.

Description

Quasi-stiff gravity coma compensation element

Specification

The present invention relates to a tunable lens.

Typically, tunable lenses, particularly when based on liquids or other materials / structures that deform under gravity, are susceptible to gravity coma, which is an optical aberration that occurs due to the influence of gravity (or upon an acceleration of the lens) on the shape of respective material.

Particularly, in a liquid lens, the liquid's surface is typically held in place by the tensile stress of a membrane that has an adjustable curvature to tune e.g. the focal power of the tunable lens. However, gravity can cause the liquid to sag, creating an asymmetrical, non-uniform surface of the membrane, particularly when the optical axis extends along the horizontal plane.

Gravity coma can significantly degrade the quality of the image produced by the tunable lens. To minimize gravity coma, liquid can be designed with compensation techniques, but it remains a challenge to provide an efficient compensation, particularly for lenses that are not used in static conditions where the influence of gravity is more easy to control, but shall be used in situations where the spatial orientation of the lens changes dynamically as is e.g. the case for lens applications in mobile devices or in the field of human vision, such as vision correction (e.g. head-worn glasses, particularly smart glasses) or other head-worn devices such as augmented reality (AR) glasses or virtual reality (VR) headsets.

Known passive coma compensation methods often require several liquid volumes that interact with one another so that properties of involved liquids and refractive indices need to be properly matched which restricts the design possibilities due to material constraints.

Based on the above, it is an objective of the present invention to provide a tunable lens facilitating a gravity coma compensation that is improved regarding the above stated difficulties.

This problem is solved by a tunable lens having the features of claim 1. Preferred embodiments of this aspect of the present invention are stated in the corresponding dependent claims and are described below.

According to an aspect, a tunable lens is disclosed, comprising:

- a container enclosing an internal space filled with a transparent fluid,

- an element configured for creating a higher order (particularly non-spherical) wavefront distortion of incoming light impinging on the element, wherein the element forms a wall of the container and contacts the fluid,

- a support structure configured to support a circumferential boundary region of the element, and

- at least one actuator configured to operatively interact with the element to deform the element from a first state to a second state.

The element may be transparent. The element may be thin. The element may be flexurally rigid. The element may be a plate. The element may be a thin plate. The element may be a plate in that the element is flexurally rigid, i.e., can sustain or withstand bending stresses or loads. The element may be formed out of a resilient material. The element may be configured to be deformed, e.g., elastically deformed, from a first state to a second state.

Further, according to an aspect of the present invention, a tunable lens is disclosed, comprising:

- a container enclosing an internal space filled with a transparent fluid,

- a transparent and flexurally rigid (e.g. quasi-stiff) thin element configured for creating a higher order (particularly non-spherical) wavefront distortion of incoming light impinging on the thin element, wherein the thin element is formed out of a resilient material and is configured to be elastically deformed from a first state to a second state, wherein the thin element forms a wall of the container and contacts the fluid,

- a support structure configured to support a circumferential boundary region of the thin element (the support structure facilitating said elastic deformation of the thin element), and at least one actuator configured to operatively interact with the thin element to deform the thin element from the first state to the second state. Particularly, the thin element is configured to create a higher order (particularly non- spherical) wavefront distortion of said incoming light in order to perform gravity coma compensation and/or compensation of aberrations due to an acceleration of the lens, particularly of a fluid of the tunable lens.

However, the thin element does not need to comprise an initial (first) flat state in which the thin element comprises a completely planar shape.

Furthermore, in a preferred embodiment, an outer edge of the thin element (which is also an outer edge of the circumferential boundary region) comprises a circular shape. Thus, the thin element can be a circular disk. Alternatively, in a preferred embodiment, the outer edge of the thin element can be non-circular in at least one state of the thin element. However, the outer edge may also be generally non-circular (i.e. in all states the thin element can assume)

Particularly the support structure may be integrated or comprise in, or formed by, a lateral wall of the container.

According to a preferred embodiment, the thin element comprises or is formed out of one of the following materials: a glass, a polymer, a thermoplastic material, polycarbonate (PC), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyimide (PI), polystyrene (PE), cyclic olefin copolymer (COC), cyclic olefin polymer (COP, e.g., Zeonex), a duroplastic material, a silicone (polysiloxane), epoxy, acrylic.

In certain preferred embodiments, the material does not contain a significant plastic creep under stress. Furthermore, in preferred embodiments, the thin element / said material is used in a regime, where its deformations are of elastic nature, and the original stress and strain states are reversible between different states. The transition between the two states might contain a hysteresis, however, the hysteresis preferably remains constant.

Furthermore, according to a preferred embodiment, the thin element is monolithic.

Furthermore, the thin element (particularly when taken alone) can be elastically bent out of its extension plane (against its flexural rigidity) and thereby generates restoring forces that try to bend the thin element back to its initial (e.g. flat) state. In this sense, the thin element can also be considered as a self-supporting element.

Particularly, according to a preferred embodiment of the present invention, the nondimensional tension parameter k of the thin element is smaller than 5. This nondimensional tension parameter k is defined as wherein No is the initial in plane radial tension load, a is the radius of the thin element and D is the bending stiffness. It is defined as

Eh³

^D ~ 12(1 - v²) where E is the modulus of elasticity, h is the thickness of the thin element 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).

Furthermore, particularly, according to a preferred embodiment, the bending stiffness D of the thin element is in the range from 0.001 Nmm to 50 Nmm. However, the bending stiffness can be less in small systems, and significantly larger in large systems.

Particularly, in the framework of the present invention, the feature that the element is a thin element means that its thickness is significantly smaller compared to its extension in the two linear independent directions extending orthogonal to the direction of the thickness. Thus, the thin element has a sheet-like form and depending on its material typically has a thickness in the range from 0.01 mm (e.g. for glass-like high stiffness materials) to 2 mm (e.g. for rubber-like low stiffness materials).

Furthermore, according to a preferred embodiment, the fluid can be one of: a liquid, a gel, a gas. Thus, in the framework of the present invention, a fluid is understood to encompass all states of matter that can flow, including liquids, gases, and gels. In this regard, a liquid is a state of matter with a definite volume but no fixed shape, taking the shape of its container. Furthermore, a gas is a state of matter without a fixed shape or volume, expanding to fill its container, and a gel is a semi-solid state of matter with a cross-linked network that can flow under stress but maintains a shape under low stress conditions. Particularly in an embodiment, the fluid is one of: a liquid polymer, a silicone-based liquid, a silicone based-gel, a mineral oil, a glycol-based liquid, a water based or water containing liquid, liquid mixtures or solutions, air. The fluid may be one of a polyol or a fatty acid.

According to a preferred embodiment, the thin element comprises a thickness being smaller compared to its extension in two linear independent directions extending orthogonal to a direction of the thickness which runs parallel to an optical axis of the tunable lens.

Furthermore, according to a preferred embodiment, the tunable lens is configured to control a boundary condition of the thin element at least at two different points of the circumferential boundary region. Particularly, said control is exerted by the at least one actuator and the supporting structure.

In certain preferred embodiments, the at least one actuator is one of: an electromagnetic polymer actuator (EPM), a piezo actuator, e.g. a bending piezo such as a piezo strip actuator (e.g. in an unimorph or bimorph configuration), a shape memory alloy (SMA) actuator, an electromagnetic actuator, a reluctance actuator, a thermal actuator, an electrostatic actuator.

Particularly, an electromagnetic polymer actuator (EPM) can utilizes the ability of a certain polymer to convert electrical energy into mechanical motion. Furthermore, a piezo actuator can use the piezoelectric effect to convert electrical energy into mechanical motion or force. Particularly, a piezo actuator comprises a piezoelectric material that expands or contracts when an electric field is applied). Furthermore, particularly SMAs exhibit the shape memory effect, i.e., they can return to their original, pre-defined shape after being deformed when heated above the transformation temperature. This transformation occurs due to a reversible phase change between martensite (low-temperature phase) and austenite (high-temperature phase) crystal structures within the SMA. SMA actuators typically operate by applying heat (e.g. via applying an electrical current) to the shape memory alloy. When heated above its transformation temperature, the SMA undergoes a phase change from martensite to austenite, causing it to revert to its original shape. This movement can used by a corresponding actuator comprising the SMA. Conversely, cooling the SMA below its transformation temperature allows it to retain a deformed shape until reheated. Furthermore, an electromagnetic actuator / voice coil actuator can employ an electrical coil and a permanent magnet, wherein an electrical current flowing in the coil can interact with the field of the permanent magnet generating a Lorentz force that can be used to move coil and magnet relative to one another. Furthermore, a reluctance actuator is configured to generate a magnetic flux that seeks the path of least reluctance which is used to induce a movement, e.g. by generating a magnetic flux with an electrical coil and guiding the magnetic flux via an air gap which gets minimized to minimize magnetic reluctance. Further, a thermal actuator typically comprises a material that expands or contracts significantly when heated or cooled, e.g. a bimetallic strip actuator. Finally, an electrostatic actuator can comprise two opposing electrodes that can attract and/or repel one another depending on their charge (as also described further down below)

Furthermore, according to yet another preferred embodiment, in the first state the thin element comprises a curvature in the direction of an optical axis of the tunable lens.

Further, according to a preferred embodiment, the at least one actuator is connected to the circumferential boundary region and configured to be bent for deforming the thin element from the first state to the second state, wherein particularly the at least one actuator is a piezo actuator, particularly a bending piezo, particularly a piezo strip actuator.

Furthermore, in a preferred embodiment, the tunable lens comprises a further actuator connected to the circumferential boundary region opposite the at least one actuator, wherein the further actuator is configured to be bent (particularly in conjunction with the at least one first actuator) for deforming the thin element from the first state to the second state, wherein particularly the further actuator is a piezo actuator, particularly a bending piezo, particularly a piezo strip actuator-

According to a further preferred embodiment, tunable lens comprises a plurality of actuators configured to operatively interact with the thin element to deform the thin element from the first state to the second state.

According to yet another preferred embodiment, the respective actuator is configured to press onto an actuation point of the circumferential boundary region of the thin element in a direction parallel to the optical axis.

Further, in a preferred embodiment, the support structure supports the circumferential boundary region of the thin element via a plurality of bearing points spaced apart from one another along the boundary, the bearing points being arranged offset with respect to the actuation points along the circumferential boundary region of the thin element.

Furthermore, according to a preferred embodiment, each actuator comprises a first and a second electrode opposing one another in the direction of the optical axis, wherein the first electrode is connected to the circumferential boundary region of the thin element and the second electrode is connected to the container, wherein the first and the second electrodes of the respective actuator are chargeable with opposite charges to move the first electrode towards the second electrode, or wherein the first and the second electrodes of the respective actuator are chargeable with like charges to move the first electrode away from the second electrode. Furthermore, according to a preferred embodiment, the at least one actuator is a piezo stack comprising a first and a second piezo element connected to the circumferential boundary region, and wherein the tunable lens comprises a further actuator in form of a piezo stack comprising a first and a second piezo element connected to the circumferential boundary region opposite the at least one actuator, wherein the respective first piezo element is configured to be shortened in a direction running parallel to the optical axis, and wherein the respective second piezo element is configured to be elongated in said direction to deform the thin element from the first state to the second state.

Further, in yet another preferred embodiment, the at least one actuator is configured to exert a force in direction orthogonal to the optical axis or in a direction forming an angle with the optical axis in the range from 45° to 90°.

Furthermore, in a preferred embodiment, the support structure is elastically deformable and said force (being e.g. orthogonal to the optical axis or e.g. forming said angle with the optical axis) acts on the thin element.

Alternatively, in a preferred embodiment, the support structure is elastically deformable and said force acts on a component coupled to the thin element via the support structure, wherein particularly said component is a rigid optical element arranged opposite the thin element.

Particularly, according to a preferred embodiment, the tunable lens comprises a sensor configured to provide an output signal indicative of one of: a spatial orientation of the tunable lens (particularly on orientation of the optical axis of the tunable lens with respect to the direction of gravity), a velocity of the tunable lens, an acceleration of the tunable lens.

In a preferred embodiment, the tunable lens comprises a control unit configured to control the at least one actuator (or said plurality of actuators) based on the output signal.

According to yet another preferred embodiment, the control unit controls the at least one actuator (or said plurality of actuators) to deform the thin element from the first state to the second state when the spatial orientation of the tunable lens changes from a first spatial orientation to a different second spatial orientation, wherein particularly the first spatial orientation corresponds to the optical axis extending along the horizontal plane (e.g. corresponding to the gaze of a person wearing the tuneable lens in front of an eye and looking forward) and the second spatial orientation corresponds to the optical axis forming a steeper angle with the horizontal plane (e.g. corresponding to the gaze of a person wearing the tuneable lens in front of an eye and looking downwards) or vice versa.

Particularly, in case multiple actuators are used, the control unit may be configured to prompt an appropriate selection of actuators to deform the thin element from the first state to a desired second state, thus not all actuators are necessarily used/moved to deform the thin element from the first state to the desired second state.

Furthermore, according to a preferred embodiment, the tunable lens comprises a transparent rigid optical element, particularly a rigid lens opposing the thin element (particularly in the direction of the optical axis).

Further, according to a preferred embodiment, the rigid optical element contacts the fluid.

According to yet another preferred embodiment, the tunable lens comprise a transparent and elastically deformable membrane (particularly the membrane is not a flexurally rigid member as the thin element) arranged opposite the thin element, and wherein the tunable lens comprises a further fluid contacting the membrane. Particularly, the further fluid can be one of: a liquid, a gel, a gas (see also above). Particularly, the membrane can be made of materials like silicone elastomer, silicone elastomer-based materials such as fluorine-modified silicone or a phenyl-containing silicone, and may have a thickness in the range from 5 microns to 200 microns, particularly up to 500 microns. In some embodiments the membrane can be an injection-molded membrane with a thickness of more than 500 microns (e.g. up to 2mm).

In a further preferred embodiment, the further fluid contacts the rigid optical element.

Furthermore, according to a preferred embodiment, the further fluid is separated from the fluid by the rigid optical element.

According to a further preferred embodiment, the further fluid contacts the thin element.

Furthermore, according to a preferred embodiment, the further liquid is separated from the thin element by a further transparent rigid optical element, wherein particularly the further transparent rigid optical element is a transparent rigid flat plate.

Further, according to a preferred embodiment, the tunable lens comprises an annular lens shaper connected to the membrane so that a circumferential edge of the lens shaper defines a curvature-adjustable area of the membrane. Particularly, in a preferred embodiment, the tunable lens comprises a lens shaper actuator configured to operatively interact with the lens shaper to adjust one, several or all of: a spherical power of the tunable lens, a cylindrical power of the tunable lens, a prismatic power of the tunable lens (as measured in prism diopters), wherein for tuning the spherical power the lens shaper actuator is configured to push the lens shaper against the membrane or to pull on the membrane in a direction parallel to the optical axis thus altering the curvature of the curvature-adjustable area accordingly, and wherein for adapting the cylindrical power of the tunable lens, the lens shaper element is configured to be bent out of its extension plane, and wherein for facilitating an adjustable prismatic power, the lens shaper is configured to be tilted by a desired angle with respect to the optical axis.

Furthermore, according to a preferred embodiment, the lens shaper is configured to operatively interact with the transparent membrane to compensate an astigmatism generated by the thin element.

According to a further preferred embodiment, the thin element comprises at least one state having a curvature with a wavy pattern in a first direction (the first direction being orthogonal to the optical axis) comprising a hill and a succeeding valley (connected by an inflection point of the curvature), wherein the opposing transparent rigid optical element comprises a cylindrical surface having a cylinder axis running parallel to said first direction.

Furthermore, in a preferred embodiment, the tunable lens 1 comprises a further transparent and flexurally rigid thin element configured to perform gravity coma compensation, wherein the further thin element is configured to be elastically deformed from a first state to a second state, wherein the further thin element is arranged opposite the thin element. Particularly, the thin element comprises at least one state having a curvature with a wavy pattern in a first direction comprising a hill and a succeeding valley (the first direction being orthogonal to the optical axis), and wherein the further thin element comprises at least one state having a curvature with a wavy pattern in a second direction y comprising a hill and a succeeding valley (the second direction y being orthogonal to the optical axis A), and wherein the first and the second direction are orthogonal to one another.

Some of the aforementioned aspects refer to a thin element, and it will be appreciated that the expression ‘thin’ refers to a thickness dimensions being much less than planar or width dimensions. The term ‘thin element’ may be replaced by ‘element’ or ‘plate element’ or ‘plate’ or ‘thin plate’ or ‘thin plate element’. In the following, further advantages, features as well as embodiments of the present invention are described with reference to the Figures, wherein:

Fig. 1 shows a schematic cross-sectional view of an embodiment of a tunable lens according to the present invention;

Fig. 2 shows a perspective view of a possible curved state of a thin element of the tunable lens that performs gravity coma compensation;

Fig. 3 shows a top view onto the thin element being in said curved state, the curves state essentially corresponding to a wavy pattern having a hill and an adjacent value connected via an inflection point;

Fig. 4 shows an embodiment of a tunable lens, wherein the thin element is actuated by bending actuators (e.g. piezo actuators) leading to a lateral displacement of a rigid optical element opposing the thin element with respect to the thin element;

Fig. 5 shows a perspective view of an embodiment, wherein the thin element is supported on multiple bearings via bearing points and actuated by actuators that act on actuation points offset from the bearing points;

Fig. 6 shows a schematic cross-sectional view of an embodiment of the tunable lens with the thin element being supported on bearings and actuated by actuators, e.g. in the form of piezo piston actuators;

Fig. 7 shows a schematic cross-sectional view of an embodiment of the tunable lens with the thin element being actuated by bending actuators, e.g. piezo strip actuators;

Fig. 8 shows a perspective view of an embodiment of a tunable lens according to the present invention, wherein the thin element is actuated by two opposing bending actuators (e.g. piezo strip actuators);

Fig. 9 shows a modification of the embodiment shown in Fig. 8;

Fig. 10 shows a schematic cross-sectional view of a further embodiment of a tunable lens according to the present invention, comprising multiple electrostatic actuators;

Fig. 11 shows a schematic perspective view of an embodiment of a tunable lens according to the present invention, wherein the thin element is arranged opposite a membrane to which a lens shaper is bonded that is configured to be deformed to correct aberrations introduced by the thin element, wherein in addition an optical power (e.g. spherical power) of the tunable lens may also be adjusted by means of the lens shaper;

Fig. 12 shows a schematic cross-sectional view of a further embodiment of a tunable lens according to the present invention, comprising two opposing thin elements for facilitating coma compensation in different directions;

Fig. 13 shows a schematic top view of an embodiment of the present invention, wherein multiple actuators (or components thereof) are arranged on the circumferential boundary region of the thin element in form of adjacent segments, particularly without gaps between neighboring segments;

Fig. 14 shows a schematic top view of an embodiment of the present invention, wherein multiple actuators are arranged on the circumferential boundary region of the thin element spaced apart from one another along the circumferential boundary region of the thin element,

Fig. 15 is a schematic representation of forces exerted by actuators of certain embodiments of the tunable lens, wherein the generated forces act essentially parallel to the optical axis of the tunable lens;

Fig. 16 shows a schematic cross-section of a further embodiment using e.g. piezo stacks as actuators, each stack comprises a first and a second piezo element (other actuators that can be shortened and elongated can be used as well);

Fig. 17 illustrates how the thin element can be deformed using momenta introduced into the thin element at its boundary;

Fig. 18 shows a schematic cross-section of a further embodiment using an elastic support and an actuator exerting a force on the thin element in a direction orthogonal to the optical axis of the tunable lens; and

Fig. 19 shows a modification of the embodiment shown in Fig. 18.

Fig. 1 shows an embodiment of a tunable lens 1 according to the present invention, comprising a container 10 enclosing an internal space filled with a transparent fluid F1 , a transparent and flexurally rigid thin element 11 , which may be considered to be a plate or a thin plate which can sustain bending loads, e.g., can support its own weight in bending, configured to perform gravity coma compensation, wherein the thin element 11 is configured to be elastically deformed from a first state to a second state, wherein the thin element 11 forms a wall of the container 10 and contacts the fluid F1. Further, the tunable lens 1 comprises a support structure 12 configured to support a circumferential boundary region 11a of the thin element 11 , wherein the support structure 12 facilitates said elastic deformation of the thin element 11. Particularly the support structure 12 can be integrated or formed by a lateral wall 19 of the container 10. Furthermore, the lateral wall 19 can comprise a bellows as a sealing element (or another elastic sealing element).

Furthermore, the tunable lens comprises at least one actuator 13 (or several such actuators as described herein and further down below) configured to operatively interact with the thin element 11 to deform the thin element 11 from the first state to the second state. Particularly, this deformation can also utilize the support structure 12 as a counter bearing.

Furthermore, the tunable lens 1 can comprise a transparent rigid optical element 16 (e.g. a rigid lens) that can be connected to the lateral wall 19 and can encloses the first fluid F2 together with the lateral wall 19 and the thin element 11.

Particularly, the thin element 11 does not need to comprise an initial (first) flat state in which the thin element 11 comprises a completely planar shape, but can be precurved, particularly with a wavy pattern comprising a hill and an adjacent valley.

Furthermore, as indicated in Fig. 1 (cf. also Fig. 2), a thickness of the thin element 11 is significantly smaller compared to its extensions orthogonal to the optical axis A.

Figs. 2, 3, 5, and 6 show embodiments, where the tunable lens 1 comprises a plurality of actuators 13 configured to operatively interact with the thin element 11 to deform the thin element 11 from the first state to the second state.

Particularly, the respective actuator 13 is configured to exert a force (or momentum) onto an actuation point 13a of the circumferential boundary region 11a of the thin element 11 in a direction parallel to the optical axis A. In this respect, the support structure 12 can support the circumferential boundary region 11a of the thin element 11 via a plurality of bearing points 12a (provided e.g. by several bearings) spaced apart from one another along the circumferential boundary region 11a, wherein the bearing points 12a are arranged offset from the actuation points 13a along the circumferential boundary region 11 a of the thin element 11 , which particularly allows to deform the thin element in a wavy pattern comprising a hill and an adjacent valley as indicated in Figs. 2, 3 and 5. In Fig. 2, some specific areas of deflection have leaders and reference numerals attached, and the deflections of the corresponding part of the thin element 11 is provided below:

• D21 : approximately 0.03 mm;

• D22: approximately -0.03 mm;

• D23: approximately 0.00 mm;

• D24: approximately -0.01 mm; and

• D25: approximately 0.01 mm.

Similarly, the deflections indicated in Fig. 3 are provided as follows:

• D31 : approximately 0.025 mm;

• D32: approximately -0.025 mm;

• D33: approximately -0.005 mm; and

• D34: approximately 0.005 mm.

The following list is provided for Fig. 5:

• D51 : approximately 0.03 mm;

• D52: approximately -0.03 mm;

• D53: approximately-0.01 mm; and

• D54: approximately 0.01 mm.

It will be appreciated that the displacement values in Figs. 2, 3 and 5 are exemplary only, and that these may be greater in magnitude, for example by reducing a stiffness of the thin element 11 and/or by increasing the amount of actuation force.

Particularly, in all embodiments described herein, the tunable lens 1 can comprise a transparent and elastically deformable membrane 17 (particularly the membrane is not a flexurally rigid member as the thin element 11 , i.e., a membrane cannot support its own weight in bending) arranged opposite the thin element 11 , wherein the tunable lens 1 can comprise a further fluid F2 contacting the membrane 17. The membrane can be connected to a further lateral wall 119 (cf. e.g. Figs. 6 and 7) or may be connected to a common lateral wall 19 (cf. e.g. Figs. 1 , 8, 9). Furthermore, the tunable lens 1 can comprises an annular lens shaper 18 connected to the membrane 17 so that a circumferential inner edge of the lens shaper 18 defines a curvature-adjustable area 17a of the membrane 17. Particularly, the lens shaper 18 can also be configured to operatively interact with the membrane 17 to compensate an astigmatism generated by the thin element 11 (to this end the lens shaper may be appropriately deformed by a suitable actuator). Using the lens shaper 18, the membrane 17, particularly its area 17a, can be deformed to tune focal and/or cylindrical power of the tunable lens and the lens shaper may be tilted to tune prismatic power of the tunable lens. In certain preferred embodiments of the tunable lens 1 , light may pass through the tunable lens 1 by passing first through the membrane and the adjacent further fluid F2 and thereafter through the thin element 11 for gravity coma compensation (the fluid F1 can be arranged in different ways with respect to the further fluid F2 as indicated e.g. in Figs. 8 and 9). The further fluid F2 adjacent the membrane 17 is generally susceptible to gravity sag due to the elastic properties of the membrane 17 so that the tunable lens 1 can develop gravity coma aberrations, particularly in case the optical axis A extends perpendicular to the direction of gravity (as an example, the direction of gravity is indicated in Figs. 6, 7, 8, 9 on the left side by an arrow). The induced gravity coma aberration can be compensated by lending the thin element 11 a corresponding curvature that compensates for the sag of the further fluid F2. This curvature can be adapted to different situations, particularly orientations (and/or velocities and/or accelerations) of the tunable lens 1 by actively adapting the curvature of the thin element 11 as described herein.

The embodiment shown in Fig. 1 corresponds to a configuration where the thin element separates the two fluids F1 and F2 from one another, wherein both fluids F1 , F2 contact the thin element 11 from opposite sides.

Fig. 6 and Fig. 7 show an alternative configuration, wherein the fluid F1 and the further fluid F2 are separated by a further rigid optical element 160 that can be connected to the rigid optical element 16 by a connecting member 191 that can encapsulate the thin element 11 together with the rigid optical elements 160, 16. Furthermore, in Figs. 6 and 7, the thin element 11 can form an interface with air arranged between the thin element 11 and the further transparent rigid optical element 160.

Furthermore, as indicated in Fig. 6, the tunable 1 can comprise a plurality of actuators 13 that can act on actuation points 13a as described above, wherein the thin element can be supported on bearing points 12a provided by the support structure 12 (e.g. in form of multiple bearings 12a) as also described above. Particularly, the actuators 13 are linear actuators exerting a force in a direction parallel to the optical axis A. Particularly, piezo piston actuators 13 can be used.

Fig. 7 shows a modification of the embodiment shown in Fig. 6, wherein bending actuators 13 are used instead of linear actuators. These bending actuators 13 can be formed by piezo strip actuators 13 as shown in the upper part of Fig. 8. According thereto, two opposing actuators 13 can be used, wherein each actuator is connected to the circumferential boundary region 11a and configured to be bent (e.g. in a direction parallel to the optical axis A) for deforming the thin element 11 from the first state to the second state.

As alternative, bending actuators 13 may also be employed as shown in Fig. 4, wherein here the individual actuator 13 is connected to the circumferential boundary region 11a and may also be a piezo actuator that is now configured to bend laterally in accordance with an opposing actuator 13, i.e., in a direction orthogonal to the optical axis A, leading to a lateral displacement of the rigid optical element 16 relative to the thin element 11 as well as to a corresponding curvature of the thin element 11 .

Furthermore, Figs. 8 and 9 show embodiments of the tunable lens, where the further fluid F2 is either in contact with the thin element 11 (Fig. 8), or wherein the two fluids are merely separated by the rigid optical element 16 and the thin element 11 can form an interface with air.

In the heat map of Fig. 8, the high point, or peak, of deflection is labelled ‘HP’ and the low point, or trough, of deflection is labelled ‘LP’. These indicators are also used in subsequent heat maps in the same way, to distinguish between peaks and troughs.

Further, Fig. 10 schematically indicates an embodiment of the tunable lens 1 comprising a plurality of actuators 13 in form of electrostatic actuators, wherein each actuator 13 comprises a first and a second electrode 131 , 132 opposing one another in a direction running parallel to the optical axis A, wherein the first electrode 131 is connected to the circumferential boundary region 11a of the thin element 11 and the second electrode 132 is connected to the container 10, wherein the first and the second electrodes of the respective actuator 13 are chargeable with opposite charges to move the first electrode 131 towards the second electrode 132, or wherein the first and the second electrodes of the respective actuator 13 are chargeable with like charges to move the first electrode 131 away from the second electrode 132. Charging of the electrodes 131 , 132 can be performed by connecting the electrodes to a corresponding voltage source 130 of the tunable lens 1 .

Furthermore, Fig. 11 shows a further embodiment of a tunable lens 1 wherein the thin element 11 comprises at least one state having a curvature with a wavy pattern in a first direction D1 (the first direction being orthogonal to the optical axis A) comprising a hill and a succeeding valley (e.g. connected by an inflection point of the curvature along direction D1). However, despite being able to correct gravity coma at least in central area of the thin element 11 , such a shape is prone to introducing additional errors at its boundary. Therefore, a lens shaper 18 bonded to an opposing transparent and elastically deformable membrane 17 of the tunable lens can be configured to adjust the shape of a curvature adjustable area 17a of the membrane 17 (which area 17a is defined by the lens shaper 18) to correct for aberrations introduced by the shape of the thin element 11 shown in Fig. 11. Particularly, the lens shaper 18 is configured to be deformed in a manner to form the area 17a of the membrane 17 into a trefoil shape as shown in Fig. 11 on the upper left-hand side. Here a trefoil shape is configured to be a deformation of the area 17a of the membrane comprising three valleys and three hills arranged in an alternating fashion along a circumferential boundary of the area 17a, with the center of the area 17a being essentially flat. In conjunction with the shape of the thin element 11 , this results in an (essentially aberration free) effective gravity coma compensation shape as shown on the lower right-hand side of Fig. 11. In addition, the lens shaper 18 can be used to tune the optical (e.g. spherical) power of the tunable lens as described herein.

Further, Fig. 12 shows an embodiment the tunable lens 1 , wherein the tunable lens 1 comprises further transparent and flexurally rigid thin element 1 T configured to perform gravity coma compensation, wherein the further thin element 1 T is configured to be elastically deformed from a first state to a second state, and wherein the further thin element 1 T is arranged opposite the thin element 11 . Particularly, the thin element 11 comprises at least one state having a curvature with a wavy pattern in a first direction x (the first direction x being orthogonal to the optical axis A) comprising a hill and a succeeding valley, and wherein the further thin element 1 T comprises at least one state having a curvature with a wavy pattern in a second direction y (the second direction y being orthogonal to the optical axis A) comprising a hill and a succeeding valley, and wherein the first and the second direction are orthogonal to one another.

Furthermore, Fig. 13 shows a schematic top view of an embodiment of the present invention, wherein multiple actuators 13 (or components thereof such as electrodes 131 described herein) are arranged on the circumferential boundary region 11a of the thin element 11 in form of adjacent segments, particularly without substantial gaps between neighboring segments. The tunable lens 1 may comprise one of: 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16 such actuators / electrodes.

Further, Fig. 14 shows a schematic top view of an embodiment of the present invention, wherein multiple actuators 13 are arranged on the circumferential boundary region of the thin element spaced apart from one another along the circumferential boundary region 11 a of the thin element 11. The tunable lens 1 may comprise one of: 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16 such actuators 13 (or corresponding actuation points).

Fig. 15 shows a schematic representation of forces exerted by actuators of certain embodiments of the tunable lens 1 , wherein the generated forces act essentially parallel to the optical axis A of the tunable lens 1 . Such forces are utilized in the embodiments of Fig. 2, 3, 5 and 6 for example by providing actuation points 13a and bearing points 12a offset with respect to the actuation points 13a. Using such a configuration, the thin element 11 can e.g. be deformed into the shapes shown in Figs. 2, 3, and 5 to perform gravity coma compensation.

In a similar fashion, Fig. 16 shows a preferred embodiment of a tunable lens 1 wherein the tunable lens 1 comprises two opposing actuators 13, particularly in form of piezo stacks, each actuator 13 comprising a first and a second piezo element 13a, 13b (or a first and a second actuator that can be shortened and elongated) connected to the circumferential boundary region 11a, wherein the respective first piezo element 13a is configured to be shortened in a direction running parallel to the optical axis A, and wherein the respective second piezo element 13b is configured to be elongated in said direction to deform the thin element 11 from the first (e.g. flat) state shown in the upper part of Fig. 16 to the (e.g. wavy) second state shown in the lower part of Fig. 16. The actuators 13 may be sealed by appropriate lateral sealing elements 19a and top sealing elements 19b.

Generally, the thin element 11 can be formed into e.g. coma gravity compensation shapes by applying the proper momentum at the boundary 11a of the thin element 11 as shown in the middle and lower part of Fig. 17.

As indicated in Fig. 18 and 19, such momenta can be generated by applying forces to e.g. the thin element 11 directly (or to another component coupled to the thin element 11) in a direction extending orthogonal (or at an angle in the range from 45° to 90°) to the optical axis A of the tunable lens.

Fig. 18 shows an embodiment of the tunable lens 1 , wherein the support structure 12 is elastically deformable and an actuator 13 of the tunable lens 1 exerts a force on the thin element 11 e.g. orthogonal to the optical A axis leading to the curved state of the thin element 11 shown in the middle part of Fig. 18. In case this force acts in the opposite direction the curved stated can be inverted as shown in the lower part of Fig. 18. Alternatively, in the embodiment shown in Fig. 19, the thin element 11 is also supported on an elastically deformable support structure 12, and a force generated by the at least one actuator 13 of the tunable lens 1 acts orthogonal to the optical axis A on a component coupled to thin element 11 via the support structure 12, wherein particularly said component is a rigid optical element 160 of the tunable lens 1 arranged opposite the thin element 11.

Furthermore, in all embodiments described herein, the tunable lens 1 can comprise a sensor 14 (as indicated for example in Fig. 1) configured to provide an output signal indicative of one of: a spatial orientation of the tunable lens 1 (particularly an orientation of the optical axis A) of the tunable lens 1 with respect to the direction of gravity), a velocity of the tunable lens 1 , an acceleration of the tunable lens 1.

Furthermore, in all embodiments described herein, the tunable lens can further comprise a control unit 15 (as indicated for example in Fig. 1) configured to control the at least one actuator 13 or said plurality of actuators 13 based on the output signal.

Particularly, the control unit 15 can control the at least one actuator 13 (or said plurality of actuators 13) to deform the thin element 11 from the first state to the second state when the spatial orientation of the tunable lens 1 changes from a first spatial orientation to a different second spatial orientation, wherein particularly the first spatial orientation corresponds to the optical axis A extending along the horizontal plane (e.g. corresponding to the gaze of a person wearing the tuneable lens in front of an eye and looking forward) and the second spatial orientation corresponds to the optical axis A forming a steeper angle with the horizontal plane (e.g. corresponding to the gaze of a person wearing the tuneable lens in front of an eye and looking downwards) or vice versa.

Particularly, in case multiple actuators 13 are used, the control unit 15 may be configured to prompt an appropriate selection of actuators 13 to deform the thin element 11 from the first state to a desired second state, thus not all actuators are necessarily used/moved to deform the thin element 11 from the first state to the desired second state. Particularly, in all embodiments described herein, in the second state, the stiff element can assume one specific curvature profile out of a plurality of different possible curvature profiles that can be achieved with the actuator(s) 13 that are utilized.

*****

Claims

1. A tunable lens, comprising:

- a container (10) enclosing an internal space filled with a transparent fluid (F1),

- a transparent and flexurally rigid thin element (11) for creating a higher order wavefront distortion, wherein the thin element is configured to be elastically deformed from a first state to a second state, wherein the thin element (11) forms a wall of the container (10) and contacts the fluid (F1),

- a support structure (12) configured to support a circumferential boundary region (11a) of the thin element (11), and

- at least one actuator (13) configured to operatively interact with the thin element (11) to deform the thin element (11) from the first state to the second state.

2. The tunable lens according to claim 1 , wherein the thin element (11) comprises a thickness being smaller compared to its extension in two linear independent directions extending orthogonal to a direction of the thickness which runs parallel to an optical axis (A) of the tunable lens (1).

3. The tunable lens according to claim 1 or 2, wherein the tunable lens (1) is configured to control a boundary condition of the thin element (11) at least at two different points of the circumferential boundary region (11a).

4. The tunable lens according to one of the preceding claims, wherein the at least one actuator (13) is one of: an electromagnetic polymer actuator (EPM), a piezo actuator, a shape memory alloy (SMA) actuator, an electromagnetic actuator, a voice coil actuator, a reluctance actuator, a thermal actuator, an electrostatic actuator.

5. The tunable lens according to one of the preceding claims, wherein in the first state the thin element (11) comprises a curvature in the direction of an optical axis (A) of the tunable lens (1).

6. The tunable lens according to one of the preceding claims, wherein the at least one actuator (13) is connected to the circumferential boundary region (11a) and configured to be bent for deforming the thin element (11) from the first state to the second state, wherein particularly the at least one actuator (13) is a piezo actuator.

7. The tunable lens according to claim 6, wherein the tunable lens (1) comprises a further actuator (13) connected to the circumferential boundary region (11a) opposite the at least one actuator (13), wherein the further actuator (13) is configured to be bent for deforming the thin element (11) from the first state to the second state, wherein particularly the further actuator (13) is a piezo actuator.

8. The tunable lens according to one of the preceding claims, wherein tunable lens (1) comprises a plurality of actuators (13) configured to operatively interact with the thin element (11) to deform the thin element (11) from the first state to the second state.

9. The tunable lens according to claims 2 and 8, wherein the respective actuator (13) is configured to press onto an actuation point (13a) of the circumferential boundary region (11a) of the thin element (11) in a direction parallel to the optical axis (A).

10. The tunable lens according to claim 9, wherein the support structure (12) supports the circumferential boundary region (11a) of the thin element (11) via a plurality of bearing points (12a) spaced apart from one another along the circumferential boundary region (11a), the bearing points (12a) being arranged offset with respect to the actuation points (13a) along the circumferential boundary region (11a) of the thin element (11).

11. The tunable lens according to claims 2 and 8, wherein each actuator (13) comprises a first and a second electrode (131 , 132) opposing one another in a direction running parallel to the optical axis (A), wherein the first electrode (131) is connected to the circumferential boundary region (11a) of the thin element (11) and the second electrode (132) is connected to the container (10), wherein the first and the second electrodes of the respective actuator (13) are chargeable with opposite charges to move the first electrode (131) towards the second electrode (132), or wherein the first and the second electrodes of the respective actuator (13) are chargeable with like charges to move the first electrode (131) away from the second electrode (132).

12. The tunable lens according to one of the claims 2 to 8, wherein the at least one actuator (13) is a piezo stack comprising a first and a second piezo element (13a, 13b) connected to the circumferential boundary region (11a), and wherein the tunable lens (1) comprises a further actuator (13) in form of a piezo stack comprising a first and a second piezo element (13a, 13b) connected to the circumferential boundary region (11a) opposite the at least one actuator (13), wherein the respective first piezo element (13a) is configured to be shortened in a direction running parallel to the optical axis (A), and wherein the respective second piezo element (13b) is configured to be elongated in said direction to deform the thin element (11) from the first state to the second state.

13. The tunable lens according to one of the claims 2 to 8, wherein the at least one actuator (13) is configured to exert a force in direction orthogonal to the optical axis (A) or forming an angle with the optical axis (A) in the range from 45° to 90°.

14. The tunable lens according to claim 13, wherein the support structure (12) is elastically deformable and said force acts on the thin element (11).

15. The tunable lens according to claim 13, wherein the support structure (12) is elastically deformable and said force acts on a component coupled to thin element (11) via the support structure (12), wherein particularly said component is a rigid optical element (160) arranged opposite the thin element (11).

16. The tunable lens according to one of the preceding claims, wherein the tunable lens (1) comprises a sensor (14) configured to provide an output signal indicative of one of: a spatial orientation of the tunable lens (1), a velocity of the tunable lens (1), an acceleration of the tunable lens (1).

17. The tunable lens according to claim 16, wherein the tunable lens (1) comprises a control unit (15) configured to control the at least one actuator (13) based on the output signal.

18. The tunable lens according to one of the preceding claims, wherein the tunable lens (1) comprises a transparent rigid optical element (16), particularly a rigid lens opposing the thin element (11).

19. The tunable lens according to claim 18, wherein the rigid optical element (16) contacts the fluid (F1).

20. The tunable lens according to one of the preceding claims, wherein the tunable lens (1) comprise a transparent and elastically deformable membrane (17) arranged opposite the thin element (11), and wherein the tunable lens (1) comprises a further fluid (F2) contacting the membrane (17).

21. The tunable lens according to claims 18 and 20, wherein the further fluid (F2) contacts the rigid optical element (16).

22. The tunable lens according to claim 18 and according to claim 20 or 21 , wherein the further fluid (F2) is separated from the fluid (F1) by the rigid optical element (16).

23. The tunable lens according to claim 20 wherein the further fluid (F2) contacts the thin element (11).

24. The tunable lens according to claim 20, wherein the further fluid (F2) is separated from the thin element (11) by a further transparent rigid optical element (160).

25. The tunable lens according to claim 20 or one of the claims 21 to 24 insofar referring to claim 20, wherein the tunable lens (1) comprises an annular lens shaper (18) connected to the membrane (17) so that a circumferential edge of the lens shaper defines a curvature-adjustable area (17a) of the membrane (17).

26. The tunable lens according to claim 25, wherein the lens shaper (18) is configured to operatively interact with the membrane (17) to compensate an aberration, particularly an astigmatism, generated by the thin element (11).

27. The tunable lens according to claim 18 or one of the claims 19 to 26 insofar referring to claim 18, wherein the thin element (11) comprises at least one state having a curvature with a wavy pattern in a first direction (D1) comprising a hill and a succeeding valley.

28. The tunable lens according to one of the preceding claims, wherein the tunable lens (1) comprises further transparent and flexurally rigid thin element (1 T) configured to perform gravity coma compensation, wherein the further thin element (1 T) is configured to be elastically deformed from a first state to a second state, wherein the further thin element (1 T) is arranged opposite the thin element (11).