Optical devices equipped with electroactive lenses

Abstract

The present disclosure relates to an electro-active unit for use in eyewear, the electro-active unit comprising: an electro-active element including first and second optically transparent substrates between which are disposed at least one liquid crystal layer including nematic liquid crystals and a Fresnel lens structure; first and second transparent electrodes formed on the first and second substrates, respectively; an alignment layer present on the first substrate and in contact with the liquid crystal layer and configured to align the nematic liquid crystals in a first direction; and a polarizing element configured to condition light having polarization in a second direction perpendicular to the first direction, wherein the liquid crystals of the liquid crystal layer are in the Morgan regime.

Description

[Technical Field]

[0001] This disclosure relates to an optical device for use in eyeglasses, the optical device including a first electroactive lens for adjustable light transmission. This disclosure also relates to a lens unit including such an optical device, eyeglasses including a frame on which the optical device is provided, and a method for operating the optical device. [Background technology]

[0002] An optical device incorporating a liquid crystal (LC) layer and a Fresnel lens structure as part of an electroactive lens can be switched from a state where the refractive index of the LC in the optical axis direction of the lens matches the refractive index of the lens, to a state where the refractive index in the direction perpendicular to the optical axis does not match the refractive index of the lens. In the latter state, the lens turns on for polarizations whose polarization angle depends on LC alignment. The liquid crystal lens may be a lens made entirely of liquid crystal, or a lens made of an isotropic material filled with liquid crystal.

[0003] Several approaches have been proposed to make such lenses suitable for non-polarized light, such as natural light: 1. Two similar lenses are stacked on top of each other so that the alignment of the liquid crystals within each lens is perpendicular to each other (Patent Document 1). 2. The lens is used in combination with a linear polarizer of a certain orientation (Patent Document 2).

[0004] Several patent documents relating to liquid crystal tunable lenses describe lens stacking, but tend to use planar alignment and do not consider how the Fresnel lens structures within the LC cavity are oriented relative to each other. Even if this were the case, the Fresnel lens structures are generally stacked with their surfaces oriented in the same direction. See, for example, Patent Documents 3, 4, 5, 6, 1, or 2.

[0005] This disclosure relates to an electroactive lens made from an isotropic polymer material combined with a vertically aligned liquid crystal. This type of electroactive lens is known, for example, from Patent Document 7. These known electroactive lenses have many drawbacks. For example, the orientation in a plane perpendicular to the optical axis is affected by the structure of the lens in the optical device. This orientation differs in different parts of the optical device. Therefore, in the above approach, the device transmits not only a magnified image but also a non-magnified image in some parts. This causes a double image.

[0006] The double image appears when the homeotropically oriented liquid crystal has a small tilt angle and a large off-axis (with respect to unidirectional tilt orientation) local lens surface tilt, while the electroactive unit is ON.

[0007] A switchable lens consisting of an isotropic polymer lens and a coated vertically aligned liquid crystal is known from Patent Document 7. This lens is made by imprinting a polymer layer onto a single substrate. This process also forms a spacer, which keeps a second substrate at a constant distance from the lens. The cavity between the substrates, covered with transparent electrodes, is filled with liquid crystal. Along the substrate, the orientation of the liquid crystal is determined by several factors. The orientation in the off state is controlled by a polyimide layer acting as an alignment layer. Generally, this layer aligns the liquid crystal director (defined as the average direction of the long molecular axis of the liquid crystal molecules) uniformly perpendicular to the surface, also known as vertical alignment. Then, when a voltage is applied to the electrodes, the liquid crystal randomly realigns in a plane along the surface. If the alignment layer on the substrate is rubbed, for example, if the polyimide coated substrate is rubbed, a small deviation of the director from the vertical alignment in the off state occurs. An additional explanation of the concept of pretilting by rubbing the alignment layer within an electroactive lens (or similar techniques such as optical alignment) is presented in Patent Document 8, which is incorporated herein by reference.

[0008] The misalignment of the director is related to the direction of friction and is called pre-tilt. When a voltage is applied, the orientation on the substrate opposite the lens is determined solely by the direction of friction. On a substrate with a lens, the situation becomes more complex. The orientation of the liquid crystal director is also affected by the direction of friction and even the geometric shape of the lens surface. Since the orientation of the lens surface differs at different locations, the liquid crystal director is also non-uniform on the lens substrate. This is why the orientation of the director differs in some parts between the top and bottom substrates, resulting in director twisting. It should be noted that similar alignment (i.e., the application of suitable pre-tilt) can be achieved by optical alignment techniques. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] U.S. Patent Application Publication No. 2017 / 15787082 [Patent Document 2] U.S. Patent No. 4,190,330 [Patent Document 3] U.S. Patent Application Publication No. 2007 / 0216851 [Patent Document 4] U.S. Patent No. 9,448,456 [Patent Document 5] U.S. Patent No. 9,690,116 [Patent Document 6] U.S. Patent No. 10,863,949[[ID=2,1]] [Patent Document 7] U.S. Patent No. 8,587,734 [Patent Document 8] International Publication No. 2019 / 038439 [Patent Document 9] International Publication No. 2019 / 101966 [Patent Document 10]<000V072>U.S. Patent No. 7,724,347 [Non-Patent Document]

[0010] [Non-Patent Document 1] V.G. Chigrinov et al., "Photoalignment of liquid crystal materials: Physics and applications" [Non-Patent Document 2] Gooch, C.H. and H.A. Tarry, "The optical properties of twisted nematic liquid crystal structures with twist angles less than or equal to 90 degrees", Applied Physics Vol. 8 (1975): pp. 1575 - 1584 [Summary of the Invention] [Problems to be Solved by the Invention]

[0011] The object of the present disclosure is to provide an optical device including at least one adjustable electroactive lens that provides improved optical quality and / or reduced risk of double image occurrence.

[0012] A further object is to improve the optical quality and reduce the occurrence of optical artifacts such as double images when the light focused or dispersed by the electroactive lens is non-polarized.

Means for Solving the Problems

[0013] According to a first aspect, there is provided an optical device for use in spectacles, the optical device comprising a first electroactive lens for adjustable focusing or dispersing of light, the electroactive lens - a first and a second optically transparent substrate, the first and second optically transparent substrates extending generally parallel to each other and defining an axial direction (z) and a transverse direction (x, y), the substrates; - a diffractive lens structure such as a Fresnel lens structure disposed between the first optically transparent substrate and the second optically transparent substrate on the side of the second optically transparent substrate; - a first optically transparent electrode formed on the first optically transparent substrate and a second optically transparent electrode formed on the second optically transparent substrate or on the diffractive lens structure; - a sealed cavity (108) between the first optically transparent substrate and the second optically transparent substrate, in which at least one LC layer of a diffractive structure and a nematic liquid crystal (LC) material is disposed, and the liquid crystals in the nematic liquid crystal (LC) material are generally aligned axially in an off state; The first optically transparent electrode has a contact surface in contact with the LC layer and is provided with an alignment layer configured to linearly align the liquid crystals in the nematic liquid crystal material in a first horizontal direction in an on state by introducing a pretilt in an off state, the sealed cavity (108); and a polarization element configured to adjust light having polarization in a second horizontal direction perpendicular to the first horizontal direction. The LC layer of the nematic liquid crystal material has a thickness (D) measured between the portion of the diffraction lens structure closest to the first optically transparent electrode and the contact surface of the aligned layer on the first optically transparent electrode. The thickness (D) is given by condition 1 < (πD(n e -n o Selected such that ) / (φλ)<200, n o n is the ordinary refractive index of the LC layer, and e θ is the anomalous refractive index of the LC layer, φ is the torsion angle of the liquid crystal director of the LC layer, and λ is the wavelength of light, with the wavelength λ being in the range of 350 nm to 750 nm.

[0014] The angle of twist may be assumed to be within the range of 0 to 180 degrees.

[0015] The pre-tilt caused by the alignment layer, and, if present, by any further alignment layers described below, results in a relatively small deviation from perfect axial alignment. In embodiments of this disclosure, the pre-tilt (which defines a small deviation from perfect axial (perpendicular) alignment) typically varies between 1 and 6 degrees with respect to the axial (z-) direction. See also Patent Document 8, filed by the same inventors, which provides further explanation of how including a small pre-tilt may aid in proper alignment of LC materials in off and on states.

[0016] When this condition is met, the liquid crystals in the liquid crystal layer fit well within the Mauguin regime so that wave guidance occurs within the liquid crystal layer. This makes it possible to maintain the linear polarization of light traveling through the optical device. Furthermore, a specific linear alignment direction can be applied to the first optically transparent electrode by using an alignment layer of the first optically transparent electrode, so that a uniform and favorable response of the optical device can be achieved on the surface optical device. In addition, by maintaining linear polarization, it is possible to filter out unwanted artifacts such as double images. Filtering can be achieved in some embodiments by incorporating a linear polarizer into the optical device, while in other embodiments it is achieved by providing a second electroactive lens stacked on top of the first electroactive element, as described below. For example, in embodiments of the present disclosure, the polarization element described above includes a polarizer (preferably a linear polarizer) configured to allow light having a first linear polarization to pass through and substantially block light having a second linear polarization perpendicular to the first linear polarization. Alternatively, or in addition, in other embodiments of the present disclosure, the polarizing element described above includes a second electroactive lens, preferably similar to the first electroactive lens, stacked on top of the first electroactive lens.

[0017] The optical devices as defined herein may comprise first and second substrates, and / or first or second alignment layers, which are substantially flat and arranged to extend generally parallel to one another. In these embodiments, axial alignment corresponds to vertical alignment when the flat substrates and / or flat alignment layers are arranged to extend horizontally. In other embodiments, the first and second substrates and / or first or second alignment layers may be curved elements, which are still arranged to extend generally parallel to one another. In these embodiments, axial alignment of a nematic liquid crystal (LC) material defines alignment in a direction that is locally perpendicular to the surface of the substrate / align layer facing the sealed cavity. In other words, at all locations on the surface, an axial direction can be defined that is perpendicular to the local orientation of the surface of the substrate / align layer. This direction generally differs for different arrangements on the surface. Therefore, in embodiments having curved substrates and alignment layers, it is preferable to refer to “axial alignment” rather than “vertical alignment.”

[0018] In the off state, an alignment layer is generally required on the diffractive lens structure to align the liquid crystals axially (vertically), but introducing directional pretilt is not strictly necessary. In the on state, a non-uniform director profile exists in the diffractive lens structure, resulting in various twist angles that depend heavily on the local diffractive lens structure. However, introducing pretilt in the same transverse (horizontal) direction as the linear alignment direction of the alignment layer on the first optically transparent electrode generally reduces the value of the twist angle, thereby increasing the Morgan condition. This results in better optical performance.

[0019] Throughout this disclosure, when referring to liquid crystals in nematic liquid crystal (LC) materials, axial alignment generally means that a substantial portion of the liquid crystal is aligned in one axis direction.

[0020] According to embodiments of the present disclosure, the diffraction lens structure located between the first and second optically transparent substrates on the side of the second optically transparent substrate is located on the second optically transparent layer. The second optically transparent electrode may be formed on the diffraction lens structure. According to embodiments of the present disclosure, the diffraction lens structure located between the first and second optically transparent substrates on the side of the second optically transparent substrate is located on the second optically transparent electrode, and the second optically transparent electrode is located on the second optically transparent substrate.

[0021] According to embodiments of the present disclosure, the polarizing element includes a second electroactive lens stacked on a first electroactive lens. The first optically transparent layer of the first electroactive lens has a contact surface in contact with the LC layer and comprises an alignment layer configured to linearly align the liquid crystals in the nematic liquid crystal material in a first horizontal direction when on, while the first optically transparent layer of the second electroactive lens has a contact surface in contact with the LC layer and comprises an alignment layer configured to linearly align the liquid crystals in the nematic liquid crystal material in a second horizontal direction when on, wherein the first direction is perpendicular to the second horizontal direction. In this configuration, the optical device can transmit (i.e., disperse or focus) unpolarized light to the electroactive lens with improved precision, thereby avoiding or at least reducing the possibility of double image formation.

[0022] Preferably, the refractive power of the first electroactive lens corresponds to the refractive power of the second electroactive lens, so that, when the optical device is ON, the lensing action provided by the optical device with respect to the first linear polarization direction corresponds to the lensing action with respect to the second linear polarization direction (the second direction being perpendicular to the first direction).

[0023] The first and second electroactive lenses may be identical, which may be advantageous from a manufacturing cost standpoint. However, the first and second electroactive lenses may also be different. For example, in embodiments where the diffracting lens elements of both electroactive lenses are Fresnel lens structures, the blaze axial height and / or blaze transversal position of the Fresnel lens structure of the first electroactive lens may differ, at least partially, from the blaze axial height and / or blaze transversal position of the Fresnel lens structure of the second electroactive lens. This may help reduce parallax and moiré effects when observed from an oblique direction, for example.

[0024] In addition, or alternatively, the nematic liquid crystal material of the first electroactive lens may differ from that of the second electroactive lens. Using different nematic liquid crystal materials may help reduce parallax and moiré effects when observed from oblique angles. Furthermore, the selection of nematic liquid crystal materials may affect the desired position of the blaze in the diffraction structure and / or reduce the occurrence of chromatic aberration.

[0025] In some embodiments where the first and second electroactive lenses are stacked, the first optically transparent substrate of the first electroactive lens and the first optically transparent substrate of the second electroactive lens are combined into a single common optically transparent substrate. The stack of electroactive lenses may then have only three substrates.

[0026] Instead of stacking two electroactive lenses on top of each other, a single electroactive lens may be provided with at least one linear polarizer. The linear polarizer is configured to allow light having a first linear polarization to pass through and substantially block light having a second linear polarization perpendicular to the first linear polarization. Furthermore, the polarizer is preferably aligned on the side of the first optically transparent layer such that the first linear polarization is substantially parallel to the alignment of liquid crystals in the liquid crystal layer near the first electrode. In other words, the polarizer axis can be aligned in the direction of the liquid crystal director in the nematic liquid crystal (LC) material of the first electroactive lens when it is turned on. In this configuration, when unpolarized light is incident (when the optical device is turned on), a magnified image originating from the first polarization along the first linear alignment direction and a non-magnified image originating from the second polarization perpendicular to the first direction are produced. The non-magnified image can then be easily removed by a suitable polarizer.

[0027] In a preferred embodiment, the linear polarizer comprises one or more polarizing layers attached to a first substrate and / or a first optically transparent electrode, and more preferably, the linear polarizer comprises polarizing layers attached to an alignment layer, aligned in the alignment direction of the alignment layer. It should be noted that the alignment direction may be achieved in a different manner and may correspond to the direction of rubbing when the alignment layer is subjected to a rubbing action, or to the optical alignment direction when the alignment layer is subjected to an optical alignment treatment.

[0028] In a further embodiment, the optical device comprises at least one polarizing layer formed on the surface of a diffractive lens structure facing an LC layer, wherein the polarization director of at least one further polarizing layer is tuned within different regions of the diffractive lens structure to match a local liquid crystal director on the lens surface.

[0029] The optical device may be of a type in which at least one electroactive lens is configured to adjust the focusing or dispersion of light by changing the alignment of liquid crystals in the LC layer when a voltage is applied to the optically transparent electrode. As will be understood by those skilled in the art, the voltage can be applied in different ways. One specific example in which the electrodes of one or more electroactive lenses are attached to a power source, such as a battery located in different parts of an eyeglass frame, is described in Patent Document 9. Furthermore, the optically transparent electrodes of the electroactive lenses may be electrically connected for simultaneous switching of the first and second electroactive lenses. Adjustment of the focusing or dispersion of light can be caused by changing the refractive index of the LC layer in the transverse direction when a voltage is applied to the optically transparent electrode, because this reorients the LC director in the transverse direction.

[0030] The optical device may be configured such that, upon application of a voltage to the optically transparent electrode of at least one electroactive lens, at least one electroactive lens is switched from an off state, where it substantially does not exhibit lensing action, to an on state, where it exhibits lensing action. Depending on the type of diffractive lens element, the lensing action may involve magnification of the incident image.

[0031] In the off state, the liquid crystals in the nematic liquid crystal material are oriented such that the refractive index of the LC layer in the transverse direction substantially matches the refractive index of the diffraction structure, and / or in the on state, the orientation of the liquid crystals is tilted so that the orientation is parallel to the alignment direction of the aligned layer.

[0032] The optical device may comprise a plurality of spacers arranged in the liquid crystal layer and extending perpendicular to the plane on which the second electrode extends, preferably formed on a diffraction lens structure. The spacers ensure that the required minimum and maximum thicknesses of the LC layer can be precisely achieved. In a specific embodiment, the spacers are configured to provide an additional height of 1 to 20 μm, preferably between 2 and 12 μm, when measured from the portion of the diffraction lens structure closest to the second substrate.

[0033] The liquid crystal material of the LC layer is preferably selected to have a birefringence Δn in the range of 0.15 to 0.40.

[0034] In another embodiment, a lens unit for use in eyeglasses is provided, the lens unit comprising a first lens component, a second lens component, and an optical device as defined herein, wherein an electroactive lens is positioned, preferably sandwiched, between the first lens component and the second lens component.

[0035] In yet another embodiment, eyeglasses are provided, comprising a frame on which first and second lens units, or first and second optical devices, as defined herein, are mounted.

[0036] In yet another embodiment, a method is provided for operating an optical device including first and second electroactive lenses as defined herein, wherein an alternating voltage is applied to the first and second electrodes of the first electroactive lens and the second electroactive lens stacked on the first electroactive lens, thereby aligning liquid crystals in a direction substantially perpendicular to the first and second substrates. The disclosure also relates to the use of optical devices, lens units, and / or eyeglasses as defined herein.

[0037] overview Although it is a uniaxial material, liquid crystals have birefringence properties. This is due to a specific phase delay.

number

Equation

[0038] In a liquid crystal lens, the refractive index of the lens material can be made to match either the refractive index of the liquid crystal, i.e., n e or n o This means that there is no lens effect on linearly polarized light in the direction of the matching refractive index. For polarized light perpendicular to this, all light is refracted by the lens. When unpolarized light that can be decomposed into two orthogonal polarization directions is transmitted, half of the light is subject to the lens effect and half is not. Therefore, a double image is transmitted. To make all light subject to the lens effect, one solution is to add a second liquid crystal lens perpendicular to the first liquid crystal lens. This has also been proposed in Patent Document 10 and Patent Document 1. However, in both patents, the arrangement of the liquid crystal is different from the present disclosure in terms of the method of stacking two liquid crystal layers.

[0039] In this disclosure, the liquid crystal director has a non-uniform orientation on a substrate having a Fresnel lens structure, but a uniform orientation on an opposing substrate (which does not have a Fresnel lens structure). When stacking two lenses, if the substrate having a Fresnel lens structure touches the other lens, it is impossible to orient the liquid crystal director perpendicular to the substrate touching the second lens in all parts of the lens. This is only possible when the two lenses are stacked together with opposing substrates facing each other.

[0040] Another solution to make an electroactive lens function for non-polarized light is to add a polarizer to the lens. In this case, the polarizer axis should coincide with the liquid crystal director. Since the liquid crystal director is uniform only on the substrate opposite the lens, the (linear) polarizer should be mounted on this substrate and aligned in the direction of the liquid crystal (=rubbing or light alignment).

[0041] In a further solution, a polarizer is also added to the electroactive lens. However, in this case, this is a special type of polarizer in which the polarizer director is tuned within different regions of the lens so as to match a local liquid crystal director on the lens surface. This polarizer is mounted on the lens substrate. This type of polarizer can be made by optical alignment (see, for example, Non-Patent Document 1).

[0042] As mentioned earlier, in order to achieve a pure separation between one polarization for the magnified image and one polarization for the non-magnified image, the liquid crystal twist should extend widely in the waveguide regime. This means that the Morgan condition should be satisfied, which we rewrite for simplicity as 0.5pΔn >> λ, where λ is the wavelength of light, p is the helical pitch (equal to 2πd / φ), and Δn is the birefringence. The pitch is the length over which the liquid crystal director twists with respect to 360 degrees.

[0043] For example, under certain conditions, λ is the wavelength of light, typically 0.5 microns. Δn is the difference in refractive index along the steady and abnormal axes, typically 0.2, and p is the helical pitch. This means that, in order to satisfy the Morgan condition, considering the aligned geometric shape, the helical pitch p should be considerably larger than 0.5 / (0.5 × 0.2) = 5 microns.

[0044] The amount of twist within the electroactive lens depends on how much the lens structure changes the direction of the director between the two surfaces of the liquid crystal contact, which in this application is between the lens surface and the substrate (opposing substrate).

[0045] Numerical calculations using the finite element method were applied by the inventors to determine the torsional behavior of liquid crystals within an electroactive lens, and it was found that this behavior depends on the pre-tilt angle of the liquid crystals on the lens surface. This pre-tilt angle can be influenced by the alignment material, rubbing or illumination conditions, and even the surface angle of the polymer (Fresnel) lens relative to the substrate on which it is mounted. Generally, the lower the pre-tilt, the greater the torsion. For example, a pre-tilt of 87 degrees on a surface with a 3-degree angle oriented perpendicular to the alignment direction results in a total torsion of 45 degrees.

[0046] Considering the cross-section of an electroactive lens perpendicular to aligned surfaces, the torsion value changes with the azimuth angle. When the side of the cross-section coincides with the direction of friction, the torsion between the lens and the opposing substrate should be 0 degrees. However, the value of the torsion angle increases with the azimuth angle, and theoretically can reach a value of 180 degrees. In this case, the directors on the Fresnel lens surface and the opposing substrate are oriented parallel to each other, and the directors choose torsion instead of bending deformation. This choice occurs when the system is about to reach equilibrium, and the overall minimum energy state corresponds to a torsion of 180 degrees. The larger the torsion value, the greater the distance between the two substrates must be than 2.5 microns. For this reason, a spacer at least 4 microns higher than the top of the blaze is provided for a lens with a lens power of 1.5 diopters (diameter 21 mm, Δn=0.2).

[0047] Depending on the lens power and diameter, the height of the spacer on the lens should be optimized to span the entire lens surface and fill the Morgan regime.

[0048] When the conditions for the waveguide / Morgan regime are met, the linear polarization of light coincides with the twisting of liquid crystal molecules. The inventors have found that this effect can be used to improve the quality of electroactive lenses.

[0049] This ensures that linear polarization is maintained through the lens cell, and when a linear alignment direction is applied to the opposing substrate, the optical response to this surface is uniform. More specifically, there will be a magnified image along the linear alignment direction and a non-magnified image perpendicular to it. Therefore, if a linear polarizer is placed on that side, the non-magnified image can be easily eliminated. Furthermore, assuming that both opposing substrates are oriented toward each other and placed at a 90-degree angle, it is also possible to create a polarization-independent switchable lens by stacking a similar electroactive lens on top of the first electroactive lens. [Brief explanation of the drawing]

[0050] [Figure 1] This figure illustrates one embodiment of an optical device equipped with an electroactive lens. [Figure 2] This diagram illustrates the twisting of liquid crystals within an electroactive lens. [Figure 3A] This diagram illustrates the alignment of liquid crystals within an electroactive lens. [Figure 3B] This diagram illustrates the alignment of the liquid crystals in the two liquid crystal layers of each electroactive lens. [Figure 4] This figure illustrates an example of polarization-dependent magnification using an electroactive lens. [Figure 5] This figure illustrates an electroactive lens provided with a polarizer layer according to one embodiment of the present disclosure. [Figure 6] This figure illustrates an electroactive lens provided with a polarizer layer according to another embodiment of the present disclosure. [Figure 7] This figure illustrates one embodiment of a lens unit comprising a first lens component, a second lens component, and the optical device shown in Figure 5, which is sandwiched between the two lens components. [Figure 8] This figure illustrates one embodiment of an optical device comprising two stacked electroactive lenses, corresponding to the embodiment in Figure 1. [Figure 9] This figure illustrates an electroactive unit comprising a stack of two electroactive lenses according to the present disclosure. [Figure 10A] This figure illustrates exemplary test results of an electroactive lens according to an embodiment of the present disclosure. [Figure 10B] This figure illustrates exemplary test results of an electroactive lens according to an embodiment of the present disclosure. [Figure 10C] This figure illustrates exemplary test results of an electroactive lens according to an embodiment of the present disclosure. [Modes for carrying out the invention]

[0051] The following description includes numerous specific details to enable a complete understanding of this disclosure, for illustrative purposes only. However, it will be clear that this disclosure can be carried out without these specific details. In other cases, well-known structures and devices are not described in detail to avoid unnecessarily obscuring this disclosure.

[0052] As will be apparent to those skilled in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features that can be readily separated from or combined with features of any of the other embodiments without departing from the scope of this disclosure. Any described method may be performed in the order of the described events or in any other logically possible order.

[0053] Note that, as used herein and in the accompanying claims, the singular form (the articles “a,” “an,” and “the” in the original text) includes multiple referents unless the context clearly indicates otherwise. Furthermore, note that the claims may be written to exclude any additional elements. As such, this sentence is intended to serve as a prerequisite for the exclusive use of “exclusive,” “only,” and similar words, or for the use of “negative” limitation, in relation to the description of the claims.

[0054] Figure 1 shows an electroactive lens 101. The electroactive lens 101 may be part of a lens. The electroactive lens 101 comprises a first substrate 104 on which a first electrode 106 is formed, a second substrate 105 on which a second electrode 107 is formed, and a volume or cavity 108 surrounded between the first substrate 104 and the second substrate 106, and in certain embodiments between the electrodes 106 and 107, and sealed by two boundaries 103 located at the opposing ends of the electroactive lens 101. The first substrate 104, the second substrate 105, the first electrode 106, and the second electrode 107 may be made from optically transparent materials. For example, electrodes 106, 107 may include a tin-doped indium oxide (ITO) layer and / or an indium zinc oxide (IZO) layer. The first and second electrodes 106, 107 may be connected to a power source (not shown). The power supply may be configured to apply a voltage difference between the first electrode and the second electrode when the optical device is switched on, while substantially no voltage difference exists between the first electrode and the second electrode when the device is off.

[0055] The sealing volume or sealing cavity 108 between the optically transparent electrodes 106 and 107 includes a diffractive lens structure 102 and at least one nematic liquid crystal (LC) layer 113 formed from nematic liquid crystal. The cavity 108 of the electroactive lens 101 may include a diffractive lens structure in the form of a Fresnel lens structure, but other types of diffractive structures may also be employed. In the illustrated embodiment, the diffractive structure 102 extends only over a portion of the width of the cavity 108 such that intermediate spaces 108a and 108b exist at both ends of the diffractive structure. However, in other embodiments, the diffractive structure extends to contact two boundaries 103 (which may be formed by a plug positioned between a first substrate 104 and a second substrate 105). Furthermore, the Fresnel lens structure 102 is positioned at the center of the cavity 108, but in other embodiments, the Fresnel lens structure may be positioned closer to either of the boundaries 103 of the electroactive lens 101. The Fresnel lens structure 103 can be made from transparent materials, for example, from isotropic polymer materials.

[0056] In addition, one or more spacers 109 may also be placed inside the volume 108. The spacers 109 may be placed between the Fresnel lens structure 102 and the counter electrodes 106, 107. For example, as illustrated in Figure 1, the Fresnel lens structure 102 may be placed on the second electrode 107. Then, one or more spacers 109 are placed between the Fresnel lens structure 102 and the first electrode 106 and pass through the volume 108. One or more spacers (not shown) may also be placed between the electrodes 106, 107 and extend from the first electrode 106 through the volume 108 to the second electrode 107.

[0057] Furthermore, an alignment layer 111 is positioned on (or as part of) the first electrode 106 to align the LC material 113 inside the cavity 108. Optionally, a second alignment layer 112 is positioned on the diffraction structure 102, i.e., on the surface of the diffraction structure 102 facing the LC material in the cavity 108. In embodiments (not shown in Figure 1) where the second electrode layer is located on the diffraction structure instead of between the second substrate 105 and the diffraction structure 102, the second alignment layer 102 may be part of the second electrode 102.

[0058] Electrodes 106 and 107 are configured to alter the alignment of liquid crystals within the liquid crystal (LC) layer, thereby altering the refractive index of the liquid crystal (LC) layer in the transverse direction (x-direction in Figure 1) of the electroactive lens 101. More specifically, this is the refractive index in the transverse direction (horizontal direction), which needs to either match or not match the refractive index of the diffracted structure. This allows for variations in the refractive power of the electroactive lens 101. The alignment of the liquid crystals can be altered by activating the electroactive lens 101. The electroactive lens 101 is configured to be activated using a voltage applied to the optically transparent electrodes 106 and 107, as will be described later.

[0059] When no voltage is applied to electrodes 106 and 107, the orientation of liquid crystal molecules in the nematic liquid crystal (LC) is determined by the alignment layer. More specifically, the liquid crystal molecules in the nematic liquid crystal (LC) layer exhibit both in-planar and out-of-planar orientations, and the in-planar alignment direction of the liquid crystal typically coincides with the rubbing or illumination direction. The average upward tilt angle of the liquid crystal from the alignment surface plane is then referred to as the (unidirectional) pre-tilt angle. When a voltage is applied to electrodes 106 and 107, the electric field generated between electrodes 106 and 107 causes different alignment directions of the liquid crystal.

[0060] For example, in the first state, also referred to here as the off state, i.e., when no voltage is applied to the optically transparent electrodes 106 and 107, the liquid crystal can be oriented such that the refractive index of the LC layer in the transverse direction (x direction) of the electroactive lens 101 substantially matches the refractive index of the diffractive lens structure 102. As a result, the diffractive lens structure 102 and the LC layer effectively form a combined optical layer having the same refractive index in the transverse direction (x direction) (i.e., substantially no optical interface within the volume portion 108). In other words, the combined optical layer has a substantially constant refractive index within the volume portion 108, regardless of the width position (i.e., the position along the x direction shown in Figure 1). Furthermore, the combined optical layer also has two parallel surfaces. As a result, light rays incident on the electroactive lens 101 when in the first state are not collimated or dispersed.

[0061] In the second state, also referred to as the ON state, where a voltage is applied to the first electrode 106 and the second electrode 107, the orientation of the liquid crystal molecules is typically parallel to the alignment direction of the aligned layer, and thus an additional optical interface is formed between the liquid crystal in the LC layer and the diffractive lens structure 102. This additional optical interface results in different refractive indices for the combined layers. Thus, light rays incident on the electroactive lens 101 are refracted by the optical interface between the diffractive lens structure 102 and the LC layer, thereby collimating or dispersing the light rays incident on the diffractive lens structure 102.

[0062] In summary, the first state may be a state in which no voltage is applied to electrodes 106 and 107, and the second state is a state in which a suitable voltage is applied to electrodes 106 and 107, and the refractive indices of the combined optical layers in the transverse direction of the electroactive element 101 match and differ from the refractive indices of the diffractive lens structure 102 (e.g., Fresnel lens structure), respectively. Similarly, in the following description, the switch-on state refers to a state in which additional refractive power is provided to the electroactive lens 101 by forming a refractive optical interface between the diffractive lens structure 102 and the liquid crystal in the volume portion 108, and the switch-off state refers to a state in which the refractive index of the liquid crystal in the transverse direction of the electroactive lens 101 matches the refractive index of the diffractive lens structure 102 as a result of no additional refractive power being provided to the electroactive lens 101. Preferably, the refractive indices of the LC layer (switch-off state) and the Fresnel lens structure 102 also match the refractive indices of the first substrate 104 and / or the second substrate 105.

[0063] The Fresnel lens structure 102 may be a positive Fresnel lens structure or a negative Fresnel lens structure. Preferably, the Fresnel lens structure 102 is a negative Fresnel lens structure (as illustrated in Figure 1). The type of Fresnel lens structure 102 used may vary depending on the application of the electroactive lens 101, for example, Fresnel lens structures 102 of different sizes, strengths, and shapes may be used. The Fresnel lens structure 102 may be placed on an electrode 107 connected to a second substrate, or, in embodiments where the electrode is placed on the Fresnel structure 102, the Fresnel structure may be connected to the second substrate. In embodiments where the Fresnel lens structure 102 is placed on the electrode 107, the Fresnel lens structure 102 may be formed on the electrode 107 by any technique, for example, nanoimprint lithography. The Fresnel lens structure 102 may be formed by a plurality of concentric ring-shaped shapes referred to as blazes 110. The blaze 110 is formed by a ring-shaped cross-section having a triangular shape, with a side extending axially (i.e., in the z-direction) of the electroactive lens 101, a side facing the electrode where the Fresnel lens structure 102 is formed (i.e., the xy-plane), and an oblique side (which may be curved), which provides a refractive optical interface between the Fresnel lens structure 102 and the liquid crystal when switched on. The shape of the blaze 110 may be optimized to suit the specific application of the electroactive lens 101, and the examples or illustrative figures described above are not limiting.

[0064] The first substrate 104 and the second substrate 105 are joined by applying an adhesive between the two substrates, thereby forming at least a portion of the boundary 103. The adhesive joining the first substrate 104 and the second substrate 105 may be, for example, NOA71 or NOA160. The boundary 103 or a portion of the boundary may further be formed during the formation of the Fresnel lens structure 102, for example, in the nanoimprinting step in which the Fresnel lens structure 102 is formed.

[0065] The same explanation as above, taking Figure 1 into consideration, may also apply to the embodiments shown in Figures 5 to 7, where similar reference figures may refer to similar elements.

[0066] A nematic liquid crystal in an electroactive lens, as shown in Figure 1, can undergo birefringence due to the birefringence properties of the liquid crystal. As illustrated in Figure 4, in the ON state of the electroactive lens, the electroactive lens provides a lens power. However, due to the birefringence properties of the liquid crystal, different polarizations are refracted in different ways. For example, dots 402 and 403 ideally coincide and form a single dot. However, due to the different refraction of different polarizations, these dots appear separated in the magnified image 401. In the following description, this problem will be stated more clearly considering Figures 2-4, and then how this problem is solved will be revealed considering Figures 5, 6, and / or 7. Figures 8A-8C are exemplary measurements illustrating the success of the proposed solution.

[0067] Figure 2 illustrates a liquid crystal layer containing liquid crystal 205 positioned between two surfaces 200 and 210. Although it is a uniaxial material, the liquid crystal has birefringence properties. This is due to the phase delay.

number

number

[0068] In the liquid crystal layer within the electroactive lens as described with reference to Figure 1, the refractive lens material 102 has a refractive index of the liquid crystal, i.e., (n e or n o This coincides with that of the other. This means that there is no lensing effect on linearly polarized light in the direction of the coincident refractive index. For polarized light with polarization perpendicular to this, all the light is refracted by the lens. When unpolarized light, which can be described as a superposition of light with two orthogonal polarization directions, is transmitted, half of the light is lensed and the other half is not. Thus, a double image is transmitted.

[0069] In other words, the birefringent liquid crystal 205 disposed between surface 201 and surface 210 tends to twist with respect to angle φ over distance d. As described above, the liquid crystal 205 guides the incident polarization when the Morgan condition is met. For example, when light is incident on the transparent surface 200 in the z direction, the polarization of the light in the x direction produces a refractive index of the liquid crystal layer that is different from that of another polarization of light having a polarization direction (on surface 200) in the y direction.

[0070] The twisting of the liquid crystal 205 is affected not only by the thickness of the layer between surfaces 200 and 210, but also by known methods such as rubbing or optical alignment of the alignment layer. Furthermore, the orientation of the second surface 210 relative to the first surface 200 also affects the twisting of the liquid crystal 205. For example, if the second surface is rotated in the yz plane, the liquid crystal 205 will rotate in a manner different from that illustrated in Figure 2. This can occur, for example, at the position of the blaze 110.

[0071] This can be illustrated in Figure 3A illustrating a lens outline 300. Such a lens outline may be a lens that includes an electroactive lens, as shown in Figure 1's electroactive lens 101. In the lens of Figure 3, both the first electrode 106 and the Fresnel structure 102 provided on the second electrode 107 are provided with alignment layers, and these alignment layers are aligned in direction 306. This will probably cause the liquid crystals in both the first electrode 106 and the Fresnel structure 102 to align in direction 306. However, the Fresnel structure 102 does not provide a surface parallel to the surface of the first electrode 106, and as such, the surface of the Fresnel structure 102 affects the orientation of the liquid crystals on it, as schematically illustrated by arrows 301, 302, 303, 304 and 305. Even if the alignment at the center of the lens outer diameter 300 (as illustrated by arrow 301) is parallel to the alignment direction 306, the alignment of the liquid crystals in the first lower-left alignment 302, the first lower-right alignment 303, the first upper-left alignment 304, and the first upper-right alignment 305 has a substantial component that is not parallel to the rubbing direction (306). As such, applying a linear polarizer is insufficient to obtain a single image because the emitted light contains multiple polarizations that transversely have different refractive properties of the birefringent liquid crystal.

[0072] To obtain a stack of two elements having an outline 310 as shown in Figure 3B, it can be assumed that the above problem can be solved by placing an additional electroactive lens, such as element 101 in Figure 1, on top of the electroactive lens of outline 300. The above explanation also applies to the additional electroactive lens, but if there is an additional electroactive lens, it will be aligned in a direction 316 perpendicular to the alignment direction 306. In fact, the first central alignment 301 is perpendicular to the second central alignment 311, and as such, polarization-independent refraction is obtained near the center of the lens outline 310. However, in places away from the center, for example, where the first lower-left alignment 302 and the second lower-left alignment 312 overlap, their alignments are not perpendicular to each other, resulting in different refractions for two different elliptical polarizations, and therefore, in the region where the first lower-left alignment 302 and the second lower-left alignment 312 overlap, the lens forms a double image. The same applies to the region where the first lower-right orientation 303 overlaps with the second lower-right orientation 313, the first upper-left orientation 304 overlaps with the second upper orientation 314, and the first upper-right orientation 305 overlaps with the second upper-right orientation 315.

[0073] In other words, light can be decomposed into two independent polarization states (twice linear, twice circular, or twice elliptical), and unpolarized light includes a superposition of these two states. Liquid crystals consist of elongated molecules with different refractive index values ​​along different axes. When using a single lens cell and ideal linear alignment directions at the top and bottom surfaces, in the ON state, linearly polarized light along the longitudinal direction of the molecules is lensed, while other polarized light perpendicular to the linearly polarized light is not lensed. Therefore, the resulting image obtained through the lens is a double image, both magnified and unmagnified.

[0074] However, by positioning the linear polarizer parallel to the linear alignment direction, the non-magnified image can be eliminated. In the case of a double-layered lens cell with a 90-degree angle, both polarizations are amplified, and the incident unpolarized light is magnified overall. However, in reality, while linear alignment within the lens cell is desirable, it introduces lens misalignment. As a result, there is a location-dependent twist that transforms the linearly polarized light into location-dependent elliptical polarization (such as the location-dependent elliptical polarization state illustrated in Figure 3B). Consequently, it is not possible to eliminate the non-magnified image with the help of the linear polarizer. More specifically, the elliptical polarization resulting from independent linearly polarized light (each containing either a magnified or non-magnified image) can no longer be resolved by the linear polarizer.

[0075] Furthermore, it is difficult to create a fully polarized independent lens with two stacked cells. Ultimately, it must be possible to ensure that at each position, the polarization changes in both cells are the same but rotated by 90 degrees, which is not possible with two equal lens cells as illustrated in Figure 3B.

[0076] Figure 4 illustrates an image of the electroactive lens 101 in the switched-off state, such as in the embodiment described with reference to Figure 1. In the switched-off state, the uniaxial liquid crystal molecules are preferably aligned in the axial direction of the electroactive lens 101, i.e., substantially perpendicular to the surface of the first electrode 106. In such a state, the refractive index of the liquid crystal matches the refractive index of the Fresnel lens structure 102. In such a state, there is no lensing effect. An image of a light screen containing a plurality of black dots arranged in a repeating pattern (as seen through the electroactive lens 101) is illustrated in 401. Here, the dots on the screen also appear as a repeating pattern. Pattern 401 is the same pattern of dots arranged on the screen.

[0077] When the electroactive lens 101 is switched on, the liquid crystal is preferably aligned radially, i.e., substantially parallel to the surface of the first electrode 106. In such a case, the refractive index of the liquid crystal does not match that of the Fresnel lens structure 102, and a lensing effect is obtained. The image of the light screen containing multiple dots is magnified as illustrated in image 401. However, the magnification is not the same for two orthogonal polarizations. For example, dots 402 and 403 are separate dots belonging to different polarizations, and ideally these dots would coincide to form a single dot, i.e., ideally polarization-independent magnifications would be obtained.

[0078] This problem primarily occurs when an electric field is applied to the liquid crystal layer by electrodes; therefore, the following explanation will deal with such conditions unless otherwise clearly stated.

[0079] Figure 5 illustrates one embodiment of the electroactive lens 501 in which the problems identified above have been resolved. The electroactive lens 501 includes substantially the same components as the electroactive lens 101 in Figure 1, and similar reference numbers (above 400) refer to similar elements. In order not to obscure the disclosure, the same descriptions that also apply to this figure are not repeated here. The electroactive lens 501 includes (from top to bottom in the figure) a first substrate 504, a first electrode layer 506, an alignment layer 506, a cavity 508 filled with a layer of LC material 513 and a diffraction structure 502, a further alignment layer 512, a second electrode layer, and a second substrate 505. In addition, the electroactive lens 501 comprises a polarizer layer 560 positioned between the first substrate 504 and the electrode layer 506.

[0080] Figure 6 also illustrates another embodiment of the electroactive lens 801 in which the problems identified above have been resolved. The electroactive lens 801 includes substantially the same components as the electroactive lens 501 in Figure 5, and similar reference numbers (above 300) refer to similar elements. In order not to obscure the disclosure, the same descriptions that also apply to this figure will not be repeated here. In addition, the electroactive lens 801 comprises a polarizer layer 860, the function of which will be described later. In this embodiment, the polarizer layer 860 is located on the first substrate 604 (i.e., on the outer surface of the first substrate 804).

[0081] Figure 7 shows an exploded view of a lens unit 650 consisting of the optical device of Figure 5, positioned between two lens components 651 and 652. These two lens units 650 may be placed within the frame of eyeglasses to be worn by a person, allowing the person to change the refractive power of the lens units between an off state and an on state.

[0082] In embodiments shown in Figures 5 to 7, linear polarizers forming polarizer layers 560, 860 are provided. The polarizer layers are configured to allow a first linear polarization to pass through and substantially block a second linear polarization perpendicular to the first linear polarization. Furthermore, the polarizer layers are aligned such that the first linear polarization is substantially parallel to the alignment of liquid crystals in the liquid crystal layers 508, 808 near the first electrodes 506, 806. For example, the linear polarizers 560, 860 may allow polarization in a first transverse direction (e.g., the x-direction) of an electromagnetic wave traveling in the axial direction (z-direction) to pass through, while blocking polarization in a second transverse direction (e.g., the y-direction perpendicular to the first transverse direction and the z-direction, i.e., perpendicular to the xz-plane). In this example, the alignment of liquid crystals near the first electrodes 506, 806 is in the x-direction. Furthermore, the thickness d0 of the liquid crystal layers 508, 808, measured from the outer surface of any blaze 510 of the diffraction structures 502, 802 (or the outer surface of any blaze of the second alignment layer provided on top of the diffraction structures 502, 802) to the outer surface of the alignment layers 561, 861 facing the cavities 508, 808, is such that the liquid crystal layer satisfies the Morgan condition (Equation 1). This prevents the double image 401 illustrated in Figure 4.

[0083] Those skilled in the art will recognize that the thickness d0 can also be chosen such that the Morgan condition (Equation 1) is not completely satisfied, but that some degree of waveguide effect will still occur. For example, with respect to thickness d0,

number

number

[0084] In many devices, a first minimum value of transmittance is used to define the required minimum thickness, but the main drawback here is that the first minimum value is held only for a single wavelength. Physically, this means that for thicknesses of the first minimum value, the resulting polarization state is not purely linear for most other wavelengths. In general, the polarization state becomes elliptic, and its primary contribution is still along the preferred direction (i.e., the alignment direction on the opposing substrate). By increasing the integer M and performing calculations for multiple wavelengths, we can obtain an optimal thickness d0 with approximately similar transmittance values, and it can be considered that the waveguide condition is well satisfied. Thus, substituting the thickness value into the left-hand side of the Morgan condition, we find that f is approximately 1, 2, 5, or 10, depending on the desired purity of the resulting polarization state, the target wavelength range, and the birefringence of the LC material.

[0085] The above solution can still substantially solve the problem because the thickness of most of the liquid crystal layer 508 is substantially greater than d0 when measured from the portion of the blaze 510 closest to the first electrode 506.

[0086] Furthermore, the polarizing layer 560 may be placed between the first substrate 504 and the first electrode 506 (as shown in Figure 5), between the first electrode 806 and the first alignment layer 811, or on top of the first substrate 804 (Figure 6).

[0087] In principle, a polarizer layer can be provided on the side of the second substrates 505, 805, for example, between the second substrate and the diffraction structure. In this case, a location-dependent quasi-spherical polarizer layer should be added. Such a location-dependent quasi-spherical polarizer can be specifically formed to remove light in the polarization direction that emerges from the Fresnel lens structure 502, 802 after passing through the first substrates 504, 804, the first electrodes 506, 806, the alignment layers 511, 811, and the liquid crystal layers 508, 808. A location-dependent quasi-spherical polarizer would have a spherical shape that precisely removes the non-refractory polarization component of the emerging light. For this purpose, the electroactive lens 501 would have a specified pattern. For example, referring to Figure 3, a location-dependent quasi-spherical polarizer, when incorporated into an electroactive lens having an outline 300, would block light having a polarization direction perpendicular to each of the arrows 301, 302, 303, 304, and 305 at the location where each of the arrows 301, 302, 303, 304, and 305 is positioned. In this case, it is necessary to perform measurements regarding the polarization direction of light for each thickness d0, each Fresnel lens structure 502, and each liquid crystal layer, so that the Fresnel lens structure 502 appears in each of its configurations (in the xy plane) within the electroactive lens and form a location-dependent quasi-spherical polarizer according to such measurements.

[0088] Furthermore, in embodiments described with a polarizer layer on the side of the second substrate, the second solution, the thickness d0 of the liquid crystal layer measured between the end of any blaze 510 and the opposite end of the liquid crystal layer 508 (i.e., near the first electrode 506), is such that the liquid crystal layer satisfies Morgan's condition (Equation 1). This prevents the double image illustrated in Figure 4.

[0089] Those skilled in the art will also know that the thickness d0 can be selected such that the Morgan condition (Equation 1) is not fully satisfied, for example, that it can be partially satisfied with respect to the thickness d0, i.e.

number

[0090] Those skilled in the art will recognize that the first and second solutions can be combined, which may adequately solve the problems described above. However, in some embodiments, having two polarizing layers may be undesirable as it reduces the light transmission intensity.

[0091] Figure 8 illustrates a third solution to the above problem. In the embodiment of this figure, the electroactive lenses 601 and 601' substantially contain the same components as the electroactive lens 101 in Figure 1 (i.e., a lens without one or more polarizer layers), and similar reference numbers refer to similar elements (above the number 500). In order not to obscure the disclosure, the same explanations that also apply to this figure are not entirely repeated here.

[0092] Figure 8 shows an optical device 600 including a first electroactive lens 601 and a second electroactive lens 601' stacked on top of the first electroactive lens 601. Similar to the electroactive lens 101 in Figure 1, each of the first and second electroactive lenses 601, 601' comprises a first optically transparent substrate 604, 604' and a second optically transparent substrate 605, 605'. The first and second optically transparent substrates 604, 604', 605, 605' extend generally parallel to each other, as shown in the figure, defining the axial (z) and transverse (x,y) directions. The first and second electroactive lenses 601, 601' are stacked in such a manner that the second substrates 605, 605' of each electroactive lens 601, 601' are located on the outside of the stack, and each of the first substrates 604, 604' is located on the inside of the stack.

[0093] The first electroactive lens 601 and the further electroactive lens 601' are in optical communication; that is, the second substrate 604 and the further second substrate 604' are optically coupled such that there is preferably no optical interface between the two substrates. Similar to the electroactive lenses described with reference to Figure 5, the first and further electroactive lenses 601 and 601' have thicknesses d1 and d2, respectively, measured between the diffraction structure 602 or 602' (or the alignment layers 612, 612' provided thereon) and the electrodes opposite the diffraction lens structure, i.e., the electrode 606 of the first electroactive lens 601 or the electrode 606' of the second electroactive lens 601, and their respective alignment layers 611, 611'. Each of the thicknesses d1 and d2 is such that the liquid crystal layer 613 of the first electroactive lens 601 and the liquid crystal layer 613' of the second electroactive lens 601' satisfy the Morgan condition (Equation 1). This prevents, or at least significantly reduces, the double image 401 as illustrated in Figure 4.

[0094] The first electrode 606 and the further first electrode 606' each include an alignment layer 611, 611', for example, a polyimide layer treated by rubbing. The alignment of liquid crystals on opposing surfaces of the alignment layers 611 and 611' is mutually orthogonal. For example, the liquid crystals of the first liquid crystal layer 613 are aligned in the x-direction on the surface of the first electrode 606 closest to the alignment layer 611, and the liquid crystals of the second liquid crystal layer 613' are aligned in the y-direction (perpendicular to the x and z directions, not shown) on the surface of the further first electrode 606' closest to the alignment layer 611'. As a result, if the first polarization of light incident on the first electroactive lens 601 is amplified by the first electroactive lens 601, and the second polarization of light incident on the first electroactive lens 601 (which is orthogonal to the first polarization direction) is not amplified, then the amplified first polarization of light incident on the further electroactive lens 601' is not further amplified by the further electroactive lens 601', while the second polarization of light incident on the further electroactive lens 601' is amplified. Thus, the first electroactive lens 601 and the further electroactive lens 601', which constitute the optical device 600, work together to provide polarization-independent amplified light.

[0095] For manufacturing purposes, it may be preferable that d1 and d2 are identical, or that the first electroactive lens 601 and the further electroactive lens 601' are substantially identical. This allows both elements to be formed using the same parameters in the production method. However, in some embodiments, d1 and d2 may be different (i.e., the blaze height may differ if the diffractive lens element is a Fresnel lens element). The blaze position of the Fresnel lens element of the first electroactive lens may even differ from the blaze position of the Fresnel lens element of the second electroactive lens. For example, the blaze height may differ slightly in both electroactive lenses when the blaze edges do not need to be precisely aligned. In a preferred embodiment, however, the refractive power of the first electroactive lens 601 is the same as that of the second electroactive lens 601'.

[0096] This third solution may offer advantages over the first and second solutions in that the intensity of light incident on the electroactive lenses 601 and 601' is substantially preserved, whereas the first and second solutions reduce the light intensity due to at least one polarizer. On the other hand, the units according to the first and second solutions can be relatively thinner than those according to the third solution. Depending on the application, any one of the first, second, or third solutions, or any combination thereof, may be applied.

[0097] Depending on the dimensions of the electroactive lens and the desired optical quality, the alignment layer (e.g., alignment layer 512) on top of the diffractive lens structure may also include pre-tilt, and the alignment layer has a preferred direction parallel to the linear alignment direction of the alignment layer on the first electrode. Introducing this pre-tilt generally reduces the value of the twist angle and increases the Morgan condition value, resulting in better optical performance.

[0098] Figure 9 is a schematic exploded view of the electroactive unit shown in Figure 8. For illustrative purposes, some components have been omitted. The first electroactive lens 701 and the further electroactive lens 711 are actually in optical communication.

[0099] A liquid crystal layer and a Fresnel lens structure (not shown) are disposed between the second electrode 707 and the first electrode 706. The distance between the second electrode 707 and the first electrode 706 is such that the liquid crystal disposed between them satisfies Morgan's condition (Equation 1). The first electrode 706 is provided with an alignment layer, schematically illustrated in 730, because the liquid crystal is aligned on the first electrode 706 parallel to the alignment direction 730. On the second electrode 707, the liquid crystal can be aligned according to a schematic pattern 731 due to the geometric shape of the first Fresnel lens structure (not shown). This schematic pattern may be a star shape starting from the center. Note that the alignment pattern on the second electrode 707 may differ, for example, by leaving the surface in contact with the liquid crystal close to the second electrode 707 (e.g., the Fresnel lens structure or the surface of electrode 707 or a layer provided on it (excluding the liquid crystal layer)). For example, due to rubbing of the surface near electrode 707, the arrangement on the electrode may resemble the orientation described with reference to Figure 3A.

[0100] A liquid crystal layer and a Fresnel lens structure (not shown) are disposed between a further second electrode 717 and a further first electrode 716. The distance between the further second electrode 717 and the further first electrode 716 is such that the liquid crystal disposed between them satisfies Morgan's condition (Equation 1). The further first electrode 716 is provided with an alignment layer schematically illustrated in 740. Since we want to obtain a uniform linearly polarized state at the further first electrode 716, the liquid crystal in the further electroactive lens 711 aligns on the further first electrode 716 parallel to the alignment direction 740. On the further second electrode 717, the liquid crystal can be aligned according to a schematic pattern 741 due to the geometric shape of a second Fresnel lens structure (not shown). It should be noted that the alignment pattern on the further second electrode 717 may differ, for example, by leaving a surface in contact with the liquid crystal near the further second electrode 717 (e.g., a Fresnel lens structure or the surface of electrode 717 or a layer provided on it (excluding the liquid crystal layer)). For example, due to rubbing of a surface near electrode 717, the alignment on the electrode may resemble the alignment described with reference to Figure 3A.

[0101] The alignment of the first alignment direction 730 with respect to a further first alignment direction 740 is orthogonal. Thus, if the first polarization is magnified by the first electroactive lens 701 and the second polarization direction (orthogonal to the first polarization direction) is not magnified, as described above, then the second polarization is magnified by the further electroactive lens 711 and the first polarization direction (orthogonal to the first polarization direction) is not magnified. Thus, both orthogonal polarization directions are magnified, and polarization-independent magnification is achieved.

[0102] Exemplary Embodiments In the following non-limiting embodiment, the exemplary lens diameter is 21 mm, i.e., the Fresnel lens structures (102, 502, 602, and 612, etc.) have diameters in the x and y directions, both of which are 21 mm.

[0103] In addition to the birefringence of the liquid crystal and the maximum torsion within the cell, the cell thickness is also an important parameter. It is crucial to design the spacer height above the Fresnel lens structure to be sufficiently high to ensure that the Morgan regime is achieved throughout the lens and that the thickness varies within the Fresnel blaze. In this way, the regime is preferably achieved even above the highest point of the blaze.

[0104] Using this regime, it is even possible to completely specify the linear alignment direction on the lens surface and use only circularly symmetric alignment resulting from a homeotropic alignment layer that is not rubbed or undergoes optical alignment treatment. Nevertheless, this may still be the case in some embodiments. Ultimately, there is a trade-off relationship between the height of the spacer on the lens, the degree to which the Morgan regime is achieved, and the switching voltage and speed of the lens. A lens cell with a certain spacer height and a (quasi) linear alignment direction on the lens surface (as in Figure 3A) has better optical quality than the same lens cell with a circularly symmetric alignment direction on the lens surface, because the former is deeper in the Morgan regime. A lens cell with a smaller spacer height than a lens cell with both (quasi) linear and circularly symmetric alignment directions may have similar optical quality, but the switching between the off and on states is faster.

[0105] The Hartmann test was used to inspect electroactive lenses. The quality of the electroactive lens was determined by using the contrast values ​​of a projection dot matrix (such as that shown in Figure 4). In the following example, the electroactive lens is divided into three concentric zones C1, C2, and C3 from the inside out. The average contrast value across the entire zone summarizes the quality within that zone.

[0106] (Example 1 (not based on this disclosure)) Hartmann inspection image of an electroactive lens in the off state with minimal Morgan regime. This electroactive lens has a blaze height of 16 microns, an additional spacer height of 3 microns, and liquid crystals with Δn=0.2. This electroactive lens was rubbed on both sides of the liquid crystal layer. Presumably, the LCs are linearly aligned on the top substrate, with the alignment direction on the bottom substrate (near the Fresnel lens structure), and the alignment approximates the alignment shown in Figure 3A. The off state result is illustrated in item 400 in Figure 4. In the on state, the image resembles item 401, where the non-magnified and magnified images overlap each other.

[0107] (Example 2 (not based on the present disclosure)) An electroactive lens in the off state with almost no Morgan regime (Figure 10A). The electroactive lens in this embodiment is substantially the same as the electroactive lens in Embodiment 1. Figure 10A illustrates the on state, supplemented by the contrast values ​​of the individual contrast values ​​of the dots in the Hartmann inspection. This result is obtained using a linear polarizer on the side of the upper substrate, parallel to the linear alignment direction of the upper substrate. As can be seen from the values ​​of C1, C2, and C3, the contrast values ​​are only moderate.

[0108] As can be derived from Figure 10A, the value of C1 is 0.553 and corresponds to region AA1, the value of C2 is 0.434 and corresponds to region AA2, and the value of C3 is 0.377 and corresponds to region AA3.

[0109] (Example 3 (According to the first solution of this disclosure)) An electroactive lens in the ON state in the Morgan regime (Figure 10B). This embodiment relates to an electroactive lens in the Morgan regime where the surface of the Fresnel lens structure is rubbed. The blaze height is 15 microns, with an additional spacer height of 10 microns, and Δn = 0.25. The electroactive lens is measured using a linear polarizer on the upper substrate side, parallel to the linear alignment direction of the opposing electrode substrate. This electroactive lens has the best contrast value (of Examples 2-4) because the maximum twist of the electroactive lens is limited.

[0110] As can be seen in Figure 10B, the value of C1 is 0.532, corresponding to region BA1; the value of C2 is 0.48, corresponding to region BA2; and the value of C3 is 0.453, corresponding to region BA3.

[0111] (Example 4 (According to the first solution of this disclosure)) An electroactive lens in the ON state in the Morgan regime (Figure 10C). This embodiment relates to an electroactive lens in the Morgan regime where the surface of the Fresnel lens structure was not rubbed. The blaze height is 15 microns, with an additional spacer height of 10 microns, and Δn = 0.25. The electroactive lens is measured using a linear polarizer on the upper substrate side, parallel to the linear alignment direction of the counter electrodes. The electroactive lens shows a better contrast value compared to the second embodiment, mainly in the outer C3 zone.

[0112] As can be seen in Figure 10C, the value of C1 is 0.562, corresponding to region CA1; the value of C2 is 0.487, corresponding to region CA2; and the value of C3 is 0.442, corresponding to region CA3.

[0113] From the above embodiments, it can be objectively and quantitatively demonstrated that the present disclosure improves the quality of electroactive lenses.

[0114] This disclosure is not limited to the specific embodiments described, and it should be understood that such embodiments may differ. Furthermore, since the scope of this disclosure is limited only by the accompanying claims, it should be understood that the terminology used herein is intended to describe only specific embodiments and is not intended to be restrictive. [Explanation of Symbols]

[0115] 101 Electroactive Lens 102 Diffractive lens structure 103 Boundary 104 First substrate 105 Second substrate 106 First electrode 107 Second electrode 108 Cavity 108a, 108b intermediate space 109 Spacer 110 Blaze 111 Aligned Layer 112 Second Alignment Layer 113 Nematic Liquid Crystal (LC) Layer 201 Surface 200, 210 surface 205 LCD 300 Lens Outer Diameter 301, 302, 303, 304, 305 Arrows 306 directions 310 Lens Outer Diameter 311 Second central orientation 312 Second lower-left orientation 313 Second lower-right orientation 314 Second upward orientation 315 Second upper right orientation 400 items 401 Enlarged image 402 dots 403 dots 501 Electroactive Lens 502 Diffraction structure Diffraction structures of 502 and 802 504 First substrate 505 Second substrate 506 First electrode layer 506 Aligned Layer 506, 806 First electrode 508 Cavity 508, 808 liquid crystal layer 510 Blaze 511 Aligned layer 512 Aligned Layer 513 Layer of LC material 560 Polarizer layer 561, 861 Aligned Layer 600 Optical Devices 601, 601' Electroactive Lens 602, 602' diffraction structure 604 First substrate 604, 604' First optically transparent substrate 605, 605' Second optically transparent substrate 606' electrode 611, 611' Aligned layer 612, 612' Aligned layer 613, 613' Liquid crystal layer 701 First electroactive lens 706 First electrode 707 Second electrode 711 Electroactive Lens 716 First electrode 717 Second electrode 730 Alignment direction 731 General Pattern 740 Alignment direction 741 General Pattern 801 Electroactive Lens 804 First substrate 806 First electrode 811 First Alignment Layer 860 Polarizer layer

Claims

1. An optical device for use in eyeglasses, wherein the optical device comprises a first electroactive lens for adjustable light transmission, and the first electroactive lens is - First and second optically transparent substrates, wherein the first and second optically transparent substrates extend generally parallel to each other and define the axial direction (z) and transverse direction (x, y), - A Fresnel lens structure is disposed between the first optically transparent substrate and the second optically transparent substrate on the side of the second optically transparent substrate, - A first optically transparent electrode formed on the first optically transparent substrate, and a second optically transparent electrode formed on the second optically transparent substrate or on the Fresnel lens structure, - A sealed cavity (108) between the first optically transparent substrate and the second optically transparent substrate, wherein the Fresnel lens structure and at least one LC layer of the nematic liquid crystal (LC) material are disposed within the sealed cavity, and the liquid crystals in the nematic liquid crystal (LC) material are generally aligned axially when off. The first optically transparent electrode has a contact surface that contacts the LC layer and comprises an alignment layer configured to linearly align the liquid crystals in the nematic liquid crystal material in a first horizontal direction in the ON state by introducing pretilt in the OFF state, and a sealed cavity (108), A polarizing element configured to block light having polarization in a second horizontal direction that is perpendicular to the first horizontal direction, Equipped with, The LC layer of the nematic liquid crystal material has a thickness (D) measured between the portion of the Fresnel lens structure closest to the first optically transparent electrode and the contact surface of the aligned layer on the first optically transparent electrode. The aforementioned thickness (D) is given by condition 1 < (πD(n ｅ -n ｏ ) / (φλ) < 200 is selected, n ｏ n is the ordinary refractive index of the LC layer, and ｅ An optical device in which is the anomalous refractive index of the LC layer, φ is the twist angle of the liquid crystal director of the LC layer, and λ is the wavelength of the light, with the wavelength λ being in the range of 350 nm to 750 nm.

2. The optical device according to claim 1, wherein the Fresnel lens structure, which is disposed between the first optically transparent substrate and the second optically transparent substrate on the side of the second optically transparent substrate, is disposed on the second optically transparent electrode.

3. The optical device according to claim 1 or 2, wherein the polarizing element includes a second electroactive lens stacked on the first electroactive lens, the second optically transparent substrate of the first electroactive lens includes an alignment layer having a contact surface in contact with the LC layer and configured to linearly align the liquid crystals in the nematic liquid crystal material in a first horizontal direction, the second optically transparent substrate of the second electroactive lens includes an alignment layer having a contact surface in contact with the LC layer and configured to linearly align the liquid crystals in the nematic liquid crystal material in a second horizontal direction, and the first horizontal direction is perpendicular to the second horizontal direction.

4. The optical device according to claim 3, wherein the first and second electroactive lenses are stacked together with each of the first optically transparent substrates facing each other, and / or the first and second electroactive lenses are stacked together such that the second optically transparent substrate is located on the outside of the stack and the first optically transparent substrate is located on the inside of the stack.

5. The optical device according to claim 3 or 4, wherein the first optically transparent substrate of the first electroactive lens and the first optically transparent substrate of the second electroactive lens are combined into a single common optically transparent substrate.

6. The optical device according to claim 3 or 4, wherein the refractive power of the first electroactive lens corresponds to the refractive power of the second electroactive lens.

7. The optical device according to any one of claims 3 to 6, wherein the Fresnel lens structure is a Fresnel lens structure, and the blaze axial height and / or blaze transverse position of the Fresnel lens structure of the first electroactive lens is at least partially different from the blaze axial height and / or blaze transverse position of the Fresnel lens structure of the second electroactive lens.

8. The optical device according to any one of claims 3 to 7, wherein the Fresnel lens structure of the first electroactive lens faces the Fresnel lens structure of the second electroactive lens.

9. The optical device according to any one of claims 3 to 8, wherein the first and second electroactive lenses are identical.

10. The optical device according to any one of claims 3 to 8, wherein the nematic liquid crystal material of the first electroactive lens is different from the nematic liquid crystal material of the second electroactive lens.

11. The optical device according to claim 1 or 2, comprising a linear polarizer configured to allow light having a first linear polarization to pass through and substantially block light having a second linear polarization perpendicular to the first linear polarization, wherein the linear polarizer is aligned such that the first linear polarization is substantially parallel to the alignment of the liquid crystals in the liquid crystal layer at a position near the first optically transparent electrode.

12. The optical device according to claim 11, wherein the first linearly polarized light is parallel to the first transverse direction (x), and the second linearly polarized light is parallel to the second transverse direction (y), which is perpendicular to the first transverse direction.

13. The optical device according to claim 11 or 12, wherein the linear polarizer includes one or more polarizing layers attached to the first optically transparent substrate and / or the first optically transparent electrode, the polarizing layers being attached to the alignment layer and aligned in the alignment direction of the alignment layer.

14. The optical device according to any one of claims 11 to 13, comprising at least one further polarizing layer formed on the surface of the Fresnel lens structure facing the LC layer, wherein the polarizing director of the at least one further polarizing layer is adjusted in different regions of the Fresnel lens structure to match the local liquid crystal director on the lens surface.

15. The optical device according to any one of claims 1 to 14, wherein the second optically transparent electrode comprises a further alignment layer configured to linearly align the liquid crystals in the nematic liquid crystal material in the first horizontal direction in the ON state by introducing pretilt in the OFF state.

16. The optical device according to any one of claims 1 to 15, wherein the first and / or second electroactive lens is configured to adjust the focusing or dispersion of light by changing the alignment of the liquid crystals in the LC layer when a voltage is applied to the optically transparent electrode.

17. The optical device according to any one of claims 1 to 16, wherein the first and / or second electroactive lens is configured to change the refractive power of the first and / or second electroactive lens by changing the refractive index of the LC layer in the transverse direction when a voltage is applied to the optically transparent electrode.

18. The optical device according to claim 16 or 17, configured to switch the first and / or second electroactive lens from an off state that substantially does not exhibit lensing action to an on state that exhibits lensing action when a voltage is applied to the optically transparent electrode of the first and / or second electroactive lens.

19. The optical device according to any one of claims 1 to 18, wherein in the off state, the liquid crystal in the nematic liquid crystal material is oriented such that the refractive index of the LC layer in the transverse direction substantially matches the refractive index of the Fresnel lens structure, and / or in the on state, the orientation of the liquid crystal is tilted such that the orientation is parallel to the alignment direction of the alignment layer.

20. The optical device according to any one of claims 1 to 19, wherein an alignment layer facing the LC layer is provided on the second optically transparent electrode.

21. The optical device according to any one of claims 3 to 10, wherein the optically transparent electrodes of the first and second electroactive lenses are electrically connected to switch the first electroactive lens and the second electroactive lens simultaneously.

22. The optical device according to any one of claims 1 to 21, wherein a plurality of spacers are arranged in the liquid crystal layer and extend in a direction perpendicular to the plane on which the second optically transparent electrode extends, and the spacers are formed on the Fresnel lens structure.

23. The optical device according to claim 22, wherein the spacer is configured to provide an additional height of between 1 and 20 μm when measured from the portion of the Fresnel lens structure closest to the second optically transparent substrate.

24. The optical device according to any one of claims 1 to 23, wherein the nematic liquid crystal material of the first and / or second electroactive lens has a birefringence Δn in the range of 0.15 to 0.

40.

25. The optical device according to any one of claims 1 to 24, wherein the optical device is configured to provide light transmission that is independent of polarization.

26. A lens unit for use in eyeglasses, wherein the lens unit comprises a first lens component, a second lens component, and an optical device according to any one of claims 1 to 25, and the electroactive lens is disposed between the first lens component and the second lens component.

27. Eyeglasses comprising a frame on which the first and second lens units according to claim 26, or the first and second optical devices according to any one of claims 1 to 25, are mounted.

28. Use of the optical device according to any one of claims 1 to 25.

29. A method for operating the optical device according to any one of claims 3 to 10, wherein an alternating voltage is applied to the first and second optically transparent electrodes of the first electroactive lens and the second electroactive lens stacked on the first electroactive lens to align the liquid crystal in a direction substantially perpendicular to the first and second optically transparent substrates.

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