Lens with adjustable focal length through at least one alignable liquid crystal elastomer layer

Abstract

Spectacle lens, characterized in that it has at least one layer of a transparent liquid crystal elastomer (LCE layers), • where each LCE layer has a reconfigurable anisotropic mesogen structure, • each LCE layer is surrounded by at least one alignment layer which determines the orientation of the mesogens along a fixed azimuth direction, • where polarization independence is ensured by either providing two LCE layers with orthogonally offset azimuth axes or dividing a single LCE layer into segments whose main azimuth axes are alternately orthogonally offset or using a retardation foil for the necessary phase shift, • wherein the mesogens within the LCE layers are locally variably alignable to produce an optically effective phase profile - which preferably represents a Fresnel phase profile - by means of which the effective focal length of the spectacle lens is reconfigurable, • wherein each LCE layer is based on a reversibly cross-linkable polymer network that allows multiple rearrangement of the mesogen alignment, and wherein the LCE layers together have high transparency in the visible wavelength range and the ophthalmic lens is free from perceptible optical distortions, scattering effects or interference, regardless of the polarization of the incident light.

Description

Technical area

[0001] The invention relates to optical devices, in particular prescription spectacles, whose focal length can be specifically adjusted. This allows for subsequent adjustment of the prescription without remaking the lenses. State of the art

[0002] Eyeglass lenses are individually ground and manufactured, which results in high production costs and requires the entire lens to be replaced every time your prescription changes. Furthermore, because prescriptions change gradually, glasses often no longer fully meet your current visual needs months before the next change, leaving you with a suboptimal prescription over this period. Systems such as electrically focusable lenses (e.g., liquid-based or liquid crystal-based) exist, but are technically complex, expensive, energy-dependent, and lack the simplicity of normal eyeglasses due to the large amount of built-in electronics. Mechanically adjustable glasses with external adjustment wheels or other adjustable elements are also available, but they appear clunky, disruptive in design terms and deviate significantly from the usual appearance of classic glasses. Technical background and problem

[0003] Conventional ophthalmic lenses have traditionally been designed and manufactured for a specific refractive power. Changes in prescription or adjustments to meet individual needs require the lens or the entire optical system to be remade. This is costly, resource-consuming, and associated with long waiting times. This leads to increased costs for both consumers and manufacturers, particularly in cases of frequent changes (e.g., due to age, for adolescents during growth, after medical procedures, or for specific occupational requirements). Object of the invention

[0004] The goal is to provide an optical system whose focal length can be subsequently modified. The focal length is not changed continuously during operation, but exclusively as part of a targeted reconfiguration process, for example by an optician. The simplicity and plainness of the glasses should not be compromised. The solution should be material- and cost-efficient, compatible with common optical standards, and enable rapid reconfiguration, for example by opticians. For this purpose, at least one thin layer of a liquid crystal elastomer (LCE) is combined with the lens. By specifically controlling the anisotropic molecular alignment of the mesogens within the LCE layers, the refractive index of the entire system can be specifically modified and the polarization sensitivity of the anisotropic medium can be controlled. Solution to the task

[0005] This task is solved by a lens structure featuring at least one reconfigurable layer made of a liquid crystal elastomer (LCE). By temporarily removing the cross-linking and subsequently re-fixing, the molecular alignment of the mesogens can be locally altered; the associated refractive index shift modulates the focal length of the entire system. A Fresnel-like phase profile is provided either by the LCE layer itself or by a separately structured substrate surface. Various methods are possible for implementation, including, but not limited to, electrically, optically, mechanically, or chemically induced pattern formation.

[0006] To compensate for the polarization sensitivity of an anisotropic LCE, two measures can be considered: (i) a stack arrangement of at least two LCE layers with different, preferably orthogonal azimuth axes or (ii) a single layer in which adjacent segments have alternating different azimuth directions or (iii) a retardation film.

[0007] To ensure that the mesogens are reproducibly fixed in their 0° or 90° direction during each reconfiguration, each LCE layer contains at least one alignment layer. The alignment layers define a fixed azimuth axis (0° or 90°) across the entire LCE thickness. During reconfiguration, the mesogens can be preferentially tilted along this axis or their degree of order can be changed without deviating from the specified direction.

[0008] To ensure the functionality and longevity of the glasses and the LCE layer, protective layers are applied to the LCE layer.

[0009] The LCE layer is based on a reversibly cross-linkable polymer network that allows for multiple subsequent rearrangements of the molecular alignment. Various reversible chemical cross-linking mechanisms are possible for this, including thermally, chemically, photo-, or mechanically activated systems. Such mechanisms make it possible to temporarily dissolve or weaken the original cross-linking structure without permanently damaging the material.

[0010] During this reversible phase, the orientation of the mesogens can be altered by external stimuli such as electric or magnetic fields, mechanical stretching, targeted irradiation (e.g., UV or IR), or by a combination of both. By controlling the stimulus, a defined phase structure can be created, allowing for the targeted manipulation of the refractive behavior in the visible wavelength range.

[0011] After the external stimulus has been removed and stable environmental conditions have been returned (e.g. cooling or relaxation), the new alignment can be permanently fixed by refixing the network structure.

[0012] The transparency of the layer is crucial for optical quality. This can be achieved by selecting suitable materials, controlled processing, and low layer thicknesses (e.g., in the range of a few to a maximum of one hundred micrometers). Clean mesogen orientation and precise cross-linking also contribute to high light transmittance. This allows for very high transparency in the visible range without any visible tint.

[0013] To avoid reflections at the interface, the refractive indices of the spectacle material and the elastomer should be similar. Advantages of the invention • Significant reduction in production and material costs, as the optical system can be reused multiple times, eliminating the need to completely remake the lenses every time a prescription changes. Furthermore, the costs for new frames or reworking the new lenses into the old frame are eliminated. • Complete focusing of the light without loss of intensity or contrast. • The system requires no moving parts, no additional controls such as dials, actuators, or sliding mechanisms, and no visible additional structure. This fully preserves the appearance of a classic, optically simple pair of prescription glasses. • High sustainability and resource conservation: The repeatable adaptation reduces waste and saves energy, as a glass produced only once can be used for years. • Fast and customer-friendly prescription adjustment: Glasses can be adjusted to a new prescription at your local optician within a short time - without waiting time, shipping or new lens production. • Ideal for users with changing vision, such as younger people or those in transition (e.g., those at the beginning of presbyopia), who would require frequent correction. This eliminates the need to buy new lenses every year. Adjustments can also be made at short intervals for optimal individual fit. • The spectacle lens according to the invention is particularly suitable for applications in progressive lenses and augmented reality systems where adjustable optical correction combined with transparency is required. • Compatible with existing eyeglass frames and established manufacturing processes, making market entry easier for both manufacturers and service providers. • In addition, new business models are emerging, for example for recurring adjustment services at the optician. Example 1

[0014] One possible embodiment of the invention comprises a spectacle lens made of an optically transparent material, such as CR-39 or polycarbonate, which is provided with two thin layers of a liquid crystal elastomer (LCE) on the inner side facing the eye. The two layers are arranged orthogonally to each other to compensate for polarization sensitivity.

[0015] The LCE used is preferably based on an acrylate chemistry that exhibits high transparency in the visible wavelength range. Acrylate-based liquid crystal elastomers achieve transparency values ​​of up to approximately 94% at a wavelength of 590 nm, ensuring largely unchanged light transmission of the optical system.

[0016] The thickness of the LCE layer is approximately 15 to 30 micrometers. This thickness represents a compromise between sufficient optical efficiency (focal length adjustment) and maintaining high transparency and mechanical stability.

[0017] The liquid crystal elastomer (LCE) layers are each sandwiched between two alignment layers and fixed therein. These alignment layers can be applied directly to the lens substrate, for example, by spin coating.

[0018] To reliably compensate for the volume swelling of the LCE layer that occurs during reconfiguration, the acrylate prepolymer is mixed with low concentrations of fillers such as SiO2 nanoparticles (10-50 nm). This significantly reduces the thermal expansion coefficient while maintaining high transmission in the visible spectrum. The cell edges are sealed with a transparent silicone or PU adhesive, whose elasticity allows slight yielding upon heating, thus preventing excessive mechanical stress on the alignment and substrate layers. Optionally, structured buffer zones and flexible alignment substrates can be used to further increase system compliance without sacrificing optical precision.

[0019] To protect the sensitive surface, a thin transparent protective layer, such as a UV-curing clear coat or a sputter-deposited silicon dioxide layer, is applied after application. This protective layer provides mechanical protection and increases durability.

[0020] The change in refractive power is achieved by a targeted reconfiguration of the mesogen alignment. For this purpose, the lens is moderately heated, for example, to temperatures in the range of approximately 60 °C to 90 °C. During this process, the reversible cross-linking within the liquid crystal elastomers is temporarily dissolved, based on reversible chemical mechanisms such as Diels-Alder reactions. This dissolution of the network structure increases the mobility of the mesogens, enabling a new orientation. Depending on the polymer composition and the reaction conditions, approximately 10 complete cycles can be achieved.

[0021] While the LCE layers are in this reconfigurable state, an electric field is applied to specifically realign the mesogens. For this purpose, a structured electrode array is used, whereby the electrodes can be controlled pixel by pixel or have a graduated resistance that results in a spatially varying electric field. This controlled field distribution causes the mesogens to align in a Fresnel-like manner across the surface of the lens, enabling a defined local adjustment of the refractive index and thus the focal length. To control both LCEs equally during this process and maintain their orthogonal alignment to each other, a thin transparent electrode - such as ITO - is placed between the two layers, which allows each LCE layer to be controlled individually. Alternatively, both LCE layers can be aligned with the same electric field, without an intermediate electrode.

[0022] After the reconfiguration phase is complete, the glass is cooled back to ambient temperature. The decreasing temperature refixes the network structure within the elastomer, thus stably freezing the new alignment of the mesogens. The modified optical property is thus retained until another reconfiguration is performed.

[0023] The achievable diopter change is about 2 diopters, which is more than sufficient for the intended application.

[0024] The prescription of the lens can be adjusted without the need to replace the lens. Example 2

[0025] In contrast to Example 1, only one LCE layer is used to generate the Fresnel phase profile, with neighboring segments having alternating orthogonal azimuth directions, thus ensuring polarization independence. As in Example 1, thermal stimulation can loosen the network structure, and an electric field causes a new orientation of the mesogens.

[0026] These are also covered by at least one alignment layer to ensure long-term stability and a uniform azimuth axis. Example 3

[0027] In contrast to Example 1, in this example, the Fresnel phase profile is engraved as a micro-relief directly into the glass surface facing the eye, or rather, imprinted using a nanoimprint. A homogeneous, monodomain-oriented LCE layer is applied over the relief, which serves to fine-tune the focal length electrically; the basic focus is maintained by the fixed relief. A collective change in the alignment of the mesogens results in a new focal length during reconfiguration.

[0028] In this design, due to the monodomain alignment of the mesogens, the polarization independence can be further implemented by a retardation film.

[0029] In this version, too, at least one alignment layer is included to ensure long-term stability and a uniform azimuth axis. Example 4

[0030] In contrast to Example 1, a linearly polarized laser creates ring-shaped bright / dark zones on the LCE layer. In the bright rings, methyl red molecules absorb light, isomerize from trans to cis, and align perpendicular to the polarization direction. The directors, originally at 0°, locally tilt to 90°. The dark rings remain unchanged. This creates a binary 0° / 90° pattern in the LC volume, which imparts a phase difference to neighboring zones, thus forming a Fresnel zone plate.

[0031] In this example, at least one alignment layer is combined with the LCE layer so that all mesogens are initially parallel.

[0032] Optionally, an electric field can be applied for adjustment, tilting all directors a few degrees out of plane. This allows the effective refractive index to be changed and the focal length to be fine-tuned without losing the basic optical pattern. If the prescription needs to be significantly changed later, the optician briefly heats the cell to approximately 70°C; the dye relaxes into the trans form, the 0° / 90° profile disappears, and a new Fresnel interference pattern can be irradiated with a modified zone geometry. After cooling, the new focal length remains permanently fixed until it is rewritten again. The system thus combines maskless light patterning with electro-optical fine control.

Claims

[1] spectacle lens, characterized by that it has at least one layer of a transparent liquid crystal elastomer (LCE layers), • where each LCE layer has a reconfigurable anisotropic mesogen structure, • each LCE layer is surrounded by at least one alignment layer which determines the orientation of the mesogens along a fixed azimuth direction, • where polarization independence is ensured by either providing two LCE layers with orthogonally offset azimuth axes or dividing a single LCE layer into segments whose main azimuth axes are alternately orthogonally offset or using a retardation foil for the necessary phase shift, • wherein the mesogens within the LCE layers are locally variably alignable to produce an optically effective phase profile - which preferably represents a Fresnel phase profile - by means of which the effective focal length of the spectacle lens is reconfigurable, • wherein each LCE layer is based on a reversibly cross-linkable polymer network that allows multiple rearrangement of the mesogen alignment, and wherein the LCE layers together have high transparency in the visible wavelength range and the ophthalmic lens is free from perceptible optical distortions, scattering effects or interference, regardless of the polarization of the incident light. [2] Spectacle lens according to claim 1, characterized bythat the polarization independence is achieved by either providing two LCE layers with main orientation axes rotated by approximately 90° with respect to one another, each of these layers focusing one of the two orthogonal polarization components, or by dividing a single LCE layer into segments whose main orientation axes are alternately offset by approximately 90° with respect to one another, so that each segment focuses a corresponding polarization component, and the combined effect of the layers or segments brings about a complete, polarization-independent change in the refractive index of the spectacle lens. [3] Spectacle lens according to any preceding claim, characterized bythat the reversible polymer network structure of the LCE layers is loosened by applying an external stimulus (e.g. thermally, photo- or chemically activated), so that the mesogens can then be specifically realigned along the fixed alignment axes into the desired phase profile. [4] Spectacle lens according to any preceding claim, characterized by that the mesogen alignment of the LCE layers can be changed by external stimuli, the stimuli being selected from the group consisting of electric fields, magnetic fields, mechanical strain or optical irradiation, preferably electric fields, [5] Spectacle lens according to any preceding claim, characterized bythat in order to achieve polarization independence, two LCE layers are stacked on top of each other with azimuth axes that are offset by orthogonal axes, the layer structure of which is designed in such a way that a homogeneous electric field can be applied over both LCE layers, or a transparent electrode layer (e.g. ITO) is arranged between the two LCE layers, by means of which each LCE layer can alternatively be controlled individually in the reconfiguration process, or that polarization independence is achieved by a single LCE layer whose surface is divided into segments with alternating orthogonal azimuth directions. [6] Spectacle lens according to one of the preceding claims, characterized by that the LCE layer is designed in such a way that, in conjunction with a structured electrode arrangement whose structure enables locally varying field strengths, it enables a gradient-like, pixelated or segmented alignment of the mesogens. [7] Spectacle lens according to any preceding claim, characterized by that the phase profile is already imprinted as a fine micro-relief on a substrate surface. Above this layer lies an LCE layer, whose mesogens are finely adjusted during reconfiguration to adjust the focal length without changing the basic profile. [8] Spectacle lens according to any preceding claim, characterized by The desired phase profile is not mechanically or electrically predetermined, but rather generated by photochemical reorientation of the mesogens in the LCE layer. A spatially structured exposure to polarized light locally tilts the mesogens into different azimuth directions, and this new orientation remains stable after exposure until another photochemical reconfiguration occurs. Electrical reorientation of the mesogens is optional. [9] Spectacle lens according to any preceding claim, characterized bythat the reversible polymer network is based, for example, on Diels-Alder reaction, whose re-crosslinking is possible at low temperatures, using an acrylate LCE which has a high transparency in the visible range. [10] Spectacle lens according to any preceding claim, characterized by that the glasses have covering, transparent protective layers that provide mechanical protection and weather resistance. [11] Spectacle lens according to one of the preceding claims, characterized by that the following measures are provided to compensate for thermally induced stresses: a) the selection of an LCE material with a low thermal expansion coefficient, b) the use of a flexible, transparent adhesive to seal the layer system, c) the introduction of low concentrations of fillers to compensate for the thermomechanical properties. d) the use of a flexible substrate as a base for the alignment layers e) the use of structured buffer zones on or around the alignment layers