Lens with adjustable focal length through an alignable liquid crystal elastomer layer

Abstract

Spectacle lens, characterized in that it has a liquid crystal elastomer layer (LCE layer) whose anisotropic mesogen structure is reconfigurable, wherein the alignment of the mesogens is locally variable in order to produce an optically effective structure by means of which the effective focal length of the spectacle lens can be subsequently changed, and wherein the LCE layer is based on a reversibly cross-linkable network structure which enables multiple rearrangement of the mesogen alignment, and wherein the LCE layer has a transparency in the visible wavelength range suitable for spectacle use and is free from optical distortions, scattering effects or interference perceptible to the user.

Description

Technical FieldThe invention relates to optical devices, in particular correction glasses, the focal length of which can be adjusted in a targeted manner. This enables a subsequent adjustment of the vision without re-making the glasses.Prior ArtLenses are ground and manufactured individually, causing high production costs and requiring replacement of the entire lens with each change in vision. Systems such as electrically focusable lenses (e.g. liquid-based or liquid-crystal-based) exist, but are technically complex, expensive, energy-dependent and, owing to the many incorporated electronics, do not have the smoothness of normal eyeglasses.Mechanically adjustable eyeglasses with external adjusting wheels or other adjustable elements are also available, but have a bulky, design-related disturbing effect and differ greatly from the usual appearance of conventional eyeglasses.Technical Background and Problem SettingConventional spectacle lenses have hitherto been designed and manufactured permanently for a specific refractive power. Changes in vision or adaptations to individual needs have hitherto required a re-production of the glass or of the entire optical system. This is cost-intensive, resource-consuming and associated with long waiting times. In particular in the case of frequent changes (e.g. age-related, in the case of juveniles in the growth phase, after medical interventions or in the case of special occupation requirements), this leads to increased outlay for consumers and manufacturers.Object of the InventionThe aim is to provide an optical system whose focal length can be subsequently modified. The change of the focal length does not take place continuously during operation, but exclusively in the context of a targeted reconfiguration process, for example by an optician. The simplicity and simplicity of the spectacles should not be impaired. The solution approach is intended to be material- and cost-effective, compatible with common optical standards, and to enable rapid reconfiguration, for example by opticians. For this purpose, a thin layer of a liquid crystal elastomer (LCE) is connected to the spectacle lens. By controlled anisotropic molecular orientation of the mesogenics within the LCE layer, the refractive index of the overall system can be changed in a controlled manner. This alignment is preferably effected in a gradient-like or segmented manner in order to produce optically effective profiles.Solution of the ProblemThe spectacle lenses are provided with a layer of a functionalized liquid crystal elastomer (LCE), which has a location-dependent, in particular gradient-like or segmented, alignment of the mesogenics. By means of a targeted reconfigurable orientation of these mesogens and the optically anisotropic properties of the material, the refractive index can be locally changed-and therefore also the effective focal length of the optical system. The programmed orientation of the mesogenics remains securely frozen until the next conversion.In order to bond the LCE layer to the inner glass surface, there are various approaches, for example UV-curing adhesives or a wide variety of chemical methods.To ensure the functionality and longevity of the eyeglasses and the LCE layer, a protective layer is applied to the LCE layer.The LCE layer is based on a reversibly crosslinkable polymer network which allows multiple subsequent rearrangement of the molecular orientation. Various reversible chemical crosslinking mechanisms are suitable for this purpose, including thermally, chemically, photo- or mechanically activatable systems. Such mechanisms allow the original cross-linking structure to be temporarily released or weakened without permanently damaging the material.During this phase of reversion, the orientation of the mesogenics can be altered by external stimuli such as electric or magnetic fields, mechanical stretching, targeted irradiation (e.g. UV or IR) or by combined methods. By controlled control of the stimulus, a defined mesogenic structure can be produced which enables a targeted influencing of the refractive behavior in the visible wavelength range.After the external excitation is omitted and the system returns to stable ambient conditions (e.g. cooling or relaxation), the new alignment can be permanently fixed by refixing the network structure.The transparency of the layer is essential for the optical quality. This can be achieved by selecting suitable materials and by controlled processing and small layer thickness (e.g. in the range of less than to a maximum of a hundred micrometers). Clean mesogenic orientation and precise crosslinking also contribute to high light transmission. As a result, a very high transparency in the visible range can be produced without visible tint.In order 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, since the optical system can be used multiple times and no complete remanufacturing of the spectacle lenses is required with each change in vision. In addition, the costs of new racks or the remanufacturing of the new glasses into the old rack are dispensed with.• The system requires no moving parts, no additional operating elements such as wheels, adjusting motors or sliding mechanisms, and also no visible additional structure. As a result, the appearance of classic, optically smooth correction glasses is completely maintained.• High sustainability and resource conservation: Repeatable matching reduces waste and saves energy because only one glass produced once can be used for years.• Rapid and Customized Visual Strength Adaptation: The eyeglasses can be adapted to a new visual strength at the optician on site within a short time-without waiting time, shipping or new lens production.• Ideal for users with changing vision, for example in more recent persons or in the transitional age (for example beginning of age vision), in which a new correction would frequently be necessary. The need to buy new glasses every year is eliminated. Adjustments for optimum individual adjustment can also be made at short time intervals.• The spectacle lens according to the invention is also suitable in particular for applications in progressive glasses and augmented reality systems in which an adaptable optical correction with simultaneous transparency is required.• Compatible with existing spectacle frames and established manufacturing processes, thus facilitating market entry - both for manufacturers and for service providers.• In addition, new business models are obtained, for example for recurrent adaptation services at the optician.Exemplary EmbodimentOne possible embodiment of the invention comprises a spectacle lens made of an optically transparent material, for example CR-39 or polycarbonate, which is provided on the inner side facing the eye with a thin layer of a liquid crystal elastomer (LCE).The LCE used is preferably based on acrylate chemistry which has high transparency in the visible wavelength range. Acrylate-based liquid crystal elastomers reach transparency values of up to about 94% at a wavelength of 590 nm, which ensures largely unchanged light transmission of the optical system.The thickness of the LCE layer is typically about 20 to 40 microns. This thickness represents a compromise between sufficient optical efficiency (adjustment of the focal length) and the maintenance of high transparency and mechanical stability.To attach the LCE layer to the glass surface, the glass surface is preferably initially silanized in order to enable chemical bonding. An optically clear UV curable adhesive having a refractive index in the range of about 1.5 to 1.52 is then applied to provide a bubble free, durable and transparent bond.The refractive indices of the eyeglass lens, the LCE and the adhesive are chosen so that reflections at the interfaces are minimized. Typical refractive indices for CR-39 glass are about 1.50, for suitable LCEs in the range of about 1.52 to 1.54.To protect the sensitive LCE surface, a thin transparent protective layer is applied after application, for example a UV-curing clear lacquer or a sputter deposited silicon dioxide layer. This protective layer serves for mechanical protection and for increasing durability.The change in the refractive power takes place by a targeted reconfiguration of the mesogenic alignment. For this purpose, the spectacle lens is moderately heated, for example to temperatures in the range from about 60° C. to 90° C. During this process, the reversible crosslinking within the liquid crystal elastomer is temporarily dissolved, based on reversible chemical mechanisms such as Diels-Alder reactions. This dissolution of the network structure increases the mobility of the mesogenics, thus enabling a new orientation.While the LCE layer is in this reconfigurable state, an electric field is applied to selectively reorient the mesogenics. For this purpose, a structured electrode arrangement is used, wherein the electrodes have a graduated resistance which leads to a spatially varying electric field. This gradient-like field distribution also results in the alignment of the mesogens in a gradient manner over the surface of the spectacle lens, which enables a defined local adaptation of the refractive index and thus of the focal length.After the reconfiguration phase has ended, the glass is cooled back to ambient temperature. As a result of the falling temperature, the network structure is refixed within the elastomer, with the result that the new orientation of the mesogenics is stably frozen. The modified optical property is thus retained until reconfiguration is performed.By this method, the vision of the spectacle lens can be adjusted without the need for replacement of the lens.

Claims

Spectacle lens, characterized in that it has a liquid crystal elastomer (LCE) layer, the anisotropic mesogenic structure of which can be reconfigured, wherein the orientation of the mesogenics is locally variable in order to produce an optically effective structure, by means of which the effective focal length of the spectacle lens can be changed subsequently, and wherein the LCE layer is based on a reversibly crosslinkable network structure which enables multiple rearrangement of the mesogenic orientation, and wherein the LCE layer has a transparency in the visible wavelength range suitable for the use of the spectacle and is free of optical distortions, scattering effects or interference perceptible to the user.Eyeglass lens according to claim 1, characterized in that the LCE layer is designed such that its mesogenic orientation can be changed by external stimuli, the stimuli being from the group: electric fields, magnetic fields, mechanical strain or optical irradiation, the structure of the layer preferably being optimized for electric fields.Spectacle lens according to one of the preceding claims, characterized in that the LCE layer is designed such that, in conjunction with a structured electrode arrangement whose structure generates locally varying field strengths, it enables a gradient-like or segmented alignment of the mesogens.Eyeglass lens according to any of the preceding claims, characterized in that the network structure of the LCE layer is designed such that it can be temporarily transferred to a reconfigurable state by thermal, photoactive or chemical stimuli in order to enable readjustment of the mesogens, and that the structure experiences self-healing or re-crosslinking after removal of the stimulus, wherein in the case of thermal stimuli the reversion is preferably effected by a Diels-Alder reaction.Spectacle lens according to one of the preceding claims, characterized in that the LCE layer has a thickness which is designed for a focal length change suitable in spectacle use with simultaneously high light transmission in the visible spectrum.Spectacle lens according to one of the preceding claims, characterized in that, for example, an acrylate-based liquid crystal elastomer is used to achieve the optical transparency within the LCE layer, as a result of which high light transmission and low scattering effects in the visible range are achieved.Spectacle lens according to one of the preceding claims, characterized in that the LCE layer is connected to the lens surface by an optically clear adhesive.Spectacle lens according to one of the preceding claims, characterized in that the LCE layer has a covering, transparent protective layer which gives mechanical protection and weathering resistance.Spectacle lens according to one of the preceding claims, characterized in that the refractive indices of the spectacle lens, of the adhesive, of the protective layer and of the LCE layer are matched to one another such that reflections at the boundary surfaces are minimized and a high transmittance is achieved.Spectacle lens according to one of the preceding claims, characterized in that it is constructed in such a way that a specific change of the mesogenic orientation is made possible by external stimuli within the scope of a expert application, in particular by an optician or by a company adapted thereto.