WO2023067152A2

WO2023067152A2 - Method for producing an optical structure and optical structure

Info

Publication number: WO2023067152A2
Application number: PCT/EP2022/079400
Authority: WO
Original assignee: Meta Platforms Technologies, Llc
Priority date: 2021-10-21
Filing date: 2022-10-21
Publication date: 2023-04-27
Also published as: CN117940275A; WO2023067152A3

Abstract

A method for producing an optical structure (1), in particular a lens structure, comprising a substrate (2), an optical layer (4) and a buffer layer (3) arranged between the substrate (2) and the optical layer (4), is proposed, wherein the method comprises at least the following steps: - in a first step, the substrate (2) is provided, - in a second step, the buffer layer (3) is printed on the substrate (2), - in a third step, the optical layer (4) is printed on at least parts of the buffer layer (3), wherein the buffer layer (3) comprises a predetermined and preferably non-uniform thickness.

Description

DESCRIPTION

TITLE

Method for producing an optical structure and optical structure

BACKGROUND

The present invention relates to a method for producing an optical structure, in particular a lens structure, comprising a substrate, an optical layer and a buffer layer arranged between the substrate and the optical layer.

Such optical structures are known. Typically, the substrate is generally optically transparent and a lens is attached to it by means of the buffer layer. The buffer layer is applied to the substrate in advance and may act as an adhesive layer. The buffer layer may be applied by spraying, pouring, spreading etc. and comprises a constant, i.e. a uniform thickness along the extension of the substrate’s surface. A separately produced lens is then attached to the buffer layer to yield the optical structure.

In recent years, additive manufacturing has been employed to produce lenses. By means of additive manufacturing, e.g. three-dimensional printing, the lens may alternatively be produced directly on the substrate. Yet, as the lens material and the substrate material usually differ substantially, defects and/or inner tensions may arise, which deteriorates the structural integrity and/or the optical properties of the resulting optical structure.

Furthermore, without a buffer layer, the bonding between the lens and the substrate may be insufficient, whereas a buffer layer adds an undesirable thickness to the lens. For optical and aesthetic reasons, the total lens thickness should be as small as possible.

SUMMARY

Hence, it is a purpose of the present invention to provide a method for producing an optical structure, in particular a lens structure, comprising a substrate, an optical layer and a buffer layer arranged between the substrate and the optical layer, which does not show the described disadvantages of the prior art, but allows for an easy and quick production of an optical structure with high structural integrity and excellent optical properties. According to the present invention, this object is achieved by a method for producing an optical structure, in particular a lens structure, comprising a substrate, an optical layer and a buffer layer arranged between the substrate and the optical layer, wherein the method comprises at least the following steps:

- in a first step, the substrate is provided,

- in a second step, the buffer layer is printed on the substrate,

- in a third step, the optical layer is printed on at least parts of the buffer layer, wherein the buffer layer comprises a predetermined and preferably non-uniform thickness.

The method according to the invention advantageously allows for a very flexible production of an optical structure. Due to the non-uniform thickness of the buffer layer, its material may be saved at locations where the buffering properties are less needed, and reinforced, i.e. provided with a higher thickness, in areas where its properties are needed more. Hence, the overall thickness of the buffer layer may advantageously be minimized which allows for a very thin optical structure. The printing of the buffer layer is highly advantageous, because in this way, no additional production step is required and a good connection between the buffer layer and the substrate on the one hand and between the buffer layer and the optical layer on the other hand is provided. Advantageously, the buffer layer ensures a sufficient bonding between the optical layer and the substrate, prevents deformations of the optical layer due to different material properties, such as thermal coefficients, thermal expansion and/or different elasticities.

The embodiments described in conjunction with this subject matter of the present invention also apply to the further subject matters of the present invention and vice versa.

Preferably, within the context of the present invention, it is assumed that the substrate is generally flat and therefore comprises a substantially flat surface area. Of course, the substrate may as well comprise a curved surface. All features and explanations apply equivalently in this case. Preferably, the buffer layer is applied to at least a part of the substrate’s surface. Its extension in the plane of extension of the substrate surface will generally be denoted as a lateral extension. The thickness of all layers is preferably measured in a direction perpendicular to the surface area. The person skilled in the art acknowledges that this holds true for a generally curved surface area as well. Due to the non-uniformity of the buffer layer thickness, i.e. due to the fact that the thickness of the buffer layer is not constant at all points over its lateral extension, the thickness of the buffer layer is dependent on its location on the substrate. For the sake of simplicity, within the present application, in particular circular shapes are discussed, because in this case, the edges of the layers correspond to their outer circumference and their center is well defined. Yet, other and in particular more complex shapes are encompassed by the present invention as well. All corresponding explanation apply equivalently.

Within the context of the present invention, a layer is meant to denote at least one molecular and/or atomic layer. In particular, the printing of the second and third steps preferably comprises ejecting droplets of ink side by side and if applicable one above the other such as to built up a three-dimensional structure. The optical structure is therefore a three- dimensional structure intended to at least partially transmit light. All layers according to the present invention may therefore comprise one or more atomic and/or molecular layers by themselves. Light in particular may pass at least partially through the substrate and/or be emitted by the substrate and preferably passes through the buffer layer and the optical layer. Both layers form an optical system with a specific spatial pattern of refraction, diffraction, interference, transmission and/or absorption. In particular, the substrate may contribute to the optical properties of the optical structure or may merely serve as an (optically neutral) emitter or source for light. The optical structure is preferably intended for use with the visible spectrum. In particular, the optical structure may be a lens structure intended to focus and/or disperse a light beam using refraction. Preferably, the optical properties of the optical structure results from the combination of the optical properties of all layers.

Preferably, in order to serve an optical purpose, all applicable layers are at least partially optically transparent, in particular at least for a predetermined range of wavelengths.

According to the present invention, the buffer layer and the optical layer are produced by three-dimensional printing, in particular ink-jet printing, e.g. multi-jet printing, which is a known additive manufacturing technique. Additive manufacturing is well known and a particularly versatile and reliable production technique. In the sense of the present invention, printing, in particular three-dimensional printing, of a structure comprises building up the structure from layers of printing ink, preferably through a targeted placement of droplets of printing ink at least partially side by side and in vertically stacked layers. The droplets of printing ink are ejected from one or more nozzles of a print head, typically towards a substrate. Droplets of layers constituting a second and subsequent layers are at least partly ejected towards a previously deposited layer, such that the three-dimensional structure is built up layer by layer. The printing ink preferably comprises a translucent or transparent component. More preferably, the printing ink comprises at least one photo-polymerizable component. The at least one photo-polymerizable component is even more preferably a monomer that polymerizes upon exposure to radiation, e.g. ultra-violet (UV) light. The deposited droplets are preferably pin cured, i.e. partially cured, after deposition. In particular, the viscosity of at least one component of the printing ink is increased. Pin curing is preferably carried out after deposition of the respective droplet or after deposition of an entire or only part of a layer. Alternatively, pin curing is carried out at certain intervals, e.g. after printing of every second layer. Hence, in case of ink-jet printing, the second and third step according to the present invention preferably comprise a plurality of substeps, wherein at least one substep consists in depositing droplets of printing ink in accordance with a predetermined pattern, wherein at least one further substep consists in passively or actively curing the deposited droplets. In this context, passively curing preferably includes letting the droplets dry or cure over time, whereas actively curing preferably includes acting upon the deposited droplets, e.g. submitting the droplets to additional energy such as electromagnetic radiation, in particular UV light. The substeps are preferably carried out at least partially subsequently. In particular, the substeps more preferably at least partially overlap.

According to an advantageous embodiment of the present invention, the buffer layer is printed such that its thickness corresponds to a predetermined fraction of the optical layer’s thickness or vice versa, wherein the fraction is preferably constant over the lateral extension of the optical structure. More preferably, the thickness of the buffer layer corresponds to 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15% of the thickness of the optical layer at the same location, i.e. in particular above the buffer layer. It is herewith advantageously possible to provide additional buffering properties at locations where a higher amount of optical layer material is deposited. Furthermore, as the printing is performed according to a predetermined printing pattern, it is easy to determine the required shape of the buffer layer.

According to an advantageous embodiment of the present invention, the buffer layer is printed such that it comprises a thickness at its edges which is higher than a thickness at its center. This embodiment is highly advantageous, because it has been found that in particular at the edges of the optical structure, due to the boundary conditions, higher buffering properties are required.

According to an advantageous embodiment of the present invention, the buffer layer comprises a lateral extension which is larger than the lateral extension of the optical layer. It has been surprisingly found by the applicant that the buffer layer performs better if its diameter (i.e. generally its lateral extension) is larger than the one of the optical layer. This means in particular that according to this embodiment, there are locations where there is no optical layer material on top of buffer layer material.

According to an advantageous embodiment of the present invention, in a fourth step, a coating layer is printed on the optical layer and/or the buffer layer, preferably only at locations where the optical layer is deposited on the buffer layer. Such a coating layer is particularly advantageous, because it may prevent damage to the optical layer from outside influences. Furthermore, the coating layer preferably is designed such as to provide at least one of the following functions: color correction, UV protection and anti-reflection.

According to an advantageous embodiment of the present invention, the coating layer and/or the optical layer comprises a uniform thickness. In particular, the coating layer and/or the optical layer comprises a constant thickness over its entire lateral extension. More preferably, the coating layer comprises a lower thickness than the optical layer and/or the buffer layer. This is particularly advantageous, because in this way, the preferably merely protective coating layer does not substantially influence the optical properties of the optical structure.

According to an advantageous embodiment of the present invention, during the second step, the third step and/or the fourth step, different printing parameters and/or inks with different structural properties are used, wherein the printing properties preferably comprise at least one of droplet size, printing speed and droplet density, wherein more preferably the structural properties of the ink comprise at least one of glass transition temperature, elasticity, thermal coefficient, refractive index, dispersion, transmission coefficient, absorption, reflection coefficient and color, wherein in particular the ink used for the buffer layer comprises at least a lower glass transition temperature than the ink used for the optical layer. The person skilled in the art understands that a lower glass transition temperature means in particular that the layer is more flexible, but also more prone to damage. Hence, by printing the layers according to predetermined shapes and/or thicknesses and preferably with different inks, the mechanical and optical properties of the resulting optical structure can advantageously be tuned as desired.

According to an advantageous embodiment of the present invention, there is at least one region of the optical structure in which no buffer layer, optical layer and/or coating layer is printed. In particular, this means that the lens structure comprises a hole or cut-out. This is particularly advantageous in case the substrate comprises a waveguide. In this case, it may be desired to not print any layers on, e.g. the entry and/or exit openings of the waveguide. According to traditional techniques, material has to be removed subsequently, which may prove cumbersome. In particular by means of three-dimensional printing, an omission of one or more layers in a predetermined region is readily feasible.

According to an advantageous embodiment of the present invention, a layer is at least partially cured before a subsequent layer is printed. Preferably, a layer (e.g. the buffer layer and/or the optical layer) is substantially fully cured before the subsequent (e.g. the optical layer and/or the coating layer) is printed. This advantageously allows for a precise shaping of the optical structure. On the other hand, printing a layer above a not-fully cured layer may advantageously improve the bonding of the layers.

A further subject matter of the present invention is an optical structure, in particular produced by a method according to the present invention, wherein the optical structure comprises a substrate, a buffer layer and an optical layer, wherein the buffer layer is arranged between the substrate and the optical layer, wherein the buffer layer and the optical layer are produced by means of additive manufacturing, in particular three-dimensional printing, wherein the buffer layer comprises a predetermined and preferably non-uniform thickness.

For this subject-matter, the same advantages hold true as for the method according to the present invention, in particular an easily produced optical structure with high flexibility and excellent optical and structural properties may be provided, wherein the non-uniform thickness of the buffer layer advantageously allows for a precise tuning of the optical and mechanical properties of the optical structure, while allowing for a minimal total lens thickness.

According to an advantageous embodiment of the present invention, the substrate comprises glass and/or a polymer, in particular cellulose triacetate (TAC), cyclic olefin copolymer (COC), polyethylene terephthalate (PET), polycarbonate (PC) and/or Polymethyl methacrylate (PMMA), which is also known as acrylic glass or plexiglass. Those materials are well-known and tested materials for optical purposes and therefore advantageously allow for flexible optical structures.

According to an advantageous embodiment of the present invention, the substrate comprises a waveguide and/or a display, e.g. an LCD or OLED display. It is herewith advantageously possible to print an optical structure directly on top of a waveguide and/or display. According to an advantageous embodiment of the present invention, the optical structure further comprises a coating layer, wherein the coating layer is produced by means of additive manufacturing, in particular three-dimensional printing and is preferably deposited on the optical layer. Such a coating layer is particularly advantageous, because it may prevent damage to the optical layer from outside influences. Preferably, the coating layer comprises a uniform thickness, in particular the coating layer comprises a constant thickness over its entire lateral extension. More preferably, the coating layer comprises a lower thickness than the optical layer and/or the buffer layer. This is particularly advantageous, because in this way, the preferably merely protective coating layer does not substantially influence the optical properties of the optical structure.

According to an advantageous embodiment of the present invention, the coating layer provides shielding of the optical structure against ultraviolet radiation, color correction and/or anti-reflective properties. It is herewith advantageously possible to protect the optical structure from external damaging and/or deteriorating influences.

According to an advantageous embodiment of the present invention, the materials used for the buffer layer, the optical layer and/or the coating layer comprise at least one different parameter, wherein the parameter is at least one of glass transition temperature, elasticity, thermal coefficient, refractive index, dispersion, transmission coefficient, absorption, reflection coefficient and color, wherein in particular the material used for the buffer layer comprises at least a lower glass transition temperature than the material used for the optical layer. Hence, by printing the layers according to predetermined shapes and/or thicknesses and preferably with different inks, the mechanical and optical properties of the resulting optical structure can advantageously be tuned as desired.

According to an advantageous embodiment of the present invention, the buffer layer, the optical layer and/or the coating layer form a lens. It is herewith particularly advantageously possible to print a lens directly on a display and/or waveguide with sufficient mechanical stability due to the buffering properties of the buffer layer and with excellent optical properties.

According to an advantageous embodiment of the present invention, the optical structure comprises at least one region in which no buffer layer, optical layer and/or coating layer is printed, wherein the region is preferably arranged at an opening of the waveguide. Preferably, the region is vertically arranged over an entrance and/or exit opening of a waveguide. It is herewith advantageously possible to account for a waveguide already during the production of the optical structure. Hence, removing material of the optical structure, in particular of the buffer layer, the optical layer and/or the coating layer, is advantageously not necessary.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an optical structure produced by a method according to a first advantageous embodiment of the present invention;

Figure 2 shows an optical structure produced by a method according to a second advantageous embodiment of the present invention;

Figure 3 shows an optical structure produced by a method according to a third advantageous embodiment of the present invention;

Figure 4 shows an optical structure produced by a method according to a fourth advantageous embodiment of the present invention;

Figure 5 shows an optical structure produced by a method according to a fifth advantageous embodiment of the present invention; and

Figure 6 shows an optical structure produced by a method according to a sixth advantageous embodiment of the present invention.

DETAILED DESCRIPTION

The present invention will be described with respect to particular embodiments and with target to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and for illustrative purposes may not be drawn to scale.

Where an indefinite or definite article is used when referring to a singular noun, e.g. “a”, “an”, “the”, this includes a plural of that noun unless something else is specifically stated. Furthermore, the terms first, second, further and the like in the description and in the claims are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order, except for the method steps. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

In figure 1, an optical structure 1 produced by a method according to a first advantageous embodiment of the present invention is illustrated.

Here, the optical structure 1 is a circular lens. Of course, the explanations also apply to a different type of optical structure and/or different shapes. A circular lens is merely an exemplary embodiment chosen for its relative simplicity.

A substrate 2, which is e.g. made of glass and may be part of a display and/or a waveguide is provided in a first step. On the substrate 2 surface, which is here flat, a buffer layer 3 is printed, e.g. by means of three-dimensional multi-jet printing, in a second step. In particular, droplets of printing ink are ejected from a plurality of nozzles simultaneously and according to a predetermined pattern chosen by a control unit (not depicted). The nozzles are deposited side by side and one above the other in layers. Preferably, the buffer layer 3 comprises at least one layer of droplets. The entire buffer layer 3 is preferably made of droplets of the same ink, which is chosen such as to exhibit specific buffering properties. In particular, the buffer layer ink comprises a relatively low glass transition temperature and a high elasticity, therefore providing a relatively high flexibility albeit being prone to mechanical damage. Due to its high flexibility, the buffer layer 3 conforms to the substrate 2 surface and provides a good bonding. In order to allow for good performance of the resulting optical structure 1, the buffer layer ink is at least partially transparent and provides desired optical properties.

Here, the buffer layer 3 is printed such that it has a substantially constant thickness at the center and in adjacent areas, but comprises a higher thickness at the edge region. Thickness is in particular the extension of the buffer layer 3 in the y-direction, as denoted in figure 1 , i.e. perpendicular to the surface of the substrate. The thickness of the buffer layer 3 may increase in a radial direction linearly or exponentially, i.e. gradually, or it may increase stepwise, e.g. from a first value to a second value such that from radius 0 to a predetermined radius, the thickness comprises the first value and from the predetermined radius to the radially outer edges the thickness comprises the second value. The person skilled in the art understands that different combinations or variations are possible as well. In the case of the gradually increasing thickness, at least from the predetermined radius radially outwards, the thickness may increase according to any desired mathematical function. By printing the buffer layer, the total thickness of the optical structure may advantageously be minimized in particular when compared to prior art techniques.

After printing the buffer layer 3 and preferably after at least partially actively or passively curing the monomer of the buffer layer printing ink, e.g. by means of UV radiation, an optical layer 4, here a lens layer, is printed on top of the buffer layer 4 in a third step. This optical layer 4 is here provided as a substantially plano-concave layer, i.e. at the interface to the buffer layer 3, the optical layer comprises a substantially plane surface (and is slightly convex at its outer circumference) and towards the top of the lens, the optical layer 4 is concave. The resulting lens, here consisting of the buffer layer 3 and the optical layer 4, on top of the substrate is therefore a plano-concave lens.

The optical layer 4 is preferably printed using a different ink, e.g. an ink comprising a higher glass transition temperature than the buffer layer 3 ink. It is therefore more rigid and in particular allows for well-defined optical behavior. Notwithstanding the above, the ink used for printing the optical layer 4 is similar enough to the one used for printing the buffer layer 3, e.g. comprising the same color and substantially the same optical properties, that a good bonding is achieved between the buffer layer 3 and the optical layer 4. Furthermore, in particular the refractive indices of both inks are substantially identical such that the interface between both layers preferably does not count as an interface between different media with regard to refraction.

In figure 2, an optical structure 1 produced by a method according to a second advantageous embodiment of the present invention is illustrated. The second embodiment substantially corresponds to the first embodiment. Reference is therefore made to the explanations given with regard to the first embodiment. In the following, special attention is given to the differentiating features.

According to the second embodiment, the buffer layer 3 comprises a thickness which corresponds to a fixed percentage of the thickness of the optical layer 4 at a given location. E.g., the thickness of the buffer layer 3 may correspond to about 50% of the thickness of the optical layer 4 at the same given radius. In this way, higher buffering capacities are provided at locations where they are required due to a larger amount of optical layer 4 material. Optionally, in a further, here fourth, step, a protective coating layer 5 may be applied to the optical layer 4. This is indicated in figure 2. Here, the coating layer 5 is preferably printed on top of the optical layer 4, in particular with a uniform, i.e. constant, thickness.

The coating layer 5 may provide a color correction for the lens and/or it may provide UV protection, mechanical protection and/or anti-reflective properties.

In figure 3, an optical structure 1 produced by a method according to a third advantageous embodiment of the present invention is depicted. The third embodiment substantially corresponds to the first and/or second embodiment. Reference is therefore made to the explanations given with regard to those embodiments. In the following, special attention is given to the differentiating features.

In particular, this embodiment is substantially opposite to the first embodiment. Wherein according to the first embodiment, the thickness of the buffer layer 3 is constant and smaller over a large area and is higher at the circumferentially outer region, according to the third embodiment, the thickness of the buffer layer 3 is constant and relatively high at a large, radially outer region and smaller at the center. At the center, the optical layer 4 is very thin, hence, fewer buffering is required and therefore the buffer layer 3 only comprises a low thickness at the center of the lens.

It is important to mention that in particular a combination of the second and the third embodiment may be particularly advantageous.

Finally, in figure 4, an optical structure 1 produced by a method according to a fourth advantageous embodiment of the present invention is illustrated. The fourth embodiment substantially corresponds to the first, second and/or third embodiment. Reference is therefore made to the explanations given with regard to those embodiments. In the following, special attention is given to the differentiating features.

According to this fourth embodiment, the shape and/or curvature of the lens is substantially defined by the buffer layer 3. Here, the buffer layer 3 itself acts as a plano-concave lens. The optical layer 4 is printed on top of the buffer layer 3 with a relatively low and in particular constant thickness. It is important to mention that, although a coating layer 5 has only been described with regard to the second embodiment, the optical structures 1 according to the first, third and fourth embodiment may comprise such a coating layer 5 as well.

In figure 5, an optical structure 1 produced by a method according to a fifth advantageous embodiment of the present invention is depicted. The fifth embodiment substantially corresponds to the third embodiment. Reference is therefore made to the explanations given with regard to that embodiment. In the following, special attention is given to the differentiating features.

The fifth embodiment comprises an optical structure 1 with a buffer layer 3 comprising a constant thickness over the entire extension of the substrate 2 or optical structure 1. In contrast, the optical layer 4 comprises a varying thickness, such as according to the firs, second or third embodiment.

In figure 6, an optical structure 1 produced by a method according to a sixth advantageous embodiment of the present invention is illustrated. The sixth embodiment substantially corresponds to the first embodiment. Reference is therefore made to the explanations given with regard to that embodiment. In the following, special attention is given to the differentiating features.

While the form, thickness distribution etc. of the optical structure 1 is in this case substantially similar to the first embodiment (although it could as well be as illustrated in conjunction with the second, third, fourth or fifth embodiment), the optical structure 1 comprises a region, which is here depicted on the left in an exaggerated manner, in which there is no buffer layer 3, optical layer 4 and/or coating layer 5. This region is e.g. located (vertically) above an entrance opening of a waveguide.

Although the region is here depicted at an edge of the optical structure 1 , the person skilled in the art acknowledges that the region could as well be arranged at any location of the optical structure 1. In particular, the region could be provided at the center of the optical structure 1. In particular, the region is produced by not printing any droplets of material in that particular region. REFERENCE SIGN LIST

1 Optical structure

2 Substrate 3 Buffer layer

4 Optical layer

5 Coating layer x dimension parallel to substrate surface y dimension perpendicular to substrate surface

Claims

PATENT CLAIMS

1. Method for producing an optical structure (1), in particular a lens structure, comprising a substrate (2), an optical layer (4) and a buffer layer (3) arranged between the substrate (2) and the optical layer (4), wherein the method comprises at least the following steps:

- in a first step, the substrate (2) is provided,

- in a second step, the buffer layer (3) is printed on the substrate (2),

- in a third step, the optical layer (4) is printed on at least parts of the buffer layer (3), wherein the buffer layer (3) comprises a predetermined and preferably non-uniform thickness.

2. Method according to claim 1, wherein the buffer layer (3) is printed such that its thickness corresponds to a predetermined fraction of the optical layer’s (4) thickness or vice versa, wherein the fraction is preferably constant over the lateral extension of the optical structure (1).

3. Method according to any one of the preceding claims, wherein the buffer layer (3) is printed such that it comprises a thickness at its edges which is higher than a thickness at its center.

4. Method according to any one of the preceding claims, wherein the buffer layer (3) comprises a lateral extension which is larger than the lateral extension of the optical layer (4).

5. Method according to any one of the preceding claims, wherein in a fourth step, a coating layer (5) is printed on the optical layer (4) and/or the buffer layer (3), preferably only at locations where the optical layer (4) is deposited on the buffer layer (3).

6. Method according to any one of the preceding claims, wherein the coating layer (5) and/or the optical layer (4) comprises a uniform thickness.

7. Method according to any one of the preceding claims, wherein during the second step, the third step and/or the fourth step, different printing parameters and/or inks with different structural properties are used, wherein the printing properties preferably comprise at least one of droplet size, printing speed and droplet density, wherein more preferably the structural properties of the ink comprise at least one of glass transition temperature, elasticity, thermal coefficient, refractive index, dispersion, transmission coefficient, absorption, reflection coefficient and color, wherein in particular the ink used for the buffer layer (3) comprises at least a lower glass transition temperature than the ink used for the optical layer (4).

8. Method according to any one of the preceding claims, wherein there is at least one region of the optical structure (1) in which no buffer layer (3), optical layer (4) and/or coating layer (5) is printed.

9. Method according to any one of the preceding claims, wherein a layer is at least partially cured before a subsequent layer is printed.

10. Optical structure (1), in particular produced by a method according to any one of the preceding claims, wherein the optical structure (1) comprises a substrate (2), a buffer layer (3) and an optical layer (4), wherein the buffer layer (3) is arranged between the substrate (2) and the optical layer (4), wherein the buffer layer (3) and the optical layer (4) are produced by means of additive manufacturing, in particular three-dimensional printing, characterized in that the buffer layer (3) comprises a predetermined and preferably non-uniform thickness.

11. Optical structure (1) according to claim 10, wherein the substrate (2) comprises glass and/or a polymer, in particular cellulose triacetate, cyclic olefin copolymer, polycarbonate and/or polymethylmethacrylate.

12. Optical structure (1) according to any one of claims 10 or 11 , characterized in that the optical structure (1) further comprises a coating layer (5), wherein the coating layer (5) is produced by means of additive manufacturing, in particular three-dimensional printing and is preferably deposited on the optical layer (4).

13. Optical structure (1) according to any one of claims 10 to 12, characterized in that the substrate (2) comprises a waveguide and/or a display.

14. Optical structure (1) according to any one of claims 10 to 13, characterized in that the materials used for the buffer layer (3), the optical layer (4) and/or the coating layer (5) comprise at least one different parameter, wherein the parameter is at least one of glass transition temperature, elasticity, thermal coefficient, refractive index, dispersion, transmission coefficient, absorption, reflection coefficient and color, wherein in particular the material used for the buffer layer (3) comprises at least a lower glass transition temperature than the material used for the optical layer (4). Optical structure (1) according to any one of claims 10 to 14, characterized in that the coating layer (5) provides shielding of the optical structure (1) against ultraviolet radiation, color correction and/or anti-reflective properties. Optical (1) structure according to any one of claims 10 to 15, characterized in that the buffer layer (3), the optical layer (4) and/or the coating layer (5) form a lens. Optical structure (1) according to any one of claims 10 to 16, characterized in that the optical structure (1) comprises at least one region in which no buffer layer (3), optical layer (4) and/or coating layer (5) is printed, wherein the region is preferably arranged at an opening of the waveguide.