TITLE

Method for producing a three-dimensional optical structure and three-dimensional optical structure

BACKGROUND

The present invention relates to a method for producing a three-dimensional optical structure, in particular an ophthalmic lens, wherein in a first step a base structure is printed by depositing droplets of a first printing ink at least partially side by side and preferably at least partially on top of each other. The optical structure shall comprise an anti-reflective coating.

Printed three-dimensional optical structures such as ophthalmic lenses are well known from the prior art. In recent years, with the rise of rapid prototyping and in particular additive manufacturing, it has become clear that such optical structures can easily be produced by three-dimensional printing. An advantage of three-dimensionally printed optical structures and in particular ophthalmic lenses is their variability and versatility, especially with regard to individual customizability and the possibilities of special uses. Not only is it easy to customize optical functions of the optical structures during their production, but the optical structures may also be specially adapted for the integration of functional components. For example, it is conceivable that the three-dimensional optical structure is used as the lens in a pair of glasses through which information is displayed to the wearer, which is the case in so-called augmented reality glasses.

For reasons of safety and/or comfort, it is desirable that the lens comprises an anti-reflective coating. Typically, such coatings are applied in a separate production step after printing (and curing) of the optical structure is finished. The optical structures, e.g. the lens, is transferred to another apparatus and the anti-reflective coating is applied e.g. by means of spin coating, dip coating, physical vapor deposition or chemical vapor deposition. These are all well-known techniques.

Due to the underlying physical principles of anti-reflective coatings, their thickness is usually very small, i.e. in the order of 100nm to 200 nm. Yet, due to technical limitations, in particular due to the droplet size of printing ink, a three-dimensionally printed layer comprises a thickness which is usually rather in the order of pm.

Hence, with currently known techniques, three-dimensional printing of an anti-reflective coating is not possible.

SUMMARY

Hence, it is a purpose of the present invention to provide a method for producing a three- dimensional optical structure, in particular an ophthalmic lens, comprising a printed anti- reflective coating.

According to the present invention, this object is achieved by a method for producing a three- dimensional optical structure, in particular an ophthalmic lens, wherein in a first step a base structure is printed by depositing droplets of a first printing ink at least partially side by side and preferably at least partially on top of each other, wherein in a second step an anti- reflective coating is printed in at least a region of a surface of the base structure by depositing droplets of a second printing ink at least partially side by side, wherein the second printing ink is different from the first printing ink, wherein the second printing ink comprises at least a first component and a second component, wherein the first component is a structural component and the second component is a solvent, wherein in a third step the solvent is evaporated, wherein in an optional fourth step the anti-reflective coating is cured.

The method according to the invention advantageously allows for the production of an optical structure, in particular an ophthalmic lens, comprising an anti-reflective coating completely by means of three-dimensional printing. Hence, the production of the optical structure is quick and may completely be performed in the same apparatus, thus preventing possible damages sustained during transport.

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

The person skilled in the art acknowledges that as the second component is at least substantially evaporated in the third step, it could be said that in the optional fourth step the remaining second printing ink is cured yielding the anti-reflective coating. This means in particular that the anti-reflective coating obtains its anti-reflective properties by the third step of evaporating the second component.

The person skilled in the art understands that usually, in three-dimensional printing, the resulting structure comprise one or more, preferably a plurality of, layers of printing ink. Within the context of the present invention, the anti-reflective coating is preferably an anti- reflective coating layer in the broader sense that it is a layer applied on at least parts of the base structure. While in particular the anti-reflective coating may be printed in the second step as one or more layers of printing ink, due to the evaporation during the third step, the anti-reflective coating is not identifiable as a layer in the sense of vertically stacked layers of printing ink, but rather a layer in the broader sense of a layer covering the base structure surface at least partially. Therefore, the term “layer” preferably comprises different meanings before and after carrying out the third step.

Preferably, the third step involves waiting a predetermined time, until the second component, i.e. the solvent, evaporates by itself. More preferably, the evaporation is supported, e.g. by directing heat and/or an air flow to the surface of the anti-reflective coating.

Preferably, the anti-reflective coating comprises, at least prior to printing and/or curing at least one further component. This may be an additive, a suspension fluid and/or a color component.

Preferably, the anti-reflective coating comprises a uniform thickness, in particular a constant thickness over its entire lateral extension. It is thus advantageously possible to allow for uniform optical, in particular (anti-)reflective, properties of the optical structure.

According to a preferred embodiment, the anti-reflective coating is also a hard coating, which in particular prevents damage to the optical structure from external influences. More preferably, the coating comprises a uniform thickness, in particular the coating comprises a constant thickness over its entire lateral extension. This is particularly advantageous, because in this way, the anti-reflective coating does not substantially influence the optical power of the optical structure. Even more preferably, the coating comprises a lower thickness than the base structure. Additionally or alternatively, the coating provides shielding against e.g. ultraviolet radiation and/or color correction. It is herewith advantageously possible to protect the optical structure or the eye of a user from external damaging and/or deteriorating influences, in particular mechanical, chemical or radiation influences. The optical structure is a three-dimensional structure preferably intended to at least partially transmit light. The optical structure is more preferably intended for use with the visible spectrum. Preferably, the optical structure is at least partially optically transparent, in particular at least for a predetermined range of wavelengths, such as the visible spectrum. In particular, the optical structure may be a lens and even more preferably an ophthalmic lens. Ophthalmic lenses comprise concave, convex, biconcave, biconvex, plano-concave, planoconvex and meniscus lenses. Ophthalmic lenses in the sense of the present invention also comprise multifocal lenses as well as gradient-index lenses. Ophthalmic lenses comprise in particular spectacle lenses or other lenses that are used in eyewear.

In the context of the present invention, printing of an optical structure comprises building up the structure from layers of printing ink. These are obtained through a targeted placement of droplets of printing ink at least partially side by side. The droplets of printing ink are preferably ejected from nozzles of a print head, typically in a substantially vertical direction towards a substrate or another suitable surface, though ejecting at an angle is possible as well, wherein the print head is controlled by a controller according to predetermined print data. The print data preferably comprises slicing data, wherein in particular, a predetermined shape of the optical structure is converted into print data by dividing it into a plurality of layers, i.e. slices, which are at least partially stacked upon each other. Droplets of layers constituting the following layer are at least partly ejected towards the previously deposited layer, such that the three-dimensional structure is built up layer by layer. Preferably, the three-dimensional printing is a multi-jet printing. This means in particular that the printing system used for carrying out the method according to the present invention comprises a three-dimensional printer which preferably is a multi-jet printer.

According to a preferred embodiment of the present invention, the optical structure, in particular the base structure and/or the anti-reflective coating, is at least partially printed in a multi-pass printing mode, wherein preferably a layer printed in a multi-pass printing mode comprises multiple sublayers which are printed in subsequent sublayer printing steps, wherein at least one sublayer printing step is followed by an at least partial curing step. This allows in a very advantageous manner for a highly flexible and customizable production of an optical structure. A multi-pass printing mode preferably comprises the printing head making several passes, in particular back and/or forth, wherein during each pass, a sublayer of the layer is printed. Each sublayer may be subjected to a separate curing step, only the completed layer may be subjected to a curing step or a curing step is performed in regular or irregular intervals, e.g. as soon as a predetermined amount of sublayers are printed and/or after a predetermined time after printing has passed. Alternatively or additionally, at least one layer of the base structure and/or at least one layer of an anti-reflective coating is printed in a multi-pass printing mode, wherein at least one further layer is printed in a non-multi-pass printing mode. By including a multi-pass printing mode, it is advantageously possible to correct errors in the optical structure. This process is detailed in the previous application EP 3722073 A1 of the present applicant. The disclosure of the aforementioned application, at least regarding the application of a multi-pass printing mode for approximation error reduction, is incorporated in the present disclosure.

Preferably, the first printing ink and/or the second printing ink comprises a translucent or transparent component. More preferably, the first and/or second printing ink, in particular the first component, comprises at least one polymerizable component, in particular a photo- polymerizable and/or thermo-polymerizable component. The at least one polymerizable component is most preferably a monomer and/or an initiator that polymerizes upon exposure to radiation, e.g. ultra-violet (UV) and/or infrared (IR) light, and/or upon exposure to heat. The deposited droplets are preferably pin cured, i.e. partially cured, after deposition. More preferably, the viscosity of the at least one deposited droplet of the (first and/or second) printing ink is increased. Pin curing is most preferably carried out after deposition of the respective droplet or after deposition of an entire (sub)layer or only part of a layer.

Alternatively, pin curing is carried out at certain intervals, e.g. after printing of every second (sub)layer. In particular for an optical structure, it is desirable that the structure is at least partly translucent and/or transparent. Preferably, curing may comprise actively and/or passively curing, wherein in particular passively curing includes letting the droplets dry or cure over time, whereas actively curing includes acting upon the deposited droplets, e.g. submitting the droplets to additional energy such as electromagnetic radiation, in particular UV and/or IR light, and/or thermal energy, in particular heat.

Preferably, the first component of the second printing ink comprises at least one of a monomer, a photoinitiator, an additive, an oligomer. Preferably, the first component comprises more than 70% by volume of a monomer and/or an oligomer, more preferably more than 80%, even more preferably more than 90%, in particular around 99%. Preferably, the first component comprises less than 20% by volume of a photoinitator, more preferably less than 10%, even more preferably less than 1%. Preferably, the first component comprises between 0,1% and 10% by volume of an additive. More preferably, the first component is substantially the same as the first printing ink.

Preferably, the second component comprises an organic solvent. More preferably, the second component comprises at least one of toluene, acetone, butyl acetate, ethyl acetate, ethanol, xylene, white spirit, cyclohexanone, butanol, pentane, hexane, benzene, chloroform, ammonia, ethylenglycolmonoethylether (also called ethyl cellosolve), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), formic acid, methanol and water.

According to a preferred embodiment of the present invention, the base structure is printed on a substrate, a lens blank and/or a three-dimensionally printed structure. In particular, the base structure is printed upon a base layer, wherein the base layer is (three-dimensionally) printed upon a substrate. This is particularly advantageous as the resulting surface, upon which the base structure is printed, may be produced such as to comprise a very smooth surface, which is of particular importance for high-quality optical structures. Furthermore, the material of the base layer may be chosen such as to allow for an optimal bonding to both the substrate on the one side and the base structure on the other side. Preferably, the substrate, the lens blank and/or the base layer comprises glass and/or a polymer, in particular cellulose triacetate (TAC), cyclic olefin copolymer (COC), polyethylene terephthalate (PET), polycarbonate (PC) and/or Polymethyl methacrylate (PM MA), which is also known as acrylic glass or plexiglass. Those materials are well-known and tested materials for optical purposes and therefore particularly suited for the production of the optical structure according to the present invention. Preferably, within the context of the present invention, it is assumed and preferred that the bottom of the base structure is generally flat and therefore comprises a substantially flat surface area. Of course, the base structure may as well comprise a curved surface at its bottom. All features and explanations apply accordingly in this case.

According to a preferred embodiment of the present invention, the third or fourth step is performed such that the anti-reflective coating comprises a textured surface. Preferably, the textured surface is configured such as to reduce reflections of irradiation, in particular light, incident on the textured surface. It is known that textured coating may be used to reduce reflections, e.g. so called “moth-eye” antireflective textures. Such textured coatings may e.g. be produced by the Langmuir-Blodgett method. Yet, it has not yet been known to produce such textured coatings by means of three-dimensional printing. By evaporating the second component of the second printing ink, passively and/or actively, structures created by the first component define the surface of the anti-reflective coating. Preferably, such a textured surface comprises e.g. wrinkles, elevations and/or depressions. The roughness of such a textured surface is in particular significantly higher than that of the surface of the antireflective coating after printing and before evaporation of the second component of the second ink. Preferably, the size of the texture structures is smaller than the predetermined wavelength. More preferably, the texture acts like a gradient-index film and thus reduces reflections. Preferably, after the third step, the anti-reflective coating comprises a liquid, semi-solid and/or viscous state. Hence, after the third step, the fourth step, i.e. a curing step, is required to solidify the anti-reflective coating.

According to a preferred embodiment of the present invention, the third step is performed such that the anti-reflective coating comprises a thickness corresponding to one quarter or an uneven multiple of one quarter of a predetermined wavelength, wherein the predetermined wavelength is preferably within a range of 400 nm to 800 nm. The person skilled in the art acknowledges that this wavelength range substantially corresponds to the visible spectrum. A layer with a thickness of one quarter of such a wavelength causes destructive interferences at its boundaries, thus cancelling out reflections. Preferably, the amount of the second component is chosen such that after evaporation of the second component, the resulting anti-reflective coating layer comprises the above-claimed thickness. It is herewith advantageously possible to print an anti-reflective coating with known three- dimensional printing techniques and still yield an anti-reflective coating layer with a thickness small enough to fulfill the A/4 requirement, wherein A denotes the wavelength. A printed layer preferably comprises a thickness of at least about 10 pm, whereas the thickness of the anti- reflective coating consequently may comprise about 100 nm. In order to reach such a reduction in thickness, the second printing ink comprises roughly 99% of the second component. Thus, about 99% of the anti-reflective coating layer as printed is evaporated during the third step.

According to a preferred embodiment of the present invention, the second printing ink, in particular the first component comprises a reflective index lower than the reflective index of the base structure and/or the first printing ink. It is herewith advantageously possible to create and interface between the base structure and the anti-reflective coating with respect to their refractive indices. Light is reflected at this interface.

According to a preferred embodiment of the present invention, the second, third and preferably the fourth step are repeated at least once such that the optical structure and in particular the anti-reflective coating comprises at least two anti-reflective coating layers, wherein the anti-reflective coating layers comprise at least one different parameter, in particular a different thickness and/or a different surface texture. Additionally or alternatively, at least two consecutive anti-reflective coating layers are printed using different second printing inks, in particular different first components. It is herewith particularly advantageously possible to print a plurality of anti-reflective coating layers, wherein each layer is configured for another wavelength or wavelength range. Thus, a low reflectivity over a broad wavelength range may be obtained. Preferably, after the second step and/or before the third step, each anti-reflective coating layer comprises one or more, preferably a plurality of, layers of printing ink. More preferably, the at least two anti-reflective coating layers are at least partially vertically stacked.

According to a particularly preferred embodiment, the relative amount of the second component of the second printing ink is chosen individually for each anti-reflective coating layer, in particular prior to the second step. Additionally or alternatively, the predetermined thickness of each anti-reflective coating layer is chosen individually. The person skilled in the art acknowledges, that in particular by tuning the amount of the second component, the final thickness of an anti-reflective coating layer may advantageously be chosen. Additionally or alternatively, the thickness (of the anti-reflective coating and/or of each anti-reflective coating layer) is determined by adjusting the droplet volume, the droplet ejection frequency, the amount of ejected droplets and/or the printing speed. It is thus in particular advantageously possible to tune the total thickness of the anti-reflective coating by choosing the thickness of anti-reflective coating layers accordingly.

According to a preferred embodiment of the present invention, the second printing ink comprises at least 80%, preferably at least 90%, more preferably at least 95% and in particular at least 99% of the second component by volume. By tuning the amount of solvent which is evaporated during the third step, it is advantageously possible to tune the resulting thickness of the anti-reflective coating.

A further subject matter of the present invention is a three-dimensional optical structure, in particular an ophthalmic lens, in particular produced by a method according to the present invention, with a base structure comprising a cured first printing ink, wherein at least one region of a surface of the base structure comprises an anti-reflective coating, wherein the anti-reflective coating comprises a, preferably cured, second printing ink, wherein before printing the second printing ink comprises at least a first component and a second component, wherein the first component is a structural component and the second component is a solvent, wherein after printing and in particular before curing the second component is evaporated such that the anti-reflective coating is free of the second component. The embodiments and advantages described in conjunction with this subject matter of the present invention also apply to the further subject matter of the present invention and vice versa.

It is hence advantageously possible to provide an optical structure such as an ophthalmic lens which comprises an anti-reflective coating, wherein both the optical structure and the anti-reflective coating are three-dimensionally printed objects. Hence, a relatively cost- and time-efficiently produced optical structure may be realized.

According to a preferred embodiment of this subject matter of the present invention, the anti- reflective coating comprises a textured surface. It is herewith advantageously possible to print an optical structure including an anti-reflective coating. Preferably, the textured coating is a result of the third step, i.e. the evaporation of the second component of the second printing ink.

According to a preferred embodiment of this subject matter of the present invention, the second printing ink, in particular the first component, comprises a refractive index which is lower than the refractive index of the first printing ink. It is herewith advantageously possible to create an interface or an interface between the base structure and the anti-reflective coating with respect to their refractive indices. As reflections only occur at interfaces between media with different refractive indices, an interference-type of anti-reflective coating may thus advantageously be provided.

According to a preferred embodiment of this subject matter of the present invention, after evaporation of the second component the anti-reflective coating comprises a thickness corresponding to one quarter or an uneven multiple of one quarter of a predetermined wavelength, wherein the predetermined wavelength is preferably within a range of 400 nm to 800 nm. The person skilled in the art acknowledges that this wavelength range substantially corresponds to the visible spectrum. A layer with a thickness of one quarter of such a wavelength will hence in particular yield an interference-type of anti-reflective coating.

Preferably, the amount of the second component is chosen such that after evaporation of the second component, the resulting anti-reflective coating layer comprises the above-claimed thickness. It is herewith advantageously possible to print an anti-reflective coating with known three-dimensional printing techniques.

According to a preferred embodiment of this subject matter of the present invention, the optical structure, in particular the anti-reflective coating, comprises at least two anti-reflective coating layers at least partially stacked upon each other, wherein the at least two anti- reflective coating layers comprise different surface textures and/or thicknesses. It is herewith particularly advantageously possible to provide an optical structure comprising a plurality of anti-reflective coating layers, wherein each layer is configured for another wavelength or wavelength range. Thus, a low reflectivity over a broad wavelength range may advantageously be obtained.

According to a preferred embodiment of this subject matter of the present invention, the optical structure, in particular the anti-reflective coating, comprises at least two anti-reflective coating layers at least partially stacked upon each other, wherein the at least two anti- reflective coating layers comprise a different second printing ink, in particular a different first component. Preferably, the different first components comprise different refractive indices. It is herewith particularly advantageously possible to provide an optical structure comprising a plurality of anti-reflective coating layers, wherein each layer is configured for another wavelength or wavelength range. Thus, a low reflectivity over a broad wavelength range may advantageously be obtained.

According to a preferred embodiment of this subject matter of the present invention, the surface of the base structure on which the anti-reflective coating is provided is an interface surface to air, in particular to ambient air and/or to an air gap within the optical structure. Preferably, this includes that an upper/outer surface of the optical structure is at least partially provided with the anti-reflective coating. Furthermore, inner surfaces of the optical structure may at least partially be provided with the anti-reflective coating. Such inner surfaces occur e.g. in the case of optical structures, in particular lenses, with further embedded components, in particular waveguides. Such lenses may then advantageously be used for augmented reality applications.

According to a preferred embodiment of this subject matter of the present invention, the base structure comprises a diffraction grating, wherein a region of the surface of the base structure in which the diffraction grating is located is preferably free of the anti-reflective coating. Such diffraction gratings are in particular produced by means of naturally occurring print lines during three-dimensional printing. They may be used for a variety of optical purposes. It is herewith advantageously possible to provide an optical structure comprising both a diffraction grating and an anti-reflective coating, wherein all parts are produced by means of three- dimensional printing. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an optical structure produced by a method according to an advantageous embodiment of the present invention immediately after printing.

Figure 2 shows an optical structure produced by a method according to an advantageous embodiment of the present invention after evaporation.

DETAILED DESCRIPTION

The present invention will be described with respect to a particular embodiment and with reference to the drawing, but the invention is not limited thereto but only limited by the claims. The drawing described herein is only schematic and are non-limiting. In the drawing, the sizes may be exaggerated and non-proportional and may not be drawn to scale for illustrative purposes.

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.

In Fig. 1, an optical structure 1 produced by a method according to an advantageous embodiment of the present invention immediately after printing is shown. The optical structure 1 may e.g. be an ophthalmic lens. According to this embodiment, the optical structure 1 comprises at least two parts, a base structure 2, which constitutes the main lens body, and an anti-reflective coating 3 applied on its upper surface.

According to the present invention, the optical structure 1 is produced by means of the additive manufacturing technique known as three-dimensional printing. Printing systems used for this technique are well known and are therefore not shown within the drawings or explained in detail. Such a printing system usually comprises at least a print head comprising at least one nozzle, preferably a plurality of nozzles, at least one reservoir for providing a printing ink and a controller for controlling the print head according to predetermined printing data. Such printing data may e.g. comprise slicing data. This means that a desired final shape of the optical structure 1 is sliced into layers and the controller controls the print head such as to subsequently build up those layers by ejecting printing ink and depositing droplets of printing ink at least partially side by side. Subsequent layers are deposited in a similar manner at least partially on top of the previous layer. The printing ink preferably comprises a polymerizable monomer, which may be cured under irradiation, e.g. by ultraviolet (UV) light, infrared (IR) light and/or heat. According to the specific layer shape and/or the specific requirements, a curing step can be performed after depositing a layer, after depositing parts of a layer and/or after finishing multiple layers.

Another well-known three-dimensional printing technique, which may be used in conjunction with the method according to the present invention is multi-pass printing. In a multi-pass printing mode, a layer is divided into sublayers. During each pass of the print-head (e.g. a movement in one linear direction, wherein preferably moving back in the opposite direction constitutes another pass), a sublayer is printed. Thus, a layer is printed in multiple substeps, wherein during each substep, a sublayer is printed. Each sublayer may be cured after printing or a curing step is performed after a predetermined number of substeps.

The base structure 2 preferably comprises a thickness which is significantly larger than that of the anti-reflective coating 3. In particular, such an anti-reflective coating 3 may comprise a thickness of about 100 nm to 200 nm. There are several known approaches to anti-reflective coatings. One such approach makes use of destructive interferences. Light is reflected at interfaces between media of different refractive indices. If a layer with two such interfaces is as thin as A/4 or uneven multiples of A/4, wherein A denotes the wavelength of incoming light, destructive interferences occur, thus effectively cancelling out reflections. Another approach to create anti-reflective coatings are textured coatings. Such coatings comprise a textured surface, in particular gratings. Depending on the relative size of the structures compared to the wavelength A, different explanations apply. E.g., if the size of the structures is considerably greater than the wavelength A, the light will be reflected so many times in oblique angles that only a negligible part is reflected back at its source.

As mentioned above, an interference-type of anti-reflecting coating 3, which is configured for visible light, i.e. in the range of 400 nm to 800 nm, requires a thickness, here in the vertical direction z, of about 100 nm to 200 nm. With the currently known three-dimensional printing techniques, the minimal thickness of a layer is about 5 pm.

According to the present invention, this problem is solved by using a second printing ink for the anti-reflective coating 3, which is different from the first printing ink used for the base structure 2. The second printing ink comprises at least a first component 4 and a second component 5. The first component 4 is a structural component and comprises a material with a refractive index which is preferably significantly lower than that of the first printing ink. The second component 5 comprises a solvent. The second component 5 is hence preferably volatile, whereas the first component 4 is non-volatile. For usual applications, the second component 5 may e.g. amount to ca. 99% by volume of the second printing ink.

In order to produce the optical structure 1, in a first step, the base structure 2 is printed using the first printing ink. As the optical structure 1 may e.g. be a lens, it is preferred that the base structure 2 is substantially translucent. The first step may e.g. be carried out in a multi-pass mode.

Subsequently, in a second step, the anti-reflective coating 3 is printed using the second printing ink. After the second step and in particular before curing, the solvent is evaporated in a third step. The person skilled in the art acknowledges that a solvent will evaporate under ambient conditions. Additionally, this process may be supported by adjusting ambient conditions. E.g., the ambient temperature may be changed, in particular increased, and/or an air flow may be directed at the surface of the anti-reflective coating.

After the evaporation of the second component 5 and due to the amount of volatile components in the second printing ink, only a small fraction of the second printing ink remains as a coating layer. Preferably, the thus produced coating layer comprises a thickness of A/4, i.e. in particular of 100 nm to 200 nm.

Finally, in an optional fourth step, the anti-reflective coating layer 3 is cured, hence yielding an optical structure 1 comprising a thin anti-reflective coating 3 on a base structure 2.

Additionally or alternatively, the first component 4 of the second printing ink is chosen such and/or deposited such that after the evaporation, i.e. the third step, the remaining coating layer comprises a textured surface, wherein the textured surface comprises regular and/or irregular structure of suitable shape and sizes to provide the coating layer with anti-reflective properties. REFERENCE SIGN LIST

1 optical structure

2 base structure 3 anti-reflective coating

4 first component

5 second component z vertical direction