WO2023179923A1

WO2023179923A1 - Method for producing an optical structure and optical structure

Info

Publication number: WO2023179923A1
Application number: PCT/EP2023/050131
Authority: WO
Original assignee: Meta Platforms Technologies, Llc
Priority date: 2022-03-23
Filing date: 2023-01-04
Publication date: 2023-09-28

Abstract

A method for producing an optical structure, in particular an optical lens, wherein the method comprises the following steps: - a) providing a base structure with a protruding element; - b) obtaining a first substructure of the optical structure by means of depositing an ink on the base structure, wherein the protruding element provides a negative imprint on the first substructure, wherein the negative imprint on the first substructure is shaped and/or configured to provide a recess in the first substructure to at least partly accommodate an additional structure and/or an airgap; - c) separating the first substructure from the base structure.

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 an optical lens. Moreover, the present invention relates to an optical structure.

In recent years, with the rise of rapid prototyping and in particular additive manufacturing, three-dimensional printing techniques making use of various ink materials have started to be employed for producing optical structures, especially optical lenses. As an additive method, printing is more flexible and less wasteful than conventional techniques, thereby providing highly individualized, non-standard, low-waste and low-cost optical structures. As such, printing techniques for optical structures are generally known.

It is desirable, e.g., for ophthalmic lenses, microscopy or semiconductor production, to create optical structures with very small dimensions, e.g., in the region of microns or even nanometers, with high accuracy. Yet, this poses problems for the current three-dimensional printing technology as the structures that may be printed by modern 3d-printers are larger than those required for such microstructures or nanostructures. Moreover, it is desirable to produce optical structures that are able to realize or accommodate more complex or varying optical properties.

SUMMARY

Hence, it is an object of the present invention to provide an advantageous method for producing an optical structure, preferably such that optical structures may be produced with desired optical properties and/or with high accuracy. It is a further object of the present invention to provide a corresponding optical structure.

According to the present invention, the object is achieved by a method for producing an optical structure, in particular an optical lens, wherein the method comprises the following steps: - a) providing a base structure with a protruding element;

- b) obtaining a first substructure of the optical structure by means of depositing an ink on the base structure, wherein the protruding element provides a negative imprint on the first substructure, wherein the negative imprint on the first substructure is shaped and/or configured to provide a recess in the first substructure to at least partly accommodate an additional structure and/or an airgap;

- c) separating the first substructure from the base structure.

By means of the present invention, optical structures with advantageous properties may be produced with a high level of customization by means of an ink. The method according to the invention advantageously allows for a particularly efficient way to produce optical microstructures, such as microlenses or diffraction gratings. In particular, it is possible to advantageously incorporate additional structures and/or optical properties/features and/or functional layers into such optical structures by means of the present invention. According to the present invention, the shape of the recess in the first substructure is advantageously defined by means of the shape of the protruding element. It is advantageously possible that the shape of the protruding element is chosen such that the recess in the first substructure is configured to a accommodate an additional structure and/or an airgap. Thereby, additional structures and/or airgaps can be incorporated into an optical structure in a particularly efficient and precise manner.

It is to be understood that an airgap according to the present may be a gap that is filled with air or with a fluid such as a gas or gas mixture that is different from air. It is to be understood that an airgap according to the present invention may comprise a vacuum.

According to the present invention, the protruding element may be configured to extend from a surface of the base structure and/or protrude from a surface of the base structure.

According to the present invention, the protruding element may be understood to be an insert. As such, the step of “providing a base structure with a protruding element” may be understood such that a base structure with an insert is provided.

According to the present invention, it is conceivable that the base structure is a substrate. Preferably, the base structure is a substrate which is used for producing the optical structure, especially for producing the first substructure of the optical structure. In particular, the base structure may comprise a base layer printed upon a substrate. This is particularly advantageous as the resulting base structure may be produced such as to comprise a very smooth surface, which is advantageous when creating optical microstructures. Preferably, the base structure 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 particularly suited for the production of the optical structure according to the present invention. However, other materials are conceivable as well. Preferably, within the context of the present invention, it is assumed and preferred that 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. For instance, it is conceivable that the base structure is or comprises a PMMA sheet. The protruding element preferably protrudes from said mainly flat base structure. It is conceivable that the protruding element extends perpendicularly from the base structure. It is conceivable that the protruding element and the base structure are formed as a single piece or that the protruding element is a separate structure (separate from the base structure), e.g., a layer, that is placed on top of the base structure. It is conceivable that the protruding element is fixed to the substrate, e.g., glued to the base structure, or alternatively that the protruding element is placed on the substrate without fixing the protruding element to the substrate. However, the protruding element should preferably be placed on the base structure such that the protruding element does not move relative to the base structure during the printing process, especially in step b). It is possible that the protruding element is made of the same material as the base structure. According to an alternative embodiment, it is conceivable that the base structure and the protruding element are made of different materials. It is conceivable that the protruding element and/or the base structure are partially or fully covered by an intermediate material, especially a wetting promoter. By means of said intermediate material, the flow of the ink can be stimulated. In particular, the intermediate material, especially the wetting promoter, is configured to stimulate the flow on the one side and has a strong enough adhesion on the other side to hold the first substructure during printing. However, the adhesion should not be too strong, because the first substructure preferably needs to be peeled off after printing and curing.

Preferably, the protruding element is also separated from the first substructure as part of step c). As part of step c), it is conceivable that the base structure and the protruding element are separated from the first substructure together. This is, e.g., advantageous in case that the base structure and the protruding element are made of a single piece or in case that the protruding element is fixed to the base structure. According to an alternative embodiment, especially if the protruding element is not attached or fixed to the base structure, it is also conceivable that the first substructure and the protruding element are first removed from the base structure and that the protruding element is subsequently removed from first substructure.

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 in the visible spectrum. Preferably, in order to serve an optical purpose, the optical structure is at least partially optically transparent, in particular at least for in range of wavelengths, such as the visible spectrum.

It is conceivable that the optical structure is a microstructure. In the context of the present invention, the term microstructure is not intended to be limited to structures with sizes in the range of several micrometers, but also covers smaller structures with sizes in the range of several nanometers, i.e., nanostructures.

In the context of the present invention, it is conceivable that step b) comprises printing the first substructure by means of the ink. It is conceivable that printing the first substructure comprises building up the first substructure from one or more layers of printing ink. It preferred that said layers of ink are obtained through a targeted placement of droplets of printing ink at least partially side by side and/or partially overlapping with each other. The droplets of ink are preferably ejected from one or more nozzles of a print head, typically in a substantially vertical direction towards the base structure, although ejecting the droplets at an angle is possible as well. Droplets of layers constituting the following layer are at least partly ejected towards the previously deposited layer, such that the three-dimensional structure (especially the first substructure) is built up layer by layer. Preferably, the three-dimensional printing is a multi-jet printing.

According to a preferred embodiment of the present invention, one or more curing steps may be carried out as part of step b). In particular, curing steps may generally be performed at any time in the process; e.g., a partial curing may be carried out after finishing printing a layer. Preferably, a layer is at least partially cured before a subsequent layer is printed. Fully curing a layer before printing the next layer allows for a precise shaping of the optical structure. On the other hand, printing a layer on top of a not-fully cured layer may advantageously improve the bonding between the layers or elements.

According to an embodiment of the present invention, it is conceivable that obtaining the first substructure of the optical structure in step b) comprises: - b1) depositing ink at one or more grid points and/or voxels on the base structure, especially at least partly in the region of the protruding element, by drop on demand;

- b2) curing the deposited ink; and

- b3) preferably repeating at least steps b1) through b3) until the first substructure is formed and cured. Thereby, an advantageous printing process for the first structure may be realized. The first substructure is printed on the base structure with the protruding element such that a negative imprint of the protruding element is obtained in the first substructure. The negative imprint of the protruding element that is obtained in the first substructure advantageously forms a recess in the first substructure.

Preferably, the ink, especially the printing ink, 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 most 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. More preferably, 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 layer or after deposition of only part of a layer. Alternatively, pin curing is carried out at certain intervals, e.g., after printing of every second layer. Preferably, curing may comprise active and/or passive curing, wherein in particular passive curing includes letting the droplets dry or cure over time, whereas active curing includes acting upon the deposited droplets, e.g., subjecting the droplets to additional energy such as electromagnetic radiation, in particular UV light.

According to an embodiment of the present invention, it is conceivable

- that the additional structure comprises a light guiding structure and/or a functional layer; and/or

- that the airgap is located between the additional structure and the first substructure.

The shape of the recess is advantageously defined by means of the shape of the protruding element. It is advantageously possible that the shape of the protruding element is chosen such that the recess in the first substructure is configured to accommodate an additional structure, especially a light guiding structure and/or a functional layer. The functional layer may be a functional layer that is part of an optical element, such as a light guiding structure. As such, the shape of the protruding element is advantageously chosen according to the shape of the additional structure that is to be arranged in the recess. The functional layer is preferably an optical functional layer that may be part of an optical element (or optical structure), such as a waveguide. A waveguide typically comprises two functional layers and a TIR (total internal reflection) layer. The TIR layer may be formed by means of the airgap. Therein, by means of arranging a functional layer and an airgap in the recess of the first substructure, it is possible to form at least a part of a waveguide.

According to an embodiment of the present invention, it is conceivable that the method further comprises:

- d) arranging the additional structure in the recess of the first substructure, preferably such that the additional structure is flush with the first substructure. Thereby, it is preferably possible that a generally flat surface is created, as the additional structure (e.g., a light guiding structure, such as a waveguide) is flush with the first substructure (especially the first lens half). It is particularly advantageous to print a second substructure on said flat surface, which is formed by the additional structure being flush with the first substructure.

According to an embodiment of the present invention, it is conceivable that the air in the airgap is replaced by a further layer. According to an embodiment of the present invention, it is conceivable that the airgap is partially or fully filled with a further layer, especially after step c). The further layer may be produced by means of an ink. In particular, it is conceivable that the further layer is printed layer. It is particularly preferred that the further layer is constructed from an ink that comprises a refractive index (Rl) between 1 and 1.4, e.g., of around 1.35, after curing. By replacing the air in the airgap by said further layer, a stronger and better optical structure (especially a lens) can be created as there is less deformations/bending possible, while still total internal reflection can be achieved.

- e) printing or casting a second substructure of the optical structure, preferably wherein the additional structure and/or the air gap is at least partially enclosed between the first substructure and second substructure. Accordingly, the produced optical structure is constructed by means of the first and second substructures.

According to a preferred embodiment of the present invention, the parameters of the printing process comprise at least one of an ambient temperature, gas composition of the atmosphere, oxygen level, temperature of the printing ink, a composition of the printing ink, a viscosity of the printing ink, a droplet size, a droplet ejection velocity, a droplet density and a printing velocity, and/or the parameters of the curing process comprise at least one of a curing temperature, a curing time, an irradiation intensity and an irradiation wavelength. It is conceivable according to the present invention that at least one of those parameters is adjusted such as to create the optical structure, in particular the first substructure and/or the second substructure, with predetermined dimensions. It is hence, e.g., possible to create the optical structure, in particular the first substructure and/or the second substructure, as microstructures.

According to still another preferred embodiment of the present invention, it is possible that the first substructure and the second substructure are produced with the same ink or with different inks. By means of selecting appropriate inks the properties of the first and second substructures may be influenced and/or adjusted.

According to a preferred embodiment of the present invention, a further airgap is located between the additional structure and the second substructure, preferably wherein:

- the second substructure is fabricated in the same way as the first substructure and/or

- the second substructure is produced by a method according to an embodiment of the present invention for producing the first substructure. In particular, the second substructure is constructed according to steps a) to c) as well, thereby comprising a further recess in the second substructure to at least partly accommodate the further airgap. For instance, the second substructure can be constructed by means of the following steps:

- providing a base structure with a protruding element;

- obtaining the second substructure of the optical structure by means of depositing an ink on said base structure, wherein the protruding element provides a negative imprint on the second substructure, wherein the negative imprint on the second substructure is shaped and/or configured to provide a further recess in the second substructure to at least partly accommodate a further airgap;

- separating the second substructure from said base structure.

According to a preferred embodiment of the present invention, a rim is printed on the first substructure or the second substructure before connecting the first and second substructure, wherein the first substructure and the second substructure are placed on top of each other at least in the region of the rim, wherein the rim is cured for connecting, especially gluing, the first substructure to the second substructure. Preferably, before connecting the first and second substructure, an additional structure is placed in the recess of the first substructure. Thereby, an optical structure comprising a further airgap located between the additional structure and the second substructure can be constructed in an efficient manner. According to an embodiment of the present invention, the base structure and/or the protruding element comprises a relief structure, especially on a surface of the base structure and/or the protruding element. The relief structure is preferably a nanostructure. The relief structure preferably comprises feature sizes in the range of several nanometers. However, it is conceivable that the relief structure comprises feature sizes in the range of several micrometers.

According to an embodiment of the present invention, it is conceivable that, especially in step b), the first substructure is obtained with a further negative imprint of the relief structure. As such, by means of obtaining a further negative imprint of the relief structure in the first substructure an advantageous customization of the optical properties of the first substructure may be achieved. In particular, the shape and dimensions of the relief structure may be chosen in dependence of the desired shape and dimension of the further negative imprint of the relief structure in the first substructure. It is, e.g., conceivable that the relief structure is present over the entire protruding element or only in parts thereof.

According to an embodiment of the present invention, the further negative imprint of the relief structure is shaped and/or configured to provide anti-reflection properties, especially an antireflection surface, and/or a diffraction grating. The relief structure may be configured and/or formed such that the further negative imprint of the relief structure provides an optical metastructure, in particular a diffraction grating and/or an anti-reflection surface, in the first substructure. Thereby, a particularly advantageous process for customizing the optical properties of the first substructure, especially locally, may be realized.

According to an embodiment of the present invention, the further negative imprint of the relief structure in the first substructure is at least partially enclosed between the first substructure and second substructure. As such, the further negative imprint may be partially or fully enclosed and/or encapsulated inside the optical structure.

According to an embodiment of the present invention, the protruding element comprises one or more recesses and/or additional ridges, wherein by means of the one or more recesses and/or additional ridges of the protruding element one or more spacers are created - in step b) - in the recess in the first substructure that is provided by means of the negative imprint of the protruding element. The one or more spacers are preferably formed during the printing process of the first substructure. As such, the spacers preferably are made of the same ink as the first substructure. Such spacers may, e.g., be formed to provide for a stable and well- defined air gap between an additional structure, located in the recess of the first substructure, and the first substructure or a main body of the first substructure. It is conceivable that the spacer is arranged parallel to an outer edge of the first substructure and/or the second substructure, at least partially circumferentially.

Alternatively, it is also conceivable according to an embodiment of the present invention that the protruding element is flat or substantially flat, i.e. , such that the protruding element does not comprise any recesses or extra ridges.

Furthermore, the present invention relates to an optical structure, in particular produced by a method according to an embodiment of the present invention, wherein the optical structure comprises a first substructure, wherein the first substructure comprises a recess to at least partly accommodate an additional structure and/or an airgap, wherein the recess is shaped and/or provided by a negative imprint of a protruding element of a base structure. As such, the optical structure at least comprises a first substructure, wherein a negative imprint of a protruding element on the first substructure is shaped and/or configured to provide a recess in the first substructure to at least partly accommodate an additional structure and/or an airgap.

According to an embodiment of the present invention, the optical structure comprises a second substructure, being printed or casted on the first substructure, preferably wherein the first substructure is a first lens half and the second substructure is a second lens half. Advantageously by means of the first lens half and the second lens half an optical lens is formed.

According to a preferred embodiment of the present invention, especially of the inventive optical structure, a further airgap is located between the additional structure and the second substructure. It is thus possible that the optical structure comprises an airgap on one side of the additional structure as well as a further airgap on the opposite side of the additional structure. Preferably the second substructure is fabricated in the same way as the first substructure. In particular, the second substructure is constructed according to steps a) to c) as well, thereby comprising a further recess in the second substructure to at least partly accommodate the further airgap. For instance, the second substructure can be constructed by means of the following steps:

- providing a base structure with a protruding element;

- separating the second substructure from said base structure.

According to a preferred embodiment of the present invention, especially of the inventive optical structure, the first and second substructures are connected to each other, especially glued to each other, by means of a rim that is printed on the first substructure or the second substructure before connecting the first and second substructure, wherein the first substructure and the second substructure are placed on top of each other at least in the region of the rim, wherein the rim is cured for connecting, especially gluing, the first substructure to the second substructure. Preferably, before connecting the first and second substructure, an additional structure is placed in the recess of the first substructure. Thereby, an optical structure comprising a further airgap located between the additional structure and the second substructure can be realized in an efficient manner.

According to an embodiment of the present invention, by means of the recess in the first substructure:

- the additional structure, especially a light guiding structure and/or a functional layer, and/or

- the airgap is at least partially enclosed between the first substructure and second substructure. As such, additional structures and/or airgaps may be provided inside the optical structure, partially or fully enclosed in between the first and second substructures. The additional structure that is partially or fully enclosed between the first and second substructure may advantageously comprise a waveguide and/or a functional layer, said functional layer preferably being part of a waveguide and/or configured for realizing a waveguide.

According to an embodiment of the present invention, the first substructure comprises a further negative imprint of a relief structure, preferably wherein the further negative imprint of the relief structure is shaped and/or configured to provide anti-reflection properties, especially an anti-reflection surface, and/or a diffraction grating. Thereby, a particularly advantageous optical structure may be obtained, wherein the optical properties may be customized, preferably locally, by means of the further negative imprint of the relief structure. According to an embodiment of the present invention, the further negative imprint of a relief structure is at least partially enclosed between the first substructure and second substructure.

According to a preferred embodiment of the present invention, especially of the inventive optical structure, one or more spacers are located in the recess in the first substructure, preferably wherein said one or more spacers are constructed by means of the protruding element comprising one or more recesses and/or additional ridges for creating said one or more spacers. It is preferred that the one or more spacers are created by means of the one or more recesses and/or additional ridges of the protruding element when printing the first substructure in step b).

In the context of the present invention, the dimensions of structures and elements comprise, but are not limited to, a height, i.e., a vertical extension perpendicular to the area of the base structure, and a lateral width, i.e., a horizontal extension parallel to the area of the base structure. A person skilled in the art understands that the first substructure and/or the second substructure may comprise substantially any outer contour and/or shape as desired. It is additionally or alternately conceivable that the first substructure and/or the second substructure may comprise varying heights and/or different lateral widths in different orientations.

According to an embodiment of the present invention, the optical structure comprises a coating layer, especially a functional layer. The coating layer, especially a functional layer, may be located on the outside of the optical structure, in particular on the outside of the first substructure and/or the second substructure. It is hence advantageously possible to protect the optical structure from chemical and/or mechanical deterioration.

The embodiments and advantages described above with respect to the method according to the present invention or with respect to an embodiment of the method according to the present invention are also applicable for the optical structure according to the present invention. The embodiments and advantages described above with respect to the optical structure according to the present invention or with respect to an embodiment of an optical structure according to the present invention are also applicable for the method according to the present invention.

These and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1A and 1B illustrate a method for producing an optical structure according to an embodiment of the present invention;

Figure 2 shows a further embodiment of the present invention;

Figures 3A, 3B and 3C illustrate a method for producing an optical structure according to an embodiment of the present invention;

Figures 4A and 4B illustrate the production of a further negative imprint of a relief structure according to an embodiment of the present invention;

Figures 5A and 5B illustrate the production of a further negative imprint of a relief structure according to an embodiment of the present invention;

Figures 6A, 6B and 6C illustrate a method for producing an optical structure according to an embodiment of the present invention;

Figure 7 illustrates the concept of a waveguide.

DETAILED DESCRIPTION

The present invention will be described with respect to particular embodiments and with reference 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 not drawn on 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. Furthermore, the terms first, second, third 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.

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 Figures 1A and 1 B a method for producing an optical structure according to an embodiment of the present invention is schematically illustrated. In Fig. 1A a base structure 3, especially a substrate is shown. Such mainly flat substrates, e.g., PMMA sheets, are used for printing optical lenses. According to the present invention, a protruding element 2 is provided on top of the flat base structure 3, wherein the protruding element 2 protrudes from the base structure 3. The protruding element 2 may be understood to be an insert. The protruding element 2 is preferably shaped like a light guiding element and may, e.g., be made of the same material as the base structure 3 (e.g., PMMA) or another material, as long as it doesn't bind to a cured lens material. The protruding element 2 may be attached (e.g., glued) to the base structure 3 or could also lay loosely on the base structure 3. However, in any case the protruding element 2 should be on a fixed position on the base structure 3. The base structure 3 and protruding element 2 may be formed as a single element or may be separate elements.

On the base structure 3, and in particular on the protruding element 2, a first substructure 1 of an optical structure is printed. The first substructure 1 is a first lens half. By means of the protruding element 2, a negative imprint of the protruding element 2 is created in first substructure 1 when printing the first substructure 1 , especially in step b) of a method according to an embodiment of the present invention. After the first substructure 1 has been printed and cured, it is removed from the base structure 3 and the protruding element 2. Optionally, if the protruding element 2 is not attached to the base structure 3, the first substructure 1 and the protruding element 2 can be removed from the base structure 3 together and - in a next step - the protruding element 2 is removed from the first substructure 1 . The result is a first substructure 1 that is provided with a recess 11 . In this recess 11 , an additional structure 5, preferably a light guiding element, such as a waveguide, can be placed. In this way, it is possible to create a generally flat surface, as the surface of the additional structure 5 is aligned with the surface of the first substructure 1. This situation, with an additional structure 5 being located in the recess 11 of the first substructure 1 , is shown in Fig. 1 B. Afterward, a second substructure, especially a second lens half, may be printed or casted on top of the first substructure 1, thereby at least partially encapsulating the additional structure 5 (compare Fig. 3C).

In Fig. 2 a further embodiment of the present invention is schematically illustrated. In contrast to the embodiment shown in Figures 1 A and 1 B, the protruding element 2 is shaped such that it creates a recess 11 in the first substructure 1 , the recess 11 being configured for accommodating an additional structure 5, in particular a light guiding element, and an airgap 4, wherein the air gap 4 may be arranged between the additional structure 5 and first substructure 1.

In Figures 3A, 3B and 3C a method for producing an optical structure 100 according to another embodiment of the present invention is schematically illustrated. Therein, Fig. 3A illustrates the structure after the first substructure 1 has been printed. Fig. 3B illustrates the structure after the base structure 3 and protruding element 2 have been separated from the first substructure 1 , wherein an additional structure 5 and an airgap 4 are located in the recess 11. Fig. 3C shows the produced optical structure 100 after the second substructure 9 has been fabricated, especially printed or casted.

In the embodiment according to Figures 3A, 3B and 3C, one or more spacers 7 are created by using a protruding element 2 provided with an additional ridge 6 or recess. The extra ridge 6 is located at the outer side of the protruding element 2. It is conceivable that said extra ridge 6 is formed circumferentially around the protruding element 2 or only partly.

Alternatively or additionally, it is also possible that one or more additional recesses/ridges are located in other regions of the protruding element 2, i.e., not at the outer edge of the protruding element.

By means of the additional recess or ridge 6 in the protruding element 2, spacers 7 are created when printing the first substructure 1. Thereby, an optical structure 100 comprising a printed first substructure 1 (especially a first lens half), a printed second substructure 9 (especially a second lens half), and an enclosed additional structure 5, arranged between the first and second substructure 1 , 9, may be produced, wherein an air gap 4 is arranged between the enclosed additional structure 5 and the first substructure 1 and/or second substructure 9. The air gap 4 advantageously allows total reflection (TIR) in the optical structure to be used to transport information in the form of light. The transport mechanism is extremely efficient. In the illustrated embodiment according to Figures 3A to 3C, the spacer 7 is arranged between the first substructure 1 and the enclosed additional structure 5, thus providing a well-defined air gap 4. Advantageously the spacer 7 is printed, preferably when printing the first substructure 1. Thereby, a particularly stable and well-defined air gap 4 may be created. It is conceivable that the spacer 7 is arranged parallel to an outer edge of the first substructure and/or the second substructure, at least partially circumferentially.

In summary, by means of the embodiments described with respect to Figures 1A to 3C, a method for manufacturing an optical structure, in particular an optical lens, may be realized, wherein the method comprises the following steps:

- a) providing a base structure 3 with a protruding element 2;

- b) obtaining a first substructure 1 of the optical structure by means of depositing an ink on the base structure, wherein the protruding element 2 provides a negative imprint on the first substructure 1 , wherein the negative imprint on the first substructure is shaped and/or configured to provide a recess 11 in the first substructure 1 to at least partly accommodate an additional structure 5 and/or an airgap 4;

- c) separating the first substructure 1 from the base structure 3. In other word, according to the invention, it is conceivable that the protruding element 2 provides a negative imprint on the first substructure 1 , wherein the negative imprint is shaped to create a complementary recess 11 to at least partly accommodate the additional structure 5, such as a light guiding structure, and/or an air gap 4, preferably an airgap 4 between the light guiding structure and the first substructure 1.

In particular, step b) may be realized by:

- b1) depositing ink at one or more voxels on the base structure 3 provided with the protruding element 2 by drop on demand;

- b2) curing the deposited ink; and,

- b3) repeating at least steps b1) through b3) until the first substructure 1 is formed and cured.

It is preferably conceivable that step c) is followed by an optional step d) and/or e), wherein in step d) the additional structure 5 is arranged in the recess of the first substructure 1 , and/or wherein in step e), a second substructure 9, in particular a second lens half, is printed or casted such that the additional structure 5 and/or airgap 4 is at least partially enclosed between the first substructure 1 and the second substructure 9.

Figures 4A and 4B illustrate the production of a further negative imprint 10 (or “copy”) of a relief structure 8 according to an embodiment of the present invention. A base structure 3, especially a flat substrate, is provided with a relief structure 8, such as a negative relief of a diffraction grating or an anti-reflection surface. A first optical substructure 1 is printed on the base structure 3. As such, by printing on a base structure 3, provided with a relief structure 8, such as a nano relief (also called nanostructure), a further negative imprint of said relief structure is made.

In Fig. 4A, only one relief type is shown over the entire surface. However, it is also conceivable that the relief structure 8 comprises more than one different type of relief, especially in different regions of the base structure 3. Thereby, different reliefs (such as a diffraction grating relief and an anti-reflective relief) may be imprinted in different regions. The resulting first substructure 1 , i.e., lens half, provided with a further negative imprint 10 of the relief structure 8 is shown in Fig. 4B after the base structure 3 has been removed from the first substructure 1. The further negative imprint 10 of the relief structure 8 is a functional imprint on the first substructure 1. Thereby, an advantageous way of tailoring the properties and functionality of the first substructure 1 may be achieved. Fabricating a further negative imprint of a relief structure (i.e., a functional imprint) in this manner allows for creating such functional imprints with high accuracy and quality. This is, e.g., particularly promising in the field of making a diffraction grating in a lens. Therein, the further negative imprint 10 of the relief structure 8 comprises a diffraction grating or forms a diffraction grating. Thereby and in contrast to fabricating a diffraction grating by post processing a transparent material/lens, by means of the present invention a diffraction grating may be formed as part of a further negative imprint 10 of a relief structure 7 during the printing process of a lens half. In Figures 5A and 5B an alternative to Figures 4A and 4B is shown. According to Figures 5A, only a part of the base structure 3 is provided with a relief structure 8, wherein other parts 8’ of the base structure are smooth, i.e., free of a relief structure 8. This may be advantageous if the functions created by the relief in the first substructure 1, such as anti-reflection properties, are only required on part of the surface of the first substructure 1. The resulting first substructure 1 (in the form of a lens half) provided with a functional imprint (i.e., a further negative imprint of the relief structure) on parts of the first substructure 1 shown in Fig. 5B.

According to an embodiment of the present invention, it is advantageously possible to combine such a diffraction grating with an airgap 4 to ensure total internal reflection, as further illustrated in Figures 6A, 6B and 6C. By combining a diffraction grating with an airgap 4, it is possible to omit using an ‘off the shelf’ waveguide as an at least partially encapsulated object within the optical structure (e.g., optical lens). Instead, the functions of the waveguide can be integrated in the optical structure (e.g., the optical lens) itself, allowing an advantageous production method, thinner end products, more control over the product, and more flexibility in lens design. Waveguides typically consist of two or more functional layers, wherein - in between these functional layers - a layer that allows total internal reflection (TIR), such as an air layer, is located.

According to the present invention, it becomes possible to produce a first substructure 1 (especially a first lens half) with one of the two functional layers imprinted in it, so that only the other functional layer of the waveguide needs to be at least partially encapsulated. This leads to a thinner and lighter end product, reduced production time and/or cost and more flexibility in lens design. The concept of a waveguide will be briefly illustrated with respect to Fig. 7 later.

In Figures 6A, 6B and 6C, an embodiment according to the present invention is schematically illustrated. A base structure 3 is provided with a protruding element 2. The protruding element 2 is at least partially provided with a relief structure 8. A first substructure 1 is printed on the base structure 2, resulting in first substructure 1 that comprises a recess 11 , formed by means of the protruding element 2, as well as a further negative imprint 10 of the relief structure 8. Optionally, the recess 11 in resulting first substructure 1 is then filled with an additional structure 5, such as a waveguide and/or a functional layer, or a functional layer may be provided on top the first substructure (instead of in the recess 11). Optionally, an airgap 4 is created by means of the protruding element 2 during the printing process as well. Optionally, as shown in Fig. 6C, a second substructure 9, especially a second lens half, is printed or casted on top of the first substructure 1 , thereby at least partially encapsulating the additional structure 5, the airgap 4 and the further negative imprint 10 of the relief structure.

Therein, according to the embodiment shown in Figures 6A to 6C, a protruding element 2 and/or a base structure 3, which the first substructure 1 is printed on, are at least partly provided with a relief structure 8, such as a nano relief. After printing, the base structure 3 and protruding element 2 are separated from the first substructure 1 (compare Fig. 6B), thereby leaving an imprint 10 of the (nano)relief in the first substructure 1. The imprinted relief 10 creates, e.g., anti-reflective properties, preferably in the airgap 4 between the first substructure 1 and an at least partially encapsulated additional element 5, such as a light guiding element (e.g., moth-eye nanostructure). Anti-reflective surfaces advantageously decrease the light-reflecting properties of specific wavelengths, thereby reducing unwanted reflections, causing ghosting or other artefacts in the projected image. The imprinted relief, i.e. , the further negative imprint 10, may also provide a diffraction grating, next to, combined with, or instead of anti-reflective properties. Diffraction gratings are used to change a direction of light waves, e.g., to couple light in or out of an airgap 4, thereby creating an input pupil or an output pupil, or to change a direction of light within the airgap 4.

This concept is schematically illustrated in Fig. 7. By means of a surface- re lief grating for incoupling 20, light is coupled into the waveguide. In an intermediate region, two reflective surfaces 22, 23 provide a planar waveguide. By means of a surface-relief grating for out- coupling 21 , the light is coupled out of the waveguide. A waveguide typically consists of a (plurality of) two functional layers with a TIR layer, typically air, in between. On at least one functional layer, a grating, such as diffraction grating, is provided. Typically, not the entire surface is covered with a grating. The rest of the surface is usually covered with an anti- reflective coating to increase efficiency and decrease unwanted reflections/ghosting. An anti- reflective coating is usually wavelength specific, so that the wavelength intended to be guided through the air gap is not quenched by the anti-reflective coating, but most other wavelengths are. It is possible that the waveguide comprises several pairs of functional layers, each pair typically comprising two layers. Commonly, there are three pairs of two layers for RGB (red green blue) wavelengths. It is possible that blue is in one pair of layers and green and red are together in the other pair of layers. A person skilled in the art understands that there are different configurations of waveguides known in the state of the art. By means of the present invention, especially by means of producing a further negative imprint 10 of the relief structure 8, such waveguide concepts may advantageously be realized in an optical structure 100.

REFERENCE SIGN LIST

1 first substructure

2 protruding element

3 base structure

4 airgap

5 additional structure

6 additional ridge

7 spacer

8 relief structure

8’ smooth part of the base structure

9 second substructure

10 further negative impring

11 recess

20 surface- re lief grating for in-coupling

21 surface- re lief grating for out-coupling

22 surface

23 surface

100 optical structure

Claims

PATENT CLAIMS

1. Method for producing an optical structure (100), in particular an optical lens, wherein the method comprises the following steps:

- a) providing a base structure (3) with a protruding element (2);

- b) obtaining a first substructure (1) of the optical structure (100) by means of depositing an ink on the base structure (3), wherein the protruding element (2) provides a negative imprint on the first substructure, wherein the negative imprint on the first substructure (1) is shaped and/or configured to provide a recess (11) in the first substructure (1) to at least partly accommodate an additional structure (5) and/or an airgap (4);

- c) separating the first substructure (1) from the base structure (3).

2. Method according to claim 1 , wherein obtaining the first substructure (1) of the optical structure (100) in step b) comprises:

- b1) depositing ink at one or more grid points and/or voxels on the base structure (3), especially at least partly in the region of the protruding element (2), by drop on demand;

- b2) curing the deposited ink; and

- b3) preferably repeating at least steps b1) through b3) until the first substructure (1) is formed and cured.

3. Method according to one of the preceding claims,

- wherein the additional structure (5) comprises a light guiding structure and/or a functional layer; and/or

- wherein the airgap (4) is located between the additional structure (5) and the first substructure (1).

4. Method according to one of the preceding claims, wherein the method further comprises:

- d) arranging the additional structure (5) in the recess (11) of the first substructure (1), preferably such that the additional structure (5) is flush with the first substructure (1).

5. Method according to one of the preceding claims, wherein the method further comprises:

- e) printing or casting a second substructure (9) of the optical structure (100), preferably wherein the additional structure (5) and/or the air gap (4) is at least partially enclosed between the first substructure (1) and second substructure (9).

6. Method according to claim 5, wherein a further airgap is located between the additional structure (5) and the second substructure (9), preferably wherein:

- the second substructure (9) is fabricated in the same way as the first substructure (1) and/or

- the second substructure (9) is produced by a method according to any of the preceding claims for producing said first substructure (1).

7. Method according to one of claims 5 or 6, wherein a rim is printed on the first substructure (1) or the second substructure (9) before connecting the first and second substructure (1, 9), wherein the first substructure (1) and the second substructure (9) arranged together at least in the region of the rim, wherein the rim is cured for connecting, especially gluing, the first substructure (1) to the second substructure (9).

8. Method according to one of the preceding claims, wherein the base structure (100) and/or the protruding element (2) comprises a relief structure (8), especially on a surface of the base structure (3) and/or the protruding element (2), preferably wherein, especially in step b), the first substructure (1) is obtained with a further negative imprint (10) of the relief structure (8).

9. Method according to claim 8, wherein the further negative imprint (10) of the relief structure (8) is shaped and/or configured to provide anti-reflection properties, especially an anti-reflection surface, and/or a diffraction grating, preferably wherein the further negative imprint (10) of the relief structure (8) in the first substructure (1) is at least partially enclosed between the first substructure (1) and second substructure (9).

10. Method according to one of the preceding claims, wherein the protruding element (2) comprises one or more recesses and/or additional ridges (6), wherein by means of the one or more recesses and/or additional ridges (6) of the protruding element (2) one or more spacers (7) are created - in step b) - in the recess (11) in the first substructure (1) that is provided by means of the negative imprint of the protruding element (2).

11. Optical structure (100), produced by a method according to any one of the preceding claims, wherein the optical structure (100) comprises a first substructure (1), wherein the first substructure (1) comprises a recess (11) to at least partly accommodate an additional structure (5) and/or an airgap (4), wherein the recess (11) is shaped and/or provided by a negative imprint of a protruding element (2) of a base structure (3).

12. Optical structure (100) according to claim 11 , wherein the optical structure (100) comprises a second substructure (9), being printed or casted on the first substructure (1), preferably wherein the first substructure (1) is a first lens half and the second substructure (9) is a second lens half.

13. Optical structure (100) according to claim 12, wherein by means of the recess (11) in the first substructure (1):

- the additional structure (5), especially a light guiding structure and/or a functional layer, and/or

- the airgap (4) is at least partially enclosed between the first substructure (1) and second substructure (9).

14. Optical structure (100) according to one of claims 11 to 13, wherein the first substructure (1) comprises a further negative imprint (10) of a relief structure (8), preferably wherein the further negative imprint (10) of the relief structure (8) is shaped and/or configured to provide anti-reflection properties, especially an anti-reflection surface, and/or a diffraction grating, more preferably wherein the further negative imprint (10) of the relief structure (8) is at least partially enclosed between the first substructure (1) and second substructure (9).

15. Optical structure (100) according to one of claims 11 to 14, wherein one or more spacers (7) are located in the recess (11) in the first substructure (1), preferably wherein said one or more spacers (7) are constructed by means of the protruding element (2) comprising one or more recesses and/or additional ridges (6) for creating said one or more spacers (7).