METHOD FOR MANUFACTURING A GLASS WAFER OF HIGH QUALITY, GLASS WAFER, GLASS PART ELEMENT, STACK, AUGMENTED REALITY DEVICE AND USE

Abstract

A method for manufacturing a glass wafer for augmented reality applications includes the steps of: providing the raw wafer; edge-grinding of the raw wafer; lapping the raw wafer; rough polishing the raw wafer; fine polishing the raw wafer to obtain an intermediate wafer; gluing the intermediate wafer on a flat carrier; performing single-side polishing of a first main side of the intermediate wafer; and performing single-side polishing of a second main side of the intermediate wafer.

Claims

1. A method for manufacturing a glass wafer for a plurality of augmented reality applications from a raw wafer, the method comprising the steps of: providing the raw wafer; edge-grinding of the raw wafer; lapping the raw wafer; rough polishing the raw wafer; fine polishing the raw wafer to obtain an intermediate wafer; gluing the intermediate wafer on a flat carrier; performing single-side polishing of a first main side of the intermediate wafer; and performing single-side polishing of a second main side of the intermediate wafer.

2. The method according to claim 1, wherein the step of providing the raw wafer includes: melting a glass and obtaining a glass strip from a molten glass, the glass strip being solid; annealing the glass strip; cutting the glass strip into at least one glass block; gluing at least two of the glass block together and thereby obtaining a glass batch; and at least one of: wire-sawing the glass batch so as at least one of: (a) to manufacture a plurality of thin substrates close to a final thickness of a proposed glass wafer; and (b) to saw a plurality of the glass block simultaneously; and cutting the raw wafer out of the glass batch.

3. The method according to claim 2, wherein at least one of: (i) a glass material of the glass wafer has a refractive index of between 1.3 and 2.5 at 587.562 nm; (ii) a maximal extension of the glass waferwhich has been manufacturedis: (a) 100 mm, 150mm, 200 mm, or 300 mm and/or (b) between 100 mm and 500 mm; (iii) a thickness of the glass waferwhich has been manufacturedis between 0.2 and 2 mm; (iv) a Knoop-hardness expressed as Knoop-hardness number HK.sub.0.1/20 of a glass material of the glass waferwhich has been manufacturedis between 400 and 900; and (v) a Young-Modulus of a glass material of the glass waferwhich has been manufacturedis between 1 GPa and 1000 GPa.

4. The method according to claim 2, wherein at least one of: (i) a size of the glass strip is 64021025 mm.sup.3; (ii) a size of the at least one glass block is 20520522 mm.sup.3; (iii) the step of wire-sawing is carried out having at least one of: a wire-speed of 30 m/min; a feed of 15 to 20 mm/h; a density of SiC of 1.1 to 1.3 g/cm.sup.3; and a tilt angle between a wire and a glass material of 3 to 5 degrees; (iv) the step of cutting the raw wafer out is carried out so that a maximal extension of the raw wafer of a glass material is between 180 mm and 220 mm and having at least one of: a pressure of 0.1 to 0.2 MPa; and a speed of 1 m/min; (v) the step of edge-grinding is carried out by having at least one of: a chamfer size of between 0.05 to 0.25; a number of cycles of 2 to 5; a feed of between 500 to 1000 mm/min; and a turning speed of a tool of 20000 to 40000 rpm; (vi) the step of lapping is carried out by having at least one of: a removal of between 150 to 400 m; a pressure of between 800 N to 2000 N; a rotational speed of between 10 to 25 rpm; and a slurry density of between 1.08 to 1.3 g/cm.sup.3; (vii) the step of rough polishing is carried out by having at least one of: a removal of between 25 to 45 m; a pressure of between 800 N to 2000 N; a rotational speed of between 10 to 25 rpm; and a slurry density of between 1.08 to 1.3 g/cm.sup.3; (viii) the step of fine polishing is carried out by having at least one of: a removal of between 1 to 5 m; a pressure of between 400 N to 1000 N; a rotational speed of between 10 to 25 rpm; and a slurry density of between 1.08 to 1.3 g/cm.sup.3; (ix) the step of performing single-side polishing of the first main side is carried out by having at least one of: a pressure of between 500 N to 2000 N; a rotational speed of between 10 to 25 rpm; a slurry density of between 1.08 to 1.3 g/cm.sup.3; a hardness of a pad of between 55 and 80; and a groove distance of between 5 mm and 30 mm; and (x) the step of performing single-side polishing of the second main side is carried out by having at least one of: a pressure of between 500 N to 2000 N; a rotational speed of between 10 to 25 rpm; a slurry density of between 1.08 to 1.3 g/cm.sup.3; a hardness of a pad of between 55 and 80; and a groove distance of between 5 mm and 30 mm.

5. A glass wafer, comprising: a first main surface; and a second main surface opposite the first main surface, a material of the glass wafer having a refractive index N, wherein, for each of a plurality of sub-domains of a maximal extension D of the glass wafer, the plurality of sub-domains are located within an effective domain of the glass wafer: from a thickness distribution of the glass wafer between the first main surface and the second main surface of a respective one of the plurality of sub-domains, a specific angle is configured for being determined, wherein the specific angle is determined as an angle of a planar contribution to a change in the thickness distribution; wherein the glass wafer has a maximal thickness of 2 mm or less, wherein the glass wafer has a specific thickness t, wherein the glass wafer is configured with respect to at least one parameter of the glass wafer such that for each of the plurality of sub-domains a local quality index LQI of the glass wafer is equal to or smaller than a threshold T, with the threshold T being defined as $T=\frac{{}_{\max }}{D}$ wherein .sub.max is 360 arcsec or less, wherein the local quality index LQI is defined as: $\mathrm{LQI}=\frac{.Math..Math.}{t}\sqrt{N^2-1}$

6. The glass wafer according to claim 5, wherein at least one of: (i) the refractive index N of the material of the glass wafer is at least one of (a) between 1.4 and 3; (b) 1.4 or more; and (c) 3 or less; and (ii) the material of the glass wafer has the refractive index N for a wavelength of between 587 nm and 588 nm.

7. The glass wafer according to claim 5, wherein at least one of: (i) a thickness of the glass wafer varies for each of two positions by at most 5000 nms; and (ii) the maximal thickness of the glass wafer is at least one of: (a) 1.9 mm or less; (b) 0.01 mm or more; and (c) between 0.01 mm and 1.8 mm.

8. The glass wafer according to claim 5, wherein each of the plurality of sub-domains at least one of: (i) is or is configured for being defined; (ii) includes at least one part of a body of the glass wafer between and inclusive of the first main surface and the second main surface; (iii) includes at least one of (a) at least 0.1%, and (b) at most 80%, respectively, of a total glass material of the glass wafer; (iv) is disk-like shaped; (v) has a same said maximal extension D; and (vi) includes in at least one cross-sectional plane a circular, an oval, or a rectangular circumferential shape.

9. The glass wafer according to claim 5, wherein at least one of: (i) each of the plurality of sub-domains at least one of is of a disk-like shape, of a rectangular shape, and has a same said maximal extension relative to one another; (ii) the plurality of sub-domains are at least partly overlapping relative to one another; and (iii) the plurality of sub-domains cover at least one of: (a) more than 50% of the glass wafer; and (b) less than 99.9% of the glass wafer.

10. The glass wafer according to claim 5, wherein at least one of: the maximal extension D of each of the plurality of sub-domains is a respective diameter of a plurality of disk-like sub-domains when the plurality of sub-domains is the plurality of disk-like sub-domains; and the maximal extension D of each of the plurality of sub-domains is: (i) 1 mm or more; (ii) 100 mm or less; and (iii) between 1 mm and 100 mm.

11. The glass wafer according to claim 5, wherein the effective domain at least one of: (i) is or is configured for being defined; (ii) includes at least one part of a body of the glass wafer between and inclusive of the first main surface and the second main surface; (iii) includes at least one of (a) at least 10%, and (b) at most 99.99% a total glass material of the glass wafer; (iv) is disk-like shaped; and (v) includes in at least one cross-sectional plane a circular, an oval, or a rectangular circumferential shape.

12. The glass wafer according to claim 5, wherein the specific thickness t is a minimal thickness, the maximal thickness, and/or a mean thickness of the glass wafer.

13. The glass wafer according to claim 5, wherein the planar contribution is determined by a contribution of orders 1 and 2 of an expression of the thickness distribution using a least-squares-approximation with Zernike-Polynomials, and wherein the orders 1 and 2 are expressed by an indexing scheme of James C. Wyant.

14. The glass wafer according to claim 5, wherein the at least one parameter is selected from the group comprising: a global wedge; at least one of a global dome and a global bowl; a topology of the first main surface; a topology of the second main surface; the maximal thickness of the glass wafer at least within the effective domain; a minimal thickness of the glass wafer at least within the effective domain; a thickness variation of the glass wafer at least within the effective domain; a roughness of the first main surface; and a roughness of the second main surface.

15. The glass wafer according to claim 5, wherein the .sub.maxwhich is a specific angle .sub.maxis 300 arcsec or less.

16. The glass wafer according to claim 5, wherein the local quality index LQI of the glass wafer is equal to or larger than 0.001 arcsec/mm.

17. The glass wafer according to claim 5, wherein the glass wafer forms, at least within the effective domain, an optical light guide.

18. The glass wafer according to claim 5, wherein the glass wafer is configured such that a plurality of light beams which are parallel or quasi-parallel relative to one another and which are coupled into any of the plurality of sub-domains at a feeding point of a respective one of the plurality of sub-domains under an angle of incidence propagates within the respective one of the plurality of sub-domains along a propagation path by experiencing a plurality of total inner reflections at the first main surface and the second main surface until the light beams are released out of the respective one of the plurality of sub-domains at an end point of the glass wafer under an angle of release, wherein a difference between a plurality of the angle of release for at least two of the plurality of light beams is at least one of (a) equal to or smaller than 120 arcsec, and (b) equal to or larger than 0.001 arcsec.

19. The glass wafer according to claim 18, wherein at least one of: (i) the plurality of light beams have a wavelength of between 587 nm and 588 nm; (ii) the plurality of light beams are coupled into the respective one of the plurality of sub-domains at the feeding point by way of at least one first coupling structure of the glass wafer; and (iii) the plurality of light beams are coupled out of the respective one of the plurality of sub-domains at the end point by way of at least one second coupling structure.

20. The glass wafer according to claim 5, wherein the material of the glass wafer is a glass material which comprises the following components in weight percent (wt.-%): TABLE-US-00011 SiO.sub.2 0-30 P.sub.2O.sub.5 0-25 B.sub.2O.sub.3 0-20 Na.sub.2O 0-15 K.sub.2O 0-10 CaO 0-5 BaO 0-25 ZnO 0-15 La.sub.2O.sub.3 0-50 Gd.sub.2O.sub.3 0-10 Y.sub.2O.sub.3 0-5 ZrO.sub.2 0-10 TiO.sub.2 0-30 Nb.sub.2O.sub.5 0-50.

21. A glass part element, comprising: a first main surface; and a second main surface opposite the first main surface, a material of the glass part element having a refractive index N, wherein, for the glass part element of a maximal extension D: from a thickness distribution of the glass part element between the first main surface and the second main surface of the glass part element, a specific angle is determined as an angle of a planar contribution to a change in the thickness distribution; wherein the glass part element has a maximal thickness of 2 mm or less, wherein the glass part element has a specific thickness t, wherein the glass part element is configured with respect to at least one parameter of the glass element such that a local quality index LQI of the glass part element is equal to or smaller than a threshold T, with the threshold T being defined as $T=\frac{{}_{\max }}{D}$ wherein .sub.max is 360 arcsec or less; wherein the local quality index LQI is defined as: $\mathrm{LQI}=\frac{.Math..Math.}{t}\sqrt{N^2-1}$

22. The glass part element according to claim 21, wherein the specific thickness t is at least one of a minimal thickness, the maximal thickness, and a mean thickness of the glass part element.

23. The glass part element according to claim 21, wherein at least one of: the maximal extension D of the glass part element is a respective diameter of a disk-like glass part element when the glass part element is the disk-like glass part element; and the maximal extension D of the glass part element is: (i) 1 mm or more; (ii) 100 mm or less; and (iii) between 1 mm and 100 mm.

24. The glass part element according to claim 21, wherein the glass part element has in at least one cross-sectional plane a circular, an oval, or a rectangular circumferential shape.

25. The glass part element according to claim 21, wherein the glass part element is configured for forming a part of a stack including at least two of the glass part element, such that at least one of: (i) each of the glass part element within the stack includes a wedge that is in the same or quasi-same manner; (ii) the at least two glass part element are stacked vertically relative to one another; (iii) wherein the .sub.maxwhich is a specific angle .sub.maxof each of the at least two glass part element is 300 arcsec or less; and (iv) each of the glass part element within the stack includes a wedge which are oriented opposed relative to one another, wherein the glass part element is configured for formingand thereby being used asa part of an augmented reality device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0301] The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

[0302] FIG. 1 shows a schematic illustration of a part of a glass wafer according to the second aspect of the invention;

[0303] FIG. 2 shows a schematic illustration of a sub-domain of a glass wafer according to the second aspect of the invention;

[0304] FIGS. 3A, 3B, 4A, 4B, 5A, 5B, 6A, 6B, 7A, 7B, 8A, 8B, 9A, 9B, 10A, 10B, 11A, 11B, 12A, 12B, 13A, and 13B show thickness distribution profiles of different glass wafers according to the second aspect of the invention;

[0305] FIG. 14 shows a first stack having three glass part elements;

[0306] FIG. 15 shows a second stack having two glass part elements;

[0307] FIG. 16 shows a third stack having two glass part elements;

[0308] FIG. 17 shows a fourth stack having three glass part elements; and

[0309] FIG. 18 shows principles of exemplary Wedge and Dome contributions.

[0310] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

[0311] FIG. 1 shows a schematic illustration of a part, such as at least one part of a sub-domain, of a glass wafer 1 according to the second aspect of the present invention in a cross-sectional plane.

[0312] The glass wafer 1 has a mean thickness t, a first main surface 3 and a second main surface 5. The first main surface 3 has a slope with respect to the second main surface 5. Due to the slope, the first main surface 3 and the second main surface 5 enclose an angle . Or in other words, between the normal vector of the first main surface 3 and the normal vector of the second main surface 5 the angle is enclosed. If based on a thickness distribution of the glass wafer 1 a Zernike-Polynomial regression is obtained, this angle can be obtained. Likewise, from a thickness distribution of sub-domains of the glass wafer 1, the respective specific angle can be obtained for that sub-domain from the corresponding Zernike-Polynomial regression.

[0313] Within the glass wafer 1 a light beam 7 propagates in FIG. 1 from left to right along a main propagation direction X by way of total inner reflections at the first main surface 3 and the second main surface 5.

[0314] In FIG. 1, the light beam 7 encloses an angle with the normal vector of the second main surface 5, after experiencing a total inner reflection at a certain position 9a at the second main surface 5. Apparently, due to the slope between the two main surfaces 3 and 5, after a further total inner reflection at the position 9b, the angle enclosed between the light beam 7 and the first main surface 3 is +. After the next total inner reflection at a position 9c, light beam 7 encloses an angle +2 with the normal vector of the second main surface 5. Likewise, after a further total inner reflection at the position 9d, the angle between the light beam 7 and the first main surface 3 is +3. And so on.

[0315] It is clear from this illustration that due to the slope between the two main surfaces 3 and 5, the angle of total inner reflection of the light beam 7 increases over the propagation path along direction X. In other words, the larger the distance is that the light beam 7 propagates within the glass wafer 1 before it leaves the glass wafer 1 (e.g. via some coupling structures provided on the first main surface 3 which, however, is not shown in FIG. 1), the larger is the last angle of total inner reflection that the light beam 7 has. And, therefore, the larger the angle of release (i.e. the angle enclosed between the released light beam and the normal vector of the first main surface 3 for the case the coupling structure has a refractive index lower than or equal to the one of the glass wafer) is.

[0316] For a plurality of sub-domains within the effective domain of the wafer 1, the ratio of the value of || and the value of the specific thickness t (taking into account the refractive index of the glass material), i.e. the local quality index, LQI, is limited, that is, basically the maximal angle of total inner reflection is limited, that is, the maximal angle of total inner reflection for a particular propagation distance.

[0317] It is clear for the person skilled in the art that the illustration of the glass wafer 1 shown in FIG. 1 corresponds also to the shape of its thickness distribution. This is especially because the bottom surface is flat. Therefore, the illustration of FIG. 1 can be referred to for both cases: discussing the principles of reflection occurring for the glass wafer 1 and discussion aspects concerning the thickness distribution of the respective wafer 1.

[0318] FIG. 2 shows a schematic illustration of a sub-domain 10 of a glass wafer 1 according to the second aspect of the invention in a cross-sectional plane. (Indeed, the sub-domain 10 might correspond to a glass part element according to the third aspect of the invention.) In principle, the glass wafer 1 is similar to the glass wafer 1 described above with respect to FIG. 1. Therefore, for the glass wafer 1 the same structural features as for the glass wafer 1 have same reference signs but single dashed.

[0319] It is again noted that the illustration of the sub-domain 10 corresponds at the same time to the thickness distribution of the sub-domain 10. Therefore, the illustration of FIG. 2 can be referred to for both cases: discussing the principles of reflection occurring for the glass wafer 1 and discussion aspects concerning the thickness distribution of the respective sub-domain.

[0320] A bundle of parallel light beams 11a and 11b (only two of which are shown in FIG. 2) is coupled at a feeding area 13 of the glass wafer 1/sub-domain 10 via a first coupling structure 15 into the glass wafer 1. The light beams correspond to one pixel of the computer-generated visual information. Initially, each light beam 11a, 11b encloses an angle with the normal vector of the first main surface 3, i.e. the light beams 11a and 11b are parallel to each other. After a first total inner reflection at a position 17a, each light beam 7a, 7b encloses an angle + with the normal vector of the second main surface 5. At a position 17b the light beam 7a is coupled out of the glass wafer 1 at a releasing area 19 by way of a second coupling structure 21 which covers the releasing area 19.

[0321] The feeding area 13 and the releasing area 19 here correspond to the contact surface between the glass wafer 1 (to be more precise, its first main surface 3) and, respectively, the first coupling structure 15 and the second coupling structure 21.

[0322] In the actual application in AR the coupling structures may be surface gratings to couple light in and out. Then, there is a statistical likelihood that the light beam is coupled out or refracted back and eventually coupled out only after more bounces. It has to be understood that a light beam which hits the releasing area 19 experiences a total inner reflection with a certain probability P1 and is released out of the glass wafer 1 with a certain probability P2, where P1+P2=1 (neglecting minor absorption effects or the like).

[0323] While light beam 11a leaves the glass wafer 1 at a position 17b, the light beam 11b experiences a further total inner reflection at position 17b and at position 17c. At position 17d, light beam 11b finally also leaves the glass wafer 1 via the second coupling structure 19.

[0324] Since the light beam 11a experienced in total three total inner reflections, hence, one more than light beam 11b did, the angle of release 1 enclosed between the normal vector of the first main surface 3 and the light beam 11b and the angle of release 2 enclosed between the normal vector of the first main surface 3 and the light beam 11a are different.

[0325] The coupling elements 15 and 21 are designed in form of surface-gratings provided on the first main surface 3. It is noted that the refractions of the light beam entering the coupling structure 15 and leaving the coupling structure 21 have not been illustrated in FIG. 2. In other embodiments, the coupling elements 15 and 21 may be designed in form of prisms made of a glass material having a refractive index which is lower than that of the glass material of the glass wafer 1.

[0326] Since the glass wafer 1 meets the local quality index for the sub-domain 10 shown in FIG. 2, the slope c between the first and second main surfaces 3, 5 of the glass wafer 1 is limited. Therefore, also the difference between the angles of release 1 and 2 is limited, i.e. |12| is smaller than some threshold value. In other words, although light beams 11a and 11b are no longer parallel to each other after leaving the glass wafer 1/sub-domain 10, they still allow to present the respective pixel of the computer-generated visual information in high visual quality to a person. This is because the two light beams 11a and 11b have still a similar angle of release, hence, the light beams 11a and 11b still reach the same or nearly the same point on the retina (or in general on some detecting way).

[0327] To be more precise, the main surfaces 3, 5 of the wafer 1/sub-domain 10 are specifically designed with respect to the wedge, hence , which is a parameter of the wafer. The glass wafer 1 obtained that way allows a light propagation between the first and second main surfaces 3, 5 with angles of total inner reflection of limited accumulation. Thus, along the extension of the coupling interface 19, the difference between the angles of total inner reflection is restricted to certain limits for the sub-domain shown in FIG. 2.

[0328] Again, the specific angle can be obtained from the thickness distribution of the sub-domain or glass wafer. At the same time, this angle correspond to the wedge as shown in the FIGS. 1 and 2.

[0329] The sub-domain 10 is, therefore, well-suited for AR applications. For example, a glass part element can be cut out from the sub-domain 10 (or it can be directly used as glass part element) which in turn can be used as basic parts for eye-pieces in glasses for AR devices.

[0330] FIGS. 3A, 4A, 5A, 6A, 7A, 8A, 9A, 10A, 11A, 12A, 13A each shows the thickness distribution profile of a glass wafer according to the second aspect of the invention, which has been manufactured with a method according to the first aspect of the invention. FIGS. 3B, 4B, 5B, 6B, 7B, 8B, 9B, 10B, 11B, 12B, 13B each shows a top view of the thickness distribution profile. On the top view there is shown superimposed a cutting line. FIGS. 3B, 4B, 5B, 6B, 7B, 8B, 9B, 10B, 11B, 12B, 13B further include the course of the thickness distribution profile of the glass wafer for a slice through the wafer along the cutting line.

[0331] The properties of each of the glass wafers concerning its general shape, its diameter Dw, the refractive index N of its glass material for a wavelength of 632.8 nm and its physical thickness t, are listed in the table below. Here, the specific thickness t corresponds to a mean thickness of the glass wafer.

TABLE-US-00009 Glass Representation Diameter wafer shown in General Dw N t ID FIG. . . . shape [mm] [1] [mm] 1 3 Dom 300 2.0010 0.5 2 4 Dom 300 2.0010 0.5 3 5 Dom 300 2.0010 0.5 4 6 Bowl 300 1.9037 0.3 5 7 Wedge 300 1.9037 0.3 6 8 Dom 200 1.9037 0.5 7 9 Dom 200 1.9037 0.5 8 10 Dom 200 2.0010 0.5 9 11 Dom 200 2.0010 0.5 10 12 Wedge 200 1.9220 0.7 11 13 Wedge 200 1.9220 0.7

[0332] Next, the quality of the wafers with respect to the visual quality of computer-generated visual information is investigated.

[0333] For this purpose, for each glass wafer the local quality index, LQI, has been determined for different pluralities of disk-like shaped sub-domains with diameter Ds defined within an effective domain of the respective wafers. The effective domain of each wafer includes the central portion of the respective glass wafer and has a diameter De. In other words, the effective domain corresponds to the part of the wafer with reduced diameter of De.

[0334] In the table below the results for the average and maximal LQI for each wafer and for each plurality of sub-domains thereof are shown. To be more precise, for each wafer and for each plurality of sub-domains the mean value of the LQI (across all sub-domains of same diameter Ds for a particular wafer) and the maximal value of the LQI (across all sub-domains of same diameter Ds for a particular wafer) are provided. Of course, the LQI has to be checked for each sub-domain in order to check if the wafer is a proposed wafer.

[0335] Here, the maximal extension D of a sub-domain corresponds to the diameter Ds, because the sub-domain is here disk-like shaped.

[0336] Indeed, the maximal value of the LQI would be sufficient in order to verify whether the glass wafer is a glass wafer according to the second aspect of the invention, because for all sub-domains the LQI has to be met.

[0337] Note that the same glass wafer ID indicates the same glass wafer in both tables.

TABLE-US-00010 Glass Number Mean Maximum wafer Ds of sub- De LQI LQI ID [mm] domains [mm] [arcsec/mm] [arcsec/mm] 1 60 48 284 2.91 4.61 40 125 284 3.05 5.20 30 236 284 3.15 5.44 20 559 284 3.19 6.41 2 60 48 284 2.57 4.33 40 125 284 2.77 4.64 30 236 284 2.84 5.10 20 559 284 2.95 6.17 3 60 48 284 1.66 3.33 40 125 284 1.84 4.02 30 236 284 1.94 4.44 20 559 284 2.01 4.89 4 60 48 290 2.00 4.37 40 125 290 2.16 4.91 30 236 290 2.27 5.35 20 559 290 2.38 5.94 5 60 48 290 1.35 3.19 40 125 290 1.46 4.37 30 236 290 1.57 6.53 20 559 290 1.78 8.69 6 60 19 190 1.10 2.24 40 50 190 1.13 3.01 30 94 190 1.26 3.60 20 240 190 1.59 5.51 7 60 19 190 1.23 2.33 40 50 190 1.39 3.30 30 94 190 1.46 4.21 20 240 190 1.68 5.09 8 60 19 190 1.11 1.46 40 50 190 1.18 2.43 30 94 190 1.25 3.54 20 240 190 1.59 5.79 9 60 19 190 1.39 2.08 40 50 190 1.46 2.53 30 94 190 1.46 3.19 20 240 190 1.59 3.92 10 60 19 190 0.70 1.34 40 50 190 0.77 1.48 30 94 190 0.82 1.69 20 240 190 0.89 2.06 11 60 19 190 1.06 1.45 40 50 190 1.10 1.78 30 94 190 1.10 2.09 20 240 190 1.17 2.91

[0338] According to the results listed in the table above, for example, for the glass wafer ID 1 of diameter Dw=300 mm, a plurality of 48 different sub-domains (each sub-domain having a defined diameter of Ds=60 mm) has been defined within the effective domain of the glass wafer ID 1, the effective domain being a defined central portion of the wafer and having a diameter of De=284 mm. For each of the 48 sub-domains a specific angle has been determined based on the thickness distribution profile of that sub-domain. Subsequently, along with the physical mean thickness t of the glass wafer ID 1 (i.e. t=0.5 mm) and the refractive index N of the glass material (i.e. N=2.0010), an LQI for each of the respective sub-domains has been determined. For the glass wafer ID 1, the maximal LQI determined for one of the sub-domains of diameter Ds=60 mm was LQI=4.61 arcsec/mm, while the mean value for the LQI determined across all of the 48 sub-domains of diameter Ds=60 mm was LQI=2.91 arcsec/mm.

[0339] Consequently, for sub-domains of diameter Ds=60 mm, all sub-domains have an LQI which is below the threshold value of 360/60 arcsec/mm.

[0340] Obviously, the LQI of all sub-domains of all wafers have an LQI which is smaller than 360/60 arcsec/mm. Thus, all of the eleven glass wafers meet the LQI criterion even for sub-domains having the smallest diameter of Ds=20 mm.

[0341] All of the glass wafers shown in FIGS. 3A-13B are well-suited for AR application. For example, glass part elements (for example of the size of the defined sub-domains) can be cut out of the glass wafer, hence, serving as basic parts for eye-pieces for glasses in AR devices.

[0342] FIG. 14 shows a stack 23 which includes three glass part elements 25a, 25b and 25c according to the third aspect of the invention. The glass part elements 25a-c are vertically stacked. Here, each glass part element is used for the propagation of a light beam 27a-c of an individual color. The top glass part element 25a is used for red colored light beam transmission. The glass part element 25b in the middle is used for green colored light beam transmission. The bottom glass part element 25c is used for blue colored light beam transmission.

[0343] The three light beams 27a, 27b, 27c all correspond to the same pixel of the visual information. Thus, the three light beams 27a, 27b, 27c are initially coupled into the respective glass part element 25a-c parallel to each other. Ideally, the light beams 27a-c are also parallel to each other once they left the respective glass part element 25a-c, hence the stack 23.

[0344] This can be ensured in that the change of the angle of total inner reflection during propagation of the light beams 27a-c within the individual glass part elements 25a-c is the same (ideally zero, as it is the case here for stack 23) or at least similar. The similar change of the angle of total inner reflection is achieved in that the glass part elements 25a-c are designed such that the local quality index is met for each glass part element 25a-c. Hence, the change of the angle of the total inner reflection is limited for all light beams 27a-c in all glass part elements 25a-c.

[0345] In FIG. 14 each incoming light beam 27a-c has three outgoing light beams for illustration purposes. It is clear, that light beams 27a-c may be a continuous light beam and depending on the probability, light is coupled out at different positions of the respective glass part element 25a-c. In FIG. 14 three outgoing beams are illustrated per glass part element. However, the internal total reflections of the light beams are not shown in FIG. 14.

[0346] FIG. 15 shows another stack 29 which includes two identical glass part elements 31a and 31b. In principle the same situation is present for stack 29 as for stack 23 described above with respect to FIG. 14. However, each of the glass part elements 31a, 31b has a wedge, i.e. an angle is enclosed between the two (ideally flat) main surfaces of the glass part elements 31a and 31b. As a consequenceand as described above in greater detaila light beam 33a, 33b which leaves the glass part element after a longer propagation distance within the glass material, hence, experiencing more total inner reflections, has a greater change of the angle of release compared to a light beam which leaves the glass part element earlier (for example via a respective coupling structure, which is not shown here). This is also evident from FIG. 15, where for each glass part element 31a, 31b three outgoing light beams are shown (solid lines) having propagation paths of different length. For example, it can be taken from FIG. 15 in a qualitative manner, that for the glass part element 31a, the third outgoing beam (solid line) encloses a larger angle with the first outgoing beam (dashed line) than the second outgoing beam (solid line) does. The same applies to the glass part element 31b.

[0347] For the situation shown in FIG. 15, the wedge is oriented for both glass part elements 31a and 31b in the same manner, i.e., the rising edge is from left to right in FIG. 15 for both glass part elements 31a-b. In this case, all changes of the angle of the total inner reflections occur in the same direction. Hence, the light beams leaving the stack 29 have the same properties (especially angle of release) as they would have for a single glass part element.

[0348] FIG. 16 shows a stack 29 which is similar to the stack 29 of FIG. 15. Hence, the same structural features have the same reference numerals but single dashed. However, the glass part elements 31a and 31b of stack 29 are oriented opposing to one another, i.e. the rising edge is from right to left in FIG. 16 for glass part element 31a and from left to right in FIG. 16 for glass part element 31b. In such a case, each glass part element may contribute not more than 50% of the total error budget. Or, in other words, it might be required to reduce the maximal allowed local quality index for the individual glass part elements, for example reduced by 50% compared to the situation described with respect to stack 29 shown in FIG. 15.

[0349] FIG. 17 shows a stack 35 which includes three glass part elements 37a, 37b and 37c. The glass part elements 37a and 37b have a wedge while the glass part element 37c has ideally parallel main surfaces (similar to the glass part elements of stack 23). Also, the three parallel incoming laser beams 39a, 39b and 39c are illustrated. It is evident from FIG. 17 that also for a stack having more than two glass part elements, such as stack 35, the maximal effect of the change of the angle of the total inner reflection is present, if the orientation of the glass part elements 37a and 37b is opposed.

[0350] Thus, if two or more glass part elements are included by a stack, it is optional that each glass part element contributes only 50% of the total error budget. Or, in other words, each glass part element has a reduced maximal allowed local quality index, for example reduced by 50%.

[0351] FIG. 18 shows principles of exemplary Wedge and Dome contributions, H.sub.w and H.sub.d respectively. To be more precise, FIG. 18 shows a thickness distribution profile of a glass wafer of radius R which has a wedge contribution H.sub.w and a dome contribution H.sub.d. The angle is the slope angle of the wedge with height H.sub.w and basis 2R.

[0352] The features disclosed in the description, the figures as well as the claims could be essential alone or in every combination for the realization of the invention in its different embodiments.

REFERENCES

[0353] 1, 1 Glass wafer [0354] 3, 3 First main surface [0355] 5, 5 Second main surface [0356] 7 Light beam [0357] 9a, 9b, 9c, 9d Position [0358] 10 Sub-Domain [0359] 11a, 11b Light beam [0360] 13 Feeding area [0361] 15 First coupling structure [0362] 17a, 17b, 17c, 17d Position [0363] 19 Releasing area [0364] 21 Second coupling structure [0365] 23 Stack [0366] 25a, 25b, 25c Glass part element [0367] 27a, 27b, 27c Light beam [0368] 29, 29 Stack [0369] 31a, 31b, 31a, 31b Glass part element [0370] 33a, 33b, 33a, 33b Light beam [0371] 35 Stack [0372] 37a, 37b, 37c Glass part element [0373] 39a, 39b, 39c Light beam [0374] H.sub.d Dome contribution [0375] H.sub.w Wedge contribution [0376] t Thickness [0377] R Radius [0378] X Direction [0379] Angle [0380] 1, 2 Angle of release [0381] Angle

[0382] While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.