Magic Leap Patent | Biased total thickness variations in waveguide display substrates

Patent: Biased total thickness variations in waveguide display substrates

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Publication Number: 20210255387

Publication Date: 20210819

Applicants: Magic Leap

Abstract

A plurality of waveguide display substrates, each waveguide display substrate having a cylindrical portion having a diameter and a planar surface, a curved portion opposite the planar surface defining a nonlinear change in thickness across the substrate and having a maximum height D with respect to the cylindrical portion, and a wedge portion between the cylindrical portion and the curved portion defining a linear change in thickness across the substrate and having a maximum height W with respect to the cylindrical portion. A target maximum height D.sub.t of the curved portion is 10.sup.-7 to 10.sup.-6 times the diameter, D is between about 70% and about 130% of D.sub.t, and W is less than about 30% of D.sub.t.

Claims

1.-19. (canceled)

20. A waveguide display substrate comprising: a cylindrical portion having a diameter and a planar surface; a curved portion opposite the planar surface, defining a nonlinear change in thickness across the substrate; and a wedge portion between the cylindrical portion and the curved portion, defining a linear change in thickness across the substrate, wherein a target maximum height D.sub.t of the curved portion is 10.sup.-7 to 10.sup.-6 times the diameter.

21. The waveguide display substrate of claim 20, wherein W is a maximum height of the wedge portion with respect to the cylindrical portion, and wherein W is less than 30% of D.sub.t.

22. The waveguide display substrate of claim 20, wherein D is a maximum height of the curved portion with respect to the cylindrical portion, and wherein D is between 70% and 130% of D.sub.t.

23. The waveguide display substrate of claim 20, wherein the nonlinear change in thickness is a quadratic change in thickness.

24. The waveguide display substrate of claim 20, wherein the curved portion in is the form of a dome.

25. The waveguide display substrate of claim 24, wherein the dome is spherical.

26. The waveguide display substrate of claim 20, wherein an average thickness of the waveguide display substrate is between about 200 microns and about 2000 microns.

27. The waveguide display substrate of claim 20, wherein an average diameter of the waveguide display substrate is between about 2 centimeters and about 50 centimeters.

28. The waveguide display substrate of claim 20, wherein the waveguide display substrate comprises a molded polymer.

29. The waveguide display substrate of claim 20, wherein the waveguide display substrate comprises at least one of a polished glass, silicon, or a metal substrate.

30. A method comprising: fabricating a waveguide display substrate such that the display substrate comprises: a cylindrical portion having a diameter and a planar surface; a curved portion opposite the planar surface and defining a nonlinear change in thickness across the substrate; and a wedge portion between the cylindrical portion and the curved portion and defining a linear change in thickness across the substrate, wherein the waveguide display substrate fabricated such as a target maximum height Dt of the curved portion is 10.sup.-7 to 10.sup.-6 times the diameter.

31. The method of claim 30, wherein W is a maximum height of the wedge portion with respect to the cylindrical portion, and wherein the waveguide display substrate is fabricated such that W is less than 30% of D.sub.t.

32. The method of claim 30, wherein D is a maximum height of the curved portion with respect to the cylindrical portion, and wherein the waveguide display substrate is fabricated such that D is between 70% and 130% of D.sub.t.

33. The method of claim 30, wherein the waveguide display substrate is fabricated such that the nonlinear change in thickness is a quadratic change in thickness.

34. The method of claim 30, wherein the waveguide display substrate is fabricated such that the curved portion in is the form of a dome.

35. The method of claim 34, wherein the waveguide display substrate is fabricated such that the dome is spherical.

36. The method of claim 30, wherein the waveguide display substrate is fabricated such that an average thickness of the waveguide display substrate is between about 200 microns and about 2000 microns.

37. The method of claim 30, wherein the waveguide display substrate is fabricated such that an average diameter of the waveguide display substrate is between about 2 centimeters and about 50 centimeters.

38. The method of claim 30, wherein the waveguide display substrate is fabricated using a molded polymer.

39. The method of claim 30, wherein the waveguide display substrate is fabricated using at least one of a polished glass, silicon, or a metal substrate.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent application Ser. No. 16/792,083 filed Feb. 14, 2020, which claims the benefit of U.S. Patent Application Nos. 62/805,832 filed Feb. 14, 2019, and 62/820,769 filed Mar. 19, 2019, all of which are herein incorporated by reference in their entirety.

TECHNICAL FIELD

[0002] This invention relates to biased total thickness variations in waveguide display substrates.

BACKGROUND

[0003] Optical imaging systems, such as wearable head-mounted systems, typically include one or more eyepieces that present projected images to a user. Eyepieces can be constructed using thin layers of one or more refractive materials. As examples, eyepieces can be constructed from one or more layers of highly refractive glass, silicon, metal, or polymer substrates.

[0004] In some cases, an eyepiece layer can be patterned (e.g., with one or more light diffractive nanostructures) such that it displays received light incoupled from an external projector. Further, multiple eyepieces layers (or "waveguides") can be used in conjunction to project a simulated three-dimensional image. For example, multiple waveguides--each having a specific pattern--can be layered, and each waveguide can relay specific light information of a portion of a volumetric image (e.g., wavelength or focal distance) such that in the aggregate of specific light information from each of the waveguides, the entire coherent volumetric image is viewable. Thus, the eyepieces can collectively present the full color volumetric image to the user across three-dimensions. This can be useful, for example, in presenting the user with a "virtual reality" environment.

[0005] Unintended variations in an eyepiece can reduce the quality of a projected image. Examples of such unintended variations include wrinkles, uneven thicknesses, and other physical distortions that can negatively affect the performance of the eyepiece.

SUMMARY

[0006] A first general aspect includes a plurality of waveguide display substrates, each waveguide display substrate having a cylindrical portion having a diameter and a planar surface, a curved portion opposite the planar surface defining a nonlinear change in thickness across the substrate and having a maximum height D with respect to the cylindrical portion, and a wedge portion between the cylindrical portion and the curved portion defining a linear change in thickness across the substrate and having a maximum height W with respect to the cylindrical portion. A target maximum height D.sub.t of the curved portion is 10.sup.-7 to 10.sup.-6 times the diameter, D is between about 70% and about 130% of D.sub.t, and W is less than about 30% of D.sub.t. For the plurality of waveguide display substrates, an average of D is D.sub.mean, a maximum D for the plurality of waveguide display substrates is D.sub.max, a minimum D for the plurality of waveguide display substrates is D.sub.min, and a maximum W for the plurality of waveguide display substrates is W.sub.max.

[0007] A second general aspect includes fabricating the plurality of waveguide display substrates of the first general aspect.

[0008] Implementations of the first and second general aspects may include one or more of the following features.

[0009] In some implementations, the nonlinear change in thickness is a quadratic change in thickness. The curved portion may be in the form of a dome. In some cases, the dome is spherical.

[0010] An average thickness of the plurality of waveguide display substrates is typically between about 200 microns and about 2000 microns. An average diameter of the plurality of waveguide display substrates is typically between about 2 centimeters and about 50 centimeters. W.sub.max/D.sub.mean is typically less than about 0.3. (D.sub.mean-D.sub.min)/D.sub.mean is typically less than about 0.3. (D.sub.max-D.sub.min)/D.sub.mean is typically less than about 0.3. D is typically in a range of about 0.1 microns to about 5 microns. W is typically in a range of 0 to about 1.5 microns. An average total thickness variation of the plurality of substrates is typically between about 0.1 microns and about 6.5 microns.

[0011] In some implementations, the waveguide display substrates comprise a molded polymer. In certain implementations, the waveguide display substrates comprise a polished glass, silicon, or metal substrate.

[0012] Implementations of the second general aspect may include one or more of the following features.

[0013] In some cases, fabricating the plurality of waveguide display substrates may include polishing the waveguide display substrates, where the waveguide display substrates are formed of glass, metal, or silicon. In certain cases, fabricating the plurality of waveguide display substrates includes molding polymeric waveguide display substrates.

[0014] The second general aspect may further include forming one or more waveguides on each of the waveguide display substrates. The one or more waveguides may include at least two waveguides, and the waveguides may be positioned in a radial pattern on each waveguide display substrate.

[0015] The details of one or more embodiments of the subject matter of this disclosure are set forth in the accompanying drawings and the description. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

[0016] FIG. 1 depicts a sample waveguide display substrate with waveguide areas.

[0017] FIGS. 2A-2C depict polished waveguide display substrates having flat, convex, and concave cross-sectional shapes, respectively.

[0018] FIGS. 3A and 3B depict total thickness variation (TTV) comparisons of waveguide display substrates.

[0019] FIG. 4 depicts TTV of a polished waveguide display substrate with a convex surface.

[0020] FIG. 5 shows a cross section of a waveguide display substrate with a biased TTV having linear (wedge) and nonlinear (dome) components.

[0021] FIGS. 6A-6C show waveguide display substrate yield versus TTV, dome height, and wedge height for ultra-low TTV waveguide display substrates. FIGS. 6D-6F show waveguide display substrate yield versus TTV, dome height, and wedge height for biased TTV waveguide display substrates.

[0022] FIG. 7 shows waveguide eyebox efficiency versus "dome" height TTV (nm) of a spherical waveguide display substrate on a 6 inch waveguide display substrate for a typical diffractive waveguide display with 300 .mu.m average thickness and 0 nm "wedge" TTV.

DETAILED DESCRIPTION

[0023] Total thickness variation (TTV) is one metric for improving performance of an optical waveguide. As used herein, TTV generally refers to the difference between the maximum and minimum values of the thickness of the waveguide or the waveguide display substrate on which the waveguide is formed. As light travels through an optical waveguide, typically by total internal reflection, variations in the thickness alter the light propagation path(s). Angular differences in the light propagation path(s) can affect image quality with field distortions, image blurring, and sharpness loss.

[0024] Waveguide preparation and processing typically occurs by arranging a number of waveguides to designated areas onto a waveguide display substrate (e.g., a wafer). FIG. 1 depicts waveguide display substrate 100 with a radial arrangement of waveguides 102. TTV can be reduced by fabricating a flat waveguide display substrate (i.e., a waveguide display substrate with zero TTV), for example, by polishing the substrate (e.g., a metal, glass or silicon substrate) or originally molding the substrate (e.g., a polymer substrate) with high-precision. However, polishing can produce a certain amount of curvature upon the waveguide display substrate and the resultant waveguides formed thereon. FIG. 2A depicts polished flat waveguide display substrate 200. FIGS. 2B and 2C depict polished convex waveguide display substrate 202 and polished concave waveguide display substrate 204, respectively. Though polishing can yield convex or concave curvatures, embodiments described herein are explained with reference to a convex curvature, such as that depicted in FIG. 2B.

[0025] Since completely flat polishing or molding, such as that depicted in FIG. 2A, requires extensive and costly processing to achieve, a certain degree of TTV is typically tolerated. With most low TTV processes for waveguide display substrates (e.g., 20 nmX

(D.sub.mean-D.sub.min)/D.sub.mean<Y

(D.sub.max-D.sub.mean)/D.sub.mean<Z

With these relationships, X, Y, and Z typically range from 0 to 10 among different substrate polishing or molding processes. FIGS. 6A-6C show a set of waveguide display substrates that result in higher values of X, Y, and Z than the set of waveguide display substrates shown in FIGS. 6D-6F. As X, Y, and Z approach zero, as opposed to having TTV itself approach zero, overall efficiency of a plurality of waveguides produced on numerous subsections of numerous waveguide display substrates both increases and has fewer variations. Also, as X, Y, and Z approach zero, luminance uniformity and color uniformity among the resultant waveguides also increases and has fewer variations. In a typical substrate polishing or molding process, X, Y, and Z increase as the targeted TTV.sub.max approaches zero. Ultra-low TTV waveguide display substrates typically have X, Y and Z in the range of 1-10, and biased TTV waveguide display substrates have X, Y and Z in the range of 0 to 0.3, so a biased (or nonzero target) TTV can contribute toward improved waveguide display image quality.

[0034] FIG. 7 shows waveguide eyebox efficiency versus "dome" TTV (nm) of a spherical waveguide display substrate shape on a 6 inch wafer for a typical diffractive waveguide display with 300 .mu.m average thickness and 0 nm "wedge" TTV. As seen in FIG. 7, eyebox efficiency is a maximum between a TTV of 400 nm and a TTV of 600 nm. Waveguide eyebox efficiency here refers to the sum of light entering a 15.times.20 mm.sup.2 rectangular area 15 mm.sup.2 away from the eye-side of a diffractive waveguide display's output grating relative to the sum of light incident on the waveguide display's input coupling grating as calculated by a typical diffractive waveguide simulation.

[0035] Although this disclosure contains many specific embodiment details, these should not be construed as limitations on the scope of the subject matter or on the scope of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in this disclosure in the context of separate embodiments can also be implemented, in combination, in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments, separately, or in any suitable sub-combination. Moreover, although previously described features may be described as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

[0036] Particular embodiments of the subject matter have been described. Other embodiments, alterations, and permutations of the described embodiments are within the scope of the following claims as will be apparent to those skilled in the art. While operations are depicted in the drawings or claims in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed (some operations may be considered optional), to achieve desirable results.

[0037] Accordingly, the previously described example embodiments do not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure.