Magic Leap Patent | Customized polymer/glass diffractive waveguide stacks for augmented reality/mixed reality applications
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Publication Number: 20210382221
Publication Date: 20211209
Applicants: Magic Leap
Abstract
A diffractive waveguide stack includes first, second, and third diffractive waveguides for guiding light in first, second, and third visible wavelength ranges, respectively. The first diffractive waveguide includes a first material having first refractive index at a selected wavelength and a first target refractive index at a midpoint of the first visible wavelength range. The second diffractive waveguide includes a second material having a second refractive index at the selected wavelength and a second target refractive index at a midpoint of the second visible wavelength range. The third diffractive waveguide includes a third material having a third refractive index at the selected wavelength and a third target refractive index at a midpoint of the third visible wavelength range. A difference between any two of the first target refractive index, the second target refractive index, and the third target refractive index is less than 0.005 at the selected wavelength.
Claims
1-14. (canceled)
15. A method of fabricating diffractive waveguides for a waveguide stack, the method comprising: combining a first monomer and a second monomer in a first ratio to yield a first polymerizable material; casting the first polymerizable material in a first diffractive waveguide mold and polymerizing the first polymerizable material to yield a first diffractive waveguide for guiding light in a first visible wavelength range, wherein the first diffractive waveguide has a first yellowness index and a first refractive index at a selected wavelength; combining the first monomer and the second monomer in a second ratio to yield a second polymerizable material; and casting the second polymerizable material in a second diffractive waveguide mold and polymerizing the second polymerizable material to yield a second diffractive waveguide for guiding light in a second visible wavelength range, wherein the second diffractive waveguide has a second yellowness index and a second refractive index at the selected wavelength, wherein: a wavelength in the first visible wavelength range exceeds a wavelength in the second visible wavelength range, the first refractive index exceeds the second refractive index at the selected wavelength, and the first yellowness index exceeds the second yellowness index at the selected wavelength.
16. The method of claim 15, further comprising: combining the first monomer and the second monomer in a third ratio to yield a third polymerizable material; and casting the third polymerizable material in a third diffractive waveguide mold and polymerizing the third polymerizable material to yield a third diffractive waveguide for guiding light in a third visible wavelength range, wherein the third diffractive waveguide has a third yellowness index and a third refractive index at the selected wavelength, wherein: a wavelength in the second visible wavelength range exceeds a wavelength in the third visible wavelength range, and the second yellowness index exceeds the third yellowness index at the selected wavelength.
17. The method of claim 16, wherein the second refractive index exceeds the third refractive index at the selected wavelength.
18. The method of claim 15, wherein the selected wavelength is 589 nm.
19. A diffractive waveguide stack comprising: a first diffractive waveguide for guiding light in a first visible wavelength range, the first diffractive waveguide comprising a first material and having a first refractive index at a selected wavelength and a first target refractive index at a midpoint of the first visible wavelength range; and a second diffractive waveguide for guiding light in a second visible wavelength range, the second diffractive waveguide comprising a second material and having a second refractive index at the selected wavelength and a second target refractive index at a midpoint of the second visible wavelength range; and a third diffractive waveguide for guiding light in a third visible wavelength range, the third diffractive waveguide comprising a third material and having a third refractive index at the selected wavelength and a third target refractive index at a midpoint of the third visible wavelength range, wherein: the first visible wavelength range comprises red light, the second visible wavelength range comprises green light, and the third visible wavelength range comprises blue light, and a difference between any two of the first target refractive index, the second target refractive index, and the third target refractive index at the selected wavelength is less than 0.005 at the selected wavelength.
20. The diffractive waveguide stack of claim 19, wherein the selected wavelength is 589 nm.
21. The method of claim 15, wherein casting the first polymerizable material comprises providing the first polymerizable material to a first casting the second polymerizable material comprises providing the second polymerizable material to a second casting head.
22. The method of claim 21, wherein the first casting head and the second casting head are different.
23. The method of claim 15, wherein casting the first polymerizable material and the second polymerizable material comprises providing the first polymerizable material and the second polymerizable material to a multi-head casting system.
24. The method of claim 23, wherein the multi-head casting system comprises a first casting head and a second casting head, and the first casting head and the second casting head are different.
25. The method of claim 15, wherein the first ratio and the second ratio are different.
26. The method of claim 15, further comprising selecting first conditions for polymerizing the first polymerizable material and second conditions for polymerizing the second polymerizable material yields a first combination of the first refractive index and the first yellowness index and a second combination of the second refractive index and the second yellowness index, wherein first conditions differ from the second conditions, and the first combination differs from the second combination.
27. The method of claim 15, wherein polymerizing the first polymerizable material, the second polymerizable material, or both yields a thiol-ene or a polycarbonate.
28. The method of claim 15, further comprising superimposing the first diffractive waveguide and the second diffractive waveguide to yield a waveguide stack.
29. The waveguide stack of claim 19, wherein the first material differs from the second material and the third material, and the second material differs from the third material.
30. The waveguide stack of claim 19, wherein the first yellowness index is less than about 1.2, the second yellowness index is less that about 0.8, and the third yellowness index is less than about 0.4 at the selected wavelength.
31. The waveguide stack of claim 19, wherein the first material comprises a first copolymer comprising a first monomer and a second monomer, the second material comprises a second copolymer comprising the first monomer and the second monomer, and a ratio of the first monomer and the second monomer in the first copolymer differs from a ratio of the first monomer and the second monomer in the second copolymer.
32. The waveguide stack of claim 19, wherein the first material, the second material, and the third material each independently comprises a polymer or a glass.
33. The waveguide stack of claim 19, wherein: the first material comprises a first glass, the second material comprises a second glass, and the third material comprises a third glass, wherein the first glass, the second glass, and the third glass are different, or the first material comprises a first polymer, the second material comprises a second polymer, and the third material comprises a third polymer, wherein the first polymer, the second polymer, and the third polymer are different
34. The waveguide stack of claim 19, wherein a field of view the first diffractive waveguide differs from the field of view of the second diffractive waveguide.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application Ser. No. 16/909,201 filed on Jun. 23, 2020, which claims the benefit of U.S. Patent Application No. 62/865,808 filed on Jun. 24, 2019, which are incorporated by reference herein in their entirety.
TECHNICAL FIELD
[0002] This invention relates to customized polymer/glass diffractive waveguide stacks with improved performance for augmented reality/mixed reality applications.
BACKGROUND
[0003] Augmented reality/mixed reality devices typically exploit a single type of glass or polymer material for all layers (e.g., red (R), green (G), and blue (B) layers). The overall performance of the device can be dictated by the performance of the RGB layers. Some key performance indicators, such as modulation transfer function (MTF), efficiency, field of view (FOV), contrast, and uniformity of an eyepiece depend on optical properties of the individual layers. These optical properties include refractive index, yellowness index, haze, optical transmission, surface roughness, and the like. For a given material, optical properties such as refractive index and optical transmission are a function of wavelength. See, for example, FIGS. 1A and 1B, which show typical dispersion curves (refractive index versus wavelength) for polymer waveguides, and FIG. 2, which shows typical optical absorption curves (optical transmission versus wavelength) for polymer waveguide materials. Other properties such as haze and yellowness index do not depend as heavily on wavelength. This particular relationship of waveguide materials with incident wavelength can impose challenges related to optical suitability if the refractive index and corresponding yellowness index values are above a certain threshold.
SUMMARY
[0004] In a first general aspect, a diffractive waveguide stack includes a first diffractive waveguide for guiding light in a first visible wavelength range and a second diffractive waveguide for guiding light in a second visible wavelength range. The first diffractive waveguide includes a first material and having a first yellowness index and a first refractive index at a selected wavelength, and the second diffractive waveguide includes a second material and having a second yellowness index and a second refractive index at the selected wavelength. A wavelength in the first visible wavelength range exceeds a wavelength in the second visible wavelength range, the first refractive index exceeds the second refractive index at the selected wavelength, and the first yellowness index exceeds the second yellowness index at the selected wavelength.
[0005] Implementations of the first general aspect may include one or more of the following features.
[0006] The diffractive waveguide stack of the first general aspect may include a third diffractive waveguide for guiding light in a third visible wavelength range. The third diffractive waveguide includes a third material and having a third yellowness index and a third refractive index at the selected wavelength. A wavelength in the second visible wavelength range exceeds a wavelength in the third visible wavelength range, and the second yellowness index exceeds the third yellowness index at the selected wavelength. The second refractive index may exceed the third refractive index at the selected wavelength. The first visible wavelength range includes red light, the second visible wavelength range includes green light, and the third visible wavelength range includes blue light. The first yellowness index is less than about 1.2, the second yellowness index is less than about 0.8, and the third yellowness index is less than about 0.4 at the selected wavelength.
[0007] In some cases, the first material includes a first polymer and the second material includes a second polymer. The first polymer and the second polymer may be different. In certain cases, the first material includes a first copolymer having a first monomer and a second monomer, and the second material includes a second copolymer having the first monomer and the second monomer. A ratio of the first monomer to the second monomer in the first copolymer may differ from a ratio of the first monomer to the second monomer in the second copolymer. The first material may include a first additive, and the second material may include a second additive. The first additive and the second additive can be the same, with a ratio of the first additive to the first polymer differing from a ratio of the second additive to the second polymer.
[0008] In some cases, the first material includes a first glass and the second material comprises a second glass. In certain cases, the first material comprises one of a polymer and a glass, and the second material comprises the other of a polymer and a glass.
[0009] In a second general aspect, a diffractive waveguide stack includes a first diffractive waveguide for guiding light in a first visible wavelength range, a second diffractive waveguide for guiding light in a second visible wavelength range, and a third diffractive waveguide for guiding light in a third visible wavelength range. The first diffractive waveguide includes a first material and having a first refractive index at a selected wavelength and a first target refractive index at a midpoint of the first visible wavelength range. The second diffractive waveguide includes a second material and having a second refractive index at the selected wavelength and a second target refractive index at a midpoint of the second visible wavelength range. The third diffractive waveguide includes a third material and having a third refractive index at the selected wavelength and a third target refractive index at a midpoint of the third visible wavelength range. The first visible wavelength range corresponds to red light, the second visible wavelength range corresponds to green light, and the third visible wavelength range corresponds to blue light. A difference between any two of the first target refractive index, the second target refractive index, and the third target refractive index is less than 0.005 at the selected wavelength.
[0010] In some implementations of the second general aspect, the selected wavelength is 589 nm.
[0011] In a third general aspect, fabricating diffractive waveguides for a waveguide stack includes combining a first monomer and a second monomer in a first ratio to yield a first polymerizable material, casting the first polymerizable material in a first diffractive waveguide mold and polymerizing the first polymerizable material to yield a first diffractive waveguide for guiding light in a first visible wavelength range, combining the first monomer and the second monomer in a second ratio to yield a second polymerizable material, and casting the second polymerizable material in a second diffractive waveguide mold and polymerizing the second polymerizable material to yield a second diffractive waveguide for guiding light in a second visible wavelength range. The first diffractive waveguide has a first yellowness index and a first refractive index at a selected wavelength, and the second diffractive waveguide has a second yellowness index and a second refractive index at the selected wavelength. A wavelength in the first visible wavelength range exceeds a wavelength in the second visible wavelength range, the first refractive index exceeds the second refractive index at the selected wavelength, and the first yellowness index exceeds the second yellowness index at the selected wavelength.
[0012] Implementations of the third general aspect may include one or more of the following features.
[0013] The third general aspect may further include combining the first monomer and the second monomer in a third ratio to yield a third polymerizable material, casting the third polymerizable material in a third diffractive waveguide mold, and polymerizing the third polymerizable material to yield a third diffractive waveguide for guiding light in a third visible wavelength range. The third diffractive waveguide has a third yellowness index and a third refractive index at the selected wavelength. A wavelength in the second visible wavelength range exceeds a wavelength in the third visible wavelength range, and the second yellowness index exceeds the third yellowness index at the selected wavelength. The second refractive index may exceed the third refractive index at the selected wavelength. In some cases, the selected wavelength is 589 nm.
[0014] 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
[0015] FIGS. 1A and 1B show typical dispersion curves for polymer waveguides.
[0016] FIG. 2 shows typical optical absorption curves for waveguide materials.
[0017] FIG. 3 shows a plot of efficiency versus yellowness index for red-green-blue (RGB) waveguides.
[0018] FIGS. 4A and 4B show RGB configurations based on three different base materials.
[0019] FIGS. 5A and 5B show RGB configurations based on the same base materials with different refractive indices.
[0020] FIGS. 6A-6D show RGB configurations based on combinations of glass and polymer waveguides with different refractive indices.
[0021] FIG. 7 depicts a multi-head system for fabricating RGB layers based on a two-part liquid resin.
DETAILED DESCRIPTION
[0022] This disclosure relates to the use of optically tuned materials for various color layers (e.g., RGB) in an augmented reality (AR)/mixed reality (MR) diffractive waveguide-based eyepiece to optimize the overall optical performance of the eyepiece. The material for each color waveguide can be tuned for optimal optical properties (refractive index, yellowness index, transmission) according to operating wavelength. Various implementations of glass and polymer-based waveguides configured to achieve optimal optical properties are described.
[0023] Differences in refractive indices (dispersion curve) for a given waveguide material at RGB wavelengths typically result in a different field of view (FOV) for each layer and can limit the overall FOV of a waveguide stack. In addition, materials with higher refractive indices (e.g., glass as well as polymers) tend to exhibit a greater yellowness index (b*), which is related to the optical transmission of a waveguide and overall efficiency of an eyepiece. Above a certain value of yellowness index (b*.sub.lim), the material absorption limits the overall efficiency of an eyepiece due at least in part to light absorption by the bulk of the waveguide. The threshold values of b*.sub.lim are spectrally dependent: b*.sub.lim is different for various colors (R, G, B, C, . . . ) in the order B.sub.TH
