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US-20260126651-A1 - POLARIZATION INSENSITIVE DIFFRACTION GRATING AND DISPLAY INCLUDING THE SAME

US20260126651A1US 20260126651 A1US20260126651 A1US 20260126651A1US-20260126651-A1

Abstract

Polarization insensitive gratings and displays including the same are disclosed.

Inventors

  • MohammadSadegh FARAJI-DANA
  • Robert D. TeKolste
  • Chinmay Khandekar
  • Liyi Hsu
  • Vikramjit Singh
  • Mauro MELLI
  • Victor Kai LIU

Assignees

  • MAGIC LEAP, INC.

Dates

Publication Date
20260507
Application Date
20231107

Claims (20)

  1. 1 . A head-mounted display system comprising: a head-mountable frame; a light projection system configured to output light to provide image content; a waveguide supported by the frame, the waveguide configured to guide at least a portion of the light from the light projection system coupled into the waveguide; a grating structure optically coupled to the waveguide, the grating structure being configured to couple light from the light projection system into the waveguide, the grating structure comprising: a grating layer comprising a plurality of ridges having a blaze profile in at least one cross-section; and one or more dielectric layers disposed on the grating layer, wherein, for unpolarized incident light at at least one operative wavelength of the output light, the grating structure has a mean launch efficiency of 40% or more and a mean back reflection of 15% or less over a field of view of 10° or more in at least one direction.
  2. 2 . The head mounted display system of claim 1 , wherein, for unpolarized incident light at at least two operative wavelengths of the output light at least 100 nm apart, the grating structure has a mean launch efficiency of 40% or more and a mean back reflection of 15% or less over a field of view of 10° or more in at least one direction.
  3. 3 . The head mounted display system of claim 2 , wherein, for unpolarized incident light at three operative wavelengths of the output light spanning a spectral range of 120 nm or more, the grating structure has a mean launch efficiency of 40% or more and a mean back reflection of 15% or less over a field of view of 10° or more in at least one direction.
  4. 4 . The head mounted display system of claim 3 , wherein the three wavelengths are a blue wavelength, a green wavelength, and a red wavelength.
  5. 5 - 7 . (canceled)
  6. 8 . The head mounted display system of claim 1 , wherein the grating structure is a reflection grating structure.
  7. 9 . The head mounted display system of claim 1 , wherein the grating structure is a transmission grating structure.
  8. 10 . (canceled)
  9. 11 . The head mounted display system of claim 1 , wherein the grating structure further comprises a metal layer disposed on the one or more dielectric layers.
  10. 12 . The head mounted display system of claim 1 , wherein the one or more dielectric layers comprise at least one continuous layer.
  11. 13 . The head mounted display system of claim 1 , wherein the one or more dielectric layers comprise at least one discontinuous layer.
  12. 14 . The head mounted display system of claim 1 , wherein the one or more dielectric layers comprises a first dielectric layer disposed directly on the grating layer and a second dielectric layer disposed directly on the first dielectric layer, the first dielectric layer have a larger refractive index at the operative wavelength than a refractive index of the grating layer and a refractive index of the second dielectric layer.
  13. 15 . The head mounted display system of claim 1 , wherein the one or more dielectric layers comprise a layer having a thickness in a range from 1 nm to 150 nm.
  14. 16 - 21 . (canceled)
  15. 22 . The head mounted display system of claim 1 , wherein the launch efficiency of the grating structure corresponds to a first order diffraction efficiency of the grating structure.
  16. 23 . The head mounted display system of claim 1 , wherein the grating structure is a first grating structure and the system further comprises a second grating structure on an opposite side of the waveguide form the first grating structure.
  17. 24 . The head mounted display system of claim 23 , wherein the first grating structure is a reflection grating structure and the second grating structure is a transmission grating structure.
  18. 25 . The head mounted display system of claim 23 , wherein the second grating structure comprises a grating layer comprising a plurality of ridges and at least one dielectric layer supported by the grating layer.
  19. 26 - 30 . (canceled)
  20. 31 . The head-mounted display system of claim 1 , wherein the grating structure comprises a cross-linked polymer that has a refractive index in a range from 1.5 to 2.25.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to Provisional Application No. 63/423,286, titled “POLARIZATION INSENSITIVE DIFFRACTION GRATING AND DISPLAY INCLUDING THE SAME,” filed on Nov. 7, 2022, the contents of which are hereby incorporated by reference. BACKGROUND Field The present disclosure relates to display systems and, more particularly, to augmented and virtual reality display systems and input coupling gratings (ICGs) or output coupling gratings for use therewith. Description of the Related Art Modern computing and display technologies have facilitated the development of systems for so called “virtual reality” or “augmented reality” experiences, wherein digitally reproduced images or portions thereof are presented to a user in a manner wherein they seem to be, or may be perceived as, real. A virtual reality, or “VR”, scenario typically involves presentation of digital or virtual image information without transparency to other actual real-world visual input; an augmented reality, or “AR”, scenario typically involves presentation of digital or virtual image information as an augmentation to visualization of the actual world around the user. A mixed reality, or “MR”, scenario is a type of AR scenario and typically involves virtual objects that are integrated into, and responsive to, the natural world. For example, in an MR scenario. AR image content may be blocked by or otherwise be perceived as interacting with objects in the real world. Referring to FIG. 1, an augmented reality scene 10 is depicted wherein a user of an AR technology sees a real-world park-like setting 20 featuring people, trees, buildings in the background, and a concrete platform 30. In addition to these items, the user of the AR technology also perceives that he “sees” “virtual content” such as a robot statue 40 standing upon the real-world platform 30, and a cartoon-like avatar character 50 flying by which seems to be a personification of a bumble bee, even though these elements 40, 50 do not exist in the real world. Because the human visual perception system is complex, it is challenging to produce an AR technology that facilitates a comfortable, natural-feeling, rich presentation of virtual image elements amongst other virtual or real-world imagery elements. Systems and methods disclosed herein address various challenges related to AR and VR technology. SUMMARY Grating structures suitable for input coupling gratings (ICGs) for coupling light into a waveguide are described that are substantially insensitive to polarization, have low back reflection, and allow operation over a wide range of input angles are disclosed. Such grating structures can be used in inline alignment configurations where the ICG for multiple stacked waveguides are aligned along a common optical path. Such ICGs can be particularly useful for head-mounted displays using a microLED (μLED) light projection system, which can emit unpolarized light over a wide range of angles. Examples of the grating structures include asymmetric blazed gratings either formed from a high index material and/or coated with a high index material (such as titanium dioxide, gallium phosphide, silicon carbide and others). Such high index layers can provide grating structures with relatively low optical losses. However, because the high index film the reflected light can be significant (e.g., >10% for some incident angles), unwanted back reflection coupling and ghosting, reduced contrast etc. in the virtual images can be an undesirable result. Reducing this back reflection can lead to more light being diffracted and coupled in the right order in TIR in the waveguide and thus benefits of reduced reflection can outweigh advantages of light recycling that may occur from the reflections. The grating structures described herein can have low reflection with high diffraction efficiency in both TE and TM polarization modes. Such optical performance can enable overall eyepiece efficiency per Watt of energy used by the projectors, e.g., μLED projections systems, e.g., that use unpolarized light and ideally operate with reduced back reflection from grating structures into the lens of the projection system. Such grating structures can also work well for single active layer architectures where all colors (e.g., R, G, B) get waveguided in a single high index active layer but use grating structures working in transmission mode to harness use of high diffraction efficiency in orthogonal polarization states, e.g., enabling use of μLED projection systems. Various aspects of the disclosed subject matter are summarized as follows. In general, in a first aspect, the disclosure features a head-mounted display system including: a head-mountable frame; a light projection system configured to output light to provide image content; a waveguide supported by the frame, the waveguide configured to guide at least a portion of the light from the light projection system coup