Slanted surface relief grating replication by optical proximity recording

Patent metadata

Field	Value
Publication number	US-12422677-B2
Application number	US-202217592383-A
Country	US
Kind code	B2
Filing date	Feb 3, 2022
Priority date	Feb 3, 2022
Publication date	Sep 23, 2025
Grant date	Sep 23, 2025

Abstract

Slanted surface relief gratings for use in an optical display system in an HMD device are replicated in a manufacturing process that utilizes non-contact optical proximity recording into a specialized photo-sensitive resin that is disposed over a waveguide substrate. The recording process comprises selective resin exposure to ultraviolet light through a mask to spatially record grating structures by interferential exposure and polymerization. Subsequent resin development evacuates unexposed resin down to the waveguide substrate to remove flat surfaces, referred to as a bias layer, that remain in the grating trenches after exposure. The resin development reduces Fresnel reflections that could otherwise be induced at the media interface between the bias layer and the waveguide substrate. Fresnel reflections may cause a loss of diffraction efficiency and thereby reduce the field of view that may be guided by the SRGs in the optical display system.

First claim

What is claimed is:

1. A method for replicating a surface relief grating (SRG) using optical proximity recording, wherein the SRG is usable in a mixed-reality display system, having a real-world side and an eye side, that combines light for virtual images and real-world images for display to a user, the method comprising:
dispensing a layer of polymer dispersed liquid crystal mixture between a top plate and a bottom waveguide substrate; placing a mask in optical proximity to the layer of polymer dispersed liquid crystal mixture;
directing at least one recording beam from a light source to the mask which interacts with the at least one recording beam to diffract at least a portion of the at least one recording beam to the layer of polymer dispersed liquid crystal mixture;
recording diffraction grating features for the SRG in the layer of polymer dispersed liquid crystal mixture onto the bottom waveguide substrate, in which the recorded diffraction grating features result from interferential exposure formed from the diffracted portion of the at least one recording beam; and
and developing the layer of polymer dispersed liquid crystal mixture to realize the SRG with a minimal bias layer by evacuating one or more portions of interferentially-unexposed mixture substantially down to the bottom waveguide substrate using plasma ashing, wherein the evacuation of the interferentially-unexposed mixture reduces virtual image light being diffracted by the SRG towards the real-world side of the display system.

2. The method of claim 1 further including removing the top plate prior to developing the layer of polymer dispersed liquid crystal mixture.

3. The method of claim 1 in which the developing comprises ashing the SRG using an oxygen plasma.

4. The method of claim 1 in which the light source comprises a laser emitting light in the ultraviolet range of wavelengths.

5. The method of claim 1 in which the layer of polymer dispersed liquid crystal mixture comprises a reactive monomer liquid crystal mixture.

6. The method of claim 1 further comprising utilizing atomic layer deposition processing on the realized SRG.

7. The method of claim 1 in which the mask is a binary mask comprising a chromium layer deposed on a glass substrate.

8. The method of claim 1 in which the diffraction grating features in the SRG are slanted.

9. The method of claim 1 in which a refractive index of the SRG is lower than a refractive index of the waveguide substrate.

10. The method of claim 1 further comprising controlling the interferential exposure by adjusting the optical proximity spacing between the mask and the layer of polymer dispersed liquid crystal mixture.

11. The method of claim 1 further comprising controlling the interferential exposure by adjusting optical characteristics of the at least one recording beam.

12. The method of claim 1 further comprising controlling the interferential exposure by adjusting characteristics of the mask including one or more of aperture size, shape, spacing, or pattern.

13. The method of claim 1 in which the evacuation provides the SRG with minimal residual mixture in trenches between grating features to reduce Fresnel reflections.

14. The method of claim 1 further comprising configuring the SRG grating features with an aspect ratio and refractive index for one of maximizing Bragg selectivity at an interface between the SRG and waveguide substrate or tuning the Bragg selectivity.

15. A system for replicating a surface relief grating (SRG) on an optical waveguide using optical proximity recording, wherein the SRG is usable in a mixed-reality display system, having a real-world side and an eye side, that combines light for virtual images and real-world images for display to a user, comprising:
a top plate configured to contain a layer of polymer dispersed liquid crystal mixture in an enclosed volume between the top plate and a waveguide substrate;
a binary mask configured for adjustable optical proximity to the top plate;
a controllable laser source for directing at least one recording beam to the binary mask which interacts with the at least one recording light beam to diffract at least a portion of the at least one recording beam to the layer of polymer dispersed liquid crystal mixture to record diffraction grating features for the SRG in the layer of polymer dispersed liquid crystal mixture on the waveguide substrate; and
and a plasma source configured for subjecting the SRG to plasma ashing to evacuate residual polymer dispersed liquid crystal mixture forming a bias layer between the diffraction grating features, wherein the evacuation of the residual polymer dispersed liquid crystal mixture reduces virtual image light being ex-raced diffracted by the SRG towards the real-world side of the display system.

16. The system of claim 15 in which the top plate is removable from the enclosed volume and is optically transparent to a range of wavelengths produced by the controllable laser source.

17. The system of claim 15 in which the controllable source is configured for directing a plurality of recording beams of the same frequency that interfere with each other to produce an interference pattern in the layer of polymer dispersed liquid crystal mixture.

18. A head-mounted display (HMD) device wearable by a user and supporting a mixed-reality experience including viewing virtual images from a virtual world that are combined with real-world images of objects in a physical world, comprising:
a display engine configured for producing virtual images;
a see-through waveguide combiner through which the user can view the physical world and on which the virtual images are rendered within a field of view (FOV) of the HMD device; and
an out-coupling diffractive optical element (DOE) disposed on a waveguide portion of the see-through waveguide combiner, the DOE comprising a surface relief grating (SRG) configured with grating features directly disposed on the waveguide portion, and wherein a refractive index of the grating features is lower relative to a refractive index of the waveguide portion,
wherein SRG is produced using a method for optical proximity recording comprising:
dispensing a layer of polymer dispersed liquid crystal mixture between a top plate and a bottom waveguide substrate;
placing a mask in optical proximity to the layer of polymer dispersed liquid crystal mixture;
directing at least one recording beam from a light source to the mask which interacts with the at least one light beam to diffract at least a portion of the at least one recording beam to the layer of polymer dispersed liquid crystal mixture;
recording diffraction grating features for the SRG in the layer of polymer dispersed liquid crystal mixture onto the bottom waveguide substrate, in which the recorded diffraction grating features result from interferential exposure formed from the diffracted portion of the at least one recording beam; and
and developing the layer of polymer dispersed liquid crystal mixture to realize the SRG by evacuating one or more portions of interferentially-unexposed mixture substantially down to the bottom waveguide substrate using plasma ashing, wherein the evacuation of the interferentially-unexposed mixture reduces virtual image light being diffracted by the SRG towards the real-world side of the display system.

19. The HMD device of claim 18 in which the SRG includes slanted grating features.

Assignees

• Microsoft Technology Licensing Llc

Inventors

• Kress Bernard Charles
• Chatterjee Ishan
• Kollin Joel Steven
• Pace Maria Esther

Classifications

• G02B2027/0178

  Eyeglass type (eyeglass details G02C) · CPC title

• G02B27/0101

  characterised by optical features (G02B27/0172 takes precedence) · CPC title

• G02B5/1876

  Diffractive Fresnel lenses; Zone plates; Kinoforms (G02B5/1842, G02B5/1847 take precedence; optical systems having diffractive correction means G02B27/0037; Fresnel lenses operating by refraction G02B3/08) · CPC title

• G02B5/1814

  structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings (G02B5/189 takes precedence) · CPC title

• G02B5/1857

  using exposure or etching means, e.g. holography, photolithography, exposure to electron or ion beams · CPC title