Holographic waveguides incorporating birefringence control and methods for their fabrication

Patent metadata

Field	Value
Publication number	US-11150408-B2
Application number	US-202016906872-A
Country	US
Kind code	B2
Filing date	Jun 19, 2020
Priority date	Mar 16, 2018
Publication date	Oct 19, 2021
Grant date	Oct 19, 2021

Abstract

Many embodiments in accordance with the invention are directed towards waveguides implementing birefringence control. In some embodiments, the waveguide includes a birefringent grating layer and a birefringence control layer. In further embodiments, the birefringence control layer is compact and efficient. Such structures can be utilized for various applications, including but not limited to: compensating for polarization related losses in holographic waveguides; providing three-dimensional LC director alignment in waveguides based on Bragg gratings; and spatially varying angular/spectral bandwidth for homogenizing the output from a waveguide. In some embodiments, a polarization-maintaining, wide-angle, and high-reflection waveguide cladding with polarization compensation is implemented for grating birefringence. In several embodiments, a thin polarization control layer is implemented for providing either quarter wave or half wave retardation.

First claim

What is claimed is:

1. A waveguide comprising:
at least one waveguide substrate;
at least one birefringent grating;
at least one birefringence control layer;
a light source for outputting light;
an input grating coupler for directing the light into total internal reflection paths within the at least one waveguide substrate; and
an output grating coupler for extracting light from the at least one waveguide substrate, wherein light in the total internal reflection paths undergoes multiple interactions along the at least one waveguide substrate with each of the birefringent grating and the birefringence control layer, wherein the interaction of the light with the birefringence control layer and the birefringent grating provides a predefined characteristic of light extracted from the at least one waveguide substrate.

2. The waveguide of claim 1 , wherein the interaction of light with the birefringence control layer provides at least one selected from the group of: an angular or spectral bandwidth variation; a polarization rotation; a birefringence variation; an angular or spectral dependence of at least one of beam transmission or polarization rotation; and a light transmission variation in at least one direction in the plane of the at least one waveguide substrate.

3. The waveguide of claim 1 , wherein the predefined characteristic varies across the waveguide.

4. The waveguide of claim 1 , wherein the predefined characteristic results from the cumulative effect of the interaction of the light with the birefringence control layer and the birefringent grating along at least one direction of light propagation within the at least one waveguide substrate.

5. The waveguide of claim 1 , wherein the predefined characteristic comprises at least one of: uniform illumination and uniform polarization over the angular range of the light.

6. The waveguide of claim 1 , wherein the birefringence control layer provides compensation for polarization rotation introduced by the birefringent grating along at least one direction of light propagation within the waveguide.

7. The waveguide of claim 1 , wherein the birefringence control layer is aligned by at least one of: electromagnetic radiation; electrical or magnetic fields; mechanical forces; chemical reaction; and thermal exposure.

8. The waveguide of claim 1 , wherein the birefringence control layer influences the alignment of LC directors in a birefringent grating formed in a liquid crystal and polymer system.

9. The waveguide of claim 1 , wherein the birefringence control layer comprises at least one stack of refractive index layers disposed on at least one optical surface of the waveguide, wherein at least one layer in the stack of refractive index layers has an isotropic refractive index and at least one layer in the stack of refractive index layers has an anisotropic refractive index.

10. The waveguide of claim 1 , wherein the birefringence control layer has a gradient index structure.

11. The waveguide of claim 1 , wherein the birefringence control layer is formed by stretching a layer of an optical material to spatially vary its refractive index in the plane of the waveguide substrate.

12. The waveguide of claim 1 , wherein the light source provides collimated light in angular space.

13. The waveguide of claim 1 , wherein at least one selected from the group of: said birefringent grating; said input grating coupler; and said output grating coupler is at least one selected from the group of: a switchable grating; a grating recorded in a liquid crystal and polymer material system; a birefringent grating; a switchable Bragg grating; a switchable Bragg grating used in a non-switching mode; a uniform modulation grating; a Raman Nath grating; a Bragg grating; a surface relief grating; and a grating recorded in a liquid crystal and polymer system aligned using directional ultraviolet radiation.

14. The waveguide of claim 1 , wherein said at least one birefringent control layer is at least one selected from the group of: a layer formed on at least one internal or external optical surface of said waveguide; a layer in contact with said birefringent grating layer; a layer having a spatial distribution of birefringence; and a layer in at least partial overlap with said birefringent grating.

15. The waveguide of claim 1 , wherein the birefringence control layer provides at least one selected from the group of: an anisotropic refractive index; optical power; a high reflectivity layer; a spatial variation of birefringence; and an environmental isolation layer for the waveguide.

16. The waveguide of claim 1 , wherein the at least one birefringent grating comprises at least one birefringent grating for providing at least one of the functions of: beam expansion in a first direction; beam expansion in a second direction and light extraction from the waveguide; and coupling light from the source into a total internal reflection path in the waveguide.

17. The waveguide of claim 1 , wherein the light source comprises a laser, and the alignment of LC directors in the birefringent grating spatially vary to compensate for illumination banding.

18. The waveguide of claim 1 , further comprising a surface relief grating.

19. The waveguide of claim 1 , further comprising a fold grating.

20. The waveguide of claim 1 , wherein said input grating coupler is replaced by a prism.

Assignees

• Digilens Inc

Inventors

• Waldern Jonathan David
• Popovich Milan Momcilo
• Grant Alastair John

Classifications

• G02B6/122

  Basic optical elements, e.g. light-guiding paths · CPC title

• G02B27/01

  Head-up displays · CPC title

• G02B5/30

  Polarising elements (light-modulating devices with active elements G02F1/00) · CPC title

• G02B27/0172

  characterised by optical features · CPC title

• G02F1/1334

  based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals · CPC title