Holographic waveguides incorporating birefringence control and methods for their fabrication

Patent metadata

Field	Value
Publication number	US-10690851-B2
Application number	US-201916357233-A
Country	US
Kind code	B2
Filing date	Mar 18, 2019
Priority date	Mar 16, 2018
Publication date	Jun 23, 2020
Grant date	Jun 23, 2020

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 coupler for directing the light into total internal reflection paths within the waveguide; and
an output coupler for extracting light from the waveguide, wherein light in the total internal reflection paths undergoes multiple interactions along the waveguide 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 waveguide.

2. The waveguide of claim 1 , wherein the interaction of light with the birefringence control layer provides at least one 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 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 waveguide.

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 a liquid crystal and polymer material system.

8. The waveguide of claim 1 , wherein the birefringence control layer is a liquid crystal and polymer system aligned using directional ultraviolet radiation.

9. 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.

10. 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.

11. The waveguide of claim 1 , wherein the birefringence control layer has an anisotropic refractive index.

12. The waveguide of claim 1 , wherein the birefringence control layer is formed on at least one internal or external optical surface of the waveguide.

13. 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.

14. The waveguide of claim 1 , wherein the birefringence control layer provides a high reflection layer.

15. The waveguide of claim 1 , wherein the birefringence control layer provides optical power.

16. The waveguide of claim 1 , wherein the birefringence control layer provides an environmental isolation layer for the waveguide.

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

18. 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.

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

20. The waveguide of claim 1 , wherein at least one of the input coupler and output coupler comprises a birefringent grating.

21. The waveguide of claim 1 , wherein the birefringent grating is recorded in a material system comprising at least one polymer and at least one liquid crystal.

22. 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.

23. 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.

24. A method of fabricating a waveguide, the method comprising:
providing a first transparent substrate;
depositing a layer of grating recording material, wherein the layer of grating recording material is deposited onto the first substrate;
exposing the layer of grating recording material to form a grating layer;
forming a birefringence control layer;
applying a second transparent substrate;
depositing a layer of liquid crystal polymer material; and
aligning the liquid crystal polymer material using directional UV light, wherein the second transparent substrate is applied over the aligned liquid crystal polymer layer.

25. The method of claim 24 , wherein:
the layer of grating recording material is deposited onto the substrate;
the birefringence control layer is formed on the grating layer; and
the second transparent substrate is applied over the birefringence control layer.

26. The method of claim 24 , wherein:
the layer of grating recording material is deposited onto the substrate;
the second transparent substrate is applied over the grating layer; and
the birefringence control layer is formed on second transparent substrate.

27. The method of claim 24 , wherein:
the birefringence control layer is formed on the first transparent substrate;
the layer of grating recording material is deposited onto the birefringence control layer; and
the second transparent substrate is applied over the grating layer.

28. The method of claim 24 , wherein the layer of liquid crystal polymer material is deposited onto one of either the grating layer or the second transparent substrate.

29. The method of claim 24 , wherein:
the layer of liquid crystal polymer material is deposited onto the first transparent substrate;
the layer of grating recording material is deposited onto the aligned liquid crystal polymer material; and
the second transparent substrate is applied over the grating layer.

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