Holographic waveguides incorporating birefringence control and methods for their fabrication

• US 10,690,851 B2
• Filed: 03/18/2019
• Issued: 06/23/2020
• Est. Priority Date: 03/16/2018
• Status: Active Grant

• Current Assignee: DigiLens Inc
• Original Assignee: DigiLens Inc
• Inventors: Waldern, Jonathan David, Popovich, Milan Momcilo, Grant, Alastair John
• Primary Examiner(s): Rahll, Jerry
• Application Number:
  US16/357,233
• Publication Number:
  US 20190285796A1
• Time in Patent Office: 463 Days
• Field of Search: None
• CPC Class Codes: G02B 2006/12116 Polariser; Birefringent
• CPC Class Codes: G02B 2027/0109 comprising details concerning the making of holograms
• CPC Class Codes: G02B 2027/0125 Field-of-view increase by wavefront division
• CPC Class Codes: G02B 2027/0174 holographic
• CPC Class Codes: G02B 27/0081 with means for altering, e.g. enlarging, the entrance or exit pupil
• CPC Class Codes: G02B 27/0103 comprising holographic elements
• CPC Class Codes: G02B 27/0172 characterised by optical features
• CPC Class Codes: G02B 5/3016 involving passive liquid crystal elements optical properties of liquid crystals G02F1/0063; polarising elements associated with active liquid crystal devices G02F1/133528
• CPC Class Codes: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001
• CPC Class Codes: G02B 6/1221 made from organic materials
• CPC Class Codes: G02B 6/126 using polarisation effects G02B6/1226 takes precedence
• CPC Class Codes: G02B 6/13 Integrated optical circuits characterised by the manufacturing method
• CPC Class Codes: G02B 6/2726 in or on light guides, e.g. polarisation means assembled in a light guide
• CPC Class Codes: G02B 6/274 based on light guide birefringence, e.g. due to coupling between light guides G02B6/105, G02B6/024 take precedence; mechanically induced birefringence G02F1/0134
• CPC Class Codes: G02B 6/34 utilising prism or grating G02B6/293 takes precedence

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.

Claims

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.