Display Waveguide High-Index Region for Wide Field of View
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Solution Overview
Problem
Conventional head-mounted displays (HMDs) for virtual reality (VR), augmented reality (AR), and mixed reality (MR) face challenges in achieving a compact and lightweight design while maintaining a wide field of view and uniform color and brightness across the field of view, due to the complexity of managing different color channels and their propagation angles within the display waveguide.
Innovation Solution
A display waveguide system with a refractive index that varies in thickness, featuring a high-index layer between lower-index regions, allows for the efficient coupling and propagation of image light across a wider field of view by using input and output gratings to direct light within the waveguide, ensuring uniformity and reducing the number of ray-grating interactions across different angles and colors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a conventional waveguide design is used, then the display device structure is simple, but the field of view is limited and color uniformity cannot be maintained
Solution Approach 1:
The waveguide is divided into multiple functional layers: a core layer for light propagation, cladding layers for confinement, and buffer layers for stress management. This segmentation allows each layer to be optimized for its specific function, enabling wider field of view while maintaining manageable structural complexity
Solution Approach 2:
Different layers of the waveguide are assigned different refractive indices tailored to their specific functions. The core layer has higher refractive index for light guidance, while cladding and buffer layers have progressively lower indices. This local variation in optical properties enables precise control of light propagation paths across different viewing angles, expanding field of view without requiring complex overall restructuring
2Stability of the object's composition
If the waveguide thickness is increased to accommodate multiple color channels, then color uniformity can be maintained, but the device becomes bulkier and heavier
Solution Approach 1:
The patent employs precise control of layer thicknesses and refractive indices to manage polychromatic light propagation. By adjusting these parameters, the design maintains uniform color and brightness across the field of view while keeping the overall waveguide thickness minimized for compact form factor
Solution Approach 2:
The waveguide uses a composite multi-layer structure with different materials having distinct refractive indices. This composite approach allows independent optimization of each layer's thickness and optical properties, achieving color uniformity without requiring uniform increases in overall waveguide volume
3Ease of manufacture
If the refractive index is made uniform throughout the waveguide, then manufacturing is simpler, but light propagation control across different angles and colors becomes difficult
Solution Approach 1:
The waveguide structure implements spatially varying refractive indices through its multi-layer composition. Each layer is engineered with specific optical properties tailored to its function: the core layer for light guidance, cladding layers for confinement, and buffer layers for stress management. This local differentiation enables precise control of light propagation for multiple colors and angles while maintaining manufacturability through standardized layering processes
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the display's compactness, maintains a wide field of view, and ensures uniform color and brightness across the viewing area by optimizing the refractive index distribution and grating configurations within the waveguide, addressing the challenges of managing polychromatic light and diverse propagation angles.
Implementation Method 1
first rays of the image light coupled into the waveguide at the first propagation angle are guided toward the output area by total internal reflection at the outer surfaces of the waveguide
Implementation Method 2
An input coupler may be disposed in the input area and configured to couple the image light into the waveguide body
Implementation Method 3
An output coupler may be disposed in the output area and configured to couple the image light out of the waveguide body
Data Source
AI summary
A display waveguide configured for conveying image light to a viewer has a waveguide body whose refractive index varies in the thickness direction to include a high-index region between lower-index regions. Multi-layer and gradient index implementations are described. The waveguide transmits a portion of image light within the high-index region of the waveguide to provide a wider field of view.