Symmetrical Waveguide Pupil Expansion for Wide-FOV Near-Eye Displays
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Solution Overview
Problem
Existing two-dimensional array waveguides in augmented reality displays suffer from asymmetry, limited angle of view, and increased volume when using high refractive index materials, leading to processing difficulties and deviations from the optimal eye position for image display.
Innovation Solution
A symmetrical pupil expansion apparatus comprising a first and second waveguide sheet with mirror-symmetrical turning structures and a geometric in-coupling prism, which evenly divides luminous energy between the sheets, ensuring symmetrical angles of view and reducing the required volume by allowing half the field of view to be transmitted by each sheet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a high refractive index material is used to increase the angle of view, then the angle of view is improved, but the processing difficulty and cost of the waveguide plate are greatly increased
Solution Approach 1:
The patent changes the refractive index parameter from high to low (using materials like H-BAK5 with n=1.56), and compensates for the reduced angle of view by optimizing the geometric configuration of the in-coupling prism and waveguide structure, thereby reducing processing difficulty while maintaining acceptable angle of view performance
Solution Approach 2:
The patent introduces an asymmetric in-coupling prism structure with specific angle configurations (α=60°-80°, β=20°-40°) that compensates for the limitations of low refractive index materials, enabling improved angle of view without requiring high refractive index materials
2Illumination intensity
If the field of view is increased, then the angle of view is improved, but the volume of the device is increased
Solution Approach 1:
The patent segments the waveguide structure into multiple functional regions (in-coupling region with prism, turning structure region, out-coupling region with beam splitters), allowing each segment to be optimized independently for compactness while collectively achieving a large field of view
Solution Approach 2:
The patent utilizes three-dimensional spatial arrangement of optical components, particularly the asymmetric in-coupling prism and folded optical path, to achieve large field of view in a compact form factor by exploiting dimensional space efficiently
3Area of stationary object
If a turning structure is added to expand the pupil, then the eye box is improved, but the center of the effective display region deviates from the optimal eye position
Solution Approach 1:
The patent introduces an asymmetric design where the in-coupling prism and turning structure are positioned and angled differently (α≠β) to shift the effective display region center to align with the optimal eye position while maintaining a large eye box through the turning structure
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
The apparatus achieves a large angle of view with high luminous energy utilization, reduces processing complexity, and maintains symmetry, effectively displaying a complete field of view while minimizing the device's size.
Implementation Method 1
a light incident edge and a light emission edge that are opposite to each other, and a first side edge and a second side edge that are opposite to each other, where the light incident edge and the first side edge form an acute angle θ, the acute angle θ=60° to 80°
Implementation Method 2
a first turning mirror and a first turning structure that are sequentially arranged along a second direction, where the first turning structure includes multiple first beam splitters parallel to each other
Implementation Method 3
the first waveguide structure includes a first turning mirror and a first turning structure that are sequentially arranged along a second direction
Data Source
AI summary
Provided are a near-eye display device and a symmetrical pupil expansion apparatus including: a first waveguide sheet and a second waveguide sheet are parallel to each other and are stacked, and a first turning mirror and a second turning mirror are arranged correspondingly; a first waveguide structure is mirror-symmetrical to a second waveguide structure, a turning reflection slope of the first turning mirror is parallel to first beam splitters; a turning reflection slope of the second turning mirror is parallel to second beam splitters; a cementing layer is disposed between two waveguide sheets; a geometric in-coupling prism is disposed in a middle region between turning structures, the projected surface of the geometric in-coupling prism facing the second direction is a quadrilateral including a light incident edge and a light emission edge opposite to each other, and a first side edge and a second side edge opposite to each other.