Overlapping EPE and OC Gratings for AR Waveguides
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Solution Overview
Problem
Augmented reality (AR) display systems using waveguides with surface relief gratings suffer from rainbow artifacts due to light diffraction and are sensitive to incident angles, leading to poor color uniformity and limited display brightness.
Innovation Solution
Implementing a diffractive waveguide with a combined exit pupil expander (EPE) and output coupler (OC) using surface relief gratings, where the EPE and OC gratings at least partially overlap laterally, reducing the overall lateral area occupied by gratings and shortening the light path between the input coupler and output coupler.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If surface relief gratings are used for EPE and OC in the waveguide, then the eyebox can be expanded and light can be output, but rainbow artifacts are introduced due to diffraction of real environment light
Solution Approach 1:
The patent combines the EPE and OC gratings into a single integrated structure where the EPE grating and OC grating are laterally overlapping. This merging reduces the total lateral area occupied by gratings, thereby reducing diffraction of real environment light and minimizing rainbow artifacts while maintaining eyebox expansion and light output functionality
Solution Approach 2:
The patent transitions from separate, non-overlapping grating structures to laterally overlapping gratings in the same lateral dimension. This dimensional reconfiguration allows the gratings to share the same lateral space, reducing the overall grating area and associated diffraction effects while maintaining the necessary optical functions
2Ease of operation
If surface relief gratings are used for EPE and OC, then light propagation and output are achieved, but the waveguide becomes very sensitive to incident angles of display light
Solution Approach 1:
By merging the EPE and OC gratings into a laterally overlapping structure, the patent creates a more robust optical path that is less sensitive to incident angle variations. The overlapping configuration provides a broader tolerance range for display light angles compared to separate grating structures
3Ease of manufacture
If separate EPE and OC gratings are used, then each function can be optimized independently, but the overall lateral area occupied by gratings is large
Solution Approach 1:
The patent merges the EPE and OC gratings into a laterally overlapping configuration, significantly reducing the total lateral area occupied by gratings. The overlapping design allows both gratings to share the same lateral space, achieving compact integration while maintaining independent optimization of each grating's optical function
Solution Approach 2:
The patent reconfigures the grating arrangement from a sequential, non-overlapping layout to a laterally overlapping layout in the same dimension. This dimensional change allows both EPE and OC functions to occupy the same lateral footprint, minimizing the overall area while preserving independent function optimization
4Adaptability or versatility
If the light path between IC and OC is long, then more optical components can be integrated, but the maximum efficiency of the waveguide is reduced
Solution Approach 1:
By merging the EPE and OC gratings into a laterally overlapping structure, the patent shortens the light path between the input coupler and the combined EPE/OC structure. This reduced path length minimizes optical losses and improves waveguide efficiency while still allowing for necessary component integration
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 reduces the risk and magnitude of rainbow effects and other visual artifacts, while enhancing the maximum efficiency of the waveguide, allowing for improved color uniformity and increased display brightness, even in daylight conditions.
Implementation Method 1
an exit pupil expander (EPE) may be implemented in the light path between the IC and OC in the waveguide. In some implementations, the IC, EPE, and OC are implemented at the waveguide in the form of surface relief gratings
Implementation Method 2
Display light from the light source enters the waveguide through an incoupler (IC) and is propagated through the waveguide via total internal reflection (TIR) or other internal propagation techniques
Data Source
AI summary
An augmented reality (AR) display system includes a light source and a lens element having a waveguide to direct display light from the light source toward a user's eye. The waveguide includes an incoupler (IC) having surface relief gratings (SRGs) in a first region of the waveguide to incouple the display light and a combined exit pupil expander (EPE) and outcoupler (OC) having surface relief gratings at a second region of the waveguide for exit pupil expansion and surface relief gratings at a third region of the waveguide for outcoupling the display light from the waveguide. The second and third regions at least partially overlap laterally relative to the expected position of the user's eye, with the surface relief gratings of the second region being formed on the same or opposite side of the waveguide as the surface relief gratings of the third region.