Waveguide Facet Layout for 2D Image Expansion With Fewer Ghosts
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Solution Overview
Problem
Existing optical systems for near-eye displays face challenges in minimizing the size of optical components while maintaining a given angular field of view, particularly in coupling-in configurations, leading to issues with glints and ghost images.
Innovation Solution
The optical system employs a light-guide optical element with optimized deployment of partially-reflecting surfaces, including a coupling-in prism bonded to the LOE, and facets oriented to minimize unnecessary reflections, reducing the size of the system by injecting image illumination at shallow angles and using concave polygon facet locations to enhance efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional coupling-in configurations are used, then the angular field of view can be maintained, but the size of optical components increases and glints and ghost images are generated
Solution Approach 1:
The waveguide is divided into multiple functional regions: a coupling-in region with a coupling-in prism, a first region with a first set of partially-reflecting surfaces for lateral expansion, and a second region with a second set of partially-reflecting surfaces for vertical expansion. This segmentation allows each region to perform its specific function efficiently, reducing unnecessary reflections and minimizing glints and ghost images while maintaining a compact overall size.
Solution Approach 2:
The coupling-in prism is extracted as a separate component bonded to the coupling-in surface of the waveguide. This allows the coupling-in function to be performed outside the main waveguide volume, reducing the size of the integrated optical components while maintaining the angular field of view. The prism extracts and directs light into the waveguide at optimized angles, preventing harmful reflections.
2Volume of moving object
If the size of optical components is reduced, then the system becomes more compact, but maintaining a given angular field of view becomes difficult
Solution Approach 1:
The optical system uses two-dimensional aperture expansion by implementing both lateral expansion (first dimension) and vertical expansion (second dimension) through sets of partially-reflecting surfaces at different orientations. This allows the system to maintain a large angular field of view while using a compact waveguide thickness, effectively trading physical volume for angular coverage in a different dimensional space.
Solution Approach 2:
The system optimizes the angles and orientations of the partially-reflecting surfaces to achieve efficient light propagation and expansion. By carefully selecting the parameters of the coupling-in prism (thickness greater than waveguide thickness, specific bonding configuration) and the orientations of the facet sets, the system maintains a given angular field of view while minimizing component sizes.
3Area of moving object
If multiple sets of partially-reflecting surfaces are used for two-dimensional expansion, then aperture expansion is achieved, but device complexity increases
Solution Approach 1:
The coupling-in prism is merged with the waveguide by bonding it to the coupling-in surface, creating an integrated component that performs both coupling and protection functions. The first and second sets of partially-reflecting surfaces are integrated into the waveguide structure at defined orientations, combining multiple functions (lateral expansion, vertical expansion, and reflection management) into a single unified optical path, thereby reducing overall device complexity.
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 size of optical components and minimizes glints and ghost images, improving the efficiency and performance of near-eye displays by optimizing the deployment of partially-reflecting surfaces and facets.
Implementation Method 1
image illumination propagating within the LOE by internal reflection at the major external surfaces
Implementation Method 2
first set of planar, mutually-parallel, partially-reflecting surfaces having a first orientation; a second region containing a second set of planar, mutually-parallel, partially-reflecting surfaces
Data Source
Figure 1A~1C
Figure 1D
Figure 2A~2C
AI summary
An optical system employs a waveguide including a first set of partially-reflecting surfaces ("facets") for progressively redirecting image illumination propagating from a coupling-in region towards a second region, and a second set of facets in the second region for progressively coupling-out the redirected image illumination towards the eye of a viewer. The first set of facets includes at least a first facet close to the coupling-in region, a third facet fare from the coupling-in region, and a second facet located on a medial plane between the first and the third facets. The second facet is located in a subregion of the medial plane such that image illumination propagating from the coupling-in region to the third facet passes through the medial plane without passing through the second facet.