Prismatic Waveguide with Semi-Reflecting Surfaces
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Solution Overview
Problem
One-dimensional waveguides without holograms face issues such as achromatic reflections and sharp edges, leading to pupil banding limitations, necessitating the incorporation of diffractive processes to create an inexpensive and effective waveguide solution.
Innovation Solution
A prismatic waveguide incorporating diffraction gratings and semi-reflecting surfaces made from glass, with a coating that reacts with cement to cause controlled reflection and transmission, utilizing titanium dioxide gratings to modulate the optical field and achieve uniform illumination, while absorbing stray light to prevent ghost images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If diffraction gratings are incorporated into the waveguide, then pupil banding and edge sharpness are reduced, but device complexity increases
Solution Approach 1:
The patent combines multiple functions into a single integrated waveguide structure: diffraction gratings are incorporated directly into the waveguide body, semi-reflecting surfaces are formed at internal junctions, and multiple optical paths are merged into one compact device. This integration achieves pupil banding reduction while maintaining manufacturability through unified construction rather than separate components.
Solution Approach 2:
The patent modifies optical parameters by incorporating diffraction gratings with specific groove densities and patterns that control the diffraction of light. By changing the grating parameters (groove spacing, depth, profile), the waveguide achieves softened pupil edges and reduced banding effects. The semi-reflecting surfaces are designed with specific reflectivity characteristics to further control light distribution.
2Illumination intensity
If multiple make-up pieces are used to create semi-reflecting surfaces, then illumination control is improved, but manufacturing complexity increases
Solution Approach 1:
The waveguide is divided into multiple make-up pieces (first make-up piece, second make-up piece, third make-up piece) that can be manufactured separately and then assembled. Each piece contains specific optical features (diffraction gratings, semi-reflecting surfaces) that are optimized for its function. This segmentation allows for specialized manufacturing of each component while maintaining overall illumination control through precise assembly interfaces.
Solution Approach 2:
The patent uses cement as an intermediary material to bond the make-up pieces together. The cement serves multiple functions: mechanical adhesion, optical coupling, and creating semi-reflecting surfaces at the junctions. This intermediary approach simplifies assembly compared to direct bonding, as the cement layer provides tolerance for alignment and automatically creates the desired optical reflection properties at the interfaces.
3Shape
If diffraction gratings are used to modulate optical field, then edge sharpness is reduced, but loss of energy increases
Solution Approach 1:
The patent converts the potential harm of energy loss at diffraction gratings into a beneficial effect by strategically placing semi-reflecting surfaces at specific locations within the waveguide. These surfaces reflect light that would otherwise be lost or stray, redirecting it toward the exit pupil. The diffraction gratings' inherent energy distribution is thus converted into controlled illumination, where previously lost light becomes useful illumination.
Solution Approach 2:
The waveguide design incorporates feedback mechanisms through the semi-reflecting surfaces that monitor and redirect light paths. When light is diffracted by the gratings, the semi-reflecting surfaces detect and reflect portions of this diffracted light back into the waveguide core, creating a feedback loop that recovers energy. This feedback system ensures that energy distributed by diffraction is not lost but rather redistributed to achieve uniform illumination at the exit.
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 solution results in a cost-effective, compact, and high-quality waveguide that reduces pupil banding and edge sharpness, enhancing optical performance and manufacturability for applications like head-mounted displays.
Implementation Method 1
The waveguide including the diffraction gratings (106, 108) comprising a structure that is configured to cause diffraction within the waveguide such that an optical field is modulated in the prism (102)
Implementation Method 2
the semi-reflecting surfaces (114, 116) each reflect a different amount of illumination towards an exit point (118) to produce an output image
Implementation Method 3
The waveguide including the waveguide being configured for the illumination to undergo total internal reflection within the prism (102)
Data Source
AI summary
A waveguide for use in a head-up or head-worn display, the waveguide comprising: a prism having an entrance pupil for receiving an image; a plurality of gratings configured to direct illumination through the prism towards first and second semi-reflecting surfaces; wherein the semi-reflecting surfaces each reflect a different amount of illumination towards an exit point to produce an output image.