Dual Waveguide Pupil Expansion for HUD Image Quality
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Solution Overview
Problem
Existing waveguide systems for head-up displays face challenges in achieving large exit pupil size without increasing the size and weight of input optics, while maintaining uniform light distribution and preserving image quality across different wavelengths.
Innovation Solution
A dual waveguide system with orthogonal diffraction gratings is used to replicate the input pupil in two dimensions, utilizing rectangular profiled gratings fabricated through photolithography to achieve efficient pupil expansion without degrading image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a single waveguide with diffraction gratings is used to expand the exit pupil, then the pupil size increases, but chromatic dispersion degrades image quality
Solution Approach 1:
The system divides the waveguide into two separate waveguides (first and second waveguides), each handling a portion of the pupil expansion function. This segmentation allows each waveguide to be optimized for minimal chromatic dispersion while collectively achieving the desired large exit pupil size through their orthogonal arrangement.
Solution Approach 2:
The second waveguide is arranged orthogonal to the first waveguide, expanding the exit pupil in a second dimension. This dimensional approach distributes the chromatic dispersion effects across different spatial orientations, allowing each waveguide to maintain better image quality while achieving overall pupil expansion.
2Ease of manufacture
If rectangular profiled gratings are used instead of blazed gratings, then fabrication cost decreases, but diffraction efficiency may be affected
Solution Approach 1:
The patent changes the grating profile parameter from blazed (triangular) to rectangular, which simplifies the fabrication process significantly. The rectangular profile can be manufactured using standard photolithography techniques, reducing fabrication cost while the orthogonal waveguide arrangement compensates for any diffraction efficiency losses.
3Volume of moving object
If the waveguide system is made compact, then device size decreases, but maintaining large exit pupil becomes more difficult
Solution Approach 1:
By arranging the second waveguide orthogonal to the first waveguide, the system expands the exit pupil in multiple dimensions rather than requiring a single large waveguide. This orthogonal configuration allows compact device volume while achieving a large effective exit pupil area through the combined optical paths of both waveguides.
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 system provides a compact waveguide design with a large exit pupil and uniform light distribution, maintaining image quality by compensating for chromatic dispersion and reducing fabrication costs through the use of simpler grating structures.
Implementation Method 1
the first diffraction grating diffracts a portion of light trapped in the first waveguide by total internal reflection
Implementation Method 2
light trapped in the first waveguide by total internal reflection
Implementation Method 3
the second optical waveguide comprising a second diffraction grating wherein the first and second gratings are arranged to be rotated relative to one another
Data Source
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AI summary
An optical waveguide device for use in a head up display. The waveguide device provides pupil expansion in two dimensions. The waveguide device comprise a primary waveguide and a secondary waveguide, the secondary waveguide being positioned on a face of the primary waveguide. The secondary waveguide has a diffraction grating on a face opposite to the face which contacts the primary waveguide. The diffraction grating diffracts light into more than diffraction order. Rays diffracted into a non-zero order are trapped in the secondary waveguide by total internal reflection.