Compact Projection Display Using Waveguide Diffraction
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Solution Overview
Problem
Conventional head-up displays are bulky and space-intensive due to their spherical lens systems, which limits their use in compact environments like aircraft cockpits, and waveguide displays with multi-spectral light sources face challenges with color aberration and space constraints, especially with large panoramic canopies and the need for head-down displays.
Innovation Solution
A projection display using a waveguide assembly with diffraction regions to expand the input pupil in orthogonal dimensions, combined with a separate combiner oriented at an angle relative to the waveguide assembly to direct the image-bearing light towards the viewer, allowing for a compact and efficient use of space while minimizing chromatic aberration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional spherical lens systems are used for head-up displays, then the display can be implemented, but the system becomes large and bulky, limiting space availability in the cockpit
Solution Approach 1:
The patent replaces conventional spherical lens systems with a waveguide-based optical system. The waveguide uses diffraction gratings and total internal reflection to guide and expand light, eliminating the need for bulky spherical lenses while maintaining collimated display functionality. This substitution of mechanical/optical components reduces the overall system volume significantly.
Solution Approach 2:
The waveguide expands the input pupil in two orthogonal dimensions (first and second transverse directions) through sequential diffraction regions, transforming a small input aperture into a large exit pupil. This dimensional expansion approach allows compact light source placement while achieving large effective display area.
2Volume of moving object
If waveguide displays with multi-spectral light sources are used to reduce space, then the display becomes more compact, but chromatic aberration occurs
Solution Approach 1:
The patent addresses chromatic aberration by using a reflective combiner that reflects all wavelengths equally, rather than attempting to eliminate dispersion at the diffraction gratings. The combiner's reflective surface converts the dispersed spectral components back into a coherent image, transforming the potential harm of chromatic aberration into a manageable optical path configuration.
Solution Approach 2:
The combiner acts as an intermediary optical element between the waveguide and the viewer. It receives the dispersed multi-spectral light from the waveguide and redirects it toward the viewer's eye, serving as a mediator that manages the optical paths of different wavelengths and enables compact multi-spectral display without severe chromatic aberration.
3Volume of moving object
If a separate combiner is used to direct light towards the viewer, then the waveguide assembly can be oriented at an angle for compactness, but the device complexity increases
Solution Approach 1:
The patent combines the waveguide assembly and combiner into an integrated head-up display system where the combiner is positioned at an angle to the waveguide. This merging of components allows the system to achieve compact angular orientation while maintaining efficient light guidance and display functionality, reducing overall space requirements despite the additional component.
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 provides a compact and efficient head-up display that reduces space requirements and minimizes chromatic aberration, enabling the use of a small, cost-effective light source for displaying multi-spectral images, even in environments with large panoramic canopies and the need for head-down displays.
Implementation Method 1
a waveguide assembly arranged to receive the input pupil of image bearing light and including first and second diffraction regions arranged respectively to expand the input pupil in first and second generally orthogonal dimensions
Implementation Method 2
The input pupil is coupled into a first waveguide and propagates by total internal reflection along the waveguide reflecting between each of two opposed and parallel sides of the generally rectilinear waveguide
Implementation Method 3
a combiner arranged separately from the waveguide assembly and orientated at an angle relative to the plane of the waveguide assembly to direct the image bearing light from the exit pupil towards a viewer
Data Source
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Figure 4
AI summary
The present invention provides a projection display (10), for displaying an image to a viewer (12). An image-providing light source device (60) is arranged to inject an input pupil (61) of multi-spectral image bearing light into a waveguide assembly (50). The waveguide assembly (50) comprises first and second diffraction regions arranged respectively for expanding the input pupil in first and second generally orthogonal dimensions and outputting an exit pupil (54) expanded in the first and second dimensions from the waveguide assembly (50). The diffractive regions of the waveguide assembly (50) are matched to cause zero or substantially zero net chromatic aberration. A combiner (16) is arranged to direct the exit pupil (54) towards theviewer (12) for viewing an image (18) and to transmit light (52) from a real world scene through the combiner (16) so that the image (18) overlays the light (52) from the real world scene.