Waveguide Display with Inverted Light Path for Compact HUD
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Solution Overview
Problem
Waveguide displays in limited spaces, such as vehicles or helmets, face challenges due to the need for a vertical orientation, which restricts head-clearance and reduces the instantaneous field of view because the output direction of image-bearing light is perpendicular to the waveguide plane, and alternative overhead arrangements lead to increased path lengths and space constraints.
Innovation Solution
Positioning a waveguide display unit between a combiner unit and the viewer, directing the output back through the waveguide for reflection, allowing a compact arrangement with a planar waveguide and obliquely oriented combiner to combine image-bearing and external scene light efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the waveguide is oriented vertically to permit output light to be viewed in the horizontal direction, then the image-bearing light can be output perpendicular to the waveguide plane, but the vertical space/height required increases, which is problematic in space-limited environments
Solution Approach 1:
The waveguide is reoriented from a vertical arrangement to a horizontal arrangement, changing the dimensional orientation of the system. This allows the waveguide to extend in the horizontal plane rather than vertically, reducing the vertical space requirement while maintaining the perpendicular output capability through the use of a combiner for indirect viewing
2Length of stationary object
If the waveguide is positioned overhead with a combiner in front of the viewer, then the vertical space requirement is reduced, but the path length from waveguide output to viewer's eye increases, reducing the instantaneous field of view
Solution Approach 1:
Instead of positioning the waveguide overhead and having light travel downward to a combiner, the waveguide is positioned between the combiner and the viewer, with light traveling upward. This inverted arrangement shortens the effective path length through the air gap while maintaining the overhead positioning benefit, as the light now travels a shorter distance from the waveguide output through the combiner to the viewer's eye
3Length of moving object
If the waveguide output part is positioned close to the combiner, then the path length is reduced, but the arrangement becomes more complex in terms of positioning and alignment
Solution Approach 1:
The combiner serves multiple functions: it reflects image-bearing light from the waveguide back toward the viewer, transmits external scene light from the environment, and combines these two light paths. This multi-functionality allows for a compact arrangement where the combiner and waveguide can be positioned close together without requiring separate components for each function, thereby reducing overall system complexity despite the close positioning
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 configuration enables a compact and efficient display setup in space-limited environments, maintaining a wide field of view while allowing image overlay on the external scene, without the need for bulky light sources, and mitigates chromatic aberration by matching diffraction grating periods.
Implementation Method 1
image-bearing light may be focussed at infinity, and a viewer views/receives the released light directly. In this way, the viewer focusses on an image seen by looking at/through the transparent waveguide output area
Implementation Method 2
inserted light propagates along the waveguide by total internal reflection towards an output part arranged to release guided light from the waveguide
Implementation Method 3
output part arranged to release guided light from the waveguide by a further process of diffraction, for viewing
Implementation Method 4
a combiner arranged adjacent to the output part of the optical waveguide for reflecting image-bearing light output by the waveguide in a direction which passes back through the optical waveguide and for allowing light from an external scene to pass through the combiner
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A display apparatus for use in displaying an image to a viewer (4), comprising an optical waveguide (8) arranged to receive image-bearing light (2) into the optical waveguide to guide the received image-bearing light therealong to an output part (5) of the optical waveguide for output therefrom. A combiner (70) is arranged adjacent to the output part of the optical waveguide for reflecting image-bearing light output by the waveguide in a direction which passes back through the optical waveguide and for allowing light (6) from an external scene to pass through the combiner in said direction through the optical waveguide to combine with the reflected image-bearing light so that the image-bearing light overlays light from the external scene for viewing by a viewer.