HUD Waveguide Output Coupling Structure With Air-Gap Isolation
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Solution Overview
Problem
Existing head-up displays face challenges in coupling light efficiently from an image source to the user's eye while maintaining image quality, often due to irregularities in the optical waveguide structure, which increases manufacturing costs and time.
Innovation Solution
The use of a saw-tooth grating as an output coupling structure, combined with an optical coating and an air gap, allows for improved light coupling and reduced mechanical processing, minimizing distortions and stresses in the waveguide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the output coupling structure is formed by stamping or engraving into the waveguide surface, then the light coupling function is achieved, but stress and irregularities are induced in the waveguide leading to poor optical performance
Solution Approach 1:
The output coupling structure is separated from the waveguide body and placed in an air gap, dividing the system into distinct functional components. This segmentation prevents stress transfer between the coupling structure and waveguide, eliminating the source of optical distortions while maintaining manufacturing simplicity.
Solution Approach 2:
An air gap is introduced as an intermediary between the output coupling structure and the waveguide body. This intermediary layer isolates the two components, preventing mechanical stress and irregularities from being transmitted to the waveguide, thereby preserving optical performance.
2Device complexity
If the output coupling structure is formed directly in the waveguide surface, then the structure is simple, but the manufacturing cost and time increase due to induced stress and irregularities
Solution Approach 1:
By separating the output coupling structure from the waveguide body and positioning it in an air gap, the system achieves better optical performance that increases manufacturing yield. The slight increase in structural complexity is offset by the elimination of defective products requiring rework or rejection.
3Ease of manufacture
If mechanical processing is used to form the output coupling structure, then the structure is created, but distortions and stresses are introduced in the waveguide
Solution Approach 1:
The air gap acts as a mediator that allows the output coupling structure to be formed using mechanical processing methods while preventing the transmission of stresses and distortions to the waveguide body, thereby maintaining optical quality and reliability.
Solution Approach 2:
The output coupling structure is extracted from the waveguide body and positioned separately in an air gap. This extraction removes the source of mechanical stresses and distortions from the optical path, preserving waveguide integrity and optical performance.
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 enhances image quality and reduces manufacturing costs by increasing the yield of usable waveguides through precise alignment and reduced mechanical processing.
Implementation Method 1
Ray 13 then propagates along the length of the waveguide, guided by total internal reflection at the surfaces of the waveguide
Implementation Method 2
The optical waveguide may further comprise an optical coating on the face of the waveguide body in the region of the air gap
Implementation Method 3
Image light (shown as an example ray, 13) from a projector (mounted, for example in the cockpit or helmet, out of the line-of-sight of the user) is injected into a first end 11 of the waveguide using a coupling device 12, for example a prism
Data Source
Figure 1
Figure 2(a)~2(e)
Figure 3
AI summary
A waveguide structure for ahead up display in which a reflective output coupling structure is formed of a separate, but connected, component to a main waveguide. Light is coupled from the main waveguide to the output coupling structure by evanescent wave coupling. In a method of manufacture for such a waveguide the output coupling structure is attached to the main waveguide using an optical feedback technique.