Segmented Waveguide Projection Display for Reduced Obscuration
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Solution Overview
Problem
Prior art projection displays using waveguide techniques result in obscuration of the outside world scene due to the large size of the first plate-like waveguide, which is unsuitable for restricted environments like aircraft cockpits or helmet-mounted displays, and reduces the observer's view.
Innovation Solution
A projection display design that includes a smaller dimensioned first waveguide element, allowing for reduced obscuration and increased suitability in restricted spaces, achieved by dividing the image into sub-images and injecting each into different input regions of the first waveguide, with a transmission or reflection grating to direct light internally and an exit grating to diffract light out towards the observer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a large first plate-like waveguide is used to maintain a large exit pupil and field of view, then the display performance is improved, but the obscuration of the outside world scene increases and the device becomes unsuitable for restricted environments
Solution Approach 1:
The first waveguide is divided into multiple segments (first, second, third waveguides) arranged in series. Each segment contributes to the overall optical path and pupil expansion, allowing the system to achieve a large exit pupil without requiring a single large waveguide that would cause obscuration. The segmented approach distributes the optical function across multiple smaller components.
Solution Approach 2:
The patent introduces a temporal dimension to the optical path by using a movable mirror that scans light across different input regions of the waveguide segments over time. This dynamic scanning approach allows the system to maintain a large effective exit pupil and field of view without requiring all waveguide segments to be simultaneously visible to the observer, thereby reducing obscuration.
2Area of stationary object
If a large first plate-like waveguide is used to maintain a large exit pupil and field of view, then the display performance is improved, but the device mass and size increase making it unsuitable for helmet-mounted or head-mounted displays
Solution Approach 1:
The waveguide system is segmented into multiple smaller waveguide elements connected in series. This segmentation allows the total optical path length to be achieved with smaller, lighter individual components rather than one large heavy waveguide. The segmented structure reduces overall mass while maintaining the required field of view and exit pupil characteristics.
Solution Approach 2:
The patent adds temporal dimension through movable mirror scanning, which allows the system to achieve a large field of view over time rather than requiring all field angles to be simultaneously present. This temporal multiplexing reduces the spatial dimensions and mass of the waveguide system, making it suitable for helmet-mounted and head-mounted displays.
3Area of stationary object
If a large first plate-like waveguide is used to maintain a large exit pupil and field of view, then the display performance is improved, but the complexity of the optical system increases
Solution Approach 1:
The optical system is divided into modular segments (multiple waveguides with input/output couplings) that can be independently optimized and assembled. This modularity simplifies the design and alignment process compared to a single complex large waveguide, as each segment can be characterized and adjusted separately while contributing to the overall large exit pupil 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 reduces the size and mass of the projection display, allowing for a clearer view of the outside world scene while maintaining a large exit pupil and field of view, making it more suitable for head-up or helmet-mounted displays.
Implementation Method 1
a first grating associated with the first waveguide element arranged to direct the image bearing light internally along the first waveguide element
Implementation Method 2
the incidence angle of the light on the internal surfaces of the first plate-like waveguide 12 is greater than the critical angle for the material from which the first plate-like waveguide 12 is made. The image bearing light is constrained within the first plate-like waveguide 12 to propagate along the first plate-like waveguide 12 reflecting from each internal surface in turn
Implementation Method 3
an exit grating arranged to diffract received image bearing light out of the second waveguide element towards an observer
Implementation Method 4
a coupling grating arranged to receive the image bearing light from the first waveguide element and to direct the image bearing light along the second waveguide element
Implementation Method 5
the coupling grating 24 is operable to diffract each impinging ray of image bearing light received from the transmission grating 18 of the first plate-like waveguide 12 at an angle that is larger than the critical angle for the material from which the second plate-like waveguide 14 is made
Data Source
AI summary
A projection display which includes first and second waveguide elements, wherein the first waveguide element has a two input regions for injecting image bearing light into the first waveguide element. In this manner, the total field of view of the image to be displayed at the second waveguide element is divided into two sub-images prior to injection of one sub-image into one input region and the other sub-image into the other input region of the first waveguide element. This results in a smaller first waveguide element, thereby reducing obscuration of an observers view of a forward scene over which to the image to be displayed is overlaid.