LED Waveguide Projector Pupil Shaping for Reduced Reinteraction
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Solution Overview
Problem
Existing diffractive waveguide projection displays suffer from reinteraction of light, leading to efficiency loss and banding issues, particularly in thin waveguides where reducing the input pupil size is necessary but undesirable.
Innovation Solution
The projection display employs an input pupil shape larger in the direction parallel to the linear diffractive features and uses a tapered light pipe array to efficiently relay light, reducing angular range and preventing reinteraction while maintaining image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the input pupil size is reduced to prevent reinteraction, then reinteraction is avoided, but banding effects occur in the output image
Solution Approach 1:
The patent applies asymmetry by changing the input pupil shape from a conventional symmetric circular shape to an asymmetric shape that is elongated in the direction perpendicular to the linear diffractive features. This asymmetric shaping allows the pupil to be smaller in the critical dimension (parallel to features) to prevent reinteraction, while being larger in the perpendicular dimension to maintain sufficient light throughput and avoid banding effects.
Solution Approach 2:
The patent changes the geometric parameters of the input pupil by defining specific dimensional relationships: the pupil is shaped such that its extent in the direction parallel to the linear diffractive features is limited to prevent reinteraction, while its extent perpendicular to the features is maintained at a larger size. This parameter optimization resolves the contradiction between preventing reinteraction and avoiding banding.
2Reliability
If the waveguide thickness is increased to reduce reinteraction, then reinteraction is prevented, but the device becomes less efficient and harder to manufacture
Solution Approach 1:
The patent changes the input pupil size and shape parameters to compensate for the thin waveguide design. By optimizing the pupil dimensions and asymmetric shape, the system achieves effective reinteraction prevention without requiring increased waveguide thickness, thereby maintaining manufacturing feasibility and device efficiency.
3Reliability
If the input pupil is made too small to prevent reinteraction, then reinteraction is avoided, but gaps appear in the output image causing banding
Solution Approach 1:
The asymmetric pupil shape maintains image continuity by being larger in the dimension perpendicular to the linear diffractive features, ensuring sufficient light distribution across the output image to prevent gaps and banding, while being appropriately limited in the parallel dimension to prevent reinteraction.
Solution Approach 2:
The patent optimizes the pupil dimensional parameters by setting the extent perpendicular to the linear features at a larger value than the extent parallel to them. This parameter adjustment ensures continuous image coverage and eliminates banding effects while maintaining reinteraction prevention.
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 enhances efficiency and reduces banding, allowing for compact projector designs without compromising image quality, suitable for applications like augmented and virtual reality headsets.
Implementation Method 1
The input grating 4 diffracts the light of the input pupil 8 towards the output grating 10 through a series of total internal reflections within the waveguide 2
Implementation Method 2
The input grating 4 diffracts the light of the input pupil 8 towards the output grating 10 through a series of total internal reflections within the waveguide 2
Implementation Method 3
At the output grating 10 the input pupil 8 is replicated as a series of output pupils 12. At each interaction of the light with the output grating 10 some of the light is diffracted out of the waveguide as an output pupil replication 12 forming the image
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
There is provided a projection display (200), and a method for illuminating a projection display (200). The projection display (200) comprising a waveguide (2) comprising an input grating (4) having a plurality of linear diffractive features (6), the input grating (4) configured to couple in light into the waveguide (2), and an array of LEDs configured to form an illumination pupil which is optically relayed as an input pupil (8) onto the input grating (4), such that at the input grating (4) the input pupil (8) has a shape that is larger in a direction parallel to the linear diffractive features (6) than in a direction perpendicular to the linear diffractive features (6).