Waveguide Stack Gratings for Wide-FOV Color Uniformity
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Solution Overview
Problem
Conventional in-coupling solutions for waveguide displays suffer from cross-coupling issues and require large surface areas, limiting their practical applications, especially in high-field-of-view (FOV) displays.
Innovation Solution
A waveguide element with an in-coupling grating that splits incoming light into two separate directions using opposite diffraction orders and sets a threshold wavelength below the visible range, combined with reflective gratings to optimize light propagation and reduce cross-coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multiple waveguides are stacked on top of each other to maximize field of view, then the field of view is improved, but cross-coupling between layers occurs leading to color variations
Solution Approach 1:
The patent changes the wavelength parameter by configuring the in-coupling grating to couple only wavelengths below a threshold (e.g., blue light below 480nm) while leaving longer wavelengths (green, red) uncoupled. This wavelength-based parameter differentiation prevents cross-coupling between stacked waveguide layers, as each layer handles specific wavelength ranges, thereby maintaining color uniformity across the field of view.
2Illumination intensity
If conventional in-coupling solutions are used to achieve large field of view, then the field of view is improved, but the waveguide surface area required increases
Solution Approach 1:
The patent segments the field of view into two separate directions using opposite diffraction orders (+1 and -1 orders). This segmentation allows the in-coupling grating to direct different portions of the incoming light into separate propagation paths within the waveguide, effectively doubling the utilized field of view without proportionally increasing the waveguide surface area.
Solution Approach 2:
The patent utilizes the angular dimension by splitting light into two separate directions (upward and downward angles) through opposite diffraction orders. This dimensional approach to light routing allows efficient use of the waveguide's internal space, achieving large field of view without requiring proportional increases in surface area.
3Ease of manufacture
If surface relief gratings are used for in-coupling, then the manufacturing is simplified, but polarization sensitivity issues cause cross-coupling and color variations
Solution Approach 1:
The patent changes the operational parameter from polarization-based differentiation to wavelength-based differentiation. By configuring the grating period to couple only wavelengths below a threshold, the system achieves polarization-insensitive operation while maintaining manufacturing simplicity of surface relief gratings. This parameter shift eliminates cross-coupling issues without sacrificing ease of manufacture.
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 approach enables high-quality, multi-color displays with reduced cross-coupling and efficient use of surface area, maintaining a large field of view.
Implementation Method 1
The in-coupling grating is configured to couple incoming light into the waveguide body into two separate directions using opposite diffraction orders for splitting the field of view of the incoming light
Implementation Method 2
the in-coupling grating is configured, typically by setting its period suitably short, such that said coupling takes place only at wavelengths below a threshold wavelength residing in the visible wavelength range
Implementation Method 3
a waveguide body and an in-coupling grating arranged to the waveguide body
Data Source
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AI summary
The invention relates to a waveguide display element comprising a waveguide body and an in-coupling grating (21) arranged to the waveguide body. The in-coupling grating (21) is configured to couple incoming light into the waveguide body into two separate directions (26A, 26B) using opposite diffraction orders (IC:+1, IC:-1) for splitting the field of view of the incoming light. Further the in-coupling grating (21) is configured, typically by setting its period suitably short, such that said coupling takes place only at wavelengths below a threshold wavelength residing in the visible wavelength range. The invention also relates to a waveguide stack (51 A, 51 B, 51 C).