Waveguide Volume Bragg Gratings Pupil Expansion Haze Reduction
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Solution Overview
Problem
Compact planar optical components in near-eye displays, such as waveguides, face limitations in image resolution, image quality, and field of view, while also causing haze when trying to observe the real world due to the density of volume Bragg gratings.
Innovation Solution
A waveguide design incorporating multiple input ports and diffraction gratings configured for pupil expansion along different axes, allowing for increased field of view and reduced haze by using wavelength division to distribute different wavelengths of the same color channel at different locations, thereby reducing the required density of volume Bragg gratings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the density of volume Bragg gratings is increased to improve image resolution and quality, then image quality is improved, but haze increases when observing the real world
Solution Approach 1:
The patent transitions from two-dimensional surface relief gratings to three-dimensional volume Bragg gratings embedded within the waveguide bulk. This dimensional change enables higher diffraction efficiency and better spectral control, improving image quality while the volumetric distribution reduces surface-related haze artifacts
Solution Approach 2:
The patent optimizes key parameters of the volume Bragg gratings including grating period, orientation angle, and embedding depth within the waveguide. By carefully tuning these parameters, the system achieves high diffraction efficiency for desired wavelengths while minimizing scattering and haze effects that would degrade real-world visibility
2Weight of moving object
If compact planar optics are used to reduce size and weight, then weight is reduced, but field of view and image quality are limited
Solution Approach 1:
The diffraction gratings are embedded within the waveguide structure itself, with the grating patterns integrated into the waveguide bulk. This nesting approach eliminates separate optical components, maintaining compactness while the volumetric grating structure enables enhanced field of view compared to surface-only implementations
Solution Approach 2:
The patent employs composite waveguide structures combining transparent substrate materials with embedded diffractive elements. This composite approach allows the waveguide to simultaneously function as a light guiding medium and a diffraction element, achieving enhanced performance without increasing overall size or weight
3Adaptability or versatility
If multiple volume Bragg gratings are used to expand pupil along one axis, then pupil expansion is achieved, but haze increases due to grating density
Solution Approach 1:
The patent implements a two-stage pupil expansion process: first expanding along the horizontal axis using one set of volume Bragg gratings, then expanding along the vertical axis using a second set. This sequential expansion in different dimensions achieves full 2D pupil expansion while keeping the grating density in each individual layer manageable, thereby reducing haze
Solution Approach 2:
The pupil expansion function is segmented into multiple independent volume Bragg grating layers, each responsible for expansion along a specific axis. This segmentation allows each layer to use lower grating density optimized for its specific function, reducing cumulative haze compared to a single high-density grating attempting to perform all expansion
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 field of view while minimizing haze, allowing users to perceive a larger, clear field of view and reducing the overall size and weight of the waveguide, improving user experience in near-eye displays.
Implementation Method 1
a first diffraction grating including a first plurality of volume Bragg gratings configured to expand a beam of image light along a first axis and to redirect the beam of image light towards a second diffraction grating
Implementation Method 2
a second diffraction grating including a second plurality of volume Bragg gratings configured to receive the beam of image light from the first diffraction grating, to expand the beam of image light along a second axis, and to out-couple the beam of image light from the waveguide
Data Source
Figure 1A~1B
Figure 2A
Figure 2B~2C
AI summary
A waveguide is provided for conveying image light. The waveguide includes an input port for receiving a first beam of image light carrying an image in a wavelength band. A first diffraction grating of the waveguide includes a plurality of volume Bragg gratings (VBGs) configured to expand the first beam along a first axis and to redirect the first beam towards a second diffraction grating of the waveguide. The second diffraction grating includes a plurality of VBGs configured to receive the first beam from the first diffraction grating and to out-couple different portions of the first wavelength band of the first beam along a second axis, thereby expanding the first beam along the second axis for observation of the image by a user.