Cross-Polarized Eye Pupil Expanders for Waveguide Vertical FoV
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Solution Overview
Problem
Existing waveguide-based AR/VR glasses suffer from limited field of view (FoV), particularly in vertical directions, due to the use of conventional diffraction gratings that restrict the angular bandwidth, limiting the immersive experience.
Innovation Solution
Employing cross-polarized eye pupil expanders (EPEs) on opposite surfaces of the waveguide, where each EPE preferentially diffracts light of a specific polarization state, allowing for independent control of light propagation in different image portions, thereby expanding the vertical FoV without compromising image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional diffraction gratings are used in waveguide-based AR/VR glasses, then the device structure is simple and fabrication is easier, but the field of view (FoV) is limited
Solution Approach 1:
The patent divides the waveguide into multiple sections, each containing different types of diffraction gratings (first type for s-polarized light, second type for p-polarized light). This segmentation allows independent optimization of each section for specific polarization states, enabling expanded field of view while maintaining fabrication feasibility through modular design
Solution Approach 2:
Different regions of the waveguide are assigned different grating characteristics tailored to local requirements. The first diffraction grating is optimized for s-polarized light while the second is optimized for p-polarized light, creating local quality variations that collectively expand the overall field of view without compromising manufacturing ease
2Device complexity
If the angular bandwidth is restricted by conventional diffraction gratings, then the device complexity is reduced, but the field of view is limited
Solution Approach 1:
The patent changes the diffraction grating parameters (grating period, orientation, and type) to match the polarization state of incident light. By adjusting these parameters, the system achieves broader angular bandwidth and expanded field of view while maintaining manageable device complexity through systematic parameter optimization
3Area of stationary object
If cross-polarized eye pupil expanders are employed on opposite surfaces, then the vertical FoV is doubled, but the device structure becomes more complex
Solution Approach 1:
The patent employs asymmetric positioning of diffraction gratings on opposite waveguide surfaces, with first gratings for s-polarized light and second gratings for p-polarized light. This asymmetric configuration enables vertical field of view expansion while the systematic arrangement keeps structural complexity manageable
Solution Approach 2:
The waveguide structure is designed to perform multiple functions simultaneously: it guides light, expands pupil, and differentiates polarization states using integrated diffraction gratings. This multi-functionality achieves doubled vertical FoV while avoiding the need for separate dedicated components that would increase complexity
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 use of cross-polarized EPEs significantly enhances the vertical FoV, doubling it compared to conventional systems, ensuring a more immersive experience by optimizing light propagation through the waveguide.
Implementation Method 1
a diffraction grating configured to diffract a light of at least one given wavelength incident on the optical waveguide
Implementation Method 2
light propagates into the optical waveguide by TIR (for Total Internal Reflection)
Implementation Method 3
each EPE preferentially diffracts light of a specific polarization state
Implementation Method 4
each EPE preferentially diffracts light of a specific polarization state
Data Source
Figure 1A
Figure 1B~1C
Figure 1D~1E
AI summary
Embodiments include an optical system that may be included in a waveguide display. An example apparatus includes an image generator configured to generate an image having an upper portion and a lower portion. A waveguide is provided with an in-coupler and an out-coupler, the in-coupler being arranged to couple the upper and lower portions of the image along an optical path to the out-coupler. Along the optical path, at least first and second polarization-selective diffraction gratings are configured to cooperatively direct the upper portion of the image toward the out-coupler. At least third and fourth polarization-selective diffraction gratings are configured to cooperatively direct the lower portion of the image toward the out-coupler.