Display device having diffraction gratings with reduced polarization sensitivity
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Solution Overview
Problem
Conventional augmented reality (AR) and virtual reality (VR) systems face challenges in providing a comfortable and natural presentation of virtual image elements amidst real-world imagery due to polarization sensitivity in diffractive optical coupling elements, leading to reduced efficiency and coherent artifacts, and mismatched accommodative and vergence states causing user discomfort.
Innovation Solution
The use of blazed diffraction gratings with reduced polarization sensitivity, formed in high refractive index materials like lithium niobate, coupled with a waveguide system that provides controlled wavefront divergence to match accommodative and vergence cues, enhancing the perception of depth and reducing user discomfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional diffractive optical coupling elements are used in AR/VR systems, then light coupling can be achieved, but polarization sensitivity causes reduced efficiency and coherent artifacts
Solution Approach 1:
The patent changes the physical parameters of the diffraction grating by using high refractive index materials (n ≥ 1.9) and optimizing the grating geometry (blazed profile with specific blaze angles). These parameter changes reduce polarization sensitivity while maintaining high diffraction efficiency, resolving the contradiction between light coupling efficiency and polarization sensitivity
Solution Approach 2:
The patent employs composite material structures combining high refractive index substrates with specifically designed grating layers. This composite approach allows optimization of both the substrate's light-guiding properties and the grating's diffraction characteristics, achieving reduced polarization sensitivity while maintaining coupling efficiency
2Reliability
If waveguide systems provide controlled wavefront divergence to match accommodative and vergence cues, then depth perception is enhanced, but device complexity increases
Solution Approach 1:
The waveguide system is designed to perform multiple functions simultaneously: light transmission, wavefront control, and depth cue provision. By integrating these functions into a single system rather than separate components, the patent enhances depth perception while minimizing the increase in device complexity
Solution Approach 2:
The patent utilizes parameter changes in the waveguide's physical structure (such as varying refractive index profiles or geometric configurations) to control wavefront divergence. This allows the system to provide accurate depth cues through modifications to existing structural parameters rather than adding complex control mechanisms
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 achieves improved efficiency and uniformity of light coupling, reducing polarization sensitivity and aligning accommodative and vergence states, resulting in a more realistic and comfortable three-dimensional imagery experience.
Implementation Method 1
a blazed diffraction grating formed in the substrate or in a layer disposed over the substrate
Implementation Method 2
The blazed diffraction grating has a first diffraction efficiency for a first polarization over a range of angles of light incident thereon and has a second diffraction efficiency for a second polarization
Implementation Method 3
The substrate is configured to guide light coupled into the waveguide within the waveguide via total internal reflection
Data Source
AI summary
Blazed diffraction gratings provide optical elements in head-mounted display systems to, e.g., incouple light into or out-couple light out of a waveguide. These blazed diffraction gratings may be configured to have reduced polarization sensitivity. Such gratings may, for example, incouple or outcouple light of different polarizations with similar level of efficiency. The blazed diffraction gratings and waveguides may be formed in a high refractive index substrate such as lithium niobate. In some implementations, the blazed diffraction gratings may include diffractive features having a feature height of 40 nm to 120 nm, for example, 80 nm. The diffractive features may be etched into the high index substrate, e.g., lithium niobate.