Volume Holographic Grating Waveguide for Expanded Field of View
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Solution Overview
Problem
Conventional optical reflective devices, including dielectric mirrors and grating structures, face limitations such as a reflective axis constrained to the surface normal, inadequate light reflectivity across a range of incidence angles, and optical clarity issues, particularly in head-mounted display (HMD) devices, leading to suboptimal image projection and reduced field of view (FOV).
Innovation Solution
The use of volume holographic light coupling elements with grating structures that allow for pupil expansion by reflecting light about a reflective axis not constrained to the surface normal, enabling a constant angle of reflection across a range of incidence angles and increasing the field of view (FOV) through the incorporation of skew mirror technology and holographic optical elements within waveguides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional dielectric mirrors are used, then light reflectivity is improved, but the reflective axis is constrained to surface normal
Solution Approach 1:
The patent changes the fundamental parameter of reflection mechanism from surface-based Fresnel reflection to volume-based Bragg diffraction. This allows the reflective axis to be independently controlled from the surface normal by adjusting the grating vector orientation and magnitude in the volume holographic structure, while maintaining high reflectivity through constructive interference of diffracted waves.
Solution Approach 2:
The patent replaces the mechanical constraint of surface-normal reflection with an optical field-based solution using volume holographic gratings. The grating structures encode directional information in the volume, allowing light to be reflected at arbitrary angles determined by the grating vector rather than being constrained by surface geometry.
2Adaptability or versatility
If conventional grating structures are used, then reflective axis independence from surface normal is improved, but angle of reflection varies with wavelength
Solution Approach 1:
The patent employs composite volume holographic grating structures that combine multiple grating vectors and orientation states within a single volume. This composite structure creates a superposition of diffraction effects that collectively maintain a constant reflective axis across a broad wavelength range, overcoming the wavelength-dependent behavior of conventional single-wavelength gratings.
Solution Approach 2:
The volume holographic grating structure serves multiple functions simultaneously: it provides wavelength-independent reflection, maintains constant reflective axis orientation, and enables arbitrary angle control. The single structure replaces multiple conventional components that would be needed to achieve the same performance across different wavelengths and angles.
3Ease of manufacture
If conventional reflective devices are used, then manufacturing simplicity is improved, but optical clarity and field of view are reduced
Solution Approach 1:
The patent transitions from two-dimensional surface gratings to three-dimensional volume holographic gratings. This dimensional change enables the encoding of multiple reflection angles and wavelength compensations within the volume, expanding the field of view and angular acceptance while maintaining manufacturability through standard holographic recording techniques.
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 enhances the viewing capability and optical clarity of image projection systems by providing a more expansive FOV and reducing impedances to optical clarity, while maintaining image quality and compactness, particularly in HMD devices.
Implementation Method 1
a first volume holographic light coupling element disposed between the first waveguide surface and the second waveguide surface. The first volume holographic light coupling element may be configured to reflect at least a portion of incident light as reflected light
Implementation Method 2
The incident light may have a first angle of incidence within a TIR range with respect a first axis corresponding to a surface normal of the waveguide
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A device including a waveguide having a first waveguide surface and a second waveguide surface parallel to the first waveguide surface is disclosed. The device may include a first volume holographic light coupling element disposed between the first waveguide surface and the second waveguide surface. The first volume holographic light coupling element may be structured to reflect at least a portion of incident light as reflected light. Incident light for which the first volume holographic light coupling element is structured to reflect may have a first angle of incidence within a total internal reflection (TIR) range with respect a first axis corresponding to a surface normal of the waveguide. Incident light for which the first volume holographic light coupling element is structured to reflect may have a second angle of incidence with respect to a second axis different from the first axis.