Holographic Bragg Grating Waveguide for Near-Eye Display FOV
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Solution Overview
Problem
Conventional near-eye displays with waveguide systems face limitations in achieving a large field-of-view (FOV) while maintaining compactness and light weight, due to the need for high refractive index materials and multiple waveguides, which results in thickness and weight increase, and also suffer from ghost images and low in-coupling efficiency.
Innovation Solution
The use of a waveguide with a holographic Bragg grating generated by multiple exposures within a recording band, allowing for efficient diffraction of light across different optical bands and angles, enabling a larger FOV and reducing ghost images by directly coupling image light without external gratings, thus supporting multiple channels in a single output waveguide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If conventional surface-relief grating elements are used to achieve large FOV, then FOV can be increased, but the device thickness and weight increase significantly
Solution Approach 1:
The patent changes the grating structure from surface-relief to volume holographic grating, and modifies the recording parameters (using UV band with wavelengths 300-400nm) to achieve broader diffraction bandwidth. This allows the waveguide to achieve large FOV without requiring high refractive index materials or multiple waveguides, thereby reducing device weight while maintaining FOV performance
2Adaptability or versatility
If multiple waveguides are used for full-color display, then color performance is improved, but device thickness and weight increase
Solution Approach 1:
The volume holographic grating is designed to diffract multiple wavelength bands (blue 450-480nm, green 500-550nm, red 600-680nm) simultaneously through multiple exposures during recording. This allows a single waveguide to perform full-color display functionality that would traditionally require multiple separate waveguides, thereby reducing device thickness
Solution Approach 2:
The patent combines multiple grating functions for different color channels into a single volume holographic grating structure within one waveguide. By recording multiple gratings at different orientations and wavelengths during the manufacturing process, the single grating element handles all color channels, eliminating the need for stacked multiple waveguides
3Productivity
If surface-relief grating elements are used, then light coupling is achieved, but ghost images are generated due to external light diffraction
Solution Approach 1:
The volume holographic grating provides selective diffraction based on wavelength and angle, creating localized diffraction zones for different color channels. This angular and spectral selectivity ensures that only the intended image light is diffracted to the user's eyes, while external ambient light at different angles and wavelengths passes through undiffracted, thereby eliminating ghost images while maintaining high coupling efficiency
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 achieves a significantly larger FOV with reduced weight and ghost image issues, while enhancing in-coupling efficiency to over 90% for any polarization, allowing for a more compact and efficient near-eye display system.
Implementation Method 1
the holographic Bragg grating diffracts light in one or more bands of light (e.g., different portions of a visible band) that are at a longer wavelength than the recording band
Implementation Method 2
an occurrence of total internal reflection of image light coupled into a waveguide
Data Source
AI summary
A near-eye display includes a light source assembly, a first waveguide, an output waveguide, and a controller. The light source assembly emits image light including light within a first band and a second band. The first waveguide receives the image light, expands the received image light in at least one dimension, and outputs an image light. The output waveguide includes an output area and a plurality of input areas. Each input area receives the image light from the first waveguide. The output waveguide includes a holographic Bragg grating and the output waveguide expands the image light at least along two dimensions to form an expanded image light, and outputs the expanded image light toward an eyebox. The controller controls the scanning of the light source assembly and the first waveguide.