Holographic Diffractive Grating for Wide Field of View AR
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Solution Overview
Problem
Current augmented reality (AR) devices with holographic diffractive grating structures face challenges in providing a wide field of view without increasing the size and weight of the device, due to limitations in refractive index and diffraction efficiency of recording materials, leading to limited angular selectivity and image uniformity.
Innovation Solution
The apparatus and method involve a light source, beam splitter, and triangular prisms to split and attenuate light beams, creating interference patterns on diffractive grating material, forming expanding and out-coupling diffractive gratings with equal surface periods, allowing for a wide field of view while maintaining compactness and low weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If an expanding element is added to increase the field of view, then the field of view is improved, but the weight and dimensions of the device increase
Solution Approach 1:
The patent combines the expanding element and out-coupling element into a single integrated diffractive grating structure formed by recording interference patterns in a photosensitive material. This merging eliminates the need for separate expanding and out-coupling elements, thereby increasing the field of view while avoiding the weight and dimensional penalties of multiple discrete components.
Solution Approach 2:
The diffractive grating structure serves multiple functions simultaneously: it acts as both the expanding element (to widen the field of view) and the out-coupling element (to extract light from the waveguide). This multi-functionality resolves the contradiction by achieving field of view expansion without adding dedicated expanding hardware that would increase device weight.
2Area of stationary object
If multiple separate elements are used for inputting light, expanding the exit pupil, and outputting the light, then the field of view is improved, but the device becomes significantly bulky and heavy
Solution Approach 1:
The patent merges the in-coupling grating, expanding element, and out-coupling grating into a single integrated diffractive grating structure. This is achieved by recording multiple interference patterns in different orientations within the same photosensitive material layer, thereby simplifying the device structure while maintaining the field of view enhancement benefits.
3Ease of manufacture
If photopolymer materials are used for holographic optical element, then the device is easy to manufacture, but the diffraction efficiency is low due to insufficient refractive index and refractive index change
Solution Approach 1:
The patent uses a photosensitive material with specific properties (refractive index n and refractive index change Δn) that balances manufacturability with diffraction efficiency. The material is formulated to achieve sufficient diffraction efficiency while maintaining ease of holographic recording, resolving the contradiction between manufacturing simplicity and optical performance.
Solution Approach 2:
The patent optimizes the thickness of the photosensitive material layer and the recording conditions (exposure time, light intensity) to maximize diffraction efficiency within the constraints of the material's refractive index properties. By carefully controlling these parameters, the system achieves adequate diffraction efficiency while maintaining the manufacturing advantages of photopolymer materials.
4Loss of energy
If a thick layer of material is used to achieve high diffraction efficiency, then the diffraction efficiency is improved, but the angular selectivity of the grating worsens and the field of view decreases
Solution Approach 1:
The patent optimizes the thickness of the photosensitive material layer to achieve the optimal balance between diffraction efficiency and angular selectivity. By carefully controlling the layer thickness and recording conditions, the system maintains high diffraction efficiency while preserving wide angular acceptance, thereby achieving both high efficiency and wide field of view.
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 enables an AR device with a wide field of view, minimizing light loss and improving image uniformity, while being easy to manufacture and lightweight, thus overcoming the limitations of existing technologies.
Implementation Method 1
creating interference patterns on diffractive grating material
Implementation Method 2
holographic diffractive grating structure
Implementation Method 3
triangular prisms to split and attenuate light beams
Implementation Method 4
the beams propagate in the waveguide and are incident on or arrive at the out-coupling diffractive grating (HOE/DOE) through total internal reflection
Data Source
AI summary
Provided is an augmented reality (AR) device based on a waveguide with a holographic diffractive grating structure and an apparatus for recording the holographic diffractive grating structure. The apparatus includes a light source, a beam splitter, a first amplitude filter and a first triangular prism that are arranged on a path of a first light beam, and a second amplitude filter and a second triangular prism that are arranged on a path of a second light beam, in which a first part of the first light beam passes through the first triangular prism without attenuation, a second part of the first light beam passes through the first triangular prism after being attenuated, and the second light beam passes through the second triangular prism after being attenuated, and the holographic diffractive grating structure is recorded between the first triangular prism and the second triangular prism.