Dual-Layer Holographic Optical Element for Wearable HUDs
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Solution Overview
Problem
Current holographic optical elements in wearable heads-up displays face limitations in achieving high index modulation and diffraction efficiency due to the distribution of multiple holograms across a single layer, which restricts angular bandwidth and overall performance.
Innovation Solution
The use of a dual-layer holographic optical element with each layer containing multiple holograms responsive to distinct wavebands, allowing for greater index modulation and diffraction efficiency, with each hologram having an index modulation of at least 0.016 and an angular bandwidth of at least 12°, distributed across two layers of photopolymer material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple holograms are recorded in a single layer of holographic material, then the device complexity is reduced, but the index modulation and diffraction efficiency of each hologram decrease
Solution Approach 1:
The patent divides the holographic optical element into multiple layers, with each layer containing a subset of holograms. This segmentation allows each layer to dedicate its full index modulation capability to fewer holograms, thereby maintaining high diffraction efficiency while still achieving multi-wavelength functionality through the combination of layers.
Solution Approach 2:
The patent transitions from a single-layer two-dimensional structure to a multi-layer three-dimensional structure. By adding the layer dimension, the system can distribute holograms across multiple planes, allowing each hologram to achieve sufficient index modulation and diffraction efficiency while collectively covering multiple wavebands.
2Ease of manufacture
If a single layer of holographic material is used, then the manufacturing process is simpler, but the angular bandwidth and diffraction efficiency are limited
Solution Approach 1:
The patent segments the holographic functionality across multiple layers, where each layer is optimized for specific angular bandwidth requirements. This segmentation allows each layer to be manufactured with precise angular characteristics while the overall device achieves broader spectral coverage through layer combination.
Solution Approach 2:
The patent varies optical parameters such as index modulation depth, hologram spacing, and layer thickness across different layers to optimize angular bandwidth for each wavelength. This parameter variation enables precise control over diffraction characteristics while maintaining manufacturing feasibility.
3Reliability
If the holographic material thickness is increased to improve diffraction efficiency, then the light manipulation capability improves, but the device becomes less suitable for wearable applications
Solution Approach 1:
The patent divides the total required optical path length into multiple thinner layers. Each layer contributes to the overall diffraction efficiency through its own index modulation, and the cumulative effect of multiple layers achieves the desired light manipulation capability while keeping individual layer thicknesses suitable for wearable applications.
Solution Approach 2:
The patent uses composite multi-layer structures where each layer may have different optical properties optimized for specific wavelengths. This composite approach allows the system to achieve high overall diffraction efficiency across multiple wavebands while maintaining thin individual layers that are compatible with wearable form factors.
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 configuration enhances the diffraction efficiency and angular bandwidth of each hologram, enabling better light manipulation and image display in wearable heads-up displays while maintaining thinness, thus overcoming the limitations of single-layer elements.
Implementation Method 1
a photopolymer film may be controllably exposed/illuminated with a particular interference pattern of light to cause surface relief patterns to form in/on the photopolymer film
Implementation Method 2
The index modulation of a holographic optical element is the change in the holographic material refractive index from before the hologram is recorded to after the hologram is recorded and is an indication of the ability of the holographic optical element to diffract light
Data Source
AI summary
Systems, devices, and methods for holographic optical elements are described. A holographic optical element includes a first layer of holographic material and a second layer of holographic material. The first layer of holographic material includes a first hologram responsive to light in a first waveband and a second hologram responsive to light in a second waveband. The second layer of holographic material includes a third hologram responsive to light in a third waveband and may include a fourth hologram responsive to light in a fourth waveband. The first, second, third, and fourth wavebands are distinct and may comprise light of red, blue, green, and infrared wavelengths, respectively. Distribution of the three or four holograms on two layers of holographic material allows each hologram to have an index modulation of greater than 0.016, a diffraction efficiency of greater than 15%, and an angular bandwidth of greater than 12°.