Lightguide Reflective Coatings for Wide Field-of-View
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Solution Overview
Problem
High refractive index materials, necessary for wider field-of-view in augmented, mixed, and virtual reality devices, are cost-prohibitive and limited by total internal reflection constraints, restricting the range of angles light can propagate within lightguides.
Innovation Solution
The use of refractive index interfaces combined with reflective coatings in lightguides increases the range of angles at which light can propagate, providing a wider field-of-view without the need for high index materials, by reflecting light between the guide's front and back sides based on common reflective wavebands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If high refractive index materials are used in lightguides, then the field-of-view and range of propagation angles are improved, but the manufacturing cost increases significantly
Solution Approach 1:
The patent combines low refractive index material (such as glass or polymer with index 1.4-1.7) with reflective coatings (metallic or dielectric layers) to create a composite lightguide structure. This composite approach achieves wide-angle light propagation comparable to high index materials while using cost-effective low index materials, thereby resolving the contradiction between performance and manufacturing cost
Solution Approach 2:
The patent changes the optical parameters of the lightguide by introducing reflective coatings with specific reflectivity characteristics. By adjusting the coating properties (reflectivity, wavelength selectivity, angular dependence), the system achieves enhanced light confinement and wider propagation angles without changing the base material's refractive index, thus improving performance without increasing material cost
2Adaptability or versatility
If high refractive index materials are used in lightguides, then the range of propagation angles is improved, but material availability and cost-effectiveness worsen
Solution Approach 1:
The patent replaces expensive high index materials with inexpensive low index materials combined with reflective coatings. This substitution uses readily available, cost-effective materials (common glass or polymers) instead of specialized high index materials, improving material availability while achieving comparable optical performance through the coating enhancement
Solution Approach 2:
The reflective coating acts as an intermediary element that enhances the optical performance of low index materials. The coating mediates between the limitations of low index materials (narrow propagation angles) and the desired performance (wide propagation angles), enabling the use of abundant, inexpensive materials while achieving high performance
3Reliability
If total internal reflection is used for light confinement, then light propagation is achieved, but the range of confusable angles is inherently limited
Solution Approach 1:
The patent merges two light confinement mechanisms: total internal reflection (TIR) at the lightguide boundaries and reflective coating reflection at specific interfaces. This combination allows light to be confined effectively while propagating at a wider range of angles than TIR alone would permit, as the reflective coatings provide additional reflection pathways that extend the angular acceptance range
Solution Approach 2:
The reflective coatings serve multiple functions: they enhance light confinement at angles where TIR is insufficient, they can provide wavelength-selective reflection for color management, and they can control the directional distribution of out-coupled light. This multi-functionality allows a single coating structure to address multiple optical requirements simultaneously
4Ease of manufacture
If low refractive index materials are used in lightguides, then manufacturing cost is reduced, but the field-of-view and propagation angle range decrease
Solution Approach 1:
The patent changes the optical parameters of the low index material system by introducing reflective coatings with tailored reflectivity characteristics. By adjusting coating properties (material composition, layer thickness, optical constants), the system compensates for the inherently narrow propagation angles of low index materials, achieving wide field-of-view performance while maintaining the cost advantages of using inexpensive base materials
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 solution enhances the field-of-view of display devices by allowing light to propagate at a wider range of angles, making high index materials unnecessary, thus reducing costs while maintaining performance.
Implementation Method 1
The reflective coatings may complement the refractive index interfaces and increase the angles at which rays propagate through the guide
Implementation Method 2
confinement within the guide is based on TIR
Data Source
AI summary
A display device may include a guide, a back side coating, a front side coating, an input couple, and output coupler, and an image source. The guide may include a guide front side and a guide back side opposite the guide front side. The back side coating may line the guide back side and may reflect rays in a first waveband. The front side coating may line the guide front side and may reflect rays in a second waveband. The image source may emit rays toward the guide. The input coupler may receive the rays emitted by the image source and couple the rays into the guide. The output coupler may receive rays propagated along the guide between the guide back side and the guide front side and emit the received rays from the guide front side.