Multilayer Waveguide Coatings for Thin AR Display Resolution
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Solution Overview
Problem
Existing optical head-mounted displays face challenges in achieving reduced weight without compromising image resolution due to the use of high index glasses that increase device weight and result in coarse mode spacing when thin, leading to unacceptable resolution reductions.
Innovation Solution
Incorporating a multilayer coating on the waveguide surfaces with varying refractive indices to enhance modal density and reduce mode spacing, allowing thinner waveguides to maintain high image resolution while reducing overall device weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If high index glass is used to increase field of view, then field of view is improved, but device weight increases
Solution Approach 1:
The waveguide employs a composite structure combining high index glass core with low index glass substrate and dielectric coating layers. This composite material approach allows the system to achieve high field of view through the high index core while reducing overall weight by using lighter low index materials for substrate and coating, resolving the contradiction between field of view and device weight.
Solution Approach 2:
Different regions of the waveguide are assigned different material properties: the core uses high index glass for optical performance (field of view), while the substrate and coating use low index materials for weight reduction. This local differentiation of material quality allows simultaneous optimization of field of view and weight.
2Weight of stationary object
If high index glass thickness is reduced to decrease weight, then device weight is reduced, but mode spacing becomes coarse resulting in unacceptable resolution reduction
Solution Approach 1:
The patent changes the optical parameters of the waveguide by introducing dielectric coating layers with specific refractive indices and thicknesses. These parameter changes in the coating structure compensate for the reduced core thickness, maintaining fine mode spacing and high image resolution even when the high index glass thickness is reduced for weight reduction.
Solution Approach 2:
The dielectric coating acts as an intermediary structure between the high index glass core and the surrounding medium. This intermediary layer modifies the boundary conditions for light propagation, enabling the thinner core to support the necessary mode density for high resolution while maintaining the weight benefits of reduced thickness.
3Weight of stationary object
If lower index material is used with thinner high index glass to reduce weight, then device weight is reduced, but mode spacing becomes coarse reducing image resolution
Solution Approach 1:
The waveguide uses a composite material system where low index glass is employed for the substrate and coating layers, reducing overall weight. Simultaneously, the high index glass core maintains optical performance, and the combined structure achieves fine mode spacing through the interaction of different index materials, resolving the contradiction between weight reduction and resolution.
Solution Approach 2:
The patent applies local quality differentiation by using low index materials specifically for the substrate and coating regions where weight reduction is prioritized, while reserving high index material for the core region where optical performance and mode spacing are critical. This spatial differentiation resolves the contradiction between weight and resolution.
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
The multilayer coating configuration increases modal density, enabling thinner waveguides to transport images with higher fidelity and reduce device weight without sacrificing resolution.
Implementation Method 1
The in-coupler may be configured for coupling light emitted by the display into the waveguide at a first location of the waveguide such that the light is propagated through the waveguide via total internal reflection to a second location of the waveguide
Implementation Method 2
A refractive index of at least one of the thin films may differ from that of the core. Adjacent thin films may have different refractive indices from one another
Data Source
AI summary
A device for projecting a virtual- or augmented-reality image may include a waveguide and an in-coupler directing light into the waveguide such that the light is propagated through the waveguide via total internal reflection. The waveguide may include a core, a substrate, and a stack of thin films overlaying a surface of the core. A refractive index of at least one of the thin films of the stack may differ from that of the core. Adjacent thin films may have different refractive indices from one another.