Reflective Waveguide Inactive Facet Reflection Mitigation
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Solution Overview
Problem
Current reflective waveguide fabrication processes face challenges in minimizing reflections from inactive facets, leading to artifacts such as ghost images and light scattering, while also dealing with the 'louver effect' that affects see-through transmission of environmental light.
Innovation Solution
A non-selective coating technique is employed using a directional deposition method to apply a partially reflective coating that is thicker on active facets than on inactive facets, with the coating's refractive index closely matched to the substrate. This approach minimizes reflections from inactive facets and mitigates the 'louver effect' by ensuring uniform transmission of environmental light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a reflective coating is applied to inactive facets to reduce reflections, then artifacts such as ghost images and light scattering are reduced, but the coating process becomes more complex and costly
Solution Approach 1:
The patent applies a non-uniform coating thickness across the waveguide surface, with thicker coating on inactive facets and thinner or no coating on active facets. This local differentiation allows the inactive facets to have reduced reflectivity while preserving the reflective functionality of active facets, thereby reducing ghost images and light scattering without requiring complete re-coating of the entire waveguide
Solution Approach 2:
Instead of applying a uniform reflective coating and then masking inactive facets (which would be complex), the patent inverts the approach by applying a non-selective coating that is inherently non-uniform in thickness. The coating process naturally deposits more material on inactive facets due to their geometric orientation, eliminating the need for complex masking or selective coating procedures
2Ease of manufacture
If the coating is made non-selective to simplify the coating process, then manufacturing complexity is reduced, but reflections from inactive facets increase causing artifacts
Solution Approach 1:
The patent changes the parameter of coating thickness rather than applying a binary selective/non-selective coating. By controlling the deposition process to create a thickness gradient (thicker on inactive facets, thinner on active facets), the patent achieves both goals: the non-selective application simplifies manufacturing while the varied thickness provides the necessary optical control to reduce reflections from inactive facets
Solution Approach 2:
The patent applies coating material in excess to inactive facets, where the thicker coating layer completely blocks or absorbs stray light that would otherwise cause reflections and artifacts. This partial or excessive coating on specific regions (inactive facets) achieves the desired effect without requiring precise selective application across the entire surface
3Object-affected harmful factors
If the coating thickness is increased on inactive facets to reduce reflections, then artifact reduction is improved, but the transmission of environmental light through active facets may be affected
Solution Approach 1:
The patent creates local quality differences in the coating by making it non-uniform in thickness. Inactive facets receive thicker coating to suppress reflections, while active facets receive thinner coating to maintain their optical functionality. This local differentiation ensures that environmental light transmission through active facets is preserved while artifact reduction is achieved on inactive facets
Solution Approach 2:
The patent introduces asymmetry in the coating distribution across the waveguide surface. The coating thickness is deliberately made asymmetric relative to the facet types, with inactive facets having significantly thicker coating than active facets. This asymmetric coating pattern optimizes the balance between artifact reduction and light transmission by tailoring the coating properties to the specific functional requirements of each facet type
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 solution effectively reduces reflections from inactive facets, minimizing artifacts and improving display efficiency, while also ensuring uniform see-through transmission of environmental light, thus enhancing the overall performance of augmented reality eyewear.
Implementation Method 1
A non-selective coating technique is employed using a directional deposition method to apply a partially reflective coating
Implementation Method 2
the coating's refractive index closely matched to the substrate. This approach minimizes reflections from inactive facets
Data Source
AI summary
A reflective waveguide includes active and inactive facets that are non-selectively coated with a partially reflective coating while minimizing reflections from the inactive facets without using a stencil mask. The partially reflective coating has a refractive index that is closely matched to a refractive index of a polymer substrate of the waveguide, is applied using a directional deposition technique such that the coating is thicker on the active prism facets than on the inactive prism facets, and the backside of the prism facets is angled such that the angle of incidence of display light on the backside of the prism facets is less than approximately 80 degrees.