ALD Thickness-Modulated Conformal Coatings for Waveguide Reflection Control
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Solution Overview
Problem
Existing mixed reality computing devices face challenges in maintaining optical performance and durability due to environmental exposure and handling, particularly in head-mounted display devices where sharp transitions in conformal coatings degrade the modulation transfer function and cause undesirable reflections.
Innovation Solution
A thickness-modulated conformal coating is applied using atomic layer deposition (ALD) techniques, with variations in refractive index and reflectivity tailored to meet design requirements, enhancing durability and minimizing reflections by smoothly transitioning from high to low refractive index areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conformal coating is applied to protect optical components from environmental exposure and handling damage, then durability and reliability are improved, but sharp transitions in coating thickness degrade the modulation transfer function and cause undesirable reflections
Solution Approach 1:
The patent applies different coating thicknesses to different regions of the optical component. The coating thickness is locally optimized: thicker in regions requiring protection and durability, thinner in optical regions where sharp transitions would degrade the modulation transfer function. This spatial variation in coating quality resolves the contradiction between durability and optical precision.
Solution Approach 2:
The patent introduces gradual thickness transitions instead of sharp boundaries between different coating regions. By making the coating thickness dynamic and continuous rather than static and abrupt, the modulation transfer function is preserved while still providing protective coverage. The gradual transition eliminates unwanted reflections that would occur at sharp interfaces.
2Reliability
If a conformal coating is applied to enhance durability and resist wear, then reliability is improved, but reflections occur that degrade see-through characteristics
Solution Approach 1:
The patent applies anti-reflection optimized thin coating layers specifically in the see-through regions where reflections would be harmful to the user experience. Meanwhile, thicker protective coatings are applied in non-critical regions. This local differentiation provides wear resistance while minimizing reflections in optical paths.
Solution Approach 2:
The patent uses multiple layers of conformal coating with different material properties and thicknesses. By combining materials with different refractive indices and optical properties, the coating structure provides both protective durability and anti-reflection functionality. The composite structure allows each layer to address specific requirements: protection against wear and control of reflections.
3Ease of manufacture
If uniform thickness conformal coating is applied for simplicity, then ease of manufacture is improved, but optical performance degrades due to sharp transitions and unwanted reflections
Solution Approach 1:
The patent implements spatially varying coating thicknesses tailored to different functional regions of the optical component. This local optimization requires sophisticated manufacturing control but delivers superior optical performance by eliminating sharp transitions in critical areas while maintaining protection in non-critical areas.
Solution Approach 2:
The patent transitions from static uniform coating thickness to dynamic graduated thickness profiles. This allows the coating to adapt to different functional requirements across the component surface, providing smooth transitions that preserve optical performance while still being manufacturable through controlled deposition processes.
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 improves the reliability and optical performance of mixed reality devices by reducing wear and damage while maintaining clear see-through characteristics, optimizing the modulation transfer function, and minimizing reflections.
Implementation Method 1
the conformal coating that is thickness-modulated over different areas of the display to enable tuning of the optical parameters such as refractive index and reflectivity
Implementation Method 2
The thickness-modulated conformal coating may be implemented using spatial ALD (atomic layer deposition)
Implementation Method 3
which may be enhanced with plasma in a technique known as plasma enhanced ALD (PEALD)
Data Source
AI summary
A near-eye optical display system that may be utilized in mixed reality applications and devices includes a see-through waveguide on which diffractive optical elements (DOEs) are disposed that are configured for in-coupling, exit pupil expansion, and out-coupling. The optical display system includes a conformal coating that is thickness modulated over different areas of the display to enable tuning of the optical parameters such as refractive index and reflectivity to meet various design requirements. The conformal coating may also be utilized to enhance physical characteristics of the optical display system to thereby improve reliability and resist wear and damage from handling and exposure to environmental elements.