Thickness-modulated conformal coatings on optical components
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Solution Overview
Problem
Existing optical display systems in mixed reality devices face challenges in maintaining optical performance and durability due to environmental exposure and handling, with conventional coatings leading to degradation of modulation transfer function (MTF) and undesirable reflections.
Innovation Solution
A thickness-modulated conformal coating is applied using atomic layer deposition (ALD) techniques, with varying refractive index and reflectivity to enhance optical parameters, minimizing degradation and reflections, and applied to diffractive optical elements (DOEs) in waveguides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional uniform coating is applied to protect optical components, then durability and resistance to environmental exposure are improved, but degradation of modulation transfer function (MTF) occurs and undesirable reflections are generated
Solution Approach 1:
The patent applies thickness-modulated conformal coatings with spatially varying thickness and refractive index to different regions of the optical component. The coating thickness transitions from thicker at the in-coupling DOE to thinner at the out-coupling DOE, providing localized optical properties that prevent MTF degradation and reduce reflections while maintaining protective durability.
Solution Approach 2:
The patent modifies the coating parameters by varying the thickness and refractive index of the conformal coating across different areas of the optical component. This parameter modulation allows the coating to simultaneously provide protection and maintain optical performance by adjusting local optical properties rather than using a uniform coating.
2Strength
If a thick conformal coating is applied to enhance protection, then resistance to wear and damage is improved, but MTF degradation occurs due to sharp transitions
Solution Approach 1:
The patent implements a dynamic thickness profile in the conformal coating that gradually transitions from thicker to thinner regions. This dynamic variation in coating thickness eliminates sharp transitions that cause MTF degradation while maintaining adequate protective thickness in critical areas, thus preserving both strength and optical performance.
Solution Approach 2:
Different regions of the optical component receive coating with locally optimized thickness. The in-coupling DOE area receives thicker coating for protection, while the out-coupling DOE area receives thinner coating to maintain optical performance, with smooth transitions between regions preventing MTF degradation.
3Ease of manufacture
If a uniform refractive index coating is applied, then manufacturing simplicity is maintained, but optical parameter tuning flexibility is reduced
Solution Approach 1:
The patent utilizes thickness-modulated conformal coatings with spatially varying refractive index to enable tuning of optical parameters. By controlling the coating thickness and material composition at different locations, the system achieves versatile optical parameter adjustment while maintaining a relatively simple conformal coating application process.
4Reliability
If a thick conformal coating is applied at the out-coupling DOE, then protection is improved, but undesirable reflections increase in the real-world view area
Solution Approach 1:
The patent applies a thinner conformal coating specifically at the out-coupling DOE region where real-world environment is viewed. This localized thinning reduces the coating's reflective properties in the critical viewing area while maintaining adequate protection in other regions through thicker coating application.
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 reliability and reduces wear and damage, maintaining optical performance by avoiding MTF degradation and minimizing reflections, while enabling cost-effective manufacturing of multiple DOE configurations.
Implementation Method 1
The conformal coating may comprise layers of different materials in a thickness-modulated thin film stack that may be utilized to enhance physical characteristics of the optical display system... varying refractive index and reflectivity to enhance optical parameters
Implementation Method 2
The relatively thinner conformal coating on the out-coupling DOE reduces undesirable reflections in the area of the optical display through which a user looks to see the real-world environment
Implementation Method 3
The thickness-modulated conformal coating may be implemented using spatial ALD (atomic layer deposition) which may be enhanced with plasma in a technique known as plasma enhanced ALD (PEALD)
Implementation Method 4
diffractive optical elements (DOEs) are disposed that are configured for in-coupling, exit pupil expansion, and out-coupling
Data Source
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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.