Multi-Layer Birefringent Optical Element Suppressing Rainbow Diffraction
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Solution Overview
Problem
Conventional optical devices with single-layer polarization volume holograms (PVHs) suffer from significant diffraction artifacts, particularly the 'rainbow effect,' which degrades image quality in see-through views, especially when users view bright light sources from certain angles, due to the dispersion of polychromatic light into its constituent wavelengths.
Innovation Solution
A multi-layer optical element comprising a first birefringent medium layer with a specific in-plane and vertical pitch configuration, optically coupled with a second birefringent medium layer having a similar in-plane pitch but a smaller vertical pitch, designed to reduce diffraction efficiency and suppress undesirable diffraction orders, thereby minimizing the rainbow effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer PVH is used, then the device complexity is low, but diffraction artifacts (rainbow effect) occur
Solution Approach 1:
The single-layer PVH is divided into multiple layers, each with specific pitch configurations. The first layer has a first pitch and the second layer has a second pitch that is different from the first pitch, allowing each layer to address specific diffraction orders independently, thereby reducing the rainbow effect while maintaining manageable complexity
Solution Approach 2:
The patent combines multiple PVH layers with different pitch characteristics to create a composite structure. This composite approach allows the system to leverage the advantages of each layer, suppressing both positive and negative diffraction orders simultaneously, thus reducing diffraction artifacts without requiring excessively complex individual components
2Power
If the vertical pitch is increased, then the diffraction efficiency is improved, but the rainbow effect is enhanced
Solution Approach 1:
The diffraction control function is segmented across multiple layers with different vertical pitches. The first layer with a larger vertical pitch handles certain diffraction orders efficiently, while the second layer with a smaller vertical pitch addresses other orders, thereby maintaining high overall diffraction efficiency without concentrating all efficiency in one layer which would cause severe rainbow effects
Solution Approach 2:
Each layer is assigned a specific pitch characteristic optimized for controlling certain diffraction orders. The first layer has a first vertical pitch optimized for its function, while the second layer has a second vertical pitch optimized for its function, allowing each layer to have local quality tailored to its specific role in reducing the rainbow effect
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 multi-layer configuration significantly reduces the rainbow effect by minimizing perceivable diffraction orders, enhancing image quality in see-through views by uniformly distributing diffraction efficiency across various viewing angles.
Implementation Method 1
configured to reduce a diffraction of a light by the first birefringent medium layer
Implementation Method 2
a first birefringent medium layer with orientations of directors of first optically anisotropic molecules spatially varying
Data Source
AI summary
An optical element includes a first birefringent medium layer with orientations of directors of first optically anisotropic molecules spatially varying with a first in-plane pitch and a first vertical pitch. The optical element also includes a second birefringent medium layer with orientations of directors of second optically anisotropic molecules spatially varying with a second in-plane pitch and a second vertical pitch. The second birefringent medium layer is optically coupled with the first birefringent medium layer and configured to reduce a diffraction of a light by the first birefringent medium layer. The first in-plane pitch is substantially the same as the second in-plane pitch, and the second vertical pitch is smaller than the first vertical pitch.