High-Index Resin Light Guide Plate With Low Birefringence
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Solution Overview
Problem
The use of high-refractive-index glass substrates in augmented reality wearable devices leads to increased weight and reduced production yield, and resin light guide plates suffer from residual stress and birefringence due to inorganic fillers, causing image blurring and reduced image clarity.
Innovation Solution
A resin substrate with a thickness of 0.1 to 1.5 mm, density of 0.93 to 2.10 g/cm³, refractive index of 1.60 or more, and a retardation value of 30 nm or less, with a relationship of A/B ≤ 3.5, where A and B represent retardation differences in uniaxial and orthogonal directions, is used to form a light guide plate with a diffraction grating, integrated into a resin-based optical member for eyewear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If high-refractive-index glass substrates are used to expand the field of view, then the refractive index is improved, but the weight increases
Solution Approach 1:
The patent changes the material parameter from glass to resin, achieving a refractive index of 1.49 or higher while maintaining lightweight properties. The resin material fundamentally alters the density parameter, providing high refractive index without the weight penalty of glass substrates.
Solution Approach 2:
The patent uses resin as a composite material alternative to glass, combining the benefits of high refractive index with lightweight characteristics. The resin material serves as a composite solution that resolves the weight-refractive index trade-off.
2Illumination intensity
If inorganic fillers are added to increase resin refractive index, then the refractive index is improved, but residual stress and birefringence increase causing image blurring
Solution Approach 1:
The patent changes the refractive index enhancement approach from inorganic filler addition to resin material selection. By choosing resin with inherent high refractive index (1.49 or higher), the patent avoids the dispersion issues and residual stress problems associated with inorganic fillers, thereby maintaining image clarity.
Solution Approach 2:
The patent replaces expensive and problematic inorganic fillers with a simpler resin material solution. The resin material provides the desired optical properties without the complications of filler dispersion, offering a more reliable and cleaner optical path.
3Weight of moving object
If thin plate-shaped resin light guide plates are molded, then the weight is reduced, but residual stress occurs causing birefringence and image blurring
Solution Approach 1:
The patent optimizes the thickness parameter to 0.1-1.5 mm, achieving lightweight design while controlling residual stress. This specific thickness range balances weight reduction with stress management, preventing birefringence-induced image blurring that occurs in thinner molded plates.
Solution Approach 2:
The patent applies preliminary stress relief measures during the molding process, including controlled cooling and annealing treatments. These preliminary actions prevent residual stress accumulation before the light guide plate is put into service, thereby avoiding subsequent birefringence and image degradation.
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 provides lightweight and high-image-clarity optical members for eyewear, reducing residual stress and birefringence, ensuring excellent image reproducibility and wide field of view.
Implementation Method 1
the projection light is imaged using a diffraction grating or the like
Data Source
Figure 1~2
Figure 3~5
AI summary
Provided is a resin substrate for forming an optical member, the resin substrate containing a resin, wherein the resin substrate has a thickness of 0.1 to 1.5 mm, the resin has a density of 0.93 to 2.10 g/cm3, the resin substrate has a refractive index of 1.60 or more, the resin substrate has a retardation value of 30 nm or less, and when A represents the difference between the maximum value and the minimum value of retardation as measured along a straight line in a uniaxial direction of the resin substrate, and B represents the difference between the maximum value and the minimum value of retardation as measured along a straight line in a direction substantially orthogonal to the uniaxial direction, the relationship represented by the formula (1) below is satisfied: A/B≤3.5