High Elastic Glass Substrate for Double-Sided Diffractive Optical Elements
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Solution Overview
Problem
Conventional glass wafers experience warping during the formation of diffractive optical elements due to heating, leading to misregistration and decreased positional accuracy of diffractive optical elements, which affects the precision and quality of light guide plates used in smart glasses and other display devices.
Innovation Solution
A glass wafer with a thickness of 3.0 mm or less, a Young's modulus of 100 GPa or greater, and a refractive index of 1.9 or greater, along with a diffractive optical element part having a periodic uneven structure with a period of 500 nm or less, is used to minimize warpage and ensure high precision in forming diffractive optical elements on both surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If glass wafer is heated on hot plate during diffractive optical element formation, then photoresist thermal crosslinking and organic material baking are achieved, but warping occurs due to temperature difference between main surfaces
Solution Approach 1:
The patent applies parameter changes by modifying the physical properties of the glass wafer - specifically setting the Young's modulus to 100 GPa or greater and thickness to 3.0 mm or less. These parameter changes enable the glass wafer to maintain dimensional stability during heating processes, preventing warping while still allowing thermal crosslinking and baking to proceed effectively.
Solution Approach 2:
The patent implements beforehand cushioning by pre-configuring the glass wafer with specific material properties (high Young's modulus, thin thickness) before the heating process begins. This pre-prepared structural configuration acts as a cushion against thermal warping, ensuring that the wafer maintains its flatness throughout the photoresist thermal crosslinking and organic material baking processes.
2Manufacturing precision
If glass wafer thickness is reduced to minimize warpage, then thermal conductivity improves and warping decreases, but mechanical strength and handling difficulty are affected
Solution Approach 1:
The patent resolves this contradiction through parameter changes by establishing a specific thickness range (3.0 mm or less) and Young's modulus requirement (100 GPa or greater). This parameter optimization ensures that the glass wafer is thin enough to minimize warpage during heating while maintaining sufficient mechanical strength for practical handling and processing.
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 proposed glass wafer design reduces warpage and enhances the precision of diffractive optical elements, resulting in improved positional accuracy and quality of light guide plates, which in turn improves the performance and image quality of image display devices like smart glasses.
Implementation Method 1
light emitted from an image light source is allowed to enter the interior of a light guide plate by a diffractive optical element formed on the surface of the light guide plate. Then, the light that has entered the interior of the light guide plate travels while repeatedly undergoing total reflection inside the light guide plate and is emitted to the direction of the wearer's pupils by a diffractive optical element provided in front of the wearer's pupils.
Implementation Method 2
Glass has a relatively low thermal conductivity, and when the glass wafer is heated on a hot plate, a large temperature difference occurs between the main surface in contact with the hot plate, that is, the main surface facing downward, and the main surface on the opposite side, that is, the main surface facing upward. Since the amount of expansion of the main surface at a high temperature facing downward is greater than the amount of expansion of the main surface at a low temperature facing upward, the glass wafer warps in a downward convex shape.
Implementation Method 3
After the exposure, the wafer is placed on a hot plate and heated to about 120° C. to 150° C. (post-baking) in order to thermally crosslink the photoresist.
Data Source
AI summary
A glass wafer for manufacturing a light guide plate, the glass wafer including: a glass part in a thin sheet shape; and a diffractive optical element part on two main surfaces of the glass part, in which one main surface of the glass part has an area of 1950 mm2 or greater, the glass part has a thickness of 3.0 mm or less, and the glass part has a Young's modulus of 100 GPa or greater.