High Index Low Density Glass for AR/VR
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Solution Overview
Problem
The development of high refractive index glasses suitable for augmented reality and virtual reality devices poses challenges due to the need for low density, high elastic modulus, and compatibility with conventional manufacturing processes, while avoiding undesirable increases in density and thermal expansion, and the use of harmful oxides like PbO, Sb2O3, and Ta2O5.
Innovation Solution
A glass composition comprising at least 30 mol % SiO2, free of iron, lead, antimony, and tantalum oxides, with a refractive index greater than 1.75, a linear thermal expansion coefficient less than 65×10−7 K−1, and a Young's elastic modulus greater than 100 GPa, achieved through specific ratios of SiO2, Al2O3, TiO2, ZnO, and rare earth metal oxides, which also maintains a moderate melting temperature and glass transition temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the refractive index is increased to meet augmented reality device requirements, then the optical performance is improved, but the glass density increases making the glasses heavier
Solution Approach 1:
The patent changes the chemical composition parameters of the glass by using specific ratios of SiO2 (30-45 mol%), Al2O3 (5-20 mol%), TiO2 (5-15 mol%), ZnO (5-15 mol%), and rare earth metal oxides (1-5 mol%), while excluding heavy metals like PbO, Sb2O3, and Ta2O5. This compositional parameter change achieves high refractive index (nd ≥ 1.75) without the harmful effects of traditional heavy metal oxides, maintaining low density (≤ 4.00 g/cm³).
Solution Approach 2:
The patent creates a composite glass system combining multiple oxide components (silica, alumina, titania, zinc oxide, and rare earth metal oxides) to achieve the desired optical properties. This composite approach allows the glass to have high refractive index through the synergistic effect of different components while avoiding reliance on single heavy metal oxide additives.
2Ease of manufacture
If the melting temperature is reduced by lowering high-temperature viscosity, then the manufacturing process is simplified, but devitrification occurs during glass article formation
Solution Approach 1:
The patent adjusts the viscosity-temperature parameters of the glass melt by incorporating specific oxide components. The Al2O3 (5-20 mol%) and SiO2 (30-45 mol%) content modifies the melt viscosity to achieve appropriate working characteristics at reduced temperatures while preventing devitrification. The TiO2 (5-15 mol%) and ZnO (5-15 mol%) further tune the melt properties to maintain stability during forming operations.
3Ease of manufacture
If the glass transition temperature is decreased, then the manufacturing process is easier, but the coefficient of thermal expansion increases
Solution Approach 1:
The patent modifies the thermal expansion characteristics by controlling the oxide composition ratios. The Al2O3 (5-20 mol%) content is particularly effective in suppressing thermal expansion while maintaining acceptable glass transition temperature. The combination of Al2O3 with SiO2 (30-45 mol%) and other network modifiers creates a balanced thermal property profile that achieves low CTE without excessive Tg reduction.
4Strength
If the elastic modulus is increased to above 95 GPa, then the mechanical strength is improved, but the glass transition temperature rises
Solution Approach 1:
The patent achieves high elastic modulus (≥ 95 GPa) through the specific oxide composition, particularly Al2O3 (5-20 mol%) and TiO2 (5-15 mol%), which reinforce the glass network structure. The ZnO (5-15 mol%) content helps maintain appropriate Tg levels while the rare earth metal oxides (1-5 mol%) fine-tune the mechanical properties. This compositional balance achieves the desired elastic modulus without excessive Tg increase.
Data Source
AI summary
A glass comprising greater or equal to 30.0 mol % SiO2, the glass being free of iron, lead, antimony ant tantalum oxides, and having a refractive index nd greater than or equal to 1.75 and a linear thermal expansion coefficient α20-300, in the temperature range 20-300° C., that is less than or equal to about 65×10−7 K−1.