Layered Infrared Transmitting Optical Elements Void-Free Bonding
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Solution Overview
Problem
Existing infrared optics face challenges in bonding infrared transmitting glasses without interlayer voids, limiting the precision and performance of infrared lens elements due to the lack of suitable IR-transparent optical cements and the unsuitability of ion-exchange processes for IR materials, which restricts the fabrication of gradient index optics and increases system size, weight, and complexity.
Innovation Solution
A method involving the sequential application of vacuum, high isostatic pressure, and annealing to bond infrared transmitting glasses with different refractive indices and dispersions, ensuring similar viscosities and thermal expansion coefficients, without using optical cements, to create layered optical elements with controlled internal optical properties and void-free interfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ion-exchange process is used to fabricate gradient index optics, then optical properties can be controlled within the bulk of the optical element, but the process is not suitable for IR transparent materials and limits element size to about 1 inch in diameter
Solution Approach 1:
The patent changes the fundamental processing parameters from ion-exchange at moderate temperatures to direct bonding at elevated temperatures (above glass transition temperature). This parameter change enables the use of IR-transparent materials like chalcogenide glasses that cannot undergo ion-exchange, while still achieving precise control of optical properties through controlled bonding conditions and material selection.
Solution Approach 2:
The patent replaces the chemical ion-exchange mechanism with a physical thermal bonding mechanism. By heating the glass layers above their transition temperature and applying pressure, the glasses soften and bond together, eliminating the need for ion-exchange chemistry that is incompatible with IR materials. This mechanical/thermal approach enables fabrication of large-scale IR optics.
2Reliability
If multiple separate optical elements are used to manipulate infrared light, then chromatic dispersion and thermal drift problems can be reduced, but system size, weight, and complexity increase
Solution Approach 1:
The patent merges multiple separate optical elements into a single integrated layered optical element. By bonding multiple IR-transparent glass layers with different optical properties (refractive indices, dispersions) together, the system achieves the functionality of multiple elements while reducing overall size, weight, and complexity. The layered structure corrects chromatic dispersion through material selection rather than requiring separate corrective elements.
Solution Approach 2:
The patent uses composite material structures where multiple glass layers with different optical properties are bonded together. Each layer is selected for specific optical characteristics, and their combination creates an integrated element that corrects chromatic aberrations and thermal drift inherently through the material composition rather than requiring additional separate corrective elements.
3Manufacturing precision
If vacuum pressure is applied to remove trapped air between glass sheets, then bonding quality improves, but volatile components outgas and increase bubble formation in infrared glasses
Solution Approach 1:
The patent replaces the vacuum environment with an inert atmosphere (argon or nitrogen) during the bonding process. This inert environment prevents volatile components from outgassing and forming bubbles, while still allowing the glass layers to bond effectively through thermal softening and pressure. The inert atmosphere dissolves or suppresses the outgassing of volatile species that would otherwise create defects in the bonded structure.
Solution Approach 2:
The patent utilizes the phase transition of volatiles from gas to dissolved state by introducing an inert gas atmosphere. Instead of vacuum that causes volatiles to outgas as bubbles, the inert atmosphere allows volatiles to remain dissolved or be suppressed, preventing bubble formation during the bonding process while maintaining effective bonding through controlled thermal and pressure conditions.
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
This method enables the fabrication of infrared optical elements with improved performance, reduced size and weight, and enhanced precision, allowing for the design of advanced imagers and broadband infrared systems, such as achromatic dual-band IR imaging systems, by eliminating air spaces and internal voids, and enabling operation across a wide wavelength range from SWIR to LWIR.
Implementation Method 1
applying a vacuum to the vessel
Implementation Method 2
applying an isostatic pressure of at least 1500 psi
Implementation Method 3
annealing at a temperature within 10° C. of the glass transition temperature
Data Source
AI summary
A method for bonding infrared transmitting glasses into an optical element without interlayer voids by stacking at least two different infrared transmitting glasses inside a vessel where each glass has a different refractive index, a different dispersion, or both, and where the glasses all have similar viscosities, thermal expansion coefficients, and glass transition temperatures; placing a weight on top of the stack; applying a vacuum to the vessel; applying an isostatic pressure of at least 1500 psi; and after releasing the isostatic pressure, annealing at a temperature within 10° C. of the glass transition temperature at a pressure between 0 and 1000 psi. Applying the vacuum, applying the isostatic pressure, and annealing are done sequentially and with no intermediate transitions to ambient temperature or pressure. Also disclosed is the related optical element made by this method.