AR Waveguide Thermo-Optical Effect Control
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Solution Overview
Problem
Augmented and mixed reality devices face image quality impairment due to thermo-optical effects caused by inhomogeneous temperature distributions in waveguides, resulting from partial light absorption, which affects the guidance of image pixel light.
Innovation Solution
A waveguide with a solid body made of an optical material that is transparent to visible light, featuring specific absorption coefficients, thermal conductivity, and refractive index properties, allowing for quantitative control of thermally induced changes in optical path length, thereby minimizing thermo-optical effects. The waveguide includes in-coupling and out-coupling surfaces and optional diffractive structures for redirecting image pixel light, with the geometry and material properties optimized to manage heat and radiation-induced changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the in-coupling surface is made small to reduce waveguide size, then the device compactness is improved, but the local heat absorption increases causing inhomogeneous temperature distribution and thermo-optical effects that impair image quality
Solution Approach 1:
The patent applies parameter changes by carefully selecting and optimizing the absorption coefficient κ460nm, thermal conductivity k, coefficient of thermal expansion α20°C, refractive index nF, and its temperature derivative dnF/dT20°C. These material parameters are chosen to satisfy specific inequalities that balance heat absorption and thermal conduction, minimizing thermo-optical effects while maintaining a compact waveguide design
Solution Approach 2:
The patent employs composite material strategies by selecting optical materials with specific combinations of thermal and optical properties. The material is engineered to have controlled absorption and thermal conductivity characteristics, effectively combining properties to achieve both compactness and thermal stability
2Reliability
If the optical material absorbs more light to enable waveguide function, then the light guidance capability is improved, but the thermal heating increases causing inhomogeneous temperature distribution
Solution Approach 1:
The patent optimizes the absorption coefficient κ460nm to a specific range that enables sufficient light guidance while limiting excessive heat generation. The thermal conductivity k is simultaneously optimized to efficiently conduct away the absorbed heat, maintaining relatively uniform temperature distribution throughout the waveguide
Solution Approach 2:
The patent converts the harmful effect of light absorption (heat generation) into a beneficial outcome by carefully controlling the absorption coefficient and thermal conductivity. The absorbed light energy is managed through optimized thermal conduction, transforming potential thermal damage into controlled thermal management that maintains waveguide functionality
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 effectively controls thermo-optical effects, ensuring stable image quality by balancing thermal and optical phenomena, allowing for precise guidance of image pixel light in augmented and mixed reality applications.
Implementation Method 1
The light guidance from the in-coupling surface to the out-coupling surface is usually achieved by total reflection in the waveguide
Implementation Method 2
The in-coupling surface is usually comparatively small so that the waveguide may be locally heated by partial absorption of light intensity
Implementation Method 3
The optical material has an absorption coefficient κ460nm for light having a wavelength of 460 nm, a thermal conductivity k
Implementation Method 4
a coefficient of thermal expansion α20° C. at a temperature of 20° C.
Implementation Method 5
a derivative dnF/dT20° C., wherein the derivative dnF/dT20° C. characterizes the change of the refractive index with the temperature
Data Source
AI summary
A waveguide for guiding an image pixel light includes: a solid body including an optical material which is transparent for at least a light with a wavelength of 460 nm; an in-coupling surface located on the solid body; and an out-coupling surface located on the solid body, wherein the optical material has an absorption coefficient κ460 nm for light having a wavelength of 460 nm, a thermal conductivity k, a coefficient of thermal expansion α20° C. at a temperature of 20° C., a refractive index nF related to the hydrogen F-line, and a derivative dnF/dT20° C. which are related in such a way that a thermally induced change of an optical path length within the waveguide due to an absorption of at least one of heat and an optical radiation is quantitatively described by a merit function.