Input Diffractive Optical Element for Uniform Virtual Image Display
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Solution Overview
Problem
Existing virtual image display devices suffer from compromised spatial uniformity of the image light at the eyebox due to unevenness in the image light distribution, which is not adequately addressed by current diffractive display elements.
Innovation Solution
A virtual image display device and optical unit that include a display panel, a projection optical system, and a light guide member with an input diffractive optical element having a diffraction efficiency distribution that cancels the unevenness of the image light entering it, ensuring uniform image guidance into the light guide plate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional diffractive display element with uniform diffraction efficiency is used, then the device structure is simple, but the spatial uniformity of the image at the eyebox is compromised due to unevenness in the image light distribution
Solution Approach 1:
The patent applies local quality by varying the diffraction efficiency of different regions of the input diffractive optical element according to the beam profile characteristics. Specifically, the diffraction efficiency is adjusted locally to compensate for unevenness in the image light distribution, with higher efficiency in regions where light intensity is lower and lower efficiency where light intensity is higher, thereby achieving uniform spatial distribution at the eyebox
Solution Approach 2:
The patent changes the diffraction efficiency parameter of the input diffractive optical element to resolve the contradiction. By modifying the diffraction efficiency distribution across different regions of the element, the system transforms the uneven beam profile into a uniform distribution, improving spatial uniformity while managing the increased design complexity through systematic parameter optimization
2Illumination intensity
If the diffraction efficiency of the input diffractive optical element is increased to improve image brightness, then the image brightness improves, but the unevenness of the image light is amplified resulting in worse spatial uniformity
Solution Approach 1:
The patent applies local quality by implementing non-uniform diffraction efficiency distribution across the input diffractive optical element. Different regions have different diffraction efficiency values tailored to the local beam intensity, allowing simultaneous achievement of high overall brightness through increased average efficiency while maintaining spatial uniformity through localized efficiency modulation
Solution Approach 2:
The patent converts the harmful effect of uneven beam profile into a benefit by using the diffraction efficiency variation as a compensatory mechanism. The unevenness in image light distribution is transformed into a design parameter for the diffraction efficiency profile, where the varying efficiency selectively enhances or suppresses light in different regions to achieve both brightness and uniformity
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 cancels the unevenness of the image light, resulting in improved spatial uniformity of the image at the eyebox, thereby enhancing the display quality and reducing display unevenness such as pixel luminance variation due to line-of-sight movement.
Implementation Method 1
an input diffractive optical element configured to cause the image light to enter the light guide plate
Implementation Method 2
a light guide plate configured to guide the image light
Implementation Method 3
an output diffractive optical element configured to cause the image light to be emitted from the light guide plate
Data Source
AI summary
A virtual image display device includes a display panel that emits image light, a projection optical system that collimates the image light from the display panel, and a light guide member that includes a light guide plate that guides the image light, an input diffractive optical element that causes the image light to enter the light guide plate, and an output diffractive optical element that causes the image light to be emitted from the light guide plate, wherein the input diffractive optical element has a diffraction efficiency distribution having a tendency to cancel unevenness of the image light entering the input diffractive optical element.