Segmented Input Diffractive Optical Element for Virtual Image Display
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Solution Overview
Problem
Existing virtual image display devices suffer from color and luminance non-uniformity due to the wavelength and angle of incidence dependencies of surface relief type diffraction gratings, which affect the diffraction efficiency and lead to uneven brightness across different angles of view.
Innovation Solution
A virtual image display device with a light guide member that includes a light guide plate and diffractive optical elements, where the input diffractive optical element is divided into regions with different inclined angles of gratings to optimize diffraction efficiency based on the angle of incidence of the image light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a surface relief type diffraction grating is used as a diffraction optical element, then the device structure is simplified and manufacturing is easier, but color non-uniformity and luminance non-uniformity occur due to wavelength and angle of incidence dependencies
Solution Approach 1:
The input diffractive optical element is divided into a plurality of regions, with each region having a different inclined angle of grating. This segmentation allows each region to be optimized for specific angles of incidence, reducing color non-uniformity and luminance non-uniformity while maintaining the simplicity of surface relief type diffraction grating manufacturing
Solution Approach 2:
Different regions of the input diffractive optical element are assigned different local properties (different inclined angles of grating) according to the angle of incidence characteristics in each region. This local optimization reduces color non-uniformity and luminance non-uniformity without complicating the overall manufacturing process
2Illumination intensity
If the diffraction efficiency is enhanced by inclining the grating surface, then luminance uniformity in the eyebox is improved, but luminance non-uniformity occurs depending on the angle of view
Solution Approach 1:
The input diffractive optical element is divided into multiple regions with different inclined angles, allowing each region to handle specific angle ranges optimally. This prevents luminance non-uniformity across different viewing angles while maintaining good luminance uniformity within the eyebox
Solution Approach 2:
The grating inclined angle is made variable across different regions rather than uniform throughout. This dynamic adaptation of the grating angle to different incident angle requirements resolves the contradiction between eyebox luminance uniformity and angle-of-view luminance 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 improves the uniformity of luminance and reduces color non-uniformity by optimizing the diffraction efficiency across different angles of incidence, resulting in enhanced light use efficiency and a more consistent virtual image display.
Implementation Method 1
an input diffractive optical element that causes the image light to enter the light guide plate
Implementation Method 2
a surface relief type diffraction grating is used as a diffraction optical element. The surface relief type diffraction grating has dependency on a wavelength and an angle of incidence, and diffraction efficiency changes depending on the wavelength and the angle of incidence
Implementation Method 3
a light guide plate configured to guide the image light
Data Source
AI summary
A virtual image display device includes a display panel configured to emit image light, a projection optical system configured to collimate the image light from the display panel, and a light guide member that includes a light guide plate configured to guide the image light, an input diffractive optical element configured to cause the image light to enter the light guide plate, and an output diffractive optical element configured to cause the image light to be emitted from the light guide plate, wherein the input diffractive optical element is divided into a plurality of regions, and the plurality of regions are different from each other in an inclined angle of a grating in accordance with an angle of incidence of the image light.