Holographic Grating Light Guide for Uniform Brightness
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Solution Overview
Problem
Existing virtual image display devices using hologram diffraction gratings struggle to maintain uniform brightness across the image viewed by an observer, as the diffraction efficiency changes significantly with wavelength, leading to variations in image brightness on the left, center, and right sides.
Innovation Solution
The optical device employs a light guide plate with three hologram diffraction gratings, where the first and second gratings are configured to deflect light through total reflection, and the third grating is positioned to emit light, with specific relations between their slant angles and pitches to optimize diffraction efficiency and uniformity, and includes two light sources to form images based on their peak wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the thickness of the first deflection unit configured with a hologram diffraction grating is increased to increase diffraction efficiency, then the diffraction efficiency increases, but the diffraction efficiency change curve has a sharp peak causing significant brightness variation across the image
Solution Approach 1:
The first deflection unit is divided into multiple hologram diffraction gratings (first, second, and third gratings) with different slant angles. Each grating handles a specific wavelength range, segmenting the overall diffraction function to achieve both high efficiency and broad spectral coverage without sharp peaks
Solution Approach 2:
Different regions of the optical device have different grating configurations optimized for their specific functions. The first deflection unit uses gratings with specific slant angles for incoming wavelengths, while the second deflection unit uses gratings with different slant angles for outgoing wavelengths, creating locally optimized quality for each function
2Device complexity
If a single hologram diffraction grating is used to deflect light, then the device structure is simple, but the brightness uniformity across the image deteriorates due to wavelength-dependent diffraction efficiency
Solution Approach 1:
The single grating is segmented into multiple gratings with different slant angles, where each grating is responsible for diffracting light within a specific wavelength range. This segmentation maintains relatively simple individual grating structures while collectively achieving uniform brightness across the spectrum
Solution Approach 2:
Multiple hologram diffraction gratings are designed to perform overlapping functions of diffracting different wavelength ranges. The first, second, and third gratings each contribute to the overall diffraction function, with their combined effect achieving universal coverage across the visible spectrum with uniform brightness
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 configuration increases the brightness and uniformity of the image viewed by the observer, ensuring consistent brightness across the image, addressing the issue of non-uniform brightness in existing systems.
Implementation Method 1
a light guide plate configured to cause incident light to propagate inside the light guide plate through total reflection and then emit the light
Implementation Method 2
The first deflection unit is constituted by a first hologram diffraction grating and a second hologram diffraction grating
Data Source
AI summary
To provide a display device in which the brightness of the image viewed by the observer is bright, and the brightness of the image is as uniform as possible. The display device according to the present invention includes a frame 10 and an image display device 100, the image display device 100 includes an image forming apparatus 11 and an optical device 120, the optical device 120 includes a light guide plate 121, a first deflection unit 130 configured with a first hologram diffraction grating 131 and a second hologram diffraction grating 135, and a second deflection unit 140 configured with a third hologram diffraction grating 141, and slant angles and pitches of the first hologram diffraction grating 131, the second hologram diffraction grating 135, and the third hologram diffraction grating 141 satisfy a predetermined relation.