Volume Hologram Exit Pupil Diffuser for Display Luminance Uniformity
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Solution Overview
Problem
Existing display apparatuses, such as head-mounted displays, face challenges in suppressing luminance unevenness and color unevenness due to the use of diffraction elements with constant or stepwise varying interference fringes, leading to streaky irregularities in images, especially at the boundaries of regions with varying fringe inclinations.
Innovation Solution
The display apparatus incorporates a multi-layered optical system with a first diffraction element and a second diffraction element, where the second diffraction element is a volume hologram with continuously varying interference fringes in pitch and inclination, forming an exit pupil, and is configured to handle different wavelength bands, ensuring uniform light distribution and reduced color and luminance unevenness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a diffraction element with constant or stepwise varying interference fringes is used, then the optical system can be simplified, but luminance unevenness and color unevenness cannot be suppressed
Solution Approach 1:
The patent applies parameter changes by continuously varying the pitch and inclination of interference fringes in the volume hologram diffraction element. This continuous variation of geometric parameters enables uniform diffraction of light across different regions, suppressing luminance unevenness and color unevenness while maintaining optical system performance
2Ease of manufacture
If a diffraction element with stepwise varying interference fringes is used, then manufacturing is simplified, but streaky irregularity is visually recognized at boundaries
Solution Approach 1:
The patent transitions from stepwise to continuous parameter variation of interference fringe pitch and inclination. This continuous variation eliminates abrupt transitions at boundaries, preventing streaky irregularities while remaining compatible with volumetric hologram manufacturing processes
3Illumination intensity
If a diffraction element with continuously varying interference fringes is used, then luminance and color unevenness are suppressed, but device complexity increases
Solution Approach 1:
The patent uses a volume hologram to record and reproduce the complex continuously varying interference fringe pattern. The holographic copying process enables the complex pitch and inclination variations to be stored and reproduced efficiently, achieving uniform luminance and color without proportionally increasing device complexity
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 effectively minimizes luminance and color unevenness in the displayed images by compensating for peripheral wavelengths and maintaining high resolution, resulting in a more uniform and clear visual experience.
Implementation Method 1
the second diffraction element is constituted of a volume hologram and has, in a cross-sectional view of the volume hologram, interference fringes continuously varying in pitch and inclination thereof
Implementation Method 2
a volume hologram and has, in a cross-sectional view of the volume hologram, interference fringes continuously varying in pitch and inclination
Data Source
AI summary
The display apparatus of the present disclosure includes an imaging light generating device and an optical system on which imaging light emitted from the imaging light generating device is incident. The optical system includes a first optical unit having positive power, a second optical unit having a positive power and including a first diffraction element, a third optical unit having positive power, and a fourth optical unit having positive power and including a second diffraction element forming an exit pupil, the first optical unit, the second optical unit, the third optical unit, and the fourth optical unit being aligned in order along an optical path of the imaging light. The second diffraction element is constituted of a volume hologram and has, in a cross-sectional view of the volume hologram, interference fringes continuously varying in pitch and inclination thereof from one end toward another end of the second diffraction element.