Virtual Image Display Apparatus with Luminance Adjustment
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Solution Overview
Problem
Existing virtual image display apparatuses face challenges in reducing size while maintaining image quality due to interference between optical components, particularly when varying the angles of diffraction between hologram elements, which affects pupil diameter and observer viewing directions.
Innovation Solution
The apparatus employs a light-guiding unit with a specific configuration of optical systems, including a first optical system forming an intermediate image, a second optical system with a diffraction element, a third optical system forming another intermediate image, and a fourth optical system with a second diffraction element, where the luminance of pixels at end positions is adjusted to be greater than or equal to 60% of those at the central position, and includes a luminance adjustment member to optimize image distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the angles of diffraction of the first hologram element and the second hologram element are varied to reduce apparatus size, then the distance between optical members can be reduced, but the pupil diameter becomes insufficient and image quality deteriorates
Solution Approach 1:
The patent applies parameter changes by systematically varying the diffraction angles of the first and second hologram elements (specifically setting the first diffraction angle to 10 degrees and the second diffraction angle to 20 degrees in the embodiment) to optimize the balance between apparatus size and image quality. This allows the optical path to be folded within a compact form factor while maintaining adequate pupil diameter for acceptable image quality
Solution Approach 2:
The patent introduces a third dimension by adding a luminance adjustment member (such as a gray filter or electrochromic layer) that modulates light intensity along the optical path. This additional degree of freedom allows compensation for image quality degradation caused by compact diffraction angle design, enabling the system to maintain acceptable luminance distribution across the pupil even with reduced apparatus size
2Power
If the diffraction angles are increased to improve optical efficiency, then the apparatus size increases due to required intervals between optical members, but compact design is achieved
Solution Approach 1:
The patent segments the optical system into distinct functional modules: a first hologram element for initial diffraction, a second hologram element for further diffraction and wavelength compensation, and a luminance adjustment member for intensity control. This segmentation allows each component to be optimized independently, enabling the use of moderate diffraction angles (10 and 20 degrees) that balance optical efficiency with compact overall dimensions
3Volume of moving object
If the diffraction angles are decreased to reduce apparatus size, then the first mirror and second mirror interfere with each other, but compact design is achieved
Solution Approach 1:
The patent introduces a luminance adjustment member as an intermediary element between the first and second hologram elements. This mediator not only adjusts luminance distribution but also serves as a spatial separator that prevents direct optical interference between the first mirror and second mirror, allowing compact diffraction angles to be used without causing harmful optical interactions
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 allows for a reduction in the size of the display apparatus while ensuring consistent and high-quality image luminance across different viewing directions, reducing user discomfort and maintaining image clarity.
Implementation Method 1
a first diffraction element that deflects imaging light emitted from an imaging light generating device
Implementation Method 2
a second diffraction element disposed on an optical path starting at a light source unit of the imaging light generating device and ending at the first diffraction element
Implementation Method 3
a first mirror that reflects imaging light toward the first hologram element
Data Source
AI summary
A virtual image display apparatus includes an imaging light emitting unit configured to emit imaging light, and a light-guiding unit configured to guide the imaging light. The light-guiding unit is configured by arranging a first, a second, a third, and a fourth optical system in the stated order in a travel direction of the imaging light. The first optical system forms a first intermediate image of the imaging light. The second optical system includes a first diffraction element forming a pupil between the second and the fourth optical system. The third optical system forms a second intermediate image. The fourth optical system includes a second diffraction element forming an exit pupil by diffracting the imaging light. At the exit pupil, luminance of pixels at a central position of the imaging light and luminance of pixels at end positions of the imaging light differ.