HMD Image Display Device with Overlapping Exit Pupils
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Solution Overview
Problem
Image display devices for head-mounted displays (HMDs) face challenges in achieving a wide eye box with high light use efficiency while minimizing brightness unevenness, as existing technologies either lead to brightness inconsistencies or low light use efficiency due to inefficient pupil duplication methods.
Innovation Solution
The implementation of an image display device with a projection optical unit that includes at least one projection lens, where the image light duplication unit duplicates the image light at an interval smaller than the outer diameter of the projection lens, utilizing a light-guiding unit with a pupil enlargement prism and a light-guiding plate featuring partial reflection surfaces to achieve uniform image projection and high light use efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the exit pupil is duplicated using a light-guiding plate with diffraction grating, then the eye box area is enlarged, but the light use efficiency becomes low because not all incident lights can be used
Solution Approach 1:
The patent replaces the diffraction grating optical system with a mirror-based optical system. Specifically, it uses a projection lens to project the image and mirrors to duplicate the exit pupil, substituting the diffraction-based mechanism with a reflection-based mechanism that can utilize all incident light effectively.
Solution Approach 2:
The patent changes the optical parameters by using a projection lens with a specific focal length and arranging mirrors at specific positions and angles. The duplication interval is set to be smaller than the outer diameter of the projection lens, creating overlapping exit pupils that ensure uniform brightness while maximizing light utilization.
2Area of stationary object
If the exit pupil is duplicated using multiple partial reflection surfaces, then the eye box is enlarged, but brightness unevenness occurs in the displayed image
Solution Approach 1:
The patent merges multiple exit pupils by setting the duplication interval smaller than the outer diameter of the projection lens. This causes the duplicated exit pupils to overlap spatially, combining their light distributions to produce a uniform brightness profile across the enlarged eye box area.
Solution Approach 2:
The patent creates different optical paths for different regions of the incident light. By strategically positioning mirrors at specific angles and distances, each region of the light beam is directed to appropriate locations, ensuring uniform brightness distribution across the entire eye box area.
3Device complexity
If the duplication interval is large, then the device structure is simpler, but brightness unevenness occurs and light use efficiency decreases
Solution Approach 1:
The patent optimizes the duplication interval parameter by setting it smaller than the outer diameter of the projection lens. This parameter choice creates overlapping exit pupils that eliminate brightness unevenness and maximize light utilization, while the overall device structure remains relatively simple with only a projection lens and a few mirrors.
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 results in a wide eye box with uniform image display and reduced brightness unevenness, enhancing the light use efficiency and usability of HMDs for extended periods.
Implementation Method 1
a light-guiding unit that projects the image light duplicated by the image light duplication unit to a user
Implementation Method 2
a light-guiding plate featuring partial reflection surfaces to achieve uniform image projection
Data Source
AI summary
An image display device projecting an image to a user includes: an image generation unit that generates image light; a projection optical unit that projects the image light generated by the image generation unit; an image light duplication unit that duplicates and emits the image light projected by the projection optical unit; and a light-guiding unit that projects the image light duplicated by the image light duplication unit to a user, in which the projection optical unit includes at least one projection lens, and in which an interval at which the image light duplication unit duplicates the image light is smaller than an outer diameter of the projection lens.