Head-Mounted Image Display Optics for Depth-Separated Images
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Solution Overview
Problem
Existing head-mounted HUDs have limited depth direction freedom for image display, leading to increased field of view occupation and difficulty in visually distinguishing multiple images.
Innovation Solution
An image display device utilizing a first image projection unit, beam splitters, retroreflection and reflection units, and an image forming optical unit to create distinct image positions in the depth direction, allowing for improved depth direction freedom and separation of images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If a head mounted HUD directly irradiates eyes with light from a light source to project an image on the retina, then the device size and weight are reduced, but the image forming position in depth direction becomes fixed and degree of freedom is limited
Solution Approach 1:
The patent introduces optical path folding using beam splitters and retroreflectors to create multiple image forming positions along the depth direction (optical axis). This transforms the single fixed display position into multiple adjustable positions by manipulating light paths in different spatial dimensions, resolving the contradiction between compact device size and display position flexibility.
Solution Approach 2:
The patent employs nested optical components where beam splitters, retroreflectors, and lenses are arranged in a compact nested configuration. The optical paths are folded back on themselves within a small form factor, allowing multiple image forming positions to be achieved without increasing device weight or size proportionally.
2Area of stationary object
If multiple images are displayed in parallel to expand display area, then the display area is increased, but the ratio of image occupying field of view increases and background becomes difficult to visually recognize
Solution Approach 1:
The patent distributes multiple images along the depth direction (optical axis) rather than arranging them side-by-side in the lateral field of view. This vertical stacking in the depth dimension increases display area while maintaining good background visibility, as each image occupies a different focal plane.
3Area of stationary object
If multiple images are displayed in parallel, then the display area is expanded, but it becomes difficult to separate and identify each image intuitively and individually
Solution Approach 1:
The patent uses depth positioning along the optical axis to separate multiple images, making them identifiable at different focal distances. This depth-based organization provides intuitive separation compared to lateral arrangement, as users can focus at different depths to distinguish between images.
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
Enhances the degree of freedom in depth direction for image display, enabling clear visualization of multiple images with reduced background interference.
Implementation Method 1
a beam splitter configured to reflect a part of light emitted from the first image projection unit in a first direction and transmit remaining light in a second direction
Implementation Method 2
a retroreflection unit configured to retroreflect, to the beam splitter, light traveling from the beam splitter in one of the first direction and the second direction
Data Source
AI summary
An image display device includes: a first image projection unit configured to project a first image; a beam splitter configured to reflect a part of light emitted from the first image projection unit in a first direction and transmit remaining light in a second direction; a retroreflection unit configured to retroreflect, to the beam splitter, light traveling from the beam splitter in one of the first direction and the second direction; a reflection unit configured to reflect, to the beam splitter, light traveling from the beam splitter in the other of the first direction and the second direction; and an image forming optical unit configured to form an image of the light reflected by the retroreflection unit and the reflection unit in a space.