Prism Member Optical System for Compact Head-Mounted Display
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Solution Overview
Problem
Existing head-mounted displays face challenges in reducing the size of the optical system while maintaining a wide angle of view, as the inclination angle of the half mirror affects the system's width and complexity.
Innovation Solution
The design incorporates a prism member with a first and second prism, along with a semi-transmissive reflection surface, which allows for the projection and reflection of image light while reducing the thickness of the prism member, enabling a smaller optical system with an equivalent or wider angle of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the inclination angle of the half mirror is set to approximately 45° to achieve proper light reflection, then the light path can be properly redirected, but the occupying width in the optical axis direction increases and the size of the optical system cannot be reduced
Solution Approach 1:
The optical system is segmented into multiple functional components: a light condensing optical system with multiple lenses (first through fourth lenses) arranged in sequence, a half mirror positioned at a specific angle, and a reflecting mirror. This segmentation allows each component to perform its specific function efficiently, reducing the overall optical path length and system size while maintaining proper light redirection
Solution Approach 2:
The patent positions the half mirror to be inclined at approximately 45° relative to the optical axis, utilizing angular orientation in a different dimensional space. This angular arrangement allows the light path to be redirected efficiently without increasing the linear occupying width along the optical axis, effectively using spatial orientation to resolve the size-complexity contradiction
2Adaptability or versatility
If the half mirror and its periphery are enlarged to secure the angle of view, then the angle of view can be maintained or improved, but the occupying width in the optical axis direction increases
Solution Approach 1:
The patent employs a light condensing optical system with specifically designed lens arrangements where each lens has particular focal lengths and positions optimized for its function. The first lens has a positive focal length to converge light, while subsequent lenses have negative focal lengths to diverge and redirect light. This localized optimization of optical properties allows the system to maintain a wide angle of view without requiring overall enlargement of the half mirror and its periphery
Solution Approach 2:
The patent introduces a light condensing optical system with multiple lenses as an intermediary between the image source and the half mirror. This intermediary system condenses and conditions the light before it reaches the half mirror, enabling the half mirror to operate at optimal dimensions while still achieving the desired angle of view. The reflecting mirror also acts as an intermediary to further optimize the light path without requiring enlargement of the half mirror
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 more compact optical system while maintaining or enhancing the angle of view, reducing the risk of image unevenness and stray light, and improving light utilization efficiency.
Implementation Method 1
a first joining surface that is joined with the second prism via a semi-transmissive reflection surface that reflects the image light totally reflected by the reflection surface toward the reflection surface
Implementation Method 2
a light condensing and reflecting surface disposed at an external side of the prism member, with the external side being an opposite side from the exit pupil across the prism member, and configured to return at least a portion of the image light, which has been emitted from the prism member, to the prism member
Implementation Method 3
a reflection surface that totally reflects the image light from the incident surface
Data Source
AI summary
A head-mounted display includes a display device, a projection optical member, a prism member, and a light condensing and reflecting surface. The prism member includes a first prism, and a second prism that is disposed further toward an exit pupil side than the first prism. The first prism includes an incident surface, a reflection surface that totally reflects the image light, and a first joining surface that is joined with the second prism via a semi-transmissive reflection surface. The second prism includes a second joining surface that is joined with the first joining surface, and an opposing flat surface that is disposed parallel to the reflection surface to face the reflection surface and configured to transmit the image light, reflected by the semi-transmissive reflection surface and then by the light condensing and reflecting surface and thereafter passing through the semi-transmissive reflection surface.