Curved Light Guide Member for Compact HMD Display
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Solution Overview
Problem
Existing virtual image display apparatuses face challenges in achieving a wide viewing angle and reduced size and weight while maintaining high performance, as they often require large projection lenses, concave mirrors, or thick prism arrays, which can obstruct the field of view and compromise video quality.
Innovation Solution
A virtual image display apparatus featuring a light guide member with non-axisymmetric curved surfaces that form an intermediate image, where video light is totally reflected and transmitted through specific surfaces to achieve a wide viewing angle and correct aberration, using conditional expressions to optimize surface shapes and coefficients for minimal size and weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a relay optical system uses a parallel planar light guide plate with a parabolic mirror and projection lens, then an intermediate image can be formed inside the light guide plate, but the projection lens becomes large in size, obstructing reduction in size and weight
Solution Approach 1:
The patent replaces the planar light guide plate with a light guide member having curved surfaces (first surface, second surface, third surface) that are non-planar. The curved surfaces enable total internal reflection and light guidance while forming the intermediate image, eliminating the need for a large parabolic mirror and projection lens combination, thus reducing the overall size and weight while maintaining image quality
2Volume of moving object
If a relay optical system uses a concave mirror and half mirror to reduce the size of projection lens, then the appearance is damaged and video light becomes very dark due to multiple reflections
Solution Approach 1:
The patent replaces the mechanical reflection system (concave mirror and half mirror) with a light guide member that uses total internal reflection at curved surfaces. This substitution eliminates the need for multiple external reflections, preventing light loss and maintaining video brightness while achieving compact size through the integrated light guide structure
3Ease of operation
If a diffusion plate is placed at the position of intermediate image to diffuse light beam, then the light beam flux width in the pupil is expanded, but the image on the diffusion plate is enlarged and video quality is damaged
Solution Approach 1:
The patent uses curved surfaces (first, second, and third surfaces) in the light guide member to guide and expand the light beam flux. The curved geometry enables smooth light diffusion and expansion without the need for a separate diffusion plate, thereby maintaining image quality while achieving wide viewing angle through the inherent optical design of the curved light guide surfaces
4Ease of operation
If a prism array is inserted between the eyepiece optical system and the eyes to spread the light beam flux, then the viewing angle is improved, but the distance between the eyepiece optical system and the eyes is extended, and the optical system increases in size
Solution Approach 1:
The patent merges the light guidance function and the light beam expansion function into a single integrated light guide member with curved surfaces. This consolidation eliminates the need for separate prism arrays and eyepiece optical systems, achieving wide viewing angle while maintaining a compact overall size through functional integration
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
The solution enables a small and lightweight virtual image display apparatus with a wide viewing angle and high performance by effectively correcting aberration and reducing the thickness of the light guide member, allowing for bright and clear image display without obstructing the external field of view.
Implementation Method 1
video light from the video element is totally reflected by the third surface, is totally reflected by the first surface
Data Source
AI summary
An optical system of a virtual image display apparatus is configured such that, in regard to a width in a first direction and a width in a second direction at a first surface position, and a width in a first direction and a width in a second direction at a second surface position corresponding to the width in the first direction and the width in the second direction at the first surface position, predetermined conditional expressions are established. With this, in an optical system for an HMD which includes a light guide member having a free-form surface, it is possible to allow video light to be emitted toward eyes in an appropriate state while controlling the light guide of video light accurately and maintaining high performance.