Virtual Image Display Prism with Nested Projection Lens
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Solution Overview
Problem
Existing virtual image display devices face challenges in providing a wide angle of view, minimizing size and weight, while allowing simultaneous observation of external light and image light without interference, and maintaining high image quality and brightness.
Innovation Solution
A virtual image display device with a prism having three or more non-axisymmetric curved surfaces, where external light passes through specific surfaces to maintain visibility and image light is totally reflected to form an intermediate image, reducing the size and weight of the optical system, and incorporating a half mirror for seamless observation of external light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a relay optical system with a projection lens is used to form an intermediate image, then the image can be displayed with good quality, but the size and weight of the device increase
Solution Approach 1:
The patent combines the projection lens and light guide plate into a single integrated optical system. The projection lens is positioned to directly form an intermediate image on the light guide plate without requiring separate mounting structures, thereby reducing the overall device size and weight while maintaining image quality.
Solution Approach 2:
The optical system is designed with a compact nested structure where the projection lens is positioned within or adjacent to the light guide plate assembly. This nesting arrangement allows the optical components to occupy overlapping or adjacent spatial volumes, significantly reducing the device footprint and weight.
2Volume of moving object
If the optical system is made compact to reduce size, then the device becomes more wearable, but the image light may be folded back and reflected at the half mirror, causing the observed image to become dark
Solution Approach 1:
Instead of having the image light fold back and reflect off the half mirror as in conventional designs, the patent inverts the light path arrangement. The projection lens directly forms the intermediate image on the light guide plate, and the light emerges through the light guide plate without folding back, thereby maintaining image brightness while achieving compact size.
Solution Approach 2:
The patent extracts and eliminates the half mirror reflection step from the optical path. By directly forming the intermediate image on the light guide plate and using it as the final output, the design removes the unnecessary reflection component that would otherwise cause light loss and image darkening in compact configurations.
3Adaptability or versatility
If a half mirror is used to allow outside viewing, then the observer can see both the image and outside, but the image light is reflected twice on the half mirror surface, making the image very dark
Solution Approach 1:
The patent removes the half mirror from the optical path entirely. Instead, it uses a light guide plate that can transmit both image light and external light without requiring reflection. This extraction of the half mirror eliminates the double reflection that causes image darkening while preserving the capability for outside viewing through the light guide plate's transmission properties.
Solution Approach 2:
The patent replaces the mechanical reflection-based half mirror system with an optical transmission-based light guide plate system. The light guide plate transmits light through refraction and total internal reflection rather than requiring a separate half mirror component, thereby eliminating the image darkening problem while maintaining outside viewing functionality.
4Manufacturing precision
If the projection lens is made large to ensure good image forming performance, then the image quality improves, but it becomes difficult to reduce the size and weight of the device
Solution Approach 1:
The patent merges the projection lens with the light guide plate assembly, positioning the lens to directly focus the intermediate image onto the light guide plate. This integration allows for a more compact arrangement where the lens does not require large clearance space, thereby maintaining image forming performance while reducing overall device size.
Solution Approach 2:
The patent utilizes the thickness dimension of the light guide plate as part of the optical path. By forming the intermediate image on the rear surface of the light guide plate and using its front surface as the output, the design effectively uses the plate's thickness to accommodate the optical path, allowing for a compact overall size while maintaining proper image forming performance.
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 high-quality, wide-angle display with reduced weight and size, allowing for clear observation of both external and image light without distortion or ghosting, improving wearability and external visibility.
Implementation Method 1
the image light is totally reflected at the first surface, totally reflected at the third surface, totally reflected again at the first surface and reflected at the second surface, and then transmits through the first surface
Data Source
AI summary
An intermediate image is formed inside the prism by a projection lens or the like, and since an image light that is totally reflected at three or more surfaces; at a third surface firstly, at a first surface firstly, at a third surface secondly, at the first surface secondly, and at the second surface in the order specified, transmits the first surface, and then arrives at an observer's eye, the size and weight of the prism can be reduced and it is possible to realize a display of high performance and brightness with a wide angle of view. In addition, since the external light can be observed after passing through the first surface and the third surface, and the visibility at that time becomes substantially zero, it is possible to reduce the defocus or distortion of the external light when observing the see-through external light.