Light Guiding Prism Negative Inclination Ghost Image Reduction
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Solution Overview
Problem
Small and thin light guiding prisms in attachable image display devices generate ghost images due to unnecessary reflected light, which affects the user's field of view.
Innovation Solution
The light guiding prism is designed with an outer peripheral surface that surrounds the light path and a reflection surface, where the intersection line of the outer peripheral surface and a plane including the optical axis has a negative inclination angle downstream of the light path, with a tangential inclination angle that gradually increases from the upstream to the downstream side, preventing multiple reflections and reducing ghost images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the light guiding prism is made smaller and thinner to fit the field of view, then the device size is reduced, but ghost images are generated due to unnecessary reflected light
Solution Approach 1:
The patent applies local quality by giving different surface characteristics to different regions of the light guiding prism. Specifically, the outer peripheral surface has a negative inclination angle in the downstream direction, while the intersection line has a gradually increasing tangential inclination angle from upstream to downstream. This localized variation in surface geometry targets the specific regions where ghost images are generated, allowing the prism to maintain its small and thin overall dimensions while eliminating harmful reflections in critical areas.
2Device complexity
If the light guiding prism is made smaller and thinner, then the device becomes more compact, but multiple reflections occur that degrade image quality
Solution Approach 1:
The patent applies inversion by reversing the conventional approach to prism surface design. Instead of using traditional flat or positively inclined surfaces that cause light to reflect back toward the optical path, the invention uses a negative inclination angle for the outer peripheral surface. This inverted geometry causes reflected light to diverge away from the optical axis, effectively eliminating multiple reflections and improving image quality while maintaining the compact prism structure.
3Object-generated harmful factors
If the outer peripheral surface has a negative inclination angle, then reflected light is diverted from the pupil, but the manufacturing precision requirements increase
Solution Approach 1:
The patent applies curvature by designing the intersection line between the outer peripheral surface and the plane including the optical axis to have a gradually increasing tangential inclination angle from upstream to downstream. This curved geometry, rather than a simple flat surface, provides a progressive change in light reflection angles, which helps divert reflected light away from the pupil while distributing the precision requirements across a gradual transition rather than a sharp angle, thereby balancing optical performance with manufacturability.
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 effectively reduces or eliminates ghost images by ensuring that light reflected off the prism sides is diverted away from the pupil, improving image clarity and reducing aberrations in the ocular optical system.
Implementation Method 1
a portion of or the entirety of an intersection line of the outer peripheral surface and a plane including a first optical axis of the image light before the image light is reflected off the reflection surface has a negative inclination angle to the first optical axis in a direction downstream of the light path
Implementation Method 2
a light guiding prism that guides image light from the display element
Data Source
AI summary
An attachable image display device includes a light guiding prism that guides image light from a display element, and an eyepiece that emits the image light guided by the light guiding prism, wherein the light guiding prism includes an outer peripheral surface, and a reflection surface off which the image light is reflected to the eyepiece; and a portion of or the entirety of an intersection line of the outer peripheral surface and a plane including an optical axis of the image light before the image light is reflected off the reflection surface has a negative inclination angle to the optical axis in a direction downstream of the light path, and a tangential inclination angle of the portion of or the entirety of the intersection line becomes gradually larger from an upstream side to a downstream side of the light path.