Retroreflective Light Guide for Wide Vertical Viewing Angle
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Solution Overview
Problem
Existing virtual image display devices face challenges in achieving a wide viewing angle, particularly in the vertical direction, while preventing stray light and uneven brightness, due to the configuration of light guides with multiple mirrors or microstructures that lead to dispersion and reflection issues.
Innovation Solution
A light guide with a retroreflection portion and an extraction portion, featuring a plurality of surfaces that reverse the direction of image light and guide it to an exit portion, ensuring a wide viewing angle and reducing stray light and brightness unevenness by optimizing the inclination angles and surface configurations of the first, second, and third surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a light guide includes multiple mirrors or microstructures to extract image light, then light extraction is achieved, but the vertical viewing angle becomes insufficient and stray light increases
Solution Approach 1:
The light guide is divided into multiple functional regions: a first light guide portion with extraction surfaces for image light extraction, and a second light guide portion with a retroreflection film for viewing angle expansion. This segmentation allows each portion to specialize in one function, resolving the contradiction between light extraction and viewing angle.
Solution Approach 2:
A retroreflection film is introduced as an intermediary element in the second light guide portion. This film reflects divergent light rays back toward the observer, effectively expanding the vertical viewing angle without interfering with the image light extraction function of the first portion.
2Area of stationary object
If a retroreflection portion is added to reverse light direction and expand viewing angle, then vertical viewing angle improves, but stray light and brightness unevenness increase
Solution Approach 1:
The light guide is divided into a first portion for image light extraction and a second portion for viewing angle expansion. This spatial segmentation prevents the retroreflection film from interfering with image light extraction, thereby reducing stray light and brightness unevenness while maintaining wide viewing angle.
Solution Approach 2:
Different regions of the light guide are assigned different optical properties: the first portion has extraction surfaces optimized for image light extraction, while the second portion has a retroreflection film optimized for viewing angle expansion. This local differentiation allows each region to perform its specific function without causing harmful effects to the other.
3Speed
If light rays are dispersed and propagated in vertical viewing direction within light-guide plate, then light propagation is achieved, but sufficient field of view in vertical direction cannot be obtained
Solution Approach 1:
The light guide is divided into two portions: the first portion propagates light in the vertical viewing direction for efficient light transport, while the second portion uses a retroreflection film to expand the field of view in the vertical direction, resolving the contradiction between light propagation efficiency and field of view.
Solution Approach 2:
The retroreflection film in the second light guide portion utilizes the principle of retroreflection to redirect light rays back toward the observer from multiple angles, effectively adding a dimensional aspect to light propagation that expands the vertical field of view without compromising the efficiency of light transport in the first portion.
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 effectively achieves a sufficient vertical viewing angle and prevents stray light, ensuring even brightness and improved image observation in virtual image display devices by carefully designing the surface angles and configurations within the light guide.
Implementation Method 1
a retroreflection portion to reverse a direction of travel of image light propagating through the light-guide member
Implementation Method 2
a light guide that guides image light therethrough by totally reflecting the image light
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A light guide (50) includes a light-guide member (100) including an incidence portion (101) through which image light emitted from an image display element (10) enters the light-guide member (100); an exit portion (104) through which the image light exits the light-guide member (100) to an outside of the light-guide member (100); a retroreflection portion (106) to reverse a direction of travel of the image light guided through the light-guide member (100); and an extraction portion (103) to guide the image light reversed by the retroreflection portion (106) to the exit portion (104). The retroreflection portion (106) has a plurality of surfaces.