Light Guide for Virtual Image Display with Wide Viewing Angle
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Solution Overview
Problem
Existing virtual image display devices, such as transmissive head-mounted displays (HMDs), face challenges in achieving a compact and thin design with a wide viewing angle while maintaining effective see-through characteristics.
Innovation Solution
A light guide system comprising a light-guide member with an incidence portion, a reflective portion, an extraction portion, and an exit portion, integrated with an optical member, which guides image light from an image display element to the observer, utilizing inclined and parallel planes to enhance viewing angle and compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a conventional light guide structure is used, then the device can guide image light, but the viewing angle is limited and the device thickness cannot be reduced below a certain level
Solution Approach 1:
The light guide is divided into multiple functional portions: an incidence portion for receiving image light, a reflective portion for guiding light into the guide, an extraction portion with alternating inclined and parallel planes for light extraction, and an exit portion for emitting light. This segmentation allows each portion to be optimized independently, achieving a wide viewing angle through the extraction portion's plane configuration while maintaining compact overall thickness.
Solution Approach 2:
The extraction portion utilizes alternating inclined and parallel planes to extract light in multiple directions, effectively expanding the viewing angle in the horizontal dimension while keeping the device thickness constrained in the vertical dimension. This dimensional approach resolves the contradiction between wide viewing angle and thin profile.
2Length of stationary object
If the light guide structure is made compact and thin, then portability is improved, but see-through characteristics may be compromised
Solution Approach 1:
Different portions of the light guide have different optical properties optimized for their specific functions. The incidence portion, reflective portion, extraction portion, and exit portion each have tailored structures that optimize light management locally. This allows the compact design to maintain effective see-through characteristics by ensuring adequate light extraction and emission at each stage.
3Area of stationary object
If the viewing angle is increased, then user comfort is improved, but the device complexity increases
Solution Approach 1:
Multiple optical functions (light reception, guidance, extraction, and emission) are merged into a single integrated light guide structure. The alternating inclined and parallel planes in the extraction portion simultaneously achieve light extraction and viewing angle expansion without requiring separate optical components, thereby reducing overall device complexity while maintaining wide viewing angle.
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 compact transmissive light guide with a wide viewing angle of greater than or equal to 40 degrees, ensuring successful see-through characteristics and reducing the size and weight of the display device.
Implementation Method 1
a reflective portion inclined relative to the incidence portion to guide the image light received by the incidence portion into the light guide
Implementation Method 2
an extraction portion including at least one first plane inclined relative to the exit portion and at least one second plane parallel with the exit portion, to guide the image light from the at least one first plane to the exit portion and extract the image light
Data Source
AI summary
A light guide for a virtual image device to guide and emit image light output from an image display element to display a virtual image. The light guide includes a light-guide member and an optical member. The light-guide member includes an incidence portion to receive the image light and an exit portion to emit the image light to an outside, and a reflective portion inclined relative to the incidence portion to guide the image light received by the incidence portion into the light guide. The light-guide member also includes an extraction portion including first planes each inclined relative to the exit portion and second planes each parallel with the exit portion, to guide the image light from each first plane to the exit portion and extract the image light. The optical member includes a parallel plane and an inclined portion.