Light Guide Device for Head-Mounted Display with Reflection Unit
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Solution Overview
Problem
Existing head-mounted display light guide devices suffer from luminance non-uniformity and ghosting due to multiple reflections through half mirrors, leading to reduced image quality and increased complexity in design.
Innovation Solution
A light guide device with a reflection unit where image light rays are reflected without hitting the boundary surface between the light guide and the reflection unit, using a configuration with inclined half mirrors that reduce the number of reflections and enhance image precision, while maintaining high-precision image formation and suppressing diffraction non-uniformity and moire.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple half mirrors are arranged in the light guide plate to guide image light rays, then the image light can be reflected to the observer, but luminance non-uniformity occurs and luminance is reduced
Solution Approach 1:
The light guide plate is divided into multiple regions with different reflectance characteristics. The first region (closer to the incident section) has lower reflectance while the second region (farther from the incident section) has higher reflectance. This segmentation allows different parts of the light guide to handle light distribution differently, compensating for luminance non-uniformity caused by multiple reflections.
Solution Approach 2:
Different regions of the light guide plate are assigned different optical properties (reflectance values). The reflectance is not uniform across the entire plate but is locally optimized: lower reflectance in the first region to maintain luminance, and higher reflectance in the second region to ensure sufficient light reaches the observer after multiple reflections.
2Loss of energy
If the reflectance of half mirrors is increased to improve image light efficiency, then more light reaches the observer, but external light (see-through light) non-uniformity occurs
Solution Approach 1:
The light guide plate implements local quality variation by assigning different reflectance values to different regions. The first region has lower reflectance to maintain good see-through performance and external light uniformity, while the second region has higher reflectance to improve image light efficiency for rays that undergo multiple reflections.
3Illumination intensity
If the thickness of the reflection unit is reduced to allow light rays to reach internal HMs without transmitting other HMs, then non-uniformity in light amount is suppressed, but reflection efficiency decreases due to multiple reflections from paired HM surfaces
Solution Approach 1:
The invention extracts the problematic paired HM structure and replaces it with a simplified reflection unit configuration. Instead of using paired half mirrors that cause double reflection, the light guide plate uses a single-layer reflection structure with spatially varying reflectance, eliminating the need for light rays to pass through multiple HM layers while maintaining uniform light distribution.
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 prevents luminance non-uniformity and ghosting, allowing for high-quality image display with reduced light loss and simplified manufacturing by minimizing reflections through the mirrors, thus enhancing the overall image quality and usability of the head-mounted display.
Implementation Method 1
image light rays guided to the light guide plate propagate while being totally reflected in the light guide plate
Implementation Method 2
image light rays are reflected from the HMs so as to be presented to the observer
Data Source
AI summary
A light guide device that does not cause non-uniformity in image light and external light and does not cause ghosts, and a virtual image display apparatus provided with the light guide device. The light guide device includes a parallel light guide, an incident section, and an emission section. Here, the light guide device is set such that image light rays are reflected without reflecting from a boundary surface between the parallel light guide and the reflection unit and head for an observer. Thus, the image light rays only pass through half mirrors, which are positioned in positions where the image light rays are emitted from the reflection unit of the emission section or are positioned therearound. Accordingly, it is possible to prevent luminance non-uniformity or light reduction by reducing the number of times of the image light rays to be observed pass through the half mirrors.