See-Through Virtual Image Optics for High Center-Field Transmittance
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Solution Overview
Problem
Existing virtual image display devices of a see-through type face challenges in maintaining high see-through transmittance near the center of the visual field due to the treatment of light emitting regions, necessitating larger optical systems to achieve this.
Innovation Solution
A virtual image display device with a light modulating element, a light shielding member, a backlight irradiating in a time-division manner, polarizing plates, an image selection conversion member, and a polarization separation lens element to manage light polarization and transmission, enhancing see-through transmittance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the light emitting region of the light guiding plate is subjected to treatment such as formation of dots and application of a scattering agent, then the backlight light can be effectively emitted, but the see-through transmittance near the center of the visual field is reduced
Solution Approach 1:
The light guiding plate is divided into a light emitting region with dots/scattering agents and a light transmitting region without such treatments. This segmentation allows different regions to serve different functions: the light emitting region effectively emits backlight light while the light transmitting region maintains high see-through transmittance, thus resolving the contradiction between illumination intensity and see-through transmittance.
Solution Approach 2:
Different regions of the light guiding plate are given different optical properties. The light emitting region has scattering properties to enhance backlight emission, while the light transmitting region maintains high transparency for environmental light. This local differentiation of quality allows the system to achieve both effective backlight emission and high see-through transmittance without requiring additional optical systems.
2Reliability
If additional optical systems with high see-through transmittance are added to achieve high see-through transmittance near the center of the visual field, then the see-through transmittance is improved, but the device size increases
Solution Approach 1:
The light guiding plate is designed to perform multiple functions within a single component: it serves as both a backlight diffusion element (in the light emitting region) and a high-transmittance optical element (in the light transmitting region). This multi-functionality eliminates the need for additional separate optical systems, thereby maintaining high see-through transmittance without increasing device size.
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 improves see-through transmittance by selectively managing light polarization and transmission, allowing for clearer overlapping of external and display images without increasing device size.
Implementation Method 1
a light modulating element including a liquid crystal pixel
Implementation Method 2
a polarizing plate configured to limit external light that passes through the first light transmitting region of the light modulating element and image light that is emitted from the liquid crystal pixel, to polarized light in a first polarization direction
Implementation Method 3
a polarization separation lens element being arranged on the face side of the image selection conversion member and having refractive power acting on polarization of the image light
Data Source
AI summary
A virtual image display device includes a light modulating element including a liquid crystal pixel and a light transmitting region, a light shielding member being arranged on an external side of the light modulating element, a backlight being arranged between the light modulating element and the light shielding member and being configured to irradiate the liquid crystal pixel, a polarizing plate configured to limit external light that passes through the light transmitting region of the light modulating element and image light that is emitted from the liquid crystal pixel, to polarized light, and cause the light to pass therethrough, an image selection conversion member configured to selectively change a polarization direction of the image light emitted from the polarizing plate, and a polarization separation lens element being arranged on the face side of the image selection conversion member.