Virtual Image Display Device Reducing Luminance Unevenness
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Solution Overview
Problem
Existing virtual image display devices, such as head-mounted displays, suffer from image unevenness and ghost light due to the use of thin, wide-angle optical systems, particularly in the horizontal direction, which affects image quality and luminance.
Innovation Solution
A virtual image display device configuration that includes a semi-transmissive polarizing plate with a polarizing transmission axis in the horizontal direction, combined with a polarization converting member like a ¼ wavelength plate, and a concave half mirror, reduces luminance unevenness and prevents ghost light by optimizing the polarization state of image light, while using low-birefringence lenses and a reflective wire-grid polarizing plate to enhance image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a thin, wide-angle optical system is applied to achieve a wide angle of view and downsizing, then the device can be made compact with wide viewing capability, but the optical system becomes complicated causing image degradation including luminance unevenness and ghost light
Solution Approach 1:
The optical system is divided into distinct functional components: a half mirror for optical path folding, a display-side lens for image formation, an observer-side lens for light collection, and a semi-transmissive polarizing plate for luminance correction. Each component performs a specific function, allowing the complex wide-angle system to be managed through modular design while reducing overall complexity.
Solution Approach 2:
A semi-transmissive polarizing plate is introduced as an intermediary component between the display-side lens and observer-side lens. This intermediate element specifically addresses luminance unevenness by selectively transmitting and reflecting light based on polarization state, thereby correcting the image degradation caused by the thin optical system without requiring complete redesign of the entire optical path.
2Length of stationary object
If a thin, wide-angle optical system is used to downsize the device, then the device thickness is reduced, but ghost light occurs due to the partial optical returning portion using the half mirror
Solution Approach 1:
The half mirror, which initially causes ghost light as a harmful effect, is combined with a semi-transmissive polarizing plate that converts the problematic reflected light into useful transmitted light through polarization control. The ghost light path is transformed into a beneficial optical path that contributes to the main image, converting the harmful reflection into a useful function.
Solution Approach 2:
The polarization state of light is used as a controlling parameter to distinguish between the main image path and ghost light path. By adjusting the polarization characteristics of the semi-transmissive plate, the system selectively transmits the desired light while blocking or redirecting the ghost light, thereby eliminating the harmful effect through parameter control.
3Ease of manufacture
If the optical system is simplified to reduce complexity, then the device becomes easier to manufacture, but image quality degrades due to luminance unevenness in the horizontal direction
Solution Approach 1:
The semi-transmissive polarizing plate is positioned specifically in the region where luminance unevenness occurs (between the lenses in the horizontal direction). This localized intervention addresses the image quality issue only where needed, without requiring complex modifications to the entire optical system, thereby maintaining ease of manufacture while improving image quality.
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 provides a high-quality image with reduced luminance unevenness and ghost light, maintaining a wide angle of view and downsizing the device, effectively addressing the challenges of image quality in virtual image display devices.
Implementation Method 1
a semi-transmissive polarizing plate provided between the display-side lens and the observer-side lens and having a polarizing transmission axis in a horizontal direction
Implementation Method 2
a half mirror provided before the display-side lens
Implementation Method 3
the polarization converting member may be a 1⁄4 wavelength plate and be provided between the display-side lens and the semi-transmissive polarizing plate, and configured to convert a component of light traveling toward the semi-transmissive polarizing plate into linearly-polarized light
Implementation Method 4
at least one of the display-side lens and the observer-side lens may be a resin lens having at least one of an oriented birefringence of not greater than 0.01 and not less than −0.01 and a photoelastic constant of not greater than 10
Data Source
AI summary
A half mirror 21 provided in an optical path bends the optical path, and a semi-transmissive polarizing plate 23 increases the transmittance of image light GL in a direction along alignment of the eyes of an observer while the virtual image display device has a wide angle of view and is downsized, thus reducing luminance unevenness between the central region and the peripheral region in the image in the direction and allowing the observer to view a high quality image.