Flat Mirror Projection Optical System Color Uniformity
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Solution Overview
Problem
Conventional projection type image display devices using free-form surface mirrors face challenges in design and manufacturing complexity, leading to high costs, and suffer from color unevenness due to differences in reflectance between P-polarized and S-polarized light at large incident angles, which affect image quality.
Innovation Solution
A projection type image display device utilizing a flat mirror as the projection mirror, which reduces color unevenness by employing a diagonal projection optical system and a polarization converter, such as a quarter wavelength plate, to ensure equal reflectance of differently polarized light colors, thereby improving image quality and reducing manufacturing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a free-form surface mirror is used as a projection mirror, then the optical system can be designed to prevent light return to the projector body, but the design and manufacturing complexity increases and costs rise
Solution Approach 1:
Instead of using a complex free-form surface mirror to prevent light return, the invention inverts the approach by using a simple flat mirror combined with a diagonal projection optical system. The diagonal projection angle of 45° or more ensures that reflected light does not return to the projector body, achieving the same reliability benefit with much simpler and cheaper flat mirror technology.
2Device complexity
If a flat mirror is used as a projection mirror, then design and manufacturing complexity is reduced, but color unevenness occurs due to reflectance differences between P-polarized and S-polarized light at large incident angles
Solution Approach 1:
The invention introduces a polarization converter as an intermediary component between the light source and the flat mirror. This converter transforms the polarization state of incident light to ensure that both P-polarized and S-polarized light components have equal reflectance at the large incident angles required for diagonal projection, thereby eliminating color unevenness while maintaining the simplicity of flat mirror design.
Solution Approach 2:
The invention changes the polarization state parameter of the incident light through the polarization converter. By adjusting the polarization characteristics of the light before it reaches the flat mirror, the system achieves equal reflectance for different polarization components at large incident angles, resolving the color uniformity issue without compromising the simplicity of using a flat mirror.
3Area of stationary object
If a large incident angle is used for projection on a large image projection surface, then the projection area is increased, but color unevenness due to polarization-dependent reflectance differences worsens
Solution Approach 1:
The polarization converter serves as a mediator that compensates for the polarization-dependent reflectance differences that occur at large incident angles. By preprocessing the light's polarization state, it enables the system to maintain color uniformity across the entire large projection surface even when using the large incident angles necessary for wide-area coverage.
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 use of a flat mirror and polarization converter in the projection system effectively minimizes color unevenness, enhances image quality, and simplifies the design and manufacturing process, making the device more cost-effective and efficient.
Implementation Method 1
a polarization converter, such as a quarter wavelength plate, to ensure equal reflectance of differently polarized light colors
Implementation Method 2
By using a flat mirror as a projection mirror, there can be a reduction in color unevenness and improve the quality of image projection
Data Source
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AI summary
A projection type image display device using, in a projection optical system thereof, a flat mirror, which is easy to design and manufacture, as a projection mirror is provided. The projection optical system is a diagonal projection optical system and includes plural lenses. Among the plural lenses, the one disposed closest to the flat mirror has an effective area, along the vertical direction of an image, through which a light beam passes and which is off the optical axis, among optical axes of the plural lenses, shared by the most lenses so as not to allow light reflected from the projection mirror to return to the projector body. A polarization converter using, for example, a quarter wavelength plate is provided at an output surface of a crossed prism to decrease reflectance differences between differently colored light and to thereby prevent the occurrence of color unevenness.