Projection Display Optical System Stray Light Reduction
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Solution Overview
Problem
Existing projection-type display apparatuses face challenges in reducing size while minimizing stray light, as the use of field lenses leads to increased size and cost due to long focal lengths and imperfect light separation.
Innovation Solution
A projection-type display apparatus is designed with a first optical system including a negative lens, a positive lens, and a positive lens, along with a second optical system consisting of two positive lenses, and incorporates a reflective flat surface mirror to separate illumination and projection light effectively, reducing stray light and apparatus size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a field lens is used to separate illumination light and projection light, then light separation is achieved, but the focal length must be long which increases apparatus size
Solution Approach 1:
The optical system is divided into two separate optical systems: a first optical system for illumination light and a second optical system for projection light. This segmentation allows each system to be optimized independently, eliminating the need for a single complex field lens with long focal length while achieving effective light separation.
Solution Approach 2:
A reflective optical element is introduced as an intermediary between the light source unit and the projection lens. This mirror reflects illumination light into the first optical system while allowing projection light to pass through the second optical system, achieving light separation without requiring a long-focal-length field lens.
2Length of stationary object
If the focal length of the field lens is reduced to decrease apparatus size, then compactness is improved, but curvature of field occurs and stray light increases
Solution Approach 1:
By separating the optical paths into distinct first and second optical systems, each with its own positive lenses, the patent eliminates the need for a single field lens. This segmentation allows optimal design of each subsystem without the compromise of reducing focal length, thereby minimizing stray light while maintaining compact size.
Solution Approach 2:
The patent replaces the traditional refractive field lens with a reflective optical element (mirror) in the first optical system. This substitution allows for more flexible optical path design and better control of light rays, reducing stray light generation while enabling compact apparatus configuration.
3Ease of manufacture
If a total reflection prism is used to separate illumination and projection light, then light separation is achieved, but apparatus size and cost increase
Solution Approach 1:
The patent extracts the light separation function from a single complex component (total reflection prism) and distributes it across multiple simpler components: a reflective optical element and two separate optical systems. This extraction reduces apparatus size and complexity while maintaining effective light separation.
Solution Approach 2:
Instead of using a single expensive total reflection prism, the patent creates separate optical paths with simpler optical elements that replicate the light separation function. The first and second optical systems with positive lenses provide equivalent separation functionality at reduced cost and complexity.
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 achieves a compact projection-type display apparatus with reduced stray light and cost, while maintaining effective light separation, by utilizing a reflective flat surface mirror and a field lens configuration with two positive lenses to minimize curvature of field and stray light.
Implementation Method 1
the first optical system includes at least one reflective optical element
Implementation Method 2
the second optical element consists essentially of two positive lenses
Data Source
AI summary
A projection-type display apparatus includes a light source unit, a first optical system that rays from the light source unit enter, a second optical system that rays from the first optical system enter, an image display device that rays from the second optical system enter, and a projection lens that magnifies and projects an optical image formed by rays that have been optically modulated by the image display device onto a screen. The second optical system is configured to pass again the rays that have been output from the image display device, and to make the rays enter the projection lens. The first optical system includes at least one reflective optical element, and the second optical element consists essentially of two positive lenses.