Projection Display Stray Light Reduction via Polarization Separation
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Solution Overview
Problem
Existing projection display apparatuses face challenges in reducing stray light entering the imaging element, particularly when the optical path branching element uses polarization separation coating, leading to increased noise and decreased signal-to-noise ratio.
Innovation Solution
The apparatus incorporates an optical path separation element with a partial reflection coating or polarization separation coating, combined with a condensing optical system and a polarizing plate, to manage the image and external light paths, ensuring that only the desired polarization state of light reaches the imaging element, thereby reducing stray light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an optical path branching element with polarization separation coating is used to share optical paths, then angle of view adjustment can be omitted and device complexity is reduced, but stray light is generated and incident on the imaging element deteriorating image quality
Solution Approach 1:
The harmful stray light is extracted and separated from the main optical path using a beam splitter. The beam splitter divides the optical path into a transmission path for image light and a reflection path for stray light, extracting the harmful component before it reaches the imaging element.
Solution Approach 2:
A beam splitter is introduced as an intermediary element between the projection lens and imaging element. This mediator selectively transmits image light while reflecting stray light, preventing stray light from directly reaching the imaging element while maintaining the optical path sharing structure.
2Use of energy by moving object
If polarization separation coating is used in the optical path branching element, then image light transmission efficiency is improved, but stray light generation increases and signal-to-noise ratio deteriorates
Solution Approach 1:
The beam splitter acts as an intermediary that preserves the high transmission efficiency of the polarization separation coating for image light while simultaneously redirecting stray light into a separate reflection path, preventing information loss due to stray light contamination.
Solution Approach 2:
The optical path is segmented into separate transmission and reflection paths by the beam splitter. This segmentation allows the polarization separation coating to efficiently transmit image light in the transmission path while directing stray light into the reflection path, maintaining signal-to-noise ratio.
3Measurement precision
If the capturing angle of the condensing optical system is increased to collect more external light, then imaging sensitivity is improved, but stray light from the optical path branching element is also captured increasing noise
Solution Approach 1:
The beam splitter performs preliminary separation of stray light from the main optical path before the light reaches the condensing optical system. This preliminary action ensures that when the condensing optical system collects external light with a wide capturing angle, it does not simultaneously collect the already-separated stray light, thus maintaining imaging sensitivity without increasing noise.
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
This configuration effectively attenuates stray light, improving the signal-to-noise ratio and enhancing image quality by ensuring only the intended light is captured by the imaging element.
Implementation Method 1
the optical path branching element branches the image light incident on the imaging element by using a polarization separation coating
Implementation Method 2
The condensing optical system condenses the part of the external light reflected by the optical path separation element on the imaging element
Implementation Method 3
a 1/4 wave plate that is disposed between the optical path separation element and the projection lens unit, converts the image light in the first polarization state into circularly polarized image light, and converts the circularly polarized image light reflected by the projection target into image light in the second polarized state
Implementation Method 4
a polarizing plate that is disposed between the optical path separation element and the imaging element, and transmits the external light in the second polarization state
Data Source
AI summary
A projection display apparatus includes an image light emitter that includes a light modulation element that emits image light, a projection lens unit that projects the image light on a projection target, an optical path separation element, an imaging element that images external light incident via the projection lens unit and the optical path separation element, and a condensing optical system. The optical path separation element transmits a part of the image light to the projection lens unit, and reflects a part of the external light emitted from the projection lens unit to the condensing optical system. The condensing optical system condenses the part of the external light reflected by the optical path separation element on the imaging element. A capturing angle of the external light in the condensing optical system is equal to or less than a condensing angle of a lens F-number of the projection lens unit.