Prism Optical Unit for Two-Axis DMD Projectors
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Solution Overview
Problem
Existing digital micromirror devices that drive micromirrors with respect to two axes orthogonal to each other face challenges in separating unnecessary OFF light from ON light, leading to contrast reduction and temperature rises due to stray light, as conventional methods like increasing prism height are ineffective for this operation type.
Innovation Solution
The optical unit includes a digital micromirror device that modulates light intensity by controlling micromirror inclination over two axes and a prism optical system with a TIR prism and color synthesizing cross prism, where the OFF light is directed differently from ON light, using a reflecting surface with total reflection characteristics and optimizing the height of the color synthesizing cross prism to secure a separate optical path for OFF light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a heat releasing body is used to absorb OFF light, then OFF light processing is improved, but bonding problems occur at the cross prism surface
Solution Approach 1:
The patent extracts the heat releasing body from direct contact with the cross prism by introducing an air gap between them. The OFF light is reflected by the cross prism's reflecting surface toward the heat releasing body, which is positioned separately. This extraction eliminates the bonding problem while maintaining OFF light absorption functionality.
2Object-affected harmful factors
If the height of the synthesizing prism is increased to secure OFF light optical path, then OFF light separation is improved, but device complexity increases and is only applicable to one-axis DMD
Solution Approach 1:
The patent changes the approach from increasing prism height (vertical dimension) to utilizing the lateral dimension by introducing an air gap and positioning the heat releasing body horizontally. The OFF light optical path is secured by reflecting OFF light at an angle toward a laterally positioned heat releasing body, avoiding the need to increase prism height and making the solution applicable to two-axis DMDs.
3Object-affected harmful factors
If conventional prism height increase method is used, then OFF light path is secured for one-axis DMD, but OFF light from two-axis DMD hits unexpected surfaces causing temperature rise and contrast reduction
Solution Approach 1:
The patent changes the optical path parameters by introducing an air gap and utilizing total internal reflection at the cross prism's reflecting surface. This parameter change directs OFF light from two-axis DMDs along a controlled path that reflects off the cross prism and travels laterally to the heat releasing body, preventing OFF light from hitting unexpected surfaces and causing temperature rise.
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 separates OFF light from ON light, preventing temperature rises and stray light, thereby achieving high contrast and stable performance in three-plate projectors.
Implementation Method 1
a prism optical system configured to emit, to an image projection side, ON light reflected at the micromirror in an ON state among emitted light the intensity of which has been modulated by the digital micromirror device... a reflecting surface with total reflection characteristics
Implementation Method 2
the OFF light reflected at an upper surface of the color synthesizing cross prism can be separated from the ON light on an emission surface of the color synthesizing cross prism
Data Source
AI summary
An image projection optical unit includes a digital micromirror device and a prism optical system. The digital micromirror device is configured to drive micromirrors, which are subjected to ON/OFF control, with respect to two axes. The prism optical system is configured to emit, to an image projection side, ON light reflected at the micromirror in an ON state among emitted light the intensity of which has been modulated by the digital micromirror device. An optical path, which is configured to emit, to the image projection side in a direction different from the ON light, OFF light reflected at the micromirror in an OFF state among the emitted light the intensity of which has been modulated by the digital micromirror device, is secured in the prism optical system.