Asymmetric Mirror Tilting Axis for Projection Contrast
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Solution Overview
Problem
Existing spatial light modulators (SLMs) with digital mirror devices (DMDs) face challenges in achieving high contrast and spatial resolution due to issues with stray and diffracted light reaching the aperture, primarily caused by mirror tilting inefficiencies and variations in tilting angles.
Innovation Solution
A mirror system with tiltable mirrors arranged on a support surface, where each mirror has discrete tilting positions with asymmetrical angles relative to the center of gravity, utilizing stopper structures and actuation electrodes to control precise tilting and reduce diffraction, and incorporating a Blazed grating condition for mirrors in the OFF state to deflect light away from the aperture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mirror pitch is reduced to achieve fine pixel pitch and high spatial resolution, then spatial resolution is improved, but optical efficiency decreases and contrast deteriorates due to insufficient mirror tilting capability
Solution Approach 1:
The patent applies asymmetry by positioning the tilting axis below the center of gravity of each mirror rather than passing through it. This asymmetric placement creates different lever arms for the electrostatic forces, enabling greater tilting angles. The mirrors achieve sufficient tilting to redirect stray and diffracted light away from the aperture, thereby maintaining high contrast and optical efficiency while using small mirror pitch for high spatial resolution
2Area of stationary object
If mirror pitch is reduced to increase fill factor, then fill factor is improved, but contrast decreases due to difficulty in preventing stray light and diffracted light from reaching the aperture
Solution Approach 1:
The asymmetric tilting axis placement below the center of gravity enables mirrors to achieve larger tilting angles even with small mirror pitch. This allows mirrors in the OFF state to effectively redirect stray and diffracted light away from the aperture, preventing these harmful light components from degrading image contrast while maintaining high fill factor
Solution Approach 2:
The patent converts the potentially harmful stray light and diffracted light into beneficial redirected light by using the asymmetric tilting mechanism. The mirrors in the OFF state deflect these light components at angles that direct them away from the aperture and toward light absorbers, transforming what would be contrast-degrading elements into controlled light paths that do not interfere with image quality
3Object-affected harmful factors
If mirror tilting angle is increased to prevent stray light from reaching the aperture, then contrast is improved, but unwanted variations in tilting angles occur leading to additional contrast loss
Solution Approach 1:
The asymmetric tilting axis design creates a self-aligning mechanism where the electrostatic forces naturally converge toward the tilted position. The geometry of the electrode-mirror arrangement provides inherent stability that reduces sensitivity to manufacturing tolerances and electrical variations, enabling consistent tilting angles across all mirrors in the array without requiring complex active control mechanisms
Solution Approach 2:
The patent changes the geometric parameter of the tilting axis position from the conventional center-of-gravity location to a position below it. This parameter change fundamentally alters the force balance and torque characteristics, creating a more robust system where the tilting angle is less sensitive to variations in drive voltage and manufacturing tolerances, thereby improving reliability and consistency
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 enhances image contrast and spatial resolution by minimizing stray and diffracted light, achieving high contrast ratios and efficient tilting control while maintaining a high fill factor and small mirror pitch.
Implementation Method 1
each mirror in the first tilting position is arranged to reflect a light beam that is emitted from the light source onto the aperture; wherein each mirror in the second tilting position is arranged to reflect the light beam that is emitted from the light source away from the aperture
Implementation Method 2
a tilting axis of each of the plurality of mirrors passes through or lies below the center of gravity of the mirror
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
The invention relates to a mirror system (10) for a projection apparatus (60), wherein the projection apparatus (60) comprises a light source (61) and an aperture (62), wherein the mirror system (10) comprises a support surface (11); and a plurality of mirrors (12) arranged on the support surface (11); wherein each of the plurality of mirrors (12) is arranged tiltable between a first and a second tilting position, wherein the first and the second tilting position are discrete positions; wherein each mirror (12) in the first tilting position is arranged to reflect a light beam (63) that is emitted from the light source (61) onto the aperture (62); wherein each mirror (12) in the second tilting position is arranged to reflect the light beam (63) that is emitted from the light source (61) away from the aperture (62); wherein a tilting axis of each of the plurality of mirrors (12) passes through or lies below the center of gravity (C) of the mirror (12); and wherein the first and the second tilting position of each of the plurality of mirrors (12) are asymmetrical to each other, especially relative to an axis that is perpendicular to the support surface (11).