Blazed Grating Mirror System for Projection Contrast
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Solution Overview
Problem
Spatial light modulators with digital mirror devices face challenges in achieving high contrast images due to stray and diffracted light from mirrors in the OFF state reaching the aperture, particularly when trying to maintain small mirror pitch and high fill factor, which affects optical efficiency and color contrast.
Innovation Solution
A mirror system where mirrors in the OFF state form a Blazed grating, efficiently focusing diffraction orders away from the aperture, maximizing diffraction efficiency for the Blazed order and reducing unwanted diffraction light, while mirrors in the ON state focus light efficiently onto the aperture, enhancing contrast for all primary colors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If mirror pitch is reduced to achieve fine pixel pitch and high fill factor, then spatial resolution is improved, but optical efficiency decreases and contrast deteriorates due to increased stray light and diffraction
Solution Approach 1:
The patent applies local quality by differentiating the functional properties of mirrors in different states: ON-mirrors are optimized for reflecting light onto the aperture with high efficiency, while OFF-mirrors are specifically designed to form a blazed grating that directs diffracted light away from the aperture. This localized functional differentiation allows the system to maintain high fill factor and fine pixel pitch while minimizing the harmful effects of stray light and diffraction from OFF-mirrors.
Solution Approach 2:
The patent utilizes parameter changes by adjusting the tilting angle of OFF-mirrors to satisfy the blazed condition for specific diffraction orders. By changing the orientation parameter of OFF-mirrors to a specific angle that creates constructive interference in desired directions and destructive interference toward the aperture, the system maximizes diffraction efficiency away from the aperture while maintaining high contrast and optical efficiency.
2Manufacturing precision
If fill factor is increased to achieve high spatial resolution, then pixel density is improved, but contrast decreases due to difficulty in preventing stray light from reaching the aperture
Solution Approach 1:
The patent converts the harmful effect of diffraction from OFF-mirrors into a beneficial effect by designing OFF-mirrors to form a blazed grating. Instead of allowing diffraction to occur in random directions and create stray light that degrades contrast, the controlled diffraction from the blazed grating directs light into specific diffraction orders that are steered away from the aperture. This transforms the previously harmful diffraction phenomenon into a useful mechanism for enhancing contrast while maintaining high fill factor.
3Illumination intensity
If mirror array density is increased to achieve wide color gamut and high resolution, then image quality is improved, but optical efficiency decreases due to increased diffraction losses
Solution Approach 1:
The patent optimizes optical efficiency by changing the orientation parameter of OFF-mirrors to satisfy the blazed condition. This parameter adjustment ensures that diffraction orders are concentrated in specific directions away from the aperture, maximizing the efficiency of light redirection. By carefully selecting the tilting angle to match the blazed condition for the given geometry and wavelength range, the system achieves high optical efficiency across the visible spectrum, supporting wide color gamut while minimizing energy loss from stray light.
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 high spatial resolution and contrast images by effectively managing light reflection and diffraction, reducing stray light and improving color contrast across red, green, and blue channels.
Implementation Method 1
at least some of the mirrors that are arranged in the second tilting position form a Blazed grating for the light beam, wherein the angle at which the light beam is reflected off the at least some of the mirrors in the second tilting corresponds to a Blaze angle of the Blazed grating
Implementation Method 2
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
Data Source
Figure 1
Figure 2a~2b
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 to be tiltable between a first and a second tilting position, wherein the first and the second tilting positions 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) towards 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), and wherein at least some of the mirrors (12) that are arranged in the second tilting position form a blazed grating for the light beam (63), wherein the angle at which the light beam (63) is reflected off the at least some of the mirrors (12) in the second tilting position corresponds to a blaze angle of the blazed grating.