Projection Optical System F-Number Optimization for DMD Diffraction Loss
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Solution Overview
Problem
High-definition digital micromirror devices suffer from significant light transfer loss due to diffraction effects, particularly when using laser light sources, as the smaller pixel pitches act as diffraction gratings, spreading reflected light and reducing efficiency, and existing solutions to mitigate this are not applicable to image projection apparatus where uniform imaging across a screen is required.
Innovation Solution
The image projection apparatus employs a configuration where the f-number of the projection optical system is set such that it captures the diffracted light closest to the mirror-reflected light, ensuring efficient energy transfer by fulfilling conditional formula FP≦1/(2·sin {sin−1[1/(2·FI)]+Δ}), where Δ represents the largest diffraction angle, thereby reducing light transfer loss and maintaining high-quality projection imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel pitch of the digital micromirror device is reduced to increase definition, then the imaging resolution is improved, but the diffraction effect increases causing light transfer efficiency to deteriorate
Solution Approach 1:
The patent changes the parameter of the projection optical system's f-number to optimize light collection. By setting the f-number to satisfy the conditional formula FP≦1/(2·sin{sin−1[1/(2·FI)]+Δ}), the system captures diffracted light more effectively, reducing energy loss while maintaining high-definition imaging with small pixel pitches
2Loss of energy
If the digital micromirror device is inclined at a large angle to suppress diffraction influence, then light transfer efficiency is improved, but proper imaging across the entire screen becomes difficult to achieve
Solution Approach 1:
Instead of changing the inclination angle of the digital micromirror device, the patent optimizes the f-number parameter of the projection optical system. This allows the system to capture diffracted light effectively without tilting the device, thereby maintaining proper imaging across the entire screen while reducing light transfer loss
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 reduces light transfer loss and ensures high-quality projection images by capturing the most concentrated diffracted light, even with high-definition digital micromirror devices, while maintaining a compact and cost-effective projection optical system design.
Implementation Method 1
A digital micromirror device has an image display surface composed of a plurality of minute mirrors; it controls the inclination of the individual mirror surfaces on the image display surface, thereby modulating the intensity of illumination light
Implementation Method 2
the smaller the pixel pitch, the more a digital micromirror device acts as a diffraction grating, and this spreads the reflected light to a degree commensurate with the diffraction angle
Data Source
AI summary
An image projector has a light source emitting blue, green, and red illumination light, a digital micromirror device forming blue, green, and red images, and a projection system enlarging the images, and fulfills the formula FP≦1/(2·sin {sin−1[1/(2·FI)]+Δ}), where, when mirror surfaces forming pixels are referred to as pixel surfaces, mirror-reflected light on the pixel surface along the illumination axis is referred to as mirror-reflected light, and angles between, of the diffracted light produced as a result of the rays along the illumination axis being diffracted, the part traveling in a direction closest to the mirror-reflected light and the normal line to the image display surface is defined as diffraction angles βB, βG, and βR, then Δ represents the largest of the angles βB, βG, and βR, FI represents f-number of illumination light, and FP represents f-number of projection system.