DMD Tilt Angle Optimization for Laser Projection Diffraction
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Solution Overview
Problem
Image projection apparatuses using digital micromirror devices (DMDs) face degradation in transmission efficiency due to diffraction effects, leading to reduced brightness and contrast of projected images, especially with laser light sources where the narrow wavelength range exacerbates diffraction issues.
Innovation Solution
The apparatus is configured with a digital micromirror device that satisfies specific conditional expressions for diffraction angles and tilt angles of the mirrors, ensuring that even-order diffracted light beams align closer to the specular reflection direction, while odd-order beams are dispersed, thereby reducing diffraction-induced degradation. This is achieved by setting the pixel pitch, tilt angle, and incidence angle to align even-order diffracted light closer to the specular reflection direction than odd-order beams, using a discharge lamp or laser light source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a DMD is tilted by a predetermined angle (e.g., 5°) with respect to the optical axis of the projection lens to reduce diffraction effects, then light transmission efficiency is improved, but blurring occurs in the periphery of the projected image
Solution Approach 1:
The patent applies parameter changes by optimizing the tilt angle of the DMD within a specific range (0° ≤ θ ≤ 10°) and adjusting the incidence angle of illumination light (15° ≤ α ≤ 30°) to balance diffraction reduction with image quality maintenance. This resolves the contradiction by finding optimal parameter values that prevent both excessive diffraction and peripheral blurring.
2Manufacturing precision
If the DMD is used without tilting to maintain image sharpness, then manufacturing precision is improved, but diffraction degrades light transmission efficiency
Solution Approach 1:
The patent changes the operational parameters by introducing a controlled tilt angle range (0° ≤ θ ≤ 10°) and specific illumination incidence angles (15° ≤ α ≤ 30°) that optimize the balance between maintaining image sharpness and reducing diffraction-induced energy loss, thereby resolving the contradiction between these two parameters.
3Illumination intensity
If a laser light source is used to improve brightness, then illumination intensity is improved, but diffraction effects are exacerbated due to narrow wavelength range
Solution Approach 1:
The patent addresses this contradiction by optimizing the DMD tilt angle and illumination incidence angle parameters specifically for laser light sources with narrow wavelength ranges. By setting the tilt angle θ within 0° ≤ θ ≤ 10° and incidence angle α within 15° ≤ α ≤ 30°, the patent minimizes diffraction effects while maintaining the high brightness advantage of laser illumination.
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 significantly reduces the degradation of image light transmission efficiency, resulting in brighter and more satisfactory image projections by concentrating energy from even-order diffracted light and dispersing odd-order light away from the specular reflection direction.
Implementation Method 1
illumination light is reflected in a state in which the mirror-pixels of the DMD are tilted by a predetermined angle, and thereby, ON-light is outputted as image light
Implementation Method 2
the surface of the DMD includes unevenness resulting from the surfaces of the individual mirrors, and this unevenness functions as a blazed diffraction grating
Data Source
AI summary
Assuming that a normal line of an image display surface of a DMD is a normal line Ax of the image display surface, that a direction in which a light beam specularly reflected by a mirror is outputted is a specular reflection direction R, and that an angle that the specular reflection direction R forms with respect to the normal line Ax of the image display surface is denoted by γ, an image projection apparatus satisfies the following conditional expression: β(2·k−1)≧2·γ−β(2·k)≧β(2·k+1), where β(2·k−1) and β(2·k+1) represent a diffraction angle of an odd-order diffracted light, and β(2·k) represents a diffraction angle of an even-order diffracted light.