Digital Micromirror Device Speckle Reduction in Laser Projection
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Solution Overview
Problem
Coherent light sources, such as lasers, produce speckle noise when scattered by rough surfaces in projection display systems, which is objectionable to viewers and current speckle reduction techniques like acousto-optic deflectors and galvanometric mirrors have limitations in speed and aperture size.
Innovation Solution
A system and method using a digital micromirror device (DMD) to continuously steer coherent light beams with large optical apertures and wide steering angles, allowing for rapid movement and reduction of speckle noise, while also being cost-effective and reliable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If acousto-optic deflectors are used to steer coherent light beams for speckle reduction, then speckle reduction is achieved through high speed operation, but the aperture size is limited to small rectangular apertures
Solution Approach 1:
The patent replaces acousto-optic deflectors (acoustic field-based) and galvanometric mirrors (mechanical rotation-based) with a digital micromirror device that uses electronically controlled micromirror tilting. This substitution enables large aperture coverage while maintaining fast response times through electronic addressing of individual micromirrors, resolving the contradiction between aperture size and steering speed.
2Area of stationary object
If galvanometric mirrors are used to steer coherent light beams for speckle reduction, then various optical aperture sizes and wide steering angles are achieved, but the response time is slow with non-linear scan response
Solution Approach 1:
The patent divides the aperture into numerous independently controllable micromirrors arranged in an array. Each micromirror can be tilted independently and rapidly in response to digital control signals, enabling both large overall aperture coverage and fast local response times. This segmentation eliminates the mechanical inertia limitations of galvanometric mirrors while maintaining wide steering angles.
3Illumination intensity
If coherent light sources are used in projection display systems, then compactness, brightness, and energy efficiency are improved, but speckle noise is generated when light scatters off rough surfaces
Solution Approach 1:
The patent introduces dynamic control of the coherent light beam by rapidly tilting individual micromirrors in the array. This dynamic steering creates time-varying speckle patterns that average out over time, reducing the visibility of speckle noise while maintaining the brightness and efficiency benefits of coherent light sources. The system transitions from static to dynamic light modulation to eliminate the harmful speckle effect.
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 DMD-based approach effectively reduces speckle noise, is cost-effective, and provides high reliability due to its ability to operate with low drive power and mature support electronics, with fault tolerance from independent micromirror operation.
Implementation Method 1
a first digital micromirror device having a first plurality of micromirrors, optically coupled to the coherent light source and positioned in a light path of the coherent light source after the coherent light source
Implementation Method 2
A coherent light source, such as a laser, may be used to replace a wideband light (light that encompasses a wide range of wavelengths) source
Implementation Method 3
One such technique involves the use of an acousto-optic deflector to steer the coherent light beam using a radio frequency signal
Implementation Method 4
Galvanometric mirrors may also be used to reduce speckles by steering the phase-front of the coherent light beam
Data Source
AI summary
A system and method for reducing visible speckle in images displayed using coherent light. In an embodiment, a system for displaying images includes a light source to produce coherent light, an array of light modulators optically coupled to the light source and positioned in a light path of the light source after the light source, and a controller electronically coupled to the array of light modulators and to the light source. The light source includes a coherent light source, and a first digital micromirror device (DMD) having a first plurality of micromirrors. The first DMD is optically coupled to the coherent light source and positioned in a light path of the coherent light source after the coherent light source. The first DMD directs coherent light by moving the micromirrors of the first plurality of micromirrors through a first range of tilt angles substantially continuously.