Rotating Optical Plate Despeckling for Laser Projection
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Solution Overview
Problem
Laser projection systems face significant challenges in reducing speckle artifacts, which degrade image quality due to the high coherence of laser light, leading to shimmer effects and reduced resolution, with existing solutions often causing additional image resolution loss.
Innovation Solution
A despeckling device with a rotating optical element, such as a tilted optical plate, is positioned between the projection lens and the display surface to increase angular diversity and temporally average speckle patterns, reducing speckle visibility while minimizing image dither and maintaining image resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a rotating optical element is used to increase angular diversity and reduce speckle visibility, then speckle contrast is reduced, but image resolution may be degraded due to image dither
Solution Approach 1:
The patent applies the dynamics principle by implementing a rotating optical element (such as a rotating diffuser or rotating wedge prism) that continuously changes the angular orientation of the projected light beam. This dynamic rotation creates temporal averaging of speckle patterns while the rotation speed is carefully controlled to remain below the threshold that causes perceptible image dither, thus reducing speckle visibility while maintaining image resolution
Solution Approach 2:
The patent applies periodic action by using the rotating optical element to periodically modulate the light path at a frequency that creates multiple uncorrelated speckle patterns over time. The rotation period is designed so that the temporal averaging occurs at a rate sufficient to reduce speckle contrast, while the periodic nature of the rotation ensures consistent speckle reduction without introducing chaotic image movement that would degrade resolution
2Object-affected harmful factors
If screen vibration is used to reduce speckle visibility through temporal averaging, then speckle contrast is reduced, but variations in screen tension and position cause inconsistent speckle reduction quality
Solution Approach 1:
The patent applies the taking out principle by extracting the vibration function from the screen itself and relocating it to a dedicated optical element (such as a vibrating diffuser or rotating component) positioned in the light path between the projector and screen. This separation allows the speckle reduction mechanism to operate independently of screen tension variations, ensuring consistent speckle reduction quality regardless of screen mounting conditions
Solution Approach 2:
The patent applies the intermediary principle by introducing a vibrating or rotating optical element as a mediator between the projected light and the screen surface. This intermediary component performs the temporal averaging function in the light path itself, creating speckle reduction that is independent of screen properties and positioning, thereby ensuring reliable and consistent speckle contrast reduction
3Object-affected harmful factors
If axial vibration of a mirror is used to increase spatial diversity and reduce speckle, then speckle visibility is reduced, but image dither is created that reduces image resolution
Solution Approach 1:
The patent applies parameter changes by carefully controlling the amplitude and frequency parameters of the optical element's rotation or vibration. The rotation speed is set to a specific range that provides sufficient angular diversity for speckle reduction while remaining below the threshold that creates perceptible image dither. This precise parameter optimization allows speckle visibility reduction while maintaining image resolution
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 effectively reduces speckle contrast and visibility, enhancing image quality by increasing angular diversity and temporal averaging of speckle patterns without significant loss in image resolution or introducing additional optical aberrations.
Implementation Method 1
The deflector subsystem includes an optical element that is rotatable about the optical axis to temporally and angularly deflect the convergent light beam through angular orientations toward the location on the target surface
Implementation Method 2
An example of the optical element is an optical plate that can be rotated by a motor or other actuator about an axis to deflect, angularly and temporally, a beam of light that is incident to the inner surface and that emerges from the outer surface and directed to a given location on a display surface
Data Source
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AI summary
Speckle artifacts as viewed in images projected on a display surface by a projector can be reduced. At least one spatial light modulator, illuminated by one or more light sources, can be imaged to a screen by a projection lens. A deflector subsystem can be provided in image space, proximate to the lens, where the image light emerges. In this location, image light directed to any given field point on the display surface is convergent, but can appear collimated. The deflector subsystem can include a tilted optical plate that is rotated in a plane along an axis. As the deflector subsystem is temporally rotated, the image light to any given field point traverses different optical paths, varying the angular diversity to reduce perceivable speckle by changing at least the angle of incidence to the screen.