Laser Beam Combining Optics for Speckle Reduction
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Solution Overview
Problem
Scanning laser projectors face the issue of speckle, a sparkling phenomenon caused by the spatial coherence of laser light, which interferes with the quality of the displayed image due to the reflection off diffuse surfaces.
Innovation Solution
The implementation of beam combining optics with speckle reduction, which splits and recombines laser beams to make them temporally incoherent, using non-polarizing and polarizing beam splitters, dichroic mirrors, and polarization rotation devices to create unequal optical path lengths and cross-polarize the beams, thereby reducing speckle patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If laser beams are combined to create an image, then image brightness and coherence are improved, but speckle patterns appear causing image quality to deteriorate
Solution Approach 1:
The patent divides the laser beam into multiple separate beams that travel through different optical paths with varying lengths. Each beam is independently manipulated through beam splitting and path differentiation, causing them to generate independent speckle patterns that do not correlate with each other, thereby reducing overall speckle visibility in the combined image
Solution Approach 2:
The patent introduces an additional dimension of optical path length variation to differentiate the laser beams. By creating unequal path lengths through various optical components, the beams acquire different temporal phases and spatial characteristics, which transforms the speckle reduction problem from a two-dimensional spatial interference issue into a three-dimensional problem involving time, space, and path length
2Object-affected harmful factors
If beam combining optics are used to reduce speckle, then image quality is improved, but device complexity increases
Solution Approach 1:
The patent designs optical components that serve multiple functions simultaneously. The beam combining optics not only combine multiple laser beams to maintain image brightness but also introduce unequal optical path lengths to reduce speckle. The polarization rotation devices and beam splitters perform both beam routing and speckle pattern differentiation, reducing the need for separate dedicated components for each function
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 approach achieves a maximum speckle reduction factor of √2, resulting in a 30% improvement in image quality by ensuring the speckle patterns are uncorrelated and non-interfering, leading to a clearer and more consistent image projection.
Implementation Method 1
beam combining optics with speckle reduction, which splits and recombines laser beams to make them temporally incoherent
Implementation Method 2
Laser light is spatially coherent, and when reflected off a diffuse surface, the reflected coherent light waves interfere with each other in a regular pattern that results in a user perceiving speckle
Implementation Method 3
polarization rotation devices to create unequal optical path lengths and cross-polarize the beams
Data Source
AI summary
A beam combining device combines laser beams and performs speckle reduction of the laser light. Two laser beams are incident on a non-polarizing beam splitter and combined beams are split into two light paths with different optical path lengths. The two light paths may have different geometric path lengths and/or different indices of refraction in the paths to produce the different optical path lengths. One of the light paths is passed through a polarization rotation device and then the two light paths are recombined with a polarizing beam splitter to produce a combined reduced speckle laser beam.