Laser Line Generation Using Beam Sweep for Speckle Reduction
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Solution Overview
Problem
Speckle patterns in laser line projectors limit the precision of 3D imaging systems due to the lumpy and asymmetric irregularity of the received line light, leading to errors in height measurements, and existing speckle reduction techniques are mechanically complex, costly, or deteriorate the quality of the line profile.
Innovation Solution
A coherent light beam moves laterally across a stationary linear diffuser, such as an engineered diffuser or hologram, using a moving mirror structure like a MEMS mirror or AOM, to generate a planar fan of diffused light with rapid phase changes, reducing speckle contrast by averaging uncorrelated patterns within exposure times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a moving diffuser is placed within the path of a stationary beam to reduce speckle, then speckle reduction is achieved, but the beam quality deteriorates and mechanical complexity increases
Solution Approach 1:
Instead of moving the diffuser as in conventional approaches, this patent moves the laser beam source laterally across a stationary linear diffuser. This inversion of the moving component resolves the technical contradiction by eliminating the need for a heavy moving diffuser while still achieving speckle reduction through temporal averaging of uncorrelated speckle patterns.
Solution Approach 2:
The patent replaces the mechanical moving diffuser system with a lateral beam movement system using optical deflectors or galvanometer mirrors. This substitution reduces mechanical complexity and mass while achieving the same speckle reduction effect through faster beam positioning.
2Reliability
If a moving diffuser is used to reduce speckle, then speckle patterns are averaged, but the frame rate is limited and beam quality deteriorates
Solution Approach 1:
By moving the lightweight beam source laterally across the stationary diffuser rather than moving the heavy diffuser, the system achieves faster modulation speeds. This allows the beam to sweep across multiple diffuser features within a single camera exposure, enabling higher frame rates while maintaining speckle reduction.
Solution Approach 2:
The system uses dynamic beam positioning with galvanometer mirrors or acousto-optic deflectors to rapidly sweep the beam laterally across the diffuser during each camera exposure. This dynamic movement creates temporal averaging of speckle patterns without limiting the frame rate, as the beam can be repositioned faster than traditional mechanical diffusers could be moved.
3Reliability
If conventional speckle reduction techniques are applied, then speckle is reduced, but cost and complexity increase
Solution Approach 1:
The system uses the camera's own exposure time to capture multiple uncorrelated speckle patterns as the beam sweeps across the diffuser. This self-service approach leverages existing system components (camera exposure, beam deflection) to achieve speckle reduction without adding expensive specialized hardware like moving diffusers or complex optical trains.
Solution Approach 2:
The patent employs a simple linear diffuser with a specific scattering angle that is stationary and low-cost. Combined with the lateral beam movement, this creates an effective speckle reduction system that is more economical than conventional approaches requiring expensive moving diffusers or complex optical assemblies.
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 allows for high-quality, speckle-free illumination lines with reduced mechanical complexity and cost, enhancing the accuracy of 3D imaging systems by averaging speckle patterns effectively.
Implementation Method 1
a linear diffuser positioned in an optical path between an illumination target and the light source, the linear diffuser being configured to diffuse the coherent light into diffused light that spreads in one dimension
Implementation Method 2
a beam deflector positioned between the light source and the linear diffuser on the optical path; wherein the controller is configured to operate the beam deflector to direct the coherent light incident on the beam deflector to sweep across different locations
Data Source
AI summary
An illumination apparatus for reducing speckle effect in light reflected off an illumination target includes a laser; a linear diffuser positioned in an optical path between an illumination target and the laser to diffuse collimated laser light in a planar fan of diffused light that spreads in one dimension across at least a portion of the illumination target; and a beam deflector to direct the collimated laser light incident on the beam deflector to sweep across different locations on the linear diffuser within an exposure time for illumination of the illumination target by the diffused light. The different locations span a distance across the linear diffuser that provides sufficient uncorrelated speckle patterns, at an image sensor, in light reflected from an intersection of the planar fan of light with the illumination target to add incoherently when imaged by the image sensor within the exposure time.