Patterned Metasurfaces for VCSEL Speckle Reduction
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Solution Overview
Problem
Coherent laser light from VCSELs causes speckle interference when illuminating rough surfaces, leading to inaccurate image processing due to random patterns of varying signal intensity, which existing technologies fail to effectively suppress.
Innovation Solution
The use of metasurfaces to introduce angular diversity, wavelength diversity, and temporal diversity in illumination by replicating light sources, diffusing wavelengths, and creating spatial incoherence through patterned nanostructures and optical elements, such as diffraction gratings and patterned metasurfaces, to reduce speckle contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If coherent laser light from VCSELs is used to illuminate rough surfaces, then high illumination intensity and narrow bandwidth are achieved, but speckle interference patterns with large signal intensity variations occur
Solution Approach 1:
The VCSEL array is divided into multiple independent VCSELs, each emitting coherent light. By spatially separating the illumination sources across the aperture, the system maintains high illumination intensity while reducing the coherence area, thereby suppressing speckle interference patterns and improving measurement precision.
2Reliability
If a single VCSEL array is used for illumination, then narrow bandwidth and high coherence are maintained, but wavelength diversity is insufficient leading to speckle formation
Solution Approach 1:
Different regions of the VCSEL array are assigned different local optical properties through the use of a diffractive optical element. Each region contributes to the overall illumination with slightly different wavelength characteristics, providing local wavelength diversity while maintaining overall system coherence and reliability.
3Device complexity
If direct illumination from VCSEL array is used, then simple optical path is maintained, but angular diversity is insufficient causing speckle interference
Solution Approach 1:
A diffractive optical element is introduced as an intermediary between the VCSEL array and the illumination target. This element modifies the angular distribution of light without significantly increasing optical path complexity, thereby enhancing angular diversity and suppressing speckle interference to improve image processing accuracy.
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 described solution significantly reduces speckle contrast and improves image processing accuracy by increasing angular and wavelength diversity, ensuring more uniform and coherent illumination, thereby enhancing the performance of machine vision systems.
Implementation Method 1
A suitable optical element for functioning as a metasurface comprises a diffusing element that is robust to both placement and assembly error and that forms an ensemble metasurface. These forms of diversity are referred to herein as angular diversity, wavelength diversity, polarization diversity, and temporal diversity.
Implementation Method 2
After having undergone total internal reflection within the light bar and after having interacted with the patterned metasurface, the light exits the light bar and propagates toward the object.
Implementation Method 3
Because of its low cost, narrow output beam, narrow bandwidth, and high levels of illumination, a commonly used device for such illumination a vertical-cavity surface-emitting laser, or 'VCSEL.' Like most lasers, a VCSEL outputs coherent light.
Implementation Method 4
In another aspect, the invention features a metasurface-enabled design diversifies the output wavelengths of VCSELs in a single VCSEL array individually, thereby increasing wavelength diversity.
Data Source
AI summary
An apparatus that relies on patterned metasurfaces to reduce speckle when illuminating an object with coherent light. The metasurfaces serve to increase one or more of angle diversity and wavelength diversity resulting from illumination by a coherent source.