Beam Expander Using Composite Waveguide for Speckle Reduction
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Solution Overview
Problem
Existing beam expanders face challenges in achieving high homogeneity and coherency of laser beams while maintaining a miniaturized size, efficient energy use, and reducing speckle contrast, especially when dealing with coherent laser beams and non-collimated outputs.
Innovation Solution
A beam expander comprising a composite waveguide with dichroic coatings and multiple waveguide elements, which splits and mixes collimated incident beams into multiple wavefronts through total internal reflection, achieving a desired cross-sectional shape and homogeneity with reduced speckle contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a microlens array is used for beam homogenization, then beam homogeneity is improved, but coherency is lost and speckle suppression is insufficient
Solution Approach 1:
The beam is divided into multiple wavefronts using a wavefront division element, which segments the incident coherent beam into several separate wavefronts. This segmentation allows subsequent mixing of the wavefronts to achieve homogeneity while maintaining the coherent nature of the original beam, unlike microlens arrays that destroy coherence.
Solution Approach 2:
A wavefront mixing element is introduced as an intermediary component between the wavefront division element and the output. This intermediary mixes the divided wavefronts through controlled interference and superposition, achieving intensity homogenization without the random phase disruptions caused by microlens arrays, thus preserving beam coherency.
2Volume of moving object
If a beam expander is miniaturized, then device size is reduced, but beam homogeneity and cross-section control become difficult
Solution Approach 1:
The patent transitions from traditional two-dimensional beam manipulation to three-dimensional wavefront control. By using volume Bragg gratings and wavefront mixing in the third dimension (depth), the system achieves compact miniaturization while maintaining precise control over beam homogeneity and cross-sectional shape that would be difficult in planar configurations.
Solution Approach 2:
The beam expander employs composite optical structures combining different functional elements (wavefront division element, volume Bragg gratings, wavefront mixing element) in an integrated compact design. This composite approach enables simultaneous achievement of miniaturization and high beam quality control within a reduced device volume.
3Use of energy by moving object
If coherent laser beams are used, then beam efficiency is improved, but speckle patterns are generated
Solution Approach 1:
The coherent laser beam is segmented into multiple wavefronts with different optical paths. When these wavefronts are mixed at the output, their interference patterns create averaged intensity distributions that suppress speckle while maintaining the high efficiency of coherent light sources.
Solution Approach 2:
The patent converts the harmful speckle effect into a beneficial homogenization mechanism. By deliberately controlling the interference of multiple wavefronts through the wavefront mixing element, the random speckle patterns are replaced with controlled interference that produces uniform intensity distribution, transforming the harmful interference effect into a useful homogenization tool.
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 enhances beam homogeneity and reduces speckle contrast, maintaining coherency and collimation, and allows for the same output effect as using multiple light sources without adjustments, while also miniaturizing the beam expander size.
Implementation Method 1
the plurality of wavefronts are mixed by total internal reflection in the composite waveguide
Implementation Method 2
the plurality of wavefronts are mixed by total internal reflection in the composite waveguide
Data Source
AI summary
There is provided a beam expander including a first optical element, a second optical element, a composite waveguide including a plurality of waveguide elements, and a dichroic coating provided between the plurality of waveguide elements. The first optical element inputs a collimated incident beam from the outside into the composite waveguide, and the second optical element outputs, from the composite waveguide, collimated incident beam, input to the composite waveguide, wherein the collimated incident beam input into the composite waveguide is divided into multiple wavefronts by the dichroic coating, and the multiple wavefronts are mixed by total internal reflection in the composite waveguide. When the beam expander is used, coherency and collimation of an output beam may be maintained and speckles may be reduced or eliminated while improving the efficiency of an optical system.