Speckle Reduction via Multi-Stage Coherence Control
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Solution Overview
Problem
Coherent radiation sources, such as lasers, suffer from speckle interference patterns caused by reflection or transmission from rough surfaces, which affect measurement accuracy and require effective reduction or elimination.
Innovation Solution
A series arrangement of coherence-reducing components, comprising arrays of transparent elements that split and recombine light beams to traverse different optical lengths, significantly reducing the coherence level of the output beam and minimizing speckle effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If coherent light is used for illumination, then high brightness and directionality are achieved, but speckle interference patterns are generated that reduce measurement accuracy
Solution Approach 1:
The patent segments the coherent light beam into multiple sub-beams by passing it through an array of transparent elements (prisms, lenses, or flat plates). Each element creates a separate sub-beam that traverses a different optical path length, effectively dividing the original beam into incoherent components that reduce speckle when recombined.
Solution Approach 2:
The patent introduces an additional dimension by varying the optical path length of each sub-beam through different element thicknesses or configurations. This dimensional variation in optical path length causes phase differences between sub-beams, transforming the coherent beam into an incoherent superposition that eliminates speckle patterns.
2Object-affected harmful factors
If optical elements are added to reduce coherence, then speckle is reduced, but device complexity increases
Solution Approach 1:
The patent merges multiple transparent optical elements into a single integrated array structure. These elements can be cemented or optically coupled together to form one compact component, reducing the number of separate optical elements and simplifying alignment while maintaining the coherence-reducing function.
Solution Approach 2:
The transparent elements in the array serve multiple functions simultaneously: they divide the beam into sub-beams, introduce different optical path lengths, and can be designed with anti-reflective coatings to minimize losses. This multi-functionality reduces the need for additional separate components.
3Reliability
If multiple transparent elements with different optical lengths are used, then coherence is significantly reduced, but energy loss increases
Solution Approach 1:
The patent optimizes the optical path length differences between elements to be sufficient for coherence reduction (exceeding the coherence length of the light source) while minimizing the total number of elements. By carefully selecting thickness variations and refractive indices, the patent achieves effective decoherence with minimal energy loss through absorption or scattering.
Solution Approach 2:
The patent uses transparent materials with high transmission properties (low absorption) and designs the element geometry to minimize scattering losses. The elements are optimized to provide just sufficient optical path differences for decoherence without excessive thickness that would increase energy loss.
4Object-affected harmful factors
If an array of transparent elements is introduced, then speckle is reduced through multiple optical paths, but alignment difficulty increases
Solution Approach 1:
The patent combines multiple transparent elements into a single integrated array where elements are cemented or optically coupled together. This merging eliminates the need for precise alignment between separate elements during operation, as they function as a unified component with fixed relative positions.
Solution Approach 2:
The patent designs each transparent element with specific local properties (thickness, shape, material) that are optimized for its position in the array. This local optimization ensures that each element contributes appropriately to the overall decoherence function while maintaining ease of assembly and alignment for the entire array.
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 effectively reduces speckle by generating a large number of incoherent sub-beams with minimal energy loss and no damage to apparatus components, preserving beam collimation and polarization, and simplifying optical alignment.
Implementation Method 1
The first elements receive different respective first portions of a light beam incident on the first component, cause the first portions to traverse at least two different optical lengths generated by the first elements
Implementation Method 2
Coherent light scattered by reflection or transmission from a rough surface forms an interference pattern in the space away from the rough surface
Data Source
AI summary
Apparatus for reducing speckle, including a first coherence-reducing component, having a first array of transparent first elements arranged to receive different, respective first portions of a collimated light beam that is incident on the first component, the first elements generating different, respective optical lengths with respect to the light beam passing therethrough and outputting the respective first portions as respective first collimated sub-beams. The apparatus further includes a second coherence-reducing component, having a second array of transparent second elements arranged to receive different, respective second portions of each of the first collimated sub-beams of the light beam, the second elements generating different, respective optical lengths with respect to the light beam passing therethrough and outputting the respective second portions as respective second collimated sub-beams. The apparatus also includes a light combiner, which is arranged to combine the second collimated sub-beams into a collimated output beam.