Twisted Fiber Mode Scrambler for Stable Light Distribution
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Solution Overview
Problem
Existing mode scramblers for stabilizing outgoing light from a light source, particularly in step index multimode fibers, face challenges in reproducing a steady mode distribution equivalent to long-distance propagation and suffer from significant light loss due to stress-induced dispersion and varying mode distributions with wound diameter and incident light characteristics.
Innovation Solution
A mode scrambler with a twisted fiber structure, where the fiber is wound around bobbins that rotate in opposing directions, generating a twisted portion that attenuates higher-order modes without reducing the bending radius, allowing for stable mode distribution output by adjusting the number of rotations and turns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If microbending is generated by pressurizing a fiber core wire to enable attenuation of higher-order mode distribution, then mode distribution can be controlled, but light leaks out of the fiber causing large loss
Solution Approach 1:
The fiber is divided into distinct sections: an incident light receiving section, a twisted section with controlled twist pitch, and an outgoing light emitting section. This segmentation allows mode scattering to occur only in the twisted section while maintaining light confinement in the core, preventing light leakage and reducing loss.
Solution Approach 2:
The twisted structure is applied locally to a specific section of the fiber rather than the entire fiber. The twist pitch is carefully controlled to be within a specific range (0.1 to 10 times the fiber diameter) to achieve mode scattering only in the twisted section, maintaining core light confinement and preventing excessive loss.
2Adaptability or versatility
If the fiber is continuously wound in the same direction to create mode scattering, then mode distribution changes, but the mode distribution varies depending on wound diameter and incident light characteristics making it difficult to output stable steady mode distribution
Solution Approach 1:
The twist pitch is controlled within a specific parameter range (0.1 to 10 times the fiber diameter) to achieve stable mode scattering. This parameter control ensures that the mode distribution becomes independent of incident light characteristics and wound diameter, producing a stable steady mode distribution.
3Adaptability or versatility
If stress acts on the fiber to disperse mode distribution, then mode scattering occurs, but the steady mode distribution equivalent to long distance propagation is not reproduced
Solution Approach 1:
A twisted structure with a specific twist pitch is introduced to create controlled curvature in the fiber. This curvature causes mode scattering that accurately reproduces the steady mode distribution equivalent to long-distance propagation, unlike simple stress application which does not achieve the same effect.
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 enables stable mode distribution output with reduced attenuation and light loss, reproducing long-distance propagation characteristics, and allows for easy switching between mode distributions, including higher-order modes, at a low cost and with improved versatility for various fiber types.
Implementation Method 1
dispersion of the mode distribution occurs in the twisted portion of the fiber
Implementation Method 2
the mode scrambler includes a support structure and a cylindrical sleeve that work in tandem to maintain the predetermined spiral curvature of the helical mode scrambler
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
Provided is a low-loss mode scrambler in which a steady mode distribution can be obtained in a short distance and switch to an entire mode distribution state is easy even when incident light is smaller than a numerical aperture of a fiber to be measured in a multimode fiber having a core diameter exceeding several tens of µm and a numerical aperture of 0.2 or more. One fiber 2 is wound around a plurality of bobbins 3a and 3b having a radius larger than a minimum bending radius of the fiber to form a bundle, and the fiber 2 is twisted by rotating the bobbins 3a and 3b to form a twisted portion 5, whereby it is possible to perform output of a steady mode from light incident on the fiber 2.