Optical Fiber Strain Gradient for SBS Suppression
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Solution Overview
Problem
Existing techniques for suppressing stimulated Brillouin scattering (SBS) in high-power optical fiber amplifiers are limited, as they require significant temperature or strain gradients that are impractical for long fibers, and current methods for applying strain are not feasible for high-power applications.
Innovation Solution
The application of a mechanical strain gradient to the optical fiber by embedding it in a deformable structure with a neutral axis, where the fiber is positioned at varying distances from the axis to create a compressive strain, combined with a temperature gradient to enhance SBS suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If temperature gradient is applied to broaden SBS linewidth, then SBS suppression is improved, but fiber temperature becomes impractical for high power applications
Solution Approach 1:
The patent replaces the thermal field approach (temperature gradient) with a mechanical field approach (strain gradient). Instead of using temperature to broaden the SBS linewidth, the invention applies mechanical strain through a deformable structure that imposes a strain gradient along the fiber length, achieving the same SBS suppression effect without the harmful thermal side effects.
Solution Approach 2:
The patent changes the physical parameter used for SBS suppression from temperature to strain. By deformable structure, a strain gradient is created along the fiber length, which broadens the SBS linewidth and suppresses SBS effects. This parameter substitution allows achieving the desired SBS suppression while avoiding the practical limitations of high fiber temperatures.
2Object-affected harmful factors
If large tensile strain is applied to broaden SBS linewidth, then SBS suppression is improved, but fiber degradation and reliability concerns increase
Solution Approach 1:
The patent inverts the conventional approach of applying tensile strain by instead applying compressive strain to the fiber. The deformable structure is designed to impose a compressive strain gradient along the fiber length, which broadens the SBS linewidth and suppresses SBS effects. This inversion from tensile to compressive strain eliminates the fiber degradation and reliability concerns associated with large tensile strains while maintaining the desired SBS suppression performance.
3Object-affected harmful factors
If standard SBS suppression technique is used to broaden laser bandwidth, then SBS gain is reduced below threshold, but compatibility with high power scaling techniques is lost
Solution Approach 1:
The patent changes the parameter used for SBS suppression from optical bandwidth to mechanical strain. Instead of broadening the laser bandwidth, the invention applies a strain gradient along the fiber length that broadens the SBS linewidth directly. This approach is compatible with narrowband laser signals and high power scaling techniques, as it does not require modifying the optical properties of the laser or the fiber's bandwidth characteristics.
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 broadens the SBS linewidth, reducing SBS effects in high-power optical fibers, allowing for efficient power transmission without fiber degradation, and is scalable for longer fibers handling high powers.
Implementation Method 1
SBS is a well known nonlinear phenomenon that affects various types of optical components, including optical fibers. SBS is often explained in terms of three waves that propagate in a fiber: an incident wave, an acoustic wave and a reflected wave
Implementation Method 2
Researchers in this field have observed a temperature induced enhancement of SBS resonance by a factor of approximately 2.5 for a temperature gradient of 100° C.
Implementation Method 3
Strain has been observed to affect the SBS resonance frequency by approximately 100 kHz/μE, where PE refers to 'microstrain' (i.e. a fractional change in length of 10−6)
Data Source
AI summary
A technique for suppressing stimulated Brillouin scattering (SBS) in fibers intended to handle high powers. A fiber is embedded in an elongated embedding material to form an embedded fiber structure. The embedded fiber structure is formed either as a cantilevered beam or as one or more turns around a circular or elliptical path, and then the entire structure is deformed to apply a desired strain that varies along the fiber length and results in suppression of SBS. In one embodiment, the embedded fiber structure is deformed by applying lateral and generally diametric force across the turns of the structure, resulting in changes to its curvature. In another embodiment the embedded fiber structure initially has a helical shape, which is deformed by stretching or twisting to change its radius. In either embodiment, a desired strain profile is obtained by selecting the position of the fiber with respect to a neutral axis.