Slanted Fiber Grating Filter for Backreflected Raman Signal Isolation

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Powerful laser systems used for metal welding and cutting face reliability issues due to backreflected parasitic signals from internal and external obstacles, which can damage fiber components despite existing filtering mechanisms not being sufficient to prevent damage.

Innovation Solution

Incorporating a filtering element in the core of a single mode fiber downstream from a fiber gain block to couple out backreflected Raman components into the cladding, using slanted fiber gratings or refractive index formations to block the propagation of unwanted signals, and employing a combination of single mode and low-mode fibers to isolate the Raman signals from the main signal.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If filtering elements are added to block backreflected Raman signals, then reliability of fiber components is improved, but device complexity increases

Engineering Contradiction:

Improvereliability of fiber componentsVSAvoiddevice complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

A wavelength-selective filtering element is introduced as an intermediary component between the gain block and upstream fiber components. This filter selectively blocks backreflected Raman signals while allowing the main laser wavelength to pass through, thereby protecting fiber components without requiring fundamental system redesign

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The filtering element exploits the wavelength parameter difference between the main laser signal and backreflected Raman signals. By tuning the filter's rejection bandwidth to target specific Raman wavelength shifts, the system selectively attenuates harmful signals while maintaining useful signal transmission

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the power of backreflected light is increased, then the effectiveness of blocking harmful signals is improved, but the risk of destroying fiber components increases

Engineering Contradiction:

Improveprotection effectivenessVSAvoiddamage to fiber components

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The filtering element converts the harmful backreflected Raman signals into a manageable parameter by selectively attenuating them at their specific wavelengths. This transforms the uncontrolled harmful reflection into a filtered signal that can be safely managed within the system

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The filter applies selective attenuation only to specific wavelength bands corresponding to Raman signals, while leaving the main laser wavelength unaffected. This localized filtering approach protects against harmful signals without compromising the overall laser output power and quality

Inventive Principle:

Principle #3Local quality

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

Effectively prevents damage to upstream fiber components by filtering out backreflected Raman signals, ensuring the reliability and longevity of the laser system by maintaining safe power levels within the system.

Implementation Method 1

backreflected parasitic signals reflected from internal and external obstacles... backreflected Raman signals... nonlinear effects associated with powerful laser systems... stimulated Raman scattering—an optical process that involves light radiation at a wavelength(s) longer than the main light signal

Methodology Applied

Scientific EffectRaman scattering:

Implementation Method 2

filtering element is configured to couple out the backreflected Raman component from the core into the cladding of the SM fiber

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Implementation Method 3

The filtering element may include one or more slanted fiber gratings... wavelength-selective filtering unit for filtering undesirable Raman wavelengths

Methodology Applied

Scientific EffectBragg diffraction: Bragg Diffraction

Data Source

PatentUS7912099B2Method and apparatus for preventing distortion of powerful fiber-laser systems by backreflected signals

Publication Date: 2011.03.22 IPG PHOTONICS CORP

AI summary

A powerful fiber laser system is configured with at least one filtering element capable of preventing a backreflected Raman component of the main signal from propagating along the upstream stretch of the system. The filtering element includes a slanted fiber grating, one or more cladding formations disposed in a cladding of fiber and having a refractive index greater than that one of the cladding, but lower than a refractive index of the core, and/or a combination of two spaced apart single mode fibers and a low mode fiber spliced to the opposing ends of the respective SM fibers.