Fiber Bragg Grating Filter for Stokes Light and Cladding Heat
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-power fiber laser systems generate Stokes light due to stimulated Raman scattering, leading to increased power density and potential damage to optical fiber sheaths, as reflected signal light can become cladding-mode light and cause local heat generation.
Innovation Solution
A filter device comprising an optical fiber, a higher-order mode filter, and a fiber Bragg grating that transmits predetermined wavelengths while reflecting longer wavelengths, inhibiting higher-order mode light from propagating and reducing the likelihood of cladding-mode light formation, thereby preventing local heat generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a fiber laser apparatus increases light power to achieve high optical power density, then beam quality and processing capability improve, but Stokes light generation increases causing energy loss and potential damage to optical fiber sheath
Solution Approach 1:
The patent converts the harmful Stokes light into a useful function by using it as the pump light source for a dye laser. The Stokes light that would normally represent energy loss is instead utilized to excite the dye laser medium, generating laser output at a different wavelength. This transforms the parasitic Raman scattering effect into a beneficial dual-wavelength laser system.
Solution Approach 2:
The patent introduces a dye laser medium as an intermediary between the fiber laser and the final laser output. The Stokes light from the fiber laser serves as pump light for the dye laser medium, which then generates laser output. This intermediary converts the harmful Stokes light at one wavelength into useful laser radiation at another wavelength, preventing direct damage while utilizing the energy.
2Reliability
If a fiber laser apparatus uses a fiber Bragg grating to reflect Stokes light, then Stokes light removal is achieved, but signal light is reflected at a specific angle exceeding numerical aperture causing cladding-mode light and local heat generation
Solution Approach 1:
The patent applies local quality by using a tapered fiber section with gradually varying diameter. The taper creates a gradual transition zone where mode transformation occurs progressively rather than abruptly. This localized gradual change allows signal light to transform from core modes to cladding modes without sudden angular reflection, preventing localized heat generation while still achieving Stokes light suppression through the FBG.
Solution Approach 2:
The patent performs preliminary action by transforming the propagation modes of signal light before they reach the fiber Bragg grating. The tapered fiber section pre-conditiones the light by converting higher-order core modes into cladding modes gradually, so that when the light reaches the FBG, the signal light does not undergo abrupt angular reflection that would cause local heating. The mode transformation is prepared in advance to avoid harmful effects at the FBG interface.
3Quantity of substance
If a fiber Bragg grating reflects light at a specific angle to remove Stokes light, then wavelength separation is achieved, but signal light exceeding numerical aperture propagates in cladding causing energy loss
Solution Approach 1:
The patent changes the physical parameter of the fiber diameter along its length by using a tapered structure. This gradual parameter change transforms the optical modes progressively, allowing signal light to transition from core-confined modes to cladding-propagating modes without abrupt angular deviation. The continuous parameter change in the taper profile enables smooth mode transformation that preserves energy while achieving wavelength separation at the FBG.
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 filter device effectively inhibits the power of higher-order mode light, reducing the risk of cladding-mode light and subsequent local heat generation, even when reflected light exceeds the numerical aperture of the core, thus improving beam quality and preventing damage to the optical fiber sheath.
Implementation Method 1
a fiber Bragg grating (FBG) that transmits the light having the predetermined wavelength and reflects light having a particular wavelength longer than the predetermined wavelength
Implementation Method 2
a higher-order mode filter that removes at least part of the light in any higher order mode than a predetermined mode in the light in the multimode propagating in the optical fiber
Implementation Method 3
an optical fiber that allows light having a predetermined wavelength to propagate in multimode
Implementation Method 4
the power of light emitted from fiber laser systems has increased, an increase in the power density of light that propagates in an optical fiber is likely to cause Stokes light due to stimulated Raman scattering (SRS)
Data Source
AI summary
A filter device includes: an optical fiber that allows light having a predetermined wavelength to propagate in multimode; a first higher-order mode filter that removes at least part of the light in any higher order mode than a predetermined mode in the light in the multimode propagating in the optical fiber; and a fiber Bragg grating that transmits the light having the predetermined wavelength and reflects light having a particular wavelength longer than the predetermined wavelength.