Fiber Laser Stabilization via Asymmetric FBG Wavelengths
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Solution Overview
Problem
The existing fiber laser devices experience unstable output intensity due to modulation instability caused by anomalous dispersion properties of Fiber Bragg Gratings (FBGs), which affect the refractive index and lead to significant changes in laser light output with slight changes in input light.
Innovation Solution
A fiber laser device is designed with a first FBG having a high reflectance and a second FBG with lower reflectance, where the Bragg wavelength of the second FBG is on the short wavelength side of the first FBG, preventing modulation instability by ensuring normal dispersion and stabilizing the output intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two FBGs have the same Bragg wavelength to enable light resonance, then laser light output is achieved, but the output intensity becomes unstable due to anomalous dispersion and modulation instability
Solution Approach 1:
The patent applies asymmetry by setting different Bragg wavelengths for the first and second FBGs. Specifically, the Bragg wavelength of the second FBG is set to be shorter than that of the first FBG, creating an asymmetric configuration that eliminates the resonance condition causing modulation instability while maintaining laser output functionality
Solution Approach 2:
The patent changes the wavelength parameter of the FBGs to resolve the contradiction. By adjusting the Bragg wavelength of the second FBG to be shorter than the first FBG's Bragg wavelength, the system transitions from a symmetric resonance configuration to an asymmetric non-resonance configuration, thereby suppressing modulation instability and stabilizing output intensity
2Stability of the object's composition
If light with wavelength shifted from Bragg wavelength is reflected by FBGs, then dispersion occurs, but this causes anomalous dispersion leading to modulation instability
Solution Approach 1:
The asymmetric Bragg wavelength configuration prevents light with wavelengths shifted from the Bragg wavelength from being reflected by both FBGs in a way that causes anomalous dispersion. The wavelength mismatch between the two FBGs ensures that the dispersion characteristics are controlled and remain in the normal dispersion regime
Solution Approach 2:
By changing the Bragg wavelength parameter of the second FBG to be shorter than that of the first FBG, the patent controls the dispersion characteristics of the system. This parameter adjustment ensures that the refractive index changes remain stable and prevent anomalous dispersion from occurring
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 configuration stabilizes the intensity of the laser light output by preventing modulation instability, ensuring consistent laser light production.
Implementation Method 1
light reflected by one or both of the FBGs includes not only light having a wavelength same as Bragg wavelength of the FBGs but also light having a wavelength slightly shifted from the Bragg wavelength
Implementation Method 2
the FBGs causes normal dispersion on the short length side from the Bragg wavelength of the FBGs since the refractive index becomes larger on a light having a shorter wavelength, while causing anomalous dispersion on the long length side from the center wavelength of the FBGs
Implementation Method 3
light emitted from the rare earth-doped fiber is reflected by one of FBGs (Fiber Bragg Grating) formed on both sides of the rare earth-doped fiber. The light that is reflected is again input to the rare earth-doped fiber and amplified
Implementation Method 4
a time required for reflection is minimum when light has a wavelength same as the Bragg wavelength of the FBGs means that the refractive index of the FBGs is minimum when light input to the FBGs has the wavelength same as the Bragg wavelength of the FBGs, while the refractive index of the FBGs becomes larger as the wavelength is shifted farther away from Bragg wavelength of the FBGs
Data Source
AI summary
[Object] An object of the invention is to provide a fiber laser device capable of stabilizing intensity of laser light output therefrom.[Means to attain the object] A fiber laser device 100 includes: an pumping light source 11 configured to output pumping light; a rare earth-doped fiber 20 to which the pumping light is input; and a first FBG 30 formed on one side of the rare earth-doped fiber 20 and a second FBG 40 formed on the other side of the rare earth-doped fiber 20 that are configured to reflect light amplified in the rare earth-doped fiber 20, wherein the second FBG 40 has a reflectance lower than that of the first FBG 30, a reflection wavelength band in that of the first FBG 30, and Bragg wavelength on short wavelength side of Bragg wavelength of the first FBG 30.