FBG Wavelength Reflection in Double-Clad MMF for 910 nm Laser Diode

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SUMMARY

The discussion centers on the use of Fiber Bragg Gratings (FBGs) in double-clad multimode optical fibers, specifically with a 20 µm core diameter and a 910 nm laser diode. The participant, Gilbert, inquires whether an FBG reflects multiple guided modes or only a fixed wavelength, given that his FBG is designed for 99% reflection at the LP01 mode. The presence of additional guided modes (LP11, LP02, and LP21) raises questions about the FBG's behavior in this context. The need for resources to better understand FBG behavior in multimode fibers is also highlighted.

PREREQUISITES
  • Understanding of Fiber Bragg Gratings (FBGs)
  • Knowledge of multimode optical fibers and their guided modes
  • Familiarity with the concept of effective refractive index (neff)
  • Basic principles of laser diodes, specifically at 910 nm
NEXT STEPS
  • Research the principles of FBG operation in multimode fibers
  • Study the impact of guided modes on FBG reflection characteristics
  • Explore resources on effective refractive index calculations for multimode fibers
  • Investigate advanced texts or websites dedicated to optical fiber technology
USEFUL FOR

Optical engineers, fiber optic researchers, and professionals working with multimode fiber systems who seek to optimize FBG performance and understand guided mode interactions.

Gilbert
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Hi everyone!

I use a FBG in a double-clad multimode optical fiber of 20 µm core diameter, and a laser diode working at 910 nm as ligth source.

As the Bragg reflection wavelength of a FBG depends on the effective refractive index of the different guided modes (λFBG=2.neff.Λ , where Λ is the period), is it right to say that the FBG will reflect each of these modes? Or is a FBG only used to carry out reflection of a fixed wavelength, independantly of the modes?

Because in my case, the FBG has been designed to have a maximized reflection (99%) at 910 nm, which is the LP01 wavelength. But there are 3 other guided modes : LP11, LP02 and LP21.

Thanks in advance.

Gilbert.
 
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Edit : is there any book or website that could explain the behavior of FBG with multimode fiber ?