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

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The discussion focuses on the use of a Fiber Bragg Grating (FBG) in a double-clad multimode optical fiber with a core diameter of 20 µm and a 910 nm laser diode. It raises the question of whether the FBG can reflect multiple guided modes or if it is limited to a specific wavelength. The FBG is designed for maximum reflection at 910 nm, corresponding to the LP01 mode, while other modes such as LP11, LP02, and LP21 are also present. The inquiry seeks clarification on the behavior of FBGs with multimode fibers and requests resources for further understanding. Overall, the discussion highlights the complexities of FBG reflection in multimode fiber applications.
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 ?
 

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