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.