Bragg gratings in the germanium-doped concentric rings of an Yb3+- doped core solid photonic bandgap fibre

International audienceWe demonstrate the inscription of Bragg gratings in each of the three, concentric, germanium-doped rings of an ytterbium-doped-core photonic-bandgap fibre. These rings can support several modes and the effective indices of these modes are derived experimentally from the grating peaks. They are found to be in excellent agreement with numerical simulation