Bragg gratings in the germanium-doped concentric rings of a Yb 3+-doped core solid photonic bandgap fiber

The inscription of Bragg gratings into the germanium-phosphorous co-doped rings of a photonic bandgap fiber with a ytterbium-doped core is reported. These cladding layers are observed to exhibit interesting modal properties, with each ring supporting near-degenerate modes that agree well with numerical modeling. Besides fiber laser applications, there are several potential sensing applications of gratings in such a fiber. © 2006 IEEE.