Inscription of Bragg gratings in nanostructured graded index single-mode fibers

We report on efficient inscription of fiber Bragg gratings (FBGs) in a new type of single mode fiber with nanostructured core and with an effective parabolic graded index profile, using the standard phase mask method and a 248 nm pulsed laser. A nanostructured core allows to obtain high concentration of GeO₂ in subwavelength glass rods and simultaneously to maintain low average germanium dopant level of silica similarly to standard single mode fibers. We showed that in a nanostructured core fiber, a factor of 3 better efficiency in gratings inscription was achieved, although the fiber has 20% lower average concentration of GeO₂ with respect to SMF-28. In the nanostructured fiber we obtained a significant improvement in temperature sensitivity, while the strain sensitivity of FBG in nGRIN optical fiber is the same as in case of standard single-mode fiber (SMF-28). We have measured the strain sensitivity of 0.72 × 10^-6 1/με (1.11 pm/με@1.53μm), and the temperature sensitivity is about 30% higher than for FBG in SMF-28 and equals to 10.2 × 10^-6 1/K (15.6 pm/K@1.53μm).