Fiber Bragg grating inscription in pure-silica and Ge-doped photonic crystal fibers

We report on fiber Bragg gratings (FBGs) inscribed in pure-silica and Ge-doped photonic crystal fibers (PCFs) with a two-beam interference technique and a femtosecond or excimer laser. Such a technique enables the inscription of FBGs for different Bragg wavelengths with high flexibility. Effects of H2-loading and Ge doping on the efficiency of grating inscription were investigated by measuring the development of Bragg wavelength and attenuation in the transmission spectra with an increased exposure dose. H2-loading dramatically enhances the laser-induced index modulation not only in Ge-doped PCFs but also in pure-silica PCFs. We observed a reversible Bragg wavelength shift during femtosecond pulse irradiation, which indicates an internal temperature rise of approximately 77 °C.