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 H-2-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. H-2-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 degrees C. (C) 2009 Optical Society of America