Fabrication of high-reflectivity superimposed multiple-fiber Bragg gratings with unequal wavelength spacing

We report the inscription of as many as 10 superimposed Bragg gratings of high reflectivity in a 25-mm segment of fiber. Using hydrogenated boron codoped and germanosilicate fibers, we inscribed 10 superimposed gratings with reflectivities above 80% and 6 superimposed gratings with reflectivities above 98%, respectively. The superimposed gratings had unequal wavelength spacing and were written over a 20-nm wavelength span in the region of 1530 nm. The inscription of each new grating caused an increase in the FWHM linewidth of the existing gratings, while their reflectivity was unaffected.