Realization of periodic transmission filter based on a pair of cascaded long-period fibre gratings of different strength/wavelength position

► Inscription of long-period fibre gratings (LPFGs) in Ge/B-codoped fibre. ► Realization of Mach-Zehnder interferometer using fs UV recording of cascaded LPFGs. ► Comb filter based on a pair of LPFGs with different strength and peak position. ► Strong non-uniformity of photosensitivity along the axis of Ge/B-codoped fibre.