FABRICATION AND CHARACTERIZATION OF BANDPASS-FILTERS BASED ON CONCATENATED CHIRPED FIBER GRATINGS

Practical, low-loss (<2 dB), fiber Bragg grating single-passband trans mission filters have been realized with >30 dB out of-band rejection o ver similar to 25 nm spectral widths. The approach adopted is based on the concatenation of two or more tailored broadband chirped gratings fabricated with low short-wavelength loss to maximize the rejection an d stopband width in a filter with similar to 1 nm passband. The effect of thermal aging for similar complex structures is considered in the context of three different fiber types: standard telecommunication, hi gh germania(Ge)-doped and boron/germania(B/Ge)-codoped. It is shown th at while hydrogenated B/Ge-codoped fiber exhibits excellent photosensi tivity, the resulting decrease in guiding strength and thermal stabili ty may make germania-doped fiber the more attractive choice.