| Abstract: | We used the Modified Chemical Vapor Deposition (MCVD) method to fabricate a B/Ge codoped fiber with a depressed cladding in which boron and germanium were also doped, the depressed cladding was photosensitive, which can greatly suppress the cladding mode coupling. The transmission spectrum of written grating in this fiber made by the phase mask method verified its larger photosensitivity and great suppression of the cladding mode coupling. We then analyzed the Bragg wavelength tuning theory in the phase mask method in detail which gave us a more exact equation. The ultra-violet (UV) exposure system was modified, and eight cascaded Fiber Bragg Gratings (FBG) centered at different wavelengths were written in this photosensitive fiber successfully using a 248 nm KrF excimer laser and one piece of 1067 nm phase mask. Each channel spacing was 100 GH according to the Densed Wavelength Division Multiplexing (DWDM) standards of the International Telecommunication Union (ITU-T). At the same time, we also wrote in chirp in each grating by tilting the phase mask to realize dispersion compensation. The dispersion in 44 km SMF was successfully compensated by the cascaded chirped gratings in the eight channel WDM system with each channel being 10 Gbit/s. |
