Abstract
Since the excellent proposal of a dual-wavelength pumping scheme by Kasamatsu et al., 1 the gain-shifted Tm-doped fiber amplifiers (GS-TDFA) attract a great interest, because they can utilize the wavelength region between the C-band Er-doped fiber amplifier (EDFA) and the conventional S+band TDFA. The development of S-band amplifiers is important because few other amplifiers can operate in this unexplored gap of the low-loss window. The key principle of this pumping scheme is the use of an auxiliary pumping laser at 1.56 µm to control the population inversion factor between the initial 3H4 and the terminal 3F4 level, in addition to the main pumping laser source at 1.05 µm or 1.4 µm, which is used for the excited state absorption (ESA).1 The comparison of the 1.05 µm-pumping and 1.4 µm-pumping was discussed in terms of the power conversion efficiency and the noise figure performances.2,3 The spectral properties and upconversion characteristics of Tm-doped glasses are well studied4,5 also by using tunable lasers.6,7 The spectroscopic tunability of rare earth doped glasses is based on the inhomogeneous broadening and the Stark splitting of 4f-electronic levels. It is known that the absorption to the first-excited 3F4 level shows a broad band at around 1.7 µm, which is longer than the wavelength of the auxiliary pump of the previous dual-wavelength-pumped GS-TDFA.1–3 The absorption coefficient of the Tm3+: 3F4 ← 3H6 transition in a fluoride glass increases rapidly from 1.55 µm to 1.65 µm.6 This fact suggests much improved pumping efficiency by L-band lasers, which has a longer wavelength than 1.56 µm. In this study, the gain characteristics of a TDF were investigated with a 1051 nm-laser and a tunable L-band source to investigate the optimization of dual-wavelength pumping scheme.
© 2002 Optical Society of America
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