Fluorescence and superfluorescence line narrowing and tunability of Nd3+ doped fibers

The inhomogeneous behavior of the 1.06 μm-neodymium transitions in doped optical fibers have been investigated, using the fluorescence line narrowing technique, pumping on the ⁴F_3/2 and ⁴F_5/2 sublevels at 4 K. Each observed transition has been identified. As the pump wavelength varies, the shift of the main fluorescence line is 40 nm, with the two pumping levels. We have studied the spectral behavior of the superfluorescence as a function of the pump wavelength, the temperature, and the absorbed power. The spectral evolution depends on λ_p with 19 nm-tuning range at low temperature. At 300 K, the quasihomogeneous behavior of the transition decreases the tunability to 14 nm. Based on these results, we present a simple technique permitting precise prediction of gain and spectral line shapes of superfluorescent Nd-doped fiber sources