2017 , Volume 22, № 6, p.98-103

This work addresses the following goals and objectives: 1) theoretical calculation of the spectrum of amplified spontaneous emission (ASE) for the active ytterbium fiber at different pump wavelengths and different lengths of the active fiber; 2) experimental determination of the ASE and comparison with the theoretical spectrum; 3) finding of the optimal length of active fiber from the intensity of the amplified spontaneous emission spectrum at the signal wavelength; 4) experimental verification of the results.

The numerical solution of the systems of velocity equations by the fourth-order Runge-Kutta method is given in the paper. The calculation was based on a two-level model of the fiber amplifier. The calculation was performed simultaneously for several wavelengths of ASE in the range from 910 to 1150 nm in 0.5 nm steps. Parameters of the active fiber under study are the following: core diameter is 6 µ m, clad diameter is 125 µ m, doping concentrations in active core is N = 8 . 5 · 1025 m3. The study was carried out for the 915 and 975 nm pump wavelengths, and active fiber lengths of 16 and 20 m.

The spectra of ASE were obtained as a result of the calculation. These spectra were well matched with the experimentally spectra, both from the spectral range of the ASE, either from the position of the main maxima. Also, the change of the shape of the theoretical ASE spectra with increasing length of the active fiber, was consistent with the experimental results. It was shown that the gain increases as the length of the active fiber changes from 16 to 20 m for the amplification at 1062 nm, as predicted theoretically.