Fibre-optic Raman amplifier of signals at the 1.3 μm wavelength, pumped by a Cr4+ : forsterite crystal laser

A report is given of the experimental results of an investigation of the parameters of a fibre-optic Raman amplifier pumped by radiation from a highly stable laser with a forsterite (Mg₂SiO₄) crystal doped with Cr⁴⁺ ions. The nonabsorbed part of the pump radiation was returned to an active fibre waveguide by a fibre Bragg grating in order to increase the amplifier efficiency. A high measurement precision was ensured by a system for stabilisation of the pump power coupled into the active fibre. When the pump power was 800 mW and the noise factor was 4 dB, the gain was 30 dB; when the gain was 15 dB, the gain saturation power – expressed in terms of the output signal —was 15 dBm.