3. Experimental Setup
Fig. 1 shows the free-running experimental setup used to obtain the value of the Raman gain
coefficient of the optical fibers under test. A 1064 nm CW fiber laser (FL) pumps a fiber and at its
end an optical spectrum analyzer (OSA) is recording changes in the emission lines when the pump
power is varied. A power meter (PM) measures the average power of the output signal. S1 stands
for a splice between the fiber laser and the fiber under test.
With this experimental configuration the pump level was gradually increased to find the PF0, and
critical power. When the pumping power is released, instantaneously spontaneous Raman
scattering occurs. The pump increases and the energy transfer to the signal Stokes starts, we stop
pumping until finding the Raman threshold.