Dynamic characteristics of a multi-wavelength Brillouin–Raman fiber laser assisted by multiple four-wave mixing processes in a ring cavity

• The n  th Stokes threshold is less than the (n−1)th(n−1)th Stokes saturation power for n≻3n≻3.
• The nth anti-Stokes power is about the (n+4)th Stokes power before threshold.
• A linear relation is found between the Stokes threshold reduction and the gain GOn−OffGOn−Off.
• The Stokes threshold powers of the MBRFL can be estimated by using the relation.

Dynamic characteristics of a multi-wavelength Brillouin–Raman fiber laser (MBRFL) assisted by four-wave mixing have been investigated through the development of Stokes and anti-Stokes lines under different combinations of Brillouin and Raman pump power levels and different Raman pumping schemes in a ring cavity. For a Stokes line of order higher than three, the threshold power was less than the saturation power of its last-order Stokes line. By increasing the Brillouin pump power, the nth order anti-Stokes and the (n+4)th order Stokes power levels were unexpectedly increased almost the same before the Stokes line threshold power. It was also found out that the SBS threshold reduction (SBSTR) depended linearly on the gain factor for the 1st and 2nd Stokes lines, as the first set. This relation for the 3rd and 4th Stokes lines as the second set, however, was almost linear with the same slope before SBSTR −6 dB, then, it approached to the linear relation in the first set when the gain factor was increased to 50 dB. Therefore, the threshold power levels of Stokes lines for a given Raman gain can be readily estimated only by knowing the threshold power levels in which there is no Raman amplification.