The stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) threshold powers in passive small mode area optical fibers (SMAFs) and large mode area optical fibers (LMAFs) are determined from a distributed light scattering model. The model employs the pump and Stokes rate equations together with the equivalent thermal Brillouin and Raman noise powers to provide a numerical solution for the evolution of the pump and Stokes powers along the fiber length without approximation and is applicable in the non-depleted and depleted pump regimes. A simple transcendental equation for the threshold powers is obtained in the non-depleted pump, low fiber loss regime that is of similar form to the standard threshold relations first derived by Smith: P_th=κA_eff/gL_eff where Pth is the threshold power, g is the non-linear gain coefficient and Leff is the fiber effective interaction length. The numerical coefficient κ=ln(P_S/P_N) is found to be a weak function of the Stokes power P_S and the thermal noise power PN and differs for the two types of fibers due to the differing order-of-magnitude Stokes powers and noise powers. It is found that the SRS threshold power of the LMAF exceeds that first derived by Smith by 1.7 dB and that the SBS threshold power in the SMAF is 1.2 dB less than that derived by Smith. The SRS threshold in SMAF and the SBS threshold in the LMAF are in agreement to within <1.0 dB with the Smith relations. The transcendental approximation is useful for estimating the threshold powers in all fibers at any pump power and pump-to-Stokes conversion efficiency η<0.1. It is found that the Smith relations do not apply to the pump-depletion regime although they are defined for conversion efficiencies η of 0.5 and 1.0.

Date Published: 15 February 2012
PDF: 9 pages
Proc. SPIE 8237, Fiber Lasers IX: Technology, Systems, and Applications, 82371A (15 February 2012); doi: 10.1117/12.906824

Published in SPIE Proceedings Vol. 8237:
Fiber Lasers IX: Technology, Systems, and Applications
Eric C. Honea; Sami T. Hendow, Editor(s)