Dynamic effects of the stimulated brillouin scattering in fibers due to acoustic diffraction

The influence of acoustic-wave diffraction on nonstationary backward stimulated Brillouin scattering (SBS) in the presence of feedback for a Stokes electromagnetic wave is numerically investigated. The cases of an acoustic-waveguide and -antiwaveguide fibers are considered. The Kerr nonlinearity is taken into account. For fibers with a small core radius (r0<3 µm), the influence of sound diffraction on the nonstationary SBS can lead to new features. The importance of the acoustic-mode structure of the fiber for the process of forming a pulse train is shown in the case of synchronous pumping in Brillouin fiber lasers. It has been found that the acoustic-antiwaveguide fibers with a small core, r0<3 µm, can be preferable for obtaining a stable train of compressed pulses. Under a constant input pump, an acoustic diffraction can essentially reduce the threshold of the modulation instability under SBS in the presence of the feedback.