Recently, stimulated Brillouin scattering in a forward direction (FSBS) in a dual-mode single-core optical fiber was reported for the first time. Frequency shifts on the order of 17 MHz were seen in fiber supporting LP01 and LP11 modes at 514.5 nm. The phenomenon is examined here in more detail, and the governing differential equations of the three-wave parametric process (involving laser pump, Brillouin signal, and acoustic flexural-wave phonon) are derived and solved. FSBS is possible because although the overlap integral between a flexural fiber mode and the light is small, the phonon lifetime is much longer than in conventional SBS. FSBS may also be the first example of a nonlinear effect which is enhanced by increasing the optical mode area at constant pump power
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