Numerical study of phase conjugation in stimulated Brillouin scattering from an optical waveguide

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Abstract
Phase conjugation in stimulated Brillouin scattering (SBS) from an optical waveguide is studied numerically, using a Cartesian two-dimensional propagation code (BOUNCE) that includes pump depletion. The simulations show that light scattered back through a phase aberrator produces a far-field profile closely matching that of the incident beam; however, the near-field intensity exhibits large and rapid spatial inhomogeneities across the entire aberrator, even for conjugation fidelities H as high as 98%. This effect can be only partially removed by spatial-filtering techniques. The dependence of H on SBS gain, scattering length L, and the average intensity Ī and angular divergence θD of the pump beam is first studied in the low-reflectivity regime (i.e., ignoring pump depletion). For amplitude gains ≳e10, H decreases monotonically with the factor Ī/θD that is due to a small-scale intensity pulling effect. This result appears to be independent of whether θD arises entirely from the aberrator or from a combination of the aberrator plus curvature introduced by a lens. In all cases, pump depletion is found to enhance the fidelity by inhibiting the small-scale pulling effect. Under appropriate conditions, this can actually reverse the intensity dependence of H seen in the absence of pump depletion.