This article presents and analyzes an approximated exponential integrator for the (inhomogeneous) stochastic Manakov system. This system of SPDE occurs in the study of pulse propagation in randomly birefringent optical fibers. For a globally Lipschitz-continuous nonlinearity, we prove that the strong order of the time integrator is $ 1/2 $. This is then used to prove that the approximated exponential integrator has convergence order $ 1/2 $ in probability and almost sure order $ 1/2^{-} $, in the case of the cubic nonlinear coupling which is relevant in optical fibers. Finally, we present several numerical experiments in order to support our theoretical findings and to illustrate the efficiency of the approximated exponential integrator as well as a modified version of it.
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Figure 1. $ 3d $ space-time evolution (Figure 1a) and colormap (Figure 1b) of the intensity of the first component (left) and the second component (right) of the numerical solution to the stochastic Manakov system (1) with initial value (8) computed using the approximated exponential integrator (3). The discretization parameters are $ h = 3/625 $ and $ \Delta x = 1/4 $
Figure 2. Strong rates of convergence for the stochastic Manakov system (1) with initial value (8): Error $ {\mathbb E}\left[\left\lVert{X^N-X_{\text{ref}}(T)}\right\rVert_{ {\mathbb H}^1}^2\right] $ at the time $ T = 1 $ as a function of the time step $ h $ in loglog scale. The discretization parameters are $ h $ from $ 2^{-6} $ to $ 2^{-16} $ and $ \Delta x = 0.4 $
Figure 3. Efficiency of the time integrators for the stochastic Manakov system (1) with initial value (8): Computational time as a function of the averaged final error $ {\mathbb E}\left[\left\lVert{X^N-X_{\text{ref}}(T)}\right\rVert_{ {\mathbb L}^2}^2\right] $ at $ T = 0.5 $ over $ 500 $ samples (loglog scale). The discretization parameters are $ h $ from $ 2^{-9} $ to $ 2^{-17} $ and $ \Delta x = 0.2 $
Figure 5. Left: Evolution of the (squared) $ {\mathbb L}^2 $-norm along the numerical solutions of both exponential schemes applied to the stochastic Manakov system (1) with initial values (8). The discretization parameters are $ h = 0.006 $ and $ \Delta x = 0.25 $. Right: Strong rates of convergence for the stochastic Manakov system (1) with initial value (8): Error $ {\mathbb E}\left[\left\lVert{X^N-X_{\text{ref}}(T)}\right\rVert_{ {\mathbb H}^1}^2\right] $ at the time $ T = 1 $ as a function of the time step $ h $ in loglog scale. The discretization parameters are $ h $ from $ 2^{-6} $ to $ 2^{-16} $ and $ \Delta x = 0.4 $
Figure 6. Strong rate of convergence (left) and evolution of the (squared) $ {\mathbb L}^2 $-norm (right) of the approximated exponential scheme when applied to the inhomogeneous stochastic Manakov equation (9). The discretization parameters are $ h $ from $ 2^{-13} $ to $ 2^{-19} $ and $ \Delta x = 0.4 $ (left) and $ h = 0.006 $ and $ \Delta x = 0.25 $ (right)
Figure 7. Weak rates of convergence of three time integrators when applied to the inhomogeneous stochastic Manakov equation (9). The test functions are $ \phi_1(X) = \left\lVert{X_1}\right\rVert_{L^2} $ (left) and $ \phi_2(X) = \exp(-\left\lVert{X_2}\right\rVert_{L^2}^2) $ (right). The discretization parameters are $ h $ from $ 2^{-6} $ to $ 2^{-13} $ and $ \Delta x = 0.4 $
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Strong rates of convergence for the stochastic Manakov system (1) with initial value (8): Error
Efficiency of the time integrators for the stochastic Manakov system (1) with initial value (8): Computational time as a function of the averaged final error
Evolution of the (squared)
Left: Evolution of the (squared)
Strong rate of convergence (left) and evolution of the (squared)
Weak rates of convergence of three time integrators when applied to the inhomogeneous stochastic Manakov equation (9). The test functions are