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The nonlinear interaction between amplified spontaneous emission noise and copropagating signal in a dispersive optical fiber is investigated both theoretically and experimentally. A transfer matrix formulation is used to solve the nonlinear propagation equation. A continuous wave (CW) input optical signal format isolates the effect of modulation instability (MI) from the signal self-phase modulation. The change of the relative intensity noise (RIN) spectrum at an optical receiver caused by MI has been analyzed extensively in multispan optical amplified systems, and thus the impact of MI in the performance of intensity modulation and direct detection (IMDD) systems is evaluated. Performance of systems with distributed dispersion compensation (DC) and a lumped DC at the receiver are compared in terms of the effect of MI, the results show that the highest efficiency of DC to reduce the effect of MI can be achieved by putting a lumped DC module at the receiver side. Excellent agreement between theory and experiment demonstrates a good understanding of the mechanism of MI and its impact in the performance of terrestrial optical transmission systems.