Under certain conditions a changing speckle pattern exists at the output plane of a multimode fiber, resulting in modal noise which can degrade the error performance of a fiber data link. Fiber motion is the usual cause of such speckle change, and Daino et al. have studied the first-order statistics of such modal noise, assuming a single frequency source. But source frequency variation can also cause modal noise; and source frequency diversity has been shown effective in its reduction. In this paper we use a speckle theory approach to study the frequency dependence of modal noise. We have measured and analyzed the correlation of two speckle patterns as a function of source frequency difference, and the speckle spatial frequency distribution as a function of fiber parameters. We have also measured the speckle contrast as a function of fiber length for several sources and fiber types. Such information permits the prediction of the modal noise statistics, from which corresponding changes in error rates can be derived.
© 1980 Optical Society of America
Eric G. Rawson, Joseph W. Goodman, and Robert E. Norton, "Frequency dependence of modal noise in multimode optical fibers," J. Opt. Soc. Am. 70, 968-976 (1980)