= Solution
Different transverse <normal modes> have different cutoff <frequencies> and <group velocities>. A pulse exciting several of them reaches the output in delayed modal components, causing <intermodal dispersion>, pulse distortion and overlap of successive signals. Their <interference> also makes the transverse <wave intensity> pattern depend on propagation distance; irregularities can transfer <energy> between modes.
Mitigations are to operate between the first and second <cutoff frequencies of a membrane waveguide>, excite only the desired <mode shape> with a suitable source, and use smooth uniform boundaries or gradual transitions to reduce mode conversion. Reducing the signal bandwidth keeps its spectrum inside the single-mode interval and reduces <group velocity dispersion> within the selected mode. Single-mode operation removes <intermodal dispersion> but does not remove the dispersion derived in part (b).
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