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Using selective mode excitation via the cladding of an etched step-index weakly multimode fibre, and spatial mode separation at the output using a similarly etched section, intermodal coupling has been measured, mode-by-mode in the first seven guided modes of the fibre. Experimentally the observation has been made that most coupling terms remain less than −20dB after 500 m of fibre.
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Stuart Shaklan (1990) studied this question.
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