Changes in transmission characteristics caused by an outer layer have been investigated for graded-index fibers. Equations have been derived using the WKB method for calculating baseband frequency response and excess loss in a general type of the graded-index fiber. Numerical examples have been given for a square-law fiber, mainly with cladding thickness and index difference between outer layer and cladding as parameters. Measurement of the excess loss has been carried out for fibers with various cladding thickness and outer layer-cladding index differences. The measured loss is in agreement with the theoretical value.
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