Gain characteristics of ER/sup 3+/ doped fiber with a quasi-confined structure

The fiber-structure dependence of the gain characteristics of Er/sup 3+/ doped fibers pumped at 1.48 mu m is analyzed. The optimum V value is derived theoretically and experimentally. For step-index fibers, the optimum V value is 1.6, which is smaller than that needed to minimize spot size. The fiber with a small V value enjoys a large Er/sup 3+/ confinement effect. For laser diode pumping, an efficiency of 1.7 dB/mW is achieved at 1.536 mu m. The bending characteristics are also described.<
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