| 摘要 |
PROBLEM TO BE SOLVED: To provide a multimode (MM) fiber which allows substantially excitation of a fundamental mode only and has high nonlinearity.SOLUTION: An MM fiber has a step refractive-index profile configured with a dip positioned at the center of a core 12 and includes, along the length thereof, an end region 36 at each end, frustoconically shaped transformer regions 39 that run inwards from the respective end regions 36, and a central region 38 that bridges the transformer regions 39. Width of the dip is relatively small at the end regions 36 such that only a fundamental mode with a Gaussian profile is supported. As the dip becomes larger along the input-side transformer region 39, the Gaussian profile is gradually transformed into a ring profile of the fundamental mode and is guided along the central region 38 of the MM core. The dip gradually becomes smaller along the output-side transformer region 39 such that the ring profile is substantially transformed back into the Gaussian profile of the fundamental mode to be radiated from the output-side end region 36 of the MM core. |
