| 摘要 |
An optical fiber preform, and method for fabricating, having a first core, a second core spaced from the first core and first and second regions, the first region having an outer perimeter having a first substantially straight length and the second region having an outer perimeter having a second substantially straight length facing the first straight length. One of the regions can comprise the first core and the other comprises the second core. The preform can be drawn with rotation to provide a fiber wherein a first core of the fiber is multimode at a selected wavelength of operation and a second core of the fiber is spaced from and winds around the first core and has a selected longitudinal pitch. The second core of the fiber can couple to a higher order mode of the first core and increase the attenuation thereof relative to the fundamental mode of the first core.
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