| 摘要 |
Disclosed is a fiber optic filter that includes a central core, a ring core concentric with the central core, an inner cladding region of refractive index ni between the central and ring cores, and a cladding layer of refractive index nc surrounding the ring core. The maximum refractive index n1 of the central core and the maximum refractive index n2 of the ring core are greater than nc and ni. The propagation constants of one core mode and one ring mode are different at wavelengths except for at least one wavelength lambd0 whereby power transfers between the two cores at lambd0. At least a portion of the fiber optic filter fiber is wound around a reel to subject it to a continuous curvature, the radius of which determines the amplitude of the attenuation. Such fibers are useful in fiber amplifiers in which the central core contains active dopant ions.
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