| 摘要 |
The present invention provides an optical fiber equipped with a grating that functions as a narrow-band loss filter. The optical fiber has a core, an inner cladding, an intermediate cladding, and an outer cladding, which have refractive indexes n0, n1, n2, and n3, respectively, the refractive indexes having a relationship of n0>n3>=n1n2. At least a part of the inner cladding has a grating. The refractive index of the intermediate cladding is lower than the refractive indexes of the inner cladding and the outer cladding such that a recession is formed in the refractive index profile of the clad. The grating is provided on the inner side relative to the recession.
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