| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical fiber grating which is increased the confinement index of light power by increasing the ratio of the light power propagating in a core, can be easily produced, and can be handled in the same manner as for ordinary light. SOLUTION: The constitution of the optical fiber has the core having the max. refractive index n1 in the central part, has a first clad having a refractive index n2 on the outer side thereof and, further, has a second clad having a refractive index n3 on the outer side thereof. The respective refractive indices are n1 >n3 >n2 . The normalization frequency V expressed by V=2πa/λx(n1 <2> -n2 <2> )<1/2> when a core radius is (a) and a use wavelength isλis >=2.405. The refractive index n3 of the second clad in the optical fiber constitution described above is made larger than the effective refractive index N2 of a secondary mode and is made smaller than the effective refractive index N1 of a base mode, by which the loss of a short wavelength band is suppressed. |
