| 摘要 |
PROBLEM TO BE SOLVED: To obtain an optical fiber having a large effective core area, low loss, small absolute value of dispersion and small bending loss susceptibility by controlling the difference in the propagation constant between the lowest mode and the second-order mode to be twice or more of the difference in the propagation constant between adjacent modes of higher-order modes. SOLUTION: The distribution structure of the refractive index is designed in such a manner that when light signal enters, three or more modes of linearly polarized waves are present as the propagation modes. In this state, the difference in the propagation constant between LP01 mode and LP11 mode is specified to be twice or more, preferably three times or more, of the difference in the propagation constant of the LP11 mode or higher-order mode and the adjacent higher mode. As a result, this structure enables such an arrangement of modes that only the LP11 mode or higher-order modes are coupled to the crack mode and that only the LP01 mode substantially propagates after the light propagates at a proper distance. If the difference is less than twice, proper attenuation for only the higher-order modes is impossible and a single mode transmission is made difficult. |
