| 摘要 |
PURPOSE:To reduce an error in measurement due to axial deviation and to take a measurement with good reproducibility by using a grated filter which has the same core diameter with and maximum difference in specific refractive index smaller than a fiber to be measured as a mold filter. CONSTITUTION:A set of stepped fibers 7 and 9 and the grated fiber 8 operates as a mold scrambler and the grated fiber 10 is excited to have a constant mode distribution even if the light emission pattern of a light source 1 and the position relation between the light source 1 and fiber 7 change. The maximum specific refractive index difference of the fiber 10 is less than that of a fiber 2 to be measured, so the mode distribution that the fiber 2 is excited to have varies with the maximum specific refractive index difference of the fiber 10 and this value is set 0.28-0.53 time as large as the value of the fiber 2, thereby realizing an excitation mode distribution close to a stationary mode distribution. On the other hand, if there is axial deviation at the connection point of the fibers 2 and 10 in excitation, the excitation mode distribution varies, but its ratio decreases and the reproducibility of transmission characteristics is improved. |
