| 摘要 |
PURPOSE:To reduce the shift of a cut-off wavelength, by inserting a polarization maintaining optical fiber between a polarizer for linearily polarizing light and an optical fiber to be measured and allowing the linearily polarized light to be incident to said polarized wave holding optical fiber in matching relation to the double refraction axis of said fiber. CONSTITUTION:The wavelength of a wavelength variable light source 1 is determined so that the mode propagating through an optical fiber 6 to be measured is brought to a single mode state. When the polarizing direction of a polarizer 4 and the double refraction of a polarization maintaining optical fiber 14 are taken on an X-axis in this state, a LP01 mode is cut off by an analyser 7. When the wavelength of the wavelength variable light source 1 is successively changed to the side of a short wavelength, the mode propagating through the optical fiber 6 to be measured changes from the single mode state to two modes. The LP01 mode is cut off by the analyser 7 but a LP11 mode is not cut off by the analyser 7 but detected by a light detector 10. |
