| 摘要 |
PURPOSE:To measure a cut-off wavelength by arranging a polarizer to at least one of the input and output terminals of a single mode optical fiber. CONSTITUTION:A polarizer 10 is provided between a monochrometer 3 and the input terminal of an optical fiber 1. A fundamental mode LP01 and a tertiary mode LP02 are linear polarization and, in a secondary mode LP11, degeneracy is released in the vicinity of a cut-off wavelength and said mode LP11 is not linear polarization. The excitation of the secondary mode is removed by inserting the plarizer 10 and the cut-off wavelength of the tertiary mode to the fundamental mode is measured. A wavelength of difference is drawn using a waveform (b) in a case inserting no polarizer 10 and a wavelength (a) in a case inserting the polarizer 10 to know the cut-off wavelength lambdac only of the secondary mode. By this constitution, the effect of other modes is removed to make it possible to perform measurement with high accuracy. When a detector is also provided on an emitting side in parallel to an incident side, the extinction ratio of the fundamental mode and the tertiary mode can be increased. |
