| 摘要 |
PROBLEM TO BE SOLVED: To obtain a reflecting light with a required loss with respect to an incident light by reducing the insertion loss of a variable attenuator. SOLUTION: Zero dispersion fibers 9A, 9B of different spot sizes are connected to an input and an output of a variable attenuator 10 which can vary the attenuation amount at a predetermined step distance, so that the difference of level of back scattering lights when an optical pulse is inputted becomes larger than the insertion loss of the variable attenuator 10. The spot size is larger at the input side than at the output side of the variable attenuator 10. The 1.3μm zero dispersion fiber 9A is connected to the input side of the variable attenuator 10, and the 1.55μm zero dispersion fiber 9B is connected to the output side of the variable attenuator 10.
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