Patent ID: 6914669

Claim:
A method for determining a cause of defect in an unused optical fiber comprising: measuring, from both ends of said optical fiber, backscattering-light-strengths S(λ 1 ,z) and S(λ 2 ,z) of said optical fiber for two wavelengths λ 1 and λ 2 , where λ 1 <λ 2 ; calculating an amount of change in a backscattering-light-collect-coefficient I(λ 1 ,z) and I(λ 2 ,z ) for said two wavelengths λ 1 and λ 2 ; comparing said amount of change in a backscattering-light-collect-coefficient I(λ 1 ,z) and I(λ 2 ,z) for said two wavelengths λ 1 and λ 2 to determine whether said amount of change satisfies a predetermined relationship; and determining said cause of defect in said optical fiber according to said comparison.