Patent ID: 6519026
Filing Date: 2003-02-11
Classification: G01M

Abstract:
An optical time-domain reflectometer having a light source means for launching a test light pulse into a test fiber carrying traffic signals, and means for measuring, as a function of time after the launching of the test light pulse, the test signal back-scatter from the test fiber, wherein the improvement comprises said means for measuring including means for offsetting the test signal back-scatter so as to compensate for Raman non-linearities present in the test fiber which Raman non-linearities extract energy from the traffic signals and amplify the test signal back-scatter, wherein the offsetting of the test signal back-scatter is made on the basis of the Raman gain G present over the length of the test fiber, and the Raman gain G is calculated from a measured â€œout-of-bandâ€  back-scattering PBS in accordance with the following equations: G=&ee;Î³â€²&it;LPBSPo&TildeTilde;Î±Raman&it;Î±Rayliegh&it;â€ƒ&it;S&af;(1-&ee;-2&it;(Î±-Î³â€²)&it;L)2&it;(Î±-Î³â€²)where PBS is the back-scattering reaching the optical time-domain reflectometer that occurs at the wavelength of the test light pulse without the presence of the test light pulse, but while there is still live traffic, &agr; is the attenuation coefficient of the fiber, &ggr;â€² is the effective Raman gain coefficient, &agr;Raman is the Raman scattering coefficient, &agr;Rayleigh is Rayleigh scattering coefficient, S is the back-scattering capture coefficient, Po is the average power of the traffic signals, and L is the length of the test fiber.