Patent ID: 7190442

Claim:
A method for measuring polarization mode dispersion in an optical fiber having a longitudinal axis and a length along the longitudinal axis, the method comprising: (a) sending a first polarized input light pulse into a first end of the length of the optical fiber, thereby causing a first backscattered light signal to exit the first end of the optical fiber; (b) obtaining a first backscatter intensity trace corresponding to the length of the optical fiber by effecting a polarization sensitive measurement of the first backscattered light signal; (c) sending a second polarized input light pulse into a second end of the length of the optical fiber, thereby causing a second backscattered light signal to exit the second end of the optical fiber; (d) obtaining a second backscatter intensity trace corresponding to the length of the optical fiber by effecting a polarization sensitive measurement of the second backscattered light signal; (e) analyzing the variation of intensity of the first backscatter intensity trace, wherein the analyzing step comprises analyzing the variation of intensity over a sliding window of data from the first backscatter intensity trace and moving the window of data lengthwise along the length of the fiber while continuing to analyze the variation of intensity to thereby produce a first variation of intensity trace comprising information related to the local variation in intensity along the length of the fiber; (f) analyzing the variation of intensity of the second backscatter intensity trace, wherein the analyzing step comprises analyzing the variation of intensity over a sliding window of data from the second backscatter intensity trace and moving the window of data lengthwise along the length of the fiber while continuing to analyze the variation of intensity to thereby produce a second variation of intensity trace comprising information related to the local variation in intensity along the length of the fiber; and (g) generating an absolute intensity variation difference trace corresponding to the length of optical fiber by determining the absolute magnitude of the difference between the second variation of intensity trace and the first variation of intensity trace.