Patent ID: 7164469
Filing Date: 2007-01-16
Classification: G01M,H04B

Abstract:
1. 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 plurality of polarized input light pulses into a first end of the length of the optical fiber via an optical path, each polarized input light pulse thereby causing a respective backscattered light signal to exit the first end of the optical fiber and to enter the optical path, whereby a plurality of pulse-signal pairs are generated from the input light pulses and respective backscattered light signals; (b) effecting a polarization sensitive measurement of the backscattered light signals, thereby obtaining backscatter intensity traces corresponding to a portion of the length of optical fiber; (c) nondegenerately modifying the polarization of the optical path between the passage of at least two pulse-signal pairs; (d) generating an intensity level composite trace corresponding to the portion of the length of optical fiber by summing (i) at least one of the backscatter intensity traces, multiplied by a first weighting coefficient, and (ii) at least one other backscatter intensity trace, multiplied by another weighting coefficient of opposite sign to the first weighting coefficient; (e) analyzing the variation of intensity level of the composite trace, wherein the analyzing step comprises analyzing the variation of intensity over a sliding window of data from the composite trace and moving the window of data lengthwise along the portion of the length of the fiber while continuing to analyze the variation of intensity to thereby produce information related to the local variation in intensity along the portion of the length of the fiber, and relating the level of variation of intensity level to the polarization mode dispersion (PMD) distribution in the fiber.