Image Number 3 for United States Patent #6658215.
A compensation arrangement for addressing the problem of first-order and second-order polarization mode dispersion (PMD) in an optical fiber communication system includes separate, independent elements for each type of PMD. First-order PMD may be compensated using conventional techniques related to adjusting the transit time differential between the polarization states. The second-order polarization mode dispersion is compensated by recognizing the separate sources of second-order PMD (pulse broadening analogous to chromatic dispersion, additional pulse broadening due to optical filtering (narrowing), and coupling of a portion of the optical signal into the orthogonal polarization relative to the main pulse with a different transmit time. A chirped fiber grating with a variable temperature gradient, a complementary optical filter with variable spectral transmission and a polarizer, respectively, can be used to compensate for these three sources of second-order PMD.