Measurement of polarization-mode dispersion of optical fibers

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Helsinki University of Technology | Diplomityö
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Polarization-Mode Dispersion (PMD) has the same effect on light signals in optical fibers as any other kind of dispersion. Locally, PMD is due to the presence of two group velocities, one for each polarization mode. Globally, this effect is combined with random polarization mode coupling, which results in the stochastic nature of PMD. PMD is a major limitation in optical transmission systems and an ultimate limitation for ultra-high speed single channel systems based on standard single-mode fibers. In this work, the concept of polarization is discussed prior to the elaboration of the fundamental theory, causes and impact of PMD. Then, PMD of seven standard single mode fibers are measured using the Jones Matrix Eigenanalysis (JME) measurement method. The motivation of this work is to derive a method to predict the PMD of fiber cables. Standard single-mode fibers samples are provided wound on a small, large spool or un-spooled for the measurement of their PMD values. A special fiber holder is developed for measuring PMD of un-spooled fibers. The sensitivity of PMD measurement to mechanical perturbations is investigated and the stability of our measurement setup is demonstrated. Next, the distribution of PMD along the fiber length is analyzed from measurement of PMD of different 500 m pieces of the fibers. It is then shown that for each fiber, the variation of the measured PMD value, with respect to the spool radius and un-spooled condition, follows a similar pattern regardless of the fiber pieces considered. This result indicates that the distribution of PMD appears to be uniform along the fiber length. The average PMD values of all fibers in each measurement condition (small spool, large spool or un-spooled) are determined, and variation of the average PMD value with respect to the spool radius and un-spooled condition is analysed. The results indicate that the effect of scrambling of un-spooled fibers on the measurement of PMD is similar to measuring PMD of a fiber by re-spooling it after each measurement. They also indicate that the average PMD value of the fiber when un-spooled could be predicted from the measured PMD values of the fiber when wound on small and large spools. In general, there is no drastic change between the average PMD value of the fiber when spooled and un-spooled.
Ikonen, Erkki
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Niemi, Tapio
polarization, polarization-mode dispersion, birefringence, polarization mode coupling, optical fibers
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