Abstract
Environmental conditions affect the birefringence of an optical fibre which in turn leads to fluctuations in its Polarization mode dispersion (PMD). Fluctuations in PMD make compensation for it in optical fibres very complicated. In this paper, fluctuations of first-order polarization mode dispersion (FO-PMD), FO-PMD coefficients and second-order polarization mode dispersion (SO-PMD) are monitored over time and also with respect to the environmental conditions. Long term measurements of FO-PMD have been done before by Mudau (2008) using the Generalized Interferometry Technique (GINTY) only. However, in this current study the FO-PMD coefficients and SO-PMD fluctuations were also monitored in addition to making a comparison between the measurements obtained using the Single-ended Dispersion Analyzer (FTB-5700) and the GINTY. These measurements were made on a 14.8 km long deployed aerial optical fibre that links St. Albans to Rockland transmission stations in Port Elizabeth, South Africa. The weather information was obtained from the Kestrel 4500 pocket weather tracker that was set up at St. Albans transmission station. So, for good PMD compensation, PMD should be monitored for a very long period of time or use an instrument that can accurately measure it even when the optical fibre is exposed to harsh environmental conditions.
Highlights
Polarization Mode Dispersion is a form of modal dispersion where two different polarizations of light in a waveguide, which normally travel at the same speed, travel at different speeds due to random imperfections and asymmetries, causing random spreading of optical pulses
Environmental conditions affect the birefringence of an optical fibre which in turn leads to fluctuations in its Polarization mode dispersion (PMD)
After 12:00 noon, the temperature variations became quite small. This implies that the random fluctuations of the first-order polarization mode dispersion (FO-PMD) in both instruments are mainly due to the rapid fluctuations in the wind speeds. This is in agreement with Mudau (2008), Karlsson, Brentel, & Andrekson (2000) and Zhang, Bao, Yu, & Chen (2007) who made long-term FO-PMD measurements only that they did not make a comparison of the Generalized Interferometry Technique (GINTY) with the FTB-5700 during their measurements and did not show FO-PMD variations for short time
Summary
Polarization Mode Dispersion is a form of modal dispersion where two different polarizations of light in a waveguide, which normally travel at the same speed, travel at different speeds due to random imperfections and asymmetries, causing random spreading of optical pulses. Within the amorphous matrix of mechanically unstressed pure glass the SiO2 molecules are randomly distributed This makes it a medium which is isotropic in the sense that the physical properties of the glass are uniformly random in all directions. Extrinsic factors on the other hand are such stresses introduced during cabling and the deployment process Environmental factors such as temperature, stress and fibre movement (including wind for an aerial optical fibre) can lead to changes in the birefringence (Cameron, Chen, Bao, & Stears, 1998). These effects cause the fibre PMD to vary stochastically in time making PMD difficult to manage. Bends, twists and splices are other extrinsic sources of mode coupling (Kaminow, 1981)
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