The backbone optical networks have high transfer speed therefore they are very sensitive to the changes of the optical parameters. These parameters are influenced by environmental effects. In this study I try to find out how the optical parameters are changed by the environmental conditions. The changes are observed on an aerial optical fiber.
The fiber has three major optical parameters. These are the attenuation, the dispersion and the cut off wavelength.
The distance between the two sides of the link depends mainly to the attenuation. The attenuation of optical fiber depends on the wavelength and the temperature.
The dispersion is the scattering of the pulse. The three kinds of dispersions are the mode dispersion, the chromatic dispersion and the polarization mode dispersion. I studied the polarization mode dispersion more detailed than the other two dispersions. PMD originates from birefringence which causes a delay between the two orthogonal polarization modes.
Not only the fiber’s attenuation will vary by the environment but the three kinds of dispersions will vary too. Dispersions are one of the major factors limiting high data transmission rates, this is why we have to know how it is influenced by environmental conditions.
I am going to describe the major measurement methods of optical parameters. I will introduce the Optical Time-Domain Reflectometer (OTDR) and the Optical Spectrum Analyzer (OSA) to measure the attenuation with them. The Pulse-delay and the Phase-shift methods will show us how the chromatic dispersion is measured. I am going to describe the following PMD measurements techniques: Fixed Analyzer (AF), Jones-Matrix-Eigen Analysis (JME), Interferometry: Traditional method (TINTY), Interferometry: Generalized method (GINTY), and the State-of polarization Scrambling Analysis (SSA).
I measured the PMD’s changes on an aerial fiber because I would like to find a relation between the PMD’s variations and the environmental conditions. I used the FTB-5700 and the FTB-5500B test units. The FTB-5700 uses the SSA method while the FTB-5500B uses the GINTY method.
The measurement results show that the PMD will be higher if the temperature grows and they show that the higher wind speed causes smaller PMD, but this is not the same what I expected. The relation between the PMD and the wind speed is not a correct result because I have only a few measured PMD values at high wind speed. Maybe I would have correct result, if I had more measured PMD values at high wind speed and had more PMD values at different wind speeds.
The FTB-5500B measured more accurate than the single-ended FTB-5700. The aerial optical fibers are measured with FTB-5500B more suitable than the FTB-5700. ITU-T recommends the usage of the GINTY method in test units for the measurement on an aerial optical cable. The FTB-5700’s results are accurate enough to show us the aerial optical fiber’s PMD value, but it has not enough accuracy to analyse the influence of environmental conditions on the PMD.