| This thesis describes an experimental investigation of Brillouin scattering in silica based single mode optical fibers at IR communication wavelengths (lambda = 1550nm).; We have investigated the scattering process in spontaneous and stimulated regimes by taking into account of the gain spectrum evolution, stimulated Brillouin scattering (SBS) threshold and polarization properties using laser sources with different spectral lineshapes.; We have shown that several acoustic resonance modes, depending on the waveguide properties, exist in the spontaneous regime, but they decay as the process becomes stimulated. In the stimulated regime, only the main Brillouin peak persists with a linewidth approximately 10 times narrower than that in the spontaneous regime. Our results on the linewidth narrowing are in an agreement with the theory, which considers thermal noise fluctuations as the origin of Brillouin scattering in undepleted-pump regime. Moreover, we have found that the lineshape of the SBS light is identical to the input laser lineshape, with a resolution bandwidth that is equal to the SBS linewidth of the medium (7--12 MHz), which makes SBS a practical tool for laser linewidth measurements.; In the study of polarization properties of Brillouin scattering, we specifically determined the SBS threshold and Degree of Polarization (DOP) of Brillouin light with respect to the state of polarization (SOP) and DOP of the input laser source. It is found that, for linearly polarized input signal (100% DOP); Rayleigh and Spontaneous Brillouin scattered signals have the DOP of 33%, while the Stimulated Brillouin scattered light has a DOP of 95%. On the other hand, for a depolarized input signal (DOP of 0%); Rayleigh, Spontaneous and Stimulated Brillouin scattered light have the same DOP of 5%. We also found that the depolarized signal yields 1dB higher SBS threshold than the polarized signal as oppose to earlier prediction of 3dB. A possible explanation for the discrepancy is given by taking into account of the gain contribution from the incoherent orthogonal signal via longitudinal elasto-optic coefficients.; We have also proposed a novel polarization multiplexing technique, which can provide 3dB suppression of SBS. In this technique, an optical signal is converted to two orthogonal incoherent signals with a frequency shift with respect to each other. We have studied the interference effects of this technique in terms of coherence and polarization orientation of the two signals in order to determine the resultant spectrum. Finally, we have shown that this technique can be utilized in conjunction with conventional SBS suppression techniques such as frequency modulation (FM) and external phase modulation (PM) in order to obtain an additional SBS suppression. |
