Fibre Raman studies

The gain mechanism in Raman amplification is the stimulated Raman scattering (SRS), a process by which energy is transferred from the pump wavelength to a longer (100 nm shift) signal wavelength through nonlinear inelastic photon scattering on an optical phonon. It has been found recently that unlike the other optical amplifiers (semiconductor optical amplifier, linear optical amplifier, erbium doped fiber amplifier), only the discrete and lumped fiber Raman amplifiers (FRAs) can provide the wide bandwidth gain to develop a long-distance metro/access network by enlarging the power budget for coarse wavelength-division multiplexing transmission systems. However, the polarization-dependent gain (PDG) (difference between the maximum and minimum gain) and gain fluctuations (GF) in FRAs can degrade the performance of a fiber optic communication system. Therefore, the dependences of PDG and GF on fiber birefringence (polarization mode dispersion (PMD), birefringence and beat correlation lengths) and on the pump state of polarization (SOP) have to be found.

In our previous papers we demonstrated experimentally and theoretically that the dependence of the PDG on PMD split into two branches of maximum and minimum values for different pump SOPs. Results obtained in some other experiments describing the PDG, in which the pump SOP was not controlled, correspond to intermediate values between the maximum and minimum PDG. In the approach developed by Lin and Agrawal, the evolution of the birefringence vector for a signal wave was presented as a three-dimensional (3D) Gaussian process in the reference frame of the pump polarization. As a result, the PDG and GF were obtained as independent of the pump SOP. Unlike this approach, we used a more general representation of randomly varying birefringence in the form of fixed birefringence strength, and the birefringence vector orientation was driven by a white-noise process (fixed modulus model). As a result, we have found the PDG as a function of pump SOP and PMD value.

For further information, please see the links to revelevant publications on the various researcher pages.