Dispersion-compensating fiber Raman amplifiers with step, parabolic, and triangular refractive index profiles

This paper presents a comprehensive analysis of the performance of a gain-flattened coaxial fiber Raman amplifier with respect to the refractive index profile. The variation of the dispersion coefficient and the end-end gain spectrum of the coaxial fiber Raman amplifier against the core structure as a function of the step, parabolic, and triangular profiles are analyzed. The analysis shows that the dispersion coefficient is sensitive to the variation of the core structure of the fiber, whereas the effective Raman gain coefficient remains nearly constant as the structure changes. Simulations of transmissions employing the coaxial fiber Raman amplifier with the three different structures are carried out individually, and the results show that the parabolic and triangular profiles perform better than the step profile, where the parabolic profile gives the best performance over 80 km of G.652 fiber, with a transmission rate of 20 Gb/s and a gain ripple of +/- 1 dB. In addition, the analysis shows that the maximum negative dispersion wavelength of the fiber exhibits a linear relationship with the normalized core radius. Hence, a coaxial fiber Raman amplifier providing A possible operation over the L-band is proposed.