Flat-Gain Fiber Raman Amplifiers Using Equally Spaced Pumps

Abstract—This paper analyzes the gain flatness of mul-tiwavelength pumped fiber Raman amplifiers using equally spaced pumps with both a fixed and an optimized central pump wavelength. The signal gain ripple using equally spaced pumps is compared with the case in which the pump wavelengths are allowed to vary for two, four, and eight pumps with 20-, 40-, and 80-nm signal bandwidths. The paper shows that using an optimized central pump wavelength with equal pump spacing simplifies system design, while the gain ripple is no more than 0.4 dB larger than the ripple obtained when the pump wavelengths are optimized for the cases considered. Index Terms—Modeling, optical fiber amplifiers, optical fiber communication, Raman scattering. I