Gain Optimization of Germanosilicate Fiber Raman Amplifier and Its Applications in the Compensation of Raman-Induced Crosstalk Among Wavelength Division Multiplexing Channels

Abstract—Spectral characteristics of stimulated Raman scattering (SRS) process were theoretically investigated for step-index silica optical fibers with various GeO 2 concentrations. Optimal-fiber lengths and germanium concentration, where the first Stokes power reaches maximum, were calculated at various pump power levels for application in Raman amplifiers. Based on this analysis, we proposed and experimentally demonstrated a new channel-equalizing technique to simultaneously compensate Raman-induced crosstalk and amplify wavelength-division-mul-tiplexing (WDM) signals using a discrete Raman amplifier in the 1.5- m range. As a further application of SRS in germanosilicate glass fibers, we introduce an all-optical variable attenuator for channel equalization that could be used in dynamic optical power tilt control in WDM systems. Index Terms—Amplifier design, optical fiber, power equaliza-tion, Raman amplifier, variable optical attenuator (VOA). I