Broadband Raman Amplifier for WDM

Yoshihiro EMORI  Shu NAMIKI  

IEICE TRANSACTIONS on Communications   Vol.E84-B    No.5    pp.1219-1223
Publication Date: 2001/05/01
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section INVITED PAPER (Joint Special Issue on Recent Progress in Optoelectronics and Communications)
Category: Optical Fibers and Cables
Raman amplifier,  multi-wavelength pumping,  broadband amplifier,  gain flatness,  

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We have developed the design procedure of multi-wavelength pumped Raman amplifiers, introducing superposition rule and account for pump-to-pump energy transfer. It is summarized with respect to the pumping wavelength and power allocation. The comparisons between simulated and experimental results are presented. Section 2 reviews the fundamentals of Raman amplifier. In this section, Raman gain spectra measured for different fibers are presented and the difference among the spectra is discussed. Section 3 describes the way to determine the pumping wavelength allocation by introducing superposition method. By means of this design method, some optimized design examples are presented, where the peak levels of Raman gain are fixed to 10 dB for the wavelength range from 1525 nm to 1615 nm (C- plus L-band) in all cases. From these results, it is confirmed that better gain flatness can be obtained by using the larger number of pumps. Section 4 explains how the pump-to-pump energy transfer changes the gain profile by experimental and simulated results. In this section, simulation modeling to perform precise numerical simulation is also presented. From the above discussion, the design procedure can be simplified: (1) one determines pump wavelengths with which a desired composite Raman gain can be obtained by adding in logarithmic scale individual Raman gain spectra shifted by the respective wavelength differences with adequate weight factors. And (2), one predicts how much power should be launched in order to realize the weight factors through precise numerical simulations. Section 5 verifies the superposition rule and the effect of pump-to-pump energy transfer by comparing a measured Raman gain with a superposed one. The agreement of two gain profiles shows that the multi-wavelength pumped Raman gain profile contains only the individual gain profiles created by the respective pump wavelengths. Section 6 concludes this paper.