Abstract
Multi-wavelength pumped Raman amplifiers have many advantages over Erbium doped fiber amplifiers (EDFAs) such as a broad and flat gain spectrum and low noise due to the distributed nature of Raman amplifiers. These advantages have been particularly realized by the progress of multi-wavelength pumping technique and increasing output power of laser diodes.1 This pumping technique would also allow us to obtain a high Raman gain without polarization combined LDs. However polarization dependence of Raman gain (PDG) remains when pump light is polarized. In order to offset the PDG, polarization-combining or depolarization technique is usually used because it can reduce the DOP of the pump source. Considering a cost and size of pumping sources as well as flatness of Raman gain, one attractive solution is to have the same number of LDs as the number of pump channels, or at least a single pump laser in one of the pump channels.2 In either case, DOP of each LD should be as small as possible. For example, PDG would occur up to 3 dB in a forward pumping scheme and up to 1.5 dB in a backward pumping scheme against 4 dB Raman gain.3
© 2002 Optical Society of America
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