Abstract:
The paper examines the influence of the delivery scheme and spectral characteristics of remote optically pumped amplifiers (ROPA) on the maximum length of unrepeatered communication lines. It is established that in the backward ROPA (BROPA) scheme, signal amplification due to stimulated Raman scattering (SRS) in the working telecommunication fiber causes a small shift (∼5 nm) of optimal pump wavelength toward shorter wavelengths relative to the maximum gain-to-noise ratio of the erbium-doped fiber (max[GainEDF(λpump)/NFEDF(λpump)]). The pump delivery through the working fiber in the case of BROPA has been found to increase the transmission distance due to additional signal amplification caused by SRS and the absence of significant depletion of pump power delivered to the erbium-doped fiber. Conversely, when the signal and pump propagate forward (FROPA) along the working fiber, the pump power decays due to SRS, which makes its delivery via an additional fiber more efficient. It has been determined that for a pump spectral width exceeding 4 GHz, the effect of the Mandelstam-Brillouin stimulated scattering on pump power can be disregarded. Approximate formulas are derived for calculating the dependence of the BROPA gain on the microparameters of the erbium-doped fiber, the signal spectrum, and on the delivered power and pump spectrum subject to the amplified spontaneous emission.
Keywords:unrepeatered communication line, erbium amplifier, remote optical pumping.
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