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Distributed Raman amplification in an optical fiber. The input Stokes field is amplified by stimulated Raman scattering (SRS) in the fiber. The amplified Stokes field is detected by the optical spectrum analyzer.
Experimental demonstration of Raman amplification at 808 nm in a single-mode fiber. The presence of the pump field amplified the Stokes field by 4.7 dB. The contribution of the fluorescence noise from the Ti:Sapphire crystal to the amplified Stokes field is negligible as the difference in power between them is more than 10 dB. The noise can be further reduced by backward pumping.
Measured Raman gain coefficient of the Ge-doped silica-core single-mode fiber at 808 nm as a function of the frequency difference between the Stokes and pump fields. We measured the Raman gain spectrum by tuning the pump wavelength for about 25 nm while keeping the Stokes wavelength fixed. Based on this data and Eq. (3), the Raman gain coefficient was deduced and used in our Raman amplifier model (Fig. 4).
Net gain (gain minus fiber loss) as a function of the propagation length and pump power. A dual pumping (forward and backward) architecture is considered here. The pump powers shown in the figure are for each of the forward and backward pumps. While the maximum pump power available to us was 0.2 W, the model predicts that at a pump power level of 1 W (a value within the range of commercial amplified Ti:Sapphire lasers), a net gain of 30 dB may be possible.
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