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Optical Amplifiers 285

14
P p (0) = 24 dBm
12

10

8 P (0) = 22 dBm
G (dB)
p
6
P (0) = 20 dBm
p
4
2

0
0 10 20 30 40 50
Length (Km)
Figure 6.24 The gain of the Raman amplifier becomes roughly independent of length for large L. Signal launch power =
2
−1
−1
2
−6dBm, g = 6 × 10 −14 m/W, A = 40 μm , A = 50 μm , = 9.21 × 10 −5 m , = 4.605 × 10 −5 m .
s
s
p
R
p
a certain gain for Raman amplifiers is larger than that needed for EDFA in the unsaturated regime. However,
as the signal power increases because of the increase in number of channels of a WDM system, the gain
of a Raman amplifier is greater than that of an EDFA [10]. This is because of the higher saturation power of
the Raman amplifier.
0
In the presence of the pump
–5
Signal Power (dBm) –10

–15 In the absence of the pump

–20
0 10 20 30 40 50
Length (km)
Figure 6.25 Evolution of signal power in the Raman amplifier with and without the pump. P (0)= 23 dBm for the solid
p
line. The parameters are the same as those of Fig. 6.24.