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Optical Amplifiers 279

20
18
P p
16
14
Power (mW) 12 8
10

6
P s
4
2
0
0 2 4 6 8 10
Amplifier length (m)
Figure 6.17 Evolution of signal and pump power in EDFA.

g = N , (6.193)
T 12
s
and from Eq. (6.187) we obtain
P (L)= P (0) exp[(Γ N − )L]. (6.194)
s
s
s T 12
s
Typically, ≪ Γ N and therefore, signal power grows exponentially with distance. Fig. 6.18 shows the
s T 12
s
amplifier gain G as a function of the amplifier length for various pump powers. For the given pump power,
30
20 P p (0) = 12 dBm

10 P p (0) = 6 dBm
P p (0) = 3 dBm
0 P p (0) = 0 dBm
G (dB) –10

–20

–30

–40

–50
0 5 10 15 20
Length (m)

Figure 6.18 Amplifier gain vs. length in EDFA. The amplifier gain becomes maximum at a certain amplifier length
which is a function of pump power.