Page 346 - Fiber Optic Communications Fund

Transmission System Design 327

1.4 2.5

1.2
2
1
1.5
0.8
Current, I 0.6 Current, I 1

0.4
0.5
0.2
0 0
–0.5 0 0.5 1 –0.5 0 0.5 1
Time (s) x 10 –10 Time (s) x 10 –10
(a) (b)

Figure 7.19 Eye diagrams for a direct detection system. Amplifier spacing = 100 km, number of amplifiers = 10. ASE
2
2
is turned off. (a) =−1ps /km and (b) =−5ps /km.
2
2
1.4 2.5
1.2
2
1
1.5
0.8
Current, I 0.6 Current, I 1

0.4
0.5
0.2

0 0
–0.5 0 0.5 1 –0.5 0 0.5 1
Time (s) x 10 –10 Time (s) x 10 –10
(a) (b)
Figure 7.20 Eye diagrams for a direct detection system. The parameters are the same as those of Fig. 7.19, except that
2
2
ASE is turned on. n = 1.5, number of amplifiers = 10. (a) =−1ps /km and (b) =−5ps /km.
2
2
sp
7.5 Additional Examples
Example 7.6

In the fiber-optic system of Fig. 7.5, = 0.18 dB/km and fiber length L = 190 km, T = 298 K, P = 1dBm,
in
R = 1.1A/W, R = 200 Ω, f = 7.5 GHz, and f = 20 GHz. The noise figure and gain of the preamplifier are
e
L
o