Page 347 - Fiber Optic Communications Fund

328 Fiber Optic Communications

4.5 dB and 20 dB, respectively. Find the Q-factor at the receiver, assuming that the operating wavelength is
1.55 μm.
Solution:
The optical power at the receiver after the preamplifier is
P (dBm)= P (dBm)− loss(dB)+ gain of the preamplifier(dB),
in
out
loss(dB)= 0.18 × 190 dB

= 34.2dB.
Gain of the preamplifier(dB)= G(dB)= 20 dB,

P (dBm)= 1 − 34.2 + 20 dBm
out
=−13.2dBm.

P = 10 −13.2∕10 mW = 4.78 × 10 −2 mW,
out
= hf(G − 1)n ,
ASE sp
c 3 × 10 8
f = = = 193.54 THz.
1.55 × 10 −6
From Eq. (6.105), we have

F ≅ 2n ,
n
sp
F (dB)= 4.5dB,
n
F = 10 4.5∕10 = 2.818,
n
n = 1.409,
sp
G = 10 G(dB)∕10 = 100,

12
= 6.626 × 10 −34 × 193.54 × 10 ×(100 − 1)× 1.409
ASE
= 1.78 × 10 −17 W/Hz,
I = RP + 2 f
1 out ASE o
9
= 1.1 × 4.7 × 10 −5 + 2 × 1.78 × 10 −17 × 20 × 10 A
= 5.32 × 10 −2 mA,

f
I = 2R ASE o
0
9
= 2 × 1.1 × 1.78 × 10 −17 × 20 × 10 A
= 7.83 × 10 −4 mA,