Page 282 - Fiber Optic Communications Fund

Optical Amplifiers 263

Example 6.5
An amplifier operating at 1545 nm has a gain G = 25 dB, F = 6 dB, and input power P =−22 dBm. Cal-
in
n
culate the OSNR in a bandwidth of 12.49 GHz.
Solution:

P out = GP ,
in
P (dBm)= G(dB)+ P (dBm)
out
in
= 25 dB − 22 dBm
= 3dBm,
P out = 10 P out (dBm)∕10 mW

= 2mW.
From Eq. (6.102), we have

hf 0
ASE =(GF − 1) ,
n
2
F = 10 F n (dB)∕10 = 3.98,
n
G(dB)∕10
G = 10 = 316.22,
c 3 × 10 8
f = = = 194.17 THz,
0 −9
1545 × 10
0
12
ASE =(316.22 × 3.98 − 1)× 6.626 × 10 −34 × 194.17 × 10 ∕2W/Hz
= 8.09 × 10 −17 W/Hz

B opt = 12.49 GHz,

P out 2 × 10 −3
OSNR = = = 989,
2 ASE B opt 2 × 8.09 × 10 −17 × 12.49 × 10 9

OSNR(dB) = 10 log (OSNR)= 29.95 dB.
10

6.6 Semiconductor Optical Amplifiers

A semiconductor optical amplifier (SOA) or semiconductor laser amplifier (SLA) is nothing but a laser oper-
ating slightly below threshold. The optical field incident on one facet is amplified at the other accompanied
by the ASE. The SOAs can be divided into two types: (i) cavity-type SOA or Fabry–Perot amplifier (FPA),
(ii) traveling wave amplifier (TWA).