Page 420 - Fiber Optic Communications Fund

Channel Multiplexing Techniques 401

2 × 110
l = = 117.74 μm. (9.62)
2
0
(b)
d d d d df
= = 2 , (9.63)
d d d d d
c
f = , (9.64)

c
df =− d, (9.65)
2
−3 × 10 8
df | −1 −1 20 −1 −1
| = m s =−1.24 × 10 m s (9.66)
−9 2
d | 1 =1550 nm (1550 × 10 )
d | −9
= | = 4.86 × 10 s/m. (9.67)
1
d |=1550 nm
Eq. (9.63) may be written as
d | df |
| = 2 1 |
d | 1 =1550 nm d | 1 =1550 nm
−2
12
=−3.81 × 10 m . (9.68)
From Eqs. (9.49) and (9.54), we have
( )= ( )l
2
2 1
1
d |
= ( )l +( − )l |
1 1
2
1 1
d | 1 =1550 nm
12
= 2 × 100 − 0.8 × 10 −9 × 107.04 × 10 −6 × 3.81 × 10 rad
2
= 6.279 × 10 rad, (9.69)
( )= ( )l
2 2 2 2
d |
= ( )l +( − )l
1 2 2 1 2 |
d | 1 =1550 nm
12
= 2 × 110 − 0.8 × 10 −9 × 117.74 × 10 −6 × 3.81 × 10 rad
2
= 6.907 × 10 rad. (9.70)
9.3.2 WDM Experiments
WDM has been studied extensively and is used in commercial transmission systems. Early WDM experiments
were carried out using direct detection [13]. With the advent of digital coherent receivers, the information
capacity and spectral efficiency have increased significantly. A data rate of 7.2 Tb/s over a distance of 7040 km
with a spectral efficiency of 2 bit/s/Hz is achieved using PDM and QPSK [14]. The baud rate of each WDM
channel in this experiment is 25 GBaud, excluding the FEC overhead. Because of QPSK modulation forma-
tion, the bit rate of each PDM channel is 50 Gb/s. Since there are two PDM channels for each optical carrier, the
total bit rate per WDM channel is 100 Gb/s. The total number of WDM channels is 72, leading to a total bit rate