Image Processing Reference
In-Depth Information
(1
st
Stage)
(N
th
Stage)
A/D
A/D
LO
Data
out
A/D
A/D
Correlated NLC step
x pol
signal
delay
* exp( j)
| |
2
weighted
average
| |
2
y pol
signal
delay
* exp( j)
Fig. 7. Block diagram of coherent receiver with correlated backward propagation module
(CBP) (Li et al., 2011; Rafique et al., 2011c).
c
k
a
b
exp
E
i
y
t
E
i
x
t
+(
N
−
1
)
/2
2
2
k
T
s
2
k
T
s
2
E
out
y
E
i
y
·
∑
=
−
j
·
−
+
−
(21)
k
=
−
(
N
−
1
)
/2
Whereas,
E
is the electric field envelope of the orthogonal polarization states, a and b
represent intra-polarization and inter-polarization parameters (Oda et al., 2009),
N
represents
the number of symbols to be considered for a non-linear phase shift,
c
k
is the weighing vector,
K
is the delay order, and
T
s
is the symbol period. In (Li et al., 2011) the investigations depict
the results in 100GHz channel spaced DP-QPSK transmission and multi-span DBP shows a
reduction of DBP stages upto 75%. While in (Rafique et al., 2011c) the algorithm is investigated
for single channel DP-QPSK transmission. In this article upto 80% reduction in required
back-propagation stages is shown to perform non-linear compensation in comparison to the
standard back-propagation algorithm. By using this method the number of DBP stages are
significantly reduced.
4.2 Optical backward Propagation (OBP)
The DBP improves the transmission performance significantly by compensating dispersion
and non-linearities. However, it requires a considerable amount of computational resources
as described in previous sections thus upto now no real time experimental implementations
are reported. In (Kumar et al., 2011) an alternative technique for real-time implementation
is proposed in optical domain, realized by an effective non-linear coefficient using a pair of
highly non-linear fibers (HNLFs). In this method the linear compensation is realized by using
