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Physical Layer impairments
on C-band networks: Part II
This article analyzes some physical layer calculated for the optimal power per channel,
impairments (PLIs) of the hardware which is different for all architectures.
components belonging to the nodes and of the Therefore, the OSNRs calculated considering
overall network, such as non-linear only ASE noise power or both ASE noise
interference (NLI) noise and crosstalk powers and NLI power cannot be directly
influence. The analysis will focus on the most compared.
feasible and cheaper horseshoe network
solutions (which results from a study made
through the data present in Source 1), CD
ROADM B&S (which is the most common
solution for metropolitan networks), and FD&W
using coherent detection (ChD) nodes N1, both
combined with CD ROADM R&S nodes N2 (see
my article on newDataMagazine nº11).
Table 1: OSNR for the cases of Figure 1 (see my article on nDm
nº13) with 10 and 60 km spans, for the N1 CD ROADM B&S and
NON-LINEAR INTERFERENCE NOISE FD&W ChD node architectures, after signal extraction,
considering NLI power and for the optimal power per channel,
The study of the impact of the NLI on P ch,opt .
systems performance with coherent detection
is performed in this section. The influence of As shown in Table 1, the node architecture
this impairment is quantified using the where the OSNR decreases the most is the
Gaussian-Noise model for NLI assessment. FD&W ChD, compared with the OSNRs
We can evaluate the system performance just obtained considering only ASE noise. These
by correcting the OSNR, by adding the NLI values of OSNR are justified because in
noise power, p , to the accumulated ASE noise networks with N1 FD&W ChD nodes, the
NLI
power at the optical R input by (Source 1). The optimal power is around -3.5 dBm, which is
x
NLI noise can be modeled as Gaussian additive lower than 0 dBm. For the case of Figure 1 (b),
noise, independent of ASE noise. Thus, the NLI the OSNR is between 4.8 dB and 5.1 dB lower
power can be computed using expressions than for the case of Figure 1 (a) because the
presented in (Source 2). It is possible to NLI power is higher, which depends on the
calculate the OSNR penalty due to NLI by the optimal power per channel twice higher in the
difference between the OSNR without NLI second case for FD&W ChD-based networks
given by and the OSNR in the presence of NLI. and at least 0.1 dB higher in the case of
For the optimum channel power, the OSNR ROADM-based networks, which contributes to
penalty is 1.76 dB (Source 3). The OSNRs at the a higher OSNR degradation on FD&W ChD-
optical R input considering the NLI are shown based networks. The OSNRs obtained for CD
x
in Table 1 and were obtained using the ROADM B&S-based networks are the lowest for
equations from Source 1. Note that the OSNRs all network types. When the signal insertion
for only ASE noise are calculated for a p = 0 occurs at the N1 node, the OSNR is higher
Rx
dBm, while the values presented in Table 1 are between 0.8 dB and 1 dB than in the case of the
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