Recommendation G.957 (06/99)
27
T1517740-95
%
0
E
100
E
1
P
1
P
2
P
0
M
Eye
opening
Received power
Adding
interference noise
Figure III.2/G.957 – Eye opening due to intersymbol interference
III.2
S/X test method
To simulate intersymbol
interference noise, the
S/
X test is performed by using an NRZ signal
modulated at a low frequency compared to the system operating bit rate.
This interfering signal is
combined optically with a normal optical signal and injected into the receiver under test.
In the
S/X test, the normal optical signal power is usually set to
P
1
. The
amount of the optical power
of the interference noise,
X, can be determined by a relationship
between eye opening and S/X ratio
whose characteristics are shown in Figure III.3. From Figure III.3, the
S/X ratio can be determined as
(
S/X)
E
by the
relationship between E
1
and
E. The aging margin
M and (
S/X)
E
are given by:
(
)
X
P
X
S
P
P
M
E
1
0
1
/
=
−
=
T1509090-92
%
0
E
100
E
1
P
1
P
2
(
S/
X)
E
1
¥
Eye
opening
S/
X ratio
Figure III.3/G.957 – Eye opening and S/X ratio parameter
