Optical Modulation Analyzer
72
PDL
The Polarization Dependent Loss is calculated within the Polarization Demultiplexing Algorithm and its
value is presented in dB. The resolution of this measurement is determined by the number of samples per
baud.
PDL
𝑑𝑑𝑑𝑑
= �20 log
10
�
|max (𝑇𝑇𝑀𝑀𝑇𝑇
𝑋𝑋𝑋𝑋
)| + |max (𝑇𝑇𝑀𝑀𝑇𝑇
𝑋𝑋𝑋𝑋
)|
|max (𝑇𝑇𝑀𝑀𝑇𝑇
𝑋𝑋𝑋𝑋
)| + |max (𝑇𝑇𝑀𝑀𝑇𝑇
𝑋𝑋𝑋𝑋
)|��
Equation 8 - Polarization Dependent Loss calculation
where max(Tap) gives the maximum of the corresponding array of tap values.
XY Skew
The skew between X and Y polarization signals is the difference between the X polarization and Y
polarization symbol centers. It is calculated within the Polarization Demultiplexing Algorithm. The
resolution of this measurement is determined by the number of samples per baud.
Q-Factor
Q-Factor is an alternate representation of the signal to noise ratio that is commonly used since its
relationship with the BER is more intuitive. Q factor is often represented in dB.
Q factor = �
3 log
2
𝐿𝐿
𝐿𝐿
2
− 1
2
(𝐸𝐸𝐸𝐸𝑀𝑀%/100)
2
log
2
2
𝑅𝑅𝑝𝑝𝑑𝑑
Equation 9- Q-Factor calculation
Q factor
𝑑𝑑𝑑𝑑
= 20 log
10
(𝑄𝑄 𝑓𝑓𝑀𝑀𝑓𝑓𝑀𝑀𝐸𝐸𝐸𝐸)
Equation 10- Q-Factor in dB
BER Estimate
The BER Estimate is calculated from the Q-factor through the relationship given by Equation 11. This
provides an instantaneous estimation of the bit error rate to act as an alternative to actual BER counting,
which can be time consuming.
BERest =
1 − 1𝐿𝐿
log
2
𝐿𝐿 𝑀𝑀𝐸𝐸𝑓𝑓𝑓𝑓 �
𝑄𝑄 𝑓𝑓𝑀𝑀𝑓𝑓𝑀𝑀𝐸𝐸𝐸𝐸
√2
�
Equation 11 - BER estimate calculation
where erfc is the complimentary error function, which applies the assumption of Gaussian distribution of
constellation points.
Summary of Contents for IQS25
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Page 3: ...Optical Modulation Analyzer Operator s Manual August 2016 ...
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Page 88: ...927295 00 Rev A August 2016 ...
