EXFO FTB-5500B PMD Analyzer - Manual (Page 113)

Using Third-Party Broadband Light Sources
Polarization Mode Dispersion Analyzer 105
Uncertainty Formula
Uncertainty Formula
The following formula can be used to determine the mean uncertainty as a
function of the auto-correlation rms width,
, the measured PMD value,
and the number of measurements performed with distinct I/O-SOPs (using
scramblers at the input and output of the DUT),
³
all cases:
Equation 4
³
large PMD:
when
Note: The uncertainty on the mean-PMD is decreased considerably when
performing a sufficient number N of measurements with distinct I/O-SOPs.
For randomly distributed I/O-SOPs, the uncertainty is decreased by a factor
of
according to Equation 3 on page 104. However, using an
appropriate, deterministic set of I/O-SOPs covering the Poincaré sphere
with a regularly spaced grid, the improvement factor tends toward
instead, which is much more efficient.
σ
0
σ
PMD
PMD
--------------
1
N
----
1
8
3 π
------ –
⎝ ⎠
⎛ ⎞
1
1
4
---
PMD
σ
0
-------------
⎝ ⎠
⎛ ⎞
2
⋅ +
------------------------------------------ ⋅ =
σ
PMD
PMD
--------------
1
N
----
σ
0
PMD
------------- ⋅
0.55
∼
PMD
σ
0
------------- 1 »
1 N ⁄
1 N ⁄