are aligned 45° from each other, producing higher order PMD. This higher order PMD
generation capability is not available in previous DGD generator designs in which the
polarization rotators can only generate ± 45°. polarization rotations. The 0 degree
polarization rotation is essential for the generation of higher order PMD.
The total number of PMD values that can be generated with N+1 sections of birefringent
material and N rotator pairs is 3
N
. For N=8, the total number of PMD states is 6561. The
total number of DGD-only (1
st
order PMD) states is 2
N
. For N=8, the total number of
DGD-only states is 256.
Unlike the analog crystal rotators used in other PMD source designs, which suffer from
slow speed and low repeatability, the digital ternary operation method of this PMD
source makes PMD generation fast and highly repeatable.
In addition to the digital ternary rotators described above, the PMDPro uses a quasi-
continuous rotator to achieve independent DGD and SOPMD control, allowing it to
uniformly cover the PMD space, as shown in Figure 35. Note that the SOPMD values
generated using this method are wavelength independent, so there are no FSR issues.
90ps PMDPro
0
500
1000
1500
2000
2500
0
20
40
60
80
100
DGD (ps)
SO
PM
D
(ps
2
)
180ps PMDPro
0
2000
4000
6000
8000
10000
0
50
100
150
200
DGD (ps)
SO
PM
D (
p
s
2
)
Figure 35 DGD and wavelength independent SOPMD range
A)
90
ps
PMDPro™
B)
180
ps
PMDPro™
Document #: GP-UM-PMD-1000-21
Page 113 of 122
