Tap stabilizer method and structure for coherent optical receiver
A method and structure for a coherent optical receiver device. Timing recovery (TR) is implemented after channel dispersion (i.e., chromatic dispersion (CD) and polarization mode dispersion (PMD)) compensation blocks. This architecture provides both improves performance and reduces power consumption of the device. Also, a TR loop is provided, enabling computing, by an error evaluation module, a first sampling phase error (SPE) and computing, by a timing phase information (TPI) module coupled to the error evaluation module, a second SPE from a plurality of CD equalizer taps PMD equalizer taps. The first and second SPE are combined into a total phase error (TPE) in a combining module, and the resulting TPE is filtered by a timing recovery (TR) filter coupled to an interpolated timing recovery (ITR) module and the combining module. The ITR module then synchronizes an input signal of the coherent optical receiver according to the TPE.
1. A coherent optical receiver device, the device comprising:
an input signal;
a chromatic dispersion (CD) equalizer module receiving the input signal, the CD equalizer module being configured to compensate for CD affecting the input signal;
a polarization mode dispersion (PMD) equalizer module coupled to the CD equalizer, the PMD equalizer module having a plurality of PMD taps and being configured to compensate for PMD affecting the input signal following compensation by the CD equalizer module; and
an evaluation module coupled to the PMD equalizer module, the evaluation module being configured to compute a first sampling phase error (SPE) and a second SPE from the plurality PMD taps; the evaluation module being configured to combine the first and second SPE into a total phase error (TPE).
2. The device of claim 1 wherein the input signal is a dual-polarization input with an x-type polarization input and a y-type polarization input.
3. The device of claim 1 wherein the CD equalizer module includes a non-adaptive frequency-domain (FD) equalizer, and wherein the PMD equalizer module includes an adaptive FD equalizer.
4. The device of claim 1 wherein the first SPE is computed according to a baud rate synchronization technique based on a Muller and Mueller phase error.
5. The device of claim 1 wherein the first SPE is computed according to the following equation:
ɛ
mm
=
K
mm
ℜ
(
∑
nN
p
+
2
(
n
+
1
)
N
p
a
^
*
(
k
)
q
(
k
-
1
)
-
a
^
*
(
k
-
1
)
q
(
k
)
)
where K mm is a certain gain,
where refers to real component of a complex number,
where N p is a parallelism factor,
where q(k) is an input of slicer and error evaluation module, and
where â* is an output of the slicer and error evaluation module.
6. The device of claim 1 wherein the second SPE is computed from the plurality of PMD taps according to the following equation:
ε fse =−K fse angle(det( M f ))
where K fse =[2 −1 , . . . , 2 −4 ], and
where M f =e −j2ω 0 τ |P(ω 0 )| 2 Z(ω 0 , −ω 0 , t),
where ω 0 is a given frequency,
where
τ
=
Δ
T
(
T
+
Δ
T
)
t
<
200
×
10
-
6
t
,
where P(ω 0 ) is a CD parameter, and
where Z(ω 0 , −ω 0 , t) is a unitary matrix for all (ω 0 , t).
7. The device of claim 1 wherein the second SPE is computed from the plurality of PMD taps according to the following equation:
ε fse =2ω 0 τ
where ω 0 is a given frequency, and
where
τ
=
Δ
T
(
T
+
Δ
T
)
t
<
200
×
10
-
6
t
,
where t is a given time, and
where T is a symbol period.
8. The device of claim 1 wherein the evaluation module includes a slicer module configured to derive a data stream from the input signal.
9. The device of claim 1 further comprising a zero padding module coupled to the evaluation module and the PMD equalizer module, the zero padding module being configured to increase a sampling rate of the input signal.
10. A method of operating a coherent optical receiver device, the method comprising:
providing an input signal;
compensating, by a chromatic dispersion (CD) equalizer module receiving the input signal, for CD affecting the input signal;
compensating, by a polarization mode dispersion (PMD) equalizer module coupled to the CD equalizer module and having a plurality of PMD taps, for PMD affecting the input signal following the compensation by the CD equalizer module;
computing, by an evaluation module coupled to the PMD equalizer module, a first sampling phase error (SPE);
computing, by the evaluation module, a second SPE from the plurality of PMD taps; and
combining, by the evaluation module, the first and second SPE into a total phase error (TPE).
11. The method of claim 10 wherein the input signal is a dual-polarization input with an x-type polarization input and a y-type polarization input.
12. The method of claim 10 wherein compensating by the CD equalizer module includes compensating by a non-adaptive frequency-domain (FD) equalizer, and wherein compensating by the PMD equalizer module includes compensating by an adaptive FD equalizer.
13. The method of claim 10 wherein the first SPE is computed according to a baud rate synchronization technique based on a Muller and Mueller phase error.
14. The method of claim 10 wherein the first SPE is computed according to the following equation:
ɛ
mm
=
K
mm
ℜ
(
∑
nN
p
+
2
(
n
+
1
)
N
p
a
^
*
(
k
)
q
(
k
-
1
)
-
a
^
*
(
k
-
1
)
q
(
k
)
)
where K mm is a certain gain,
where refers to real component of a complex number,
where N p is a parallelism factor,
where q(k) is an input of slicer and error evaluation module, and
where â* is an output of the slicer and error evaluation module.
15. The device of claim 10 wherein the second SPE is computed from the plurality of PMD taps according to the following equation:
ε fse =−K fse angle(det( M f ))
where K fse =[2 −1 , . . . , 2 −4 ], and
where M f =e −j2ω 0 τ |P(ω 0 )| 2 Z(ω 0 , −ω 0 , t),
where ω 0 is a given frequency,
where
τ
=
Δ
T
(
T
+
Δ
T
)
t
<
200
×
10
-
6
t
,
where P(ω 0 ) is a CD parameter, and
where Z(ω 0 , −ω 0 , t) is a unitary matrix for all (ω 0 , t).
16. The device of claim 10 wherein the second SPE is computed from the plurality of PMD taps according to the following equation:
ε fse =2ω 0 τ
where ω 0 is a given frequency, and
where
τ
=
Δ
T
(
T
+
Δ
T
)
t
<
200
×
10
-
6
t
,
where t is a given time, and
where T is a symbol period.
17. The method of claim 10 further comprising deriving, by a slicer module configured with the evaluation module, a data stream from the input signal.
18. The method of claim 10 further comprising increasing, by a zero padding module coupled between the evaluation module and the PMD equalizer module, a sampling rate of the input signal.
19. A compensation module configured within a coherent optical receiver, the module comprising:
a compensated input signal;
an error evaluation module receiving the compensated input signal, the error evaluation module being configured to compute a first sampling phase error (SPE);
a timing phase information (TPI) module coupled to the error evaluation module and receiving a plurality of Polarization Mode Dispersion (PMD) taps signals, the TPI module being configured to compute a second SPE from the plurality of PMD taps signals;
a combining module coupled to the TPI module and the error evaluation module, the combining module being configured to combine the first and second SPE into a total phase error (TPE);
a timing recovery (TR) filter coupled to the combining module, the TR filter being configured to filter the TPE; and
an interpolated timing recovery (ITR) module coupled to the combining module and receiving the compensated input signal, the ITR module being configured to synchronize the input signal using the TPE.
20. The module of claim 19 wherein the compensated input signal comprises an input signal compensated by a Chromatic Dispersion (CD) equalizer module and by a PMD equalizer module.
21. The module of claim 19 wherein the first SPE is computed according to a baud rate synchronization technique based on a Muller and Mueller phase error.
22. The module of claim 19 wherein the first SPE is computed according to the following equation:
ɛ
mm
=
K
mm
ℜ
(
∑
nN
p
+
2
(
n
+
1
)
N
p
a
^
*
(
k
)
q
(
k
-
1
)
-
a
^
*
(
k
-
1
)
q
(
k
)
)
where K mm is a certain gain,
where refers to real component of a complex number,
where N p is a parallelism factor,
where q(k) is an input of slicer and error evaluation module, and
where â* is an output of the slicer and error evaluation module.
23. The module of claim 19 wherein the second SPE is computed from the plurality of PMD taps according to the following equation:
ε fse =−K fse angle(det( M f ))
where K fse =[2 −1 , . . . , 2 −4 ], and
where M f =e −j2ω 0 τ |P(ω 0 )| 2 Z(ω 0 , −ω 0 , t),
where ω 0 is a given frequency,
where
τ
=
Δ
T
(
T
+
Δ
T
)
t
<
200
×
10
-
6
t
,
where P(ω 0 ) is a CD parameter, and
where Z(ω 0 , −ω 0 , t) is a unitary matrix for all (ω 0 , t).
24. The module of claim 19 wherein the second SPE is computed from the plurality of PMD taps according to the following equation:
ε fse =2ω 0 τ
where ω 0 is a given frequency, and
where
τ
=
Δ
T
(
T
+
Δ
T
)
t
<
200
×
10
-
6
t
,
where t is a given time, and
where T is a symbol period.
25. A method of error compensation by an evaluation module configured within a coherent optical receiver device, the method comprising:
providing a compensated input signal;
computing, by an error evaluation module receiving the compensated input signal, a first sampling phase error (SPE);
computing, by a timing phase information (TPI) module coupled to the error evaluation module and receiving a plurality of Polarization Mode Dispersion (PMD) taps signals, a second SPE from the plurality of PMD taps signals;
combining, by a combining module coupled to the TPI module and the error evaluation module, the first and second SPE into a total phase error (TPE);
filtering, by a timing recovery (TR) filter coupled to an interpolated timing recovery (ITR) module and the combining module, the TPE; and
synchronizing, by an ITR module coupled to the PMD equalizer module, the input signal according to the TPE.
26. The method of claim 25 wherein the compensated input signal comprises an input signal compensated by a Chromatic Dispersion (CD) equalizer module and by a PMD equalizer module.
27. The method of claim 25 wherein the first SPE is computed according to a baud rate synchronization technique based on a Muller and Mueller phase error.
28. The method of claim 25 wherein the first SPE is computed according to the following equation:
ɛ
mm
=
K
mm
ℜ
(
∑
nN
p
+
2
(
n
+
1
)
N
p
a
^
*
(
k
)
q
(
k
-
1
)
-
a
^
*
(
k
-
1
)
q
(
k
)
)
where K mm is a certain gain
where refers to real component of a complex number
where N p is a parallelism factor,
where q(k) is an input of slicer and error evaluation module, and
where â* is an output of the slicer and error evaluation module.
29. The device of claim 25 wherein the second SPE is computed from the plurality of PMD taps signals according to the following equation:
ε fse =−K fse angle(det( M f ))
where K fse =[2 −1 , . . . , 2 −4 ], and
where M f =e −j2ω 0 τ |P(ω 0 )| 2 Z(ω 0 , −ω 0 , t),
where ω 0 is a given frequency,
where
τ
=
Δ
T
(
T
+
Δ
T
)
t
<
200
×
10
-
6
t
,
where P(ω 0 ) is a CD parameter, and
where Z(ω 0 , −ω 0 , t) is a unitary matrix for all (ω 0 , t).
30. The device of claim 25 wherein the second SPE is computed from the plurality of PMD taps signals according to the following equation:
ε fse =2ω 0 τ
where ω 0 is a given frequency, and
where
τ
=
Δ
T
(
T
+
Δ
T
)
t
<
200
×
10
-
6
t
,
where t is a given time, and
where T is a symbol period.