US 8,265,491 B2Granted

Method for improving the performance of digital coherent optical receiver using single ended photo-detection

AssigneeAT&T Intellectual Property I, L.P.

InventorXiang Zhou

Life of this patent

Estimating the term…

Abstract

A method and system for mitigating distortion in coherent single-ended photo-detection is disclosed. The methodology comprises: receiving an optical signal carried on an optical transmission medium and coherently detecting the received optical signal to produce a digitized signal; estimating a time-dependent random variable introducing distortion to the coherently detected signal; and subtracting the distortion from digitized signal to produce a distortion mitigated output signal.

Claims6

Dependent claims

A method for mitigating distortion in coherent single-ended photo-detection comprising

receiving an optical signal carried on an optical transmission medium and coherently detecting the received optical signal to produce a digitized signal;
estimating a time-dependent random variable introducing distortion to the coherently detected signal;
subtracting the distortion from the digitized signal to produce a distortion mitigated output signal;
wherein signal power received by photo-detectors in the coherent detection is represented by:
P
I
⁡
(
t
)
=
P
S
⁡
(
t
)
+
P
L
⁡
(
t
)
+
2
⁢
P
S
⁡
(
t
)
⁢
P
L
⁡
(
t
)
⁢
cos
⁡
(
θ
⁡
(
t
)
)
P
Q
⁡
(
t
)
=
P
S
⁡
(
t
)
+
P
L
⁡
(
t
)
+
2
⁢
P
S
⁡
(
t
)
⁢
P
L
⁡
(
t
)
⁢
sin
⁡
(
θ
⁡
(
t
)
)
wherein PS(t) denotes the signal power and PL(t) denotes local oscillator power of a reference optical signal, and θ(t) represents a relative phase between the received optical signal and the reference optical signal, and further, wherein a digitized signal with AC coupling is represented by:
I
I
⁡
(
n
)
≅
I
~
S
⁡
(
n
)
+
2
⁢
I
S
⁡
(
n
)
⁢
I
L
⁡
(
n
)
⁢
cos
⁡
(
θ
⁡
(
t
n
)
)
I
Q
⁡
(
n
)
≅
I
~
S
⁡
(
n
)
+
2
⁢
I
S
⁡
(
n
)
⁢
I
L
⁡
(
n
)
⁢
sin
⁡
(
θ
⁡
(
t
n
)
)
and IS(n) denotes the coherently detected signal and IL(n) denotes a local oscillator signal, and ĨS(n) is the time-dependent random variable introducing distortion;
wherein a first-order approximation is represented by:
I
I
⁡
(
n
)
≈
2
⁢
I
S
⁡
(
n
)
⁢
I
L
⁡
(
n
)
⁢
cos
⁡
(
θ
⁡
(
t
n
)
)
I
Q
⁡
(
n
)
≈
2
⁢
I
S
⁡
(
n
)
⁢
I
L
⁡
(
n
)
⁢
sin
⁡
(
θ
⁡
(
t
n
)
)
and
⁢
:
I
I
2
⁡
(
n
)
+
I
Q
2
⁡
(
n
)
≈
4
⁢
I
~
S
⁡
(
n
)
⁢
I
_
L
⁡
(
n
)
+
4
⁢
I
_
S
⁢
I
_
L
I
I
2
+
I
Q
2
_
=
4
⁢
I
_
S
⁢
I
_
L
and ĪS(n) and ĪL(n) denote a DC component of IS(n) and IL(n) respectively, and II2+Iq2 denotes a DC component of II2(n)=Iq2(n), and, the first-order approximation of ĨS(n) is represented by:
I
~
S
(
1
)
⁡
(
n
)
=
I
I
2
⁡
(
n
)
+
I
Q
2
⁡
(
n
)
-
I
I
2
+
I
Q
2
_
4
⁢
I
_
L
and, a known local-oscillator-to-signal power ratio (LOSPR), defined as PL/ PS, is approximated as ĪL/ĪS such that ĪL is represented by:
I
_
L
≈
I
I
2
+
I
Q
2
_
·
LOSPR
2
.

366 more elements

A system for mitigating distortion in coherent single-ended photo-detection, comprising:

a coherent detector including a plurality of phase and polarization diverse hybrids and polarization beam splitters, photo-detectors and analog-to-digital converters, the detector configured to receive an optical signal carried on an optical transmission medium and coherently detect the received optical signal to produce a digitized signal;
a digital signal processor including a module for estimating a time-dependent random variable introducing distortion to the coherently detected signal and subtracting the distortion from the digitized signal to produce a distortion mitigated output signal;
wherein signal power received by the photo-detectors is represented by:
P
I
⁡
(
t
)
=
P
S
⁡
(
t
)
+
P
L
⁡
(
t
)
+
2
⁢
P
S
⁡
(
t
)
⁢
P
L
⁡
(
t
)
⁢
cos
⁡
(
θ
⁡
(
t
)
)
P
Q
⁡
(
t
)
=
P
S
⁡
(
t
)
+
P
L
⁡
(
t
)
+
2
⁢
P
S
⁡
(
t
)
⁢
P
L
⁡
(
t
)
⁢
sin
⁡
(
θ
⁡
(
t
)
)
wherein PS(t) denotes the signal power and PL(t) denotes local oscillator power of a reference optical signal, and θ(t) represents a relative phase between the received optical signal and the reference optical signal, and further, wherein a digitized electrical signal with AC coupling is represented by:
I
I
⁡
(
n
)
≅
I
~
S
⁡
(
n
)
+
2
⁢
I
S
⁡
(
n
)
⁢
I
L
⁡
(
n
)
⁢
cos
⁡
(
θ
⁡
(
t
n
)
)
I
Q
⁡
(
n
)
≅
I
~
S
⁡
(
n
)
+
2
⁢
I
S
⁡
(
n
)
⁢
I
L
⁡
(
n
)
⁢
sin
⁡
(
θ
⁡
(
t
n
)
)
and IS(n) denotes the coherently detected signal and IL(n) denotes a local oscillator signal, and ĨS(n) is the time-dependent random variable introducing distortion;
wherein a first-order approximation is represented by:
I
I
⁡
(
n
)
≈
2
⁢
I
S
⁡
(
n
)
⁢
I
L
⁡
(
n
)
⁢
cos
⁡
(
θ
⁡
(
t
n
)
)
I
Q
⁡
(
n
)
≈
2
⁢
I
S
⁡
(
n
)
⁢
I
L
⁡
(
n
)
⁢
sin
⁡
(
θ
⁡
(
t
n
)
)
and
⁢
:
I
I
2
⁡
(
n
)
+
I
Q
2
⁡
(
n
)
≈
4
⁢
I
~
S
⁡
(
n
)
⁢
I
_
L
⁡
(
n
)
+
4
⁢
I
_
S
⁢
I
_
L
I
I
2
+
I
Q
2
_
=
4
⁢
I
_
S
⁢
I
_
L
where, ĪS(n) and ĪLdenote a DC component of IS(n) and IL(n), respectively, and II2+Iq2 denotes a DC component of II2(n)+Iq2(n) , and the first order approximation of ĨS(n) is represented by:
I
~
S
(
1
)
⁡
(
n
)
=
I
I
2
⁡
(
n
)
+
I
Q
2
⁡
(
n
)
-
I
I
2
+
I
Q
2
_
4
⁢
I
_
L
and a known local-oscillator-to-signal power ratio (LOSPR), defined as PL/ PS, is approximated as IL/ IS such that IL is represented by:
I
_
L
≈
I
I
2
+
I
Q
2
_
·
LOSPR
2
.

365 more elements

A non-transitory computer-readable medium having encoded machine executable instructions that, when executed by at least one processor, causes an apparatus to mitigate distortion in coherent single-ended photo-detection by:

estimating a time-dependent random variable introducing distortion to a digitized signal from a coherently detected optical signal;
and
subtracting the distortion from the digitized signal to produce a distortion mitigated output signal;
wherein signal power received by photo-detectors in the coherent detection is represented by:
P
I
⁡
(
t
)
=
P
S
⁡
(
t
)
+
P
L
⁡
(
t
)
+
2
⁢
P
S
⁡
(
t
)
⁢
P
L
⁡
(
t
)
⁢
cos
⁡
(
θ
⁡
(
t
)
)
P
Q
⁡
(
t
)
=
P
S
⁡
(
t
)
+
P
L
⁡
(
t
)
+
2
⁢
P
S
⁡
(
t
)
⁢
P
L
⁡
(
t
)
⁢
sin
⁡
(
θ
⁡
(
t
)
)
wherein PS(t) denotes the signal power and PL(t)denotes local oscillator power of a reference optical signal, and θ(t) represents a relative phase between the received optical signal and the reference optical signal, and further, wherein a digitized electrical signal with AC coupling is represented by:
I
I
⁡
(
n
)
≅
I
~
S
⁡
(
n
)
+
2
⁢
I
S
⁡
(
n
)
⁢
I
L
⁡
(
n
)
⁢
cos
⁡
(
θ
⁡
(
t
n
)
)
I
Q
⁡
(
n
)
≅
I
~
S
⁡
(
n
)
+
2
⁢
I
S
⁡
(
n
)
⁢
I
L
⁡
(
n
)
⁢
sin
⁡
(
θ
⁡
(
t
n
)
)
and IS(n) denotes the coherently detected signal and IL(n) denotes a local oscillator signal, and ĨS(n) is the time-dependent random variable introducing distortion;
and
wherein a first-order approximation is represented by:
I
I
⁡
(
n
)
≈
2
⁢
I
S
⁡
(
n
)
⁢
I
L
⁡
(
n
)
⁢
cos
⁡
(
θ
⁡
(
t
n
)
)
I
Q
⁡
(
n
)
≈
2
⁢
I
S
⁡
(
n
)
⁢
I
L
⁡
(
n
)
⁢
sin
⁡
(
θ
⁡
(
t
n
)
)
and
⁢
:
I
I
2
⁡
(
n
)
+
I
Q
2
⁡
(
n
)
≈
4
⁢
I
~
S
⁡
(
n
)
⁢
I
_
L
⁡
(
n
)
+
4
⁢
I
_
S
⁢
I
_
L
I
I
2
+
I
Q
2
_
=
4
⁢
I
_
S
⁢
I
_
L
where ĪS(n) and ĪL(n), denote a DC component of IS(n) and IL(n), respectively, and II2+Iq2 denotes a DC component of II2(n)+Iq2(n), and, the first-order approximation of IS (n) is represented by:
I
~
S
(
1
)
⁡
(
n
)
=
I
I
2
⁡
(
n
)
+
I
Q
2
⁡
(
n
)
-
I
I
2
+
I
Q
2
_
4
⁢
I
_
L
and a known local-oscillator-to-signal power ratio (LOSPR), defined as PL/ PS is approximated as ĪL/ĪS such that ĪL is represented by:
I
_
L
≈
I
I
2
+
I
Q
2
_
·
LOSPR
2
.

367 more elements

Dependencies are inferred from the claim text.

Facts

Application: 12/386,837Filed 23 Apr 2009 · us provisional application
Priority: 22 Sep 2008
Published: US 2010/0074632 A125 Mar 2010
Granted: 11 Sep 2012
Term ends: Not estimatedThe source records don’t support an estimate.

Classification10 codes

H04B 10/6971
Arrangements for reducing noise and distortion: using equalisation
H04B 10/2513
For the reduction or elimination of distortion or dispersion: due to chromatic dispersion
H04B 10/25133
Due to chromatic dispersion: including a lumped electrical or optical dispersion compensator
H04B 10/61
Receivers: coherent receivers

Family

Application61/192,776Us provisional application · filed 22 Sep 2008
US 2010/0074632 A1Pre-grant publication · published 25 Mar 2010
US 8,265,491 B2This patent

From the US filing history. Foreign family members aren’t listed.

Timeline

Citations

Open elsewhere

patentgrep

Loading patent…

Abstract

A method for mitigating distortion in coherent single-ended photo-detection comprising

receiving an optical signal carried on an optical transmission medium and coherently detecting the received optical signal to produce a digitized signal;
estimating a time-dependent random variable introducing distortion to the coherently detected signal;
subtracting the distortion from the digitized signal to produce a distortion mitigated output signal;
wherein signal power received by photo-detectors in the coherent detection is represented by:
P
I
⁡
(
t
)
=
P
S
⁡
(
t
)
+
P
L
⁡
(
t
)
+
2
⁢
P
S
⁡
(
t
)
⁢
P
L
⁡
(
t
)
⁢
cos
⁡
(
θ
⁡
(
t
)
)
P
Q
⁡
(
t
)
=
P
S
⁡
(
t
)
+
P
L
⁡
(
t
)
+
2
⁢
P
S
⁡
(
t
)
⁢
P
L
⁡
(
t
)
⁢
sin
⁡
(
θ
⁡
(
t
)
)
wherein PS(t) denotes the signal power and PL(t) denotes local oscillator power of a reference optical signal, and θ(t) represents a relative phase between the received optical signal and the reference optical signal, and further, wherein a digitized signal with AC coupling is represented by:
I
I
⁡
(
n
)
≅
I
~
S
⁡
(
n
)
+
2
⁢
I
S
⁡
(
n
)
⁢
I
L
⁡
(
n
)
⁢
cos
⁡
(
θ
⁡
(
t
n
)
)
I
Q
⁡
(
n
)
≅
I
~
S
⁡
(
n
)
+
2
⁢
I
S
⁡
(
n
)
⁢
I
L
⁡
(
n
)
⁢
sin
⁡
(
θ
⁡
(
t
n
)
)
and IS(n) denotes the coherently detected signal and IL(n) denotes a local oscillator signal, and ĨS(n) is the time-dependent random variable introducing distortion;
wherein a first-order approximation is represented by:
I
I
⁡
(
n
)
≈
2
⁢
I
S
⁡
(
n
)
⁢
I
L
⁡
(
n
)
⁢
cos
⁡
(
θ
⁡
(
t
n
)
)
I
Q
⁡
(
n
)
≈
2
⁢
I
S
⁡
(
n
)
⁢
I
L
⁡
(
n
)
⁢
sin
⁡
(
θ
⁡
(
t
n
)
)
and
⁢
:
I
I
2
⁡
(
n
)
+
I
Q
2
⁡
(
n
)
≈
4
⁢
I
~
S
⁡
(
n
)
⁢
I
_
L
⁡
(
n
)
+
4
⁢
I
_
S
⁢
I
_
L
I
I
2
+
I
Q
2
_
=
4
⁢
I
_
S
⁢
I
_
L
and ĪS(n) and ĪL(n) denote a DC component of IS(n) and IL(n) respectively, and II2+Iq2 denotes a DC component of II2(n)=Iq2(n), and, the first-order approximation of ĨS(n) is represented by:
I
~
S
(
1
)
⁡
(
n
)
=
I
I
2
⁡
(
n
)
+
I
Q
2
⁡
(
n
)
-
I
I
2
+
I
Q
2
_
4
⁢
I
_
L
and, a known local-oscillator-to-signal power ratio (LOSPR), defined as PL/ PS, is approximated as ĪL/ĪS such that ĪL is represented by:
I
_
L
≈
I
I
2
+
I
Q
2
_
·
LOSPR
2
.

366 more elements

Facts

Application

12/386,837Filed 23 Apr 2009 · us provisional application

Priority

22 Sep 2008

Published

US 2010/0074632 A125 Mar 2010

Granted

11 Sep 2012

Term ends

Not estimatedThe source records don’t support an estimate.

Classification10 codes

H04B 10/6971
Arrangements for reducing noise and distortion: using equalisation
H04B 10/2513
For the reduction or elimination of distortion or dispersion: due to chromatic dispersion
H04B 10/25133
Due to chromatic dispersion: including a lumped electrical or optical dispersion compensator
H04B 10/61
Receivers: coherent receivers