U.S. patent application number 09/109252 was filed with the patent office on 2002-06-20 for multi-wavelength all-optical regenerators ( mars).
Invention is credited to CAO, XIANG-DONG.
Application Number | 20020075536 09/109252 |
Document ID | / |
Family ID | 22326651 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020075536 |
Kind Code |
A1 |
CAO, XIANG-DONG |
June 20, 2002 |
MULTI-WAVELENGTH ALL-OPTICAL REGENERATORS ( MARS)
Abstract
In an optical regenerator for use in an optical transmission
system, an optical input signal to the regenerator comprising N
wavelength division multiplexed channel signals is received in a
signal synchronizing arrangement which synchronizes the phase of
all of the N channels, where N.multidot.2. An optical output signal
from the signal synchronizing arrangement has N phase-synchronized
wavelength division multiplexed channels and is provided as an
optical input signal to a nonlinear optical loop mirror (NOLM)
arrangement. The NOLM has a high nonlinearity fiber loop that
propagates equal parts of the optical input signal from the signal
synchronizing arrangement in both a clockwise (CW) and a
counterclockwise (CCW) direction. An optical clock signal from a
laser having a phase that matches the phase of the CW and CCW
propagating signals is multiplexed with the CW signal to provide a
180 degree phase shift between the CW and CCW propagating signals
while propagating in the optical fiber loop. The NOLM retimes and
reshapes the optical pulses of the optical synchronized N
wavelength division multiplexed channels, and generates a
corresponding optical NOLM output signal to an Erbium-doped fiber
amplifier (EDFA). The EDFA amplifies the NOLM output signal, and
generates an amplified and phase-synchronized optical N wavelength
division multiplexed channel output signal that is transmitted from
the optical regenerator.
Inventors: |
CAO, XIANG-DONG; (BOYNTON
BEACH, FL) |
Correspondence
Address: |
SIEMENS CORPORATION
INTELLECTUAL PROPERTY DEPARTMENT
186 WOOD AVENUE SOUTH
ISELIN
NJ
08830
|
Family ID: |
22326651 |
Appl. No.: |
09/109252 |
Filed: |
June 30, 1998 |
Current U.S.
Class: |
398/97 ; 398/154;
398/161; 398/180 |
Current CPC
Class: |
H04B 2210/258 20130101;
H04B 10/299 20130101 |
Class at
Publication: |
359/124 ;
359/176 |
International
Class: |
H04J 014/02; H04B
010/00; H04B 010/02 |
Claims
What is claimed is:
1. An optical regenerator for use in an optical transmission system
comprising: an optical N wavelength division multiplexed channel
signal synchronizing arrangement responsive to the reception of an
optical input signal to the regenerator comprising N wavelength
division multiplexed channel signals for synchronizing the phase of
all of the N channel signals, and for generating an optical output
signal comprising N synchronized wavelength division multiplexed
channel signals, where N.multidot.2; an optical pulse retiming and
reshaping arrangement comprising a nonlinear optical loop mirror
(NOLM) arrangement which is responsive to the optical output signal
from the signal synchronizing arrangement for retiming and
reshaping optical pulses of the optical synchronized N wavelength
division multiplexed channel signals, and for generating a
corresponding optical NOLM output signal; and an Erbium-doped fiber
amplifier (EDFA) responsive to the optical NOLM output signal for
amplifying the retimed and reshape optical NOLM output signal, and
for generating an amplified and phase-synchronized optical N
wavelength division multiplexed channel output signal for
transmission as an output signal from the optical regenerator.
2. The optical regenerator of claim 1 wherein the optical N
wavelength division multiplexed channel signal synchronizing
arrangement comprises: an optical wavelength division demultiplexer
(WDD) responsive to the optical input signal to the regenerator for
directing the N wavelength division multiplexed channels onto
separate N output paths; a plurality of N-1 selectively changeable
optical delays coupled in predetermined N-1 output paths of the
WDD, each optical delay being responsive to a delay control signal
for selectively adjusting the phase of an associated one of the N-1
optical channel signals so that all of the N-1 optical channel
signals are synchronized in phase with an Nth optical channel
signal; an optical wavelength division multiplexer (WDM) for
multiplexing the Nth optical channel signal and the N-1 optical
channel signals from the plurality of N-1 optical delays to
generate a synchronized N wavelength division multiplexed channel
optical output signal; and a phase controller responsive to a
portion of the optical output signal from the WDM for detecting a
phase difference between the Nth channel signal and each of the N-1
delayed channel signals, and for generating a separate delay
control signal to each of the optical delays for synchronizing the
phase of each of the N-1 delayed optical channel signals to the
phase of the Nth optical channel signal.
3. The optical regenerator of claim 2 wherein the phase controller
comprises: a wavelength division demultipexer (WDD) responsive to a
portion of the optical output signal from the WDM for directing the
N channels onto separate N output paths; a power splitter for
splitting the power of a first one of the synchronized N wavelength
division multiplexed optical channel signals in a first output path
from the WDD into N-1 parts; a plurality of N-1 optical combiners,
each optical combiner combining a separate one of the N-1 parts of
the first one of the optical channel signals from the power
splitter and a separate one of second-to-N optical channel signals
in a second-to-N output path from the WDD for generating an optical
output signal corresponding to the combined associated channel
signals; and a plurality of N-1 filters, each filter being coupled
to receive a separate one of the optical output signals from the
plurality of N-1 combiners, and to generate a phase error control
signal as an output signal to a separate predetermined one of the
plurality of N-1 selectively changeable optical delays.
4. The optical regenerator of claim 3 wherein the phase controller
further comprises: a plurality of N-1 photodetectors, each
photodetector being coupled to receive a separate one of the
optical output signals from the plurality of N-1 optical combiners,
and to convert said separate one of the optical output signals into
a corresponding electrical signal; and the plurality of N-1 filters
are N-1 bandpass filters, each bandpass filter being coupled to
receive a separate one of the electrical signals from the plurality
of N-1 photodetectors and to generate a phase error control signal
as an output signal to a separate predetermined one of the
plurality of N-1 selectively changeable optical delays.
5. The optical regenerator of claim 1 wherein the optical pulse
retiming and reshaping arrangement further comprises: a clock
recovery circuit responsive to a predetermined one of the N channel
signals propagating in the optical N wavelength division
multiplexed channel signal synchronizing arrangement for generating
a clock output signal having a frequency corresponding to the bit
rate frequency of the predetermined one of the N channel signals,
and being responsive to the output signal from the EDFA for
synchronizing the phase of the clock output signal to the phase of
the output signal from the EDFA; and a laser responsive to the
clock output signal from the clock recovery circuit for generating
a corresponding optical clock output signal which is coupled into
the NOLM.
6. The optical regenerator of claim 5 wherein the NOLM comprises:
an optical fiber loop wherein at least a portion thereof comprises
a high nonlinearity optical fiber section; an optical coupler for
receiving the optical synchronized N wavelength division
multiplexed channel output signal from the signal synchronizing
arrangement at a first port thereof, and for directing first and
second halves of the received synchronized N channel output signal
for propagation in first and second opposite directions,
respectively, in the optical fiber loop; and a wavelength division
multiplexer (WDM) for multiplexing the optical clock output signal
from the laser with the first half of the optical synchronized N
wavelength division multiplexed channel output signal from the
signal synchronizing arrangement propagating in the first direction
in the optical fiber loop in order to shift the phase of the first
half of the optical synchronized N channel signal by a
predetermined amount and cause the first and second halves of the
synchronized N channel signals to be switched out of a second port
of the WDM to the EDFA.
7. The optical regenerator of claim 6 wherein the NOLM further
comprises a filter for blocking any of the optical clock output
signal from the laser from propagating to the optical coupler of
the NOLM after the phase of the first half signal has been shifted
by a predetermined amount.
8. The optical regenerator of claim 6 wherein the NOLM further
comprises: a first polarization controller coupled between the
laser and the WDM; and a second polarization controller coupled
between the optical coupler and the WDM of the NOLM, wherein the
first and second polarization controllers provide a proper optical
biasing of the optical fiber loop for stabilizing the NOLM when the
optical fiber loop is not polarization independent.
9. The optical regenerator of claim 1 wherein the NOLM comprises:
an optical fiber loop wherein at least a portion thereof comprises
a high nonlinearity fiber; an optical coupler for receiving the
optical synchronized N wavelength division multiplexed channel
output signal from the signal synchronizing arrangement at a first
port thereof, and for directing first and second halves of the
received synchronized N channel output signal for propagation in
first and second opposite directions, respectively, in the optical
fiber loop; and a wavelength division multiplexer (WDM) for
multiplexing the optical clock output signal from the laser with
the first half of the optical synchronized N wavelength division
multiplexed channel output signal from the signal synchronizing
arrangement propagating in the first direction in the optical fiber
loop in order to shift the phase of the first half of the optical
synchronized N channel signal by a predetermined amount and cause
the first and second halves of the synchronized N channel signals
to be switched out of a second port of the WDM to the EDFA.
10. The optical regenerator of claim 9 wherein the NOLM further
comprises a filter for blocking any of the optical clock output
signal from the laser from returning to the optical coupler of the
NOLM after the phase of the first half signal has been shifted by a
predetermined amount.
11. The optical regenerator of claim 9 wherein the NOLM further
comprises: a first polarization controller coupled between the
laser and the WDM; and a second polarization controller coupled
between the coupler and the WDM of the NOLM, wherein the first and
second polarization controllers provide a proper optical biasing of
the optical fiber loop for stabilizing the NOLM when the optical
fiber loop is not polarization independent.
12. An optical regenerator for use in an optical transmission
system comprising: an optical wavelength division demultiplexer
(WDD) responsive to an optical input signal to the regenerator
comprising N wavelength division multiplexed channels for directing
the N channels onto separate N output paths, where N.multidot.2; a
plurality of N-1 selectively changeable optical delays, each
optical delay being coupled in a separate predetermined one of N-1
output paths of the WDD, and being responsive to a delay control
signal for selectively adjusting the phase of the channel signal in
an associated one of an N-1 output paths so that all N-1 optical
channel signals are synchronized in phase with an Nth optical
channel signal propagating in an output path not including an
optical delay; an optical wavelength division multiplexer (WDM) for
multiplexing the Nth optical channel signal and the N-1 optical
channel signals from the plurality of N-1 optical delays into a
synchronized N wavelength division multiplexed channel optical
output signal; a phase controller responsive to a portion of the
optical output signal from the WDM for detecting a phase difference
between the Nth channel signal and each of the remaining N-1
delayed channel signals, and for generating a separate delay
control signal to each of the optical delays for synchronizing the
phase of each of the N-1 delayed optical channel signals to the
phase of the Nth optical channel signal; an optical pulse retiming
and reshaping arrangement comprising a nonlinear optical loop
mirror (NOLM) arrangement which is responsive to the optical
synchronized N wavelength division multiplexed channel output
signal from the WDM for retiming and reshaping optical pulses of
the optical synchronized N wavelength division multiplexed channels
and for generating a corresponding optical NOLM output signal; and
an Erbium-doped fiber amplifier (EDFA) responsive to the optical
NOLM output signal for amplifying NOLM output signal, and for
generating an amplified and phase-synchronized optical N wavelength
division multiplexed channel output signal for transmission as an
output signal from the optical regenerator.
13. The optical regenerator of claim 12 wherein the phase
controller comprises: a wavelength division demultipexer (WDD)
responsive to a portion of the optical output signal from the WDM
for directing the N channels onto separate N output paths; a power
splitter for splitting the power of a first one of the synchronized
N wavelength division multiplexed optical channel signals into N-1
parts; a plurality of N-1 optical combiners, each combiner
combining a separate one of the N-1 parts of the first one of the
synchronized N wavelength division multiplexed optical channel
signals from the power splitter for generating an optical output
signal corresponding to the combined associated channel signals;
and a plurality of N-1 filters, each filter being coupled to
receive a separate one of the output signals from the plurality of
N-1 combiners and to generate a phase error control signal as an
output signal to a separate predetermined one of the plurality of
N-1 selectively changeable optical delays.
14. The optical regenerator of claim 13 wherein the phase
controller further comprises: a plurality of N-1 photodetectors,
each photodetector being coupled to receive a separate one of the
optical output signals from the plurality of N-1 optical combiners
and to convert said separate one of the optical output signal into
a corresponding electrical signal; and the plurality of N-1 filters
are N-1 bandpass filters, each bandpass filter being coupled to
receive a separate one of the electrical signals from the plurality
of N-1 photodetectors and to generate a phase error control signal
as an output signal to a separate predetermined one of the
plurality of N-1 selectively changeable optical delays.
15. The optical regenerator of claim 12 wherein the optical pulse
retiming and reshaping arrangement further comprises: a clock
recovery circuit responsive to the predetermined Nth optical
channel signal in the Nth output path from the WDD for generating a
clock output signal having a frequency corresponding to the bit
rate frequency of the predetermined Nth optical channel signal, and
being responsive to the output signal from the EDFA for
synchronizing the phase of the clock output signal to the phase of
the amplified and phase-synchronized optical N wavelength division
multiplexed channel in the output signal from the EDFA; and a laser
responsive to the clock output signal from the clock recovery
circuit for generating a corresponding optical clock output signal
which is coupled into the NOLM.
16. The optical regenerator of claim 15 wherein the NOLM comprises:
an optical fiber loop wherein at least a portion thereof comprises
a high nonlinearity fiber section; an optical coupler for receiving
the optical synchronized N wavelength division multiplexed channel
output signal from the WDM at a first port thereof, and for
directing first and second halves of the received synchronized N
wavelength division multiplexed channel output signal for
propagation in first and second opposite directions, respectively,
in the optical fiber loop; and a wavelength division multiplexer
(WDM) for multiplexing the optical clock output signal from the
laser with the first half of the optical N channel signal
propagating in the first direction in the optical fiber loop in
order to shift the phase of the first half optical N channel signal
by a predetermined amount and cause the first and second halves of
the N channel signals to be switched out of a second port of the
WDM to the EDFA.
17. The optical regenerator of claim 16 wherein the NOLM further
comprises a filter for blocking any of the optical clock output
signal from the laser from returning to the optical coupler after
phase of the first half signal in the optical fiber loop has been
shifted by a predetermined amount.
18. The optical regenerator of claim 16 wherein the NOLM further
comprises: a first polarization controller coupled between the
laser and the WDM; and a second polarization controller coupled
between the coupler and the WDM, wherein the first and second
polarization controllers provide a proper optical biasing of the
optical fiber loop for stabilizing the NOLM when the optical fiber
loop is not polarization independent.
19. The optical regenerator of claim 12 wherein the NOLM comprises:
an optical fiber loop wherein at least a portion thereof comprises
a high nonlinearity fiber; an optical coupler for receiving the
optical synchronized N wavelength division multiplexed channel
output signal from the WDM at a first port thereof, and for
directing first and second halves of the received synchronized N
channel output signal for propagation in first and second opposite
directions, respectively, in the optical fiber loop; and a
wavelength division multiplexer (WDM) for multiplexing an optical
clock output signal with the first half of the optical N channel
signal from the WDM that is propagating in the first direction in
the optical fiber loop in order to shift the phase of the first
half signal by a predetermined amount and cause the first and
second halves of the synchronized N channel signals to be switched
out of a second port of the optical coupler of the NOLM to the
EDFA.
20. The optical regenerator of claim 19 wherein the NOLM further
comprises a filter for blocking any of the optical clock signal
from returning to optical coupler of the NOLM after the phase of
the first half signal has been shifted by a predetermined amount in
the optical fiber loop.
21. The optical regenerator of claim 19 wherein the NOLM further
comprises: a first polarization controller coupled between a source
of the optical clock signal and the WDM; and a second polarization
controller coupled between the coupler and the WDM, wherein the
first and second polarization controllers provide a proper optical
biasing of the optical fiber loop when the optical fiber loop is
not polarization independent.
22. An optical regenerator for use in an optical transmission
system comprising: an optical N wavelength division multiplexed
channel signal synchronizing arrangement responsive to the
reception of an optical input signal to the regenerator comprising
N wavelength division multiplexed channels for synchronizing the
phase of all of the N channel signals, and for generating an
optical synchronized N wavelength division multiplexed channel
output signal, where N.multidot.2; an optical pulse retiming and
reshaping arrangement comprising: a nonlinear optical loop mirror
(NOLM) arrangement which is responsive to the optical output signal
from the signal synchronizing arrangement for retiming and
reshaping optical pulses of the N channel signals, and for
generating a corresponding optical NOLM output signal; a clock
recovery circuit responsive to a predetermined one of the N channel
signals propagating in the optical synchronizing arrangement for
generating a clock output signal having a frequency corresponding
to the bit rate frequency of the predetermined one of the N channel
signals, and being responsive to an output signal from the optical
regenerator comprising N phase-synchronized optical channel signals
for synchronizing the phase of the clock output signal to the phase
of the N channel signals in the output signal from the optical
regenerator; and a laser responsive to the clock output signal from
the clock recovery circuit for generating a corresponding optical
clock output signal which is coupled into the NOLM; and an
Erbium-doped fiber amplifier (EDFA) for amplifying the optical NOLM
output signal, and for generating an amplified and
phase-synchronized optical N wavelength division multiplexed
channel output signal for transmission as the output signal from
the optical regenerator.
23. The optical regenerator of claim 22 wherein the NOLM comprises:
an optical fiber loop wherein at least a portion thereof comprises
a high nonlinearity optical fiber section; an optical coupler for
receiving the optical synchronized N wavelength division
multiplexed channel output signal from the signal synchronizing
arrangement at a first port thereof, and for directing first and
second halves of the received synchronized N channel output signal
for propagation in first and second opposite directions,
respectively, in the optical fiber loop; and a wavelength division
multiplexer (WDM) for multiplexing the optical clock output signal
from the laser with the first half of the optical synchronized N
wavelength division multiplexed channel output signal from the
signal synchronizing arrangement propagating in the first direction
in the optical fiber loop in order to shift the phase of the first
half signal by a predetermined amount and cause the first and
second halves of the N channel signals to be switched out of a
second port of the WDM to the EDFA.
24. The optical regenerator of claim 23 wherein the NOLM further
comprises a filter for blocking any of the optical clock output
signal from the laser returning to optical coupler after the phase
of the first half signal has been shifted by a predetermined amount
in the optical fiber loop.
25. The optical regenerator of claim 23 wherein the NOLM further
comprises: a first polarization controller coupled between the
laser and the WDM of the NOLM; and a second polarization controller
coupled between the coupler and the WDM of the NOLM, wherein the
first and second polarization controllers provide a proper optical
biasing of the optical fiber loop for stabilizing the NOLM when the
optical fiber loop is not polarization independent.
26. The optical regenerator of claim 22 wherein the optical N
wavelength division multiplexed channel signal synchronizing
arrangement comprises: an optical wavelength division demultiplexer
(WDD) responsive to the optical input signal to the regenerator for
directing the N wavelength division multiplexed channels onto
separate N output paths; a plurality of N-1 selectively changeable
optical delays coupled in predetermined N-1 output paths of the
WDD, each optical delay being responsive to a delay control signal
for selectively adjusting the phase of an associated one of N-1
optical channel signals so that all of the N-1 optical channel
signals are synchronized in phase with an Nth optical channel
signal not associated with an optical delay; an optical wavelength
division multiplexer (WDM) for multiplexing the Nth optical channel
signal and the N-1 optical channel signals from the plurality of
N-1 optical delays into a synchronized N wavelength division
multiplexed channel optical output signal; and a phase controller
responsive to a portion of the synchronized N wavelength division
multiplexed channel output signal from the WDM for detecting a
phase difference between the Nth channel signal and each of the N-1
delayed channel signals, and for generating a separate delay
control signal to each of the optical delays for synchronizing the
phase of each of the N-1 delayed optical channel signals to the
phase of the Nth optical channel signal.
27. The optical regenerator of claim 26 wherein the phase
controller comprises: a wavelength division demultipexer (WDD)
responsive to a portion of the synchronized N wavelength division
multiplexed channel output signal from the WDM for directing the N
channels onto separate N output paths; a power splitter for
splitting the power of a first one of the synchronized N wavelength
division multiplexed optical channel signals into N-1 parts; a
plurality of N-1 optical combiners, each optical combiner combining
a separate one of the N-1 parts from the power splitter and a
separate one of the remaining second-to-N wavelength division
multiplexed optical channel signals for generating an optical
output signal corresponding to the combined associated channel
signals; and a plurality of N-1 filters, each filter being coupled
to receive a separate one of the output signals from the plurality
of N-1 combiners and to generate a phase error control signal as an
output signal to a separate predetermined one of the plurality of
N-1 selectively changeable optical delays.
28. The optical regenerator of claim 27 wherein the phase
controller further comprises: a plurality of N-1 photodetectors,
each photodetector being coupled to receive a separate one of the
optical output signals from the plurality of N-1 optical combiners,
and to convert said separate one of the optical output signal into
a corresponding electrical signal; and the plurality of N-1 filters
are N-1 bandpass filters, each bandpass filter being coupled to
receive a separate one of the electrical signals from the plurality
of N-1 photodetectors and to generate a phase error control signal
as an output signal to a separate predetermined one of the
plurality of N-1 selectively changeable optical delays.
29. A method of regenerating a received optical N wavelength
division multiplexed channel signal in an optical regenerator of an
optical transmission system, where N.multidot.2, comprising the
steps of: (a) concurrently and separately synchronizing the phase
of all of the N channel signals in the received optical N
wavelength division multiplexed channel signal for generating an
optical output signal comprising N synchronized wavelength division
multiplexed channel signals, where N.multidot.2; (b) splitting the
optical output signal from step (a) into two halves in an optical
coupler so that a first half propagates in a first direction around
an optical fiber loop wherein at least a portion thereof comprises
a high nonlinearity optical fiber section and a second half
propagates in a second opposite direction around the optical fiber
loop; (c) multiplexing an optical clock output signal from a laser
with the first half signal propagating in the first direction in
the optical fiber loop in step (b) in an optical wavelength
division multiplexer for shifting the phase of the first half
signal by a predetermined amount and causing the first and second
halves of the N channel signals to be switched out of a second port
of the optical coupler as a NOLM output signal when they return to
the entry point of the optical fiber loop; and (d) amplifying the
optical NOLM output signal in an Erbium-doped fiber amplifier
(EDFA) for generating an amplified and phase-synchronized optical N
wavelength division multiplexed channel output signal for
transmission as an output signal from the optical regenerator.
30. The method of claim 29 wherein in performing step (a),
performing the steps of: (e) directing the N channel signals of the
received optical N wavelength division multiplexed channel signal
onto separate N output paths of an optical wavelength division
demultiplexer (WDD); (f) selectively adjusting the phase of each of
N-1 optical channel signals in N-1 output paths of the WDD in
separate one of a plurality of N-1 selectively changeable optical
delays so that all of the N-1 optical channel signals are
synchronized in phase with an Nth optical channel signal not
associated with an optical delay; (g) multiplexing the Nth optical
channel signal and the N-1 optical channel signals from the
plurality of N-1 optical delays into a synchronized N wavelength
division multiplexed channel optical output signal in an optical
wavelength division multiplexer (WDM); (h) detecting a phase
difference between the Nth channel signal and each of the N-1
delayed channel signals in the optical output signal from step (g)
in a phase controller; and (i) generating a separate delay control
signal from the phase controller to each of the optical delays for
synchronizing the phase of each of the N-1 delayed optical channel
signals to the phase of the Nth optical channel signal.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to multi-wavelength,
all-optical, regenerators for use in high speed optical
communication systems, and to a method for regenerating an optical
N wavelength division multiplexed channel signal received by a
regenerator.
BACKGROUND OF THE INVENTION
[0002] Conventional regenerators that are used in optical networks
convert received optical signals to electronic signals and then
back to optical signals for transmission to a next regenerator or
terminal station. The problem with such conventional type of
regenerators is that they have a bandwidth which is limited to 10
gigahertz and each channel has to be processed on a
channel-by-channel basis. As point-to-point transmission speeds in
communication systems approach 10 gigabits/second (e.g., in OC-192
systems) and beyond, it is highly desirable to use all-optical
regenerators to extend transmission distances between regenerators
(repeaters) instead of using the conventional type of regenerators
that convert received optical signals to electronic signals and
then back to optical signals. From a network point of view, the
conventional electronic type of regenerators become bottlenecks for
high capacity optical networks. In contrast, all-optical
regenerators can provide a larger bandwidth and have many
advantages when considering network scalability, management, and
capacity. Therefore, all-optical regenerators will be key
components for future all-optical communication networks.
[0003] It is desirable to provide a regenerator system and a method
which simultaneously reamplifies, retimes, and reshapes received
multiple wavelength division multiplexed channels entirely in the
optical domain before retransmission along a next section of an
optical communication system.
SUMMARY OF THE INVENTION
[0004] The present invention is directed to multi-wavelength
all-optical regenerators, where each regenerator reamplifies,
retimes, and reshapes multiple wavelength channels in a received N
wavelength division multiplexed optical channel signal entirely in
the optical domain.
[0005] Viewed from one aspect, the present invention is directed to
an optical regenerator for use in an optical transmission system
comprising an optical N wavelength division multiplexed channel
signal synchronizing arrangement, an optical pulse retiming and
reshaping arrangement comprising a nonlinear optical loop mirror
(NOLM) arrangement, and an Erbium-doped fiber amplifier (EDFA). The
optical N wavelength division multiplexed channel signal
synchronizing arrangement is responsive to the reception of an
optical input signal to the regenerator comprising N wavelength
division multiplexed channel signals for synchronizing the phase of
all of the N channel signals, and for generating an optical output
signal comprising synchronized N wavelength division multiplexed
channel signals, where N.multidot.2. The nonlinear optical loop
mirror (NOLM) arrangement in the optical pulse retiming and
reshaping arrangement is responsive to the optical output signal
from the signal synchronizing arrangement for retiming and
reshaping optical pulses of the optical synchronized N wavelength
division multiplexed channel signals, and for generating a
corresponding optical NOLM output signal. The Erbium-doped fiber
amplifier (EDFA) amplifies the optical NOLM output signal, and
generates an amplified and phase-synchronized optical N wavelength
division multiplexed channel output signal for transmission as an
output signal from the optical regenerator.
[0006] Viewed from another aspect, the present invention is
directed to an optical regenerator for use in an optical
transmission system comprising an optical wavelength division
demultiplexer (WDD), a plurality of N-1 selectively changeable
optical delays, an optical wavelength division multiplexer (WDM),
an optical pulse retiming and reshaping arrangement comprising a
nonlinear optical loop mirror (NOLM) arrangement, and an
Erbium-doped fiber amplifier (EDFA), where N.multidot.2. The WDD is
responsive to an optical input signal to the regenerator comprising
N wavelength division multiplexed channels for directing the N
channels onto separate N output paths. Each of the plurality of N-1
selectively changeable optical delays is coupled in a separate
predetermined one of N-1 output paths of the WDD. Still further,
each selectively changeable optical delay is responsive to a delay
control signal for selectively adjusting the phase of the channel
signal propagating in an associated one of an N-1 output path so
that all N-1 optical channel signals are synchronized in phase with
an Nth optical channel signal. The WDM multiplexes the Nth optical
channel signal and the N-1 optical channel signals from the
plurality of N-1 optical delays into a synchronized N wavelength
division multiplexed channel optical output signal. The phase
controller is responsive to a portion of the output signal from the
WDM for detecting a phase difference between the Nth channel signal
and each of the remaining N-1 delayed channel signals. In turn, the
phase controller generates a separate delay control signal to each
of the optical delays for synchronizing the phase of each of the
N-1 delayed optical channel signals to the phase of the Nth optical
channel signal. The optical pulse retiming and reshaping
arrangement comprising a nonlinear optical loop mirror (NOLM)
arrangement which is responsive to the optical output signal from
the WDM for retiming and reshaping optical pulses of the optical
synchronized N wavelength division multiplexed channel signals and
for generating a corresponding optical NOLM output signal. The EDFA
amplifies the NOLM output signal, and generates an amplified and
phase-synchronized optical N wavelength division multiplexed
channel output signal for transmission as an output signal from the
optical regenerator.
[0007] Viewed from still another aspect, the present invention is
directed to an optical regenerator for use in an optical
transmission system comprising an optical N wavelength division
multiplexed channel signal synchronizing arrangement, an
Erbium-doped fiber amplifier (EDFA), and an optical pulse retiming
and reshaping arrangement comprising a nonlinear optical loop
mirror (NOLM) arrangement, a clock recovery circuit, and a laser.
The optical N wavelength division multiplexed channel signal
synchronizing arrangement is responsive to the reception of an
optical input signal to the regenerator comprising N wavelength
division multiplexed channels for synchronizing the phase of all of
the N channel signals, and for generating an optical synchronized N
wavelength division multiplexed channel output signal, where
N.multidot.2. The nonlinear optical loop mirror (NOLM) arrangement
is responsive to the optical output signal from the signal
synchronizing arrangement for retiming and reshaping optical pulses
of the N channel signals, and for generating a corresponding
optical NOLM output signal. The clock recovery circuit is
responsive to a predetermined one of the N channel signals
propagating in the optical synchronizing arrangement for generating
a clock output signal having a frequency corresponding to the bit
rate frequency of the predetermined one of the N channel signals.
The clock recovery circuit is also responsive to an output signal
from the optical regenerator comprising N phase-synchronized
optical N channel signals for synchronizing the phase of the clock
output signal to the phase of the N channel signals in the output
signal from the optical regenerator. The laser is responsive to the
clock output signal from the clock recovery circuit for generating
a corresponding optical clock output signal which is coupled into
the NOLM. The Erbium-doped fiber amplifier (EDFA) is used to
amplify the optical NOLM output signal, and generate an amplified
and phase-synchronized optical N wavelength division multiplexed
channel output signal for transmission as the output signal from
the optical regenerator.
[0008] Viewed from still another aspect, the present invention is
directed to a method of regenerating a received optical N
wavelength division multiplexed channel signal in an optical
regenerator of an optical transmission system, where N.multidot.2,
comprising the following steps. In a first step, the phase of all
of the N channel signals in the received optical N wavelength
division multiplexed channel signal are concurrently and separately
synchronized for generating an optical output signal comprising N
synchronized wavelength division multiplexed channel signals. In a
second step, the optical output signal from step (a) is split into
two halves in an optical coupler so that a first half propagates in
a first direction around an optical fiber loop wherein at least a
portion thereof comprises a high nonlinearity optical fiber section
and a second half propagates in a second opposite direction around
the optical fiber loop. In a third step, an optical clock output
signal from a laser is multiplexed with the first half signal
propagating in the first direction in the optical fiber loop in the
second step in an optical wavelength division multiplexer. This
shifts the phase of the first half signal in the optical fiber loop
by a predetermined amount and causes the first and second halves of
the N channel signals to be switched out of a second port of the
optical coupler as a NOLM output signal when the two halves return
to the entry point of the optical fiber loop. In a fourth step, the
optical NOLM output signal from the third step is amplified in an
Erbium-doped fiber amplifier (EDFA) for generating an amplified and
phase-synchronized optical N wavelength division multiplexed
channel output signal for transmission as an output signal from the
optical regenerator.
[0009] The invention will be better understood from the following
more detailed description taken with the accompanying drawings and
claims.
BRIEF DESCRIPTION OF THE DRAWING
[0010] FIG. 1 shows a block diagram of a multi-wavelength,
all-optical, regenerator system (MARS) in accordance with the
present invention; and
[0011] FIG. 2 is a block diagram of a phase controller for use in
the multi-wavelength, all-optical, regenerator system (MARS) of
FIG. 1 in accordance with the present invention.
DETAILED DESCRIPTION
[0012] Referring now to FIG. 1, there is shown a block diagram of a
multi-wavelength, all-optical, regenerator system (MARS) 10 (shown
within a dashed line rectangle) in accordance with the present
invention. The MARS 10 is a photonic device that simultaneously
performs the functions of reamplification, retiming, and reshaping
of N wavelength division multiplexed channels in the optical domain
without converting the received signal format from an optical
signal to an electronic signal and back to an optical signal (a
so-called o-e-o conversion) before retransmission along another
section of an optical communication system.
[0013] The MARS 10 comprises an optical wavelength division
demultiplexer (WDD) 20, first, second, and third optical taps 22,
32, and 44, respectively, a plurality of N-1 selectively changeable
optical delays (DELAY) (of which only three delays 24, 25, and 26
are shown), an optical wavelength division multiplexer (WDM) 30, an
optical isolator 34, a phase controller 40, an Erbium-doped fiber
amplifier (EDFA) 42, a clock recovery circuit 50, a laser 52, and a
nonlinear optical loop mirror (NOLM) 60 (shown within a dashed line
rectangle). The combination of the WDD 20, the first and second
optical taps 22 and 32, the plurality of N-1 selectively changeable
optical delays 24, 25, and 26, the WDM 30, and the phase controller
40 can be considered as a signal synchronizing arrangement.
similarly, the combination of the clock recovery circuit 50, the
laser 52, and the NOLM 60 can be considered as a pulse retiming and
reshaping arrangement. The NOLM 60 comprises a 50:50 coupler 70
that is coupled to both ends of a nonlinear optical loop 71. The
nonlinear optical loop 71 provides a serial coupling of a optional
first polarization controller (POLAR. CONT.) 72 (shown within a
dashed line rectangle), an optical wavelength division multiplexer
(WDM) 76, a loop of a dispersion-shifting high nonlinearity fiber
80, and a filter (FILT.) 82. The NOLM 60 further comprises a second
optional polarization controller (POLAR. CONT.) 74 (shown within a
dashed line rectangle) which couples an output of the laser 52 to
an input of the WDM 76.
[0014] In the MARS 10, an optical input signal comprising N
wavelength division multiplexed channels is provided at an input 18
as an input to the WDD 20, where N can comprise any integer
.multidot.2 such as 4, 8, 16, 32, etc. However, for purposes of
explanation hereinafter, it is assumed that N=4. The WDD 20 is a
wavelength division demultiplexer which directs the N wavelength
division multiplexed channels along N separate output paths. A
first channel (CH.1) of the N wavelength division multiplexed
channels, which is hereinafter considered as a reference channel,
is directed to an input of the first optical tap 22. The second
channel (CH.2), the third channel (CH.3), and the Nth channel
(CH.N) of the N wavelength division multiplexed channels are
directed to inputs of the first optical delay 24, the second
optical delay 25, and the third optical delay 26, respectively. A
first output from the first optical tap 22 is coupled to a first
input of the clock recovery circuit 50. A second output from the
first optical tap 22, and outputs from the first, second, and third
selectively changeable optical delays 24, 25, and 26 are
multiplexed in the wavelength division multiplexer (WDM) 30 to
generate an output signal comprising N phase synchronized
wavelength division multiplexed channels. The output signal from
the WDM 30 is coupled to an input of the second optical tap 32.
[0015] A first output of the second optical tap 32 is coupled to an
input of the phase controller 40 to divert a small amount (e.g.,
2%) of the output signal from the WDM 30 to the phase controller 40
as an error control signal. Separate N-1 outputs from the phase
controller 40 are coupled to separate ones of the first, second,
and third selectively changeable optical delays 24, 25, and 26. The
phase controller 40 is responsive to the error control signal
received from the second optical tap 32 to generate separate delay
control signals to each of the first, second, and third selectively
changeable optical delays 24, 25, and 26. A second output of the
second optical tap 32 is coupled to an input of the optical
isolator 34, and an output of the optical isolator 34 is coupled to
the NOLM 60 via a first port of the 50:50 optical coupler 70.
[0016] A second port of the 50:50 optical coupler 70 is coupled to
an input of the Erbium-doped fiber amplifier (EDFA) 42 which
generates an amplified output signal that is coupled to an input of
the third optical tap 44. The third optical tap 44 directs a small
portion (e.g., 2%) of the output signal from the EDFA 42 to the
photodetector 46, and the remaining portion of the output signal
from the EDFA 42 as an amplified and synchronized N wavelength
division multiplexed optical output signal from the MARS 10 on
optical fiber 48. The photodetector 46 converts the received
portion of the N wavelength division multiplexed optical output
signal into a corresponding electrical control signal which is
coupled to an second input of the clock recovery circuit 50. An
output of the clock recovery circuit 50 is coupled to a control
input of the laser 52. The laser 52 is preferably a continuous wave
laser which has its frequency and phase controlled by a control
signal from the clock recovery circuit 50. The output from the
laser 52 is coupled to the WDM 76 via the optional polarization
controller (POLAR. CONT.) 74 of the NOLM 60.
[0017] In an operation of the MARS 10, the input optical signal
comprising N different wavelength division multiplexed channels
from input 18 is provided as an input to the WDD 20, where the N
channels are separated and directed to the first optical tap 22,
and the first, second, and third selectively changeable optical
delays 24, 25, and 26, respectively. In the first, second, and
third delays 24, 25, and 26, control signals generated in the phase
controller 40 cause the phase of each of the second-to-N channels
of the input signal to be synchronized to the phase of the
reference channel (CH.1) before being multiplexed and recombined in
the WDM 30. An error control signal from the second optical tap 32
is used by the phase controller 40 to determine any phase
differences between each of the second-to-N channels and the first
channel. If any phase differences are detected, the phase
controller 40 generates appropriate control signals to the first,
second, and third selectively changeable optical delays 24, 25, and
26 to cause the phases of all of the N channels to be synchronized.
An exemplary arrangement of the phase controller 40 will be
discussed hereinafter in relation to FIG. 2.
[0018] The synchronized and recombined N channels from the WDM 30
are coupled to the 50:50 optical coupler 70 of the NOLM 60 via the
second optical tap 32 and the isolator 34. The isolator 34 is used
to block any signals from the NOLM 70 from propagating back towards
the input 18 of the MARS 10.
[0019] In the NOLM 60, the synchronized and recombined N channel
input signal is split into two parts by the 50:50 optical coupler
70. A first part of the split signal propagates in a clockwise (CW)
direction in the nonlinear optical loop 71, while the second part
of the split signal propagates in a counterclockwise (CCW)
direction in the nonlinear optical loop 71. Both the first part
(CW) and second part (CCW) of the input signal propagate through
physically the same path in the nonlinear optical loop 71. Without
the introduction of the clock signal from the laser 52, the two
parts of the input signal will still be in phase when they reach
the 50:50 optical coupler 70 after traversing the loop 71. Under
such condition, the first and second parts would be switched out of
the 50:50 combiner 70 back towards the input 18 of the MARS 10. The
isolator 34, in turn, would block any signal from the 50:50
combiner 70 from propagating back towards the input 18 of the MARS
10.
[0020] However, a phase shift (e.g., D or 180 degrees) can be
introduced into the first (CW) propagating signal when the local
controlled laser 52 is coupled into the NOLM 60 via the WDM 76 and
co-propagates with the first (CW) signal. This is due to a
cross-phase modulation occurring between the control laser 52 and
the first (CW) propagating signal. More particularly, the clock
signal from the laser 52 cause a phase modulation (shifts the
phase) of the first CW signal. The amount of phase modulation or
shifting of the phase of the first CW signal is dependent on the
power of clock signal from the laser 52. The dispersion-shifted
high nonlinearity optical fiber coil 80 inside the loop 71 is used
to increase the normal nonlinear phase shift. This enhancing of the
phase shift or phase modulation of the first CW signal permits a
decreasing of the power needed of the control laser 52 to cause a
same amount of phase shift. Since the wavelength of the optical
signal from the control laser 52 is different from the wavelengths
of the N channel signals propagating the CW direction, a 2.times.1
WDM 76 is used to couple the signal from laser 52 into the loop 71.
The filter 82 is arranged to pass the N channel signals propagating
in the CW and CCW directions and block any of the signal of the
control laser 52 from reaching the 50:50 optical coupler 70.
[0021] When the first CW signal and the second CW signal are 180
degrees out of phase on returning to the 50:50 coupler 70, the two
signals from the loop 71 are not switched out towards the input 18
of the MARS 10. Instead, the two signals from the loop 71 are
switched out of the other port of the 50:50 optical combiner 70 and
coupled to an input of the Erbium-doped fiber amplifier (EDFA) 42.
If some small portion of the two signals from the loop 71 is
switched out of the 50:50 coupler 70 towards the input 18 of the
MARS 10 because the two signals are not exactly 180 degrees out of
phase, the isolator 34 blocks such signal from reaching the input
18 of the MARS 10. The EDFA 42 amplifies the output signal from the
50:50 optical combiner 70 by a predetermined amount and generates
an output signal that is coupled to an input of the third optical
tap 44. The third optical tap 44 diverts a small portion (e.g., 2%)
of the amplified optical signal from the EDFA 42 to the
photodetector 46, and the remaining amplified optical signal as the
output from the MARS 10 for transmission along an output optical
fiber 48. The photodetector 46 converts the optical signal received
from the third optical tap 44 into a corresponding electrical
control signal to the clock recovery circuit 50.
[0022] The clock recovery circuit 50 is responsive to the portion
of the channel 1 signal obtained from the first optical tap 22 to
generate an output clock signal that has a same frequency (bit
rate) as the pulses of the channel 1 signal. The electrical control
signal from the photodetector 46 is used by the clock recovery
circuit 50 to adjust the phase of the output clock signal so as to
match the phase of the N synchronized wavelength division
multiplexed signal obtained from the output of the MARS 10. More
particularly, the phase of the clock generated by the clock
recovery circuit 50 is adjusted in such a way by the electrical
control signal from the photodetector 46 that the output clock
signal from the clock recovery circuit 50 is at a maximum value.
Such maximum value of the output clock signal corresponds to an
in-phase condition between the control laser 52 and the
synchronized and amplified N division multiplexed channel signals
at the output of the MARS 10. The output clock signal from the
clock recovery circuit 50 is used to directly drive the laser 52,
which is then used to switch out the synchronized clock and N
channel signals from the NOLM 60 to the EDFA 42. In this manner,
the laser output signal is in phase with the first CW N channel
signal propagating in the loop 71 of the NOLM 60.
[0023] The polarization controllers 72 and 74 are optional devices
and are used only if switching of the synchronized N division
multiplexed channels out of the NOLM 60 is dependent on
polarization states of the signals. When the NOLM 60 is
polarization dependent, then the polarization controllers 72 and 74
are used to optimize the extinction ratio and the efficiency of the
nonlinear transmissions in the loop 71. More particularly, when a
field in the loop 71 of the NOLM 60 produces some birefringence
(double refraction) therein, the polarization controllers 72 and 74
are needed to properly optically bias the switching of the NOLM 60.
Since the polarization state within the loop 71 does not depend on
the conditions of the input signal, once the optical bias within
the NOLM 60 is properly adjusted, the bias and the loop 71 is
stabilized and the bias remains fixed. Because of such optical
biasing to control the polarization state in the loop 71, the
efficiency of the nonlinear transmissions from the loop to the EDFA
42 are improved. However, when the design of the NOLM 60 is made
polarization insensitive, then the optional polarization
controllers 72 and 74 are not required.
[0024] In accordance with the present invention, all output signals
from the MARS 10 are retimed by a retiming arrangement comprising
the clock recovery circuit 50 and the laser 52 to have a same
timing as the clock generated in the clock recovery circuit 50, and
thereby cause any timing jitter in the input signal to the MARS 10
to be corrected. Still further, the pulse amplitudes of all of the
N channel signals are restored to a predetermined level by using
the EDFA 42 at the output of the NOLM 60. Additionally, since the
switching timing window is determined by the pulses of the control
laser 52, the switched out pulses will have a same pulse shape as
the pulse of the control laser 52. Therefore, the output pulses
from the MARS 10 are reshaped according to the pulse shape of the
control laser 52. By a proper design of the NOLM 60 and the
waveform of the control laser 52, the output pulse shape from the
MARS 10 can be adjusted to optimize the system performance of the
MARS 10.
[0025] Other advantages can be obtained from the design of the MARS
10. A first advantage is that any noise in each channel is reduced
by the NOLM 60, which is a well known property of a NOLM. More
particularly, the NOLM 60 operates as a timing gate, where it opens
periodically at times when the MARKS (or 1's) of each channel
arrive, and closes in between. Therefore, any noise between MARKS
will be blocked out.
[0026] A second advantage is that in order to optimize the system
performance, there exists an optimal frequency chirp for a best Q
factor, or an equivalent bit error rate (BER). In the MARS 10, it
is possible to control the chirp of the output signal from the MARS
10 by adjusting the power level of the control laser 52. More
particularly, modifying the switching power of the laser 52 is
strictly done at the laser 52 and not within the loop 71 since the
loop 71 is a passive device. If the control laser 52 is stronger
than required, it will introduce a larger phase shift between the
two oppositely propagating N channel signals. Any phase difference
between the two oppositely propagating N channel signals is
proportional to the poser of the laser 52. The higher the power of
the laser 52, the larger the phase difference that is introduced.
Two effects occur--first, there is an intense demodulation because
of the interference effect, and second, there is also a phase
factor which chirps the pulses. By controlling the laser power, the
amount of chirp and the transmission from the NOLM 60 will be
controlled. Chirp indicates that the frequency across a pulse is
not uniform because the frequency changes over time across the
pulse. For example, when a pulse is launched through a chromatic
dispersant element such as an optical fiber, the pulse will become
chirped because the lower frequency portion moves faster when
compared to the higher frequency portion. Therefore, the leading
edge of the pulse has a lower frequency than the trailing edge of
the pulse and is referred to as a "chirp".
[0027] A third advantage is that (a) the input signal to the MARS
10 can either be a NonReturn to Zero (NRZ) or Return to Zero (RZ)
format, or (b) the output signal format from the MARS 10 can be a
RZ format or quasi RZ format. Since the RZ format provides better
performance than the NRZ format for OC-192 systems and beyond, the
MARS 10 is able to optimize an existing NRZ transmission
performance by modifying the pulse format to a quasi NRZ. The
built-in chirp control function available in the MARS 10 is also
very useful in dealing with high chromatic dispersion. Still
further, the MARS 10 is also compatible with solitron systems.
[0028] Referring now to FIG. 2, there is shown a block diagram of
an exemplary arrangement of a block diagram of a phase controller
40 (shown within a dashed line rectangle) for use in the
multi-wavelength, all-optical, regenerator system (MARS) of FIG. 1
in accordance with the present invention. The phase controller 40
comprises an optical wavelength division demultiplexer (WDD) 100, a
power splitter 102, a plurality of N-1 optical combiners (of which
only first, second, and third optical combiners 104A, 104B, and
104N, respectively, are shown), a plurality of N-1 photodetectors
(of which only first, second, and third photodetectors 107A, 107B,
and 107N, respectively, are shown), and a plurality of N-1 bandpass
filters (BPF) (of which only first, second, and third bandpass
filters 110A, 110B, and 110N, respectively, are shown). For
purposes of discussion hereinafter, it is assumed that N=4. An N
synchronized wavelength division multiplexed channel signal from
the second optical tap 32 of the MARS 10 of FIG. 1 is provided as
an input signal to the WDD 100. The WDD 20 is a wavelength division
demultiplexer which separates the N channels and directs the N
different wavelength division multiplexed channels along N separate
output paths. A first channel (CH.1), which is hereinafter
considered as a reference channel, is directed along a first path
to an input of the power splitter 102. The power splitter 102
divides the first channel signal into N-1 parts which are coupled
to first inputs of separate ones of the optical combiners 104A,
104B, and 104N. The second channel (CH.2) signal from the WDD 100
is coupled to a second input of the optical combiner 104A, the
third channel (CH.3) from the WDD 100 is coupled to a second input
of the optical combiner 104B, and the Nth channel (CH.N) from the
WDD 100 is coupled to a second input of the optical combiner 104N.
Outputs from the optical combiners 104A, 104B, and 104N are coupled
to inputs of the photodetectors 107A, 107B, and 107N, respectively.
Outputs from the photodetectors 107A, 107B, and 107N are coupled to
inputs of the BPFs 110A, 110B, and 110N, respectively. The outputs
from the BPFs 110A, 110B, and 110N are provided as delay control
signals to the first, second, and third optical delays 22, 23, and
24, respectively, of the MARS 10 of FIG. 1.
[0029] In operation, the N synchronized wavelength division
multiplexed channel signals from the second optical tap 32 of the
MARS 10 of FIG. 1 are demultiplexed in the WDD 100. The optical
combiner 104A combines the second channel (CH.2) signal from the
WDD 100 with the part of the reference channel (CH.1) signal
provided by the power splitter 102. The photodetector 107A converts
the optical signal from the optical combiner 104A into a
corresponding electrical signal which is coupled to the BPF 110A.
An output error control signal from the BPF 110A is proportional to
a phase error between the demultiplexed channel 2 signal and the
reference channel (CH. 1). Each of the combinations of the optical
combiner 104B, photodetector 107B, and BPF 110B for the third
channel, and the optical combiner 104N, photodetector 107N, and BPF
110N for the Nth channel operate in the same manner as described
hereinabove for the combination of the optical combiner 104A,
photodetector 107A, and BPF 110A for the second channel. The error
control signals from the BPFs 110A, 110B, and 110N are
simultaneously fed back to optical delays 22, 23, and 24,
respectively, to synchronize the phases of all of the N channels
prior to being multiplexed in the WDM 30 (shown in FIG. 1).
[0030] It is to be appreciated and understood that the specific
embodiments of the present invention described hereinabove are
merely illustrative of the general principles of the invention.
Various modifications may be made by those skilled in the art which
are consistent with the principles set forth.
* * * * *