U.S. patent application number 10/281152 was filed with the patent office on 2003-04-03 for optical exchanger.
This patent application is currently assigned to Fujitsu Limited. Invention is credited to Kuroyanagi, Satoshi, Maeda, Takuji, Nakajima, Ichiro, Nishi, Tetsuya, Tsuyama, Isao.
Application Number | 20030063347 10/281152 |
Document ID | / |
Family ID | 12526429 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030063347 |
Kind Code |
A1 |
Kuroyanagi, Satoshi ; et
al. |
April 3, 2003 |
Optical exchanger
Abstract
In addition to the configuration of a conventional optical XC
node, a former-stage regenerator for converting optical signals to
electrical signals and regenerating optical signals again is
provided at an output stage of a demultiplexer and at the input
stage of an optical switch unit. Since the regenerator has a 3R
function, the regenerator compensates for the influence of the
noise and crosstalk generated during propagation in the
transmission line, and improves the S/N ratio of the optical
signals. Since the optical signals with S/N ratios improved in this
way are inputted to the optical switch unit, it is sufficient only
if a latter-stage regenerator compensates for the S/N ratio
degradation generated in the optical switch unit, and thereby the
error rate characteristic of the optical signals can be
improved.
Inventors: |
Kuroyanagi, Satoshi;
(Kanagawa, JP) ; Nishi, Tetsuya; (Kanagawa,
JP) ; Maeda, Takuji; (Kanagawa, JP) ; Tsuyama,
Isao; (Kanagawa, JP) ; Nakajima, Ichiro;
(Kanagawa, JP) |
Correspondence
Address: |
STAAS & HALSEY LLP
700 11TH STREET, NW
SUITE 500
WASHINGTON
DC
20001
US
|
Assignee: |
Fujitsu Limited
Kawasaki
JP
|
Family ID: |
12526429 |
Appl. No.: |
10/281152 |
Filed: |
October 28, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10281152 |
Oct 28, 2002 |
|
|
|
09111770 |
Jul 8, 1998 |
|
|
|
6496289 |
|
|
|
|
Current U.S.
Class: |
398/43 |
Current CPC
Class: |
H04J 14/02 20130101 |
Class at
Publication: |
359/128 ;
359/117 |
International
Class: |
H04J 014/00; H04J
014/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 20, 1998 |
JP |
10-038480 |
Claims
What is claimed is:
1. An optical exchanger for accommodating a plurality of
wavelength-multiplexed input/output optical links, routing
wavelength-multiplexed optical signals inputted from each input
link, and outputting the optical signals to output links,
comprising: demultiplexing means for demultiplexing
wavelength-multiplexed optical signals inputted from the input link
to optical signals of each wavelength; first regenerating means for
regenerating optical signals of each wavelength outputted from the
demultiplexing means; optical switch means for receiving each input
optical signal outputted from the first regenerating means, routing
the input and outputting the input optical signals; second
regenerating means for regenerating optical signals of each
wavelength outputted from the optical switch means and compensating
for an S/N ratio degradation; and multiplexing means for
multiplexing optical signals of each wavelength outputted from the
second regenerating means, generating wavelength-multiplexed
optical signals and transmitting the optical signals to a
transmission line.
2. The optical exchanger according to claim 1, wherein said first
regenerating means does not convert the wavelengths of inputted
optical signals.
3. The optical exchanger according to claim 2, further comprising;
noise elimination filter means for eliminating wavelength
components different from inputted optical signals, provided at the
former-stage of said second regenerating means and on the output
side of said optical switch means.
4. The optical exchanger according to claim 1, wherein when
outputting inputted optical signals, said first regenerating means
converts the wavelength so that all the wavelengths of the optical
signals inputted to said optical switch means are different from
each other.
5. The optical exchanger according to claim 1, further comprising;
noise elimination filter means for enabling changing of the
transmission band thereof, provided at the former-stage of said
second regenerating means and on the output side of said optical
switch means, wherein said first regenerating means converts the
wavelength when regenerating and outputting optical signals so that
all the wavelengths of the optical signals inputted to said optical
switch means are different from each other.
6. The optical exchanger according to claim 1, wherein all the
output wavelengths of optical signals from said first regenerating
means are the same.
7. The optical exchanger according to claim 6, further comprising:
noise elimination filter means for eliminating wavelength
components different from inputted optical signals, provided at the
former-stage of said second regenerating means and on the output
side of said optical switch means.
8. The optical exchanger according to claim 1, further comprising:
noise elimination filter means for enabling changing of the
transmission band thereof, provided at the former-stage of said
second regenerating means and on the output side of said optical
switch means, wherein said first regenerating means regenerates and
outputs inputted optical signals without converting the
wavelengths.
9. An optical exchanger for accommodating a plurality of
wavelength-multiplexed input/output optical links, routing
wavelength-multiplexed optical signals inputted from each input
link, and outputting the optical signals to output links,
comprising: a demultiplexer demultiplexing wavelength-multiplexed
optical signals inputted from the input link to optical signals of
each wavelength; a first regenerator regenerating optical signals
of each wavelength outputted from the demultiplexer; an optical
switch receiving each input optical signal outputted from the first
regenerator, routing the input and outputting the input optical
signals; a second regenerator regenerating optical signals of each
wavelength outputted from the optical switch and compensating for
an S/N ratio degradation; and a multiplexer multiplexing optical
signals of each wavelength outputted from the second regenerator,
generating wavelength-multiplexed optical signals and transmitting
the optical signals to a transmission line.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a configuration for
preventing a waveform of an optical signal from degrading in an
optical exchanger (cross-connect node).
[0003] 2. Description of the Related Art
[0004] As information is being exchanged at high speed and in large
volumes, a demand for networks and transmission systems with a
broad band and large capacity has increased. As one means for
meeting this demand the construction of an optical network is
desired. An optical transmission system is a key factor in the
construction of an optical network, and there is a
wavelength-multiplexed optical cross-connect (XC) system as one
system for such an optical transmission network. A
wavelength-multiplexed optical XC refers to a photonic switching
system of wavelength-multiplexed optical signals.
[0005] FIG. 1 shows the configuration of a wavelength-multiplexed
optical XC and an optical network using the wavelength-multiplexed
optical XC.
[0006] In the diagram the optical network comprises optical
amplifiers 1500-1 through 1500-4 and optical transmission line
1501-1 through 1501-4 for connecting these optical amplifiers. A
wavelength-multiplexed optical XC 1502 accommodates a plurality of
optical input/output transmission line, and routes
wavelength-multiplexed optical signals inputted from input optical
transmission line to the desired output optical transmission line
for each wavelength. The routing is controlled by an operating
system 1503 provided in another network controller (not shown in
the diagram). The operating system 1503 controls switching in the
wavelength-multiplexed optical XC 1502, and monitors from which
transmission line optical signals are inputted and to which
transmission line optical signals are outputted to.
[0007] It is desirable from the viewpoint of miniaturized hardware
that the configuration of the wavelength-multiplexed optical XC
1502 can be implemented without converting optical signals to
electrical signals. However, as transmission distance and the
number of passed nodes increase, noise generated by the optical
amplifiers (spontaneous emission light) and crosstalk from other
channels are accumulated, and thereby the waveforms of optical
signals are degraded (that is, the error rate characteristic is
degraded).
[0008] There are two systems in a wavelength-multiplexed optical XC
system; that is, one is a system in which the wavelength is not
converted in the node (fixed wavelength type) and the other is a
system in which the wavelength is converted, if necessary
(converted wavelength type).
[0009] FIGS. 2A and 2B, respectively, show the general
configurations of fixed and converted wavelength type
wavelength-multiplexed optical XCs using an optical switch.
[0010] The fixed wavelength type shown in FIG. 2A comprises a
demultiplexer 1600, a wavelength-corresponding optical switch
(optical SW) unit 1601, a multiplexer 1603 and a regenerator 1602
(consisting of an electrical/optical converter and an
optical/electrical converter), and routes an input optical signal
to the desired output transmission line with the wavelength
unchanged by controlling the optical switch unit 1601. On the other
hand, the converted wavelength type shown in FIG. 2B uses an
optical switch unit 1604 with such a capacity that the same number
of optical signals as the product of the number of wavelengths n
multiplied by a port number k can be accommodated, and the optical
switch unit 1604 is controlled so that the wavelength of an optical
signal can be converted to the desired wavelength of the desired
output transmission line.
[0011] FIGS. 3A and 3B, respectively, show the general
configurations of fixed and converted wavelength type
wavelength-multiplexed optical XCs using a wavelength filter.
[0012] The fixed wavelength type shown in FIG. 3A comprises a
wavelength selector unit 1700, a demultiplexer 1701, a multiplexer
1703 and a regenerator 1702, and the wavelength selector 1700
controls using a wavelength selection filter, etc. so that optical
signals of the same wavelength may not be outputted to the same
output. On the other hand, the converted wavelength type shown in
FIG. 3B uses a wavelength selector unit 1704 with such a capacity
that the wavelength-multiplexed optical signals and the same number
of optical signals as the product of the number of wavelengths n
multiplied by a port number k can be accommodated for the input and
output, respectively, and the wavelength selector unit 1704 is
controlled so that the wavelength of an optical signal can be
converted to the desired wavelength of the desired output
transmission line.
[0013] As described above, the regenerators in the converted
wavelength types shown in FIGS. 2B and 3B are used to convert a
wavelength in addition to the regeneration function.
[0014] In the conventional configurations, although a regenerator
is used, the noise and crosstalk generated in an optical XC node
are combined with the noise and crosstalk generated in the
transmission line. Accordingly, the error rate characteristic is
degraded.
[0015] Therefore, it is necessary to prevent the noise and
crosstalk generated in the optical XC node from mixing with the
noise and crosstalk generated in the transmission line or to
suppress the noise and crosstalk themselves in order to solve the
conventional problems.
SUMMARY OF THE INVENTION
[0016] It is an object of the present invention to provide an
optical XC node with a configuration for suppressing the noise and
crosstalk generated in the transmission line and the noise and
crosstalk generated in an optical XC node, and thereby suppressing
the degradation of the error rate characteristic.
[0017] The optical exchanger of the present invention is a photonic
switching apparatus for accommodating a plurality of
wavelength-multiplexed optical input/output optical links, routing
wavelength-multiplexed optical signals inputted from each input
link, and outputting the optical signals to output links, and is
characterized in comprising a demultiplexer for demultiplexing
wavelength-multiplexed optical signals inputted from the input link
to optical signals of each wavelength, a first regenerator for
regenerating the optical signals of each wavelength outputted from
the demultiplexer and compensating for the S/N ratio degradation
due to propagation in the transmission line, an optical switch unit
for receiving the optical signals outputted from the first
regenerator, and routing and outputting the optical signals, a
second regenerator for regenerating the optical signals outputted
from the optical switch unit and compensating for the S/N ratio
degradation generated in the optical exchanger, and a multiplexer
for multiplexing the optical signals of each wavelength outputted
from the second regenerator to wavelength-multiplexed optical
signals and outputting the wavelength-multiplexed optical signals
to the transmission line.
[0018] The optical exchanger in another aspect of the present
invention is a photonic switching apparatus for accommodating a
plurality of wavelength-multiplexed optical input/output optical
links, routing wavelength-multiplexed optical signals inputted from
each input link, and outputting the optical signals to output
links, and is characterized in comprising a first demultiplexer for
demultiplexing wavelength-multiplexed optical signals inputted from
the input link to optical signals of each wavelength, a first
regenerator for regenerating the optical signals of each wavelength
outputted from the demultiplexer and compensating for the S/N ratio
degradation due to propagation in the transmission line, a first
multiplexer for multiplexing the optical signals of each wavelength
outputted from the first regenerator, a wavelength selector unit,
consisting of two optical couplers and one multi-wavelength
selection filter for routing the wavelength-multiplexed optical
signals from the first multiplexer, a second demultiplexer for
demultiplexing the optical signals outputted from the wavelength
selector unit to optical signals of each wavelength, a second
regenerator for regenerating the optical signals of each wavelength
from outputted from the second demultiplexer and compensating for
the S/N ratio degradation generated in an optical exchanger, and a
second multiplexer for multiplexing the optical signals outputted
from the second regenerator and outputting the
wavelength-multiplexed optical signals to the transmission
line.
[0019] The optical exchanger in another aspect of the present
invention is a photonic switching apparatus for accommodating a
plurality of wavelength-multiplexed optical input/output optical
links, routing wavelength-multiplexed optical signals inputted from
each input link, and outputting the optical signals to output
links, and is characterized in comprising a demultiplexer for
demultiplexing wavelength-multiplexed optical signals inputted from
the input link to optical signals of each wavelength, a first
regenerator for regenerating the optical signals of each wavelength
outputted from the demultiplexer and compensating for the S/N ratio
degradation due to propagation in the transmission line, a first
multiplexer for multiplexing the optical signals of each wavelength
outputted from the first regenerator, a wavelength selector unit,
consisting of two optical couplers and one wavelength selection
filter for routing the wavelength-multiplexed optical signals
inputted from the first multiplexer, a second regenerator for
regenerating optical signals from the optical signals of each
wavelength outputted from the wavelength selector unit and
compensating for the S/N ratio degradation generated in an optical
XC node, and a second multiplexer for multiplexing the optical
signals of each wavelength outputted from the second regenerator
and transmitting then to the transmission line.
[0020] According to the present invention, by providing a
regenerator for optical signals on the input side of an optical
exchanger and eliminating noise and crosstalk degrading the S/N
ratio of optical signals prior to routing, only the compensation
for the S/N ratio degradation due to the noise generated by optical
amplifiers provided in the optical exchanger and the crosstalk due
to routing, is needed in a regenerating means provided on the
output side of the optical exchanger. That is, since the
regeneration means on the input side of the optical exchanger
compensates for the S/N ratio degradation due to the transmission
line beforehand, and the error rate characteristic in the case
where optical signals are regenerated on the output side is
improved. Accordingly, the error rate characteristic of the entire
optical exchanger is also improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 shows the configuration of a wavelength-multiplexed
optical XC and an optical network using the wavelength-multiplexed
optical XC.
[0022] FIGS. 2A and 2B, respectively, show the general
configurations of fixed and converted wavelength type
wavelength-multiplexed optical XCs using an optical switch.
[0023] FIGS. 3A and 3B, respectively, show the general
configurations of fixed and converted wavelength type
wavelength-multiplexed optical XCs using a wavelength filter.
[0024] FIG. 4 shows a configuration of the fixed wavelength type
wavelength-multiplexed optical XC using optical switches of the
present invention.
[0025] FIGS. 5A through 5C show one-stage and three-stage
configurations using optical space switches as a general
configuration of an optical switch unit.
[0026] FIG. 6 shows a configuration in which a noise elimination
filter is provided before the latter-stage regenerator shown in the
configuration shown in FIG. 4.
[0027] FIG. 7 shows a configuration in which the output wavelength
of the former-stage regenerator is set in the configuration shown
in FIG. 4 so that all the input wavelengths to a certain optical
switch unit may be different from each other.
[0028] FIG. 8 shows a configuration in which a noise elimination
filter capable of changing transmission wavelength is provided
before the latter stage regenerator in the configuration shown in
FIG. 7.
[0029] FIG. 9 is a flowchart showing the control process of the
noise elimination filter in the configuration shown in FIG. 8.
[0030] FIG. 10 shows a configuration of the converted wavelength
type wavelength-multiplexed optical XC using optical switches.
[0031] FIG. 11 shows a configuration in which a noise elimination
filter is provided before the latter-stage regenerator in the
configuration shown in FIG. 10.
[0032] FIG. 12 shows a configuration in which the wavelength of
output optical signals from the former-stage regenerator are the
same as the wavelength of the input optical signals in the
configuration shown in FIG. 10.
[0033] FIG. 13 shows a configuration in which a noise elimination
filter capable of changing transmission wavelength is provided
before the latter-stage regenerator in the configuration shown in
FIG. 12.
[0034] FIG. 14 shows a configuration of the fixed wavelength type
wavelength-multiplexed optical XC using a wavelength selector
unit.
[0035] FIGS. 15A and 15B show configurations of the wavelength
selector unit.
[0036] FIG. 16 shows a configuration of the converted wavelength
type wavelength-multiplexed optical XC using a wavelength selector
unit.
[0037] FIG. 17 shows a configuration in which a noise elimination
filter capable of changing transmission wavelength is provided
before the latter-stage regenerator in the configuration shown in
FIG. 16.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] FIG. 4 shows a configuration of the fixed wavelength type
wavelength-multiplexed optical XC using optical switches of the
present invention.
[0039] FIG. 4 shows a configuration in which a regenerator 101 is
also provided on the output of a demultiplexer 100 in a
conventional configuration (FIG. 2A). In the regenerator 101 the
wavelengths of output optical signals remain the same as the
wavelengths of input optical signals. The former-stage regenerator
101 of this configuration can regenerate optical signals by
compensating for the degradation due to the noise and crosstalk
generated in the transmission line only. The latter stage
regenerator 103 can regenerate optical signals by compensating for
the degradation of the noise and crosstalk generated in the
wavelength-multiplexed optical XC only.
[0040] The regenerators 101 and 103 comprise an optical receiver
(OR) and an optical sender (OS), convert the electrical signals to
optical signals again after converting optical signals to
electrical signals, and transmit the optical signals. In this case,
when optical signals are converted to electrical signals, in the
optical receiver a so-called 3R function is used to reshape the
signal waveforms. Therefore, when optical signals with degraded
waveforms transmitted from the transmission line are received and
converted to electrical signals by the optical receiver, the
waveforms are reshaped and outputted. That is, the waveforms
degraded by noise, etc. are compensated for and the signals are
outputted as electrical signals. Since a transmitter is driven by
these electrical signals with reshaped waveforms, optical signals
outputted from the regenerators 101 and 103 are outputted with the
noise and crosstalk suppressed, that is, with the S/N ratio
improved.
[0041] In the drawing a wavelength-multiplexed optical signal is
inputted to a demultiplexer 100, and is demultiplexed to optical
signals of each wavelength (.lambda.1 to .lambda.n). The optical
signals of each wavelength are inputted to corresponding
regenerators 101 provided for each wavelength. The optical signals
of each wavelength outputted from the regenerators 101 are
outputted after the S/N ratio degraded by the noise and crosstalk
generated in the transmission line are improved. The optical
signals of each wavelength (.lambda.1 to .lambda.n) outputted from
these regenerators 101 are inputted to corresponding optical switch
units 102 provided for each wavelength, and routed. The optical
signals routed and outputted are inputted to corresponding
regenerators 103 provided for each signal.
[0042] In the regenerator 103 the optical signals are outputted
with the waveform degraded by the noise and crosstalk generated in
the optical switch unit 102 compensated for as described above.
Thus, the optical signals with improved S/N ratios are outputted
from the regenerators 103, and are inputted to multiplexers 104.
The multiplexers 104 are configured so that optical signals of
different wavelengths may be inputted, the received optical signals
different in wavelengths from each other are
wavelength-multiplexed, and the optical signals are outputted to
the transmission line.
[0043] In this way, by providing a regenerator 101 before the
optical switch unit 102, optical signals are inputted to the
optical switch unit 102 after the S/N ratio degradation generated
in the transmission line is compensated for, and the S/N ratio
degradation generated by the optical switch unit 102 is compensated
for by the regenerator 103. In this manner, since it is sufficient
if the regenerator 103 compensates for the S/N ratio degradation
generated in the optical switch unit 102 only, optical signals can
be prevented from being degraded so badly that the optical signals
may not be regenerated because of the degraded S/N ratio. On the
other hand, conventionally, since a regenerator 101 is not
provided, not only the S/N ratio degradation generated in the
optical switch unit 102 but also the S/N ratio degradation
generated in the transmission line had to be compensated for by the
latter-stage regenerator 103, and the optical signals are only
regenerated by the latter-stage regenerator 103. Thus, since the
optical signals are regenerated after the waveform degradation of
the optical signals becomes great, there is a possibility that the
error rate of the signals become great. However, according to the
present invention, the error rate can be suppressed to be low.
[0044] FIGS. 5A through 5C show one-stage and three-stage
configurations using optical space switches as a general
configuration of an optical switch unit.
[0045] FIG. 5A and FIG. 5B show the cases where optical space
switches are configured in one stage and where optical space
switches are configured in three stages, respectively. Although in
this way an optical switch unit can be configured using optical
space switches, it is necessary to provide the optical space
switches in multi-stages according to the numbers of lines and
channels (wavelengths) accommodated by the optical switch unit.
Since particularly an 8.times.8 optical space switch with eight
inputs and eight outputs is currently popular, it is necessary to
provide optical space switches in multi-stages when an optical
switch unit is actually introduced into an optical network. On the
other hand, in an optical space switch the loss of an optical
signal increases proportional to the numbers of accommodated lines
and channels. For this reason, it is necessary to insert optical
amplifiers before and after the optical space switch. In FIGS. 5A
and 5B the inserted locations of an optical amplifier are marked by
arrows.
[0046] FIG. 5C shows a configuration of a 4.times.4 optical space
switch. The 4.times.4 optical space switch shown in FIG. 5C is
configured so that optical waveguides are crossed at many points on
the substrate. A configuration for modifying the path of an optical
signal is provided at a point where these waveguides are crossed,
the path of the optical signal is determined by applying a control
signal from a controller circuit (not shown in the diagram). The
path of an optical signal inputted from the left of FIG. 5C is
determined at the crossing of waveguides, and the optical signal is
properly routed and outputted to the output side on the right of
FIG. 5C.
[0047] The details of an optical space switch like this are, for
example, described in the Japanese Laid-open Patent Publication No.
6-66982.
[0048] FIG. 6 show a configuration in which a noise elimination
filter is provided before the latter stage regenerator shown in the
configuration shown in FIG. 4.
[0049] In FIG. 6 the same components as in FIG. 4 are given the
same reference numbers as in FIG. 4.
[0050] The object of a noise elimination filter 300 is to eliminate
noise generated in an optical switch unit 102 when an optical
amplifier is provided in the optical switch unit 102. However, some
noise in the neighborhood of the wavelength of an optical signal
remains. But, the error rate characteristic in the latter-stage
regenerator 103 can be improved.
[0051] When wavelength-multiplexed optical signals are inputted to
a demultiplexer 100, the optical signals are demultiplexed to
optical signals of each wavelength by the demultiplexer 100. The
optical signals of each wavelength are regenerated by regenerators
101 provided for each wavelength, and are inputted to corresponding
optical switch units 102 provided for each wavelength. In this
case, the optical signals of which the S/N ratio degradation due to
the noise and crosstalk generated in the transmission line are
partly compensated for are inputted to the optical switch unit
102.
[0052] The optical signals of each wavelength are routed by the
optical switch unit 102, and are outputted to each port. The
optical switch units 102 at the top and at the bottom of FIG. 6 are
for optical signals of wavelengths .lambda.1 and .lambda.n,
respectively. The optical switch units for optical signals of
wavelengths .lambda.2 to .lambda.n-1 are also provided, although
these optical switch units are not shown in the diagram.
[0053] When the optical signals are outputted from each optical
switch unit, the optical signals are inputted to noise elimination
filters 300 provided for each port. The noise elimination filters
300 are configured so as to pass the wavelength of the main signal
of the optical signals, and eliminate other noise and crosstalk
generated in the wavelengths. Thus, the noise generated in the
optical switch unit 102, and particularly, almost all the noise
generated by the optical amplifier provided in the optical switch
unit 102 is eliminated. Accordingly, the S/N ratio of each optical
signal is improved, and the noise is eliminated.
[0054] Then, after the optical signals pass through the noise
elimination filter 300, the optical signals are inputted to the
corresponding regenerator 103 provided for each port. Since the S/N
ratio of the optical signal inputted to the regenerator 103 is
improved by the noise elimination filter 300, the regenerator 103
can regenerate an optical signal with an improved S/N ratio. Thus,
the S/N ratio of the optical signals is further improved by
regenerating the optical signals. Particularly, the noise and
crosstalk with almost the same wavelength as the main signal of the
optical signal which cannot be eliminated by the noise elimination
filter 300, can be suppressed by regenerating. Accordingly, both
the noise and crosstalk of the optical signals inputted to the
multiplexer 104 at the next stage which are present when the
optical signals are inputted to the wavelength-multiplexed optical
XC in the diagram, and the noise and crosstalk generated in the
optical switch unit 102, are significantly suppressed.
[0055] The multiplexer 104 receives optical signals different in
wavelength with each other out of optical signals outputted from
the optical switch unit 102, wavelength-multiplexes the optical
signals, and transmits the optical signals to the transmission
line. In this way, wavelength-multiplexed optical signals with
improved SIN ratios can be outputted to the transmission line by
providing a regenerator 101 on the input side of the
wavelength-multiplexed optical XC and providing a noise elimination
filter 300.
[0056] FIG. 7 shows a configuration in which the output wavelength
of the former-stage regenerator is set in the configuration shown
in FIG. 4 so that all the input wavelengths to a certain optical
switch unit may be different from each other.
[0057] In FIG. 7 the same components as in FIG. 4 are given the
same reference numbers as in FIG. 4.
[0058] By differentiating all the wavelengths of optical signals
inputted to one optical switch unit 401 in the same way as shown in
FIG. 7, coherent crosstalk (the wavelength of a crosstalk light
beam being the same as the wavelength of a signal light beam)
generated in the optical switch unit 401 can be eliminated. Thus,
the error rate characteristic in the latter-stage regenerator 402
can be improved.
[0059] As described earlier, although an optical switch unit is
configured using optical space switches as shown in FIG. 5C, there
is a possibility that the crosstalk of optical signals is
generated, since optical waveguides cross at many points.
Particularly, since the characteristics of the optical signals are
similar, crosstalk is easily generated where the optical waveguides
cross in an optical space switch. For this reason, by
differentiating the wavelengths of optical signals inputted to an
optical space switch, crosstalk can be reduced.
[0060] When wavelength-multiplexed optical signals are inputted to
a demultiplexer 100, the optical signals are demultiplexed to
optical signals of each wavelength Al to An. A former-stage
regenerator 400 regenerates the optical signals of each wavelength
and improves the S/N ratio, and changes the wavelengths and
differentiates the wavelengths of the optical signals.
[0061] In the configuration shown in FIG. 7 each optical signal is
sequentially led from a demultiplexer 100 at the top of FIG. 7 to a
different optical switch unit 401. That is, an optical signal is
inputted from a plurality of different demultiplexers 100 to each
optical switch unit 401. Therefore, if all the optical signals from
one demultiplexer 100 have the same wavelength, and different
demultiplexers 100 process optical signals of different
wavelengths, all the optical signals inputted to one optical switch
unit 401 have different wavelengths. Accordingly, in FIG. 7, a
regenerator 400 corresponding to the demultiplexer 100 at the top
of FIG. 7 is designed to convert the wavelengths of all the
received optical signals to .lambda.1. In the same way, a
regenerator 400 corresponding to the demultiplexer 100 at the
bottom of FIG. 7 is designed to convert the wavelengths of all the
received optical signals to .lambda.k. In the same way, the other
regenerators 400 corresponding to the other demultiplexers 100
located between are designed to convert the wavelengths of all the
received optical signals to wavelengths different from each other,
although this is not shown in the diagram.
[0062] In this way, when optical signals are inputted to the
optical switch unit 401, the optical signals are routed and
outputted. The output optical signals are inputted to a regenerator
402, and are wavelength-converted again. In this case, each optical
signal is wavelength-converted so as to be convenient to be
transmitted to the transmission line. That is, a regenerator 402
corresponding to an optical switch unit 401 at the top of FIG. 7
inputs each of the received optical signals to different
multiplexers. In the same way, each of the other optical signals
from another regenerator 402 corresponding to another optical
switch unit 401 is inputted to a different multiplexer 104. It is
necessary for all the wavelengths of input optical signals to be
different from each other in order to be wavelength-multiplexed by
the multiplexer 104. For this purpose, it is sufficient only if a
regenerator 402 corresponding to each optical switch unit 401
converts all the received optical signals to optical signals of the
same wavelength.
[0063] In this way, in the diagram a regenerator 402 corresponding
to an optical switch unit 401 at the top of FIG. 7 is designed to
convert the wavelengths of all the received optical signals to
.lambda.1. In the same way, a regenerator 402 corresponding to an
optical switch unit 401 at the bottom of FIG. 7 is designed to
convert the wavelengths of all the received optical signals to
.lambda.n. In the same way, the other regenerators 402
corresponding to the other demultiplexers 100 located between are
designed to convert the wavelengths of all the received optical
signals to wavelengths different with each other, although this is
not shown in the diagram.
[0064] In this way, optical signals different from each other
inputted to the multiplexer 104 are wavelength-multiplexed and
outputted to the transmission line.
[0065] According to the configuration shown in FIG. 7, since
received optical signals inputted to one optical switch unit 401
all have different wavelengths, no coherent crosstalk is generated
in the optical switch unit 401, and the S/N ratio of the optical
signals transmitted from the wavelength-multiplexed optical XC in
the diagram can be favorably maintained. Particularly, when
coherent crosstalk is generated, it is difficult to eliminate the
crosstalk and to extract only a main signal, since the wavelengths
of the main signal and crosstalk are the same. However, the
configuration has an advantage that the main signal can be quite
easily extracted when the wavelengths of the main signal and
crosstalk are different.
[0066] FIG. 8 shows the configuration in which a noise elimination
filter capable of changing a transmission wavelength is provided
before the latter-stage regenerator in the configuration shown in
FIG. 7.
[0067] In FIG. 8 the same components as in FIG. 7 are given the
same reference numbers as in FIG. 7.
[0068] In FIG. 8 the wavelength of the former-stage regenerator 400
is set in the same way as in FIG. 7 so that all the input optical
signals may differ in wavelength. Thus, the error rate
characteristic in the latter-stage regenerator 402 can be improved.
In addition to this, since a noise elimination filter 500 is
provided, the error rate characteristic of the latter-stage
regenerator 402 can be further improved.
[0069] When the wavelength-multiplexed optical signals are inputted
to a demultiplexer 100, the optical signals are demultiplexed to
optical signals of each wavelength by the demultiplexer 100. The
optical signals are regenerated by the regenerator 400, the S/N
ratios are improved, and the wavelengths are converted to
wavelengths corresponding to each of the demultiplexers 100, as
described with reference to FIG. 7. The optical signals of
different wavelengths from the regenerators 400 are inputted to one
optical switch unit 401. After each optical signal is routed, the
optical signal is outputted from the optical switch 401, and is
inputted to a noise elimination filter 500. The noise elimination
filter 500 is designed so as to pass only a main signal, and
thereby the noise and crosstalk are eliminated.
[0070] After the optical signals pass through the noise elimination
filter 500, the optical signals are inputted to a regenerator 402
and regenerated, and as described with reference to FIG. 7, are
wavelength-multiplexed and inputted to each multiplexer 104.
Optical signals of different wavelengths are inputted to each
multiplexer 104, and the optical signals are wavelength-multiplexed
and outputted to the transmission line.
[0071] Since optical signals inputted to one optical switch unit
401 have different wavelengths, it is unknown of which wavelength
an optical signal is outputted from which port, which depends on
the routing status. Therefore, unlike a filter with a fixed
transmission band, the transmission band of the noise elimination
filter 500 has to be able to be changed according to the wavelength
of an input optical signal. For this reason, a controller circuit
503 for managing and controlling the routing of the optical switch
unit 401 is also designed so as to control the transmission bands
of the noise elimination filters 500.
[0072] The controller circuit 503 receives a path setting signal
being routing information from the operation system of an optical
network. The controller circuit 503 controls an optical switch
driver circuit 502 based on this signal, and establishes a path for
each optical switch unit 401. Although in the above-mentioned
configuration the controller circuit (not shown in FIG. 8 of the
above-mentioned configuration) only controls the optical switch
unit, in this configuration the controller circuit also judges from
the path setting signal which wavelength optical signal should be
outputted from which port of the optical switch unit 401. Based on
the result of this judgement the controller circuit 503 provides a
filter driver circuit 501 with a control signal, and properly sets
the transmission band of each noise elimination filter 500.
[0073] For a filter with a variable transmission band, an
acousto-optical filter, fiber Fabry-Perot filter, etc. can be
used.
[0074] FIG. 9 is a flowchart showing the control process of the
noise elimination filter in the configuration of FIG. 8.
[0075] The operation system inputs a path setting signal to the
controller circuit when routing optical signals using a
wavelength-multiplexed optical XC. This path setting signal
comprises an input optical link number, an input wavelength value,
an output optical link number, an output wavelength value (used
only in the case of converted wavelength type
wavelength-multiplexed optical XC described below), etc.
[0076] When the controller circuit receives a path setting signal,
the controller circuit analyzes this signal, and calculates the
output wavelengths of optical signals immediately after the
former-stage regenerator, the control point of an optical switch
unit and the transmission wavelength of a noise elimination filter.
Based on these values, the controller circuit outputs control
signals for the optical space switch and the noise elimination
filter to the driver circuit.
[0077] When the optical switch and the filter driver circuit
receive the control signals for the optical space switch and the
noise elimination filter, respectively, the optical switch and the
filter driver circuit respectively convert these signals to drive
signals for the optical space switch and the noise elimination
filter, and output the drive signals for the optical space switch
and the noise elimination filter to the optical space switch and
noise elimination filter, respectively.
[0078] Since the more concrete contents of the analysis method of
the path setting signal of the above-mentioned controller circuit
would be properly and optimally designed by a person having
ordinary skill in the art, the analysis method is not described in
detail here. However, the analysis method will be easily
implemented by the person having ordinary skill in the art.
[0079] The above-mentioned configurations are all for a fixed
wavelength type wavelength-multiplexed optical XC, in that optical
signals of a specific wavelength immediately after the
demultiplexer 100 are inputted to the optical switch unit
corresponding to the wavelength, and are wavelength-multiplexed
with the wavelengths as they are or are converted to the same
wavelengths again immediately before the multiplexer 104.
[0080] Configurations for a converted wavelength type
wavelength-multiplexed optical XC for routing optical signals after
converting the original wavelengths of optical signals and
outputting the optical signals with wavelengths different from the
original are described below.
[0081] FIG. 10 shows a configuration of the converted wavelength
type wavelength-multiplexed optical XC using optical switches.
[0082] FIG. 10 shows a configuration in which a regenerator is
provided on the output side of a demultiplexer in a conventional
configuration (FIG. 2B), and all the wavelengths of the regenerated
optical signals are the same (.lambda.1 in FIG. 10). In this
configuration, in the former-stage regenerator, optical signals can
be regenerated by compensating for only the degradation due to the
noise and crosstalk generated in the transmission line. In the
latter-stage regenerator, optical signals can be regenerated by
compensating for only the noise and crosstalk generated in the
optical XC.
[0083] When wavelength-multiplexed optical signals are inputted to
a demultiplexer 700, the optical signals are demultiplexed to
optical signals of each wavelength, and are inputted to a
regenerator 701 provided for each optical signal of each
wavelength. After the optical signals are regenerated by the
regenerator 701 and the S/N ratio degradation due to the
transmission line is compensated for, the wavelength of the optical
signals are converted. In the diagram all the wavelengths of
optical signals outputted from the regenerator 701 are .lambda.1.
These optical signals are inputted to an optical switch unit 702
and are routed. In the diagram, unlike the fixed wavelength type
described earlier, the optical switch unit 702 is configured so as
to route all the received optical signals equally. In this
configuration, since the wavelengths of any optical signals
immediately after the demultiplexer 700 are routed equally, all the
optical signals do not necessarily have the same wavelengths as
when first inputted, when the optical signals are outputted from a
multiplexer 704. That is, the optical signals are routed with the
wavelengths converted.
[0084] The optical signals routed in the optical switch unit 702
are regenerated by a regenerator 703 provided for each output port
of the optical switch unit 702, and the S/N ratio degradation
generated in the optical switch unit 702 is compensated for.
Furthermore, in the regenerator 703, the wavelengths of the optical
signals inputted to one multiplexer 704 are converted to be
different from each other so as to be wavelength-multiplexed by the
multiplexer 704. Then, the optical signals are
wavelength-multiplexed by the multiplexer 704, and are outputted to
the transmission line.
[0085] Even in the configuration shown in FIG. 10, in the same way
as in FIG. 4, if a regenerator 701 is provided on the input side of
the optical switch unit so as to compensate for the degradation of
the S/N generated in the transmission line, it is sufficient if the
latter-stage regenerator 703 compensate for only the S/N ratio
degradation generated in the optical switch unit 702, and thereby
the error rate characteristic of the optical signals can be
improved.
[0086] FIG. 11 shows the configuration in which a noise elimination
filter is provided before the latter-stage regenerator in the
configuration shown in FIG. 10.
[0087] In FIG. 11 the same components as in FIG. 10 are given the
same reference numbers as in FIG. 10.
[0088] The object of a noise elimination filter 800 is to eliminate
noise generated in the optical switch unit 702 when an optical
amplifier is provided in the optical switch unit 702. (However,
some noise remains in the neighborhood of a wavelength of an
optical signal.) Thus, the error rate characteristic of the
latter-stage regenerator can be improved.
[0089] When wavelength-multiplexed optical signals are inputted to
a demultiplexer 700, the optical signals are demultiplexed to
optical signals of each wavelength, and are regenerated by a
regenerator 701. That is, the influence of the loss and crosstalk
generated in the transmission line is removed. Furthermore, as
described with reference to FIG. 10, the wavelength of all the
optical signals are converted to the same wavelength (.lambda.1 in
the diagram). These optical signals are inputted to an optical
switch unit 702, are routed, and are outputted. The outputted
optical signals are outputted with the noise and crosstalk
generated in the optical switch unit 702 eliminated by the noise
elimination filter 800. In the diagram, since the wavelength of the
main signal of the optical signals outputted from the optical
switch unit 702 is determined to be .lambda.1, the transmission
band of the noise elimination filter can be fixed. The optical
signals passed through the noise elimination filter 800 are
inputted to a regenerator 703, are regenerated there, and the
wavelengths of the optical signals are converted. The S/N ratio of
the optical signals and the error rate characteristics are further
improved by the regeneration in the regenerator 703. The wavelength
conversion by the regenerator 703 is performed so that all the
optical signals inputted to one multiplexer 704 differ in
wavelength. In the diagram the converted wavelengths are .lambda.1
to .lambda.n.
[0090] In this way, optical signals of wavelengths of .lambda.1 to
.lambda.n are wavelength-multiplexed by the multiplexer 704, and
are outputted to the transmission line.
[0091] As described with reference to FIG. 10, since each optical
signal outputted from a plurality of demultiplexers 700 are equally
routed, the wavelength is not necessarily the original wavelength
when the optical signal is outputted from the regenerator 703.
[0092] FIG. 12 shows a configuration in which the wavelengths of
output optical signals from the former-stage regenerator are the
same as the wavelengths of the input optical signals in the
configuration shown in FIG. 10.
[0093] In FIG. 12 the same components as in FIG. 10 are given the
same reference numbers as in FIG. 10.
[0094] According to the configuration shown in FIG. 12, since the
volume of coherent crosstalk generated in an optical switch unit
702 can be reduced compared with the configuration shown in FIG.
10, the error rate characteristic in the latter-stage regenerator
can be improved.
[0095] When wavelength-multiplexed optical signals are inputted to
a demultiplexer 700, the optical signals are demultiplexed to
optical signals of wavelengths of .lambda.1 to .lambda.n. Each
signal is regenerated by a regenerator 900, and the noise and
crosstalk generated in the transmission line are removed. In FIG.
12, since the wavelengths of the optical signals are not converted,
the optical signals are inputted to the optical switch unit 702 as
they are. Thus, since all the optical signals demultiplexed in one
demultiplexer 700 differ in wavelength, in FIG. 12 the number of
optical signals of the same wavelength is the same as the number of
demultiplexers. Accordingly, the number of optical signals of the
same wavelength among optical signals inputted to the optical
switch unit 702 is reduced compared with the configurations of
FIGS. 10 and 11, and thereby the influence of the coherent
crosstalk can be reduced. That is, since the S/N ratio degradation
generated in the optical switch unit 702 is suppressed, the error
rate characteristic in the regenerator 901 can be improved.
[0096] When optical signals are outputted from the optical switch
unit 702, the optical signals are regenerated by a regenerator 901,
and the wavelengths are converted. As described earlier, the
wavelength conversion by the regenerator 901 is performed so that
all the optical signals inputted to one multiplexer 704 differ in
wavelength. In FIG. 12 the converted wavelengths are .lambda.1 to
.lambda.n. Then, the optical signals are wavelength-multiplexed by
the multiplexer 704, and are outputted to the transmission
line.
[0097] Although in the configuration shown in FIG. 12 there is no
wavelength conversion in a regenerator 900, the regenerator can
also be configured as to convert the wavelengths of optical
signals. That is, optical signals with a high possibility of the
optical path crossing in the optical switch unit 702 can also be
detected by a controller circuit (not shown in the diagram) of the
optical switch unit 702 beforehand, and the wavelength conversion
function of the regenerator 900 can also be controlled so that the
optical signals differ in wavelength. Alternatively, all the
optical signals from the regenerator 900 can be made to differ in
wavelength. Thus, since all the optical signals inputted to the
optical switch unit 702 can be made to differ in wavelength, the
occurrence of coherent crosstalk in the optical switch unit 702 can
be further suppressed.
[0098] FIG. 13 shows the configuration in which a noise elimination
filter capable of changing a transmission wavelength is provided
before the latter-stage regenerator in the configuration shown in
FIG. 12.
[0099] In FIG. 13 the same components as in FIG. 12 are given the
same reference numbers as in FIG. 12.
[0100] In FIG. 13, in a former-stage regenerator 900, the
wavelengths of the output optical signals are the same as the
wavelengths of the input optical signals. For this reason, the
error rate characteristic in a latter-stage regenerator 901 can be
improved as described with reference to FIG. 12. The error rate
characteristic in the latter-stage regenerator 901 can be further
improved by providing a noise elimination filter 1000.
[0101] When wavelength-multiplexed optical signals are inputted to
a demultiplexer 700, the optical signals are demultiplexed to
optical signals of wavelengths .lambda.1 to .lambda.n, and are
inputted to regenerators 900 provided for each of the wavelength of
.lambda.1 to .lambda.n. The regenerators 900 regenerate the optical
signals, improve the S/N ratio, and input the optical signals to an
optical switch unit 702 without converting the wavelengths. The
inputted optical signals are routed and are outputted from each
output port of the optical switch unit 702. Then, each optical
signal is inputted to a noise elimination filter 1000 provided for
each output port. Since the noise elimination filter 1000 passes
only main signals of inputted optical signals of each wavelength,
the noise and crosstalk generated by the optical amplifiers in the
optical switch unit 702 can be removed. In this way, optical
signals with an improved S/N ratio are regenerated and inputted to
a regenerator 901, the wavelengths are converted, and the optical
signals are wavelength-multiplexed in a multiplexer 704 and
transmitted to the transmission line.
[0102] Like the configuration as described with reference to FIG.
8, the noise elimination filter 1000 is designed so that the
transmission band may be changed according to the wavelengths of
optical signals inputted from the optical switch unit 702. The
configuration for this purpose is like the configuration described
with reference to FIG. 8. That is, a controller circuit (not shown
in the diagram) obtains information on routing from the operating
system of an optical network, controls the optical paths in the
optical switch unit 702, estimates the wavelengths of the optical
signals outputted from each port, and properly adjusts the
transmission band of the noise elimination filter 1000. As
described earlier, for example, an acousto-optic filter, fiber
Fabry-Perot filter, etc. are used for the noise elimination filter
1000.
[0103] As described with reference to FIG. 12, a regenerator 900
can also be provided with a wavelength conversion function, and can
convert the wavelength of each optical signal to an optimal
wavelength, if necessary.
[0104] FIG. 14 shows a configuration of the fixed wavelength type
wavelength-multiplexed optical XC using a wavelength selector
unit.
[0105] This is a configuration in which each node input part is
provided with a demultiplexer 1100, the same number of regenerators
1101 as the number of the wavelengths and a multiplexer 1102. In
the regenerators 1101 the wavelengths of output optical signals are
the same as the wavelengths of the input optical signals. According
to this configuration, in the former-stage regenerator 1101,
optical signals can be regenerated by compensating for only the
degradation due to the noise and crosstalk generated in the
transmission line. In the latter-stage regenerator 1105, optical
signals can be regenerated by compensating for only the degradation
due to the noise and crosstalk generated in the
wavelength-multiplexed optical XC.
[0106] When wavelength-multiplexed optical signals are inputted to
the demultiplexer 1100, the optical signals are demultiplexed to
optical signals of each wavelength, and are inputted to a
regenerator 1101. The S/N ratio degradation of optical signals
generated in the transmission line is removed by the
above-mentioned function when the optical signals are regenerated
by the regenerator 1101. The regenerator 1101 does not convert the
wavelengths, and inputs each regenerated optical signal to a
multiplexer 1102. In the multiplexer 1102 optical signal
demultiplexed by the demultiplexer are wavelength-multiplexed again
and are inputted to a wavelength selector unit 1103. The wavelength
selector unit 1103 routes the wavelength-multiplexed optical
signals as they are, and outputs the optical signals from output
ports. The outputted optical signals are inputted to the
multiplexers 1104 provided for each output port of the wavelength
selector unit 1103, and are demultiplexed to optical signals of
each wavelength. The optical signals of each wavelength are
regenerated by a regenerator 1105 provided for each wavelength.
When optical signals are regenerated, the S/N ratio degradation
generated in the wavelength selector unit 1103 of each optical
signal is compensated for, and the optical signals are inputted to
a multiplexer 1106. The multiplexer 1106 wavelength-multiplexes the
optical signals of each wavelength, and the multiplexed optical
signals are transmitted to the transmission line.
[0107] In this way, since both degradations of the S/N ratio due to
the propagation in the transmission line and that generated by
optical amplifiers, etc. provided in the wavelength selector unit
1103, can be compensated for by providing the regenerators 1101 and
1105, respectively, on the input and output sides of the wavelength
selector unit 1103, the error rate characteristic of optical
signals can be improved.
[0108] FIGS. 15A and 15B show configurations of a wavelength
selector unit.
[0109] FIG. 15A shows a general configuration of a fixed wavelength
type wavelength selector unit, wherein a multi-wavelength filter
1201 is a filter for selecting a plurality of desired wavelengths
out of wavelength-multiplexed input optical signals. For this
example, an acousto-optic filter can be considered. In this
configuration, loss increases as the number of ports increases.
Accordingly, an optical amplifier has to be inserted. In FIG. 15A
examples of the inserted locations of the optical amplifier are
indicated by the arrow marks.
[0110] When wavelength-multiplexed optical signals are inputted to
an optical coupler 1200, the optical signals are distributed to a
plurality of optical signals of each output port. The distributed
optical signals are inputted to different multi-wavelength filters
1201. Each multi-wavelength filter 1201 extracts a specific optical
signal, and outputs the optical signal. Then, the optical signals
selected by each multi-wavelength filter 1201 are coupled by an
optical coupler 1202, and are transmitted as wavelength-multiplexed
optical signals of wavelengths of .lambda.1 to .lambda.n.
[0111] FIG. 15B shows a general configuration of a converted
wavelength type wavelength selector unit, wherein a wavelength
filter 1204 is a filter for selecting a desired wavelength out of
wavelength-multiplexed input optical signals. For this example, an
acousto-optic filter can be considered. In this configuration, loss
increases as the numbers of both ports and wavelengths increase.
Accordingly, an optical amplifier has to be inserted. In FIG. 15B
examples of the inserted locations of the optical amplifier are
indicated by the arrow marks.
[0112] When wavelength-multiplexed optical signals are inputted to
an optical coupler 1203, the optical signals are distributed to a
plurality of optical signals of each output port. The distributed
optical signals are inputted to different wavelength filters 1204.
Each wavelength filter 1204 extracts a specific optical signal. The
same number of optical couplers 1205 as the product of the number
of wavelengths n multiplied by the number of input ports k are
provided, and optical signals of a single wavelength are outputted
from each optical coupler 1205. That is, the wavelength-multiplexed
optical signals are routed, by passing through a wavelength
selector unit shown in FIG. 15B, for each optical signal of each
wavelength inputted to each input port, and are outputted without
being wavelength-multiplexed.
[0113] For details of such a wavelength selector unit as shown in
FIG. 15B, see the Japanese Laid-open Patent Publication
No.8-019964.
[0114] FIG. 16 shows a configuration of the converted wavelength
type wavelength-multiplexed optical XC using a wavelength selector
unit.
[0115] In FIG. 16 the same components as in FIG. 14 are given the
same reference numbers as in FIG. 14.
[0116] This is a configuration in which each node input port is
provided with a demultiplexer 1100, the same number of regenerators
1101 as the number of the wavelengths, and a multiplexer 1102. In
the regenerators 1101 the wavelengths of the output optical signals
are the same as the wavelengths of the input optical signals.
According to this configuration, in the former-stage regenerator
1101, optical signals can be regenerated by compensating for only
the degradation due to the noise and crosstalk generated in the
transmission line. In the latter-stage regenerator 1301, optical
signals can be regenerated by compensating for only the degradation
due to the noise and crosstalk generated in the wavelength selector
unit 1300.
[0117] When wavelength-multiplexed optical signals are inputted to
a demultiplexer 1100, the optical signals are demultiplexed to
optical signals of each wavelength by the demultiplexer 1100, and
are inputted to regenerators 1101 provided for each wavelength.
When the optical signals are regenerated by the regenerators 1101,
the S/N ratio degradation generated in the transmission line can be
compensated for.
[0118] When the optical signals are outputted from the regenerators
1101, the optical signals are inputted to a multiplexer 1102, are
multiplexed to wavelength-multiplexed optical signals consisting of
the same optical signals as the input sinal, and are inputted to
the wavelength selector unit 1300.
[0119] The wavelength selector unit 1300 has the configuration as
shown in FIG. 15B, and after routing the optical signals, it
outputs demultiplexed optical signals of each wavelength from the
output ports. The optical signals outputted from each output port
are inputted to regenerators 1301 provided corresponding to each
output port, and are regenerated. Thus, the S/N ratio degradation
generated in the wavelength selector unit 1300 can be compensated
for. When the optical signals are outputted from the regenerators
1301, the wavelengths of the optical signals are converted to
appropriate wavelengths in order to be wavelength-multiplexed, and
are inputted to a multiplexer 1106. The multiplexer 1106
multiplexes the inputted optical signals and transmits the
multiplexed optical signals to the transmission line.
[0120] In the configuration shown in FIG. 16, since the wavelengths
of optical signals each having a specific wavelength when being
inputted are converted by the regenerators 1301, generally speaking
the input and output wavelengths of the optical signals of the
wavelength optical XC are different.
[0121] FIG. 17 shows the configuration in which a noise elimination
filter capable of changing a transmission wavelength is provided
before the latter-stage regenerator in the configuration shown in
FIG. 16.
[0122] In FIG. 17 the same components as in FIG. 16 are given the
same reference numbers as in FIG. 16.
[0123] The object of a noise elimination filter 1400 is to
eliminate noise generated in a wavelength selector unit 1300 when
optical amplifiers are provided in the wavelength selector unit
1300 (However, some noise remains in the neighborhood of the
wavelengths of optical signals). Thus, the error rate
characteristic of the latter-stage regenerator 1301 can be
improved.
[0124] In FIG. 17, in the same way as described in FIG. 16, when
wavelength-multiplexed optical signals are inputted to a
demultiplexer 1100, the optical signals are demultiplexed to
optical signals of each wavelength, and are regenerated by a
regenerator 1101. Thus, the S/N ratio degradation generated in the
transmission line is compensated for. Then, the optical signals of
each wavelength are multiplexed to wavelength-multiplexed optical
signals again by a multiplexer 1102, and are inputted to the
wavelength selector unit 1300. The wavelength selector unit 1300
routes the optical signals, and outputs the optical signals from
the output ports for each wavelength of the optical signals. The
outputted optical signals of each wavelength are inputted to the
noise elimination filter 1400, and the noise, etc. degrading the
S/N ratio of the main signals is eliminated.
[0125] When the optical signals have passed through the noise
elimination filter 1400, the optical signals are regenerated by the
regenerators 1301, the wavelengths are converted, and the optical
signals are inputted to a multiplexer 1106. The wavelength
conversion is performed so that all the optical signals inputted to
one multiplexer differ in wavelength and each wavelength may
conform to the standards of an optical network, when the optical
signals are wavelength-multiplexed by the multiplexer 1106.
[0126] Since the optical signals inputted to the noise elimination
filter 1400 differ in wavelength depending on the routing status in
the wavelength selector unit 1300, as described with reference to
FIG. 8, a controller circuit (not shown in the diagram) for
controlling the routing of the wavelength selector unit 1300 checks
based on routing information (pass setting signal) provided by the
operating system, as to which wavelength is to be outputted from
which output port, and controls so as to appropriately change the
transmission band of the noise elimination filter, when
establishing a call.
[0127] For concrete examples of the noise eliminating filters an
acousto-optic filter, fiber Fabry-Perot filter, etc. can be
considered.
[0128] In the configuration shown in FIG. 17, since the S/N ratio
of optical signals can be improved by providing a regenerator at
the former- and latter-stages of the wavelength selection unit, and
further providing a noise elimination filter, the error rate
characteristic can be improved when the latter-stage regenerator
regenerates the optical signals.
[0129] As described above, optical signals in the former- and
latter-stage regenerators can be regenerated by compensating for
the noise and crosstalk generated in the transmission line, and the
optical switch unit and the wavelength selection unit,
respectively, by providing a regenerator after demultiplexing the
wavelength on the input side (at the former-stage) and a noise
elimination filter before the regenerator on the output side (at
the latter-stage), and thereby the error rate characteristic of the
entire network can be improved. Accordingly, the present invention
greatly contributes to the functional improvement of an optical
transmission system using these configurations.
* * * * *