Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-07-08
2002-12-17
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
Reexamination Certificate
active
06496289
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a configuration for preventing a waveform of an optical signal from degrading in an optical exchanger (cross-connect node).
2. Description of the Related Art
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.
FIG. 1
shows the configuration of a wavelength-multiplexed optical XC and an optical network using the wavelength-multiplexed optical XC.
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.
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).
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).
FIGS. 2A and 2B
, respectively, show the general configurations of fixed and converted wavelength type wavelength-multiplexed optical XCs using an optical switch.
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.
FIGS. 3A and 3B
, respectively, show the general configurations of fixed and converted wavelength type wavelength-multiplexed optical XCs using a wavelength filter.
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.
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.
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.
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
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.
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.
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 si
Kuroyanagi Satoshi
Maeda Takuji
Nakajima Ichiro
Nishi Tetsuya
Tsuyama Isao
Pascal Leslie
Singh Dalzid
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