Patent Description:
A wavelength division multiplexing (WDM) method of multiplexing and transmitting optical signals at various wavelengths for achieving high-capacity communication is used in a trunk long-distance optical communication system.

Signal transmission is controlled on a per-wavelength basis in a WDM-based optical communication system. PTLs <NUM> and <NUM> describe examples of an optical add/drop multiplexer (OADM) device and a reconfigurable optical add/drop multiplexer (ROADM) device that are provided in WDM-based optical communication systems. An OADM device and a ROADM device perform adding and dropping of a signal on a per-wavelength basis. Consequently, signal transmission can be controlled on a per-wavelength basis. In recent years, OADM devices and ROADM devices have started to be applied to optical submarine cable systems, and flexible network control has started to be also required in optical submarine cable systems. PTL <NUM> describes an example of an optical submarine cable system including a submarine branching device having an OADM function. A submarine branching device is laid on the seabed and is provided on an optical submarine cable connecting land terminal stations. A submarine branching device performs adding and dropping of a signal on a wavelength-multiplexed optical signal (WDM signal) input from a land terminal station on a per-wavelength basis and outputs a WDM signal to each land terminal station.

<CIT> relates to an extended branch device. <CIT> discloses an optical branching unit for optical add drop multiplexing. <CIT> discloses an optical add/drop multiplexing device and method. <CIT> relates to an optical multiplexing and demultiplexing device and a respective control method.

With recent increase in communication traffic, for example, an optical transmission system using a plurality of wavelength bands, such as both of a wavelength band in a conventional band (C-band: <NUM> band) and a wavelength band in a long wavelength band (L-band: <NUM> band), is under study in an optical submarine cable system, in order to achieve higher capacity communication.

In order to provide a submarine optical transmission system using a plurality of wavelength bands, a submarine branching device applicable to any WDM signal in the plurality of wavelength bands is required.

Then, an object of the present invention is to provide a submarine branching device, a submarine optical communication system, and an optical communication method that are applicable to WDM signals in a plurality of wavelength bands.

The present invention can provide a submarine branching device, an optical submarine cable system, and an optical communication method that are applicable to WDM signals in a plurality of wavelength bands.

Next, example embodiments of the present invention will be described in detail with reference to drawings.

<FIG> illustrates a configuration example of an optical submarine cable system according to a first example embodiment of the present invention. The optical submarine cable system <NUM> in <FIG> includes a terminal station <NUM>, a terminal station <NUM>, a terminal station <NUM>, an optical submarine cable <NUM>, and a submarine branching device <NUM>. The terminal station <NUM>, the terminal station <NUM>, the terminal station <NUM>, and the submarine branching device <NUM> are connected to one another through the optical submarine cable <NUM>. Each of the terminal stations <NUM>, <NUM>, and <NUM> is a station office installed on land and includes an optical communication device capable of transmitting and receiving optical signals. The terminal stations <NUM>, <NUM>, and <NUM> perform transmission of WDM signals through the optical submarine cable <NUM>.

The submarine branching device <NUM> has a function of adding/dropping a wavelength-multiplexed optical signal. A WDM signal <NUM> and a WDM signal <NUM> are input to the submarine branching device <NUM> from the terminal station <NUM> and the terminal station <NUM>, respectively. The submarine branching device <NUM> outputs a WDM signal <NUM> and a WDM signal <NUM> to the terminal station <NUM> and the terminal station <NUM>, respectively. While <FIG> illustrates a signal transmitted in a direction from the terminal station <NUM> to the terminal station <NUM> (upstream direction), an unillustrated signal is also transmitted in a direction from the terminal station <NUM> to the terminal station <NUM> (downstream direction) through the optical submarine cable <NUM>. The optical submarine cable <NUM> includes a plurality of fibers, and a signal in the upstream direction and a signal in the downstream direction may be transmitted through different fibers. Each of the upstream direction and the downstream direction may be configured with a plurality of optical fibers. Submarine repeaters each of which including an amplifier, or the like may be placed between the terminal stations <NUM>, <NUM>, and <NUM> and the submarine branching device <NUM>.

<FIG> illustrates a configuration example of the submarine branching device <NUM> according to the first example embodiment. According to <FIG>, the submarine branching device <NUM> includes a demultiplexing unit <NUM>, an optical add/drop unit <NUM>, and a multiplexing unit <NUM>. An arrow illustrated in <FIG> indicates a transmission direction of a WDM signal. While the C-band and the L-band will be described as an example of a plurality of wavelength bands in the following description about the present example embodiment, a plurality of wavelength bands applied to the present example embodiment are not limited to the above.

The demultiplexing unit <NUM> demultiplexes the WDM signal <NUM> input from the terminal station <NUM>. The WDM signal <NUM> includes a WDM signal (C-band signal) <NUM> having a C-band wavelength and a WDM signal (L-band signal) <NUM> having an L-band wavelength. The demultiplexing unit <NUM> demultiplexes the WDM signal <NUM> into the C-band signal <NUM> and the L-band signal <NUM>, and outputs the C-band signal <NUM> to the optical add/drop unit <NUM> and outputs the L-band signal <NUM> to the multiplexing unit <NUM>. For example, the demultiplexing unit <NUM> may be a wavelength selective switch (WSS) selectively switching a wavelength output to a specific port, an optical filter selectively transmitting or reflecting a specific wavelength, or a combination of an optical coupler and an optical filter selectively transmitting a specific wavelength. A wavelength band demultiplexed by the demultiplexing unit <NUM> may be changeable. A change of a wavelength band may be performed in accordance with control from an unillustrated control device.

The optical add/drop unit <NUM> has a function of adding/dropping a specific wavelength. The C-band signal <NUM> input to the optical add/drop unit <NUM> includes a band signal <NUM> and a band signal <NUM>. The optical add/drop unit <NUM> outputs the WDM signal <NUM> including the band signal <NUM> included in the C-band signal <NUM> to the terminal station <NUM>. Further, the optical add/drop unit <NUM> multiplexes the band signal <NUM> included in the C-band signal <NUM> and a band signal <NUM> included in the WDM signal <NUM> input from the terminal station <NUM>, and outputs a C-band signal <NUM> to the multiplexing unit <NUM>. Each of the band signals <NUM>, <NUM>, and <NUM> may be a WDM signal or a single-wavelength signal. Data to be received by the terminal station <NUM> may be superposed on the band signals <NUM> and <NUM>. Data to be received by the terminal station <NUM> may be superposed on the band signal <NUM>. Wavelength bands of the band signal <NUM> and the band signal <NUM> are not limited to be uniform as illustrated in <FIG>. Furthermore, a wavelength band added/dropped by the optical add/drop unit <NUM> may be changeable. A change of a wavelength band may be performed in accordance with control from an unillustrated control device.

The WDM signal <NUM> output to the terminal station <NUM> by the optical add/drop unit <NUM> has only to include at least the band signal <NUM>. Accordingly, for example, the optical add/drop unit <NUM> may output the WDM signal <NUM> including the band signal <NUM> and the band signal <NUM> to the terminal station <NUM>. While the WDM signal <NUM> input to the optical add/drop unit <NUM> may include a dummy signal having a wavelength band corresponding to the band signal <NUM>, the optical add/drop unit <NUM> in this case may output the WDM signal <NUM> including the dummy signal and the band signal <NUM> to the terminal station <NUM>.

The multiplexing unit <NUM> multiplexes the L-band signal <NUM> input from the demultiplexing unit <NUM> and the C-band signal <NUM> input from the optical add/drop unit <NUM> and outputs the WDM signal <NUM> to the terminal station <NUM>. For example, the multiplexing unit <NUM> may be a WSS or an optical coupler.

An operation example of the submarine branching device according to the first example embodiment will be described below by use of <FIG>.

The demultiplexing unit <NUM> demultiplexes the WDM signal <NUM> input from the terminal station <NUM> into the C-band signal <NUM> and the L-band signal <NUM> (S101).

The optical add/drop unit <NUM> outputs the WDM signal <NUM> including the band signal <NUM> included in the C-band signal <NUM> to the terminal station <NUM> (S102).

The optical add/drop unit <NUM> outputs, to the multiplexing unit <NUM>, the C-band signal <NUM> acquired by multiplexing the band signal <NUM> included in the C-band signal <NUM> and the band signal <NUM> included in the WDM signal <NUM> input from the terminal station <NUM> (S103). An order in which S102 and S103 are executed is not limited, and S102 may be executed after S103 is executed. S102 and S103 may be executed simultaneously.

The multiplexing unit <NUM> multiplexes the L-band signal <NUM> input from the demultiplexing unit <NUM> and the C-band signal <NUM> input from the optical add/drop unit <NUM> and outputs the WDM signal <NUM> to the terminal station <NUM> (S104).

The submarine branching device according to the present example embodiment demultiplexes an input WDM signal into a plurality of wavelength bands, such as a C-band signal and an L-band signal, and performs add/drop on one of the signals. Consequently, an output destination of a WDM signal including a plurality of wavelength bands can be controlled on a per-wavelength basis. Accordingly, a submarine branching device capable of providing an optical transmission system using a plurality of wavelength bands can be provided.

As exemplified in the present example embodiment, by demultiplexing an input WDM signal into a C-band signal and an L-band signal, an output destination of the WDM signal including the C-band signal and the L-band signal can be controlled on a per-wavelength basis. Consequently, an output destination of the WDM signal including the C-band signal and the L-band signal can be controlled on a per-wavelength basis. Accordingly, a submarine branching device capable of providing an optical transmission system using the C-band and the L-band can be provided.

While it is assumed that the submarine branching device according to the present example embodiment performs add/drop on a C-band signal, the submarine branching device may perform add/drop on an L-band signal. In this case, the demultiplexing unit <NUM> outputs the L-band signal <NUM> to the optical add/drop unit <NUM>, and the optical add/drop unit <NUM> performs add/drop on the L-band signal <NUM>. A wavelength band added/dropped by the submarine branching device may be set during manufacture or may be dynamically controlled. A change of a wavelength band may be performed in accordance with control from an unillustrated control device.

When performing add/drop on a C-band signal, the optical add/drop unit <NUM> in the submarine branching device according to the present example embodiment may be applied to part of an OADM device or a ROADM device used in a C-band optical transmission system. Accordingly, an effect of reducing a manufacture cost of a submarine branching device applicable to an optical transmission system using the C-band and the L-band is provided.

While a signal output in the direction from the terminal station <NUM> to the terminal station <NUM> (upstream direction) has been described in the present example embodiment, the same may similarly apply to a signal output in the direction from the terminal station <NUM> to the terminal station <NUM> (downstream direction).

A second example embodiment of the present invention will be described. A submarine branching device according to the second example embodiment of the present invention comprises a configuration to be capable of flexibly controlling an output destination of an input wavelength-multiplexed optical signal on a per-wavelength basis. Description of a configuration similar to that in the first example embodiment of the present invention is omitted in the second example embodiment of the present invention.

A configuration example of an optical submarine cable system according to the second example embodiment of the present invention is similar to the configuration example of the optical submarine cable system <NUM> illustrated in <FIG>.

Compared with the configuration illustrated in <FIG>, the submarine branching device according to the second example embodiment of the present invention includes an optical add/drop unit 52A in place of the optical add/drop unit <NUM>. The optical add/drop unit 52A comprises a configuration to be capable of flexibly controlling an output destination of an input wavelength-multiplexed optical signal on a per-wavelength basis. <FIG> illustrates a configuration example of the optical add/drop unit 52A according to the second example embodiment of the present invention. The optical add/drop unit 52A includes a branching unit <NUM>, a wavelength selection unit <NUM>, and a multiplexing unit <NUM>.

The branching unit <NUM> branches a C-band signal <NUM> input from a demultiplexing unit <NUM>. The branching unit <NUM> outputs one of the branched C-band signals <NUM> to the wavelength selection unit <NUM>. The branching unit <NUM> outputs the other of the branched C-band signals <NUM> to a terminal station <NUM> as a WDM signal <NUM>. For example, the branching unit <NUM> may be an optical coupler.

The wavelength selection unit <NUM> transmits a band signal <NUM> included in a C-band signal <NUM> input from the branching unit <NUM>. The wavelength selection unit <NUM> outputs the transmitted band signal <NUM> to the multiplexing unit <NUM>. The wavelength selection unit <NUM> may block a band signal <NUM> included in the C-band signal <NUM> input from the branching unit <NUM>. The wavelength selection unit <NUM> may be an optical filter selectively transmitting a specific wavelength and blocking the other wavelength bands. A wavelength band transmitted by the wavelength selection unit <NUM> may be changeable. A change of a wavelength band may be performed in accordance with control from an unillustrated control device.

The multiplexing unit <NUM> multiplexes the band signal <NUM> input from the wavelength selection unit <NUM> and a band signal <NUM> included in a WDM signal <NUM> input from the terminal station <NUM> and outputs a C-band signal <NUM>. For example, the multiplexing unit <NUM> may be an optical coupler.

The wavelength selection unit <NUM> and the multiplexing unit <NUM> may be a WSS combining the aforementioned functions. In this case, the WSS performs add/drop on the input C-band signal <NUM> and the input WDM signal <NUM>, and outputs the C-band signal <NUM>.

An operation example of the optical add/drop unit 52A according to the second example embodiment will be described below by use of <FIG>. Description of an operation example similar to that in the first example embodiment of the present invention is omitted in the second example embodiment of the present invention.

The branching unit <NUM> branches the C-band signal <NUM> input from the demultiplexing unit <NUM> to the optical add/drop unit <NUM> (S201).

The wavelength selection unit <NUM> transmits the band signal <NUM> included in the C-band signal <NUM> input from the branching unit <NUM> (S202).

The multiplexing unit <NUM> multiplexes the band signal <NUM> input from the wavelength selection unit <NUM> and the band signal <NUM> included in the WDM signal <NUM> and outputs the multiplexed signal to the multiplexing unit <NUM> as the C-band signal <NUM> (S203).

The optical add/drop unit according to the present example embodiment comprises a configuration to be capable of selectively transmitting a band signal included in an input C-band signal and outputting a WDM signal including the transmitted band signal. Consequently, an output destination of a WDM signal can be flexibly controlled on a per-wavelength basis. Accordingly, a submarine branching device capable of providing an optical transmission system using the C-band and the L-band can be provided.

A third example embodiment of the present invention will be described. A submarine branching device according to the third example embodiment of the present invention comprises a configuration to be capable of ensuring data confidentiality. Description of a configuration similar to that in another example embodiment of the present invention is omitted in the third example embodiment of the present invention.

A configuration example of an optical submarine cable system according to the third example embodiment of the present invention is similar to the configuration example of the optical submarine cable system <NUM> illustrated in <FIG>.

The optical add/drop unit <NUM> according to the aforementioned second example embodiment of the present invention outputs the WDM signal <NUM> including the band signal <NUM> to the terminal station <NUM>. Data to be received by the terminal station <NUM> may be superposed on the band signal <NUM>, but at this time, the band signal <NUM> is output to the terminal station <NUM> not being an original destination.

Then, the submarine branching device according to the third example embodiment of the present invention performs predetermined waveform processing on a band signal on which data to be received by the terminal station <NUM> are superposed. Consequently, even when a signal is output to a terminal station not being an original destination, data confidentiality can be ensured.

Compared with the configuration illustrated in <FIG>, the submarine branching device according to the third example embodiment of the present invention includes an optical add/drop unit 52B in place of the optical add/drop unit <NUM>. <FIG> illustrates a configuration example of the optical add/drop unit <NUM> according to the third example embodiment of the present invention. In addition to the configuration illustrated in <FIG>, the optical add/drop unit 52B includes a demultiplexing unit <NUM>, a processing unit <NUM>, and a multiplexing unit <NUM>.

The demultiplexing unit <NUM> demultiplexes a C-band signal <NUM> input from a branching unit <NUM> into a band signal <NUM> and a band signal <NUM>. The demultiplexing unit <NUM> outputs the band signal <NUM> to the processing unit <NUM> and outputs the band signal <NUM> to the multiplexing unit <NUM>. For example, the demultiplexing unit <NUM> may be a WSS selectively switching a wavelength output to a specific port, an optical filter selectively transmitting or reflecting a specific wavelength, or a combination of an optical coupler and an optical filter selectively transmitting a specific wavelength. A wavelength band demultiplexed by the demultiplexing unit <NUM> may be changeable. A change of a wavelength band may be performed in accordance with control from an unillustrated control device.

The processing unit <NUM> generates a processed signal <NUM> by applying predetermined waveform processing to the band signal <NUM> input from the demultiplexing unit <NUM>. The processing unit <NUM> outputs the processed signal <NUM> to the multiplexing unit <NUM>. As the predetermined waveform processing, the processing unit <NUM> may add a predetermined pattern to the band signal <NUM>. For example, the predetermined pattern may be a dummy pattern in which <NUM> and <NUM> are randomly arranged or a fixed pattern in which <NUM> and <NUM> are arranged in a specific pattern. Further, as the predetermined waveform processing, the processing unit <NUM> may perform scrambling processing on the band signal <NUM>. Further, as the predetermined waveform processing, the processing unit <NUM> may degrade a transmission characteristic of the band signal <NUM>. Furthermore, the processing unit <NUM> may delay the band signal <NUM> and cause the multiplexing unit <NUM> to multiplex the delayed signal as a delayed optical signal. The predetermined waveform processing executed by the processing unit <NUM> may be changeable. A change of the waveform processing may be performed in accordance with control from an unillustrated control device.

The multiplexing unit <NUM> multiplexes the band signal <NUM> and the processed signal <NUM> and outputs the multiplexed signal to the terminal station <NUM> as a WDM signal <NUM>. The multiplexing unit <NUM> may be an optical coupler.

Operation examples of the demultiplexing unit <NUM>, the processing unit <NUM>, and the multiplexing unit <NUM>, according to the third example embodiment, will be described below by use of <FIG>. An operation example of a configuration not illustrated in <FIG> is similar to that in the second example embodiment, and therefore description thereof is omitted.

The demultiplexing unit <NUM> demultiplexes the C-band signal <NUM> input from the branching unit <NUM> into the band signal <NUM> and the band signal <NUM> (S301).

The processing unit <NUM> generates the processed signal <NUM> by applying predetermined waveform processing on the band signal <NUM> input from the demultiplexing unit <NUM> (S302).

The multiplexing unit <NUM> multiplexes the band signal <NUM> input from the demultiplexing unit <NUM> and the processed signal <NUM> input from the processing unit <NUM> (S303).

The optical add/drop unit according to the present example embodiment comprises a configuration to apply predetermined waveform processing to a signal on which data output to a terminal station not being an original destination are superposed. Consequently, the data cannot be extracted from the signal to which the waveform processing is applied, at the terminal station not being the original destination. Accordingly, an effect of allowing ensured data confidentiality while achieving flexible signal transmission control is provided.

A fourth example embodiment of the present invention will be described. A submarine branching device according to the fourth example embodiment of the present invention comprises a configuration to be capable of compensating for strength of a WDM signal by use of a dummy signal. Description of a configuration similar to that in another example embodiment of the present invention is omitted in the fourth example embodiment of the present invention.

A configuration example of an optical submarine cable system according to the fourth example embodiment of the present invention is similar to the configuration example of the optical submarine cable system <NUM> illustrated in <FIG>.

A WDM signal input to a submarine branching device <NUM> from a terminal station <NUM> may include a dummy signal, according to the fourth example embodiment. A dummy signal is a signal multiplexed onto a band signal on which data are superposed, in order to compensate for signal strength. The submarine branching device according to the fourth example embodiment of the present invention comprises a configuration to multiplex a dummy signal input from the terminal station <NUM> onto a WDM signal output to the terminal station <NUM>. Consequently, strength of the WDM signal output to the terminal station <NUM> from the submarine branching device can be compensated for.

Compared with the configuration illustrated in <FIG>, the submarine branching device according to the fourth example embodiment of the present invention includes an optical add/drop unit 52C in place of the optical add/drop unit <NUM>. <FIG> illustrates a configuration example of the optical add/drop unit 52C according to the fourth example embodiment of the present invention. In addition to the configuration illustrated in <FIG>, the optical add/drop unit 52C includes a branching unit <NUM>, wavelength selection units <NUM>, <NUM>, and <NUM>, and a multiplexing unit <NUM>. A WDM signal <NUM> input from the terminal station <NUM> includes a dummy signal <NUM>. A WDM signal <NUM> output to the terminal station <NUM> includes the dummy signal <NUM>. The dummy signal <NUM> may have a wavelength band corresponding to a wavelength band of a band signal <NUM>.

The branching unit <NUM> branches the WDM signal <NUM> input from the terminal station <NUM>. The branching unit <NUM> outputs the branched WDM signals <NUM> to the wavelength selection units <NUM> and <NUM>. The branching unit <NUM> may be an optical coupler.

Each of the wavelength selection units <NUM>, <NUM>, and <NUM> transmits a signal at a specific wavelength in an input signal. The wavelength selection unit <NUM> transmits a band signal <NUM> in a C-band signal <NUM> input from a branching unit <NUM>. The wavelength selection unit <NUM> transmits a band signal <NUM> in a WDM signal input from the branching unit <NUM>. The wavelength selection unit <NUM> transmits the dummy signal <NUM> in the WDM signal input from the branching unit <NUM>. Each of the wavelength selection units <NUM>, <NUM>, and <NUM> may block a band signal not to be transmitted. Further, each of the wavelength selection units <NUM>, <NUM>, and <NUM> may be an optical filter selectively transmitting a specific wavelength. A wavelength band transmitted by each of the wavelength selection units <NUM>, <NUM>, and <NUM> may be changeable. A change of a wavelength band may be performed in accordance with control from an unillustrated control device.

The multiplexing unit <NUM> multiplexes the band signal <NUM> input from the wavelength selection unit <NUM> and the dummy signal <NUM> input from the wavelength selection unit <NUM> and outputs the WDM signal <NUM> to the terminal station <NUM>. For example, the multiplexing unit <NUM> may be an optical coupler.

An operation example of the optical add/drop unit 52C according to the fourth example embodiment will be described below by use of <FIG>. An operation example of a configuration not illustrated in <FIG> is similar to that in the first example embodiment, and therefore description thereof is omitted.

The branching unit <NUM> branches the C-band signal <NUM> input from the demultiplexing unit <NUM> (S401).

The wavelength selection unit <NUM> transmits the band signal <NUM> included in the branched C-band signal <NUM> (S402).

The wavelength selection unit <NUM> transmits the band signal <NUM> included in the branched C-band signal <NUM> (S403).

The branching unit <NUM> branches the WDM signal <NUM> input from the terminal station <NUM> (S404).

The wavelength selection unit <NUM> transmits the band signal <NUM> included in the branched WDM signal <NUM> (S405).

The wavelength selection unit <NUM> transmits the dummy signal <NUM> included in the branched WDM signal <NUM> (S406).

The multiplexing unit <NUM> multiplexes the band signal <NUM> and the band signal <NUM> (S407).

The multiplexing unit <NUM> multiplexes the band signal <NUM> and the dummy signal <NUM> (S408).

The submarine branching device according to the fourth example embodiment of the present invention comprises a configuration to output a WDM signal onto which an input dummy signal is multiplexed. Consequently, strength of the WDM signal output from the submarine branching device can be compensated for. In this case, even when an optical signal is amplified in a submarine repeater or the like being an output destination, excessive amplification of the optical signal can be prevented by the dummy signal, and by extension, degradation of the optical signal due to a nonlinear effect can be prevented.

A fifth example embodiment of the present invention will be described. The submarine branching device according to the fifth example embodiment of the present invention comprises a configuration to add/drop an L-band signal. Description of a configuration similar to that in another example embodiment of the present invention is omitted in the fifth example embodiment of the present invention.

A configuration example of an optical submarine cable system according to the fifth example embodiment of the present invention is similar to the configuration example of the optical submarine cable system <NUM> illustrated in <FIG>.

The submarine branching devices according to the aforementioned example embodiments perform add/drop on a C-band signal. However, the submarine branching devices do not have a function of adding/dropping an L-band signal.

Then, the submarine branching device according to the fifth example embodiment of the present invention comprises a configuration to add/drop an L-band signal. Consequently, flexible transmission control of a WDM signal can be achieved in an optical transmission system using the C-band and the L-band.

<FIG> illustrates a configuration example of the submarine branching device according to the fifth example embodiment of the present invention. The submarine branching device <NUM> in <FIG> includes demultiplexing units <NUM> and <NUM>, a C-band optical add/drop unit <NUM>, an L-band optical add/drop unit <NUM>, and multiplexing units <NUM> and <NUM>. A WDM signal <NUM> output from a terminal station <NUM> is input to the submarine branching device <NUM>. A WDM signal <NUM> output from a terminal station <NUM> is input to the submarine branching device <NUM>.

The demultiplexing unit <NUM> demultiplexes the WDM signal <NUM> input from the terminal station <NUM> into a C-band signal <NUM> and an L-band signal <NUM>. The demultiplexing unit <NUM> outputs the C-band signal <NUM> to the C-band optical add/drop unit <NUM>. The demultiplexing unit <NUM> outputs the L-band signal <NUM> to the L-band optical add/drop unit <NUM>.

For example, each of the demultiplexing units <NUM> and <NUM> may be a WSS selectively switching a wavelength output to a specific port, an optical filter selectively transmitting or reflecting a specific wavelength, or a combination of an optical coupler and an optical filter selectively transmitting a specific wavelength. A wavelength band demultiplexed by each of the demultiplexing units <NUM> and <NUM> may be changeable. A change of a wavelength band may be performed in accordance with control from an unillustrated control device.

The C-band optical add/drop unit <NUM> performs add/drop on a C-band signal. The C-band optical add/drop unit <NUM> outputs a band signal <NUM> included in the C-band signal <NUM> input from the demultiplexing unit <NUM> to the multiplexing unit <NUM>. Further, the C-band optical add/drop unit <NUM> multiplexes a band signal <NUM> included in the C-band signal <NUM> and the C-band signal <NUM> and outputs a C-band signal <NUM> to the multiplexing unit <NUM>.

The L-band optical add/drop unit <NUM> performs add/drop on an L-band signal. The L-band optical add/drop unit <NUM> outputs a band signal <NUM> in the L-band signal <NUM> input from the demultiplexing unit <NUM> to the multiplexing unit <NUM>. Further, the L-band optical add/drop unit <NUM> multiplexes a band signal <NUM> in the L-band signal <NUM> input from the demultiplexing unit <NUM> and the L-band signal <NUM> input from the demultiplexing unit <NUM> and outputs an L-band signal <NUM> to the multiplexing unit <NUM>.

The multiplexing unit <NUM> multiplexes the C-band signal <NUM> input from the C-band optical add/drop unit <NUM> and the L-band signal <NUM> input from the L-band optical add unit and outputs the multiplexed signal to a terminal station <NUM> as a WDM signal <NUM>.

The multiplexing unit <NUM> multiplexes the band signal <NUM> input from the C-band optical add/drop unit <NUM> and the band signal <NUM> input from the L-band optical add/drop unit <NUM> and outputs the multiplexed signal to the terminal station <NUM> as a WDM signal <NUM>.

An operation example of the submarine branching device according to the fifth example embodiment will be described below by use of <FIG>.

The demultiplexing unit <NUM> demultiplexes the WDM signal <NUM> input from the terminal station <NUM> into the C-band signal <NUM> and the L-band signal <NUM> (S501).

The demultiplexing unit <NUM> demultiplexes the WDM signal <NUM> input from the terminal station <NUM> into the C-band signal <NUM> and the L-band signal <NUM> (S502).

The C-band optical add/drop unit <NUM> multiplexes the band signal <NUM> included in the C-band signal <NUM> and the C-band signal <NUM> and outputs the C-band signal <NUM> to the multiplexing unit <NUM> (S503).

Further, the C-band optical add/drop unit <NUM> drops the band signal <NUM> included in the C-band signal <NUM> input from the demultiplexing unit <NUM> and outputs the band signal <NUM> to the multiplexing unit <NUM> (S504).

The L-band optical add/drop unit <NUM> multiplexes the band signal <NUM> in the L-band signal <NUM> input from the demultiplexing unit <NUM> and the band signal <NUM> input from the demultiplexing unit <NUM> and outputs the L-band signal <NUM> to the multiplexing unit <NUM> (S505).

Further, the L-band optical add/drop unit <NUM> drops the band signal <NUM> in the L-band signal <NUM> input from the demultiplexing unit <NUM> and outputs the band signal <NUM> to the multiplexing unit <NUM> (S506).

The multiplexing unit <NUM> multiplexes the C-band signal <NUM> input from the C-band optical add/drop unit <NUM> and the L-band signal <NUM> input from the L-band optical add unit and outputs the WDM signal <NUM> to the terminal station <NUM> (S507).

The multiplexing unit <NUM> multiplexes the band signal <NUM> input from the C-band optical add/drop unit <NUM> and the band signal <NUM> input from the L-band optical add/drop unit <NUM> and outputs the WDM signal <NUM> to the terminal station <NUM> (S508).

The submarine branching device according to the present example embodiment performs add/drop on each of a C-band signal and an L-band signal. Accordingly, a submarine branching device capable of flexible transmission control on a per-wavelength basis in an optical transmission system using the C-band and the L-band can be provided.

A sixth example embodiment of the present invention will be described. A submarine branching device according to the sixth example embodiment of the present invention comprises a configuration to be capable of controlling an output destination of a signal in response to occurrence of a failure. Description of a configuration similar to that in another example embodiment of the present invention is omitted in the sixth example embodiment of the present invention.

<FIG> illustrates a configuration example of an optical submarine cable system according to the sixth example embodiment of the present invention. Compared with the configuration illustrated in <FIG>, the optical submarine cable system <NUM> illustrated in <FIG> includes a submarine branching device 7A in place of the submarine branching device <NUM>. <FIG> illustrates a configuration example in a case of a failure occurring on a transmission line through an optical submarine cable <NUM> between a terminal station <NUM> and the submarine branching device 7A. A configuration example under normal operation is similar to the configuration example illustrated in <FIG>. As illustrated in <FIG>, in response to occurrence of a failure, the submarine branching device 7A controls an output destination of a WDM signal and outputs a WDM signal <NUM> input from a terminal station <NUM> to a terminal station <NUM>.

<FIG> illustrates a configuration example of the submarine branching device 7A according to the sixth example embodiment of the present invention. The submarine branching device 7A includes a failure detection unit <NUM>, a demultiplexing unit <NUM>, an optical add/drop unit <NUM>, and a multiplexing unit <NUM>. A solid arrow in <FIG> indicates a signal flow in the case of a failure occurring on the transmission line through the optical submarine cable <NUM> between the terminal station <NUM> and the submarine branching device 7A. A signal flow under normal operation is similar to the configuration example illustrated in <FIG>. A broken arrow in <FIG> indicates a signal flow between the terminal station <NUM> and the submarine branching device 7A under normal operation.

The demultiplexing unit <NUM> and the multiplexing unit <NUM> are similar to the demultiplexing unit <NUM> and the multiplexing unit <NUM> in <FIG>, respectively, and therefore detailed description thereof is omitted.

The failure detection unit <NUM> detects a failure on the transmission line through the optical submarine cable <NUM> between the terminal station <NUM> and the submarine branching device 7A. The failure detection unit <NUM> may also detect a failure on a transmission line between another terminal station and the submarine branching device. Further, in response to detection of a failure, the failure detection unit <NUM> instructs the optical add/drop unit <NUM> to change a wavelength band to be multiplexed and demultiplexed. The failure detection unit <NUM> may monitor a WDM signal input to the submarine branching device 7A and detect a failure on the transmission line in response to signal quality degradation or signal interruption of the monitored WDM signal. The failure detection unit <NUM> may detect a failure by receiving failure occurrence information from a terminal station or another submarine branching device. In place of the failure detection unit <NUM>, an unillustrated monitor unit may detect a failure on the transmission line. In this case, the failure detection unit <NUM> issues an instruction to the optical add/drop unit <NUM> in response to detection of a failure by the monitor unit.

The optical add/drop unit <NUM> has a function of being capable of changing a wavelength band to be multiplexed and demultiplexed. In response to occurrence of a failure, the optical add/drop unit <NUM> changes a wavelength band to be multiplexed and demultiplexed and switches an output destination of a signal. The optical add/drop unit <NUM> outputs a C-band signal <NUM> input from the demultiplexing unit <NUM> to the multiplexing unit <NUM>.

An operation example of the submarine branching device 7A according to the sixth example embodiment at occurrence of a failure will be described below by use of <FIG>. An operation example of the submarine branching device 7A under normal operation is similar to the operation example illustrated in <FIG>.

The failure detection unit <NUM> detects a failure on the transmission line through the optical submarine cable <NUM> between the terminal station <NUM> and the submarine branching device 7A (S601).

In response to the detection of the failure, the failure detection unit <NUM> instructs the optical add/drop unit <NUM> to change a wavelength band to be multiplexed and demultiplexed (S602).

In accordance with the instruction from the failure detection unit <NUM>, the optical add/drop unit <NUM> changes a wavelength band to be multiplexed and demultiplexed (S603).

The demultiplexing unit <NUM> demultiplexes the WDM signal <NUM> (S604).

The optical add/drop unit <NUM> transmits the C-band signal <NUM> input from the demultiplexing unit <NUM> and outputs the C-band signal <NUM> to the multiplexing unit <NUM> (S605).

The multiplexing unit <NUM> multiplexes the C-band signal <NUM> and an L-band signal <NUM> and outputs the WDM signal <NUM> to the terminal station <NUM> (S606).

The submarine branching device according to the present example embodiment comprises a configuration to be capable of controlling an output destination of a signal in response to occurrence of a failure. Accordingly, a submarine branching device being capable of providing an optical transmission system using the C-band and the L-band and also being capable of handling occurrence of a failure can be provided.

A Seventh example embodiment of the present invention will be described. A submarine branching device according to the seventh example embodiment of the present invention comprise a configuration to be capable of controlling an output destination of a signal in response to occurrence of a failure. The submarine branching device further comprises a configuration to be capable of ensuring data confidentiality. Description of a configuration similar to that in another example embodiment of the present invention is omitted in the seventh example embodiment of the present invention.

Compared with the configuration illustrated in <FIG>, an optical submarine cable system according to the seventh example embodiment of the present invention includes a submarine branching device 7B in place of the submarine branching device 7A.

The submarine branching device 7A according to the aforementioned sixth example embodiment of the present invention outputs the WDM signal <NUM> including the band signal <NUM> to the terminal station <NUM>. Data to be received by the terminal station <NUM> may be superposed on the band signal <NUM>, but at this time, the band signal <NUM> is output to the terminal station <NUM> not being an original destination.

Then, the submarine branching device 7B according to the seventh example embodiment of the present invention performs predetermined waveform processing on a band signal on which data to be received by the terminal station <NUM> are superposed. Consequently, even when a signal is output to a terminal station not being an original destination, data confidentiality can be ensured.

<FIG> illustrates a configuration example of the submarine branching device 7B according to the seventh example embodiment. In addition to the configuration of the submarine branching device 7A in <FIG>, the submarine branching device 7B in <FIG> includes a demultiplexing unit <NUM>, a processing unit <NUM>, and a multiplexing unit <NUM>. A solid arrow in <FIG> indicates a signal flow in a case of a failure occurring on a transmission line through an optical submarine cable <NUM> between the terminal station <NUM> and the submarine branching device 7B. A signal flow under normal operation is similar to the configuration example illustrated in <FIG>. A broken arrow in <FIG> indicates a signal flow between the terminal station <NUM> and the submarine branching device 7B under normal operation.

The demultiplexing unit <NUM> demultiplexes a C-band signal <NUM> input from an optical add/drop unit <NUM> into a band signal <NUM> and a band signal <NUM>. For example, the demultiplexing unit <NUM> may be a WSS selectively switching a wavelength output to a specific port, an optical filter selectively transmitting or reflecting a specific wavelength, or a combination of an optical coupler and an optical filter selectively transmitting a specific wavelength. A wavelength band demultiplexed by the demultiplexing unit <NUM> may be changeable. A change of a wavelength band may be performed in accordance with control from an unillustrated control device or may be performed in response to detection of a failure by the failure detection unit <NUM>.

The processing unit <NUM> generates a processed signal <NUM> by applying predetermined waveform processing to the band signal <NUM> input from the demultiplexing unit <NUM>. The processing unit <NUM> outputs the processed signal <NUM> to the multiplexing unit <NUM>. As the predetermined waveform processing, the processing unit <NUM> may add a predetermined pattern to the band signal <NUM>. For example, the predetermined pattern may be a dummy pattern in which <NUM> and <NUM> are randomly arranged or a fixed pattern in which <NUM> and <NUM> are arranged in a specific pattern. Further, as the predetermined waveform processing, the processing unit <NUM> may perform scrambling processing on the band signal <NUM>. Further, as the predetermined waveform processing, the processing unit <NUM> may degrade a transmission characteristic of the band signal <NUM>. Furthermore, the processing unit <NUM> may delay the band signal <NUM> and cause the multiplexing unit <NUM> to multiplex the delayed signal as a delayed optical signal. The predetermined waveform processing executed by the processing unit <NUM> may be changeable. A change of the waveform processing may be performed in accordance with control from an unillustrated control device or may be performed in response to detection of a failure by the failure detection unit <NUM>.

The multiplexing unit <NUM> multiplexes the band signal <NUM> and the processed signal <NUM> and outputs the multiplexed signal to the multiplexing unit <NUM>. The multiplexing unit <NUM> may be an optical coupler.

Operations of the demultiplexing unit <NUM>, the processing unit <NUM>, and the multiplexing unit <NUM>, according to the seventh example embodiment, are similar to the operation example illustrated in <FIG>. In this case, the demultiplexing unit <NUM>, the processing unit <NUM>, and the multiplexing unit <NUM> correspond to the demultiplexing unit <NUM>, the processing unit <NUM>, and the multiplexing unit <NUM>, respectively.

The optical add/drop unit according to the present example embodiment comprises a configuration to apply predetermined waveform processing to a signal on which data output to a terminal station not being an original destination are superposed, when changing an output destination of a signal in response to occurrence of a failure. Consequently, the data cannot be extracted from the signal to which the waveform processing is applied, at the terminal station not being the original destination. Accordingly, an effect of allowing ensured data confidentiality while achieving flexible signal transmission control is provided.

An eighth example embodiment of the present invention will be described. A submarine branching device according to the eighth example embodiment of the present invention comprises a configuration to be capable of controlling an output destination of a signal in response to occurrence of a failure. Description of a configuration similar to that in another example embodiment of the present invention is omitted in the eighth example embodiment of the present invention.

Compared with the configuration illustrated in <FIG>, an optical submarine cable system according to the eighth example embodiment of the present invention includes a submarine branching device 8A in place of the submarine branching device 7A. <FIG> illustrates a configuration example of the submarine branching device 8A according to the eighth example embodiment of the present invention. In addition to the configuration illustrated in <FIG>, the submarine branching device 8A includes a failure detection unit <NUM>, a demultiplexing unit <NUM>, an optical add/drop unit <NUM>, a multiplexing unit <NUM>, and switching units <NUM> and <NUM>. A solid arrow in <FIG> indicates a signal flow under normal operation.

The demultiplexing unit <NUM>, the optical add/drop unit <NUM>, and the multiplexing unit <NUM> are similar to the demultiplexing unit <NUM>, the optical add/drop unit <NUM>, and the multiplexing unit <NUM> in <FIG>, respectively, and therefore detailed description thereof is omitted. The optical add/drop unit <NUM> may also be similar to the optical add/drop unit <NUM> in <FIG>.

The failure detection unit <NUM> detects a failure on a transmission line through an optical submarine cable <NUM> between a terminal station <NUM> and the submarine branching device 8A. The failure detection unit <NUM> may also detect a failure on a transmission line between another terminal station and the submarine branching device. Further, the failure detection unit <NUM> instructs the switching units <NUM> and <NUM> to switch signal paths in response to detection of a failure. The failure detection unit <NUM> may monitor a WDM signal input to the submarine branching device 8A and detect a failure on the transmission line in response to signal quality degradation or signal interruption of the monitored WDM signal. Further, the failure detection unit <NUM> may detect a failure by receiving failure occurrence information from a terminal station or another submarine branching device. When the submarine branching device 8A receives power supply from at least one of terminal stations <NUM>, <NUM>, and <NUM>, a failure may be detected in response to interruption of the power supply. In place of the failure detection unit <NUM>, an unillustrated monitor unit may detect a failure on the transmission line. In this case, the failure detection unit <NUM> issues an instruction to the switching units <NUM> and <NUM> in response to detection of a failure by the monitor unit.

The switching unit <NUM> outputs a WDM signal <NUM> input from the terminal station <NUM> to the demultiplexing unit <NUM>. The switching unit <NUM> outputs a WDM signal <NUM> input from the multiplexing unit <NUM> to the terminal station <NUM>.

The switching units <NUM> and <NUM> switch signal paths in accordance with an instruction from the failure detection unit <NUM>. <FIG> illustrates a configuration example of the submarine branching device 8A in a case of the switching units <NUM> and <NUM> switching the signal paths. A solid arrow in <FIG> indicates a signal flow in the case of the switching units <NUM> and <NUM> switching the signal paths. The switching unit <NUM> switches the signal path and outputs the WDM signal <NUM> input from the terminal station <NUM> to the switching unit <NUM>. The switching unit <NUM> switches the signal path and outputs the WDM signal <NUM> input from the switching unit <NUM> to the terminal station <NUM>.

An operation example of the submarine branching device 8A according to the present example embodiment will be described by use of <FIG>. An operation example of the submarine branching device 8A under normal operation is similar to the operation example illustrated in <FIG>.

The failure detection unit <NUM> detects a failure on the transmission line through the optical submarine cable <NUM> between the terminal station <NUM> and the submarine branching device 8A (S801).

In response to the detection of the failure, the failure detection unit <NUM> instructs the switching units <NUM> and <NUM> to switch the signal paths (S802).

The switching unit <NUM> switches the signal path (S803).

The switching unit <NUM> switches the signal path (S804). An order in which S803 and S804 are executed is not limited. For example, S803 may be executed after S804 is executed, or S803 and S804 may be executed simultaneously.

The switching unit <NUM> outputs the WDM signal <NUM> input from the terminal station <NUM> to the switching unit <NUM> (S805).

The switching unit <NUM> outputs the WDM signal <NUM> input from the switching unit <NUM> to the terminal station <NUM> (S806).

A ninth example embodiment of the present invention will be described. A submarine branching device according to the ninth example embodiment of the present invention comprises a configuraion to be capable of controlling an output destination of a signal in response to occurrence of a failure. The submarine branching device further comprises a configuration to ensure data confidentiality. Description of a configuration similar to that in another example embodiment of the present invention is omitted in the ninth example embodiment of the present invention.

Compared with the configuration illustrated in <FIG>, an optical submarine cable system according to the ninth example embodiment of the present invention includes a submarine branching device 8B in place of the submarine branching device 7A.

The submarine branching device 8A according to the aforementioned eighth example embodiment of the present invention outputs the WDM signal <NUM> included in the band signal <NUM> to the terminal station <NUM>. Data received by the terminal station <NUM> may be superposed on the band signal <NUM>, but at this time, the band signal <NUM> is output to the terminal station <NUM> not being an original destination.

Then, the submarine branching device 8B according to the ninth example embodiment of the present invention performs predetermined waveform processing on a band signal on which data to be received by the terminal station <NUM> are superposed. Consequently, even when a signal is output to a terminal station not being an original destination, data confidentiality can be ensured.

<FIG> illustrates a configuration example of the submarine branching device 8B according to the ninth example embodiment. In addition to the configuration of the submarine branching device 8A in <FIG>, the submarine branching device 8B in <FIG> includes a demultiplexing unit <NUM>, a processing unit <NUM>, and a multiplexing unit <NUM>. A solid arrow in <FIG> indicates a signal flow in a case of switching units <NUM> and <NUM> switching signal paths, and a broken arrow indicates a signal flow before the switching units <NUM> and <NUM> switch the signal paths.

The demultiplexing unit <NUM> demultiplexes a WDM signal <NUM> input from the switching unit <NUM>. The demultiplexing unit <NUM> outputs a band signal <NUM> to the processing unit <NUM> and outputs a band signal <NUM> and an L-band signal <NUM> to the multiplexing unit <NUM>. For example, the demultiplexing unit <NUM> may be a WSS selectively switching a wavelength output to a specific port, an optical filter selectively transmitting or reflecting a specific wavelength, or a combination of an optical coupler and an optical filter selectively transmitting a specific wavelength. A wavelength band demultiplexed by the demultiplexing unit <NUM> may be changeable. A change of a wavelength band may be performed in accordance with control from an unillustrated control device.

The processing unit <NUM> generates a processed signal <NUM> by applying predetermined waveform processing to the band signal <NUM> input from the demultiplexing unit <NUM>. The processing unit <NUM> outputs the processed signal <NUM> to the multiplexing unit <NUM>. As the predetermined waveform processing, the processing unit <NUM> may add a predetermined pattern to the band signal <NUM>. For example, the predetermined pattern may be a dummy pattern in which <NUM> and <NUM> are randomly arranged or a fixed pattern in which <NUM> and <NUM> are arranged in a specific pattern. Further, as the predetermined waveform processing, the processing unit <NUM> may perform scrambling processing on the band signal <NUM>. Furthermore, the processing unit <NUM> may delay the band signal <NUM> and cause the multiplexing unit <NUM> to multiplex the delayed signal as a delayed optical signal. Further, as the predetermined waveform processing, the processing unit <NUM> may degrade a transmission characteristic of the band signal <NUM>. The predetermined waveform processing executed by the processing unit <NUM> may be changeable. A change of the waveform processing may be performed in accordance with control from an unillustrated control device or may be performed in response to detection of a failure by the failure detection unit <NUM>.

The multiplexing unit <NUM> multiplexes the band signal <NUM> and the L-band signal <NUM> that are input from the demultiplexing unit <NUM>, and the processed signal <NUM> input from the processing unit <NUM> and outputs a WDM signal <NUM> to the terminal station <NUM>. The multiplexing unit <NUM> may be an optical coupler.

Operations of the demultiplexing unit <NUM>, the processing unit <NUM>, and the multiplexing unit <NUM> in this example are similar to the operation example illustrated in <FIG>. In this case, the demultiplexing unit <NUM>, the processing unit <NUM>, and the multiplexing unit <NUM> correspond to the demultiplexing unit <NUM>, the processing unit <NUM>, and the multiplexing unit <NUM>, respectively.

A tenth example embodiment of the present invention will be described. A submarine branching device according to the tenth example embodiment of the present invention comprises a configuration to be capable of switching control of a signal path in response to occurrence of a failure. The submarine branching device according to the tenth example embodiment of the present invention further comprises a configuration to be capable of outputting an optical signal without causing traffic interruption due to switching control of a signal path. Description of a configuration similar to that in another example embodiment of the present invention is omitted, in the tenth example embodiment of the present invention.

Compared with the configuration illustrated in <FIG>, an optical submarine cable system according to the tenth example embodiment of the present invention includes a submarine branching device 9A in place of the submarine branching device 7A. <FIG> illustrates a configuration example of the submarine branching device 9A according to the tenth example embodiment of the present invention. The submarine branching device 9A includes a failure detection unit <NUM>, a branching unit <NUM>, an optical add/drop unit <NUM>, a multiplexing unit <NUM>, switching units <NUM> and <NUM>, and wavelength selection units <NUM> and <NUM>. A solid arrow in <FIG> indicates a signal flow under normal operation. <FIG> illustrates a configuration example of the submarine branching device 9A in a case of the switching units <NUM> and <NUM> switching signal paths. A solid arrow in <FIG> indicates a signal flow in the case of the switching units <NUM> and <NUM> switching the signal paths.

The failure detection unit <NUM> detects a failure on a transmission line through an optical submarine cable. According to the present example embodiment, the failure detection unit <NUM> detects a failure on a transmission line through an optical submarine cable <NUM> between a terminal station <NUM> and the submarine branching device 9A. The failure detection unit <NUM> may detect a failure on a transmission line between another terminal station and the submarine branching device. In response to detection of a failure, the failure detection unit <NUM> instructs the switching units <NUM> and <NUM>, to be described later, to switch signal paths. The failure detection unit <NUM> may monitor a WDM signal input to the submarine branching device 9A and detect a failure on the transmission line in response to signal quality degradation or signal interruption of the monitored WDM signal. Further, the failure detection unit <NUM> may detect a failure by receiving failure occurrence information from a terminal station or another submarine branching device. When the submarine branching device 9A receives power supply from at least one of terminal stations <NUM>, <NUM>, and <NUM>, a failure may be detected in response to interruption of the power supply. In place of the failure detection unit <NUM>, an unillustrated monitor unit may detect a failure on the transmission line. In this case, the failure detection unit <NUM> issues an instruction to the switching units <NUM> and <NUM> in response to detection of a failure by the monitor unit.

The branching unit <NUM> branches an input WDM signal and outputs the branched signals. For example, the branching unit <NUM> may be configured with an optical coupler.

The optical add/drop unit <NUM> has a function of adding/dropping a specific wavelength. Further, the optical add/drop unit <NUM> has a function and a configuration similar to those of the optical add/drop devices <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> according to the aforementioned example embodiments.

The multiplexing unit <NUM> multiplexes input optical signals and outputs the multiplexed signal. For example, the multiplexing unit <NUM> may be an optical coupler.

The switching units <NUM> and <NUM> switch optical signal paths by switching input/output ends of the optical signals. As described above, the switching units <NUM> and <NUM> switch optical signal paths in accordance with an instruction from the failure detection unit <NUM>. For example, each of the switching units <NUM> and <NUM> is configured with an optical switch.

Each of the wavelength selection units <NUM> and <NUM> selectively transmits and outputs a specific wavelength in an input WDM signal. According to the present example embodiment, the wavelength selection unit <NUM> selectively outputs a signal at a wavelength band of an L-band signal <NUM>, and the wavelength selection unit <NUM> outputs signals at wavelength bands of C-band signals <NUM> and <NUM>. For example, each of the wavelength selection units <NUM> and <NUM> may be configured with an optical filter. Further, each of the wavelength selection units <NUM> and <NUM> may be configured with an optical switch and optical filters. In this case, a selectively transmitted wavelength band can be changed by switching, by the optical switch, an optical filter to which an optical signal is input.

The multiplexing unit <NUM> and the wavelength selection units <NUM> and <NUM> may be integrally configured with a three-port optical filter or a WSS.

Switching of signal paths in response to occurrence of a failure will be described along a signal path of a WDM signal <NUM> input from the terminal station <NUM>.

In signal paths illustrated in <FIG>, the WDM signal <NUM> input to the branching unit <NUM> is branched and is output to the switching unit <NUM> and the wavelength selection unit <NUM>.

The WDM signal input to the switching unit <NUM> is input to the optical add/drop unit <NUM> and undergoes add/drop with a WDM signal <NUM> from the terminal station <NUM>. A WDM signal output from the optical add/drop unit <NUM> is input to the wavelength selection unit <NUM> through the switching unit <NUM>, and the C-band signal <NUM> transmitted in the wavelength selection unit <NUM> is input to the multiplexing unit <NUM>. Although not illustrated in <FIG>, the WDM signal <NUM> may include dummy signals at wavelength bands related to a band signal <NUM> and the L-band signal <NUM>. A WDM signal <NUM> output from the optical add/drop unit <NUM> may include not only a band signal <NUM> but also the band signal <NUM> and the L-band signal <NUM>, or may include dummy signals at wavelength bands related to the band signal <NUM> and the L-band signal <NUM>. When the optical add/drop unit <NUM> does not support add/drop of a wavelength band in the L-band, the wavelength selection unit <NUM> may be provided on a signal path input from the branching unit <NUM> to the optical add/drop unit <NUM> through the switching unit <NUM>, and a wavelength band of the L-band signal <NUM> may be blocked. With the above configuration, a wavelength band being an add/drop target of the optical add/drop unit <NUM> becomes the C-band signals <NUM> and <NUM>. Further, an optical signal having an L-band wavelength band is not transmitted over the transmission line between the terminal station <NUM> and the submarine branching device 9A.

The band signal <NUM> in the WDM signal input to the wavelength selection unit <NUM> is selectively transmitted and is input to the multiplexing unit.

The multiplexing unit <NUM> multiplexes the optical signals input from two directions and outputs a WDM signal <NUM> to the terminal station <NUM>.

Next, signal paths after switching by the switching units <NUM> and <NUM> will be described. The switching units <NUM> and <NUM> switch the signal paths in <FIG>. By the failure detection unit <NUM> issuing an instruction to switch the signal paths in response to detection of a failure, the switching units <NUM> and <NUM> execute switching of the signal paths. By switching of the signal paths, the WDM signal output by the branching unit <NUM> is input to the multiplexing unit <NUM> through the wavelength selection unit <NUM> without being input to the optical add/drop unit <NUM>.

On the other hand, the L-band signal <NUM> in the WDM signal branched and output by the branching unit <NUM> is input to the multiplexing unit <NUM> through the wavelength selection unit <NUM> regardless of the switching of the signal paths by the switching units <NUM> and <NUM>.

An operation of the failure detection unit <NUM> instructing the switching units <NUM> and <NUM> to switch the signal paths, in response to occurrence of a failure, is similar to the sequence diagram illustrated in <FIG>, and therefore detailed description thereof is omitted.

In general, when a signal path is switched by an optical switch, the signal is interrupted for a very short period of time before the switching is completed. It is assumed in a submarine cable system that signal quality is affected even by signal interruption for a very short period of time. In the submarine branching device 9A, a signal path of the L-band signal <NUM> transmitted between the terminal station <NUM> and the terminal station <NUM> is not changed before and after the switching units <NUM> and <NUM> switch signal paths. Accordingly, the submarine branching device 9A can keep signal quality unaffected by not interrupting traffic transmitted between the terminal station <NUM> and the terminal station <NUM> while executing switching of signal paths at occurrence of a failure in traffic transmitted to/from the terminal station <NUM>.

The configuration of the present example embodiment may be changed as appropriate within the scope thereof. For example, a demultiplexing unit demultiplexing an input WDM signal and outputting specific wavelengths may be provided in place of the branching unit <NUM> in <FIG> and <FIG>. <FIG> and <FIG> illustrate a configuration in which a demultiplexing unit <NUM> is provided in place of the branching unit <NUM>. <FIG> and <FIG> further illustrate signal paths before and after switching by the switching units <NUM> and <NUM>.

A WDM signal input from the terminal station <NUM> is demultiplexed into the C-band signal <NUM> and the L-band signal <NUM>, and the signals are input to the switching unit <NUM> and the multiplexing unit <NUM>, respectively. As illustrated in <FIG> and <FIG>, a signal path of the L-band signal <NUM> is not changed by switching by the switching units <NUM> and <NUM>. Accordingly, occurrence of traffic interruption can be prevented similarly to the configuration illustrated in <FIG> and <FIG>.

While the C-band and the L-band have been described as an example of a plurality of wavelength bands similarly to the aforementioned example embodiments, a plurality of wavelength bands applied to the present example embodiment are not limited thereto. For example, both of the band signals <NUM> and <NUM> may be WDM signals having wavelengths in the C-band or the L-band.

An eleventh example embodiment of the present invention will be described. A submarine branching device according to the eleventh example embodiment of the present invention comprises a configuration to be capable of controlling a configuration in the submarine branching device in response to a control signal input from a terminal station.

<FIG> illustrates a configuration example of an optical submarine cable system <NUM> according to the eleventh example embodiment. The optical submarine cable system <NUM> includes a terminal station 1A and a submarine branching device 5A. The optical submarine cable system <NUM> may include a plurality of other terminal stations, similarly to the configuration illustrated in <FIG>.

The terminal station 1A includes a transmission device <NUM>, a control device <NUM>, and a multiplexing unit <NUM>.

The transmission device <NUM> generates a main signal <NUM> transmitted to a facing terminal station. The transmission device outputs the main signal <NUM> to the multiplexing unit <NUM>. For example, the transmission device <NUM> generates the main signal <NUM> with a light source and a modulator. The terminal station device may include a plurality of transmission devices equivalent to the transmission device <NUM>.

The control device <NUM> generates a control signal <NUM> targeting the submarine branching device <NUM>. The control device <NUM> outputs the control signal <NUM> to the multiplexing unit <NUM>. For example, the control device <NUM> may generate the control signal <NUM> by modulating light at a wavelength not included in the main signal <NUM>.

The multiplexing unit <NUM> generates a WDM signal <NUM> from the main signal <NUM> and the control signal <NUM>. The multiplexing unit <NUM> may include a modulator and modulate the main signal <NUM> in accordance with the control signal <NUM>. Further, the multiplexing unit <NUM> may modulate a specific wavelength band in accordance with the control signal <NUM> or may modulate the entire main signal <NUM>. When the multiplexing unit <NUM> modulates the entire main signal <NUM>, for example, the modulation may be performed with a sufficiently low-frequency component compared with the main signal.

The transmission device <NUM> may be configured to include the control device <NUM> and the multiplexing unit <NUM>.

The submarine branching device 5A includes a branching unit <NUM>, a reception unit <NUM>, a control unit <NUM>, and an optical component <NUM>. Although not illustrated, the submarine branching device <NUM> may include a configuration included in the submarine branching device according to another example embodiment.

The branching unit <NUM> branches the WDM signal <NUM> input from the terminal station <NUM> and outputs the branched signals to the reception unit <NUM> and the optical component <NUM>. For example, the branching unit <NUM> may be an optical coupler.

The reception unit <NUM> extracts the control signal <NUM> from the WDM signal <NUM>. The reception unit <NUM> outputs the control signal <NUM> to the control unit <NUM>. <FIG> illustrates a configuration example of the reception unit <NUM> according to the eleventh example embodiment. When the control signal <NUM> is generated by modulating light at a wavelength not included in the main signal <NUM> as described above, the reception unit <NUM> may include an optical filter <NUM> and a photoelectric conversion unit <NUM>, as illustrated in <FIG>. The optical filter <NUM> extracts a wavelength band of the control signal <NUM> from the WDM signal <NUM>. The photoelectric conversion unit <NUM> converts the extracted control signal <NUM> into an electric signal and outputs the converted signal to the control unit <NUM>. <FIG> illustrates another configuration example of the reception unit <NUM> according to the eleventh example embodiment. When the control signal <NUM> is generated by modulating the entire wavelength band of the main signal <NUM> as described above, the reception unit <NUM> may include a photoelectric conversion unit <NUM> and a low-pass filter (LPF) <NUM>, as illustrated in <FIG>. The photoelectric conversion unit <NUM> converts the WDM signal <NUM> into an electric signal. The LPF <NUM> extracts a low-frequency modulation component in the converted electric signal and outputs the control signal <NUM>.

In <FIG>, the control unit <NUM> executes control over the optical component <NUM> in accordance with the control signal <NUM> input from the reception unit <NUM>.

The WDM signal <NUM> is input to the optical component <NUM> from the branching unit <NUM>. The optical component <NUM> is an optical part controllable in accordance with an instruction from the control unit <NUM>. For example, as illustrated in <FIG>, optical components <NUM> being control targets of the control unit <NUM> may include a demultiplexing unit <NUM>, an optical add/drop unit <NUM>, and a multiplexing unit <NUM>. Without being limited to the above, the optical component <NUM> may have a configuration changeable by a control device, according to another example embodiment.

An operation example according to the present example embodiment will be described by use of <FIG>.

The transmission device <NUM> outputs the main signal <NUM> to the multiplexing unit <NUM> (S901).

The control device <NUM> outputs the control signal <NUM> to the multiplexing unit <NUM> (S902). An order in which S901 and S902 are executed is not limited. For example, S901 may be executed after S902 is executed, or S901 and S902 may be executed simultaneously.

The multiplexing unit <NUM> generates the WDM signal <NUM> from the main signal <NUM> input from the transmission device <NUM> and the control signal <NUM> input from the control device <NUM> (S903).

The branching unit <NUM> branches the WDM signal <NUM> input from the terminal station <NUM> and outputs the branched signals to the reception unit <NUM> and the optical component <NUM> (S904).

The reception unit <NUM> extracts the control signal <NUM> from the WDM signal <NUM> input from the branching unit <NUM> and outputs the extracted signal to the control unit <NUM> (S905).

The control unit <NUM> executes control over the optical component <NUM> in accordance with the control signal <NUM> input from the reception unit <NUM> (S906).

The submarine branching device according to the eleventh example embodiment of the present invention comprises a configuration to be capable of controlling a configuration in the submarine branching device in accordance with a control signal input from a terminal station. Consequently, an output destination of a WDM signal can be flexibly controlled on a per-wavelength basis. Accordingly, a submarine branching device capable of providing an optical transmission system using the C-band and the L-band can be provided.

Claim 1:
A submarine branching device (9A) comprising:
branching means (<NUM>) configured to branch a wavelength multiplexed optical signal (<NUM>) input from a first terminal station (<NUM>) and outputting a first branch signal and a second branch signal;
optical add/drop means (<NUM>) configured to output at least a first wavelength-multiplexed optical signal (<NUM>) included in the first branch signal to a second terminal station (<NUM>), and to multiplex at least a second wavelength-multiplexed optical signal included in the first branch signal and a wavelength-multiplexed optical signal (<NUM>) input from the second terminal station (<NUM>) and to output at least a third wavelength-multiplexed optical signal;
multiplexing means (<NUM>) comprising wavelength selection means (<NUM>,<NUM>) configured to multiplex a fourth wavelength-multiplexed optical signal included in the second branch signal and the third wavelength-multiplexed optical signal in normal operation or a fifth-multiplexed optical signal included in the first branch signal in case of failure and to output the multiplexed signal to a third terminal station (<NUM>);
first switching means (<NUM>) configured to output first branch light input from the branching means (<NUM>) to the optical add/drop means (<NUM>) or the second switching means
second switching means (<NUM>) configured to output a third wavelength-multiplexed optical signal input from the optical add/drop means (<NUM>) or the first switching means to the multiplexing means (<NUM>); and
failure detection means (<NUM>) configured to detect a failure of a transmission line between the second terminal station (<NUM>) and the submarine branching device (9A), wherein,
in response to detecting a failure by the failure detection means (<NUM>), the first switching means is configured to switch a signal path from the optical add/drop means (<NUM>) to the second switching means (<NUM>) and to output the first branch signal to the second switching means (<NUM>), and
the second switching means is configured to switch a signal path from the optical add/drop means to the first switching means and outputting the first branch signal to the multiplexing means (<NUM>).