Patent Description:
An optical submarine cable system includes a terminal station A, a terminal station B, and a terminal station C provided on the land. The terminal station A and the terminal station B provided to face each other are connected by an optical submarine cable. The terminal station A and the terminal station B are terminal stations terminating the optical submarine cable. The terminal station A and the terminal station B are referred to as trunk stations. A submarine optical branching device (BU) is inserted midway of the optical submarine cable between the terminal station A and the terminal station B. The submarine optical branching device (BU) is placed on the seabed. The terminal station C is referred to as a branch station.

In the optical submarine cable system, it is often the case that a configuration of connecting a submarine optical branching device (BU) and a reconfigurable optical add/drop multiplexer (ROADM) device is employed as a device for branching a part of a wavelength-multiplexed optical signal on a branch station side. Since the submarine optical branching device (BU) and the ROADM device cannot be integrally configured due to constraints on a size of a casing of submarine equipment, a configuration may be employed in which an ROADM device connected to the vicinity of a submarine optical branching device (BU) via a submarine cable is disposed. It is possible to dynamically change a path route of a network by the ROADM device. As an optical device for achieving the ROADM device, a wavelength selective switch (WSS) is known. A part of a wavelength multiplexed optical signal is dropped by the wavelength selective switch, and a new optical signal to be transmitted to an opposing station is added, as the ROADM device.

<CIT> relates to an optical network system including a branching device, and proposes control of switching a power supply path according to a control signal received from a terminal station device. <CIT> relates to a submarine cable system including a branching device, and proposes a submarine cable system capable of maximally continuing an existing function by utilizing a facility in which a fault has not occurred, even when a fault occurs in a submarine cable and the like.

<CIT> relates to an extended branch device and method of control, in which construction work is easy, and communication is not significantly affected by the construction work. The extended branch device is provided with a first branch unit provided with a first port coupled to a first terminal station, a second port coupled to a second terminal station, a third port, a fourth port, and a switch for coupling the first port with the second or third port and for coupling the second port with the fourth port. A first separation unit provided with a fifth port coupled to the third port, a sixth port coupled to the fourth port, and a seventh port coupled to a third terminal station is provided. The first separation unit outputs, from the sixth port, an optical signal having a first wavelength among the optical signals inputted from the fifth port, and outputs, from the seventh port, an optical signal having a second wavelength from among the optical signals inputted from the fifth port. The extended branch device is further provided with a second branch unit configured so as to be separable from the first branch unit.

<CIT> discloses a device and method for an OADM submarine system. A branching unit for an optical transmission system is described. The branching unit comprises a first and a second input port configured to be coupled to a first and a second incoming fiber, respectively; a first output port configured to be coupled to a first outgoing fiber; wherein the second incoming fiber is part of an optical cable comprising an electrical conductor; wherein the branching unit is configured to receive electrical power via the optical cable; and an optical by-pass switch configured to switch between a first mode, and a second mode; wherein in the first mode, the by-pass switch is configured to couple the second incoming fiber to the first outgoing fiber; and wherein in the second mode, the by-pass switch is configured to couple the first incoming fiber to the first outgoing fiber.

<CIT> relates to a feedline branching apparatus and feedline branching method. The feedline branching apparatus makes it possible for additional submarine cables to be installed easily. The feedline branching apparatus comprises a branching unit and an earth unit. First, second and third terminal stations are connected to the branching unit via first, second and third cables, respectively. When the first and second cables are normal, the branching unit connects a feedline of the first cable to a feedline of the second cable, thereby forming a feedline using a first current. If one of the first and second cables is faulty, the branching unit grounds the feedline of the one of the first and second cables, while connecting the feedline of the other cable to the earth unit. The earth unit grounds a feedline of the third cable, thereby forming a feedline using a second current. When the feedline of the other cable is connected to the earth unit from the branching unit, the earth unit grounds the feedline of the other cable, thereby forming a feedline using the first current.

<FIG> is a block diagram for describing a configuration of a branching device for use in the submarine cable system of the background art. The branching device for use in the submarine cable system of the background art includes a branching unit (BU) constituted of an optical switch circuit, and an ROADM unit provided with an ROADM function such as a WSS. The branching unit (BU) of the branching device includes a portion of an optical circuit configuration and a portion of an electric circuit configuration, and the ROADM unit of the branching device also includes a portion of the optical circuit configuration and a portion of the electric circuit configuration. For convenience of description, the portion of the optical circuit configuration and the portion of the electric circuit configuration in the branching unit (BU) of the branching device are respectively referred to as a branching unit <NUM>-<NUM> (BU <NUM>-<NUM>) and a branching unit <NUM>-<NUM> (BU <NUM>-<NUM>). For convenience of description, the portion of the optical circuit configuration and the portion of the electric circuit configuration in the ROADM unit of the branching device are respectively referred to as an ROADM unit <NUM>-<NUM> and an ROADM unit <NUM>-<NUM>.

The branching unit <NUM>-<NUM> (BU <NUM>-<NUM>) includes optical switches 102a to 102d (optical SWs 102a to 102d) inserted into an optical fiber connecting terminal stations, and configured to change a connection route between the terminal stations by a control signal. The branching unit <NUM>-<NUM> (BU <NUM>-<NUM>) includes an optical switch circuit <NUM> (optical SW circuit <NUM>) for detecting current in a power supply path between the ROADM unit <NUM>-<NUM> and the sea earth.

In a normal state of the branching device in <FIG>, the ROADM unit <NUM>-<NUM> is connected to the branch station side of the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>), and is operated by electric power supply from the branch station side of the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>). The optical switch circuit <NUM> (optical SW circuit <NUM>) is provided on the branch station side of the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>), and has a control function of the optical switches 102a to 102d (optical SWs 102a to 102d) of the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>), and a detection function of electric power supply in a power supply path of the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>).

Herein, when electric power from the branch station side is applied to the branching unit of the branching device in <FIG>, the optical switches 102a to 102d (optical SWs 102a to 102d) of the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>) become switchable by a command signal from a terminal station on the land.

At a time of a normal operation, as illustrated in <FIG>, the optical switches 102a to 102d (optical SWs 102a to 102d) within the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>) are connected to a contact point on the branch station side, and an optical signal on a trunk station side is added to or dropped from the branch station side.

A case where a ground fault has occurred in the branching device in <FIG> is described with reference to <FIG> illustrates a case where a ground fault has occurred in a power supply path on the branch station side of the branching device in <FIG>. In particular, <FIG> illustrates a case where a ground fault has occurred in a power supply path between a branch station and an ROADM unit of the branching device, in the branching device in <FIG>. Herein, it is assumed that a ground fault has occurred in a power supply path between the branch station and the ROADM unit of the branching device, but an optical fiber is not disconnected.

In a case where a ground fault has occurred in a power supply path between the branch station and the ROADM unit <NUM>-<NUM> of the branching device, electric power from the branch station does not reach the ROADM unit <NUM>-<NUM>, and the branching device becomes a state that electric power to the ROADM unit <NUM>-<NUM> is not applied. Consequently, the branching device becomes a state in which electric power to the branch station side of the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>) is also not applied.

In this state, the ROADM unit <NUM>-<NUM> becomes inoperable due to no supply of electric power, and it is presumed that all the trunk stations and the branch station are disconnected in a state that the optical switches 102a to 102d (optical SWs 102a to 102d) of the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>) are switched to the branch station side. However, herein, the optical switch circuit <NUM> (optical SW circuit <NUM>) provided on the branch station side of the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>) detects that there is no electric power supply from the branch station, and a connection state of the optical switches 102a to 102d (optical SWs 102a to 102d) of the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>) is initialized. By the initialization of the connection state of the optical switches 102a to 102d (optical SWs 102a to 102d), as illustrated in <FIG>, the optical switches 102a to 102d (optical SWs 102a to 102d) are switched to the trunk station side. In this way, it is possible to configure the branching device in such a way that an optical signal of a trunk station does not undergo line disconnection, even when a ground fault occurs on the branch station side of the branching device.

Next, occurrence of another ground fault is described in association with the problem to be solved by the present invention.

<FIG> illustrates a case where a ground fault has occurred in a power supply path on the branch station side of the branching device in <FIG>. Herein, unlike <FIG>, <FIG> illustrates a case where a ground fault has occurred in a power supply path between the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>) and the ROADM unit <NUM>-<NUM>. When a ground fault has occurred in a power supply path between the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>) and the ROADM unit <NUM>-<NUM> as in this case, electric power supply from the branch station to the ROADM unit <NUM>-<NUM> is maintained, and electric power from the branch station is applied to the ROADM unit <NUM>-<NUM>. Therefore, the ROADM unit <NUM>-<NUM> is operable, and a branch line of the branch station is not disconnected.

However, the optical switch circuit <NUM> (optical SW circuit <NUM>) provided on the branch station side of the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>) detects that there is no electric power supply from the branch station, and initializes a connection state of the optical switches 102a to 102d (optical SWs 102a to 102d) of the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>). In this way, the optical switch circuit <NUM> (optical SW circuit <NUM>) detects that there is no electric power supply from the branch station, and, as illustrated in <FIG>, the optical switch circuit <NUM> (optical SW circuit <NUM>) automatically switches to the trunk station side.

The optical switch circuit <NUM> (optical SW circuit <NUM>) is provided on the branch station side of the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>), and thus detects that there is no electric power supply from the branch station side. Therefore, until power supply on the branch station side of the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>) is recovered, it is not possible to switch to the branch station side by controlling the optical switch circuit <NUM> (optical SW circuit <NUM>). Therefore, in a case where a ground fault has occurred in a power supply path between the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>) and the ROADM unit <NUM>-<NUM>, as illustrated in <FIG>, there is a problem that it is not possible to save a branch line until power supply on the branch station side of the branching unit <NUM>-<NUM> (BU <NUM>-<NUM>) is recovered.

There is a voltage difference equal to or more than several kilo voltages between a power supply path of a trunk station, and a power supply path of a branch station in a branching device (BU), and it is technically difficult to provide, in a power supply path on the trunk station side, a detection circuit for branch power supply as exemplified by the optical switch circuit <NUM> (optical SW circuit <NUM>) in <FIG>.

We have therefore appreciated that it would be desirable to provide a branching device, and a submarine cable system that are capable of saving a branch line when a ground fault occurs in a power supply path on a branch station side.

A branching device according to the present invention is a branching device inserted into a transmission path and a power supply path connecting a first trunk station and a second trunk station, the branching device including: a branching unit that is connected to a branch station by a transmission path and a power supply path, and switches a route by controlling a switch inserted into the transmission path and the power supply path; and a reconfigurable optical add/drop multiplexer (ROADM) device that is inserted into a transmission path and a power supply path connecting the branch station and the branching unit, and supplies, to the branching unit, a control signal for controlling the switch of the branching unit.

The branching device further includes a current detection means for detecting that there is no current flowing through a power supply path between the branch station and the branching unit, a first optical signal detection means for detecting an optical signal in a transmission path connecting the branch station and the branching unit, second optical signal detection means for detecting an optical signal in the transmission path connecting the first trunk station and the second trunk station, and a switching means for controlling the switch in such a way as to connect a transmission path between either of the first trunk station and the second trunk station, and the branch station, according to the detection results obtained by the second optical signal detection means, when the current detection means detects that there is no current flowing through a power supply path between the branch station and the branching unit, and the first optical signal detection means detects an optical signal in a transmission path connecting the branch station and the branching unit.

A submarine cable system according to the present invention includes: the first trunk station and the second trunk station installed on the land; a submarine cable connecting the first trunk station and the second trunk station; the above-described branching device inserted midway of the submarine cable; and a branch station connected to the branching device, and installed on the land.

A control method of a branching device according to the present invention is a control method of a branching device inserted into a transmission path and a power supply path connecting a plurality of trunk stations and a branch station, the plurality of trunk stations including a first trunk station and a second trunk station, the control method including: detecting that there is no current flowing through a power supply path between the branch station and the branching device; detecting an optical signal in a transmission path connecting the branch station and the branching device; and, when current flowing through a power supply path between the branch station and the branching device is detected, and an optical signal in a transmission path connecting the branch station and the branching device is detected, switching an optical switch on a route of a transmission path in such a way as to connect a transmission path between one of the plurality of trunk stations and the branch station, according to the detection results obtained by the detecting of the optical signal in the transmission path connecting the first trunk station and the second trunk station.

The present invention is able to provide a branching device, and a submarine cable system that are capable of saving a branch line when a ground fault occurs in a power supply path on a branch station side.

Preferred example embodiments according to the present invention are described in detail with reference to the drawings. In a branching device and a submarine cable system according to the preferred example embodiments of the present invention, it becomes possible to detect both of power supply from a branch station, and an optical signal from the branch station, and switch an optical switch of the branching device to an appropriate state according to a condition. It also becomes possible to achieve a branching device and a submarine cable system capable of controlling an optical switch solely by power supply from a branch station, or solely by power supply from a trunk station.

A branching device and a submarine cable system according to a first example embodiment of the present invention are described. <FIG> is a configuration diagram for describing a submarine cable system according to the first example embodiment of the present invention. The submarine cable system in <FIG> includes a terminal station A (50A) as one example of a first trunk station installed on the land, a terminal station B (50B) as one example of a second trunk station, and a submarine cable connecting the terminal station A (50A) and the terminal station B (50B). The submarine cable system in <FIG> further includes a branching device inserted midway of the submarine cable, and a terminal station C (50C) as one example of a branch station connected to the branching device, and installed on the land. The submarine cable includes transmission paths <NUM> to <NUM> constituted of an optical fiber, and power supply paths <NUM> to <NUM>. The power supply path <NUM> is provided along the transmission path <NUM>, the power supply path <NUM> is provided along the transmission path <NUM>, and the power supply path <NUM> is provided along the transmission path <NUM>.

The branching device of the submarine cable system in <FIG> includes a branching unit <NUM> (BU <NUM>) as a device for splitting a part of a wavelength-multiplexed optical signal on the terminal station C (50C) side, and a reconfigurable optical add/drop multiplexer (ROADM) unit <NUM>. The branching unit <NUM> (BU <NUM>) is a branching unit connected to the terminal station C (50C) as a branch station by the transmission path <NUM> and the power supply path <NUM>. The branching unit <NUM> (BU <NUM>) is constituted of an optical switch circuit, and switches a route by controlling a switch inserted into a transmission path and a power supply path reaching the terminal station A or the terminal station B. The ROADM unit <NUM> has an ROADM function such as a WSS. The ROADM unit <NUM> is inserted into the transmission path <NUM> and the power supply path <NUM> connecting the terminal station C (50C) as a branch station, and the branching unit <NUM> (BU <NUM>), and supplies, to the branching unit <NUM> (BU <NUM>), a control signal for controlling a switch of the branching unit <NUM> (BU <NUM>).

<FIG> is a configuration diagram for describing the branching device according to the first example embodiment of the present invention. In particular, the branching device in <FIG> is provided in the branching unit <NUM> (BU <NUM>) in <FIG>. The branching device in <FIG> includes a current detection means <NUM>, an optical signal detection means <NUM><NUM>, an optical signal detection means <NUM><NUM>, and a switching means <NUM>.

The current detection means <NUM> monitors current flowing through the power supply path <NUM> between the terminal station C (50C) as a branch station, and the branching unit <NUM> (BU <NUM>), and detects that there is no current flowing through the power supply path <NUM>. The current detection means <NUM> detects that there is no current flowing through the power supply path <NUM> by particularly monitoring current in a power supply path between the ROADM unit <NUM> and the sea earth among the power supply path <NUM> between the terminal station C (50C) and the branching unit <NUM> (BU <NUM>). The optical signal detection means <NUM><NUM> detects an optical signal in the transmission path <NUM> connecting the terminal station C (50C) as a branch station, and the branching unit <NUM> (BU <NUM>). The optical signal detection means <NUM><NUM> detects an optical signal in the transmission path <NUM> or the transmission path <NUM> connecting the terminal station A (50A) as one example of a first trunk station, and the terminal station B (50B) as one example of a second trunk station.

When the current detection means <NUM> detects that there is no current flowing through the power supply path <NUM> between the terminal station C (50C) and the branching unit <NUM> (BU <NUM>), and the optical signal detection means <NUM><NUM> detects an optical signal in the transmission path <NUM> connecting the terminal station C (50C) and the branching unit <NUM> (BU <NUM>), the switching means <NUM> controls a switch of the branching unit <NUM> (BU <NUM>) in such a way as to connect a transmission path between either of the terminal station A (50A) and the terminal station B (50B), and the terminal station C (50C). In particular, the switching means <NUM> performs control of a switch of the branching unit <NUM> (BU <NUM>), which connects a transmission path between either of the terminal station A (50A) and the terminal station B (50B), and the terminal station C (50C), when the optical signal detection means <NUM><NUM> detects an optical signal in the transmission path <NUM> or the transmission path <NUM> connecting the terminal station A (50A) and the terminal station B (50B).

Next, an operation of the branching device, and the submarine cable system according to the first example embodiment is described. For example, it is assumed that the branching device is in a normal state, as illustrated in <FIG> that is referred to in the description of the background art. In this normal state, when electric power from the terminal station C (50C) as a branch station is applied to the branching unit <NUM> (BU <NUM>) of the branching device in <FIG>, the branching unit <NUM> (BU <NUM>) becomes switchable by a command signal from a terminal station on the land. At a time of a normal operation, an optical signal on the trunk station side is added to or dropped from the branch station side by being connected to the branch station side within the branching unit <NUM> (BU <NUM>).

The branching device according to the present example embodiment detects that there is no current flowing through the power supply path <NUM> by monitoring current flowing through the power supply path <NUM> between the terminal station C (50C) as a branch station, and the branching unit <NUM> (BU <NUM>). The current detection means <NUM> detects that there is no current flowing through the power supply path <NUM> by particularly monitoring current in a power supply path between the ROADM unit <NUM> and the sea earth among the power supply path <NUM> between the terminal station C (50C) and the branching unit <NUM> (BU <NUM>). The optical signal detection means <NUM><NUM> detects an optical signal in the transmission path <NUM> connecting the terminal station C (50C) as a branch station, and the branching unit <NUM> (BU <NUM>). The optical signal detection means <NUM><NUM> detects an optical signal in the transmission path <NUM> or the transmission path <NUM> connecting the terminal station A (50A) as one example of a first trunk station, and the terminal station B (50B) as one example of a second trunk station. The switching means <NUM> controls a switch of the branching unit <NUM> (BU <NUM>) in such a way as to connect a transmission path between either of the terminal station A (50A) and the terminal station B (50B), and the terminal station C (50C), when the current detection means <NUM> detects that there is no current flowing through the power supply path <NUM> between the terminal station C (50C) and the branching unit <NUM> (BU <NUM>), and the optical signal detection means <NUM><NUM> detects an optical signal in the transmission path <NUM> connecting the terminal station C (50C) and the branching unit <NUM> (BU51).

For example, when a ground fault has occurred in a power supply path between the ROADM unit <NUM> and the sea earth, the current detection means <NUM> detects that there is no current flowing through the power supply path <NUM>. The optical signal detection means <NUM><NUM> detects an optical signal in the transmission path <NUM> connecting the terminal station C (50C) as a branch station, and the branching unit <NUM> (BU <NUM>).

Then, the switching means <NUM> controls a switch of the branching unit <NUM> (BU <NUM>) in such a way as to connect a transmission path between either of the terminal station A (50A) and the terminal station B (50B), and the terminal station C (50C), when the current detection means <NUM> detects that there is no current flowing through the power supply path <NUM> between the terminal station C (50C) and the branching unit <NUM> (BU <NUM>), and the optical signal detection means <NUM><NUM> detects an optical signal in the transmission path <NUM> connecting the terminal station C (50C) and the branching unit <NUM> (BU <NUM>). Thus, even when a ground fault occurs in a power supply path between the ROADM unit <NUM> and the sea earth, the branching device can save a branch line. Thus, it is possible to save a branch line without waiting for recovery of power supply on the branch station side of the branching device.

In the branching device according to the present example embodiment, even when a ground fault occurs in a power supply path between the terminal station C (50C) as a branch station, and the ROADM unit <NUM>, which is described with reference to <FIG> in the background art, the current detection means <NUM> detects that there is no current flowing through the power supply path <NUM>. However, in this case, since electric power is not supplied to the ROADM unit <NUM>, an optical signal is not detected in the transmission path <NUM> connecting the terminal station C (50C) and the branching unit <NUM> (BU <NUM>). Therefore, similarly to the case described in the background art in <FIG>, a switch of the branching device is initialized, and the switch is switched to the trunk station side. In this way, it is possible to configure the branching device in such a way that an optical signal of a trunk station does not undergo line disconnection even when a ground fault occurs on the branch station side of the branching device.

Next, a branching device and a submarine cable system according to a second example embodiment of the present invention are described. The branching device and the submarine cable system according to the second example embodiment have a configuration in which the branching device according to the first example embodiment is further specified. Same reference numerals are appended to elements similar to those in the first example embodiment, and detailed description thereof is omitted. <FIG> is a configuration diagram for describing a configuration of a submarine cable system according to the present example embodiment. <FIG> is a configuration diagram for describing a switch switching operation of the submarine cable system in <FIG>. <FIG> is a configuration diagram for describing a configuration of an optical switch in the branching device according to the present example embodiment.

As illustrated in <FIG>, the branching device according to the second example embodiment includes an optical switch circuit <NUM> (optical SW circuit <NUM>) as one example of a current detection means for detecting that there is no current flowing through a power supply path between a terminal station C as a branch station, and a branching unit <NUM>. The branching device according to the second example embodiment further includes a first optical switch circuit <NUM><NUM> (first optical SW circuit <NUM><NUM>) as one example of a first optical signal detection means for detecting an optical signal in a transmission path between the terminal station C as a branch station, and the branching unit <NUM>. In the branching device according to the present example embodiment, the current detection means and the first optical signal detection means are integrated, and the optical switch circuit <NUM> (optical SW circuit <NUM>) is incorporated within the first optical switch circuit <NUM><NUM> (first optical SW circuit <NUM><NUM>). The branching device according to the second example embodiment further includes a second optical switch circuit <NUM><NUM> (second optical SW circuit <NUM><NUM>) as one example of a second optical signal detection means for detecting an optical signal in a transmission path <NUM> or a transmission path <NUM> connecting a terminal station A (50A) as one example of a first trunk station, and a terminal station B (50B) as one example of a second trunk station. A control command signal of an optical switch to be transmitted from a terminal station device in a land station building is divided by an optical coupler <NUM> in <FIG>, and the divided signals are respectively transmitted to the first optical SW circuit <NUM><NUM> and the second optical SW circuit <NUM><NUM>.

<FIG> illustrates a state in which a repeater 53A is inserted into a transmission path between the unillustrated terminal station A and the branching unit <NUM>, a repeater 53B is inserted into a transmission path between the unillustrated terminal station B and the branching unit <NUM>, and a repeater 53C is inserted into a transmission path between the unillustrated terminal station C and the branching unit <NUM>. The repeater 53A, the repeater 53B, and the repeater 53C are operated by electric power supply from a power supply path provided along a transmission path, and amplify an optical signal in the transmission path.

An optical switch <NUM>-<NUM> (optical SW <NUM>-<NUM>), an optical switch <NUM>-<NUM> (optical SW <NUM>-<NUM>), an optical switch <NUM>-<NUM> (optical SW <NUM>-<NUM>), and an optical switch <NUM>-<NUM> (optical SW <NUM>-<NUM>) in <FIG> are each a <NUM>×<NUM> type optical switch that switches to a trunk station side or a branch station side, and controlled by the first optical SW circuit <NUM><NUM>.

An optical switch <NUM>-<NUM> (optical SW <NUM>-<NUM>), an optical switch <NUM>-<NUM> (optical SW <NUM>-<NUM>), an optical switch <NUM>-<NUM> (optical SW <NUM>-<NUM>), and an optical switch <NUM>-<NUM> (optical SW <NUM>-<NUM>) in <FIG> are each a <NUM>×<NUM> type optical switch that switches to the trunk station side or the branch station side, and controlled by the second optical SW circuit <NUM><NUM>.

As illustrated in a lower left portion of <FIG>, a <NUM>×<NUM> type optical switch is switched between an ON-state and an OFF-state, and a <NUM>×<NUM> type optical switch is switched between an ON-state and an OFF-state. In an operation of an optical SW illustrated in the lower left portion of <FIG>, when a <NUM>×<NUM> type optical switch and a <NUM>×<NUM> type optical switch are in an ON-state, a transmission path between one trunk station and a branch station is set to a connected state, and when the <NUM>×<NUM> type optical switch and the <NUM>×<NUM> type optical switch are in an OFF-state, a transmission path between one trunk station and another trunk station is set to a connected state.

When there is no power supply from the branch station side, the optical SW circuit <NUM> of the first optical SW circuit <NUM><NUM> detects such state, and automatically sets the optical SW <NUM>-<NUM>, the optical SW <NUM>-<NUM>, the optical SW <NUM>-<NUM>, and the optical SW <NUM>-<NUM> to an OFF-state.

The first optical SW circuit <NUM><NUM> controls the optical SW <NUM>-<NUM>, the optical SW <NUM>-<NUM>, the optical SW <NUM>-<NUM>, and the optical SW <NUM>-<NUM>. As a control method of the first optical SW circuit <NUM><NUM>, there are two methods, namely, a method of setting the optical SWs <NUM>-<NUM> to <NUM>-<NUM> to an ON-state or an OFF-state by a control command signal from a land station, and a method of detecting current disconnection on the branch station side by the optical SW circuit <NUM> of the first optical SW circuit <NUM><NUM>, and automatically setting the optical SWs <NUM>-<NUM> to <NUM>-<NUM> to an OFF-state. The first optical SW circuit <NUM><NUM> is operated by power supply from the branch station side of the branching device.

The second optical SW circuit <NUM><NUM> controls the optical SW <NUM>-<NUM>, the optical SW <NUM>-<NUM>, the optical SW <NUM>-<NUM>, and the optical SW <NUM>-<NUM>. As a control method of the second optical SW circuit <NUM><NUM>, there are two methods, namely, a method of setting the optical SWs <NUM>-<NUM> to <NUM>-<NUM> to an ON-state or an OFF-state by a control command signal from a land station, and a method of detecting an optical signal on the trunk station side and an optical signal on the branch station side, and automatically setting the optical SWs <NUM>-<NUM> to <NUM>-<NUM> to an ON-state or an OFF-state. The second optical SW circuit <NUM><NUM> is operated by power supply from the trunk station side of the branching device.

Next, an operation of the branching device according to the present example embodiment is described. An upper portion of <FIG> illustrates a configuration of a transmission path of an optical signal directing from the terminal station A to the terminal station B, and a lower right portion of <FIG> illustrates a configuration of a transmission path of an optical signal directing from the terminal station B to the terminal station A. For convenience, a direction directing from the terminal station A to the terminal station B in <FIG> may be referred to as "downstream", and a direction directing from the terminal station B to the terminal station A may be referred to as "upstream". A configuration of a downstream transmission path in <FIG>, and a configuration of an upstream transmission path in <FIG> are substantially the same.

Control and an operation of the downstream transmission path in <FIG> are described. In the downstream transmission path in <FIG>, the optical SW <NUM>-<NUM> and the optical SW <NUM>-<NUM> are controlled by the first optical SW circuit <NUM><NUM> in <FIG>, and the optical SW <NUM>-<NUM> and the optical SW <NUM>-<NUM> are controlled by the second optical SW circuit <NUM><NUM> in <FIG>. When there is an optical signal from the branch station side, the first optical SW circuit <NUM><NUM> detects the optical signal. When there is an optical signal from the trunk station side, the second optical SW circuit <NUM><NUM> detects the optical signal.

Control and an operation of the upstream transmission path in <FIG> are described. In the upstream transmission path in <FIG>, the optical SW <NUM>-<NUM> and the optical SW <NUM>-<NUM> are controlled by the first optical SW circuit <NUM><NUM> in <FIG>, and the optical SW <NUM>-<NUM> and the optical SW <NUM>-<NUM> are controlled by the second optical SW circuit <NUM><NUM> in <FIG>. When there is an optical signal from the branch station side, the first optical SW circuit <NUM><NUM> detects the optical signal. When there is an optical signal from the trunk station side, the second optical SW circuit <NUM><NUM> detects the optical signal.

<FIG> is a configuration diagram for describing a switch switching operation of the submarine cable system in <FIG>. In particular, <FIG> illustrates a block diagram of a power supply circuit of the branching unit <NUM> (BU <NUM>). The first optical SW circuit <NUM><NUM> is operated by power supply from the branch station side. It is possible to set the optical SW <NUM>-<NUM> and the optical SW <NUM>-<NUM> in the downstream transmission path of <FIG> to an ON-state or an OFF-state, and set the optical SW <NUM>-<NUM> and the optical SW <NUM>-<NUM> in the upstream transmission path of <FIG> to an ON-state or an OFF-state by a command control signal from a terminal station device in a land station building, for example, the land station A in <FIG>. Herein, when there is no power supply from the branch station side, a function of the first optical SW circuit <NUM><NUM> of detecting branch power supply current is activated, and the control is switched to the trunk station side by automatically setting the optical SWs <NUM>-<NUM> to <NUM>-<NUM> to an OFF-state.

By power supply from the trunk station side, the second optical SW circuit <NUM><NUM> is operated, and it is possible to set the optical SW <NUM>-<NUM> and the optical SW <NUM>-<NUM> in the downstream transmission path of <FIG> to an ON-state or an OFF-state, and set the optical SW <NUM>-<NUM> and the optical SW <NUM>-<NUM> in the upstream transmission path of <FIG> to an ON-state or an OFF-state by a command control signal from a terminal station device in a land station building, for example, the land station A in <FIG>. Herein, when there is no power supply from the branch station side, a function of the first optical SW circuit <NUM><NUM> of detecting branch power supply current is activated, and the control is switched to the trunk station side by automatically setting the optical SWs <NUM>-<NUM> to <NUM>-<NUM> to an OFF-state.

An optical signal detection unit <NUM> has a function of detecting an optical signal input from a branch station, and particularly detects an optical signal in a transmission path directing from the terminal station C as a branch station to the terminal station A as a first trunk station. An optical signal detection unit <NUM> has a function of detecting an optical signal input from a branch station, and particularly detects an optical signal in a transmission path directing from the terminal station C as a branch station to the terminal station B as a second trunk station.

An optical signal detection unit <NUM> has a function of detecting an optical signal input from a trunk station, and particularly detects an optical signal in a transmission path directing from the terminal station A as a first trunk station to the terminal station B as a second trunk station. An optical signal detection unit <NUM> has a function of detecting an optical signal input from a trunk station, and particularly detects an optical signal in a transmission path directing from the terminal station B as a second trunk station to the terminal station A as a first trunk station.

Detection results of the optical signal detection unit <NUM>, the optical signal detection unit <NUM>, the optical signal detection unit <NUM>, and the optical signal detection unit <NUM> are sent to the second optical SW circuit <NUM><NUM>, and the optical SW <NUM>-<NUM>, the optical SW <NUM>-<NUM>, the optical SW <NUM>-<NUM>, and the optical SW <NUM>-<NUM> are controlled to an ON-state or an OFF-state. Herein, it is preferable to send, to the second optical SW circuit <NUM><NUM> via an optical fiber by way of an optical signal, detection results of the optical signal detection unit <NUM>, the optical signal detection unit <NUM>, the optical signal detection unit <NUM>, and the optical signal detection unit <NUM>, taking into consideration a withstand voltage difference between a branch station and a trunk station.

As an example of control of the downstream transmission path in <FIG>, when both of the optical signal detection unit <NUM> and the optical signal detection unit <NUM> detect that an optical signal is coming, the second optical SW circuit <NUM><NUM> is operated, and the control is switched to the branch station side by automatically setting the optical SW <NUM>-<NUM> and the optical SW <NUM>-<NUM> to an ON-state. When a signal is not detected by either or both of the optical signal detection unit <NUM> and the optical signal detection unit <NUM>, the optical SW <NUM>-<NUM> and the optical SW <NUM>-<NUM> are automatically set to an OFF-state. It is also possible to switch the optical SW <NUM>-<NUM> and the optical SW <NUM>-<NUM> to the ON side or the OFF-side by a command control signal from a terminal station device in a land station building.

As an example of control of the upstream transmission path in <FIG>, when both of the optical signal detection unit <NUM> and the optical signal detection unit <NUM> detect that an optical signal is coming, the second optical SW circuit <NUM><NUM> is operated, and the control is switched to the branch station side by automatically setting the optical SW <NUM>-<NUM> and the optical SW <NUM>-<NUM> to an ON-state. When a signal is not detected by either or both of the optical signal detection unit <NUM> and the optical signal detection unit <NUM>, the optical SW <NUM>-<NUM> and the optical SW <NUM>-<NUM> are automatically set to an OFF-state. It is also possible to switch the optical SW <NUM>-<NUM> and the optical SW <NUM>-<NUM> to the ON side or the OFF-side by a command control signal from a terminal station device in a land station building.

At a time of a normal operation of the branching device and the submarine cable system, electric power from the trunk station side, and electric power from the branch station side are applied to the branching unit <NUM> (BU <NUM>).

The first optical SW circuit <NUM><NUM> is operable by current supply from the branch station side. By a control command signal from the land station A, the first optical SW circuit <NUM><NUM> receives a command, and switches the optical SW <NUM>-<NUM>, the optical SW <NUM>-<NUM>, the optical SW <NUM>-<NUM>, and the optical SW <NUM>-<NUM> to an ON-state. Thus, it becomes possible to communicate an optical signal between a trunk station and a branch station.

When a ground fault has occurred in a power supply path between the terminal station C (50C) as a branch station, and the ROADM unit <NUM>, as described with reference to <FIG> of the background art, electric power from the branch station does not reach the branch station side of the branching unit <NUM> (BU <NUM>) and the ROADM unit <NUM>. Thus, the ROADM unit <NUM> becomes inoperable, and a branch line is disconnected. However, the optical SW circuit <NUM> detects that there is no power supply from the branch station, and the first optical SW circuit <NUM><NUM> automatically switches the optical SW <NUM>-<NUM>, the optical SW <NUM>-<NUM>, the optical SW <NUM>-<NUM>, and the optical SW <NUM>-<NUM> to an OFF-state. By this control, in a transmission path between trunk stations disconnection of a trunk line can be prevented without adding or dropping a signal to or from the branch station side.

When a ground fault has occurred in a power supply path between the branching unit <NUM> (BU <NUM>) of the branching device, and the ROADM unit <NUM>, as described with reference to <FIG> of the background art, although electric power from a branch station reaches the ROADM unit <NUM>, electric power from the branch station does not reach the branching unit <NUM> (BU <NUM>) of the branching device.

Also in this case, the optical SW circuit <NUM> in <FIG> detects that there is no power supply from the branch station, and the first optical SW circuit <NUM><NUM> automatically switches the optical SW <NUM>-<NUM>, the optical SW <NUM>-<NUM>, the optical SW <NUM>-<NUM>, and the optical SW <NUM>-<NUM> to an OFF-state. In this state, since electric power does not reach the branch station side, an optical switch of the branching unit <NUM> (BU <NUM>) cannot be controlled even when a control command signal from the land station A is transmitted to the first optical SW circuit <NUM><NUM>. However, in the example embodiments according to the present invention including the present example embodiment, recovery of a branch signal is enabled.

When a ground fault has occurred in a power supply path between the branching unit <NUM> (BU <NUM>) of the branching device, and the ROADM unit <NUM>, electric power from the branch station reaches the ROADM unit <NUM>, and the ROADM unit <NUM> is operated. Therefore, an optical signal from the branch station side is input to the branching unit <NUM> (BU <NUM>). An optical signal from the trunk station side is also input to the branching unit <NUM> (BU <NUM>).

In this case, the optical signal detection unit <NUM>, the optical signal detection unit <NUM>, the optical signal detection unit <NUM>, and the optical signal detection unit <NUM> detect an optical signal from a trunk station and a branch station. As illustrated in <FIG>, the optical signal detection unit <NUM>, the optical signal detection unit <NUM>, the optical signal detection unit <NUM>, and the optical signal detection unit <NUM> detect an optical signal on the branch station side and the trunk station side, and the optical signals are transmitted to the second optical SW circuit <NUM><NUM>. The optical signal detection unit <NUM>, the optical signal detection unit <NUM>, the optical signal detection unit <NUM>, and the optical signal detection unit <NUM> convert the optical signal into an electrical signal by, for example, a photodiode or the like, thereby switching the optical switch.

When the optical signal detection unit <NUM> and the optical signal detection unit <NUM> detect an optical signal, the optical signal detection unit <NUM> and the optical signal detection unit <NUM> automatically switch the optical SW <NUM>-<NUM> and the optical SW <NUM>-<NUM> to an ON-state. When the optical signal detection unit <NUM> and the optical signal detection unit <NUM> detect an optical signal, the optical signal detection unit <NUM> and the optical signal detection unit <NUM> automatically switch the optical SW <NUM>-<NUM> and the optical SW <NUM>-<NUM> to an ON-state.

Thus, even when a ground fault occurs in a power supply path between the branching unit <NUM> (BU <NUM>) of the branching device, and the ROADM unit <NUM>, it is possible to detect both of power supply from a branch station, and an optical signal from the branch station, and switch an optical switch of the branching device to an appropriate state according to a condition. In this way, even when a ground fault occurs in a power supply path between the branching unit <NUM> (BU <NUM>) of the branching device, and the ROADM unit <NUM>, recovery of a branch signal is enabled.

In the branching device according to the present example embodiment, even when power is not supplied from a branch station, it is possible to operate the second optical SW circuit <NUM><NUM> solely by power supply from a trunk station. By receiving a control command signal from a land station by the second optical SW circuit <NUM><NUM>, and turning off or on the optical SW <NUM>-<NUM>, the optical switch SW <NUM>-<NUM>, the optical switch SW <NUM>-<NUM>, and the optical SW <NUM>-<NUM>, switching is enabled between a communication state solely on the trunk station side, and a communication state in which a signal is added to or dropped from the branch station side.

In the configuration of the background art, when a ground fault has occurred between a branching unit (BU) of a branch, and an ROADM unit, it is difficult to recover a branch signal, regardless of an operation of the ROADM unit. In contrast, the configuration of the above-described example embodiment enables recovery of a branch line by detecting an optical signal from a branch, even when electric power from the branch station side is not applied to the branching unit (BU).

Further, it becomes possible to switch an optical switch of the branching unit (BU) to the trunk station side or the branch station side by a remote control command signal from a terminal station device in a land station building, regardless of whether electric power from the branch station side is present. Thus, it is possible to save a branch line without waiting for recovery of power supply on the branch station side of the branching device, and it is possible to switch between a communication state solely on the trunk station side, and a communication state in which a signal is added to or dropped from the branch station side.

In the foregoing, preferred example embodiments according to the present invention have been described. However, the present invention is not limited to these. Various modifications can be made within the scope of the invention defined by the claims, and it is needless to say that these are also included in the scope of the present invention.

While the invention has been particularly shown and described with reference to example embodiments thereof, the invention is not limited to these example embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the scope of the present invention as defined by the claims.

Claim 1:
A branching device for a transmission path (<NUM>, <NUM>) and a power supply path (<NUM>, <NUM>) connecting a first trunk station (50A) and a second trunk station (50B), the branching device comprising:
a branching unit (<NUM>) configured to be connected to a branch station (50C) by a transmission path (<NUM>) and a power supply path (<NUM>), the branching unit comprises a switch, configured to switch a route by controlling the switch to switch the transmission path (<NUM>) and the power supply path (<NUM>); and
a reconfigurable optical add/drop multiplexer, ROADM, device (<NUM>) configured to be connected to the transmission path (<NUM>) and the power supply path connecting the branch station (50C) and the branching unit (<NUM>), and which is further configured to supply, to the branching unit (<NUM>), a control signal for controlling the switch of the branching unit (<NUM>), wherein
the branching device further comprises
current detection means (<NUM>) for detecting that there is no current flowing through a power supply path between the branch station (50C) and the branching unit (<NUM>),
first optical signal detection means (<NUM><NUM>,, <NUM><NUM>) for detecting an optical signal in the transmission path (<NUM>) connecting the branch station (50C) and the branching unit (<NUM>),
second optical signal detection means (<NUM><NUM>, <NUM><NUM>) for detecting an optical signal in the transmission path connecting the first trunk station (50A) and the second trunk station (50B), and
switching means (<NUM>) for controlling the switch in such a way as to connect a transmission path between either of the first trunk station (50A) and the second trunk station (50B), and the branch station (50C), according to the detection results obtained by the second optical signal detection means (<NUM><NUM>, <NUM><NUM>), when the current detection means (<NUM>) detects that there is no current flowing through a power supply path between the branch station (50C) and the branching unit (<NUM>), and the first optical signal detection means (<NUM><NUM>,, <NUM><NUM>) detects an optical signal in a transmission path connecting the branch station (50C) and the branching unit.