Optical transmission apparatus and fault detection method

An optical transmission apparatus includes a non-reciprocal device including first to second ports, an optical signal input from the first port being provided to the second port, an optical signal input from the second port being provided to the first port, a dispersion compensator that is coupled to the first port of the non-reciprocal device and that conducts given processing to an optical signal input from the first port of the non-reciprocal device to provide the optical signal subjected to the given processing to the second port of the non-reciprocal device, a first monitor, a second monitor, and a fault determination device that compares a value monitored by the first monitor with a value monitored by the second monitor to determine one of a connection failure, at least at one of the first port, the second port, of the non-reciprocal device and a connection state of the dispersion compensator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2009-145678 filed on Jun. 18, 2009, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to an optical transmission apparatus transmitting an optical signal.

BACKGROUND

Wavelength Division Multiplexing (WDM) is currently in widespread use, in which multiple optical signals having different wavelengths are transmitted through one transmission line to increase the transmission capacity. In the WDM, the optical output power after the multiplexing of the optical signals is increased to a high level, for example, to about +20 dBm even if the optical output power per one wavelength is low, for example, is equal to a few dBm. Accordingly, it is necessary to take measures against the high optical output power.

For example, optical amplifier apparatuses used in optical communication systems include dispersion compensation devices that compensate dispersion characteristics occurring in the transmission lines. The optical amplifier apparatuses perform, for example, detection of connection failure in the dispersion compensation devices as the above measures.

FIG. 15illustrates an example of the configuration of an optical communication system in related art. Referring toFIG. 15, the optical communication system includes optical amplifier apparatuses10and20. The optical amplifier apparatus10is connected to the optical amplifier apparatus20via a transmission line1. An optical signal amplified by the optical amplifier apparatus10is provided to the optical amplifier apparatus20through the transmission line1. Since the optical amplifier apparatus10includes the same configuration as that of the optical amplifier apparatus20, the configuration of the optical amplifier apparatus20will now be described.

The optical amplifier apparatus20includes couplers (CPLs)21and22, a variable optical attenuator (VOA)23, photodiodes (PDs)24and25, a dispersion compensation device26, and an optical amplifier module27. Each of the CPLs21and22is a device that splits an optical signal.

The CPL21splits an optical signal provided from the optical amplifier apparatus10into signal components to provide one signal component to the PD24and provide the other signal component to the VOA23. The CPL22splits an optical signal provided from the VOA23into signal components to provide one signal component to the PD25and provide the other signal component to the dispersion compensation device26.

The VOA23is a device that attenuates an optical signal. The VOA23receives an optical signal from the CPL21, attenuates the received optical signal, and provides the attenuated optical signal to the CPL22.

The PD24is a device that receives an optical signal from the CPL21to convert the received optical signal into an electrical signal. The PD24provides the electrical signal to a monitor. The PD25is a device that receives an optical signal from the CPL22to convert the received optical signal into an electrical signal. The PD25provides the electrical signal to the monitor.

The dispersion compensation device26causes an appropriate delay for every wavelength in an optical signal that is received from the CPL22to compensate the dispersion existing in the optical signal. The dispersion compensation device26is connected to a To_DCF port and a From_DCF port.

The dispersion compensation device26receives an optical signal output from the CPL22through the To_DCF port to perform dispersion compensation to the received optical signal. The dispersion compensation device26provides the optical signal subjected to the dispersion compensation to the optical amplifier module27through the From_DCF port.

In order to simplify the optical communication system, to simplify the operation, and to decrease the number of menus in the dispersion compensation device, it is effective to use a dispersion compensation device including a directional device, such as a circulator as the dispersion compensation device26. The dispersion compensation device including a directional device is, for example, a variable dispersion compensation device.

The optical amplifier module27is a device that receives an optical signal from the dispersion compensation device26, amplifies the received optical signal, and outputs the amplified optical signal. The optical amplifier module27includes a PD. The optical amplifier module27converts the optical signal into an electrical signal with the PD and provides the resulting electrical signal to a monitor.

In detection of any fault in the dispersion compensation device26, the optical amplifier apparatus20detects the difference between the electrical signal output from the PD25and the electrical signal output from the PD in the optical amplifier module27. The optical amplifier apparatus20compares the detected difference with a given value to determine whether any connection failure occurs in the dispersion compensation device26.

For example, if the optical amplifier apparatus20detects a connection failure, the optical amplifier apparatus20forcedly shuts down the optical amplifier module27to prevent an abnormal optical signal from being output from the optical amplifier module27.

However, the above technology in the related art has a problem in that the optical amplifier apparatus cannot accurately detect a failure concerning the dispersion compensation device when the dispersion compensation device including a directional device is used.FIGS. 16 and 17illustrate problems in the related art.

A problem in the related art will now be described with reference toFIG. 16. The dispersion compensation device26inFIG. 16includes a circulator26aand a device26bperforming the dispersion compensation. An optical signal received through a port (1) of the dispersion compensation device26is provided to the device26bthrough the circulator26a. An optical signal output from the device26bis output from a port (2) through the circulator26a.

With the fault detection method in the related art, since “the value of the monitor for the PD25is normal” and “the value of the monitor for the optical amplifier module27is abnormal” in a case in which a failure occurs in the device26band a case in which a failure, such as port disconnection, occurs in the To_DCF port or the From_DCF port, it is not possible to discriminate the above two cases.

Another problem in the related art will now be described with reference toFIG. 17. In the dispersion compensation device26illustrated inFIG. 17, the To_DCF port and the From_DCF port are connected in a manner opposite to that in the connection inFIG. 16because of the circulator. In the connection inFIG. 17, an optical signal received through the port (2) is output from the port (1) not through the device26b.

When the To_DCF port and the From_DCF port are connected in the opposite manner, it should be determined that a failure occurs because the optical signal does not pass through the device26band expected dispersion characteristics are not received. However, since the amount of optical loss is small when the optical signal does not pass through the device26b, as in the case inFIG. 17, it is not possible to determine that the abnormal state occurs only from the value of the monitor for the PD25and the value of the monitor for the optical amplifier module27and, thus, the abnormal state cannot be detected.

SUMMARY

According to an aspect of the disclosed embodiments, an optical transmission apparatus includes a non-reciprocal device including first to second ports, an optical signal input from the first port being provided to the second port, an optical signal input from the second port being provided to the first port, a dispersion compensator that is coupled to the first port of the non-reciprocal device and that conducts given processing to an optical signal input from the first port of the non-reciprocal device to provide the optical signal subjected to the given processing to the second port of the non-reciprocal device, a first monitor configured to monitor an optical signal output from the first port, a second monitor configured to monitor an optical signal output from the second port, and a fault determination device that compares a value monitored by the first monitor with a value monitored by the second monitor to determine a connection failure at the first and/or second ports of the non-reciprocal device and/or a connection state of the dispersion compensator.

The object and advantages of the disclosed embodiments will be realized and attained by means of the elements and combinations particularly pointed out in the claims.

DESCRIPTION OF EMBODIMENTS

Embodiments of an optical transmission apparatus disclosed in the present invention will herein be described in detail with reference to the attached drawings. However, the present invention is not limited to the embodiments described below.

FIG. 1illustrates an example of the configuration of an optical communication system according to a first embodiment of the present invention. Referring toFIG. 1, the optical communication system includes an optical amplifier apparatus100aand an optical amplifier apparatus100b. The optical amplifier apparatus100ais connected to the optical amplifier apparatus100bvia a transmission line1. Since the optical amplifier apparatus100aincludes the same configuration as that of the optical amplifier apparatus100b, the configuration of the optical amplifier apparatus100bwill now be described.

The optical amplifier apparatus100bincludes couplers (CPLs)101to105, a variable optical attenuator (VOA)106, photodiodes (PDs)107to109, a dispersion compensation device110, an optical amplifier module111, and a fault determination device112.

The CPL101splits an optical signal provided from the optical amplifier apparatus100ainto signal components to provide one signal component to the PD107and provide the other signal component to the VOA106. The CPL102splits an optical signal provided from the VOA106into signal components to provide one signal component to the PD108and provide the other signal component to the CPL103.

The CPL103provides an optical signal from the CPL102to the CPL104. The CPL103provides an optical signal from the CPL104to the CPL105. The CPL104provides an optical signal from the CPL103to the dispersion compensation device110through a To_DCF port. The CPL104provides an optical signal provided from the dispersion compensation device110through the To_DCF port to the PD109.

The CPL105provides an optical signal provided from the dispersion compensation device110through a From_DCF port to the optical amplifier module111. The CPL105provides an optical signal from the CPL103to the dispersion compensation device110through the From_DCF port.

The VOA106is a device that attenuates an optical signal. The VOA106receives an optical signal from the CPL101, attenuates the received optical signal, and provides the attenuated optical signal to the CPL102. If a fault occurs in, for example, the dispersion compensation device110, the VOA106increases the amount of attenuation to prevent a high-power optical signal from being provided to the dispersion compensation device110.

The PD107is a device that receives an optical signal from the CPL101and converts the received optical signal into an electrical signal. The PD107provides the electrical signal to a monitor. The PD108is a device that receives an optical signal from the CPL102and converts the received optical signal into an electrical signal. The PD108provides the electrical signal to the monitor. The PD109is a device that receives an optical signal from the CPL104and converts the received optical signal into an electrical signal. The PD109provides the electrical signal to the fault determination device112.

The dispersion compensation device110causes an appropriate delay for every wavelength in an optical signal that is received from the CPL104to compensate the dispersion existing in the optical signal. The dispersion compensation device110includes a circulator110aand a device110bperforming the dispersion compensation.

The dispersion compensation device110is connected to the To_DCF port and the From_DCF port. A connection method in which a port (1) of the dispersion compensation device110is connected to the To_DCF port and a port (2) of the dispersion compensation device110is connected to the From_DCF port corresponds to normal connection.

An optical signal input from the port (1) of the dispersion compensation device110is input into the device110bthrough the circulator110a. The optical signal subjected to the dispersion compensation in the device110bis output from the port (2) through the circulator110a. In contrast, an optical signal input from the port (2) of the dispersion compensation device110is output from the port (1) not through the device110b.

The optical amplifier module111is a device that receives an optical signal from CPL105, amplifies the received optical signal, and outputs the amplified optical signal. The optical amplifier module111includes a PD113. The optical amplifier module111converts the optical signal into an electrical signal with the PD113and provides the resulting electrical signal to the fault determination device112.

The fault determination device112is a processor that determines any fault concerning the dispersion compensation device110. The fault determination device112includes a first given value and a second given value. The fault determination device112compares the value of the electrical signal received from the PD109with the first given value and compares the value of the electrical signal received from the PD113in the optical amplifier module111with the second given value to determine any fault on the basis of the result of the comparison.

The value of the electrical signal received from the PD109is hereinafter referred to as a first monitor value, and the value of the electrical signal received from the PD113in the optical amplifier module111is hereinafter referred to as a second monitor value. A first threshold value indicates a value that is set so as to reflect the loss of the optical signal transmitted through the port (2) and the port (1), not through the device110bin the dispersion compensation device110. A second threshold value indicates a value that is set so as to reflect the loss of the optical signal transmitted through the port (1), the device110bin the dispersion compensation device110, and the port (2).

If the first monitor value is higher than or equal to the first given value and the second monitor value is higher than or equal to the second threshold value, the fault determination device112determines that the dispersion compensation device110is in a normal state and provides the result of the determination to, for example, the monitor.

If the first monitor value is higher than or equal to the first threshold value (the first monitor value is normal) and the second monitor value is lower than the second threshold value (the second monitor value is abnormal), the fault determination device112determines that the device110bfails and provides the result of the determination to, for example, the monitor. If the first monitor value is higher than or equal to the first given value, no port connection failure occurs and the connection of the port is normal. If the second monitor value is lower than the second threshold value although no port connection failure occurs, the fault determination device112determines that any fault occurs in the device110band a loss is caused in the second monitor value.

If the first monitor value is lower than the first given value (the first monitor value is abnormal) and the second monitor value is lower than the second given value (the second monitor value is abnormal), the fault determination device112determines that a port connection failure occurs in the To_DCF port or the From_DCF port and provides the result of the determination to, for example, the monitor. When a port connection failure occurs, both of the path of the signal light provided from the CPL104to the dispersion compensation device110and the path of the signal light provided from the CPL105to the dispersion compensation device110are in a disconnection state. Accordingly, the first and second monitor values have a no input level.

A case will now be described in which the dispersion compensation device110according to the first embodiment is wrongly connected.FIG. 2illustrates the case in which the dispersion compensation device110according to the first embodiment is wrongly connected. In the dispersion compensation device110inFIG. 2, the To_DCF port is connected to the port (2) and the From_DCF port is connected to the port (1).

When the dispersion compensation device110is wrongly connected in the manner illustrated inFIG. 2, the optical signal from the To_DCF port, which is normally subjected to the dispersion compensation, is input into the dispersion compensation device110and is output from the dispersion compensation device110not through the device110b. Accordingly, the optical signal that is not subjected to the dispersion compensation is output and is provided to the optical amplifier module111. In this case, since no device loss is reflected in the optical signal input into the optical amplifier module111, the second monitor value is higher than or equal to the second given value.

In contrast, the optical signal from the From_DCF port, which is normally not subjected to the dispersion compensation, is input into the dispersion compensation device110and is output from the dispersion compensation device110through the device110b. In this case, since an unexpected device loss is reflected in the optical signal input into the PD109, the first monitor value is lower than the first given value.

Practically, if the first monitor value is lower than the first given value and the second monitor value is higher than or equal to the second given value, the fault determination device112determines that the dispersion compensation device is in the wrong connection state and provides the result of the determination to, for example, the monitor.

Upon detection of any of the failure of the device110b, the port connection failure, and the wrong connection, the fault determination device112causes the VOA106to increase the loss in the VOA106. Increasing the loss in the VOA106prevents the high-power optical signal from the To_DCF port from being provided to the dispersion compensation device110. The fault determination device112may set off an alarm to notify an abnormal state if the fault determination device112detects the abnormal state.

FIGS. 3A and 3Billustrate optical spectra in the normal state, in the state in which the device failure occurs, and in the state in which the port is wrongly connected at the To_DCF port and the From_DCF port in the first embodiment.FIG. 3Aillustrates a case in which the device110bhas flat loss characteristics.FIG. 3Billustrates a case in which the device110bhas periodic loss characteristics.

As illustrated inFIGS. 3A and 3B, the monitor value (the integral value of the signal light and the amplified spontaneous emission (ASE) light) at the PD109when the device110bhas the flat loss characteristics differs from the monitor value at the PD109when the device110bhas the periodic loss characteristics in the following manner. The periodic loss characteristics include, for example, comb-shaped loss characteristics. The optical amplifier apparatus100billustrated inFIG. 1can accurately detect any fault not only when the device having the flat loss characteristics is applied to the dispersion compensation device110but also when the device having the periodic loss characteristics is applied to the dispersion compensation device110.

In the normal state, since only the loss in the circulator110ais reflected in the signal light and the ASE light and the loss in the device is small, the spectrum that is approximately the same as that at the From_DCF port is achieved. The amount of attenuation is very low, for example, is equal to about 0.x dB. Refer to solid lines inFIGS. 3A and 3B.

In the state in which the device failure occurs, the same value as in the normal state is monitored at the PD109. However, since the input into the optical amplifier module111is abnormal, the device failure state can be determined. Refer to the solid lines inFIGS. 3A and 3B.

In the state in which the port connection failure occurs, since the port disconnection is caused, the optical signal from the dispersion compensation device110has the no input level at the To_DCF port.

In the state in which the port is wrongly connected, the loss characteristics in the device are reflected in the signal light and the ASE light and the levels of the signal light and the ASE light are decreased. Since the loss in the device is much larger than the loss in the circulator110a, the normal state, the device failure state, and the wrong connection of the port can be determined from the monitor value detected at the PD109. Refer to broken lines inFIGS. 3A and 3B.

A processing process in the optical amplifier apparatus100baccording to the first embodiment will now be described.FIG. 4illustrates an example of the processing process in the optical amplifier apparatus100baccording to the first embodiment. Referring toFIG. 4, in operation S101, the fault determination device112in the optical amplifier apparatus100bdetects the second monitor value from the optical amplifier module111. In operation S102, the fault determination device112performs determination of whether the second monitor value is higher than or equal to the second given value.

If the second monitor value is higher than or equal to the second given value (Yes in operation S103), then in operation S104, the fault determination device112detects the first monitor value from the PD109. In operation S105, the fault determination device112performs determination of whether the first monitor value is higher than or equal to the first given value.

If the first monitor value is higher than or equal to the first given value (Yes in operation S106), then in operation S107, the fault determination device112determines that the dispersion compensation device110is in the normal state. If the first monitor value is lower than the first given value (No in operation S106), then in operation S108, the fault determination device112determines that the port are in the wrong connection state.

If the second monitor value is lower than the second given value (No in operation S103), then in operation S109, the fault determination device112detects the first monitor value from the PD109. In operation S110, the fault determination device112performs determination of whether the first monitor value is higher than or equal to the first given value.

If the first monitor value is higher than or equal to the first given value (Yes in operation S111), then in operation S112, the fault determination device112determines that the device failure occurs. If the first monitor value is lower than the first given value (No in operation S111), then in operation S113, the fault determination device112determines that the port disconnection is caused.

As described above, in the optical amplifier apparatus100baccording to the first embodiment, the fault determination device112receives the first monitor value from the PD109and receives the second monitor value from the optical amplifier module111. Since the fault determination device112compares the first monitor value with the first given value and compares the second monitor value with the second given value to perform the fault determination on the basis of the results of the comparison, it is possible to accurately determine any fault in the dispersion compensation device. For example, it is possible to differentiate and determine the connection failure, the device failure, and the wrong connection in the dispersion compensation device including a directional device, such as the circulator110a.

In addition, when the optical amplifier apparatus100bis turned on, the fault determination device112performs the fault determination to provide the result of the determination to the monitor. Accordingly, it is possible to rapidly detect the abnormal connection state due to an operation error to avoid turning on the optical amplifier apparatus in the abnormal state.

Furthermore, the optical amplifier apparatus100baccording to the first embodiment can determine the abnormal state regardless of the loss characteristics of the device110b, as described above with reference toFIGS. 3A and 3B.

Although the PD113in the optical amplifier module111is used to detect the second monitor value in the first embodiment, the detection of the second monitor value is not limited to the use of the PD113. For example, a PD used to detect the second monitor value may be separately provided downstream of the dispersion compensation device110.

Alternatively, an optical switch may be provided, instead of the CPL103, to switch between the signal light and the optical signal so that the main signal light provided from the optical amplifier apparatus100adoes not interfere with the optical signal in the opposite direction provided from the dispersion compensation device110.

The configuration of an optical communication system according to a second embodiment of the present invention will now be described.FIG. 5illustrates an example of the configuration of the optical communication system according to the second embodiment. Referring toFIG. 5, the optical communication system includes an optical amplifier apparatus200aand an optical amplifier apparatus200b. Since the optical amplifier apparatus200aincludes the same configuration as that of the optical amplifier apparatus200b, the configuration of the optical amplifier apparatus200bwill now be described.

Referring toFIG. 5, the optical amplifier apparatus200bincludes CPLs201to204, a VOA205, PDs206to208, a dispersion compensation device209, an optical amplifier module210, a laser diode (LD)211, and a fault determination device212.

The CPL201splits an optical signal provided from the optical amplifier apparatus200ainto signal components to provide one signal component to the PD206and provide the other signal component to the VOA205. The CPL202splits an optical signal provided from the VOA205into signal components to provide one signal component to the PD207and provide the other signal component to the CPL203.

The CPL203provides an optical signal from the CPL202to the dispersion compensation device209. The CPL203provides an optical signal from the dispersion compensation device209to the PD208.

The CPL204provides an optical signal from the dispersion compensation device209to the optical amplifier module210. The CPL204provides an optical signal from the LD211to the dispersion compensation device209.

The VOA205is a device that attenuates an optical signal. The VOA205receives an optical signal from the CPL201, attenuates the received optical signal, and provides the attenuated optical signal to the CPL202. If a fault occurs in, for example, the dispersion compensation device209, the VOA205increases the amount of attenuation to prevent a high-power optical signal from being provided to the dispersion compensation device209.

The PD206is a device that receives an optical signal from the CPL201and converts the received optical signal into an electrical signal. The PD206provides the electrical signal to a monitor. The PD207is a device that receives an optical signal from the CPL202and converts the received optical signal into an electrical signal. The PD207provides the electrical signal to the monitor.

The PD208is a device that receives an optical signal from the CPL203and converts the received optical signal into an electrical signal. The PD208provides the electrical signal to the fault determination device212.

The dispersion compensation device209causes an appropriate delay for every wavelength in an optical signal that is received from the CPL203to compensate the dispersion existing in the optical signal. The dispersion compensation device209includes a circulator209aand a device209bperforming the dispersion compensation.

The dispersion compensation device209is connected to a To_DCF port and a From_DCF port. A connection method in which a port (1) of the dispersion compensation device209is connected to the To_DCF port and a port (2) of the dispersion compensation device209is connected to the From_DCF port corresponds to the normal connection.

An optical signal input from the port (1) of the dispersion compensation device209is input into the device209bthrough the circulator209a. The optical signal subjected to the dispersion compensation in the device209bis output from the port (2) through the circulator209a. In contrast, an optical signal input from the port (2) of the dispersion compensation device209is output from the port (1) not through the device209b.

The optical amplifier module210is a device that receives an optical signal from CPL204, amplifies the received optical signal, and outputs the amplified optical signal. The optical amplifier module210includes a PD. The optical amplifier module210converts the optical signal into an electrical signal with the PD and provides the resulting electrical signal to the fault determination device212.

The LD211is a device that provides an optical signal (LD light) to the dispersion compensation device209through the CPL204. The LD211may provide an optical signal to the CPL204during a period in which the fault detection is performed to decrease the power consumption.

The fault determination device212is a processor that determines any fault concerning the dispersion compensation device209. The fault determination device212includes a first given value and a second given value. The fault determination device212compares the value of the electrical signal received from the PD208with the first given value and compares the value of the electrical signal received from the PD in the optical amplifier module210with the second given value to determine any fault on the basis of the result of the comparison.

The value of the electrical signal received from the PD208is hereinafter referred to as a first monitor value, and the value of the electrical signal received from the PD in the optical amplifier module210is hereinafter referred to as a second monitor value. A first threshold value indicates a value that is set so as to reflect the loss of the optical signal transmitted through the port (2) and the port (1), not through the device209bin the dispersion compensation device209. A second threshold value indicates a value that is set so as to reflect the loss of the optical signal transmitted through the port (1), the device209bin the dispersion compensation device209, and the port (2).

If the first monitor value is higher than or equal to the first given value (the first monitor value is normal) and the second monitor value is higher than or equal to the second threshold value (the second monitor value is normal), the fault determination device212determines that the dispersion compensation device209is in the normal state and provides the result of the determination to, for example, the monitor.

If the first monitor value is higher than or equal to the first threshold value (the first monitor value is normal) and the second monitor value is lower than the second threshold value (the second monitor value is abnormal), the fault determination device212determines that the device209bfails and provides the result of the determination to, for example, the monitor. If the first monitor value is higher than or equal to the first given value, no port connection failure occurs and the connection of the port is normal. If the second monitor value is lower than the second threshold value although no port connection failure occurs, the fault determination device212determines that any fault occurs in the device209band a loss is caused in the second monitor value.

If the first monitor value is lower than the first given value (the first monitor value is abnormal) and the second monitor value is lower than the second given value (the second monitor value is abnormal), the fault determination device212determines that a port connection failure occurs in the To_DCF port or the From_DCF port and provides the result of the determination to, for example, the monitor. When a port connection failure occurs, both of the path of the signal light provided from the CPL203to the dispersion compensation device209and the path of the signal light provided from the CPL204to the dispersion compensation device209are in the disconnection state. Accordingly, the first and second monitor values have the no input level.

A case will now be described in which the dispersion compensation device209according to the second embodiment is wrongly connected.FIG. 6illustrates the case in which the dispersion compensation device209according to the second embodiment is wrongly connected. In the dispersion compensation device209inFIG. 6, the To_DCF port is connected to the port (2) and the From_DCF port is connected to the port (1).

When the dispersion compensation device209is wrongly connected in the manner illustrated inFIG. 6, the optical signal from the To_DCF port, which is normally subjected to the dispersion compensation, is input into the dispersion compensation device209and is output from the dispersion compensation device209not through the device209b. Accordingly, the optical signal that is not subjected to the dispersion compensation is output and is provided to the optical amplifier module210. In this case, since no device loss is reflected in the optical signal input into the optical amplifier module210, the second monitor value is higher than or equal to the second given value.

In contrast, the optical signal from the From_DCF port, which is normally not subjected to the dispersion compensation, is input into the dispersion compensation device209and is output from the dispersion compensation device209through the device209b. In this case, since an unexpected device loss is reflected in the optical signal input into the PD208, the first monitor value is lower than the first given value.

Practically, if the first monitor value is lower than the first given value (the first monitor value is abnormal) and the second monitor value is higher than or equal to the second given value (the second monitor value is normal), the fault determination device212determines that the dispersion compensation device is in the wrong connection state and provides the result of the determination to, for example, the monitor.

Upon detection of any of the failure of the device209b, the port connection failure, and the wrong connection, the fault determination device212causes the VOA205to increase the loss in the VOA205. Increasing the loss in the VOA205prevents the high-power optical signal from the To_DCF port from being provided to the dispersion compensation device209.

FIG. 7andFIGS. 8A and 8Billustrate optical spectra in the normal state, in the state in which the device failure occurs, and in the state in which the port is wrongly connected at the To_DCF port and the From_DCF port in the second embodiment.FIG. 7illustrates a case in which the device has flat loss characteristics.FIGS. 8A and 8Billustrate cases in which the device has periodic loss characteristics.

The monitor value when the device has the flat loss characteristics will now be described with reference toFIG. 7. In the normal state, since only the loss in the circulator209ais reflected in the optical signal (LD light) output from the LD211and the loss in the device is small, the spectrum that is approximately the same as that at the From_DCF port is achieved. The amount of attenuation is very low, for example, is equal to about 0.x dB. Refer to broken lines inFIG. 7.

In the state in which the device failure occurs, the same value as in the normal state is monitored at the PD208. However, since the input into the optical amplifier module210is abnormal, the device failure state can be determined. Refer to the broken line inFIG. 7.

In the state in which the port connection failure occurs, since the port disconnection is caused, the LD light at the To_DCF port has the no input level.

In the state in which the port is wrongly connected, the loss characteristics in the device are reflected in the LD light and the level of the LD light is decreased. Since the loss in the device is much larger than the loss in the circulator209a, the normal state, the device failure state, and the wrong connection of the port can be determined from the monitor value detected at the PD208. Refer to the broken lines inFIG. 7.

The monitor value when the device has the periodic loss characteristics will now be described with reference toFIGS. 8A and 8B. Since the device has the periodic loss characteristics in the case inFIGS. 8A and 8B, the LD light within the frequency band of transmission signals and the LD light outside the frequency band of the transmission signals are separately illustrated.FIG. 8Aillustrates the monitor value when the LD light is within the frequency band of the transmission signals andFIG. 8Billustrates the monitor value when the LD light is outside the frequency band of the transmission signals.

When the LD light within the frequency band in which the signals having the periodic loss characteristics are transmitted is selected in the state in which the port is wrongly connected, the device loss is reflected in the LD light monitored at the PD208to decrease the level of the LD light. Refer to alternate long and short lines inFIG. 8A.

When the LD light outside the frequency band in which the signals having the periodic loss characteristics are transmitted is selected in the state in which the port is wrongly connected, the LD light is greatly attenuated in the device and the monitor value near the no input level is detected at the PD208. The loss in the device is much larger than the loss in the circulator209aboth within the frequency band in which the signals having the periodic loss characteristics are transmitted and outside the frequency band in which the signals having the periodic loss characteristics are transmitted, so that the normal state, the device failure state, and the wrong connection of the port can be determined from the monitor value detected at the PD208.

The optical amplifier apparatus200baccording to the second embodiment can accurately detect any fault not only when the device having the flat loss characteristics is applied to the dispersion compensation device209but also when the device having the periodic loss characteristics is applied to the dispersion compensation device209, as in the optical amplifier apparatus according to the first embodiment. In addition, the LD light output from the LD211can be used to accurately detect any fault, regardless of whether the LD light is within the frequency band of the transmission signals or outside the frequency band thereof. For example, it is possible to differentiate and determine the connection failure, the device failure, and the wrong connection in the dispersion compensation device including a directional device, such as the circulator209a.

The configuration of an optical communication system according to a third embodiment of the present invention will now be described.FIG. 9illustrates an example of the configuration of the optical communication system according to the third embodiment. Referring toFIG. 9, the optical communication system includes an optical amplifier apparatus300aand an optical amplifier apparatus300b. Since the optical amplifier apparatus300aincludes the same configuration as that of the optical amplifier apparatus300b, the configuration of the optical amplifier apparatus300bwill now be described.

The optical amplifier apparatus300breceives LD light (optical signals) from an LD313through a To_DCF port and a From_DCF port and detects the monitor values of the LD light with a PD310and an optical amplifier module312to allow detection of an abnormal state even without a main signal from the optical amplifier apparatus300a.

Referring toFIG. 9, the optical amplifier apparatus300bincludes CPLs301to306, a VOA307, PDs308to310, a dispersion compensation device311, the optical amplifier module312, the LD313, an LD controller314, and a fault determination device315.

The CPL301splits an optical signal provided from the optical amplifier apparatus300ainto signal components to provide one signal component to the PD308and provide the other signal component to the VOA307. The CPL302splits an optical signal provided from the VOA307into signal components to provide one signal component to the PD309and provide the other signal component to the CPL303.

The CPL303provides an optical signal from the CPL302or an optical signal (LD light) from the CPL306to the CPL304. The CPL304provides an optical signal from the CPL303to the dispersion compensation device311. The CPL304provides an optical signal from the dispersion compensation device311to the PD310.

The CPL305provides an optical signal from the dispersion compensation device311to the optical amplifier module312. The CPL305provides an optical signal from the CPL306to the dispersion compensation device311.

The CPL306splits an optical signal (LD light) from the LD313into signal components to provide one signal component to the CPL303and provide the other signal component to the CPL305.

The VOA307is a device that attenuates an optical signal. The VOA307receives an optical signal from the CPL301, attenuates the received optical signal, and provides the attenuated optical signal to the CPL302. If a fault occurs in, for example, the dispersion compensation device311, the VOA307increases the amount of attenuation to prevent a high-power optical signal from being provided to the dispersion compensation device311.

The PD308is a device that receives an optical signal from the CPL301and converts the received optical signal into an electrical signal. The PD308provides the electrical signal to a monitor and the LD controller314. The PD309is a device that receives an optical signal from the CPL302and converts the received optical signal into an electrical signal. The PD309provides the electrical signal to the monitor.

The PD310is a device that receives an optical signal from the CPL304and converts the received optical signal into an electrical signal. The PD310provides the electrical signal to the fault determination device315.

The dispersion compensation device311causes an appropriate delay for every wavelength in an optical signal that is received from the CPL304to compensate the dispersion existing in the optical signal. The dispersion compensation device311includes a circulator311aand a device311bperforming the dispersion compensation.

The dispersion compensation device311is connected to the To_DCF port and the From_DCF port. A connection method in which a port (1) of the dispersion compensation device311is connected to the To_DCF port and a port (2) of the dispersion compensation device311is connected to the From_DCF port corresponds to the normal connection.

An optical signal input from the port (1) of the dispersion compensation device311is input into the device311bthrough the circulator311a. The optical signal subjected to the dispersion compensation in the device311bis output from the port (2) through the circulator311a. In contrast, an optical signal input from the port (2) of the dispersion compensation device311is output from the port (1) not through the device311b.

The optical amplifier module312is a device that receives an optical signal from the CPL305, amplifies the received optical signal, and outputs the amplified optical signal. The optical amplifier module312includes a PD. The optical amplifier module312converts the optical signal into an electrical signal with the PD and provides the resulting electrical signal to the fault determination device315.

The LD313is a device that provides optical signals (LD light) to the dispersion compensation device311through the corresponding CPLs and through the To_DCF port and the From_DCF port.

The LD controller314is a processor that receives an electrical signal from the PD308, determines whether an optical signal and ASE light are input into the optical amplifier apparatus300b, and controls the output from the LD313on the basis of the result of the determination.

If the LD controller314receives an electrical signal from the PD308, the LD controller314determines that an optical signal and ASE light are input into the optical amplifier apparatus300band shuts down the LD313. In contrast, if the LD controller314does not receive an electrical signal from the PD308, the LD controller314determines that no optical signal and no ASE light are input into the optical amplifier apparatus300band causes the LD313to output an optical signal (LD light).

The fault determination device315is a processor that determines any fault concerning the dispersion compensation device311. The fault determination device315includes a first given value and a second given value. The fault determination device315compares the value of the electrical signal received from the PD310with the first given value and compares the value of the electrical signal received from the PD in the optical amplifier module312with the second given value to determine any fault on the basis of the result of the comparison.

The value of the electrical signal received from the PD310is hereinafter referred to as a first monitor value, and the value of the electrical signal received from the PD in the optical amplifier module312is hereinafter referred to as a second monitor value. A first threshold value indicates a value that is set so as to reflect the loss of the optical signal transmitted through the port (2) and the port (1), not through the device311bin the dispersion compensation device311. A second threshold value indicates a value that is set so as to reflect the loss of the optical signal transmitted through the port (1), the device311bin the dispersion compensation device311, and the port (2).

If the first monitor value is higher than or equal to the first given value (the first monitor value is normal) and the second monitor value is higher than or equal to the second threshold value (the second monitor value is normal), the fault determination device315determines that the dispersion compensation device311is in the normal state and provides the result of the determination to, for example, the monitor.

If the first monitor value is higher than or equal to the first threshold value (the first monitor value is normal) and the second monitor value is lower than the second threshold value (the second monitor value is abnormal), the fault determination device315determines that the device311bfails and provides the result of the determination to, for example, the monitor. If the first monitor value is higher than or equal to the first given value, no port connection failure occurs and the connection of the port is normal. If the second monitor value is lower than the second threshold value although no port connection failure occurs, the fault determination device315determines that any fault occurs in the device311band a loss is caused in the second monitor value.

If the first monitor value is lower than the first given value (the first monitor value is abnormal) and the second monitor value is lower than the second given value (the second monitor value is abnormal), the fault determination device315determines that a port connection failure occurs in the To_DCF port or the From_DCF port and provides the result of the determination to, for example, the monitor. When a port connection failure occurs, both of the path of the signal light provided from the CPL304to the dispersion compensation device311and the path of the signal light provided from the CPL305to the dispersion compensation device311are in the disconnection state. Accordingly, the first and second monitor values have the no input level.

If the first monitor value is lower than the first given value (the first monitor value is abnormal) and the second monitor value is higher than or equal to the second given value (the second monitor value is normal), the fault determination device315determines that the dispersion compensation device311is in the wrong connection state and provides the result of the determination to, for example, the monitor.

Upon detection of any of the failure of the device311b, the port connection failure, and the wrong connection, the fault determination device315causes the VOA307to increase the loss in the VOA307. Increasing the loss in the VOA307prevents the high-power optical signal from the To_DCF port from being provided to the dispersion compensation device311.

A processing process in the optical amplifier apparatus300baccording to the third embodiment will now be described.FIG. 10illustrates an example of the processing process in the optical amplifier apparatus300baccording to the third embodiment. Referring toFIG. 10, in operation S201, the LD controller314in the optical amplifier apparatus300breceives an electrical signal from the PD308to perform determination of whether an optical signal is input into the optical amplifier apparatus300b.

If an optical signal is input into the optical amplifier apparatus300b(Yes in operation S202), then in operation S203, the LD controller314turns off the LD313for detection. In operation S204, the dispersion compensation device311is normally operated.

If an optical signal is not input into the optical amplifier apparatus300b(No in operation S202), then in operation S205, the LD controller314turns on the LD313for detection. In operation S206, the fault determination device315detects the second monitor value from the optical amplifier module312.

In operation S207, the fault determination device315performs determination of whether the second monitor value is higher than or equal to the second given value. If the second monitor value is higher than or equal to the second given value (Yes in operation S208), then in operation in S209, the fault determination device315detects the first monitor value from the PD310. In operation S210, the fault determination device315performs determination of whether the first monitor value is higher than or equal to the first given value.

If the first monitor value is higher than or equal to the first given value (Yes in operation S211), then in operation S212, the fault determination device315determines that the dispersion compensation device311is in the normal state. If the first monitor value is lower than the first given value (No in operation S211), then in operation S213, the fault determination device315determines that the port are in the wrong connection state.

If the second monitor value is lower than the second given value (No in operation S208), then in operation S214, the fault determination device315detects the first monitor value from the PD310. In operation S215, the fault determination device315performs determination of whether the first monitor value is higher than or equal to the first given value.

If the first monitor value is higher than or equal to the first given value (Yes in operation S216), then in operation S217, the fault determination device315determines that the device failure occurs. If the first monitor value is lower than the first given value (No in operation S216), then in operation S218, the fault determination device315determines that the port disconnection is caused.

As described above, the optical amplifier apparatus300baccording to the third embodiment receives LD light (optical signals) from the LD313through the To_DCF port and the From_DCF port and detects the monitor values of the LD light with the PD310and the optical amplifier module312to allow detection of the abnormal state even without a main signal from the optical amplifier apparatus300a.

In addition, the LD controller314determines that the optical signal and the ASE light are received and shuts down the LD313if an electrical signal is received from the PD308, so that the power consumption can be minimized.

When the dispersion compensation device311has flat loss characteristics, the LD313adjusts the wavelength of the LD light so as to be within the frequency band of the optical signal provided from the optical amplifier apparatus300aand outputs the adjusted LD light.

When the dispersion compensation device311has periodic loss characteristics, the LD313adjusts the wavelength of the LD light so that the LD light is transmitted through the dispersion compensation device311. This is because, if the LD light is provided to the dispersion compensation device311without the adjustment of the wavelength, a considerable loss can possibly occur in the device311beven in the normal state and the second monitor value may not be higher than or equal to the second given value.

The configuration of an optical communication system according to a fourth embodiment of the present invention will now be described.FIG. 11illustrates an example of the configuration of the optical communication system according to the fourth embodiment. Referring toFIG. 11, the optical communication system includes an optical amplifier apparatus400aand an optical amplifier apparatus400b. Since the optical amplifier apparatus400aincludes the same configuration as that of the optical amplifier apparatus400b, the configuration of the optical amplifier apparatus400bwill now be described.

When the optical amplifier apparatus400breceives no optical signal from the optical amplifier apparatus400a, an optical signal from an LD413is received through a To_DCF port and a From_DCF port to perform fault determination. In contrast, when the optical amplifier apparatus400breceives an optical signal from the optical amplifier apparatus400a, the optical signal provided through the To_DCF port, among the optical signals output from the LD413, is blocked by an optical switch (SW)414and the optical signal received from the optical amplifier apparatus400ais output through the To_DCF port to perform the fault determination.

The optical SW414blocks the LD light from the LD413on the basis of whether an optical signal is received from the optical amplifier apparatus400ain the optical amplifier apparatus400b, so that the abnormal state can be detected regardless of whether an optical signal is received from the optical amplifier apparatus400a.

Referring toFIG. 11, the optical amplifier apparatus400bincludes CPLs401to406, a VOA407, PDs408to410, a dispersion compensation device411, an optical amplifier module412, and the LD413. The optical amplifier apparatus400balso includes the optical SW414, an optical SW controller415, and a fault determination device416.

The CPL401splits an optical signal provided from the optical amplifier apparatus400ainto signal components to provide one signal component to the PD408and provide the other signal component to the VOA407. The CPL402splits an optical signal provided from the VOA407into signal components to provide one signal component to the PD409and provide the other signal component to the CPL403.

The CPL403provides an optical signal from the CPL402or an optical signal (LD light) from the CPL406to the CPL404. The CPL404provides an optical signal from the CPL403to the dispersion compensation device411. The CPL404provides an optical signal from the dispersion compensation device411to the PD410.

The CPL405provides an optical signal from the dispersion compensation device411to the optical amplifier module412. The CPL405provides an optical signal from the CPL406to the dispersion compensation device411. The CPL406splits an optical signal (LD light) provided from the LD413into signal components to provide one signal component to the CPL403through the optical SW414and provide the other signal component to the CPL405.

The VOA407is a device that attenuates an optical signal. The VOA407receives an optical signal from the CPL401, attenuates the received optical signal, and provides the attenuated optical signal to the CPL402. If a fault occurs in, for example, the dispersion compensation device411, the VOA407increases the amount of attenuation to prevent a high-power optical signal from being provided to the dispersion compensation device411.

The PD408is a device that receives an optical signal from the CPL401and converts the received optical signal into an electrical signal. The PD408provides the electrical signal to a monitor and the optical SW controller415. The PD409is a device that receives an optical signal from the CPL402and converts the received optical signal into an electrical signal. The PD409provides the electrical signal to the monitor.

The PD410is a device that receives an optical signal from the CPL404and converts the received optical signal into an electrical signal. The PD410provides the electrical signal to the fault determination device416.

The dispersion compensation device411causes an appropriate delay for every wavelength in an optical signal that is received from the CPL404to compensate the dispersion existing in the optical signal. The dispersion compensation device411includes a circulator411aand a device411bperforming the dispersion compensation.

The dispersion compensation device411is connected to the To_DCF port and the From_DCF port. A connection method in which a port (1) of the dispersion compensation device411is connected to the To_DCF port and a port (2) of the dispersion compensation device411is connected to the From_DCF port corresponds to the normal connection.

An optical signal input from the port (1) of the dispersion compensation device411is input into the device411bthrough the circulator411a. The optical signal subjected to the dispersion compensation in the device411bis output from the port (2) through the circulator411a. In contrast, an optical signal input from the port (2) of the dispersion compensation device411is output from the port (1) not through the device411b.

The optical amplifier module412is a device that receives an optical signal from the CPL405, amplifies the received optical signal, and outputs the amplified optical signal. The optical amplifier module412includes a PD. The optical amplifier module412converts the optical signal into an electrical signal with the PD and provides the resulting electrical signal to the fault determination device416.

The LD413is a device that provides optical signals (LD light) to the dispersion compensation device411through the corresponding CPLs and through the To_DCF port and the From_DCF port. The optical SW414blocks the transmission of an optical signal from the LD413on the basis of a control instruction from the optical SW controller415.

The optical SW controller415is a processor that controls the optical SW414on the basis of an electrical signal from the PD408. If the optical SW controller415receives an electrical signal from the PD408, the optical SW controller415provides a control instruction to block the transmission of an optical signal to the optical SW414. In contrast, if the optical SW controller415does not receive an electrical signal from the PD408, the optical SW controller415provides a control instruction to permit the transmission of an optical signal to the optical SW414.

The fault determination device416is a processor that determines any fault concerning the dispersion compensation device411. The fault determination device416includes a first given value and a second given value. The fault determination device416compares the value of the electrical signal received from the PD410with the first given value and compares the value of the electrical signal received from the PD in the optical amplifier module412with the second given value to determine any fault on the basis of the result of the comparison.

The value of the electrical signal received from the PD410is hereinafter referred to as a first monitor value, and the value of the electrical signal received from the PD in the optical amplifier module412is hereinafter referred to as a second monitor value. A first threshold value indicates a value that is set so as to reflect the loss of the optical signal transmitted through the port (2) and the port (1), not through the device411bin the dispersion compensation device411. A second threshold value indicates a value that is set so as to reflect the loss of the optical signal transmitted through the port (1), the device411bin the dispersion compensation device411, and the port (2).

If the first monitor value is higher than or equal to the first given value (the first monitor value is normal) and the second monitor value is higher than or equal to the second threshold value (the second monitor value is normal), the fault determination device416determines that the dispersion compensation device411is in the normal state and provides the result of the determination to, for example, the monitor.

If the first monitor value is higher than or equal to the first threshold value (the first monitor value is normal) and the second monitor value is lower than the second threshold value (the second monitor value is abnormal), the fault determination device416determines that the device411bfails and provides the result of the determination to, for example, the monitor. If the first monitor value is higher than or equal to the first given value, no port connection failure occurs and the connection of the port is normal. If the second monitor value is lower than the second threshold value although no port connection failure occurs, the fault determination device416determines that any fault occurs in the device411band a loss is caused in the second monitor value.

If the first monitor value is lower than the first given value (the first monitor value is abnormal) and the second monitor value is lower than the second given value (the second monitor value is abnormal), the fault determination device416determines that a port connection failure occurs in the To_DCF port or the From_DCF port and provides the result of the determination to, for example, the monitor. When a port connection failure occurs, both of the path of the signal light provided from the CPL404to the dispersion compensation device411and the path of the signal light provided from the CPL405to the dispersion compensation device411are in the disconnection state. Accordingly, the first and second monitor values have the no input level.

If the first monitor value is lower than the first given value (the first monitor value is abnormal) and the second monitor value is higher than or equal to the second given value (the second monitor value is normal), the fault determination device416determines that the dispersion compensation device411is in the wrong connection state and provides the result of the determination to, for example, the monitor.

Upon detection of any of the failure of the device411b, the port connection failure, and the wrong connection, the fault determination device416causes the VOA407to increase the loss in the VOA407. Increasing the loss in the VOA407prevents the high-power optical signal from the To_DCF port from being provided to the dispersion compensation device411.

A processing process in the optical amplifier apparatus400baccording to the fourth embodiment will now be described.FIG. 12illustrates an example of the processing process in the optical amplifier apparatus400baccording to the fourth embodiment. Referring toFIG. 12, in operation S401, the optical SW controller415performs determination of whether the optical amplifier apparatus400breceives an optical signal from the optical amplifier apparatus400a.

If no optical signal is received (No in operation S402), then in operation S403, the optical SW controller415sets the optical SW414to permit the transmission of an optical signal and the process goes to operation S405. If an optical signal is received (Yes in operation S402), then in operation S404, the optical SW controller415sets the optical SW414to block the transmission of an optical signal.

In operation S405, the fault determination device416detects the second monitor value from the optical amplifier module412. In operation S406, the fault determination device416performs determination of whether the second monitor value is higher than or equal to the second given value.

If the second monitor value is higher than or equal to the second given value (Yes in operation S407), then in operation S408, the fault determination device416detects the first monitor value from the PD410. In operation S409, the fault determination device416performs determination of whether the first monitor value is higher than or equal to the first given value.

If the first monitor value is higher than or equal to the first given value (Yes in operation S410), then in operation S411, the fault determination device416determines that the dispersion compensation device411is in the normal state. If the first monitor value is lower than the first given value (No in operation S410), then in operation S412, the fault determination device416determines that the port are in the wrong connection state.

If the second monitor value is lower than the second given value (No in operation S407), then in operation S413, the fault determination device416detects the first monitor value from the PD410. In operation S414, the fault determination device416performs determination of whether the first monitor value is higher than or equal to the first given value.

If the first monitor value is higher than or equal to the first given value (Yes in operation S415), then in operation S416, the fault determination device416determines that the device failure occurs. If the first monitor value is lower than the first given value (No in operation S415), then in operation S417, the fault determination device416determines that the port disconnection is caused.

As described above, the optical SW controller415causes the optical SW414to block the LD light from the LD413on the basis of whether an optical signal is received from the optical amplifier apparatus400ain the optical amplifier apparatus400baccording to the fourth embodiment. Accordingly, the abnormal state can be accurately detected regardless of whether an optical signal is received from the optical amplifier apparatus400a.

When the dispersion compensation device411has flat loss characteristics, the LD413adjusts the wavelength of the LD light so as to be within the frequency band of the optical signal provided from the optical amplifier apparatus400aand outputs the adjusted LD light.

When the dispersion compensation device411has periodic loss characteristics, the LD413adjusts the wavelength of the LD light so that the LD light is transmitted through the dispersion compensation device411. This is because, if the LD light is provided to the dispersion compensation device411without the adjustment of the wavelength, a considerable loss can possibly occur in the device411beven in the normal state and the second monitor value may not be higher than or equal to the second given value.

The configuration of an optical communication system according to a fifth embodiment of the present invention will now be described.FIG. 13illustrates an example of the configuration of the optical communication system according to the fifth embodiment. Referring toFIG. 13, the optical communication system includes an optical amplifier apparatus500aand an optical amplifier apparatus500b. Since the optical amplifier apparatus500aincludes the same configuration as that of the optical amplifier apparatus500b, the configuration of the optical amplifier apparatus500bwill now be described.

The optical amplifier apparatus500bforces an optical amplifier module513, instead of an LD, to emit light if no optical signal is received from the optical amplifier apparatus500aand provides the signal light to a dispersion compensation device512to perform fault determination.

Referring toFIG. 13, the optical amplifier apparatus500bincludes CPLs501to507, a VOA508, PDs509to511, the dispersion compensation device512, the optical amplifier module513, an optical SW514, an optical SW controller515, and a fault determination device516.

The CPL501splits an optical signal provided from the optical amplifier apparatus500ainto signal components to provide one signal component to the PD509and provide the other signal component to the VOA508. The CPL502splits an optical signal provided from the VOA508into signal components to provide one signal component to the PD510and provide the other signal component to the CPL503.

The CPL503provides an optical signal from the CPL502or an optical signal from the CPL506to the CPL504. The CPL504provides an optical signal from the CPL503to the dispersion compensation device512. The CPL504provides an optical signal from the dispersion compensation device512to the PD511.

The CPL505provides an optical signal from the dispersion compensation device512to the optical amplifier module513. The CPL505provides an optical signal from the CPL506to a From_DCF port.

The CPL506splits an optical signal that is received from the CPL507into signal components to provide one signal component to the CPL505and provide the other signal component to the CPL503through the optical SW514. The CPL507splits an optical signal that is received from the optical amplifier module513into signal components to provide one signal component to the CPL506and externally provide the other signal component.

The VOA508is a device that attenuates an optical signal. The VOA508receives an optical signal from the CPL501, attenuates the received optical signal, and provides the attenuated optical signal to the CPL502. If a fault occurs in, for example, the dispersion compensation device512, the VOA508increases the amount of attenuation to prevent a high-power optical signal from being provided to the dispersion compensation device512.

The PD509is a device that receives an optical signal from the CPL501and converts the received optical signal into an electrical signal. The PD509provides the electrical signal to a monitor and the optical SW controller515. The PD510is a device that receives an optical signal from the CPL502and converts the received optical signal into an electrical signal. The PD510provides the electrical signal to the monitor.

The PD511is a device that receives an optical signal from the CPL504and converts the received optical signal into an electrical signal. The PD511provides the electrical signal to the fault determination device516.

The dispersion compensation device512causes an appropriate delay for every wavelength in an optical signal that is received from the CPL504to compensate the dispersion existing in the optical signal. The dispersion compensation device512includes a circulator512aand a device512bperforming the dispersion compensation.

The dispersion compensation device512is connected to a To_DCF port and the From_DCF port. A connection method in which a port (1) of the dispersion compensation device512is connected to the To_DCF port and a port (2) of the dispersion compensation device512is connected to the From_DCF port corresponds to the normal connection.

An optical signal input from the port (1) of the dispersion compensation device512is input into the device512bthrough the circulator512a. The optical signal subjected to the dispersion compensation in the device512bis output from the port (2) through the circulator512a. In contrast, an optical signal input from the port (2) of the dispersion compensation device512is output from the port (1) not through the device512b.

The optical amplifier module513is a device that receives an optical signal from the CPL505, amplifies the received optical signal, and outputs the amplified optical signal. The optical amplifier module513includes a PD. The optical amplifier module513converts the optical signal into an electrical signal with the PD and provides the resulting electrical signal to the fault determination device516. When a control instruction to force the optical amplifier module513to emit light is received, the optical amplifier module513provides the optical signal to the CPL507.

The optical SW514blocks the transmission of an optical signal from the CPL506on the basis of a control instruction from the optical SW controller515.

The optical SW controller515is a processor that controls the optical SW514on the basis of an electrical signal from the PD509. If the optical SW controller515receives an electrical signal from the PD509, the optical SW controller515provides a control instruction to block the transmission of an optical signal to the optical SW514. In contrast, if the optical SW controller515does not receive an electrical signal from the PD509, the optical SW controller515provides a control instruction to permit the transmission of an optical signal to the optical SW514.

The fault determination device516is a processor that determines any fault concerning the dispersion compensation device512. The fault determination device516includes a first given value and a second given value. The fault determination device516compares the value of the electrical signal received from the PD511with the first given value and compares the value of the electrical signal received from the PD in the optical amplifier module513with the second given value to determine any fault on the basis of the result of the comparison.

The value of the electrical signal received from the PD511is hereinafter referred to as a first monitor value, and the value of the electrical signal received from the PD in the optical amplifier module513is hereinafter referred to as a second monitor value. A first threshold value indicates a value that is set so as to reflect the loss of the optical signal transmitted through the port (2) and the port (1), not through the device512bin the dispersion compensation device512. A second threshold value indicates a value that is set so as to reflect the loss of the optical signal transmitted through the port (1), the device512bin the dispersion compensation device512, and the port (2).

If the first monitor value is higher than or equal to the first given value (the first monitor value is normal) and the second monitor value is higher than or equal to the second threshold value (the second monitor value is normal), the fault determination device516determines that the dispersion compensation device512is in the normal state and provides the result of the determination to, for example, the monitor.

If the first monitor value is higher than or equal to the first threshold value (the first monitor value is normal) and the second monitor value is lower than the second threshold value (the second monitor value is abnormal), the fault determination device516determines that the device512bfails and provides the result of the determination to, for example, the monitor. If the first monitor value is higher than or equal to the first given value, no port connection failure occurs and the connection of the port is normal. If the second monitor value is lower than the second threshold value although no port connection failure occurs, the fault determination device516determines that any fault occurs in the device512band a loss is caused in the second monitor value.

If the first monitor value is lower than the first given value (the first monitor value is abnormal) and the second monitor value is lower than the second given value (the second monitor value is abnormal), the fault determination device516determines that a port connection failure occurs in the To_DCF port or the From_DCF port and provides the result of the determination to, for example, the monitor. When a port connection failure occurs, both of the path of the signal light provided from the CPL504to the dispersion compensation device512and the path of the signal light provided from the CPL505to the dispersion compensation device512are in the disconnection state. Accordingly, the first and second monitor values have the no input level.

If the first monitor value is lower than the first given value (the first monitor value is abnormal) and the second monitor value is higher than or equal to the second given value (the second monitor value is normal), the fault determination device516determines that the dispersion compensation device512is in the wrong connection state and provides the result of the determination to, for example, the monitor.

Upon detection of any of the failure of the device512b, the port connection failure, and the wrong connection, the fault determination device516causes the VOA508to increase the loss in the VOA508. Increasing the loss in the VOA508prevents the high-power optical signal from the To_DCF port from being provided to the dispersion compensation device512.

A processing process in the optical amplifier apparatus500baccording to the fifth embodiment will now be described.FIG. 14illustrates an example of the processing process in the optical amplifier apparatus500baccording to the fifth embodiment. Referring toFIG. 14, in operation S501, the optical SW controller515performs determination of whether the optical amplifier apparatus500breceives an optical signal on the basis of the electrical signal provided from the PD509.

If no optical signal is received (No in operation S502), then in operation S503, the optical SW controller515sets the optical SW514to permit the transmission of an optical signal. In operation S504, the optical SW controller515forces the optical amplifier module513to emit light and the process goes to operation S507.

If an optical signal is received (Yes in operation S502), then in operation S505, the optical SW controller515sets the optical SW514to block the transmission of an optical signal. In operation S506, the optical SW controller515normally operates the optical amplifier module513.

In operation S507, the fault determination device516detects the second monitor value from the optical amplifier module513. In operation S508, the fault determination device516performs determination of whether the second monitor value is higher than or equal to the second given value. If the second monitor value is higher than or equal to the second given value (Yes in operation S509), then in operation S510, the fault determination device516detects the first monitor value from the PD511.

In operation S511, the fault determination device516performs determination of whether the first monitor value is higher than or equal to the first given value. If the first monitor value is higher than or equal to the first given value (Yes in operation S512), then in operation S513, the fault determination device516determines that the dispersion compensation device512is in the normal state. If the first monitor value is lower than the first given value (No in operation S512), then in operation S514, the fault determination device516determines that the port are in the wrong connection state.

If the second monitor value is lower than the second given value (No in operation S509), then in operation S515, the fault determination device516detects the first monitor value from the PD511. In operation S516, the fault determination device516performs determination of whether the first monitor value is higher than or equal to the first given value.

If the first monitor value is higher than or equal to the first given value (Yes in operation S517), then in operation S518, the fault determination device516determines that the device failure occurs. If the first monitor value is lower than the first given value (No in operation S517), then in operation S519, the fault determination device516determines that the port disconnection is caused.

As described above, the optical amplifier apparatus500baccording to the fifth embodiment forces the optical amplifier module513, instead of an LD, to emit light if no optical signal is received from the optical amplifier apparatus500a, so that the optical amplifier apparatus500bcan accurately determine any fault in the dispersion compensation device512regardless of whether an optical signal is received.

Although the first monitor value and the second monitor value are compared with the first given value and the second given value, respectively, to determine any fault in the first to fifth embodiments, the present invention is not limited to the above determination. Any parameter may be used, instead of the first and second given values, as long as it can be determined whether the first monitor value and the second monitor value are abnormal.

Among the processes described in the above embodiments, all or some of the processes described to be automatically performed may be manually performed and all or some of the processes described to be manually performed may be automatically performed. Information including the processing processes, the control processes, the specific names, a variety of data, and the parameters described in the above description and illustrated in the drawings may be arbitrarily varied, except otherwise specified.

Although the dispersion compensation device is exemplified as the dispersion compensator, for example, an optical amplifier including a Mach-Zehnder external optical modulator, an optical branching device, a wavelength demultiplexer, and an optical isolator and a gain equalizer may be used.

According to an aspect of the embodiments of the invention, any combinations of one or more of the described features, functions, operations, and/or benefits can be provided. A combination can be one or a plurality. The embodiments can be implemented as an apparatus (a machine) that includes optical transceiving hardware in combination with computing hardware including hardware logic and/or circuitry (i.e., computing apparatus), such as (in a non-limiting example) any computer that can store, retrieve, process and/or output data and/or communicate (network) with other computers. According to an aspect of an embodiment, the described features, functions, operations, and/or benefits can be implemented by and/or use optical transceiving hardware, computing hardware and/or software. For example, the fault determination devices (112,212,315,416,516) can be implemented as a computing apparatus and/or software. A computing apparatus can comprise a controller (CPU) (e.g., a hardware logic and/or circuitry based computer processor that processes or executes instructions, namely software/program), computer readable recording media, transmission communication media interface (network interface), and/or an output device, such as a display device, all in communication through a data communication bus. In addition, an apparatus can include one or more apparatuses in computer network communication with each other or other apparatuses. In addition, a computer processor can include one or more computer processors in one or more apparatuses or any combinations of one or more computer processors and/or apparatuses. An aspect of an embodiment relates to causing one or more apparatuses and/or computer processors to execute the described operations. The results produced can be displayed on the display.

A program/software implementing the embodiments may be recorded on a computer-readable media, e.g., a non-transitory computer-readable medium. The program/software implementing the embodiments may also be transmitted over a transmission communication path, e.g., a network implemented via hardware. Examples of the non-transitory computer-readable recording media include a magnetic recording apparatus, an optical disk, a magneto-optical disk, and/or volatile and/or non-volatile semiconductor memory (for example, RAM, ROM, etc.). Examples of the magnetic recording apparatus include a hard disk device (HDD), a flexible disk (FD), and a magnetic tape (MT). Examples of the optical disk include a DVD (Digital Versatile Disc), DVD-ROM, DVD-RAM (DVD-Random Access Memory), BD (Blue-ray Disk), a CD-ROM (Compact Disc-Read Only Memory), and a CD-R (Recordable)/RW.