Optical add-drop multiplexer

• US 20020131116A1
• Filed: 04/30/2002
• Published: 09/19/2002
• Est. Priority Date: 07/31/1997
• Status: Active Grant

• Current Assignee: Rakuten Group, Inc.
• Original Assignee: NEC Corporation
• Inventors: Takeshita, Hitoshi, Shimomura, Hirofumi, Henmi, Naoya
• Granted Patent: US 6,895,183 B2
• Time in Patent Office: Days
• US Class Current: 398/83
• CPC Class Codes: H04B 10/03 Arrangements for fault recovery
• CPC Class Codes: H04B 10/0771 Fault location on the transmission path
• CPC Class Codes: H04B 2210/071 using alarms
• CPC Class Codes: H04B 2210/072 using an overhead signal
• CPC Class Codes: H04J 14/0212 using optical switches or wavelength selective switches [WSS]
• CPC Class Codes: H04J 14/0216 Bidirectional architectures
• CPC Class Codes: H04J 14/0227 Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
• CPC Class Codes: H04J 14/0241 Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths
• CPC Class Codes: H04J 14/0245 for downstream transmission, e.g. optical line terminal [OLT] to ONU
• CPC Class Codes: H04J 14/0249 for upstream transmission, e.g. ONU-to-OLT or ONU-to-ONU
• CPC Class Codes: H04J 14/0278 WDM optical network architectures
• CPC Class Codes: H04J 14/0283 WDM ring architectures
• CPC Class Codes: H04J 14/0287 Protection in WDM systems
• CPC Class Codes: H04J 14/0293 Optical channel protection

Abstract

An optical wavelength division coupler 11 wavelength-divides a wavelength multiplexed light to respective wavelength lights each of which is dropped to an optical gate switch 15-i (i=I˜n) and a light receiver 13-i by an optical coupler 12-i and supplied to an optical light fault monitor 14 through the light receiver 13-i. When the optical signal deterioration monitor 14 detects an optical loss of wavelength (OLOW), an optical loss of signal (OLOS) or an optical signal degrade (OSD) in wavelength lights processed by the optical coupler 12-i as a fault detection signal in an optical layer, a controller 19 controls the optical gate switch 15-i to cut off wavelength light passing therethrough and sends an optical alarm indication signal (AIS-O) to a downstream side. Therefore, when a loss of signal is detected by the light receiver 13-i, the optical signal deterioration monitor 14 can know the alarm indication signal (AIS) from the upstream side, removing the necessity of special hardware therefor.

Claims

1. An optical add-drop multiplexer comprising:

an optical wavelength division coupler for wavelength-dividing a wavelength multiplexed light input from one optical transmission line to a plurality of wavelength lights having different wavelengths;

a plurality of light receivers for receiving the respective wavelength lights having different wavelengths output from said optical wavelength division coupler;

a plurality of optical gate switches each for on-off controlling a light passing therethrough;

a plurality of light transmitters provided correspondingly to the plurality of said light receivers, each said light transmitter transmitting different one of the plurality of wavelength lights having different wavelengths constituting the wavelength multiplexed light; and

an optical wavelength multiplexer coupler for receiving light outputs of said optical gate switches and light outputs of said light transmitters and sending a wavelength multiplexed light to the other optical transmission line.

2. An optical add-drop multiplexer as claimed in claim 1, wherein each said optical gate switch comprises an input side optical transmission line for receiving a signal light, an impurity doped fiber connected to said input side optical transmission line, a pumping light source for supplying a pumping light to said impurity doped fiber and an output side optical transmission line connected to an output of said impurity doped fiber, wherein the signal light input to said input side optical transmission line is on-off controlled by controlling an intensity of the pumping light and the intensity of the signal light output to said output side optical transmission line is controlled by controlling the intensity of the pumping light during a time for which the signal light input to said input side optical transmission line is on.

3. An optical add-drop multiplexer comprising:

an optical wavelength division multiplex coupler connected to an optical circulator adapted to receive a wavelength multiplexed light from one optical transmission line and to output the wavelength multiplexed light to the other optical transmission line, for dividing a wavelength multiplexed light input from an input/output of said optical circulator to a plurality of wavelength lights having different wavelengths and for multiplexing a plurality of wavelength lights having different wavelength and supplying a resultant wavelength multiplexed light to said input/output of said optical circulator;

a plurality of first optical couplers connected to said optical wavelength division multiplex coupler, for receiving/sending a plurality of wavelength lights having different wavelengths with respect to said optical wavelength division multiplex coupler, respectively;

a plurality of light receivers connected to the plurality of said first optical couplers for receiving optical outputs of said first optical couplers, respectively;

a plurality of light transmitters provided correspondingly to the plurality of said light receivers for supplying the plurality of wavelength lights having different wavelengths constructing the wavelength multiplexed light;

a plurality of optical gate switches provided correspondingly to the plurality of wavelength-divided lights, each said optical gate switch for on-off controlling a light passing therethrough;

a plurality of second optical couplers provided correspondingly to the plurality of the wavelength-divided lights and connected to said light transmitters for receiving lights from said light transmitters, respectively, said second optical couplers being connected, on one sides thereof, to the optical inputs/outputs of said first optical couplers, respectively, and, on the other sides thereof, to one sides of said optical gate switches to input/output wavelength lights with respect thereto, respectively; and

a plurality of mirrors provided correspondingly to the plurality of wavelengthdivided lights and connected to the other sides of said optical gate switches, respectively, wherein the wavelength multiplexed light output from said light input/output of said optical circulator and received by said optical wavelength division multiplex coupler is output from said optical wavelength division multiplex coupler to said optical transmission line through said light output of said optical circulator.

4. An optical add-drop multiplexer comprising:

an optical wavelength division multiplex coupler for wavelength dividing a wavelength multiplexed light input from an optical transmission line on one hand and wavelength-multiplexing the wavelength divided lights and supplying a wavelengthmultiplexed light to said optical transmission line on the other hand;

a plurality of first optical couplers connected to said optical wavelength division multiplex coupler, said first optical couplers being adapted to input/output the wavelength lights having different wavelengths with respect to said optical wavelength division multiplex coupler on one hand and to drop the wavelength lights having different wavelengths, respectively, on the other hand;

a plurality of light receivers connected to the plurality of said first optical couplers for receiving the dropped optical outputs of said first optical couplers, respectively;

a plurality of light transmitters provided correspondingly to the plurality of said light receivers for supplying the plurality of wavelength lights having different wavelengths constructing the wavelength multiplexed light, respectively;

a plurality of optical gate switches provided correspondingly to the plurality of wavelength-divided lights, each said optical gate switch for on-off controlling a light passing therethrough;

a plurality of optical isolators provided correspondingly to the respective wavelength divided lights and adapted to pass only corresponding light outputs of said optical gate switches, respectively;

a plurality of second optical couplers provided correspondingly to the plurality of the wavelength-divided lights, said second optical couplers being connected to said light inputs/outputs of said first optical couplers, said second optical couplers being adapted to drop the respective wavelength-divided lights and to receive lights from respective said light transmitters; and

a plurality of third optical couplers provided correspondingly to the plurality of the wavelength-divided lights, said third optical couplers being connected to said light inputs/outputs of said second optical couplers, said second optical couplers being adapted to receive the light outputs of respective said optical isolators and output wavelength lights having different wavelengths from the wavelength of the output light of said optical isolators to said optical gate switches, wherein one of the respective wavelength-divided lights is passed through a path including one of said first optical couplers, one of said second optical couplers, one of said third optical couplers, one of said optical gate switches and one of said optical isolators, corresponding to one wavelength light, and returned to said optical wavelength division multiplex coupler through a path including another of said third optical couplers and another of said second optical coupler, corresponding to another wavelength light having wavelength adjacent to that of the one wavelength light, and said optical wavelength division multiplex coupler wavelength-multiplexes the returned lights.

5. An optical add-drop multiplexer comprising optical signal deterioration monitor means, wherein said optical signal deterioration monitor means comprises:

means for monitoring an optical signal fault by either detecting the optical loss of signal by determining presence or absence of a signal light on a basis of calculation of an optical S/N ratio from a ratio of intensity of light having wavelength within a wavelength range of a certain width including at least the signal light to intensity of spontaneously emitted light having wavelength within a different wavelength range of substantially the same width as the predetermined width or determining presence or absence of the signal light from intensity of light within a wavelength range of a certain width including the signal light, or detecting the optical loss of wavelength by monitoring wavelength deviation of the signal light from intensity of light within the wavelength range;

means for calculating an optical S/N ratio from a ratio of intensity of light within a wavelength range of a predetermined width including at least the signal light to intensity of spontaneously emitted light having wavelength within a different wavelength range of substantially the same width as the predetermined width and detecting the optical signal degrade when the optical SIN ratio becomes smaller than a predetermined threshold value; and

means for converting a fault signal into the optical alarm indication signal in an optical layer by cutting off a signal output correspondingly to an input when said optical signal deterioration monitor means detects in the input the fault signal of either the optical loss of signal, the optical loss of wavelength or the optical signal degrade.

6. An optical signal deterioration monitor system in which an optical add-drop multiplexer provided in each of nodes of an optical network, for adding, dropping or passing a wavelength multiplexed optical signal, monitors an optical signal fault within the optical network, said optical add-drop multiplexer comprising:

optical signal deterioration monitor means comprising

means for monitoring an optical signal fault by either detecting an optical loss of signal by determining presence or absence of a signal light on a basis of calculation of an optical S/N ratio from a ratio of intensity of light within a wavelength range of a predetermined width including at least the signal light to intensity of spontaneously emitted light having wavelength within a different wavelength range of substantially the same width as the predetermined width or determining presence or absence of the signal light from intensity of light within a wavelength range of a certain width including the signal light, or detecting the optical loss of wavelength by monitoring wavelength deviation of the signal light from intensity of light within the wavelength range;

means for calculating an optical SIN ratio from a ratio of intensity of light within a wavelength range of a predetermined width including at least the signal light to intensity of spontaneously emitted light having wavelength within a different wavelength range of substantially the same width as the predetermined width and detecting the optical signal degrade when the optical S/N ratio becomes smaller than a predetermined threshold value; and

means for converting a fault signal into the optical alarm indication signal in an optical layer by cutting off a signal output correspondingly to an input when said optical signal deterioration monitor means detects in the input the fault signal of either the optical loss of signal, the optical loss of wavelength or the optical signal degrade and noticing the optical alarm indication signal to said nodes on the downstream side.

7. An optical signal deterioration monitor system as claimed in claim 6, wherein a signal reproducing repeater is arranged on an upstream side of a location of said optical add-drop multiplexer at which a network fault is detected, and at least one line terminator connected to said optical layer is arranged between said optical add-drop multiplexer and said signal reproducing repeater, and wherein the network fault is recovered by sending a monitor signal issued by said signal reproducing repeater to said line terminator so that an occurrence of the network fault is noticed from said signal reproducing repeater to said line terminator when said signal reproducing repeater detects the network fault.

8. An optical signal deterioration monitor system as claimed in claim 6, wherein a signal reproducing repeater is arranged on an upstream side of a location of said optical add-drop multiplexer at which a network fault is detected, and said signal reproducing repeater has an optical alarm indication signal issuing function in an optical layer, and wherein the network fault is recovered by an optical path switching performed by said optical add-drop multiplexer in said optical layer according to a notice of the network fault to at least one of said optical repeater/amplifier on the downstream side of said signal reproducing repeater and said optical add-drop multiplexer and by a notice of network fault performed by a transmission line connected to said optical layer from said optical layer to said transmission line by converting the optical loss of signal of the network fault in said optical layer into the optical alarm indication signal.

9. An optical signal deterioration monitor system as claimed in claim 6, wherein a network management information is assigned to a wavelength range different from a main signal wavelength range to be processed by said optical wavelength add-drop multiplexer to perform a network information communication between said nodes independently from framing format.

10. An optical signal deterioration monitor system including an optical network having;

an optical add-drop multiplexer for adding, dropping or passing a wavelength multiplexed optical signal;

an optical repeater/amplifier for amplifying and repeating a wavelength multiplexed light; and

a line terminator for terminating an optical signal and converting the optical signal into a signal of SONET/SDH standard, wherein each of said optical add-drop multiplexer and said optical repeater/amplifier comprises;

optical signal deterioration monitor means including means for monitoring an optical signal fault by either detecting the optical loss of signal by determining presence or absence of a signal light on a basis of calculation of an optical S/N ratio from a ratio of intensity of light having wavelength within a wavelength range of a predetermined width including at least the signal light to intensity of spontaneously emitted light having wavelength within a different wavelength range of substantially the same width as the predetermined width or determining presence or absence of the signal light from intensity of light having wavelength within a certain wavelength range including the signal light, or detecting the optical loss of wavelength by monitoring wavelength deviation of the signal light from intensity of light having wavelength within the wavelength range;

means for calculating an optical S/N ratio from a ratio of intensity of light having wavelength within a wavelength range of a predetermined width including at least the signal light to intensity of spontaneously emitted light having wavelength within a different wavelength range of substantially the same width as the predetermined width and detecting the optical signal degrade when the optical S/N ratio becomes smaller than a predetermined threshold value; and

means for converting a fault signal into an optical alarm indication signal in an optical layer by cutting off a signal output correspondingly to an input when said optical signal deterioration monitor means detects in the input the fault signal of either the optical loss of signal, the optical loss of wavelength or the optical signal degrade and noticing the optical alarm indication signal to said nodes on the downstream side, wherein, in order to notice a network fault occurrence to said line terminator on the downstream side on the detection location of the network fault when the network fault is detected in a section layer of the SONET/SDH in said optical network, an optical signal cut-off fault in said network is monitored by at least one of the optical loss of signal and the optical alarm indication signal in said optical layer instead of an line alarm indication signal in the SONET/SDH layer output again to said line terminator to notice the network fault to said line terminator by reading in the line alarm indication signal assigned to a line overhead to identify the network fault.

11. An optical signal deterioration monitor system as claimed in claim 10, wherein, when a network fault occurs in said optical layer, said line terminator is forced to detect the loss of signal by converting the optical loss of signal into the optical alarm indication signal and noticing the network fault from said optical layer to the SONET/SDH layer.

12. An optical signal deterioration monitor system as claimed in claim 10, wherein a signal reproducing repeater of the SONET/SDH standard is arranged on the upstream side of the network fault detection location of said optical add-drop multiplexer and at least one line terminator of the SONET/SDH standard is arranged between said optical add-drop multiplexer and said signal reproducing repeater and wherein a recovery of the network fault is performed by activating an automatic protection system of the SONET/SDH standard by sending the line alarm indication signal issued by said signal reproducing repeater to said line terminator so that the occurrence of the network fault is noticed from said signal reproducing repeater to said line terminator of the SONET/SDH standard on the downstream side when the network fault is detected by said signal reproducing repeater.

13. An optical signal deterioration monitor system as claimed in claim 10, wherein a signal reproducing repeater of the SONET/SDH standard is arranged on the upstream side of the network fault detection location of said optical add-drop multiplexer and said signal reproducing repeater has an optical alarm indication signal issuing function in an optical layer, and wherein the network fault is recovered by either a switching of at least one of optical paths performed by said optical add-drop multiplexer in said optical layer according to a notice of the network fault to at least one of said optical repeater/amplifier and said optical wavelength add-drop multiplexer on the downstream side of said signal reproducing repeater or an automatic protection system of said SONET/SDH, which is performed by a notice of the network fault from said optical layer to said SONET/SDH layer by converting the optical loss of signal of the network fault in said optical layer into the optical alarm indication signal to notify said line terminator the detection of the loss of signal.

14. An optical signal deterioration monitor system as claimed in claim 10, wherein a network management information is assigned to a wavelength range different from a main signal wavelength range to perform a network information communication between said optical add-drop multiplexers forming nodes and between said optical add-drop multiplexers and said line terminator.

15. A ring network having a plurality of nodes connected in a ring by at least one transmission line, comprising an optical add-drop multiplexer provided in each of said nodes, wherein each said optical add-drop multiplexer detects a fault by using at least one of an optical loss of signal or an optical alarm indication signal and a fault recovery is performed by at least one of a switching to a protect transmission line and a reconfiguration of network.

16. A wavelength multiplexed light monitor system comprising an optical wavelength division multiplex coupler having two or more input ports and two or more output ports, and having a function of wavelength-multiplexing signal lights input from a plurality of optical transmission lines, a function of wavelength-dividing a wavelength-multiplexed light input from an optical transmission line to wavelength lights having different wavelengths and an optical router function of providing a regular correlation between said optical input ports and said optical output ports for every wavelength, wherein signal lights input from a plurality of optical transmission lines and having mutually different wavelengths are wavelength-multiplexed by said optical wavelength division multiplex coupler and output to an optical transmission line, a portion of the wavelength-multiplexed light is dropped to said optical wavelength division multiplex coupler and wavelength-divided to signal portions having the mutually different wavelengths, the signal portions being used as monitor lights.

17. A wavelength multiplexed light monitor system for use in an optical wavelength adddrop multiplexer, comprising:

an optical wavelength division coupler for wavelength-dividing a wavelengthmultiplexed light input from one optical transmission line to wavelength lights having different wavelengths;

a plurality of light receivers for respectively receiving the wavelength lights having the different wavelengths output from said optical wavelength division coupler;

a plurality of optical gate switches provided correspondingly to the plurality of said light receivers, for respectively on-off controlling the lights passing therethrough;

a plurality of light transmitters provided correspondingly to said light receivers, for sending optical signals having the different wavelengths constituting the wavelength multiplexed light;

an optical wavelength division multiplex coupler having two or more input ports and two or more output ports, said optical wavelength division multiplex coupler being adapted to wavelength-multiplex the plurality of the signal lights having the mutually different wavelengths output from the plurality of said optical gate switches or the plurality of said light transmitters and output the wavelength-multiplexed light to another optical transmission line and being adapted to wavelength divide the wavelength- multiplex ed signal light to wavelength lights having the different wavelengths by an optical router function providing a regular correlation between said optical input ports and said optical output ports for every wavelength; and

an optical monitor for monitoring the wavelength lights having the different wavelengths output from said optical wavelength division multiplex coupler.

18. A wavelength multiplexed light monitor in an optical wavelength add drop multiplexer, comprising:

an optical wavelength division multiplex coupler having two or more input ports and two or more output ports, and having a function of wavelength-multiplexing signal lights input from a plurality of optical transmission lines, a function of wavelength-dividing a wavelength multiplexed light input from an optical transmission line to wavelength lights having different wavelengths and an optical router function of providing a regular correlation between said optical input ports and said optical output ports for every wavelength;

an optical circulator for sending a wavelength- multiplexed light input from one optical transmission line to said input/output ports of said optical wavelength division multiplex coupler and for sending the wavelength- multiplexed light output from said input/output ports of said optical wavelength division multiplex coupler to another optical transmission line;

a plurality of first optical couplers provided correspondingly to the plurality of wavelength lights wavelength-divided by said optical wavelength division multiplex coupler, for receiving/sending the plurality of wavelength lights, on one hand, and dropping the plurality of wavelength lights;

a plurality of light receivers for receiving output lights having the different wavelengths from the plurality of said first optical couplers, respectively;

a plurality of light transmitters provided correspondingly to the plurality of said light receivers, respectively, for sending optical signals having the different wavelengths constituting the wavelength multiplexed light;

a plurality of optical gate switches provided correspondingly to the plurality of the wavelength-divided lights, for on-off controlling lights passing therethrough;

a plurality of second optical couplers provided correspondingly to the wavelengthdivided lights and connected, on one hand, to optical inputs/outputs of said first optical couplers, respectively, and, on the other hand, to one sides of said optical gate switches, for receiving/sending lights with respect to said first optical couplers and said optical gate switches, said second optical couplers being adapted to receive the lights from said light transmitters;

a plurality of reflection mirrors provided correspondingly to the respective wavelength-divided lights and connected to the other sides of said optical gate switches;

a plurality of third optical couplers for dropping the wavelength multiplexed light output from said input/output ports of said optical wavelength division multiplex coupler and supplying the dropped wavelength- multiplexed light to input/output ports different from said input/output ports of said optical wavelength division multiplex coupler; and

an optical monitor for monitoring the plurality of wavelength lights obtained by redividing the wavelength- multiplexed light input from said third optical couplers by said optical wavelength division multiplex coupler.

19. In an optical add-drop multiplexer comprising:

an optical wavelength division multiplex coupler having two or more input ports and two or more output ports, and having an optical router function providing a regular correlation between the optical input ports and the optical output ports for every wavelength by wavelength-dividing an input wavelength-multiplexed light from an optical transmission line to wavelength lights having different wavelengths and wavelength multiplexing signal lights input from a plurality of optical transmission lines;

a plurality of first optical couplers provided correspondingly to the plurality of wavelength lights wavelength-divided by said optical wavelength division multiplex coupler, for receiving/sending the plurality of wavelength lights, on one hand, and dropping the plurality of wavelength lights, on the other hand;

a plurality of light transmitters provided correspondingly to the plurality of said light receivers, respectively, for sending optical signals having the different wavelengths constituting the wavelength multiplexed light;

a plurality of optical gate switches provided correspondingly to the plurality of the wavelength-divided lights, for on-off controlling lights passing therethrough;

a plurality of optical isolators provided correspondingly to the plurality of the wavelength-divided lights, for passing only lights corresponding to said gate switches;

a plurality of second optical couplers provided correspondingly to the wavelengthdivided lights and connected, on one hand, to optical inputs/outputs of said first optical couplers, respectively, and, on the other hand, to one sides of said optical gate switches, for receiving/sending lights with respect to said first optical couplers and said optical gate switches, said second optical couplers being adapted to receive the lights from said light transmitters; and

a plurality of third optical couplers provided correspondingly to the plurality of the wavelength lights for receiving/sending the plurality of the wavelength lights, receiving the light outputs of said optical isolators and supplying lights having wavelengths different from those of the light output to said optical gate switches, wherein each of the wavelength-divided lights from said optical wavelength division multiplex coupler passes through said first optical coupler, said second optical coupler, said third optical coupler, said optical gate switch and said optical isolator, and, then, through said third optical coupler for an adjacent light having wavelength adjacent to that of the each light and said second optical coupler for the adjacent light back to said optical wavelength division multiplex coupler and the lights are wavelength-multiplexed by said optical wavelength division multiplex coupler and output to another transmission line,

a wavelength-multiplexed light monitor comprising;

a fourth optical coupler for dropping a portion of the wavelength multiplexed light sent to said another optical transmission line and supplying the dropped light portion to an optical port of said optical wavelength division multiplex coupler different from said output port thereof, and

a plurality of optical monitors for receiving a plurality of wavelength lights having different wavelengths obtained by re-dividing the wavelength-multiplexed light input from the fourth optical coupler by said optical wavelength division multiplex coupler and monitoring the plurality of the different wavelength lights.

20. A wavelength multiplexed light monitor for use in a wavelength multiplexed repeater/amplifier, comprising:

an optical wavelength division coupler for wavelength-dividing a wavelengthmultiplexed light input from one optical transmission line to a plurality of wavelength lights having different wavelengths;

a plurality of optical amplifiers provided correspondingly to the plurality of the wavelength lights wavelength-divided by said optical wavelength division coupler;

an optical wavelength division multiplex coupler having two or more input ports and two or more output ports, and having an optical router function providing a regular correlation between the optical input ports and the optical output ports for every wavelength by wavelength-dividing an input wavelength-multiplexed light from an optical transmission line to wavelength lights having different wavelengths and wavelength multiplexing signal lights input from a plurality of optical transmission lines; and

an optical monitor for monitoring the wavelength-divided lights output from said optical wavelength division multiplex coupler.

21. A wavelength multiplexed light monitor for use in a wavelength multiplexed repeater/amplifier, comprising:

an optical wavelength division multiplex coupler having two or more input ports and two or more output ports, and having a function of wavelength-multiplexing signal lights input from a plurality of optical transmission lines, a function of wavelength-dividing a wavelength multiplexed light input from an optical transmission line and an optical router function providing a regular correlation between the optical input ports and the optical output ports for every wavelength;

an optical circulator for sending a wavelength-multiplexed light input from one optical transmission line to said input/output ports of said optical wavelength division multiplex coupler and sending a wavelength- multiplexed light output from said input/output ports of said optical wavelength division multiplex coupler to another optical transmission line;

a plurality of optical amplifiers connected to said optical wavelength division multiplex coupler, respectively, for amplifying the plurality of the wavelength lights wavelength-divided by said optical wavelength division multiplex coupler and sending amplified wavelength lights to said optical wavelength division multiplex coupler;

a plurality of reflection mirrors for reflecting outputs of said optical amplifiers, respectively;

a third optical coupler for dropping a portion of the wavelength multiplexed light optically amplified by said optical amplifier, wavelength-multiplexed by said optical wavelength division multiplex coupler and output from said input/output of said optical wavelength division multiplex coupler and sending the portion to a port of said optical wavelength multiplex coupler different from said input/output ports thereof; and

a plurality of optical monitors for monitoring the respective wavelength-divided signal lights obtained by re-dividing the wavelength multiplexed light input from said third optical coupler.

22. In a wavelength-multiplexed light repeater/amplifier comprising:

an optical wavelength division multiplex coupler having two or more input ports and two or more output ports, and having a function of wavelength-multiplexing signal lights input from a plurality of optical transmission lines, a function of wavelength-dividing a wavelength multiplexed light input from an optical transmission line and an optical router function providing a regular correlation between the optical input ports and the optical output ports for every wavelength;

a plurality of first optical couplers provided correspondingly to a plurality of wavelength lights obtained by wavelength-dividing a wavelength-multiplexed light input from one optical transmission line, for receiving/sending the wavelength-divided lights from said optical wavelength division multiplex coupler, respectively, on one hand, and dropping portions of the wavelength-divided lights from said optical wavelength division multiplex coupler, respectively, on the other hand;

a plurality of optical amplifiers connected to one optical input/output of said first optical couplers, respectively;

a plurality of optical isolators provided correspondingly to the wavelength-divided lights, for passing only wavelength lights corresponding to said optical amplifiers; and

a plurality of second optical couplers for receiving the optical outputs of said optical isolators and sending lights having wavelengths different from the wavelengths of the optical outputs of said optical isolators, wherein each of the wavelength-divided lights from said optical wavelength division multiplex coupler passes through said first optical coupler, said optical amplifier and said optical isolator, and, then, through said second optical coupler for an adjacent light having wavelength adjacent to that of the each light back to said optical wavelength division multiplex coupler and the lights are wavelength multiplexed by said optical wavelength division multiplex coupler and output to another transmission line,

a wavelength-multiplexed light monitor comprising;

a third optical coupler for dropping a portion of the wavelength multiplexed light sent to said another optical transmission line and supplying the dropped light portion to an optical port of said optical wavelength division multiplex coupler different from said output port thereof; and

a plurality of optical monitors for receiving a plurality of wavelength lights obtained by re-dividing the wavelength-multiplexed light input from the third optical coupler by said optical wavelength division multiplex coupler and monitoring the plurality of the wavelength lights, respectively.

23. A wavelength-multiplexed light monitor for use in a wavelength multiplexed light gain equalizer, comprising:

an optical wavelength division coupler for wavelength- dividing a wavelengthmultiplexed light input from one optical transmission line to a plurality of wavelength lights having different wavelengths;

a plurality of optical attenuators provided correspondingly to the plurality of the wavelength lights wavelength-divided by said optical wavelength division coupler, respectively;

an optical wavelength division multiplex coupler having two or more input ports and two or more output ports, and having a function of wavelength-multiplexing signal lights input from a plurality of optical transmission lines, a function of wavelength-dividing a wavelength multiplexed light input from an optical transmission line and an optical router function providing a regular correlation between the optical input ports and the optical output ports for every wavelength; and

a plurality of optical monitors for monitoring the respective wavelength lights obtained by wavelength-dividing the wavelength multiplexed light by said optical wavelength division multiplex coupler.

24. A wavelength multiplexed light monitor for use in a wavelength multiplexed light gain equalizer, comprising:

an optical wavelength division multiplex coupler having two or more input ports and two or more output ports, and having a function of wavelength-multiplexing signal lights input from a plurality of optical transmission lines, a function of wavelength-dividing a wavelength multiplexed light input from an optical transmission line and an optical router function providing a regular correlation between the optical input ports and the optical output ports for every wavelength;

an optical circulator for sending a wavelength multiplexed-light input from one optical transmission line to input/output ports of said optical wavelength division multiplex coupler and sending a wavelength multiplexed light output from said input/output ports of said optical wavelength division multiplex coupler to another optical transmission line;

a plurality of optical attenuators provided correspondingly to the plurality of the wavelength lights divided by said optical wavelength division coupler for attenuating the plurality of the wavelength lights and sending the attenuated wavelength lights to said optical wavelength division multiplex coupler, respectively;

a plurality of reflection mirrors for reflecting outputs of said optical attenuators, respectively;

a third optical coupler for dropping a portion of the wavelength multiplexed light optically attenuated by said optical attenuators, wavelength-multiplexed by said optical wavelength division multiplex coupler and output from said input/output ports of said optical wavelength division multiplex coupler and sending the portion to a port of said optical wavelength multiplex coupler different from said input/output ports thereof, and

a plurality of optical monitors for monitoring the respective wavelength lights obtained by re-dividing the wavelength-multiplexed light input from said third optical coupler by said optical wavelength division multiplex coupler.

25. In a wavelength-multiplexed light gain equalizer comprising:

an optical wavelength division multiplex coupler having two or more input ports and two or more output ports, and having a optical router function of wavelength-dividing an input wavelength-multiplexed light to a plurality of wavelength lights, wavelengthmultiplexing signal lights input from a plurality of optical transmission lines, and providing a regular correlation between the optical input ports and the optical output ports for every wavelength;

a plurality of first optical couplers provided correspondingly to the plurality of the wavelength lights obtained by wavelength-dividing a wavelength-multiplexed light input from one optical transmission line by said optical wavelength division multiplex coupler, for receiving/sending the wavelength-divided lights from said optical wavelength division multiplex coupler, respectively, on one hand, and dropping portions of the wavelengthdivided lights from said optical wavelength division multiplex coupler, respectively, on the other hand;

a plurality of optical attenuators connected to one optical inputs/outputs of said first optical couplers, respectively;

a plurality of optical isolators provided correspondingly to the wavelength-divided lights, for passing only wavelength lights corresponding to said optical attenuators, respectively; and

a plurality of second optical couplers for receiving the optical outputs of said optical isolators and sending lights having wavelengths different from the wavelengths of the optical outputs of said optical isolators to said optical attenuators, respectively, wherein each of the wavelength-divided lights from said optical wavelength division multiplex coupler passes through said first optical coupler, said optical attenuator and said optical isolator, and, then, through said second optical coupler for an adjacent light having wavelength adjacent to that of the each light back to said optical wavelength division multiplex coupler and the lights are wavelength-multiplexed by said optical wavelength division multiplex coupler and output to another transmission line, a wavelength-multiplexed light monitor comprising;

a third optical coupler for dropping a portion of the wavelength multiplexed light output to said another optical transmission line and supplying the dropped light portion to an optical port of said optical wavelength division multiplex coupler different from said output port thereof, and a plurality of optical monitors for receiving a plurality of wavelength lights obtained by re-dividing the wavelength-multiplexed light input from the third optical coupler by said optical wavelength division multiplex coupler and monitoring the plurality of the wavelength lights, respectively.