Optical multiplexing / demultiplexing device, optical transmission system, and optical multiplexing / demultiplexing method

Abstract

In order to suppress the occurrence of the optical power difference between wavelength bands by using a simple structure, this light multiplexing / demultiplexing device comprises: a first demultiplexer that demultiplexes an inputted first wavelength-multiplexed signal light into a first signal light of a first wavelength band and a second signal light of a second wavelength band and outputs the first signal light and the second signal light; a first amplifier that amplifies the second signal light inputted from the first demultiplexer; a light processor that, on the basis of the inputted second signal light and an inputted third signal light of the second wavelength band, outputs a fourth signal light; and a first multiplexer that multiplexes the fourth signal light with the first signal light outputted from the first demultiplexer. The gain of the first amplifier is set such that the difference between the optical power of the first signal light outputted from the first multiplexer and the optical power of the fourth signal light outputted from the first multiplexer is equal to or less than a predetermined value.

Description

[Technical field]

[0001] The present invention relates to an optical multiplexing / demultiplexing device and an optical multiplexing / demultiplexing method, and more particularly to an optical multiplexing / demultiplexing device and an optical multiplexing / demultiplexing method that are provided with a function for adjusting the optical power of multiplexed wavelength-multiplexed signal light. [Background technology]

[0002] In an optical transmission system including devices (submarine devices) such as optical branching devices and optical multiplexing / demultiplexing devices installed on the seabed, a wideband wavelength multiplexed signal light ranging from the C-band to the L-band is transmitted. In order to transmit such a wideband wavelength multiplexed signal light over a long distance, an optical amplifier capable of amplifying the wavelength multiplexed signal light in both the C-band and the L-band is required. In this specification, the C-band refers to a wavelength band of 1530 nm or more and less than 1565 nm, and the L-band refers to a wavelength band of 1565 nm or more and less than 1625 nm. In addition, the wavelength multiplexed signal light is hereinafter referred to as "WDM signal light". WDM is an abbreviation for Wavelength Division Multiplexed. Furthermore, WDM signal light in the wavelength band of the C-band is referred to as "C-band WDM signal light", and WDM signal light in the wavelength band of the L-band is referred to as "L-band WDM signal light". An example of the above-mentioned optical transmission system is disclosed in Patent Document 1.

[0003] Fig. 8 is a block diagram showing the configuration of a general optical amplifier 900 described in Patent Document 1. Fig. 8 also shows the spectrum of WDM signal light at each portion, with the vertical axis (height) representing optical power and the horizontal axis representing wavelength. The WDM signal light input to the optical amplifier 900 is demultiplexed into C-band WDM signal light and L-band WDM signal light by a demultiplexer 901. The demultiplexed C-band WDM signal light and L-band WDM signal light are amplified by a C-band EDFA 902 and an L-band EDFA 903, respectively. These amplified WDM signal lights are wavelength-multiplexed by a multiplexer 904 and output from the optical amplifier 900. It should be noted that EDFA stands for Erbium-Doped Optical Fiber Amplifier. [Prior art documents]

Patent Document

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a general optical submarine transmission system that transmits WDM signal light including C-band and L-band signal light, in order to compensate for the attenuation of the WDM signal light, it is necessary to install both a C-band EDFA 902 and an L-band EDFA 903 in the submarine device. Further, in order to excite these optical amplifiers, two excitation light sources are required, and two wavelength multiplexers for multiplexing the excitation light and the WDM signal light are also required. As a result, for example, when transmitting WDM signal light including C-band and L-band signal light as compared with the case of transmitting only C-band WDM signal light, the number of optical components constituting the optical amplifier doubles.

[0006] On the other hand, the accommodation space for the components inside the submarine device is limited, and in recent years, the case where components to which a plurality of optical fibers are connected (for example, a WSS (Wavelength Selective Switch)) are installed in the submarine device is also increasing. For this reason, the accommodation space for the components of the optical amplifier may be further limited. Also, in order to reduce the optical components accommodated in the submarine device, for example, when passive components such as a WSS are arranged only in the path of the C-band WDM signal light, a large difference in loss occurs in the submarine device between the C-band WDM signal light and the L-band WDM signal light. As a result, a difference occurs between the optical powers of the C-band WDM signal light and the L-band WDM signal light output from the submarine device. Such a difference in optical power between wavelength bands may affect the transmission quality. (Object of the Invention) An object of the present invention is to provide a technique for suppressing the occurrence of a difference in optical power between wavelength bands in a wavelength multiplexer / demultiplexer used in an optical submarine transmission system with a simple configuration.

Means for Solving the Problems

[0007] The optical multiplexing and demultiplexing device of the present invention includes: a first demultiplexing means for demultiplexing the input first wavelength-division multiplexed signal light into a first signal light in a first wavelength band and a second signal light in a second wavelength band and outputting each of them; a first amplification means for amplifying the second signal light input from the first demultiplexing means; an optical processing means for outputting a fourth signal light based on the input second signal light and a third signal light in the second wavelength band; and a first multiplexing means for multiplexing the fourth signal light and the first signal light output from the first demultiplexing means. The gain of the first amplification means is set such that the difference between the optical power of the first signal light output from the first multiplexing means and the optical power of the fourth signal light output from the first multiplexing means is equal to or less than a predetermined value.

[0008] The optical multiplexing and demultiplexing method of the present invention includes the steps of demultiplexing, by a demultiplexing means, the input first wavelength-division multiplexed signal light into a first signal light in a first wavelength band and a second signal light in a second wavelength band, amplifying the second signal light, outputting a fourth signal light based on the amplified second signal light and a third signal light in the second wavelength band input, and multiplexing, by a multiplexing means, the fourth signal light and the first signal light output from the demultiplexing means. The gain of the amplification of the second signal light is set such that the difference between the optical power of the first signal light output from the multiplexing means and the optical power of the fourth signal light output from the multiplexing means is equal to or less than a predetermined value.

Advantages of the Invention

[0009] The present invention can suppress the occurrence of a difference in optical power between wavelength bands with a simple configuration in an optical multiplexing and demultiplexing device.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0011] Embodiments of the present invention will be described below with reference to the drawings. The directions of the arrows shown in the figures are for illustration and are not intended to limit the direction of the signal light. In each embodiment and the drawings, the same reference numerals are assigned to the elements that have already appeared, and duplicate explanations are omitted.

[0012] (First Embodiment) FIG. 1 is a block diagram showing a configuration example of the undersea transmission system 1 in the first embodiment of the present invention. The undersea transmission system 1 includes terminal stations 101 - 103, optical repeaters 111 - 113, an optical branching device 121, and an optical multiplexer / demultiplexer 201. The terminal stations 101 - 103 are installed on land and have an interface function between the land transmission system (not shown) and the undersea transmission system 1. The optical repeaters 111 - 113, the optical branching device 121, and the optical multiplexer / demultiplexer 201 are installed underwater. The undersea cables 51 - 55 and 61 - 65 are undersea cables including optical fiber transmission paths that connect between these devices.

[0013] The terminal station 101 is equipped with an optical transmitter and transmits the WDM signal light 301 in which the C-band WDM signal light and the L-band WDM signal light are wavelength multiplexed to the optical repeater 111. The terminal station 102 is equipped with an optical receiver and receives the WDM signal light 304 from the optical repeater 112. The terminal station 103 is equipped with an optical transmitter and an optical receiver, receives the WDM signal light 302 from the optical repeater 113, and transmits the WDM signal light 303 in which the C-band WDM signal light and the L-band WDM signal light are wavelength multiplexed to the optical repeater 113.

[0014] The optical branching device 121 controls the connection between the submarine cables 52, 53, 63, and 64. In this embodiment, the optical branching device 121 connects the submarine cable 52 and the submarine cable 53, and also connects the submarine cable 63 and the submarine cable 64. By such a connection, the WDM signal light 301 transmitted by the terminal station 101 is transmitted to the optical multiplexer / demultiplexer 201 via the optical repeater 111. Also, the WDM signal light 304 transmitted by the optical multiplexer / demultiplexer 201 is transmitted to the terminal station 102 via the optical repeater 112. The function of the optical branching device 121 may be realized by an optical switch included in the optical branching device 121. The optical switch may be controlled by a control signal transmitted from any one of the terminal stations 101-103 to the optical multiplexer / demultiplexer 201.

[0015] The optical repeaters 111 and 112 each include a set of optical amplifiers for amplifying the WDM signal light in the C-band and the L-band. The optical repeaters 111 and 112 of this embodiment may include the general optical amplifier 900 described in FIG. 8 in order to amplify the signal light in the C-band and the L-band. For example, the optical repeater 111 amplifies the WDM signal light 301 received from the terminal station 101 using a C-band EDFA and an L-band EDFA. The optical repeater 112 amplifies the WDM signal light 304 received from the optical branching device 121 using a C-band EDFA and an L-band EDFA.

[0016] The optical repeater 113 may include two sets of the optical amplifier 900 described in FIG. 8. The optical repeater 113 amplifies the WDM signal light 302 received from the optical multiplexer / demultiplexer 201 and transmits it to the terminal station 103. Also, the optical repeater 113 amplifies the WDM signal light 303 received from the terminal station 103 and transmits it to the optical multiplexer / demultiplexer 201.

[0017] The optical multiplexing / demultiplexing device 201 receives a WDM signal light 301 from the optical branching device 121, and receives a WDM signal light 303 from the optical repeater 113. The optical multiplexing / demultiplexing device 201 processes the WDM signal light 301 and 303, and generates WDM signal light 302 and 304 based on the WDM signal light 301 and 303. Then, the optical multiplexing / demultiplexing device 201 transmits the WDM signal light 302 to the optical repeater 113, and transmits the WDM signal light 304 to the optical branching device 121. Details of the optical multiplexing / demultiplexing device 201 will be described with reference to FIG. 2.

[0018] 2 is a block diagram showing an example of the configuration of the optical multiplexing and demultiplexing device 201. The optical multiplexing and demultiplexing device 201 includes demultiplexers 211 and 212, multiplexers 221 and 222, C-band EDFAs 231 and 232, and a WSS 241.

[0019] The demultiplexer 211 separates the WDM signal light 301 received from the optical branching device 121 via the undersea cable 53 into a C-band WDM signal light and an L-band WDM signal light. The demultiplexer 212 separates the WDM signal light 303 received from the terminal station 103 via the undersea cable 62 into a C-band WDM signal light and an L-band WDM signal light.

[0020] The C-band EDFA 231 amplifies the C-band WDM signal light separated in the demultiplexer 211. The C-band EDFA 232 amplifies the C-band WDM signal light separated in the demultiplexer 212.

[0021] The WSS241 is a wavelength selective switch having two input ports P1 and P2, and two output ports P3 and P4. The WSS241 is a device capable of outputting a C-band WDM signal light including a signal light of a predetermined wavelength from the C-band WDM signal lights input from P1 and P2 from P3 and P4. The WSS241 has a function of setting, from outside the WSS241, the relationship between the wavelengths of the signal lights input from P1 and P2 and the wavelengths of the signal lights output from P3 and P4. Such a function of the WSS241 is well known. The optical multiplexer / demultiplexer 201 may include a control circuit for controlling the WSS241. The control circuit may control the WSS241 based on an instruction from any one of the terminal stations 101 - 103.

[0022] The C-band WDM signal light amplified in the C-band EDFA 231 is input from P1 to the WSS241. The C-band WDM signal light amplified in the C-band EDFA 232 is input from P2 to the WSS241. Based on these C-band WDM signal lights, the WSS241 generates a C-band WDM signal light to be transmitted to the terminal station 102 and a C-band WDM signal light to be transmitted to the terminal station 103. The C-band WDM signal light generated by the WSS241 and to be transmitted to the terminal station 102 is multiplexed with the L-band WDM signal light input from the demultiplexer 212 in the multiplexer 222. The WDM signal light multiplexed in the multiplexer 222 is transmitted as the WDM signal light 304 to the optical branching device 121. On the other hand, the C-band WDM signal light generated by the WSS241 and to be transmitted to the terminal station 103 is multiplexed with the L-band WDM signal light input from the demultiplexer 211 in the multiplexer 221. The WDM signal light multiplexed in the multiplexer 221 is transmitted as the WDM signal light 302 to the optical repeater 113.

[0023] In the optical multiplexer / demultiplexer 201, the L-band WDM signal light included in the WDM signal light 301 transmitted from the terminal station 101 is transmitted to the terminal station 103 via the demultiplexer 211 and the multiplexer 221. The L-band WDM signal light included in the WDM signal light 303 transmitted from the terminal station 103 is transmitted to the terminal station 102 via the demultiplexer 212 and the multiplexer 222.

[0024] In addition, the C-band WDM signal light included in the WDM signal light 301 transmitted from the terminal station 101 is processed in the WSS 241 included in the optical multiplexer / demultiplexer 201 and transmitted to one or both of the terminal station 102 and the terminal station 103. The C-band WDM signal light included in the WDM signal light 303 transmitted from the terminal station 103 is processed in the WSS 241 included in the optical multiplexer / demultiplexer 201 and transmitted to one or both of the terminal station 102 and the terminal station 103.

[0025] FIG. 3 is a diagram for explaining an operation example of the optical multiplexer / demultiplexer 201 in the first embodiment. [1] to [5] in the figure schematically show the spectra of the WDM signal light at respective locations, with the vertical axis (height) being the optical power and the horizontal axis being the wavelength. The optical multiplexer / demultiplexer 201 receives the WDM signal light 301 ([1]). The demultiplexer 211 demultiplexes the WDM signal light 301 into a C-band WDM signal light and an L-band WDM signal light. The C-band EDFA 231 amplifies the demultiplexed C-band WDM signal light and inputs the amplified C-band WDM signal light ([2]) to P1 of the WSS 241.

[0026] In FIG. 3, the WSS 241 outputs the C-band WDM signal light input to P1 as it is to the multiplexer 221. Here, the optical power of the C-band WDM signal light is attenuated by the WSS 241 ([3]). Therefore, the gain of the C-band EDFA 231 is set to a value capable of compensating for the loss in the WSS 241 of the C-band WDM signal light transmitted from the demultiplexer 211 via the WSS 241 to the multiplexer 221. The multiplexer 221 multiplexes the L-band WDM signal light ([4]) input from the demultiplexer 211 and the C-band WDM signal light ([3]) input from the WSS 241, and outputs it as the WDM signal light 302 ([5]). The WDM signal light 302 is amplified by the optical repeater 113 and transmitted to the terminal station 103.

[0027] The optical multiplexing and demultiplexing device 201 shown in FIG. 3 can compensate for the loss when the C-band WDM signal light passes through the WSS 241 by the C-band EDFA 231. As a result, even when only the C-band WDM signal light in the optical multiplexing and demultiplexing device 201 suffers the loss by the WSS 241, the generation of the optical power difference between the C-band WDM signal light and the L-band WDM signal light included in the WDM signal light 302 can be suppressed. Thereby, for example, the variation in the quality for each wavelength band of the signal light included in the WDM signal light 302 can be suppressed. In other words, the gain of the C-band EDFA 231 may be set to reduce the difference between the optical power of the L-band WDM signal light output from the multiplexer 221 and the optical power of the C-band WDM signal light output from the multiplexer 221. Alternatively, the gain of the C-band EDFA 231 may be set so that the difference between the optical power of the L-band WDM signal light output from the multiplexer 221 and the optical power of the C-band WDM signal light output from the multiplexer 221 becomes equal to or less than a predetermined value. The predetermined value is, for example, the maximum value allowed in terms of the transmission quality of the WDM signal light for the difference between the optical power of the L-band WDM signal light and the optical power of the C-band WDM signal light included in the same WDM signal light.

[0028] The optical multiplexing and demultiplexing device 201 having such a configuration can suppress the generation of the optical power difference between wavelength bands with a simple configuration. The reason is that an EDFA is prepared only for the C-band WDM signal light that undergoes the process by the WSS 241 in the optical multiplexing and demultiplexing device 201, and the decrease in the optical power of the C-band WDM signal light passing through the WSS 241 is compensated.

[0029] (Another representation of the optical multiplexing and demultiplexing device of the first embodiment) The effect of the optical multiplexing and demultiplexing device 201 described with reference to FIG. 2 can also be obtained by the following configuration. The reference numerals in parentheses indicate the corresponding reference numerals in FIG. 3. That is, the optical multiplexing and demultiplexing device (201) includes a first demultiplexing means (211), a first amplifying means (231), an optical processing means (241), and a first multiplexing means (221).

[0030] The first wavelength division means (211) divides the input first wavelength division multiplexed signal light (301) into a first signal light in a first wavelength band and a second signal light in a second wavelength band, and outputs each of them. The first amplification means (231) amplifies the second signal light input from the first wavelength division means (211). The optical processing means (241) outputs a fourth signal light based on the input second signal light and the input third signal light in the second wavelength band. The first multiplexing means (221) multiplexes the fourth signal light and the first signal light output from the first wavelength division means (211).

[0031] And the gain of the first amplification means (231) is set so that the difference between the optical power of the first signal light output from the first multiplexing means (221) and the optical power of the fourth signal light output from the first multiplexing means (221) is equal to or less than a predetermined value.

[0032] The optical multiplexer / demultiplexer having such a configuration can also suppress the occurrence of a difference in optical power between wavelength bands with a simple configuration.

[0033] (First modification example of the optical multiplexer / demultiplexer 201) FIG. 4 is a diagram showing a first modification example of the optical multiplexer / demultiplexer 201. The optical multiplexer / demultiplexer 201 shown in FIG. 4 may further include an optical attenuator 251 between the demultiplexer 211 and the multiplexer 221. The optical attenuator 251 is an optical component whose attenuation amount can be controlled by external control, and attenuates the optical power of the L-band WDM signal light ([4]). By using the optical attenuator 251, only the optical power of the L-band WDM signal light ([6]) can be independently adjusted. The attenuation amount of the optical attenuator 251 may be controlled by a control circuit provided in the optical multiplexer / demultiplexer 201.

[0034] (Second modification example of the optical multiplexer / demultiplexer 201) FIG. 5 is a diagram showing a second modification of the optical multiplexing / demultiplexing device 201. In FIG. 5, an optical monitor 261 is arranged at the output of the multiplexer 221. The optical monitor 261 is a known optical component including, for example, an optical coupler, an optical filter, and a photodiode. The optical monitor 261 outputs an electrical signal having an amplitude corresponding to the optical power of the WDM signal light 302 output from the multiplexer 221 to the control circuit 262 for each predetermined wavelength band. The predetermined wavelength band is, for example, but not limited to, the C band and the L band. The control circuit 262 controls the gain of the C-band EDFA 231 so that the optical power of the C-band WDM signal light and the optical power of the L-band WDM signal light included in the WDM signal light 302 become the same based on the amplitude of the electrical signal output from the optical monitor 261. When the optical multiplexing / demultiplexing device 201 includes the optical attenuator 251, the control circuit 262 may control the gain of the C-band EDFA 231 and the attenuation amount of the optical attenuator 251 based on the amplitude of the electrical signal output from the optical monitor 261.

[0035] Also in these first and second modifications, the optical multiplexing / demultiplexing device 201 can suppress the occurrence of a difference in optical power between wavelength bands with a simple configuration.

[0036] (Second Embodiment) FIG. 6 is a diagram for explaining an operation example of the optical multiplexing / demultiplexing device 201 in the second embodiment. The configuration of the optical multiplexing / demultiplexing device 201 in this embodiment is the same as that in FIG. 2. In the spectrum (

[11] -

[16] ) of the WDM signal light in FIG. 6, the spectrum of the WDM signal light included in the WDM signal light 301 is shown by a solid line, and the spectrum of the WDM signal light included in the WDM signal light 303 is shown by a broken line. The optical multiplexing / demultiplexing device 201 receives the WDM signal light 301 (

[11] ) from the optical branching device 121 and receives the WDM signal light 303 (

[14] ) from the optical repeater 113. The demultiplexer 211 demultiplexes the WDM signal light 301 received from the optical branching device 121 into a C-band WDM signal light and an L-band WDM signal light. The C-band EDFA 231 amplifies the C-band WDM signal light demultiplexed by the demultiplexer 211. The demultiplexer 212 demultiplexes the WDM signal light 303 received from the optical repeater 113 into a C-band WDM signal light and an L-band WDM signal light. The C-band EDFA 232 amplifies the C-band WDM signal light demultiplexed by the demultiplexer 212.

[0037] The WSS241 wavelength-division multiplexes the C-band WDM signal light input from the C-band EDFA231 to P1 and the C-band WDM signal light input from the C-band EDFA232 to P2, and outputs the result from P4 to the multiplexer 222. Here, it is assumed that the wavelengths of the carriers of the two C-band WDM signal lights wavelength-division multiplexed in the WSS241 do not overlap. The multiplexer 222 multiplexes the L-band WDM signal light (

[12] ) input from the demultiplexer 212 and the C-band WDM signal light input from the WSS241. The multiplexer 222 transmits the multiplexed WDM signal light as the WDM signal light 304 (

[16] ) to the optical branching device 121. No WDM signal light is output from P3 of the WSS241. The multiplexer 221 transmits only the L-band WDM signal light (

[12] ) included in the WDM signal light 301 as the WDM signal light 302 (

[13] ) to the terminal station 103.

[0038] In this embodiment, the C-band WDM signals included in the WDM signal light 304 include two C-band WDM signal lights, namely, the C-band WDM signal light included in the WDM signal light 301 and the C-band WDM signal light included in the WDM signal light 303. The C-band EDFA231 amplifies the C-band WDM signal light included in the WDM signal light 301. The C-band EDFA232 amplifies the C-band WDM signal light included in the WDM signal light 303. The gains of the C-band EDFA231 and 232 are each set so as to suppress the occurrence of a difference in optical power between the C-band WDM signal light and the L-band WDM signal light in the WDM signal light 304 transmitted from the multiplexer 222.

[0039] The optical multiplexer / demultiplexer 201 of this embodiment having such a configuration can transmit the C-band WDM signal light transmitted by the terminal station 101 and the L-band WDM signal light and C-band WDM signal light transmitted by the terminal station 103 to the terminal station 102. And since the optical multiplexer / demultiplexer 201 of this embodiment does not need to include an EDFA for the L-band WDM signal light, it has a simple configuration and can suppress the occurrence of a difference in optical power between wavelength bands.

[0040] (Third Embodiment) FIG. 7 is a diagram for explaining an operation example of the optical multiplexing and demultiplexing apparatus 201 in the third embodiment. In the spectra of the WDM signal lights (

[21] -

[26] ) in FIG. 7, the spectrum of the WDM signal light included in the WDM signal light 301 is indicated by a solid line, and the spectrum of the WDM signal light included in the WDM signal light 303 is indicated by a broken line.

[0041] In FIG. 7, the optical multiplexing and demultiplexing apparatus 201 receives the WDM signal light 301 (

[21] ) from the optical branching device 121 and receives the WDM signal light 303 (

[24] ) from the optical repeater 113. The demultiplexer 211 demultiplexes the WDM signal light 301 received from the optical branching device 121 into a C-band WDM signal light and an L-band WDM signal light. The C-band EDFA 231 amplifies the C-band WDM signal light demultiplexed by the demultiplexer 211. The demultiplexer 212 demultiplexes the WDM signal light 303 received from the optical repeater 113 into a C-band WDM signal light and an L-band WDM signal light. The C-band EDFA 232 amplifies the C-band WDM signal light demultiplexed by the demultiplexer 212.

[0042] In the present embodiment, the WSS 241 outputs the C-band WDM signal light input from the C-band EDFA 231 to the multiplexer 222. Further, the WSS 241 outputs the C-band WDM signal light input from the C-band EDFA 232 to the multiplexer 221. The multiplexer 221 multiplexes the L-band WDM signal light (

[22] ) input from the demultiplexer 211 and the C-band WDM signal light input from the WSS 241, and transmits the WDM signal light 302 (

[23] ) to the optical repeater 113. The multiplexer 222 multiplexes the L-band WDM signal light (

[25] ) input from the demultiplexer 212 and the C-band WDM signal light input from the WSS 241, and transmits the WDM signal light 304 (

[26] ) to the optical repeater 113.

[0043] Here, the C-band WDM signal light input to the multiplexer 221 is the one included in the WDM signal light 303 transmitted by the terminal station 103. Then, the multiplexer 221 transmits the multiplexed WDM signal light to the optical repeater 113 as the WDM signal light 302. The optical repeater 113 amplifies the WDM signal light 302 received from the optical multiplexer / demultiplexer 201 and transmits the amplified WDM signal light 302 to the terminal station 103. That is, the optical multiplexer / demultiplexer 201 of the present embodiment can loop back the C-band WDM signal light transmitted by the terminal station 103 to the terminal station 103.

[0044] On the other hand, the multiplexer 222 multiplexes the L-band WDM signal light input from the demultiplexer 212 and the C-band WDM signal light input from the WSS 241. Here, the C-band WDM signal light input to the demultiplexer 212 is the one included in the WDM signal light 301 transmitted by the terminal station 101. Then, the multiplexer 222 transmits the multiplexed WDM signal light to the optical branching device 121 as the WDM signal light 304. The optical branching device 121 transmits the WDM signal light 304 to the optical repeater 112. The optical repeater 112 amplifies the WDM signal light 304 received from the optical branching device 121 and transmits the amplified WDM signal light 304 to the terminal station 102. That is, in the present embodiment, the C-band WDM signal light transmitted by the terminal station 101 can be transmitted to the terminal station 102.

[0045] In the present embodiment, the gain of the C-band EDFA 231 is set so as to suppress the occurrence of the difference in optical power between the C-band WDM signal light and the L-band WDM signal light in the WDM signal light 304 transmitted from the multiplexer 222. Also, the gain of the C-band EDFA 232 is set so as to suppress the occurrence of the difference in optical power between the C-band WDM signal light and the L-band WDM signal light in the WDM signal light 302 transmitted from the multiplexer 221.

[0046] As described above, the optical multiplexer / demultiplexer 201 of the present embodiment has a simple configuration and can suppress the occurrence of the difference in optical power between wavelength bands. The reason is that the EDFA is prepared only for the C-band WDM signal light that undergoes the processing by the WSS 241 in the optical multiplexer / demultiplexer 201, and the decrease in the optical power of the C-band WDM signal light passing through the WSS 241 is compensated.

[0047] In addition, the optical multiplexer / demultiplexer 201 of the present embodiment can multiplex the C-band WDM signal light transmitted by the terminal station 101 with the L-band WDM signal light transmitted by the terminal station 103 and transmit it to the terminal station 102. Further, the optical multiplexer / demultiplexer 201 of the present embodiment can multiplex the C-band WDM signal light transmitted by the terminal station 103 with the L-band WDM signal light transmitted by the terminal station 101 and loop it back to the terminal station 103. By including a signal light for monitoring and control in the looped-back C-band WDM signal light, the terminal station 103 may monitor and control the optical transmission path between the terminal station 103 and the optical multiplexer / demultiplexer 201.

[0048] (Modification of the Third Embodiment) In addition, in the optical multiplexer / demultiplexer 201 described with reference to FIG. 7, the WSS 241 may multiplex a part of the C-band WDM signal light input from P1 and a part of the C-band WDM signal light input from P2 that does not overlap in wavelength therewith, and output the multiplexed signal to the multiplexer 221 or 222. That is, the WSS 241 may be set such that a part of the C-band WDM signal light included in the WDM signal light 301 transmitted by the terminal station 101 is transmitted to the terminal station 103 and the rest is transmitted to the terminal station 102. Further, the WSS 241 may be set such that a part of the C-band WDM signal light included in the WDM signal light 303 transmitted by the terminal station 103 is transmitted to the terminal station 102 and the rest is looped back to the terminal station 103.

[0049] In this modification, the gains of the C-band EDFAs 231 and 232 may be set so as to reduce the difference in optical power between the L-band WDM signal light and the C-band WDM signal light included in the WDM signal light 302 transmitted from the multiplexer 221. Alternatively, the gains of the C-band EDFAs 231 and 232 may be set so that the difference in optical power between the L-band WDM signal light and the C-band WDM signal light included in the WDM signal light 302 transmitted from the multiplexer 221 becomes equal to or less than a predetermined value.

[0050] Also, the gains of the C-band EDFAs 231 and 232 may be set so as to reduce the optical power difference between the L-band WDM signal light and the C-band WDM signal light included in the WDM signal light 304 transmitted from the multiplexer 222. Alternatively, the gains of the C-band EDFAs 231 and 232 may be set so that the optical power difference between the L-band WDM signal light and the C-band WDM signal light included in the WDM signal light 304 transmitted from the multiplexer 222 becomes equal to or less than a predetermined value.

[0051] Note that the configuration including the optical attenuator according to the first modification of the first embodiment and the configuration including the optical monitor and control circuit according to the second modification of the first embodiment can also be applied to the paths of the WDM signal lights 303 and 304 in the optical multiplexer / demultiplexer 201 of the second and third embodiments. Thereby, the optical multiplexer / demultiplexer 201 can independently adjust only the optical power of the L-band WDM signal light included in the WDM signal light 304, and can control the gains of the C-band EDFAs 231 and 232 based on the optical power for each wavelength band of the WDM signal light 304.

[0052] As described above, the present invention has been described with reference to the embodiments, but the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

[0053] For example, in each embodiment, an example in which the L-band WDM signal light is not processed by the WSS 241 and the C-band WDM signal light is processed by the WSS 241 has been described. However, the C-band WDM signal light may not be processed by the WSS 241 and the L-band WDM signal light may be processed by the WSS 241. In this case, the demultiplexers 211 and 212, the multiplexers 221 and 222, and the C-band EDFAs 231 and 232 are changed so that the L-band WDM signal light is processed by the WSS 241.

[0054] In addition, the wavelength bands included in the WDM signal light transmitted between the terminal stations 101 - 103 are not limited to the C band and the L band. The configuration of each embodiment is also applicable to a submarine transmission system in which WDM signal light including two non - overlapping bands is transmitted between the terminal stations 101 - 103, and only the WDM signal light of one band is processed by the WSS241.

[0055] Note that the configurations described in each embodiment are not necessarily mutually exclusive. The operations and effects of the present invention may be realized by a configuration combining all or part of the above - described embodiments.

[0056] The functions and procedures described in each of the above embodiments may be realized by a central processing unit (CPU) provided in the optical multiplexer / demultiplexer 201 executing a program. The program is recorded on a fixed, non - temporary recording medium. As the recording medium, a semiconductor memory or a fixed magnetic disk device is used, but is not limited thereto. The CPU is, for example, a computer provided in the control circuit 262, but may be provided at other locations of the optical multiplexer / demultiplexer 201. Alternatively, the operation of the optical multiplexer / demultiplexer 201 may be controlled by any one of the terminal stations 101 - 103.

Explanation of Reference Numerals

[0057] 1 Submarine transmission system 51 - 55, 61 - 65 Submarine cable 101 - 103 Terminal station 111 - 113 Optical repeater 121 Optical branching device 201 Optical multiplexer / demultiplexer 211, 212 Demultiplexer 221, 222 Multiplexer 231, 232 C - band EDFA 241 WSS 251 Optical attenuator 261 Optical monitor 262 Control circuit 301 - 304 WDM signal light 900 Optical amplifier 901 Demultiplexer 902 C-band EDFA 903 L-band EDFA 904 Multiplexer

Claims

1. A first demultiplexing means for demultiplexing the input first wavelength-division multiplexed signal light into a first signal light in a first wavelength band and a second signal light in a second wavelength band and outputting each of them; A first amplifying means for amplifying the second signal light input from the first demultiplexing means; An optical processing means for outputting a fourth signal light based on the input second signal light and a third signal light in the input second wavelength band; A first multiplexing means for multiplexing the fourth signal light and the first signal light output from the first demultiplexing means; A second demultiplexing means for demultiplexing the input second wavelength-division multiplexed signal light into a fifth signal light in the first wavelength band and the third signal light; A second amplifying means for amplifying the third signal light input from the second demultiplexing means; A second multiplexing means for multiplexing the sixth signal light output from the optical processing means and the fifth signal light output from the second demultiplexing means; Comprising: The optical processing means outputs the sixth signal light based on the input second signal light and the input third signal light; The gain of the first amplifying means is The optical power of the first signal light output from the first multiplexing means, The optical power of the fourth signal light output from the first multiplexing means, Set so that the difference between them is equal to or less than a predetermined value; The gain of the second amplifying means is The optical power of the fifth signal light output from the second multiplexing means, Set so that the difference between the optical power of the sixth signal light output from the second multiplexing means and the predetermined value is equal to or less than the predetermined value; An optical multiplexer / demultiplexer.

2. The optical multiplexer / demultiplexer according to claim 1, wherein the first wavelength band is the L band and the second wavelength band is the C band.

3. The optical multiplexer / demultiplexer according to claim 1 or 2, wherein the optical processing means is a wavelength selection switch.

4. The optical multiplexer / demultiplexer according to any one of claims 1 to 3, further comprising a first optical attenuator for attenuating the optical power of the first signal light output from the first demultiplexing means.

5. The optical multiplexer / demultiplexer according to claim 4, further comprising a second optical attenuator for attenuating the optical power of the fifth signal light output from the second demultiplexing means.

6. The optical multiplexer / demultiplexer according to claim 4 or 5, A first terminal station for transmitting the first wavelength-division multiplexed signal light to the optical multiplexer / demultiplexer; A second terminal station for receiving the fifth signal light and the sixth signal light output from the second multiplexing means; A third terminal station that receives the first signal light and the fourth signal light output from the first multiplexing means and outputs the second wavelength-division multiplexed signal light to the optical multiplexer / demultiplexer; An optical transmission system communicably connected. **Claim 7** The optical transmission system according to claim 6, wherein a relay station equipped with an optical amplifier is arranged in at least one of the optical transmission paths between the first to third terminal stations and the optical multiplexer / demultiplexer. **Claim 8** The input first wavelength-division multiplexed signal light is demultiplexed by first demultiplexing means into a first signal light in a first wavelength band and a second signal light in a second wavelength band. The input second wavelength-division multiplexed signal light is demultiplexed by second demultiplexing means into a fifth signal light in the first wavelength band and a third signal light in the second wavelength band. The second signal light and the third signal light are amplified. Based on the amplified second signal light and the amplified third signal light, a fourth signal light and a sixth signal light are output. The fourth signal light and the first signal light output from the first demultiplexing means are multiplexed by first multiplexing means. The sixth signal light and the fifth signal light output from the second demultiplexing means are multiplexed by second multiplexing means. The gain of amplification of the second signal light is set so that the difference between the optical power of the first signal light output from the first multiplexing means and the optical power of the fourth signal light output from the first multiplexing means is equal to or less than a predetermined value. The gain of amplification of the third signal light is set so that the difference between the optical power of the fifth signal light output from the second multiplexing means and the optical power of the sixth signal light output from the second multiplexing means is equal to or less than the predetermined value. An optical multiplexing / demultiplexing method.

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