TRANSMISSION DEVICE, TRANSMISSION METHOD, AND TRANSMISSION SYSTEM

Abstract

To provide a transmission device, a transmission method, and a transmission system capable of reducing a difference in transmission characteristics between a plurality of wavelength division multiplexing optical signals.SOLUTION: A transmission device includes a separation unit that separates a plurality of wavelength division multiplexing optical signals from a combined light obtained by combining the plurality of wavelength division multiplexing optical signals having different wavelength bands, a plurality of optical amplifiers that respectively amplify the plurality of wavelength division multiplexing optical signals, a wavelength conversion unit that converts at least some of the wavelength division multiplexing optical signals into other wavelength bands such that wavelength bands of at least some of the wavelength division multiplexing optical signals amplified by the plurality of optical amplifiers do not overlap with each other, and a combining unit that combines the plurality of wavelength division multiplexing optical signals whose wavelength bands have been converted by the wavelength conversion unit.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a transmission device, a transmission method, and a transmission system. [Background technology]

[0002] As demand for communications increases, there is a demand to increase the transmission capacity of wavelength division multiplexing (WDM) optical transmission by increasing the number of channels of wavelength-multiplexed optical signals. For example, when transmission is performed using only wavelength-multiplexed optical signals in the C (Conventional) band, the wavelength band is limited to 1530 to 1565 (nm).

[0003] In response to this, it is possible to increase the transmission capacity of WDM by expanding the wavelength band to, for example, the L (Long) band of 1565 to 1625 (nm) or the S (Short) band of 1460 to 1530 (nm). For example, Patent Document 1 describes a technology in which a C-band wavelength multiplexed optical signal is converted into an L-band and an S-band wavelength multiplexed optical signal, and the C-band, L-band, and S-band wavelength multiplexed optical signals are multiplexed and transmitted. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-188830 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the transmission characteristics of each of the C-band, L-band, and S-band wavelength multiplexed optical signals differ because the transmission path loss, power due to Raman scattering, etc. vary for each wavelength band. For this reason, the transmission performance (e.g., transmission distance) of the entire transmission system is limited by the worst transmission characteristic among the transmission characteristics of the wavelength multiplexed optical signals of the C-band, L-band, and S-band.

[0006] Therefore, an object of the present invention is to provide a transmission device, a transmission method, and a transmission system that can reduce the difference in transmission characteristics between a plurality of wavelength-multiplexed optical signals. [Means for solving the problem]

[0007] In one aspect, a transmission device includes a separation unit that separates a plurality of wavelength multiplexed optical signals from a multiplexed light obtained by multiplexing a plurality of wavelength multiplexed optical signals having different wavelength bands, a plurality of optical amplifiers that amplify the plurality of wavelength multiplexed optical signals, respectively, a wavelength conversion unit that converts each wavelength band of at least some of the wavelength multiplexed optical signals amplified by the plurality of optical amplifiers, to another wavelength band of the at least some of the wavelength multiplexed optical signals such that wavelength bands do not overlap among the plurality of wavelength multiplexed optical signals, and a multiplexing unit that multiplexes the plurality of wavelength multiplexed optical signals whose wavelength bands have been converted by the wavelength conversion unit. The wavelength conversion unit converts the wavelength band of at least one of the wavelength multiplexed optical signals from a first wavelength band in which the transmission characteristics are worse toward one of the longer and shorter wavelength sides to a second wavelength band in which the transmission characteristics are worse toward the other of the longer and shorter wavelength sides, and in this conversion, converts the wavelength of the first wavelength band of each of a plurality of optical signals wavelength-multiplexed into the wavelength multiplexed optical signal to the wavelength of the second wavelength band at a position shifted by a predetermined width on the wavelength axis. .

[0008] In another aspect, a transmission device includes a demultiplexer that demultiplexes a plurality of wavelength-multiplexed optical signals from a multiplexed light obtained by multiplexing a plurality of wavelength-multiplexed optical signals having different wavelength bands, a plurality of optical amplifiers that amplify the plurality of wavelength-multiplexed optical signals, respectively, a plurality of wavelength converters that convert the wavelength bands of the plurality of wavelength-multiplexed optical signals amplified by the plurality of optical amplifiers, respectively, to other wavelength bands of the plurality of wavelength-multiplexed optical signals, a demultiplexer that demultiplexes the plurality of wavelength-multiplexed optical signals, and a route to a destination of the plurality of wavelength-multiplexed optical signals separated from the multiplexed light by the demultiplexer that is determined by the plurality of wavelength converters. One of and a route that bypasses the wavelength converters and leads to the multiplexing unit.

[0009] In one aspect, the transmission method includes: separating a plurality of wavelength multiplexed optical signals from a multiplexed light obtained by multiplexing a plurality of wavelength multiplexed optical signals having different wavelength bands; amplifying each of the plurality of wavelength multiplexed optical signals; converting each wavelength band of at least a portion of the amplified wavelength multiplexed optical signals to another wavelength band of the at least a portion of the wavelength multiplexed optical signals such that the wavelength bands do not overlap among the plurality of wavelength multiplexed optical signals; and multiplexing the plurality of wavelength multiplexed optical signals whose wavelength bands have been converted. The conversion of the wavelength band of at least one of the wavelength multiplexed optical signals is performed by converting from a first wavelength band in which the transmission characteristics are worse toward one of the longer and shorter wavelength sides to a second wavelength band in which the transmission characteristics are worse toward the other of the longer and shorter wavelength sides, and in this conversion, the wavelength of the first wavelength band of each of the multiple optical signals wavelength-multiplexed into the wavelength multiplexed optical signal is converted to the wavelength of the second wavelength band at a position shifted by a predetermined width on the wavelength axis. This is the method.

[0010] In another aspect, the transmission method includes separating a plurality of wavelength-multiplexed optical signals from a combined light obtained by combining a plurality of wavelength-multiplexed optical signals having different wavelength bands, amplifying each of the plurality of wavelength-multiplexed optical signals, converting the wavelength bands of the amplified plurality of wavelength-multiplexed optical signals to other wavelength bands of the plurality of wavelength-multiplexed optical signals by a plurality of wavelength converters, combining the plurality of wavelength-multiplexed optical signals by a combiner, and configuring destination routes for the plurality of wavelength-multiplexed optical signals separated from the combined light by a plurality of optical switches, and One of and a route that bypasses the plurality of wavelength converters and leads to the multiplexing unit.

[0011] In one aspect, a transmission system includes a transmitting device that transmits multiplexed light obtained by multiplexing multiple wavelength multiplexed optical signals having different wavelength bands, and one or more transmission devices provided on a transmission path between a receiving device that receives the multiplexed light, the one or more transmission devices including a separation unit that separates the multiple wavelength multiplexed optical signals from the multiplexed light, a plurality of optical amplifiers that amplify the multiple wavelength multiplexed optical signals, respectively, a wavelength conversion unit that converts each wavelength band of at least some of the multiple wavelength multiplexed optical signals amplified by the plurality of optical amplifiers, to another wavelength band of the at least some of the wavelength multiplexed optical signals such that the wavelength bands do not overlap among the multiple wavelength multiplexed optical signals, and a multiplexing unit that multiplexes the multiple wavelength multiplexed optical signals whose wavelength bands have been converted by the wavelength conversion unit. The conversion of the wavelength band of at least one of the wavelength multiplexed optical signals is performed by converting from a first wavelength band in which the transmission characteristics are worse toward one of the longer and shorter wavelength sides to a second wavelength band in which the transmission characteristics are worse toward the other of the longer and shorter wavelength sides, and in this conversion, the wavelength of the first wavelength band of each of the multiple optical signals wavelength-multiplexed into the wavelength multiplexed optical signal is converted to the wavelength of the second wavelength band at a position shifted by a predetermined width on the wavelength axis. . Effect of the Invention

[0012] As one aspect, it is possible to reduce the difference in transmission characteristics between a plurality of wavelength-multiplexed optical signals. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a configuration diagram showing a comparative example of a transmission system. [Diagram 2] 1 is a diagram illustrating an example of transmission characteristics and transmission performance for each wavelength band of a wavelength multiplexed optical signal. [Diagram 3] FIG. 1 is a configuration diagram showing a first example of a transmission system in which relay devices are provided so that the number of transmission spans is a multiple of the number of wavelength-multiplexed optical signals. [Figure 4] FIG. 11 is a configuration diagram showing a second example of a transmission system in which relay devices are provided so that the number of transmission spans is a number other than a multiple of the number of wavelength-multiplexed optical signals. [Diagram 5] FIG. 11 is a configuration diagram showing a third example of a transmission system in which relay devices are provided so that the number of transmission spans is a number other than a multiple of the number of wavelength-multiplexed optical signals. [Figure 6] FIG. 13 is a configuration diagram showing a fourth example of a transmission system in which relay devices are provided so that the number of transmission spans is a number other than a multiple of the number of wavelength-multiplexed optical signals. [Figure 7] FIG. 11 is a configuration diagram showing a fifth example of a transmission system in which relay devices are provided so that the number of transmission spans is a number other than a multiple of the number of wavelength-multiplexed optical signals. [Figure 8] FIG. 1 is a configuration diagram showing an example of a repeater device that converts wavelength bands in two stages. [Figure 9] This is an example of a repeater device that performs wavelength conversion among four wavelength bands. [Figure 10] 13 is another example of a repeater device that performs wavelength conversion among four wavelength bands. [Figure 11] FIG. 1 is a configuration diagram showing an example of a relay device having a function of switching control of wavelength conversion. [Figure 12] FIG. 13 illustrates an example of control of an optical switch. [Figure 13] FIG. 1 is a diagram showing an example of a wavelength converter having a single pump light source; [Figure 14] FIG. 1 is a configuration diagram showing an example of a wavelength converter equipped with two pump light sources. [Figure 15] FIG. 13 is a configuration diagram showing another example of a wavelength converter equipped with two pumping light sources. [Figure 16] FIG. 1 is a diagram showing an example of wavelength conversion by a wavelength converter equipped with two pump light sources. [Figure 17] FIG. 13 is a diagram showing another example of wavelength conversion by a wavelength converter equipped with two pump light sources. [Figure 18] 11 is a diagram showing an example of the arrangement of wavelengths in a case where the transmission characteristics of wavelengths on the shorter wavelength side are worse before and after wavelength band conversion; FIG. [Figure 19] 11 is a diagram showing an example of an arrangement order of wavelengths in a case where the longer wavelengths have worse transmission characteristics before wavelength band conversion, and the shorter wavelengths have worse transmission characteristics after wavelength band conversion. FIG. [Figure 20] 11 is a diagram illustrating wavelength conversion of a wavelength-multiplexed optical signal in a case where all wavelength converters in each relay device of a node reverse the order of wavelengths. FIG. [Figure 21] 13 is a diagram illustrating wavelength conversion of a wavelength-multiplexed optical signal when two wavelength converters in each relay device of a node reverse the order of wavelengths. FIG. [Figure 22] 13 is a diagram illustrating wavelength conversion of a wavelength-multiplexed optical signal when one of the wavelength converters in each relay device of a node reverses the order of wavelengths. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] (Comparative example of a transmission system) 1 is a configuration diagram showing a comparative example of a transmission system 9. As an example, the transmission system 9a includes a transmission path 90 configured of an optical fiber or the like, a plurality of nodes 91 provided on the transmission path 90, and a transmitting device 2 and a receiving device 3 connected to each other via the transmission path 90.

[0015] As indicated by dotted lines, the transmitting device 2 multiplexes each of the wavelength multiplexed optical signals Sa to Sc in the C band, L band, and S band to generate multiplexed light Smux, and transmits the multiplexed light Smux to the receiving device 3 via a transmission path 90. The transmitting device 2 has a plurality of transmitters (Tx) 20a to 20c, multiplexers 21a to 21c, optical amplifiers 23a to 23c, wavelength converters (CNV) 24a and 24c, and a multiplexer 26.

[0016] The wavelength converter 24a converts the wavelength band of the wavelength multiplexed optical signal Sa from the C band to the L band, and the wavelength converter 24c converts the wavelength band of the wavelength multiplexed optical signal Sc from the C band to the S band. Therefore, the wavelength bands of the wavelength multiplexed optical signals Sa, Sb, and Sc are different.

[0017] A plurality of transmitters 20a, a multiplexer 21a, an optical amplifier 23a, and a wavelength converter 24a are provided on the path of the wavelength-multiplexed optical signal Sa. Each transmitter 20a generates an optical signal Da having a wavelength within the C-band and outputs it to the multiplexer 21a. The wavelengths of the optical signals Da from each transmitter 20a are different.

[0018] A plurality of transmitters 20b, a multiplexer 21b, and an optical amplifier 23b are provided on the path of the wavelength-multiplexed optical signal Sb. Each transmitter 20b generates an optical signal Db having a wavelength within the C-band and outputs it to the multiplexer 21b. The wavelengths of the optical signals Db of the transmitters 20b are different from each other.

[0019] A plurality of transmitters 20c, a multiplexer 21c, and an optical amplifier 23c are provided on the path of the wavelength-multiplexed optical signal Sc. Each transmitter 20c generates an optical signal Dc having a wavelength within the C-band and outputs it to the multiplexer 21c. The wavelengths of the optical signals Dc of the transmitters 20c are different.

[0020] The transmitters 20a to 20c are connected to a client-side LAN (Local Area Network), etc. The transmitters 20a to 20c generate optical signals Da to Dc, respectively, from client signals such as Ethernet (registered trademark, the same applies below) signals.

[0021] The multiplexer 21a multiplexes the optical signals Da input from the transmitters 20a to generate a wavelength-multiplexed optical signal Sa in the C band and outputs it to the optical amplifier 23a. Similarly to the multiplexer 21a, the multiplexer 21b generates a wavelength-multiplexed optical signal Sb in the C band from each optical signal Db and outputs it to the optical amplifier 23b, and the multiplexer 21c generates a wavelength-multiplexed optical signal Sc in the C band from each optical signal Dc and outputs it to the optical amplifier 23c. The multiplexers 21a to 21c are, for example, optical couplers.

[0022] The optical amplifiers 23a to 23c amplify the wavelength multiplexed optical signals Sa to Sc, respectively. The optical amplifiers 23a to 23c are, for example, EDFAs (Erbium Doped Optical Fiber Amplifiers). The optical amplifier 23a outputs the wavelength multiplexed optical signal Sa to the wavelength converter 24a. The optical amplifier 23b outputs the wavelength multiplexed optical signal Sa to the multiplexer 26. The optical amplifier 23c outputs the wavelength multiplexed optical signal Sc to the wavelength converter 24c.

[0023] The wavelength converter 24a converts the wavelength band of the wavelength multiplexed optical signal Sa from the C band to the L band, as indicated by the symbol G1. As a result, the wavelengths of the optical signals Da wavelength-multiplexed into the wavelength multiplexed optical signal Sa are converted from the C band to the L band. Moreover, the wavelength converter 24c converts the wavelength band of the wavelength multiplexed optical signal Sc from the C band to the S band. As a result, the wavelengths of the optical signals Dc wavelength-multiplexed into the wavelength multiplexed optical signal Sc are converted from the C band to the S band. The wavelength converters 24a and 24c output the converted wavelength multiplexed optical signals Sa and Sc to the multiplexer 26, respectively.

[0024] The multiplexer 26 multiplexes the wavelength-multiplexed optical signals Sa and Sc input from the wavelength converters 24a and 24c, respectively, and the wavelength-multiplexed optical signal Sb input from the optical amplifier 23b, and outputs the multiplexed light Smux to the transmission line 90. The multiplexer 26 is, for example, an optical coupler.

[0025] In this way, the transmitting device 2 multiplexes the L-band wavelength-multiplexed optical signal Sa, the C-band wavelength-multiplexed optical signal Sb, and the S-band wavelength-multiplexed optical signal Sc, in which the optical signals Da to Dc are wavelength-multiplexed, and transmits the multiplexed light Smux to the receiving device 3.

[0026] The multiplexed light Smux is relayed to the receiving device 3 by a plurality of nodes 91 on a transmission line 90. Each of the plurality of nodes 91 is provided with an optical amplifier (not shown) that amplifies each of the wavelength-multiplexed optical signals Sa, Sb, and Sc.

[0027] The receiving device 3 includes a plurality of receivers (Rx) 30a to 30c, demultiplexers 31a to 31c, optical amplifiers 32a, 32c, and 33a to 33c, wavelength converters (CNV) 34a and 34c, and a demultiplexer . The multiplexed light Smux is input from a transmission line 90 to the demultiplexer .

[0028] The demultiplexer 36 demultiplexes the multiplexed light Smux for each wavelength band and outputs the demultiplexed light from different ports. The demultiplexer 36 is, for example, an optical splitter.

[0029] The L-band wavelength-multiplexed optical signal Sa is amplified by the optical amplifier 32a and then input to the wavelength converter 34a. The wavelength converter 34a converts the wavelength band of the wavelength-multiplexed optical signal Sa from the L-band to the C-band and outputs it to the optical amplifier 33a. The optical amplifier 33a amplifies the wavelength-multiplexed optical signal Sa and outputs it to the demultiplexer 31a.

[0030] The S-band wavelength-multiplexed optical signal Sc is amplified by the optical amplifier 32c and then input to the wavelength converter 34c. The wavelength converter 34c converts the wavelength band of the wavelength-multiplexed optical signal Sc from the S-band to the C-band and outputs it to the optical amplifier 33c. The optical amplifier 33c amplifies the wavelength-multiplexed optical signal Sc and outputs it to the demultiplexer 31c. The configurations of the wavelength converters 34a and 34c will be described later.

[0031] The wavelength-multiplexed optical signal Sb in the C-band is input to the optical amplifier 33b from the demultiplexer 36. The optical amplifier 33b amplifies the wavelength-multiplexed optical signal Sb and outputs it to the demultiplexer 31b.

[0032] The demultiplexer 31a demultiplexes the wavelength multiplexed optical signal Sa into optical signals Da for each wavelength and outputs them to the receiver 30a. The demultiplexer 31b demultiplexes the wavelength multiplexed optical signal Sb into optical signals Db for each wavelength and outputs them to the receiver 30b. The demultiplexer 31c demultiplexes the wavelength multiplexed optical signal Sc into optical signals Dc for each wavelength and outputs them to the receiver 30c. The demultiplexers 31a to 31c are, for example, optical splitters.

[0033] The receivers 30a to 30c receive the optical signals Da to Dc, respectively. The receivers 30a to 30c are connected to a client-side LAN or the like, and generate client signals from the optical signals Da to Dc and transmit the client signals to the LAN, for example.

[0034] In this manner, the receiver 3 receives the multiplexed light Smux, and demultiplexes the multiplexed light Smux into an L-band wavelength multiplexed optical signal Sa, a C-band wavelength multiplexed optical signal Sb, and an S-band wavelength multiplexed optical signal Sc.

[0035] (Difference in transmission performance for each wavelength band) The wavelength-multiplexed optical signals Sa, Sb, Sc in the C-band, L-band, and S-band have different transmission characteristics because the transmission path loss, power due to Raman scattering, etc. vary for each wavelength band. For this reason, the transmission performance (e.g., transmission distance) of the entire transmission system 9 is limited by the worst transmission characteristic among the transmission characteristics of the wavelength-multiplexed optical signals Sa, Sb, Sc in the C-band, L-band, and S-band.

[0036] FIG. 2 is a diagram showing an example of the transmission characteristics and transmission performance for each wavelength band of the wavelength multiplexed optical signals Sa, Sb, and Sc.

[0037] Symbol G21 indicates an example of the change in transmission characteristics with respect to wavelength. Here, symbol Pa indicates the change in transmission characteristics when the transmission loss of the transmission line 90 is taken into consideration, symbol Pb indicates the change in transmission characteristics when the pump light of the distributed Raman amplification input from the optical amplifier of each node 91 to the transmission line 90 is taken into consideration. Symbol Pc indicates the change in transmission characteristics when the stimulated Raman scattering occurring in the transmission line 90 is taken into consideration.

[0038] The S-band wavelength-multiplexed optical signal Sc has lower amplification performance (maximum output, gain, NF (Noise Factor)) of the optical amplifier compared to the C-band and L-band wavelength-multiplexed optical signals Sa, Sb, and is also susceptible to power absorption by the C-band and L-band wavelength-multiplexed optical signals Sa, Sb due to stimulated Raman scattering. For this reason, the transmission characteristics of the S-band are often lower than those of the C-band and L-band. Note that the transmission characteristics are not limited to this, and depending on the configuration of the transmission system 9, the transmission characteristics of the C-band or L-band may be lower than the transmission characteristics of the S-band.

[0039] Reference symbol G22 indicates the transmission performance of the wavelength multiplexed optical signals Sa, Sb, and Sc. As described above, the transmission characteristics of the S band are lower than those of the C band and the L band, and therefore, among the wavelength multiplexed optical signals Sa, Sb, and Sc, the transmission performance of the wavelength multiplexed optical signal Sc is the worst. For this reason, the transmission performance (e.g., transmission distance) of the entire transmission system 9 is limited by the transmission characteristic K of the wavelength multiplexed optical signal Sc.

[0040] (Example of relay device) Therefore, by providing a repeater device at each node 91 on the transmission path 90 for converting the wavelength band of the wavelength multiplexed optical signals Sa, Sb, Sc to the wavelength band of other wavelength multiplexed optical signals Sa, Sb, Sc, the difference in the number of transmission spans in which each wavelength multiplexed optical signal Sa, Sb, Sc is transmitted in the S band is reduced. This reduces the difference in the transmission characteristics of each wavelength multiplexed optical signal Sa, Sb, Sc. Note that the process of the repeater device described below is one example of a transmission method.

[0041] Fig. 3 is a configuration diagram showing a first example of a transmission system 9 in which relay devices 1b and 1c are provided so that the number of transmission spans is a multiple of the number of wavelength multiplexed optical signals Sa, Sb, and Sc. In Fig. 3, components common to Fig. 1 are given the same reference numerals, and their explanation is omitted. For convenience, only a part of the configuration of the transmitting device 2 and the receiving device 3 shown in Fig. 1 is shown.

[0042] The number of transmission spans is the number of transmission sections of the transmission path 90 divided by the relay devices 1b and 1c of each node 91. In this example, the transmission path 90 is divided into three transmission sections by the relay devices 1b and 1c, so the number of transmission spans is three. However, in the following explanation, it is assumed that 3×(N-1) (N: an integer equal to or greater than 1) relay devices 1a are further provided between the transmitting device 2 and the relay device 1b, and the number of transmission spans is the general format of (3×N). For example, when N=1, only two relay devices 1b and 1c are provided on the transmission path 90, so the number of transmission spans is three.

[0043] The repeaters 1a, 1b, and 1c have the same configuration. The repeaters 1a, 1b, and 1c each include a demultiplexer 10 such as a WDM (Wavelength Divisional Multiplexing) filter, optical amplifiers 11a, 11b, and 11c, wavelength converters 12a, 12b, and 12c, and a multiplexer 13 such as an optical coupler. The repeaters 1a, 1b, and 1c are examples of transmission devices.

[0044] The demultiplexer 10 is an example of a separation unit, and separates each of the wavelength-multiplexed optical signals Sa, Sb, and Sc from the multiplexed light Smux of the wavelength-multiplexed optical signals Sa, Sb, and Sc. The demultiplexer 10 outputs the wavelength-multiplexed optical signals Sa, Sb, and Sc from separate output ports corresponding to the wavelength bands to optical amplifiers 11a, 11b, and 11c corresponding to the wavelength bands. The wavelength-multiplexed optical signals Sa, Sb, and Sc input to the optical amplifiers 11a, 11b, and 11c are determined according to the respective paths.

[0045] The optical amplifier 11a amplifies the wavelength multiplexed optical signals Sa, Sb, and Sc in the L band, the optical amplifier 11b amplifies the wavelength multiplexed optical signals Sa, Sb, and Sc in the C band, and the optical amplifier 11c amplifies the wavelength multiplexed optical signals Sa, Sb, and Sc in the S band. The optical amplifiers 11a, 11b, and 11c output the amplified wavelength multiplexed optical signals Sa, Sb, and Sc to the wavelength converters 12a, 12b, and 12c, respectively. The wavelength multiplexed optical signals Sa, Sb, and Sc input to the wavelength converters 12a, 12b, and 12c are determined according to the respective paths.

[0046] The wavelength converter 12a converts the wavelength multiplexed optical signals Sa, Sb, Sc in the L band into wavelength multiplexed optical signals Sa, Sb, Sc in the S band. The wavelength converter 12b converts the wavelength multiplexed optical signals Sa, Sb, Sc in the C band into wavelength multiplexed optical signals Sa, Sb, Sc in the L band. The wavelength converter 12c converts the wavelength multiplexed optical signals Sa, Sb, Sc in the S band into wavelength multiplexed optical signals Sa, Sb, Sc in the C band.

[0047] In this way, the wavelength converters 12a, 12b, and 12c convert each wavelength band of the amplified wavelength multiplexed optical signals Sa, Sb, and Sc into another wavelength band of the wavelength multiplexed optical signals Sa, Sb, and Sc such that the wavelength bands of the wavelength multiplexed optical signals Sa, Sb, and Sc do not overlap. Note that the wavelength converters 12a, 12b, and 12c are examples of wavelength conversion units.

[0048] The multiplexer 13 is an example of a multiplexing section, and multiplexes the wavelength multiplexed optical signals Sa, Sb, and Sc whose wavelength bands have been converted by the wavelength converters 12a, 12b, and 12c. Therefore, the wavelength multiplexed optical signals Sa, Sb, and Sc are transmitted again as multiplexed light to the relay devices 1b and 1c or the receiving device 3 of the subsequent node 91.

[0049] Next, the routes of the wavelength-multiplexed optical signals Sa, Sb, and Sc will be described, assuming that N=1 and there are no 3×(N−1) repeaters 1a.

[0050] The path of the wavelength multiplexed optical signal Sa is indicated by a dotted line. The wavelength band of the wavelength multiplexed optical signal Sa is converted from the C band to the L band by the wavelength converter 24a of the transmitting device 2, and is input from the multiplexer 26 to the transmission line 90 to the demultiplexer 10 of the repeater 1b. The wavelength band of the wavelength multiplexed optical signal Sa is converted from the L band to the S band by the wavelength converter 12a of the repeater 1b, and is input from the multiplexer 26 to the transmission line 90 to the demultiplexer 10 of the repeater 1c. The wavelength band of the wavelength multiplexed optical signal Sa is converted from the S band to the C band by the wavelength converter 12c of the repeater 1c, and is input from the multiplexer 26 to the transmission line 90 to the demultiplexer 36 of the receiving device 3, and is received by the receiver 30b.

[0051] In this way, the wavelength-multiplexed optical signal Sa is transmitted in the L band on the transmission path 90 between the transmitting device 2 and the repeater 1b, in the S band on the transmission path 90 between the repeater 1b and the repeater 1c, and in the C band on the transmission path 90 between the repeater 1c and the receiving device 3. In other words, the number of transmission spans for each wavelength band of the wavelength-multiplexed optical signal Sa is all one.

[0052] The path of the wavelength multiplexed optical signal Sb is indicated by a dashed line. The wavelength multiplexed optical signal Sb is input from the multiplexer 26 of the transmitting device 2 to the demultiplexer 10 of the repeater 1b via the transmission line 90. The wavelength band of the wavelength multiplexed optical signal Sb is converted from the C band to the L band by the wavelength converter 12b of the repeater 1b, and input from the multiplexer 26 to the transmission line 90 to the demultiplexer 10 of the repeater 1c. The wavelength band of the wavelength multiplexed optical signal Sb is converted from the L band to the S band by the wavelength converter 12a of the repeater 1c, and input from the multiplexer 26 to the transmission line 90 to the demultiplexer 36 of the receiving device 3. The wavelength band of the wavelength multiplexed optical signal Sb is converted from the S band to the C band by the wavelength converter 34c of the receiving device 3, and received by the receiver 30c.

[0053] In this way, the wavelength multiplexed optical signal Sb is transmitted in the C band on the transmission path 90 between the sending device 2 and the repeater 1b, in the L band on the transmission path 90 between the repeater 1b and the repeater 1c, and in the S band on the transmission path 90 between the repeater 1c and the receiving device 3. In other words, the number of transmission spans for each wavelength band of the wavelength multiplexed optical signal Sb is all one.

[0054] The path of the wavelength multiplexed optical signal Sc is indicated by a two-dot chain line. The wavelength band of the wavelength multiplexed optical signal Sc is converted from the C band to the S band by the wavelength converter 24c of the transmitting device 2, and is input to the demultiplexer 10 of the repeater 1b via the multiplexer 26 and the transmission line 90. The wavelength band of the wavelength multiplexed optical signal Sc is converted from the S band to the C band by the wavelength converter 12c of the repeater 1b, and is input to the demultiplexer 10 of the repeater 1c via the multiplexer 26 and the transmission line 90. The wavelength band of the wavelength multiplexed optical signal Sc is converted from the C band to the L band by the wavelength converter 12b of the repeater 1c, and is input to the demultiplexer 36 of the receiving device 3 via the multiplexer 26 and the transmission line 90. The wavelength band of the wavelength multiplexed optical signal Sc is converted from the L band to the C band by the wavelength converter 34a of the receiving device 3, and is received by the receiver 30a.

[0055] In this way, the wavelength-multiplexed optical signal Sc is transmitted in the C-band on the transmission line 90 between the transmitting device 2 and the repeater 1b, in the L-band on the transmission line 90 between the repeater 1b and the repeater 1c, and in the S-band on the transmission line 90 between the repeater 1c and the receiving device 3. Sc The number of transmission spans for each wavelength band is all 1.

[0056] Therefore, by converting the wavelength bands of the wavelength multiplexed optical signals Sa, Sb, Sc to other wavelength bands, the repeaters 1b and 1c transmit the three transmission spans in three different wavelength bands, respectively, and can make the number of transmission spans for each wavelength band of the wavelength multiplexed optical signals Sa, Sb, Sc the same. Therefore, the number of transmission spans in the S band, which has poor transmission characteristics, is 1 for each of the wavelength multiplexed optical signals Sa, Sb, Sc, and the difference in transmission characteristics between the wavelength multiplexed optical signals Sa, Sb, Sc is reduced.

[0057] Furthermore, when N ≠ 1, the wavelength bands of the wavelength-multiplexed optical signals Sa, Sb, and Sc are converted by 3×(N-1) repeaters 1a. Here, the 3×(N-1) repeaters 1a divide the transmission path 90 between the transmitter 2 and repeater 1b into (3×(N-1)+1) transmission spans. Furthermore, since the transmission path 90 between the repeater 1b and repeater 1c is divided into two transmission spans, the total number of transmission spans between the transmitter 2 and the receiver 3 is 3×N, that is, a multiple of 3, which is the number of wavelength-multiplexed optical signals Sa, Sb, and Sc.

[0058] Therefore, the 3×(N-1) repeater 1a and the repeater 1b, 1c can divide the (3×N) transmission spans into two transmission spans each and transmit them in three different wavelength bands, making it possible to make the number of transmission spans for each wavelength band of each wavelength multiplexed optical signal Sa, Sb, Sc the same. For example, when N=2, the number of transmission spans for each wavelength band of each wavelength multiplexed optical signal Sa, Sb, Sc is all 2, and when N=3, the number of transmission spans for each wavelength band of each wavelength multiplexed optical signal Sa, Sb, Sc is all 3.

[0059] Symbol G3 indicates the number of wavelength conversion stages of wavelength multiplexed optical signals (see "WDM signal") Sa, Sb, and Sc in this example and the comparative example in Fig. 1, the number of amplifications by S-band optical amplifiers 11c and 32c, and the number of transmission spans in the S-band. Wavelength band conversion in the comparative example is not performed at node 91 on the transmission path, but is performed only on wavelength multiplexed optical signals Sa and Sc by transmitting device 2 and receiving device 3. For this reason, the number of wavelength conversion stages of wavelength multiplexed optical signals Sa and Sc is two each, and the number of wavelength conversion stages of wavelength multiplexed optical signal Sb is zero.

[0060] In contrast, in this example, wavelength conversion of the wavelength-multiplexed optical signals Sa, Sb, and Sc is performed in each of the relay devices 1a, 1b, and 1c. Therefore, when the wavelength conversions of the transmitting device 2 and the receiving device 3 are added, the number of wavelength conversion stages of the wavelength-multiplexed optical signals Sa, Sb, and Sc becomes (4×N) stages. Here, the wavelength conversion from the L band to the S band is a wavelength conversion that exceeds the intermediate C band, so it is counted as two stages, and the other wavelength conversions are counted as one stage.

[0061] In the comparative example, an S-band optical amplifier 11c is provided in each node 91 on the transmission line 90 to amplify the wavelength-multiplexed optical signal Sc, and an optical amplifier 32c that amplifies the S-band wavelength-multiplexed optical signal Sc is also provided in the receiving device 3. Therefore, the number of S-band optical amplifiers for the wavelength-multiplexed optical signals Sa and Sb is 0, but the number of S-band optical amplifiers for the wavelength-multiplexed optical signal Sc is (3×N), which is the number of transmission spans.

[0062] In contrast, in this example, each of the repeaters 1a, 1b, and 1c amplifies one of the wavelength-multiplexed optical signals Sa, Sb, and Sc by the optical amplifier 11c, and the receiver 3 amplifies the S-band wavelength-multiplexed optical signal Sb by the optical amplifier 32c. Therefore, the wavelength-multiplexed optical signals Sa, Sb, and Sc are amplified by the optical amplifiers 11c and 32c only once per three transmission spans. Therefore, the number of times each of the wavelength-multiplexed optical signals Sa, Sb, and Sc is amplified is (3×N) times.

[0063] In the comparative example, the number of transmission spans in the S band of wavelength-multiplexed optical signals Sa, Sb is 0, and the number of transmission spans in the S band of wavelength-multiplexed optical signal Sc is (3×N). In contrast, in this example, the number of transmission spans in the S band of wavelength-multiplexed optical signals Sa, Sb, Sc is N, as described above.

[0064] Thus, in this example, unlike the comparative example, the number of S-band wavelength conversion stages, the number of optical amplifications, and the number of transmission spans are averaged among the wavelength-multiplexed optical signals Sa, Sb, and Sc. Therefore, the transmission characteristics of the wavelength-multiplexed optical signals Sa, Sb, and Sc are also averaged, and the difference in transmission performance is reduced.

[0065] The number of transmission spans is not limited to this example, and may be a number other than 3×N.

[0066] Fig. 4 is a configuration diagram showing a second example of a transmission system 9 in which relay devices 1a and 1b are provided so that the number of transmission spans is a number other than a multiple of the number of wavelength multiplexed optical signals Sa, Sb, and Sc. In Fig. 4, the same components as those in Fig. 3 are given the same reference numerals and their explanations are omitted.

[0067] In this example, the transmission line 90 is divided into (3×N-1) transmission spans by 3×(N-1) repeater devices 1a and 1b. Therefore, the number of transmission spans is a multiple of the number of wavelength multiplexed optical signals Sa, Sb, and Sc plus 2. For example, when N=1, only one repeater device 1b is provided on the transmission line 90, so the number of transmission spans is 2.

[0068] The path of wavelength-multiplexed optical signal Sa is indicated by a dotted line, the path of wavelength-multiplexed optical signal Sb is indicated by a dashed line, and the path of wavelength-multiplexed optical signal Sc is indicated by a dashed line. As can be seen from the paths of the wavelength-multiplexed optical signals Sa, Sb, and Sc, the number of transmission spans for each wavelength band is not the same for wavelength-multiplexed optical signals Sa, Sb, and Sc, unlike the example of FIG.

[0069] For example, when N=1, for each of the wavelength multiplexed optical signals Sa, Sb, and Sc, the number of transmission spans in one wavelength band among the C band, L band, and S band is 0, and the number of transmission spans in the remaining two wavelength bands is 2. For example, in the case of the wavelength multiplexed optical signal Sa, the number of transmission spans in the C band is 0, and the number of transmission spans in the L band and S band is 2.

[0070] Generalizing this, the number of transmission spans is (3×N-1), so for each of the wavelength-multiplexed optical signals Sa, Sb, and Sc, the number of transmission spans in one wavelength band is (N-1), and the number of transmission spans in the remaining two wavelength bands is N. Therefore, compared to the comparative example, the number of transmission spans for each wavelength band is averaged among the wavelength-multiplexed optical signals Sa, Sb, and Sc in this example as well.

[0071] Reference symbol G4 indicates the number of wavelength conversion stages of wavelength multiplexed optical signals Sa, Sb, and Sc, the number of amplifications by S-band optical amplifiers 11c and 32c, and the number of transmission spans in the S-band in this example and the comparative example in Fig. 1. For wavelength multiplexed optical signal Sc, the number of optical amplifications and the number of transmission spans in the S-band in the comparative example are (3 x N-1) because the number of transmission spans is (3 x N-1).

[0072] In this example, the number of stages of wavelength conversion of wavelength multiplexed optical signal Sa is (4×N), and the number of stages of wavelength conversion of wavelength multiplexed optical signals Sb and Sc is (4×N-2). As described above, the wavelength conversion from L band to S band is a wavelength conversion exceeding the intermediate C band, so it is counted as two stages, and the other wavelength conversions are counted as one stage.

[0073] In this example, the number of times that wavelength-multiplexed optical signals Sa and Sc are optically amplified in the S band is N, and the number of times that wavelength-multiplexed optical signal Sb is optically amplified in the S band is (N-1). Therefore, although the number of times that wavelength-multiplexed optical signals Sa, Sb, and Sc are optically amplified in the S band is not the same, it is averaged between wavelength-multiplexed optical signals Sa, Sb, and Sc compared to the comparative example.

[0074] In this example, the number of times that wavelength-multiplexed optical signals Sa and Sc are optically amplified in the S band is N, and the number of times that wavelength-multiplexed optical signal Sb is optically amplified in the S band is (N-1). Therefore, although the number of times that wavelength-multiplexed optical signals Sa, Sb, and Sc are optically amplified in the S band is not the same, it is averaged between wavelength-multiplexed optical signals Sa, Sb, and Sc compared to the comparative example.

[0075] In this example, the number of transmission spans in the S band of the wavelength-multiplexed optical signals Sa and Sc is N, and the number of transmission spans in the S band of the wavelength-multiplexed optical signal Sb is (N-1). Therefore, although the numbers of transmission spans in the S band of the wavelength-multiplexed optical signals Sa, Sb, and Sc are not the same, they are averaged between the wavelength-multiplexed optical signals Sa, Sb, and Sc compared to the comparative example.

[0076] Thus, in this example, unlike the comparative example, the number of S-band wavelength conversion stages, the number of optical amplifications, and the number of transmission spans are averaged among the wavelength-multiplexed optical signals Sa, Sb, and Sc. Therefore, the transmission characteristics of the wavelength-multiplexed optical signals Sa, Sb, and Sc are also averaged, and the difference in transmission performance is reduced.

[0077] Fig. 5 is a configuration diagram showing a third example of a transmission system 9 in which relay devices 1a and 1b are provided so that the number of transmission spans is a number other than a multiple of the number of wavelength multiplexed optical signals Sa, Sb, and Sc. In Fig. 5, the same components as those in Fig. 3 are given the same reference numerals and their explanations are omitted.

[0078] The number of transmission spans in this example is (3×N-1) like the example in Fig. 4, but a repeater 1b' is provided instead of the repeater 1b. The repeater 1b' has a demultiplexer 10, optical amplifiers 11a, 11b, and 11c, wavelength converters 12b' and 12c, and a multiplexer 13. Note that the repeater 1b' is an example of a transmission device.

[0079] The repeater 1b' is not provided with a wavelength converter 12a that converts a wavelength band from the L band to the S band. Therefore, the repeater 1b' is provided with a wavelength converter 12bb' that converts a wavelength band from the C band to the S band, instead of the wavelength converter 12b that converts a wavelength band from the C band to the L band.

[0080] Therefore, when the wavelength multiplexed optical signal Sa is input to the repeater 1b, it is transmitted to the receiving device 3 while maintaining its wavelength band in the L band. When the wavelength multiplexed optical signal Sb is input to the repeater 1b, its wavelength band is converted from the C band to the S band and transmitted to the receiving device 3. The position of the node 91 where the repeater 1b' is provided is not limited.

[0081] Symbol G4' indicates the number of wavelength conversion stages of wavelength multiplexed optical signals (see "WDM signal") Sa, Sb, and Sc in this example and the comparative example in Figure 1, the number of amplifications by S-band optical amplifiers 11c and 32c, and the number of transmission spans in the S-band.

[0082] In this example, since there is no wavelength conversion in the repeater 1b', the number of wavelength conversion stages of the wavelength multiplexed optical signal Sa is two (4×N-2) fewer than the number of wavelength conversion stages in the example of Fig. 4. Therefore, the number of wavelength conversion stages of the wavelength multiplexed optical signals Sa, Sb, and Sc is the same, and compared to the example of Fig. 4, the power loss due to wavelength conversion is averaged among the wavelength multiplexed optical signals Sa, Sb, and Sc.

[0083] Moreover, the number of times that wavelength-multiplexed optical signal Sa is optically amplified in the S band is (N-1) times, which is one less than the number of transmission spans in the example of Fig. 4, and the number of times that wavelength-multiplexed optical signal Sb is optically amplified in the S band is N times, which is one more than the number of transmission spans in the example of Fig. 4. Moreover, the number of transmission spans in the S band of wavelength-multiplexed optical signal Sa is (N-1) times, which is one less than the number of transmission spans in the example of Fig. 4, and the number of transmission spans in the S band of wavelength-multiplexed optical signal Sb is N, which is one more than the number of transmission spans in the example of Fig. 4.

[0084] In this way, in this example, the number of S-band wavelength conversion stages, the number of optical amplifications, and the number of transmission spans are averaged among the wavelength-multiplexed optical signals Sa, Sb, and Sc, similarly to the example in Fig. 4. Therefore, the transmission characteristics of the wavelength-multiplexed optical signals Sa, Sb, and Sc are also averaged, and the difference in transmission performance is reduced.

[0085] Fig. 6 is a configuration diagram showing a fourth example of a transmission system 9 in which relay devices 1a and 1b are provided so that the number of transmission spans is a number other than a multiple of the number of wavelength multiplexed optical signals Sa, Sb, and Sc. In Fig. 6, the same components as those in Fig. 3 are given the same reference numerals and their explanations are omitted.

[0086] In this example, the transmission line 90 is divided into (3×(N−1)) transmission spans by the repeater 1a and the repeaters 1b, 1c, and 1d, where N is an integer of 2 or more.

[0087] The number of transmission spans is a multiple of the number of wavelength multiplexed optical signals Sa, Sb, and Sc plus 1. For example, when N=2, only three repeaters 1b, 1b, and 1c are provided on the transmission line 90, so the number of transmission spans is 4. Note that the repeater 1d has the same configuration as the other repeaters 1a, 1b, and 1c.

[0088] The path of wavelength-multiplexed optical signal Sa is indicated by a dotted line, the path of wavelength-multiplexed optical signal Sb is indicated by a dashed line, and the path of wavelength-multiplexed optical signal Sc is indicated by a dashed line. As can be seen from the paths of the wavelength-multiplexed optical signals Sa, Sb, and Sc, the number of transmission spans for each wavelength band is not the same for wavelength-multiplexed optical signals Sa, Sb, and Sc, unlike the example of FIG.

[0089] For example, when N=2, for each of the wavelength multiplexed optical signals Sa, Sb, and Sc, the number of transmission spans in one wavelength band among the C band, L band, and S band is 2, and the number of transmission spans in the remaining two wavelength bands is 1. For example, in the case of the wavelength multiplexed optical signal Sa, the number of transmission spans in the L band is 2, and the number of transmission spans in the C band and S band is 1.

[0090] Generalizing this, the number of transmission spans is (3×N-2), so for each of the wavelength-multiplexed optical signals Sa, Sb, and Sc, the number of transmission spans in one wavelength band is N, and the number of transmission spans in the remaining two wavelength bands is (N-1). Therefore, compared to the comparative example, the number of transmission spans for each wavelength band is averaged among the wavelength-multiplexed optical signals Sa, Sb, and Sc in this example as well.

[0091] Reference symbol G5 indicates the number of wavelength conversion stages of wavelength multiplexed optical signals Sa, Sb, Sc, the number of amplifications by S-band optical amplifiers 11c, 32c, and the number of transmission spans in the S-band in this example and the comparative example in Fig. 1. For wavelength multiplexed optical signal Sc, the number of optical amplifications and the number of transmission spans in the S-band in the comparative example are (3 x N-2) because the number of transmission spans is (3 x N-2).

[0092] In this example, the number of stages of wavelength conversion for each of the wavelength multiplexed optical signals Sa and Sc is (4×N-2), and the number of stages of wavelength conversion for the wavelength multiplexed optical signal Sb is (4×N-4). As described above, the wavelength conversion from the L band to the S band is a wavelength conversion that exceeds the intermediate C band, so it is counted as two stages, and the other wavelength conversions are counted as one stage.

[0093] In this example, the number of times that wavelength-multiplexed optical signals Sa and Sb are optically amplified in the S band is (N-1) times, and the number of times that wavelength-multiplexed optical signal Sc is optically amplified in the S band is N. Therefore, although the number of times that wavelength-multiplexed optical signals Sa, Sb, and Sc are optically amplified in the S band are not the same, they are averaged out between wavelength-multiplexed optical signals Sa, Sb, and Sc compared to the comparative example.

[0094] Furthermore, in this example, the number of transmission spans in the S band of wavelength-multiplexed optical signals Sa and Sb is (N-1), and the number of transmission spans in the S band of wavelength-multiplexed optical signal Sc is N. Therefore, although the numbers of transmission spans in the S band of wavelength-multiplexed optical signals Sa, Sb, and Sc are not the same, they are averaged among wavelength-multiplexed optical signals Sa, Sb, and Sc compared to the comparative example.

[0095] Thus, in this example, unlike the comparative example, the number of S-band wavelength conversion stages, the number of optical amplifications, and the number of transmission spans are averaged among the wavelength-multiplexed optical signals Sa, Sb, and Sc. Therefore, the transmission characteristics of the wavelength-multiplexed optical signals Sa, Sb, and Sc are also averaged, and the difference in transmission performance is reduced.

[0096] Fig. 7 is a configuration diagram showing a fifth example of a transmission system 9 in which relay devices 1a and 1b are provided so that the number of transmission spans is a number other than a multiple of the number of wavelength multiplexed optical signals Sa, Sb, and Sc. In Fig. 7, the same components as those in Fig. 3 are given the same reference numerals and their explanations are omitted.

[0097] The number of transmission spans in this example is (3×N-2) like the example in Fig. 6, but a repeater 1d' is provided instead of the repeater 1d. The repeater 1d' has a demultiplexer 10, optical amplifiers 11a, 11b, and 11c, and a multiplexer 13. Unlike the other repeaters 1a, 1b, and 1c, the repeater 1d' does not have wavelength converters 12a, 12b, and 12c.

[0098] Therefore, when wavelength multiplexed optical signal Sa is input to repeater 1d', it is transmitted to receiving device 3 while its wavelength band is maintained in the C band. When wavelength multiplexed optical signal Sb is input to repeater 1b, it is transmitted to receiving device 3 while its wavelength band is maintained in the S band. When wavelength multiplexed optical signal Sc is input to repeater 1b, it is transmitted to receiving device 3 while its wavelength band is maintained in the L band. The position of node 91 where repeater 1d' is provided is not limited.

[0099] Symbol G5' indicates the number of wavelength conversion stages of wavelength multiplexed optical signals (see "WDM signal") Sa, Sb, and Sc in this example and the comparative example in Figure 1, the number of amplifications by S-band optical amplifiers 11c and 32c, and the number of transmission spans in the S-band.

[0100] In this example, the number of wavelength conversion stages of wavelength multiplexed optical signals Sa and Sc is two less (4×N-2) than the number of wavelength conversion stages in the example of Fig. 6 because there is no wavelength conversion in the repeater 1d'. Also, the number of wavelength conversion stages of wavelength multiplexed optical signal Sb is the same (4×N-2) as the example of Fig. 6 because there is no wavelength conversion in the repeater 1d' but wavelength conversion in the wavelength converter 34c of the receiving device 3 is added. Therefore, the number of wavelength conversion stages of wavelength multiplexed optical signals Sa, Sb, and Sc is the same, and compared to the example of Fig. 6, the power loss due to wavelength conversion is averaged between wavelength multiplexed optical signals Sa, Sb, and Sc.

[0101] Moreover, the number of times of optical amplification in the S band of wavelength-multiplexed optical signal Sb is N) times, which is one more than the number of optical amplifications in the example of Fig. 6, and the number of times of optical amplification in the S band of wavelength-multiplexed optical signal Sc is (N-1), which is one less than the number of optical amplifications in the example of Fig. 6. Moreover, the number of times of optical amplification in the S band of wavelength-multiplexed optical signal Sa is (N-1) times, the same as the number of optical amplifications in the example of Fig. 6.

[0102] Moreover, the number of transmission spans in the S band of wavelength-multiplexed optical signal Sc is one less (N-1) than the number of transmission spans in the example of Fig. 6, and the number of transmission spans in the S band of wavelength-multiplexed optical signal Sb is N, which is one more than the number of transmission spans in the example of Fig. 6. Moreover, the number of transmission spans in the S band of wavelength-multiplexed optical signal Sa is the same as the number of transmission spans in the example of Fig. 6 (N-1).

[0103] In this way, in this example, the number of S-band wavelength conversion stages, the number of optical amplifications, and the number of transmission spans are averaged among the wavelength-multiplexed optical signals Sa, Sb, and Sc, similarly to the example in Fig. 6. Therefore, the transmission characteristics of the wavelength-multiplexed optical signals Sa, Sb, and Sc are also averaged, and the difference in transmission performance is reduced.

[0104] (Design of the number of transmission spans) The number of transmission spans of the transmission line 90 can be determined within a range that satisfies, for example, the following formula (1).

[0105] α+β>0 (1)

[0106] In formula (1), α is the conversion efficiency (dB) of the wavelength converters 12a, 12b, 12b', and 12c, and β is the power (dB) of the wavelength multiplexed optical signals Sa, Sb, and Sc improved by averaging the transmission characteristics. The power β is calculated from, for example, the difference in gain and NF according to the wavelength bands of the optical amplifiers 11a, 11b, and 11c, the loss per transmission span, and the like.

[0107] (An example of a repeater that converts wavelength bands in two stages) Fig. 8 is a configuration diagram showing an example of a repeater 1e that converts wavelength bands in two stages. In Fig. 8, the same components as those in Fig. 3 are given the same reference numerals, and the description thereof will be omitted.

[0108] The repeater 1e is provided in the node 91 in place of the repeaters 1a, 1b, 1c, and 1d. The repeater 1e differs from the repeaters 1a, 1b, 1c, and 1d in that it has two wavelength converters 12a1 and 12a2 in place of the wavelength converter 12a. One wavelength converter 12a1 converts the wavelength band of the wavelength multiplexed optical signals Sa, Sb, and Sc from the L band to the C band, and the other wavelength converter 12a2 converts the wavelength band of the wavelength multiplexed optical signals Sa, Sb, and Sc from the C band to the L band.

[0109] Therefore, the wavelength bands of the wavelength multiplexed optical signals Sa, Sb, Sc are converted from the C band to the S band by two stages of wavelength conversion. This enables wavelength conversion with higher accuracy than when the wavelength bands of the wavelength multiplexed optical signals Sa, Sb, Sc are converted from the C band to the S band by one wavelength conversion. The number of stages of wavelength conversion is not limited to two stages, and may be three or more stages. Furthermore, although the repeater 1e performs wavelength band conversion from the L band to the C band in two stages, the present invention is not limited to this, and conversion between other wavelength bands may also be performed through multiple stages.

[0110] (Example of wavelength conversion between four wavelength bands) In the above embodiments, the wavelength conversion of the wavelength multiplexed optical signals Sa, Sb, and Sc in three wavelength bands has been described as an example, but the number of wavelength bands is not limited. For example, the wavelength conversion may be performed among four wavelength bands, namely, the L band, the C band, the S band, and the E band.

[0111] 9 shows an example of a repeater 5a that performs wavelength conversion among four wavelength bands. The repeater 5a is provided in each node 91, similar to the repeaters 1a to 1d. The repeater 5a transmits wavelength multiplexed optical signals Sa, Sb, Sc, and Sd in the E band, S band, C band, and L band from the transmitter 2 to the receiver 3.

[0112] The repeater 5a includes a demultiplexer 50 such as a WDM filter, optical amplifiers 51a, 51b, 51c, and 51d, wavelength converters 52a, 52b, 52c, and 52d, and a multiplexer 53 such as an optical coupler. The repeater 5a is an example of a transmission device.

[0113] The demultiplexer 50 is an example of a separation unit, and separates each of the wavelength multiplexed optical signals Sa, Sb, Sc, and Sd from the multiplexed light Smux of the wavelength multiplexed optical signals Sa, Sb, and Sc. The demultiplexer 50 outputs the wavelength multiplexed optical signals Sa, Sb, Sc, and Sd from separate output ports corresponding to the wavelength bands to optical amplifiers 51a, 51b, 51c, and 51d corresponding to the wavelength bands, respectively.

[0114] The optical amplifier 51a amplifies the wavelength multiplexed optical signal Sa in the E band, and the optical amplifier 51b amplifies the wavelength multiplexed optical signal Sb in the S band. The optical amplifier 51c amplifies the wavelength multiplexed optical signal Sc in the C band, and the optical amplifier 51d amplifies the wavelength multiplexed optical signal Sd in the L band. The optical amplifiers 51a, 51b, 51c, and 51d output the amplified wavelength multiplexed optical signals Sa, Sb, Sc, and Sd to the wavelength converters 12a, 12b, and 12c, respectively.

[0115] 9 shows an example in which the wavelength bands of the wavelength multiplexed optical signals Sa, Sb, Sc, Sd are E-band, S-band, C-band, and L-band, respectively, but the wavelength bands of the wavelength multiplexed optical signals Sa, Sb, Sc, Sd are different for each node 91, as in the embodiment in the case of the above-mentioned three wavelength bands. Therefore, the wavelength multiplexed optical signals Sa, Sb, Sc, Sd input to the optical amplifiers 51a, 51b, 51c, 51d are determined according to each route.

[0116] The wavelength converter 52a converts the wavelength multiplexed optical signal Sa in the E band into a wavelength multiplexed optical signal Sa in the S band. The wavelength converter 52b converts the wavelength multiplexed optical signal Sb in the S band into a wavelength multiplexed optical signal Sb in the C band. The wavelength converter 52c converts the wavelength multiplexed optical signal Sc in the C band into a wavelength multiplexed optical signal Sc in the L band. The wavelength converter 52d converts the wavelength multiplexed optical signal Sd in the L band into a wavelength multiplexed optical signal Sd in the E band.

[0117] In this way, the wavelength converters 52a, 52b, 52c, and 52d convert each wavelength band of the amplified wavelength multiplexed optical signals Sa, Sb, Sc, and Sd into another wavelength band of the wavelength multiplexed optical signals Sa, Sb, Sc, and Sd so that the wavelength bands of the wavelength multiplexed optical signals Sa, Sb, Sc, and Sd do not overlap. Note that the wavelength converters 52a, 52b, 52c, and 52d are an example of a wavelength conversion unit.

[0118] The multiplexer 53 is an example of a multiplexing section, and multiplexes the wavelength multiplexed optical signals Sa, Sb, Sc, and Sd whose wavelength bands have been converted by the wavelength converters 52a, 52b, 52c, and 52d. Therefore, the wavelength multiplexed optical signals Sa, Sb, Sc, and Sd are transmitted again as multiplexed light to the relay device 5a or the receiving device 3 of the subsequent node 91.

[0119] With the above configuration, the repeater 5a can convert the wavelength bands of the wavelength multiplexed optical signals Sa, Sb, Sc, and Sd in the order shown by the reference symbol G60. The wavelength bands of the wavelength multiplexed optical signals Sa, Sb, Sc, and Sd are converted by the repeater 5a of each node 91 in the order of E-band to S-band, S-band to C-band, C-band to L-band, and L-band to E-band. The order of wavelength conversion is not limited to this.

[0120] Fig. 10 shows an example of another repeater device 5b that performs wavelength conversion among four wavelength bands. In Fig. 10, the same components as those in Fig. 9 are given the same reference numerals, and the description thereof will be omitted.

[0121] The repeater 5b, like the repeaters 1a to 1d, is provided in each node 91. The repeater 5b transmits wavelength-multiplexed optical signals Sa, Sb, Sc, and Sd in E band, S band, C band, and L band from the transmitter 2 to the receiver 3.

[0122] The repeater 5b has wavelength converters 54a, 54b, 54c, and 54d instead of the wavelength converters 52a, 52b, 52c, and 52d. The wavelength converter 54a converts the wavelength multiplexed optical signal Sa in the E band from the optical amplifier 51a into a wavelength multiplexed optical signal Sa in the C band. The wavelength converter 54b converts the wavelength multiplexed optical signal Sb in the S band from the optical amplifier 51b into a wavelength multiplexed optical signal Sb in the E band. The wavelength converter 54c converts the wavelength multiplexed optical signal Sc in the C band into a wavelength multiplexed optical signal Sc in the L band. The wavelength converter 54d converts the wavelength multiplexed optical signal Sd in the L band into a wavelength multiplexed optical signal Sd in the S band.

[0123] With the above configuration, the repeater 5b can convert the wavelength bands of the wavelength multiplexed optical signals Sa, Sb, Sc, and Sd in the order shown by reference symbol G61. The wavelength bands of the wavelength multiplexed optical signals Sa, Sb, Sc, and Sd are converted by the repeater 5a of each node 91 in the order of E band to C band, C band to L band, L band to S band, and S band to E band.

[0124] In this way, the repeater 5b does not perform wavelength conversion across two or more wavelength bands on the wavelength axis (conversion from L band to E band) like the repeater 5a, and therefore can improve the accuracy of wavelength conversion compared to the repeater 5a.

[0125] As described above, the relay devices 1a to 1d, 1b', 5a, and 5b each include the wavelength converters 12a, 12b, 12b', 12c, 52a, 52b, 52c, 52d, 54a, 54b, 54c, and 54d. The wavelength converters 12a, 12b, 12b', 12c, 52a, 52b, 52c, 52d, 54a, 54b, 54c, and 54 convert each wavelength band of at least some of the wavelength multiplexed optical signals Sa, Sb, Sc, and Sd to another wavelength band of some of the wavelength multiplexed optical signals so that the wavelength bands of the wavelength multiplexed optical signals Sa, Sb, Sc, and Sd do not overlap with each other.

[0126] Therefore, the repeaters 1a-1d, 1b', 5a, and 5b can make the wavelength bands of the wavelength-multiplexed optical signals Sa, Sb, Sc, and Sd different for each transmission span. Therefore, the repeaters 1a-1d, 1b', 5a, and 5b can reduce the difference in transmission characteristics for each wavelength band and reduce the difference in transmission performance between the wavelength-multiplexed optical signals Sa, Sb, Sc, and Sd.

[0127] (Wavelength conversion switching control) The relay devices 1a to 1d, 1b', 5a, and 5b described so far do not control switching of the wavelength conversion of the wavelength-multiplexed optical signals Sa, Sb, Sc, and Sd, but may be provided with a function of controlling switching of the wavelength conversion.

[0128] 11 is a configuration diagram showing an example of a repeater 4 having a function of controlling switching of wavelength conversion. The repeater 4 is provided at each node 91 on a transmission line 90. The repeater 4 transmits wavelength multiplexed optical signals Sa, Sb, and Sc of S band, C band, and L band from a transmitter 2 to a receiver 3.

[0129] The relay device 4 includes a demultiplexer 40 such as a WDM filter, taps 41a, 41b, and 41c such as optical splitters, optical amplifiers 42a, 42b, and 42c, optical switches 43a, 43b, and 43c, wavelength converters 44a, 44b1, 44b2, and 44c, optical couplers 45a, 45b, and 45c, and a multiplexer 46. The relay device 4 is another example of a transmission device.

[0130] The demultiplexer 40 is an example of a separation unit, and separates each of the wavelength multiplexed optical signals Sa, Sb, and Sc from the multiplexed light Smux of the wavelength multiplexed optical signals Sa, Sb, and Sc. The demultiplexer 40 outputs the wavelength multiplexed optical signals Sa, Sb, and Sc from separate output ports corresponding to the wavelength bands to optical amplifiers 42a, 42b, and 42c corresponding to the wavelength bands via taps 41a, 41b, and 41c, respectively.

[0131] As an example, it is assumed that the wavelength band of wavelength multiplexed optical signal Sa is the L band, the wavelength band of wavelength multiplexed optical signal Sb is the C band, and the wavelength band of wavelength multiplexed optical signal Sc is the S band. The wavelength multiplexed optical signals Sa, Sb, and Sc are input to optical amplifiers 42a, 42b, and 42c, respectively. The optical amplifiers 42a, 42b, and 42c amplify the wavelength multiplexed optical signals Sa, Sb, and Sc, respectively, and output them to optical switches 43a, 43b, and 43c.

[0132] The optical switch 43a selects routes R1a and R2a to which the wavelength-multiplexed optical signal Sa is output in accordance with the control of the control circuit 48. The route R1a is a route from the optical switch 43a to the multiplexer 46 via the wavelength converter 44a and optical coupler 45a, and the route R2a is a route from the optical switch 43a to the multiplexer 46 via the optical coupler 45a. The wavelength converter 44a converts the wavelength band of the wavelength-multiplexed optical signal Sa from the L band to the S band. Note that instead of the optical coupler 45a, another optical switch that switches between the routes R1a and R2a in conjunction with the optical switch 43a may be provided.

[0133] The optical switch 43b selects a route R1b, R2b, or R3b for the output destination of the wavelength multiplexed optical signal Sb under the control of the control circuit 48. The route R1b is a route from the optical switch 43b to the multiplexer 46 via the wavelength converter 44b1 and the optical coupler 45b, and the route R2b is a route from the optical switch 43b to the multiplexer 46 via the optical coupler 45b. The route R3b is a route from the optical switch 43b to the multiplexer 46 via the wavelength converter 44b2 and the optical coupler 45b.

[0134] The wavelength converter 44b1 converts the wavelength band of the wavelength multiplexed optical signal Sb from the C band to the L band, and the wavelength converter 44b2 converts the wavelength band of the wavelength multiplexed optical signal Sb from the C band to the S band. Note that, instead of the optical coupler 45b, another optical switch that switches between R1b, R2b, and R3b in conjunction with the optical switch 43b may be provided.

[0135] The optical switch 43c selects routes R1c and R2c for the output destination of the wavelength-multiplexed optical signal Sc under the control of the control circuit 48. The route R2c is a route from the optical switch 43c to the multiplexer 46 via the wavelength converter 44c and the optical coupler 45c, and the route R1c is a route from the optical switch 43c to the multiplexer 46 via the optical coupler 45c. The wavelength converter 44c converts the wavelength band of the wavelength-multiplexed optical signal Sc from the S band to the C band. Note that instead of the optical coupler 45c, another optical switch that switches between the routes R1c and R2c in conjunction with the optical switch 43c may be provided.

[0136] The multiplexer 46 is an example of a multiplexing section, and multiplexes the wavelength multiplexed optical signals Sa, Sb, and Sc whose wavelength bands have been converted by the wavelength converters 12a, 12b, and 12c. Therefore, the wavelength multiplexed optical signals Sa, Sb, and Sc are transmitted again as multiplexed light to the relay device 4 or the receiving device 3 of the subsequent node 91.

[0137] The tap 41a branches the wavelength-multiplexed optical signal Sa to the optical amplifier 42a and the monitor circuit 47. The tap 41b branches the wavelength-multiplexed optical signal Sb to the optical amplifier 42b and the monitor circuit 47. The tap 41c branches the wavelength-multiplexed optical signal Sc to the optical amplifier 42c and the monitor circuit 47.

[0138] The monitor circuit 47 detects the power of the wavelength-multiplexed optical signals Sa, Sb, and Sc input from the taps 41 a, 41 b, and 41 c, respectively, using, for example, a photodiode. The control circuit 48 obtains the detection values ​​of the power of the wavelength-multiplexed optical signals Sa, Sb, and Sc from the monitor circuit 47.

[0139] The control circuit 48 is a circuit including, for example, a processor such as a CPU (Central Processing Unit), a memory, an FPGA (Field Programmable Gate Array), and an ASIC (Application Specified Integrated Circuit). The control circuit 48 controls the optical switches 43a, 43b, and 43c so as to reduce the difference in power between the wavelength-multiplexed optical signals Sa, Sb, and Sc. As a result, the repeater 4 reduces the difference in transmission characteristics between the wavelength-multiplexed optical signals Sa, Sb, and Sc in units of nodes 91.

[0140] Fig. 12 is a diagram showing control examples #1 to #3 of the optical switches 43a, 43b, and 43c. In Fig. 12, for each of control examples #1 to #3, the wavelength bands of the wavelength multiplexed optical signals Sa, Sb, and Sc, the relative level of power, the identifiers (symbols) of the optical switches 43a, 43b, and 43c to be controlled, and the identifiers (symbols) of the routes R1a, R2a, R1b, R2b, R3b, R1c, and R2c are shown in association with one another.

[0141] Control example #1 is an example in which the power of the wavelength multiplexed optical signal Sa in the L band is the highest and the power of the wavelength multiplexed optical signal Sc in the S band is the lowest. The control circuit 48 causes the optical switch 43a to select the route R1a, the optical switch 43b to select the route R1b, and the optical switch 43c to select the route R2c. This allows the repeater 4 to perform wavelength conversion similar to that of the repeaters 1a to 1d described above.

[0142] Control example #2 is an example in which the power of the wavelength multiplexed optical signal Sb in the C band is the highest and the power of the wavelength multiplexed optical signal Sc in the S band is the lowest. The control circuit 48 causes the optical switch 43a to select the route R2a, the optical switch 43b to select the route R3b, and the optical switch 43c to select the route R2c. This allows the repeater 4 to perform wavelength conversion similar to that of the repeater 1b' described above.

[0143] Control example #3 is an example in which the power of the S-band wavelength multiplexed optical signal Sc is the highest. The control circuit 48 causes the optical switch 43a to select the route R2a, the optical switch 43b to select the route R2b, and the optical switch 43c to select the route R1c. This allows the repeater 4 to perform only amplification without wavelength conversion, similar to the repeater 1d' described above.

[0144] In this way, the relay device 4 switches the wavelength conversion depending on the power of the wavelength multiplexed optical signals Sa, Sb, Sc, so that it is possible to configure a transmission system 9 as shown in Figures 3 to 7. As a result, it is possible to reduce the difference in transmission characteristics between the wavelength multiplexed optical signals Sa, Sb, Sc.

[0145] The control circuit 48 may control the optical switches 43a, 43b, and 43c in response to detection results such as the OSNR (Optical Signal-to-Noise Ratio) or BER (Bit Error Rate) of the wavelength multiplexed optical signals Sa, Sb, and Sc instead of the power of the wavelength multiplexed optical signals Sa, Sb, and Sc. The monitor circuit 47 is an example of a detection unit that detects the transmission characteristics of each of the wavelength multiplexed optical signals Sa, Sb, and Sc. The control circuit 48 is an example of a control unit that controls the optical switches 43a, 43b, and 43c so that the difference between the transmission characteristics of each of the wavelength multiplexed optical signals Sa, Sb, and Sc is reduced.

[0146] (Example of wavelength converter configuration) 13 is a configuration diagram showing an example of wavelength converters 12a-12c, 12b', 44a-44c, 52a-52c, and 54a-54c equipped with a single pumping light source 60. Wavelength converters 12a-12c, 12b', 44a-44c, 52a-52c, and 54a-54c each include pumping light source 60, an optical amplifier 61, an optical coupler 62, and a nonlinear optical medium 63.

[0147] The pumping light source 60 outputs pumping light Xa. The optical amplifier 61 amplifies the pumping light Xa and outputs it to the optical coupler 62. The optical coupler 62 receives the wavelength-multiplexed optical signals Sa-Sd and the pumping light Xa. The optical coupler 62 multiplexes the wavelength-multiplexed optical signals Sa-Sd and the pumping light Xa and outputs the multiplexed optical signals to the nonlinear optical medium 63. The nonlinear optical medium 63 generates degenerate four-wave mixing of the wavelength-multiplexed optical signals Sa-Sd and the pumping light Xa. Idler light generated by the degenerate four-wave mixing is output as wavelength-converted wavelength-multiplexed optical signals Sa-Sd.

[0148] Reference symbol G70 shows an example of wavelength conversion by this configuration. The wavelengths λ1, λ2, . . . , λn of each optical signal wavelength-multiplexed into the wavelength-multiplexed optical signals Sa to Sd are converted to wavelengths λ1', λ2', . . . , λn' at symmetrical positions on the wavelength axis with respect to the central wavelength λa of the pumping light Xa. As a result, the order of the wavelengths λ1, λ2, . . . , λn of each optical signal wavelength-multiplexed into the wavelength-multiplexed optical signals Sa to Sd is reversed. For example, the wavelength λ1 on the shortest wavelength side is converted to the wavelength λ1' on the longest wavelength side, and for example, the wavelength λn on the longest wavelength side is converted to the wavelength λn' on the shortest wavelength side.

[0149] Fig. 14 is a configuration diagram showing an example of wavelength converters 12a-12c, 12b', 44a-44c, 52a-52c, 54a-54c equipped with two pumping light sources 60, 65. In Fig. 14, components common to Fig. 13 are given the same reference numerals and their description will be omitted. Wavelength converters 12a-12c, 12b', 44a-44c, 52a-52c, 54a-54c include pumping light sources 60, 65, optical amplifiers 61, 66, optical couplers 64, 62, and a nonlinear optical medium 63.

[0150] The pumping light source 65 outputs pumping light Xb. The optical amplifier 66 amplifies the pumping light Xb and outputs it to the optical coupler 64. The optical coupler 64 receives the pumping light Xa from the optical amplifier 61 and the pumping light Xb from the optical amplifier 66. The pumping lights Xa and Xb are multiplexed by the optical coupler 64 and input to the optical coupler 62.

[0151] The wavelength-multiplexed optical signals Sa-Sd and pumping lights Xa, Xb are input to the optical coupler 62. The optical coupler 62 multiplexes the wavelength-multiplexed optical signals Sa-Sd and pumping lights Xa, Xb and outputs the multiplexed optical signals to the nonlinear optical medium 63. The nonlinear optical medium 63 generates non-degenerate four-wave mixing of the wavelength-multiplexed optical signals Sa-Sd and pumping lights Xa, Xb. Idler light generated by non-degenerate four-wave mixing is output as wavelength-converted wavelength-multiplexed optical signals Sa-Sd.

[0152] Fig. 15 is a configuration diagram showing another example of wavelength converters 12a-12c, 12b', 44a-44c, 52a-52c, 54a-54c equipped with two pumping light sources 60, 65. In Fig. 15, components common to Fig. 14 are given the same reference numerals and their description will be omitted. Wavelength converters 12a-12c, 12b', 44a-44c, 52a-52c, 54a-54c each include pumping light sources 60, 65, optical amplifiers 68, optical couplers 62, 67, and a nonlinear optical medium 63.

[0153] 14, pump light Xa, Xb are input to optical coupler 67 and multiplexed before being amplified by optical amplifier 68. The multiplexed light of pump light Xa, Xb is input from optical coupler 67 to optical amplifier 68 and amplified. In this example, too, idler light generated by non-degenerate four-wave mixing in nonlinear optical medium 63 is output as wavelength-converted wavelength-multiplexed optical signals Sa-Sd, similar to the example of FIG.

[0154] 16 is a diagram showing an example of wavelength conversion by wavelength converters 12a-12c, 12b', 44a-44c, 52a-52c, 54a-54c having two pumping light sources 60, 65. In this example, an example is given in which a wavelength band on the short wavelength side (λ1, λ2,..., λn) is converted to a wavelength band on the long wavelength side (λ1', λ2',..., λn'), such as conversion from C-band to L-band. The polarizations of the two pumping lights Xa, Xb are orthogonal to each other. The polarizations of the wavelength multiplexed optical signals Sa-Sd are arbitrary.

[0155] Reference symbol G71 indicates an example in which the wavelength bands (λ1, λ2, . . . , λn) of wavelength multiplexed optical signals Sa-Sd before conversion are located on the short wavelength side of the central wavelengths λa, λb of the pumping lights Xa, Xb, and the wavelength bands (λ1', λ2', . . . , λn') of wavelength multiplexed optical signals Sa-Sd after conversion are located on the long wavelength side of the central wavelengths λa, λb of the pumping lights Xa, Xb. Reference symbol G72 indicates an example in which the wavelength bands (λ1, λ2, . . . , λn) of wavelength multiplexed optical signals Sa-Sd before conversion are located on the short wavelength side of the central wavelengths λa, λb of the pumping lights Xa, Xb, and the wavelength bands (λ1', λ2', . . . , λn') of wavelength multiplexed optical signals Sa-Sd after conversion are located on the long wavelength side of the central wavelengths λa, λb of the pumping lights Xa, Xb.

[0156] Wavelength converters 12a-12c, 12b', 44a-44c, 52a-52c, 54a-54c convert wavelengths λ1, λ2,...,λn to wavelengths λ1', λ2',...,λn' at symmetric positions on the wavelength axis, sandwiching the intermediate wavelength ((λa+λb) / 2) between the central wavelengths λa, λb of the two pumping lights Xa, Xb. Therefore, the order on the wavelength axis of the wavelengths λ1', λ2',...,λn' included in the converted wavelength band is the reverse of the order of the wavelengths λ1, λ2,...,λn included in the wavelength band before conversion.

[0157] FIG. 17 is a diagram showing another example of wavelength conversion by wavelength converters 12a to 12c, 12b', 44a to 44c, 52a to 52c, and 54a to 54c each including two pumping light sources 60 and 65. In FIG.

[0158] Reference symbol G73 shows an example in which the wavelength bands (λ1, λ2, . . . , λn) of wavelength-multiplexed optical signals Sa-Sd before conversion are located on the short wavelength side of the central wavelength λa of pumping light Xa, and the wavelength bands (λ1', λ2', . . . , λn') of wavelength-multiplexed optical signals Sa-Sd after conversion are located on the long wavelength side of the central wavelength λa of pumping light Xa and on the short wavelength side of the central wavelength λb of pumping light Xb. Here, the polarizations of the two pumping lights Xa, Xb are orthogonal to each other. The polarizations of the wavelength-multiplexed optical signals Sa-Sd are arbitrary.

[0159] Wavelength converters 12a-12c, 12b', 44a-44c, 52a-52c, 54a-54c convert wavelengths λ1, λ2,...,λn to wavelengths λ1', λ2',...,λn' at positions shifted by a predetermined width Δλ on the wavelength axis. Therefore, the order on the wavelength axis of wavelengths λ1', λ2',...,λn' included in the converted wavelength band is the same as the order of wavelengths λ1, λ2,...,λn included in the wavelength band before conversion.

[0160] Symbol G74 shows an example in which the wavelength bands (λ1, λ2, . . . , λn) of wavelength multiplexed optical signals Sa-Sd before conversion are located on the long wavelength side of the central wavelength λa of the pump light Xa and on the short wavelength side of the central wavelength λb, and the wavelength bands (λ1', λ2', . . . , λn', λ1'', λ2'', . . . , λn'') of wavelength multiplexed optical signals Sa-Sd after conversion are located on the long wavelength side of the central wavelength λb of the pump light Xb and on the long wavelength side of the central wavelength λb of the pump light Xb. Here, the polarizations of the two pump lights Xa, Xb are V-polarized in the same direction and are orthogonal to the polarization of the wavelength multiplexed optical signals Sa-Sd, which are V-polarized.

[0161] Wavelength converters 12a-12c, 12b', 44a-44c, 52a-52c, 54a-54c convert wavelengths λ1, λ2,...,λn to wavelengths λ1', λ2',...,λn' which are shifted a predetermined width Δλ toward the longer wavelength side on the wavelength axis, and wavelengths λ1'',λ2'',...,λn'', which are shifted a predetermined width Δλ toward the shorter wavelength side on the wavelength axis. Therefore, the order on the wavelength axis of wavelengths λ1', λ2',...,λn' and λ1'',λ2'',...,λn' included in the converted wavelength band is the same as the order of wavelengths λ1, λ2,...,λn included in the wavelength band before conversion.

[0162] Wavelength converters 12a to 12c, 12b', 44a to 44c, 52a to 52c, and 54a to 54c select and output one of two converted wavelength bands (λ1', λ2', . . ., λn', λ1'', λ2'', . . ., λn'').

[0163] (Selection of wavelength order during wavelength conversion) The transmission characteristics (e.g., power, etc.) of each wavelength included in the wavelength band are biased toward the long wavelength side or the short wavelength side, for example. Therefore, as described below, the order of the wavelengths during wavelength conversion may be selected so as to reduce the bias in the transmission characteristics.

[0164] 18 is a diagram showing an example of the arrangement of wavelengths when the transmission characteristics are worse for wavelengths on the shorter wavelength side before and after wavelength band conversion. Reference symbol G80 shows an example of the transmission characteristics of wavelength band X before conversion and wavelength band Y after conversion. For wavelength band X before conversion and wavelength band Y after conversion, the transmission characteristics are worse for wavelengths on the shorter wavelength side.

[0165] Reference symbol G81 indicates an example of the order of wavelengths when converting from wavelength band X to wavelength band Y. Wavelength converters 12a-12c, 12b', 44a-44c, 52a-52c, 54a-54c convert wavelengths λ1, λ2,...,λn included in wavelength band X to wavelengths λ1', λ2',...,λn' at symmetrical positions on the wavelength axis about a predetermined center wavelength. Therefore, the order of wavelengths λ1', λ2',...,λn' included in wavelength band Y after conversion is the reverse of the order of wavelengths λ1, λ2,...,λn included in wavelength band X before conversion.

[0166] Therefore, for example, wavelengths λ1 and λ2 on the short wavelength side with poor transmission characteristics are converted to wavelengths λ1' and λ2' on the long wavelength side with good transmission characteristics. Also, for example, wavelength λn on the long wavelength side with good transmission characteristics is converted to wavelength λn' on the short wavelength side with poor transmission characteristics. As a result, the transmission characteristics are averaged among the wavelengths λ1', λ2', ..., λn' included in the converted wavelength band Y.

[0167] In this example, an example is given of conversion from the shorter wavelength side wavelength band X to the longer wavelength side wavelength band Y, but even in the opposite case of conversion from the longer wavelength side wavelength band Y to the shorter wavelength side wavelength band X, the transmission characteristics are averaged by reversing the order of the wavelengths during wavelength conversion in the same manner as above. Also, in this example, an example is given of the transmission characteristics becoming worse on the shorter wavelength side, but even in the opposite case of conversion where the transmission characteristics become worse on the longer wavelength side, the transmission characteristics are averaged by reversing the order of the wavelengths during wavelength conversion in the same manner as above.

[0168] 19 is a diagram showing an example of the arrangement of wavelengths in a case where the transmission characteristics are worse on the longer wavelength side before the wavelength band conversion, and worse on the shorter wavelength side after the wavelength band conversion. Reference symbol G90 shows an example of the transmission characteristics of wavelength band X before conversion and wavelength band Y after conversion. In wavelength band X before conversion, the transmission characteristics are worse on the longer wavelength side, and in wavelength band Y after conversion, the transmission characteristics are worse on the shorter wavelength side.

[0169] Reference symbol G91 indicates an example of the order of wavelengths when converting from wavelength band X to wavelength band Y. Wavelength converters 12a-12c, 12b', 44a-44c, 52a-52c, 54a-54c convert wavelengths λ1, λ2,...,λn included in wavelength band X to wavelengths λ1', λ2',...,λn' at positions shifted by a predetermined width on the wavelength axis. Therefore, the order of wavelengths λ1', λ2',...,λn' included in wavelength band Y after conversion is the same as the order of wavelengths λ1, λ2,...,λn included in wavelength band X before conversion.

[0170] Therefore, for example, wavelengths λ1 and λ2 on the short wavelength side with good transmission characteristics are converted to wavelengths λ1' and λ2' on the wavelength side with poor transmission characteristics. Also, for example, wavelength λn on the long wavelength side with poor transmission characteristics is converted to wavelength λn' on the short wavelength side with good transmission characteristics. As a result, the transmission characteristics are averaged among the wavelengths λ1', λ2', ..., λn' included in the converted wavelength band Y.

[0171] In this example, an example is given of conversion from the shorter wavelength side wavelength band X to the longer wavelength side wavelength band Y, but even in the opposite case of conversion from the longer wavelength side wavelength band Y to the shorter wavelength side wavelength band X, the transmission characteristics are averaged by maintaining the order of the wavelengths during wavelength conversion in the same manner as above. Also, in this example, an example is given of the transmission characteristics being worse on the longer wavelength side before conversion and worse on the shorter wavelength side after conversion, but even in the opposite case of the transmission characteristics being worse on the shorter wavelength side before conversion and worse on the longer wavelength side after conversion, the transmission characteristics are averaged by maintaining the order of the wavelengths during wavelength conversion in the same manner as above.

[0172] (The order of wavelengths at both ends of the transmission line is the same) For normal transmission and reception, it is desirable that the order of wavelengths of wavelength multiplexed optical signals Sa to Sd is the same when transmitting from the transmitting device 2 and when receiving from the receiving device 3. Since the transmitting device 2 and the receiving device 3 each perform wavelength band conversion once, it is sufficient that the order of wavelengths is the same at both ends of the transmission line 90. The relationship between the number of nodes 91 in the transmission system 9, the number of wavelength converters that reverse the order of wavelengths at each node 91, and the number of wavelength converters that maintain the same order of wavelengths will be described below.

[0173] 20 is a diagram showing wavelength conversion of wavelength multiplexed optical signals Sa, Sb, and Sc when all wavelength converters 12a, 12b, and 12c of relay devices 1 of nodes #1 and #2 reverse the order of wavelengths. Here, "(reverse)" indicates that wavelength converters 12a, 12b, and 12c perform wavelength conversion so as to reverse the order of wavelengths.

[0174] The order of wavelengths of each of the wavelength-multiplexed optical signals Sa, Sb, Sc is reversed every time it passes through the wavelength converters 12a, 12b, 12c in each repeater 1. Therefore, the order of wavelengths is reversed when passing through node #1, but is reversed again when passing through the subsequent node #2, returning to the original order. Therefore, if only the wavelength converters 12a, 12b, 12c that reverse the order of wavelengths are provided in the (2×N) nodes 91, the order of wavelengths of each of the wavelength-multiplexed optical signals Sa, Sb, Sc can be made the same at both ends of the transmission line 90.

[0175] 21 is a diagram showing wavelength conversion of wavelength multiplexed optical signals Sa, Sb, and Sc when two of the wavelength converters 12a, 12b, and 12c in each relay device 1 of nodes #1 to #3 reverse the order of the wavelengths. Here, "(reverse)" indicates that the wavelength converters 12a, 12b, and 12c perform wavelength conversion so as to reverse the order of the wavelengths, and "(same)" indicates that the wavelength converters 12a, 12b, and 12c perform wavelength conversion so as to maintain the order of the wavelengths the same as before the conversion.

[0176] In this example, as an example, each wavelength converter 12c that converts the wavelength band from S band to C band maintains the order of the wavelengths the same before and after the conversion, and the other wavelength converters 12a, 12b reverse the order of the wavelengths, but either one of the wavelength converters 12a, 12b may maintain the order of the wavelengths the same before and after the conversion.

[0177] The wavelength order of the wavelength multiplexed optical signals Sa, Sb, and Sc is reversed in the wavelength conversion of the repeater 1 of two of the nodes #1 to #3, while the order is maintained before and after the conversion in the remaining node. Therefore, the wavelength order is restored to the original order by two wavelength conversions (L-band to S-band and C-band to L-band) that reverse the wavelength order.

[0178] Therefore, if each of the wavelength-multiplexed optical signals Sa, Sb, Sc is wavelength-converted at least once each into the L band and the S band, the wavelength order is restored. Therefore, when there is an even number of wavelength converters 12a, 12b, 12c that reverse the wavelength order (two types in this example), the wavelength order of each of the wavelength-multiplexed optical signals Sa, Sb, Sc can be made the same at both ends of the transmission line 90 as long as the number of nodes is a multiple (ω×N) of the number of wavelength bands (number of bands) ω.

[0179] 22 is a diagram showing wavelength conversion of wavelength multiplexed optical signals Sa, Sb, Sc when one of the wavelength converters 12a, 12b, 12c of each relay device 1 of nodes #1 to #6 reverses the order of the wavelengths. Here, "(reverse)" indicates that the wavelength converters 12a, 12b, 12c perform wavelength conversion so as to reverse the order of the wavelengths, and "(same)" indicates that the wavelength converters 12a, 12b, 12c perform wavelength conversion so as to maintain the order of the wavelengths the same as before the conversion.

[0180] In this example, as an example, each wavelength converter 12a that converts the wavelength band from L band to S band reverses the order of the wavelengths, and the other wavelength converters 12b, 12c maintain the order of the wavelengths the same before and after the conversion, but either one of the wavelength converters 12b, 12c may maintain the order of the wavelengths the same before and after the conversion.

[0181] For the wavelength multiplexed optical signals Sa, Sb, and Sc, the order of wavelengths is reversed in the wavelength conversion of the repeater 1 of two nodes among the nodes #1 to #6, while the order is maintained before and after conversion in the other four nodes. Therefore, the order of wavelengths is restored to the original order by two wavelength conversions (wavelength conversion from L band to S band) that reverse the order of wavelengths.

[0182] Therefore, if each of the wavelength-multiplexed optical signals Sa, Sb, and Sc is wavelength-converted to the S band an even number of times, the wavelength order is restored to the original order. Therefore, if there is an odd number of types of wavelength converters 12a, 12b, and 12c that reverse the wavelength order (one type in this example), the wavelength order of each of the wavelength-multiplexed optical signals Sa, Sb, and Sc can be made the same at both ends of the transmission line 90 if the number of nodes is an even number (2×ω×N) of bands ω.

[0183] The above-described embodiment is a preferred example of the present invention, but the present invention is not limited to this embodiment and can be modified in various ways without departing from the scope of the present invention.

[0184] In addition, the following supplementary notes are provided in relation to the above description. (Note 1) A demultiplexer that demultiplexes a plurality of wavelength-multiplexed optical signals from a multiplexed light in which the plurality of wavelength-multiplexed optical signals having different wavelength bands are multiplexed; a plurality of optical amplifiers each amplifying the plurality of wavelength-multiplexed optical signals; a wavelength conversion unit that converts each wavelength band of at least some of the wavelength multiplexed optical signals amplified by the plurality of optical amplifiers into another wavelength band of the at least some of the wavelength multiplexed optical signals such that wavelength bands do not overlap among the plurality of wavelength multiplexed optical signals; a multiplexing section for multiplexing the plurality of wavelength-multiplexed optical signals whose wavelength bands have been converted by the wavelength conversion section. (Note 2) At least a portion of the wavelength multiplexed optical signals has poorer transmission characteristics as the wavelength approaches the longer wavelength side or the shorter wavelength side before and after the wavelength band conversion; The transmission device described in Appendix 1, characterized in that the wavelength conversion unit converts the wavelength of each of the multiple optical signals wavelength-multiplexed into at least some of the wavelength-multiplexed optical signals into other wavelengths at symmetric positions on the wavelength axis around a predetermined center wavelength. (Note 3) Before the wavelength band conversion, the at least some of the wavelength multiplexed optical signals have poorer transmission characteristics toward one of the longer wavelength side and the shorter wavelength side, and after the wavelength band conversion, the at least some of the wavelength multiplexed optical signals have poorer transmission characteristics toward the other of the longer wavelength side and the shorter wavelength side, The transmission device described in Appendix 1, characterized in that the wavelength conversion unit converts the wavelength of each of the multiple optical signals wavelength-multiplexed into at least some of the wavelength-multiplexed optical signals to another wavelength at a position shifted by a predetermined width on the wavelength axis. (Supplementary Note 4) The transmission device according to any one of Supplementary Notes 1 to 3, wherein the wavelength conversion unit converts at least one wavelength band of the plurality of wavelength-multiplexed optical signals to another wavelength band by multiple stages of wavelength conversion. (Additional Note 5) A demultiplexer that demultiplexes a plurality of wavelength-multiplexed optical signals from a multiplexed light in which the plurality of wavelength-multiplexed optical signals having different wavelength bands are multiplexed; a plurality of optical amplifiers each amplifying the plurality of wavelength-multiplexed optical signals; a plurality of wavelength converters each converting a wavelength band of the plurality of wavelength multiplexed optical signals amplified by the plurality of optical amplifiers into another wavelength band of the plurality of wavelength multiplexed optical signals; a multiplexing unit that multiplexes the plurality of wavelength-multiplexed optical signals; a plurality of optical switches that select, as output routes of the plurality of wavelength-multiplexed optical signals separated from the multiplexed light by the separation unit, a route that passes through the plurality of wavelength converters and leads to the multiplexing unit, and a route that bypasses the number of wavelength converters and leads to the multiplexing unit; a detection unit for detecting a transmission characteristic of each of the plurality of wavelength multiplexed optical signals; a control unit that controls each of the optical switches so as to reduce a difference in transmission characteristics of each of the wavelength-multiplexed optical signals detected by the detection unit. (Appendix 6) A plurality of wavelength-multiplexed optical signals having different wavelength bands are separated from a multiplexed light in which the plurality of wavelength-multiplexed optical signals are multiplexed; amplifying each of the plurality of wavelength multiplexed optical signals; converting each wavelength band of at least a portion of the amplified wavelength multiplexed optical signals into another wavelength band of the at least a portion of the wavelength multiplexed optical signals such that the wavelength bands do not overlap among the plurality of wavelength multiplexed optical signals; A transmission method comprising multiplexing said plurality of wavelength-multiplexed optical signals whose wavelength bands have been converted. (Note 7) At least a portion of the wavelength multiplexed optical signals has poorer transmission characteristics as the wavelength approaches the longer wavelength side or the shorter wavelength side before and after the wavelength band conversion; The transmission method described in claim 5, characterized in that the wavelengths of the optical signals wavelength-multiplexed into each of the at least some of the wavelength-multiplexed optical signals are converted to other wavelengths at symmetric positions on the wavelength axis around a predetermined center wavelength. (Additional Note 8) Before the wavelength band conversion, the at least some of the wavelength multiplexed optical signals have poorer transmission characteristics toward one of the longer wavelength side and the shorter wavelength side, and after the wavelength band conversion, the at least some of the wavelength multiplexed optical signals have poorer transmission characteristics toward the other of the longer wavelength side and the shorter wavelength side, The transmission method according to claim 7, wherein the wavelength of each of a plurality of optical signals wavelength-multiplexed into each of said at least some of the wavelength-multiplexed optical signals is converted to another wavelength at a position shifted by a predetermined width on the wavelength axis. (Supplementary Note 9) The transmission device according to any one of Supplementary Notes 6 to 8, wherein at least one wavelength band of the plurality of wavelength-multiplexed optical signals is converted into another wavelength band by a plurality of stages of wavelength conversion. (Appendix 10) A multiplexed light beam is generated by multiplexing a plurality of wavelength-multiplexed optical signals having different wavelength bands, and the multiple wavelength-multiplexed optical signals are separated from the multiplexed light beam; amplifying each of the plurality of wavelength multiplexed optical signals; converting the wavelength bands of the amplified wavelength-multiplexed optical signals into other wavelength bands of the wavelength-multiplexed optical signals by a plurality of wavelength converters, respectively; A multiplexing unit multiplexes the plurality of wavelength-multiplexed optical signals; selecting, by a plurality of optical switches, destination routes of the plurality of wavelength-multiplexed optical signals separated from the multiplexed light from among a route passing through the plurality of wavelength converters to the multiplexing unit and a route bypassing the plurality of wavelength converters to the multiplexing unit, Detecting a transmission characteristic of each of the plurality of wavelength multiplexed optical signals; A transmission method comprising controlling the plurality of optical switches so as to reduce a difference between the transmission characteristics of each of the detected plurality of wavelength-multiplexed optical signals. (Additional Note 11) At least some of the plurality of wavelength multiplexed optical signals have poorer transmission characteristics as the wavelengths become longer or shorter before and after conversion of the wavelength band; A transmission method according to claim 10, characterized in that the wavelengths of the optical signals wavelength-multiplexed into at least a portion of the wavelength-multiplexed optical signals are converted to other wavelengths at symmetric positions on the wavelength axis around a predetermined center wavelength. (Additional Note 12) At least some of the plurality of wavelength multiplexed optical signals have poorer transmission characteristics toward one of the longer wavelength side and the shorter wavelength side before conversion of the wavelength band, and have poorer transmission characteristics toward the other of the longer wavelength side and the shorter wavelength side after conversion of the wavelength band; A transmission method according to claim 10, characterized in that the wavelengths of each of the plurality of optical signals wavelength-multiplexed into at least a portion of the plurality of wavelength-multiplexed optical signals are converted to other wavelengths at positions shifted by a predetermined width on the wavelength axis. (Supplementary Note 13) The transmission device according to any one of Supplementary Notes 10 to 12, wherein at least one wavelength band of the plurality of wavelength-multiplexed optical signals is converted into another wavelength band by a plurality of stages of wavelength conversion. (Appendix 14) A system including one or more transmission devices provided on a transmission path between a transmission device that transmits a multiplexed light obtained by multiplexing a plurality of wavelength-multiplexed optical signals having different wavelength bands, and a reception device that receives the multiplexed light, The one or more transmission devices, a demultiplexer that demultiplexes the plurality of wavelength-multiplexed optical signals from the multiplexed light; a plurality of optical amplifiers each amplifying the plurality of wavelength-multiplexed optical signals; a wavelength conversion unit that converts each wavelength band of at least some of the wavelength multiplexed optical signals amplified by the plurality of optical amplifiers into another wavelength band of the at least some of the wavelength multiplexed optical signals such that wavelength bands do not overlap among the plurality of wavelength multiplexed optical signals; a multiplexing section that multiplexes the plurality of wavelength-multiplexed optical signals whose wavelength bands have been converted by the wavelength conversion section. (Additional Note 15) The one or more transmission devices are provided so as to divide the transmission line into transmission sections whose number is a multiple of the number of the plurality of wavelength-multiplexed optical signals, 15. The transmission system according to claim 14, wherein the wavelength conversion unit converts each wavelength band of the plurality of wavelength multiplexed optical signals into another wavelength band of the plurality of wavelength multiplexed optical signals. [Explanation of symbols]

[0185] 1,1a~1e,1b',1d',4,5a,5b Relay device 2. Transmitting device 3. Receiving device 9. Transmission Systems 11a to 11c, 42a to 42c, 51a to 51d Optical amplifiers 12a~12c, 12b', 44a, 44b Wavelength converter 44b2,12a1,12a2 Wavelength converter 43a~43c Optical switch 47 Monitor Circuit 48 Control Circuit 52a-52d, 54a-54d Wavelength converter 10,40,50 duplexer 13,46,53 Multiplexer 90 Transmission Line 91 nodes

Claims

1. a separation unit that separates a plurality of wavelength multiplexed optical signals from a multiplexed light obtained by multiplexing a plurality of wavelength multiplexed optical signals having different wavelength bands; a plurality of optical amplifiers each amplifying the plurality of wavelength-multiplexed optical signals; a wavelength conversion unit that converts each wavelength band of at least some of the wavelength multiplexed optical signals amplified by the plurality of optical amplifiers into another wavelength band of the at least some of the wavelength multiplexed optical signals such that wavelength bands do not overlap among the plurality of wavelength multiplexed optical signals; a multiplexing unit that multiplexes the plurality of wavelength-multiplexed optical signals whose wavelength bands have been converted by the wavelength conversion unit, The wavelength converting portion is converting at least one wavelength band of the wavelength multiplexed optical signal from a first wavelength band in which the transmission characteristics become worse toward one of the longer and shorter wavelength sides to a second wavelength band in which the transmission characteristics become worse toward the other of the longer and shorter wavelength sides; A transmission device characterized in that, in the conversion, the wavelength of the first wavelength band of each of the multiple optical signals wavelength-multiplexed into the wavelength-multiplexed optical signal is converted to the wavelength of the second wavelength band at a position shifted a predetermined width on the wavelength axis.

2. 2. The transmission device according to claim 1, wherein the wavelength conversion section converts at least one wavelength band of the plurality of wavelength multiplexed optical signals into another wavelength band through a plurality of stages of wavelength conversion.

3. a separation unit that separates a plurality of wavelength multiplexed optical signals from a multiplexed light obtained by multiplexing a plurality of wavelength multiplexed optical signals having different wavelength bands; a plurality of optical amplifiers each amplifying the plurality of wavelength-multiplexed optical signals; a plurality of wavelength converters each converting a wavelength band of the plurality of wavelength multiplexed optical signals amplified by the plurality of optical amplifiers into another wavelength band of the plurality of wavelength multiplexed optical signals; a multiplexing unit that multiplexes the plurality of wavelength-multiplexed optical signals; a plurality of optical switches that select, as the output route of the plurality of wavelength-multiplexed optical signals separated from the multiplexed light by the separation unit, from a route that passes through one of the plurality of wavelength converters to the multiplexing unit, and a route that bypasses the plurality of wavelength converters to the multiplexing unit.

4. Separating a plurality of wavelength-multiplexed optical signals from a multiplexed light in which a plurality of wavelength-multiplexed optical signals having different wavelength bands are multiplexed; amplifying each of the plurality of wavelength multiplexed optical signals; converting each wavelength band of at least a portion of the amplified wavelength multiplexed optical signals into another wavelength band of the at least a portion of the wavelength multiplexed optical signals such that the wavelength bands do not overlap among the plurality of wavelength multiplexed optical signals; multiplexing the plurality of wavelength-multiplexed optical signals whose wavelength bands have been converted; The conversion of the wavelength band of at least one of the wavelength multiplexed optical signals includes: converting from a first wavelength band in which the transmission characteristics are worse toward one of the long wavelength side and the short wavelength side to a second wavelength band in which the transmission characteristics are worse toward the other of the long wavelength side and the short wavelength side; A transmission method characterized in that, in the conversion, the wavelength of the first wavelength band of each of the multiple optical signals wavelength-multiplexed into the wavelength-multiplexed optical signal is converted to the wavelength of the second wavelength band at a position shifted by a predetermined width on the wavelength axis.

5. Separating a plurality of wavelength-multiplexed optical signals from a multiplexed light in which a plurality of wavelength-multiplexed optical signals having different wavelength bands are multiplexed; amplifying each of the plurality of wavelength multiplexed optical signals; converting the wavelength bands of the amplified wavelength-multiplexed optical signals into other wavelength bands of the wavelength-multiplexed optical signals by a plurality of wavelength converters, respectively; A multiplexing unit multiplexes the plurality of wavelength-multiplexed optical signals; A transmission method characterized in that a route to the output of the multiple wavelength multiplexed optical signals separated from the multiplexed light is selected by a plurality of optical switches from a route that passes through one of the multiple wavelength converters to the multiplexing unit, and a route that bypasses the multiple wavelength converters to the multiplexing unit.

6. a transmitting device that transmits a multiplexed light obtained by multiplexing a plurality of wavelength-multiplexed optical signals having different wavelength bands, and one or more transmitting devices that are provided on a transmission path between the transmitting device and a receiving device that receives the multiplexed light, The one or more transmission devices, a demultiplexer that demultiplexes the plurality of wavelength-multiplexed optical signals from the multiplexed light; a plurality of optical amplifiers each amplifying the plurality of wavelength-multiplexed optical signals; a wavelength conversion unit that converts each wavelength band of at least some of the wavelength multiplexed optical signals amplified by the plurality of optical amplifiers into another wavelength band of the at least some of the wavelength multiplexed optical signals such that wavelength bands do not overlap among the plurality of wavelength multiplexed optical signals; a multiplexing unit that multiplexes the plurality of wavelength-multiplexed optical signals whose wavelength bands have been converted by the wavelength conversion unit, The conversion of the wavelength band of at least one of the wavelength multiplexed optical signals includes: converting from a first wavelength band in which the transmission characteristics are worse toward one of the long wavelength side and the short wavelength side to a second wavelength band in which the transmission characteristics are worse toward the other of the long wavelength side and the short wavelength side; A transmission system characterized in that, in the conversion, the wavelength of the first wavelength band of each of the multiple optical signals wavelength-multiplexed into the wavelength-multiplexed optical signal is converted to the wavelength of the second wavelength band at a position shifted by a predetermined width on the wavelength axis.

7. the one or more transmission devices are provided so as to divide the transmission line into transmission sections whose number is a multiple of the number of the plurality of wavelength multiplexed optical signals; 7. The transmission system according to claim 6, wherein the wavelength conversion section converts each wavelength band of the plurality of wavelength multiplexed optical signals into another wavelength band of the plurality of wavelength multiplexed optical signals.

8. a transmitting device that transmits a multiplexed light obtained by multiplexing a plurality of wavelength-multiplexed optical signals having different wavelength bands, and one or more transmitting devices that are provided on a transmission path between the transmitting device and a receiving device that receives the multiplexed light, The one or more transmission devices, a demultiplexer that demultiplexes the plurality of wavelength-multiplexed optical signals from the multiplexed light; a plurality of optical amplifiers each amplifying the plurality of wavelength-multiplexed optical signals; a plurality of wavelength converters each converting a wavelength band of the plurality of wavelength multiplexed optical signals amplified by the plurality of optical amplifiers into another wavelength band of the plurality of wavelength multiplexed optical signals; a multiplexing unit that multiplexes the plurality of wavelength-multiplexed optical signals whose wavelength bands have been converted by the plurality of wavelength converters; a plurality of optical switches that select, as the output route of the plurality of wavelength-multiplexed optical signals separated from the multiplexed light by the separation unit, from a route that passes through one of the plurality of wavelength converters to the multiplexing unit, and a route that bypasses the plurality of wavelength converters to the multiplexing unit.

Images