Optical communication device

Abstract

To suppress deterioration of the quality of an optical signal in a WDM transmission system using a plurality of wavelength bands.SOLUTION: An optical communication device includes a receiving circuit that receives a WDM signal and a transmitting circuit that transmits the WDM signal to a second node. The receiving circuit includes a wavelength filter for extracting a plurality of input optical signals arranged in a first wavelength band from the received WDM signal, a wavelength selective switch, and a wavelength converter. The wavelength selective switch guides an optical signal to be transmitted to the second node from the plurality of input optical signals to the transmitting circuit. The wavelength selective switch guides an optical signal to be dropped from the received WDM signal from the plurality of input optical signals to the wavelength converter. The wavelength converter performs wavelength conversion from the first wavelength band to a second wavelength band. The wavelength-converted optical signal is transmitted to an access network.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to an optical communication device that transmits a wavelength division multiplexing (WDM) signal. [Background technology]

[0002] WDM transmission has been put to practical use to realize large-capacity optical communications. WDM can transmit multiple optical signals through a single optical fiber by multiplexing multiple wavelength channels. Each node in a WDM transmission system is provided with, for example, a reconfigurable optical add-drop multiplexer (ROADM). The ROADM can drop an optical signal of a desired wavelength from a WDM signal. The dropped optical signal is transferred to, for example, an access network. The ROADM can also add an optical signal received from the access network to an available channel of the WDM signal.

[0003] In existing WDM transmission systems, the C (Conventional) band and / or the L (Long Wavelength) band are mainly used. The wavelength range of the C band is about 1530 to 1565 nm, and the wavelength range of the L band is about 1565 to 1625 nm. Furthermore, multiple wavelength channels are set within each wavelength band.

[0004] In recent years, in order to realize a larger capacity of optical communication, WDM transmission using the S (Short Wavelength) band and / or the U (Ultra-Long Wavelength) band in addition to the C band and L band has been considered. The wavelength range of the S band is about 1460 to 1530 nm, and the wavelength range of the U band is about 1625 to 1675 nm.

[0005] However, optical devices (e.g., optical transceivers, etc.) for processing S-band / U-band optical signals have not yet been put to practical use. Or, such optical devices are very expensive. For this reason, ROADMs equipped with wavelength converters have been proposed. For example, when a WDM transmission system transmits optical signals using C-band and S-band, the ROADM is equipped with a wavelength converter that performs wavelength conversion between the S-band and C-band. Or, when a WDM transmission system transmits optical signals using L-band and U-band, the ROADM is equipped with a wavelength converter that performs wavelength conversion between the U-band and L-band. And, according to this configuration, it is possible to expand the wavelength region in which communication is possible while using existing optical devices. Note that a configuration in which a wavelength converter is implemented in each node is described in, for example, Patent Document 1. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2020-137042 A Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, by providing a wavelength converter in a ROADM, the wavelength region in which communication is possible can be expanded. However, in conventional configurations, noise generated in the wavelength converter can degrade the optical signal-to-noise ratio (OSNR). Therefore, when a WDM signal passes through multiple nodes (i.e., multiple ROADMs), the degradation of the OSNR accumulates, and communication quality may deteriorate.

[0008] An object of one aspect of the present invention is to suppress deterioration of the quality of an optical signal in a WDM transmission system using a plurality of wavelength bands. [Means for solving the problem]

[0009] An optical communication device according to one aspect of the present invention processes a WDM signal in a WDM transmission system. The optical communication device includes a receiving circuit that receives a first WDM signal from a first node of the WDM transmission system, and a transmitting circuit that transmits a second WDM signal to a second node of the WDM transmission system. The receiving circuit includes a wavelength filter that extracts a plurality of input optical signals arranged in a first wavelength band from the first WDM signal, a wavelength selective switch having a first input port, a second input port, a plurality of output ports, and a wavelength conversion port, and an optical circuit including a wavelength converter optically coupled to the wavelength selective switch. The plurality of input optical signals are guided to the first input port. The wavelength selective switch guides an optical signal that is branched from the first WDM signal among the plurality of input optical signals to the wavelength conversion port. The optical circuit performs wavelength conversion from the first wavelength band to a second wavelength band on the optical signal output via the wavelength conversion port to generate a wavelength-converted optical signal. The wavelength-converted optical signal is guided to the second input port. The wavelength selective switch guides the optical signal to be transmitted to the second node and the wavelength converted optical signal among the plurality of input optical signals to corresponding output ports among the plurality of output ports, respectively. The optical circuit guides the optical signal outputted through the plurality of output ports and located within the first wavelength band to the transmission circuit, and guides the optical signal outputted through the plurality of output ports and located within the second wavelength band to an access network connecting the optical communication device. Effect of the Invention

[0010] According to the above-described aspect, degradation of the quality of an optical signal is suppressed in a WDM transmission system using a plurality of wavelength bands. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating an example of a WDM transmission system according to an embodiment of the present invention. [Diagram 2] A diagram showing an example of the configuration of a ROADM. [Diagram 3] FIG. 1 illustrates an example of a ROADM equipped with wavelength converters for expanding the wavelength range. [Figure 4] FIG. 1 is a diagram illustrating an example of a WDM signal whose wavelength range is expanded. [Diagram 5] FIG. 13 is a diagram showing another example of a ROADM equipped with a wavelength converter for expanding the wavelength range. [Figure 6] FIG. 2 is a diagram illustrating an example of a configuration of a ROADM according to an embodiment of the present invention. [Figure 7] FIG. 2 is a diagram illustrating an example of a receiving circuit and a transmitting circuit implemented in a ROADM according to an embodiment of the present invention. [Figure 8] FIG. 2 is a diagram illustrating an example of an operation of a receiving circuit. [Figure 9] FIG. 4 is a diagram illustrating an example of an operation of a transmission circuit. [Figure 10] 11 is a flowchart showing an example of a procedure for setting a WSS in a ROADM. [Figure 11] 1 is a diagram showing an example of the level and noise figure of an optical signal transmitted by a ROADM. [Figure 12] FIG. 13 is a diagram showing an effect according to an embodiment of the present invention. [Figure 13] FIG. 11 is a diagram illustrating an example of a receiving circuit and a transmitting circuit implemented in a ROADM according to a second embodiment. [Figure 14] FIG. 11 is a diagram illustrating an example of an operation of the receiving circuit according to the second embodiment. [Figure 15] FIG. 11 is a diagram illustrating an example of an operation of the transmission circuit according to the second embodiment. [Figure 16] FIG. 13 is a diagram illustrating a variation of the second embodiment. [Figure 17] FIG. 13 is a diagram illustrating an example of a receiving circuit and a transmitting circuit implemented in a ROADM according to a third embodiment. [Figure 18] FIG. 11 is a diagram illustrating an example of the operation of a receiving circuit and a transmitting circuit in the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] FIG. 1 shows an example of a WDM transmission system according to an embodiment of the present invention. In this example, the WDM transmission system 500 connects a plurality of networks (for example, a core network, a metropolitan network, etc.) to each other. Furthermore, each node of the WDM transmission system 500 is provided with a ROADM1 (1a to 1f). The ROADM1 is an example of an optical communication device that processes a WDM signal. Therefore, the ROADM1 can drop an optical signal of a desired wavelength from the WDM signal. The optical signal dropped from the WDM signal is guided to an access network or a device under the ROADM1. Furthermore, the ROADM1 can add an optical signal transmitted from the access network or a device under the ROADM1 to an empty channel of the WDM signal.

[0013] In the WDM transmission system 500 having the above configuration, for example, it is assumed that communication is performed between the terminal 2a and the terminal 2b. At this time, a wavelength path is set between the terminal 2a and the terminal 2b by a network management system (not shown). That is, control information for performing communication between the terminal 2a and the terminal 2b is set in each ROADM 1. It is assumed that this wavelength path is realized by a wavelength channel that propagates an optical signal of wavelength λ1. Hereinafter, the optical signal of wavelength λ1 may be referred to as "optical signal λ1".

[0014] Data to be transmitted from the terminal 2a to the terminal 2b is guided to a transponder that generates an optical signal λ1. This transponder is connected to, for example, ROADM1b. Then, this transponder generates an optical signal λ1 that transmits data. The optical signal λ1 output from the transponder is guided to ROADM1b. ROADM1b adds the optical signal λ1 to a WDM signal. Each ROADM1 processes the WDM signal according to control information set by a network management system. Specifically, ROADM1b guides the optical signal λ1 to ROADM1c, and ROADM1c guides the optical signal λ1 to ROADM1e. Then, ROADM1e drops the optical signal λ1 from the WDM signal and guides it to the access network. As a result, the terminal 2b receives the data transmitted from the terminal 2a.

[0015] When communication is performed between terminal 2a and terminal 2c, a wavelength path is set between terminal 2a and terminal 2c by the network management system. This wavelength path is realized by a wavelength channel that propagates an optical signal with wavelength λ2. Hereinafter, the optical signal with wavelength λ2 may be referred to as "optical signal λ2."

[0016] Data to be transmitted from the terminal 2a to the terminal 2c is guided to a transponder that generates an optical signal λ2. This transponder generates the optical signal λ2 that transmits the data. The optical signal λ2 output from the transponder is guided to the ROADM 1b. The ROADM 1b adds the optical signal λ2 to the WDM signal. Each ROADM 1 processes the WDM signal according to control information set by the network management system. Specifically, the ROADM 1b guides the optical signal λ2 to the ROADM 1c, the ROADM 1c guides the optical signal λ2 to the ROADM 1d, and the ROADM 1d guides the optical signal λ2 to the ROADM 1f. Then, the ROADM 1f drops the optical signal λ2 from the WDM signal and guides it to the access network. As a result, the terminal 2c receives the data transmitted from the terminal 2a.

[0017] Thus, in the WDM transmission system 500, an optical signal transmitted from an access network or a terminal is added to a WDM signal and transmitted through one or more ROADMs. Then, the optical signal is dropped from the WDM signal by the ROADM that accommodates the destination terminal.

[0018] 2 shows an example of the configuration of a ROADM. In this example, the ROADM 1 is a four-way ROADM. That is, the ROADM 1 can transmit WDM signals between four nodes (N1 to N4). The ROADM 1 also includes an add / drop unit 13.

[0019] The ROADM 1 includes a pair of WSS 11 and WSS 12 for each of the paths (#1 to #4). The WSS 11 processes the WDM signal received from the corresponding node. That is, the WSS 11 processes each optical signal in the received WDM signal according to the wavelength. For example, the WSS 11 (#1) guides each optical signal in the WDM signal received from the node N1 to the WSS 12 (#2) corresponding to the path #2, the WSS 12 (#3) corresponding to the path #3, the WSS 12 (#4) corresponding to the path #4, or the add / drop unit 13 according to the wavelength. The WSS 12 generates a WDM signal to be transmitted to the corresponding node. For example, the WSS 12 (#1) multiplexes the optical signals guided from the WSS 11 (#2) corresponding to the path #2, the WSS 11 (#3) corresponding to the path #3, the WSS 11 (#4) corresponding to the path #4, and the add / drop unit 13 to generate a WDM signal.

[0020] The add / drop unit 13 includes a plurality of transponders 14 and a transponder aggregator (TPA) 15 that accommodates the plurality of transponders 14. Each transponder 14 includes an optical transmitter (TX) and an optical receiver (RX). It is preferable that different wavelengths are assigned to the plurality of transponders 14. The TPA 15 includes a WSS or MCS (Multicast Switch) and can associate any transponder 14 with any path.

[0021] For example, when a signal addressed to node N1 is generated by transponder 14, TPA 15 guides the signal to WSS 12 (#1). Also, when a signal is received from any of WSSs 11, TPA 15 guides the signal to the transponder 14 corresponding to the destination.

[0022] In this way, the ROADM processes the WDM signal using the WSS. On the other hand, in order to realize a further increase in capacity of optical communication, WDM transmission using the S band and / or the U band in addition to the C band / L band is being considered. In this case, the ROADM is required to have a WSS capable of processing the S band, the C band, the L band, and the U band. However, it is not easy to manufacture a WSS that processes a wideband WDM signal. Or, a WSS that processes a wideband WDM signal is expensive.

[0023] This problem can be solved by appropriately converting the wavelength of the optical signal using a wavelength converter in the ROADM. For example, by providing a wavelength converter that converts the wavelength of the optical signal between the S band and the C band, and a wavelength converter that converts the wavelength of the optical signal between the U band and the L band, the ROADM can process a WDM signal including the S / C / L / U bands using a WSS corresponding to the C / L bands.

[0024] FIG. 3 shows an example of a ROADM equipped with a wavelength converter for expanding a wavelength region. In the example shown in FIG. 3, the ROADM 20 has two routes (#1 and #2). That is, the ROADM 20 can transmit a WDM signal to and from the node N1 via route #1, and can transmit a WDM signal to and from the node N2 via route #2. However, in FIG. 3, in order to make the drawing easier to understand, a circuit for transmitting a WDM signal from the node N1 to the node N2 is depicted, and a circuit for transmitting a WDM signal from the node N2 to the node N1 is omitted.

[0025] The ROADM 20 transmits WDM signals including the S band, C band, L band, and U band shown in Fig. 4. Note that "S", "C", "L", and "U" shown in Fig. 3 represent the S band, C band, L band, and U band, respectively. "S / C / L / U" represents a state in which the S band, C band, L band, and U band are multiplexed. Similarly, "C / L" represents a state in which the C band and the L band are multiplexed.

[0026] The ROADM 20 includes a wavelength filter 21, wavelength converters 22 and 23, WSSs 24 to 27, wavelength converters 28 and 29, a multiplexer 30, and an add / drop unit 31. The ROADM 20 may further include other devices, circuits, or functions not shown in FIG.

[0027] The wavelength filter 21 separates the WDM signal arriving at the ROADM 20 via the path #1 into wavelength bands. Specifically, the wavelength filter 21 extracts an S-band WDM signal, a C-band WDM signal, an L-band WDM signal, and a U-band WDM signal from the received WDM signal.

[0028] The wavelength converter 22 performs wavelength conversion from the S band to the C band. Thus, the wavelength converter 22 converts the S band WDM signal extracted by the wavelength filter 21 into a C band WDM signal. The wavelength converter 23 performs wavelength conversion from the U band to the L band. Thus, the wavelength converter 23 converts the U band WDM signal extracted by the wavelength filter 21 into an L band WDM signal.

[0029] The C-band WDM signal generated by the wavelength converter 22 and the L-band WDM signal generated by the wavelength converter 23 are each guided to the WSS 24. On the other hand, the C-band WDM signal and the L-band WDM signal extracted by the wavelength filter 21 are each guided to the WSS 25 without being wavelength-converted.

[0030] WSS24 and WSS25 each process an optical signal in an input WDM signal. Specifically, WSS24 guides an optical signal to be transferred to node N2 to WSS26, and guides an optical signal to be transmitted to an access network to an add / drop unit 31. Similarly, WSS25 guides an optical signal to be transmitted to node N2 to WSS27, and guides an optical signal to be transmitted to an access network to the add / drop unit 31. The add / drop unit 31 forwards the optical signals guided from WSS24 and WSS25 to a destination terminal in the access network.

[0031] The add / drop unit 31 can generate an optical signal to be transmitted to the node N2. Here, the optical signal to be transmitted to the node N2 is guided to the WSS 26 or the WSS 27.

[0032] An optical signal to be transmitted from the ROADM 20 to the node N2 using the S band or the U band is guided from the add / drop unit 31 to the WSS 26. However, an optical signal to be transmitted to the node N2 using the S band is arranged in the C band between the add / drop unit 31 and the WSS 26. An optical signal to be transmitted to the node N2 using the U band is arranged in the L band between the add / drop unit 31 and the WSS 26. On the other hand, an optical signal to be transmitted from the ROADM 20 to the node N2 using the C band or the L band is guided from the add / drop unit 31 to the WSS 27. An optical signal to be transmitted to the node N2 using the C band is arranged in the C band between the add / drop unit 31 and the WSS 27. An optical signal to be transmitted to the node N2 using the L band is arranged in the L band between the add / drop unit 31 and the WSS 27.

[0033] The WSS 26 processes the optical signals guided from the WSS 24 and the add / drop unit 31. At this time, the optical signals arranged in the C band are guided to a wavelength converter 28, and the optical signals arranged in the L band are guided to a wavelength converter 29.

[0034] Wavelength converter 28 performs wavelength conversion from C band to S band. Thus, the optical signal guided from WSS 26 is placed in the S band by wavelength converter 28. Wavelength converter 29 performs wavelength conversion from L band to U band. Thus, the optical signal guided from WSS 26 is placed in the U band by wavelength converter 29. The optical signals output from wavelength converter 28 and wavelength converter 29 are guided to multiplexer 30.

[0035] The WSS 27 processes the optical signals guided from the WSS 25 and the add / drop unit 31. At this time, the optical signal to be transmitted to the node N2 is guided to the multiplexer 30 without being wavelength-converted.

[0036] The multiplexer 30 multiplexes the S-band WDM signal output from the wavelength converter 28, the U-band WDM signal output from the wavelength converter 29, and the C / L-band WDM signal output from the WSS 27. This generates an S / C / L / U-band WDM signal. That is, the S / C / L / U-band WDM signal is transmitted from the ROADM 20 to the node N2.

[0037] 3, optical amplifiers 32 are provided between wavelength converters 22, 23 and WSS 24, and between wavelength filter 21 and WSS 25. Optical amplifiers 33 are provided between WSS 26 and wavelength converters 28, 29, and between WSS 27 and multiplexer 30. Optical amplifiers 32, 33 amplify the WDM signal.

[0038] In this way, the ROADM 20 is equipped with wavelength converters (22, 28) that perform wavelength conversion between the S band and the C band, and wavelength converters (23, 29) that perform wavelength conversion between the U band and the L band, and thus can process S / C / L / U band WDM signals using a WSS that corresponds to the C / L band. In other words, the band of WDM signals that the ROADM can process is expanded without widening the bandwidth of the WSS.

[0039] However, in the configuration shown in Fig. 3, the addition of a wavelength converter in the ROADM causes degradation of the optical signal-to-noise ratio (OSNR). Specifically, noise is added to the optical signal in the S / U band WDM signal when it passes through the wavelength converter. Therefore, when the optical signal in the S / U band WDM signal is transmitted through multiple ROADMs, the degradation of the OSNR accumulates.

[0040] FIG. 5 shows another example of a ROADM equipped with a wavelength converter for expanding a wavelength region. In the example shown in FIG. 5, the ROADM 40 has two routes (#1 and #2). That is, the ROADM 40 can transmit a WDM signal between node N1 via route #1, and can transmit a WDM signal between node N2 via route #2. However, in FIG. 5, in order to make the drawing easier to understand, a circuit for transmitting a WDM signal from node N1 to node N2 is depicted, and a circuit for transmitting a WDM signal from node N2 to node N1 is omitted. Also, the ROADM 40 transmits S / C / L / U band WDM signals including S band, C band, L band, and U band, as in the case shown in FIG. 3.

[0041] The ROADM 40 includes a wavelength filter 41, an optical amplifier 42, WSSs 43 to 46, wavelength converters 47, 48, WSSs 49 to 52, wavelength converters 53, 54, WSSs 55 to 58, an optical amplifier 59, a multiplexer 60, and an add / drop unit 61. The ROADM 40 may further include other devices, circuits, or functions not shown in FIG.

[0042] The wavelength filter 41 separates the WDM signal arriving at the ROADM 40 via the path #1 into wavelength bands. Specifically, the wavelength filter 41 extracts an S-band WDM signal, a U-band WDM signal, a C-band WDM signal, and an L-band WDM signal from the received WDM signal. The optical amplifier 42 amplifies the WDM signals of each wavelength band extracted by the wavelength filter 41.

[0043] The WSS 43 processes the S-band WDM signal extracted by the wavelength filter 41. Specifically, the WSS 43 guides the optical signal to be transferred to the node N2 to the WSS 55, and guides the optical signal to be transmitted to the access network to the wavelength converter 47. That is, the optical signal dropped from the S-band WDM signal by the WSS 43 is guided to the wavelength converter 47, and the remaining optical signal not dropped from the S-band WDM signal is guided to the WSS 55. Similarly, the WSS 44 processes the U-band WDM signal extracted by the wavelength filter 41. Specifically, the WSS 44 guides the optical signal to be transmitted to the node N2 to the WSS 56, and guides the optical signal to be transmitted to the access network to the wavelength converter 48. That is, the optical signal dropped from the U-band WDM signal by the WSS 44 is guided to the wavelength converter 48, and the remaining optical signal not dropped from the U-band WDM signal is guided to the WSS 56.

[0044] The wavelength converter 47 performs wavelength conversion from the S band to the C band. Thus, the wavelength converter 47 places the optical signal in the S band guided from the WSS 43 in the C band. The wavelength converter 48 performs wavelength conversion from the U band to the L band. Thus, the wavelength converter 48 places the optical signal in the U band guided from the WSS 43 in the L band.

[0045] The WSS 49 processes the optical signal output from the wavelength converter 47 and the optical signal output from the wavelength converter 48. At this time, the WSS 49 guides each optical signal to the add / drop unit 61. Here, when the add / drop unit 61 includes a plurality of transponders or a plurality of transponder aggregators (TPAs), the WSS 49 can guide each optical signal to the transponder or TPA corresponding to the wavelength.

[0046] The WSS 45 processes the C-band WDM signal extracted by the wavelength filter 41. Specifically, the WSS 45 guides the optical signal to be transmitted to the node N2 to the WSS 57, and guides the optical signal to be transmitted to the access network to the WSS 50. That is, the optical signal dropped from the C-band WDM signal by the WSS 45 is guided to the WSS 50, and the remaining optical signal not dropped from the C-band WDM signal is guided to the WSS 57. Similarly, the WSS 46 processes the L-band WDM signal extracted by the wavelength filter 41. Specifically, the WSS 46 guides the optical signal to be transmitted to the node N2 to the WSS 58, and guides the optical signal to be transmitted to the access network to the WSS 50. That is, the optical signal dropped from the L-band WDM signal by the WSS 46 is guided to the WSS 50, and the remaining optical signal not dropped from the L-band WDM signal is guided to the WSS 58.

[0047] The WSS 50 processes optical signals in the C-band output from the WSS 45 and optical signals in the L-band output from the WSS 46. At this time, the WSS 50 guides each optical signal to the add / drop unit 61. Here, when the add / drop unit 61 includes a plurality of transponders or a plurality of transponder aggregators (TPAs), the WSS 50 can guide each optical signal to a transponder or TPA corresponding to the wavelength.

[0048] The WSS 51 processes optical signals traveling from the add / drop unit 61 to the node N2. At this time, the optical signals arranged in the C-band are guided to the wavelength converter 53, and the optical signals arranged in the L-band are guided to the wavelength converter .

[0049] Wavelength converter 53 performs wavelength conversion from C band to S band. Thus, the optical signal guided from WSS 51 is placed in the S band by wavelength converter 53. Wavelength converter 54 performs wavelength conversion from L band to U band. Thus, the optical signal guided from WSS 51 is placed in the U band by wavelength converter 54. The optical signals output from wavelength converter 53 and wavelength converter 54 are guided to WSS 55 and WSS 56, respectively.

[0050] The WSS 55 processes the optical signal guided from the WSS 43 and the optical signal output from the wavelength converter 53. In this way, an S-band WDM signal is generated. Similarly, the WSS 56 processes the optical signal guided from the WSS 44 and the optical signal output from the wavelength converter 54. In this way, a U-band WDM signal is generated.

[0051] The WSS 52 processes optical signals traveling from the add / drop unit 61 to the node N2. At this time, optical signals assigned to the C-band are guided to the WSS 57, and optical signals assigned to the L-band are guided to the WSS 58.

[0052] The WSS 57 processes the optical signal guided from the WSS 45 and the optical signal guided from the WSS 52. In this way, a C-band WDM signal is generated. Similarly, the WSS 58 processes the optical signal guided from the WSS 46 and the optical signal output from the WSS 52. In this way, an L-band WDM signal is generated.

[0053] The multiplexer 60 multiplexes the S-band WDM signal output from the WSS 55, the U-band WDM signal output from the WSS 56, the C-band WDM signal output from the WSS 57, and the L-band WDM signal output from the WSS 58. As a result, S / C / L / U-band WDM signals are generated. That is, the S / C / L / U-band WDM signals are transmitted from the ROADM 40 to the node N2. The WDM signals output from the WSSs 55 to 58 are each amplified by an optical amplifier 59.

[0054] The add / drop unit 61 guides the optical signals guided from the WSS 49 and WSS 50 to a destination device under the access network or ROADM 40. That is, the optical signal branched from the input WDM signal is guided by the add / drop unit 61 to a destination device under the access network or ROADM 40. The add / drop unit 61 can also add an optical signal received from a source device under the access network or ROADM 40 to an output WDM signal. At this time, a signal to be placed in the S band or U band between the ROADM 40 and node N2 is guided to the WSS 51. A signal to be placed in the C band or L band between the ROADM 40 and node N2 is guided to the WSS 52.

[0055] In this way, the ROADM 40 can process S / C / L / U band WDM signals, similarly to the ROADM 20 shown in Fig. 3. That is, even in the configuration shown in Fig. 5, the band of WDM signals that the ROADM can process is expanded.

[0056] In addition, in the ROADM 40, the optical signal forwarded to the node N2 without being dropped from the WDM signal does not pass through the wavelength converter. For example, among the optical signals included in the S-band WDM signal received from the node N1, the optical signal forwarded to the node N2 is guided to the path #2 by the WSS 43 and the WSS 55. In the following description, the optical signal forwarded to the next node without being dropped from the WDM signal in the ROADM may be referred to as the "through signal."

[0057] Thus, according to the configuration shown in Fig. 5, unlike the configuration shown in Fig. 3, the through signal does not pass through the wavelength converter. Therefore, according to the configuration shown in Fig. 5, noise added to the through signal is suppressed compared to the configuration shown in Fig. 3.

[0058] However, in the configuration shown in Fig. 5, the number of WSSs implemented in the ROADM increases. Specifically, in the case of S-band, in the configuration shown in Fig. 3, one WSS (e.g., WSS24) is implemented for the input path, and one WSS (e.g., WSS26) is implemented for the output path. In contrast, in the configuration shown in Fig. 5, two WSSs (e.g., WSS43 and WSS49) are implemented for the input path, and two WSSs (e.g., WSS51 and WSS55) are implemented for the output path. Here, WSSs are generally expensive. For this reason, the cost of manufacturing the ROADM increases in the configuration shown in Fig. 5.

[0059] <Embodiment> 6 shows an example of the configuration of a ROADM according to an embodiment of the present invention. A ROADM 100 according to the embodiment of the present invention is implemented in each node of a WDM transmission system (for example, the WDM transmission system 500 shown in FIG. 1). In this embodiment, the ROADM 100 is a four-way ROADM. That is, the ROADM 100 can transmit WDM signals between four nodes (N1 to N4).

[0060] The ROADM 100 includes a pair of a receiving circuit 110 and a transmitting circuit 130 for each of the paths (#1 to #4). The receiving circuit 110 processes the WDM signal received from the corresponding node. That is, the receiving circuit 110 processes each optical signal in the received WDM signal according to the wavelength. For example, the receiving circuit 110 (#1) guides each optical signal in the WDM signal received from the node N1 to the transmitting circuit 130 (#2) corresponding to the path #2, the transmitting circuit 130 (#3) corresponding to the path #3, the transmitting circuit 130 (#4) corresponding to the path #4, or the add / drop unit 150 according to the wavelength. The transmitting circuit 130 generates a WDM signal to be transmitted to the corresponding node. For example, the transmitting circuit 130 (#1) multiplexes optical signals guided from the receiving circuit 110 (#2) corresponding to the path #2, the receiving circuit 110 (#3) corresponding to the path #3, the receiving circuit 110 (#4) corresponding to the path #4, and the add / drop unit 150 to generate a WDM signal.

[0061] The add / drop unit 150 includes a plurality of transponders 14 and a transponder aggregator (TPA) 15 that accommodates the plurality of transponders 14. The add / drop unit 150 is connected to an access network. Note that the configuration and operation of the add / drop unit 150 are substantially the same as those of the add / drop unit 13 shown in FIG. 2, and therefore a description thereof will be omitted.

[0062] Fig. 7 shows an example of a receiving circuit and a transmitting circuit implemented in a ROADM 100 according to an embodiment of the present invention. The ROADM 100 shown in Fig. 7 shows a part of the ROADM 100 shown in Fig. 6. Specifically, Fig. 7 shows the receiving circuit 110 (#1), the transmitting circuit 130 (#2), and the add / drop unit 150 shown in Fig. 6.

[0063] The receiving circuit 110 includes a WDM filter 111, a WSS 112, and a wavelength converter 113. However, the receiving circuit 110 may further include other devices not shown in Fig. 7. For example, the receiving circuit 110 may include an optical amplifier that amplifies the optical signal.

[0064] The receiving circuit 110 receives WDM signals transmitted from other nodes. In the example shown in Fig. 7, the receiving circuit 110 (#1) receives a WDM signal transmitted from the node N1 shown in Fig. 6 via a route #1. This WDM signal includes a WDM signal arranged in the S band (hereinafter, S-band WDM signal), a WDM signal arranged in the C band (hereinafter, C-band WDM signal), a WDM signal arranged in the L band (hereinafter, L-band WDM signal), and a WDM signal arranged in the U band (hereinafter, U-band WDM signal).

[0065] The WDM filter 111 extracts an S-band WDM signal, a C-band WDM signal, an L-band WDM signal, and a U-band WDM signal from the input light. Each WDM signal extracted by the WDM filter 111 is preferably amplified by an optical amplifier 121 as shown in Fig. 7. In the following description, a configuration for processing an S-band WDM signal will be described. The S-band WDM signal includes multiple optical signals with different wavelengths arranged within the S band.

[0066] As shown in Fig. 7, the WSS 112 has an input port P1, an input port P2, and a plurality of output ports. The WSS 112 can guide an optical signal input via the input port P1 or the input port P2 to a specified output port. The optical paths in the WSS 112 are set for each wavelength. Each optical path is set in advance according to the destination of the optical signal. The WSS 112 can process optical signals arranged in the S band and optical signals arranged in the C band.

[0067] One of the multiple output ports is optically coupled to wavelength converter 113. In the following description, the output port optically coupled to wavelength converter 113 may be referred to as "wavelength conversion port W1."

[0068] The S-band WDM signal extracted by the WDM filter 111 is guided to the input port P1. Then, the WSS 112 processes a plurality of optical signals constituting the S-band WDM signal according to a preset optical path. Specifically, the WSS 112 guides one or a plurality of optical signals to be branched from the S-band WDM signal and transmitted to an access network, among the plurality of optical signals constituting the S-band WDM signal, to the wavelength conversion port W1. Then, the optical signal output via the wavelength conversion port W1 is guided to the wavelength converter 113.

[0069] The wavelength converter 113 performs wavelength conversion from the S band to the C band on the optical signal output via the wavelength conversion port W1 to generate a wavelength-converted optical signal. The wavelength-converted optical signal includes one or more optical signals to be transmitted to the access network. The wavelength-converted optical signal is then guided to the input port P2 of the WSS 112. The receiving circuit 110 may include an optical amplifier between the wavelength converter 113 and the input port P2 for amplifying the optical signal in the C band. The wavelength converter 113 is realized, for example, by PPLN (Periodically Poled Lithium Niobate). Alternatively, the wavelength converter 113 is realized by a nonlinear optical medium and a light source that generates pump light. The same applies to the wavelength converter 132 described later.

[0070] Note that the wavelength converter 113 is part of an optical circuit optically coupled to the WSS 112. In this case, this optical circuit includes a configuration for guiding an optical signal output from the WSS 112 to the transmission circuit 130 and the add / drop unit 150.

[0071] The WSS 112 guides, according to a preset optical path, an optical signal to be transmitted to another node among a plurality of optical signals constituting an optical signal (i.e., an S-band WDM signal) input via the input port P1 to a corresponding output port. The WSS 112 also guides an optical signal (i.e., one or a plurality of optical signals constituting a wavelength-converted optical signal) input via the input port P2 to a corresponding output port.

[0072] FIG. 8 shows an example of the operation of the receiving circuit 110. In this example, the S-band WDM signal includes an optical signal λS1 and an optical signal λS2. The destination of the optical signal λS1 is node N2. The destination of the optical signal λS2 is a terminal in the access network. The WSS 112 has an input port P1, an input port P2, an output port Q1, an output port Q2, and a wavelength conversion port W1. The output light of the output port Q1 is guided to the transmitting circuit 130 (#2) shown in FIG. 6 or FIG. 7. The output light of the output port Q2 is guided to the add / drop unit 150 shown in FIG. 6 or FIG. 7.

[0073] As shown in FIG. 8(a), the optical signal λS1 and the optical signal λS2 are guided to the input port P1. Here, the destination of the optical signal λS1 is another node (in this example, node N2), and the optical signal λS1 is guided to the output port Q1. In contrast, the destination of the optical signal λS2 is the access network, and the optical signal λS2 is guided to the wavelength conversion port W1. The optical signal λS2 output from the wavelength conversion port W1 is guided to the wavelength converter 113. The wavelength converter 113 performs wavelength conversion from the S band to the C band on the optical signal λS2, and generates the wavelength-converted optical signal λC2. Then, the wavelength-converted optical signal λC2 is guided to the input port P2.

[0074] 8(b), the WSS 112 guides the wavelength-converted optical signal λC2 to the output port Q2. Thus, the wavelength-converted optical signal λC2 is transmitted to the access network by the add / drop unit 150. On the other hand, the optical signal λS1 is transmitted to the node N2 by the transmission circuit 130.

[0075] In this way, the optical signal λS1 is forwarded to another node without passing through a wavelength converter. That is, the optical signal forwarded to another node without being branched in the ROADM 100 does not pass through a wavelength converter. Therefore, the quality of the through signal is good. Also, the optical signal λS2 is converted to a C-band optical signal and transmitted to the access network. That is, the optical signal branched from the S-band WDM signal in the ROADM 100 is converted to a C-band optical signal and transmitted to the access network. Therefore, even if the optical signal is transmitted using the S-band, the destination terminal can receive the optical signal using a C-band optical device that is widely used.

[0076] As shown in Fig. 7, the transmission circuit 130 includes a WSS 131, a wavelength converter 132, and a multiplexer 133. However, the transmission circuit 130 may further include other devices not shown in Fig. 7. For example, the transmission circuit 130 may include an optical amplifier that amplifies the optical signal.

[0077] As shown in FIG. 7, the WSS 131 includes a plurality of input ports, a common output port, and a wavelength conversion port W2. Then, the S-band WDM signals received from other nodes are guided to the corresponding input ports via the corresponding receiving circuits 110. In this embodiment, the S-band WDM signals received from the nodes N1, N3, and N4 are guided to the corresponding input ports. These optical signals are guided to the common output port of the WSS 131. Also, the optical signals received from the access network are guided to the corresponding input ports via the add / drop unit 150. In this embodiment, the optical signals received from the access network are arranged in the C-band. Then, the optical signals received from the access network are guided to the wavelength conversion port W2. The wavelength conversion port W2 is optically coupled to the wavelength converter 132.

[0078] The optical paths in the WSS 131 are set for each wavelength. Each optical path is set in advance according to the destination of the optical signal. The WSS 131 is also capable of processing optical signals placed in the S band and optical signals placed in the C band.

[0079] The wavelength converter 132 performs wavelength conversion from the C band to the S band on the optical signal output via the wavelength conversion port W2 to generate a wavelength-converted optical signal. The wavelength-converted optical signal includes an optical signal transmitted from an access network. The wavelength-converted optical signal is guided to an input port P3 of the WSS 131, and is further guided from the input port P3 to a common output port. Note that the transmission circuit 130 may include an optical amplifier between the wavelength converter 132 and the input port P3, which amplifies light in the S band. Note that the input port P3 is any one of the multiple input ports.

[0080] The multiple optical signals outputted through the common output port of the WSS 131 are arranged in the S-band. That is, the multiple optical signals outputted through the common output port of the WSS 131 constitute an S-band WDM signal. Then, this S-band WDM signal is guided to the multiplexer 133. The multiplexer 133 also receives a C-band WDM signal, an L-band WDM signal, and a U-band WDM signal. Here, these WDM signals are preferably amplified by the corresponding optical amplifiers 141, as shown in FIG. 7. The multiplexer 133 multiplexes these WDM signals and outputs them. In this embodiment, the WDM signal outputted from the multiplexer 133 is transmitted to the node N2.

[0081] Fig. 9 shows an example of the operation of the transmission circuit 130. In this embodiment, an optical signal λS1 is transmitted from a node N1 and guided to the transmission circuit 130 by the WSS 112 shown in Fig. 8. An optical signal λC3 is transmitted from an access network and guided to the transmission circuit 130 by the add / drop unit 150. The optical signal λS1 is placed in the S band, and the optical signal λC3 is placed in the C band. The WSS 131 has input ports P3 to P5, a common output port Q3, and a wavelength conversion port W2.

[0082] As shown in FIG. 9(a), the optical signal λS1 arrives at the input port P4. The WSS 131 guides the optical signal λS1 from the input port P4 to the common output port Q3. The optical signal λC3 received from the access network is guided to the input port P5. The WSS 131 guides the optical signal λC3 from the input port P5 to the wavelength conversion port W2. The optical signal λC3 output from the wavelength conversion port W2 is guided to the wavelength converter 132. The wavelength converter 132 performs wavelength conversion from the C band to the S band on the optical signal λC3 to generate the wavelength-converted optical signal λS3. The wavelength-converted optical signal λS3 is guided to the input port P3.

[0083] 9(b), the WSS 132 guides the wavelength-converted optical signal λS3 to the output port Q3. Thus, the WSS 132 outputs the optical signal λS1 and the optical signal λS3 via the common output port Q3. The optical signal λS1 and the optical signal λS3 are multiplexed with the C-band WDM signal, the L-band WDM signal, and the U-band WDM signal in the multiplexer 133, and transmitted to the node N2.

[0084] In this way, also in the transmitting circuit 130, the optical signal λS1 arranged in the S band is forwarded to another node without passing through a wavelength converter. That is, the optical signal forwarded to another node without being branched in the ROADM 100 does not pass through a wavelength converter in either the receiving circuit 110 or the transmitting circuit 130. Therefore, the quality of the through signal arranged in the S band is good. Also, the optical signal λC3 received from the access network is converted to an optical signal in the S band and forwarded to another node.

[0085] 7 to 9, a WDM signal placed in the S band is processed, but the ROADM 100 according to the embodiment of the present invention can also process a WDM signal placed in the U band. However, when processing a WDM signal placed in the U band, the receiving circuit 110 includes a wavelength converter that performs wavelength conversion from the U band to the L band, and the transmitting circuit 130 includes a wavelength converter that performs wavelength conversion from the L band to the U band.

[0086] Fig. 10 is a flowchart showing an example of a procedure for setting a WSS in the ROADM 100. This example shows a procedure for setting an optical path in a WSS (WSS 112 and WSS 131 in Fig. 7) that processes a WDM signal arranged in the S band. The optical path in the WSS is set by, for example, a network administrator. In this case, the network administrator sets an optical path between a desired input port and a desired output port by, for example, controlling the angle of a mirror implemented in the WSS.

[0087] In steps S1 to S3, settings are made for the WSS 112 implemented in the receiving circuit 110. S1 to S2 relate to the setting of the S band, and S3 relates to the setting of the C band.

[0088] In S1, the network administrator sets up optical paths between the common input port and output ports corresponding to destination nodes based on the wavelengths of the through signals in the received WDM signal. The through signals represent optical signals that are forwarded to other nodes without being dropped from the received WDM signal. The common input port is the optical port where the received WDM signal arrives, which corresponds to port P1 in the example shown in Figure 8.

[0089] At S2, the network administrator sets an optical path between the common input port and the wavelength conversion port for the drop signal. The drop signal represents an optical signal that is dropped from the received WDM signal and guided to the access network. The wavelength conversion port is an optical port optically coupled to the wavelength converter 113, and corresponds to the wavelength conversion port W1 shown in FIG. 8.

[0090] In S3, the network administrator sets up optical paths between the second input port and the output port corresponding to the destination transponder based on the wavelengths of the wavelength-converted drop signals. The second input port is an optical port to which the output light of the wavelength converter 113 is guided, and corresponds to the input port P2 shown in FIG.

[0091] In steps S4 to S6, settings are made for the WSS 131 implemented in the transmission circuit 130. S4 and S6 relate to the setting of the S band, and S5 relates to the setting of the C band.

[0092] In S4, the network administrator sets an optical path for the through signal between the input port and a common output port. The common output port is an optical port from which the transmitted WDM signal is output, and corresponds to the output port Q3 shown in FIG.

[0093] In S5, the network administrator sets up an optical path between an input port and a wavelength conversion port for an add signal. The add signal is an optical signal to be added to a transmission WDM signal and is received from an access network. The wavelength conversion port is an optical port optically coupled to a wavelength converter 132 and corresponds to the wavelength conversion port W2 shown in FIG. 9.

[0094] In S6, the network administrator sets up an optical path between the second input port and a common output port. The second input port is an optical port to which the output light of the wavelength converter 132 is guided, and corresponds to the input port P3 shown in FIG.

[0095] Note that the procedure shown in Fig. 10 is an example, and the order in which each step is executed is not particularly limited. For example, the setting of the transmission circuit may be performed before the setting of the reception circuit. Also, each step may be executed in parallel.

[0096] <Effects of the embodiment> Fig. 11 shows an example of the level and noise figure of an optical signal transmitted by a ROADM. Fig. 11(a) shows an example of the level and noise figure of an optical signal transmitted by the ROADM 20 shown in Fig. 3. Fig. 11(b) shows an example of the level and noise figure of an optical signal transmitted by the ROADM 100 according to an embodiment of the present invention. It is assumed that an arbitrary optical signal in an S-band WDM signal is transmitted.

[0097] In this embodiment, the input optical level of the ROADM (20, 100) is -18 dBm. The gain of the optical amplifiers (32, 33, 121, 141) is 18 dB. The conversion efficiency of the wavelength converters (22, 28) is 0 dB. The noise figure (NF) of the optical amplifier is 6 dB. The noise figure of the wavelength converter is 6 dB. The loss for the through signal in the ROADM is 18 dB.

[0098] Here, when an optical signal is transmitted through multiple ROADMs, the OSNR at each node (i.e., each ROADM) is expressed by equation (1). Pin represents the input optical power of the ROADM. NF represents the noise figure shown in FIG. 11(a) or FIG. 11(b). h represents Planck's constant. ν represents the optical frequency. Δf represents the bandwidth when the noise figure is measured.

number

[0099] When an optical signal is transmitted through multiple ROADMs, the OSNR_RX at the receiving node is expressed by the following equation (2): OSNRi represents the OSNR at each node, and is calculated by the above equation (1).

number

[0100] FIG. 12 shows the effect of the embodiment of the present invention. The horizontal axis represents the number of spans of a path through which an optical signal is transmitted. In other words, the horizontal axis represents the number of ROADMs provided between a transmitting node and a receiving node. The vertical axis represents the OSNR at the receiving node, which is calculated by the above formula (2). The triangular symbol represents the OSNR in a WDM transmission system in which each node is provided with the ROADM 20 shown in FIG. 3. The OSNR is calculated based on the model shown in FIG. 11(a). The circular symbol represents the OSNR in a WDM transmission system in which each node is provided with the ROADM 100 according to the embodiment of the present invention. The OSNR is calculated based on the model shown in FIG. 11(b).

[0101] In either case, as the number of spans increases, the received OSNR deteriorates. However, compared to the configuration shown in FIG. 3, the embodiment of the present invention suppresses deterioration of the received OSNR. That is, compared to the configuration shown in FIG. 3, the embodiment of the present invention improves the received OSNR. As a result, by implementing the ROADM according to the embodiment of the present invention, the number of spans capable of transmitting optical signals increases. For example, in order to realize high-quality optical communication, a received OSNR of 20 dB or more is required. In this case, the configuration shown in FIG. 3 allows transmission over 15 spans, but the embodiment of the present invention allows transmission over 22 spans.

[0102] In the configuration shown in FIG. 5, the optical signal passing through the node (i.e., the through signal) is not wavelength-converted in the ROADM. Therefore, the number of spans capable of transmitting an optical signal is approximately the same in the configuration shown in FIG. 5 and the configuration according to the embodiment of the present invention shown in FIG. 6 to FIG. 7. However, in the configuration shown in FIG. 5, two WSSs (e.g., WSS43 and WSS49) are implemented for the input route, and two WSSs (e.g., WSS51 and WSS55) are implemented for the output route. In contrast, according to the embodiment of the present invention, as shown in FIG. 7, one WSS (e.g., WSS112) is implemented for the input route, and one WSS (e.g., WSS131) ​​is implemented for the output route. Here, WSSs are generally expensive. Therefore, according to the embodiment of the present invention, the cost of manufacturing the ROADM can be reduced.

[0103] <Second embodiment> 13 shows an example of a receiving circuit and a transmitting circuit implemented in a ROADM according to the second embodiment. This ROADM has paths 1 to n. Fig. 13(a) shows an example of a receiving circuit 110B, and Fig. 13(b) shows an example of a transmitting circuit 130B.

[0104] 7, the receiving circuit 110B includes a WSS 112 and a wavelength converter 113. In the receiving circuit 110B, a wavelength filter 114 is coupled to each output port of the WSS 112. The wavelength filter 114 extracts an optical signal in the S band and an optical signal in the C band. The optical signal in the S band extracted by the wavelength filter 114 is guided to the transmitting circuit 130 (or 130B) B corresponding to the destination node. In addition, the optical signal in the C band extracted by the wavelength filter 114 is guided to the add / drop unit 150.

[0105] The wavelength converter 113 and the wavelength filter 114 are part of an optical circuit optically coupled to the WSS 112. In this case, the optical circuit includes a configuration for guiding an optical signal output from the WSS 112 to the transmission circuit 130 and the add / drop unit 150.

[0106] The transmitting circuit 130B includes a WSS 131 and a wavelength converter 132, similar to the transmitting circuit 130 shown in FIG. 7. In the transmitting circuit 130B, a multiplexer 134 is coupled to each input port of the WSS 131. The multiplexer 134 can multiplex an optical signal in the S band and an optical signal in the C band. Specifically, the multiplexer 134 can multiplex an optical signal in the S band output from the corresponding receiving circuit 110B and an optical signal in the C band output from the access network. When an optical signal in the S band is input, the WSS 131 guides the optical signal to a common output port, and when an optical signal in the C band is input, the WSS 131 guides the optical signal to the wavelength conversion port W2.

[0107] Fig. 14 shows an example of the operation of the receiving circuit 110B in the second embodiment. In this example, similar to the case shown in Fig. 8, the optical signal λS1 and the optical signal λS2 arrive at the input port P1. The destination of the optical signal λS1 is the node N2, and the destination of the optical signal λS2 is a terminal in the access network. Note that a wavelength filter 114 is optically coupled to the output port Q1.

[0108] The operation shown in Fig. 14(a) is substantially the same as that shown in Fig. 9(a). That is, the optical signal λS1 is guided to the output port Q1. The optical signal λS2 is converted to the optical signal λC2 by the wavelength converter 113 and guided to the input port P2.

[0109] 14(b), the WSS 112 guides the optical signal λC2 from the input port P1 to the output port Q1. Thus, the WSS 112 outputs the optical signal λS1 and the optical signal λC2 via the output port Q1. Then, the wavelength filter 114 extracts the optical signal λS1 and the optical signal λC2 from the output light of the WSS 112. The extracted optical signal λS1 is transmitted to the destination node by the transmitting circuit 130B. The extracted optical signal λC2 is transmitted to the access network by the add / drop unit 150.

[0110] FIG. 15 shows an example of the operation of the transmission circuit 130B in the second embodiment. In this example, similar to the case shown in FIG. 9, the optical signal λS1 and the optical signal λC3 are input to the WSS 131. However, as shown in FIG. 15(a), the optical signal λS1 and the optical signal λC3 are multiplexed by the multiplexer 134 and guided to the input port P4. Here, the optical signal λS1 is arranged in the S band, so it is guided to the output port Q3. On the other hand, the optical signal λC3 is arranged in the C band, so it is guided to the wavelength conversion port W2. Then, the optical signal λC3 is converted to the optical signal λS3 by the wavelength converter 132 and guided to the input port P3. After this, the WSS 131 guides the optical signal λS3 to the output port Q3. Therefore, the optical signal λS1 and the optical signal λS3 are output via the output port Q3.

[0111] In this way, in the second embodiment, each output port of the WSS implemented in the receiving circuit can be shared to output a through signal and a drop signal. The through signal represents an optical signal that passes through the ROADM without being dropped from the WDM signal. The drop signal represents an optical signal that is dropped from the WDM signal and guided to the access network. Also, each input port of the WSS implemented in the transmitting circuit can be shared to input a through signal and an add signal. The add signal represents an optical signal that is added to the WDM signal. Therefore, assuming that the number of ports of the WSS is the same and the number of transponders connected to the access network is the same, the configuration according to the second embodiment can be connected to more nodes than the configuration shown in FIG. 7. Therefore, the configuration of the second embodiment is effective, for example, when the number of paths of the ROADM is large.

[0112] In addition, this configuration allows all output ports of the WSS implemented in the receiving circuit to be used as drop ports, and all input ports of the WSS implemented in the transmitting circuit to be used as add ports. Therefore, it is possible to increase the number of transponders to be connected to the access network without increasing the number of ports of the WSS. In other words, it is possible to increase the add / drop rate.

[0113] In the embodiment shown in Fig. 13, wavelength filters 114 are provided for all output ports of the WSS implemented in the receiving circuit, and multiplexers 134 are provided for all input ports of the WSS implemented in the transmitting circuit, but the second embodiment is not limited to this configuration. That is, the receiving circuit 110B may be configured as shown in Fig. 16(a) in which wavelength filters 114 are provided for some of the output ports of the WSS. Also, the transmitting circuit 130B may be configured as shown in Fig. 16(b) in which multiplexers 134 are provided for some of the input ports of the WSS.

[0114] <Third embodiment> 17 shows an example of a receiving circuit and a transmitting circuit implemented in a ROADM according to the third embodiment. This ROADM has paths 1 to n. Fig. 17(a) shows an example of a receiving circuit 110C, and Fig. 17(b) shows an example of a transmitting circuit 130C.

[0115] The receiving circuit 110C includes a WSS 112 and a wavelength converter 113, similar to the receiving circuit 110 shown in Fig. 7. However, in the receiving circuit 110C, the wavelength converter 113 is provided on the input side of the WSS 112. Specifically, the S-band WDM signal extracted by the WDM filter 111 is guided to the input port P1 of the WSS 112, and is also branched by the optical splitter 115 and guided to the wavelength converter 113. The wavelength converter 113 performs wavelength conversion from the S-band to the C-band on the input optical signal. The wavelength-converted optical signal is then guided to the input port P2 of the WSS 112.

[0116] Among the optical signals arriving at input port P1, WSS 112 guides the optical signals to be transmitted to other nodes to an output port corresponding to the destination node. In addition, among the optical signals arriving at input port P2, WSS 112 guides the optical signals to be transmitted to the access network to an output port corresponding to the destination.

[0117] 7, the transmitting circuit 130C includes a WSS 131 and a wavelength converter 132. However, in the transmitting circuit 130C, as shown in FIG 17(b), the wavelength-converted optical signal generated by the wavelength converter 132 is not re-input to the WSS 131. The multiplexer 135 multiplexes the optical signal output from the WSS 131 and the wavelength-converted optical signal output from the wavelength converter 132.

[0118] In the example shown in FIG. 17(a), the receiving circuit 110C includes a wavelength filter 114, but the third embodiment is not limited to this configuration. That is, the receiving circuit 110C may not include the wavelength filter 114. Similarly, in the example shown in FIG. 17(b), the transmitting circuit 130C includes a multiplexer 134, but the third embodiment is not limited to this configuration. That is, the transmitting circuit 130C may not include the multiplexer 134.

[0119] Fig. 18(a) shows an example of the operation of the receiving circuit 110C in the third embodiment. In this example, similar to the case shown in Fig. 8 or 14, the optical signal λS1 and the optical signal λS2 arrive at the input port P1. However, the optical signal λS1 and the optical signal λS2 are also guided to the wavelength converter 113 by the optical splitter 115. The wavelength converter 113 performs wavelength conversion from the S band to the C band on the optical signal λS1 and the optical signal λS2, generating the optical signal λC1 and the optical signal λC2.

[0120] Of the optical signals arriving at input port P1, WSS112 guides the optical signals to be transmitted to other nodes to the corresponding ports. In this example, optical signal λS1 is guided to output port Q1. Note that the destination of optical signal λS2 is the access network, and optical signal λS2 is not guided to any port. Also, of the optical signals arriving at input port P2, WSS112 guides the optical signals to be transmitted to the access network to the corresponding ports. In this example, optical signal λC2 is guided to output port Q2. Note that the destination of optical signal λC1 is another node, and optical signal λC1 is not guided to any port. As a result, optical signal λS1 is transmitted to another node, and optical signal λC2 is transmitted to the access network.

[0121] FIG. 18(b) shows an example of the operation of the transmission circuit 130C in the third embodiment. In this example, the optical signal λS1 arrives at the input port P4, and the optical signal λC3 arrives at the input port P5. The WSS 131 guides the optical signal arranged in the S band to a common output port, and guides the optical signal arranged in the C band to the wavelength conversion port W2. In this example, the optical signal λS1 is guided to the output port Q3, and the optical signal λC3 is guided to the wavelength conversion port W2. Then, the wavelength converter 132 performs wavelength conversion from the C band to the S band on the optical signal λC3 to generate the optical signal λS3. Then, the optical signal λS1 and the optical signal λS3 are multiplexed and transmitted to the destination node. [Explanation of symbols]

[0122] 100 ROADM 110, 110B, 110C Receiver circuit 111 WDM Filter 112 WSS 113 Wavelength Converter 114 Wavelength Filter 115 Optical splitter 121 Optical Amplifier 130, 130B, 130C Transmitting circuit 131 WSS 132 Wavelength Converter 133 Multiplexer 134 Multiplexer 135 Multiplexer 141 Optical Amplifier 150 Add / Drop Section 500 WDM Transmission System

Claims

1. An optical communication device for processing a WDM signal in a WDM transmission system, comprising: a receiving circuit for receiving a first WDM signal from a first node of the WDM transmission system; a transmitter circuit for transmitting a second WDM signal to a second node of the WDM transmission system; The receiving circuit includes: a wavelength filter for extracting from the first WDM signal a plurality of input optical signals disposed within a first wavelength band; a wavelength selective switch including a first input port, a second input port, a plurality of output ports, and a wavelength conversion port; an optical circuit including a wavelength converter optically coupled to the wavelength selective switch; the plurality of input optical signals are directed to the first input port; the wavelength selective switch guides an optical signal that is dropped from the first WDM optical signal among the plurality of input optical signals to the wavelength conversion port; the optical circuit performs wavelength conversion from the first wavelength band to a second wavelength band on an optical signal output via the wavelength conversion port to generate a wavelength-converted optical signal; the wavelength-converted optical signal is directed to the second input port; the wavelength selective switch guides, among the plurality of input optical signals, an optical signal to be transmitted to the second node and the wavelength-converted optical signal to a corresponding output port among the plurality of output ports, respectively; The optical circuit guides, among the optical signals outputted via the plurality of output ports, an optical signal arranged in the first wavelength band to the transmission circuit, and guides, among the optical signals outputted via the plurality of output ports, an optical signal arranged in the second wavelength band to an access network connected to the optical communication device.

1. An optical communication device comprising:

2. the optical circuit includes a second wavelength filter for extracting an optical signal within the first wavelength band and an optical signal within the second wavelength band, At least some of the plurality of output ports are optically coupled to the second wavelength filter.

2. The optical communication device according to claim 1 .

3. The transmission circuit includes: a second wavelength selective switch including a common output port and a second wavelength conversion port; a second wavelength converter optically coupled to the second wavelength conversion port; the second wavelength selective switch directs an optical signal, which is transmitted from the access network toward the second node and is located within the second wavelength band, to the second wavelength conversion port; the second wavelength converter performs wavelength conversion from the second wavelength band to the first wavelength band on an optical signal output via the second wavelength conversion port to generate a second wavelength-converted optical signal; The second wavelength selective switch outputs the optical signal arriving at the transmission circuit from the receiving circuit and the second wavelength converted optical signal via the common output port.

2. The optical communication device according to claim 1 .

4. An optical communication device for processing a WDM signal in a WDM transmission system, comprising: a receiving circuit for receiving a first WDM signal from a first node of the WDM transmission system; a transmitter circuit for transmitting a second WDM signal to a second node of the WDM transmission system; The receiving circuit includes: a wavelength filter for extracting from the first WDM signal a plurality of input optical signals disposed within a first wavelength band; a wavelength selective switch comprising a first input port, a second input port, and a plurality of output ports; a wavelength converter that performs wavelength conversion on the plurality of input optical signals from the first wavelength band to a second wavelength band to generate a plurality of wavelength-converted optical signals; the plurality of input optical signals are directed to the first input port; the plurality of wavelength converted optical signals are directed to the second input port; the wavelength selective switch directs an optical signal to be transmitted to the second node among the plurality of input signals to an output port among the plurality of output ports that is optically coupled to the transmission circuit; The wavelength selective switch directs an optical signal to be transmitted to an access network among the plurality of wavelength converted optical signals to an output port among the plurality of output ports that is optically coupled to a device connected to the access network.

1. An optical communication device comprising:

5. The transmission circuit includes: a second wavelength selective switch including a common output port and a second wavelength conversion port; a second wavelength converter optically coupled to the second wavelength conversion port; The second wavelength selective switch comprises: directing optical signals arriving at the transmit circuit from the receive circuit to the common output port; directing an optical signal located within the second wavelength band, the optical signal being transmitted from the access network toward the second node, to the second wavelength conversion port; the second wavelength converter performs wavelength conversion from the second wavelength band to the first wavelength band on an optical signal output via the second wavelength conversion port to generate a second wavelength-converted optical signal; The optical signal outputted via the common output port and the second wavelength-converted optical signal are multiplexed.

5. The optical communication device according to claim 4.

Images