JP2019195124A - Optical communication node, optical communication system, and method of controlling optical communication node - Google Patents

Abstract

To provide an optical communication node for performing wavelength defragmentation more flexibly and easily, an optical communication system, and a method of controlling the optical communication node.SOLUTION: At least one wavelength conversion means 605 is provided on a path 612 to output multiplexing WSSs 604-1 to 604-3 or an Add port within optical communication nodes 600, 700. In a path from input ports In 1 to In 3 to output ports Out 1 to Out 3 toward multiple routes, some paths may be directly connected and wavelength conversion means is provided on the remaining part of the paths. For the wavelength conversion means, pump light for wavelength conversion is supplied from pump light generation means 601. A method of controlling the optical communication nodes interlockingly performs wavelength defragmentation operations and phase synchronizing procedures between a wavelength conversion node and a receiving terminal node for dropping information data.SELECTED DRAWING: Figure 16

Description

  The present invention relates to an optical communication system and an optical communication node included in the optical communication system.

  In current optical communication networks, a large capacity is realized by using wavelength division multiplexing (WDM) technology in which optical signals of a plurality of different wavelengths are simultaneously placed on a single optical fiber cable. An optical communication network using the WDM technology connects nodes with different wavelengths and virtually sets an optical communication path of an arbitrary connection (hereinafter, the optical communication path is referred to as a path). The wavelength configuration used for these paths was almost fixed.

  On the other hand, due to the recent development of video on demand and social media, the traffic demand on the Internet is changing every moment. An optical communication network is also required to efficiently and flexibly process such time-varying traffic. For example, it is preferable that the capacity of a path between nodes and the wavelength configuration forming the path can be flexibly changed in response to a change in traffic demand. However, newly configuring a path or changing the communication capacity of an existing path is affected by the configuration of the existing path. For example, it is affected by the start and end nodes of the existing path, the wavelength used, the wavelength bandwidth, and the like. For this reason, wavelength resources in the communication band of optical communication cannot always be efficiently used, and the traffic accommodation efficiency of the network cannot be maximized.

  FIG. 1 is a diagram illustrating an example of a change in traffic time in a conventional optical communication network. 1A shows a node configuration of the optical communication network, and FIG. 1B conceptually shows a signal on each node or path on the wavelength axis. In FIG. 1A, traffic from node A to node C is considered in an optical communication network composed of four nodes, node A, node B, node C, and node D. Here, consider a situation where a path is set as follows. Referring also to (b) of FIG. 1, first, signals 1 to 6 are added from the Add unit 1 (A: Add) in the node A and transmitted in the direction of the node B. In the node B, the signal 2 and the signal 4 among the signals 1 to 6 are dropped from the drop unit 2 of the node B (B: Drop). Further, the remaining signals 1, 3, 5, 6 are dropped (C: Drop) from the drop unit 3 of the node C. In such a situation, it is assumed that a new traffic demand is generated and it is necessary to set up a path of the signal 7 from the node B to the node C. The WDM wavelength band from the node B to the node C has a sufficient margin as a whole. However, since the wavelength band 7 of the signal 7 overlaps the entire band 5 of the signal 3 and a part of the band 6 of the signal 5, the signal 7 cannot be accommodated in the node B. Eventually, even if there is a vacancy in the entire wavelength band and there is room, the traffic cannot be accepted depending on the mode of the path for new traffic. In order to solve such a problem, for example, Non-Patent Document 1 proposes wavelength defragmentation.

  FIG. 2 is a diagram for explaining the concept of wavelength defragmentation in Non-Patent Document 1. Non-Patent Document 1 discloses wavelength defragmentation using three steps in a linear network including nodes A to D as shown in FIG. In Step 1 in the initial state, Signal 1 to Signal 4 are transmitted between node A to node D. In each step, the vertical direction represents the wavelength λ, and the horizontal axis direction represents the node position (transmission direction). Signal 1 (wideband signal) with a wide bandwidth is transmitted between nodes A and C, and Signal4 (narrowband signal) with a narrow bandwidth is transmitted between nodes A and B. The state of Step 2 is a state in which Signal 3 in which a path is set from Node C to Node D in Step 1 of the initial state is abolished. Here, the wavelengths of Signal2 (10a) and Signal1 (9a) can be gradually changed downward (for example, on the short wavelength side). As a result, in Step 3, the empty wavelength band 8 is provided in the wavelength band originally occupied by Signal 1, and the traffic accommodation efficiency in the wavelength resource can be maximized. Non-Patent Document 1 discloses an example of successful transmission of a 100 G double polarization quadrature phase shift keying (DP-QPSK) signal.

Kyosuke Sone, Xi Wang, Shoichiro Oda, Goji Nakagawa, Yasuhiko Aoki, Inwoong Kim, Paparao Palacharla, Takeshi Hoshida, Motoyoshi Sekiya, and Jens C. Rasmussen, “First Demonstration of Hitless Spectrum Defragmentation using Real-time Coherent Receivers in Flexible Grid Optical Networks, ”ECOC2012, _Th.3.D.1 (PD) Hideto Yamamoto, Kohei Saito, Akira Naka, Hideki Maeda “Realization of Uninterrupted Wavelength Defragmentation for Flexible Optical Network by Wavelength Diversity Transmission Using Maximum Ratio Combining”, Society Conference of IEICE, 2015, B -10-66

  However, the wavelength defragmentation disclosed in Non-Patent Document 1 has a complicated and troublesome control for implementation. According to the method of Non-Patent Document 1, it is necessary to change the wavelength of the optical signal on the transmission node side and the wavelength of the local oscillation light for the receiver on the reception node side in a synchronized manner between these remote nodes. There is. Furthermore, it is necessary to change the wavelength of the transmission band used in the wavelength selective switch at the node through which the optical signal passes in synchronization.

  FIG. 3 is a diagram for explaining the outline of the control operation required at each node in the wavelength defragmentation of the prior art. FIG. 3 shows control when switching the wavelength of the optical signal in synchronization between the node A11, the node B12, and the node C13. It is assumed that a signal is input from the add circuit 14 of the node A11, an optical signal having a wavelength λ1 is transmitted, and a signal is output from the drop circuit 15 of the node C13 via the node B12. Consider a case where the wavelength used here is switched from λ1 to λ2 and the wavelengths are rearranged. At this time, the Tx frequency (wavelength) of the transmitter 16 for the signal at the node A11, the transmission wavelengths of the plurality of wavelength selective switches at the nodes A to C, and the frequency (wavelength) of the local oscillator for the receiver at the node C13. ) Must be controlled synchronously. Therefore, when the wavelength is rearranged from λ1 to λ2, complicated control of the optical transmission equipment is required across three nodes at remote locations.

  In addition, due to the difference in wavelength bandwidth, wavelength rearrangement in which wavelengths cross each other, for example, wavelength rearrangement in which the relationship between Signal 1 and Signal 4 in FIG. In many cases, an optical transmission device arranged in a node uses a laser light source. When changing the wavelength of the laser light source, it is not possible to change the wavelength instantaneously digitally, but it is necessary to stabilize the oscillation light by changing the resonance length of the laser in an analog manner.

  In many optical transmission devices, it takes a certain time to change the wavelength for communication to a state where it can actually be used. From the viewpoint of the user, the optical signal is completely stopped at the time of switching, and communication is interrupted. If a wavelength in use is included in another signal in a band between two wavelengths to be switched, the signal in use may be disturbed or communication may be interrupted while the wavelength is switched. In the end, changing the wavelength during actual optical communication network operation requires cumbersome and complicated control, and there is a limit to the range that can be changed, and wavelength switching without service interruption or communication quality degradation was difficult.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a mechanism of wavelength defragmentation that is more flexible and simpler than the prior art.

  In order to achieve the above object, the present invention provides an optical communication system that multiplexes optical signals of different wavelengths and transmits information data, and uses wavelengths from different input paths. A plurality of demultiplexing wavelength selective switches for demultiplexing the division multiplexed signal, and a plurality of multiplexing for multiplexing wavelength division multiplexed signals including the demultiplexed signal light from each of the plurality of demultiplexing wavelength selective switches A plurality of paths for mutually connecting a wavelength selective switch and each of the plurality of demultiplexing wavelength selective switches and each of the plurality of multiplexing wavelength selective switches; A first optical communication node in which wavelength conversion means is installed for at least one of the paths connected to the wavelength selective switch, and the first optical communication node before wavelength conversion in the first optical communication node 1 optical signal and this Wavelength demultiplexing means for demultiplexing the second optical signal obtained by wavelength-converting the first optical signal, and the timing of information data between the first optical signal and the second optical signal are estimated. And a wavelength switching processing means including a timing adjustment unit for reducing a timing difference of information data between the first optical signal and the second optical signal, and carrying the information data And a second optical communication node that drops two optical signals. The first optical communication node is an optical communication node that performs wavelength conversion, and the second optical communication node is an optical communication node at the receiving end.

  A second aspect of the present invention is the optical communication system according to the first aspect, wherein the timing estimation unit decodes the first optical signal and the second optical signal by performing coherent detection on each of them. Timing estimation is performed on the two pieces of information data, and the timing adjustment unit adjusts the timing of the two pieces of information data so as to maximize the combined output by combining the two pieces of information data in a maximum ratio. It is a maximum ratio combining unit. For example, the maximum ratio combining unit described above may be an adaptive MIMO equalization unit that is used for communication technology by inputting the first optical signal and the second optical signal that are coherently detected. .

  The invention according to claim 3 is the optical communication system according to claim 1 or 2, wherein the at least one path of the first optical communication node is the wavelength selection switch for demultiplexing and the wavelength for multiplexing. It includes a path of at least one combination of selective switches, or a path from an Add port connected to the plurality of multiplexing wavelength selective switches.

  The invention according to claim 4 is the optical communication system according to any one of claims 1 to 3, further comprising excitation light generation means for supplying excitation light to the wavelength conversion means, wherein the wavelength conversion means is wavelength conversion Is an all-optical wavelength converting means implemented only in the optical layer.

  Invention of Claim 5 is the optical communication system of Claim 4, Comprising: The said excitation light generation means generate | occur | produced in the excitation light generation part which generate | occur | produces frequency comb light from CW light, and the said excitation light generation part Comb separating means for spatially demultiplexing the frequency comb light into a single CW light for each comb frequency, a plurality of frequency shift units for shifting the frequency of the demultiplexed single CW light, And pumping light selective distribution means for multiplexing and spatially demultiplexing the CW light whose frequency is shifted from each of a plurality of frequency shift sections.

  A sixth aspect of the present invention is the optical communication system according to the fifth aspect, wherein the pumping light selective distribution means is a multi-input multi-output wavelength selective switch.

  According to a seventh aspect of the present invention, in the optical communication system according to any one of the first to sixth aspects, the first optical communication node performs wavelength conversion on the first optical signal having the wavelength λ1. Generating the second optical signal having the wavelength λ2, and estimating the timing of the first optical signal and the second optical signal by the timing estimation unit at the second optical communication node; Operating the timing adjustment unit so that a timing difference between the first optical signal and the second optical signal is reduced in the second optical communication node; and in the second optical communication node, Switching the reception path from the first optical signal to the second optical signal and acquiring the information data from the second optical signal; and the first optical communication node and the second optical At the communication node, λ1 A control method of the optical communication nodes, characterized by carrying out the phase locking procedure including the step of deleting an optical path involved.

  According to another aspect of the present invention, in an optical communication system that multiplexes optical signals of different wavelengths and transmits information data, the optical communication node drops the optical signal carrying the information data, and the optical communication nodes are different from each other. Wavelength demultiplexing means for demultiplexing the first optical signal before wavelength conversion at the node, and the second optical signal obtained by wavelength-converting the first optical signal at the different optical communication node; A timing estimator for estimating a timing of the information data between the first optical signal and the second optical signal; and a timing of the information data between the first optical signal and the second optical signal A plurality of demultiplexing wavelength selective switches for demultiplexing wavelength division multiplexed signals from different input paths, the wavelength switching processing means including a timing adjustment unit including a timing adjustment unit for reducing the difference, A plurality of multiplexing wavelength selective switches for multiplexing wavelength division multiplexed signals including the demultiplexed signal light from each of the plurality of demultiplexing wavelength selective switches, and a plurality of demultiplexing wavelength selective switches A plurality of paths mutually connecting each of the plurality of multiplexing wavelength selective switches and at least one of paths connected to the plurality of multiplexing wavelength selective switches It can also be implemented as an optical communication node characterized in that wavelength conversion means for converting the wavelength from the first optical signal to the second optical signal is installed on the path. Here, the optical communication node is a receiving-end optical communication node, and the different optical communication node is an optical communication node that performs wavelength conversion.

  As described above, the present invention provides a wavelength defragmentation mechanism that is more flexible and simpler than the prior art.

FIG. 1 is a diagram for explaining changes in traffic time of an optical communication network. FIG. 2 is a diagram for explaining wavelength defragmentation in the prior art. FIG. 3 is a diagram for explaining wavelength defragmentation control in the prior art. FIG. 4 is a diagram showing a schematic configuration of the optical communication node of the present invention. FIG. 5 is a diagram showing the configuration of the pump light generating means of the optical communication node according to the present invention. FIG. 6 is a diagram showing the spectrum of each part in the pump light generating means. FIG. 7 is a diagram showing the configuration of the wavelength converting means of the optical communication node according to the present invention. FIG. 8 is a diagram for explaining the spectrum of each part in the wavelength converting means. FIG. 9 is a diagram for explaining the operation of wavelength conversion for exchanging two optical signals. FIG. 10 is a diagram illustrating the configuration and operation of the M × pWSS of the first embodiment. FIG. 11 is a diagram illustrating the configuration of the LCOS used in the second embodiment. FIG. 12 is a diagram showing an outline of circuit elements of the spatial beam converter. FIG. 13 is an optical path diagram of an optical system in which the three WSSs of Example 3 are integrated. FIG. 14 is a diagram illustrating the configuration of the optical communication node according to the fourth embodiment. FIG. 15 is a diagram illustrating the configuration of the optical communication node according to the fifth embodiment. FIG. 16 is a diagram illustrating the configuration of the optical communication system according to the sixth embodiment. FIG. 17 is a diagram showing a flow of a phase synchronization procedure in the receiving end node. FIG. 18 is a diagram illustrating the configuration of the optical communication system according to the seventh embodiment.

  The optical communication node of the present invention provides a novel configuration for wavelength defragmentation. In the communication node, at least one wavelength conversion means is provided in the middle of the path between the input port (demultiplexing WSS and Add port for path switching) and the output port (multiplexing WSS). Among paths from an input port to an output port directed to a plurality of routes, some paths are directly connected, and wavelength conversion means is provided on the remaining part of the paths. All paths may be provided with wavelength conversion means. Pump light used for wavelength conversion is supplied from the pump light generation means to the wavelength conversion means. An efficient and suitable configuration for supplying pump light to the wavelength converting means is also disclosed.

Further, an optical communication system in which a wavelength defragmentation operation in an optical communication node that performs wavelength switching and a phase synchronization procedure of two optical signals having different wavelengths in a receiving end node that drops information data are linked, and a control method for these optical communication nodes Is also disclosed. Hereinafter, the overall configuration, operation, and specific configuration of each component of the optical communication node according to the present invention will be described in detail with reference to the drawings.
[Configuration of optical communication node]
FIG. 4 is a diagram showing a schematic configuration of the optical communication subsystem of the present invention. The optical communication subsystem 20 in FIG. 4 corresponds to the node B or the node D having the number of routes N = 3 in FIG. Typically, the optical communication subsystem 20 corresponds to, for example, an optical communication node in a ROADM (Reconfigurable Optical Add / Drop Multiplexer) system. Hereinafter, for the sake of simplicity, the optical communication subsystem 20 of FIG. 4 is referred to as an optical communication node. The optical communication node of FIG. 4 has a configuration in which functional blocks necessary for wavelength defragmentation according to the present invention are added to the configuration of a general optical communication node of the prior art. The optical communication node 20 of FIG. 4 shows an example of the configuration of an optical network node with the number of routes N = 3. However, the number of routes N is not limited to three, and can be configured to be scalable by adapting to different number of routes N. .

  In FIG. 4, wavelength division multiplexed signals (hereinafter referred to as WDM signals) from inputs (In1, In2, In3) of different routes are respectively wavelength division selective switches 21-1 to 21-3 (WSS: Wavelength Selective Switch) ( Ingress 1 to Ingress 3). The input WDM signal is wavelength-demultiplexed by each of the demultiplexing WSSs 21-1 to 21-3, and is routed toward any desired route (Out1 to Out3) for each wavelength. The routed optical signals are wavelength-multiplexed by the corresponding multiplexing WSSs 29-1 to 29-3 (Egress1 to Egress3) in the respective paths (Out1 to Out3). The optical signals wavelength-multiplexed by the multiplexing WSSs 29-1 to 29-3 are output from the outputs (Out1 to Out3) of the WSSs 29-1 to 29-3 as WDM signals.

  In the routing in the optical communication node 20 described above, the input-side demultiplexing WSSs 21-1 to 21-3 and the output-side demultiplexing WSSs 29-1 to 29-3 are respectively represented by paths indicated by dotted lines in FIG. Connected by a path indicated by a solid line. Here, for example, a path between WSSs on the same route such as between In1 and Out1 is meaningless because a signal is routed to the same route and an optical signal is returned. Therefore, in the optical communication node 20, the demultiplexing WSS and the multiplexing WSS on the same path are not connected.

  In FIG. 4, paths 23-1 to 23-3 indicated by dotted lines are paths that directly connect the input-side demultiplexing WSS and the output-side demultiplexing WSS. On the other hand, paths (paths) 22-1 to 22-3 indicated by solid lines are paths newly added in the optical communication node of the present invention, and wavelength conversion means is inserted on each path. . In the conventional optical communication node, the WDM signal input from the route In1 is wavelength-demultiplexed via the demultiplexing WSS 21-1, and is multiplexed via the dotted path 23-1. Directly connected to 29-3. In the optical communication node 20, when the wavelength is demultiplexed via the demultiplexing WSS 21-1 and passes through the solid line 22-1, the multiplexing WSS 29-2 is routed through the wavelength conversion units 24 a to 24 d, respectively. 29-3. The optical signals demultiplexed by the demultiplexing WSS 21-1 are wavelength-converted by the wavelength conversion units 24 a to 24 d, and then routed to desired paths through the multiplexing WSSs 29-2 to 29-3. The path 22-2 from the demultiplexing WSS 22-2 to the multiplexing WSSs 29-1 and 29-3, and the path 22-3 from the demultiplexing WSS 22-3 to the multiplexing WSSs 29-1 and 29-2 The same wavelength conversion means is also installed.

  Therefore, the optical communication node of the present invention includes a plurality of demultiplexing wavelength selective switches 21-1 to 21-3 that demultiplex wavelength multiplexed signals from different input paths, and each of the demultiplexing wavelength selective switches. A plurality of multiplexing wavelength selective switches 29-1 to 29-3 that multiplex wavelength multiplexed signals including the demultiplexed optical signals from each of the plurality of demultiplexing wavelength selective switches, A plurality of paths mutually connecting with each of the wavelength selection switches for multiplexing, and at least one of paths 22-1 to 22-3 connected to the plurality of wavelength selection switches for multiplexing This can be implemented as if wavelength conversion means are installed for one path. The at least one path is a path of at least one combination of the demultiplexing wavelength selective switch and the multiplexing wavelength selective switch.

  In a specific connection path (for example, In1 → Out2), q wavelength converting means are installed. Therefore, q is the number of paths including wavelength conversion means in a specific connection path. In the configuration example of the optical communication node in FIG. 4, q = 2, and the value of q may be 1 or 3. However, the larger q is, the higher the degree of freedom when performing wavelength defragmentation in the optical communication node. In the optical communication node 20, the value of q may be different for each connection path (route to be routed) for the demultiplexing WSS of one route. Further, for some other reason, a part of the optical communication node 20 may include q = 0, that is, a path where no wavelength conversion unit is installed.

  As shown in FIG. 4, the simplest configuration includes the same number of paths in which wavelength conversion means are installed in all connection paths connecting the demultiplexing WSS and the multiplexing WSS between different paths. It ’s fine. In the following description, the configuration of wavelength conversion means used in the optical communication node of the present invention will be described on the premise of the configuration of FIG.

[Configuration of wavelength conversion means]
As the wavelength conversion means 24a to 24d in the optical communication node of FIG. 4, all-optical wavelength conversion means can be used. Here, the all-optical wavelength conversion means performs wavelength conversion only in the optical layer without performing optical-electrical-optical conversion (O / E / O conversion). As will be described later, the wavelength conversion means 24a to 24d in the optical communication node according to the present invention performs wavelength conversion using the nonlinear optical phenomenon of the optical layer. Since the all-optical wavelength converting means does not intervene an electric layer, it has advantages in all aspects such as deployment cost, power consumption, component failure rate, and operational complexity.

  Referring to FIG. 4 again, for example, the signal light 78 and the pump light 77 for generating wavelength conversion are input to one wavelength conversion unit 24a. The pump light 77 is generated by the pump light generation means 25-1 as one of a plurality of pump lights, and is input to the wavelength conversion means 24a to 24d via the WSS 26-1 having an M × p configuration. The pump light is also called excitation light, and the pump light generation means corresponds to the excitation light generation means. Hereinafter, a WSS having M input ports and a p output port number is referred to as M × p WSS. The number of output ports p in the M × p WSS 26-1 is p = (N−1) × q. Here, N is the number of routes in the optical communication node, and q is the maximum number of routes including wavelength conversion means in the connection path from one route to another route.

  In FIG. 4, the value of q is the same for all connection paths, and N = 3 and q = 2. Therefore, the number p of output ports in the M × p WSS 26-1 in the pump light generation means is 2 × 2 = 4. If the number of q is the same in all connection paths as in the optical communication node of FIG. 4, all the ports of M × p WSS can be used without excess or deficiency. The number of input ports M in the M × p WSS 26-1 will be described later. The optical communication node of the present invention shown in FIG. 4 has a configuration in which pump light is supplied from one pump light generation means to a connection path from one demultiplexing WSS. FIG. 14 illustrates an optical communication node that supplies pump light with another configuration.

  As the all-optical wavelength conversion means, wavelength conversion using four-wave mixing in an optical fiber or a nonlinear crystal can be used. In addition, mutual gain modulation of a semiconductor optical amplifier may be used. As a means for performing wavelength conversion, there is a disadvantage that power consumption increases because an electric layer is interposed, but OE conversion and EO conversion may be used without using an all-optical wavelength conversion means. In this case, the pump light generating means 25-1 to 25-3 and M × p WSS are not necessary. Next, a more specific configuration of the pump light generating means used with the wavelength converting means will be described.

[Configuration of pump light generation means]
FIG. 5 is a diagram showing a more specific configuration of the pump light generation means in the optical communication node of the present invention. The pump light generation means (excitation light generation means) shown in FIG. 5 includes an excitation light generation unit 25a and an excitation light frequency shift unit 25b. The pump light generating means shown in FIG. 5 includes M × p WSSs 26-1 to 26-3 in FIG. 4 as the excitation light selection / distribution unit 26. In the excitation light generation unit 25 a of FIG. 5, first, continuous light (CW light) output from the laser diode light source LD 41 is input to the photodetector PD 43 via the gas cell 42. The optical signal received by the PD 43 is converted into an electrical signal and input to the control circuit 44. The control circuit 44 has a mechanism for controlling the injection current to the LD 41. Therefore, the LD 41, the gas cell 42, the PD 43, and the control circuit 44 form a feedback loop that controls the output wavelength from the LD 41. In this loop, a weak control is applied to the current injected into the LD 41 to form a control loop that locks the oscillation wavelength of the LD 41 to the absorption line of the gas cell 42. As a result, at point 60, the oscillation wavelength of the output light from the LD 41 is locked to the desired wavelength very precisely.

  Part of the CW light output from the LD 41 is intensity-modulated at the frequency f by the intensity modulator 45, and a pulse is generated at a point 61. The generated pulse light is amplified by an erbium doped optical fiber amplifier (EDFA) 46 and then input to a highly nonlinear fiber HNLF 47. In the HNLF 47, supercontinuum light (frequency comb) is generated at point 62 by self-phase modulation. Here, the frequency interval of the frequency comb is the frequency f.

  For the frequency comb generated by the HNLF 47, one CW light having a desired pump frequency is selected from the frequency comb light by the 1 × M WSS 48. At point 63, the selected CW light is input to an SSB (Single Side Band) modulator 49. Accordingly, the 1 × M WSS 48 functions as a comb separation unit that spatially demultiplexes the frequency comb light into a single CW light for each comb frequency. At the output of 1 × M WSS 48, up to M SSB modulators are provided in parallel. The SSB modulator 49 driven at the modulation frequency Δf finely adjusts the frequency of the input CW light. The finely adjusted CW light is amplified by the EDFA 50 and then output from the frequency shift unit 25b. The modulation frequency Δf in the maximum M SSB modulators provided in parallel may be different.

  The maximum M finely-tuned CW lights from the frequency shift unit 25 b are first multiplexed by the M × 1 WSS 52 in the pump light selection / distribution unit 26. Further, the light is demultiplexed by the 1 × p WSS 53 and output to the predetermined output ports 54 a to 54 d as excitation light that is CW light having a desired wavelength. The CW light having a desired wavelength output to any one of the output ports 54a to 54d is supplied to the wavelength selection unit as pump light from the pump light generation unit in FIG. The output ports 54a to 54d are connection terminals connected to the wavelength converters 24a to 24d in FIG. 4, and the above-described CW light is input to the wavelength converters 24a to 24d, respectively. The CW light output from the EDFA 50 of the frequency shift unit 25b is partly branched without passing through the excitation light selection / distribution unit 26, and the branched light 51 is supplied to the pump light generation means 25-1 to 25-3. It may be pump light.

  Therefore, the pump light generation means, that is, the excitation light generation means, uses a single excitation frequency generator 25a that generates frequency comb light from CW light, and a single frequency comb light generated by the excitation light generation section for each comb frequency. Comb separating means 48 that spatially demultiplexes into CW light, a plurality of frequency shift units (SSB modulators) 49 that shift the frequency of the single demultiplexed CW light, and a plurality of frequency shift units. The present invention can be implemented as including excitation light selection / distribution means 52 and 53 for multiplexing and spatially demultiplexing the CW light whose frequency is shifted from each.

  FIG. 6 is a spectrum diagram showing the pump light generation process in the pump light generation means. Each point in the following description corresponds to points 60 to 66d of the pump light generating means in FIG. At the point 60 which is the output of the wavelength control loop, the oscillation wavelength of the LD 41 is locked to one of the absorption spectra of the gas cell, and is output as CW light. At the point 61 that is the output of the intensity modulator 45, sidebands are generated by intensity modulation of the CW light. After the intensity-modulated light wave is amplified by the EDFA 46, supercontinuum light is generated by self-phase modulation in the highly nonlinear fiber. As a result, at the point 62 which is the output of the HNLF 47, the spectrum becomes the frequency comb light 67 over a very wide band. Here, the interval of the frequency comb light is the intensity modulation frequency f.

  At the point 63 which is the 1 × M WSS 48 output of the frequency shift unit 25b, a desired spectrum of the frequency comb light 67 is output to each output port of the 1 × M WSS 48 one by one. At point 63, the CW light 68 is output as it is. The CW light is finely adjusted by shifting the frequency by Δf at the point 64 which is the output of the SSB modulator 49. Further, at point 65 which is the combined output of M × 1 WSS 52, a plurality of CW lights from different SSB modulators are combined. FIG. 6 shows a state where three waves are combined. Finally, at each of the points 66a to 66d of the output port of the 1 × p WSS 53, the pump light, which is CW light having a desired wavelength and shifted in frequency, is distributed one by one. CW light from different SSB modulators is distributed and output to each output port of the 1 × p WSS 53 one by one. As shown in FIG. 6, pump lights 69-1 and 69-2 having the same wavelength are output. May be distributed to a plurality of output ports. FIG. 6 shows an example in which CW lights 69-1 and 69-2 having the same wavelength are output to the two output ports 54b and 54d of the 1 × p WSS 53. The distribution output method will be described in detail in the embodiments described later.

  In the pump light generating means shown in FIG. 5, the pump light having the required wavelength can be extracted as CW light by the wavelength filter function of the M × 1 WSS 52 in the excitation light selective distribution unit 26. Therefore, the SSB modulator 49 of the frequency shift unit 25b in FIG. 5 may be replaced with a phase modulator or an intensity modulator that generates a double sideband. That is, unnecessary sidebands and carrier waves generated in the alternative modulator of the SSB modulator 49 can be removed by the filter function of M × 1 WSS. Next, a specific configuration of the wavelength conversion units 24a to 24d in the optical communication node of FIG. 4 will be described.

[Configuration of wavelength conversion means]
FIG. 7 is a diagram showing a configuration example of wavelength conversion means in the optical communication node of the present invention. The wavelength converter 24 includes an optical combiner 70 that combines the pump light 77 and the signal light 78 and a nonlinear optical medium 72 that converts the wavelength of the signal light. When the intensity of the pump light and the signal light combined by the optical combiner 70 is insufficient to generate a nonlinear phenomenon, the light can be input to the nonlinear optical medium 72 after being amplified by the EDFA 71.

As the optical combiner 70, an optical directional coupler or a wavelength selective switch can be used. As the nonlinear optical medium 72, a highly nonlinear optical fiber, a periodically poled LiNbO ₃ waveguide, a semiconductor optical amplifier, or the like can be used. Furthermore, instead of the optical amplifier described as an EDFA in each element of the optical communication node of the present invention, a semiconductor optical amplifier may be used.

FIG. 8 is a diagram for explaining the spectrum of each part in the wavelength conversion means of the optical communication node of the present invention. Each point in the following explanation corresponds to points 73 to 76 of the wavelength conversion means 24 in FIG. At points 73 and 74 which are two inputs of the wavelength conversion means, pump light 81 and signal light 82 having different wavelengths are respectively input. At the point 75 which is the output of the optical combiner 70, the above-mentioned two waves are combined. Next, at a point 76, idler light 84 is generated by degenerate four-wave mixing by the nonlinear optical medium 72. If the optical frequency of the pump light 81 is fp and the optical frequency of the signal light 82 is fs, the optical frequency fi of the idler light 84 is expressed by the following equation.
fi = 2fp-fs Equation (1)
In the nonlinear optical medium 72, simultaneously with the generation of fi, the idler light 83 generated using the signal light as pump light and the pump light as probe light is also generated simultaneously.

  The wavelength converters 24c and 24d in the optical communication node in FIG. 4 are connected to the multiplexing WSS 29-2 (Egress 2) in the optical communication node in FIG. The original pump light 81, signal light 82 and unnecessary idler light 83 shown in FIG. 8 are removed by the filtering function of the WSS 29-2 for multiplexing, and only the optical signal 84 (idler light) after wavelength conversion is obtained. The signal is output to the point 80-2 which is an output port of the multiplexing WSS 29-2. In FIG. 8, the spectrum of only the idler light 84 is shown for explaining the wavelength conversion operation. However, at the point 80-2 in FIG. 4, the optical signal transmitted without wavelength conversion or the light converted to another wavelength is shown. The signals are combined and output.

[Configuration for wavelength conversion of optical signals of multiple wavelengths]
In the spectrum description of FIG. 8 described above, an example in which pump light is used only for wavelength conversion of an optical signal having a specific wavelength of an optical communication node is shown. However, if the pump light generation means shown in FIG. 5 is used, it can also be used to simultaneously perform wavelength conversion of optical signals having a plurality of wavelengths in the optical communication node 20 of the present invention. In the pump light generation means of FIG. 5, one CW light is selected from the frequency comb light 67 by 1 × M WSS 48, and a plurality of SSB modulators are operated independently in parallel, and pump lights of different wavelengths are output at the same time. Because it can. This is effective when the wavelengths of two different optical signals are interchanged. That is, the present invention can be applied to a case where an optical signal having an optical frequency of fs2 is converted to fs4 and an optical signal having an optical frequency of fs4 is converted to fs2.

  FIG. 9 is a diagram illustrating a comparison between operations when the wavelength conversion of two optical signals is performed collectively and when wavelength conversion is performed by dividing the pump light generation unit shown in FIG. FIG. 9A illustrates the operation when wavelength conversion is performed by introducing the optical signal of the frequency fs2 and the optical signal of fs4 into the nonlinear optical medium 72 of the wavelength conversion means of FIG. At the point 75 which is the output of the optical combiner 70, there are three wavelengths including pump light of frequency fp. The optical spectrum at the point 76 that is the output of the nonlinear optical medium 72 is a mixture of the residual component of the signal light of fs2 and the converted fi4. Similarly, the residual component of the signal light of fs4 and the converted fi2 are mixed. Since these mixed signals have the same wavelength, they cannot be separated by the filtering function of the WSS 29-2 at the point 80-2 which is the output port of the WSS 29-2 for multiplexing of the optical communication node 20, for example.

  FIG. 9B is a diagram for explaining the operation of performing wavelength conversion with the CW lights 69-1 and 69-2 having the same wavelength in the pump light generating means shown in FIG. As shown in FIG. 9 (b), the conversion from fs2 to fi2 (= fs4) and the conversion from fs4 to fi4 (= fs2) are performed using the CW lights 69-1 and 69-2 having the same wavelength, and are separated from each other. Performed by conversion means. In this case, mixing of the residual component of one signal light and the converted light component of the other signal light described in FIG. 9A can be avoided. That is, pump lights 69-1 and 69-2 having an optical frequency of fp are distributed to the output ports 54b and 54d of the 1 × p WSS 53, respectively, and are individually performed by the wavelength conversion means 24d and 24b.

  The upper diagram in FIG. 9B shows a case where the wavelength conversion unit 24d converts the signal light fs2 into fs4. The unnecessary signal 85 of the residual component of the pump light fp and the original signal light fs2 is filtered by the multiplexing WSS 29-2, and only the signal light fs4 after wavelength conversion is extracted at the point 80-2. 9B shows a case where the signal light fs4 is converted into fs2 in the wavelength conversion unit 24b. Similar to the case of the wavelength converting unit 24d, the unnecessary signal 86 is filtered by the multiplexing WSS 29-3, and only the signal light fs4 after wavelength conversion is extracted at the point 80-3. Thus, in the optical communication node 20 of the present invention, the wavelengths of the two signal lights can be easily switched. Here, an example of exchanging wavelengths for two waves has been shown, but it is also possible to use three pump lights having the same wavelength for mutual wavelength conversion of three or more signal lights. The output of the CW light having the same wavelength at the two output port points 66b and 66d of the 1 × p WSS 53 described here is realized by using the broadcast function of the wavelength selective switch described later in the second embodiment.

  The optical communication node of the present invention shown in FIG. 4 can realize wavelength defragmentation that is more flexible and simpler than the prior art. By performing wavelength conversion on the path in the optical communication node without changing the frequency of the transmitter in the transmission node, the troublesome and complicated control required between multiple communication nodes is greatly simplified. The If the information about the wavelength change is known at the receiving node, the frequency of the local oscillator can be changed in advance to the frequency (wavelength) after the change at the receiver side of the receiving node. Even in the pump light generation means, it is sufficient to prepare pump light having a predetermined frequency in advance before the wavelength change. If the setting of the transmission wavelength of the input side WSS and the output side WSS is changed, the wavelength of the optical signal can be changed immediately. On the receiving node side, reception by the wavelength before the change and reception by the wavelength after the change can be performed in parallel. Therefore, the wavelength can be changed without interrupting communication.

  Next, in the optical communication node of the present invention, a more specific embodiment realized by using WSS in which each component is integrated will be described.

  The M × p WSSs 26-1 to 26-3 in the optical communication node of the present invention illustrated in FIG. 4 are realized by cascading the M × 1 WSS 52 and the 1 × p WSS 53 illustrated in FIG. In general, in a multi-input multi-output WSS, when the wavelengths to the input ports are all different, two WSS common ports (multiplexing side ports) can be connected as shown in FIG. If all the wavelengths to the input port are different, wavelength collision does not occur and the switch does not block internally. In the excitation light generation unit 25a and the frequency shift unit 25b in FIG. 5, all the inputs to the M × 1 WSS 52 of the frequency shift unit 25b are different in principle, and therefore no internal blockage occurs. The WSS having the same function as that of the M × p WSSs 26-1 to 26-3 can be realized by using a normal 1 × (M + p−1) configuration WSS having one multiplexing port.

  FIG. 10 is a diagram showing a configuration example of M × p WSS for selective distribution of pumping light in the optical communication node of the present invention. The example which uses WSS of a single 1 * (M + p-1) structure as WSS of the M * p structure shown in FIG. The WSS having a 1 × (M + p−1) configuration in FIG. 10 includes (M + p) input / output ports 101, a diffraction grating 102, cylindrical lenses 103 and 104, and a deflecting element 105. FIG. 10 is a view of the arrangement surface (xz plane) of the input / output ports 101 with the z direction as the light traveling direction as the horizontal direction of the drawing, and a side surface (yz plane) orthogonal thereto. It consists of a view. Of the (M + p) input / output ports 101, M are used as input ports 101a and p are used as output ports 101b. CW lights having different wavelengths are input to the M input ports 101a. For example, the CW light input from the input port 101-2 propagates along the optical path of the one-dot chain line. The CW light is first wavelength-demultiplexed by the diffraction grating 102 and dispersed in a direction corresponding to the wavelength of the CW light in the yz plane. The CW light is further refracted in the xz plane by the cylindrical lens 103, subsequently refracted in the yz plane by the cylindrical lens 104, and finally reaches the deflection element 105.

  CW light input from another input port of the M input ports, for example, the input port 101-3, propagates along the dotted optical path. Since the CW light has a wavelength different from that of the CW light input to the input port 101-2, the CW light is dispersed in different directions by the diffraction grating 102. Similarly, the CW light input from the input port 101-4 is also dispersed by the diffraction grating 102 in a direction different from the above two CW lights. Since all the CW lights input from different input ports have different wavelengths, each CW light finally reaches a different position in the y direction on the deflection element 105. The deflecting element 105 deflects each CW light so as to output to a desired port among the p output ports 101b. Each deflected CW light passes through the cylindrical lenses 104 and 103 and the diffraction grating 102, and is output to any one of the p output ports 101b.

  As described above, the multi-input multi-output M × p WSS constituting the M × 1 WSS 52 and the 1 × p WSS 53 shown in FIG. 5 is a single 1 × (M + p−1) having one multiplexing port. ) Can be realized by configuring the WSS as shown in FIG.

  In the pump light generating means shown in FIG. 5, the method of outputting CW light of the same wavelength to two two output ports (points 66b and 66d) of 1 × p WSS 53 is mentioned. In this embodiment, a configuration in which CW light having the same wavelength is output from different output ports of M × p WSS using the broadcast function of the deflecting element will be described. As the WSS deflection element in this embodiment, LCOS (Liquid Crystal on Silicon) is used. The LCOS is a spatial phase modulation element in which pixel-like phase modulation elements that can be individually controlled are two-dimensionally arranged.

  FIG. 11 is a diagram for explaining the configuration of the LCOS used in the M × p WSS for selective distribution of the excitation light according to the present embodiment. In the LCOS 105 shown in FIG. 10, the relationship between the phase pattern displayed by the two-dimensionally arranged phase modulation elements (pixels) and the CW light beam incident on the LCOS 105 is shown. On the left side of FIG. 11, a pixel arranged two-dimensionally on the LCOS is seen, and three CW lights are incident thereon, and beam surfaces 106a, 106b, and 106c of the respective CW lights are drawn. At this time, each CW light lands at the center position 105a in the x direction and at different positions in the y direction.

  Different phase modulation patterns can be displayed depending on the pixels in the area occupied by each CW light on the LCOS. For example, the phase pattern 107-2 is displayed in the area 106-2 covered by the beam surface 106a of the CW light indicated by the one-dot chain line. Similarly, the phase pattern 107-3 is displayed in the area 106-3 covered by the beam surface 106b indicated by the dotted line, and the phase pattern 107-4 is displayed in the area 106-4 covered by the beam surface 106c indicated by the solid line. To do.

  Each phase pattern is a sawtooth pattern with a phase value turned back at 2π, and the polarization direction of incident light is adjusted by the pattern period. For example, the phase pattern 107-2 has a constant pattern period Λ1, and all the CW lights on the beam surface 106a are deflected in the same direction. The phase pattern 107-3 includes phase patterns having pattern periods Λ2 and Λ3 with the center line 105a as a boundary. At this time, the component of the CW light 106b incident on the area of the pattern period Λ2 and the component of the CW light 106b incident on the area of the pattern period Λ3 are deflected in different directions. The phase pattern 107-4 includes three components having a pattern period of [Lambda] 4, [Lambda] 5, and [Lambda] 6. The components of the CW light 106c incident on the respective regions are deflected in different directions.

  As described above, the CW light is incident so that the beam surface of the CW light incident on the LCOS 105 is divided by the region on the LCOS, and is deflected by a different phase pattern in each region. Mxp WSS can be directed to different output ports. That is, it becomes possible to output CW light of the same wavelength to two different output ports of 1 × p WSS 53 in FIG. 5 and introduce them into two wavelength conversion means.

  In this embodiment, a specific configuration example of each wavelength multiplexer / demultiplexer in the pump light generation unit in FIG. 5 will be described. In the pump light generation unit shown in FIG. 5, three units of 1 × M WSS 48, M × 1 WSS 52, and 1 × p WSS 53 are required as WSSs having a wavelength multiplexing / demultiplexing function. In the second embodiment, the configuration in which the M × 1 WSS 52 and the 1 × p WSS 53 for selective distribution of the excitation light are realized with a single optical system has been described. In this embodiment, a configuration in which three WSSs are integrated in a single optical system by adding 1 × M WSS 48 will be described.

  Before describing the details of WSS integration, a spatial beam transformer (SBT) will be described. The SBT is a circuit element formed in the optical waveguide element, and is an important component for promoting the integration of WSS.

  FIG. 12 is a diagram showing an outline of the configuration of the spatial beam converter. The SBT 200 includes a plurality of input waveguides 201, a slab waveguide 202, and an arrayed waveguide 203 formed on a substrate. The optical signal input to the input waveguide 201 reaches the arrayed waveguide 203 while spreading in a plane parallel to the substrate surface in the slab waveguide 202. The arrayed waveguide 203 is configured such that the respective optical path lengths are equal between adjacent waveguides. The optical signal that has reached the arrayed waveguide 203 is output from the chip end 204 to the free space while maintaining its wavefront. Here, the direction of the wave front in the free space of the optical signal output from the chip end 204 is determined depending on which of the input waveguides 201 the optical signal is input from. For example, an optical signal input from the input waveguide 201a is output in the direction of the light beam 205a, and an optical signal input from the input waveguide 202b is output in the direction of the light beam 205b.

  FIG. 13 is an optical path diagram of an optical system in which three WSSs are integrated in the pump light generating means used in the optical communication node of the present invention. In the optical system shown in FIG. 13, three WSSs of 1 × M WSS 48, M × 1 WSS 52, and 1 × p WSS 53 in FIG. 5 are integrated. In the following description, the optical path diagram of FIG. 13 is orthogonal to the view of the arrangement plane (xz plane) of M + p input / output ports with the light traveling direction z direction as the horizontal direction of the drawing. It consists of the figure which looked at the side (yz plane). In the integrated WSS of this embodiment, an optical waveguide chip 301 including at least M + p SBT circuit elements is used as an input / output port.

  First, the operation as 1 × M WSS 48, which is a comb separating means for separating a plurality of CW lights, will be described. The CW light 300b input from the input port 301b is output to free space in the optical path direction of the dotted line 303b via the SBT circuit element 302b. The CW light is wavelength-demultiplexed by the diffraction grating 102 and then reaches the deflection element 105 via the cylindrical lenses 103 and 104. As in the second embodiment, the deflection element 105 is preferably an LCOS element. As described above, the CW light 300b is output to the free space tilted in the direction of the light ray 303b in the x-axis direction. For this reason, it also lands on the LCOS element at a position 105b offset in the x direction from the intersection 105a with the optical axis.

  The deflecting element 105 deflects the CW light in the direction of any one (SBT circuit element 305b) constituting a desired output port for each wavelength of the CW light in the SBT circuit element group 305, and then shows a dotted line 304b. Follow the light path. In the integrated WSS shown in FIG. 13, basically, one wavelength of CW light is output from one SBT circuit element. Signals having the same frequency adjustment amount Δf by the SSB modulator 49 for frequency shift in FIG. 5 may be collectively output to the same output port. In the example of the optical path diagram of FIG. 13, among the CW light deflected by the deflecting element (LCOS) 105, the optical signal having the wavelength indicated by the dotted line propagates in the direction of the light ray 304b and is output via the SBT circuit element 305b. Output from port 306b.

  The operation as the M × p WSS (M × 1 WSS 52 and 1 × p WSS 53), which is the excitation light selective distribution unit, is as follows. Of the input waveguides connected to the SBT circuit element group 305, for example, CW light is input to the SBT circuit element 305b to a waveguide that is not used as an output port of the 1 × M WSS48. This CW light becomes CW light from one of the plurality of SSB modulators of the frequency shift unit 25b in FIG. The input CW light 300c is output from the end of the SBT circuit element 305b to the free space in the direction of the solid line 303c. The CW light 300 c reaches a point 105 c on the LCOS 105 via the diffraction grating 102 and the cylindrical lenses 103 and 104. Here, the landing position 105 c is different from the intersection 105 a between the optical axis and the LCOS 105 for the same reason as in the case of the CW light 300 b described above. Since the light ray 303b and the light ray 303c which are emission directions to the space are in different directions, the two landing positions 105b and 105c are also different points. Therefore, by displaying different phase patterns in the vicinity of the points 105b and 105c in the x direction with the LCOS 105, it becomes possible to integrate the 1 × M WSS 48 and the M × p WSS into one optical system. The CW light 300c is finally output to an output waveguide connected to any one of the SBT circuit element groups 307. In FIG. 13, it is output from the output port 307c.

  As described above, according to the configuration of this embodiment, three WSSs (1 × M WSS48, M × 1 WSS52, and 1 × p WSS53) necessary for the pump light generation unit illustrated in FIG. Can be accumulated. That is, the wavelength selective switch 1 × M WSS 48 that is the comb separating means can share the same optical system as the multi-input multiple-output wavelength selective switches (M × 1 WSS 52 and 1 × p WSS 53). The components in the pump light generation means added in the optical communication node of the present invention can be efficiently integrated, and the node device in the optical communication node can be reduced in size.

  In the optical communication node of the present invention shown in FIG. 4, the configuration having the wavelength converting means and the corresponding pump light generating means for each input route has been described. That is, the pump light generating means 25-1 and the M × p WSS 26-1 are provided for the path 22-1 from the demultiplexing WSS 22-1 of the input path In1. Similarly, the pump light generating means 25-2 and the M × p WSS 26-2 are provided for the path 22-2 from the demultiplexing WSS 22-2 in the input path In2. The same applies to the route 22-3 from the demultiplexing WSS 22-3 of the input route In3. However, if the intensity of the pump light is sufficient, the pump light can be supplied from one pump light generating means across different paths.

  FIG. 14 is a diagram showing another configuration example of the optical communication node of the present invention. In the optical communication node 400 of FIG. 14, pump light is supplied from one pump light generation unit 25 to all the wavelength conversion units of the three paths (In1 to In3) via the M × p WSS 401. The output port of the M × p WSS 401 is connected not only to the wavelength conversion means 24a to 24d in the path In1, but also to all other wavelength conversion means in the paths In2 and In3. Therefore, the number p of ports in the M × p WSS 401 is equal to the total number of wavelength conversion means in this optical communication node.

  In the optical communication node of the present embodiment, an example in which p and the number of wavelength conversion means are equal is shown, but the numerical value of p is not limited to this example. By supplying pump light to the wavelength conversion means corresponding to a plurality of paths by a single pump light generation means, it is possible to realize downsizing and cost reduction of the device in the optical communication node.

  In the optical communication node of each of the embodiments described above, the wavelength converting means includes a plurality of paths that mutually connect between each of the plurality of demultiplexing wavelength selective switches and each of the plurality of multiplexing wavelength selective switches. At least one is installed. In this configuration, it cannot be applied between two adjacent nodes where no relay node exists. However, there may be a case where it is desired to immediately perform wavelength conversion on the optical signal from the Add port of the optical communication node. In the present embodiment, a configuration of an optical communication node suitable for a case where wavelength fragmentation in an added optical signal is severe is presented.

  FIG. 15 is a diagram showing still another configuration of the optical communication node of the present invention. The optical communication node 500 of FIG. 15 further adds wavelength conversion means on the path from the Add port 28 to the optical communication node 400 shown in FIG. Since other configurations are the same as those in FIG. 14, only the differences will be described. In the optical communication node of FIG. 15, two paths 503 are configured from the Add port 28 to each of the three multiplexing wavelength selective switches 29-1 to 29-3. On each path 503, wavelength conversion means 24e to 24j are installed. Pump light is supplied from one pump light generation means 25 via M × p WSS 501 to all the wavelength conversion means on the path between the input path and the output path, and on the path 503 from the Add port 28. Is done. In FIG. 15, pump light is supplied from the output 502 of the M × p WSS 501 to the wavelength conversion units 24e to 24j.

  In the optical communication node of this embodiment, the output port of the M × p WSS 401 is connected not only to the routes In1, In2, and In3 but also to all wavelength conversion means existing on the route connected to Out1, Out2, and Out3. Is done. Therefore, in the case of the configuration of FIG. 15, the number of ports p in the M × p WSS 501 is equal to the total number of wavelength conversion means in this optical communication node, and the number of output ports p is p = N × q. In the optical communication node of the present embodiment, an example is shown in which the number of ports p of the pump light selection / distribution unit 26 is equal to the number of wavelength conversion means, but the numerical value of p is not limited to this example. The pump light may be supplied to each wavelength conversion means by any number of pump light generation means and combination methods as long as an empty port in the pump light selection / distribution unit 26 is allowed.

  By supplying the pump light with a single pump light generation means to the wavelength conversion means corresponding to a plurality of routes including the Add port, it is possible to reduce the size and cost of the apparatus in the optical communication node. That is, the wavelength conversion means is installed in at least one of the paths connected to the plurality of multiplexing wavelength selective switches, and the path from the Add port connected to the plurality of multiplexing wavelength selective switches. Has been.

  By providing wavelength conversion means for the path on the Add port 28 as well, wavelength conversion is performed immediately after the transmitter, but it becomes possible to switch wavelengths more flexibly in the entire optical communication system. Wavelength defragmentation is performed by performing wavelength conversion of the added optical signal, such as when the wavelength fragmentation of the added optical signal is severer than the wavelength fragmentation state of the optical signal that has passed through In1, In2, In3, etc. In some cases, the number of wavelengths to be converted may be smaller. For this reason, in addition to the configuration of the embodiment shown in FIG. 14, by enabling wavelength conversion on the path of the Add port as in this embodiment, more flexible wavelength defragmentation can be realized. Of course, the configuration including the wavelength conversion means for the Add port of this embodiment can also be applied to the configuration of the optical communication node of FIG. 4 described first.

  According to the present invention, more flexible and simple wavelength defragmentation can be realized as compared with the prior art. By performing wavelength conversion on the path in the optical communication node without changing the frequency of the transmitter in the transmission node, troublesome and complicated control among a plurality of communication nodes is greatly simplified. If the information about wavelength change is known at the receiving node, the frequency of the local oscillator may be changed in advance to the frequency (wavelength) after the change at the receiver side of the receiving node. Even in the pump light generation means, it is sufficient to prepare pump light having a predetermined frequency in advance before the wavelength change. If the setting of the transmission wavelength of the input side WSS and the output side WSS is changed, the wavelength of the optical signal can be changed immediately. On the receiving node side, reception by the wavelength before the change and reception by the wavelength after the change can be performed in parallel. Therefore, the wavelength can be changed without interrupting communication. The components such as the pump light generation means and the pump light selection / distribution means added according to the present invention can realize a related apparatus in a small size and at low cost by using WSS integrated in an optical planar circuit.

  In the above-described first to fifth embodiments, the configuration of the optical communication node that performs flexible and simple wavelength defragmentation has been described. In order to implement wavelength defragmentation while the optical communication system is actually in operation, the operation procedure of each device in each optical communication node is important. Accordingly, the present invention has an aspect of an optical communication system including an optical communication node that performs wavelength defragmentation and an optical communication node at a receiving end that drops information data. Further, in the following embodiments, the configuration and operation procedure of an optical communication node that does not cause communication signal interruption in the optical communication system using the optical communication nodes of Embodiments 1 to 5 will be described. Therefore, the present invention also has an aspect as a method for controlling an optical communication node in an optical communication system. In addition, the optical communication system also has an aspect as a receiving-end optical communication node that implements a control method between optical communication nodes in an optical communication system.

  As described with reference to the spectrum of the pump light generation means in FIG. 6 and the wavelength conversion means in FIG. 8, wavelength defragmentation uses a wavelength conversion means that is an all-optical wavelength conversion means based on the nonlinear optical effect. In the wavelength conversion by the nonlinear optical effect, unnecessary light is generated in addition to the final converted signal light. Specifically, as shown in FIG. 8, signal light 82, pump light 81, idler light 83 using these as probe light, and idler light (signal light) 84 as desired wavelength converted light are generated simultaneously. In the node that performs wavelength conversion, it is necessary to operate the optical communication system by using only the signal light 84 that is idler light of the wavelength after wavelength conversion among these lights. The pump light 81 having an unnecessary wavelength, including the signal light 82 before wavelength conversion, and the idler light 83 generated by the nonlinear optical effect are blocked by, for example, the combining WSSs 29-1 to 29-3 in FIG.

  However, when switching the wavelength of an optical signal while the optical communication system is in an operational state, there is a problem that communication is interrupted at the moment of switching. Here, the wavelength of the optical signal before wavelength conversion is λ1, and the wavelength of the optical signal after wavelength conversion is λ2. Necessary for resetting if wavelength change setting from λ1 to λ2 is performed for each device such as WSS and other filters in the optical communication node that performs wavelength conversion and the optical communication node at the receiving end that drops optical signals Communication disruption occurs during a long period of time. Hereinafter, an optical communication node that drops an optical signal transmitting information data is referred to as a receiving end node.

  In order to avoid the above-described communication interruption, it is possible to simultaneously transmit two optical signals having different wavelengths λ1 and λ2 to the receiving end node. Also in this case, the reception timing between the two optical signals having different wavelengths depends on the influence of the chromatic dispersion in the transmission path and the length of the intra-office wiring (optical fiber) in the reception end node. Deviation occurs. At the receiving end node, the dropped optical signal is connected to a transponder or the like corresponding to the wavelength, and after the wavelength demultiplexing is performed on the downstream side of the demultiplexing WSS, the path corresponding to the wavelength may have a different delay. If a wavelength switching operation is performed between two wavelengths in a state where there is a shift in reception timing for each demultiplexed path on the receiving end node side, signal loss and data loss cannot be avoided. Therefore, in order to avoid data loss as much as possible at the receiving end node and to successfully receive information data, a mechanism for phase-synchronizing two optical signals having different wavelengths and a procedure for stably performing phase synchronization are important.

  FIG. 16 is a diagram illustrating the configuration of the optical communication system according to the sixth embodiment of the present invention. FIG. 16 illustrates a partial configuration of an optical communication network including two optical communication nodes, that is, a node B 600 and a node C 700. Wavelength switching of the optical signal is performed between the two optical communication nodes 600 and 700 without causing data loss. The two optical communication nodes 600 and 700 shown in FIG. 16 are assumed to perform information transmission from node A to node C via node B in the arrangement state of the nodes of the optical communication network shown in FIG. ing. In the node B 600, wavelength defragmentation for changing the wavelength of the optical signal is performed as described in the first to fifth embodiments. The optical signal after wavelength conversion is transmitted to the node C, and the optical signal is dropped at the node C. Therefore, the node C700 becomes a receiving end node. The route setting in each node is as follows.

  The optical signal having the wavelength λ1 input to the input port In2 of the demultiplexing WSS 603-2 at the node B600 is wavelength-converted to the wavelength λ2 by the wavelength conversion unit 605 on the path 612. The optical signal of λ2 after wavelength conversion is output from the output port Out1 of the multiplexing WSS 604-1 of the node B to the transmission path 650 and propagates to the receiving end node C. It should be noted that the optical signal of λ1 before wavelength conversion is simultaneously output from the Out1 of the WSS 604-1 for multiplexing in addition to the optical signal of λ2 after wavelength conversion until the phase synchronization procedure described later is completed. It is that. Therefore, the multiplexing WSS 604-1 of the Node B 600 has different wavelengths (λ1, λ2) before and after wavelength conversion from the path 612 in which the wavelength converting means 605 is inserted to its output port Out1 until the phase synchronization procedure is completed. Note that it is set to output two optical signals.

  As described in FIG. 8, in the optical communication nodes of the first to fifth embodiments, the original pump light 81, the signal light 82, and the unnecessary idler light 83 are removed, and the optical signal 84 (after wavelength conversion) ( It has been described that only the idler light is output to the output port of the multiplexing WSS 29-2 (FIG. 4). In the present embodiment, the original optical signal having the wavelength λ1 before wavelength conversion, which is unnecessary, is used until the phase synchronization procedure described later is completed.

  The multiplexed optical signal including at least λ1 and λ2 from the output port Out1 of the multiplexing WSS 604-1 is input to the input port In1 of the demultiplexing WSS 703-1 of the node C700 via the transmission path 650. The Multiplexed light including two optical signals of wavelengths λ1 and λ2 input to In1 is illustrated in each optical communication node of FIG. 16, for example, via a path 710 from one of the output ports of the demultiplexing WSS 703-1. Not received by transponder. The node B 600 and the node C 700 are described as having the configuration of the optical communication node according to the fourth embodiment illustrated in FIG. 14, but may be the optical communication node having the configuration according to another embodiment. Further, the setting of the number of paths and wavelengths of each optical communication node is not limited to that of the present embodiment.

  The optical communication node according to the present exemplary embodiment includes a wavelength switching processing unit 800 on a path leading to the drop port side transponder. The wavelength switching processing unit 800 realizes wavelength switching without data loss in conjunction with the wavelength defragmentation operation of the optical communication node shown in the first to fifth embodiments. The wavelength switching processing unit 800 includes a wavelength demultiplexing unit (DEMUX) 801 that demultiplexes two optical signals having different wavelengths λ1 and λ2, and at least two data reception paths that perform phase adjustment on the optical signals of the respective wavelengths. , A phase synchronization control unit 803, and a signal switching unit 806 for switching wavelengths by switching two data reception paths.

  The data reception paths are respectively phase adjustment units 802-1 and 802-2 that adjust the phase of the optical signal demultiplexed from the DEMUX 801, phase estimation units 804-1 and 804-2 that estimate the phase of each optical signal, It comprises receiving sections 805-1 and 805-2 that decode each optical signal. Next, a more detailed operation of the wavelength switching processing unit 800 in conjunction with the wavelength defragmentation operation of the optical communication node (node B) that performs wavelength switching upstream of the receiving end node will be described.

  FIG. 17 is a diagram illustrating a flow of the wavelength defragmentation operation and the phase synchronization procedure in the optical communication node according to the sixth embodiment. In the flow 1000, the operation of the node B 600 that performs wavelength switching and the operation of the wavelength switching processing unit 800 of the receiving end node C 700 are described together. As will be described later, the wavelength switching processing unit 800 operates to estimate the phases of two optical signals and adjust the two phase differences. Here, the term “phase” means “timing of information data” in an optical signal transmitted in an optical communication system. Therefore, terms such as “phase estimation”, “phase synchronization”, and “phase adjustment” are replaced with “information data timing estimation”, “information data timing synchronization”, and “information data timing adjustment”, respectively. Please keep in mind. When wavelength defragmentation is performed and the wavelength of the optical signal is switched, the information data should not be interrupted or lost. The wavelength switching processing unit 800 on the path for dropping the optical signal at the receiving end node operates to match the timing of the information data of the two optical signals. The two optical signals before and after wavelength conversion differ only in the wavelength (frequency) of light as a carrier carrying information data, and the contents of the information data being carried are the same. Therefore, in order to switch two optical signals of different wavelengths at the receiving end node, it is necessary to match the timing in consideration of not only the bits and modulation symbols but also the contents of the information data. If the wavelength is switched after the timings of the information data of the two optical signals are completely coincident, no data loss occurs downstream from the wavelength switching processing unit 800, or the data data disappears to the extent that does not hinder the use of the information data. Can be suppressed. The wavelength switching processing unit 800 in the receiving end node C is operated in conjunction with the wavelength defragmentation in the node B that performs wavelength switching, so that the optical communication system including the optical communication nodes according to the first to fifth embodiments can be operated more stably. .

  In step 1001, an optical signal of λ2 is generated by the wavelength conversion unit 605 on the path 612 for the optical signal of λ1 for which wavelength defragmentation is performed in the node B. As described above, it should be noted that at this stage, the optical signals of both λ1 and λ2 are wavelength-multiplexed and simultaneously output from the output port Out1 of the multiplexing WSS 604-1 of the Node B.

  In step 1002, the optical signals of λ1 before wavelength conversion and λ2 subjected to wavelength conversion are demultiplexed by the demultiplexing WSS 703-1 of the receiving end node C700, dropped into the path 710, and input to the DEMUX 801. As the DEMUX 801, for example, an arrayed-waveguide grating (AWG) or WSS is often used.

  In step 1003, the phases of the optical signals of λ1 and λ2 output from different ports of the DEMUX 801 are estimated by the phase estimation units 804-1 and 804-2, respectively. As described above, since the phase of the optical signal means the timing of the information data in the optical signal, the timing of the information data of the two optical signals is estimated here. In the configuration of the wavelength switching processing unit in FIG. 16, the receiving units 805-1 and 805-2 are provided on the downstream side of the phase estimation units 804-1 and 804-2, but the optical signal is branched in the phase estimation unit. Thus, at least part of the information data may be decoded to obtain the timing of the information data. Various methods can be selected as a method for obtaining the timing of information data of two optical signals. It can be processed as an optical signal, or can be processed after being converted into an electrical signal. Also, processing at an intermediate frequency before decoding, processing on a signal after decoding, or a combination thereof can be performed. As will be described later, since the wavelength switching processing unit obtains the phase difference (timing difference), the timing of the information data does not need to be an absolute time, and may be a relative timing from a specific time.

  In step 1004, a phase difference between the optical signal of λ1 and the optical signal of λ2 is calculated from the above two phase estimation values. It is determined whether or not the phase difference exceeds the variable range of the phase that can be adjusted by the phase adjustment unit 802-2 for the optical signal of λ2. As described above, the phase adjustment unit may be rephrased as a timing adjustment unit. Alternatively, the phase adjustment unit may obtain a timing difference instead of the phase difference and determine the timing adjustment variable range in the timing adjustment unit 802-2.

  In the stage from step 1001, the last-stage signal switching unit 806 in the wavelength switching processing unit 800 selects the optical signal of λ1 before wavelength conversion. Note that the decoded output of the optical signal of λ1 from the 805-1 receiving unit is further supplied to a transponder or the like at the subsequent stage, and information data is transmitted. The wavelength switching without data loss is prepared from the optical signal of λ1 to the optical signal of λ2 by the procedure after step 1003 described below. If the phase difference in step 1004 does not exceed the variable range of phase adjustment of the phase adjustment unit 802-2 (NO), the flow 1000 proceeds to step 1005.

  In step 1005, the phase synchronization control unit 803 gives the phase adjustment unit 802-2 for the optical signal of λ2 so that the two optical signals of λ1 and λ2 are phase-synchronized, that is, the timings of the information data match. The power phase shift amount is obtained. The obtained phase shift amount is applied to the phase adjustment unit 802-2, and a feedback operation for performing the phase shift of the optical signal of λ2 is performed so as to eliminate the phase difference calculated in Step 1004. The phase synchronization control unit 803 can operate as a timing synchronization control unit, and the phase shift can also be called a data information timing shift (timing adjustment). If the phase difference between the two optical signals in step 1004 exceeds the variable range of phase adjustment by the phase adjustment unit 802-2 (YES), the procedure proceeds to step 1008.

  In step 1008, the phase synchronization controller 803 controls the phase difference for the optical signal of λ1 as a phase shift amount corresponding to the phase adjustment variable range (corresponding to the remaining amount) exceeding the variable range of phase adjustment for the optical signal of λ2. The optical signal of λ1 is phase-shifted to the unit 802-1. Thereafter, the procedure returns to Step 1003, and the phases of the two optical signals λ1 and λ2 are estimated again by the phase estimation units 804-1 and 804-2. In the stage after returning from step 1008, the initial phase difference between the optical signal of λ1 and the optical signal of λ2 is reduced by the phase adjustment by the phase adjustment unit 802-1 for the optical signal of λ1 performed in step 1008. ing. Therefore, the determination in step 1004 after passing through step 1008 is NO, and the process proceeds to step 1005 described above.

  In step 1006, it is determined whether or not the phase difference between the optical signal of λ1 and the optical signal of λ2 is less than or equal to the allowable value. Needless to say, the phase difference is replaced by a timing difference between the optical signal of λ1 and the optical signal of λ2. Here, if the phase difference (timing difference) exceeds the allowable value (NO), the process proceeds to step 1009.

  In step 1009, a phase shift amount to be given to the phase adjustment unit 802-2 for the optical signal of λ2 is calculated under the control of the phase synchronization control unit 803 in order to eliminate the phase difference between the two optical signals. Returning to step 1005 again, under the control of the phase synchronization control unit 803, the phase adjustment unit 802-2 shifts the phase of the optical signal of λ2, and performs a feedback operation. The number of repetitions of step 1009 varies depending on parameters such as the phase control amount and loop gain of feedback loop control in one operation, and depends on the specific control method and algorithm of the phase synchronization control unit 803. The allowable value of the phase difference is determined according to the information transmission rate and the optical signal modulation method in the optical communication system. When the transmission rate of information data (that is, the baud rate) is high or the modulation method has a large modulation order, the allowable value of the phase difference (timing difference) can be set strictly. If the phase difference between the optical signal of λ1 and the optical signal of λ2 is equal to or smaller than an allowable value in step 1006 (YES), the procedure proceeds to step 1007.

  In step 1007, the signal switching unit 806 at the final stage in the wavelength switching processing unit 800 switches the path so as to output the optical signal of λ2, and the procedure of the flow 1000 is completed.

  In the steps 1004, 1005 and 1008 described above, the phase adjustment unit 802-2 for the wavelength-converted λ2 optical signal is used to eliminate the phase difference between the λ1 optical signal and the λ2 optical signal. Priority is given to phase adjustment. Since the optical signal having the wavelength λ1 before the wavelength conversion is the original data information and the optical signal is actually being transmitted before the wavelength switching, the optical signal having the wavelength λ1 is not inadvertently operated as much as possible. This is because it is preferable. Therefore, it is desirable to preferentially adjust the phase adjustment unit 802-2 of the optical signal of λ2 without operating the phase adjustment unit 802-1 of the optical signal of λ1 as much as possible. As in step 1008, only when the phase difference between the optical signal of λ1 and the optical signal of λ2 exceeds the operating range of the phase modulation unit 802-2 on the λ2 side, the phase adjustment unit phase modulation unit 802 of the optical signal of λ1 It is desirable to operate -1.

  Therefore, the present invention provides a plurality of demultiplexing wavelength selective switches (603-603) for demultiplexing wavelength division multiplexed signals from different input paths in an optical communication system that multiplexes optical signals of different wavelengths and transmits information data. 1-603-3), a plurality of multiplexing wavelength selective switches (604-1 to 604) for multiplexing wavelength division multiplexed signals including the demultiplexed signal light from each of the plurality of demultiplexing wavelength selective switches. -3), and a plurality of paths that mutually connect between each of the plurality of demultiplexing wavelength selective switches and each of the plurality of multiplexing wavelength selective switches, The first optical communication node 600 in which the wavelength conversion means 605 is installed and the first optical communication node are wavelength-converted with respect to at least one path 612 among the paths connected to the wavelength selective switch for use. Wavelength demultiplexing means 703-1 and 901 for demultiplexing the previous first optical signal and the second optical signal obtained by wavelength-converting the first optical signal, and the first optical signal and Timing estimation units 904-1 and 904-2 that estimate the timing of information data between the second optical signals, and the timing difference of information data between the first optical signal and the second optical signal A wavelength switching processing unit 900 including timing adjustment units 903, 904-1, and 904-2 for decreasing the frequency, and a second optical communication node 700 that drops the second optical signal carrying the information data. It can be implemented as an optical communication system.

  Further, in the above-described optical communication system, the first optical communication node performs wavelength conversion on the first optical signal having the wavelength λ1, and generates the second optical signal having the wavelength λ2. Estimating the timing of the first optical signal and the second optical signal by the timing estimation unit at the second optical communication node; and the first optical signal at the second optical communication node. And a step of operating the timing adjustment unit so that a timing difference between the second optical signals is reduced, and reception from the first optical signal to the second optical signal at the second optical communication node. Switching a route and acquiring the information data from the second optical signal; and deleting an optical path related to λ1 at the first optical communication node and the second optical communication node. phase Period procedure can also be carried out as a control method of the optical communication nodes implementing.

The phase adjustment accuracy in the phase adjustment units 802-1 and 802-2 is, for example, 0.01 to 0.00 when converted to time based on a standard in a system called 100G system or Beyond 100G that is currently being introduced. It becomes about 1 nsec. Since the information transmission speed in the current optical communication is about 25 to 50 × 10 ⁹ baud, phase (timing) adjustment accuracy corresponding to the reciprocal of this transmission speed is required. The variable range of phase adjustment requires an adjustment range of about 30 nsec if the length of the optical fiber in the station varies in terms of vacuum.

  The phase adjustment units 802-1 and 802-2, the phase synchronization control unit 803, the phase estimation units 804-1 and 804-2, the reception units 805-1 and 805-2, and the signal switching unit 806 are independent devices. It is not necessary to be a device that handles an optical signal as it is, or a device that performs processing by converting an optical signal into an electrical signal. In particular, when processing is performed by converting into an electric signal, a digital signal processor (DSP), a field-programmable gate array (FPGA), and an application specific ASPS (Application Specific Signal Processor) widely used in long-distance and large-capacity communication devices. Standard Product) can be selected. The phase estimation function already mounted for communication processing by a DSP or FPGA can be used for each element of the wavelength switching processing unit 800, and the above-described phase synchronization control processing can be realized in a compact manner.

  The elements of the wavelength switching processing unit 800 do not have to be arranged in the order and connection relationship shown in FIG. 16 as long as the same function as the phase synchronization procedure described in FIG. You don't have to. For example, the DEMUX 801 may be a general demultiplexing unit that is used in an optical communication node of the prior art to drop an optical signal and guide it to, for example, a transponder. Depending on the number of wavelengths, the demultiplexing means can be variously configured. The DEMUX 801 can be omitted, or an optical switch and WSS can be combined. It is only necessary that the two optical signals λ1 and λ2 before and after the wavelength switching can be supplied to the two data reception paths.

  In the wavelength switching processing unit shown in FIG. 16, the output of the DEMUX 801 is configured to be connected to two data reception paths, but the phase synchronization procedure of FIG. 17 can be performed simultaneously for different wavelength sets. As described above, it is also possible to configure four data reception paths so that two different wavelength switching operations (λ1 → λ2, λ3 → λ4) are performed simultaneously. In addition, the positions of the signal switching unit 806 and the receiving units 805-1 and 805-2 can be switched to make one receiving unit. Furthermore, after the wavelength switching processing unit 800 of the receiving end node, not only a transponder but also any functional block that uses a dropped optical signal can be connected. Therefore, the wavelength switching processing unit 800 does not necessarily include a receiving unit for decoding information data. In addition, since the phase adjustment (timing adjustment) can be performed on the symbols and data bits decoded by the receiving units 805-1 and 805-2, before the phase adjusting units 802-1 and 802-2. Receiving units 805-1 and 805-2 may be provided.

  By performing the procedure of the flow 1000 in FIG. 17, the two optical signals λ1 and λ2 are phase-synchronized and the timing of the information data is matched, and then the signal switching unit 806 changes the wavelength of λ2 after wavelength conversion. By switching to an optical signal, communication using an optical signal with a new wavelength is achieved. After the phase synchronization procedure by the wavelength switching processing unit 800 is completed, in the node B600 and the node C700, in the device existing in the section transmitting the optical signal of λ2, such as WSS, the optical signal of λ1 before wavelength conversion is It becomes unnecessary. The wavelength defragmentation of the entire optical communication system is completed by sequentially performing a block or the like of the optical signal of λ1 and deleting unnecessary optical path settings in the section where the optical signal of λ1 existed.

To summarize the optical communication node configuration of the optical communication system of FIG. 16 and the flow of FIG. 17, in the optical communication node of the present embodiment, in order to perform wavelength defragmentation without causing data loss, the following steps are performed. Implement sequentially. At the receiving end node, data information is received by the optical signal of λ1.
(1) At the wavelength switching node, wavelength conversion is performed on the optical signal of λ1, and an optical signal of λ2 is generated.
(2) At the receiving end node, the phase estimation unit estimates the phase of each optical signal of λ1 and λ2 (timing of information data).
(3) Based on the information from the phase estimation unit, analysis is performed by the phase synchronization control unit, and feedback control is performed on the phase adjustment unit so that the respective phases are aligned and the timing of the information data coincides.
(4) At the receiving end node, the reception path is switched from the optical signal of λ1 to the optical signal of λ2, and the optical signal is supplied to the subsequent functional block.
(5) The optical path related to the optical signal of λ1 before wavelength conversion is deleted.

  By switching the operation of the optical communication node that performs the wavelength defragmentation described as the first to fifth embodiments and the phase synchronization procedure at the receiving end node, the optical communication node according to the present embodiment can perform wavelength switching without data loss. realizable.

  In the optical communication node of Example 6 described above, the phase synchronization procedure by the wavelength switching processing unit has been described. In the phase synchronization procedure by the wavelength switching processing unit of the sixth embodiment, the phase synchronization and phase adjustment of the optical signal can be performed before and after the decoding of the optical signal, and a general configuration is shown. In the present embodiment, a more specific configuration using a MIMO equalizer that enables more efficient phase synchronization at the receiving end node will be described.

  In the experimental system described in Non-Patent Document 2 (FIG. 1), modulation is performed with the same signal for each of the two wavelengths, and maximum ratio synthesis is performed by an adaptive MIMO (Multi-Input and Multi-Output) equalizer. Implementing phase synchronization is disclosed. More specifically, in the experimental system (FIG. 1) of Non-Patent Document 2, optical signals of two wavelengths (channel 1 and channel 2) are each decoded by a coherent receiver, and the decoded signals are adaptive MIMO or the like. Connected to the generator. The adaptive MIMO equalizer controls the tap coefficients of the two signals to appropriate values and synthesizes the two signals. At this time, when the phases of the two signals are appropriately adjusted, the signal quality is maximized, and the original optical signal (channel 1) is stopped after setting the state to the maximum quality. The optical communication node of the present embodiment uses a maximum ratio combining unit (adaptive MIMO equalizer) as a more specific configuration example. Hereinafter, differences from the configuration of the sixth embodiment will be mainly described.

  FIG. 18 is a diagram showing a configuration of an optical communication system according to the seventh embodiment of the present invention. Also in FIG. 18, wavelength switching of an optical signal is performed between two optical communication nodes 600 and 700 without causing data loss. In the two optical communication nodes B 600 and C 700 shown in the optical communication system of FIG. 18, information data is transmitted to the node C via the node B as in the sixth embodiment. In the present embodiment, the wavelength conversion unit described in the first to fifth embodiments is used to generate two optical signals, and the optical signals before and after wavelength conversion are used for demultiplexing at the receiving end node C700. Input to the input port In1 of the WSS 703-1. The multiplexed light including the two optical signals having the wavelengths λ1 and λ2 input to In1 is demultiplexed by the demultiplexing WSS 703-1, and the two optical signals are routed from one of the output ports of the demultiplexing WSS to the path 710. And received by the transponder.

  The optical communication node according to the present exemplary embodiment includes a wavelength switching processing unit 900 on a route to the drop port side transponder. The wavelength switching processing unit 900 realizes wavelength switching without data loss in conjunction with the wavelength defragmentation operation of the optical communication node described in the first to fifth embodiments. The wavelength switching processing unit 900 includes a wavelength demultiplexing unit (DEMUX) 901 that demultiplexes two optical signals having different wavelengths λ1 and λ2, and at least two systems of data reception that perform detection and phase estimation on the optical signals of the respective wavelengths. A maximum ratio combining unit 907 for combining the optical signals of two wavelengths with a maximum ratio, and phase synchronization control for acquiring phase information of each wavelength and analyzing a phase adjustment amount necessary to synchronize each phase Part 903. The data reception path of each system includes coherent detection units 906-1 and 906-2 for performing coherent detection, and phase estimation units 904-1 and 904 for estimating the phase of an optical signal input for each wavelength. -2.

  The maximum ratio combining unit 907 calculates the Q value of the signal when the two optical signals are combined at the maximum ratio. The phase estimation units 904-1 and 904-2 estimate the phases of the two optical signals, and control the filter taps and the like of the maximum ratio combining unit 907 so that the Q value becomes maximum. As the maximum ratio combining unit 907, for example, an adaptive MIMO equalizer can be used. In the maximum ratio combining unit 907, as the matching degree between the two channels increases, the signal level rises above the noise level, and the Q value of the signal increases. The Q value is maximized when the phases of the two signals are synchronized and the timing of the information data coincides. Therefore, the phase of the two optical signals having the wavelengths λ1 and λ2 can be adjusted using the equalization function of the maximum ratio combining unit 907. When the optical signal of λ2 is input to the wavelength switching processing unit 900, the maximum ratio combining unit 907 immediately operates so that the Q value when the maximum ratio is combined is maximized. After entering the maximum ratio combining state, the two optical signals of λ1 before wavelength conversion are quenched as in the sixth embodiment. In the present embodiment, the coherent detectors 906-1 and 906-2 convert and decode each of the optical signals of λ1 and λ2, and the maximum ratio combining unit 907 converts each of the electrical signals. It is synthesized electrically. Therefore, the output of the maximum ratio combining unit 907 is the decoded electrical signal 910 after the logic synthesis. Therefore, the switching SW as in the sixth embodiment is not necessary. To switch to the optical signal of λ2, it is only necessary to extinguish the optical signal of λ1 while the signal of λ1 and the signal of λ2 are synchronized.

  Even in the optical communication node according to the seventh embodiment, when the wavelength conversion node B600 that performs wavelength defragmentation converts the wavelength of an optical signal by the wavelength conversion unit 605, the optical signal of λ1 before conversion and the optical signal of λ2 after conversion Can coexist at the same time. By using an adaptive MIMO equalization unit used in communication technology, a phase synchronization procedure without data loss can be realized with the minimum necessary configuration.

  In any of the sixth embodiment and the seventh embodiment described above, each block of the wavelength switching processing units 800 and 900 can be configured in a transponder corresponding to the wavelength of the optical signal on the drop side, for example. Further, the phase synchronization control units 803 and 903 can be configured as a part of a common control unit of transponders, for example.

  As described in detail above, the optical communication system of the present invention includes an optical communication node that can realize wavelength defragmentation that is more flexible and simpler than the prior art. By linking the wavelength defragmentation operation of the node that performs wavelength conversion with the phase synchronization procedure at the receiving end node, stable operation of the optical communication system is possible by wavelength switching without data loss.

  The present invention is generally applicable to communication systems. In particular, it can be used for an optical communication node of an optical communication system.

11, 12, 13, 20, 400, 500, 600, 700 Optical communication nodes 21-1 to 21-3, 603-1 to 603-3 WSS for demultiplexing
24, 24a to 24i, 605 Wavelength conversion means 25, 25-1 to 25-3, 601 Pump light generation means 25a Excitation light generation part 25b Frequency shift part 26 Excitation light selective distribution part 27 Drop port 28 Add port 26-1 26-3, 401, 501 M × p WSS
29-1 to 29-3 WSS for multiplexing
46, 50, 71 EDFA
47 HNLF
48 1 × M WSS
49 SSB modulator 52 M × 1 WSS
53 1 × p WSS
70 Optical Combiner 72 Nonlinear Optical Medium 102 Diffraction Grating 103, 104 Cylindrical Lens 105 Deflection Element (LCOS)
800, 900 Wavelength switching processing unit 801, 901 Wavelength demultiplexing unit 803, 903 Phase synchronization control unit 805-1, 805-2 Receiver 804-1, 804-2, 904-1, 904-2 Phase estimation unit 906 1,906-2 Coherent detection unit 907 Maximum ratio combining unit

Claims (8)

In an optical communication system that multiplexes optical signals of different wavelengths and transmits information data,
A plurality of demultiplexing wavelength selective switches for demultiplexing wavelength division multiplexed signals from different input paths;
A plurality of multiplexing wavelength selective switches for multiplexing wavelength division multiplexed signals including the demultiplexed signal light from each of the plurality of demultiplexing wavelength selective switches; and
A plurality of paths interconnecting each of the plurality of demultiplexing wavelength selective switches and each of the plurality of multiplexing wavelength selective switches;
A first optical communication node in which wavelength conversion means is installed for at least one of the paths connected to the plurality of multiplexing wavelength selective switches;
Wavelength demultiplexing means for demultiplexing the first optical signal before wavelength conversion in the first optical communication node, and the second optical signal obtained by converting the wavelength of the first optical signal; and
A timing estimator for estimating a timing of information data between the first optical signal and the second optical signal, and a timing difference of information data between the first optical signal and the second optical signal; And a second optical communication node for dropping the second optical signal carrying the information data. The timing estimation unit performs coherent detection on the first optical signal and the second optical signal, respectively, and performs timing estimation on the two pieces of decoded information data,
The timing adjustment unit is a maximum ratio combining unit that adjusts the timing of the two pieces of information data so as to maximize the combined output by combining the two pieces of information data with a maximum ratio. Item 4. The optical communication system according to Item 1. The at least one path of the first optical communication node is:
A path of at least one combination of the demultiplexing wavelength selective switch and the multiplexing wavelength selective switch, or a path from an Add port connected to the plurality of multiplexing wavelength selective switches. Item 3. The optical communication system according to Item 1 or 2. Further comprising excitation light generating means for supplying excitation light to the wavelength converting means,
4. The optical communication system according to claim 1, wherein the wavelength conversion unit is an all-optical wavelength conversion unit in which wavelength conversion is performed only in an optical layer. The excitation light generating means includes
An excitation light generator that generates frequency comb light from CW light;
Comb separation means for spatially demultiplexing the frequency comb light generated in the pump light generation unit into a single CW light for each comb frequency;
A plurality of frequency shifters for shifting the frequency of the demultiplexed single CW light;
5. The optical communication according to claim 4, further comprising: excitation light selective distribution means for multiplexing and spatially demultiplexing the CW light whose frequency is shifted from each of the plurality of frequency shift units. system.   6. The optical communication system according to claim 5, wherein the pumping light selective distribution means is a multi-input multi-output wavelength selective switch. The optical communication system according to any one of claims 1 to 6,
Performing wavelength conversion on the first optical signal of wavelength λ1 at the first optical communication node to generate the second optical signal of wavelength λ2.
Estimating the timing of the first optical signal and the second optical signal by the timing estimation unit in the second optical communication node;
Operating the timing adjustment unit so that a timing difference between the first optical signal and the second optical signal is reduced in the second optical communication node;
Switching the reception path from the first optical signal to the second optical signal at the second optical communication node, and obtaining the information data from the second optical signal;
A method of controlling an optical communication node, comprising: performing a phase synchronization procedure including: deleting an optical path related to λ1 at the first optical communication node and the second optical communication node. In an optical communication system that multiplexes optical signals of different wavelengths and transmits information data, an optical communication node that drops an optical signal carrying the information data,
Wavelength demultiplexing means for demultiplexing a first optical signal before wavelength conversion in a different optical communication node and a second optical signal in which the wavelength of the first optical signal is converted in the different optical communication node When,
A timing estimator for estimating a timing of the information data between the first optical signal and the second optical signal, and an information data between the first optical signal and the second optical signal. And a wavelength switching processing unit including a timing adjustment unit that reduces a timing difference. The different nodes are a plurality of demultiplexing wavelength selective switches that demultiplex wavelength division multiplexed signals from different input paths, and the plurality of demultiplexing. A plurality of multiplexing wavelength selective switches for multiplexing wavelength division multiplexed signals including the demultiplexed signal light from each of the wavelength selecting switches for use, each of the plurality of wavelength selecting switches for demultiplexing, and the plurality of A plurality of paths mutually connecting to each of the plurality of wavelength selection switches for multiplexing, and at least one path among paths connected to the plurality of wavelength selection switches for multiplexing To the first optical communication node, characterized in that the wavelength conversion means is provided for wavelength conversion to said second optical signal from the optical signal.

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