JP5858474B2 - Optical variable filter and optical signal termination device using optical variable filter - Google Patents

Description

  The present invention relates to an optical circuit used in optical communication. More specifically, the present invention relates to an optical variable filter used in an optical signal termination device for extracting or adding an optical signal having a specific wavelength from a wavelength division multiplexed optical signal, and an optical signal termination device using the optical variable filter.

  Optical communication technology using an optical fiber as a transmission medium has resulted in a long signal transmission distance, and a large-scale optical communication network has been constructed. In recent years, with the widespread use of Internet communication, communication traffic has increased rapidly, and demands for large capacity, high speed, high functionality, and low power consumption for communication networks are increasing. Up to now, it has become possible to increase the transmission capacity between two points by introducing a wavelength multiplex communication technique for simultaneously transmitting a plurality of optical signals having different wavelengths through one optical fiber transmission line. However, in a communication network, it is necessary to set (route) or switch (switch) a signal path (path) at a node where a plurality of transmission paths gather. With the rapid increase in transmission capacity in recent years, signal processing such as path setting and switching has become a bottleneck.

  Up to now, a method has been used in which a transmitted optical signal is once converted into an electrical signal, path setting or path switching is performed, the electrical signal is converted again into an optical signal, and then sent to the transmission path. However, in the future, a so-called photonic network will be realized that uses a method of performing signal path setting and switching processing without converting an optical signal into an electrical signal. By using a photonic network, it is expected that the throughput of the node will be dramatically increased and the power consumption of the node device will be greatly reduced.

  As an optical node system using a photonic network, a reconfigurable optical add drop multiplexing (ROADM) system in which a plurality of nodes are connected in a ring shape or a bus shape, and a plurality of nodes in a mesh shape An optical cross-connect (OXC: Optical Cross-Connect) system connected to the network is known. Each node of the ROADM system is connected to one input-side optical fiber transmission line and one output-side optical fiber transmission line. For each wavelength division multiplexed optical signal input from the input-side optical fiber transmission line, In addition, an optical switch that switches connections for each wavelength is equipped. This makes it possible to switch between a through state and an add / drop state for an optical signal having an arbitrary wavelength among the wavelength division multiplexed optical signals.

  The through state is a state in which an optical signal input from the input side optical fiber transmission line is output to the output side optical fiber transmission line. The add / drop state is a “drop state” in which an optical signal input from the input side optical fiber transmission line side is output to a terminal device connected to the node, or an optical signal input from the terminal device. Is an “added state” that is output to the output side optical fiber transmission line.

  On the other hand, in the OXC system, a plurality of input-side optical fiber transmission lines and a plurality of output-side optical fiber transmission lines are connected to each node, and wavelength division multiplexed optical signals input from the input-side optical fiber transmission lines are received. An optical switch that switches connection paths (routes) for each wavelength is provided. With this configuration, an optical signal having an arbitrary wavelength among wavelength division multiplexed optical signals input from an arbitrary input-side optical fiber transmission line can be output to an arbitrary output-side optical fiber transmission line. Recently, in order to build a highly flexible network, a terminal device is also connected to an OXC node, and in addition to switching connection paths between input and output optical fiber transmission lines, add / drop to the terminal device There is also a need for a system that can.

  FIG. 1 is a diagram conceptually showing the configuration of an OXC system in a photonic network. The configuration shown in FIG. 1 is obtained by adding an ad system / drop system to the original OXC system. In other words, the OXC system in FIG. 1 can be regarded as having a configuration in which the number of routes in the ROADM system is changed from one to a plurality (K). The present invention relates to a node including a plurality of input transmission line fibers and a plurality of output transmission line fibers and capable of adding / dropping an optical signal from the transmission line optical fiber. In the following description, the OXC system will be described for convenience, but it goes without saying that the present invention can also be applied to a ROADM system. In the photonic network, a node in which a plurality of transmission paths are gathered and the optical layer and the electrical layer are exchanged and a communication signal is processed is called a photonic node.

  The OXC system shown in FIG. 1 includes, as basic elements, K input side optical fiber transmission lines 2-1 to 2-K to which J wavelength division multiplexed optical signals 1-1 to 1-J are respectively input. The optical cross-connect unit 3 and K output-side optical fiber transmission lines 4-1 to 4-K from which J wavelength division multiplexed optical signals 5-1 to 5-J are output, respectively. Further, a drop system 6-1 and an add system 6-2 are added to realize the add / drop function. In FIG. 1, the number K of input side and output side optical fibers may be the same as the number J of wavelength division multiplexed optical signals.

The wavelength division multiplexed optical signal is an optical signal obtained by multiplexing a plurality of optical signals having different wavelengths. It is also possible to multiplex optical signals of a plurality of wavelengths to form one wavelength group, and further multiplex a plurality of different wavelength groups to configure a wavelength division multiplexed optical signal. Moreover, the wavelength contained in one wavelength group can be comprised from the several wavelength by which the value of the wavelength was continuously arrange | positioned in the order of the length. For example, the wavelength (number), lambda _1, lambda _2, as in the · · lambda _8, can constitute one wavelength group of eight wavelengths are arranged in succession. Moreover, it can also be comprised from the several wavelength arrange | positioned discontinuously discontinuously instead of being continuous in order of the length of a wavelength. For example, the wavelength (number), lambda _1, lambda _5, as in the lambda ₉ · · lambda _29, constituting a wavelength group of eight wavelengths arranged in a discontinuous (discretely) at a predetermined distance You can also. There are various cases where the number of wavelengths constituting one wavelength group and the above-described predetermined interval are various.

  The optical signal dropped by the drop system 6-1 is connected to a plurality of receivers 8 (also referred to as transmission lines Rx), subjected to termination signal processing, and another network 7 (for example, an electrical router) in the electrical layer, etc. The electric signal 10 supplied to is output. In addition, an electrical signal 11 supplied from another network 7 in the electrical layer is connected to a plurality of transmitters (also referred to as transmission lines Tx) 9, and an optical signal is added via an add system 6-2. The termination signal processing described above includes signal processing such as conversion between an optical signal and an electric signal, level adjustment, error detection / correction in the converted electric signal, and conversion of an appropriate signal format. The drop system 6-1 and the add system 6-2, and the receiver 8 and the transmitter 9 are collectively referred to as an optical signal terminator. The receiver 8 and the transmitter 9 are also called terminal equipment.

  In general, in the OXC system as shown in FIG. 1, as an ideal drop / add system, colorless (colorless), directionless (directionless), and contentionless These three characteristics are required. Colorless means that an optical signal of any wavelength can be output from any drop port to the receiver, and an optical signal of any wavelength can be transmitted from the transmitter via the add system to the output optical fiber transmission A configuration that can be input to a road. Directionless means that an optical signal input from an arbitrary input side optical fiber transmission line can be output from an arbitrary drop port (receiver), and an arbitrary optical signal input to an add system can be arbitrarily specified. It is the structure which can output from the output side optical fiber transmission line.

  Further, as a matter of course, if two or more optical signals having the same wavelength are simultaneously present in the same optical path of the optical fiber transmission path, the optical signals collide with each other, resulting in interference. . The optical path becomes unusable (blocking state). Such a collision may also occur in connection setting of an optical path related to an add / drop operation. In the connection setting of the optical path related to the add / drop operation, it is necessary to have a configuration in which such optical signals do not collide with each other, and it is necessary to perform the contentionless so as not to cause blocking. .

  Currently, an add / drop system that has started operation has limitations such as being able to connect only to predetermined ports and requiring manual operation to change port connections. Ideally, it is necessary to realize the above-mentioned three characteristics (CDC: Colorless, Directionless and Contentionless) in the photonic network. Next, a configuration currently proposed as an ideal photonic network will be described.

  FIG. 2 is a diagram for explaining a configuration of a conventional add / drop system using a full mesh connection optical switch in an OXC system. The configuration of FIG. 2 is a more specific example of the add / drop function portion in the schematic configuration of the OXC system shown in FIG. 1, so only the differences from the configuration shown in FIG. 1 will be described. Between the input side optical fiber transmission lines 1-1 to 1-K and the optical cross-connect unit 3, the wavelength division multiplexed optical signals from the K input side optical fiber transmission lines 2-1 to 2-K are transmitted. Branching optical couplers 21-1 to 21 -K are provided. A corresponding one of the duplexers 22-1 to 22-K is connected to one optical coupler. For example, an optical coupler 21-1 is connected to the first input side optical fiber transmission line 2-1, and the branched wavelength division multiplexed optical signal 12 is guided to the demultiplexer 22-1. In the add / drop system of FIG. 2, it goes without saying that the optical signal having the wavelength branched by the optical coupler and dropped to the receiver is appropriately processed in the optical cross-connect unit 3 so as not to overlap. The optical coupler does not have a path switching function, but can branch and output an input wavelength. The cost is very small compared with the optical matrix switch, which is about 1/100.

  The outputs of the demultiplexers 22-1 to 22-K are connected to an optical matrix switch 23 having a full mesh configuration having M inputs and L outputs. The L outputs of the optical switch 23 are connected to L receivers 24-1 to 24-L. In general, an optical matrix switch, regarding optical signals (wavelength path, wavelength group path) having an arbitrary granularity, rearranges the input optical signals in an arbitrary order (port position) and outputs them to each output port. Therefore, an optical signal entering any input port of the M inputs of the optical switch 23 appears at any output port of the L outputs. In general, the cost for realizing an optical switch device largely depends on the number of input / output ports, and increases as the number of ports increases.

  For example, when optical signals of 96 different wavelengths are multiplexed on one wavelength division multiplexed optical signal and there are K = 8 input-side optical fiber transmission lines, the optical switch 23 receives 768 as an input. With input ports. The number of add ports and the number of drop ports per node are determined at a predetermined rate (drop rate / add rate) with respect to the number of input ports. For example, if the number of add ports and the number of drop ports are 16, respectively, the optical switch 23 forms a huge matrix having 768 inputs × 16 outputs. The same applies to the add-side optical switch 28.

  As described above, the configuration of the OXC node shown in FIG. 2 can realize three characteristics of colorless, directionless, and contentionless, but requires a large and expensive optical switch. The problem of reduced reliability due to the large number of switch elements was also important. Thus, several improved configurations have been proposed for add / drop systems. For example, Patent Document 1 shows a colorless configuration example in a ROADM system. As an OXC node, Patent Document 2 proposes an example in which wavelength group demultiplexing selection and wavelength demultiplexing selection are combined with a compact optical switch.

  FIG. 3 is a diagram for explaining the configuration of another conventional add / drop system according to Patent Document 2. In FIG. The configuration of the OXC system shown in FIG. 3 is obtained by realizing the add / drop function portion with a different configuration in the configuration shown in FIG. 2, and only the differences from the configuration of FIG. 2 will be described below. The add / drop system in the OXC node shown in FIG. 3 includes a drop-side optical signal terminator 30 and an add-side optical signal terminator 31. The optical output levels of the wavelength division multiplexed optical signals from the input optical fiber transmission lines branched by the K optical couplers 21-1 to 21-K are adjusted by the optical amplifiers 31-1 to 31-K, respectively. The Thereafter, the 1 × L optical couplers (star couplers) 32-1 to 32-K are branched into L wavelength division multiplexed optical signals corresponding to the number of receivers 35-1 to 35-L.

  Therefore, the wavelength multiplexed signal from each input side optical fiber transmission line is connected to each of the fiber selection switches 33-1 to 33-L. The fiber selection switch selects the wavelength division multiplexed optical signal of any one of the K input-side optical fiber transmission lines. The fiber selection switch can be constituted by a switch of K input and 1 output. For example, in FIG. 3, the wavelength division optical signals from all K input side optical fiber transmission lines are given to the fiber selection switch 33-1, but the wavelength division multiplexing of the input side optical fiber transmission line 2-1 is performed. Only the optical signals 1-1, 36, and 37 are selected by the fiber selection switch 33-1. The selected wavelength division multiplexed optical signal 38-1 is given to an optical variable filter (tunable filter) 34-1 and only an optical signal 39-1 having a desired wavelength is selected. Since the optical variable filter selects only a desired wavelength from a wavelength division multiplexed optical signal including a plurality of wavelengths, it is also called a tunable filter (tunable filter).

  FIG. 4 is a diagram illustrating a configuration example of an A input 1 output switch. An A × 1 switch having A input and one output has the ability to extract one signal from A input signals, and can be configured by combining 1 × 2 switches 40 and 41 which are basic elements. The switch shown in FIG. 4A has a tree-type configuration and is characterized in that it can suppress variation in loss between inputs. The switch shown in FIG. 4B has a lattice type configuration, and it is necessary to correct loss variation. The fiber selection switch can be configured by an A × 1 switch.

  As described above, the add / drop system shown in FIG. 3 is characterized in the method of realizing the optical variable filters 34-1 to 34-L described above. The present invention provides an improved optical variable filter as will be described later. Therefore, the details of the optical variable filter will be further described below.

  FIG. 5 is a conceptual diagram illustrating a configuration method of an optical variable filter in a conventional add / drop system. The wavelength selection filter has a function of selecting only an optical signal having a desired wavelength (optical frequency) from a wavelength division multiplexed optical signal of one fiber transmission line selected from a plurality of input side optical fiber transmission lines. Various configurations of the optical variable filter are conceivable. As shown in FIG. 5A, the wavelength division multiplexed optical signal 50 is demultiplexed by wavelength demultiplexer 52 by the demultiplexer 52, and then the demultiplexed optical signal is selected by the selection switch 51. There is a method of obtaining an optical signal 53 having a dropped wavelength. The configuration of (a) is problematic in terms of cost and reliability because the scale of the switch is greater than or equal to the number of wavelength paths.

  In the invention disclosed in Patent Document 2, as shown in FIG. 5B, the problem of the optical variable filter having the configuration of FIG. 5A is solved by cascading multi-stage demultiplexing functions as a variable filter. It is something to try. That is, the first-stage optical variable filter 54 having the first-stage demultiplexing function unit 54-1 and the selection switch 54-2, and the n-th demultiplexing function unit 55-2 and the selection switch 55-2. The nth stage optical variable filter 55 is cascaded in n stages. As an example, taking the case of a two-stage configuration as an example, the first-stage optical variable filter 54 demultiplexes the wavelength division multiplexed optical signal into wavelength groups, and the second-stage optical variable filter 55 1 The wavelength division multiplexed optical signal of one wavelength group can be demultiplexed for each wavelength.

  FIG. 6 is a diagram illustrating a configuration example of a conventional optical variable filter having a two-stage configuration. It is a structural example of the optical variable filter 60 in the optical signal termination | terminus apparatus in the prior art add / drop system disclosed by patent document 2 shown in FIG. The optical variable filter 60 includes a first-stage wavelength group selective light variable filter 54 and a second-stage wavelength selective light variable filter 55. The first-stage wavelength group selection light variable filter 54 includes a 1 × M orbiting arrayed waveguide grating (AWG) 61 and an M × 1 selection switch 62. The second-stage wavelength selective light variable filter 55 includes a 1 × N revolving AWG 63 and an N × 1 selection switch 64. The wavelength division multiplexed optical signal 50 is supplied to the first-stage wavelength group selection optical variable filter 54, and is divided into, for example, a plurality of wavelength groups by the 1 × M orbiting AWG 61, and wavelength division of one wavelength group is performed. Multiplexed optical signal 66 is selected. Further, the wavelength division multiplexed optical signal 66 of a certain wavelength group is demultiplexed into each wavelength by the 1 × N revolving AWG 63, and the optical signal 53 of one wavelength is selected.

  Although details are described in Patent Document 2, M and N have a prime relationship with each other. Further, the FSR of the 1 × M orbiting AWG 61 corresponds to M times the channel interval δf, and the FSR of the 1 × N orbiting AWG 63 only needs to have a relationship corresponding to N times the channel interval δf. The selection switches 62 and 64 can realize a colorless, directionless, and contentless drop function by combining compact switches.

  FIG. 7 is a diagram for explaining the function of the conventional optical variable filter configured as shown in FIG. The fiber selection function 70 corresponds to the fiber selection switch in the add / drop system of FIG. Subsequent to the fiber selection function 70, a first-stage variable optical filter function 75 to an n-th optical variable filter function 77 are provided, and the first-stage variable optical filter function 75 includes wavelength group selection demultiplexing. The function 71 and the wavelength group selection function 72 are provided, and the nth stage optical variable filter function 77 is provided with a wavelength demultiplexing function 73 and a wavelength selection function 74, respectively. The optical variable filter of FIG. 6 is not necessarily limited to the configuration divided into wavelength group demultiplexing selection and wavelength demultiplexing selection, and can be made from many wavelengths regardless of the configuration of the wavelength division multiplexed optical signal. It should be noted that the configuration for selecting wavelengths to be dropped in multiple stages has its characteristics.

JP 2010-34858 A JP 2012-60622 A

  According to the optical variable filter shown in FIG. 6, since the wavelength to be dropped is selected in multiple stages, a device with a small scale optical switch can be used. The number of switches is generally expressed by the following equation. Here, n is the number of stages of the optical variable filter.

  FIG. 8 is a diagram showing the relationship between the switch scale and the number of stages n in the optical variable filter shown in FIG. The switch scale decreases as the number of stages increases regardless of the number of wavelength multiplexing. When the number of stages is three or more, the amount of reduction in the switch size is slightly peaked, and the amount of reduction in the case of the two-stage configuration is remarkable.

  However, considering the recent situation in which network traffic, such as the explosive spread of smartphones, has increased rapidly, the optical variable filter having the configuration disclosed in Patent Document 2 is also large in terms of switch size. Still not enough.

  In addition to the rapid increase in network traffic, wavelength division multiplexing (WDM) technology and the technological progress of each optical device are expected, and in the near future, in one optical fiber transmission line The maximum number of wavelengths handled is expected to exceed 200. If the number of wavelength paths (wavelengths) to be processed by the optical variable filter in the optical end signal end device increases, the number of switches will inevitably increase. Therefore, a new configuration of an optical variable filter that can further reduce the switch scale is desired.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical variable filter that can further reduce the scale of an optical switch in an optical signal termination device of a photonic node. The present invention also provides an optical signal termination device and a photonic node using the optical variable filter.

In order to solve the above-mentioned problem, the invention of claim 1 is an optical path network in which one selected from a plurality of wavelength division multiplexed lights transmitted to a relay node via each of a plurality of optical fibers. In the variable filter that selects an optical signal of a predetermined wavelength path included in the selected wavelength division multiplexed light from the two wavelength division multiplexed lights and drops it to the electrical layer, the selected wavelength division multiplexed light, A first optical switch for selectively inputting to one input port of the plurality of input ports of the first cyclic wavelength multiplexer / demultiplexer having a plurality of input ports and a plurality of output ports; A second optical switch for selecting one output port from among the plurality of output ports of the first cyclic wavelength multiplexer / demultiplexer; and the selected output of the first cyclic wavelength multiplexer / demultiplexer. From the port The plurality of second circulating wavelength multiplexers / demultiplexers having a plurality of input ports and a plurality of output ports, and having a revolving property different from that of the first circulating wavelength multiplexer / demultiplexer. A third optical switch for selectively inputting to one of the plurality of input ports, and one output port from among the plurality of output ports of the second cyclic wavelength multiplexer / demultiplexer. And an optical signal from the output port of the second cyclic wavelength multiplexer / demultiplexer selected by the fourth optical switch is dropped to the electrical layer. This is a variable optical filter. The cyclic wavelength multiplexer / demultiplexer is also called a cyclic wavelength multiplexer / demultiplexer.

  The invention according to claim 2 is the optical variable filter according to claim 1, wherein the first cyclic wavelength multiplexer / demultiplexer has M inputs and M outputs, and has an FSR corresponding to an M channel. An arrayed waveguide grating (AWG), wherein any one of the m input ports of the M inputs is selected by the first optical switch, and m ′ output ports of the M outputs. Is selected by the second optical switch, and the second cyclic wavelength multiplexer / demultiplexer is an AWG configured to have N inputs and N outputs and have an FSR corresponding to an N channel. Any one of the n input ports among the N inputs is selected by the third optical switch, and any one of the n ′ output ports among the N outputs is selected by the fourth optical switch. And M and N are relatively prime. It is selected so that it may become a relationship. M of the first cyclic wavelength multiplexer / demultiplexer is a cycle of a channel number input / output to / from the same port. Further, N of the second cyclic wavelength multiplexer / demultiplexer is a cycle of a channel number input / output to / from the same port.

The invention of claim 3 is the optical variable filter of claim 2, wherein m, m ′, n and n ′ are:
It is selected so as to further satisfy the relationship of M ≦ m × m ′ and N ≦ n × n ′.

Invention of Claim 4 is an optical variable filter in any one of Claim 1 thru | or 3, Comprising: The said 2nd optical switch and the said 3rd optical switch select one from one or more inputs, It is configured as an integral optical switch that outputs to one of one or more outputs.

  A fifth aspect of the present invention is the optical variable filter according to any one of the first to fourth aspects, comprising the first optical switch, the first recursive wavelength multiplexer / demultiplexer, and the second optical switch. In addition to the first-stage variable optical filter function section and the second-stage variable optical filter function section including the third optical switch, the second cyclic wavelength multiplexer / demultiplexer, and the fourth optical switch Further, one or more stages of optical variable filter function units including an optical switch for selecting an input port, a cyclic wavelength multiplexer / demultiplexer, and an optical switch for selecting an output port are further provided.

  A sixth aspect of the present invention is the optical variable filter according to any one of the first to fifth aspects, wherein the wavelength division multiplexed optical signal is composed of a plurality of wavelength groups, and one wavelength group includes a plurality of wavelengths. The one wavelength group is a continuously arranged wavelength group composed of a plurality of wavelengths whose wavelength values are continuously arranged in the order of their lengths. That is, it may be a continuously arranged wavelength group in which a plurality of channels are selected in which the channel numbers are continuously arranged.

  A seventh aspect of the present invention is the optical variable filter according to any one of the first to fifth aspects, wherein the wavelength division multiplexed optical signal includes a plurality of wavelength groups, and one wavelength group includes a plurality of wavelengths. The one wavelength group includes a plurality of wavelengths whose wavelength values are selected at a predetermined interval from a plurality of wavelengths continuously arranged in the order of their lengths and are arranged in a discontinuous order. It is a dispersion arrangement type wavelength group composed of: That is, the dispersion-arranged wavelength group in which channel numbers are selected discontinuously at a predetermined period may be used.

  According to a seventh aspect of the present invention, a plurality of optical branching devices branching wavelength division multiplexed light from each of the plurality of optical fibers, and a plurality of wavelength division multiplexed light respectively branched from the plurality of optical branching devices 8. An optical switch having a plurality of matrix optical switches or a plurality of inputs and one output, wherein one is selected and output to one of a number of optical variable filters corresponding to a predetermined drop rate; And an optical signal termination device for an optical path network.

  As described above, according to the present invention, it is possible to provide an optical variable filter that can further reduce the scale of an optical switch in an optical signal termination device of a photonic node. Since the scale of the optical switch constituting the optical variable filter can be greatly reduced, the configuration of the device can be simplified and the cost can be reduced. By reducing the circuit scale, device reliability can be improved.

FIG. 1 is a diagram conceptually showing the configuration of an OXC system that is a photonic network. FIG. 2 is a diagram for explaining the configuration of a conventional add / drop system using a full-mesh connection optical switch. FIG. 3 is a diagram illustrating the configuration of another conventional add / drop system. FIG. 4 is a diagram illustrating a configuration example of an A input 1 output switch. FIG. 5 is a conceptual diagram illustrating a configuration method of an optical variable filter in a conventional add / drop system. FIG. 6 is a diagram illustrating a configuration example of a conventional optical variable filter having a two-stage configuration. FIG. 7 is a diagram for explaining the function of the conventional optical variable filter shown in FIG. FIG. 8 is a diagram showing the relationship between the switch scale and the number of stages N in the conventional optical variable filter shown in FIG. FIG. 9 is a diagram for explaining a demultiplexing operation having a recursive function in the arrayed waveguide diffraction grating. FIG. 10 is a diagram for explaining the configuration of the optical variable filter of the present invention. FIG. 11 is a diagram showing a specific configuration example of the second optical switch shown in FIG. 10 in the optical variable filter of the present invention. FIG. 12 is a diagram for explaining the function of the optical signal terminator including the function of the optical variable filter of the present invention. FIG. 13 is a diagram for explaining the operation of the optical variable filter according to the first embodiment of the present invention (when the input port 4 of the first circulating AWG is selected). FIG. 14 is a diagram for explaining the operation of the optical variable filter according to the first embodiment of the present invention (when the input port 5 of the first circulating AWG is selected). FIG. 15 is a diagram for explaining the operation of the optical variable filter according to the first embodiment of the present invention (when the input port 6 of the first circulating AWG is selected). FIG. 16 is a table showing configuration examples of various other optical variable filters in the case of a two-stage configuration. FIG. 17 is a diagram showing the reduction effect of the optical switch scale by the optical variable filter of the present invention in comparison with the prior art. FIG. 18 is a diagram showing a table showing the reduction rate of the number of switches by the optical variable filter of the present invention on the basis of the configuration of the prior art.

  The present invention relates to an optical signal termination unit of an optical cross-connect device in an optical path network that performs signal path setting and switching processing while maintaining an optical signal. The optical signal termination unit includes a wavelength division multiplexed light from one wavelength division multiplexed light selected from a plurality of wavelength division multiplexed lights respectively transmitted in parallel to a relay node through a plurality of optical fibers. Are provided with a plurality of optical variable filters that select and drop optical signals of a predetermined wavelength path included in the electrical layer. The characteristic variable optical filter of the present invention can be realized by using a smaller-scale optical switch as compared with the prior art.

  The inventors have made use of the wavelength selection function by the input port of the recursive wavelength multiplexer / demultiplexer, which has not been paid attention to in the prior art optical variable filter, making the optical wavelength variable filter more compact, low cost and highly reliable. I found that it can be composed of sex devices. Determine the FSR setting of the recursive wavelength multiplexer / demultiplexer and the actual input and output ports to be used, determine the number of wavelengths to be demultiplexed under specific conditions, and output each wavelength without overlapping the same port To do. With this configuration, the scale of the optical switch is reduced. The configuration of the present invention will be described below while comparing with the configuration of the prior art.

  The wavelength division multiplexed optical signal handled by the optical tunable filter or the optical signal termination unit of the present invention is obtained by multiplexing optical signals having a plurality of different wavelengths, and the wavelength division multiplexed optical signal includes various configurations. . For example, the wavelength division multiplexed optical signal may be configured from a plurality of wavelength groups, and one wavelength group may include a plurality of wavelengths. In an optical communication system, a wavelength value or a corresponding optical frequency is associated with a channel number.

A wavelength included in one wavelength group can be composed of a plurality of wavelengths whose wavelength values are continuously arranged in the order of their length (continuous arrangement type wavelength group). For example, the wavelength (number), lambda _1, lambda _2, as in the · · lambda _8, can constitute one wavelength group in the eight that are arranged continuous wavelength (continuous even channel numbers). Moreover, it is also possible to configure from a plurality of wavelengths selected in a predetermined channel number interval and arranged in a discontinuous order instead of being continuous in order of wavelength length (dispersed arrangement type wavelength group). For example, the wavelength (number), lambda _1, lambda _5, as in the lambda ₉ · · lambda _29, constituting a wavelength group of eight wavelengths arranged in a discontinuous (discretely) at a predetermined distance You can also. The number of wavelength groups, the number of wavelengths constituting one wavelength group, the predetermined channel number interval described above, and the like can be various. The channel interval is configured with equal wavelength intervals or equal optical frequency intervals depending on the system.

  In the conventional optical variable filter, a cyclic wavelength multiplexer / demultiplexer is used. As a typical example, an arrayed waveguide diffraction grating (AWG) can be used. In the AWG, the wavelength multiplexed signal input to the input port is demultiplexed, and the demultiplexed optical signal is output to each output port. By configuring the AWG by appropriately setting the FSR (Free Spectral Range), the wavelength appearing at the output port becomes cyclic, that is, has recursive properties. Since the feature of the present invention that can greatly reduce the scale of the optical switch is obtained by using a wavelength multiplexer / demultiplexer having a recursive property, the wavelength multiplexer / demultiplexer is not limited to the AWG, In an embodiment described later, an example using a circular AWG will be described.

FIG. 9 is a diagram for explaining a demultiplexing operation having a recursive function in the arrayed waveguide diffraction grating. The AWG 90 has eight input ports and eight output ports. By appropriately configuring the structural parameters of the slab waveguide and the arrayed waveguide included in the AWG, the FSR can be adjusted to a wavelength bandwidth corresponding to eight wavelength channels. For example, when a wavelength division multiplexed optical signal including wavelengths λ ₁ to λ ₁₆ is input to the first port of the input ports 91, as shown by the wavelength group 93, the first to eighth output ports 92 are output. Optical signals of wavelengths λ ₁ to λ ₁₆ are output to the port. At this time, optical signals having wavelengths of λ ₁ and λ ₉ are output to the _first output port. In other words, the first output port outputs an optical signal having a wavelength of a number with a remainder of 1 when the wavelength number is divided by 8.

Here, when a wavelength division multiplexed optical signal including wavelengths λ ₁ to λ ₁₆ is input to the second port of the input ports 91, each wavelength is output as indicated by the wavelength group 94. Compared with the wavelength indicated by the wavelength group 93, the optical signals having the same wavelength number are shifted one by one to the adjacent output ports. Similarly, when a wavelength division multiplexed optical signal including wavelengths λ ₁ to λ ₁₆ is input to the third port of the input ports 91, each wavelength is output this time as indicated by the wavelength group 95. Compared with the wavelength indicated by the wavelength group 93, the optical signals having the same wavelength number are further shifted one by one to the adjacent output ports. That is, it can be seen that if the position of the port to which the wavelength division multiplexed optical signal is input is shifted by one, the position of the output port of the optical signal having a certain wavelength is also shifted by one. Therefore, the wavelength of the optical signal appearing at the same output port can be changed by selecting the input port for inputting the wavelength division multiplexed optical signal. The inventors focused on utilizing this wavelength selection function by selecting an input port.

  FIG. 10 is a diagram illustrating the configuration of the optical variable filter of the present invention. The variable optical filter 100 of the present invention corresponds to the conventional variable optical filter shown in FIG. Therefore, the optical variable filter 100 replaces the optical variable filters 34-1 to 34-L in the drop system 30 in the photonic node shown in FIG. A wavelength division multiplexed optical signal 50 is input to the optical variable filter 100 from one input-side optical fiber transmission line selected from a plurality of optical fibers. An optical signal having a desired wavelength is selected by the optical variable filter 100, and a dropped optical signal 53 is obtained and passed to one of the receivers 35-1 to 35-L.

  The optical variable filter 100 includes a first optical switch 101 having 1 input m output (1 × m), a first circulating AWG 102 having M input M output, and a second light having m ′ input n output. A switch 103, a second circular AWG 104 having N inputs and N outputs, and a third optical switch 105 having n ′ inputs and 1 output (n ′ × 1) are provided. The wavelength division multiplexed optical signal 50 is input to the input port 106 of the first optical switch 101, and the optical signal 53 of the dropped wavelength is obtained from the output port 107 of the third optical switch 105. In the optical signal termination device of the photonic node, the optical variable filter 100 is provided for each of the plurality of optical receivers.

  The 1 × m first optical switch 101 has a function of switching an input wavelength division multiplexed optical signal to one of m output ports. The output ports of the first optical switch 101 are respectively connected to any m of the M input ports of the first circular AWG. Therefore, a relationship of at least m ≦ M is established. The first optical switch 101 has a function of selecting any one of the input ports of the first circulating AWG 102. That is, it has an input port selection function of the first circulatory AWG 102.

  The first circulating AWG 102 receives the wavelength division multiplexed optical signal as input to any one of the selected input ports, and demultiplexes and outputs the optical signal for each wavelength (group) at the output port. The first revolving AWG 102 has M inputs and M outputs, and its demultiplexing characteristics are cyclic and have recurring properties. Therefore, the first revolving AWG 102 is called a recurring wavelength multiplexer / demultiplexer or a cyclic wavelength multiplexer / demultiplexer. M is the cycle of the channel number input / output to / from the same port. Focusing on one output port, a plurality of optical signals having different wavelength numbers for each M channel are output.

  Here, it should be noted that only a part of the demultiplexing function of the first AWG 102 is used. In the optical variable filter of the present invention, only M input ports and m ′ output ports are used among the M input ports and M output ports, respectively. Accordingly, the first circulatory AWG 102 is configured with slab waveguides and arrayed waveguides as constituent elements so as to have M-input M-output multiplexing / demultiplexing characteristics as wavelength multiplexers / demultiplexers. However, it should be noted that the input / output port wirings as a device need only include a part of m input ports and m ′ output ports.

Further, m and m ′ have the following relationship with respect to M.
M ≦ m × m ′ Formula (2)

As will be described in detail in an embodiment to be described later, according to m input ports of the first cyclic AWG selected by the first optical switch 101, m ′ output ports of the first cyclic AWG are output. The wavelength of the optical signal that appears in each is determined. Therefore, m × m ′ different wavelength groups (or wavelengths) can be selected. The first circulating AWG 102 has FSR ₁ represented by the following equation when the channel interval is δf (Hz).
FSR ₁ = M × δf Formula (3)

  Since the first circulating AWG 102 outputs optical signals having different wavelengths cyclically (cyclically) for each M channel to the same output port, the wavelength group (or the wavelength without overlapping) if Expression (2) is satisfied. ) Can be demultiplexed.

  The second optical switch 103 has a function of selecting one of m ′ outputs of the first cyclic AWG 102 and selecting n input ports of the subsequent second cyclic AWG 104. Have. That is, the second optical switch 103 is formed by cascading (m ′ × 1) switch function portions and (1 × n) switch function portions.

  FIG. 11 is a diagram showing a specific configuration example of the second optical switch 103 in the optical variable filter of the present invention. (A) shows a first configuration example, and (b) shows a second configuration example. In the first configuration example (a), the optical switch 103 includes a front-stage A input 1-output optical switch 110 on the left side of FIG. 11 and a rear-stage 1-input B-output optical switch 111 on the right side of FIG. It is connected. FIG. 11 shows an example in which A = 8 and B = 9. Any optical switch can be configured by combining 1 × 2 switch 112 which is an element element.

  An input optical signal to any one of the A input ports of the optical switch 110 is selected. Next, the selected input optical signal is connected to the input port of the optical switch 111 at the subsequent stage. Further, it is connected to one of the B output ports of the optical switch 111. After all, the optical switch 103 is a switch that selects only one input from the A input and outputs it to any one of the B outputs. Such an optical switch is not limited to the configuration shown in FIG. 11, and can be realized by any other method. As shown in FIG. 11, although the optical switch 103 is depicted as if it were composed of two switches 110 and 111, the optical switch 103 can be configured as an integrated optical switch device.

  As another configuration example, as shown in FIG. 11B, a 2 × 2 switch 113 may be used at the center. That is, in the configuration of (a), the output switch of the front switch 110 and the input switch of the rear switch 111 can be realized by one 2 × 2 switch 113. Needless to say, the second optical switch 103 can be realized by various methods other than the configurations of (a) and (b).

  Returning to FIG. 10 again, the second optical switch 103 selects any one of the m ′ output ports of the first circulatory AWG, and the subsequent second lap. It is input to one of n input ports of the sex AWG 104.

  The second circulating AWG 104 receives the wavelength division multiplexed optical signal as input to any one of the selected input ports, and demultiplexes and outputs the optical signal for each wavelength at the output port. The second circulating AWG 104 has N inputs and N outputs, and has a circulating property in its demultiplexing characteristics. N is the cycle of the channel number input / output to / from the same port. Therefore, if attention is paid to one output port, a plurality of optical signals having different channel (wavelength) numbers for each N channel can be output. Here, it should be noted that only a part of the demultiplexing function of the second circulating AWG 104 is used in the same manner as the first circulating AWG 102. That is, of the N input ports and N output ports, only n input ports and n ′ output ports are used. Therefore, in the second revolving AWG 104, a slab waveguide, an array waveguide, and the like, which are constituent elements, are set so as to have N input N output multiplexing / demultiplexing characteristics as a wavelength multiplexer / demultiplexer. However, it should be noted that the input / output port wirings as a device need only include a part of n input ports and n ′ output ports.

Further, n and n ′ have the following relationship with N.
N ≦ n × n ′ Formula (4)

As will be described in detail in an embodiment to be described later, according to n input ports selected by the second optical switch 103 in the second circular AWG 104, n ′ output ports of the second circular AWG 104 The wavelength that appears in each is determined. Therefore, the channel number (wavelength) number can be uniquely selected by the second revolving AWG 104 according to n × n ′ different combinations. The second revolving AWG 104 has FSR ₂ represented by the following expression when the channel interval is δf (Hz).
FSR ₂ = N × δf Formula (5)

  Since the second circulating AWG 104 outputs optical signals having different wavelengths cyclically (cyclically) every N channels to the same output port, if the equation (4) is satisfied, the optical signal is output for each wavelength without overlapping. Can be demultiplexed. Here, it is necessary that M of the first circular AWG 102 and N of the second circular AWG 104 have a prime relationship.

  The n ′ output ports of the second circular AWG 104 are selected by the third optical switch 105, one of which has n ′ input and 1 output. An optical signal 53 having a specific wavelength to be dropped is output from the output port 107 of the third optical switch 105. As described above, the optical variable filter 100 as a whole has the first-stage optical variable filter function of the first circulatory AWG 102 and the second-stage optical variable filter function of the second circulatory AWG 104. In this respect, it is similar to the configuration of the conventional optical variable filter shown in FIG. However, the first optical switch for selecting the input port of the first circulatory AWG 102 and the second optical switch for selecting the input port of the second circulatory AWG 104, which are not in the configuration shown in FIG. In that it is different.

  The configuration shown in FIG. 10 shows an example in which the configuration is configured in two stages. Here, the optical switch 103 in FIG. 10 is divided into two as shown in FIG. That is, the optical variable filter 100 includes a first optical variable filter function unit including the first optical switch 101, the first circulating AWG 102, and the second optical switch 110 (FIG. 11), and the third optical signal. The second stage optical variable filter function unit including the switch 111 (FIG. 11), the second circulating AWG 104, and the fourth optical switch 105 is configured. However, in addition to the two-stage configuration shown in FIG. 10, there is further provided one or more stages of another optical variable filter function unit including an optical switch for selecting an input port, a circular AWG, and an optical switch for selecting an output port. Needless to say.

  FIG. 12 is a diagram illustrating the function of the optical signal termination unit (optical signal termination device) including the function of the optical variable filter of the present invention. (A) explains the function of the optical variable filter of the present invention, and (b) explains the function of the conventional optical variable filter in comparison. In the optical signal termination unit of the present invention, as in the prior art, fiber selection switches 33-1 to 33-L (see FIG. 3) select one fiber from a plurality of input side optical fiber transmission lines (steps). 120) is executed. Further, in the optical tunable filter of the present invention shown in FIG. 10, the first optical switch 101 performs input port selection of the first circular AWG 101 (step 121). Thereafter, wavelength group demultiplexing or wavelength demultiplexing is performed by the first circular AWG 101 (step 122). Further, the output port selection of the first circulatory AWG is performed by the optical switch portion 110 (see FIG. 11) in the previous stage of the second optical switch 103 (step 123). Further, the input port selection of the second circulatory AWG is executed by the optical switch portion 111 subsequent to the second optical switch 103 (step 124). Next, wavelength demultiplexing is performed by the second circulating AWG 104 (step 124). Finally, the output port selection of the second circular AWG is performed by the third optical switch 105 (step 126).

  FIG. 12B shows the function of the conventional optical variable filter in comparison with FIG. The function of the conventional optical variable filter in FIG. 12B corresponds to the function shown in the conceptual diagram in FIG. Also, by comparing (a) and (b) of FIG. 12, the optical variable filter of the present invention can select the input port selection function 121 of the first circular AWG and the input port selection of the second circular AWG. It can be seen that there is a novel feature in that the function 124 is provided. In the optical variable filter of the present invention, by selecting an AWG input port having recurring properties, the demultiplexing function of the AWG can be used efficiently, and the FSR setting of the recurring AWG (setting of M and N) The input port and the output port to be used are selected, and the configuration in which the output wavelengths do not overlap is selected. The scale of the optical switch is further reduced as compared with the prior art by using the input port selection function 121 of the first cyclic AWG and the input port selection function 124 of the second cyclic AWG. Next, the operation of the optical variable filter of the present invention will be described in more detail with specific examples.

  13 to 15 are diagrams for explaining the operation of the optical variable filter according to the first embodiment of the present invention. FIG. 13 illustrates the wavelength selection operation of the optical tunable filter when “input port 4” of the first circular AWG is selected. Similarly, FIG. 14 shows the wavelength selection operation when “input port 5” of the first cyclic AWG is selected, and FIG. 15 shows the wavelength selection operation when “input port 6” of the first cyclic AWG is selected. Respectively. In the present embodiment, as an example, a wavelength division multiplexed optical signal including 96 channels is assumed.

In this embodiment, the first optical switch 101 is a selection switch having one input and three output ports. The wavelength division multiplexed optical signal 50 is connected to one of the input port 4, the input port 5, and the input port 6 of the first circulating AWG 102 by the first optical switch 101. The first AWG 102 has 9 inputs and 9 outputs (M = 9) and has FSR ₁ corresponding to a bandwidth (Hz) for 9 channels. Therefore, nine optical signals of different wavelengths are sequentially output to the nine output ports of the first circular AWG 102, and optical signals having the same channel number (wavelength number) when divided by 9 are used. Will appear at the same output port.

  In the present embodiment, the second, fifth and eighth output ports are used among the nine output ports. As shown in FIG. 13, when “input port 4” of the first cyclic AWG 102 is selected, channel numbers (wavelength numbers) of 1, 10, 19,. Eleven optical signal groups 130-1 are output. That is, from the second output port, an optical signal group 130-1 having a channel number with a remainder of 1 divided by 9 out of signals having channel numbers 1 to 96 is output. Similarly, from the fifth output port, there are 11 optical signal groups 130-having channel numbers (wavelength numbers) of 4, 13, 22,... 94, that is, channel numbers having a remainder of 4 divided by 9. 4 is output. Similarly, the tenth optical signal group 130 having channel numbers (wavelength numbers) of 7, 16, 25... 88 from the eighth output port, that is, a channel number of which the remainder divided by 9 is 7. -7 is output.

  Here, as shown in FIG. 14, when the “input port 5” of the first circulating AWG 102 is selected, the second, fifth and eighth output ports are shown in FIG. Note that an optical signal with a different wavelength number is output. That is, from the second output port, there are 11 optical signal groups 130-having channel numbers (wavelength numbers) of 2, 11, 20,... 92, that is, channel numbers of which the remainder divided by 9 is 2. 2 is output. From the fifth output port, there are 11 optical signal groups 130-5 having channel numbers (wavelength numbers) of 5, 14, 23... 95, that is, channel numbers having a remainder of 5 divided by 9. Is output. From the eighth output port, there are ten optical signal groups 130-8 having channel numbers (wavelength numbers) of 8, 17, 26... 89, that is, channel numbers whose remainder is 8 divided by 9. Is output.

  Further, as shown in FIG. 15, when “input port 6” of the first circulating AWG 102 is selected, the second, fifth and eighth output ports are shown in FIG. 13 and FIG. An optical signal with a wavelength number different from that of the output is output. That is, from the second output port, there are 11 optical signal groups 130-having channel numbers (wavelength numbers) of 3, 12, 21... 93, that is, channel numbers of which the remainder divided by 9 is 3. 3 is output. From the fifth output port, there are 11 optical signal groups 130-6 having channel numbers (wavelength numbers) of 6, 15, 24... 96, that is, channel numbers having a remainder of 6 divided by 9. Is output. From the eighth output port, there are ten optical signal groups 130-9 having channel numbers (wavelength numbers) of 9, 18, 27... 90, that is, channel numbers whose remainders divided by 9 are 0. Is output.

  Wavelength division multiplexed light including 96 optical signals having channel numbers 1 to 96 by the above-described selection / demultiplexing operation by the first optical switch 101 and the first circular AWG 102 shown in FIGS. The signal 50 selects one of the m = 3 (ports) input ports of the first circulatory AWG 102, so that one of the m ′ = 3 (ports) output ports of the first circulatory AWG 102 is selected. It can be seen that the wavelength group is demultiplexed and output.

One of the optical signals demultiplexed to one of the output ports of m ′ = 3 (pieces) by the first circular AWG 102 is further selected by the second optical switch 103, and the second circular AWG 104 n = 4 (number) of input ports. The second circulating AWG 103 has 11 inputs and 11 outputs (N = 11), and has FSR ₂ corresponding to a bandwidth (Hz) for 11 channels. Therefore, 11 output signals of 11 different wavelengths are sequentially output to the 11 output ports of the second circular AWG 104, and the remainder when divided by 11 is input from the same input port. However, optical signals having the same channel number (wavelength number) may appear at the same output port. Here, the number of ports (number of channels equivalent to FSR ₁ ) M = 9 in the first recursive AWG 102 and the number of ports (number of channels equivalent to FSR ₂ ) N = 11 in the _second recursive AWG 105 are relatively prime. Are in a relationship. Hereinafter, the operation of the second optical switch and the second circular AWG will be further described.

  Referring again to FIG. 13, the optical signal groups from the three output ports of the first circulatory AWG 102 are input to the input port 4, the input port 5, and the input port of the second circulatory AWG 104 by the third optical switch 103. 6 and input port 7 are connected. The second AWG 104 demultiplexes the input optical signal to a different output port according to the selected input port and outputs the demultiplexed optical signal. Here, attention is focused on the optical signal group 130-1 from the second output port of the first circulating AWG 102 in FIG. 13. The optical signal group 130-1 is connected to any one of the input port 4, the input port 5, the input port 6, and the input port 7 of the second circulating AWG 104 by the selection function of the second optical switch 103. The

  In FIG. 13, optical signals from different output ports of the first circulating AWG 102 are distinguished by the channel number character font. The channel number of the optical signal output from the second output port is a normal typeface, the channel number of the optical signal output from the fifth output port is a gray typeface, and further output from the eighth output port. The channel number of the optical signal is shown in a white font.

  Further, the correspondence between the input port selected by the second AWG 104 and the channel number of the optical signal demultiplexed and output from the output port at the time of the input port is distinguished by the type such as hatching. That is, the optical signal input to the “input port 4” of the second revolving AWG 104 is output as an optical signal having a channel number described in the belt labeled a. In addition, the optical signal input to the “input port 5” of the second circulating AWG 104 is output as an optical signal having a channel number described in the belt labeled b. Similarly, the optical signal input to the “input port 6” of the second circulating AWG 104 is output as an optical signal of the channel number indicated in the belt labeled “c”, and “input port 7”. It is shown that the optical signal input to is output as an optical signal of the channel number described in the belt labeled d.

  More specifically, the selection / demultiplexing operation of the second optical switch 103 and the second circular AWG 104 will be described as follows. Focusing on the optical signal group 130-1 from the second output port of the first circulatory AWG 102 shown in FIG. 13, when the “input port 4” of the second circulatory AWG 104 is selected, the channel number 1 Is output from the output port 2 (belt a). At the same time, the optical signal of channel number 82 is output from the output port 6 (belt a), and the optical signal of channel number 64 is output from the output port 10 (belt a).

  Next, focusing on channel numbers 10, 28, and 46 in the optical signal group 130-1, when "input port 5" is selected, the optical signal of channel number 46 is output from the output port 2. (Belt b). At the same time, the optical signal of channel number 28 is output from the output port 6 (belt b), and the optical signal of channel number 10 is output from the output port 10 (belt b).

  Furthermore, focusing on channel numbers 55, 73, and 91 in the optical signal group 130-1, when "input port 6" is selected, the optical signal of channel number 91 is output from the output port 2 ( Belt c). At the same time, the optical signal of channel number 73 is output from the output port 6 (belt c), and the optical signal of channel number 55 is output from the output port 10 (belt c).

  Focusing on channel numbers 1, 19, and 37 in the optical signal group 130-1, when "input port 7" is selected, the optical signal of channel number 37 is output from the output port 2 ( Belt d). At the same time, the optical signal of channel number 19 is output from the output port 6 (belt d), and the optical signal of channel number 1 is output from the output port 10 (belt d).

  When one of the n = 4 (ports) input ports of the second cyclic AWG 104 is selected from the above selection / demultiplexing operation, n ′ = 3 (ports) of the second cyclic AWG 104 is output. It can be seen from the port that optical signals with different channel numbers appear one by one. Further, when another input port is selected, optical signals of three different channel numbers corresponding to the selected input port appear one by one. Eventually, it can be seen that one combination of the input port and the output port of the second recursive AWG 104 and the channel number of the optical signal to be demultiplexed operate in a one-to-one relationship. That is, if one combination (n × n ′) of the input port (n = 4) and the output port (n ′ = 3) of the second circulating AWG 104 is determined, the light obtained from the output port of the combination The channel number of the signal is uniquely determined. Finally, the desired optical signal 53 to be dropped is obtained by selecting one of the n ′ output ports of the second cyclic AWG 104 by the third optical switch 105.

  The operation of the optical signal group 130-1 from the second output port described above is performed by the optical signal group 130-4 from the fifth output port of the first circulating AWG 102 shown in FIG. It can be confirmed that the same applies to the optical signal group 130-7 from the output port. Therefore, (1) the second optical switch 103 selects one output port from the m ′ output ports of the first circulating AWG 102, and (2) the second optical switch 103 selects the second output port. One input port is selected from n input ports of the cyclic AWG 104 of the second cyclic AWG 104, and (3) one of the n ′ output ports of the second cyclic AWG 104 is selected by the third optical switch 105. One output port is selected, and an optical signal having one channel number is selected from 32 of the three optical signal groups 130-1, 130-4, and 130-7.

  Similarly, in the case of FIG. 14 in which “input port 5” is selected by the first optical switch 101 by the above-described three selection operations (1), (2), and (3), three optical signal groups are used. The optical signal of one channel number out of 32 of 130-2, 130-5, and 130-8 is selected. Further, in the case of FIG. 15 in which “input port 6” is selected by the first optical switch 101, similarly, one of 32 of the three optical signal groups 130-3, 130-6, and 130-9. An optical signal with one channel number is selected. After all, as a result of the combination of the input port selection operation by the optical switch 101 and the four selection operations related to the input / output ports of the two circular AWGs 102 and 104, the wavelength division multiplexed optical signal 50 consisting of 96 channels has nine optical signal groups. Through 130-1 to 130-9, the optical signal 53 having only one channel number is uniquely selected as the optical signal to be dropped.

  As described above in detail, in the configuration of the optical tunable filter according to the first embodiment, the 9 × 9 port first AWG and the 11 × 11 port second AWG are obtained from the wavelength division multiplexed optical signal including 96 channels. An optical signal having an arbitrary channel (wavelength) number can be dropped by using the revolving AWG and three types of optical switches. With the configuration of this embodiment, the scale of the optical switch of the optical variable filter can be greatly reduced as compared with the configuration of the prior art. Details will be described later.

  In the optical variable filter of the first embodiment, the case where the number of wavelengths included in the wavelength division multiplexed optical signal is 96 is shown, but it goes without saying that the optical variable filter can be configured using various other numbers of wavelengths and AWG configurations. Further, the present invention is not limited to the configuration using the two-stage circulating AWG as shown in the first embodiment, and may be configured to have three or more stages of circulating AWG (optical variable filter section) as shown in FIG. The effect of reducing the switch scale is recognized.

FIG. 16 is a table showing configuration examples of various other optical variable filters in the case of a two-stage configuration as the second embodiment. M is the number of input ports or output ports of the first cyclic AWG, and N is the number of input ports or output ports of the second cyclic AWG. m is the number of input ports actually used as an optical variable filter in the first circulatory AWG, and m ′ is the number of output ports used in the first circulatory AWG. Further, n is the number of input ports used as an optical variable filter in the second circular AWG, and n ′ is the number of output ports used as an optical variable filter in the second circular AWG. There is a prime relationship between M and N. Further, as described above, the following relationship is established between m, m ′, n, and n ′ and M and N.
M ≦ m × m ′ Formula (2)
N ≦ n × n ′ Formula (4)

  In general, when an optical switch having a very large number of branches is multistaged, the values of the branches after the multistage are selected to be close integers in order to minimize the switch scale. For example, a 100 × 1 selection switch can be made smaller by using two 10 × 1 switches than combining a 1 × 2 switch and a 50 × 1 switch. Therefore, as shown in the table of FIG. 16, M and N are prime and close values are selected.

  FIG. 17 is a diagram showing the reduction effect of the optical switch scale by the optical variable filter of the present invention in comparison with the prior art. It is the figure which showed the scale of the optical switch in the case of the Example of each wavelength number shown in FIG. 16 compared with the case of the structure of a corresponding prior art. The scale of the optical switch can be grasped, for example, by the number of 1 × 2 switches that are the minimum element switch elements constituting the optical switch shown in FIG. The vertical axis represents the total number of 1 × 2 switch points of the first optical switch 101, the second optical switch 103, and the third optical switch 105, which is necessary in the case of the present invention in the case of the two-stage configuration. Yes.

  FIG. 18 is a diagram showing a table showing the reduction rate of the number of switches by the optical variable filter of the present invention on the basis of the configuration of the prior art. It can be seen that the reduction rate increases as the number of wavelength paths of the wavelength division multiplexed optical signal increases. In particular, when the number of wavelength paths is 240, the number of switches is reduced by 59% compared to the conventional optical variable filter, and the scale of the switch can be halved. Therefore, the configuration of the optical variable filter of the present invention can reduce the number of element switches as the number of wavelength paths increases. In the near future, it is predicted that the maximum number of wavelengths handled in one optical fiber transmission line will exceed 200, and the present invention will most effectively cope with the future explosive traffic increase. can do.

  Needless to say, the optical variable filter of the present invention can be configured as a drop-side optical signal terminator by combining a fiber selection switch and a receiver as shown in FIG. In addition, since the configuration of the optical switch can be simplified, the present invention exhibits excellent effects in terms of downsizing, simplification, and high reliability regardless of the configuration of the optical switch. Even when realized by a planar optical circuit (PLC), it can greatly contribute to miniaturization of the device.

  As described above in detail, according to the present invention, it is possible to provide an optical variable filter capable of further reducing the scale of an optical switch in an optical signal termination device of a photonic node. Since the number of element switch elements constituting the optical variable filter can be reduced and the scale of the optical switch can be greatly reduced, the configuration of the device can be simplified and the cost can be reduced. By reducing the circuit scale, device reliability can be improved.

  The present invention can be used in an optical communication system. In particular, the present invention can be used for a variable filter and an optical signal terminator for extracting or adding an optical signal having a specific wavelength from a wavelength division multiplexed optical signal.

1-1 to 1-J, 36, 37, 50 Wavelength division multiplexed optical signal 2-1 to 2-K input side optical fiber transmission line 3 optical cross-connect unit 4-1 to 4-K output side optical fiber transmission line 5 -1 to 5-J Output wavelength division multiplexed optical signal 6-1 and 30 drop system 6-2 and 31 add system 7 electrical layer network 8, 24-1 to 24-L, 35-1 to 35-L receiver 9 , 25-1 to 25-L Transmitters 21-1 to 21-K, 27-1 to 27-K Optical couplers 23 and 28 Full matrix switch 33-1 to 33-L Fiber selection switch 34-1 to 34-L , 60, 100 Optical variable filters 39-1 to 39-L, 53 Dropped optical signals 62, 64, 101, 103, 105 Optical switches 61, 63, 102, 104 Circumferential wavelength multiplexer / demultiplexer (AWG)

Claims (8)

In an optical path network, from one wavelength division multiplexed light selected from among a plurality of wavelength division multiplexed lights transmitted to a relay node via each of a plurality of optical fibers, the selected wavelength division multiplexed light is transmitted. In a variable filter that selects an optical signal of a predetermined wavelength path included therein and drops it to the electrical layer,
The selected wavelength division multiplexed light is selectively input to one input port of the plurality of input ports of the first cyclic wavelength multiplexer / demultiplexer having a plurality of input ports and a plurality of output ports. A first optical switch for
A second optical switch for selecting one output port from among the plurality of output ports of the first circulating wavelength multiplexer / demultiplexer;
Demultiplexed output light from the selected output port of the first circulating wavelength multiplexer / demultiplexer has a plurality of input ports and a plurality of output ports, and the first circulating wavelength multiplexer / demultiplexer A third optical switch for selectively inputting to one input port of the plurality of input ports of the second cyclic wavelength multiplexer / demultiplexer having a different cyclicity from
A fourth optical switch for selecting one output port from among the plurality of output ports of the second cyclic wavelength multiplexer / demultiplexer ;
An optical variable filter , wherein an optical signal selected from the output port of the second cyclic wavelength multiplexer / demultiplexer selected by the fourth optical switch is dropped to an electrical layer . The first cyclic wavelength multiplexer / demultiplexer is an arrayed waveguide grating (AWG) having an M input and an M output and having an FSR corresponding to an M channel. Are selected by the first optical switch, and m ′ output ports of the M outputs are selected by the second optical switch,
The second cyclic wavelength multiplexer / demultiplexer is an AWG that has N inputs and N outputs and is configured to have an FSR corresponding to an N channel, and any one of the n input ports of the N inputs. Is selected by the third optical switch, and any of n ′ output ports of the N outputs is selected by the fourth optical switch,
The optical variable filter according to claim 1, wherein the M and the N are selected so as to have a prime relationship with each other. m, m ′, n and n ′ are
The optical variable filter according to claim 2, wherein the optical variable filter is selected so as to further satisfy a relationship of M ≦ m × m ′ and N ≦ n × n ′. The second optical switch and the third optical switch are configured as an integrated optical switch that selects one of one or more inputs and outputs to one of the one or more outputs. The optical variable filter according to claim 1, wherein the optical variable filter is characterized in that: A first-stage variable optical filter function unit including the first optical switch, the first recursive wavelength multiplexer / demultiplexer, and the second optical switch; and the third optical switch, the second optical switch, In addition to the second-stage optical variable filter function unit including the recursive wavelength multiplexer / demultiplexer and the fourth optical switch,
2. The optical switch according to claim 1, further comprising at least one optical variable filter function unit including an optical switch for selecting an input port, a cyclic wavelength multiplexer / demultiplexer, and an optical switch for selecting an output port. 4. The optical variable filter according to any one of 4 above.   The wavelength division multiplexed optical signal is composed of a plurality of wavelength groups, one wavelength group is configured to include a plurality of wavelengths, and the wavelength values of the one wavelength group are continuous in the order of their lengths. 6. The optically variable filter according to claim 1, wherein the optically variable filter is a continuously arranged wavelength group composed of a plurality of wavelengths arranged in a continuous manner.   The wavelength division multiplexed optical signal is composed of a plurality of wavelength groups, one wavelength group is configured to include a plurality of wavelengths, and the wavelength values of the one wavelength group are continuous in the order of their lengths. 6. A dispersion arrangement type wavelength group consisting of a plurality of wavelengths arranged in a discontinuous order selected from a plurality of wavelengths arranged in a discontinuous manner. A variable optical filter according to claim 1. A plurality of optical branching devices for branching wavelength division multiplexed light from each of the plurality of optical fibers;
A plurality of matrices for selecting one of a plurality of wavelength division multiplexed lights respectively branched from the plurality of optical branching devices and outputting to one of a number of optical variable filters corresponding to a predetermined drop rate An optical switch or an optical switch having multiple inputs and one output;
An optical signal termination device for an optical path network, comprising: the optical variable filter according to claim 1.

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