JP2015158645A - optical variable filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that network traffic rapidly increases, technological development of optical devices is expected, it is predicted even that the number of wavelengths included in wavelength division multiplex light in one optical fiber transmission line may exceed 200 at a maximum in near future, a novel configuration of an optical variable filter capable of further reducing switch scale by suppressing the number of element optical switches is being expected and in an optical variable filter of the prior arts utilizing a plurality of stages of cyclic AWG, transmission loss increase becomes a new problem.SOLUTION: In an optical variable filter of the present invention, only one stage of non-cyclic AWG is used. Therefore, in comparison with a multi-stage optical variable filter of the prior arts using a plurality of cyclic AWGs, a transmission loss becomes an extremely small value equal to or less than a half. Thus, the optical variable filter suppresses increase of the transmission loss equal to or less than a half while maintaining switch scale reduction effects substantially equal to the prior arts by utilizing a transmission loss property that the non-cyclic AWG itself has, at a maximum.

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 terminator for extracting or adding an optical signal having a specific wavelength from a wavelength division multiplexed optical signal.

  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. With this configuration, it is 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 an optical component (apparatus) used in a node having 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. Is. The following description will be made based on the OXC system for the sake of convenience, but it goes without saying that the present invention can also be applied to the 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 an OXC system as shown in FIG. 1, ideal add / drop systems are 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.

  Furthermore, as a matter of course, if two or more different optical signals having the same wavelength are simultaneously present in the same optical path of the optical fiber transmission line, the optical signals collide with each other, causing interference. End up. 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. It is necessary to perform connection setting of the optical path related to the add / drop operation without contention so as not to cause blocking. The add / drop system needs to have a configuration in which such optical signals do not collide with each other.

  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 in FIG. 2 is a more specific example of the add / drop function portion in the schematic configuration of the OXC system shown in FIG. Therefore, only differences from the configuration shown in FIG. 1 will be described here. Between the input side optical fiber transmission lines 2-1 to 2-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 of 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 of the optical coupler is very small compared with the optical matrix switch, and 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 the optical switch device largely depends on the number of input / output ports, and the cost 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 the three characteristics of colorless, directionless, and contentionless, but has a drawback of requiring a large and expensive optical switch. Further, the problem that the reliability is lowered due to the large number of switch elements is 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.

  The wavelength division multiplexed optical signals from the L-side input side optical fiber transmission lines are 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 (wavelength variable 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 variation in loss between input and output caused by an input port can be suppressed. 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 the A × 1 switch described above.

  The add / drop system shown in FIG. 3 is characterized by a method for realizing the above-described optical variable filters 34-1 to 34-L. As described below, the inventors have improved the optical variable filter in the add / drop system shown in FIG. In the present invention, an optical variable filter to which the inventors have further improved is disclosed. Therefore, first, the details of the configuration and operation of the optical variable filter in the add / drop system will be further described.

  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 can be considered. FIG. 5A shows one configuration example. The optical tunable filter shown in FIG. 5A demultiplexes the wavelength division multiplexed optical signal 50 in units of wavelength paths by the demultiplexer 52, and then selects the demultiplexed optical signal by the selection switch 51. The optical signal 53 having the dropped wavelength is obtained. However, the optical variable filter having the configuration of FIG. 5A has a problem in terms of cost and reliability because the scale of the switch becomes as large as the number of wavelength paths or more.

  FIG. 5B is a diagram illustrating another configuration example of the optical variable filter, which is a configuration proposed in Patent Document 2. In the optical variable filter of FIG. 5B, the problem of the optical variable filter having the configuration of FIG. 5A is sought by cascading multi-stage demultiplexing functions. That is, from the first-stage optical variable filter 54 having the first-stage demultiplexing function unit 54-1 and the selection switch 54-2, to the n-th demultiplexing function unit 55-1 and the selection switch 55-2. Up to 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 selects a wavelength group including a desired wavelength. The second stage optical variable filter 55 demultiplexes the wavelength division multiplexed optical signal of one wavelength group for each wavelength and selects a desired wavelength.

  FIG. 6 is a diagram illustrating a more specific configuration example of a conventional optical variable filter having a two-stage configuration. In the conventional add / drop system disclosed in Patent Document 2 shown in FIG. 3, a configuration example of the optical variable filter 60 in the optical signal termination device is shown. 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 are in a relatively prime relationship with respect to the configuration of two circulating AWGs. 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. By combining compact switches as the selection switches 62 and 64, it has become possible to realize a colorless, directionless and contentless drop function.

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

It is known that the necessary switch scale decreases as the number of wavelength multiplexes is 5 or more, as the number of circulating AWGs increases. The configuration of FIG. 6 can reduce the scale of the switch configuration as compared with the optical variable filter having a single-stage configuration shown in FIG.

  However, as represented by the explosive spread of new mobile terminals such as smartphones, considering the current situation in which network traffic increases rapidly, the optical variable filter having the configuration disclosed in Patent Document 2 is also a switch. It was still not enough in terms of scale. In addition to the increase in network traffic, wavelength division multiplexing (WDM) technology and technical progress of each optical device are expected and will be handled in one optical fiber transmission line in the near future. The number of wavelengths was expected to exceed 200 at the maximum. Under such circumstances, if the number of wavelength paths (wavelengths) to be processed by the optical variable filter in the optical end signal terminal device increases, it is inevitable that the number of switches in the optical variable filter further increases. Therefore, a new configuration of an optical variable filter that can further reduce the switch scale has been desired. The inventors have made a new proposal for further improving the optical variable filter in the optical signal termination device in the prior art add / drop system shown in FIG. 3 (Patent Document 3).

  FIG. 7 is a diagram showing the configuration of an optical variable filter that can further reduce the scale of the optical switch proposed by the inventors. The inventors have made use of a wavelength selection function by the input port of the cyclic wavelength multiplexer / demultiplexer, which has not been paid attention to in the prior art optical variable filter, and makes the optical wavelength variable filter more compact, low cost and highly reliable. It has been found that it can be configured by a sex device. Set the FSR of the recursive wavelength multiplexer / demultiplexer, select the input and output ports that are actually used for demultiplexing, determine the number of wavelengths to be demultiplexed as a specific condition, and do not duplicate the same port Operates to output each wavelength. With the configuration of FIG. 7, even if the number of wavelength paths (wavelengths) increases, the scale of the optical switch can be effectively suppressed.

  The outline of the operation of the optical variable filter shown in FIG. 7 is as follows. The variable optical filter 70 proposed by the inventors corresponds to the conventional variable optical filter 60 shown in FIG. Therefore, in the drop system 30 in the photonic node shown in FIG. 3, the optical variable filters 34-1 to 34-L can be replaced by the optical variable filter 70, respectively. A wavelength division multiplexed optical signal 50 is input to the optical variable filter 70 from one input side optical fiber transmission line selected from among a plurality of optical fibers. An optical signal having a desired wavelength is selected by the optical variable filter 70, and a dropped optical signal 53 is obtained and passed to one of the receivers 35-1 to 35-L.

  The optical variable filter 70 includes a first optical switch 71 having 1 input m output (1 × m), a first circulating AWG 72 having M input M output, and a second light having m ′ input n output. A switch 73, a second circular AWG 74 having N inputs and N outputs, and a third optical switch 75 having n ′ inputs and 1 output (n ′ × 1) are provided. The wavelength division multiplexed optical signal 50 is input to the input port 76 of the first optical switch 71, and the optical signal 53 of the dropped wavelength is obtained from the output port 77 of the third optical switch 75. In the optical signal termination device of the photonic node, the optical variable filter 70 is provided for each of the plurality of optical receivers.

  The 1 × m first optical switch 71 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 71 are connected to any m of the M input ports of the first circulating AWG. Therefore, a relationship of at least m ≦ M is established. The first optical switch 71 has a function of selecting any one of the input ports of the first circulating AWG 72. That is, it has the input port selection function of the first AWG 72.

  The first circulating AWG 72 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) to the output port. The first AWG 72 has M inputs and M outputs, and its demultiplexing characteristics are cyclic and have circulatory properties. Therefore, the first AWG 72 is called a circulatory 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.

  Only a part of the demultiplexing function of the first circulating AWG 72 is used. In the optical variable filter of FIG. 7, only m input ports and m ′ output ports are used among M input ports and M output ports, respectively. Accordingly, the first circular AWG 72 has a slab waveguide, an arrayed waveguide, and the like as its constituent elements so as to have M-input M-output multiplexing / demultiplexing characteristics as a wavelength multiplexer / demultiplexer. 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)

The wavelength of the optical signal appearing at each of the m ′ output ports of the first cyclic AWG is determined according to the m input ports of the first cyclic AWG selected by the first optical switch 71. The Therefore, m × m ′ different wavelength groups (or wavelengths) can be selected. The first circulating AWG 72 has FSR ₁ represented by the following equation when the channel interval is δf (Hz).
FSR ₁ = M × δf Formula (3)

  The first circulating AWG 72 outputs optical signals having different wavelengths cyclically (cyclically) for each M channel to the same output port. Therefore, if the equation (2) is satisfied, the wavelength group (or the wavelength without overlapping) is satisfied. ) Can be demultiplexed.

  The second optical switch 73 has a function of selecting one of the m ′ outputs of the first circular AWG 72 and selecting n input ports of the subsequent second circular AWG 74. Have. In other words, the second optical switch 73 is formed by cascading (m ′ × 1) switch function part (front stage part) and (1 × n) switch function part (back stage part). The second optical switch 73 selects any one of the m ′ output ports of the first circular AWG, and n input ports of the subsequent second circular AWG 74. It is input to one of these.

  The second circular AWG 74 receives the wavelength division multiplexed optical signal at 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 74 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, as with the first AWG 72, only a part of the demultiplexing function is used for the second AWG 74 as well. That is, of the N input ports and N output ports, only n input ports and n ′ output ports are used. Accordingly, in the second revolving AWG 74, the slab waveguide and the array waveguide, which are constituent elements, are set so as to have N-input N-output multiplexing / demultiplexing characteristics as a wavelength multiplexer / demultiplexer. The input / output port wirings 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)

Depending on the n input ports selected by the second optical switch 73 in the second circular AWG 74, the wavelength appearing in each of the n ′ output ports of the second circular AWG 74 is determined. Therefore, the channel number (wavelength) number can be uniquely selected by the second revolving AWG 74 according to n × n ′ different combinations. The second AWG 74 has an FSR ₂ represented by the following equation when the channel interval is δf (Hz).
FSR ₂ = N × δf Formula (5)

  Since the second circulating AWG 74 outputs optical signals having different wavelengths cyclically (cyclically) every N channels to the same output port, the optical signal for each wavelength can be used without overlapping if Expression (4) is satisfied. Can be demultiplexed. Here, it is necessary that M of the first circulatory AWG 72 and N of the second circulatory AWG 74 are in a prime relationship.

  The n ′ output ports of the second circular AWG 74 are selected by the third optical switch 75, 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 77 of the third optical switch 75. As described above, the optical variable filter 70 as a whole has the first-stage optical variable filter function based on the first circular AWG 72 and the second-stage optical variable filter function based on the second circular AWG 74. . This is similar to the configuration of the conventional optical variable filter shown in FIG. However, the first optical switch that selects the input port of the first circulating AWG 72 and the second optical that selects the input port of the second circulating AWG 74, which are not included in the configuration shown in FIG. The proposed variable optical filter differs from the prior art in that it includes a switch.

  FIG. 8 is a diagram for explaining the function of the optical signal termination unit (optical signal termination device) including the function of the proposed optical variable filter. FIG. 8A illustrates the function of the proposed optical variable filter, and FIG. 8B illustrates the function of the conventional optical variable filter in comparison. In the proposed optical signal termination unit, as in the prior art, fiber selection switches 33-1 to 33-L (see FIG. 3) are used to select one fiber from a plurality of input side optical fiber transmission lines (steps). 80) is executed. Further, in the proposed optical variable filter shown in FIG. 7, the first optical switch 71 performs input port selection of the first circular AWG 72 (step 81). Thereafter, wavelength group demultiplexing or wavelength demultiplexing is performed by the first circulating AWG 72 (step 82). Further, the output port selection of the first circulatory AWG 72 is executed by the optical switch portion in the previous stage of the second optical switch 73 (step 83). Further, the input port selection of the second circulatory AWG 74 is executed by the optical switch portion subsequent to the second optical switch 73 (step 84). Next, wavelength demultiplexing is performed by the second revolving AWG 74 (step 85). Finally, the output port selection of the second circular AWG 74 is executed by the third optical switch 75 (step 86).

  FIG. 8B shows the function of the conventional optical variable filter in comparison with the proposed optical variable filter function (a). The function of the conventional optical variable filter of FIG. 8B corresponds to the function shown in the conceptual diagram of FIG. Further, as understood by comparing (a) and (b) of FIG. 8, the optical variable filter proposed by the inventors includes an input port selection function 81 and a second one of the first circular AWG. There is a novel feature in that it has an input port selection function 84 of the recursive AWG.

  In the optical variable filter of FIG. 7 proposed by the inventors, the demultiplexing function possessed by the AWG is efficiently used by selecting the AWG input port having the circularity. In addition to this, the FSR settings (M and N settings) of the recursive AWG and the input and output ports to be used are selected, and the configuration in which the output wavelengths do not overlap has been selected. That is, only the optical signal having the desired wavelength is output from the same output port.

  The optical variable filter of FIG. 7 proposed by the inventors uses the input port selection function 81 of the first circulatory AWG and the input port selection function 84 of the second circulatory AWG, thereby reducing the scale of the optical switch. Is further reduced as compared with the conventional optical variable filter. 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. This simplifies the configuration of the device in the drop-side optical signal termination device and enables cost reduction. Furthermore, improvement in device reliability can be expected due to the reduction in circuit scale.

Japanese Patent No. 4916489 JP 2012-60622 A JP 2014-10437 A

  However, the optical variable filter proposed by the inventors has the problem that the transmission loss of the selected and transmitted signal light increases while the scale of the optical switch constituting the optical variable filter can be greatly reduced. It was. In the two-stage variable optical filter shown in FIG. 7, transmitted signal light passes through the two circulating AWGs 72 and 74. In general, the cyclic AWG has a greater port dependency of transmission loss than a normal AWG having a sufficiently large FSR value with respect to a communication band (= channel interval × number of wavelength multiplexing). For example, the typical transmission loss of a circular AWG having about 10 input / output ports (M and N) is around 2 to 3 dB in the vicinity of the central port, similar to the transmission loss in a normal (non-circular) AWG. On the other hand, it reaches 4 to 5 dB at the end port. Therefore, in the optical variable filter shown in FIG. 7 that uses two or more round AWGs, the optical variable filter of the prior art using one-stage non-circular AWG shown in FIG. The above transmission loss occurs.

  When the loss in the optical tunable filter increases, the level of signal light must be compensated by an optical amplifier or the like in the drop-side optical signal termination device 30 shown in FIG. The amplification gain of the optical amplifier has a certain limit depending on the optical frequency band used. In addition, an increase in required gain in the optical amplifier increases the scale and configuration of the optical amplifier and increases the power consumption of the entire apparatus. In some cases, the number of branches in the optical signal termination device may be limited. If the number of stages for selecting the wavelength of the optical variable filter is further increased from two, the negative effect on the performance of other devices newly caused by the increase in transmission loss cannot be ignored, rather than the effect obtained by reducing the switch scale.

  In addition, the optical variable filter shown in FIG. 7 uses a plurality of input ports of the revolving AWGs 72 and 74. In general, when a plurality of input ports arranged adjacent to each other in the AWG are used successively. The filter characteristics are limited in the degree of design freedom in both the transmission band and the stop band. For example, multiple input ports that are adjacent to each other in response to various requests for filter characteristics, such as flattening the loss characteristics of the transmission band or making the slopes at both ends of the transmission characteristics appropriate. There is a limit to the design parameters for AWGs that use. As a result, in a recursive AWG using a plurality of adjacent input ports adjacent to each other, the filter characteristics are generally inferior to a normal type non-circumferential AWG using a single input port. Therefore, from the viewpoints of design and manufacturing flexibility and ease of transmission loss, AWG filter characteristics, etc., use of recursive AWG, especially recursive AWG using a plurality of adjacent input ports. Rather, it was accompanied by new problems in the overall performance and cost of the device.

  The present invention has been made in view of such problems, and the object of the present invention is to reduce the size of the optical switch in the optical variable filter and to suppress an increase in transmission loss and to design the filter characteristics of the AWG. It is to provide a new optical variable filter configuration that realizes manufacturing flexibility and ease.

  According to the present invention, in order to achieve such a problem, according to the first aspect of the present invention, each signal light of the plurality of channels is multiplexed in a predetermined communication band including a plurality of channels arranged continuously. In an optical variable filter that selects an optical signal of a predetermined wavelength from the wavelength division multiplexed light, a wavelength multiplexer / demultiplexer having a plurality of input ports and a plurality of output ports, and in the communication band, When the wavelength division multiplexed light is input to one of the input ports, only the signal light corresponding to one channel of the plurality of channels is output from one of the plurality of output ports. A multiplexer / demultiplexer; a first optical switch that selectively inputs the wavelength division multiplexed light to one of the plurality of input ports of the wavelength multiplexer / demultiplexer; and One of the plurality of output ports; And a second optical switch for selectively outputting the optical signal of the predetermined wavelength demultiplexed by the wavelength multiplexer / demultiplexer, and a single wavelength selection stage is configured by the wavelength multiplexer / demultiplexer This is a variable optical filter.

The invention according to claim 2 is the optical variable filter according to claim 1, wherein the first optical switch has one input port and M (natural number greater than or equal to 2) output ports, The output port is connected to an input port group continuously arranged in an adjacent position among the plurality of input ports of the wavelength multiplexer / demultiplexer,
The second optical switch has N (a natural number greater than or equal to 2) input ports and one output port, and is positioned in M repetition periods of the plurality of output ports of the wavelength multiplexer / demultiplexer. The N output ports are connected to the N input ports of the second optical switch element.

  The invention of claim 3 is the optical variable filter according to claim 1, wherein the first optical switch has one input port and M (natural number of 2 or more) output ports, The output port is connected to an input port group not adjacent to each other, which is located in a repetition period of A (natural number of 2 or more) among the plurality of input ports of the wavelength multiplexer / demultiplexer. .

  A fourth aspect of the present invention is the optical variable filter according to the second or third aspect, wherein the wavelength multiplexer / demultiplexer has an inter-port frequency interval of Δf when a channel interval of the plurality of channels is Δf. Each of the plurality of wavelength multiplexers / demultiplexers is connected to the first optical switch and the second optical switch, and the single wavelength multiplexer / demultiplexer It constitutes a wavelength selection stage.

  The invention according to claim 5 is the optical variable filter according to claim 2 or 3, wherein the wavelength multiplexer / demultiplexer sets a frequency interval between ports of B × Δf when Δf is a channel interval of the plurality of channels. And B wavelength multiplexers / demultiplexers configured such that the centers of the respective transmission bands are shifted by Δf, and each of the B wavelength multiplexers / demultiplexers includes the first optical switch. And connected to the second optical switch to constitute the single wavelength selection stage.

  A sixth aspect of the present invention is the optical variable filter according to the second or third aspect, wherein each of the plurality of wavelength multiplexers / demultiplexers has the same number of input ports and the same number of output ports. To do.

  A seventh aspect of the present invention is the optical variable filter according to any one of the first to sixth aspects, wherein at least one of the wavelength multiplexers / demultiplexers is configured by a non-circular arrayed waveguide grating (AWG). It is characterized by that.

  The invention of claim 8 is a wavelength multiplexer / demultiplexer having a plurality of input ports and a plurality of output ports in an optical variable filter that selects an optical signal of a predetermined wavelength from the multiplexed wavelength division multiplexed light. Then, in the communication band, when the wavelength division multiplexed light is input to one of the plurality of input ports, one of the plurality of output ports corresponds to one of the plurality of channels. A non-circular arrayed waveguide grating (AWG) that outputs only the signal light to be output, one input port, and M (natural number of 2 or more) output ports, and the plurality of non-circular AWGs A first optical switch that selectively inputs the wavelength division multiplexed light to one of the input ports, N (natural number greater than or equal to 2) input ports, and one output port. The above-mentioned orbiting AWG A second optical switch that selectively outputs an optical signal having the predetermined wavelength demultiplexed by the wavelength multiplexer / demultiplexer from one of the output ports, wherein the M output ports are , An input port group continuously arranged adjacent to each other among the plurality of input ports of the non-circumferential AWG, or A (two or more natural numbers) of the plurality of input ports of the non-circular AWG ), Which is connected to input port groups that are not adjacent to each other, and a non-circularity AWG constitutes a single wavelength selection stage.

  As described above, according to the present invention, the size of the optical switch of the optical variable filter used in the optical signal termination device of the photonic node is suppressed, and the device configuration is simplified and the cost is reduced. Furthermore, it is possible to realize a variable optical filter having a new configuration that suppresses an increase in transmission loss. In addition, the configuration of the optical variable filter of the present invention can also obtain design / manufacturing flexibility and ease such as filter characteristics of the AWG.

FIG. 1 is a diagram conceptually showing the configuration of an OXC system in 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 specific configuration example of a conventional optical variable filter having a two-stage configuration. FIG. 7 is a diagram showing a configuration of an optical variable filter that can further reduce the scale of the optical switch proposed by the inventors. FIG. 8 is a diagram for explaining the function of the optical signal termination unit (optical signal termination device) including the function of the proposed optical variable filter. FIG. 9 is a diagram for explaining the demultiplexing operation of the non-circumferential AWG used in the optical variable filter of the present invention. FIG. 10 is a diagram for explaining the demultiplexing operation of the circulating AWG. FIG. 11 is a diagram illustrating the configuration and operation of the first embodiment of the optical variable filter of the present invention. FIG. 12 is a diagram for explaining the configurations of the second and third embodiments of the variable optical filter of the present invention. FIG. 13 is a diagram for explaining the configuration and operation of the second embodiment of the variable optical filter of the present invention. FIG. 14 is a diagram for explaining the configuration and operation of the third embodiment of the variable optical filter of the present invention. FIG. 15 is a diagram for explaining the configuration of the optical variable filter according to the fourth embodiment of the present invention. FIG. 16 is a diagram for explaining a more specific operation of the first embodiment of the optical variable filter of the present invention. FIG. 17 is a table showing various configuration examples of the first embodiment of the variable optical filter of the present invention. FIG. 18 is a diagram for explaining a more specific operation of the third embodiment of the optical variable filter of the present invention. FIG. 19 is a table showing various configuration examples of the third embodiment of the optical variable filter of the present invention. FIG. 20 is a diagram illustrating a specific operation of the first configuration example of the fourth embodiment of the optical variable filter according to the present invention. FIG. 21 is a diagram illustrating an example of different demultiplexing characteristics of non-circumferential AWGs that can be used in the fourth embodiment. FIG. 22 is a diagram illustrating a specific operation of the second configuration example of the fourth embodiment of the optical variable filter according to the present invention. FIG. 23 is a table showing various configuration examples of the fourth embodiment of the variable optical filter of the present invention. FIG. 24 is a diagram comparing the effect of reducing the switch scale in the conventional optical variable filter and the optical variable filter of the present invention.

  The present invention relates to an optical variable filter used in an optical signal termination unit of an optical cross-connect device in an optical path network that performs signal path setting and switching processing with an optical signal as it is. The optical signal termination unit converts the wavelength division multiplexed light from one wavelength division multiplexed light selected from the plurality of wavelength division multiplexed lights respectively transmitted in parallel to the relay node via the plurality of optical fibers. A plurality of optical variable filters that select and drop an optical signal of a predetermined wavelength path included in the electrical layer are provided. Therefore, the term “optical variable filter” means a filter that can vary the center wavelength (optical frequency) of a transmission band that transmits an optical signal having a predetermined wavelength. The optical variable filter of the present invention can naturally be used for applications other than the optical signal termination unit as long as one wavelength is selected from a plurality of wavelength division multiplexed optical signals having different wavelengths.

  For example, the optical variable filter of the present invention can be applied to an optical communication system in which 192 channel optical signals are multiplexed at 25 GHz intervals. However, the present invention can also be applied to an optical communication system that handles other channel intervals and other numbers of multiplexed signals. Furthermore, the optical variable filter of the present invention can be applied not only to the optical signal termination unit but also to the use of extracting only a desired wave from a plurality of optical signals.

  The wavelength division multiplexed optical signal handled by the optical variable filter of the present invention is obtained by multiplexing a plurality of optical signals having 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 tunable filter, a cyclic wavelength multiplexer / demultiplexer is used, and a typical example is an arrayed waveguide diffraction grating (AWG). In the AWG, the wavelength division 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 an FSR (Free Spectral Range), the wavelength appearing at the output port can be made cyclic, that is, an AWG having recurring properties. The prior art variable optical filter shown in FIG. 7 is realized by using a circular AWG combined with an input port selection switch in a multistage configuration. As in the configuration of FIG. 5A, a normal non-circumferential AWG cannot multiplex / demultiplex a plurality of wavelengths as a wavelength group. The prior art optical tunable filter shown in FIG. 7 pays attention to the characteristics of the circulating AWG capable of realizing a multi-stage configuration by handling a plurality of wavelengths as a wavelength group.

  The present invention achieves a reduction in switch scale by using a normal acyclic AWG without using a recurring AWG, and at the same time, an optical variable filter that suppresses deterioration of filter characteristics such as an increase in transmission loss. provide. The prior art has reviewed the premise that an optimum multi-stage configuration has been studied by using a multi-stage circulatory AWG, and has focused on the low-loss characteristics of the non-circumferential AWG to arrive at the present invention.

  The present invention selects an optical signal having a predetermined wavelength from wavelength division multiplexed light in which signal lights of the plurality of channels are multiplexed in a predetermined communication band including a plurality of channels arranged continuously. It is an optical variable filter. A wavelength multiplexer / demultiplexer having a plurality of input ports and a plurality of output ports, wherein the wavelength division multiplexed light is input to one of the plurality of input ports in the communication band. A wavelength multiplexer / demultiplexer that outputs only signal light corresponding to one of the plurality of channels from one of the output ports, and one of the plurality of input ports of the wavelength multiplexer / demultiplexer From the first optical switch for selectively inputting the wavelength division multiplexed light and one of the plurality of output ports of the wavelength multiplexer / demultiplexer, the wavelength multiplexer / demultiplexer demultiplexes the wavelength division multiplexed light. And a second optical switch for selectively outputting the optical signal having the predetermined wavelength. In the optical variable filter of the present invention, a single wavelength selection stage is configured by the wavelength multiplexer / demultiplexer. In the optical variable filter of the present invention, a normal non-circumferential AWG that is not a recursive AWG is used. Therefore, first, the multiplexing / demultiplexing characteristics of the noncircular AWG used in the optical variable filter of the present invention will be described.

  FIG. 9 is a diagram for explaining the demultiplexing operation of the non-circumferential AWG used in the optical variable filter of the present invention. The non-circumferential AWG 90 is defined with respect to the recursive AWG described later by the number of wavelengths appearing at one output port. Therefore, it should be understood together with the demultiplexing operation of the circulating AWG described in conjunction with FIG. The non-circumferential AWG 90 includes input ports 1 to 8 as indicated by numbers on the left side and output ports 1 to 8 as indicated by numbers on the right side. When a multiplexed signal in which a plurality of different wavelengths are multiplexed is input to each input port, one wavelength is demultiplexed to each of the output ports 1 to 8.

  For example, when the multiplexed light 91-1 including wavelengths λ1 to λ8 is input to the input port 1, the signal light of λ1 appears at the output port 1, the signal light of λ2 appears at the output port 2, and similarly the output port In FIG. 8, signal light of λ8 appears. That is, the multiplexed light 91-1 is demultiplexed one by one to each of the output ports 1 to 8 by the noncircular AWG 90, and the demultiplexed wavelength 92-1 is obtained. When the multiplexed light 91-2 including wavelengths λ2 to λ9 is input to the input port 2, the signal light of λ2 appears at the output port 1, the signal light of λ3 appears at the output port 2, and the output port 8 similarly. Λ9 signal light appears. That is, the multiplexed light 91-2 is demultiplexed one by one to each of the output ports 1 to 8 by the non-circular AWG 90, and a demultiplexed wavelength 92-2 is obtained. As in the case of the input port 1, the multiplexed light 91-2 is demultiplexed one by one to each of the output ports 1 to 8 by the non-circumferential AWG 90. Similarly, when the multiplexed light 91-3 including wavelengths λ3 to λ10 is input to the input port 3, it is demultiplexed one by one to each of the output ports 1 to 8 by the noncircular AWG 90, and the demultiplexed wavelength 92− 3 is obtained.

  It should be noted that when the input port is shifted by one, the wavelength numbers that can be output from the output ports 1 to 8 are shifted one by one. This means that the signal light of the same wavelength can be output from different output ports by selecting the input port. In FIG. 9, the wavelengths included in the multiplexed lights 91-1, 91-2, and 91-3 input to the input ports do not mean that multiplexed light including only these wavelengths must be input. Please note that. That is, the input port 1 may include wavelengths λ9 to other than the wavelengths λ1 to λ8. The wavelengths described in the input port and the output port in FIG. 9 mean that when input multiplexed light of these wavelengths is input, different wavelengths appear one by one from all the output ports 1 to 8 without omission. ing.

  As described above, in the non-circumferential AWG 90, only signal light of one wavelength is demultiplexed from each output port. That is, in the optical variable filter of the present invention, in a predetermined communication band including a plurality of consecutively arranged channels, a wavelength of a predetermined wavelength is selected from wavelength division multiplexed light in which the signal lights of the plurality of channels are multiplexed. An optical signal is selected. In the non-circumferential AWG 90, when wavelength division multiplexed light is input to one of the plurality of input ports in the communication band described above, one of the plurality of output ports is changed to one of the plurality of channels. Only the signal light corresponding to the channel is output (definition of non-circularity). On the other hand, in the cyclic AWG used in the prior art, a plurality of optical signals having different wavelengths appear from one output port.

  FIG. 10 is a diagram for explaining the demultiplexing operation of the circulating AWG. The revolving AWG 100 includes input ports 1 to 8 as described on the left side and output ports 1 to 8 as illustrated on the right side. When a multiplexed signal in which a plurality of different wavelengths are multiplexed is input to each input port, a plurality of wavelengths having different wavelengths are demultiplexed to the output ports 1-8.

  For example, when the multiplexed light 101-1 including wavelengths λ1 to λ16 is input to the input port 1, signal light of λ1 and λ9 appears in the output port 1, and signal light of λ2 and λ10 appears in the output port 2, Similarly, signal light of λ8 and λ16 appears at the output port 8. That is, in the multiplexed light 101-1, signal light having two different wavelengths is demultiplexed to each of the output ports 1 to 8 by the circulating AWG 100, and a demultiplexed wavelength 102-1 is obtained. When the multiplexed light 101-2 including the wavelengths λ1 to λ16 is input to the input port 2, the signal light of λ2 and λ10 appears at the output port 1, the signal light of λ3 and λ11 appears at the output port 2, and similarly Signal light of λ1 and λ9 appears at the output port 8. That is, the multiplexed light 101-2 is demultiplexed by two at each of the output ports 1 to 8 by the circulating AWG 100, and the demultiplexed wavelength 102-2 is obtained. As in the case of the input port 1, the multiplexed light 101-2 is demultiplexed with signal light having two different wavelengths to each of the output ports 1 to 8 by the circulating AWG 100. Similarly, when the multiplexed light 101-3 including the wavelengths λ1 to λ16 is input to the input port 3, the signal light having two different wavelengths is demultiplexed to each of the output ports 1 to 8 by the circular AWG 100, A wave wavelength 102-3 is obtained.

  As is clear from FIG. 10, in the revolving AWG 100 used in the prior art, a plurality of signal lights having two or more different wavelengths appear simultaneously at one output port. In FIG. 10, for example, if the input multiplexed light 101-1 includes 48 channel signal lights of λ1 to λ48, six output signals of λ1, λ9, λ17, λ25, λ33, and λ41 are output from the output port 1. Light appears at the same time. In the prior art optical tunable filter shown in FIG. 7, in order to further separate a plurality of signal lights having different wavelengths appearing at one output port, it is essential to use at least two or more round AWGs. there were.

  It should be noted that the circulatory AWG 100 and the non-circumferential AWG 90 can be distinguished by the set FSR value. In other words, in the recursive AWG, the FSR value corresponds to the wavelength number period (8 in the example of FIG. 10) that appears repeatedly multiplied by the channel bandwidth Δf. On the other hand, in the non-circumferential AWG, the FSR value is sufficiently higher than that of the cyclic AWG so that all the channels assumed in the optical communication system targeted by the optical variable filter can be demultiplexed to one output port. It is set to a large value.

  In the non-circumferential AWG shown in FIG. 9, when the wavelength division multiplexed light is input to one input port, the inventors of the present invention demultiplex only signal light of one wavelength from each output port. Focusing on this simple function again, we examined a configuration that can simultaneously suppress both the switch scale and transmission loss. As already described, if the number of wavelengths to be demultiplexed by non-circumferential AWG increases to 96 channels, 192 channels, etc., the problem is that the scale of the switch 51 shown in FIG. Met. However, even when using a non-circumferential AWG, in addition to the wavelength selective switch for the output port after demultiplexing, it is possible to effectively demultiplex many wavelengths by combining the wavelength selection function by the input port. I found out. Hereinafter, the configuration and operation of the optical variable filter of the present invention will be described in detail.

  The optical variable filter of the present invention has a single-stage configuration in which a non-circumferential AWG is used in place of the recursive AWG, and two selection switches arranged on the input side and the output side of the non-circular AWG are combined. Provide AWG. By using the non-circumferential AWG in only one stage, it is possible to realize an optical variable filter that suppresses both the switch scale and the transmission loss.

** First embodiment **
FIG. 11 is a diagram illustrating the configuration and operation of the first embodiment of the optical variable filter of the present invention. FIG. 11A shows the optical variable filter 110 of the present invention, and FIG. 11B conceptually shows the wavelength of the optical signal selected by the optical variable filter 110. Referring to (a) of FIG. 11, the optical variable filter 110 is connected to the non-circumferential AWG 111, the input port selection switch 112 connected to the input side of the non-circular AWG 111, and the output side of the non-circular AWG 111. An output port selection switch 113 is included. Multiplexed input light 114 including a plurality of different wavelengths is input to the 1 × M input port selection switch 112. The output of the input port selection switch 112 is in the approximate center of the L × L non-circumferential AWG 111 and is connected to adjacent M input ports adjacent to each other. In the configuration of FIG. 11, adjacent consecutive M input ports of the non-circumferential AWG are used. However, in another embodiment of the present invention described later, a different form of usage of the input ports is disclosed. The

  The optical signal appearing at the output port of the non-circumferential AWG 111 is selected by the N × 1 output port selection switch 113 and output as the output light 115. Among the output ports of the non-circumferential AWG 111, the one connected to the output port selection switch 113 starts from the first output port, and is (M + 1) th, (2M + 1) every M−1 (with a repetition period M). ) Th, (3M + 1) th,... Up to ((N−1) × M + 1) th output port that does not exceed L.

  FIG. 11B conceptually shows the wavelength of the optical signal selected by the optical variable filter 110. Each arrow indicates an optical signal having a different wavelength, and the horizontal axis conceptually indicates the wavelength. The number described at the tip of the arrow indicates the input port number selected by the non-circumferential AWG 111. The M signal lights denoted by reference numeral 116 are output in order from the left when the first input port, the second input port,..., The Mth input port are selected. It represents the signal light that appears at the port. Here, it should be noted that M signal lights 116 do not appear at a time, but one signal light corresponding to the selected input port appears. Therefore, the M signal lights use the wavelength selection function of the non-circumferential AWG by selecting the input port.

  Similarly, M signal lights denoted by reference numeral 117 are selected in order from the left when the first input port, the second input port,..., The Mth input port are selected. The signal light that appears at the (M + 1) th output port is shown. Here too, the M signal lights 117 do not appear at once, but one signal light corresponding to the selected input port appears. Further, similarly, M signal lights denoted by reference numeral 118 are sequentially selected from the left when the first input port, the second input port,..., The Mth input port are selected. The signal light that appears at the (2M + 1) th output port is shown. The M signal lights 118 do not appear at once, but one signal light corresponding to the selected input port appears.

  As described above, when the M input ports adjacent to each other in the non-circumferential AWG 111 are selected by the input port selection switch 112, the output ports of the non-circular AWG are selected at M intervals. Thus, a group of signal lights having consecutive wavelength numbers can be selected without omission. Therefore, for example, when ten input ports are selected by the input port selection switch 112, for example, if the first, eleventh, and twenty-first output ports are selected, λ1 to λ10 are assigned to the first output port. Wavelengths from λ11 to λ20 can be output to the eleventh output port, and wavelengths from λ21 to λ30 can be output to the twenty-first output port.

  Therefore, in the optical variable filter of the present invention, the first optical switch (input port selection switch 112) has one input port and M (natural number of 2 or more) output ports, and the M output ports. Are connected to an input port group continuously arranged at adjacent positions among a plurality of input ports of the wavelength multiplexer / demultiplexer (non-circumferential AWG 111), and the second optical switch (output port selection switch 113) is , N (natural numbers greater than or equal to 2) input ports and one output port, and N output ports located in M repetition periods of the plurality of output ports of the wavelength multiplexer / demultiplexer are It is connected to the N input ports of the second optical switch element. Next, a more specific configuration and operation example of the first embodiment will be described.

  FIG. 16 is a diagram for explaining a more specific operation of the first embodiment of the optical variable filter of the present invention. 11 illustrates an example including the 1 × 4 input port selection switch 165, the 9 × 9 non-circumferential AWG 160, and the 3 × 1 output port selection switch 166 in the optical variable filter 110 illustrated in FIG. The input wavelength division multiplexed optical signal 167 is multiplexed with signal light having 12 different wavelengths from λ1 to λ12. The input wavelength division multiplexed optical signal 167 is input by the input port selection switch 165 to four (M = 4) consecutively arranged (M = 4) inputs in the center of the nine input ports of the non-circular AWG 160. Select one of the ports. That is, one of the fourth input port to the seventh input port is selected. 16A shows the case where the fourth input port 161 is selected, FIG. 16B shows the case where the fifth input port 162 is selected, and FIG. 16C shows the case where the sixth input port 163 is selected. (D) shows the case where the seventh input port 164 is selected.

  On the output port side of the non-circumferential AWG 160, three ports of a first output port, a fifth output port, and a ninth output port are used at intervals of four ports. By selecting one of these three output ports by the output port selection switch 166, one of twelve signal lights having different wavelengths from λ1 to λ12 is selected.

  For example, if the first output port is selected when the fourth input port 161 is selected, an optical signal of λ1 can be output as the output light 168 as shown in FIG. If the first output port is selected when the fifth input port 162 is selected, an optical signal of λ2 can be output as the output light 168 as shown in FIG. Similarly, output light of λ3 (in the case of (c) in FIG. 16) or λ4 (in the case of (d) in FIG. 16) can be output from the first output port.

  If the fifth output port is selected when the fourth input port 161 is selected, an optical signal of λ5 can be output as the output light 168 as shown in FIG. If the fifth output port is selected when the fifth input port 162 is selected, an optical signal of λ6 can be output as the output light 168 as shown in FIG. Similarly, output light of λ7 or λ8 can be output from the fifth output port.

  As described above, with the configuration of the optical variable filter shown in FIG. 16, any one of the optical signals of λ1 to λ12 can be selected and extracted from the input wavelength division multiplexed optical signal 167 without omission.

  Therefore, according to the present invention, in a predetermined communication band including a plurality of consecutively arranged channels, an optical signal having a predetermined wavelength is selected from wavelength division multiplexed light in which the signal lights of the plurality of channels are multiplexed. The optical variable filter to be selected is realized. The optical variable filter is a wavelength multiplexer / demultiplexer having a plurality of input ports and a plurality of output ports, and the wavelength division multiplexed light is input to one of the plurality of input ports in the communication band. Then, only the signal light corresponding to one of the plurality of channels is output from one of the plurality of output ports, and the plurality of the wavelength multiplexer / demultiplexer The first optical switch for selectively inputting the wavelength division multiplexed light to one of the input ports, and the wavelength multiplexing / demultiplexing from one of the plurality of output ports of the wavelength multiplexer / demultiplexer. And a second optical switch that selectively outputs the optical signal having the predetermined wavelength that has been demultiplexed by the duplexer, and a single wavelength selection stage is configured by the wavelength multiplexer / demultiplexer.

  As is clear from FIG. 11 and FIG. 16, a combination of an input port selection switch and an output port selection switch using a non-circumferential AWG that forms a single wavelength selection stage allows a plurality of different wavelengths. The signal light having a desired wavelength can be selected from the multiplexed signal light in which the signal light is multiplexed. By using M consecutively arranged input ports adjacent to each other in the center of the non-circumferential AWG and N output ports in M repetition cycles, continuous wavelengths are obtained. A series of M × N signal lights having numbers can be selected without omission. The reason why the M input ports in the central portion are used here is that, in AWG, in general, it is easy to realize a desired filter characteristic in the input port located in the central portion, and the number is not necessarily limited to the central portion. Not.

  FIG. 17 is a table showing various configuration examples of the first embodiment of the variable optical filter of the present invention. It is an example of a structure of the optical variable filter corresponding to the wavelength selection of 96 channels with a continuous wavelength number. The possible combinations of the number M of 1 × M input port selection switches, the number of non-circumferential AWG input ports and output ports (AWG size) L, and the number N of N × 1 output port selection switches are shown. . In general, in order to minimize the switch scale in the entire optical variable filter, a combination that minimizes the sum of M and N is preferable. Among such combinations, it is preferable to select a combination having the smallest AWG size L. FIG. 16 shows a configuration example in which the number of multiplexed wavelengths is equal to M × N. However, in each configuration example shown in FIG. 17, the number of selectable wavelengths is 96 depending on the combination of M, L, and N. Note that it can be large. Even in such a case, according to the optical variable filter of the first embodiment, it is still possible to select a series of 96 channel signal lights having consecutive wavelength numbers without omission.

  In the embodiment shown in FIGS. 11, 16, and 17, the input port used by the non-circumferential AWG is substantially in the center, and uses input ports that are continuously arranged adjacent to each other. However, in general, when adjacent input ports or output ports adjacent to each other are used in the AWG, crosstalk between channels can be a problem in transmission characteristics. Therefore, in the next second embodiment, different usage modes of the input port of the acyclic AWG for wavelength selection will be described.

** Second embodiment **
FIG. 12 is a diagram illustrating the configuration of the second and third embodiments of the variable optical filter of the present invention. The optical variable filter 120 includes a non-circumferential AWG 121, an input port selection switch 122 connected to the input side of the non-circular AWG 121, and an output port selection switch 123 connected to the output side of the non-circular AWG 121. Multiplexed input light 124 including a plurality of different wavelengths is input to the 1 × M input port selection switch 122. The output of the input port selection switch 122 is substantially at the center of the L × L non-circular AWG 121 and is connected to M input ports arranged at equal intervals with at least one interval. The difference from the first embodiment shown in FIG. 11 is which input port of the non-circumferential AWG is used and which output port is used in accordance with this.

  As shown in FIG. 12, as the input port of the non-circumferential AWG in the second embodiment, M input ports are used which are generally located at the center and arranged at equal intervals with at least one interval. The In the example of FIG. 12, the first input port, the third input port, the fifth input port,... (2M-1) th M input ports that are located at the center of the center are used. The In this way, when the input ports are used discontinuously at intervals, two types of methods for selecting the output port of the non-circumferential AWG are proposed. One is a method using adjacent output ports, and the other is a method not using adjacent output ports. First, a second embodiment using adjacent output ports will be described.

  FIG. 13 is a diagram for explaining the configuration and operation of the second embodiment of the variable optical filter of the present invention. FIG. 13A shows the optical variable filter 120 of the present invention, and FIG. 13B conceptually shows the wavelength of the optical signal selected by the optical variable filter 120. FIG. 13A is the same as the configuration shown in FIG. 12 except that the output port used in the non-circumferential AWG 121 is clearly indicated. In the present embodiment, a total of N adjacent two output ports are used as output ports in the acyclic AWG 121. Here, the input ports of the non-circumferential AWG 121 are used from the first to the (2M-1) th, but since every other input port is selected, only M input ports are used in total. I want to be.

  Referring to FIG. 13B, the wavelength of the optical signal selected by the optical variable filter 120 is conceptually shown in the same manner as described with reference to FIG. Each arrow indicates an optical signal having a different wavelength, and the horizontal axis conceptually indicates the wavelength. The number described at the tip of the arrow indicates the input port number selected by the non-circumferential AWG 121. M signal lights indicated by solid-line arrows labeled 131-1 are, in order from the left, the first input port, the third input port,..., The (2M-1) th input. The signal light that appears at the first output port when the port is selected is shown. Here, the input ports selected in the present embodiment are the first, third, fifth,... (2M−1) th, and a total of M input ports spaced apart from each other. Please note that. Therefore, the M signal lights 131-1 do not have consecutive wavelength numbers on the wavelength axis, and correspond to every other wavelength number.

  On the other hand, the M signal lights indicated by broken-line arrows labeled 131-2 are, in order from the left, the first input port, the third input port,... (2M-1). It represents the signal light that appears at the second output port when the first input port is selected. It should be noted that the M signal lights 131-2 are signal lights corresponding to the wavelength numbers for which no signal light appeared in the M signal lights 131-1 on the wavelength axis. This is obtained by selecting every other input port of the non-circumferential AWG and using a set of two output ports adjacent to each other at intervals of 2M (repetition period). As a result, from the first output port and the second output port, optical signals having a total of 2M continuous wavelength numbers on the wavelength axis can be selected alternately.

  Similarly, the M signal lights indicated by thick solid arrows denoted by reference numerals 131-3 are, in order from the left, the first input port, the third input port,... (2M-1 The signal light that appears at the (2M + 1) th output port when the) th input port is selected. Then, the wavelength numbers on the wavelength axis are M numbers starting from the (2M + 1) th wavelength following the 2M consecutive wavelength numbers selected by the first output port and the second output port. It becomes signal light 131-3. Further, M signal lights indicated by thick dashed arrows denoted by reference numerals 131-4 are, in order from the left, the first input port, the third input port,... (2M-1). The M signal lights appearing at the (2M + 2) th output port when the th input port is selected. It should be noted that the M signal lights 131-4 are signal lights corresponding to the wavelength numbers for which no signal light appeared in the M signal lights 131-3 on the wavelength axis.

  Eventually, as shown in FIG. 13B, every other input port of the non-circumferential AWG is selected, and a set of two adjacent output ports at intervals of 2M (repetition period). By using, a series of M × N signal lights having consecutive wavelength numbers on the wavelength axis can be selected without omission. Here, compared with the first embodiment of FIG. 11, the second embodiment shown in FIG. 13 differs in the usage mode of the input port of the non-circumferential AWG. In the first embodiment, M input ports that are arranged adjacent to each other in a substantially central portion and N output ports selected at M intervals (repetition periods) are used. Thus, a series of M × N signal lights having consecutive wavelength numbers can be selected without omission. On the other hand, in the second embodiment, at least every other input port of the non-circumferential AWG is selected M, and two adjacent ports spaced by an integer multiple of M (repetition cycle) are selected. By using a total of N output ports, a series of M × N signal lights having consecutive wavelength numbers on the wavelength axis can be selected without omission.

  In the example of FIG. 13, M input ports are selected every other (repetition period A is 2), and two output ports adjacent to each other with 2M intervals are used. However, as can be easily guessed, every two input ports (repetition period A is 3) are selected M, and a set of 3 output ports adjacent to each other with 3M intervals (repetition period) is used. However, it will be understood that a series of signal lights having consecutive wavelength numbers on the wavelength axis can be selected without omission. Therefore, a series of M × N signal lights having consecutive wavelength numbers on the wavelength axis are selected without omission by using at least one gap between the input ports of the acyclic AWG at equal intervals. be able to.

  Therefore, in the optical variable filter of the present embodiment, the first optical switch (input port selection switch 122) has one input port and M (a natural number of 2 or more) output ports, and the M outputs The port is connected to a group of input ports that are not adjacent to each other and are located in a repetition period of A (natural number of 2 or more) among the plurality of input ports of the wavelength multiplexer / demultiplexer (non-circumferential AWG 121). become.

  According to the present embodiment, since adjacent input ports are not used on the input port side, it is possible to design the required performance of the filter characteristics of the non-circumferential AWG more loosely in terms of crosstalk. With respect to the shape of transmission loss and filter characteristics, the degree of design freedom can be increased. In the second embodiment described above, the method of selecting the output port to be used can be modified to further reduce the required filter characteristics.

** Third embodiment **
FIG. 14 is a diagram for explaining the configuration and operation of the third embodiment of the variable optical filter of the present invention. 14A shows the optical variable filter 120 of the present invention, and FIG. 14B conceptually shows the wavelength of the optical signal selected by the optical variable filter 120. FIG. 14A is the same as the configuration shown in FIG. 12 except that the output port handled by the non-circumferential AWG 121 is clearly indicated. In the present embodiment, unlike the second embodiment shown in FIG. 13, the output ports in the non-circumferential AWG 121 use a total of N output ports, which are a set of two adjacent output ports. . As in the second embodiment, 2M ports from the first to (2M-1) th are used as the input ports of the non-circumferential AWG 121. Note that since every other input port is chosen, only M input ports are used in total.

  Referring to (b) of FIG. 14, the wavelength of the optical signal selected by the optical variable filter 120 is conceptually shown in the same manner as described with reference to (b) of FIG. 13. Each arrow indicates an optical signal having a different wavelength, and the horizontal axis conceptually indicates the wavelength. The number described at the tip of the arrow indicates the input port number selected by the non-circumferential AWG 121. The M signal lights indicated by solid-line arrows labeled 141-1 are, in order from the left, the first input port, the third input port,..., The (2M-1) th input. The signal light that appears at the first output port when the port is selected is shown. Here, the input ports selected in the present embodiment are the first, third, fifth,... (2M−1) th total M input ports spaced apart from each other. . Therefore, the M signal lights 141-1 do not have consecutive wavelength numbers on the wavelength axis, and correspond to signal lights with every other wavelength number.

  On the other hand, the M signal lights indicated by broken-line arrows labeled 141-2 are, in order from the left, the first input port, the third input port,... (2M-1). It represents the signal light that appears at the fourth output port when the fourth input port is selected. It should be noted that the M signal lights 141-2 are signal lights corresponding to the wavelength numbers for which no signal light appeared in the M signal lights 141-1 on the wavelength axis. However, unlike the second embodiment, when the first signal light of the M signal lights 141-1 is the wavelength number 1, the M signal lights 141-2 do not start from the second. Note that it starts with the signal light corresponding to the fourth wavelength number. Accordingly, the signal light 142 corresponding to the second wavelength number does not exist in the wavelength number that is assumed for the design of the optical variable filter, and cannot be selected.

  However, if the incomplete portion which is the non-selectable signal light 142 is ignored, a total of 2M optical signals having consecutive wavelength numbers on the wavelength axis are selected by the first output port and the fourth output port. It will be possible. Actually, since the signal light 142 cannot be used, in FIG. 14B, in order from the signal light 143 selected by the combination of the input port 3 and the output port 1 among the M signal lights 141-1. A series of a plurality of optical signals having the selected wavelength numbers can be selected.

  Similarly, M signal lights indicated by thick solid line arrows denoted by reference numerals 141-3 are, in order from the left, the first input port, the third input port,..., (2M-1 The signal light that appears at the (2M + 1) th output port when the) th input port is selected. Then, the wavelength numbers on the wavelength axis are M number of wavelengths that are newly selected from the (2M + 1) th wavelength following the consecutive wavelength numbers alternately selected by the first output port and the fourth output port. It becomes signal light 141-3. Further, M signal lights indicated by thick dashed arrows with a reference numeral 141-4 are, in order from the left, the first input port, the third input port,... (2M−1). The M signal lights appearing at the (2M + 4) th output port when the th input port is selected. The M signal lights 141-4 are signal lights corresponding to the wavelength numbers for which no signal light appeared in the M signal lights 141-3 on the wavelength axis.

  After all, according to the configuration of the optical variable filter shown in FIG. 14, a series of signal lights having consecutive wavelength numbers on the wavelength axis are selected without omission, except for an incomplete portion which is an unselectable signal light 142. be able to. In the present embodiment, the incomplete portion described above is formed by combining two output ports that are not adjacent to each other, and separating the two output ports. As a result, the end portion on the wavelength axis is selected. Wavelength, that is, an incomplete part appears. In the case where every other input port is selected, if the first output port and the third output port are selected as one set, the wavelength numbers are completely overlapped. The same applies to selecting the first output port and the fifth output port as one set. That is, in the present embodiment, one of the output port groups is at a position shifted from the other by an odd number of ports. The case of shifting by one port is the second embodiment using adjacent output ports. Accordingly, the basic configuration of the present embodiment is a case where three ports are shifted as shown in FIG. When the output port is shifted more than this, for example, if the first output port and the sixth output port are selected as one set, the incomplete portion that becomes two unselectable signal lights at the end on the wavelength axis It will be easy to see that

  FIG. 18 is a diagram for explaining a more specific operation of the third embodiment of the optical variable filter of the present invention. 14 shows an example of a 12-channel variable optical filter including the 1 × 4 input port selection switch 187, the 12 × 12 acyclic AWG 180, and the 4 × 1 output port selection switch 188 in the optical variable filter shown in FIG. In the input wavelength division multiplexed optical signal 189, signal lights having 12 different wavelengths from λ1 to λ12 are multiplexed. The input wavelength division multiplexed optical signal 189 is input by the input port selection switch 187 so that four of the 12 input ports of the non-circumferential AWG 180 are arranged at every other center (M = 4) in the central portion. Select one of the input ports. That is, one of the fourth, sixth, eighth and tenth input ports is selected. 18A shows the case where the fourth input port 181 is selected, FIG. 18B shows the case where the sixth input port 182 is selected, and FIG. 18C shows the case where the eighth input port 183 is selected. (D) shows the case where the 10th input port 184 is selected.

  On the output port side of the non-circumferential AWG 180, the 9th output port and the 12th output port are used next in a repetition period of 8 ports with the 1st output port and the 4th output port as a set. By selecting one of these four output ports by the output port selection switch 188, one of signal lights having twelve different wavelengths from λ1 to λ12 is selected.

  For example, when the fourth input port 181 is selected and the fourth output port is selected, an optical signal of λ2 can be output as the output light 190 as shown in FIG. If the first output port is selected when the sixth input port 182 is selected, an optical signal of λ1 can be output as the output light 190 as shown in FIG. Similarly, output light of λ3 (in the case of (c) in FIG. 18) or λ5 (in the case of (d) in FIG. 18) can be output from the first output port.

  If the ninth output port is selected when the eighth input port 183 is selected, an optical signal of λ11 can be output as the output light 190 as shown in FIG. If the twelfth output port is selected when the tenth input port 184 is selected, an optical signal of λ16 can be output as the output light 190 as shown in FIG.

  As described above, in the third embodiment, when signal light having twelve different wavelengths from λ1 to λ12 is to be selected, the non-circular AWG has 12 port input ports and output ports. Is required. However, as can be seen from FIG. 18, λ0 and λ15 cannot be selected, and unnecessary (λ-1) can be selected. The unselectable λ0 and λ15 correspond to the incomplete portion of the unselectable signal light 142 described in FIG. Due to this imperfection, in order to demultiplex a plurality of signal lights having a predetermined continuous series of wavelengths, the demultiplexing is performed over a wider range of wavelength numbers than the required number (12 channels). Larger size non-circumferential AWGs and selection switches are needed that have the capability to do so. For example, in this example, a 12-channel optical variable filter is assumed, but the combinations that can be selected by the input port selection switch and the output port selection switch are 4 × 4 = 16.

  In this embodiment, a non-circumferential AWG and a switch are selected to be slightly larger so as to cover a wider range than the target wavelength range, thereby avoiding an incomplete part and a series of a plurality of light beams having consecutive wavelength numbers. The signal can be selected. Although some waste occurs in the AWG and the switch, neither the input port nor the output port uses a port in a continuous position, and uses a port that is not adjacent. As a result, the filter characteristics required for the non-circumferential AWG need only be more relaxed.

  FIG. 19 is a table showing various configuration examples of the third embodiment of the optical variable filter of the present invention. It is an example of a structure of the optical variable filter corresponding to the wavelength selection of 96 channels with a continuous wavelength number. The possible combinations of the number M of 1 × M input port selection switches, the number of non-circumferential AWG input ports and output ports (AWG size) L, and the number N of N × 1 output port selection switches are shown. . In general, in order to minimize the switch scale in the entire optical variable filter, a combination that minimizes the sum of M and N is preferable. Among such combinations, it is preferable to select a combination having the smallest AWG size L.

  In the configuration of the third embodiment shown in FIGS. 14, 18, and 19, adjacent input ports and output ports do not use adjacent continuous ports but use non-adjacent ports. As a result, the specification of the filter characteristics required for the non-circumferential AWG can be more relaxed. For example, the non-circumferential AWG filter characteristics can be designed to reduce transmission loss as much as possible. Further, it is possible to design such that the shape of the transmission characteristics is close to a rectangle (higher order Gaussian) instead of a Gaussian waveform. It is possible to improve and acquire flexibility from various viewpoints of the transmission characteristic of the signal light selected by the optical variable filter. In the second embodiment shown in FIG. 13, the output port side of the non-circumferential AWG uses continuous adjacent output ports. On the other hand, in the third embodiment shown in FIG. 14, the filter characteristics of the AWG can be further effectively improved by using the output ports separated from each other on the output port side of the non-circumferential AWG. It becomes possible.

  In the configuration of the third embodiment, since there is signal light having an unselectable wavelength (incomplete portion) at the end of the wavelength range to be handled, a series of signal lights having continuous wavelength numbers without missing wavelength numbers are generated. In order to process it, it is necessary to avoid this incomplete part. In the first embodiment, signal light having continuous wavelength numbers can be selected using all of the first output port to the last output port. Therefore, if the specification of the required wavelength band and the configuration of the AWG are selected, all the output ports can be completely used without waste. On the other hand, in the present embodiment, it is necessary to select the configuration of the AWG while avoiding the above-described incomplete portion and considering the wavelength band specification of the target system. As a result, the non-circumferential AWG and the selection switch may need a slightly larger size.

  However, a degree of freedom can be obtained in the design of the filter characteristics of the non-circumferential AWG, and an allowance for errors is generated in the manufacturing process, and the merit of improving the manufacturing yield is increased. Although a detailed performance comparison will be described later, the optical variable filter configuration of the present invention shown in FIG. 14 is different from the conventional optical variable filter configuration shown in FIG. The low loss characteristic can be realized by using the non-circumferential AWG while maintaining the effect of reducing the switch scale equivalent to that of the conventional technology. By using only one AWG, the configuration of the optical variable filter becomes very simple.

  In the above-mentioned three embodiments, a single non-circumferential AWG is used in one stage and a single wavelength selection stage is configured. When the target wave band is very wide like 192 channels, the size of one AWG may become large. In such a case, the non-circumferential AWG can be divided. In the following fourth embodiment, a configuration example of a split type optical variable filter will be described.

** Fourth embodiment **
FIG. 15 is a diagram for explaining a first configuration of the fourth embodiment of the optical variable filter according to the present invention. The optical variable filter 150 of the present embodiment includes two or more non-circumferential AWGs used in parallel unlike the previous embodiments, for example, the first non-circumferential AWG 151-1 and the second non-circular AWG. AWG151-2. Each non-circumferential AWG has an L × L configuration, an input port selection switch 152 connected to the input side of each non-circumferential AWG, and an output port selection connected to the output side of each non-circumferential AWG The switch 153 is configured. Multiplexed input light 154 including a plurality of different wavelengths is input to the 1 × M input port selection switch 152. The output of the input port selection switch 152 is approximately the center of each L × L non-circumferential AWG, and is connected to consecutive adjacent M / 2 input ports. In the configuration of FIG. 15, adjacent M / 2 input ports (groups) of each non-circumferential AWG are used. However, as in the second and third embodiments, each non-circumferential AWG may use input ports (groups) arranged at equal intervals with at least one interval.

  In this embodiment, by dividing the non-circumferential AWG into two, the size of one non-circumferential AWG is reduced, and the number of optical signals carried by one non-circular AWG is reduced. Since the size of one non-circumferential AWG may be smaller than in the first to third embodiments, the center frequency deviation of the transmission characteristics obtained between the input and output ports can be suppressed to be small. With respect to other filter band characteristics, requirements for realizing the required performance are loose. Therefore, for example, the filter characteristics of the non-circumferential AWG can be designed to reduce transmission loss as much as possible. Further, it is possible to design such that the shape of the transmission characteristics is close to a rectangle (higher order Gaussian) instead of a Gaussian waveform. It is possible to improve and obtain flexibility from various viewpoints of the transmission characteristics of signal light that is wavelength-selected by the optical variable filter. Next, a more specific configuration example and operation of the optical variable filter according to the fourth embodiment will be described.

  FIG. 20 is a diagram illustrating a more specific operation of the optical variable filter according to the fourth embodiment of the present invention. The optical variable filter 200 illustrated in FIG. 20 includes an example of a 1 × 4 input port selection switch 206, two 5 × 5 non-circular AWGs 201-1 and 201-2, and a 6 × 1 output port selection switch 207. In the input wavelength division multiplexed optical signal 208, signal lights having 12 different wavelengths from λ1 to λ12 are multiplexed. By the input port selection switch 206, two of the five input ports of each of the non-circumferential AWGs 201-1 and 201-2 are arranged in succession at approximately the center (M / 2 = 2). One of the input ports is selected, and an input wavelength division multiplexed optical signal 208 is input. That is, one of the third input port and the fourth input port is selected. 20A shows the case where the third input port 203 of the first acyclic AWG 201-1 is selected, and FIG. 20B shows the case where the fourth input port 204 is selected. Shows the case where the third input port 205 of the second acyclic AWG 201-2 is selected, and (d) shows the case where the fourth input port 206 is selected.

  In the optical variable filter shown in FIG. 20, adjacent input ports are used in each non-circumferential AWG. Therefore, in each non-circumferential AWG, the wavelength can be selected by the same operation as in the first embodiment. As can be seen from FIGS. 20A and 20B, a series of signal lights having consecutive wavelength numbers from λ1 to λ6 are demultiplexed by the first acyclic AWG 201-1. Similarly, as can be seen from (c) and (d) of FIG. 20, a series of signal lights having consecutive wavelength numbers from λ7 to λ12 are demultiplexed by the second acyclic AWG 201-2.

  FIG. 21 is a diagram for explaining different demultiplexing characteristics of the non-circumferential AWG that can be used in the optical variable filter according to the fourth embodiment. A non-circumferential AWG 210 in FIG. 21A shows the demultiplexing characteristics of the non-circular AWG used in the optical variable filter shown in FIG. The non-circumferential AWG 211 in (b) shows the demultiplexing characteristics of the non-circumferential AWG used in the optical variable filter of the second configuration example of the fourth embodiment described later. ) And will be described in detail. As shown in (a), when the multiplexed light 212 is input to the first input port, the non-circumferential AWG 210 outputs one signal light 214 of λ1 to λ6 from each of the six output ports. Is done. When the input port is shifted by one and the multiplexed light 213 is input to the second input port, one signal light 215 from λ2 to λ7 is output from each of the six output ports. Therefore, one port corresponds to one channel (center wavelength λ, center optical frequency f). Assuming that the center frequency interval (channel interval) of the signals of each channel at this time is Δf, a non-circular AWG having a frequency interval between adjacent ports of Δf may be used. At this time, the transmission bandwidth of the non-circumferential AWG is also configured to be Δf. The transmission bandwidth of the AWG (one port) is designed according to the signal channel interval Δf and the signal bit rate. Therefore, in the case of the configuration of FIG. 20, two non-circular AWGs having the same frequency interval Δf are used.

  Therefore, the optical tunable filter according to the present embodiment is configured such that the wavelength multiplexer / demultiplexer (non-circumferential AWG) has an inter-port frequency of Δf, where Δf is the channel spacing of a plurality of channels in the communication band of the target system. Each of the plurality of wavelength multiplexers / demultiplexers configured to have an interval is connected to the first optical switch and the second optical switch. The single wavelength selection stage is configured.

  By dividing the non-circumferential AWG into two or more by the configuration of this embodiment, the size of one non-circumferential AWG can be reduced and the number of optical signals carried by one non-circumferential AWG can be reduced. . Thereby, the center frequency shift of the transmission characteristic obtained between each input / output port can be suppressed to a small value. It goes without saying that the division type configuration can be applied to the second and third embodiments that use input ports spaced apart from each other in a non-circumferential AWG. In the variable wavelength optical filter of FIG. 20, the wavelength assigned to one non-circumferential AWG is simply divided into two or more groups. However, by using an AWG having a different center frequency interval from that of the example of FIG. 20, it becomes possible to further relax the design conditions and manufacturing conditions of the non-circumferential AWG as in the following second configuration example.

FIG. 22 is a diagram illustrating a specific operation of the second configuration example of the optical variable filter according to the fourth embodiment of the present invention. In the first configuration example shown in FIG. 20, an example in which the non-circumferential AWG having the same structure in which the center frequency interval is set to Δf is used is shown. However, in the second configuration example shown in FIG. This is a configuration example using a non-circumferential AWG having a wider frequency interval between them. The configuration of the optical variable filter 220 is the same as the configuration of the optical variable filter 200 shown in FIG. 20, but the configuration of the non-circumferential AWG used and the method of dividing the wavelength shared by the two non-circular AWGs. Different. The following description will focus on these differences.
As can be seen from FIG. 22A, the wavelength output from the output port when the third input port 223 of the first acyclic AWG 221-1 is selected is different from the configuration example of FIG. Please be careful. That is, the signal light of λ5 is output from the third output port instead of λ3. That is, λ5 signal light having a difference of 4 channels is output instead of λ3 having a difference of 2 channels from λ1 from the first output port. In addition, signal light of λ9 is output from the fifth output port instead of λ5. That is, λ9 signal light having a difference of 8 channels is output instead of λ5 having a difference of 4 channels from λ1 of the first output port. As shown in FIG. 22B, the wavelength output from the output port by selecting the fourth input port 224 of the first acyclic AWG 221-1 is also the same as that of the first output port. A λ7 optical signal having a difference of 4 channels from λ3 and a λ11 signal light having a difference of 8 channels are output.

  Further, referring to FIG. 22 (c), the wavelength output from the output port when the third input port 225 of the second acyclic AWG 221-2 is selected is as follows. The signal light of λ6 is output from the third output port, and the signal light of λ10 is output from the fifth output port. That is, λ6 signal light having a difference of 4 channels from λ2 of the first output port is output, and λ10 signal light having a difference of 8 channels from λ2 of the first output port is output. As shown in FIG. 22D, the wavelength output from the output port by selecting the fourth input port 226 of the second acyclic AWG 221-2 is also the same as that of the first output port. λ8 signal light having a difference of 4 channels from λ4 and λ12 signal light having a difference of 8 channels are output.

  Comparing (a) to (d) of FIG. 22 showing the second configuration example and (a) to (d) of FIG. 20 showing the first configuration example, in the second configuration example, the two non-circulations The wavelength carried by the sex AWG is not a simple division, but the wavelengths are distributed alternately. That is, it can be seen that the group is divided into a group including odd-numbered wavelengths (λ1, λ3,...) And a group including even-numbered wavelengths (λ2, λ4,...). Further, in addition to one output port corresponding to one wavelength, that is, one channel, in the configuration of FIG. 22, if one non-circular AWG output port is different, two channels are output. Wavelengths (numbers) are different.

  A non-circumferential AWG that can distribute and output each wavelength in a pattern as shown in FIGS. 22A to 22D is an AWG 211 having a demultiplexing characteristic shown in FIG. realizable. When the multiplexed light 216 is inputted to the first input port, the non-circumferential AWG 211 shown in FIG. 21B has λ1, λ3, λ5 having alternate wavelength numbers from each of the six output ports. , Λ7, λ9, and λ11, one signal light 218 is output. When the input port is shifted by one and the multiplexed light 217 is input to the second input port, the wavelength number is shifted by 2 from each of the six output ports, among λ3, λ5, λ7, λ9, λ11, and λ13 The one signal light 219 is output. Such a demultiplexing characteristic is a non-circularity AWG having a frequency interval of 2 × Δf between adjacent ports, where Δf is the center frequency interval of the signal of each channel (wavelength) of the target system at this time. Use it. Accordingly, the first non-circumferential AWG 221-1 in FIG. 20 that outputs the wavelengths λ1, λ3, λ5, λ7, λ9, and λ11 is a non-circumferential AWG having a frequency interval between ports of 2 × Δf.

  On the other hand, in order to output even-numbered wavelengths (λ2, λ4,...) As in the second non-circumferential AWG 221-2 shown in (c) and (d) of FIG. An AWG configured to have the same inter-port frequency interval 2 × Δf as that of one non-circumferential AWG 221-1 and so that the center wavelength of each transmission band is shifted by Δf by one channel may be used. Note that the transmission bandwidths of the non-circumferential AWGs 221-1 and 221-2 are respectively Δf. Therefore, in order to output each wavelength shown in FIG. 22, two types of non-circumferential AWGs having different center wavelengths in the respective transmission bands and a frequency interval between ports of 2 × Δf are prepared. There is a need to. An AWG having a different center wavelength in each transmission band can be easily realized by various methods such as changing the connection position of the input waveguide in the AWG.

  Therefore, in the optical tunable filter of the present embodiment, the wavelength multiplexer / demultiplexer (non-circumferential AWG) has a port of B × Δf when Δf is the channel spacing of a plurality of channels in the communication band of the target system. Each of the B wavelength multiplexers / demultiplexers is configured to have a frequency interval between them and the center of each transmission band is shifted by Δf. One optical switch and the second optical switch are connected to constitute the single wavelength selection stage.

  The optical variable filter having the configuration shown in FIG. 22 requires a non-circumferential AWG having a different configuration as compared to the configuration of FIG. 20 using two non-circumferential AWGs having exactly the same configuration, but the channel spacing is small. Double AWG can be used. An AWG with a large frequency interval between ports has a greater degree of design freedom than a narrow AWG due to the design specifications of the filter characteristics. Further, a larger error can be allowed in manufacturing, and advantages such as improvement in manufacturing yield can be obtained.

In the second configuration example shown in FIG. 22, the target communication band is divided into two and two non-circumferential AWGs having different center wavelengths of the respective transmission bands are used. It is also possible to divide into two parts. In this case, the output wavelength is the first group of λ1, λ4, λ7,... (The remainder obtained by dividing the wavelength number by 3 is 1), and the output wavelengths are λ2, λ5, λ8,. Group (wavelength number divided by 3 gives a remainder of 2), output wavelength is λ3, λ6, λ9... Third group (wavelength number divided by 3 is a remainder of 0) Can be divided. As can be easily estimated, in this case, the first non-circumferential AWG having a frequency interval between ports of 3 × Δf may be used. Then, a total of three types of non-circularity, that is, a second non-circumferential AWG in which the center wavelength of the transmission band is shifted by Δf by one channel and a third non-circumferential AWG in which the center wavelength of the transmission band is shifted by 2Δf by two channels. What is necessary is just to provide AWG.
Therefore, if the number of channels in the system becomes very large and it is appropriate to use a smaller AWG due to other performance requirements of the filter characteristics, the number of divisions should be further increased to 4 or more. Needless to say, it can be increased. For example, in the case of B (natural number greater than or equal to 2) division, a first non-circumferential AWG having a frequency interval between ports of B × Δf is provided, and the center wavelength of each transmission band is sequentially shifted by Δf by one channel ( B-1) What is necessary is just to further provide the non-circumferential AWG. Even in the case of simple division into wavelength groups having consecutive wavelength numbers as shown in FIG. 20, there are cases where it is appropriate to use a smaller AWG due to other performance requirements of the filter characteristics. The number can be increased.

  FIG. 23 is a table showing various configuration examples of the optical variable filter according to the fourth embodiment of the present invention. FIG. 21 is a configuration example of an optical variable filter that corresponds to the configuration of FIG. 20 and that divides a band into two for 96 channels having continuous wavelength numbers and selects wavelengths by two non-circumferential AWGs. The possible combinations of the number M of 1 × M input port selection switches, the number of input ports and output ports (AWG size) L of one acyclic AWG, and the number N of selections of N × 1 output port selection switches are shown. ing. In general, in order to minimize the switch scale in the entire optical variable filter, a combination that minimizes the sum of M and N is preferable. Among such combinations, it is preferable to select a combination having the smallest AWG size L.

  As described above in detail, in each optical variable filter of the fourth embodiment having the AWG division type configuration whose specific operation has been described with reference to FIGS. 20 and 22, by dividing the non-circularity AWG, A small size AWG can be used. As a result, the design of the filter characteristics and the like of the AWG itself can be performed under more lenient specifications, and the tolerance of errors is large even in the manufacture of the AWG, and the manufacturing yield can be improved and the cost can be reduced. Furthermore, according to the configuration of the AWG division type shown in FIG. 22, it is possible to use an AWG having a larger frequency interval between ports. As a result, a further margin and a degree of design freedom are created in the design specifications of the filter characteristics. Larger errors can be tolerated in manufacturing, and the manufacturing yield can be further improved. If the number of channels in the system becomes very large in the future and it is appropriate to use a smaller AWG because of other performance requirements or restrictions on filter characteristics, etc. The configuration of the AWG division type according to the fourth embodiment of the invention can exhibit its merit.

  FIG. 24 is a diagram comparing the effect of reducing the switch scale in the conventional optical variable filter shown in FIG. 7 and the optical variable filter of each embodiment of the present invention. The horizontal axis indicates the number of wavelengths of interest (corresponding to the number of channels in the communication band), and the vertical axis indicates the number of switches converted by the number of 1 × 2 switch elements. The notation of “SW batch type” and “SW split type” shown in the legend indicates that the wavelength selection is performed collectively only on the output port side of the AWG, and the input port selection switch and output port before and after the AWG. A case where wavelength selection is performed by dividing the selection switch is shown. In addition, the notation of “one-stage selection” to “three-stage selection” in the wavelength selection method indicates the number of wavelength selection stages constituted by a recursive AWG or a non-circular AWG.

  The optical variable filter of the present invention corresponds to the “SW division type” configured by “one-stage selection” of the non-circumferential AWG, and is indicated by a solid line of a white square plot. The “one-stage selection” configuration and the “SW batch type” optical variable filter indicated by the solid line of the square plot correspond to the configuration of FIG. According to the optical variable filter of the present invention, the switch scale is drastically reduced as compared with the configuration of FIG. 5A of the prior art despite the “one-stage selection” configuration. The “2 stage selection” configuration and “SW split type” optical variable filter of the conventional circulatory AWG shown in FIG. 7 are shown by white circle plots. The reduction scale of the switch is only slightly reduced compared with the “one-stage selection” configuration of the non-circumferential AWG of the present invention and the “SW division type” configuration (white square plot). Even if the number of wavelength selection stages is increased to “2-stage selection” and “3-stage selection”, the reduction amount of the switch scale has reached its peak.

  24, the comparison result of FIG. 24 shows that the “SW split type” configuration in which the selection switch is divided into the input side and the output side in the “one-stage selection” configuration of the non-circumferential AWG of the present invention It can be seen that there is a switch reduction effect comparable to the “multi-stage selection” configuration of the circular AWG shown in FIG. Since the optical variable filter of the present invention uses only one stage of the non-circumferential AWG, the transmission loss is less than half compared with the multi-stage optical variable filter using a plurality of circular AWGs shown in FIG. It becomes a small value. In the present invention, by utilizing the characteristics of the low transmission loss of the non-circumferential AWG itself, the increase in the transmission loss is greatly suppressed while realizing the effect of reducing the switch scale to the same level as the conventional technology. An optical variable filter can be realized.

  In the above description, the non-circumferential AWG has been described as an example of the wavelength multiplexer / demultiplexer. However, the present invention has a demultiplexing characteristic similar to that of the AWG, and transmission loss is achieved by making the demultiplexing function multistage. The present invention may be applicable to other types of devices in which the increase is increased. In each of the embodiments and drawings described above, the optical signal having the first wavelength number of the target system is output from the first output port at the extreme end of the non-circumferential AWG. However, even when the first port at the extreme end is not used, the basic configuration of the optical variable filter of the present invention having the AWG port selection switches on the input side and output side of the non-circumferential AWG is provided. Of course, the effect of the present invention can be obtained as a matter of course. Therefore, it is not necessary to use the output ports of all non-circumferential AWGs.

  As described above in detail, the optical variable filter according to the present invention reduces the size of the optical switch in the optical variable filter and suppresses an increase in transmission loss while simplifying the device configuration and reducing the cost. In addition, an optical variable filter having a new configuration can be realized.

  The present invention can be used in an optical communication system. In particular, it can be used for an optical variable filter that extracts or adds 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, 70 Optical variable filters 39-1 to 39-L, 53 Dropped optical signals 62, 64, 71, 73, 75 Optical switches 90, 111, 121, 151-1, 151-2, 180, 201- 1, 20 -2 non cyclic-frequency wavelength division multiplexer (AWG)
61, 63, 72, 74, 100 orbital wavelength multiplexer / demultiplexer (AWG)
112, 122, 152, 165, 187, 206, 227 Input selection switch 113, 123, 153, 166, 188, 207, 228 Output selection switch

Claims (8)

In an optical variable filter that selects an optical signal having a predetermined wavelength from wavelength division multiplexed light in which each signal light of the plurality of channels is multiplexed in a predetermined communication band including a plurality of channels arranged continuously. ,
A wavelength multiplexer / demultiplexer having a plurality of input ports and a plurality of output ports, wherein the wavelength division multiplexed light is input to one of the plurality of input ports in the communication band. A wavelength multiplexer / demultiplexer that outputs only signal light corresponding to one of the plurality of channels from one of the output ports;
A first optical switch that selectively inputs the wavelength division multiplexed light to one of the plurality of input ports of the wavelength multiplexer / demultiplexer;
A second optical switch that selectively outputs an optical signal of the predetermined wavelength demultiplexed by the wavelength multiplexer / demultiplexer from one of the plurality of output ports of the wavelength multiplexer / demultiplexer; Prepared,
A single optical wavelength selection stage is constituted by the wavelength multiplexer / demultiplexer. The first optical switch has one input port and M (natural number of 2 or more) output ports, and the M output ports are among the plurality of input ports of the wavelength multiplexer / demultiplexer. Connected to the input ports grouped in succession at
The second optical switch has N (a natural number greater than or equal to 2) input ports and one output port, and is positioned in M repetition periods of the plurality of output ports of the wavelength multiplexer / demultiplexer. 2. The optical variable filter according to claim 1, wherein N output ports are connected to the N input ports of the second optical switch element. 3.  The first optical switch has one input port and M (natural number of 2 or more) output ports, and the M output ports are among the plurality of input ports of the wavelength multiplexer / demultiplexer. 2. The optical variable filter according to claim 1, wherein the optical variable filter is connected to a group of input ports that are not adjacent to each other and are positioned in a repetition period of A (natural number of 2 or more). The wavelength multiplexer / demultiplexer includes a plurality of wavelength multiplexers / demultiplexers configured to have an inter-port frequency interval of Δf, where Δf is a channel interval of the plurality of channels,
4. Each of the plurality of wavelength multiplexers / demultiplexers is connected to the first optical switch and the second optical switch, and constitutes the single wavelength selection stage. The optical variable filter described in 1. The wavelength multiplexer / demultiplexer has a frequency interval between ports of B × Δf where Δf is the channel spacing of the plurality of channels, and the center of each transmission band is shifted by Δf. It consists of multiple wavelength multiplexers / demultiplexers,
4. Each of the B wavelength multiplexers / demultiplexers is connected to the first optical switch and the second optical switch to constitute the single wavelength selection stage. The optical variable filter described in 1.   6. The optical variable filter according to claim 4, wherein each of the plurality of wavelength multiplexers / demultiplexers has the same number of input ports and the same number of output ports.   7. The optical variable filter according to claim 1, wherein at least one of the wavelength multiplexer / demultiplexers is configured by a non-circular arrayed waveguide diffraction grating (AWG). In an optical variable filter that selects an optical signal having a predetermined wavelength from wavelength division multiplexed light in which each signal light of the plurality of channels is multiplexed in a predetermined communication band including a plurality of channels arranged continuously. ,
A wavelength multiplexer / demultiplexer having a plurality of input ports and a plurality of output ports, wherein the wavelength division multiplexed light is input to one of the plurality of input ports in the communication band. A non-circular arrayed waveguide grating (AWG) that outputs only signal light corresponding to one of the plurality of channels from one of the output ports;
A first input port and M (a natural number greater than or equal to 2) output ports, wherein the wavelength division multiplexed light is selectively input to one of the plurality of input ports of the non-circumferential AWG; 1 optical switch,
N (natural number greater than or equal to 2) input ports and one output port, the one of the plurality of output ports of the non-circumferential AWG being demultiplexed by the wavelength multiplexer / demultiplexer A second optical switch for selectively outputting an optical signal of a predetermined wavelength,
The M output ports are input port groups that are continuously arranged adjacent to each other among the plurality of input ports of the non-circumferential AWG, or of the plurality of input ports of the non-circumferential AWG. Are connected to non-adjacent input port groups located in a repetition period of A (natural number of 2 or more),
A variable wavelength filter, wherein a single wavelength selection stage is constituted by the non-circumferential AWG.

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