House-side device, optical communication system, and sub-carrier selection method

Abstract

To provide a house-side device that communicates with two station-side devices by using one optical transceiver.SOLUTION: In an optical communication system 200, a house-side device 2 capable of optical communication with two base-side devices 1 comprises an optical transceiver 21 of a sub-carrier multiplexing system, and a control unit that sets a plurality of sub-carriers. The sub-carriers satisfy the following formulas. The sub-carriers fLmin to fH1max are used for communication with the first station-side device 1A. The sub-carriers fH2min to fLmax are used for communication with the second base-side device 1B. (a) fH1max-fLmin≥CW×N. (b) fLmax-fH2min≥CW×N. fH1max / fH2min is the maximum frequency / minimum frequency at which the optical transceivers of the first / second station-side devices can be modulated / demodulated, fLmax / fLmin is the maximum frequency / minimum frequency at which the optical transceiver of the house-side device can be modulated / demodulated, CW is a carrier width of the sub-carriers, and N is the number of one or more sub-carriers used by the house-side device.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an optical network unit, an optical communication system, and a method for selecting subcarriers. [Background technology]

[0002] Patent documents 1 and 2 describe that an optical transceiver employing a subcarrier multiplexing (SCM) method generates multiple subcarriers (subcarriers) with different wavelengths using a single light source through digital signal processing, and transmits the generated subcarriers to an optical fiber. In the optical transceivers disclosed in Patent Documents 1 and 2, the subcarriers of the upstream optical signal and the subcarriers of the downstream optical signal are divided into different wavelength bands.

[0003] Therefore, the optical transceivers disclosed in Patent Documents 1 and 2 can be installed in, for example, one optical line terminal and multiple optical network terminals, which are components of a P2MP optical communication system. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2021 / 0021365 [Patent Document 2] US Patent Application Publication No. 2022 / 0103258 Summary of the Invention [Problem to be solved by the invention]

[0005] In a P2MP optical communication system including one optical line terminal and multiple optical network terminals, it may be desirable to add an optical line terminal in order to achieve communication redundancy or load balancing. However, Patent Documents 1 and 2 do not assume that an optical network unit communicates with two optical line terminals using one optical transceiver.

[0006] In view of the above-described conventional problems, an object of the present disclosure is to provide an optical network unit that can communicate with two optical line terminals using one optical transceiver. [Means for solving the problem]

[0007] An apparatus according to one embodiment of the present disclosure is an optical line terminal (ONB) capable of optical communication with two optical line terminals, and includes a subcarrier multiplexing optical transceiver and a control unit that sets a plurality of subcarriers to be used by the optical transceiver, wherein the plurality of subcarriers satisfy the following formulas (a) and (b), and subcarriers in a range equal to or greater than fLmin and equal to or less than fH1max are used for communication with a first optical line terminal, and subcarriers in a range equal to or greater than fH2min and equal to or less than fLmax are used for communication with a second optical line terminal: fH1max-fLmin≧CW×N ……(a) fLmax-fH2min≧CW×N ……(b)

[0008] however, fH1max: The maximum frequency that the optical transceiver of the first optical line terminal can modulate and demodulate fH2min: The minimum frequency that the optical transceiver of the second optical line terminal can modulate / demodulate fLmax: The maximum frequency that the optical transceiver in the home equipment can modulate and demodulate fLmin: The minimum frequency that the optical transceiver in the home equipment can modulate / demodulate CW: Carrier width of subcarrier N: The number of subcarriers (one or more) that a home device uses to communicate with one central office device

[0009] The present disclosure can be realized not only as a system and device having the above-described characteristic configuration, but also as a program for causing a computer to execute such characteristic configuration. Furthermore, the present disclosure can be realized as a semiconductor integrated circuit that realizes part or all of the system and device. [Effects of the Invention]

[0010] According to the present disclosure, it is possible to provide an optical network unit that can communicate with two optical line terminals using one optical transceiver. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram showing an example of the configuration of an optical communication system. [Figure 2] FIG. 2 is an explanatory diagram showing an example of a problem with a LEAF that communicates with two HUBs. [Figure 3] FIG. 3 is an explanatory diagram showing an example of a solution to the problem. [Figure 4] FIG. 4 is a diagram showing a first example of allocation of subcarriers SCi to a LEAF that communicates with two HUBs 1 and 2. In FIG. [Figure 5] FIG. 5 is a diagram illustrating a second example of allocation of subcarriers SCi to a LEAF that communicates with two HUBs 1 and 2. In FIG. [Figure 6] FIG. 6 is a block diagram showing an example of the configuration of an optical transceiver in a station side device. [Figure 7] FIG. 7 is a block diagram illustrating an example of the configuration of an optical transceiver in an optical network unit. [Figure 8] FIG. 8 is a block diagram showing a modified example of the optical communication system. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Summary of Embodiments of the Present Disclosure> The following provides an outline of embodiments of the present disclosure. (1) An apparatus according to one aspect of this embodiment is an optical network unit capable of optical communication with two optical line terminals, and includes a subcarrier multiplexing optical transceiver and a control unit that sets a plurality of subcarriers to be used by the optical transceiver, wherein the plurality of subcarriers satisfy the following formulas (a) and (b), and subcarriers in a range of not less than fLmin and not more than fH1max are used for communication with a first optical line terminal, and subcarriers in a range of not less than fH2min and not more than fLmax are used for communication with a second optical line terminal. fH1max-fLmin≧CW×N ……(a) fLmax-fH2min≧CW×N ……(b)

[0013] however, fH1max: The maximum frequency that the optical transceiver of the first optical line terminal can modulate and demodulate fH2min: The minimum frequency that the optical transceiver of the second optical line terminal can modulate / demodulate fLmax: The maximum frequency that the optical transceiver in the home equipment can modulate and demodulate fLmin: The minimum frequency that the optical transceiver in the home equipment can modulate / demodulate CW: Carrier width of subcarrier N: The number of subcarriers (one or more) that a home device uses to communicate with one central office device

[0014] According to the optical network unit of this embodiment, subcarriers within the range of not less than fH2min and not more than fLmax are used for communication with one optical line terminal, and subcarriers within the range of not less than fH2min and not more than fLmax are used for communication with the other optical line terminal. This makes it possible to connect to one optical line terminal without adding an optical transceiver or halting communication with the other optical line terminal that is currently in operation. This allows a network unit to communicate with two optical line terminals using one optical transceiver. Specifically, this allows for communication redundancy or load balancing without increasing costs or causing communication outages.

[0015] (2) In the optical network unit of (1) above, the optical network unit may include a carrier selection unit that selects subcarriers to which a transmission signal is to be assigned based on a field value that indicates a type of communication frame. In this case, the subcarriers to which the transmission signals are assigned are selected based on the field value indicating the type of communication frame, so that the transmission signals can be appropriately assigned to the first optical line terminal and the second optical line terminal.

[0016] (3) A system according to one aspect of this embodiment is an optical communication system including the optical network unit (ONU) of (1) or (2) described above, the first optical line terminal (ONU) having a subcarrier multiplexing optical transceiver, and the second optical line terminal (ONU) having a subcarrier multiplexing optical transceiver, wherein the frequency bands usable by the first optical line terminal and the frequency bands usable by the second optical line terminal are adjacent to each other with a distance equal to the guard band of the subcarrier.

[0017] The optical communication system of this embodiment has the advantage of being able to prevent waste of bandwidth compared to the case (4) described below.

[0018] (4) A system according to another aspect of this embodiment is an optical communication system comprising the optical network unit (ONU) of (1) or (2) described above, the first optical line terminal (ONU) having a subcarrier multiplexing optical transceiver, and the second optical line terminal (ONU) having a subcarrier multiplexing optical transceiver, wherein an empty wavelength width corresponding to a predetermined number of the subcarriers not used by the optical network unit is interposed between the frequency band usable by the first optical line terminal (ONU) and the frequency band usable by the second optical line terminal (ONU).

[0019] The optical communication system of this embodiment has the advantage that it is easier to prevent interference between carriers than in the above-mentioned case (3).

[0020] (5) A method according to one aspect of this embodiment is a subcarrier selection method executed in an optical home device having a subcarrier multiplexing optical transceiver when the optical home device communicates optically with two optical line devices, and includes a first step of extracting a field value representing the type of transmission signal, and a second step of selecting a subcarrier corresponding to the extracted field value.

[0021] According to the selection method of this embodiment, a step of selecting subcarriers corresponding to field values ​​extracted from a transmission signal is executed in the home terminal, so that the transmission signal can be appropriately allocated to one station terminal and the other station terminal.

[0022] (6) In the selection method of (5) above, if the two optical line terminals include an optical line terminal of a working system and a optical line terminal of a standby system, the subcarriers selected in the second step may be subcarriers for either the optical line terminal of the working system or the optical line terminal of the standby system. In this way, by executing the second step, it is possible to perform redundancy switching from the active system to the standby system.

[0023] (7) In the selection method of (5) above, the two optical line terminals may include a first optical line terminal and a second optical line terminal, and the selection performed in the second step may include selecting subcarriers for the first optical line terminal for a first field value, and selecting subcarriers for the second optical line terminal for a second field value different from the first field value. In this way, by executing the second step, switching for load balancing can be performed.

[0024] <Details of the embodiment of the present disclosure> Hereinafter, details of embodiments of the present disclosure will be described with reference to the drawings. Note that at least some of the embodiments described below may be combined in any manner.

[0025] [Configuration example of optical communication system] FIG. 1 is a block diagram showing an example of the configuration of an optical communication system 200. As shown in FIG. 1, the optical communication system 200 of this embodiment is a system in which two optical line terminals 1 and multiple (three in the illustrated example) optical network terminals 2 are connected by an optical fiber line 3. In this embodiment, the direction from the optical line terminal 1 to the optical network terminal 2 is referred to as the "downstream direction," and the opposite direction is referred to as the "upstream direction."

[0026] The optical line 3 includes a downstream ODN (Optical Distribution Network) 3d through which downstream optical signals are transmitted, and an upstream ODN 3u through which upstream optical signals are transmitted. The downstream ODN 3d includes a trunk line 4d connected to the optical line terminal 1 and a branch line 5d connected to the optical line terminal 2, and the trunk line 4d and the branch line 5d are connected by an optical coupler 6d. The upstream ODN 3u includes a trunk line 4u connected to the optical line terminal 1 and a branch line 5u connected to the optical line terminal 2, and the trunk line 4u and the branch line 5u are connected by an optical coupler 6u.

[0027] The trunk lines 4d and 4u and the branch lines 5d and 5u are each a single optical fiber. The optical couplers 6d and 6u are, for example, 2:N branch optical couplers. The downstream optical coupler 6d distributes downstream optical signals from the two trunk lines 4d to N (three in the illustrated example) branch lines 5d. The upstream optical coupler 6u distributes upstream optical signals from the N branch lines 5u to two trunk lines 5u. Therefore, the two optical line devices 1 (1A, 1B) can optically communicate with the three optical network devices 2 (2A, 2B, 2C) using the optical line 3 including the downstream ODN 3d and the upstream ODN 3u as a transmission path.

[0028] Each optical line terminal 1 is installed, for example, in a central office of a telecommunications carrier. An optical line terminal 2 is installed, for example, in the building of a user who uses a communication service. Note that the terms "optical line terminal" and "optical line terminal" indicate the relative positions of the devices, and do not limit the installation locations of the devices. The two optical line terminals 1 are both connected to a higher-level network 7 such as a core network, and can be used for redundancy or load balancing, for example.

[0029] The two optical line terminals 1 are connected to a controller 10 via a management network 9 such as a LAN (Local Area Network). The controller 10 is, for example, a management computer operated by a communications administrator. Each optical network unit 2 is connected to a lower network 7 such as an in-home LAN individually constructed in a user's home. Each optical network unit 2 is connected to a controller 10 via a management network 9.

[0030] The optical transceiver 11 of the optical line terminal 1 and the optical transceiver 21 of the optical network terminal 2 are both subcarrier multiplexing (SCM) optical transceivers. In the SCM (Sub Carrier Multiplexing) system, the optical transceiver 11 (or 21) on the transmitting side modulates a baseband signal into a subcarrier signal (electrical signal) with a bandwidth of several GHz and converts the modulated subcarrier signal into an optical signal. The optical transceiver 21 (or 11) on the receiving side extracts the subcarrier assigned to itself from the electrical signal obtained by photoelectric conversion of the optical signal by filtering, and demodulates the extracted subcarrier.

[0031] The multiple optical network units 2 use different subcarriers exclusively. The two optical line terminals 1 store information about which optical network unit 2 can demodulate which subcarrier, and broadcast downstream optical signals that are generated by converting the subcarrier signals assigned to the optical network units 2 under their control. The plurality of optical network units 2 transmit optical signals obtained by modulating subcarrier signals assigned for transmission, and the two optical line terminals 1 demodulate the subcarrier signals within the demodulatable range.

[0032] In this way, each optical line terminal 1 can demodulate the subcarrier signal modulated by the optical line terminal 2 under its control. Therefore, when the subcarrier signal photoelectrically converted from the upstream optical signal originates from the optical line terminal 2 under its control, the optical line terminal 1 demodulates the subcarrier signal and extracts the received signal. The wavelengths of the carriers (main carriers) of the two optical line terminals 1 are different, and the subcarrier ranges are operated so as not to overlap each other. Therefore, in the system configuration of Figure 1, for example, communication between optical line terminal 1A and optical network unit 2A and communication between optical line terminal 1B and optical network unit 2B can be carried out simultaneously in parallel.

[0033] Specifically, one of the two optical line terminals 1 (for example, optical line terminal 1A in FIG. 1) normally communicates with one optical line terminal 2A. Therefore, optical line terminal 1A is assigned, as a transmission subcarrier, a subcarrier that can be demodulated by optical line terminal 2A. Another one of the two optical line terminals 1 (for example, optical line terminal 1B in FIG. 1) also regularly communicates with one optical line terminal 2B. Therefore, optical line terminal 1B is assigned, as a transmission subcarrier, a subcarrier that can be demodulated by optical line terminal 2B.

[0034] One of the three optical network units 2 (for example, optical network unit 2C in FIG. 1) is an optical network unit that can switch the optical line terminal 1 for redundancy or load balancing, for example. For example, optical network unit 1C normally communicates with optical line terminal 1A, and temporarily communicates with optical line terminal 1B for redundancy purposes.

[0035] Therefore, station device 1A needs to be assigned, as transmission subcarriers, subcarriers that can be demodulated not only by optical network device 1A but also by optical network device 2C. Similarly, station device 1B needs to be assigned, as transmission subcarriers, subcarriers that can be demodulated not only by optical network device 1B but also by optical network device 2C.

[0036] As shown in FIG. 1, in this embodiment, the optical line terminal 1, the optical network terminal 2, and the optical transceivers 11 and 21 may be respectively expressed as follows. Central office device 1 → "HUB" (meaning the device at the concentrator side of the optical fiber line) Home device 2 → "LEAF" (meaning the device at the end of the optical fiber line) Optical transceiver 11, 21 → "TRx"

[0037] [Configuration example of central office device] As shown in FIG. 1, the optical line terminal 1 includes an optical transceiver 11, a switch 12, and a control unit 13.

[0038] The optical transceiver 11 of the optical line terminal 1 is an optical module that converts optical signals into electrical signals and vice versa, and may be, for example, a CFP (Centum Form-factor Pluggable) type digital coherent optical transceiver conforming to the MSA (Multi-Source Agreement) standard. The optical transceiver 11 may be an SFP (Small Form Factor Pluggable) type optical transceiver. The SFP type is a general term for SFP, SFP+, SFP28, QSFP, QSFP28, and their upwardly compatible pluggable optical modules.

[0039] The optical transceiver 11 has a function of switching the wavelength λk of the optical signal, but the subcarrier used for transmission and reception may be fixed or switchable. One carrier (primary carrier) of the same wavelength λk is used for transmission and reception with the optical network unit 2. Specifically, the optical transceiver 11 uses, for communication with the optical network unit 2, subcarriers allocated to the subordinate optical network unit 2 from within the subcarrier range (subcarriers before and after the center frequency) that the optical transceiver 11 can demodulate.

[0040] The frequency range that the optical transceiver 11 of the optical line terminal 1 can modulate and demodulate is a frequency range that includes all subcarriers assigned to the subordinate optical line terminals 2. The subcarrier switching function can be realized by, for example, a subcarrier multiplexing (SCM) coherent optical transceiver (FIG. 6). The subcarrier switching function can be used, for example, to allocate logical channels (for example, VLAN: Virtual LAN) of the higher-level network 7 to subcarriers.

[0041] The optical transceiver 11 of the optical line terminal 1 is connected to the trunk lines 4d and 4u, which are single-core optical fibers. The optical transceiver 11 is electrically connected to a predetermined port of the switch 12. Specifically, the optical transceiver 11 is connected to the switch 12 via multiple interfaces. Each interface may be either a physical port or a logical port, and corresponds exclusively to one or more subcarriers SCi (see FIG. 2).

[0042] The switch 12 is an integrated circuit such as an LSI (Large Scale Integration) that has relay functions for the L2 layer and the L3 layer, for example. A control unit 13 is electrically connected to a predetermined port of the switch 12. The switch 12 and the control unit 13 may be implemented in a single integrated circuit such as a System on a Chip (SoC).

[0043] The control unit 13 is an arithmetic processing device including, for example, a CPU (Central Processing Unit) 14 and a memory 15. The memory 15 includes a non-volatile memory in which a predetermined control program and data required for executing the program (for example, subcarrier setting information described later) are recorded, and a volatile memory in which the control program and the like are temporarily loaded.

[0044] The control unit 13 may include a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC). The control unit 13 may be configured with at least one of an FPGA and an ASIC. The control unit 13 communicates with the switch 12 via, for example, Ethernet, and with the optical transceiver 11 via serial communication such as I2C (Inter-Integrated Circuit).

[0045] The control unit 13 can acquire predetermined setting information from the controller 10 through control communication with the controller 10 via the management network 9. The control unit 13 performs various setting processes for the optical line terminal 1 and the optical network terminal 2 based on the acquired setting information. For example, the control unit 13 may perform initial settings such as wavelengths and subcarriers used by the optical transceiver 11, Quality of Service (QoS) settings for the switch 12, bandwidth settings for each port of the switch 12, and Virtual LAN (VLAN) settings. Note that subcarrier settings for the optical network unit 2 are performed by the controller 10.

[0046] The controller 10 performs management communication with the control unit 13 of the optical line terminal 1. Specifically, the controller 10 transmits the setting information of the optical line terminal 1 and the setting information of the optical line terminal 2 (excluding the carrier setting information) to the control unit 13 of the optical line terminal 1. If the received setting information is setting information for the optical transceiver 11 of the optical line terminal 1, the control unit 13 of the optical line terminal 1 controls the optical transceiver 11 of the optical line terminal 1 in accordance with the received setting information via serial communication such as I2C.

[0047] The control unit 13 of the optical line terminal 1 transfers the setting information for the optical network terminal 2 to the optical network terminal 2 by control communication via the optical fiber line 3 . That is, if the received setting information is setting information for the optical transceiver 11 of the optical line terminal 1, the control unit 13 of the optical line terminal 1 generates an Ethernet ("Ethernet" is a registered trademark) control frame addressed to the optical line terminal 2 and including the received setting information, and outputs the frame to the switch 12.

[0048] The control frame is transmitted via Ethernet communication to the control unit 13 of the optical network unit 2. The control unit 13 of the optical network unit 2 controls its own optical transceiver 11 in accordance with the received setting information via serial communication such as I2C. If the TRx's can perform control communication using a dedicated control channel (control wavelength), the setting information for the optical transceiver 11 of the optical network unit 2 may be transmitted by the control communication.

[0049] [Configuration example of home device] As shown in FIG. 1, the optical network unit 2 includes an optical transceiver 21, a switch 22, and a control unit . The optical transceiver 21 may employ an optical device similar to the optical transceiver 11 of the optical line terminal 1. Therefore, the modulation and demodulation range of the optical transceiver 21 may be the same as that of the optical line terminal 1.

[0050] However, the modulation / demodulation range of the optical transceiver 21 may be limited to a range close to the subcarrier set for the optical transceiver 21. In this case, there is an advantage that the performance of the digital signal processing can be made reasonable, leading to economical results. Branch lines 5d and 5u, which are single-core optical fibers, are connected to the optical transceiver 21 of the optical network unit 2. The optical transceiver 21 is electrically connected to a predetermined port of the switch 22. Specifically, the optical transceiver 21 is connected to the switch 22 via multiple interfaces. Each interface may be either a physical port or a logical port, and corresponds exclusively to one or more subcarriers SCi (see FIG. 2).

[0051] The switch 22 may be, for example, the same as the switch 12 of the optical line terminal 1. The control unit 23 may be, for example, the same as the optical line terminal 1, a processing unit including a CPU 24 and a memory 25. A control unit 23 is electrically connected to a predetermined port of the switch 22. The switch 22 and the control unit 23 may be implemented in a single integrated circuit such as an SoC.

[0052] The memory 25 includes a non-volatile memory in which a predetermined control program and data necessary for executing the program (for example, correspondence information CT used for allocating subcarriers SCi described below) are recorded, and a volatile memory in which the control program, etc. are temporarily deployed. The control unit 23 communicates with the switch 22 via, for example, Ethernet, and communicates with the optical transceiver 21 via serial communication such as I2C.

[0053] When the switch 22 receives an Ethernet control frame addressed to the optical network unit (home device) 2, the switch 22 transfers the received control frame to the control unit 23. The control unit 23 performs various setting processes for the optical network unit 2 based on the setting information included in the control frame received via serial communication such as I2C. For example, the control unit 23 may perform initial settings such as subcarrier settings for the optical transceiver 21, QoS settings for the switch 22, bandwidth settings for each port of the switch 22, and VLAN settings.

[0054] When the TRxs can perform control communication using a dedicated control channel (control wavelength), the setting information of the optical transceiver 11 of the optical network unit 2 (except for the carrier setting information) can be transmitted by the control communication. However, the carrier setting for the optical transceiver 11 is performed directly by the controller 10 or a controller not shown, without going through the optical line terminal 1.

[0055] [Problems when installing two HUBs] Figure 2 is an explanatory diagram showing an example of a problem with a LEAF communicating with two HUBs. The meanings of the parameters in Figure 2 are as follows:

[0056] SCi: Subcarrier (i is an identification number). As an example, the carrier width of the subcarrier SCi is 4 GHz (equivalent to a data rate of 25 Gbps). A predetermined guard band (for example, 0.3 GHz) is provided between each subcarrier SCi. Gj: A group including a plurality of subcarriers SCi. Here, as an example, one group Gj includes four subcarriers.

[0057] HUB1: A HUB that is communicating with four LEAFs 1, 2, 3, and 4. As an example, let us assume that the center frequency of the wavelength band used by HUB1 is "fH1." The wavelength band includes the frequency bands of four groups G1, G2, G3, and G4. The frequency fH1 is located near the center of the wavelength grid (typically in the middle) so that the groups G1, G2, G3, and G4 are located within the same wavelength grid.

[0058] HUB2: A HUB that is communicating with one LEAF 5. As an example, let us assume that the center frequency of the wavelength band used by HUB2 is "fH2" (where fH2>fH1). The wavelength band includes the frequency bands of four groups G5, G6, G7, and G8. To ensure that groups G5, G6, G7, and G8 are located within the same wavelength grid, fH2 is located near the center of the wavelength grid (typically in the middle).

[0059] LEAF1: One of the LEAFs communicating with HUB1. As an example, it is assumed here that LEAF1 is using group G1. LEAF2: One of the LEAFs communicating with HUB1. As an example, it is assumed here that LEAF2 is using group G2.

[0060] LEAF3: One of the LEAFs communicating with HUB1. As an example, it is assumed here that LEAF3 is using group G3. LEAF4: One of the LEAFs communicating with HUB1. As an example, it is assumed here that LEAF4 is using group G4.

[0061] LEAF5: One of the LEAFs communicating with HUB2. As an example, let us assume that LEAF5 is using group G6. Therefore, there are free frequency bands in three groups, G5, G7, and G8, for communication with HUB2.

[0062] As shown in Figure 2, in an optical communication system operating with two HUBs 1 and 2 and five LEAFs 1, 2, 3, 4, and 5, it is assumed that LEAF 4, which is communicating with HUB 1, is connected to HUB 2 for communication redundancy or load sharing. In this case, for example, the following measures 1 or 2 can be adopted.

[0063] Measure 1: Add an optical transceiver for HUB2 to LEAF4, and assign the added optical transceiver to one of the available groups G5, G7, or G8. Strategy 2: Any of the vacant groups G5, G7, and G8 is assigned to the currently used optical transceiver 21 of LEAF4 that communicates with HUB1.

[0064] However, Measure 1 requires the installation of additional optical transceivers, which increases costs. On the other hand, Measure 2 requires the suspension of communication with the existing HUB 1 when setting up groups G5, G7, and G8 in the optical transceiver 21 of LEAF 4. In view of the above-mentioned problems, in this embodiment, a suitable method for allocating subcarriers SCi has been found for a LEAF4 that is in communication with HUB1 and will start connecting to HUB2, so that it can be appropriately connected to HUB1 and HUB2 even with a single optical transceiver 21. This point will be explained below.

[0065] [Solution to the problem] Fig. 3 is an explanatory diagram showing an example of a solution to the problem. The meanings of the parameters in Fig. 3 are as follows:

[0066] X: Identifier of a communication node. Identifier H1 represents HUB1. Identifier H2 represents HUB2. Identifier L represents a LEAF that communicates with HUB1 and HUB2. fXBW: A frequency band (e.g., 68.5 GHz) that can be modulated and demodulated by the optical transceiver of communication node X. Although Fig. 3 illustrates the case where fH1BW = fH2BW = fLBW, fH1BW, and fLBW may be different values ​​(including the case where any two are the same).

[0067] fXcent: The center frequency of communication node X. fXmin: The minimum frequency that the optical transceiver of communication node X can modulate / demodulate. fXmax: The maximum frequency that the optical transceiver of communication node X can modulate or demodulate. N:LEAF is the number of subcarriers (1 or more) used for communication with one HUB. CW: Carrier width of the subcarrier (for example, 4 GHz).

[0068] From the above parameter definitions, the following equalities and inequalities hold: fXBW=fXmax- fXmin fXcent=(fXmin+fXmax) / 2 fH1cent <fH2cent

[0069] Here, in order for one LEAF to communicate with HUB1, it is sufficient to satisfy the following conditions C1 and C2. Condition C1: The overlap range between the LEAF's modulatable frequency bandwidth fLBW and the HUB1's modulatable frequency bandwidth fH1BW is equal to or greater than the frequency bandwidth of the number N of subcarriers used for communication with HUB1. In other words, the following formula (a) is satisfied: fH1max-fLmin≧CW×N ……(a) Condition C2: LEAF uses subcarriers in the range of not less than fLmin and not more than fH1max.

[0070] Similarly, for one LEAF to communicate with HUB2, the following conditions C3 and C4 need to be satisfied. Condition C3: The overlapping range of the LEAF's modulatable frequency bandwidth fLBW and the HUB2's modulatable frequency bandwidth fH2BW is equal to or greater than the frequency bandwidth of the number N of subcarriers used for communication with HUB2. In other words, the following formula (b) is established: fLmax-fH2min≧CW×N ……(b) Condition C4: LEAF uses subcarriers in the range of not less than fH2min and not more than fLmax.

[0071] Therefore, in this embodiment, a subcarrier SCi that satisfies the above conditions C1 to C4 is assigned in advance to one optical transceiver 21 implemented in a LEAF.

[0072] In this way, a subcarrier SCi capable of communicating with the two HUBs 1 and 2 can be set in the optical transceiver 21, making it possible to connect to HUB 2 without adding an optical transceiver for HUB 2 or stopping communication with HUB 1. Therefore, communication redundancy or load balancing can be achieved without incurring high costs or communication outages.

[0073] [Subcarrier allocation example] FIG. 4 is a diagram showing a first example of allocation of subcarriers SCi to a LEAF that communicates with two HUBs 1 and 2. In FIG. As shown in FIG. 4, in the first allocation example, the modulation / demodulation frequency width fLBW of LEAF is eight subcarriers SCi, and the center frequency fLcent is allocated between group G4 of HUB1 and group G5 of HUB2.

[0074] Therefore, LEAF can communicate with HUB1 using subcarriers SC13 to SC16 of group G4, and can communicate with HUB1 using subcarriers SC17 to SC20 of group G5. In the first allocation example, subcarrier SC16 of group G4 and subcarrier SC17 of group G5 are adjacent to each other with the same interval as the guard band of subcarrier SCi. Therefore, compared to the second allocation example (FIG. 5) described later, this has the advantage of preventing bandwidth waste.

[0075] FIG. 5 is a diagram showing a second example of allocation of subcarriers SCi to a LEAF that communicates with two HUBs 1 and 2. In FIG. In FIG. 5, a predetermined number (for example, two) of subcarriers (hatched with diagonal lines) intervening between group G4 and group G5 are dummy subcarriers not used by LEAF.

[0076] As shown in FIG. 5, in the second allocation example, the modulation / demodulation frequency width fLBW of LEAF is 10 subcarriers SCi, and the center frequency fLcent is allocated between two dummy carriers. Therefore, LEAF can communicate with HUB1 using subcarriers SC13 to SC16 of group G4, and can communicate with HUB1 using subcarriers SC17 to SC20 of group G5.

[0077] In the second allocation example, an empty wavelength width corresponding to two subcarriers is interposed between subcarrier SC16 of group G4 and subcarrier SC17 of group G5. Therefore, compared to the first allocation example (FIG. 4) described above, this has the advantage of making it easier to prevent interference between carriers.

[0078] In the second allocation example of FIG. 5, if the modulatable frequency width fLBW of the LEAF is eight subcarriers, the LEAF may communicate with HUB1 using subcarriers SC14 to SC16 and with HUB2 using subcarriers SC17 to SC19.

[0079] [Optical transceiver in central office equipment] FIG. 6 is a block diagram showing an example of the configuration of the optical transceiver 11 of the optical line terminal 1. As shown in FIG. The optical transceiver 11 in Figure 6 is an SCM coherent optical transceiver. Since the wavelength λ (m) is a physical quantity obtained by dividing the speed of light c (m / s) by the frequency f (Hz), in the following explanation, the term "subcarrier" can also be referred to as frequency. The meanings of "TSm" and "RSm" in Figure 6 are as follows:

[0080] m: An identification number of an interface (port) used to connect the optical transceiver 11 and the switch 12. Hereinafter, this is also referred to as a "port number." TSm: an electrical signal input from the switch 12 to the optical transceiver 11. Since TSm is an electrical signal that is the source of a downstream optical signal, it is also referred to as a "transmission signal" below. RSm: An electrical signal input from the optical transceiver 11 to the switch 12. Since RSm is an electrical signal based on an upstream optical signal, it is also referred to as a "received signal" below.

[0081] The optical transceiver 11 includes a light source 101, an optical splitter 102, a first signal processing unit 103, a DAC (Digital Analog Converter) 104, an optical transmitting unit 105, an optical receiving unit 106, an ADC (Analog Digital Converter) 107, a second signal processing unit 108, and a processor 110. The multiplexed optical signal Oout output from the optical transmitter 105 is sent to the downstream optical fiber (trunk 4d). The upstream optical signal from the upstream optical fiber (trunk 4u) is input to the optical receiver 106 as the multiplexed optical signal Oin.

[0082] The processor 110 may be an integrated circuit such as an MPU (Micro Processing Unit), etc. The first signal processing unit 103 and the second signal processing unit 108 may be a digital signal processor (DSP), for example. The light source 101 is, for example, a semiconductor laser diode. The laser diode is, for example, a diode with a variable emission wavelength, but the emission wavelength may also be fixed. The wavelength of the light source 101 corresponds to the wavelength of the carrier transmitted and received by the optical line terminal 1.

[0083] The optical splitter 102 splits the output light of the light source 101 in two directions. One of the split lights is sent to the optical transmitter 105 as transmission light. The other of the split lights is sent to the optical receiver 106 as local light. The local light is used for coherent detection in the optical receiver 106. In this way, the light source 101 is used for both transmission and reception, and functions as both a transmission light source and a local light source, which contributes to the miniaturization, low power consumption, and low cost of the optical transceiver 11.

[0084] The first signal processing unit 103 generates a drive signal for the optical transmitting unit 105 according to the transmission signal (electrical signal) TSm by digital signal processing. The second signal processing unit 108 performs predetermined digital signal processing on the input signal from the ADC 107 and outputs a received signal (electrical signal) RSm. The correspondence between the port number m and the identification number i of the subcarrier SCi is specified by the processor 110 in advance.

[0085] Therefore, the first signal processing unit 103 and the second signal processing unit 108 transmit and receive at least one subcarrier SCi for each port number m. This allows multiple subcarriers SCi to be shared or divided. The digital signal processing of the second signal processing unit 108 may include at least one of dispersion compensation, sampling phase synchronization, adaptive equalization, frequency offset compensation, carrier phase recovery, and error correction decoding.

[0086] The first signal processing unit 103 and the second signal processing unit 108 can simultaneously perform transmission processing and reception processing on the transmission signal TSm and reception signal RSm for each port number m corresponding to the subcarrier SCi. In this case, the transmission signal TSm and the reception signal RSm may be a signal that aggregates a plurality of channels associated with the subcarrier SCi.

[0087] The DAC 104 converts the digital drive signal generated by the first signal processing unit 103 into an analog drive signal. The analog drive signal is amplified by a driver amplifier or the like and output to the optical transmitting unit 105. The ADC 107 converts the analog electrical signal input from the optical receiving unit 106 according to the modulation method such as the power and phase of the signal light into a digital electrical signal, and outputs the converted digital electrical signal to the second signal processing unit 108.

[0088] The optical transmitter 105 is driven by a drive signal having a signal waveform corresponding to the transmission signal TSm, modulates the transmission light with the transmission data signal, and outputs the modulated multiplexed optical signal Oout as a downstream optical signal. The modulation method may be multi-level phase shift keying (PSK), multi-level quadrature amplitude modulation (QAM), etc. Furthermore, multiplexing such as polarization multiplexing or orthogonal frequency division multiplexing (OFDM) may be performed for one wavelength.

[0089] The upstream optical signal is input to the optical receiving unit 106 as a multiplexed optical signal Oin. The optical receiving unit 106 mixes the local light and the upstream multiplexed optical signal Oin using, for example, a 90-degree hybrid mixer, and separates them into optical signals of multiple systems each including an I component and a Q component.

[0090] The optical receiving unit 106 includes a conversion unit such as a photodiode-trans impedance amplifier (PD-TIA) array, etc. The conversion unit converts the separated optical signals into electrical signals according to the received optical power. The converted electrical signal is converted into a digital signal by the ADC 107 and output to the second signal processing unit .

[0091] The processor 110 controls the components included in the optical transceiver 11 and is, for example, a one-chip microcontroller. The microcontroller may be configured by, for example, a micro processing unit (MPU), a logic circuit such as an FPGA or a complex programmable logic device (CPLD), or a combination of these.

[0092] The processor 110 is capable of serial communication with the control unit 13 acting as the master, and therefore the processor 110 is capable of executing predetermined slave processing led by the control unit 13. The predetermined slave processing includes, for example, a process of notifying the control unit 13 of the received optical power monitored in the optical receiving unit 106. If the second signal processing unit 108 has a function such as forward error correction (FEC), the above-mentioned slave processing also includes a process of notifying the control unit 13 of the monitored bit error rate.

[0093] The processor 110 can control, in response to an instruction from the control unit 13, whether to use all or a part (for example, half) of the plurality of subcarriers SCi. Specifically, the processor 110 generates a control signal CS1 that modulates the subcarrier SCi corresponding to the transmission port number m instructed by the control unit 13, and outputs the generated control signal CS1 to the optical transmitting unit 105. Similarly, the processor 110 generates a control signal CS2 for demodulating the subcarrier SCi corresponding to the receiving port number m instructed by the control unit 13, and outputs the generated control signal CS2 to the optical receiving unit .

[0094] [Optical transceiver of home device] FIG. 7 is a block diagram showing an example of the configuration of the optical transceiver 21 of the optical network unit 2. As shown in FIG. The optical transceiver 21 in Figure 7 is an SCM coherent optical transceiver. Since the wavelength λ (m) is a physical quantity obtained by dividing the speed of light c (m / s) by the frequency f (Hz), in the following explanation, "subcarrier" can also be referred to as frequency. The meanings of "TSn" and "RSn" in Figure 7 are as follows:

[0095] n: An identification number of an interface (port) used to connect the optical transceiver 21 and the switch 22. Hereinafter, this is also referred to as a "port number." TSn: an electrical signal input from the switch 22 to the optical transceiver 21. Since TSn is an electrical signal that is the source of an upstream optical signal, it is also referred to as a "transmission signal" below. RSn: An electrical signal input from the optical transceiver 21 to the switch 22. Since RSn is an electrical signal based on a downstream optical signal, it is also referred to as a "received signal" below.

[0096] The optical transceiver 21 includes a light source 201, an optical splitter 202, a first signal processing unit 203, a DAC 204, an optical transmitting unit 205, an optical receiving unit 206, an ADC 207, a second signal processing unit 208, a processor 210, and a memory 211. The multiplexed optical signal Oout output from the optical transmitter 205 is sent to an upstream optical fiber (branch line 5u). A downstream optical signal from a downstream optical fiber (branch line 5d) is input to the optical receiver 206 as a multiplexed optical signal Oin.

[0097] The processor 210 may be an integrated circuit such as an MPU, etc. The first signal processing unit 203 and the second signal processing unit 208 may be a DSP, for example. The light source 201 is, for example, a semiconductor laser diode. The laser diode is, for example, a diode with a variable emission wavelength, but the emission wavelength may be fixed. The wavelength of the light source 201 corresponds to the wavelength of the carrier transmitted and received by the optical network unit 2.

[0098] The optical splitter 202 splits the output light of the light source 201 in two directions. One of the split lights is sent to the optical transmitter 205 as transmission light. The other of the split lights is sent to the optical receiver 206 as local light. The local light is used for coherent detection in the optical receiver 206. In this way, the light source 201 is used for both transmission and reception, and functions as both a transmission light source and a local light source, which contributes to reducing the size, power consumption, and cost of the optical transceiver 21.

[0099] The first signal processing unit 203 generates a drive signal for the optical transmitting unit 205 according to the transmission signal (electrical signal) TSn by digital signal processing. The second signal processing unit 208 performs predetermined digital signal processing on the input signal from the ADC 207 and outputs a received signal (electrical signal) RSn. The correspondence between the port number n and the identification number i of the subcarrier SCi is specified in advance by the processor 210.

[0100] Therefore, the first signal processing unit 203 and the second signal processing unit 208 transmit and receive at least one subcarrier SCi for each port number n. This allows multiple subcarriers SCi to be shared or divided. The digital signal processing of the second signal processing unit 208 may include at least one of dispersion compensation, sampling phase synchronization, adaptive equalization, frequency offset compensation, carrier phase recovery, and error correction decoding.

[0101] The first signal processing unit 203 and the second signal processing unit 208 can simultaneously perform transmission processing and reception processing for the transmission signal TSn and reception signal RSn for each port number n corresponding to the subcarrier SCi. In this case, the transmission signal TSn and the reception signal RSn may be a signal that aggregates a plurality of channels associated with the subcarrier SCi.

[0102] The DAC 204 converts the digital drive signal generated by the first signal processing unit 203 into an analog drive signal. The analog drive signal is amplified by a driver amplifier or the like and output to the optical transmitting unit 205. The ADC 207 converts an analog electrical signal corresponding to the power of the signal light input from the optical receiving unit 206 into a digital electrical signal, and outputs the converted digital electrical signal to the second signal processing unit 208 .

[0103] The optical transmitter 205 is driven by a drive signal having a signal waveform corresponding to the transmission signal TSn, modulates the transmission light with the transmission data signal, and outputs the modulated multiplexed optical signal Oout as an upstream optical signal. The modulation method may be multi-level PSK, multi-level QAM, etc. Furthermore, multiplexing such as polarization multiplexing or orthogonal frequency division multiplexing (OFDM) may be performed for one wavelength.

[0104] The downstream optical signal is input to the optical receiving unit 206 as a multiplexed optical signal Oin. The optical receiving unit 206 mixes the local light and the upstream multiplexed optical signal Oin using, for example, a 90-degree hybrid mixer, and separates them into optical signals of multiple systems each including an I component and a Q component.

[0105] The optical receiving section 206 includes a conversion unit such as a PD-TIA array, etc. The conversion unit converts the separated optical signals into electrical signals according to the optical reception power. The converted electrical signal is converted into a digital signal by the ADC 207 and output to the second signal processing unit 208 .

[0106] The processor 210 controls the components included in the optical transceiver 21 and is, for example, a one-chip microcontroller. The microcontroller may be configured by, for example, an MPU, a logic circuit such as an FPGA or a CPLD, or a combination of these.

[0107] The processor 210 is capable of serial communication with the control unit 23 acting as the master, and therefore the processor 210 is capable of executing predetermined slave processing led by the control unit 23. The predetermined slave processing includes, for example, a process of notifying the control unit 23 of the received optical power monitored in the optical receiving unit 206. If the second signal processing unit 208 has a function such as forward error correction (FEC), the above-mentioned slave processing also includes a process of notifying the control unit 23 of the monitored bit error rate.

[0108] The processor 210 can control whether to use all or a part (for example, half) of the plurality of subcarriers SCi in accordance with an instruction from the control unit 23. Specifically, the processor 210 generates a control signal CS3 that modulates the subcarrier SCi corresponding to the transmission port number n instructed by the control unit 23, and outputs the generated control signal CS3 to the optical transmitting unit 105. Similarly, the processor 210 generates a control signal CS4 for demodulating the subcarrier SCi corresponding to the receiving port number n instructed by the control unit 23, and outputs the generated control signal CS2 to the optical receiving unit 206.

[0109] In this embodiment, the transmission signal TSn and reception signal RSn of the optical transceiver 21 of the home device 2 are part of the channels included in the transmission signal TSn and reception signal RSn of the optical transceiver 11 of the station side device 1, and are signals corresponding to channels allocated exclusively to other home device 2 (excluding signals of multicast channels). Therefore, the first signal processing unit 203 and the second signal processing unit 208 only need to process the subcarriers SCi corresponding to the transmission and reception channels.

[0110] [Subcarrier allocation] 1, correspondence information CT recorded in memory 25 is information that indicates the correspondence relationship between, for example, a VLAN_ID (hereinafter referred to as "VID") and a port number n. The correspondence information CT is used, for example, to allocate subcarriers SCi.

[0111] Specifically, the control unit 23 transmits the correspondence information CT recorded in the memory 25 to the switch 22, and the switch 22 switches the port number n based on the VID, thereby allocating the subcarriers. For example, it is assumed that the correspondence relationships between the correspondence information CT instructing the switch 22, the port number n set in the optical transceiver 21, and the subcarriers SC13 to SC20 in FIG. 4 are as follows:

[0112] (Support information CT) VID=101→n=1 VID=102→n=2 VID=103→n=3 VID=104→n=4 VID=105→n=5 VID=106→n=6 VID=107→n=7 VID=108→n=8

[0113] (Correspondence set in the optical transceiver) n=1 → Subcarrier SC13 n=2 → Subcarrier SC14 n=3 → Subcarrier SC15 n=4 → Subcarrier SC16 n=5 → Subcarrier SC17 n=6 → Subcarrier SC18 n=7 → Subcarrier SC19 n=8 → Subcarrier SC20

[0114] When the VID value is "101", the switch 22 in which the correspondence information CT is set inputs the transmission signal TS1 to the optical transceiver 21, and the optical transceiver 21 assigns the subcarrier SC13 to the input transmission signal TS1. Furthermore, when the VID value is "102," the switch 22 inputs the transmit signal TS2 to the optical transceiver 21, and the optical transceiver 21 assigns the subcarrier SC14 to the input transmit signal TS2. The same applies when the VID value is "103" or later.

[0115] In this way, either subcarriers SC13 to SC16 for HUB1 or subcarriers SC17 to SC20 for HUB2 are selected according to the VID value based on the correspondence information CT between the VID value and port number n and the correspondence relationship between port number n and identification number i. That is, the switch 22 of the optical network unit 2 functions as a "carrier selection unit" that selects the subcarrier SCi that the optical transceiver 21 allocates to the transmission signal TSn based on the VID value, which is a type of field value that indicates the type of communication frame.

[0116] According to the optical network unit 2 of this embodiment, the switch 22 has the above-mentioned carrier selection function, so that the transmission signal TSn can be appropriately allocated to the HUB1 and the HUB2. Therefore, by changing the correspondence relationship defined by the correspondence information CT according to the use case, the following "redundant switching" and "switching for load balancing" become possible.

[0117] 1) Redundancy switching Redundancy switching is a switching in which, when HUB1 is the active system and HUB2 is the standby system, the subcarrier used for the transmission signal TSn is shifted from the subcarrier SCi for HUB1 to the subcarrier SCi for HUB2, and optical communication is shifted from HUB1 to HUB2. A specific example of switching is to assign VID=101 to subcarrier SC13 during normal operation, and to subcarrier SC17 when a failure occurs.

[0118] 2) Switching for load balancing The load balancing switch is a switch that adds subcarriers SC17-SC20 for HUB2 to subcarriers SC13-SC16 for HUB1 during operation. In this case, if a failure occurs in either subcarriers SC13-SC15 or subcarriers SC17-SC20 after the switch, the subcarriers may be biased to the side without the failure.

[0119] In the above-described allocation of subcarriers SCi, a plurality of subcarriers SCi may be combined to form one large-capacity channel. For example, a 100 Gbps channel may be configured by combining four subcarriers SCi, each with a communication capacity of 25 Gbps. In this case, the channel configured by subcarriers SC13 to SC16 may be identified by one VID value (e.g., 101), and the channel configured by subcarriers SC17 to SC20 may be identified by another VID value (e.g., 105).

[0120] Furthermore, in the above-mentioned correspondence information CT, the information that is associated with the subcarrier identification information i via the port number n is not necessarily limited to a VID value. Specifically, the information associated with the identification information i of the subcarrier SCi via the port number n can be a destination MAC address or a predetermined field value such as EtherType that indicates the type of communication frame such as an Ethernet frame.

[0121] [Modification of Optical Communication System] FIG. 8 is a block diagram showing a modified example of the optical communication system 200. In FIG. The modified example of Figure 8 differs from the configuration example of Figure 1 in that an optical line 3 is employed in which, for example, a ROADM (Reconfigurable Optical Add / Drop Multiplexer) network 300, which is a type of core network, is interposed between each optical coupler 6d, 6u and the optical line terminal 1.

[0122] The ROADM network 300 is a network in which a plurality of ROADMs that transfer optical signals without electrical regeneration are configured in one or more ring configurations. The ROADM network 300 in the figure includes a ROADM 301, a ROADM 302, and a ROADM 303. The ROADM 301 is connected to one optical line terminal 1A via trunk lines 4d and 4u. The ROADM 302 is connected to the other optical line terminal 1B via trunk lines 4d and 4u. The ROADM 303 is connected to a downstream optical coupler 6d via trunk line 4d and to an upstream optical coupler 6u via trunk line 4u.

[0123] ROADMs 301, 302, and 303 each have two optical interfaces so that an optical path is formed between downstream trunk lines 4d in the downstream direction, and an optical path is formed between upstream trunk lines 4u in the upstream direction.

[0124] For downstream communication, the ROADM 301 transfers, within the ring, a downstream optical signal received from the trunk 4d connected to the optical line terminal 1A. The ROADM 302 transfers, within the ring, a downstream optical signal received from the trunk 4d connected to the optical line terminal 1B. The ROADM 301 transmits the downstream optical signal received from the ring to the trunk line 4d leading to the downstream optical coupler 6d.

[0125] For upstream communications, upstream optical signals sent from each optical network unit 2 are aggregated by an optical coupler 6u onto a trunk line 4u and reach the ROADM 303. The upstream optical signals are then distributed to optical paths in wavelength (grid) units by the ROADM 303 and transferred within the ring. The ROADM 301 transfers an upstream optical signal received from the ROADM 303 side of the ring to the optical line terminal 1A, and the ROADM 302 transfers an upstream optical signal received from the ROADM 303 side of the ring to the optical line terminal 1B.

[0126] As in the modification shown in FIG. 8, when the optical line 3 includes a ROADM network 300, the route of the optical path is switched depending on the wavelength in the ROADM, and therefore, an unusable area (forbidden band) may occur at the boundary between wavelengths. Therefore, when setting subcarriers SCi to an optical network unit 2A that communicates with multiple optical line terminals 1A and 1B, it is preferable to adopt the above-mentioned "second allocation example" (Figure 5) so as not to use the forbidden band between the wavelengths used by the optical line terminals 1A and 1B.

[0127] In the optical communication system 200 of FIG. 8, the network interposed between the optical coupler 6 and the optical line terminal 1 may not be the ROADM network 300, but may be an optical switch network including a plurality of optical switches connected in a predetermined topology.

[0128] [Other Modifications] The embodiments disclosed herein are illustrative in all respects and are not restrictive. The scope of the present invention is not limited to the above-described embodiments, but includes all modifications within the scope of equivalents to the configurations described in the claims.

[0129] In the above-described embodiment, the number of station side devices 1 (HUBs) is not limited to two, and three or more may be provided. When three HUBs are provided, the subcarriers SCi of two LEAFs may be set, for example, as follows.

[0130] 1) The communication partners of LEAF1 are HUB1 and HUB2, and the above-mentioned allocation policy is applied to the subcarriers SCi that can be used by HUB1 and HUB2. 2) The communication partners of LEAF2 are HUB2 and HUB3, and the above-mentioned allocation policy is applied to the subcarriers SCi that can be used by HUB2 and HUB3.

[0131] In the above-described embodiment, a single-core bidirectional optical line 3 may be used, which is made up of one ODN that transmits both downstream and upstream optical signals. In this case, when reflection at the ODN is small (for example, when the intensity of reflected light detected by the optical line terminal 1 is below a threshold), the allocation of the subcarriers SCi described above (FIGS. 3 and 4) is possible in both the upstream and downstream directions. On the other hand, when reflection from the optical line 3 is large (for example, when the intensity of reflected light detected by the optical line device 1 is equal to or greater than a threshold), the allocation of subcarriers SCi may be divided into upstream and downstream directions to halve the bandwidth. [Explanation of symbols]

[0132] 1 Station side device (HUB) 1A Station side device (HUB) 1B Station side equipment (HUB) 2. Home device (LEAF) 2A Home equipment (LEAF) 2B Home side equipment (LEAF) 2C Home equipment (LEAF) 3. Fiber optic lines 3d downstream ODN 3u upstream ODN 4d Main line (downbound) 4u trunk line (upbound) 5d Branch line (downbound) 5u branch line (upbound) 6d Optical coupler (downstream) 6u optical coupler (upstream) 7 Upper network 8 Lower network 9 Management network 10 Controller 11 Optical transceiver in central office equipment 12. Central office equipment switch 13. Control unit of central office equipment 14 CPU 15 memory 21 Optical transceiver of home equipment 22 Home device switch (carrier selection unit) 23 Control unit of home device 24 CPU 25 memory 101 Light source 102 Optical splitter 103 First signal processing section 104 DAC 105 Optical transmitter 106 Optical receiver 107 ADC 108 Second signal processing section 110 processors 200 Optical Communication Systems 201 Light source 202 Optical splitter 203 First signal processing section 204 DAC 205 Optical transmitter 206 Optical receiver 207 ADC 208 Second signal processing section 210 processors 211 memory 300 ROADM network 301 ROADM 302 ROADM 303 ROADM

Claims

1. An optical network unit capable of optical communication with two optical line terminals, a subcarrier multiplexing optical transceiver; a control unit that sets a plurality of subcarriers to be used by the optical transceiver; The plurality of subcarriers include: Satisfying the following formula (a) and formula (b): A subcarrier within a range equal to or greater than fLmin and equal to or less than fH1max is used for communication with the first optical line terminal, A home terminal that uses subcarriers in a range of not less than fH2min and not more than fLmax for communication with a second optical line terminal. fH1max-fLmin≧CW×N...(a) fLmax-fH2min≧CW×N...(b) however, fH1max: maximum frequency that the optical transceiver of the first optical line terminal can modulate / demodulate fH2min: The minimum frequency that the optical transceiver of the second optical line terminal can modulate and demodulate fLmax: Maximum frequency that the optical transceiver of the home device can modulate / demodulate fLmin: The minimum frequency that the optical transceiver of the home device can modulate and demodulate CW: Carrier width of subcarrier N: The number of subcarriers (one or more) that a home device uses to communicate with one central office device

2. The optical network device The optical network unit according to claim 1 , further comprising a carrier selection unit that selects subcarriers to which a transmission signal is to be assigned based on a field value that indicates a type of communication frame.

3. an optical network unit according to claim 1 or 2; the first optical line terminal having a subcarrier multiplexing optical transceiver; the second optical line terminal having a subcarrier multiplexing optical transceiver, An optical communication system, wherein the frequency band available to the first optical line terminal and the frequency band available to the second optical line terminal are adjacent to each other with an interval equal to the guard band of the subcarriers.

4. an optical network unit according to claim 1 or 2; the first optical line terminal having a subcarrier multiplexing optical transceiver; the second optical line terminal having a subcarrier multiplexing optical transceiver, an optical communication system in which an empty wavelength width corresponding to a predetermined number of the subcarriers that are not used by the optical network device is interposed between a frequency band that can be used by the first optical line terminal and a frequency band that can be used by the second optical line terminal.

5. A subcarrier selection method executed in an optical network unit having a subcarrier multiplexing optical transceiver when the optical network unit is optically communicating with two optical line terminals, comprising: a first step of extracting a field value representative of a type of transmitted signal; a second step of selecting subcarriers corresponding to the extracted field values.

6. The two optical line terminals The optical line terminal includes an optical line terminal of a working system and an optical line terminal of a standby system, The subcarriers selected in the second step are:

6. The subcarrier selection method according to claim 5, wherein the subcarriers are either subcarriers for the active system central office device or subcarriers for the standby system central office device.

7. The two optical line terminals a first optical line terminal and a second optical line terminal; The selection performed in the second step is:

6. The subcarrier selection method of claim 5, comprising selecting a subcarrier for the first optical line terminal with a first field value, and selecting a subcarrier for the second optical line terminal with a second field value different from the first field value.

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