Optical communication system, station-side device, and wavelength allocation method

Abstract

A system according to one aspect of the present disclosure is an optical communication system in which a plurality of house-side devices and a station-side device which are connected via an optical network perform full duplex wavelength-division multiplexed communication. The optical network includes a main line to which the station-side device is connected and a plurality of branch lines which branch from the main line and to which the plurality of house-side devices are respectively connected. The branch lines are each an optical transmission path of one core via which both an uplink optical signal and a downlink optical signal are transmitted. The station-side device has an optical transceiver in which, for both reception wavelength and transmission wavelength, there are two or more wavelengths with which operation is possible. The house-side devices each have an optical transceiver in which, for both reception wavelength and transmission wavelength, there is one or more wavelengths with which operation is possible. The reception wavelengths and transmission wavelengths of the plurality of house-side devices satisfy expression (1) and expression (2).　(1): Rλi∩Tλi=φ (2): AR1∩AT1≠φ

Description

Optical communication system, station side device, and wavelength allocation method

[0001] The present disclosure relates to an optical communication system, a station side device, and a wavelength allocation method.

[0002] Non-Patent Document 1 describes an optical transceiver that employs subcarrier multiplexing (SCM) technology, which uses digital signal processing to generate multiple subcarriers with different wavelengths using a single light source and transmits the generated subcarriers to an optical fiber. In Non-Patent Document 1, the subcarriers of upstream and downstream optical signals are separated into different wavelength bands. Therefore, even if the upstream and downstream optical signals interfere with each other, digital signal processing allows only the subcarriers of the signal light to be selectively received.

[0003] Journal of Lightwave Technology Volume:39, Issue:16, 15 August 2021

[0004] A system according to one aspect of the present disclosure is an optical communication system in which a station-side device and a plurality of optical network units connected by an optical line perform full-duplex wavelength division multiplexing communication, the optical line including a trunk line to which the station-side device is connected and a plurality of branch lines branching from the trunk line and to which the plurality of optical network units are respectively connected, the branch lines being single-core optical transmission paths through which both upstream optical signals and downstream optical signals are transmitted, the station-side device having an optical transceiver with two or more types of operable receiving wavelengths and two or more types of transmitting wavelengths, the optical network unit having an optical transceiver with one or more types of operable receiving wavelengths and one or more types of transmitting wavelengths, and the receiving wavelengths and transmitting wavelengths of the plurality of optical network units satisfy the following equations (1) and (2).

[0005] Rλi∩Tλi=φ (1) AR1∩AT1≠φ (2) where, i: identifier of at least two optical network units included in the system Rλi: set of receiving wavelengths used by the optical network unit with identifier i Tλi: set of transmitting wavelengths used by the optical network unit with identifier i AR1: set of receiving wavelengths used by at least two optical network units identified by identifier i AT1: set of transmitting wavelengths used by at least two optical network units identified by identifier i φ: empty set

[0006] 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.

[0007] FIG. 1 is a block diagram showing an example of the configuration of an optical communication system. FIG. 2 is a block diagram showing an example of the internal configuration of an optical transceiver of an optical line terminal device. FIG. 3 is a block diagram showing an example of the internal configuration of an optical transceiver of an optical network unit. FIG. 4 is an explanatory diagram of a "first allocation policy" of wavelengths. FIG. 5 is an explanatory diagram of a "second allocation policy" of wavelengths. FIG. 6 is an explanatory diagram of example 1 of wavelength allocation based on the second allocation policy. FIG. 7 is an explanatory diagram of example 2 of wavelength allocation based on the second allocation policy. FIG. 8 is an explanatory diagram of example 3 of wavelength allocation based on the second allocation policy. FIG. 9 is a flowchart showing an example of a process for determining allocation conditions. FIG. 10 is a flowchart showing an example of a process for allocating operating wavelengths. FIG. 11 is a flowchart showing another example of a process for allocating operating wavelengths. FIG. 12 is a flowchart showing another example of a process for allocating operating wavelengths. FIG. 13 is a block diagram showing a modified example of the optical transceiver of an optical line terminal device.

[0008] <Problem that the present disclosure aims to solve> In Non-Patent Document 1, in an optical communication system that connects a station side device and multiple home side devices in a P2MP format, it is not assumed that the multiple home side devices will share the receiving wavelength and the transmitting wavelength during operation, thereby effectively utilizing the communication bandwidth.

[0009] In view of the above-described conventional problems, the present disclosure aims to provide an optical communication system that can effectively utilize the communication bandwidth of optical network units.

[0010] <Effects of the Present Disclosure> According to the present disclosure, the communication band of an optical network unit can be effectively utilized.

[0011] <Outline of Embodiments of the Present Disclosure> The following is a description of outlines of embodiments of the present disclosure. (1) A system according to one aspect of the present embodiment is an optical communication system in which a station-side device and multiple optical network units connected by an optical line perform full-duplex wavelength division multiplexing communication, the optical line including a trunk line to which the station-side device is connected and multiple branch lines branching from the trunk line and to which the multiple optical network units are respectively connected, the branch lines being single-core optical transmission paths through which both upstream optical signals and downstream optical signals are transmitted, the station-side device has an optical transceiver with two or more operable receiving wavelengths and two or more operable transmitting wavelengths, the optical network unit has an optical transceiver with one or more operable receiving wavelengths and one or more operable transmitting wavelengths, and the receiving wavelengths and transmitting wavelengths of the multiple optical network units satisfy the following formulas (1) and (2):

[0012] Rλi∩Tλi=φ (1) AR1∩AT1≠φ (2) where, i: identifier of at least two optical network units included in the system Rλi: set of receiving wavelengths used by the optical network unit with identifier i Tλi: set of transmitting wavelengths used by the optical network unit with identifier i AR1: set of receiving wavelengths used by at least two optical network units identified by identifier i AT1: set of transmitting wavelengths used by at least two optical network units identified by identifier i φ: empty set

[0013] In the optical communication system of this embodiment, since the above formula (1) is satisfied, single-fiber bidirectional transmission is possible for multiple optical network units, with the wavelengths of downstream optical signals and upstream optical signals not overlapping. Furthermore, since the above formula (2) is satisfied, multiple optical network units under the central office unit share some or all of the receiving wavelength and transmitting wavelength. Therefore, the communication bandwidth of the optical network units can be effectively utilized.

[0014] (2) In the optical communication system of (1) above, if the optical signal having the wavelengths included in the set AR1 is largely reflected when the optical line terminal transmits the optical signal, the following equation (3) may be applied instead of the equation (2): AR1∩AT1=φ (3)

[0015] In this case, multiple optical network units under the optical line terminal use separate wavelengths for receiving and transmitting, preventing the optical line terminal from being unable to properly receive upstream optical signals due to reflections from optical couplers, etc.

[0016] (3) A system according to another aspect of the present embodiment is an optical communication system in which a station-side device and a plurality of optical network units connected by an optical line perform full-duplex wavelength division multiplexing communication, the optical line including a trunk line to which the station-side device is connected, a plurality of first branch lines branching from the trunk line and grouping the plurality of optical network units, and a second branch line branching from the first branch line and connecting the optical network units of the same group, the first branch line and the second branch line being a single-core optical transmission line through which both upstream optical signals and downstream optical signals are transmitted, the station-side device has an optical transceiver having two or more types of operable receiving wavelengths and two or more types of transmitting wavelengths, the optical network unit has an optical transceiver having one or more types of operable receiving wavelengths and one or more types of transmitting wavelengths, and the receiving wavelengths and transmitting wavelengths of the plurality of optical network units satisfy the following equations (4) and (5).

[0017] Rλji ∩ Tλji = φ (4) AR2 ∩ AT2 ≠ φ (5) where, j: identifiers of at least two groups included in the system i: identifier of at least one optical network unit included in the group with identifier j Rλji: set of receiving wavelengths operated by an optical network unit with identifier i in the group with identifier j Tλji: set of transmitting wavelengths operated by an optical network unit with identifier i in the group with identifier j AR2: set of receiving wavelengths operated by at least two optical network units assigned with identifier j and identifier i AT2: set of transmitting wavelengths operated by at least two optical network units assigned with identifier j and identifier i φ: empty set

[0018] In the optical communication system of this embodiment, since the above formula (4) is satisfied, single-fiber bidirectional transmission is possible for multiple optical network units, with the wavelengths of downstream optical signals and upstream optical signals not overlapping. Furthermore, since the above formula (5) is satisfied, multiple optical network units under the central office unit share some or all of the receiving wavelength and transmitting wavelength. Therefore, the communication bandwidth of the optical network units can be effectively utilized.

[0019] (4) In the optical communication system of (3) above, if the optical signal having the wavelengths included in the set AR2 is largely reflected when transmitted from the optical line terminal, the following equation (6) may be applied instead of the equation (5): AR2∩AT2=φ (6)

[0020] In this case, multiple optical network units under the optical line terminal use separate wavelengths for receiving and transmitting, preventing the optical line terminal from being unable to properly receive upstream optical signals due to reflections from optical couplers, etc.

[0021] (5) The optical line terminal of this embodiment is an optical line terminal used in the optical communication system of (2) or (4) described above, and includes the optical transceiver, a control unit that performs control communication with the plurality of optical line terminals, and a memory that stores allocation information for wavelength sharing that satisfies formula (2) or formula (5) and allocation information for wavelength divisions that satisfy formula (3) or formula (6), and when the reflection is small, the control unit determines the receiving wavelength and the transmitting wavelength during operation of the plurality of optical line terminals based on the allocation information for wavelength sharing.

[0022] According to the optical line terminal of this embodiment, the control unit determines the receiving wavelength and transmitting wavelength during operation of multiple optical line terminals based on allocation information for wavelength sharing, so that the optical line terminal can perform wavelength allocation that effectively utilizes the communication bandwidth of the optical line terminals.

[0023] (6) In the optical line terminal of the optical line terminal of the above-described (5), when the reflection is large, the control unit may determine the receiving wavelengths and transmitting wavelengths during operation of the plurality of optical network units based on the allocation information for the wavelength division. According to the optical line terminal of this embodiment, the control unit determines the receiving wavelengths and transmitting wavelengths during operation of the plurality of optical network units based on the allocation information for the wavelength division, so that the optical line terminal can perform wavelength allocation that prevents the optical line terminal from being unable to properly receive upstream optical signals.

[0024] (7) In the optical line terminal of the optical line terminal described above in (6), the control unit may notify the optical line terminals of the receiving wavelengths and transmitting wavelengths that the control unit has determined for the operation of the optical line terminals. This allows the optical line terminals to start operating at the receiving wavelengths and transmitting wavelengths that the optical line terminal has determined, making it easier to change the wavelength settings of the optical line terminals.

[0025] (8) In the optical line terminal device according to any one of (5) to (7) above, if the plurality of optical network units store their own allocation information for the wavelength sharing case and their own allocation information for the wavelength segment, the control unit may notify the plurality of optical network units of the wavelength sharing when the reflection is small, and may notify the plurality of optical network units of the wavelength segment when the reflection is large. In this way, the plurality of optical network units can autonomously select appropriate allocation information based on the notification from the optical line terminal device.

[0026] (9) A method according to one aspect of this embodiment is a wavelength allocation method executed by a station side device used in the optical communication system of (2) or (4) described above, and includes the steps of: storing allocation information for wavelength sharing that satisfies the formula (2) or the formula (5) and allocation information for wavelength divisions that satisfies the formula (3) or the formula (6); and, if the reflection is small, determining the receiving wavelengths and transmitting wavelengths during operation of the plurality of home side devices based on the allocation information for wavelength sharing.

[0027] According to the wavelength allocation method of this embodiment, when reflection is small, the method includes a step of determining the receiving wavelength and transmitting wavelength during operation of multiple optical network devices based on allocation information for wavelength sharing, thereby enabling wavelength allocation that effectively utilizes the communication bandwidth of the optical network device.

[0028] (10) The wavelength allocation method of (9) above may further include a step of determining, when the reflection is large, receiving wavelengths and transmitting wavelengths during operation of the plurality of optical network units based on the allocation information for the wavelength division. In this way, wavelength allocation that can further prevent the optical line unit from being unable to properly receive upstream optical signals can be realized.

[0029] (11) A method according to another aspect of the present embodiment is a wavelength allocation method that is applied to the optical communication system described in (1) above. Therefore, this wavelength allocation method provides the same effects as those of the optical communication system described in (1) above.

[0030] (12) A method according to another aspect of the present embodiment is a wavelength allocation method that is applied to the optical communication system described above in (2). Therefore, this wavelength allocation method provides the same effects as those of the optical communication system described above in (2).

[0031] (13) A method according to another aspect of the present embodiment is a wavelength allocation method that is applied to the optical communication system described above in (3). Therefore, this wavelength allocation method provides the same effects as those of the optical communication system described above in (3).

[0032] (14) A method according to another aspect of the present embodiment is a wavelength allocation method that is applied to the optical communication system described above in (4). Therefore, this wavelength allocation method provides the same effects as those of the optical communication system described above in (4).

[0033] <Details of Embodiments 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.

[0034] [Configuration Example of Optical Communication System] Fig. 1 is a block diagram showing a configuration example of an optical communication system 200. As shown in Fig. 1, the optical communication system 200 is a P2MP (Point to Multi Point) system in which an optical line terminal 1 and multiple optical network terminals 2 are connected via an optical fiber line 3. The optical line terminal 1 is installed, for example, in a central office of a telecommunications carrier. The optical network terminals 2 are installed, for example, in the premises of users who use communication services.

[0035] However, the terms "station side" and "residential side" are expressions that indicate the relative positions of the devices, and do not limit the installation locations of the devices. A controller 10 is connected to the station side device 1. The controller 10 is, for example, a management computer operated by a communications administrator.

[0036] In this embodiment, the direction from the optical line terminal 1 to the optical network unit 2 is referred to as the "downstream direction," and the opposite direction is referred to as the "upstream direction." The optical line terminal 1, the optical network unit 2, and the optical transceivers 11 and 21 may be expressed as follows: Optical line terminal 1 → "HUB" (meaning a device on the line concentrating side in an optical line) Optical network unit 2 → "LEAF" (meaning a device on the end side in an optical line) Optical transceivers 11 and 21 → "TRx"

[0037] The optical line 3 includes a trunk line 4 to which the optical line terminal 1 is connected, and a plurality of branch lines 5 that branch off from the trunk line 4 and to which a plurality of optical network units 2 are connected. The trunk line 4 and the branch lines 5 are connected by an optical coupler 6, which is a type of optical passive component. The trunk line 4 may be, for example, a two-core (two optical fibers) optical transmission line through which upstream and downstream optical signals are transmitted separately. The branch line 5 may be, for example, a single-core (one optical fiber) optical transmission line through which both upstream and downstream optical signals are transmitted.

[0038] In this case, the communication section from the optical line terminal 1 to the optical coupler 6 is "two-core transmission," and the communication section from the optical coupler 6 to the optical network unit 2 is "single-core bidirectional transmission." Note that a connection configuration in which another optical coupler is installed midway along the branch line 5 and the branch line 5 further branches (see FIG. 5). Furthermore, using two-core transmission for the trunk line 4 has the advantage that the optical coupler 6 reduces the impact of reflections on the optical line terminal 1 compared to the case of single-core transmission (see FIG. 13, for example).

[0039] In this embodiment, the optical line terminal 1 and optical network unit 2 communicate using full-duplex wavelength division multiplexing (WDM). Specifically, in downstream communication, an exclusive wavelength is assigned to the optical line terminal 1 and each optical network unit 2 (or each group), and each optical network unit 2 (or each group) can communicate simultaneously and individually. The same applies to upstream communication. However, the wavelengths for downstream communication and upstream communication do not have to be exclusive.

[0040] [Configuration Example of Optical Line Terminal] As shown in FIG. 1, an optical line terminal 1 includes an optical transceiver 11, a switch 12, and a control unit 13.

[0041] The optical transceiver 11 of the optical line terminal 1 is an optical module that converts optical signals into electrical signals and vice versa. For example, a CFP (Centum Form-factor Pluggable) digital coherent optical transceiver conforming to the Multi-Source Agreement (MSA) standard may be used. The optical transceiver 11 may also be an SFP (Small Form Factor Pluggable) optical transceiver. The SFP type is a general term for SFP, SFP+, SFP28, QSFP, QSFP28, and their upwardly compatible pluggable optical modules.

[0042] The optical transceiver 11 is an optical transceiver capable of operating at two or more types of receiving wavelengths and two or more types of transmitting wavelengths, and has a function for switching the wavelength λk (k = 1, 2, ...) of the optical signal used for transmission and reception. The optical signal may be a subcarrier. If the optical signal is divided into subcarriers, the optical transceiver may have a function for switching the subcarrier to wavelength λk. The wavelength λk switching function can be realized, for example, by a coherent optical transceiver using subcarrier multiplexing (SCM) (Figure 2). Multiple wavelengths λk may be bundled into one channel. Note that "channel" refers to a transmission path for an electrical signal or an optical signal.

[0043] A trunk line 4 (two optical fibers) is connected to the optical transceiver 11 of the optical line terminal 1. The optical transceiver 11 is electrically connected to a predetermined port of a switch 12. 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. A control unit 13 is electrically connected to the 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 SoC (System on a Chip).

[0044] The control unit 13 is an arithmetic processing device including, for example, a CPU (Central Processing Unit) 13A and a memory 13B. The memory 13B includes a non-volatile memory in which a predetermined control program and data required for executing the program (for example, setting information such as an operating wavelength, which will be described later) are recorded, and a volatile memory in which the control program and the like are temporarily loaded.

[0045] 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).

[0046] The control unit 13 can acquire predetermined setting information from the controller 10 through communication via a management communication interface (not shown). Based on the acquired setting information, the control unit 13 performs various setting processes for the optical line terminal 1 and the optical network terminal 2. For example, the control unit 13 can perform initial settings such as the wavelength to be 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.

[0047] The controller 10 is connected to, for example, the control unit 13 of the optical line terminal 1. However, a local area network (LAN) may be interposed between the optical line terminal 1 and the controller 10. The controller 10 transmits setting information for the optical line terminal 1 and setting information for the optical network terminal 2 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 controls the optical transceiver 11 of the optical line terminal 1 in accordance with the received setting information via serial communication such as I2C.

[0048] The control unit 13 of the optical line terminal 1 transfers the setting information for the optical network unit 2 to the optical network unit 2 by control communication (dashed arrow in FIG. 2 ) via the optical line 3. That is, if the received setting information is setting information for the optical transceiver 11 of the optical network unit 2, the control unit 13 of the optical line terminal 1 generates an Ethernet ("Ethernet" is a registered trademark) control frame addressed to the optical network unit 2 and including the received setting information, and outputs the control frame to the switch 12.

[0049] The control frame is transmitted to the control unit 13 of the optical network unit 2 via Ethernet communication. The control unit 13 of the optical network unit 2 controls its own optical transceiver 11 according to the received setting information via serial communication such as I2C. If 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 may be transmitted via that control communication.

[0050] 1, the optical network unit 2 includes an optical transceiver 21, a switch 22, and a control unit 23. The optical transceiver 21 of the optical network unit 2 is an optical module that converts optical signals into electrical signals and vice versa, and may be, for example, a CFP-type digital coherent optical transceiver conforming to the MSA standard. The optical transceiver 21 may also be an SFP-type optical transceiver.

[0051] The optical transceiver 21 is an optical transceiver capable of operating at least one type of receiving wavelength and one type of transmitting wavelength, and has a function for switching the wavelength λk (k = 1, 2, ...) of the optical signal used for transmission and reception. The optical signal may be a subcarrier. If the optical signal is divided into subcarriers, the optical transceiver may have a function for switching the subcarrier to the wavelength λk. The wavelength λk switching function can be realized, for example, by a coherent optical transceiver using subcarrier multiplexing (SCM) (Figure 3). Multiple wavelengths λk may be bundled together to form a single channel.

[0052] A branch line 5 (one optical fiber) is connected to the optical transceiver 21 of the optical network unit 2. The optical transceiver 21 is electrically connected to a predetermined port of a switch 22. The switch 22 is an integrated circuit such as an LSI that has relay functions for the L2 layer and the L3 layer. A control unit 23 is electrically connected to the 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.

[0053] The control unit 23 is an arithmetic processing unit including, for example, a CPU 23 A and a memory 23 B. The memory 23 B includes a non-volatile memory in which a predetermined control program and data required for executing the program (for example, setting information such as an operating wavelength, which will be described later) are recorded, and a volatile memory in which the control program and the like are temporarily loaded.

[0054] The control unit 23 may include an FPGA or an ASIC. The control unit 23 may be configured with at least one of an FPGA and an ASIC. The control unit 23 communicates with the switch 22 via, for example, Ethernet, and with the optical transceiver 21 via serial communication such as I2C.

[0055] When the switch 22 receives an Ethernet control frame addressed to the optical network unit (home device) 2, it transfers the received control frame to the control unit 23. The control unit 23 performs various setting processes for the optical network unit 2 via serial communication such as I2C based on the setting information included in the received control frame. For example, the control unit 23 may perform initial settings such as the wavelength used by the optical transceiver 21, QoS settings for the switch 22, bandwidth settings for each port of the switch 22, and VLAN settings.

[0056] If 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 can be transmitted through the control communication. Also, some or all of the settings of the optical network unit 2 may be performed directly from a controller (not shown) without going through the optical line terminal 1.

[0057] [Optical Transceiver of Optical Line Terminal Device] Figure 2 is a block diagram showing an example of the internal configuration of the optical transceiver 11 of the optical line terminal device 1. The optical transceiver 11 in Figure 2 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 a frequency.

[0058] The optical transceiver 11 includes a light source 101, an optical splitter 102, a first signal processing unit 103, a digital-to-analog converter (DAC) 104, an optical transmitting unit 105, an optical receiving unit 106, an analog-to-digital converter (ADC) 107, a second signal processing unit 108, and a processor 110. The processor 110 may be an integrated circuit such as an MPU (micro processing unit). The first signal processing unit 103 and the second signal processing unit 108 may be digital signal processors (DSPs). The light source 101 is, for example, a semiconductor laser diode. The laser diode may have a fixed or variable emission wavelength.

[0059] 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 processing, and functions as both a transmission light source and a local light source. This allows for the optical transceiver 11A to be made smaller, consume less power, and cost less.

[0060] The first signal processing unit 103 generates, by digital signal processing, a drive signal for the optical transmitting unit 105 in accordance with the transmission signal (electrical signal) TS. The second signal processing unit 108 performs predetermined digital signal processing on the input signal from the ADC 107 and outputs a reception signal (electrical signal) RS.

[0061] The first signal processing unit 103 and the second signal processing unit 108 can arbitrarily allocate multiple subcarriers to transmission and reception, thereby realizing sharing or division of multiple subcarriers. Note that 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, for example.

[0062] The first signal processing unit 103 and the second signal processing unit 108 can allocate the transmission signal TS and the reception signal RS to multiple subcarriers and simultaneously perform transmission processing and reception processing. In this case, the transmission signal TS and the reception signal RS may be signals that aggregate multiple channels associated with the subcarriers.

[0063] 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 corresponding to the power of the signal light input from the optical receiving unit 106 into a digital electrical signal, and outputs the converted digital electrical signal to the second signal processing unit 108.

[0064] The optical transmitter 105 is driven by a drive signal having a signal waveform corresponding to the transmission signal TS, and modulates the transmission light with a transmission data signal. The optical transmitter 105 outputs the modulated multiplexed optical signal Oout as a downstream optical signal. Modulation methods that may be used include multilevel phase shift keying (PSK) and multilevel quadrature amplitude modulation (QAM). Furthermore, multiplexing such as polarization multiplexing and orthogonal frequency division multiplexing (OFDM) may be performed on a single wavelength.

[0065] 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 the signals into multiple optical signals containing I and Q components. The optical receiving unit 106 includes a conversion unit such as a PD-TIA (Photodiode-Trans Impedance Amplifier) ​​array. The conversion unit converts the separated optical signals into electrical signals corresponding to the received optical power. The converted electrical signals are converted into digital signals by an ADC 107 and output to a second signal processing unit 108.

[0066] The processor 110 is, for example, a one-chip microcontroller that controls the components included in the optical transceiver 11 A. The microcontroller may be, for example, a microprocessing unit (MPU), a logic circuit such as an FPGA or a complex programmable logic device (CPLD), or a combination of these.

[0067] The processor 110 is capable of serial communication with the control unit 13 acting as the master. Therefore, the processor 110 can execute predetermined slave processing led by the control unit 13. The predetermined slave processing includes, for example, processing for notifying the control unit 13 of the received optical power monitored by the optical receiving unit 106. If the second signal processing unit 108 has a function such as forward error correction (FEC), the slave processing also includes processing for notifying the control unit 13 of the monitored bit error rate.

[0068] The processor 110 can control whether to use all or some (e.g., half) of the multiple subcarriers in accordance with instructions from the control unit 13. Specifically, the processor 110 generates a control signal CS1 that causes modulation of the transmission subcarriers 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 that causes demodulation of the reception subcarriers instructed by the control unit 13, and outputs the generated control signal CS2 to the optical receiving unit 106.

[0069] [Optical Transceiver of Optical Network Unit] Figure 3 is a block diagram showing an example of the internal configuration of the optical transceiver 21 of the optical network unit 2. The optical transceiver 21 in Figure 3 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 description, the term "subcarrier" can also be referred to as a frequency.

[0070] The optical transceiver 21 of the optical network unit 2 differs from the optical transceiver 11 ( FIG. 2 ) of the optical station unit 1 in that it includes an optical component 209 that branches an optical signal. The optical component 209 may be located outside the housing of the optical transceiver 21. The optical component 209 may be, for example, an optical coupler or an optical circulator. The multiplexed optical signal Oout output by the optical transmitting unit 205 is transmitted to the optical fiber (branch line 5) by the optical component 209, and the downstream optical signal from the optical fiber is branched by the optical component 209 and input to the optical receiving unit 206 as the multiplexed optical signal Oin.

[0071] 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, and a processor 210. The processor 210 may be an integrated circuit such as an MPU. The first signal processing unit 203 and the second signal processing unit 208 may be a DSP. The light source 201 is, for example, a semiconductor laser diode. The laser diode may have a fixed or variable emission wavelength.

[0072] 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 processing, and functions as both a transmission light source and a local light source. This allows for the optical transceiver 21 to be made smaller, consume less power, and cost less.

[0073] The first signal processing unit 203 generates, by digital signal processing, a drive signal for the optical transmitting unit 205 in accordance with the transmission signal (electrical signal) TS. The second signal processing unit 208 performs predetermined digital signal processing on the input signal from the ADC 207 and outputs a reception signal (electrical signal) RS.

[0074] The first signal processing unit 203 and the second signal processing unit 208 can arbitrarily allocate multiple subcarriers to transmission and reception, thereby realizing sharing or division of multiple subcarriers. Note that the digital signal processing of the second signal processing unit 208 may include, for example, at least one of dispersion compensation, sampling phase synchronization, adaptive equalization, frequency offset compensation, carrier phase recovery, and error correction decoding.

[0075] The first signal processing unit 203 and the second signal processing unit 208 can allocate the transmission signal TS and the reception signal RS to multiple subcarriers and perform transmission processing and reception processing simultaneously. In this case, the transmission signal TS and the reception signal RS may be signals that aggregate multiple channels associated with the subcarriers.

[0076] 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 the 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.

[0077] The optical transmitter 205 is driven by a drive signal having a signal waveform corresponding to the transmission signal TS, and modulates the transmission light with the transmission data signal. The optical transmitter 205 outputs the modulated multiplexed optical signal Oout as an upstream optical signal. Modulation methods that may be used include multilevel PSK and multilevel QAM. Furthermore, multiplexing such as polarization multiplexing and orthogonal frequency division multiplexing (OFDM) may be performed for a single wavelength.

[0078] The downstream optical signal is branched by an optical component 209 and 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 multiple optical signals containing I and Q components. The optical receiving unit 206 includes a conversion unit such as a PD-TIA array. The conversion unit converts the multiple separated optical signals into electrical signals corresponding to the received optical power. The converted electrical signals are converted into digital signals by an ADC 207 and output to a second signal processing unit 208.

[0079] The processor 210 is, for example, a one-chip microcontroller that controls the components included in the optical transceiver 21. The microcontroller may be, for example, an MPU, a logic circuit such as an FPGA or a CPLD, or a combination of these.

[0080] The processor 210 is capable of serial communication with the control unit 23 as the master. Therefore, the processor 210 can execute predetermined slave processing led by the control unit 23. The predetermined slave processing includes, for example, processing for notifying the control unit 23 of the received optical power monitored by the optical receiving unit 206. If the second signal processing unit 208 has a function such as forward error correction (FEC), the slave processing also includes processing for notifying the control unit 23 of the monitored bit error rate.

[0081] The processor 210 can control whether to use all or some (e.g., half) of the multiple subcarriers in accordance with instructions from the control unit 23. Specifically, the processor 210 generates a control signal CS3 that causes modulation of the transmission subcarriers 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 that causes demodulation of the reception subcarriers instructed by the control unit 23, and outputs the generated control signal CS2 to the optical receiving unit 206.

[0082] In this embodiment, the transmission signal TS and reception signal RS of the optical transceiver 21 of the optical network unit 2 are part of the channels included in the transmission signal TS and reception signal RS of the optical transceiver 11 of the optical line terminal 1, and are signals corresponding to channels (excluding multicast channel signals) exclusively assigned to other optical network units 2. Therefore, the first signal processing unit 203 and the second signal processing unit 208 only need to process subcarriers corresponding to the transmission and reception channels.

[0083] [First Wavelength Allocation Policy] Fig. 4 is an explanatory diagram of a "first wavelength allocation policy" applicable to the optical communication system 200 of this embodiment. The first allocation policy in Fig. 4 is a policy suitable for a unicast channel when the number of branching stages counted from the LEAF side is one.

[0084] As shown in Figure 4, an optical line 3 with one branching stage includes, for example, a trunk line 4 connected to a HUB, an optical coupler 6 connected to the trunk line 4, and a plurality of branch lines 5 branching from the optical coupler 6 and each connected to a plurality of LEAFs.

[0085] The parameters in the first allocation policy are defined as follows: In the following definitions, "LEAFi" means a LEAF with an identifier i. i: identifier of at least two LEAFs included in the system Rλi: set of receiving wavelengths λr operated by LEAFi Tλi: set of transmitting wavelengths λt operated by LEAFi

[0086] AR1: A set of receiving wavelengths λr operated by at least two LEAFs with an identifier i. AT1: A set of transmitting wavelengths λt operated by at least two LEAFs with an identifier i. φ: An empty set. hRλ: A set of receiving wavelengths operated by the HUB. hTλ: A set of transmitting wavelengths operated by the HUB.

[0087] In the following, a set of receiving wavelengths operated by a specific communication node is also referred to as a "receiving wavelength group," and a set of transmitting wavelengths operated by the communication node is also referred to as a "transmitting wavelength group." The receiving wavelength group and transmitting wavelength group are collectively referred to as "operating wavelengths." Since the HUB needs to transmit and receive optical signals to and from all subordinate LEAFi, the HUB's receiving wavelength group hRλ has elements of the set AT1, and the HUB's transmitting wavelength group hTλ has elements of the set AR1.

[0088] In the optical communication system 200 of this embodiment, since the LEAFi is a single-core bidirectional transmission, taking into consideration the influence of reflection on the LEAFi side, it is preferable that all LEAFi do not overlap the wavelengths of downstream optical signals and upstream optical signals. Therefore, in the first allocation policy, the following condition L1 is adopted as the "allocation condition for the operating wavelength of LEAF". Condition L1: Satisfying formula (1) Rλi∩Tλi=φ ... (1)

[0089] On the other hand, if the receiving wavelength group hRλ and the transmitting wavelength group hTλ of the HUB overlap, there is a possibility that a downstream optical signal of a certain wavelength will be reflected by the optical coupler 6 and mixed into the upstream optical signal due to the length of the trunk line 4 or individual differences in the optical coupler 6, and the HUB will not be able to properly receive the upstream optical signal of that wavelength. Therefore, in the first allocation policy, the following conditions L2 and L3 are further adopted as "allocation conditions for the operating wavelength of the LEAF". Condition L2: If the reflection on the HUB side is small, equation (2) must be satisfied. Condition L3: If the reflection on the HUB side is large, equation (3) must be satisfied. AR1∩AT1≠φ ... (2) AR1∩AT1=φ ... (3)

[0090] If condition L2 is adopted, multiple LEAFi under the HUB will share part or all of the receiving wavelength group AR1 and the transmitting wavelength group AT1. Therefore, the communication bandwidth of the entire optical communication system 200 can be effectively utilized. If condition L3 is adopted, multiple LEAFi under the HUB will use the receiving wavelength group AR1 and the transmitting wavelength group AT1 separately. Therefore, it is possible to prevent the HUB from being unable to properly receive upstream optical signals due to reflections at the optical coupler 6.

[0091] In addition, when an identifier i is assigned to some of the LEAFs included in the system, i.e., when LEAFi constitutes a subset of the LEAFs in the system, condition L2 may include satisfying "AR1 = AT1" in addition to satisfying equation (2).

[0092] [Second Wavelength Allocation Policy] Fig. 5 is an explanatory diagram of a "second wavelength allocation policy" applicable to the optical communication system 200 of this embodiment. The second wavelength allocation policy in Fig. 5 is a policy suitable for a unicast channel when the number of branching stages counted from the LEAF side is two.

[0093] The optical line 3 with two branching stages includes, for example, a trunk line 4 connected to a HUB, a first optical coupler 6A connected to the trunk line 4, and a plurality of first branch lines 5A branching from the first optical coupler 6A and grouping a plurality of LEAFs. The optical line 3 further includes a second optical coupler 6B connected to the first branch line 5A, and a plurality of second branch lines 5B branching from the second optical coupler 6B and connecting LEAFs of the same group.

[0094] The first optical coupler 6A is installed, for example, in a station building including a hub. The second optical coupler 6B is installed, for example, outside the station building. However, the first optical coupler 6A and the second optical coupler 6B may be installed in locations other than those mentioned above. Note that the number of branching stages is counted from the LEAF side, so an optical line with three or more branching stages may be created by installing another coupler upstream of the first coupler 6A.

[0095] The parameters in the second allocation policy are defined as follows: In the following definitions, "group j" means a group with identifier j. Also, "LEAFji" means a LEAF with identifier i in group j. j: identifiers of at least two groups included in the system i: identifier of at least one LEAF included in group j Rλji: set of receiving wavelengths λr operated by LEAFji Tλji: set of transmitting wavelengths λt operated by LEAFji

[0096] AR2: A set of receiving wavelengths λr operated by at least two LEAFji assigned identifiers j and i. AT2: A set of transmitting wavelengths λt operated by at least two LEAFji assigned identifiers j and i. φ: An empty set. hRλ: A set of receiving wavelengths operated by the HUB. hTλ: A set of transmitting wavelengths operated by the HUB.

[0097] Since the HUB needs to transmit and receive optical signals to and from all of the subordinate LEAFji, the receiving wavelength set hRλ of the HUB has a set AT2, and the transmitting wavelength set hTλ of the HUB has elements of AR2.

[0098] In the optical communication system 200 of this embodiment, since the LEAFji is a single-core bidirectional transmission system, taking into consideration the influence of reflection on the LEAFji side, it is preferable that all LEAFji do not overlap the wavelengths of downstream optical signals with the wavelengths of upstream optical signals. Therefore, in the second allocation policy, the following condition L4 is adopted as the "allocation condition for the operating wavelength of a LEAF." Condition L4: Satisfying formula (4) Rλji∩Tλji=φ ... (4)

[0099] On the other hand, if the receiving wavelength group hRλ and the transmitting wavelength group hTλ of the HUB overlap, due to the length of the trunk line 4 or individual differences in the first optical coupler 6A, a downstream optical signal of a certain wavelength may be reflected by the optical coupler 6 and mixed into an upstream optical signal, which may prevent the HUB from properly receiving the upstream optical signal of that wavelength. Therefore, in the second allocation policy, the following conditions L5 and L6 are further adopted as "allocation conditions for the operating wavelength of the LEAF".

[0100] Condition L5: If the reflection on the HUB side is small, then equation (5) must be satisfied. Condition L6: If the reflection on the HUB side is large, then equation (6) must be satisfied. AR2∩AT2≠φ (5) AR2∩AT2=φ (6)

[0101] If condition L5 is adopted, then the multiple LEAFji under the HUB will share part or all of the receiving wavelength set AR2 and the transmitting wavelength set AT1. This allows for effective use of the communication bandwidth of the entire optical communication system 200. If condition L6 is adopted, then the multiple LEAFji under the HUB will use the receiving wavelength set AR1 and the transmitting wavelength set AT1 separately. This prevents the HUB from being unable to properly receive upstream optical signals due to reflections at the first optical coupler 6A.

[0102] In addition, when some of the LEAFs included in the system are assigned identifiers j and i, i.e., when LEAFji constitutes a subset of the LEAFs in the system, condition L5 may include satisfying "AR2 = AT2" in addition to satisfying equation (5).

[0103] [Effects of the Allocation Policy of the Present Embodiment] Conventionally (Non-Patent Document 1) employs an allocation policy that always prevents overlap between the receiving wavelength groups AR1 and AR2 of a LEAF and the transmitting wavelength groups AT1 and AT2. That is, the conventional allocation policy uses only equation (3) or equation (6). However, with such an allocation policy, only half the number of wavelengths available in the entire optical communication system 200 can be accommodated for LEAFs.

[0104] In contrast, the allocation policy of this embodiment is a policy that allows overlap between the receiving wavelength groups AR1 and AR2 and the transmitting wavelength groups AT1 and AT2 of the LEAFs, provided that the reflection on the hub side is small. In other words, when the reflection on the hub side is small, allocation based on equation (2) or equation (5) is allowed, which has the advantage of being able to accommodate the same number of LEAFs as the number of wavelengths. Below, an example of wavelength allocation based on the allocation policy of this embodiment will be described.

[0105] [Operating Wavelengths Within a Group] Incidentally, the following condition L7 may be adopted for the allocation of operating wavelengths within group j to avoid overlap between the upstream and downstream directions. Condition L7: Formula (7) must be satisfied AR2j∩AT2j=φ (7) where, AR2j: a set of receiving wavelengths λr used by group j AT2j: a set of transmitting wavelengths λt used by group j

[0106] Adopting condition L7 has the advantage that, for example, even if an upstream optical signal transmitted by LEAFmi in a certain group m reaches LEAFni in another group n through the following events, the attenuation is large and does not affect the reception of the upstream optical signal by LEAFni. Event 1: Passes through optical coupler 6B of group m Event 2: Reflected by optical coupler 6A separating group m and group n Event 3: Passes through optical coupler 6B of group n

[0107] [Wavelength Allocation Example 1] Figure 6 is an explanatory diagram of wavelength allocation example 1 based on the second allocation policy. Allocation example 1 in Figure 6 is an allocation example in which a total of 12 LEAFs are divided into four groups, and three LEAFs belong to each group. Also, allocation example 1 in Figure 6 satisfies conditions L4 and L7, and also adopts condition L5 because there is little reflection to the hub.

[0108] In allocation example 1, LEAFs 11, 12, and 13 belonging to group 1 do not use λ21, λ22, and λ23, which are used for reception in group 1, for transmission in order to avoid the influence of reflection within group 1. Similarly, LEAFs 21, 22, and 23 belonging to group 2 do not use λ31, λ32, and λ33, which are used for reception in group 2, for transmission.

[0109] Similarly, LEAFs 31, 32, and 33 belonging to group 3 do not use λ41, λ42, and λ43 used for reception in group 3 for transmission. Similarly, LEAFs 41, 42, and 43 belonging to group 4 do not use λ11, λ12, and λ13 used for reception in group 3 for transmission.

[0110] Furthermore, in the second allocation policy, by adopting condition L5, the following sharing is performed for the receiving wavelengths and transmitting wavelengths operated by each LEAF: λ11, λ12, λ13 → shared as transmitting wavelengths for group 1 and receiving wavelengths for group 4 λ21, λ22, λ23 → shared as transmitting wavelengths for group 2 and receiving wavelengths for group 1 λ31, λ32, λ33 → shared as transmitting wavelengths for group 3 and receiving wavelengths for group 2 λ41, λ42, λ43 → shared as transmitting wavelengths for group 4 and receiving wavelengths for group 5

[0111] [Wavelength Allocation Example 2] Fig. 7 is an explanatory diagram of wavelength allocation example 2 based on the second allocation policy. Allocation example 2 in Fig. 7 is an allocation example in which a total of four LEAFs are divided into two groups, with two LEAFs belonging to each group. Allocation example 2 in Fig. 7 is also an allocation example in which the receiving wavelength group Rλji and the transmitting wavelength group Tλji of each LEAF are the following sets: Rλji = {λ1, λ2, λ3, λ4, λ5, λ6, λ7, λ8} Tλji = {λ1, λ2, λ3, λ4, λ5, λ6, λ7, λ8}

[0112] As shown in Figure 7, when the number of elements (=8) of the receiving wavelength group Rλji and the transmitting wavelength group Tλji is more than twice the number of LEAFs (=4), the wavelengths to be assigned to each LEAF can be determined by dividing or sharing the operating wavelengths depending on the amount of reflection to the HUB.

[0113] For example, in allocation example 2 of Fig. 7, as an allocation example for condition L5 (small reflection), the operating wavelengths of each LEAF are allocated as follows: Receiving wavelength of LEAF11 = λ1, λ7 Transmitting wavelength of LEAF11 = λ5, λ3 Receiving wavelength of LEAF12 = λ2, λ8 Transmitting wavelength of LEAF12 = λ6, λ4 Receiving wavelength of LEAF21 = λ3, λ5 Transmitting wavelength of LEAF21 = λ7, λ1 Receiving wavelength of LEAF22 = λ4, λ6 Transmitting wavelength of LEAF22 = λ8, λ2

[0114] In this case, the set of receiving wavelengths operated by each LEAF is {λ1, λ2, λ3, λ4, λ5, λ6, λ7, λ8}, and the set of transmitting wavelengths operated by each LEAF is also {λ1, λ2, λ3, λ4, λ5, λ6, λ7, λ8}. In this way, by overlapping Rλji and Tλji without increasing the number of LEAFs accommodated, the communication bandwidth can be doubled. Therefore, each LEAF can share the operating receiving wavelengths and the operating transmitting wavelengths to the maximum extent possible, and the communication bandwidth of each LEAF can be effectively utilized.

[0115] 7, as an example of allocation for condition L6 (high reflection), the operating wavelengths of each LEAF are allocated as follows: Receiving wavelength of LEAF11 = λ1, transmitting wavelength of LEAF11 = λ5, receiving wavelength of LEAF12 = λ2, transmitting wavelength of LEAF12 = λ6, receiving wavelength of LEAF21 = λ3, transmitting wavelength of LEAF21 = λ7, receiving wavelength of LEAF22 = λ4, transmitting wavelength of LEAF22 = λ8

[0116] In this case, the set of receiving wavelengths used by each LEAF is {λ1, λ2, λ3, λ4}, and the set of transmitting wavelengths used by each LEAF is {λ5, λ6, λ7, λ8}. Therefore, each LEAF distinguishes between the receiving wavelength during operation and the transmitting wavelength during operation, preventing the HUB from being unable to properly receive upstream optical signals due to reflection at optical coupler 6A.

[0117] [Wavelength Allocation Example 3] Fig. 8 is an explanatory diagram of wavelength allocation example 3 based on the second allocation policy. Allocation example 3 in Fig. 8 is an allocation example in which a total of eight LEAFs are divided into four groups, and two LEAFs belong to each group. Allocation example 3 in Fig. 8 is also an allocation example in which Rλ and Tλ of each LEAF are the following sets: Rλ = {λ1, λ2, λ3, λ4, λ5, λ6, λ7, λ8} Tλ = {λ1, λ2, λ3, λ4, λ5, λ6, λ7, λ8}

[0118] As shown in Figure 8, if the number of elements of Rλ and Tλ (= 8) is the same as the number of LEAFs (= 8), it is physically impossible to assign multiple receiving wavelengths or multiple transmitting wavelengths to one LEAF. Therefore, it is sufficient to share the operating wavelengths on the condition that the reflection to the hub is small, and assign one wavelength to each LEAF. Note that if the reflection to the hub is large, it is preferable not to start operation.

[0119] In allocation example 3 of Fig. 8, as an allocation example for condition L5 (small reflection), the operating wavelengths of each LEAF are allocated as follows: Receiving wavelength of LEAF11 = λ1 Transmitting wavelength of LEAF11 = λ5 Receiving wavelength of LEAF12 = λ2 Transmitting wavelength of LEAF12 = λ6 Receiving wavelength of LEAF21 = λ3 Transmitting wavelength of LEAF21 = λ7 Receiving wavelength of LEAF22 = λ4 Transmitting wavelength of LEAF22 = λ8 Receiving wavelength of LEAF31 = λ5 Transmitting wavelength of LEAF31 = λ1 Receiving wavelength of LEAF32 = λ6 Transmitting wavelength of LEAF32 = λ2 Receiving wavelength of LEAF41 = λ7 Transmitting wavelength of LEAF41 = λ3 Receiving wavelength of LEAF42 = λ8 Transmitting wavelength of LEAF42 = λ4

[0120] In this case, the set of receiving wavelengths operated by each LEAF is {λ1, λ2, λ3, λ4, λ5, λ6, λ7, λ8}, and the set of transmitting wavelengths operated by each LEAF is also {λ1, λ2, λ3, λ4, λ5, λ6, λ7, λ8}. Therefore, each LEAF shares the receiving wavelengths during operation and the transmitting wavelengths during operation, and the communication band of each LEAF can be effectively utilized.

[0121] [Manual and Automatic Setting of Operating Wavelengths of LEAFs] The methods of allocating operating wavelengths to LEAFs, which are applied to the optical communication system 200 of this embodiment, are broadly divided into "manual setting" and "automatic setting." In either setting, allocation information including the receiving wavelength λr and transmitting wavelength λt for each LEAF can be artificially determined in advance in accordance with the first or second allocation policy described above. Manual setting is a method in which an operations manager manually allocates operating wavelengths to LEAFs using the controller 10. Manual setting includes, for example, the following variations:

[0122] (Variations of manual setting) 1) Manual setting 1: Manual setting when the number of branching stages is one Manual setting 1 includes the following steps: Step P11: Make the HUB measure the reflected power through control communication. Step P12: If the measurement result shows that the reflection is small, decide to adopt the next allocation information Q1, and send the adopted allocation information Q1 to the HUB. Allocation information Q1: Rλi and Tλi for each LEAFi that satisfy L1 and L2

[0123] Step P13: If the measurement result shows high reflection, it decides to adopt the next allocation information Q2 and sends the adopted allocation information Q2 to the HUB. Allocation information Q2: Rλi and Tλi for each LEAFi that satisfies L1 and L3. Upon receiving the allocation information Q1 and Q2, the HUB notifies each subordinate LEAFi of the operating wavelength. The content of the notification may be the allocation information Q1 and Q2 themselves, or the operating wavelength for each LEAFi extracted by the HUB from the allocation information Q1 and Q2.

[0124] 2) Manual Setting 2: Manual setting when the number of branching stages is two Manual setting 2 includes the following steps: Step P21: The HUB is caused to measure the reflected power by control communication. Step P22: If the measurement result shows that the reflection is small, it is decided to adopt the next allocation information Q3, and the adopted allocation information Q3 is transmitted to the HUB. Allocation information Q3: Rλji and Tλji for each LEAFji that satisfy L4, L5, and L6

[0125] Step P23: If the measurement result shows high reflection, it is decided to adopt the next allocation information Q4, and the adopted allocation information Q4 is sent to the HUB. Allocation information Q4: Rλji and Tλji for each LEAFji that satisfy L4, L5, and L7. Upon receiving the allocation information Q3 and Q4, the HUB notifies each subordinate LEAFji of the operating wavelength. The content of the notification may be the allocation information Q3 and Q4 itself, or the operating wavelength for each LEAFji that the HUB extracted from the allocation information Q3 and Q4.

[0126] 3) Other Manual Settings For example, if it is not necessary to measure the reflection power on the HUB side, such as by using an optical coupler 6 that is less likely to cause reflection to the HUB, only step P12 or step P22 may be performed. Also, instead of using the controller 10 for setting, the operating wavelength of the HUB may be preset in the memory 13B of the HUB or the operating wavelength of the LEAF may be preset in the memory 23B of the LEAF when at least one of the HUB and the LEAF is manufactured.

[0127] The automatic setting is a method of installing the above-mentioned allocation information Q1, Q2, Q3, and Q4 and a control program for selecting the allocation information Q1, Q2, Q3, and Q4 in the memory 13B of the HUB. The automatic setting includes, for example, the following procedure.

[0128] (Variations of Automatic Setting) 1) Automatic Setting 1: Automatic setting when the number of branching stages is one Automatic setting 1 includes the following steps: Step P41: The HUB autonomously measures the reflected power. Step P42: If the measurement result shows that the reflection is small, the control unit 13 of the HUB selects allocation information Q1 and reads it from memory 13B.

[0129] Step P13: If the measurement result indicates high reflection, the control unit 13 of the HUB selects allocation information Q2 and reads it from the memory 13B. The HUB that selected the allocation information Q1 and Q2 notifies each subordinate LEAFi of the operating wavelength. The content of the notification may be the allocation information Q1 and Q2 themselves, or the operating wavelength for each LEAFi that the HUB extracted from the allocation information Q1 and Q2.

[0130] 2) Automatic setting 2: Automatic setting when the number of branching stages is two Automatic setting 2 includes the following steps: Step P51: The HUB autonomously measures the reflected power. Step P52: If the measurement result shows that the reflection is small, the control unit 13 of the HUB selects allocation information Q3 and reads it from memory 13B.

[0131] Step P53: If the measurement result indicates high reflection, the control unit 13 of the HUB selects allocation information Q4 and reads it from the memory 13B. The HUB that selected the allocation information Q3 and Q4 notifies each subordinate LEAFji of the operating wavelength. The content of the notification may be the allocation information Q3 and Q4 itself, or the operating wavelength for each LEAFji that the HUB extracted from the allocation information Q3 and Q4.

[0132] 3) Other automatic settings For example, if it is not necessary to measure the reflected power on the HUB side, such as by using an optical coupler 6 that is less likely to cause reflection to the HUB, it is possible to omit the measurement of the reflected power and perform automatic settings that include only step P42 or step P52.

[0133] [Allocation Condition Determination Process] Figure 9 is a flowchart showing an example of allocation condition determination process executed by the control unit 13 of the HUB. The determination process of Figure 9 is executed when the system is installed or restarted, with transmission from the LEAF stopped. As shown in Figure 9, the control unit 13 of the HUB causes its own optical transceiver 11 to emit light at a wavelength to be determined (step ST11). The wavelength to be determined is a wavelength selected from the set of wavelengths Tλi and Tλij of optical signals that can be transmitted by the LEAF.

[0134] Next, the control unit 13 of the HUB measures the reception power of reflected light that may occur at the optical coupler 6 (hereinafter referred to as "reflection power") (step ST12). Next, the control unit 13 of the HUB determines whether the ratio obtained by dividing the minimum reception power by the reflection power exceeds a predetermined threshold (step ST13). The "minimum reception power" refers to the minimum reception power (set value) that the HUB can receive.

[0135] If the determination result in step ST13 is positive (small reflection), the control unit 13 of the HUB sets the allocation condition for the operating wavelength of the LEAF to "shared" (step ST14). "Shared" means that condition L2 or condition L5 is adopted as the allocation condition. If the determination result in step ST13 is negative (large reflection), the control unit 13 of the HUB sets the allocation condition for the operating wavelength of the LEAF to "classified" (step ST15). "Classified" means that condition L3 or condition L7 is adopted as the allocation condition.

[0136] However, if the number of connected LEAFs is the same as the number of wavelengths of optical signals that the LEAFs can transmit (number of elements of Tλi and Tλji), when the judgment result of step ST13 is negative (high reflection), the control unit 13 of the HUB will stop operation of the system or limit the number of connected LEAFs.

[0137] 10 is a flowchart showing an example of an operation wavelength allocation process executed by the HUB control unit 13 and the LEAF control unit 13. The operation wavelength allocation process 1 in FIG. 10 is a process that requires the satisfaction of the following preconditions.

[0138] Precondition C11: The memory 13B of the HUB holds the IDs of the subordinate LEAFs. Precondition C12: The memory 13B of the HUB holds the above-mentioned allocation information Q1, Q2, Q3, and Q4 that define the operating wavelengths for each LEAF ID. The format of the allocation information Q1, Q2, Q3, and Q4 may be a table format such as the allocation table T1 in FIG. 7 or the allocation table T2 in FIG. 8, or may be a text-based data format such as CSV (Comma Separated Values) or XML (Extensible Markup Language).

[0139] Precondition C13: The memory 13B of the LEAF holds its own ID. Precondition C14: The memory 13B of the LEAF holds allocation information for the LEAF that defines its own operating wavelength. The allocation information for the LEAF may be the same information as the allocation information Q1, Q2, Q3, and Q4 described above, or may be information obtained by extracting the parts corresponding to the identifiers of the LEAFs from the allocation information Q1, Q2, Q3, and Q4.

[0140] 10, the control unit 13 of the HUB determines the receiving wavelength and transmitting wavelength to be used by each LEAF during operation according to the determination result of the allocation condition (shared or divided) (step ST21). This determination is made based on the allocation information for the HUB. Next, the control unit 13 of the HUB notifies the LEAF of the start of registration, including the determination result of the allocation condition (shared or divided) (step ST22).

[0141] Next, the control unit 13 of the HUB registers the LEAF that has responded and starts operation (step ST23). Note that the control unit 13 of the HUB repeats the processes of steps ST21 and ST22 for all subordinate LEAFs.

[0142] As shown in Fig. 10, the control unit 13 of the LEAF waits for a notification of registration start from the HUB at the receiving wavelength of the wavelength segment (step ST31). Next, the control unit 13 of the LEAF determines its own operating wavelength according to the determination result (shared or segmented) of the allocation condition included in the registration start (step ST32). This determination is made based on the allocation information for the LEAF described above. Next, the control unit 13 of the LEAF responds to the HUB and then starts operation (step ST33).

[0143] 11 is a flowchart showing another example of the operation wavelength allocation process executed by the HUB control unit 13 and the LEAF control unit 13. The operation wavelength allocation process 2 in FIG. 11 is a process that requires the satisfaction of the following preconditions.

[0144] Precondition C21: The memory 13B of the HUB holds the IDs of the subordinate LEAFs. Precondition C22: The memory 13B of the HUB holds the aforementioned allocation information Q1, Q2, Q3, and Q4 that define the operating wavelength for each LEAF ID. Precondition C23: The memory 13B of a LEAF holds only its own ID and does not hold its own allocation information at the time of installation, but holds allocation information notified from the HUB. Precondition C24: The memory 13B of a LEAF holds the receiving wavelength λr and transmitting wavelength λt for discovery as seen from the LEAF.

[0145] As shown in Fig. 11, the control unit 13 of the HUB periodically notifies the LEAF of the start of registration, specifying the ID of the LEAF (step ST41). The transmission wavelength of the registration notification is the receiving wavelength λr for discovery for the LEAF. The registration start notification includes the operating wavelengths to be used by the LEAF (receiving wavelength group Rλi, Rλji and transmitting wavelength group Tλi, Tλji). The operating wavelengths to be used by the LEAF are determined according to the determination result of the allocation conditions (shared or classified).

[0146] Next, the control unit 13 of the HUB waits for a response from the LEAF on the notified wavelength channel (step ST42). Next, the control unit 13 of the HUB registers the LEAF that has responded and starts operation (step ST43). The control unit 13 of the HUB repeats the processes from step ST41 to step ST43 for all subordinate LEAFs.

[0147] As shown in Figure 11, the control unit 13 of the LEAF waits for a registration start notification from the HUB at the discovery receiving wavelength (step ST51). Next, the control unit 13 of the LEAF determines its own operating wavelength in accordance with the registration start notification addressed to itself (step ST52). Specifically, the control unit 13 of the LEAF sets the wavelength of its own TRx to the receiving wavelength and transmitting wavelength included in the registration start notification. Next, the control unit 13 of the LEAF responds to the HUB and then starts operation (step ST53).

[0148] 12 is a flowchart showing another example of the operation wavelength allocation process executed by the HUB control unit 13 and the LEAF control unit 13. The operation wavelength allocation process 3 in FIG. 12 is a process that requires the satisfaction of the following preconditions.

[0149] Precondition C31: The memory 13B of the HUB holds set information (specifically, the aforementioned allocation information Q3 and Q4) that defines usable receiving wavelengths and transmitting wavelengths for each group ID. The set information includes allocation information Q3 for sharing an operating wavelength and allocation information Q4 for separating an operating wavelength. Precondition C32: The memory 13B of the LEAF holds its own ID. Precondition C33: The memory 13B of the LEAF holds the ID of its own group.

[0150] 12, the control unit 13 of the hub periodically notifies the start of registration specifying the group ID (step ST61). The notification of registration start includes set information including the receiving wavelength and transmitting wavelength that can be used in the group. Next, the control unit 13 of the hub waits for a response from the LEAF on the notified wavelength channel (step ST62).

[0151] Next, the control unit 13 of the HUB determines whether or not the response from the LEAF has been received normally (step ST63). If the determination result of step ST63 is negative, the control unit 13 of the HUB returns the process to step ST61. If the determination result of step ST63 is positive, the control unit 13 of the HUB registers the wavelength allocation of the LEAF and marks the allocated wavelength as in use (step ST64).

[0152] Next, the control unit 13 of the HUB notifies the LEAF of the completion of registration and starts operation (step ST65). Note that the control unit 13 of the HUB repeats the processes from step ST61 to step ST65 for all subordinate LEAFs.

[0153] 12, the control unit 13 of the LEAF waits for a registration start notification from the HUB at a predetermined receiving wavelength (step ST71). Next, the control unit 13 of the LEAF determines whether the group ID included in the registration start notification matches its own group ID (step ST72).

[0154] If the determination result of step ST72 is negative, the control unit 13 of the LEAF returns the process to step ST71. If the determination result of step ST72 is positive, the control unit 13 of the LEAF waits a random time and then determines its own operating wavelength in accordance with the notification of registration start (step ST73). Specifically, the control unit 13 of the LEAF sets the wavelength of its own TRx to the receiving wavelength and transmitting wavelength included in the notification of registration start.

[0155] Next, the control unit 13 of the LEAF responds to the HUB and waits for a notification of registration completion (step ST74), and determines whether or not the notification has been received (step ST75). If the determination result of step ST75 is negative, the control unit 13 of the HUB returns the process to step ST71. If the determination result of step ST75 is positive, the control unit 13 of the HUB starts operation (step ST76).

[0156] [First Modification] In the above-described embodiment, the trunk line 4 of the optical line 3 is a two-core optical transmission line, but the trunk line 3 may be a single-core optical transmission line. Fig. 13 is a block diagram showing a modification of the optical transceiver 11 of the optical line terminal 1 when the trunk line 4 is a single-core optical transmission line.

[0157] The optical transceiver 11 in Fig. 13 differs from the optical transceiver 11 (Fig. 2) of the optical station device 1 described above in that it includes an optical component 109 that branches an optical signal. The optical component 109 may be located outside the housing of the optical transceiver 21. The optical component 109 may be, for example, an optical coupler or an optical circulator. The multiplexed optical signal Oout output by the optical transmitting unit 105 is transmitted to the optical fiber (trunk line 4) by the optical component 109, and the downstream optical signal from the optical fiber is branched by the optical component 109 and input to the optical receiving unit 106 as the multiplexed optical signal Oin.

[0158] [Second Modification] In the above-mentioned operating wavelength allocation process 2 (FIG. 11) and allocation process 3 (FIG. 12), the control unit 13 of the HUB may notify the subordinate LEAF of the operating wavelength in the case of sharing without determining the allocation conditions.

[0159] In the above-described embodiment, the allocation policy (FIGS. 4 and 5) may be applied to only some of the LEAFs rather than to all of the LEAFs connected to the HUB. In this case, the allocation condition determination process (FIG. 9) and the operating wavelength allocation process (FIGS. 10 to 12) may be performed for only those LEAFs.

[0160] [Fourth Modification] In the above-described embodiment, the formula using the empty set (φ) can also be written as a formula using the number of elements of the set (the number of wavelengths in this embodiment). Specifically, it is as follows.

[0161] Formula (1) is equivalent to the following formula (11): [Number of wavelengths used by LEAFi=Number of wavelengths of Rλi+Number of wavelengths of Tλi] (11) Formula (2) is equivalent to the following formula (12): [Number of wavelengths used by all LEAFi<Number of wavelengths of AR1+Number of wavelengths of AT1] (12) Formula (3) is equivalent to the following formula (13): [Number of wavelengths used by all LEAFi=Number of wavelengths of AR1+Number of wavelengths of AT1] (13)

[0162] Equation (4) is equivalent to the following equation (14): [Number of wavelengths used by LEAFji=Number of wavelengths of Rλji+Number of wavelengths of Tλji] (14) Equation (5) is equivalent to the following equation (15): [Number of wavelengths used by all LEAFji<Number of wavelengths of AR2+Number of wavelengths of AT2] (15)

[0163] Equation (6) is equivalent to the following equation (16): [Number of wavelengths used by all LEAFji=Number of wavelengths in AR2+Number of wavelengths in AT2] (16) Equation (7) is equivalent to the following equation (17): [Number of wavelengths used by group j=Number of wavelengths in AR2j+Number of wavelengths in AT2j] (17)

[0164] [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.

[0165] DESCRIPTION OF SYMBOLS 1 Line side device (HUB) 2 Network side device (LEAF) 3 Optical line 4 Trunk line 5 Branch line 5A First branch line 5B Second branch line 6 Optical coupler 6A First optical coupler 6B Second optical coupler 10 Controller 11 Optical transceiver of line side device 12 Switch of line side device 13 Control unit of line side device 13A CPU 13B Memory 21 Optical transceiver of line side device 22 Switch of line side device 23 Control unit of line side device 23A CPU 23B Memory 101 Light source 102 Optical splitter 103 First signal processing unit 104 DAC 105 Optical transmitting unit 106 Optical receiving unit 107 ADC 108 Second signal processing unit 109 Optical component (optical coupler, optical circulator) 110 Processor 200 Optical communication system 201 Light source 202 Optical splitter 203 First signal processing unit 204 DAC 205 Optical transmitting unit 206 Optical receiving unit 207 ADC 208 Second signal processing unit 209 Optical components (optical coupler, optical circulator) 210 Processor T1, T2 Allocation information Q1, Q2, Q3, Q4 Allocation information

Claims

1. An optical communications system in which a station side device and multiple home appliances connected by an optical line perform full-duplex wavelength division multiplexing communications, wherein the optical line includes a trunk line to which the station side device is connected, and multiple branch lines branching off from the trunk line and to which the multiple home appliances are respectively connected, wherein the branch lines are single-core optical transmission lines through which both upstream optical signals and downstream optical signals are transmitted, wherein the station side device has an optical transceiver having two or more operational receiving wavelengths and two or more operational transmitting wavelengths, wherein the home appliances have an optical transceiver having one or more operational receiving wavelengths and one or more operational transmitting wavelengths, and wherein the receiving wavelengths and transmitting wavelengths of the multiple home appliances satisfy the following equations (1) and (2). Rλi ∩ Tλi = φ ... (1) AR1 ∩ AT1 ≠ φ ... (2) where, i: identifier of at least two optical network units included in the system Rλi: set of receiving wavelengths operated by an optical network unit with identifier i Tλi: set of transmitting wavelengths operated by an optical network unit with identifier i AR1: set of receiving wavelengths operated by at least two optical network units assigned with identifier i AT1: set of transmitting wavelengths operated by at least two optical network units assigned with identifier i φ: empty set 2. The optical communication system according to claim 1, wherein the following formula (3) is applied instead of formula (2) when reflection is large when the optical signal of the wavelength included in the set AR1 is transmitted from the optical line terminal. AR1 ∩ AT1 = φ ... (3) 3. An optical communications system in which a station side device and a plurality of home unit devices connected by an optical line perform full-duplex wavelength division multiplexing communications, the optical line including a trunk line to which the station side device is connected, a plurality of first branches branching from the trunk line and grouping the plurality of home unit devices, and a second branch branching from the first branch line and connecting the home unit devices of the same group, the first branch line and the second branch line being a single-core optical transmission line through which both upstream optical signals and downstream optical signals are transmitted, the station side device has an optical transceiver having two or more operational receiving wavelengths and two or more operational transmitting wavelengths, the home unit has an optical transceiver having one or more operational receiving wavelengths and one or more operational transmitting wavelengths, and the receiving wavelengths and transmitting wavelengths of the plurality of home unit devices satisfy the following formulas (4) and (5). Rλji ∩ Tλji = φ ... (4) AR2 ∩ AT2 ≠ φ ... (5) where, j: identifier of at least two groups included in the system i: identifier of at least one optical network unit included in the group with identifier j Rλji: set of receiving wavelengths operated by an optical network unit with identifier i in the group with identifier j Tλji: set of transmitting wavelengths operated by an optical network unit with identifier i in the group with identifier j AR2: set of receiving wavelengths operated by at least two optical network units assigned with identifier j and identifier i AT2: set of transmitting wavelengths operated by at least two optical network units assigned with identifier j and identifier i φ: empty set 4. The optical communication system according to claim 3, wherein the following formula (6) is applied instead of formula (5) when reflection is large when the optical signal of the wavelength included in the set AR2 is transmitted from the optical line terminal. AR2 ∩ AT2 = φ ... (6) 5. A station side device used in an optical communication system as described in claim 2 or claim 4, comprising: the optical transceiver; a control unit which performs control communication with the plurality of home-side devices; and a memory which stores allocation information for wavelength sharing which satisfies the formula (2) or the formula (5) and allocation information for wavelength divisions which satisfies the formula (3) or the formula (6), wherein when the reflection is small, the control unit determines the receiving wavelengths and transmitting wavelengths during operation of the plurality of home-side devices based on the allocation information for wavelength sharing.

6. The optical line terminal according to claim 5, wherein the control unit, when the reflection is large, determines the receiving wavelengths and transmitting wavelengths for operation of the plurality of optical line terminals based on allocation information for the wavelength division.

7. The optical line device according to claim 6, wherein the control unit notifies the plurality of optical line devices of the receiving wavelengths and transmitting wavelengths during operation of the plurality of optical line devices that the control unit has determined.

8. A station side device as described in any one of claims 5 to 7, wherein the multiple home appliances store their own allocation information in the case of wavelength sharing and their own allocation information in the case of wavelength division, and the control unit notifies the multiple home appliances of the wavelength sharing when the reflection is small, and notifies the multiple home appliances of the wavelength division when the reflection is large.

9. A wavelength allocation method executed by a station side device used in an optical communication system according to claim 2 or claim 4, comprising the steps of: storing allocation information for wavelength sharing that satisfies said formula (2) or said formula (5) and allocation information for a wavelength division that satisfies said formula (3) or said formula (6); and, when the reflection is small, determining the receiving wavelengths and transmitting wavelengths during operation of said plurality of home side devices based on the allocation information for wavelength sharing.

10. The wavelength allocation method according to claim 9, further comprising a step of determining, when the reflection is large, receiving wavelengths and transmitting wavelengths during operation of the plurality of optical network devices based on allocation information for the wavelength section.

11. A wavelength allocation method applied to an optical communications system in which a station side device and multiple home device devices connected by an optical line perform full-duplex wavelength division multiplexing communications, the wavelength allocation method comprising the steps of: determining receiving wavelengths and transmitting wavelengths to be operated by the multiple home device devices in accordance with a predetermined allocation policy; and setting the determined receiving wavelengths and transmitting wavelengths in the multiple home device devices, respectively, wherein the allocation policy includes a first allocation policy that satisfies the following equations (1) and (2). Rλi ∩ Tλi = φ ... (1) AR1 ∩ AT1 ≠ φ ... (2) where, i: identifier of at least two optical network units included in the system Rλi: set of receiving wavelengths operated by an optical network unit with identifier i Tλi: set of transmitting wavelengths operated by an optical network unit with identifier i AR1: set of receiving wavelengths operated by at least two optical network units assigned with identifier i AT1: set of transmitting wavelengths operated by at least two optical network units assigned with identifier i φ: empty set 12. The optical communication system according to claim 11, wherein the first allocation policy is a policy that applies the following formula (3) instead of the formula (2) when reflection is large when the optical line terminal transmits an optical signal having a wavelength included in the set AR1. AR1 ∩ AT1 = φ ... (3) 13. A wavelength allocation method applied to an optical communications system in which a station side device and a plurality of home appliances connected by an optical line including a branch line for grouping the plurality of home appliances perform full-duplex wavelength division multiplexing communication, the wavelength allocation method comprising the steps of: determining receiving wavelengths and transmitting wavelengths to be operated by the plurality of home appliances in accordance with a predetermined allocation policy; and setting the determined receiving wavelengths and transmitting wavelengths in the plurality of home appliances, respectively, wherein the allocation policy includes a second allocation policy that satisfies the following equations (4) and (5). Rλji ∩ Tλji = φ ... (4) AR2 ∩ AT2 ≠ φ ... (5) where, j: identifier of at least two groups included in the system i: identifier of at least one optical network unit included in the group with identifier j Rλji: set of receiving wavelengths operated by an optical network unit with identifier i in the group with identifier j Tλji: set of transmitting wavelengths operated by an optical network unit with identifier i in the group with identifier j AR2: set of receiving wavelengths operated by at least two optical network units assigned with identifier j and identifier i AT2: set of transmitting wavelengths operated by at least two optical network units assigned with identifier j and identifier i φ: empty set 14. The optical communication system according to claim 13, wherein the second allocation policy is a policy that applies the following formula (6) instead of the formula (5) when reflection is large when the optical line terminal transmits an optical signal having a wavelength included in the set AR2. AR2 ∩ AT2 = φ ... (6)

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