JP7560003B1 - COMMUNICATION DEVICE, WAVELENGTH DETERMINATION METHOD, OPTICAL TRANSCEIVER, AND OPTICAL COMMUNICATION SYSTEM - Google Patents

Abstract

An apparatus according to one embodiment of the present disclosure is a communication apparatus that performs optical communication using a single core bidirectional transmission, and includes an optical transceiver capable of transmitting and receiving optical signals of multiple wavelengths to an opposing device, and a control unit that determines the wavelengths to be used for communication with the opposing device, and the control unit determines whether the multiple wavelengths are divided into upstream and downstream wavelengths or shared for both upstream and downstream depending on the degree of reflection of the optical signal transmitted from the apparatus itself.

Description

The present disclosure relates to a communication device, a wavelength determination method, an optical transceiver, and an optical communication system.

Non-Patent Document 1 specifies that the standard specifications for 100GBASE-LR4 are to transmit optical signals of 25 Gbps per lane to a single-mode fiber using wavelength division multiplexing (WDM) of four wavelengths in the O-band (1260 to 1360 nm).
Non-Patent Document 2 specifies that the standard specifications for GE-PON (Gigabit Ethernet-Passive Optical Network) are that the wavelength of the upstream optical signal is 1310 nm and the wavelength of the downstream optical signal is 1490 nm ("Ethernet" and "Ethernet" are registered trademarks).

Non-Patent Document 3 describes that an optical transceiver employing a subcarrier multiplexing (SCM) method generates multiple subcarriers with different wavelengths using a single light source through digital signal processing, and transmits the generated subcarriers (optical signals) to an optical fiber.
In Non-Patent Document 3, the subcarriers of the upstream optical signal and the downstream optical signal are divided into different wavelength bands. Therefore, even if the upstream optical signal and the downstream optical signal interfere with each other, only the subcarriers of the signal light are selectively received by digital signal processing.

IEEE Std 802.3ba-2010 [88. Physical Medium Dependent sublayer and medium, type 100GBASE-LR4 and 100G-BASE-ER4] IEEE Std 802.3ah-2004 [59.1 Overview] Journal of Lightwave Technology Volume:39, Issue:16, 15 August 2021

An apparatus according to one embodiment of the present disclosure is a communication apparatus that performs optical communication using a single core bidirectional transmission, and includes an optical transceiver capable of transmitting and receiving optical signals of multiple wavelengths to an opposing device, and a control unit that determines the wavelengths to be used for communication with the opposing device, and the control unit determines whether the multiple wavelengths should be divided into upstream and downstream wavelengths or shared for both upstream and downstream wavelengths depending on the degree of reflection of the optical signal transmitted from the apparatus itself.

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

FIG. 1 is an explanatory diagram showing variations of optical communication transmission methods. FIG. 2 is an explanatory diagram showing a variation of the configuration of the optical communication system. FIG. 3 is an explanatory diagram showing variations of the control path from the controller to the optical transceiver. FIG. 4 is an explanatory diagram showing an overview of the first wavelength setting process. FIG. 5A is a flowchart showing a specific example of the first wavelength setting process. FIG. 5B is a flowchart showing a specific example of the first wavelength setting process. FIG. 6 is an explanatory diagram showing an overview of the second wavelength setting process. FIG. 7A is a flowchart showing a specific example of the second wavelength setting process. FIG. 7B is a flowchart showing a specific example of the second wavelength setting process. FIG. 8 is an explanatory diagram showing an overview of the third wavelength setting process. FIG. 9A is a flowchart showing a specific example of the third wavelength setting process. FIG. 9B is a flowchart showing a specific example of the third wavelength setting process. FIG. 10 is a block diagram showing an example of the internal configuration of an optical transceiver. FIG. 11 is a block diagram showing another example of the internal configuration of the optical transceiver. FIG. 12 is an explanatory diagram showing variations in the connection form (topology) of an optical communication system.

<Problems to be Solved by the Present Disclosure>
The above-mentioned non-patent literature does not anticipate dividing multiple types of wavelengths into upstream and downstream wavelengths depending on the reflection conditions of the optical signal in single-core bidirectional transmission, or sharing multiple types of wavelengths for both upstream and downstream.
In view of the above-mentioned problems in the related art, the present disclosure has an object to provide a communication device capable of appropriately dividing and sharing a plurality of types of wavelengths.

<Effects of the present disclosure>
According to the present disclosure, it is possible to appropriately classify and share a plurality of types of wavelengths.

Overview of the embodiments of the present disclosure
Below, an overview of the embodiments of the present disclosure will be listed and described.
(1) An apparatus according to one aspect of this embodiment is a communication device that performs optical communication via single-core bidirectional transmission, and includes an optical transceiver capable of transmitting and receiving optical signals of multiple wavelengths to an opposing device, and a control unit that determines the wavelengths to be used for communication with the opposing device, and the control unit determines whether the multiple wavelengths should be divided into upstream and downstream wavelengths or shared for both upstream and downstream wavelengths depending on the degree of reflection of the optical signal transmitted from the apparatus itself.

According to the communication device of this embodiment, the control unit determines whether to divide multiple types of wavelengths into upstream and downstream use or to share them for both upstream and downstream use depending on the degree of reflection of the optical signal transmitted from the device, thereby enabling appropriate division and sharing of multiple types of wavelengths.

(2) In the communication device of (1) described above, when the opposing device performs optical communication using a single-core bidirectional transmission, the control unit may further determine whether the multiple types of wavelengths are to be divided into upstream and downstream wavelengths or shared by both upstream and downstream wavelengths depending on the degree of reflection of the optical signal transmitted from the opposing device.
In this way, it is possible to more accurately determine whether to separate or share a plurality of types of wavelengths, compared to a case where only the amount of reflection on the communication device side is used as a criterion.

(3) In the communication device of (2) described above, the control unit may divide the plurality of types of wavelengths into those for upstream and downstream use when the reflection is large, and may share the plurality of types of wavelengths for both upstream and downstream use when the reflection is small.
In this way, when reflection is large, stable bidirectional transmission over a single core is possible by dividing multiple types of wavelengths into upstream and downstream directions, and when reflection is small, large-capacity bidirectional transmission over a single core is possible by sharing multiple types of wavelengths for both upstream and downstream directions.

(4) In the communication device of (2) or (3) described above, the control unit may determine the amount of reflection based on a first reflected power measured by the control unit itself, a first received power measured by the control unit itself or a predetermined first minimum received power, a second reflected power measured by the opposing device, and a second received power measured by the opposing device or a predetermined second minimum received power.
In this case, the amount of reflection in the transmission path is determined based on the measured power or predetermined power on the own side and the measured power or predetermined power on the opposing device side, so that the amount of reflection can be determined accurately.

(5) In the communication device of (4) described above, the control unit may determine to classify the plurality of types of wavelengths when a ratio of the first received power or the first minimum received power to the first reflected power is equal to or less than a threshold value, or when a ratio of the second received power or the second minimum received power to the second reflected power is equal to or less than a threshold value.
In this way, when the influence of reflection is large, it is possible to stabilize one-core bidirectional transmission by dividing the wavelengths.

(6) In the communication device according to (4) or (5) described above, the control unit may determine to share the multiple types of wavelengths when a ratio of the first received power or the first minimum received power to the first reflected power exceeds a threshold value and a ratio of the second received power or the second minimum received power to the second reflected power exceeds a threshold value.
In this way, when the effect of reflection is small, large-capacity bidirectional transmission over a single fiber becomes possible by sharing wavelengths.

(7) In any of the communication devices described above in (2) to (6), the control unit may determine the amount of reflection based on a first error rate that is a bit error rate of a first communication frame and a second error rate that is a bit error rate of a second communication frame, where the first communication frame is a frame that the device itself detects when transmitting and receiving optical signals of the same wavelength simultaneously, and the second communication frame is a frame that the opposing device detects when transmitting and receiving optical signals of the same wavelength simultaneously.
In this case, the amount of reflection in the transmission path is determined based on the first error rate on the own side and the second error rate on the opposite device side, so that the amount of reflection can be easily determined even if the optical power cannot be measured.

(8) In the communication device according to (7) above, the control unit may determine to separate the plurality of types of wavelengths when the first error rate is equal to or greater than a threshold value or when the second error rate is equal to or greater than a threshold value.
In this way, in cases where the influence of reflection is estimated to be large, it is possible to stabilize one-core bidirectional transmission by dividing the wavelengths.

(9) In the communication device according to (7) or (8) described above, the control unit may determine to share the multiple types of wavelengths when the first error rate is less than a threshold and the second error rate is less than a threshold.
In this way, in the case where the influence of reflection is estimated to be small, large-capacity bidirectional transmission over a single fiber becomes possible by sharing wavelengths.

(10) In any of the communication devices described above in (1) to (9), the control unit may determine the amount of reflection based on the result of a loopback test performed with the same transmission wavelength for upstream and downstream.
In this way, for example, the amount of reflection can be easily determined based on the presence or absence of a loss of a test frame in a loopback test, even if the optical power cannot be measured.

(11) In the communication device according to (10) above, the control unit may determine to separate the plurality of types of wavelengths when a result of the loopback test indicates that a test frame is lost.
In this way, in cases where the influence of reflection is estimated to be large, it is possible to stabilize one-core bidirectional transmission by dividing the wavelengths.

(12) In the communication device according to (10) or (11) above, the control unit may determine to share the plurality of types of wavelengths when a result of the loopback test indicates that there is no loss of a test frame.
In this way, in the case where the influence of reflection is estimated to be small, large-capacity bidirectional transmission over a single fiber becomes possible by sharing wavelengths.

(13) A method according to one aspect of the present embodiment is a wavelength determination method executed by any one of the communication devices described above in (1) to (12).
Therefore, the wavelength determination method of the present embodiment has the same effects as any one of the communication devices (1) to (12) described above.

(14) A device according to another aspect of this embodiment is an optical transceiver comprising an optical transmitting unit capable of transmitting optical signals of multiple wavelengths, an optical receiving unit capable of receiving optical signals of multiple wavelengths, and a processor that determines the wavelengths to be used for communication with a counterpart device, and the processor determines whether the multiple wavelengths are to be divided into upstream and downstream wavelengths or shared by both upstream and downstream wavelengths depending on the degree of reflection of the optical signal transmitted from the device itself.

According to the optical transceiver of this embodiment, the processor determines whether to divide multiple types of wavelengths into upstream and downstream use or to share them for both upstream and downstream use depending on the degree of reflection of the optical signal transmitted from the device itself, thereby enabling appropriate division and sharing of multiple types of wavelengths.

(15) A system according to one aspect of this embodiment is an optical communications system including a communication device capable of transmitting and receiving optical signals of multiple wavelengths, which performs optical communications in a single-core bidirectional transmission; an opposing device capable of transmitting and receiving optical signals of multiple wavelengths, which performs optical communications with the communication device; and a controller that manages the wavelengths to be used by the communication device and the opposing device, and the controller determines whether the multiple wavelengths are to be divided into upstream and downstream wavelengths or shared by both upstream and downstream wavelengths depending on the degree of reflection of the optical signal transmitted from the communication device.

According to the communication system of this embodiment, the controller determines whether to divide multiple types of wavelengths into upstream and downstream use or to share them for both upstream and downstream use depending on the degree of reflection of the optical signal transmitted from the communication device, thereby enabling appropriate division and sharing of multiple types of wavelengths.

<Details of the embodiment of the present disclosure>
Hereinafter, the details of the 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 combination.

[Optical communication transmission method]
Fig. 1 is an explanatory diagram showing variations of the transmission method of optical communication. In the figure, "TRx" is an abbreviation of optical transceiver. In this embodiment, the direction from communication device 1 to communication device 2 is referred to as the "downstream direction," and the opposite direction is referred to as the "upstream direction."
As shown in FIG. 1, the transmission methods of the optical communication system are roughly classified into the following methods.
Transmission method 1: 2-core transmission Transmission method 2: 1-core bidirectional transmission

Two-core transmission (transmission method 1) is a transmission method in which upstream and downstream communications are performed using separate optical fibers. Therefore, even if the same wavelength is shared for both upstream and downstream, optical signals do not interfere with each other. For example, two-core transmission is used in metro networks or core networks.
This is because metro and core networks use dense wavelength division multiplexing (DWDM), which means there is no freedom to assign different wavelengths for upstream and downstream. Also, it is difficult to share upstream and downstream transmissions (single-core transmission) because optical amplifiers are installed in the middle of the transmission line.

Single-core bidirectional transmission (transmission method 2) is a transmission method in which upstream and downstream communications are carried out using a single optical fiber. Therefore, if the same wavelength is shared for both upstream and downstream, optical signals may be interfered with by reflections along the transmission path. For example, single-core bidirectional transmission is used in access networks.
This is because single-core bidirectional transmission can reduce the cost of laying optical fiber, and is therefore suitable for access networks that have many installation locations.

In single-core bidirectional transmission, in order to suppress interference of optical signals caused by reflection along the transmission path, different wavelengths are generally used for upstream and downstream optical signals.
As shown in FIG. 1, wavelength allocation methods in single-core bidirectional transmission (transmission method 2) can be classified into, for example, "allocation method 1" in which a single wavelength is allocated to each of the upstream and downstream communications, and "allocation method 2" in which multiple wavelengths are allocated to each of the upstream and downstream communications.

Allocation method 1 is a method in which one wavelength λ1 is used for upstream communication and one wavelength λ2 is used for downstream communication. For example, Non-Patent Document 2 specifies the values of the wavelengths λ1 and λ2 of a PON that employs allocation method 1.
Allocation method 2 is a method in which multiple wavelengths λi (i=1, 2...m) are used for upstream communication, and multiple wavelengths λj (j=1, 2...n) are used for downstream communication. Wavelengths λi and λj may be subcarriers in a predetermined wavelength band. For example, Non-Patent Document 3 describes an optical transceiver that uses different subcarriers for upstream and downstream.

Incidentally, when performing bidirectional transmission over a single fiber using the intensity-modulated direct detection (IMDD) method, different wavelengths are assigned to the upstream optical signal and the downstream optical signal so that even if the upstream optical signal and the downstream optical signal interfere with each other, they can be separated and received using a wavelength filter.
Coherent systems are not usually suitable for single-core bidirectional transmission because, in order to make optical transceivers more compact, the transmitting light source and the receiving light source (the interference light for detection) are often shared, and the transmitting wavelength and the receiving wavelength are often aligned.

However, to assign different wavelengths to the upstream and downstream optical signals, it is necessary to have separate light sources for transmission and reception, which leads to high costs. Therefore, when connecting optical fibers with relatively little reflection, bidirectional transmission over a single fiber can be performed using the same wavelength without dividing the wavelength.
Furthermore, even in the case of a coherent system, an optical transceiver that uses a subcarrier multiplexing (SCM) system (see, for example, non-patent document 3) can transmit using multiple subcarriers with different wavelengths from a single light source by using digital signal processing (DSP).

In other words, in the SCM method, by assigning different subcarriers to the upstream optical signal and the downstream optical signal, even if the upstream optical signal and the downstream optical signal interfere with each other, the optical signal of the desired subcarrier can be selectively received by digital signal processing.

[Issues and solutions for single-core bidirectional transmission]
As described above, in single-core bidirectional transmission, if different wavelengths (which may be subcarriers) are assigned to upstream and downstream communications, even if the upstream optical signal and the downstream optical signal interfere with each other, it is possible to selectively receive only the desired optical signal.
On the other hand, the approach of always dividing limited wavelength band resources into upstream and downstream communications has the problem that transmission capacity cannot be expanded significantly.

In this embodiment, in order to solve the above problem, the amount of reflection in the transmission path between communication devices connected by a single optical fiber is determined, and depending on the result of the determination, it is decided whether multiple types of wavelengths should be divided into upstream and downstream use, or whether they should be shared for both upstream and downstream use.
Specifically, when the reflection is large, it is assumed that there is a lot of interference between optical signals, and multiple types of wavelengths are divided into upstream and downstream use. Conversely, when the reflection is small, it is assumed that there is little interference between optical signals, and multiple wavelengths are shared by both the upstream and downstream use.

In this way, it is possible to appropriately divide and share a plurality of types of wavelengths depending on the amount of reflection along the transmission path.
In other words, when reflection is large, stable bidirectional transmission over a single fiber is possible by dividing multiple types of wavelengths into upstream and downstream directions, and when reflection is small, large-capacity bidirectional transmission over a single fiber is possible by sharing multiple types of wavelengths for both upstream and downstream directions.

[Method for determining the amount of reflection]
The amount of reflection can be determined, for example, by the following method.
Determination method 1: Power measurement method Determination method 2: Error rate measurement method Determination method 3: Test frame method In the following description of the determination methods, "itself" is, for example, communication device 1 in FIG. 1, and "opposing device" is, for example, communication device 2 in FIG.

The power measurement method (judgment method 1) is a method for judging the amount of reflection based on the reception power R1 and reflection power T1 measured by the device itself and the reception power T2 and reflection power R2 measured by the opposing device (see Figures 4, 5A and 5B).

The error rate measurement method (judgment method 2) is a method for judging the amount of reflection. This judgment is made based on the bit error rate E1 of the communication frame detected by the device itself when simultaneously transmitting and receiving optical signals of the same wavelength, and the bit error rate E2 of the communication frame detected by the opposing device when simultaneously transmitting and receiving optical signals of the same wavelength (see Figures 6, 7A, and 7B).

The test frame method (judgment method 3) is a method for judging the amount of reflection based on the results of a loopback test (specifically, whether or not a test frame is lost) performed with the same transmission wavelength for both upstream and downstream (see Figures 8, 9A, and 9B).
The above-mentioned determination methods 1 to 3 will be described in detail later.

[Example of optical communication system configuration]
FIG. 2 is an explanatory diagram showing a variation of the configuration of the optical communication system.
2, the optical communication system includes a communication device 1, a communication device 2, and a controller 3 that manages them. The communication device 1 and the communication device 2 are connected one-to-one by a single optical fiber 4.

In this embodiment, communication device 1 is the "master device" and communication device 2 is the "slave device", but this correspondence may be reversed.
The communication device 1 and the communication device 2 are mechanically substantially the same optical communication device, and each include an optical transceiver 11, a switch 12, and a control unit 13.

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

The optical transceiver 11 has a function of switching the wavelength of an optical signal used for optical communication with a counterpart device. The optical signal may be a subcarrier. When the optical signal is divided into subcarriers, the optical transceiver 11 may have a switching function using the subcarriers as a wavelength.
The optical transceiver 11 having a wavelength switching function may be a coherent optical transceiver 11A (see FIG. 10) using the SCM method, or a multi-channel WDM (Wavelength Division Multiplexing) optical transceiver 11B (see FIG. 11) using a wavelength multiplexing method. A "channel" refers to a transmission path that transmits an electric signal or an optical signal (a specific wavelength in the case of an optical signal), and a plurality of wavelengths may be bundled together to form one channel. The internal configuration of the optical transceiver 11 will be described later.

An optical fiber 4 is connected to an optical port of the optical transceiver 11. The optical transceiver 11 is electrically connected to a predetermined port of the switch 12.
The switch 12 is an integrated circuit such as an LSI (Large Scale Integration) having a relay function of the L2 layer and the L3 layer. A control unit 13 is electrically connected to a predetermined port of the switch 12. The switch 12 and the control unit 13 may be implemented in a single integrated circuit such as a SoC (System on a Chip).

The control unit 13 is, for example, an arithmetic processing device including a central processing unit (CPU) 13A and a volatile memory 13B. 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 communicates with the optical transceiver 11 via serial communication such as I2C (Inter-Integrated Circuit).

The control unit 13 can acquire predetermined setting information from the controller 3 through communication via a management communication interface (not shown). The control unit 13 performs various setting processes for the communication device 1 and the communication device 2 based on the acquired setting information.
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.

The controller 3 is, for example, a management computer operated by a communications manager. As shown in Fig. 2, the connection methods between the communication device 1 and the communication device 2 and the controller 3 include a "cloud method" and a "proximity method."
The cloud method is a method in which the controller 3 is connected to the control units 13 of the communication devices 1 and 2 via a wide area communication network 5 including the Internet. In this case, the controller 3 can provide setting information to the communication devices 1 and 2 individually.

The proximity method is a method in which the controller 3 is connected to the control unit 13 of the master communication device 1 without going through the wide area communication network 5. However, a LAN (Local Area Network) may be interposed between the communication device 1 and the controller 3.
In this case, the controller 3 transmits the setting information of both communication devices 1 and 2 to the communication device 1. The control unit 13 of the communication device 1 transfers the setting information for the communication device 2 to the communication device 2 by control communication via the optical fiber 4 (dashed arrow in FIG. 2).

[Optical transceiver control path]
FIG. 3 is an explanatory diagram showing variations of the control path from the controller 3 to the optical transceiver 11 in the case of the proximity method of FIG.
3, control path P1 is a path for transmitting setting information to optical transceiver 11 of communication device 1. Control paths P2 and P3 are paths for transmitting setting information to optical transceiver 11 of communication device 2.

(Control path P1)
If the setting information received from the controller 3 is setting information for the optical transceiver 11 of the communication device 1, the control unit 13 controls the optical transceiver 11 of the communication device 1 in accordance with the received setting information via serial communication such as I2C.
In this way, control path P1 includes a path from controller 3 to control unit 13 in communication device 1 and a path from control unit 13 in communication device 1 to optical transceiver 11.

(Control path P2)
If the setting information received from the controller 3 is setting information for the optical transceiver 11 of the communication device 2, the control unit 13 of the communication device 1 generates an Ethernet control frame addressed to the communication device 2, including the received setting information, and outputs it to the switch 12.

The control frame is transmitted to the control unit 13 of the communication device 2 by Ethernet communication via the optical fiber 4. The control unit 13 of the communication device 2 controls its own optical transceiver 11 in accordance with the received setting information by serial communication such as I2C.
Thus, control path P2 includes a path from controller 3 to communication device 1, a path from communication device 1 to control unit 13 of communication device 2, and a path from control unit 13 in communication device 2 to optical transceiver 11.

(Control path P3)
The control path P3 is a path in which opposing TRx can exchange control information using a dedicated control channel (control wavelength).
In this case, if the setting information received from the controller 3 is setting information for the optical transceiver 11 of the communication device 2, the control unit 13 of the communication device 1 transfers the received setting information to its own optical transceiver 11.

The optical transceiver 11 of the communication device 1 transmits the received setting information to the optical transceiver 11 of the communication device 2 via a dedicated control channel.
In this way, the control path P3 includes a path from the controller 3 to the communication device 1, a path from the control unit 13 in the communication device 1 to the optical transceiver 11, and a control path of a dedicated channel between the TRxs.

[Outline of the first wavelength setting process]
FIG. 4 is an explanatory diagram showing an overview of the first wavelength setting process.
In the figure, "Dλ" is the initial setting value of the transmission wavelength. Therefore, in the initial state, the transmission wavelength of communication device 1 is "λ1" and the transmission wavelength of communication device 2 is "λ2". At this time, the reception wavelength of communication device 1 is λ2 and the reception wavelength of communication device 2 is λ1. Furthermore, the first wavelength setting process is premised on the conditions listed below.

Condition C11: The TRx of the communication device 1 can be switched to either transmit at λ1 and receive at λ2, or transmit at (λ1+λ2) and receive at (λ1+λ2), where (λ1+λ2) means that both wavelengths are used to form one channel.
Condition C12: TRx of the communication device 2 is switchable between transmitting at λ2 and receiving at λ1, or transmitting at (λ1+λ2) and receiving at (λ1+λ2).

Condition C13: Communication device 1 is the master device, and communication device 2 is the slave device. The master device is, for example, a communication device that communicates with the controller 3, or a communication device designated as the master by zero-touch provisioning or the like.
Condition C14: The control communication and the data communication use the same wavelength.

Condition C15: The transmission power of the optical signal with wavelength λ1 transmitted by the communication device 1 is approximately equal to the transmission power of the optical signal with wavelength λ2 transmitted by the communication device 2. Furthermore, the reflection does not depend on the wavelengths λ1 and λ2.
Condition C16: In order to prevent instability in the control communication, the reflection status is checked using different wavelengths for upstream communication and downstream communication.
Condition C17: The TRx of the communication device 1 and the TRx of the communication device 2 are capable of monitoring the received optical power of the optical signal.

As shown in FIG. 4, the first wavelength setting process includes the following steps.
Step ST11: Measurement of reflected power T1 Step ST12: Measurement of received power R1 Step ST13: First judgment based on the measurement results (T1, R1) Step ST14: Measurement of reflected power T2 Step ST15: Measurement of received power R2 Step ST16: Second judgment based on the measurement results (T2, R2)

The measurement of the reflected power T1 (step ST11) is a step of measuring the light receiving power (reflected power T1) on the communication device 1 side while the communication device 2 is not transmitting and the communication device 1 is transmitting at the wavelength λ1. The measurement is performed by the control unit 13 of the communication device 1.
The measurement of the reception power R1 (step ST12) is a step of measuring the reception power (reception power R1) on the communication device 1 side while the communication device 1 is stopping transmission and the communication device 2 is transmitting at the wavelength λ2. The measurement is performed by the control unit 13 of the communication device 1.

The first judgment (step ST13) based on the measurement results (T1, R1) is a step of judging whether to classify the wavelengths λ1 and λ2 as upstream and downstream, or to have the communication device 2 measure them, based on the measured values of the reflected power T1 and the received power R1. The judgment is made by the control unit 13 of the communication device 1.
Specifically, when R1/T1 is equal to or less than a predetermined threshold Th, the control unit 13 of the communication device 1 determines that the wavelengths λ1 and λ2 are to be divided into upstream and downstream wavelengths. Therefore, the transmission wavelengths of the communication devices 1 and 2 are maintained at the initial settings. This is because reflection on the communication device 1 side is large in this case.

If R1/T1 exceeds the predetermined threshold value Th, the control unit 13 of the communication device 1 transitions the process to step ST14.
The reason is that even if the reflection is small on the communication device 1 side, the amount of reflection on the communication device 2 side must be determined before a final decision can be made as to whether the wavelengths λ1 and λ2 should be shared for the upstream and downstream.

The measurement of the reflected power T2 (step ST14) is a step of measuring the light receiving power (reflected power T2) on the communication device 2 side while the communication device 1 is stopping transmission and the communication device 2 is transmitting at the wavelength λ2. The measurement is performed by the control unit 13 of the communication device 2, and the measurement value is notified to the communication device 1.
The measurement of the reception power R2 (step ST15) is a step of measuring the reception power (reception power R2) on the communication device 2 side while the communication device 2 is stopping transmission and the communication device 1 is transmitting at the wavelength λ1. The measurement is performed by the control unit 13 of the communication device 2, and the measurement value is notified to the communication device 1.

The second determination (step ST16) based on the measurement results (T2, R2) is a step of determining whether the wavelengths λ1 and λ2 are divided into upstream and downstream or shared based on the measured values of the reflected power T2 and the received power R2. The determination is made by the control unit 13 of the communication device 1.
Specifically, when R2/T2 is equal to or less than a predetermined threshold Th, the control unit 13 of the communication device 1 determines that the wavelengths λ1 and λ2 are to be divided into upstream and downstream wavelengths. Therefore, the transmission wavelengths of the communication devices 1 and 2 are maintained at the initial settings. This is because reflection on the communication device 2 side is large in this case.

When R2/T2 exceeds a predetermined threshold value Th, the control unit 13 of the communication device 1 determines that the wavelengths λ1 and λ2 are shared for both the upstream and downstream. The reason is that if the reflection based on the received power measured by both communication devices 1 and 2 is small, it is acceptable to share the wavelengths λ1 and λ2 between them to expand the transmission capacity.
Therefore, the control unit 13 of the communication device 1 instructs the communication device 2 to set the transmission wavelength and reception wavelength to two types, λ1 and λ2, and changes its own transmission wavelength and reception wavelength to two types, λ1 and λ2.

[Specific example of first wavelength setting process]
5A and 5B are flowcharts showing a specific example of the first wavelength setting process.
5A and 5B, "ni" (i=1 to 5) is a node of the flowchart. "Device 1" is an abbreviation for communication device 1. "Device 2" is an abbreviation for communication device 2. The dashed arrows represent request frames or response frames transmitted and received between device 1 and device 2.

(Initial state of wavelength)
At the start of the initialization sequence, device 1 sets its transmission wavelength to "λ1" and its reception wavelength to "λ2" (step S101).
At the start of the initialization sequence, device 2 sets its transmission wavelength to "λ2" and its receiving wavelength to "λ1" (step S201).

(Processing of communication device 1)
When the initialization sequence starts, the device 1 requests the device 2 to stop transmission (step S103), and then waits for a response from the device 2 (step S104).
Next, upon receiving the response to stop transmission, the device 1 measures the reception power after the device 2 stops transmission (step S105), thereby measuring the reflection power T1 (step S106).

Next, device 1 requests device 2 to start transmission (step S107), and waits for a response from device 2 (step S108).
Next, upon receiving the response to start transmission, the device 1 stops its own transmission (step S109) and then measures the reception power R1 (step S110).

Next, the device 1 starts its own transmission (step S111), and then determines whether or not "R1/T1>threshold" is satisfied (step S112).
If the result of the determination in step S112 is negative (if the reflection is large), the device 1 requests the device 2 to start operation (step S113), and then waits for a response from the device 2 (step S114). Upon receiving the response to start operation, the device 1 starts operation at λ1 (step S115). In this case, operation is started with the device 1's transmission wavelength set to λ1 and its reception wavelength set to λ2.

If the determination result in step S112 is positive (if the reflection is small), the device 1 requests the device 2 to measure the reflection power T2 (step S116), and then stops its own transmission (step S117).
Next, after waiting for a response of the reflected power T2 from the device 2 (step S118), the device 1 starts its own transmission (step S119), requests the device 2 to measure the received power R2 (step S120), and waits for a response to the measurement (step S121).

The measurement request for the receiving power R2 transmitted from device 1 to device 2 is, specifically, a control command for causing device 2 to execute the following processes in the order of stop transmission/power measurement/start transmission.

Having received the response including the reception power R2, the device 1 determines whether or not "R2/T2>threshold" is satisfied (step S122).
If the result of the determination in step S122 is negative (if the reflection is large), the device 1 requests the device 2 to start operation (step S128), and then waits for a response from the device 2 (step S129). Having received the response from the device 2 to start operation, the device 1 starts operation at λ1 (step S115). In this case, operation is started with the device 1's transmission wavelength set to λ1 and its reception wavelength set to λ2.

If the determination result in step S122 is positive (if the reflection is small), the device 1 requests the device 2 to start operation at (λ1+λ2) (step S123), and then waits for a response from the device 2 (step S124).
Next, upon receiving the response from device 2, device 1 changes the wavelength used for transmission and reception to (λ1+λ2) (step S125), and then starts operation at the changed wavelength (λ1+λ2) (step S126). In this case, device 1 starts operation with the transmission wavelength being (λ1+λ2) and the reception wavelength being (λ1+λ2).

(Processing of communication device 2)
When the initialization sequence starts, device 2 waits for a request to stop transmission from device 1 (step S202).
Next, device 2 that has received the request to stop transmission returns a response to device 1 (step S203), and then stops its own transmission (step S204).

Next, device 2 waits for a request to start transmission from device 1 (step S205), and when a request is received, starts its own transmission (step S206) and returns a transmission start response to device 1 (step S207).
Next, the device 2 waits for a request from the device 1 to start operation (large reflection) or to measure the reflected power (step S208).

If the request from the device 1 is to start operation (high reflection), the device 2 returns a response to the device 1 (step S209) and then starts operation at λ2 (step S210). In this case, operation is started with the transmission wavelength of the device 2 being λ2 and the reception wavelength being λ1.
If the request from device 1 is to measure the reflected power, device 2 waits for device 1 to stop transmitting (step S211), measures the reflected power T2 (step S212), and returns a response including the measured reflected power T2 to device 1 (step S213).

Next, the device 2 waits for a request for measuring the reception power from the device 1 (step S214). Upon receiving the request for measuring the reception power, the device 2 sequentially stops its own transmission (step S215), measures the reception power R2 (step S216), and starts its own transmission (step S217), and returns a response including the measurement result, the reception power R2, to the device 1 (step S218).
Next, the device 2 waits for a request to start operation (large reflection) or start operation (small reflection) from the device 1 (step S219).

If the request from the device 1 is to start operation (high reflection), the device 2 returns a response to the device 1 (step S223) and then starts operation at λ2 (step S210). In this case, the device 2 starts operation with the transmission wavelength of λ2 and the reception wavelength of λ1.
If the request from device 1 is to start operation (low reflection), device 2 returns a response to device 1 (step S220), and after changing the wavelength used for transmission and reception to (λ1+λ2) (step S221), starts operation with the changed wavelength (step S222). In this case, device 2 starts operation with the transmission wavelength being (λ1+λ2) and the reception wavelength being (λ1+λ2).

[Outline of second wavelength setting process]
FIG. 6 is an explanatory diagram showing an overview of the second wavelength setting process.
In the figure, "Dλ" is the initial setting value of the transmission wavelength. Therefore, in the initial state, the transmission wavelength of communication device 1 is "λ1" and the transmission wavelength of communication device 2 is "λ2". At this time, the reception wavelength of communication device 1 is λ2 and the reception wavelength of communication device 2 is λ1. The second wavelength setting process is based on the following prerequisites:

Condition C21: TRx of communication device 1 can be switched to either transmit at λ1 and receive at λ2, or transmit at (λ1+λ2) and receive at (λ1+λ2), where (λ1+λ2) means that both wavelengths are used to form one channel.
Condition C22: TRx of the communication device 2 is switchable between transmitting at λ2 and receiving at λ1, or transmitting at (λ1+λ2) and receiving at (λ1+λ2).

Condition C23: Communication device 1 is the master device, and communication device 2 is the slave device. The master device is, for example, a communication device that communicates with the controller 3, or a communication device designated as the master by zero-touch provisioning or the like.
Condition C24: The control communication and the data communication use the same wavelength.

Condition C25: The transmission power of the optical signal with wavelength λ1 transmitted by the communication device 1 is approximately equal to the transmission power of the optical signal with wavelength λ2 transmitted by the communication device 2. Furthermore, the reflection does not depend on the wavelengths λ1 and λ2.
Condition C26: In order to prevent instability in the control communication, the reflection status is checked using different wavelengths for upstream communication and downstream communication.
Condition C27: The TRx of communication device 1 and communication device 2 are capable of encoding and decoding error correction, and monitoring the bit error rate before correction during decoding.

As shown in FIG. 6, the second wavelength setting process includes the following steps.
Step ST21: Measurement of bit error rate E1. Step ST22: First decision based on the measurement result (E1). Step ST23: Measurement of bit error rate E2. Step ST24: Second decision based on the measurement result (E2).

The measurement of the bit error rate E1 (step ST21) is a step of measuring the bit error rate E1 contained in the communication frame received by the communication device 1 when the communication device 1 simultaneously transmits and receives an optical signal with a wavelength λ2. The measurement is performed by the control unit 13 of the communication device 1.
The first judgment (step ST22) based on the measurement result (E1) is a step of judging whether to classify the wavelengths λ1 and λ2 as upstream and downstream, or to have the communication device 2 measure it, based on the measured value of the bit error rate E1. The judgment is made by the control unit 13 of the communication device 1.

Specifically, when E1 is equal to or greater than a predetermined threshold Th, the control unit 13 of the communication device 1 determines that the wavelengths λ1 and λ2 are to be divided into upstream and downstream wavelengths. In this case, the transmission wavelength of the communication device 1 is returned to the initial state.
The reason is that if the bit error rate E1 is relatively high when optical signals of the same wavelength λ2 are transmitted and received simultaneously, it can be assumed that this is due to the large reflection of the optical signal of wavelength λ2.

If E1 is less than the predetermined threshold value Th, the control unit 13 of the communication device 1 transitions the process to step ST23.
The reason is that the state of the optical signal transmission path is not necessarily the same when viewed from communication device 1 and when viewed from communication device 2, so a final decision on whether or not wavelengths λ1 and λ2 should be shared cannot be made simply by measuring the bit error rate E1 on the communication device 1 side.

The measurement of the bit error rate E2 (step ST23) is a step of measuring the bit error rate E2 contained in the communication frame received by the communication device 2 when the communication device 2 simultaneously transmits and receives an optical signal with wavelength λ1. The measurement is performed by the control unit 13 of the communication device 2, and the measurement value is notified to the communication device 1.
The second judgment (step ST24) based on the measurement result (E2) is a step of judging whether the wavelengths λ1 and λ2 are divided into upstream and downstream or shared by both the upstream and downstream based on the measured value of the bit error rate E2. The judgment is made by the control unit 13 of the communication device 1.

Specifically, when E2 is equal to or greater than a predetermined threshold Th, the control unit 13 of the communication device 1 determines that the wavelengths λ1 and λ2 are to be divided into upstream and downstream wavelengths. In this case, the transmission wavelength of the communication device 2 is returned to the initial state.
The reason is that if the bit error rate E2 is relatively high when optical signals of the same wavelength λ1 are transmitted and received simultaneously, it can be assumed that this is due to the large reflection of the optical signal of wavelength λ1.

When E2 is less than a predetermined threshold Th, the control unit 13 of the communication device 1 determines that the wavelengths λ1 and λ2 are shared for both the upstream and downstream. The reason is that if the reflection of the optical signals of the wavelengths λ1 and λ2 is small, the communication devices 1 and 2 may share the wavelengths λ1 and λ2 to expand the transmission capacity.
Therefore, the control unit 13 of the communication device 1 instructs the communication device 2 to set the transmission wavelength and reception wavelength to two types, λ1 and λ2, and changes its own transmission wavelength and reception wavelength to two types, λ1 and λ2.

[Specific example of second wavelength setting process]
7A and 7B are flowcharts showing a specific example of the second wavelength setting process.
7A and 7B, "ni" (i=6 to 10) is a node of the flowchart. "Device 1" is an abbreviation for communication device 1. "Device 2" is an abbreviation for communication device 2. The dashed arrows represent request frames or response frames transmitted and received between device 1 and device 2.

(Initial state of wavelength)
At the start of the initialization sequence, device 1 sets its transmission wavelength to "λ1" and its reception wavelength to "λ2" (step S301).
At the start of the initialization sequence, device 2 sets its transmitting wavelength to "λ2" and its receiving wavelength to "λ1" (step S401).

(Processing of communication device 1)
When the initialization sequence starts, the device 1 sets its own transmission wavelength to λ2 (the wavelength of the device 2) (step S302), and then measures the uncorrected bit error rate E1 (step S303).
Next, the device 1 returns its own transmission wavelength to λ1 (step S304), and then determines whether or not "E1<threshold" is satisfied (step S305).

If the result of the determination in step S305 is negative (determined to be high reflection), the device 1 requests the device 2 to start operation (step S113), and then waits for a response from the device 2 (step S307). Having received the response to start operation, the device 1 starts operation at λ1 (step S308). In this case, operation is started with the transmission wavelength of the device 1 being λ1 and the reception wavelength being λ2.
If the determination result in step S305 is positive (reflection is determined to be small), the device 1 requests the device 2 to measure the bit error rate E2 (step S309), and then waits for a response from the device 2 (step S310).

The measurement request for bit error rate E2 sent from device 1 to device 2 is, specifically, a control command to cause device 2 to execute the following processes in the order of wavelength change to λ1/error rate measurement/wavelength change to λ2.

Next, upon receiving the response including the bit error rate E2, the device 1 determines whether or not "E2<threshold" is satisfied (step S311).
If the result of the determination in step S311 is negative (determined to be high reflection), the device 1 requests the device 2 to start operation (step S312), and then waits for a response from the device 2 (step S317). Having received the response to start operation, the device 1 starts operation at λ1 (step S308). In this case, operation is started with the device 1's transmission wavelength set to λ1 and its reception wavelength set to λ2.

If the determination result in step S311 is positive (reflection is determined to be small), the device 1 requests the device 2 to start operation at (λ1+λ2) (step S313), and then waits for a response from the device 2 (step S314).
Next, upon receiving the response from device 2, device 1 changes the wavelength used for transmission and reception to (λ1+λ2) (step S315), and then starts operation at the changed wavelength (λ1+λ2) (step S316). In this case, device 1 starts operation with the transmission wavelength being (λ1+λ2) and the reception wavelength being (λ1+λ2).

(Processing of communication device 2)
When the initialization sequence starts, the device 2 waits for a request from the device 1 to start operation (large reflection) or to measure an error rate (step S402).
If the request from the device 1 is to start operation (high reflection), the device 2 returns a response to the device 1 (step S403) and then starts operation at λ2 (step S404). In this case, operation is started with the transmission wavelength of the device 2 being λ2 and the reception wavelength being λ1.
If the request from the device 1 is to measure the error rate, the device 2 sets its own transmission wavelength to λ1 (the wavelength of the device 1) (step S405).

Furthermore, the device 2 measures the bit error rate E2 (step S406), changes the transmission wavelength back to λ2 (step S407), and returns a response including the measurement result, the bit error rate E2, to the device 1 (step S408).
Next, the device 2 waits for a request to start operation (large reflection) or start operation (small reflection) from the device 1 (step S409).

If the request from the device 1 is to start operation (high reflection), the device 2 returns a response to the device 1 (step S413) and then starts operation at λ2 (step S404). In this case, operation is started with the transmission wavelength of the device 2 being λ2 and the reception wavelength being λ1.
If the request from device 1 is to start operation (low reflection), device 2 returns a response to device 1 (step S410), and after changing the wavelength used for transmission and reception to (λ1+λ2) (step S411), starts operation with the changed wavelength (step S412). In this case, operation is started with device 2's transmission wavelength set to (λ1+λ2) and its reception wavelength set to (λ1+λ2).

[Outline of the third wavelength setting process]
FIG. 8 is an explanatory diagram showing an overview of the third wavelength setting process.
"Dλ" in the figure is the initial setting value of the transmission wavelength. Therefore, in the initial state, the transmission wavelength of communication device 1 is "λ1" and the transmission wavelength of communication device 2 is "λ2". At this time, the reception wavelength of communication device 1 is λ2 and the reception wavelength of communication device 2 is λ1. Furthermore, the third wavelength setting process is premised on the conditions listed below.

Condition C31: The TRx of the communication device 1 can be switched to either transmit at λ1 and receive at λ2, or transmit at (λ1+λ2) and receive at (λ1+λ2), where (λ1+λ2) means that both wavelengths are used to form one channel.
Condition C32: TRx of the communication device 2 is switchable between transmitting at λ2 and receiving at λ1, or transmitting at (λ1+λ2) and receiving at (λ1+λ2).

Condition C33: Communication device 1 is the master device, and communication device 2 is the slave device. The master device is, for example, a communication device that communicates with the controller 3, or a communication device designated as the master by zero-touch provisioning or the like.
Condition C34: The control communication and the data communication use the same wavelength.

Condition C35: The transmission power of the optical signal with wavelength λ1 transmitted by the communication device 1 is approximately equal to the transmission power of the optical signal with wavelength λ2 transmitted by the communication device 2. Furthermore, the reflection does not depend on the wavelengths λ1 and λ2.
Condition C36: In order to prevent instability in the control communication, the reflection status is checked using different wavelengths for upstream communication and downstream communication.
Condition C37: The control units 13 of the communication devices 1 and 2 are capable of performing a loopback test based on, for example, Ethernet OAM (Operations Administration Maintenance).

6, the third wavelength setting process includes the following steps: Note that the first loopback test (step ST31) is a test for the communication device 1 to check whether or not there is any defect other than reflection, and is not a test essential for estimating the amount of reflection.
Step ST31: Executing a first loopback test. Step ST32: Making a first judgment based on the result of the first loopback test. Step ST33: Executing a second loopback test. Step ST34: Making a second judgment based on the result of the second loopback test.

Execution of the first loopback test (step ST31) is a step in which the communication device 1 performs a loopback test in a state in which the transmission wavelengths for the upstream and downstream are different.
FIG. 8 illustrates an example in which a downstream test frame is transmitted at a wavelength λ1 (Dλ of communication device 1) and an upstream test frame is transmitted at a wavelength λ2 (Dλ of communication device 2).

The first determination based on the result of the first loopback test (step ST32) is a step of determining whether to abnormally terminate the first loopback test or to proceed to a second loopback test based on the quality (number of bit errors, etc.) of the test frame received by the communication device 1 in the first loopback test. The determination is made by the control unit 13 of the communication device 1.
Specifically, if the test frame received in the first loopback test is missing, the control unit 13 of the communication device 1 executes an abnormal termination.
Note that "missing test frames" refers to a defect in the quality of the test frames, and means, for example, that the frame loss rate of multiple test frames is equal to or greater than a predetermined value, or that at least one test frame cannot be received.

The abnormal termination is to terminate the communication between the communication devices 1 and 2 when some abnormality is detected. The control unit 13 of the communication device 1 notifies the controller 3 of the occurrence of the abnormality.
The reason is that if the loopback test is not passed when the wavelengths λ1 and λ2 are separated, there is a fundamental abnormality unrelated to the reflection of the optical signal.
If there is no loss in the test frame received in the first loopback test, the control unit 13 of the communication device 1 proceeds to step ST33.

Execution of the second loopback test (step ST32) is a step in which the communication device 1 performs a loopback test by using the same transmission wavelength for the upstream and downstream.
FIG. 8 illustrates an example in which a downstream test frame is transmitted at wavelength λ2 (Dλ of communication device 2) and an upstream test frame is transmitted at wavelength λ2 (Dλ of communication device 2).

The second judgment based on the second loopback test result (step ST34) is a step in which it is judged whether the wavelengths λ1 and λ2 are divided into upstream and downstream or shared for both upstream and downstream based on the quality (number of bit errors, etc.) of the test frame received by the communication device 1 in the second loopback test. The judgment is made by the control unit 13 of the communication device 1.

Specifically, if the test frame received by the second loopback test has a missing portion, the control unit 13 of the communication device 1 determines that the wavelengths λ1 and λ2 are to be divided into upstream and downstream wavelengths. In this case, the transmission wavelength of the communication device 2 is returned to the initial state.
The reason is that if the loopback test is not passed when the wavelength λ2 is the same for the upstream and downstream, it can be assumed that there is a location in the transmission path where the optical signal is highly reflected.

If there is no loss in the test frame received by the second loopback test, the control unit 13 of the communication device 1 determines that the wavelengths λ1 and λ2 are shared between the upstream and downstream. The reason for this is that if the loopback test passes even when the wavelength λ2 is the same for the upstream and downstream, it can be assumed that the reflection of the optical signal in the transmission path is low, and it is acceptable to share the wavelengths λ1 and λ2 for the upstream and downstream to expand the transmission capacity.
Therefore, the control unit 13 of the communication device 1 changes its own transmission wavelength to two types, λ1 and λ2, and instructs the communication device 2 to set the transmission wavelength to two types, λ1 and λ2.

[Details of the third wavelength setting process]
9A and 9B are flowcharts showing a specific example of the third wavelength setting process.
9A and 9B, "ni" (i=11 to 15) is a node of the flowchart. "Device 1" is an abbreviation for communication device 1. "Device 2" is an abbreviation for communication device 2. The dashed arrows represent request frames or response frames transmitted and received between device 1 and device 2.

(Initial state of wavelength)
At the start of the initialization sequence, device 1 sets its transmission wavelength to "λ1" and its reception wavelength to "λ2" (step S501).
At the start of the initialization sequence, device 2 sets its transmission wavelength to "λ2" and its receiving wavelength to "λ1" (step S601).

(Processing of communication device 1)
When the initialization sequence starts, the device 1 requests the device 2 to perform a loopback test (step S502), and then waits for a response from the device 2 (step S503).
Next, upon receiving the response to the loopback test, the device 1 waits for a predetermined time required for changing the configuration of the device 2 (step S504), and then transmits a test frame for the loopback test to the device 2 (step S506).

Next, the device 1 waits for a predetermined time required for changing the configuration of the device 2 (step S506), and then judges whether or not there is a loss of a test frame (step S507).
If the determination result in step S506 is "YES", device 1 requests device 2 to abnormally terminate (step S508), and then abnormally terminates itself (step S509).

If the determination result in step S506 is "no", the device 1 requests the device 2 to perform a loopback test (step S512), and then waits for a response from the device 2 (step S513).
Next, upon receiving the loopback test response, device 1 changes its own transmission wavelength to λ2 (the wavelength of device 2) (step S514), waits for a predetermined time required for the configuration change (step S515), and then transmits a test frame for the loopback test to device 2 (step S517).

Next, the device 1 waits for a predetermined time required for changing the configuration of the device 2 (step S518), and then judges whether or not there is a loss of the test frame (step S518).
If the result of the determination in step S518 is "Yes" (determined to be high reflection), the device 1 requests the device 2 to start operation (step S519), and then waits for a response from the device 2 (step S510). After that, upon receiving the response from the device 2, the device 1 starts operation at λ1 (step S511). In this case, operation is started with the device 1's transmission wavelength as λ1 and its reception wavelength as λ2.

If the determination result in step S518 is "none" (determined to be low reflection), the device 1 requests the device 2 to start operation at (λ1+λ2) (step S520), and then waits for a response from the device 2 (step S521).
Next, upon receiving the response from device 2, device 1 changes the wavelength used for transmission and reception to (λ1+λ2) (step S522), and then starts operation at the changed wavelength (λ1+λ2) (step S523). In this case, device 1 starts operation with the transmission wavelength being (λ1+λ2) and the reception wavelength being (λ1+λ2).

(Processing of communication device 2)
When the initialization sequence starts, device 2 waits for a loopback test request from device 1 (step S602).
Next, upon receiving the request for the loopback test, the device 2 returns a response to the device 1 (step S603), then changes its own control configuration to loopback (step S604), and returns a test frame for the loopback test to the device 1 (step S605).

Next, the device 2 releases the loopback control configuration (step S606), and then waits for an abnormal termination or a loopback test request from the device 1 (step S607).
If the request from device 1 is for abnormal termination, device 2 executes its own abnormal termination (step S608).

If the request from device 1 is a loopback test, device 2 returns a response to device 1 (step S611), then changes its own control configuration to loopback (step S612), and returns a test frame for the loopback test to device 1 (step S613).
Next, the device 2 releases the control configuration of the loopback test (step S614), and then waits for a request to start operation (large reflection) or start operation (small reflection) from the device 1 (step S615).

If the request from the device 1 is to start operation (high reflection), the device 2 returns a response to the device 1 (step S609) and then starts operation at λ2 (step S610). In this case, operation is started with the transmission wavelength of the device 2 being λ2 and the reception wavelength being λ1.
If the request from device 1 is to start operation (low reflection), device 2 returns a response to device 1 (step S616), and after changing the wavelength used for transmission and reception to (λ1+λ2) (step S617), starts operation with the changed wavelength (step S618). In this case, device 2 starts operation with the transmission wavelength (λ1+λ2) and the reception wavelength (λ1+λ2).

[Optical Transceiver Configuration Example 1]
FIG. 10 is a block diagram showing an example of the internal configuration of the optical transceiver 11. As shown in FIG.
The optical transceiver 11 in Fig. 10 is a coherent optical transceiver 11A that employs the SCM method. Hereinafter, the coherent optical transceiver 11A will be abbreviated as "optical transceiver 11A." Note that since the wavelength λ (m) is a physical quantity obtained by dividing the speed of light c (m/s) by the frequency f (Hz), the "subcarrier" can also be rephrased as the frequency.

The optical transceiver 11A includes a light source 101, an optical splitter 102, a first signal processing unit 103, a DA (Digital-Analog) conversion unit 104, an optical transmitting unit 105, an optical receiving unit 106, an AD (Analog-Digital) conversion unit 107, a second signal processing unit 108, an optical circulator 109, and a processor 110.
The light source 101 is, for example, a semiconductor laser diode. The laser diode may have a fixed emission wavelength or a variable emission wavelength.

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

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 AD conversion unit 107 and outputs a received signal (electrical signal) RS.

The first signal processing unit 103 and the second signal processing unit 108 can arbitrarily allocate multiple subcarriers to transmission and reception. This allows multiple subcarriers to be shared or divided. The digital signal processing of the second signal processing unit 108 may include at least one of the following processes: dispersion compensation, sampling phase synchronization, adaptive equalization, frequency offset compensation, carrier phase recovery, and error correction decoding.

The DA conversion unit 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 transmission unit 105.
The AD conversion unit 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 .

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 the transmission data signal. The optical transmitter 105 outputs the modulated optical signal as a multiplexed optical signal Oout.
As a modulation method, multi-level phase shift keying (PSK), multi-level quadrature amplitude modulation (QAM), etc. Also, multiplexing such as polarization multiplexing and orthogonal frequency division multiplexing (OFDM) may be performed for one wavelength.

The optical receiving unit 106 mixes the local light and the multiplexed optical signal Oin using, for example, a 90-degree hybrid mixer, and separates the mixed light into optical signals of multiple systems each including an I component and a Q component.
The optical receiving unit 106 includes a conversion unit such as a photodiode-trans impedance amplifier (PD-TIA) 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 AD conversion unit 107 and output to a second signal processing unit 108.

The output side of the optical transmitter 105 is connected to port P1 of the optical circulator 109, a single-core bidirectional optical fiber 4 is connected to port P2, and the input side of the optical receiver 106 is connected to port P3. The optical circulator 109 may be provided outside the housing of the optical transceiver 11A.

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

The processor 110 is capable of serial communication with the control unit 13 of the communication devices 1 and 2 acting as a master. Therefore, the processor 110 is capable of executing a predetermined slave process under the initiative of the control unit 13.
The above slave processing includes, for example, a process of notifying the control unit 13 of the received light power monitored in the optical receiving unit 106. If the second signal processing unit 108 has a function such as forward error correction (FEC), the above slave processing also includes a process of notifying the control unit 13 of the monitored bit error rate.

The processor 110 can control which of the multiple subcarriers to use in response to an instruction from the control unit 13 .
Specifically, the processor 110 generates a control signal CS1 for executing modulation of a subcarrier for transmission instructed by the control unit 13, and outputs the generated control signal CS to the optical transmitting unit 105. Similarly, the processor 110 generates a control signal CS2 for executing demodulation of a subcarrier for reception instructed by the control unit 13, and outputs the generated control signal CS2 to the optical receiving unit 106.

[Optical Transceiver Configuration Example 2]
FIG. 11 is a block diagram showing another example of the internal configuration of the optical transceiver 11. In FIG.
11 is a multi-channel WDM optical transceiver 11B that utilizes wavelength division multiplexing. Hereinafter, the WDM optical transceiver 11B will be abbreviated to "optical transceiver 11B."

Here, the optical transceiver 11B that supports four wavelengths for both transmission and reception is illustrated as an example, but the number of wavelengths of the optical transceiver 11B may be two or more.
Moreover, the WDM may be either CWDM (Coarse WDM) or DWDM (Dense WDM).

As shown in FIG. 11, the optical transceiver 11A includes a TOSA (Transmitter Optical Sub-Assembly) 121, an LDD (Laser Diode Driver) 122, a transmitting side CDR (Clock Data Recovery) 123, a ROSA (Receiver Optical Sub-assembly) 124, a TIA (Trans-Impedance Amplifier) 125, a receiving side CDR 126, an optical circulator 127, and a processor 128.

The transmitting CDR 123 is a circuit unit capable of shaping the waveforms of up to four electrical signals TX. The signals to be shaped are selected based on a control signal CS1 from the control unit 13.
When the quality of the electrical signal input to the LDD 122 is improved by shaping the waveform, the waveform quality of the drive signal is improved. As a result, the waveform of the optical signal output by the laser diode is shaped, which contributes to improving the communication performance of the optical transceiver 11A.

The LDD 122 is a circuit unit capable of driving up to four laser diodes. The laser diodes to be driven are selected based on a control signal CS1 from the control unit 13.
The LDD 122 generates a drive signal for driving a laser diode in the TOSA 121 based on an electrical signal TX from the transmitting CDR 123. The LDD 122 may be built into the TOSA 121.

The TOSA 121 is an optical device that converts an electrical signal to be transmitted into an optical signal, that is, the TOSA 121 causes each laser diode to output an optical signal modulated in response to a drive signal.
The TOSA 121 includes, for example, four laser diodes for generating up to four channels of optical signals (four optical signals each having a different peak wavelength), and an optical multiplexer.

The laser diode of TOSA121 is an optical transmitting element that converts an electrical signal into an optical signal. As mentioned above, a channel refers to a transmission path that transmits an electrical or optical signal. Multiple channels refer to multiple transmission paths that are installed in parallel with each other and each transmit an independent signal.

The TOSA 121 generates optical signals having different wavelengths based on up to four channels of electrical signals (input signals) TX generated within the communication devices 1 and 2 .
The TOSA 121 multiplexes (combines) the generated optical signals using an optical multiplexer and outputs the multiplexed optical signal Oout. The multiplexed optical signal Oout includes up to four optical signals with wavelengths λ1, λ2, λ3, and λ4, each of which has a different wavelength and transmits independent information.

The ROSA 124 is an optical device that converts the received optical signal into an electrical signal.
The ROSA 124 includes, for example, four photodiodes for receiving optical signals of up to four wavelength channels, and an optical splitter.
The photodiode of the ROSA 124 is an optical receiving element that converts an optical signal into an electrical signal. The ROSA 124 demultiplexes the multiplexed optical signal Oin received from the outside into optical signals with different wavelengths. The ROSA 124 converts each of the optical signals demultiplexed into a maximum of four wavelengths into a photocurrent (electrical signal).

The TIA 125 is a circuit unit that converts a photocurrent into an electrical signal (output signal) RX.
The TIA 125 converts the photocurrents output from up to four photodiodes into electrical signals RX. The conversion target is selected based on a control signal CS2 from the control unit 13. The TIA 125 may be built in the ROSA 124.

The receiving side CDR 126 is a circuit unit capable of shaping the waveforms of up to four electrical signals RX. The signals to be shaped are selected based on a control signal CS2 from the control unit 13.
The electrical signal output by the TIA 125 has jitter removed by the receiving CDR 126 and is output in a state that is easy to handle as a digital signal.
The transmitting CDR 123 and the receiving CDR 126 may be configured as an integrated integrated circuit, i.e., the CDRs 123 and 126 may be integrated as a transmitting and receiving CDR.

The output side of the TOSA 121 is connected to port P1 of the optical circulator 127, a single-core bidirectional optical fiber 4 is connected to port P2, and the input side of the ROSA 124 is connected to port P3. The optical circulator 127 may be provided outside the housing of the optical transceiver 11B.

The processor 128 is, for example, a one-chip microcontroller that controls the components included in the optical transceiver 11A. The microcontroller may be, for example, an MPU, a logic circuit such as an FPGA or a CPLD (Complex Programmable Logic Device), or a combination of these.

The processor 128 is capable of serial communication with the control unit 13 of the communication devices 1 and 2 acting as a master. Therefore, the processor 128 is capable of executing a predetermined slave process under the initiative of the control unit 13.
The slave process includes, for example, a process of notifying the control unit 13 of the received light power monitored in the ROSA 124. The control unit 13 has a function such as forward error correction (FEC) and calculates a bit error rate based on the electrical signal RX.

The processor 128 can control, in response to an instruction from the control unit 13, which of a plurality of (four in the illustrated example) wavelengths λ1, λ2, λ3, and λ4 to use.
Specifically, the processor 128 generates a control signal CS1 that enables a transmission wavelength instructed by the control unit 13, and outputs the generated control signal CS1 to the transmitting-side CDR 123 and the LDD 122. Similarly, the processor 128 generates a control signal CS2 that enables a reception wavelength instructed by the control unit 13, and outputs the generated control signal CS2 to the TIA 125 and the receiving-side CDR 126.

[First Modification: Modification of the First Wavelength Setting Process]
In the first wavelength setting process (FIGS. 4, 5A, and 5B), it may be determined whether the wavelengths λ1 and λ2 are to be used for upstream and downstream, or whether they are to be used for both, based on the results of comparing the reflected powers T1 and T2 with the following minimum received powers L1 and L2 that are preset. In this case, it is not necessary to measure the received powers R1 and R2.
First minimum reception power L1: the minimum reception power that the communication device 1 can receive (set value)
Second minimum reception power L2: the minimum reception power that the communication device 2 can receive (set value)
Since communication device 1 and communication device 2 are opposed to each other, normally L1=L2.

Specifically, the control unit 13 may execute the following process 1 and process 2.
Process 1: If L1/T1≦Tha or L2/T2≦Thb, the wavelengths λ1 and λ2 are divided into upstream and downstream wavelengths. In this case, there is a possibility that the optical signal cannot be received by either the communication device 1 or the communication device 2 due to the influence of reflection.
Process 2: When L1/T1>Tha and L2/T2>Thb, the wavelengths λ1 and λ2 are shared for both the upstream and downstream. In this case, the influence of reflection is small in both communication device 1 and communication device 2, and the optical signal can be properly received.

[Second Modification: Variation in Connection Form of Optical Communication System]
In the above-described embodiment, the transmission method of the master-side communication device 1 needs only to be “single-core bidirectional transmission” (transmission method 1), and the transmission method of the slave-side communication device 2 may be either “single-core bidirectional transmission” (transmission method 1) or “two-core transmission” (transmission method 2).

Furthermore, the transmission path between the master communication device 1 and the slave communication device 2 is not limited to a direct connection via a single optical fiber 4, but may be in a form that involves one or more optical couplers, optical networks, etc.
A modified example of the connection topology of the optical communication system will be described below with reference to Fig. 12. Fig. 12 is an explanatory diagram showing variations of the connection topology of the optical communication system.

"Pattern 1" in FIG. 12 is a connection configuration in which one-core bidirectional transmission is used from communication device 1 to optical coupler 201, and two-core transmission is used from optical coupler 201 to communication device 2.
Specifically, in pattern 1, a single-core optical fiber 4 connected to a communication device 1 is branched into two single-core optical fibers 202, 202 by an optical coupler (e.g., a power splitter) 201, and each of the optical fibers 202, 202 is connected to a communication device 2. Note that an optical circulator may be adopted instead of the optical coupler 201 to multiplex or demultiplex optical signals in both upstream and downstream directions.

In the case of pattern 1 in which communication device 2 is a two-core transmission device, if one optical fiber 202 is divided into an upstream optical fiber and the other optical fiber 202 is divided into a downstream optical fiber, the optical signals will not interfere with each other even if communication device 2 shares the same wavelength for both upstream and downstream.
For this reason, in pattern 1, the decision of whether to separate or share multiple types of wavelengths can be determined based only on the amount of reflection of the optical signal transmitted by the master communication device 1, and there is no need to take into account the amount of reflection of the slave communication device 2.

Therefore, in the case of pattern 1, the first wavelength setting process (FIG. 4) and the second wavelength setting process (FIG. 5) can be changed as follows. Note that the third wavelength setting process (FIG. 8) can be applied to pattern 1 as well because it does not use the measurement results on the communication device 2 side.
First setting process (FIG. 4): Steps ST14 to ST16 in FIG. 4 are omitted. If the result of the determination in step ST13 is positive, the wavelength is shared.
Second setting process (FIG. 6): Steps ST23 to ST24 in FIG. 6 are omitted. If the result of the determination in step ST22 is positive, the wavelength is shared.

12 is a connection configuration in which a communication device 1 and a plurality of communication devices 2 (two in the illustrated example) are connected via an ODN (Optical Distribution Network) 203. In the connection configuration shown in FIG.
Specifically, the ODN 9 includes an optical fiber 4 connected to the communication device 1, an optical coupler 204 connected to the optical fiber 4, and a plurality of optical fibers 205, 205 branching off from the optical coupler 204, and a communication device 2 is respectively connected to each of the optical fibers 205, 205.

In pattern 2 including ODN 203, there are multiple slave-side communication devices 2 performing single-core bidirectional transmission, so the master-side communication device 1 can individually decide whether to share or separate multiple wavelengths with at least one of the multiple slave-side communication devices 2.
For example, as shown in the figure, assume that the wavelengths available to communication device 1 are "λ1, λ2, λ3, λ4," the wavelengths available to communication device 2A are "λ1, λ2," and the wavelengths available to communication device 2B are "λ3, λ4."

In this case, communication device 1 executes any one of the first to third setting processes described above for communication device 2A to determine whether wavelengths λ1 and λ2 are to be divided into upstream and downstream or shared for optical communication with communication device 2A.
Similarly, communication device 1 may determine whether wavelengths λ3 and λ4 are to be divided into upstream and downstream or shared for optical communication with communication device 2B by executing any one of the first to third setting processes described above for communication device 2B.

In addition, in pattern 2, if the reflection of the optical signal at the master side communication device 1 is large for any one of the multiple wavelengths λ1, λ2, λ3, and λ4, the wavelengths may be divided for all communication devices 2A and 2B.

A "pattern 3" in FIG. 12 is a connection configuration in which an APN (All Photonics Network) 206 is included in the transmission path between the communication device 1 and the communication device 2.
Specifically, the APN 206 is an example of an APN that transfers optical signals without electrical regeneration. The APN 206 is, for example, a network in which communication nodes are configured in one or more ring configurations, and within the APN 206, upstream optical signals and downstream optical signals are transmitted through separate cores. As the communication nodes, for example, a ROADM (Reconfigurable Optical Add/Drop Multiplexer) or an optical switch may be adopted.

However, the connection topology of the APN 206 is not limited to a ring topology, and any topology such as a mesh may be adopted.
In this case, multiplexing and demultiplexing of optical signals may be performed by an optical circulator at a portion where the optical fibers 4 and 207, in which optical signals are multiplexed in both directions, are connected to the APN 206. This point is similar to the case of the optical fiber 4 and the optical fiber 210 of pattern 4 described later.

As shown in the figure, in the pattern 3 including the APN 206, the master communication device 1 may be connected to the APN 206 by one optical fiber 4 for single-core bidirectional transmission.
The slave communication device 2 may be configured as a single-core bidirectional transmission device connected to the APN 206 via one optical fiber 207, or as a two-core transmission device connected to the APN 206 via two optical fibers 208, 208.

In this embodiment, the control unit 13 of the communication device 1 on the master side performs a process (hereinafter referred to as the "decision process") to determine whether multiple types of wavelengths should be divided into upstream and downstream use or shared by both upstream and downstream, and in pattern 3, the communication device 1 is connected to one of the communication devices 2 by setting the optical path of the APN 206.
In this case, the decision process for the communication device 2 connected with one core is the same as in the above embodiment, and the decision process for the communication device 2 connected with two cores is the same as in pattern 1 of this modified example.

"Pattern 4" in FIG. 12 is a connection configuration in which the transmission path between communication device 1 and communication device 2 includes APN 206 and ODN 209.
Specifically, the master-side communication device 1 is configured for single-core bidirectional transmission connected to the APN 206 by one optical fiber 4, similar to pattern 3. The ODN 209 includes an optical fiber 210 leading to the APN 206, an optical coupler 211 connected to the optical fiber 210, and a plurality of optical fibers 212, 212 branching from the optical coupler 211, and a communication device 2 is connected to each of the optical fibers 212, 212. The process of determining pattern 4 is similar to that of pattern 2.

[Third Modification: Decision Process by Controller]
In the above embodiment, the control unit 13 of the master communication device 1 performs the above-mentioned determination process regarding whether or not the wavelength can be shared, but this determination process may be performed by the cloud-based controller 3 (see FIG. 2).

In particular, when the transmission path includes the APN 206 as in the patterns 3 and 4 in FIG. 12, the wavelengths used by the communication devices 1 and 2 need to be coordinated with the wavelengths of the communication nodes in the APN 206.
Therefore, it is preferable that the process of determining the wavelengths to be used by the communication devices 1 and 2 be performed by the cloud-based controller 3 that collectively manages the wavelengths to be used by the APN 206 .

In this case, the controller 3 first sets up an optical path between the communication devices 1 and 2 for the divided wavelengths, and then instructs the communication devices 1 and 2 to set the wavelengths. Next, the controller 3 receives notification of the result, performs a decision process, and if it decides to share the wavelengths, it releases the optical path of the unused wavelength.
However, when subcarrier division multiplexing is performed within one wavelength (carrier), the controller 3 needs to set one optical path for each of the upstream and downstream directions in a fixed manner. Even when the determination process is performed in a communication device or an optical transceiver, the controller 3 needs to set the optical paths in the same manner.

The alternative decision process by the controller 3 is, for example, as follows.
For the first wavelength setting process (FIG. 4):
The communication device 1 notifies the controller 3 of the reflected power T1 and the received power R1.
The controller 3 performs the determination in step ST13 based on the notified data.
The communication device 2 notifies the controller 3 of the reflected power T2 and the received power R2.
The controller 3 performs the determination in step ST16 based on the notified data, and notifies the communication device of the result of the determination process.

In the case of the second wavelength setting process (FIG. 6):
The communication device 1 notifies the controller 3 of the bit error rate E1.
The controller 3 performs the determination in step ST22 based on the notified data.
The communication device 2 notifies the controller 3 of the bit error rate E2.
The controller 3 performs the determination in step ST24 based on the notified data.

[Other Modifications]
The embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is not limited to the above-described embodiments, but includes all modifications within the scope of the equivalents of the configurations described in the claims.
In the above-described embodiment, at least one of the first wavelength setting process, the second wavelength setting process, and the third wavelength setting process may be executed by the processor 110, 128 of the optical transceiver 11 instead of the control unit 13 of the communication devices 1, 2.

1. Communication device (master device)
2. Communication device (slave device)
3 Controller 4 Optical fiber 5 Wide area communication network 11 Optical transceiver 11A Coherent optical transceiver 11B WDM optical transceiver 12 Switch 13 Control unit 13A CPU
13B Memory 101 Light source 102 Optical splitter 103 First signal processing unit 104 DA conversion unit 105 Optical transmission unit 106 Optical reception unit 107 AD conversion unit 108 Second signal processing unit 109 Optical circulator 110 Processor (control unit)
121 TOSA (optical transmitter)
122 L.D.D.
123 Transmitting CDR
124 ROSA (optical receiver)
125 TIA
126 Receiver CDR
127 Optical circulator 128 Processor (control unit)
201 Optical coupler 202 Optical fiber 203 ODN
204 Optical coupler 205 Optical fiber 206 APN
207 Optical fiber 208 Optical fiber 209 ODN
210 Optical fiber 211 Optical coupler 212 Optical fiber R1 Reception power (first reception power)
R2 reception power (second reception power)
T1 reflected power (first reflected power)
T2 reflected power (second reflected power)
E1 bit error rate (first error rate)
E2 bit error rate (second error rate)
P1 Control path P2 Control path P3 Control path

Claims (15)

A communication device for performing optical communication using a single-core bidirectional transmission,
an optical transceiver capable of transmitting and receiving optical signals of a plurality of wavelengths to and from a counterpart device;
a control unit that determines a wavelength to be used for communication with the opposite device,
The control unit is
A communication device that determines whether the plurality of types of wavelengths are to be divided into upstream and downstream wavelengths or to be shared by both upstream and downstream wavelengths depending on the degree of reflection of an optical signal transmitted from the device itself. When the opposing device performs optical communication using a single-core bidirectional transmission,
The control unit further
2. The communication device according to claim 1, further comprising: a determining unit configured to determine whether said plurality of types of wavelengths are to be divided into upstream and downstream wavelengths or to be shared by both upstream and downstream wavelengths, depending on a degree of reflection of an optical signal transmitted from said opposite device. The control unit is
If the reflection is large, the plurality of types of wavelengths are divided into upstream and downstream wavelengths;
The communication device according to claim 2 , wherein when the reflection is small, the plurality of types of wavelengths are shared between upstream and downstream. The control unit is
a first reflected power measured by the device itself and a first received power measured by the device itself or a predetermined first minimum received power;
The communication device according to claim 2 , wherein the amount of reflection is determined based on a second reflected power measured by the opposite device and a second received power or a predetermined second minimum received power measured by the opposite device. The control unit is
A ratio of the first received power or the first minimum received power to the first reflected power is equal to or less than a threshold value, or
When the ratio of the second reception power or the second minimum reception power to the second reflection power is equal to or less than a threshold value,
The communication device according to claim 4 , further comprising: determining to separate the plurality of types of wavelengths. The control unit is
a ratio of the first received power or the first minimum received power to the first reflected power exceeds a threshold; and
If a ratio of the second received power or the second minimum received power to the second reflected power exceeds a threshold value,
The communication device according to claim 4 or 5, wherein the communication device determines to share the plurality of types of wavelengths. The control unit is
determining whether the reflection is large or small based on a first error rate, which is a bit error rate of the first communication frame, and a second error rate, which is a bit error rate of the second communication frame;
The first communication frame is
This is the frame that is detected when simultaneously transmitting and receiving optical signals of the same wavelength.
The second communication frame is
3. The communication device according to claim 2 , wherein the frame is detected by the opposing device when optical signals of the same wavelength are simultaneously transmitted and received. The control unit is
If the first error rate is equal to or greater than a threshold, or
If the second error rate is equal to or greater than a threshold,
The communication device according to claim 7 , further comprising: determining to separate the plurality of types of wavelengths. The control unit is
the first error rate is less than a threshold; and
If the second error rate is less than a threshold,
The communication device according to claim 7 or 8, wherein the communication device determines to share the plurality of types of wavelengths. The control unit is
3. The communication device according to claim 2 , wherein the amount of reflection is determined based on the result of a loopback test that is performed with the same transmission wavelength for upstream and downstream. The control unit is
If the result of the loopback test indicates that the test frame is missing,
The communication device according to claim 10 , further comprising: determining to separate the plurality of types of wavelengths. The control unit is
If the result of the loopback test is that there is no loss of test frames,
The communication device according to claim 10 or 11, which determines to share the plurality of types of wavelengths. A wavelength determination method executed by a communication device that performs single-core bidirectional optical communication using an optical transceiver capable of transmitting and receiving optical signals of multiple wavelengths to and from a counterpart device, comprising the steps of:
A step of determining the amount of reflection of an optical signal transmitted from the own device;
and determining whether the plurality of types of wavelengths are to be divided into upstream and downstream wavelengths or to be shared by both upstream and downstream wavelengths depending on the result of the determination of the amount of reflection. an optical transmitter capable of transmitting optical signals of a plurality of wavelengths;
an optical receiving unit capable of receiving optical signals of a plurality of wavelengths;
a processor for determining a wavelength to be used for communication with a counterpart device,
The processor,
An optical transceiver that determines whether the plurality of types of wavelengths are to be divided into upstream and downstream wavelengths or to be shared by both upstream and downstream wavelengths depending on the degree of reflection of an optical signal transmitted from the transceiver itself. A communication device capable of transmitting and receiving optical signals of a plurality of wavelengths, the communication device performing optical communication via single-core bidirectional transmission;
A counterpart device that optically communicates with the communication device and is capable of transmitting and receiving optical signals of a plurality of wavelengths;
a controller for managing wavelengths to be used by the communication device and the opposing device,
The controller:
an optical communication system that determines whether the plurality of types of wavelengths are divided into upstream and downstream wavelengths or are shared by both upstream and downstream wavelengths depending on the degree of reflection of the optical signal transmitted from the communication device;

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