Polarization state monitoring device, polarization state monitoring method and program

Abstract

To provide a novel technique for monitoring a polarization state of an optical reception signal.SOLUTION: A polarization state monitoring device calculates polarization state change vectors representing polarization states of an optical reception signal in respective different periods, and specifies features of change in polarization state of the optical reception signal based upon directions of the respective polarization state change vectors, lengths of the respective polarization state change vectors, or both of them.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a polarization state monitoring device, a polarization state monitoring method, and a program. [Background technology]

[0002] Technologies for monitoring changes in the polarization state of optical signals have been developed for optical communication systems. For example, Non-Patent Document 1 discloses a technology for monitoring changes in the polarization state of received optical signals modulated with QPSK (Quadrature Phase-Shift Keying). The system in Non-Patent Document 1 calculates multiple Jones vectors from the received optical signal and maps each calculated Jones vector to a point in Stokes space. Next, the system in Non-Patent Document 1 divides the multiple points obtained by mapping into four groups and calculates the center point of each group. Furthermore, the system in Non-Patent Document 1 calculates a normal vector based on the four calculated center points. The system in Non-Patent Document 1 monitors the polarization state of the received optical signal based on the rotation speed of the normal vector calculated in this way. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Jingnan Li, Yangyang Fan, Zhenning Tao, Hisao Nakashima, and Takeshi Hoshida, "Polarization Change Monitor Based on Geometrical Analysis in Stokes Space", 2021 European Conference on Optical Communication (ECOC), November 22, 2021 [Non-patent document 2] Bogdan Szafraniec, Todd S. Marshall, and Bernd Nebendahl, "Performance Monitoring and Measurement Techniques for Coherent Optical Systems," Journal of Lightwave Technology, February 15, 2013, vol. 31, no. 4, pp. 648-663 Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors of the present disclosure have discovered a new technique for monitoring the polarization state of a received optical signal. An object of the present disclosure is to provide a new technique for monitoring the polarization state of a received optical signal. [Means for solving the problem]

[0005] The polarization state monitoring device according to the present disclosure includes a calculation means for calculating a polarization state change vector representing a change in the polarization state of an optical reception signal for each different period, and an identification means for identifying characteristics of the change in the polarization state of the optical reception signal based on the direction of each of the polarization state change vectors, the length of each of the polarization state change vectors, or both.

[0006] A polarization state monitoring method according to the present disclosure is executed by a computer and includes a calculation step of calculating polarization state change vectors representing changes in the polarization state of a received optical signal for different time periods, and an identification step of identifying characteristics of the changes in the polarization state of the received optical signal based on the direction of each of the polarization state change vectors, the length of each of the polarization state change vectors, or both.

[0007] The program according to the present disclosure causes a computer to execute a calculation step of calculating polarization state change vectors representing changes in the polarization state of the received optical signal for different periods, and an identification step of identifying characteristics of changes in the polarization state of the received optical signal based on the direction of each of the polarization state change vectors, the length of each of the polarization state change vectors, or both. [Effects of the Invention]

[0008] According to the present disclosure, a new technique for monitoring the polarization state of a received optical signal is provided. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating an optical transmission and reception system handled by a polarization state monitoring device according to the present disclosure; [Figure 2] FIG. 1 is a diagram illustrating an example of an outline of the operation of a polarization state monitoring device. [Figure 3] FIG. 2 is a block diagram illustrating a functional configuration of a polarization state monitoring device. [Figure 4] FIG. 1 is a block diagram illustrating a hardware configuration of a computer that realizes a polarization state monitoring device. [Figure 5] 10 is a flowchart illustrating a flow of processing executed by a polarization state monitoring device. [Figure 6] FIG. 10 is a diagram illustrating a case (Case 1) in which the end point of the polarization state vector rotates greatly and quickly. [Figure 7] FIG. 10 is a diagram illustrating a case (Case 2) in which the end point of the polarization state vector rotates significantly and slowly. [Figure 8] FIG. 10 is a diagram illustrating a case (Case 3) in which the end point of the polarization state vector rotates slightly. [Figure 9] FIG. 10 is a diagram illustrating a case (Case 4) in which the end point of the polarization state vector does not rotate. [Figure 10] 10 is a flowchart illustrating a process for identifying the characteristics of a change in the polarization state from four cases. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are designated by the same reference numerals, and duplicate explanations will be omitted as necessary for clarity. Furthermore, unless otherwise specified, predetermined values ​​such as predetermined values ​​and threshold values ​​are stored in advance in a storage device accessible from a device that uses the values. Furthermore, unless otherwise specified, the storage unit is composed of one or any number of storage devices.

[0011] [Embodiment 1] <Summary> 1 is a diagram illustrating an optical transmission and reception system handled by the polarization state monitoring device of the present disclosure. The optical transmission and reception system 1 includes a transmitting device 100, a receiving device 200, and an optical communication path 300. The receiving device 200 receives an optical signal transmitted from the transmitting device 100 via the optical communication path 300. The optical communication path 300 is a communication path capable of transmitting an optical signal, and is configured using, for example, an optical fiber. Here, the optical signal transmitted from the transmitting device 100 and the optical signal received by the receiving device 200 are referred to as an optical transmission signal 10 and an optical reception signal 20, respectively.

[0012] Communication between the transmitting device 100 and the receiving device 200 is performed, for example, as follows. The transmitting device 100 generates an optical transmission signal 10 from data (hereinafter referred to as a message) to be transmitted to the receiving device 200. Specifically, the transmitting device 100 divides the message into multiple frames and encodes the data of each frame into symbols to generate a symbol sequence. The transmitting device 100 then generates a polarization-multiplexed optical transmission signal 10 by modulating the X polarization and Y polarization of an optical carrier wave based on the symbol sequence.

[0013] The receiving device 200 recovers the message from the optical reception signal 20. To do this, the receiving device 200 converts the optical reception signal 20 into a digital signal. The receiving device 200 then divides the digital signal into multiple frames and converts each frame into a symbol to obtain a symbol sequence. The receiving device 200 then decodes each symbol in the symbol sequence to obtain the message.

[0014] Fig. 2 is a diagram illustrating an example of an outline of the operation of the polarization state monitoring device 2000. Here, Fig. 2 is a diagram for facilitating understanding of the outline of the polarization state monitoring device 2000, and the operation of the polarization state monitoring device 2000 is not limited to that shown in Fig. 2.

[0015] The polarization state monitoring device 2000 monitors changes in the State of Polarization (SOP) of the received optical signal 20. More specifically, the polarization state monitoring device 2000 identifies, for each of one or more periods (hereinafter referred to as monitoring periods), the characteristics of changes in the SOP of the received optical signal 20 during that period. For example, the characteristics of changes in the SOP are classified into one of a number of predetermined cases.

[0016] The monitoring period can be determined arbitrarily. For example, a plurality of monitoring periods can be obtained by dividing the period during which the polarization state monitoring device 2000 receives the optical reception signal 20 into predetermined intervals.

[0017] Hereinafter, the monitoring period for which the characteristics of the change in the polarization state are to be identified will be referred to as the target monitoring period. For example, suppose that the polarization state monitoring device 2000 is attempting to identify the characteristics of the change in the polarization state for the i-th monitoring period. In this case, the i-th monitoring period will be referred to as the target monitoring period.

[0018] The polarization state monitoring device 2000 identifies the characteristics of changes in the polarization state during each monitoring period by treating each of the multiple monitoring periods as a target monitoring period. For example, the multiple monitoring periods are treated as target monitoring periods in chronological order.

[0019] The polarization state of the optical reception signal 20 can be represented by a vector in the Stokes space. Hereinafter, the vector in the Stokes space representing the polarization state of the optical reception signal 20 will be referred to as the "polarization state vector (SOP vector)." The polarization state vector is a vector whose start point is the origin of the Stokes space and whose end point is a point in the Stokes space representing the polarization state of the optical reception signal 20. Hereinafter, the point in the Stokes space representing the polarization state of the optical reception signal 20 will be referred to as the "polarization state point."

[0020] The polarization state monitoring device 2000 calculates a plurality of polarization state change vectors (SOP change vectors) representing changes in the polarization state during a target monitoring period. A polarization state change vector is represented by, for example, the difference between two polarization state vectors.

[0021] More specifically, the polarization state monitoring device 2000 calculates a polarization state vector representing the polarization state during each of a plurality of partial periods included in the target monitoring period. The partial periods are obtained, for example, by dividing the monitoring period into predetermined intervals. The polarization state monitoring device 2000 calculates a plurality of polarization state change vectors using the plurality of polarization state vectors calculated for the target monitoring period. For example, the polarization state change vector is calculated by calculating the difference between the polarization state vectors calculated for two partial periods adjacent to each other in time series.

[0022] The polarization state monitoring device 2000 uses the multiple polarization state change vectors calculated for the target monitoring period to identify the characteristics of the change in the polarization state of the optical reception signal 20 during the target monitoring period, based on the direction of the polarization state change vector, the length of the polarization state change vector, or both.

[0023] <Examples of effects> The polarization state monitoring device 2000 identifies the characteristics of the change in the polarization state as one of the indicators for monitoring the polarization state of the optical reception signal 20 received by the receiving device 200. The identification is performed based on the direction of the polarization state change vector, the length of the polarization state change vector, or both. In this way, the polarization state monitoring device 2000 provides a new technique for monitoring the polarization state of the optical reception signal.

[0024] The polarization state monitoring device 2000 of this embodiment will be described in more detail below.

[0025] <Example of functional configuration> 3 is a block diagram illustrating the functional configuration of the polarization state monitoring device 2000. The polarization state monitoring device 2000 includes a calculation unit 2020 and an identification unit 2040. The calculation unit 2020 calculates a plurality of polarization state change vectors for a target monitoring period. The identification unit 2040 identifies the characteristics of the change in the polarization state of the optical reception signal 20 during the target monitoring period based on the directions of the plurality of polarization state change vectors, the lengths of the plurality of polarization state vectors, or both.

[0026] Understanding the characteristics of changes in the polarization state of the optical reception signal 20 has the advantage of being useful, for example, for selecting an appropriate monitoring method for the polarization state of the optical reception signal 20. For example, a case in which the end point of the polarization state vector of the optical reception signal 20 rotates slightly (Case 3 described below) is less suitable for a geometric method (e.g., a method using a Stokes vector) than a case in which the end point of the polarization state vector of the optical reception signal 20 rotates significantly (Cases 1 and 2 described below). Therefore, for example, by using the polarization state monitoring device 2000, it becomes possible to address the issue by selecting a monitoring method other than the geometric method when the characteristics of changes in the polarization state of the optical reception signal 20 are those of Case 3.

[0027] <Example of hardware configuration> Each functional component of the polarization state monitoring device 2000 may be realized by hardware that realizes the functional component (e.g., a hardwired electronic circuit, etc.), or may be realized by a combination of hardware and software (e.g., a combination of an electronic circuit and a program that controls it, etc.). Below, a case where each functional component of the polarization state monitoring device 2000 is realized by a combination of hardware and software will be further described.

[0028] 4 is a block diagram illustrating an example of a hardware configuration of a computer 1000 that realizes the polarization state monitoring apparatus 2000. The computer 1000 is any computer. For example, the computer 1000 is a stationary computer such as a PC (Personal Computer) or a server machine. Alternatively, the computer 1000 may be a portable computer such as a smartphone or a tablet terminal. Alternatively, the computer 1000 may be a semiconductor chip such as an SoC (System on Chip). The computer 1000 may be a dedicated computer designed to realize the polarization state monitoring apparatus 2000, or may be a general-purpose computer.

[0029] For example, by installing a predetermined application on the computer 1000, the computer 1000 realizes each function of the polarization state monitoring device 2000. The application is configured with a program for realizing each functional component of the polarization state monitoring device 2000. The program can be acquired by any method. For example, the program can be acquired from a storage medium (such as a DVD (Digital Versatile Disk) or a USB (Universal Serial Bus) memory) on which the program is stored. Alternatively, the program can be acquired by downloading the program from a server device that manages a storage device on which the program is stored.

[0030] The computer 1000 has a bus 1020, a processor 1040, a memory 1060, a storage device 1080, an input / output interface 1100, and a network interface 1120. The bus 1020 is a data transmission path for the processor 1040, the memory 1060, the storage device 1080, the input / output interface 1100, and the network interface 1120 to transmit and receive data to and from each other. However, the method for connecting the processor 1040 and the like to each other is not limited to a bus connection.

[0031] The processor 1040 is a variety of processors, such as a central processing unit (CPU), a graphics processing unit (GPU), a digital signal processor (DSP), or a field-programmable gate array (FPGA). The memory 1060 is a main storage device realized using a random access memory (RAM) or the like. The storage device 1080 is an auxiliary storage device realized using a hard disk, a solid state drive (SSD), a memory card, a read only memory (ROM), or the like.

[0032] The input / output interface 1100 is an interface for connecting the computer 1000 to an input / output device. For example, the input / output interface 1100 is connected to an input device such as a keyboard and an output device such as a display device.

[0033] The network interface 1120 is an interface for connecting the computer 1000 to a network. This network may be a LAN (Local Area Network) or a WAN (Wide Area Network).

[0034] The storage device 1080 stores a program (a program that realizes the above-mentioned application) that realizes each functional component of the polarization state monitoring device 2000. The processor 1040 reads this program into the memory 1060 and executes it, thereby realizing each functional component of the polarization state monitoring device 2000.

[0035] The polarization state monitoring device 2000 may be realized by one computer 1000 or by multiple computers 1000. In the latter case, the configurations of the computers 1000 do not need to be the same, and can be different from each other.

[0036] The polarization state monitoring device 2000 may be realized as a separate entity from the receiving device 200, or may be realized as an integrated entity with the receiving device 200. In the latter case, each functional component of the polarization state monitoring device 2000 is implemented inside the receiving device 200. This allows the receiving device 200 to function as the polarization state monitoring device 2000 as well.

[0037] <Processing flow> Fig. 5 is a flowchart illustrating the flow of processing executed by the polarization state monitoring device 2000. The series of processing shown in Fig. 5 is executed for each of a plurality of monitoring periods.

[0038] The calculation unit 2020 identifies a polarization state vector for each of a plurality of partial periods included in the target monitoring period (S102). The calculation unit 2020 calculates a polarization state change vector for each of a plurality of pairs of polarization state vectors (S104).

[0039] The identifying unit 2040 identifies the characteristics of the change in the polarization state of the optical reception signal 20 during the target monitoring period based on the directions of the multiple polarization state change vectors, the lengths of the multiple polarization state change vectors, or both (S106).

[0040] <Identification of polarization state vector: S102> The calculation unit 2020 determines the polarization state vector for each of the plurality of partial periods (S102). Below, several examples of methods for determining the polarization state vector will be described.

[0041] <<Example 1 of how to identify the polarization state vector>> For example, the calculation unit 2020 uses a polarimeter to identify the polarization state vector for each partial period. When a polarimeter is used to identify the polarization state vector, the polarimeter is installed in advance in the receiving device 200. The optical reception signal 20 is input to the polarimeter.

[0042] A polarimeter is a device that measures the polarization state of input light. For example, when an optical reception signal 20 is input, the polarimeter outputs time series data {S[t]} of the Stokes vector S, which represents the polarization state of the optical reception signal 20. Here, t represents time. The Stokes vector S is a list of four Stokes parameters s0, s1, s2, and s3.

[0043] Stokes space is a three-dimensional space defined by three axes: s1-axis, s2-axis, and s3-axis. Therefore, the polarization state vector v[t] of the optical received signal 20 at time t can be expressed as v[t]=(s1[t],s2[t],s3[t]) using the three Stokes parameters s1[t], s2[t], and s3[t] output from the polarimeter to which the optical received signal 20 at time t is input.

[0044] Therefore, the calculation unit 2020 acquires time-series data of the Stokes vector output from a polarimeter provided in the receiving device 200. Then, for each partial period, the calculation unit 2020 identifies the polarization state vector for that partial period using one or more Stokes vectors for that partial period.

[0045] For example, the calculation unit 2020 obtains a representative Stokes vector S[rj] for each subperiod j. The time rj is, for example, a specific time point related to the subperiod j (such as the start or end of the subperiod j). The calculation unit 2020 then extracts Stokes parameters s1[rj], s2[rj], and s3[rj] from the representative Stokes vector S[rj]. The calculation unit 2020 then determines the vector (s1[rj], s2[rj], s3[rj]) specified by these parameters as the polarization state vector for the subperiod j.

[0046] Alternatively, for example, the calculation unit 2020 may calculate statistical values ​​ss1[j], ss2[j], and ss3[j] of the Stokes parameters s1, s2, and s3, respectively, using a plurality of Stokes vectors for the subperiod j. Then, the calculation unit 2020 identifies the vector (ss1[j], ss2[j], ss3[j]) identified by the calculated statistical values ​​as the polarization state vector for the subperiod j.

[0047] There are various methods by which the calculation unit 2020 acquires the Stokes vector output from the polarimeter. For example, the receiving device 200 transmits the Stokes vector output from the polarimeter to the polarization state monitoring device 2000. In this case, the calculation unit 2020 acquires the Stokes vector by receiving the Stokes vector transmitted from the receiving device 200. As another example, the receiving device 200 stores the Stokes vector output from the polarimeter in a storage unit accessible from the polarization state monitoring device 2000. In this case, the calculation unit 2020 acquires the Stokes vector from this storage unit.

[0048] In addition, when only the representative Stokes vector is used to identify the polarization state vector, the receiving device 200 may be configured to transmit only the representative Stokes vector or store only the representative Stokes vector in a memory unit.

[0049] <<Example 2 of how to identify the polarization state vector>> The calculation unit 2020 obtains sample data representing the polarization state of the optical reception signal 20 for each frame of the optical reception signal 20. For example, the sample data is a Jones vector. Furthermore, the calculation unit 2020 obtains corresponding points for each sample data by mapping the sample data for each frame to points in Stokes space.

[0050] The Stokes vector S[t]=(s0[t],s1[t],s2[t],s3[t]) can be obtained from the sample data at time t. Therefore, the calculation unit 2020 obtains the point (s1[t],s2[t],s3[t]) as the corresponding point corresponding to the sample data at time t.

[0051] The Stokes vector S[t] at time t can be calculated using the sample data at time t as follows:

number

[0052] Here, the number of frames included in the optical reception signal 20 in each partial period is denoted as n. In this case, the calculation unit 2020 calculates one polarization state vector for each partial period based on n corresponding points obtained for the n frames included in that partial period. Hereinafter, a set of corresponding points obtained for multiple frames included in a partial period will be referred to as a corresponding point cloud corresponding to that frame. The corresponding point cloud for each frame includes n corresponding points.

[0053] For example, the calculation unit 2020 performs the following process for each subperiod. First, the calculation unit 2020 calculates a plane in Stokes space that fits the corresponding point cloud obtained for the target subperiod (in other words, fits n corresponding points included in the corresponding point cloud). The calculation unit 2020 identifies, as a polarization state vector, a vector whose end point is the intersection point of the normal vector of the plane and the Poincaré sphere and whose start point is the origin of the Stokes space.

[0054] Here, the normal vector is determined to pass through the origin of the Stokes space. Also, there can be two normal vectors that pass through a specific point on a certain plane. Therefore, it is assumed that a rule for selecting a normal vector to be used for calculating a polarization state point from these two normal vectors is determined in advance.

[0055] Here, the plane in the Stokes space can be expressed as follows:

number

[0056] For this reason, for example, the calculation unit 2020 uses the corresponding point group to calculate A, B, C, and D that satisfy formula (2), thereby calculating a plane that fits the corresponding point group. For example, the calculation unit 2020 substitutes each corresponding point included in the corresponding point group into formula (2) and performs singular value decomposition (SVD). As a result, A, B, C, and D in formula (2) are calculated, and a plane that fits the corresponding point group is calculated.

[0057] Here, when QAM (Quadrature Amplitude Modulation) is used, the corresponding points are located inside a lens-shaped area that combines the area defined by the following equation (3) and the area defined by the following equation (4).

number

number

[0058] The method for deriving equation (3) is disclosed in Non-Patent Document 2. In deriving equation (3), for the H polarization state, the point with the maximum amplitude is selected. For the V polarization state, all points within the unit circle on the imaginary plane are considered. This is expressed by the Jones vector:

number

[0059] Equation (3) is obtained by converting the Jones vectors in equation (5) into Stokes vectors.

[0060] In contrast, in the derivation of equation (4), for the V polarization state, the point with the maximum amplitude is selected, and for the H polarization state, any point within the unit circle on the imaginary plane is considered. This is expressed by the Jones vector:

number

[0061] Equation (4) is obtained by converting the Jones vectors in equation (6) into Stokes vectors.

[0062] From equations (3) and (4), the above lens-shaped region is a point-symmetric region with the origin as the center. Therefore, a plane that fits the corresponding points distributed within this lens-shaped region passes through the origin. Therefore, we can assume that D = 0 in equation (2).

[0063] Therefore, the calculation unit 2020 may calculate a plane that fits the corresponding points by calculating A, B, and C that satisfy the following using the corresponding points:

number

[0064] When formula (7) is used, a plane that fits the corresponding points can be calculated by a method such as singular value decomposition, just like when formula (2) is used.

[0065] The method for calculating one polarization state vector based on multiple corresponding points is not limited to the method using a plane that fits the multiple corresponding points described above. For example, the calculation unit 2020 may use the method disclosed in Non-Patent Document 1 to calculate one corresponding point based on multiple corresponding points and calculate a polarization state vector that has the calculated corresponding point as its end point.

[0066] There are various methods for the calculation unit 2020 to acquire the sample data. For example, the receiving device 200 is configured to generate sample data for each frame of the optical reception signal 20 and transmit the generated sample data to the polarization state monitoring device 2000. In this case, the calculation unit 2020 acquires the sample data by receiving the sample data transmitted from the receiving device 200. As another example, the receiving device 200 is configured to store the sample data generated for each frame of the optical reception signal 20 in a storage unit accessible from the polarization state monitoring device 2000. In this case, the calculation unit 2020 acquires the sample data from this storage unit.

[0067] When the calculation unit 2020 acquires sample data only for the representative frame, the receiving device 200 may be configured to generate sample data only for the representative frame.

[0068] <Calculation of polarization state change vector: S104> The calculation unit 2020 calculates a polarization state change vector for each of a plurality of pairs of polarization state vectors (S104). A pair of polarization state vectors is, for example, composed of polarization state vectors that are adjacent to each other in the time-series data of the polarization state vectors (a plurality of polarization state vectors arranged in time series). For example, from the time-series data of the polarization state vectors (v[1],v[2],v[3],...,v[m]), a set of pairs of polarization state vectors {(v[1],v[2]),(v[2],v[3]),...,(v[m-1],v[m])} is obtained.

[0069] The polarization state monitoring device 2000 calculates a polarization state change vector for each pair included in this set. Specifically, the polarization state monitoring device 2000 calculates the polarization state change vector u[1] for the polarization state vector pair (v[1],v[2]), the polarization state change vector u[2],...,u[m-1] for the polarization state vector pair (v[2],v[3]), and the polarization state change vector u[m-1] for the polarization state vector pair (v[m-1],v[m]). This provides time-series data of the polarization state change vector (u[1],u[2],...,u[m-1]) for the set of polarization state vector pairs {(v[1],v[2]),(v[2],v[3]),...,(v[m-1],v[m])}. Here, the i-th polarization state change vector u[i] represents the difference between the polarization state vectors v[i] and v[i+1].

[0070] The pair of polarization state vectors used to calculate the polarization state change vector is not limited to a pair of polarization state vectors adjacent to each other in time series. For example, the polarization state monitoring device 2000 may calculate the polarization state change vector u[i] by pairing polarization state vectors v[k] and v[i+k] that are k degrees apart from each other (k is an integer equal to or greater than 2). Alternatively, the calculation unit 2020 may generate a pair of polarization state vectors by randomly combining polarization state vectors. In this case, the calculation unit 2020 repeats the process of "extracting any two polarization state vectors from the set of polarization state vectors and calculating a polarization state change vector for the pair of these two polarization state vectors" until the set of polarization state vectors is empty.

[0071] <Identifying the characteristics of changes in polarization state: S106> The identifying unit 2040 identifies the characteristics of the change in the polarization state of the optical reception signal 20 during the target monitoring period based on the directions of the multiple polarization state change vectors, the lengths of the multiple polarization state change vectors, or both (S106). The characteristics of the change in the polarization state can be classified as follows, for example, depending on the characteristics of the movement of the end points of the polarization state vectors. (Case 1) The end point of the polarization state vector rotates rapidly and greatly. (Case 2) The end point of the polarization state vector rotates large and slowly. (Case 3) The end point of the polarization state vector is rotated slightly. (Case 4) The endpoints of the polarization state vector are not rotated.

[0072] 6 to 9 are diagrams illustrating four cases showing characteristics of changes in the polarization state. Five polarization state vectors, v1, v2, v3, v4, and v5, are shown in all of Figures 6 to 9. Four polarization state change vectors are also shown: u1, which represents the difference between v1 and v2; u2, which represents the difference between v2 and v3; u3, which represents the difference between v3 and v4; and u4, which represents the difference between v4 and v5.

[0073] Fig. 6 is a diagram illustrating a case (Case 1) in which the end point of the polarization state vector rotates rapidly and significantly. Fig. 7 is a diagram illustrating a case (Case 2) in which the end point of the polarization state vector rotates rapidly and significantly. In both cases of Fig. 6 and Fig. 7, the end point of the polarization state vector rotates in a large circle. However, in the case of Fig. 7, the end point of the polarization state vector rotates more slowly than in the case of Fig. 6.

[0074] 8 is a diagram illustrating a case (Case 3) in which the end points of the polarization state vector rotate slightly. In the case of Fig. 8, the circle described by the end points of the polarization state vector is smaller than the circles described by the end points of the polarization state vector in the cases of Fig. 6 and Fig. 7.

[0075] Fig. 9 is a diagram illustrating a case (Case 4) in which the end point of the polarization state vector does not rotate. In the case of Fig. 9, unlike the cases of Fig. 6 to Fig. 8, the end point of the polarization state vector does not rotate.

[0076] For example, the identifying unit 2040 uses a plurality of polarization state change vectors to identify which of Case 1 to Case 4 the characteristics of the change in the polarization state of the optical reception signal 20 during the target monitoring period corresponds to. Fig. 10 is a flowchart illustrating the flow of a process for identifying the characteristics of the change in the polarization state from among the four cases.

[0077] The identification unit 2040 determines whether the end points of the multiple polarization state vectors are close to each other (S202). Here, when the polarization state vectors are rotating rapidly and significantly (i.e., in case 1), the end points of the multiple polarization state vectors are located far from each other (see FIG. 6). On the other hand, in cases other than case 1, the end points of the multiple polarization state vectors are located close to each other (see FIGS. 7, 8, and 9).

[0078] Therefore, if the endpoints of the multiple polarization state vectors are not close to each other (S202: NO), the identifying unit 2040 determines that the characteristics of the change in the polarization state of the optical reception signal 20 during the target monitoring period apply to Case 1 (S204).

[0079] If the endpoints of the multiple polarization state vectors are located close to each other (S202: YES), the identification unit 2040 determines whether the multiple polarization state change vectors are pointing in directions close to each other (S206). Here, if the endpoints of the polarization state vectors are rotating large and slowly as shown in Fig. 7, the multiple polarization state change vectors are pointing in directions close to each other. On the other hand, if the endpoints of the polarization state vectors are rotating small or are not rotating, the multiple polarization state change vectors are not pointing in directions close to each other (see Figs. 8 and 9).

[0080] Therefore, if the multiple polarization state change vectors are oriented in directions close to each other (S206: YES), the identifying unit 2040 determines that the characteristics of the change in the polarization state of the optical reception signal 20 during the target monitoring period apply to Case 2 (S208).

[0081] If the multiple polarization state changing vectors are not pointing in directions close to each other (S206: NO), the identifying unit 2040 determines whether the variation in the lengths of the multiple polarization state changing vectors is small (S210). Here, if the endpoints of the polarization state vectors are rotated slightly as shown in Fig. 8, the variation in the lengths of the multiple polarization state changing vectors is small. On the other hand, if the endpoints of the polarization state vectors are not rotated as shown in Fig. 9, the variation in the lengths of the multiple polarization state changing vectors is large.

[0082] Therefore, if the variation in the lengths of the multiple polarization state change vectors is small (S210: YES), the identifying unit 2040 determines that the characteristics of the change in the polarization state of the optical reception signal 20 during the target monitoring period apply to Case 3 (S212). On the other hand, if the variation in the lengths of the multiple polarization state change vectors is not small (S210: NO), the identifying unit 2040 determines that the characteristics of the change in the polarization state of the optical reception signal 20 during the target monitoring period apply to Case 4 (S214).

[0083] Here, whether the variation in the lengths of the multiple polarization state change vectors is small can be determined, for example, by determining whether the variation in the lengths of the multiple polarization state change vectors is equal to or less than a predetermined threshold value.

[0084] <<S202について> > In S202, the determination unit 2040 determines whether the end points of the plurality of polarization state vectors are located close to each other. There are various specific methods for this determination. For example, the determination unit 2040 determines whether the end points of the plurality of polarization state vectors are located close to each other based on statistics (such as average, maximum, or minimum values) of the lengths of the polarization state change vectors.

[0085] When the endpoints of multiple polarization state vectors are located close to each other, it is considered that the lengths of the multiple polarization state change vectors are all short. From this, it can be seen that when the statistical value of the lengths of the polarization state change vectors is equal to or less than a predetermined threshold, the endpoints of the multiple polarization state vectors are located close to each other. On the other hand, when the statistical value of the lengths of the polarization state change vectors is greater than the predetermined threshold, it can be seen that the endpoints of the multiple polarization state vectors are not located close to each other.

[0086] Therefore, the determination unit 2040 determines whether the statistical value of the lengths of the polarization state change vectors is equal to or smaller than a predetermined threshold value. The threshold value is determined in advance to determine whether the statistical value of the lengths of the polarization state change vectors is small enough to indicate that the end points of multiple polarization state vectors are located close to each other.

[0087] If the statistical value of the length of the polarization state change vector is not equal to or less than the predetermined threshold, the identifying unit 2040 determines that the characteristics of the change in the polarization state of the optical reception signal 20 during the target monitoring period apply to Case 1 (S204). If the statistical value of the length of the polarization state change vector is equal to or less than the predetermined threshold, the identifying unit 2040 executes S206.

[0088] Whether the end points of a plurality of polarization state vectors are located close to each other may be determined based on the magnitude of the rotation angles of the polarization state vectors. In this case, the specifying unit 2040 calculates the rotation angles of the polarization state vectors for each pair of the polarization state vectors. Then, the specifying unit 2040 calculates statistics (such as the average, maximum, or minimum value) of the calculated rotation angles.

[0089] When the end points of multiple polarization state vectors are located close to each other, the rotation angles of the polarization state vectors are all considered to be small. From this, it can be seen that when the statistical value of the rotation angles of the polarization state vectors is equal to or smaller than a predetermined threshold, the end points of multiple polarization state vectors are located close to each other. On the other hand, when the statistical value of the rotation angles of the polarization state vectors is greater than the predetermined threshold, it can be seen that the end points of multiple polarization state vectors are not located close to each other.

[0090] Therefore, the determination unit 2040 determines whether the statistical value of the rotation angles of the polarization state vectors is equal to or smaller than a predetermined threshold value. The threshold value is determined in advance to determine whether the statistical value of the rotation angles of the polarization state vectors is small enough to indicate that the end points of the multiple polarization state vectors are located close to each other.

[0091] If the statistical value of the rotation angle of the polarization state vector is not equal to or less than the predetermined threshold, the identifying unit 2040 determines that the characteristics of the change in the polarization state of the optical reception signal 20 during the target monitoring period apply to Case 1 (S204). If the statistical value of the rotation angle of the polarization state vector is equal to or less than the predetermined threshold, the identifying unit 2040 executes S206.

[0092] <<S206について> > In S206, the identification unit 2040 determines whether the multiple polarization state changing vectors are oriented in directions close to each other. Whether the multiple polarization state changing vectors are oriented in directions close to each other can be determined based on, for example, variations in the orientations of the multiple polarization state changing vectors.

[0093] When multiple polarization state changing vectors are pointing in directions close to each other, it is considered that the variation in the directions of the multiple polarization state changing vectors is small. From this, it can be seen that when the variation in the directions of the polarization state changing vectors is equal to or less than a predetermined threshold, the multiple polarization state changing vectors are pointing in directions close to each other. On the other hand, when the variation in the directions of the polarization state changing vectors is greater than the predetermined threshold, it can be seen that the multiple polarization state changing vectors are not pointing in directions close to each other.

[0094] Therefore, the determination unit 2040 calculates the variation in the orientation of the polarization state changing vector and determines whether the variation is equal to or smaller than a predetermined threshold value. The threshold value is determined in advance to determine whether the variation in the orientation of the polarization state changing vector is small enough to indicate that multiple polarization state changing vectors are oriented in directions close to each other.

[0095] If the variation in the direction of the polarization state change vector is equal to or smaller than the predetermined threshold, the identifying unit 2040 determines that the characteristics of the change in the polarization state of the optical reception signal 20 during the target monitoring period apply to Case 2 (S208). On the other hand, if the variation in the direction of the polarization state change vector is greater than the predetermined threshold, the identifying unit 2040 executes S210.

[0096] <Output of processing results> The polarization state monitoring device 2000 may be configured to output information indicating the results of the processing (hereinafter referred to as result information). The result information indicates, for example, information indicating a target monitoring period and information indicating characteristics of changes in the polarization state of the optical reception signal 20 during the target monitoring period. The information indicating the target monitoring period indicates, for example, the start and end points of the target monitoring period. The information indicating characteristics of changes in the polarization state of the optical reception signal 20 indicates, for example, a label indicating one of the above-mentioned cases 1 to 4.

[0097] The result information may be output in various ways. For example, the polarization state monitoring device 2000 stores the result information in an arbitrary storage unit. Alternatively, for example, the polarization state monitoring device 2000 outputs the result information to a display device, thereby displaying the contents of the result information on the display device. Alternatively, for example, the polarization state monitoring device 2000 transmits the result information to another device (for example, a terminal operated by a user of the polarization state monitoring device 2000).

[0098] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0099] Each drawing is merely an example for describing one or more embodiments. Each drawing may relate not only to one particular embodiment, but also to one or more other embodiments. As will be understood by those skilled in the art, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings to create, for example, an embodiment not explicitly shown or described. Not all features or steps shown in any one drawing are necessary to describe an exemplary embodiment, and some features or steps may be omitted. The order of steps described in any drawing may be changed as appropriate.

[0100] In the above examples, the program includes instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable media or tangible storage media include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disc (DVD), Blu-ray (registered trademark) disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The program may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, transitory computer-readable media or communication media include electrical, optical, acoustic, or other forms of propagated signals.

[0101] A part or all of the above-described embodiments can be described as, but not limited to, the following supplementary notes. (Appendix 1) a calculation means for calculating a polarization state change vector representing a change in the polarization state of the optical reception signal for each different period; and an identification means for identifying characteristics of a change in the polarization state of the optical reception signal based on the direction of each of the polarization state change vectors, the length of each of the polarization state change vectors, or both. (Appendix 2) The polarization state monitoring device described in Appendix 1, wherein the identification means determines whether or not the change in the polarization state of the optical reception signal is characterized by a large and slow rotation of the polarization state vector representing the polarization state of the optical reception signal, based on the closeness of the directions of the plurality of polarization state change vectors. (Appendix 3) The polarization state monitoring device according to claim 2, wherein the identifying means identifies that the change in the polarization state of the received optical signal is characterized by the polarization state vector rotating significantly and slowly when the variation in the orientation of the plurality of polarization state change vectors is equal to or less than a threshold value. (Appendix 4) The polarization state monitoring device described in Appendix 1, wherein the identification means determines whether or not the change in the polarization state of the optical reception signal is characterized by a small rotation of the polarization state vector representing the polarization state of the optical reception signal, based on the variation in the lengths of the plurality of polarization state change vectors. (Appendix 5) The polarization state monitoring device according to claim 4, wherein the identifying means identifies that the change in the polarization state of the received optical signal is characterized by a small rotation of the polarization state vector when the variation in the lengths of the plurality of polarization state change vectors is equal to or less than a threshold value. (Appendix 6) The polarization state monitoring device described in Appendix 1, wherein the specifying means determines whether or not the change in the polarization state of the optical reception signal is characterized by a large and fast rotation of the polarization state vector representing the polarization state of the optical reception signal, based on the proximity of the end points of multiple polarization state vectors representing the polarization state of the optical reception signal. (Appendix 7) The identification means If a statistical value of the magnitude of the rotation angles of the plurality of polarization state vectors is equal to or greater than a threshold value, the change in the polarization state of the optical reception signal is characterized by the polarization state vector rotating rapidly and greatly, or 7. The polarization state monitoring device according to claim 6, wherein, when a statistical value of the lengths of a plurality of the polarization state change vectors is equal to or greater than a threshold value, the change in the polarization state of the received optical signal is characterized by the polarization state vector rotating rapidly and significantly. (Appendix 8) a calculation step of calculating a polarization state change vector representing a change in the polarization state of the optical reception signal for each different period; and identifying a characteristic of a change in the polarization state of the optical reception signal based on the orientation of each of the polarization state change vectors, the length of each of the polarization state change vectors, or both. (Appendix 9) 9. The polarization state monitoring method according to claim 8, wherein in the identifying step, it is determined whether or not the change in the polarization state of the received optical signal is characterized by a large and slow rotation of the polarization state vector representing the polarization state of the received optical signal, based on the closeness of the directions of the plurality of polarization state change vectors. (Appendix 10) a calculation step of calculating a polarization state change vector representing a change in the polarization state of the optical reception signal for each different period; and a specifying step of specifying characteristics of a change in the polarization state of the optical reception signal based on the direction of each of the polarization state change vectors, the length of each of the polarization state change vectors, or both.

[0102] Some or all of the elements (e.g., configurations and functions) described in Supplementary Notes 2 to 6 that are dependent on Supplementary Note 1 (device) may also be dependent on Supplementary Note 8 (method) in the same dependency relationship as Supplementary Note 2 to 6. Some or all of the elements (e.g., configurations and functions) described in Supplementary Note 2 to 7 that are dependent on Supplementary Note 1 (device) may also be dependent on Supplementary Note 10 (program) in the same dependency relationship as Supplementary Note 2 to 7. Some or all of the elements described in any Supplementary Note may be applied to various hardware, software, recording means for recording software, systems, and methods. [Explanation of symbols]

[0103] 10 Optical transmission signal 20 Optical receiving signal 100 Transmitting device 200 receiving device 300 Optical Communication Channel 1000 computers 1020 Bus 1040 processor 1060 memory 1080 storage device 1100 Input / Output Interface 1120 Network Interface 2000 Polarization Status Monitoring Device 2020 Calculation Department 2040 Specific section

Claims

1. a calculation means for calculating a polarization state change vector representing a change in the polarization state of the optical reception signal for each different period; and an identification means for identifying characteristics of a change in the polarization state of the optical reception signal based on the direction of each of the polarization state change vectors, the length of each of the polarization state change vectors, or both.

2. 2. The polarization state monitoring device according to claim 1, wherein the specifying means determines whether or not the change in the polarization state of the received optical signal is characterized by a large and slow rotation of the polarization state vector representing the polarization state of the received optical signal, based on the similarity of the directions of the plurality of polarization state change vectors.

3. 3. The polarization state monitoring device according to claim 2, wherein the identifying means identifies that the change in the polarization state of the received optical signal is characterized by the polarization state vector rotating significantly and slowly when the variation in the orientation of the plurality of polarization state change vectors is equal to or less than a threshold value.

4. 2. The polarization state monitoring device according to claim 1, wherein the identifying means determines whether or not a characteristic of the change in the polarization state of the optical reception signal is characterized by a small rotation of the polarization state vector representing the polarization state of the optical reception signal, based on the variation in lengths of the plurality of polarization state change vectors.

5. 5. The polarization state monitoring device according to claim 4, wherein the identifying means identifies the change in the polarization state of the received optical signal as being characterized by a small rotation of the polarization state vector when the variation in lengths of the plurality of polarization state change vectors is equal to or less than a threshold value.

6. 2. The polarization state monitoring device according to claim 1, wherein the specifying means determines whether or not a change in the polarization state of the received optical signal is characterized by a large and fast rotation of the polarization state vector, based on the proximity of the end points of a plurality of polarization state vectors representing the polarization state of the received optical signal.

7. The identification means If a statistical value of the magnitude of the rotation angles of the plurality of polarization state vectors is equal to or greater than a threshold value, the change in the polarization state of the optical reception signal is characterized by the polarization state vector rotating rapidly and greatly, or 7. The polarization state monitoring device according to claim 6, wherein, when a statistical value of lengths of a plurality of the polarization state change vectors is equal to or greater than a threshold value, the change in the polarization state of the received optical signal is determined to be characterized by the polarization state vector rotating significantly and rapidly.

8. a calculation step of calculating a polarization state change vector representing a change in the polarization state of the optical reception signal for each different period; and identifying a characteristic of a change in the polarization state of the optical reception signal based on the orientation of each of the polarization state change vectors, the length of each of the polarization state change vectors, or both.

9. 9. The polarization state monitoring method according to claim 8, wherein in the identifying step, it is determined whether or not the change in the polarization state of the optical reception signal is characterized by a large and slow rotation of the polarization state vector representing the polarization state of the optical reception signal, based on the closeness of the directions of the plurality of polarization state change vectors.

10. a calculation step of calculating a polarization state change vector representing a change in the polarization state of the optical reception signal for each different period; and a specifying step of specifying characteristics of a change in the polarization state of the optical reception signal based on the direction of each of the polarization state change vectors, the length of each of the polarization state change vectors, or both.

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