Apparatus and method for estimating the characteristics of optical fiber transmission lines

Abstract

To provide a characteristic estimation device and method, and an optical transmission system that reduce the cost or burden of the work of estimating characteristics of an optical fiber transmission line.SOLUTION: In an optical transmission system that transmits an optical signal via an optical fiber transmission line, a fiber type estimation device for estimating characteristics of the optical fiber transmission line includes a profile generation unit, a span detection unit, and a dispersion coefficient calculation unit. The profile generation unit generates a power profile representing a relation between an amount of dispersion corresponding to a transmission distance from a transmitting node or an optical transmission device and power of the optical signal, based on a received electric field information signal representing an electric field of the optical signal received by the optical transmission device via the optical fiber transmission line. The span detection unit detects one or more spans forming the optical fiber transmission line using the power profile. The dispersion coefficient calculation unit calculates a dispersion coefficient of the optical fiber transmission line by dividing the amount of dispersion estimated based on the power profile for each span by a corresponding span length.SELECTED DRAWING: Figure 6

Description

【Technical Field】 【0001】 The present invention relates to an apparatus and method for estimating the characteristics of an optical fiber transmission line. 【Background Art】 【0002】 The type of optical fiber used in an optical communication network is determined according to the application, cost, etc. In recent years, single-mode optical fiber (SMF), dispersion-shifted single-mode optical fiber (DSF), or non-zero dispersion-shifted single-mode optical fiber (NZ-DSF) etc. are used in optical communication networks. Examples of NZ-DSF include LEAF (registered trademark), TWRS (True Wave RS (registered trademark)). 【0003】 SMF is an optical fiber in which only one mode propagates by reducing the core diameter. General-purpose SMF has a zero-dispersion wavelength in the 1310 nm band, so it has low transmission loss and is often used in trunk networks where high-quality and stable communication is required. DSF has a zero-dispersion wavelength in the 1550 nm band with low transmission loss, so it is often used in long-distance transmission. The zero-dispersion wavelength of NZ-DSF is slightly shifted from the 1550 nm band. As an example, NZ-DSF has a zero-dispersion wavelength at about 1500 nm. Therefore, since the non-linear effect in the 1550 nm band is suppressed, NZ-DSF is suitable for wavelength division multiplexing transmission and is often used in ultra-high-speed long-distance transmission. 【0004】 Optical transmitters / receivers and optical amplifiers installed in each optical node of an optical transmission system need to be designed according to the type of optical fiber. For this reason, communication carriers check the type of optical fiber laid in each span. In the following description, the type of optical fiber may be simply referred to as "fiber type". 【0005】 Figure 1 shows an example of a method for estimating the fiber type. In this example, the type of optical fiber 503 laid between nodes 501 and 502 shown in Figure 1(a) is estimated. In this case, a multi-wavelength OTDR (Optical Time Domain Reflectometer) 504 is connected to one of the nodes. The OTDR detects the reflected light from the optical fiber after an optical pulse is incident on it. By measuring the propagation time of the optical pulse based on the timing of the reception of the reflected light, the distance to the discontinuity point or endpoint of the optical fiber is detected. 【0006】 The multi-wavelength OTDR504 measures the characteristics of the optical fiber 503 using multiple wavelengths (λ1 to λ4). Here, the propagation speed of light in the optical fiber depends on the wavelength. Therefore, the propagation time of the optical pulse measured by the multi-wavelength OTDR504 depends on the wavelength, as shown in Figure 1(b). Thus, by plotting this measurement result against the wavelength, the dispersion coefficient of the optical fiber being measured can be calculated, as shown in Figures 1(c) to 1(d). Based on this dispersion coefficient, the fiber type can then be estimated. 【0007】 Furthermore, methods for monitoring the state of each section of a transmission line have been proposed (for example, Patent Document 1). In addition, methods for estimating the characteristics of a transmission line based on dispersion coefficients used to compensate for the wavelength dispersion of a received optical signal have been proposed (for example, Patent Document 2). [Prior art documents] [Patent Documents] 【0008】 [Patent Document 1] Japanese Patent Publication No. 2018-133725 [Patent Document 2] WO2021 / 124415 [Overview of the Initiative] [Problems that the invention aims to solve] 【0009】 As mentioned above, methods are known for estimating the characteristics of an optical transmission path in order to determine the fiber type. However, conventional methods (for example, the method shown in Figure 1) use multi-wavelength OTDRs to estimate transmission characteristics. However, multi-wavelength OTDRs are expensive, making the cost of estimating transmission characteristics high. In addition, when estimating transmission characteristics using multi-wavelength OTDRs, it is necessary to either leave the fiber end open or connect a reflector to the fiber end, which increases the workload. 【0010】 One aspect of the present invention is to reduce the cost or burden of the work involved in estimating the characteristics of optical fiber transmission lines. [Means for solving the problem] 【0011】 This relates to one aspect of the present invention. Special The characteristic estimation device is a characteristic estimation device for estimating the characteristics of an optical fiber transmission path in an optical transmission system in which an optical signal is transmitted from a first node to a second node via an optical fiber transmission path, before A power profile representing the relationship between the amount of dispersion corresponding to the transmission distance from the first node or the second node and the power of the optical signal. Ru A span detection unit is used to detect one or more spans constituting the optical fiber transmission path, and for each span detected by the span detection unit, the amount of dispersion is estimated based on the power profile. , stored in the storage section The system includes a dispersion coefficient calculation unit that calculates the dispersion coefficient of the optical fiber transmission line by dividing it by the corresponding span length. [Effects of the Invention] 【0012】 According to the above-described embodiment, the cost or burden of the work of estimating the characteristics of optical fiber transmission lines is reduced. [Brief explanation of the drawing] 【0013】 [Figure 1] This figure shows an example of a method for estimating fiber type. [Figure 2]It is a diagram showing an example of a method for measuring the power of an optical signal at an arbitrary position on an optical transmission line. [Figure 3] It is a diagram showing an example of the function of a digital signal processing unit. [Figure 4] It is a diagram showing an example of changes in the power and wavelength dispersion of an optical signal. [Figure 5] It is a flowchart showing an example of a process for measuring the power of an optical signal at a plurality of positions on an optical transmission line. [Figure 6] It is a diagram showing an example of a fiber type estimation device according to an embodiment of the present invention. [Figure 7] It is a diagram showing another example of a fiber type estimation device according to an embodiment of the present invention. [Figure 8] It is a diagram showing an example of an embodiment of a method for generating a received electric field information signal and a reference signal. [Figure 9] It is a diagram showing an example of a method for generating a power profile. [Figure 10] It is a diagram showing an example of a method for detecting a span. [Figure 11] It is a diagram showing an example of design information and a constructed optical transmission system. [Figure 12] It is a flowchart showing the process of a fiber type estimation device according to the first embodiment. [Figure 13] It is a diagram showing the estimation results for the dispersion amount and dispersion coefficient of each span. [Figure 14] It is a flowchart showing the process of a fiber type estimation device according to the second embodiment. [Figure 15] (a) shows an example of fiber data, and (b) shows an example of a determination result regarding the fiber type. [Figure 16] It is a diagram showing an example of design information and a constructed optical transmission system according to the third embodiment. [Figure 17] It is a diagram showing an example of a fiber type estimation device according to the third embodiment. [Figure 18] It is a flowchart showing the process of a fiber type estimation device according to the third embodiment. [Figure 19] This figure shows the calculation results and determination results according to the third embodiment. [Figure 20] This figure shows design information relating to the third embodiment and other examples of constructed optical transmission systems. [Figure 21] This figure shows examples of optical fiber transmission paths with different optical fiber connection sequences. [Figure 22] This figure shows an example of a fiber type estimation device according to the fourth embodiment. [Figure 23] This is a flowchart showing the processing of the fiber type estimation device according to the fourth embodiment. [Figure 24] This figure illustrates a method for estimating the fiber type in the fifth embodiment. [Figure 25] This figure shows an example of a fiber type estimation device according to the fifth embodiment. [Figure 26] This is a flowchart showing the processing of the fiber type estimation device according to the fifth embodiment. [Figure 27] This is a diagram showing an optical transmission system according to the sixth embodiment. [Figure 28] This figure shows an example of the measurement results obtained in the sixth embodiment. [Figure 29] This is a flowchart showing the processing of the fiber type estimation device according to the sixth embodiment. [Figure 30] This is a diagram showing an optical transmission system according to the seventh embodiment. [Figure 31] This is a flowchart showing the processing of the fiber type estimation device according to the seventh embodiment. [Modes for carrying out the invention] 【0014】 The transmission characteristics estimation device according to an embodiment of the present invention includes a function to measure the optical power at any position on the optical fiber transmission path based on the received optical signal. Therefore, before describing the function for estimating the fiber type, we will describe the function for measuring the power of the optical signal at any position on the optical fiber transmission path. 【0015】 Figure 2 shows an example of a method for measuring the power of an optical signal at any point on an optical transmission path. In this example, the optical signal transmitted from the transmitting node 100 is transmitted via the optical fiber transmission path 2. The optical transmission device 1 receives the optical signal via the optical fiber transmission path 2. 【0016】 The optical transmission device 1 comprises a coherent receiver 11, an analog-to-digital converter (ADC) 12, a digital signal processing unit 13, a transmission waveform reconstruction unit 14, a memory circuit 15, and a feature extraction unit 16. Note that the optical transmission device 1 may also include other functions or circuits not shown in Figure 1. 【0017】 The coherent receiver 11 includes a 90-degree optical hybrid circuit and generates an electric field information signal (or electric field data) representing the electric field of the received optical signal. The electric field information signal includes the in-phase (I) and quadrature (Q) components of the received optical signal. When the optical signal is a polarization-multiplexed optical signal, the electric field information signal includes the I and Q components of the H polarization and the I and Q components of the V polarization. The ADC 12 converts the electric field information signal into a digital signal. 【0018】 Figure 3 shows an example of the functions of the digital signal processing unit 13. As shown in Figure 3, the digital signal processing unit 13 includes a dispersion compensation unit 13a, an adaptive equalization unit 13b, a frequency correction unit 13c, a phase correction unit 13d, an identification unit 13e, and an error correction unit 13f. The digital signal processing unit 13 processes the electric field information of the received optical signal. 【0019】 The dispersion compensation unit 13a is a fixed equalizer and compensates for the wavelength dispersion of the optical transmission path. The adaptive equalization unit 13b performs adaptive equalization. For example, the adaptive equalization unit 13b can compensate for residual dispersion. When the received optical signal is a polarization-multiplexed optical signal, the adaptive equalization unit 13b includes a function to separate the received optical signal by polarization. The frequency correction unit 13c compensates for the frequency offset between the light source of the transmitting node 100 and the local light source provided by the optical transmission device 1. The phase correction unit 13d compensates for the phase offset between the transmitting node 100 and the optical transmission device 1 and estimates the phase of the optical signal transmitted from the transmitting node 100. That is, for each symbol, the signal point on the constellation is reconstructed. The identification unit 13e reconstructs the transmission data based on the constellation information (phase and amplitude) output from the phase correction unit 13d. The error correction unit 13f corrects errors in the reconstructed data. 【0020】 The transmit waveform reconstruction unit 14 maps the transmitted data reconstructed by the digital signal processing unit 13 onto a constellation to generate an electric field information signal. Here, this mapping is substantially the same as the mapping performed at the transmit node 100. Therefore, the electric field information signal generated by the transmit waveform reconstruction unit 14 is substantially the same as the electric field information signal used to generate the optical signal at the transmit node 100. In other words, the output signal of the transmit waveform reconstruction unit 14 represents the electric field of the optical signal at the transmit node 100. In the following description, the output signal of the transmit waveform reconstruction unit 14 (i.e., the electric field information signal used to generate the optical signal at the transmit node 100) may be referred to as the "reference signal". 【0021】 The memory circuit 15 stores an electric field information signal representing the electric field of the received optical signal. In Figure 2, the input signal of the digital signal processing unit 13 is stored in the memory circuit 15 as the received electric field information signal, but the embodiments of the present invention are not limited to this configuration. For example, the output signals of the dispersion compensation unit 13a, the adaptive equalization unit 13b, the frequency correction unit 13c, or the phase correction unit 13d may be stored in the memory circuit 15 as the received electric field information signal. 【0022】 The feature extraction unit 16 includes a first dispersion compensation unit 16a, a nonlinear compensation unit 16b, a second dispersion compensation unit 16c, and a correlation calculation unit 16d, and performs chromatic dispersion and nonlinear distortion compensation on an electric field information signal representing the electric field of the received optical signal. The first dispersion compensation unit 16a compensates for a portion of the chromatic dispersion of the optical transmission path (hereinafter referred to as the first chromatic dispersion) in the electric field information signal. The nonlinear compensation unit 16b compensates for the nonlinear distortion of the optical transmission path in the output signal of the first dispersion compensation unit 16a. The second dispersion compensation unit 16c compensates for the remaining chromatic dispersion of the optical transmission path (hereinafter referred to as the second chromatic dispersion) in the output signal of the nonlinear compensation unit 16b. The correlation calculation unit 16d calculates the correlation between the output signal of the second dispersion compensation unit 16c and the output signal of the transmission waveform reconstruction unit 14. Here, the output signal of the transmission waveform reconstruction unit 14 represents the electric field of the optical signal at the transmission node 100, as described above. In other words, the correlation calculation unit 16d calculates the correlation between the electric field information signal, which has been compensated for wavelength dispersion and nonlinear distortion, and the electric field information signal representing the electric field of the optical signal at the transmitting node 100. It is preferable that the output signal of the second dispersion compensation unit 16c and the output signal of the transmitting waveform reconstruction unit 14 are appropriately normalized. 【0023】 The correlation value calculated by the feature extraction unit 16 represents the power of the optical signal transmitted through the optical transmission path. In other words, the optical transmission device 1 can measure the power of the optical signal transmitted through the optical transmission path by calculating this correlation value. Here, with reference to Figure 4, the relationship between the correlation value and the power of the optical signal is described. 【0024】 Figure 4 shows an example of changes in the power and chromatic dispersion of an optical signal. In this example, an optical signal is transmitted from the transmitting node 100 to the optical transmission device 1. An optical amplifier is provided on the optical transmission path. 【0025】 The power of the optical signal attenuates as it moves away from the transmitting node 100. The optical signal is then amplified by the optical amplifier. Subsequently, the power of the optical signal attenuates as it moves away from the optical amplifier. The cumulative chromatic dispersion added to the optical signal increases in proportion to the distance from the transmitting node 100. Note that "CD" in Figure 4 represents the total chromatic dispersion of the optical transmission path between the transmitting node 100 and the optical transmission device 1. 【0026】 Here, the optical transmission device 1 measures the power of the optical signal at position P shown in Figure 4. The chromatic dispersion of the optical transmission path between the optical transmission device 1 and position P is CD1. The chromatic dispersion between the transmitting node 100 and position P is CD2. The sum of CD1 and CD2 is CD. 【0027】 As described above, the feature extraction unit 16 compensates for chromatic dispersion and nonlinear distortion. Specifically, the first dispersion compensation unit 16a compensates for chromatic dispersion CD1 in the electric field information signal representing the received optical signal. The nonlinear compensation unit 16b compensates for nonlinear distortion in the output signal of the first dispersion compensation unit 16a. At this time, the nonlinear compensation unit 16b compensates for a predetermined amount of nonlinear distortion. Then, the second dispersion compensation unit 16c compensates for chromatic dispersion CD2 in the output signal of the nonlinear compensation unit 16b. 【0028】 Here, the magnitude of the nonlinear distortion that occurs in the optical transmission line depends on the power of the optical signal. Specifically, the greater the power of the optical signal, the greater the nonlinear distortion. In this embodiment, the nonlinear compensation unit 16b is designed to compensate for the nonlinear distortion that occurs when the power of the optical signal is sufficiently large. For example, although not limited to this example, the nonlinear compensation unit 16b is designed to compensate for the nonlinear distortion that occurs with respect to the output optical power of the transmitting node 100. 【0029】 On the other hand, the correlation value calculated by the correlation calculation unit 16d represents the correlation between the electric field information signal, which has been compensated for wavelength dispersion and nonlinear distortion in the feature extraction unit 16, and the electric field information signal representing the electric field of the optical signal at the transmission node 100. Therefore, if the nonlinear distortion is appropriately compensated in the nonlinear compensation unit 16b, the correlation value calculated by the correlation calculation unit 16d will increase. 【0030】 Specifically, when the power of the optical signal at position P is high, the amount of nonlinear distortion at position P increases, and the difference between the amount of nonlinear distortion at position P and the amount of nonlinear distortion compensated by the nonlinear compensation unit 16b decreases. As a result, the nonlinear distortion is appropriately compensated by the nonlinear compensation unit 16b, and the difference between the output signal of the second dispersion compensation unit 16c and the electric field information signal at the transmission node 100 decreases, so the correlation value calculated by the correlation calculation unit 16d increases. On the other hand, when the power of the optical signal at position P is low, the amount of nonlinear distortion at position P decreases, and the difference between the amount of nonlinear distortion at position P and the amount of nonlinear distortion compensated by the nonlinear compensation unit 16b increases. As a result, the nonlinear distortion is not appropriately compensated by the nonlinear compensation unit 16b, and the difference between the output signal of the second dispersion compensation unit 16c and the electric field information signal at the transmission node 100 increases, so the correlation value calculated by the correlation calculation unit 16d decreases. In other words, the correlation value increases when the power of the optical signal at position P is high, and decreases when the power of the optical signal at position P is low. Therefore, the correlation value calculated in the feature extraction unit 16 essentially represents the power of the optical signal at a predetermined position (position P in Figure 4) on the optical transmission path. 【0031】 Furthermore, the position P shown in Figure 4 is specified by a combination of wavelength-dispersive CD1 and wavelength-dispersive CD2. Therefore, the feature extraction unit 16 can measure the power of the optical signal at a desired position on the optical transmission path by changing the combination of wavelength-dispersive CD1 and wavelength-dispersive CD2 with respect to the electric field information signal representing the electric field of the received optical signal. 【0032】 Figure 5 is a flowchart illustrating an example of a process for measuring the power of an optical signal at multiple locations along an optical transmission path. This process is performed when the optical transmission device 1 receives an optical signal transmitted from the transmitting node 100 via the optical transmission path. 【0033】 In S101, the feature extraction unit 16 acquires the transmitted electric field information signal generated by the transmitted waveform reconstruction unit 14. The transmitted electric field information signal represents the electric field of the optical signal at the transmitting node 100. In S102, the feature extraction unit 16 acquires the electric field information signal of the received optical signal. This electric field information signal is assumed to be generated by the coherent receiver 11 or the digital signal processing unit 13 and stored in the memory circuit 15. 【0034】 In S103, the feature extraction unit 16 initializes the chromatic dispersion CD1 to "zero". The value of chromatic dispersion CD1 corresponds to the transmission distance relative to the optical transmission device 1. The chromatic dispersion CD2 is calculated from "CD1 + CD2 = CD". CD represents the total chromatic dispersion of the transmission path between the transmitting node 100 and the optical transmission device 1, and its value is assumed to be known. In S104, the feature extraction unit 16 determines whether the chromatic dispersion CD1 is less than or equal to CD. If the chromatic dispersion CD1 is less than or equal to CD, the processing of the feature extraction unit 16 proceeds to S105. 【0035】 In S105, the feature extraction unit 16 sequentially performs compensation for wavelength dispersion CD1, nonlinear compensation, and wavelength dispersion CD2 on the electric field information signal of the received optical signal. In S106, the feature extraction unit 16 calculates the correlation between the electric field information signal compensated in S105 and the transmitted electric field information signal acquired in S101. 【0036】 In S107, the feature extraction unit 16 adds ΔCD to the chromatic dispersion CD1. It is preferable that ΔCD is sufficiently small compared to the total chromatic dispersion CD. After this, the feature extraction unit 16 returns to processing S104. That is, in S104 to S107, the feature extraction unit 16 calculates the correlation value while increasing the chromatic dispersion CD1 by ΔCD until the chromatic dispersion CD1 becomes greater than CD. Here, the value of chromatic dispersion CD1 corresponds to the transmission distance relative to the optical transmission device 1. Therefore, the step of increasing the chromatic dispersion CD1 by ΔCD is equivalent to the step of shifting the position on the optical transmission path by a distance corresponding to ΔCD. Thus, by repeatedly executing the processing in S104 to S107, the feature extraction unit 16 can obtain correlation values ​​at multiple positions on the optical transmission path. 【0037】 When the chromatic dispersion CD1 becomes greater than CD, in S108, the feature extraction unit 16 outputs the correlation value calculated in S104 to S107. Here, the correlation value essentially represents the power of the optical signal at a predetermined position on the optical transmission path corresponding to the combination of chromatic dispersion CD1 and CD2. In other words, the feature extraction unit 16 can detect the power of the optical signal at multiple positions on the optical transmission path. In the following description, the information representing the power of the optical signal at multiple positions on the optical transmission path may be referred to as a "power profile". In this way, the optical transmission device 1 can measure the power of the optical signal at a desired position on the optical transmission path and create a power profile of the optical transmission path. 【0038】 Figure 6 shows an example of a fiber type estimation device according to an embodiment of the present invention. In this embodiment, the fiber type estimation device 20 according to an embodiment of the present invention is connected to an optical transmission device 1. The optical transmission device 1 includes a coherent receiver 11 and a digital signal processing unit 13. The coherent receiver 11 generates a received electric field information signal (or electric field data) that represents the electric field of the received optical signal. The digital signal processing unit 13 reconstructs data based on the received electric field information signal, as described with reference to Figure 3. 【0039】 The fiber type estimation device 20 comprises a profile generation unit 21, a span detection unit 22, a dispersion coefficient calculation unit 23, and a fiber type estimation unit 24. Note that the fiber type estimation device 20 may have other functions not shown in Figure 6. 【0040】 The fiber type estimation device 20 is implemented by a digital signal processor that processes digital signals. The digital signal processor can be implemented by an FPGA (Field Programmable Gate Array), a large-scale integrated circuit (LSI), or a central processing unit (CPU). When the fiber type estimation device 20 is implemented by a CPU, the CPU provides the functions of the fiber type estimation device 20 by executing a software program. 【0041】 Figure 7 shows another example of a fiber type estimation device according to an embodiment of the present invention. In the embodiment shown in Figure 6, the fiber type estimation device 20 is provided outside the optical transmission device 1. In contrast, in the embodiment shown in Figure 7, the fiber type estimation device 20 is implemented inside the optical transmission device 1. The configuration of the fiber type estimation device 20 is substantially the same in Figures 6 and 7. 【0042】 The fiber type estimation device 20 estimates the type of optical fiber connecting the transmitting node 100 and the optical transmission device 1 using the received electric field information signal and the reference signal. The received electric field information signal represents the electric field information of the optical signal received by the optical transmission device 1 from the transmitting node 100. For example, although not limited to this, as shown in Figure 8, the output signal of the adaptive equalization unit 13b is used as the received electric field information signal. Alternatively, the output signal of the phase correction unit 13d may be used as the received electric field information signal. The reference signal represents the electric field information for generating the optical signal at the transmitting node 100. In this embodiment, the reference signal is generated by the transmission waveform reconstruction unit 14 based on data reconstructed by the digital signal processing unit 13. 【0043】 The fiber type estimation device 20 may refer to dispersion data, span length data, and fiber data when estimating the fiber type. The dispersion data, span length data, and fiber data are stored in a storage unit 30, as shown in Figure 6 or Figure 7. The storage unit 30 is implemented, for example, by a semiconductor memory. Alternatively, the storage unit 30 may be implemented using hardware circuitry. 【0044】 The dispersion data represents the total chromatic dispersion of the optical fiber transmission path 2 between the transmitting node 100 and the optical transmission device 1. The total chromatic dispersion of the optical fiber transmission path 2 is assumed to be pre-measured, for example. The span length data represents the length (or transmission distance) of each span. In this embodiment, a span refers to the interval between an optical node and an adjacent optical node. Optical nodes include transmitting nodes, relay stations, and receiving nodes. The fiber data represents the dispersion coefficient for each fiber type. For example, the fiber data represents the dispersion coefficients for SMF, DSF, and NZ-DSF. 【0045】 The profile generation unit 21 generates a power profile for a dispersion amount corresponding to the transmission distance from the transmitting node 100 or the optical transmission device 1, based on the received electric field information signal which represents the electric field of the optical signal received by the optical transmission device 1. At this time, the profile generation unit 21 generates the power profile according to the flowchart shown in Figure 5. 【0046】 Figure 9 shows an example of a method for generating a power profile. In this embodiment, the total dispersion of the optical fiber transmission path 2 between the transmitting node 100 and the optical transmission device 1 is 1000 ps / nm. The profile generation unit 21 acquires a received electric field information signal representing the electric field of the optical signal received by the optical transmission device 1. The profile generation unit 21 also acquires a reference signal representing the electric field information for generating the optical signal at the transmitting node 100. Furthermore, the ΔCD used in the flowchart shown in Figure 5 is 10 ps / nm. 【0047】 The profile generation unit 21 sets "CD1=10" and "CD2=990". The first dispersion compensation unit 16a compensates for dispersion of 10 ps / nm in the received electric field information signal. The nonlinear compensation unit 16b compensates for nonlinear distortion in the output signal of the first dispersion compensation unit 16a. The second dispersion compensation unit 16c compensates for dispersion of 990 ps / nm in the output signal of the nonlinear compensation unit 16b. Then, the correlation calculation unit 16d calculates the correlation between the reference signal and the output signal of the second dispersion compensation unit 16c. Here, this correlation value represents the power of the optical signal at position P1 shown in Figure 9(a). Position P1 corresponds to the position reached by a transmission distance corresponding to a dispersion of 10 ps / nm from the optical transmission device 1 toward the transmission node 100. In this example, the power of the optical signal at position P1 is Q1. 【0048】 Next, the profile generation unit 21 sets "CD1=20" and "CD2=980". The first dispersion compensation unit 16a compensates for dispersion of 20 ps / nm in the received electric field information signal. The nonlinear compensation unit 16b compensates for nonlinear distortion in the output signal of the first dispersion compensation unit 16a. The second dispersion compensation unit 16c compensates for dispersion of 980 ps / nm in the output signal of the nonlinear compensation unit 16b. Then, the correlation calculation unit 16d calculates the correlation between the reference signal and the output signal of the second dispersion compensation unit 16c. Here, this correlation value represents the power of the optical signal at position P2 shown in Figure 9(b). Position P2 corresponds to the position reached by a transmission distance corresponding to a dispersion of 20 ps / nm from the optical transmission device 1 toward the transmission node 100. In this example, the power of the optical signal at position P2 is Q2. 【0049】 Similarly, the profile generation unit 21 calculates the optical power for each dispersion amount while shifting the dispersion amounts compensated by the first dispersion compensation unit 16a and the second dispersion compensation unit 16c by ΔCD. As a result, as shown in Figure 9(c), a power profile is generated that represents the relationship between the dispersion amount corresponding to the transmission distance from the optical transmission device 1 and the power of the optical signal. 【0050】 The span detection unit 22 uses the power profile generated by the profile generation unit 21 to detect one or more spans that make up the optical fiber transmission line 2. For example, the interval between each peak appearing in the power profile and adjacent peaks is detected as a span. In the example shown in Figure 10, three spans (SP1 to SP3) are detected between the transmitting node and the receiving node. At this time, the span detection unit 22 may correct the peak positions using pre-prepared calibration values. 【0051】 The dispersion coefficient calculation unit 23 estimates the dispersion amount for each span detected by the span detection unit 22. The dispersion amount for a span corresponds to the difference between the dispersion value at which a peak appears in the power profile and the dispersion value at which the adjacent peak appears. The dispersion coefficient calculation unit 23 then calculates the dispersion coefficient of the optical fiber transmission line 2 for each span. At this time, the dispersion coefficient is calculated, for example, by dividing the dispersion amount estimated based on the power profile by the span length. The span length of each span is known and is represented by span length data stored in the storage unit 30. The fiber type estimation unit 24 estimates the type of optical fiber constituting the optical fiber transmission line 2 for each span detected by the span detection unit 22, based on the dispersion coefficient calculated by the dispersion coefficient calculation unit 23. The processing of the dispersion coefficient calculation unit 23 and the fiber type estimation unit 24 will be explained in detail in the embodiments described later. 【0052】 <First Embodiment> Figure 11 shows design information relating to the first and second embodiments and an example of a constructed optical transmission system. In this embodiment, relay stations A1 and A2 are provided on the optical fiber transmission path between the transmitting node TX and the receiving node RX. That is, the optical fiber transmission path consists of spans SP1 and SP3. Span SP1 corresponds to the section between the transmitting node TX and relay station A1, span SP2 corresponds to the section between relay station A1 and relay station A2, and span SP3 corresponds to the section between relay station A2 and the receiving node RX. 【0053】 The design information relating to the first and second embodiments represents the configuration shown in Figure 11(a). That is, the optical transmission system is designed so that spans SP1 to SP3 are each composed of SMF. Here, the span lengths of each span SP1 to SP3 are known. The dispersion coefficient of the SMF is also known. Therefore, it is possible to create a power profile corresponding to the design information. Figure 11(b) shows the power profile corresponding to the design information shown in Figure 11(a). Note that the power profiles shown in Figure 11 and other drawings only schematically show the relationship between dispersion and optical power, and the dispersion, optical power, and the slope of the graph are not important. 【0054】 Figure 11(c) shows an optical transmission system constructed based on design information. Here, spans SP1 and SP3 are composed of the correct optical fibers. However, span SP2 is composed of the wrong optical fiber. Specifically, the design information specifies SMF, but in reality, NZ-DSF is laid in span SP2. The fiber type estimation device 20 then acquires electric field information from the receiving node RX of the optical transmission system shown in Figure 11(c). 【0055】 Figure 12 is a flowchart showing the processing of the fiber type estimation device 20 according to the first embodiment. Below, the processing of the fiber type estimation device 20 will be described based on the design information and measurement results shown in Figure 11. 【0056】 In S1, the profile generation unit 21 generates a power profile based on the electric field information acquired from the receiving node. Figure 11(d) shows the power profile of the optical transmission system shown in Figure 11(c). 【0057】 In S2, the span detection unit 22 detects one or more spans using the power profile generated by the profile generation unit 21. In the embodiment shown in Figure 11(d), three spans SP1 to SP3 are detected. 【0058】 In S3, the dispersion coefficient calculation unit 23 estimates the dispersion amount of the optical fiber transmission path for each span detected by the span detection unit 22 based on the power profile. Here, in the power profile, the power of the optical signal is plotted against the dispersion amount of the optical fiber transmission path. Therefore, by identifying the dispersion value at which the peak of optical power appears in the power profile, the dispersion amount of each span can be estimated. The estimated values ​​of the dispersion amount of each span are shown in Figure 11(d) or Figure 13. 【0059】 In S4, the dispersion coefficient calculation unit 23 calculates the dispersion coefficient of the optical fiber transmission line for each span. The dispersion coefficient is calculated by dividing the amount of dispersion estimated based on the power profile by the span length. The span length of each span is stored as span length data in the storage unit 30. For example, the dispersion coefficient of span SP1 is obtained by dividing "680 ps / nm" by "60 km". The calculation results for each span are shown in Figure 13. 【0060】 Thus, in the first embodiment, the fiber type estimation device 20 can calculate the dispersion coefficient for each span of the optical transmission system. That is, in the first embodiment, the fiber type estimation device 20 is used as a characteristic estimation device to estimate the characteristics of the optical fibers constituting each span of the optical transmission system. 【0061】 Here, the dispersion coefficients for each fiber type are known. For example, the dispersion coefficient for SMF is 14-17 ps / nm, the dispersion coefficient for NZ-DSF is 3-7 ps / nm, and the dispersion coefficient for DSF is -2-2 ps / nm. Therefore, the network system administrator can estimate the type of optical fiber laid in each span based on the dispersion coefficient calculated by the dispersion coefficient calculation unit 23. In the example shown in Figure 13, it can be estimated that SMF is laid in spans SP1 and SP3, and NZ-DSF is laid in span SP2. 【0062】 Furthermore, by measuring the dispersion amount of each span, it is possible to estimate the type of optical fiber laid in each span. However, in large-scale networks, dozens of relay stations may be provided between the transmitting node and the receiving node. In other words, the optical fiber transmission path may consist of dozens of spans. Therefore, measuring the dispersion amount of the corresponding span at each relay station requires considerable effort. In contrast, the fiber type estimation device 20 can estimate the dispersion amount and dispersion coefficient of each span based on the electric field information generated at the receiving node, thus reducing the workload for network system administrators. 【0063】 <Second Embodiment> In the first embodiment, the dispersion coefficient for each span of the optical transmission system is calculated. In the second embodiment, the fiber type for each span is estimated using the dispersion coefficient calculated in the first embodiment. In the second embodiment as well, the processing of the fiber type estimation device 20 will be explained with reference to Figure 11. 【0064】 Figure 14 is a flowchart showing the processing of the fiber type estimation device 20 according to the second embodiment. Note that S1 to S4 are the same in Figures 12 and 14. That is, the fiber type estimation device 20 calculates the dispersion coefficient for each span. 【0065】 In S11, the fiber type estimation unit 24 estimates the type of optical fiber constituting the optical fiber transmission line based on the dispersion coefficient calculated by the dispersion coefficient calculation unit 23 for each span detected by the span detection unit 22. At this time, the fiber type estimation unit 24 refers to the fiber data shown in Figure 15(a). The fiber data represents the dispersion coefficient of each fiber type. For example, the dispersion coefficient of SMF is 14 to 17 ps / nm, the dispersion coefficient of NZ-DSF is 3 to 7 ps / nm, and the dispersion coefficient of DSF is -2 to 2 ps / nm. 【0066】 In the example shown in Figures 11(c) to 11(d), the dispersion coefficient calculated for span SP1 by the dispersion coefficient calculation unit 23 is 16.3 ps / nm. This value corresponds to the dispersion coefficient of SMF. Therefore, the fiber type estimation unit 24 estimates that the optical fiber laid in span SP1 is SMF. Similarly, the optical fiber laid in span SP3 is also estimated to be SMF. In contrast, the dispersion coefficient calculated for span SP2 by the dispersion coefficient calculation unit 23 is 4.5 ps / nm. This value corresponds to the dispersion coefficient of NZ-DSF. Therefore, the fiber type estimation unit 24 estimates that the optical fiber laid in span SP2 is NZ-DSF. 【0067】 In S12, the fiber type estimation unit 24 determines whether the optical fiber transmission path in each span is correctly constructed according to the design information. In this embodiment, the optical transmission system is designed so that SMF is laid in each span SP1 to SP3. Here, the fiber type estimation unit 24 estimates that spans SP1 and SP3 are composed of SMF. Therefore, the fiber type estimation unit 24 determines that the correct optical fibers are laid in spans SP1 and SP3. On the other hand, the fiber type estimation unit 24 estimates that span SP2 is composed of NZ-DSF. Therefore, the fiber type estimation unit 24 determines that the wrong optical fiber is laid in span SP2. Figure 15(b) shows the estimation and determination results by the fiber type estimation unit 24. 【0068】 <Third Embodiment> In the first and second embodiments, the fiber type for each span is estimated. However, multiple fiber types may be present within a single span. Therefore, in the third embodiment, the fiber type estimation device 20 estimates multiple fiber types that are present within a span. 【0069】 Figure 16 shows an example of design information and a constructed optical transmission system relating to the third embodiment. The design information specifies the fiber type for each span, as shown in Figure 16(a). In this example, it is designed so that SMF is laid in each span SP1 to SP3. The design information may also include information representing the span length of each span. Figure 16(b) shows the power profile obtained for the design information. 【0070】 Figure 16(c) shows the configuration of the optical transmission system built based on the design information. In this example, the correct optical fibers are laid in spans SP1 and SP3. However, the wrong optical fibers are laid in span SP2. Specifically, the optical fiber transmission path in span SP2 is composed of SMF and NZ-DSF. 【0071】 Figure 16(d) shows the power profile of the optical fiber transmission line shown in Figure 16(c). This power profile is generated based on the electric field information detected at the receiving node RX, as described above. 【0072】 Figure 17 shows an example of a fiber type estimation device 20 according to the third embodiment. In the third embodiment, the fiber type estimation unit 24 includes a combination detection unit 24b. Furthermore, the fiber type estimation device 20 does not necessarily have to calculate the dispersion coefficient for each span. 【0073】 The combination detection unit 24b detects the combination of optical fibers constituting each span by referring to the fiber type list. The fiber type list is an example of fiber data stored in the storage unit 30 and represents the dispersion coefficient for each fiber type. 【0074】 Figure 18 is a flowchart showing the processing of the fiber type estimation device 20 according to the third embodiment. Note that S1 to S3 are the same in Figures 12 and 18. That is, the fiber type estimation device 20 calculates the dispersion amount for each span. In the example shown in Figures 16(c) to 16(d), the dispersion amounts calculated for spans SP1, SP2, and SP3 are 980 ps / nm, 645 ps / nm, and 980 ps / nm, respectively. 【0075】 The processes S21 to S23 are executed for each span. In the context of Figure 18, the span in which the processes S21 to S23 are executed is sometimes referred to as the "target span". 【0076】 In S21, the fiber type estimation unit 24 compares the estimated dispersion amount with the design value for the target span. The estimated dispersion amount is obtained in S1 to S3. The design value for the dispersion amount is assumed to be calculated in advance based on design information representing the fiber type and span length. If the difference between the estimated value and the design value is smaller than the threshold, the fiber type estimation unit 24 determines that the correct optical fiber is laid in the target span. In this case, in S22, the fiber type estimation unit 24 estimates the fiber type of the target span based on the dispersion coefficient. The method for calculating the dispersion amount of the target span and the method for estimating the fiber type of the target span based on the dispersion coefficient are as described in the second embodiment. The threshold is not particularly limited, but for example, it may be set to about 10 percent of the design value. 【0077】 If the difference between the estimated value and the design value is greater than a threshold, the fiber type estimation unit 24 determines that the wrong optical fiber has been laid in the target span. In this case, in S23, the combination detection unit 24b uses the span length of the target span and the fiber type list to determine a combination of fiber types that satisfies the estimated value of the dispersion amount. 【0078】 Here, the processing of S21 to S23 will be explained with reference to the cases shown in Figures 16(c) to 16(d). First, in span SP1, the design value of the dispersion is 990 ps / nm, and the estimated value of the dispersion is 980 ps / nm. That is, the difference between the design value and the estimated value is sufficiently small. In this case, the fiber type estimation unit 24 calculates the dispersion coefficient of span SP1 in S22. In this embodiment, "16.3 ps / nm / km" is obtained by dividing "980 ps / nm" by "60 km". Then, according to the fiber data shown in Figure 15(a) or the fiber type list shown in Figure 17, this dispersion coefficient corresponds to the dispersion coefficient of SMF. Therefore, the fiber type estimation unit 24 estimates that the optical fiber laid in span SP1 is SMF. The same applies to span SP3. 【0079】 Furthermore, if the difference between the design value and the estimated value is sufficiently small, the fiber type estimation unit 24 determines that the correct optical fiber is laid in the target span. In this case, according to the design information shown in Figure 16(a), SMF is used in span SP1. Therefore, the fiber type estimation unit 24 may refer to the design information and estimate that the optical fiber laid in span SP1 is SMF. 【0080】 In span SP2, the design value for dispersion is 990 ps / nm, while the estimated value for dispersion is 645 ps / nm. In other words, there is a large difference between the design value and the estimated value. In this case, the combination detection unit 24b determines the fiber type combination in S23. 【0081】 For the sake of simplicity, let's assume that the only fiber types that may be used in optical fiber transmission lines are SMF and NZ-DSF. In this case, equation (1) holds for span SP2. CD_2 represents the amount of dispersion in span SP2 estimated based on the power profile. L_2 represents the span length of span SP2. D_SMF represents the dispersion coefficient of SMF. D_NZDSF represents the dispersion coefficient of NZ-DSF. X represents the ratio of the length of SMF to the span length of span SP2. 【number】 【0082】 Then, by substituting "CD_2=645ps / nm", "D_SMF=17ps / nm / km", "D_NZDSF=4.5ps / nm / km", and "L_2=60km" into equation (1), we obtain "X=0.5". In this case, multiplying the span length of span SP2 (60km) by "X" calculates that the length of the SMF is 30km. Also, multiplying the span length of span SP2 (60km) by "1-X" calculates that the length of the NZ-DSF is 30km. In other words, the combination detection unit 24b estimates that span SP2 is composed of an SMF of 30km and an NZ-DSF of 30km. 【0083】 As shown in the flowchart in Figure 18, the S23 process is executed only for spans where the difference between the estimated and design values ​​of the dispersion is large. Therefore, the processing load for estimating the fiber type of each span in the optical fiber transmission line can be reduced. In particular, in large-scale networks with a large number of spans, the reduction in the computational load of the fiber type estimation device 20 is significant. 【0084】 In addition, the number of optical fibers constituting the target span and the length of each optical fiber may be known. For example, in the cases shown in Figures 16(c) to 16(d), it is known that span SP2 is composed of two optical fibers, and the length of each optical fiber is 30 km. Furthermore, it is assumed that at least one of the two optical fibers constituting span SP2 is SMF. Moreover, it is assumed that the dispersion coefficients of SMF, NZ-DSF, DSF, and LS are 17 ps / nm, 4.5 ps / nm, zero ps / nm, and -1.75 ps / nm, respectively. 【0085】 In this case, the combination detection unit 24b estimates the fiber type of span SP2 using equation (2). D_1 represents the dispersion coefficient of one of the two optical fibers constituting span SP2 (in this case, SMF), and D_2 represents the dispersion coefficient of the other optical fiber (in this case, SMF, NZ-DSF, DSF, or LS). 【number】 【0086】 Assuming that both optical fibers constituting the span in question are SMF, equation (2) is given by "CD_2=645ps / nm", "D_1=17ps / nm / km", "D_2=17ps / nm / km", and "L_2=60km". In this case, "X" is not determined. Therefore, the assumption that "the other optical fiber is SMF" is determined to be incorrect. 【0087】 If we assume that the other optical fiber is DSF, then we get "D_2 = zero". In this case, we obtain "X = 38 km". That is, it is inconsistent with "the length of each optical fiber is 30 km". Therefore, the assumption that "the other optical fiber is DSF" is determined to be incorrect. 【0088】 Assuming the other optical fiber is LS, we get "D_2 = -1.75 ps / nm / km". In this case, we obtain "X = 40km". That is, it is inconsistent with "the length of each optical fiber is 30km". Therefore, the assumption that "the other optical fiber is LS" is determined to be incorrect. 【0089】 Assuming the other optical fiber is NZ-DSF, we get "D_2 = 4.5 ps / nm / km". In this case, we obtain "X = 30km". This is consistent with "the length of each optical fiber is 30km". Therefore, the assumption that "the other optical fiber is NZ-DSF" is determined to be correct. Figure 19 shows the determination result by the combination detection unit 24b. 【0090】 Figure 20 shows design information and other examples of constructed optical transmission systems. The design information specifies the fiber type for each span, as shown in Figure 20(a). In this example, spans SP1 and SP3 are each composed of 60 km of SMF, and span SP2 is composed of 40 km of SMF and 20 km of NZ-DSF. 【0091】 However, in reality, as shown in Figure 20(b), span SP2 consists of a 40km SMF and a 20km SMF. Figure 20(c) shows the power profile generated for the optical transmission system shown in Figure 20(b). 【0092】 The fiber type estimation device 20 estimates the fiber type of each span based on the power profile shown in Figure 20(c). Specifically, it estimates the fiber type using equation (1) described above. Here, when estimating the fiber type of span SP2, "CD_2=980ps / nm", "D_SMF=17ps / nm / km", "D_NZDSF=4.5ps / nm / km", and "L_2=60km" are given to equation (1). Then, "X=0.944" is obtained. Here, considering the error, "X=1" is acceptable. Also, "X=1" indicates that the entire span SP2 is composed of SMF. Therefore, the combination detection unit 24b estimates that span SP2 is composed of 40km SMF and 20km SMF. 【0093】 A span may be composed of three or more optical fibers. Also, optical fibers other than SMF or NZ-DSF may be used. Therefore, the combination detection unit 24b may estimate the fiber types in the span using equation (3). CD represents the estimated value of the dispersion amount of the target span. L represents the span length of the target span. D_i identifies the dispersion coefficient of the i-th optical fiber among the n optical fibers when the target span is composed of n optical fibers. X_i represents the ratio of the length of the i-th optical fiber to the span length of the target span. 【0094】 【number】 The combination detection unit 24b then solves an optimization problem (or mathematical programming problem) to find D_i (i=1~n) and X_i (i=1~n). This estimates the fiber types within the target span. 【0095】 <Fourth Embodiment> In the third embodiment, the types of fibers mixed within the span are estimated. For example, as shown in Figure 21, suppose the span SP2 is composed of SMF and NZ-DSF. In this case, using equation (1) described above, it is possible to estimate that the span SP2 is composed of SMF and NZ-DSF, and the length of each optical fiber. 【0096】 In the fourth embodiment, in addition to estimating the fiber type, the order in which different types of optical fibers are connected is also estimated. For example, in the case shown in Figure 21(a), an SMF is provided on the transmitting node side and an NZ-DSF is provided on the receiving node side. On the other hand, in the case shown in Figure 21(b), an NZ-DSF is provided on the transmitting node side and an SMF is provided on the receiving node side. In the fourth embodiment, the two cases shown in Figure 21 can be identified. 【0097】 In the fourth embodiment, the optical transmission system includes a function to detect connection points between two or more optical fibers when two or more optical fibers are provided within a single span. This function is realized, for example, by an OTDR. The OTDR injects an optical pulse into the optical fiber and detects the reflected light from the optical fiber. Then, by measuring the propagation time of the optical pulse based on the reception timing of the reflected light, the distance to the discontinuity point in the optical fiber transmission path is detected. Therefore, for example, if an OTDR is provided at each node and each relay station, the connection points of the optical fibers within each span can be detected. That is, when two or more optical fibers are provided within a single span, the length of each optical fiber can be detected. The connection point information, which represents the position of the connection points between the optical fibers, is then provided to the fiber type estimation device 20. Note that the connection points between optical fibers may be detected using a single-wavelength OTDR without using an expensive multi-wavelength OTDR. 【0098】 Figure 22 shows an example of a fiber type estimation device 20 according to the fourth embodiment. In the fourth embodiment, the fiber type estimation unit 24 includes a combination detection unit 24b and a connection order determination unit 24c. Note that the fiber type estimation device 20 does not need to calculate the dispersion coefficient for each span. 【0099】 The combination detection unit 24b detects combinations of optical fibers constituting each span, similar to the third embodiment. The connection order determination unit 24c determines the order in which the optical fibers detected by the combination detection unit 24b are connected. At this time, the connection order determination unit 24c uses connection point information to determine the order in which the optical fibers are connected. 【0100】 Figure 23 is a flowchart showing the processing of the fiber type estimation device 20 according to the fourth embodiment. Steps S1 to S3 are the same in Figures 12 and 23. That is, the fiber type estimation device 20 calculates the dispersion amount for each span. Steps S21 to S23 are the same in Figures 18 and 23. That is, the fiber type estimation device 20 estimates the type and characteristics of each optical fiber within the target span. 【0101】 In S31, the connection order determination unit 24c acquires connection point information. As described above, the connection point information represents the position of the connection point between optical fibers within the span. Therefore, the connection point information essentially represents the length of each optical fiber. The connection point information can be acquired using OTDR. In S32, the connection order determination unit 24c determines the connection order of each optical fiber within the target span based on the connection point information and the fiber type estimated in S23. 【0102】 For example, in the optical transmission system shown in Figure 21, the combination detection unit 24b estimates that the span SP2 consists of SMF with a span of 20 km and NZ-DSF with a span of 40 km. Furthermore, it is assumed that a connection point between optical fibers is detected at a location 20 km away from relay station A1 by using an OTDR or the like. In this case, the connection order determination unit 24c estimates that the optical fiber connected to relay station A1 is SMF and the optical fiber connected to relay station A2 is NZ-DSF. 【0103】 <Fifth Embodiment> In the fourth embodiment, as described above, the order in which different types of optical fibers are connected within the span is estimated. However, in the fourth embodiment, it is necessary to detect the location of the optical fiber connection points within the span. In contrast, in the fifth embodiment, even if the location of the optical fiber connection points is unknown, the order in which multiple optical fibers are connected within the span can be estimated. 【0104】 Figure 24 illustrates a method for estimating fiber types in a fifth embodiment. In this embodiment, as shown in Figure 24(a), span SP2 is composed of SMF and NZ-DSF. Figure 24(b) shows the power profile of span SP2 generated by the profile generation unit 21. Note that the power profiles of spans SP1 and SP3 are omitted. 【0105】 Figure 25 shows an example of a fiber type estimation device 20 according to the fifth embodiment. In the fifth embodiment, the fiber type estimation unit 24 includes a feature detection unit 24d and a connection order determination unit 24e. The fiber type estimation device 20 does not need to calculate the dispersion coefficient for each span. 【0106】 The feature detection unit 24d detects the shape characteristics of the power profile generated by the profile generation unit 21. In this embodiment, the feature detection unit 24d detects the slope of the power profile of the target span (here, span SP2). Then, the connection order determination unit 24e determines the connection order of the optical fibers within the target span based on the features detected by the feature detection unit 24d. 【0107】 In the power profile shown in Figure 24(b), span SP2 consists of two sections with different slopes. That is, span SP2 consists of a first section with a slope of G1 and a second section with a slope of G2. Here, the slope of the power profile corresponds to the type of optical fiber. Specifically, when the dispersion coefficient and transmission loss of the optical fiber are CD [ps / nm / km] and LOS [dB / km], respectively, the slope G of the power profile is expressed by equation (4). 【number】 【0108】 For example, when the dispersion coefficient and transmission loss of SMF are 17 ps / nm / km and 0.3 dB / km, respectively, the slope of the SMF power profile is 0.018 dB / (ps / nm). Also, when the dispersion coefficient and transmission loss of NZ-DSF are 4.5 ps / nm / km and 0.3 dB / km, respectively, the slope of the NZ-DSF power profile is 0.067 dB / (ps / nm). 【0109】 Therefore, the connection order determination unit 24e can estimate the fiber type of each section by calculating the slopes of the first and second sections shown in Figure 24(b). Specifically, when the slope G1 is close to 0.018 dB / (ps / nm), the optical fiber laid in the first section is estimated to be SMF. Also, when the slope G2 is close to 0.067 dB / (ps / nm), the optical fiber laid in the second section is estimated to be NZ-DSF. The slope of the power profile is calculated, for example, by differentiating the power profile with respect to the dispersion. 【0110】 Figure 26 is a flowchart showing the processing of the fiber type estimation device 20 according to the fifth embodiment. Steps S1 to S3 are the same in Figures 12 and 26. That is, the fiber type estimation device 20 calculates the dispersion amount for each span. Steps S21 to S23 are the same in Figures 18 and 26. That is, the fiber type estimation device 20 estimates the type and length of optical fibers within the target span. 【0111】 In S41, the feature detection unit 24d calculates the slope of the power profile within the target span. In S42, the connection order determination unit 24e determines the connection order of each optical fiber within the target span based on the fiber type estimated in S23 and the slope of the power profile calculated in S41. 【0112】 In the flowchart shown in Figure 26, steps S41 to S42 are executed after determining the fiber type combination in S23, but the fiber type estimation unit 24 does not need to execute S23. That is, if the dispersion coefficient and transmission loss of each fiber type are known, the fiber type estimation unit 24 can estimate the type, length, and connection order of each optical fiber constituting the target span based solely on the power profile, as explained with reference to Figure 24(b). 【0113】 Furthermore, in the above embodiment, the slope of the power profile within the target span is calculated, but the feature detection unit 24d may detect other features. For example, when the combination of optical fibers within the target span is estimated by the combination detection unit 22b shown in Figure 22, the connection order of the optical fibers can be determined based on the shape of the power profile. 【0114】 <Sixth Embodiment> In the above-described embodiment, the fiber type is estimated assuming that SMF or NZ-DSF may be laid on the optical fiber transmission line. Here, since the dispersion coefficients of SMF and NZ-DSF are significantly different from each other, SMF and NZ-DSF can be accurately distinguished based on the power profile. In other words, if the dispersion coefficients of optical fibers are similar to each other, it is not easy to identify the fiber type based on the power profile. For example, NZ-DSF (hereinafter referred to as NZ-DSF1 and NZ-DSF2) with dispersion coefficients that are only slightly different from each other are known. In this case, it is not easy to distinguish between NZ-DSF1 and NZ-DSF2 simply by generating a power profile of the optical fiber transmission line. 【0115】 Figure 27 shows an optical transmission system according to the sixth embodiment. In this example, the transmitting node 100 is equipped with a tunable light source 101. The tunable light source 101 can generate test light of a corresponding wavelength according to the wavelength instruction given by the fiber type estimation device 20. Therefore, the fiber type estimation device 20 can receive test light of a desired wavelength from the transmitting node 100. The tunable light source 101 can be implemented, for example, by an ASE light source and a wavelength selective switch (WSS). 【0116】 The fiber type estimation device 20 comprises a profile generation unit 21, a span detection unit 22, a dispersion coefficient calculation unit 23, a fiber type estimation unit 24, and a dispersion slope calculation unit 25. The fiber type estimation device 20 then transmits a wavelength instruction to the transmission node 100. The wavelength instruction specifies the wavelength of the test light. Therefore, when the wavelength instruction specifies λ1, the transmission node 100 transmits a test light with wavelength λ1, and when the wavelength instruction specifies λ2, the transmission node 100 transmits a test light with wavelength λ2. 【0117】 The profile generation unit 21 generates a power profile for each wavelength of test light. The dispersion coefficient calculation unit 23 calculates the dispersion coefficient for each span using the power profile for each wavelength of test light. The dispersion slope calculation unit 25 calculates the dispersion slope for each span using the dispersion coefficient obtained by the dispersion coefficient calculation unit 23. Then, the fiber type estimation unit 24 estimates the type of optical fiber laid in each span based on the dispersion coefficient and dispersion slope. 【0118】 Figure 28 shows an example of measurement results obtained in the sixth embodiment. Figure 28(a) shows the power profile generated for each wavelength over the target span. Figure 28(b) shows the dispersion coefficient calculated based on the power profile shown in Figure 28(a). The span length of the target span is 60 km. 【0119】 In the example shown in Figure 28, power profiles are generated for three wavelengths. The dispersion coefficient calculation unit 23 then calculates the dispersion coefficient for each wavelength. When the wavelength of test light λ1 is 1542 nm, the dispersion amount in the target span is 246 ps / nm, and the dispersion coefficient is 4.0 ps / nm / km. When the wavelength of test light λ2 is 1552 nm, the dispersion amount in the target span is 270 ps / nm, and the dispersion coefficient is 4.5 ps / nm / km. When the wavelength of test light λ3 is 1562 nm, the dispersion amount in the target span is 300 ps / nm, and the dispersion coefficient is 5.0 ps / nm / km. 【0120】 The dispersion slope calculation unit 25 calculates the dispersion slope of the target span. For example, the difference in dispersion coefficients obtained by test light λ1 and λ2 is 0.5 ps / nm / km, and the wavelength difference between test light λ1 and λ2 is 10 nm. Therefore, the dispersion slope obtained by test light λ1 and λ2 is 0.05 ps / nm. 2 It is / km. 【0121】 The fiber type estimation unit 24 estimates the type of optical fiber laid in the target span based on the dispersion coefficient and dispersion slope of the target span. At this time, the fiber type estimation unit 24 refers to a pre-prepared fiber type list. As shown in Figure 27, this fiber type list represents the dispersion coefficient and dispersion slope for each fiber type. Note that the dispersion coefficient and dispersion slope for each fiber type are known. 【0122】 In this embodiment, the dispersion coefficient is 4-5 ps / nm / km, so it is estimated that the optical fiber laid in the target span is NZ-DSF1. However, considering the error, it is also possible that the optical fiber laid in the target span is NZ-DSF2. Therefore, the fiber type estimation unit 24 considers the dispersion slope in addition to the dispersion coefficient. In this case, the dispersion slope is 0.05, so it is estimated that the optical fiber laid in the target span is NZ-DSF1. 【0123】 Figure 29 is a flowchart showing the processing of the fiber type estimation device 20 according to the sixth embodiment. Note that steps S1 to S4 are the same in Figures 12 and 29. That is, the fiber type estimation device 20 calculates the dispersion coefficient for each span. However, in the sixth embodiment, steps S1 to S4 are performed for each of multiple wavelengths. That is, the dispersion coefficient is calculated for each of multiple wavelengths. 【0124】 In S51, the dispersion slope calculation unit 25 calculates the dispersion slope for each span. In S52, the fiber type estimation unit 24 estimates the fiber type for each span based on the dispersion coefficient and the dispersion slope. 【0125】 Thus, in the sixth embodiment, the fiber type is estimated using the dispersion coefficient and dispersion slope obtained based on the power profile. Therefore, optical fibers with similar dispersion coefficients can be identified. 【0126】 <Seventh Embodiment> Figure 30 shows an optical transmission system according to the seventh embodiment. In this embodiment, the optical signal transmitted from the transmitting node TX is transmitted to the receiving node RX via relay stations A1 and A2. Each node (transmitting node TX, relay station A1, and relay station A2) controls the transmission power of the optical signal according to the design information. For example, the transmitting node TX transmits the optical signal with a power corresponding to the fiber type of span SP1 (i.e., the type of optical fiber between the transmitting node TX and relay station A1). 【0127】 Therefore, if an optical fiber that is not correct according to the design information is laid, the optical signal will be transmitted at an inappropriate power. And when an optical signal is transmitted at an inappropriate power, the OSNR or GSNR will deteriorate. In the seventh embodiment, the transmission power of each node is controlled according to the fiber type estimated by the fiber type estimation device 20. 【0128】 The fiber type estimation device 20 includes a profile generation unit 21, a span detection unit 22, a dispersion coefficient calculation unit 23, and a fiber type estimation unit 24, as well as a setting control unit 26. The setting control unit 26 generates setting control information to control the transmission power according to the fiber type estimated by the fiber type estimation unit 24. The setting control unit 26 then transmits the generated setting control information to the corresponding node. For example, when a span is detected in which the estimated fiber type differs from the design information, the setting control unit 26 transmits the setting control information to the source node of that span. The setting control unit 26 may be implemented inside the fiber type estimation device 20 or it may be provided outside the fiber type estimation device 20. 【0129】 As an example, suppose the design information indicates that span SP2 is composed of SMF. In this case, relay station A1 transmits the optical signal at a power suitable for SMF by controlling the gain of the optical amplifier implemented within relay station A1. Now, suppose the fiber type estimation device 20 estimates that the optical fiber laid in span SP2 is NZ-DSF. In this case, the setting control unit 26 transmits setting control information representing a power suitable for NZ-DSF to relay station A1. As a result, relay station A1 transmits the optical signal at a power suitable for NZ-DSF. This improves the OSNR or GSNR. 【0130】 Figure 31 is a flowchart showing the processing of the fiber type estimation device 20 according to the seventh embodiment. Steps S1 to S4 are the same in Figures 12 and 31. That is, the fiber type estimation device 20 calculates the dispersion coefficient for each span. Steps S11 to S12 are the same in Figures 14 and 31. That is, the fiber type estimation device 20 detects spans where the wrong optical fiber is laid by estimating the fiber type for each span. When a span with the wrong optical fiber is detected, the process in S61 is executed. 【0131】 In S61, the setting control unit 26 transmits setting control information to the optical node to which the incorrect optical fiber is connected (i.e., the source-side optical node in the span where the incorrect optical fiber is laid). This setting control information represents the transmission power appropriate for the estimated fiber type. The optical node that receives the setting control information then controls the transmission optical power by adjusting the gain of the optical amplifier according to that setting control information. 【0132】 In the embodiment shown in Figure 31, the setting control unit 26 generates setting control information based on the fiber type estimated by the fiber type estimation unit 24, but the present invention is not limited to this configuration. For example, the setting control unit 26 may generate setting control information based on the dispersion coefficient calculated by the dispersion coefficient calculation unit 23. [Explanation of symbols] 【0133】 1. Optical transmission device 11 Coherent Receiver 13 Digital signal processing unit 13a Dispersion compensation section 13b Adaptive Equalization Section 13c Frequency Correction Section 13d Phase correction section 13e Identification unit 13f Error Correction Section 14. Transmitted waveform reconstruction section 16a First Dispersion Compensation Unit 16b Nonlinear compensation section 16c Second Dispersion Compensation Unit 16d Correlation Calculation Unit 20 Fiber type estimation device 21 Profile Generation Unit 22 Span detection unit 23. Variance Coefficient Calculation Unit 24 Fiber type estimation unit 24b Combination detection unit 24c, 24e Connection order determination unit 24d Feature detection unit 25 Distributed Slope Calculation Unit 26 Setting Control Unit 100 transmitting nodes

Claims

[Claim 1] In an optical transmission system in which an optical signal is transmitted from a first node to a second node via an optical fiber transmission path, a characteristic estimation device for estimating the characteristics of the optical fiber transmission path, A span detection unit that detects one or more spans constituting the optical fiber transmission path using a power profile that represents the relationship between the amount of dispersion corresponding to the transmission distance from the first node or the second node and the power of the optical signal, A dispersion coefficient calculation unit calculates the dispersion coefficient of the optical fiber transmission line by dividing the amount of dispersion estimated based on the power profile for each span detected by the span detection unit by the corresponding span length stored in the storage unit. A characteristic estimation device equipped with the following features. [Claim 2] The system further includes a fiber type estimation unit that estimates the type of optical fiber constituting the optical fiber transmission path based on the dispersion coefficient calculated by the dispersion coefficient calculation unit for each span detected by the span detection unit. The characteristic estimation device according to feature 1. [Claim 3] The dispersion coefficient calculation unit uses the power profile to estimate the amount of dispersion for each span detected by the span detection unit. When the first span among the one or more spans detected by the span detection unit is composed of multiple optical fibers, the fiber type estimation unit: We obtain fiber data representing the known dispersion coefficients for each of several types of optical fibers. Using the aforementioned fiber data, the type and fiber length of each optical fiber are estimated such that the sum of the fiber lengths of the plurality of optical fibers matches the span length of the first span, and the sum of the products of the fiber length of each optical fiber and the corresponding dispersion coefficient matches the dispersion amount of the first span. The characteristic estimation device according to feature 2. [Claim 4] The fiber type estimation unit, Connection point information representing the positions of the connection points between the plurality of optical fibers within the first span is obtained. The connection order of the plurality of optical fibers is determined based on the connection point information. The characteristic estimation device according to claim 3. [Claim 5] The fiber type estimation unit determines the connection order of the plurality of optical fibers based on the characteristics of the power profile shape within the first span. The characteristic estimation device according to claim 3. [Claim 6] The system further comprises a profile generation unit that generates the power profile for each of multiple wavelengths, The dispersion coefficient calculation unit calculates the dispersion coefficient for each span for each of the plurality of wavelengths using the corresponding power profile. The fiber type estimation unit estimates the type of optical fiber constituting the optical fiber transmission path for each span based on the slope of the dispersion coefficient with respect to wavelength. The characteristic estimation device according to feature 2. [Claim 7] The setting control unit further comprises a setting control unit that generates setting control information that instructs the transmission power of the optical signal based on the dispersion coefficient calculated by the dispersion coefficient calculation unit or the fiber type estimated by the fiber type estimation unit for a target span among one or more spans detected by the span detection unit, and transmits the setting control information to an optical node located on the transmission side of the target span. The characteristic estimation device according to feature 2. [Claim 8] The profile generation unit, A first dispersion compensation unit that compensates for a first dispersion among the known dispersions in the optical fiber transmission path in a received electric field information signal representing the electric field of the optical signal received by the second node via the optical fiber transmission path, The output signal of the first dispersion compensation unit includes a nonlinear compensation unit that compensates for the nonlinear distortion of the optical fiber transmission line, A second variance compensation unit compensates for the remaining variance of the known variance in the output signal of the nonlinear compensation unit, The system comprises a calculation unit that calculates the optical power corresponding to the combination of the first dispersion and the remaining dispersion based on the correlation between a reference signal representing the electric field of the optical signal at the first node and the output signal of the second dispersion compensation unit, The profile generation unit calculates the corresponding optical power for multiple dispersion amounts by changing the amount of the first dispersion and calculating the corresponding optical power for each. The characteristic estimation device according to feature 6. [Claim 9] The first optical transmission device, A second optical transmission device that receives an optical signal transmitted from the first optical transmission device via an optical fiber transmission path, The system includes a characteristic estimation device for estimating the characteristics of the optical fiber transmission line, The characteristic estimation device is A span detection unit that detects one or more spans constituting the optical fiber transmission path using a power profile that represents the relationship between the amount of dispersion corresponding to the transmission distance from the first optical transmission device or the second optical transmission device and the power of the optical signal, The system includes a dispersion coefficient calculation unit that calculates the dispersion coefficient of the optical fiber transmission line by dividing the amount of dispersion estimated based on the power profile for each span detected by the span detection unit by the corresponding span length stored in the storage unit. An optical transmission system characterized by the following: [Claim 10] In an optical transmission system in which an optical signal is transmitted from a first node to a second node via an optical fiber transmission path, a characteristic estimation method for estimating the characteristics of the optical fiber transmission path, Using a power profile that represents the relationship between the amount of dispersion corresponding to the transmission distance from the first node or the second node and the power of the optical signal, one or more spans constituting the optical fiber transmission path are detected. For each detected span, the dispersion coefficient of the optical fiber transmission line is calculated by dividing the amount of dispersion estimated based on the power profile by the corresponding span length stored in the storage unit. A method for estimating characteristics characterized by the following:

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