Optical Fiber Measurement System, Optical Fiber Measurement Method, Control Arithmetic Unit, and Program

Abstract

The purpose of the present invention is to provide an optical fiber measurement system, an optical fiber measurement method, a control and calculation device, and a program that make it possible to measure the loss and the XT that occur at each of a plurality of locations on an optical fiber that propagates a plurality of modes.　This optical fiber measurement system comprises a light inputting circuit that inputs probe light into one end of an optical fiber and inputs secondary probe light and pump light that is a light pulse into the other end of the optical fiber, a light receiver that measures the optical intensity of a single arbitrary propagation mode of the probe light propagated by the optical fiber, and a control and calculation device that sets propagation modes for the probe light, the secondary probe light, and the pump light, an optical frequency difference for the secondary probe light, and an optical frequency difference for the pump light for the light inputting circuit and, from the optical intensity measured by the light receiver, calculates the loss and the crosstalk at points along the longitudinal direction of a measured optical fiber that has been connected as the optical fiber.

Description

Technical Field

[0001] The present disclosure relates to a measurement system that independently measures losses and crosstalk (XT) generated at each point in an optical fiber transmission line, a measurement method thereof, a control arithmetic unit thereof, and a program.

Background Art

[0002] In recent years, with the rapid increase in transmission traffic, few-mode fibers (FMFs) and multimode fibers (MMFs) that can utilize multiple propagation modes have attracted great attention as enabling further increases in capacity, replacing the single-mode fibers (SMFs) currently used in transmission lines. In these fibers, when passing through devices such as connection points and mode combiners / splitters, mode-to-mode loss differences (DMAs) and crosstalk (XT) occur due to different losses received for each mode, and a part of the incident mode is coupled to a different mode. Since DMAs and XT are important parameters for signal processing on the receiving side, it is desirable to be able to measure the losses and XT of each mode in the transmission line for each section in order to evaluate the quality of the transmission line.

[0003] Heretofore, a method for obtaining propagation characteristics for each mode using Brillouin gain analysis has been disclosed (see, for example, Non-Patent Document 1). In this measurement method, by controlling the frequency difference between the pump light and the probe light incident on the fiber, the loss and XT received by the pump light can be obtained from the generated gain amount.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When there are multiple locations where loss and XT occur, the XT component of the probe light is generated in the fiber, and the gain due to this XT component becomes a factor of error. For this reason, the method of the non-patent literature has a problem that it is difficult to measure the loss and XT occurring at multiple locations for each location.

[0006] Therefore, in order to solve the above problems, an object of the present invention is to provide an optical fiber measurement system, an optical fiber measurement method, a control arithmetic device, and a program capable of measuring loss and XT occurring at multiple locations of an optical fiber in which multiple modes propagate for each location.

Means for Solving the Problems

[0007] In order to achieve the above object, the optical fiber measurement system according to the present invention uses two probe lights and the Brillouin gain coefficient between each mode in order to decompose the gain component into loss and XT components.

[0008] Specifically, the optical fiber measurement system according to the present invention An optical incident circuit that injects a probe light into one end of the optical fiber and injects a secondary probe light and a pump light that is an optical pulse into the other end of the optical fiber, A light receiver that measures the light intensity of any one propagation mode among the probe lights that have propagated through the optical fiber, For the optical incident circuit, the propagation modes of the probe light, the secondary probe light, and the pump light, and the optical frequency difference of the secondary probe light and the optical frequency difference of the pump light are set, and from the light intensity measured by the light receiver, the loss and crosstalk at each point in the longitudinal direction of the optical fiber to be measured connected as the optical fiber are calculated. A control arithmetic unit, Comprising The control arithmetic unit When the optical fiber to be measured is connected as the optical fiber, for the optical incident circuit, Injecting the probe light into one end of the optical fiber in an arbitrary propagation mode, Causing the secondary probe light having an optical frequency difference from the probe light to enter the other end of the optical fiber in a propagation mode that becomes a crosstalk component of the probe light on the low frequency side; Causing the pump light having an optical frequency difference from the probe light to enter on the high frequency side in an arbitrary propagation mode; Obtaining a distribution of the Brillouin amplification amount of the probe light with respect to the longitudinal direction of the optical fiber to be measured from the light intensity, and Calculating the loss and crosstalk using the step of the Brillouin amplification amount appearing in the distribution, and the Brillouin gain coefficient determined by the optical frequency difference and the propagation mode between the pump light and the probe light. It is characterized by the above.

[0009] Further, the optical fiber measurement method according to the present invention is An optical input circuit for injecting a probe light into one end of an optical fiber, and injecting a secondary probe light and a pump light which is an optical pulse into the other end of the optical fiber; A light receiver for measuring the light intensity of an arbitrary one propagation mode among the probe lights propagated through the optical fiber; Setting the propagation modes of the probe light, the secondary probe light, and the pump light, and the optical frequency differences of the secondary probe light and the pump light with respect to the optical input circuit, and calculating the loss and crosstalk at each point in the longitudinal direction of the optical fiber to be measured connected as the optical fiber from the light intensity measured by the light receiver by a control arithmetic unit; Using an optical fiber measurement system including: When connecting an optical fiber to be measured as the optical fiber, Causing the probe light to enter one end of the optical fiber in an arbitrary propagation mode; Causing the secondary probe light having an optical frequency difference from the probe light to enter the other end of the optical fiber in a propagation mode that becomes a crosstalk component of the probe light on the low frequency side; Causing the pump light having an optical frequency difference from the probe light to enter on the high frequency side in an arbitrary propagation mode; Obtaining a distribution of the Brillouin amplification amount of the probe light with respect to the longitudinal direction of the optical fiber under measurement from the light intensity, and Calculating the loss and crosstalk using the step of the Brillouin amplification amount appearing in the distribution, and the Brillouin gain coefficient determined by the optical frequency difference between the pump light and the probe light and the propagation mode characterized by.

[0010] Furthermore, the control arithmetic unit according to the present invention is an optical incident circuit that injects probe light into one end of an optical fiber, and injects secondary probe light and pump light that is an optical pulse into the other end of the optical fiber, a control arithmetic unit of an optical fiber measurement system including a light receiver that measures the light intensity of any one propagation mode among the probe light propagated through the optical fiber, a control unit that sets the propagation modes of the probe light, the secondary probe light, and the pump light with respect to the optical incident circuit, and the optical frequency differences of the secondary probe light and the pump light, an arithmetic unit that calculates the loss and crosstalk at each point in the longitudinal direction of the optical fiber under measurement connected as the optical fiber from the light intensity measured by the light receiver, comprising, when the optical fiber under measurement is connected to the optical fiber measurement system as the optical fiber, the control unit, with respect to the optical incident circuit, causes the probe light to be incident on one end of the optical fiber in an arbitrary propagation mode, causes the secondary probe light having an optical frequency difference from the probe light on the low frequency side to be incident on the other end of the optical fiber in a propagation mode that becomes a crosstalk component of the probe light, and causes the pump light having an optical frequency difference from the probe light on the high frequency side to be incident in an arbitrary propagation mode, performs, the arithmetic unit obtains a distribution of the Brillouin amplification amount of the probe light with respect to the longitudinal direction of the optical fiber under measurement from the light intensity, and Calculating the loss and crosstalk using the step of the Brillouin amplification amount appearing in the distribution, and the Brillouin gain coefficient determined by the optical frequency difference between the pump light and the probe light and the propagation mode It is characterized by performing the following steps.

[0011] This optical fiber measurement system obtains the distribution of the Brillouin amplification amount of the probe light in the longitudinal direction of the optical fiber while suppressing the XT component of the probe light using the secondary probe light. The loss and XT can be calculated for each point using the steps of the plurality of Brillouin amplification amounts appearing in this distribution and the separately obtained Brillouin gain coefficient. Therefore, the present invention can provide an optical fiber measurement system, an optical fiber measurement method, and a control arithmetic device that can measure the loss and XT generated at a plurality of points of an optical fiber in which a plurality of modes propagate, for each point.

[0012] The Brillouin gain coefficient can be obtained as follows. The control arithmetic device When a reference optical fiber having the same characteristics as the measured optical fiber and no mode coupling is connected as the optical fiber to the optical incidence circuit, While changing the combination of all propagation modes propagating through the measured optical fiber and changing the optical frequency difference between the probe light and the pump light, the probe light is incident on one end of the optical fiber and the pump light is incident on the other end of the optical fiber, and Obtaining the Brillouin gain coefficient for each optical frequency difference and each combination of propagation modes from the light intensity It is characterized by the following steps.

[0013] The control arithmetic device is characterized in that the optical frequency difference between the secondary probe light and the probe light is set to an optical frequency difference that gives only Brillouin loss to the crosstalk component of the probe light. Loss and XT can be measured accurately.

[0014] The present invention is a program for causing a computer to function as the control arithmetic unit. This control arithmetic unit can also be realized by a computer and a program, and it is possible to record the program on a recording medium or provide it through a network.

Advantages of the Invention

[0015] The present invention can provide an optical fiber measurement system, an optical fiber measurement method, a control arithmetic unit, and a program capable of measuring losses and XT generated at multiple points of an optical fiber in which a plurality of modes propagate, for each point.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0017] Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In this specification and the drawings, components having the same reference numerals indicate the same components as each other.

[0018] (Embodiment 1) [Device Configuration] FIG. 1 is a diagram for explaining an optical fiber measurement system 301 according to the present embodiment. The optical fiber measurement system 301 is an example of a configuration for realizing the present invention. The optical fiber measurement system 301 includes an optical input circuit 11 that injects a probe light Pb1 into one end of an optical fiber 50 and injects a secondary probe light Pb2 and a pump light Pm that is an optical pulse into the other end of the optical fiber 50, a light receiver 12 that measures the light intensity of any one propagation mode among the probe lights Pb1 propagated through the optical fiber 50, a control arithmetic unit 13 that sets the propagation modes of the probe light Pb1, the secondary probe light Pb2, and the pump light Pm with respect to the optical input circuit 11, and the optical frequency differences of the secondary probe light Pb2 and the pump light Pm, and calculates the loss and crosstalk at each point in the longitudinal direction of the optical fiber to be measured connected as the optical fiber 50 from the light intensity measured by the light receiver 12, and includes. The control arithmetic unit 13 when connecting the optical fiber to be measured as the optical fiber 50, with respect to the optical input circuit 11, injecting the probe light Pb1 into one end of the optical fiber 50 in an arbitrary propagation mode, injecting a secondary probe light Pb2 having an optical frequency difference from the probe light Pb1 to the low frequency side into the other end of the optical fiber 50 in a propagation mode that becomes a crosstalk component of the probe light Pb1, injecting a pump light Pm having an optical frequency difference from the probe light Pb1 to the high frequency side in an arbitrary propagation mode, obtaining the distribution of the Brillouin amplification amount of the probe light Pb1 with respect to the longitudinal direction of the optical fiber to be measured from the light intensity, and calculating the loss and crosstalk using the step of the Brillouin amplification amount appearing in the distribution and the Brillouin gain coefficient determined by the optical frequency difference and propagation mode between the pump light Pm and the probe light Pb1. It is characterized by.

[0019] The light incident circuit 11 includes a laser light generation means 21, a mode multiplexing / demultiplexing means 22, an optical frequency control means (23, 24), a branching element 25, an optical pulse generation means 26, and a mode selection multiplexing / demultiplexing means 27.

[0020] The light output from the laser light generation means 21 that generates coherent light is branched into three by the branching element 25, and becomes a probe light Pb1, a pump light Pm, and a secondary probe light Pb2, respectively. The pump light Pm is given a frequency difference corresponding to the Brillouin frequency shift of the optical fiber under measurement by the optical frequency control means 23 to the higher frequency side, and then pulsed by the optical pulse generation means 26. On the other hand, the secondary probe light Pb2 is given a frequency difference corresponding to the Brillouin frequency shift of the optical fiber under measurement by the optical frequency control means 24 to the lower frequency side. Since it is only necessary to give a frequency difference corresponding to the Brillouin frequency shift to the pump light Pm and the secondary probe light Pb2 with respect to the probe light Pb1, three laser light generation means 21 with different optical frequencies can be prepared without using the optical frequency control means (23, 24), and the optical frequency difference between the three lasers can be controlled by separating the light sources of the pump light Pm, the probe light Pb1, and the secondary probe light Pb2.

[0021] The probe light Pb1 is converted into an arbitrary mode by the mode multiplexing / demultiplexing means 22 and then incident on one end of the optical fiber under measurement (optical fiber 50). The mode multiplexing / demultiplexing means 22 in FIG. 1 has inputs 1 and 2 and is structured to be switched by a switch. When light is incident on input 1 of the mode multiplexing / demultiplexing means 22, it is output as the first propagation mode, and when light is incident on input 2, it is output as the second propagation mode. That is, the mode multiplexing / demultiplexing means 22 can arbitrarily select the propagation mode of the probe light emitted by the switch. Also, the pump light Pm and the secondary probe light Pb2 are converted into an arbitrary mode by the mode selection multiplexing / demultiplexing means 27 and then incident on the other end of the optical fiber under measurement.

[0022] The probe light Pb1 and the secondary probe light Pb2 incident on the optical fiber to be measured generate Brillouin interaction in the entire section of the optical fiber to be measured, and thereby the probe light Pb1 undergoes Brillouin loss. Here, by controlling the frequency difference between the probe light Pb1 and the secondary probe light Pb2 by the optical frequency control means 24, loss is imparted to an arbitrary mode of the probe light Pb1. Thereby, only the probe light Pb1 of a specific mode exists in the optical fiber to be measured.

[0023] Also, for the pulsed pump light Pm and the probe light Pb1 incident on the optical fiber to be measured, Brillouin interaction is generated in the entire section of the optical fiber to be measured, and thereby the probe light Pb1 is Brillouin amplified. Here, since the pump light Pm is pulsed, the amplification amount of the probe light Pb1 at each time with reference to the incident time of the pump light Pm corresponds to the optical intensity of the pump light Pm at each point in the optical fiber to be measured. The amplified probe light Pb1 is converted into an electrical signal by the light receiver 12 after the mode is selected by the mode selection multiplexing / demultiplexing means 27. The mode selection multiplexing / demultiplexing means 27 in FIG. 1 has outputs 1 and 2 and is structured to be switched by a switch. The mode selection multiplexing / demultiplexing means 27 can selectively extract the mode components of the probe light Pb1 emitted from the mode multiplexing / demultiplexing means 22 by the switch. That is, the mode selection multiplexing / demultiplexing means 27 can output the component of the first propagation mode of the probe light Pb1 from output 1 and the component of the second propagation mode of the probe light Pb1 from output 2 by switching the switch.

[0024] The control arithmetic unit 13 includes a control unit 32 that sets the propagation modes of the probe light Pb1, the secondary probe light Pb2, and the pump light Pm for the light incident circuit 11, as well as the optical frequency difference of the secondary probe light Pb2 and the optical frequency difference of the pump light Pm, and an arithmetic unit 31 that calculates the loss and crosstalk at each point in the longitudinal direction of the fiber under test connected as the optical fiber 50 from the light intensity measured by the light receiver 12. The arithmetic unit 31 has a digitization processing means 31a and a numerical arithmetic means 31b. The reception signal from the light receiver 12 is digitized by the digitization processing means 31a, and the Brillouin gain is obtained by the numerical arithmetic means 31b. The specific method for analyzing the Brillouin gain is as follows. First, the reference intensity of the probe light Pb1 when the pump light Pm is not incident is obtained. Then, the signal intensity when the pump light Pm and the probe light Pb1 are incident is obtained. The Brillouin gain can be obtained by calculating the increase amount of the reference intensity from the signal intensity.

[0025] The control unit 32 controls the operation of the light incident circuit 13. Specifically, the control unit 32 sets the optical frequency difference between the probe light Pb1 and the pump light Pm and the optical frequency difference between the probe light Pb1 and the secondary probe light Pb2 for the optical frequency control means (23, 24). Also, the control unit 32 sets the time for the pump light Pm, which is pulsed light, to be incident on the optical fiber 50 for the optical pulse forming means 26 (setting of the position in the optical fiber 50 to be measured). Further, the control unit 32 sets the propagation modes of the probe light Pb1, the pump light Pm, and the secondary probe light Pb2 incident on the optical fiber 50 for the mode multiplexing means 22 and the mode selective multiplexing means 27. That is, the control unit 32, for the light incident circuit 11, causes the probe light Pb1 to be incident on one end of the optical fiber 50 in an arbitrary propagation mode, causes the secondary probe light Pb2 having an optical frequency difference from the probe light Pb1 on the low frequency side to be incident on the other end of the optical fiber 50 in the propagation mode that becomes the crosstalk component of the probe light Pb1, and causes the pump light Pm having an optical frequency difference from the probe light Pb1 on the high frequency side to be incident in an arbitrary propagation mode, and performs the above operations.

[0026] This configuration is an example. Any means can be used as long as it can provide an optical frequency difference and an incident time difference corresponding to a frequency (wavelength) shift among the pump light Pm, the probe light Pb1, and the secondary probe light Pb2, and can excite an arbitrary propagation mode and extract the amplified probe light Pb1 in the time domain. Also, even for a general single-mode optical fiber (SMF), by making the incident wavelength shorter than the cut-off wavelength, the optical fiber measurement system 301 can measure the SMF. Therefore, the fiber to be measured may have a condition in which a plurality of modes propagate.

[0027] [Brillouin gain and Brillouin loss generated between multiple modes] In the optical fiber 50, the Brillouin frequency shift ν at which the Brillouin amplification and loss are maximum b is [Equation] is given as. Here, n i is the effective refractive index of the mode, V a is the effective velocity of the acoustic wave, and λ is the wavelength in vacuum.

[0028] That is, in an optical fiber in which a plurality of modes propagate, it means that the Brillouin frequency shift differs depending on the propagating mode, and the Brillouin gain spectrum in each mode is different for each propagating mode. The present invention utilizes this feature.

[0029] For simplicity, a few-mode optical fiber (FMF) in which only two modes propagate will be described. When each of the pump light Pm and the probe light (or the probe light Pb1 and the secondary probe light Pb2) has an amplitude in both the LP 01 and LP 11 modes, (i) v01-01 (interaction between the pump and probe components of LP 01 with each other) (ii) v01-11 (pump component of LP 01 and LP11 between the probe components of 11 the pump component of LP and 01 the probe components of (iii) v11 - 11 (LP 11 interaction between the pump and probe components of There exist three different Brillouin gain spectra. By utilizing this characteristic and adjusting the optical frequency differences among the pump light Pm, the probe light Pb1, and the secondary probe light Pb2 incident on the optical fiber, the amplification and suppression of any mode in the optical fiber can be controlled.

[0030] [Brillouin Gain Coefficient Acquisition] In the present invention, the Brillouin gain coefficient is utilized for measurement. Therefore, it is necessary to acquire the Brillouin gain coefficient by some method. In this embodiment, the Brillouin gain coefficient is acquired using a reference optical fiber that has the same characteristics as the optical fiber under measurement except for no mode coupling. The control arithmetic unit 13 when connecting a reference optical fiber having the same characteristics as the optical fiber under measurement and no mode coupling as the optical fiber 50 to the optical incident circuit 11, while changing the optical frequency difference between the probe light Pb1 and the pump light Pm for all combinations of propagation modes propagating in the optical fiber under measurement, making the probe light Pb1 incident on one end of the optical fiber 50 and the pump light Pm incident on the other end of the optical fiber 50, and acquiring the Brillouin gain coefficient for each optical frequency difference and each combination of propagation modes from the light intensity. is characterized by the above.

[0031] Since the Brillouin gain spectrum generally has a full width at half maximum (FWHM) of about 30 MHz, the Brillouin frequency shift ν for each mode bIf they are not sufficiently separated, Brillouin action will also occur simultaneously for other mode components. That is, when observing the gain, gain due to modes other than the desired propagation mode occurs, resulting in a gain in which the loss component and the XT component are mixed. To decompose the gain component into the loss and XT components, the Brillouin gain coefficient between each mode is utilized. The decomposition into the loss and XT components using the gain coefficient will be described in the multi-connection point model described later. Below, the procedure for obtaining the gain coefficient between each mode will be explained.

[0032] In an optical fiber in which multiple modes propagate, the Brillouin frequency shift and the gain amount differ depending on the combination of modes to be used. Utilize this difference to obtain the gain coefficient of each mode. First, prepare a reference optical fiber that exhibits the same characteristics as the fiber under measurement and in which mode coupling does not occur in the optical fiber. Then, obtain the gain coefficient of each mode corresponding to the frequency difference between the pump light Pm and the probe light Pb1 in that optical fiber. Here, the reference optical fiber is a fiber having the same number of propagation modes as the optical fiber under measurement, and the Brillouin gain spectrum (the frequency difference between the pump and probe lights Pb1 at which gain occurs and the gain coefficient at that frequency difference) generated between each mode is the same, but it is an optical fiber without mode coupling. That is, the reference optical fiber is used to obtain in advance the Brillouin gain coefficient in a state without mode coupling.

[0033] The gain coefficient is obtained by combining the pump light Pm of all propagation modes propagating in the optical fiber under measurement and the probe light Pb1 of any one propagation mode. That is, in a fiber in which only two modes propagate, when using the LP 01 mode for the probe light Pb1, the combinations for obtaining the gain coefficient are (i) v01 - 01 (interaction between the pump and probe components of LP 01 with each other) (ii) v01 - 11 (interaction between the pump component of LP 11 and the probe component of LP 01 ) This results. FIG. 2 is a diagram for explaining an example of the Brillouin gain spectrum in a two-mode fiber. From FIG. 2, it can be confirmed that the gain coefficients of the modes generated by the frequency difference between the pump light and the probe light are different.

[0034] Note that the gain coefficient can be obtained by fixing the powers of the propagation modes of the pump light and the probe light, fixing the propagation mode of the incident probe light Pb1, changing the propagation mode of the incident pump light Pm, and measuring the gain amount at that time.

[0035] [Suppression of Probe Light XT Component by Brillouin Loss] When there are a plurality of loss and XT generation points in the optical fiber under measurement, gain occurs due to components other than the mode of the probe light Pb1 used to obtain the gain coefficient (XT of the probe light Pb1), making it difficult to accurately measure the loss and XT. Therefore, in order to apply loss only to the XT component of the probe light Pb1, the Brillouin action of the probe light Pb1 and the secondary probe light Pb2 is utilized. That is, the control arithmetic unit 13 sets the optical frequency difference between the probe light Pb1 and the secondary probe light Pb2 to be the optical frequency difference that gives Brillouin loss only to the crosstalk component of the probe light Pb1.

[0036] Specifically, in an optical fiber in which only two modes propagate, when the mode of the probe light Pb1 for measuring loss and XT is LP 01 in the case of, the LP 11 mode that becomes the XT component of the probe light Pb1 in the secondary probe light Pb2 is utilized (iii) v11 - 11 (LP 11 [Interaction between Probe and Secondary Probe Components of the Same Kind) is utilized. By causing this action to occur over the entire section of the optical fiber under measurement, it is possible to suppress the XT component of the probe light Pb1.

[0037] [Measurement of Loss and XT Using Brillouin Gain and Brillouin Loss] For the description of this embodiment, as an example, consider an optical fiber transmission line model in which there are n connection points (loss and XT generation points) as shown in Fig. 3. In this model, the LP 11 mode is used for the pump light Pm, and the LP 01 mode is used for the probe light Pb1. By comparing the amplification amount of Brillouin amplification generated in the probe light Pb1 at the time of collision with the pump light Pm in the longitudinal direction, the loss and XT amount generated at each connection point are measured. Also, a frequency difference at which strong Brillouin interaction occurs in the combination of v11-11 is imparted to the probe light Pb1 and the secondary probe light Pb2, and the secondary probe light Pb2 in the LP 11 mode is incident from the incident side of the pump light Pm.

[0038] As shown in Fig. 3, at each connection point, when the pump light Pm and the probe light Pb1 pass through, two phenomena occur: loss and XT that couples to other mode components. Here, the Brillouin interaction between the LP 11 mode, which is the XT component of the probe light Pb1 generated at each connection point, and the LP 11 mode of the secondary probe light Pb2 is generated over the entire section of the optical fiber under test. By applying only the Brillouin loss Db to the LP 11 mode of the probe light Pb1, only the probe light Pb1 in the LP 01 exists in the fiber.

[0039] Let the optical intensities of the pump light Pm and the probe light Pb1 incident on the optical fiber be P r and P p respectively. Then, the Brillouin amplification amount ΔPs 01 of the probe light Pb1 generated at the point z on the transmission line can be expressed as follows with respect to z. 01 It can be expressed as follows with respect to z.

Equation

Equation

Equation

Equation

Number

[0040] When comparing the Brillouin amplification amounts of equations (2) to (5) in the longitudinal direction, the step L of the probe amplification amount observed at each connection point (see Figure 6) can be expressed as follows.

Number

Number

Number

Number

[0041] From equations (7) to (10), it can be seen that the observed step is a value including the loss component and the XT component suffered by the pump light Pm. Also, L 2 in equation (8) and L 3 in equation (9) are values including the losses and XT generated at the previous connection points, and it can be seen that they are in the form of substituting 2 and 3 into n of L n shown in equation (10).

[0042] Next, using the step and gain coefficient observed at each connection point, information on loss and XT is obtained. Here, L 2 ~L n For all of them, they can be represented by L n Therefore, below, the loss occurring at the first connection point using L 1 and the XT measurement procedure and the loss occurring at the nth connection point using L n will be described.

[0043] (i) Loss and XT at the first connection point As shown in Equation (7), L 1 is represented by the loss of LP 11 , XT, and the gain coefficient between modes. Here, L 1 and the gain coefficient utilize characteristics that depend on the frequency difference ν between the pump and the probe. Considering the frequency difference, L 1 in Equation (7) can be expressed as follows.

Equation

Equation

Equation

[0044] (ii) Loss and XT at the nth connection point Similar to the process in (i), L nand utilizes the characteristic that the gain coefficient depends on the frequency difference ν between the pump and the probe. Considering the frequency difference, L in Equation (10) n can be expressed as follows.

Equation

Equation

Equation

Equation

[0045] That is, the arithmetic unit 31 acquires the distribution of the Brillouin amplification amount of the probe light Pb1 with respect to the longitudinal direction of the optical fiber under measurement from the light intensity, and calculates the losses and crosstalk using the step L of the Brillouin amplification amount appearing in the distribution, the Brillouin gain coefficient determined by the optical frequency difference between the pump light Pm and the probe light Pb1, and the propagation mode.

[0046] Figures 4 and 5 are diagrams for explaining the optical fiber measurement method performed by the optical fiber measurement system 301. This optical fiber measurement method is an example of obtaining a Brillouin gain coefficient using a reference optical fiber first.

[0047] Figure 4 is a flowchart for explaining Step 1 of obtaining the Brillouin gain coefficient. In Step 1, first, a reference optical fiber without mode coupling having the same characteristics as the optical fiber to be measured is prepared and connected to the optical fiber measurement system 301 (Step S11). Next, the control unit 32 sets the optical frequency difference between the probe light Pb1 and the pump light Pm for the optical frequency control means 23 (Step S12). Further, the control unit 32 sets the propagation modes of the pump light Pm and the probe light Pb1 to be propagated in the reference optical fiber for the mode multiplexing means 22 and the mode selective multiplexing means 27 (Step S13). The mode multiplexing means 22 and the mode selective multiplexing means 27 make the pump light Pm and the probe light Pb1 enter the reference optical fiber (Step S14). The arithmetic unit 31 obtains the gain coefficient of the Brillouin gain generated by the probe light Pb1 (Step S16). The control unit 32 determines whether all the Brillouin gain coefficients to be used in the optical fiber to be measured (for all combinations of the pump light Pm and the probe light Pb1 for all propagation modes propagating in the optical fiber to be measured) have been obtained (Step S16). If there is an unobtained combination (\"No\" in Step S16), the operations from Step S12 are repeated. If all combinations have been obtained (\"Yes\" in Step S16), proceed to Step 2.

[0048] FIG. 5 is a flowchart for explaining step 2 of measuring loss and XT at the connection point of the optical fiber under measurement. First, the optical fiber under measurement is connected to the optical fiber measurement system 301 (step S20). Next, the control unit 32 sets the optical frequency difference between the probe light Pb1, the pump light Pm, and the secondary probe light Pb2 for the optical frequency control means (23, 24) (step S21). The control unit 32 sets the incident time of the pump light Pm for the optical pulse generation means 26 (step S22). Further, the control unit 32 sets the propagation modes of the pump light Pm, the probe light Pb1, and the secondary probe light Pb2 to be propagated through the reference optical fiber for the mode multiplexing means 22 and the mode selective multiplexing means 27 (step S23). Then, the optical incident circuit 11 makes the probe light Pb1 and the secondary probe light Pb2 incident on the optical fiber under measurement in order to suppress the XT component of the probe light Pb1 (step S24). Also, the optical incident circuit 11 makes the pump light Pm incident on the optical fiber under measurement at the set incident time (step S25). The calculation unit 31 obtains the step L observed at each connection point from the distribution of the probe light amplification amount in FIG. 6 (step S26). The calculation unit 31 uses the Brillouin gain coefficient obtained in step 1 and the step L of the probe light amplification amount observed in FIG. 6 to calculate the loss and XT at the first connection point as viewed from the pump light Pm incident side (the other end of the optical fiber 50) using equations (11) to (13) (step S27). The control unit 32 determines whether the loss and XT of the desired connection point have been obtained (step S28). If the loss and XT of the desired connection point have been obtained (Yes in step S28), the measurement is terminated. On the other hand, if the loss and XT of the desired connection point have not been obtained, the calculation unit 31 calculates the loss and XT of the connection point zi using equations (14) to (17) with the loss, XT, Brillouin gain coefficient, and the step Li of the amplification amount of the i-th connection point up to the connection points z1 to zi-1 (step S29).

[0049] (Embodiment 2) The control arithmetic unit 13 can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided through a network. Figure 7 shows a block diagram of system 100. System 100 includes a computer 105 connected to a network 135.

[0050] Network 135 is a data communication network. Network 135 can be a private network or a public network and can include any or all of (a) a personal area network covering, for example, a room, (b) a local area network covering, for example, a building, (c) a campus area network covering, for example, a campus, (d) a metropolitan area network covering, for example, a city, (e) a wide area network covering, for example, an area spanning city, regional, or national boundaries, or (f) the Internet. Communications are performed via network 135 by electronic and optical signals.

[0051] Computer 105 includes a processor 110 and a memory 115 connected to processor 110. Although computer 105 is represented herein as a stand-alone device, it is not so limited and may rather be connected to other devices not shown in a distributed processing system.

[0052] Processor 110 is an electronic device composed of logic circuits that responds to and executes instructions.

[0053] Memory 115 is a tangible computer-readable storage medium encoded with a computer program. In this regard, memory 115 stores data and instructions, i.e., program code, readable and executable by processor 110 to control the operation of processor 110. Memory 115 can be implemented with random access memory (RAM), a hard drive, read-only memory (ROM), or a combination thereof. One of the components of memory 115 is program module 120.

[0054] Program module 120 includes instructions for controlling processor 110 to execute the processes described herein. Although operations are described herein as being performed by computer 105 or a method or process or a sub-process thereof, those operations are actually performed by processor 110.

[0055] The term "module" is used herein to refer to a functional operation that can be embodied as either a stand-alone component or an integrated configuration consisting of a plurality of sub-components. Thus, program module 120 can be implemented as a single module or as a plurality of modules operating in cooperation with each other. Further, although program module 120 is described herein as being installed in memory 115 and thus implemented in software, it can be implemented in either hardware (e.g., an electronic circuit), firmware, software, or any combination thereof.

[0056] Program module 120 is shown as already loaded into memory 115, but may be configured to be located on storage device 140 for later loading into memory 115. Storage device 140 is a tangible computer-readable storage medium that stores program module 120. Examples of storage device 140 include a compact disk, magnetic tape, read-only memory, optical storage medium, a memory unit composed of a hard drive or a plurality of parallel hard drives, and a universal serial bus (USB) flash drive. Alternatively, storage device 140 may be a random access memory or other type of electronic storage device located in a remote storage system (not shown) and connected to computer 105 via network 135.

[0057] System 100 further includes data sources 150A and 150B, collectively referred to herein as data source 150 and communicatively coupled to network 135. In practice, data source 150 can include any number of data sources, i.e., one or more data sources. Data source 150 includes unstructured data and can include social media.

[0058] System 100 further includes user device 130, which is operated by user 101 and connected to computer 105 via network 135. Examples of user device 130 include input devices, such as a keyboard or voice recognition subsystem, that enable user 101 to convey selections of information and commands to processor 110. User device 130 further includes an output device, such as a display device, a printer, or a voice synthesizer. A cursor control, such as a mouse, trackball, or touch-sensitive screen, enables user 101 to manipulate a cursor on a display device to convey additional selections of information and commands to processor 110.

[0059] Processor 110 outputs the result 122 of the execution of program module 120 to user device 130. Alternatively, processor 110 can direct the output to a storage device 125, such as a database or memory, or to a remote device (not shown) via network 135.

[0060] For example, a program that performs the flowcharts of FIGS. 4 and 5 can be used as program module 120. System 100 can be operated as a control arithmetic unit 13.

[0061] The terms "comprising" or "including" are to be construed as specifying the presence of the features, integers, steps, or components stated therein, but not precluding the presence of one or more other features, integers, steps, or components, or groups thereof. The terms "a" and "an" are indefinite articles and, therefore, do not preclude embodiments having a plurality of the same.

[0062] (Other embodiments) It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. In short, the present invention is not limited to the upper embodiments as they are, and the components can be modified within the scope not departing from the gist at the implementation stage.

[0063] In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiments. Further, components from different embodiments may be appropriately combined.

[0064] (Advantages of the invention) According to the present invention, it is possible to suppress the loss by Brillouin gain analysis method and the XT component of the probe light Pb1 in the fiber that causes problems in XT measurement in the measurement optical fiber, and it is possible to measure the loss and XT generated at each point independently.

Description of reference numerals

[0065] 11: Optical input circuit 12: Light receiver 13: Control arithmetic unit 21: Laser light generation means 22: Mode multiplexing / demultiplexing means 23, 24: Optical frequency control means 25: Branch element 26: Optical pulse generation means 27: Mode selection multiplexing / demultiplexing means 31: Arithmetic unit 31a: Digitization processing means 31b: Numerical calculation means 32: Control unit 50: Optical fiber 100: System 101: User 105: Computer 110: Processor 115: Memory 120: Program module 122: Result 125: Storage device 130: User device 135: Network 140: Storage device 150: Data source 301: Optical fiber measurement system

Claims

1. An optical fiber measurement system, comprising: an optical input circuit configured to inject a probe light into one end of an optical fiber, and inject a secondary probe light which is a continuous light and a pump light which is an optical pulse into the other end of the optical fiber; a light receiver configured to measure the light intensity of any one propagation mode among the probe lights propagated through the optical fiber; a control arithmetic unit configured to set the propagation modes of the probe light, the secondary probe light, and the pump light with respect to the optical input circuit, and the optical frequency differences of the secondary probe light and the pump light, and calculate losses and crosstalk at each point in the longitudinal direction of a measured optical fiber connected as the optical fiber from the light intensity measured by the light receiver; wherein: the control arithmetic unit: when connecting the measured optical fiber as the optical fiber to the optical input circuit, inject the probe light into one end of the optical fiber in an arbitrary propagation mode; inject the secondary probe light having an optical frequency difference from the probe light to the low frequency side into the other end of the optical fiber in a propagation mode that becomes a crosstalk component of the probe light; inject the pump light having an optical frequency difference from the probe light to the high frequency side into the optical fiber in an arbitrary propagation mode; obtain a distribution of Brillouin amplification amounts of the probe light with respect to the longitudinal direction of the measured optical fiber from the light intensity; and calculate the losses and crosstalk using the steps in the distribution of the Brillouin amplification amount and the Brillouin gain coefficient determined by the optical frequency difference and propagation mode between the pump light and the probe light; characterized in that: furthermore, the control arithmetic unit: when connecting a reference optical fiber having the same characteristics as the measured optical fiber and no mode coupling as the optical fiber to the optical input circuit, inject the probe light into one end of the optical fiber and the pump light into the other end of the optical fiber in all combinations of propagation modes propagating through the measured optical fiber while changing the optical frequency difference between the probe light and the pump light; and obtain the Brillouin gain coefficient for each optical frequency difference and each combination of propagation modes from the light intensity; characterized by an optical fiber measurement system.

2. An optical fiber measurement system, comprising: an optical input circuit configured to inject a probe light into one end of an optical fiber, and inject a secondary probe light which is a continuous light and a pump light which is an optical pulse into the other end of the optical fiber; A light receiver that measures the light intensity of any one propagation mode among the probe light that has propagated through the optical fiber, A control arithmetic unit that sets the propagation modes of the probe light, the secondary probe light, and the pump light with respect to the light incident circuit, and the optical frequency differences of the secondary probe light and the pump light, and calculates the loss and crosstalk at each point in the longitudinal direction of the optical fiber under measurement connected as the optical fiber from the light intensity measured by the light receiver, Comprising, The control arithmetic unit, When connecting the optical fiber under measurement as the optical fiber, with respect to the light incident circuit, Injecting the probe light into one end of the optical fiber in an arbitrary propagation mode, Injecting the secondary probe light having an optical frequency difference from the probe light to the low frequency side into the other end of the optical fiber in the propagation mode that becomes the crosstalk component of the probe light, Injecting the pump light having an optical frequency difference from the probe light to the high frequency side in an arbitrary propagation mode, Obtaining the distribution of the Brillouin amplification amount of the probe light with respect to the longitudinal direction of the optical fiber under measurement from the light intensity, and Calculating the loss and crosstalk using the step of the Brillouin amplification amount appearing in the distribution and the Brillouin gain coefficient determined by the optical frequency difference and propagation mode between the pump light and the probe light Characterized by, Furthermore, the control arithmetic unit, An optical fiber measurement system characterized in that the optical frequency difference between the secondary probe light and the probe light is set to an optical frequency difference that gives only Brillouin loss to the crosstalk component of the probe light.

3. An optical fiber measurement method, A light incident circuit that injects probe light into one end of an optical fiber and injects secondary probe light that is continuous light and pump light that is an optical pulse into the other end of the optical fiber, A light receiver that measures the light intensity of any one propagation mode among the probe light that has propagated through the optical fiber, A control arithmetic unit that sets the propagation modes of the probe light, the secondary probe light, and the pump light with respect to the light incident circuit, and the optical frequency differences of the secondary probe light and the pump light, and calculates the loss and crosstalk at each point in the longitudinal direction of the optical fiber under measurement connected as the optical fiber from the light intensity measured by the light receiver, Using an optical fiber measurement system comprising, When connecting the optical fiber under measurement as the optical fiber, Injecting the probe light into one end of the optical fiber in an arbitrary propagation mode; Injecting the secondary probe light having an optical frequency difference from the probe light into the other end of the optical fiber in a propagation mode that becomes a crosstalk component of the probe light on the low-frequency side; Injecting the pump light having an optical frequency difference from the probe light into the high-frequency side in an arbitrary propagation mode; Obtaining a distribution of the Brillouin amplification amount of the probe light with respect to the longitudinal direction of the optical fiber to be measured from the light intensity; and Calculating the loss and crosstalk using the step of the Brillouin amplification amount appearing in the distribution and the Brillouin gain coefficient determined by the optical frequency difference and propagation mode between the pump light and the probe light is characterized in that; Furthermore, when a reference optical fiber having the same characteristics as the optical fiber to be measured and no mode coupling is connected as the optical fiber, with respect to the optical incident circuit, Injecting the probe light into one end of the optical fiber in all combinations of propagation modes propagating through the optical fiber to be measured and while changing the optical frequency difference between the probe light and the pump light, and injecting the pump light into the other end of the optical fiber; and Obtaining the Brillouin gain coefficient for each optical frequency difference and each combination of propagation modes from the light intensity; An optical fiber measurement method characterized by the above.

4. An optical fiber measurement method, An optical incident circuit for injecting a probe light into one end of an optical fiber and injecting a secondary probe light which is continuous light and a pump light which is an optical pulse into the other end of the optical fiber; A light receiver for measuring the light intensity of an arbitrary one propagation mode among the probe lights propagated through the optical fiber; With respect to the optical incident circuit, setting the propagation modes of the probe light, the secondary probe light, and the pump light, and the optical frequency difference of the secondary probe light and the optical frequency difference of the pump light, and calculating the loss and crosstalk at each point in the longitudinal direction of the optical fiber to be measured connected as the optical fiber from the light intensity measured by the light receiver; a control arithmetic unit; Using an optical fiber measurement system comprising: When connecting an optical fiber to be measured as the optical fiber, Injecting the probe light into one end of the optical fiber in an arbitrary propagation mode; Injecting the secondary probe light having an optical frequency difference from the probe light into the other end of the optical fiber in a propagation mode that becomes a crosstalk component of the probe light on the low-frequency side; Injecting the pump light having an optical frequency difference from the probe light in an arbitrary propagation mode on the high-frequency side, obtaining a distribution of the Brillouin amplification amount of the probe light with respect to the longitudinal direction of the optical fiber to be measured from the optical intensity, and calculating the loss and crosstalk using the step of the Brillouin amplification amount appearing in the distribution, the optical frequency difference between the pump light and the probe light, and the Brillouin gain coefficient determined by the propagation mode is characterized in that, Furthermore, an optical fiber measurement method is characterized in that the optical frequency difference between the secondary probe light and the probe light is set to an optical frequency difference that gives only Brillouin loss to the crosstalk component of the probe light.

5. An optical incident circuit for injecting a probe light into one end of an optical fiber and injecting a secondary probe light that is continuous light and a pump light that is an optical pulse into the other end of the optical fiber, a light receiver for measuring the optical intensity of an arbitrary one propagation mode among the probe lights propagated through the optical fiber, and a control arithmetic unit of an optical fiber measurement system comprising: a control unit for setting the propagation modes of the probe light, the secondary probe light, and the pump light, the optical frequency difference of the secondary probe light, and the optical frequency difference of the pump light with respect to the optical incident circuit; an arithmetic unit for calculating the loss and crosstalk at each point in the longitudinal direction of the optical fiber to be measured connected as the optical fiber from the optical intensity measured by the light receiver, comprising: When the optical fiber to be measured is connected to the optical fiber measurement system as the optical fiber, the control unit, with respect to the optical incident circuit, injecting the probe light into one end of the optical fiber in an arbitrary propagation mode, injecting the secondary probe light having an optical frequency difference from the probe light on the low-frequency side into the other end of the optical fiber in a propagation mode that becomes the crosstalk component of the probe light, and injecting the pump light having an optical frequency difference from the probe light on the high-frequency side in an arbitrary propagation mode, performing, the arithmetic unit, obtaining a distribution of the Brillouin amplification amount of the probe light with respect to the longitudinal direction of the optical fiber to be measured from the optical intensity, and calculating the loss and crosstalk using the step of the Brillouin amplification amount appearing in the distribution, the optical frequency difference between the pump light and the probe light, and the Brillouin gain coefficient determined by the propagation mode is characterized by performing. Furthermore, when a reference optical fiber having the same characteristics as the optical fiber to be measured and no mode coupling is connected to the optical fiber measurement system as the optical fiber, the control unit, with respect to the optical incidence circuit, performs the operation of injecting the probe light into one end of the optical fiber and the pump light into the other end of the optical fiber while changing the optical frequency difference between the probe light and the pump light in all combinations of propagation modes propagating through the optical fiber to be measured, the arithmetic unit, performs the operation of obtaining the Brillouin gain coefficient for each optical frequency difference and each combination of propagation modes from the optical intensity, A control arithmetic device characterized by the above.

6. An optical incidence circuit for injecting a probe light into one end of an optical fiber, a secondary probe light which is a continuous light and a pump light which is an optical pulse into the other end of the optical fiber, A control arithmetic device for an optical fiber measurement system, comprising a light receiver for measuring the optical intensity of any one propagation mode among the probe lights propagated through the optical fiber, a control unit for setting the propagation modes of the probe light, the secondary probe light, and the pump light with respect to the optical incidence circuit, and the optical frequency difference of the secondary probe light and the optical frequency difference of the pump light, an arithmetic unit for calculating the loss and crosstalk at each point in the longitudinal direction of the optical fiber to be measured connected as the optical fiber from the optical intensity measured by the light receiver, comprising, when the optical fiber to be measured is connected to the optical fiber measurement system as the optical fiber, the control unit, with respect to the optical incidence circuit, performs the operation of injecting the probe light into one end of the optical fiber in an arbitrary propagation mode, performs the operation of injecting the secondary probe light having an optical frequency difference from the probe light to the low frequency side into the other end of the optical fiber in the propagation mode that becomes the crosstalk component of the probe light, and performs the operation of injecting the pump light having an optical frequency difference from the probe light to the high frequency side in an arbitrary propagation mode, performs, the arithmetic unit, performs the operation of obtaining the distribution of the Brillouin amplification amount of the probe light with respect to the longitudinal direction of the optical fiber to be measured from the optical intensity, and performs the operation of calculating the loss and crosstalk using the step of the Brillouin amplification amount appearing in the distribution and the Brillouin gain coefficient determined by the optical frequency difference between the pump light and the probe light and the propagation mode, characterized by performing the above, furthermore, the control unit, A control arithmetic unit characterized in that a optical frequency difference between the probe light and the secondary probe light is set to an optical frequency difference that gives Brillouin loss only to a crosstalk component of the probe light.

7. A program for causing a computer to function as the control arithmetic unit according to claim 5 or 6.

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