Optical transmission line testing device and testing method

Abstract

The objective of the present invention is to provide an optical transmission path testing device and testing method capable of employing an optical time domain reflectometer (OTDR) to measure, from one end side of an optical transmission path obtained by connecting in series a plurality of uncoupled multicore fibers, cumulative crosstalk in the optical transmission path.　An optical transmission path testing device 301 according to the present invention measures cumulative crosstalk in an optical transmission path 50 obtained by connecting in series a plurality of uncoupled multicore fibers 50-i. The optical transmission path testing device 301 comprises: a test light input unit 10 for inputting a light pulse into each core of an uncoupled multicore fiber 50-1 at one end 50a of an optical transmission path 50; a receiving unit 20 for receiving backscattered light from each core, output from the one end 50a; and a computing unit 30 for acquiring a loss distribution arising in each core from the backscattered light, and calculating the cumulative crosstalk from a connection loss at connecting points zj of the uncoupled multicore fibers, obtained from the loss distribution, and known inter-core mode couplings of each uncoupled multicore fiber 50-i.

Description

[Technical Field]

[0001] The present disclosure relates to an optical transmission line testing device and a testing method for testing an optical transmission line in which a plurality of uncoupled multi-core fibers are connected in series. [Background technology]

[0002] Uncoupled multicore fibers are one of the promising optical fibers for realizing future high-capacity optical communications. Crosstalk between cores in uncoupled multicore fibers is an important parameter that limits the transmission capacity. Therefore, to ensure the desired transmission capacity, it is necessary to evaluate whether the cumulative crosstalk of the entire transmission path is within the acceptable range. Crosstalk generated in the optical fiber itself and input / output devices can be measured when they are manufactured.

[0003] For example, Non-Patent Documents 1 and 2 disclose crosstalk measurement methods using an optical time domain reflectometer (OTDR). These methods involve inputting an optical pulse into one core of a multicore fiber, measuring the intensities of backscattered light output from that core (input core) and an adjacent core, and calculating the crosstalk from the ratio between the intensities. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] M. Nakazawa et al., “Nondestructive measurement of mode couplings along a multi-core fiber using a synchronous multi-channel OTDR,” Optics Express, vol. 20, no. 11, pp. 12530-12540, 2012. [Non-patent document 2] M. Ohashi et al., “Simple backscattered power technique for measuring crosstalk of multi-core fibers,” in Proc. 17th Opto-Electronics and Communications Conference, P1_25, 2012. Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, in the case of an optical transmission line in which multiple uncoupled multicore fibers are connected in series, the connection points have an effect on cumulative crosstalk, so they must be evaluated when the optical transmission line is constructed.When constructing an optical transmission line, it is operationally difficult to test from both ends of the optical fiber, so it is necessary to input test light from one end of the optical transmission line and perform the test using the backscattered light.

[0006] However, the intensity of the backscattered light output from the core (adjacent core) adjacent to the core (input core) where the test light is input is extremely small compared to the intensity of the backscattered light from the input core. Therefore, unless the cumulative crosstalk is in a region with a certain degree of cumulative crosstalk, the dynamic range of the OTDR is insufficient, making it difficult to directly measure the cumulative crosstalk.

[0007] Therefore, in order to solve the above-mentioned problems, an object of the present invention is to provide an optical transmission line testing device and a testing method that can measure the accumulated crosstalk of an optical transmission line in which multiple uncoupled multi-core fibers are connected in series from one end side using an OTDR. [Means for solving the problem]

[0008] In order to achieve the above object, the optical transmission line testing device according to the present invention calculates the cumulative crosstalk of the entire optical transmission line from loss characteristics that can be easily measured with an OTDR.

[0009] Specifically, the optical transmission line testing apparatus according to the present invention is an optical transmission line testing apparatus that measures cumulative crosstalk in an optical transmission line in which a plurality of uncoupled multi-core fibers are connected in series, and a test light input unit that inputs an optical pulse from one end of the optical transmission line to each core of the uncoupled multi-core fiber; a receiving unit that receives backscattered light for each core at one end of the optical transmission line; a calculation unit that acquires a loss distribution occurring in each of the cores from the backscattered light for each of the cores, and calculates the cumulative crosstalk from a connection loss at a connection point of the uncoupled multicore fibers obtained from the loss distribution and known inter-core mode coupling of each of the uncoupled multicore fibers; Equipped with.

[0010] Further, an optical transmission line testing method according to the present invention is a testing method for measuring cumulative crosstalk of an optical transmission line, comprising the steps of: the optical transmission line is a series-connected multi-core fiber; an optical pulse is input from one end of the optical transmission line to each core of the uncoupled multicore fiber; receiving backscattered light for each of the cores at one end of the optical transmission line; Obtaining a loss distribution occurring in each of the cores from the backscattered light for each of the cores; and calculating the cumulative crosstalk from the splice loss at the splice point of the uncoupled multi-core fibers obtained from the loss distribution and the known inter-core mode coupling of each of the uncoupled multi-core fibers; It is characterized by:

[0011] The optical transmission line testing device and method calculates the output of each core from the other end of the optical transmission line using a matrix representing the mode coupling at the connection point and a (known) matrix representing the mode coupling of the uncoupled multicore fiber, and then calculates the cumulative crosstalk. Here, because the mode coupling between cores that occurs at the connection point is negligibly small compared to the mode coupling between cores that occurs in each section of the uncoupled multicore fiber, only the element of connection loss between identical cores that can be obtained from the backscattered light in a pulse test is taken into account for the matrix representing the mode coupling at the connection point. In other words, the cumulative crosstalk of the entire optical transmission line can be calculated by measuring only the intensity of the backscattered light from the input core.

[0012] Therefore, the present invention can provide an optical transmission line testing device and testing method that can measure the accumulated crosstalk of an optical transmission line in which a plurality of uncoupled multi-core fibers are connected in series from one end side using an OTDR.

[0013] Specifically, the calculation unit: a ratio of the optical intensity of light input to the one core at one end of the optical transmission line, propagating through the optical transmission line, and output from the one core and the other core at the other end of the optical transmission line is defined as the cumulative crosstalk; The optical intensity ratio is calculated using the product of a splice point matrix representing the splice loss of the one core and the other core at each of the splice points and a fiber section matrix representing the inter-core mode coupling of each of the uncoupled multicore fibers.

[0014] Furthermore, since bending loss and splice loss are wavelength dependent, it is preferable to calculate the cumulative crosstalk for each wavelength of the optical pulse.

[0015] The calculation unit of the optical transmission line testing device can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network.

[0016] The above inventions can be combined as much as possible. [Effects of the Invention]

[0017] The present invention can provide an optical transmission line testing device and testing method that can measure the accumulated crosstalk of an optical transmission line in which a plurality of uncoupled multi-core fibers are connected in series from one end side using an OTDR. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a diagram illustrating an optical transmission line testing device according to the present invention; [Figure 2] 1A and 1B are diagrams illustrating an optical transmission line testing method according to the present invention. [Figure 3] FIG. 2 is a diagram illustrating input and output of an optical transmission line. DETAILED DESCRIPTION OF THE INVENTION

[0019] The following description of the preferred embodiments of the present invention will be given with reference to the accompanying drawings. The preferred embodiments described below are examples of the present invention, and the present invention is not limited to the preferred embodiments. In this specification and the drawings, components having the same reference numerals are intended to represent the same components.

[0020] (Embodiment 1) FIG. 1 is a diagram illustrating the configuration of an optical transmission line testing device 301 according to this embodiment. The optical transmission line testing device 301 includes: An optical transmission line testing device for measuring cumulative crosstalk in an optical transmission line 50 in which a plurality of uncoupled multi-core fibers 50-i (i is an integer from 1 to N) are connected in series, a test light input unit 10 for inputting an optical pulse to each core of the uncoupled multi-core fiber 50-1 at one end 50a of the optical transmission line 50; a receiving unit (20) that receives backscattered light for each core output from one end (50a) of the optical transmission line (50); a calculation unit 30 that acquires a loss distribution occurring in each of the cores from the backscattered light for each of the cores, and calculates the cumulative crosstalk from a connection loss at a connection point zj (j=i−1, and is 1 or more) of the uncoupled multi-core fiber obtained from the loss distribution and known inter-core mode coupling of each uncoupled multi-core fiber 50-i; Equipped with.

[0021] The test light input section 10 has a pulse light source 11, an optical circulator 12, an optical switch 13, and an input / output device 14. The pulse light source 11 outputs an optical pulse of an arbitrary wavelength. The optical circulator 12 passes the optical pulse from the pulse light source 11 toward the optical transmission line 50. The input / output device 14 can input the optical pulse to each of multiple cores appearing at one end 50a of the optical transmission line 50. For example, the input / output device 14 is a fan-in / fan-out device for a multicore fiber. The optical switch 13 selects a path to input the optical pulse from the pulse light source 11 to one of the multiple cores appearing at one end 50a of the optical transmission line 50.

[0022] The receiving unit 20 has an opto-electrical converter 21 and an AD converter 22. When an optical pulse is input to one of the cores (e.g., core #m) appearing at one end 50a of the optical transmission line 50, the optical pulse propagates through the optical transmission line 50, generating backscattered light (Rayleigh scattered light). The backscattered light is received by the opto-electrical converter 21 via the input / output device 14, the optical switch 13, and the optical circulator 12. The opto-electrical converter 21 is, for example, a photodiode. The opto-electrical converter 21 converts the light intensity of the received backscattered light (light intensity relative to the distance from the one end 50a of the optical transmission line 50) into an electrical signal. The AD converter 22 converts the analog electrical signal into a digital signal.

[0023] The calculation unit 30 includes a waveform analysis unit 31 and a crosstalk calculation unit 32. The operation of the calculation unit 30 will be described later.

[0024] 2 is a diagram illustrating a test method performed by the optical transmission line testing device 301. This test method includes an input step (step S01) of inputting an optical pulse to each core of an uncoupled multi-core fiber from one end 50a of the optical transmission line 50; a receiving step (step S02) of receiving backscattered light for each core at one end 50a of the optical transmission line 50; an acquisition step (step S03) of acquiring a loss distribution occurring in each of the cores from the backscattered light for each of the cores; and a calculation step (step S04) of calculating the cumulative crosstalk from the splice loss at the splice point zj of the uncoupled multi-core fibers obtained from the loss distribution and the known inter-core mode coupling of each of the uncoupled multi-core fibers; It is characterized by:

[0025] The input process through the acquisition process will now be described in detail. First, an arbitrary core (for example, core #m) is selected by the optical switch 13. An optical pulse P is transmitted from one end 50a of the optical transmission line 50 to the core #m. in Input the backscattered light BC from core #m. m Then, the calculation unit 30 calculates the backscattered light BC m From the loss distribution, the waveform analyzer 31 of the calculator 30 obtains the loss distribution in the longitudinal direction of the optical transmission line 50. Furthermore, the waveform analyzer 31 of the calculator 30 obtains the splice loss η at the splice point zj between the uncoupled multi-core fiber 50-i and the uncoupled multi-core fiber 50-i+1 from the loss distribution. (j) 11 is obtained from the change in backscattered light intensity.

[0026] Next, another core (for example, core #n) is selected by the optical switch 13. An optical pulse P is transmitted from one end 50a of the optical transmission line 50 to the core #n. in (The wavelength is the optical pulse P in (same as BC) and the backscattered light from core #n n Then, the calculation unit 30 calculates the backscattered light BC nFrom the loss distribution, the waveform analyzer 31 of the calculator 30 obtains the loss distribution in the longitudinal direction of the optical transmission line 50. Furthermore, the waveform analyzer 31 of the calculator 30 obtains the splice loss η at the splice point zj between the uncoupled multi-core fiber 50-i and the uncoupled multi-core fiber 50-i+1 from the loss distribution. (j) 22 is obtained from the change in backscattered light intensity.

[0027] The calculation process performed by the crosstalk calculation unit 32 of the calculation unit 30 will be described with reference to FIG. The crosstalk calculation unit 32 An optical pulse P is input to one core (for example, core #m) at one end 50a of the optical transmission line 50. in is propagated through the optical transmission line 50, and the ratio of the optical intensity output from one core (core #m) at the other end 50b of the optical transmission line 50 to the other core (core #n) is defined as cumulative crosstalk, The ratio of the optical intensities is calculated by the connection point matrix T j and a fiber section matrix M representing the inter-core mode coupling of each uncoupled multi-core fiber 50-i. i It is calculated using the product of

[0028] FIG. 3 shows an optical pulse P in and the optical transmission line 50 transmits an optical pulse P m propagates and is output from each of the cores (#m and #n) at the other end 50b of the optical transmission line 50. out This explains the matrix P in Since the optical pulse is input only to core #m, the optical power is P m(in) =1, P n(in) = 0. When an optical pulse is input only to core #n, the elements are reversed. Also, the matrix P out The element of is the optical power P of the optical pulse output from core #m. m(out) and the optical power P of the optical pulse output from core #n n(out) is.

[0029] matrix P outcan be expressed by the following equation:

number

number

number

number

[0030] M in formula (1) i is a matrix representing the mode coupling between cores occurring in each uncoupled multi-core fiber 50-i.

number

[0031] matrix M i The elements of the uncoupled multi-core fiber 50-i are the loss coefficient α, the power coupling coefficient h, and the fiber length L as shown in the following equation. i can be obtained from

number

[0032] In this way, the crosstalk calculation unit 32 calculates the crosstalk coefficient α, the power coupling coefficient h, and the fiber length L of the uncoupled multi-core fiber 50-i measured before the construction of the optical transmission line 50. i , and the mode coupling matrix of the connection point zj obtained in the input step (step S01) to the acquisition step (step S03), the optical intensity (P m(out) , P n(out) ) can be calculated.

[0033] Then, the crosstalk calculation unit 32 calculates the cumulative crosstalk XT (logarithmic notation) taking into account the influence of all the connection points zj of the optical transmission line 50 as the optical intensity (P m(out) , P n(out) ) is calculated by substituting it into the following formula:

number

[0034] The calculation method performed by the crosstalk calculation unit 32 described above is for the case where the optical transmission line 50 has two cores, but even if the optical transmission line 50 has three or more cores, it is sufficient to measure the connection loss at each connection point zj for each core. j and M i is a determinant whose number of rows and columns is the number of cores.

[0035] (Embodiment 2) The optical transmission line testing apparatus of this embodiment has the same configuration as the optical transmission line testing apparatus 301 described in embodiment 1. This optical transmission line testing apparatus is characterized in that a pulse light source 11 outputs optical pulses of different wavelengths, and a calculation unit 30 calculates the cumulative crosstalk XT for each wavelength of the optical pulse.

[0036] By testing with optical pulses of different wavelengths, the mode coupling matrix T j It is possible to calculate the cumulative crosstalk XT for the optical fiber in the vicinity of the splice point zj, including the influence of the bending of the fiber. In other words, this optical transmission line testing equipment can obtain the cumulative crosstalk XT in the communication wavelength band, which is easily affected by the bending of the fiber.

[0037] The greater the inter-core loss difference at the splice point zj, the greater the impact on cumulative crosstalk XT. Because bending loss and splice loss are wavelength dependent, it is preferable to perform tests using optical pulses of multiple wavelengths in order to determine the quality of the splice point (splice point + accommodated bend). For example, because the shorter the wavelength, the more pronounced the change in splice loss, it is preferable to perform tests using optical pulses with wavelengths on the short side of the communication wavelength band. On the other hand, because the longer the wavelength, the more pronounced the change in bending loss, it is preferable to perform tests using optical pulses with wavelengths on the long side of the communication wavelength band.

[0038] (Other embodiments) The calculation unit 30 of the optical transmission line testing device 301 can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network. [Explanation of symbols]

[0039] 10: Test light input section 11: Pulsed light source 12: Optical circulator 13: Optical switch 14: Input / output devices 20: Receiving unit 21: Photoelectric conversion unit 22: AD conversion section 30: Arithmetic section 31: Waveform analysis section 32: Crosstalk calculation section 50: Optical transmission line 50-1, 50-2, , 50-i, , 50-N: Uncoupled multicore fibers 301: Optical transmission line testing equipment z1, z2, , zj, , zN-1: connection points

Claims

1. An optical transmission line testing device for measuring cumulative crosstalk in an optical transmission line in which a plurality of uncoupled multi-core fibers are connected in series, comprising: a test light input unit that inputs an optical pulse from one end of the optical transmission line to each core of the uncoupled multi-core fiber; a receiving unit that receives backscattered light for each core at one end of the optical transmission line; a calculation unit that acquires a loss distribution occurring in each of the cores from the backscattered light for each of the cores, and calculates the cumulative crosstalk from a connection loss at a connection point of the uncoupled multicore fibers obtained from the loss distribution and known inter-core mode coupling of each of the uncoupled multicore fibers; An optical transmission line testing device comprising:

2. The calculation unit a ratio of the optical intensity of light input to one of the cores at one end of the optical transmission line, propagating through the optical transmission line, and output from the one core and the other core at the other end of the optical transmission line is defined as the cumulative crosstalk; 2. The optical transmission line testing device according to claim 1, wherein the ratio of the optical intensities is calculated using a product of a splice point matrix representing the splice loss of the one core and the other core at each of the splice points and a fiber section matrix representing the inter-core mode coupling of each of the uncoupled multicore fibers.

3. 3. The optical transmission line testing device according to claim 1, wherein the calculation unit calculates the cumulative crosstalk for each wavelength of the optical pulse.

4. A test method for measuring cumulative crosstalk in an optical transmission line, comprising: the optical transmission line is a series-connected multi-core fiber; an optical pulse is input from one end of the optical transmission line to each core of the uncoupled multicore fiber; receiving backscattered light for each of the cores at one end of the optical transmission line; Obtaining a loss distribution occurring in each of the cores from the backscattered light for each of the cores; and calculating the cumulative crosstalk from the splice loss at the splice point of the uncoupled multi-core fibers obtained from the loss distribution and the known inter-core mode coupling of each of the uncoupled multi-core fibers; A test method characterized by:

5. a ratio of the optical intensity of light input to one of the cores at one end of the optical transmission line, propagating through the optical transmission line, and output from the one core and the other core at the other end of the optical transmission line is defined as the cumulative crosstalk; 5. The test method according to claim 4, wherein the ratio of the optical intensities is calculated using a product of a splice point matrix representing the splice loss of the one core and the other core at each of the splice points and a fiber section matrix representing the inter-core mode coupling of each of the uncoupled multicore fibers.

6. 6. The test method according to claim 4, wherein the cumulative crosstalk is calculated for each wavelength of the optical pulse.

Images