TERMINATION DETERMINATION DEVICE AND TERMINATION DETERMINATION METHOD

Abstract

An object of the present invention is to provide a terminal determination device and a terminal determination method, which enable identification of a reflection signal from a terminal portion of an optical fiber to be measured even in a case where a reflection signal caused by multiple reflection appears in an OTDR waveform in a mode in which an OTDR and the optical fiber to be measured are connected at a bent portion.

The reflection signal caused by multiple reflection inevitably propagates through a distance equal to a distance between true reflection points more than the other reflection point, because of multiple reflection. Therefore, a distance between the reflection signal and another reflection signal is inevitably coincident with a distance between the other reflection signals. In contrast, in a case of a reflection signal from a terminal portion 51 of the optical fiber, the distance between the reflection signal and another reflection signal is not coincident with the distance between the other reflection signals.

Claims

1. A terminal determination device, comprising: an optical reflectance distribution measurement device configured to measure reflectance distribution of an optical fiber to be measured by receiving reflection light of test light entering the optical fiber to be measured; a side light input/output unit configured to form a bent portion in a predetermined bent shape at an arbitrary position of the optical fiber to be measured, to cause the test light to enter from the bent portion to a core of the optical fiber to be measured, and to output the reflection light propagating through the core of the optical fiber to be measured from the bent portion to outside; and a measurement data analysis unit configured to perform a determination operation by detecting a plurality of peaks included in the reflectance distribution, and comparing the peaks to determine a terminal of the optical fiber to be measured from the peaks.

2. The terminal determination device according to claim 1, wherein, when N is a total number of peaks, i is a number of each of the peaks from the optical reflectance distribution measurement device side, and x.sub.i is a distance of each of the peaks from the optical reflectance distribution measurement device side, the determination operation by the measurement data analysis unit includes, with respect to a farthest peak farthest from the optical reflectance distribution measurement device from the peaks: representing the distances of the peaks except for the farthest peak, by an (N−1)-order column vector d.sub.N-1 in an expression C1; representing the distances between any two of the peaks, by an N×N matrix A in an expression C2; representing components in an N-th column of the matrix A, by a column vector {x} in an expression C3; comparing components of the column vector {x} with components of the column vector d.sub.N-1 and components of the matrix A except for the components in the N-th column; and in a case where values of the components are not coincident with one another, determining the farthest peak as a terminal of the optical fiber to be measured, or in a case where the values of the components are coincident with one another, repeating the determination operation by changing N to N−1. $\begin{array}{cc}\left[\mathrm{Math}.C1\right]& \\ d_{N-1}=\left(\begin{array}{c}{x}_1\\ x_2\\ .Math.\\ x_i\\ .Math.\\ x_{N-1}\end{array}\right)& \left(C1\right)\end{array}$ $\begin{array}{cc}\left[\mathrm{Math}.C2\right]& \\ A=\left[\Delta x_{\mathrm{ij}}\right]=\left(\begin{array}{cccccc}0& \Delta x_{21}& .Math.& \Delta x_{i1}& .Math.& \Delta x_{N1}\\ *& 0& .Math.& \Delta x_{i2}& .Math.& \Delta x_{N2}\\ *& *& \ddots & .Math.& \ddots & .Math.\\ *& *& *& 0& .Math.& .Math.\\ *& *& *& *& \ddots & .Math.\\ *& *& *& *& *& 0\end{array}\right)& \left(C2\right)\end{array}$ where Δx.sub.ij is a distance between an i-th reflection signal and a j-th reflection signal, represented by Δx.sub.ij=|x.sub.i−x.sub.j|, and a symbol “*” represents an unnecessary component. $\begin{array}{cc}\left[\mathrm{Math}.C3\right]& \\ \left\{x\right\}=\left(\begin{array}{c}\Delta x_{N1}\\ \Delta x_{N2}\\ .Math.\\ \Delta x_{\mathrm{NN}-1}\end{array}\right)& \left(C3\right)\end{array}$

3. The terminal determination device according to claim 1, wherein the optical reflectance distribution measurement device causes the test light with a plurality of wavelengths to enter the optical fiber to be measured, and the determination operation by the measurement data analysis unit includes determining the peak that is present in all of the wavelengths and is farthest from the optical reflectance distribution measurement device, as the terminal of the optical fiber to be measured.

4. A terminal determination method, comprising: forming a bent portion in a predetermined bent shape, at an arbitrary position of an optical fiber to be measured; causing test light to enter a core of the optical fiber to be measured from the bent portion; outputting reflection light of the test light from the bent portion to outside of the optical fiber to be measured; measuring reflectance distribution of the optical fiber to be measured, by receiving the reflection light; and performing a determination operation by detecting a plurality of peaks included in the reflectance distribution, and comparing the peaks to determine a terminal of the optical fiber to be measured from the peaks.

5. The terminal determination method according to claim 4, wherein, when N is a total number of peaks, i is a number of each of the peaks from an optical reflectance distribution measurement device side, and x.sub.i is a distance of each of the peaks from the optical reflectance distribution measurement device side, the determination operation includes, with respect to a farthest peak farthest from the optical reflectance distribution measurement device from the peaks: representing the distances of the peaks except for the farthest peak, by an (N−1)-order column vector d.sub.N-1 in an expression C1; representing the distances between any two of the peaks, by an N×N matrix A in an expression C2; representing components in an N-th column of the matrix A, by a column vector {x} in an expression C3; comparing components of the column vector {x} with components of the column vector d.sub.N-1 and components of the matrix A except for the components in the N-th column; and in a case where values of the components are not coincident with one another, determining the farthest peak as a terminal of the optical fiber to be measured, or in a case where the values of the components are coincident with one another, repeating the determination operation by changing N to N−1. $\begin{array}{cc}\left[\mathrm{Math}.C1\right]& \\ d_{N-1}=\left(\begin{array}{c}{x}_1\\ x_2\\ .Math.\\ x_i\\ .Math.\\ x_{N-1}\end{array}\right)& \left(C1\right)\end{array}$ $\begin{array}{cc}\left[\mathrm{Math}.C2\right]& \\ A=\left[\Delta x_{\mathrm{ij}}\right]=\left(\begin{array}{cccccc}0& \Delta x_{21}& .Math.& \Delta x_{i1}& .Math.& \Delta x_{N1}\\ *& 0& .Math.& \Delta x_{i2}& .Math.& \Delta x_{N2}\\ *& *& \ddots & .Math.& \ddots & .Math.\\ *& *& *& 0& .Math.& .Math.\\ *& *& *& *& \ddots & .Math.\\ *& *& *& *& *& 0\end{array}\right)& \left(C2\right)\end{array}$ where Δx.sub.ij is a distance between an i-th reflection signal and a j-th reflection signal, represented by Δx.sub.ij=|x.sub.i−x.sub.j|, and a symbol “*” represents an unnecessary component. $\begin{array}{cc}\left[\mathrm{Math}.C3\right]& \\ \left\{x\right\}=\left(\begin{array}{c}\Delta x_{N1}\\ \Delta x_{N2}\\ .Math.\\ \Delta x_{\mathrm{NN}-1}\end{array}\right)& \left(C3\right)\end{array}$

6. The terminal determination method according to claim 4, wherein the test light has a plurality of wavelengths, and the determination operation includes determining the peak that is present in all of the wavelengths and is farthest from an optical reflectance distribution measurement device, as the terminal of the optical fiber to be measured.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0023] FIG. 1 is a configuration diagram illustrating a terminal determination device according to the present invention.

[0024] FIG. 2 is a diagram illustrating an OTDR waveform including multiple reflection.

[0025] FIG. 3 is a flowchart illustrating a terminal determination method according to the present invention.

[0026] FIG. 4 is a flowchart illustrating the terminal determination method according to the present invention.

[0027] FIG. 5 is a diagram illustrating an OTDR waveform acquired by the terminal determination device according to the present invention.

DESCRIPTION OF EMBODIMENTS

[0028] Some embodiments of the present invention are described with reference to accompanying drawings. The embodiments described below are implementation examples of the present invention, and the present invention is not limited to the following embodiments. Note that, in the present specification and the drawings, the same components are denoted by the same reference numerals.

Embodiment 1

[0029] FIG. 1 is a configuration diagram illustrating a terminal determination device 301 according to the present embodiment. The terminal determination device 301 includes: an optical reflectance distribution measurement device 11 configured to measure reflectance distribution of an optical fiber to be measured 50 by receiving reflection light of test light entering the optical fiber to be measured 50; a side light input/output unit 12 configured to form a bent portion in a predetermined bent shape at an arbitrary position of the optical fiber to be measured 50, to cause the test light to enter a core of the optical fiber to be measured 50 from the bent portion, and to output the reflection light propagating through the core of the optical fiber to be measured 50 from the bent portion to outside; and a measurement data analysis unit 13 configured to perform a determination operation by detecting a plurality of peaks included in the reflectance distribution and comparing the peaks to determine a terminal portion 51 of the optical fiber to be measured 50 from the peaks.

[0030] The side light input/output unit 12 outputs light propagating through the core of an optical fiber as leakage light to the outside by applying the predetermined bent shape to the optical fiber to be measured 50, and inputs light from the outside into the core of the optical fiber. The optical reflectance distribution measurement device 11 measures the reflectance distribution of the optical fiber to be measured 50 at a plurality of wavelengths. The measurement data analysis unit 13 analyzes the reflectance. The terminal determination device 301 uses the three components to determine whether an ONU in a power-off state is connected to the terminal portion 51 of the optical fiber, from an arbitrary position where the core of the optical fiber to be measured 50 is exposed, on a downstream of an external SP.

[0031] The optical reflectance distribution measurement device 11 has functions to emit test light with a plurality of different center wavelengths and to receive optical reflectance distribution in a longitudinal direction of the optical fiber. A multi-wavelength OTDR or an OFDR (Optical Frequency Domain Reflectometer) is usable. In the present embodiment, measurement by the OTDR is used and described.

[0032] The test light output from the OTDR 11 enters a probe optical fiber 11b including a gradient index (GRIN) lens 11a attached at a front end. In this example, a general-purpose single mode fiber is used for the probe optical fiber 11b, and a GRIN lens 11a has a focal length of 1090 μm at a beam waist width of 27 μm.

[0033] The condensed test light output from the GRIN lens 11a passes through a concave block 12a, and then enters the optical fiber to be measured 50 that has the predetermined bent shape (bent portion) formed by being sandwiched between a convex block 12b and the concave block 12a. The convex block 12b is made of a material having a refractive index greater than a refractive index (approximately 1.5) of an optical fiber coating, in order to reduce reflection of the light leaking from the optical fiber to be measured 50 by the convex block 12b. For example, the convex block 12b is made of glass or polycarbonate having a refractive index of 1.57. Further, the bent shape of the optical fiber to be measured 50 has a radius of curvature of 2 mm and a bent angle of 90 degrees in a plane illustrated in FIG. 1.

[0034] A length of the optical fiber to be measured 50 is approximately 1000 m. The test light input the optical fiber to be measured 50 propagates through the optical fiber to be measured 50, and enters the terminal portion 51 thereof. The test light entering the terminal portion 51 is reflected at a reflectance corresponding to a state of an optical fiber end surface of the terminal portion 51 and a refractive index of a layer contacting with the optical fiber end surface.

[0035] The reflection light from the terminal portion 51 passes through the same path as the test light in an opposite direction, propagates through the optical fiber to be measured 50 by 1000 m. Thereafter, the reflection light leaks from the bent portion of the optical fiber to be measured 50 bent by the side light input/output unit 12, passes through the concave block 12a, and then enters the GRIN lens 11a. The reflection light having entered the GRIN lens 11a enters the OTDR 11 through the probe fiber 11b. The reflection light having entered the OTDR 11 is analyzed by the measurement data analysis unit 13. As a result, optical reflectance distribution in the longitudinal direction of the optical fiber to be measured 50, namely, an OTDR wave form is obtained.

[0036] FIG. 2 illustrates an example of the OTDR waveform measured by the terminal determination device 301. In this example, a wavelength of the test light is 1550 nm, a pulse width of the test light is 10 ns, and the number of averaging times of the measurement is 2.sup.13 (=8192). In the OTDR waveform, six reflection signals (peaks) are present other than reflection at a port of the OTDR 11 (reflection by bent portion). Therefore, it is not possible to visually determine whether a reflection signal caused by multiple reflection is included, and which peak represents reflection from the terminal portion 51 of the optical fiber to be measured 50.

[0037] Therefore, the terminal determination device 301 performs the determination operation by the measurement data analysis unit 13, to identify a reflection signal representing reflection from the terminal portion 51 of the optical fiber, in addition to determination whether multiple reflection is included in the OTDR waveform. An example of the determination operation is described below.

[0038] As a principle of the determination operation, it is determined whether a distance between the reflection signal to be determined and another reflection signal is coincident with a distance between the other reflection signals, and the determination is performed in order from the reflection signal farthest from the OTDR 11. At this time, as the premise, “distance from OTDR 11 to each of reflection signals is not equal to distance between reflection signals”. Under the above-described premise, the reflection signal caused by multiple reflection inevitably propagates through a distance equal to a distance between true reflection points more than the other reflection point, because of multiple reflection. Therefore, the distance between the reflection signal and another reflection signal is inevitably coincident with the distance between the other reflection signals. In contrast, in a case of the reflection signal from the terminal portion 51 of the optical fiber, the distance between the reflection signal and another reflection signal is not coincident with the distance between the other reflection signals.

[0039] The method of the determination operation is generalized and described.

[0040] A case where N reflection signals are present in the OTDR waveform, and i-th reflection signal counted from the port of the OTDR 11 is reflection from the terminal portion 51 of the optical fiber is considered. At this time, i=1, 2, . . . , N, and the reflection signal by the port of the OTDR 11 is handled as an origin, namely, as a 0-th reflection signal. When a distance of the i-th reflection signal from the OTDR 11 is denoted by x.sub.i, distances of the N reflection signals from the OTDR 11 are represented by the following N-order column vector {d.sub.N}.

[00003]$\begin{array}{cc}\left[\mathrm{Math}.0\right]& \\ \left\{d_N\right\}=\left(\begin{array}{c}{x}_1\\ x_2\\ .Math.\\ x_i\\ .Math.\\ x_N\end{array}\right)& \left(0\right)\end{array}$

[0041] Further, a distance Δx.sub.ij between the i-th reflection signal and a j-th reflection signal is in an expression (1).

[Math. 1]

Δx.sub.ij=|x.sub.j−x.sub.i|  (1)

where j=1, 2, . . . , Ni

[0042] From the expression (1), all distances between any two of the reflection signals in the OTDR waveform are represented by the following N×N matrix A.

[00004]$\begin{array}{cc}\left[\mathrm{Math}.2\right]& \\ A=\left[\Delta x_{\mathrm{ij}}\right]=\left(\begin{array}{cccccc}\Delta x_{11}& \Delta x_{21}& .Math.& \Delta x_{i1}& .Math.& \Delta x_{N1}\\ \Delta x_{12}& \Delta x_{22}& .Math.& \Delta x_{i2}& .Math.& \Delta x_{N1}\\ .Math.& .Math.& \ddots & .Math.& \ddots & .Math.\\ \Delta x_{1j}& \Delta x_{2j}& .Math.& \Delta x_{ij}& .Math.& \Delta x_{Nj}\\ .Math.& .Math.& \ddots & .Math.& \ddots & .Math.\\ \Delta x_{1N}& \Delta x_{2N}& .Math.& \Delta x_{\mathrm{iN}}& .Math.& \Delta x_{\mathrm{NN}}\end{array}\right)& \left(2\right)\end{array}$

At this time, in a case of i=j, Δx.sub.ij=0 is established. Therefore, diagonal components of the matrix in the expression (2) are all zero. In addition, Δx.sub.ij=Δx.sub.ji is established because of symmetry of the expression (1). Therefore, the matrix A only with significant components is represented as follows.

[00005]$\begin{array}{cc}\left[\mathrm{Math}.3\right]& \\ A=\left(\begin{array}{cccccc}0& \Delta x_{21}& .Math.& \Delta x_{i1}& .Math.& \Delta x_{N1}\\ *& 0& .Math.& \Delta x_{i2}& .Math.& \Delta x_{N1}\\ *& *& \ddots & .Math.& \ddots & .Math.\\ *& *& *& 0& .Math.& .Math.\\ *& *& *& *& \ddots & .Math.\\ *& *& *& *& *& 0\end{array}\right)& \left(3\right)\end{array}$

In the expression, a symbol “*” represents an unnecessary component that is not handled in the following calculation.

[0043] FIG. 3 is a flowchart illustrating a terminal determination method performed by the terminal determination device 301. The terminal determination method determines a state of the terminal portion 51 by using the matrix A. Note that, as described above, as the premise, the distance from the OTDR 11 to each of the reflection signals is not equal to the distance between the reflection signals.

[0044] The terminal determination method includes: forming a bent portion in a predetermined bent shape, at an arbitrary position of the optical fiber to be measured 50 (work 1); causing test light to enter a core of the optical fiber to be measured 50 from the bent portion (work 2); outputting reflection light of the test light from the bent portion to outside of the optical fiber to be measured 50 (work 3); measuring reflectance distribution of the optical fiber to be measured 50, by receiving the reflection light (work 4); and performing a determination operation by detecting a plurality of peaks included in the reflectance distribution, and comparing the peaks to determine the terminal portion 51 of the optical fiber to be measured 50 from the peaks (work 5).

[0045] The work 1 to the work 4 correspond to step S01 in FIG. 3, and the work 5 corresponds to step S02 and subsequent steps in FIG. 3.

[0046] First, processing in step S01 is performed by the side light input/output unit 12 and the OTDR 11, to measure the optical reflectance distribution of the optical fiber to be measured 50.

[0047] The determination operation in step S02 and subsequent steps includes, with respect to the farthest peak farthest from the optical reflectance distribution measurement device 11 from the peaks: representing the distances of the peaks except for the farthest peak, by a (N−1)-order column vector d.sub.N-1 in an expression (4); representing the distances between any two of the peaks, by an N×N matrix A in the expression (2); representing components in the N-th column of the matrix A, by a column vector {x} in an expression (4); comparing components of the column vector {x} with components of the column vector d.sub.N-1 and the components of the matrix A except for the components in the N-th column; and in a case where values of the components are not coincident with one another, determining the farthest peak as a terminal of the optical fiber to be measured, or in a case where the values of the components are coincident with one another, repeating the determination operation by changing N to N−1.

[0048] The measurement data analysis unit 13 acquires the distance Δx.sub.ij between any two of the peaks from the optical reflectance distribution (step S02). The measurement data analysis unit 13 calculates the matrix A in the expression (3) from the distance Δx.sub.ij (step S03).

[0049] Next, the determination operation to determine whether the reflection signal is a reflection signal caused by multiple reflection is performed in order from, among the N peaks (reflection signals), the N-th reflection signal farthest from the port of the OTDR 11 (step S04.sub.N). The determination operation uses the above-described principle that the distance between the reflection signal caused by multiple reflection and each of the other reflection signals is inevitably coincident with the distance between the true reflection signals.

[0050] First, a vector {x.sub.N-1} that indicates relative distances between the N-th reflection signal and each of the other reflection signals becomes an (N−1)-order column vector in the N-th column of the matrix A in the expression (3).

[00006]$\begin{array}{cc}\left[\mathrm{Math}.4\right]& \\ \left\{x_{N-1}\right\}=\left(\begin{array}{c}\Delta x_{N1}\\ \Delta x_{N2}\\ .Math.\\ \Delta x_{\mathrm{NN}-1}\end{array}\right)& \left(4\right)\end{array}$

[0051] Next, as distances among the reflection signals except for the N-th reflection signal, distances {d.sub.N-1} between reflection from a connection point with the optical fiber to be measured 50 at the port of the OTDR 11 and each of the N−1 reflection signals are in an expression (5).

[00007]$\begin{array}{cc}\left[\mathrm{Math}.5\right]& \\ \left\{d_{N-1}\right\}=\left(\begin{array}{c}{x}_1\\ x_2\\ .Math.\\ x_i\\ .Math.\\ x_{N-1}\end{array}\right)& \left(5\right)\end{array}$

In other words, distances between any two of the reflection signals except for the reflection from the connection point at the port of the OTDR 11 and the N-th reflection are all of remaining components except for the components in the N-th column of the matrix A.

[0052] Therefore, the components of the (N−1)-order column vector {x.sub.N-1} in the N-th column of the matrix A are compared with all of the remaining components except for the components of the (N−1)-order column vector of the distance {d.sub.N-1} and the components in the N-th column of the matrix A, thereby determining whether components having coincident values are present.

[0053] As a result of the determination, in a case where components having coincident values are not present (all components of vector {x.sub.N-1} are not coincident with components of distances {d.sub.N-1} of reflection signals and components of column vectors in first to (N−1)-th columns of matrix A) (“Yes” in step S04.sub.N), the N-th reflection signal is identified as being reflection from the terminal portion 51 of the optical fiber to be measured 50 (step S05.sub.N).

[0054] In contrast, as a result of the determination, in a case where components having coincident values are present (all components of vector {x.sub.N-1} are coincident with any of components of distances {d.sub.N-1} of reflection signals and components of column vectors in first to (N−1)-th columns of matrix A) (“No” in step S04.sub.N), it is determined that the N-th reflection signal is caused by multiple reflection.

[0055] In a case where it is determined that the N-th reflection signal is caused by multiple reflection, the measurement data analysis unit 13 then performs determination of the (N−1)-th reflection signal (step S04.sub.N-1) in order to identify the terminal portion 51 of the optical fiber to be measured 50. The determination of the (N−1)-th reflection signal is performed in the following manner.

[0056] A vector {x.sub.N-2} that indicates relative distances between the (N−1)-th reflection signal and each of the other reflection signals (except for N-th reflection signal) becomes (N−2)-order column vector in the (N−1)-th column of the matrix A in the expression (3). The vector {x.sub.N-2} is in an expression (6).

[00008]$\begin{array}{cc}\left[\mathrm{Math}.6\right]& \\ \left\{x_{N-2}\right\}=\left(\begin{array}{c}\Delta x_{N-11}\\ \Delta x_{N-12}\\ .Math.\\ \Delta x_{N-1j}\\ .Math.\\ \Delta x_{N-1N-2}\end{array}\right)& \left(6\right)\end{array}$

[0057] Next, as distances among the reflection signals except for the N-th reflection signal and the (N−1)-th reflection signal, distances {d.sub.N-2} between the reflection from the connection point with the optical fiber to be measured 50 at the port of the OTDR 11 and each of the N−1 reflection signals are in an expression (7).

[00009]$\begin{array}{cc}\left[\mathrm{Math}.7\right]& \\ \left\{d_{N-2}\right\}=\left(\begin{array}{c}{x}_1\\ x_2\\ .Math.\\ x_i\\ .Math.\\ x_{N-2}\end{array}\right)& \left(7\right)\end{array}$

In other words, distances between any two of the reflection signals except for the reflection from the connection point at the port of the OTDR 11, the N-th reflection, and the (N−1)-th reflection are all of remaining components except for the components in the N-th column and the (N−1)-th column of the matrix A.

[0058] Likewise, the components of the (N−2)-order column vector {x.sub.N-2} in the (N−1)-th column of the matrix A are compared with all of the remaining components except for the components of the (N−2)-order column vector of the distances {d.sub.N-2} and the components in the N-th column and the (N−1)-th column of the matrix A, thereby determining whether components having coincident values are present.

[0059] As a result of the determination, in a case where components having coincident values are not present (all components of vector {x.sub.N-2} are not coincident with components distances {d.sub.d-2} of reflection signals and components of column vectors in first to (N−2)-th columns of matrix A) (“Yes” in step S04.sub.N-1), the (N−1)-th reflection signal is identified as being reflection from the terminal portion 51 of the optical fiber to be measured 50 (step S05.sub.N-1).

[0060] In contrast, as a result of the determination, in a case where components having coincident values are present (all components of vector {x.sub.N-2} are coincident with any of components of distances {d.sub.N-2} of reflection signals and components of column vectors in first to (N−2)-th columns of matrix A) (“No” in step S04.sub.N-1), it is determined that the (N−1)-th reflection signal is caused by multiple reflection.

[0061] In a case where the (N−1)-th reflection signal is also caused by multiple reflection, the measurement data analysis unit 13 then performs determination of the (N−2)-th reflection signal. In the above-described manner, the measurement data analysis unit 13 sequentially performs determination in order from the N-th reflection signal farthest from the OTDR 11.

[0062] Likewise, in a case where determination is performed on an i-th reflection signal (step S04.sub.i), when the reflection signal is a reflection signal from the terminal portion 51 of the optical fiber to be measured 50 (“Yes” in step S04.sub.i), all components of an (N−i)-order column vector in an i-th column of the matrix A in an expression (8) are not coincident with all components of (i−1)-order column vector in an expression (9) as distances of up to (i−1)-th reflection signal, and all of components of the column vectors in the first to (i−1)-th columns of the matrix A.

[00010]$\begin{array}{cc}\left[\mathrm{Math}.8\right]& \\ \left\{x_{i-1}\right\}=\left(\begin{array}{c}\Delta x_{i1}\\ \Delta x_{i2}\\ .Math.\\ \Delta x_{\mathrm{ii}-1}\end{array}\right)& \left(8\right)\end{array}$$\begin{array}{cc}\left[\mathrm{Math}.9\right]& \\ \left\{d_{i-1}\right\}=\left(\begin{array}{c}{x}_1\\ x_2\\ .Math.\\ x_{i-1}\end{array}\right)& \left(9\right)\end{array}$

[0063] As described above, using the determination flow in FIG. 3 makes it possible to identify that N reflection signals are present in the OTDR waveform and the i-th reflection signal counted from the port of the OTDR 11 is reflection from the terminal portion 51 of the optical fiber to be measured 50.

[0064] When the above-described method is applied to the OTDR waveform illustrated in FIG. 2, fourth to sixth reflection signals are determined as reflection signals caused by multiple reflection, and a third reflection signal is identified as a reflection signal from the terminal portion 51 of the optical fiber.

Embodiment 2

[0065] In the present embodiment, another example of the determination operation is described.

[0066] In the determination operation according to the present embodiment, multiple reflection and reflection from the terminal portion 51 are identified based on reflectance distribution acquired at a plurality of wavelengths, in place of the premise condition “distance from OTDR 11 to each of reflection signals is not equal to distance between reflection signals” for the determination operation described in Embodiment 1.

[0067] As a principle of the determination operation according to the present embodiment, it is determined whether a reflection signal present in a certain acquired distance is present common to all of measurement wavelengths. The farthest reflection signal present in the distance common to all of the measurement wavelengths is a reflection signal from the terminal portion 51 of the optical fiber, and reflection signals farther from the reflection signal are all reflection signals caused by multiple reflection. This is established on an assumption that at least one measurement wavelength at which the reflection signal caused by multiple reflection does not appear exists.

[0068] A terminal determination device according to the present embodiment has the configuration same as the configuration of the terminal determination device 301 described in Embodiment 1. The terminal determination device according to the present embodiment is different in the analysis method by the measurement data analysis unit 13 from the terminal determination device 301.

[0069] FIG. 4 is a flowchart illustrating a terminal determination method performed by the terminal determination device according to the present embodiment. Step S11 corresponds to the work 1 to the work 4 described in Embodiment 1. To acquire reflectance distribution at the plurality of wavelengths, the OTDR 11 causes test light with the plurality of wavelengths to enter the optical fiber to be measured 50.

[0070] After the OTDR waveform at each of the wavelengths is measured, the measurement data analysis unit 13 acquires distances of the reflection signals at each of the wavelengths (step S12). Next, determination is performed on the reflection signals at each of the wavelengths. The determination is performed in order from the reflection signal farthest from the OTDR 11 based on the above-described principle of the determination operation (step S13.sub.N). In a case where the reflection signal of the target distance is present common to the reflectance distribution of all of the wavelengths (“Yes” in step S13.sub.N), the N-th reflection signal is identified as being reflection from the terminal portion 51 of the optical fiber to be measured 50 (step S14.sub.N). The measurement data analysis unit 13 ends the determination operation at a time when the reflection signal from the terminal portion 51 of the optical fiber to be measured 50 is identified.

[0071] In contrast, in a case where the reflection signal of the target distance is not present common to all of the measurement wavelengths (“No” in step S13.sub.N), it is determined that the N-th reflection signal is a reflection signal caused by multiple reflection. In a case where it is determined that the N-th reflection signal is caused by multiple reflection, the measurement data analysis unit 13 performs determination of next farthest reflection signal (step S13.sub.N-1). In step S13.sub.N-1, the determination is also performed in a manner similar to step S13.sub.N, and it is determined whether the (N−1)-th reflection signal is reflection from the terminal portion 51 of the optical fiber to be measured 50, or is caused by multiple reflection.

[0072] As described above, the measurement data analysis unit 13 performs the determination in order from the reflection signal farthest from the OTDR 11 (step S13.sub.i), and identifies the reflection signal that is first determined to be present in the distance common to all of the measurement wavelengths, as the reflection signal from the terminal portion 51 of the optical fiber to be measured 50 (step S14.sub.i). Other reflection signals are caused by multiple reflection. Therefore, the measurement data analysis unit 13 ends the determination operation at a time when the reflection signal from the terminal portion 51 of the optical fiber to be measured 50 is identified.

[0073] FIG. 5 is a diagram illustrating reflectance distribution (OTDR waveforms) acquired by the OTDR 11 according to the present embodiment. FIGS. 5(a), 5(b), and 5(c) respectively illustrate the reflectance distribution at the measurement wavelengths of 1310 nm, 1550 nm, and 1650 nm. A pulse width of the test light and the number of averaging times of the measurement are respectively 10 ns and 2.sup.13 (=8192) as in Embodiment 1.

[0074] Fourth to sixth reflection signals in the OTDR waveform in each of FIG. 5(b) and FIG. 5(c) are not present in the OTDR waveform in FIG. 5(a). Therefore, these reflection signals are determined as reflection signals caused by multiple reflection. On the other hand, a third reflection signal in the OTDR waveform is present at a distance common to the OTDR waveforms at all of the measurement wavelengths in FIGS. 5(a) to 5 (c). Therefore, the third reflection signal can be identified as a reflection signal from the terminal portion 51 of the optical fiber.

OTHER EMBODIMENTS

[0075] The measurement data analysis unit 13 can be realized by a computer and programs, and the programs can be recorded in a recording medium or provided through a network.

[0076] (Effects)

[0077] According to the present invention, in the mode in which the OTDR 11 and the optical fiber to be measured 50 are connected at the bent portion, even in the case where the reflection signal caused by multiple reflection appears in the OTDR waveform, it is possible to identify the reflection signal from the terminal portion 51 of the optical fiber.

INDUSTRIAL APPLICABILITY

[0078] The present invention is applicable to a work in which, in an optical line in a PON (Passive Optical Network) mode, test light is caused to enter an optical fiber on a downstream of an external branch splitter, from a side of the optical fiber, to determine a terminal state of a target optical fiber on a user home side, from an arbitrary position on the downstream of the external branch splitter.

REFERENCE SIGNS LIST

[0079] 11 Optical reflectance distribution measurement device (OTDR) [0080] 11a GRIN lens [0081] 11b Probe optical fiber [0082] 12 Side light input/output unit [0083] 12a Concave block [0084] 12b Convex block [0085] 13 Measurement data analysis unit [0086] 50 Optical fiber to be measured [0087] 51 Terminal portion [0088] 301 Terminal determination device