Optical characteristic evaluation device and method

Abstract

An optical characteristic evaluation device 20 according to the present disclosure comprises: a test light generation unit 30 that generates test light; an input / output unit 40 that injects the test light in a given polarization state into one end of an optical fiber 10 under test, and acquires, from the one end, backscattered light from points along the optical fiber 10 under test and outputs the backscattered light; a backscattered light complex electric field amplitude acquisition unit 50 that acquires, for each point along the optical fiber 10 under test, the complex electric field amplitude of the backscattered light output from the input / output unit 40; and an arithmetic processing unit 60 that converts the complex electric field amplitude into a matrix for each point along the optical fiber 10 under test and evaluates polarization-dependent loss using the singular values of the matrix.

Description

Optical property evaluation apparatus and method

[0001] The present disclosure relates to a technique for evaluating optical properties of an optical fiber.

[0002] In communication using an optical fiber, optical power loss occurs due to various causes. Conventionally, such optical power loss has been evaluated. For example, mode-dependent loss (MDL: Mode Dependent Loss) is one of the important parameters of a transmission system using a multi-core fiber and a few-mode fiber (hereinafter sometimes referred to as a "space division multiplexing fiber" in this specification). Since the mode-dependent loss depends on external factors applied to the transmission line, it is necessary to identify abnormal locations of the mode-dependent loss during transmission line construction and operation.

[0003] As a conventional technique for evaluating polarization-dependent loss, for example, as shown in Non-Patent Document 1, light in various polarization states is incident on the measured single-mode fiber, and the polarization-dependent loss of the entire measured single-mode fiber is evaluated from the transmitted light intensity output from the measured single-mode fiber. A method is known.

[0004] As a conventional technique for evaluating mode-dependent loss, for example, Non-Patent Document 2 discloses a method of estimating the transfer matrix of the entire measured space division multiplexing fiber and evaluating the mode-dependent loss of the entire measured space division multiplexing fiber based on the complex electric field amplitude of the propagated light output from the measured space division multiplexing fiber.

[0005] B. Koch1, R. Noe1, V. Mirvoda1, D. Sandel and M. F. Panhwar, 2014 OptoElectronics and Communication Conference and Australian Conference on Optical Fiber Technology, July 2014, “Simple polarization-dependent loss measurement based on polarization scrambling” N. K. Fontaine; Roland Ryf; Miquel A. Mestre; Binbin Guan; Xavi Palou; Sebastian Randel, 2013 Optical Fiber Communication Conference and Exposure and the National Fiber Optic Engineers Conference (OFC / NFOEC), “Characterization of Space-Division Multiplexing Systems using a Swept-Wavelength Interferometer”

[0006] In the technique described in Non-Patent Document 1, the polarization-dependent loss is obtained from the light input from one end of the single-mode fiber under test and output from the other end. Therefore, it was not possible to evaluate the polarization-dependent loss with a single-end measurement. Furthermore, the technique in Non-Patent Document 1 evaluates the polarization-dependent loss of the entire transmission line. Consequently, the technique in Non-Patent Document 1 could not identify abnormal locations of polarization-dependent loss in the transmission line.

[0007] According to the technology disclosed in Non-Patent Document 2, it is possible to evaluate the mode-dependent loss over the entire length of the spatial division multiplexed fiber under test. However, the technology disclosed in Non-Patent Document 2 could not identify the location of abnormalities in the mode-dependent loss in the transmission line.

[0008] To solve the aforementioned problems, the first objective of this disclosure is to provide a technology that enables the evaluation of polarization-dependent loss at each point in an optical fiber by single-end measurement.

[0009] Furthermore, in order to solve the aforementioned problems, a second objective of this disclosure is to provide a technology that can evaluate mode-dependent loss at each point in an optical fiber.

[0010] To achieve the first objective described above, the optical property evaluation apparatus and method of this disclosure employ a method of matrixing the complex electric field amplitude at each point in the optical fiber under test and evaluating the polarization-dependent loss using the singular values ​​of the matrix.

[0011] Specifically, the optical property evaluation apparatus of this disclosure comprises: a test light generation unit that generates test light; an input / output unit that incidents the test light from one end of the optical fiber under test in an arbitrary polarization state and acquires and outputs backscattered light from each point of the optical fiber under test from the one end; a backscattered light complex electric field amplitude acquisition unit that acquires the complex electric field amplitude of the backscattered light output from the input / output unit for each point of the optical fiber under test; and a calculation processing unit that, for each point of the optical fiber under test, creates a matrix of the complex electric field amplitude and evaluates the polarization-dependent loss using the singular values ​​of the matrix.

[0012] In the above configuration, the calculation processing unit calculates the complex electric field amplitude E' of the backscattered light in the X-polarization state when the test light is incident from one end of the optical fiber under test in a predetermined X-polarization state. Ｘｘ (z) and Y polarization states of backscattered light complex field amplitude E' Ｙｘ (z) and the complex electric field amplitude E' of the backscattered light in the X-polarized state when the test light is incident from one end of the optical fiber under test in a predetermined Y-polarized state. Ｘｙ (z) and Y polarization states of backscattered light complex field amplitude E' Ｙｙ Alternatively, a matrix H shown in equation (4) below may be constructed using (z) and and then subjected to singular value decomposition.

[0013] Furthermore, the arithmetic processing unit may use the ratio of singular values ​​in the matrix H to evaluate the polarization-dependent loss at any point in the optical fiber under test.

[0014] More specifically, the optical property evaluation method of this disclosure involves generating test light, injecting the test light into the optical fiber under test from one end in an arbitrary polarization state, acquiring and outputting backscattered light from each point in the optical fiber under test from the one end, acquiring the complex electric field amplitude of the output backscattered light for each point in the optical fiber under test, creating a matrix of the complex electric field amplitudes for each point in the optical fiber under test, and evaluating the polarization-dependent loss using the singular values ​​of the matrix.

[0015] The apparatus of this disclosure (for example, an optical property evaluation apparatus) can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided over a network. The program of this disclosure is a program that causes a computer to realize each function of the apparatus of this disclosure, and a program that causes a computer to execute each procedure of the method performed by the apparatus of this disclosure.

[0016] To achieve the second objective described above, the optical property evaluation apparatus and method of this disclosure employ a method of matrixing the complex electric field amplitude at each point in the optical fiber under test and evaluating the mode-dependent loss using the singular values ​​of the matrix.

[0017] Specifically, the optical property evaluation apparatus of this disclosure comprises: a test light generation unit that generates test light; an input / output unit that incidents the test light onto an optical fiber under test in an arbitrary propagation mode of the optical fiber under test from one end, and separates the backscattered light from each point in the optical fiber under test according to the propagation mode, acquires it from the one end, and outputs it; a backscattered light complex electric field amplitude acquisition unit that acquires the complex electric field amplitude of the backscattered light output from the input / output unit for each point in the optical fiber under test; and a calculation processing unit that, for each point in the optical fiber under test, matrices the complex electric field amplitude according to the propagation mode, and evaluates the mode-dependent loss using the singular values ​​of the matrix.

[0018] The distribution of the backscattered complex field amplitude at position z in the longitudinal direction of the optical fiber under measurement is E'. ｋｌIn the case represented as (z), the backscattered light complex electric field amplitude acquisition unit acquires the distribution of the backscattered light complex electric field amplitudes for any n propagation modes k corresponding to each of the n propagation modes l of the optical fiber under test when the test light is incident on it while switching modes to any n propagation modes l. The calculation processing unit may construct a matrix H shown in equation (24) described later and perform singular value decomposition based on the n × n sets of backscattered light complex electric field amplitude distributions acquired by the backscattered light complex electric field amplitude acquisition unit.

[0019] Furthermore, the optical fiber under test is a spatially divided multiplexed optical fiber, and the arithmetic processing unit may evaluate the mode-dependent loss at any point in the optical fiber under test using the ratio or variance of the singular values ​​of the matrix H.

[0020] The calculation processing unit can calculate the singular value λ for each point of the optical fiber under measurement for each of the n propagation modes using equation (21), which will be described later.

[0021] The backscattered light complex electric field amplitude acquisition unit may acquire n × n sets of the backscattered light complex electric field amplitude multiple times for each point in the optical fiber under measurement. In this embodiment, the calculation processing unit can use the complex electric field amplitudes acquired by the backscattered light complex electric field amplitude acquisition unit to construct multiple matrices for each point in the optical fiber under measurement, and perform averaging processing for each of the n singular values.

[0022] The calculation processing unit may calculate the ratio of the maximum and minimum values ​​in the averaged n singular values ​​for each point in the optical fiber under test. The calculation processing unit may also calculate the variance of the averaged n singular values ​​for each point in the optical fiber under test.

[0023] Furthermore, the backscattered light complex electric field amplitude acquisition unit may acquire the complex electric field amplitude for each point in the optical fiber under test multiple times. In this embodiment, the calculation processing unit uses the complex electric field amplitude acquired by the backscattered light complex electric field amplitude acquisition unit to construct a plurality of matrices for each point in the optical fiber under test, and uses the maximum and minimum values ​​of the n singular values ​​in each of the plurality of matrices to calculate the mode-dependent loss in each of the plurality of matrices for each point in the optical fiber under test, and can perform an averaging process of the calculated mode-dependent losses in each of the plurality of matrices for each point in the optical fiber under test.

[0024] More specifically, the optical property evaluation method of this disclosure involves generating test light, injecting the test light into an arbitrary propagation mode of the optical fiber under test from one end of the optical fiber under test, separating the backscattered light from each point in the optical fiber under test according to the propagation mode, acquiring and outputting it from the one end, acquiring the complex electric field amplitude of the backscattered light output from the input / output unit for each point in the optical fiber under test, creating a matrix of the complex electric field amplitudes for each point in the optical fiber under test according to the propagation mode, and evaluating the mode-dependent loss using the singular values ​​of the matrix.

[0025] The apparatus of this disclosure (for example, an optical property evaluation apparatus) can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided over a network. The program of this disclosure is a program that causes a computer to realize each function of the apparatus of this disclosure, and a program that causes a computer to execute each procedure of the method performed by the apparatus of this disclosure.

[0026] Furthermore, the above disclosures can be combined as much as possible.

[0027] According to this disclosure, polarization-dependent losses at each point in an optical fiber can be evaluated by one-end measurement.

[0028] According to this disclosure, mode-dependent losses at each point in an optical fiber can be evaluated.

[0029] This figure illustrates an overview of the optical property evaluation system according to an embodiment of the present disclosure. This figure illustrates the acquisition of the backscattered light complex electric field amplitude corresponding to each polarization state of the test light, where (A) shows the acquisition of the backscattered light complex electric field amplitude corresponding to the X polarization state, and (B) shows the acquisition of the backscattered light complex electric field amplitude corresponding to the Y polarization state. This figure illustrates an example of backscattered light intensity measurement using an OTDR. This figure illustrates the configuration of the optical property evaluation system according to an embodiment of the present disclosure. This figure illustrates the processing flow by the optical property evaluation system according to an embodiment of the present disclosure. This figure illustrates the acquisition of the backscattered light complex electric field amplitude corresponding to each propagation mode of the optical fiber under test, where (A) shows the acquisition of the backscattered light complex electric field amplitude corresponding to the first mode, and (B) shows the acquisition of the backscattered light complex electric field amplitude corresponding to the second mode. This figure illustrates the configuration of the optical property evaluation system according to an embodiment of the present disclosure. This figure illustrates the processing flow by the optical property evaluation system according to an embodiment of the present disclosure. This figure illustrates the configuration of the optical property evaluation system according to an embodiment of the present disclosure. This figure illustrates the processing flow by the optical property evaluation system according to an embodiment of the present disclosure. A specific example of a mode-dependent loss evaluation procedure is shown.

[0030] Embodiments of this disclosure will be described in detail below with reference to the drawings. However, this disclosure is not limited to the embodiments shown below. These examples are illustrative, and this disclosure can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. In this specification and in the drawings, components with the same reference numerals refer to the same components.

[0031] (First Embodiment) [Overview of Optical Characteristic Evaluation System] Figure 1 is a diagram illustrating the overview of the optical characteristic evaluation system 100. The optical characteristic evaluation system 100 acquires backscattered light based on the OTDR (Optical Time Domain Reflectometry) method. The optical characteristic evaluation system 100 comprises an optical fiber under test 10 and an optical characteristic evaluation device 20 that acquires and processes backscattered light corresponding to test light incident on the optical fiber under test 10. In this embodiment, the optical fiber under test 10 is any single-mode fiber. The optical characteristic evaluation device 20 comprises a test light generation unit 30, an input / output unit 40, a backscattered light complex electric field amplitude acquisition unit 50, and a calculation processing unit 60.

[0032] The test light generation unit 30 generates test light. The input / output unit 40 inputs the test light generated by the test light generation unit 30 to the optical fiber under test 10 in an arbitrary polarization state. The input / output unit 40 also separates the backscattered light from each point of the optical fiber under test 10 into each polarization and outputs it to the backscattered light complex electric field amplitude acquisition unit 50. The backscattered light complex electric field amplitude acquisition unit 50 calculates the complex electric field amplitude for each polarization at each point of the optical fiber under test 10. The calculation processing unit 60 calculates the polarization-dependent loss evaluation value at each point of the optical fiber under test 10.

[0033] In particular, the optical characteristic evaluation system 100 according to this embodiment inputs light from one end of the optical fiber 10 under test and acquires the complex electric field amplitude of the backscattered light from each point on the optical fiber 10 under test from that end. Then, the optical characteristic evaluation system 100 creates a matrix of the acquired complex electric field amplitudes and evaluates the polarization-dependent loss at each point on the optical fiber 10 under test from its singular values.

[0034] According to this embodiment, it is possible to identify abnormal locations of polarization-dependent loss in a single-mode fiber by measuring at one end.

[0035] As described above, the optical property evaluation apparatus 20 according to the present embodiment includes a test light generation unit 30 that generates test light, an input / output unit 40 that causes the test light to enter one end of the fiber under test 10 in an arbitrary polarization state and acquires and outputs the backward scattered light from each point of the fiber under test 10 from the one end, a backward scattered light complex electric field amplitude acquisition unit 50 that acquires the complex electric field amplitude of the backward scattered light output from the input / output unit 40 for each point of the fiber under test 10, and an arithmetic processing unit 60 that matrixes the complex electric field amplitude for each point of the fiber under test 10 and evaluates the polarization-dependent loss using the singular values of the matrix.

[0036] [Polarization-Dependent Loss Evaluation Procedure] Here, a specific polarization-dependent loss evaluation procedure will be described. First, the polarization-dependent loss is a parameter representing the loss difference when the fiber under test receives different losses for each polarization. When considering a transmission transfer matrix H as in the following equation (1), its singular value matrix Λ (a matrix having the losses λ １ , λ ２ as diagonal elements) represents the loss characteristics of each channel (polarization in the present disclosure). Therefore, by taking the ratio (λ ｍｉｎ / λ ｍａｘ ) of the maximum value and the minimum value of the diagonal components of the singular value matrix, it is possible to evaluate the loss difference between polarizations.

[0037] Next, a method for obtaining the transfer matrix H will be described. As shown in FIG. 2(A), the backward scattered light complex electric field amplitude acquisition unit 50 acquires the complex electric field amplitudes E' Ｘｘ (z) and E' Ｙｘ (z) of the backward scattered light in the X polarization state and the Y polarization state at the position z in the fiber longitudinal direction when test light in the X polarization state is input to the fiber under test 10. The complex electric field amplitudes E' Ｘｘ (z) and E' Ｙｘ (z) of the backward scattered light in the X polarization state and the Y polarization state are represented by the following equations (2-1) and (2-2). Note that E represents the complex electric field amplitude of the test light.

[0038] Furthermore, as shown in Figure 2(B), the backscattered light complex electric field amplitude acquisition unit 50 acquires the backscattered light complex electric field amplitude E' in the X-polarization and Y-polarization states in the longitudinal direction z of the fiber when test light in the Y-polarization state is input to the optical fiber 10 under test. Ｘｙ (z) and E' Ｙｙ (z) is obtained. The complex electric field amplitude E' of the backscattered light in the X-polarization state and the Y-polarization state. Ｘｙ (z) and E' Ｙｙ (z) is expressed by the following equations (3-1) and (3-2).

[0039] In practice, the backscattered light intensity corresponding to each polarization, as shown in Figure 3, is measured, and E' is used as backscattered light information at any point z. Ｘｘ (z), E' Ｙｘ (z), E' Ｘｙ (z) and E' Ｙｙ (z) is acquired by the backscattered light complex electric field amplitude acquisition unit 50.

[0040] Next, a method for evaluating polarization-dependent loss from the backscattered complex electric field amplitude obtained as described above will be explained. The arithmetic processing unit 60 matrixizes the backscattered complex electric field amplitudes for each polarization at each point of the optical fiber 10 under test as shown in equation (4) below. The arithmetic processing unit 60 performs singular value decomposition on each of the transfer matrices H at each point of the optical fiber 10 under test and calculates singular values ​​as shown in equation (1) above. Then, the arithmetic processing unit 60 evaluates the polarization-dependent loss at each point from the ratio of the maximum and minimum values ​​of the singular values.

[0041] As shown in equation (4) above, since H is given at any position z, it is possible to identify the location of polarization-dependent loss anomalies in a single-mode fiber by measuring at one end.

[0042] As described above, the arithmetic processing unit 60 calculates the complex electric field amplitude E' of the backscattered light in the X-polarized state when the test light is incident from one end of the optical fiber 10 under test in a predetermined X-polarized state. Ｘｘ (z) and Y polarization states of backscattered light complex field amplitude E' Ｙｘ(z) and the complex electric field amplitude E' of the backscattered light in the X-polarized state when the test light is incident from one end of the optical fiber 10 under test in a predetermined Y-polarized state. Ｘｙ (z) and Y polarization states of backscattered light complex field amplitude E' Ｙｙ Using (z) and , we construct the matrix H shown in equation (4) and perform singular value decomposition.

[0043] Furthermore, the arithmetic processing unit 60 evaluates the polarization-dependent loss at any point in the optical fiber 10 under test using the ratio of singular values ​​in matrix H.

[0044] [Configuration of the Optical Characteristics Evaluation System] Figure 4 is a diagram illustrating the configuration of the optical characteristics evaluation system. The test light generation unit 30 includes a light source 31 and an acousto-optic modulator 32. The light source 31 outputs continuous light. The acousto-optic modulator 32 generates test light pulses based on the continuous light from the light source 31.

[0045] The input / output unit 40 includes input / output devices 41 and 42, and an optical circulator 43. The test light pulse generated by the test light generation unit 30 is input to the optical fiber under test 10 via the input / output devices 41 and the optical circulator 43 in an arbitrary polarization state. The backscattered light from each point of the optical fiber under test 10 is separated into its respective polarizations via the optical circulator 43 and the input / output device 42.

[0046] The backscattered light complex electric field amplitude acquisition unit 50 comprises a pair of optical multiplexers 51A and 51B, a pair of photoelectric converters 52A and 52B, an AD converter 53, and a waveform analysis unit 54. Each of the pair of optical multiplexers 51A and 51B combines the backscattered light from the optical fiber 10 under test, separated into its respective polarizations, with the continuous light from the light source 31. Each of the pair of photoelectric converters 52A and 52B converts the combined light of each polarization into an electrical signal. The AD converter 53 converts the electrical signal from the photoelectric converter into a digital signal.

[0047] The waveform analysis unit 54 calculates the in-phase and quadrature-phase components of the combined light by performing a Hilbert transform on the digital signal from the AD converter 53. Then, the waveform analysis unit 54 calculates the complex electric field amplitude of each polarization at each point of the optical fiber 10 under test from the in-phase and quadrature-phase components of the combined light of each polarization.

[0048] In this embodiment, a means for obtaining complex electric field amplitude using a Hilbert transform has been described, but the scope of this disclosure is not limited thereto. For example, a Short Fourier transform may be applied to the combined light of each acquired polarization to obtain the complex electric field amplitude of the beat frequency component of the combined light. Alternatively, the in-phase and quadrature-phase components of the combined light of each polarization may be directly received using a 90-degree hybrid, and then these in-phase and quadrature-phase components may be converted into digital signals using a photoelectric converter and an AD converter to calculate the complex electric field amplitude.

[0049] In particular, in this embodiment, the input / output unit 40 is controlled to switch the polarization state when a test optical pulse is input, and the complex electric field amplitude corresponding to each polarization state at each point of the optical fiber 10 under test is acquired when a test optical pulse of each polarization state is incident.

[0050] The arithmetic processing unit 60 includes a polarization-dependent loss evaluation unit 61P. The polarization-dependent loss evaluation unit 61P calculates the transfer matrix at each point of the optical fiber 10 under test from the complex electric field amplitude corresponding to each polarization at each point of the optical fiber 10 under test when a test optical pulse for each polarization state is incident on it. The polarization-dependent loss evaluation unit 61P obtains a singular value matrix by singular value decomposition of the calculated transfer matrix at each point of the optical fiber 10 under test. The polarization-dependent loss evaluation unit 61P calculates a polarization-dependent loss evaluation value from the obtained singular value matrix.

[0051] In this embodiment, a means for acquiring the complex electric field amplitude of backscattered light based on the OTDR method has been described, but the scope of this disclosure is not limited thereto. For example, the complex electric field amplitude of the optical fiber 10 under test may be acquired using the OFDR (Optical Frequency Domain Reflectometry) method.

[0052] [Processing Flow of the Optical Characteristics Evaluation System] Figure 5 is a flowchart illustrating the processing flow of the optical characteristics evaluation system. In particular, steps S11 to S14, enclosed by the dotted line, correspond to the procedure for acquiring the complex electric field amplitude of backscattered light.

[0053] In step S11, the optical characteristic evaluation system 100 generates test light in the test light generation unit 30 and inputs the X-polarized test light from one end of the optical fiber 10 under test via the input / output unit 40.

[0054] In step S12, the optical characteristic evaluation system 100 acquires backscattered light corresponding to the test light in the X-polarized state from one end of the optical fiber 10 under test and sends it to the backscattered light complex electric field amplitude acquisition unit 50 via the input / output unit 40. The backscattered light complex electric field amplitude acquisition unit 50 acquires the complex electric field amplitude of the backscattered light at each point of the optical fiber 10 under test from the backscattered light corresponding to the test light in the X-polarized state.

[0055] In step S13, the optical characteristic evaluation system 100 generates test light in the test light generation unit 30 and inputs the Y-polarized test light from one end of the optical fiber 10 under test via the input / output unit 40.

[0056] In step S14, the optical characteristic evaluation system 100 acquires backscattered light corresponding to the test light in the Y-polarized state from one end of the optical fiber 10 under test and sends it to the backscattered light complex electric field amplitude acquisition unit 50 via the input / output unit 40. The backscattered light complex electric field amplitude acquisition unit 50 acquires the complex electric field amplitude of the backscattered light at each point of the optical fiber 10 under test from the backscattered light corresponding to the test light in the Y-polarized state.

[0057] In step S15, the arithmetic processing unit 60 of the optical characteristic evaluation system 100 calculates the transfer matrix at each point of the optical fiber 10 under test from the complex electric field amplitude of each polarization at each point of the optical fiber 10 under test that has been acquired. Then, the arithmetic processing unit 60 calculates the polarization-dependent loss evaluation value from the singular value matrix obtained by singular value decomposition of the calculated transfer matrix at each point of the optical fiber 10 under test.

[0058] The apparatus of this disclosure (for example, an optical property evaluation apparatus) can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided over a network. The program of this disclosure is a program that causes a computer to realize each function of the apparatus of this disclosure, and a program that causes a computer to execute each procedure of the method performed by the apparatus of this disclosure.

[0059] In the following embodiments, the optical fiber 10 under test will be referred to as the optical fiber 10 being measured.

[0060] (Second Embodiment) [Overview of Optical Characteristic Evaluation System] Figure 1 is a diagram illustrating the overview of the optical characteristic evaluation system 100. The optical characteristic evaluation system 100 acquires backscattered light based on the OTDR (Optical Time Domain Reflectometry) method. The optical characteristic evaluation system 100 comprises an optical fiber to be measured 10 and an optical characteristic evaluation device 20 that acquires and processes backscattered light corresponding to test light incident on the optical fiber to be measured 10. In this embodiment, the optical fiber to be measured 10 is a coupled two-core fiber (multicore optical fiber). However, the optical fiber to be measured 10 is not limited to being a multicore optical fiber, and the optical fiber to be measured 10 may be any spatial division multiplexed fiber. For example, the optical fiber to be measured 10 may be a multimode fiber. The optical characteristic evaluation device 20 comprises a test light generation unit 30, an input / output unit 40, a backscattered light complex electric field amplitude acquisition unit 50, and a calculation processing unit 60.

[0061] The test light generation unit 30 generates test light. The input / output unit 40 inputs the test light generated by the test light generation unit 30 to an arbitrary propagation mode of the optical fiber 10 under test. The input / output unit 40 also separates the backscattered light from each point of the optical fiber 10 under test into each propagation mode and outputs it to the backscattered light complex electric field amplitude acquisition unit 50. The backscattered light complex electric field amplitude acquisition unit 50 calculates the complex electric field amplitude for each propagation mode at each point of the optical fiber 10 under test. The calculation processing unit 60 calculates the mode-dependent loss evaluation value at each point of the optical fiber 10 under test.

[0062] In particular, the optical characteristic evaluation system 100 according to this embodiment inputs light from one end of the optical fiber 10 to be measured, and acquires the complex electric field amplitude of the backscattered light from each point on the optical fiber 10 to be measured from that end. Then, the optical characteristic evaluation system 100 creates a matrix of the acquired complex electric field amplitudes and evaluates the mode-dependent loss at each point on the optical fiber 10 to be measured from its singular values.

[0063] According to this embodiment, it is possible to identify abnormal locations of mode-dependent loss in a spatially multiplexed fiber by measuring at one end.

[0064] As described above, the optical characteristic evaluation apparatus 20 according to this embodiment comprises: a test light generation unit 30 that generates test light; an input / output unit 40 that incidents the test light onto an arbitrary propagation mode of the optical fiber 10 to be measured from one end of the optical fiber 10 to be measured, and separates the backscattered light from each point on the optical fiber 10 to be measured according to the propagation mode, acquires it from the aforementioned end, and outputs it; a backscattered light complex electric field amplitude acquisition unit 50 that acquires the complex electric field amplitude of the backscattered light output from the input / output unit 40 for each point on the optical fiber 10 to be measured; and a calculation processing unit 60 that, for each point on the optical fiber 10 to be measured, matrices the complex electric field amplitude according to the propagation mode and evaluates the mode-dependent loss using the singular values ​​of the matrix.

[0065] [Mode-Dependent Loss Evaluation Procedure] Here, we will explain the specific evaluation procedure for mode-dependent loss. First, mode-dependent loss is a parameter that represents the loss difference when different losses are experienced for each propagation mode in the optical fiber 10 under test. When considering the transmission matrix H as shown in equation (21) below, its singular value matrix Λ (loss for each propagation mode λ) １ , λ ２ , ..., λ ｎ The matrix (which has as its diagonal elements) represents the loss characteristics of each propagation mode. Therefore, the MDL, which is expressed as the ratio of the maximum and minimum values ​​of the singular value matrix, ｐ－ｐ :λ ｍｉｎ / λ ｍａｘ Using this, the difference in losses between modes, i.e., mode-dependent loss, can be evaluated. Furthermore, MDL, which is expressed as the variance of singular values, can be used. ｒｍｓMode-dependent loss can also be evaluated using V(λ). Note that the subscripts in the lower right of the complex electric field amplitude E' indicate the propagation mode of the test light input to the optical fiber 10 under test (right subscript), and the subscript on the left indicates the propagation mode of the backscattered light output from the optical fiber 10 under test (left subscript).

[0066] However, W and V' represent special unitary matrices. When an N×N matrix is ​​decomposed into singular values, it is decomposed into the form W (special unitary matrix) × Λ (singular value matrix) × V' (special unitary matrix).

[0067] Also, MDL ｒｍｓ This represents the variance of singular values. In V(λ), "V" stands for Variance and is unrelated to V' described in (21). The variance is given by each λ ｎ The average value of λ from λ ｍｅａｎ It is obtained by summing the squares of the results after subtracting [a certain value] and dividing by the number of data points n. For example, it can be expressed as follows: MDL ｒｍｓ = {(λ １ -λ ｍｅａｎ ) ２ + (λ ２ -λ ｍｅａｎ ) ２ +... +(λ ｎ -λ ｍｅａｎ ) ２} / n

[0068] Next, we will explain how to obtain the transfer matrix H. First, for simplicity, we will explain the acquisition of each component of the transfer matrix H by assuming that both the propagation mode of the test light input to the optical fiber 10 under test and the propagation mode of the backscattered light output from the optical fiber 10 under test consist of two modes: a first mode (subscript "1") and a second mode (subscript "2").

[0069] As shown in Figure 6(A), the backscattered light complex electric field amplitude acquisition unit 50 acquires the backscattered light complex electric field amplitude E' of the first mode and the second mode at position z in the longitudinal direction of the fiber when the test light is input to the first mode of the optical fiber 10 under measurement. １１ (z) and E' ２１(z) is obtained. The complex electric field amplitude E' of the backscattered light of the first and second modes. １１ (z) and E' ２１ (z) is expressed by the following equations (22-1) and (22-2). Note that E represents the complex electric field amplitude of the test light.

[0070] As shown in Figure 6(B), the backscattered light complex electric field amplitude acquisition unit 50 acquires the backscattered light complex electric field amplitude E' of the first mode and the second mode at position z in the longitudinal direction of the fiber when the test light is input to the second mode of the optical fiber 10 under measurement. １２ (z) and E' ２２ (z) is obtained. The complex electric field amplitude E' of the backscattered light of the first and second modes. １２ (z) and E' ２２ (z) is expressed by the following equations (23-1) and (23-2).

[0071] For simplicity, the above description assumes that both the propagation mode of the test light input to the optical fiber 10 under test and the propagation mode of the backscattered light output from the optical fiber 10 under test consist of two modes, a first mode and a second mode. However, the scope of this disclosure is not limited to this, and mode-dependent losses can be evaluated for any number of modes.

[0072] This section describes the case where both the propagation mode of the test light input to the optical fiber 10 under test and the propagation mode of the backscattered light output from the optical fiber 10 under test consist of an arbitrary N modes. In this case, the test light is input to one propagation mode i in the propagation modes (l = 1 to n) of the optical fiber 10 under test, and the complex electric field amplitude E' of the backscattered light at position z in the longitudinal direction of the fiber for all propagation modes (k = 1 to n) is described. １ｉ (z) ~ E' ｎｉ (z) is obtained. This is performed for all propagation modes (l = 1 to n) of the optical fiber 10 under test, and the backscattered optical field amplitude distribution E' is obtained in n × n sets. ｋｌ Get (z).

[0073] In practice, the backscattered light intensity corresponding to each propagation mode, as shown in Figure 3, is measured, and E' is used as backscattered light information at any point z. ｋｌ (z) is acquired by the backscattered light complex electric field amplitude acquisition unit 50.

[0074] The processing unit 60 calculates the backscattered light complex electric field amplitude distribution E' of each spatial mode at each point of the optical fiber 10 under measurement, as acquired as described above. ｋｌ The transfer matrix H is obtained by transforming (z) into a matrix as shown in equation (24) below.

[0075] Next, a method for evaluating mode-dependent loss based on the acquired transfer matrix H will be described. The arithmetic processing unit 60 performs singular value decomposition on each of the transfer matrix H at each point of the optical fiber 10 under test and calculates singular values ​​as shown in equation (21) above. Then, the arithmetic processing unit 60 calculates the ratio of the maximum and minimum values ​​of the singular values ​​(MDL ｐ－ｐ ), or the variance of singular values ​​(MDL ｒｍｓ Based on this, the mode-dependent loss at each point of the optical fiber 10 under test is evaluated.

[0076] As shown in equation (24) above, since the transfer matrix H is given at any position z, it is possible to identify the location of the mode-dependent loss in a spatially multiplexed fiber by measuring at one end.

[0077] As described above, the optical characteristic evaluation device 20 determines that the distribution of the backscattered light complex electric field amplitude at position z in the longitudinal direction of the optical fiber 10 under measurement is E'. ｋｌ In the case represented as (z), the backscattered complex electric field amplitude acquisition unit 50 acquires the distribution of backscattered complex electric field amplitudes for any n propagation modes k corresponding to each of the n propagation modes l of the optical fiber 10 under test when test light is incident on it while switching modes to any n propagation modes l. The calculation processing unit 60 constructs the matrix H shown by equation (24) and performs singular value decomposition based on the n × n sets of backscattered complex electric field amplitude distributions acquired by the backscattered complex electric field amplitude acquisition unit 50.

[0078] Furthermore, the optical fiber 10 under test is a spatially divided multiplexed optical fiber, and the arithmetic processing unit 60 evaluates the mode-dependent loss at any point in the optical fiber 10 under test using the ratio or variance of singular values ​​in the transfer matrix H.

[0079] [Configuration of the Optical Characteristics Evaluation System] Figure 7 is a diagram illustrating the configuration of the optical characteristics evaluation system 100. The test light generation unit 30 includes a light source 31 and an acousto-optic modulator 32. The light source 31 outputs continuous light. The acousto-optic modulator 32 generates test light pulses based on the continuous light from the light source 31.

[0080] The input / output unit 40 includes input / output devices 41 and 42, and an optical circulator 43. The test light pulse generated by the test light generation unit 30 is input to any propagation mode of the optical fiber 10 under test via the input / output device 41 and the optical circulator 43. The backscattered light from each point of the optical fiber 10 under test is separated into each propagation mode via the optical circulator 43 and the input / output device 42.

[0081] The backscattered light complex electric field amplitude acquisition unit 50 comprises a pair of optical multiplexers 51A and 51B, a pair of photoelectric converters 52A and 52B, an AD converter 53, and a waveform analysis unit 54. Each of the pair of optical multiplexers 51A and 51B combines the backscattered light from the optical fiber 10 under test, separated into each propagation mode, with the continuous light from the light source 31. Each of the pair of photoelectric converters 52A and 52B converts the combined light of each propagation mode into an electrical signal. The AD converter 53 converts the electrical signals from the photoelectric converters 52A and 52B into digital signals.

[0082] The waveform analysis unit 54 calculates the in-phase and quadrature-phase components of the combined wave by performing a Hilbert transform on the digital signal from the AD converter 53. Then, the waveform analysis unit 54 calculates the complex electric field amplitude of each propagation mode at each point of the optical fiber 10 under measurement from the in-phase and quadrature-phase components of the composite wave of each propagation mode.

[0083] In this embodiment, a means for obtaining complex electric field amplitude using a Hilbert transform has been described, but the scope of this disclosure is not limited thereto. For example, a Short Fourier transform may be applied to the combined light of each propagation mode to obtain the complex electric field amplitude of the beat frequency component of the combined light. Alternatively, the in-phase and quadrature-phase components of the combined light of each propagation mode may be directly received using a 90-degree hybrid, and then the in-phase and quadrature-phase components may be converted into digital signals using a photoelectric converter and an AD converter to calculate the complex electric field amplitude.

[0084] In this embodiment, the above measurement is performed while switching the propagation mode into which the test light pulse is input, thereby obtaining the complex electric field amplitude of each propagation mode at each point of the optical fiber 10 under test when the test light pulse is incident on each propagation mode.

[0085] The arithmetic processing unit 60 includes a mode-dependent loss evaluation unit 61M. The mode-dependent loss evaluation unit 61M calculates the transfer matrix at each point of the optical fiber 10 under test from the complex electric field amplitude of each propagation mode at each point of the optical fiber 10 under test when a test optical pulse is incident on each propagation mode. The mode-dependent loss evaluation unit 61M obtains a singular value matrix by singular value decomposition of the calculated transfer matrix at each point of the optical fiber 10 under test. The mode-dependent loss evaluation unit 61M calculates a mode-dependent loss evaluation value from the obtained singular value matrix.

[0086] In this embodiment, a means for acquiring the complex electric field amplitude of backscattered light based on the OTDR method has been described, but the scope of this disclosure is not limited thereto. For example, the complex electric field amplitude of the fiber 10 under measurement may be acquired using the OFDR (Optical Frequency Domain Reflectometry) method.

[0087] [Processing Flow of the Optical Characteristics Evaluation System] Figure 8 is a flowchart illustrating the processing flow of the optical characteristics evaluation system 100. In particular, steps S21 to S24, enclosed by the dotted line, correspond to the procedure for acquiring the complex electric field amplitude of backscattered light.

[0088] In step S21, the optical property evaluation system 100 increments the variable i, which corresponds to the propagation mode of the optical fiber 10 under test. At the start of the processing flow, i is stored as 0. Therefore, subsequent processing is carried out by switching between propagation modes one by one, from the first propagation mode to the last propagation mode.

[0089] Here, the variable i may be stored, for example, in the memory of the backscattered light complex electric field amplitude acquisition unit 50. In this case, the backscattered light complex electric field amplitude acquisition unit 50 may refer to the current variable i and control which propagation mode the test light is input to.

[0090] In step S22, the optical characteristic evaluation system 100 inputs test light from one end of the optical fiber 10 to the i-th propagation mode of the optical fiber 10 to be measured, according to the current variable i.

[0091] In step S23, the backscattered light complex electric field amplitude acquisition unit 50 acquires the complex electric field amplitude of the backscattered light at each point on the optical fiber 10 to be measured from the backscattered light corresponding to the i-th propagation mode incident on the optical fiber 10 to be measured.

[0092] In step S24, the backscattered light complex electric field amplitude acquisition unit 50 incidents test light on all propagation modes of the optical fiber 10 under test and determines whether or not it has acquired the corresponding complex electric field amplitude. If the backscattered light complex electric field amplitude acquisition unit 50 determines that it has not acquired the complex electric field amplitude for all propagation modes (step S24: No), the optical characteristic evaluation system 100 repeats steps S21 to S24 until it has acquired the complex electric field amplitude for all propagation modes.

[0093] If the backscattered light complex electric field amplitude acquisition unit 50 determines that it has acquired the complex electric field amplitudes for all propagation modes (step S24: Yes), the calculation processing unit 60 calculates the transfer matrix at each point of the optical fiber 10 under test from the acquired complex electric field amplitudes for each propagation mode at each point of the optical fiber 10 under test. Then, the calculation processing unit 60 calculates a mode-dependent loss evaluation value from the singular value matrix obtained by singular value decomposition of the calculated transfer matrix at each point of the optical fiber 10 under test.

[0094] The apparatus of this disclosure (for example, an optical property evaluation apparatus) can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided over a network. The program of this disclosure is a program that causes a computer to realize each function of the apparatus of this disclosure, and a program that causes a computer to execute each procedure of the method performed by the apparatus of this disclosure.

[0095] (Third Embodiment) In general loss measurement using backscattered light, signal-to-noise ratio (SN) improvement is achieved by averaging the intensity waveforms acquired continuously. However, in the method described in Non-Patent Document 2, phase information is required in addition to the intensity information of the backscattered light. Since the phase information at each point of the optical fiber 10 under measurement changes with each measurement, it is not possible to perform averaging on the measurement waveform as in the conventional method. Therefore, in order to observe smaller MDL changes, a different SN improvement method is required.

[0096] On the other hand, the singular value of the transmission matrix H, which represents the characteristics of the transmission line, shows the same value regardless of the phase change for each measurement. Therefore, in this embodiment, the signal-to-noise ratio (SN) in the second embodiment is improved using the transmission matrix H.

[0097] Figure 9 shows an example of the system configuration of this embodiment. In this embodiment, the arithmetic processing unit 60 in the second embodiment comprises a propagation matrix calculation unit 62, a singular value average calculation unit 63, and a mode-dependent loss evaluation unit 61M.

[0098] (Test light generation unit 30) The test light generation unit 30 generates test light pulses. The method for generating test light pulses is arbitrary, but for example, continuous light from the light source 31 can be intensity-modulated using an acousto-optic modulator.

[0099] (Input / Output Unit 40) The input / output unit 40 inputs the test light pulse generated by the test light generation unit 30 to the desired propagation mode of the optical fiber 10 under test via the input / output device 41 and the optical circulator 43. Subsequently, the backscattered light from each point of the optical fiber 10 under test is separated into each propagation mode via the optical circulator 43 and the input / output device 42.

[0100] (Backscattered Light Complex Electric Field Amplitude Acquisition Unit 50) The backscattered light from the optical fiber 10 under test, separated into each propagation mode by the input / output unit 40, is combined with the continuous test light by the optical multiplexers 51A and 51B, respectively. The combined light of each propagation mode is converted into a digital signal by the photoelectric converters 52A and 52B and the AD converter 53. The waveform analysis unit 54 performs a Hilbert transform on the obtained combined light of each propagation mode to calculate the in-phase and orthogonal phase components of the combined light. The waveform analysis unit 54 calculates the complex electric field amplitude of each propagation mode at each point in the optical fiber 10 under test from the in-phase and orthogonal phase components of the combined light of each propagation mode.

[0101] In this embodiment, a means for acquiring complex electric field amplitude using a Hilbert transform has been described, but this embodiment is not limited thereto. For example, a Short Fourier transform may be applied to the combined light of each acquired propagation mode to obtain the complex electric field amplitude of the beat frequency component of the combined light. Alternatively, a 90° hybrid may be used to directly receive the in-phase and quadrature-phase components of the combined light of each propagation mode, convert them into digital signals using a photoelectric converter and an AD converter, and calculate the complex electric field amplitude. The propagation mode into which the test light pulse is input is switched, and the complex electric field amplitude of each propagation mode at each point in the optical fiber 10 under test is acquired when the test light pulse is incident on each propagation mode.

[0102] Figure 10 is a flowchart showing an example of the optical properties evaluation method of this embodiment. The optical properties evaluation method of this embodiment comprises steps S31 to S35.

[0103] (Procedure S31) The test light generation unit 30 generates test light, and the test light of an arbitrary propagation mode is incident from one end of the optical fiber 10 to be measured, which is a spatial division multiplexed fiber, via the input / output unit 40.

[0104] (Procedure S32) The optical characteristic evaluation device 20 sends the backscattered light from the optical fiber 10 to be measured to the backscattered light complex electric field amplitude acquisition unit 50 via the input / output unit 40. The backscattered light complex electric field amplitude acquisition unit 50 acquires the complex electric field amplitude of the backscattered light at each point on the optical fiber 10 to be measured from the backscattered light.

[0105] (Procedures S33 and S34) In this embodiment, light is input from one end of the optical fiber 10 to be measured (S31), and the complex electric field amplitude of the backscattered light from each point on the optical fiber 10 to be measured is acquired at the same end as the input (S32). Procedures S31 and S32 are performed for N averaging cycles (S33), and the complex electric field amplitudes of all propagation modes for N averaging cycles are acquired (S34). The order of the loop for acquiring the complex electric field amplitude of each mode (S33) and the loop for acquiring the complex electric field amplitude for the number of averaging cycles (S34) does not matter.

[0106] For example, in the propagation modes (l=1 to n) of the optical fiber 10 under test, a test light is input to one propagation mode i (S31), and the complex electric field amplitude E' in the longitudinal direction z of the fiber is calculated for all propagation modes (k=1 to n). １ｉ (z) ~ E' ｎｉ (z) is acquired (S32). This is performed N times for all propagation modes (l=1 to n) (S33, S34). As a result, the backscattered light complex electric field amplitude acquisition unit 50 acquires n × n sets of complex electric field amplitudes E' for each point z of the optical fiber 10 under measurement. ｋｌ (z) is obtained N times.

[0107] In the two mode measurements shown in Figure 6(A), the complex electric field amplitude E' is expressed by equations (22-1) and (22-2). １１ (z) and E' ２１ (z) is acquired by the backscattered light complex electric field amplitude acquisition unit 50. In the measurement of the two modes shown in Figure 6(B), the complex electric field amplitude E' is expressed by equations (23-1) and (23-2). １２ (z) and E' ２２ (z) is acquired by the backscattered light complex electric field amplitude acquisition unit 50. In this embodiment, these complex electric field amplitudes are acquired N times.

[0108] (Procedure S35) The calculation processing unit 60 calculates the complex electric field amplitude E' of the backscattered light for the number of averaging iterations. ｋｌ If (z) is obtained (Yes in S34), the mode-dependent loss evaluation procedure S35 is executed. Figure 11 shows a specific example of the mode-dependent loss evaluation procedure. The mode-dependent loss evaluation procedure comprises steps S351 to S355 in order.

[0109] (Procedure S351) The propagation matrix calculation unit 62 uses the complex electric field amplitudes acquired by the backscattered light complex electric field amplitude acquisition unit 50 to construct a plurality of matrices H for each point z of the optical fiber 10 under test. For example, the propagation matrix calculation unit 62 calculates the complex electric field amplitude distribution E' of each of the n spatial modes at each point z of the optical fiber 10 under test. ｋｌ (z) is transformed into an n × n matrix H as shown in equation (24). This creates N matrices H for each point z of the optical fiber 10 under measurement.

[0110] (Procedure S352) The singular value average calculation unit 63 decomposes the matrix H into a singular value matrix Λ as shown in formula (24). This yields n singular values ​​λ １ , λ ２ ,...λ ｎ This is obtained for each point z of the optical fiber 10 under measurement. That is, the longitudinal distribution λ(z) of the singular value λ is obtained.

[0111] (Procedure S353) Procedures S351 and S352 are repeated until the number of averaging steps N is reached. This yields the longitudinal distribution λ(z) of N singular values.

[0112] (Procedure S354) In this embodiment, N singular values ​​λ １ , N singular values ​​λ ２ ..., N singular values ​​λ ｎ However, this is obtained for each point z of the optical fiber 10 under measurement. The singular value average calculation unit 63 calculates the N singular value components λ １ , λ ２ ,...λ ｎ Then, an averaging process is performed for each singular value component. This results in N singular values ​​λ １ The average value, N singular values ​​λ ２ The average value, ..., N singular values ​​λ ｎ The average value is obtained for each point z of the optical fiber 10 under measurement. That is, the longitudinal distribution λ'(z) of the average value λ' of the singular values ​​is obtained.

[0113] Here, the type of averaging process in the singular value average calculation unit 63 is not specified. For example, averaging may be used, weighted averaging, or frequency averaging which averages singular values ​​obtained from multiple test light pulses of different frequencies can be used.

[0114] (Step S355) The singular value averaging unit 63 evaluates the mode-dependent loss using the averaged singular value λ'(z). (i) For example, the singular value averaging unit 63 evaluates the mode-dependent loss based on the ratio of the maximum value to the minimum value of the averaged singular value λ'(z). Specifically, the singular value averaging unit 63 calculates, for each point z of the measured optical fiber 10, the ratio of the maximum value to the minimum value among the n averaged singular values λ １ ', λ ２ ', …, λ ｎ '. (ii) For example, the singular value averaging unit 63 evaluates the mode-dependent loss based on the variance of the averaged singular value λ'(z). Specifically, the singular value averaging unit 63 calculates, for each point z of the measured optical fiber 10, the variance value of the n averaged singular values λ １ ', λ ２ ', …, λ ｎ '.

[0115] Note that the order of Step S354 and Step S355 is not limited to this. For example, Step S354 may be executed after Step S355. That is, the singular value averaging unit 63 may average after calculating the mode-dependent loss instead of averaging the singular values.

[0116] As described above, since the optical characteristic evaluation system of the present embodiment performs an averaging process on the singular value distribution, the SNR can be improved, and measurement of a smaller MDL and improvement of measurement accuracy can be realized.

[0117] (Fourth Embodiment) In the third embodiment, the singular value averaging unit 63 evaluated the mode-dependent loss using the averaged singular value λ'(z). Instead of this, in the present embodiment, the singular value averaging unit 63 sequentially executes the following processes.

[0118] (First Step) The singular value averaging unit 63 calculates the n singular values λ １ , λ ２ , ··· λ ｎUsing the maximum and minimum values, the mode-dependent loss in each of the N matrices H is calculated for each point z of the optical fiber 10 under test. This provides N mode-dependent losses for each point z of the optical fiber 10 under test.

[0119] (Second step) The singular value average calculation unit 63 performs an averaging process of the mode-dependent losses in each of the N calculated matrices H for each point z of the optical fiber 10 under test. As a result, the average value of the N mode-dependent losses is obtained for each point z of the optical fiber 10 under test.

[0120] (Other Embodiments) In the embodiments described above, a means for acquiring the complex electric field amplitude of backscattered light based on the OTDR method has been described, but this embodiment is not limited thereto. For example, the complex electric field amplitude of the spatial division multiplexed fiber under test may be acquired using OFDR.

[0121] The optical properties evaluation system described herein can be applied to the information and communication industry.

[0122] 10: Optical fiber under test 20: Optical property evaluation device 30: Test light generation unit 31: Light source 32: Acousto-optic modulator 40: Input / output unit 41, 42: Input / output devices 43: Optical circulator 50: Backscattered light complex field amplitude acquisition unit 51A, 51B: Optical multiplexer 52A, 52B: Photoelectric converter 53: AD converter 54: Waveform analysis unit 60: Calculation processing unit 61P: Polarization-dependent loss evaluation unit 61M: Mode-dependent loss evaluation unit 100: Optical property evaluation system

Claims

1. An optical characteristic evaluation apparatus comprising: a test light generation unit that generates test light; an input / output unit that incidents the test light from one end of an optical fiber under test in an arbitrary polarization state and acquires and outputs backscattered light from each point on the optical fiber under test from the one end; a backscattered light complex electric field amplitude acquisition unit that acquires the complex electric field amplitude of the backscattered light output from the input / output unit for each point on the optical fiber under test; and a calculation processing unit that creates a matrix of the complex electric field amplitudes for each point on the optical fiber under test and evaluates the polarization-dependent loss using the singular values ​​of the matrix.

2. The calculation processing unit calculates the complex electric field amplitude E' of the backscattered light in the X-polarization state when the test light is incident on the optical fiber under test from one end in a predetermined X-polarization state. Ｘｘ (z) and Y polarization states of backscattered light complex field amplitude E' Ｙｘ (z) and the complex electric field amplitude E' of the backscattered light in the X-polarized state when the test light is incident from one end of the optical fiber under test in a predetermined Y-polarized state. Ｘｙ (z) and Y polarization states of backscattered light complex field amplitude E' Ｙｙ An optical property evaluation apparatus according to claim 1, comprising constructing a matrix H represented by equation (C1) using (z) and and performing singular value decomposition. z: Position in the longitudinal direction of the optical fiber under test 3. The optical property evaluation apparatus according to claim 2, wherein the arithmetic processing unit evaluates the polarization-dependent loss at any point in the optical fiber under test using the ratio of singular values ​​in the matrix H.

4. An optical characteristic evaluation apparatus comprising: a test light generation unit that generates test light; an input / output unit that incidents the test light onto an optical fiber under test in an arbitrary propagation mode of the optical fiber under test from one end, and separates the backscattered light from each point in the optical fiber under test according to the propagation mode, acquires it from the one end, and outputs it; a backscattered light complex electric field amplitude acquisition unit that acquires the complex electric field amplitude of the backscattered light output from the input / output unit for each point in the optical fiber under test; and a calculation processing unit that, for each point in the optical fiber under test, matrices the complex electric field amplitude according to the propagation mode, and evaluates the mode-dependent loss using the singular values ​​of the matrix.

5. The distribution of the complex electric field amplitude of the backscattered light at position z in the longitudinal direction of the optical fiber under measurement is E'. ｋｌ In the case where (z) is used, the backscattered light complex electric field amplitude acquisition unit acquires the distribution of the complex electric field amplitudes of the backscattered light for any n propagation modes k corresponding to each of the n propagation modes l of the optical fiber under test when the test light is incident on it while switching modes to any n propagation modes l of the optical fiber under test, and the calculation processing unit constructs a matrix H shown by equation (C2) and performs singular value decomposition based on the n × n sets of backscattered light complex electric field amplitude distributions acquired by the backscattered light complex electric field amplitude acquisition unit, according to the optical property evaluation apparatus of claim 4. z: Position in the longitudinal direction of the optical fiber under measurement 6. The optical property evaluation apparatus according to claim 4, wherein the optical fiber under test is a spatially divided multiplexed optical fiber, and the arithmetic processing unit evaluates the mode-dependent loss at any point in the optical fiber under test using the ratio or variance of singular values ​​of the matrix H.

7. The optical property evaluation apparatus according to claim 5, wherein the calculation processing unit calculates the n propagation modes for each point of the optical fiber under measurement using the following formula. However, W and V' represent special unitary matrices.

8. The optical property evaluation apparatus according to claim 7, wherein the backscattered light complex electric field amplitude acquisition unit acquires the n × n sets of the complex electric field amplitude multiple times for each point of the optical fiber under test, and the calculation processing unit constructs a plurality of matrices for each point of the optical fiber under test using the complex electric field amplitudes acquired by the backscattered light complex electric field amplitude acquisition unit, and performs averaging processing for each of the n singular value components.

9. The optical property evaluation apparatus according to claim 8, wherein the calculation processing unit calculates the ratio of the maximum and minimum values ​​in the averaged n singular values ​​for each point in the optical fiber under measurement.

10. The optical property evaluation apparatus according to claim 8, wherein the calculation processing unit calculates the variance of the averaged n singular values ​​for each point on the optical fiber under measurement.

11. The optical characteristic evaluation apparatus according to claim 7, wherein the backscattered light complex electric field amplitude acquisition unit acquires the complex electric field amplitude multiple times for each point of the optical fiber under test, the calculation processing unit constructs a plurality of matrices for each point of the optical fiber under test using the complex electric field amplitudes acquired by the backscattered light complex electric field amplitude acquisition unit, calculates the mode-dependent loss for each of the plurality of matrices for each point of the optical fiber under test using the maximum and minimum values ​​of the n singular values ​​in each of the plurality of matrices, and performs an averaging process of the calculated mode-dependent losses for each of the plurality of matrices for each point of the optical fiber under test.

12. An optical characteristic evaluation method comprising: generating test light; injecting the test light into an optical fiber under test from one end in an arbitrary polarization state; acquiring and outputting backscattered light from each point in the optical fiber under test from the one end; acquiring the complex electric field amplitude of the output backscattered light for each point in the optical fiber under test; creating a matrix of the complex electric field amplitudes for each point in the optical fiber under test; and evaluating the polarization-dependent loss using the singular values ​​of the matrix.

13. An optical characteristic evaluation method comprising: generating test light; injecting the test light into an arbitrary propagation mode of the optical fiber under test from one end of the optical fiber under test; separating the backscattered light from each point in the optical fiber under test according to the propagation mode, acquiring it from the one end and outputting it; acquiring the complex electric field amplitude of the output backscattered light for each point in the optical fiber under test; creating a matrix of the complex electric field amplitudes for each point in the optical fiber under test according to the propagation mode; and evaluating the mode-dependent loss using the singular values ​​of the matrix.

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