Optical property evaluation device and method

Abstract

An optical property 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 inputs the test light from one end of an optical fiber 10 under test in any polarization state, and acquires and outputs, from the one end, backscattered light from each point of the optical fiber 10 under test; a backscattered light complex electric field amplitude acquisition unit 50 that acquires, for each point of the optical fiber 10 under test, a 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 of the optical fiber 10 under test, and evaluates polarization dependent loss using a singular value of the matrix.

Description

Apparatus and method for evaluating optical properties

[0001] This disclosure relates to a technique for evaluating the optical properties of optical fibers.

[0002] In optical fiber communication, optical power loss occurs due to various reasons. Evaluating such optical power loss has been a common practice. For example, polarization-dependent loss (PDL) is one of the important parameters in transmission systems using single-mode fiber. Since polarization-dependent loss depends on external factors acting on the transmission line, it is necessary to identify abnormalities in polarization-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, a method is known in which light with various polarization states is incident on a single-mode fiber under test, and the polarization-dependent loss of the entire single-mode fiber under test is evaluated from the transmitted light intensity output from the single-mode fiber under test.

[0004] However, the technique described in Non-Patent Document 1 involves inputting light from one end of the single-mode fiber under test and obtaining polarization-dependent loss from the light output from the other end. Therefore, it was not possible to evaluate polarization-dependent loss with a single-end measurement. Furthermore, the technique described in Non-Patent Document 1 evaluates polarization-dependent loss for the entire transmission line. Consequently, the technique described in Non-Patent Document 1 could not identify abnormal locations in polarization-dependent loss within the transmission line.

[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”

[0006] To solve the aforementioned problems, this disclosure aims to provide a technology that enables the evaluation of polarization-dependent loss at each point in an optical fiber by single-end measurement.

[0007] To achieve the above objective, the optical property evaluation apparatus and method of this disclosure employ a method in which the complex electric field amplitude is matrixed for each point of the optical fiber under test, and the polarization-dependent loss is evaluated using the singular values ​​of the matrix.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] Furthermore, the above disclosures can be combined as much as possible.

[0014] According to this disclosure, polarization-dependent losses at each point in an optical fiber can be evaluated by one-end measurement.

[0015] 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 complex electric field amplitude of backscattered light corresponding to each polarization state of the test light, where (A) shows the acquisition of the complex electric field amplitude of backscattered light corresponding to the X polarization state, and (B) shows the acquisition of the complex electric field amplitude of backscattered light 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.

[0016] 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.

[0017] [Overview of the Optical Characteristics Evaluation System] Figure 1 is a diagram illustrating the overview of the optical characteristics evaluation system 100. The optical characteristics evaluation system 100 acquires backscattered light based on the OTDR (Optical Time Domain Reflectometry) method. The optical characteristics evaluation system 100 comprises an optical fiber under test 10 and an optical characteristics evaluation device 20 that acquires and processes backscattered light corresponding to the test light incident on the optical fiber under test 10. The optical fiber under test 10 is any single-mode fiber. The optical characteristics 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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 inputs the test light into 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 forms a matrix of the complex electric field amplitudes for each point of the fiber under test 10 and evaluates the polarization-dependent loss using the singular values of the matrix.

[0022] [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 shown 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.

[0023] 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 the 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). Here, E represents the complex electric field amplitude of the test light.

[0024] 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).

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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 backward scattered light in the X polarization state when test light is incident from one end of the test optical fiber 10 in a predetermined Y polarization state Ｘｙ (z) and the complex electric field amplitude E' of the backward scattered light in the Y polarization state Ｙｙ (z) and are used to construct the matrix H shown in Equation (4) and perform singular value decomposition.

[0029] Further, the arithmetic processing unit 60 evaluates the polarization-dependent loss at an arbitrary point of the test optical fiber 10 using the ratio of the singular values of the matrix H.

[0030] [Configuration of Optical Characteristic Evaluation System] FIG. 4 is a diagram for explaining the configuration of the optical characteristic 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.

[0031] The input / output unit 40 includes input / output devices 41, 42, and an optical circulator 43. The test light pulses generated by the test light generation unit 30 are input to the test optical fiber 10 in an arbitrary polarization state via the input / output device 41 and the optical circulator 43. The backward scattered light from each point of the test optical fiber 10 is separated into each polarization via the optical circulator 43 and the input / output device 42.

[0032] The backward scattered light complex electric field amplitude acquisition unit 50 includes 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 multiplexes the backward scattered light from the test optical fiber 10 separated into each polarization 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.

[0033] The waveform analysis unit 54 calculates the in-phase component and the quadrature phase component of the combined light by performing a Hilbert transform on the digital signal from the AD converter 53. Moreover, the waveform analysis unit 54 calculates the complex electric field amplitude of each polarization at each point of the test optical fiber 10 from the in-phase component and the quadrature phase component of the combined light of each polarization.

[0034] Note that, in this embodiment, the complex electric field amplitude acquisition means using Hilbert transform has been described, but the scope of the present disclosure is not limited thereto. For example, a short Fourier transform may be applied to the combined light of each polarization wave obtained, and the complex electric field amplitude of the beat frequency component of the combined light may be obtained. Further, after directly receiving the in-phase component and the quadrature phase component of the combined light of each polarization wave using a 90-degree hybrid, the in-phase component and the quadrature phase component may be converted into digital signals using a photoelectric converter and an AD converter, and the complex electric field amplitude may be calculated.

[0035] In particular, in this embodiment, while switching the polarization state when inputting the test light pulse by controlling the input / output unit 40, the complex electric field amplitude corresponding to each polarization state at each point of the test optical fiber 10 when the test light pulse in each polarization state is incident is acquired.

[0036] The arithmetic processing unit 60 includes a polarization-dependent loss evaluation unit 61. The polarization-dependent loss evaluation unit 61 calculates the transfer matrix at each point of the test optical fiber 10 from the complex electric field amplitude corresponding to each polarization at each point of the test optical fiber 10 when the test light pulse in each polarization state is incident. The polarization-dependent loss evaluation unit 61 acquires a singular value matrix by performing singular value decomposition on the calculated transfer matrix at each point of the test optical fiber 10. The polarization-dependent loss evaluation unit 61 calculates a polarization-dependent loss evaluation value from the acquired singular value matrix.

[0037] Note that, in this embodiment, the complex electric field amplitude acquisition means of the backscattered light based on the OTDR method has been described, but the scope of the present disclosure is not limited thereto. For example, the complex electric field amplitude of the test optical fiber 10 may be acquired using an OFDR (Optical Frequency Domain Reflectometry) method.

[0038] [Processing Flow of Optical Characteristic Evaluation System] FIG. 5 is a flowchart for explaining the processing flow of the optical characteristic evaluation system. In particular, steps S1 to S4 surrounded by a dotted line correspond to the procedure for acquiring the complex electric field amplitude of the backscattered light.

[0039] In step S1, 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.

[0040] In step S2, 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.

[0041] In step S3, the optical property evaluation system 100 generates test light in the test light generation unit 30 and inputs the test light in a Y-polarized state from one end of the optical fiber 10 under test via the input / output unit 40.

[0042] In step S4, 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.

[0043] In step S5, 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.

[0044] 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.

[0045] The optical properties evaluation system described herein can be applied to the information and communication industry.

[0046] 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 61: Polarization-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 method comprising: 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.

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