Analytical apparatus, measurement system, measurement method and procedure

Abstract

The purpose of this disclosure is to reduce instrument noise without complicating the receiving system or increasing analysis time. This disclosure uses multiple spectral data measured at different times by the same OFDR instrument to generate a spectrum representing the time-varying frequency characteristics, and filters the spectrum in both the time and frequency directions.

Description

Technical Field

[0001] This disclosure relates to techniques for analyzing the spectrum of backscattered light in an optical fiber. Background Technology

[0002] By measuring the time-series data (spectral graph) of the Rayleigh backscattered light spectrum in an optical fiber using OFDR (Optical Frequency Domain Reflectometry), and analyzing the spectral shift, temperature strain sensing can be performed (Non-Patent Literature 1, 2). However, in the presence of phase noise in the laser used in OFDR, the spectral structure changes at each moment, deteriorating reproducibility. Therefore, the phase noise of the laser becomes the noise in the analysis of spectral shift caused by temperature strain.

[0003] Non-Patent Document 3 proposes a technique for monitoring and compensating for the phase noise of a laser while simultaneously sensing temperature strain. However, because the technique in Non-Patent Document 3 adds a receiving channel for monitoring, it leads to increased complexity in the receiving system and extended analysis time due to heavy signal processing.

[0004] Existing technical documents

[0005] Non-patent literature

[0006] Non-patent document 1: Mark Froggatt, and Jason Moore. "High-spatial-resolution distributed strain measurement in optical fiber with Rayleigh scatter." Applied Optics 37.10 (1998): 1735-1740.

[0007] Non-patent document 2: DP Zhou, Z. Qin, W. Li, L. Chen, and X. Bao, "Distributed vibration sensing with time-resolved optical frequency-domain reflectometry," Opt. Exp., vol. 20, no. 12, pp. 13138-13145, 2012.

[0008] Non-patent document 3: Z. Zhang, Summary of the Invention

[0009] The problem the invention aims to solve

[0010] The purpose of this disclosure is to reduce instrument noise without complicating the receiving system or extending the analysis time.

[0011] Problem-solving methods

[0012] The analytical apparatus disclosed herein

[0013] A spectrum representing the time-varying frequency characteristics is generated using multiple spectral data measured at different times by the same OFDR instrument.

[0014] The spectrum is filtered in both the time and frequency directions.

[0015] The measurement system disclosed herein includes: an OFDR and the analytical apparatus disclosed herein.

[0016] The measurement method disclosed herein includes the following steps:

[0017] Multiple spectral data were obtained by measuring backscattered light at different times using the same OFDR measuring instrument;

[0018] Using the multiple spectral data, a spectrum representing the time variation of frequency characteristics is generated;

[0019] The spectrum is filtered in both the time and frequency directions.

[0020] The program disclosed herein is a program for enabling a computer to implement the various functional units included in the analysis apparatus of this disclosure, and a program for enabling a computer to execute the various steps of the method performed by the analysis apparatus of this disclosure.

[0021] Invention Effects

[0022] According to this disclosure, it is possible to suppress changes in the spectral structure caused by the phase noise of the laser, and to reduce instrument noise without complicating the receiving system or prolonging the analysis time. Attached Figure Description

[0023] Figure 1 An example of the system architecture of this disclosure is shown.

[0024] Figure 2 An example of the structure of an OFDR measuring instrument is shown.

[0025] Figure 3 An example of a spectrum obtained by an OFDR measuring instrument is shown.

[0026] Figure 4 An example of a spectrum obtained by an OFDR measuring instrument is shown.

[0027] Figure 5 This is an example of the spectrum before filtering.

[0028] Figure 6 An example of the filter characteristics of a Gaussian filter is shown.

[0029] Figure 7 This is an example of a filtered spectrum.

[0030] Figure 8 An example of the time waveform of strain obtained from spectral shift analysis is shown when the filter of this disclosure is applied.

[0031] Figure 9 An example of the time waveform of strain without the application of a filter is shown.

[0032] Figure 10 An example of the spectral density of strain is shown. Detailed Implementation

[0033] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. However, the present disclosure is not limited to the embodiments shown below. These examples are merely illustrations, and the present disclosure can be implemented in various modified and altered ways based on the knowledge of those skilled in the art. Furthermore, in this specification and the accompanying drawings, the same structural elements are designated as identical structural elements.

[0034] Figure 1 An example of the system architecture of this disclosure is shown. The measurement system of this disclosure includes: an OFDR measuring instrument 10 for measuring the spectrum of backscattered light reflected or scattered in the measured optical fiber 4; and a spectrum analysis unit 20 for acquiring and analyzing the spectrum data obtained by the OFDR measuring instrument 10. The spectrum analysis unit 20 functions as the analysis device of this disclosure and can also be implemented by a computer and a program, which can be stored in a storage medium or provided via a network.

[0035] Figure 2An example of the structure of an OFDR measuring instrument 10 is shown. The OFDR measuring instrument 10 includes: a laser 1 as a frequency scanning light source, a coupler 2, a circulator 3, a coupler 5, a balanced optical receiver 6, an A / D converter 7, and an analysis unit 8.

[0036] Coupler 2 branches the light from laser 1 into a reference optical path for local light and a measurement optical path for probe light. The probe light branched into the measurement optical path passes through coupler 2 and circulator 3 and is incident on the fiber 4 under test. Coupler 5 combines the backscattered light (signal light) in the fiber 4 under test with the local light branched by coupler 2. Balanced optical receiver 6 receives the interference light after combining by coupler 5. This interference light has a beat frequency corresponding to the difference in optical path length between the reference optical path and the measurement optical path. A / D converter 7 converts the output signal of balanced optical receiver 6 into a digital signal. Analysis unit 8 uses the digital signal from A / D converter 7 to analyze and measure the spectrum of the backscattered light in the fiber 4 under test.

[0037] Figure 3 as well as Figure 4 An example of a spectrum obtained by OFDR measuring instrument 10 is shown. This is done when the phase noise of laser 1 does not affect the spectrum measurement, such as... Figure 3 As shown, the spectral structure is the same for each measurement, and the spectral shift is performed based on the temperature strain while maintaining the spectral structure. On the other hand, when the phase noise of laser 1 affects the spectral measurement, as... Figure 4 As shown, the spectral structure changes with each measurement, making it impossible to calculate the spectral shift corresponding to the temperature strain.

[0038] The spectrum analysis unit 20 of this disclosure uses multiple spectrum data to generate a spectrum representing the time variation of frequency characteristics. Figure 5 An example of a spectrum without the filtering described in this disclosure is shown. Figure 5 In the middle, only the bands with relatively large spectral intensities were not found.

[0039] The spectrum analysis unit 20 of this disclosure reduces the changes in the spectral structure caused by the phase noise of the laser 1 by applying Gaussian filters f(t,n) in both the time and frequency directions to the generated spectrum.

[0040] [Mathematical Expression 1]

[0041]

[0042] Where t is time, ν is the optical frequency, Δt is the width of the Gaussian filter in the time direction, and Δν is the width in the frequency direction.

[0043] Figure 6This example illustrates the filter characteristics of a Gaussian filter with Δt = 10 ms and Δν = 30.3 MHz. The time width Δt of the Gaussian filter determines the cutoff frequency f of the low-pass filter relative to the spectral shift. c ~1 / Δt. Furthermore, by making the width Δν in the frequency direction smaller than the frequency resolution of the measured spectrum, the original spectral structure can be maintained. Therefore, the width Δν is made smaller than the frequency resolution of the OFDR measuring instrument 10. On the other hand, if the ambiguity is greater than the frequency resolution, the original spectral structure may be lost.

[0044] The noise of the OFDR measuring instrument 10 can be measured by measuring the measured optical fiber 4 in a stationary state. Therefore, the noise of the OFDR measuring instrument 10 is evaluated by analyzing the spectral image of the measured optical fiber 4 at one location in a stationary state. Specifically, the noise of the OFDR measuring instrument 10 is... Figure 4 The Gaussian filter with the characteristics shown was applied to a spectrum analyzed at a spectral analysis length of 1.3 m (corresponding to a frequency resolution of 77 MHz).

[0045] Figure 7 An example of the spectrum of this disclosure is shown. Figure 7 Only the bands with higher spectral intensities are shown. (And...) Figure 5 Compared to the case without a Gaussian filter, Figure 7 The spectrum shown can suppress the reproducibility degradation of the spectral structure caused by the phase noise of the laser by applying a Gaussian filter, and obtain the same spectral structure at all times.

[0046] Figures 8-10 This illustrates an example of the effect of filtering the measured strain. Figure 8 as well as Figure 9 An example of the time waveform of strain derived from spectral shift analysis is shown. Figure 8 The application of the Gaussian filter disclosed herein is illustrated. Figure 9 This shows the case where no filter is applied. Figure 10 It is the spectral density of strain. From Figure 10 As can be seen from the spectral density shown, the high-frequency components above 40Hz are reduced by the low-pass filtering with a Gaussian filter. Therefore, according to this disclosure, the changes in the spectral structure caused by the phase noise of the laser are suppressed, resulting in a reduction in instrument noise. Therefore, this disclosure allows for the calculation of the spectral shift using the filtered spectrum, enabling temperature strain sensing with suppressed spectral structure changes.

[0047] Industrial application possibilities

[0048] This disclosure can be applied to the information and communication industry.

[0049] Explanation of reference numerals in the attached figures

[0050] 1: Laser

[0051] 2: Coupler

[0052] 3: Circulator

[0053] 4: The fiber being measured

[0054] 5: Coupler

[0055] 6: Balanced optical receiver

[0056] 7: A / D converter

[0057] 8: Analysis Department

[0058] 10: OFDR measuring instrument

[0059] 20: Spectrum Analysis Department.

Claims

1. Analytical apparatus, A spectrum representing the time-varying frequency characteristics is generated using multiple spectral data measured at different times by the same OFDR instrument. The spectrum is filtered in both the time and frequency directions.

2. The analysis apparatus according to claim 1, wherein the filtered spectrum is used to calculate the spectral shift.

3. In the analysis apparatus according to claim 1 or 2, the width Δt of the filter in the time direction is determined by the cutoff frequency relative to the spectral shift.

4. In the analysis apparatus according to claim 1 or 2, the width Δν of the filter in the frequency direction is less than the frequency resolution of the OFDR measuring instrument.

5. The analysis apparatus according to claim 1 or 2, wherein filtering is performed using a Gaussian filter.

6. Measurement system, equipped with: OFDR measuring instrument; and, The analysis apparatus according to any one of claims 1 to 5 acquires multiple spectral data measured by the OFDR measuring instrument at different times.

7. Measurement method, including the following steps: Multiple spectral data were obtained by measuring backscattered light at different times using the same OFDR measuring instrument; Using the multiple spectral data, a spectrum representing the time variation of frequency characteristics is generated; The spectrum is filtered in both the time and frequency directions.

8. A computer program product having stored computer-readable program medium code thereon, which, when executed by a computer, causes the computer to implement the measurement method of claim 7.

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