Optical fiber characteristic measuring device and optical fiber characteristic measuring method

Abstract

The optical fiber characteristic measuring device (1-3) comprises: a light detecting unit (15, 15A) for detecting Brillouin scattered light (LS) obtained by causing light to be incident on an optical fiber (FUT); an intensity acquiring unit (16, 16A) for acquiring the signal intensity at a predetermined reference frequency (f1, f2) based on a detection signal (S1-S3) output by the light detecting unit; and a measuring unit (18, 18A, 18B) for determining the peak frequency of a Brillouin gain spectrum, which is a spectrum of the Brillouin scattered light, based on the signal intensity at the reference frequency acquired by the intensity acquiring unit, and measuring the characteristics of the optical fiber.

Description

Technical Field

[0001] The present invention relates to an optical fiber characteristic measuring device and an optical fiber characteristic measuring method. Background Art

[0002] The optical fiber characteristic measuring device is a device that allows continuous light or pulsed light to be incident on the optical fiber to be measured, detects scattered light or reflected light generated in the optical fiber to be measured, and measures the temperature distribution or deformation distribution (distortion) of the optical fiber to be measured in the longitudinal direction, the vibration of the optical fiber to be measured, and other characteristics. In the optical fiber characteristic measuring device, since the detected scattered light or reflected light changes according to the physical quantity (such as temperature or deformation) that affects the optical fiber to be measured, the optical fiber to be measured itself is used as a sensor.

[0003] One such optical fiber characteristic measuring device is a BOCDR (Brillouin Optical Correlation Domain Reflectometry) type device. The BOCDR type optical fiber characteristic measuring device allows pump light, which is a frequency-modulated continuous light, to be incident from one end of the optical fiber to be measured, and detects light obtained by interfering Brillouin scattered light emitted from one end of the optical fiber to be measured with reference light (the same frequency-modulated light as the pump light). Then, the spectrum of the Brillouin scattered light (hereinafter referred to as the "Brillouin gain spectrum") is obtained based on the obtained detection signal, and the characteristics of the optical fiber to be measured are measured by obtaining the frequency shift amount of the incident light with respect to the Brillouin scattered light (hereinafter referred to as the "Brillouin frequency shift amount").

[0004] In a BOCDR-based optical fiber characteristic measuring device, Brillouin scattered light and reference light are interfered to selectively extract Brillouin scattered light at a specific position where a "correlation peak" appears in the measured optical fiber. Here, by scanning the modulation frequency of the pump light and the reference light, the correlation peak can be moved along the length direction of the measured optical fiber. Therefore, by moving the correlation peak while obtaining the Brillouin frequency shift amount at the position where each correlation peak appears, the temperature distribution or deformation distribution in the length direction of the measured optical fiber can be measured. In addition, for details of the BOCDR-based optical fiber characteristic measuring device, it is recommended to refer to, for example, the following patent document 1.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 5105302 Summary of the invention

[0008] Problems to be solved by the invention

[0009] However, the Brillouin frequency shift amount obtained by the optical fiber characteristic measuring device of the BOCDR method is the difference between the frequency of the incident light and the peak frequency of the Brillouin gain spectrum. Therefore, in order to obtain the Brillouin frequency shift amount, it is necessary to obtain the peak frequency of the Brillouin gain spectrum. Here, since it is necessary to perform a frequency scan of the detection signal in order to obtain the Brillouin gain spectrum, there is a problem that the measurement time becomes longer.

[0010] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an optical fiber characteristic measuring device and an optical fiber characteristic measuring method capable of measuring the characteristics of an optical fiber to be measured in a shorter time.

[0011] Means for solving problems

[0012] In order to solve the above-mentioned problems, an optical fiber characteristic measuring device (1-3) involved in one embodiment of the present invention comprises: a light detection unit (15, 15A) for detecting Brillouin scattered light (LS) obtained by causing light to be incident on an optical fiber (FUT); an intensity acquisition unit (16, 16A) for obtaining the signal intensity at a predetermined reference frequency (f1, f2) based on the detection signal (S1-S3) output by the light detection unit; and a measuring unit (18, 18A, 18B) for determining the peak frequency of a Brillouin gain spectrum which is a spectrum of the Brillouin scattered light based on the signal intensity at the reference frequency obtained by the intensity acquisition unit, and measuring the characteristics of the optical fiber.

[0013] In the optical fiber characteristics measurement device according to one aspect of the present invention, the reference frequency is a frequency within a frequency band of a reference Brillouin gain spectrum obtained when the optical fiber is placed under a predetermined reference environment.

[0014] Furthermore, in the optical fiber characteristics measurement device according to one aspect of the present invention, the reference frequency is a frequency at which a slope of the reference Brillouin gain spectrum becomes maximum.

[0015] Furthermore, in the optical fiber characteristics measuring device according to one aspect of the present invention, the reference frequency is two frequencies sandwiching a peak frequency of the reference Brillouin gain spectrum.

[0016] In addition, an optical fiber characteristic measuring device involved in one embodiment of the present invention comprises: a storage unit (18a) storing transformation information for converting the signal intensity at the reference frequency into the peak frequency of the Brillouin gain spectrum, and the measuring unit uses the transformation information stored in the storage unit to obtain the peak frequency of the Brillouin gain spectrum based on the signal intensity at the reference frequency obtained by the intensity acquisition unit.

[0017] In addition, an optical fiber characteristic measuring device involved in one embodiment of the present invention comprises: a light source unit (11) that outputs frequency-modulated continuous light (L1); a first light branching unit (12) that branches the continuous light into pump light (LP) and reference light (LR); and a second light branching unit (14) that allows the pump light to be incident from one end of the optical fiber and outputs the Brillouin scattered light generated in the optical fiber, and the light detection unit detects interference light between the Brillouin scattered light and the reference light.

[0018] Here, in an optical fiber characteristic measuring device according to one aspect of the present invention, the light detecting section comprises: a first separation element (22a) for separating the reference light into a first reference light (LR1) and a second reference light (LR2) having polarization directions orthogonal to each other; a second separation element (22b) for separating the Brillouin scattered light into a first scattered light (LS1) having the same polarization direction as the first reference light and a second scattered light (LS2) having the same polarization direction as the second reference light; a first detector (23a) for detecting interference light between the first scattered light and the first reference light; and a second detector (23b) for detecting interference light between the second scattered light and the second reference light, the intensity acquiring section obtaining a first signal intensity as a signal intensity at the reference frequency based on a detection signal output by the first detector, and obtaining a second signal intensity as a signal intensity at the reference frequency based on a detection signal output by the second detector, and the measuring section obtains a peak frequency of the Brillouin gain spectrum based on the first signal intensity and the second signal intensity obtained by the intensity acquiring section.

[0019] Alternatively, an optical fiber characteristic measuring device according to one embodiment of the present invention comprises a polarization switcher (30) for alternately switching the polarization direction of the reference light into a first direction and a second direction orthogonal to each other, the intensity acquisition unit obtains a first signal intensity as a signal intensity in the reference frequency based on the detection signal output from the light detection unit when the polarization direction of the reference light is switched to the first direction through the polarization switcher, and obtains a second signal intensity as a signal intensity in the reference frequency based on the detection signal output from the light detection unit when the polarization direction of the reference light is switched to the second direction through the polarization switcher, and the measuring unit obtains the peak frequency of the Brillouin gain spectrum based on the first signal intensity and the second signal intensity obtained by the intensity acquisition unit.

[0020] Alternatively, an optical fiber characteristics measuring device according to one aspect of the present invention includes a polarization scrambler (40) for randomly changing the polarization state of the reference light over time.

[0021] Furthermore, the optical fiber characteristic measurement device according to one aspect of the present invention includes an optical delay unit (13) for delaying the pump light between the first optical branching unit and the second optical branching unit.

[0022] A method for measuring optical fiber characteristics according to one aspect of the present invention detects Brillouin scattered light (LS) obtained by causing light to be incident on an optical fiber (FUT) by means of a light detection unit (15, 15A), obtains a signal intensity at a predetermined reference frequency (f1, f2) based on a detection signal (S1 to S3) output from the light detection unit by means of an intensity acquisition unit (16, 16A), obtains a peak frequency of a Brillouin gain spectrum, which is a spectrum of the Brillouin scattered light, based on the signal intensity at the reference frequency obtained by the intensity acquisition unit by means of a measurement unit (18, 18A, 18B), and measures the characteristics of the optical fiber.

[0023] Furthermore, in the optical fiber characteristic measurement method according to one aspect of the present invention, the reference frequency is a frequency within a frequency band of a reference Brillouin gain spectrum obtained when the optical fiber is placed under a predetermined reference environment.

[0024] Furthermore, in the optical fiber characteristic measurement method according to one aspect of the present invention, the reference frequency is a frequency at which a slope of the reference Brillouin gain spectrum becomes maximum.

[0025] Furthermore, in the optical fiber characteristic measurement method according to one aspect of the present invention, the reference frequency is two frequencies sandwiching a peak frequency of the reference Brillouin gain spectrum.

[0026] Furthermore, in an optical fiber characteristic measuring method according to one aspect of the present invention, a storage unit (18a) stores transformation information for transforming the signal intensity at the reference frequency into the peak frequency of the Brillouin gain spectrum, and the measuring unit uses the transformation information stored in the storage unit to obtain the peak frequency of the Brillouin gain spectrum based on the signal intensity at the reference frequency obtained by the intensity acquisition unit.

[0027] Furthermore, in an optical fiber characteristic measuring method according to one aspect of the present invention, a frequency-modulated continuous light (L1) is outputted by a light source section (11), the continuous light is branched into a pump light (LP) and a reference light (LR) by a first optical branching section (12), the pump light is incident from one end of the optical fiber by a second optical branching section (14), the Brillouin scattered light generated in the optical fiber is outputted, and interference light between the Brillouin scattered light and the reference light is detected by the optical detection section.

[0028] In addition, in an optical fiber characteristic measuring method according to one embodiment of the present invention, the light detection unit comprises a first separation element (22a), a second separation element (22b), a first detector (23a) and a second detector (23b), the reference light is separated into a first reference light and a second reference light whose polarization directions are orthogonal to each other by the first separation element, the Brillouin scattered light is separated into a first scattered light having the same polarization direction as the first reference light and a second scattered light having the same polarization direction as the second reference light by the second separation element, and the first detector detects the reference light. The first scattered light and the interference light of the first reference light are detected by the second detector, the first signal intensity as the signal intensity in the reference frequency is obtained by the intensity acquisition unit according to the detection signal output by the first detector, the second signal intensity as the signal intensity in the reference frequency is obtained according to the detection signal output by the second detector, and the peak frequency of the Brillouin gain spectrum is obtained by the measuring unit according to the first signal intensity and the second signal intensity obtained by the intensity acquisition unit.

[0029] In addition, in an optical fiber characteristic measuring method involved in one embodiment of the present invention, the polarization direction of the reference light is alternately switched to a first direction and a second direction orthogonal to each other by a polarization switcher (30), and the first signal intensity as the signal intensity in the reference frequency is obtained by the intensity acquisition unit based on the detection signal output from the light detection unit when the polarization direction of the reference light is switched to the first direction by the polarization switcher. The second signal intensity as the signal intensity in the reference frequency is obtained by the intensity acquisition unit based on the detection signal output from the light detection unit when the polarization direction of the reference light is switched to the second direction by the polarization switcher. The peak frequency of the Brillouin gain spectrum is obtained by the measuring unit based on the first signal intensity and the second signal intensity obtained by the intensity acquisition unit.

[0030] Furthermore, in the optical fiber characteristic measuring method according to one aspect of the present invention, the polarization state of the reference light is randomly changed over time by a polarization scrambler (40).

[0031] Furthermore, in the optical fiber characteristic measuring method according to one aspect of the present invention, the pump light is delayed between the first optical branching section and the second optical branching section by an optical delay section (13).

[0032] Further features and aspects of the present invention will become apparent from the detailed description of the embodiments described below with reference to the accompanying drawings.

[0033] Effects of the Invention

[0034] According to the present invention, there is an effect that the characteristics of the optical fiber to be measured can be measured in a shorter time. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a block diagram showing the main part configuration of the optical fiber characteristics measuring device according to the first embodiment of the present invention.

[0036] Figure 2 This is a diagram showing the relationship between the signal intensity at a predetermined reference frequency and the peak frequency of the Brillouin gain spectrum in the first embodiment of the present invention.

[0037] Figure 3 This is a flowchart showing an operation example of the optical fiber characteristics measuring device according to the first embodiment of the present invention.

[0038] Figure 4 It is a block diagram showing the main part configuration of an optical fiber characteristics measuring device according to a second embodiment of the present invention.

[0039] Figure 5 This is a flowchart showing an operation example of the optical fiber characteristics measurement device according to the second embodiment of the present invention.

[0040] Figure 6 It is a block diagram showing the main part structure of the optical fiber characteristic measurement device according to the third embodiment of the present invention.

[0041] Figure 7 This is a diagram showing the relationship between the signal intensity and the peak frequency of the Brillouin gain spectrum at a plurality of predetermined reference frequencies. DETAILED DESCRIPTION

[0042] Hereinafter, an optical fiber characteristic measuring device and an optical fiber characteristic measuring method according to embodiments of the present invention will be described in detail with reference to the accompanying drawings. Hereinafter, an overview of embodiments of the present invention will be described first, and then the details of each embodiment of the present invention will be described.

[0043] [summary]

[0044] The embodiments of the present invention can measure the characteristics of the measured optical fiber in a shorter time. Here, in order to measure the characteristics of the measured optical fiber, it is necessary to obtain the peak frequency based on the Brillouin gain spectrum obtained at each measurement point set in the length direction of the measured optical fiber. In order to obtain the Brillouin gain spectrum, it is necessary to perform a frequency scan of the detection signal. For example, when the frequency band of 10.6 to 11.1 [GHz] is frequency scanned in units of frequency 1 [MHz] scale, it is necessary to perform 501 measurements (sampling) of the detection signal. In addition, since the Brillouin scattered light emitted from the measured optical fiber is very weak, the obtained Brillouin gain spectrum is almost superimposed with noise. In the optical fiber characteristic measuring device, in order to remove the noise superimposed on the Brillouin gain spectrum, a process of obtaining the Brillouin gain spectrum over multiple times and averaging is performed. Since this process is performed at each measurement point set in the length direction of the measured optical fiber, the measurement time will be longer.

[0045] In the embodiment of the present invention, the signal intensity at a predetermined reference frequency is obtained based on the detection signal of Brillouin scattered light obtained by causing light to be incident on the optical fiber to be measured. Then, the peak frequency of the Brillouin gain spectrum is obtained based on the obtained signal intensity at the reference frequency to measure the characteristics of the optical fiber to be measured. That is, in this embodiment, the detection signal of Brillouin scattered light does not need to be frequency scanned, but the peak frequency of the Brillouin gain spectrum is obtained based on the signal intensity at the predetermined reference frequency to measure the characteristics of the optical fiber to be measured. As a result, the characteristics of the optical fiber to be measured can be measured in a shorter time.

[0046] [First embodiment]

[0047] <Structure of Optical Fiber Characteristics Measurement Device>

[0048] Figure 1 FIG. 1 is a block diagram showing the main structure of the optical fiber characteristic measuring device according to the first embodiment of the present invention. Figure 1 As shown, the optical fiber characteristic measuring device 1 of this embodiment includes a light source unit 11, a first optical branching unit 12, an optical delay unit 13, a second optical branching unit 14, a light detection unit 15, an intensity acquisition unit 16, a digitizer 17, and a measuring unit 18. The optical fiber characteristic measuring device 1 of this structure is a measuring device of the so-called BOCDR method that measures the characteristics of the optical fiber FUT to be measured based on the Brillouin scattered light LS obtained by causing the pump light LP to be incident on the optical fiber FUT to be measured.

[0049] The above-mentioned pump light LP is the continuous light after frequency modulation. The above-mentioned Brillouin scattered light LS is the backscattered light produced by the Brillouin scattering in the measured optical fiber FUT. In addition, the measured optical fiber FUT can use any optical fiber based on the wavelength of the pump light LP etc. In addition, in the present embodiment, in order to make the description simple, only 1 correlation peak value appears in the measured optical fiber FUT.

[0050] Here, the light source section 11 and the first optical branching section 12, the first optical branching section 12 and the optical detection section 15, and the interior of the optical detection section 15 are connected by, for example, a polarization maintaining fiber (PMF). This is to maintain the polarization state of the continuous light L1 and the reference light LR (described in detail later). In contrast, the first optical branching section 12 and the second optical branching section 14 (including the optical delay section 13) and the second optical branching section 14 and the optical detection section 15 are connected by, for example, a single mode fiber (SMF). In addition, in this embodiment, it is assumed that the optical fiber FUT to be measured is a single mode fiber.

[0051] The light source unit 11 includes a light source 11a and a modulation unit 11b, and outputs a frequency-modulated continuous light L1 under the control of the measuring unit 18. The light source 11a includes a semiconductor laser element such as a distributed feedback laser diode (DFB-LD), and outputs a linearly polarized continuous light L1 that is frequency-modulated according to a modulation signal m1 output from the modulation unit 11b. Under the control of the measuring unit 18, the modulation unit 11b outputs a modulation signal m1 for frequency-modulating the continuous light L1 output from the light source 11a. The modulation signal m1 is, for example, a sinusoidal signal, and its frequency (modulation frequency fm) and amplitude are controlled by the measuring unit 18.

[0052] The first optical branching unit 12 branches the continuous light L1 output from the light source unit 11 into a pump light LP and a reference light LR of a predetermined intensity ratio (e.g., 1 to 1). The optical delay unit 13 delays the pump light LP branched by the first optical branching unit 12 by only a predetermined time. The optical delay unit 13 includes, for example, an optical fiber (e.g., a single-mode optical fiber) of a predetermined length. By changing the length of the optical fiber, the delay time can be adjusted. Such an optical delay unit 13 is provided in order to configure the 0th-order correlation peak outside the measured optical fiber FUT, the position of which will not move even if the modulation frequency fm is scanned. In addition, the optical delay unit 13 can also be provided between the first optical branching unit 12 and the optical detection unit 15.

[0053] The second optical branching section 14 includes a first port, a second port, and a third port. The first port is connected to the first optical branching section 12 via the optical delay section 13. The second port is connected to the optical fiber FUT to be measured. The third port is connected to the optical detection section 15. The second optical branching section 14 outputs the pump light LP input from the first port to the second port. In addition, the Brillouin scattered light LS from the optical fiber FUT to be measured input from the second port is output to the third port. Such a second optical branching section 14 can be, for example, an optical circulator.

[0054] The light detection unit 15 detects the Brillouin scattered light LS (Brillouin scattered light LS from the optical fiber FUT under test) output from the third port of the second optical branching unit 14. Specifically, the light detection unit 15 performs optical heterodyne detection by interfering the Brillouin scattered light LS output from the third port of the second optical branching unit 14 with the reference light LR output from the first optical branching unit 12.

[0055] The light detection unit 15 includes a polarization rotator 21, a polarization separation element 22a (first separation element), a polarization separation element 22b (second separation element), a detector 23a (first detector), and a detector 23b (second detector). The polarization rotator 21 rotates the polarization direction of the reference light LR output from the first light branching unit 12 by only π / 4 (45°). The polarization rotator 21 may be, for example, a Faraday rotator.

[0056] The polarization separation element 22a separates the reference light LR that has passed through the polarization rotator 21 into a reference light LR1 (first reference light) and a reference light LR2 (second reference light) whose polarization directions are orthogonal to each other. In addition, for easy understanding, the polarization direction of the reference light LR1 is referred to as the "X direction", and the polarization direction of the reference light LR2 is referred to as the "Y direction". In addition, the X direction is the same direction as the polarization direction of the reference light LR output from the first optical branching unit 12 (the reference light LR before passing through the polarization rotator 21), for example.

[0057] The polarization separation element 22b separates the Brillouin scattered light LS output from the third port of the second optical branching unit 14 into scattered light LS1 (first scattered light) and scattered light LS2 (second scattered light) whose polarization directions are orthogonal to each other. Here, the polarization direction of the scattered light LS1 is the same as the polarization direction of the reference light LR1, which is the X direction, and the polarization direction of the scattered light LS2 is the same as the polarization direction of the reference light LR2, which is the Y direction.

[0058] The detector 23a performs optical heterodyne detection by interfering the reference light LR1 separated by the polarization separation element 22a with the scattered light LS1 separated by the polarization separation element 22b. For example, the detector 23a includes a balanced photodiode formed by connecting two photodiodes (PD) in series, and the interference light of the reference light LR1 and the scattered light LS1 is received by the two photodiodes. The detector 23a outputs a detection signal S1 as an interference signal (beat signal) indicating the frequency difference between the reference light LR1 and the scattered light LS1.

[0059] The detector 23b performs optical heterodyne detection by interfering the reference light LR2 separated by the polarization separation element 22a with the scattered light LS2 separated by the polarization separation element 22b. The detector 23b is similar to the detector 23a, for example, and includes a balanced photodiode, and receives the interference light of the reference light LR2 and the scattered light LS2 through two photodiodes. The detector 23b outputs a detection signal S2 as an interference signal (beat signal) indicating the frequency difference between the reference light LR2 and the scattered light LS2.

[0060] Here, in the light detection unit 15, as described above, the components with polarization directions in the X direction (scattered light LS1, reference light LR1) and components with polarization directions in the Y direction (scattered light LS2, reference light LR2) are separated. Then, the detection signal S1 of the component with polarization directions in the X direction and the detection signal S2 of the component with polarization directions in the Y direction are obtained separately. This is done to suppress the variation of the Brillouin gain spectrum depending on the relative polarization states of the reference light LR and the Brillouin scattered light LS.

[0061] The intensity acquisition unit 16 obtains a predetermined reference frequency f1 (reference frequency f1) based on the detection signals S1 and S2 outputted from the light detection unit 15. Figure 2 : Details will be described later). Specifically, the intensity acquisition unit 16 includes two spectrum analyzers (ESA: Electrical Spectrum Analyzer) 24a and 24b. The spectrum analyzer 24a obtains the signal strength (first signal strength) at the reference frequency f1 based on the detection signal S1 output by the detector 23a of the light detection unit 15. The spectrum analyzer 24b obtains the signal strength (second signal strength) at the reference frequency f1 based on the detection signal S2 output by the detector 23b of the light detection unit 15.

[0062] Like this, in intensity acquisition part 16, according to the signal intensity in reference frequency f1 obtained by the detection signal S1, S2 output by light detection part 15, it is to measure the characteristic of measured optical fiber FUT in a shorter time.That is, in this embodiment, the detection signal S1, S2 output from light detection part 15 is not carried out to carry out frequency scanning to obtain the processing of Brillouin gain spectrum, but by only obtaining the signal intensity in reference frequency f1, thus shortening the time required for measurement.

[0063] The digitizer 17 includes A / D converters 25a and 25b, and converts the signal strength obtained by the strength acquisition unit 16 into a digital signal. Specifically, the A / D converter 25a converts the signal strength obtained by the spectrum analyzer 24a of the strength acquisition unit 16 into a digital signal. The A / D converter 25b converts the signal strength obtained by the spectrum analyzer 24b of the strength acquisition unit 16 into a digital signal. In addition, the signal strength converted into a digital signal by the A / D converter 25a is used as I X , the signal strength converted into a digital signal by the A / D converter 25b is taken as I Y .

[0064] The measuring unit 18 uses two digital signals (I X , I Y ) to obtain the peak frequency of the Brillouin gain spectrum. Specifically, the measuring unit 18 performs a first process to obtain the square root of the sum of the squares of the two digital signals output by the digitizer 17 (√(I X 2 +I Y 2 )) The measuring unit 18 performs a second process of multiplying the square root of the square sum obtained by the first process by the conversion coefficient stored in the storage unit 18a to obtain the peak frequency of the Brillouin gain spectrum.

[0065] Here, the conversion coefficient stored in the storage unit 18a is a coefficient (conversion information) for converting the signal intensity at the reference frequency f1 into the peak frequency of the Brillouin gain spectrum. In addition, in order to reduce the influence of noise, the measuring unit 18 can also perform the above-mentioned first processing multiple times to obtain the average value of the square root of the obtained multiple squares.

[0066] In addition, the measuring unit 18 is to measure the characteristic of the measured optical fiber FUT by obtaining the Brillouin frequency shift according to the peak frequency of the Brillouin gain spectrum obtained. The measuring unit 18 can include a display unit that displays the Brillouin frequency shift obtained as physical information such as deformation or temperature. In addition, the information such as the deformation or temperature of the measured optical fiber FUT can also be interpreted as the information meaning the state of the object as its measuring object and displayed in the display unit. The display unit is, for example, a liquid crystal display device or an organic EL (Electro Luminescence, electroluminescence) display device, etc.

[0067] In addition, the measuring unit 18 controls the operation of the optical fiber characteristic measuring device 1 in a unified manner. For example, the measuring unit 18 controls the modulating unit 11b provided in the light source unit 11 to change the modulation frequency fm of the continuous light L1 output from the light source unit 11. The modulation frequency fm of the continuous light L1 is changed in order to move the correlation peak along the length direction of the optical fiber FUT to be measured, for example. In addition, the measuring unit 18 can be implemented by a computer such as a personal computer.

[0068] Figure 2 This is a diagram showing the relationship between the signal intensity at a predetermined reference frequency and the peak frequency of the Brillouin gain spectrum in the first embodiment of the present invention. Figure 2 FIG. 8 shows an example of a Brillouin gain spectrum in which the horizontal axis represents frequency and the vertical axis represents signal intensity. Figure 2 In the example shown, three Brillouin gain spectra are shown, namely G0, G1, and G2.

[0069] The Brillouin gain spectrum G0 is obtained when the optical fiber FUT is placed in a predetermined reference environment (reference Brillouin gain spectrum). Figure 2 The Brillouin gain spectra G1 and G2 in the figure are obtained in an environment different from the reference environment. Here, the predetermined reference environment refers to an environment in which, for example, the temperature around the measured optical fiber FUT is a predetermined temperature (e.g., room temperature 25°C) and no deformation is applied to the measured optical fiber FUT. In addition, an environment different from the reference environment refers to an environment in which, for example, a deformation is applied to the measured optical fiber FUT.

[0070] like Figure 2 As shown, the peak frequency of the Brillouin gain spectrum G0 obtained when the measured optical fiber FUT is placed in a predetermined reference environment is fp0. By applying deformation to the measured optical fiber FUT, the Brillouin gain spectrum shifts to the low-frequency side or the high-frequency side. Thus, it is clear that the peak frequency of the Brillouin gain spectrum G1 becomes fp1, and the peak frequency of the Brillouin gain spectrum G2 becomes fp2.

[0071] The aforementioned reference frequency f1 is defined as a frequency within the frequency band of the Brillouin gain spectrum G0 obtained when the measured optical fiber FUT is placed under a predetermined reference environment. Specifically, the reference frequency f1 is defined as a frequency at which the signal intensity changes significantly due to the Brillouin gain spectrum shift. For example, the reference frequency f1 is defined as a frequency at which the slope of the Brillouin gain spectrum G0 becomes the maximum.

[0072] exist Figure 2 In the example shown, the signal intensity at the reference frequency f1 when the Brillouin gain spectrum G0 is obtained is I2. In contrast, the signal intensity at the reference frequency f1 when the Brillouin gain spectrum G1 is obtained is I3 which is larger than I2, and on the other hand, the signal intensity at the reference frequency f1 when the Brillouin gain spectrum G2 is obtained is I1 which is smaller than I2.

[0073] Here, the shift amount of the Brillouin gain spectrum (the change amount of the peak frequency of the Brillouin gain spectrum) and the change amount of the signal intensity at the reference frequency f1 are in a one-to-one relationship. Therefore, if the signal intensity at the reference frequency f1 is known, the peak frequency of the Brillouin gain spectrum can be obtained. The storage unit 18a of the measuring unit 18 stores, as information representing the above relationship, coefficients for converting the signal intensity at the reference frequency f1 to the peak frequency of the Brillouin gain spectrum. The measuring unit 18 uses the coefficients stored in the storage unit 18a to convert the signal intensity at the reference frequency f1 (√(I X 2 +I Y 2 )) is transformed into the peak frequency of the Brillouin gain spectrum.

[0074] <Operation of the Optical Fiber Characteristics Measurement Device>

[0075] Figure 3 This is a flowchart showing an operation example of the optical fiber characteristics measuring device according to the first embodiment of the present invention. Figure 3 The flowchart shown in the figure shows the operation when measuring the characteristics of one measurement point set in the length direction of the optical fiber FUT to be measured. Figure 3 The flowchart shown is started by, for example, instructing the optical fiber characteristic measurement device 1 to start measurement.

[0076] when Figure 3 When the process of the flowchart shown in the figure starts, first, the modulator 11b provided in the light source unit 11 is controlled by the measuring unit 18, and the linearly polarized continuous light L1 frequency-modulated by the modulation frequency fm is output from the light source 11a (step S11). The continuous light L1 output from the light source 11a is incident on the first light branching unit 12 and branched into the pump light LP and the reference light LR (step S12).

[0077] The branched pump light LP is incident on the measured optical fiber FUT (step S13) via the optical delay unit 13 and the second optical branching unit 14 in sequence, and propagates in the measured optical fiber FUT. Thereupon, Brillouin scattered light LS (backscattered light) is generated in sequence in the measured optical fiber FUT. Here, the Brillouin scattered light LS generated in the measured optical fiber FUT is affected by the sound wave whose speed depends on the deformation or temperature of the measured optical fiber FUT, and its frequency will shift.

[0078] For example, if it is assumed that the wavelength of the continuous light L1 output from the light source unit 11 is about 1.55 [μm], the Brillouin scattered light LS generated in the measured optical fiber FUT will shift the frequency of the above-mentioned continuous light L1 by, for example, 10.8 [GHz]. The Brillouin frequency shift varies according to the deformation or temperature applied to the measured optical fiber FUT.

[0079] The Brillouin scattered light LS generated in the measured optical fiber FUT propagates in the direction opposite to the propagation direction of the pump light LP and is emitted from one end of the measured optical fiber FUT. The Brillouin scattered light LS emitted from one end of the optical fiber FUT is incident on the light detection unit 15 via the second light branching unit 14. Then, the light detection unit 15 detects the Brillouin scattered light LS using the reference light LR branched by the first light branching unit 12 (step S14: detection step).

[0080] Specifically, the Brillouin scattered light LS incident on the light detection unit 15 is separated into scattered light LS1 with a polarization direction in the X direction and scattered light LS2 with a polarization direction in the Y direction by the polarization separation element 22b. In addition, the reference light LR incident on the light detection unit 15 is firstly rotated in polarization direction by π / 4 by the polarization rotator 21, and then separated into reference light LR1 with a polarization direction in the X direction and reference light LR2 with a polarization direction in the Y direction by the polarization separation element 22a.

[0081] Then, the detector 23a performs optical heterodyne detection by interfering the reference light LR1 separated by the polarization separation element 22a and the scattered light LS1 separated by the polarization separation element 22b. Thus, the detector 23a outputs a detection signal S1 as an interference signal (beat signal) representing the frequency difference between the reference light LR1 and the scattered light LS1. Similarly, the detector 23b performs optical heterodyne detection by interfering the reference light LR2 separated by the polarization separation element 22a and the scattered light LS2 separated by the polarization separation element 22b. Thus, the detector 23b outputs a detection signal S2 as an interference signal (beat signal) representing the frequency difference between the reference light LR2 and the scattered light LS2.

[0082] The detection signals S1 and S2 output from the light detection unit 15 are input to the intensity acquisition unit 16. The intensity acquisition unit 16 obtains the signal intensity at the predetermined reference frequency f1 based on the detection signals S1 and S2 (step S15: intensity acquisition step). Specifically, the spectrum analyzer 24a obtains the signal intensity (first signal intensity) at the reference frequency f1 based on the detection signal S1. In addition, the spectrum analyzer 24b obtains the signal intensity (second signal intensity) at the reference frequency f1 based on the detection signal S2.

[0083] The signal strength at the reference frequency f1 acquired by the strength acquisition unit 16 is converted into a digital signal (I X , I Y ) and input to the measuring unit 18. In this way, the measuring unit 18 uses the two digital signals (I X , I Y ) to obtain the peak frequency of the Brillouin gain spectrum (step S16: measurement step).

[0084] Specifically, first, the measuring unit 18 obtains the square root of the sum of the squares of the two digital signals output from the digitizer 17 (√(I X 2 +I Y 2 ))(first processing). Next, the measuring unit 18 obtains the peak frequency of the Brillouin gain spectrum by multiplying the square sum square root obtained by the first processing by the transformation coefficient stored in the storage unit 18a (second processing). In addition, in order to reduce the influence of noise, the processing of steps S14 and S15 can be performed multiple times, and the above-mentioned first processing can be performed multiple times to obtain the average value of the multiple square sum square roots obtained.

[0085] For example, when the square root of the square sum obtained by the first process is Figure 2 In the case of the intensity I1 shown in FIG. 1 , by performing the above-mentioned second processing, fp2, which is the peak frequency of the Brillouin gain spectrum, is obtained. In addition, the square root of the sum of squares obtained by the above-mentioned first processing is Figure 2 In the case of the intensity I2 shown in FIG. 1 , by performing the above-mentioned second processing, fp0, which is the peak frequency of the Brillouin gain spectrum, is obtained. In addition, the square root of the sum of squares obtained by the above-mentioned first processing is Figure 2 In the case of the intensity I3 shown in FIG. 1 , by performing the above-mentioned second processing, fp1 which is the peak frequency of the Brillouin gain spectrum is obtained.

[0086] When the above processing is finished, the measuring unit 18 measures the characteristics of the measured optical fiber FUT by obtaining the Brillouin frequency shift according to the peak frequency of the Brillouin gain spectrum (step S17: measuring step). For example, the measuring unit 18 obtains the deformation in one measuring point set in the length direction of the measured optical fiber FUT according to the peak frequency of the Brillouin gain spectrum.

[0087] As above, in the present embodiment, according to the detection signals S1 and S2 of the Brillouin scattered light LS obtained by making the pump light LP incident on the measured optical fiber FUT, the signal intensity in the predetermined reference frequency f1 is obtained. Then, the peak frequency of the Brillouin gain spectrum is obtained according to the signal intensity in the obtained reference frequency f1 to measure the characteristics of the measured optical fiber FUT. That is, in the present embodiment, the detection signals S1 and S2 of the Brillouin scattered light LS are not subjected to frequency scanning, and the peak frequency of the Brillouin gain spectrum is obtained only according to the signal intensity in the predetermined reference frequency f1 to measure the characteristics of the measured optical fiber FUT. Thus, the characteristics of the measured optical fiber can be measured in a shorter time.

[0088] [Second embodiment]

[0089] <Structure of Optical Fiber Characteristics Measurement Device>

[0090] Figure 4 FIG. 2 is a block diagram showing the main structure of the optical fiber characteristic measuring device according to the second embodiment of the present invention. Figure 4 In, about Figure 1 The same structures as shown are assigned the same reference numerals. Figure 4 As shown, the optical fiber characteristic measuring device 2 of this embodiment is Figure 1 The optical fiber characteristics measuring device 1 shown has a configuration in which the light detection unit 15, the intensity acquisition unit 16, the digitizer 17, and the measurement unit 18 are replaced by a light detection unit 15A, an intensity acquisition unit 16A, a digitizer 17A, and a measurement unit 18A, and a polarization switcher 30 is added.

[0091] The optical fiber characteristic measurement device 1 of the first embodiment described above simultaneously obtains the detection signal S1 of the component with polarization direction in the X direction (scattered light LS1, reference light LR1) and the detection signal S2 of the component with polarization direction in the Y direction (scattered light LS2, reference light LR2). In contrast, the optical fiber characteristic measurement device 2 of the present embodiment obtains the detection signal of the component with polarization direction in the X direction and the detection signal of the component with polarization direction in the Y direction alternately (in a time-sharing manner).

[0092] The light detection unit 15A and Figure 1The light detecting unit 15 shown in FIG. 1 detects the Brillouin scattered light LS output from the third port of the second light branching unit 14 (the Brillouin scattered light LS from the optical fiber FUT under test). Figure 1 The light detection unit 15 shown in the figure is different from that of the light detection unit 15, and only includes a detector 23. The detector 23 is Figure 1 The detectors 23a and 23b shown are the same. The detector 23 performs optical heterodyne detection by interfering the Brillouin scattered light LS output from the third port of the second optical branching unit 14 with the reference light LR output from the first optical branching unit 12 and passing through the polarization switcher 30. The detector 23 outputs a detection signal S3 which is an interference signal (beat signal) indicating the frequency difference between the reference light LR and the Brillouin scattered light LS.

[0093] The intensity acquisition unit 16A includes a spectrum analyzer 24, and obtains the signal intensity at a predetermined reference frequency f1 based on the detection signal S3 output by the light detection unit 15. Figure 1 The spectrum analyzers 24a and 24b shown in the figure are the same. The digitizer 17A includes an A / D converter 25, which converts the signal strength obtained by the strength acquisition unit 16 into a digital signal. Figure 1 The A / D converters 25a and 25b shown in FIG. 1 are the same. Figure 1 The measuring unit 18 shown is substantially the same as that shown in FIG. 1 , but the point that the polarization switch 30 is controlled is different from that shown in FIG. Figure 1 The measuring section 18 shown is different.

[0094] The polarization switcher 30 is provided between the first light branching unit 12 and the light detection unit 15A. Under the control of the measurement unit 18A, the polarization switcher 30 switches the polarization direction of the reference light LR branched by the first light branching unit 12. Specifically, the polarization switcher 30 alternately switches the polarization direction of the reference light LR to the X direction (first direction) and the Y direction (second direction) which are orthogonal to each other.

[0095] <Operation of the Optical Fiber Characteristics Measurement Device>

[0096] Figure 5 FIG. 1 is a flowchart showing an example of the operation of the optical fiber characteristic measuring device according to the second embodiment of the present invention. Figure 5 In, about Figure 3 The same steps in the flowcharts are assigned the same reference numerals. Figure 5 The flowchart shown is similar to Figure 3 Similarly, the operation when measuring the characteristics of one measurement point set in the length direction of the optical fiber FUT to be measured is shown.

[0097] when Figure 5When the process of the flowchart shown in the figure starts, similarly to the first embodiment, the linearly polarized continuous light L1 after frequency modulation by the modulation frequency fm is output from the light source 11a (step S11), and the continuous light L1 is incident on the first optical branching unit 12 and branched into the pump light LP and the reference light LR (step S12). Then, the branched pump light LP is incident on the optical fiber FUT to be measured via the optical delay unit 13 and the second optical branching unit 14 in sequence (step S13). In addition, as the pump light LP propagates in the optical fiber FUT to be measured, Brillouin scattered light LS (backscattered light) is sequentially generated in the optical fiber FUT to be measured.

[0098] Then, the measuring unit 18A switches the polarization direction of the reference light LR to the X direction by controlling the polarization switch 30 (step S21). Then, the light detection unit 15A detects the Brillouin scattered light LS using the reference light LR that has passed through the polarization switch 30 (step S22). Specifically, the detector 23 performs optical heterodyne detection by interfering the reference light LR whose polarization direction is the X direction with the Brillouin scattered light LS. As a result, the detector 23 outputs a detection signal S3 that is an interference signal (beat signal) indicating the frequency difference between the reference light LR whose polarization direction is the X direction and the scattered light LS.

[0099] The detection signal S3 outputted from the light detection unit 15A is inputted to the intensity acquisition unit 16A. The intensity acquisition unit 16A obtains the signal intensity (first signal intensity) at a predetermined reference frequency f1 based on the detection signal S3 (step S23). The signal intensity at the reference frequency f1 obtained by the intensity acquisition unit 16A is converted into a digital signal (I X ) is input to the measuring unit 18A.

[0100] Then, the measuring unit 18A switches the polarization direction of the reference light LR to the Y direction by controlling the polarization switch 30 (step S24). Then, the light detection unit 15A detects the Brillouin scattered light LS using the reference light LR that has passed through the polarization switch 30 (step S25). Specifically, the detector 23 performs optical heterodyne detection by interfering the reference light LR whose polarization direction is the Y direction with the Brillouin scattered light LS. As a result, the detector 23 outputs a detection signal S3 that is an interference signal (beat signal) indicating the frequency difference between the reference light LR whose polarization direction is the Y direction and the scattered light LS.

[0101] The detection signal output from the light detection unit 15A is input to the intensity acquisition unit 16A. The intensity acquisition unit 16A obtains the signal intensity (second signal intensity) at a predetermined reference frequency f1 based on the detection signal S3 (step S26). The signal intensity at the reference frequency f1 obtained by the intensity acquisition unit 16A is converted into a digital signal (I Y) and input to the measuring unit 18A.

[0102] In this way, the measuring unit 18A uses the two digital signals (I X , I Y ) to obtain the peak frequency of the Brillouin gain spectrum (step S16). Specifically, first, the measuring unit 18A obtains the square root of the sum of the squares of the two digital signals sequentially output from the digitizer 17A (√(I X 2 +I Y 2 ))(first processing). Next, the measuring unit 18A obtains the peak frequency of the Brillouin gain spectrum by multiplying the square root of the sum of squares obtained by the first processing by the transformation coefficient stored in the storage unit 18A (second processing). In addition, in order to reduce the influence of noise, the processing of steps S23 and S25 can be performed multiple times, and the above-mentioned first processing can be performed multiple times to obtain the average value of the square roots of the multiple squares obtained.

[0103] When the above processing is finished, the measuring unit 18A measures the characteristics of the measured optical fiber FUT by obtaining the Brillouin frequency shift according to the peak frequency of the Brillouin gain spectrum (step S17). For example, the measuring unit 18A obtains the deformation in one measuring point set in the length direction of the measured optical fiber FUT according to the peak frequency of the Brillouin gain spectrum.

[0104] As mentioned above, in the present embodiment, according to the detection signal S3 of the Brillouin scattered light LS obtained by making the pump light LP incident on the measured optical fiber FUT, the signal intensity in the predetermined reference frequency f1 is obtained. Then, according to the signal intensity in the obtained reference frequency f1, the peak frequency of the Brillouin gain spectrum is obtained to measure the characteristic of the measured optical fiber FUT. Like this, in the present embodiment, similarly to the first embodiment, the detection signal S3 of the Brillouin scattered light LS is not subjected to frequency scanning, and only the peak frequency of the Brillouin gain spectrum is obtained according to the signal intensity in the predetermined reference frequency f1 to measure the characteristic of the measured optical fiber FUT. Thus, the characteristic of the measured optical fiber can be measured in a shorter time.

[0105] In addition, in this embodiment, the polarization direction of the reference light LR is alternately switched between the X direction and the Y direction orthogonal to each other by the polarization switcher 30 provided between the first light branching unit 12 and the light detection unit 15A. Figure 1 The light detection unit 15 , the intensity acquisition unit 16 , and the digitizer 17 shown are replaced with a light detection unit 15A, an intensity acquisition unit 16A, and a digitizer 17A, so that the structure can be simplified and the cost can be reduced.

[0106] [Third embodiment]

[0107] <Structure of Optical Fiber Characteristics Measurement Device>

[0108] Figure 6 FIG. 1 is a block diagram showing the main structure of an optical fiber characteristic measuring device according to a third embodiment of the present invention. Figure 6 In, about Figure 4 The same structures are assigned the same reference numerals. Figure 6 As shown, the optical fiber characteristic measuring device 3 of this embodiment is Figure 4 The optical fiber characteristic measuring device 2 shown has a configuration in which the measuring section 18A is replaced by a measuring section 18B, and the polarization switcher 30 is replaced by a polarization scrambler 40 .

[0109] The optical fiber characteristic measuring device 2 of the second embodiment described above obtains the detection signal of the component with the polarization direction in the X direction and the detection signal of the component with the polarization direction in the Y direction alternately (in a time-sharing manner). In contrast, the optical fiber characteristic measuring device 3 of the present embodiment separates the component with the polarization direction in the X direction and the component with the polarization direction in the Y direction, and randomly changes the polarization direction of the reference light LR by the polarization scrambler 40. This is done to suppress the variation of the Brillouin gain spectrum that depends on the relative polarization states of the reference light LR and the Brillouin scattered light LS.

[0110] The process of obtaining the peak frequency of the Brillouin gain spectrum in the measuring unit 18B is slightly different from that in the measuring unit 18A. Specifically, the measuring unit 18B does not perform the first process (the process of obtaining the square root of the sum of the squares of the two digital signals sequentially output from the digitizer 17A) performed by the measuring unit 18A. The measuring unit 18B performs the process of obtaining the peak frequency of the Brillouin gain spectrum by multiplying the digital signal output from the digitizer 17A by the conversion coefficient stored in the storage unit 18a. In addition, in the measuring unit 18B, the function of controlling the polarization switch 30 of the measuring unit 18A is omitted.

[0111] The polarization scrambler 40 is provided between the first optical branching unit 12 and the optical detection unit 15A, and randomly changes the polarization state of the reference light LR branched by the first optical branching unit 12 over time. The polarization scrambler 40 changes the polarization state of the reference light LR at a speed significantly faster than the speed at which the polarization switch 30 switches the polarization direction of the reference light LR. For example, the polarization scrambler 40 changes the polarization state of the reference light LR at a high speed (at a frequency of about MHz) to average out the influence of the polarization state.

[0112] <Operation of the Optical Fiber Characteristics Measurement Device>

[0113] The basic operation of the optical fiber characteristic measurement device 3 of this embodiment is the same as that of the optical fiber characteristic measurement device 1 of the first embodiment. Figure 3 The following uses the flowchart shown in Figure 3 The operation of the optical fiber characteristics measuring device 3 will be described.

[0114] When the operation of the optical fiber characteristic measuring device 3 starts, similarly to the first embodiment, the linearly polarized continuous light L1 frequency modulated at the modulation frequency fm is output from the light source 11a (step S11), and the continuous light L1 is incident on the first optical branching unit 12 and branched into the pump light LP and the reference light LR (step S12). Then, the branched pump light LP is incident on the optical fiber FUT to be measured via the optical delay unit 13 and the second optical branching unit 14 in sequence (step S13). In addition, as the pump light LP propagates in the optical fiber FUT to be measured, Brillouin scattered light LS (backscattered light) is sequentially generated in the optical fiber FUT to be measured.

[0115] Then, the light detection unit 15A detects the Brillouin scattered light LS using the reference light LR that has passed through the polarization scrambler 40 (step S14). Specifically, the detector 23 performs optical heterodyne detection by interfering the reference light LR whose polarization direction changes randomly with time with the Brillouin scattered light LS. As a result, the detector 23 outputs a detection signal S3 that is an interference signal (beat signal) indicating the frequency difference between the reference light LR and the scattered light LS.

[0116] The detection signal S3 output from the light detection unit 15A is input to the intensity acquisition unit 16A. The intensity acquisition unit 16A obtains the signal intensity at the predetermined reference frequency f1 based on the detection signal S3 (step S15). The signal intensity at the reference frequency f1 obtained by the intensity acquisition unit 16A is converted into a digital signal by the digitizer 17A and input to the measurement unit 18B.

[0117] Next, the measuring unit 18B uses the digital signal output from the digitizer 17A to obtain the peak frequency of the Brillouin gain spectrum (step S16). Specifically, the measuring unit 18B obtains the peak frequency of the Brillouin gain spectrum by multiplying the digital signal output from the digitizer 17A by the conversion coefficient stored in the storage unit 18a. In addition, in order to reduce the influence of noise, the processing of steps S14 and S15 can be performed multiple times to obtain the average value of the multiple digital signals obtained.

[0118] When the above processing is finished, the measuring unit 18B obtains the Brillouin frequency shift amount according to the peak frequency of the Brillouin gain spectrum, and measures the characteristics of the measured optical fiber FUT (step S17). For example, the measuring unit 18B obtains the deformation in one measuring point set in the length direction of the measured optical fiber FUT according to the peak frequency of the Brillouin gain spectrum.

[0119] As described above, in the present embodiment, according to the detection signal S3 of the Brillouin scattered light LS obtained by making the pump light LP incident on the measured optical fiber FUT, the signal intensity in the predetermined reference frequency f1 is obtained. Then, according to the signal intensity in the obtained reference frequency f1, the peak frequency of the Brillouin gain spectrum is obtained to measure the characteristic of the measured optical fiber FUT. Like this, in the present embodiment, similarly to the first embodiment, the detection signal S3 of the Brillouin scattered light LS is not subjected to frequency scanning, but only according to the signal intensity in the predetermined reference frequency f1, the peak frequency of the Brillouin gain spectrum is obtained to measure the characteristic of the measured optical fiber FUT. Thus, the characteristic of the measured optical fiber can be measured in a shorter time.

[0120] In addition, in this embodiment, the polarization direction of the reference light LR is randomly changed over time by the polarization scrambler 40 provided between the first light branching unit 12 and the light detection unit 15A. Figure 1 The light detection unit 15 , the intensity acquisition unit 16 , and the digitizer 17 shown are replaced with a light detection unit 15A, an intensity acquisition unit 16A, and a digitizer 17A, so that the structure can be simplified and the cost can be reduced.

[0121] The optical fiber characteristic measuring device and the optical fiber characteristic measuring method according to the embodiment of the present invention have been described above, but the present invention is not limited to the above embodiment, but can be freely changed within the scope of the present invention. For example, in the above embodiment, the signal intensity at a predetermined reference frequency f1 is obtained by the intensity acquisition unit 16, 16A, and the peak frequency of the Brillouin gain spectrum is obtained based on the signal intensity at the obtained reference frequency f1 by the measurement unit 18, 18A, 18B. However, the signal intensity at a plurality of predetermined reference frequencies may be obtained by the intensity acquisition unit 16, 16A, and the peak frequency of the Brillouin gain spectrum may be obtained based on the signal intensity at the obtained plurality of reference frequencies by the measurement unit 18, 18A, 18B.

[0122] Figure 7 Graph showing the relationship between the signal intensity and the peak frequency of the Brillouin gain spectrum at a plurality of predetermined reference frequencies. Figure 7 In, with Figure 2 Similarly, the horizontal axis represents frequency and the vertical axis represents signal intensity, showing three Brillouin gain spectra G0, G1, and G2.

[0123] exist Figure 7 In the example shown, in addition to the aforementioned reference frequency f1, a reference frequency f2 is also set. Both reference frequencies f1 and f2 are defined as frequencies within the frequency band of the Brillouin gain spectrum G0 obtained when the measured optical fiber FUT is placed under a predetermined reference environment. Specifically, the reference frequencies f1 and f2 are defined as the peak frequency fp0 sandwiching the Brillouin gain spectrum G0. For example, the reference frequencies f1 and f2 may also be defined as the peak frequency fp0 sandwiching the Brillouin gain spectrum G0 at equal intervals. The reference frequency f2, like the reference frequency f1, is defined as a frequency at which the signal intensity changes significantly due to the Brillouin gain spectrum shift. For example, the reference frequency f2, like the reference frequency f1, may also be defined as the frequency at which the slope (absolute value) of the Brillouin gain spectrum G0 becomes the maximum.

[0124] like Figure 2 In the example shown, the signal strengths at the reference frequencies f1 and f2 when the Brillouin gain spectrum G0 is obtained are both I2. The signal strength at the reference frequency f1 when the Brillouin gain spectrum G1 is obtained is I3 which is larger than I2, and the signal strength at the reference frequency f2 is I1 which is smaller than I2. On the contrary, the signal strength at the reference frequency f1 when the Brillouin gain spectrum G2 is obtained is I1 which is smaller than I2, and the signal strength at the reference frequency f2 is I3 which is larger than I2.

[0125] Here, the shift amount of the Brillouin gain spectrum (the change amount of the peak frequency of the Brillouin gain spectrum) and the change amount of the signal intensity at the reference frequency f1 have a one-to-one relationship. Similarly, the shift amount of the Brillouin gain spectrum (the change amount of the peak frequency of the Brillouin gain spectrum) and the change amount of the signal intensity at the reference frequency f2 have a one-to-one relationship. Therefore, if the signal intensity at the reference frequencies f1 and f2 is known, the peak frequency of the Brillouin gain spectrum can be obtained.

[0126] When the signal strengths of two reference frequencies f1 and f2 are obtained, information indicating the relationship between the signal strength at the reference frequency f1, the signal strength at the reference frequency f2, and the peak frequency of the Brillouin gain spectrum is stored in the storage unit 18a of the measuring unit 18. Then, in the measuring unit 18, a process of obtaining the peak frequency of the Brillouin gain spectrum using the information stored in the storage unit 18a is performed. When the signal strengths at a plurality of reference frequencies are obtained, the error of the peak frequency of the Brillouin gain spectrum can be reduced compared to the case of obtaining the signal strength at one reference frequency.

[0127] In addition, in the above-mentioned embodiment, an optical fiber characteristic measuring device of the BOCDR method is described as an example, but it can also be applied to a device other than the optical fiber characteristic measuring device of the BOCDR method. Specifically, it can be applied to a device that obtains a Brillouin gain spectrum and analyzes the obtained Brillouin gain spectrum to obtain the Brillouin frequency shift amount. Such a device can be, for example, an optical fiber characteristic measuring device of the BOCDA (Brillouin Optical Correlation Domain Analysis) method.

[0128] In addition, in the above-mentioned embodiment, in order to make the description simple, it is described with only one correlation peak appearing in the measured optical fiber FUT. In the case where multiple correlation peaks appear in the measured optical fiber FUT, for example, a method called a time gate method can be used to select one of the multiple correlation peaks, and only the Brillouin scattered light in the position where the selected correlation peak appears is extracted.

[0129] In addition, the optical delay unit 13 may be provided between the second optical branching unit 14 and the optical detection unit 15, 15A, in addition to being provided between the first optical branching unit 12 and the second optical branching unit 14, or between the first optical branching unit 12 and the optical detection unit 15, 15A. In addition, a first optical amplifier for amplifying the pump light LP may be provided between the first optical branching unit 12 and the second optical branching unit 14. In addition, a second optical amplifier for amplifying the Brillouin scattered light LS may be provided between the second optical branching unit 14 and the optical detection unit 15, 15A. In addition, a third optical amplifier for amplifying the reference light LR may be provided between the first optical branching unit 12 and the optical detection unit 15, 15A.

[0130] Furthermore, in the optical fiber characteristic measurement device 1 of the first embodiment, a first signal amplifier for amplifying the detection signal S1 may be provided between the detector 23a and the spectrum analyzer 24a, and a second signal amplifier for amplifying the detection signal S2 may be provided between the detector 23b and the spectrum analyzer 24b. Furthermore, in the optical fiber characteristic measurement devices 2 and 3 of the second and third embodiments, a signal amplifier for amplifying the detection signal S3 may be provided between the detector 23 and the spectrum analyzer 24.

[0131] The words "front, back, up, down, right, left, vertical, horizontal, longitudinal, transverse, row and column" in this specification, which indicate directions, refer to these directions in the device of the present invention. Therefore, these words in the specification of the present invention should be interpreted relatively in the device of the present invention.

[0132] The term “configured” is used to indicate being configured to perform the function of the present invention, or to indicate the structure, element, or part of a device.

[0133] Furthermore, the term "means plus action" in the claims should include any structure that can be used to perform the functions included in the present invention.

[0134] The term "unit" is used to refer to a structural element, a unit, hardware, or a part of software that is programmed to perform a desired function. Typical examples of hardware are devices and circuits, but are not limited thereto.

[0135] The preferred embodiments of the present invention are described above, but the present invention is not limited to these embodiments. Additions, omissions, substitutions and other changes to the structure can be made without departing from the spirit of the present invention. The present invention is not limited by the above description, but only by the attached claims.

[0136] Description of symbols

[0137] 1~3 Optical fiber characteristic measurement device

[0138] 11 Light source

[0139] 12. 1st optical branching unit

[0140] 13. Optical Delay Unit

[0141] 14 Second optical branching unit

[0142] 15.15A Light detection unit

[0143] 16.16A Strength acquisition unit

[0144] 18, 18A, 18B Measurement unit

[0145] 18a Storage

[0146] 22a, 22b Polarization separation element

[0147] 23a, 23b Detector

[0148] 30 Polarization switcher

[0149] 40 Polarization Scrambler

[0150] f1, f2 reference frequency

[0151] FUT Fiber under test

[0152] L1 Continuous light

[0153] LP pump light

[0154] LR reference light

[0155] LR1, LR2 reference light

[0156] LS Brillouin scattered light

[0157] LS1, LS2 Scattered light

[0158] S1~S3 detection signal

Claims

1. An optical fiber characteristic measuring device, comprising: a light detection unit for detecting Brillouin scattered light obtained by causing light to be incident on the optical fiber; an intensity acquisition unit, which obtains a plurality of signal intensities at a predetermined reference frequency based on the detection signal output from the light detection unit; as well as a measuring unit that obtains a square root of a sum of squares of the plurality of signal intensities at the reference frequency obtained by the intensity obtaining unit, multiplies the square root of the sum of squares by a transformation coefficient, thereby obtaining a peak frequency of a Brillouin gain spectrum that is a spectrum of the Brillouin scattered light, and measures a characteristic of the optical fiber; The reference frequency is a frequency within a frequency band of a reference Brillouin gain spectrum of the Brillouin gain spectrum obtained when the optical fiber is placed in a predetermined reference environment. The reference environment is an environment in which the temperature around the optical fiber is a predetermined temperature and no deformation is applied to the optical fiber.

2. The optical fiber characteristic measuring device according to claim 1, wherein: The reference frequency is a frequency at which the slope of the reference Brillouin gain spectrum becomes maximum.

3. The optical fiber characteristic measuring device according to claim 1 or claim 2, wherein: The reference frequencies are two frequencies sandwiching the peak frequency of the reference Brillouin gain spectrum.

4. The optical fiber characteristic measuring device according to claim 1 or claim 2, wherein: The device comprises: a storage unit storing conversion information for converting the signal intensity at the reference frequency into the peak frequency of the Brillouin gain spectrum; The measuring unit obtains the peak frequency of the Brillouin gain spectrum from the signal intensity at the reference frequency acquired by the intensity acquiring unit, using the conversion information stored in the storage unit.

5. The optical fiber characteristic measuring device according to claim 1 or claim 2, comprising: A light source part, outputting frequency-modulated continuous light; a first light branching unit that branches the continuous light into a pump light and a reference light; and The second optical branching section allows the pump light to be incident from one end of the optical fiber and outputs the Brillouin scattered light generated in the optical fiber. The light detection unit detects interference light between the Brillouin scattered light and the reference light.

6. The optical fiber characteristic measuring device according to claim 5, wherein: The light detection unit comprises: a first separation element for separating the reference light into a first reference light and a second reference light having polarization directions orthogonal to each other; a second separation element for separating the Brillouin scattered light into a first scattered light having the same polarization direction as the first reference light and a second scattered light having the same polarization direction as the second reference light; a first detector for detecting interference light between the first scattered light and the first reference light; as well as a second detector for detecting interference light between the second scattered light and the second reference light, The intensity acquisition unit obtains a first signal intensity as the signal intensity at the reference frequency based on the detection signal output from the first detector, and obtains a second signal intensity as the signal intensity at the reference frequency based on the detection signal output from the second detector, The measuring unit obtains a peak frequency of the Brillouin gain spectrum based on the first signal intensity and the second signal intensity obtained by the intensity acquiring unit.

7. The optical fiber characteristic measuring device according to claim 5, wherein: The device comprises: a polarization switcher for alternately switching the polarization direction of the reference light into a first direction and a second direction that are orthogonal to each other; The intensity acquisition unit obtains a first signal intensity as a signal intensity at the reference frequency based on the detection signal output from the light detection unit when the polarization direction of the reference light is switched to the first direction by the polarization switcher, and obtains a second signal intensity as a signal intensity at the reference frequency based on the detection signal output from the light detection unit when the polarization direction of the reference light is switched to the second direction by the polarization switcher. The measuring unit obtains a peak frequency of the Brillouin gain spectrum based on the first signal intensity and the second signal intensity obtained by the intensity acquiring unit.

8. The optical fiber characteristic measuring device according to claim 5, comprising: A polarization scrambler causes the polarization state of the reference light to change randomly over time.

9. The optical fiber characteristic measuring device according to claim 5, comprising: The optical delay unit delays the pump light between the first optical branching unit and the second optical branching unit.

10. A method for measuring optical fiber characteristics, wherein: The light detection unit detects the Brillouin scattered light obtained by injecting light into the optical fiber. The intensity acquisition unit obtains a plurality of signal intensities at a predetermined reference frequency based on the detection signal output from the light detection unit. The measuring unit obtains the square root of the sum of squares of the plurality of signal intensities at the reference frequency obtained by the intensity obtaining unit, and multiplies the square root of the sum of squares by a transformation coefficient to obtain the peak frequency of the Brillouin gain spectrum which is the spectrum of the Brillouin scattered light, thereby measuring the characteristics of the optical fiber. The reference frequency is a frequency within a frequency band of a reference Brillouin gain spectrum of the Brillouin gain spectrum obtained when the optical fiber is placed in a predetermined reference environment. The reference environment is an environment in which the temperature around the optical fiber is a predetermined temperature and no deformation is applied to the optical fiber.

11. The optical fiber characteristic measurement method according to claim 10, wherein: The reference frequency is a frequency at which the slope of the reference Brillouin gain spectrum becomes maximum.

12. The optical fiber characteristic measurement method according to claim 10 or claim 11, wherein: The reference frequencies are two frequencies sandwiching the peak frequency of the reference Brillouin gain spectrum.

13. The optical fiber characteristic measurement method according to claim 10 or claim 11, wherein: The storage unit stores conversion information for converting the signal intensity at the reference frequency into the peak frequency of the Brillouin gain spectrum. The measurement unit uses the conversion information stored in the storage unit to obtain the peak frequency of the Brillouin gain spectrum from the signal intensity at the reference frequency acquired by the intensity acquisition unit.

14. The optical fiber characteristic measurement method according to claim 10 or claim 11, wherein: Through the light source, the frequency modulated continuous light is output. The continuous light is branched into pump light and reference light by a first light branching unit, The pump light is input from one end of the optical fiber through the second optical branching section, and the Brillouin scattered light generated in the optical fiber is output. The light detection unit detects interference light between the Brillouin scattered light and the reference light.

15. The optical fiber characteristic measurement method according to claim 14, wherein: The light detection unit includes a first separation element, a second separation element, a first detector, and a second detector. The reference light is separated into a first reference light and a second reference light whose polarization directions are orthogonal to each other by the first separation element. The Brillouin scattered light is separated into a first scattered light having the same polarization direction as the first reference light and a second scattered light having the same polarization direction as the second reference light by the second separation element. detecting interference light between the first scattered light and the first reference light by the first detector, detecting interference light between the second scattered light and the second reference light by the second detector, The intensity acquisition unit obtains a first signal intensity as the signal intensity at the reference frequency based on the detection signal output from the first detector, and obtains a second signal intensity as the signal intensity at the reference frequency based on the detection signal output from the second detector, The peak frequency of the Brillouin gain spectrum is obtained by the measuring unit based on the first signal intensity and the second signal intensity obtained by the intensity acquiring unit.

16. The optical fiber characteristic measurement method according to claim 14, wherein: By using a polarization switcher, the polarization direction of the reference light is alternately switched to a first direction and a second direction that are orthogonal to each other, The intensity acquisition unit obtains a first signal intensity as a signal intensity at the reference frequency based on the detection signal output from the light detection unit when the polarization direction of the reference light is switched to the first direction by the polarization switcher, The intensity acquisition unit obtains a second signal intensity as a signal intensity at the reference frequency based on the detection signal output from the light detection unit when the polarization direction of the reference light is switched to the second direction by the polarization switcher, The peak frequency of the Brillouin gain spectrum is obtained by the measuring unit based on the first signal intensity and the second signal intensity obtained by the intensity acquiring unit.

17. The optical fiber characteristic measurement method according to claim 14, wherein: The polarization state of the reference light is randomly changed over time by a polarization scrambler.

18. The optical fiber characteristic measurement method according to claim 14, wherein: The pump light is delayed by an optical delay unit between the first optical branching unit and the second optical branching unit.

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