JP6796043B2 - Light reflection measuring device and its method - Google Patents

Description

The present invention relates to a light reflection measurement technique for measuring reflected light or rear Rayleigh scattered light amplitude distribution in an optical fiber.

One of the optical reflection measuring methods used for optical fiber loss distribution measurement and optical fiber sensing is the optical frequency domain reflection measuring method (OFDR) (see, for example, Non-Patent Document 1). The OFDR splits the frequency-swept continuous light into two, uses one of them as test light to enter the fiber under test, and combines the reflected light or backward scattered light from the fiber under test with the other continuous light that has branched. This is a method of analyzing the reflection (scattering) point from the frequency region of the obtained beat signal. Assuming that the test light in OFDR is E (t) and the beat signal is I (t), they are expressed as follows.

Here, E ₀ , ν ₀ , and γ are the optical amplitude of the test light, the initial optical frequency, and the frequency sweep rate, and r _FUT and τ _FUT are the reflectance and optical reciprocating propagation time at the reflection (scattering) point of the fiber under test. θ _FUT (t) is phase noise due to disturbance such as vibration applied to the fiber to be measured. For the sake of simplicity, the phase noise derived from the light source is ignored here. Also, since τ _FUT is sufficiently small, the square term of τ _FUT is ignored.

As can be seen from equation (2), if the phase noise θ _FUT (t) is ignored, I (t) is a sine wave with a frequency of γτ _FUT . Therefore, the reflected position of the reflected (scattered) light by the Fourier transform of I (t). And the amplitude is analyzed.

W. Eickhohh et al, “Optical frequency domain reflectometry in single-mode fiber,” Applied Physics Letters 39 (9), pp.693-695 (1981). S. Kreger et al, “Distributed Rayleigh scatter dynamic strain sensing above the scan rate with optical frequency domain reflectometry,” Proc. SPIE 9480, Fiber Optic Sensors and Applications XII, 948006 (2015).

However, although the phase noise θ _FUT (t) due to disturbance such as vibration can be ignored in the above description, there is a problem that the spatial resolution of OFDR deteriorates because the spectrum of the beat signal is widened by the disturbance in the actual measurement scene.

The present invention has been made in view of the above circumstances, and an object of the present invention is light reflection measurement that analyzes or compensates for disturbances in an environment where disturbances such as vibrations are applied to the fiber to be measured to realize high spatial resolution. The purpose is to provide an apparatus and a method thereof.

In order to solve the above problems, the present invention is a light reflection measuring device, which divides a light source that emits frequency-swept continuous light and the continuous light into a first optical path and a second optical path. It is an interferometer that outputs a beat signal by merging the continuous light after propagating the first optical path and the continuous light after propagating the second optical path, and the first optical path is The continuous light after the first optical path propagation includes the orbital optical path that gives a delay time τ _Loop, and the continuous light before the orbital optical path propagation and the continuous light after the orbital optical path propagation are incident on the optical fiber to be measured. The interferometer, which is the reflected light or scattered light generated by the optical fiber to be measured, the light detecting means for converting the beat signal into an electric signal, and the optical amplitude distribution waveform of the reflected light or the scattered light using the electric signal. The arithmetic processing means is provided with an arithmetic processing means for calculating the above, and the arithmetic processing means divides the beat signal into τ _Loop units and performs Fourier conversion, calculates a plurality of complex spectra for each τ _Loop unit, and performs a plurality of complex spectra. The phase component at an arbitrary point of the reflected light or scattered light amplitude distribution waveform appearing on the highest frequency side of each of the complex spectra is extracted, the time change of the phase of the reflected light or the scattered light is calculated, and the time change of the phase is obtained. The beat signal is resampled according to the time sequence calculated based on the above, and the resampled beat signal is Fourier-transformed to calculate the optical amplitude distribution waveform of the reflected light or the scattered light in which the phase fluctuation of the optical fiber to be measured is compensated. A light reflection measuring device characterized by

The invention according to claim 2 is a light reflection measuring device, wherein a light source that emits continuous light whose frequency has been swept and the continuous light are demultiplexed into a first optical path and a second optical path. An interferometer that outputs a beat signal by combining the continuous light after the first optical path propagation and the continuous light after the second optical path propagation, and the first optical path has a delay time τ _Loop. The continuous light after the propagation of the first optical path includes the continuous light before the propagation of the orbital optical path and the continuous light after the propagation of the orbital optical path is incident on the optical fiber to be measured, and the optical fiber to be measured The interferometer, which is the reflected light or scattered light generated in the above, the light detecting means for converting the beat signal into an electric signal, and the calculation for calculating the light amplitude distribution waveform of the reflected light or the scattered light using the electric signal. The arithmetic processing means includes a processing means, and the arithmetic processing means divides the beat signal into τ _Loop units in a time region and performs Fourier conversion, calculates a plurality of complex spectra for each τ _Loop unit, and obtains a plurality of complex spectra of the plurality of complex spectra. The phase component at an arbitrary point of the reflected light or scattered light amplitude distribution waveform appearing on the highest frequency side of each is extracted, the time change of the phase of the reflected light or the scattered light is calculated, and the measured light is measured from the time change of the phase. It is characterized by analyzing the frequency of vibration generated in the fiber.

The invention according to claim 3 is the light reflection measuring apparatus according to claim 1 or 2, wherein the first optical path is a phase reference dummy light between the circumferential optical path and the optical fiber to be measured. The arithmetic processing means includes a fiber, and the arithmetic processing means determines the time change of the phase difference between the reflected light or the scattered light of the optical fiber to be measured and the reflected light or the scattered light of the dummy optical fiber for phase reference as the time change of the phase. It is characterized by being used.

The invention according to claim 4 is a method for measuring light reflection, in which a first step of emitting continuous light frequency-swept from a light source and the continuous light are divided into a first optical path and a second optical path. It is a second step of wavening and combining the continuous light after propagating the first optical path and the continuous light after propagating the second optical path to output a beat signal, which is the first optical path. Includes an orbital optical path that gives a delay time τ _Loop, and the continuous light after the first optical path propagation is incident on the optical fiber to be measured by the continuous light before the orbital optical path propagation and the continuous light after the orbital optical path propagation. The second step of outputting the beat signal, which is the reflected light or scattered light generated by the optical fiber to be measured, the third step of converting the beat signal into an electric signal, and the reflected light using the electric signal. Alternatively, it has a fourth step of calculating the optical amplitude distribution waveform of the scattered light, and the fourth step divides the beat signal into τ _Loop units in the time region and performs Fourier conversion, and for each τ _Loop unit. The 41st step of calculating a plurality of complex spectra and the phase of the reflected light or the scattered light by extracting the phase component at an arbitrary point of the reflected light or scattered light amplitude distribution waveform appearing on the highest frequency side of each of the plurality of complex spectra. The 42nd step of calculating the time change of the above, the 43rd step of resampling the beat signal with the time sequence calculated based on the time change of the phase, and the Fourier transform of the resampled beat signal to be measured. It is characterized by having a 44th step of calculating an optical amplitude distribution waveform of reflected light or scattered light in which phase fluctuation of an optical fiber is compensated.

The invention according to claim 5 is a method for measuring light reflection, in which a first step of emitting continuous light frequency-swept from a light source and the continuous light are divided into a first optical path and a second optical path. a second step of outputting a beat signal by multiplexing the continuous light after the second optical path and propagation continuous light after propagating the first optical path to the wave, the first optical path Includes an orbital optical path that gives a delay time τ _Loop, and the continuous light after the first optical path propagation is incident on the optical fiber to be measured by the continuous light before the orbital optical path propagation and the continuous light after the orbital optical path propagation. The second step of outputting the beat signal, which is the reflected light or scattered light generated by the optical fiber to be measured, the third step of converting the beat signal into an electric signal, and the reflected light using the electric signal. Alternatively, it has a fourth step of calculating the light amplitude distribution waveform of the scattered light, and the fourth step divides the beat signal into τ _Loop units in a time region and performs Fourier conversion, and for each τ _Loop unit. The 41st step of calculating a plurality of complex spectra and the phase component of the reflected light or scattered light amplitude distribution waveform appearing on the highest frequency side of each of the plurality of complex spectra are extracted and the phase of the reflected light or scattered light is extracted. and 42 calculating a time variation of, characterized in that the time variation of the previous SL phase having a 45th step of analyzing the frequency of the vibration generated in the optical fiber to be measured.

The invention according to claim 6 is the light reflection measuring method according to claim 4 or 5, wherein the first optical path includes a phase reference dummy optical fiber between the circumferential optical path and the measured optical fiber. In the 42nd step , as the time change of the phase, the time change of the phase difference between the reflected light or the scattered light of the optical fiber to be measured and the reflected light or the scattered light of the dummy optical fiber for phase reference is used. It is characterized by.

According to the present invention, it is possible to realize an application using OFDR such as loss distribution measurement and optical fiber sensing with high resolution even in an environment where disturbance such as vibration is applied. Further, by Fourier transforming the phase change of the reflected (scattered) light obtained in the present invention and performing frequency analysis, the frequency of vibration generated in the fiber to be measured can be analyzed, so that it can be applied as optical fiber vibration sensing. is there. The conventional vibration sensing method using OFDR (for example, Non-Patent Document 2) requires reference data acquired in advance in a vibration-free state, but the method according to the present invention does not require reference data, so that it is compared with the conventional method. Vibration sensing can be easily performed.

It is a conceptual diagram of the phase analysis method of the reflected (scattered) light in the present invention, (a) is a diagram showing a beat signal, and (b) is a diagram showing a complex spectrum obtained by Fourier transforming a beat signal. , (C) is a diagram showing the time change of the phase of the reflected (scattered) light. This is an example of the time change of the phase of the beat signal calculated in the present invention. This is an example of the power spectrum waveform of the beat signal obtained by the present invention. It is a block diagram which shows an example of the structure of the light reflection measuring apparatus which concerns on 1st and 2nd Embodiment of this invention. It is a flowchart which shows the flow of measurement in the light reflection measuring apparatus which concerns on 1st Embodiment of this invention. It is a flowchart which shows the flow of measurement in the light reflection measuring apparatus which concerns on 2nd Embodiment of this invention.

In the present invention, an orbiting optical path is provided in the OFDR measurement system, and by passing the frequency sweep continuous light used for the test light through the orbiting optical path, a plurality of test lights are incident on the fiber to be measured for each orbit time, and the plurality of test lights are used. The above problem is solved by measuring the phase change for each orbital time by individually analyzing the phase of the reflected (scattered) light and compensating for the influence of the phase noise based on the obtained phase change information.

In order to compensate for the influence of the phase noise derived from the disturbance in the suppression OFDR, it is necessary to obtain the time change information of the phase of the reflected (scattered) light within the beat signal acquisition time, but the test light of the conventional OFDR measurement Is one frequency sweep continuous light per OFDR measurement, so it was impossible to obtain the phase change information generated during one measurement.

On the other hand, in the present invention, a plurality of frequency sweep continuous lights can be produced by passing through the orbiting optical path, and since they have different arrival times of the fibers to be measured, the reflected (scattered) light signals by each frequency sweep continuous light are individually generated. The phase change information of the reflected (scattered) light can be obtained by the analysis.

Furthermore, by continuing the frequency sweep with the light source during the orbital optical path propagation (instead of repeating the sweep, one sweep is continued for a long time), the conventional OFDR beat signal (signal by non-circumferential light) at the same time as the signal by the orbital optical path propagation light. ) Can be obtained at the same time, and noise compensation can be applied to the signal due to non-circumferential light by using the phase change information obtained from the orbital optical path propagating light. The test light E'(t) after propagating in the orbiting optical path in the present invention is expressed by the following equation.

Here, n is the number of laps in the lap optical path, and τ _Loop and Δφ are the propagation delay time and the phase change per lap. Since the τ _Loop is sufficiently small, the square term of the τ _Loop is ignored. At this time, the time width T related to the frequency sweep of the light source satisfies T> 2τ _Loop , and N (t) is an integer of 1 or more and T / τ _Loop or less. When E'(t) is used as the test light, the obtained beat signal I'(t) is as follows.

Here, the squared terms of the delay times τ _FUT and τ _Loop are ignored.

FIG. 1 shows a conceptual diagram of phase analysis of reflected (scattered) light using the beat signal I'(t). The phase change information of the reflected (scattered) light is a complex spectrum obtained by short-time Fourier transforming the beat signal I'(t) in the range of iτ _Loop <t <(i + 1) τ _Loop (i is an integer of 0 or more). S _i (f) is calculated for each number of orbits in the orbiting optical path, and is obtained from the phase component of each calculated complex spectrum S _i (f). Considering only the positive frequency component (f> 0), the short-time Fourier transform of I'(t) is as follows.

Here, the propagation delay time τ _Loop per circuit of the orbiting optical path is sufficiently shorter than the fluctuation period of the phase noise θ _FUT (t) of the fiber 200 to be measured, and the time interval of iτ _Loop <t <(i + 1) τ _Loop . Then, θ _FUT (t) is almost constant and can be regarded as θ _FUT (iτ _Loop ).

As shown in the equation (6), in S ₀ (f), one reflected (scattered) light amplitude distribution waveform appears in the beat frequency domain, and S _i (f) (i is an integer of 1 to N-1). Then, N reflected (scattered) light amplitude distribution waveforms appear in the beat frequency region (FIG. 1 (b)). That is, when i is an integer of 1 to N-1, S _i (f) includes a plurality of reflected (scattered) light amplitude distribution waveforms corresponding to beat signals with lights having different numbers of orbits in the orbiting optical path. The value of S _i (f) at f = γ (τ _FUT + iτ _Loop ) (i is an integer of 0 to N-1) is iτ _Loop <t <at the point corresponding to the propagation delay time τ _FUT of the measured fiber 200. (I + 1) Indicates the electric field complex amplitude of the reflected (scattered) light at the time of τ _Loop .

When S _i (f) is calculated for different i, the reflection (scattered) light amplitude distribution waveform (f = γ (τ _FUT + iτ _Loop )) on the highest frequency side in each S _i (f), that is, the number of orbits of the orbiting optical path is The reflected (scattered) light amplitude distribution waveform corresponding to the beat signal with the most light shows the reflected (scattered) light amplitude distribution waveform of the same light frequency generated at different times. Therefore, by obtaining the phase component of S _i (γ (τ _FUT + iτ _Loop )) for each value of i, it is possible to analyze the time change of the phase of the reflected (scattered) light as shown in FIG. 1 (c). it can. The phase component of S _i (γ (τ _FUT + iτ _Loop )) is as follows.

Here, since the beat frequency difference (γτ _FUT ) of the plurality of reflected (scattered) light amplitude distribution waveforms appearing in S _i (f) is sufficiently larger than the spectral resolution (~ 1 / τ _Loop ), it is as follows. Approximate.

Replacing iτ _Loop = t', Eq. (7) is rewritten as follows.

Therefore, the phase noise θ _FUT (t') is obtained by the following equation.

Next, as shown in FIG. 2, the time change of the phase of the OFDR beat signal on which the phase noise θ _FUT (t) is superimposed is calculated, the time sequence corresponding to the unit phase change is calculated, and I'in each time sequence. By arranging (resampling) (t) at equal intervals on the time axis, the influence of phase noise at I'(t) is compensated. That is, I'(t) is resampled in the time sequence t _m (m is a natural number) satisfying the following equation.

Here, ω is an arbitrary angular frequency, and δ is an arbitrary phase constant.

If replaced with, the beat signal after resampling

Is as follows.

An example of the Fourier transform of is shown in FIG. In the beat frequency region, the reflected (scattered) light amplitude distribution waveforms of n = 0, 1, 2, ... Appear in order from the low frequency side. In the waveform on the lowest frequency side (n = 0), the phase noise θ _FUT (t) term becomes 0 at the point corresponding to the delay τ _FUT = ω / 2πγ, and the phase noise is compensated. At other points, phase noise compensation is possible by performing the above-mentioned series of processes from phase analysis to resampling for different τ _FUTs .

Embodiments of the present invention will be described with reference to the accompanying drawings. The following embodiments are examples of the configurations of the present invention, and the present invention is not limited to the following embodiments.

(First Embodiment)
The first embodiment described below is carried out for the purpose of compensating for phase noise due to disturbance and performing high spatial resolution light reflection measurement in an environment where disturbance such as vibration is applied to the fiber to be measured.

FIG. 4 shows the configuration of the light reflection measuring device 100 according to the first embodiment of the present invention. A frequency sweep light source 101 having a frequency sweep means is used as the light source, and continuous light whose frequency is swept linearly with respect to time is emitted. The emitted continuous light is branched into two by an optical demultiplexer 111, one is incident on the orbiting optical path 102 from the photosynthetic demultiplexer 112, and the other is local light for coherent detection of reflected (scattered) light.

The continuous light incident on the orbiting optical path 102 propagates through the delay fiber 104 having a length of twice or more the length of the fiber to be measured, and then the optical amplifier 103 compensates for the optical loss due to the delay fiber propagation. It should be noted that the optical amplifier 103 here does not necessarily have to be used if sufficient signal intensity can be obtained for the phase analysis of the reflected (scattered) light even if the light loss due to the propagation of the orbiting optical path 102 occurs.

The continuous light after propagating in the orbiting optical path 102 is incident on the measured fiber 200 via the optical junction demultiplexer 112, the optical circulator 108, and the optical phase reference dummy fiber 109, and is in the phase reference dummy fiber 109 and the measured fiber 200. Reflected and Rayleigh scattered. The phase reference dummy fiber 109 here is installed in an environment where disturbance such as vibration is not applied.

The reflected (scattered) light from the phase reference dummy fiber 109 and the fiber under test 200 is incident on the optical combiner 113 via the optical circulator 108 and combined with the local light, and a beat signal is output from the optical combiner 113. Will be done. In this way, in the light reflection measuring device 100, the optical interferometer is configured by the optical demultiplexer 111, the optical combiner 113, and the optical path between them.

The beat signal output from the optical combiner 113 is converted into an electric signal by the receiver 105, and converted into a digital signal by the A / D converter 106. The A / D converter 106 records a beat signal having a time width Nτ _Loop (N is a natural number, τ _Loop is a delay time related to one-round propagation of the orbital optical path 102).

Next, the arithmetic processing apparatus 107 performs signal processing to compensate for the phase noise caused by the disturbance generated in the fiber 200 to be measured, and obtains a reflected (scattered) light amplitude distribution in the longitudinal direction of the fiber 200 to be measured.

FIG. 5 shows a flowchart showing the flow of arithmetic processing performed by the arithmetic processing unit 107 of the light reflection measuring apparatus 100 according to the first embodiment of the present invention.

First, in step S501, as shown in FIG. 1, the beat signal is Fourier-transformed for a short time in the range of iτ _Loop <t <(i + 1) τ _Loop (i = 0 to N-1), and each divided signal is Fourier-transformed. To obtain N complex spectra S _i (f).

Next, in step S502, the phase component of S _i (γ (τ _Ref + iτ _Loop )) is obtained for each i to obtain the phase change Θ _Ref (iτ _Loop ) of the scattered light at an arbitrary point of the phase reference dummy fiber 109. To analyze. As τ _Ref here, an arbitrary value of 2 L _Ref / v (v is the speed of light in the fiber) or less is used, where the fiber length of the phase reference dummy fiber 109 is L _Ref . At this time, Θ _Ref (iτ _Loop ) is given by the following equation.

Since the phase reference dummy fiber 109 is installed in an environment where disturbance is not applied, the phase noise propagating through the phase reference dummy fiber 109 can be ignored.

Next, in step S503, the phase change Θ _FUT (iτ _Loop ) of the scattered light at an arbitrary point of the measured fiber 200 is analyzed by obtaining the phase component of S _i (γ (τ _FUT + iτ _Loop )) for each i. .. Here, τ _FUT is an arbitrary value that satisfies 2L _Ref / v <τ _FUT <2L _FUT / v, where the length of the fiber to be measured is L _FUT . Θ _FUT (iτ _Loop ) is given by the following equation.

The order in which steps S502 and S503 are performed may be reversed.

Next, in step S504, the phase noise is calculated from the phase difference between Θ _FUT (iτ _Loop ) and Θ _Ref (iτ _Loop ). Theta _FUT phase difference ΔΘ of (iτ _Loop) and _{Θ Ref (iτ Loop) (iτ} Loop) is given by the following equation.

Substituting iτ _Loop = t', equation (15) is rewritten as:

Next, in step S505, the time sequence used for the resampling process performed in step S506 is calculated. The time sequence t _m is calculated by the following formula.

Next, in step S506, the beat signal is resampled based on the time sequence t _m . As a result of resampling, the beat signal has the form shown in Eq. (12).

Finally, in step S507, the beat signal resampled in step S506 is Fourier transformed to obtain a reflected (scattered) light amplitude distribution waveform. Of the multiple amplitude distribution waveforms that appear after the Fourier transform, the lowest frequency side shows the waveform after phase noise compensation.

By the above arithmetic processing, the phase noise of the reflected (scattered) light at the point corresponding to the delay τ _FUT is compensated. When compensating for phase noise at different points, steps S503 to S507 are performed for different τ _FUTs . Reflected (scattered) light amplitude distribution obtained for different τ _FUT Reflected (scattered) light compensated for phase noise at multiple points by cutting out the waveform data of an arbitrary section centered on each τ _FUT and connecting them. Amplitude distribution waveform can be obtained.

(Second Embodiment)
The second embodiment described below is carried out for the purpose of analyzing the frequency of vibration applied to the fiber 200 to be measured.

The apparatus configuration used in this embodiment is the same as that of the first embodiment, and the arithmetic processing performed by the arithmetic processing unit 107 in FIG. 4 is different from that of the first embodiment.

First, the beat signal generated by the combined wave of the reflected light of the fiber 200 to be measured and the local light is acquired by using the apparatus shown in FIG. The beat signal is acquired in the same manner as in the first embodiment.

Next, the arithmetic processing unit 107 analyzes the frequency of the vibration applied to the fiber 200 to be measured by using the beat signal.

FIG. 6 shows a flowchart showing the flow of arithmetic processing performed by the arithmetic processing unit 107 of the light reflection measuring apparatus 100 according to the second embodiment of the present invention.

First, the time change ΔΘ (t') of the phase of the reflected (scattered) light of the fiber to be measured is analyzed by the processing of steps S601 to S604. Since steps S601 to S604 are the same processes as those in the first embodiment, the description thereof will be omitted here.

Next, in step S605, the frequency of the vibration applied to the fiber to be measured is analyzed using ΔΘ (t'). When vibration is applied to the fiber 200 to be measured, the reflected (scattered) light is phase-modulated at the vibration frequency. That is, ΔΘ (t') is described by the following equation.

Here, θ _v is the phase modulation amplitude due to vibration, and f _v is the vibration frequency. As is clear from the equation (18), the frequency of the vibration applied to the fiber 200 to be measured can be analyzed by Fourier transforming ΔΘ (t') and performing frequency analysis.

The arithmetic processing unit 107 in the first and second embodiments can also be realized by a general-purpose computer and a program for executing the light reflection measurement method, and the program can be recorded on a recording medium or communication. It can also be provided through the network.

100 Optical reflection measuring device 101 Frequency sweep light source 102 Circular optical path 103 Optical amplifier 104 Delayed fiber 105 Receiver 106 A / D converter 107 Computational processing device 108 Optical circulator 109 Optical phase reference dummy fiber 111 Optical duplexer 112 Optical duplexer Instrument 113 Optical combiner 200 Fiber under test

Claims (6)

A light source that emits continuous light whose frequency has been swept,
The continuous light is demultiplexed into a first optical path and a second optical path, and the continuous light after the propagation of the first optical path and the continuous light after the propagation of the second optical path are combined. An interferometer that outputs a beat signal, the first optical path includes an orbiting optical path that gives a delay time τ _Loop, and the continuous light after the first optical path propagation is the continuous light before the orbital optical path propagation and The interferometer, which is the reflected light or scattered light generated by the measured optical fiber by incident the continuous light after propagating in the orbiting optical path onto the measured optical fiber,
An optical detection means that converts the beat signal into an electric signal,
An arithmetic processing means for calculating the light amplitude distribution waveform of reflected light or scattered light using the electric signal, and
The arithmetic processing means is provided with
The beat signal is divided into τ _Loop units in the time domain and Fourier transformed, and a plurality of complex spectra for each τ _Loop unit are calculated.
The phase component of an arbitrary point of the reflected light or scattered light amplitude distribution waveform appearing on the highest frequency side of each of the plurality of complex spectra is extracted, and the time change of the phase of the reflected light or scattered light is calculated.
The beat signal is resampled by the time sequence calculated based on the time change of the phase.
An optical reflection measuring apparatus, characterized in that the resampled beat signal is Fourier transformed to calculate an optical amplitude distribution waveform of reflected light or scattered light in which the phase fluctuation of the optical fiber to be measured is compensated. A light source that emits continuous light whose frequency has been swept,
The continuous light is demultiplexed into a first optical path and a second optical path, and the continuous light after the propagation of the first optical path and the continuous light after the propagation of the second optical path are combined. An interferometer that outputs a beat signal, the first optical path includes an orbiting optical path that gives a delay time τ _Loop, and the continuous light after the first optical path propagation is the continuous light before the orbital optical path propagation and wherein continuous light after round optical path propagating incident on the measured optical fiber is reflected light or scattered light generated in the optical fiber to be measured, and the interferometer,
An optical detection means that converts the beat signal into an electric signal,
And arithmetic processing means for calculating the optical amplitude distribution waveform of the reflected light or scattered light using the electric signal,
The arithmetic processing means is provided with
The beat signal is divided into τ _Loop units in the time domain and Fourier transformed, and a plurality of complex spectra for each τ _Loop unit are calculated.
The phase component of an arbitrary point of the reflected light or scattered light amplitude distribution waveform appearing on the highest frequency side of each of the plurality of complex spectra is extracted, and the time change of the phase of the reflected light or scattered light is calculated.
A light reflection measuring apparatus characterized in that the frequency of vibration generated in the optical fiber to be measured is analyzed from the time change of the phase. The first optical path includes a phase reference dummy optical fiber between the circumferential optical path and the optical fiber to be measured.
The arithmetic processing means uses as the time change of the phase the time change of the phase difference between the reflected light or the scattered light of the optical fiber to be measured and the reflected light or the scattered light of the dummy optical fiber for phase reference. The light reflection measuring device according to claim 1 or 2. The first step of emitting continuous light frequency-swept from the light source,
The continuous light is demultiplexed into a first optical path and a second optical path, and the continuous light after the propagation of the first optical path and the continuous light after the propagation of the second optical path are combined. In the second step of outputting a beat signal, the first optical path includes an orbiting optical path that gives a delay time τ _Loop, and the continuous light after the first optical path propagation is the continuous light before the orbital optical path propagation. The second step of outputting the beat signal, which is the reflected light or scattered light generated by the measured optical fiber by incident the continuous light after propagating in the orbiting optical path into the measured optical fiber, and the second step.
The third step of converting the beat signal into an electric signal and
The fourth step of calculating the light amplitude distribution waveform of the reflected light or the scattered light using the electric signal, and
The fourth step is
The 41st step of dividing the beat signal into τ _Loop units in the time domain and performing a Fourier transform to calculate a plurality of complex spectra for each τ _Loop unit.
The 42nd step of extracting the phase component of an arbitrary point of the reflected light or scattered light amplitude distribution waveform appearing on the highest frequency side of each of the plurality of complex spectra and calculating the time change of the phase of the reflected light or scattered light.
The 43rd step of resampling the beat signal in the time sequence calculated based on the time change of the phase, and
The 44th step of Fourier transforming the resampled beat signal to calculate the optical amplitude distribution waveform of the reflected light or the scattered light in which the phase fluctuation of the optical fiber to be measured is compensated.
A method for measuring light reflection, which comprises. The first step of emitting continuous light frequency-swept from the light source,
The continuous light is demultiplexed into a first optical path and a second optical path, and the continuous light after the propagation of the first optical path and the continuous light after the propagation of the second optical path are combined. In the second step of outputting a beat signal, the first optical path includes an orbiting optical path that gives a delay time τ _Loop, and the continuous light after the first optical path propagation is the continuous light before the orbital optical path propagation. The second step of outputting the beat signal, which is the reflected light or scattered light generated by the measured optical fiber by incident the continuous light after propagating in the orbiting optical path into the measured optical fiber, and the second step.
The third step of converting the beat signal into an electric signal and
The fourth step of calculating the light amplitude distribution waveform of the reflected light or the scattered light using the electric signal, and
The fourth step is
The 41st step of dividing the beat signal into τ _Loop units in the time domain and performing a Fourier transform to calculate a plurality of complex spectra for each τ _Loop unit.
The 42nd step of extracting the phase component of an arbitrary point of the reflected light or scattered light amplitude distribution waveform appearing on the highest frequency side of each of the plurality of complex spectra and calculating the time change of the phase of the reflected light or scattered light .
The 45th step of analyzing the frequency of vibration generated in the optical fiber to be measured from the time change of the phase, and
A method for measuring light reflection, which comprises. The first optical path includes a phase reference dummy optical fiber between the circumferential optical path and the optical fiber to be measured.
In the 42nd step , as the time change of the phase, the time change of the phase difference between the reflected light or the scattered light of the optical fiber to be measured and the reflected light or the scattered light of the dummy optical fiber for phase reference is used. The light reflection measuring method according to claim 4 or 5.

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