KR102171888B1 - Sensing device and sensing mehtod using brillouin scattering - Google Patents

Abstract

Embodiments include a light source unit for generating laser light using a modulation frequency; An optical modulator for distributing the light output by the light source to generate a pump optical signal and a probe optical signal having a frequency different from that of the pump optical signal; A test optical fiber through which the pump optical signal or the probe optical signal is incident at one end optically connected to the optical modulator and the pump optical signal or the probe optical signal is reflected at the other end; An optical detection unit optically connected to one end of the test optical fiber to detect a Brillouin scattering optical signal generated at a plurality of correlation points by propagating the probe optical signal and the pump optical signal in opposite directions within the test optical fiber; And a calculation unit that calculates changes in Brillouin frequencies at the plurality of correlation points from the detected optical signal, and relates to a sensor and sensing method using Brillouin scattering of an optical fiber.

Description

Sensor and sensing method using Brillouin scattering in an optical fiber with an open one end {SENSING DEVICE AND SENSING MEHTOD USING BRILLOUIN SCATTERING}

The embodiments relate to a sensor and a sensing method using Brillouin scattering, and in more detail, measuring physical changes in a wide measurement area using an optical fiber with an open end such as a single access type optical fiber. It's all about possible technology.

The Brillouin frequency shift caused by Brillouin scattering in the optical fiber has a characteristic that changes linearly according to the temperature and stress experienced by the optical fiber, so the physical change of the point by measuring the amount of Brillouin frequency shift Can be seen. The distributed sensor using the Brillouin scattering has various methods such as a time domain, a frequency domain, or a correlation domain.

Among them, the sensor of the spatially selective Brillouin Optical Correlation Domain Analysis (BOCDA) method is a point where the frequency difference between the pump light and the probe light is constant, and a correlation point that appears periodically as a sensing point. It is very useful because it has advantages such as high spatial resolution and selectivity of arbitrary sensing points.

However, in the BOCDA method according to the conventional embodiment, both ends of the measurement optical fiber, which are areas where physical changes are detected, must be connected to the sensor. This is because pump light and probe light are input in opposite directions to form a correlation point in the measurement optical fiber. A conventional BOCDA sensor including a measurement optical fiber (that is, a dual access type optical fiber) connected to both ends thereof has a problem in that the flexibility of the optical fiber arrangement is low in arranging the measurement optical fiber in an environment to be measured. . For this reason, there is a problem that the efficiency of the measurement range is also low.

To compensate for this, a method capable of measuring even if only one end of the measuring fiber is connected to a sensor is being tried. However, this attempt has a limitation in that the measurement range is limited because only one correlation point must be formed in the measurement optical fiber. In addition, the frequency modulation width of the probe light and the pump light is limited to analyze the Brillouin frequency, so there is a limit to obtaining a high spatial resolution.

Registered Patent Publication No. 10-1823454

According to an aspect of the present invention, it is possible to provide a sensor and a sensing method capable of measuring a physical change in a wide measurement area by using an optical fiber with an open end such as a single access type optical fiber.

A sensor using Brillouin scattering of an optical fiber according to an aspect of the present invention includes: a light source unit for generating laser light using a modulation frequency; An optical modulator for distributing the light output by the light source to generate a pump optical signal and a probe optical signal having a frequency different from that of the pump optical signal; A test optical fiber that is optically connected to the optical modulator and includes one end to which the pump optical signal or the probe optical signal is incident and the other end to which the pump optical signal or the probe optical signal is reflected; An optical detection unit optically connected to one end of the test optical fiber to detect a Brillouin scattering optical signal generated at a plurality of correlation points by propagating the probe optical signal and the pump optical signal in opposite directions within the test optical fiber; And a calculation unit that calculates a change in Brillouin frequency at the plurality of correlation points from the detected optical signal.

In one embodiment, the pump optical signal may be a pulse signal having a time width equal to the reciprocal of the modulation frequency, and the probe optical signal may be a continuous signal.

In one embodiment, the light source unit may include a first waveform generator that generates a modulated signal having the modulated frequency.

In one embodiment, the optical modulator comprises: a first modulator configured to generate the probe optical signal by shifting the frequency of the light by a predetermined offset frequency; A second waveform generator for generating a gating signal synchronized with the modulated signal; And a second modulator for generating a pump optical signal in the form of a pulse by using the gating signal.

In one embodiment, the optical modulator generates a pump optical signal having a period of 4 times (4 L / vg) or more of the time ( L / vg) passing through the length of the test fiber ( L ) at the speed (vg) of the optical signal. It can be further configured to do. In this period, from the moment the pump pulsed optical signal is incident to the incident end, the pump pulsed optical signal is reflected from the other end and exits to the incident end, and at this time, the newly incident continuous probe optical signal is reflected from the other end and exits all to the incident end. This is the time it takes to get out.

In one embodiment, the other end of the test optical fiber reflecting may be configured to have a reflectance of 80% or more.

In one embodiment, the optical modulator generates a pump optical signal having a period of 2 times (2 L / vg) or more of the time ( L / vg) passing through the length of the test fiber ( L ) at the speed (vg) of the optical signal. It can be further configured to do. This period is the time it takes from the moment when the pump pulse optical signal is incident to the incident end and the pump pulse optical signal is reflected from the other end and exits to the incident end.

In one embodiment, the other end of the test optical fiber reflecting may be configured to have a reflectance of less than 20%.

In an embodiment, the operation unit may be further configured to calculate a Brillouin gain at each correlation point by segmenting the detected optical signal by one period of the probe optical signal.

A sensing method using Brillouin scattering according to another aspect of the present invention includes: generating laser light modulated by a modulated signal having a modulated frequency; Generating a probe optical signal by shifting the frequency of the laser light by a predetermined offset frequency; Generating a pump optical signal as a pulse signal by gating the laser light to have a time width determined based on the modulation frequency; And detecting Brillouin scattered light generated by the pump optical signal and the probe optical signal at a plurality of correlation points located on the test optical fiber, wherein the pump optical signal or the probe optical signal is incident at one end of the test optical fiber. And detecting the Brillouin scattered light from which the incident optical signal is reflected at the other end.

In one embodiment, the pump optical signal may be a pulse signal having a time width equal to the reciprocal of the modulation frequency, and the probe optical signal may be a continuous signal.

In one embodiment, the step of generating the pump optical signal, having a period of 4 times (4 L / vg) or more of the time ( L / vg) passing through the length of the test fiber ( L ) at the speed of the optical signal (vg) It may include generating a pump optical signal. In this period, from the moment the pump pulsed optical signal is incident to the incident end, the pump pulsed optical signal is reflected from the other end and exits to the incident end, and at this time, the newly incident continuous probe optical signal is reflected from the other end and exits all to the incident end. This is the time it takes to get out.

In an embodiment, the detecting of the Brillouin scattered light may include detecting the Brillouin scattered light generated between half cycles of the pump optical signal from the moment when the pump optical signal is incident and the probe light is amplified.

In one embodiment, the step of generating the pump optical signal, having a period of 2 times (2 L / vg) or more of the time ( L / vg) passing through the length of the test fiber ( L ) at the speed of the optical signal (vg) It may include generating a pump optical signal. This period is the time it takes from the moment when the pump pulse optical signal is incident to the incident end and the pump pulse optical signal is reflected from the other end and exits to the incident end.

In an embodiment, the detecting of the Brillouin scattered light may include detecting the Brillouin scattered light generated between one cycle of the pump optical signal from the moment when the pump optical signal is incident and the probe light is amplified.

In one embodiment, generating the pump optical signal comprises: generating a gating signal synchronized with the modulated signal; And gating-modulating the laser light using the gating signal.

In an embodiment, the sensing method may further include calculating a Brillouin gain at each correlation point by segmenting the Brillouin scattered light into a period of the probe optical signal.

In an embodiment, the sensing method may further include calculating a Brillouin frequency at each of the plurality of correlation points based on the Brillouin gain.

In the sensor according to an aspect of the present invention, since only one end of the test optical fiber, which is a measurement area, is connected to other components in the sensor, the test optical fiber can be arranged more flexibly. Accordingly, there is an advantage in that the measurable area is expanded compared to the case where both sides are connected.

In addition, it is possible to increase the measurement range while maintaining high spatial resolution by allowing a number of correlation points to be located on the optical fiber measurement optical fiber and dividing and analyzing it by the period of the probe optical signal.

1 is a schematic configuration diagram of a sensor 1 using Brillouin scattering according to an embodiment of the present invention.
2 is a view for explaining an optical signal proceeding in a single access type test optical fiber according to an embodiment of the present invention.
3 is a diagram showing a Brillouin gain spectrum at a plurality of correlation points obtained by a sensor according to an embodiment of the present invention.
4 is a diagram illustrating a Brillouin gain at one of a plurality of correlation points of FIG. 3 according to an embodiment of the present invention.
5A to 5B are diagrams illustrating measurement results when a stress is applied to a test optical fiber according to an embodiment of the present invention.
6 is a diagram illustrating a change in Brillouin gain according to a change in stress magnitude according to an embodiment of the present invention.
7 is a diagram illustrating a change in Brillouin frequency according to a change in a stress magnitude according to an embodiment of the present invention.
8 is a shape of a signal measured by a sensor for explaining a process of amplifying a probe optical signal due to an interaction between a pump optical signal and a probe optical signal according to the first embodiment of the present invention. It is a diagram schematically showing.
9 is a shape of a signal measured by a sensor for explaining a process of amplifying a probe optical signal due to an interaction between a pump optical signal and a probe optical signal according to a second embodiment of the present invention. It is a diagram schematically showing.
10 is a flowchart of a sensing method using Brillouin scattering according to an exemplary embodiment.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings.

1 is a schematic configuration diagram of a sensor 1 using Brillouin scattering according to an embodiment of the present invention.

The sensor according to the embodiments uses a Brillouin Optical Correlation Domain Analysis (BOCDA). Specifically, when the frequency difference between the pump light and the probe light traveling in opposite directions within the optical fiber coincides with or approaches the inherent Brillouin transition frequency of the optical fiber, the induction brill over the entire section of the optical fiber Luang scattering amplification occurs and the intensity of the probe light is amplified.

At this time, by modulating the optical signal so that the frequencies of the pump light and the probe light have a spatially sine wave, a Brillouin scattering signal can be selectively obtained only at a specific position in the optical fiber. Specifically, at a specific position in the optical fiber, the difference between the frequency of the pump light and the frequency of the probe light is constant over time, and this is referred to as a correlation point (CP). The correlation point where the frequency difference between the pump light and the probe light is constant appears every half cycle of the modulation frequency of the pump light and the probe light, and if the frequency difference between the pump light and the probe light coincides with the inherent Brillouin transition frequency of the optical fiber, induced Brillouin scattering occurs at the correlation point. You can get scattered light. Induced Brillouin scattering appears in the form of a peak with a Brillouin gain in the spectrum of the scattered light.

The measuring point may be determined based on the modulation frequency of the laser light for generating the pump light and the probe light. It is possible to measure the Brillouin gain spectrum by varying the offset frequency between the pump light and the probe light. Since the Brillouin transition frequency of the test fiber to which the pump light and probe light are applied depends on physical properties such as temperature or stress acting outside, the physical properties of the test fiber change using the frequency at which the Brillouin gain spectrum has the maximum value. Can be measured.

Since only one correlation point must be located within the measurement range of the BOCDA type sensor, the measurement range is a distance between two adjacent correlation points and can be expressed as Equation 1 below.

In Equation 1, R represents the measurement range, vg represents the speed of the optical signal in the test optical fiber, f _m represents the modulation frequency of the optical signal, c represents the speed during the vibration of light, and n represents It shows the effective refractive index of the optical fiber.

In addition, the spatial resolution Δz in the BOCDA sensor can be expressed as Equation 2 below.

In Equation 2, Δf represents the amount of change in the actual frequency of the optical signal modulated with the modulation frequency f _m . For example, if the current of the laser is modulated using a signal of a waveform generator having a frequency f _m , the modulated current The optical frequency of the actual laser is modulated in proportion to the size of, which corresponds to the magnitude of the modulated optical frequency. In addition, in Equation 2, Δv _B is the line width of the Brillouin gain spectrum, and although the Brillouin scattering signal has a maximum value at the Brillouin frequency v _B , a considerable amount of signal is observed at frequencies near it. _B is located in both directions around the peak and corresponds to the width between the two points where the signal strength is reduced by half.

According to embodiments of the present invention, the BOCDA system allows a plurality of correlation points to be located within a measurement range and processes signals in a time domain to analyze measurement results for a plurality of correlation points. Specifically, for signal processing in the time domain, the pump light is modulated in the form of pulses instead of continuous light, and the amplified probe light by interaction with the pump light traveling in the opposite direction is divided into time intervals (e.g., for each period of the probe light). ) Each correlation point can be analyzed by segmenting. As a result, it is possible to use a plurality of, for example, N correlation points located within the measurement range at the same time, and as a result, while maintaining a high spatial resolution, the measurement range is expanded N times.

Referring to FIG. 1, the spatially selective sensor according to this embodiment includes a light source unit 10, a light modulator 20, a test optical fiber 30, and a light detection unit 50. The test optical fiber 30 may be disposed at a position in which a change in a physical quantity is to be measured using Brillouin scattering on an optical path. For example, the test optical fiber 30 may be disposed on a measurement object or may be disposed in a measurement environment.

The light source unit 10 is a device for supplying light to be used in the operation of the distributed optical fiber sensor. In an embodiment, the light source unit 10 may include a Distrubuted Feed-Back Laser Diode (DFB LD) 110 and a waveform generator 120. In one example, the light source unit 10 may include a distributed feedback laser diode 110 having a wavelength of 1550 nm. The light source unit 10 modulates the supply current to the DFB LD 110 using the waveform generator 120 to output the modulated laser light in the form of a sine wave having a predetermined frequency. However, this is exemplary, and in other embodiments, the light source unit 10 may be configured to include other different types of laser generating devices.

The optical modulator 20 is configured to receive the modulated laser light from the light source unit 10, generate a pump optical signal and a probe optical signal therefrom, and apply it to one end of the test optical fiber 30. At this time, the optical modulator 20 generates a pump optical signal in the form of a pulse signal so that probe amplification caused by Brillouin scattering occurring at a plurality of correlation points can be individually analyzed. The pump optical signal is generated by gating the output light of the light source unit 100 to have a time width determined based on the modulation frequency of the laser light.

In one embodiment, the time width of the pulse of the pump optical signal is for modulation of laser light, and may be one period of the modulated signal having a modulation frequency f _m of 1/f _m . In other words, in order to individually analyze the amplification of probe light due to Brillouin scattering occurring at multiple correlation points, the pulse width (τ _m ) of the gating signal for the pump optical signal is a sine-shaped modulation with a modulation frequency (f _m ). It must be equal to or less than one period of the signal. In an embodiment, in order to maximize the magnitude of the Brillouin gain, the pulse width may be determined equal to one period of the modulated signal.

Meanwhile, the probe optical signal may be a continuous wave (CW).

In one embodiment, the optical modulator 20 includes an optical splitter 210, a first modulator 220, and a second modulator 230. The optical splitter 210 divides the light source signal output from the light source unit 10 into two paths. For example, the optical splitter 210 may divide the laser light applied from the light source unit 10 into a first output light for generating a probe optical signal and a second output light for generating a pump optical signal. In one embodiment, the optical splitter 210 may divide the light source signal into 50:50, but is not limited thereto.

The first modulator 220 is optically connected between the optical splitter 210 and one end of the test optical fiber 30 to which the probe optical signal and/or the pump optical signal is incident, and transmits the first output light of the optical splitter 210. By using this, a probe optical signal including a sideband signal is generated. That is, the first modulator 220 generates a probe optical signal by shifting the frequency of the first output light by a predetermined offset frequency. For example, the first modulator 220 receives the first output light having a frequency (v ₀ ), and then a sideband signal of a frequency (v ₀ -v _B ) whose frequency is shifted by an offset frequency (v _B ). It may be a single side band modulator (SSBM) that generates a probe optical signal to include.

On the other hand, the second modulator 230 is optically connected between the optical splitter 210 and one end of the test optical fiber 30 into which the pump optical signal and/or the probe optical signal is incident, and the second output of the optical splitter 210 By gating-modulating light according to a predetermined gating signal, a pump optical signal in the form of a pulse is generated. For example, the second modulator 230 may be a semiconductor optical amplifier (SOA). The optical modulator 20 may further include a waveform generator 231 that supplies a modulated signal to the second modulator 230. The waveform generator 231 may be a pulse generator capable of supplying a gating signal. The gating signal of the waveform generator 231 may be synchronized with the modulated signal of the waveform generator 120 of the light source unit 10. Accordingly, even when the modulation frequency modulated in a sine shape is changed to move the position of the correlation point, the shape and phase of the pump optical signal in the form of a pulse can be kept constant.

The second modulator 230 and/or the waveform generator 231 may be set to have a first period or a second period different from the first period (eg, half of the first period) of the pump optical signal. . Each period may be set according to the state of the reflective surface of the test optical fiber 30. This will be described in more detail with reference to FIGS. 8 to 9 below.

In addition, in an embodiment, the optical modulator 20 may further include a phase modulator (PM) 240. The phase modulator 240 is configured to turn on/off the reference signal to remove noise, and to modulate the pump optical signal using the on/off reference signal. In the above embodiment, the optical modulator 20 may further include a waveform generator 241 that supplies the predetermined reference signal to the phase modulator 240. The phase modulator 240 controls the on/off of the pump optical signal, and since the optical signal modulated by the phase modulator 240 has the same frequency before and after input and output, the frequency of the pump optical signal is the output of the light source unit 10 Is the frequency (fm).

In addition, in one embodiment, the optical modulator 20 uses the output light of the optical splitter 210 to polarize the first and second output lights of the optical splitter 210 before generating the pump and probe optical signals. It further includes a first polarization controller (PC) 250 and a second polarization controller 255 for adjusting in a linear direction. That is, the first and second polarization controllers 250 and 255 polarize the incident laser light in a linear direction.

In addition, in one embodiment, the optical modulator 20 further includes a polarization switch (PSW) 260. Since the induced Brillouin scattering amplification occurs when the polarization of the probe optical signal and the pump optical signal coincide, the polarization of the pump optical signal and the probe optical signal can be equally adjusted using the polarization switch 260. In this embodiment, the polarization switch 260 is optically connected between the second modulator 230 and the test optical fiber 30 to adjust the polarization of the pump optical signal, but in another embodiment, the polarization switch 260 It is also possible to adjust the polarization of the signal.

In one embodiment, the polarization switch 260 is configured to alternately rotate the polarization of the pump optical signal or the probe optical signal to 0° once and 90° the other. Induced Brillouin scattering amplification occurs when the polarization of the pump optical signal and the probe optical signal coincide, but the polarization of the pump optical signal and/or the probe optical signal may change according to time and space. Accordingly, the polarization problem can be solved by performing measurement while changing the polarization of the pump optical signal or the probe optical signal using the polarization switch 260 and using the average value of the measured values. More specifically, after obtaining the Brillouin gain in the case where the polarization direction of the pump optical signal is 90° before and after the rotation by the polarization switch 260 (that is, after obtaining two Brillouin gains), the average is calculated. By obtaining, it compensates for the change in the Brillouin gain according to polarization. The polarization angles of 0° and 90° described above are merely exemplary, and the polarization of the pump optical signal or the probe optical signal may be periodically changed to another angle different therefrom.

In one embodiment, the optical modulator 20 further includes first and second optical fiber amplifiers 270 and 275 for amplifying the optical probe signal and the optical pump signal, respectively. The first optical fiber amplifier 270 may be optically connected between the first modulator 220 and one end of the test optical fiber 30. Also, the second optical fiber amplifier 275 may be optically connected between the second modulator 230 and the other end of the test optical fiber 30. The first and second optical fiber amplifiers 270 and 275 may be Erbium-Doped Fiber Amplifier (EDFA), but are not limited thereto.

In one embodiment, the optical modulator 20 further includes a delay optical fiber 280 that is optically connected to the test optical fiber 30. The delayed optical fiber 280 is used to prevent a correlation point (order q=0) located in the test optical fiber 30 in the middle of the path of the pump optical signal and the probe optical signal, which does not change its position even when the modulation frequency is changed. As an auxiliary optical fiber, the order of the correlation point at which the Brillouin gain peak occurs in the test optical fiber 30 can be adjusted by appropriately adjusting the length of the delay optical fiber 280.

The pump optical signal and the probe optical signal generated by the optical modulator 20 are combined by the optical splitter 215 and proceed to one optical path.

In one embodiment, the optical modulator 20 may further include an optical filter 290. The optical filter 290 removes noise components such as amplified spontaneous emission noise generated by the optical fiber amplifiers 270 and/or 275. In one embodiment, the optical filter 290 may remove a noise component of an optical pump signal as shown in FIG. 1.

The pump optical signal and the probe optical signal are coupled by an optical coupler 215. The optical combiner 215 is a device that combines two or more input optical signals into one. In one embodiment, the optical coupler 215 may be a 50:50 optical coupler, but is not limited thereto.

The pump optical signal and the probe optical signal combined in the optical coupler 215 travel in one optical path.

2 is a view for explaining an optical signal proceeding in a single access type test optical fiber according to an embodiment of the present invention.

The test optical fiber 30 is optically connected to the optical modulator 20 and is a region where Brillouin scattering occurs. In one embodiment, the test optical fiber 30 has an open end structure and includes a single access type optical fiber through which an optical signal can be incident on one end. Referring to FIG. 2, one end of the test optical fiber 30 is optically connected to the optical modulator 20 so that an optical signal can be incident, and a part or all of the optical signal incident from the other end is reflected. In one example, the other end of the test optical fiber 30 may be cleave to reflect the optical signal. However, the present invention is not limited thereto, and the test optical fiber 30 may have various structures such that an incident signal can be reflected.

The pump optical signal and the probe optical signal generated by the optical modulator 20 are incident on the same end of the test optical fiber 30. The incident pump optical signal and the probe optical signal travel toward the reflection end of the test optical fiber 30, are reflected, and return to the incident end.

The Brillouin scattering generated inside the test optical fiber 30, which is the single-access optical fiber, depends on the pump optical signal. As described above, since the pump optical signal generated by the optical modulator 20 is in the form of a pulse, Brillouin scattering in the test optical fiber 30 is caused by the interaction of the two situations, depending on the direction of the pump optical signal. Can occur.

First, Brillouin scattering may occur in a situation in which the pump optical signal incident on one end of the test optical fiber 30 proceeds to the other end of the test optical fiber 30 (hereinafter, “first situation”). During the progress of the pump optical signal, the incident pump optical signal encounters a probe optical signal that is reflected from the other end and proceeds to one end, and interacts with each other to generate Brillouin scattering. As a result, the probe optical signal amplified by the first situation may be detected.

Meanwhile, Brillouin scattering may occur in a situation in which the pump optical signal reflected from the other end of the test optical fiber 30 proceeds to one end of the test optical fiber 30 (hereinafter, "second situation"). During the progress of the pump optical signal, the reflected pump optical signal encounters a probe optical signal that is incident from one end and proceeds to the other end, and interacts with each other to generate Brillouin scattering. Accordingly, the probe optical signal amplified by the second situation may be detected.

Therefore, a plurality of correlation points are formed by Brillouin scattering according to each situation. For example, in the first situation, N correlation points (CP-1, CP-2, ..., CP-n) are formed, and in the second situation, N correlation points (CP'-1, CP' -2, ..., CP'-n) is formed.

In one embodiment, the reflective end may be configured to have a high reflectivity. For example, the reflectance may be about 100%, or 80% or more, but is not limited thereto, and may be a reflectance that makes the intensity of the reflected signal similar to the intensity of the incident signal. In another embodiment, the reflective end may be configured to have a very low reflectivity. For example, the reflectance may be less than about 20%, or less than 4%, but is not limited thereto, and the intensity of the reflected signal has a significant difference from the intensity of the incident signal. Intensity can be of negligible reflectivity.

Brillouin scattering that may occur in the test optical fiber 30 may vary in correlation point information, intensity, and the like included in the cycle of the pump optical signal and the reflectance of the test optical fiber 30. This will be described in more detail with reference to FIGS. 8 and 9 below.

As described above, when the additionally modulated pump light is incident to a continuous wave type probe optical signal and a pulse signal having a frequency-modulated width of one cycle, Brillouin scattering occurs individually at a plurality of correlation points in the test optical fiber 30. The Brillouin scattered light generated in the test optical fiber 30 is output through the incident end again and is input to the light detection unit 50 below. When the Brillouin scattering signal generated from each of the correlation points is measured and analyzed in the time domain, the Brillouin scattering of a plurality of correlation points of the single-sided open test optical fiber 30 can be analyzed, respectively.

The light detection unit 50 detects the Brillouin scattered light generated at a plurality of correlation points or a specific correlation point located in the test optical fiber 30, and provides the detected Brillouin scattered light information to the data processing unit 70.

In one embodiment, the light detection unit 50 includes an optical circulator 510 optically connected between the light modulator 20 and the test optical fiber 30. The optical circulator 510 applies a pump optical signal in the form of a pulse modulated to become a gating signal and/or a probe optical signal, which is a continuous signal, to the test optical fiber 30, and Brillouin scattered light generated from the test optical fiber 30 It serves to branch in the direction of other components of the photodetector 50. That is, the optical circulator 510 may serve to block the pump optical signal and/or the probe optical signal output from the optical modulator 20 from entering the optical modulator 20 again.

In one embodiment, the photodetector 50 includes a variable optical intensity adjuster (VOA) 520 and a photo detector (PD) 530 for adjusting and converting a signal size. The Brillouin scattered light generated while the pump optical signal and the probe optical signal pass through the test optical fiber 30 in opposite directions is diverged from the optical circulator 510 and is incident on the VOA 520, and the VOA 520 is The size of the Rouen scattered light is attenuated to be incident on the PD 530, and the PD 530 may convert the incident optical signal into an electric signal.

The data processing unit 70 includes a data acquisition (DAQ) 710 and an operation unit 750. For example, the DAQ 710 includes an oscilloscope for obtaining an electrical signal output from the PD 530 in a time domain, and the data processing unit 750 includes one or more processes for analyzing the signal of the oscilloscope. It may include a personal computer (Personal Computer). However, this is exemplary, and in other embodiments, signal processing and analysis may be performed by further using one or more different data processing means.

The sensor 1 can obtain an electrical signal in the time domain by the data collection unit 710, so that the correlation point can be measured in the time domain.

The operation unit 750 may calculate a Brillouin gain based on the optical signal detected from the photodetector 50 and calculate a Brillouin frequency. In addition, the change in the Brillouin frequency can be calculated. Accordingly, the operation unit 750 can easily separate the unamplified probe light, the probe light amplified by Brillouin scattering, the pump pulse light, and the like.

In some embodiments, the data processing unit 70 may further include a control unit (not shown) electrically connected to control one or more components included in the sensor 1. The control unit may control the overall operation of the sensor 1.

In an embodiment, the calculator 750 may calculate a Brillouin gain from the Brillouin scattered light detected from a plurality of correlation points. For example, by processing Brillouin scattered light generated at a plurality of correlation points in a time domain, a Brillouin gain at each of a plurality of correlation points through which a pump optical signal modulated with a pulsed gating signal passes is calculated. As a result, when the frequency modulation width is widened to improve the spatial resolution, the frequencies of the two lights overlap and can be easily separated in the time domain, unlike in the frequency domain where the two lights cannot be separated.

In addition, the Brillouin frequency at the correlation point may be calculated based on the calculated Brillouin gain. In the sensor 1, when the frequency difference of the pump light and the frequency of the probe light are changed, the frequency difference when the Brillouin scattering occurs best becomes the Brillouin frequency of each correlation point. By changing the modulation frequencies of the two lights, the positions of the correlation points can be changed, and thus the Brillouin frequencies of all the measurable optical fibers can be measured. In addition, it is possible to measure the change in physical properties at which point through the detection of the Brillouin frequency change.

As a result, since the sensor 1 uses a plurality of correlation points, a measurement range of a single open optical fiber increases by a multiple of the number of correlation points, so that long distance measurement is possible. In addition, since there is no change in the modulation frequency or modulation width during this process, the spatial resolution remains high as it is.

As an example, in the conventional BOCDA system, when the light source is modulated with f _m = 10 MHz and △ f = 1.95 GHz, and the effective refractive index n value of the test optical fiber is 1.45, the adjacent calculated by Equation 1 and Equation 2 The distance between the correlation points is about 10.34 m, and when Δv _B of the single mode fiber is 30 MHz, the spatial resolution is about 5 cm.

In the case of additionally modulating the pump light in a pulse form and in a pulse form having a width of 100 ns and a repetition rate of 50 kHz, and incident with a single open measurement optical fiber together with a continuous probe light, the frequency offset of the pump light and the probe light using examples The Brillouin frequency at multiple correlation points can be individually measured by varying the Brillouin frequency at 2 MHz intervals in the 200 MHz section around the Brillouin frequency. As a result, a total of 146 correlation points are placed within the measurement range, and the measurement range increases to about 1.51 km.

3 is a diagram showing a Brillouin gain spectrum at a plurality of correlation points obtained by a sensor according to an embodiment of the present invention. 4 is a diagram illustrating a Brillouin gain at one of a plurality of correlation points of FIG. 3 according to an embodiment of the present invention.

3 and 4, as a result of applying the present embodiment, the measurement range is increased by about 150 times compared to the measurement range of the conventional BOCDA system. When Δv _B of the single mode optical fiber is 30 MHz, the spatial resolution is calculated to be about 5 cm by Equation 2 above. That is, the measurement range increases while maintaining the spatial resolution of the conventional BOCDA system.

5A to 5B are diagrams illustrating measurement results when a stress is applied to a test optical fiber according to an embodiment of the present invention.

By changing the modulation frequency from 9.9915 MHz to 10.15 MHz and measuring the Brillouin frequency over the entire range of the single-access type test optical fiber 30 while moving the positions of the correlation points by about 1 cm, the stress in the test optical fiber 30 It can detect whether it is applied or not.

As shown in Fig. 5A, when a stress is applied in a range of about 2.5 cm from the most end of the incident end in the test optical fiber 30, a Brillouin frequency different from the unapplied portion in the stressed portion is obtained. . The user of the sensor 1 is provided with information on the change in the Brillouin frequency and can know whether a stress is applied.

As shown in FIG. 5B, as the intensity of the applied stress increases, the change in the Brillouin frequency increases. Therefore, when obtaining a measurement result having a large change in the Brillouin frequency, it is possible to obtain a result that the strength of the stress applied to the test optical fiber 30 is large.

6 is a diagram showing a change in Brillouin gain according to a change in a stress level according to an embodiment of the present invention, and FIG. 7 is a view showing a change in Brillouin according to a change in the stress level according to an embodiment of the present invention. It is a diagram showing the frequency change.

The sensor 1 according to the present embodiment may detect whether or not stress is applied to the test optical fiber 30 as described above. In addition, the applied stress can be calculated based on the change in the Brillouin frequency. When a change in the Brillouin frequency is sensed, the calculator 750 may calculate the applied stress based on Equation 3 below.

Here, V _B (ε) is the currently obtained Brillouin frequency, Cε is the stress effective factor (MHz/με), and ε is the currently applied strain. V _B0 represents the reference Brillouin offset frequency when there is no strain.

Referring to FIG. 6, when a stress is applied to the test optical fiber 30 while changing the size, the Brillouin gain moves as the size of the stress increases. Based on the change in the Brillouin gain, the change in the Brillouin frequency can be calculated.

Referring to FIG. 6, when a stress is applied to the test optical fiber 30 while changing the size, the Brillouin gain moves as the size of the stress increases. Based on the change in the Brillouin gain, the change in the Brillouin frequency can be calculated.

Referring to FIG. 7, the Brillouin frequency increases as the stress increases. The slope of FIG. 7 is the sensitivity of the Brillouin frequency according to the stress, and represents the stress effective coefficient of the above equation. The stress effective coefficient of this embodiment may be 0.052MHz/με

When the Brillouin scattered light is detected, the sensor 1 of the present embodiment may calculate a Brillouin gain to calculate a Brillouin frequency. In addition, the applied stress may be measured based on the above equation.

In FIGS. 5 to 7, only the stress is described as the change in which the test optical fiber 30 is measurable, but it will be apparent to those skilled in the art that the sensor 1 is not limited to being measurable only for the stress. This is merely exemplary, and the sensor 1 may measure various physical changes (eg, temperature, etc.) other than stress.

Additionally, in the sensor 1 of FIG. 1, the Brillouin scattered light may be differently generated according to the period of the pump optical signal.

8 is a shape of a signal measured by a sensor for explaining a process of amplifying a probe optical signal due to an interaction between a pump optical signal and a probe optical signal according to the first embodiment of the present invention. It is a diagram schematically showing.

In the first embodiment, the period of the pump optical signal (T _Pump1 ) is from the moment when the pump pulse optical signal is incident to the incident end, the pump pulse optical signal is reflected from the other end and exits to the incident end. It can be set as the time it takes for the probe optical signal to be reflected from the other end and exit all of the incident end. For example, the period of the pump optical signal may be set to 4 times (4 L /vg) of the time ( L /vg) passing through the length of the test fiber ( L ) at the speed (vg) of the optical signal.

When a pump optical signal having such a period is incident on the test optical fiber 30, one pump optical signal exists in the test optical fiber 30 per period of the pump optical signal, so that the probe optical signal already amplified by Brillouin scattering is a different pump. It is not further amplified by the optical signal. The Brillouin scattering that occurs during the half cycle of the pump optical signal is the Brillouin scattering (0~1/2 T _Pump1 ) that occurs while the incident pump optical signal proceeds to the other end, or the pump optical signal reflected from the other end. It includes Brillouin scattering (1/2 T _Pump1 to 1 T _Pump1 ) that occurs during the process to the first stage.

Specifically, when the pump optical signal having the period is incident on the test optical fiber 30, the shape of the signal detected in the time domain is as shown in FIG. 8. As shown in FIG. 8, the Brillouin scattered light detected between 1/ _{2T Pump1} from the moment when the probe light starts to be amplified when the pump pulsed optical signal is incident is the Brillouin scattered light generated in the first situation. On the other hand, the Brillouin scattered light detected between 1/2 T _Pump1 and T _Pump1 is the Brillouin scattered light generated in the second situation.

That is, during one period of the pump optical signal (T _Pump1 ), the Brillouin scattered light generated in the first situation and the Brillouin scattered light generated in the second situation are detected for each half period, and the detected Brillouin scattered light is the first situation and the second situation. Each contains information on the Brillouin gains that occurred in the situation. The Brillouin gain generated by the reflected and returned pump pulse may not be neglected depending on the reflectivity.

By dividing and analyzing only the Brillouin scattered light detected between 1/ _{2T Pump1} from the moment when the probe optical signal is amplified by the period of the probe optical signal, it is possible to analyze the Brillouin gain information at a plurality of correlation points formed only in the first situation. have.

The degree of amplification of the probe light decreases as it moves away from the incident end. The Brillouin gain is proportional to the intensity of the pump optical signal. Since the intensity of the incident pump optical signal decreases due to the loss of the optical fiber as it travels through the optical fiber, the Brillouin gain that occurs far from the incident end decreases.

Further, in the first embodiment, the test optical fiber 30 may be further configured to have a reflecting end having a high reflectance.

In one example, the reflectivity of the reflective end may be about 100%, or may be 80% or more. However, the present invention is not limited thereto, and the test optical fiber 30 of the first embodiment may have various reflectances such that the intensity of the signal after the reflection is not neglected by comparing before and after the reflected signal. In this way, if the reflective end of the test optical fiber 30 is set high (maximum 100%), even if the intensity of the probe optical signal incident to the incident end is small, the intensity of the reflected probe light can be greater than the threshold intensity. This is because the intensity of the probe optical signal reflected by the high reflectivity does not change significantly from before reflection.

In addition, in some embodiments, the cycle of the pump optical signal may be set to 4 L / vg or more. The only difference is that the longer the pulse period, the longer the measurement time. In other words, the Brillouin scattered light generated in the optical fiber has only minor differences (e.g., different shapes) due to the difference in periods, and the cause of the Brillouin scattered light generated by period and the process of analyzing the Brillouin scattered light are the same. Do. In this case, the measurement time becomes the minimum when the period of the pump optical signal is 4 L /vg.

9 is a shape of a signal measured by a sensor for explaining a process of amplifying a probe optical signal due to an interaction between a pump optical signal and a probe optical signal according to a second embodiment of the present invention. It is a diagram schematically showing.

In the second embodiment, the period of the pump optical signal (T _Pump2 ) may be set from the moment when the pump pulse optical signal is incident to the incident end, and the time it takes for the pump pulse optical signal to be reflected from the other end and exit to the incident end. . For example, the speed (vg) of the optical signal may be set to twice (2 L /vg) the time ( L /vg) passing through the length of the test fiber ( L ).

When the pump optical signal having such a period is incident on the test optical fiber 30, the probe optical signal amplified in the first situation may be reflected and newly incident on the way back and then amplified by the pump optical signal. That is, one pump optical signal is always present in the test optical fiber 30 per cycle of the pump optical signal, and the probe optical signal already amplified by Brillouin scattering is further amplified by another pump optical signal. When a pump optical _signal having such a period T _Pump2 is incident on the test optical fiber 30, the shape of the signal detected in the time domain is shown in FIG. 9. Until the pump optical signal is first incident and reflected, Brillouin scattering occurs due to the interaction of the first situation as shown in FIG. 8, but when the pump optical _signal continues to be incident in the period (T _Pump2 ), Brillouin scattering is different from that of FIG. do.

Specifically, the probe optical signal amplified by the pump optical signal reflected and returned is newly incident and then amplified again by the pump optical signal. That is, the Brillouin scattering is applied once again in the first situation to the Brillouin scattering in the second situation. Accordingly, as shown in FIG. 9, the Brillouin scattered light detected during one period T _Pump2 has both Brillouin gain information at the correlation points formed in the first and second situations.

The degree of amplification of the probe light decreases as it moves away from the incident end. The Brillouin gain is proportional to the intensity of the pump optical signal. Since the intensity of the incident pump optical signal decreases due to the loss of the optical fiber as it travels through the optical fiber, the Brillouin gain that occurs far from the incident end decreases.

Further, in the second embodiment, the test optical fiber 30 may be further configured to have a reflective end having a low reflectance. For example, the reflectivity can be less than about 4%, or less than 20%. However, the present invention is not limited thereto, and the test optical fiber 30 of the second embodiment generates a significant difference in the intensity of the reflected signal from the intensity of the incident signal, so that the signal after reflection is negligible when comparing the signal intensity before and after reflection. , Can have various reflectivity.

In this way, if the reflection end of the test optical fiber 30 is set very low, the intensity of the Brillouin scattered light generated by the pump optical signal reflected and returned becomes very small. The intensity of the Brillouin scattered light is proportional to the intensity of the pump optical signal, because the intensity of the reflected pump optical signal decreases due to the low reflectivity. Accordingly, even if the Brillouin scattered light detected during T _Pump2 includes both Brillouin gain information generated in the first and second situations, the Brillouin gain generated by the reflected pump pulse can be ignored. Therefore, only the Brillouin gain information generated at the correlation point formed by the incident pump optical signal is substantially included in the amplified probe optical signal, and if this is divided and analyzed, the Brillouin at a plurality of correlation points formed in the first situation. Each gain information can be analyzed.

In addition, in some embodiments, the cycle of the pump optical signal may be set to 2 L / vg or more. The only difference is that the longer the pulse period, the longer the measurement time. That is, the Brillouin scattered light generated in the optical fiber has only a difference in shape due to the difference in period, and the cause of the Brillouin scattered light generated for each period and the process of analyzing the Brillouin scattered light are the same. In this case, the measurement time becomes the minimum when the period of the pump optical signal is 2 L /vg.

8 and 9, in the second embodiment, the period in which the pump optical signal is incident is shorter than in the first embodiment, and the measurement cycle time is shortened. Consequently, the second embodiment also shortens the total measurement time compared to the first embodiment.

10 is a flowchart of a sensing method using Brillouin scattering according to an exemplary embodiment.

Referring to FIG. 10, first, a laser light modulated by a modulated signal having a modulation frequency f _m may be generated (S1). Next, a probe optical signal may be generated by moving the frequency of the laser light by a predetermined offset frequency (S2). In addition, a pump optical signal in the form of a pulse signal may be generated by gating the laser light to have a time width determined based on the modulation frequency (S3). At this time, in order to individually analyze the amplification of the probe light due to Brillouin scattering that occurs at multiple correlation points, the width of the pulse of the pump optical signal can be determined equal to one period of a sine-shaped modulated signal having a modulation frequency f _m . have.

Next, the generated pump optical signal and the probe optical signal may be applied to one end of the test optical fiber (S4). In the test optical fiber, the amplification of the probe optical signal occurs due to the interaction between the pulse of the pump optical signal and the continuous probe optical signal. For example, when a pump optical signal incident on one end of the test optical fiber 30 proceeds to the other end of the test optical fiber 30, Brillouin scattering may occur. In addition, Brillouin scattering may occur in a situation in which the pump optical signal reflected from the other end of the test optical fiber 30 proceeds to one end of the test optical fiber 30.

Thereafter, the Brillouin scattered light generated from the test optical fiber is detected by the pump optical signal and the probe optical signal (S5), and the detected Brillouin scattered light is segmented in a time domain, so that the Brill at a plurality of correlation points on the test optical fiber. Rouen gain can be calculated (S6).

The Brillouin scattered light detected in step S5 may be different Brillouin scattered light according to the period of the pump optical signal.

In one embodiment, in step S3, from the moment the pump pulse optical signal is incident to the incident end, the pump pulse optical signal is reflected from the other end and exits the incident end, and at this time, the newly incident continuous probe optical signal is transmitted to the other end. It is possible to generate a pump optical signal having a period of time it takes to reflect and exit all of the incident ends. In this case, as described above with reference to FIG. 8, the Brillouin scattering that occurs during the half cycle of the pump optical signal is the Brillouin scattering that occurs while the incident pump optical signal travels to the other end or is reflected from the other end. It may include Brillouin scattering generated while the pump optical signal proceeds to the first stage.

In the above embodiment, only the Brillouin scattered light between 1/ _{2T Pump1} is detected from the moment when the probe optical signal is amplified (S5), and the detected Brillouin scattered light is divided and analyzed by the period of the probe optical signal. Brillouin gain information at the formed plurality of correlation points may be analyzed (S6).

In another embodiment, in step S3, from the moment the pump pulse optical signal is incident to the incident end, the pump pulse optical signal is reflected from the other end to generate a pump optical signal having a period of time it takes to exit the incident end. have. In this case, as described above with reference to FIG. 9, the Brillouin scattering that occurs during one period of the pump optical signal is the Brillouin scattering that occurs while the incident pump optical signal travels to the other end and is reflected from the other end. It may include Brillouin scattering that occurs while the generated pump optical signal proceeds to the first stage.

In the above embodiment, when the reflectance of the test optical fiber 30 is low, the Brillouin scattered light in the second situation due to the reflected probe light may be ignored. Therefore, if the Brillouin scattered light between T _Pump2 is detected from the moment the probe optical signal starts to be amplified (S5), and the detected Brillouin scattered light is divided and analyzed by the period of the probe optical signal, a plurality of correlation points formed only in the first situation The Brillouin gain information of can be analyzed (S6).

Since the Brillouin frequency at which the Brillouin gain is maximized has a characteristic that changes linearly with the temperature and stress experienced by the optical fiber, the physical properties of the corresponding point change by calculating the Brillouin gain at multiple correlation points on the test optical fiber. Can be measured. In addition, the above process is repeated by gradually changing the modulation frequency f _m and gradually moving the positions of the correlation points, so that the entire range of the test optical fiber can be measured (S7).

The present invention described above has been described with reference to the embodiments shown in the drawings, but these are merely exemplary, and those of ordinary skill in the art will understand that various modifications and variations of the embodiments are possible therefrom. However, such modifications should be considered to be within the technical protection scope of the present invention. Accordingly, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims.

Claims (18)

As a sensor that uses the Brillouin scattering of optical fibers,
A light source unit that generates laser light using the modulation frequency;
An optical modulator for distributing the light output by the light source to generate a pump optical signal and a probe optical signal having a frequency different from that of the pump optical signal;
A test optical fiber having an end optically connected to the optical modulator to which the pump optical signal or the probe optical signal is incident, and the other end to which the pump optical signal or the probe optical signal is reflected;
Optically connected to one end of the test optical fiber, the probe optical signal and the pump optical signal propagate in opposite directions to each other in the test optical fiber to detect Brillouin scattering optical signals generated at a plurality of correlation points in a time domain ; And
Comprising a calculation unit for calculating a change in Brillouin frequency at the plurality of correlation points from the detected optical signal,
The optical modulator,
The sensor, characterized in that further configured to generate a pump optical signal having a cycle of 4 times (4L/vg) or more of the time (L/vg) passing through the test optical fiber length (L) at the speed (vg) of the optical signal.
The method of claim 1,
A sensor, characterized in that the other end of the test optical fiber reflecting is configured to have a reflectance of 80% or more.
As a sensor that uses the Brillouin scattering of optical fibers,
A light source unit that generates laser light using the modulation frequency;
An optical modulator for distributing the light output by the light source to generate a pump optical signal and a probe optical signal having a frequency different from that of the pump optical signal;
A test optical fiber having an end optically connected to the optical modulator to which the pump optical signal or the probe optical signal is incident, and the other end to which the pump optical signal or the probe optical signal is reflected;
Optically connected to one end of the test optical fiber, the probe optical signal and the pump optical signal propagate in opposite directions to each other in the test optical fiber to detect Brillouin scattering optical signals generated at a plurality of correlation points in a time domain ; And
Comprising a calculation unit for calculating a change in Brillouin frequency at the plurality of correlation points from the detected optical signal,
The optical modulator,
The sensor, characterized in that further configured to generate a pump optical signal having a cycle of at least twice (2L/vg) of a time (L/vg) passing through the test optical fiber length (L) at a speed (vg) of the optical signal.
The method of claim 3,
A sensor, characterized in that the other end of the test optical fiber is configured to have a reflectance of less than 20%.
The method of claim 1 or 3,
The optical pump signal is a pulse signal having a time width equal to the reciprocal of the modulation frequency, and the optical probe signal is a continuous signal.
The method of claim 1 or 3,
The light source unit includes a first waveform generator that generates a modulated signal having the modulated frequency.
The method of claim 6, wherein the optical modulation unit,
A first modulator configured to generate the probe optical signal by shifting the frequency of the light by a predetermined offset frequency;
A second waveform generator for generating a gating signal synchronized with the modulated signal; And
And a second modulator for generating a pump optical signal in the form of a pulse using the gating signal.
The method of claim 1 or 3, wherein the calculation unit,
And a sensor further configured to calculate a Brillouin gain at each correlation point by segmenting the detected optical signal by one period of the probe optical signal.
As a sensing method using Brillouin scattering,
Generating a laser light modulated by a modulated signal having a modulation frequency;
Generating a probe optical signal by shifting the frequency of the laser light by a predetermined offset frequency;
Generating a pump optical signal as a pulse signal by gating the laser light to have a time width determined based on the modulation frequency; And
A step of detecting Brillouin scattered light generated by the pump optical signal and the probe optical signal at a plurality of correlation points located on the test optical fiber, wherein the pump optical signal or the probe optical signal is incident at one end of the test optical fiber, At the other end, it includes the step of detecting in the time domain the Brillouin scattered light from which the incident optical signal is reflected,
The step of generating the pump optical signal,
A sensing method comprising the step of generating a pump optical signal having a cycle of 4 times (4L/vg) or more of the time (L/vg) passing through the test fiber length (L) at the speed (vg) of the optical signal. .
The method of claim 9, wherein detecting the Brillouin scattered light,
And detecting the Brillouin scattered light generated between a half cycle of the pump optical signal from the moment when the pump optical signal is incident and the probe light starts to be amplified.
As a sensing method using Brillouin scattering,
Generating a laser light modulated by a modulated signal having a modulation frequency;
Generating a probe optical signal by shifting the frequency of the laser light by a predetermined offset frequency;
Generating a pump optical signal as a pulse signal by gating the laser light to have a time width determined based on the modulation frequency; And
A step of detecting Brillouin scattered light generated by the pump optical signal and the probe optical signal at a plurality of correlation points located on the test optical fiber, wherein the pump optical signal or the probe optical signal is incident at one end of the test optical fiber, At the other end, it includes the step of detecting in the time domain the Brillouin scattered light from which the incident optical signal is reflected,
The step of generating the pump optical signal,
A sensing method comprising the step of generating a pump optical signal having a cycle of at least twice (2L/vg) of the time (L/vg) passing through the length of the test optical fiber (L) at the speed (vg) of the optical signal. .
The method of claim 11, wherein detecting the Brillouin scattered light comprises:
And detecting the Brillouin scattered light generated between one cycle of the pump optical signal from the moment when the pump optical signal is incident and the probe light is amplified.
The method of claim 9 or 11, wherein the pump optical signal,
The optical pump signal is a pulse signal having a time width equal to the reciprocal of the modulation frequency, and the optical probe signal is a continuous signal.
The method of claim 9 or 11,
The step of generating the pump optical signal,
Generating a gating signal synchronized with the modulated signal; And
A sensing method comprising the step of gating-modulating the laser light using the gating signal.
The method of claim 9 or 11,
The sensing method further comprising the step of calculating a Brillouin gain at each correlation point by segmenting the detected Brillouin scattered light into a period of the probe optical signal.
The method of claim 15,
The sensing method further comprising calculating a Brillouin frequency at each of the plurality of correlation points based on the Brillouin gain.
delete delete

Images