KR20180134253A - Fiber-optic acoustic sensor module apparatus and system using coherent optical time-domain reflectormeter method - Google Patents

Abstract

The present invention relates to an optical fiber acoustic sensor system using a coherent optical time-domain reflectormeter method (OTDR), which comprises: a coherent laser providing a laser pulse; a plurality of optical fibers transferring the laser pulse provided by the coherent laser, and including a glass molecule causing a Rayleigh backscatter of the laser pulse; a plurality of optical circulators installed between the optical fibers; a plurality of photodetectors connected to each of the optical circulators; and a computer measuring sound waves around the optical fibers by analyzing a signal detected by each of the photodetectors.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a fiber optic acoustic sensor system using a coherent OTDR method and a modular apparatus using the coherent OTDR method,

The present invention relates to an optical fiber acoustic sensor system and a modular apparatus using the coherent OTDR method.

The technology that uses optical fiber as sensor is divided into OTDR (Optical Time Domain Reflectometry) and FBG (Fiber Bragg Grating sensor) method. Distributed OTDR can be classified into Interferometer sensor And an intensity sensor.

Scattering occurs in various directions when a laser pulse is incident on a distributed OTDR sensor. Back scattering is scattered in the opposite direction and there are three types of scattering: Rayleigh, Raman, and Brillouin. It is possible to know the backscattering scattered at a certain position of the cable by the time difference between the incident and observation times. In general, the position is determined by using a Rayleigh scattering wave having the same frequency as the incident light. Rayleigh scattering with large scattering numbers is generally associated with changes in the density of the optical fiber material that makes up the cable and there is no change in wavelength.

An object of the present invention is to provide an optical fiber acoustic sensor system and a module device using the coherent OTDR method.

The problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems which are not mentioned can be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided an optical fiber acoustic sensor system using a coherent optical time-domain reflectometer (hereinafter referred to as " coherent optical time-domain reflectometer & A plurality of optical fibers that transmit the laser pulses provided from the coherent laser and include glass molecules that cause Rayleigh backscattering of the laser pulses, a plurality of optical circulators provided between the plurality of optical fibers, a plurality of photodetectors connected to the plurality of optical circulators, and a computer for analyzing signals detected from the plurality of optical detectors and observing the sound waves around the plurality of optical fibers.

Each of the plurality of optical circulators may include a first port through which the laser pulse is input from a first optical fiber that is one of the plurality of optical fibers, a second port through which the laser pulse is transmitted to the second optical fiber that is one of the plurality of optical fibers, And a third port connected to the first photodetector which is one of the plurality of photodetectors.

Each of the plurality of optical circulators may transmit light scattered back from the second optical fiber to the first photodetector through the third port.

The computer may further include a controller for analyzing a signal detected from each of the plurality of photodetectors to determine characteristics of Rayleigh back scattering generated in at least one of the plurality of optical fibers, The position where the vibration is transmitted to at least one of the optical fibers can be determined.

In addition, the system includes a sensing section having a predetermined length, and the plurality of optical circulators are installed at a predetermined interval between a start point of the sensing section and an end point of the sensing section, The plurality of optical fibers may be connected between the plurality of optical circulators and may be connected from the optical circulator closest to the end of the sensing section to the end of the sensing section.

The maximum sensing distance and the maximum repetition rate of the laser pulses that can be applied to the plurality of optical fibers are inversely proportional to each other using the optical fiber acoustic sensor system, The maximum repetition rate of the laser pulse may be proportional to the number of the optical circulators.

The maximum sensing distance for observing the sound waves using the optical fiber acoustic sensor system and the maximum frequency of sound waves measurable in the plurality of optical fibers are inversely proportional to each other, It can be proportional to the number of circulators.

According to another aspect of the present invention, there is provided a modular apparatus for constructing an optical fiber acoustic sensor system using a coherent OTDR method. The module includes an optical circulator, an optical circulator connected to the optical circulator, An optical fiber including a glass molecule for transmitting a laser pulse and causing Rayleigh backscatter of the laser pulse and a light circulator connected to the optical circulator for detecting light scattered back from the optical fiber through the optical circulator And a photodetector.

The optical circulator is connected to an optical fiber of another modular device, and the optical circulator transmits the laser pulse to a first port through which the laser pulse is inputted from the optical fiber of the other modular device to the optical fiber of the modular device And a third port coupled to the photodetector.

The optical fiber may be connected to an optical circulator of another modular device, and the optical fiber may transmit the laser pulse to an optical circulator of the other modular device.

Other specific details of the invention are included in the detailed description and drawings.

According to the disclosed embodiment, the maximum pulse repetition rate is increased at the same sensing distance as the conventional system, and the frequency range of the sound wave that can be measured is increased.

In addition, when the maximum pulse repetition rate is equal to that of the existing system, the sensing distance is increased.

The maximum pulse repetition rate, the frequency range of the measurable sound waves and the sensing distance increase in proportion to the number of optical circulators included in the optical fiber acoustic sensor system according to the disclosed embodiment.

The effects of the present invention are not limited to the above-mentioned effects, and other effects not mentioned can be clearly understood by those skilled in the art from the following description.

FIG. 1 is a diagram illustrating an optical fiber acoustic sensor system using a coherent optical time-domain reflectometer method according to an exemplary embodiment. Referring to FIG.
2 is a diagram of an optical fiber acoustic sensor system including a plurality of optical circulators according to one embodiment.
FIG. 3 is a block diagram of a modular apparatus constituting an optical fiber acoustic sensor system using the coherent OTDR method according to an embodiment.
FIG. 4 is a view showing a module device constituting an optical fiber acoustic sensor system using the coherent OTDR method according to another embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, Is provided to fully convey the scope of the present invention to a technician, and the present invention is only defined by the scope of the claims.

The terminology used herein is for the purpose of illustrating embodiments and is not intended to be limiting of the present invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. The terms " comprises " and / or " comprising " used in the specification do not exclude the presence or addition of one or more other elements in addition to the stated element. Like reference numerals refer to like elements throughout the specification and " and / or " include each and every combination of one or more of the elements mentioned. Although " first ", " second " and the like are used to describe various components, it is needless to say that these components are not limited by these terms. These terms are used only to distinguish one component from another. Therefore, it goes without saying that the first component mentioned below may be the second component within the technical scope of the present invention.

Unless defined otherwise, all terms (including technical and scientific terms) used herein may be used in a sense that is commonly understood by one of ordinary skill in the art to which this invention belongs. In addition, commonly used predefined terms are not ideally or excessively interpreted unless explicitly defined otherwise.

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

FIG. 1 is a diagram illustrating an optical fiber acoustic sensor system using a coherent optical time-domain reflectometer method according to an exemplary embodiment. Referring to FIG.

The system 10 shown in Figure 1 represents a Distributed Acoustic Sensor (DAS).

The OTDR method uses a pulse as a signal to input a laser pulse to a measured optical fiber to detect Fresnel reflection at a break point or Rayleigh scattering in the optical fiber to detect a defect point And loss characteristics are measured.

In the disclosed embodiment, a Rayleigh backscatter is used.

Referring to FIG. 1, a system 10 includes a coherent laser 100, a photodetector 200, an optical circulator 300, an optical fiber 400, and a computer 500.

A laser pulse is applied using the coherent laser 100.

The laser pulse applied from the coherent laser 100 is transmitted to the optical fiber 400 through the optical circulator 300.

In one embodiment, optical circulator 300 includes one or more ports. One or more ports included in the optical circulator 300 are connected to the coherent laser 100, the optical fiber 400, and the photodetector 200, respectively.

The optical fiber 400 includes glass molecules that transmit a laser pulse applied from the coherent laser 100 and cause Rayleigh backscatter of the laser pulse.

The laser pulse causes Rayleigh back scattering by the glass molecules contained in the optical fiber 400 and causes internal interference among the back scattered light in the optical fiber 400.

In one embodiment, the optical circulator 300 includes a first port through which a laser pulse is input from the coherent laser 100, a second port through which a laser pulse is transmitted to the optical fiber, and a third port connected to the optical detector 200. [ .

The optical circulator 300 transmits the back scattered light from the optical fiber 400 to the photodetector 200 through the third port.

The computer 500 analyzes the signals detected from each of the plurality of photodetectors and observes the sound waves around the optical fiber 400.

For example, when external vibration around the optical fiber 400 is transmitted to the optical fiber 400, a specific scattering phenomenon due to external vibration occurs in the optical fiber 400.

The computer 500 can determine the position of the vibration by analyzing the signal change due to the scattering phenomenon through the photodetector 200.

In the distributed acoustic sensor shown in FIG. 1, the sensing distance and the external frequency to be sensed vary depending on the repetition rate of the light source.

However, due to the physical characteristics of the laser and the optical fiber, there is a theoretical limit on the repetition rate of the light source. Therefore, the distributed acoustic sensor shown in FIG. 1 has a limit of the maximum frequency and sensing distance that can be theoretically measured. In the distributed acoustic sensor shown in Fig. 1, a measurable frequency range is determined according to the sensing distance.

In one embodiment, the length of the optical fiber 400 shown in FIG. 1 may be the sensing distance of the distributed acoustic sensor shown in FIG. Assuming that the sensing distance of the distributed acoustic sensor is X (km), the maximum pulse repetition rate that can be applied by the distributed acoustic sensor shown in FIG. 1 and the maximum frequency that can be measured are calculated according to Equation 1 below .

In Equation (1), v represents the speed of light in the optical fiber, and c represents the speed of light in vacuum. And n represents the refractive index of the optical fiber.

Therefore, according to Equation (1), the maximum pulse repetition rate that can be applied by the distributed acoustic sensor shown in FIG. 1 and the maximum frequency that can be measured according to Equation (2) are calculated.

In Equation (2), the maximum frequency that can be measured is calculated by the Nyquist rate.

2 is a diagram of an optical fiber acoustic sensor system including a plurality of optical circulators according to one embodiment.

The optical fiber acoustic sensor system 10 shown in FIG. 2 is an embodiment of FIG. 1 and is a distributed acoustic sensor using a coherent OTDR method.

Therefore, the contents already described with reference to FIG. 1 apply to FIG. 2 even if omitted from FIG.

Referring to FIG. 2, the system 10 includes a coherent laser 100 that applies a laser pulse.

The system 10 also includes a plurality of optical fibers 400-430 that include glass molecules that deliver laser pulses applied from the coherent laser 100 and cause Rayleigh back scattering of the laser pulses.

In addition, the system 10 includes a plurality of optical circulators 300 to 330 installed between a plurality of optical fibers 400 to 430, respectively.

The system 10 also includes a plurality of photodetectors 200-230 coupled to a plurality of optical circulators 300-330, respectively.

The system 10 also includes a computer 500 that analyzes the signals detected from each of the plurality of photodetectors 200 to 230 and observes the sound waves around the plurality of optical fibers.

In one embodiment, each of the plurality of optical circulators 300 to 330 includes a first port through which a laser pulse is input from a first optical fiber that is one of a plurality of optical fibers 400 to 430, a plurality of optical fibers 400 to 430, A second port for delivering a laser pulse to a second optical fiber, and a third port coupled to a first photodetector, one of the plurality of photodetectors 200-230.

In one embodiment, each of the plurality of optical circulators 300 to 330 transmits light backscattered from the second optical fiber to the first photodetector through the third port.

In one embodiment, the computer 500 analyzes signals detected from each of the plurality of photodetectors 200-230 to determine Rayleigh backscattering characteristics occurring in at least one of the plurality of optical fibers 400-430 , And determines the position at which vibration is transmitted to at least one of the plurality of optical fibers (400 to 430) from outside using the determined characteristics.

In one embodiment, the system 10 includes a sensing interval having a predetermined length.

In FIG. 2, a section indicated by the total X (km) represents a sensing period.

In one embodiment, the plurality of optical circulators 300 to 330 are installed at a predetermined interval between the start point of the sensing section and the start point of the sensing section and the end point of the sensing section.

In one embodiment, the plurality of optical fibers 400 to 430 connect between the plurality of optical circulators 300 to 330, and the optical circulators 300 to 330 closest to the end of the sensing section of the plurality of optical circulators 300 to 330 And is connected to the end point of the sensing section from the lighter 330.

2, the maximum sensing distance for observing the sound waves using the optical fiber acoustic sensor system 10 and the maximum repetition rate of laser pulses that can be applied to the plurality of optical fibers 400 to 430 are inversely proportional to each other.

The maximum sensing distance for observing the sound waves using the optical fiber acoustic sensor system 10 and the maximum repetition rate of laser pulses that can be applied to the plurality of optical fibers 400 to 430 are determined by the optical circulators 300 to 330, . ≪ / RTI >

Likewise, the maximum sensing distance at which the sound waves can be observed using the optical fiber acoustic sensor system 10 and the maximum frequency of the sound waves measurable at the plurality of optical fibers 400 to 430 are inversely proportional to each other.

The maximum sensing distance at which the sound waves can be observed using the optical fiber acoustic sensor system 10 and the maximum frequency of the sound waves that can be measured at the plurality of optical fibers 400 to 430 are measured by the optical circulators 300 to 330 It is proportional to the number.

In Fig. 2, when the total sensing distance is X (km) and the total number of optical circulators is N, the spacing of each optical circulator can be assumed to be X / N (km).

Therefore, it can be assumed that the total sensing distance is that N optical fibers of X / N (km) length are connected to each other.

At this time, the maximum pulse repetition rate that can be applied to the system 10 and thus the maximum sound wave frequency that can be measured in the system 10 is calculated by the following equation (3).

In Equation (3), v represents the speed of light in the optical fiber, and c represents the speed of light in vacuum. And n represents the refractive index of the optical fiber.

Therefore, according to Equation (3), the maximum pulse repetition rate that can be applied by the distributed acoustic sensor shown in FIG. 2 and the maximum sound wave frequency that can be measured according to Equation (3) are calculated as follows.

In Equation (4), the maximum sound wave frequency that can be measured is calculated by the Nyquist rate.

Assuming that the pulse repetition rate is fixed instead of the sensing distance in Equation (3), the sensing distance increases N times as N increases.

Therefore, by adding the optical circulator to the system 10, it is possible to obtain the sensing distance proportional to the number of all optical circulators, or the maximum sound frequency that can be applied and measured.

For example, when it is desired to increase the maximum frequency that can be applied and measured in the installed system 10 as shown in FIG. 1 or FIG. 2, an optical circulator may be added in the middle of the existing optical fiber.

As another example, when it is desired to increase the sensing distance in the installed system 10 as shown in FIG. 1 or FIG. 2, a new sensing module device may be added (connected) to the end of the existing optical fiber.

FIG. 3 is a block diagram of a modular apparatus constituting an optical fiber acoustic sensor system using the coherent OTDR method according to an embodiment.

Referring to FIG. 3, the module device 20 includes an optical circulator 22, a glass molecule which is connected to the optical circulator and transmits a laser pulse output from the optical circulator and causes a Rayleigh rear scattering of the laser pulse And a photodetector 26 connected to the optical fiber 24 and the optical circulator 22 for detecting the light scattered back from the optical fiber 24 through the optical circulator 22.

In one embodiment, the modular device 20 shown in Figure 3 is coupled to other modular devices or to the system shown in Figures 1-2.

In one embodiment, the optical circulator 22 is coupled to the optical fiber of another modular device.

The optical circulator 22 has a first port for inputting laser pulses from the optical fibers of other modular devices, a second port for delivering laser pulses to the optical fibers 24 of the modular device 20, Lt; / RTI >

In one embodiment, the optical fiber 24 is connected to the optical circulator of another modular device, and the optical fiber 24 transfers the laser pulse to the optical circulator of another modular device.

In one embodiment, the modular device 20 is standardized such that the first port of the optical circulator 22 is input and the end of the optical fiber 24 is output.

Therefore, an optical fiber acoustic sensor system including a plurality of optical circulators 22 is constructed by connecting the outputs and inputs of a plurality of modular devices respectively and applying laser pulses to the front modular device using a coherent laser can do.

As another example, a modular arrangement for building an optical fiber acoustic sensor system including a plurality of optical circulators in a manner that adds a new optical circulator in the middle of an existing optical fiber acoustic sensor system can be used.

FIG. 4 is a view showing a module device constituting an optical fiber acoustic sensor system using the coherent OTDR method according to another embodiment.

Referring to FIG. 4, the modular device 30 includes an optical circulator 32 and a photodetector 34.

The module device 30 shown in Fig. 4 is one embodiment of the module device 20 shown in Fig. 3, and the contents already described with reference to Fig. 3 also apply to Fig.

The optical circulator 32 shown in FIG. 4 includes a first port for inputting a laser pulse, a second port for outputting a laser pulse, and a third port connected to the optical detector 34.

In one embodiment, the modular device 30 is standardized such that the first port of the optical circulator 32 is input and the second port portion is output.

When the modular device 30 is added in the middle of the optical fiber acoustic sensor, the middle of the existing optical fiber is cut off, and a connection part for connecting the optical circulator 32 is added. The module device 30 can be added.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, You will understand. Therefore, it should be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

10: Fiber optic acoustic sensor system
100: Coherent laser
200 to 230: photodetector
300 to 330: Optical circulator
400 to 430: Optical fiber
500: computer

Claims (10)

A fiber optic acoustic sensor system using a Coherent Optical Time-Domain Reflectormeter Method,
A coherent laser providing a laser pulse;
A plurality of optical fibers including glass molecules that transmit the laser pulses provided from the coherent laser and cause Rayleigh backscatter of the laser pulses;
A plurality of optical circulators provided between the plurality of optical fibers;
A plurality of photodetectors connected to each of the plurality of optical circulators; And
A computer for analyzing a signal detected from each of the plurality of photodetectors and observing a sound wave around the plurality of optical fibers; . The method according to claim 1,
Wherein each of the plurality of optical circulators comprises:
A first port through which the laser pulse is inputted from a first optical fiber which is one of the plurality of optical fibers;
A second port for transmitting the laser pulse to a second optical fiber, which is one of the plurality of optical fibers; And
A third port coupled to a first photodetector that is one of the plurality of photodetectors; . 3. The method of claim 2,
Wherein each of the plurality of optical circulators comprises:
And transmits backscattered light from the second optical fiber to the first photodetector through the third port. The method according to claim 1,
The computer,
And a controller configured to analyze signals detected from each of the plurality of optical detectors to determine characteristics of Rayleigh back scattering generated in at least one of the plurality of optical fibers, and to oscillate at least one of the plurality of optical fibers from the outside To determine the delivered location. The method according to claim 1,
The system includes a sensing period having a predetermined length,
Wherein the plurality of optical circulators are provided at a predetermined interval between a start point of the sensing section and a start point of the sensing section and an end point of the sensing section,
Wherein the plurality of optical fibers connect between the plurality of optical circulators and are connected from an optical circulator closest to an end point of the sensing section among the plurality of optical circulators to an end point of the sensing section. The method according to claim 1,
Wherein a maximum sensing distance for observing a sound wave using the optical fiber acoustic sensor system and a maximum repetition rate of the laser pulse that can be applied to the plurality of optical fibers are inversely proportional to each other,
Wherein the maximum sensing distance and the maximum repetition rate of the laser pulse are proportional to the number of optical circulators. The method according to claim 1,
Wherein a maximum sensing distance for observing a sound wave using the optical fiber acoustic sensor system and a maximum frequency of a sound wave measurable in the plurality of optical fibers are inversely proportional to each other,
Wherein the maximum sensing distance and the maximum frequency are proportional to the number of optical circulators. Optical circulator;
An optical fiber connected to the optical circulator for transmitting a laser pulse output from the optical circulator and including glass molecules for causing Rayleigh backscatter of the laser pulse; And
A photodetector coupled to the optical circulator and detecting light scattered back from the optical fiber through the optical circulator;
A module device constituting an optical fiber acoustic sensor system using a coherent OTDR method. 9. The method of claim 8,
The optical circulator is connected to an optical fiber of another module device,
The optical circulator includes:
A first port through which the laser pulse is input from an optical fiber of the other modular device;
A second port for delivering the laser pulse to an optical fiber of the module device; And
A third port coupled to the photodetector; A module device constituting an optical fiber acoustic sensor system using a coherent OTDR method. 9. The method of claim 8,
The optical fiber is connected to an optical circulator of another module device,
The optical fiber includes:
And transmits the laser pulse to the optical circulator of the other modular device. The module device constitutes the optical fiber acoustic sensor system using the coherent OTDR method.

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