KR101727091B1 - Apparatus and method of distributed fiber sensor using optical frequency domain reflectometry based on Brillouin dynamic grating - Google Patents

Abstract

The present invention relates to a distributed optical fiber sensor apparatus using frequency domain reflectometry of a Brillouin dynamic grating. The distributed optical fiber sensor apparatus using frequency domain reflectometry of a Brillouin dynamic grating comprises: a pump light source to generate pump light; a first light distributor to distribute the pump light into first pump light and second pump light; a first single side wave modulator to move a frequency of the first pump light to output the first pump light; polarization maintaining optical fiber connected to allow the first and the second pump light propagating through the first single side wave modulator to enter an identical first optical axis in opposite directions; a probe light source to generate probe light; a second light distributor to distribute the probe light into first probe light and second probe light; an optical circulator to allow the first probe light to enter a different second optical axis of the polarization maintaining optical fiber in a direction identical to the first pump light; a second single side wave modulator to move a frequency of the second probe light to output the second probe light; an optical multiplexer to multiplex the second probe light and first probe reflection light reflected from a Brillouin dynamic grating formed in the polarization maintaining optical fiber for the first probe light to be outputted to a first optical circulator; and a photodetector to detect light outputted by the optical multiplexer. According to the distributed optical fiber sensor apparatus using frequency domain reflectometry of a Brillouin dynamic grating and a sensing method thereof, high spatial resolution and a narrowband Brillouin gain curve can be simultaneously acquired. Also, a short pulse generator and a high speed digitizer are not required to obtain high spatial resolution to simplify a structure.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed optical fiber sensor device using frequency domain reflection measurement of a Brillouin dynamic grating and a sensing method thereof,

The present invention relates to a distributed optical fiber sensor device using a frequency domain reflection measurement of a Brillouin dynamic grating and a sensing method thereof, and more particularly, to a distributed optical fiber sensor device using a frequency domain reflection measurement of a Brillouin dynamic grating An optical fiber sensor device and a sensing method thereof.

Brillouin dynamic grating (BDG) is a method of stimulating Brillouin scattering (SBS) in a directionally polarized light wave in a polarization maintaining fiber (PMF) or other medium with birefringence It refers to the generated sound wave. When the sound wave satisfies an appropriate phase matching condition, the light wave generating the sound wave and the polarized light are perpendicular to each other, and the light wave acts as a grating to the light wave having a different optical frequency to reflect the light wave.

Since the intensity of the BDG is proportional to the magnitude of the Brillouin gain of the light wave used to generate this grating, the Brillouin gain curve can be obtained by measuring the intensity of the BDG reflected light and the Brillouin frequency, which is the center frequency thereof, can be detected.

The prior art for measuring the Brillouin gain curves in a distributed fashion is the time domain analysis technique of Brillouin frequency.

This technique, called BOTDA, allows the pump light, which is a pulse in the optical fiber, and the probe light, which is a continuous oscillation light, to be incident in opposite directions. The interference between the pump light and the probe light in the optical fiber generates a sound wave and generates a Brillouin gain signal. The Brillouin gain signal is acquired from the intensity change of the probe light while the frequency difference between the pump light and the probe light is changed to detect the Brillouin frequency.

In this method, a short pulse light is used as the pump light in order to obtain a high spatial resolution. Since the short pulse light corresponds to a wide band on the frequency component, a broadband Brillouin gain curve is obtained.

As the Brillouin gain curve becomes wider, the Brillouin frequency, which is the center frequency thereof, can not be accurately obtained, so there is a limit to improve the spatial resolution.

Another conventional technique is the time domain analysis of Brillouin dynamic grating (BDG), which is disclosed in Korean Patent No. 10-1130344. In this method, BDG is generated in a polarization maintaining optical fiber (PMF) by using a long pump beam instead of using a short pump beam, and a short probe light is incident on a polarization perpendicular to the pump light to measure the reflection of the probe light from the BDG to be.

In this method, since the pump pulse light is only involved in the generation of the BDG but does not determine the spatial resolution, a long pump can be used. Thus, a narrow Brillouin gain curve can be obtained, The spatial resolution can be obtained. In addition, when the frequency difference between the two pump lights traveling in both directions in the form of pulse light and continuous oscillation light is changed, the Brillouin gain appears depending on the position, which is represented by the reflectance of the BDG. When this reflectance change is measured using a short probe light, the Brillouin gain curve can be obtained while changing the frequency difference between the two pump lights.

However, in order to obtain a high spatial resolution using this technique, short pulse light is used for the probe light, so a pulse generator of a high bandwidth is required and a high-speed digitizer is used for signal processing.

The present invention has been made in order to solve the above problems, and it is an object of the present invention to provide a distributed optical fiber sensor device using a Brillouin dynamic grating, which can simplify the structure and provide a high spatial resolution, The purpose is to provide.

In order to achieve the above object, a distributed optical fiber sensor device using frequency domain reflection measurement of a Brillouin dynamic grating according to the present invention comprises a pump light source for generating a pump light; A first optical splitter for distributing the pump light to the first pump light and the second pump light; A first single-sided wave modulator for shifting and outputting the frequency of the first pump light; A polarization maintaining optical fiber in which a first pump light traveling through the first single side wave modulator and the second pump light are connected to the same first optical axis so as to be mutually incident in opposite directions; A probe light source for generating probe light; A second optical splitter for distributing the probe light to the first probe light and the second probe light; An optical circulator for causing the first probe light to enter the other second optical axis of the polarization maintaining optical fiber in the same direction as the first pump light; A second single side wave modulator for shifting and outputting the frequency of the second probe light; A combiner for multiplexing the first probe light and the second probe light reflected from the Brillouin diffractive element formed on the polarization maintaining optical fiber with respect to the first probe light and outputted to the first optical circulator; And a photodetector for detecting light output from the optical multiplexer.

And a signal processing unit for processing the signal output from the photodetector, wherein the signal processing unit is configured to detect a frequency difference between the first pump light and the second pump light and a frequency difference between the first probe light and the second probe light And detects the Brillouin transition frequency acquired from the photodetector while changing the frequency difference.

The probe light source is a wavelength tunable laser capable of varying the wavelength.

According to another aspect of the present invention, there is provided a distributed optical fiber sensing method using frequency domain reflection measurement of a Brillouin dynamic grating, comprising: generating a pump light; A pump light distribution step of distributing the pump light to the first pump light and the second pump light; Outputting the first pump light by shifting the frequency by a first single side wave modulator; A pump light incident step of causing the first pump light and the second pump light to move in the opposite directions to the same first optical axis of the polarization maintaining optical fiber; A probe light generating step of generating probe light; A probe light distribution step of distributing the probe light to the first probe light and the second probe light; Moving the frequency of the second probe light by a second single side wave modulator and outputting the same; A probe light incidence step of causing a first probe light to enter the other second optical axis of the polarization maintaining optical fiber in the same direction as the first pump light; Generating interference light by multiplexing first reflected light from the first probe light from the polarization maintaining optical fiber and second probe light whose frequency has been shifted through the second single side wave modulator to generate interference light; And a light detecting step of detecting the interference light.

According to the distributed optical fiber sensor device and the sensing method using the frequency domain reflection measurement of the Brillouin dynamic grating according to the present invention, a high spatial resolution and a Brillouin gain curve of a narrow margin can be simultaneously obtained. In addition, short pulse generators and high-speed digitizers are not required to obtain a high spatial resolution, which simplifies the structure.

1 is a view showing a distributed optical fiber sensor device using frequency domain reflection measurement of a Brillouin dynamic grating according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A distributed optical fiber sensor device and a sensing method thereof using frequency domain reflection measurement of a Brillouin dynamic grating according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a view showing a distributed optical fiber sensor device using frequency domain reflection measurement of a Brillouin dynamic grating according to the present invention.

Referring to FIG. 1, a distributed optical fiber sensor apparatus 100 using frequency domain reflection measurement of a Brillouin dynamic grating according to the present invention includes a Brillouin dynamic grating generating unit (BDG generating unit) 110, (OFDR: Optical Frequency Domain Reflectometry Measurement Unit)

The BDG generating unit 110 is capable of generating a Brillouin dynamic grating in the polarization maintaining optical fiber PMF.

The BDG generating unit 110 includes a pump light source 111, a first optical splitter 113, a first single side wave modulator (SSBM) 115, an optical amplifier 117, a first polarizer 121, A first polarization splitter 125, a second polarization splitter 126, and a polarization maintaining optical fiber 130.

The pump light source (Pump LD) 111 is a continuously oscillating laser light source that continuously oscillates and emits a pump light.

The first optical splitter 113 distributes the pump light emitted from the pump light source 111 to the first pump light and the second pump light at a ratio of 50 to 50 percent.

The first single-sided wave modulator 115 moves the frequency of the first pump light upward or downward according to the output signal of the microwave generator 141 and outputs the same.

The first single side wave modulator 115 may be constructed to move the frequency of the first pump light upward by a predetermined frequency in accordance with the Brillouin frequency of the polarization maintaining optical fiber 130 set by the microwave generator 141.

The optical amplifier 117 is an EDFA.

The first polarizer 121 transmits the polarization component of the first optical axis and the first polarization splitter 125 causes the light propagated in the first polarization splitter 121 to propagate to the polarization maintaining optical fiber 130, The light reflected from the holding optical fiber 130 is propagated in a direction toward the first optical circulator 171.

The second pump light is incident on the polarization maintaining optical fiber 130 via the optical isolator 127 and the first polarization splitter 126.

A power meter was applied to monitor light traveling in the direction of the isolator 127 from the polarization maintaining optical fiber 130 and a second photocoupler 121 connected between the optical amplifier 117 and the first polarizer 121 It is needless to say that the lighter 121 and the photodetector PD are applied to monitor the light reflected by the first polarizer 121 and can be omitted.

The second polarizer 122 is connected between the first optical circulator 171 and the first polarization splitter 125 of the optical frequency region reflection measuring unit 160 to pass the polarized light of the second optical axis.

The polarization maintaining optical fiber 130 is arranged such that the first pump beam Pump1 and the second pump beam Pump2 propagating through the first single side wave modulator 115 are incident on the same first optical axis in opposite directions, And the second polarization splitter 126, and functions as a distributed sensor.

 The optical frequency domain reflectometry (OFDR) 160 modulates the frequency of the probe light and combines the light reflected from the BDG generator 110 and the reference light to obtain a desired physical quantity, for example, temperature or strain So that it can be measured.

The optical frequency domain reflectometry (OFDR) measuring unit 160 includes a probe light source 161, a second optical splitter 163, a second single side wave modulator 165, An optical combiner 173, a photodetector 180 and a signal processing unit (DAQ & Signal Processing)

The probe light source 161 generates and outputs the probe light. The probe light source 161 is a continuous oscillation light source.

Further, the probe light source 161 is applied with a wavelength tunable laser whose wavelength is varied by the signal processing unit 185.

The second optical splitter 163 divides the probe light generated by the probe light source 161 into 50 to 50 percent of the first probe light Probe 1 and the second probe light Probe 2.

The first optical circulator 171 causes the first probe light to enter the other second optical axis of the polarization maintaining optical fiber 130 in the same direction as the first pump light and reflects the first probe light reflected from the polarization maintaining optical fiber 130 To the multiplexer (173).

A second single-sided wave modulator (SSBM) 165 shifts the frequency of the second probe light upward or downward to output.

Preferably, the second single-sided wave modulator (SSBM) 165 is also configured to shift the frequency of the second probe light to the same frequency as that of the first pump light in accordance with a signal output from the microwave generator 141.

The third polarizer 167 outputs the polarization component of the first optical axis to the second probe light.

The optical multiplexer 173 multiplexes the first probe light reflected from the Brillouin scattering optical element 130 formed on the polarization maintaining optical fiber 130 with respect to the first probe light and the first probe light reflected from the first optical circulator 171 and the second probe light And outputs it to the photodetector 180.

The photodetector 180 detects light output from the optical multiplexer 173 and outputs an electrical signal corresponding to the detected light to the signal processor 185.

The signal processor 185 processes the signal output from the photodetector 180.

The signal processing unit 185 detects the Brillouin transition frequency acquired from the photodetector 180 while changing the frequency difference between the first pump light and the second pump light and the frequency difference between the first probe light and the second probe light.

Here, the magnitude of the first probe reflected light is proportional to the reflectance of the Brillouin dynamic grating due to the Brillouin gain between the first pump and the second pump.

Therefore, when the intensity of the first probe reflected light is measured by the OFDR measurement method while changing the frequency difference between the first pump light and the second pump light at a constant interval, the signal processor 185 obtains a Brillouin gain curve according to the position Which can detect the Brillouin frequency.

The signal processing unit 185 detects the change of the signal while changing the wavelength of the probe light in a constant band, and acquires information of the reflectance according to the position through Fourier transform.

Hereinafter, the sensing process of the sensing device will be described.

First, the pump light generated in the pump light source 111 is distributed to the first pump light and the second pump light via the first optical splitter 113. [

Thereafter, the frequency of the first pump light is shifted by the first side wave modulator 115, and the first pump light and the second pump light of which frequency is shifted are incident on the same first optical axis of the polarization maintaining optical fiber 130 in opposite directions . In this process, a Brillouin dynamic grating is generated in the polarization maintaining optical fiber 130.

Meanwhile, the probe light generated by the pump light source 161 is distributed to the first probe light and the second probe light via the second optical splitter 163.

The frequency of the second probe light is shifted by the second single side wave modulator 165.

Also, the first probe light is incident on the other second optical axis of the polarization maintaining optical fiber 130 in the same direction as the first pump light, and the first probe reflected light generated from the first probe light and the second probe light reflected from the second single- And the optical detector 173 detects the interference light generated by combining the second probe light having the frequency shifted through the first and second probe lights.

The first probe light is incident on the polarization axis perpendicular to the polarization axis of the polarization maintaining optical fiber into which the first light second pump light is incident, and proceeds in the same direction as the first pump light.

The second probe light passed through the other arm of the second optical splitter 163 passes through a second single-sided wave modulator (SSBM) 165 and is reflected by a reference light ).

The first probe reflected light generated in the polarization maintaining optical fiber 130 passes through the first polarization splitter 125 and the first optical circulator 171 and then interferes with the reference light through the multiplexer 173, ) ≪ / RTI >

The signal detected by the photodetector PD is processed in the signal processing unit 185 described above.

The above measurement is repeated while gradually changing the frequency of the first pump light in a predetermined region near the Brillouin frequency to obtain a Brillouin gain curve at each position.

The optical fiber sensor device according to the present invention is a method (BDG-OFDR) for replacing a conventional time domain analysis method with an optical frequency domain reflectometry (OFDR) The advantage is that it is used for all probe light and does not use a high-speed digitizer.

In addition, the present apparatus can simultaneously acquire a Brillouin gain curve of a narrow band, which is an advantage of the high spatial resolution of the OFDR and the measurement method using the BDG.

Further, since the change of Brillouin frequency linearly depends on the change of the temperature or the strain acting on the optical fiber, the apparatus and method according to the present invention are useful as a distributed optical fiber sensor for temperature or strain measurement with high spatial resolution Can be used.

111: pump light source 113: first optical splitter
115: first single side wave modulator 117: optical amplifier
121: first polarizer 125: first polarizing splitter
126: second polarization splitter 130: polarization maintaining optical fiber
161: probe light source 163: second optical splitter
165: second single side wave modulator 167: third polarizer
171: optical circulator 173:
180: photodetector 185: signal processor

Claims (4)

A pump light source for generating a pump light;
A first optical splitter for distributing the pump light to the first pump light and the second pump light;
A first single-sided wave modulator for shifting and outputting the frequency of the first pump light;
A polarization maintaining optical fiber in which a first pump light traveling through the first single side wave modulator and the second pump light are connected to the same first optical axis so as to be mutually incident in opposite directions;
A probe light source for generating probe light;
A second optical splitter for distributing the probe light to the first probe light and the second probe light;
An optical circulator for causing the first probe light to enter the other second optical axis of the polarization maintaining optical fiber in the same direction as the first pump light;
A second single side wave modulator for shifting and outputting the frequency of the second probe light;
A combiner for multiplexing the first probe light and the second probe light reflected from the Brillouin diffractive element formed on the polarization maintaining optical fiber with respect to the first probe light and outputted to the optical circulator;
And a photodetector for detecting light output from the optical multiplexer. The distributed optical fiber sensor device using the frequency-domain reflection measurement of the Brillouin dynamic grating. The apparatus of claim 1, further comprising: a signal processor for processing a signal output from the photodetector,
The signal processing unit detects the Brillouin transition frequency acquired from the photodetector while changing the frequency difference between the first pump light and the second pump light and the frequency difference between the first probe light and the second probe light A distributed optical fiber sensor device using frequency domain reflection measurement of Brillouin dynamic grating. The distributed optical fiber sensor device according to claim 1, wherein the probe light source is a wavelength tunable laser capable of varying the wavelength. A pump light generating step of generating a pump light;
A pump light distribution step of distributing the pump light to the first pump light and the second pump light;
Outputting the first pump light by shifting the frequency by a first single side wave modulator;
A pump light incident step of causing the first pump light and the second pump light to move in the opposite directions to the same first optical axis of the polarization maintaining optical fiber;
A probe light generating step of generating probe light;
A probe light distribution step of distributing the probe light to the first probe light and the second probe light;
Moving the frequency of the second probe light by a second single side wave modulator and outputting the same;
A probe light incidence step of causing a first probe light to enter the other second optical axis of the polarization maintaining optical fiber in the same direction as the first pump light;
Generating interference light by multiplexing first reflected light from the first probe light from the polarization maintaining optical fiber and second probe light whose frequency has been shifted through the second single side wave modulator to generate interference light;
And a light detecting step of detecting the interference light. The distributed optical fiber sensing method using frequency domain reflection measurement of Brillouin dynamic grating.

Images