CN103335666A - Dynamic distributed Brillouin optical fiber sensing device and method - Google Patents

Abstract

The invention relates to a dynamic distributed Brillouin optical fiber sensing device and method, belonging to the field of optics. The invention aims to solve the problem that the strain measurement range is small based on the dynamic sensing technology based on the Brillouin gain slope method. The invention includes a laser, a coupler, a polarization-maintaining fiber to be tested, an erbium-doped fiber amplifier, an adjustable optical attenuator, a data acquisition module, a first polarization controller PC1, a second polarization controller PC2, a third polarization controller PC3, The fourth polarization controller PC4, the probe light intensity modulator IM1, the pump light intensity modulator IM2, the arbitrary waveform generator AWG, the first circulator R1, the second circulator R2, the first signal amplifier Amp1 and the second signal The amplifier Amp2, using the arbitrary wave to drive the intensity modulator, realizes the frequency agility of the probe light, solves the problem of rapid frequency scanning, realizes distributed Brillouin dynamic sensing, and measures the strain of the polarization-maintaining fiber to be tested .

Description

Dynamic Distributed Brillouin Optical Fiber Sensing Device and Method

technical field

The invention relates to a dynamic distributed Brillouin optical fiber sensing device and method, belonging to the field of optics.

Background technique

Distributed dynamic sensing technology is used for distributed monitoring of transient signals. This sensing technology can realize fast and real-time measurement of the stress information of the monitored object. This sensing technology can be used to monitor the health status of infrastructure such as bridges, and can also be used to study the impact of external transient conditions such as explosions and earthquakes on the structure of the monitored object. In the traditional Brillouin optical time-domain analysis (BOTDA) technology, the frequency scanning speed is lower than the signal change, which makes the traditional BOTDA technology only suitable for the monitoring of steady-state signals, not suitable for transient signals. The existing BOTDA technology that can be used to measure dynamic signals mostly adopts the Brillouin gain slope method. This method is limited by the length of the linear segment of the Brillouin gain curve, and the measured strain range is small, which limits the practicality of this method. Application Ability.

Contents of the invention

The purpose of the present invention is to solve the problem of small strain measurement range based on the Brillouin gain slope method dynamic sensing technology, and provide a dynamic distributed Brillouin optical fiber sensing device and method with a large measurement range.

The dynamic distributed Brillouin optical fiber sensing device of the present invention includes a laser, a coupler, a polarization-maintaining optical fiber to be tested, an erbium-doped optical fiber amplifier, an adjustable optical attenuator, a data acquisition module, a first polarization controller PC1, The second polarization controller PC2, the third polarization controller PC3, the fourth polarization controller PC4, the probe optical intensity modulator IM1, the pump optical intensity modulator IM2, the arbitrary waveform generator AWG, the first circulator R1, the second Two circulators R2, the first signal amplifier Amp1 and the second signal amplifier Amp2,

The RF signal output terminal of the arbitrary waveform generator AWG is connected to the modulation terminal of the probe light intensity modulator IM1 through the first signal amplifier Amp1; the rectangular pulse signal output terminal of the arbitrary waveform generator AWG is connected to the pump light through the second signal amplifier Amp2 The modulation terminal of the intensity modulator IM2 is connected; the trigger signal output terminal of the arbitrary waveform generator AWG is connected with the trigger terminal of the data acquisition module;

The laser beam emitted by the laser is divided into two laser beams through the coupler;

One of the laser beams enters the probe optical intensity modulator IM1 through the first polarization controller PC1, and the probe light modulated by the optical intensity modulator IM1 is output to the A port of the first circulator R1, and passes through the B port of the first circulator R1. The fiber grating at the port is reflected and output from the C port, and the probe light output from the C port of the first circulator R1 passes through the third polarization controller PC3 and then enters the polarization-maintaining fiber to be tested;

The other beam of laser light enters the pumping light intensity modulator IM2 through the second polarization controller PC2, and the pumping light modulated by the pumping light intensity modulator IM2 is output to the input end of the erbium-doped fiber amplifier, and the output of the erbium-doped fiber amplifier is The end is connected to the input end of the adjustable optical attenuator, and the pump light output by the adjustable optical attenuator enters from the C port of the second circulator R2, and is output from the A port, and enters the polarization-maintaining optical fiber to be tested from another direction;

In the polarization-maintaining fiber to be tested, the probe light satisfying the Brillouin scattering condition and the pump light undergo Brillouin amplification interaction; the probe light amplified by Brillouin enters the A port of the second circulator R2, and Output from the B port of the second circulator R2 to the data acquisition module.

Based on the method of the dynamic distributed Brillouin optical fiber sensing device, the method may further comprise the steps:

Step 1. The coupler divides the laser beam into two beams, one of which is modulated into probe light by probe light intensity modulator IM1, and the other beam is modulated into pump light by pump light intensity modulator IM2.

The radio frequency signal input to the modulation terminal of the probe optical intensity modulator IM1 is a wave train with N frequency step changes

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; [</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ]</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; ,</span>$

为取整，t是时间；Among them: f _m0 is the initial frequency of the wave train, f _s is the frequency step, T is any frequency scanning period,

is rounded, t is time;

The probe light intensity modulator IM1 modulates an input beam of laser light into probe light f _tzg (t)=f ₀ -2f _m (t),

Where: f ₀ is the frequency of an input laser beam;

The pumping light is pulsed light consisting of N pulses with a period of T,

Step 2, the light modulated and output by the probe light intensity modulator IM1 is filtered by the fiber grating to filter the second-order lower side frequency signal as the probe light;

Step 3, the probe light and the pump light interact in the polarization-maintaining fiber to be tested through stimulated Brillouin scattering, and the polarization-maintaining fiber to be tested outputs amplified probe light;

Step 4. After completing the scanning of a frequency scanning period T, obtain the Brillouin gain spectrum at each spatial point on the polarization-maintaining fiber to be tested under the frequency state;

Step 5. According to the linear functional relationship between Brillouin frequency shift ν _B and strain ε ν _B =ν _B0 +C _s ε, complete the measurement of the strain of the polarization-maintaining fiber under test at this frequency state,

where ν _B0 is the Brillouin frequency shift without strain and C _s is the gauge coefficient.

Advantages of the present invention: the method of the present invention utilizes arbitrary wave to drive the intensity modulator, realizes the frequency agility of the probe light, solves the problem of rapid frequency scanning, and realizes distributed Brillouin dynamic sensing. A large strain measurement range can be obtained by increasing the probe optical frequency scanning range, which overcomes the small strain measurement problem in the Brillouin gain slope method.

Description of drawings

Figure 1 is a timing diagram of probe light and pump light;

Fig. 2 is the structural representation of dynamic distributed Brillouin optical fiber sensing device of the present invention;

Figure 3 is a schematic diagram of stress measurement.

Detailed ways

Specific embodiment one: the present embodiment is described below in conjunction with Fig. 1 and Fig. 2, and the dynamic distributed Brillouin optical fiber sensing device described in the present embodiment includes a laser 1, a coupler 2, a polarization-maintaining optical fiber 3 to be tested, a doped Bait fiber amplifier 4, adjustable optical attenuator 5, data acquisition module 6, first polarization controller PC1, second polarization controller PC2, third polarization controller PC3, fourth polarization controller PC4, probe light intensity modulation IM1, pump light intensity modulator IM2, arbitrary waveform generator AWG, first circulator R1, second circulator R2, first signal amplifier Amp1 and second signal amplifier Amp2,

The RF signal output terminal of the arbitrary waveform generator AWG is connected to the modulation terminal of the probe light intensity modulator IM1 through the first signal amplifier Amp1; the rectangular pulse signal output terminal of the arbitrary waveform generator AWG is connected to the pump light through the second signal amplifier Amp2 The modulation terminal of the intensity modulator IM2 is connected; the oscilloscope trigger signal output terminal of the arbitrary waveform generator AWG is connected with the trigger terminal of the data acquisition module 6;

The laser beam emitted by laser 1 is divided into two laser beams by coupler 2;

One of the laser beams enters the probe optical intensity modulator IM1 through the first polarization controller PC1, and the probe light modulated by the optical intensity modulator IM1 is output to the A port of the first circulator R1, and passes through the B port of the first circulator R1. The fiber grating at the port is reflected and output from the C port, and the probe light output from the C port of the first circulator R1 passes through the third polarization controller PC3 and then enters the polarization-maintaining optical fiber 3 to be tested;

Wherein another beam of laser light enters the pump light intensity modulator IM2 through the second polarization controller PC2, and the pump light modulated by the pump light intensity modulator IM2 is output to the input end of the erbium-doped fiber amplifier 4, and the erbium-doped fiber amplifier 4 The output end of the adjustable optical attenuator 5 is connected to the input end of the adjustable optical attenuator 5, and the pump light output by the adjustable optical attenuator 5 enters from the C port of the second circulator R2, and is output from the A port, and enters the protection device under test from another direction. Polarizing fiber 3;

In the polarization-maintaining fiber 3 to be tested, the probe light and the pump light satisfying the Brillouin amplification condition undergo a Brillouin amplification process; the probe light amplified by the Brillouin enters the A port of the second circulator R2, and Output from the B port of the second circulator R2 to the oscilloscope 6 for display.

The arbitrary waveform generator AWG adopts the arbitrary waveform generator produced by Tek Company, the model is 7122C.

Laser 1 adopts an ultra-narrow linewidth laser with a linewidth of 50 kHz, which is used as a light source with a wavelength of about 1550 nm. The output laser is divided into two beams through a 3dB coupler (Coupler), and the one through the probe light intensity modulator IM1 is used to generate probe light; the one through the pump light intensity modulator IM2 is used to generate pump light. The probe light intensity modulator IM1 works in the first-order side frequency suppression mode, driven by the RF signal with frequency step change from the arbitrary waveform generator AWG, and produces a second-order frequency shift effect on the injected laser. The low frequency Stokes signal is filtered out by the fiber Bragg grating FBG. The pump light intensity modulator IM2 is used to modulate the continuous pump laser light into pulsed light. After the pulsed light is amplified by the erbium-doped fiber amplifier 4 (EDFA), it passes through the SBS effect with the probe light in the polarization-maintaining fiber 3 to be tested. interaction. The third polarization controller PC3 and the fourth polarization controller PC4 are used to adjust the polarization states of the probe light and the pump light to be within the same optical axis of the polarization-maintaining fiber 3 to be tested. The amplified probe light is monitored by the data acquisition module 6 . The data acquisition module 6 works in an external trigger mode, and the trigger signal is provided by an arbitrary waveform generator AWG.

The arbitrary waveform generator AWG model 7122C generates three electrical signals in total, which are the radio frequency signal, the rectangular pulse signal and the trigger signal of the oscilloscope 6 respectively. AWG works in dual-channel multiplexing mode with a bandwidth of 9.6GHz and a sampling rate of up to 24GHz. The radio frequency signal is provided by the arbitrary wave output terminal. Marker output terminal 1 (Marker1) is used to output rectangular pulses, marker output terminal 2 (Marker2) is used to provide trigger signals for the oscilloscope, and the three channels work in burst mode (intermittent working mode).

Specific Embodiment Two: The present embodiment will be described below in conjunction with FIG. 2 . This embodiment will further describe Embodiment 1. It also includes a first DC power supply DC1 and a second DC power supply DC2.

The first DC power supply DC1 provides DC working power for the probe light intensity modulator IM1;

The second DC power supply DC2 provides DC working power for the pumping optical intensity modulator IM2.

Specific embodiment three: the present embodiment is described below in conjunction with Fig. 1 to 3, and present embodiment is based on the method for the dynamic distributed Brillouin optical fiber sensing device described in embodiment one, and this method comprises the following steps:

Step 1. The coupler 2 splits the laser beam into two beams, one of which is modulated into probe light by probe light intensity modulator IM1, and the other beam is modulated into pump light by pump light intensity modulator IM2.

The radio frequency signal input to the modulation terminal of the probe optical intensity modulator IM1 is a wave train with N frequency step changes

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; [</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ]</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; ,</span>$

为取整，t是时间；Among them: f _m0 is the initial frequency of the wave train, f _s is the frequency step, T is any frequency scanning period,

is rounded, t is time;

The probe light intensity modulator IM1 modulates an input beam of laser light into probe light f _tzg (t)=f ₀ -2f _m (t),

Where: f ₀ is the frequency of an input laser beam;

The pumping light is pulsed light consisting of N pulses with a period of T,

Step 2, the light modulated and output by the probe light intensity modulator IM1 is filtered by the fiber grating to filter the second-order lower side frequency signal as the probe light;

Step 3, the probe light and the pump light interact through stimulated Brillouin scattering in the polarization-maintaining fiber 3 to be tested, and the polarization-maintaining fiber 3 to be tested outputs amplified probe light;

Step 4. After completing the scanning of a frequency scanning period T, obtain the Brillouin gain spectrum at each spatial point on the polarization-maintaining fiber 3 to be tested under the frequency state;

Step 5. According to the linear functional relationship between the Brillouin frequency shift ν _B and the strain ε, ν _B =ν _B0 +C _s ε, complete the measurement of the strain of the polarization-maintaining optical fiber 3 to be tested at this frequency state,

where ν _B0 is the Brillouin frequency shift without strain and C _s is the gauge coefficient.

The principle of this method:

In this method, the probe light is continuous light, the pump light is pulsed light, and the frequency agility technology is used to realize the rapid frequency conversion of the probe light. By measuring the intensity of the probe light in each frequency state as a function of time, the Brillouin gain information of each spatial point on the polarization-maintaining fiber 3 to be tested can be deduced in this frequency state. When a After the frequency scanning cycle, the Brillouin gain spectrum at each spatial point on the polarization-maintaining fiber 3 to be tested can be obtained; the relationship between the measured physical quantity (strain) and the Brillouin frequency shift can be used to obtain Strain on polarizing fiber 3. When the frequency sweep speed is much greater than the stress change speed, the data measured by one frequency sweep is the transient data. The dynamic change information of the signal to be measured can be measured by sampling and measuring the signal to be measured within the time to be measured.

The wave trains with N frequency step changes are input to the modulation end of the probe optical intensity modulator IM1, and the probe optical intensity modulator IM1 performs frequency shift on the input beam of laser light, so that the probe output from the probe optical intensity modulator IM1 The needle light is scanned step by step within a certain range, and the scan step is 2f _s .

The timing of the output probe light and pump light modulated by the probe light intensity modulator IM1 and the pump light intensity modulator IM2 is set according to the form shown in FIG. 1 . The highest frequency of the signal that can be measured by this method is:

$\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; NT</span>}}$

For example, the frequency range of the radio frequency signal is 5.4GHz to 5.5GHz, and the frequency step f _s =2MHz, then N=51, f ₁ =10.8GHz, f ₂ =11.0GHz.... If any frequency scan period T is set to 1.4μs, the above formula requirements are met. It takes 71.4μs to complete a scan, and the sampling rate under this parameter can reach up to 14kHz, that is, dynamic signals with a maximum frequency of 7kHz can be measured.

Referring to FIG. 3 , two eccentric motors are placed on the polarization-maintaining optical fiber 3 to be tested, and a pressed object 8 is placed on the polarization-maintaining optical fiber 3 to be tested, and then the measurement is performed with the device shown in FIG. 2 .

The Brillouin frequency shift of each point of the optical fiber to be tested can be obtained by performing the following processing on the amplified probe light waveform data measured by the data acquisition module 6 . Using the linear relationship between the Brillouin frequency shift and the physical quantity to be sensed-strain (dynamic signal), the value of the dynamic signal at each point of the optical fiber to be tested can be measured.

1) The amplified data (that is, one frame of data) corresponding to a single frequency scan is intercepted according to the time length T, and divided into N segments. Let the number of points of each piece of data be L, then this data is divided into an N×L matrix, and the name of the matrix is A;

2) According to the linear functional relationship between the physical quantity to be sensed (strain) and the Brillouin gain spectrum, calculate the value of the sensed physical quantity (stress) at each point on the optical fiber to be measured at this time of frequency scanning, and obtain the matrix B, dimension It is N×L, that is, the data of one frame of the dynamic signal.

3) For the data of each frequency scan, do the above steps 1) and 2) to obtain the data of all frames of the dynamic signal to be tested, thereby completing the measurement of the dynamic signal.

Claims (4)

1. dynamic distributed Brillouin light fiber sensing equipment, it is characterized in that, it comprises laser instrument (1), coupling mechanism (2), polarization maintaining optical fibre to be measured (3), Erbium-Doped Fiber Amplifier (4), adjustable optical attenuator (5), data acquisition module (6), the first Polarization Controller PC1, the second Polarization Controller PC2, the 3rd Polarization Controller PC3, the 4th Polarization Controller PC4, probe light intensity modulator IM1, pump light intensities modulator IM2, AWG (Arbitrary Waveform Generator) AWG, the first circulator R1, the second circulator R2, the first signal amplifier Amp1 and secondary signal amplifier Amp2

The radiofrequency signal output terminal of AWG (Arbitrary Waveform Generator) AWG links to each other with the modulated terminal of probe light intensity modulator IM1 by the first signal amplifier Amp1; The rectangular pulse signal output terminal of AWG (Arbitrary Waveform Generator) AWG links to each other with the modulated terminal of pump light intensities modulator IM2 by secondary signal amplifier Amp2; The trigger pip output terminal of AWG (Arbitrary Waveform Generator) AWG links to each other with the trigger end of data acquisition module (6);

The laser beam that laser instrument (1) sends is divided into two bundle laser by coupling mechanism (2);

Wherein beam of laser enters probe light intensity modulator IM1 through the first Polarization Controller PC1, the probe light that light intensity modulator IM1 modulates exports the A port of the first circulator R1 to, from the output of C port, the probe light of the C port output of the first circulator R1 enters in the polarization maintaining optical fibre to be measured (3) after through the 3rd Polarization Controller PC3 through the fiber grating reflection back of the B port of the first circulator R1;

Wherein another Shu Jiguang enters pump light intensities modulator IM2 through the second Polarization Controller PC2, the pump light that pump light intensities modulator IM2 modulates exports the input end of Erbium-Doped Fiber Amplifier (4) to, the output terminal of Erbium-Doped Fiber Amplifier (4) connects the input end of adjustable optical attenuator (5), the pump light of adjustable optical attenuator (5) output enters from the C mouth of the second circulator R2, and from the output of A mouth, enter the polarization maintaining optical fibre to be measured (3) from another direction;

In polarization maintaining optical fibre to be measured (3), the probe light and the pump light generation Brillouin that satisfy the Brillouin scattering condition amplify interaction; The probe light that amplifies through Brillouin enters the A port of the second circulator R2, and exports data acquisition module (6) to from the B port of the second circulator R2.

2. according to the described dynamic distributed Brillouin light fiber sensing equipment of claim 1, it is characterized in that it also comprises the first direct supply DC1 and the second direct supply DC2,

The first direct supply DC1 provides dc supply for probe light intensity modulator IM1;

The second direct supply DC2 provides dc supply for pump light intensities modulator IM2.

3. according to the described dynamic distributed Brillouin light fiber sensing equipment of claim 1, it is characterized in that AWG (Arbitrary Waveform Generator) AWG employing Tek company produces, model is the AWG (Arbitrary Waveform Generator) of 7122C.

4. based on the method for the described dynamic distributed Brillouin light fiber sensing equipment of claim 1, it is characterized in that this method may further comprise the steps:

Step 1, coupling mechanism (2) are divided into two bundles with laser beam, and wherein beam of laser is modulated into probe light by probe light intensity modulator IM1, and another Shu Jiguang is modulated into pump light by pump light intensities modulator IM2,

The radiofrequency signal of the modulated terminal input of probe light intensity modulator IM1 is the wave train that N frequency step changes

$f_m\left(t\right)=f_{m0}+\left[\frac{t}{T}\right]f_s,$

Wherein: f _M0Be the original frequency of the wave train, f _sBe number of frequency steps, T is arbitrary frequency sweeping cycle,

For rounding, t is the time;

Probe light intensity modulator IM1 is modulated into probe light f with the beam of laser of input _Tzg(t)=f ₀-2f _m(t),

Wherein: f ₀The frequency of beam of laser for input;

The pulsed light that described pump light is formed for the pulse that is T by N cycle,

Step 2, the light of being exported by probe light intensity modulator IM1 modulation leach second order lower side frequency signal as probe light by fiber grating;

Step 3, described probe light and described pump light interact by stimulated Brillouin scattering in polarization maintaining optical fibre to be measured (3), the probe light that polarization maintaining optical fibre to be measured (3) output is amplified;

Step 4, after the scanning of finishing a frequency sweeping period T, obtain polarization maintaining optical fibre to be measured (3) under this frequency state and go up brillouin gain spectrum on each spatial point, and shown by data acquisition module (6);

Step 5, according to Brillouin shift ν _BLinear functional relation ν with strain stress _B=ν _B0+ C _sε finishes the measurement of the strain of polarization maintaining optical fibre to be measured (3) under this frequency state,

Wherein, ν _B0Brillouin shift when being no strain, C _sIt is the coefficient of strain.

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