CN109781154B - Brillouin correlation domain analysis system with high spatial resolution based on intensity modulation - Google Patents
Brillouin correlation domain analysis system with high spatial resolution based on intensity modulation Download PDFInfo
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- CN109781154B CN109781154B CN201910115322.3A CN201910115322A CN109781154B CN 109781154 B CN109781154 B CN 109781154B CN 201910115322 A CN201910115322 A CN 201910115322A CN 109781154 B CN109781154 B CN 109781154B
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Abstract
The invention discloses a Brillouin correlation domain analysis system with high spatial resolution based on intensity modulation, belongs to the technical field of distributed optical fiber sensing, and aims to solve the problem of low spatial resolution caused by non-perfect phase modulation code patterns of the existing Brillouin correlation domain analysis method. Laser emitted by the laser is divided into an upper path and a lower path after being modulated by the phase modulator; the upper path of the detection light is modulated into down-shift frequency detection light by a single-side band electro-optic modulator, and the modulated detection light enters the optical fiber to be detected through a first erbium-doped optical fiber amplifier and a delay optical fiber; the lower path as pump light enters a second erbium-doped fiber amplifier, then is input into a circulator, and enters the optical fiber to be detected after being output from the circulator; the detection light interacts with the pump light in the optical fiber to be detected, then the detection light is input into the circulator, the detection light enters the photoelectric detector after being output from the circulator, and the oscilloscope acquires signals of the photoelectric detector, and then the temperature and strain information of a related peak in the optical fiber to be detected is obtained through average noise removal and demodulation. The invention is used for seamless detection.
Description
Technical Field
The invention relates to a Brillouin correlation domain analysis system, and belongs to the technical field of distributed optical fiber sensing.
Background
The distributed Brillouin optical fiber sensing technology has the advantages of high sensitivity, electromagnetic interference resistance, corrosion resistance, convenience in layout and the like. Compared with other point type sensors, the sensing units of the distributed Brillouin optical fiber sensing technology are all positions on the optical fiber line, and seamless detection can be achieved. The method can be widely applied to the fields of building structure health monitoring, power cable health monitoring, petroleum and natural gas pipeline monitoring and the like at present, and has great research value.
The spatial resolution is a key parameter for representing the performance of the distributed sensing technology, the parameter not only represents the spatial positioning precision of the sensing system, but also represents the minimum spatial scale of the system which can sense the event, and only the event of which the spatial scale is larger than the spatial resolution can be sensed. The Brillouin correlation domain analysis (BOCDA) technology is a Brillouin optical fiber sensing technology with the highest spatial resolution at present. According to the technology, a correlation peak is constructed in the optical fiber to be detected, and the Brillouin scattering effect is limited in the correlation peak, so that high-spatial resolution sensing is realized. Phase modulation, which imparts random 0 and pi phase shifts to the pump and probe light, is an effective means of constructing correlation peaks. The spatial resolution of the technique is determined by the code width of the phase modulation, and the optimal spatial resolution of the existing BOCDA technique based on the phase modulation is 14 mm. The fundamental reason limiting the increase in its spatial resolution is the imperfect modulation pattern due to the limited bandwidth of the device: due to the limitation of bandwidth of devices related to modulation such as an arbitrary wave source, a radio frequency amplifier and the like, a modulation code pattern is represented as an imperfect code pattern with non-0 and pi phase shifts, so that the Brillouin scattering effect cannot be limited to a correlation peak, Brillouin amplification exists in a non-correlation peak region, the signal-to-noise ratio is reduced, and the spatial resolution is reduced.
Disclosure of Invention
The invention aims to solve the problem of low spatial resolution caused by non-perfect phase modulation code patterns of the existing Brillouin correlation domain analysis method, and provides a Brillouin correlation domain analysis method with high spatial resolution based on intensity modulation.
According to the Brillouin correlation domain analysis system with high spatial resolution based on intensity modulation, laser emitted by a laser is modulated by a phase modulator and then divided into an upper path and a lower path;
the upper path is used as detection light and is modulated by a single-side band electro-optic modulator, a microwave source generates a sinusoidal signal and loads the sinusoidal signal on the single-side band electro-optic modulator, the single-side band electro-optic modulator modulates an input optical signal into detection light with a frequency shift down, and the modulated detection light enters an optical fiber to be detected through a first erbium-doped optical fiber amplifier and a delay optical fiber;
the lower path as pump light enters a second erbium-doped fiber amplifier, then is input into a first port of the circulator, and enters the optical fiber to be detected after being output from a second port of the circulator;
after the probe light interacts with the pump light in the optical fiber to be detected, the probe light is input into a second port of the circulator, the probe light is output from a third port of the circulator and enters the photoelectric detector, and after the oscilloscope collects signals of the photoelectric detector, the temperature and strain information of a related peak in the optical fiber to be detected is obtained through average noise removal and demodulation;
the phase modulator adopts an electro-optic intensity modulator, firstly, a bias voltage equal to half-wave voltage of the electro-optic intensity modulator is loaded by a direct-current power supply, and then a coding signal generated by an arbitrary waveform generator is loaded on the electro-optic intensity modulator after being amplified by a microwave amplifier.
Preferably, the laser adopts a distributed feedback type optical fiber laser, and the output wavelength is 1550 nm.
Preferably, the length of the delay fiber is selected according to the correlation peak distance and the length of the optical fiber to be measured.
Preferably, the photodetector is implemented as a photodiode.
Preferably, the microwave source generates a sinusoidal signal which is loaded on the single-sideband electro-optic modulator, and the probe light is swept by changing the frequency of the microwave source.
Preferably, the pump light is input to the pulse module before entering the second erbium-doped fiber amplifier, so as to enhance the identification of the signal and the related peak.
The invention has the advantages that: the invention realizes the phase modulation of a perfect phase shift code pattern through intensity modulation, and the phase shift is irrelevant to the size of a radio frequency electric signal and only relevant to the polarity of the radio frequency signal; when the voltage of the radio-frequency electric signal is positive, the phase shift of the output optical field relative to the input optical field is 0, and when the voltage of the radio-frequency electric signal is negative, the phase shift of the output optical field relative to the input optical field is pi. Therefore, even if the modulation pattern is not perfect, the phase shift pattern is still a perfect 0, pi pattern. The invention obviously reduces the requirements of the BOCDA technology on the bandwidth and the output power of the modulation device; the generation of a perfect phase shift code pattern is realized, and the spatial resolution of the Brillouin correlation domain analysis technology is improved.
Drawings
FIG. 1 is a schematic diagram of an intensity modulation based high spatial resolution Brillouin correlation domain analysis system in accordance with the present invention;
fig. 2 is a schematic diagram of implementing perfect phase shift coding by using the brillouin correlation domain analysis system with high spatial resolution based on intensity modulation according to the present invention, where a represents an input perfect modulated electrical signal pattern, b represents an imperfect electrical signal pattern limited by bandwidth, c represents a phase change of an optical signal modulated by a phase modulator using an electrical signal shown in b, and d represents a phase change of an optical signal modulated by an intensity modulator via an electrical signal shown in b.
Detailed Description
The first embodiment is as follows: in the following description of the present embodiment, with reference to fig. 1, in the brillouin correlation domain analysis system with high spatial resolution based on intensity modulation according to the present embodiment, laser light emitted by a laser is modulated by a phase modulator and then divided into an upper path and a lower path;
the upper path is used as detection light and is modulated by a single-side band electro-optic modulator, a microwave source generates a sinusoidal signal and loads the sinusoidal signal on the single-side band electro-optic modulator, the single-side band electro-optic modulator modulates an input optical signal into detection light with a frequency shift down, and the modulated detection light enters an optical fiber to be detected through a first erbium-doped optical fiber amplifier and a delay optical fiber;
the lower path as pump light enters a second erbium-doped fiber amplifier, then is input into a first port of the circulator, and enters the optical fiber to be detected after being output from a second port of the circulator;
after the probe light interacts with the pump light in the optical fiber to be detected, the probe light is input into a second port of the circulator, the probe light is output from a third port of the circulator and enters the photoelectric detector, and after the oscilloscope collects signals of the photoelectric detector, the temperature and strain information of a related peak in the optical fiber to be detected is obtained through average noise removal and demodulation;
the phase modulator adopts an electro-optic intensity modulator, firstly, a bias voltage equal to half-wave voltage of the electro-optic intensity modulator is loaded by a direct-current power supply, and then a coding signal generated by an arbitrary waveform generator is loaded on the electro-optic intensity modulator after being amplified by a microwave amplifier.
In this embodiment, the second erbium-doped fiber amplifier amplifies the pump light to the order of several watts of peak power.
The second embodiment is as follows: in this embodiment, the first embodiment is further described, the laser employs a distributed feedback fiber laser, and the output wavelength is 1550 nm.
The third concrete implementation mode: in this embodiment, the length of the delay fiber is selected according to the correlation peak distance and the length of the optical fiber to be measured.
In this embodiment, the length of the delay fiber is generally about several kilometers.
The fourth concrete implementation mode: in this embodiment mode, a photoelectric detector is implemented by using a photodiode.
The fifth concrete implementation mode: in this embodiment, the first embodiment is further described, in which the microwave source generates a sinusoidal signal and loads the sinusoidal signal to the single-sideband electro-optic modulator, and the frequency of the microwave source is changed to sweep the probe light.
The sixth specific implementation mode: in this embodiment, the first embodiment is further described, before the pump light enters the second erbium-doped fiber amplifier, the pump light is input into the pulse module to enhance the discrimination between the signal and the correlation peak.
In the present invention, the principle of implementing perfect phase shift coding by intensity modulation is as follows:
the electro-optical intensity modulator adopts an M-Z type electro-optical modulator.
Input light field E of M-Z type electro-optical modulatorinAnd an output light field EoutSatisfies the following conditions:
Eout＝Einh；
where h represents the transfer function:
wherein, VπDCIs a DC half-wave voltage, VDCIs a DC bias voltage, VπRFIs a radio frequency half-wave voltage, Vm(t) is a radio frequency electrical signal;
here ignoring the constant phase shift introduced by the optical transmission;
when the DC bias voltage VDCEqual to half-wave voltage V of direct currentπDCThe transfer function is then:
when the radio frequency electric signal Vm(t) output light field with value of positive
Comprises the following steps:
when the radio frequency electric signal VmOutput light field when the value of (t) is negative
Comprises the following steps:
therefore, when the radio frequency electric signal Vm(t) a positive voltage, outputting the light field
With respect to the input light field EinIs 0, neglecting the constant phase shift introduced by the optical transmission, when the radio frequency electrical signal V ism(t) when it is negative voltage, the light field is output
With respect to the input light field EinThe phase shift of (d) is pi.
The phase shift is therefore independent of the magnitude of the radio frequency electrical signal and only of the sign. Therefore, although the pattern of the modulated electrical signal is not perfect, the phase-shifted pattern is still a perfect 0, pi pattern, as shown in fig. 2.
Claims (6)
1. The Brillouin correlation domain analysis system with high spatial resolution based on intensity modulation is characterized in that:
laser emitted by the laser is modulated by the intensity modulator and then divided into an upper path and a lower path;
the upper path is used as detection light and is modulated by a single-side band electro-optic modulator, a microwave source generates a sinusoidal signal and loads the sinusoidal signal on the single-side band electro-optic modulator, the single-side band electro-optic modulator modulates an input optical signal into detection light with a frequency shift down, and the modulated detection light enters an optical fiber to be detected through a first erbium-doped optical fiber amplifier and a delay optical fiber;
the lower path as pump light enters a second erbium-doped fiber amplifier, then is input into a first port of the circulator, and enters the optical fiber to be detected after being output from a second port of the circulator;
after the probe light interacts with the pump light in the optical fiber to be detected, the probe light is input into a second port of the circulator, the probe light is output from a third port of the circulator and enters the photoelectric detector, and after the oscilloscope collects signals of the photoelectric detector, the temperature and strain information of a related peak in the optical fiber to be detected is obtained through average noise removal and demodulation;
the intensity modulator adopts an electro-optic intensity modulator, firstly, a bias voltage equal to the half-wave voltage of the electro-optic intensity modulator is loaded by a direct-current power supply, and then a coding signal generated by an arbitrary waveform generator is loaded on the electro-optic intensity modulator after being amplified by a microwave amplifier;
the phase modulation of the perfect phase-shifted pattern is achieved by an intensity modulator.
2. The intensity modulation based high spatial resolution brillouin correlation domain analysis system of claim 1, wherein the laser employs a distributed feedback fiber laser with an output wavelength of 1550 nm.
3. The intensity modulation based high spatial resolution brillouin correlation domain analysis system according to claim 1, wherein the length of the delay fiber is selected according to the correlation peak distance and the length of the optical fiber to be measured.
4. The intensity modulation based high spatial resolution brillouin correlation domain analysis system according to claim 1, wherein the photodetector is implemented with a photodiode.
5. The intensity modulation based high spatial resolution brillouin correlation domain analysis system of claim 1, wherein the microwave source generates a sinusoidal signal loaded on the single-sideband electro-optic modulator, and the probe light is swept by changing the frequency of the microwave source.
6. The intensity modulation based high spatial resolution brillouin correlation domain analysis system of claim 1, wherein the pump light is input to the pulse module before entering the second erbium doped fiber amplifier to enhance discrimination of signal and correlation peaks.
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