CN112414584B - Brillouin optical time domain analysis device and method based on pi-pulse Gray code coding - Google Patents
Brillouin optical time domain analysis device and method based on pi-pulse Gray code coding Download PDFInfo
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Abstract
The invention belongs to the technical field of distributed optical fiber sensing, and discloses a Brillouin optical time domain analysis device and method based on pi pulse Gray code coding, wherein the method comprises the following steps: dividing continuous laser generated by a laser into two paths, wherein one path is used as probe light to be input into a sensing optical fiber after being modulated, amplified and isolated, and the other path is used as pumping light to be input into the sensing optical fiber from the other end after being subjected to pi pulse Gray code coding phase modulation and amplification by a phase modulator; the detection light which is output from the other end of the sensing optical fiber and contains the Brillouin scattering signal is amplified and subjected to grating filtering, then the detection light is input into the photoelectric detector to be detected and converted into an electric signal, a single-pulse Brillouin scattering signal is obtained through decoding operation, and then the demodulation is carried out to obtain the Brillouin frequency shift distribution along the optical fiber.
Description
Technical Field
The invention belongs to the technical field of distributed optical fiber sensing, and particularly relates to a Brillouin optical time domain analysis device and method based on pi pulse and Gray code mixed coding, which are used for simultaneously realizing the sensing performance of long distance and high spatial resolution.
Background
The distributed optical fiber sensing technology utilizes the scattering effect of light in an optical fiber medium to realize the measurement of physical quantities such as temperature strain and the like along the optical fiber, and has the advantages of strong anti-electromagnetic interference capability, high sensitivity, corrosion resistance, low cost and the like. Among a plurality of distributed optical fiber sensing systems, the stimulated Brillouin scattering-based Brillouin Optical Time Domain Analysis (BOTDA) technology has obvious advantages in the aspect of long-distance distributed optical fiber sensing and has wide application prospects in the aspect of large building structure detection.
In the BOTDA system, continuous probe light and pulsed pump light are injected into a sensing fiber from opposite ends of the fiber, respectively, and when the frequency difference between the probe light and the pump light satisfies the brillouin gain condition, energy transfer occurs between the two in the fiber. And scanning the frequency difference of the probe light and the pump light, and obtaining Brillouin frequency shift distribution along the optical fiber according to a pulse time domain positioning technology. And analyzing the temperature strain change of the optical fiber according to the relationship between the Brillouin frequency shift and the temperature and the strain. The spatial resolution in the BOTDA system depends on the pulse width of the pump light pulses, the smaller the pulse width, the higher the spatial resolution. However, when the pulse width is reduced to be equal to or far less than the phonon lifetime (10 ns), a significant broadening effect occurs on the spectral width of the brillouin gain spectrum, and meanwhile, the peak value of the gain spectrum is also sharply reduced, which seriously affects the measurement accuracy and the signal-to-noise ratio of the sensing system. Thus, for the conventional BOTDA system, there is a relationship between spatial resolution and sensing distance that is mutually constrained. Reducing the width of the pump pulse can improve the spatial resolution, but can limit the sensing distance of the system, and in order to increase the sensing distance of the system, the method of increasing the peak power of the pump pulse is usually adopted to improve the signal-to-noise ratio without changing the spatial resolution. But the injection power of the pulsed pump light may be limited due to modulation instability, phase modulation, etc. In addition, the effect of the loss of the pump light and the transmission loss of the optical fiber also affect the sensing distance.
In order to increase the sensing distance of the system, researchers have proposed various schemes, such as a multiplexing technique, a raman amplification technique, and an encoding technique. The time division multiplexing technology needs time-division frequency scanning, so that the complexity of the system is increased; the raman amplification technique can realize ultra-long distance transmission, but can cause the intensity noise of the system to increase, and the signal-to-noise ratio of the system is deteriorated. The coding technology realizes the coding of the pulse by changing the modulation waveform of the pump light, does not increase the complexity of the system and does not introduce a new noise source, can obviously improve the signal-to-noise ratio of the system and increase the sensing distance. However, the spatial resolution of the pulse coding technique is still limited by the lifetime of phonons, and is difficult to break through 1m. Therefore, there is a need to provide a new apparatus and method to solve the problem of mutual restriction between sensing distance and spatial resolution in the BOTDA system.
Disclosure of Invention
The invention overcomes the defects of the prior art, and solves the technical problems that: provided are a Brillouin optical time domain analysis device and method based on pi pulse and Gray code mixed coding.
In order to solve the technical problems, the invention adopts the technical scheme that: a Brillouin optical time domain analysis method based on pi pulse and Gray code mixed coding comprises the following steps:
s1, dividing continuous laser generated by a laser into two paths, wherein one path of continuous laser is input into a sensing optical fiber as probe light after being modulated, amplified and isolated, and the other path of continuous laser is input into the sensing optical fiber from the other end after being used as pump light and subjected to pi pulse Gray code coding phase modulation and amplification by a phase modulator;
s2, the detection light containing the Brillouin scattering signal output from the other end of the sensing optical fiber is amplified and subjected to grating filtering, and then is input into a photoelectric detector for detection and converted into an electric signal;
and S3, collecting the Brillouin signal detected by the photoelectric detector, obtaining a single-pulse Brillouin scattering signal through decoding operation, and demodulating to obtain Brillouin frequency shift distribution along the optical fiber.
In the pi pulse gray code coding, the gray code is a unipolar gray code after polarity conversion, and the conversion process is as follows:
wherein:
when the number of coded bits is L, two bipolarity mutual electrodes of bipolarity Gray codeThe sequence is complemented,
are respectively as
The obtained sequences of the two unipolar gray codes are converted,
are respectively as
And converting the obtained sequences of the two unipolar gray codes.
The pi pulse gray code specifically refers to that when the code bit of the gray code converted into the unipolar character is 1, the input pulse is a pi pulse.
In addition, the invention also provides a brillouin optical time domain analysis device based on pi pulse and gray code mixed coding, which comprises: the device comprises a laser, a first optical isolator, a light splitter, a first electro-optic modulator, a first optical amplifier, a second optical isolator, a sensing optical fiber, a second electro-optic modulator, an optical polarization scrambler, a second optical amplifier, a first optical circulator, a third optical amplifier, a second optical circulator, an optical fiber Bragg grating filter, a photoelectric detector and a data acquisition and processing system;
continuous laser output by the laser is divided into two paths after passing through a first optical isolator and a light splitter, one path of continuous laser as probe light is input into a sensing optical fiber after passing through a first electro-optical modulator, a first optical amplifier and a second optical isolator, and the other path of continuous laser as pump light sequentially passes through a second electro-optical modulator, an optical polarization scrambler, a second optical amplifier and a first optical circulator and then enters the sensing optical fiber from the other end of the sensing optical fiber; the second electro-optical modulator is used for carrying out pi pulse Gray code encoding phase modulation on the pump light;
the detection light output from the other end of the sensing optical fiber is output by the first optical circulator, amplified by the third optical amplifier, then incident to the fiber Bragg grating filter through the second optical circulator, reflected by the fiber Bragg grating filter, returned to the second optical circulator and output to the photoelectric detector for detection, and a detection signal is acquired and processed by the data acquisition and processing system.
The brillouin optical time domain analysis device based on pi pulse and gray code mixed coding further comprises: the polarization controller is arranged between the optical fiber coupler and the first electro-optical modulator, and the second polarization controller is arranged between the optical fiber coupler and the second electro-optical modulator and is respectively used for adjusting the polarization states of the detection light entering the first polarization controller and the pump light entering the second electro-optical modulator.
The optical splitter is a 1x2 optical fiber coupler.
In the Gray code coding with pi phase shift, the Gray code is a unipolar Gray code with polarity conversion, and the conversion process is as follows:
wherein:
when the coding number is L, two bipolar complementary sequences of the bipolar Gray code,
are respectively as
The obtained sequences of the two unipolar gray codes are converted,
are respectively as
Converting the obtained sequences of the two unipolar gray codes;
the pi pulse gray code specifically means that when the code bit of the gray code converted into the unipolar character is 1, the input pulse is a pi pulse.
The Brillouin optical time domain analysis device based on the pi pulse and Gray code mixed coding further comprises an arbitrary waveform generator and a signal generator, wherein the arbitrary waveform generator and the signal generator are respectively used for driving the second electro-optic modulator and the first electro-optic modulator.
In the Brillouin optical time domain analysis device based on the pi pulse and Gray code mixed coding, a laser, a first optical isolator and an optical splitter are connected in sequence through a single-mode optical fiber jumper; the optical splitter, the first electro-optic modulator, the first optical amplifier and the second optical isolator are connected through a single-mode optical fiber jumper in sequence; the optical splitter, the second electro-optical modulator, the optical polarization scrambler, the second optical amplifier and the first optical circulator are connected in sequence through a single-mode optical fiber jumper; the first optical circulator, the third optical amplifier and the second optical circulator are connected through a single-mode optical fiber jumper in sequence; the second optical circulator is connected with the optical fiber Bragg grating filter and the photoelectric detector through optical fiber jumpers respectively.
The wavelength of continuous laser light output by the laser is 1550nm.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention adopts the Gray code coding technology, effectively improves the signal-to-noise ratio of the system and increases the sensing distance. Meanwhile, by adopting a pi pulse coding technology, the spatial resolution is improved by reducing the pulse width of phase shift pulses in the pi pulses, so that the limit of the phonon service life is broken through, the centimeter-level spatial resolution is realized, the broadening of a Brillouin gain spectrum is avoided, and the measurement accuracy of the system is ensured.
2. The pumping light adopts pi pulse coding, the spatial resolution is determined by the pulse width of the phase shift pulse in the pi pulse, and the rapid mutation of the pumping light is realized by phase shifting the pulse, so that the gain of the detection light disappears rapidly when the pi phase shift pulse arrives, the width of the sensing pulse can be smaller, and the higher spatial resolution is realized.
3. The BOTDA system based on the pi pulse and the Gray code effectively solves the problem that the spatial resolution and the sensing distance of the BOTDA system are mutually restricted, does not increase the complexity and the hardware cost of the traditional BOTDA system, and is simple to operate and easy to realize.
Drawings
Fig. 1 is a schematic structural diagram of a brillouin optical time domain analysis device based on pi pulse and gray code mixed coding according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a pi-pulse Gray code encoding employed in an embodiment of the present invention; in the figure, (a) represents a single pulse timing chart of unipolar Gray code coding, and (b) represents a pi pulse timing chart of the Gray code coding, wherein the position corresponding to a symbol pi in the figure is a pi pulse;
FIG. 3 is a BGS distribution along the line of an optical fiber with a phase-shifted pulse of 2ns obtained by MATLAB simulation, the horizontal axis representing the position of the optical fiber;
fig. 4 is a schematic diagram of a relationship between the number of gray code encoding bits, a signal-to-noise ratio, and a sensing distance in the embodiment of the present invention.
In the figure: the system comprises a laser 1, a first optical isolator 2, an optical splitter 3, a first polarization controller 4, a first electro-optic modulator 5, a signal generator 6, a first optical amplifier 7, a second optical isolator 8, a sensing optical fiber 9, a second polarization controller 10, a second electro-optic modulator 11, an arbitrary waveform generator 12, an optical scrambler 13, a second optical amplifier 14, a first optical circulator 15, a third optical amplifier 16, a second optical circulator 17, a fiber Bragg grating filter 18, an optical detector 19 and a data acquisition and processing system 20.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments; all other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
As shown in fig. 1, an embodiment of the present invention provides a brillouin optical time domain analysis device based on pi pulse and gray code mixed coding, including: the device comprises a laser 1, a first optical isolator 2, an optical splitter 3, a first polarization controller 4, a first electro-optic modulator 5, a signal generator 6, a first optical amplifier 7, a second optical isolator 8, a sensing optical fiber 9, a second polarization controller 10, a second electro-optic modulator 11, an arbitrary waveform generator 12, an optical scrambler 13, a second optical amplifier 14, a first optical circulator 15, a third optical amplifier 16, a second optical circulator 17, an optical fiber Bragg grating filter 18, a photoelectric detector 19 and a data acquisition and processing system 20.
The emergent end of the laser 1 is connected with the incident end of the first optical isolator 2 through a single-mode optical fiber jumper; the emergent end of the first optical isolator 2 is connected with the optical splitter 3 with two emergent ends through a single-mode optical fiber jumper.
One emergent end of the 1 multiplied by 2 optical splitter 3 is connected with an incident end of the first polarization controller 4 through a single mode fiber jumper; the emergent end of the first polarization controller 4 is connected with the optical fiber incident end of the first electro-optic modulator 5 through a single-mode optical fiber jumper; the radio frequency output end of the signal generator 6 is connected with the radio frequency incident end of the first electro-optical modulator 5 through a high-frequency cable; the fiber exit end of the first electro-optical modulator 5 is connected with the incident end of the first optical amplifier 7 through a single-mode fiber jumper; the emergent end of the first optical amplifier 7 is connected with the incident end of a second optical isolator 8 through a single-mode optical fiber jumper; the emergent end of the second optical isolator 8 is connected with one end of a sensing optical fiber 9; the other end of the sensing fiber 9 is connected with the reflection end of the first optical circulator 15.
The other emergent end of the optical splitter 3 is connected with the incident end of the second polarization controller 10 through a single-mode optical fiber jumper; the emergent end of the second polarization controller 10 is connected with the fiber incident end of the second electro-optic modulator 11 through a single-mode fiber jumper; the radio frequency output end of the arbitrary waveform generator 12 is connected with the radio frequency input end of the second electro-optical modulator 11 through a high-frequency cable; the fiber exit end of the second electro-optical modulator 11 is connected with the optical interference polarizer 13 through a single-mode fiber jumper; the exit end of the optical polarization scrambler 13 is connected with the second optical amplifier 14 through a single-mode optical fiber jumper; the exit end of the second optical amplifier 14 is connected to the entrance end of the first optical circulator 15 through a single-mode optical fiber jumper.
The emergent end of the optical circulator 15 is connected with the incident end of a third optical amplifier 16 through a single-mode optical fiber jumper; the exit end of the third optical amplifier 16 is connected with the entrance end of the second optical circulator 17 through a single-mode optical fiber jumper; the exit end of the fiber Bragg grating filter 18 is connected with the reflection end of the second optical circulator 17 through a single mode fiber; the exit end of the second optical circulator 17 is connected with the input end of the photoelectric detector 19 through a single-mode optical fiber jumper; the output end of the photodetector 19 is connected to the data acquisition and processing system 20 by a single-mode fiber jumper.
Specifically, in this embodiment, the optical splitter 3 is a 1 × 2 fiber coupler. The wavelength of the continuous laser light output by the laser 1 is 1550nm. The first polarization controller 4 and the second polarization controller 10 are used to adjust the polarization states of the probe light entering the first polarization controller 4 and the pump light entering the second electro-optical modulator 11, respectively. The arbitrary waveform generator 12 and the signal generator 6 are used to drive the second electro-optical modulator 11 and the first electro-optical modulator 5, respectively. The second electro-optical modulator 11 is configured to perform phase modulation of a pi pulse gray code on the pump light, where the pi pulse gray code specifically indicates that when a gray code bit converted into a unipolar character is 1, an input pulse is a pi pulse.
The working principle of the invention is as follows:
a. the laser 1 generates continuous laser with the working wavelength of 1550nm, and the continuous laser sequentially passes through the first optical isolator 2 and the optical splitter 3 and then is divided into two light paths, wherein one light path is used as a detection light signal, and the other light path is used as a pumping light signal. The detection light signal passes through a first polarization controller 4, a first electro-optic modulator 5, a first optical amplifier 7 and a second optical isolator 8 in sequence to adjust, modulate, amplify and isolate the polarization state of the light signal and then enters a sensing optical fiber 9;
b. the other path of output light of the optical splitter 3 is adjusted in polarization state through a second polarization controller 10, and the output light passes through a second electro-optical modulator 11 controlled by an arbitrary waveform generator 12 to generate a gray code encoded pump light signal with pi phase shift, and then enters a sensing optical fiber 9 after being subjected to polarization disturbance, amplification and circulation sequentially through an optical polarization scrambler 13, a second optical amplifier 14 and a first optical circulator 15;
c. after the detection optical signal and the pumping optical signal enter the sensing optical fiber 9, stimulated brillouin scattering occurs through interaction, the detection light containing the brillouin scattering signal is output through the first optical circulator 15, then enters the third optical amplifier 16, the second optical circulator 17 and the optical fiber bragg grating filter 18 for amplification, circulation and filtering, the optical signal output from the second optical circulator 17 enters the photoelectric detector 19 for photoelectric conversion, and the data acquisition and processing system 20 acquires and processes the signal from the photoelectric detector 19 to obtain brillouin gain spectrum information along the optical fiber.
In specific implementation, compared with the traditional Gray code, the Gray code provided by the invention introduces a pi pulse technology, obtains the distribution of Brillouin frequency shift by decoding, normalizing and Lorentz fitting detected optical signals, obtains information along an optical fiber through the relationship between the Brillouin frequency shift and temperature or strain, and realizes long-distance and high-spatial-resolution distributed optical fiber sensing.
The conventional gray code is composed of a pair of complementary sequences which only contain '1', '1' and are equal in length. Unipolar pulses are transmitted in a BOTDA system, so that a bipolar gray code needs to be converted into unipolar pulses, two complementary sequences a and a code B of an L-bit gray code are respectively converted into two unipolar gray codes, and the specific conversion process is as follows:
wherein:
when the coding number is L, two bipolar complementary sequences of the bipolar Gray code,
are respectively as
The order of two unipolar gray codes obtained by conversionThe columns of the image data are arranged in rows,
are respectively as
Converting the obtained sequences of the two unipolar gray codes; as shown in fig. 2, a schematic diagram of pi-pulse gray code encoding in the embodiment of the present invention is shown, where a +, a-, B +, and B-are four gray code sequences converted into monopolarity, respectively.
And after the pump light is subjected to pi pulse Gray code coding modulation by the Gray code converted into the unipolar characteristic, the pump light is injected into the sensing optical fiber to perform Brillouin action, and a single-pulse Brillouin scattering signal can be obtained by decoding the detected optical signal. Assuming a single pulse response of
The timing signals of the two sequences of L-bit Gray codes A and B are
The corresponding response of each group of unipolar codes is respectively
The specific decoding operation process is as follows:
from the above process, the response obtained by the gray code coded system is 2L times of the single pulse response. The improvement of the response can improve the signal-to-noise ratio of the system, and further increase the sensing distance.
Therefore, gray code coding is carried out on the pi pulse, the signal to noise ratio of the BOTDA system can be improved, and long-distance sensing is realized. Fig. 3 is the BGS distribution along the fiber obtained by MATLAB simulation, with the horizontal axis representing the fiber position, and the width of the corresponding phase shifted pulse (pi-pulse) from fig. 3 being 2ns, which can achieve 20cm spatial resolution. As shown in FIG. 4, compared with the conventional BOTDA system, the signal-to-noise ratio of the Gray code system is increased with the increase of the number of encoding bits, the signal-to-noise ratio of the Gray code with 256 bits of encoding is improved (encoding gain) by about 9.03dB, the sensing distance can be increased by 45km, and the signal-to-noise ratio of the system with 512 bits of encoding can be improved by over 10dB, but the encoding process does not affect the spatial resolution, so the spatial resolution of the system still depends on the width of the phase-shifted pulse in the pi pulse. Because the pulse coding technology provided by the invention really determines the spatial resolution as the width of the phase-shifted pulse in the pi pulse, the pulse input before the phase-shifted pulse is used for pre-excitation of an acoustic wave field to generate a stable acoustic wave field, when the phase-shifted pulse enters the sensing optical fiber, although the phase of the phase-shifted pulse is changed, the phase and amplitude of the acoustic wave field are basically unchanged because the pulse width of the phase-shifted pulse is far smaller than the phonon life, and the acoustic wave field is not ready to be phase-matched again, so that the bandwidth of the BGS keeps the bandwidth under the steady state, and the high spatial resolution is realized under the condition that the Brillouin gain spectrum is not widened. Therefore, the Brillouin optical time domain analysis device based on the mixed coding of the pi pulse and the Gray code can realize long-distance and high-spatial-resolution optical fiber sensing.
In addition, the invention also provides a Brillouin optical time domain analysis method based on pi pulse and Gray code mixed coding, which comprises the following steps:
s1, dividing continuous laser generated by a laser into two paths, wherein one path of continuous laser is input into a sensing optical fiber as probe light after being modulated, amplified and isolated, and the other path of continuous laser is input into the sensing optical fiber from the other end after being modulated and amplified by a Gray code coding phase with pi phase shift generated by a phase modulator as pump light; the pi pulse gray code specifically means that when the coded bit converted into the unipolar gray code is 1, the input pulse is a pi pulse.
S2, amplifying and grating-filtering the detection light containing the Brillouin scattering signal output from the other end of the sensing optical fiber, and then inputting the detection light into a photoelectric detector for detection and converting the detection light into an electric signal;
and S3, collecting the Brillouin signal detected by the photoelectric detector, obtaining a single-pulse Brillouin scattering signal through decoding operation, and demodulating to obtain Brillouin frequency shift distribution along the optical fiber.
In summary, the present invention provides a brillouin optical time domain analysis method and apparatus based on pi pulse and gray code mixed coding, which adopts gray code coding technology to perform phase modulation on pump light, effectively improves the signal-to-noise ratio of the system, and increases the sensing distance. Meanwhile, by adopting a pi pulse coding technology, the spatial resolution is improved by reducing the pulse width of phase shift pulses in the pi pulses, so that the limit of the phonon service life is broken through, the centimeter-level spatial resolution is realized, the broadening of a Brillouin gain spectrum is avoided, and the measurement accuracy of the system is ensured.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and these modifications or substitutions do not depart from the spirit of the corresponding technical solutions of the embodiments of the present invention.
Claims (7)
1. A Brillouin optical time domain analysis method based on pi pulse Gray code coding is characterized by comprising the following steps:
s1, dividing continuous laser generated by a laser into two paths, wherein one path is modulated, amplified and isolated and then is used as detection light to be input into a sensing optical fiber, and the other path is used as pumping light to be input into the sensing optical fiber from the other end after the pumping light is subjected to pi pulse Gray code phase modulation and amplification by a phase modulator;
s2, the detection light containing the Brillouin scattering signal output from the other end of the sensing optical fiber is amplified and subjected to grating filtering, and then is input into a photoelectric detector for detection and converted into an electric signal;
s3, collecting the Brillouin signal detected by the photoelectric detector, obtaining a single-pulse Brillouin scattering signal through decoding operation, and demodulating to obtain Brillouin frequency shift distribution along the optical fiber; in the pi pulse gray code coding, the gray code is a unipolar gray code after polarity conversion, and the conversion process is as follows:
wherein:
when the number of the coding bits is L, two bipolar complementary sequences of the bipolar Gray code,
are respectively as
The obtained sequences of the two unipolar gray codes are converted,
are respectively as
Converting the obtained sequences of the two unipolar gray codes;
the pi pulse gray code specifically means that when the code bit of the gray code converted into the unipolar character is 1, the input pulse is a pi pulse.
2. A Brillouin optical time domain analysis device based on pi-pulse Gray code coding is characterized by comprising the following components: the device comprises a laser (1), a first optical isolator (2), an optical splitter (3), a first electro-optic modulator (5), a first optical amplifier (7), a second optical isolator (8), a sensing optical fiber (9), a second electro-optic modulator (11), an optical deflector (13), a second optical amplifier (14), a first optical circulator (15), a third optical amplifier (16), a second optical circulator (17), an optical fiber Bragg grating filter (18), an optical detector (19) and a data acquisition and processing system (20);
continuous laser output by the laser (1) is divided into two paths after passing through a first optical isolator (2) and a light splitter (3), one path of continuous laser is used as detection light and is input into a sensing optical fiber (9) after passing through a first electro-optical modulator (5), a first optical amplifier (7) and a second optical isolator (8), and the other path of continuous laser is used as pumping light and enters the sensing optical fiber (9) from the other end of the sensing optical fiber after passing through a second electro-optical modulator (11), an optical polarization scrambler (13), a second optical amplifier (14) and a first optical circulator (15) in sequence; the second electro-optical modulator (11) is used for carrying out pi pulse Gray code coding phase modulation on the pump light;
the detection light output from the other end of the sensing optical fiber is output by a first optical circulator (15), amplified by a third optical amplifier (16), then incident to a fiber Bragg grating filter (18) through a second optical circulator (17), reflected by the fiber Bragg grating filter (18), returned to the second optical circulator (17), and output to a photoelectric detector (19) for detection, and the detection signal is collected and processed by a data collecting and processing system (20);
in the pi pulse gray code coding, the gray code is a unipolar gray code after polarity conversion, and the conversion process is as follows:
wherein:
when the coding number is L, two bipolar complementary sequences of the bipolar Gray code,
are respectively as
The obtained sequences of the two unipolar gray codes are converted,
are respectively as
Converting the obtained sequences of the two unipolar gray codes;
the pi pulse gray code specifically means that when the code bit of the gray code converted into the unipolar character is 1, the input pulse is a pi pulse.
3. The brillouin optical time domain analysis device according to claim 2, further comprising: the polarization state adjusting device comprises a first polarization controller (4) and a second polarization controller (10), wherein the first polarization controller (4) is arranged between the optical splitter (3) and the first electro-optical modulator (5), and the second polarization controller (10) is arranged between the optical splitter (3) and the second electro-optical modulator (11) and is respectively used for adjusting the polarization states of detection light entering the first polarization controller (4) and pump light entering the second electro-optical modulator (11).
4. A brillouin optical time domain analysis device based on pi-pulse gray code coding according to claim 2, characterized in that the optical splitter (3) is a 1x2 fiber coupler.
5. A brillouin optical time domain analysis device based on pi-pulse gray code coding according to claim 2, further comprising an arbitrary waveform generator (12) and a signal generator (6), the arbitrary waveform generator (12) and the signal generator (6) being respectively used to drive the second electro-optical modulator (11) and the first electro-optical modulator (5).
6. The Brillouin optical time domain analysis device based on pi-pulse Gray code coding according to claim 2, wherein the laser (1), the first optical isolator (2) and the optical splitter (3) are connected sequentially through a single-mode optical fiber jumper; the optical splitter (3), the first electro-optic modulator (5), the first optical amplifier (7) and the second optical isolator (8) are connected through single-mode optical fiber jumpers in sequence; the optical splitter (3), the second electro-optical modulator (11), the optical polarization scrambler (13), the second optical amplifier (14) and the first optical circulator (15) are connected in sequence through single-mode optical fiber jumpers; the first optical circulator (15), the third optical amplifier (16) and the second optical circulator (17) are connected in sequence through a single-mode optical fiber jumper; the second optical circulator (17) is respectively connected with the optical fiber Bragg grating filter (18) and the photoelectric detector (19) through optical fiber jumpers.
7. The Brillouin optical time domain analysis device based on pi-pulse Gray code coding according to claim 2, wherein the wavelength of the continuous laser light output by the laser (1) is 1550nm.
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