CN111912514B - Distributed vibration sensing system adopting multimode optical fiber and vibration measurement method - Google Patents
Distributed vibration sensing system adopting multimode optical fiber and vibration measurement method Download PDFInfo
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- CN111912514B CN111912514B CN202010811580.8A CN202010811580A CN111912514B CN 111912514 B CN111912514 B CN 111912514B CN 202010811580 A CN202010811580 A CN 202010811580A CN 111912514 B CN111912514 B CN 111912514B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
Abstract
The invention discloses a distributed vibration sensing system adopting multimode optical fibers and a vibration measuring method, wherein the distributed vibration sensing system comprises a pulse laser, an optical gyrator and multimode optical fibers to be measured, and the resource waste phenomenon caused by using the distributed sensing system with the single-mode optical fibers in the occasions needing single-point detection is effectively solved. According to the invention, the multimode fiber coupler is added between the optical gyrator and the multimode fiber to be detected, the optical pulse laser emitted by the pulse laser enters the multimode fiber coupler after passing through the port 1 and the port 2 of the optical gyrator, the multimode fiber coupler is connected with the fiber to be detected, and the multimode fiber to be detected is detected by using the optical pulse generated by the pulse laser, so that the cost of the distributed sensing system is saved, the phenomenon of resource waste generated when the distributed vibration sensing system is used in the occasion that detection is not needed at multiple points but only at a single point is avoided, and the detection of the vibration position of the multimode fiber to be detected is realized.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to a distributed vibration sensing system adopting multimode optical fibers and a vibration measuring method.
Background
The distributed vibration sensing system of the optical fiber adopts the backscattering characteristic of the optical fiber to detect the vibration level of an optical fiber link, most distributed vibration sensors are based on the interference phenomenon among Rayleigh scattered light, an ultra-narrow linewidth laser with long coherence length is used as a light source, the vibration of the optical fiber is utilized to cause the change of the refractive index and the length of the optical fiber, the phase among the Rayleigh scattered light is further changed, and the intensity of a scattered light signal fluctuates.
In order to ensure the coherence of rayleigh scattered light, single-mode optical fibers are generally adopted to avoid the influence of factors such as modal dispersion and the like in the optical fibers on the optical coherence, and an ultra-narrow linewidth laser with long coherence length is used as a light source, but the ultra-narrow linewidth laser is expensive, and when a distributed vibration sensing system using the single-mode optical fibers is used in an occasion which does not need multi-point detection but only needs single-point detection, such as the security industry, the phenomenon of resource waste can be caused.
The present invention therefore provides a new solution to this problem.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a distributed vibration sensing system adopting a multimode optical fiber and a vibration measuring method, which effectively solve the problem of resource waste caused by using the distributed sensing system with the single-mode optical fiber in the occasions needing only single-point detection.
The distributed vibration sensing system comprises a pulse laser, an optical gyrator and a multimode optical fiber to be detected, wherein the multimode optical fiber coupler is arranged between the optical gyrator and the multimode optical fiber to be detected, optical pulse laser emitted by the pulse laser enters the multimode optical fiber coupler after passing through a port 1 and a port 2 of the optical gyrator, and the multimode optical fiber coupler is connected with the optical fiber to be detected.
A vibration measurement method using the distributed vibration sensing system as claimed in claim 1, comprising in particular the steps of:
s1, after the pulse laser generates the light pulse to enter the multimode fiber to be tested, the light energy is randomly distributed into a plurality of modes of the multimode fiber to be tested;
s2, distributing Rayleigh scattered light signals generated by the multimode fiber to be tested among a plurality of modes of the multimode fiber to be tested, and returning to the multimode fiber coupler in a primary path due to the fiber characteristics;
s3, the Rayleigh scattering optical signal is divided into two paths to be output from two ports of the multimode fiber coupler respectively, one path is detected by a photodiode PD1, the other path is input to a 2 port of the optical gyrator, and the other path is detected by a photodiode PD2 from a 3 port of the optical gyrator;
and the Rayleigh scattered light signals detected by the S4, the photodiode PD1 and the photodiode PD2 are subjected to data processing after passing through an A/D converter.
Due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages:
by adding the multimode fiber coupler between the optical gyrator and the multimode fiber to be detected, the optical pulse laser emitted by the pulse laser enters the multimode fiber coupler through the port 1 and the port 2 of the optical gyrator, the multimode fiber coupler is connected with the fiber to be detected and detects the multimode fiber to be detected by using the optical pulse generated by the pulse laser, so that the cost of a distributed sensing system is saved, the phenomenon of resource waste generated when the distributed vibration sensing system is used in the occasion that the detection is not needed at multiple points but only at a single point is avoided, and the detection of the vibration position of the multimode fiber to be detected is realized.
Drawings
FIG. 1 is a block diagram of the system of the present invention.
Fig. 2 is a schematic diagram of vibration monitoring according to the present invention.
Detailed Description
The foregoing and other technical and functional aspects of the present invention will be apparent from the following detailed description of the embodiments, which proceeds with reference to the accompanying figures 1-2. The structural contents mentioned in the following embodiments are all referred to the attached drawings of the specification.
Exemplary embodiments of the present invention will be described below with reference to the accompanying drawings.
A distributed vibration sensing system adopting multimode optical fibers comprises a pulse laser, an optical gyrator and multimode optical fibers to be detected, wherein the optical gyrator and the multimode optical fibers to be detected also pass through a multimode optical fiber coupler, optical pulse laser emitted by the pulse laser enters the multimode optical fiber coupler after passing through a port 1 and a port 2 of the optical gyrator, and the multimode optical fiber coupler is connected with the optical fibers to be detected;
a vibration measurement method using the distributed vibration sensing system as claimed in claim 1, as shown in fig. 1, specifically comprising the steps of:
s1, after the pulse laser generates the light pulse to enter the multimode fiber to be tested, the light energy is randomly distributed into a plurality of modes of the multimode fiber to be tested;
s2, distributing Rayleigh scattered light signals generated by the multimode fiber to be tested among a plurality of modes of the multimode fiber to be tested, and returning to the multimode fiber coupler in a primary path due to the fiber characteristics;
s3, the Rayleigh scattering optical signal is divided into two paths to be output from two ports of the multimode fiber coupler respectively, one path is detected by a photodiode PD1, the other path is input to a 2 port of the optical gyrator, and the other path is detected by a photodiode PD2 from a 3 port of the optical gyrator;
s4, the data processing is carried out after Rayleigh scattered light signals detected by the photodiode PD1 and the photodiode PD2 pass through an A/D converter;
the data processing in step S4 is to perform subtraction processing on the rayleigh scattered light signals detected by the photodiode PD1 and the photodiode PD2 to obtain a light intensity difference, that is, to obtain light intensity variation information of the two rayleigh scattered light signals;
as shown in fig. 2, when the multimode optical fiber to be tested is vibrated, the backward detection pulse energy from the vibration position is redistributed among the modes in the multimode optical fiber to be tested, the mode distribution of the rayleigh scattered light signal behind the vibration position in the multimode optical fiber to be tested is also changed correspondingly, and when the state of the multimode optical fiber to be tested is unchanged and is not affected by the vibration, the mode distribution of the optical pulse in the multimode optical fiber to be tested and the returned rayleigh scattered light signal is also kept unchanged, so the light intensities detected by the photodiode PD1 and the photodiode PD2 are also kept unchanged, and the difference value of the light intensities of the two rayleigh scattered light signals is kept stable and unchanged, that is, the vibration position of the multimode optical fiber to be tested is obtained according to the time when the light intensities of the rayleigh scattered light signals detected by the photodiode PD1 and the photodiode PD2 start to change;
in step S3, the energy distribution ratio of the rayleigh scattered light signals in the multimode optical fiber to be tested in different modes is different between the two output ports of the multimode optical fiber coupler, and when the mode distribution of the returned rayleigh scattered light signals changes, the intensity distribution of the rayleigh scattered light signals obtained at the two ports of the multimode optical fiber coupler also changes, and the light intensity difference between the rayleigh scattered light signals detected by the photodiode PD1 and the photodiode PD2 also changes.
When the invention is used specifically, a multimode fiber coupler is added between an optical gyrator and a multimode fiber to be tested, optical pulse laser emitted by the pulse laser enters the multimode fiber coupler through a port 1 and a port 2 of the optical gyrator, the multimode fiber coupler is connected with the fiber to be tested, Rayleigh scattered light signals generated by the multimode fiber to be tested are distributed in a plurality of modes of the multimode fiber to be tested, the Rayleigh scattered light signals return to the multimode fiber coupler because of the fiber characteristics, the Rayleigh scattered light signals are divided into two paths and output from two ports of the multimode fiber coupler respectively, one path is detected by a photodiode PD1, the other path is input to a port 2 of the optical gyrator, the Rayleigh scattered light signals detected by the photodiode PD1 and the photodiode PD2 are detected by a port 3 of the optical gyrator by a photodiode PD2, and then are subjected to data processing after passing through an A/D converter, obtaining the difference value of the light intensity of the two paths of Rayleigh scattering light signals;
by adding the multimode fiber coupler between the optical gyrator and the multimode fiber to be detected and detecting the multimode fiber to be detected by using the optical pulse generated by the pulse laser, the cost of a distributed sensing system is saved, the phenomenon of resource waste generated by adopting an ultra-narrow linewidth laser is avoided, and the detection of the vibration position of the multimode fiber to be detected is realized.
Claims (3)
1. A distributed vibration sensing system adopting multimode optical fibers comprises a pulse laser, an optical gyrator and multimode optical fibers to be detected, and is characterized in that the optical gyrator and the multimode optical fibers to be detected also pass through a multimode optical fiber coupler, optical pulse laser emitted by the pulse laser enters the multimode optical fiber coupler after passing through a port 1 and a port 2 of the optical gyrator, and the multimode optical fiber coupler is connected with the multimode optical fibers to be detected;
the vibration measurement method adopted by the distributed vibration sensing system specifically comprises the following steps:
s1, after the pulse laser generates the light pulse to enter the multimode fiber to be tested, the light energy is randomly distributed into a plurality of modes of the multimode fiber to be tested;
s2, distributing Rayleigh scattered light signals generated by the multimode fiber to be tested among a plurality of modes of the multimode fiber to be tested, and returning to the multimode fiber coupler in a primary path due to the fiber characteristics;
s3, the Rayleigh scattering optical signal is divided into two paths to be output from two ports of the multimode fiber coupler respectively, one path is detected by a photodiode PD1, the other path is input to a 2 port of the optical gyrator, and the other path is detected by a photodiode PD2 from a 3 port of the optical gyrator;
s4, the data processing is carried out after Rayleigh scattered light signals detected by the photodiode PD1 and the photodiode PD2 pass through an A/D converter;
the data processing in step S4 is to perform subtraction processing on rayleigh scattered light signals detected by the photodiode PD1 and the photodiode PD2 to obtain a light intensity difference;
and obtaining the vibration position of the multimode optical fiber to be tested according to the time when the light intensity of the Rayleigh scattered light signals detected by the photodiode PD1 and the photodiode PD2 begins to change.
2. The distributed vibration sensing system according to claim 1, wherein the multimode optical fiber under test is vibrated, the pulse energy detected from the vibration location is redistributed among the modes in the multimode optical fiber under test, and the mode distribution of the rayleigh scattered light signal behind the vibration location in the multimode optical fiber under test is changed accordingly.
3. The distributed vibration sensing system according to claim 1, wherein in step S3, energy distribution ratios of rayleigh scattered light signals in different modes of the multimode optical fiber to be detected are different between two output ports of the multimode optical fiber coupler, and when mode distribution of returned rayleigh scattered light signals is changed, intensity distribution of rayleigh scattered light signals obtained at two ports of the multimode optical fiber coupler is also changed, and light intensity difference of rayleigh scattered light signals detected by the photodiode PD1 and the photodiode PD2 is also changed.
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| CN102147236B (en) * | 2011-03-23 | 2012-09-26 | 南京大学 | Fully distributed optical fiber strain and vibration sensing method and sensor |
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