CN115128728A - Distributed acoustic vibration sensing optical fiber and acoustic vibration monitoring system - Google Patents
Distributed acoustic vibration sensing optical fiber and acoustic vibration monitoring system Download PDFInfo
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 91
- 238000012544 monitoring process Methods 0.000 title claims abstract description 8
- 239000000835 fiber Substances 0.000 claims abstract description 60
- 238000005253 cladding Methods 0.000 claims abstract description 57
- 108700041286 delta Proteins 0.000 claims abstract description 9
- 239000010410 layer Substances 0.000 claims description 106
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 claims description 31
- 239000011737 fluorine Substances 0.000 claims description 31
- 229910052731 fluorine Inorganic materials 0.000 claims description 31
- 229910052732 germanium Inorganic materials 0.000 claims description 27
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 claims description 27
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 23
- 235000012239 silicon dioxide Nutrition 0.000 claims description 16
- 239000000377 silicon dioxide Substances 0.000 claims description 11
- 239000011347 resin Substances 0.000 claims description 7
- 229920005989 resin Polymers 0.000 claims description 7
- 239000011247 coating layer Substances 0.000 claims description 6
- HHFCFXJTAZTLAO-UHFFFAOYSA-N fluorogermanium Chemical compound [Ge]F HHFCFXJTAZTLAO-UHFFFAOYSA-N 0.000 claims description 2
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
-
- 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
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02395—Glass optical fibre with a protective coating, e.g. two layer polymer coating deposited directly on a silica cladding surface during fibre manufacture
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/028—Optical fibres with cladding with or without a coating with core or cladding having graded refractive index
- G02B6/0283—Graded index region external to the central core segment, e.g. sloping layer or triangular or trapezoidal layer
- G02B6/0285—Graded index layer adjacent to the central core segment and ending at the outer cladding index
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
- G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
- G02B6/03638—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 3 layers only
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Abstract
The application discloses a distributed acoustic vibration sensing optical fiber and an acoustic vibration monitoring system, wherein the optical fiber sequentially comprises a fiber core and a cladding from inside to outside, the fiber core has disordered relative refractive index distribution on a path radiating from the center to the periphery of the optical fiber, the fiber core comprises a central layer and an annular layer arranged on the periphery of the central layer, the relative refractive index of an inner side area close to the central layer in the annular layer meets the requirement that the relative refractive index is 0.1% < delta 1-delta 2 ≦ 0.3%, and delta 1 and delta 2 are respectively the relative refractive index of the central layer and the inner side area; the relative refractive index of an outer region close to the cladding in the annular layer is gradually increased by taking the inner region as a reference, the maximum relative refractive index delta 3 of the edge part of the outer region meets 0.1% < delta 3-delta 2 ≦ 0.4%, and the thickness of the outer region accounts for 30-50% of the thickness of the annular layer; the invention arranges that the fiber core has disordered relative refractive index distribution on a path radiating to the periphery along the center of the optical fiber; by increasing the nonuniformity of the refractive index distribution of the fiber core, the Rayleigh scattering coefficient of the optical fiber is obviously improved.
Description
Technical Field
The application relates to the technical field of optical fiber communication, in particular to a distributed acoustic vibration sensing optical fiber with a high Rayleigh scattering coefficient and an acoustic vibration monitoring system.
Background
The optical fiber has the advantages of light weight, small size, electromagnetic interference resistance, high transmission rate, large information capacity, long transmission distance and the like. Optical fibers have been heavily deployed and used in optical communication networks worldwide. With the continuous development of special optical fibers and optical fiber application technologies thereof, optical fibers have been widely used in fields other than conventional communications.
With the continuous development of optical fiber sensing technology, distributed optical fiber sensing has been widely used in recent years due to the characteristics of long distance, multiple parameters, high sensitivity, and the like. Among them, the phi-OTDR technology based on the fiber Rayleigh scattering effect is used as an application of distributed fiber sensing to detect the vibration signal along the sensing fiber in real time, and has been successfully applied in the fields of geological detection, oil exploration, pipeline safety monitoring and the like in recent years.
At present, most of commonly used distributed sensing fibers mainly use a G652D single-mode communication fiber, but the backscattering intensity of a common single-mode communication fiber G652D is too low, so that the strength of a sensing signal reflected back to a demodulation end is weak, and a sufficient signal-to-noise ratio cannot be provided, so that the distributed sensing fiber cannot be applied to the field with high-precision detection requirements.
Disclosure of Invention
The invention provides a distributed acoustic vibration sensing fiber with a high Rayleigh scattering coefficient and an acoustic vibration monitoring system, aiming at solving the problems that the existing common single-mode fiber has too low backscattering intensity, so that the intensity of a sensing signal reflected to a demodulation end is weak, and a sufficient signal-to-noise ratio cannot be provided.
To achieve the above object, according to one aspect of the present invention, there is provided a distributed acoustic vibration sensing fiber, the fiber including, in order from inside to outside, a core and a cladding, the core having a disordered relative refractive index profile on a path radiating to the outside along the center of the fiber when a relative refractive index of the core is defined with a refractive index of pure silica as a reference;
the fiber core comprises a central layer and an annular layer arranged on the periphery of the central layer, the relative refractive index of an inner side area close to the central layer in the annular layer meets 0.1% < delta 1-delta 2 ≦ 0.3%, wherein delta 1 and delta 2 are the relative refractive index of the inner side area of the central layer and the inner side area of the annular layer respectively;
the relative refractive index of the annular layer in the outer region close to the cladding layer is gradually increased by taking the inner region as a reference, the maximum relative refractive index delta 3 of the edge part of the outer region meets the condition that the value is 0.1% < delta 3-delta 2 ≦ 0.4%, and the thickness of the outer region accounts for 30-50% of the thickness of the annular layer.
Further, in the distributed acoustic vibration sensing fiber, the central layer is doped with fluorine and/or germanium under the condition that the relative refractive index Δ 1 of the central layer satisfies 0.5% and Δ 1% and 0.6%;
the inner region of the annular layer is doped with fluorine and/or germanium under the condition that the relative refractive index delta 2 thereof satisfies 0.3% and delta 2 < 0.4%;
the annular layer is doped with fluorine and/or germanium under the condition that the relative refractive index Δ 3 at the edge portion of the outer region thereof satisfies 0.5% to Δ 3% to 0.7%.
Further, in the above-mentioned distributed acoustic vibration sensing optical fiber, the inner region and the outer region of the central layer and the annular layer are silicon dioxide layers doped with fluorine and germanium, wherein,
the fluorine doping amount of the central layer is-0.1% to-1.0%, and the germanium doping amount is 0.6% to 1.6%;
the fluorine doping amount of the inner side area of the annular layer is-0.1% to-1.0%, and the germanium doping amount is 0.5% to 1.6%;
the outer region of the annular layer has a germanium doping amount of 0.6% to 1.7% and a fluorine doping amount of-0.1% to-1.0%.
Further, in the above distributed acoustic vibration sensing optical fiber, the diameter D1 of the central layer is 2.1 μm to 3 μm;
the diameter D2 of the inner region of the annular layer is 3.5 μm to 4.5 μm;
the diameter D3 of the outer region of the annular layer is 6 μm to 9 μm.
Further, the above-mentioned distributed acoustic vibration sensing optical fiber, the cladding includes an inner cladding and an outer cladding;
the inner cladding is a fluorine-doped silicon dioxide layer, and the relative refractive index delta 4 of the inner cladding is more than or equal to-0.02% and less than or equal to-0.01%, and the relative refractive index delta 4 of the inner cladding is more than or equal to-0.8% and less than or equal to-4-delta 3 and less than or equal to-0.5% of fluorine doping; the outer cladding layer is a pure silicon dioxide layer.
Further, in the distributed acoustic vibration sensing optical fiber, the diameter of the inner cladding is 14 μm to 18 μm;
the diameter of the outer cladding layer is 124-126 μm.
Furthermore, the distributed acoustic vibration sensing optical fiber also comprises a resin coating layer coated on the outer surface of the outer cladding layer, and the outer diameter of the resin coating layer is 190-210 μm.
Further, in the distributed acoustic vibration sensing optical fiber, the rayleigh scattering coefficient of the optical fiber is larger than 1.4, or the attenuation at the 1550nm waveband is smaller than 0.4dB/km, or the attenuation at the 1310nm waveband is smaller than 0.7dB/km, or the mode field diameter at the 1550nm waveband is 8.5-9.5 um.
According to another aspect of the present invention there is also provided a distributed acoustic vibration monitoring system using a distributed acoustic vibration sensing optical fibre according to any one of the above as an acoustic signal transmission medium.
In general, compared with the prior art, the above technical solutions conceived by the present invention can achieve the following beneficial effects:
(1) the fiber core of the distributed acoustic vibration sensing fiber provided by the invention has disordered relative refractive index distribution on a path radiating to the periphery along the center of the fiber, the central layer of the fiber and the inner side area of the annular layer form step-shaped relative refractive index distribution, the relative refractive index is slowly increased in the outer side area of the annular layer close to the cladding, and gradual change distribution with the maximum relative refractive index at the edge position close to the cladding is formed, the waveguide structure can enable the optical power to be more distributed in the fiber core area, and the backward Rayleigh scattering intensity of the fiber core is favorably improved; in addition, the distribution structure gradually disperses the stress in the optical fiber to the cladding, and the overall material structure of the optical fiber can be changed, so that the stress distribution of the optical fiber after drawing is optimized. The layering bears the tensile stress formed in the drawing process, the stress borne by the core layer is the compressive stress, and the stress distribution is beneficial to improving the disorder degree of doping elements in the optical fiber, so that the Rayleigh scattering coefficient of the optical fiber is improved.
(2) According to the distributed acoustic wave vibration sensing optical fiber provided by the invention, the viscosity of the cladding region is adjusted by adjusting the fluorine doping amount of the inner cladding and combining with the diameter size design, so that the viscosity of the cladding region is equivalent to that of the fiber core region, and the increase of loss caused by the generation of defects due to the relative viscous flow of the interface of the fiber core and the cladding in the high-temperature wire drawing process is avoided.
(3) According to the distributed acoustic wave vibration sensing optical fiber provided by the invention, the Rayleigh scattering coefficient of the optical fiber is effectively improved by reasonably arranging the waveguide structures of the fiber core and the cladding, and the Rayleigh scattering coefficient of the optical fiber is obviously superior to that of the existing G652D optical fiber; the technical problems that optical fiber Rayleigh scattering signals in the distributed acoustic vibration sensing system are weak and the signal to noise ratio of the system is insufficient are solved, and therefore the detection sensitivity of the distributed acoustic vibration sensing system is improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is a schematic structural composition diagram of a distributed acoustic vibration sensing optical fiber provided in this embodiment;
fig. 2 is a schematic diagram of a refractive index profile of a cross section of the distributed acoustic vibration sensing optical fiber provided in this embodiment.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application.
The terms "first," "second," "third," and the like in the description and claims of this application and in the above-described drawings are used for distinguishing between different objects and not for describing a particular order. Furthermore, the terms "include" and "have," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements listed, but may alternatively include other steps or elements not listed, or inherent to such process, method, article, or apparatus.
In other instances, well-known or widely used techniques, elements, structures and processes may not have been described or shown in detail to avoid obscuring the understanding of the present invention by the skilled artisan. Although the drawings represent exemplary embodiments of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated or omitted in order to better illustrate and explain the present invention.
The following are definitions and descriptions of some terms involved in the present invention:
optical fiber or optical fiber preform construction: starting from the most central axis of the fiber, the central portion of the fiber cross section is defined as the core, the annular region immediately adjacent to the core in the fiber cross section is defined as the inner cladding, and the annular region of pure silica immediately adjacent to the inner cladding in the fiber cross section is defined as the outer cladding, according to the change in refractive index.
Relative refractive index:
wherein n is i Representing the refractive indices, n, corresponding to the different deposited layers 0 Is pure SiO 2 1.457;
the doping amount or doping concentration, in%, represents the proportion of the doping element to the relative refractive index contribution of the region in which it is located.
Fig. 1 is a schematic structural diagram of a distributed acoustic vibration sensing fiber provided in this embodiment, please refer to fig. 1, where the distributed acoustic vibration sensing fiber includes a fiber core 1 and a cladding 2 in sequence from inside to outside, and in order to improve the rayleigh scattering coefficient of the sensing fiber, in this embodiment, when the refractive index of pure silica is used as a reference to define the relative refractive index of the fiber core, the fiber core 1 has a disordered relative refractive index distribution on a path radiating from the center to the outer periphery of the fiber; the rayleigh scattering coefficient of the optical fiber is increased by increasing the unevenness of the refractive index distribution of the core 1.
In a specific example, the fiber core 1 includes a central layer 3 at the innermost side, and a ring layer 4 disposed on the periphery of the central layer 3, wherein the relative refractive index of an inner region 4-1 of the ring layer 4 near the central layer 3 satisfies 0.1% < Δ 1- Δ 2 ≦ 0.3%, where Δ 1 and Δ 2 are the relative refractive indexes of the inner region 4-1 of the central layer 3 and the inner region 4-1 of the ring layer 4, respectively; the relative refractive index of the outer region 4-2 of the annular layer 4 close to the cladding 2 is gradually increased based on the inner region 4-1, the maximum relative refractive index Δ 3 of the edge portion 4-3 of the outer region 4-2 satisfies the condition 0.1% < Δ 3- Δ 2 ≦ 0.4%, and the thickness of the outer region 4-2 accounts for 30-50% of the thickness of the annular layer 4.
In the distributed acoustic vibration sensing fiber provided by the embodiment, the central layer of the fiber and the inner side region of the annular layer form a stepped relative refractive index distribution, the relative refractive index is slowly increased in the outer side region of the annular layer close to the cladding, and a graded distribution with the maximum relative refractive index is formed at the edge position close to the cladding, so that the waveguide structure can enable the optical power to be more distributed in the core region, and the backward rayleigh scattering intensity of the fiber core is favorably improved; in addition, the distribution structure gradually disperses the stress in the optical fiber to the cladding, and the overall material structure of the optical fiber can be changed, so that the stress distribution of the optical fiber after drawing is optimized. The layering bears the tensile stress formed in the drawing process, the stress borne by the core layer is the compressive stress, and the stress distribution is beneficial to improving the disorder degree of the doped elements in the optical fiber, so that the Rayleigh scattering coefficient of the optical fiber is improved.
The core layer 3 and the ring layer 4 are described above only for distinguishing the respective regions of the core 1 having different relative refractive indices and for characterizing the disorder of the relative refractive index profile of the core 1, and the number of layers in the physical structure of the core 1 is not limited. For example: the central layer 3 further comprises two or more sublayers having different relative refractive indices but each larger than the relative refractive index of the inner region 4-1 of the annular layer 4; similarly, the inner region 4-1 and the outer region 4-2 of the annular layer 4 each include two or more sublayers, and the relative refractive indices of these sublayers may satisfy the above relationship.
Further, the present embodiment increases the non-uniformity of the refractive index profile of the core 1 by introducing a certain amount of doping into the pure silica of the fiber, in particular, in the core 1,
the core layer is doped with fluorine and/or germanium under the condition that the relative refractive index thereof satisfies 0.5% to Δ 1% to 0.6%;
the inner region of the annular layer is doped with fluorine and/or germanium under the condition that the relative refractive index thereof satisfies 0.3% to less than delta 2 < 0.4%;
the annular layer is doped with fluorine and/or germanium under the condition that the relative refractive index at the edge portion of the outer region thereof satisfies 0.5% to Δ 3% to 0.7%.
Doping elements such as fluorine and germanium in the optical fiber to regulate and control the relative refractive indexes of different areas in the optical fiber, and further increasing the Rayleigh scattering coefficient of the optical fiber, specifically, defining:
a c ＝a 0 (1+0.62[GeO 2 ]+0.6[F] 2 +0.44[GeO 2 ][F] 2 )
wherein, a c Represents a concentration factor, a 0 Denotes the intrinsic concentration of the quartz glass [. [ ]]Represents the doping concentration of the doping element, i.e. the proportion of the doping element to the relative refractive index contribution of the region in which it is located.
Concentration factor a of different regions in an optical fiber c The difference of (2) affects the Rayleigh scattering coefficient of the optical fiber, and therefore, the elements of fluorine and germanium are adjustedThe relative refractive indexes of the central layer 3 and the annular layer 4 are adjusted by the doping amount in different layers of the fiber core 1, so that the Rayleigh scattering coefficient of the optical fiber is adjusted.
In order to realize the above-mentioned relative refractive index distribution relationship of each core layer, different element doping schemes may be adopted, such as:
only germanium element is doped in the central layer 3 and the outer region 4-2 of the annular layer, and fluorine element and germanium element are doped in the inner region 4-1 of the annular layer; the central layer 3 and the outer region 4-2 of the annular layer are then germanium-doped silicon dioxide layers and the inner region 4-1 of the annular layer is a fluorogermanium co-doped silicon dioxide layer. Or,
the central layer 3, the inner region 4-1 and the outer region 4-2 of the annular layer are respectively doped with fluorine and germanium, and the central layer 3, the inner region 4-1 and the outer region 4-2 of the annular layer are fluorine-germanium co-doped silicon dioxide layers.
In one specific example, the fluorine doping amount of the core layer 3 is-0.75%, and the germanium doping amount is 1.35%;
the fluorine doping amount of the inner region 4-1 of the annular layer is-0.75%, and the germanium doping amount is 1.15%;
the fluorine doping level of the outer region 4-2 of the annular layer is-0.75% and the germanium doping level is 1.45%.
In another specific example, the fluorine doping amount of the core layer 3 is-0.8%, and the germanium doping amount is 1.4%;
the fluorine doping amount of the inner region 4-1 of the annular layer is-0.8%, and the germanium doping amount is 1.2%;
the fluorine doping level of the outer region 4-2 of the annular layer is-0.8% and the germanium doping level is 1.5%.
Further, in the core 1, the diameter D1 of the central layer 3 is 2.1 μm to 3 μm; the diameter D2 of the inner region 4-1 of the annular layer is 3.5 μm to 4.5 μm; the outer region 4-2 of the annular layer has a diameter D3 of 6 μm to 9 μm.
The sizes of the layers in the fiber core 1 are designed by combining the relative refractive indexes of the layers, the relative refractive index difference between the fiber core and the cladding is balanced through size optimization, the normalized frequency of the optical fiber is ensured, and the attenuation in the optical transmission process is reduced.
With reference to fig. 1, in the distributed acoustic vibration sensing optical fiber provided in the present embodiment, the cladding 2 includes an inner cladding 2-1 and an outer cladding 2-2;
wherein the inner cladding 2-1 is a fluorine-doped silicon dioxide layer, and the relative refractive index delta 4 of the inner cladding is more than or equal to-0.02% and less than or equal to-0.01% and more than-0.8% and less than or equal to-4-delta 3 and less than or equal to-0.5% of fluorine doping. The refractive index depressed cladding of the inner cladding has viscosity matching effect, can improve the bending resistance of the optical fiber, and has positive effect on improving the bending resistance of the optical fiber. The design of the layered structure is beneficial to reducing the macrobend additional loss of the optical fiber in a small bending radius state. In addition, the viscosity of the cladding region is adjusted by adjusting the fluorine doping amount of the inner cladding and combining with the diameter size design, so that the viscosity of the cladding region is equivalent to that of the core 1 region, and the increase of loss caused by the generation of defects due to the relative viscous flow of the interface of the core 1 and the cladding in the high-temperature drawing process is avoided.
The diameter D4 of the inner cladding 2-1 is 14-18 μm; the outer cladding layer 2-2 is a pure silicon dioxide layer with a diameter D5 of 124 μm to 126 μm, and the cross-sectional shape is not particularly limited, and may be generally circular, and may be other shapes such as regular hexagon and regular octagon.
In an alternative embodiment, the distributed acoustic vibration sensing optical fiber further includes a resin coating layer 5 coated on the outer surface of the outer cladding 2-2, and the outer diameter of the resin coating layer 5 is 190 μm to 210 μm. The single-layer coating is adopted, the large-modulus resin material is adopted, the coating outer diameter is reduced, in practical application, external stress change can be effectively transmitted, and transmission lag generated by an inner coating is reduced.
The cut-off wavelength of the distributed acoustic vibration sensing optical fiber provided by the embodiment is 1300nm to 1400 nm.
According to the scheme, the mode field diameter of the optical fiber at the 1550nm waveband is 8.5-9.5 microns.
According to the scheme, the Rayleigh scattering coefficient of the optical fiber is 1.4-1.5.
According to the scheme, the attenuation of the optical fiber in the 1550nm wave band is less than 0.4 dB/km.
According to the scheme, the attenuation of the optical fiber in the 1310nm wave band is less than 0.7 dB/km.
Table 1 shows structural parameters of the distributed acoustic vibration sensing fiber of different embodiments:
table 1 examples 1-3 structural parameters of distributed acoustic vibration sensing optical fiber
The performance test of the distributed acoustic vibration sensing optical fiber provided in the above embodiments 1 to 3 was performed, and the test results are shown in table 2:
table 2 examples 1-3 performance parameters of distributed acoustic vibration sensing optical fiber
As can be seen from table 2, the rayleigh scattering coefficient of the distributed acoustic vibration sensing fiber provided in this embodiment is greater than 1.4, while the rayleigh scattering coefficient of the ordinary communication G652D fiber is only 0.8-0.9, and the rayleigh scattering coefficient of the fiber provided in the present invention is significantly greater than that of the comparative ordinary G652D fiber.
The distributed acoustic wave vibration sensing optical fibers of the embodiments 1, 2 and 3 and the ordinary G652D optical fiber are respectively connected to a distributed acoustic wave vibration sensing system (DAS/DVS host), 2m of the optical fibers are respectively taken out from the tail of the optical fibers to form a ring with a diameter of 50cm (the ring is reserved about 30m away from the tail end of the optical fiber to prevent rayleigh scattering light influence on a signal area due to end face reflection at the tail end), the rings are completely overlapped together and tightly attached to the surface of a loudspeaker, the loudspeaker outputs acoustic wave signals with fixed frequency and amplitude by a signal generator, and response conditions of the optical fibers to external acoustic waves are respectively demodulated and compared. In the experiment, data of 1s is collected under external sound waves every time for demodulation, 3 times of collection are carried out, an average value is taken, and the operation is repeated for 3 times.
The signal generator is utilized to drive the loudspeaker, the sensitivity of the optical fiber is defined as the increasing rate (slope) of the amplitude obtained by demodulation, 500Hz and 1000Hz frequency points are selected to sequentially increase the output voltages 0v, 1v, 3v and 5v of the signal generator, and the test results are as follows in the following table 3:
TABLE 3 response data of different optical fibers to acoustic signals
As can be seen from table 3, the maximum signal-to-noise ratios of the sensing fibers provided in embodiments 1 to 3 of the present invention are all greater than those of the ordinary communication G652D optical fiber, and the fiber sensitivities of the sensing fibers provided in embodiments 1 to 3 are all greater than those of the ordinary communication G652D optical fiber when the signal generators output voltages 1v, 3v, and 5v at 500Hz and 1000 Hz. The signal-to-noise ratio is the ratio of signal power to noise power, the strength of a backward Rayleigh scattering signal in distributed acoustic sensing determines the strength of the signal power, and the sensitivity is the slope of a demodulation amplitude; generally, the larger the rayleigh scattering coefficient of the optical fiber, the higher the signal power intensity, and the signal-to-noise ratio of the sensing optical fiber is increased. The above data show that compared with the common communication G652D optical fiber, the rayleigh scattering coefficient of the sensing optical fiber provided in embodiments 1 to 3 of the present invention is significantly greater than that of the common communication G652D optical fiber, and the amplitude slope of the backward rayleigh scattering signal of the sensing optical fiber and the system demodulation is improved, so that the signal-to-noise ratio and the detection sensitivity of the distributed sensing acoustic wave vibration sensing system are improved, and the technical problems that the strength of the sensing signal reflected to the demodulation end is weak, a sufficient signal-to-noise ratio cannot be provided, and the test sensitivity is insufficient are solved.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
It will be understood by those skilled in the art that the foregoing is only an exemplary embodiment of the present invention, and is not intended to limit the invention to the particular forms disclosed, since various modifications, substitutions and improvements within the spirit and scope of the invention are possible and within the scope of the appended claims.
Claims (9)
1. A distributed acoustic vibration sensing optical fiber comprises a fiber core and a cladding in sequence from inside to outside, and is characterized in that when the relative refractive index of the fiber core is defined by taking the refractive index of pure silica as a reference, the fiber core has disordered relative refractive index distribution on a path radiating from the center to the periphery of the optical fiber;
the fiber core comprises a central layer and an annular layer arranged on the periphery of the central layer, the relative refractive index of an inner side area close to the central layer in the annular layer meets 0.1% < delta 1-delta 2 ≦ 0.3%, wherein delta 1 and delta 2 are the relative refractive index of the inner side area of the central layer and the inner side area of the annular layer respectively;
the relative refractive index of the annular layer in the outer region close to the cladding layer is gradually increased by taking the inner region as a reference, the maximum relative refractive index delta 3 of the edge part of the outer region meets the condition that the value is 0.1% < delta 3-delta 2 ≦ 0.4%, and the thickness of the outer region accounts for 30-50% of the thickness of the annular layer.
2. A distributed acoustic vibration sensing optical fiber according to claim 1, wherein said central layer is doped with fluorine and/or germanium under conditions such that its relative refractive index Δ 1 satisfies 0.5% to Δ 1% to 0.6%;
the inner region of the annular layer is doped with fluorine and/or germanium under the condition that the relative refractive index delta 2 thereof satisfies 0.3% and delta 2 < 0.4%;
the annular layer is doped with fluorine and/or germanium under the condition that the relative refractive index Δ 3 at the edge portion of the outer region thereof satisfies 0.5% to Δ 3% to 0.7%.
3. A distributed acoustic vibration sensing optical fiber as defined in claim 2, wherein said central layer, inner region and outer region of said annular layer are each a layer of silicon dioxide co-doped with fluoro-germanium,
the fluorine doping amount of the central layer is-0.1% to-1.0%, and the germanium doping amount is 0.6% to 1.6%;
the fluorine doping amount of the inner side area of the annular layer is-0.1% to-1.0%, and the germanium doping amount is 0.5% to 1.6%;
the outer region of the annular layer has a germanium doping amount of 0.6% to 1.7% and a fluorine doping amount of-0.1% to-1.0%.
4. A distributed acoustic vibration sensing optical fiber as defined in claim 1, wherein said central layer has a diameter D1 of 2.1 μm to 3 μm;
the diameter D2 of the inner region of the annular layer is 3.5 μm to 4.5 μm;
the diameter D3 of the outer region of the annular layer is 6 μm to 9 μm.
5. A distributed acoustic vibration sensing optical fiber as claimed in any of claims 1 to 4, wherein said cladding comprises an inner cladding and an outer cladding;
the inner cladding is a fluorine-doped silicon dioxide layer, and the relative refractive index delta 4 of the inner cladding is more than or equal to-0.02% and less than or equal to-0.01%, and the relative refractive index delta 4 of the inner cladding is more than or equal to-0.8% and less than or equal to-4-delta 3 and less than or equal to-0.5% of fluorine doping; the outer cladding layer is a pure silicon dioxide layer.
6. A distributed acoustic vibration sensing optical fiber as defined in claim 5, wherein said inner cladding has a diameter of 14 μm to 18 μm;
the diameter of the outer cladding layer is 124-126 μm.
7. The distributed acoustic vibration sensing fiber of claim 5, further comprising a resin coating layer coated on an outer surface of the outer cladding layer, the resin coating layer having an outer diameter of 190-210 μm.
8. A distributed acoustic vibration sensing optical fiber as claimed in any of claims 1 to 7, wherein the optical fiber has a Rayleigh scattering coefficient of greater than 1.4, or an attenuation of less than 0.4dB/km at 1550nm, or an attenuation of less than 0.7dB/km at 1310nm, or a mode field diameter of 8.5 to 9.5um at 1550 nm.
9. A distributed acoustic vibration monitoring system, characterized in that the system uses the distributed acoustic vibration sensing optical fiber according to any one of claims 1 to 8 as an acoustic signal transmission medium.
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