CN115128728B - 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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- CN115128728B CN115128728B CN202210616293.0A CN202210616293A CN115128728B CN 115128728 B CN115128728 B CN 115128728B CN 202210616293 A CN202210616293 A CN 202210616293A CN 115128728 B CN115128728 B CN 115128728B
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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
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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
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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
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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
- G02B6/028—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 wave vibration sensing optical fiber and an acoustic wave 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 along the center of the optical fiber to the outer periphery, the fiber core comprises a center layer and an annular layer arranged on the periphery of the center layer, the relative refractive index of an inner side area close to the center layer in the annular layer is 0.1% < delta 1-delta 2 +.0.3%, and delta 1 and delta 2 are the relative refractive indexes of the center layer and the inner side area 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 satisfies 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 application provides a fiber core with unordered relative refractive index distribution along the path of the radiation from the center to the periphery of the fiber; by increasing the non-uniformity of the refractive index distribution of the fiber core, the Rayleigh scattering coefficient of the optical fiber is significantly improved.
Description
Technical Field
The application relates to the technical field of optical fiber communication, in particular to a distributed acoustic wave vibration sensing optical fiber with a high Rayleigh scattering coefficient and an acoustic wave 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. Worldwide, optical fibers have been widely laid and applied in optical communication networks. With the continuous development of special optical fibers and optical fiber application technologies thereof, optical fibers have been increasingly used in fields other than conventional communication.
With the continuous development of optical fiber sensing technology, distributed optical fiber sensing is widely applied in recent years with the characteristics of long distance, multiple parameters, high sensitivity and the like. The phi-OTDR technology based on the fiber Rayleigh scattering effect is applied to distributed optical fiber sensing, and is used for detecting vibration signals along sensing optical fibers in real time, and is successfully applied to the fields of geological detection, petroleum exploration, pipeline safety monitoring and the like in recent years.
The current common distributed sensing optical fiber mainly uses a G652D single-mode communication optical fiber, but because the backscattering strength of the common single-mode communication optical fiber G652D is too low, the strength of the sensing signal reflected back to the demodulation end is weak, and a sufficient signal-to-noise ratio cannot be provided, so that the distributed sensing optical fiber cannot be applied to the field with high-precision detection requirement.
Disclosure of Invention
Aiming at least one defect or improvement requirement of the prior art, the application provides a distributed acoustic vibration sensing optical fiber with a high Rayleigh scattering coefficient and an acoustic vibration monitoring system, and aims to solve the problems that the back scattering intensity of the conventional common single-mode optical fiber 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.
In order to achieve the above object, according to one aspect of the present application, there is provided a distributed acoustic vibration sensing optical fiber including a core and a cladding in this order from inside to outside, the core having a disordered relative refractive index distribution along a path radiating from the center to the outer circumference of the optical fiber when the relative refractive index of the core is defined with reference to the refractive index of pure silica;
the fiber core comprises a central layer and an annular layer arranged outside the central layer, wherein the relative refractive index of an inner region of the annular layer, which is close to the central layer, is 0.1% < delta 1-delta 2 +.0.3%, wherein delta 1 and delta 2 are the relative refractive indexes of the inner regions of the central layer and the annular layer respectively;
the relative refractive index of the annular layer in the outer region close to the cladding layer is gradually increased based on the inner region, the maximum relative refractive index delta 3 of the edge part of the outer region meets the condition that delta 3-delta 2 is less than or equal to 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 wave vibration sensing optical fiber, the central layer is doped with fluorine and/or germanium under the condition that the relative refractive index delta 1 of the central layer is 0.5% -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 of the inner region satisfies 0.3 percent or less than delta 2 < 0.4 percent;
the annular layer is doped with fluorine and/or germanium under the condition that the relative refractive index delta 3 of the edge part of the outer side area of the annular layer is 0.5 percent or less and delta 3 or less than 0.7 percent.
Further, the inner region and the outer region of the central layer and the annular layer of the distributed acoustic vibration sensing optical fiber are silicon dioxide layers co-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 region 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 distributed acoustic wave vibration sensing optical fiber, the diameter D1 of the center 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 distributed acoustic vibration sensing optical fiber 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 less than or equal to minus 0.02 percent and less than or equal to minus 0.01 percent, and the relative refractive index delta 4 is less than or equal to minus 0.8 percent and less than or equal to minus 0.5 percent; the outer cladding is a pure silica layer.
Further, in the distributed acoustic vibration sensing optical fiber, the diameter of the inner cladding is 14-18 μm;
the diameter of the outer cladding is 124-126 mu m.
Further, the distributed acoustic vibration sensing optical fiber further comprises a resin coating layer coated on the outer surface of the outer cladding, and the outer diameter of the resin coating layer is 190-210 mu m.
Further, the Rayleigh scattering coefficient of the distributed acoustic wave vibration sensing optical fiber is larger than 1.4, or the attenuation of the optical fiber in 1550nm wave band is smaller than 0.4dB/km, or the attenuation of the optical fiber in 1310nm wave band is smaller than 0.7dB/km, or the mode field diameter of the optical fiber in 1550nm wave band is 8.5-9.5 um.
According to another aspect of the present application, there is also provided a distributed acoustic vibration monitoring system using the distributed acoustic vibration sensing optical fiber of any one of the above as an acoustic signal transmission medium.
In general, the above technical solutions conceived by the present application, compared with the prior art, enable the following beneficial effects to be obtained:
(1) The distributed acoustic vibration sensing optical fiber provided by the application has the advantages that the fiber core has disordered relative refractive index distribution on a path radiating along the center of the optical fiber to the periphery, the central layer of the optical fiber and the inner area of the annular layer form stepped relative refractive index distribution, the relative refractive index is slowly increased in the outer area of the annular layer close to the cladding, and the graded distribution with the maximum relative refractive index is formed in the edge position close to the cladding; in addition, the distribution structure enables the stress in the optical fiber to be gradually dispersed to the cladding, and the material structure of the whole optical fiber can be changed, so that the stress distribution after the optical fiber is drawn is optimized. The layering bears tensile stress formed in the drawing process, the stress borne by the core layer is compressive stress, and the stress distribution is favorable for improving the disorder degree of doped elements in the optical fiber, so that the Rayleigh scattering coefficient of the optical fiber is improved.
(2) According to the distributed acoustic vibration sensing optical fiber provided by the application, 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 phenomenon that the relative viscous flow is generated at the interface of the fiber core and the cladding in the high-temperature wire drawing process, so that the loss is increased due to defects is avoided.
(3) According to the distributed acoustic vibration sensing optical fiber, 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 distributed acoustic vibration sensing optical fiber is obviously superior to the existing G652D optical fiber; the technical problems of weak optical fiber Rayleigh scattering signals and insufficient system signal-to-noise ratio in the distributed acoustic wave vibration sensing system are solved, so that the detection sensitivity of the distributed acoustic wave vibration sensing system is improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present application, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural diagram of a distributed acoustic vibration sensing optical fiber according to the present embodiment;
fig. 2 is a schematic diagram of a refractive index profile of a cross section of a distributed acoustic vibration sensing optical fiber according to the present embodiment.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application.
The terms first, second, third and the like in the description and in the claims and in the above drawings, are used for distinguishing between different objects and not necessarily for describing a particular sequential or chronological order. Furthermore, the terms "comprise" and "have," as well as any variations thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those listed steps or elements but may include other steps or elements not listed or inherent to such process, method, article, or apparatus.
Furthermore, well-known or widely-used techniques, elements, structures, and processes may not be described or shown in detail in order to avoid obscuring the understanding of the present application by the skilled artisan. Although the drawings represent exemplary embodiments of the present application, the drawings are not necessarily to scale and certain features may be exaggerated or omitted in order to better illustrate and explain the present application.
The following are definitions and illustrations of some terms involved in the present application:
optical fiber or optical fiber preform structure: the central part of the cross section of the optical fiber is defined as the fiber core, the annular region of the fiber section immediately adjacent to the fiber core is the inner cladding, and the annular region of the pure silica immediately adjacent to the inner cladding is the outer cladding, based on the change in refractive index, starting from the centermost axis of the fiber.
Relative refractive index:
wherein n is i Representing refractive indexes corresponding to different deposition layers, n 0 Is pure SiO 2 Is 1.457;
the doping amount or doping concentration, in units, represents the ratio of the relative refractive index contribution of the doping element to the region in which it is located.
Fig. 1 is a schematic structural diagram of a distributed acoustic wave vibration sensing optical fiber provided in this embodiment, referring to fig. 1, the distributed acoustic wave vibration sensing optical fiber includes a fiber core 1 and a cladding 2 sequentially from inside to outside, in order to improve the rayleigh scattering coefficient of the sensing optical 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 along the path of the central to peripheral radiation of the optical fiber; the rayleigh scattering coefficient of the optical fiber is improved by increasing the non-uniformity of the refractive index profile of the core 1.
In a specific example, the fiber core 1 includes a center layer 3 at the innermost side, an annular layer 4 disposed at the outer periphery of the center layer 3, the relative refractive index of the annular layer 4 at the inner region 4-1 near the center layer 3 satisfying 0.1% < Δ1- Δ2+.0.3%, wherein Δ1, Δ2 are the relative refractive indices of the center layer 3, the inner region 4-1 of the annular layer 4, respectively; the relative refractive index of the annular layer 4 in the outer region 4-2 near the cladding layer 2 is gradually increased based on the inner region 4-1, the maximum relative refractive index Δ3 of the edge portion 4-3 of the outer region 4-2 satisfies the condition 0.1% < Δ3- Δ2+.0.4%, and the thickness of the outer region 4-2 is 30-50% of the thickness of the annular layer 4.
The distributed acoustic wave vibration sensing optical fiber provided by the embodiment has the advantages that the central layer of the optical fiber and the inner side area of the annular layer form a stepped 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 the gradient distribution with the maximum relative refractive index is formed in the edge position close to the cladding; in addition, the distribution structure enables the stress in the optical fiber to be gradually dispersed to the cladding, and the material structure of the whole optical fiber can be changed, so that the stress distribution after the optical fiber is drawn is optimized. The layering bears tensile stress formed in the drawing process, the stress borne by the core layer is compressive stress, and the stress distribution is favorable for improving the disorder degree of doped elements in the optical fiber, so that the Rayleigh scattering coefficient of the optical fiber is improved.
The central layer 3 and the annular layer 4 are only for distinguishing the regions of the core 1 having different relative refractive indices to characterize the disorder of the relative refractive index distribution of the core 1, and do not limit the number of layers on the physical structure of the core 1. For example: the central layer 3 further comprises two or more sub-layers having different relative refractive indices but each being 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 may each include two or more sub-layers, and the relative refractive indices of these sub-layers may satisfy the above-described relationship.
Further, this 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 central layer is doped with fluorine and/or germanium under the condition that the relative refractive index of the central layer is 0.5 percent or less and delta 1 percent or less and 0.6 percent;
the inner region of the annular layer is doped with fluorine and/or germanium under the condition that the relative refractive index of the inner region satisfies 0.3 percent or less than delta 2 and less than 0.4 percent;
the annular layer is doped with fluorine and/or germanium under the condition that the relative refractive index of the edge part of the outer side area of the annular layer is 0.5% -0.7%.
Doping fluorine, germanium and other elements into the optical fiber to regulate and control the relative refractive indexes of different areas in the optical fiber, so as to increase the Rayleigh scattering coefficient of the optical fiber, and specifically, defining:
a c ＝a 0 (1+0.62[GeO 2 ]+0.6[F] 2 +0.44[GeO 2 ][F] 2 )
wherein a is c Represents concentration factor, a 0 Represents the intrinsic concentration of quartz glass, [ + ]]The doping concentration of the doping element, i.e. the ratio of the relative refractive index contribution of the doping element to the region in which it is located, is expressed.
Concentration factor a for different regions in an optical fiber c The difference of the (2) influences the Rayleigh scattering coefficient of the optical fiber, so that the respective relative refractive indexes of the central layer 3 and the annular layer 4 are regulated by regulating the doping amounts of fluorine and germanium elements in different layers of the fiber core 1, and the Rayleigh scattering coefficient of the optical fiber is regulated.
In order to achieve the above-described relative refractive index profile of the respective core layers, an unused doping scheme of elements may be employed, such as:
only germanium is doped in the central layer 3 and the outer region 4-2 of the annular layer, and fluorine and germanium 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 fluorine germanium co-doped silicon dioxide layer. Or,
fluorine and germanium are doped in the central layer 3, the inner region 4-1 and the outer region 4-2 of the annular layer respectively, and the central layer 3, the inner region 4-1 and the outer region 4-2 of the annular layer are silicon dioxide layers co-doped with fluorine and germanium.
In one specific example, the fluorine doping amount of the center 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 amount of the outer region 4-2 of the annular layer was-0.75%, and the germanium doping amount was 1.45%.
In another specific example, the fluorine doping amount of the center layer 3 is-0.8%, and the germanium doping amount is 1.4%;
the fluorine doping amount of the inner side area 4-1 of the annular layer is-0.8%, and the germanium doping amount is 1.2%;
the fluorine doping amount of the outer region 4-2 of the annular layer was-0.8%, and the germanium doping amount was 1.5%.
Further, in the core 1, the diameter D1 of the center 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 diameter D3 of the outer region 4-2 of the annular layer is 6 μm to 9 μm.
The dimensions of each layer 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 dimension optimization, the normalized frequency of the optical fiber is ensured, and the attenuation in the optical transmission process is reduced.
With continued reference to fig. 1, the cladding 2 of the distributed acoustic vibration sensing optical fiber provided in this embodiment includes an inner cladding 2-1 and an outer cladding 2-2;
wherein the inner cladding 2-1 is a fluorine-doped silica layer, and the relative refractive index delta 4 thereof satisfies-0.02% delta 4-0.01% and-0.8% delta 4-delta 3-0.5% fluorine. The refractive index depressed cladding of the inner cladding has viscosity matching function, 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 macrobend additional loss of the optical fiber in a state with a small bending radius. 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 fiber core 1 region, and the phenomenon that the relative viscous flow is generated at the interface of the fiber core 1 and the cladding layer in the high-temperature wire drawing process, and the loss is increased due to defects is avoided.
The diameter D4 of the inner cladding 2-1 is 14-18 mu m; the outer cladding 2-2 is a pure silica layer, the diameter D5 of which is 124 μm to 126 μm, and the cross-sectional shape thereof is not particularly limited, and is generally circular, but may be other shapes such as regular hexagons, regular octagons, and the like.
In an alternative embodiment, the distributed acoustic vibration sensing optical fiber further includes a resin coating layer 5 applied to 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, and the large-modulus resin material is adopted, so that the coating outer diameter is reduced, and in practical application, the external stress change can be effectively transmitted, and the transmission hysteresis generated by the inner coating is reduced.
The cutoff wavelength of the distributed acoustic wave vibration sensing optical fiber provided by the embodiment is 1300 nm-1400 nm.
According to the scheme, the mode field diameter of the optical fiber in 1550nm wave band is 8.5-9.5 mu m.
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 at 1550nm wave band is less than 0.4dB/km.
According to the scheme, the attenuation of the optical fiber at the 1310nm wave band is less than 0.7dB/km.
Table 1 shows the structural parameters of the distributed acoustic vibration sensing fibers of the different embodiments:
table 1 examples 1 to 3 structural parameters of distributed acoustic vibration sensing optical fibers
Performance tests were performed on the distributed acoustic wave vibration sensing optical fibers provided in the above examples 1 to 3, and the test results are shown in table 2:
table 2 examples 1-3 distributed acoustic vibration sensing fiber performance parameters
As can be seen from table 2, the rayleigh scattering coefficient of the distributed acoustic vibration sensing optical fiber provided by the embodiment is greater than 1.4, while the rayleigh scattering coefficient of the ordinary communication G652D optical fiber is only 0.8-0.9, and the rayleigh scattering coefficient of the optical fiber provided by the application is obviously greater than that of the comparative ordinary G652D optical fiber.
The distributed acoustic vibration sensing optical fibers and the common G652D optical fibers in the embodiments 1, 2 and 3 are respectively connected into a distributed acoustic vibration sensing system (DAS/DVS host), the optical fibers are respectively taken out from the tail part to form circular rings with the diameter of 50cm (the circular rings are reserved for about 30m from the tail end of the light to prevent the influence of the end face reflection on the Rayleigh scattered light of the signal area), the circular rings are completely overlapped and are tightly attached to the surface of a loudspeaker, the loudspeaker outputs acoustic signals with fixed frequency and amplitude by a signal generator, and the response conditions of the optical fibers to external acoustic waves are respectively demodulated and compared. The experiment is carried out by collecting 1s data under external sound wave for demodulation, collecting 3 times, taking average value, repeating 3 times.
The loudspeaker is driven by the signal generator, the sensitivity of the optical fiber is defined as the increasing rate (slope) of the amplitude obtained by demodulation, the frequency points of 500Hz and 1000Hz are selected to sequentially increase the output voltages of 0v, 1v, 3v and 5v of the signal generator, and the test results are shown in the following table 3:
TABLE 3 response data of different fibers to Acoustic wave signals
As can be seen from Table 3, the maximum signal-to-noise ratios of the sensing optical fibers provided in embodiments 1 to 3 of the present application are all larger than those of the ordinary communication G652D optical fibers, and the optical fiber sensitivities of the sensing optical fibers provided in embodiments 1 to 3 are all larger than those of the ordinary communication G652D optical fibers when the signal generator outputs voltages of 1v, 3v and 5v at 500Hz and 1000 Hz. The signal-to-noise ratio, namely the ratio of signal power to noise power, is characterized in that the signal power intensity is determined by the strength of the back Rayleigh scattering signal in distributed acoustic wave sensing, and the sensitivity is the slope of the demodulation amplitude; in general, the larger the Rayleigh scattering coefficient of the optical fiber is, the larger the signal power intensity is, and the signal-to-noise ratio of the sensing optical fiber is increased. Compared with the common communication G652D optical fiber, the Rayleigh scattering coefficient of the sensing optical fiber provided by the embodiments 1-3 is obviously larger than that of the common communication G652D optical fiber, and the backward Rayleigh scattering signal of the sensing optical fiber and the amplitude slope of system demodulation are improved, so that the signal-to-noise ratio and the detection sensitivity of the distributed sensing acoustic vibration sensing system are improved, and the technical problems that the strength of the sensing signal reflected back to the demodulation end is weak, the sufficient signal-to-noise ratio cannot be provided, and the test sensitivity is insufficient are solved.
The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the application and is not intended to limit the application, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the application are intended to be included within the scope of the application.
Claims (9)
1. A distributed acoustic vibration sensing optical fiber, the optical fiber sequentially comprising a fiber core and a cladding from inside to outside, wherein 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 along the path of radiation from the center of the optical fiber to the periphery;
the fiber core comprises a central layer and an annular layer arranged outside the central layer, wherein the relative refractive index of an inner region of the annular layer, which is close to the central layer, is 0.1% < delta 1-delta 2 +.0.3%, wherein delta 1 and delta 2 are the relative refractive indexes of the inner regions of the central layer and the annular layer respectively;
the relative refractive index of the annular layer in the outer region near the cladding layer is gradually increased based on the inner region, and a gradient type distribution with the maximum relative refractive index is formed in the edge region near the cladding layer, the maximum relative refractive index delta 3 of the edge region of the outer region satisfies the condition of 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, the central layer is doped with fluorine and/or germanium under the condition that the relative refractive index delta 1 of the central layer is 0.5 percent or less and delta 1 percent or less and 0.6 percent;
the inner region of the annular layer is doped with fluorine and/or germanium under the condition that the relative refractive index delta 2 of the inner region satisfies 0.3 percent or less than delta 2 < 0.4 percent;
the annular layer is doped with fluorine and/or germanium under the condition that the relative refractive index delta 3 of the edge part of the outer side area of the annular layer is 0.5 percent or less and delta 3 or less than 0.7 percent.
3. The distributed acoustic vibration sensing optical fiber of claim 2 wherein the inner and outer regions of the central layer, annular layer are each fluorine-germanium co-doped silica layers, 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 region 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. The distributed acoustic vibration sensing optical fiber of claim 1, wherein 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.
5. The distributed acoustic vibration sensing optical fiber of any of claims 1-4, 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 less than or equal to minus 0.02 percent and less than or equal to minus 0.01 percent, and the relative refractive index delta 4 is less than or equal to minus 0.8 percent and less than or equal to minus 0.5 percent; the outer cladding is a pure silica layer.
6. The distributed acoustic wave vibration sensing optical fiber of claim 5 wherein the inner cladding has a diameter of 14 μm to 18 μm;
the diameter of the outer cladding is 124-126 mu m.
7. The distributed acoustic vibration sensing optical fiber of claim 5, further comprising a resin coating layer applied to an outer surface of the overclad layer, the resin coating layer having an outer diameter of 190-210 μm.
8. A distributed acoustic wave vibration sensing optical fibre according to any of claims 1 to 7 wherein the optical fibre has a rayleigh scattering coefficient greater than 1.4, or an attenuation of less than 0.4dB/km at 1550nm or 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 using the distributed acoustic vibration sensing optical fiber of any one of claims 1 to 8 as an acoustic signal transmission medium.
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| CN202210616293.0A CN115128728B (en) | 2022-06-01 | 2022-06-01 | Distributed acoustic vibration sensing optical fiber and acoustic vibration monitoring system |
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