CN113568090B - Multi-core microstructure optical fiber for distributed sensing system - Google Patents
Multi-core microstructure optical fiber for distributed sensing system Download PDFInfo
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- CN113568090B CN113568090B CN202110796129.8A CN202110796129A CN113568090B CN 113568090 B CN113568090 B CN 113568090B CN 202110796129 A CN202110796129 A CN 202110796129A CN 113568090 B CN113568090 B CN 113568090B
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 147
- 239000000835 fiber Substances 0.000 claims abstract description 134
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- 230000005540 biological transmission Effects 0.000 abstract description 7
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- VTYDSHHBXXPBBQ-UHFFFAOYSA-N boron germanium Chemical compound [B].[Ge] VTYDSHHBXXPBBQ-UHFFFAOYSA-N 0.000 description 2
- 229910052732 germanium Inorganic materials 0.000 description 2
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 description 2
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Classifications
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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
- G02B6/02042—Multicore optical fibres
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/3537—Optical fibre sensor using a particular arrangement of the optical fibre itself
- G01D5/3538—Optical fibre sensor using a particular arrangement of the optical fibre itself using a particular type of fiber, e.g. fibre with several cores, PANDA fiber, fiber with an elliptic core or the like
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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
- G02B6/02047—Dual mode fibre
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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
- G02B6/02295—Microstructured optical fibre
- G02B6/02314—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes
- G02B6/02319—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes characterised by core or core-cladding interface features
- G02B6/02323—Core having lower refractive index than cladding, e.g. photonic band gap guiding
- G02B6/02328—Hollow or gas filled core
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Couplings Of Light Guides (AREA)
- Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)
Abstract
The invention discloses a multi-core microstructure optical fiber for a distributed sensing system, which belongs to the technical field of optical fiber sensing and comprises the following components: the multimode fiber core is arranged at the central position of the optical fiber; at least one single-mode fiber core arranged at a non-central position with the optical fiber; an air hole, the multimode core and the at least one single mode core being separated by the air hole; the cladding is coated on the peripheries of the multimode fiber core, the at least one single-mode fiber core and the air holes. The invention has the beneficial effects that: meanwhile, the fiber has a multimode fiber core and a single-mode fiber core, so that the distributed sensing of DTS and DAS is realized in the same optical fiber, the energy coupling between different fiber cores in the optical fiber is effectively controlled, and the loss of multimode and single-mode long-distance transmission in a plurality of fiber cores is ensured to be lower; by introducing the air hole structure, the energy crosstalk between fiber cores is greatly reduced, and meanwhile, the applicability of the optical fiber is ensured for different optical fiber outer diameters.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to a multi-core microstructure optical fiber for a distributed sensing system.
Background
The distributed optical fiber sensing system is one utilizing optical fiber as sensing sensor and signal transmission medium. Distributed fiber optic sensing systems are now widely used in various industries, such as: the power industry comprises surface temperature detection and monitoring of a power cable, an accident point positioning cable tunnel, interlayer fire monitoring, additional temperature monitoring of a power plant and a transformer substation, fault point detection and fire alarm; structural health monitoring of large civil engineering, seepage of dams and river levees, fission monitoring of bridges and other concrete structures, concrete solidification and maintenance temperature and strain monitoring of the dams and river levees and the bridges; the system is further applied to fire monitoring and alarming, and fire monitoring and alarming of tunnels, subways and highways; the system can also be used for the petroleum and natural gas industry, including leakage monitoring of petroleum and natural gas conveying pipelines or storage tanks, temperature monitoring of oil reservoirs, oil pipes and oil tanks and fault point detection.
With the development of distributed optical fiber sensing technology, not only distributed temperature sensing (Distributed temperature sensor, DTS) but also distributed acoustic wave sensing (Distributed acoustic sensor, DAS) can be realized. However, at present, the DTS system mainly adopts multimode optical fibers, while the DAS system mainly uses single mode optical fibers, and the types of the optical fibers used are different due to different technical principles of the DTS and DAS technologies.
In order to realize the joint use of DTS and DAS technologies to meet more application requirements, such as leakage monitoring of oil and gas transmission pipelines, fracturing monitoring in petroleum exploitation processes, and the like, it is required to have both multimode fiber cores and single-mode fiber cores. When the multimode fiber cores and the single-mode fiber cores are integrated in one optical fiber, because the areas of the multimode fiber cores are larger, the larger fiber core spacing and the smaller outer diameter of the optical fiber form contradiction in structural design, when the fiber core spacing is insufficient, the energy coupling between the fiber cores can increase the loss of each fiber core, and the requirement of long-distance transmission in the distributed sensing technology can not be met, so that the research on the multi-core microstructure optical fiber for the distributed sensing system is urgently needed to meet the requirement of practical use.
Disclosure of Invention
In order to solve the technical problems, the invention provides a multi-core microstructure optical fiber for a distributed sensing system, which realizes the transmission of single mode and multiple modes in the same optical fiber through an air hole, and greatly reduces the crosstalk between the single-mode fiber core and the multi-mode fiber core of the optical fiber and between the single-mode fiber core and the single-mode fiber core.
The technical problems solved by the invention can be realized by adopting the following technical scheme:
wherein, a multicore microstructure fiber for a distributed sensing system, comprising:
the multimode fiber core is arranged at the central position of the optical fiber;
at least one single-mode core disposed at a non-central location with the optical fiber;
an air hole, said multimode core and at least one of said single mode cores being separated by said air hole;
and the cladding is coated on the peripheries of the multimode fiber cores, at least one single-mode fiber core and the air holes.
Preferably, when the single-mode fiber cores are more than one, the single-mode fiber cores and the multimode fiber cores are distributed in a regular triangle, and two adjacent single-mode fiber cores are separated by the air hole.
Preferably, the single mode core has a core diameter in the range of 3 to 15 μm and a numerical aperture in the range of 0.1 to 0.18.
Preferably, the multimode core has a core diameter in the range of 25 to 80 μm and a numerical aperture in the range of 0.15 to 0.3.
Preferably, the air hole is spaced apart from the Shan Moqian core by a first predetermined distance;
the first preset distance is not less than 2 times the diameter of the single-mode fiber core.
Preferably, the air hole is spaced apart from the multimode fiber core by a second predetermined distance;
the second preset distance is not less than 0.2 times the diameter of the multimode fiber core.
Preferably, the center of the air hole is located at the midpoint of the center line of the single-mode core and the multimode core.
Preferably, the aperture of the air hole is 0.05-0.8 times of the center distance between the single-mode fiber core and the multi-mode fiber core.
Preferably, at least one of said single mode cores is rotatable about said multimode core to form a helical core having a helical period in the range of 3mm to 1m.
Preferably, the midpoint of the single-mode core is in the range of 10 to 200 μm from the outer edge of the cladding of the optical fiber.
The invention has the beneficial effects that:
the multi-core microstructure optical fiber prepared by the invention has the multi-mode fiber cores and the single-mode fiber cores, realizes the distributed sensing of DTS and DAS in the same optical fiber, effectively controls the energy coupling between different fiber cores in the optical fiber, and ensures lower loss in long-distance transmission of multi-mode and single-mode in a plurality of fiber cores; by introducing the air hole structure, the energy crosstalk between fiber cores is greatly reduced, and meanwhile, the applicability of the optical fiber is ensured for different optical fiber outer diameters.
Drawings
FIG. 1 is a schematic diagram of a multi-core microstructured optical fiber embodiment 1 for a distributed sensing system according to the present invention;
FIG. 2 is a schematic diagram of a stack of an embodiment 1 of the multi-core microstructured optical fiber of FIG. 1;
FIG. 3 is a schematic diagram of a multi-core microstructured optical fiber embodiment 2 for a distributed sensing system according to the present invention;
FIG. 4 is a schematic diagram of a stack of an embodiment 2 of the multi-core microstructured optical fiber of FIG. 3;
FIG. 5 is a schematic diagram of an embodiment 3 of a multi-core microstructured optical fiber for a distributed sensing system according to the present invention;
FIG. 6 is a schematic diagram of a stack of an embodiment 3 of the multi-core microstructured optical fiber of FIG. 5;
FIG. 7 is a schematic diagram of an embodiment 4 of a multi-core microstructured optical fiber for a distributed sensing system according to the present invention;
FIG. 8 is a schematic diagram of a stack of an embodiment 4 of the multi-core microstructured optical fiber of FIG. 7 according to the present invention.
Reference numerals:
the fiber comprises a multimode fiber core (1), a first capillary rod (11), a first capillary tube (12), a single-mode fiber core (2), a second capillary rod (21), a second capillary tube (22), an air hole (3), a third capillary tube (31), a cladding layer (4), an outer sleeve (41) and a third capillary rod (5).
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.
The invention is further described below with reference to the drawings and specific examples, which are not intended to be limiting.
The invention provides a multi-core microstructure optical fiber for a distributed sensing system, which belongs to the technical field of optical fiber sensing, and is shown in fig. 1-8, and comprises the following components:
a multimode fiber core 1 arranged at the center of the optical fiber;
at least one single-mode core 2 arranged at a non-central position with respect to the optical fiber;
an air hole 3, the multimode core 1 and the at least one single-mode core 2 being separated by the air hole 3;
the cladding 4, the cladding 4 is coated on the multimode fiber core 1, at least one single mode fiber core 2 and the periphery of the air hole 3.
Specifically, in this embodiment, the multi-core microstructured optical fiber includes a cladding layer 4, and a core disposed in the cladding layer 4, where the core includes at least one single-mode core 2 and a multi-mode core 1, and one or more air holes 3 are further included in the cladding layer 4, and the air holes 3 are disposed between the multi-mode core 1 and the at least one single-mode core 2, for separating the multi-mode core 1 from each single-mode core 2, so as to reduce energy crosstalk between the multi-mode core 1 and the single-mode core 2.
Specifically, the cladding layer 4 is generally prepared from pure quartz material.
As a preferred embodiment, the multimode core 1 is arranged at the very center of the optical fiber, and the diameter of the multimode core 1 is in the range of 25 to 80 μm, typically 50 μm or 62.5 μm; the numerical aperture of the multimode core 1 ranges from 0.15 to 0.3, typically from 0.18 to 0.22; the multimode fiber core 1 is prepared from a doped quartz glass material, and the doped quartz glass material can be germanium-doped quartz glass, boron-germanium co-doped quartz glass or the like.
As a preferred embodiment, the single-mode cores 2 are disposed at a non-central position of the optical fiber, and at least one single-mode core 2, preferably 1 to 6 single-mode cores 2 are provided. The core diameter of each single-mode core 2 is in the range of 3 to 15 μm, typically 8 to 10 μm; the numerical aperture of the single-mode fiber core 2 ranges from 0.05 to 0.18, typically from 0.1 to 0.15; the single-mode fiber core 2 is also made of doped quartz glass material, and the doped quartz glass material can be germanium-doped quartz glass, boron-germanium co-doped quartz glass or the like.
As a preferred embodiment, the midpoint of the single-mode core 2 is in the range of 10 to 200 μm from the outer edge of the cladding 4 of the fiber.
Specifically, the range between the midpoint of the single-mode core 2 and the outer edge of the cladding 4 of the optical fiber is 10 to 200 μm, and the value is typically 30 to 100 μm.
Further, in order to improve the sensing sensitivity of the DAS system, it is necessary to appropriately improve the nonlinear coefficient of the single-mode core 2 in the multi-core microstructured optical fiber, further optimize the size range thereof, the core diameter range of the single-mode core 2 may be 3 to 5 μm, the numerical aperture may be 0.1 to 0.18, and simultaneously use the highly germanium-doped quartz glass as the preparation material of the single-mode core 2.
In a preferred embodiment, when the number of single-mode cores 2 is more than one, the single-mode cores 2 are arranged in a regular triangle with the multimode cores 1, and two adjacent single-mode cores 2 are separated by the air hole 3.
Specifically, if the multi-core microstructure optical fiber includes two or more single-mode fiber cores 2, the single-mode fiber cores 2 and the multi-mode fiber cores 1 are distributed in a regular triangle, that is, the center distances between the single-mode fiber cores 2 and between the single-mode fiber cores 2 and the multi-mode fiber cores 1 are equal.
Further, the center-to-center distance between the single-mode core 2 and the multimode core 1 is in the range of 10 to 300. Mu.m, and is generally 30 to 150. Mu.m.
Preferably, when there are two or more single-mode cores 2, the air holes 3 are provided between the single-mode cores 2 and the multimode cores 1, and in addition to reducing crosstalk between the single-mode cores 2 and the multimode cores 1, the air holes 3 are also required to be provided between adjacent single-mode cores 2 and single-mode cores 2 to reduce crosstalk between the single-mode cores 2. I.e. if the single-mode core 2 is one, the number of air holes 3 is at least one; when the number of the single-mode fiber cores 2 is two, the number of the air holes 3 is at least three, and the number of the air holes 3 can be adaptively increased on the basis.
As a preferred embodiment, the center of the air hole 3 is located at the midpoint of the center line of the single-mode core 2 and the multimode core 1.
Specifically, the center position of the air hole 3 is set at the midpoint of the center line between the single-mode fiber core 2 and the multi-mode fiber core 1; similarly, the air hole 3 provided between two adjacent single-mode cores 2 may be provided at the midpoint of the center line of the two adjacent single-mode cores 2.
As a preferred embodiment, the air holes 3 are spaced apart from the single-mode core 2 by a first predetermined distance;
the first preset distance is not less than 2 times the diameter of the single-mode core 2.
As a preferred embodiment, the air hole 3 is spaced apart from the multimode core 1 by a second predetermined distance;
the second preset distance is not less than 0.2 times the diameter of the multimode core 1.
Specifically, the distance between the air hole 3 and the single-mode fiber core 2 is not smaller than 2 times of the diameter of the single-mode fiber core 2, the distance between the air hole 3 and the multi-mode fiber core 1 is not smaller than 0.2 times of the diameter of the multi-mode fiber core 1, and the optical fiber sensor system is suitable for long-distance transmission of optical signals for a distributed optical fiber sensing system (DAS system and DTS system).
In a preferred embodiment, the aperture of the air hole 3 is 0.05 to 0.8 times the center distance between the single-mode core 2 and the multimode core 1, and is generally 0.35 to 0.6 times.
As a preferred embodiment, at least one single-mode core 2 is rotatable around the multimode core 1 to form a helical core with a helical period in the range 3mm to 1m.
Specifically, in order to improve the sensing sensitivity of the DAS system, the single-mode fiber core 2 may rotate around the geometric center of the multi-core microstructured optical fiber (i.e., the multi-mode fiber core 1 located at the central position) to form a spiral fiber core optical fiber, where the spiral period ranges from 3mm to 1m, and the value range is generally from 4 mm to 20mm.
In the preferred embodiment, the multi-core microstructured optical fiber is manufactured by a stacking method, the multi-mode optical fiber includes a first capillary 12 and a plurality of first capillary rods 11 positioned in the first capillary 12, the first capillary 12 is melted to form a part of the cladding 4 in the subsequent optical fiber drawing manufacturing process, and the plurality of first capillary rods 11 are melted to form the multi-mode fiber core 1;
the single-mode optical fiber comprises a second capillary 22 and a second capillary rod 21 positioned in the second capillary 22, wherein the second capillary 22 is melted to form a part of the cladding 4 in the subsequent optical fiber drawing preparation process, and the second capillary rod 21 is melted to form a single-mode fiber core 2;
before preparation, a plurality of multimode optical fibers and a plurality of single-mode optical fibers are prepared for standby by a stacking method, and the specific stacking method of the multi-core microstructure optical fiber comprises the following steps:
stacking the multimode optical fibers, at least one single mode optical fiber and the third capillary tube 31 together in a regular triangle distribution mode, wherein the multimode optical fibers are positioned at the central position, the single mode optical fibers are positioned at the non-central position, and the third capillary tube 31 is arranged between the single mode optical fibers and the multimode optical fibers and between two adjacent single mode optical fibers;
after stacking, the third capillary rod 5 with different diameters is inserted into the outer sleeve 41, then the third capillary rod 5 with different diameters is used for filling gaps in the outer sleeve 41, the diameter of the third capillary rod 5 is smaller than or equal to that of a single-mode optical fiber, when the third capillary rod 5 with the same diameter as that of the single-mode optical fiber and the multimode optical fiber is stacked with the single-mode optical fiber to form a regular hexagon, the third capillary rod 5 with smaller diameter is used for filling gaps, such as gaps between the single-mode optical fiber and the outer sleeve 41, between the single-mode optical fiber and the single-mode optical fiber or between the single-mode optical fiber and the multimode optical fiber.
The outer diameter of the multimode fiber (i.e., the outer diameter of the first capillary 12), the outer diameter of the single-mode fiber (i.e., the outer diameter of the second capillary 22) and the outer diameter of the third capillary 31 are all the same, and the ratio of the tube thickness of the outer jacket 41 to the outer diameter of the first capillary 12 is in the range of 0.3-7, and is generally 1.5-5.
Further, in the subsequent optical fiber drawing process, the first capillary 12, the second capillary 22, the third capillary 31, and the outer jacket 41 are all melted to form the cladding 4.
Hereinafter, four specific examples are provided to further illustrate and describe the present technical solution:
example 1
The multi-core microstructure optical fiber for the distributed sensing system comprises 6 single-mode fiber cores 2 and 1 multi-mode fiber core 1 which are distributed in a regular triangle shape, wherein the single-mode fiber cores 2 and the multi-mode fiber cores 1 are separated by air holes 3;
the cladding layer 4 is made of pure quartz material;
the multimode fiber core 1 is arranged at the right center of the optical fiber, the fiber core diameter is 50 mu m, and the numerical aperture value is 0.2+/-0.01; the preparation material adopts germanium-doped quartz glass;
the single-mode cores 2 are arranged at non-central positions of the optical fiber, the number of the single-mode cores 2 is 6, and the core diameter is 9 μm. The numerical aperture of the single-mode fiber core 2 takes a value of 0.12; the single-mode fiber core 2 is made of germanium-doped quartz glass;
the distance between the geometric midpoint of the single-mode fiber core 2 and the edge of the optical fiber is 71 mu m, and the center distance between the single-mode fiber core 2 and the multimode fiber core 1 is 120 mu m;
the air hole 3 is located between two adjacent single-mode cores 2, between the single-mode cores 2 and the multimode cores 1, and the air hole 3 is located at the midpoint of the center line of the two adjacent cores, preferably, the aperture of the air hole 3 is 40 μm.
The multi-core microstructured optical fiber in embodiment 1 is shown in fig. 2 after stacking, i.e. one multimode optical fiber, 6 single-mode optical fibers and a third capillary tube 31 are stacked together according to a regular triangle distribution mode, the multimode optical fiber is located at a central position, the single-mode optical fiber is located at a non-central position, the third capillary tube 31 is arranged between the single-mode optical fiber and the multimode optical fiber and between two adjacent single-mode optical fibers, more preferably, the 6 single-mode optical fibers can be distributed in a regular hexagon around the multimode optical fiber at the central position, and one multimode optical fiber, 6 single-mode optical fibers and the third capillary tube 31 are integrally stacked to form a regular hexagon;
after stacking, it is inserted into the outer sleeve 41, and the gap in the outer sleeve 41 is filled with third capillary rods 5 of different diameters.
Example 2
A multi-core microstructure optical fiber for a distributed sensing system, as shown in fig. 3, comprises 3 single-mode fiber cores 2 and 1 multi-mode fiber core 1 distributed in a regular triangle, wherein the single-mode fiber cores 2 and the multi-mode fiber cores 1 are separated by air holes 3.
The cladding layer 4 is made of pure quartz material;
the multimode fiber core 1 is arranged at the right center of the optical fiber, the fiber core diameter is 50 mu m, and the numerical aperture value is 0.2+/-0.01; the preparation material adopts germanium-doped quartz glass;
the single-mode fiber cores 2 are arranged at the non-central position of the optical fiber, the number of the single-mode fiber cores 2 is 3, the 3 single-mode fiber cores 2 surround the multimode fiber cores 1 in a central symmetry mode, the center distances of each single-mode fiber core 2 and the multimode fiber cores 1 are equal, and the fiber core diameter is 5 mu m. The numerical aperture of the single-mode fiber core 2 takes a value of 0.14; the single-mode fiber core 2 is made of high germanium doped quartz glass, and the single-mode fiber core 2 is a high nonlinear fiber core so as to improve the sensitivity of the DAS system;
the distance between the geometric midpoint of the single-mode fiber core 2 and the edge of the optical fiber is 60 mu m, and the center distance between the single-mode fiber core 2 and the multimode fiber core 1 is 100 mu m;
the air holes 3 are located between two adjacent single-mode cores 2, between a single-mode core 2 and a multimode core 1, and the air holes 3 are located at the midpoints of the central lines of the two adjacent cores, preferably, the aperture of the air holes 3 is 45 μm, and more preferably, a plurality of air holes 3 are surrounded around the multimode core 1.
The multi-core microstructured optical fiber in example 2 is shown in fig. 4 after stacking, i.e. the multi-mode optical fiber is located at the center, 6 third capillaries 31 are circumferentially distributed around the multi-mode optical fiber, 3 single-mode optical fibers are arranged in a "regular triangle" distribution manner, and a plurality of third capillary rods 5 are stacked with the multi-mode optical fiber, 3 single-mode optical fibers and 6 third capillaries 31 to form a regular hexagon, where the diameter of each third capillary rod 5 is the same as the diameter of each third capillary 31.
After stacking, it is inserted into the outer sleeve 41, and the gap in the outer sleeve 41 is filled with a third capillary rod 5 of a different diameter, where the diameter of the third capillary rod 5 is smaller than the diameter of the third capillary tube 31.
Example 3
A multi-core microstructured optical fiber for a distributed sensing system, as shown in fig. 5, comprises 1 single-mode fiber core 2, 1 multi-mode fiber core 1,1 single-mode fiber core 2 is arranged at one side of the multi-mode fiber core 1, and the single-mode fiber core 2 and the multi-mode fiber core 1 are separated by an air hole 3.
The cladding layer 4 is made of pure quartz material;
the multimode fiber core 1 is arranged at the right center of the optical fiber, the fiber core diameter is 50 mu m, and the numerical aperture value is 0.2+/-0.01; the preparation material adopts germanium-doped quartz glass;
the single-mode cores 2 are arranged at non-central positions of the optical fiber, the number of the single-mode cores 2 is 1, and the core diameter is 5 μm. The numerical aperture of the single-mode fiber core 2 takes a value of 0.14; the single-mode fiber core 2 is made of high germanium doped quartz glass, and the single-mode fiber core 2 is a high nonlinear fiber core so as to improve the sensitivity of the DAS system;
the distance between the geometric midpoint of the single-mode fiber core 2 and the edge of the optical fiber is 70 mu m, and the center distance between the single-mode fiber core 2 and the multimode fiber core 1 is 100 mu m;
1 air hole 3 is located between the single-mode core 2 and the multimode core 1 to separate the single-mode core 2 and the multimode core 1, and the air hole 3 is located at the midpoint of the center line of the adjacent two cores, preferably, the aperture of the air hole 3 is 45 μm.
The multi-core microstructured optical fiber of example 3 is shown in fig. 6 after stacking, i.e. the multi-mode optical fiber is located at the center, 1 single-mode optical fiber is placed on one side of the multi-mode optical fiber, the third capillary tube 31 is located between the single-mode optical fiber and the multi-mode optical fiber, and several third capillary rods 5 are stacked with the multi-mode optical fiber, the single-mode optical fiber and the third capillary tube 31 to form a regular hexagon, and the diameter of the third capillary rod 5 is the same as that of the third capillary tube 31.
After stacking, it is inserted into the outer sleeve 41, and the gap in the outer sleeve 41 is filled with a third capillary rod 5 of a different diameter, where the diameter of the third capillary rod 5 is smaller than the diameter of the third capillary tube 31.
Example 4
In example 3, since the multimode core 1 and the air holes 3 are closer, the distance thereof is shorter, and the single air hole 3 affects the mode field shape of the multimode core 1, and thus affects certain parameters in the optical fiber, such as polarization, dispersion, etc., in order to avoid this problem, example 4 is optimized on the basis of example 3.
Example 4 provides a multi-core microstructured optical fiber for a distributed sensing system, as shown in fig. 7, which is also only 1 single-mode core 2, 1 multi-mode core 1, and differs from example 3 in that: in example 3, only one air hole 3 is provided between the single-mode core 2 and the multimode core 1; while in this embodiment 4, 6 air holes 3 are distributed around the multimode core 1;
further, the optical fiber prepared in this embodiment may be in a spiral shape, that is, the single-mode core 2 extends spirally around the central multimode core 1 in the axial direction, and the spiral period is 10mm.
In the multi-core microstructured optical fiber of example 4, referring to fig. 8, in which the multi-mode optical fiber is located at the center, 6 third capillaries 31 are distributed around the multi-mode optical fiber core 1,1 single-mode optical fiber is placed on one side of the multi-mode optical fiber, one of the third capillaries 31 is located at the midpoint of the central line between the single-mode optical fiber and the multi-mode optical fiber, and several third capillary rods 5 are stacked with the multi-mode optical fiber, the single-mode optical fiber and the third capillaries 31 to form a regular hexagon, and the diameter of each third capillary rod 5 is the same as that of the third capillary tube 31.
After stacking, inserting the capillary rods into the outer sleeve 41, and filling gaps in the outer sleeve 41 by using third capillary rods 5 with different diameters, wherein the diameter of the third capillary rods 5 is smaller than that of the third capillary tubes 31;
further, the single-mode optical fiber rotates the preform at a high speed during the preparation process, and the preform is spirally extended around the central multimode core 1 in the axial direction by controlling the rotation speed and the optical fiber drawing speed.
The invention has the beneficial effects that:
the multi-core microstructure optical fiber prepared by the invention has the multi-mode fiber cores and the single-mode fiber cores, realizes the distributed sensing of DTS and DAS in the same optical fiber, effectively controls the energy coupling between different fiber cores in the optical fiber, and ensures lower loss in long-distance transmission of multi-mode and single-mode in a plurality of fiber cores; by introducing the air hole structure, the energy crosstalk between fiber cores is greatly reduced, and meanwhile, the applicability of the optical fiber is ensured for different optical fiber outer diameters.
The foregoing description is only illustrative of the preferred embodiments of the present invention and is not to be construed as limiting the scope of the invention, and it will be appreciated by those skilled in the art that equivalent substitutions and obvious variations may be made using the description and illustrations of the present invention, and are intended to be included within the scope of the present invention.
Claims (8)
1. A multi-core microstructured optical fiber for a distributed sensing system, comprising:
the multimode fiber core is arranged at the central position of the optical fiber;
at least one single-mode fiber core arranged at a non-central position of the optical fiber;
an air hole, said multimode core and at least one of said single mode cores being separated by said air hole;
the cladding is coated on the peripheries of the multimode fiber cores, at least one single-mode fiber core and the air holes;
the air hole is separated from the Shan Moqian core by a first preset distance;
the first preset distance is not smaller than 2 times of the diameter of the single-mode fiber core;
the air hole is separated from the multimode fiber core by a second preset distance;
the second preset distance is not less than 0.2 times the diameter of the multimode fiber core.
2. The multi-core microstructured optical fiber for a distributed sensing system according to claim 1, wherein when the single-mode fiber cores are more than one, the single-mode fiber cores and the multi-mode fiber cores are in regular triangle distribution, and two adjacent single-mode fiber cores are separated by the air hole.
3. The multi-core microstructured optical fiber for a distributed sensing system according to claim 1, wherein the single-mode core has a core diameter ranging from 3 to 15 μm and a numerical aperture ranging from 0.1 to 0.18.
4. The multi-core microstructured optical fiber for a distributed sensing system according to claim 1, wherein the multi-mode core has a core diameter ranging from 25 to 80 μm and a numerical aperture ranging from 0.15 to 0.3.
5. A multi-core microstructured optical fiber for a distributed sensing system according to claim 1, characterized in that a center of the air hole is located at a midpoint of a center line of the single-mode core and the multi-mode core.
6. The multi-core microstructured optical fiber for a distributed sensing system according to claim 1, characterized in that the air holes have a diameter of 0.05 to 0.8 times the center-to-center distance between the single-mode core and the multi-mode core.
7. A multi-core microstructured optical fiber for a distributed sensing system according to claim 1, characterized in that at least one of the single-mode cores is rotatable around the multi-mode core to form a spiral core having a spiral period ranging from 3mm to 1m.
8. A multi-core microstructured optical fiber for a distributed sensing system according to claim 1, characterized in that a midpoint of the single-mode core is in a range of 10 to 200 μm from an outer edge of a cladding of the optical fiber.
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