CN116893471A - Low-loss optical fiber and manufacturing method thereof - Google Patents
Low-loss optical fiber and manufacturing method thereof Download PDFInfo
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 98
- 238000004519 manufacturing process Methods 0.000 title claims description 12
- 238000005253 cladding Methods 0.000 claims abstract description 247
- 239000010410 layer Substances 0.000 claims abstract description 229
- 239000012792 core layer Substances 0.000 claims abstract description 92
- 230000002829 reductive effect Effects 0.000 claims abstract description 20
- 230000003287 optical effect Effects 0.000 claims description 37
- 238000000034 method Methods 0.000 claims description 31
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 23
- 239000011521 glass Substances 0.000 claims description 23
- 238000000151 deposition Methods 0.000 claims description 16
- 238000012545 processing Methods 0.000 claims description 15
- 230000008021 deposition Effects 0.000 claims description 10
- 229910052732 germanium Inorganic materials 0.000 claims description 10
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 claims description 10
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims description 9
- 229910052796 boron Inorganic materials 0.000 claims description 9
- 238000005234 chemical deposition Methods 0.000 claims description 9
- 238000001816 cooling Methods 0.000 claims description 9
- 235000012239 silicon dioxide Nutrition 0.000 claims description 9
- 239000006004 Quartz sand Substances 0.000 claims description 7
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 7
- 229910052710 silicon Inorganic materials 0.000 claims description 7
- 239000010703 silicon Substances 0.000 claims description 7
- 239000000377 silicon dioxide Substances 0.000 claims description 7
- 238000007493 shaping process Methods 0.000 claims description 6
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 3
- 229910052782 aluminium Inorganic materials 0.000 claims description 3
- 239000011248 coating agent Substances 0.000 claims description 3
- 238000000576 coating method Methods 0.000 claims description 3
- 238000010438 heat treatment Methods 0.000 claims description 3
- 238000002844 melting Methods 0.000 claims description 3
- 230000008018 melting Effects 0.000 claims description 3
- 238000010309 melting process Methods 0.000 claims description 3
- 238000004804 winding Methods 0.000 claims description 3
- 238000005491 wire drawing Methods 0.000 claims description 3
- 239000000758 substrate Substances 0.000 claims description 2
- 238000002360 preparation method Methods 0.000 abstract 1
- 230000035882 stress Effects 0.000 description 141
- 238000009826 distribution Methods 0.000 description 18
- 230000005540 biological transmission Effects 0.000 description 9
- 230000008569 process Effects 0.000 description 9
- 230000008646 thermal stress Effects 0.000 description 6
- 238000012360 testing method Methods 0.000 description 5
- 238000010586 diagram Methods 0.000 description 4
- 229910052731 fluorine Inorganic materials 0.000 description 4
- 239000011737 fluorine Substances 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- PXGOKWXKJXAPGV-UHFFFAOYSA-N Fluorine Chemical compound FF PXGOKWXKJXAPGV-UHFFFAOYSA-N 0.000 description 3
- 238000005452 bending Methods 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 230000010287 polarization Effects 0.000 description 3
- YZCKVEUIGOORGS-OUBTZVSYSA-N Deuterium Chemical compound [2H] YZCKVEUIGOORGS-OUBTZVSYSA-N 0.000 description 2
- 238000000137 annealing Methods 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 229910052805 deuterium Inorganic materials 0.000 description 2
- 230000009365 direct transmission Effects 0.000 description 2
- 238000000691 measurement method Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
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- 230000008054 signal transmission Effects 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
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- 230000009471 action Effects 0.000 description 1
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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
- G02B6/036—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
- G02B6/03661—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 4 layers only
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/02—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor
- C03B37/022—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor from molten glass in which the resultant product consists of different sorts of glass or is characterised by shape, e.g. hollow fibres, undulated fibres, fibres presenting a rough surface
- C03B37/023—Fibres composed of different sorts of glass, e.g. glass optical fibres, made by the double crucible technique
-
- 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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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
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- General Life Sciences & Earth Sciences (AREA)
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- Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)
Abstract
The application discloses a low-loss optical fiber and a preparation method thereof, wherein the low-loss optical fiber comprises the following components: a core layer; the first cladding layer is coated on the outer side of the core layer, and a core cladding stress area is formed between the core layer and the first cladding layer; the second cladding layer is coated on the outer side of the first cladding layer, the first cladding layer is provided with a second cladding layer stress layer positioned on the outer side of the first cladding layer and a second cladding layer body layer positioned on the outer side of the second cladding layer stress layer, and the second cladding layer stress layer is used for applying inward compressive stress to the first cladding layer to offset or partially offset the influence of the core cladding stress area on the core layer, so that loss is reduced. According to the application, the second cladding stress layer is added when the second cladding is manufactured, and the second cladding stress layer can apply inward compressive stress to the first cladding to offset or partially offset the influence of the core cladding stress layer on the core layer, so that the influence of structural stress on the optical fiber loss is reduced.
Description
Technical Field
The application relates to the field of optical fibers, in particular to a low-loss optical fiber and a manufacturing method thereof.
Background
The structure of an optical fiber generally includes a core layer and a cladding layer. The core layer is made of silicon-based quartz glass doped with germanium (for example); the cladding is made of undoped pure silica-based quartz glass, the refractive index of the core is higher than that of the cladding, and a certain value must be reached between the two, expressed by the relative refractive index, for example, delta=0.35%.
As shown in fig. 1 (the upper graph is a cross-sectional view of the optical fiber, and the lower graph is a refractive index distribution line corresponding to each layer of the optical fiber), in order to further reduce the attenuation of the optical fiber, the following methods are generally adopted to manufacture the low-loss optical fiber: by lowering the refractive index of the core layer 1, the doping amount of the core layer 1 is reduced. In order to make the refractive index difference between the core layer 1 and the cladding layer reach a certain value, a structure that the first cladding layer 2 is doped with fluorine is adopted to reduce the refractive index value of the first cladding layer 2, so that the refractive index difference between the core layer 1 and the first cladding layer 2 is unchanged (for example, the refractive index difference is still 0.35%). The second cladding layer 3 is made of undoped pure silica-based glass, the first cladding layer 2 surrounding the core layer 1 has a refractive index lower than that of the core layer 1, and the refractive index of the second cladding layer 3 surrounding the first cladding layer 2 is lower than that of the core layer 1 but higher than that of the first cladding layer 2.
Thus, the structure is improved, and the loss is reduced to a certain extent. But since two impurities having opposite refractive indexes are introduced between the core layer 1 and the first cladding layer 2 (for example, the core layer is germanium element for increasing the refractive index, and the first cladding layer is fluorine element for decreasing the refractive index). Thus, a larger structural stress exists between the core layer 1 and the first cladding layer 2, and a core cladding stress region exists between the core layer 1 and the first cladding layer 2, and the core layer 1 is subjected to outward tensile stress due to the existence of the core cladding stress region, so that the attenuation of the optical fiber is increased, and further reduction of the loss of the optical fiber is limited. Therefore, the attenuation of the optical fiber with the structure is only at least 0.170dB/Km, and cannot be reduced any more.
Patent document publication No. CN114994830a discloses a low-loss bending-resistant single-mode optical fiber and a manufacturing method thereof. In the document, the relative refractive index difference of the core layer is reduced from delta 1 to delta 2 from inside to outside, the distortion degree of the refractive index profile in a bending state is reduced, the viscosity matching of the core package is further optimized, the defects in the drawing process are reduced, the loss value of the optical fiber is reduced, the bending resistance of the optical fiber is improved, the relative refractive index difference of the inner cladding layer is increased from delta 2 to delta 3 from inside to outside, the viscosity of the core layer and the cladding layer of the optical fiber are well matched, and the stress between the core package is reduced.
The disadvantage of the above method is that by adding a refractive index transition layer between the core layer and the cladding layer, the refractive index structure of the optical fiber is complicated, and other performance indexes of the optical fiber such as macrobend loss, mode field diameter and the like are affected. Therefore, the optical fiber structure design needs to be changed to make up for other index differences, which leads to the optical fiber structure becoming more and more complex, the manufacturing process becoming more and more complicated, the quality control being more difficult and the cost increasing correspondingly.
Disclosure of Invention
The application aims at solving the problems and at least one defect, and provides a low-loss optical fiber and a manufacturing method thereof, and the aim of reducing attenuation is fulfilled by a method for adjusting the stress distribution of an optical fiber structure.
The technical scheme adopted by the application is as follows:
a low loss optical fiber comprising:
a core layer;
the first cladding layer is coated on the outer side of the core layer, and a core cladding stress area is formed between the core layer and the first cladding layer;
the second cladding is coated on the outer side of the first cladding, the first cladding is provided with a second cladding stress layer positioned on the outer side of the first cladding and a second cladding body layer positioned on the outer side of the second cladding stress layer, and the second cladding stress layer is used for applying inward compressive stress to the first cladding to offset or partially offset the influence of a core cladding stress area on the core layer, so that loss is reduced.
Stress is classified into temporary stress and permanent stress according to the existing characteristics:
1. temporary stress. When the glass is heated or cooled below the strain point temperature, the thermal conductivity of the glass is poor, and temperature gradients are formed at all parts, so that certain thermal stress is generated. Such thermal stress exists with the existence of a temperature difference, and the larger the temperature difference is, the larger the temporary stress is and vanishes with vanishing of the temperature difference. Such thermal stresses are referred to as temporary stresses.
2. Structural stress. Structural stress is stress produced by the fact that two partial areas in glass have different expansion coefficients due to the fact that the chemical composition is not uniform. Such as different doping properties, different viscosities, different refractive indices, etc. The method is characterized in that structural stress cannot be eliminated by measures such as annealing. The stress formed by the second cladding stress layer is structural stress.
According to the application, the second cladding stress layer is added when the second cladding is manufactured, and the second cladding stress layer can apply inward compressive stress to the first cladding to offset or partially offset the influence of the core cladding stress layer on the core layer, so that the influence of structural stress on the optical fiber loss is reduced.
The added second cladding stress layer is positioned on the second cladding, and does not participate in the direct transmission of optical signals, so that the transmission performance of the optical fiber cannot be directly influenced, the requirements on the material purity and the dimensional accuracy of the area are lower, the realization process is simpler, and the cost is lower.
In the prior art, the loss of the optical fiber is reduced mainly by reducing the Rayleigh scattering of the core layer of the optical fiber, so that the loss is as close to the intrinsic loss of the material as possible. At present, the method is mainly realized in China by reducing the doping amount of the optical fiber core layer. According to the application, under the condition that the refractive index structure and the doping amount of the core layer are not changed, the Rayleigh scattering of the optical fiber is reduced in a mode of reducing and counteracting the stress of the core layer by changing the structural stress of the optical fiber cladding, so that the aim of reducing the optical fiber loss is fulfilled.
In one embodiment of the present application, the core layer has a relative refractive index difference of Δ 1 The relative refractive index difference of the first cladding layer is delta 2 The relative refractive index difference of the second cladding stress layer is delta 3 The relative refractive index difference of the second cladding body layer is delta 4 The relative refractive index difference of the second cladding stress layer is the same as the relative refractive index difference of the second cladding body layer.
The relative refractive index difference of the present application refers to the relative difference between the refractive index of the layer and that of pure silicon dioxide, e.g. pure silicon has a refractive index n 0 The refractive index of the i layer is n i The calculation formula of the relative refractive index difference Δ of the i layer is:
the relative refractive index difference of the second cladding stress layer is the same as the relative refractive index difference of the second cladding body layer, so that the refractive index distribution structure of the core rod and the optical rod can not be changed. The method has little influence on other transmission indexes of the optical fiber, and does not need to be optimized by a more complex optical fiber structure.
In one embodiment of the present application, the relative refractive index difference Δ of the core layer 1 In the range of-0.1% to 0.1%, the relative refractive index difference delta of the first cladding layer 2 In the range of-0.4% to-0.2%, the second cladding stress layer having a relative refractive index difference delta 3 In the range of-0.3% to-0.15%, the relative refractive index difference of the second cladding body layer being delta 4 Ranging from-0.3% to-0.15%.
In one embodiment of the present application, the thickness of the core layer is t 1 ，t 1 Ranging from 4 μm to 7 μm; the thickness of the first cladding layer is t 2 ，t 2 Is in the range of 12 μm to 35 μm; the thickness of the second cladding stress layer is t 3 ，t 3 Ranging from 4 μm to 12 μm; the thickness of the second cladding body layer is t 4 ，t 4 In the range of 8 μm to 42 μm.
In one embodiment of the present application, the thickness of the first cladding layer is 2 to 5 times the radius of the core layer; the thickness of the second cladding stress layer is 1 to 3 times the radius of the core layer.
The stress expression in the application is expressed by adopting a double refraction method test, and the magnitude of the stress is expressed by the magnitude of the optical path difference. In one embodiment of the present application, the stress optical path difference of the core layer is R 1 ，R 1 In the range of 100nm.cm -1 To 200nm.cm -1 The stress optical path difference of the core-spun stress area is R 2 ，R 2 In the range of 100nm.cm -1 To 300nm.cm -1 The stress optical path difference of the first cladding stress layer is R 3 ，R 3 In the range of 0nm.cm -1 To 100nm.cm -1 The stress optical path difference of the second cladding stress layer is R 4 ，R 4 In the range of 100nm.cm -1 To 300nm.cm -1 The stress optical path difference of the second cladding body layer is R 5 ，R 5 Is of (2)Around 50nm.cm -1 To 100nm.cm -1 。
In practical use, the stress distribution can be gradient distribution or gradual change distribution.
In one embodiment of the present application, the core layer is made of silica-based glass doped with an element for improving refractive index, so that more than 80% of optical signals can be transmitted in the optical fiber; the first cladding is a pure silicon dioxide layer or is made of silicon-based glass doped with elements for reducing refractive index, a certain refractive index difference is formed between the first cladding and the core layer, the transmission condition of the optical fiber core is met, and the thickness is about 2-5 times of the radius of the core layer. Acting as a protective core layer while about 20% of the optical signal is able to be transmitted at this layer; the second cladding layer is formed by doping aluminum and boron and germanium together or improving the density, and mainly acts to offset structural stress between the core layer and the first cladding layer, the thickness of the second cladding layer is 1 to 3 times of the radius of the core layer, the second cladding layer does not directly participate in transmission of optical signals, the second cladding layer body layer has the same refractive index as the first cladding layer, and can also have a tiny refractive index difference with the first cladding layer, and the second cladding layer body layer mainly acts to protect the first cladding layer and the core layer and not directly participate in transmission of the optical signals.
The refractive index increasing element may be various, such as germanium; the refractive index reducing element may be various, such as fluorine.
The application also discloses a manufacturing method of the low-loss optical fiber, which comprises the following steps:
s1, preparing a core rod, wherein the core rod comprises a core layer and a first cladding layer coated on the outer side of the core layer;
s2, processing a second cladding outside the first cladding to obtain an optical fiber preform, wherein the first cladding is provided with a second cladding stress layer positioned outside the first cladding and a second cladding body layer positioned outside the second cladding stress layer, and the second cladding stress layer is used for applying inward compressive stress to the first cladding;
s3, heating the optical fiber preform through a wire drawing furnace, and melting the lower end of the optical fiber preform to form a silk thread;
s4, cooling and shaping the drooping silk thread through a shaping pipe, and then further cooling through a cooling pipe;
and S5, coating the cooled optical fiber, performing a curing procedure operation, and then winding to obtain the optical fiber.
In practical use, the core layer and the first cladding layer can be deposited by MCVD, PCVD, OVD, VAD and other processes, and finally the core rod is formed. In either case, the core rod is produced by the process described above, and the core layer is doped with an element that increases the refractive index, and the first cladding layer is pure silica or doped with an element that decreases the refractive index, so that a stress layer (i.e., a core-cladding stress region) is formed at the core-cladding interface between the core layer and the first cladding layer.
In practice, the wire diameter in step S3 is typically 125. Mu.m. After the optical fiber is wound, the optical fiber with the diameter meeting the requirements is subjected to the steps of tension intensity screening, deuterium treatment and the like, and then the optical fiber is sent to a detection procedure, so that various index tests are completed, and qualified products are put in storage.
In one embodiment of the present application, the processing manner of the second cladding stress layer is as follows: fused deposition of quartz sand doped with 10 to 30ppm of Al element onto the core rod;
the processing mode of the second cladding body layer is as follows: and depositing a second cladding body layer outside the substrate by using a chemical deposition method, or depositing the second cladding body layer by using a quartz sand melting process.
In one embodiment of the present application, the processing manner of the second cladding stress layer is as follows: the boron element is obtained by deposition through a chemical deposition method, and boron element with the molar concentration of 10% and germanium element with the molar concentration of 4% are doped during deposition;
the processing mode of the second cladding body layer is as follows: is deposited by a chemical deposition method.
The beneficial effects of the application are as follows: according to the application, the second cladding stress layer is added when the second cladding is manufactured, and the second cladding stress layer can apply inward compressive stress to the first cladding to offset or partially offset the influence of the core cladding stress layer on the core layer, so that the influence of structural stress on the optical fiber loss is reduced.
Drawings
FIG. 1 is a graph of a combination of fiber cross-sections and refractive index profiles of layers of an optical fiber;
FIG. 2 is a graph of the refractive index and stress distribution combinations of layers of an optical fiber without a second cladding stress layer;
FIG. 3 is a schematic representation of a cross-section of an optical fiber of the present application;
FIG. 4 is a graph showing the combination of refractive index profile and stress profile of layers of an optical fiber according to the present application;
FIG. 5 is a schematic diagram of the optical path difference principle;
fig. 6 is a basic schematic diagram of a compensator measurement method.
The reference numerals in the drawings are as follows:
1. a core layer; 2. a first cladding layer; 100. a core wrap stress region; 3. a second cladding layer; 31. a second cladding stress layer; 32. and a second cladding body layer.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of 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. It will be apparent that the described embodiments are some, but not all, embodiments of the application. The components of the embodiments of the present application generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
In the description of the present application, it should be noted that, the azimuth or positional relationship indicated by the terms "inner", "outer", etc. are based on the azimuth or positional relationship shown in the drawings, or the azimuth or positional relationship that is commonly put in use of the product of this application, are merely for convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element to be referred to must have a specific azimuth, be configured and operated in a specific azimuth, and therefore should not be construed as limiting the present application. Furthermore, the terms "first," "second," and the like, are used merely to distinguish between descriptions and should not be construed as indicating or implying relative importance.
In the description of the present application, it should also be noted that, unless explicitly specified and limited otherwise, the terms "disposed", "connected" and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected or integrally connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present application will be understood in specific cases by those of ordinary skill in the art.
The present application will be described in detail with reference to the accompanying drawings.
As shown in fig. 3, a low-loss optical fiber includes:
a core layer 1;
a first cladding layer 2 which is coated on the outer side of the core layer 1, wherein a core cladding stress region 100 is formed between the core layer 1 and the first cladding layer 2;
the second cladding layer 3 is wrapped on the outer side of the first cladding layer 2, the first cladding layer 2 is provided with a second cladding stress layer 31 positioned on the outer side of the first cladding layer 2 and a second cladding body layer 32 positioned on the outer side of the second cladding stress layer 31, and the second cladding stress layer 31 is used for applying inward compressive stress to the first cladding layer 2 to offset or partially offset the influence of the core cladding stress region 100 on the core layer 1, so that loss is reduced.
Stress is classified into temporary stress and permanent stress according to the existing characteristics:
1. temporary stress. When the glass is heated or cooled below the strain point temperature, the thermal conductivity of the glass is poor, and temperature gradients are formed at all parts, so that certain thermal stress is generated. Such thermal stress exists with the existence of a temperature difference, and the larger the temperature difference is, the larger the temporary stress is and vanishes with vanishing of the temperature difference. Such thermal stresses are referred to as temporary stresses.
2. Structural stress. Structural stress is stress produced by the fact that two partial areas in glass have different expansion coefficients due to the fact that the chemical composition is not uniform. Such as different doping properties, different viscosities, different refractive indices, etc. The method is characterized in that structural stress cannot be eliminated by measures such as annealing. The stress formed by the second cladding stress layer 31 is structural stress.
As shown in fig. 2, the refractive index and stress distribution combination diagram of each layer of the optical fiber, which is not provided with the second cladding stress layer 31, is shown by the solid line, which is the refractive index structure distribution of the optical fiber, and the broken line, which is the normal structure stress distribution diagram of the structure, is shown by the larger numerical value as the position is higher, and the larger structure stress exists at the boundary due to the different doping amounts of the core layer 1 and the first cladding layer 2, so that the stress is generated to the core layer 1, thereby increasing the rayleigh scattering of the light transmission and increasing the light loss. Referring to fig. 4, in order to make up the refractive index distribution and stress distribution of each layer of the optical fiber according to the present application, the solid line is the refractive index structure distribution of the optical fiber, and the dotted line is the normal structure stress distribution of the structure, in the present application, a second cladding stress layer 31 is added when the second cladding layer 3 is fabricated, and the second cladding stress layer 31 can apply inward compressive stress to the first cladding layer 2 to counteract or partially counteract the influence of the core cladding stress layer on the core layer 1, thereby reducing the influence of the structure stress on the optical fiber loss.
The added second cladding stress layer 31 is positioned on the second cladding layer 3, and does not participate in the direct transmission of optical signals, so that the transmission performance of the optical fiber is not directly affected, the requirements on the material purity and the dimensional accuracy of the area are lower, the realization process is simpler, and the cost is lower.
In the prior art, the loss of the optical fiber is reduced mainly by reducing the Rayleigh scattering of the optical fiber core layer 1, so that the loss is as close to the intrinsic loss of the material as possible. At present, the doping amount of the optical fiber core layer 1 is mainly reduced at home. According to the application, under the condition that the refractive index structure and doping amount of the core layer 1 are not changed, the Rayleigh scattering of the optical fiber is reduced in a mode of reducing and counteracting the stress of the core layer 1 by changing the structural stress of the optical fiber cladding, so that the aim of reducing the optical fiber loss is fulfilled.
In the optical fiber, the relative refractive index difference of the core layer 1 is delta 1 The relative refractive index difference of the first cladding 2 is delta 2 The relative refractive index difference of the second cladding stress layer 31 is delta 3 The relative refractive index difference of the second cladding body layer 32 is delta 4 The relative refractive index difference of the second clad stress layer 31 is the same as the relative refractive index difference of the second clad body layer 32.
The relative refractive index difference of the present application refers to the relative difference between the refractive index of the layer and that of pure silicon dioxide, e.g. pure silicon has a refractive index n 0 Refractive index of i layerIs n i The calculation formula of the relative refractive index difference Δ of the i layer is:
the relative refractive index difference of the second clad stress layer 31 is the same as the relative refractive index difference of the second clad body layer 32, and this arrangement makes it possible to avoid changing the refractive index distribution structure of the core rod and the optical rod. The method has little influence on other transmission indexes of the optical fiber, and does not need to be optimized by a more complex optical fiber structure.
In practice, the relative refractive index difference Deltaof the core layer 1 1 In the range of-0.1% to 0.1%, the relative refractive index difference delta of the first cladding 2 2 Ranging from-0.4% to-0.2%, the relative refractive index difference delta of the second cladding stress layer 31 3 Ranging from-0.3% to-0.15%, the relative refractive index difference of the second cladding body layer 32 being delta 4 Ranging from-0.3% to-0.15%.
In practical use, the thickness of the core layer 1 is t 1 ，t 1 Ranging from 4 μm to 7 μm; the thickness of the first cladding layer 2 is t 2 ，t 2 Is in the range of 12 μm to 35 μm; the second cladding stress layer 31 has a thickness t 3 ，t 3 Ranging from 4 μm to 12 μm; the second cladding body layer 32 has a thickness t 4 ，t 4 In the range of 8 μm to 42 μm.
In actual use, the thickness of the first cladding layer 2 is 2 to 5 times the radius of the core layer 1; the thickness of the second cladding stress layer 31 is 1 to 3 times the radius of the core layer 1.
The stress expression in the application is expressed by adopting a double refraction method test, and the magnitude of the stress is expressed by the magnitude of the optical path difference. In practical use, the stress optical path difference of the core layer 1 is R 1 ，R 1 In the range of 100nm.cm -1 To 200nm.cm -1 The stress optical path difference of the core-spun stress region 100 is R 2 ，R 2 In the range of 100nm.cm -1 To 300nm.cm -1 The stress optical path difference of the stress layer of the first cladding layer 2 is R 3 ，R 3 In the range of 0nm.cm -1 To 100nm.cm -1 The second cladding stress layer 31 shouldThe force optical path difference is R 4 ，R 4 In the range of 100nm.cm -1 To 300nm.cm -1 The second cladding body layer 32 has a stress optical path difference R 5 ，R 5 In the range of 50nm.cm -1 To 100nm.cm -1 。
In practical use, the stress distribution can be gradient distribution or gradual change distribution.
The optical path difference was used to calculate internal stress of glass, which is an isotropic body having isotropic properties, as shown in fig. 5, and the light velocity was independent of the propagation direction and the polarization plane of the light wave when the monochromic tube was passed therethrough, without occurrence of birefringence. However, when the glass has residual stress or the mechanical action of the outside, the isotropic glass becomes an anisotropic body optically, and when the monochromatic light passes through the glass, the light is separated into two beams, and as shown in the right graph of fig. 5, the light velocity of the O light in the glass, the propagation direction thereof and the polarization plane of the light wave are unchanged, so that the O light still advances along the original incident direction, the time required for reaching the second surface is less, and the path to be travelled is shorter; the speed of light in the glass, the propagation direction of the light and the polarization plane of the light wave are changed, so that the light deviates from the original incidence direction, the time required for reaching the second surface is longer, and the distance covered by the light is longer. This difference in path length between the O light and the E light is called an optical path length difference. By measuring the optical path difference, the internal stress of the glass can be calculated.
The optical path difference is measured by several methods such as a polarimeter observation method, an interference color method and a compensator measurement method. The first method can roughly estimate the magnitude of the optical path difference, which is inconvenient for quantitative determination. The second type can perform quantitative measurement, but the accuracy is not high. And thirdly, relatively precise measurement can be performed. The basic principle of the compensator measurement is shown in FIG. 6, in which a light source 4, a polarizer 5, a stressed glass sample 6, a 1/4 wave plate 7, an analyzer 8 and an eye 9 are used, and it is known from theoretical deduction that the optical path difference of the glass sample is proportional to the deflection angle, i.e
R＝λθ/π
Wherein R is the optical path difference of glass, and the unit is nm.cm -1 The method comprises the steps of carrying out a first treatment on the surface of the Lambda is the wavelength of the irradiation light source, singlyThe position is nm; pi=180°. When a fluorescent lamp is used as a light source, λ=540 (nm), and r=3θ.
In practical use, the core layer 1 is made of silicon-based glass doped with elements for improving refractive index, so that more than 80% of optical signals can be transmitted in the optical fiber; the first cladding layer 2 is a pure silicon dioxide layer or is made of silicon-based glass doped with elements for reducing refractive index, forms a certain refractive index difference with the core layer 1, meets the transmission condition of the optical fiber core, plays a role in protecting the core layer 1, and simultaneously can transmit about 20% of optical signals at the layer; the second cladding layer 3 forms a second cladding layer stress layer 31 by doping aluminum and boron and germanium together or improving the density, and the second cladding layer stress layer 31 mainly acts to counteract structural stress between the core layer 1 and the core of the first cladding layer 2, does not directly participate in optical signal transmission, and the second cladding layer body layer 32 has the same refractive index as the first cladding layer 2, can also have a small refractive index difference with the first cladding layer 2, and mainly acts to protect the first cladding layer 2 and the core layer 1 and not directly participate in optical signal transmission. The refractive index increasing element may be various, such as germanium; the refractive index reducing element may be various, such as fluorine.
The application also discloses a manufacturing method of the low-loss optical fiber, which comprises the following steps:
s1, preparing a core rod, wherein the core rod comprises a core layer 1 and a first cladding layer 2 coated on the outer side of the core layer 1;
s2, processing a second cladding layer 3 outside the first cladding layer 2 to obtain an optical fiber preform, wherein the first cladding layer 2 is provided with a second cladding stress layer 31 positioned outside the first cladding layer 2 and a second cladding body layer 32 positioned outside the second cladding stress layer 31, and the second cladding stress layer 31 is used for applying inward compressive stress to the first cladding layer 2;
s3, heating the optical fiber preform through a wire drawing furnace, and melting the lower end of the optical fiber preform to form a silk thread;
s4, cooling and shaping the drooping silk thread through a shaping pipe, and then further cooling through a cooling pipe;
and S5, coating the cooled optical fiber, performing a curing procedure operation, and then winding to obtain the optical fiber.
In practical use, the core layer 1 and the first cladding layer 2 can be deposited by MCVD, PCVD, OVD, VAD and other processes, and finally the core rod is formed. In the core rod manufactured by any of the above processes, since the core layer 1 is doped with an element for improving the refractive index and the first cladding layer 2 is pure silica or doped with an element for reducing the refractive index, a stress layer (i.e., the core cladding stress region 100) is formed on the core cladding interface between the core layer 1 and the first cladding layer 2, and the optical fiber manufactured by the present application has a structure for protecting the second cladding stress layer 31, and the second cladding stress layer 31 can exert inward compressive stress on the first cladding layer 2 to offset or partially offset the influence of the core cladding stress layer on the core layer 1, thereby reducing the influence of the structural stress on the optical fiber loss.
In practice, the wire diameter in step S3 is typically 125. Mu.m. After the optical fiber is wound, the optical fiber with the diameter meeting the requirements is subjected to the steps of tension intensity screening, deuterium treatment and the like, and then the optical fiber is sent to a detection procedure, so that various index tests are completed, and qualified products are put in storage.
In practice, the second cladding layer 3 having the second cladding stress layer 31 may be formed by a variety of processes, and the following description will describe three embodiments in which only the second cladding layer 3 is formed by a different process.
Example 1
The processing mode of the second cladding stress layer is as follows: fused deposition of quartz sand doped with 10 to 30ppm of Al element onto the core rod;
the processing mode of the second cladding body layer is as follows: and depositing a second cladding body layer by using a chemical deposition method.
Example 2
The processing mode of the second cladding stress layer is as follows: fused deposition of quartz sand doped with 10 to 30ppm of Al element onto the core rod;
the processing mode of the second cladding body layer is as follows: and depositing by a quartz sand melting process to obtain a second cladding body layer.
Example 3
The processing mode of the second cladding stress layer is as follows: the boron element is obtained by deposition through a chemical deposition method, and boron element with the molar concentration of 10% and germanium element with the molar concentration of 4% are doped during deposition;
the processing mode of the second cladding body layer is as follows: is deposited by a chemical deposition method.
The following table shows the data parameters and attenuation test results of the corresponding optical fibers of three embodiments:
as can be seen from the above table, the application can effectively reduce the loss of the optical fiber by forming the second cladding stress layer.
The foregoing description is only of the preferred embodiments of the present application, and is not intended to limit the scope of the application, but rather is intended to cover all equivalent structures as modifications within the scope of the application, either directly or indirectly, as may be contemplated by the present application.
Claims (10)
1. A low loss optical fiber comprising:
a core layer;
the first cladding layer is coated on the outer side of the core layer, and a core cladding stress area is formed between the core layer and the first cladding layer;
the second cladding is coated on the outer side of the first cladding, the first cladding is provided with a second cladding stress layer positioned on the outer side of the first cladding and a second cladding body layer positioned on the outer side of the second cladding stress layer, and the second cladding stress layer is used for applying inward compressive stress to the first cladding to offset or partially offset the influence of a core cladding stress area on the core layer, so that loss is reduced.
2. The low loss optical fiber according to claim 1, wherein said core layer has a relative refractive index difference of Δ 1 The relative refractive index of the first cladding layerThe difference is delta 2 The relative refractive index difference of the second cladding stress layer is delta 3 The relative refractive index difference of the second cladding body layer is delta 4 The relative refractive index difference of the second cladding stress layer is the same as the relative refractive index difference of the second cladding body layer.
3. The low loss optical fiber according to claim 2, wherein the core layer has a relative refractive index difference delta 1 In the range of-0.1% to 0.1%, the relative refractive index difference delta of the first cladding layer 2 In the range of-0.4% to-0.2%, the second cladding stress layer having a relative refractive index difference delta 3 In the range of-0.3% to-0.15%, the relative refractive index difference of the second cladding body layer being delta 4 Ranging from-0.3% to-0.15%.
4. The low loss optical fiber according to claim 1, wherein said core layer has a thickness t 1 ，t 1 Ranging from 4 μm to 7 μm; the thickness of the first cladding layer is t 2 ，t 2 Is in the range of 12 μm to 35 μm; the thickness of the second cladding stress layer is t 3 ，t 3 Ranging from 4 μm to 12 μm; the thickness of the second cladding body layer is t 4 ，t 4 In the range of 8 μm to 42 μm.
5. The low-loss optical fiber according to claim 4, wherein the thickness of said first cladding layer is 2 to 5 times the radius of the core layer; the thickness of the second cladding stress layer is 1 to 3 times the radius of the core layer.
6. The low loss optical fiber according to claim 1, wherein said core layer has a stress optical path difference R 1 ，R 1 In the range of 100nm.cm -1 To 200nm.cm -1 The stress optical path difference of the core-spun stress area is R 2 ，R 2 In the range of 100nm.cm -1 To 300nm.cm -1 The stress optical path difference of the first cladding stress layer is R 3 ，R 3 Is in the range of 0nm.cm -1 To 100nm.cm -1 The stress optical path difference of the second cladding stress layer is R 4 ，R 4 In the range of 100nm.cm -1 To 300nm.cm -1 The stress optical path difference of the second cladding body layer is R 5 ，R 5 In the range of 50nm.cm -1 To 100nm.cm -1 。
7. The low-loss optical fiber according to claim 2, wherein said core layer is made of silica-based glass doped with an element for increasing refractive index; the first cladding is a pure silicon dioxide layer or is made of silicon-based glass doped with elements for reducing refractive index; and the second cladding layer is formed into the second cladding stress layer by doping aluminum, boron and germanium or increasing the density.
8. A method of making a low loss optical fiber comprising the steps of:
s1, preparing a core rod, wherein the core rod comprises a core layer and a first cladding layer coated on the outer side of the core layer;
s2, processing a second cladding outside the first cladding to obtain an optical fiber preform, wherein the first cladding is provided with a second cladding stress layer positioned outside the first cladding and a second cladding body layer positioned outside the second cladding stress layer, and the second cladding stress layer is used for applying inward compressive stress to the first cladding;
s3, heating the optical fiber preform through a wire drawing furnace, and melting the lower end of the optical fiber preform to form a silk thread;
s4, cooling and shaping the drooping silk thread through a shaping pipe, and then further cooling through a cooling pipe;
and S5, coating the cooled optical fiber, performing a curing procedure operation, and then winding to obtain the optical fiber.
9. The method for manufacturing a low-loss optical fiber according to claim 8, wherein the second cladding stress layer is manufactured by: fused deposition of quartz sand doped with 10 to 30ppm of Al element onto the core rod;
the processing mode of the second cladding body layer is as follows: and depositing a second cladding body layer outside the substrate by using a chemical deposition method, or depositing the second cladding body layer by using a quartz sand melting process.
10. The method for manufacturing a low-loss optical fiber according to claim 8, wherein the second cladding stress layer is manufactured by: the boron element is obtained by deposition through a chemical deposition method, and boron element with the molar concentration of 10% and germanium element with the molar concentration of 4% are doped during deposition;
the processing mode of the second cladding body layer is as follows: is deposited by a chemical deposition method.
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