CN116626805B - Ultra-low loss optical fiber and preparation method thereof - Google Patents
Ultra-low loss optical fiber and preparation method thereof Download PDFInfo
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- CN116626805B CN116626805B CN202310905845.4A CN202310905845A CN116626805B CN 116626805 B CN116626805 B CN 116626805B CN 202310905845 A CN202310905845 A CN 202310905845A CN 116626805 B CN116626805 B CN 116626805B
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- 238000002360 preparation method Methods 0.000 title abstract description 12
- 238000005253 cladding Methods 0.000 claims abstract description 130
- 239000010410 layer Substances 0.000 claims abstract description 126
- 239000012792 core layer Substances 0.000 claims abstract description 53
- 238000010438 heat treatment Methods 0.000 claims description 107
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- 230000003287 optical effect Effects 0.000 abstract description 8
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- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 17
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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
- G02B6/03688—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 5 or more layers
-
- 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
- C03B37/025—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor from reheated softened tubes, rods, fibres or filaments, e.g. drawing fibres from preforms
- C03B37/027—Fibres composed of different sorts of glass, e.g. glass optical fibres
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- 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
- C03B37/025—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor from reheated softened tubes, rods, fibres or filaments, e.g. drawing fibres from preforms
- C03B37/027—Fibres composed of different sorts of glass, e.g. glass optical fibres
- C03B37/02718—Thermal treatment of the fibre during the drawing process, e.g. cooling
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- 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
- C03B37/025—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor from reheated softened tubes, rods, fibres or filaments, e.g. drawing fibres from preforms
- C03B37/027—Fibres composed of different sorts of glass, e.g. glass optical fibres
- C03B37/02718—Thermal treatment of the fibre during the drawing process, e.g. cooling
- C03B37/02727—Annealing or re-heating
-
- 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
- C03B37/025—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor from reheated softened tubes, rods, fibres or filaments, e.g. drawing fibres from preforms
- C03B37/029—Furnaces therefor
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P40/00—Technologies relating to the processing of minerals
- Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping
- Y02P40/57—Improving the yield, e-g- reduction of reject rates
Abstract
The application provides an ultralow-loss optical fiber and a preparation method thereof. The optical fiber includes: the radius width R0 of the core layer is in the range of 4.2 μm to 4.8 μm, and the maximum relative refractive index difference Delta1 of the core layer max Ranging from 0.2% to 0.3%; the inner cladding is coated on the outer side of the core layer, the outer radius of the inner cladding is R1, the width R1-R0 of the inner cladding is in the range of 4.0 mu m to 4.3 mu m, and the minimum relative refractive index difference delta 2 of the inner cladding min Ranging from-0.25% to-0.3%; the width of the concave cladding layer ranges from 30 mu m to 40 mu m, the width of the concave platform layer is larger than that of the deep concave layer, and the width of the concave platform layer is larger than that of the concave platform layer; the outer cladding layer is coated on the outer side of the concave cladding layer. The 1550nm wavelength attenuation coefficient corresponding to the ultra-low loss optical fiber is smaller than or equal to 0.170dB/km, and the 1480nm wavelength attenuation coefficient corresponding to the ultra-low loss optical fiber is smaller than or equal to 0.210dB/km. The ultra-low loss optical fiber has the optical cable cut-off wavelength not more than 1400nm, meets the G.654.C optical fiber standard, preferably has the optical cable cut-off wavelength less than or equal to 1260nm, and meets the G.652 optical fiber standard.
Description
Technical Field
The application relates to the field of communication, in particular to an ultralow-loss optical fiber and a preparation method thereof.
Background
According to the current development trend of the power grid, the construction of a power information communication system with large capacity, long distance and high reliability is a trend. Conventional optical fibers are usually constrained by attenuation loss, and the communication distance is usually not more than 400km, so that the problems of difficult site selection, difficult power supply of a relay station and the like are encountered in ultra-high voltage power communication. The reduction of the attenuation coefficient of the optical fiber is an effective means for improving the optical fiber performance and prolonging the transmission distance, and the use of the ultra-low loss optical fiber can reduce the number of relay stations, reduce the loss of links as a whole and reduce the construction cost.
Typically by doping GeO in the core of the fiber 2 The refractive index is increased, but a large doping of Ge element introduces rayleigh scattering, which in turn causes an increase in fiber loss. Pure silicon core optical fiber eliminates GeO in the core 2 The optical fiber 1550nm wavelength attenuation can theoretically achieve about 0.145dB/km, but in order to design a proper refractive index difference of the core cladding, the cladding deep doping can cause a great increase in preparation cost. In order to solve the problem, the refractive index structure of the low-loss optical fiber generally adopts a step type structure, but the viscosity between the core layer and the cladding layer is suddenly changed due to the change of doping concentration, so that the stress difference is generated, and the additional attenuation is easily increased.
And, corresponding to the preparation process of optic fibre, in the optic fibre drawing melting process, usually set up a heating unit in the wire drawing stove. The cone head of the prefabricated member is divided into a high-temperature melting area, the temperature in the upper direction and the lower direction is rapidly reduced, the temperature gradient in the drawing furnace is larger, the temperature field distribution in the drawing furnace is sensitive to the change of drawing conditions, the unstable convection state of the gas in the furnace is caused, the diameter of an optical fiber forming area is uneven, the density distribution in the optical fiber is possibly suddenly changed, and the attenuation of the optical fiber is increased.
How to solve the above problems, it is considered by those skilled in the art to reduce the attenuation of the optical fiber.
Disclosure of Invention
In order to solve the problems in the prior art, the embodiment of the application provides an ultralow-loss optical fiber and a preparation method thereof.
The ultra-low loss optical fiber provided by the embodiment of the application comprises:
a core layer having a radius width R0 in the range of 4.2 μm to 4.8 μm and a maximum relative refractive index difference Delta1 max Ranging from 0.2% to 0.3%;
an inner cladding layer which is coated on the outer side of the core layer, wherein the outer radius of the inner cladding layer is R1, the width R1-R0 of the inner cladding layer is in the range of 4.0 mu m to 4.3 mu m, and the minimum relative refractive index difference delta 2 of the inner cladding layer min Ranging from-0.25% to-0.3%;
the deep concave layer, the concave platform layer and the concave platform layer are sequentially coated on the outer side of the inner cladding layer, the width range of the concave cladding layer is 30-40 mu m, the width of the concave platform layer is larger than that of the deep concave layer, and the width of the concave platform layer is larger than that of the concave platform layer;
and the outer cladding layer is coated on the outer side of the concave cladding layer.
In an embodiment, the refractive index structures of the core layer and the inner cladding layer change nonlinearly, and the radial position r of the core layer changes with respect to the refractive index Δ1 (r) and the radial position r of the inner cladding layer changes with respect to the refractive index Δ2 (r) obeying the following formula (1):
wherein g is the refractive index distribution parameter of the core layer, and g is more than or equal to 2 and less than or equal to 6; h is the refractive index distribution parameter of the inner cladding, and the refractive index distribution parameter satisfies that h is more than or equal to 3 and less than or equal to 10.
In one embodiment, the refractive index of the core layer has a plateau structure, and the refractive index junction of the inner cladding layerNonlinear variation is constructed, the radial position r of the core layer is relative to the refractive index delta 1 (r) = delta 1 max The change in the radial position r of the inner cladding relative to the refractive index Δ2 (r) obeys the following formula (2):
wherein m is the refractive index distribution parameter of the inner cladding, and the refractive index distribution parameter is more than or equal to 3 and less than or equal to 10.
In one embodiment, the outer radius of the deep recess layer is R2, the width R2-R1 of the deep recess layer is in the range of 5.0 μm to 6.0 μm, and the relative refractive index difference Delta3 of the deep recess layer is in the range of-0.45% to-0.48%.
In one embodiment, the outer radius of the recessed step is R3, the width R3-R2 of the recessed step is in the range of 6.0 μm to 15 μm, and the relative refractive index difference Delta4 of the recessed step is in the range of-0.25% to-0.3%.
In one embodiment, the outer radius of the recessed land layer is R4, the width of the recessed land layer R4-R3 is in the range of 12 μm to 22 μm, and the relative refractive index difference Delta5 of the recessed land layer is in the range of-0.35% to-0.4%.
In one embodiment, the ratio of the width of the inner cladding to the radial width of the core is in the range of 0.85 to 1.
In an embodiment, the core layer and the inner cladding layer are both doped with fluorine, the doping concentration of fluorine in the core layer ranges from 0.01% to 0.3%, and the doping concentration of fluorine in the inner cladding layer ranges from 0.01% to 2.0%.
In an embodiment, the residual stress in the core layer, the inner cladding layer and the depressed cladding layer is a compressive stress, and the compressive stress ranges from 40MPa to 100MPa.
In one embodiment, the 1550nm wavelength attenuation coefficient of the ultra-low loss optical fiber is less than or equal to 0.170dB/km, and the 1480nm wavelength attenuation coefficient of the ultra-low loss optical fiber is less than or equal to 0.210dB/km.
The preparation method of the ultralow-loss optical fiber provided by the embodiment of the application comprises the following steps: constructing a preform according to the refractive index structure of the optical fiber; performing fusion drawing on the prefabricated member through a drawing heating system to prepare the optical fiber;
the wire drawing heating system comprises a wire drawing furnace internal heating unit, a high-temperature annealing heating unit and a low-temperature annealing heating unit, wherein the wire drawing furnace internal heating unit comprises a melting deformation unit, a heating forming unit, a heating melting unit and a preheating unit, and the preheating unit, the heating melting unit, the melting deformation unit, the heating forming unit, the high-temperature annealing heating unit and the low-temperature annealing heating unit are sequentially arranged at intervals along the processing direction of the prefabricated member;
the highest heating temperature of the melting deformation unit is T1, the highest heating temperature of the heating forming unit is T2, the highest heating temperature of the heating melting unit is T3, the highest heating temperature of the preheating unit is T4, the highest heating temperature of the high-temperature annealing heating unit is T200, the highest heating temperature of the low-temperature annealing heating unit is T300, the glass transition temperature is Tg, and the conditions that T1 & gtT 200 & gtTg & gtT 4 & gtT 300 & gtT 1 & gtT 2 & gtTg & gtT 3 & gtTg & gtT 4 are satisfied.
The ultra-low loss optical fiber adopts a wide concave cladding structure with the width ranging from 30 mu m to 40 mu m, the width of a concave platform layer is larger than that of a deep concave layer, and the width of a concave platform layer is larger than that of the concave platform layer. On one hand, the viscosity difference between the core layer and the cladding layer can be reduced, the stress difference is reduced, and the attenuation performance of the optical fiber is improved; and the relative refractive index difference is reduced by doping fluorine element in the depressed cladding, and the viscosity is reduced, so that the viscosity difference between the depressed cladding and the core layer is relatively reduced. On the other hand, the wide concave cladding structure can also prevent the leakage of the conducted light, reduce the loss of the optical signal in the long wavelength section and improve the bending resistance of the optical fiber. Maintaining the fiber at a low attenuation level in the 1520nm to 1625nm range facilitates expansion of the communication application to the L-band window.
And the core layer adopts a low germanium doping mode, so that GeO is reduced 2 The Rayleigh scattering effect is reducedThe optical fiber loss is low, and meanwhile, fluorine is doped in the core layer to reduce the relative refractive index of the core layer and the viscosity of the core layer. By controlling the concentration of fluorine doped in the inner cladding, the refractive index difference is slowly excessive, the difference of thermal expansion coefficients caused by abrupt change of doping concentration is reduced, and the additional loss caused by uneven stress is avoided. Residual stress in the core layer, the inner cladding layer and the concave cladding layer is compressive stress, and the existence of the compressive stress can prevent the expansion of micro defects in the optical fiber and further reduce Rayleigh scattering.
According to the preparation method of the optical fiber, the prefabricated part is subjected to heat treatment in a multi-unit independent heating mode, so that the temperature difference between the melting heating part and the upper and lower furnace parts is greatly reduced, the crowing number is reduced, the unstable flow in the wire drawing furnace is prevented, the thermal field in the furnace is kept stable, and the diameter of the cladding is kept stable. The preheating section, the high-temperature annealing and the low-temperature annealing units are arranged, so that the internal stress of the prefabricated member is fully released above the glass transition temperature point, and the attenuation coefficient is reduced.
Drawings
Fig. 1 is a schematic cross-sectional view of an optical fiber according to an embodiment of the present application.
Fig. 2 is a schematic diagram of refractive index distribution of an optical fiber according to an embodiment of the present application.
Fig. 3 is a schematic diagram of another refractive index distribution of an optical fiber according to an embodiment of the present application.
Fig. 4 is a schematic diagram of an optical fiber according to an embodiment of the present application for testing attenuation of an optical fiber by a truncation method.
Fig. 5 is a schematic diagram of reducing a cut-off wavelength of an optical fiber according to an embodiment of the present application.
Fig. 6 is a schematic structural diagram of a drawing heating system used in the method for manufacturing an optical fiber according to an embodiment of the present application.
Fig. 7 is a schematic diagram of temperature distribution of an improved heating mode corresponding to the preparation method of an optical fiber according to an embodiment of the present application and a comparative heating mode corresponding to a conventional preparation method.
Description of the main reference signs
Optical fiber 1
Core layer 10
Inner cladding 20
Depressed cladding 30
Deep recess layer 31
Recessed step level 32
Recessed land layer 33
Outer cladding 40
Heating unit 100 in wire drawing furnace
Fusion deformation heating unit 101
Thermoforming unit 102
Heating and melting unit 103
Preheating units 104, 105
High temperature annealing heating unit 200
Low temperature annealing heating unit 300
The application will be further described in the following detailed description in conjunction with the above-described figures.
Detailed Description
The following description will make reference to the accompanying drawings to more fully describe the application. Exemplary embodiments of the present application are illustrated in the accompanying drawings. This application may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. These exemplary embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art. Like reference numerals designate identical or similar components. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, as used herein, "comprises" and/or "comprising" and/or "having," integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, and/or groups thereof. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Furthermore, unless the context clearly defines otherwise, terms such as those defined in a general dictionary should be construed to have meanings consistent with their meanings in the relevant art and the present disclosure, and should not be construed as idealized or overly formal meanings. The following description of exemplary embodiments will be provided with reference to the accompanying drawings. It is noted that the components depicted in the referenced figures are not necessarily shown to scale; and the same or similar components will be given the same or similar reference numerals or similar technical terms.
The embodiment of the application provides an ultralow-loss optical fiber, which comprises the following components: a core layer having a radius width R0 in the range of 4.2 μm to 4.8 μm and a maximum relative refractive index difference Delta1 max Ranging from 0.2% to 0.3%; an inner cladding layer which is coated on the outer side of the core layer, wherein the outer radius of the inner cladding layer is R1, the width R1-R0 of the inner cladding layer is in the range of 4.0 mu m to 4.3 mu m, and the minimum relative refractive index difference delta 2 of the inner cladding layer min Ranging from-0.25% to-0.3%; the deep concave layer, the concave platform layer and the concave platform layer are sequentially coated on the outer side of the inner cladding layer, the width range of the concave cladding layer is 30-40 mu m, the width of the concave platform layer is larger than that of the deep concave layer, and the width of the concave platform layer is larger than that of the concave platform layer; and the outer cladding layer is coated on the outer side of the concave cladding layer.
The following describes the embodiments of the present application in further detail with reference to the accompanying drawings. Wherein, the optical fiber 1 refers to an ultra-low loss optical fiber, and the ultra-low loss optical fiber refers to an optical fiber with 1550nm wavelength attenuation coefficient smaller than or equal to 0.170dB/km.
As shown in fig. 1, an embodiment of the present application provides an optical fiber 1. The optical fiber 1 comprises a core layer 10, an inner cladding layer 20, a concave cladding layer 30 and an outer cladding layer 40, wherein the inner cladding layer 20 is coated and arranged on the outer side of the core layer 10, the concave cladding layer 30 is coated and arranged on the outer side of the inner cladding layer 20, and the outer cladding layer 40 is coated and arranged on the outer side of the concave cladding layer 30. That is, the inner cladding 20, the depressed cladding 30, and the outer cladding 40 are sequentially wrapped around the core 10.
The depressed cladding 30 has a wide depressed structure, the depressed cladding 30 includes a deep depressed layer 31, a depressed mesa layer 32 and a depressed mesa layer 33, the deep depressed layer 31, the depressed mesa layer 32 and the depressed mesa layer 33 are sequentially coated on the outer side of the inner cladding 20, the width of the depressed mesa layer 32 is greater than the width of the deep depressed layer 31, and the width of the depressed mesa layer 33 is greater than the width of the depressed mesa layer 32.
It will be appreciated that the depressed cladding 30 of the wide depressed structure serves to confine the guided wave transmission of the fiber, to enhance the bending resistance of the fiber, and that its width and relative refractive index difference affect the cut-off wavelength and macrobend loss of the fiber. Generally, the wider the depressed cladding 30, the greater the relative refractive index difference, the greater the cut-off wavelength of the fiber and the smaller the macrobend loss. To control the cutoff wavelength and macrobend size, the design parameters are balanced to limit the width of depressed cladding 30. To reduce long wavelength transmission loss, a depressed mesa layer is provided which is wide and has a low relative refractive index to prevent leakage of the conducted light.
In one embodiment, the depressed cladding 30 has a width in the range of 30 μm to 40 μm, and further may be 32 μm to 36 μm.
As further shown in FIG. 2, in one embodiment, the radial width R0 of the core 10 is in the range of 4.2 μm to 4.8 μm, and the maximum relative refractive index difference Delta1 of the core 10 max Ranging from 0.2% to 0.3%.
In this embodiment, the radial width R0 of the core layer 10 may be specifically 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, and 4.7 μm. Maximum relative refractive index difference Δ1 of core layer 10 max Specifically, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28% and 0.29% may be used.
In one embodiment, the inner cladding 20 has an outer radius R1, the width R1-R0 of the inner cladding 20 is in the range of 4.0 μm to 4.3 μm, and the minimum relative refractive index difference Δ2 of the inner cladding 20 min Ranging from-0.25% to-0.3%.
In this embodiment, the widths R1-R0 of the inner cladding 20 may be specifically 4.1 μm and 4.2 μm. Minimum relative refractive index difference Δ2 of inner cladding 20 min Specifically, it may be-0.26%, -0.27%, -0.28% and-0.29%.
In one embodiment, the refractive index structures of the core 10 and the inner cladding 20 vary nonlinearly, and the radial position r of the core 10 relative to the refractive index Δ1 (r) and the radial position r of the inner cladding 20 relative to the refractive index Δ2 (r) vary according to the following formula (1):
wherein g is the refractive index distribution parameter of the core layer 10, and g is more than or equal to 2 and less than or equal to 6; h is a refractive index distribution parameter of the inner cladding 20, which satisfies 3.ltoreq.h.ltoreq.10.
As further shown in connection with fig. 3, in another embodiment, the radial width R0 of the core layer 10 is in the range of 4.2 μm to 4.8 μm, the maximum relative refractive index difference Δ1 of the core layer 10 max Ranging from 0.2% to 0.3%.
In this embodiment, the radial width R0 of the core layer 10 may be specifically 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, and 4.7 μm. Maximum relative refractive index difference Δ1 of core layer 10 max Specifically, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28% and 0.29% may be used.
In one embodiment, the inner cladding 20 has an outer radius R1, the width R1-R0 of the inner cladding 20 is in the range of 4.0 μm to 4.3 μm, and the minimum relative refractive index difference Δ2 of the inner cladding 20 min Ranging from-0.25% to-0.3%.
In this embodiment, the widths R1-R0 of the inner cladding 20 may be specifically 4.1 μm and 4.2 μm. Minimum relative refractive index difference Δ2 of inner cladding 20 min Specifically, it may be-0.26%, -0.27%, -0.28% and-0.29%.
In one embodiment, the refractive index of the core layer 10 has a plateau structure, and the radial position r of the core layer 10 has a relative refractive index Δ1 (r) = Δ1 max The refractive index structure of the inner cladding 20 varies nonlinearly, and the variation of the radial position r of the inner cladding 20 with respect to the refractive index Δ2 (r) obeys the following formula (2):
wherein m is the refractive index distribution parameter of the inner cladding, and the refractive index distribution parameter satisfies that m is more than or equal to 3 and less than or equal to 10.
It can be understood that the refractive index profiles of the optical fibers 1 shown in fig. 2 and 3 are different from each other only in the refractive index structures of the core layers 10, and are otherwise identical.
As further shown in fig. 2 and 3, in one embodiment, the outer radius of the deep recess layer 31 is R2, and the width R2-R1 of the deep recess layer 31 is in the range of 5.0 μm to 6.0 μm. The relative refractive index difference Δ3 of the deep concave layer 31 ranges from-0.45% to-0.48%.
In the present embodiment, the widths R2-R1 of the deep recess layer 31 may be specifically 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm and 5.9 μm. The relative refractive index difference Δ3 of the deep concave layer 31 may be specifically-0.46% and-0.47%.
In one embodiment, the outer radius of the recessed step 32 is R3, and the width R3-R2 of the recessed step 32 is in the range of 6.0 μm to 15 μm. The relative refractive index difference Δ4 of the depressed step level 32 ranges from-0.25% to-0.3%.
In this embodiment, the widths R3-R2 of the recessed step 32 may be 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, and 14.5 μm. The relative refractive index difference Δ4 of the recessed step level 32 may be specifically-0.25%, -0.26%, -0.27%, -0.28% and-0.29%.
In one embodiment, the outer radius of the recessed land layer 33 is R4, and the width R4-R3 of the recessed land layer 33 is in the range of 12 μm to 22 μm. The relative refractive index difference Δ5 of the recessed land layer 33 ranges from-0.35% to-0.4%.
In this embodiment, the widths R4-R3 of the recessed land layer 33 may be 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm,16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, 20.5 μm, 21 μm and 21.5 μm. The relative refractive index difference Δ5 of the recessed land layer 33 ranges from-0.36%, -0.37%, -0.38% and-0.39%.
The radius of the core 10, the width of the inner cladding 20, and the relative refractive index design range are the basis for achieving ultra-low loss performance of the fiber, reaching a specific mode field diameter range. The width of the deep concave layer 31 is designed to limit the cut-off wavelength of the optical fiber, if the deep concave layer 31 is too wide, the cut-off wavelength may be too large and exceed the standard, so that single-mode transmission is affected; the refractive index of the deep concave layer 31 is designed to achieve a sufficient relative refractive index difference with the core layer 10, thereby reducing the additional loss of the optical fiber in the bent state and improving the transmission capability. The depressed mesa layer 33 has a refractive index relatively lower than that of the depressed mesa layer 32, and the width of the depressed mesa layer 33 is increased to prevent the long wavelength optical signal from leaking into the outer cladding 40, reduce the long wavelength loss, reduce the maximum attenuation coefficient difference between the C-band and the long wavelength L-band, and facilitate the expansion of the optical fiber c+l communication window. Too large a width of the depressed mesa 33 may result in too small a width of the outer cladding 40, and the tensile stress formed by the outer cladding 40 may not generate sufficient compressive stress on the core 10, inner cladding 20, and depressed cladding 30, which may be detrimental to attenuation reduction.
In one embodiment, the material of the outer cladding 40 may be SiO 2 The relative refractive index n0 defaults to 0. The outer cladding 40 has a diameter in the range of 100 μm to 130 μm, and may further be 125 μm.
In one embodiment, the ratio of the width R1-R0 of the inner cladding 20 to the radial width R0 of the core 10 is in the range of 0.85 to 1.
It will be appreciated that the wide depressed cladding 30 structure can constrain the guided wave transmission of the optical fiber, improving the bending resistance of the optical fiber 1, the width and relative refractive index of the deep depressed layer 31 affect the cut-off wavelength and macrobending loss of the optical fiber 1, and the wide depressed cladding 30 has a lower relative refractive index difference for reducing the transmission attenuation coefficient of the optical fiber. The ratio of the width of the inner cladding 20 to the radial width of the core 10 is controlled to be between 0.85 and 1 for balancing the cut-off wavelength and macrobending loss of the optical fiber 1.
The fluorine doping amount of the inner cladding 20 is controlled, so that the refractive index difference of the inner cladding 20 is in nonlinear distribution and is slowly excessive, the difference of thermal expansion coefficients generated by abrupt change of doping concentration is reduced, further, abrupt change of viscosity between the core layer 10 and the concave cladding 30 is reduced, additional loss caused by uneven stress is avoided, and the attenuation performance of the optical fiber 1 is improved.
In one embodiment, the core layer 10 and the inner cladding layer 20 are doped with fluorine, the doping concentration of fluorine in the core layer 10 is in the range of 0.01% to 0.3%, and the doping concentration of fluorine in the inner cladding layer 20 is in the range of 0.01% to 2.0%.
In this embodiment, the doping concentration of fluorine in the core layer 10 may be 0.03%, 0.05%, 0.08%, 0.1%, 0.13%, 0.15%, 0.18%, 0.2%, 0.23%, 0.25% and 0.28%. The doping concentration of fluorine in the inner cladding layer 20 may be 0.03%, 0.08%, 0.1%, 0.3%, 0.5%, 1.0%, 1.5% and 1.8%. In this embodiment, the above-described doping concentration range represents the mass percentage of fluorine element to silicon dioxide.
It will be appreciated that the core 10 is low germanium doped, and the refractive index of conventional low loss optical fiber cores is typically around 0.4%. Reducing GeO 2 The resulting Rayleigh scattering effect reduces the loss of the fiber 1 and, in combination with fluorine doping, reduces the relative refractive index of the core layer 10 while reducing the viscosity of the core layer 10. According to the designed refractive index structure, the fluorine doping amount of the inner cladding 20 is controlled, so that the refractive index difference is slowly excessive, the thermal expansion coefficient difference generated by the abrupt change of doping concentration is reduced, and the additional loss caused by uneven stress is avoided.
It can be appreciated that the main material of the optical fiber 1 is SiO 2 The core layer 10 increases refractive index by doping Ge, geO 2 With SiO in glass 2 As well as acting as a network former to increase the polarizability of quartz glass, thereby doping GeO 2 The refractive index of the glass can be increased. The inner cladding 20 and the depressed cladding 30 are adjusted to lower the refractive index by doping fluorine in different proportions, and fluorine exists as a network intermediate in the silica glass, thereby being able to lower the refractive index of the silica glass. The doping of Ge and F can weaken the action of silicon-oxygen bond, and SiO is formed at high temperature 2 The chemical bonds are more likely to break, thus reducing the viscosity of the quartz glass.
In one embodiment, the residual stresses in the core 10, inner cladding 20 and depressed cladding 30 are compressive stresses ranging from 40MPa to 100MPa.
In this embodiment, the compressive stress may be 40Mpa, 50Mpa, 60Mpa, 70Mpa, 80Mpa, and 90Mpa.
It will be appreciated that the presence of compressive stress may prevent the interiorThe spread of microdefects reduces Rayleigh scattering. The outer cladding 40 is pure SiO 2 The material has a relatively high viscosity, and is drawn by a certain tension to provide a tensile stress.
In one embodiment, the optical fiber 1550nm wavelength mode field has a diameter in the range of 10 μm to 11 μm. The cut-off wavelength of the 22m optical fiber 1 is tested according to the standard GBT 15972.44-2017 optical fiber test method standard cut-off wavelength, the optical fiber 1 has the optical cable cut-off wavelength not more than 1400nm, the G.654.C optical fiber standard is met, the optical cable cut-off wavelength is preferably less than or equal to 1260nm, and the G.652 optical fiber standard is met.
Further referring to fig. 4 and 5, the attenuation coefficients of the wavelengths of the optical fiber 1 are tested according to the standard GBT 15972.40-2008 optical fiber test method standard attenuation method a cut-off method.
In the test process, a 22m optical fiber is used as a high-order mode filter, when the cut-off wavelength of the optical fiber is larger than 1260nm, the high-order mode cannot be completely filtered through a mode of adding 24 large rings H1 with the radius of 140mm and 2 small rings H2 with the radius of 40mm by using a conventional winding, and the test of the attenuation coefficient of the optical fiber in the range from over 1260nm to the cut-off wavelength of the optical fiber is inaccurate. Therefore, 1 small ring H3 with radius not more than 15mm is additionally added during the test, and the position of the cut-off wavelength of the optical cable is changed from lambda cc 1 to lambda cc 2, ensuring the cut-off wavelength lambda of the optical cable during test cc 2 is below 1260nm, the higher order modes are further filtered, and the attenuation coefficient above 1260nm is accurately tested. The 1550nm wavelength attenuation coefficient of the optical fiber is less than or equal to 0.170dB/km, preferably less than or equal to 0.165dB/km; the 1480nm wavelength attenuation coefficient is 0.210dB/km or less, preferably 0.20dB/km or less, and more preferably 0.19dB/km or less; meanwhile, the wide concave layer design ensures that the optical fiber has a lower attenuation coefficient in the wavelength range of 1520nm to 1625nm, so that the communication window of the optical fiber is expanded from a conventional C wave band to an L wave band, and the optical fiber is suitable for a C+L wave band wavelength division multiplexing communication system. The difference between the maximum attenuation coefficient and the minimum attenuation coefficient in the wavelength range of 1520nm to 1625nm is smaller, the difference Deltaα1520 less than or equal to 0.02dB/km between 1520nm and the minimum attenuation coefficient in the wavelength range, the difference Deltaα1625 less than or equal to 0.02dB/km between 1625nm and the minimum attenuation coefficient in the wavelength range, and the absolute value Deltaα1520 less than or equal to 0.009dB/km of the arithmetic difference between Deltaα1625 and Deltaα1625, preferablyDelta alpha is less than or equal to 0.006dB/km. Wherein Δα satisfies the following formula (3):
with further reference to fig. 6, an embodiment of the present application provides a method for preparing an optical fiber 1 in the foregoing embodiment, where the method for preparing an optical fiber includes:
preform a is constructed according to the refractive index structure of the optical fiber.
In this embodiment, the preform a may be prepared by MCVD or VAD or OVD methods.
Preform a is melt drawn by a drawing heating system b to produce an optical fiber.
The wire drawing heating system b comprises a wire drawing furnace heating unit 100, a high-temperature annealing heating unit 200 and a low-temperature annealing heating unit 300, wherein the wire drawing furnace heating unit 100 comprises a melting deformation heating unit 101, a heating forming unit 102, a heating melting unit 103 and a preheating unit 104 (105). The preheating unit 104 (105), the heating and melting unit 103, the melting and deforming heating unit 101, the thermoforming unit 102, the high-temperature annealing heating unit 200, and the low-temperature annealing heating unit 300 are sequentially arranged at intervals along the processing direction of the preform a (from top to bottom in correspondence with fig. 6).
The maximum heating temperature of the melt deformation heating unit 101 is T1, the maximum heating temperature of the heating forming unit 102 is T2, the maximum heating temperature of the heating melting unit 103 is T3, and the maximum heating temperature of the preheating unit 104 (105) is T4. The highest heating temperature of the high temperature annealing heating unit 200 is T200, the highest heating temperature of the low temperature annealing heating unit 300 is T300, and the glass transition temperature is Tg. It satisfies T1 > T200 > Tg > T4 > T300, T1 > T2 > Tg and T1 > T3 > Tg > T4.
In one embodiment, the glass transition temperature Tg is the temperature at which the physical properties such as refractive index, specific heat capacity, thermal expansion coefficient of the glass are abrupt. And after the fusion wire drawing and shaping, high-temperature heating annealing is carried out, wherein the heating temperature T200 is above the glass transition temperature Tg, so that the quick release of the internal stress of the optical fiber can be promoted, and the attenuation coefficient is effectively reduced. In this embodiment, the difference between T200 and Tg may range from 50 ℃ to 100 ℃.
In one embodiment, the temperature of the fiber at the low temperature annealing section is slowly reduced, and the temperature of the fiber at the outlet of the annealing tube reaches 1000 ℃ to 1200 ℃ and is controlled in combination with controlling the drawing speed. Too high an outlet temperature may cause surface turbulence, which is detrimental to cladding diameter control. Optionally, a thermal insulation annealing device is arranged below the low-temperature annealing section to further anneal the optical fiber and reduce the attenuation of the optical fiber.
In an embodiment, the preheating unit 104 (105), the heating and melting unit 103, the melting and deforming heating unit 101, the heating and forming unit 102, the high-temperature annealing heating unit 200 and the low-temperature annealing heating unit 300 can all adopt a graphite heating or coil heating mode, and the preheating unit 104 (105), the heating and melting unit 103, the melting and deforming heating unit 101, the heating and forming unit 102, the high-temperature annealing heating unit 200 and the low-temperature annealing heating unit 300 can all independently heat and control temperature and are connected with a host PLC control system (not shown), and the temperature is remotely adjusted according to different process settings, which is not described herein.
In an embodiment, the preheating unit 104 (105), the melting unit 103, the fusion deformation heating unit 101, the forming unit 102, the high-temperature annealing heating unit 200 and the low-temperature annealing heating unit 300 may be provided with high-temperature detectors (not shown) at corresponding positions, so as to monitor the temperatures around the preform a and the optical fiber in real time.
In an embodiment, the outer sides of the preheating unit 104 (105), the heating and melting unit 103, the melting and deforming unit 101, the heating and forming unit 102, the high temperature annealing and heating unit 200 and the low temperature annealing and heating unit 300 may be provided with heat insulation members (not shown), and a water circulation cooling system (not shown) may be provided outside the heat insulation members.
In one embodiment, the axes of the preheating unit 104 (105), the heating and melting unit 103, the melting and deforming unit 101, the thermoforming unit 102, the high temperature annealing heating unit 200, and the low temperature annealing heating unit 300 are kept at one center from top to bottom.
In one embodiment, the wire drawing heating system b is filled with inert gas, and the inert gas may be Ar gas or a mixture of Ar gas and He gas. The flow instability or unsteadiness of the shielding gas can be quantified as the glas' number (Gr). The gruff number (Gr) can be interpreted as the ratio of the buoyancy of the gas system to the viscous force. When the buoyancy becomes significantly larger than the viscous force, the flow becomes unstable, is susceptible to changes in external conditions, and the glas-fv number (Gr) is expressed numerically to satisfy the following formula (4):
where g is the gravitational acceleration, β is the thermal expansion coefficient of the shielding gas, L c Is the characteristic length (e.g., the length of the space into which the gas is introduced), Δt is the temperature difference (e.g., the temperature difference between the bottom and the upper portion of the preform of the drawing furnace), and v is the dynamic viscosity of the shielding gas.
It will be appreciated that the lower the Gray dawn number (Gr), the better it is to prevent unsteady flow in the drawing furnace; from the above formula (4), g, β, L can be found c Variations in parameters such as Δ T, v affect the value of the grazing number (Gr).
He gas and Ar gas can be selected as the shielding gas. When He gas is used as the shielding gas, the He gas has high dynamic viscosity, so that the He gas can effectively resist unsteady buoyancy driving flow, but the He gas has high cost. When a protective gas having a low dynamic viscosity such as Ar gas is used, it is considered to reduce the temperature difference DeltaT in the drawing furnace, reduce the occurrence of unstable convection, and improve the thermal field distribution to reduce the value of the Skoto number (Gr). Therefore, in the preparation method of the optical fiber, the temperature difference (delta T) between the melting heating part and the upper furnace and the lower furnace is greatly reduced by a multi-unit independent temperature control heating mode, so that the diameter of the cladding is kept stable, and the improved temperature distribution is schematically shown in fig. 7.
In one embodiment, the fiber tension is controlled to be in the range of 80g to 150g so that the cable cut-off wavelength of the optical fiber is controlled within the target range. After the optical fiber is annealed and cooled, the surface of the optical fiber can be further coated with two layers of resin for protection, wherein the material of the resin can be polymethacrylic acid resin. Wherein the modulus of the inner resin is relatively low and may range from 0.3 Mpa to 1Mpa; the modulus of the outer resin is relatively high and may range from greater than 500Mpa. And (3) after the resin is cured and molded by ultraviolet, preparing the optical fiber.
Hereinabove, the specific embodiments of the present application are described with reference to the accompanying drawings. However, those of ordinary skill in the art will appreciate that various modifications and substitutions can be made to the specific embodiments of the application without departing from the spirit and scope thereof. Such modifications and substitutions are intended to be included within the scope of the present application.
Claims (7)
1. An ultra-low loss optical fiber comprising:
a core layer having a radius width R0 in the range of 4.2 μm to 4.8 μm and a maximum relative refractive index difference Delta1 max Ranging from 0.2% to 0.3%;
an inner cladding layer which is coated on the outer side of the core layer, wherein the outer radius of the inner cladding layer is R1, the width R1-R0 of the inner cladding layer is in the range of 4.0 mu m to 4.3 mu m, and the minimum relative refractive index difference delta 2 of the inner cladding layer min Ranging from-0.25% to-0.3%;
the deep concave layer, the concave platform layer and the concave platform layer are sequentially coated on the outer side of the inner cladding layer, the width range of the concave cladding layer is 30-40 mu m, the width of the concave platform layer is larger than that of the deep concave layer, and the width of the concave platform layer is larger than that of the concave platform layer; the outer radius of the deep concave layer is R2, the width R2-R1 of the deep concave layer ranges from 5.0 mu m to 6.0 mu m, and the relative refractive index difference delta 3 of the deep concave layer ranges from-0.45% to-0.48%; the outer radius of the concave step is R3, the width R3-R2 of the concave step ranges from 6.0 mu m to 15 mu m, and the relative refractive index difference delta 4 of the concave step ranges from-0.25% to-0.3%; the outer radius of the concave platform layer is R4, the width R4-R3 of the concave platform layer ranges from 12 mu m to 22 mu m, and the relative refractive index difference delta 5 of the concave platform layer ranges from-0.35% to-0.4%;
an outer cladding layer which is coated on the outer side of the concave cladding layer;
wherein fluorine is doped in the core layer and the inner cladding layer, the doping concentration of fluorine in the core layer ranges from 0.01% to 0.3%, and the doping concentration of fluorine in the inner cladding layer ranges from 0.01% to 2.0%; the refractive index structures of the core layer and the inner cladding layer are nonlinear, or the refractive index of the core layer has a platform structure, and the refractive index structure of the inner cladding layer is nonlinear.
2. The ultra-low loss optical fiber according to claim 1, wherein the refractive index structures of said core and said inner cladding vary non-linearly, and the radial position r of said core relative to the refractive index Δ1 (r) and the radial position r of said inner cladding relative to the refractive index Δ2 (r) vary according to the following formula (1):
wherein g is the refractive index distribution parameter of the core layer, and g is more than or equal to 2 and less than or equal to 6; h is the refractive index distribution parameter of the inner cladding, and the refractive index distribution parameter satisfies that h is more than or equal to 3 and less than or equal to 10.
3. The ultra-low loss optical fiber according to claim 1, wherein the refractive index of said core layer has a plateau structure, the refractive index structure of said inner cladding layer varies non-linearly, and the radial position r of said core layer is relative to the refractive index Δ1 (r) = Δ1 max The change in the radial position r of the inner cladding relative to the refractive index Δ2 (r) obeys the following formula (2):
wherein m is the refractive index distribution parameter of the inner cladding, and the refractive index distribution parameter is more than or equal to 3 and less than or equal to 10.
4. The ultra-low loss optical fiber according to claim 1, wherein the ratio of the width of said inner cladding to the width of said core radius ranges from 0.85 to 1.
5. The ultra-low loss optical fiber according to claim 1, wherein residual stresses in said core, said inner cladding and said depressed cladding are compressive stresses, said compressive stresses ranging from 40MPa to 100MPa.
6. The ultra-low loss optical fiber according to claim 1, wherein said ultra-low loss optical fiber has a 1550nm wavelength attenuation coefficient less than or equal to 0.170dB/km, and said ultra-low loss optical fiber has a 1480nm wavelength attenuation coefficient less than or equal to 0.210dB/km.
7. A method for preparing an ultra-low loss optical fiber, wherein the method for preparing an optical fiber according to claim 1 comprises: constructing a preform according to the refractive index structure of the optical fiber; performing fusion drawing on the prefabricated member through a drawing heating system to prepare the optical fiber;
the wire drawing heating system comprises a wire drawing furnace internal heating unit, a high-temperature annealing heating unit and a low-temperature annealing heating unit, wherein the wire drawing furnace internal heating unit comprises a melting deformation unit, a heating forming unit, a heating melting unit and a preheating unit, and the preheating unit, the heating melting unit, the melting deformation unit, the heating forming unit, the high-temperature annealing heating unit and the low-temperature annealing heating unit are sequentially arranged at intervals along the processing direction of the prefabricated member;
the highest heating temperature of the melting deformation unit is T1, the highest heating temperature of the heating forming unit is T2, the highest heating temperature of the heating melting unit is T3, the highest heating temperature of the preheating unit is T4, the highest heating temperature of the high-temperature annealing heating unit is T200, the highest heating temperature of the low-temperature annealing heating unit is T300, the glass transition temperature is Tg, and the conditions that T1 & gtT 200 & gtTg & gtT 4 & gtT 300 & gtT 1 & gtT 2 & gtTg & gtT 3 & gtTg & gtT 4 are satisfied.
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