CN111694088A - Single-mode optical fiber and preparation method thereof - Google Patents
Single-mode optical fiber and preparation method thereof Download PDFInfo
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- CN111694088A CN111694088A CN202010406925.1A CN202010406925A CN111694088A CN 111694088 A CN111694088 A CN 111694088A CN 202010406925 A CN202010406925 A CN 202010406925A CN 111694088 A CN111694088 A CN 111694088A
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02395—Glass optical fibre with a protective coating, e.g. two layer polymer coating deposited directly on a silica cladding surface during fibre manufacture
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- 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
- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
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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
Abstract
A single-mode optical fiber and its preparation method, the bare fiber includes the core layer and the cladding, the core layer includes the first core layer, the second core layer, the inner cladding, the relative refractive index difference of the first core layer is 0.2% delta1Not more than 0.35 percent, and the relative refractive index difference of the second core layer is not less than 0.15 percent and not more than delta2Not more than 0.25 percent, the radius of the refractive index of the inner cladding is between 24 and 36 mu m, and the difference value of the relative refractive index of the inner cladding is between-0.12 and delta3Less than or equal to 0 percent. The cladding comprises a depressed cladding and an outer cladding, the relative refractive index difference of the depressed cladding is-0.40% < delta >4Less than or equal to-0.28 percent, and the outer cladding is a high-hardness pure quartz sleeve. The method of online assembling and drawing the two-stage sleeve and the core rod is adopted, optical fiber annealing is carried out for many times in the drawing process, and a coating with low modulus and high modulus is coated inside and outside the surface of the optical fiber, so that the optical fiber with low loss, large effective area and high strength is prepared. Simple method, coreThe rod can be used for viscosity adjustment according to requirements, the optical fiber attenuation is reduced without adopting a pure silicon core scheme, and the mass production is facilitated.
Description
Technical Field
The invention relates to a single mode fiber and a preparation method thereof.
Background
As is known, with the rapid development of optical fiber communication technology, the existing conventional g.652 optical fiber cannot meet the requirement of high-speed optical communication trunk transmission such as 400G or even 1T, and the construction of a long-distance backbone network is continuously developed towards ultra-long distance, ultra-high speed and ultra-large capacity. As a main index and syndrome of optical fiber signal transmission, reducing optical fiber loss and increasing effective area are widely considered as key factors for increasing optical fiber transmission capacity and transmission distance in the industry.
Currently, when the method is used for preparing low-loss and large-effective-area optical fibers in the industry, the VAD method and the PCVD method are mostly adopted to prepare the core rod, the refractive index of the optical fiber prepared by the VAD method is difficult to control, and the PCVD method cannot improve the single-fiber capacity due to the influence of the size of the liner tube. In the investigation, it has been found that the production of fluorine-doped core rods by the Outside Vapor Deposition (OVD) method has been rarely reported. SiO removal for attenuation of communication optical fibers2Outside of the intrinsic absorptionDoped GeO2Is the most dominant source of attenuation in optical communication fibers, reducing the core layer GeO2The content is an effective means and a main direction for reducing the attenuation of the optical fiber, and meanwhile, the attenuation of the optical fiber is reduced by reasonably proportioning the viscosity of the core layer and the cladding layer of the optical fiber, reducing the internal stress of the optical fiber, reducing the interface defects, reducing Rayleigh scattering and other factors.
Chinese patent ZL201310409732 discloses a method for preparing a low-loss optical fiber by using a pure silicon core scheme, but the method adopts a pure silicon core design, so that the viscosity matching difficulty of a core layer and a cladding layer is extremely high, the uniformity of the radial refractive index is poor, and the method adopts a PCVD (plasma chemical vapor deposition) in-tube method for preparation, has a complex process and extremely high requirements on optical fiber drawing, and is not beneficial to realizing mass production. 201510355895.5 discloses a method for preparing a low-loss large-effective-area high-strength single-mode optical fiber under a germanium-fluorine co-doped core, which is not beneficial to mass production because the refractive index profile design is very complicated and the steps are complicated although a VAD method is adopted to prepare a core rod.
Disclosure of Invention
Aiming at the problems in the prior art, the invention develops and designs the single-mode optical fiber with low loss, large effective area and high strength, and the method for preparing the optical fiber core rod by an Outside Vapor Deposition (OVD) method.
In addition, the application further designs a method for online assembling and drawing by adopting a two-stage sleeve and a prepared core rod, optical fiber annealing is carried out for many times in the drawing process, a coating with low modulus and high modulus is coated inside and outside the surface of the optical fiber, and the optical fiber with low loss, large effective area and high strength is prepared. The method is simple, the core rod can be subjected to viscosity adjustment according to requirements, the pure silicon core scheme is not needed to reduce the optical fiber attenuation, and the large-scale production is facilitated.
The technical scheme adopted by the invention for realizing the aim is as follows:
a single mode optical fiber includes a first core layer having a circular cross-section,the material is a quartz-based germanium-doped material with a radius of R1Refractive index of n1Refractive index difference of Δ relative to pure quartz10.20 to 0.35 percent; the outer side of the first core layer is provided with a second core layer which is made of quartz-based phosphorus-doped material, the cross section of the second core layer is annular, and the radius of the second core layer is R2Refractive index of n2Refractive index difference Δ relative to pure quartz20.15% -0.25%; the outer side of the second core layer is provided with an inner cladding layer made of quartz-based fluorine-doped material, the cross section of the inner cladding layer is annular, and the radius of the inner cladding layer is R3Refractive index of n3Refractive index difference Δ relative to pure quartz3-0.12% -0; the first core layer, the second core layer and the inner cladding layer jointly form a core rod of the optical fiber, wherein the high-temperature viscosity of the second core layer is matched with that of the inner cladding layer: the viscosity ratio is 1-1.3 at 1900-2060 ℃; the outer side of the inner cladding is a depressed cladding made of quartz-based fluorine-doped material with an annular cross section and a radius of R4Refractive index of n4Refractive index difference Δ relative to pure quartz4-0.40% to-0.28%; the outer side of the depressed cladding is an outer cladding made of pure quartz with a radius of R5Refractive index of n5Refractive index difference Δ relative to pure quartz5＝0～0.02％。
The above relative refractive index (. DELTA.)i)：Δi＝(ni 2-n0 2)/ni 2100% of n, wherein niIs the refractive index of the ith layer of optical fiber material, i is an integer; n is0Is a pure quartz refractive index.
Preferably, the viscosity ratio of the second core layer to the inner cladding layer at the temperature of 1900-2060 ℃ is 1.1-1.15.
Preferably, the first core radius R13.5-5.5 μm, second core radius R25.0 to 7 μm, inner cladding radius R3Is 24-36 μm, the core-spun ratio of the core rod is 4.5-6, and the radius R of the concave cladding layer440-50 μm, outer cladding radius R560 to 62.5 mu m.
The core-spun ratio of the core rod is as follows: the ratio of the diameter of the inner cladding to the diameter of the core.
Preferably, the germanium doped in the first core layer accounts for 3% -10% of the total mass of the core rod; the phosphorus doped in the second core layer accounts for 1-3% of the total mass of the core rod, and the doping concentration of fluorine in the inner cladding layer is not higher than 1200 ppm.
Optionally, in a refractive index profile of the optical fiber, the refractive index of the first core layer is a flat top profile or a sharp top profile.
Optionally, the outer side of the outer cladding is further coated with an inner coating and an outer coating, the modulus of the inner coating is lower than 0.5Mpa, the modulus of the outer coating is higher than 1000Mpa, and the coating is polyacrylate paint.
The present application further provides a method for preparing the single mode optical fiber, comprising the following steps
1) Arranging vertical blowlamps right below a horizontally and transversely arranged target rod on an OVD (over-the-horizon) deposition lathe, and respectively arranging inclined blowlamps at two axial sides of the target rod, wherein the spraying directions of the inclined blowlamps form an included angle with the axial direction of the target rod;
2) introducing a silicon source and a germanium source into a vertical torch, depositing a first core layer loose body outside a target rod, and after the deposition is finished, starting an inclined torch to sinter the first core layer loose body into a compact first core layer;
3) starting a vertical torch, introducing a silicon source, depositing silicon dioxide outside a first core layer, then closing the vertical torch, starting an inclined torch, introducing the silicon source and a phosphorus source, depositing a phosphorus-doped second core layer loose body, after the deposition is finished, starting the inclined torch to sinter the second core layer loose body into a compact second core layer, and controlling the sintering density of the second core layer to be lower than that of the first core layer;
4) starting the vertical torch, introducing a silicon source, depositing silicon dioxide outside the second core layer, then starting the inclined torch, introducing the silicon source and a fluorine source, depositing the fluorine-doped inner cladding loose body together with the vertical torch in operation, and taking out the target rod after deposition is finished;
5) putting the core rod obtained in the step 4) into a dehydration furnace, and introducing He and Cl into the dehydration furnace2Dehydrating the inner cladding loose body; sintering the mixture into a transparent mother rod at the temperature of 1500-1650 ℃ after dehydration is finished;
6) annealing the transparent mother rod, extending the mother rod into a sub-rod, straightening and polishing the sub-rod, annealing again to obtain a transparent core rod, sleeving the transparent core rod into the fluorine-doped sleeve, performing fusion shrinkage to form a combined core rod, then plugging the combined core rod into the pure quartz sleeve, and performing fusion drawing in a drawing furnace to obtain a quartz optical fiber;
7) annealing the quartz optical fiber;
8) and (4) coating the surface.
Compared with the prior art, the method has the following advantages
The single-mode optical fiber has the advantages of low loss, large effective area and high strength:
(1) the attenuation value of the optical fiber at the wavelength of 1550nm is less than or equal to 0.175dB/km, and the typical attenuation value is 0.170 dB/km.
(2) On the basis of the single-mode optical fiber preparation method, the base mode optical power distribution of the low-loss large-effective-area high-strength single-mode optical fiber is flat-top distribution, and the effective area of the single-mode optical fiber at the wavelength of 1550nm is 110-140 um2。
(3) When the single-mode optical fiber is wound for 100 circles under the bending radius of 30mm, the macrobending loss at the wavelength of 1625nm is less than or equal to 0.1dB, and the preferable macrobending loss value is less than or equal to 0.03 dB.
(II) preparing a single-mode optical fiber: the method comprises the steps of respectively depositing a first core layer, a second core layer and an inner cladding layer through an external vapor deposition mode to jointly form a core rod part, doping germanium into the first core layer, doping phosphorus into the second core layer, doping fluorine into the inner cladding layer, enabling three doping elements to respectively enter a design area through a deposition blowtorch oxyhydrogen flame spraying mode, matching a sunken cladding layer and a high-hardness pure quartz outer cladding layer outside a core rod, and performing viscosity matching and multiple annealing in the preparation process.
(1) The second core layer is doped with P element, so that the viscosity of the quartz glass is effectively reduced, and P is oxidized into P2O5The internal structure of the glass is damaged, the viscosity can be reduced on one hand, the refractive index can be improved on the other hand, the hypothetical temperature and the Rayleigh scattering coefficient of the optical fiber are effectively reduced, and the attenuation of the optical fiber is further reduced. This is because P effectively increases the viscosity matching value between the core layer and the inner cladding layer, so that the network structure of silica is relaxed and the core is balancedThe difference between the structure relaxation time of the layer and the structure relaxation time of the inner cladding reduces stress mismatch at the center of the core layer, reduces over-high interface defects caused by viscosity difference and expansion coefficient difference in the wire drawing process, and is favorable for reducing the fictive temperature of the optical fiber. P is mostly doped in the second core layer, and the application reduces the diffusion of P to the first core layer by controlling the sintered density of the first core layer to be larger than that of the second zinc layer, but does not affect the matching of the overall viscosity.
(2) The inner cladding layer is doped with fluorine in the OVD deposition process, so that the bending loss of the optical fiber can be greatly improved.
(3) Besides the vertical blowtorch arranged right below the target rod, the OVD deposition blowtorch (inclined blowtorch) is respectively designed on two sides of the target rod and is specially used for permeation doping of phosphorus-containing gas and fluorine-containing gas and burning of a compact layer. It is reasonable that the angle of the inclined torch is adjustable, but when the torch is operated, the angle of the torch should be fixed to ensure uniform axial deposition density and doping concentration.
(4) The design of the refractive index profile is beneficial to stabilizing optical fiber parameters such as the diameter of an optical fiber mode field and the like, and the optical fiber drawing qualification rate is effectively improved. Meanwhile, the power density of the core fundamental mode electric field is designed to be flat-top distribution, so that the optical power density can be effectively reduced, the optical power intensity of a core layer is improved, and the effective area of the optical fiber is increased. The final 1550nm window attenuation of the obtained optical fiber is less than or equal to 0.175dB/km, the mode field diameter is stabilized at 11.8 +/-0.8 mu m, the preparation requirements of the low-loss G.654.E optical fiber are met, and the method is suitable for high-speed large-scale production.
Drawings
FIG. 1 is a schematic cross-sectional view of an optical fiber according to an embodiment of the present invention;
FIG. 2 is a schematic view of the arrangement of a deposition burner for manufacturing a core rod structure by OVD method according to the present invention;
FIG. 3 is a schematic diagram of a refractive index profile under a flat top profile;
FIG. 4 is a schematic diagram of a refractive index profile under a peaked profile;
fig. 5 is a schematic diagram of the core fundamental mode optical power intensity distribution.
In the figure, 1-first core layer, 2-second core layer, 3-inner cladding layer, 4-depressed cladding layer, 5-outer cladding layer, 6-first blast lamp, 7-second blast lamp, 8-third blast lamp, 9-fourth blast lamp, 10-ceramic target rod, 11-first core layer sintered layer, 12-second core layer sintered layer and 13-OVD mother rod loose body.
Detailed Description
The invention is described in further detail below with reference to the embodiments of the drawing, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
The terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
Deposition: the optical fiber raw material is subjected to a chemical reaction under a certain environment to generate (doped) quartz glass.
And (3) OVD: outside vapor deposition.
And (3) melting and shrinking: the deposited hollow glass tube is gradually burnt into a solid glass rod under a certain heat source, and the solid glass rod is also collapsed.
Sleeving a sleeve: can meet the requirements of high-hardness quartz glass tubes with certain cross section and size uniformity or fluorine-doped quartz glass tubes.
Refractive Index Profile (RIP): between the refractive index of the optical fibre or optical fibre preform (including the core rod) and its radius
A relationship curve.
Core-spun ratio b/a: representing the ratio of the inner cladding diameter to the core diameter.
Relative refractive index (Δ)i)：Δi＝(ni 2-n0 2)/ni 2100% of n, wherein niIs the refractive index of the ith layer of optical fiber material, i is an integer; n is0Is a pure quartz refractive index.
Optical fiber effective area Aeff:
where E is the electric field associated with propagation and r is the distance from the axis to the point of electric field distribution.
MFD is the fiber mode field diameter. The larger the MFD, the larger the effective area of the fiber.
Rayleigh scattering coefficient R: r ═ Rc+Rd，RcRayleigh scattering due to concentration fluctuations, RdIs rayleigh scattering caused by density fluctuation. Rd＝4.1*10-4(K) R can be lowered by lowering the fictive temperatured。
Example 1
As shown in FIG. 1, which is a cross-sectional view of a single mode optical fiber, the bare fiber includes a core layer and an inner cladding layer, the core layer includes a first core layer 1 and a second core layer 2, the first core layer 1 has a radius R13.5 to 5.5 μm,the difference value of the relative refractive index is more than or equal to delta of 0.2 percent1Less than or equal to 0.35 percent, and the radius R of the second core layer 225-7 mu m, and the difference value of the relative refractive indexes is more than or equal to delta of 0.15 percent2Not more than 0.25 percent, the radius of the refractive index of the inner cladding layer 3 is 24 to 36 mu m, the radius ratio of the inner cladding layer 3 to the second core layer 2 is 4.5 to 6, and the difference value of the relative refractive index is not less than minus 0.12 percent and not more than delta3Less than or equal to 0 percent. The cladding comprises a depressed cladding 4 and an outer cladding 5, the radius of the depressed cladding 4 is 40-50 μm, and the relative refractive index difference is-0.40% < delta >4Less than or equal to-0.28 percent, the outer cladding 5 is a high-hardness pure quartz sleeve, the radius of the outer cladding 5 is 62.5 mu m, and the refractive index difference delta relative to the pure quartz is5＝0～0.02％。
The first core layer has a peaked distribution (as shown in fig. 4) or a flat-topped distribution (as shown in fig. 3) in the middle. In the single mode fiber, except SiO2, the content of germanium needs to be controlled in the first core layer, so that the contribution refractive index of germanium to the first core layer is 0.04-0.12%, and the content of germanium in the core layer accounts for 5-8% of the weight of the core rod. The content of phosphorus element in the second core layer is controlled, so that the contribution refractive index of phosphorus to the second core layer is 0.02-0.06%, the phosphorus content of the core layer accounts for 1-2.4% of the total mass, and the phosphorus raw material can be POCl3. The inner cladding is doped with a small amount of fluorine, so that the fluorine contributes to the inner cladding with a refractive index of-0.01 to-0.03 percent, and the fluorine-doped concentration is 800-1200 ppm. The fluorine-doped material may be SF6、CF4、SiF4One kind of (1).
For the depressed cladding 4 part, an externally purchased deep fluorine-doped sleeve (Heraeus, F520-40) and a core rod are adopted for carrying out fusion shrinkage, and the fluorine-doped part can also be sintered by OVD process outsourcing. The outer cladding 5 is made of high-hardness pure quartz sleeve.
The viscosity of the optical fiber core layer material and the inner cladding layer material needs to be matched at high temperature, and the ratio of the optical fiber core layer material to the inner cladding layer material ranges from 1.0 to 1.15 under the condition of wire drawing temperature of 1900-2060 ℃.
An inner coating and an outer coating are also arranged outside the outer coating, wherein the modulus of the inner coating is lower than 0.5Mpa, the diameter of the inner coating is more than 192 mu m, the modulus of the outer coating is higher than 1000Mpa, the diameter of the outer coating is 245 +/-3 mu m, and the strength of the optical fiber is more than or equal to 200 kpsi.
The single-mode optical fiber has low loss, large effective area and high strengthSingle-mode fiber: the effective area at 1550nm wavelength is 110-150 μm2. The attenuation value of the optical fiber at the wavelength of 1550nm is less than or equal to 0.175dB/km, and the typical attenuation value is 0.170 dB/km. The mode field diameter of the single mode optical fiber at 1550nm wavelength is 11.0-14.0, and the effective area is 110-140 um2. When the single-mode optical fiber is wound by 100 turns under the bending radius of 30mm, the macrobending loss at the wavelength of 1625nm is equal to or less than 0.1dB, and the preferable macrobending loss value is equal to or less than 0.03 dB.
Example 2
A method for preparing single-mode optical fiber with flat-top distribution at the center of first core layer in Refractive Index Profile (RIP) comprises the following steps
Preparing a core rod by adopting OVD (over-the-counter deposition) external vapor deposition, wherein the core rod is divided into a first core layer 1, a second core layer 2 and an inner cladding layer 3, four blowlamps are arranged in a deposition lathe, two vertical blowlamps are arranged at 200-300 mm positions under a pre-installed ceramic target rod (the length is 2000-2200 mm, and the diameter is 6-8 mm), the vertical blowlamps are arranged in parallel along a straight line, the injection direction is vertical to the ceramic target rod, and the vertical blowlamps are named as a first blowlamp and a second blowlamp respectively; the other two blowlamps are distributed on two sides of the main axis of the pre-installed ceramic target rod, are respectively fixed in advance at an angle of 45 degrees with the horizontal plane and are respectively named as a third blowlamp and a fourth blowlamp, the ceramic target rod can reciprocate back and forth along the axial direction, namely the horizontal direction, and meanwhile, the ceramic target rod can rotate per se. The distance between the third blowtorch and the main axis of the ceramic rod is 180 mm-300 mm, the distance between the fourth blowtorch and the main axis of the ceramic rod is 220 mm-270 mm, and the distance between the fourth blowtorch and the main axis is larger than that between the third blowtorch and the fourth blowtorch. The positions of the third blowtorch and the fourth blowtorch can be adjusted on the designed semicircular track, so that the spray angles of the third blowtorch and the fourth blowtorch are controlled to be 30-60 degrees relative to the horizontal plane. The third torch is used for spraying POCl3The fourth torch is used for spraying SF6Or CF4Or SiF4. The specific implementation steps are as follows:
s1: first, a first core layer is deposited, and SiCl is supplied in a first torch and a second torch4、GeCl4、H2、O2As a raw material, SiCl4Flow rate: 2.8-3.2 g/min, GeCl4Flow rate: 1.3-1.6 gMin, keeping the flow stable in the deposition process, reducing the fluctuation, along with the back-and-forth rotary motion of the ceramic rod, the forward motion speed is slow, the moving speed is 2000mm/min, the reverse motion speed is fast, the moving speed is 10000mm/min, the rotating speed of the target rod is 200rpm, and the SiO obtained by oxyhydrogen flame hydrolysis2And GeO2The particles are deposited on the surface of the ceramic rod layer by layer, and the deposition density of the first core layer is controlled to be 0.6-0.9 g/cm3Stopping the supply of the blowtorch after the deposition of the core layer is finished, starting the third deposition blowtorch and the fourth deposition blowtorch (the injection angle is 40 degrees), heating and sintering the outer surface of the core layer by using large-flow oxyhydrogen flame, and H in the blowtorch2And O2The flow rates are respectively 35L/min and 18L/min, so that a compact layer is formed, and the density of the compact layer is controlled to be 1.4g/cm3～2.0g/cm3。
S2: depositing a second core layer, supplying SiCl in the first torch4、H2、O2SiCl in the first torch4The flow rate is controlled to be larger, the flow rate is 3.0-3.3 g/min, and the raw material supply in the first blast lamp is stopped after the deposition is carried out until the weight is 2.3-2.5 kg; introducing SiCl into the third blast lamp4、POCl3、H2、O2Wherein SiCl4Flow rate of 0.5-0.8 g/min, POCl3The flow rate is 0.3-0.5 g/min, before the operation of the third blast lamp, the spraying angle of the third blast lamp is adjusted to 30 degrees and is fixed, and the third blast lamp continuously diffuses phosphorus elements into the second core layer in a deposition mode. The deposition density of the second core layer is controlled to be 0.8-1.0 g/cm3And the deposition radius of the second core layer reaches 55 mm. Turning off the third torch, turning on the third and fourth torches, and heating the outer surface of the core layer with large flow oxyhydrogen flame, wherein H is in the torch2And O2The flow rates are respectively 30L/min and 15L/min, so that a compact layer is formed on the surface of the material, and the density of the compact layer is controlled to be 1.2g/cm3～1.8g/cm3And the sintered density of the second core layer is smaller than that of the first core layer.
The reason why the densities of the first core layer prepared in the step S1 and the second core layer prepared in the step S2 are different is that the first core layer has a high density and the second core layer has a low density because the penetration of the doping element is controlled, so that the phosphorus element can only enter the second core layer and cannot enter or is difficult to enter the first core layer.
S3: depositing the inner cladding, starting the first and second torches (vertical torches) to supply SiCl separately4、H2、O2As raw material, after depositing about 22-25 kg, SiCl is added in the first and second blowlamps4Reducing the flow by 50%, starting a fourth blast lamp, and spraying SiCl in the fourth blast lamp4、SF6、H2、O2So that a small amount of fluorine is diffused into the inner cladding, and SiCl in a fourth torch4The flow rate is controlled to be 2.8g/min, SF6The flow rate is controlled to be 0.2-0.4L/min, the deposition density of the inner cladding is controlled to be 0.5-0.8 g/cm3. When the outer diameter reaches 280 mm-300 mm, the deposition of the loose body of the core rod is finished, the central ceramic rod is taken out after the deposition of the loose body of the inner cladding is finished, and the core rod is in a central hole state.
S4: placing the loose core rod body into a dehydration furnace, controlling the rotation speed of the loose core rod body at 3r/min, and introducing He and Cl into the dehydration furnace2And He flow rate: 15-20L/min, Cl2The flow rate is 0.8-1.2L/min, and the dehydration temperature is as follows: 1100-1150 ℃, dehydration time: 200-300 min; and then transferring the loose core rod body from the dehydration furnace to a sintering furnace, controlling the vacuum degree in the furnace at 100 millipascals and the He flow at 28-35L/min, sintering at 1500-1600 ℃ for 6-8 h to obtain a transparent glass mother rod, wherein the diameter of the mother rod is 140-150 mm, the length of the mother rod is 1-1.1 m, the center hole is well closed and has no air line, annealing the sintered transparent glass mother rod at 1000-1100 ℃ for 8-10 h, extending the transparent glass mother rod into a sub-rod with the corresponding diameter through an extension furnace, the diameter of the sub-rod is 38 +/-0.5 mm, the length of the sub-rod is 1-1.1 m, performing micro-alignment treatment on alignment equipment, transversely installing the transparent glass mother rod on a lathe, performing surface polishing treatment by using oxyhydrogen flame, performing forward and reverse polishing for 1 time respectively, aligning and performing polishing treatment, annealing the core rod at 1100-1150 ℃ for 4-8 h again, and finally obtaining.
S5: the method comprises the steps of arranging a core rod and a deep fluorine-doped pipe, wherein the inner diameter of the fluorine-doped pipe is 40 +/-0.5 mm, the wall thickness is 9mm, the length is 1100mm, the fluorine-doped depth is-0.0045 to-0.005, carrying out high-temperature fusion on the fluorine-doped pipe on an MCVD lathe by using oxyhydrogen flame, arranging the core rod and the deep fluorine-doped pipe on a lathe fixture, burning the flame by using the oxyhydrogen flame, heating the surface temperature of the deep fluorine-doped pipe to 2000 to 2250 ℃, continuously moving a heat source in the longitudinal direction of the fluorine-doped pipe at the speed of 20 to 60mm/min, and keeping a negative pressure state of-40 to-60 kpa in the pipe until the fluorine-doped pipe and the core rod are all collapsed into an integral rod.
S6: and (2) placing the combined core rod into a high-hardness pure quartz sleeve (with the inner diameter of 60mm, the wall thickness of 45 +/-0.5 mm and the length of 1100mm), carrying out online vacuum-pumping wire drawing, wherein the wire drawing temperature is 1980-2100 ℃, the bare fiber tension is 150g, the wire drawing speed is 1200-1700 mpm, 1-3 sections of annealing furnaces are arranged below a wire drawing furnace, the temperature of the annealing furnaces is set to be 1100-1300 ℃, and annealing treatment is carried out on the optical fiber. And coating the inner layer and the outer layer by using a special coating, wherein the diameter of the inner coating is preferably 195 micrometers, the diameter of the outer coating is 245 +/-3 micrometers, the modulus of the inner coating is lower than 0.5Mpa, and the modulus of the outer coating is higher than 1000 Mpa.
The optical fiber prepared in the mode has the 1550nm attenuation value of 0.170dB/km and the optical fiber strength of more than 200 kpsi.
The structural design of the single mode fiber is shown in table 1:
TABLE 1 design for fiber structure and doping content
The main technical indexes of the single-mode optical fiber are shown in table 2:
table 2 shows the main technical indexes of the optical fiber
The modulus of the coating is larger than 1000MPa, and the strength of the optical fiber is improved, and the modulus of the coating selected by serial numbers 2 and 4 is smaller than 1000MPa, and the strength of the optical fiber is also lower than the design requirement of 200 kpsi.
Although preferred embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that modifications and variations of the present invention are possible to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (4)
1. A method for preparing a single mode optical fiber, comprising: comprises the following steps
1) Arranging vertical blowlamps right below a horizontally and transversely arranged target rod on an OVD (over-the-horizon) deposition lathe, and respectively arranging inclined blowlamps at two axial sides of the target rod, wherein the spraying directions of the inclined blowlamps form an included angle with the axial direction of the target rod;
2) introducing a silicon source and a germanium source into a vertical torch, depositing a first core layer loose body outside a target rod, and after the deposition is finished, starting an inclined torch to sinter the first core layer loose body into a compact first core layer;
3) starting a vertical torch, introducing a silicon source, depositing silicon dioxide outside a first core layer, then closing the silicon source deposition vertical torch, starting an inclined torch, introducing the silicon source and a phosphorus source, beginning to deposit a phosphorus-doped second core layer loose body, after the deposition is finished, starting the inclined torch to sinter the second core layer loose body into a compact second core layer, and controlling the sintering density of the second core layer to be lower than that of the first core layer;
4) starting the vertical torch, introducing a silicon source, depositing silicon dioxide outside the second core layer, then starting the inclined torch, introducing the silicon source and a fluorine source, depositing the fluorine-doped inner cladding loose body together with the vertical torch in operation, and taking out the target rod after deposition is finished;
5) putting the core rod obtained in the step 4) into a dehydration furnace, and introducing He and Cl into the dehydration furnace2Dehydrating the inner cladding loose body; sintering the mixture into a transparent mother rod at the temperature of 1500-1650 ℃ after dehydration is finished;
6) annealing the transparent mother rod, extending the mother rod into a sub-rod, straightening and polishing the sub-rod, annealing again to obtain a transparent core rod, sleeving the transparent core rod into the fluorine-doped sleeve, performing fusion shrinkage to form a combined core rod, then plugging the combined core rod into the pure quartz sleeve, and performing fusion drawing in a drawing furnace to obtain a quartz optical fiber;
7) annealing the quartz optical fiber;
8) and (4) coating the surface.
2. The method of making a single mode optical fiber according to claim 1, wherein: the included angle between the spraying direction of the inclined blowtorch and the central axis of the target rod is 30-60 degrees, and the vertical distance between the inclined blowtorch for spraying the fluorine source and the target rod is larger than that between the inclined blowtorch for spraying the phosphorus source and the target rod.
3. The method of making a single mode optical fiber according to claim 1, wherein: in the deposition process, the target rod moves back and forth along the self axial direction while spinning.
4. The method of making a single mode optical fiber according to claim 1, wherein: in the step 6, annealing the sintered transparent mother rod at 1000-1100 ℃ for 8-10 h, mounting the transparent mother rod on a rod hanging platform, sending the transparent mother rod into a wire drawing furnace to extend into a sub-rod, carrying out micro-alignment treatment on the sub-rod on alignment equipment, then polishing the sub-rod in the axial direction by using oxyhydrogen flame in the forward and reverse directions, annealing the core rod at 1100-1150 ℃ for 1-2 h again, and finally obtaining the transparent core rod;
sleeving a transparent core rod into a fluorine-doped quartz tube with the fluorine-doped depth of-0.0045 to-0.005, installing the core rod and the deep fluorine-doped tube on a clamp of MCVD equipment, heating the surface of the deep fluorine-doped tube to 2000-2250 ℃ by using oxyhydrogen flame, continuously reciprocating the oxyhydrogen flame in the axial direction of the fluorine-doped tube at the speed of 20-60 mm/min, and keeping the negative pressure state of-40 to-60 kpa in the tube until the fluorine-doped tube and the core rod are completely collapsed into an integral rod, thereby finishing the processing of the combined core rod;
and (3) placing the combined core rod in a high-hardness pure quartz sleeve, and vacuumizing and drawing, wherein the drawing temperature is controlled to be 1900-2060 ℃.
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| CN110794509B (en) | 2020-09-11 |
| CN111694088B (en) | 2022-06-14 |
| CN110794509A (en) | 2020-02-14 |
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