阅读说明：本技术 一种单模光纤及其制备方法 (Single-mode optical fiber and preparation method thereof ) 是由 宋海瑞 冯术娟 孙周 徐亮 侯树虎 缪振华 卞新海 韩婷婷 于 2019-09-29 设计创作，主要内容包括：一种单模光纤及其制备方法,裸光纤包括芯层和包层,芯层包括第一芯层、第二芯层、内包层,第一芯层相对折射率差值为0.2％≤Δ<Sub>1</Sub>≤0.35％,第二芯层相对折射率差值为0.15％≤Δ<Sub>2</Sub>≤0.25％,内包层折射率半径为24μm～36μm,内包层相对折射率差值为-0.12％≤Δ<Sub>3</Sub>≤0％。包层,包括凹陷包层和外包层,凹陷包层相对折射率差值为-0.40％≤Δ<Sub>4</Sub>≤-0.28％,外包层为高硬度纯石英套管。采用两级套管与芯棒在线组装拉丝的方法,在拉丝过程中进行多次光纤退火,在光纤表面内涂低模量、外涂高模量的涂层,制备低损耗大有效面积高强度光纤。方法简单,芯棒可根据需求进行粘度调整,无需采用纯硅芯方案来降低光纤衰减,有利于规模化生产。(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% delta 1 Not 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 delta 2 Not 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 delta 3 Less 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 > 4 Less than or equal to-0.28 percent, and the outer cladding is a high-hardness pure quartz sleeve. Using a two-stage sleeve andthe method for online assembling and drawing the core rod is characterized in that optical fiber annealing is carried out for multiple 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.)

1. A single mode optical fiber, characterized by: comprises that

A first core layer (1) with a circular cross section and made of quartz-based germanium-doped material with a radius of R₁Refractive index of n₁Refractive index difference of Δ relative to pure quartz₁＝0.20％～0.35％；

The outer side of the first core layer (1) is provided with a second core layer (2) 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 quartz₂＝0.15％～0.25％；

The outer side of the second core layer (2) is provided with an inner cladding layer (3) which is 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 (1), the second core layer (2) and the inner cladding layer (3) jointly form a core rod of the optical fiber, wherein the viscosity ratio of the second core layer (2) to the inner cladding layer (3) at the temperature of 1900-2060 ℃ is 1-1.3;

the outer side of the inner cladding (3) is a sunken cladding (4) made of quartz-based fluorine-doped material, the cross section of the inner cladding is annular, and the radius of the inner cladding is R₄Refractive index of n₄Refractive index difference Δ relative to pure quartz₄＝-0.40％～-0.28％；

The outer side of the depressed cladding (4) is provided with an outer cladding (5) made of pure quartz with the radius of R₅Refractive index of n₅Refractive index difference Δ relative to pure quartz₅＝0～0.02％。

2. The single mode optical fiber of claim 1, wherein: the viscosity ratio of the second core layer (2) to the inner cladding layer (3) at the temperature of 1900-2060 ℃ is 1.1-1.15.

3. The single mode optical fiber of claim 1, wherein: the first core radius R₁3.5-5.5 μm, second core radius R₂5.0 to 7 μm, inner cladding radius R₃24-36 μm, the core-spun ratio of the core rod is 4.5-6, and the depressed cladding layer is a halfDiameter R₄40-50 μm, outer cladding radius R₅60 to 62.5 mu m.

4. The single mode optical fiber of claim 1, wherein: the germanium doped in the first core layer (1) accounts for 3% -10% of the total mass of the core rod; the phosphorus doped in the second core layer (2) accounts for 1-3% of the total mass of the core rod, and the doping concentration of fluorine in the inner cladding layer (3) is not higher than 1200 ppm.

5. The single mode optical fiber of claim 1, wherein: on the refractive index profile of the optical fiber, the refractive index of the first core layer is in flat top distribution or sharp top distribution.

6. The single mode optical fiber of claim 1, wherein: the outer side of the outer cladding layer (5) is also coated with an inner coating and an outer coating, the modulus of the inner coating is lower than 0.5MPa, and the modulus of the outer coating is higher than 1000 MPa.

7. 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.

8. The method of making a single mode optical fiber according to claim 7, 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.

9. The method of making a single mode optical fiber according to claim 7, wherein: in the deposition process, the target rod moves back and forth along the self axial direction while spinning.

10. The method of making a single mode optical fiber according to claim 7, 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 ℃.

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 fibers₂Doped with GeO in addition to intrinsic absorption₂Is the most dominant source of attenuation in optical communication fibers, reducing the core layer GeO₂In an amount to reduce attenuation of the optical fiberMeanwhile, 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 comprises a first core layer with a circular cross section made of quartz-based germanium-doped material and 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)：Δ_i＝(n_i ²-n₀ ²)/n_i ²100% of n, wherein n_iIs 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. The reason is that the viscosity matching value of the core layer and the inner cladding is effectively improved by the P, so that the network structure of the silicon dioxide is loosened, the difference between the structure relaxation time of the core layer and the structure relaxation time of the inner cladding is balanced, the stress mismatch of the central position of the core layer is reduced, and the viscosity in the wire drawing process is reducedThe difference and the expansion coefficient difference cause too high interface defects, and are beneficial to 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): the refractive index of an optical fiber or an optical fiber preform (including a core rod of an optical fiber) versus its radius.

Core-spun ratio b/a:

representing the ratio of the inner cladding diameter to the core diameter.

Relative refractive index (Δ)_i)：Δ_i＝(n_i ²-n₀ ²)/n_i ²100% of n, wherein n_iIs 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 ═ R_c+R_d，R_cRayleigh scattering due to concentration fluctuations, R_dIs rayleigh scattering caused by density fluctuation. R_d＝4.1*10^-4(K) R can be lowered by lowering the fictive temperature_d。