Method for preparing optical fiber having large effective area and ultralow loss

Abstract

Disclosed in the present invention is a method for preparing an optical fiber having a large effective area and an ultralow loss. The method comprises the following steps: S1, preparing a chlorine-doped non-porous glass tube; S2, preparing an alkali-metal-doped core; S3, inserting the core into the chlorine-doped non-porous glass tube to form an assembly, and collapsing the assembly under a fluorine-containing atmosphere, so as to prepare a core rod; and S4, forming a cladding layer outside of the prepared core rod, and subjecting same to deeply-fluorine-doped sintering, wherein during the collapsing process in step S3, a clean gas, which is a gas mixture of Cl2 and He, is introduced for cleaning the surfaces of the core and the glass tube. In the present invention, an annular cross-section structure design is used, and the clean gas is introduced during the preparation process to clean an optical transmission region; and the prepared optical fiber has an effective area of 130 μm2 to 150 μm2 at 1550 nm, and is capable of achieving an ultralow attenuation loss.

Description

A method for preparing large effective area ultra-low loss optical fiber Technical field:

[0001] The present invention belongs to the technical field of optical fibers, and in particular relates to a method for preparing an optical fiber with a large effective area and ultra-low loss. Background technology:

[0002] Large capacity and long distance transmission systems can greatly increase the optical power transmitted and passed through the optical fiber, which also puts forward higher requirements for reducing nonlinear effects. The magnitude of nonlinearity is generally expressed by the nonlinear refractive index n2 of the optical fiber and the effective area A of the optical fiber. eff The ratio of n2 / A eff Effective measures to suppress nonlinearity include reducing the nonlinear refractive index of the optical fiber and increasing the effective area of ​​the optical fiber. Since the nonlinear refractive index is an inherent property of the optical fiber material and cannot be significantly reduced, current measures to suppress nonlinearity mainly focus on increasing the effective area of ​​the optical fiber.

[0003] Patent CN109298482A proposes a method for producing single-mode optical fibers with large effective areas, low attenuation and low bending loss. This method utilizes a double-fluorine-doped depressed cladding design to effectively improve the bending loss performance of large effective area optical fibers. However, its drawback is that the PCVD method used to prepare the core rod limits its diameter. Furthermore, the optical fiber produced by this process exhibits a transmission loss of 0.170 dB / km at 1550 nm, exceeding that of ultra-low-loss optical fibers produced by other methods.

[0004] Patent CN109683233A proposes a method for preparing a single-mode optical fiber with ultra-low attenuation and large effective area. The ultra-low loss optical fiber prepared by this method has an effective area of ​​137μm at 1550nm. 2 The transmission loss at 1550nm is 0.154dB / Km, but its defect is that it adopts a multi-depression layer profile structure. The complex profile design makes it difficult to control in actual production and difficult to carry out large-scale mass production.

[0005] Patent US9097834B2 proposes a method for preparing a chlorine-doped ring structure core. The ultra-low loss optical fiber prepared by this method has an effective area of ​​140μm at 1550nm. 2 The mode field diameter at 1550nm is 12.7 μm, but the patent involves the process of directly depositing the cladding on the surface of the alkali metal-doped core and preparing the core chlorine-doped layer, which will cause hydroxyl groups to diffuse into the core, resulting in the risk of high water peak attenuation loss in the optical fiber.

[0006] In response to the shortcomings of the above-mentioned existing technologies, the present invention provides a method for preparing ultra-low-loss optical fiber with a large effective area. It not only has the advantage of low manufacturing cost, but also can solve the problem of interface contamination between the fluorine-doped inner cladding and the core during the preparation of the chlorine-doped core.

[0007] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0008] Summary of the invention:

[0009] The object of the present invention is to provide a method for preparing a large effective area ultra-low loss optical fiber, thereby overcoming the above-mentioned defects in the prior art.

[0010] In order to achieve the above object, the present invention provides a method for preparing a large effective area ultra-low loss optical fiber, comprising the following steps:

[0011] S1: Preparation of chlorine-doped non-porous glass tubes;

[0012] S2: preparing alkali metal-doped cores;

[0013] S3: inserting the core into a chlorine-doped non-porous glass tube to form an assembly, and collapsing the assembly in a fluorine-containing atmosphere to form a core rod;

[0014] S4: forming a cladding layer on the outer surface of the prepared core rod and performing deep fluorine doping sintering;

[0015] During the collapse process of step S3, a cleaning gas is introduced, wherein the cleaning gas is a mixture of Cl2 and He, and is used to clean the surface of the core and the glass tube.

[0016] Furthermore, as a preference, the order of step S1 and step S2 is not limited.

[0017] Furthermore, preferably, in step S1, when preparing the chlorine-doped non-porous glass tube, a chlorine-doped silica loose body doped with chlorine atoms is first deposited on the surface of the glass tube by an external vapor deposition method, and then placed in a muffle furnace for sintering to form a dense chlorine-doped non-porous glass tube.

[0018] Furthermore, preferably, the raw materials used in the external vapor deposition method are SiCl4, H2 and O2, and one or a mixture of two or more gases selected from Cl2, Si2Cl6, SiCl4, CF4, C2F6, SiF4 and SF6 are introduced during sintering in the muffle furnace.

[0019] Furthermore, preferably, when preparing the alkali metal-doped core in step S2, the alkali metal is first doped into the pure silicon glass tube, and then melted into the alkali metal-doped core.

[0020] Furthermore, preferably, when preparing the core rod in step S3, firstly, a silicon dioxide loose body is deposited outside the chlorine-doped non-porous glass tube by an external vapor deposition method, and then the core is inserted into the chlorine-doped non-porous glass tube to form an assembly.

[0021] Furthermore, preferably, the optical fiber has, from the inside to the outside, an alkali metal-doped region, a chlorine-doped region, a fluorine-doped inner cladding region and a cladding region.

[0022] Furthermore, preferably, the effective area of ​​the optical fiber at 1550 nm is greater than or equal to 130 μm 2 and less than or equal to 150μm 2 .

[0023] Furthermore, preferably, the mode field diameter of the optical fiber at 1550 nm is greater than or equal to 12 μm and less than or equal to 13 μm.

[0024] Furthermore, preferably, the attenuation of the optical fiber at 1550 nm is less than or equal to 0.155 dB / Km.

[0025] Compared with the prior art, one aspect of the present invention has the following beneficial effects:

[0026] (1) The present invention adopts an annular cross-sectional structure design of an alkali metal doped region, a chlorine doped region, and a fluorine doped inner cladding region, and the prepared optical fiber has a 130 μm optical fiber at 1550 nm. 2 -150μm 2 The effective area;

[0027] (2) The core rod of the optical fiber is treated with chlorine doping, which can effectively improve the structural relaxation phenomenon of silica glass and reduce the structural defects of the optical fiber caused by rapid cooling after drawing, thereby reducing the attenuation loss of the optical fiber;

[0028] (3) During the preparation of the core rod, clean gas is introduced to clean the light transmission area, which can avoid the risk of hydroxyl groups diffusing into the core during the deposition process on the core surface, causing the water peak attenuation to be too high; at the same time, it solves the contamination problem between the fluorine-doped inner cladding of the core rod and the core interface. Description of the drawings:

[0029] FIG1 is a schematic diagram of depositing a chlorine-doped loose body on a target rod according to the present invention;

[0030] FIG2 is a schematic diagram of sintering a chlorine-doped non-porous glass tube according to the present invention;

[0031] FIG3 is a schematic diagram of forming a loose silica body on a chlorine-doped glass tube according to the present invention;

[0032] FIG4 is a schematic diagram of the preparation of a core rod according to the present invention;

[0033] FIG5 is a schematic diagram of depositing a loose silica body on the surface of a core rod according to the present invention;

[0034] FIG6 is a schematic cross-sectional view of an optical fiber made according to the present invention;

[0035] Figure numerals: 1-assembly of target rod and chlorine-doped loose body, 10-target rod, 11-deposition handle, 12-chlorine-doped loose body, 13-burner, 14-plug with capillary structure, 15-gas in furnace, 16-sintering handle, 17-muffle furnace, 21-alkali metal-doped core, 3-assembly of alkali metal-doped core and chlorine-doped glass tube, 31-section chlorine-doped glass tube, 32-silica loose body, 33-centerline gas, 4-optical rod precursor, 41-section core rod, 42-handle, 43-quartz extension section. Specific implementation method:

[0036] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0037] The following is a brief summary of one or more aspects to provide a basic understanding of these aspects. This summary is not an exhaustive overview of all conceivable aspects and is neither intended to identify key or critical elements of all aspects nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that will be provided later.

[0038] Example 1:

[0039] A method for preparing a large effective area ultra-low loss optical fiber comprises the following steps:

[0040] S1: Preparation of chlorine-doped non-porous glass tubes;

[0041] Specifically, as shown in FIG1 , a target rod 10 with a diameter of 30 mm is passed through a deposition handle 11. The target rod 10 is made of alumina ceramic. A layer of chlorine-doped loose body 12 is deposited on the surface of the target rod 10 by a burner 13. After the deposition is completed, the target rod 10 is pulled out from the chlorine-doped loose body 12.

[0042] When depositing the chlorine-doped soot body 12, a chlorine-containing precursor is selected as the silicon dioxide soot body precursor. Specifically, one of SiCl4 and Si2Cl6 or a mixture of the two precursors is selected as the raw material.

[0043] As shown in FIG2 , a sintered handle 16 is welded to the end face of the deposition handle 11, and a capillary plug 14 is welded to the other end. The chlorine-doped loose body 12 including the handle and the plug is hung as an assembly 1 in a muffle furnace 17 for doping and sintering to form a densified chlorine-doped non-porous glass tube.

[0044] During doping and sintering, a gas 15 is introduced into the muffle furnace 17, where the gas 15 is a mixture of a doping gas and a diluent gas, wherein the doping gas is selected from one or a mixture of two or more of Cl2, SiCl4, Si2Cl6, CF4, C2F6, SiF4 and SF6, and the diluent gas is selected from one or a mixture of two or more of He, Ar and N2; at the same time, the above-mentioned chlorine-containing precursor is introduced into the muffle furnace 17, and the partial pressure of the chlorine-containing precursor in the mixed gas is greater than or equal to 10 atmospheres and less than or equal to 25 atmospheres;

[0045] After testing, the chlorine content in the chlorine-doped non-porous glass tube prepared above is greater than or equal to 5000 ppm and less than or equal to 30000 ppm;

[0046] The chlorine-doped non-porous glass tube prepared above is stretched, and the stretched tube is cut into sections of chlorine-doped glass tubes 31;

[0047] S2: preparing alkali metal-doped cores;

[0048] Alkali metal elements are doped into a pure silica glass tube, and then an alkali metal-doped core 21 is produced by a collapse process. The alkali metal is selected from one or two or more elements selected from lithium, sodium, potassium, and rubidium. A more preferred solution is to select two or more alkali metal elements for doping.

[0049] According to the test, the average concentration of alkali metal in the alkali metal-doped core 21 is greater than or equal to 100 ppm and less than or equal to 300 ppm;

[0050] S3: prepare the mandrel;

[0051] As shown in FIG3 , a deposition handle 11 is first welded to one end of a chlorine-doped glass tube 31, and a capillary plug 14 is welded to the other end. A layer of silicon dioxide loose material 32 is deposited on the surface of the chlorine-doped glass tube 31 using a burner. After the deposition is completed, a sintered handle 16 is welded to one end of the deposition handle 11.

[0052] As shown in FIG4 , an alkali metal-doped core 21 is inserted into a chlorine-doped glass tube 31 to form an assembly 3. The assembly 3 is then placed in a muffle furnace 17 for cleaning and fluorine doping. During this process, the temperature in the muffle furnace 17 is controlled between 1000° C. and 1250° C., more preferably between 1150° C. and 1200° C. During the fluorine doping process, gas 15 and centerline gas 33 are introduced into the furnace. The gas 15 is a mixture of a doping gas and a diluent gas, wherein the doping gas is selected from one or a mixture of two or more of Cl2, SiCl4, Si2Cl6, CF4, C2F6, SiF4, and SF6, and the diluent gas is selected from one or a mixture of two or more of He, Ar, and N2. The centerline gas 33 is a mixture of Cl2 and He, which is used to clean the outer surface of the alkali metal-doped core 21 and the inner surface of the chlorine-doped glass tube 31, while preventing the formation of seed crystals on the contact surface between the two. The cleaning and fluorine doping process takes about 1-5 hours, more preferably 2-3.5 hours.

[0053] After the cleaning and fluorine doping process is completed, the assembly 3 is sintered and melted in a muffle furnace 17. The sintering temperature is controlled at 1400°C-1600°C, so that the silicon dioxide loose body 32 forms a dense glass body. At the same time, during this process, the chlorine-doped glass tube 31 collapses onto the alkali metal-doped core 21, and the two gradually fuse into one. After fusion, the core rods 41 are stretched and cut into sections.

[0054] S4: forming a cladding layer on the outer surface of the prepared core rod and performing deep fluorine doping sintering;

[0055] As shown in FIG5 , a handle 42 and a quartz extension section 43 are welded to both ends of the section core rod 41 , and then a layer of silica loose body 32 is deposited on the surface of the section core rod 41 to obtain a light rod precursor 4 . The light rod precursor 4 is then placed in a muffle furnace 17 for fluorine doping and sintering treatment, and the silica loose body 32 is densified to form a deep fluorine-doped cladding.

[0056] During this process, the temperature in the muffle furnace 17 is controlled between 1000°C and 1250°C, and the more preferred temperature range is 1150°C to 1200°C. During the fluorine doping process, gas 15 and centerline gas 33 are introduced into the furnace. Gas 15 is a mixture of doping gas and dilution gas, wherein the doping gas is selected from one or a mixture of two or more of Cl2, SiCl4, Si2Cl6, CF4, C2F6, SiF4 and SF6, and the dilution gas is selected from one or a mixture of two or more of He, Ar and N2.

[0057] After deep fluorine doping and sintering, an ultra-low loss optical rod is obtained.

[0058] The cross-section of the ultra-low-loss optical fiber after the light rod is drawn is shown in Figure 6, where regions r1, r2, r3, and r4 are the alkali metal doped region, chlorine doped region, fluorine-doped inner cladding region, and deep fluorine-doped cladding region, respectively. The effective area of ​​the optical fiber is related to the electric field intensity distribution of the propagating light. The ring structure can change the electric field intensity distribution and thus change the effective area. Therefore, the optical fiber produced by the above ring design has a transmission loss of 0.152dB / Km at 1550nm and an effective area of ​​135μm 2 , the mode field diameter is 12.6μm;

[0059] In addition, the core rod of the optical fiber is treated with chlorine doping, which can effectively improve the structural relaxation phenomenon of silica glass and reduce the structural defects of the optical fiber caused by rapid cooling after drawing, thereby reducing the attenuation loss of the optical fiber; and in the process of preparing the core rod, clean gas is introduced to clean the light transmission area, which can avoid the risk of hydroxyl groups diffusing into the core during the deposition process on the core surface, causing the water peak attenuation to be too high; at the same time, it solves the contamination problem between the fluorine-doped inner cladding of the core rod and the core interface.

[0060] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many variations and modifications are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the invention and various options and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing a large effective area ultra-low loss optical fiber, characterized in that: The following steps are involved: S1: preparing chlorine-doped non-porous glass tubes; S2: preparing alkali metal-doped core; S3: inserting the core into a chlorine-doped non-porous glass tube to form an assembly, and collapsing the assembly in a fluorine-containing atmosphere to form a core rod; S4: forming a cladding layer on the outside of the manufactured core rod and performing deep fluorine doping sintering; In the step S3, a cleaning gas is introduced during the collapse process. The cleaning gas is a mixed gas of Cl2 and He, which is used to clean the surface of the core and the glass tube.

2. The method for preparing a large effective area ultra-low loss optical fiber according to claim 1, characterized in that: The order of step S1 and step S2 is not limited.

3. The method for preparing a large effective area ultra-low loss optical fiber according to claim 1, characterized in that: In the step S1, when preparing the chlorine-doped non-porous glass tube, a chlorine-doped silicon dioxide loose body doped with chlorine atoms is first deposited on the surface of the glass tube by an external vapor deposition method, and then placed in a muffle furnace for sintering to form a dense chlorine-doped non-porous glass tube.

4. The method for preparing a large effective area ultra-low loss optical fiber according to claim 3, characterized in that: The raw materials used in the external vapor deposition method are SiCl4, H2 and O2. During sintering in the muffle furnace, one or a mixed gas of two or more of Cl2, Si2Cl6, SiCl4, CF4, C2F6, SiF4 and SF6 is introduced.

5. The method for preparing a large effective area ultra-low loss optical fiber according to claim 1, characterized in that: When preparing the alkali metal-doped core in step S2, the alkali metal is firstly doped into a pure silicon glass tube, and then melted and shrunk into the alkali metal-doped core.

6. The method for preparing a large effective area ultra-low loss optical fiber according to claim 1, characterized in that: When preparing the core rod in step S3, firstly, a loose body of silicon dioxide is deposited outside the chlorine-doped non-porous glass tube by an external vapor deposition method, and then the core is inserted into the chlorine-doped non-porous glass tube to form an assembly.

7. The method for preparing a large effective area ultra-low loss optical fiber according to claim 1, characterized in that: The optical fiber has an alkali metal doped region, a chlorine doped region, a fluorine doped inner cladding region and a cladding region from the inside to the outside.

8. The method for preparing a large effective area ultra-low loss optical fiber according to claim 1, characterized in that: The effective area of ​​the optical fiber at 1550nm is greater than or equal to 130μm 2 And less than or equal to 150μm 2 .

9. The method for preparing a large effective area ultra-low loss optical fiber according to claim 1, characterized in that: The mode field diameter of the optical fiber at 1550 nm is greater than or equal to 12 μm and less than or equal to 13 μm.

10. The method for preparing a large effective area ultra-low loss optical fiber according to claim 1, characterized in that: The attenuation of the optical fiber at 1550 nm is less than or equal to 0.155 dB / Km.

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