A low-loss optical fiber preform, its fabrication method, and the optical fiber.

Abstract

This invention discloses a low-loss optical fiber preform, its preparation method, and an optical fiber. The optical fiber preform includes an outer core layer and an inner core layer. The outer core layer is a four-hole quartz tube doped with alkali metal, and the inner core layer is a quartz rod doped with alkali metal. The inner core layer is located inside the four-hole quartz tube, and the outer and inner core layers are fused together. The preparation method includes the following steps: S1: preparing the alkali metal-doped inner core layer; S2: grinding the outer circumference of the inner core layer, then extending the inner core layer, and slicing it for later use; S3: preparing the alkali metal-doped outer core layer; S4: inserting the inner core layer from S2 into the outer core layer from S3 and fusing it to form a low-loss optical fiber preform. This invention, by inserting an alkali metal-doped quartz rod into a four-hole quartz tube doped with alkali metal and then fusing it together to form the optical fiber preform, can produce larger-sized optical fiber preforms, increase the alkali metal content of the optical fiber preform, and reduce optical fiber attenuation.

Description

Technical fields:

[0001] This invention belongs to the field of optical fiber preform preparation technology, and specifically relates to a low-loss optical fiber preform, preparation method and optical fiber. Background technology:

[0002] Optical fiber communication features large transmission capacity, long transmission distance, and high transmission speed, and is widely used in long-haul backbone networks, metropolitan area networks, and access networks. Reducing the fiber attenuation coefficient can effectively increase the transmission distance of optical fiber communication systems, significantly reduce the number and cost of repeater stations, and is of great significance for optimizing transmission system structure and reducing operating costs, especially for submarine optical fibers.

[0003] Alkali metal doping of the core and cladding of optical fibers can optimize viscosity matching between the core and cladding, effectively reducing fiber attenuation. Currently, the diffusion method is commonly used to dope alkali metal elements into quartz glass tubes. This method utilizes heated vapors of high-purity alkali metal elements (purity above 99.9%) to introduce the alkali metal elements into the tube. Then, an external localized heat source is used to heat the glass tube, causing diffusion to the inner surface. After doping, the glass tube is heated to shrink. To remove transition metal elements such as Ni and Fe added during alkali metal doping, a certain thickness of etching is required on the inner surface of the glass tube. Patents such as US20140127507A1, US9229160B2, CN102627400B, and CN102603179A all involve heating alkali metal raw materials placed inside a glass tube with a continuously moving heat source, and then doping the alkali metal into the inner wall of the glass tube via in-tube diffusion. However, this process limits the core size of the optical fiber preform, restricts the doping concentration when preparing large-size preforms, and consequently, large-size preforms cannot achieve the goal of reducing attenuation. This application addresses the shortcomings of the prior art by providing a method for preparing large-size, high-concentration preform cores of optical fiber preforms.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention:

[0005] The purpose of this invention is to provide a low-loss optical fiber preform, a preparation method, and an optical fiber, thereby overcoming the defects in the prior art.

[0006] To achieve the above objectives, the present invention provides a low-loss optical fiber preform, comprising an outer core layer and an inner core layer, wherein the outer core layer is a four-hole quartz tube doped with alkali metal, and the inner core layer is a quartz rod doped with alkali metal, wherein the inner core layer is located inside the four-hole quartz tube, and the outer core layer and the inner core layer are fused together as one unit.

[0007] This invention also provides a method for preparing a low-loss optical fiber preform, comprising the following steps:

[0008] S1: Prepare an alkali metal-doped inner core layer, wherein the alkali metal refers to a group IA metal element selected from Li, Na, K, Rb, Cs, and Fr. In this invention, the alkali metal is selected from potassium.

[0009] S2: Grind the outer circle of the inner core layer, then extend the inner core layer, and cut it for later use. When grinding the outer circle, test the alkali metal concentration of each part of the outer circle and grind away the part with relatively low concentration.

[0010] S3: Prepare an alkali metal-doped outer core layer, wherein the alkali metal refers to a group IA metal element selected from Li, Na, K, Rb, Cs, and Fr. In this invention, the alkali metal is selected from potassium.

[0011] S4: The inner core layer of S2 is inserted into the outer core layer of S3 and fused together to form a low-loss optical fiber preform.

[0012] Furthermore, as a preferred embodiment, after S2 polishing, the fiber is soaked in hydrofluoric acid solution for 10-20 minutes before being extended; after polishing, cleaning with hydrofluoric acid solution can remove impurities from the outer surface of the inner core layer, ensuring the quality of the optical fiber.

[0013] Furthermore, preferably, the concentration of the hydrofluoric acid solution is 15-40%; more preferably, the concentration of hydrofluoric acid is 30% in this invention. If the concentration is too low, it will not have the effect of pickling, while if the concentration is too high, it will cause damage to the outer surface of the inner core layer.

[0014] Furthermore, preferably, the preparation of the alkali metal-doped outer core layer in step S3 includes the following steps:

[0015] S31: Select quartz tubes and process them by drilling holes to form four-hole quartz tubes.

[0016] S32: Immerse the four-hole quartz tube in a 15-40% hydrofluoric acid solution for 10-20 minutes. This removes impurities from the inner wall surface of the holes and ensures the quality of the optical fiber. In this invention, a 30% concentration of hydrofluoric acid and an immersion time of 15 minutes are preferred.

[0017] S33: After removing the four-hole quartz tube from the hydrofluoric acid solution, etch the inner and outer surfaces;

[0018] S34: After etching is completed, alkali metal hot vapor is introduced into the four-hole quartz tube, so that the alkali metal hot vapor diffuses into the inner surface of the quartz tube.

[0019] S35: Secondary etching is performed on the four-hole quartz tube to remove excessive alkali metal elements.

[0020] Furthermore, as a preferred embodiment, in step S33, the inner wall of the four-hole quartz tube is etched using an etching gas; the etching gas can be SF6, and the etching temperature is controlled at 1450-1850℃.

[0021] Furthermore, as a preferred embodiment, the four-hole quartz tube in S34 is placed in a graphite furnace, and the heating temperature of the graphite furnace is 2000℃-2500℃; more preferably, the heating temperature of the graphene is 2350-2450℃.

[0022] The present invention also provides a low-loss optical fiber, which is formed by drawing the above-mentioned optical fiber preform.

[0023] Compared with the prior art, one aspect of the present invention has the following beneficial effects:

[0024] (1) In this invention, an alkali metal-doped quartz rod is loaded into a four-hole quartz tube and then fused together to form an optical fiber preform. This can produce larger optical fiber preforms, increase the alkali metal content of the optical fiber preforms, and reduce optical fiber attenuation.

[0025] (2) The present invention performs outer circle grinding after doping of quartz rod, which can remove the part of the outer surface of quartz rod with relatively low alkali metal concentration, thereby increasing the alkali metal content and uniformity of alkali metal distribution of optical fiber preform and reducing optical fiber attenuation. Attached image description:

[0026] Figure 1 This is a schematic diagram of a low-loss optical fiber preform according to the present invention.

[0027] Figure 2 This is a schematic diagram of welding auxiliary tubes to both ends of the four-hole liner tube according to the present invention.

[0028] Figure reference numerals: 1-outer core layer, 2-inner core layer. Detailed implementation method:

[0029] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0030] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive 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 to prepare for the more detailed descriptions that follow.

[0031] Example 1:

[0032] like Figure 1 As shown, a low-loss optical fiber preform includes an outer core layer 1 and an inner core layer 2. The outer core layer 1 is a four-hole quartz tube doped with alkali metal, and the inner core layer 2 is a quartz rod doped with alkali metal. The inner core layer is located inside the four-hole quartz tube, and the outer core layer and the inner core layer are fused together as one piece.

[0033] A specific method for preparing a low-loss optical fiber preform includes the following steps:

[0034] S1: Alkali metal-doped quartz rods are prepared by diffusion method. Specifically, the diffusion method involves placing the quartz rod in a high-temperature furnace and introducing alkali metal hot vapor into the furnace, causing the alkali metal to deposit and diffuse on the outer surface of the quartz rod. This technology is existing technology and will not be described in detail here. Alkali metal refers to Group IA metal elements, selected from Li, Na, K, Rb, Cs, and Fr. In this embodiment, the alkali metal is selected from potassium, and the alkali metal vapor is selected from potassium bromide. In this embodiment, the amount of potassium bromide vapor introduced is 5g.

[0035] S2: The outer circle of the quartz rod is ground off by cold working. The quartz rod with the outer circle ground off is immersed in a 30% hydrofluoric acid solution for 15 minutes and then extended into a quartz rod with a diameter of 6 mm. After extension, it is cut into 4 pieces with a length of about 600 mm for later use.

[0036] During the grinding of the outer circle, the alkali metal concentration of each part of the outer circle of the quartz rod was tested. The peak value of the alkali metal content on the surface of the quartz rod was measured to be 1850 ppm. Parts with a concentration lower than 1850 ppm were ground off.

[0037] Soaking in hydrofluoric acid solution can clean the fiber, remove impurities from the outer surface of the inner core layer, and ensure the quality of the optical fiber.

[0038] S31: Select a quartz tube with a length of 600mm and an outer diameter of φ34mm, and process the quartz tube into a four-hole liner using machining methods;

[0039] S32: Immerse the four-hole liner in a 30% hydrofluoric acid solution for 15 minutes; similarly, immersion in hydrofluoric acid solution can clean the liner, remove impurities from the inner wall of the hole, and ensure the quality of the optical fiber.

[0040] S33: As Figure 2As shown, the four-hole liner is removed and cleaned. Auxiliary tubes are welded to both ends of the four-hole liner. After welding, a high-temperature graphite furnace and etching gas are used to etch the inner surface of the four-hole liner. Gas etching involves placing the four-hole liner in a high-temperature graphite furnace and then introducing etching gas into the furnace, which gives the inner wall of the four-hole liner a certain roughness, making it easier for alkali metals to deposit and diffuse into the inner wall of the four-hole liner. SF6 can be used as the etching gas, and the etching temperature is controlled at 1450-1850℃. Gas etching of quartz liners is an existing technology and will not be described in detail here.

[0041] S34: After etching is completed, a carrier gas is used to transport potassium bromide vapor heated by an external heat source to the four holes of the liner tube, so that potassium element diffuses from the inner surface of the four holes of the quartz liner tube to the outside of the quartz tube. At this time, the heating temperature of the graphite furnace is constant at 2450-2500℃. Under this temperature range, potassium element can be deposited more quickly and uniformly on the inner wall of the four holes of the quartz tube. In this embodiment, the amount of potassium bromide vapor introduced is 5g.

[0042] S35: Etch the four-hole liner again to remove excessive potassium elements from the inner wall of the four holes; similarly, place the four-hole liner in a high-temperature graphite furnace, and then introduce etching gas into the graphite furnace to remove excessive potassium elements from the inner wall of the four holes. The etching gas can be SF6, and the etching temperature is controlled at 1450-1850℃.

[0043] S4: Insert four quartz rods, each approximately 600 mm long and 6 mm in diameter, into the holes of the four-hole liner tube. Then, through a melting and shrinking process, melt and shrink the four-hole liner tube and the four quartz tubes to form a potassium-doped optical fiber preform with a length of 550 mm and an outer diameter of φ31 mm.

[0044] The above-mentioned optical fiber preform can be drawn into optical fiber.

[0045] Example 2:

[0046] Unlike Example 1, the heating temperature of the S34 graphite furnace is constant at 2250-2300℃.

[0047] Example 3:

[0048] Unlike Example 1, the amount of potassium bromide vapor introduced in S34 is 10g.

[0049] Example 4:

[0050] Unlike Example 3, the heating temperature of the S34 graphite furnace is kept constant at 2250-2300℃.

[0051] Example 5:

[0052] Unlike Example 1, the amount of potassium bromide vapor introduced in S34 was 15g.

[0053] Example 6:

[0054] Unlike Example 5, the heating temperature of the S34 graphite furnace is kept constant at 2250-2300℃.

[0055] Example 7:

[0056] Unlike Example 1, the amount of potassium bromide vapor introduced in S34 is 20g.

[0057] Example 8:

[0058] Unlike Example 7, the heating temperature of the S34 graphite furnace is kept constant at 2250-2300℃.

[0059] Example 9:

[0060] Unlike Example 5, S2 does not involve grinding off the outer diameter. Instead, the quartz rod is directly immersed in a 30% hydrofluoric acid solution for 15 minutes before being stretched and slit.

[0061] The alkali metal content and attenuation at 1500 nm of the optical fiber preforms in Examples 1-9 were tested, and the test results are shown in Table 1 below.

[0062]

[0063] Based on the above test results, the method of the invention can be used to prepare large-diameter optical fiber preforms, and the prepared optical fiber preforms can achieve a high concentration of alkali metal doping effect, with attenuation at 1500nm controlled within 0.155dB / km; especially when preparing four-hole quartz liner tubes, the doping effect is best when the alkali metal vapor introduction amount is 15g; and when the quartz rod is ground to remove the outer circle with low alkali metal content before acid washing, the overall doping effect of the optical fiber preform is better; in addition, the doping effect is better when the temperature is controlled at 2450-2500℃ when performing alkali metal doping on four-hole quartz liner tubes.

[0064] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A low-loss optical fiber preform, characterized by: The outer core layer is a four-hole quartz tube doped with alkali metal by inner surface deposition and diffusion, and the inner core layer is a quartz rod doped with alkali metal by outer surface deposition and diffusion. The outer core layer is a four-hole quartz tube doped with alkali metal by inner surface deposition and diffusion, and the inner core layer is a quartz rod doped with alkali metal by outer surface deposition and diffusion.

2. A low-loss optical fiber preform according to claim 1, characterized in that: The preparation method of the preform rod comprises the following steps: S1: preparing an alkali metal-doped inner core layer, which is a quartz rod doped with alkali metal by outer surface deposition and diffusion; S2: polishing the outer circle of the inner core layer, and then extending the inner core layer, and then cutting the extended inner core layer for use; S3: preparing an alkali metal-doped outer core layer, which is a four-hole quartz tube doped with alkali metal by inner surface deposition and diffusion; S4: loading the inner core layer of S2 into the outer core layer of S3 to fuse and shrink into a low-loss optical fiber preform rod.

3. A low-loss optical fiber preform according to claim 2, characterized in that, The S2 is polished and then soaked in a hydrofluoric acid solution for 10-20 minutes before being extended.

4. A low-loss optical fiber preform according to claim 3, characterized in that, The concentration of the hydrofluoric acid solution is 15-40%.

5. A low-loss optical fiber preform according to claim 2, characterized in that, The S3 of preparing the alkali metal-doped outer core layer comprises the following steps: S31: selecting a quartz tube material, and processing the quartz tube material into a four-hole quartz tube by punching; S32: soaking the four-hole quartz tube in a hydrofluoric acid solution for 10-20 minutes; S33: etching the inner and outer surfaces of the four-hole quartz tube after taking it out of the hydrofluoric acid solution; S34: after etching is completed, introducing alkali metal hot steam into the four-hole quartz tube to diffuse the alkali metal hot steam to the inner surface of the quartz tube; S35: performing secondary etching on the four-hole quartz tube to remove excessive alkali metal elements.

6. A low-loss optical fiber preform according to claim 5, characterized in that, In the S33, the inner wall of the four-hole quartz tube is etched by etching gas.

7. A low-loss optical fiber preform according to claim 5, characterized in that, In the S34, the four-hole quartz tube is placed in a graphite furnace, and the heating temperature of the graphite furnace is 2000-2300°C.

8. A low-loss optical fiber, characterized by, The optical fiber is drawn from the optical fiber preform rod of claim 1.

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