A doped optimized ultra-low attenuation single mode optical fiber

Abstract

This invention discloses a doped and optimized ultra-low attenuation single-mode optical fiber, comprising a core, an inner cladding covering the core, and an outer cladding covering the inner cladding. The fiber fabrication method includes the following steps: 1) selecting a glass tube and a solid glass rod, and fitting the glass tube over the solid glass rod; 2) welding quartz rods to both ends of the glass tube; 3) placing the glass tube in a graphite furnace and doping the inner surface of the glass tube and the outer surface of the solid glass rod with alkali metals; 4) controlling the pressure and temperature inside the graphite furnace to fuse the glass tube and the solid glass rod into a single unit, forming the core; 5) forming an inner cladding around the core, followed by forming an outer cladding, to obtain the ultra-low attenuation single-mode optical fiber. The core obtained by this invention has the characteristics of large outer diameter, low hydroxyl content, high potassium concentration, and good longitudinal uniformity. By selecting appropriate inner and outer claddings to fabricate the optical fiber, the resulting fiber exhibits extremely superior ultra-low loss performance.

Description

Technical fields:

[0001] This invention belongs to the field of optical fiber technology, and specifically relates to a doped and optimized ultra-low attenuation single-mode optical fiber. Background technology:

[0002] Ultra-low loss optical fiber is characterized by increased transmission distance, which can reduce the number of relays and reduce network complexity, and can significantly reduce construction costs. With the advancement of 5G network trials and commercialization, the demand for bandwidth is increasing, and low-loss and ultra-low loss optical fibers are becoming more and more popular in the market.

[0003] Optical fibers with alkali metal-doped silica cores are known to have low Rayleigh scattering and low transmission loss. If the core of the optical fiber preform contains alkali metal elements, the viscosity of the core is reduced when the fiber is drawn, making the silica mesh structure looser and the density more uniform. This would presumably lower the temperature, reducing Rayleigh scattering loss caused by density fluctuations and thus reducing fiber attenuation.

[0004] Optical fibers based on existing alkali metal doping technologies, such as those described in WO2004020357A2 and CN100545113C, utilize diffusion methods to diffuse alkali metal elements into the inner surface of the glass tube. To achieve a good alkali metal doping effect, the inner surface temperature needs to reach 1700℃ to 2150℃. To obtain quartz glass with a higher average alkali metal concentration, solutions include increasing the wall thickness to reduce the heat source's movement speed or decreasing the quartz tube wall thickness and increasing the tube length. However, with thicker quartz tubes, increasing the diffusion temperature to achieve alkali metal doping concentrations above 500ppm can lead to crystallization on the inner wall due to excessively high alkali metal concentrations as potassium diffuses from the inner wall, causing a significant increase in attenuation across all wavelengths. Conversely, reducing the alkali metal doping amount makes it difficult to increase the overall concentration of the solid quartz glass rod after doping, thus preventing the production of large quantities of quartz glass with alkali metal concentrations above 500ppm in a single process. Increasing the length of the quartz tube results in a significant difference in longitudinal distance between the alkali metal evaporation source and the diffusing quartz glass tube, leading to a large concentration difference of alkali metal ions along the longitudinal direction. When the quartz tube exceeds a certain length, crystallization begins at the front, and the potassium concentration at the rear still does not reach 500 ppm. Therefore, the existing in-tube diffusion method cannot obtain a large-sized alkali metal-doped quartz glass rod with a uniform alkali metal concentration distribution in one step, which can be used as the core of the alkali metal-doped preform.

[0005] 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:

[0006] The purpose of this invention is to provide a doped-optimized ultra-low attenuation single-mode optical fiber, thereby overcoming the defects in the prior art.

[0007] To achieve the above objectives, the present invention provides a doped-optimized ultra-low attenuation single-mode optical fiber, comprising a core, an inner cladding covering the core, and an outer cladding covering the inner cladding. The method for fabricating the optical fiber includes the following steps:

[0008] 1) Select a glass tube and a solid glass rod, and put the glass tube over the solid glass rod;

[0009] 2) Weld quartz rods to both ends of the glass tube;

[0010] 3) Place the glass tube into a graphite furnace and dope the inner surface of the glass tube and the outer surface of the solid glass rod with alkali metals.

[0011] 4) Control the pressure and temperature inside the graphite furnace to fuse the glass tube and solid glass rod into one piece to form the core;

[0012] 5) An inner cladding is made on the core, followed by an outer cladding, to obtain an ultra-low attenuation single-mode fiber.

[0013] Furthermore, as a preferred embodiment, the glass tube has a length of 580-650 mm, and the solid glass rod has a length of 600-670 mm.

[0014] Furthermore, as a preferred embodiment, the diameter of the glass tube is φ35*25mm, and the diameter of the solid glass rod is φ15mm.

[0015] Furthermore, preferably, the average alkali metal concentration in the core reaches 500 ppm.

[0016] Furthermore, preferably, the quartz rod has two or more holes.

[0017] Furthermore, as a preferred option, the alkali metal is potassium bromide.

[0018] Furthermore, as a preferred option, the temperature inside the graphite furnace during doping is controlled at 2000℃-2300℃.

[0019] Furthermore, as a preferred option, impurities on the core surface are removed before the inner cladding is applied, and then the fluorine-containing inner cladding is applied after the extension.

[0020] Furthermore, as a preferred option, an ultra-low attenuation single-mode fiber is obtained by applying an outer cladding layer and then drawing it into a fiber.

[0021] Compared with the prior art, one aspect of the present invention has the following beneficial effects:

[0022] This invention combines a glass tube and a solid glass rod, simultaneously doping both the glass tube and the solid glass rod with alkali metals, and then collapsing them into a large-diameter potassium-doped quartz rod. The core obtained by this method has the characteristics of large outer diameter, low hydroxyl content, high potassium content, and good longitudinal uniformity. Then, by selecting appropriate inner and outer cladding, optical fiber is made, and the resulting optical fiber has extremely superior ultra-low loss performance. Attached image description:

[0023] Figure 1 This is a cross-sectional view of the structure of a doped and optimized ultra-low attenuation single-mode fiber according to the present invention.

[0024] Figure 2 This is a schematic diagram of the synthetic pure silica quartz tube and the solid synthetic pure silica quartz rod of the present invention;

[0025] Figure 3 This is a cross-sectional schematic diagram of the double-hole quartz rod of the present invention;

[0026] Figure 4 This is a potassium concentration detection diagram of the core cross-section of the present invention;

[0027] Figure 5 This is a statistical graph showing the attenuation of the optical fiber of the present invention at a wavelength of 1550nm;

[0028] Figure 6 This is a schematic diagram of the refractive index distribution of the optical fiber cross-section according to the present invention;

[0029] Reference numerals: 1-core, 2-inner casing, 3-outer casing, 4-synthetic pure silicon quartz tube, 5-solid synthetic pure silicon quartz rod, 6-quartz rod. Detailed implementation method:

[0030] 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.

[0031] 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.

[0032] Example 1:

[0033] like Figure 1 As shown, a doped-optimized ultra-low attenuation single-mode optical fiber includes a core 1, an inner cladding 2 covering the core 1, and an outer cladding 3 covering the inner cladding 2. The fabrication method of the optical fiber includes the following steps:

[0034] 1) Select a 600mm long, φ35*25mm synthetic pure silica quartz tube 4 and a 620mm long, φ15mm solid synthetic pure silica quartz rod 5. Fit the synthetic pure silica quartz tube 4 over the solid synthetic pure silica quartz rod 5, as follows: Figure 2 As shown;

[0035] 2) Select a double-hole quartz rod (material 6) as the welding auxiliary material. Use a handheld hydrogen-oxygen welding torch to weld the quartz rod (material 6) to both ends of the synthetic pure silicon quartz tube, such as... Figure 2 As shown, the cross-section of the double-hole quartz rod 6 is as follows. Figure 3 As shown;

[0036] 3) The synthetic pure silicon quartz tube 4 is placed in a graphite furnace. Etching gas is introduced into the synthetic pure silicon quartz tube 4 through the hole in the quartz rod 6. The etching gas etches the inner surface of the synthetic pure silicon quartz tube 4 and the outer surface of the solid synthetic pure silicon quartz rod 5. After etching, a carrier gas is used to carry potassium bromide vapor, which has been heated by an external heat source, to the inner surface of the synthetic pure silicon quartz tube 4 and the outer surface of the solid synthetic pure silicon quartz rod 5. During this process, the graphite furnace is heated to 2000℃-2300℃. Potassium diffuses into the interior through the inner surface of the synthetic pure silicon quartz tube 4 and into the interior through the outer surface of the solid synthetic pure silicon quartz rod 5. This achieves the purpose of alkali metal doping on the inner surface of the synthetic pure silicon quartz tube 4 and the outer surface of the solid synthetic pure silicon quartz rod 5.

[0037] 4) Controlling the pressure and temperature inside the graphite furnace allows the synthetic pure silica quartz tube 4 and the solid synthetic pure silica quartz rod 5 to be fused together, resulting in a potassium-doped quartz rod core 1 with a length of over 500 mm and an outer diameter of approximately 27 mm. The potassium concentration at the cross-section of core 1 is as follows: Figure 4 As shown;

[0038] 5) After removing impurities from the surface of the potassium-doped quartz rod core 1, it is first extended, then wrapped with 2 layers of fluorine-containing inner cladding to form a potassium-doped core rod, and then wrapped with 3 layers of outer cladding to obtain an ultra-low attenuation single-mode optical fiber.

[0039] The optical parameters of the above-mentioned optical fiber were tested and confirmed using a PK2200 device (cutoff wavelength measuring instrument), and the additional loss performance of the optical fiber at a wavelength of 1625nm was tested. Specifically, the additional loss measured at 1625nm with a 30mm radius loosely wound 100 turns was 0.03-0.06dB.

[0040] The attenuation of optical fiber at a wavelength of 1550 nm was measured using an OTDR (Optical Time Domain Reflectometer). The test results are as follows: Figure 5 As shown;

[0041] The refractive index profile of the optical fiber was tested using an NR9200 instrument (optical fiber profile analyzer), and the test results are as follows: Figure 6 As shown.

[0042] Based on the above experimental results, the optical parameters of the optical fiber of the present invention, such as mode field diameter, cutoff wavelength, and fiber loss, can fully comply with the requirements of ITU-T G.652D / G.654.E standards. Furthermore, the optical fiber produced by loosely winding 100 turns with a radius of 30mm has an additional loss of no more than 0.06dB at a wavelength of 1625nm, and its bending performance is better than the requirement of G.652D standard by 0.1dB. On this basis, the attenuation value at a wavelength of 1550nm is ≤0.155dB / km. The process route is mature, has good repeatability, can produce large-size ultra-low loss optical rods, and is easy to carry out industrial production.

[0043] The ultra-low-loss optical fiber obtained by this invention, due to its ultra-low loss characteristics, is highly suitable for ultra-long-distance, high-capacity, and high-speed network transmission applications. For example, its use in a 400G ultra-long-distance wavelength division multiplexing transmission system can reduce the number of regenerator stations by approximately 40%, resulting in significant benefits. Ultra-low-loss optical fiber can not only be widely used by operators, but also, considering its ultra-low attenuation characteristics, can be used in supporting communication projects for AC / DC power grid interconnection, enabling ultra-long-distance repeater-free optical transmission exceeding 300km. Furthermore, the excellent characteristics of ultra-low-loss optical fiber provide network margins for expanding network hop spans, increasing access points, upgrading to faster bit rates, increasing the flexibility of network components, or extending the distance between regenerators, thereby enabling longer and wider regional networks to meet the ever-growing global demand for bandwidth.

[0044] 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 doped optimized ultra-low attenuation single mode optical fiber comprising a core, an inner cladding surrounding the core, an outer cladding surrounding the inner cladding, characterized in that: The preparation method of the optical fiber comprises the following steps: 1) selecting a glass tube and a solid glass rod, and sleeving the glass tube outside the solid glass rod; 2) welding quartz rods at two ends of the glass tube respectively; 3) placing the glass tube into a graphite furnace to dope alkali metal on the inner surface of the glass tube and the outer surface of the solid glass rod; 4) controlling the pressure and temperature in the graphite furnace, so that the glass tube and the solid glass rod are fused and shrunk into one body, and a potassium-doped quartz rod core part with a length of more than 500 mm and an outer diameter of 27 mm is prepared; 5) sleeving an inner cladding layer outside the core part, and then sleeving an outer cladding layer, so that an ultra-low attenuation single-mode optical fiber is prepared. The quartz rod in the step 2) is punched with two or more than two holes.

2. A doped optimised ultra-low-loss single-mode optical fibre according to claim 1, characterised in that: The length of the glass tube is 580-650 mm, and the length of the solid glass rod is 600-670 mm.

3. A doped optimised ultra-low-loss single-mode optical fibre according to claim 1, characterised in that: The diameter of the glass tube is φ35*25 mm, and the diameter of the solid glass rod is φ15 mm.

4. The optimally-doped, ultra-low-loss single-mode optical fiber of claim 1, wherein: The average alkali metal concentration of the core part reaches 500 ppm.

5. A doped optimized ultra-low-loss single-mode optical fiber according to claim 1, characterized in that: The alkali metal is potassium bromide.

6. A doped optimised ultra-low-loss single-mode optical fibre according to claim 1, characterised in that: The temperature in the graphite furnace during the doping is controlled at 2000-2300 °C.

7. A doped optimised ultra-low-loss single-mode optical fibre according to claim 1, characterised in that: The impurities on the surface of the core part are removed before the inner cladding layer is sleeved, and then the fluorine-containing inner cladding layer is sleeved after extension.

8. The optimally-doped, ultra-low-loss single-mode optical fiber of claim 1, wherein: After the outer cladding layer is sleeved, the ultra-low attenuation single-mode optical fiber is obtained after drawing.

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