Layered doping-based multi-layer fusion shrinkage device and method for optical fiber preform

Abstract

The invention belongs to the related field of optical fiber preform processing, and discloses an optical fiber preform multilayer fusion shrinkage device based on layered doping, the device comprises a glass tube, a multilayer isolation ring, an upper cover plate, a lower cover plate, a heating furnace and the like, the two ends of the glass tube are respectively connected with the two cover plates, and a sealed integrated space is formed; the multi-layer isolation circular ring is used for being placed in a glass tube and dividing an inner cavity of the glass tube into multiple layers of independent isolation cavities in the radial direction, and filling particles and doping gas which serve as reactants are independently and controllably guided into the isolation cavities. The heating furnace is used for heating the glass tube and reactants in each layer of isolation chamber at different temperatures so as to start the reaction. The invention further discloses a corresponding process method. According to the invention, multiple layers of independent cavities can be fully utilized and matched with dopants with different flows and reaction conditions, so that smooth transition of the refractive index and viscosity of each layer of interface is smoothly realized, and the scattering loss at the interface is effectively reduced.

Description

Technical Field

[0001] The present invention belongs to the field related to optical fiber preform processing, and more specifically, relates to an optical fiber preform multi-layer melting and shrinking device and method based on layered doping. Background Art

[0002] The preform manufacturing process is the most cutting-edge and core technology in the entire optical fiber industry. With the development of optical communication technology, the performance requirements of optical fibers are becoming increasingly higher. Currently, the use of sunken and multi-layer profiles to achieve low attenuation and anti-bending is becoming a mainstream optical fiber profile structure.

[0003] To prepare optical fiber preform products with multi-layer cross-sections, conventional doping routes in the prior art generally employ a multi-step process. However, further research has revealed that this prior art still suffers from the following drawbacks or deficiencies: First, this multi-step process requires layer-by-layer doping, requiring each layer to be completed before the next layer can be doped. This leads to complex processes, low production efficiency, and high production costs. Second, when customizing preforms with complex multi-layer cross-sections, the doping path must diffuse layer by layer, resulting in difficulties in controlling the refractive index distribution, insufficient doping uniformity, and low yield rates. Finally, the prior art preparation process typically only produces preforms with a size of no more than 200 mm, which also limits its use in many applications.

[0004] Accordingly, there is an urgent need in this field to improve the optical fiber preform processing technology so as to better meet the high quality control requirements of optical fiber products. Summary of the Invention

[0005] In response to one or more of the above-mentioned defects or needs in the prior art, the present invention provides a multi-layer melting and shrinking device and method for optical fiber preform based on layered doping, wherein, by studying and improving the overall structural composition and working principle of the relevant melting and shrinking device, as well as the process route and key reaction conditions, it is possible to fully utilize the multi-layer independent chambers and cooperate with different flow rates of dopants and reaction conditions to smoothly achieve a smooth transition of the refractive index and viscosity of each layer interface, and effectively reduce the scattering loss at the interface caused by factors such as stress mismatch and imperfect refractive index waveguide interface. At the same time, it has the advantages of compact equipment structure, easy operation, high production efficiency and yield rate, and is therefore particularly suitable for preform manufacturing applications with multi-layer complex cross-sections and large sizes.

[0006] To achieve the above objectives, according to one aspect of the present invention, a multi-layer melting and shrinking device for optical fiber preform based on layered doping is provided, the device comprising a glass tube, a multi-layer isolation ring, an upper cover plate, a lower cover plate, and a heating furnace, wherein:

[0007] The upper and lower ends of the glass tube are detachably connected to the upper cover plate and the lower cover plate respectively, to form a sealed integrated space;

[0008] The multi-layer isolation ring is used to be placed in the glass tube and divide the inner cavity of the glass tube into multiple layers of independent isolation chambers along the radial direction;

[0009] The upper cover plate is provided with a plurality of air inlets, which are respectively allocated to the isolation chambers of each layer and are used to sequentially introduce the filler particles and the doping gas as reactants; the lower cover plate is provided with a plurality of air outlets, which are respectively allocated to the isolation chambers of each layer and are used to discharge the residue after the reaction;

[0010] The heating furnace is used to perform synchronous preheating and layered doping reactions on the glass tube and the reactants in the isolation chambers of each layer when the multi-layer isolation rings are placed in the glass tube; and after the multi-layer isolation rings are removed from the glass tube, the glass tube is subjected to step sintering until the desired preform product with a multi-layer cross-sectional structure is obtained.

[0011] As a further preferred embodiment of the present invention, the specifications and dimensions of the glass tube are preferably designed as follows: an outer diameter of 150 mm to 350 mm, and a length of 400 mm to 2500 mm.

[0012] As a further preference of the present invention, the multi-layer isolation ring is made of high temperature resistant and corrosion resistant material, the number of layers is preferably 3 to 5 and the radial size of each layer is adjustable.

[0013] As a further preferred embodiment of the present invention, the upper cover plate and the lower cover plate are preferably screw-fastened and pressed tightly together by means of the raised steps at the ends of the glass tube.

[0014] As a further preferred embodiment of the present invention, a hanging ring is preferably provided at the top of the upper cover plate for withdrawing the upper cover plate and the multi-layer isolation ring connected thereto from the glass tube.

[0015] According to another aspect of the present invention, a corresponding optical fiber preform multilayer melting and shrinking method is also provided, wherein the method comprises the following steps:

[0016] Step 1: hoist the multi-layer isolation ring as a whole into the glass tube, and assemble the upper cover plate and the lower cover plate at the same time; then, independently and controllably fill the isolation chambers of each layer in the glass tube with silica soot particles until they are full;

[0017] Step 2: starting the heating furnace to synchronously preheat the glass tube and the silica soot particles in each layer of the isolation chamber;

[0018] Step 3: After the preheating reaches a specified temperature, the same or different doping gas sources are independently and controllably introduced into the isolation chambers corresponding to each layer in the glass tube, and a multi-layer synchronous doping reaction is performed;

[0019] Step 4: After the doping gas source has reacted with the silica soot particles and the glass tube, the multi-layer isolation ring is removed from the glass tube, and the upper end of the glass tube is pressed against the upper cover plate again to complete the sealing.

[0020] Step 5: Start the heating furnace again and perform step sintering on the glass tube until the desired preform product with a multi-layer cross-section structure is obtained.

[0021] As a further preferred embodiment of the present invention, in step 2, the critical value of the preheating temperature is preferably maintained at about 1000°C.

[0022] As a further preferred embodiment of the present invention, in step three, before performing the synchronous doping reaction, it is preferred to start the exhaust unit to extract the reaction residues in the glass tube, and the exhaust pressure is controlled to be below -1000 Pa.

[0023] As a further preference of the present invention, in step three, the doping gas source is preferably at least one of the following substances: chlorine, helium, oxygen, nitrogen, fluorine-containing gases such as F2, HF or C2F4, and dopants containing boron or phosphorus; wherein the pressure in the glass tube during the doping reaction is preferably controlled in the range of -100Pa to -1000Pa.

[0024] As a further preferred embodiment of the present invention, in step five, before performing step sintering, it is preferred to start an exhaust unit to extract the reaction residues in the glass tube, and the exhaust pressure is controlled to be below 100 Pa.

[0025] As a further preferred embodiment of the present invention, in step five, the key parameters of the step sintering are preferably designed as follows: the sintering start temperature is above 1500° C., and the step speed is 3 mm / min to 6 mm / min.

[0026] In general, the above technical solutions conceived by the present invention have the following technical advantages compared with the existing technology:

[0027] (1) Realizing complex cross-sections of multiple layers with different depths and widths: The present invention closely combines the working characteristics and actual needs of processing optical fiber preforms with complex cross-sections. By studying and improving the overall structural composition and working mechanism of the relevant melting and shrinking device, it can flexibly adopt isolation tooling with different numbers of layers and different spacings. At the same time, it cooperates with various appropriate doping gas sources to achieve a smooth transition of the refractive index and viscosity of each layer interface, and effectively reduce the scattering loss at the interface, so as to customize glass preforms with multiple layers and complex cross-sections accordingly.

[0028] (2) Multi-layer simultaneous doping, one-step molding, greatly simplified doping process: The present invention adopts a multi-layer simultaneous online doping process technology. Compared with the prior art process that requires doping layer by layer and only proceeding to the next layer after completing one layer, the doping time is significantly shortened and the process is greatly simplified. In particular, the efficiency is greatly improved for glass rods with complex multi-layer cross-sections.

[0029] (3) Deep doping rods with fine refractive index control and more uniform distribution: Compared with the layer-by-layer diffusion doping in the prior art, the doping path of the present invention does not need to be diffused layer by layer, but is directly doped in the corresponding layers. The corresponding refractive index distribution is more finely controlled, and a more uniform and consistent deep doping effect can be achieved;

[0030] (4) Ultra-large deep-doped rods: Compared with conventional doping methods, the vertical particle doping equipment of the present invention is suitable for using larger glass tubes and can realize deep-doped rods with a size exceeding 200 mm. At the same time, it has the advantages of compact equipment structure, easy operation, high production efficiency and yield rate, etc., and is therefore particularly suitable for the manufacture of preform rods with multi-layer complex cross-sections and large sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the main components of the multi-layer melting and shrinking device of the preferred embodiment of the present application, which is in the process of filling silica soot particles and synchronous doping;

[0032] Figure 2 This is a schematic diagram of the main components of the multi-layer melting and shrinking device of the preferred embodiment of the present application, which is in the step sintering process;

[0033] Figure 3 is a schematic diagram for exemplarily showing a typical multilayer doping profile obtained according to the present invention;

[0034] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0035] 1-air inlet; 2-hanging ring; 3-upper cover; 4-multi-layer isolation ring; 5-lower cover; 6-air outlet; 7-glass tube; 8-raised step; 9-heating furnace; 10-exhaust unit. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0037] It should be understood that expressions such as "include" and "may include" used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as "include" and / or "have" may be interpreted as indicating a specific characteristic, number, operation, constituent element, component, or combination thereof, but may not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0038] It should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0039] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0040] In this application, unless otherwise specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they can refer to fixed connection, detachable connection, or integral connection; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0041] Figure 1 and Figure 2The following are schematic diagrams of the main components of the multi-layer melting and shrinking device of the preferred embodiment of the present application, which are respectively in the process of filling silica soot particles and synchronous doping process and progressive sintering process. Figure 1 and Figure 2 The present invention will be explained in more detail.

[0042] See Figure 1 and Figure 2 The device of the present invention mainly includes a glass tube 7, a multi-layer isolation ring 4, an upper cover plate 3, a lower cover plate 5 and a heating furnace 9, and can be equipped with an exhaust unit 10, an exhaust control system, a multi-layer air intake control system pressure detection system, a silica soot particle filling system and other auxiliary parts.

[0043] Specifically, the upper and lower ends of the glass tube 7 are detachably connected to the upper cover plate 3 and the lower cover plate 5, respectively, to form a sealed integrated space; the multi-layer isolation ring 4 is used to be placed in the glass tube 7, and divides the inner cavity of the glass tube 7 into multiple layers of independent isolation chambers along the radial direction; the upper cover plate 3 is provided with a plurality of air inlets 1, which correspond to the isolation chambers allocated to each layer, and are used to successively introduce filling particles and doping gases as reactants; the lower cover plate 5 is provided with a plurality of air outlets 6, which correspond to the isolation chambers allocated to each layer, and are used to discharge the residues after the reaction.

[0044] More specifically, the upper cover plate 3 and the multi-layered isolation ring 4 can be either integrated or separate structures. The upper cover plate 3 has an air inlet 1 for each layer, and the lower cover plate has an air outlet 6 for each layer. The multi-layered isolation ring 4 can be constructed with three, four, or five layers. The upper cover plate 3 has a lifting ring 2 at its top for later removal from the glass tube. The upper and lower cover plates 3 and 5 are screwed together via raised steps 8 on the glass tube 7, and then pressed together tightly. Furthermore, the multi-layered isolation tooling is entirely constructed of high-temperature and corrosion-resistant materials, including but not limited to ceramics and glass.

[0045] The heating furnace 9 can be in the form of a resistance furnace or an induction furnace, and is used to perform synchronous preheating and layered doping reactions on the glass tube 7 and the reactants in each layer of the isolation chamber when the multi-layer isolation rings 4 are placed in the glass tube 7; and after the multi-layer isolation rings 4 are removed from the glass tube 7, the glass tube 7 is subjected to step sintering until the desired preform product with a multi-layer cross-sectional structure is obtained.

[0046] According to a preferred embodiment of the present invention, the specifications and dimensions of the glass tube 7 are preferably designed as follows: an outer diameter of 150 mm to 350 mm, and a length of 400 mm to 2500 mm.

[0047] The multi-layer melting and shrinking process of the optical fiber preform according to the present invention will be explained in detail below.

[0048] Step 1: Filling with silica soot particles

[0049] In this step, the multi-layer isolation ring 4 is hoisted into the glass tube 7 as a whole, and the upper cover plate 3 and the lower cover plate 5 are assembled at the same time. Then, the isolation chambers corresponding to each layer in the glass tube 7 are independently and controllably filled with silica soot particles until they are full.

[0050] More specifically, the outer diameter of the glass tube 7 can range from 150 mm to 350 mm, and the length can range from 400 mm to 2500 mm. The silica soot particles are not limited to the μm level, and higher or lower grades can be of any size. They can be directly synthesized using the VAD / OVD method, or natural quartz sand particles can be used.

[0051] Step 2: Preheat the glass tube and silica soot particles

[0052] In this step, the heating furnace 9 is started to perform synchronous preheating on the glass tube 7 and the silica soot particles in the isolation chambers of each layer;

[0053] More specifically, in order to avoid melting of soot particles, the temperature of the heating furnace 9 during the heating process should not exceed 1000° C.; when the furnace temperature reaches 1000° C., the doping stage begins.

[0054] Step 3: Multi-component multi-layer simultaneous doping

[0055] In this step, after the preheating reaches the specified temperature, the same / different doping gas sources are independently and controllably introduced into the isolation chambers corresponding to each layer in the glass tube 7, and a synchronous doping reaction of the multiple layers is performed;

[0056] More specifically, after the temperature of the heating furnace 9 reaches 1000°C, the exhaust unit 10 is first started to extract the gas that may remain in the tube, and the pressure can be controlled at about -1000Pa; after the residual gas is extracted, each chamber is separately introduced with a corresponding doping gas source, including but not limited to: chlorine, helium, oxygen, nitrogen, fluorine-containing gas (F2, HF, C2F4), boron, phosphorus and other dopants; the chlorine flow rate is generally set to 50~200sccm, the helium flow rate is generally set to 10~2slm; the oxygen flow rate is generally set to 50~200sccm; the argon flow rate is generally set to 1~2slm; the pressure in the glass tube 7 is appropriately controlled in a slightly negative pressure state, which can be -100Pa~-1000Pa, which can further improve the impregnation effect.

[0057] In addition, based on the size of the silica soot particles and the filling weight, the process gas filling and doping time can be adjusted appropriately. Generally, the outer diameter of the glass tube is 200 mm and the length is about 1800 mm, and the time is controlled within 4 hours. When the glass tube 7 is longer and has a thicker outer diameter, the doping time can be appropriately extended.

[0058] Step 4: Remove the multi-layer isolation ring

[0059] After the doping gas source has completed the reaction with the silica soot particles and the glass tube, the multi-layer isolation ring 4 is removed from the glass tube 7, and then the upper cover plate 3 is used to press the upper end of the glass tube 7 to complete the sealing;

[0060] More specifically, for example, a lifting rope can be used to slowly pull the upper cover plate 3 and the multi-layer isolation ring 4 out of the glass tube 7 and remove them from the lifting ring 2 of the upper cover plate 3 .

[0061] Step 5: Step Sintering

[0062] In this step, the heating furnace 9 is started again to perform step-by-step sintering on the glass tube 7 until the desired preform product with a multi-layer cross-sectional structure is obtained.

[0063] More specifically, after the upper cover plate 3 is pulled out and the multi-layer isolation ring 9 is disassembled, the upper cover plate 3 is pressed against the upper end of the glass tube again; after the screw tightens the lid, the melting and vitrification stage begins: in this melting stage, the exhaust unit 10 is first started to reduce the pressure in the tube to below 100 Pa absolute pressure, and maintained for 3 to 5 hours, and all residual gas is extracted as much as possible. In case of larger workpiece size or higher filling weight, the suction force can be appropriately increased or the vacuuming time can be extended.

[0064] Next, continue heating the furnace 9 to a temperature above 1500°C. Set a suitable stepping speed, preferably around 3mm to 6mm / min, to gradually sinter the entire glass tube from top to bottom. The thicker the glass tube, the slower the stepping speed, typically set at 0.1 to 1kg per minute. When the furnace reaches its final stepping position, turn off the power to the furnace 9 and allow the sintered transparent glass rod to cool before removing it.

[0065] Table 1 below shows data related to several examples of doping with layered silica soot particles according to the present invention.

[0066]

[0067] Table 1

[0068] Figure 2 A typical multilayer doping profile obtained according to the present invention is shown in FIG. Figure 2It can be seen that even with complex profiles of different depths and widths, the present application can still achieve the processing process in a highly efficient, low-cost and easy-to-control manner.

[0069] In summary, compared with the existing technology, the present application can make full use of multi-layer independent chambers and cooperate with dopants of different flow rates and reaction conditions to smoothly achieve a smooth transition of the refractive index and viscosity of each layer interface, and effectively reduce the scattering loss generated at the interface. At the same time, it has the advantages of compact equipment structure, easy operation, high production efficiency and yield rate. Therefore, it is particularly suitable for preform rod manufacturing applications with multi-layer complex cross-sections and large sizes, and has good practical value and application prospects.

[0070] It is easy for those skilled in the art to understand that the above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A multi-layer melting and shrinking device for optical fiber preform based on layered doping, characterized in that: The device comprises a glass tube (7), a multi-layer isolation ring (4), an upper cover plate (3), a lower cover plate (5) and a heating furnace (9), wherein: The upper and lower ends of the glass tube (7) are detachably connected to the upper cover plate (3) and the lower cover plate (5), respectively, to form a sealed integrated space; The multi-layer isolation ring (4) is used to be placed in the glass tube (7) and to separate the inner cavity of the glass tube (7) into multiple layers of independent isolation chambers along the radial direction; The upper cover plate (3) is provided with a plurality of air inlets (1), which are respectively allocated to the isolation chambers of each layer and are used to sequentially introduce filler particles and doping gases as reactants; the lower cover plate (5) is provided with a plurality of air outlets (6), which are respectively allocated to the isolation chambers of each layer and are used to discharge residues after the reaction; The heating furnace (9) is used to perform synchronous preheating and layered doping reactions on the glass tube (7) and the reactants in the isolation chambers of each layer when the multi-layer isolation ring (4) is placed in the glass tube (7); and after the multi-layer isolation ring (4) is removed from the glass tube (7), the glass tube (7) is subjected to step sintering until a desired preform product with a multi-layer cross-sectional structure is obtained.

2. The optical fiber preform multi-layer melting and shrinking device according to claim 1, wherein: The specifications and dimensions of the glass tube (7) are preferably designed as follows: an outer diameter of 150 mm to 350 mm, and a length of 400 mm to 2500 mm.

3. The optical fiber preform multi-layer melting and shrinking device according to claim 1 or 2, characterized in that: The multi-layer isolation ring (4) is made of high-temperature resistant and corrosion-resistant material, and the number of layers is preferably 3 to 5, and the radial size of each layer is adjustable.

4. The optical fiber preform multi-layer melting and shrinking device according to any one of claims 1 to 3, characterized in that: The upper cover plate (3) and the lower cover plate (5) are preferably screw-fastened and pressed together via the raised step (8) at the end of the glass tube (7).

5. The optical fiber preform multi-layer melting and shrinking device according to any one of claims 1 to 4, characterized in that: The top end of the upper cover plate (3) is preferably provided with a hanging ring (2) for withdrawing the upper cover plate (3) and the connected multi-layer isolation ring (4) from the glass tube (7).

6. A multi-layer melting and shrinking method for an optical fiber preform, characterized in that: The method is implemented using the device according to any one of claims 1 to 5, and comprises the following steps: Step 1: hoist the multi-layer isolation ring (4) into the glass tube (7) as a whole, and assemble the upper cover plate (3) and the lower cover plate (5) at the same time; then, independently and controllably fill the isolation chambers corresponding to each layer in the glass tube (7) with silica soot particles until they are full; Step 2: starting the heating furnace (9) to synchronously preheat the glass tube (7) and the silica soot particles in the isolation chambers of each layer; Step 3, after the preheating reaches a specified temperature, the same / different doping gas sources are independently and controllably introduced into the isolation chambers corresponding to each layer in the glass tube (7), and a multi-layer synchronous doping reaction is performed; Step 4: After the doping gas source has completed the reaction with the silica soot particles and the glass tube, the multi-layer isolation ring (4) is removed from the glass tube (7), and then the upper cover plate (3) is used to press the upper end of the glass tube (7) to complete the sealing; Step five: start the heating furnace (9) again and perform step sintering on the glass tube (7) until the desired preform product with a multi-layer cross-section structure is obtained.

7. The optical fiber preform multi-layer melting and shrinking method according to claim 6, wherein: In step 2, the critical value of the preheating temperature is preferably maintained at about 1000°C.

8. The optical fiber preform multi-layer melting and shrinking method according to claim 6, wherein: In step three, the doping gas source is preferably at least one of the following substances: chlorine, helium, oxygen, nitrogen, fluorine-containing gases such as F2, HF or C2F4, and dopants containing boron or phosphorus; wherein the pressure in the glass tube (7) during the doping reaction is preferably controlled in the range of -100Pa to -1000Pa.

9. The optical fiber preform multi-layer melting and shrinking method according to claim 8, wherein: In step five, the key parameters of the step sintering are preferably designed as follows: the sintering start temperature is above 1500° C., and the step speed is 3 mm / min to 6 mm / min.

10. The optical fiber preform multi-layer melting and shrinking method according to any one of claims 6 to 9, characterized in that: Before performing the synchronous doping reaction, it is preferred to start the exhaust unit (10) to extract the reaction residues in the glass tube (7), and the exhaust pressure is controlled to be below -1000 Pa; In addition, before performing step sintering, it is preferred to start the exhaust unit (10) to extract the reaction residues in the glass tube (7), and the exhaust pressure is controlled to be below 100 Pa.

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