A device and method for collapsing and sintering a fiber preform cane

Abstract

The application relates to a melting and sintering device and method for a fiber preform core rod, which comprises a bed body, a horizontal guide rail arranged on the bed body, an air inlet rotary sealing chuck and an air outlet rotary sealing chuck respectively arranged at two ends of the bed body, a sleeve-shaped heating furnace arranged between the air inlet rotary sealing chuck and the air outlet rotary sealing chuck, and a reciprocating moving device connected with the sleeve-shaped heating furnace, characterized in that the air inlet rotary sealing chuck is connected with a freon gas source and an oxygen gas source through air inlet connecting pipes, and the air outlet rotary sealing chuck is connected with a gas pressure control device through air outlet connecting pipes. The quartz sleeve and the initial core rod are combined, cleaned and sintered into one body by adopting the combination of high-pressure corrosion reaction cleaning treatment and low-pressure melting and sintering treatment, and a solid core fiber preform is prepared, so that the core rod inner combination interface defects can be reduced, the melting and sintering quality of the fiber preform core rod is effectively improved, and the processing efficiency of the fiber preform core rod is improved.

Description

Technical Field

[0001] This invention relates to a melting and sintering apparatus and method for optical fiber preform core rods, belonging to the field of optical fiber preform manufacturing technology. Background Technology

[0002] Currently, the most commonly used process in the fabrication of optical fiber preform cores is vapor phase reaction deposition (VPD). Typical VPD processes include in-tube VPD, such as plasma-induced chemical vapor deposition (PCVD) and modified chemical vapor deposition (MCVD), as well as out-of-tube VPD processes, such as outside vapor deposition (OVD) and vapor axial deposition (VAD). For some preforms with complex optical fiber profiles and high performance requirements, actual production often requires a combination of two or more processes. The core fabrication process is carried out in multiple steps. A crucial step is that after the initial core vapor deposition, it needs to be fused and sintered together with a sleeve of a specific refractive index to form a larger final core.

[0003] Existing fusion-bonding processes often result in small air bubbles at the bonding interface within the core rod after fusion-bonding. Since these bubbles remain within the light-guiding portion of the core rod, they significantly negatively impact the final fiber performance. To reduce these bubbles, higher fusion-bonding temperatures are typically used, but this increases the core rod's bow value, reducing the effective rod length and thus manufacturing efficiency. Furthermore, existing processes involve localized contact friction between the ferrule and the initial core rod during fusion-bonding, generating numerous small powder highlights. These highlights cannot be promptly removed, resulting in significant reflection peaks during downstream OTDR testing, ultimately leading to fiber failure. Additionally, the inner surface of the ferrule and the surface of the initial core rod are contaminated by upstream processes, typically containing high impurities. Existing processes cannot completely eliminate these contaminants, easily leading to quality issues such as increased localized attenuation in the drawn fiber. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a melting and sintering apparatus and method for optical fiber preform core rods, which can reduce interface defects within the core rod, effectively improve the melting and sintering quality of optical fiber preform core rods, and enhance the processing efficiency of optical fiber preform core rods.

[0005] The technical solution of the melting and sintering apparatus adopted by the present invention to solve the above-mentioned problems is as follows:

[0006] The device includes a bed with horizontal guide rails, an inlet rotary sealing chuck and an outlet rotary sealing chuck at both ends of the bed, a sleeve-shaped heating furnace between the inlet and outlet rotary sealing chucks, and the sleeve-shaped heating furnace connected to a reciprocating moving device. The inlet rotary sealing chuck is connected to a Freon gas source and an oxygen gas source via an inlet pipe, and the outlet rotary sealing chuck is connected to a gas pressure control device via an outlet pipe.

[0007] According to the above scheme, the air pressure control device includes a low-pressure control device and a high-pressure control device, which are connected to the air outlet pipe through a switching valve or a control valve.

[0008] According to the above scheme, the low-pressure control device includes a vacuum pump and a filter connected in series. One end of the low-pressure control device is connected to the gas outlet pipe through a control valve, and the other end is connected to the gas outlet.

[0009] According to the above scheme, the high-pressure control device includes a connected gas supply pipeline. One end of the high-pressure control device is connected to the gas outlet pipe through a control valve, and the other end is connected to the gas outlet.

[0010] According to the above scheme, the air intake rotary sealing clamp is fixed at one end of the bed, and the air exhaust rotary sealing clamp is installed on the movable slide, forming an axially movable air exhaust rotary sealing clamp.

[0011] According to the above scheme, the air intake rotary sealing chuck and the air outlet rotary sealing chuck are connected to the synchronous rotary drive device.

[0012] According to the above scheme, the packaged heating furnace is a graphite resistance heating furnace or an induction furnace, with a heating axial area of ​​100-350mm. The furnace cavity of the packaged heating furnace is equipped with a protective gas source for filling with protective gas; the protective gas is an inert gas such as Ar or N2.

[0013] According to the above scheme, the Freon gas source and the oxygen gas source are respectively connected to flow meters. The oxygen is controlled by two flow meters, a large flow meter and a small flow meter. The large flow meter is used to control the purging of dust and impurities, and the small flow meter is used to control the corrosion reaction.

[0014] The technical solution of the present invention using the above-mentioned melting and sintering apparatus and melting and sintering method is as follows:

[0015] A quartz sleeve with a specific refractive index and an initial mandrel are assembled into a sleeve assembly and installed on a melting and sintering device. The quartz sleeve and the initial mandrel of the sleeve assembly are aligned and fitted together with a radial gap. One end of the quartz sleeve is clamped to an inlet rotary sealing chuck, and the other end is clamped to an outlet rotary sealing chuck. After clamping, the synchronous rotation of the inlet and outlet rotary sealing chucks drives the sleeve assembly to rotate at a uniform speed. At the same time, a sleeve-shaped heating furnace fitted around the outer periphery of the sleeve assembly begins heating at a temperature of 1800–2250°C. The heating furnace reciprocates along the axial direction of the sleeve assembly from one end to the other. The process begins by introducing Freon and oxygen into the inlet rotary sealing chuck, which then enters the radial gap between the quartz sleeve and the initial core rod. Simultaneously, the outlet rotary sealing chuck is connected to a high-pressure control device to perform high-pressure corrosion cleaning on the inner wall of the quartz sleeve and the outer periphery of the initial core rod. After the high-pressure corrosion cleaning, the Freon and oxygen sources are shut off at the inlet rotary sealing chuck end, and the outlet pipe at the outlet rotary sealing chuck end is connected to a low-pressure control device to perform low-pressure melting and sintering treatment on the sleeve assembly until the quartz sleeve and the initial core rod are melted and sintered into one piece to form a solid optical fiber preform.

[0016] According to the above scheme, after high-pressure corrosion reaction cleaning treatment and before melting and shrinking sintering, a large flow of oxygen is used to purge the inner wall of the quartz sleeve and the outer periphery of the initial mandrel.

[0017] According to the above scheme, the relative pressure of the high-pressure corrosion reaction cleaning treatment is controlled within the range of 50 to 200 Pa.

[0018] According to the above scheme, the ratio of Freon to oxygen flow rate in the high-pressure corrosion reaction cleaning treatment is 1:1 to 1:2.

[0019] According to the above scheme, the absolute pressure of the low-pressure melting and shrinking sintering treatment is controlled within the range of 10 to 100 mbar.

[0020] According to the above scheme, the rotational speed of the sleeve assembly is 10 to 30 rad / min (revolutions per minute).

[0021] According to the above scheme, the speed at which the sleeve-shaped heating furnace moves axially is 10-30 mm / min, the axial heating area of ​​the sleeve-shaped heating furnace is 100-350 mm, and the radial gap between the furnace cavity and the sleeve assembly of the sleeve heating furnace is filled with protective gas during heating.

[0022] According to the above scheme, the gap between the quartz sleeve and the initial mandrel (the difference between the inner diameter of the sleeve and the outer diameter of the mandrel) is 3 to 15 mm.

[0023] According to the above scheme, the specifications of the quartz sleeve before melting and sintering are: outer diameter of 30-60mm and length of 1.0-2.5m.

[0024] The beneficial effects of this invention are as follows: 1. By introducing corrosive gas under high pressure, the inner surface of the sleeve and the outer surface of the core rod are corroded, removing the interface portion with high impurity content, improving the core rod's shrinkage quality, and reducing optical fiber attenuation. 2. By using higher internal pressure during the corrosion reaction, the corrosion amount is increased, the corrosion pass time is reduced, and the production efficiency of the equipment is improved. 3. Using extremely low internal pressure during shrinkage, there are virtually no defects such as bubbles and bright spots at the interface of the core rod after shrinkage and sintering, greatly improving the core rod quality and ensuring the performance of the optical fiber. 4. Due to the lower internal pressure used during shrinkage, the pressure difference between the inside and outside of the tube is large, requiring only lower heat to solidify. On the one hand, the bow value of the core rod is significantly improved after shrinkage; on the other hand, the temperature and power of the heating furnace during shrinkage can be significantly reduced, increasing the service life of graphite components such as heating elements, while reducing the consumption of protective gas. 5. This invention uses a large flow of oxygen to purge before shrinkage and a large vacuum force during shrinkage, which helps to remove powder particles generated by friction between the core rod and the sleeve, preventing them from remaining at the interface. 6. This invention provides favorable preconditions for the preparation of large-sized optical fiber preforms with complex cross-sections, thereby contributing to the improvement of optical fiber performance and manufacturing efficiency. Attached Figure Description

[0025] Figure 1 This is a general structural diagram of one embodiment of the melting and shrinking sintering apparatus of the present invention.

[0026] Figure 2 This is a cross-sectional assembly view of the sleeve assembly in one embodiment of the present invention.

[0027] Figure 3 This is a comparison diagram of fiber attenuation after drawing the core rod prepared by the present invention and the prior art.

[0028] Figure 4 This is a statistical distribution diagram of the bow values ​​of the mandrels prepared by the present invention and existing technologies. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0030] Examples of implementation of the device of the present invention Figure 1As shown, the device includes a bed 1 with horizontal guide rails 2. An inlet rotary sealing clamp 4 and an outlet rotary sealing clamp 5 are respectively installed at both ends of the bed. The inlet rotary sealing clamp is fixed to one end of the bed, and the outlet rotary sealing clamp is mounted on a movable slide, forming an axially movable outlet rotary sealing clamp. The inlet rotary sealing clamp is connected to a Freon gas source and an oxygen gas source via an inlet pipe. The Freon and oxygen gas sources are respectively connected to flow meters. The oxygen gas source is controlled by two separate flow meters, a large flow meter for controlling the purging of dust and impurities, and a small flow meter for controlling corrosion reactions. The rotary sealing clamp for venting air is connected to a pneumatic pressure control device via a venting pipe. The pneumatic pressure control device includes a low-pressure control device and a high-pressure control device. The low-pressure control device and the high-pressure control device are connected to the venting pipe via control valves. The low-pressure control device includes a vacuum pump 10 and a filter 12 connected in series. One end of the low-pressure control device is connected to the venting pipe via a control valve 7, and the other end is connected to the venting port. The high-pressure control device includes a connected air supply line 9 and a filter 11 connected in series. One end of the high-pressure control device is connected to the venting pipe via a control valve 8, and the other end is connected to the venting port. A pressure gauge 6 is connected to the venting pipe. A sleeve-shaped heating furnace 3 is installed between the inlet rotary sealing chuck and the outlet rotary sealing chuck. The sleeve-shaped heating furnace is a graphite resistance heating furnace or an induction furnace. The axial heating area is 100-350mm. The furnace cavity of the sleeve-shaped heating furnace is equipped with a protective gas source for filling with protective gas. The protective gas is an inert gas such as Ar or N2. The outer shell of the furnace body is also equipped with a water cooling structure. At the same time, the sleeve-shaped heating furnace is connected to a reciprocating moving device. During heating, the sleeve-shaped heating furnace moves slowly along the axial direction of the sleeve assembly, reciprocating multiple times from one end to the other to complete the corrosion and shrinkage process of the sleeve assembly.

[0031] The corrosion and shrinkage process of this invention is as follows: Quartz sleeves 14 with a specific refractive index and initial mandrel 13 are assembled into sleeve assemblies in a cleanroom. The specific assembly method is as follows: Figure 2As shown, the initial mandrel and the quartz sleeve are fixed at both ends by fixing devices. The fixing devices include a hollow tightening cone sleeve 15, with a threaded front end that mates with a tightening nut. The outer periphery of the tightening cone sleeve is fitted with flanges 16 fixed to the inner holes at both ends of the quartz sleeve. The flanges have evenly distributed vent holes. The initial mandrel is prepared using a vapor deposition process such as PCVD, MCVD, or VAD. The assembled sleeve assembly is installed onto the melting and sintering device. The quartz sleeve and the initial mandrel of the sleeve assembly are aligned and fitted together with a radial gap. One end of the quartz sleeve is clamped to the inlet rotary sealing clamp, and the other end is clamped to the outlet rotary sealing clamp. After clamping, the inlet rotary sealing clamp 4 and the outlet rotary sealing clamp 5 are turned on to rotate synchronously, causing the sleeve assembly to rotate at a uniform speed. At the same time, the sleeve-shaped heating furnace 3, which is fitted around the outer periphery of the sleeve assembly, begins heating. When the temperature of the heating element rises to 1900℃, the first high-pressure corrosion reaction cleaning treatment begins. The relative pressure inside the sleeve is controlled at 100 Pa (higher than the maximum pressure). The heating furnace moves back and forth along the axial direction of the casing assembly from one end to the other at a speed of 18 mm / min. The reaction gases Freon and oxygen enter the gap between the casing and the mandrel from the inlet end through the rotary sealing clamp 4 at a flow ratio of 1:1.5. A corrosion reaction occurs under high temperature and high pressure. The tail gas after the reaction passes through the outlet rotary sealing clamp 5, connects to the high pressure control device, and passes through the control valve 8, filter 11 and gas supply line 9 to the outlet. The gas supply line can provide the gas required for high pressure control. The corrosion cycle can be 3 to 5 times (one reciprocating cycle is one pass). After multiple corrosion cycles, the furnace temperature is raised to approximately 2000℃ to initiate the sintering and melting cycle, performing low-pressure melting and sintering. At this point, the reaction gas at the inlet is shut off, and the pressure control device switches from high-pressure to low-pressure control. Control valve 8 closes, and control valve 7 opens, maintaining an absolute pressure of 60 mbar. The pressure throughout the process is monitored by pressure gauge 6. Gas and impurities remaining between the sleeve and mandrel are extracted by the air pump through control valve 7 and filter 12, entering the waste gas treatment system. This process continues until the quartz sleeve and initial mandrel are melted and sintered into a single unit. After the melting and melting cycle, the furnace begins to cool down and continues its reciprocating motion, gradually and slowly lowering the mandrel temperature until room temperature.

[0032] In this embodiment, the interface with high impurity content is removed by etching the inner surface of the sleeve with a specific refractive index and the outer surface of the small mandrel. Figure 3 Experimental data shows that the unstable phenomenon of sudden increase in the intermediate decay of the existing core rods, which account for about 10% of the total, has basically disappeared, and the overall decay is stable.

[0033] In this embodiment, due to the introduction of a low-pressure system during melting and compaction, a lower internal tube pressure is used during melting and compaction, resulting in a larger pressure difference between the inside and outside of the tube. This requires only a lower furnace heat to achieve compaction, significantly improving the bow value of the mandrel after melting and compaction. Figure 4 As shown, the bow value statistics before and after the implementation of the invention clearly show a significant improvement in bending performance, which greatly enhances the effective length of the mandrel and manufacturing efficiency.

Claims

1. A melting and sintering apparatus for optical fiber preform core rods, comprising a bed, a horizontal guide rail mounted on the bed, an inlet rotary sealing chuck and an outlet rotary sealing chuck respectively mounted at both ends of the bed, a sleeve-shaped heating furnace mounted between the inlet rotary sealing chuck and the outlet rotary sealing chuck, the sleeve-shaped heating furnace being connected to a reciprocating moving device, characterized in that... The inlet rotary sealing clamp is connected to both a Freon gas source and an oxygen gas source via an inlet pipe, and the outlet rotary sealing clamp is connected to a pressure control device via an outlet pipe. The pressure control device includes a low-pressure control device and a high-pressure control device, which are connected to the outlet pipe via a switching valve or a control valve. The Freon gas source and the oxygen gas source are respectively connected to flow meters, with the oxygen source controlled by two separate flow meters, a large flow meter for controlling the purging of dust and impurities, and a small flow meter for controlling corrosion reactions.

2. The fusion-shrinking sintering apparatus for optical fiber preform core rods according to claim 1, characterized in that... The low-pressure control device includes a vacuum pump and a filter connected in series. One end of the low-pressure control device is connected to the gas outlet pipe through a control valve, and the other end is connected to the gas outlet.

3. The fusion-shrinking sintering apparatus for optical fiber preform core rods according to claim 1 or 2, characterized in that... The high-pressure control device includes a connected gas supply pipeline. One end of the high-pressure control device is connected to the gas outlet pipe through a control valve, and the other end is connected to the gas outlet.

4. The fusion-shrinking sintering apparatus for optical fiber preform core rods according to claim 1 or 2, characterized in that... The air intake rotary sealing chuck is fixed at one end of the bed, and the air exhaust rotary sealing chuck is installed on the movable slide, forming an axially movable air exhaust rotary sealing chuck.

5. The fusion-shrinking sintering apparatus for optical fiber preform core rods according to claim 1 or 2, characterized in that... The air intake rotary sealing chuck and the air outlet rotary sealing chuck are connected to a synchronous rotary drive device.

6. The fusion-shrinking sintering apparatus for optical fiber preform core rods according to claim 1 or 2, characterized in that... The sleeve-shaped heating furnace is a graphite resistance heating furnace or an induction furnace, with a heating axial area of ​​100~350mm. The furnace cavity of the sleeve-shaped heating furnace is equipped with a protective gas source for filling with protective gas.

7. A method for melting and sintering optical fiber preform core rods, characterized in that... Using any one of the devices described in claims 1-6, a quartz sleeve with a specific refractive index and an initial mandrel are assembled into a sleeve assembly and installed on a melting and sintering apparatus. The quartz sleeve and the initial mandrel of the sleeve assembly are aligned and fitted together with a radial gap. One end of the quartz sleeve is clamped to an inlet rotary sealing chuck, and the other end is clamped to an outlet rotary sealing chuck. After clamping, the synchronous rotation of the inlet and outlet rotary sealing chucks drives the sleeve assembly to rotate at a uniform speed. Simultaneously, a sleeve-shaped heating furnace fitted around the outer periphery of the sleeve assembly begins heating at a temperature of 1800~2250℃, and the heating furnace moves axially along the sleeve assembly from... The device moves back and forth from one end to the other. First, Freon and oxygen are introduced into the inlet rotary sealing chuck and enter the radial gap between the quartz sleeve and the initial core rod. At the same time, the outlet rotary sealing chuck is connected to the high-pressure control device to perform high-pressure corrosion reaction cleaning on the inner wall of the quartz sleeve and the outer periphery of the initial core rod of the sleeve assembly. After the high-pressure corrosion reaction cleaning, the Freon and oxygen gas sources are shut off at the inlet rotary sealing chuck end, and the outlet pipe at the outlet rotary sealing chuck end is connected to the low-pressure control device to perform low-pressure melting and sintering treatment on the sleeve assembly until the quartz sleeve and the initial core rod are melted and sintered into one piece to form a solid optical fiber preform.

8. The fusion-shrink sintering method for the optical fiber preform core rod according to claim 7, characterized in that... After high-pressure corrosion reaction cleaning treatment, and before melting and shrinking sintering, a large flow of oxygen is used to purge the inner wall of the quartz sleeve and the outer periphery of the initial mandrel.

9. The fusion-shrink sintering method for the optical fiber preform core rod according to claim 7, characterized in that... The relative pressure of the high-pressure corrosion reaction cleaning treatment is controlled within the range of 50~200 Pa.

10. The method for melting and sintering the optical fiber preform core rod according to claim 7 or 9, characterized in that... The ratio of Freon to oxygen flow rate in the high-pressure corrosion reaction cleaning treatment is 1:1 to 1:

2.

11. The fusion-shrink sintering method for the optical fiber preform core rod according to claim 7, characterized in that... The absolute pressure of the low-pressure melting and sintering process is controlled within the range of 10~100mbar.

12. The fusion-shrink sintering method for the optical fiber preform core rod according to claim 7, characterized in that... The rotational speed of the sleeve assembly is 10~30 rad / min.

13. The fusion-shrink sintering method for the optical fiber preform core rod according to claim 7, characterized in that... The axial movement speed of the sleeve-shaped heating furnace is 10~30mm / min, the axial heating area of ​​the sleeve-shaped heating furnace is 100~350mm, and the radial gap between the furnace cavity and the sleeve assembly is filled with protective gas during heating.

14. The fusion-shrink sintering method for the optical fiber preform core rod according to claim 7, characterized in that... The gap between the quartz sleeve and the initial mandrel is 3~15mm.

15. The fusion-shrink sintering method for the optical fiber preform core rod according to claim 7 or 14, characterized in that... The specifications of the quartz sleeve before melting and sintering are: outer diameter of 30~60mm and length of 1.0~2.5m.

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