Degassing device and degassing method for optical fiber preform

Abstract

The present invention discloses a degassing device and a degassing method for an optical fiber preform, and belongs to the technical field of manufacturing optical fiber preforms. The device comprises a frame, a rod feeding mechanism arranged on the frame, a rotating machine and a guide rod arranged on the output end of the rod feeding mechanism, a cylindrical quartz glass cavity, a sealing cover plate that can be sealed and connected with the quartz glass cavity to form a closed space, a heating furnace installed on the periphery of the quartz glass cavity, a quartz clamp arranged in the closed space, a circulation pipeline connected to the quartz glass cavity, a vacuum pumping device connected in series on the circulation pipeline, and a mixed gas storage tank for storing deuterium gas. The present invention utilizes the excellent thermal conductivity of deuterium gas to allow the residual gas in the optical fiber preform to overflow quickly, and effectively remove the bubbles in the optical fiber preform; the rotation function of the guide rod allows the optical fiber preform to be heated more evenly and fully, which can further shorten the annealing time of the optical fiber preform and improve efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber preform manufacturing, in particular to a degassing device and a degassing method for an optical fiber preform. Background Art

[0002] At present, the window of single-mode optical fiber communication is 1260nm to 1675nm, but due to the influence of the water peak at 1383nm, the actual use is still the O-band near 1310nm and the S-, C-, and L-bands in the range of 1460-1625nm. With the advancement and development of optical fiber manufacturing technology, the optical fiber is treated with deuterium gas after the optical fiber preform is drawn, and the disordered Si-O free radicals generated during the optical fiber drawing process react with deuterium to form Si-OD, preventing hydrogen from replacing the position of deuterium, so that the optical fiber can withstand long-term corrosion in hydrogen-containing environments and improve the hydrogen insensitivity of the optical fiber. The optical fiber treated with deuterium gas effectively eliminates and reduces the OH ion absorption peak at 1383nm in the optical fiber, allowing the optical fiber to be used in the entire communication window.

[0003] At present, the international preform preparation technology adopts a two-step process, that is, the core rod is prepared by one of the methods of axial vapor deposition (VAD), external vapor deposition (OVD), plasma chemical vapor deposition (PCVD), and modified chemical vapor deposition (MCVD), and the outer cladding is prepared by the casing method, plasma spraying method, flame hydrolysis method, etc. The development of outer cladding technology makes the optical fiber preform rod thicker in diameter and longer in length, further improving the optical fiber production efficiency and reducing the manufacturing cost.

[0004] Axial vapor deposition and external vapor deposition are carried out by SiXCl 4 The raw materials are subjected to high temperature hydrolysis reaction and thermophoresis principle to prepare large-sized preform loose bodies, and then undergo dehydration and sintering processes to obtain dense transparent glass. Since the loose bodies will inevitably contain free water and silanol groups during the deposition process, chlorine (Cl 2 ), thionyl chloride (SOCl 2 ) and other chemical reagents for high-temperature dehydroxylation, and finally helium (He) is introduced for sintering and vitrification, but it is impossible to completely remove the Cl in the pores of the loose body. 2 , He, etc. are removed so that a small amount of gas will remain in the preform to form bubble defects.

[0005] Bubbles in preforms are extremely harmful defects. Large bubbles can easily cause the tower to break during the drawing process, affecting production efficiency; small bubbles can easily form air lines in the optical fiber, affecting the fusion loss and optical fiber life. Preforms usually need to be degassed. The conventional degassing principle is to heat the sintered preform to 800℃-1200℃, and slowly let the bubbles overflow through thermal diffusion. Normally, it takes 10-40 hours. The larger the size of the optical fiber preform, the longer the insulation and degassing time.

[0006] Chinese patent CN105753311A proposes a high temperature negative pressure treatment method to make the Cl2, He and other gases remaining in the optical fiber preform quickly overflow and remove the bubbles in the preform. However, in the results of this embodiment, the diameter of the optical fiber preform is only 90mm, and it still takes 10 hours to basically remove the bubbles.

[0007] In addition, optical fiber deuterium treatment requires 36-48 hours to achieve the purpose of reducing hydrogen sensitivity. Although patent CN101838114A describes an optical fiber deuterium treatment method that reduces the deuterium treatment time, it is still considered from the perspective of optical fiber processing and fails to solve this problem from the source of optical fiber preform manufacturing. Summary of the invention

[0008] In order to overcome the above technical defects, the present invention provides a degassing device and a degassing method for an optical fiber preform to solve the problems involved in the background technology.

[0009] The present invention provides a degassing device for an optical fiber preform, comprising:

[0010] The mounting assembly includes a frame, a rod feeding mechanism disposed on the frame and movable up and down, a rotating mechanism disposed on an output end of the rod feeding mechanism, and a guide rod disposed at the bottom of the rotating mechanism;

[0011] The heat preservation furnace comprises a semi-enclosed cylindrical quartz glass cavity with an opening at the top, a sealing cover plate arranged at the lower part of the guide rod and capable of being sealed and connected with the quartz glass cavity to form a closed space, and a heating furnace installed at the periphery of the quartz glass cavity;

[0012] A quartz fixture is installed at the bottom of the lead rod and is arranged in the enclosed space through the sealing cover plate.

[0013] The gas circulation component comprises a circulation pipeline with two ends respectively connected to the quartz glass cavity, a vacuum pumping device connected in series on the circulation pipeline and a mixed gas storage tank for storing deuterium gas.

[0014] Preferably or optionally, a sealing quartz ring is provided at the bottom of the sealing cover plate, and is sealed and connected to the quartz glass cavity through the sealing quartz ring.

[0015] Preferably or optionally, the lower end surface of the sealing quartz ring is a frosted surface.

[0016] Preferably or optionally, an annular step is provided on the top of the quartz glass cavity;

[0017] The sealing cover plate falls on the top of the quartz glass cavity, and the annular step can accommodate the sealing quartz ring.

[0018] Preferably or optionally, the quartz fixture comprises: a fixture body made of quartz material, and a plurality of through holes arranged on the lower side of the fixture body and distributed along the circumferential direction.

[0019] Preferably or optionally, the mixed gas includes deuterium gas and other inert gases; the concentration of deuterium gas in the mixed gas is 1% to 5%.

[0020] Preferably or optionally, the heating furnace is a silicon-molybdenum rod furnace, a silicon-carbon rod furnace or an induction furnace.

[0021] Preferably or optionally, the gas outlet of the mixed gas storage tank is connected to the lower end of the quartz glass cavity through an air inlet pipeline, and a first control valve is provided on the air inlet pipeline;

[0022] The air inlet end of the vacuum pump is connected to the upper end of the quartz glass cavity through an air outlet pipeline, and a pressure sensor is arranged on the air outlet pipeline;

[0023] The gas outlet end of the vacuum pumping device and the gas inlet of the mixed gas storage tank are connected via a connecting pipeline, and a second control valve is also arranged on the connecting pipeline;

[0024] An exhaust pipeline is also provided on the gas outlet end of the vacuum pumping device, and an exhaust valve is provided on the exhaust pipeline.

[0025] The present invention also provides a degassing method based on the degassing device for the optical fiber preform, comprising the following steps:

[0026] The optical fiber preform rods after deposition and sintering are fixed and hung on the fixture body through the through holes through the pins in turn, and the rod feeding mechanism is controlled to drive the guide rod to slowly lower the optical fiber preform rod into the quartz glass cavity, and the sealing quartz ring and the sealing cover plate fall on the step and the top of the quartz glass cavity in turn, and are sealed and connected to form a closed space;

[0027] Control the rotating mechanism to drive the guide rod to rotate, start the vacuum device, open the exhaust valve, and exhaust the gas in the quartz glass cavity. Keep it for 3 to 5 minutes. When the quartz glass cavity reaches a stable negative pressure of 200 mbar, close the vacuum device;

[0028] Open the first control valve of the air inlet pipeline, introduce deuterium-nitrogen mixed gas into the closed space, wait until the quartz glass cavity reaches a stable positive pressure of 500 mbar, close the first control valve of the air inlet pipeline, start the heating furnace, and perform deuterium gas treatment and degassing treatment;

[0029] After the insulation and degassing time is reached, the heating furnace is turned off. After the quartz glass cavity is cooled to room temperature, the vacuum device is turned on, the control valve on the recovery pipeline is opened, and the deuterium nitrogen mixed gas is discharged to the mixed gas storage tank.

[0030] The rod feeding mechanism is controlled to drive the guide rod to lift, so as to lift the optical fiber preform rod out of the quartz glass cavity.

[0031] Preferably or optionally, the concentration of deuterium gas in the deuterium-nitrogen mixed gas is 1% to 5%.

[0032] Preferably or optionally, the target temperature of the deuterium treatment and degassing treatment is 800-1000° C., and the insulation and degassing time is 5-10 hours.

[0033] The present invention relates to a degassing device and a degassing method for an optical fiber preform, which have the following beneficial effects compared with the prior art:

[0034] (1) By utilizing the excellent thermal conductivity of deuterium gas, the residual gas in the optical fiber preform can be quickly released, effectively removing the bubbles in the optical fiber preform. At the same time, the rotation function of the lifting and lowering rod is added, so that the optical fiber preform is heated more evenly and fully, which can further shorten the annealing time of the optical fiber preform and improve the efficiency.

[0035] (2) Deuterium treatment is carried out simultaneously under high temperature conditions during the degassing process. The diffusion of deuterium molecules is accelerated under high temperature conditions. The structural defects in the optical fiber preform are pre-combined with deuterium to reduce hydrogen sensitivity. The deuterium treatment time after subsequent optical fiber preform drawing can be reduced or even the deuterium treatment process can be eliminated, thereby improving production efficiency;

[0036] (3) Using a quartz clamp to clamp multiple optical fiber preform rods for degassing and deuterium treatment at the same time, effectively improving equipment production capacity, saving equipment space, and reducing production energy consumption.

[0037] (4) After degassing and deuterium treatment, the stress inside the optical fiber preform can be effectively released, promoting the adjustment of the internal structure, thereby reducing the overall attenuation level of the optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a simplified structural diagram of the degassing device in the present invention.

[0039] Figure 2 It is a structural schematic diagram and a bottom view of the quartz fixture in the present invention.

[0040] Figure 3 This is the result of a hydrogen aging test of an optical fiber prepared by drawing the preform rod in Example 1 of the present invention and treated with deuterium gas for 12 hours.

[0041] Figure 4 This is the result of a hydrogen aging test of an optical fiber prepared by drawing the preform rod in Example 1 of the present invention and treated with deuterium gas for 18 hours.

[0042] Figure 5 This is the result of a hydrogen aging test of an optical fiber prepared by drawing the preform rod in Example 1 of the present invention and treated with deuterium gas for 24 hours.

[0043] Figure 6 This is the result of a hydrogen aging test on an optical fiber prepared by drawing the preform rod in Application Example 2 of the present invention without deuterium treatment.

[0044] The numbers in the accompanying drawings are: 11, frame; 12, rod feeding mechanism; 13, rotating mechanism; 14, guide rod; 21, quartz glass cavity; 22, sealing cover plate; 23, sealing quartz ring; 24, heating furnace; 30, quartz fixture; 31, fixture body; 32, through hole; 41, vacuum device; 42, mixed gas storage tank; 43, air inlet pipeline; 431, first control valve; 44, air outlet pipeline; 441, pressure sensor; 45, connecting pipeline; 451, second control valve; 46, exhaust pipeline; 461, drain valve; 50, optical fiber preform. DETAILED DESCRIPTION

[0045] In the following description, a large number of specific details are provided to provide a more thorough understanding of the present invention. However, it is apparent to those skilled in the art that the present invention can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present invention, some technical features well known in the art are not described.

[0046] Device Embodiment

[0047] See attached Figures 1 to 2A degassing device for an optical fiber preform 50 comprises: a frame 11, a rod feeding mechanism 12 arranged on the frame 11 in a vertical direction, a rotating mechanism 13, a guide rod 14, a quartz glass cavity 21, a sealing cover plate 22, a sealing quartz ring 23, a heat preservation furnace, a vacuum device 41 connected to the heat preservation furnace, and a mixed gas storage tank 42. The rod feeding mechanism 12 is a linear motion module such as a screw rod and a cylinder, which can drive the guide rod 14 to move in a vertical direction so that the optical fiber preform 50 is annealed in the quartz glass cavity 21. A rotating mechanism 13 is arranged at the output end of the rod feeding mechanism 12, and the rotating mechanism 13 is connected to the guide rod 14 to drive the guide rod 14 to rotate so that the optical fiber preform 50 rotates in the quartz glass cavity 21 along the central axis of the guide rod 14. A quartz fixture 30 is disposed at the lower end of the guide rod 14. The quartz fixture 30 includes: a fixture body 31 made of quartz material, a plurality of through holes 32 arranged on the lower side of the fixture body 31 and distributed along the circumferential direction, and the optical fiber preform 50 is fixed to the lower side of the fixture body 31 by a pin. A sealing quartz ring 23 and a sealing cover plate 22 are disposed at the lower part of the guide rod 14, and the sealing quartz ring 23 and the sealing cover plate 22 are located at a predetermined distance above the quartz fixture 30. The insulation furnace includes a cylindrical quartz glass cavity 21 and a heating furnace 24 arranged on the outer periphery of the quartz glass cavity 21. The quartz glass cavity 21 is cylindrical, open at the top, and is made of high-purity quartz sand. The heating furnace 24 is a silicon-molybdenum rod furnace, a silicon-carbon rod furnace or an induction furnace. The sealing quartz ring 23 is disposed with the quartz glass cavity 21 to form the same closed space. The mixed gas storage tank 42 for storing deuterium gas is connected to the vacuum device 41 and the air inlet pipeline 43, forming a mixed gas gas circulation component. The gas outlet of the mixed gas storage tank 42 is connected to the lower end of the quartz glass cavity 21 through the air inlet pipeline 43, and a first control valve 431 is provided on the air inlet pipeline 43; the gas inlet end of the vacuum device 41 is connected to the upper end of the quartz glass cavity 21 through the air outlet pipeline 44, and a pressure sensor 441 is provided on the air outlet pipeline 44; the gas outlet end of the vacuum device 41 and the gas inlet of the mixed gas storage tank 42 are connected through a connecting pipeline 45, and a second control valve 451 is also provided on the connecting pipeline 45; the gas outlet end of the vacuum device 41 is also provided with an exhaust pipeline 46, and an exhaust valve 461 is provided on the exhaust pipeline 46. The mixed gas storage tank 42 recovers the mixed gas in the quartz glass cavity 21 through the vacuum pumping device 41 , and realizes the recycling of the mixed gas through the air intake pipeline 43 .

[0048] In a further embodiment, a sealing quartz ring 23 is provided at the bottom of the sealing cover plate 22, and the lower end surface of the sealing quartz ring 23 is a frosted surface to increase the sealing effect. In contrast, an annular step is provided at the top of the quartz glass cavity 21; the sealing quartz ring 23 falls on the step at the top of the quartz glass cavity 21, and the sealing cover plate 22 falls on the top of the quartz glass cavity 21, so that the sealing quartz ring 23 is sealed and connected to the quartz glass cavity 21 to form a closed space.

[0049] The present invention will be further described below in conjunction with application examples. The examples of the application examples are intended to explain the present invention and should not be construed as limiting the present invention.

[0050] Application Example 1

[0051] The method for degassing the optical fiber preform 50 using the degassing device as described in the equipment embodiment comprises the following steps:

[0052] S1. The optical fiber preform rod 50 after deposition and sintering is fixed and suspended on the quartz fixture 30 through the through hole 32 on the lower side of the quartz fixture 30 through the pins in turn, and the rod feeding mechanism 12 is controlled to drive the guide rod 14 to slowly lower the optical fiber preform rod 50 into the quartz glass cavity 21. When the sealing quartz ring 23 and the sealing cover plate 22 fall on the step and the top of the quartz glass cavity 21 in turn, they reach the target position and are sealed and connected to form a closed space.

[0053] S2. Control the rotating mechanism 13 to drive the guide rod 14 to rotate, start the vacuum device 41, open the exhaust valve 461, and exhaust the gas in the quartz glass cavity 21. Maintain for 3 to 5 minutes, wait until the quartz glass cavity 21 reaches a stable negative pressure of 200 mbar, and then close the vacuum device 41.

[0054] S3. Open the control valve of the air inlet line 43, control the mixed gas storage tank 42 to pass the deuterium nitrogen mixed gas into the quartz glass cavity 21, the concentration of deuterium gas in the deuterium nitrogen mixed gas is 1% to 5%, wait until the quartz glass cavity 21 reaches a stable positive pressure of 500 mbar, close the control valve of the air inlet line 43, turn on the heating furnace 24, raise the furnace temperature to the target temperature of 800 to 1000° C., and simultaneously perform deuterium treatment and degassing treatment, and the insulation and degassing time is 5-8 hours.

[0055] S4. After the insulation and degassing time is reached, the heating furnace 24 is turned off, and after the quartz glass cavity 21 is cooled to room temperature, the vacuum pump 41 is turned on, and the control valve on the recovery pipeline is opened to discharge the deuterium nitrogen mixed gas into the mixed gas storage tank 42.

[0056] S5. Control the rod feeding mechanism 12 to drive the guide rod 14 to lift up, and lift the optical fiber preform 50 out of the quartz glass cavity 21.

[0057] In this embodiment, the optical fiber preform 50 is prepared by VAD process. After sintering, the diameter of the preform is 120 mm. Three optical fiber preforms 50 are sequentially suspended in the quartz fixture 30 for degassing. The deuterium concentration in the deuterium gas mixture is 1%, and the degassing time is 5 hours. The optical fiber preform 50 is stretched into a core rod with a diameter of 45 mm, and no bubbles are found.

[0058] The preforms were prepared by OVD process using the core rods. The optical fibers prepared by drawing the preforms were treated with deuterium in batches, with a deuterium concentration of 2.5% and the treatment time was 12h, 18h and 24h respectively. One disk of optical fiber was selected for hydrogen aging test to detect the hydrogen sensitivity of the optical fiber. Figure 3 , Figure 4 , Figure 5 These are the results of hydrogen aging tests after deuterium gas treatment for 12h, 18h, and 24h, respectively.

[0059] Application Example 2

[0060] In this embodiment, the optical fiber preform 50 is prepared by VAD+OVD process. After sintering, the diameter of the preform reaches 150 mm. The optical fiber preforms 50 are suspended in sequence in the quartz fixture 30 for degassing. The deuterium concentration in the deuterium gas mixture is 1.5%. The heat preservation degassing time is 10 hours. Other process parameters are the same as those in Application Example 1.

[0061] The batch of optical fiber preform rods 50 were directly drawn, and no gas lines were found in the optical fiber detection. The selected optical fiber was directly subjected to hydrogen aging test without deuterium gas treatment process. Figure 6 This is the result of the optical fiber hydrogen aging test. From the test results, it can be seen that the optical fiber that has not been treated with deuterium still has good hydrogen insensitivity.

[0062] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

Claims

1. A degassing device for an optical fiber preform, It is characterized in that include: The mounting assembly includes a frame, a rod feeding mechanism disposed on the frame and movable up and down, a rotating mechanism disposed on an output end of the rod feeding mechanism, and a guide rod disposed at the bottom of the rotating mechanism; The heat preservation furnace comprises a semi-enclosed cylindrical quartz glass cavity with an opening at the top, a sealing cover plate arranged at the lower part of the guide rod and capable of being sealed and connected with the quartz glass cavity to form a closed space, and a heating furnace installed at the periphery of the quartz glass cavity; a sealing quartz ring is arranged at the bottom of the sealing cover plate, and is sealed and connected with the quartz glass cavity through the sealing quartz ring, and the lower end surface of the sealing quartz ring is a frosted surface, and an annular step is arranged at the top of the quartz glass cavity, and the sealing cover plate falls on the top of the quartz glass cavity, and the annular step can accommodate the sealing quartz ring; A quartz fixture is installed at the bottom of the guide rod and is disposed in the enclosed space through the sealing cover plate; A gas circulation component comprises a circulation pipeline whose two ends are respectively connected to the quartz glass cavity, a vacuum pumping device on the circulation pipeline and a mixed gas storage tank for storing deuterium gas connected in series; the circulation pipeline comprises an air inlet pipeline, an air outlet pipeline, a connecting pipeline and an exhaust pipeline, the air outlet of the mixed gas storage tank is connected to the lower end of the quartz glass cavity through the air inlet pipeline, and a first control valve is arranged on the air inlet pipeline; the air inlet end of the vacuum pumping device is connected to the upper end of the quartz glass cavity through the air outlet pipeline, the air outlet end of the vacuum pumping device and the air inlet of the mixed gas storage tank are connected through a connecting pipeline, and a second control valve is also arranged on the connecting pipeline; the air outlet end of the vacuum pumping device is also provided with an exhaust pipeline, and an exhaust valve is arranged on the exhaust pipeline.

2. The degassing device for optical fiber preform according to claim 1, It is characterized in that The quartz fixture comprises: a fixture body made of quartz material, and a plurality of through holes arranged on the lower side of the fixture body and distributed along the circumferential direction.

3. The degassing device for optical fiber preform according to claim 1, It is characterized in that The mixed gas stored in the mixed gas storage tank includes deuterium gas and other inert gases; the concentration of deuterium gas in the mixed gas is 1% to 5%.

4. The degassing device for optical fiber preform according to claim 1, It is characterized in that The heating furnace is a silicon-molybdenum rod furnace, a silicon-carbon rod furnace or an induction furnace.

5. The optical fiber preform degassing device according to claim 1, It is characterized in that A pressure sensor is arranged on the air outlet pipeline.

6. A degassing method based on the degassing device for an optical fiber preform according to any one of claims 1 to 5, It is characterized in that The steps include: The optical fiber preform rods after deposition and sintering are fixed and hung on the fixture body through the through holes through the pins in turn, and the rod feeding mechanism is controlled to drive the guide rod to slowly lower the optical fiber preform rod into the quartz glass cavity, and the sealing quartz ring and the sealing cover plate fall on the step and the top of the quartz glass cavity in turn, and are sealed and connected to form a closed space; Control the rotating mechanism to drive the guide rod to rotate, start the vacuum device, open the exhaust valve, and exhaust the gas in the quartz glass cavity. Keep it for 3 to 5 minutes. When the quartz glass cavity reaches a stable negative pressure of 200 mbar, close the vacuum device; Open the first control valve of the air inlet pipeline, introduce deuterium-nitrogen mixed gas into the closed space, wait until the quartz glass cavity reaches a stable positive pressure of 500 mbar, close the first control valve of the air inlet pipeline, start the heating furnace, and perform deuterium gas treatment and degassing treatment; After the insulation and degassing time is reached, the heating furnace is turned off, and after the quartz glass cavity is cooled to room temperature, the vacuum device is turned on, and the control valve on the recovery pipeline is opened to discharge the deuterium nitrogen mixed gas into the mixed gas storage tank; The rod feeding mechanism is controlled to drive the guide rod to lift, so as to lift the optical fiber preform rod out of the quartz glass cavity.

7. The degassing method according to claim 6, It is characterized in that The concentration of deuterium gas in the deuterium-nitrogen mixed gas is 1% to 5%.

8. The degassing method according to claim 7, It is characterized in that The target temperature of the deuterium treatment and degassing treatment is 800-1000° C., and the insulation and degassing time is 5-10 hours.

Images