CN116409922A - Preparation device and method of fluorine-based glass active optical fiber preform - Google Patents

Abstract

The invention discloses a preparation device and method for a fluorine-based glass active optical fiber preform with a core-clad structure designed based on temperature-viscosity dependence. In this device, through the synchronous cooling of the core and cladding, when the cladding glass liquid just solidifies, the rare earth-doped glass liquid fills the preform core layer under the condition of relatively high viscosity, which can suppress the core glass to the cladding glass. The reheating process can effectively reduce the erosion of the core layer to the cladding layer, so as to obtain a high-quality core-in-pack interface, stable core-in-pack ratio and high core-in-pack concentricity, and better optical performance. This preparation method can realize a fully automatic/semi-automatic preparation process with a short preparation cycle, and is expected to be applied in fields such as medical treatment, industrial processing, and gas detection.

Description

Preparation device and method of a fluorine-based glass active optical fiber preform

technical field

The invention relates to a preparation device and method for a glass optical fiber preform, and is especially suitable for the preparation of a rare earth ion-doped fluorine-based glass optical fiber preform with a core-clad structure. It has a good core-cladding interface, high core-clad concentricity, and The advantage of layer diameter stability.

Background technique

2-5μm near-mid-infrared lasers have a wide range of applications in medical surgery, ophthalmic surgery, molecular absorption spectroscopy, organic polymer laser cutting, and national defense infrared countermeasures. Fiber laser has become a major direction of laser research due to its advantages of small size, good beam quality, low cost, high light-to-light conversion efficiency, and low thermal effect. A method of generating laser light in the mid-infrared band is based on the unique energy level structure of rare earth ions, which can emit mid-infrared light of different wavelengths, and is widely used in mid-infrared band fluorescence and laser emission. Fluorine-based glass materials are widely used in the preparation of mid-infrared devices due to their high solubility of rare earth ions, high infrared transmittance, far infrared cut-off edge and high laser damage threshold. Fluorine-based glass fiber doped with rare earth ions as a gain medium requires high optical quality of the fluorine-based glass fiber, which brings challenges in the preparation process. The difficulties in the preparation of rare earth-doped fluorine-based glass gain fibers with a core-clad structure are reflected in the eccentricity of the core-clad layer, the quality of the core-clad layer interface, easy crystallization, and large internal stress. At present, the traditional preparation process uses the pouring method. First, the cladding is cast and the central glass liquid is poured out to form a hollow tube, and then the core glass liquid is poured into it to form a preform. Usually, the core package is not concentric, and the core package is smaller than the bottom and the top is large. Inhomogeneous, high-temperature core layer erodes the cladding layer, resulting in a non-step distribution of the refractive index. A new type of preparation device and preparation process is urgently needed. Therefore, we have designed a preparation device and process technology for core-clad optical fiber preform based on temperature-viscosity dependence, which can obtain fluorine-based glass gain fiber prefabrication with high core-clad interface quality, high core-clad concentricity, and high optical quality. Great.

Contents of the invention

The object of the present invention is to provide a preparation device and method for a core-clad structure glass optical fiber preform. Compared with the previous preparation methods and devices, the device can prepare fluorine-based glass gain optical fiber preforms with high-quality core-clad interface and high core-clad concentricity.

Technical solution of the present invention is as follows:

A preparation device for a fluorine-based glass optical fiber preform, comprising a core liquid container for containing the core glass liquid, a cladding liquid container for containing the cladding glass liquid, a preform molding mold, and a molding mold holder , which is characterized in that it also includes a glass liquid isolation tube;

The preform forming mold is a hollow cylindrical tube, placed in the forming mold holder, and a traction mechanism is arranged under the forming mold holder to drive the forming mold holder to move up and down;

The glass liquid isolating tube is placed in the preform forming mold, so that the core glass liquid and the cladding glass are respectively flowed into the preform forming mold along the inner wall and the outer wall of the glass liquid isolating tube, and the preform is formed In the mould, the bottom of the molten glass isolating tube is closely attached to the upper part of the mold holder, so that the cladding glass is isolated from the core glass, and the cladding glass is cooled faster than the core glass. When the cladding glass When the liquid is solidified into glass, the core glass liquid is in a slightly higher temperature, higher viscosity, and still liquid state. At this time, the forming mold holder is pulled down by the traction mechanism, and the bottom of the glass liquid isolation tube is always is lower than the solid-liquid interface of the cladding glass, so that the core glass liquid is slowly spread and solidified in the preform molding mold to form a fluorine-based glass optical fiber preform with a core-clad structure.

Further, it also includes an annealing temperature control system, which is used for preheating the preform molding mold, providing temperature control for glass cooling, preventing the glass from cooling too fast to cause bursting or early solidification of the core layer, and providing a stable temperature for the formed glass preform. Provide an annealing environment;

The preform forming mold is a hollow cylindrical tube formed by combining three arc columns with an arc angle of 120°, and is fixed by three screws with an included angle of 120° outside the forming mold holder.

The lower part of the molding die fixer is connected with the traction mechanism through screws.

The core liquid container and the cladding liquid container are provided with openings at the bottom, and are connected with drainage wires, the glass liquid can be added manually and the opening size is controlled by the automation system to control the flow of the glass liquid.

The core liquid container and the cladding liquid container are precious metals such as platinum and gold, and the drainage wires connected to the lower openings are precious metals such as platinum or gold or glassy carbon.

Further, a casting positioning plate is also included, which is used for positioning the molten glass isolating tube, so that the molten glass isolating tube is stably located in the center of the preform molding mold, so as to ensure the detachable and replaceable of the molten glass isolating tube.

The casting positioning plate is made of stainless steel, the glass liquid isolating tube is made of platinum, and the surface is mirror polished.

A method for preparing a fluorine-based glass optical fiber preform, comprising the steps of:

Step 1. Continuously casting cladding and core layer glass liquid into the preform molding mold;

Step 2. Pull down the forming mold holder through the traction mechanism, and ensure that the bottom of the glass liquid isolation tube is always lower than the solid-liquid interface of the cladding glass, so that the core glass liquid is slowly spread in the preform forming mold to form core structure;

Step 3. Annealing is performed by an annealing temperature control system after the preform with a core-clad structure is cast.

Compared with prior art, the beneficial effect of the present invention:

1) The present invention controls the temperature of the molten glass and the solid-liquid interface in the mould, by automatically/semi-automatically regulating the addition of the core layer and the clad glass liquid, so that the temperature of the core glass is slightly higher than that of the clad glass. The mold has been solidified but the core layer glass is not solidified but has a relatively high viscosity, so that the core layer with a slightly higher temperature is slowly spread in the center, effectively reducing the number of bubbles at the interface of the core layer and reducing the temperature difference between the core layer and the cladding layer. In order to obtain a fluorine-based glass gain fiber preform with high-quality core-clad interface and stable core diameter;

2) The obtained fluorine-based glass gain fiber preform core-clad interface quality is high, the core layer diameter is stable, the core-clad concentricity is high, the preparation method is simple and automatic, and the preparation cycle is short. It is expected to be applied to the preparation of mid-infrared optical fiber preforms.

Description of drawings

1 is a schematic diagram of a preparation device for a core-clad glass optical fiber preform;

Fig. 2 is the optical microscope image of the cross-section of the glass optical fiber preform of embodiment 1;

Fig. 3 is the refractive index distribution of embodiment 1 glass optical fiber preform;

Fig. 4 is the optical microscope image of the cross-section of the glass optical fiber preform of Comparative Example 1;

Fig. 5 is the refractive index distribution of the glass optical fiber preform of Comparative Example 1.

Detailed ways

The following specific examples illustrate the present invention and help to further understand the present invention, but the specific details of the implementation cases are only to illustrate the present invention, and do not represent all technical solutions under the present invention, so it should not be interpreted as a comprehensive understanding of the present invention. The limitations of the technical solution, some insubstantial additions and changes that do not deviate from the concept of the present invention in the eyes of a skilled person, such as simple replacement or replacement of technical features with the same or similar technical effects, all belong to the protection scope of the present invention.

Fig. 1 is the schematic diagram of the preparation device of core-clad structure glass optical fiber preform, as shown in the figure, comprises core liquid container (1), cladding liquid container (2), cast positioning plate (3), glass liquid isolating tube (4 ), cladding glass fluid diversion plate (5), preform molding mold (6), molding mold holder (7), traction rod (8), annealing temperature control system (9) and traction mechanism (10);

The core liquid container (1) and the cladding liquid container (2) are provided with openings at the bottom, and connected with platinum drainage wires, glass liquid can be manually added and the opening size is controlled by the automation system to control the flow of glass liquid;

The casting positioning plate (3), the glass liquid isolation tube (4), and the cladding glass liquid drainage plate (5) are connected and fixed by screws, and the preform rod forming mold (6) is formed by splicing three curved columns with an arc angle of 120° The hollow cylindrical tube is placed in the forming mold holder (7), and the bottom surface is closely fitted, and is tightened and fixed on the outside of the forming mold holder (7) with three screws at an angle of 120°;

A screw connection structure is set under the forming mold holder (7), and it is connected with the drawing rod (8) through screw thread matching, and an annealing temperature control system (9) is installed on both sides of the drawing rod (8) to provide an appropriate temperature for forming Annealing procedures for preforms;

The lower part of the drawing rod (8) is connected with the drawing mechanism (10), and the drawing mechanism (10) provides the precise and adjustable pull-down speed for the preform molding mold (6) and the molding mold holder (7).

The core liquid container (1) and the cladding liquid container (2) are precious metals such as platinum and gold, and the drainage tube connected to the opening below them is precious metals such as platinum or gold or glassy carbon; the casting positioning plate (3) is stainless steel; glass The liquid isolation tube (4) and the cladding glass liquid drainage plate (5) are made of platinum, and the surface is mirror polished; the preform forming mold (6) and the forming mold holder (7) are stainless steel, and the internal surface is mirror polished Processing; the overall device is in an inert gas such as Ar, N2 protective atmosphere.

The method for preparing a high-quality core-clad interface fluorine-based gain optical fiber preform by using the above-mentioned preparation device for a glass optical fiber preform comprises the following steps:

Step 1. Weigh the raw materials for cladding melting and core layer melting respectively in a glove box under a nitrogen protective atmosphere, grind them into powder, and melt them in an inert protective atmosphere or a fluoride atmosphere such as NF ₃ , SF The clarified rare earth ion-doped fluorine-based glass and pure fluorine-based glass respectively obtained in ₆ are transferred to the core liquid container (1) and the cladding liquid container (2) by automatic or manual addition;

Step 2. Raise the temperature of the annealing temperature control system (9) to 180°C to 220°C, preheat the preform molding mold (6) and the molding mold holder (7), and pass through the traction mechanism (10) when the temperature is stable Raise the preform molding die (6) and the molding die holder (7), and make the bottom of the glass liquid isolation tube (4) closely fit the upper part of the molding die holder (7);

Step 3. Make the high-temperature and low-viscosity glass liquid in the cladding liquid container (2) flow into the preform forming mold along the outer surface of the cladding glass liquid diversion plate (5) and the glass liquid isolation tube (4) through automatic control or manual control In (6), gradually cool at the bottom of the preform rod molding die (6);

Step 4. After 10 to 20 seconds after the preform cladding glass liquid starts feeding, the high-temperature and low-viscosity glass liquid in the core liquid container (1) is moved along the glass liquid isolation tube (4) through automatic control or manual control. The inner surface flows into the preform molding mold (6), but is temporarily isolated from the cladding glass liquid by the glass liquid isolation tube (4). At this time, the temperature of the core layer is higher and the viscosity is lower, and the temperature of the cladding layer is lower and the viscosity is lower. larger cases;

Step 5. Along with the further cooling of the molten glass, the cladding glass has been cooled and solidified, while the core glass is in a state of slightly higher temperature, higher viscosity and about to solidify. At this time, the preform molding mold (6) is pulled down by the traction mechanism (10) ) and forming mold holder (7), and ensure that the bottom of the glass liquid isolating tube (4) is lower than the solid-liquid interface of the cladding glass. The opening at the bottom of the tube (4) flows into the center of the cladding glass and is slowly spread and filled to form a prefabricated rod core structure;

Step 6. According to the position of the solid-liquid interface of the cladding glass, the addition rate and the pull-down rate of the cladding glass liquid and the core glass liquid are adjusted at any time, so that the preform is gradually formed;

Step 7. When step 2 is completed, the temperature of the annealing temperature control system (9) is raised and maintained at 220°C to 240°C. After step 6 is completed, the preform forming mold (6), forming mold holder (7) and forming After the prefabricated rod is kept warm in the annealing temperature control system (9) for 150 to 200 minutes, the annealing temperature control system (9) is turned off and gradually cooled to room temperature to obtain a finished product.

Example 1

The preparation device for preparing the core-clad structure glass optical fiber preform is shown in Figure 1. The raw materials used for cladding melting and core layer melting were weighed in a glove box under nitrogen protection atmosphere, and the raw materials for cladding melting and core layer melting were weighed respectively, and then ground into powders and placed on platinum respectively. The liquid container is melted to obtain clear and transparent glass liquid, which is transferred to the core liquid container and the cladding liquid container respectively. Set the annealing temperature control system according to the temperature of 1# in Table 1. After the temperature of the preform molding mold and the molding mold holder is stable, control the traction mechanism to raise the molding mold holder and the preform molding mold until the upper part of the molding mold holder is in contact with the glass. The lower end of the liquid isolation tube is in close contact, and the temperature of the annealing temperature control system is changed according to the holding temperature of the annealing temperature control system of 1# in Table 1. Turn on the switch below the cladding liquid container to make the cladding glass continuously and slowly flow into the forming mold along the outside of the glass liquid isolation tube, and turn on the switch below the core liquid container according to the time difference of 1# in Table 1 to make the core glass The liquid continues to slowly flow into the glass liquid isolating tube along the inside of the glass liquid isolating tube. After the lower part of the cladding glass begins to solidify, open the traction mechanism to pull down the preform molding mold and the molding mold holder, and ensure that the bottom of the glass liquid isolation tube is not higher than the solid-liquid interface of the cladding glass, so that the high-viscosity core glass passes through the glass The opening at the bottom of the liquid isolation tube flows into the center of the cladding glass and is slowly spread and filled to form a prefabricated rod core structure. A fluorine-based glass gain optical fiber preform with high core-clad interface quality is obtained after the down-drawing is completed. After the holding time is over, turn off the annealing temperature control system and cool down to room temperature naturally to fully remove the internal stress of the glass. Finally, a complete fluorine-based glass gain fiber preform with a high-quality core-clad interface is obtained.

The tests on the glass optical fiber preform are as follows:

1. Cut the glass optical fiber preform along the end face and place it under an optical microscope. As shown in Figure 2, it can be observed that the core layer is completely circular, the core layer is located in the center of the cladding layer, and the diameter of the core layer at the top and bottom of the preform rod is similar;

2. Test the refractive index of the glass optical fiber preform, as shown in Figure 3, the refractive index presents an obvious step distribution, indicating that the core layer has a very low degree of erosion of the cladding;

Comparative example 1

The raw materials for cladding melting and core melting were weighed in a glove box under a nitrogen protection atmosphere, ground into powders, and then melted in platinum crucibles to obtain clear and transparent glass liquids. Place the preform mold with the same structure as the preform molding mold in Example 1 on a preheating plate heated to 180°C. After the temperature stabilizes, slowly pour the cladding glass into the preform mold, wait for 15 seconds, and pour out the center For the unsolidified cladding glass liquid, slowly pour the core glass liquid into the preform mold. After the glass is fully cooled, the formed optical fiber preform sample is transferred to a muffle furnace that has been heated to 220°C, and after 170 minutes of heat preservation, the muffle furnace is closed and naturally cooled to room temperature.

The test results of the glass optical fiber preform are as follows:

1. Cracks occur in the preform, and the relatively complete part is cut along the end face, and placed under an optical microscope. As shown in Figure 4, the core layer is deformed, there is a certain degree of eccentricity, and there are a large number of bubbles at the interface;

2. Test the refractive index of the complete part of the glass optical fiber preform. As shown in Figure 5, the cladding thickness is different, the core layer is eccentric, and the refractive index step decreases at the interface, indicating that there is a certain erosion.

Table 1:

Claims (10)

1. A preparation device for a fluorine-based glass optical fiber preform, comprising a core liquid container for holding the core glass liquid, a cladding liquid container for holding the cladding glass liquid, a preform forming mold and a forming mold The fixer is characterized in that it also includes a glass liquid isolation tube; The preform forming mold is a hollow cylindrical tube, placed in the forming mold holder, and a traction mechanism is arranged under the forming mold holder to drive the forming mold holder to move up and down; The glass liquid isolating tube is placed in the preform forming mold, so that the core glass liquid and the cladding glass are respectively flowed into the preform forming mold along the inner wall and the outer wall of the glass liquid isolating tube, and the preform is formed In the mould, the bottom of the molten glass isolating tube is closely attached to the upper part of the mold holder, so that the cladding glass is isolated from the core glass, and the cladding glass is cooled faster than the core glass. When the cladding glass When the liquid is solidified into glass, the core glass liquid is in a slightly higher temperature, higher viscosity, and still liquid state. At this time, the forming mold holder is pulled down by the traction mechanism, and the bottom of the glass liquid isolation tube is always is lower than the solid-liquid interface of the cladding glass, so that the core glass liquid is slowly spread and solidified in the preform molding mold to form a fluorine-based glass optical fiber preform with a core-clad structure. 2. The preparation device of fluorine-based glass optical fiber preform according to claim 1, further comprising an annealing temperature control system for preheating the preform forming mold and providing temperature control for glass cooling , to prevent the glass from cooling too fast to cause bursting or the core layer to solidify in advance, and to provide an annealing environment for the formed glass preform. 3. The preparation device of fluorine-based glass optical fiber preform according to claim 1, characterized in that, the preform forming mold is a hollow cylindrical tube formed by splicing three arc-shaped columns with an arc of 120°. The outside of the mold holder is tightened and fixed by three screws with an included angle of 120°. 4. The preparation device for fluorine-based glass optical fiber preform according to claim 1, characterized in that, the lower part of the molding die holder is connected to the traction mechanism through screws. 5. The preparation device of fluorine-based glass optical fiber preform according to claim 1, characterized in that, the bottoms of the core liquid container and the cladding liquid container are provided with openings, and are connected with drainage wires, and the glass liquid can be added manually And the opening size is controlled by the automation system to control the flow of glass liquid. 6. The preparation device of fluorine-based glass optical fiber preform according to claim 5, characterized in that the core liquid container and the cladding liquid container are precious metals such as platinum and gold, and the drainage wire connected to the opening below is Platinum, gold and other precious metals or glassy carbon. 7. The preparation device for fluorine-based glass optical fiber preform according to claim 1, further comprising a casting positioning plate for positioning the glass liquid isolation tube, so that the glass liquid isolation tube is stably located in the The center of the preform rod forming mold ensures the detachability and replaceability of the glass liquid isolation tube. 8. The device for preparing a fluorine-based glass optical fiber preform according to claim 7, wherein the casting positioning plate is made of stainless steel. 9 . The device for preparing a fluorine-based glass optical fiber preform according to claim 1 , wherein the glass liquid isolation tube is made of platinum, and its surface is mirror-polished. 10. The method for preparing a fluorine-based glass optical fiber preform using the device for preparing a glass optical fiber preform described in any one of claims 1-9, wherein the method comprises the following steps: Step 1. Continuously casting cladding and core layer glass liquid into the preform molding mold; Step 2. Pull down the forming mold holder through the traction mechanism, and ensure that the bottom of the glass liquid isolation tube is always lower than the solid-liquid interface of the cladding glass, so that the core glass liquid is slowly spread in the preform forming mold to form core structure; Step 3. Annealing is performed by an annealing temperature control system after the preform with a core-clad structure is cast.

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