CN105060700B - Soft glass preform producing device and method - Google Patents

Abstract

A device and method for making a soft glass optical fiber preform based on double-crucible laminar flow leakage injection, the device includes a coaxial inner crucible and an outer crucible, the outer crucible is longer than the inner crucible, so that it can be completely sealed after fusing Surrounding the inner crucible, a stirring device is arranged in the inner crucible and the outer crucible respectively, and the lower part of the inner crucible has an outlet connected with the mold, and the mold has a built-in piston and its electric drive mechanism. The inner crucible and outer crucible are placed in a high-temperature furnace, the mold is placed in a heating body, and the mold and electric drive mechanism are placed on a lifting platform; the inner crucible, outer crucible, stirring device, high-temperature furnace , the heating element and the lifting platform are respectively installed on the tower. In the present invention, the rate of leakage is determined by the downward movement speed of the piston, and the Reynolds number of the process of leakage can be controlled by controlling the viscosity of the glass liquid and the rate of leakage, so as to ensure that the process of leakage is laminar flow.

Description

Device and method for making soft glass optical fiber preform

technical field

The invention relates to a soft glass optical fiber, also known as a multi-component glass optical fiber manufacturing technology, in particular to a soft glass optical fiber preform manufacturing device and method based on double-crucible laminar flow leakage injection.

Background technique

Soft glass fiber refers to non-quartz-based multi-component glass fiber, which has some unique optical and spectroscopic properties. Such as high rare earth solubility, wide gain spectrum, high nonlinearity, etc. It can be widely used in single-frequency lasers, ultrashort pulse lasers and Raman lasers. Some soft glass fibers are transparent in the mid-infrared and can be widely used in fiber laser devices in the mid-infrared band. This is an important application that silica fiber cannot replace at all. Mid-infrared laser sources have important applications in the fields of national defense, biomedicine, and cutting-edge scientific research.

So far, soft glass fibers have had high losses. High loss is a major factor restricting the wide application of soft glass optical fiber. The loss of the optical fiber mainly depends on the quality of the preform. Due to the complex composition and the lack of corresponding gaseous compounds, soft glass optical fiber preforms cannot be vapor-phase deposited like silica optical fiber preforms. Commonly used methods include tube-rod method and suction injection method.

The tube-and-rod method is the most commonly used preform production method. Its main feature is that the core rod and cladding glass tube are made separately, and the tube and rod are put together to form a prefabricated rod. There are insurmountable defects in the tube rod method. When machining tubes or rods, the surface of the tube and rod is easily polluted by polishing materials and impurity particles in the environment. When drawing optical fiber, the inner surface of the tube and the surface of the core rod are actually exposed to the environment and are easily contaminated by environmental impurities. Therefore, the tube rod method has very strict requirements on the production environment. In addition, due to the existence of the surface energy of the material, the glass is easy to crystallize on the surface when it is softened, so the inner surface of the tube and the surface of the mandrel are also easy to crystallize when heated and softened. For some soft glasses, this kind of crystallization will be more serious, resulting in a large loss of optical fiber.

When the preform is made by the suction injection method. The mold is placed on the base plate, both the base plate and the mold have been preheated. The molten cladding glass is poured into the mold, and then the core glass is poured on the cladding glass. Lift the mold upwards quickly so that a small amount of cladding glass fluid leaks from the bottom of the mold. Since the temperature of the interface between the glass liquid and the mold is in contact with the mold, the temperature is low and the viscosity is high, and the temperature at the center is high and the viscosity is low. The process of the cladding glass liquid flowing down due to gravity mainly occurs at the center of the liquid column, so a core-clad structure can be formed. .

The biggest advantage of the suction injection method is that it no longer needs to process the sleeve and core rod like the tube-rod method, so there is no problem of increased core-clad interface loss caused by the tube-rod method. The suction injection method can obtain excellent core cladding interface quality. But the disadvantage of this method is also very obvious. First of all, it is difficult to accurately grasp the timing and lifting height of the mold, which is difficult, poor in stability and consistency; secondly, the core material for suction injection often presents a tapered shape, and it is difficult to obtain a preform with a constant core diameter; The pouring method adopted by the method determines that it is difficult to produce high-quality glass rods with excellent optical uniformity.

To sum up, there is currently no suitable preform production equipment and technology that can produce soft glass optical fiber preforms with a closed core-cladding interface, constant longitudinal dimensions, and good optical uniformity.

Contents of the invention

The invention is a new optical fiber preform production equipment and its application technology. The invention is proposed in order to solve the problems existing in the current optical fiber preform production technology. This equipment adopts double-crucible laminar flow leakage injection method to make preform rods. The rod-making technology based on this equipment can solve the technical problems that are difficult to overcome in the current tube-rod method and suction injection method.

Technical solution of the present invention is as follows:

A soft glass optical fiber preform production device based on double-crucible laminar flow leak injection, which is characterized in that it includes a coaxial inner crucible and an outer crucible, the outer crucible is longer than the inner crucible, so that it can be completely sealed after fusing Surrounding the inner crucible, a stirring device is arranged in the inner crucible and the outer crucible respectively, and the lower part of the inner crucible has an outlet connected with the mold, and the mold has a built-in piston and its electric drive mechanism. The inner crucible and outer crucible are placed in a high-temperature furnace, the mold is placed in a heating body, and the mold and electric drive mechanism are placed on a lifting platform; the inner crucible, outer crucible, stirring device, high-temperature furnace , the heating element and the lifting platform are respectively installed on the tower.

Both the inner crucible and the outer crucible are made of platinum, the volume of the outer crucible is 2.5L, the diameter of the lower outlet is 3cm, the volume of the inner crucible is 0.8L, and the diameter of the lower outlet is 1cm.

The mold is made of heat-resistant stainless steel and is three-lobed, with a length of 2.5m, an inner diameter of 3cm, and an outer diameter of 5cm.

The furnace body of the high-temperature furnace is made of alumina or magnesia, the heating element is made of silicon-molybdenum rods, the maximum temperature is 1500 degrees, and the temperature control accuracy is ±0.5 degrees.

The heating element is cylindrical and surrounds the mould. The heat preservation furnace body of the heating element is divided into two parts to facilitate the removal of the mold. The heating element of the heating element is made of resistance wire, and the heat preservation material is refractory brick.

The piston can seal the outlet of the crucible and move up and down in the mold with a stroke of 2m.

The gap is less than 0.3mm.

The stroke of the lifting platform is 0.3m, and the maximum load-bearing capacity is 200kg.

The method for making a soft glass optical fiber preform using the soft glass optical fiber preform manufacturing device is characterized in that the method comprises the following steps:

①Heating up the high-temperature furnace, melting the core glass frit and cladding glass frit in the inner and outer crucibles respectively;

②Preheat the heating element, and after the core and cladding glass melt are melted, the piston is moved down, and the glass melt is leaked into the mold to form a preform;

③ Cool the heating element to room temperature according to the annealing temperature process, lower the lifting platform, take out the mold, and obtain a preform.

The speed at which the piston moves down in the step ② determines the rate of leakage. By controlling the viscosity of the glass liquid and the rate of leakage, the Reynolds number of the process of leakage is controlled to ensure that the process of leakage is laminar.

The manufacturing equipment of the optical fiber preform described in the present invention is used in the process of raising the temperature of a high-temperature furnace, and melting the cladding and core glass material in two crucibles respectively. Preheat the heating element, and after the core and the cladding glass melt are melted, the piston moves down to leak the glass melt into the mold to form a preform. The speed at which the plunger moves down determines the leak rate. By controlling the viscosity of the glass liquid and the leakage rate, the Reynolds number of the leakage process can be controlled to ensure that the leakage process is laminar flow. According to the annealing temperature process, the heating body is cooled to room temperature, the lifting base is lowered, the mold is taken out, and a preform is obtained. The surface of the preform can be machined as required, such as grinding, polishing, etc. (since the machined outer surface is far away from the interface between the core and the cladding, the loss of the optical fiber will not be increased).

Technical principle of the present invention:

When the fluid flows, if the trajectory of the fluid particles is a regular smooth curve (the simplest case is a straight line), this flow is called laminar flow. A flow without this property is called turbulent flow. Turbulent flow is the irregular motion of fluid, and various quantities in the flow field change chaotically with time and space coordinates.

Whether the fluid is meant to be in laminar flow or turbulent flow can be judged according to the Reynolds number (Reynolds number, abbreviated as Re):

Re=ρvd/μ (1)

(1) In the formula, ρ is the fluid density, v is the flow velocity, d is the diameter of the tube where the fluid is located, and μ is the fluid viscosity.

Reynolds number is a dimensionless number to distinguish the flow state of viscous fluid. When the Reynolds number is small, the influence of the viscous force on the flow field is greater than that of the inertial force. If a small random disturbance occurs during the flow process, the disturbance will gradually attenuate due to the viscous force as time goes on. Therefore, the fluid flow is stable and is a layer Conversely, if the Reynolds number is large, the inertial force has a greater influence on the flow field than the viscous force, the fluid flow is unstable, and small changes in the flow velocity are easy to develop and strengthen, forming a chaotic and irregular turbulent flow field. In pipe flow, the flow with Reynolds number less than 2300 is laminar flow, the flow with Reynolds number between 2300 and 4000 is a transition state, and the flow with Reynolds number greater than 4000 is turbulent flow.

If the viscosity of the glass liquid is controlled by the temperature, and the speed of the piston moving down is controlled, the Reynolds number can be controlled in a lower range, so as to obtain a good laminar flow effect, thus ensuring a good core-clad interface. At the same time, the good laminar flow effect can also make the uniformity of the core layer and the cladding glass liquid close to the homogenized state when it is in the crucible, so that the finally obtained preform has good optical uniformity.

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

1. Closed core-cladding interface: The core-cladding interface is not separated like the tube-and-rod method, so that the pollution of environmental particles and the surface devitrification effect can be avoided.

2. Excellent optical uniformity: The formation of the rod body is a speed-controllable leakage process, rather than pouring like the suction method, so the optical uniformity of the preform can be guaranteed.

3. Good longitudinal core diameter consistency: preforms with consistent core diameters along the length of the preform can be produced, instead of tapered cores like the suction injection method.

Description of drawings

Figure 1 The overall equipment diagram of the double crucible laminar flow leakage injection equipment

Fig. 2 Schematic diagram of partial section of double crucible and stirrer

Figure 3 Schematic diagram of the process of making soft glass preform by double crucible laminar flow leak injection method

Fig. 4 demoulding after annealing to obtain a preform

detailed description

The present invention will be further described below in conjunction with the accompanying drawings, but the protection scope of the present invention should not be limited thereby.

As shown in Figure 1-2, a soft glass optical fiber preform manufacturing device based on double-crucible laminar flow leak injection includes a coaxial inner crucible 1 and an outer crucible 2, the outer crucible is longer than the inner crucible, In order to completely surround the inner crucible after fusing, a stirring device 3 is respectively arranged in the inner crucible 1 and the outer crucible 2, and an outlet communicating with the mold 4 is provided at the bottom of the inner crucible 1. The mold 4 is built with a piston and its electric drive mechanism 5, the inner crucible 1 and the outer crucible 2 are placed in the high temperature furnace 6, the mold 4 is placed in the heating body 7, the mold 4 and the electric drive mechanism 5 is placed on the lifting platform 8; the inner crucible, outer crucible, stirring device, high temperature furnace, heating element and lifting platform are installed on the tower 9 respectively. Both the inner crucible and the outer crucible are made of platinum, the volume of the outer crucible is 2.5L, the diameter of the lower outlet is 3cm, the volume of the inner crucible is 0.8L, and the diameter of the lower outlet is 1cm. The mold is made of heat-resistant stainless steel and is three-lobed, with a length of 2.5m, an inner diameter of 3cm, and an outer diameter of 5cm. The furnace body of the high-temperature furnace is made of alumina or magnesia, the heating element is made of silicon-molybdenum rods, the maximum temperature is 1500 degrees, and the temperature control accuracy is ±0.5 degrees. The heating element is cylindrical and surrounds the mould. The heat preservation furnace body of the heating element is divided into two parts to facilitate the removal of the mold. The heating element of the heating element is made of resistance wire, and the heat preservation material is refractory brick. The piston can seal the crucible outlet, and move up and down in the mold with a stroke of 2m, and the assembly gap with the mold is less than 0.3mm. The stroke of the lifting platform is 0.3m, and the maximum load-bearing capacity is 200kg.

The method for making a soft glass optical fiber preform using the soft glass optical fiber preform manufacturing device comprises the following steps:

① heating up the high-temperature furnace, melting the core glass frit 10 and the cladding glass frit 11 in inner and outer crucibles respectively;

② Preheating the heating element, after the core and cladding glass melt is melted, the piston is moved down, and the glass melt is leaked into the mold to form a preform 12;

③ Cool the heating element to room temperature according to the annealing temperature process, lower the lifting platform, take out the mold, and obtain a preform.

The speed at which the piston moves down in the step ② determines the rate of leakage. By controlling the viscosity of the glass liquid and the rate of leakage, the Reynolds number of the process of leakage is controlled to ensure that the process of leakage is laminar.

Take the tellurite glass optical fiber preform as an example: when making the preform, first raise the piston to the bottom of the crucible and seal the crucible outlet. Operate the control button of the lifting table to lower the liftable base to the lowest level, and install the mold on the base. The base has a sunken interface for mold embedding. Lift the base up to connect with the outlet at the bottom of the crucible. Close the mold heating element, and raise the temperature to 500 degrees within 30 minutes and keep it. Put 3 kg of core glass frit and 10 kg of cladding glass frit in the inner and outer crucibles, and heat up to 800 degrees within one hour to melt the glass. During the melting process, ventilation protection and stirring homogenization. After about 1 hour, operate the piston control button to move the piston down to the bottom at a speed of 0.1m/s to complete the leakage injection process. Rapidly lower the temperature of the heating element to the annealing temperature of 320 degrees. Anneal for 3 hours and cool down to room temperature at 30°C/hour. Then operate the control button of the liftable base to lower the liftable base to the minimum, remove the mold containing the preform, and demould to obtain the preform. The preform is about 2m long, with a core diameter of 1cm and an outer diameter of 3cm. The prefabricated rod can be cut into 30-50cm long rods according to the needs.

Claims (9)

1. a kind of soft glass preform producing device based on double crucible laminar flows leakage note, it is characterised in that including coaxial Interior crucible (1) and outer crucible (2), the outer crucible are longer than the interior crucible, can surround the interior earthenware completely after sealing Crucible, agitating device (3) is respectively arranged with interior crucible (1) and outer crucible (2), is had in the bottom of described interior crucible (1) The outlet being connected with mould (4), described mould (4) are built-in with piston and its electric drive mechanism (5), described interior crucible (1) it is placed on outer crucible (2) in high temperature furnace (6), described mould (4) is placed in heater (7), described mould (4) And electric drive mechanism (5) is placed on hoistable platform (8)；Described interior crucible, outer crucible, agitating device, high temperature furnace, heater It is separately mounted to hoistable platform on pylon (9).

2. soft glass preform producing device according to claim 1, it is characterised in that described interior crucible and outer Crucible is platinum material, and the volume of outer crucible is 2.5L, lower end outlet diameter 3cm, the volume 0.8L of interior crucible, and lower end exports Diameter 1cm.

3. soft glass preform producing device according to claim 1, it is characterised in that described mould is heat-resisting Stainless steel material, in three-clove style, length 2.5m, internal diameter 3cm, external diameter 5cm.

4. soft glass preform producing device according to claim 1, it is characterised in that the stove of described high temperature furnace Body uses aluminum oxide or magnesium oxide material, and heat generating component uses Si-Mo rod, and maximum temperature is 1500 degree, temperature-controlled precision ± 0.5 degree.

5. soft glass preform producing device according to claim 1, it is characterised in that described heater is circle Column, mould is surrounded, the thermal insulation furnace body of heater is split up into two parts, and convenient to take out mould, the heat generating component of heater is adopted With resistance silk material matter, insulation material is refractory brick, and maximum temperature is 800 degree.

6. soft glass preform producing device according to claim 1, it is characterised in that described piston can be by outside Crucible outlet seals, and moves up and down in a mold, stroke 2m, is less than 0.3mm with mould fit-up gap.

7. soft glass preform producing device according to claim 1, it is characterised in that described hoistable platform Stroke is 0.3m, maximum capacity 200kg.

8. the method for soft glass preform is made using the soft glass preform producing device described in claim 1, Characterized in that, this method comprises the following steps：

1. heat up high temperature furnace, by core glass material (10) and cladding glass material (11) respectively including, found in outer crucible；

2. preheating heater, after core and cladding glass liquid melt, move down piston, by glass metal leakage note to shape in mould Into prefabricated rods (12)；

3. heater is cooled into room temperature according to annealing temperature flow, hoistable platform is fallen, mould is taken out, obtains prefabricated rods.

9. it is according to claim 8 make soft glass preform method, it is characterised in that described step 2. in Piston moves down speed and determines Lou note speed, by controlling the viscosity and leakage note speed of glass metal, the Reynolds of control leakage note process Number, to ensure to leak note process as laminar flow.