Active optical fiber preform, preparation method therefor and use thereof

Abstract

The present invention provides an optical fiber preform, and a preparation method therefor and a use thereof. The preparation method comprises the following steps: immersing a silicon dioxide loose body into a solution containing a rare earth chloride to obtain a first intermediate; placing the first intermediate in an MCVD lathe, introducing oxygen and helium simultaneously for a pre-oxidation treatment, and continuing introducing oxygen and helium for an oxidation treatment to obtain a second intermediate, wherein the introduction flow rate of oxygen for the pre-oxidation treatment is V1, the introduction flow rate of oxygen for the oxidation treatment is V2, and V1 and V2 satisfy V1:V2 = 1:(5-10); the temperature for the oxidation treatment is greater than the temperature for the pre-oxidation treatment; and the pressure for the pre-oxidation treatment is greater than the pressure for the oxidation treatment; and sequentially subjecting the second intermediate to a sintering treatment and a melting shrinkage treatment to obtain the optical fiber preform. Sufficient oxidation of a rare earth element and maximized removal of hydroxyl can be achieved, facilitating the reduction of the optical fiber loss. The preparation method has an excellent environmentally friendly performance and safety and is suitable for mass production.

Description

Active optical fiber preform and its preparation method and application Technical Field

[0001] The present invention belongs to the technical field of optical fibers, and in particular relates to an optical fiber preform rod, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of laser materials and laser technology, researchers have discovered that by doping active optical fibers with rare earth elements to form a doping layer of a certain concentration, the optical fiber can have significant absorption and emission characteristics for light of a certain wavelength, achieving better spectral characteristics and optical efficiency. This rare earth-doped active optical fiber is currently widely used in optical fiber sensors. As an important gain medium in fiber lasers, the performance of rare earth-doped active optical fibers directly determines the performance of the laser. Preforms are the basis for the preparation of optical fibers, and the performance of preforms directly affects the performance of optical fibers. Therefore, how to produce optical fiber preforms with excellent performance is a research focus in this field.

[0003] Currently, the methods for doping active optical fibers with rare earth elements include gas phase method and liquid phase method. The gas phase method includes rare earth chloride vapor deposition and rare earth chelate vapor deposition; the liquid phase method includes in-tube rare earth solution immersion method and out-tube rare earth solution immersion method. Among them, the gas phase method relies on large-scale deposition equipment, and the doping concentration and uniformity are difficult to control, which is not conducive to improving the performance of the optical fiber; the liquid phase method is to first use an MCVD lathe to deposit an optical fiber preform in a deposition tube, and then immerse the optical fiber preform in a rare earth solution. After oxidation, drying, and sintering, a rare earth-doped active optical fiber preform is obtained. Among them, the rare earth solution immersion method in the tube refers to immersing the rare earth solution in the deposition tube. This process requires the use of chlorine drying to remove the hydroxyl groups brought by the solution immersion, thereby achieving low loss of the preform. However, long-term introduction of chlorine will cause pipeline corrosion and damage to the lathe; the rare earth solution immersion method outside the tube refers to immersing the rare earth solution outside the deposition tube. This process does not require the introduction of chlorine in the subsequent drying step, but without the use of chlorine, the hydroxyl groups in the preform cannot be completely removed, which ultimately leads to increased loss of the prepared optical fiber. High-loss optical fiber used in fiber lasers will further cause a decrease in laser power.

[0004] Therefore, how to provide a method for preparing an optical fiber preform that is environmentally friendly, safe, and can effectively reduce optical fiber loss is a technical problem that needs to be urgently solved in this field. Summary of the Invention

[0005] The present invention provides a method for preparing an optical fiber preform rod, which utilizes pre-oxidation treatment and oxidation treatment to achieve gradual oxidation and limits the oxygen inlet flow rate, thereby achieving full oxidation of rare earth elements and maximal removal of hydroxyl groups, thereby helping to reduce optical fiber loss. In addition, the preparation method has excellent environmental protection and safety and is suitable for mass production.

[0006] The present invention provides an optical fiber preform rod. As it is manufactured by the above-mentioned manufacturing method, the optical fiber manufactured by using the optical fiber preform rod has the advantage of low loss.

[0007] The present invention also provides an optical fiber, which has the advantage of low loss due to being prepared by using the optical fiber preform rod.

[0008] A first aspect of the present invention provides a method for preparing an optical fiber preform, comprising the following steps:

[0009] Immersing the silicon dioxide loose body in a solution containing rare earth chloride to obtain a first intermediate;

[0010] The first intermediate is placed in an MCVD lathe, and oxygen and helium are introduced simultaneously to perform a pre-oxidation treatment, and oxygen and helium are continued to be introduced to perform an oxidation treatment to obtain a second intermediate; wherein the oxygen introduction flow rate in the pre-oxidation treatment is V1, and the oxygen introduction flow rate in the oxidation treatment is V2, satisfying V1:V2=1:(5-10); the temperature of the oxidation treatment is greater than the temperature of the pre-oxidation treatment; and the pressure of the pre-oxidation treatment is greater than the pressure of the oxidation treatment;

[0011] The second intermediate is subjected to sintering treatment and melting treatment in sequence to obtain an optical fiber preform.

[0012] In the preparation method as described above, the flow rate of helium in the pre-oxidation treatment is V3, and the flow rate of helium in the oxidation treatment is V4, satisfying V3:V4=(2-3):1.

[0013] The preparation method as described above, wherein, in the pre-oxidation treatment, the flow rate of oxygen is 50-200 sccm, and the flow rate of helium is 500-2000 sccm; and / or,

[0014] During the oxidation treatment, the flow rate of oxygen gas is 500-1000 sccm, and the flow rate of helium gas is 500-1000 sccm.

[0015] The preparation method as described above, wherein the pre-oxidation treatment temperature is 200-500° C., the pressure is 0.9-1.5 atmospheres, and the time is 1.8-3.5 hours; and / or,

[0016] The oxidation treatment is performed at a temperature of 400 to 800° C., a pressure of 0.6 to 0.9 atmospheres, and a time of 1.5 to 2 hours.

[0017] The preparation method as described above, wherein the MCVD lathe comprises at least a flame torch, a first clamping unit and a second clamping unit;

[0018] The first clamping unit and the second clamping unit rotate along their own axes, and the first clamping unit and the second clamping unit are used to cooperate with each other to clamp the first intermediate body;

[0019] The flame torch reciprocates along the axial direction of the first intermediate body, and the spraying direction of the flame torch is toward the first intermediate body;

[0020] During the pre-oxidation treatment, the flame burner is started to make a first reciprocating movement along the axial direction of the first intermediate body; the first clamping unit and the second clamping unit drive the first intermediate body to make a first rotation;

[0021] During the oxidation treatment, the flame burner is started to make a second reciprocating movement along the axial direction of the first intermediate body; the first clamping unit and the second clamping unit drive the first intermediate body to make a second rotation;

[0022] The rotation speed of the first rotation is 10 to 30 rpm; the rotation speed of the second rotation is 10 to 30 rpm;

[0023] The speed of the first reciprocating movement is 50-100 mm / min; the speed of the second reciprocating movement is 50-100 mm / min.

[0024] The preparation method as described above, wherein the solution containing rare earth chloride contains at least one element of Y, Ce, Nd, Yd, Tm, and Er; and / or,

[0025] The solvent in the solution containing rare earth chloride includes at least one of methanol, ethanol and ethylene glycol.

[0026] In the preparation method as described above, the solution containing rare earth chloride further contains at least one element selected from Al and P.

[0027] The preparation method as described above, wherein the sintering treatment and the melting treatment are both carried out in a mixed atmosphere containing oxygen and helium;

[0028] In the mixed atmosphere, the volume ratio of oxygen to helium is 1:(1-2)

[0029] A second aspect of the present invention provides an optical fiber preform, which is produced by the production method described in the first aspect.

[0030] A third aspect of the present invention provides an optical fiber, which is prepared using the optical fiber preform described in the second aspect.

[0031] The implementation of the present invention has at least the following beneficial effects:

[0032] The method for preparing an optical fiber preform provided by the present invention utilizes a liquid phase method to dope a silica soot body with rare earth elements, and then performs a pre-oxidation treatment and an oxidation treatment to achieve gradual oxidation, thereby effectively removing hydroxyl groups on the silica soot body. In addition, by limiting the oxygen flow rate during the pre-oxidation treatment and the oxidation treatment, it is possible to fully oxidize the rare earth elements and remove hydroxyl groups to the maximum extent, thereby helping to reduce optical fiber loss. Moreover, the preparation method can remove hydroxyl groups without using chlorine gas, has excellent environmental protection and safety, and is suitable for mass production.

[0033] The optical fiber preform provided by the present invention is manufactured by the above-mentioned manufacturing method, and the optical fiber manufactured by using the optical fiber preform has the advantage of low loss.

[0034] The present invention also provides an optical fiber, which is obtained by drawing the optical fiber preform rod, and has the advantage of low loss. DETAILED DESCRIPTION

[0035] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0036] A first aspect of the present invention provides a method for preparing an optical fiber preform, comprising the following steps: immersing a silica soot body in a solution containing a rare earth chloride to obtain a first intermediate; placing the rare earth-doped silica soot body in an MCVD lathe, and simultaneously introducing oxygen and helium to perform a pre-oxidation treatment, and continuing to introduce oxygen and helium to perform an oxidation treatment to obtain a second intermediate; wherein the oxygen flow rate during the pre-oxidation treatment is V1, and the oxygen flow rate during the oxidation treatment is V2, satisfying V1:V2=1:(5-10); the oxidation treatment temperature is greater than the pre-oxidation treatment temperature; the pre-oxidation treatment pressure is greater than the oxidation treatment pressure; and the second intermediate is sequentially sintered and melted to obtain an optical fiber preform.

[0037] The silica soot body of the present invention is formed by aggregation of nano-silica particles. The present invention does not limit the preparation method of the silica soot body. For example, the silica soot body can be prepared by chemical vapor deposition using a silicon-containing compound as a raw material. The specific preparation process may include the following steps: mounting a substrate tube on an MCVD lathe, polishing the substrate tube by passing SF6 into the substrate tube at high temperature, and then passing silicon tetrachloride gas into the substrate tube after the inner wall of the substrate tube is bright and free of impurities, and sequentially depositing an inner cladding layer and a core layer to obtain the silica soot body.

[0038] Among them, the substrate tube can be a conventional deposition tube in this field, and the MCVD lathe is a conventional device in this field for preparing optical fiber preform rods, which is mainly composed of a glass lathe, a feeding system, a temperature measurement and control system, a tube diameter measurement and control system, and a microcomputer control system.

[0039] In the present invention, a substrate tube is mounted on an MCVD lathe, and a silica soot body is deposited within the substrate tube. A solution containing a rare earth chloride is then directly injected into the substrate tube with the deposited silica soot body, allowing the silica soot body to be immersed in the rare earth chloride solution for 0.5 to 2 hours at a temperature of 30 to 45°C. Excess solution is then removed to obtain a first intermediate. The first intermediate is essentially a silica soot body doped with a rare earth element.

[0040] A solution containing rare earth chloride is injected into the substrate tube. After soaking, excess solution is removed. The substrate tube after the excess solution is removed can be directly installed in an MCVD lathe to perform pre-oxidation treatment and oxidation treatment.

[0041] In the present invention, when oxygen and helium are introduced simultaneously for pre-oxidation treatment and oxidation treatment, since the gas phase itself has good diffusivity and can fully contact with the first intermediate, and has a small molecular weight, oxygen can, on the one hand, oxidize the rare earth elements and promote the effective doping of rare earth elements, and on the other hand, can remove the hydroxyl groups on the surface, effectively reducing the negative impact of the hydroxyl groups on the optical properties of the optical fiber.

[0042] By implementing pre-oxidation and oxidation treatments and gradually increasing the oxygen content, it helps achieve full oxidation of rare earth elements and gradual oxidation of hydroxyl groups. In addition, by limiting the oxygen flow rate ratio between pre-oxidation and oxidation treatments, it helps to maximize the removal of hydroxyl groups.

[0043] The oxygen flow rate in the pre-oxidation treatment is V1, and the oxygen flow rate in the oxidation treatment is V2, satisfying V1:V2=1:(5~10), for example, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10 or a range consisting of any two of them.

[0044] In the present invention, the temperature of the oxidation treatment is higher than the temperature of the pre-oxidation treatment, and the pressure of the pre-oxidation treatment is higher than the pressure of the oxidation treatment, which is conducive to achieving gradual oxidation.

[0045] In the present invention, the sintering process essentially promotes the vitrification of the intermediate body, while the melting process essentially promotes the formation of a solid optical fiber preform from the hollow second intermediate body. Because both the pre-oxidation and oxidation processes are performed on an MCVD lathe, the sintering and melting processes can be performed directly on the MCVD lathe after these processes, which improves production efficiency.

[0046] The present invention can employ conventional methods for sintering and melting processes. For example, the second intermediate can be heated to a sintering temperature, sintered, and then heated again for melting. The optical fiber preform can then be cooled to obtain the optical fiber preform. During the sintering process, the heating process can be maintained at a constant heating rate, ensuring that the second intermediate is fully and evenly heated and then slowly undergoes the vitrification process, thereby ensuring that the optical fiber preform has good optical uniformity. After the sintering process, the temperature is again raised for melting. After the melting, the temperature is then cooled at a constant cooling rate. Slow cooling helps to improve internal stress defects in the optical fiber preform and enhance its uniformity.

[0047] The present invention does not limit the flow rate of helium, as long as oxygen and helium are introduced simultaneously. For example, in some embodiments, the flow rate of helium during the pre-oxidation treatment is V3, and the flow rate of helium during the oxidation treatment is V4, satisfying V3:V4 = (2-3):1, such as 2:1, 2.5:1, 3:1, or any combination thereof.

[0048] The present invention does not limit the specific flow rates of oxygen and helium, as long as the above-mentioned proportional relationship is satisfied. For example, in some embodiments, in the pre-oxidation treatment, the flow rate of oxygen is 50 to 200 sccm, for example, 50 sccm, 100 sccm, 150 sccm, 200 sccm, or a range consisting of any two thereof, and the flow rate of helium is 500 to 2000 sccm, for example, 500 sccm, 550 sccm, 1000 sccm, 1500 sccm, 2000 sccm, or a range consisting of any two thereof; and / or, in the oxidation treatment, the flow rate of oxygen is 500 to 1000 sccm, for example, 500 sccm, 550 sccm, 1000 sccm, or a range consisting of any two thereof, and the flow rate of helium is 500 to 1000 sccm, for example, 500 sccm, 550 sccm, 1000 sccm, or a range consisting of any two thereof.

[0049] The present invention does not limit the specific temperature and pressure of the pre-oxidation treatment and the oxidation treatment. For example, in some embodiments, the temperature of the pre-oxidation treatment is 200-500° C., such as 200° C., 250° C., 300° C., 350° C., 400° C., 450° C., 500° C., or a range consisting of any two thereof, and the pressure is 0.9-1.5 atmospheres, such as 0.9 atmosphere, 1 atmosphere, 1.2 atmospheres, 1.5 atmospheres, or a range consisting of any two thereof. The time is 1.8 to 3.5 hours; and / or, the temperature of the oxidation treatment is 400 to 800°C, for example, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, or a range consisting of any two thereof, and the pressure is 0.6 to 0.9 atmospheres, for example, 0.6 atmospheres, 0.7 atmospheres, 0.8 atmospheres, 0.9 atmospheres, or a range consisting of any two thereof, and the time is 1.5 to 2 hours. It should be noted that the selection of the above temperature and pressure needs to meet the following requirements: the oxidation treatment temperature is greater than the pre-oxidation treatment temperature, and the oxidation treatment pressure is less than the pre-oxidation treatment pressure.

[0050] In the present invention, the first intermediate body can be heated by a heating unit. By supplying temperature to the first intermediate body by the heating unit, the temperature conditions for the pre-oxidation treatment and the oxidation treatment can be ensured.

[0051] The present invention does not limit the specific type of MCVD lathe, which can be a conventional MCVD lathe in the field. For example, in some embodiments, the MCVD lathe includes at least a flame burner, a first clamping unit, and a second clamping unit; the first clamping unit and the second clamping unit rotate along their own axes, and the first clamping unit and the second clamping unit are used to cooperate with each other to clamp the first intermediate; the flame burner reciprocates along the axial direction of the first intermediate, and the spray direction of the flame burner is toward the first intermediate; during the pre-oxidation treatment process, the flame burner is started to make a first reciprocating movement along the axial direction of the first intermediate; the first clamping unit and the second clamping unit drive the first intermediate to make a first rotation; during the oxidation treatment process, the flame burner is started to make a second reciprocating movement along the axial direction of the first intermediate; the first clamping unit and the second clamping unit drive the first intermediate to make a second rotation.

[0052] The first intermediate body, the first clamping unit and the second clamping unit are coaxially extended. As the first clamping unit and the second clamping unit rotate along their own axes, the first intermediate body can rotate along its own axis.

[0053] The flame torch is used to spray flame onto the first intermediate body to bring the temperature of the first intermediate body to the temperature required for the pre-oxidation treatment and the oxidation treatment. During the pre-oxidation treatment and the oxidation treatment, the flame torch sprays toward the first intermediate body and reciprocates along the axial direction of the first intermediate body.

[0054] wherein, the rotation speed of the first rotation is 10 to 30 rpm, for example, 10 rpm, 15 rpm, 20 rpm, 25 rpm, 30 rpm or a range consisting of any two thereof; the rotation speed of the second rotation is 10 to 30 rpm, for example, 10 rpm, 15 rpm, 20 rpm, 25 rpm, 30 rpm or a range consisting of any two thereof; the speed of the first reciprocating movement is 50 to 100 mm / min, for example, 50 mm / min, 60 mm / min, 70 mm / min, 80 mm / min, 90 mm / min, 100 mm / min or a range consisting of any two thereof; the speed of the second reciprocating movement is 50 to 100 mm / min, for example, 50 mm / min, 60 mm / min, 70 mm / min, 80 mm / min, 90 mm / min, 100 mm / min or a range consisting of any two thereof, the number of the first reciprocating movement is 5 to 20 times, and the number of the second reciprocating movement is 5 to 20 times.

[0055] Among them, the first reciprocating movement and the second reciprocating movement both refer to the reciprocating movement of the flame torch along the axial direction of one end of the first intermediate body to the other end, and then from the other end to one end of the axial direction of the first intermediate body; the distance of the first reciprocating movement is twice the longitudinal length of the first intermediate body itself, and the first rotation and the second rotation both refer to the rotation of the first intermediate body along its own axis.

[0056] Taking the first reciprocating movement as an example, the flame torch moves from one end to the other end of the first intermediate body in the axial direction, and then from the other end to one end of the first intermediate body in the axial direction, which is one reciprocating movement.

[0057] In the present invention, the first clamping unit and the second clamping unit can adjust the rotation speed through the chuck.

[0058] During the pre-oxidation process, the H2 flow rate of the flame torch is 25 to 50 slm; during the oxidation process, the H2 flow rate of the flame torch is 35 to 55 slm, where slm represents liters per minute under standard conditions (0°C, 1 atm).

[0059] The present invention is not limited to the specific type of solution containing rare earth chloride, as long as it contains rare earth chloride. For example, in some embodiments, the solution containing rare earth chloride contains at least one element of Y, Ce, Nd, Yd, Tm, and Er; and / or, the solvent in the solution containing rare earth chloride includes at least one of methanol, ethanol, and ethylene glycol.

[0060] In a possible embodiment, the solution containing rare earth chloride further contains at least one element of Al and P.

[0061] The present invention does not limit the specific implementation methods of the sintering and melting treatments, and conventional sintering and melting treatment methods in the art can be used. In some embodiments, the sintering and melting treatments are both performed in a mixed atmosphere containing oxygen and helium; the volume ratio of oxygen to helium in the mixed atmosphere is 1:(1-2).

[0062] The second aspect of the present invention provides an optical fiber preform, which is produced by the production method provided in the first aspect. Due to the production method, the optical fiber produced by using the optical fiber preform has the advantage of low loss.

[0063] The third aspect of the present invention provides an optical fiber, which has the advantage of low loss due to being prepared using the optical fiber preform. The optical fiber of the present invention can be prepared by subjecting the optical fiber preform to conventional fiber drawing methods in the art.

[0064] The present invention is further described below by way of specific examples and comparative examples. Unless otherwise specified, the reagents, materials, and instruments used below are all conventional reagents, materials, and instruments, all of which are commercially available, and the reagents and materials involved can also be synthesized by conventional synthesis methods.

[0065] Example 1

[0066] (1) The substrate tube was mounted on an MCVD lathe, and SF6 was introduced into the substrate tube at a heating temperature of 1600°C for preheating and polishing. SiCl4 was introduced into the substrate tube at a heating temperature of 1400°C at a flow rate of 3 g / min to deposit a loose silica body in the substrate tube.

[0067] (2) introducing a methanol solution containing ytterbium chloride, aluminum chloride, and phosphoric acid into the substrate tube on which the silica loose body is deposited for 0.5 h, and removing excess solution to obtain a first intermediate;

[0068] (3) The substrate tube containing the first intermediate was reinstalled on the MCVD lathe, and oxygen and helium were introduced simultaneously for pre-oxidation treatment; during the pre-oxidation treatment, the oxygen flow rate was 50 sccm, the helium flow rate was 1000 sccm, the pressure in the substrate tube was 1.1 atmospheres, the reciprocating speed of the flame torch was 100 mm / min, the chuck speed was 30 rpm, the heating temperature was 300° C., and the pre-oxidation treatment time was 2 h;

[0069] (4) continuing to introduce oxygen and helium to carry out oxidation treatment to obtain a second intermediate; during the oxidation treatment, the oxygen flow rate is 500 sccm, the helium flow rate is 500 sccm, the pressure in the tube is 0.7 atmospheres, the reciprocating speed of the flame burner is 100 mm / min, the heating temperature is 400°C, and the oxidation treatment time is 1.5 h;

[0070] (5) The second intermediate is subjected to sintering and melting treatments, with the sintering temperature being 2000° C. and the melting temperature being 2150° C., to obtain a solid optical fiber preform.

[0071] Example 2

[0072] (1) The substrate tube was mounted on an MCVD lathe, and SF6 was introduced into the substrate tube at a heating temperature of 1700°C for preheating and polishing. SiCl4 was introduced into the substrate tube at a flow rate of 2.6 g / min at a heating temperature of 1500°C to deposit a loose silica body in the substrate tube.

[0073] (2) introducing an ethanol solution containing erbium chloride and aluminum chloride into the substrate tube on which the silica loose body is deposited for 1 hour, and removing excess solution to obtain a first intermediate;

[0074] (3) The substrate tube containing the first intermediate was reinstalled on the MCVD lathe, and oxygen and helium were introduced simultaneously for pre-oxidation treatment; during the pre-oxidation treatment, the oxygen flow rate was 100 sccm, the helium flow rate was 1500 sccm, the pressure in the substrate tube was 1.3 atmospheres, the reciprocating speed of the flame torch was 70 mm / min, the chuck speed was 15 rpm, the heating temperature was 500° C., and the pre-oxidation treatment time was 1.8 h;

[0075] (4) continuing to introduce oxygen and helium to carry out oxidation treatment to obtain a second intermediate; during the oxidation treatment, the oxygen flow rate is 700 sccm, the helium flow rate is 700 sccm, the pressure in the tube is 0.9 atmospheres, the reciprocating speed of the flame burner is 70 mm / min, the heating temperature is 700°C, and the oxidation treatment time is 2 h;

[0076] (5) The second intermediate is subjected to sintering and melting treatments, with the sintering temperature being 1950° C. and the melting temperature being 2200° C., to obtain a solid optical fiber preform.

[0077] Example 3

[0078] (1) The substrate tube was mounted on an MCVD lathe, and SF6 was introduced into the substrate tube at a heating temperature of 1800°C for preheating and polishing. SiCl4 was introduced into the substrate tube at a flow rate of 3.3 g / min at a heating temperature of 1600°C to deposit a loose silica body in the substrate tube.

[0079] (2) introducing an ethanol solution containing thulium chloride and aluminum chloride into the substrate tube on which the silica loose body is deposited for 2 hours, and removing excess solution to obtain a first intermediate;

[0080] (3) The substrate tube containing the first intermediate was reinstalled on the MCVD lathe, and oxygen and helium were introduced simultaneously for pre-oxidation treatment; during the pre-oxidation treatment, the oxygen flow rate was 200 sccm, the helium flow rate was 2000 sccm, the pressure in the substrate tube was 1.5 atmospheres, the reciprocating speed of the flame torch was 50 mm / min, the chuck speed was 10 rpm, the heating temperature was 250° C., and the pre-oxidation treatment time was 3.5 h;

[0081] (4) continuing to introduce oxygen and helium to perform oxidation treatment to obtain a second intermediate; wherein the oxygen flow rate is 1000 sccm, the helium flow rate is 1000 sccm, the pressure in the tube is 0.6 atmospheres, the reciprocating speed of the flame burner is 50 mm / min, the heating temperature is 400°C, and the oxidation treatment time is 1.5 h;

[0082] (5) The second intermediate is subjected to sintering and melting treatments, with the sintering temperature being 2050° C. and the melting temperature being 2280° C., to obtain a solid optical fiber preform.

[0083] Comparative Example 1 (Active Optical Fiber Prepared by the Out-of-Tube Method)

[0084] A VAD process was used to deposit a thin film with an outer diameter of 150 mm, a length of 754 mm, and a density of 2.1 g / cm 3 Pure SiO2 powder rod was pre-sintered in a sintering furnace at 1400℃ to obtain a 75mm, 526mm long, and 2.72g / cm3 density rod. 3 Pure SiO2 powder rod; weigh the ethanol solution of aluminum chloride, ytterbium chloride and phosphoric acid, soak the pre-sintered powder rod in the above solution for 48 hours, and then slowly take out the powder rod.

[0085] The extracted powder rod is placed in a drying jar at -40°C and 2.4 standard atmospheres to dry. It is then melted and sintered in a sintering furnace to form a transparent solid preform rod with an outer diameter of 51 mm, which is the rare earth-doped optical fiber preform rod.

[0086] Comparative Example 2

[0087] (1) The substrate tube was mounted on an MCVD lathe, and SF6 was introduced into the substrate tube for preheating and polishing at a heating temperature of 1550°C. When the heating temperature was 1500°C, SiCl4 at a flow rate of 2.3 g / min and Cl2 at a flow rate of 50 sccm were introduced into the substrate tube to deposit a loose silica body in the substrate tube.

[0088] (2) introducing an ethanol solution containing ytterbium chloride, aluminum chloride, and phosphoric acid into the substrate tube on which the silica loose body is deposited, the immersion time is 0.6 h, the temperature is 35° C., and after removing the excess solution, a first intermediate is obtained;

[0089] (3) The substrate tube containing the first intermediate is reinstalled on the MCVD lathe, and oxygen and helium are introduced at the same time for pre-oxidation treatment; during the pre-oxidation treatment, the oxygen flow rate is 1000 sccm; the helium flow rate is 1000 sccm, the pressure in the substrate tube is 1.1 atmospheres, the reciprocating speed of the flame torch is 100 mm / min; the rotation speed of the chuck is 60 rpm, the heating temperature is 400°C, and the pre-oxidation treatment time is 3 hours; (4) Oxygen and helium are continued to be introduced for oxidation treatment to obtain the second intermediate; during the drying treatment, the oxygen flow rate is 500 sccm, the helium flow rate is 1500 sccm, the chlorine flow rate is 500 sccm, the pressure in the tube is 1.2 atmospheres, the reciprocating speed of the flame torch is 120 mm / min, the rotation speed of the chuck is 56 rpm, the heating temperature is 400°C, and the oxidation treatment time is 6 hours;

[0090] (5) The second intermediate is subjected to sintering and melting treatments, with the sintering temperature being 2000° C. and the melting temperature being 2300° C., to obtain a solid optical fiber preform.

[0091] Comparative Example 3

[0092] (1) The substrate tube was mounted on an MCVD lathe, and SF6 was introduced into the substrate tube at a heating temperature of 1550°C for preheating and polishing. SiCl4 was introduced into the substrate tube at a heating temperature of 1500°C at a flow rate of 2.6 g / min to deposit a loose silica body in the substrate tube.

[0093] (2) introducing an aqueous solution containing ytterbium chloride, aluminum chloride, and phosphoric acid into the substrate tube on which the silica loose body is deposited, the immersion time is 0.4 h, the temperature is 25° C., and after removing the excess solution, a first intermediate is obtained;

[0094] (3) The substrate tube containing the first intermediate was reinstalled on the MCVD lathe, and oxygen and helium were introduced simultaneously for pre-oxidation treatment; wherein the oxidation flow rate was 250 sccm; the helium flow rate was 450 sccm, the pressure in the substrate tube was 0.8 atmospheres, the reciprocating speed of the flame torch was 42 mm / min; the chuck rotation speed was 60 rpm, the heating temperature was 600°C, and the pre-oxidation treatment time was 4 h;

[0095] (4) continuing to introduce oxygen and helium to perform oxidation treatment to obtain a second intermediate; wherein the oxygen flow rate is 1000 sccm, the helium flow rate is 450 sccm, the pressure in the tube is 1.2 atmospheres, the reciprocating speed of the flame burner is 120 mm / min, the chuck speed is 56 rpm, the heating temperature is 400°C, and the oxidation treatment time is 1 h;

[0096] (5) The second intermediate is subjected to sintering and melting treatments, with the sintering temperature being 1900° C. and the melting temperature being 2300° C., to obtain a solid optical fiber preform.

[0097] Test example

[0098] The optical fiber preform was directly drawn at a drawing temperature of 2000°C and a drawing speed of 15 mm / min to obtain an optical fiber. The optical fiber loss at a wavelength of 1200 nm and a wavelength of 1380 nm were tested using a cutoff valve. The test results are shown in Table 1.

[0099] Table 1

[0100] As can be seen from Table 1, the present invention utilizes pre-oxidation and oxidation treatments to achieve gradual oxidation, and limits the oxygen flow rate, which can achieve full oxidation of rare earth elements and maximize the removal of hydroxyl groups, thereby helping to reduce optical fiber loss. In addition, this preparation method has excellent environmental protection and safety, and is suitable for mass production.

[0101] After nearly 50 optical fiber preforms were produced using the preparation method of Example 1, the air intake duct of the MCVD lathe remained clean and had no obvious rust. However, after 50 optical fiber preforms were produced using the chlorine-containing process of Comparative Example 2, the air intake duct of the MCVD lathe was severely corroded, and the air intake duct needed to be replaced regularly.

[0102] The above describes in detail the preferred embodiments of the present invention and their experimental verification. It should be understood that a person skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solution that can be derived by a person skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art shall be within the scope of protection of the present invention.

Claims

1. A method for preparing an active optical fiber preform, characterized in that: The following steps are involved: Immersing the silicon dioxide loose body in a solution containing rare earth chloride to obtain a first intermediate; The first intermediate is placed in an MCVD lathe, and oxygen and helium are introduced simultaneously to perform a pre-oxidation treatment, and oxygen and helium are continued to be introduced to perform an oxidation treatment to obtain a second intermediate; wherein the oxygen introduction flow rate in the pre-oxidation treatment is V1, and the oxygen introduction flow rate in the oxidation treatment is V2, satisfying V1:V2=1:(5-10); the temperature of the oxidation treatment is greater than the temperature of the pre-oxidation treatment; and the pressure of the pre-oxidation treatment is greater than the pressure of the oxidation treatment; The second intermediate is subjected to sintering treatment and melting treatment in sequence to obtain an optical fiber preform.

2. The preparation method according to claim 1, characterized in that The flow rate of helium gas in the pre-oxidation treatment is V3, and the flow rate of helium gas in the oxidation treatment is V4, satisfying V3:V4=(2-3):

1.

3. The preparation method according to claim 2, characterized in that In the pre-oxidation treatment, the flow rate of oxygen is 50-200 sccm, and the flow rate of helium is 500-2000 sccm; and / or, During the oxidation treatment, the flow rate of oxygen gas is 500-1000 sccm, and the flow rate of helium gas is 500-1000 sccm.

4. The preparation method according to claim 1, characterized in that The pre-oxidation treatment is performed at a temperature of 200 to 500° C., a pressure of 0.9 to 1.5 atmospheres, and a time of 1.8 to 3.5 hours; and / or The oxidation treatment is performed at a temperature of 400 to 800° C., a pressure of 0.6 to 0.9 atmospheres, and a time of 1.5 to 2 hours.

5. The preparation method according to claim 1, characterized in that The MCVD lathe comprises at least a flame torch, a first clamping unit and a second clamping unit; The first clamping unit and the second clamping unit rotate along their own axes, and the first clamping unit and the second clamping unit are used to cooperate with each other to clamp the first intermediate body; The flame torch reciprocates along the axial direction of the first intermediate body, and the spraying direction of the flame torch is toward the first intermediate body; During the pre-oxidation treatment, the flame burner is started to make a first reciprocating movement along the axial direction of the first intermediate body; the first clamping unit and the second clamping unit drive the first intermediate body to make a first rotation; During the oxidation treatment, the flame burner is started to make a second reciprocating movement along the axial direction of the first intermediate body; the first clamping unit and the second clamping unit drive the first intermediate body to make a second rotation; The rotation speed of the first rotation is 10 to 30 rpm; the rotation speed of the second rotation is 10 to 30 rpm; The speed of the first reciprocating movement is 50-100 mm / min; the speed of the second reciprocating movement is 50-100 mm / min.

6. The preparation method according to claim 1, characterized in that The rare earth chloride-containing solution contains at least one element selected from the group consisting of Y, Ce, Nd, Yd, Tm, and Er; and / or The solvent in the solution containing rare earth chloride includes at least one of methanol, ethanol and ethylene glycol.

7. The preparation method according to claim 6, characterized in that The solution containing rare earth chloride further contains at least one element of Al and P.

8. The preparation method according to any one of claims 1 to 7, characterized in that The sintering treatment and the melting treatment are both carried out in a mixed atmosphere containing oxygen and helium; In the mixed atmosphere, the volume ratio of oxygen to helium is 1:(1-2).

9. An active optical fiber preform, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. An active optical fiber, characterized in that: It is prepared using the active optical fiber preform described in claim 9.

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