An active optical fiber preform, its preparation method and application

Abstract

This invention provides an active optical fiber preform, its preparation method, and its application, comprising the following steps: immersing a loose silica mass in a solution containing rare earth chlorides to obtain a first intermediate; placing the first intermediate in an MCVD lathe, simultaneously introducing oxygen and helium for pre-oxidation treatment, and continuing to introduce oxygen and helium for oxidation treatment to obtain a second intermediate; wherein, 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); the oxidation treatment temperature is higher than the pre-oxidation treatment temperature; the pre-oxidation treatment pressure is higher than the oxidation treatment pressure; and the second intermediate is subjected to sintering and melting / shrinking treatments sequentially to obtain an active optical fiber preform. This method enables the full oxidation of rare earth elements and maximizes the removal of hydroxyl groups, helping to reduce optical fiber loss. Furthermore, this preparation method has excellent environmental friendliness and safety, making it suitable for mass production.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber technology, specifically relating to an active optical fiber preform, its preparation method, and its application. Background Technology

[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 doped layer of a certain concentration, the fiber can exhibit significant absorption and emission characteristics for a specific wavelength of light, achieving superior spectral characteristics and optical efficiency. This rare earth-doped active fiber is currently widely used in fiber optic sensors. As an important gain medium in fiber lasers, the performance of rare earth-doped active fibers directly determines the performance of the laser. The preform is the foundation for fiber fabrication, and its performance directly affects the fiber's performance. Therefore, how to fabricate high-performance fiber preforms is a key research focus in this field.

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

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

[0005] This invention provides a method for preparing an active optical fiber preform, which utilizes pre-oxidation treatment and oxidation treatment to achieve stepwise oxidation and limits the oxygen flow rate, thereby achieving full oxidation of rare earth elements and maximizing the removal of hydroxyl groups, which helps to reduce optical fiber loss. Moreover, this preparation method has excellent environmental protection and safety, and is suitable for mass production.

[0006] This invention provides an active optical fiber preform. Because it is prepared by the above-described method, the optical fiber made from this preform 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 using the above-mentioned active optical fiber preform.

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

[0009] The first intermediate was obtained by immersing the porous silica in a solution containing rare earth chlorides.

[0010] The first intermediate is placed in an MCVD lathe, and oxygen and helium are simultaneously introduced for pre-oxidation treatment. Oxygen and helium are then introduced for oxidation treatment to obtain the second intermediate. 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 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.

[0011] The second intermediate is subjected to sintering and shrinkage treatments in sequence to obtain an active optical fiber preform.

[0012] In the preparation method described above, 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.

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

[0014] In the oxidation process, the oxygen flow rate is 500-1000 sccm, and the helium flow rate is 500-1000 sccm.

[0015] In the preparation method described above, the pre-oxidation treatment is carried out at a temperature of 200–500°C, a pressure of 0.9–1.5 atmospheres, and a time of 1.8–3.5 h; and / or,

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

[0017] The preparation method described above, wherein the MCVD lathe includes 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 spray direction of the flame torch is towards the first intermediate body;

[0020] During the pre-oxidation process, the flame torch is activated to cause the flame torch to reciprocate along the axial direction of the first intermediate body; the first clamping unit and the second clamping unit drive the first intermediate body to rotate.

[0021] During the oxidation process, the flame torch is activated to cause the flame torch to reciprocate along the axial direction of the first intermediate body in a second reciprocating motion; the first clamping unit and the second clamping unit drive the first intermediate body to rotate in a second direction.

[0022] The rotational speed of the first rotation is 10-30 rpm; the rotational speed of the second rotation is 10-30 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] In the preparation method described above, the solution containing rare earth chlorides contains at least one element selected from Y, Ce, Nd, Yd, Tm, and Er; and / or,

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

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

[0027] In the preparation method described above, the sintering treatment and the melting and shrinking 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] In a second aspect, the present invention provides an active optical fiber preform, which is prepared by the preparation method described in the first aspect.

[0030] In a third aspect, the present invention provides an optical fiber prepared using the active optical fiber preform described in the second aspect.

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

[0032] The active optical fiber preform preparation method provided by this invention utilizes a liquid-phase method to dope rare earth elements into porous silica, followed by pre-oxidation and oxidation treatments to achieve gradual oxidation, effectively removing hydroxyl groups from the porous silica. Furthermore, by limiting the oxygen flow rate during the pre-oxidation and oxidation treatments, sufficient oxidation of rare earth elements and maximum removal of hydroxyl groups can be achieved, which helps to reduce optical fiber loss. Moreover, this preparation method can remove hydroxyl groups without using chlorine gas, exhibiting excellent environmental friendliness and safety, and is suitable for mass production.

[0033] The active optical fiber preform provided by the present invention is prepared by the above-described preparation method, and the optical fiber prepared using the active optical fiber preform has the advantage of low loss.

[0034] The present invention also provides an optical fiber, which is obtained by drawing the above-mentioned active optical fiber preform into fibers, and the optical fiber has the advantage of low loss. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0036] In a first aspect, the present invention provides a method for preparing an active optical fiber preform, comprising the following steps: immersing a porous silica mass in a solution containing rare earth chlorides to obtain a first intermediate; placing the rare earth-doped porous silica mass in an MCVD lathe, simultaneously introducing oxygen and helium for pre-oxidation treatment, and continuing to introduce oxygen and helium for oxidation treatment to obtain a second intermediate; wherein 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); the temperature of the oxidation treatment is higher than the temperature of the pre-oxidation treatment; the pressure of the pre-oxidation treatment is higher than the pressure of the oxidation treatment; and subjecting the second intermediate to sintering and shrinkage treatments in sequence to obtain an active optical fiber preform.

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

[0038] The base tube can be a conventional deposition tube in the field, and the MCVD lathe is a conventional device in the field for preparing active optical fiber preforms, 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 this invention, a base tube is mounted on an MCVD lathe, and a silica porous body is deposited inside the base tube. A solution containing rare earth chlorides can be directly injected into the base tube containing the silica porous body, immersing the silica porous body in the solution for 0.5–2 hours at a temperature of 30–45°C. Excess solution is then removed to obtain the first intermediate. The first intermediate is essentially a silica porous body doped with rare earth elements.

[0040] A solution containing rare earth chlorides is injected into the base tube. After soaking and removing excess solution, the base tube after removing excess solution can be directly installed in an MCVD lathe for pre-oxidation and oxidation treatment.

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

[0042] By setting up pre-oxidation and oxidation treatments and gradually increasing the oxygen content, it is beneficial to achieve full oxidation of rare earth elements and gradual oxidation of hydroxyl groups. Furthermore, by limiting the oxygen flow rate ratio during the pre-oxidation and oxidation treatments, it is advantageous 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 any combination thereof.

[0044] In this invention, the temperature of the oxidation treatment is higher than that of the pre-oxidation treatment, and the pressure of the pre-oxidation treatment is higher than that of the oxidation treatment, which helps to achieve gradual oxidation.

[0045] In this invention, sintering essentially promotes the vitrification of the intermediate; melting and shrinking essentially promotes the formation of a solid active optical fiber preform from the hollow second intermediate. Since the above pre-oxidation and oxidation processes are both performed on an MCVD lathe, sintering and melting and shrinking processes can be directly performed on the MCVD lathe after pre-oxidation and oxidation, which is beneficial to improving production efficiency.

[0046] This invention employs conventional methods for sintering and shrinkage treatment. For example, the second intermediate can be heated to the sintering temperature and sintered. After sintering, it is heated again for shrinkage treatment, and then cooled to obtain the active optical fiber preform. During sintering, the heating process can maintain a certain heating rate, allowing the second intermediate to be fully and uniformly heated and slowly complete the vitrification process, thereby ensuring that the obtained active optical fiber preform has good optical uniformity. After sintering, it is heated again for shrinkage treatment, and then the temperature is reduced at a certain cooling rate. Slow cooling helps to improve the internal stress defects of the active optical fiber preform and enhance its uniformity.

[0047] This 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 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, for example, a range of 2:1, 2.5:1, 3:1, or any two of them.

[0048] This invention does not limit the specific flow rates of oxygen and helium, as long as the above-mentioned ratio is satisfied. For example, in some embodiments, in the pre-oxidation treatment, the oxygen flow rate is 50-200 sccm, such as 50 sccm, 100 sccm, 150 sccm, 200 sccm or any combination thereof, and the helium flow rate is 500-2000 sccm, such as 500 sccm, 550 sccm, 1000 sccm, 1500 sccm, 2000 sccm or any combination thereof; and / or, in the oxidation treatment, the oxygen flow rate is 500-1000 sccm, such as 500 sccm, 550 sccm, 1000 sccm or any combination thereof, and the helium flow rate is 500-1000 sccm, such as 500 sccm, 550 sccm, 1000 sccm or any combination thereof.

[0049] This 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 any combination thereof, and the pressure is 0.9–1.5 atmospheres, such as 0.9 atmospheres, 1 atmosphere, 1.2 atmospheres, 1.5 atmospheres, or any combination thereof. The time is 1.8–3.5 hours; and / or, the oxidation treatment temperature is 400–800°C, for example, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, or any combination thereof, and the pressure is 0.6–0.9 atmospheres, for example, 0.6 atmospheres, 0.7 atmospheres, 0.8 atmospheres, 0.9 atmospheres, or any combination thereof, and the time is 1.5–2 hours. It should be noted that the selection of the above temperature and pressure must satisfy the following conditions: the oxidation treatment temperature is higher than the pre-oxidation treatment temperature, and the oxidation treatment pressure is lower than the pre-oxidation treatment pressure.

[0050] In this invention, a heating unit can be used to heat the first intermediate. By supplying temperature to the first intermediate through the heating unit, the temperature conditions for the pre-oxidation treatment and the oxidation treatment can be guaranteed.

[0051] This invention does not limit the specific type of MCVD lathe; it can be any conventional MCVD lathe in the art. For example, in some embodiments, the MCVD lathe includes at least a flame torch, a first clamping unit, and a second clamping unit; the first and second clamping units rotate along their own axes and are used to cooperate in clamping a first intermediate body; the flame torch reciprocates along the axial direction of the first intermediate body, and the flame torch's spray direction is towards the first intermediate body; during the pre-oxidation process, the flame torch is activated to cause a first reciprocating movement along the axial direction of the first intermediate body; the first and second clamping units drive the first intermediate body to undergo a first rotation; during the oxidation process, the flame torch is activated to cause a second reciprocating movement along the axial direction of the first intermediate body; the first and second clamping units drive the first intermediate body to undergo a second rotation.

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

[0053] A flame torch is used to spray a flame onto a first intermediate to bring the temperature of the first intermediate to the temperature required for pre-oxidation and oxidation treatments. During the pre-oxidation and oxidation treatments, the flame torch is directed towards the first intermediate and moves back and forth along the axial direction of the first intermediate.

[0054] The rotational speed of the first rotation is 10–30 rpm, for example, a range of 10 rpm, 15 rpm, 20 rpm, 25 rpm, 30 rpm, or any two of these ranges; the rotational speed of the second rotation is 10–30 rpm, for example, a range of 10 rpm, 15 rpm, 20 rpm, 25 rpm, 30 rpm, or any two of these ranges; the speed of the first reciprocating movement is 50–100 mm / min, for example, a range of 50 mm / min, 60 mm / min, 70 mm / min, 80 mm / min, 90 mm / min, 100 mm / min, or any two of these ranges; the speed of the second reciprocating movement is 50–100 mm / min, for example, a range of 50 mm / min, 60 mm / min, 70 mm / min, 80 mm / min, 90 mm / min, 100 mm / min, or any two of these ranges; the number of reciprocating movements of the first reciprocating movement is 5–20 times; the number of reciprocating movements of the second reciprocating movement is 5–20 times.

[0055] The first reciprocating movement and the second reciprocating movement both refer to the reciprocating movement of the flame torch along the axial direction of the first intermediate body from one end to the other, and then from the other end to one end along 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 along the axial direction of the first intermediate body, and then from the other end to the first end along the axial direction of the first intermediate body, which constitutes one reciprocating movement.

[0057] In this invention, the rotation speed of the first clamping unit and the second clamping unit can be adjusted by the chuck.

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

[0059] This invention does not limit the specific type of solution containing rare earth chlorides, as long as it contains rare earth chlorides. For example, in some embodiments, the solution containing rare earth chlorides contains at least one element selected from Y, Ce, Nd, Yd, Tm, and Er; and / or, the solvent in the solution containing rare earth chlorides includes at least one element selected from methanol, ethanol, and ethylene glycol.

[0060] In one possible implementation, the solution containing rare earth chlorides also contains at least one element selected from Al and P.

[0061] This invention does not limit the specific implementation of sintering and melting treatment, and can be implemented using conventional sintering and melting treatment methods in the art. In some embodiments, both sintering and melting treatment are 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).

[0062] In a second aspect, the present invention provides an active optical fiber preform, which is prepared using the preparation method provided in the first aspect. Because it is prepared using the above-described preparation method, the optical fiber prepared using this active optical fiber preform has the advantage of low loss.

[0063] A third aspect of the present invention provides an optical fiber that, due to being fabricated using the aforementioned active optical fiber preform, exhibits the advantage of low loss. The optical fiber of the present invention can be fabricated by performing conventional fiber drawing methods in the art on the active optical fiber preform.

[0064] The present invention will be further described below through specific embodiments 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 synthetic methods.

[0065] Example 1

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

[0067] (2) A methanol solution containing ytterbium chloride, aluminum chloride, and phosphoric acid was passed into the base tube deposited with silica loose body and soaked for 0.5 h. After removing the excess solution, the first intermediate was obtained.

[0068] (3) The base tube containing the first intermediate was reinstalled on the MCVD lathe, and oxygen and helium were introduced at the same time 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 inside the base 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℃, and the pre-oxidation treatment time was 2 h.

[0069] (4) Continue to introduce oxygen and helium for oxidation treatment to obtain the second intermediate; during the oxidation treatment, the oxygen flow rate is 500 sccm, the helium flow rate is 500 sccm, the pressure inside the tube is 0.7 atmospheres, the reciprocating speed of the flame torch is 100 mm / min, the heating temperature is 400℃, and the oxidation treatment time is 1.5 h.

[0070] (5) The second intermediate is subjected to sintering and melting treatment at a sintering temperature of 2000℃ and a melting temperature of 2150℃ to obtain a solid active optical fiber preform.

[0071] Example 2

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

[0073] (2) An ethanol solution containing erbium chloride and aluminum chloride was passed into the base tube deposited with silica loose body and soaked for 1 hour. After removing the excess solution, the first intermediate was obtained.

[0074] (3) The base tube containing the first intermediate was reinstalled on the MCVD lathe, and oxygen and helium were introduced at the same time 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 inside the base tube was 1.3 atmospheres, the reciprocating speed of the flame torch was 70 mm / min, the chuck rotation speed was 15 rpm, the heating temperature was 500℃, and the pre-oxidation treatment time was 1.8 h;

[0075] (4) Continue to introduce oxygen and helium for oxidation treatment to obtain the second intermediate; during the oxidation treatment, the oxygen flow rate is 700 sccm, the helium flow rate is 700 sccm, the pressure inside the tube is 0.9 atmospheres, the reciprocating speed of the flame torch is 70 mm / min, the heating temperature is 700℃, and the oxidation treatment time is 2h.

[0076] (5) The second intermediate is subjected to sintering and melting treatment at a sintering temperature of 1950℃ and a melting temperature of 2200℃ to obtain a solid active optical fiber preform.

[0077] Example 3

[0078] (1) The base tube is installed on an MCVD lathe. Under the condition of heating temperature of 1800℃, SF6 is introduced into the base tube for preheating and polishing. Under the condition of heating temperature of 1600℃, SiCl4 is introduced into the base tube at a flow rate of 3.3g / min to deposit a loose silica body in the base tube.

[0079] (2) An ethanol solution containing thulium chloride and aluminum chloride was passed into the base tube deposited with silica loose body and soaked for 2 hours. After removing the excess solution, the first intermediate was obtained.

[0080] (3) The base tube containing the first intermediate was reinstalled on the MCVD lathe, and oxygen and helium were introduced at the same time 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 inside the base tube was 1.5 atmospheres, the reciprocating speed of the flame torch was 50 mm / min, the chuck rotation speed was 10 rpm, the heating temperature was 250℃, and the pre-oxidation treatment time was 3.5 h;

[0081] (4) Continue to introduce oxygen and helium for oxidation treatment to obtain the second intermediate; wherein the oxygen flow rate is 1000 sccm, the helium flow rate is 1000 sccm, the pressure inside the tube is 0.6 atmospheres, the reciprocating speed of the flame torch is 50 mm / min, the heating temperature is 400℃, and the oxidation treatment time is 1.5 h.

[0082] (5) The second intermediate is subjected to sintering and melting treatment at a sintering temperature of 2050℃ and a melting temperature of 2280℃ to obtain a solid active optical fiber preform.

[0083] Comparative Example 1 (Active optical fiber fabricated by the external tube method)

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

[0085] The extracted powder rods are dried in a drying oven at -40°C and 2.4 atmospheres. Then, the powder rods are melted and shrunk in a sintering furnace into transparent solid preforms with an outer diameter of 51 mm, which are the rare earth doped optical fiber preforms.

[0086] Comparative Example 2

[0087] (1) The base tube is installed on an MCVD lathe. Under the condition of heating temperature of 1550℃, SF6 is introduced into the base tube for preheating and polishing. At the heating temperature of 1500℃, SiCl4 with a flow rate of 2.3g / min is introduced into the base tube, and Cl2 with a flow rate of 50sccm is introduced at the same time to deposit a loose silica body in the base tube.

[0088] (2) An ethanol solution containing ytterbium chloride, aluminum chloride, and phosphoric acid was passed into the base tube deposited with silica loose body. The soaking time was 0.6 h and the temperature was 35 °C. After removing the excess solution, the first intermediate was obtained.

[0089] (3) The base 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 inside the base tube is 1.1 atmospheres, the reciprocating speed of the flame torch is 100 mm / min; the chuck speed is 60 rpm, the heating temperature is 400℃, and the pre-oxidation treatment time is 3h; (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 inside the tube is 1.2 atmospheres, the reciprocating speed of the flame torch is 120 mm / min, the chuck speed is 56 rpm, the heating temperature is 400℃, and the oxidation treatment time is 6h;

[0090] (5) The second intermediate is subjected to sintering and melting treatment at a sintering temperature of 2000℃ and a melting temperature of 2300℃ to obtain a solid optical fiber preform.

[0091] Comparative Example 3

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

[0093] (2) An aqueous solution containing ytterbium chloride, aluminum chloride and phosphoric acid was passed into the base tube deposited with silica loose body. The soaking time was 0.4 h and the temperature was 25 °C. After removing the excess solution, the first intermediate was obtained.

[0094] (3) The base 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; wherein the oxidation flow rate is 250 sccm; the helium flow rate is 450 sccm, the pressure inside the base tube is 0.8 atmospheres, the reciprocating speed of the flame torch is 42 mm / min; the rotation speed of the chuck is 60 rpm, the heating temperature is 600℃, and the pre-oxidation treatment time is 4h;

[0095] (4) Continue to introduce oxygen and helium for oxidation treatment to obtain the second intermediate; wherein the oxygen flow rate is 1000 sccm, the helium flow rate is 450 sccm, the pressure inside the tube is 1.2 atmospheres, the reciprocating speed of the flame torch is 120 mm / min, the chuck speed is 56 rpm, the heating temperature is 400℃, and the oxidation treatment time is 1 h.

[0096] (5) The second intermediate is subjected to sintering and melting treatment at a sintering temperature of 1900℃ and a melting temperature of 2300℃ to obtain a solid optical fiber preform.

[0097] Test case

[0098] The above-mentioned optical fiber preform was directly drawn into optical fiber at a drawing temperature of 2000℃ and a drawing speed of 15mm / min. The loss of the optical fiber at a wavelength of 1200nm and a wavelength of 1380nm was tested using a cutoff valve. The test results are shown in Table 1.

[0099] Table 1

[0100]

[0101] As shown in Table 1, the present invention utilizes pre-oxidation treatment and oxidation treatment to achieve stepwise oxidation, and limits the oxygen flow rate, which can achieve full oxidation of rare earth elements and maximum removal of hydroxyl groups, thus helping to reduce optical fiber loss. Moreover, the preparation method has excellent environmental protection and safety, and is suitable for mass production.

[0102] After nearly 50 active optical fiber preforms were prepared using the preparation method of Example 1, the air intake pipe of the MCVD lathe remained clean and showed no obvious corrosion. However, in Comparative Example 2, after 50 active optical fiber preforms were prepared using the chlorine-containing process, the air intake pipe of the MCVD lathe was severely corroded, requiring regular replacement of the air intake pipe.

[0103] The preferred embodiments and experimental verifications of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the protection scope of the present invention.

Claims

1. A method for preparing an active optical fiber preform, characterized in that, Includes the following steps: The first intermediate was obtained by immersing the porous silica in a solution containing rare earth chlorides. The first intermediate is placed in an MCVD lathe, and oxygen and helium are simultaneously introduced for pre-oxidation treatment. Oxygen and helium are then introduced for oxidation treatment to obtain the second intermediate. 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 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. The second intermediate is subjected to sintering and shrinkage treatments in sequence to obtain an active 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 oxygen flow rate is 50–200 sccm, and the helium flow rate is 500–2000 sccm; and / or, In the oxidation process, the oxygen flow rate is 500-1000 sccm, and the helium flow rate 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 200–500°C, a pressure of 0.9–1.5 atmospheres, and a time of 1.8–3.5 hours; and / or, The oxidation treatment is carried out at a temperature of 400–800°C, a pressure of 0.6–0.9 atmospheres, and a time of 1.5–2 hours.

5. The preparation method according to claim 4, characterized in that, The MCVD lathe includes 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 spray direction of the flame torch is towards the first intermediate body; During the pre-oxidation process, the flame torch is activated to cause the flame torch to reciprocate along the axial direction of the first intermediate body; the first clamping unit and the second clamping unit drive the first intermediate body to rotate. During the oxidation process, the flame torch is activated to cause the flame torch to reciprocate along the axial direction of the first intermediate body in a second reciprocating motion; the first clamping unit and the second clamping unit drive the first intermediate body to rotate in a second direction. The rotational speed of the first rotation is 10-30 rpm; the rotational speed of the second rotation is 10-30 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 solution containing rare earth chlorides contains at least one element selected from Y, Ce, Nd, Yd, Tm, and Er; and / or, The solvent in the solution containing rare earth chlorides 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 chlorides also contains at least one element from Al and P.

8. The preparation method according to any one of claims 1-7, characterized in that, The sintering and melting processes 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, It is prepared by the preparation method according to any one of claims 1-8.

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

Images