Device and method for reducing growth temperature gradient of single crystal optical fiber

Abstract

The invention discloses a device for reducing the growth temperature gradient of a single crystal optical fiber. The device comprises a heating and feeding assembly and a temperature gradient lifting and reducing assembly, the heating assembly emits laser and focuses a light beam on the top of the raw material rod to form a local heating area; the feeding assembly and the lifting assembly each comprise a displacement table and a motor, the temperature gradient reducing assembly comprises an upper heat preservation structure and a lower heat preservation structure, the upper heat preservation structure and the lower heat preservation structure are fixedly connected to the displacement tables of the feeding assembly and the lifting assembly respectively, and the lower displacement table adjusts a raw material rod penetrating through the lower heat preservation structure to be located on the same center line with a laser focus point. A corresponding motor drives the raw material rod to be fed in the vertical direction, so that the top of the raw material rod reaches a laser focus point; the upper displacement table adjusts the single-crystal optical fiber penetrating through the upper heat preservation structure to be coaxial with the raw material rod, and the corresponding motor drives the single-crystal optical fiber to be lifted in the vertical direction so as to achieve growth of the single-crystal optical fiber. The whole temperature gradient in the growth process of the single crystal optical fiber can be remarkably reduced, and stable growth of the single crystal optical fiber in the vertical direction is kept.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of single crystal fiber preparation, in particular to a device and method for reducing the temperature gradient of single crystal fiber growth. BACKGROUND

[0002] Single crystal fiber is a kind of crystal material with fiber structure, which has the intrinsic properties of bulk crystal and the structural characteristics of glass fiber, and has excellent physical and chemical properties. It has broad application prospects in the fields of laser, radiation detection and high temperature sensing. At present, the preparation methods of single crystal fiber mainly include mode guiding method, micro-pulling method and laser heating base method. Among them, the laser heating base method does not need crucible, requires less raw materials, and can quickly realize the preparation of single crystal fiber with high length-diameter ratio. Therefore, this method is widely studied and applied. However, the preparation of single crystal fiber has the problem of easy cracking, especially for high melting point single crystal fiber, because the temperature gradient during the growth of high melting point single crystal fiber is larger, so the thermal stress is larger, which leads to the easy cracking of the crystal. The temperature gradient of the laser heating base method can reach 100-1000K / cm, so a device and method for reducing the temperature gradient of single crystal fiber growth are urgently needed. SUMMARY

[0003] In view of the deficiencies of the prior art, the present application provides a device and method for reducing the temperature gradient of single crystal fiber growth, and the specific technical solutions are as follows:

[0004] A device for reducing the temperature gradient of single crystal fiber growth, comprising a heating assembly, a feeding assembly, a pulling assembly and a temperature gradient reducing assembly;

[0005] The heating assembly comprises a laser, a cone lens group, a turning mirror and a parabolic mirror, the laser is used for emitting laser, the cone lens group is used for converting the laser into a ring-shaped beam, and the turning mirror and the parabolic mirror are used for focusing the ring-shaped beam on the top of the raw material rod to form a local heating area;

[0006] The feeding assembly comprises a center double-axis linear displacement table with a threaded hole and a lower motor, the pulling assembly comprises a center double-axis linear displacement table with a threaded hole and an upper motor, the temperature gradient reducing assembly comprises an upper heat preservation structure and a lower heat preservation structure, the lower heat preservation structure is fixedly connected to the center double-axis linear displacement table with a threaded hole, the center double-axis linear displacement table with a threaded hole is used to adjust the raw material rod passing through the lower heat preservation structure to be on the same center line as the laser focus point, and the lower motor is used to drive the raw material rod to feed in the vertical direction so that the top of the raw material rod reaches the laser focus point;

[0007] The upper heat preservation structure is fixed on the double-axis linear displacement table two with a central threaded hole, which is used to adjust the single crystal optical fiber passing through the upper heat preservation structure to be coaxial with the raw material rod, and the upper motor is used to drive the single crystal optical fiber to be pulled in the vertical direction to realize the growth of the single crystal optical fiber.

[0008] The upper heat preservation structure is used to reduce the temperature gradient of the single crystal optical fiber growth zone and limit the movement of the single crystal optical fiber along the central axis, and the lower heat preservation structure is used to reduce the temperature gradient of the heating zone of the raw material rod and limit the movement of the raw material rod along the central axis, and the upper heat preservation structure and the lower heat preservation structure cooperate to reduce the axial and radial temperature gradient during the growth of the single crystal optical fiber, and keep the single crystal optical fiber to grow at a uniform speed in the vertical direction.

[0009] Further, the upper heat preservation structure is a coaxial three-layer hollow structure, which is sequentially composed of an upper quartz glass tube, an upper zirconia cylinder and an upper alumina cylinder from inside to outside.

[0010] The inner diameter of the upper quartz glass tube is equal to the diameter of the single crystal optical fiber passing therethrough.

[0011] The upper zirconia cylinder is composed of a cylinder one at the upper part and a cone one at the lower part, and the center of the upper zirconia cylinder is provided with a through shaft hole one, and the diameter of the shaft hole one is equal to the outer diameter of the upper quartz glass tube; the outer diameter of the cylinder one of the upper zirconia cylinder is equal to the diameter of the bottom surface of the cone one.

[0012] The upper alumina cylinder includes a stud two at the upper part, a cylinder two at the middle part and a cone two at the lower end, the center of the upper alumina cylinder is provided with a through shaft hole two, the shaft hole two is a three-section hole with variable diameter, including an upper section cylinder hole, a middle section cone hole and a lower end cylinder hole; the upper section cylinder hole is located in the stud two and the cylinder two, and the diameter of the upper section cylinder hole is equal to the outer diameter of the cylinder one of the upper zirconia cylinder; the middle section cone hole is located in the cone two and matches the cone one of the upper zirconia cylinder, and the diameter of the middle section cone hole is equal to the outer diameter of the cone one of the upper zirconia cylinder; the lower end cylinder hole is located in the cone two and matches the upper quartz glass tube, and the diameter of the lower end cylinder hole is equal to the outer diameter of the upper quartz glass tube; the outer diameter of the cylinder two at the middle part of the upper alumina cylinder is equal to the diameter of the bottom surface of the cone two.

[0013] Further, the outer diameter of the cylinder one of the upper zirconia cylinder and the diameter of the bottom surface of the cone one are both selected from 6-10mm.

[0014] Further, the length of the cylinder two at the middle part of the upper alumina cylinder is selected from 100-200mm, and the height of the cone two is designed according to the focusing path of the annular laser beam to avoid beam blocking.

[0015] Further, the ratio of the height of the first cone of the upper zirconia cylinder to the height of the second cone of the upper alumina cylinder is equal to the ratio of the diameters of the bottom surfaces of the two, and the bottom end of the upper quartz glass tube is flush with the top of the second cone of the upper alumina cylinder.

[0016] Further, the lower heat preservation structure is a coaxial three-layer hollow structure, which comprises, from inside to outside, a lower quartz glass tube, a lower zirconia cylinder and a lower alumina cylinder;

[0017] The inner diameter of the lower quartz glass tube is equal to the diameter of the raw material rod passing therethrough;

[0018] The lower zirconia cylinder is a cylindrical shell with an axial hole at the bottom, and the inner diameter of the cylindrical shell is equal to the outer diameter of the lower quartz glass tube; the diameter of the bottom axial hole of the cylindrical shell of the lower zirconia cylinder is between the inner diameter and the outer diameter of the lower quartz glass tube;

[0019] The lower alumina cylinder comprises a cylindrical shell and a threaded stud with an axial hole, the inner diameter of the cylindrical shell of the lower alumina cylinder is equal to the outer diameter of the lower zirconia cylinder; the diameter of the axial hole of the lower alumina cylinder is greater than the diameter of the bottom axial hole of the lower zirconia cylinder and less than the outer diameter of the lower zirconia cylinder; the bottom end of the lower quartz glass tube coincides with the inner bottom of the lower zirconia cylinder, and the outer bottom of the lower zirconia cylinder coincides with the inner bottom of the lower alumina cylinder.

[0020] Further, the inner diameter of the cylindrical shell of the lower zirconia cylinder and the outer diameter of the lower quartz glass tube are selected from 6 to 10 mm; the bottom thickness of the cylindrical shell of the lower zirconia cylinder is selected from 3 to 5 mm;

[0021] The inner diameter of the cylindrical shell of the lower alumina cylinder and the outer diameter of the lower zirconia cylinder are selected from 8 to 12 mm;

[0022] The length of the cylindrical shell of the lower alumina cylinder is selected from 100 to 200 mm, and the height of the threaded stud of the lower alumina cylinder is 3 to 5 mm.

[0023] Further, the top of the first cylinder of the upper zirconia cylinder is 5 to 10 mm higher than the top of the second threaded stud of the upper alumina cylinder, so as to facilitate the embedding and taking out of the upper zirconia cylinder into and out of the upper alumina cylinder;

[0024] The top end of the upper quartz glass tube is 5 to 10 mm higher than the top of the first cylinder of the upper zirconia cylinder, so as to facilitate the embedding and taking out of the upper quartz glass tube into and out of the upper zirconia cylinder.

[0025] Further, the size of the stud of the upper alumina cylinder matches the central threaded hole of the biaxial linear displacement table II with a central threaded hole to fix the upper heat preservation structure; the size of the stud of the lower alumina cylinder matches the threaded hole of the biaxial linear displacement table I with a threaded hole to fix the lower heat preservation structure.

[0026] A method for reducing a temperature gradient of single crystal fiber growth, which is implemented based on a device for reducing a temperature gradient of single crystal fiber growth, and the method comprises the following steps:

[0027] Step one: adjust the lower heat preservation structure so that the top of the lower alumina cylinder is located at a first preset distance below a laser focus point generated by the heating assembly; pass the raw material rod through the lower heat preservation structure, and locate the top of the raw material rod at the laser focus point;

[0028] Step two: adjust the upper heat preservation structure so that the conical top of the upper alumina cylinder is located at a second preset distance above the top of the raw material rod; pass the single crystal fiber through the upper heat preservation structure, and the bottom end of the single crystal fiber is different from the top of the raw material rod by the third preset distance;

[0029] Step three: turn on the laser to focus on the top of the raw material rod to form a hemispherical molten zone;

[0030] Step four: control the upper motor to drive the single crystal fiber to move downward to contact the hemispherical molten zone;

[0031] Step five: control the upper motor to uniformly pull up the single crystal fiber upward, and control the lower motor to uniformly feed the raw material rod upward to realize continuous growth of the single crystal fiber.

[0032] The beneficial effects of the present application are as follows:

[0033] The device and method for reducing a temperature gradient of single crystal fiber growth can significantly reduce the overall temperature gradient in the single crystal fiber growth process through the synergistic effect of the upper and lower heat preservation structures, and maintain stable growth in the vertical direction, thereby effectively inhibiting the cracking and deflection growth of the single crystal fiber, and improving the structural integrity and product quality of the single crystal fiber. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a structural diagram of a device for reducing a temperature gradient of single crystal fiber growth according to an exemplary embodiment.

[0035] Figure 2 is a schematic diagram of an upper heat preservation structure (left) and a lower heat preservation structure (right) according to an exemplary embodiment.

[0036] Figure 3 is a sectional view of the upper temperature maintaining structure according to an exemplary embodiment.

[0037] Figure 4 is a sectional view of the lower temperature maintaining structure according to an exemplary embodiment. DETAILED DESCRIPTION

[0038] The present application will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, as the purposes and advantages of this application will become more readily apparent, and the detailed description set forth below should not be taken as limiting the presently claimed application. While the specification concludes with claims particularly pointing out applications of the various embodiments, it is believed that the application will be better understood from the description and drawings.

[0039] As shown in Figure 1 , the device for reducing the temperature gradient of single crystal fiber growth of the present embodiment comprises a laser 1, a conical lens group 2, a turning mirror 3, a parabolic mirror 4, an upper temperature maintaining structure 5, a lower temperature maintaining structure 6, a raw material rod 7, a double-axis linear displacement stage 1 8 with a central threaded hole, a lower motor 9, a single crystal fiber 10, a double-axis linear displacement stage 2 11 with a central threaded hole, and an upper motor 12.

[0040] Among them, the laser 1, the conical lens group 2, the turning mirror 3, and the parabolic mirror 4 constitute a heating assembly. The laser emitted by the laser 1 is converted into a ring-shaped beam through the conical lens group 2, and the ring-shaped beam is focused on the top of the raw material rod 7 through the turning mirror 3 and the parabolic mirror 4, forming a local heating zone.

[0041] The double-axis linear displacement stage 1 8 with a central threaded hole and the lower motor 9 constitute a feeding assembly, the double-axis linear displacement stage 2 11 with a central threaded hole and the upper motor 12 constitute a pulling assembly, and the upper temperature maintaining structure 5 and the lower temperature maintaining structure 6 constitute a temperature gradient reducing assembly. The lower temperature maintaining structure 6 is fixedly connected to the double-axis linear displacement stage 1 8 with a central threaded hole, which is used to adjust the raw material rod 7 passing through the lower temperature maintaining structure to be on the same center line as the laser focal point. The lower motor 9 is used to drive the raw material rod 7 to feed in the vertical direction, so that the top of the raw material rod 7 reaches the laser focal point. The upper temperature maintaining structure 5 is fixedly connected to the double-axis linear displacement stage 2 11 with a central threaded hole, which is used to adjust the single crystal fiber 10 passing through the upper temperature maintaining structure 5 to be coaxial with the raw material rod 7. The upper motor 12 is used to drive the single crystal fiber 10 to pull in the vertical direction to realize the growth of the single crystal fiber 10.

[0042] The upper temperature maintaining structure 5 is used to reduce the temperature gradient of the single crystal fiber growth zone and limit its movement along the central axis. The lower temperature maintaining structure 6 is used to reduce the temperature gradient of the raw material rod heating zone and limit its movement along the central axis. The upper and lower temperature maintaining structures work together to reduce the axial and radial temperature gradients during the growth of the single crystal fiber, and keep the single crystal fiber growing at a uniform speed in the vertical direction.

[0043] AsFigure 2 As shown in FIG. 1, the upper heat preservation structure 5 and the lower heat preservation structure 6 are schematic diagrams, and the upper heat preservation structure is a coaxial three-layer hollow structure, which comprises, from inside to outside, an upper quartz glass tube 501, an upper zirconia cylinder 502, and an upper alumina cylinder 503. Figure 3 The single crystal optical fiber 10 passes through the upper quartz glass tube 501, the upper quartz glass tube 501 passes through the upper zirconia cylinder 502, and the upper zirconia cylinder 502 is placed in the upper alumina cylinder 503. The diameter of the single crystal optical fiber 10 is 0.1-0.5 mm, and the inner diameter of the upper quartz glass tube 501 is equal to the diameter of the single crystal optical fiber 10, so as to limit the movement of the single crystal optical fiber 10 along the central axis and prevent the single crystal optical fiber 10 from shaking during the pulling process. The inner surface of the upper quartz glass tube 501 is smooth, which can reduce the friction to maintain the uniform speed of the pulling of the optical fiber. The upper zirconia cylinder 502 and the upper alumina cylinder 503 effectively reduce the temperature gradient and prevent the single crystal optical fiber 10 from cracking due to rapid cooling.

[0044] The upper zirconia cylinder 502 comprises a cylinder I at the upper part and a cone I at the lower part, and the center of the upper zirconia cylinder 502 is provided with a through shaft hole I, the diameter of the shaft hole I is equal to the outer diameter of the upper quartz glass tube 501; the outer diameter of the cylinder I of the upper zirconia cylinder 502 and the diameter of the bottom surface of the cone I are equal, and are selected from 6-10 mm.

[0045] The upper alumina cylinder 503 comprises a stud II at the upper part, a cylinder II at the middle part, and a cone II at the lower end, and the center of the upper alumina cylinder 503 is provided with a through shaft hole II, which is a three-section hole with variable diameters, comprising an upper section cylinder hole, a middle section cone hole, and a lower end cylinder hole; the upper section cylinder hole is located in the stud II and the cylinder II, and the diameter of the upper section cylinder hole is equal to the outer diameter of the cylinder I of the upper zirconia cylinder 502; the middle section cone hole is located in the cone II and matches the cone I of the upper zirconia cylinder 502, and the diameter of the middle section cone hole is equal to the outer diameter of the cone I of the upper zirconia cylinder 502; the lower end cylinder hole is located in the cone II and matches the upper quartz glass tube 501, and the diameter of the lower end cylinder hole is equal to the outer diameter of the upper quartz glass tube 501. The outer diameter of the cylinder II at the middle part of the upper alumina cylinder 503 and the diameter of the bottom surface of the cone II are equal, and are selected from 8-12 mm; the length of the cylinder II at the middle part of the upper alumina cylinder 503 is selected from 100-200 mm, and the height of the cone II is designed according to the focusing path of the annular laser beam to avoid the blocking of the light beam; the size of the stud II matches the central threaded hole of the double-axis linear displacement stage II 11 with a central threaded hole, so as to fix the upper heat preservation structure 5.

[0046] The top of the first cylinder of the upper zirconia cylinder 502 is 5-10 mm higher than the top of the second cylinder of the upper alumina cylinder 503, so as to facilitate the embedding and taking out of the upper alumina cylinder 503 by the upper zirconia cylinder 502; the ratio of the height of the first cone of the upper zirconia cylinder 502 to the height of the second cone of the upper alumina cylinder 503 is equal to the ratio of the diameters of the bottom surfaces of the two, so as to ensure that the first cone of the upper zirconia cylinder 502 is tightly fitted with the second cone of the upper alumina cylinder 503 without falling off. The bottom end of the upper quartz glass tube 501 is flush with the top of the second cone of the upper alumina cylinder 503, and the top end of the upper quartz glass tube 501 is 5-10 mm higher than the top of the first cylinder of the upper zirconia cylinder 502, so as to facilitate the embedding and taking out of the upper zirconia cylinder 502 by the upper quartz glass tube 501.

[0047] As shown in Figure 4 , the lower heat preservation structure 6 is also a coaxial three-layer hollow structure, which comprises, from inside to outside, a lower quartz glass tube 601, a lower zirconia cylinder 602 and a lower alumina cylinder 603. The raw material rod 7 passes through the lower quartz glass tube 601, the lower quartz glass tube 601 is placed in the lower zirconia cylinder 602, and the lower zirconia cylinder 602 is placed in the lower alumina cylinder 603.

[0048] The inner surface of the lower quartz glass tube 601 is smooth, which can reduce friction and maintain uniform feeding of the raw material rod 7; the lower zirconia cylinder 602 and the lower alumina cylinder 603 effectively reduce the temperature gradient and prevent the raw material rod 7 from cracking due to rapid cooling.

[0049] As shown in Figure 4 , the lower zirconia cylinder 602 is a cylindrical shell with an axial hole at the bottom, and the inner diameter of the cylindrical shell is equal to the outer diameter of the lower quartz glass tube 601, which is selected from 6-10 mm; the bottom thickness of the cylindrical shell of the lower zirconia cylinder 602 is selected from 3-5 mm, and the diameter of the axial hole at the bottom of the cylindrical shell of the lower zirconia cylinder 602 is between the inner diameter and the outer diameter of the lower quartz glass tube 601. Such size design can not only ensure that the lower quartz glass tube 601 does not fall off, but also leave a gap between the raw material rod 7 and the wall surface of the axial hole at the bottom of the zirconia cylinder, so that the raw material rod does not contact the zirconia heat preservation, thereby reducing the friction during feeding and reducing the pollution of the raw material.

[0050] The lower alumina cylinder 603 comprises a cylindrical shell and a threaded stud with an axial hole, the inner diameter of the cylindrical shell of the lower alumina cylinder 603 is equal to the outer diameter of the lower zirconia cylinder 602, and is selected from 8-12 mm; the length of the cylindrical shell of the lower alumina cylinder 603 is selected from 100-200 mm, and the height of the threaded stud is 3-5 mm; the diameter of the axial hole of the lower alumina cylinder 603 is greater than the diameter of the bottom axial hole of the lower zirconia cylinder 602 and less than the outer diameter of the lower zirconia cylinder 602; such a size design ensures that the lower zirconia cylinder 602 does not slide off, and at the same time, the gap between the raw material rod 7 and the axial hole wall of the lower alumina cylinder 603 ensures that the raw material rod 7 is not in contact with the lower alumina cylinder 603 during heat preservation, reduces the frictional force during feeding, and reduces the pollution of the raw material; in addition, the gap also facilitates the removal of the lower zirconia cylinder 602 from the lower alumina cylinder 603. The size of the threaded stud of the lower alumina cylinder 603 matches the threaded hole of the double-axle linear displacement table 8 with a threaded hole in the center. The bottom end of the lower quartz glass tube 601 coincides with the inner bottom of the lower zirconia cylinder 602, and the outer bottom of the lower zirconia cylinder 602 coincides with the inner bottom of the lower alumina cylinder 603.

[0051] The raw material rod 7 passes through the lower quartz glass tube 601 in the lower heat preservation structure 6, and has a diameter of 0.5-2 mm; the inner diameter of the lower quartz glass tube 601 is equal to the diameter of the raw material rod 7, so as to limit the movement of the raw material rod 7 along the central axis and prevent the raw material rod 7 from shaking during feeding; the inner surface of the lower quartz glass tube 601 is smooth, which can reduce friction and maintain a uniform feeding speed.

[0052] During the growth of the single crystal optical fiber, the raw material rod 7, the single crystal optical fiber 10 and the upper and lower heat preservation structures are coaxially arranged.

[0053] The zirconia and alumina used in the upper heat preservation structure 5 and the lower heat preservation structure 6 both have the characteristics of low thermal conductivity and high melting point, and the thermal conductivity of the zirconia is lower than that of the alumina, and the melting point of the zirconia is higher than that of the alumina. The zirconia cylinder is adjacent to the quartz glass tube, and the alumina cylinder is adjacent to the zirconia cylinder, so as to effectively reduce the temperature gradient and prevent the cracking of the optical fiber caused by rapid cooling.

[0054] Another embodiment of the present application provides a method for reducing the temperature gradient of the growth of a single crystal optical fiber, which is realized based on the device for reducing the temperature gradient of the growth of a single crystal optical fiber in the above embodiment, and specifically comprises the following steps:

[0055] Step one: installing the lower heat preservation structure 6: sequentially coaxially installing the lower alumina cylinder 603, the lower zirconia cylinder 602 and the lower quartz glass tube 601, and making the top of the lower alumina cylinder 603 be located 3 mm below the laser focal point, and fixing the threaded stud of the lower alumina cylinder 603 in the threaded hole of the double-axle linear displacement table 8 with a threaded hole in the center through threaded connection;

[0056] Step two: adjusting the position of the raw material rod: making the raw material rod 7 pass through the lower heat preservation structure 6, and making the top of the raw material rod 7 be located at the laser focal point;

[0057] Step three: install the upper heat preservation structure 5: install the upper alumina cylinder 503, the upper zirconia cylinder 502 and the upper quartz glass tube 501 coaxially in sequence, so that the conical top of the upper alumina cylinder 503 is located 3mm above the top of the raw material rod 7, and the upper alumina cylinder 503 is fixed to the double-axis linear displacement table two 11 with a threaded hole by screwing;

[0058] Step four: adjust the position of the single crystal optical fiber 10 so that it passes through the upper heat preservation structure 5 and the bottom end is 1mm different from the top of the raw material rod 7;

[0059] Step five: turn on the laser 1, and focus the laser on the top of the raw material rod 7 to form a hemispherical molten zone;

[0060] Step six: control the upper motor 12 to drive the single crystal optical fiber 10 to move downward and make it contact with the hemispherical molten zone;

[0061] Step seven: control the upper motor 12 to uniformly pull up the single crystal optical fiber 10, and control the lower motor 9 to uniformly feed the raw material rod 7 upward, so as to realize the continuous growth of the single crystal optical fiber.

[0062] Those skilled in the art can understand that the above description is only a preferred example of the application and is not used to limit the application, although the application has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions recorded in the foregoing examples or make equivalent replacement for part of the technical features. Any modification, equivalent replacement, etc. within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. An apparatus for reducing the temperature gradient of a single crystal fiber growth, comprising: Includes heating components, feeding components, lifting components, and temperature gradient reduction components; The heating assembly includes a laser, a conical lens group, a steering mirror, and a parabolic reflector. The laser is used to emit laser light; the conical lens group is used to convert the laser light into a ring beam; and the steering mirror and parabolic reflector are used to focus the ring beam onto the top of the raw material bar to form a localized heating zone. The feeding assembly includes a biaxial linear displacement stage with a central threaded hole and a lower motor; the lifting assembly includes a biaxial linear displacement stage with a central threaded hole and an upper motor; the temperature gradient reduction assembly includes an upper insulation structure and a lower insulation structure. The lower insulation structure is fixedly connected to the biaxial linear displacement stage with a central threaded hole. The biaxial linear displacement stage with a central threaded hole is used to adjust the raw material bar passing through the lower insulation structure to be on the same center line as the laser focusing point. The lower motor is used to drive the raw material bar to feed vertically so that the top of the raw material bar reaches the laser focusing point. The upper insulation structure is fixedly connected to the second biaxial linear displacement stage with a central threaded hole. The second biaxial linear displacement stage with a central threaded hole is used to adjust the single crystal optical fiber passing through the upper insulation structure to be coaxial with the raw material rod. The upper motor is used to drive the single crystal optical fiber to be pulled vertically to achieve the growth of the single crystal optical fiber. The upper insulation structure is used to reduce the temperature gradient in the growth region of the single crystal fiber and restrict the movement of the single crystal fiber along the central axis. The lower insulation structure is used to reduce the temperature gradient in the heating region of the raw material rod and restrict the movement of the raw material rod along the central axis. The upper and lower insulation structures work together to reduce the axial and radial temperature gradients during the growth process of the single crystal fiber and maintain the single crystal fiber growing at a uniform speed in the vertical direction.

2. The apparatus for reducing the temperature gradient during single-crystal fiber growth according to claim 1, characterized in that, The upper insulation structure is a three-layer hollow structure coaxially assembled, consisting of an upper quartz glass tube, an upper zirconium oxide tube, and an upper alumina tube from the inside out. The inner diameter of the upper quartz glass tube is equal to the diameter of the single-crystal optical fiber passing through it; The upper zirconia tube is composed of a cylinder at the top and a cone at the bottom. A through shaft hole is provided in the center of the upper zirconia tube. The diameter of the shaft hole is equal to the outer diameter of the upper quartz glass tube. The outer diameter of the cylinder and the bottom diameter of the cone are equal. The upper alumina cylinder includes an upper stud, a middle cylinder, and a lower cone. A through-hole is formed at the center of the upper alumina cylinder. This through-hole is a three-section hole with varying diameters, consisting of an upper cylindrical hole, a middle conical hole, and a lower cylindrical hole. The upper cylindrical hole is located within the stud and cylinder, and its diameter is equal to the outer diameter of the cylinder of the upper zirconia cylinder. The middle conical hole is located within the cone and matches the cone of the upper zirconia cylinder, and its diameter is equal to the outer diameter of the cone. The lower cylindrical hole is located within the cone and matches the upper quartz glass tube, and its diameter is equal to the outer diameter of the upper quartz glass tube. The outer diameter of the cylinder in the middle of the upper alumina cylinder is equal to the bottom diameter of the cone.

3. The apparatus for reducing the temperature gradient during single-crystal fiber growth according to claim 2, characterized in that, The outer diameter of the cylinder and the bottom diameter of the cone of the upper zirconia tube are both selected from 6 to 10 mm.

4. The apparatus for reducing the temperature gradient during single-crystal fiber growth according to claim 2, characterized in that, The length of the second cylinder in the middle of the upper alumina cylinder is selected from 100 to 200 mm, and the height of the second cone is designed according to the focusing path of the annular laser beam to avoid beam obstruction.

5. The apparatus for reducing the temperature gradient during single-crystal fiber growth according to claim 2, characterized in that, The ratio of the height of the first cone of the upper zirconia tube to the height of the second cone of the upper alumina tube is equal to the ratio of their bottom diameters. The bottom end of the upper quartz glass tube is flush with the top of the second cone of the upper alumina tube.

6. The apparatus for reducing the temperature gradient during single-crystal fiber growth according to claim 2, characterized in that, The lower insulation structure is a coaxial three-layer hollow structure, consisting of a lower quartz glass tube, a lower zirconium oxide tube, and a lower alumina tube from the inside out. The inner diameter of the lower quartz glass tube is equal to the diameter of the raw material rod passing through it; The lower zirconia cylinder is a cylindrical shell with a shaft hole at the bottom, and the inner diameter of the cylindrical shell is equal to the outer diameter of the lower quartz glass tube; the diameter of the shaft hole at the bottom of the cylindrical shell of the lower zirconia cylinder is between the inner diameter and the outer diameter of the lower quartz glass tube. The lower alumina cylinder includes a cylindrical shell and a stud with a shaft hole. The inner diameter of the cylindrical shell of the lower alumina cylinder is equal to the outer diameter of the lower zirconia cylinder. The diameter of the shaft hole of the lower alumina cylinder is larger than the diameter of the bottom shaft hole of the lower zirconia cylinder and smaller than the outer diameter of the lower zirconia cylinder. The bottom end of the lower quartz glass tube coincides with the inner bottom of the lower zirconia cylinder, and the outer bottom of the lower zirconia cylinder coincides with the inner bottom of the lower alumina cylinder.

7. The apparatus for reducing the temperature gradient during single-crystal fiber growth according to claim 6, characterized in that, The inner diameter of the cylindrical shell of the lower zirconia cylinder and the outer diameter of the lower quartz glass tube are both selected from 6 to 10 mm; the bottom thickness of the cylindrical shell of the lower zirconia cylinder is selected from 3 to 5 mm. The inner diameter of the cylindrical shell of the lower alumina cylinder and the outer diameter of the lower zirconia cylinder are both selected from 8 to 12 mm; The length of the cylindrical shell of the lower alumina cylinder is selected from 100 to 200 mm, and the stud height of the lower alumina cylinder is 3 to 5 mm.

8. The apparatus for reducing the temperature gradient during single-crystal fiber growth according to claim 7, characterized in that, The top of the cylinder of the upper zirconia tube is 5-10 mm higher than the top of the stud of the upper alumina tube, so as to facilitate the insertion and removal of the upper zirconia tube from the upper alumina tube. The top of the upper quartz glass tube extends 5-10 mm above the top of the upper zirconia cylinder to facilitate the insertion and removal of the upper quartz glass tube from the upper zirconia cylinder.

9. The apparatus for reducing the temperature gradient during single-crystal fiber growth according to claim 2, characterized in that, The size of the stud of the upper alumina cylinder is matched with the central threaded hole of the biaxial linear displacement stage II with a central threaded hole to fix the upper insulation structure; the size of the stud of the lower alumina cylinder is matched with the threaded hole of the biaxial linear displacement stage I with a central threaded hole to fix the lower insulation structure.

10. A method for reducing the temperature gradient during the growth of a single-crystal optical fiber, characterized in that, This method is implemented based on the device for reducing the temperature gradient during single-crystal fiber growth as described in claim 1, and includes the following steps: Step 1: Adjust the lower insulation structure so that the top of the lower alumina cylinder is located at a first preset distance below the laser focal point generated by the heating component; The raw material rod is passed through the lower insulation structure, and the top of the raw material rod is positioned at the laser focusing point; Step 2: Adjust the upper insulation structure so that the top of the cone of the upper alumina cylinder is located at a second preset distance above the top of the raw material rod; allow the single-crystal optical fiber to pass through the upper insulation structure, and the bottom end of the single-crystal optical fiber is at a third preset distance from the top of the raw material rod; Step 3: Turn on the laser and focus it on the top of the raw material bar to form a hemispherical melting zone; Step 4: Control the upper motor to drive the single-crystal optical fiber downwards so that it contacts the hemispherical molten zone; Step 5: Control the upper motor to pull the single-crystal optical fiber upward at a uniform speed, and control the lower motor to feed the raw material rod upward at a uniform speed, so as to realize the continuous growth of the single-crystal optical fiber.

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