Apparatus and method for regulating temperature gradient of single crystal fiber growth

Abstract

This invention discloses a device and method for controlling the temperature gradient during single-crystal fiber growth, belonging to the field of crystal growth equipment technology. It includes a beam generation unit, a heating beam unit, a multi-stage post-heating beam unit, a multi-stage parabolic mirror, a raw material rod feeding roller device, a fiber lifting roller device, an infrared thermometer, and a control system. The multi-stage parabolic mirror includes an outermost parabolic mirror and several stages of inner parabolic mirrors, used to form the crystal growth melting zone and the post-heating zone, respectively. The position of the post-heating zone is adjusted by regulating the aperture and focal position of each stage of the inner parabolic mirrors. The temperature of the post-heating zone is adjusted by regulating the ratio of post-heating power to heating power through adjusting the reflectivity of the beam splitter. The post-heating gradient is set by adjusting the number of stages of the inner parabolic mirrors. This invention, employing the above-mentioned device and method for controlling the temperature gradient during single-crystal fiber growth, can regulate the temperature gradient while ensuring high-quality crystal growth.

Description

Technical Field

[0001] This invention relates to the technical field of crystal growth equipment, and in particular to a device and method for controlling the temperature gradient during the growth of single-crystal optical fibers. Background Technology

[0002] Single-crystal optical fiber, also known as crystal fiber, is a type of "quasi-one-dimensional" functional crystal material. Unlike traditional glass optical fiber, single-crystal optical fiber retains the structural advantages of the large aspect ratio of traditional optical fibers while also possessing the excellent physical and chemical properties of crystal materials, exhibiting higher melting points, higher thermal conductivity, higher mechanical strength, and stronger environmental adaptability. Single-crystal optical fiber has a wide range of applications, covering defense and civilian fields such as temperature, pressure, and stress sensing, radiation environment sensing, high-energy fiber lasers, chemical detection, medical imaging, and electromagnetic wave environment sensing. In recent years, as a core component and key new material for extreme harsh environments and fiber lasers, single-crystal optical fiber has gradually become one of the world's cutting-edge technologies.

[0003] Laser-Heated Pedestal Growth technique (LHPG) is a single-crystal growth technique developed based on the traditional optical floating zone method. It employs a ring-shaped... Laser heating of the growth bar forms a molten zone, and the diameter of the single-crystal fiber is controlled by adjusting the seed crystal pulling speed and the growth bar feed speed, thus achieving controllable fabrication of single-crystal fibers. This technology features high heating temperature, low raw material consumption, fast growth rate, and crucible-free growth, making it the primary method for fabricating ultra-fine single-crystal fibers with diameters in the tens of micrometers. However, because traditional LHPG technology lacks post-heating and insulation devices, the raw material, crystal, and molten zone are directly exposed to the atmosphere, resulting in an extremely high temperature gradient at the crystal growth interface, reaching [amount missing]. The temperature gradient can reach ℃ / cm, leading to excessive internal stress in the crystal. This makes the crystal prone to defects such as dissociation and cracking, significantly reducing crystal quality. Traditional solutions involve reducing the crystal growth rate or diameter to alleviate internal stress concentration and inhibit cracking to some extent. However, this does not fundamentally control the temperature gradient and only slightly improves crystal quality. Summary of the Invention

[0004] The purpose of this invention is to provide a device and method for regulating the temperature gradient during the growth of single-crystal optical fibers, which can adjust the temperature gradient while ensuring high-quality crystal growth.

[0005] To achieve the above objectives, the present invention provides a device for controlling the temperature gradient of single-crystal fiber growth, comprising a beam generation unit, a heating beam unit, a multi-stage post-heating beam unit, a multi-stage parabolic mirror, a raw material rod feeding roller device, an fiber lifting roller device, an infrared thermometer, and a control system. A beam generation unit is used to generate heated beams and multi-stage post-heated beams; The heating beam unit is used to receive the heating beam, generate a ring-shaped heating beam, and reflect the ring-shaped heating beam to the multi-stage parabolic mirror. The multi-stage post-thermal beam unit is used to receive the multi-stage post-thermal beam and generate a multi-stage annular post-thermal beam, and reflect the multi-stage annular post-thermal beam to the multi-stage parabolic mirror. Multi-stage parabolic mirrors are used to converge the annular heating beam and the multi-stage annular back-heating beam, forming the crystal growth melting zone and the back-heating zone, respectively. The raw material rod feeding roller device is used to stably feed the single crystal fiber growth raw material rod to the appropriate position; Fiber optic pulling roller device, used to stabilize the pulling of single-crystal fiber growth products; The control system is connected to the beam generating unit and the infrared thermometer respectively, and controls the beam power according to the temperature test results of the infrared thermometer.

[0006] Preferably, the beam generating unit includes Lasers, beam expanders, and multi-stage beam splitters; The Lasers are used to generate laser; The beam expander is disposed in the Laser generation One side of the laser is used for beam expansion. laser; The multi-stage beam splitter is specifically configured with several stages, wherein the first-stage beam splitter is used to split the expanded beam... The laser beam is split into a heating beam and a post-heated beam. The heating beam is injected into the heating beam unit, and the post-heated beam is split into multiple post-heated beams by a subsequent multi-stage beam splitter and injected into the multi-stage post-heated beam unit.

[0007] Preferably, the heating beam unit includes a heating beam conical mirror group and a heating beam plane mirror arranged sequentially along the optical path; The heating beam conical mirror group is used to receive the heating beam and generate a ring-shaped heating beam. The heated beam plane mirror is used to receive the annular heated beam and reflect it to the multi-stage parabolic mirror.

[0008] Preferably, the multi-level post-thermal beam unit is specifically set to several levels, and each level of the post-thermal beam unit includes a conical mirror group and a plane mirror arranged sequentially along the optical path of the corresponding level. The various levels of conical mirror groups are used to receive the corresponding level of back-heated beam and generate the corresponding level of annular back-heated beam. The plane mirrors at each level are used to receive the corresponding level of annular back-heated beam and reflect it to the multi-level parabolic mirror.

[0009] Preferably, the multi-stage parabolic mirror includes an outermost parabolic mirror with a larger aperture and several stages of inner parabolic mirrors with smaller apertures, wherein the stages of the inner parabolic mirrors correspond to the stages of the multi-stage rear hot beam unit. The outermost parabolic mirror is used to converge the annular heating beam as a heat source to form a crystal growth melting zone. The several levels of inner parabolic mirrors are used to converge multi-level annular back-heated beams to form multi-position gradient back-heated zones, the temperature of which is 100-2000℃.

[0010] Preferably, each stage of the multi-stage parabolic mirror is centrally symmetrical, and each focal point is on the central axis of the parabolic mirror. The focal point of the outermost parabolic mirror is located lower, and the focal point of the innermost parabolic mirror is located higher. The central axis coincides with the central axis of the reflected light path and the crystal growth direction.

[0011] Preferably, the substrate material of the multi-stage parabolic mirror is copper, aluminum, silicon, stainless steel, or aluminum alloy.

[0012] Preferably, the aperture of the multi-stage parabolic mirror is 20-200 mm, the radius of curvature is 10-200 mm, and the distance between the focal point of the multi-stage parabolic mirror and the bottom surface of the multi-stage parabolic mirror is 5-100 mm.

[0013] A method for controlling the temperature gradient during the growth of single-crystal optical fibers includes the following steps: S1. Install multi-stage parabolic mirrors, adjust the reflection ratio of each stage beam splitter so that the heating beam and the post-heating beam of each stage converge onto each stage parabolic mirror. Use thermal paper to determine the focal point position of each stage, and select a parabolic mirror with a specific aperture and focal length for auxiliary heating according to the required heating area. S2. Install the seed crystal and single-crystal fiber growth material rod required for crystal growth; S3. Close the furnace of the laser heating base equipment, introduce the growth atmosphere, move the seed crystal and the single crystal fiber growth material rod horizontally to make them coaxial with the focal point, and move the single crystal fiber growth material rod to the focal point of the heating light source to prepare for crystal growth. S4, Turn on Laser, converged by the outermost parabolic mirror The laser heating beam forms a hemispherical melting zone at the top of the single-crystal fiber growth rod, which is then converged by multiple levels of inner parabolic mirrors. The multi-stage post-thermal beam of the laser forms a post-thermal temperature field above the molten zone; S5. After the temperature field stabilizes, the seed crystal is lowered and combined with the melt of the single crystal fiber growth material rod to form a solid-liquid interface. S6. After the solid-liquid interface stabilizes, proceed with the growth of single-crystal optical fibers.

[0014] Preferably, the position of the rear hot zone is adjusted by adjusting the aperture and focal position of the inner parabolic mirrors at each stage; the temperature of the rear hot zone is adjusted by adjusting the reflectivity of the beam splitters at each stage to adjust the ratio between the rear hot power and the heating power at each stage; and the rear hot gradient is set by adjusting the number of stages of the inner parabolic mirrors.

[0015] Therefore, the present invention, employing the above-described device and method for controlling the growth temperature gradient of single-crystal optical fibers, has the following advantages: (1) In this invention, a multi-stage laser optical path with a heating beam and a multi-stage post-heating beam is set up, and a multi-stage parabolic mirror is used to achieve controlled heating of the upper region of the solid-liquid interface while heating the molten zone. The device has a high degree of integration and uses a single laser light source and a single integrated parabolic mirror to achieve coupling between the molten zone and the post-heating zone.

[0016] (2) In this invention, the heating beam and the laser path of each stage of the post-heated beam do not interfere with each other. The position of the post-heated zone can be controlled by adjusting the aperture and focal position of the parabolic mirror. Furthermore, the power of the post-heated zone can be adjusted by adjusting the reflectivity of the beam splitter. This allows for temperature gradient adjustment while ensuring high-quality crystal growth.

[0017] (3) In this invention, a multi-level parabolic mirror is designed to realize the design of complex temperature fields and meet the fabrication requirements of multi-system and multi-size single crystal optical fibers.

[0018] (4) In this invention, temperature gradient adjustment can be achieved simply by replacing parabolic mirrors with different apertures and focal positions, or by adjusting the reflectivity of each level of beam splitter. The parts are easy to process, have low requirements for the surrounding environment, and are easy to repair and replace.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a device for regulating the temperature gradient during the growth of single-crystal optical fibers according to the present invention. Figure 2 The high-quality novel [material] obtained in Example 1 of this invention (TSAG) Single-crystal fiber photograph; Figure 3 This is a photograph of the cracked TSAG single-crystal fiber grown in Comparative Example 1 of this invention. Figure label: 1, 1. Laser; 2. Beam expander; 3. First-stage beam splitter; 4. Second-stage beam splitter; 5. Heated beam conical mirror group; 6. Heated beam plane mirror; 7. First-stage conical mirror group; 8. First-stage plane mirror; 9. Outermost parabolic mirror; 10. First-stage inner parabolic mirror; 11. Raw material rod feeding roller device; 12. Fiber lifting roller device; 13. Single crystal fiber growth raw material rod; 14. Single crystal fiber growth finished product; 15. Crystal growth melting zone; 16. Back heating zone; 17. Infrared thermometer. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Specific model specifications need to be selected and determined according to the actual specifications of the device, etc. The specific selection calculation method adopts existing technology in the art, and therefore will not be described in detail.

[0022] Example 1 like Figure 1 As shown, the present invention provides a device for regulating the temperature gradient of single-crystal fiber growth, including a beam generation unit, a heating beam unit, a multi-stage post-heating beam unit, a multi-stage parabolic mirror, a raw material rod feeding roller device 11, an optical fiber lifting roller device 12, an infrared thermometer 17, and a control system. In this embodiment, a single-stage rear thermal beam is used, and the level of the multi-stage rear thermal beam unit is specifically set to single-stage. The level of the inner parabolic mirror of the multi-stage parabolic mirror is also set to single-stage accordingly. The beam generating unit includes Laser 1, beam expander 2, first-stage beam splitter 3 with 10% reflectivity, and second-stage beam splitter 4 with 100% reflectivity. Laser 1 is used to generate Laser, beam expander 2 is set Laser 1 generates One side of the laser is used for beam expansion. Laser, first-order beam splitter 3 is used to expand the beam The laser is split into a heating beam and a post-heating beam. The heating beam enters the heating beam unit, and the post-heating beam enters the second-stage beam splitter 4. The second-stage beam splitter 4 is used to receive the post-heating beam and reflect the first-stage post-heating beam to the first-stage post-heating beam unit. The heating beam unit includes a heating beam conical mirror group 5 and a heating beam plane mirror 6 arranged sequentially along the optical path. The heating beam conical mirror group 5 is used to receive the heating beam and generate a ring-shaped heating beam, and the heating beam plane mirror 6 is used to receive the ring-shaped heating beam and reflect it to a multi-stage parabolic mirror. The first-stage post-thermal beam unit includes a first-stage conical mirror group 7 and a first-stage plane mirror 8 arranged sequentially along the optical path. The first-stage conical mirror group 7 is used to receive the first-stage post-thermal beam and generate a first-stage annular post-thermal beam. The first-stage plane mirror 8 is used to receive the first-stage annular post-thermal beam and reflect it to the multi-stage parabolic mirror. The aperture of the multi-stage parabolic mirror is 20-200 mm, the radius of curvature is 10-200 mm, and the distance between the focal point and the bottom surface of the multi-stage parabolic mirror is 5-100 mm. The base material of the multi-stage parabolic mirror is copper, aluminum, silicon, stainless steel or aluminum alloy. A multi-stage parabolic mirror is obtained by mechanically integrating multiple parabolic mirrors with different apertures and focal positions into a single reflector. In this embodiment, the multi-stage parabolic mirror includes an outermost parabolic mirror 9 with a larger aperture and a first-stage inner parabolic mirror 10 with a smaller aperture. The outermost parabolic mirror 9 is used to converge a ring-shaped heating beam as a heat source to form a crystal growth melting zone 15. The first-stage inner parabolic mirror 10 is used to converge a first-stage ring-shaped back heating beam to form a multi-position gradient back heating zone 16. The outermost parabolic mirror 9 has a diameter of 100 mm and a radius of curvature of 75 mm, with its focal point 50 mm from the bottom surface of the multi-stage parabolic mirror. The first-stage inner parabolic mirror 10 has a diameter of 50 mm and a radius of curvature of 68 mm, with its focal point 45 mm from the bottom surface of the multi-stage parabolic mirror. Both the outermost parabolic mirror 9 and the first-stage inner parabolic mirror 10 are centrally symmetrical, and each focal point is on the central axis of the parabolic mirror. The focal point of the outermost parabolic mirror 9 is located lower, and the focal point of the first-stage inner parabolic mirror 10 is located higher. Furthermore, the central axis of the mirror coincides with the central axis of the reflected light path and the crystal growth direction. The raw material rod feeding roller device 11 is used to stably feed the single crystal optical fiber growth raw material rod 13 to the appropriate position. Fiber pulling roller device 12 is used to stably pull the grown fiber; The control system is connected to the beam generating unit and the infrared thermometer 17 respectively, and controls the beam temperature according to the temperature test results of the infrared thermometer 17.

[0023] A method for controlling the temperature gradient during the growth of single-crystal optical fibers includes the following steps: S1. Install multi-stage parabolic mirrors, adjust the reflection ratio of the first-stage beam splitter to make the heating beam and the post-heating beams of each stage converge onto the parabolic mirrors of each stage, use thermal paper to determine the focal position of each stage, and select a parabolic mirror with a specific aperture and focal length for auxiliary heating according to the required heating area. S2. Install the seed crystal and single-crystal fiber growth material rod 13 required for crystal growth. Both the seed crystal and the single-crystal fiber growth material rod 13 are fixed on a three-dimensional displacement platform. The horizontal position can be adjusted to achieve coaxiality with the focal point of the parabolic mirror. In this embodiment, the single-crystal fiber growth material rod 13 is a sintered TSAG ceramic rod with a diameter of 3 mm, and the seed crystal is a YAG single crystal that also belongs to the garnet structure. S3. Close the furnace of the laser heating base equipment, introduce the growth atmosphere, and horizontally move the seed crystal and the single crystal fiber growth material rod 13 to make them coaxial with the focal point of the multi-stage parabolic mirror. Move the single crystal fiber growth material rod 13 to the focal point of the heating light source to prepare for crystal growth. S4, Turn on Laser 1 has a laser power of 25 watts. After being expanded by beam expander 2, the laser beam is split into a heating beam and a post-heating beam by a first-stage beam splitter 3 with a reflectivity of 10%. The heating beam passes through heating beam conical mirror group 5 and heating beam plane mirror 6 to form a ring-shaped heating beam with a diameter of 60 mm. The ring-shaped heating beam is converged by the outermost parabolic mirror 9 to the top of the single-crystal fiber growth rod 13 to form a hemispherical melting zone. At the same time, the post-heating beam passes through a second-stage beam splitter 4 with a reflectivity of 100%, a first-stage conical mirror group 7 and a first-stage plane mirror 8 to form a first-stage ring-shaped post-heating beam with a diameter of 30 mm. The ring-shaped post-heating beam is converged by the inner first-stage parabolic mirror 10 to form a post-heating zone 16 5 mm above the focal point of the outermost parabolic mirror 9 to reduce the temperature gradient. The temperature of the post-heating zone 16 is measured to be 1200℃ by infrared thermometer 17. S5. After the temperature field stabilizes, YAG single crystal, which also belongs to the garnet structure, is used as seed crystal. The seed crystal is lowered and combined with the melt of single crystal fiber growth raw material rod 13 to form a solid-liquid interface. S6. After the solid-liquid interface stabilizes, set the lifting speed of the fiber lifting roller device 12 to 0.9 mm / min, lift the single crystal fiber to grow the finished product 14, and set the feeding speed of the raw material rod feeding roller device 11 to 0.1 mm / min. The diameter reduction ratio is 1:3 to grow TSAG single crystal fiber.

[0024] The position of the rear hot zone 16 is adjusted by adjusting the aperture and focal position of the first-stage inner parabolic mirror 10. The temperature of the rear hot zone 16 is adjusted by adjusting the reflectivity of the first-stage beam splitter 3 to adjust the ratio of rear thermal power to heating power. The rear thermal gradient is set by adjusting the number of stages of the inner parabolic mirror.

[0025] like Figure 2 As shown, TSAG single-crystal optical fiber was fabricated based on this scheme. The resulting TSAG single-crystal optical fiber has a uniform diameter, is transparent without cracks, and has high crystal quality.

[0026] Comparative Example 1 As shown in Example 1, but unlike Example 1, in Comparative Example 1... Laser 1 turned on The laser power was 22.5 watts, and the first-stage beam splitter 3 was removed, while other growth parameters remained the same.

[0027] like Figure 3 As shown, the crystal quality of TSAG single-crystal fiber without post-heating is poor, the stress concentration problem still exists, and obvious crystal cracking occurs.

[0028] Therefore, the present invention employs the above-mentioned device and method for regulating the temperature gradient of single-crystal fiber growth, which can regulate the temperature gradient while ensuring high-quality crystal growth. The design of the multi-stage parabolic mirror can meet the preparation requirements of multi-system and multi-size single-crystal fibers. The accessories are easy to process, have low requirements for the surrounding environment, and are easy to repair and replace.

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A device for regulating the temperature gradient during the growth of single-crystal optical fibers, characterized in that: It includes a beam generation unit, a heating beam unit, a multi-stage post-heating beam unit, a multi-stage parabolic mirror, a raw material bar feeding roller device, an optical fiber lifting roller device, an infrared thermometer, and a control system. A beam generation unit is used to generate heated beams and multi-stage post-heated beams; The heating beam unit is used to receive the heating beam, generate a ring-shaped heating beam, and reflect the ring-shaped heating beam to the multi-stage parabolic mirror. The multi-stage post-thermal beam unit is used to receive the multi-stage post-thermal beam and generate a multi-stage annular post-thermal beam, and reflect the multi-stage annular post-thermal beam to the multi-stage parabolic mirror. Multi-stage parabolic mirrors are used to converge the annular heating beam and the multi-stage annular back-heating beam, forming the crystal growth melting zone and the back-heating zone, respectively. The raw material rod feeding roller device is used to stably feed the single crystal fiber growth raw material rod to the appropriate position; Fiber optic pulling roller device, used to stabilize the pulling of single-crystal fiber growth products; The control system is connected to the beam generating unit and the infrared thermometer respectively, and controls the beam power according to the temperature test results of the infrared thermometer. The beam generating unit includes Lasers, beam expanders, and multi-stage beam splitters; The Lasers are used to generate laser; The beam expander is disposed in the Laser generation One side of the laser is used for beam expansion. laser; The multi-stage beam splitter is specifically configured with several stages, wherein the first-stage beam splitter is used to split the expanded beam... The laser beam is split into a heating beam and a post-heated beam. The heating beam is injected into the heating beam unit, and the post-heated beam is split into multiple post-heated beams by a subsequent multi-stage beam splitter and injected into the multi-stage post-heated beam unit. The heating beam unit includes a heating beam conical mirror group and a heating beam plane mirror arranged sequentially along the optical path; The heating beam conical mirror group is used to receive the heating beam and generate a ring-shaped heating beam. The heating beam plane mirror is used to receive the annular heating beam and reflect it to the multi-stage parabolic mirror; The multi-level post-thermal beam unit is specifically set to several levels, and each level of the post-thermal beam unit includes a conical mirror group and a plane mirror arranged sequentially along the optical path of the corresponding level. The various levels of conical mirror groups are used to receive the corresponding level of back-heated beam and generate the corresponding level of annular back-heated beam. The plane mirrors at each level are used to receive the corresponding level of annular back thermal beams and reflect them to the multi-level parabolic mirrors; The multi-stage parabolic mirror includes an outermost parabolic mirror with a larger aperture and several stages of inner parabolic mirrors with smaller apertures. The stages of the inner parabolic mirrors correspond to the stages of the multi-stage rear thermal beam unit. The outermost parabolic mirror is used to converge the annular heating beam as a heat source to form a crystal growth melting zone. The several levels of inner parabolic mirrors are used to converge the multi-level annular back-heat beam to form a multi-position gradient back-heat zone, the temperature of which is 100-2000℃. Each stage of the multi-stage parabolic mirror is centrally symmetrical, and each focal point is on the central axis of the parabolic mirror. The focal point of the outermost parabolic mirror is located lower, and the focal point of the innermost parabolic mirror is located higher. The central axis coincides with the central axis of the reflected light path and the crystal growth direction.

2. The device for regulating the temperature gradient of single-crystal fiber growth according to claim 1, characterized in that: The substrate material of the multi-stage parabolic mirror is copper, aluminum, silicon, stainless steel, or aluminum alloy.

3. The device for regulating the temperature gradient of single-crystal fiber growth according to claim 1, characterized in that: The multi-stage parabolic mirror has an aperture of 20-200 mm and a radius of curvature of 10-200 mm. The distance between the focal point of the multi-stage parabolic mirror and the bottom surface of the multi-stage parabolic mirror is 5-100 mm.

4. A method for controlling the temperature gradient during single-crystal fiber growth, using the apparatus for controlling the temperature gradient during single-crystal fiber growth as described in any one of claims 1-3, characterized in that: Includes the following steps: S1. Install multi-stage parabolic mirrors, adjust the reflection ratio of each stage beam splitter so that the heating beam and the post-heating beam of each stage converge onto each stage parabolic mirror. Use thermal paper to determine the focal point position of each stage, and select a parabolic mirror with a specific aperture and focal length for auxiliary heating according to the required heating area. S2. Install the seed crystal and single-crystal fiber growth material rod required for crystal growth; S3. Close the furnace of the laser heating base equipment, introduce the growth atmosphere, move the seed crystal and the single crystal fiber growth material rod horizontally to make them coaxial with the focal point, and move the single crystal fiber growth material rod to the focal point of the heating light source to prepare for crystal growth. S4, Turn on Laser, converged by the outermost parabolic mirror The laser heating beam forms a hemispherical melting zone at the top of the single-crystal fiber growth rod, which is then converged by multiple levels of inner parabolic mirrors. The multi-stage post-thermal beam of the laser forms a post-thermal temperature field above the molten zone; S5. After the temperature field stabilizes, the seed crystal is lowered and combined with the melt of the single crystal fiber growth material rod to form a solid-liquid interface. S6. After the solid-liquid interface stabilizes, proceed with the growth of single-crystal optical fibers.

5. The method for controlling the temperature gradient during single-crystal fiber growth according to claim 4, characterized in that: The position of the rear hot zone is adjusted by adjusting the aperture and focal position of the inner parabolic mirrors at each stage. The temperature of the rear hot zone is adjusted by adjusting the ratio between the rear thermal power and the heating power at each stage by adjusting the reflectivity of the beam splitters at each stage. The rear thermal gradient is set by adjusting the number of stages of the inner parabolic mirrors.

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