CN112593283A - Crucible for growing bendable flexible rare earth single crystal optical fiber and method for growing bendable flexible rare earth single crystal optical fiber by micro-pulling-down method - Google Patents

Crucible for growing bendable flexible rare earth single crystal optical fiber and method for growing bendable flexible rare earth single crystal optical fiber by micro-pulling-down method Download PDF

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CN112593283A
CN112593283A CN202011460099.5A CN202011460099A CN112593283A CN 112593283 A CN112593283 A CN 112593283A CN 202011460099 A CN202011460099 A CN 202011460099A CN 112593283 A CN112593283 A CN 112593283A
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single crystal
crucible
rare earth
optical fiber
growth
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薛冬峰
陈昆峰
潘婷钰
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Changchun Institute of Applied Chemistry of CAS
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Changchun Institute of Applied Chemistry of CAS
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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
    • C30B15/10—Crucibles or containers for supporting the melt
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
    • C30B15/08—Downward pulling
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/16—Oxides
    • C30B29/22—Complex oxides
    • C30B29/28—Complex oxides with formula A3Me5O12 wherein A is a rare earth metal and Me is Fe, Ga, Sc, Cr, Co or Al, e.g. garnets

Abstract

The invention provides a crucible for growing a bendable flexible rare earth single crystal optical fiber by a micro-pulling-down method, wherein the bottom of the crucible is communicated with a capillary tube through a tapered hole; the big hole of the conical hole is positioned at the bottom of the crucible, and the small hole of the conical hole is communicated with the capillary tube; the bottom of the crucible is an inclined plane; the rare earth single crystal comprises gadolinium gallium garnet single crystal or doped gadolinium gallium garnet single crystal. According to the crucible with the special structure, the inner wall of the crucible close to the opening at the bottom end and the capillary hole are connected by the tapered tube, so that the fluidity of the melt is guaranteed, and the controllable growth of the bendable single crystal optical fiber is realized. The invention also provides a method for calculating the growth rate of the rare earth single crystal optical fiber in the micro-pulling-down method, and the micro-pulling-down method growth of the bendable single crystal optical fiber is realized by utilizing the crucible matched temperature field structure and combining theoretical calculation, so that the high-quality flexible single crystal optical fiber is finally obtained.

Description

Crucible for growing bendable flexible rare earth single crystal optical fiber and method for growing bendable flexible rare earth single crystal optical fiber by micro-pulling-down method
Technical Field
The invention belongs to the technical field of rare earth single crystal materials, and particularly relates to a crucible for growing a bendable flexible rare earth single crystal optical fiber by a micro-pulling-down method, a method for growing the bendable flexible rare earth single crystal optical fiber by the micro-pulling-down method, and a method for calculating the growth rate of the bendable flexible rare earth single crystal optical fiber in the micro-pulling-down method.
Background
In recent years, with the increasingly updated and rapid development of optical fiber technology, research and application of flexible optical fibers have become one of the important development directions of fiber optics development. The high-resolution flexible optical fiber image transmission bundle has been widely applied in the fields of medicine, industry, scientific research, military and aerospace as a core optical device in a high-resolution imaging instrument due to the advantages of good flexibility and bending performance, thin monofilament diameter, high resolution and the like. The flexible infrared optical fiber image transmission bundle is used as a transmission element and is connected with an infrared imaging detector, so that high-quality infrared image transmission can be realized, the weight of the system is greatly reduced, the volume of the system is reduced, the cost of the infrared system is obviously reduced, the performance of the system is improved, the flexible infrared optical fiber image transmission bundle can be used for detecting the heat distribution of objects in strong electromagnetic places, dangerous environments, narrow spaces or small holes, and the flexible infrared optical fiber image transmission bundle has very important application prospects in the fields of national defense, medical treatment, industrial detection and the like.
Due to the long-wave infrared multi-phonon absorption of the common oxide glass, the optical fiber image transmission beam can not be applied to the infrared band with the wavelength more than 2.5 mu m. In recent years, minimally invasive laser medicine through endoscopes requires corresponding flexible optical fibers. Most of the current laser transmission in the endoscope is quartz optical fiber because the quartz optical fiber can be safely applied to the human body. Nd with a wavelength of 1.06 μm was transmitted with a quartz fiber in a medical endoscope: YAG laser and Ho with wavelength of 2.1 μm: YAG lasers have been reported. But mid-infrared lasers with a wavelength of 2 μm have reached the transmission limit of quartz fibers. In the field of lighting, special glass manufacturers schottky latest lighting technology uses light pipes made of rigid and flexible glass fibers in combination with novel light sources. Because glass fibers have good flexibility, they can be easily embedded in a narrow space, and functional lighting and ambient lighting are integrated into an excellent overall solution.
As one of the important branches of rare earth materials, a rare earth crystal refers to a crystal in which rare earth elements can completely occupy a certain lattice point in a crystallographic structure, and a rare earth laser crystal is widely applied to the national key fields of optical fiber communication, national defense safety, civil health and the like. In various types of crystal materials, the single crystal optical fiber has the advantages of high length-diameter ratio and large specific surface area of the glass optical fiber and the performance of the crystal bulk material. When the material is used as a laser gain medium, the material is between a traditional bulk single crystal and a glass optical fiber, and combines the core concepts of single crystal gain and optical fiber laser, and the novel material not only has excellent optical and thermal properties of single crystal, but also has the advantage of high laser conversion efficiency of the glass optical fiber. Compared with the glass optical fiber with multi-phonon absorption, the rare earth doped single crystal optical fiber has the light-emitting waveband reaching the mid-infrared waveband of 3.0 mu m.
At present, there are two main international methods for growing single crystal optical fibers: laser susceptor heating methods and micro-pulldown methods. Doped YAG single crystals with the diameter of tens of microns can be grown by a laser pedestal heating method to be used as fiber cores, and cladding structures are synthesized by a direct drawing or post-processing mode to finally obtain the flexible bendable single crystal fiber with the cladding. However, the crystal quality is difficult to guarantee due to the excessive temperature gradient of the method at the growth interface. The defect of crystal quality caused by a laser pedestal method can be well made up by using a micro-pulling-down method to grow the single crystal fiber. However, since the minimum diameter of the single crystal optical fiber grown by the micro-pulling-down method is 1mm or more, the single crystal optical fiber of the quality is rigid.
Therefore, it is necessary to find a more convenient way to overcome the limitations of the existing growth technology, and to obtain high-quality flexible and bendable single crystal optical fiber has become one of the focuses of great attention of the leading researchers in the application field.
Disclosure of Invention
In view of the above, the technical problem to be solved by the present invention is to provide a crucible for growing a bendable flexible rare earth single crystal optical fiber by a micro-pulling-down method.
The invention provides a crucible for growing a bendable flexible rare earth single crystal optical fiber by a micro-pulling-down method, wherein the bottom of the crucible is communicated with a capillary tube through a tapered hole;
the big hole of the conical hole is positioned at the bottom of the crucible, and the small hole of the conical hole is communicated with the capillary tube;
the bottom of the crucible is an inclined plane;
the rare earth single crystal comprises gadolinium gallium garnet single crystal or doped gadolinium gallium garnet single crystal.
Preferably, the diameter of a large hole of the conical hole is 0.1-3 mm;
the diameter of the capillary tube is 0.1-0.95 mm;
the included angle between the conical bevel edge of the conical hole and the bottom of the crucible is 0-45 degrees;
and a circular chamfer is arranged at the joint of the conical bevel edge of the conical hole and the bottom of the crucible.
Preferably, the height of the tapered hole is 0.1-10 mm;
the number of the conical holes is 1;
the thickness of the bottom of the crucible is 0.5-1.5 mm;
the diameter of the crucible is 10-15 mm;
the height of the crucible is 25-50 mm.
Preferably, the material of the crucible preferably comprises one or more of Pt, Ir, Re, Mo and graphite;
the length of the capillary tube is 0.2-3 mm;
the appearance and parameters of the crucible are obtained by calculating the growth rate formula of the rare earth single crystal optical fiber;
the appearance of the crucible comprises one or more of appearance selection of the bottom of the crucible, whether a tapered hole is arranged in the crucible and whether a circular chamfer angle is arranged at the joint of a tapered bevel edge of the tapered hole and the bottom of the crucible;
the parameters of the crucible comprise one or more of the diameter of a large hole of the tapered hole, the diameter of the capillary tube, the included angle between the tapered bevel edge of the tapered hole and the bottom of the crucible, the height of the tapered hole and the length of the capillary tube.
Preferably, the diameter of the capillary is obtained by calculating the growth rate formula of the rare earth single crystal optical fiber;
the diameter of the large hole of the conical hole is obtained by calculating the growth rate formula of the rare earth single crystal optical fiber;
the included angle between the tapered bevel edge of the tapered hole and the bottom of the crucible is obtained by calculating the growth rate formula of the rare earth single crystal optical fiber;
the bottom of the crucible is selected by a growth rate formula of the rare earth single crystal optical fiber and is obtained by calculation;
and calculating the parameters of the crucible based on one or more of the viscosity, wettability and density of the rare earth single crystal.
Preferably, the growth rate formula of the rare earth single crystal optical fiber is shown as a formula (II);
Figure BDA0002831222380000031
wherein m is the mass of the rare earth single crystal in the crucible, r is the radius of a capillary hole at the bottom of the crucible, and r is1Is the physical distance from the center of the capillary to the wall of the tube, r2The distance from the center of the capillary to the boundary layer, l is the length of the capillary at the bottom end of the crucible, t is unit time, D is the diameter of the single crystal optical fiber, D is 0.1-0.95 mm, RfiberThe growth rate of the single crystal optical fiber with the diameter D;
(Ebond/Auvwduvw)radialis the chemical bonding energy density of the rare earth single crystal along the radial direction;
(Ebond/Auvwduvw)axialis the chemical bonding energy density of the rare earth single crystal along the axial direction.
Preferably, the formula (II) is obtained by:
a) obtaining the pressure difference delta P of the downward flowing of the rare earth single crystal melt by referring to the formula (1), and calculating to obtain the driving force F of the downward flowing of the material by referring to the formula (1');
Figure BDA0002831222380000041
F＝ΔP·S1 (1`)，
where F is the driving force for the downward flow of the melt in the capillary, Δ P is the pressure difference, S1Is the capillary end face area;
g is the gravity of the melt in the crucible, r is the radius of the capillary pores at the bottom of the crucible, (E)bond/Auvwduvw)axialIs the chemical bonding energy density of the rare earth single crystal along the axial direction;
deriving and obtaining the friction force f in the capillary at the bottom end of the crucible based on the formula (2), and referring to the formula (3);
Figure BDA0002831222380000042
Figure BDA0002831222380000043
wherein f is the internal friction of the capillary at the bottom end of the crucible, eta is the viscosity coefficient of the melt, and S2The area of the side surface of the capillary tube, r is the radius of the capillary hole at the bottom of the crucible, and dv/dr is the velocity gradient of the melt; t is unit time, (E)bond/Auvwduvw)radialThe chemical bonding energy density of the rare earth single crystal along the radial direction, and l is the length of a capillary at the bottom end of the crucible;
b) based on the fact that in a steady-state growth state, in the growth process of the micro-pulling-down single crystal optical fiber, the force in the capillary tube along the vertical direction is balanced, and the driving force of the downward flow of the melt in the capillary tube is equal to the internal friction force of the capillary tube at the bottom end of the crucible, according to the formula (4);
Figure BDA0002831222380000044
c) establishing a boundary condition, wherein r ═ r1，v＝0；r＝r2，v＝vporeCombining the formula (4) to obtain the downward flow rate of the melt in the capillary, and referring to the formula (5);
Figure BDA0002831222380000051
wherein r is1Is the physical distance from the center of the capillary to the wall of the tube, r2Distance from capillary center to boundary layer, vporeThe rate of melt flow down the capillary;
d) based on the rate of downward flow of the melt in the capillary obtained in the above steps, after the fluid flows out of the capillary and infiltrates the bottom end of the crucible, the fluid grows in the solid/liquid/solid interface region, and according to the conservation of mass, the growth rate R of the single crystal optical fiber with the diameter D is obtainedfiberAs shown in formula (II);
the specific steps of the derivation are as follows:
based on the tendency of the melt to heterogeneously nucleate within the capillary at the solid/liquid interface of the tube wall, formula (2') is obtained, and formula (2) is then combined to obtain formula (3);
Figure BDA0002831222380000052
wherein t is a unit time, (E)bond/Auvwduvw)radialIs the chemical bonding energy density of the rare earth single crystal along the radial direction.
The invention provides a method for growing a bendable flexible rare earth single crystal optical fiber by using a micro-pulling-down method, which comprises the following steps:
(1) calculating the growth rate of the rare earth single crystal optical fiber by using a growth rate formula of the rare earth single crystal optical fiber;
(2) designing and building a temperature field structure for growing the rare earth single crystal optical fiber according to the growth rate obtained in the step; designing the appearance and parameters of the crucible according to the growth rate obtained in the step;
(3) filling a crystal material into a crucible, setting growth parameters required by the growth of the rare earth single crystal according to the parameters and the growth rate in the growth rate calculation process of the rare earth single crystal optical fiber, and then heating;
(4) when the heating temperature is higher than the melting point of the rare earth single crystal, moving the seed crystal upwards to contact the bottom end of the crucible, forming a meniscus at the bottom of the crucible, and then growing according to the growth parameters set in the step to obtain the rare earth single crystal optical fiber;
the crucible is the crucible of any one of the above technical schemes.
Preferably, the growth rate of the rare earth single crystal optical fiber is 0.05-12 mm/min;
the diameter of the rare earth single crystal optical fiber is 0.1-0.95 mm;
in the temperature field structure, the centers of the heat insulating material, the seed crystal, the crucible and the rear heater are kept on the same straight line in the vertical direction;
the method also comprises the following steps before the growth is carried out according to the set growth parameters:
finely adjusting the temperature of the melt, and growing according to set growth parameters when the melt infiltrates the bottom end of the whole crucible and the side surface of the melt is not protruded outwards;
the fine adjustment range is 10-40 ℃ higher than the melting point of the rare earth single crystal;
the difference between the heating temperature and the melting point of the rare earth single crystal is more than 0 ℃ and less than or equal to 50 ℃.
The invention provides a method for calculating the growth rate of a bendable flexible rare earth single crystal optical fiber in a micro-pulling-down method, which comprises the following steps,
1) determining the thermodynamic growth form of the rare earth single crystal according to the chemical bonding theory of crystal growth;
2) determining a radial growth direction corresponding to the axial growth direction and an anisotropic chemical bonding structure at a growth interface based on the thermodynamic growth form of the rare earth single crystal obtained in the step;
3) calculating the anisotropic chemical bonding energy density of the rare earth single crystal along the axial direction and the anisotropic chemical bonding energy density of the rare earth single crystal along the radial direction based on the anisotropic chemical bonding structure at the growth interface obtained in the step (I);
Figure BDA0002831222380000061
wherein the content of the first and second substances,
Figure BDA0002831222380000062
is along [ uvw ]]A directionally grown chemical bonding energy;
Auvwfor growth of elementary edges [ uvw ]]The projected area of the direction;
duvwis a single crystal edge [ uvw ]]The step height of the direction;
4) calculating the growth rate of the rare earth single crystal fiber based on the isotropic chemical bonding energy density of the rare earth single crystal obtained in the step along the axial direction and the radial direction, wherein the growth rate is shown as a formula (II);
Figure BDA0002831222380000063
wherein m is the mass of the rare earth single crystal in the crucible, r is the radius of a capillary hole at the bottom of the crucible, and r is1Is the physical distance from the center of the capillary to the wall of the tube, r2The distance from the center of the capillary to the boundary layer, l is the length of the capillary at the bottom end of the crucible, t is unit time, D is the diameter of the single crystal optical fiber, D is 0.1-0.95 mm, RfiberThe growth rate of the single crystal optical fiber with the diameter D;
(Ebond/Auvwduvw)radialis the chemical bonding energy density of the rare earth single crystal along the radial direction;
(Ebond/Auvwduvw)axialis the chemical bonding energy density of the rare earth single crystal along the axial direction.
The invention provides a crucible for growing a bendable flexible rare earth single crystal optical fiber by a micro-pulling-down method, wherein the bottom of the crucible is communicated with a capillary tube through a tapered hole; the big hole of the conical hole is positioned at the bottom of the crucible, and the small hole of the conical hole is communicated with the capillary tube; the bottom of the crucible is an inclined plane; the rare earth single crystal comprises gadolinium gallium garnet single crystal or doped gadolinium gallium garnet single crystal. Compared with the prior art, the invention aims at the single crystal optical fiber grown by the existing micro-pulling-down method, and can well make up the defect of crystal quality caused by the laser pedestal method. However, since the minimum diameter of the single crystal optical fiber grown by the micro-pulling-down method is 1mm or more, the single crystal optical fiber has a defect of rigidity although a high quality single crystal optical fiber can be obtained, and the problems of the application field and the subsequent development of the rare earth doped single crystal optical fiber are greatly limited.
The invention is based on a melt crystal growth technology of a micro-pulling-down method, and the growth technology is used for realizing the growth of a crystal optical fiber by using a micro-through hole at the bottom of a crucible as a melt transmission channel, transferring mass to a solid/liquid interface and pulling a seed crystal downwards. The invention starts from the growth mechanism of rare earth crystal optical fiber, designs the crucible with a special structure, and the crucible with the special bottom opening structure adopts the connection design of the inner wall of the crucible and the capillary hole which are close to the bottom opening by adopting a tapered tube (tapered hole), thereby ensuring the fluidity of melt and realizing the controllable growth of the bendable single crystal optical fiber. The invention also starts from the growth mechanism of the rare earth crystal optical fiber, provides a calculation method of the growth rate of the rare earth single crystal optical fiber in the micro-pulling-down method, establishes a micro-pulling-down growth model, utilizes the crucible matched temperature field structure with a special structure and combines theoretical calculation, realizes the micro-pulling-down growth of the bendable gadolinium gallium garnet single crystal optical fiber, and finally obtains the high-quality flexible rare earth single crystal optical fiber.
Experimental results show that the crucible with the special structure provided by the invention is used for growing the gadolinium gallium garnet single crystal optical fiber by a micro-pulling-down method, so that the single crystal optical fiber with the diameter of 0.1-0.95 mm can be obtained, and the single crystal optical fiber has a higher curvature radius.
Drawings
FIG. 1 is a simplified schematic diagram of a crucible structure provided by the present invention;
FIG. 2 is a schematic diagram of a simple state of a taper hole and a capillary of the crucible provided by the invention in the process of growing rare earth single crystal;
FIG. 3 shows Er: gd (Gd)3Ga5O12Appearance diagram of single crystal fiber.
Detailed Description
In order to further understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
All of the starting materials of the present invention, without particular limitation as to their source, may be purchased commercially or prepared according to conventional methods well known to those skilled in the art.
All the raw materials of the present invention are not particularly limited in their purity, and the present invention preferably employs a purity which is conventional in the field of analytical purification or rare earth single crystal production.
The invention provides a crucible for growing a bendable flexible rare earth single crystal optical fiber by a micro-pulling-down method, wherein the bottom of the crucible is communicated with a capillary tube through a tapered hole;
the big hole of the conical hole is positioned at the bottom of the crucible, and the small hole of the conical hole is communicated with the capillary tube;
the rare earth single crystal comprises gadolinium gallium garnet single crystal or doped gadolinium gallium garnet single crystal.
The rare earth single crystal comprises gadolinium gallium garnet single crystal or doped gadolinium gallium garnet single crystal, and the crucible is only used for growing the bendable flexible gadolinium gallium garnet or doped gadolinium gallium garnet single crystal optical fiber by a micro-pull-down method based on calculation and selection of growth modes.
In the present invention, the definition of said gadolinium gallium garnet or doped gadolinium gallium garnet single crystal is not particularly limited, as is the conventional definition well known to those skilled in the art.
The conventional size of the crucible is not particularly limited in principle, and a person skilled in the art can select and adjust the crucible according to actual production conditions, raw material conditions and product requirements, the flexible rare earth single crystal optical fiber can be better grown, the performance of the flexible rare earth single crystal optical fiber is guaranteed, and the thickness of the bottom of the crucible is preferably 0.5-1.5 mm, more preferably 0.7-1.3 mm, and more preferably 0.9-1.1 mm. The diameter of the crucible is preferably 10-15 mm, more preferably 11-14 mm, and more preferably 12-13 mm. The height of the crucible is preferably 25-50 mm, more preferably 30-45 mm, and more preferably 35-40 mm.
The crucible material is preferably selected from one or more of Pt, Ir, Re, Mo and graphite, and more preferably from Pt, Ir, Re, Mo or graphite, and is preferably selected and adjusted by a person skilled in the art according to actual production conditions, raw material conditions and product requirements.
The invention has no special limitation on the conventional structure of the crucible in principle, and the crucible for growing the rare earth crystal by the micro-pulling-down method well known by the technicians in the field can be selected and adjusted according to the actual production condition, the raw material condition and the product requirement, the invention is better for growing the flexible rare earth single crystal optical fiber and ensuring the performance of the flexible rare earth single crystal optical fiber, the bottom opening of the crucible is a conical hole, and the number of the conical holes is preferably 1. The bottom of the crucible of the present invention needs to be a bevel.
In the invention, the large hole of the conical hole, namely the horn hole or the countersunk hole, is positioned at the bottom of the crucible, and the small hole of the conical hole is communicated with the capillary tube.
The diameter of the large hole of the conical hole of the crucible is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to actual production conditions, raw material conditions and product requirements, the diameter of the conical hole on the inner wall of the bottom of the crucible, namely the diameter of the large hole, is preferably 0.1-3 mm, more preferably 0.5-2.5 mm, and more preferably 1-2 mm, so that the bendable flexible rare earth single crystal optical fiber can be better grown and the performance of the bendable flexible rare earth single crystal optical fiber can be guaranteed.
The diameter of the small hole of the conical hole of the crucible is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to actual production conditions, raw material conditions and product requirements, the flexible rare earth single crystal optical fiber is better grown, the performance of the flexible rare earth single crystal optical fiber is guaranteed, and the diameter of the small hole of the conical hole is preferably the same as that of the capillary, preferably 0.1-0.95 mm, more preferably 0.3-0.8 mm, and more preferably 0.5-0.6 mm.
The height of the tapered hole of the crucible is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to actual production conditions, raw material conditions and product requirements, the height of the tapered hole is preferably 0.1-10 mm, more preferably 0.5-9 mm, more preferably 2-7 mm, and more preferably 4-5 mm, in order to better grow the bendable flexible rare earth single crystal optical fiber and ensure the performance of the bendable flexible rare earth single crystal optical fiber.
The included angle between the conical hole of the crucible and the bottom of the crucible is not particularly limited in principle, and can be selected and adjusted by a person skilled in the art according to the actual production condition, the raw material condition and the product requirement, the flexible rare earth single crystal optical fiber is better grown, the performance of the flexible rare earth single crystal optical fiber is ensured, and the included angle between the conical bevel edge of the conical hole and the bottom of the crucible is preferably 0-45 degrees, more preferably 10-35 degrees, and more preferably 20-25 degrees.
In order to better grow the bendable flexible rare earth single crystal optical fiber, ensure the performance of the bendable flexible rare earth single crystal optical fiber and the proper fluidity of a melt, a round chamfer angle is preferably arranged at the joint of the conical bevel edge of the conical hole and the bottom of the crucible.
The small hole end of the conical hole is connected with a capillary tube. The invention has no special limitation on the specific parameters of the capillary tube in principle, and a person skilled in the art can select and adjust the specific parameters according to the actual production condition, the raw material condition and the product requirement, in order to better grow the bendable flexible rare earth single crystal optical fiber and ensure the performance of the bendable flexible rare earth single crystal optical fiber, the diameter of the capillary tube is preferably 0.1-1 mm, more preferably 0.1-0.95 mm, more preferably 0.3-0.8 mm, and more preferably 0.5-0.6 mm. The length of the capillary tube is preferably 0.2-3 mm, more preferably 0.7-2.5 mm, and more preferably 1.2-2 mm.
In the invention, the shape of the crucible preferably comprises one or more of shape selection of the bottom of the crucible, whether a tapered hole is arranged in the crucible and whether a round chamfer is arranged at the joint of the tapered bevel edge of the tapered hole and the bottom of the crucible, and more preferably, the shape selection of the bottom of the crucible, whether the tapered hole is arranged in the crucible and whether the round chamfer is arranged at the joint of the tapered bevel edge of the tapered hole and the bottom of the crucible.
The parameters of the crucible preferably comprise one or more of the diameter of the large hole of the tapered hole, the diameter of the capillary tube, the angle between the tapered bevel edge of the tapered hole and the bottom of the crucible, the height of the tapered hole and the length of the capillary tube, and more preferably, the diameter of the large hole of the tapered hole, the diameter of the capillary tube, the angle between the tapered bevel edge of the tapered hole and the bottom of the crucible, the height of the tapered hole and the length of the capillary tube.
The method is characterized in that the shape and parameters of the crucible are determined according to a growth rate formula of the rare earth single crystal optical fiber, and the shape and parameters of the crucible are obtained by calculation. More specifically, the diameter of the capillary is preferably calculated from the growth rate formula of the rare earth single crystal optical fiber. The diameter of the large hole of the conical hole is preferably obtained by calculating the growth rate formula of the rare earth single crystal optical fiber. The included angle between the tapered bevel edge of the tapered hole and the bottom of the crucible is preferably obtained by calculating the growth rate formula of the rare earth single crystal optical fiber. The bottom of the crucible is preferably selected by calculating the growth rate formula of the rare earth single crystal optical fiber.
In the present invention, the calculation of the parameters of the crucible is preferably also performed based on one or more of the viscosity, wettability and density of the rare earth single crystal. More preferably, the calculation is performed based on a plurality of kinds of viscosity, wettability and density of the rare earth single crystal. In the invention, a specific rare earth single crystal has specific parameters, and the parameters can directly influence the subsequent calculation result of formula (II), and related influence factors are involved in the formulas (1) to (3) in the calculation process of formula (II), so that the results have difference.
The steps of the invention start from the growth mechanism of the rare earth crystal optical fiber, a crucible with a special structure is designed, the crucible with the special bottom opening structure is obtained by calculating the obtained parameters through a calculation method, the inner wall of the crucible close to the bottom opening and the capillary holes are connected by adopting a tapered tube (tapered hole), the angles, the chamfers and the shape of the bottom of the crucible are selected, the melt fluidity is ensured, the controllable growth of the bendable specific single crystal optical fiber is realized, and the rigid rare earth single crystal optical fiber produced by the existing micro-pulling-down method has the bendable characteristic.
The growth rate formula of the rare earth single crystal optical fiber is not particularly limited in principle, and a person skilled in the art can select and adjust the growth rate formula according to the actual production condition, the raw material condition and the product requirement;
Figure BDA0002831222380000111
wherein m is the mass of the rare earth single crystal in the crucible, r is the radius of a capillary hole at the bottom of the crucible, and r is1Is the physical distance from the center of the capillary to the wall of the tube, r2The distance from the center of the capillary to the boundary layer, l is the length of the capillary at the bottom of the crucible, t is the unit time, D is the diameter of the single crystal optical fiber, RfiberThe growth rate of the single crystal optical fiber with the diameter D;
(Ebond/Auvwduvw)radialis the chemical bonding energy density of the rare earth single crystal along the radial direction;
(Ebond/Auvwduvw)axialis the chemical bonding energy density of the rare earth single crystal along the axial direction;
D＝0.1～0.95mm。
more specifically, said formula (II) is obtained by the following steps:
a) obtaining the pressure difference delta P of the downward flowing of the rare earth single crystal melt by referring to the formula (1), and calculating to obtain the driving force F of the downward flowing of the material by referring to the formula (1');
Figure BDA0002831222380000112
F＝ΔP·S1 (1`)，
where F is the driving force for the downward flow of the melt in the capillary, Δ P is the pressure difference, S1Is the capillary end face area;
g is the gravity of the melt in the crucible, r is the radius of the capillary pores at the bottom of the crucible, (E)bond/Auvwduvw)axialIs the chemical bonding energy density of the rare earth single crystal along the axial direction;
deriving and obtaining the friction force f in the capillary at the bottom end of the crucible based on the formula (2), and referring to the formula (3);
Figure BDA0002831222380000121
Figure BDA0002831222380000122
wherein f is the internal friction of the capillary at the bottom end of the crucible, eta is the viscosity coefficient of the melt, and S2The area of the side surface of the capillary tube, r is the radius of the capillary hole at the bottom of the crucible, and dv/dr is the velocity gradient of the melt; t is unit time, (E)bond/Auvwduvw)radialThe chemical bonding energy density of the rare earth single crystal along the radial direction, and l is the length of a capillary at the bottom end of the crucible;
b) based on the fact that in a steady-state growth state, in the growth process of the micro-pulling-down single crystal optical fiber, the force in the capillary tube along the vertical direction is balanced, and the driving force of the downward flow of the melt in the capillary tube is equal to the internal friction force of the capillary tube at the bottom end of the crucible, according to the formula (4);
Figure BDA0002831222380000123
c) establishing a boundary condition, wherein r ═ r1，v＝0；r＝r2，v＝vporeCombining the formula (4) to obtain the downward flow rate of the melt in the capillary, and referring to the formula (5);
Figure BDA0002831222380000124
wherein r is1Is the physical distance from the center of the capillary to the wall of the tube, r2Distance from capillary center to boundary layer, vporeThe rate of melt flow down the capillary;
d) based on the rate of downward flow of the melt in the capillary obtained in the above steps, after the fluid flows out of the capillary and infiltrates the bottom end of the crucible, the fluid grows in the solid/liquid/solid interface region, and according to the conservation of mass, the growth rate R of the single crystal optical fiber with the diameter D is obtainedfiberD is 0.1-0.95 mm, as shown in formula (II);
the specific steps of the derivation are as follows:
based on the tendency of the melt to heterogeneously nucleate within the capillary at the solid/liquid interface of the tube wall, formula (2') is obtained, and formula (2) is then combined to obtain formula (3);
Figure BDA0002831222380000131
wherein t is a unit time, (E)bond/Auvwduvw)radialIs the chemical bonding energy density of the rare earth single crystal along the radial direction.
Referring to fig. 1, fig. 1 is a simple schematic diagram of a crucible structure provided by the present invention.
The invention also provides a method for calculating the growth rate of the bendable flexible rare earth single crystal optical fiber in the micro-pulling-down method, which comprises the following steps,
1) determining the thermodynamic growth form of the rare earth single crystal according to the chemical bonding theory of crystal growth;
2) determining a radial growth direction corresponding to the axial growth direction and an anisotropic chemical bonding structure at a growth interface based on the thermodynamic growth form of the rare earth single crystal obtained in the step;
3) calculating the anisotropic chemical bonding energy density of the rare earth single crystal along the axial direction and the anisotropic chemical bonding energy density of the rare earth single crystal along the radial direction based on the anisotropic chemical bonding structure at the growth interface obtained in the step (I);
Figure BDA0002831222380000132
wherein the content of the first and second substances,
Figure BDA0002831222380000133
is along [ uvw ]]A directionally grown chemical bonding energy;
Auvwfor growth of elementary edges [ uvw ]]The projected area of the direction;
duvwis a single crystal edge [ uvw ]]The step height of the direction;
4) calculating the growth rate of the bendable flexible rare earth single crystal optical fiber based on the all-directional chemical bonding energy density of the rare earth single crystal obtained in the steps along the axial direction and the radial direction, wherein the growth rate is shown as a formula (II);
Figure BDA0002831222380000134
wherein m is the mass of the rare earth single crystal in the crucible, r is the radius of a capillary hole at the bottom of the crucible, and r is1Is the physical distance from the center of the capillary to the wall of the tube, r2Distance from capillary center to boundary layer, l is crucible bottomThe length of the end capillary, t is unit time, D is the diameter of the single crystal optical fiber, D is 0.1-0.95 mm, RfiberThe growth rate of the single crystal optical fiber with the diameter D;
(Ebond/Auvwduvw)radialis the chemical bonding energy density of the rare earth single crystal along the radial direction;
(Ebond/Auvwduvw)axialis the chemical bonding energy density of the rare earth single crystal along the axial direction;
the crucible is the crucible of any one of the above technical schemes.
In the method for calculating the growth rate of the rare earth single crystal optical fiber in the micro-pulling down method, if no particular reference is made to the selection of the parameters such as the material and the structure of the crucible and the corresponding preferred principles, the selection of the parameters such as the material and the structure of the crucible in the crucible for growing the flexible rare earth single crystal optical fiber in the micro-pulling down method provided by the steps of the invention and the corresponding preferred principles are preferably in one-to-one correspondence, and the details are not repeated herein.
The size of the rare earth single crystal optical fiber prepared by the invention is not particularly limited, the conventional size of the rare earth single crystal optical fiber known by the technicians in the field can be used, the technicians in the field can select and adjust the conventional size according to the actual application condition, the raw material condition and the product requirement, and the equal diameter size of the rare earth single crystal optical fiber prepared by the invention is preferably 0.1-0.95 mm, more preferably 0.3-0.8 mm, and more preferably 0.5-0.6 mm.
The invention firstly determines the thermodynamic growth form of the rare earth single crystal according to the chemical bonding theory of crystal growth.
The concept of the chemical bonding theory for the crystal growth is not particularly limited in the present invention, and may be defined by conventional definitions well known to those skilled in the art, and may be selected and adjusted by those skilled in the art according to practical application conditions, raw material conditions and product requirements.
The definition of the thermodynamic growth form of the rare earth single crystal is not particularly limited, and the definition of the thermodynamic growth form of the conventional rare earth single crystal, which is well known to those skilled in the art, can be selected and adjusted by those skilled in the art according to the actual application situation, the raw material situation and the product requirement.
The definition of the thermodynamic growth form of the rare earth single crystal is not particularly limited, and the definition of the thermodynamic growth form of the conventional rare earth single crystal, which is well known to those skilled in the art, can be selected and adjusted by those skilled in the art according to the actual application situation, the raw material situation and the product requirement. Specifically, the main exposed crystal planes of the thermodynamic growth morphology of the gadolinium gallium garnet single crystal or the doped gadolinium gallium garnet single crystal are {110} crystal planes and {111} crystal planes.
The invention then determines the radial growth direction corresponding to the axial growth direction and the anisotropic chemical bonding structure at the growth interface based on the thermodynamic growth morphology of the rare earth single crystal obtained in the above step.
The concept of the growth direction of the rare earth single crystal according to the present invention is not particularly limited, and may be defined by conventional definitions well known to those skilled in the art, and the growth direction according to the present invention preferably refers to a thermodynamically micro-pulling down growth direction.
The specific method for determining is not particularly limited in the present invention, and the method for performing calculation determination by using thermodynamic growth morphology, which is well known to those skilled in the art, may be selected and adjusted by those skilled in the art according to the actual application situation, the raw material situation and the product requirement. The axial growth direction can be set according to actual conditions, and then the radial growth direction corresponding to the axial growth direction is determined according to the axial growth direction, so that the anisotropic chemical bonding structure at the growth interface is obtained. The anisotropic chemical bonding structure at the growth interface according to the present invention preferably comprises an anisotropic chemical bonding structure at the growth interface in the axial growth direction and an anisotropic chemical bonding structure at the growth interface in the radial growth direction.
Based on the anisotropic chemical bonding structure at the growth interface obtained in the step, calculating the anisotropic chemical bonding energy density of the rare earth single crystal along the axial direction and the anisotropic chemical bonding energy density along the radial direction by referring to a formula (I);
Figure BDA0002831222380000151
wherein the content of the first and second substances,
Figure BDA0002831222380000152
is along [ uvw ]]A directionally grown chemical bonding energy; a. theuvwFor growth of elementary edges [ uvw ]]The projected area of the direction; duvwIs a single crystal edge [ uvw ]]Directional step height.
The definition and selection of the parameters in the formula (I) are not particularly limited in the present invention, and may be defined by conventional definitions well known to those skilled in the art, consistent with the general knowledge of the persons skilled in the art. The selection range of the above parameters of the present invention is applicable to all inorganic single crystal materials, and the specific values and selection thereof, and those skilled in the art can select and adjust the parameters in the tool books or documents according to the actual application conditions, raw material conditions and product requirements.
In the process of calculating the anisotropic chemical bonding energy density of the rare earth single crystal growth along the axial direction and the anisotropic chemical bonding energy density along the radial direction, the calculation mode and the bonding mode of the rare earth ions and other elements preferably have correlation. The preferable bonding mode of the rare earth ions and other elements can be judged by a theoretical model between the coordination number of the central ions of the rare earth and the bonding mode of outer-layer orbital hybridization. More specifically, in calculating the anisotropic chemical bonding energy density, the difference in bonding mode between the rare earth ions and other elements is considered. When the 4f orbit participates in bonding, the bonding of the rare earth ions is weaker, the isotropy is stronger, the bonding energy is weak, and the judgment can be carried out through a theoretical model between the coordination number of the central ions and the hybridization bonding mode of the outer layer orbit. Taking gadolinium gallium garnet single crystal doped as an example, the coordination number of rare earth ions is equal to 8, and the 4f orbital of the outer layer does not participate in bonding, so that the processing mode is consistent with other compositions.
Finally, calculating the growth rate of the bendable flexible rare earth single crystal fiber based on the all-directional chemical bonding energy density of the rare earth single crystal obtained in the steps along the axial direction and the radial direction, wherein the growth rate is shown as a formula (II);
Figure BDA0002831222380000161
wherein m is the mass of the rare earth single crystal in the crucible, r is the radius of a capillary hole at the bottom of the crucible, and r is1Is the physical distance from the center of the capillary to the wall of the tube, r2The distance from the center of the capillary to the boundary layer, l is the length of the capillary at the bottom of the crucible, t is the unit time, D is the diameter of the single crystal optical fiber, RfiberThe growth rate of the single crystal optical fiber with the diameter D;
(Ebond/Auvwduvw)radialis the chemical bonding energy density of the rare earth single crystal along the radial direction;
(Ebond/Auvwduvw)axialis the chemical bonding energy density of the rare earth single crystal along the axial direction;
the crucible is the crucible of any one of the above technical schemes.
Finally, parameters such as the chemical bonding energy density of the rare earth single crystal along the axial direction and the radial direction, the size of a capillary hole at the bottom end of the crucible, the outer diameter of the bottom of the crucible, the feeding amount and the like are substituted into a formula (II) to calculate the growth rate of the rare earth single crystal optical fiber.
The invention has no special limitation on the scope and source of each parameter in the formula (II), and the scope and source of each parameter can be determined by the conventional parameters known to those skilled in the art, and the skilled in the art can select and adjust the parameters according to the actual application situation, the raw material situation and the product requirement, and the crucible of the invention is a crucible with only a single capillary. The quality of the rare earth single crystal in the crucible, the radius of the capillary hole at the bottom of the crucible, the physical distance from the center of the capillary tube to the tube wall, the distance from the center of the capillary tube to the boundary layer and the length of the capillary tube at the bottom of the crucible can be obtained from actual equipment.
The present invention has no particular limitation on the specific derivation process of the formula (II) for calculating the growth rate of the rare earth single crystal optical fiber, and it is only required to use the conventional derivation process known to those skilled in the art, and those skilled in the art can select and adjust the derivation process according to the actual application situation, the raw material situation and the product requirement, and in order to further ensure the calculation accuracy of the final growth rate, complete and refine the calculation method, the formula (II) has the following steps:
based on the balance of the friction force in the capillary at the bottom of the crucible and the driving force of the downward flow of the material, the growth of the single crystal optical fiber is pushed.
a) Obtaining the pressure difference delta P of the downward flowing of the rare earth single crystal melt by referring to the formula (1), and calculating to obtain the driving force F of the downward flowing of the material by referring to the formula (1');
Figure BDA0002831222380000171
F＝ΔP·S1 (1`)，
where F is the driving force for the downward flow of the melt in the capillary, Δ P is the pressure difference, S1Is the capillary end face area;
g is the gravity of the melt in the crucible, r is the radius of the capillary pores at the bottom of the crucible, (E)bond/Auvwduvw)axialIs the chemical bonding energy density of the rare earth single crystal along the axial direction;
deriving and obtaining the friction force f in the capillary at the bottom end of the crucible based on the formula (2), and referring to the formula (3);
Figure BDA0002831222380000172
Figure BDA0002831222380000173
wherein f is the internal friction of the capillary at the bottom end of the crucible, eta is the viscosity coefficient of the melt, and S2The area of the side surface of the capillary tube, r is the radius of the capillary hole at the bottom of the crucible, and dv/dr is the velocity gradient of the melt; t is unit time, (E)bond/Auvwduvw)radialThe chemical bonding energy density of the rare earth single crystal along the radial direction, and l is the length of a capillary at the bottom end of the crucible;
b) based on the fact that in a steady-state growth state, in the growth process of the micro-pulling-down single crystal optical fiber, the force in the capillary tube along the vertical direction is balanced, and the driving force of the downward flow of the melt in the capillary tube is equal to the internal friction force of the capillary tube at the bottom end of the crucible, according to the formula (4);
Figure BDA0002831222380000181
c) establishing a boundary condition, wherein r ═ r1，v＝0；r＝r2，v＝vporeCombining the formula (4) to obtain the downward flow rate of the melt in the capillary, and referring to the formula (5);
Figure BDA0002831222380000182
wherein r is1Is the physical distance from the center of the capillary to the wall of the tube, r2Distance from capillary center to boundary layer, vporeIs the rate of melt flow down the capillary.
d) Based on the rate of downward flow of the melt in the capillary obtained in the above steps, after the fluid flows out of the capillary and infiltrates the bottom end of the crucible, the fluid grows in the solid/liquid/solid interface region, and according to the conservation of mass, the growth rate R of the single crystal optical fiber with the diameter D is obtainedfiberAs shown in formula (II).
The present invention has no particular limitation on the specific definitions and ranges of the various calculation formulas and parameters in the above steps, and the general definitions and ranges are well known to those skilled in the art, and those skilled in the art can select and adjust the specific definitions and ranges according to the actual application, raw material conditions and product requirements. Furthermore, in the step a), the specific steps of derivation are preferably:
based on the tendency of the melt to heterogeneously nucleate within the capillary at the solid/liquid interface of the tube wall, formula (2') is obtained, and formula (2) is then combined to obtain formula (3);
Figure BDA0002831222380000183
wherein t is a unit time, (E)bond/Auvwduvw)radialIs the chemical bonding energy density of the rare earth single crystal along the radial direction.
The growth rate of the rare earth single crystal fiber is obtained through the calculation of the steps, namely the growth rate of each size interval in the process of preparing the rare earth single crystal fiber by the micro-pulling-down method, the specific range of the growth rate is not particularly limited, and the growth rate can be calculated by referring to the description by a person skilled in the art, and the person skilled in the art can select and adjust the growth rate according to the actual application condition, the raw material condition and the product requirement, wherein the growth rate of the rare earth single crystal fiber is preferably 0.05-12 mm/min, more preferably 0.1-11 mm/min, more preferably 0.5-10 mm/min, more preferably 1-9 mm/min, more preferably 2-8 mm/min, and also can be 4-6 mm/min. The specific growth rate variation range of the rare earth single crystal is obtained by calculation according to the calculation method.
The concept of the growth rate of the rare earth single crystal optical fiber is not particularly limited by the present invention, and the conventional definition well known to those skilled in the art can be used, the growth rate of the single crystal optical fiber in the present invention preferably refers to the increase of the single crystal mass per unit time, specifically, the growth rate of the rare earth single crystal optical fiber more preferably refers to the thermodynamically allowable growth rate in the growth process of the single crystal optical fiber, and the fastest growth rate thereof preferably refers to the thermodynamically allowable fastest growth rate in the growth process of the single crystal optical fiber. Therefore, the growth rate of the rare earth single crystal optical fiber of the present invention includes the fastest growth rate of the rare earth single crystal optical fiber.
The invention has no special restriction on the specific process of calculating the fastest growth rate of the rare earth single crystal optical fiber by using the calculation method, and the calculation method is carried out by specific calculation known by technicians in the field, and the technicians in the field can select and adjust the process according to the actual application condition, the raw material condition and the product requirement, in order to ensure the accuracy, the integrity and the refinement of the calculation process of the fastest growth rate, the calculation method of the fastest growth rate is preferably as follows:
of the chemical bonding energy density in the axial direction and the chemical bonding energy density in the radial direction, a direction in which a ratio of the chemical bonding energy density in the axial direction to the chemical bonding energy density in the radial direction is large is a growth direction having a fastest growth rate.
The direction in which the ratio of the chemical bonding energy density in the axial direction to the chemical bonding energy density in the radial direction is large in the invention specifically means that in each chemical bonding energy density, which direction has a large ratio of the chemical bonding energy density in the axial direction to the chemical bonding energy density in the radial direction is the growth direction with the fastest growth rate.
The invention provides a method for calculating the growth rate of the bendable flexible rare earth single crystal optical fiber in the micro-pulling-down method, which is based on the fundamental of rare earth single crystal growth and aims at the current situations that the mechanism of single crystal growth is not clear and the multi-scale growth process is lack of effective control, and the growth control system is considered to lack of a front-end theoretical design function, so that the period of the micro-pulling-down method growth technology is prolonged, and the early investment of rare earth single crystal growth is increased. The invention starts from the growth mechanism of the rare earth single crystal optical fiber, establishes a micro pull-down growth model, establishes a rapid growth process of the rare earth single crystal optical fiber, provides a calculation method and a calculation system of the micro pull-down growth rate in the rare earth single crystal growth process, combines various growth parameters in actual growth, calculates the growth speeds of different size intervals, further finds the rapid growth direction of the rare earth single crystal optical fiber, obtains the fastest growth rate of the rare earth single crystal optical fiber, and matches a temperature field structure to realize rapid growth, thereby obtaining the rapid growth process of the rare earth single crystal optical fiber, and solving the problems that the design period of the rare earth single crystal growth technology is long, the growth parameters need to be repeatedly optimized, and the like.
The invention also provides a method for growing the bendable flexible rare earth single crystal optical fiber by using the micro-pulling-down method, which comprises the following steps:
(1) calculating the growth rate of the rare earth single crystal optical fiber by using a growth rate formula of the rare earth single crystal optical fiber;
(2) designing and building a temperature field structure for growing the rare earth single crystal optical fiber according to the growth rate obtained in the step; designing the appearance and parameters of the crucible according to the growth rate obtained in the step;
(3) filling a crystal material into a crucible, setting growth parameters required by the growth of the rare earth single crystal according to the parameters and the growth rate in the growth rate calculation process of the rare earth single crystal optical fiber, and then heating;
(4) when the heating temperature is higher than the melting point of the rare earth single crystal, moving the seed crystal upwards to contact the bottom end of the crucible, forming a meniscus at the bottom of the crucible, and then growing according to the growth parameters set in the step to obtain the rare earth single crystal optical fiber;
the crucible is the crucible of any one of the above technical schemes.
In the method for growing a bendable flexible rare earth single crystal optical fiber by using the micro-pulling-down method provided by the present invention, the calculation method, the selection of the mode, the selection of the parameters, and the corresponding preferred principles thereof are preferably in one-to-one correspondence with the calculation method, the selection of the mode, the selection of the parameters, and the corresponding preferred principles thereof in the method for calculating the growth rate of a rare earth single crystal optical fiber in the micro-pulling-down method provided by the foregoing steps of the present invention, and thus, no further description is provided herein.
According to the invention, the growth rate of the rare earth single crystal optical fiber is calculated by using the calculation method or the calculation system in any one of the above technical schemes, and then the fastest growth rate of the rare earth single crystal optical fiber can be preferably obtained. And then designing and building a temperature field structure for growing the rare earth single crystal optical fiber according to the growth rate obtained in the step.
The specific process and mode for designing and constructing the temperature field structure for growing the rare earth single crystal optical fiber are not particularly limited, and the conventional mode and process known by the technicians in the field can be adopted, and the technicians in the field can select and adjust the temperature field structure according to the actual application condition, the raw material condition and the product requirement. In the temperature field structure of the present invention, the centers of the insulating material, the seed crystal, the crucible, and the post-heater are preferably kept on the same straight line in the vertical direction (i.e., vertical direction).
Then, the invention fills crystal material into the crucible, sets the growth parameters needed by the growth of the rare earth single crystal according to the parameters and the growth rate in the growth rate calculation process of the rare earth single crystal optical fiber, and then heats up.
The setting mode is not particularly limited, and the setting mode can be selected manually, can be adjusted continuously in the growth process, and can also be preset in a system in a computer automatic control mode.
Finally, when the heating temperature is higher than the melting point of the rare earth single crystal, the seed crystal is moved upwards to contact the bottom end of the crucible, a meniscus is formed at the bottom of the crucible, and then the rare earth single crystal optical fiber is grown according to the growth parameters set in the steps.
The specific temperature difference of the heating temperature higher than the melting point of the rare earth single crystal in the process is not particularly limited, and a person skilled in the art can select and adjust the temperature difference according to the actual application condition, the raw material condition and the product requirement, in order to further ensure the performance of the final product and complete and refine the growth process, the difference between the heating temperature and the melting point of the rare earth single crystal is preferably greater than 0 ℃ and less than or equal to 50 ℃, more preferably 5-45 ℃, more preferably 10-40 ℃, more preferably 15-35 ℃ and more preferably 20-30 ℃.
The present invention has no particular limitation on the specific operation and process in the above process, and the conventional operation and process for growing the rare earth single crystal optical fiber by the micro-pulling-down method known to those skilled in the art can be selected and adjusted by those skilled in the art according to the actual application situation, the raw material situation and the product requirement, and in order to further ensure the performance of the final product, complete and refine the growth process, the present invention preferably further comprises the following steps before the growth is performed according to the set growth parameters:
and (4) finely adjusting the temperature of the melt, and growing according to the set growth parameters when the melt infiltrates the bottom end of the whole crucible and the side surface of the melt is not protruded outwards.
The specific parameters of the fine adjustment are not particularly limited, and a person skilled in the art can select and adjust the parameters according to the actual application condition, the raw material condition and the product requirement, wherein the fine adjustment range is preferably 10-40 ℃ higher than the melting point of the rare earth single crystal, more preferably 15-35 ℃ and more preferably 20-30 ℃.
In the method for growing the bendable flexible rare earth single crystal optical fiber by the micro-pulling-down method, part of the steps can be as follows:
designing and building a temperature structure for growing the rare earth single crystal optical fiber by a micro-pulling-down method, and keeping the centers of the heat insulating material, the seed crystal, the crucible and the rear heater on the same straight line.
The crucible is filled with crystal material, the CCD position and the observation hole position are adjusted, the observation in the growth process is convenient, the growth parameters required by the growth of the rare earth single crystal are set, and the temperature is programmed.
And (4) entering a temperature rising stage, moving the seed crystal upwards when the temperature is slightly higher than the melting point of the rare earth single crystal, contacting the bottom end of the crucible, and forming a meniscus at the bottom of the crucible. And (4) finely adjusting the temperature of the melt, and growing according to set growth parameters when the melt infiltrates the bottom end of the whole crucible and the side surface of the melt is not protruded outwards.
After the growth is finished, the rare earth single crystal optical fiber is taken out after programmed cooling and natural self-cooling.
The invention discloses a method for growing bendable flexible rare earth single crystal optical fiber by using micro-pull-down method, which comprises the following steps:
the specific scheme of the front-end calculation in the invention is as follows:
(1) rate analytic formula for determining rare earth single crystal optical fiber growth process
The friction force in the capillary at the bottom of the crucible and the driving force of the downward flow of the material balance to push the growth of the single crystal optical fiber.
Figure BDA0002831222380000221
(2) Determining the anisotropic chemical bonding energy density of the rare earth single crystal optical fiber growth by utilizing the chemical bonding theory of crystal growth;
1) calculating the thermodynamic form of the rare earth single crystal according to the chemical bonding theory of crystal growth;
2) determining a radial growth direction corresponding to the axial growth direction and a chemical bonding structure at an interface according to a thermodynamic growth form;
3) calculating the chemical bonding energy density of the rare earth single crystal along the axial direction and the radial direction by the anisotropic chemical bonding structure at the bonding interface
Figure BDA0002831222380000222
(3) The rare earth single crystal optical fiber calculated according to the formula (II) has a large ratio of chemical bonding energy density along the axial direction to the radial direction, and can realize rapid growth.
(4) The crucible with a special bottom opening structure is adopted, the inner wall of the crucible close to the bottom opening and capillary holes are connected by adopting a tapered tube, the fluidity of a melt is guaranteed, and the growth of a single crystal optical fiber with the diameter phi of 0.1-0.95 mm is realized.
(5) And (II) carrying parameters such as the chemical bonding energy density of the rare earth single crystal along the axial direction and the radial direction, the size of a capillary hole at the bottom end of the crucible, the outer diameter of the bottom of the crucible, the feeding amount and the like into the formula (II), and calculating the growth rate of the rare earth single crystal optical fiber.
(6) And calculating the growth rate of the rare earth single crystal optical fiber with phi of 0.1-0.95 mm according to the size of the optical fiber under different crucible sizes, wherein the lower pulling rate is 0.10-0.88 mm/min.
(7) Designing and building a temperature structure for growing the rare earth single crystal optical fiber by a micro-pulling-down method, and keeping the centers of the heat insulating material, the seed crystal, the crucible and the rear heater on the same straight line.
(8) The crucible is filled with crystal material, the CCD position and the observation hole position are adjusted, the observation in the growth process is convenient, the growth parameters required by the growth of the rare earth single crystal are set, and the temperature is programmed.
(9) And (4) entering a temperature rising stage, moving the seed crystal upwards when the temperature is slightly higher than the melting point of the rare earth single crystal, contacting the bottom end (outlet of the capillary tube) of the crucible, and forming a meniscus at the bottom of the crucible. And (4) finely adjusting the temperature of the melt, and growing according to set growth parameters when the melt infiltrates the bottom end of the whole crucible and the side surface of the melt is not protruded outwards.
(10) After the growth is finished, the rare earth single crystal optical fiber is taken out after programmed cooling and natural self-cooling.
Referring to fig. 2, fig. 2 is a schematic view showing a simple state of a tapered hole and a capillary of the crucible provided by the invention in a rare earth single crystal growth process.
Referring to fig. 3, fig. 3 is a graph of Er prepared in example 1 of the present invention: gd (Gd)3Ga5O12Appearance diagram of single crystal fiber.
The invention provides a crucible for growing the bendable flexible rare earth single crystal optical fiber by the micro-pulling-down method, a calculation method of the growth rate of the bendable flexible rare earth single crystal optical fiber in the micro-pulling-down method, a calculation system of the growth rate of the bendable flexible rare earth single crystal optical fiber in the micro-pulling-down method and a method for growing the bendable flexible rare earth single crystal optical fiber by the micro-pulling-down method. According to the invention, a high-quality flexible single crystal fiber is obtained by utilizing the micro-pull-down method, a micro-pull-down growth model is established starting from the growth mechanism of the rare earth crystal fiber, a crucible with a special bottom opening structure is designed, the inner wall of the crucible close to the bottom opening and capillary holes are connected by adopting a tapered tube, the fluidity of a melt is ensured, and the micro-pull-down method controllable growth of a bendable gadolinium gallium garnet single crystal or gadolinium gallium garnet doped single crystal fiber is realized by combining the specially designed crucible matched temperature field structure with theoretical calculation.
The invention also starts from the growth mechanism of the rare earth single crystal optical fiber, establishes a micro pull-down growth model, establishes a rapid growth process of the rare earth single crystal optical fiber, provides a calculation method and a calculation system of the micro pull-down growth rate in the rare earth single crystal growth process, combines various growth parameters in actual growth, calculates the growth speeds of different size intervals, further finds the rapid growth direction of the rare earth single crystal optical fiber, obtains the fastest growth rate of the rare earth single crystal optical fiber, and matches a temperature field structure to realize rapid growth, thereby obtaining the rapid growth process of the rare earth single crystal optical fiber, and solving the problems that the design period of the rare earth single crystal growth technology is long, the growth parameters need to be repeatedly optimized, and the like.
Experimental results show that the crucible with the special structure provided by the invention is used for growing the gadolinium gallium garnet single crystal optical fiber by a micro-pulling-down method, so that the single crystal optical fiber with the diameter of 0.1-0.95 mm can be obtained, and the single crystal optical fiber has a higher curvature radius.
For further illustration of the present invention, the calculation method and the growth method of the bendable flexible rare earth single crystal optical fiber by the micro-pulling-down method are described in detail with reference to the following examples, but it should be understood that the embodiments are implemented on the premise of the technical solution of the present invention, and the detailed embodiments and the specific operation procedures are given only for further illustration of the features and advantages of the present invention, not for limitation of the claims of the present invention, and the scope of the present invention is not limited to the following examples.
Example 1
Er with purity higher than 99.995% is prepared according to the above process2O3、Ga2O3、Gd2O3Powder material, Er is formed according to the composition of consistent melting zone oxide raw material in the growing process of gadolinium gallium garnet crystal2O3∶Gd2O3∶Ga2O3The raw materials are prepared according to the molar ratio of 1.5: 2.5, and the ingredients are fully mixed for 8 hours by grinding so as to uniformly mix the raw materials. Then pressing the mixture into a raw material cake under 20MPa, putting the raw material cake into a high-purity crucible, and sintering the raw material cake at 1050 ℃ to form a cake-shaped Er: gd (Gd)3Ga5O12Polycrystalline feedstock. 0.09g of raw material is put into a special Ir crucible, and the raw material is put into a 100]Directional seed crystal. Wherein the crucible parameters are as follows: the diameter of a large hole of the conical hole is 1.0-1.5 mm, the included angle is 40-45 degrees, the length of the capillary tube is 0.2-1.5 mm, the height of the conical hole is 2-8 mm, the bottom of the crucible is an inclined plane, and the inclined edge of the conical hole and the crucible are connected with each otherAnd a round chamfer angle is arranged at the joint of the crucible bottom.
And (3) building a temperature structure for growing the rare earth doped yttrium aluminum garnet crystal fiber by a micro-pulling-down method, and keeping the centers of the heat-insulating material, the seed crystal, the crucible and the rear heater on the same vertical line. The position of the CCD is adjusted to be kept on the same horizontal line with the position of the observation hole. After the hearth is vacuumized, high-purity Ar gas is filled as protective gas, and the melting is carried out by heating.
The growth rate calculation method provided by the invention is used for calculation.
Firstly, determining the thermodynamic growth form of the rare earth single crystal according to the chemical bonding theory of crystal growth, and then determining the radial growth direction corresponding to the axial growth direction and the anisotropic chemical bonding structure at the growth interface based on the thermodynamic growth form of the rare earth single crystal obtained in the step; calculating the anisotropic chemical bonding energy density of the rare earth single crystal along the axial direction and the anisotropic chemical bonding energy density of the rare earth single crystal along the radial direction according to the formula (I) based on the anisotropic chemical bonding structure at the growth interface obtained in the step; and finally, calculating the growth rate of the rare earth single crystal fiber by using a formula (II) based on the anisotropic chemical bonding energy density of the rare earth single crystal obtained in the steps along the axial direction and the radial direction.
Er with phi of 0.3mm and the total length of 55mm is calculated by the theory: gd (Gd)3Ga5O12Edge [100 ]]The pulling growth rate in the direction is 0.2-1.00 mm/min. And (4) entering a temperature rising stage, moving up the seed crystal when the temperature is slightly higher than the melting point of the rare earth crystal, contacting the bottom end of the crucible, and forming a meniscus at the bottom of the crucible. And (4) finely adjusting the temperature of the melt, and growing according to set growth parameters when the melt infiltrates the bottom end of the whole crucible and the side surface of the melt is not protruded outwards. After the growth is finished, Er with the diameter of 0.3mm and the total length of 55mm is obtained: gd (Gd)3Ga5O12A crystal fiber.
When the single crystal optical fiber prepared in the embodiment 1 of the invention is detected, the curvature radius can reach 66.7 mm.
Example 2
Nd with purity higher than 99.995% is prepared according to the above process2O3、Ga2O3、Gd2O3Powder material, according to the composition Nd of consistent melting zone oxide raw material in the growing process of gadolinium gallium garnet crystal2O3∶ Gd2O3∶Ga2O3The raw materials are prepared according to the molar ratio of 1.5: 2.5, and the ingredients are fully mixed for 8 hours by grinding so as to uniformly mix the raw materials. Then, pressing the raw material cake under 20MPa, putting the raw material cake into a high-purity crucible, and sintering the raw material cake at 1050 ℃ to form a round cake-shaped Nd: gd (Gd)3Ga5O12Polycrystalline feedstock. 0.07g of raw material is put into a special Ir crucible, and the front end of a pull-down seed crystal rod is filled with [100 ]]Directional seed crystal. Wherein the crucible parameters are as follows: the diameter of a large hole of the conical hole is 1.0-1.5 mm, the included angle is 40-45 degrees, the length of the capillary tube is 0.2-1.9 mm, the height of the conical hole is 3-10mm, and a round chamfer angle is not arranged at the joint of the inclined edge of the conical hole and the bottom of the crucible.
And (3) building a temperature structure for growing the rare earth doped yttrium aluminum garnet crystal fiber by a micro-pulling-down method, and keeping the centers of the heat-insulating material, the seed crystal, the crucible and the rear heater on the same vertical line. The position of the CCD is adjusted to be kept on the same horizontal line with the position of the observation hole. After the hearth is vacuumized, high-purity Ar gas is filled as protective gas, and the melting is carried out by heating.
The growth rate calculation method provided by the invention is used for calculation.
Firstly, determining the thermodynamic growth form of the rare earth single crystal according to the chemical bonding theory of crystal growth, and then determining the radial growth direction corresponding to the axial growth direction and the anisotropic chemical bonding structure at the growth interface based on the thermodynamic growth form of the rare earth single crystal obtained in the step; calculating the anisotropic chemical bonding energy density of the rare earth single crystal along the axial direction and the anisotropic chemical bonding energy density of the rare earth single crystal along the radial direction according to the formula (I) based on the anisotropic chemical bonding structure at the growth interface obtained in the step; and finally, calculating the growth rate of the rare earth single crystal fiber by using a formula (II) based on the anisotropic chemical bonding energy density of the rare earth single crystal obtained in the steps along the axial direction and the radial direction.
The Nd with phi of 0.3mm and the total length of 100mm is calculated by the theory: gd (Gd)3Ga5O12Edge [100 ]]Directional pull growthThe speed is 0.25 to 0.80 mm/min. And (4) entering a temperature rising stage, moving up the seed crystal when the temperature is slightly higher than the melting point of the rare earth crystal, contacting the bottom end of the crucible, and forming a meniscus at the bottom of the crucible. And (4) finely adjusting the temperature of the melt, and growing according to set growth parameters when the melt infiltrates the bottom end of the whole crucible and the side surface of the melt is not protruded outwards. Nd with phi of 0.3mm and a total length of 100mm is obtained after the growth is finished: gd (Gd)3Ga5O12A crystal fiber.
When the single crystal optical fiber prepared in the embodiment 3 of the invention is detected, the curvature radius can reach 45.3 mm.
The crucible for growing the bendable flexible rare earth single crystal optical fiber by the micro-pulling down method, the method for calculating the growth rate of the bendable flexible rare earth single crystal optical fiber in the micro-pulling down method, the system for calculating the growth rate of the bendable flexible rare earth single crystal optical fiber in the micro-pulling down method, and the method for growing the bendable flexible rare earth single crystal optical fiber by the micro-pulling down method according to the present invention have been described in detail above, and specific examples are applied herein to illustrate the principles and embodiments of the present invention. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention. The scope of the invention is defined by the claims and may include other embodiments that occur to those skilled in the art. Such other embodiments are intended to be within the scope of the claims if they have structural elements that approximate the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims (10)

1. The crucible for growing the bendable flexible rare earth single crystal optical fiber by the micro-pulling-down method is characterized in that the bottom of the crucible is communicated with a capillary tube through a tapered hole;
the big hole of the conical hole is positioned at the bottom of the crucible, and the small hole of the conical hole is communicated with the capillary tube;
the bottom of the crucible is an inclined plane;
the rare earth single crystal comprises gadolinium gallium garnet single crystal or doped gadolinium gallium garnet single crystal.
2. The crucible as claimed in claim 1, wherein the diameter of the macropores of the tapered hole is 0.1 to 3 mm;
the diameter of the capillary tube is 0.1-0.95 mm;
the included angle between the conical bevel edge of the conical hole and the bottom of the crucible is 0-45 degrees;
and a circular chamfer is arranged at the joint of the conical bevel edge of the conical hole and the bottom of the crucible.
3. The crucible as claimed in claim 1, wherein the height of the tapered hole is 0.1 to 10 mm;
the number of the conical holes is 1;
the thickness of the bottom of the crucible is 0.5-1.5 mm;
the diameter of the crucible is 10-15 mm;
the height of the crucible is 25-50 mm.
4. The crucible as claimed in claim 1, wherein the material of the crucible preferably comprises one or more of Pt, Ir, Re, Mo and graphite;
the length of the capillary tube is 0.2-3 mm;
the appearance and parameters of the crucible are obtained by calculating the growth rate formula of the rare earth single crystal optical fiber;
the appearance of the crucible comprises one or more of appearance selection of the bottom of the crucible, whether a tapered hole is arranged in the crucible and whether a circular chamfer angle is arranged at the joint of a tapered bevel edge of the tapered hole and the bottom of the crucible;
the parameters of the crucible comprise one or more of the diameter of a large hole of the tapered hole, the diameter of the capillary tube, the included angle between the tapered bevel edge of the tapered hole and the bottom of the crucible, the height of the tapered hole and the length of the capillary tube.
5. The crucible of claim 4, wherein the diameter of the capillary is calculated from the growth rate formula of the rare earth single crystal fiber;
the diameter of the large hole of the conical hole is obtained by calculating the growth rate formula of the rare earth single crystal optical fiber;
the included angle between the tapered bevel edge of the tapered hole and the bottom of the crucible is obtained by calculating the growth rate formula of the rare earth single crystal optical fiber;
the bottom of the crucible is selected by a growth rate formula of the rare earth single crystal optical fiber and is obtained by calculation;
and calculating the parameters of the crucible based on one or more of the viscosity, wettability and density of the rare earth single crystal.
6. The crucible of claim 4, wherein the rare earth single crystal fiber has a growth rate formula as shown in formula (II);
Figure FDA0002831222370000021
wherein m is the mass of the rare earth single crystal in the crucible, r is the radius of a capillary hole at the bottom of the crucible, and r is1Is the physical distance from the center of the capillary to the wall of the tube, r2The distance from the center of the capillary to the boundary layer, l is the length of the capillary at the bottom end of the crucible, t is unit time, D is the diameter of the single crystal optical fiber, D is 0.1-0.95 mm, RfiberThe growth rate of the single crystal optical fiber with the diameter D;
(Ebond/Auvwduvw)radialis the chemical bonding energy density of the rare earth single crystal along the radial direction;
(Ebond/Auvwduvw)axialis the chemical bonding energy density of the rare earth single crystal along the axial direction.
7. Crucible according to claim 6, characterized in that said formula (II) results from the following steps:
a) obtaining the pressure difference delta P of the downward flowing of the rare earth single crystal melt by referring to the formula (1), and calculating to obtain the driving force F of the downward flowing of the material by referring to the formula (1');
Figure FDA0002831222370000022
F＝ΔP·S1 (1`)，
where F is the driving force for the downward flow of the melt in the capillary, Δ P is the pressure difference, S1Is the capillary end face area;
g is the gravity of the melt in the crucible, r is the radius of the capillary pores at the bottom of the crucible, (E)bond/Auvwduvw)axialIs the chemical bonding energy density of the rare earth single crystal along the axial direction;
deriving and obtaining the friction force f in the capillary at the bottom end of the crucible based on the formula (2), and referring to the formula (3);
Figure FDA0002831222370000031
Figure FDA0002831222370000032
wherein f is the internal friction of the capillary at the bottom end of the crucible, eta is the viscosity coefficient of the melt, and S2The area of the side surface of the capillary tube, r is the radius of the capillary hole at the bottom of the crucible, and dv/dr is the velocity gradient of the melt; t is unit time, (E)bond/Auvwduvw)radialThe chemical bonding energy density of the rare earth single crystal along the radial direction, and l is the length of a capillary at the bottom end of the crucible;
b) based on the fact that in a steady-state growth state, in the growth process of the micro-pulling-down single crystal optical fiber, the force in the capillary tube along the vertical direction is balanced, and the driving force of the downward flow of the melt in the capillary tube is equal to the internal friction force of the capillary tube at the bottom end of the crucible, according to the formula (4);
Figure FDA0002831222370000033
c) establishing a boundary condition, wherein r ═ r1，v＝0；r＝r2，v＝vporeCombining the formula (4) to obtain the downward flow rate of the melt in the capillary, and referring to the formula (5);
Figure FDA0002831222370000034
wherein r is1Is the physical distance from the center of the capillary to the wall of the tube, r2Distance from capillary center to boundary layer, vporeThe rate of melt flow down the capillary;
d) based on the rate of downward flow of the melt in the capillary obtained in the above steps, after the fluid flows out of the capillary and infiltrates the bottom end of the crucible, the fluid grows in the solid/liquid/solid interface region, and according to the conservation of mass, the growth rate R of the single crystal optical fiber with the diameter D is obtainedfiberAs shown in formula (II);
the specific steps of the derivation are as follows:
based on the tendency of the melt to heterogeneously nucleate within the capillary at the solid/liquid interface of the tube wall, formula (2') is obtained, and formula (2) is then combined to obtain formula (3);
Figure FDA0002831222370000041
the resultant energy density.
8. The method for growing the bendable flexible rare earth single crystal optical fiber by utilizing the micro-pulling-down method is characterized by comprising the following steps of:
(1) calculating the growth rate of the rare earth single crystal optical fiber by using a growth rate formula of the rare earth single crystal optical fiber;
(2) designing and building a temperature field structure for growing the rare earth single crystal optical fiber according to the growth rate obtained in the step; designing the appearance and parameters of the crucible according to the growth rate obtained in the step;
(3) filling a crystal material into a crucible, setting growth parameters required by the growth of the rare earth single crystal according to the parameters and the growth rate in the growth rate calculation process of the rare earth single crystal optical fiber, and then heating;
(4) when the heating temperature is higher than the melting point of the rare earth single crystal, moving the seed crystal upwards to contact the bottom end of the crucible, forming a meniscus at the bottom of the crucible, and then growing according to the growth parameters set in the step to obtain the rare earth single crystal optical fiber;
the crucible is as claimed in any one of claims 1 to 7.
9. The method according to claim 8, wherein the rare earth single crystal optical fiber has a growth rate of 0.05 to 12 mm/min;
the diameter of the rare earth single crystal optical fiber is 0.1-0.95 mm;
in the temperature field structure, the centers of the heat insulating material, the seed crystal, the crucible and the rear heater are kept on the same straight line in the vertical direction;
the method also comprises the following steps before the growth is carried out according to the set growth parameters:
finely adjusting the temperature of the melt, and growing according to set growth parameters when the melt infiltrates the bottom end of the whole crucible and the side surface of the melt is not protruded outwards;
the fine adjustment range is 10-40 ℃ higher than the melting point of the rare earth single crystal;
the difference between the heating temperature and the melting point of the rare earth single crystal is more than 0 ℃ and less than or equal to 50 ℃.
10. A method for calculating the growth rate of a bendable flexible rare earth single crystal optical fiber in a micro-pulling-down method is characterized by comprising the following steps,
1) determining the thermodynamic growth form of the rare earth single crystal according to the chemical bonding theory of crystal growth;
2) determining a radial growth direction corresponding to the axial growth direction and an anisotropic chemical bonding structure at a growth interface based on the thermodynamic growth form of the rare earth single crystal obtained in the step;
3) calculating the anisotropic chemical bonding energy density of the rare earth single crystal along the axial direction and the anisotropic chemical bonding energy density of the rare earth single crystal along the radial direction based on the anisotropic chemical bonding structure at the growth interface obtained in the step (I);
Figure FDA0002831222370000051
wherein the content of the first and second substances,
Figure FDA0002831222370000052
is along [ uvw ]]A directionally grown chemical bonding energy;
Auvwfor growth of elementary edges [ uvw ]]The projected area of the direction;
duvwis a single crystal edge [ uvw ]]The step height of the direction;
4) calculating the growth rate of the rare earth single crystal fiber based on the isotropic chemical bonding energy density of the rare earth single crystal obtained in the step along the axial direction and the radial direction, wherein the growth rate is shown as a formula (II);
Figure FDA0002831222370000053
wherein m is the mass of the rare earth single crystal in the crucible, r is the radius of a capillary hole at the bottom of the crucible, and r is1Is the physical distance from the center of the capillary to the wall of the tube, r2The distance from the center of the capillary to the boundary layer, l is the length of the capillary at the bottom end of the crucible, t is unit time, D is the diameter of the single crystal optical fiber, D is 0.1-0.95 mm, RfiberThe growth rate of the single crystal optical fiber with the diameter D;
(Ebond/Auvwduvw)radialis the chemical bonding energy density of the rare earth single crystal along the radial direction;
(Ebond/Auvwduvw)axialis the chemical bonding energy density of the rare earth single crystal along the axial direction.
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