CN109518270B - Cladding preparation method of single crystal optical fiber - Google Patents
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- CN109518270B CN109518270B CN201811179140.4A CN201811179140A CN109518270B CN 109518270 B CN109518270 B CN 109518270B CN 201811179140 A CN201811179140 A CN 201811179140A CN 109518270 B CN109518270 B CN 109518270B
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- 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
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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
- 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
- C30B29/34—Silicates
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02295—Microstructured optical fibre
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Abstract
The invention relates to a cladding preparation method of a single crystal optical fiber, which comprises the following steps: (1) preparing a cladding layer: taking a single crystal optical fiber as a preform raw material, and drilling a hole on the central axis of the single crystal optical fiber to obtain a cladding; (2) preparing a prefabricated rod: taking a monocrystal with the outer diameter equivalent to the central aperture of the cladding as a fiber core, and inserting the monocrystal into the central aperture of the cladding to obtain a prefabricated rod; (3) preparation of single crystal optical fiber: and performing crystal growth by using the prefabricated rod as a seed crystal to form the single crystal optical fiber with a cladding structure and a fiber core structure. Compared with the prior art, the invention has the advantages of less raw materials, high growth speed, small-size noble metal crucible, low cost and the like.
Description
Technical Field
The invention belongs to the technical field of preparation of crystal optical fiber materials, and relates to a cladding preparation method of a single crystal optical fiber.
Background
The application potential of single crystal optical fiber in the fields of optical communication, optical fiber sensing, nonlinear optics and the like has been receiving wide attention. Because the substrate is composed of single crystal, compared with the traditional glass fiber and photonic crystal fiber, the material has the advantages of good thermal property, low phonon energy and wide emission section. Recently, the growth and application of crystal fiber have made a major breakthrough, and the laser output in the crystal fiber is realized: YAG single crystal fiber with Nd content of 0.2% realizes continuous laser output at 946nm, the inclined efficiency can reach 53%, and the maximum output is 34W.
The cladding technology is an important link for realizing commercialization of the single crystal optical fiber, however, the traditional cladding technology based on the glass matrix optical fiber, including the sol-gel cladding, the air pressure cladding, the liquid crystal filling cladding and the like, is not suitable for the single crystal optical fiber. The reason is that the single crystal fiber is melted and chemically reacted when contacting with the melt of the cladding, resulting in damage to the core or failure to realize the cladding structure.
Recently, Japanese scientists proposed a technique for growing a periodic structure of a quasicrystal, and obtained a single crystal of a periodic structure of a quasicrystal with a pitch of 100 μm, in which the periodic structure of a quasicrystal is used as a seed crystal, and a lattice competition phenomenon does not occur during the growth of the crystal, but the periodic structure of a quasicrystal is inherited (see FIG. 2). The fiber core and the cladding in the prefabricated rod of the single crystal fiber can realize synchronous directional growth according to the growth mechanism of the quasi-lattice crystal, and the single crystal fiber with the cladding structure is obtained.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a cladding preparation method of a single crystal optical fiber, which changes a periodic structure into a cladding structure and changes the preparation of the quasi-lattice periodic structure into the preparation of the cladding of the single crystal optical fiber in the application field.
The purpose of the invention can be realized by the following technical scheme: a method for preparing a cladding of a single crystal optical fiber, comprising the steps of:
(1) preparing a cladding layer: taking a single crystal optical fiber as a preform raw material, and drilling a hole on the central axis of the single crystal optical fiber to obtain a cladding;
(2) preparing a prefabricated rod: taking a monocrystal with the outer diameter equivalent to the central aperture of the cladding as a fiber core, and inserting the monocrystal into the central aperture of the cladding to obtain a prefabricated rod;
(3) preparation of single crystal optical fiber: and performing crystal growth by using the prefabricated rod as a seed crystal to form the single crystal optical fiber with a cladding structure and a fiber core structure.
The ratio of the outer diameter of the single crystal optical fiber adopted by the cladding to the outer diameter of the single crystal used as the fiber core is 2-5: 1, and the inner diameter of the central hole of the cladding is equivalent to the outer diameter of the fiber core.
And (2) drilling holes in the step (1) by adopting ultrasonic waves.
The crystal growth in the step (3) adopts a micro-pulling-down crystal growth method: fixing the prefabricated rod on a seed rod and placing the prefabricated rod below a crucible, growing crystals downwards after contacting a melt below the microtube, naturally closing a gap between a cladding and a fiber core, and simultaneously growing the cladding and the fiber core to form the single crystal optical fiber with a cladding structure and a fiber core structure.
The micro-pull-down crystal growth method adopts a micro-pull-down crystal growth furnace, which comprises a top cover plate (1), a side heat-insulating baffle (3), an upper heating body (4), an electrode (5), a lower heat-insulating layer (6), a crucible (7), a lower heating body (8), a support (10), a seed crystal rod (11) and a lifting motor (12), wherein the top cover plate (1) and the side heat-insulating baffle (3) are respectively arranged at the top and the side part of the upper heating body (4), the electrode (5) is fixedly connected with the crucible (7), the crucible (7) is arranged between the upper heating body (4) and the lower heating body (8), the lower heating body (8) is positioned in the lower heat-insulating layer (6), the seed crystal rod (11) is arranged on the support (10), the bottom of the crucible is connected with the lifting motor (12), and seed crystals (9) to be grown are inserted into the seed crystal rod (11), the lifting motor (12) drives the seed crystal rod (11) to drive the seed crystal (9) to be pulled down from the crucible (7).
The bottom of the crucible (7) is provided with a micro tube, and a crystal melt which is the same as the seed crystal to be grown is arranged in the micro tube.
The single crystal optical fiber has a symmetrical crystal system, such as a crystal of a tetragonal crystal system, a monoclinic crystal system and the like. These optical crystals of crystal system generally have different refractive indices in different crystal directions, and thus have the possibility of realizing the function of an optical fiber. Including but not limited to oxide-matrix single crystal optical fibers, and also to the cladding preparation of fluoride-matrix single crystal optical fibers based on the same concept.
Compared with the prior art, the single crystal optical fiber prepared by the method has the following characteristics:
1. the cladding and the fiber core are both single crystals, and the cladding and the fiber core are in closed contact without other media.
2. Refractive index n of the cladding2Refractive index n lower than core1(see FIG. 1), and for single-mode single-crystal fibers, (n)1-n2)/n1<0.5 percent. Wherein n is3Is an environmental medium.
3. The cladding material has suitable optical properties including absorption peak position, fluorescence peak position, etc.
4. The thermal property of the cladding material is close to that of the fiber core, so that the mechanical stress generated in the working environment is avoided, and the service life of the optical fiber is prolonged.
5. The preparation method has the advantages of less raw materials, high growth speed, small-size precious metal crucible, low cost and the like.
Drawings
FIG. 1 is a schematic cross-sectional view of a single crystal optical fiber;
FIG. 2 is a periodic structure that can inherit a seed crystal during crystal growth;
FIG. 3 is a schematic view of a micro-downdraw furnace configuration;
FIG. 4 is a schematic view of the structure of the crucible;
FIG. 5 is a schematic view showing a process of growing an LGS single crystal optical fiber.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
Example 1
A method for preparing a cladding of a single crystal optical fiber comprises the following steps:
(1) preparing a cladding layer: taking a single crystal optical fiber as a preform raw material, and drilling a hole on the central axis of the single crystal optical fiber by adopting ultrasonic waves to obtain a cladding;
(2) preparing a prefabricated rod: taking a monocrystal with the outer diameter equivalent to the central aperture of the cladding as a fiber core, and inserting the monocrystal into the central aperture of the cladding to obtain a prefabricated rod;
(3) preparation of single crystal optical fiber: and performing crystal growth by using the prefabricated rod as a seed crystal to form the single crystal optical fiber with a cladding structure and a fiber core structure.
The crystal growth adopts a micro-pull-down crystal growth method: fixing the prefabricated rod on a seed rod and placing the prefabricated rod below a crucible, growing crystals downwards after contacting a melt below the micro tube, naturally closing a gap between a cladding and a fiber core, and simultaneously growing the cladding and the fiber core to form the single crystal optical fiber with a cladding structure and a fiber core structure.
Wherein the micro pull-down crystal growth method adopts a micro pull-down crystal growth furnace, the structure is shown in figure 3, the micro pull-down crystal growth furnace comprises a top cover plate (1), a side heat preservation baffle plate (3), an upper heating body (4), an electrode (5), a lower heat preservation layer (6), a crucible (7), a lower heating body (8), a bracket (10), a seed rod (11) and a lifting motor (12), the top cover plate (1) and the side heat preservation baffle plate (3) are respectively arranged at the top and the side part of the upper heating body (4), the electrode (5) and the crucible (7) are fixedly connected through a bolt 2, the crucible (7) is arranged between the upper heating body (4) and the lower heating body (8), the lower heating body (8) is positioned in the lower heat preservation layer (6), the seed rod (11) is arranged on the bracket (10), the bottom of the seed rod is connected with the lifting motor (12), and seed crystals (9) to be grown are inserted into the seed rod (11), the lifting motor (12) drives the seed rod (11) to drive the seed crystal (9) to be pulled down from the crucible (7). The bottom of the crucible (7) is provided with a micro tube, and a crystal melt which is the same as the seed crystal to be grown is arranged in the micro tube. The above components are described in detail as follows:
the top cover plate 1 is made of alumina ceramic and is used for top heat preservation and heat insulation;
the bolt 2 is made of alumina or stainless steel and is used for fixedly connecting the crucible 7 of the electrode 5 together;
the side heat-preservation baffle 3 is made of alumina ceramics or alumina foam refractory bricks and is used for laterally preserving heat and protecting the bolt 2;
the upper heating body 4 uses a silicon-molybdenum rod or a metal resistance wire and is used for adjusting a temperature field;
the stainless steel electrode 5 is externally connected with a power supply and is fixedly connected with the crucible 7 by using a bolt 2 to form a current path;
a lower heat-insulating layer 6, alumina foam refractory bricks for heat insulation of a thermal field below the crucible, a support electrode 5, a side heat-insulating baffle 3, a crucible 7 and a top cover plate 1;
the crucible 7 is made of platinum or platinum-rhodium alloy, generates heat through the self resistance of the crucible, is used for melting raw materials, and grows crystals, and has a structure shown in figure 4.
The lower heating body 8 uses a silicon-molybdenum rod or a metal resistance wire and is used for adjusting the temperature gradient of a thermal field and protecting crystals;
a seed crystal 9 having a cladding and core structure;
the support 10 is used for placing the top cover plate (1), the side heat-preservation baffle plate (3), the upper heating body (4), the electrode (5) and the lower heat-preservation layer (6);
a seed rod 11 for fixing the seed crystal 9;
and the lifting motor 12 is used for lifting the seed rod 11.
The growth of langasite is specifically described as an example:
1. growing siliconLanthanum gallium oxide (La)3Ga5Si2O14Langasite, hereinafter abbreviated as LGS) single crystal optical fiber, in which a-oriented LGS crystals are processed into a clad of a preform and c-oriented LGS crystals are inserted as a core.
2. La of 99.99% purity2O3，Ga2O3And SiO2As raw materials, the solid phase sintering was carried out at 1100 ℃ for 12 hours after thorough mixing to form a pure LGS phase. 15g of sintered LGS solid raw material was weighed into a crucible. The upper heater 4 is set to 1000 deg.C and the lower heater 8 is set to 800 deg.C. The power supply is 100v, 20A, and the platinum crucible generates heat under the action of current and melts the raw materials.
3. The preform was placed on the seed rod 11 of a micro-downdraw furnace (see fig. 5). The LGS melt in the microtube at the bottom of the crucible 7 is butted upwards and left stand for about 5 minutes, so that the melt is fully contacted with the seed crystal 9 and the monocrystalline fiber starts to grow downwards after reaching a thermal equilibrium state (shown in figure 5). The core and the cladding grow independently and synchronously to form a single crystal fiber with a cladding structure (see fig. 5 c). In this example, the pull-down rate of the LGS single-crystal optical fiber was 1.5mm/min (90mm/h), and the growth time was 2 hours, to obtain an LGS single-crystal optical fiber of 180 mm.
Example 2
Lanthanum gallium tantalate (La) was prepared using the method and apparatus as in example 13Ga5.5Ta0.5O14Langate, LGT), langasite (La)3Ga5.5Nb0.5O14Langanite, LGN) single crystal optical fiber, the properties of the obtained product are shown in the following table:
TABLE 1 refractive indices of LGS, LGN, LGT
As can be seen from the above table, the refractive indexes of the single crystal optical fiber with the cladding structure and the core structure, which are prepared by the method of the present invention, in the a direction and the c direction are different by about 0.005, which proves that the single crystal optical fiber with the oriented growth which meets the requirements is obtained.
As in table 1.As shown, the LGN and LGT crystals differ in refractive index in the a-direction and the c-direction, with the c-direction as the core (refractive index n)1) a direction is cladding (refractive index n)2) (n) in a partial band in the visible band and the near infrared band1-n2)/n1<0.5%, and can also be used for growing single crystal optical fiber with cladding structure.
Claims (6)
1. A method for preparing a cladding of a single crystal optical fiber, comprising the steps of:
(1) preparing a cladding layer: taking a single crystal optical fiber as a preform raw material, and drilling a hole on the central axis of the single crystal optical fiber to obtain a cladding;
(2) preparing a prefabricated rod: taking a monocrystal with the outer diameter equivalent to the central aperture of the cladding as a fiber core, and inserting the monocrystal into the central aperture of the cladding to obtain a prefabricated rod;
(3) preparation of single crystal optical fiber: taking the prefabricated rod as a seed crystal to carry out crystal growth to form a single crystal optical fiber with a cladding structure and a fiber core structure; the crystal growth adopts a micro-pull-down crystal growth method: fixing the prefabricated rod on a seed rod and placing the prefabricated rod below a crucible, growing a crystal downwards after contacting a melt below a micro tube, naturally closing a gap between a cladding and a fiber core, and simultaneously growing the cladding and the fiber core by using the same melt to form a single crystal optical fiber with a cladding structure and a fiber core structure;
refractive index n of the cladding2Refractive index n lower than core1。
2. The method for preparing the cladding of the single crystal optical fiber according to claim 1, wherein the ratio of the outer diameter of the single crystal optical fiber used for the cladding to the outer diameter of the single crystal used as the core is 2-5: 1, and the inner diameter of the central hole of the cladding is equivalent to the outer diameter of the core.
3. The method of claim 1, wherein the drilling in step (1) is performed by ultrasonic drilling.
4. The cladding preparation method of the single crystal optical fiber according to claim 1, wherein the micro-pulling-down crystal growth method adopts a micro-pulling-down crystal growth furnace, which comprises a top cover plate (1), a side heat preservation baffle (3), an upper heating body (4), an electrode (5), a lower heat preservation layer (6), a crucible (7), a lower heating body (8), a bracket (10), a seed rod (11) and a lifting motor (12), wherein the top cover plate (1) and the side heat preservation baffle (3) are respectively arranged at the top and the side of the upper heating body (4), the electrode (5) is fixedly connected with the crucible (7), the crucible (7) is arranged between the upper heating body (4) and the lower heating body (8), the lower heating body (8) is positioned in the lower heat preservation layer (6), the seed rod (11) is arranged on the bracket (10), and the bottom of the seed rod is connected with the lifting motor (12), the seed crystal (9) to be grown is inserted into the seed rod (11), and the lifting motor (12) drives the seed rod (11) to drive the seed crystal (9) to be pulled down from the crucible (7).
5. The method for preparing the cladding of the single crystal optical fiber according to claim 4, wherein the bottom of the crucible (7) is provided with a microtube in which the same crystal melt as the seed crystal to be grown is arranged.
6. The method of claim 1, wherein the substrate of the single crystal fiber has different refractive indices in different crystal orientations, such as langasite, langasite or langasite niobate.
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