CN110217981A - A kind of single crystal fiber and preparation method thereof - Google Patents

Abstract

The invention discloses a single-crystal optical fiber and a preparation method thereof. The single-crystal optical fiber includes a fiber core, an inner cladding and an outer cladding, and the fiber core is a solid single-crystal fiber. The preparation method includes preparing a plurality of tubular glass prefabricated rods with matching inner and outer diameters; drawing the prefabricated rods to obtain a glass cladding with a two-layer structure; inserting solid single crystal fibers into the inner cladding and heating and tapering to obtain glass clad single crystal fiber. The material, quantity, size and position of the tubular element used in the present invention can be adjusted, and its optical and thermal properties can be matched with the single crystal material to the greatest extent, so as to ensure the mode quality and high power operation of the single crystal optical fiber; at the same time, it also has The advantages of simple structure and convenient preparation have broken the bottleneck of the difficulty in preparing the cladding of traditional single crystal optical fibers, and are ideal cladding preparation solutions for single crystal optical fibers.

Description

A kind of single crystal optical fiber and its preparation method

technical field

The invention belongs to the field of crystal optical fibers, and more specifically relates to a single crystal optical fiber and a preparation method thereof.

Background technique

Crystal fiber is different from traditional silica fiber. It uses crystal (such as sapphire, YAG, sesquioxide crystal) as the medium and waveguide structure as the beam transmission channel. It is a special structure between traditional fiber and bulk crystal. Therefore, crystal fiber has the advantages of optical fiber and crystal medium at the same time. Compared with traditional silica fibers, crystal fibers have better physical properties. Taking YAG crystal as an example, its thermal conductivity is an order of magnitude higher than that of glass optical fiber, so YAG crystal optical fiber has better heat dissipation performance; secondly, YAG crystal has a melting point of about 2000°C and has a greater damage threshold than silica optical fiber. In addition, the stimulated Brillouin scattering coefficient of YAG crystal fiber is 10 times that of silica glass fiber, so it has a higher stimulated Brillouin scattering threshold. These physical characteristics may essentially solve the output power bottleneck of current high-power fiber lasers, break the power limit of fiber lasers, and obtain higher power outputs. In addition, extreme environments such as high temperature, high pressure, strong radiation, strong electromagnetic interference, flammable, explosive, and strong corrosion widely exist in many fields such as industry, national defense, and aerospace, such as: metallurgy, oil extraction, thermal power generation, nuclear power generation, Aerospace detection, missile guidance, and internal combustion engines, motors, turbines and rocket propulsion, etc. However, currently, under these extreme conditions, few sensors can provide accurate and reliable information on temperature, pressure, healthy operation, etc., which has become a difficult problem in the scientific and industrial circles. Since crystal fibers have a higher melting point and better corrosion resistance, it has become a development trend in the industry to use crystal fibers instead of silica fibers for sensing in extreme environments.

The cladding of a single crystal fiber must at least meet the following characteristics: a lower refractive index than the crystal core, a thermal expansion coefficient close to the core, thermochemical and mechanical stability, and a stable chemical structure and phase equilibrium at the core-cladding interface. . The cladding materials of single crystal optical fiber mainly include glass materials and crystal materials. The cladding of crystal materials generally adopts a specific physical or chemical coating process, which requires high reaction conditions, and the preparation process is relatively complicated, and the prepared crystal cladding The refractive index cannot be adjusted. In contrast, the optical and thermal properties of glass materials such as lanthanide glass, quartz glass, silicate glass, etc. Power running.

The current hot drawing process suitable for materials such as traditional silica optical fibers is not suitable for crystal materials. Crystal materials will become glassy in a hot drawing environment, and the existing crystal optical fiber preparation process does not have a cladding structure. In the strict sense of optical fiber, the bare fiber is susceptible to serious attenuation due to the influence of pollutants in the environment. In addition, the refractive index difference between the bare fiber and the air is too large, and the refractive index in the air is not uniform and fluctuates greatly. Good control. Crystal bare fiber plus cladding can enhance mechanical properties, thermal properties, form an optical waveguide, control the transmission mode, and then apply it to fiber laser, so the crystal material needs to be further processed to add a cladding structure to form a crystal optical fiber.

Contents of the invention

In view of the defects of the prior art, the purpose of the present invention is to provide a single crystal optical fiber and its preparation method, which aims to solve the problems that the cladding preparation of traditional crystal optical fibers has high requirements for experimental equipment and reaction conditions, and the preparation process is relatively complicated. .

In order to achieve the above object, according to one aspect of the present invention, a single crystal fiber is provided, including a core, an inner cladding and an outer cladding; the core is a solid single crystal fiber; the outside of the core is coated with Inner cladding and outer cladding.

Preferably, the shape of the inner cladding is circular, hexagonal or octagonal.

Preferably, single-layer or multi-layer glass tubes are evenly arranged between the inner cladding and the outer cladding, and the number thereof is 3-200.

Preferably, the cladding material of the single crystal optical fiber is lanthanide glass, quartz glass, silicate glass, or phosphate glass.

Preferably, the inner diameter of the cladding of the single crystal optical fiber ranges from 10 μm to 1 mm, matching the size of the fiber core.

Preferably, the material of the single crystal fiber core is sapphire, yttrium aluminum garnet (YAG), lutetium oxide (Lu ₂ O ₃ ), zirconia (ZrO ₂ ), borate (Ca ₄ O(BO ₃ ) ₃ ) or Rare earth element doping and transition metal element doping of any of the above single crystals, the doped rare earth ions include Nd ³⁺ , Yb ³⁺ , Tm ³⁺ , Ho ³⁺ , Er ³⁺ , Pr ³⁺ , Sm ^{2 +} , etc., transition metal ions include Cr ³⁺ , Ti ³⁺ , Ni ²⁺ , Co ²⁺ , etc.

The glass cladding of the single crystal optical fiber provided by the present invention and the refractive index of the single crystal core material are as shown in Table 1:

Table 1

According to another aspect of the present invention, a method for preparing a single crystal optical fiber is provided, comprising:

(1) Prepare a plurality of tubular glass preforms with matching inner and outer diameters;

(2) drawing the preform to obtain a glass cladding with a two-layer structure;

(3) inserting the solid single crystal fiber into the inner cladding layer of the glass cladding, heating and tapering, and obtaining the single crystal optical fiber with the glass cladding.

The first is to design the structure, prepare the glass-clad prefabricated rod, and hot-draw to obtain the glass cladding; then use the micro-structured optical fiber tapering process to melt the cladding structure on the solid single-crystal fiber to form a single-crystal fiber.

Further, preparing a plurality of tubular glass preforms with matched inner and outer diameters specifically includes the following steps:

(1) uniformly fixing a plurality of first glass tubes according to the preset shape of the inner cladding to obtain a stack;

(2) Insert the stacked element into the second glass tube.

Preferably, preparing a plurality of tubular glass preform rods with matching inner and outer diameters further includes fixing the stacking element to the same end of the second glass tube.

Preferably, two-stage pressure control is adopted when drawing the preform, wherein a slight positive pressure is used inside the stack; a slightly positive pressure or a slightly negative pressure is used between the second glass tube and the stack, which is smaller than the former.

Preferably, the thickness of the glass cladding prepared by heating the taper is controlled at 10um-2mm.

Preferably, the length of the prepared single crystal optical fiber ranges from 1 cm to 100 cm.

Through the above technical solutions conceived by the present invention, compared with the prior art, the following beneficial effects can be obtained:

1. The present invention provides a single crystal optical fiber with a glass cladding structure. Compared with the preparation of the traditional crystal optical fiber, the physical/chemical vapor deposition process is used to grow the crystal cladding with a low refractive index on the surface of the bare fiber. The requirements for experimental equipment and reaction conditions are high, the refractive index of the prepared amorphous cladding is uncontrollable, and the crystal growth rate is limited. The optical properties and thermal properties between the glass material and the single crystal material used in the present invention Matching, the process method is simple and feasible, the cost of materials and preparation is low, which greatly reduces the difficulty of the cladding preparation process of single crystal optical fiber, and breaks the traditional high demand for experimental equipment and reaction conditions. , the preparation process is relatively complicated, and the optical/thermal properties cannot be adjusted;

2. The present invention provides a single crystal optical fiber heating taper process with a glass cladding, which directly inserts the center of the glass cladding prepared by wire drawing into the existing solid single crystal fiber, ensuring that the gap between the core and the cladding is After the relative movement between them does not occur, by controlling the heating temperature, stretching speed and stretching time, the glass cladding is just nested on the solid single crystal fiber, and the special shape and structure of the glass tube itself is not changed, so that a core cladding is obtained. Structural single crystal fiber;

3. The present invention uses glass materials with close refractive index and thermal expansion coefficient as the cladding material to study the influence of glass cladding with different shapes and structures on the performance of single crystal optical fiber waveguides, optical properties and thermal properties such as glass material refractive index and thermal expansion coefficient Both can achieve a wide range of regulation, so as to ensure the mode quality and high power operation of single crystal fiber;

4. The single crystal optical fiber with glass cladding obtained in the present invention provides a research basis for lasers or sensors based on single crystal optical fiber. Single crystal optical fiber not only has many advantages of optical fiber, such as good light guiding, light weight, small volume, Anti-electromagnetic interference, and because its material is a single crystal, it has the inherent characteristics of a single crystal. In theory, the output energy of a single crystal fiber can reach 50 times that of the current glass fiber. The single crystal fiber is expected to break the existing fiber laser. The output limit enables the output power of fiber lasers to increase by leaps and bounds. In addition, it can also be widely used in extreme environments such as high temperature, high pressure, strong radiation, strong electromagnetic interference, flammable, explosive, and strong corrosive.

Description of drawings

Fig. 1 is a schematic diagram of the structure of a single crystal optical fiber provided by the present invention;

Fig. 2 is a schematic diagram of the cladding structure of the single crystal optical fiber provided by the embodiment of the present invention;

Fig. 3 is a schematic diagram of the cladding structure of a single crystal optical fiber provided by another embodiment of the present invention;

4 is a schematic structural view of a cladding preparation device for a single crystal optical fiber provided by an embodiment of the present invention;

Fig. 5 is a schematic structural diagram of a single crystal fiber provided by an embodiment of the present invention;

6 is a schematic diagram of a tapered single crystal fiber provided by an embodiment of the present invention;

Fig. 7 is a block diagram of a tapered system of a single crystal fiber provided by an embodiment of the present invention;

Notes on drawings:

1. Outer cladding, 2. Inner cladding, 3. Preform clamp, 4. Two-stage pressure control joint, 5. Preform, 6. Heating furnace, 7. Laser caliper, 8. Traction device, 9. Cutting device , 10, glass cladding, 11, fiber core.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute conflicts with each other.

As shown in Fig. 1, the present invention provides a kind of single crystal optical fiber, comprises fiber core, inner cladding and outer cladding; Fiber core is a solid single crystal fiber; The outside of fiber core is coated with inner cladding and outer cladding successively from inside to outside Floor.

Specifically, the shape of the inner cladding is circular, hexagonal or octagonal.

Specifically, single-layer or multi-layer glass tubes are evenly arranged between the inner cladding and the outer cladding, and the number thereof is 3-200.

Specifically, the cladding material of the single crystal optical fiber is lanthanide glass, quartz glass, silicate glass, or phosphate glass.

Specifically, the inner diameter of the cladding of the single crystal optical fiber ranges from 10 μm to 1 mm, matching the size of the fiber core.

Specifically, the material of the fiber core is sapphire, yttrium aluminum garnet (YAG), lutetium oxide (Lu ₂ O ₃ ), zirconium oxide (ZrO ₂ ), borate (Ca ₄ O(BO ₃ ) ₃ ) or any of the above A single crystal doped with rare earth elements and transition metal elements. The doped rare earth ions include Nd ³⁺ , Yb ³⁺ , Tm ³⁺ , Ho ³⁺ , Er ³⁺ , Pr ³⁺ , Sm ²⁺ , etc. , transition metal ions include Cr ³⁺ , Ti ³⁺ , Ni ²⁺ , Co ²⁺ , etc.

According to another aspect of the present invention, a method for preparing a single crystal optical fiber is provided, comprising:

(1) Prepare a plurality of tubular glass preforms with matching inner and outer diameters;

(2) drawing the preform to obtain a glass cladding with a two-layer structure;

(3) inserting the solid single crystal fiber into the inner cladding layer of the glass cladding, heating and tapering, and obtaining the single crystal optical fiber with the glass cladding.

Further, preparing a plurality of tubular glass preforms with matched inner and outer diameters specifically includes the following steps:

(1) uniformly fixing a plurality of first glass tubes according to the preset shape of the inner cladding to obtain a stack;

(2) Insert the stacked element into the second glass tube.

Specifically, preparing a plurality of tubular glass preform rods with matching inner and outer diameters further includes fixing the stacking element to the same end of the second glass tube.

Specifically, two-stage pressure control is adopted when drawing the preform, wherein a slight positive pressure is used inside the stack; a slightly positive or slightly negative pressure is used between the second glass tube and the stack, which is smaller than the former.

Specifically, the length of the prepared single crystal optical fiber ranges from 1 cm to 100 cm.

As shown in Figure 2, the cladding of a single crystal fiber includes an outer cladding located on the outermost layer, an inner cladding composed of stacked tubular elements and a core defined by the inner cladding are arranged on the inner surface of the outer cladding. The inner cladding is centered on a tubular element and evenly surrounds a layer of several tubular elements. As shown in Fig. 3, the inner cladding is centered on a tubular element and evenly surrounds several tubular elements in multiple layers.

The cladding material is silicate glass and air, and the core is single crystal Lu ₂ O ₃ fiber. The preparation method of single crystal optical fiber with glass cladding is summarized as follows: designing structure, arranging structure and drawing capillary, making the micron size The bare single crystal fiber is inserted into the inner cladding of the capillary, and the single crystal optical fiber with glass cladding is obtained by local heating and tapering.

The preparation method of preform comprises the following steps:

(1) Use silicate glass tubes with an outer diameter of 20mm, an inner diameter of 14mm, an outer diameter of 13mm, an inner diameter of 9mm, and a length of 40cm for casing, and wrap the joint at one end of the two tubes with a raw material tape.

(2) Take 5 silicate glass thin tubes with an outer diameter of 2.50 mm, an inner diameter of 1.95 mm, and a length of 45 cm. With one of them as the center, arrange the other 4 thin tubes evenly around it, and fix one end with AB glue. Ensure that it does not move relative to each other.

(3) Insert the 5-hole stacking element into the annular sleeve in (1), and one end of the stacking element should be about 3cm longer. This port is wound with the port of the outer ring of the raw material tape, and the port of the stacking element is fixed with AB glue In the same direction, the junction between the stacking element and the outer ring sleeve should also be tightly fixed with a raw material tape to ensure that it does not move relative to each other.

The preparation device is shown in FIG. 4 , including a preform holder 3 , a two-stage pressure control joint 4 , a heating furnace 6 , a laser caliper 7 , a pulling device 8 and a cutting device 9 .

The drawing method of preform comprises the following steps:

(1) Put the fixed end of the preform 6 into the special two-stage pressure control joint 4, the two-stage pressure control interface 5 is clamped by the preform rod clamp 3, and a micro positive pressure of 50 mbar is applied to the inside of the stacked element, and the outer ring is set The inside of the tube adopts a slight negative pressure of -2.50KPa, inserts the preform into the medium temperature furnace, and ensures that the preform is located in the middle of the medium temperature furnace.

(2) Wait for the temperature of the medium-temperature furnace 6 to rise. The temperature settings of the four heating zones of the medium-temperature furnace are 880°C, 983°C, 740°C, and 400°C, respectively, and the last section is the annealing section. After the temperature in the heating zone reaches the set temperature slowly, observe the heating condition of the preform rod in the furnace with a reflector at the lower furnace mouth of the medium temperature furnace. , the traction device 8, and finally cut the glass capillary at the cutting device 9 to a fixed length

(3) Control the feeding speed (preset ν _feed = 0.5mm/min), adjust the drawing speed (preset ν _draw = 0.32m/min) to achieve the required fiber size (d _fiber = 800μm, capillary central aperture 78 μm). A glass capillary with a length of 40 cm is cut to length at the cutting device 10 to obtain the glass cladding 10 to be processed later.

As shown in FIG. 5 , a single crystal fiber 11 with an outer diameter of 30 μm and a length of 45 cm is inserted into the glass cladding, and one end is fixed to ensure that it does not move relative to each other.

The taper of the single crystal fiber includes the following steps: as shown in Figure 6, fix the single crystal fiber obtained in Figure 5 on the taper stand, wait for the temperature in the heating zone to rise to 850°C, and draw the taper at both ends along the taper direction. The speed is controlled at 100 μm/min. The section of the fiber before tapering shows that there is a certain gap between the single crystal fiber and the capillary sleeve. The section of the single crystal fiber after tapering shows that the cladding has been nested on the single crystal fiber, and the cladding The special morphological structure of the layer has not changed. Fig. 7 is the optical fiber tapering system used in the example of the present invention, which mainly includes the main frame of the tapering machine, a pneumatic control system and so on. The outer diameter of the single crystal optical fiber after tapering is 310 μm, and the cladding thickness is 280 μm.

Those skilled in the art can easily understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (10)

1. A single crystal optical fiber, characterized in that, comprises a core, an inner cladding and an outer cladding; The fiber core is a solid single crystal fiber; the outside of the fiber core is covered with an inner cladding layer and an outer cladding layer sequentially from the inside to the outside. 2. The single crystal optical fiber according to claim 1, wherein the shape of the inner cladding is circular, hexagonal or octagonal. 3. The single crystal optical fiber according to claim 1, wherein the cladding material of the single crystal optical fiber is lanthanide glass, quartz glass, silicate glass or phosphate glass. 4. The single crystal optical fiber according to any one of claims 1 to 3, characterized in that the inner diameter of the cladding of the single crystal optical fiber ranges from 10 μm to 1 mm. 5. The single crystal optical fiber according to claim 1, characterized in that, the material of the core is sapphire, yttrium aluminum garnet, lutetium oxide, zirconia, borate or a rare earth element doped crystal of any of the above crystals. Doping with heterogeneous and transition metal elements. 6. A method for preparing a single crystal optical fiber, comprising the following steps: (1) Prepare a plurality of tubular glass preforms with matching inner and outer diameters; (2) drawing the preform to obtain a glass cladding with a two-layer structure; (3) inserting the solid single crystal fiber into the inner cladding of the glass cladding, heating and tapering to obtain a single crystal optical fiber with a glass cladding. 7. The preparation method according to claim 6, wherein the preparation of a plurality of tubular glass preforms with matching inner and outer diameters specifically comprises the following steps: (1) uniformly fixing a plurality of first glass tubes according to the preset shape of the inner cladding to obtain a stack; (2) Insert the stack into the second glass tube. 8. The preparation method according to claim 6, characterized in that there are uniformly arranged single-layer or multi-layer hollow glass tubes between the inner cladding and the outer cladding. 9 . The preparation method according to claim 7 , wherein the preparation of a plurality of tubular glass preforms with matched inner and outer diameters further comprises fixing the stacked part to the same end of the second glass tube. 10 . 10. The preparation method according to claim 6, characterized in that two-stage pressure control is adopted when drawing the preform, wherein a positive pressure is used inside the stack; Positive or negative pressures less than the former are used.