阅读说明：本技术 D形光子晶体光纤预制棒及其d形光子晶体光纤拉制方法 (D-shaped photonic crystal optical fiber preform and D-shaped photonic crystal optical fiber drawing method thereof ) 是由 程同蕾 李斌 闫欣 李曙光 王方 张学楠 于 2020-10-29 设计创作，主要内容包括：一种D形光子晶体光纤预制棒及其D形光子晶体光纤拉制方法,属于光纤制造领域。D形光子晶体光纤预制棒,包括固定延长端和D形端；位于固定延长管内的纤芯和空气孔的阵列结构部分延长至D形管中,并填满D形管内径空间,D形管中,填充的为纤芯和空气孔,D形管空气孔保留的个数为：其中,M为纤芯的个数,M为≥1的正整数；N为光纤包层层数,N为≥1的正整数。将D形光子晶体光纤预制棒进行控温拉制,拉制中向毛细玻璃管中通入惰性气体调整其内部气压,从而控制气孔大小,通过控制拉丝速度调节得到D形光子晶体光纤。该方法容易实施,能够实现保证产品均一性,降低D形光子晶体光纤的残品率,并且能够实现大批量生产。(A D-shaped photonic crystal optical fiber preform and a D-shaped photonic crystal optical fiber drawing method thereof belong to the field of optical fiber manufacturing. The D-shaped photonic crystal optical fiber preform comprises a fixed extension end and a D-shaped end; the array structure part of fibre core and air hole that is located fixed extension intraductal prolongs to the D venturi tube in to fill up D venturi tube internal diameter space, in the D venturi tube, the packing be fibre core and air hole, the number that D venturi tube air hole reserved is: wherein M is the number of fiber cores, and M is a positive integer more than or equal to 1; n is the number of optical fiber cladding layers, and N is a positive integer not less than 1. Converting D-shaped photonic crystal lightAnd (3) carrying out temperature-controlled drawing on the fiber preform, introducing inert gas into the capillary glass tube during drawing to adjust the internal gas pressure of the capillary glass tube, so as to control the size of the gas hole, and adjusting the drawing speed to obtain the D-shaped photonic crystal fiber. The method is easy to implement, can ensure the product uniformity, reduce the defective rate of the D-shaped photonic crystal fiber and realize mass production.)

1. A D-shaped photonic crystal fiber preform is characterized by comprising a fixed extension end and a D-shaped end; the outermost layer of the fixed extension end is a fixed extension pipe, and the outermost layer of the D-shaped end is a D-shaped pipe; the fixed extension tube is internally provided with a fiber core and air hole array structure, and a fixed extension end capillary glass fiber is arranged in a hole between the fiber core and air hole array structure and the fixed extension tube; the array structure of the fiber core and the air holes takes a solid glass rod as the fiber core, and the capillary glass tubes are arranged on the periphery of the fiber core in a regular hexagon arrangement mode to serve as a fiber cladding;

wherein, be located the array structure part extension of fibre core and the air hole in the fixed extension pipe to the D venturi tube to fill up D venturi tube internal diameter space, in the D venturi tube, the packing be fibre core and air hole, the number that D venturi tube air hole reserved is:wherein M is the number of fiber cores, and M is a positive integer more than or equal to 1; n is the number of optical fiber cladding layers, and N is a positive integer not less than 1;

and the fixed extension end capillary glass filaments extend into the gap between the D-shaped tube and the array structure of the remaining fiber cores and air holes.

2. The preform of claim 1, wherein the diameter of the fixed extension end is equal to the diameter of a circle formed by the extension of the D-shaped end;

the length of the array structure of the fiber core and the air holes is less than or equal to the length of the D-shaped tube and the length of the fixed extension tube, wherein the shortest length from the array structure of the fiber core and the air holes to the fixed extension tube is 5cm, and the length of the fixed extension tube is more than or equal to the length of the D-shaped tube.

3. The preform of claim 1, wherein the fixed extension tube and the D-shaped tube are integrally formed or fusion-formed.

4. A method of fabricating a D-shaped photonic crystal fiber preform according to any of claims 1 to 3, comprising the steps of:

step 1: preparation of array structure of fiber core and air hole

Selecting M solid glass rods as fiber cores according to the number of the fiber cores and the number of cladding layers of the prepared D-shaped photonic crystal fibers, taking a capillary glass tube or a solid glass rod as a center according to the structure of the prepared D-shaped photonic crystal fibers, arranging the capillary glass tubes on the periphery of the center as fiber cladding, arranging each layer of the capillary glass tubes in a regular hexagon, replacing the capillary glass tubes with the solid glass rods according to the number and the position of the fiber cores of the D-shaped photonic crystal fibers after arrangement, and fixing and compacting each fiber cladding to form an array structure of the fiber cores and air holes;

wherein, N layers of capillary glass tubes are arranged according to the number of layers of the optical fiber cladding, and N is a positive integer more than or equal to 1;

the array structure of the fiber core and the air holes is an N-layer hexagonal cross section structure;

the diameter of the solid glass rod is the same as the outer diameter of the capillary glass tube;

step 2: preparation of preform

Selecting one end of an outer sleeve and/or a hollow glass tail pipe as a fixed extension pipe according to the connection mode of the fixed extension pipe and the D-shaped pipe;

when one end of the outer sleeve is selected as a fixed extension pipe, the following method is adopted for preparation:

selecting a hollow glass tube as an outer sleeve, wherein the inner diameter of the outer sleeve is more than or equal to 3 XN +1 capillary glass tube diameters, horizontally sectioning the outer sleeve along the axial direction to form a sectioning notch, the chord length of the sectioning aperture to the section is less than the diameter of the outer sleeve, the minimum vertical distance between the axial section of the sectioning notch and the axis of the outer sleeve is the radius of a solid glass rod, the axial length of the axial section of the sectioning notch is the length of the prepared D-shaped photonic crystal optical fiber preform, one end of the rest of the non-sectioned outer sleeve is used as a fixed extension tube, and after sectioning, the cross section of one end of the outer sleeve is D-shaped, and the cross section of;

arranging the array structure of the fiber core and the air hole in an inner hole of an outer sleeve, filling a capillary glass fiber in a gap between the array structure of the fiber core and the air hole and the outer sleeve for fixation, then cutting off the capillary glass tube with a cut on the outer sleeve, and reserving the part provided with the fiber core to obtain a reinforced prefabricated rod with a stable internal structure, namely a D-shaped photonic crystal fiber prefabricated rod;

when the hollow glass tail pipe is selected as the fixed extension pipe, the hollow glass tail pipe is prepared by the following method:

selecting a hollow glass tube as an outer sleeve, wherein the inner diameter of the outer sleeve is more than or equal to 3 multiplied by N +1 capillary glass tube outer diameters, horizontally cutting the outer sleeve along the axial direction, and after cutting, the chord length of the cut bore to the section is less than the diameter of the outer sleeve, and the minimum vertical distance between the axial section of the cutting opening and the axis of the outer sleeve is the radius of the solid glass rod to form a D-shaped tube; welding a hollow glass tail pipe at one end of the D-shaped pipe as a fixed extension pipe, wherein the inner diameter and the outer diameter of the hollow glass tail pipe and the outer sleeve pipe are the same;

arranging the array structure of the fiber core and the air hole in an inner hole of the D-shaped tube, extending the array structure of the fiber core and the air hole into the inner diameter of a tail tube of the hollow glass, filling a capillary glass fiber in a gap between the array structure of the fiber core and the air hole and the tail tube of the hollow glass for fixation, extending the capillary glass fiber into the D-shaped tube, cutting off the capillary glass tube outside the D-shaped tube, and reserving a part provided with the fiber core of the optical fiber to obtain a reinforced prefabricated rod with a stable internal structure, namely the D-shaped photonic crystal fiber prefabricated rod;

when one end of the outer sleeve and the hollow glass tail pipe are selected as fixed extension pipes, the prepared reinforced prefabricated rod with the stable internal structure is welded at one end of the outer sleeve to serve as a D-shaped photonic crystal optical fiber prefabricated rod on the basis that one end of the outer sleeve serves as the fixed extension pipes.

5. The method of claim 4, wherein the solid glass rod and the capillary glass tube are heated and melted according to the structural size requirement of the D-shaped photonic crystal fiber, and then drawn to the size requirement, and screened to obtain the D-shaped photonic crystal fiber preform.

6. The method for preparing a D-shaped photonic crystal fiber preform according to claim 4, wherein in the step 1, the array structure of the fiber core and the air holes is prepared by a stacking process, specifically: the single-core D-shaped photonic crystal fiber takes a solid glass rod as a fiber core, a first layer of capillary glass tubes are uniformly stacked outside the fiber core along the circumferential direction, a second layer of capillary glass tubes … … are uniformly stacked outside the first layer of capillary glass tubes along the circumferential direction, and so on, a Nth layer of capillary glass tubes are stacked, and each layer of capillary glass tubes are arranged in a regular hexagon;

the double-core D-shaped photonic crystal fiber takes two solid glass rods as fiber cores, the centers of the fiber cores and the array structure of the air holes are central capillary glass tubes, first layer of capillary glass tubes are uniformly stacked outside the central capillary glass tubes along the circumferential direction, two centrosymmetric peak positions of the first layer of capillary glass tubes are selected to be replaced by the solid glass rods, the solid glass rods are used as the fiber cores of the double-core D-shaped photonic crystal fiber, second layer of capillary glass tubes are uniformly stacked outside the first layer of capillary glass tubes along the circumferential direction, third layer of capillary glass tubes … … are uniformly stacked outside the second layer of capillary glass tubes along the circumferential direction, and the rest is done in sequence, the N layer of capillary glass tubes are stacked, and each layer of capillary glass tubes are arranged in a regular hexagon shape.

7. A drawing method of a D-shaped photonic crystal fiber is characterized in that the D-shaped photonic crystal fiber preform of any one of claims 1 to 3 is drawn, and the drawing method specifically comprises the following steps:

placing the D-shaped photonic crystal optical fiber preform in a drawing tower, introducing inert gas into the capillary glass tube in the temperature-controlled drawing process, adjusting the size of an air hole by controlling the air pressure in the capillary glass tube, and adjusting the size of the obtained optical fiber by controlling the drawing speed to finally obtain the D-shaped photonic crystal optical fiber;

wherein the air pressure is 1-4 kPa, the drawing temperature is 1780-1830 ℃, the rod feeding speed is 1-2 mm/min, and the drawing speed is 10-18 m/min.

8. A D-shaped photonic crystal fiber prepared by the drawing method of claim 7, wherein the number of the air holes formed in the D-shaped photonic crystal fiber is different according to the number of the fiber cores and the number of the cladding layers, and the number and the positions of the air holes are corresponding to those of the fiber cores and the air holes filled in the D-shaped photonic crystal fiber preform.

9. The D-shaped photonic crystal fiber according to claim 8, wherein when the D-shaped photonic crystal fiber is a single-core D-shaped photonic crystal fiber, the number of air holes of the single-core D-shaped photonic crystal fiber is:

wherein, the number of the capillary glass tubes of each layer is as follows: 3 XN + 1;

wherein N is the number of optical fiber cladding layers, and N is a positive integer not less than 1; m is the number of fiber cores, M is 1, and the fiber cores are located on the symmetry axis of the D-shaped photonic crystal fiber.

10. The D-shaped photonic crystal fiber of claim 8, wherein when the D-shaped photonic crystal fiber is a dual-core D-shaped photonic crystal fiber, the number of air holes of the dual-core D-shaped photonic crystal fiber is:

wherein, the center is a capillary glass tube, the number of the capillary glass tubes in the first layer is 2, and from the second layer, the number of the capillary glass tubes in each layer is 3 multiplied by N + 1;

wherein N is the number of optical fiber cladding layers, and N is a positive integer more than or equal to 2; m is the number of fiber cores, M is 2, and the fiber cores in the double-core D-shaped photonic crystal fiber are axisymmetric.

Technical Field

The invention belongs to the technical field of optical fiber manufacturing, and particularly relates to a D-shaped photonic crystal optical fiber preform and a D-shaped photonic crystal optical fiber drawing method thereof.

Background

The photonic crystal fiber is composed of two-dimensional photonic crystals with lattice constants of the optical wavelength magnitude, and air holes with a cross section usually in a periodic arrangement surround the fiber core. The photonic crystal fiber is prepared into a D shape, and sensing is realized by mainly utilizing the interaction between evanescent waves leaked from the fiber core and external substances of some fiber sensors, so that light transmitted in the fiber core has a leakage window.

The current preparation method of the D-shaped photonic crystal fiber mainly adopts a femtosecond laser ablation method, a hydrofluoric acid corrosion method and a side polishing method. The surface of the photonic crystal fiber ablated by femtosecond laser is rough, and air holes of a cladding are seriously cracked, so that the photonic crystal fiber is not beneficial to use; the leakage of evanescent waves can be realized by corroding the cladding of the optical fiber by using hydrofluoric acid with strong corrosivity, but the hydrofluoric acid has very strong toxicity and extremely damages the skin, the respiratory tract and the like of a human body, and the corrosion condition and the surface uniformity of the optical fiber are difficult to accurately control; although the side polishing method is the most common method, due to technical reasons, the polishing range is limited, air holes are easily blocked after the optical fiber is polished, the performance of the optical fiber is affected, and the mechanical property of the optical fiber is greatly reduced.

Therefore, the manufacturing of the D-shaped optical fiber still has great challenges, the D-shaped photonic crystal optical fiber cannot be prepared in large batch, and the D-shaped photonic crystal optical fiber is extremely fragile after being processed, so that the subsequent use of the optical fiber is difficult, and the application of the D-shaped photonic crystal optical fiber is limited.

Disclosure of Invention

The invention provides a D-shaped photonic crystal fiber preform and a D-shaped photonic crystal fiber drawing method thereof, aiming at solving the technical problems that the existing preparation method of the D-shaped photonic crystal fiber needs secondary treatment on commercial fibers and cannot realize mass preparation; the method for drawing the D-shaped photonic crystal fiber through the prepared D-shaped photonic crystal fiber preform is easy to implement, can ensure the product uniformity, reduce the defective rate of the D-shaped photonic crystal fiber, and can realize mass production.

In order to solve the technical problems, the technical scheme adopted by the invention is to provide a D-shaped photonic crystal fiber preform which comprises a fixed extension end and a D-shaped end; the outermost layer of the fixed extension end is a fixed extension pipe, and the outermost layer of the D-shaped end is a D-shaped pipe; the fixed extension tube is internally provided with a fiber core and air hole array structure, and a fixed extension end capillary glass fiber is arranged in a hole between the fiber core and air hole array structure and the fixed extension tube; the array structure of the fiber core and the air holes takes a solid glass rod as the fiber core, and the capillary glass tubes are arranged on the periphery of the fiber core in a regular hexagon arrangement mode to serve as a fiber cladding;

wherein, be located the array structure part extension of fibre core and the air hole in the fixed extension pipe to the D venturi tube to fill up D venturi tube internal diameter space, in the D venturi tube, the packing be fibre core and air hole, the number that D venturi tube air hole reserved is:wherein M is the number of fiber cores, and M is a positive integer more than or equal to 1; preferably M ═ 1 or 2; n is the number of optical fiber cladding layers, and N is a positive integer not less than 1; when the corresponding M is equal to 1, N is a positive integer which is more than or equal to 1; when M is 2, N is a positive integer more than or equal to 2.

The fixed elongated end capillary glass filaments extend into the gap between the D-tube and the remaining array of fiber cores and air holes.

Furthermore, the diameter of the fixed extension end is equal to the diameter of a circle formed by extending the D-shaped end.

Furthermore, the length of the array structure of the fiber core and the air holes is less than or equal to the length of the D-shaped tube and the length of the fixed extension tube, wherein the shortest length from the extension of the array structure of the fiber core and the air holes to the fixed extension tube is 5cm, and the length of the fixed extension tube is greater than or equal to the length of the D-shaped tube.

Furthermore, the fixed extension pipe and the D-shaped pipe are integrally formed or welded.

Furthermore, the solid glass rod, the capillary glass fiber, the capillary glass tube, the hollow glass tube and the hollow glass tail tube are made of silicon dioxide.

The invention relates to a preparation method of a D-shaped photonic crystal optical fiber preform, which comprises the following steps:

step 1: preparation of array structure of fiber core and air hole

Selecting M solid glass rods as fiber cores according to the number of the fiber cores and the number of cladding layers of the prepared D-shaped photonic crystal fibers, taking a capillary glass tube or a solid glass rod as a center according to the structure of the prepared D-shaped photonic crystal fibers, arranging the capillary glass tubes on the periphery of the center as fiber cladding, arranging each layer of the capillary glass tubes in a regular hexagon, replacing the capillary glass tubes with the solid glass rods according to the number and the position of the fiber cores of the D-shaped photonic crystal fibers after arrangement, and fixing and compacting each fiber cladding to form an array structure of the fiber cores and air holes;

wherein, N layers of capillary glass tubes are arranged according to the number of layers of the optical fiber cladding, and N is a positive integer more than or equal to 1;

the array structure of the fiber core and the air holes is an N-layer hexagonal cross section structure;

the diameter of the solid glass rod is the same as the outer diameter of the capillary glass tube;

step 2: preparation of preform

Selecting one end of an outer sleeve and/or a hollow glass tail pipe as a fixed extension pipe according to the connection mode of the fixed extension pipe and the D-shaped pipe;

when one end of the outer sleeve is selected as a fixed extension pipe, the following method is adopted for preparation:

selecting a hollow glass tube as an outer sleeve, wherein the inner diameter of the outer sleeve is more than or equal to 3 XN +1 capillary glass tube diameters, horizontally sectioning the outer sleeve along the axial direction to form a sectioning notch, the chord length of the sectioning aperture to the section is less than the diameter of the outer sleeve, the minimum vertical distance between the axial section of the sectioning notch and the axis of the outer sleeve is the radius of a solid glass rod, the axial length of the axial section of the sectioning notch is the length of the prepared D-shaped photonic crystal optical fiber preform, one end of the rest of the non-sectioned outer sleeve is used as a fixed extension tube, and after sectioning, the cross section of one end of the outer sleeve is D-shaped, and the cross section of;

arranging the array structure of the fiber core and the air hole in an inner hole of an outer sleeve, filling a capillary glass fiber in a gap between the array structure of the fiber core and the air hole and the outer sleeve for fixation, then cutting off the capillary glass tube with a cut on the outer sleeve, and reserving the part provided with the fiber core to obtain a reinforced prefabricated rod with a stable internal structure, namely a D-shaped photonic crystal fiber prefabricated rod;

when the hollow glass tail pipe is selected as the fixed extension pipe, the hollow glass tail pipe is prepared by the following method:

selecting a hollow glass tube as an outer sleeve, wherein the inner diameter of the outer sleeve is more than or equal to 3 multiplied by N +1 capillary glass tube outer diameters, horizontally cutting the outer sleeve along the axial direction, and after cutting, the chord length of the cut bore to the section is less than the diameter of the outer sleeve, and the minimum vertical distance between the axial section of the cutting opening and the axis of the outer sleeve is the radius of the solid glass rod to form a D-shaped tube; welding a hollow glass tail pipe at one end of the D-shaped pipe as a fixed extension pipe, wherein the inner diameter and the outer diameter of the hollow glass tail pipe and the outer sleeve pipe are the same;

arranging the array structure of the fiber core and the air hole in an inner hole of the D-shaped tube, extending the array structure of the fiber core and the air hole into the inner diameter of a tail tube of the hollow glass, filling a capillary glass fiber in a gap between the array structure of the fiber core and the air hole and the tail tube of the hollow glass for fixation, extending the capillary glass fiber into the D-shaped tube, cutting off the capillary glass tube outside the D-shaped tube, and reserving a part provided with the fiber core of the optical fiber to obtain a reinforced prefabricated rod with a stable internal structure, namely the D-shaped photonic crystal fiber prefabricated rod;

when one end of the outer sleeve and the hollow glass tail pipe are selected as fixed extension pipes, the prepared reinforced prefabricated rod with the stable internal structure is welded at one end of the outer sleeve to serve as a D-shaped photonic crystal optical fiber prefabricated rod on the basis that one end of the outer sleeve serves as the fixed extension pipes.

In the preparation method of the D-shaped photonic crystal fiber preform, the solid glass rod and the capillary glass tube are adopted, and are prepared by firstly heating and melting, then drawing to meet the size requirement and screening according to the structural size requirement of the prepared D-shaped photonic crystal fiber.

Further, in step 1, the array structure of the fiber core and the air hole is prepared by a stacking process, which specifically comprises: the single-core D-shaped photonic crystal fiber takes a solid glass rod as a fiber core, a first layer of capillary glass tubes are uniformly stacked outside the fiber core along the circumferential direction, a second layer of capillary glass tubes … … are uniformly stacked outside the first layer of capillary glass tubes along the circumferential direction, and so on, a Nth layer of capillary glass tubes are stacked, and each layer of capillary glass tubes are arranged in a regular hexagon;

the double-core D-shaped photonic crystal fiber takes two solid glass rods as fiber cores, the centers of the fiber cores and the array structure of the air holes are central capillary glass tubes, first layer of capillary glass tubes are uniformly stacked outside the central capillary glass tubes along the circumferential direction, two centrosymmetric peak positions of the first layer of capillary glass tubes are selected to be replaced by the solid glass rods, the solid glass rods are used as the fiber cores of the double-core D-shaped photonic crystal fiber, second layer of capillary glass tubes are uniformly stacked outside the first layer of capillary glass tubes along the circumferential direction, third layer of capillary glass tubes … … are uniformly stacked outside the second layer of capillary glass tubes along the circumferential direction, and the rest is done in sequence, the N layer of capillary glass tubes are stacked, and each layer of capillary glass tubes are arranged in a regular hexagon shape.

Further, in step 2, the array structure of the fiber core and the air holes extends to the length of the hollow glass tail tube which is more than or equal to the length of the D-shaped tube.

Further, in step 2, the length of the glass wool filaments is equal to the length of the outer sleeve; or the length of the capillary glass filaments is the length of the D-shaped tube plus the length of the hollow glass tail tube.

The invention discloses a drawing method of a D-shaped photonic crystal fiber, which comprises the following steps:

placing the D-shaped photonic crystal optical fiber preform in a drawing tower, introducing inert gas into the capillary glass tube in the temperature-controlled drawing process, adjusting the size of an air hole by controlling the air pressure in the capillary glass tube, and adjusting the size of the obtained optical fiber by controlling the drawing speed to finally obtain the D-shaped photonic crystal optical fiber;

wherein the air pressure is 1-4 kPa, the drawing temperature is 1780-1830 ℃, the rod feeding speed is 1-2 mm/min, and the drawing speed is 10-18 m/min.

The D-shaped photonic crystal fiber has different numbers of air holes according to the number of fiber cores and the number of layers of claddings, and the number and the positions of the air holes are corresponding to those of the fiber cores and the air holes filled in the D-shaped photonic crystal fiber preform.

The method specifically comprises the following steps:

the number of the air holes of the single-core D-shaped photonic crystal fiber is as follows:

wherein, the number of the capillary glass tubes of each layer is as follows: 3 XN + 1;

wherein N is the number of optical fiber cladding layers, and N is a positive integer not less than 1; m is the number of fiber cores, M is 1, and the fiber cores are located on the symmetry axis of the D-shaped photonic crystal fiber.

The number of the air holes of the double-core D-shaped photonic crystal fiber is as follows:

wherein, the center is a capillary glass tube, the number of the capillary glass tubes in the first layer is 2, and from the second layer, the number of the capillary glass tubes in each layer is 3 multiplied by N + 1;

wherein N is the number of optical fiber cladding layers, and N is a positive integer more than or equal to 2; m is the number of fiber cores, M is 2, and the fiber cores in the double-core D-shaped photonic crystal fiber are axisymmetric.

The invention has the beneficial effects that:

the invention realizes the manufacturing of the D-shaped photonic crystal optical fiber preform by cutting the outer sleeve and the capillary glass tube by an accumulation method, utilizes the optical fiber drawing tower to melt the preform at high temperature to draw the optical fiber, can ensure the purity of the D-shaped photonic crystal optical fiber material, can avoid the optical fiber damage caused by external operation, and can be used for manufacturing various photonic crystal optical fibers with different air hole layers, thereby realizing the high-efficiency and large-scale preparation of the D-shaped photonic crystal optical fiber, and ensuring that the prepared optical fiber has good performance and good application prospect.

Drawings

FIG. 1 is a schematic structural view of a cross section of a single-core D-shaped photonic crystal fiber in example 1 of the present invention;

FIG. 2 is a schematic structural view of a cross section of a dual-core D-shaped photonic crystal fiber according to example 2 of the present invention;

FIG. 3 is a schematic diagram of an outer sleeve of a D-shaped photonic crystal fiber prepared according to an embodiment of the present invention.

FIG. 4 is a schematic view of a single core D-shaped photonic crystal fiber preform fabricated in example 1 of the present invention.

FIG. 5 is a schematic view of a dual-core D-shaped photonic crystal fiber preform prepared in example 2 of the present invention.

FIG. 6 is a cross-sectional microscopic view of a D-shaped photonic crystal fiber prepared in example 1 of the present invention.

FIG. 7 is a schematic diagram of a single-core D-shaped photonic crystal fiber with three air hole claddings according to an embodiment of the present invention.

In the above figures, 1 is a solid glass rod; 2 is an air hole; 3 is a gap between the capillary glass tubes; 4 is a capillary glass tube; 5 is a gap between the capillary glass tube and the glass outer sleeve; 6 is a glass outer sleeve;

d₁the diameter of a solid glass rod; d₂The outer diameter of the capillary glass tube; d₃The pore diameter of the pores of the capillary glass tube; d₄The thickness of the tube wall of the glass outer sleeve; l is₁、L₂And L₃Respectively corresponding to the first layer, the second layer and the third layer of capillary glass tube arrays.

Detailed Description

The invention provides a D-shaped photonic crystal fiber preform and a D-shaped photonic crystal fiber drawing method thereof, which can be used for efficiently manufacturing D-shaped photonic crystal fibers in a large scale at low cost and can ensure that the manufactured optical fibers have controllable lengths. The present invention will be described in further detail with reference to examples.

Example 1

The embodiment provides a manufacturing method of a single-core D-shaped photonic crystal fiber preform with a three-layer air hole cladding structure and a drawing method of a D-shaped photonic crystal fiber, which comprise the following steps:

step 1: selective material drawing

According to the structural size (shown in figure 4) of a single-core D-shaped photonic crystal optical fiber preform, selecting a high-purity (the mass purity is more than 99.9%) silicon dioxide solid glass rod, heating and melting the silicon dioxide solid glass rod, and drawing the silicon dioxide solid glass rod to form the solid glass rod 1 through a conventional drawing method of an optical fiber drawing tower, wherein the solid glass rod is used as an optical fiber core.

The specific process of the conventional drawing method by adopting the optical fiber drawing tower comprises the following steps: clamping and positioning a high-purity (more than 99.9% of quality purity) silicon dioxide solid glass rod with the length of 50cm and the diameter of 20mm by using a three-jaw chuck right above a high-temperature graphite furnace of a wire drawing tower, sleeving a graphite sheet with the diameter of 2mm larger than that of the silicon dioxide solid glass rod, and allowing the lower end of the silicon dioxide solid glass rod to enter the central part of the high-temperature graphite furnace by a descending and moving device. The graphite furnace needs to be vacuumized for three times repeatedly, then argon protection materials and equipment are introduced into an upper gas path and a lower gas path in the furnace, and the upper path and the lower path of gas flow in the furnace are set to be 9L/min and 5L/min through a computer control panel. Setting heating temperature, slowly raising the temperature of the graphite furnace to 2000 ℃, dropping and leaving the graphite furnace to automatically finish cooling after the silicon dioxide solid glass rod is melted at high temperature, pulling the thinned solid glass rod through a belt pulley transmission device, adjusting the pulling speed to 2m/min to obtain the required size of the solid glass rod 1, and cutting a plurality of glass rods 1 with the length of about 50cm for later use so as to facilitate the stacking method tube arrangement.

Meanwhile, the capillary glass tube is also prepared by adopting a conventional fiber drawing method of an optical fiber drawing tower, and the specific process is as follows: the required capillary glass tube 4 can be obtained by repeating the above steps by replacing the silica solid glass rod fixed by the three-jaw chuck with a glass tube having an outer diameter of 20mm and an inner diameter of 16 mm. The outer diameter of the capillary glass tube needs to be consistent with the diameter of the solid glass rod, and the diameter of the solid glass rod and the outer diameter of the capillary glass tube can be obtained in real time through an infrared diameter measuring instrument and a vernier caliper of a drawing tower. All materials need to be cleaned by ultrasound and absolute ethanol to avoid being carried into the material.

Step 2: preparation of array structure of fiber core and air hole

Taking a solid glass rod as a center, arranging 6 capillary glass tubes in a regular hexagon shape along the axis direction, fixing and pressing the glass tubes to be used as a first layer of air hole cladding of the optical fiber; on the basis of the previous step, 12 capillary glass tubes are arranged in a regular hexagon at the outer side of a regular hexagon formed by 6 capillary glass tubes, and are fixed and compressed to be used as a second layer of air hole cladding of the optical fiber; and on the basis of the previous step, continuously arranging 18 capillary glass tubes in a regular hexagon, fixing and compacting the glass tubes to be used as a third layer of air hole cladding of the optical fiber, and obtaining an array structure of the fiber core and the air holes.

And step 3: preparation of preform

The outer sleeve with the outer diameter of 20mm and the inner diameter of 16mm is horizontally cut along the axial direction, the cutting length is half of that of the outer sleeve, a cutting notch is formed after cutting, the chord length of the cutting opening radial section is smaller than the diameter of the outer sleeve, the minimum vertical distance between the axial section of the cutting opening and the axis of the outer sleeve is the radius of a solid glass rod, the cross section of one end of the cut outer sleeve is D-shaped and serves as a D-shaped pipe, the cross section of the other end of the cut outer sleeve is circular hollow and serves as a fixed extension pipe, and the schematic diagram of the formed D-shaped photonic crystal optical.

The arrayed fiber core and air hole array structure of the arranged three-layer outer cladding is put into an outer sleeve, and one end of a fixed extension tube is fixed, wherein the specific fixing operation method comprises the following steps: and filling capillary glass filaments in a gap between the array structure of the fiber core and the air hole and the outer sleeve to prevent the structure in the sleeve from falling and deforming, wherein the filling quantity is determined by the structural stability. And cutting off 15 capillary glass tubes on the upper part of the fiber core of the optical fiber in three layers of the regular hexagon outside the D-shaped tube, wherein the final exposed length of the capillary glass tubes is consistent with the length of the cut part of the D-shaped tube. And fixing and pressing the capillary glass tubes on the rest part in the array structure of the fiber cores and the air holes. And finishing the preparation of the first part of the three-layer air hole D-shaped photonic crystal optical fiber preform.

Another glass outer sleeve with the outer diameter of 20mm and the inner diameter of 16mm is selected as a hollow glass tail pipe of the prefabricated rod, and the hollow glass tail pipe is connected by a glass welding machine tool. The glass welding machine tool has the main functions of reasonably proportioning hydrogen and oxygen, spraying the hydrogen and the oxygen through a high-pressure nozzle, and igniting the gas to generate high-temperature flame at 2500-3000 ℃ after the mixed gas flow is stable. The temperature of the flame can be varied by adjusting the ratio of hydrogen to oxygen.

At the moment, the prefabricated rod and the hollow glass tail pipe which are fixed on two sides of the machine tool need to be slowly rotated to be close to each other, the part to be contacted between the prefabricated rod and the hollow glass tail pipe is heated by flame, the butt joint is realized by the highlight softening of the glass, the phenomenon that the fixing table is moved too fast is avoided, and otherwise, the expansion of a welding point is caused, and the welding effect is influenced. After the fusion welding is finished, the whole preform rod is required to be placed into a thermostat, the temperature in the thermostat is adjusted to 120 ℃, the preform rod is continuously baked for 30 minutes to completely evaporate the water in the preform rod, and OH is prevented from being introduced into glass^-Increasing the loss of the fabricated optical fiber. And finishing the preparation of the preform of the continuous hollow glass tail tube to obtain the single-core D-shaped photonic crystal optical fiber preform, wherein the schematic diagram of the single-core D-shaped photonic crystal optical fiber preform is shown in figure 4.

In the preparation of the single-core D-shaped photonic crystal fiber preform, the data indexes of the adopted related materials are shown in Table 1:

size of D-shaped photonic crystal optical fiber preform with air hole structure in layer 13

And 4, step 4: drawing (D)

Clamping the single-core D-shaped photonic crystal optical fiber perform rod by using a three-jaw chuck, feeding the single-core D-shaped photonic crystal optical fiber perform rod into a graphite furnace for heating, controlling the temperature within the range of 1820 ℃, and waiting for the heating part of the single-core D-shaped photonic crystal optical fiber perform rod to soften and fall.

The same way of drawing solid glass rods and capillary glass tubes, D-shaped photonic crystal fibers with different diameters need to be obtained through a traction device. In the drawing process, whether the cross section and the diameter of the drawn optical fiber meet the requirements or not is observed at any time through an optical microscope and an infrared detector, the air pressure control device is adjusted, the pressure of argon gas introduced into the prefabricated rod is controlled to be kept at 2kPa, the change condition of air holes is observed, the rod feeding speed of the prefabricated rod is kept at 2mm/min, the drawing speed is 18m/min, the D-shaped photonic crystal optical fiber is finally obtained, the size of the D-shaped photonic crystal optical fiber is shown in a table 2, the schematic sectional structure diagram of the D-shaped photonic crystal optical fiber is shown in a figure 1, and the microscopic cross section diagram of the D-shaped photonic crystal optical.

Size of single-core D-shaped photonic crystal fiber with air hole structure of table 23 layer

Type (B)	Fiber core	Diameter of air hole	Diameter of optical fiber
				Diameter of	15μm	5μm	125μm

The air hole cladding of the D-shaped photonic crystal fiber prepared in this example is 21 holes, and includes a first air hole cladding, a second air hole cladding and a third air hole cladding, where the number of the first capillary glass tube, the second capillary glass tube and the third capillary glass tube is 4, 7 and 10, respectively.

Example 2

A drawing method of a dual-core D-shaped photonic crystal fiber comprises the following steps:

step 1: selective material drawing

According to the size and the structure of the prepared double-core D-shaped photonic crystal fiber, two solid glass rods are prepared as fiber cores by the same method as the embodiment 1, and capillary glass tubes are drawn as fiber cladding by the same method as the embodiment 1;

step 2: preparation of array structure of fiber core and air hole

The method comprises the steps of taking a capillary glass tube as a center, uniformly stacking a first layer of capillary glass tube on the outer portion of the capillary glass tube along the circumferential direction, selecting two centrosymmetric vertex positions to replace by a solid glass rod to serve as a double-fiber core, forming a first cladding through fixing and compacting, arranging a second layer of capillary glass tubes in a regular hexagon mode in sequence, arranging a third layer of capillary glass tubes in a regular hexagon mode, and finishing fixing and compacting, wherein the requirement is met that the number of layers of the cladding is the same as that of air hole claddings of the processed double-core D-shaped photonic crystal fiber, the diameters of all the capillary glass tubes are the same as that of the solid glass rod, and obtaining an array structure of the fiber core and air holes. The cross section of the arrayed fiber core and air hole structure is of a three-layer hexagonal structure.

And step 3: preparation of preform

Selecting an outer sleeve with the inner diameter not less than 3 × N +1 capillary glass tubes. The outer sleeve is horizontally cut along the axial direction, after cutting, the chord length of the cut bore radial section is less than the diameter of the outer sleeve, and the minimum vertical distance between the axial section of the cutting opening and the axis of the outer sleeve is the radius of the solid glass rod, so that a D-shaped pipe is formed;

welding a hollow glass tail pipe at one end of the D-shaped pipe as a fixed extension pipe, wherein the inner diameter and the outer diameter of the hollow glass tail pipe and the outer sleeve pipe are the same; the welding method was the same as in example 1.

And after the well-arranged fiber core and air hole array structure is placed, the capillary glass tube positioned outside the groove of the D-shaped tube is cut off, the fiber core of the optical fiber is reserved, and the length of the cut-off fiber core and air hole array structure is consistent with the length of the groove of the outer sleeve.

In order to ensure the stability of the internal structure, a large amount of capillary glass filaments are required to be filled into the fixed extension tube and the gap between the D-shaped tube and the array structure of the fiber core and the air hole to reinforce the preform, and finally the double-core D-shaped photonic crystal fiber preform is obtained, wherein the structural schematic diagram of the double-core D-shaped photonic crystal fiber preform is shown in FIG. 5.

And 4, step 4: drawing (D)

And (3) placing the double-core D-shaped photonic crystal optical fiber preform in a drawing tower, introducing inert gas into the capillary glass tube in the temperature-controlled drawing process, regulating the size of the air hole by controlling the air pressure in the capillary glass tube, and regulating the size of the obtained optical fiber by controlling the drawing speed to finally obtain the double-core D-shaped photonic crystal optical fiber, wherein the structural schematic diagram of the cross section of the double-core D-shaped photonic crystal optical fiber is shown in figure 2.

Wherein the air pressure is 3kPa, the drawing temperature is 1810 ℃, the rod feeding speed is 1.8mm/min, and the drawing speed is 15 m/min.

The air holes of the dual-core D-shaped photonic crystal fiber prepared in this embodiment are 20 holes, and include 1 central air hole, 2 first air hole claddings, 7 second air hole claddings, and 10 third air hole claddings, where the number of the first capillary glass tubes is 2, the number of the second capillary glass tubes is 7, and the number of the third capillary glass tubes is 10.

Example 3

A method for drawing a single-core D-shaped photonic crystal fiber, which is similar to example 1, is different in that a hollow glass tail tube is not welded, and a portion of the outer tube, which is not cut off, is used as a fixed extension tube.

And the size requirement of the prepared single-core D-shaped photonic crystal optical fiber preform is as follows:

dimension of single-core D-shaped photonic crystal optical fiber preform with surface 33-layer air hole structure

The dimensions of the single-core D-shaped photonic crystal fiber after drawing are as follows:

single-core D-shaped photonic crystal fiber size of air hole structure of surface 43 layer

Type (B)	Fiber core	Diameter of air hole	Diameter of optical fiber
				Diameter of	10μm	2μm	100μm

Example 4

A method for drawing a single-core D-shaped photonic crystal fiber, which is the same as example 1 except that:

and step 3: preparation of preform

Selecting an outer sleeve with the inner diameter not less than 3 × N +1 capillary glass tubes. The outer sleeve is horizontally cut along the axial direction, after cutting, the chord length of the cut bore radial section is less than the diameter of the outer sleeve, and the minimum vertical distance between the axial section of the cutting opening and the axis of the outer sleeve is the radius of the solid glass rod, so that a D-shaped pipe is formed;

welding a hollow glass tail pipe at one end of the D-shaped pipe as a fixed extension pipe, wherein the inner diameter and the outer diameter of the hollow glass tail pipe and the outer sleeve pipe are the same; the welding method was the same as in example 1.

And after the well-arranged fiber core and air hole array structure is placed, the capillary glass tube positioned outside the groove of the D-shaped tube is cut off, the fiber core of the optical fiber is reserved, and the length of the cut-off fiber core and air hole array structure is consistent with the length of the groove of the outer sleeve.

In order to ensure the stability of the internal structure, a large amount of capillary glass filaments are required to be filled into the fixed extension tube and gaps between the D-shaped tube and the array structure of the fiber core and the air hole to reinforce the preform, and finally the single-core D-shaped photonic crystal optical fiber preform is obtained.

The flow diagram is shown in FIG. 7.