CN114751638B - Panda type elliptical core few-mode erbium-doped optical fiber and preparation method thereof - Google Patents
Panda type elliptical core few-mode erbium-doped optical fiber and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a panda type elliptical core few-mode erbium-doped fiber and a preparation method thereof, wherein the method comprises the following steps: sequentially preparing an outer fiber core layer and an inner fiber core layer on the inner wall of the quartz tube to form a double-fiber core layer; the outer wall of the quartz tube is provided with four poles, each pole is heated along the axial direction, and positive pressure or negative pressure is applied to the interior of the double-fiber core layer to obtain a hollow tube with an elliptical double-fiber core layer; performing high-temperature reverse collapse treatment on the hollow pipe, and polishing to obtain an optical fiber preform with a circular outer surface section and a solid inner part; sleeving the optical fiber preform rod, and symmetrically punching two holes on two sides of a long axis close to the elliptical double-fiber core layer in the quartz tube; and respectively inserting the boron-doped stress rods into the holes of the optical fiber preform, drawing at high temperature and coating an outer cladding layer to obtain the finished optical fiber. The preparation method has simple process steps, reduces the processing difficulty, and obviously improves the yield of mass production; meanwhile, the influence on the refractive index of the elliptical fiber core is effectively avoided, and the fiber is not easy to crack.
Description
Technical Field
The invention relates to the field of photoelectric communication, in particular to a panda type elliptical core few-mode erbium-doped optical fiber and a preparation method thereof.
Background
With the development of the internet, the demand of people for communication capacity is continuously increasing. The capacity increase of the commercial single-mode fiber communication system nowadays has been a bottleneck due to the influence of fiber nonlinear effect and spontaneous radiation noise of optical amplifier. In order to meet the requirement of mass data transmission, the space division multiplexing technology has attracted research interest in all countries around the world. Therefore, a multi-core fiber and a few-mode fiber are proposed as two effective methods for implementing the space division multiplexing technology.
The multi-core optical fiber is the most direct solution, but the multi-core optical fiber has many defects in the aspects of expandability and compatibility, and the crosstalk among the fiber cores is very serious in long-distance transmission; in order to avoid cross talk between the cores, a certain distance needs to be maintained between the cores. However, the larger the distance between the cores, the larger the cladding required, and the larger cladding size reduces the reliability of the fiber.
The few-mode optical fiber can break the nonlinear Shannon limit of single-mode optical fiber theoretically, and has high transmission capacity density. However, modal coupling occurring in the transmission of the multimode fiber is a problem which is difficult to solve, and for the traditional round core multimode fiber, a Multiple-Input Multiple-Output Digital Signal Processing (MIMO-DSP for short) must be adopted at a receiving end to recover all spatial channels; however, as the number of guided modes increases, both cost and computational complexity are prohibitive. Researchers have therefore begun working on achieving MIMO-less transmission, proposing polarization-maintaining few-mode fibers with elliptical cores to eliminate mode degeneracy. It is generally accepted that the difference in effective refractive index between adjacent modes in an optical fiber is greater than 1 x 10 -4 The effect of mode degeneracy can be achieved.
At present, the preparation method of the elliptical core optical fiber is reported as follows: in both schemes, before a core layer is manufactured, a stress action zone layer is deposited, partial stress zones on two symmetrical sides of the stress action zone layer are removed by etching, and finally the elliptical polarization-maintaining optical fiber is obtained through the processes of shrinking and wire drawing; however, in the actual manufacturing process, the quality of the fiber core is poor due to the stress region introduced around the fiber core, so that the fiber core and the periphery of the fiber core are easy to crack when the optical fiber is cut. Patent CN111620558A discloses a method for manufacturing an elliptic core polarization maintaining optical fiber, in which corrosive gas is introduced to directionally etch the opposite side of a deposited fiber core layer, and in an actual manufacturing process, a chemical etching means is used to affect the refractive index and quality of the fiber core. Patent CN106199827A "an elliptical-core panda-type polarization maintaining fiber and its manufacturing method" is to perform flat polishing and stretching on a core rod, then reshape the core rod into an elliptical-core preform, finally drill and plug a stress rod, and perform wire drawing to obtain an elliptical-core panda-type polarization maintaining fiber; in the actual manufacturing process of the method, the preform needs to be mechanically processed for many times, the polishing degree is not easy to control, the processing difficulty is high, and the yield is not good in batch production. Therefore, the existing preparation method of the elliptical fiber core optical fiber has various problems in the practical application process, and a new preparation method of the elliptical fiber core optical fiber needs to be provided for solving the problems.
Disclosure of Invention
The invention aims to provide a panda type elliptical core few-mode erbium-doped fiber and a preparation method thereof, which are used for solving various defects existing in the preparation process of the elliptical core fiber in the prior art.
In order to solve the above technical problem, a first solution provided by the present invention is: a preparation method of a panda-shaped elliptical core few-mode erbium-doped fiber comprises the following steps: s1, sequentially preparing an outer fiber core layer and an inner fiber core layer on the inner wall of a quartz tube to form a double-fiber core layer; s2, four poles are arranged on the outer wall of the quartz tube, each pole is heated along the axis direction, and positive pressure or negative pressure is applied to the interior of the double-fiber core layer to obtain a hollow tube with an elliptical double-fiber core layer; s3, performing high-temperature reverse collapse treatment on the hollow pipe, and polishing to obtain an optical fiber preform with a circular outer surface cross section and a solid inner part; s4, sleeving the optical fiber preform, adjusting the core cladding ratio, and symmetrically punching two holes on two sides of the long axis close to the elliptical double-fiber core layer in the quartz tube; s5, inserting two boron-doped stress rods into holes of the optical fiber preform respectively, drawing at high temperature and coating an outer cladding layer to obtain a panda-shaped elliptical-core few-mode erbium-doped optical fiber; and in the step S3, the interval between two adjacent poles is 90 degrees, the interval between two opposite poles is 180 degrees, negative pressure is applied to the inside of the inner fiber core layer when one group of opposite poles are heated, and positive pressure is applied to the inside of the inner fiber core layer when the other group of opposite poles are heated.
Wherein, the step S1 specifically comprises the following steps: s11, preparing an erbium-doped outer fiber core layer on the inner wall of the quartz tube by adopting a liquid phase doping method; and S12, carrying out vapor deposition on the inner wall of the outer fiber core layer to obtain an undoped inner fiber core layer.
Wherein, the step S11 is as follows: introducing SiCl into the quartz tube 4 、POCl 3 、SF 6 、O 2 And He, and depositing a loose layer on the inner wall of the quartz tube after heating reaction; soaking the quartz tube containing the loose layer in ErCl 3 And AlCl 3 Soaking in the solution, taking out, and adding N 2 Drying the water in the loose layer; introduction of Cl 2 Drying the loose layer, and introducing O 2 And doping ions in the oxidation loose layer and sintering at high temperature to obtain the erbium-doped outer fiber core layer.
Preferably, in the step of depositing a porous layer on the inner wall of the quartz tube, siCl 4 、POCl 3 、SF 6 、O 2 And He in a molar ratio of 2 to 4, 0.5 to 0.5, and (c) 5 to 8); in the step of preparing the erbium-doped outer fiber core layer, the high-temperature sintering temperature is 2000 ℃.
Wherein, the step S12 is as follows: introducing SiCl into the outer fiber core layer 4 、GeCl 4 And O 2 Reacting at 2000 deg.C, vitrifying and sintering to obtain undoped inner fiber core layer; wherein, siCl 4 、GeCl 4 And O 2 1.
Wherein, the step S2 is as follows: the outer wall of the quartz tube is sequentially provided with a pole A, a pole B, a pole C and a pole D along the clockwise direction, and the interval between every two adjacent poles is 90 degrees; adjusting the interior of the double-fiber core layer to negative pressure of-1 to-3 torr, heating the pole A along the axial direction at 2000 ℃, rotating the quartz tube 180 degrees, heating the pole C along the axial direction at 2000 ℃, wherein the heating time of the pole A and the pole C is the same; adjusting the internal pressure of the double-fiber core layer to 1-3 torr, heating the pole B along the axial direction at 2000 ℃, rotating the quartz tube 180 degrees, and heating the pole D along the axial direction at 2000 ℃, wherein the heating time of the pole B and the pole D is the same.
Wherein, the step S3 is as follows: at O 2 The hollow pipe is reversely collapsed and compacted at 2100 ℃ under the atmosphere, then the outer surface of the hollow pipe is ground until the cross section becomes circular, and the surface is removed by flame polishingSurface impurities and defects.
Preferably, in the S5 step, melt-drawing is performed at 2000 ℃, and then an outer cladding is applied.
Preferably, in the cross section direction of the panda elliptical core few-mode erbium-doped fiber, the radius ratio of the erbium-doped region in the fiber core is 30% -50%, the ellipticity is 1.3% -3, the refractive index difference between the fiber core and the cladding is 0.5% -2%, and the refractive index difference between the stress region and quartz glass is-0.008% -0.018.
In order to solve the above technical problem, a second solution provided by the present invention is: a panda type elliptical core few-mode erbium-doped fiber is prepared by the preparation method of the panda type elliptical core few-mode erbium-doped fiber in the first solution.
The invention has the beneficial effects that: the panda elliptical core few-mode erbium-doped fiber and the preparation method thereof are different from the prior art, the preparation method is simple in process step, the processing difficulty is reduced, the mass production yield is remarkably improved, the tensile strength is improved, and the fiber is not easy to crack; meanwhile, the influence on the refractive index of the elliptical fiber core is effectively avoided, and a better mode degeneracy effect is shown.
Drawings
FIG. 1 is a diagram of a manufacturing process of an embodiment of a panda-type elliptical core few-mode erbium-doped fiber according to the present invention;
in the figure: 1-quartz tube, 2-double fiber core layer, 21-outer fiber core layer, 22-inner fiber core layer, 3-stress rod and 4-outer cladding layer.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
Referring to fig. 1, for the first solution provided by the present invention, the preparation method of the panda-type elliptical core erbium-doped fiber with few modes includes the following steps:
s1, preparing an outer fiber core layer and an inner fiber core layer on the inner wall of a quartz tube in sequence to form a double-fiber core layer. As shown in fig. 1 (a), the method specifically includes the following steps:
and S11, preparing the erbium-doped outer fiber core layer on the inner wall of the quartz tube by adopting a liquid phase doping method. In this step, siCl was introduced into the quartz tube 1 4 、POCl 3 、SF 6 、O 2 And He, after heating reaction, depositing a loose layer on the inner wall of the quartz tube 1; soaking a quartz tube containing a loose layer in ErCl 3 And AlCl 3 Mixing the obtained mixture with the doped solution, soaking thoroughly, taking out, and adding N 2 Drying the water in the loose layer; introduction of Cl 2 Drying the loose layer, and introducing O 2 And doping ions in the oxidation loose layer and performing high-temperature vitrification sintering to obtain the erbium-doped outer fiber core layer 21. In this embodiment, siCl 4 、POCl 3 、SF 6 、O 2 The molar ratio of He to SiCl is from 2 to 4:0.5 to 2:0.1 to 0.5:5 to 8 4 、POCl 3 、SF 6 、O 2 And He in a molar ratio of 2.5; in the step of preparing the erbium-doped outer fiber core layer, the high-temperature sintering temperature is 2000 ℃.
And S12, carrying out vapor deposition on the inner wall of the outer fiber core layer to obtain an undoped inner fiber core layer. In this step, siCl is introduced into the outer fiber core layer 21 4 、GeCl 4 And O 2 ，SiCl 4 、GeCl 4 And O 2 The molar ratio of (1).
S2, four poles are arranged on the outer wall of the quartz tube, each pole is heated along the axis direction, and positive pressure or negative pressure is applied to the interior of the double-fiber core layer to obtain the hollow tube with the elliptical double-fiber core layer. In the step, two adjacent poles are spaced by 90 degrees, two opposite poles are spaced by 180 degrees, one group of opposite poles applies negative pressure to the inside of the inner fiber core layer when heated, the other group of opposite poles applies positive pressure to the inside of the inner fiber core layer when heated, and the quartz tube 1 and the double fiber core layers 2 are converted into elliptical structures through two groups of different internal pressure applying processes.
In this embodiment, as shown in fig. 1 (B), the outer wall of the quartz tube is provided with a pole a, a pole B, a pole C and a pole D in sequence along the clockwise direction, and an interval between two adjacent poles is 90 °; adjusting the interior of the double-fiber core layer to negative pressure of-1 to-3 torr, heating the pole A along the axial direction at 2000 ℃, rotating the quartz tube 180 degrees, heating the pole C along the axial direction at 2000 ℃, wherein the heating time of the pole A and the pole C is the same; adjusting the internal pressure of the double-fiber core layer to 1-3 torr, heating the pole B along the axial direction at 2000 ℃, rotating the quartz tube 180 degrees, and heating the pole D along the axial direction at 2000 ℃, wherein the heating time of the pole B and the pole D is the same. When the two points of the pole A and the pole C are heated, negative pressure is applied to the interior of the double-fiber core layer, and the acting force is from outside to inside, so that the pole A and the pole C form two ends of an elliptical short shaft; when the two positions of the pole B and the pole D are heated, positive pressure is applied to the interior of the double-fiber core layer, and the acting force is from inside to outside, so that the pole B and the pole D form two ends of a long axis of an ellipse, and a hollow ellipse structure is formed. In other embodiments, the suitable location of the pole heating and the positive and negative pressure can be selected according to actual conditions, and are not limited herein.
And S3, performing high-temperature reverse collapse treatment on the hollow pipe, and polishing to obtain the optical fiber perform rod with a circular outer surface section and a solid inner part. As shown in FIG. 1 (c), in this step, O is added 2 The method comprises the following steps of reversely collapsing and compacting the hollow pipe at 2100 ℃ under high temperature in an atmosphere, then grinding the outer surface of the hollow pipe until the cross section becomes circular, and removing impurities and defects on the surface by flame polishing.
S4, sleeving the optical fiber preform, adjusting the core cladding ratio, and symmetrically punching two holes on two sides of the long axis close to the elliptical double-fiber core layer in the quartz tube; this step is shown as (d) in FIG. 1.
And S5, respectively inserting the two boron-doped stress rods into holes of the optical fiber preform, drawing at a high temperature, and coating an outer cladding layer to obtain the panda elliptical-core few-mode erbium-doped optical fiber. As shown in (e) in fig. 1, in this step, two boron-doped stress rods 3 are respectively inserted into two holes of an optical fiber preform, placed in a heating furnace of a drawing tower, drawn at a high temperature of 2000 ℃, and then coated with an outer cladding 4, to obtain a panda-shaped elliptical-core erbium-doped fiber with few modes. According to the prepared panda type elliptical core few-mode erbium-doped fiber, in the cross section direction, the erbium-doped region accounts for 30-50% of the radius ratio of the fiber core, the ovality is 1.3-3, the refractive index difference between the fiber core and the cladding is 0.5-2%, the refractive index difference of a stress region relative to quartz glass is-0.008-0.018, and the fiber has good mechanical strength and elliptical fiber core quality. Compared with the existing mechanical polishing method, the preparation process has the advantages that the process steps are simple, the processing difficulty is reduced, and the yield of mass production is obviously improved; meanwhile, the problems that the refractive index of the elliptical fiber core is influenced by the traditional chemical corrosion method and the fiber is easy to crack in the preparation process are solved.
The second solution provided by the invention is a panda elliptical core few-mode erbium-doped fiber which is prepared by the preparation method of the panda elliptical core few-mode erbium-doped fiber in the first solution, and the structure and the performance of the panda elliptical core few-mode erbium-doped fiber are kept consistent.
The following is a representation and analysis of the effect of the panda-type elliptical core few-mode erbium-doped fiber according to the present invention by specific examples.
Example 1
The preparation procedure of this example is as follows:
(1) SiCl was introduced into the quartz tube at a molar ratio of 2.5 4 、POCl 3 、SF 6 、O 2 And He, wherein the total flow of the gas is 2000sccm, and the gas is heated and reacted at 1500-1600 ℃, so that a loose layer is deposited on the inner wall of the quartz tube. Soaking the quartz tube in ErCl 3 、AlCl 3 Soaking in the mixed solution for 1h, taking out, and adopting N 2 And blowing the water in the loose layer by inert gas. Introducing Cl with the gas flow of 200sccm 2 Repeating the loose layer for multiple times until the loose layer is fully dried, and introducing O with the gas flow of 1000sccm 2 Oxidizing the loose layer, doping ions in the loose layer, and vitrifying and sintering the loose layer at 2000 deg.C to obtain erbium-doped outer fiber core layer。
(2) Introducing SiCl into a quartz tube according to a molar ratio of 1 4 、GeCl 4 And O 2 The total flow of the gases is 1000sccm, the reaction is carried out at 2000 ℃, the gases are vitrified and sintered into a passive inner fiber core layer, and a hollow double-fiber core layer is formed by the outer fiber core layer and the inner fiber core layer.
(3) The outer wall of the quartz tube is sequentially provided with a pole A, a pole B, a pole C and a pole D along the clockwise direction, and the interval between every two adjacent poles is 90 degrees; adjusting the interior of the double-fiber core layer to negative pressure of-2 torr, heating the pole A along the axial direction at 2000 ℃, then rotating the quartz tube 180 degrees, and heating the pole C along the axial direction at 2000 ℃, wherein the heating time of the pole A and the pole C is the same; adjusting the internal of the double-fiber core layer to be at a positive pressure of 2 torr, heating the pole B along the axial direction at 2000 ℃, then rotating the quartz tube by 180 degrees, heating the pole D along the axial direction at 2000 ℃, wherein the heating time of the pole B and the pole D is the same.
(4) At O 2 The method comprises the following steps of carrying out 2100 ℃ high-temperature reverse collapse compaction on a hollow tube in an atmosphere, polishing the outer surface of the hollow tube after the collapse is finished until the cross section becomes circular, and then carrying out flame polishing to remove surface impurities and defects.
(5) And sleeving the optical fiber preform, and after adjusting the core cladding ratio, symmetrically punching two holes on two sides of the long axis close to the elliptic double-fiber core layer in the quartz tube.
(6) And respectively inserting two boron-doped stress rods into two holes of the optical fiber preform, placing the optical fiber preform into a drawing tower heating furnace, drawing at a high temperature of 2000 ℃, and then coating an outer cladding layer to obtain the panda-shaped elliptical core few-mode erbium-doped optical fiber.
Example 2
This example is based on the preparation procedure of example 1, with the difference that in step (1) SiCl is introduced in a molar ratio of 3 4 、POCl 3 、SF 6 、O 2 And He, the total flow rate of the above gases was 2000sccm, and other preparation conditions were consistent with the examples.
Comparative example 1
This comparative example is based on the preparation procedure of example 1The difference lies in that in the step (1), siCl is introduced into the reaction system according to the molar ratio of 1 4 、POCl 3 、SF 6 、O 2 And He, the total flow rate of the above gases was 2000sccm, and other preparation conditions were the same as in example 1.
Comparative example 2
This comparative example is based on the preparation procedure of example 1, except that the heating temperature of the four poles in step (3) is 1800 ℃, and other preparation conditions are identical to those of example 1.
Comparative example 3
This comparative example is based on the preparation procedure of example 1, except that the heating temperature of the four poles in step (3) is 2100 ℃, and other preparation conditions are identical to those of example 1.
Comparative example 4
This comparative example is based on the production procedure of example 1 except that the negative pressure condition inside the double core layer in step (3) is-4 torr and the positive pressure condition is 4 torr, and other production conditions are the same as those of example 1.
Comparative example 5
This comparative example is based on the production procedure of example 1 except that the negative pressure condition inside the double core layer in step (3) is-0.5 torr and the positive pressure condition is 0.5 torr, and other production conditions are the same as those of example 1.
The samples prepared in examples 1 to 2 and comparative example 1 were tested, and the specific optical fiber parameters are shown in table 1, and the refractive index effect, mode degeneracy effect, strength effect, and cracking condition are shown in table 2. As can be seen by combining the characterization data of tables 1 and 2:
1) The difference between the comparative example 1 and the example 1 is that the proportion of the gas raw materials adopted in the deposition of the loose layer in the comparative example 1 is different and exceeds the range of the gas proportion, so that the strength of the erbium-doped optical fiber product finally prepared in the comparative example 1 is lower; the reason is that the process conditions for preparing the loose layer and the process conditions for preparing the elliptical hollow tube with the double-fiber core layer are matched, and when the process parameters for preparing the loose layer are changed and the process parameters for subsequently preparing the elliptical hollow tube with the double-fiber core layer are not changed, the process parameters before and after the change are not matched, so that the erbium-doped optical fiber with better performance is difficult to obtain.
2) Comparative examples 2 to 3 are different from example 1 in that heating temperatures are different when an elliptical hollow tube with double fiber core layers is prepared, and too high or too low heating temperature affects the performance of the final erbium-doped optical fiber, wherein a low temperature greatly affects the degenerating effect of an optical fiber mode, and a high temperature greatly affects the tensile strength of the optical fiber, which indicates that the heating temperature needs to be strictly controlled to obtain the erbium-doped optical fiber with good performance.
3) Comparative examples 4 to 5 are different from example 1 in that positive and negative pressures are different when an elliptical hollow tube with double fiber core layers is prepared, and it is not difficult to find that the positive and negative pressures exceed the above-mentioned limited range and then affect the performance of the final erbium-doped optical fiber, wherein a higher positive and negative pressure set value has a greater influence on the tensile strength, and a lower positive and negative pressure set value has a greater influence on the degeneracy effect of the optical fiber mode, which indicates that the positive and negative pressures need to be controlled within an appropriate range to obtain the erbium-doped optical fiber with better performance.
TABLE 1 parameters of erbium-doped fiber samples in examples 1 to 2 and comparative examples 1 to 5
TABLE 2 comparison of the effects of the erbium-doped fiber samples of examples 1 to 2 and comparative examples 1 to 5
The panda elliptical core few-mode erbium-doped fiber and the preparation method thereof are different from the prior art, the preparation method is simple in process step, the processing difficulty is reduced, the mass production yield is remarkably improved, the tensile strength is improved, and the fiber is not easy to crack; meanwhile, the influence on the refractive index of the elliptical fiber core is effectively avoided, and a better mode degeneracy effect is shown.
The above embodiments only express the embodiments of the present invention, and the description thereof is specific and detailed, but not to be understood as limiting the scope of the invention. It should be noted that various changes and modifications can be made by those skilled in the art without departing from the spirit of the invention, and these changes and modifications are all within the scope of the invention. Therefore, the protection scope of the present patent should be subject to the appended claims.
Claims (4)
1. A preparation method of a panda elliptical core few-mode erbium-doped fiber is characterized by comprising the following steps:
s1, sequentially preparing an outer fiber core layer and an inner fiber core layer on the inner wall of a quartz tube to form a double-fiber core layer;
s2, four poles are arranged on the outer wall of the quartz tube, each pole is heated along the axial direction, and positive pressure or negative pressure is applied to the interior of the double-fiber core layer to obtain a hollow tube with an elliptical double-fiber core layer;
s3, performing high-temperature reverse collapse treatment on the hollow pipe, and polishing to obtain an optical fiber preform with a circular outer surface cross section and a solid inner part;
s4, sleeving the optical fiber preform, adjusting the core cladding ratio, and symmetrically punching two holes on two sides of a long axis close to the elliptic double-fiber core layer in the optical fiber preform;
s5, respectively inserting two boron-doped stress rods into holes of the optical fiber preform, drawing at a high temperature and coating an outer cladding layer to obtain a panda elliptical core few-mode erbium-doped optical fiber;
the step S1 specifically comprises the following steps:
s11, preparing an erbium-doped outer fiber core layer on the inner wall of the quartz tube by adopting a liquid phase doping method;
s12, carrying out vapor deposition on the inner wall of the outer fiber core layer to obtain an undoped inner fiber core layer;
the step S11 is as follows: introducing SiCl into the quartz tube 4 、POCl 3 、SF 6 、O 2 Heating to react with He, and depositing a loose layer on the inner wall of the quartz tube; soaking a quartz tube containing a loose layer in ErCl 3 And AlCl 3 Soaking in the solution, taking out, and adding N 2 Blow-dry loose layerThe moisture content therein; introduction of Cl 2 Drying the loose layer, and introducing O 2 Doping ions in the oxidation loose layer and sintering at high temperature to prepare an erbium-doped outer fiber core layer;
in the step of depositing the porous layer on the inner wall of the quartz tube, siCl is adopted 4 、POCl 3 、SF 6 、O 2 And He in a molar ratio of 2 to 4, 0.5 to 0.5, and (c) 5 to 8); in the step of preparing the erbium-doped outer fiber core layer, the high-temperature sintering temperature is 2000 ℃;
the step S12 is specifically as follows: introducing SiCl into the outer fiber core layer 4 、GeCl 4 And O 2 Reacting at 2000 ℃, and vitrifying and sintering to obtain an undoped inner fiber core layer; wherein, siCl 4 、GeCl 4 And O 2 1;
the step S2 is specifically as follows:
the outer wall of the quartz tube is sequentially provided with a pole A, a pole B, a pole C and a pole D along the clockwise direction, and the interval between every two adjacent poles is 90 degrees;
adjusting the interior of the double-fiber core layer to negative pressure of-1 to-3 torr, heating the pole A along the axial direction at 2000 ℃, rotating the quartz tube by 180 degrees, heating the pole C along the axial direction at 2000 ℃, wherein the heating time of the pole A and the pole C are the same;
adjusting the internal pressure of the double-fiber core layer to 1-3 torr, heating the pole B along the axial direction at 2000 ℃, rotating the quartz tube by 180 degrees, and heating the pole D along the axial direction at 2000 ℃, wherein the heating time of the pole B and the heating time of the pole D are the same.
2. The method for preparing a panda-shaped elliptical core erbium-doped fiber with few modes according to claim 1, wherein the step S3 is as follows:
at O 2 And (3) performing high-temperature reverse collapse compaction on the hollow pipe at 2100 ℃ in the atmosphere, then grinding the outer surface of the hollow pipe until the cross section becomes circular, and performing flame polishing to remove surface impurities and defects.
3. The method for preparing panda-type elliptical-core erbium-doped fiber as claimed in claim 1, wherein the S5 step is melt-drawn at 2000 ℃ and then coated with an outer cladding.
4. A panda type elliptical core few-mode erbium-doped fiber is characterized in that the panda type elliptical core few-mode erbium-doped fiber is prepared by the preparation method of the panda type elliptical core few-mode erbium-doped fiber in any one of claims 1 to 3.
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