Preparation method of a tapered optical fiber and tapered optical fiber

Abstract

The present invention relates to the technical field of optical fiber preparation, and provides a method for preparing a tapered optical fiber and a tapered optical fiber. The preparation method includes performing a deposition operation of a core layer on the inner wall surface of a first quartz tube; simultaneously performing a rod shrinking operation and an extending operation on the first quartz tube deposited with the core layer to obtain a conical core rod; polishing the outer wall surface of the conical core rod to obtain a cylindrical optical fiber preform; and successively performing a drawing operation and a coating operation on the optical fiber preform to fabricate a tapered optical fiber with a double cladding. The preparation process of the tapered optical fiber in the present invention is simple, can achieve one-time forming of the tapered optical fiber, does not require multiple polishings during the whole process, reduces the processing difficulty of the tapered optical fiber, can save costs, shorten the preparation time, and improve the preparation efficiency and precision of the tapered optical fiber.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber preparation, and particularly to a method for preparing a tapered optical fiber and the tapered optical fiber. Background Art

[0002] Compared with ordinary optical fibers having a uniform core and cladding, tapered optical fibers can increase the effective mode field area of the optical fiber by introducing a large core diameter end, and have the advantage of effectively suppressing the nonlinear effect. At the same time, tapered optical fibers also have excellent mode instability suppression performance, beam quality maintenance characteristics, and amplified spontaneous emission (ASE) suppression effect, and have great potential in the field of high-power lasers.

[0003] Tapered optical fibers usually adopt methods such as the fused biconical taper method, mechanical polishing method, or chemical etching method, and form a tapered region by changing the radius of the optical fiber axially to achieve applications in fields such as optical coupling, optical sensing, nonlinear optics, micro-nano optics, optical fiber devices, and other research fields.

[0004] However, in the processing of existing tapered optical fibers, the core rod and the glass rod need to be ground separately, and the preparation process is complex and cumbersome. In particular, it is difficult to polish the inner wall of the glass rod, the processing difficulty is large, the precision is low, and at the same time, the inner grinding also limits the length of the glass rod, and there are disadvantages such as poor adaptability. Summary of the Invention

[0005] The present invention provides a method for preparing a tapered optical fiber and the tapered optical fiber, so as to solve the problem that in the processing of existing tapered optical fibers, the core rod and the glass rod need to be ground separately, and the preparation process is complex and cumbersome.

[0006] The present invention provides a method for preparing a tapered optical fiber, including:

[0007] Performing a deposition operation of a core layer on the inner wall surface of a first quartz tube;

[0008] Simultaneously performing a rod shrinking and an extending operation on the first quartz tube deposited with the core layer to obtain a conical core rod;

[0009] Polishing the outer wall surface of the conical core rod to obtain a cylindrical optical fiber preform;

[0010] Performing a drawing and a coating operation on the optical fiber preform in sequence to make a tapered optical fiber with a double cladding.

[0011] According to the method for preparing a tapered optical fiber provided by the present invention, the step of performing a deposition operation of a core layer on the inner wall surface of a first quartz tube includes:

[0012] Performing pickling on the first quartz tube;

[0013] Deposit a loose layer of glass particles on the inner wall surface of the first quartz tube, and dope the loose layer of glass particles with rare earth ions.

[0014] According to a method for preparing a tapered optical fiber provided by the present invention, the step of doping the loose layer of glass particles with rare earth ions includes:

[0015] Introduce a solution containing the rare earth ions into the first quartz tube;

[0016] After soaking for a preset time, drain the remaining solution containing the rare earth ions.

[0017] According to a method for preparing a tapered optical fiber provided by the present invention, the rare earth ions are Nd 3+ , Yb 3+ , Er 3+ , Tm 3+ Any one or a combination of at least two of them.

[0018] According to a method for preparing a tapered optical fiber provided by the present invention, the step of simultaneously performing rod shrinking and stretching operations on the first quartz tube deposited with the core layer includes:

[0019] While sintering the first quartz tube deposited with the core layer, also perform a stretching operation on the first quartz tube to obtain the conical core rod formed by melting and shrinking the first quartz tube and the core layer.

[0020] According to a method for preparing a tapered optical fiber provided by the present invention, the step of drawing the optical fiber preform includes:

[0021] Place the optical fiber preform on a drawing tower, and draw the tapered optical fiber by adjusting the drawing parameters.

[0022] According to a method for preparing a tapered optical fiber provided by the present invention, the drawing parameters include the heating rate, drawing temperature, drawing tension, drawing atmosphere, and drawing gas flow rate.

[0023] According to a method for preparing a tapered optical fiber provided by the present invention, before performing the drawing operation on the optical fiber preform, it further includes:

[0024] According to the core-cladding ratio of the tapered optical fiber to be prepared and the geometric parameters of the optical fiber preform, prepare a second quartz tube adapted to the optical fiber preform;

[0025] Assemble the second quartz tube and the optical fiber preform, and perform a sleeving operation on a sleeving lathe to prepare a solid optical fiber preform.

[0026] A method for preparing a tapered optical fiber according to the present invention, the steps of coating the optical fiber preform include:

[0027] The peripheral wall of the drawn optical fiber preform is coated twice in sequence to form an optical fiber coating.

[0028] The present invention also provides a tapered optical fiber, which is obtained by using the method for preparing a tapered optical fiber as described above.

[0029] A method for preparing a tapered optical fiber and the tapered optical fiber provided by the present invention deposit a core layer on the inner wall surface of the first quartz tube, and the first quartz tube can be subjected to rod shrinking and stretching operations to obtain a conical core rod. The stretching operation can be segmented stretching or continuous stretching. After the conical core rod is polished into a cylindrical optical fiber preform, the optical fiber preform can be drawn and coated in sequence, and a tapered optical fiber with a double cladding can be obtained.

[0030] As can be seen from the above, the preparation process of the tapered optical fiber of the present invention is simple, the one-time forming of the tapered optical fiber can be realized, multiple polishings are not required in the whole process, the processing difficulty of the tapered optical fiber is reduced, the cost can be saved, the preparation time is shortened, and the preparation efficiency and precision of the tapered optical fiber are improved. Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0032] Figure 1 is a schematic flow chart of the method for preparing a tapered optical fiber provided by the present invention;

[0033] Figure 2 is a schematic structural diagram of the first quartz tube provided by the present invention;

[0034] Figure 3 is a schematic structural diagram of the first quartz tube deposited with a core layer provided by the present invention;

[0035] Figure 4 is a schematic structural diagram of the conical core rod provided by the present invention;

[0036] Figure 5 is a schematic structural diagram of the optical fiber preform provided by the present invention;

[0037] Figure 6 is a schematic structural diagram of the tapered optical fiber provided by the present invention.

[0038] Reference Signs:

[0039] 1. First quartz tube; 2. Core layer; 3. Conical mandrel; 4. Optical fiber preform;

[0040] 5. Tapered optical fiber; 51. Fiber core; 52. Optical fiber cladding. Detailed implementation manners

[0041] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the protection scope of the present invention.

[0042] Below in conjunction with Figures 1 - 6 , the preparation method and the tapered optical fiber provided by the embodiments of the present invention will be described in detail through specific embodiments and their application scenarios.

[0043] As Figure 1 shown, the embodiments of the present invention provide a preparation method for a tapered optical fiber, including the following steps:

[0044] Step 110, perform a deposition operation on the inner wall surface of the first quartz tube for the core layer.

[0045] It can be understood that, as Figure 2 shown, the first quartz tube 1 is cylindrical, and the inner wall surface and the outer wall surface of the first quartz tube 1 are coaxially arranged. Along the axial direction of the first quartz tube 1, the outer diameters of all positions of the first quartz tube 1 are the same, and the inner diameters of all positions of the first quartz tube 1 are the same.

[0046] Among them, according to actual requirements, a quartz tube material with matching thermal properties and meeting the optical property requirements can be selected to prepare the first quartz tube 1 shown in this embodiment.

[0047] Furthermore, after the preparation of the first quartz tube 1 is completed, the first quartz tube 1 can be placed on a deposition lathe. During the process of driving the first quartz tube 1 to rotate by the deposition lathe, a gas raw material is introduced into the first quartz tube 1 to deposit a core layer 2 on the inner wall surface of the first quartz tube 1, as Figure 3 shown.

[0048] Among them, in this embodiment, the thickness of the deposited core layer 2 can be determined according to the size parameters of the fiber core of the tapered optical fiber to be prepared.

[0049] Step 120, simultaneously perform a rod shrinking and an extending operation on the first quartz tube deposited with the core layer to obtain a conical mandrel.

[0050] It is understandable that after the core layer is deposited on the inner wall surface of the first quartz tube, the first quartz tube is placed on a lathe, and the first quartz tube and the core layer on its inner wall surface can be fused and shrunk by heating and sintering to form a solid preform core rod, that is, the rod shrinking operation of the first quartz tube is completed.

[0051] Meanwhile, by performing a stretching operation on the preform core rod, the preform core rod can be elongated along the axial direction to obtain a conical core rod.

[0052] As Figure 4 shown, the conical core rod 3 is a solid rod body. The conical core rod 3 has a core corresponding to the core layer and a cladding corresponding to the first quartz tube 1 in terms of structural characteristics, and the cladding covers the peripheral wall of the core.

[0053] Among them, from the first end to the second end of the conical core rod 3, the overall cross-sectional area of the conical core rod 3 gradually decreases, and the cross-sectional area of the core also gradually decreases.

[0054] It should be noted here that the core of the conical core rod 3 can be prepared by a drawing process to form the core of the tapered optical fiber, and the cladding of the conical core rod 3 can be prepared by a drawing process to form the optical fiber cladding of the tapered optical fiber.

[0055] Step 130: Grind the outer wall surface of the conical core rod to obtain a cylindrical optical fiber preform.

[0056] It is understandable that as Figure 4 and Figure 5 shown, by grinding and processing the outer wall surface of the conical core rod 3, an optical fiber preform 4 can be prepared to ensure that the diameters at all positions along the axial direction of the optical fiber preform 4 are consistent, so that the optical fiber preform 4 is cylindrical.

[0057] Step 140: Perform drawing and coating operations on the optical fiber preform in sequence to make a tapered optical fiber with a double cladding.

[0058] After the optical fiber preform is made, the optical fiber preform is placed on a drawing tower, and according to actual requirements, drawing parameters are set to perform a drawing operation on the optical fiber preform, and then a coating operation is performed on the peripheral wall of the drawn optical fiber preform to obtain a tapered optical fiber with a gradually changing core-cladding ratio.

[0059] As Figure 6 shown, the tapered optical fiber 5 includes a core 51 for conducting light along the axial direction of the tapered optical fiber and an optical fiber cladding 52 surrounding the core 51.

[0060] Specifically, the core-cladding ratio of the tapered optical fiber 5 is gradually changing, that is, the tapered optical fiber 5 has a gradually changing core diameter and a constant cladding diameter, and the core-cladding ratio of the tapered optical fiber 5 gradually changes along its axial direction.

[0061] Among them, according to actual requirements, the core-cladding ratio of the tapered optical fiber can be adjusted within a certain range and can be specifically adjusted according to the requirements of passive optical fiber devices and optical systems.

[0062] The preparation method of the present invention deposits a core layer on the inner wall surface of the first quartz tube, and the first quartz tube can be rod-drawn and extended to obtain a conical core rod. After the conical core rod is ground into a cylindrical optical fiber preform, the optical fiber preform can be drawn and coated in sequence to obtain a tapered optical fiber with a double cladding.

[0063] As can be seen from the above, the preparation process of the tapered optical fiber of the present invention is simple, and the tapered optical fiber can be formed in one step. There is no need for multiple grindings during the whole process, which reduces the processing difficulty of the tapered optical fiber, saves costs, shortens the preparation time, and improves the preparation efficiency and precision of the tapered optical fiber.

[0064] It should be noted here that the tapered optical fiber prepared in this embodiment can be either an active optical fiber doped with rare earth ions or a passive optical fiber not doped with rare earth ions, and no specific limitation is made thereto.

[0065] In some embodiments, the step of depositing the core layer on the inner wall surface of the first quartz tube shown in this embodiment includes:

[0066] Pickle the first quartz tube.

[0067] Deposit a loose layer of glass particles on the inner wall surface of the first quartz tube and dope the loose layer of glass particles with rare earth ions.

[0068] It can be understood that after the first quartz tube is selected or prepared, pickling the first quartz tube can effectively reduce the introduction of impurities and ensure the processing quality of the tapered optical fiber.

[0069] In some examples, this embodiment can soak the first quartz tube in a hydrofluoric acid solution and set the soaking time to be greater than or equal to 200 min to achieve the purpose of removing impurities.

[0070] After the pickling of the first quartz tube is completed, install a rotary joint at the gas inlet end of the first quartz tube. The first quartz tube is installed on a deposition lathe, and the improved chemical vapor deposition method (Modified Chemical Vapor Deposition, MCVD) can be used to deposit a loose layer of glass particles on the inner wall surface of the first quartz tube, and then dope the loose layer of glass particles with rare earth ions.

[0071] Specifically, first, externally preheat the first quartz tube with a hydrogen-oxygen flame. During the preheating process, gradually raise the temperature of the first quartz tube to 1200 °C.

[0072] Then, feed gas raw materials into the first quartz tube according to a preset flow rate. The gas raw materials are any one or a combination of at least two of SiCl 4 , BCl 3 , GeCl 4 , POCl 3 . Prior to this, it is also necessary to feed SF 6 into the first quartz tube to etch the inner sidewall of the first quartz tube for several passes, then continue to heat the first quartz tube and feed the gas raw materials.

[0073] Among them, when feeding the gas raw materials, control the temperature of the first quartz tube to be heated to 1500 °C to 1800 °C, and control the first quartz tube to rotate until a glass particle loose layer with a specified thickness is deposited on the inner wall surface of the first quartz tube.

[0074] During the process of depositing the glass particle loose layer, or after completing the deposition of the glass particle loose layer, rare earth ions can be doped into the glass particle loose layer.

[0075] It should be noted that according to actual needs, methods such as Outside Vapour Deposition (OVD), Vapour phase Axial Deposition (VAD), or Plasma Chemical Vapor Deposition (PCVD) can also be used to deposit the glass particle loose layer and dope rare earth ions into the glass particle loose layer.

[0076] In some embodiments, the steps of doping rare earth ions into the glass particle loose layer shown in this embodiment include:

[0077] Feed a solution containing rare earth ions into the first quartz tube.

[0078] After soaking for a preset time, drain the remaining solution containing rare earth ions, and a glass particle loose layer containing rare earth ions can be obtained.

[0079] Specifically, feed a solution containing rare earth doped ions into the first quartz tube and soak for a preset time, for example, the soaking time is more than 30 minutes, to dope rare earth ions into the glass particle loose layer.

[0080] Furthermore, in this embodiment, the rare earth doped ions and the dissolution solution can be mixed according to a preset ratio to obtain a solution containing rare earth doped ions. Among them, the rare earth ions are Nd 3+ , Yb 3+ , Er 3+ , Tm 3+Any one or a combination of at least two of them; the dissolving solution is a chloride solution or a nitrate solution.

[0081] After preparing the solution containing rare earth doped ions, take out the first quartz tube, and then immerse the first quartz tube in the solution of rare earth doped ions with a specified concentration. After the immersion, the solution containing rare earth ions can be drained and dried, and a loose layer of glass particles containing rare earth ions can be obtained on the inner wall surface of the first quartz tube.

[0082] In some embodiments, the steps of simultaneously performing rod shrinking and stretching operations on the first quartz tube deposited with the core layer shown in this embodiment include:

[0083] While sintering the first quartz tube deposited with the core layer, a stretching operation is also performed on the first quartz tube to obtain a conical core rod formed by melting and shrinking the first quartz tube and the core layer. The stretching operation can be a continuous stretching or a segmented stretching operation.

[0084] Specifically, after depositing the core layer on the inner wall surface of the first quartz tube, sinter the first quartz tube deposited with the core layer to vitrify the loose layer of glass particles containing rare earth ions. Among them, the sintering temperature of the first quartz tube deposited with the core layer is 1200°C to 2000°C.

[0085] Then, perform melting and shrinking on the vitrified loose layer of glass particles and the first quartz tube, and control the melting and shrinking temperature to be 1400°C to 2200°C, so as to effectively remove the gap between the loose layer of glass particles and the first quartz tube by means of rod shrinking, and obtain a solid rod.

[0086] While performing rod shrinking on the first quartz tube deposited with the core layer, a traditional stretching process can also be used to stretch the first quartz tube deposited with the core layer, and control the pulling force and stretching speed, so as to obtain a solid conical core rod.

[0087] Based on the solutions of the above embodiments, the steps of performing drawing operation on the optical fiber preform shown in this embodiment include:

[0088] Place the optical fiber preform on the drawing tower, and draw a tapered optical fiber by adjusting the drawing parameters.

[0089] Specifically, in this embodiment, the optical fiber preform can be placed on the drawing tower, and the optical fiber preform is heated and softened using a resistance wire furnace or a graphite furnace. Then, based on the drawing tower, the softened optical fiber preform is drawn to draw a tapered optical fiber.

[0090] As Figure 6 shown, after performing a drawing (drawing) operation on the optical fiber preform through the drawing tower, the obtained tapered optical fiber 5 includes a fiber core 51 that conducts light along the axial direction of the tapered optical fiber 5 and an optical fiber cladding 52 that surrounds the fiber core 51.

[0091] In some examples, the adjustable drawing parameters in the wire drawing operation include the heating rate, drawing temperature, drawing tension, drawing atmosphere, drawing gas flow rate, etc.

[0092] Specifically, in this embodiment, the drawing parameters can be determined according to the material of the first quartz tube. Among the above drawing parameters, the heating rate is 10°C / min to 25°C / min; the drawing temperature is 300°C to 1000°C; the drawing tension is 0.5 g to 50 g; the drawing atmosphere is a high-purity single reactive gas, a single inert gas, or a high-purity gas mixture made of the above gases in a certain proportion. The single reactive gas includes oxygen and nitrogen, the single inert gas includes argon and helium, and the high-purity gas mixture includes a gas mixture of nitrogen plus oxygen and a gas mixture of helium plus oxygen; the drawing gas flow rate is 0.5 L / min to 5 L / min.

[0093] Based on the solution of the above embodiment, before the drawing operation of the fiber preform, this embodiment further includes:

[0094] Prepare a second quartz tube adapted to the fiber preform according to the core-cladding ratio of the pre-prepared tapered fiber and the geometric parameters of the fiber preform.

[0095] Assemble the second quartz tube and the fiber preform, and perform a sleeving operation on a sleeving lathe to prepare a solid fiber preform.

[0096] Specifically, after the fiber preform is made, if it is found that the core-cladding ratio of the fiber preform does not meet the requirements, a second quartz tube that meets the process requirements needs to be prepared. Then, by sleeving the second quartz tube, the cladding thickness of the fiber preform is increased to make the core-cladding ratio meet the requirements.

[0097] In actual operation, after the sleeving operation on the fiber preform, it is melted and shrunk into a solid fiber preform, which is placed on a drawing tower to perform drawing and coating operations to make the tapered fiber with a double cladding shown in this embodiment.

[0098] It should be noted here that after the second quartz tube is sleeved on the peripheral wall of the fiber preform, it can also be placed in a resistance wire furnace for drawing operation. After continuing to complete the coating process, the tapered fiber can be obtained. Among them, by performing drawing after sleeving the fiber preform, the sealing performance can be fully guaranteed, the drawing is easier to control, and the concentricity error can be suppressed.

[0099] Based on the solution of the above embodiment, the steps of the coating operation on the fiber preform shown in this embodiment include:

[0100] The circumferential wall of the drawn optical fiber preform is coated twice in sequence to form an optical fiber coating. Among them, the optical fiber coating includes an inner optical fiber coating and an outer coating.

[0101] It can be understood that the circumferential wall of the drawn optical fiber preform is coated for the first time to form an inner optical fiber coating; the circumferential wall of the inner optical fiber coating is coated for the second time to form an outer coating.

[0102] In the above preparation process, this embodiment is essentially to coat the inner optical fiber coating on the circumferential wall of the optical fiber cladding. Among them, the inner optical fiber coating is a low refractive index coating, and the refractive index of the inner optical fiber coating is lower than that of the optical fiber cladding to ensure the reliability of the tapered optical fiber.

[0103] Furthermore, the outer coating formed on the circumferential wall of the inner optical fiber coating through the coating process is specifically a polymer protective layer, and the internal structure of the tapered optical fiber can be protected based on the polymer protective layer.

[0104] In addition, the present invention also provides the following two specific embodiments to specifically describe the preparation method of the tapered optical fiber.

[0105] Example 1:

[0106] To prepare a double-clad ytterbium-doped tapered optical fiber, the following steps are adopted:

[0107] Step 1, place a cylindrical quartz tube on a deposition lathe, and uniformly deposit a core layer with a set thickness on the inner wall surface of the quartz tube.

[0108] Step 2, place the quartz tube deposited with the core layer on a lathe, and perform both rod shrinking and stretching operations on the quartz tube to obtain a conical core rod;

[0109] Step 3, polish the outer wall surface of the conical core rod to obtain a cylindrical optical fiber preform, and the outer diameter of the optical fiber preform at each position along the axial direction remains the same for subsequent wire drawing operations;

[0110] Step 4, place the optical fiber preform on a wire drawing tower, perform wire drawing operations by setting different wire drawing parameters, and after coating the drawn optical fiber, a double-clad tapered optical fiber is made.

[0111] Among them, the core diameter range of the tapered optical fiber is 30 μm - 35 μm, and the cladding diameter range is 400 μm - 600 μm.

[0112] Example 2,

[0113] To prepare a double-clad ytterbium-doped tapered optical fiber, the following steps are adopted:

[0114] Step 1, place the cylindrical quartz tube on the deposition lathe, and evenly deposit a core layer with a set thickness on the inner wall surface of the quartz tube.

[0115] Step 2, place the quartz tube deposited with the core layer on the lathe, and simultaneously perform rod shrinking and stretching operations on the quartz tube to obtain a conical core rod;

[0116] Step 3, polish the outer wall surface of the conical core rod to obtain a cylindrical optical fiber preform, and the outer diameter at each position along the axis of the optical fiber preform remains the same; then, assemble the optical fiber preform with a quartz tube and perform a sleeving operation on the sleeving lathe to obtain a solid optical fiber preform;

[0117] Step 4, place the optical fiber preform on the drawing tower, set different drawing parameters for drawing operations, and after successively performing coating operations on the drawn optical fiber preform, a tapered optical fiber with a double cladding is made.

[0118] Among them, the core diameter range of the tapered optical fiber is 30μm - 35μm, and the cladding diameter range is 400μm - 600μm.

[0119] In some embodiments, as Figure 6 shown, the embodiment of the present invention also provides a tapered optical fiber, and the tapered optical fiber is obtained by using the preparation method of the tapered optical fiber described above.

[0120] Specifically, the above-mentioned tapered optical fiber 5 includes a core 51 and an optical fiber cladding 52. The optical fiber cladding 52 is coated on the outside of the core 51. An optical fiber inner coating and an outer coating are successively formed on the outside of the optical fiber cladding 52 through a coating process, and the refractive index of the optical fiber inner coating is lower than that of the optical fiber cladding.

[0121] Since the tapered optical fiber is obtained by using the preparation method of the tapered optical fiber described in the above embodiment, the tapered optical fiber in this embodiment includes all the technical solutions of the above embodiment. Therefore, it has at least all the beneficial effects obtained by all the technical solutions of the above embodiment, and will not be elaborated here one by one.

[0122] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a tapered optical fiber, characterized in that, comprising: performing a deposition operation of a core layer on the inner wall surface of a first quartz tube; simultaneously performing a rod shrinking and an extending operation on the first quartz tube deposited with the core layer to obtain a conical core rod, and from the first end to the second end of the conical core rod, both the cross-sectional area of the conical core rod and the cross-sectional area of the fiber core of the conical core rod gradually decrease; grinding the outer wall surface of the conical core rod to obtain a cylindrical optical fiber preform, and the diameter of the optical fiber preform remains consistent at each position along its axis; successively performing a drawing and a coating operation on the optical fiber preform to fabricate a tapered optical fiber with a double cladding; the step of simultaneously performing a rod shrinking and an extending operation on the first quartz tube deposited with the core layer includes: while sintering the first quartz tube deposited with the core layer, also performing a stretching operation on the first quartz tube to obtain the conical core rod formed by the fusion and shrinking of the first quartz tube and the core layer.

2. The method for preparing a tapered optical fiber according to claim 1, characterized in that, the step of performing a deposition operation of a core layer on the inner wall surface of the first quartz tube includes: performing pickling on the first quartz tube; depositing a loose layer of glass particles on the inner wall surface of the first quartz tube, and doping the loose layer of glass particles with rare earth ions.

3. The method for preparing a tapered optical fiber according to claim 2, characterized in that, the step of doping the loose layer of glass particles with rare earth ions includes: introducing a solution containing the rare earth ions into the first quartz tube; after soaking for a preset time, discharging the remaining solution containing the rare earth ions.

4. The method for preparing a tapered optical fiber according to claim 2, characterized in that, The rare earth ion is Nd 3+ , Yb 3+ , Er 3+ , Tm 3+ or a combination of any one or at least two of them.

5. The method for preparing a tapered optical fiber according to any one of claims 1 to 4, characterized in that, the step of performing a drawing operation on the optical fiber preform includes: placing the optical fiber preform on a drawing tower, and by adjusting drawing parameters, drawing out the tapered optical fiber.

6. The method for preparing a tapered optical fiber according to claim 5, characterized in that, the drawing parameters include a heating rate, a drawing temperature, a drawing tension, a drawing atmosphere, and a drawing gas flow rate.

7. The method for preparing a tapered optical fiber according to any one of claims 1 to 4, characterized in that, before performing a drawing operation on the optical fiber preform, further comprising: preparing a second quartz tube adapted to the optical fiber preform according to the core-cladding ratio of the tapered optical fiber to be prepared and the geometric parameters of the optical fiber preform; assembling the second quartz tube and the optical fiber preform, and performing a sleeving operation on a sleeving lathe to prepare a solid optical fiber preform.

8. The method for preparing a tapered optical fiber according to any one of claims 1 to 4, characterized in that, the step of performing a coating operation on the optical fiber preform includes: performing two coatings on the peripheral wall of the drawn optical fiber preform in sequence to form an optical fiber coating.

9. A tapered optical fiber, characterized in that, the tapered optical fiber is prepared by using the method for preparing a tapered optical fiber according to any one of claims 1 to 8.

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