Method for preparing tapered optical fiber

Abstract

The present invention provides a method for preparing a tapered optical fiber, comprising: preparing a first tapered quartz tube having a first through-hole therein; depositing a core layer within the first through-hole of the first tapered quartz tube; shrinking the first tapered quartz tube, in which the core layer is deposited, to form a tapered preform; and drawing the tapered preform into a tapered optical fiber, the tapered optical fiber comprising a core that conducts light along the axial direction of the tapered optical fiber and a cladding surrounding the core. The tapered optical fiber preparation method provided by the present invention eliminates the need for multiple polishing steps throughout the entire process, resulting in a simple, one-step formation process. This significantly reduces the difficulty of processing the tapered optical fiber and improves the efficiency and precision of tapered optical fiber preparation.

Description

Technical Field

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

[0002] Compared to conventional fibers with uniform core and cladding, tapered fibers, by introducing a large core diameter end, can increase the effective mode area of the fiber, effectively suppressing nonlinear effects. Furthermore, tapered fibers also offer excellent performance in suppressing mode instabilities, maintaining beam quality, and suppressing amplified spontaneous emission (ASE), showing great potential in the high-power laser field.

[0003] Tapered optical fibers are often produced using methods such as melt tapering, mechanical polishing, or chemical etching. By varying the fiber radius along the axial direction to create a tapered region, these techniques enable applications in optical coupling, optical sensing, nonlinear optics, micro-nano optics, optical fiber devices, and other research fields. However, existing tapered optical fibers require separate grinding of the core rod and glass rod during processing, resulting in a complex and tedious preparation process. Polishing the inner wall of the glass rod is particularly difficult and results in low precision. Furthermore, internal grinding limits the length of the glass rod and poses drawbacks such as poor adaptability. Summary of the Invention

[0004] The present invention provides a method for preparing a tapered optical fiber, which is used to solve the problem that during the processing of the existing tapered optical fiber, a core rod and a glass rod need to be ground and processed separately, resulting in a complicated and tedious preparation process.

[0005] The present invention provides a method for preparing a tapered optical fiber, comprising:

[0006] Making a first tapered quartz tube having a first through hole therein;

[0007] depositing a core layer in the first through hole of the first tapered quartz tube;

[0008] shrinking the first tapered quartz tube on which the core layer is deposited to form a tapered preform;

[0009] The tapered preform is drawn into a tapered optical fiber, which includes a core for guiding light along the axial direction of the tapered optical fiber and a cladding surrounding the core.

[0010] According to a method for preparing a tapered optical fiber provided by the present invention, the step of preparing a first tapered quartz tube having a first through hole therein comprises:

[0011] The outer wall of the first quartz tube is processed into a tapered shape to prepare a first tapered quartz tube having the first through hole therein.

[0012] According to a method for preparing a tapered optical fiber provided by the present invention, the step of depositing a core layer in the first through hole of the first tapered quartz tube includes:

[0013] acid-washing the first tapered quartz tube;

[0014] A loose layer is uniformly deposited in the first through hole of the first tapered quartz tube, and rare earth ions are doped into the loose layer.

[0015] According to a method for preparing a tapered optical fiber provided by the present invention, the step of doping the loose layer with rare earth ions comprises:

[0016] Passing a solution containing the rare earth ions into the first through hole;

[0017] After soaking for a preset time, the remaining solution containing the rare earth ions is discharged.

[0018] According to a method for preparing a tapered optical fiber provided by the present invention, the step of shrinking the first tapered quartz tube for depositing the core layer to form a tapered preform comprises:

[0019] The first tapered quartz tube and the loose layer are sintered to melt and shrink the first tapered quartz tube and the loose layer into the tapered preform rod.

[0020] According to a method for preparing a tapered optical fiber provided by the present invention, the rare earth ion is Nd 3+ 、Yb 3+ 、Er 3+ 、Tm 3+ Any one or combination of .

[0021] According to a method for preparing a tapered optical fiber provided by the present invention, the step of drawing the tapered preform into the tapered optical fiber comprises:

[0022] The tapered preform rod is placed on a drawing tower and drawn into the tapered optical fiber.

[0023] According to a method for preparing a tapered optical fiber provided by the present invention, the step of drawing the tapered preform into the tapered optical fiber comprises:

[0024] Processing the outer wall of the second quartz tube into a tapered shape to construct a second tapered quartz tube having a second through hole therein;

[0025] Assembling the second tapered quartz tube and the tapered preform rod, and placing them on a sleeve lathe to obtain a solid tapered optical fiber preform rod;

[0026] According to a method for preparing a tapered optical fiber provided by the present invention, the tapered optical fiber preform is placed on a drawing tower and drawn into the tapered optical fiber.

[0027] The step of placing the tapered optical fiber preform on a drawing tower and drawing it into the tapered optical fiber comprises:

[0028] The tapered optical fiber preform is placed on the drawing tower, and the tapered optical fiber is drawn by adjusting the drawing parameters.

[0029] According to a method for preparing a tapered optical fiber provided by the present invention, after the step of drawing the tapered preform into the tapered optical fiber, the method further comprises:

[0030] The outer periphery of the cladding is coated twice to form an optical fiber coating.

[0031] The method for preparing a tapered optical fiber provided by the present invention involves first polishing the outer wall of a cylindrical quartz tube with a through hole into a conical shape, depositing a core layer within the first tapered quartz tube, shrinking the tube into a tapered preform, and finally drawing the tapered preform into a tapered optical fiber. The entire process eliminates the need for multiple polishing steps and is completed in a single step. This simplifies the process, significantly reduces the difficulty of processing the tapered optical fiber, and improves the efficiency and precision of tapered optical fiber preparation. Furthermore, because the quartz tube is polished in the early stages, the invention can reduce costs and ensure production efficiency compared to existing processes that require polishing at a later stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 This is one of the flow diagrams of the method for preparing a tapered optical fiber provided by an embodiment of the present invention;

[0034] Figure 2 is a schematic diagram of a first tapered quartz tube provided in an embodiment of the present invention;

[0035] Figure 3 Schematic diagram of the first tapered quartz tube after the core layer is deposited, provided by an embodiment of the present invention;

[0036] Figure 4 is a schematic diagram of a tapered preform provided by an embodiment of the present invention;

[0037] Figure 5 is one of the schematic diagrams of a tapered optical fiber provided by an embodiment of the present invention;

[0038] Figure 6 This is a second flow chart of a method for preparing a tapered optical fiber provided by an embodiment of the present invention;

[0039] Figure 7 This is the third flow chart of the method for preparing a tapered optical fiber provided by an embodiment of the present invention;

[0040] Figure 8 is a schematic diagram of a tapered optical fiber preform provided by an embodiment of the present invention;

[0041] Figure 9 This is the second schematic diagram of the tapered optical fiber provided by an embodiment of the present invention;

[0042] Reference numerals:

[0043] 1. First tapered quartz tube; 10. First through hole; 2. Core layer; 3. Tapered preform rod; 4. Tapered optical fiber; 41. Fiber core; 42. Cladding layer; 5. Second quartz tube. DETAILED DESCRIPTION

[0044] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0045] In the description of the embodiments of the present invention, it should be noted that the terms "upper," "lower," "front," "back," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the embodiments of the present invention and to simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0046] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0047] The following combination Figure 1 The method for preparing a tapered optical fiber provided by the present invention comprises the following steps:

[0048] Step S101: manufacturing a first tapered quartz tube with a first through hole therein.

[0049] First, select a quartz tube with matching thermal properties and optical properties that meet the requirements, such as Figure 2 As shown, the outer wall of the quartz tube is polished to produce a first tapered quartz tube 1 having a first through hole 10 .

[0050] In this embodiment, the first through hole 10 is provided at the center of the first tapered quartz tube 1 , and the first through hole 10 extends from one end of the first tapered quartz tube 1 to the other end of the first tapered quartz tube 1 .

[0051] Step S102: depositing a core layer in the first through hole of the first tapered quartz tube.

[0052] After the first tapered quartz tube 1 with the first through hole 10 is manufactured, the gas raw material can be introduced through the first through hole 10 while controlling the rotation of the first tapered quartz tube 1, and deposited on the inner wall of the first through hole 10 to form the core layer 2. Figure 3 shown.

[0053] Step S103: shrinking the first tapered quartz tube on which the core layer is deposited to form a tapered preform.

[0054] After the core layer 2 is deposited in the first through hole 10 of the first tapered quartz tube 1, the first tapered quartz tube 1 with the core layer 2 deposited thereon is shrunk to form a tapered preform rod 3, as shown in FIG. Figure 4 shown.

[0055] During the shrinking and melting process, oxygen is introduced to purge the core layer 2 and the first tapered quartz tube 1, and the temperature is gradually raised to 1700°C. The temperature is continued to rise, and the heat source movement speed is reduced to 2.5 to 20 mm / min. The pressure difference between the gas outlet and atmospheric pressure is maintained, and the temperature is controlled between 1850 and 2150°C. The first tapered quartz tube 1, on which the core layer 2 is deposited, is formed into a tapered preform 3.

[0056] Step S104: drawing the tapered preform into a tapered optical fiber.

[0057] After the conical preform rod 3 is produced, the conical preform rod 3 is placed on a drawing tower, as shown in FIG. Figure 5 As shown, a tapered optical fiber 4 with a core-to-cladding ratio gradient is drawn. The tapered optical fiber 4 comprises a core 41 for guiding light along the axial direction of the tapered optical fiber and a cladding 42 surrounding the core 41.

[0058] The tapered optical fiber 4 with a gradient core-to-cladding ratio has a constant core 41 diameter and a gradient cladding diameter. The core-to-cladding ratio of the optical fiber gradually changes with the length of the optical fiber. Moreover, the diameter of the core 41, the core-to-cladding ratio, etc. can be controlled within a certain range according to the needs, and can be specifically adjusted according to the requirements of the passive optical fiber device and the optical system.

[0059] The method for preparing a tapered optical fiber provided in this embodiment is to first grind the outer wall of a cylindrical quartz tube with a through hole into a cone shape, deposit a core layer in the first tapered quartz tube, shrink the rod into a tapered preform rod, and finally place the tapered preform rod on a drawing tower to draw it into a tapered optical fiber. The entire process does not require multiple grindings and is formed in one step. The process is simple, greatly reducing the processing difficulty of the tapered optical fiber and improving the preparation efficiency and precision of the tapered optical fiber. Moreover, since the quartz tube is polished in the early stage in this embodiment, compared with the existing process of polishing in the later stage, it can reduce costs and ensure production efficiency.

[0060] It should be noted that, during the deposition of the core layer 2, the introduction speed of the gas or liquid raw material can be gradually adjusted to adjust the deposition amount of the core layer 2 along the direction of the first through hole 10, so that the deposition amount of the core layer 2 changes with the position of the first through hole 10, so that the core layer 2 is deposited uniformly or non-uniformly in the first through hole 10, as shown in FIG. Figure 3 shown.

[0061] Optionally, the introduction speed of the gas or liquid raw material can be continuously changed so that the core layer 2 gradually increases or decreases with the deposition amount of the first through hole 10; or, the introduction speed of the gas or liquid raw material can be changed step by step so that the core layer 2 gradually increases or decreases with the deposition amount of the first through hole 10.

[0062] Since the thickness of the core layer 2 changes gradually, it will melt and shrink to form a conical or other shaped core layer 2 during the rod shrinking process, that is, melt and shrink to form a conical preform rod 3, so that the fiber core 41 can form a conical or stepped shape after drawing.

[0063] In one embodiment, step S101: a step of making a first tapered quartz tube having a first through hole therein, such as Figure 6 As shown, the following steps are included:

[0064] Step S1012: processing the outer wall of the first quartz tube into a tapered shape to construct a first tapered quartz tube having a first through hole therein.

[0065] Specifically, first select the first quartz tube with matching thermal properties and optical properties that meet the requirements, such as Figure 2 As shown, the first quartz tube is generally a cylindrical quartz tube. In the actual production and processing process, the selected cylindrical quartz tube itself has a first through hole 10 that meets the specifications. Then the outer wall of the first quartz tube is processed into a cone to construct a first tapered quartz tube with the first through hole 10 therein.

[0066] Based on the above embodiment, in another embodiment, step S102: depositing a core layer in the first through hole of the first tapered quartz tube, such as Figure 7 As shown, the following steps are included:

[0067] Step S1021: pickling the first tapered quartz tube.

[0068] Step S1022: uniformly depositing a loose layer in the first through hole of the first tapered quartz tube, and doping the loose layer with rare earth ions.

[0069] Specifically, if Figure 3 As shown, after the first tapered quartz tube with the first through hole 10 is produced, the first tapered quartz tube is first cleaned by pickling. For example, the entire first tapered quartz tube can be pickled with a hydrofluoric acid solution. The pickling effectively reduces the introduction of impurities and ensures the processing quality.

[0070] After pickling, the air inlet section of the first conical quartz tube is installed with a rotary joint, and the first conical quartz tube is installed on a deposition lathe. Modified Chemical Vapor Deposition (MCVD) can be used to deposit a loose layer, and rare earth ions are doped into the loose layer.

[0071] Specifically, the first conical quartz tube is preheated externally using an oxyhydrogen flame. During the preheating process, the temperature of the first conical quartz tube is gradually raised to 1200°C. A gas feedstock is then introduced into the first conical quartz tube at a preset flow rate. The gas feedstock is any one or a combination of SiCl4, BCl3, GeCl4, and POCl3. Prior to this, SF6 and O2 are introduced into the first conical quartz tube to perform several passes of etching on the inner sidewall of the first conical quartz tube. The first conical quartz tube is then heated and the gas feedstock is introduced. When the gas feedstock is introduced, the temperature of the reaction tube must be heated to 1500°C to 1800°C. During the repeated rotation of the first conical quartz tube, a loose layer of a specified thickness is deposited on its inner sidewall. During or after the deposition process, the loose layer can be doped with rare earth ions.

[0072] It should be noted that, according to actual needs, the loose layer can also be deposited by outside vapor deposition (OVD), axial chemical vapor deposition (VAD) or plasma chemical vapor deposition (PCVD), and rare earth ions can be doped into the loose layer.

[0073] In this embodiment, during the process of doping rare earth ions, a solution containing rare earth ions may be first passed into the first through hole. After soaking for a preset time, the remaining solution containing rare earth ions is discharged to obtain a loose layer containing rare earth ions.

[0074] Specifically, a solution containing rare earth doping ions is passed into the first tapered quartz tube and soaked for a preset time, which is more than 30 minutes, to dope the loose layer with rare earth ions. Specifically, the rare earth doping ions and the dissolving solution are mixed according to a preset ratio to obtain a rare earth doping ion solution, wherein the rare earth ions are Nd 3+ 、Yb 3+ 、Er 3+ 、Tm 3+ Any one or a combination of the following. The dissolving liquid is a chloride solution or a nitrate solution. After preparing the solution containing rare earth dopant ions, the first tapered quartz tube is removed and then immersed in a solution of rare earth dopant ions at a specified concentration. After immersion, the solution containing rare earth ions can be drained and dried to obtain a loose layer containing rare earth ions within the first through-hole. Furthermore, when producing passive tapered optical fibers, rare earth ion doping is not required.

[0075] Based on the above embodiments, in some embodiments, step S103: shrinking the first conical quartz tube on which the core layer is deposited to form a conical preform rod, includes: sintering the first conical quartz tube and the loose layer to melt and shrink the first conical quartz tube and the loose layer into the conical preform rod.

[0076] like Figure 4 As shown, after the core layer is deposited, the first tapered quartz tube and the loose layer are sintered at high temperature to vitrify the loose layer containing rare earth ions. The vitrified loose layer and the first tapered quartz tube are then melted and shrunk into a solid tapered preform rod 3. The gap between the loose layer and the first tapered quartz tube is effectively removed by shrinking the rod.

[0077] Based on the above embodiments, in some embodiments, step S104: drawing the tapered preform into a tapered optical fiber specifically includes: after the tapered preform is produced, Figure 4 As shown, the tapered preform rod 3 can be placed on a drawing tower and heated and softened using a resistance wire furnace. The adjustable experimental parameters include heating rate, drawing temperature, drawing tension, etc. The softened tapered preform rod is drawn in the resistance wire furnace to form a tapered optical fiber. Figure 5 As shown, the tapered optical fiber 4 includes a core 41 that conducts light along the tapered optical fiber axis and a cladding 42 surrounding the core 41. The tapered optical fiber 4 with a graded core-to-cladding ratio has a constant core 41 diameter and a graded cladding diameter. The core-to-cladding ratio gradually changes along the length of the optical fiber. Furthermore, the core 41 diameter and core-to-cladding ratio can be controlled within a certain range based on requirements, and can be specifically adjusted based on the requirements of passive optical fiber devices and optical systems.

[0078] Based on the above embodiment, in other embodiments, step S104: drawing the tapered preform into a tapered optical fiber specifically includes: after the tapered preform is produced, if it is found that the tapered preform does not meet the specifications and requires a sleeve, such as Figure 8 As shown, firstly, a second quartz tube 5 is selected with matching thermal properties and optical properties that meet the requirements. The second quartz tube is generally a cylindrical quartz tube with a through hole. In the actual production and processing process, the selected cylindrical quartz tube itself has a second through hole that meets the specifications. A second through hole that matches the tapered preform rod 3 is constructed in the second quartz tube 5, and the second through hole extends from one end of the second quartz tube 5 to the other end. The second tapered quartz tube is then assembled with the tapered preform rod, placed on a sleeve lathe, and melted to obtain a solid tapered optical fiber preform rod. The tapered optical fiber preform rod is then placed on a drawing tower, and a resistance wire furnace is used to heat and soften the tapered optical fiber preform rod. The adjustable experimental parameters include heating rate, drawing temperature, drawing tension, etc. In the resistance wire furnace, the softened tapered optical fiber preform rod is drawn into a tapered optical fiber. Drawing after the sleeve can fully guarantee the sealing performance, make it easier to control the drawing, and suppress concentricity errors. As shown Figure 5 As shown, the tapered optical fiber 4 includes a core 41 that conducts light along the tapered optical fiber axis and a cladding 42 surrounding the core 41. The tapered optical fiber 4 with a graded core-to-cladding ratio has a constant core 41 diameter and a graded cladding diameter. The core-to-cladding ratio gradually changes along the length of the optical fiber. Furthermore, the core 41 diameter and core-to-cladding ratio can be controlled within a certain range based on requirements, and can be specifically adjusted based on the requirements of passive optical fiber devices and optical systems.

[0079] Finally, if Figure 9 As shown, the outer periphery of the cladding 42 may be coated with a low-refractive coating twice, thereby forming an optical fiber coating outside the cladding 42 .

[0080] Specifically, the first coating is performed to form an inner coating of the optical fiber; and the second coating is performed on the peripheral wall of the inner coating of the optical fiber to form an outer coating.

[0081] In the above-mentioned preparation process, this embodiment essentially applies an inner coating to the peripheral wall of the optical fiber cladding. The inner coating is a low-refractive-index coating, and the refractive index of the inner coating is lower than that of the optical fiber cladding to ensure the reliability of the tapered optical fiber.

[0082] In addition, this application also provides two specific embodiments.

[0083] Example 1:

[0084] A double-clad ytterbium-doped tapered optical fiber is prepared using the following steps:

[0085] Step 1: Grind the outer wall of the cylindrical high-purity quartz tube into a tapered shape.

[0086] Step 2: Place the first tapered quartz tube on a lathe to evenly deposit the core layer.

[0087] Step 3: Place the deposited core rod on a lathe to shrink it into a tapered preform rod.

[0088] Step 4: Place the tapered preform on a drawing tower and draw it into a tapered optical fiber. By setting different drawing parameters, the cladding diameter of the double-clad ytterbium-doped tapered optical fiber is in the range of 400μm-600μm and the core diameter is 20μm.

[0089] Example 2:

[0090] A double-clad ytterbium-doped tapered optical fiber is prepared using the following steps:

[0091] Step 1: Grind the outer wall of the cylindrical high-purity quartz tube into a tapered shape.

[0092] Step 2: Place the first tapered quartz tube on a lathe to evenly deposit the core layer.

[0093] Step 3: Place the deposited core rod on a lathe to shrink it into a tapered preform rod.

[0094] Step 4: Place the tapered preform on a drawing tower and draw it into a tapered optical fiber. By setting different drawing parameters, the cladding diameter of the double-clad ytterbium-doped tapered optical fiber is 400μm and the core diameter ranges from 30μm to 35μm.

[0095] The device embodiments described above are merely illustrative, and some or all of the modules may be selected according to actual needs to achieve the purpose of the present embodiment. Those skilled in the art may understand and implement the present invention without inventive effort.

[0096] 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 it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a tapered optical fiber, characterized in that: include: Making a first tapered quartz tube having a first through hole therein; The step of manufacturing the first tapered quartz tube having the first through hole therein comprises: machining the outer wall of the first quartz tube into a tapered shape to prepare the first tapered quartz tube having the first through hole therein; depositing a core layer in the first through hole of the first tapered quartz tube; shrinking the first tapered quartz tube on which the core layer is deposited to form a tapered preform; The outer wall of the second quartz tube is processed into a tapered shape to construct a second tapered quartz tube with a second through hole therein; the second tapered quartz tube is assembled with the tapered preform rod and placed on a sleeve lathe to obtain a solid tapered optical fiber preform rod; the tapered optical fiber preform rod is placed on a drawing tower and drawn into the tapered optical fiber; the tapered optical fiber includes a core that conducts light along the axial direction of the tapered optical fiber and a cladding surrounding the core.

2. The method for preparing a tapered optical fiber according to claim 1, wherein: The step of depositing a core layer in the first through hole of the first tapered quartz tube comprises: acid-washing the first tapered quartz tube; A loose layer is uniformly deposited in the first through hole of the first tapered quartz tube, and rare earth ions are doped into the loose layer.

3. The method for preparing a tapered optical fiber according to claim 2, wherein: The step of doping rare earth ions in the loose layer comprises: Passing a solution containing the rare earth ions into the first through hole; After soaking for a preset time, the remaining solution containing the rare earth ions is discharged.

4. The method for preparing a tapered optical fiber according to claim 2, wherein: The step of shrinking the first tapered quartz tube for depositing the core layer to form a tapered preform comprises: The first tapered quartz tube and the loose layer are sintered to melt and shrink the first tapered quartz tube and the loose layer into the tapered preform rod.

5. The method for preparing a tapered optical fiber according to claim 2, wherein: The rare earth ion is Nd 3+ 、Yb 3+ 、Er 3+ 、Tm 3+ Any one or combination of .

6. The method for preparing a tapered optical fiber according to claim 1, wherein: The step of placing the tapered optical fiber preform on a drawing tower and drawing it into the tapered optical fiber comprises: The tapered optical fiber preform is placed on the drawing tower, and the tapered optical fiber is drawn by adjusting the drawing parameters.

7. The method for preparing a tapered optical fiber according to any one of claims 1 to 6, characterized in that: After the step of drawing the tapered preform into a tapered optical fiber, the step further includes: The outer periphery of the cladding is coated twice to form an optical fiber coating.

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