Preparation method of 1*N one-time tapering broadband single-mode optical fiber coupler

Abstract

The invention discloses a preparation method of a 1 * N one-time tapering broadband single-mode optical fiber coupler. The preparation method comprises the following steps: S1, drawing two capillary tubes of which the inner diameters of the end parts are greater than the inner diameter of a waist region; s2, preparing a first optical fiber bundle; s3, preparing a second optical fiber bundle; s4, the first optical fiber bundle and the second optical fiber bundle are welded, and it is ensured that fiber cores of the first center optical fiber and the second center optical fiber are aligned; and S5, inputting input light with a predetermined wavelength into the first central optical fiber, connecting a port of the second central optical fiber and a port of any one surrounding single-mode optical fiber into a photoelectric detector, heating a second optical fiber beam waist area at a high temperature and synchronously stretching until the output optical power of the second central optical fiber tends to 0, and stopping heating and stretching to obtain the 1 * N one-time tapering broadband single-mode optical fiber coupler. The invention has the characteristics of miniaturization and high performance.

Description

Technical Field

[0001] This invention relates to the field of optical fiber technology, and in particular to a method for fabricating a 1xN single-tapered broadband single-mode optical fiber coupler. Background Technology

[0002] Since their practical application, single-mode fiber couplers have been widely used in fiber optic communication networks, optical amplification, fiber optic sensing, fiber optic lasers, and optical instruments. Among them, 1x2 or 2x2 single-mode fiber couplers are the most common, while 1x3 and 1x4 single-tapered couplers are less common, and their design structure does not achieve optimal performance, resulting in deficiencies in beam splitting uniformity and the polarization dependence of the beam splitting ratio within the broadband operating band.

[0003] For 1xN fused tapered single-mode fiber couplers with N values ​​of 8, 16, or 32, current technologies typically employ cascaded combinations of 1x2, 1x3, or 1x4 devices to form optical splitter modules. These modules suffer from large size, and as the number of cascaded stages increases, key parameters such as splitting ratio uniformity and polarization-dependent loss (PDL) continuously deteriorate. To achieve miniaturization of optical splitter modules, planar waveguide technology was developed in the early 1990s. While this reduces splitter size and improves splitting ratio uniformity, its insertion loss and polarization dependence are almost an order of magnitude higher than fused tapered devices, making it difficult to meet the demands of high-precision applications. Therefore, the manufacturing of 1xN fused tapered single-mode fiber couplers with N values ​​of 8, 16, or 32 requires further improvement. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for fabricating a 1xN single-tapered broadband single-mode fiber coupler, which features miniaturization and high performance.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for fabricating a 1xN single-tapered broadband single-mode fiber coupler, characterized by comprising the following steps: S1. Draw two capillary tubes with an end inner diameter greater than the waist inner diameter, and the waist inner diameters of the two capillary tubes are the same. S2. Preparation of the first optical fiber bundle: (1) Prepare N+1 optical fibers, including one cored first central optical fiber and N coreless optical fibers; (2) Remove the coating layer from one end of the first central fiber and the coreless fiber, and insert N+1 fibers into the first capillary in such a way that the first central fiber is located at the axis and N coreless fibers are evenly wrapped around it, so that the uncoated part of the first central fiber and the coreless fiber is located in the waist region of the capillary and the coated part is located at both ends of the capillary. (3) The waist region of the first capillary is heated at high temperature to fuse N+1 optical fibers with the capillary into one piece, and then the first optical fiber bundle is obtained by cutting along the waist region. S3. Fabrication of the second fiber bundle: (1) Prepare N+1 optical fibers, including one second central optical fiber with the same specifications as the first central optical fiber and N single-mode optical fibers. (2) Remove the coating layer from one end of the second central fiber and the single-mode fiber, and insert N+1 fibers into the second capillary in such a way that the second central fiber is located at the axis and N single-mode fibers are evenly wrapped around it, so that the uncoated part of the second central fiber and the single-mode fiber is located in the waist region of the capillary and the coated part is located at both ends of the capillary. (3) The waist region of the second capillary is heated at high temperature to fuse the N+1 optical fibers with the capillary into one piece, and then the second optical fiber bundle is obtained by cutting along the waist region. S4. Fusion splice the first fiber bundle and the second fiber bundle to ensure that the cores of the first central fiber and the second central fiber are aligned. S5. Input light of a predetermined wavelength into the first central fiber, connect the port of the second central fiber and the port of any one of the surrounding single-mode fibers to the photodetector, heat the waist region of the second fiber at high temperature and stretch it synchronously until the output optical power of the second central fiber approaches 0, stop heating and stretching, and obtain a 1xN single-tapered broadband single-mode fiber coupler.

[0006] Preferably, the sum of the diameters of the first central optical fiber and the two coreless optical fibers is equal to the inner diameter of the waist region of the capillary.

[0007] Preferably, in steps S2 (3) and S3 (3), during high-temperature heating, the N+1 optical fibers and the capillary rotate synchronously at a uniform speed.

[0008] Preferably, the capillary is a pure quartz capillary.

[0009] Preferably, N is 4, 6, 8, 16, or 32.

[0010] Preferably, when N is less than 6, coreless fibers need to be filled during the fabrication of the second fiber bundle so that the total number of single-mode fibers and coreless fibers in the second fiber bundle is ≥6.

[0011] The advantages of this invention are: 1. The process is simple and easy to operate. The process route of "dual fiber bundle preparation, precise fusion splicing, and one-time tapering" reduces the operating threshold and facilitates large-scale production. 2. One-time tapered forming eliminates the need for component series connection, significantly reducing the coupler size; 3. Based on the evanescent field theory and coupled mode theory, it has good beam splitting uniformity and small optical power deviation at each output end; 4. Low insertion loss, with polarization-dependent loss (PDL) significantly superior to cascaded modules and planar waveguide technology; 5. Highly practical, couplers of various specifications such as 1x4, 1x6, 1x8, 1x16, and 1x32 can be flexibly manufactured to meet the application needs of different fields such as optical communication, fiber optic sensing, and testing instruments. Attached Figure Description

[0012] Figure 1 This is the fabrication process for the 1xN single-tapered broadband single-mode fiber coupler provided in this embodiment; Figure 2 This is a schematic diagram of the cross-section of the first fiber bundle before and after melting during the fabrication process of the 1x8 coupler provided in this embodiment; Figure 3 This is a schematic diagram of the cross-section of the second fiber bundle before and after melting during the fabrication process of the 1x8 coupler provided in this embodiment; Figure 4 This is a schematic diagram illustrating the variation of the output optical power of the second fiber bundle with wavelength when fabricating a 1x8 coupler as provided in this embodiment; Figure 5 This is a schematic diagram illustrating the insertion loss as a function of wavelength when fabricating a 1x8 coupler as provided in this embodiment; Figure 6 This is a schematic diagram of the cross-section of the first fiber bundle before and after melting during the fabrication process of the 1x6 coupler provided in this embodiment; Figure 7 This is a schematic diagram of the cross-section of the second fiber bundle before and after melting during the fabrication process of the 1x6 coupler provided in this embodiment; Figure 8 This is a schematic diagram illustrating the variation of the output optical power of the second fiber bundle with wavelength when fabricating a 1x6 coupler as provided in this embodiment; Figure 9 This is a schematic diagram of the cross-section of the first fiber bundle before and after melting during the fabrication process of the 1x4 coupler provided in this embodiment; Figure 10 This is a schematic diagram of the cross-section of the second fiber bundle before and after melting during the fabrication process of the 1x4 coupler provided in this embodiment; Figure 11 This is a schematic diagram showing the change of the output optical power of the second fiber bundle with wavelength when preparing a 1x4 coupler in this embodiment. Detailed Implementation

[0013] Combination Figures 1 to 11 The method for fabricating a 1xN single-tapered broadband single-mode fiber coupler according to the present invention will be further described.

[0014] like Figure 1-3 As shown, a method for fabricating a 1xN single-tapered broadband single-mode fiber coupler is characterized by the following steps: S1. Draw two capillaries with an end inner diameter larger than the waist inner diameter. The waist inner diameters of the two capillaries are the same. The capillaries are pure quartz capillaries. This material is the same as the material of the optical fiber cladding, which facilitates subsequent melting operations and the acquisition of devices with low additional loss.

[0015] S2. Preparation of the first optical fiber bundle: (1) Prepare N+1 optical fibers, including one cored first central fiber and N coreless optical fibers. When N is greater than 6, the performance of the first central fiber is the same as that of the standard communication fiber except for its diameter; when N is between 4 and 6, the first central fiber is a conventional standard communication fiber.

[0016] (2) Remove the coating layer from one end of the first central fiber and the coreless fiber, and insert N+1 fibers into the first capillary tube with the first central fiber at the axis and N coreless fibers evenly wrapped around it, so that the uncoated part of the first central fiber and the coreless fiber is located in the waist region of the capillary tube, and the coated part is located at both ends of the capillary tube; the diameter of the end of the first central fiber after removing the coating layer and the sum of the diameters of the ends of the two coreless fibers after removing the coating layer are the same as the inner diameter of the waist region of the capillary tube, so that one first central fiber and N coreless fibers are closely arranged in the waist region of the capillary tube, which facilitates synchronous rotation and uniform melting during high-temperature heating later.

[0017] (3) The waist region of the first capillary is heated at a high temperature, slightly higher than the melting point of a pure quartz capillary. In this embodiment, 1700℃ is selected. During the process, the capillary and N+1 optical fibers rotate synchronously and uniformly, so that the N+1 optical fibers and the capillary are fused together, and a high degree of symmetry is obtained. Then, the first fiber bundle is obtained by cutting along the waist region. It should be noted that the fusion of the N+1 optical fibers and the capillary together refers to fusing the cladding of the first central optical fiber, the coreless optical fiber, and the capillary together.

[0018] S3. Fabrication of the second fiber bundle: (1) Prepare N+1 optical fibers, including one second central optical fiber with the same specifications as the first central optical fiber and N single-mode optical fibers. The single-mode optical fiber is a communication single-mode optical fiber G.652.

[0019] (2) Remove the coating layer from one end of the second central fiber and the single-mode fiber, and insert N+1 fibers into the second capillary with the second central fiber at the axis and N single-mode fibers evenly wrapped around it, so that the uncoated part of the second central fiber and the single-mode fiber is located in the waist region of the capillary, and the coated part is located at both ends of the capillary; similarly, the diameter of the end of the second central fiber after removing the coating layer and the sum of the diameters of the ends of the two single-mode fibers after removing the coating layer are the same as the inner diameter of the waist region of the capillary, so that one second central fiber and N single-mode fibers are closely arranged in the waist region of the capillary, which facilitates synchronous rotation and uniform melting during high-temperature heating later.

[0020] (3) The waist region of the second capillary is heated at high temperature, and the temperature is also selected as 1700℃. During the process, the capillary and N+1 optical fibers rotate synchronously and uniformly, so that the N+1 optical fibers and the capillary are fused together. Then, the second optical fiber bundle is obtained by cutting along the waist region. It should be noted that the fusion of the N+1 optical fibers and the capillary means that the cladding of the second central optical fiber, the cladding of the single-mode optical fiber and the capillary are fused together, while the core of the second central optical fiber and the core of the single-mode optical fiber are still independent and there is no optical coupling between them.

[0021] S4. Fusion splice the first fiber bundle and the second fiber bundle at a temperature of 1700℃, ensuring that the cores of the first central fiber and the second central fiber are aligned. S5. Input light of a predetermined wavelength into the first central fiber, and connect the port of the second central fiber and the port of any one of the surrounding single-mode fibers to a photodetector. Heat the waist region of the second fiber bundle containing N+1 fiber cores at high temperature and stretch it synchronously, so that its overall diameter is reduced. According to the evanescent field theory, when this region is stretched to a certain extent, the optical power in the second central fiber will be coupled to the surrounding N single-mode fibers in equal amounts. When the optical power in the second central fiber approaches 0, under ideal conditions, the optical power in the surrounding N single-mode fibers all reach their maximum value. Therefore, when the output optical power of the second central fiber approaches 0, stop heating to obtain a 1xN single-tapered broadband single-mode fiber coupler.

[0022] In the above methods, the power coupling law can be uniformly expressed as: To obtain the coupling curves.

[0023] in, The curve represents the change in optical power output from the second central fiber as a function of wavelength. This represents the curve representing the change of output optical power of any one of the surrounding N single-mode optical fibers as a function of wavelength, where i = 1, 2, ..., 31, 32; N represents the number of single-mode fibers arranged around the second central fiber. L is the effective length of the optical power coupling region; denoted as the coupling coefficient between the second central fiber and any one of the surrounding N single-mode fibers.

[0024] This embodiment is mainly used to fabricate couplers with N values ​​of 6, 8, 16, and 32, but it can also be applied to couplers with N values ​​of 3 and 4. When N is 3 or 4, coreless optical fibers need to be filled in during the fabrication of the second optical fiber bundle. The coreless optical fibers have the same specifications as the coreless optical fibers in the first optical fiber bundle, so that the number of optical fibers wrapped around the second central optical fiber is at least 6. In this embodiment, 6 fibers are preferred to tightly fill the waist region of the capillary.

[0025] The following explanation uses coupler fabrication methods with N values ​​of 4, 6, and 8 as examples: Example 1 Figure 2-5 The following describes the fabrication method for a coupler with N=8: A 1x8 single-tapered broadband single-mode fiber coupler, characterized by comprising the following steps: S1. Draw two pure quartz capillary tubes with an end inner diameter greater than the waist inner diameter. The waist inner diameter of the two capillary tubes is the same, both being 450μm, and the end inner diameter is 1000μm.

[0026] S2. Preparation of the first optical fiber bundle: (1) Prepare 8+1 optical fibers, such as Figure 2 The diagram shows one cored first central fiber and eight coreless fibers; the first central fiber, except for its diameter, has the same performance as a standard communication fiber.

[0027] (2) Remove the coating from one end of the first central fiber and the coreless fiber. Insert 8+1 fibers into the first capillary tube with the first central fiber at the axis and N coreless fibers evenly surrounding it. The uncoated portions of the first central fiber and the coreless fiber are located in the waist region of the capillary tube, while the coated portions are located in the regions at both ends of the capillary tube. The diameter of the end of the first central fiber after removing the coating is 200μm, and the diameter of the end of the coreless fiber after removing the coating is 125μm. This ensures that the coated portions of the one first central fiber and the eight coreless fibers are closely distributed in the waist region of the capillary tube, facilitating synchronous rotation and uniform melting during subsequent high-temperature heating.

[0028] (3) The waist region of the first capillary is heated at high temperature. During the process, the capillary and 8+1 optical fibers rotate synchronously and uniformly, so that the 8+1 optical fibers and the capillary are fused together. Then, the first optical fiber bundle is obtained by cutting along the waist region.

[0029] S3. Fabrication of the second fiber bundle: (1) Prepare 8+1 optical fibers, such as Figure 3 The diagram shows one second central fiber with the same specifications as the first central fiber and eight single-mode fibers. The single-mode fibers are communication-grade single-mode fiber G.652 with a diameter of 125 μm.

[0030] (2) Remove the coating from one end of the second central fiber and the single-mode fiber. Insert 8+1 fibers into the second capillary with the second central fiber at the axis and N single-mode fibers evenly wrapped around it. The uncoated portions of the second central fiber and the single-mode fibers are located in the waist region of the capillary, while the coated portions are located at both ends of the capillary. Similarly, the diameter of the end of the second central fiber after removing the coating is 200μm, and the diameter of the end of the single-mode fiber after removing the coating is 125μm. This ensures that the coated portions of the one second central fiber and the eight single-mode fibers are closely distributed in the waist region of the capillary, facilitating synchronous rotation and uniform melting during subsequent high-temperature heating.

[0031] (3) The waist region of the second capillary is heated at high temperature. During the process, the capillary and the 8+1 optical fibers rotate synchronously and uniformly, so that the 8+1 optical fibers and the capillary are fused together. Then, the second optical fiber bundle is obtained by cutting along the waist region.

[0032] S4. Fiber fusion of the first fiber bundle and the second fiber bundle, ensuring that the cores of the first central fiber and the second central fiber are aligned.

[0033] S5. Input light with a predetermined wavelength of 1550nm into the first central fiber. Connect the port of the second central fiber and the port of any one of the surrounding single-mode fibers to a photodetector. Heat the waist region of the second fiber bundle at high temperature and stretch it synchronously. At the same time, the first and second fiber bundles rotate synchronously at a uniform speed, reducing their overall diameter. According to the evanescent field theory, when this region is stretched to a certain extent, the optical power in the second central fiber will be coupled to the surrounding 8 single-mode fibers in equal amounts. When the optical power in the second central fiber approaches 0, under ideal conditions, the optical power in the surrounding 8 single-mode fibers all reach their maximum value. Therefore, when the output optical power of the second central fiber approaches 0, stop heating to obtain a 1x8 single-tapered broadband single-mode fiber coupler.

[0034] If the predetermined wavelength of the input light is 1550nm, then according to the power coupling law, the change in optical power received at each output terminal with wavelength is as follows: Figure 4 As shown.

[0035] Insertion loss as a function of wavelength is as follows Figure 5 As shown, IL0 and ILi represent the insertion loss of the second central fiber and any one of the surrounding N single-mode fibers, respectively, which are calculated from the splitting percentage.

[0036] Example 2, as Figure 6-8 The method for fabricating a coupler with N=6 is shown below: A 1x6 single-tapered broadband single-mode fiber coupler, characterized by comprising the following steps: S1. Draw two pure quartz capillary tubes with end inner diameters larger than waist inner diameters. The waist inner diameters of the two capillary tubes are the same, both being 375μm, and the end inner diameters are both 850μm.

[0037] S2. Preparation of the first optical fiber bundle: (1) Prepare 6+1 optical fibers, such as Figure 6 The diagram shows one cored first central fiber and six coreless fibers; the first central fiber is a conventional single-mode communication fiber, G.652 fiber.

[0038] (2) Remove the coating from one end of the first central fiber and the coreless fiber. Insert 6+1 fibers into the first capillary tube with the first central fiber at the axis and the 6 coreless fibers evenly surrounding it. The uncoated portions of the first central fiber and the coreless fibers are located in the waist region of the capillary tube, while the coated portions are located in the regions at both ends of the capillary tube. The diameter of the end of the first central fiber after removing the coating is 125μm, and the diameter of the end of the coreless fiber after removing the coating is 125μm. This ensures that the coated portions of the first central fiber and the 6 coreless fibers are closely distributed in the waist region of the capillary tube, facilitating synchronous rotation and uniform melting during subsequent high-temperature heating.

[0039] (3) The waist region of the first capillary is heated at high temperature. During the process, the capillary and 6+1 optical fibers rotate synchronously and uniformly, so that the 6+1 optical fibers and the capillary are fused together. Then, the first optical fiber bundle is obtained by cutting along the waist region.

[0040] S3. Fabrication of the second fiber bundle: (1) Prepare 6+1 optical fibers, such as Figure 7 The diagram shows one second central fiber with the same specifications as the first central fiber and six single-mode fibers, which are communication-grade single-mode fibers, G.652.

[0041] (2) Remove the coating from one end of the second central fiber and the single-mode fiber. Insert 6+1 fibers into the second capillary with the second central fiber at the axis and N single-mode fibers evenly surrounding it. This ensures that the uncoated portions of the second central fiber and the single-mode fibers are located in the waist region of the capillary, while the coated portions are located at both ends of the capillary. Similarly, the diameter of the second central fiber end after removing the coating is 125μm, and the diameter of the single-mode fiber end after removing the coating is also 125μm. This ensures that the coated portions of the one second central fiber end and the six single-mode fiber ends are closely distributed within the waist region of the capillary, facilitating synchronous rotation and uniform melting during subsequent high-temperature heating.

[0042] (3) The waist region of the second capillary is heated at high temperature. During the process, the capillary and the 6+1 optical fibers rotate synchronously and uniformly, so that the 6+1 optical fibers and the capillary are fused together. Then, the second optical fiber bundle is obtained by cutting along the waist region.

[0043] S4. Fiber fusion of the first fiber bundle and the second fiber bundle, ensuring that the cores of the first central fiber and the second central fiber are aligned.

[0044] S5. Input light of a predetermined wavelength into the first central fiber, connect the port of the second central fiber and the port of any one of the surrounding single-mode fibers to a photodetector, heat the waist region of the second fiber bundle at high temperature and stretch it synchronously, while the first and second fiber bundles rotate synchronously at a uniform speed, causing their overall diameter to decrease. According to the evanescent field theory, when this region is stretched to a certain extent, the optical power in the second central fiber will be coupled to the surrounding 6 single-mode fibers in equal amounts; when the optical power in the second central fiber approaches 0, under ideal conditions, the optical power in the surrounding 6 single-mode fibers all reach their maximum value; therefore, when the output optical power of the second central fiber approaches 0, stop heating, and obtain a 1x6 single-tapered broadband single-mode fiber coupler.

[0045] If the predetermined wavelength of the input light is 1550nm, then according to the power coupling law, the change in optical power received at each output terminal with wavelength is as follows: Figure 8 As shown.

[0046] Example 3, as Figure 9-11 The method for fabricating a coupler with N=4 is shown below: A 1x4 single-tapered broadband single-mode fiber coupler, characterized by comprising the following steps: S1. Draw two pure quartz capillary tubes with end inner diameters larger than waist inner diameters. The waist inner diameters of the two capillary tubes are the same, both being 375μm, and the end inner diameters are both 850μm.

[0047] S2. Preparation of the first optical fiber bundle: (1) Prepare 6+1 optical fibers, such as Figure 9 The diagram shows one cored central fiber and six coreless fibers. The six coreless fibers are of uniform specification, resulting in six coreless fibers wrapped around the central fiber, thus improving the tightness of the arrangement between the central fiber and the six coreless fibers. The central fiber is a standard single-mode communication fiber, G.652, with a diameter of 125 μm.

[0048] (2) Remove the coating from one end of the first central fiber and the coreless fiber. Insert 6+1 fibers into the first capillary tube with the first central fiber at the axis and the 6 coreless fibers evenly surrounding it. The uncoated portions of the first central fiber and the coreless fibers are located in the waist region of the capillary tube, while the coated portions are located in the regions at both ends of the capillary tube. The diameter of the end of the first central fiber after removing the coating is 125μm, and the diameter of the end of the coreless fiber after removing the coating is 125μm. This ensures that the coated portions of the first central fiber and the 6 coreless fibers are closely distributed in the waist region of the capillary tube, facilitating synchronous rotation and uniform melting during subsequent high-temperature heating.

[0049] (3) The waist region of the first capillary is heated at high temperature. During the process, the capillary and 6+1 optical fibers rotate synchronously and uniformly, so that the 6+1 optical fibers and the capillary are fused together. Then, the first optical fiber bundle is obtained by cutting along the waist region.

[0050] S3. Fabrication of the second fiber bundle: (1) Prepare 4+1+2 optical fibers, such as Figure 10 The structure includes one second central fiber with the same specifications as the first central fiber, four single-mode fibers, and two coreless fibers with the same specifications as the coreless fibers in the first fiber bundle. The single-mode fibers are conventional communication single-mode fibers G.652.

[0051] (2) Remove the coatings from one end of the second central fiber, single-mode fiber, and coreless fiber. Insert 4+1+2 fibers into the second capillary tube with the second central fiber at the axis and the 4 single-mode fibers and 2 coreless fibers evenly surrounding it. This ensures that the uncoated portions of the second central fiber, single-mode fiber, and coreless fiber are located in the waist region of the capillary tube, while the coated portions are located at both ends. Similarly, the diameter of the second central fiber end after removing the coating is 125 μm, the diameter of the single-mode fiber end after removing the coating is 125 μm, and the diameter of the coreless fiber end after removing the coating is 125 μm. This ensures that the coated portions of the 1 second central fiber end, the 4 single-mode fiber ends, and the 2 coreless fiber ends are closely distributed within the waist region of the capillary tube, facilitating synchronous rotation and uniform melting during subsequent high-temperature heating.

[0052] (3) The waist region of the second capillary is heated at high temperature. During the process, the capillary and the 4+1+2 optical fibers rotate synchronously and uniformly, so that the 4+1+2 optical fibers and the capillary are fused together. Then, the second optical fiber bundle is obtained by cutting along the waist region.

[0053] S4. Fiber fusion of the first fiber bundle and the second fiber bundle, ensuring that the cores of the first central fiber and the second central fiber are aligned.

[0054] S5. Input light of a predetermined wavelength into the first central fiber, connect the port of the second central fiber and the port of any one of the surrounding single-mode fibers to a photodetector, heat the waist region of the second fiber bundle at high temperature and stretch it synchronously, while the first and second fiber bundles rotate synchronously at a uniform speed, so that their overall diameter is reduced. According to the evanescent field theory, when this region is stretched to a certain extent, the optical power in the second central fiber will be coupled to the four surrounding single-mode fibers in equal amounts; when the optical power in the second central fiber approaches 0, under ideal conditions, the optical power in the four surrounding single-mode fibers all reach their maximum value; therefore, when the output optical power of the second central fiber approaches 0, stop heating, and obtain a 1x4 single-tapered broadband single-mode fiber coupler.

[0055] If the predetermined wavelength of the input light is 1550nm, then according to the power coupling law, the change in optical power received at each output terminal with wavelength is as follows: Figure 11 As shown.

[0056] according to Figure 4 , 5 From points 8 and 11, we can conclude that the splitting ratio of the coupler is dependent on the wavelength. We can also conclude that the fabrication method described in this paper has the characteristics of low insertion loss, good uniformity, and low polarization-dependent loss.

[0057] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for fabricating a 1xN single-tapered broadband single-mode fiber coupler, characterized in that, Includes the following steps: S1. Draw two capillary tubes with an end inner diameter greater than the waist inner diameter, and the waist inner diameters of the two capillary tubes are the same. S2. Preparation of the first optical fiber bundle: (1) Prepare N+1 optical fibers, including one cored first central optical fiber and N coreless optical fibers; (2) Remove the coating layer from one end of the first central fiber and the coreless fiber, and insert N+1 fibers into the first capillary in such a way that the first central fiber is located at the axis and N coreless fibers are evenly wrapped around it, so that the uncoated part of the first central fiber and the coreless fiber is located in the waist region of the capillary and the coated part is located at both ends of the capillary. (3) The waist region of the first capillary is heated at high temperature to fuse N+1 optical fibers with the capillary into one piece, and then the first optical fiber bundle is obtained by cutting along the waist region. S3. Fabrication of the second fiber bundle: (1) Prepare N+1 optical fibers, including one second central optical fiber with the same specifications as the first central optical fiber and N single-mode optical fibers. (2) Remove the coating layer from one end of the second central fiber and the single-mode fiber, and insert N+1 fibers into the second capillary in such a way that the second central fiber is located at the axis and N single-mode fibers are evenly wrapped around it, so that the uncoated part of the second central fiber and the single-mode fiber is located in the waist region of the capillary and the coated part is located at both ends of the capillary. (3) The waist region of the second capillary is heated at high temperature to fuse the N+1 optical fibers with the capillary into one piece, and then the second optical fiber bundle is obtained by cutting along the waist region. S4. Fusion splice the first fiber bundle and the second fiber bundle to ensure that the cores of the first central fiber and the second central fiber are aligned. S5. Input light of a predetermined wavelength into the first central fiber, connect the port of the second central fiber and the port of any one of the surrounding single-mode fibers to the photodetector, heat the waist region of the second fiber at high temperature and stretch it synchronously until the output optical power of the second central fiber approaches 0, stop heating and stretching, and obtain a 1xN single-tapered broadband single-mode fiber coupler.

2. The method for fabricating a 1xN single-tapered broadband single-mode fiber coupler according to claim 1, characterized in that: The sum of the diameters of the first central optical fiber and the two coreless optical fibers is equal to the inner diameter of the waist region of the capillary.

3. The method for fabricating a 1xN single-tapered broadband single-mode fiber coupler according to claim 1, characterized in that: In steps S2 (3) and S3 (3), during high-temperature heating, N+1 optical fibers and capillary tube rotate synchronously at a uniform speed.

4. The method for fabricating a 1xN single-tapered broadband single-mode fiber coupler according to claim 1, characterized in that: The capillary is a pure quartz capillary.

5. The method for fabricating a 1xN single-tapered broadband single-mode fiber coupler according to claim 1, characterized in that: The value of N is 4, 6, 8, 16, or 32.

6. The method for fabricating a 1xN single-tapered broadband single-mode fiber coupler according to claim 5, characterized in that: When N is less than 6, coreless fibers need to be filled during the fabrication of the second fiber bundle so that the total number of single-mode fibers and coreless fibers in the second fiber bundle is ≥ 6.

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