Optical fiber hot melting method and optical waveguide adapter

Abstract

The invention belongs to the technical field of optical communication, and discloses an optical fiber hot melting method and an optical waveguide adapter. According to the invention, the solid-core optical fiber and the hollow-core optical fiber are respectively subjected to oblique angle cutting, so that the solid-core optical fiber has a first oblique cutting angle, the hollow-core optical fiber has a second oblique cutting angle, and the first oblique cutting angle is smaller than the second oblique cutting angle; and then the solid-core optical fiber with the first beveling angle and the hollow-core optical fiber with the second beveling angle are subjected to hot melting. According to the invention, through an unequal-angle optical fiber welding mode, low welding loss and low return loss are realized at the same time, and meanwhile, the method is a non-coating type welding method, the operation process is simpler, outdoor site construction is more convenient, and the requirement on welding equipment can be reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical communication, and more specifically, relates to a thermal fusion method for optical fibers and an optical waveguide adapter. Background Art

[0002] In the practical application of hollow-core anti-resonant optical fiber, it is often necessary to solve the connection problem between single-mode optical fiber and hollow-core anti-resonant optical fiber. Domestic and foreign scholars have done a lot of research and experiments on how to achieve low fusion loss (mainly insertion loss) and low return loss in the connection between single-mode optical fiber and hollow-core optical fiber. The current mainstream solution is to thermally expand the core of single-mode optical fiber or fuse a section of multimode transition fiber through single-mode optical fiber to achieve mode field matching with hollow-core optical fiber, and to reduce return loss by coating a layer of anti-reflection film after angle cutting of the thermally expanded single-mode optical fiber end or the multimode transition fiber end. The connection between the single-mode optical fiber and the hollow-core optical fiber treated as above is coupled and packaged using a micro-machining platform, and the conventional optical fiber thermal fusion method is rarely used to achieve optical fiber connection. The reason is that the traditional thermal fusion process cannot meet the mode field matching accuracy and has high requirements on the heat resistance of the coated layer. It is difficult to achieve low insertion loss and low return loss connection between single-mode optical fiber and hollow-core optical fiber by thermal fusion.

[0003] For example, a conventional optical fiber thermal fusion splicing method is to fuse the single-mode optical fiber to the transition fiber and then cut it at an angle, and then directly perform discharge thermal fusion splicing with the hollow-core optical fiber cut at the same angle. By adjusting the fusion splicing procedure, a non-collapse weak fusion splice between the transition fiber and the hollow-core optical fiber can be achieved. When the optical fiber cutting angle is larger (≤8°), the return loss is lower, but the fusion loss is higher, so it is difficult to obtain low return loss and fusion loss at the same time.

[0004] Similar to the above method, for example, the angled single-mode fiber is directly fused with the hollow-core fiber of the same angle. In this method, the larger the angle of the single-mode fiber is, the lower the return loss is. However, due to the refraction of the core beam at the angled end face of the fiber, the propagation direction of the core beam will have a certain angle with the axial direction of the fiber, see Figure 1 This is also the main reason why the fusion splicing of angled single-mode optical fiber and hollow-core optical fiber at the same angle has a larger fusion loss. This fusion splicing method also makes it difficult to simultaneously obtain low return loss and fusion loss.

[0005] Another conventional optical fiber thermal fusion splicing method is to reversely taper the single-mode optical fiber and then cut it in the middle of the tapered area to obtain a core-expanded single-mode optical fiber. The core-expanded single-mode optical fiber is then coated and directly thermally fused with a 0° hollow-core optical fiber. However, the above-mentioned fusion splicing technology has high requirements on the thermal field uniformity, coating uniformity, and heat resistance of the fusion splicing equipment, and the fusion splicing process is relatively complicated, which is not convenient for outdoor on-site construction.

[0006] Considering that thermal fusion splicing of optical fibers is more convenient, using a fusion splicer to splice optical fibers is more suitable for outdoor operations, and the volume of the heat shrink tube fixed outside the fusion point is smaller than that of the coupler package, making it easier to achieve wiring in a small space. Therefore, using thermal fusion splicing technology to solve the connection problem between single-mode optical fiber and hollow-core optical fiber is a key technology that needs to be solved urgently for the promotion and laying of hollow-core optical fibers. Summary of the invention

[0007] The invention provides an optical fiber thermal fusion method and an optical waveguide adapter to solve the problem that the existing optical fiber thermal fusion method is difficult to achieve low return loss and low fusion loss in connecting a single-mode optical fiber with a hollow-core optical fiber.

[0008] The present invention provides a method for thermally welding optical fibers, comprising the following steps: Performing bevel cutting on the solid core optical fiber and the hollow core optical fiber respectively, so that the solid core optical fiber has a first bevel cutting angle, and the hollow core optical fiber has a second bevel cutting angle, and the first bevel cutting angle is smaller than the second bevel cutting angle; A solid core optical fiber having a first bevel angle and a hollow core optical fiber having a second bevel angle are thermally fused.

[0009] Preferably, the solid core optical fiber is a single-mode optical fiber, and the mode field diameter of the hollow core optical fiber is larger than the mode field diameter of the single-mode optical fiber.

[0010] Preferably, the solid core optical fiber is one of thermally expanded core single-mode optical fiber, reverse tapered single-mode optical fiber, and single-mode optical fiber fusion-splicing transition optical fiber; when the solid core optical fiber is a single-mode optical fiber fusion-splicing transition optical fiber, the end side where the transition optical fiber is located is heat-fused to the hollow core optical fiber.

[0011] Preferably, the transition optical fiber is a gradient refractive index optical fiber.

[0012] Preferably, the heat welding is performed in a two-step welding manner.

[0013] Preferably, the discharge parameters during the initial welding include a first time, a first power and a first fiber overlap, wherein the first time is 1-3s, the first power is 1900-3000bit, and the first fiber overlap is 10-20μm; the discharge parameters during the secondary welding include a second time, a second power and a second fiber overlap, wherein the second time is 3-6s, the second power is 1300-1800bit, and the second fiber overlap is 1-5μm.

[0014] Preferably, the first bevel angle is determined according to the requirement on return loss, and the range of the first bevel angle is 1° to 6°.

[0015] Preferably, after aligning the claddings of the solid core optical fiber and the hollow core optical fiber and before discharge welding, it also includes: performing displacement correction in the oblique direction so that the core light beam propagation direction of the oblique solid core optical fiber coincides with the optical axis direction of the oblique hollow core optical fiber.

[0016] Preferably, with the goal of obtaining the lowest fusion loss, the optimal bevel angle and the optimal displacement correction amount of the hollow core optical fiber are determined; the optimal bevel angle is used as the second bevel angle, and the displacement correction is performed in the bevel direction according to the optimal displacement correction amount.

[0017] On the other hand, the present invention provides an optical waveguide adapter, comprising a solid core optical fiber and a hollow core optical fiber, wherein the solid core optical fiber and the hollow core optical fiber are fused by the above-mentioned optical fiber thermal fusion splicing method.

[0018] One or more technical solutions provided in the present invention have at least the following technical effects or advantages: (1) The present invention performs bevel cutting on the solid core optical fiber and the hollow core optical fiber respectively, so that the solid core optical fiber has a first bevel cutting angle and the hollow core optical fiber has a second bevel cutting angle, and the first bevel cutting angle is smaller than the second bevel cutting angle; then the solid core optical fiber with the first bevel cutting angle and the hollow core optical fiber with the second bevel cutting angle are thermally fused. The solid core optical fiber can be a single-mode optical fiber, or a thermally expanded single-mode optical fiber, a reversely tapered single-mode optical fiber, or a single-mode optical fiber fusion-splicing transition optical fiber. In order to solve the connection problem between single-mode optical fiber and hollow-core optical fiber, the present invention is different from the equal-angle welding scheme adopted in the conventional optical fiber thermal welding method. The bevel angle of the hollow-core optical fiber is greater than the bevel angle of the single-mode optical fiber. When the optical fiber welding occurs between optical fibers at different angles, the optical fibers on both sides will bend to a certain extent near the welding point. However, due to the different bending strengths of the single-mode optical fiber and the hollow-core optical fiber used, after the two unequal-angle optical fibers are welded, only the beveled single-mode optical fiber will bend to a greater extent, forming a non-axially parallel beveled optical fiber welding form. This welding form can make the propagation direction of the core light beam of the beveled single-mode optical fiber parallel to the optical axis direction of the hollow-core optical fiber again, thereby eliminating the additional welding loss caused by the refraction of the core light beam at the end face of the beveled single-mode optical fiber. In addition, due to the hollow structure of the hollow-core optical fiber, the bevel angle of the core position of the beveled single-mode optical fiber will not change significantly due to welding, so the return loss at the welding point can also be guaranteed. Therefore, the present invention can achieve low return loss and low fusion loss when connecting single-mode optical fiber to hollow-core optical fiber. That is, the present invention achieves both low fusion loss and low return loss through unequal-angle optical fiber fusion splicing (i.e. non-axial parallel fusion splicing). At the same time, the present invention is also a non-coating fusion splicing method. Compared with some existing fusion splicing methods that require coating, the operation process of the present invention is simpler, more convenient for outdoor on-site construction, and can also reduce the requirements for fusion splicing equipment.

[0019] (2) The present invention adopts a two-step fusion splicing method for thermal fusion splicing. The first fusion splicing is a short-term high-power discharge with a larger fiber overlap, and the second fusion splicing is a long-term low-power discharge with a smaller fiber overlap. The two-step fusion splicing method is used to fusion the angled hollow-core fiber and the angled single-mode fiber, and the resulting fusion splicing strength is higher and the fusion additional loss is lower.

[0020] (3) The present invention can obtain lower fusion loss by scanning and optimizing the bevel angle of the hollow core optical fiber.

[0021] (4) After aligning the cladding of the solid core fiber and the hollow core fiber and before discharge welding, the present invention can further optimize by performing displacement correction in the oblique direction, so that the core beam propagation direction of the oblique solid core fiber coincides with the optical axis direction of the oblique hollow core fiber, thereby further reducing the welding loss. The present invention combines the scanning optimization of the bevel angle of the hollow core fiber and the displacement correction amount before welding discharge, so as to optimize the welding loss of non-axial parallel welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the propagation direction of the oblique optical fiber beam; Figure 2 A schematic diagram of the effect of unequal-angle optical fiber fusion splicing achieved by a method for thermal fusion splicing of optical fibers provided in Example 1 of the present invention; Figure 3 A flow chart of scanning and optimizing the bevel angle and displacement correction parameter of a hollow core optical fiber in a thermal fusion splicing method of an optical fiber provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0023] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0024] Embodiment 1: Embodiment 1 provides a method for thermally welding optical fibers, comprising the following steps: Step 1: bevel cutting the solid core optical fiber and the hollow core optical fiber respectively, so that the solid core optical fiber has a first bevel angle, and the hollow core optical fiber has a second bevel angle, and the first bevel angle is smaller than the second bevel angle.

[0025] The solid core fiber may be a single-mode fiber, and the mode field diameter of the hollow core fiber is greater than the mode field diameter of the single-mode fiber. The solid core fiber may also be one of a thermally expanded core single-mode fiber, a reverse tapered single-mode fiber, and a single-mode fiber fusion-splicing transition fiber; when the solid core fiber is a single-mode fiber fusion-splicing transition fiber, the end side where the transition fiber is located is heat-spliced ​​with the hollow core fiber, and the transition fiber may be a gradient refractive index fiber. Compared with the solution of directly heat-splicing the single-mode fiber and the hollow core fiber, pre-treating the single-mode fiber (for example, fusing the single-mode fiber to the transition fiber) and then heat-splicing it with the hollow core fiber can achieve lower splicing loss.

[0026] Specifically, the first bevel angle may be determined according to the requirement on return loss, and the range of the first bevel angle is 1° to 6°.

[0027] Step 2: thermally fuse the solid core optical fiber having the first bevel angle and the hollow core optical fiber having the second bevel angle.

[0028] Specifically, the present invention adopts a two-step fusion method for thermal fusion. The first fusion is a short-term high-power discharge with a large fiber overlap, and the second fusion is a long-term low-power discharge with a small fiber overlap. During the two-step fusion, the optical fiber is discharged at the center of the electrode. The two-step fusion method is used to fuse the angled hollow-core optical fiber and the angled single-mode optical fiber, and the obtained fusion strength is higher and the fusion additional loss is lower.

[0029] The discharge parameter setting of the first discharge during fusion splicing can be based on the maximum discharge amount that does not cause additional loss due to the collapse of the internal structure of the hollow-core fiber when the solid-core fiber and the hollow-core fiber are fused at the same bevel angle. That is, the discharge parameters of the first discharge can refer to the discharge parameters of the low-loss fusion splicing of two optical fibers at a right angle.

[0030] During the fusion splicing, the second discharge is performed and the fiber overlap is increased to enhance the angled fiber fusion splicing strength. The discharge parameter setting can increase the additional loss caused by the collapse of the internal structure of the hollow-core fiber very little after the second discharge (for example, the increased additional loss can be set to meet the condition of less than 0.05dB), and the fusion splicing point of the fusion-spliced ​​fiber can be taken out and protected by an external heat shrink tube as standard.

[0031] For example, the fusion splicer can be a Fujikura fusion splicer. The discharge parameters during the initial fusion splicing include the first time, the first power and the first fiber overlap. The first time is 1-3s, the first power is 1900-3000bit, and the first fiber overlap is 10-20μm. The discharge parameters during the secondary fusion splicing include the second time, the second power and the second fiber overlap. The second time is 3-6s, the second power is 1300-1800bit, and the second fiber overlap is 1-5μm.

[0032] In addition, after aligning the cladding of the solid core fiber and the hollow core fiber and before the discharge welding, the method may further include: performing displacement correction in the oblique direction so that the core beam propagation direction of the oblique solid core fiber coincides with the optical axis direction of the oblique hollow core fiber. That is, the motor may be controlled to preset an axial offset correction value before the initial welding discharge. This operation may make the core beam propagation direction of the oblique solid core fiber coincide with the optical axis direction of the oblique hollow core fiber, thereby further reducing the welding loss.

[0033] Specifically, with the goal of obtaining the lowest splicing loss, the optimal bevel angle and the optimal displacement correction amount of the hollow-core optical fiber are determined; the optimal bevel angle is used as the second bevel angle, and displacement correction is performed in the bevel direction according to the optimal displacement correction amount. The present invention combines the scanning optimization of the bevel angle of the hollow-core optical fiber and the displacement correction amount before the splicing discharge, so that the splicing loss of non-axial parallel splicing can be optimized.

[0034] The present invention is further described below by taking the angled fusion splicing of a single-mode optical fiber with a cladding diameter of 125 μm and a hollow-core optical fiber with a cladding diameter of 230-250 μm as an example.

[0035] First, a cutting knife with a rotation angle function is used to cut the hollow core fiber and the single-mode fiber at an angle, and the angle of the hollow core fiber is greater than that of the single-mode fiber. Then, the two angled fibers are welded using the above-mentioned welding method.

[0036] When fiber fusion splicing occurs between fibers at different angles, the fibers on both sides will bend to a certain extent near the fusion point. However, due to the different bending strengths of the single-mode fiber and the hollow-core fiber used, after the two unequal-angle fibers are fused, only the angled single-mode fiber will bend to a greater extent, i.e., a non-axially parallel angled fiber fusion form. Figure 2 This type of fusion splicing can make the core beam propagation direction of the angled single-mode fiber parallel to the optical axis direction of the hollow-core fiber, thereby eliminating the additional fusion loss caused by the refraction of the core beam at the end face of the angled single-mode fiber. In addition, due to the hollow structure of the hollow-core fiber, the bevel angle of the core position of the angled single-mode fiber will not change significantly due to fusion splicing, so the return loss at the fusion point can also be guaranteed.

[0037] When the unequal angled hollow-core fiber is fused with the angled single-mode fiber, although the angled single-mode fiber beam will be parallel to the axial direction, there will be a certain axial misalignment, that is, the propagation direction of the beam after fusion does not coincide with the axial direction of the hollow-core fiber, such as Figure 2Therefore, after the claddings of the two angled optical fibers are aligned and before the electrodes are discharged, the X or Y motor can be controlled to add a small displacement correction in the angled direction to ensure that the angled single-mode optical fiber beam coincides with the axial direction of the angled hollow-core optical fiber, thereby achieving the lowest fusion loss with the angled hollow-core optical fiber.

[0038] The flow chart for determining the minimum splicing loss between angled hollow core fiber and angled single mode fiber is as follows: Figure 3 As shown, the bevel angle of the single-mode fiber is usually determined according to the application needs. Taking the bevel angle of the single-mode fiber as an example, the bevel angle of the hollow-core fiber is initially set to 5 degrees (i.e. Figure 3 In the example, let A=5), and set the initial value of the welding loss c to a larger value (to ensure the normal operation of the scanning optimization process), for example, let c=10, and gradually change the value of the displacement correction amount B, for example, increase it by 1μm each time (i.e. Figure 3 B=B+1), compare splice loss (including comparison Figure 3 The optimal displacement correction and the minimum splicing loss under the bevel angle condition can be obtained by calculating the splicing loss a and splicing loss b in the figure. Then, the bevel angle of the hollow core fiber is gradually increased, for example, by 0.5 degrees each time (i.e. Figure 3 The displacement correction is optimized again to obtain another set of minimum splicing losses and compare them with the previous set of splicing losses. If the splicing losses are lower than the previous set of splicing losses, the bevel angle of the hollow-core fiber is increased continuously and the procedure is repeated until the minimum splicing loss is obtained.

[0039] After the first discharge welding, a second welding operation is added. The discharge is in the form of long-term low-power discharge, and the stepping of the Z-axis motor is set to further increase the fiber overlap and strengthen the fiber welding point.

[0040] The thermal fusion splicing method for optical fibers provided in Example 1 can achieve lower fusion loss while ensuring low return loss at the fusion point.

[0041] Embodiment 2: Embodiment 2 provides an optical waveguide adapter, comprising a solid core optical fiber and a hollow core optical fiber, wherein the solid core optical fiber and the hollow core optical fiber are fused by the thermal fusion splicing method for optical fibers as described in Embodiment 1.

[0042] For example: (1) Thermally fuse the single-mode optical fiber and the hollow-core optical fiber; (2) Thermally fuse the thermally expanded core single-mode optical fiber and the hollow core optical fiber; (3) Thermally fuse the reverse tapered single-mode optical fiber to the hollow-core optical fiber; (4) After the single-mode optical fiber is fused to the transition optical fiber, the end where the transition optical fiber is located is then heat-fused to the hollow-core optical fiber.

[0043] Since the solid core optical fiber and the hollow core optical fiber in the optical waveguide adapter provided in Example 2 are fused by the thermal fusion splicing method for optical fibers as described in Example 1, Example 2 can be understood by referring to the description of Example 1, which will not be repeated here.

[0044] In summary, the present invention provides a thermal fusion splicing technology of non-axially parallel hollow-core optical fiber and solid-core optical fiber, which can simultaneously obtain lower return loss and fusion loss. At the same time, the present invention is also a non-coated angled hollow-core optical fiber and angled solid-core optical fiber fusion splicing technology, which not only simplifies the fusion splicing process, but also can obtain lower return loss.

[0045] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for thermally welding optical fibers, characterized in that: The following steps are involved: Performing bevel cutting on the solid core optical fiber and the hollow core optical fiber respectively, so that the solid core optical fiber has a first bevel cutting angle, and the hollow core optical fiber has a second bevel cutting angle, and the first bevel cutting angle is smaller than the second bevel cutting angle; A solid core optical fiber having a first bevel angle and a hollow core optical fiber having a second bevel angle are thermally fused.

2. The optical fiber thermal fusion splicing method according to claim 1, characterized in that: The solid core optical fiber is a single mode optical fiber, and the mode field diameter of the hollow core optical fiber is greater than the mode field diameter of the single mode optical fiber.

3. The optical fiber thermal fusion splicing method according to claim 1, characterized in that: The solid core optical fiber is one of a thermally expanded core single-mode optical fiber, a reverse tapered single-mode optical fiber, and a single-mode optical fiber fusion-splicing transition optical fiber; when the solid core optical fiber is a single-mode optical fiber fusion-splicing transition optical fiber, the end side where the transition optical fiber is located is heat-fused to the hollow core optical fiber.

4. The optical fiber thermal fusion splicing method according to claim 3, characterized in that: The transition optical fiber is a graded refractive index optical fiber.

5. The optical fiber thermal fusion splicing method according to claim 1, characterized in that: The heat welding is carried out by a two-step welding method.

6. The optical fiber thermal fusion splicing method according to claim 5, characterized in that: The discharge parameters during the initial fusion splicing include the first time, the first power and the first fiber overlap, the first time is 1-3s, the first power is 1900-3000bit, and the first fiber overlap is 10-20μm; the discharge parameters during the secondary fusion splicing include the second time, the second power and the second fiber overlap, the second time is 3-6s, the second power is 1300-1800bit, and the second fiber overlap is 1-5μm.

7. The optical fiber thermal fusion splicing method according to claim 1, characterized in that: The first bevel angle is determined according to the requirement on return loss, and the range of the first bevel angle is 1° to 6°.

8. The optical fiber thermal fusion splicing method according to claim 1, characterized in that: After aligning the claddings of the solid core optical fiber and the hollow core optical fiber and before discharge welding, the method further includes: performing displacement correction in the oblique direction to make the core beam propagation direction of the oblique solid core optical fiber coincide with the optical axis direction of the oblique hollow core optical fiber.

9. The optical fiber thermal fusion splicing method according to claim 8, characterized in that: With the goal of obtaining the lowest fusion loss, the optimal bevel angle and the optimal displacement correction amount of the hollow core optical fiber are determined; the optimal bevel angle is used as the second bevel angle, and displacement correction is performed in the bevel direction according to the optimal displacement correction amount.

10. An optical waveguide adapter, comprising a solid core optical fiber and a hollow core optical fiber, characterized in that: The solid core optical fiber and the hollow core optical fiber are fused by using the thermal fusion splicing method for optical fibers according to any one of claims 1 to 9.

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