Method for manufacturing hollow-core optical fiber preform, hollow-core optical fiber preform, and anti-resonance hollow-core optical fiber

Abstract

The invention provides a manufacturing method of a hollow-core optical fiber prefabricated member, the hollow-core optical fiber prefabricated member and an anti-resonance hollow-core optical fiber, and relates to the technical field of hollow-core optical fiber preparation, and the manufacturing method comprises the steps: S1, processing the inner wall of an outer sleeve along the axial direction to form at least one non-continuous smooth region; s2, a capillary tube is tightly attached to the discontinuous smooth area, and an assembly is formed; s3, the assembly is heated, so that the capillary tube and the outer sleeve are selectively welded and fixed on the contact surface between the capillary tube and the outer sleeve; and S4, cooling and curing the outer sleeve after heating is completed, so as to prepare the hollow-core optical fiber prefabricated member. The method has the advantages that the axial discontinuous smooth area is machined on the inner wall of the outer sleeve, the capillary tube is tightly attached to the discontinuous smooth area to form a contact face, heat radiation is generated by means of the photo-thermal absorption difference between the discontinuous smooth area and the adjacent smooth area, selective welding is achieved, and the service life of the capillary tube is prolonged. And the problem of capillary position deviation in the traditional method is successfully solved.

Description

Technical Field

[0001] This invention relates to the field of hollow optical fiber fabrication technology, and in particular to a method for manufacturing a hollow optical fiber preform, the hollow optical fiber preform, and an anti-resonant hollow optical fiber. Background Technology

[0002] Hollow-core fiber (HCF) has been a research hotspot due to its unique advantages in transmitting light within an air or vacuum core, such as low nonlinearity, low delay, low dispersion, and ultra-low loss. In recent years, with advancements in fabrication processes, HCF has gradually moved from the laboratory to engineering applications. Compared to traditional optical fibers, HCF uses air or a vacuum instead of glass as the transmission medium, significantly increasing the difficulty of light confinement and guidance, typically requiring microstructured cladding tubes to restrict light transmission.

[0003] In the technological evolution of hollow-core optical fibers, novel anti-resonant hollow-core fibers (HC ARF) have attracted attention due to their simpler cladding structures (such as single-ring nodeless negative curvature and nodeless nested tubes) and excellent optical performance. Their loss was reduced to 0.28 dB / km in 2020, and their light-guiding band covers the ultraviolet to mid-infrared range. However, HC ARF has extremely high requirements for the shape and thickness of the cladding quartz wall, making its fabrication quite challenging.

[0004] Taking nodeless fiber in HC ARF as an example, it consists of an outer sheath and a hollow cladding, with the cladding tubes evenly spaced on the inner wall of the sheath and not in contact with each other. Nested-tube hollow anti-resonant fiber, as an important branch of nodeless fiber, achieves high performance by nesting capillaries and fixing them to the inner wall of the sheath. The key advantage of this type of fiber lies in the precise geometry between the nested tubes. However, traditional methods for preparing hollow fiber preforms have many problems, such as the capillaries being prone to shifting during stretching, the oxyhydrogen flame heating method being laterally asymmetrical and unsuitable for thick-walled glass tubes, and the cumbersome and complex preparation process, making large-scale production difficult. In recent years, although there have been improved methods, such as additive fusion and laser processing, these methods cannot achieve continuous capillary fixation in practice. During the stretching process, a suspended diameter contraction often appears at the lower end of the capillary, making it extremely prone to shifting and severely affecting the structural uniformity and optical performance of the fiber preform. Furthermore, due to limitations in wall thickness and size, it is difficult to apply to large-sized thick-walled outer sheaths, hindering the widespread promotion and application of hollow fiber preparation technology. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a method for manufacturing hollow optical fiber preforms, comprising:

[0006] Step S1: At least one discontinuous smooth area is formed along the axial direction on the inner wall of the outer sleeve;

[0007] Step S2: Fit the capillary tube tightly into the discontinuous smooth area to form an assembly;

[0008] Step S3: Heat the assembly to selectively weld and fix the capillary tube and the outer tube at their contact surfaces.

[0009] Step S4: After heating is completed, the outer jacket is cooled and solidified to prepare a hollow optical fiber preform.

[0010] Preferably, the discontinuous smooth region is any one or more of a V-shaped groove, a U-shaped groove, a rectangular groove, and a rough surface.

[0011] Preferably, the number of discontinuous smooth regions corresponds to the number of capillaries, and each discontinuous smooth region has a depth of 10-100 μm, a width of 20-200 μm, and a length the same as that of the outer sheath.

[0012] Preferably, the processing method for the discontinuous smooth region includes any one of laser processing, mechanical processing, or chemical etching.

[0013] Preferably, in step S3, the temperature at which the assembly is heated is within 50°C below the glass transition temperature of the outer tube.

[0014] Preferably, the wall thickness of the outer sleeve is 0.5-10 mm.

[0015] Preferably, the capillary has a diameter of 0.5-5 mm and a wall thickness of 50-500 μm.

[0016] Preferably, in step S2, the capillary is fixed by a fixing mold that matches the spatial arrangement of the capillary, so that the capillary fits tightly against the discontinuous smooth area.

[0017] In step S3, the assembly is fed into a heating furnace for heating, and the fixed mold is removed simultaneously during the process of feeding the assembly into the heating furnace, and the feeding speed of the assembly is consistent with the removal speed of the fixed mold.

[0018] The present invention also provides a hollow optical fiber preform, which is prepared by the above-described manufacturing method.

[0019] The present invention also provides an anti-resonant hollow optical fiber, which is formed by drawing the above-mentioned hollow optical fiber preform.

[0020] The above technical solution has the following advantages or beneficial effects:

[0021] 1) By processing an axially discontinuous smooth area on the inner wall of the outer sleeve, the capillary is tightly attached to the discontinuous smooth area to form a contact surface. Then, by taking advantage of the difference in photothermal absorption between the discontinuous smooth area and the adjacent smooth area, thermal radiation is generated to achieve selective welding, which successfully solves the problem of capillary position displacement in the traditional method.

[0022] 2) By tightly attaching the capillary to the discontinuous smooth region, the contact surface of the capillary can be partially embedded in the discontinuous smooth region, so that the capillary can remain more stable during the stretching process, which significantly improves the structural uniformity of the optical fiber preform and lays a solid foundation for the preparation of high-quality hollow optical fibers.

[0023] 3) Selective fusion splicing is achieved by utilizing the difference in photothermal absorption, which eliminates the need for complex optical contact, greatly reduces the difficulty of preparation, simplifies the preparation process, and makes it more suitable for automated production. This is expected to promote the large-scale production and widespread application of hollow optical fibers.

[0024] 4) This method is applicable not only to thick-walled glass tubes but also to thin-walled glass tubes, and has wide applicability, which can meet the requirements of hollow fiber wall thickness in different application scenarios. Attached Figure Description

[0025] Figure 1 A schematic flowchart of a method for manufacturing a hollow optical fiber preform is shown in a preferred embodiment of the present invention.

[0026] Figure 2 This is a schematic diagram of the structure in Example 1, where a discontinuous smooth region is formed by machining a V-shaped local surface defect;

[0027] Figure 3 This is a schematic diagram of the structure in Example 2, which uses laser processing to create a discontinuous smooth region by processing a U-shaped local surface defect;

[0028] Figure 4 This is a schematic diagram of the structure in Example 3, which uses mechanical machining to form a discontinuous smooth region. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The present invention is not limited to this embodiment; other embodiments that conform to the spirit of the present invention may also fall within the scope of the present invention.

[0030] In a preferred embodiment of the present invention, based on the above-mentioned problems existing in the prior art, a method for manufacturing hollow optical fiber preforms is provided, such as... Figure 1 As shown, it includes:

[0031] Step S1: At least one discontinuous smooth area is formed along the axial direction on the inner wall of the outer sleeve;

[0032] Step S2: The capillary tube is tightly fitted to the discontinuous smooth area to form an assembly;

[0033] Step S3: Heat the assembly to selectively weld and fix the capillary tube and the outer tube at the contact surface between them.

[0034] Step S4: After heating is completed, the outer jacket is cooled and solidified to prepare the hollow fiber preform.

[0035] Specifically, in this embodiment, a discontinuous smooth region is formed along the axial direction on the inner wall of the outer jacket, so that the inner wall of the outer jacket is not entirely smooth, but has local surface defects. When the capillary is tightly bonded to the discontinuous smooth region, the presence of local surface defects can physically limit the capillary. Specifically, the contact surface of the capillary can be partially embedded in the discontinuous smooth region, forming a kind of interlocking relationship, which effectively limits the displacement space of the capillary under axial tension or radial force. Compared with the traditional unconstrained bonding or the method of temporary fixation by hydrogen-oxygen flame, the physical limiting effect of the discontinuous smooth region is more stable and precise, which can ensure that the capillary maintains the preset geometric position throughout the preform drawing process, avoid the misalignment of the cladding structure caused by offset, and thus ensure the structural uniformity and optical transmission performance of the final optical fiber.

[0036] Furthermore, surface defects in discontinuous smooth regions increase the absorption efficiency of lasers or other heat sources of specific wavelengths, while adjacent smooth regions, due to their high surface flatness, have higher light reflectivity and less heat absorption. Therefore, selective welding can be achieved by utilizing the difference in photothermal absorption between discontinuous smooth regions and adjacent smooth regions to generate thermal radiation, eliminating the need for complex optical contact, greatly reducing the difficulty of fabrication, and simplifying the fabrication process. Specifically, after the capillary is tightly bonded to the discontinuous smooth region to form an assembly, when a heat source is applied to the assembly, the discontinuous smooth region preferentially absorbs heat and reaches the softening temperature of quartz glass, while the smooth region remains at a relatively low temperature. The softened discontinuous smooth region fuses with the outer wall of the embedded capillary, forming a stable weld node. At the same time, because the smooth region is not overheated, the overall deformation of the outer tube or accidental adhesion between the capillary and non-target areas can be avoided. Compared with traditional oxyhydrogen flame heating (which has uneven lateral temperature and is prone to deformation) or additive fusion technology (which requires precise control of the fusion path and relies on complex equipment), this selective welding process has significant advantages:

[0037] On the one hand, there is no need to manually adjust the position of the heat source or calibrate the optical contact state, reducing the dependence on operational precision; on the other hand, the welding process only acts on the non-continuous smooth area, with a small heat-affected zone, which can effectively protect the overall structural integrity of the capillary and outer tube, reduce the scrap rate caused by improper heating, and at the same time greatly simplify the assembly and fixing process and shorten the preparation cycle.

[0038] This invention also solves the problem that existing oxyhydrogen flame heating is only suitable for thin-walled tubes, while some laser fusion techniques are difficult to adapt to the fusion requirements of thick-walled tubes due to insufficient heat penetration depth, thus failing to meet the fabrication requirements of large-core, thick-walled HC ARF (such as optical fibers used for high-power laser transmission). It can achieve bidirectional compatibility with both thick-walled and thin-walled glass tubes.

[0039] For thin-walled outer tubes, shallow defects in discontinuous smooth areas can effectively limit and weld the capillary, and the low heat-affected zone of selective welding can prevent the thin-walled tube from collapsing due to overheating.

[0040] For thick-walled outer tubes, the depth of defects in discontinuous smooth areas (such as deepening micro-grooves) can be adjusted to ensure that the outer wall of the capillary can be fully embedded and form a stable engagement with the inner wall of the thick-walled tube. At the same time, by utilizing the difference in photothermal absorption, the heat source energy can be concentrated on the defect area of ​​the inner wall, so that even if the outer wall temperature of the thick-walled tube is low, the inner wall and the capillary can still be effectively welded.

[0041] This wide applicability breaks through the wall thickness limitations of existing technologies, and can meet the wall thickness requirements of hollow optical fibers in different application scenarios. It is suitable for both thin-walled hollow optical fibers commonly used in the communication field and thick-walled hollow optical fibers required for high-power transmission, sensing and other scenarios, which significantly improves the application scenario coverage of the technology and provides a process foundation for the multi-field promotion of hollow optical fibers.

[0042] In a preferred embodiment of the present invention, the discontinuous smooth region is any one or more of a V-shaped groove, a U-shaped groove, a rectangular groove, and a rough surface.

[0043] In a preferred embodiment of the present invention, the number of discontinuous smooth regions corresponds to the number of capillaries, and each discontinuous smooth region has a depth of 10-100 μm, a width of 20-200 μm, and a length the same as that of the outer sheath.

[0044] Specifically, in this embodiment, taking a non-continuous smooth area as a V-shaped groove as an example, it can be a whole groove extending along the length direction of the outer sleeve, or it can be multiple grooves arranged in a straight line along the length direction of the outer sleeve. There is no limitation here.

[0045] In a preferred embodiment of the present invention, the processing method for the discontinuous smooth region includes any one of laser processing, mechanical processing or chemical etching.

[0046] Specifically, in this embodiment, when laser processing is used, a CO2 laser or an ultrafast laser is preferably used to form a discontinuous smooth area. When machining is used, a lathe tool is preferably used to form a groove-shaped discontinuous smooth area, or a grinding tool is used to form a rough surface.

[0047] In a preferred embodiment of the present invention, in step S3, the temperature at which the assembly is heated is within 50°C below the glass transition temperature of the outer tube.

[0048] In a preferred embodiment of the present invention, the wall thickness of the outer sleeve is 0.5-10 mm.

[0049] In a preferred embodiment of the present invention, the diameter of the capillary is 0.5-5 mm and the wall thickness is 50-500 μm.

[0050] In a preferred embodiment of the present invention, in step S2, a fixing mold matching the spatial arrangement of the capillary is used to fix the capillary so that the capillary fits tightly against the discontinuous smooth area.

[0051] In step S3, the assembly is fed into a heating furnace for heating, and the fixed mold is removed simultaneously during the process of feeding the assembly into the heating furnace, and the feeding speed of the assembly is consistent with the removal speed of the fixed mold.

[0052] Specifically, in this embodiment, one end of the assembly is fed into the heating furnace, and the other end is removed from the fixed mold. The feeding speed of the assembly is consistent with the removal speed of the fixed mold, so that the capillary and the defect surface are kept in stable contact during the heating process, and displacement or uneven welding caused by inconsistent speed is prevented.

[0053] The present invention also provides a hollow optical fiber preform, which is prepared by the above-described manufacturing method.

[0054] The present invention also provides an anti-resonant hollow optical fiber, which is formed by drawing the above-mentioned hollow optical fiber preform.

[0055] Example 1

[0056] In this embodiment, V-shaped local surface defects are machined to form discontinuous smooth regions. The specific implementation steps are as follows:

[0057] 1. A V-shaped local defect surface is machined on the inner wall of the outer sleeve, such as... Figure 2 As shown.

[0058] In the figure: 1. V-shaped local defect surface (non-smooth continuous area); 2. Capillary; 3. Outer tube; 4. Core area; 5. Hollow capillary area.

[0059] Quartz glass with an outer diameter of 20 mm and a wall thickness of 1.5 mm was selected as the outer tube 3, and a diamond turning tool was used for precision machining to form a V-shaped local defect surface. During machining, the tool inclination angle was 60° and the feed speed was 0.1 mm / s.

[0060] Preferably, 12 sets of equally spaced V-shaped local surface defects are machined on the inner wall of the outer sleeve, with a groove depth of 50±2μm and a groove width of 100±5μm.

[0061] Preferably, the groove depth is monitored in real time by a laser displacement sensor during the processing, with the accuracy controlled within ±1μm.

[0062] 2. Fit the capillary tube 2 tightly onto the V-shaped local defect surface 1, and use a fixing mold that matches the spatial arrangement of the capillary tube to make the capillary tube 2 and the inner wall of the outer tube 3 in close contact.

[0063] Preferably, a quartz capillary tube 2 with an outer diameter of 1.2 mm and a wall thickness of 150 μm is selected, and its size matches the V-groove to ensure stable embedding.

[0064] 3. Feed the assembly into the vertical heating furnace at a speed of 5 mm / min.

[0065] The heating furnace has a temperature of 1150℃±5℃. Through the thermal radiation effect, the temperature of the local defect location is brought to near the softening point of the quartz, so that the capillary light can be accurately fixed on the outer tube.

[0066] After 30 minutes of thermal radiation, a fusion interface with a width of approximately 20 μm is formed in the weld zone.

[0067] After 30 minutes of thermal radiation, a fusion interface with a width of about 20 μm is formed in the fusion splice area. The temperature is then gradually reduced to 800℃ at a gradient of 10℃ / min for annealing. The optical fiber preform is then removed from the heating furnace and allowed to cool naturally to room temperature for curing.

[0068] Example 2

[0069] In this embodiment, laser processing is used to create discontinuous smooth regions by processing U-shaped local surface defects. The specific implementation steps are as follows:

[0070] 1. Use a laser to process a U-shaped localized defect surface on the inner wall of the outer sleeve, such as... Figure 3 As shown.

[0071] In the figure: 1. U-shaped local defect surface (non-smooth continuous area); 2. Capillary; 3. Outer tube; 4. Core area; 5. Hollow capillary area.

[0072] Preferably, a pulsed CO2 laser (wavelength 10.6 μm) is used, the beam is shaped into a focused spot with a diameter of 30 μm, and the pulse energy is set to 50 mJ and the frequency to 1 kHz.

[0073] Preferably, a U-shaped local surface defect is machined on the inner wall of the outer sleeve using a scanning system. The groove depth is 80±3μm and the radius of the bottom arc is 40μm. Helium gas is introduced during processing to protect against the expansion of the heat-affected zone.

[0074] 2. Fit the capillary tube 2 tightly onto the U-shaped local defect surface 1, and use a fixing mold that matches the spatial arrangement of the capillary tube 2 to make the capillary tube 2 and the inner wall of the outer sleeve 3 in close contact.

[0075] Preferably, a quartz capillary tube 2 with an outer diameter of 1.2 mm and a wall thickness of 150 μm is selected.

[0076] 3. Feed the assembly into the vertical heating furnace at a speed of 5 mm / min.

[0077] The temperature of the heating furnace is 1150℃±5℃. Through the thermal radiation effect, the temperature of the local defect location is brought to near the softening point of the quartz, so that the capillary light is accurately fixed on the outer tube.

[0078] After 30 minutes of thermal radiation, a fusion interface with a width of about 20 μm is formed in the fusion splice area. The temperature is then reduced to 800℃ at a gradient of 10℃ / min for annealing. The optical fiber preform is then removed from the heating furnace and allowed to cool naturally to room temperature for curing.

[0079] Example 3

[0080] In this embodiment, a non-discontinuous smooth region is formed by machining a rough surface. The specific implementation steps are as follows:

[0081] 1. Use abrasive tools or chemical etching methods to create a rough surface on the inner wall of the outer sleeve, such as... Figure 4 As shown.

[0082] In the figure: 1. Rough surface (non-smooth continuous area); 2. Capillary; 3. Outer tube; 4. Core area; 5. Hollow capillary core area.

[0083] 2. Embed the capillary tube 2 into the rough surface 1, and use a fixing mold that matches the spatial arrangement of the capillary tube 2 to make the capillary tube 2 and the inner wall of the outer tube 3 in close contact.

[0084] 3. Place the outer tube 3 and capillary tube 2 together into the heating furnace and feed them at a speed of 5 mm / min.

[0085] Specifically, the heating furnace temperature is set below the glass transition temperature (the appropriate temperature is selected based on the different glass tube materials), which is about 50°C lower, so that only local surface defect areas reach or exceed the glass transition temperature due to the thermal radiation effect.

[0086] During the heating process, the temperature of the local surface defect area is monitored to ensure that the capillary tube and the outer tube are fused together.

[0087] 4. After the fusion splicing is completed, remove the optical fiber preform from the heating furnace and allow it to cool naturally to room temperature for curing.

[0088] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made using the content of this specification and illustrations should be included within the protection scope of the present invention.

Claims

1. A method for manufacturing a hollow optical fiber preform, characterized in that, include: Step S1: At least one discontinuous smooth area is formed along the axial direction on the inner wall of the outer sleeve; Step S2: Fit the capillary tube tightly into the discontinuous smooth area to form an assembly; Step S3: Heat the assembly to selectively weld and fix the capillary tube and the outer tube at their contact surfaces. Step S4: After heating is completed, the outer jacket is cooled and solidified to prepare a hollow optical fiber preform.

2. The manufacturing method according to claim 1, characterized in that, The discontinuous smooth region is any one or more of the following: V-shaped groove, U-shaped groove, rectangular groove, and rough surface.

3. The manufacturing method according to claim 1, characterized in that, The number of discontinuous smooth regions corresponds to the number of capillaries, and each discontinuous smooth region has a depth of 10-100 μm, a width of 20-200 μm, and a length the same as that of the outer sheath.

4. The manufacturing method according to claim 1, characterized in that, The processing method for the discontinuous smooth region includes any one of laser processing, mechanical processing, or chemical etching.

5. The manufacturing method according to claim 2, characterized in that, In step S3, the temperature at which the assembly is heated is within 50°C below the glass transition temperature of the outer tube.

6. The manufacturing method according to claim 1, characterized in that, The wall thickness of the outer tube is 0.5-10mm.

7. The manufacturing method according to claim 1, characterized in that, The capillary has a diameter of 0.5-5 mm and a wall thickness of 50-500 μm.

8. The manufacturing method according to claim 1, characterized in that, In step S2, the capillary is fixed by a fixing mold that matches the spatial arrangement of the capillary, so that the capillary fits tightly against the discontinuous smooth area. In step S3, the assembly is fed into a heating furnace for heating, and the fixed mold is removed simultaneously during the process of feeding the assembly into the heating furnace, and the feeding speed of the assembly is consistent with the removal speed of the fixed mold.

9. A hollow optical fiber preform, characterized in that, It is prepared by the manufacturing method described in any one of claims 1-8.

10. An anti-resonant hollow-core optical fiber, characterized in that, It is formed by drawing the hollow optical fiber preform according to claim 9.

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