A method for preparing an air-core optical fiber based on partial pressure control and an air-core optical fiber

Abstract

This invention provides a method for fabricating hollow optical fibers based on pressure-dividend control, and the hollow optical fiber itself, relating to the field of optical fiber fabrication technology. The method includes: assembling capillary stacks to form a preform; dividing the capillary into at least two independent pressure-dividend control regions; applying different control pressures to each region during the fiber drawing process; and inducing geometric deformation of the capillary using the pressure difference to finally draw the fiber. The beneficial effects are: by tolerating contact nodes, the requirements for raw material precision and assembly fixtures are reduced, simplifying the process and improving yield; the introduction of multi-region pressure division overcomes the limitations of single pressure, achieving fine compensation of the microstructure and solving the problem of uneven stacking; and the realization of an active structure formation mechanism, using pressure difference as the core variable to dynamically shape the structure, greatly enhancing the flexibility of control and making it possible to fabricate various high-performance hollow optical fibers using the same preform.

Description

Technical Field

[0001] This invention relates to the field of optical fiber fabrication technology, and in particular to a method for fabricating hollow optical fibers based on voltage divider control and the hollow optical fibers themselves. Background Technology

[0002] Hollow-core optical fiber, with its air core, possesses unique advantages such as low nonlinearity, low latency, and a high damage threshold, demonstrating great potential in fields such as high-speed communication and high-power laser transmission. In recent years, with companies like Microsoft announcing large-scale deployments of hollow-core optical fiber, this technology has once again become a focus of the industry.

[0003] However, existing hollow fiber fabrication technologies, especially those pursuing low-loss double-nested nodeless hollow antiresonant fiber technology, still face severe challenges in structural design, pressure control, and process adaptability. The structural design relies on the requirement of no nodes: Existing technologies generally believe that contact nodes formed by capillary stacking will lead to local concentration of light field and a surge in scattering loss. Therefore, a node-free structure is taken as a core prerequisite. This requires high-precision capillary screening, complex stack positioning fixtures, and strict control of drawing parameters to avoid node formation, resulting in an exceptionally complex manufacturing process, low fault tolerance, high equipment cost, and difficulty in improving product yield.

[0004] The pressure control method is simplistic: existing pressure control methods in fiber drawing processes mostly employ uniform pressure or simple gradient pressure schemes, which cannot perform differentiated and precise control on capillary units at the same level and coaxially symmetrical positions in the stack. Therefore, it cannot effectively compensate for structural deviations generated during stack assembly or fiber drawing, and the uniformity of the fiber structure is entirely dependent on the initial uniformity of the preform stack.

[0005] Rigid Structure Formation Mechanism: In existing technologies, the formation of low-loss fiber structures mainly relies on the pre-precision design of capillary geometric parameters (inner diameter, wall thickness, and arrangement), and is formed in one step through stacking and pulling. Pressure in this process is only used as an auxiliary means to counteract surface tension or fine-tune dimensions, rather than an active control tool to shape the core structural morphology. This results in a lack of flexibility in performance optimization and makes it difficult to prepare multiple performance structures from the same preform.

[0006] In summary, there is an urgent need for a new technology for preparing hollow optical fibers that can overcome the limitations of no nodes, achieve precise pressure control, and make the structure formation mechanism more flexible. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a method for fabricating hollow optical fibers based on voltage divider control, comprising: Step S1: Perform stacking and assembling of at least one layer of capillaries to form an optical fiber preform; Step S2: Divide the capillary in the optical fiber preform into at least two independent voltage-dividing control regions. Step S3: During the wire drawing process, different control pressures are applied to at least two independent pressure control regions respectively; Step S4: The pressure difference between each pressure control region is used to induce geometric deformation in the capillary, which is then drawn into the target optical fiber.

[0008] Preferably, the voltage divider control region includes a plurality of first capillary units and a plurality of second capillary units, wherein the first capillary units and the second capillary units are distributed at the same level and coaxially symmetrically in the optical fiber preform; The control pressures applied to the first capillary unit and the second capillary unit are different.

[0009] Preferably, each of the first capillary unit and the second capillary unit is alternately disposed on the inner wall of the outer cladding layer; The pressure control region also includes the gap region formed by the adjacent first group of capillary units and the second group of capillary units and the outer cladding.

[0010] Preferably, the pressure control region further includes a hollow fiber core region enclosed by the first capillary unit and the second capillary unit at the center of the outer cladding.

[0011] Preferably, the control pressure includes positive pressure expansion control and negative pressure contraction control; The control pressure of the second capillary unit, the hollow fiber core region, and the gap region is negative pressure contraction control; The control pressure of the first capillary unit is positive pressure expansion control.

[0012] Preferably, the pressure control region further includes a secondary sleeve unit disposed inside the first capillary unit.

[0013] Preferably, there are two secondary sleeve units, which are symmetrically arranged on the inner wall of the first capillary unit.

[0014] Preferably, the secondary bushing unit is under positive pressure expansion control.

[0015] Preferably, the optical fiber preform comprises a stacked structure formed by multiple capillaries, wherein each layer of the stacked structure has multiple independent voltage divider control regions.

[0016] The present invention also provides a hollow optical fiber, which is prepared by the above-described preparation method.

[0017] The above technical solution has the following advantages or beneficial effects: 1. By tolerating contact nodes, the stringent requirements on capillary precision and assembly fixtures are significantly reduced, simplifying the process flow from the source and greatly improving production tolerance and yield.

[0018] 2. By introducing multi-region independent pressure control, this method breaks through the limitations of traditional single pressure, realizes refined and asymmetric compensation of the microstructure of optical fiber, and effectively solves the non-uniformity problem caused by initial stacking deviation.

[0019] 3. The structure formation mechanism has been made more proactive, elevating pressure difference from an auxiliary parameter to a core control variable. By dynamically inducing capillary deformation rather than simply relying on the initial geometry, the flexibility of structure control has been greatly enhanced, making it possible to fabricate various high-performance hollow fiber structures using the same preform. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of a method for preparing hollow optical fiber based on voltage divider control in Embodiment 1 of the present invention. Figure 2 This is a schematic diagram of the optical fiber preform in Embodiment 2 of the present invention; Figure 3 This is a schematic diagram of the structure of the hollow optical fiber prepared based on the optical fiber preform in Example 2; Figure 4 This is a schematic diagram of the optical fiber preform in Embodiment 6 of the present invention; Figure 5 This is a schematic diagram of the structure of the hollow optical fiber prepared based on the optical fiber preform in Example 6; Figure 6 This is a schematic diagram of the structure of the multilayer stacked optical fiber preform in Embodiment 7 of the present invention; Figure 7 This is a schematic diagram of the hollow optical fiber prepared by applying different control pressures to the optical fiber preform in Example 2. Figure 8 A schematic diagram of the Fiber1 fiber end face and its transmission spectrum; Figure 9 A schematic diagram of the Fiber2 fiber end face and its transmission spectrum; Figure 10 A schematic diagram of the Fiber3 fiber end face and its transmission spectrum; Figure 11 This is a schematic diagram of the fiber end face and transmission spectrum of the hollow fiber prepared based on the fiber preform in Example 6. Detailed Implementation

[0021] 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.

[0022] Example 1: In this embodiment, based on the aforementioned problems existing in the prior art, a method for fabricating hollow-core optical fiber based on voltage divider control is provided, such as... Figure 1 As shown, it includes: Step S1: Perform stacking and assembling of at least one layer of capillaries to form an optical fiber preform; Step S2: Divide the capillary in the optical fiber preform into at least two independent voltage-dividing control regions. Step S3: During the wire drawing process, different control pressures are applied to at least two independent pressure control regions respectively; Step S4: The pressure difference between each pressure control region is used to induce geometric deformation in the capillary, which is then drawn into the target optical fiber.

[0023] Specifically, this embodiment provides the most basic preparation method flow of the present invention. For example... Figure 1 As shown, the structural design is first carried out based on the performance indicators of the final required optical fiber (such as type, loss target, etc.). Figure 3 , Figure 5 The fiber structure in the image is the designed target fiber structure, and based on this, at least one layer of capillaries is stacked and assembled in an orderly manner to form the initial fiber preform (such as...). Figure 2 , Figure 4 This refers to the initial optical fiber preform, which corresponds to... Figure 3 , Figure 5 The target desired fiber structure. This fiber preform has a central hollow core region and a cladding region composed of capillaries. Unlike the stringent requirements of prior art that strives for node-free operation, this method allows natural contact nodes between capillaries during stack assembly. This significantly reduces the requirements for capillary accuracy, stacking fixtures, and initial alignment, thereby simplifying the process at its source and improving production tolerance.

[0024] Subsequently, the capillaries in the preform are divided into at least two independent pressure control regions according to their spatial location and pre-defined function. For example, a portion of the capillaries can be divided into one region, and another portion into another. This step establishes the basic unit of differentiated control, breaking through the limitations of uniform pressure or single gradient pressure in existing technologies, and laying the foundation for subsequent fine, asymmetric pressure intervention.

[0025] Next comes the crucial fiber drawing stage. The preform is heated to a drawable temperature (the basic physical process of optical fiber drawing involves reheating and softening a solid quartz preform, then drawing it thinner. This process is fundamental knowledge in the industry. The principle is: the preform is placed in a heating furnace at the top of the drawing machine, and drawing is performed after the furnace temperature reaches approximately 2000-2200℃). During the thinning process, different gas pressures (i.e., control pressures) are input to at least two pressure control zones defined in step S2 through an independent pressure control system. Due to the different pressures experienced by different zones, the forces acting on different parts of the capillary differ under the high-temperature softened state.

[0026] Finally, by utilizing the pressure difference between the various pressure-controlled regions, non-uniform, pre-defined geometric deformations (such as local expansion, contraction, or bending) are actively induced in the capillary wall. This deformation process continues until the optical fiber is drawn and cooled to set, resulting in a hollow-core optical fiber with the target microstructure. The core of this embodiment lies in establishing a basic process paradigm of dividing regions, applying differential pressure, and inducing deformation. This means that the final low-loss structure is not simply drawn directly from the initial geometry of the preform, but is dynamically shaped during the drawing process using pressure difference as the core method. This fundamentally changes the mechanism of structure formation, transforming pressure from an auxiliary parameter into a core control variable, achieving flexible and adjustable structure.

[0027] Therefore, even the most basic method described in this embodiment has systematically provided solutions to the technical problems in the prior art: simplifying the initial stacking by tolerating nodes, achieving differentiated pressure control by partitioning settings, and replacing rigid direct drawing with active shaping by pressure difference, providing a new and flexible process path for the preparation of high-performance hollow optical fibers.

[0028] Example 2: In this embodiment, the voltage divider control region includes a plurality of first capillary units 1 and a plurality of second capillary units 2, wherein the first capillary units 1 and the second capillary units 2 are distributed at the same level and coaxially symmetrically in the optical fiber preform. The control pressures applied to the first capillary unit 1 and the second capillary unit 2 are different.

[0029] Specifically, this embodiment, based on Embodiment 1, provides a more specific definition of the voltage divider control region, reflecting the idea of ​​refined control. For example... Figure 2 As shown, in one specific embodiment of this example, the pressure-distributing control region includes multiple first capillary units 1 and multiple second capillary units 2. These capillary units are located at the same level in the preform and are coaxially symmetrically distributed around the center. For example, in Figure 2In the diagram, the two sets of capillary units labeled 1 and 2 constitute this relationship.

[0030] During the fiber drawing process, different control pressures are applied to the two symmetrically distributed first capillary units 1 and second capillary units 2. This asymmetric pressure application to the symmetrical units is key to the flexible structural control of this invention. It allows for direct compensation or correction of minor asymmetries that may exist in the stack, or the proactive creation of a non-uniform structure with superior optical performance. For example, by applying a slightly higher positive pressure to one group to cause it to expand slightly, and applying a normal or negative pressure to the other group to keep it in its original state or shrink it, a periodic modulation structure can be formed in the final fiber cross-section, thereby optimizing the optical field distribution and reducing the loss of specific modes.

[0031] Example 3: In this embodiment, each of the first capillary unit 1 and the second capillary unit 2 is alternately disposed on the inner wall of the outer cladding layer 5; The pressure control region also includes the gap region 3 formed by the adjacent first group of capillary units 1 and the second group of capillary units 2 and the outer cladding layer 5.

[0032] Specifically, this embodiment further incorporates Embodiment 2, considering a stack structure that more closely resembles the actual fabricated structure. For example... Figure 2 As shown, the first capillary unit 1 and the second capillary unit 2 are arranged alternately and disposed on the inner wall of an outer sheath tube 5. In this way, some triangular gap regions 3 are naturally formed between adjacent first and second capillary units and the inner wall of the outer sheath 5.

[0033] In this embodiment, these gap regions 3 are also defined as independent pressure-controlled regions. During fiber drawing, in addition to applying differential pressure to the capillary unit itself, independent control pressures (e.g., negative pressure) can be applied to these gap regions. The advantage of doing so is that the deformation environment outside the capillary unit can be further affected by the pressure regulation of the gap regions, thereby more precisely controlling the overall shape and position of the capillary unit, resulting in a more regular and periodic cladding structure, which is crucial for the performance of photonic bandgap or anti-resonant optical fibers.

[0034] Example 4: In this embodiment, the pressure control region further includes a hollow fiber core region 4 formed by the first capillary unit 1 and the second capillary unit 2 at the center of the outer cladding.

[0035] Specifically, this embodiment extends the concept of voltage divider control to the hollow core region 4 of the optical fiber, based on embodiment 3. For example... Figure 2 As shown, the blank circular area enclosed by all the capillary units at the center is the channel for optical signal transmission.

[0036] In this embodiment, the hollow fiber core region is also defined as an independent pressure-controlled region. During the fiber drawing process, by applying a specific control pressure (e.g., applying a negative pressure) to the core region, an additional radial-inward force can be provided in addition to the force of capillary contraction towards the center. This helps to better maintain the roundness and dimensional stability of the fiber core during high-temperature drawing, preventing distortion due to material flow or surface tension, which is of positive significance for ensuring the fundamental mode field quality of the optical fiber and reducing coupling loss.

[0037] Example 5: In a preferred embodiment of the present invention, the control pressure includes positive pressure expansion control and negative pressure contraction control; The control pressure of the second capillary unit 2, the hollow fiber core region 4, and the gap region 3 is negative pressure contraction control; The control pressure of the first capillary unit 1 is positive pressure expansion control.

[0038] Specifically, this embodiment combines embodiments 2 to 4 and clarifies the specific type of control pressure and a typical application strategy. The control pressure is mainly divided into two types: positive pressure expansion control and negative pressure contraction control. Positive pressure makes the internal pressure of the capillary higher than the external pressure, causing its wall to expand outward; negative pressure, on the contrary, causes its wall to contract inward.

[0039] refer to Figure 2 and 3 One specific scheme is illustrated: positive pressure expansion control is applied to the first capillary unit 1, causing it to expand moderately during the drawing process. Simultaneously, negative pressure contraction control is applied to the second capillary unit 2, the hollow fiber core region 4, and the gap region 3. This combination of positive and negative pressure creates a strong pressure contrast. The expansion of the first capillary unit 1 brings it closer to the fiber core, enhancing the anti-resonance effect; while the negative pressure in the hollow fiber core region 4 and the gap region 3 helps to tighten the structure and reduce unnecessary spatial scattering; the negative pressure in the second capillary unit 2 balances the overall structure, forming a compact and efficient optical field confinement structure. Figure 2 This demonstrates the fiber end-face morphology that may form under this pressure strategy.

[0040] Example 6: In this embodiment, the pressure control region further includes a secondary sleeve unit 1.1, which is disposed inside the first capillary unit 1.

[0041] In this embodiment, there are two secondary sleeve units 1.1, which are symmetrically arranged on the inner wall of the first capillary unit 1.

[0042] In this embodiment, the secondary bushing unit 1.1 is under positive pressure expansion control.

[0043] Specifically, this embodiment, based on embodiment 5, introduces a more complex structure to pursue better performance. For example... Figure 4 As shown in the figure, in order to further suppress higher-order modes and optimize bandwidth and loss, a finer secondary sleeve unit 1.1 is pre-embedded inside part of the first capillary unit 1 in this embodiment.

[0044] In a preferred embodiment, two secondary sleeve units 1.1 are symmetrically arranged inside each first capillary unit 1 that requires nesting. This symmetrical double-sleeve design ensures that the deformation of the capillary unit is uniform and controllable when pressure is applied, avoiding structural distortion caused by unilateral deformation, thereby ensuring that the final fiber structure has good geometric symmetry and consistent optical performance.

[0045] These secondary bushing units 1.1 constitute a new, independent pressure control zone. Independent control pressure can be applied to them during wire drawing.

[0046] Positive pressure expansion control is applied to the secondary sleeve unit 1.1. When the first capillary unit 1 is also under positive pressure, it expands simultaneously inside and out, forming a unique multi-layered thin-walled structure within the capillary wall. If the first capillary unit 1 is under negative pressure while the sleeve is under positive pressure, a complex stress distribution can be formed. This active positive pressure control of the nested sleeve is key to finely controlling the local wall thickness and shape of the capillary, providing a new means for customizing the dispersion, nonlinearity, and other characteristics of optical fibers.

[0047] This capillary-nested sleeve structure, combined with independent internal and external pressure control, forms a dual regulation mechanism. By carefully designing the pressure combination between the capillary body and the inner sleeve, an extremely complex refractive index distribution can be created, thereby achieving strong suppression of higher-order modes within a specific wavelength range and further reducing transmission loss. The resulting target fiber structure is shown in the image. Figure 5 As shown.

[0048] Example 7: In this embodiment, the optical fiber preform includes a stacked structure formed by multiple capillaries, and each layer of the stacked structure has multiple independent voltage divider control regions.

[0049] Specifically, this embodiment extends the voltage divider control method of the present invention to a wider range of hollow optical fiber types. The optical fiber preform can be a complex stacked structure composed of multiple capillary layers, for example... Figure 6 The Kagome-type multilayer stack shown, or other photonic crystal fiber stacks.

[0050] The key to this invention lies in the ability to independently set multiple pressure-dividing control regions within each layer of this multi-layered stack. This means that the pressure of capillaries at symmetrical or specific locations within each layer can be independently regulated. This layer-by-layer, region-by-region fine-grained pressure control capability makes it possible to fabricate large, complex, and high-performance microstructured hollow optical fibers, with process controllability far exceeding that of traditional methods.

[0051] The present invention also provides a hollow optical fiber, which is prepared by the above-described preparation method.

[0052] Specifically, this embodiment protects hollow-core optical fiber products prepared by the methods described in any of the above embodiments. Specifically, in the cladding cross-section of the optical fiber, there are observable, non-uniform geometrical differences between different groups of capillary units, or between different parts of a capillary unit (such as the main body and the nested sleeve). For example, some capillaries have thinner walls and greater curvature, while others remain thicker and straighter; or the thickness of different sidewalls of the same capillary is inconsistent. These morphological differences directly stem from the different control pressures experienced by the pressure-controlled regions to which they belong during the preparation process. It is these pre-set deformations induced by pressure differences that collectively constitute the unique microstructure of the optical fiber and endow it with excellent comprehensive optical properties such as low loss, high bandwidth, and weak nonlinearity.

[0053] Specifically, in actual fabrication, to cope with various application scenarios, intermediates with the same structure in the same batch can be used to achieve the fabrication of diverse optical fiber structures through differentiated voltage division control. The optical fibers actually fabricated also have the light guiding mechanism of hollow core anti-resonance intrinsic and excellent transmission effect.

[0054] like Figure 7 As shown, the end faces of various target optical fibers (Fiber1, Fiber2, Fiber3) obtained by applying different control pressures to at least two independent pressure-dividing control regions based on the optical fiber preform in Example 4 are illustrated. Figure 8-10 These are schematic diagrams of the fiber end faces and their transmission spectra for (Fiber1, Fiber2, Fiber3).

[0055] Figure 11 This refers to the target fiber end face and its transmission spectrum obtained by using a fiber preform with secondary sleeve units in Example 6. To address the signal distortion problem caused by high-order mode transmission in the basic structure, and to further reduce transmission loss, adapting to scenarios with higher requirements for mode field purity and transmission loss, in this example, secondary sleeve units are embedded in a single-layer capillary stack. Through the synergistic mechanism of primary and secondary capillary voltage division control plus nested tube structure constraints, dual optimization of low loss and high-order mode suppression is achieved.

[0056] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize 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 fabricating hollow-core optical fiber based on voltage divider control, characterized in that, include: Step S1: Perform stacking and assembling of at least one layer of capillaries to form an optical fiber preform; Step S2: Divide the capillary in the optical fiber preform into at least two independent voltage-dividing control regions. Step S3: During the wire drawing process, different control pressures are applied to at least two independent pressure control regions respectively; Step S4: The pressure difference between each pressure control region is used to induce geometric deformation in the capillary, which is then drawn into a hollow optical fiber.

2. The preparation method according to claim 1, characterized in that, The voltage divider control region includes multiple first capillary units and multiple second capillary units, wherein the first capillary units and the second capillary units are distributed at the same level and coaxially symmetrically in the optical fiber preform. The control pressures applied to the first capillary unit and the second capillary unit are different.

3. The preparation method according to claim 2, characterized in that, Each of the first capillary unit and the second capillary unit is alternately disposed on the inner wall of the outer cladding layer; The pressure control region also includes the gap region formed by the adjacent first group of capillary units and the second group of capillary units and the outer cladding.

4. The preparation method according to claim 3, characterized in that, The pressure control region also includes a hollow fiber core region enclosed by the first capillary unit and the second capillary unit at the center of the outer cladding.

5. The preparation method according to claim 4, characterized in that, The control pressure includes positive pressure expansion control and negative pressure contraction control; The control pressure of the second capillary unit, the hollow fiber core region, and the gap region is negative pressure contraction control; The control pressure of the first capillary unit is positive pressure expansion control.

6. The preparation method according to claim 5, characterized in that, The pressure control region also includes a secondary sleeve unit, which is disposed inside the first capillary unit.

7. The preparation method according to claim 6, characterized in that, The number of secondary sleeve units is two, which are symmetrically arranged on the inner wall of the first capillary unit.

8. The preparation method according to claim 7, characterized in that, The secondary bushing unit is under positive pressure expansion control.

9. The preparation method according to claim 1, characterized in that, The optical fiber preform includes a stacked structure formed by multiple capillaries, and each layer of the stacked structure has multiple independent voltage divider control regions.

10. A hollow-core optical fiber, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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