Method for manufacturing a preform of a reverse-harmonic hollow-core optical fiber with nested capillaries; preform and intermediate product

Abstract

The invention relates to the manufacturing of an anti-resonant hollow core fiber consisting of a capillary blank and a sleeve. The capillary blank comprises an outer capillary and a nested inner capillary and is stretched to a maximum outer diameter ODARE_cap and a maximum wall thickness WTARE_cap. The blank is mounted on the inside of the sleeve. In order to keep the advantages of the pre-manufactured capillary blank in terms of ease and precision of assembly while keeping the associated drawbacks due to ovality low and predictable, it is suggested that the inner and outer diameters of the outer and inner capillary and ODARE_cap and WTARE_cap are aligned with respect to each other in a way that the ARE outer capillary of the capillary blank has an ovality degree of less than 1.025.

Description

TECHNICAL FIELD

[0001] The present invention belongs to the field of optical fiber technology and in particular to the field of anti-resonant hollow core optical fibers. The optical fibers enable light to be guided in a "hollow" core which is evacuated or filled with a gas. This optical fiber technology guarantees low optical attenuation, a very broad transmission spectrum (in particular also in the UV or IR wavelength range) and low latency in data transmission. Furthermore, these optical fibers are suitable for spectroscopy and the transmission of short laser pulses.

[0002] In particular, the present invention relates to a method for manufacturing an anti-resonant hollow core optical fiber comprising a hollow core extending along a longitudinal axis of the optical fiber and a cladding region surrounding the hollow core, the cladding region comprising a plurality of anti-resonant elements, the method comprising the following steps:

[0003] (a) providing a sleeve comprising an inner bore of the sleeve and a longitudinal axis of the sleeve, a sleeve wall which is bounded by an inner side and an outer side extends along the longitudinal axis,

[0004] (b) providing a tubular anti-resonant element preform, at least a portion of the tubular anti-resonant element preform exists as a capillary blank comprising at least one ARE outer capillary and at least one nested NE inner capillary connected to an inner side surface of the ARE outer capillary, wherein the manufacturing of the capillary blank comprises the following method steps:

[0005] (b1) fixing an NE inner tube having an outer diameter OD NE and an inner diameter ID NE on an inner side surface of an ARE outer tube having an outer diameter OD ARE and an inner diameter ID ARE to form a capillary blank entirety,

[0006] (b2) heat stretching the capillary blank entirety to form the capillary blank, the capillary blank having a maximum outer diameter OD ARE_cap and a maximum wall thickness WT ARE_cap ,

[0007] (c) mounting the capillary blank at a target position on the inner side of the sleeve wall to form a nascent preform comprising a hollow core region and a cladding region, and

[0008] (d) elongating the nascent preform to form the hollow core optical fiber or further processing the nascent preform to form a secondary preform from which the hollow core optical fiber is drawn.

[0009] The present invention also relates to a method for manufacturing a preform of an anti-resonant hollow optical fiber, the anti-resonant hollow optical fiber comprising a hollow core extending along the longitudinal axis of the optical fiber and an inner sheath region surrounding the hollow core, the sheath region comprising a plurality of anti-resonant elements, the method comprising the following steps:

[0010] (a) A sleeve is provided, the sleeve including an inner bore and a longitudinal axis of the sleeve, with a sleeve wall defined by an inner side and an outer side extending along the longitudinal axis.

[0011] (b) Providing a tubular anti-resonant element preform, at least a portion of which exists as a capillary blank comprising at least one outer capillary of the ARE and at least one nested inner capillary of the NE connected to the inner surface of the outer capillary of the ARE, wherein the manufacture of the capillary blank comprises the following method steps:

[0012] (b1) will have an outer diameter OD NE and inner diameter ID NE The NE inner tube is fixed to a tube with an outer diameter OD. ARE and inner diameter ID ARE On the inner surface of the ARE outer tube, to form a whole capillary blank.

[0013] (b2) The capillary blank is hot-drawn integrally to form the capillary blank having a maximum outer diameter OD. ARE_cap and maximum wall thickness WT ARE_cap ,

[0014] (c) The capillary preform is installed at a target location on the inner side of the sleeve wall to form a nascent preform including a hollow region and a sheath region, and

[0015] (d) Optionally, the primary preform is further processed to form a secondary preform of the hollow optical fiber, wherein the further processing includes performing one or more of the following thermoforming processes once or repeatedly:

[0016] (i) Lengthen,

[0017] (ii) collapse.

[0018] (iii) Collapse and elongation at the same time.

[0019] (iv) Collapse of the additional sheath material.

[0020] (v) Collapse and subsequent elongation of the additional sheath material.

[0021] (vi) Collapse and simultaneous elongation of the additional sheath material.

[0022] Furthermore, the present invention relates to a capillary blank as an intermediate product for manufacturing anti-resonant hollow optical fiber, the capillary blank comprising at least one outer capillary ARE and at least one nested inner capillary connected to the inner surface of the outer capillary ARE.

[0023] Furthermore, the present invention relates to a preform for anti-resonant hollow optical fiber, wherein the preform has a hollow region and a sheath region, the sheath region including a sheath having a sheath wall and a plurality of tubular anti-resonant element preforms disposed on the inner side of the sheath wall.

[0024] Conventional single-mode optical fibers made of solid materials have a core region made of glass, which is surrounded by a sheath region made of glass with a lower refractive index. Light guidance is thus based on total internal reflection between the core and sheath regions. However, the interaction of the guided light with the solid material is associated with increased delay in data transmission and a relatively low damage threshold (relative to high-energy radiation).

[0025] Hollow-core fiber prevents or reduces these drawbacks, with the core consisting of an evacuated cavity filled with gas or liquid. The interaction between light and glass in hollow-core fiber is less than that in solid-core fiber. The refractive index of the core is lower than that of the sheath, making total internal reflection impossible for light guidance, and light normally escapes from the core into the sheath. Based on the physical mechanism of light guidance, hollow-core fiber is classified into "photonic bandgap fiber" and "anti-resonant reflection fiber".

[0026] In the case of "photonic bandgap fiber," the hollow core region is surrounded by a sheath in which small hollow channels are periodically arranged. Based on semiconductor technology, the periodic structure of the hollow channels in the sheath produces an effect known as the "photonic bandgap." According to this effect, light of a specific wavelength range scattered at the sheath structure can constructively interfere due to Bragg reflection in the central cavity and cannot propagate laterally within the sheath.

[0027] In an implementation of a hollow fiber known as "anti-resonant hollow fiber" (ARHCF), the hollow core region is surrounded by an inner sheath region in which so-called "anti-resonant elements" (or "AREs" for short) are arranged. The walls surrounding the anti-resonant elements, which are uniformly distributed around the hollow core, can act as a Fabry-Perot cavity operating in anti-resonance mode, reflecting and guiding the incident light through the fiber core.

[0028] This fiber optic technology ensures low optical attenuation, a very wide transmission spectrum (even in the UV or IR wavelength range), and low latency in data transmission.

[0029] Hollow-core optical fibers are used in data transmission, high-power beam guiding (e.g., for materials processing), modal filtering, and nonlinear optics (particularly for supercontinuum generation, from ultraviolet to infrared wavelengths). Furthermore, these fibers are suitable for spectral applications and for transmitting short laser pulses. Existing technology

[0030] The disadvantage of anti-resonant hollow fiber is that higher-order modes are not necessarily suppressed, which means that they are usually not pure single-mode over long transmission lengths, and the quality of the output beam is degraded.

[0031] Francesco Poletti's paper, "Nested anti-resonant nodeless hollow core fiber," *Optics Letters*, Vol. 22, No. 20 (2014); DOI: 10.1364 / OE 22.023807, proposes a fiber design in which the anti-resonant element is not designed as a simple single-structure element, but rather consists of multiple nested structural elements. The nested anti-resonant elements are designed so that higher-order core modes (rather than the fundamental core mode) are phase-matched with and suppressed by the sheath mode. Therefore, the propagation of the fundamental core mode is always ensured, and the hollow core fiber can be effectively single-mode over a finite wavelength range.

[0032] Preforms of this type of "nested anti-resonant nodeless hollow fiber" (NANF) consist of multiple anti-resonant elements (AREs). They are typically manufactured using a method known as "stacking and drawing". For example, in the fabrication of a preform for hollow fiber in a "NANF" design, multiple anti-resonant element preforms are attached to the inside of a sleeve. Each of these preforms consists of an outer anti-resonant element tube (hereinafter referred to as the ARE outer tube) and an inner anti-resonant element tube (hereinafter referred to as the NE inner tube) disposed on one side of the inner surface of the ARE outer tube.

[0033] Each element in an anti-resonant preform has a specific deviation from the geometry of its set point, and each positioning and forming step inevitably leads to geometrical deviations, which can be aggregated into an absolute geometrical error in the preform. High accuracy is required when positioning and fixing the output elements at their respective target locations, especially when the output elements are arranged compactly and close together. To achieve low attenuation and a wide transmission range, in addition to the uniform wall thickness of the anti-resonant elements, their azimuth position on the inner wall of the sheath is also critical. The attachment point of the NE inner tube to the ARE outer tube should have the same azimuth position as the attachment point of the ARE outer tube to the inner wall of the sheath. Furthermore, both the distance between individual attachment points and the peripheral distance between the ARE outer tubes must be as uniform as possible. This cannot be easily achieved through "stack and pull" techniques.

[0034] This simplification stems from a technique in which a pre-fabricated capillary preform is manufactured, comprising an outer ARE capillary and at least one inner NE capillary fixed to the inner wall of the outer ARE capillary. This technique is described, for example, in the paper “Hollow-core revolver fiber with a double-capillary reflective cladding” by A.F. Kosolapov, G.K. A. Lagashev, A.N. Kolyadin, A.D. Ryamikov, A.S. Biriukov, I.A. Bufetov, and E.M. Dianov, published in Quantum Electronics, 2016, Vol. 46, No. 3, pp. 267-270. In this case, the pre-fabrication of the capillary preform involves drawing together an outer ARE made of quartz glass and an inner NE capillary made of quartz glass welded to its inner wall to form the capillary preform. Therefore, the elongated capillary preform consists of an outer ARE capillary and an inner NE capillary fixedly connected to the outer ARE capillary. Five elongated capillary preforms are mounted on the inner wall of a sleeve made of quartz glass. A template with fivefold symmetry is used for this mounting. The capillary preforms are fused to the inner wall and the whole is elongated to form a nascent preform, from which hollow optical fibers are subsequently drawn.

[0035] Technical Objectives

[0036] While pre-fabricated capillary blanks offer advantages in terms of ease of assembly and precision, it has been shown that when the entire component is elongated, an oval (elliptical) deformation of the initially circular tube cross-section can easily occur. During softening and stretching, the NE inner tube melts on the inner surface of the ARE outer tube. Due to this contact, forces that cause cross-sectional deformation and result in an oval cross-sectional shape act on the inner surface of the ARE outer tube.

[0037] Therefore, in the known method, the elongated capillary blank has an elliptical cross-section with a long cross-sectional axis of 6.28 mm and a short cross-sectional axis of 6.12 mm. The longest cross-sectional axis is A. L and the shortest cross-sectional axis A K The ratio of the axis length A L / A K Therefore, the value is 1.026. This axis ratio is also referred to in this paper as “ovalness” or “oval degree”.

[0038] The oval shape of the capillary preform makes precise mounting on the inner wall of the sleeve more difficult. For example, the template used for mounting is often designed with a circular cross-section. Furthermore, this template makes it difficult to determine its outer diameter for subsequent drawing processes, and thus hinders accurate and reproducible prediction of the drawing results in the form of hollow optical fibers.

[0039] However, in order to maintain the resonant or anti-resonant conditions, even small size variations on the order of the operating wavelength of the light to be guided cannot be tolerated.

[0040] Therefore, one object of the present invention is to provide a method for manufacturing anti-resonant hollow optical fibers and a preform for anti-resonant hollow optical fibers, wherein the advantages of pre-manufactured capillary blanks can be maintained in terms of ease of assembly and precision, while the associated disadvantages due to ovalness can be kept so low and predictable that high precision of anti-resonant elements and accurate positioning in hollow optical fibers can be reproducibly achieved.

[0041] In addition, capillary blanks with low ovalness will be provided, which will facilitate precise positioning of the sleeve at a predetermined azimuth angle and reproducible prediction of the drawing results.

[0042] Furthermore, the object of the present invention is to specify a preform from which an anti-resonant hollow optical fiber having geometrically precise anti-resonant elements with the most accurate possible positioning can be drawn. Summary of the Invention

[0043] Regarding the method for manufacturing antiresonant hollow optical fibers, this objective is achieved according to the present invention based on a method of the type described above, wherein the cross-sectional dimension OD NE ID NEOD ARE ID ARE and OD ARE_cap and WT ARE_cap Alignment is performed in such a way that the outer capillary (11) of the capillary blank (5) has an oval shape of less than 1.025.

[0044] The starting point for manufacturing antiresonant hollow optical fibers is a preform referred to herein as a "nascent preform." Typically, the manufacture of the nascent preform involves mounting and connecting the antiresonant element preform to a sleeve. At least a portion of the antiresonant element preform exists in the form of a pre-manufactured capillary blank with nested antiresonant elements. This is understood herein to refer to a blank comprising an outer ARE capillary, on the inner surface of which at least one inner NE capillary is fixed, and which extends parallel to the longitudinal axis of the outer capillary. In the case of multiple nested antiresonant elements, at least one additional inner NE capillary, also extending parallel to the longitudinal axis of the outer capillary, is fixed to the inner surface of the outer NE capillary. The outer ARE capillary and one or more inner NE capillary tubes are fused together to form the antiresonant element preform.

[0045] A nascent preform manufactured using a pre-fabricated capillary preform can be directly drawn to form a hollow optical fiber. In principle, the nascent preform can be further processed to manufacture a preform referred to herein as a "secondary preform." Optionally, a hollow optical fiber is drawn from the secondary preform. The manufacture of the secondary preform includes method steps of manufacturing output elements of the hollow optical fiber therethrough and positioning these output elements relative to each other, as well as at least one thermoforming step.

[0046] Primary and secondary preforms are part of a monolithic body or coaxial integral of a component, having one or more collection cylinders, which are drawn to directly form hollow optical fibers. The general term "preform" should be understood herein to refer to the component or coaxial integral from which hollow optical fibers are ultimately drawn.

[0047] For example, the addition of sheath material is achieved by causing the collecting cylinder to collapse onto the nascent preform. When the collecting cylinder collapses, the coaxial arrangement of the nascent preform and the collecting cylinder may or may not be elongated. Here, the shape or arrangement of the anti-resonant element preforms may be altered, or their shape or arrangement may remain unchanged.

[0048] To manufacture a capillary blank with a simple nested NE inner capillary, an outlet tube with a circular cross-section is used, referred to herein as the ARE outer tube and the NE inner tube. The NE inner tube is fixed to the inner surface of the ARE outer tube. The connection is preferably made at the two opposite end faces of the whole, and the connection is made, for example by means of a structural retaining device, and preferably by local spot bonding or thermal bonding (spot welding).

[0049] The component is softened and stretched (elongated) in sections to form a pre-manufactured capillary blank, wherein the outer capillary ARE and the inner capillary NE have fixed, predetermined, and verifiable positions and orientations relative to each other. Pre-manufacturing eliminates the positioning and alignment measures that would otherwise be necessary for manufacturing the nascent preform during assembly. In this respect, it facilitates these assembly steps and improves the dimensional stability of the anti-resonant element preform.

[0050] However, it has been shown that when the component is elongated as a whole, an oval (elliptical) deformation of the initial circular tube cross-section can easily occur. While this also applies to the internal capillaries of the NE, it specifically relates to the external capillaries of the ARE. It has been shown that the degree of oval deformation of the external capillaries of the ARE is essentially determined by the cross-sectional geometry (OD) of the outlet tube. NE ID NE OD ARE ID ARE ) and the cross-sectional geometry (OD) of the external capillary of ARE ARE_cap WT ARE_cap The ovalness is determined by the taper ratio during hot drawing (but also as a function of the cross-sectional geometry of the outlet tube and the ARE external capillary). In contrast, drawing parameters (such as temperature, feed, and draw speed) have a relatively small effect on the ovalness. However, other drawing parameters (such as pressure and gas flow rate) have a significant effect on the ovalness of the ARE external capillary. For example, gas flow rate can cause localized cooling, which affects the geometry of the ARE external capillary. By predetermining additional drawing parameters, the ovalness of the ARE external capillary is primarily a function of the geometric cross-sectional dimensions of the outlet tube and the ARE external capillary.

[0051] The present invention specifies the following teachings: how to set the geometric parameters so that a predetermined maximum ovalness (e.g., 1.025) of the outer capillary of the ARE can be reproducibly maintained in a capillary blank manufactured by hot stretching.

[0052] In a preferred variation of the method, the following factors (F1) to (F4) are specified for setting the geometric dimensions:

[0053] (F1) Equilibrium pressure p of the inner tube of NE eg_NE Balance pressure p with ARE outer tubeeq_ARE The ratio,

[0054] (F2) The distance between the ARE outer tube and the NE inner tube relative to the inner diameter of the ARE outer tube (ID) ARE -OD NE ) / ID ARE ,

[0055] (F3) Taper ratio OD during the overall hot stretching of the capillary blank according to method step (b2) ARE / OD ARE_cap ,

[0056] (F4) The ratio of the outer diameter to the wall thickness of the capillary blank (OD) ARE_cap / WT ARE_cap .

[0057] Balance pressure p eq This is the pressure applied during the elongation of the glass tube to prevent it from collapsing or expanding. The equilibrium pressure p of the inner tube of NE. eq；NE It is generated by the following formula:

[0058] p eq；NE =(2 / OD) NE +2 / ID NE )×σ (1),

[0059] And the ARE outer tube's balancing pressure p eq；ARE It is generated by the following formula:

[0060] p eq,ARE =(2 / OD) ARE +2 / ID ARE )×σ (2),

[0061] Where σ is the surface tension at the drawing temperature, which can be 0.4 N / m and is applicable to quartz glass.

[0062] Advantageously, the diameter of the ARE outer tube made of quartz glass or the NE inner tube made of quartz glass is selected such that the pressure p is balanced. eq,NE Within the range of 60 Pa to 90 Pa, preferably within the range of 65 Pa to 80 Pa, and the equilibrium pressure p eq_ARE The range is from 25 Pa to 50 Pa, preferably from 30 Pa to 40 Pa.

[0063] The ratio p of the equilibrium pressure based on factor (F1) eq；NE / p eq；ARE It is a measure of the effectiveness of the surface tension of individual capillaries in a capillary preform. The larger the value, the more dominant the influence of the inner capillary (NE) on the ovalness of the outer capillary (ARE).

[0064] Therefore, the equilibrium pressure p eq；NE and p eq；ARE It is advantageously configured such that the factor (F1) takes a value in the range of 1.5 to 2.5, preferably in the range of 1.5 to 2.

[0065] On the one hand, the greater the free distance between the ARE outer tube and the NE inner tube, the more complex and difficult the final processing of the optical fiber becomes, because the inner diameter ID... NE_cap The pressure becomes smaller with a greater free distance between the outer AR tube and the inner NE tube. Therefore, for example, high-temperature connections with pressure connections become technically more complex. On the other hand, the pressure balancing ratio becomes larger with a greater free distance between the outer AR tube and the inner NE tube.

[0066] In view of this, it has proven advantageous to set the factor (F2) to a value in the range of 0.2 to 0.5, preferably in the range of 0.3 to 0.4.

[0067] To reduce absolute geometric error, during hot stretching, a large taper ratio OD is used. ARE / OD ARE_cap This is desirable. On the other hand, a large drawing reduction ratio is associated with a corresponding large forming process and material movement, which can easily lead to undesirable deformation in precision anti-resonant element preforms.

[0068] It has been shown that a suitable compromise is to set the taper ratio based on the factor (F3) to a value in the range of 5 to 10, preferably in the range of 5 to 8.

[0069] The ratio of the outer diameter to the wall thickness of the capillary blank (OD) ARE_cap / WT ARE_cap It is a measure of the dimensional stability of capillary blanks. The thinner the wall is compared to the outer diameter, the more easily it deforms.

[0070] Regarding the possible minimum ovalness, it has been proven successful to set the factor (F4) to a value in the range of 15 to 25, preferably in the range of 15 to 20.

[0071] In addition, the measurements provide an indication of the dimensional stability of the drawn capillary.

[0072] In a particularly preferred variation of the method, factors (F1) to (F4) are set such that the capillary blank has an ovalness of less than 1.020.

[0073] It has been shown that the mathematical product of factors (F1) through (F4) is a measure of the degree of ovalness. The smaller the product, the smaller the ovalness of the ARE external capillary in the capillary blank. This measure is referred to below as the "geometric parameter" (P(geometric)).

[0074]

[0075] Each individual factor (F1) through (F4) influences the geometric parameters. The smaller the factor, the less it contributes to the ovalness of the ARE outer capillary. Based on the geometric parameters, those skilled in the art can reliably estimate how the cross-sectional dimensions of the outlet tubes (NE inner tube and ARE outer tube) will affect the degree of ovalness through their planned taper ratio. This prevents empirical testing and failures, or at least reduces their number. For example, with a geometric parameter of 94, an ovalness of 1.04 is expected. If the ovalness will be less than 1.025, then the geometric parameter must not be greater than 77.5. If only an ovalness of 1.010 is acceptable, then the geometric parameter will be set to 55 or less.

[0076] To achieve the minimum ovalness, the geometric parameters are set to values ​​in the range of 35 to 75, preferably in the range of 40 to 60.

[0077] Especially in the case of multiple nested capillary blanks, the effort required for positioning and alignment is significantly reduced compared to individual components.

[0078] During its further processing to form the nascent preform, multiple pre-manufactured capillary blanks are mounted on the inner surface of the sleeve.

[0079] The nascent preform manufactured by the method preferably has an outer diameter in the range of 26 mm to 230 mm, and particularly preferably in the range of 30 mm to 200 mm.

[0080] During the elongation of the nascent preform to form a hollow optical fiber or a secondary preform, additional sheath material may or may not be applied. During elongation, the nascent preform is heated zone by zone within a heating zone. The larger the diameter, the slower the advance rate into the heating zone, and the longer the duration of exposure of each axial portion of the preform to the high temperature of the heating zone. However, if the advance rate is too slow during elongation, the anti-resonant element preform will deform. Therefore, the diameter of the nascent preform is preferably at most 230 mm, preferably at most 200 mm. Furthermore, the diameter of the nascent preform is preferably at least 26 mm, particularly preferably at least 30 mm. This is because it has been found that with smaller diameters, the thermal inertia of the preform is too low to compensate for any temperature fluctuations in the heating zone.

[0081] When drawing a primary or secondary preform to form a hollow fiber according to method step (d), it is preferable to generate and maintain overpressure relative to the elongated hollow region in the outer capillary of the ARE and in the inner capillary of the NE. The pressure in the outer capillary of the ARE is typically different from the pressure in the inner capillary of the NE. A hollow fiber with a hollow region and an inner sheath region is obtained, wherein the previous outer capillary of the ARE forms an anti-resonant element with a preferably circular or slightly oval cross-section.

[0082] The accuracy of the preform's positioning on the inner surface of the sleeve is further improved by machining, particularly by drilling, milling, grinding, honing and / or polishing, to manufacture the inner and / or outer sides of the sleeve and / or the inner and / or outer sides of the ARE outer tube.

[0083] Compared to other known forming techniques, these machining techniques provide more precise and refined structures by using heat and pressure, and they avoid surface contamination from molding tools such as nozzles, presses, or fusion molds.

[0084] Furthermore, the procedure has proven successful, wherein the ARE outer tube is composed of quartz glass containing at least one dopant that reduces the viscosity of quartz glass, and / or at least one NE inner tube is composed of quartz glass containing at least one dopant that increases the viscosity of quartz glass.

[0085] Dopants used to reduce the viscosity of quartz glass are preferably fluorine, chlorine, and / or hydroxyl groups. Dopants that increase the viscosity of quartz glass are considered to be Al2O3 (at a concentration of up to 15 ppm by weight) and nitrogen.

[0086] Doping allows for adaptation of the coefficient of thermal expansion of adjacent preform components to avoid or reduce stress. It can also be used to reduce the thermal stability of the outer ARE tube relative to the thermal stability of at least one nested NE inner tube.

[0087] In this regard, it is advantageous, for example, if the quartz glass of the outer ARE tube has a viscosity at least 0.1 dPa·s lower than that of the quartz glass of the nested inner NE tube at a measurement temperature of 1250°C, preferably at least 0.2 dPa·s lower (if the viscosity is given as a logarithm in dPa·s).

[0088] In the preferred method, the accuracy of the capillary blank's positioning within the sleeve is further improved, wherein the outer capillary of the ARE has a wall thickness ranging from 0.2 mm to 3 mm, preferably from 0.25 mm to 1 mm, and wherein a sleeve with an outer diameter ranging from 90 mm to 230 mm, preferably from 120 mm to 200 mm, is used. Each component has a length of at least 700 mm, preferably at least 1 m. They are relatively large structural elements, which simplifies their handling. Furthermore, through the vertical arrangement of the sleeve and the capillary blank, gravity supports the parallel and vertical alignment of the capillary's longitudinal axis when the capillary blank is positioned and fixed at its target location at its upper end.

[0089] Regarding the manufacturing of preforms for hollow optical fibers, the above-mentioned technical objectives are achieved by the method of the type described above, wherein the geometric dimension OD... NE ID NE OD ARE ID ARE and OD ARE_cap and WT ARE_cap The capillary blank is configured in such a way that the outer capillary of the ARE has an oval shape of less than 1.025.

[0090] For this purpose, a pre-manufactured capillary blank is provided, wherein an outer capillary ARE is fused with at least one inner capillary NE, and wherein the outer capillary ARE and the inner capillary NE have fixed, predetermined and verifiable positions and orientations relative to each other.

[0091] Pre-fabrication eliminates the positioning and alignment measures that would otherwise be necessary for manufacturing nascent preforms during assembly. In this respect, it facilitates these assembly steps and improves the dimensional stability of the anti-resonant element preforms.

[0092] The fabrication of the pre-manufactured capillary blank involves the integral hot stretching of the component, consisting of the ARE outer tube and the NE inner tube, which readily leads to an oval (elliptical) deformation of the initially circular tube cross-section. This applies to the NE inner capillary, but particularly to the ARE outer capillary. It has been shown that the degree of oval deformation of the ARE outer capillary is essentially determined by the cross-sectional geometry (OD) of the outlet tube. NE ID NE OD ARE ID ARE ) and the cross-sectional geometry (OD) of the external capillary of ARE ARE_cap WT ARE_capThe ovalness is determined by the taper ratio during hot stretching (but also as a function of the cross-sectional geometry of the outlet tube and the ARE external capillary). In contrast, drawing parameters (such as temperature, feed, and pull-out speed) have a relatively small effect on the ovalness. However, other drawing parameters (such as pressure and gas flow rate) have a significant effect on the ovalness of the ARE external capillary. For example, gas flow rate can cause localized cooling, which affects the geometry of the ARE external capillary. However, by predetermining additional drawing parameters, the ovalness of the ARE external capillary is primarily a function of the geometric cross-sectional dimensions of the outlet tube and the elongated ARE external capillary.

[0093] The present invention specifies the following teachings: how to set the geometric parameters so that a predetermined maximum ovalness (e.g., 1.025) of the outer capillary of the ARE can be reproducibly maintained in a capillary blank manufactured by hot stretching.

[0094] The above explanation of the manufacturing process of hollow optical fibers explains the measures used to manufacture preforms, and these explanations are included in this document.

[0095] Regarding the pre-manufactured capillary blanks used as intermediate products for manufacturing anti-resonant hollow optical fibers, the above-mentioned technical objectives are achieved by capillary blanks of the type mentioned at the beginning of this invention, wherein the outer capillary of the ARE has an ovalness of less than 1.025.

[0096] In a pre-manufactured capillary preform, at least two capillaries are integrally connected to each other to form a tubular component. Pre-manufacturing eliminates the positioning and alignment measures that would otherwise be necessary during assembly for manufacturing the nascent preform. In this respect, it facilitates these assembly steps and improves the dimensional stability of the anti-resonant element preform.

[0097] The cross-section of the outer capillary of the capillary preform is circular or has at most a low ovalness of less than 1.025, preferably less than 1.020. This is beneficial for the precise positioning of the capillary preform on the inner wall of the sleeve and for fixing its outer diameter in the subsequent drawing process, as well as for accurate and reproducible prediction of the drawing results and more precise manufacturing of hollow optical fibers.

[0098] The above explanation, combined with the fabrication of hollow optical fibers, explains the capillary blanks and procedures used to manufacture preforms, and these explanations are hereby incorporated.

[0099] Regarding the preform, the above-mentioned technical objective is achieved based on the preform of the above type according to the present invention, wherein at least a portion of the anti-resonant element preform is designed as a capillary blank according to the present invention.

[0100] The preform is the nascent preform within the meaning of this invention. The sheathing region of the preform includes a sleeve, which can be enclosed by at least one additional sleeve. The anti-resonant element preform is disposed on the inside of the sleeve and is attached to the sleeve, for example, by adhesive or thermal bonding. At least a portion (preferably all) of the anti-resonant element preform is in the form of a pre-manufactured capillary blank, wherein at least two capillaries are integrally connected to each other. Pre-manufacturing eliminates the positioning and alignment measures that would otherwise be necessary for manufacturing the nascent preform during assembly. In this respect, these assembly steps are advantageous, and the dimensional stability of the anti-resonant element preform is improved.

[0101] The cross-section of the outer capillary of the capillary preform is circular or has at most a low ovalness of less than 1.025, preferably less than 1.020. This is beneficial for the precise positioning of the capillary preform on the inner wall of the sleeve and for fixing its outer diameter in the subsequent drawing process, as well as for accurate and reproducible prediction of the drawing results and more precise manufacturing of hollow optical fibers.

[0102] The above explanation, combined with the fabrication of hollow optical fibers, explains the capillary blanks and procedures used to manufacture preforms, and these explanations are hereby incorporated.

[0103] Definitions

[0104] The various method steps and terms described above are further defined below. These definitions form part of this specification. In the event of any factual conflict between any of the following definitions and the remainder of the specification, the definitions expressed in the specification shall prevail.

[0105] Anti-resonance element

[0106] Anti-resonant elements can be simple or nested structural elements of hollow optical fibers. They have at least two walls that, when viewed from the hollow direction, have negative curvature (convex) or no curvature (planar, straight). They are typically composed of materials transparent to the working light (e.g., glass, especially doped or undoped SiO2, plastics, especially polymers, composites, or crystalline materials).

[0107] Anti-resonance element preform

[0108] So-called anti-resonant element preforms are components or parts of preforms that are essentially transformed into anti-resonant elements in hollow optical fibers through simple elongation during the fiber drawing process. Nested anti-resonant element preforms form nested anti-resonant elements in hollow optical fibers. They consist of an ARE outer tube and at least one additional structural element arranged in the inner hole of the ARE outer tube. The additional structural element can be another tube supported against the inner surface of the outer tube. The additional tube is simply referred to as a "nested element" or "NE inner tube," or also as a "nested NE inner tube."

[0109] In the case of multiple nested anti-resonant element preforms, at least one additional structural element (e.g., a third tube abutting against the inner surface of the nested NE inner tube) may be arranged in the inner hole of the NE inner tube. In the case of multiple nested anti-resonant element preforms, in order to distinguish the multiple tubes arranged in the ARE outer tube, the "outer NE inner tube" and the "inner NE inner tube" may be optionally distinguished.

[0110] The term “cross section” in conjunction with cylindrical anti-resonant element preforms and their cylindrical structural elements and capillary blanks always refers to a cross section perpendicular to the relevant longitudinal axis of the cylinder, that is, unless otherwise specified, the cross section of the outer contour of the tubular component (not the cross section of the inner contour).

[0111] Further processing of the nascent preform (particularly through a thermoforming step) can produce an intermediate product in which the initial anti-resonant element preform exists in a modified shape compared to the initial shape. The modified shape is also referred to herein as the anti-resonant element preform.

[0112] Preform / primary preform / secondary preform / core preform (billet)

[0113] A preform is a component from which antiresonant hollow optical fiber is drawn. It is a primary preform or a secondary preform manufactured through further processing of the primary preform. The primary preform may exist as a whole, consisting of at least one sleeve and a preform or precursor loosely housed or securely fastened within the sleeve to an antiresonant element. Further processing the primary preform into a secondary preform from which hollow optical fiber is drawn may include performing one or more of the following thermoforming processes, either once or repeatedly:

[0114] (i) Lengthen,

[0115] (ii) collapse.

[0116] (iii) Collapse and elongation at the same time.

[0117] (iv) Collapse of the additional sheath material.

[0118] (v) Collapse and subsequent elongation of the additional sheath material.

[0119] (vi) Collapse and simultaneous elongation of the additional sheath material.

[0120] As a blank, this document relates to a preform obtained by the collapse and / or elongation of a primary preform and thus falling under the definition of a secondary preform. Typically, it is covered with an additional sheath material before or during the drawing of the hollow fiber.

[0121] Stretching / collapse

[0122] During stretching, the nascent preform is hot-stretched. Stretching can be performed without simultaneous collapse. Stretching can be done to scale, such that the shape and arrangement of parts or components of the nascent preform are reflected in the stretched, elongated final product. However, during stretching, the nascent preform can also be stretched out of scale, and its geometry can be modified.

[0123] During collapse, the inner bore narrows or the annular gap between tubular components closes or narrows. Collapse is often accompanied by elongation.

[0124] Hollow core / inner jacket region / outer jacket region

[0125] The entirety comprising at least one sleeve and an ARE preform loosely housed or securely fastened within that sleeve is also referred to herein as a “nascent preform.” The nascent preform includes a hollow core and a sheath region. If an “outer sheath region” has also been manufactured (e.g., by collapsing into the entirety), and if this sheath region is to be distinguished, it is also referred to as an “inner sheath region.” The terms “inner sheath region” and “outer sheath region” are also used for corresponding regions in hollow optical fibers or in intermediate products obtained through further processing of the nascent preform.

[0126] The term "inner side of the pipe" is also used as a synonym for "inner surface of the pipe," and the term "outer side of the pipe" is also used as a synonym for "outer surface of the pipe." The term "internal bore" in conjunction with "pipe" does not imply that the internal bore has been created through a drilling process.

[0127] Balancing pressure

[0128] Balance pressure p eq It is the pressure applied during the stretching of the glass tube to prevent the glass tube from collapsing or expanding.

[0129] According to K.Schuster; J.Kobelke; A.Schwuchow; M.Leich; M.Becker; M.Rothhardt; U. J. Kirchhof; H. Bartelt; T. Geernaert, “Preparation and applications of germanium and fluorine doped microstructured fibers”; Proceedings of the International Society for Optical Engineering Conference 6588, Photonic Crystal Fiber, 658804 (May 22, 2007); doi: 10.1117 / 12.722470; Based on the inner radius (r) of the glass tube 内 ) and outer radius (r) 外 Perform the calculation according to the following formula:

[0130] p eq =(1 / r 外 +1 / r 内 )×σ (4),

[0131] Where σ is the surface tension at the drawing temperature. At the drawing temperature, σ = 0.4 N / m is suitable for quartz glass.

[0132] Ovality

[0133] In a tube with a circular cross-section, the degree of ovality is 1. In the case of a tube with an elliptical cross-section, the degree of ovality is determined by the longest cross-sectional axis A. L and the shortest cross-sectional axis A K The ratio is generated. The ovalness of the capillary blank is generated by the ovalness of its external capillaries. Attached Figure Description

[0134] The invention will now be explained in more detail with reference to exemplary embodiments and accompanying drawings. Detailed Description:

[0135] Figure 1 A photograph of the loosely assembled ARE outer tube and NE inner tube used to manufacture the capillary preform is shown in cross-sectional view.

[0136] Figure 2 This shows the result of securing the pipe ends together using a heat-bonding process. Figure 1 A complete photo of the ARE outer tube and NE inner tube.

[0137] Figure 3 The diagram illustrates the explanation of its use. Figure 2 A sketch of the steps involved in manufacturing a capillary blank as a whole.

[0138] Figure 4 a shows a cross-section of several integral parts used to manufacture capillary blanks in an idealized form.

[0139] Figure 4 b shows the use of Figure 4 A photograph of the cross-section of a capillary blank manufactured as a whole.

[0140] Figure 5 A graph is shown to illustrate the relationship between the degree of ovality and geometric parameters, and

[0141] Figure 6 A schematic cross-sectional view of a nascent preform manufactured using multiple capillary blanks is shown. Detailed Implementation

[0142] Figure 1 A precursor for manufacturing a pre-fabricated capillary preform is shown. The precursor is in the form of a loose integral 4 consisting of multiple nested outlet tubes (i.e., ARE outer tube 1 and NE inner tube 2). All tubes (1; 2) are made of quartz glass and have a circular cross-section. Their longitudinal axes extend parallel to each other and perpendicular to the plane of the paper in the given view. NE inner tube 2 abuts against the inner surface of ARE outer tube 1 through its outer surface. The outlet tubes (1; 2) differ in diameter but are substantially the same in wall thickness and length. Figure 4 Table a and Table 1 contain detailed information on the radial dimensions of the outlet pipes (1; 2) and other overall outlet pipes.

[0143] The outlet pipes (1; 2) are fused together at points in the regions of their two end faces. Local connection points are located at... Figure 2 The figure is marked with 6 in the attached diagram.

[0144] Figure 3 The method steps for further processing the integral 4 to form the capillary blank 5 are schematically illustrated. The outlet tube integral 4, fixed by means of the connection point 6, is conveyed from top to bottom through a vertically oriented longitudinal axis to an annular heating zone 7, where it is softened zone by zone, and the blank (5) is removed from the softened zone by means of the pull-out roller 8, from which the capillary blank 5 is cut. During the stretching process, the inner bore of the capillary blank is flushed with a constant helium gas flow rate of 25 ml / min. The inner bore of the outlet tubes (1; 2) remains open during this process, so that approximately the same internal pressure is established within them.

[0145] Following the softening and stretching processes, capillary blanks 5 are obtained, in which the previous outlet tubes (1; 2) are elongated and fused together along their contact surfaces. Due to the effective surface tension in the softened region, they change their cross-sectional shape to an oval shape.

[0146] This shows from Figure 4 The idealized representation of the whole of samples 1 to 6 of a and from Figure 4Comparison of photographs of capillary blanks manufactured from b. In capillary blank 5, the previous ARE outer tube (1) forms the ARE outer capillary 11, and the previous NE inner tube (2) forms the nested NE inner capillary 12. All capillaries (11; 12) show more or less oval cross-sectional areas. For one of the capillary blanks, dimension arrows are drawn by way of example, where dimension arrow A 径向 This indicates the outer diameter of the outer capillary 11 of the ARE, measured at the contact point with the inner capillary 12 of the nested NE. Here, this is also the maximum outer diameter of the outer capillary 11 of the ARE. Dimension arrow A 切向 Indicates perpendicular to A 径向 The cross-sectional dimensions of the ARE outer capillary 11 are measured. This dimension also corresponds to the minimum outer diameter of the ARE outer capillary 11. A is similarly determined for other capillary blanks. 径向 and A 切向 .

[0147] Table 1 shows the geometric cross-sectional dimensions of the outlet tubes (1; 2) of samples 1 to 6 and the capillary blanks drawn from them, as well as factors 1 to 4 for the above equation (3) for the geometric parameters calculated based on these data.

[0148] Table 1

[0149]

[0150] Here :

[0151] OD_ARE: Outer diameter of the ARE outer tube

[0152] ID_ARE: Inner diameter of the outer tube of the ARE pipe.

[0153] OD_NE: Outer diameter of the NE inner tube

[0154] ID_NE: Inner diameter of the NE inner tube

[0155] OD_ARE _cap ARE outer capillary diameter

[0156] WT_ARE _cap : ARE external capillary wall thickness

[0157] p eq_ARE The equilibrium pressure of the ARE inner tube is calculated according to formula (2), where σ = 400 N / mm.

[0158] p eq_NE The equilibrium pressure of the inner tube of NE is calculated according to formula (1), where σ = 400 N / mm.

[0159] A 径向 : The short elliptical axis of the external capillary of ARE

[0160] A 切向 : The short elliptical axis of the external capillary of ARE

[0161] Cross-sectional area of ​​CSA_ARE AR outer tube

[0162] CSA_ARE _cap Cross-sectional area of ​​the external capillary of ARE

[0163] *1) These are not measurement data, but rather target diameter values ​​calculated under assumed ratios (the actual proportional diameter reduction due to elongation).

[0164] In samples 1 and 2, the geometric parameters are less than 77.5 and the ovalness is less than 1.025. These are examples of the present invention; samples 3 to 6 are comparative examples.

[0165] exist Figure 5 In the illustration, the degree of ovalness “O” determined on the capillary blanks of samples 1 to 6 is plotted relative to the dimensionless geometric parameter “P(geometry)”. Accordingly, the degree of ovalness and the geometric parameter scale very well, i.e., largely independent of the drawing temperature and the feed and draw speeds. The linear equation of the regression line is y = 0.9682 + 0.008x, where R0 2 = 0.9886. This relationship allows for specific adjustments or predictions of the desired ovalness of the capillary blank by specifying the geometric cross-sectional dimensions.

[0166] Samples 1 through 7, exhibiting a linear relationship, have medium to large wall thicknesses. More specifically, they cover 238.8 mm² of the cross-sectional area (CSA cross-sectional area) of the ARE outer tube. 2 up to 863.9mm 2 The large span and the 5.95mm² cross-sectional area of ​​the ARE external capillary 2 Up to 15.17mm 2 The same wide range. Cross-sectional area ratio (CSA_ARE / CSA_ARE) _cap It ranges from 28.75 to 57.68.

[0167] It cannot be ruled out that, in the case of very thin-walled samples with a large surface area to volume ratio, other effects (such as, for example, the heating and cooling behavior of the sample) may take effect, leading to slightly different regression lines. Cross-sectional area ratio (CSA_ARE / CSA_ARE) _cap The ovalness of samples with a value higher than 25, especially higher than 28, can also be predicted very well using the above linear equation.

[0168] In samples 1 through 6, the outlet tube is composed of undoped quartz glass. The linear relationship according to formula (3) also applies to doped quartz glass. Optionally, different surface tensions result in different equilibrium pressures depending on the factor (F1).

[0169] Figure 6 A cross-section of the nascent preform 15 constructed using the capillary blank 5 of Sample 1 (Table 1) is schematically shown. This represents an intermediate product for manufacturing hollow optical fibers. The nascent preform 15 consists of a sleeving 14 made of quartz glass, with a length of 1000 mm, an outer diameter of 30 mm, and an inner diameter of 24 mm. In each case, all capillary blanks 5 exist as a combined unit consisting of a nested structural element composed of an outer ARE capillary 11 and a nested inner NE capillary 12. The outer ARE tube 11 has an outer diameter of 7.46 mm, and the nested inner NE tube 12 has an outer diameter in the region of 4.6 mm. All structural elements (11; 12) have the same wall thickness of 0.37 mm. The lengths of the outer ARE tube 11 and the nested inner ARE tube 12 correspond to the length of the sleeving 14.

[0170] The sleeve 14 is manufactured in a vertical drawing process with a two-stage elongation process without molding tools. In the first stage, a hollow outlet cylinder made of glass is mechanically processed to set the final dimensions of the hollow outlet cylinder. According to the final dimensions, the outer diameter is 90 mm, and the diameter ratio of the outer diameter to the inner diameter is 2.5. In the first elongation process, the outlet cylinder with a vertically oriented longitudinal axis is continuously fed into a heating zone with a length of 200 mm, in which it is softened by region, and the intermediate cylinder is removed from the softened zone. In the second elongation process, the intermediate cylinder with a vertically oriented longitudinal axis is continuously fed into different heating zones with a length of 100 mm, in which it is softened by region, and the tube portion is removed from the softened zone. The sleeve is obtained from the continuous tube by cutting the continuous tube to a certain length.

[0171] The capillary blank 5 is secured to the inner wall of the sleeve 14 by means of a SiO2-based bonding compound 16. The bonding compound 16 is locally applied to the inner surface of the sleeve in the end region, and the capillary blank 5 is placed thereon using a positioning template having a structurally predetermined star-shaped retaining arm arrangement for the individual capillary blank 5. In this case, the positioning template is limited to the region around the ends of both end faces of the sleeve.

[0172] The nascent preform 15 thus manufactured is thermally stretched during the elongation process to form a so-called "blank bar" with an outer diameter of 20 mm. In this case, the capillary blank 5 is attached to the inner wall of the sleeve 14 along its entire length. The stretched sleeve 14 is then collected by a collecting cylinder made of quartz glass, wherein the collecting cylinder collapses onto the stretched sleeve 14, and simultaneously, the entire assembly is elongated to form a secondary preform. The collecting cylinder has an outer diameter of 75 mm and a wall thickness of 25 mm.

[0173] During the collapse and elongation process, the coaxial arrangement of the sleeve 1 and the buffer tube from below in the vertically oriented longitudinal axis is fed into the temperature-controlled heating zone, where it is softened zone by zone starting from the upper end of the arrangement.

[0174] The heating zone is maintained at a target temperature of 1600℃, with a control accuracy of + / -0.1℃. Temperature fluctuations during the thermoforming process can thus be limited to less than + / -0.5℃.

[0175] During the collapse and elongation steps, the gap between the collecting cylinder and the billet is evacuated.

[0176] The secondary preform formed in this way during the collapse and elongation process has an outer diameter of 50 mm and a sheath wall thickness of 19.55 mm (inner diameter: 10.9 mm), consisting of an outer sheath and an inner sheath. The secondary preform is elongated to form an anti-resonant hollow fiber. For this purpose, all structural elements of the prior capillary preform 5 are closed using the aforementioned sealing or bonding compound. The sealing compound is applied only to the upward-facing end face of the capillary preform during the fiber drawing process.

[0177] The same end face is then connected to a retaining tube made of quartz glass, which also serves as a gas connection. The retainer is secured to the collecting cylinder and sleeve by means of a sealing or adhesive compound. During fiber drawing, with the longitudinal axis oriented vertically, the secondary preform is fed from above into a temperature-controlled heating zone, where it is softened zone by zone, starting from the lower end. The heating zone is maintained at a target temperature of approximately 2100°C, with a control accuracy of + / -0.1°C. Temperature fluctuations during the thermoforming process are thus limited to less than + / -0.5°C. Simultaneously, gas is supplied to the core region (hollow core) to establish an internal pressure of 4 mbar within the core region.

[0178] By using this controlled fiber drawing process, an anti-resonant hollow fiber with an embedded anti-resonant element was obtained, which has a circular cross-sectional shape.

Claims

1. A method for manufacturing an anti-resonant hollow optical fiber, the anti-resonant hollow optical fiber comprising a hollow core extending along the longitudinal axis of the optical fiber and an inner sheath region surrounding the hollow core, The inner sheath region includes multiple anti-resonant elements, and the method includes the following steps: (a) Providing a sleeve (14), the sleeve including an inner bore and a longitudinal axis of the sleeve, with sleeve walls defined by inner and outer sides extending along the longitudinal axis. (b) Providing a tubular anti-resonant element preform, at least a portion of which exists as a capillary blank (5) comprising at least one ARE outer capillary (11) and at least one nested NE inner capillary (12) connected to the inner surface of the ARE outer capillary (11), wherein the manufacture of the capillary blank comprises the following method steps: (b1) will have an outer diameter OD NE and inner diameter ID NE The NE inner tube (2) is fixed to a tube with an outer diameter OD. ARE and inner diameter ID ARE On the inner surface of the ARE outer tube (1), To form a complete capillary blank, (b2) The capillary blank is hot-stretched integrally to form the capillary blank (5). The capillary blank has a maximum outer diameter OD ARE_cap and maximum wall thickness WT ARE_cap , (c) The capillary blank (5) is mounted at a target position on the inner side of the sleeve wall to form a nascent preform (15) including a hollow region and an inner sheath region, and (d) Lengthening the primary preform (15) to form the hollow fiber, or further processing the primary preform (15) to form a secondary preform from which the hollow fiber is drawn. Its characteristic is that the geometric dimension OD NE ID NE OD ARE ID ARE and OD ARE_cap and WT ARE_cap The capillary blanks (5) are aligned relative to each other in such a way that the outer capillaries (11) of the ARE have an ovalness of less than 1.

025. The geometric dimensions are set by combining the following factors F1 to F4: The equilibrium pressure p of the NE inner tube (2) mentioned in F1 eg_NE The balancing pressure p of the outer tube (1) of the ARE eq_ARE The ratio, The distance between the ARE outer tube (1) and the NE inner tube (2) relative to the inner diameter (ID) of the ARE outer tube (1) is... ARE -OD NE ) / ID ARE , F3 during the overall hot stretching of the capillary blank according to method step (b2) has a taper ratio OD. ARE / OD ARE_cap , The ratio of the outer diameter to the wall thickness of the capillary blank (5) described in F4 is OD ARE_cap / WT ARE_cap ,as well as The diameter of the ARE outer tube or NE inner tube is selected such that the balancing pressure p eq,NE Within the range of 60 Pa to 90 Pa, and the equilibrium pressure p eq_ARE Within the range of 25 Pa to 50 Pa.

2. The method according to claim 1, characterized in that, The diameter of the ARE outer tube or NE inner tube is selected such that the balancing pressure p eq,NE Within the range of 65 Pa to 80 Pa, and the equilibrium pressure p eq_ARE Within the range of 30Pa to 40Pa.

3. The method according to claim 1, characterized in that, The equilibrium pressure p eq；NE and p eq；ARE It is advantageously configured such that the factor F1 takes a value in the range of 1.5 to 2.

5.

4. The method according to claim 1, characterized in that, The equilibrium pressure p eq；NE and p eq；ARE It is advantageously configured such that the factor F1 takes a value in the range of 1.5 to 2.

5. The method according to claim 1, characterized in that, Set the factor F2 to a value in the range of 0.2 to 0.

5.

6. The method according to claim 1, characterized in that, The factor F2 is set to a value in the range of 0.3 to 0.

4.

7. The method according to claim 1, characterized in that, Set the factor F3 to a value in the range of 5 to 10.

8. The method according to claim 1, characterized in that, Set the factor F3 to a value in the range of 5 to 8.

9. The method according to claim 1, characterized in that, Set the factor F4 to a value in the range of 15 to 25.

10. The method according to claim 1, characterized in that, Set the factor F4 to a value in the range of 15 to 20.

11. The method according to claim 1, characterized in that, The mathematical product of factors F1 to F4 restricts the geometric parameters. It is in the range of 35 to 75.

12. The method according to claim 1, characterized in that, The mathematical product of factors F1 to F4 restricts the geometric parameters. It falls within the range of 40 to 60.

13. The method according to any one of claims 1-12, characterized in that, The nascent preform (15) has an outer diameter in the range of 26 mm to 230 mm.

14. The method according to any one of claims 1-12, characterized in that, The nascent preform (15) has an outer diameter in the range of 30 mm to 200 mm.

15. A method for manufacturing a nascent preform (15) of an anti-resonant hollow optical fiber, the anti-resonant hollow optical fiber comprising a hollow core extending along the longitudinal axis of the optical fiber and an inner sheath region surrounding the hollow core, the inner sheath region comprising a plurality of anti-resonant elements, the method comprising the following steps: (a) Providing a sleeve (14), the sleeve including an inner bore and a longitudinal axis of the sleeve, with sleeve walls defined by inner and outer sides extending along the longitudinal axis. (b) Providing a tubular anti-resonant element preform, at least a portion of which exists as a capillary blank (5) comprising at least one ARE outer capillary (11) and at least one nested NE inner capillary (12) connected to the inner surface of the ARE outer capillary (11), wherein the manufacture of the capillary blank (5) comprises the following method steps: (b1) will have an outer diameter OD NE and inner diameter ID NE The NE inner tube (2) is fixed to a tube with an outer diameter OD. ARE and inner diameter ID ARE On the inner surface of the ARE outer tube (1), To form a complete capillary blank, (b2) The capillary blank is hot-stretched integrally to form the capillary blank (5). The capillary blank has a maximum outer diameter OD ARE_cap and maximum wall thickness WT ARE_cap , (c) The capillary blank (5) is mounted at a target position on the inner side of the sleeve wall to form a nascent preform (15) including a hollow region and an inner sheath region, and (d) Optionally, the primary preform (15) is further processed to form a secondary preform of the hollow optical fiber, wherein the further processing includes performing one or more of the following thermoforming processes once or repeatedly: (i) Lengthen, (ii) collapse. (iii) Collapse and elongation at the same time. (iv) Collapse of the additional sheath material. (v) Collapse and subsequent elongation of the additional sheath material. (vi) Collapse and simultaneous elongation of the additional sheath material. Its characteristic is that the geometric dimension OD NE ID NE OD ARE ID ARE and OD ARE_cap and WT ARE_cap The capillary blanks are aligned relative to each other in such a way that the outer capillaries of the ARE have an ovalness of less than 1.

025. The geometric dimensions are set by combining the following factors (F1) to (F4): The equilibrium pressure p of the NE inner tube (2) mentioned in F1 eg_NE The balancing pressure p of the outer tube (1) of the ARE eq_ARE The ratio, The distance between the ARE outer tube (1) and the NE inner tube (2) relative to the inner diameter (ID) of the ARE outer tube (1) is... ARE -OD NE ) / ID ARE , F3 during the overall hot stretching of the capillary blank according to method step (b2) has a taper ratio OD. ARE / OD ARE_cap , The ratio of the outer diameter to the wall thickness of the capillary blank (5) described in F4 is OD ARE_cap / WT ARE_cap ,as well as The diameter of the ARE outer tube or NE inner tube is selected such that the balancing pressure p eq,NE Within the range of 60 Pa to 90 Pa, and the equilibrium pressure p eq_ARE Within the range of 25 Pa to 50 Pa.

16. A capillary blank (5) as an intermediate product for manufacturing anti-resonant hollow optical fiber, the capillary blank comprising at least one ARE outer capillary (11) and at least one nested NE inner capillary (12) connected to the inner surface of the ARE outer capillary (11), The manufacturing of the capillary blank includes the following steps: (b1) will have an outer diameter OD NE and inner diameter ID NE The NE inner tube (2) is fixed to a tube with an outer diameter OD. ARE and inner diameter ID ARE On the inner surface of the ARE outer tube (1), To form a complete capillary blank, (b2) The capillary blank is thermally stretched integrally to form the capillary blank (5), the capillary blank having a maximum outer diameter OD. ARE_cap and maximum wall thickness WT ARE_cap , Its features are, Geometric Dimensions (OD) NE ID NE OD ARE ID ARE and OD ARE_cap and WT ARE_cap The capillary blanks (5) are aligned relative to each other in such a way that the outer capillaries (11) of the ARE have an ovalness of less than 1.

025. The geometric dimensions are set by combining the following factors F1 to F4: The equilibrium pressure p of the NE inner tube (2) mentioned in F1 eg_NE The balancing pressure p of the outer tube (1) of the ARE eq_ARE The ratio, The distance between the ARE outer tube (1) and the NE inner tube (2) relative to the inner diameter (ID) of the ARE outer tube (1) is... ARE -OD NE ) / ID ARE , F3 during the overall hot stretching of the capillary blank according to method step (b2) has a taper ratio OD. ARE / OD ARE_cap , The ratio of the outer diameter to the wall thickness of the capillary blank (5) described in F4 is OD ARE_cap / WT ARE_cap ,as well as The diameter of the ARE outer tube or NE inner tube is selected such that the balancing pressure p eq,NE Within the range of 60 Pa to 90 Pa, and the equilibrium pressure p eq_ARE Within the range of 25 Pa to 50 Pa.

17. A preform for anti-resonant hollow optical fiber, wherein the preform includes a hollow region and a sheath region, the sheath region including a sleeve (14) having a sleeve wall and a plurality of tubular anti-resonant element preforms disposed on the inner side of the sleeve wall, characterized in that, At least a portion of the anti-resonant element preform is designed as the capillary blank (5) according to claim 16.

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