Quartz-based hollow core optical fiber with a composite cladding structure

Abstract

This application relates to the field of optical fiber technology and discloses a quartz-based hollow-core optical fiber with a composite cladding structure, comprising: a first cladding, configured as a honeycomb structure with a hollow rectangular region in the center, the honeycomb structure including periodically arranged air holes; a second cladding, disposed within the rectangular region, the second cladding including paired arc-shaped walls protruding towards the geometric center of the rectangular region, the paired arc-shaped walls being symmetrically bonded to at least one pair of opposite sides of the first cladding within the rectangular region; a core region, the first and second claddings enclosing the core region; and a sleeve layer covering the outside of the first cladding. Thus, based on the photonic bandgap cladding, the directional introduction of anti-resonant arc-shaped wall cladding suppresses the coupling between the surface mode and the core mode within the core wall in the corresponding direction, achieving precise control of the coupling between different polarization states of the surface mode and the core mode, reducing the difficulty of controlling the coupling between the surface mode and the core mode, facilitating the generation of high birefringence, and realizing polarization-maintaining transmission in the hollow-core optical fiber.

Description

Technical Field

[0001] This application relates to the field of optical fiber technology, and in particular to a quartz-based hollow optical fiber with a composite cladding structure. Background Technology

[0002] In recent years, with the continuous improvement of microstructure hollow fiber fabrication technology and characterization measurement techniques, the optical performance of hollow fibers has been significantly developed. Photonic Bandgap Hollow-core Fiber (PBG-HCF) is one of the mainstream hollow fibers. It forms a photonic bandgap through a periodically distributed quartz cladding structure, confining light of specific wavelengths within the hollow core region to achieve low-loss transmission. This unique light-guiding mechanism fundamentally overcomes the limitations imposed on optical waveguide performance by material response in traditional solid fibers. Compared to traditional solid fibers, PBG-HCF offers advantages such as low transmission loss, low nonlinearity, low dispersion, and low transmission delay, demonstrating unique application potential in fields such as optical fiber communication, optical fiber sensing, industrial processing, and biomedicine.

[0003] However, controlling the polarization state of the transmission mode is one of the key issues that urgently needs to be addressed in the further application of PBG-HCF. Since the guiding medium of this type of fiber is air, it cannot achieve mode polarization-maintaining transmission by applying thermal or mechanical stress to induce birefringence, as is the case with traditional solid-core fibers. Existing solutions mainly introduce geometric birefringence by constructing special core geometries, but geometric deformation disrupts the fiber's structural uniformity, leading to higher transmission losses. A special type of cladding mode, called the surface mode (SM), exists in PBG-HCF and is located within the core wall structure. When the phase-matching condition is met, the surface mode couples with the core mode, causing a sudden change in core mode dispersion. This characteristic can be used to control the dispersion of different polarization modes, thereby controlling the overall birefringence of the fiber and achieving high birefringence optical properties. The coupling wavelength and intensity of the surface mode and the core mode are directly related to the distribution of the core wall material. Theoretically, the surface mode can be controlled by adjusting the core wall thickness. However, during the actual fiber drawing process, the core wall material flows laterally in the molten state due to surface tension, causing the material distribution to deviate from ideal conditions, making it difficult to precisely control the coupling wavelength of surface modes with different polarization states. Summary of the Invention

[0004] The summary section introduces a series of simplified concepts, which will be further explained in detail in the detailed description section. This section of the application is not intended to limit the key features and essential technical features of the claimed technical solution, nor is it intended to determine the scope of protection of the claimed technical solution.

[0005] An embodiment of this application provides a quartz-based hollow-core optical fiber with a composite cladding structure, comprising: a first cladding layer configured as a honeycomb structure of a rectangular region with a hollow center, the honeycomb structure including periodically arranged hexagonal air holes; a second cladding layer disposed within the rectangular region, the second cladding layer including paired arcuate walls protruding toward the geometric center of the rectangular region, the paired arcuate walls being symmetrically bonded to the first cladding layer containing at least one pair of opposite sides of the rectangular region; a core region, the first cladding layer and the second cladding layer together forming the core region, the core region and the rectangular region being concentrically disposed; and a sheath layer covering the outside of the first cladding layer.

[0006] For example, pairs of arcuate walls are symmetrically bonded to a set of opposite sides of a rectangular region. The minimum distance between the geometric center of the rectangular region and the first cladding is the first distance, and the minimum distance between the geometric center of the rectangular region and the second cladding is the second distance. The first distance and the second distance may be equal or unequal. The first distance is 5 to 20 times the center wavelength of the transmitted light, and the second distance is 5 to 20 times the center wavelength of the transmitted light.

[0007] For example, pairs of curved walls are symmetrically bonded to two sets of opposite sides of a rectangular area, and the wall thicknesses of the curved walls corresponding to the two sets of opposite sides are not equal.

[0008] For example, the rectangular region includes a first side that coincides with the chord of the arcuate wall and a second side adjacent to the first side, wherein the chord length of the arcuate wall is less than or equal to the side length of the first side and the arc height of the arcuate wall is less than or equal to half the side length of the second side.

[0009] For example, the number of arc-shaped walls located on the same side of the rectangular area is one or at least two, with at least two arc-shaped walls arranged in a nested manner.

[0010] For example, the honeycomb structure includes a first wall that encloses a rectangular area and a second wall located outside the rectangular area and not adjacent to the sleeve layer. The thickness of the first wall is greater than half the thickness of the second wall and less than twice the thickness of the second wall.

[0011] For example, the porosity of the honeycomb structure is greater than 90%, the center wavelength of the transmitted light ranges from 800 nm to 3500 nm, and the spacing between the air holes is from 2.4 μm to 10.6 μm.

[0012] For example, the honeycomb structure is formed by stacking circular capillaries in a hexagonal close-packing manner, and the rectangular area is formed by removing part of the capillaries. The gap between adjacent capillaries is eliminated by heating and drawing negative pressure. The number of capillary layers in the honeycomb structure from the inside out is greater than or equal to 5 layers.

[0013] For example, the wall thickness t of the arc-shaped wall satisfies the principle of the anti-resonant reflecting waveguide, that is, it satisfies the following:

[0014] Where, λ res The resonant wavelength, n 1 represents the refractive index of the second cladding quartz glass. n 0 represents the refractive index of the medium filling the fiber core region, and m is a positive integer.

[0015] For example, the wall thickness of the sleeve layer is greater than or equal to 30 μm, and the refractive index of the quartz glass used in the sleeve layer is not higher than the refractive index of the quartz glass used in the first cladding layer.

[0016] The embodiments of this application provide a design for a quartz-based hollow fiber with a composite cladding structure. The hollow fiber is based on a photonic bandgap cladding, and an anti-resonant arc-shaped wall cladding is directionally introduced to suppress the coupling between the surface mode and the core mode in the core wall in this direction without affecting the coupling between the surface mode and the core mode in the orthogonal direction. This significantly reduces the difficulty of controlling the coupling between the surface mode and the core mode, and makes it easy to achieve optical characteristics of high birefringence and low confinement loss in the transmission band.

[0017] Compared with the prior art, the advantages of the quartz-based hollow-core optical fiber with composite cladding structure provided in this application are as follows: 1. Conventional low-loss birefringent photonic bandgap hollow-core fibers introduce birefringence through core geometry deformation, but the order of magnitude of birefringence can only reach 10. -5 This design achieves up to 10 through the coupling of surface mode and core mode. -3 Up to 10 -2 It exhibits birefringence while simultaneously satisfying low-loss transmission.

[0018] 2. Conventional birefringent photonic bandgap hollow fiber achieves surface mode control and birefringence by adjusting the core wall thickness. However, the surface tension of the material during the fabrication process leads to imperfect distribution of the core wall structure material, resulting in irregular coupling between core modes and surface modes of different polarization states. Using the arc-shaped wall structure of quartz glass can effectively suppress the coupling between surface modes and core modes in specific directions, thereby achieving effective control of the coupling between surface modes and core modes.

[0019] 3. This solution allows for adjustable movement of the transmission window from visible light to infrared light by adjusting the spacing between the hexagonal air holes. The coupling wavelength between the surface mode and the core mode can be adjusted by regulating the wall thickness of the second cladding arc-shaped wall.

[0020] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0021] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. Wherein: Figure 1 A schematic diagram of the cross-section of the hollow optical fiber provided in Embodiment 1 of this application is shown; Figure 2 A cross-sectional structural schematic diagram of the first cladding layer provided in Embodiment 1 of this application is shown; Figure 3 A schematic diagram of the cross-section of the rectangular regions of the second cladding and the first cladding provided in Embodiment 1 of this application is shown; Figure 4 A schematic diagram of the cross-section of the hollow optical fiber provided in Embodiment 2 of this application is shown; Figure 5 A schematic diagram of the cross-section of the rectangular regions of the second cladding and the first cladding provided in Embodiment 2 of this application is shown; Figure 6 The diagram shows the variation of effective refractive index and confinement loss of hollow-core optical fiber under different polarization modes provided in Embodiment 1 of this application; Figure 7 The diagram shows the mode field distribution of fundamental modes of different polarization states near the surface mode coupling wavelength of the hollow optical fiber provided in Embodiment 1 of this application; Figure 8 The diagram showing the relationship between group birefringence and wavelength of the hollow-core optical fiber provided in Embodiment 1 of this application is illustrated. Figure 9 The diagram shows the variation of effective refractive index and confinement loss of hollow-core optical fiber under different polarization modes provided in Embodiment 2 of this application; Figure 10 The diagram shows the mode field distribution of fundamental modes of different polarization states near the surface mode coupling wavelength of the hollow optical fiber provided in Embodiment 2 of this application; Figure 11 The diagram shows the relationship between group birefringence and wavelength of the hollow fiber provided in Embodiment 2 of this application.

[0022] in, Figures 1 to 5 The correspondence between the reference numerals and component names in the attached drawings is as follows: 110 First cladding, 111 Rectangular region, 1111 First side, 1112 Second side, 112 Air hole, 113 First wall, 114 Second wall, 115 Capillary, 120 Second cladding, 121 Outer arcuate wall, 122 Inner arcuate wall, 130 Core region, 140 Sleeve layer. Detailed Implementation

[0023] The following description provides numerous specific details to offer a more thorough understanding of the technical solutions provided in this application. However, it will be apparent to those skilled in the art that the technical solutions provided in this application can be implemented without one or more of these details.

[0024] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or combinations thereof.

[0025] Exemplary embodiments according to this application will now be described in more detail with reference to the accompanying drawings. However, these exemplary embodiments may be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. It should be understood that these embodiments are provided so that the disclosure of this application is thorough and complete, and that the concept of these exemplary embodiments is fully conveyed to those skilled in the art.

[0026] like Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown in the embodiment of this application, a quartz-based hollow-core optical fiber with a composite cladding structure is provided, comprising: a first cladding 110, which is configured as a honeycomb structure of a rectangular region 111 with a hollow center, the honeycomb structure including periodically arranged hexagonal air holes 112; a second cladding 120, disposed within the rectangular region 111, the second cladding 120 including paired arcuate walls protruding toward the geometric center of the rectangular region 111, the paired arcuate walls being symmetrically bonded to the first cladding 110 where at least one pair of opposite sides of the rectangular region 111 are located; a core region 130, which is formed by the first cladding 110 and the second cladding 120, the core region 130 and the rectangular region 111 being concentrically disposed; and a sleeve layer 140, which covers the outside of the first cladding 110.

[0027] The quartz-based hollow optical fiber with a composite cladding structure provided in this application embodiment includes a first cladding 110, a second cladding 120, a core region 130, and a sheath layer 140. That is, the hollow optical fiber is a composite cladding structure including the first cladding 110 and the second cladding 120, and its material is quartz glass. The core region 130 is a hollow region located at the center of the hollow optical fiber, and its boundary is jointly defined by the composite cladding composed of the first cladding 110 and the second cladding 120. The first cladding 110 is a honeycomb structure formed by periodically arranged capillaries 115 and air holes 112 made of quartz glass. The shape of the air holes 112 can be hexagonal; specifically, the air holes 112 can be rounded hexagons. A hollow rectangular region 111 is set in the middle of the honeycomb structure. The geometric center of the rectangular region 111 is concentric with the geometric center of the core region 130, that is, the geometric center of the rectangular region is the center of the hollow optical fiber. The second cladding 120 consists of paired arc-shaped walls. Specifically, the arc-shaped walls are made of quartz glass, with the convex side of the arc-shaped walls facing the center of the optical fiber, i.e., the convex part of the arc-shaped walls facing the geometric center of the rectangular region 111. The paired arc-shaped walls are symmetrically bonded to the first cladding 110 where at least one pair of opposite sides of the rectangular region 111 are located. That is, the arc-shaped walls can be bonded to one or two pairs of opposite sides of the rectangular region 111. The paired arc-shaped walls are centrally symmetrically distributed with respect to the geometric center of the rectangular region 111. The sleeve layer 140 is made of quartz glass and is wrapped around the outside of the first cladding 110. The sleeve layer 140 and the honeycomb structure of the first cladding 110 are fused together without gaps.

[0028] Therefore, the quartz-based hollow-core optical fiber with a composite cladding structure provided in this embodiment utilizes the structure of the first cladding 110 to form a photonic bandgap, confining light of a specific wavelength within the hollow core region 130 to achieve low-loss transmission. Simultaneously, a second cladding 120 with an anti-resonant arcuate wall is directionally introduced to suppress coupling between surface modes and core modes within the core wall in this direction without affecting the coupling between surface modes and core modes in orthogonal directions. This significantly reduces the difficulty of controlling surface mode and core mode coupling, making it easier to achieve high birefringence and low confinement loss optical characteristics within the transmission light bandwidth. Furthermore, compared to the typical core wall thickness of tens of nanometers in photonic bandgap hollow-core optical fibers, the thickness of the quartz glass arcuate wall of the second cladding 120 is typically in the hundreds of nanometers or even micrometers, greatly reducing the fabrication pressure during control and making it easier to implement.

[0029] Specifically, this type of hollow optical fiber can be used as a main device for optical fiber communication and optical fiber sensing, and has a wide range of applications in industrial manufacturing, engineering technology and biomedicine.

[0030] Furthermore, such as Figure 2 and Figure 5As shown, the paired arcuate walls of the second cladding layer 120 can be symmetrically bonded to the first cladding layer 110 containing a pair of opposite sides of the rectangular region 111. In this case, the number of pairs of arcuate walls can be one or at least two pairs. Alternatively, the paired arcuate walls of the second cladding layer 120 can be symmetrically bonded to the first cladding layer 110 containing two pairs of opposite sides of the rectangular region 111. In this case, the number of pairs of arcuate walls corresponding to a pair of opposite sides can be one or at least two pairs.

[0031] The matrix material of the hollow optical fiber includes pure quartz glass or doped quartz glass. Doped quartz glass includes germanium-doped, fluorine-doped, or other ion-doped quartz glass, such as aluminum-doped (Al) or titanium-doped quartz glass. That is, the materials of the first cladding 110, the second cladding 120, and the sleeve layer 140 can be pure quartz glass or doped quartz glass.

[0032] like Figures 1 to 5 As shown, in some embodiments provided in this application, pairs of arc-shaped walls are symmetrically bonded to a set of opposite sides of a rectangular region 111. That is, in this embodiment, arc-shaped walls are provided on a set of opposite sides of a honeycomb-structured rectangular region 111, and the fiber core region 130 is formed by at least another set of opposite sides of the rectangle and the pairs of arc-shaped walls. Thus, the hollow fiber utilizes the structure of the first cladding 110 to form a photonic bandgap, confining light of a specific wavelength within the hollow core region 130 for low-loss transmission. Then, on one hand, a surface mode is introduced using a set of opposite core walls in the central rectangular region 111 of the first cladding 110, and coupled with a certain polarization state of the fiber core fundamental mode, causing a change in the effective refractive index of the mode. On the other hand, the arc-shaped wall of the second cladding 120 is used to suppress the coupling between another polarization state of the fiber core fundamental mode and the surface mode in another set of opposite core walls in the rectangular region 111 through anti-resonant reflection. This generates high birefringence, achieving polarization-maintaining transmission in the hollow fiber, significantly reducing the difficulty of controlling the coupling between the surface mode and the core mode, and easily achieving high birefringence and low confinement loss optical characteristics within the bandwidth of the transmitted light.

[0033] like Figure 2 and Figure 3 As shown, in the above embodiment, the minimum distance between the geometric center of the rectangular region 111 and the first cladding 110 is the first distance, and the minimum distance between the geometric center of the rectangular region 111 and the second cladding 120 is the second distance. The first distance and the second distance may be equal or unequal. The first distance is 5 to 20 times the center wavelength of the transmitted light, and the second distance is 5 to 20 times the center wavelength of the transmitted light.

[0034] In this case, the geometric center of the rectangular region 111 coincides with the geometric center of the fiber core region 130, as shown below. Figure 3 As shown by point O in the diagram, the first distance can be as follows: Figure 3 As shown in a1, the second distance can be as follows: Figure 3As shown by distance a2, a1 can be equal to, less than, or greater than a2, and the center wavelength range of the transmission band can be from 800nm ​​to 3500nm, meaning the transmission band is located in the near- and mid-infrared bands. Therefore, by reasonably setting the first distance, the first distance, and the range of the center wavelength of the transmitted light, it is possible to ensure that the transmitted light in the near- and mid-infrared bands achieves high birefringence and low confinement loss optical characteristics in the fiber core region 130, thus realizing polarization-maintaining transmission in hollow-core optical fibers.

[0035] In some embodiments provided in this application, pairs of arc-shaped walls are symmetrically bonded to two sets of opposite sides of the rectangular region 111, and the wall thicknesses of the arc-shaped walls corresponding to the two sets of opposite sides are not equal. That is, in this embodiment, arc-shaped walls are provided on both sets of opposite sides of the honeycomb-structured rectangular region 111, that is, arc-shaped walls are introduced into the rectangular region 111 in two orthogonal directions, that is, arc-shaped walls are provided on all four sides of the rectangular region 111, and the core region 130 is enclosed by arc-shaped walls in at least four directions. By making the wall thicknesses of the arc-shaped walls corresponding to the two sets of opposite sides of the rectangular region 111 unequal, the mode coupling degree between the core mold and the arc-shaped walls is different, thereby introducing birefringence and achieving a polarization-maintaining effect.

[0036] like Figure 3 and Figure 5 As shown, in some embodiments provided in this application, the rectangular region 111 includes a first side 1111 that coincides with the chord of the arcuate wall and a second side 1112 that is adjacent to the first side 1111. The chord length of the arcuate wall is less than or equal to the side length of the first side 1111, and the arc height of the arcuate wall is less than or equal to half the side length of the second side 1112.

[0037] In this embodiment, the chord of the arc-shaped wall coincides with the edge of the rectangular region 111 on the same side. The edge in the rectangular region 111 that coincides with the arc-shaped wall is defined as the first edge 1111, and the edge in the rectangular region 111 that is adjacent to the first edge 1111 is defined as the second edge 1112. That is, the rectangular region 111 includes a pair of first edges 1111 and a pair of second edges 1112. By reasonably setting the chord length and arc height of the arc-shaped wall, the chord length of the arc-shaped wall is less than or equal to the side length of the first edge 1111, and the arc height of the arc-shaped wall is less than or equal to half the side length of the second edge 1112. This ensures that the two ends of the arc-shaped wall can coincide with the first cladding 110 of the first edge 1111 on the same side, and that the paired arc-shaped walls will not interfere with each other. They can be reasonably arranged within the rectangular region 111, so that there is a medium-space gap between the arc-shaped wall and the first edge 1111 on the same side. The double-layer arc-shaped wall enhances reflection, further reduces loss, and suppresses mode coupling.

[0038] like Figure 3 and Figure 5As shown, in some embodiments provided by the present application, the number of arc-shaped walls on the same side of the rectangular region 111 is one or at least two, and at least two arc-shaped walls are arranged in a nested manner in sequence.

[0039] In this embodiment, the number of arc-shaped walls provided on a pair of opposite sides of the rectangular region 111 can be one pair, two pairs, three pairs, or other numbers of pairs to meet different polarization-maintaining effects. Specifically, Figure 3 in the rectangular region 111, the number of arc-shaped walls provided on a pair of opposite sides is one pair, Figure 5 in the rectangular region 111, the number of arc-shaped walls provided on a pair of opposite sides is two pairs.

[0040] As Figure 5 shown, when at least two pairs of arc-shaped walls are provided on a pair of opposite sides of the rectangular region 111, that is, when the number of arc-shaped walls on the same side of the rectangular region 111 is at least two, at least two arc-shaped walls are arranged in a nested manner in sequence. Thus, it is ensured that there is a middle space gap between adjacent arc-shaped walls, and the reflection is strengthened by the double-layer arc-shaped walls to further reduce the loss and suppress the mode coupling.

[0041] Furthermore, each pair of arc-shaped walls has an axisymmetric structure, and at least two arc-shaped walls on the same side of the rectangular region 111 are arranged in a nested manner with each other.

[0042] As Figure 1 shown, in some embodiments provided by the present application, the honeycomb structure includes a first wall 113 surrounding the rectangular region 111 and a second wall 114 located outside the rectangular region 111 and not adjacent to the sleeve layer 140. The thickness of the first wall 113 is greater than half of the thickness of the second wall 114 and less than twice the thickness of the second wall 114. Among them, the wall thickness of the first wall 113 is as Figure 1 shown by T in Figure 1 and the wall thickness of the second wall is as

[0043] shown by d in

[0044] In some embodiments provided in this application, the porosity of the honeycomb structure is greater than 90%, the center wavelength of the transmitted light ranges from 800 nm to 3500 nm, and the spacing between the air holes 112 is from 2.4 μm to 10.6 μm.

[0045] In this embodiment, by matching the high porosity of the first cladding layer 110 with a suitable pore spacing, a photonic bandgap is formed in the 800nm ​​to 3500nm band, realizing low-loss constrained transmission of light, while taking into account wide transmission bandwidth, high damage threshold and low nonlinearity.

[0046] Porosity refers to the percentage of pore volume in a material to its total volume. Setting the porosity of the honeycomb structure of the first cladding layer 110 to be greater than 90% results in a lower overlap between light and quartz glass, thereby avoiding additional optical coupling leakage and facilitating the formation of a wider photonic bandgap to ensure low-loss transmission of the target light wavelength.

[0047] The air holes 112 in the honeycomb structure have a spacing of 2.4μm to 10.6μm, matching the center wavelength of the bandgap from 800nm ​​to 3500nm. Specifically, the 800nm ​​short wavelength can be matched with a 2.4μm spacing, while the 3500nm mid-infrared long wavelength can be matched with a 10.6μm spacing. Thus, the adjustment of the spacing from 2.4μm to 10.6μm can realize the position shift of the photonic bandgap with a center wavelength from 800nm ​​to 3500nm, adapting to the transmission needs of different scenarios such as laser processing, spectral detection, communication, and biomedicine.

[0048] Specifically, the porosity of the honeycomb structure can be 91%, 94%, 96%, 98%, or other values. The center wavelength of the transmitted light can be 920nm, 1064nm, 1550nm, or other wavelengths. The spacing between the air holes 112 can be 2.4μm, 3.6μm, 4.4μm, 6.6μm, 8.6μm, 10.6μm, or other sizes.

[0049] like Figure 2 As shown, in some embodiments provided in this application, the honeycomb structure is formed by stacking circular capillaries 115 in a hexagonal close-packing manner, the rectangular region 111 is configured to be formed by removing part of the capillaries 115, the gap between adjacent capillaries 115 is eliminated by heating and drawing negative pressure, and the number of layers of capillaries 115 in the honeycomb structure from the inside out is greater than or equal to 5.

[0050] This embodiment provides the manufacturing process of the first cladding layer 110. Specifically, circular quartz glass capillaries 115 are stacked in a hexagonal close-packing manner to form a honeycomb structure. A hollow rectangular region 111 is formed in the middle of the honeycomb structure by removing part of the capillaries 115. The gaps between adjacent capillaries 115 are eliminated by heating and then drawing negative pressure. The hollow structure formed by the inner wall of the capillaries 115 is the air hole 112, thus making the air hole 112 approximately a rounded hexagon.

[0051] In this embodiment, the gap between adjacent capillaries 115 is eliminated by thermal fusion and vacuuming, which can form a photonic bandgap and enhance the mechanical stability and dimensional uniformity of the fiber structure.

[0052] Among them, the number of capillary layers 115 from the inside out of the honeycomb structure is greater than or equal to 5, which can construct a lower loss photonic bandgap. At the same time, it can improve the bending resistance of hollow fiber. By scaling the size of the honeycomb structure proportionally, the center wavelength of the hollow fiber transmission band can cover the near and mid-infrared bands from 800nm ​​to 3500nm.

[0053] Specifically, the number of capillary layers 115 in the honeycomb structure from the inside out can be 5, 6, 7, or other positive integers.

[0054] In some embodiments provided in this application, the wall thickness t of the arc-shaped wall satisfies the principle of anti-resonant reflective waveguide, that is, it satisfies the following formula:

[0055] Where, λ res The resonant wavelength, n 1 represents the refractive index of the quartz glass in the second cladding layer of 120. n 0 represents the refractive index of the medium filling the 130 core region, and m is a positive integer.

[0056] In this embodiment, the wall thickness t of the arc-shaped wall satisfies the principle of an anti-resonant reflection waveguide, and the resonant wavelength λ can be determined based on the wall thickness t of the arc-shaped wall. res This causes the target wavelength λ0 to deviate from the resonant wavelength λ. res This ensures that the target light wavelength is in the anti-resonance region where low-loss transmission is possible.

[0057] The medium filled in the fiber core region 130 can be gas, liquid or vacuum.

[0058] Furthermore, the hollow / air hole 112 portion between the first cladding layer 110, the second cladding layer 120, and the first cladding layer 110 and the second cladding layer 120 can be evacuated or filled with gas or liquid.

[0059] In some embodiments provided in this application, the wall thickness of the sleeve layer 140 is greater than or equal to 30 μm, and the refractive index of the quartz glass used in the sleeve layer 140 is not higher than the refractive index of the quartz glass used in the first cladding layer 110.

[0060] In this embodiment, the wall thickness of the sheath layer 140 is greater than or equal to 30 μm, which ensures that the hollow optical fiber has good mechanical strength and bending resistance. Specifically, the wall thickness of the sheath layer 140 can be 30 μm, 50 μm, 70 μm, 90 μm, or other sizes.

[0061] The refractive index of the quartz glass used in the sleeve layer 140 is not higher than that of the quartz glass used in the first cladding layer 110. Thus, by designing a refractive index gradient or step, an internal reflection waveguide structure is formed, which can enhance the light confinement effect and suppress its leakage to the coating layer. This has a beneficial effect on avoiding the coating layer from burning due to high temperature in high-power laser transmission.

[0062] Example 1: Please refer to Figure 1 , Figure 2 and Figure 3 As shown, a quartz-based hollow optical fiber with a composite cladding structure is provided. Its structure consists of, from the inside out, a core region 130, a second cladding 120, a first cladding 110, and a sleeve layer 140.

[0063] The core region 130 is a hollow region located at the center of the hollow fiber, and its boundary is defined by a composite cladding consisting of a first cladding 110 and a second cladding 120. The second cladding 120 consists of a pair of arc-shaped walls made of quartz glass, with the convex side of the arc-shaped walls facing the center of the hollow fiber. The first cladding 110 is a honeycomb structure formed by periodically arranged circular quartz glass capillaries 115. The inner walls of the capillaries 115 form air holes 112. The center of the honeycomb structure is a hollow rectangular region 111. The geometric center of the rectangular region 111 is concentric with the geometric center of the fiber. A pair of arc-shaped walls are symmetrically bonded to the short side of the rectangular region 111, and are centrally symmetrically distributed. The sleeve layer 140 wraps around the second cladding 120 and is fused together without gaps.

[0064] In this embodiment, the hollow fiber matrix is ​​made of pure silica material. The air holes 112 formed by the capillaries 115 in the first cladding 110 have a spacing of 4.95µm, and the porosity of the honeycomb structure is 0.96. The chord length of the arc-shaped wall is 12.2µm, and the arc height is 3.85µm. The wall thickness t of the arc-shaped wall satisfies the principle of anti-resonant reflection waveguide, i.e. .

[0065] in, λ res The resonant wavelength; n1 represents the refractive index of the quartz glass with a second cladding layer of 120, i.e. n 1 can be understood as the refractive index of the capillary 115 of quartz glass; n 0 represents the refractive index of the gas filling region 130 in the fiber core; m is a positive integer. In this embodiment, the operating wavelength is the infrared band, and the target wavelength is... λ 0 is 1550nm, the second cladding layer is 120, and the capillary has a refractive index of 115. n 1. Based on the dispersion formula of pure quartz material, the value is fitted and taken as 1.44402. Air refractive index... n 0 is set to 1, m is set to 1, the wall thickness t of the arc-shaped wall is 650nm, corresponding to a resonant wavelength of 1354nm, and the target wavelength is far from the resonant wavelength.

[0066] The hollow fiber structure of Example 1 was simulated using the finite element simulation software COMSOL Multiphysics to analyze the coupling effect of different polarization states and surface modes. Figure 6 This is a graph showing the variation of effective refractive index and confinement loss for different polarization modes. Figure 7 This is a mode field distribution diagram of fundamental modes in different polarization states near the surface mode coupling wavelength. Figure 8 This is a graph showing the relationship between birefringence and wavelength.

[0067] Depend on Figure 6 It can be seen that within the entire calculation transmission window, the effective refractive index of the fundamental mode in the x-direction polarization state does not undergo significant abrupt changes, and the overall trend is relatively smooth. However, the effective refractive index of the mode in the y-direction polarization state exhibits significant abrupt changes near the wavelengths of 1524 nm and 1552 nm, causing corresponding changes in the mode dispersion of the y-direction polarization state near these wavelengths. These abrupt changes in the effective refractive index near these wavelengths indicate that the surface mode and this polarization state are coupled. Figure 7 The calculated mode field distribution near the corresponding wavelength shows that the polarization state fundamental mode in the x-direction does not change significantly at the corresponding wavelength, and the fundamental mode is confined to the core region 130 by the cladding for transmission. However, the polarization state fundamental mode in the y-direction shows significant coupling between the calculated wavelength and the surface mode, with part of the core mode field being coupled to the cladding, leading to abrupt changes in the effective refractive index of the mode at the corresponding wavelength. Furthermore, Figure 6 The fiber confinement loss curve calculated in the figure also shows that the fiber has a loss as low as 10. -3 Limiting loss in dB / m.

[0068] Depend on Figure 8It can be seen that, due to the coupling between the polarization state and the surface mode in the y-direction, the dispersion of the polarization state in the y-direction undergoes a significant abrupt change within the calculated wavelength range, while the polarization state in the x-direction shows no significant change throughout the entire calculation window, resulting in a gradual overall dispersion trend. Therefore, the highest calculated fiber group birefringence can reach 10. -2 Even higher. The above results indicate that the quartz glass arc-shaped wall added to the fiber end face structure plays a role in suppressing the coupling between the surface mode and the core mode in this direction, and achieving high birefringence performance.

[0069] Example 2: Please refer to Figure 4 and Figure 5 A quartz-based hollow optical fiber with a composite cladding structure is provided, wherein the structure consists of a core region 130, a second cladding 120, a first cladding 110, and a sleeve layer 140, from the inside out.

[0070] The core region 130 is a hollow region located at the center of the hollow fiber, and its boundary is jointly defined by a composite cladding consisting of a first cladding 110 and a second cladding 120. The second cladding 120 consists of two pairs of curved walls made of quartz glass, with the convex side of the curved walls facing the center of the hollow fiber. The first cladding 110 is a honeycomb structure formed by periodically arranged circular quartz glass capillaries 115. The inner walls of the capillaries 115 form air holes 112. The center of the honeycomb structure is a hollow rectangular region 111, and the geometric center of the rectangular region 111 is concentric with the geometric center of the optical fiber. Two pairs of arc-shaped walls are symmetrically bonded to the short side of the rectangular region 111, arranged in a centrally symmetrical manner. The two arc-shaped walls on the same side of the rectangular region 111 are nested sequentially. Specifically, the two pairs of arc-shaped walls include an outer arc-shaped wall 121 and an inner arc-shaped wall 122. The outer arc-shaped wall 121 is close to the geometric center of the rectangular region 111, and the inner arc-shaped wall 122 is nested inside the outer arc-shaped wall 121. The sleeve layer 140 wraps around the second cladding layer 120, and the two layers are fused together without gaps.

[0071] In this example, the hollow fiber matrix is ​​made of pure silica. The air holes 112 formed by the capillaries 115 in the first cladding 110 have a spacing of 4.95µm, and the porosity of the honeycomb structure is 0.96. The outer arc-shaped wall 121 has a chord length of 12.2µm and an arc height of 3.85µm, while the inner arc-shaped wall 122 nested within it has a chord length of 11.2µm and an arc height of 2.76µm. The wall thickness t of the arc-shaped wall satisfies the principle of an anti-resonant reflection waveguide, and its corresponding resonant wavelength is far from the current target wavelength band, i.e. .

[0072] Where, λ res The resonant wavelength; n 1 represents the refractive index of the quartz glass with a second cladding layer of 120, i.e.n 1 can be understood as the refractive index of the capillary 115 of quartz glass; n 0 represents the refractive index of the gas filling region 130 in the fiber core; m is a positive integer. In this embodiment, the operating wavelength is the infrared band, the target wavelength λ0 is 1550 nm, and the refractive index of the capillary 115 of the second cladding 120 is... n 1. Based on the dispersion formula of pure quartz material, the value is fitted and taken as 1.44402. Air refractive index... n 0 is set to 1, m is set to 1, the wall thickness t is 600nm, the corresponding resonant wavelength is 1250nm, and the target wavelength is far from the resonant wavelength.

[0073] The fiber optic structure of Example 2 was simulated using the finite element simulation software COMSOL Multiphysics to analyze the coupling effects of different polarization states and surface modes. Figure 9 This is a graph showing the changes in effective refractive index and corresponding confinement loss for different polarization modes. Figure 10 This is a mode field distribution diagram of fundamental modes in different polarization states near the surface mode coupling wavelength. Figure 11 It is a graph showing the relationship between the calculated group refractive index and wavelength.

[0074] Depend on Figure 9 It can be seen that within the entire computational transmission window, the effective refractive index of the fundamental mode in the y-direction polarization state does not undergo significant abrupt changes, showing a generally gradual trend. However, the effective refractive index of the mode in the x-direction polarization state undergoes a significant abrupt change near the wavelength of 1548 nm, leading to a corresponding change in the mode dispersion in the x-direction polarization state. This abrupt change in the effective refractive index near this wavelength indicates that the surface mode and this polarization state are coupled. Figure 10 The calculated mode field distribution near the corresponding wavelength shows that the polarization state fundamental mode in the y-direction shows no significant change, as it is confined to the core region by the cladding for propagation. However, the polarization state fundamental mode in the x-direction exhibits significant coupling between the calculated wavelength and the surface mode, with part of the core mode field being coupled to the cladding, leading to abrupt changes in the effective refractive index of the mode at the corresponding wavelength. Furthermore, Figure 9 The fiber confinement loss curve calculated in the figure also shows that the fiber has a loss as low as 10. -3 Limiting loss in dB / m.

[0075] Depend on Figure 11 It can be seen that, due to the coupling between the polarization state and the surface mode in the x-direction, the dispersion of the polarization state in the x-direction undergoes a significant abrupt change within the calculated wavelength range, while the polarization state in the y-direction shows no significant change throughout the entire calculation window, resulting in a gradual overall dispersion trend. Therefore, the highest calculated fiber group birefringence can reach 10. -2Even higher. The above results indicate that the curved glass wall added to the fiber end face structure plays a role in suppressing the coupling between the surface mode and the core mode in this direction, and achieving high birefringence performance.

[0076] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0077] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A quartz-based hollow core optical fiber of a composite cladding structure, characterized by, include: The first cladding layer is configured as a honeycomb structure with a hollow rectangular region in the middle, and the honeycomb structure includes periodically arranged hexagonal air holes. A second cladding layer is disposed within the rectangular area. The second cladding layer includes a pair of arcuate walls that are arranged and protrude toward the geometric center of the rectangular area. The pair of arcuate walls are symmetrically bonded to the first cladding layer containing at least one pair of opposite sides of the rectangular area. The fiber core region is formed by the first cladding layer and the second cladding layer, and the fiber core region and the rectangular region are concentrically arranged. A sheath layer, which covers the outside of the first sheath layer.

2. The quartz-based hollow optical fiber with a composite cladding structure according to claim 1, characterized in that, The paired arcuate walls are symmetrically bonded to a set of opposite sides of the rectangular region. The minimum distance between the geometric center of the rectangular region and the first cladding is the first distance, and the minimum distance between the geometric center of the rectangular region and the second cladding is the second distance. The first distance and the second distance may be equal or unequal. The first distance is 5 to 20 times the center wavelength of the transmitted light, and the second distance is 5 to 20 times the center wavelength of the transmitted light.

3. The quartz-based hollow optical fiber with a composite cladding structure according to claim 1, characterized in that, The paired arc-shaped walls are symmetrically bonded to two sets of opposite sides of the rectangular region, and the wall thicknesses of the arc-shaped walls corresponding to the two sets of opposite sides are not equal.

4. The quartz-based hollow-core optical fiber with a composite cladding structure according to any one of claims 1 to 3, characterized in that, The rectangular region includes a first side that coincides with the chord of the arcuate wall and a second side adjacent to the first side. The chord length of the arcuate wall is less than or equal to the side length of the first side, and the arc height of the arcuate wall is less than or equal to half the side length of the second side.

5. The quartz-based hollow-core optical fiber with a composite cladding structure according to any one of claims 1 to 3, characterized in that, The number of the arc-shaped walls located on the same side of the rectangular area is one or at least two, and at least two of the arc-shaped walls are arranged in a nested manner.

6. The quartz-based hollow-core optical fiber with a composite cladding structure according to any one of claims 1 to 3, characterized in that, The honeycomb structure includes a first wall that encloses the rectangular area and a second wall located outside the rectangular area and not adjacent to the sleeve layer. The thickness of the first wall is greater than half the thickness of the second wall and less than twice the thickness of the second wall.

7. The quartz-based hollow-core optical fiber with a composite cladding structure according to any one of claims 1 to 3, characterized in that, The porosity of the honeycomb structure is greater than 90%, the center wavelength of the transmitted light ranges from 800nm ​​to 3500nm, and the spacing between the air holes is from 2.4μm to 10.6μm.

8. The quartz-based hollow-core optical fiber with a composite cladding structure according to any one of claims 1 to 3, characterized in that, The honeycomb structure is formed by stacking circular capillaries in a hexagonal close-packing manner. The rectangular area is formed by removing part of the capillaries. The gaps between adjacent capillaries are eliminated by heating and drawing negative pressure. The number of capillary layers in the honeycomb structure from the inside out is greater than or equal to 5 layers.

9. The quartz-based hollow-core optical fiber of the composite cladding structure according to any one of claims 1 to 3, characterized in that, The wall thickness t of the arc-shaped wall satisfies the principle of anti-resonant reflective waveguide, that is, it satisfies the following equation: Where, λ res The resonant wavelength, n 1 represents the refractive index of the second cladding quartz glass. n 0 represents the refractive index of the medium filling the fiber core region, and m is a positive integer.

10. The quartz-based hollow-core optical fiber with a composite cladding structure according to any one of claims 1 to 3, characterized in that, The wall thickness of the sleeve layer is greater than or equal to 30 μm, and the refractive index of the quartz glass used in the sleeve layer is not higher than the refractive index of the quartz glass used in the first cladding layer.

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