Hollow-core optical fiber

Abstract

A hollow-core optical fiber comprises an outer cladding (10) and N anti-resonant components (20) located inside the outer cladding (10), wherein N is an integer greater than or equal to 1. Among the N anti-resonant components (20), there is an anti-resonant component (20) comprising at least one tubular structure. The tubular structure comprises a first surface (201) and a second surface (202), the first surface (201) is a curved surface, and the second surface (202) is a plane, or the second surface (202) is a curved surface convex in the opposite direction to the first surface (201).

Description

Hollow core optical fiber

[0001] Cross Reference to Related Applications

[0002] The present disclosure is based on and claims priority to Chinese Patent Application No. 202410994044.4, filed on July 23, 2024, entitled “Hollow Core Optical Fiber”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of transmission and bearing, and relates to, but is not limited to, a hollow core optical fiber. BACKGROUND

[0004] The mechanism of the hollow core anti-resonant optical fiber is to use the cavity composed of air and high refractive glass wall to produce anti-resonance when light passes through the high refractive glass wall, to realize the confinement of the optical field, and to realize the propagation of light in the core. In the related art, the components inside the outer cladding of the hollow core optical fiber are usually a circular hollow core nested tube or a non-closed hollow core semi-circular nested ring, and the circular hollow core nested tube is only connected to other structures at a point or a line area, and the non-closed hollow core semi-circular nested ring has poor structural stability in the high-temperature processing process of the preform rod preparation or the optical fiber drawing, and has high preparation process requirements, thereby increasing the manufacturing difficulty of the hollow core optical fiber. SUMMARY

[0005] The present disclosure provides a hollow core optical fiber, which comprises an outer cladding and N anti-resonance components located inside the outer cladding, N being an integer greater than or equal to 1; wherein there is at least one tubular structure in the N anti-resonance components, the tubular structure comprising a first face and a second face, the first face being a curved surface, and the second face being a flat surface, or the second face being a curved surface that is convex in the opposite direction to the first face.

[0006] In some embodiments, the cross section of the first face is a circular arc line or an elliptical arc line, the cross section of the second face is a circular arc line or an elliptical arc line, and the included angle between the center line of the cross section of the first face and the center line of the cross section of the second face is less than 60 degrees.

[0007] In some embodiments, each of the at least one tubular structure is a closed tubular structure.

[0008] In some embodiments, there are two or more lines on the second face that are connected to the inner surface of the outer cladding.

[0009] In some embodiments, when the second face is a curved surface, the outer surface of the second face and the inner surface of the outer cladding have a part of the curved surface that fits each other.

[0010] In some embodiments, each of the N anti-resonant components comprises the at least one tubular structure.

[0011] In some embodiments, when N is greater than 1, the difference between the thickness of the tube wall of any two of the N anti-resonant components in the direction towards the core is less than a first set value.

[0012] In some embodiments, when N is greater than 1, the difference between the refractive parameters of any two of the N anti-resonant components is less than a second set value, the refractive parameter being the product of the thickness of the tube wall of the anti-resonant component in the direction towards the core and the refractive index of the tubular structure.

[0013] In some embodiments, the refractive index of the tubular structure of at least one of the N anti-resonant components is greater than the refractive index of the outer cladding.

[0014] In some embodiments, the refractive index of each of the N anti-resonant components is greater than the refractive index of the outer cladding.

[0015] In some embodiments, the refractive index of the inner surface of the outer cladding is greater than the refractive index of the outer surface of the outer cladding.

[0016] In some embodiments, the at least one tubular structure is formed by nesting a plurality of tubular structures.

[0017] In some embodiments, the refractive index of the outermost tubular structure of the plurality of tubular structures is greater than the refractive index of the outer cladding.

[0018] In some embodiments, the refractive index of one or more of the tubular structures nested inside of the plurality of tubular structures is greater than the refractive index of the outer cladding.

[0019] In some embodiments, the second face of the tubular structure nested inside of the plurality of tubular structures has at least two lines connected to the adjacent outer tubular structure.

[0020] It can be seen that, in the embodiments of the present disclosure, the tubular structure located inside the outer cladding of the hollow core fiber is not a circular nested tube or a semi-circular nested ring. Compared with the circular nested tube or the semi-circular nested ring, the second face of the tubular structure in the embodiments of the present disclosure can have two or more lines connected to the inner surface of the outer cladding, so that the stable connection between the outer cladding and the tubular structure can be more easily achieved during the fiber drawing process, thereby reducing the process requirements, manufacturing difficulty and manufacturing cost of the hollow core fiber. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the related art, the following will briefly introduce the drawings needed to be used in the embodiments or the related art description. Obviously, the drawings in the following description only constitute some embodiments of the present disclosure, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor

[0022] Fig. 1 is a schematic diagram of the working principle of a related art hollow core anti-resonant optical fiber;

[0023] Fig. 2 is a schematic diagram of the working principle of a related art hollow core anti-resonant optical fiber;

[0024] Fig. 3 is a schematic diagram of the working principle of a related art hollow core anti-resonant optical fiber;

[0025] Fig. 4 is a schematic diagram of the working principle of a related art hollow core anti-resonant optical fiber;

[0026] Fig. 5 is a schematic diagram of the cross section of a first hollow core optical fiber according to an embodiment of the present disclosure;

[0027] Fig. 6 is a schematic diagram of the cross section of a second hollow core optical fiber according to an embodiment of the present disclosure;

[0028] Fig. 7 is a schematic diagram of the cross section of a third hollow core optical fiber according to an embodiment of the present disclosure;

[0029] Fig. 8 is a schematic diagram of the cross section of a fourth hollow core optical fiber according to an embodiment of the present disclosure;

[0030] Fig. 9 is a schematic diagram of the cross section of a fifth hollow core optical fiber according to an embodiment of the present disclosure;

[0031] Fig. 10 is a schematic diagram of the cross section of a sixth hollow core optical fiber according to an embodiment of the present disclosure;

[0032] Fig. 11 is a schematic diagram of the cross section of a seventh hollow core optical fiber according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0033] From the late 1980s to the early 1990s, hollow core photonic bandgap optical fibers were proposed, and reducing the loss of hollow core photonic bandgap optical fibers has been a hot topic in the industry. However, due to the influence of fiber surface modes, the loss of hollow core photonic bandgap optical fibers cannot be reduced to below 2 dB / km.

[0034] Since 2011, the industry has proposed anti-resonant hollow core fibers, and with the continuous research of the industry, the transmission loss of the anti-resonant hollow core fiber has been reduced to 0.28 dB / km, which is close to the transmission loss of quartz optical fiber, laying a foundation for its application in the optical communication industry. Due to the advantages of small time delay, low nonlinear effect, large mode field area, etc., the industry has paid extensive attention. For this reason, the industry has proposed different structures of anti-resonant hollow core fibers, such as nested anti-resonant hollow core fibers, single-ring anti-resonant hollow core fibers, connected tube type anti-resonant hollow core fibers, and mixed structure type anti-resonant hollow core fibers, each of which has its own advantages.

[0035] The mechanism of the anti-resonant hollow core fiber is to use the cavity composed of air and high refractive glass wall to produce anti-resonance when light passes through the high refractive glass wall, realize the confinement of the optical field, and realize the propagation of light in the core. Figures 1 to 4 are schematic diagrams of the working principles of the anti-resonant hollow core fiber in the related art. In Figures 1 and 2, a represents the core radius, b represents the radius of the outer cladding sleeve, φ represents the optical path phase, t represents the thickness of the outer cladding sleeve, n1 represents the refractive index of the outer cladding sleeve, n0 represents the refractive index of air, and the outer cladding sleeve can be a glass wall; in Figure 2, W represents the inner diameter of the hollow core fiber; in Figure 3, k T represents the transverse wave vector, k L represents the longitudinal wave vector, Φ1 represents the optical path phase of light after passing through at least one pair of reflections in high refractive material (such as glass), and Φ0 represents the optical path phase of light without reflection; in Figure 4, the horizontal axis is the radial direction of the fiber cross section, and the vertical axis is |E| 2 / |E max | 2 , which is the normalized optical transverse mode electric field intensity square distribution, E represents the optical transverse mode electric field intensity square distribution, E max represents the maximum value of the optical transverse mode electric field intensity. As can be seen from Figure 4, the structure obtained by the mode matching method and the finite element method (Finite Element Method, FEM) is consistent.

[0036] In combination with Figure 3, the resonance condition in the related art can be represented by formula (1), ΔΦ=Φ1-Φ0=2mπ (1)

[0037] wherein m is any positive integer, and formula (2) can be derived according to formula (1)

[0038] wherein λ is the wavelength of the optical signal satisfying the resonance condition.

[0039] In combination with FIG. 3, the anti-resonance condition in the related art can be expressed by formula (3). ΔΦ = Φ1- Φ0= (2m-1)π (3)

[0040] According to formula (3), formula (4) can be derived.

[0041] In the related art, the related parameters of the hollow core fiber can be designed based on the above formula (3) and formula (4). The first scheme of the related art proposes a hollow core fiber, which includes a first tubular cladding element, a plurality of second tubular elements and a plurality of third tubular elements, the first tubular cladding element defines an inner cladding surface, the plurality of second tubular elements are attached to the cladding surface and together define a core with an effective radius, the second tubular elements are arranged at intervals, and the second tubular elements have an interval between adjacent second tubular elements, and each of the plurality of third tubular elements is respectively nested in a corresponding second tubular element.

[0042] The second technical scheme of the related art proposes a Bragg format hollow core anti-resonance optical fiber in the technical field of microstructured optical fibers, which includes a fiber support part, an inner cladding of the fiber and a core, the inner cladding of the fiber and the core are located inside the fiber support part, the inner cladding of the fiber includes a plurality of inner cladding units, and the adjacent inner cladding units have air therebetween. The Bragg cladding of the present scheme has strict periodicity in structure arrangement, each quartz layer has consistent thickness, and the thickness of the air layer is also consistent, forming a strict Bragg quartz air cladding. By using the anti-resonance effect of the quartz layer and the Bragg effect formed by the Bragg cladding composed of the quartz layer and the air, the energy can be strictly limited in the core by the double effects, and the fiber loss can be greatly reduced.

[0043] The third technical scheme of the related art proposes a partial hollow core anti-resonance optical fiber, the inner layer of the partial hollow core anti-resonance optical fiber includes a first thin wall, a second thin wall and a third thin wall. The present disclosure introduces high birefringence through the difference in wall thickness between the first thin wall and the second thin wall, and effectively amplifies the birefringence effect realized by the difference in wall thickness through the quasi-multiple symmetry structure of the first thin wall and the second thin wall. In addition, by using the present scheme, the transmission loss can be reduced, and the leakage of light through the inner layer, especially through the third thin wall of the inner layer, can be suppressed, so that the optical fiber can realize polarization maintaining while reducing the loss as much as possible.

[0044] A fourth technical solution of the related art proposes an air-core optical fiber preform, an optical fiber and a preparation method thereof, which belong to the technical field of optical fiber communication. The air-core optical fiber preform provided by the solution comprises a sleeve and a reverse resonance unit. The sleeve is in a tubular structure, and a plurality of reverse resonance units are fixedly arranged on the inner wall of the sleeve at equal intervals. The area surrounded by the plurality of reverse resonance units constitutes a central hole of the air-core optical fiber preform. The reverse resonance unit is composed of one or more capillary tubes. At least one capillary tube in the reverse resonance unit has a non-circular structure. The solution can realize accurate positioning of the reverse resonance unit in the air-core optical fiber.

[0045] In the first technical solution of the related art, the inner cladding is realized by an air-core circular tube or an air-core nested tube. In the solution, the nested tube is difficult to fix during fiber drawing, resulting in high manufacturing process requirements and high costs. In the second, third and fourth technical solutions of the related art, the inner cladding is realized by an air-core semicircular nested ring, that is, the inner cladding is realized by a complex air-core structure, so it is necessary to maintain a good structure during manufacturing, which is difficult to manufacture.

[0046] In summary, the preparation process of the air-core optical fiber in the related art requires a high degree of difficulty, thereby increasing the manufacturing difficulty of the air-core optical fiber.

[0047] In view of the above technical problems, the technical solution of the embodiments of the present disclosure is proposed.

[0048] The embodiments of the present disclosure will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the embodiments provided herein are only used to explain the embodiments of the present disclosure and not to limit the embodiments of the present disclosure. In addition, the embodiments provided below are used to implement some embodiments of the present disclosure, and the technical solutions described in the embodiments of the present disclosure can be implemented in any combination manner without conflict.

[0049] It should be noted that in the embodiments of the present disclosure, the terms "comprise", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the method or device comprising a series of elements not only includes the elements explicitly described, but also includes other elements not explicitly listed or inherent to the implementation of the method or device.

[0050] Referring to FIGS. 5 to 11, the air-core optical fiber proposed by the embodiments of the present disclosure comprises an outer cladding 10 and N reverse resonance assemblies 20 located inside the outer cladding 10, N being an integer greater than or equal to 1; for example, the air-core optical fiber in FIGS. 5, 6, 7, 8, 10 and 11 comprises 5 reverse resonance assemblies 20, and the air-core optical fiber in FIG. 9 comprises 4 reverse resonance assemblies.

[0051] Here, the N anti-resonant components include at least one tubular structure, and N is an integer greater than or equal to 3. Referring to FIGS. 5-11, each of the at least one tubular structure includes a first face 201 and a second face 202. The first face 201 is a curved face. The second face 202 is a flat face, or the second face 202 is a curved face that is convex in the opposite direction relative to the first face 201. For example, referring to FIGS. 5, 6, 9, and 11, the second face 202 is a flat face. Referring to FIGS. 7 and 10, the second face 202 is a curved face that is convex in the opposite direction relative to the first face 201.

[0052] As can be seen, when the first face 201 is a curved face and the second face 202 is a flat face, the shape of the cross section of the tubular structure is the shape of the letter "D".

[0053] As can be seen, in the embodiments of the present disclosure, the tubular structure located inside the cladding of the hollow core fiber is not a circular nested tube or a semi-circular nested ring. Compared with the circular nested tube or the semi-circular nested ring, the second face of the tubular structure in the embodiments of the present disclosure can have two or more lines connected to the inner surface of the cladding. Thus, it is easier to achieve stable connection between the cladding and the tubular structure during fiber drawing, thereby reducing the process requirements, manufacturing difficulty, and manufacturing cost of the hollow core fiber.

[0054] In some embodiments of the present disclosure, the cross section of the first face 201 is a circular arc or an elliptical arc, and the cross section of the second face 202 is a circular arc or an elliptical arc. The angle between the center line of the cross section of the first face 201 and the center line of the cross section of the second face 202 is less than 60 degrees.

[0055] Here, when the cross section of the first face 201 is an arc (circular arc or elliptical arc), the center line of the cross section of the first face 201 can be a line between the midpoint of the arc and the midpoint of the line connecting the two ends of the arc. When the cross section of the second face 202 is an arc (circular arc or elliptical arc), the center line of the cross section of the second face 202 can be a line between the midpoint of the arc and the midpoint of the line connecting the two ends of the arc. In one example, the center line of the cross section of the first face 201 and the center line of the cross section of the second face 202 are on the same straight line, i.e., the angle between the center line of the cross section of the first face 201 and the center line of the cross section of the second face 202 is 0 degrees.

[0056] In some embodiments of the present disclosure, each of the at least one tubular structure is a closed tubular structure. The closed tubular structure has good stability during fiber drawing.

[0057] In some embodiments of the present disclosure, the second face 202 has two or more lines connected to the inner surface of the cladding 10. In this way, it is easier to achieve stable connection between the cladding and the tubular structure during fiber drawing.

[0058] In some embodiments of the present disclosure, referring to FIGS. 7 and 10, when the second surface 202 is a curved surface, the outer surface of the second surface 202 and the inner surface of the outer cladding 10 have a mutually adhered partial curved surface. In this way, the close connection between the tubular structure and the outer cladding can be achieved, and the stability of the prepared hollow core fiber is enhanced.

[0059] In some embodiments of the present disclosure, each of the N anti-resonant components comprises at least one tubular structure comprising a first surface 201 and a second surface 202.

[0060] In some embodiments of the present disclosure, when N is greater than 1, the difference between the thicknesses of the tubular walls of any two anti-resonant components in the N anti-resonant components towards the core direction is less than a first set value.

[0061] For example, the thicknesses of the tubular walls of any two anti-resonant components in the N anti-resonant components towards the core direction can be equal, and the first set value can be set according to actual needs. For example, the N anti-resonant components comprise a first anti-resonant component and a second anti-resonant component, the difference between the thicknesses of the tubular walls of the first anti-resonant component and the second anti-resonant component towards the core direction is less than the first set value, the first set value can be the product of the thickness of the tubular wall of the first anti-resonant component towards the core direction and a first set ratio, or the product of the thickness of the tubular wall of the second anti-resonant component towards the core direction and the first set ratio, and the first set ratio can be 15%, 20% or 25%. As can be seen, when the difference between the thicknesses of the tubular walls of any two anti-resonant components in the N anti-resonant components towards the core direction is less than the first set value, it can be considered that the thicknesses of the tubular walls of the corresponding two anti-resonant components towards the core direction are relatively close, thereby facilitating the reduction of the preparation process requirements of the anti-resonant components.

[0062] In some embodiments of the present disclosure, when N is greater than 1, the difference between the refractive parameters of any two anti-resonant components in the N anti-resonant components is less than a second set value, the refractive parameter being the product of the thickness of the tubular wall of the anti-resonant component towards the core direction and the refractive index of the tubular structure.

[0063] For example, the second set value can be set according to actual needs. For example, the N anti-resonant components comprise a third anti-resonant component and a fourth anti-resonant component, the difference between the refractive parameters of the third anti-resonant component and the fourth anti-resonant component is less than the second set value, the second set value can be the product of the refractive parameter of the third anti-resonant component and a second set ratio, or the product of the refractive parameter of the fourth anti-resonant component and the second set ratio, and the second set ratio can be 15%, 20% or 25%.

[0064] It can be seen that when the difference between the refractive parameters of any two of the N anti-resonance components is less than the second set value, it can be considered that the refractive parameters of the two anti-resonance components are relatively close, thereby facilitating the reduction of the preparation process requirements of the anti-resonance components.

[0065] In some embodiments of the present disclosure, the refractive index of the tubular structure of at least one of the N anti-resonance components is greater than the refractive index of the outer cladding. It can be understood that when the refractive index of the tubular structure of at least one of the N anti-resonance components is greater than the refractive index of the outer cladding, the loss of optical signal transmission in the hollow core optical fiber can be reduced.

[0066] In some embodiments of the present disclosure, the refractive index of each of the N anti-resonance components is greater than the refractive index of the outer cladding. It can be understood that when the refractive index of each of the N anti-resonance components is greater than the refractive index of the outer cladding, the loss of optical signal transmission in the hollow core optical fiber can be reduced.

[0067] In some embodiments of the present disclosure, the refractive index of the inner surface of the outer cladding is greater than the refractive index of the outer surface of the outer cladding, that is, the refractive index of the inner part of the outer cladding is greater than the refractive index of the outer part of the outer cladding, so that the loss of optical signal transmission in the hollow core optical fiber can be reduced.

[0068] In some embodiments of the present disclosure, referring to FIGS. 6-10, the tubular structure in the at least one tubular structure described above is formed by nesting a plurality of tubular structures of different sizes.

[0069] In some embodiments of the present disclosure, when the tubular structure in the at least one tubular structure described above is formed by nesting a plurality of tubular structures, the refractive index of the outermost tubular structure in the plurality of nested tubular structures is greater than the refractive index of the outer cladding, so that the loss of optical signal transmission in the hollow core optical fiber can be reduced.

[0070] In some embodiments of the present disclosure, when the tubular structure in the at least one tubular structure described above is formed by nesting a plurality of tubular structures, the refractive index of one or more tubular structures nested inside the plurality of nested tubular structures is greater than the refractive index of the outer cladding, so that the loss of optical signal transmission in the hollow core optical fiber can be reduced.

[0071] In some embodiments of the present disclosure, when the tubular structure in the at least one tubular structure described above is formed by nesting a plurality of tubular structures, the second surface of the tubular structure nested inside the plurality of nested tubular structures has at least two lines connected to the adjacent outer tubular structure. In this way, it is easier to achieve reliable connection between adjacent tubular structures in the plurality of nested tubular structures during fiber drawing, which facilitates the reduction of the preparation process requirements of the hollow core optical fiber.

[0072] The above description of the various embodiments is intended to be illustrative of the various embodiments and is not intended to be limiting. Other embodiments can be apparent to those of ordinary skill in the art from a review of the description of the various embodiments. Other embodiments can be utilized and changes can be made without departing from the scope of the various embodiments and the claims.

[0073] The features disclosed in the above product embodiments of the present disclosure can be combined arbitrarily without conflict, to obtain new product embodiments.

[0074] The embodiments of the present disclosure are described above with reference to the accompanying drawings, but the present disclosure is not limited to the specific embodiments described above, which are merely illustrative rather than limiting, and those of ordinary skill in the art can make many forms under the inspiration of the present disclosure without departing from the purpose of the present disclosure and the scope of the claims, which are all within the protection of the present disclosure.

Claims

1. A hollow core optical fiber comprising: An outer cladding and N anti-resonant components inside the outer cladding, N being an integer greater than or equal to 1; wherein there is at least one anti-resonant component containing at least one tubular structure in the N anti-resonant components, the tubular structure comprising a first face and a second face, the first face being a curved face, and the second face being a flat face, or the second face being a curved face convexly opposite to the first face.

2. The hollow core fiber according to claim 1, wherein, A cross section of the first face is a circular arc or an elliptical arc, and a cross section of the second face is a circular arc or an elliptical arc, and an included angle between a center line of the cross section of the first face and a center line of the cross section of the second face is less than 60 degrees.

3. The hollow core fiber according to claim 1, wherein, Each of the at least one tubular structure is a closed tubular structure.

4. The hollow core fiber according to claim 1, wherein, There are two or more lines connecting the second face and an inner surface of the outer cladding.

5. The hollow core fiber according to claim 4, wherein, When the second face is a curved face, there is a part of the curved face of the outer surface of the second face and the inner surface of the outer cladding that are mutually fitted.

6. The hollow core fiber according to any of claims 1 to 5, wherein, Each of the N anti-resonant components contains the at least one tubular structure.

7. The hollow core fiber according to any of claims 1 to 5, wherein, When N is greater than 1, a difference between thicknesses of tube walls of any two anti-resonant components in the N anti-resonant components in a direction towards a core is less than a first set value.

8. The hollow core fiber according to any of claims 1 to 5, wherein, When N is greater than 1, a difference between refractive parameters of any two anti-resonant components in the N anti-resonant components is less than a second set value, the refractive parameter being a product of thickness of a tube wall of an anti-resonant component in a direction towards a core and a refractive index of the tubular structure.

9. The hollow core fiber according to any of claims 1 to 5, wherein, A refractive index of the tubular structure of at least one anti-resonant component in the N anti-resonant components is greater than a refractive index of the outer cladding.

10. The hollow core optical fiber according to claim 9, wherein, A refractive index of each of the N anti-resonant components is greater than a refractive index of the outer cladding.

11. The hollow core fiber according to claim 10, wherein, A refractive index of an inner surface of the outer cladding is greater than a refractive index of an outer surface of the outer cladding.

12. The hollow core fiber according to any of claims 1 to 5, wherein, The at least one tubular structure is formed by nesting a plurality of tubular structures.

13. The hollow core optical fiber according to claim 12, wherein, A refractive index of an outermost tubular structure in the plurality of tubular structures is greater than a refractive index of the outer cladding.

14. The hollow core fiber according to claim 12, wherein, A refractive index of one or more tubular structures nested inside in the plurality of tubular structures is greater than a refractive index of the outer cladding.

15. The hollow core fiber according to claim 12, wherein, The second face of the tubular structure nested inside in the plurality of tubular structures has at least two lines connected with an adjacent outer tubular structure.

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