Hollow-core optical fiber with crescent-shaped fiber core

Abstract

A hollow-core optical fiber with a crescent-shaped fiber core. The optical fiber comprises a crescent-shaped air fiber core (1) and a cladding microstructure region (2), wherein the cladding structure of the optical fiber uses a multi-tubular structure; the crescent-shaped fiber core is located between the outer side of an inner tube and the inner side of an outer tube of the cladding microstructure region (2), thereby forming a crescent-shaped structure; and an inner layer (21) of the cladding microstructure region (2) consists of a plurality of air layers (23) and tubular structures, and an outer layer (22) of the cladding microstructure region (2) also consists of a plurality of air layers (23) and tubular structures. By means of adjusting the size of the air layers and the wall thickness of the tubular structures, anti-resonant light guiding can be realized. The hollow-core optical fiber with a crescent-shaped fiber core has advantages such as an ultra-low transmission loss, a wide light-guide passband, polarization maintenance and an adjustable mode, and is suitable for applications in the fields of optical communications, fiber-optic gyroscopes, etc.

Description

A crescent-shaped hollow core optical fiber Technical Field

[0001] The present invention relates to the technical field of optical fibers, and in particular to a crescent-shaped hollow-core optical fiber. Background Art

[0002] The versatility of optical fiber depends on its ability to combine ultra-low transmission loss with a wide light-guiding passband, a crucial factor in its widespread adoption in applications such as fiber-based optical communications, laser systems, interferometric sensing systems, and spectral analysis. Ultra-low-loss optical fiber will play an indispensable role in future ultra-high-speed, ultra-large-capacity, and ultra-long-distance fiber transmission systems. As one of the cutting-edge advances in fiber optics, hollow-core fiber, with its low nonlinearity, low dispersion, high photodamage threshold, and flexible filling capabilities, has attracted widespread research interest.

[0003] In addition to low loss and broadband, polarization-maintaining performance is also a key indicator of optical fiber performance. Polarization-maintaining hollow-core fiber is expected to be used in fiber-optic gyroscopes (FOGs). It is expected to overcome the impact of non-reciprocal noise caused by backscattering, Faraday effect, Kerr effect, and Shupe effect, which exist in the sensitive loops of traditional solid-core fibers, on the precision and long-term stability of FOGs. This has become a hot research topic for the next generation of high-precision FOGs. Polarization-maintaining hollow-core fiber also has potential applications in the laser field, maintaining the polarization direction during laser transmission.

[0004] Existing hollow-core microstructured optical fibers, such as nested tube-type antiresonant optical fibers, conjoined tube-type antiresonant optical fibers, Bragg optical fibers, and polarization-maintaining antiresonant hollow-core optical fibers, have the following problems:

[0005] (1) Nested tube antiresonant fiber: This structure has good symmetry, but has high requirements for uniformity and certain requirements for gap size (for example, when achieving ultra-low loss at 1550nm, the light guide requires a gap of less than 7μm), so it is difficult to draw. This structure uses a nested tube structure to construct the cladding structure of the antiresonant hollow-core fiber. The loss of the latest reported double-nested tube structure has reached 0.174dB / km. Further optimization of the structure in the future may achieve lower loss, but it is more difficult to continue to increase the number of layers. Due to the symmetrical structure, the nested tube antiresonant fiber does not have polarization-maintaining performance without introducing wall thickness differences.

[0006] (2) Conjoined tube-type antiresonant fiber: The nodes of its cladding microstructure exist not only at the connection with the outer tube, but also in the internal structure. Therefore, the quartz mode loss in the fiber is significantly reduced and its interaction with the core air mode is significantly enhanced, so the loss spectrum calculated by simulation has an oscillation phenomenon. At the same time, precisely because of the significant enhancement of the interaction between the air mode and the quartz wall mode, this type of structure cannot achieve broadband ultra-low loss optical transmission.

[0007] (3) Bragg fiber: It uses two materials with different refractive indices as cladding, which requires a high cladding thickness and is difficult to draw. Moreover, this structure can only be drawn with soft glass materials. The optimal light guide window is in the mid-infrared band. The drawing process involves rolling the film onto a glass core and then etching away the glass core. The contact points of the film will undergo a sudden change, greatly increasing its loss. The lowest loss currently achievable is 1dB / m.

[0008] (4) Polarization-maintaining antiresonant hollow-core fiber: By introducing wall thickness inhomogeneity and designing a four-fold rotationally symmetric structure, polarization-maintaining performance is achieved, but at the expense of fiber loss characteristics and broadband characteristics.

[0009] Therefore, in view of the problems that the current hollow-core optical fiber has a single ultra-low loss structure and cannot achieve ultra-low loss, broadband and polarization maintenance at the same time, and is difficult to draw, it is necessary to design a type of anti-resonant hollow-core optical fiber with a loss comparable to or even lower than the current mainstream optical fiber design, a wider light-guiding passband, and certain polarization-maintaining performance.

[0010] Summary of the Invention

[0011] The present invention aims to address these issues by providing a crescent-shaped hollow-core optical fiber. This structure is achieved by placing the optical fiber core between two tangential or interlocking tubular structures. The crescent-shaped core divides the cladding microstructure into an inner and outer layer, both composed of multiple tubes with adjustable air spaces between them. While achieving ultra-low loss and a wide light transmission band, the present invention effectively addresses the difficulty of achieving polarization maintenance in existing hollow-core optical fibers.

[0012] To achieve the above object, the present invention provides the following technical solutions:

[0013] According to a first aspect of the present invention, a crescent-shaped hollow-core optical fiber is provided. The optical fiber comprises an air core and a cladding microstructure region. The air core is a crescent-shaped core positioned between the outer side of an inner tube and the inner side of an outer tube of the cladding microstructure region, forming a crescent-shaped structure. It should be understood that this crescent-shaped core design facilitates polarization-maintaining transmission in hollow-core optical fibers.

[0014] As a further solution of the present invention, the air core is a crescent-shaped air core, and the crescent shape of the air core is composed of an outward convex area along the inner layer of the cladding microstructure area and an inward concave area along the outer layer.

[0015] As a further solution of the present invention, the cladding microstructure region adopts a multi-tubular structure, wherein the tubular structure is a full-circular tube, a quasi-circular tube, a semi-circular tube, etc. In this way, flexibility in designing the cladding microstructure region is provided.

[0016] As a further solution of the present invention, the inner layer of the cladding microstructure region is composed of multiple air layers and multiple tubular structures.

[0017] As a further solution of the present invention, the outer layer of the cladding microstructure region is composed of multiple air layers and multiple tubular structures, and the inner layer and the outer layer are tangent or embedded in each other.

[0018] As a further solution of the present invention, the air core is placed between the inner and outer tubular structures, and an air layer with adjustable degrees of freedom is provided between the inner and outer multi-tubular structures.

[0019] As a further solution of the present invention, the inner and outer quartz thin walls of the cladding microstructure region are 1 to 10 layers.

[0020] As a further solution of the present invention, the optical fiber cladding in the cladding microstructure region is made of quartz, soft glass or plastic high refractive index thin-walled material.

[0021] As a further solution of the present invention, the thickness of the quartz wall of the optical fiber is between 0.1um and 4um.

[0022] As a further solution of the present invention, the area of ​​the air layer in the cladding of the optical fiber is 0.8 times or less of the core area. In this way, the crescent-shaped core can be achieved.

[0023] According to a second aspect of the present disclosure, an antiresonant hollow-core optical fiber is provided, comprising: an air core and a cladding microstructure; the air core is a crescent-shaped core, one side of the crescent-shaped core being concave and the other side being convex; the cladding microstructure comprising a convex region microstructure and a concave region microstructure, the convex region microstructure and the concave region microstructure constituting an antiresonant layer, and the crescent-shaped core being formed between the convex region microstructure and the concave region microstructure. It should be understood that the crescent-shaped core design facilitates polarization-maintaining transmission in hollow-core optical fibers.

[0024] As a further embodiment of the present invention, the protruding region microstructure is located on the side of the optical fiber facing the inner concave shape of the crescent-shaped core, and the recessed region microstructure is located on the side of the optical fiber facing the outer convex shape of the crescent-shaped core. As a further embodiment of the present invention, the protruding region microstructure includes the outermost wall element closest to the inner concave shape of the crescent-shaped core, and the recessed region microstructure includes the outermost recessed region wall element closest to the outer convex shape of the crescent-shaped core. As a further embodiment of the present invention, the protruding region microstructure also includes at least two protruding region nested elements nested within the outermost protruding region wall element, such as a first protruding region nested element and a second protruding region nested element, wherein the second protruding region nested element is nested within the first protruding region nested element. As a further embodiment of the present invention, the at least one protruding region nested element includes two to six protruding region nested elements in a nested relationship with each other. As a further embodiment of the present invention, the at least two protruding region nested elements include three protruding region nested elements in a nested relationship with each other. When three elements are nested within the protruding region, the antiresonance effect is optimal, thereby achieving lower fundamental mode loss and a better crescent-shaped core shape. As a further aspect of the present invention, all elements within the protruding region microstructure are arranged so as to intersect at the same point on the inner cladding surface of the outer tubular element, which serves as the cladding element of the optical fiber. As a further aspect of the present invention, an air layer is defined between any two adjacent elements within the protruding region microstructure.

[0025] It should be understood that in the above manner, the above-mentioned protruding area microstructure and the crescent-shaped air layer between any two adjacent elements can be easily realized, thereby providing an anti-resonance element layer on the side where the concave shape edge of the crescent-shaped fiber core is located.

[0026] As a further aspect of the present invention, the recessed area microstructure further includes at least two recessed area nested elements nested between the outermost wall element of the recessed area and the inner cladding surface of the outer tubular element of the optical fiber, such as a first recessed area nested element and a second recessed area nested element, wherein the second recessed area nested element is nested between the first recessed area nested element and the inner cladding surface of the outer tubular element of the optical fiber. As a further aspect of the present invention, the at least one recessed area nested element includes 2 to 8 recessed area nested elements nested with one another. As a further aspect of the present invention, the at least two recessed area nested elements include 3 recessed area nested elements nested with one another. As a further aspect of the present invention, all elements in the recessed area microstructure are arranged so as to be tangent to each other at the same point on the inner cladding surface of the outer tubular element of the optical fiber, serving as the cladding element. As a further aspect of the present invention, an air layer is defined between any two adjacent elements in the recessed area microstructure.

[0027] It should be understood that in the above manner, the above-mentioned recessed area microstructure and the crescent-shaped air layer between any two adjacent elements can be easily realized, thereby providing an anti-resonance element layer on the side where the convex edge of the crescent-shaped fiber core is located.

[0028] As a further aspect of the present invention, the at least one recessed area nested element comprises multiple groups of sub-recessed area nested elements, each of which is spaced apart from the other and each of which contacts the inner cladding surface. As a further aspect of the present invention, the multiple groups of sub-recessed area nested elements comprise two to six groups of sub-recessed area nested elements, wherein each group of sub-recessed area nested elements comprises the sub-recessed area outermost wall element that is most adjacent to the recessed area outermost wall element. As a further aspect of the present invention, each group of sub-recessed area nested elements further comprises multiple sub-recessed area nested elements nested within the corresponding sub-recessed area outermost wall element.

[0029] It should be understood that in the above manner, the above-mentioned recessed region microstructure and the air layer defined between any two adjacent elements can be alternatively implemented, and the anti-resonance element layer on the side where the convex edge of the crescent-shaped core is located is also provided.

[0030] As a further solution of the present invention, the elements in the recessed area microstructure and the protruding area microstructure are selected from full tubes, arc-shaped structures, and straight walls.

[0031] As a further embodiment of the present invention, adjacent elements in the recessed region microstructure define multiple first air layers on the side of the optical fiber facing the outward convex shape, and adjacent elements in the protruding region microstructure define multiple second air layers on the side of the optical fiber facing the inward concave shape, wherein the cross-sectional area of ​​each of the first and second air layers is less than 0.8 times the cross-sectional area of ​​the crescent-shaped core. As a further embodiment of the present invention, the loss of light transmitted within the crescent-shaped core is minimized compared to the multiple concave side cavities and the multiple convex side cavities. As a further embodiment of the present invention, the wall thickness of the elements in the recessed region microstructure and the protruding region microstructure is between 0.1 μm and 4 μm.

[0032] The crescent-shaped hollow-core optical fiber of the present invention features ultra-low transmission loss and a wide light-guiding passband. It utilizes a crescent-shaped air core design and a multi-tubular cladding structure. The inner layer of the cladding microstructure consists of multiple air layers and multiple tubular structures, while the outer layer of the cladding microstructure also consists of multiple air layers and multiple tubular structures. By adjusting the radius, wall thickness, and size of the tubular structure, the fiber's performance can be tuned to achieve specific polarization maintenance, loss values, and light-guiding wavelengths, tailored to the application's needs.

[0033] Compared with the prior art, the crescent-shaped hollow-core optical fiber of the present invention has the following beneficial effects:

[0034] 1. Ultra-low transmission loss: Crescent-core hollow-core fiber utilizes a crescent-shaped core design with one side concave and one side convex, effectively minimizing the interaction between the optical signal and the core, thereby reducing transmission loss. Because the thickness of the cladding quartz wall and the air layer of crescent-core hollow-core fiber meet the antiresonant reflection conditions, when the optical signal in the core leaks into the cladding, it is reflected back to the core by multiple antiresonant reflections from the cladding quartz wall and air, significantly reducing transmission loss.

[0035] 2. Wide light guiding passband: Since the cladding quartz wall thickness and air layer thickness of the crescent-shaped core hollow-core fiber can meet the anti-resonance reflection conditions within a wider passband, wide passband light guiding can be achieved.

[0036] 3. Polarization-maintaining performance: Since the crescent-shaped fiber core is asymmetric in the horizontal and vertical directions, shape birefringence can be used to produce polarization-maintaining performance, so that the optical signal can maintain its original polarization direction during transmission.

[0037] 4. Adjustable Multi-layer Tubes: The inner and outer layers are constructed of multiple air layers and tubular structures. The air layers between the tubes are adjustable. This design allows for adjustable air layer thickness, enabling single-mode or multi-mode transmission, and supporting optical fibers of varying sizes and performance requirements.

[0038] In summary, the crescent-shaped hollow-core optical fiber of the present invention has the beneficial effects of ultra-low transmission loss, wide light-guiding passband, polarization-maintaining performance, and mode adjustability by optimizing the core structure, cladding structure, and air layer design. It is suitable for applications in optical communications, fiber optic gyroscopes, and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG1 is a schematic structural diagram of a nested tube-type antiresonant optical fiber in the prior art;

[0040] FIG2 is a schematic diagram of another structure of a nested tube-type antiresonant optical fiber in the prior art;

[0041] FIG3 is a schematic structural diagram of a conjoined tube-type antiresonant optical fiber in the prior art;

[0042] FIG4 is a schematic diagram of the structure of another conjoined tube-type anti-resonant optical fiber in the prior art;

[0043] FIG5 is a schematic diagram of the structure of a Bragg fiber in the prior art;

[0044] FIG6 is a schematic structural diagram of a polarization-maintaining antiresonant hollow-core optical fiber in the prior art;

[0045] FIG7 is a schematic structural diagram of another polarization-maintaining antiresonant hollow-core optical fiber in the prior art;

[0046] FIG8 is a schematic structural diagram of another polarization-maintaining anti-resonant hollow-core optical fiber in the prior art;

[0047] FIG9 is a schematic structural diagram of a crescent-shaped hollow-core optical fiber provided by the present invention;

[0048] FIG10 is a schematic structural diagram of a crescent-shaped hollow-core optical fiber provided in Example 1 of the present invention;

[0049] FIG11 is a schematic diagram of a simulated loss spectrum of a crescent-shaped hollow-core optical fiber provided in Example 1 of the present invention;

[0050] FIG12 is a schematic diagram of a birefringence spectrum of a crescent-shaped hollow-core optical fiber provided in Example 1 of the present invention;

[0051] FIG13 is a schematic structural diagram of a crescent-shaped hollow-core optical fiber provided in Example 2 of the present invention;

[0052] FIG14 is a schematic diagram of a simulated loss spectrum of a crescent-shaped hollow-core optical fiber provided in Example 2 of the present invention;

[0053] FIG15 is a schematic diagram of a birefringence spectrum of a crescent-shaped hollow-core optical fiber provided in Example 2 of the present invention;

[0054] FIG16 is a schematic structural diagram of a crescent-shaped hollow-core optical fiber provided in Example 3 of the present invention;

[0055] FIG17 is a schematic diagram of a simulated loss spectrum of a crescent-shaped hollow-core optical fiber provided in Example 3 of the present invention;

[0056] FIG18 is a schematic diagram of a birefringence spectrum of a crescent-shaped hollow-core optical fiber provided in Example 3 of the present invention;

[0057] FIG19 is a schematic structural diagram of a crescent-shaped hollow-core optical fiber provided in Example 4 of the present invention;

[0058] FIG20 is a schematic structural diagram of another crescent-shaped hollow-core optical fiber provided in Example 4 of the present invention;

[0059] FIG21 is a schematic structural diagram of a crescent-shaped hollow-core optical fiber provided in Example 5 of the present invention;

[0060] FIG22 is a schematic structural diagram of another crescent-shaped hollow-core optical fiber provided in Example 5 of the present invention;

[0061] FIG23 is a schematic structural diagram of a crescent-shaped hollow-core optical fiber provided in another embodiment of the present invention.

[0062] FIG24 is a schematic structural diagram of another crescent-shaped hollow-core optical fiber provided in another embodiment of the present invention.

[0063] Wherein, the reference numerals are: 1- air core, 2- cladding microstructure region, 21- inner layer, 22- outer layer, 23- air layer, 24- tubular structure. DETAILED DESCRIPTION

[0064] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this application relates; the terms used in the specification of the application are for the purpose of describing specific embodiments only and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned drawings are intended to cover non-exclusive inclusions. The terms "first", "second", etc. in the specification and claims of this application or the above-mentioned drawings are used to distinguish different objects, not to describe a specific order.

[0065] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0066] The existing hollow-core microstructured optical fibers include nested tube-type antiresonant optical fibers, conjoined tube-type antiresonant optical fibers, Bragg optical fibers, and polarization-maintaining antiresonant hollow-core optical fibers.

[0067] (1) Nested tube antiresonant fiber

[0068] As shown in Figures 1 and 2, the nested tube antiresonant fiber uses the principle of antiresonant planar waveguide to guide light. The light that can be transmitted in the core is mainly determined by the thickness of the quartz wall in the cladding. Only when the thickness of the quartz wall meets the resonance condition will the light be significantly leaked. The resonant wavelength can be expressed as Where t is the quartz wall thickness, n² is the quartz refractive index, and m is a positive integer. Wavelengths that do not resonate are allowed to pass.

[0069] This nested-tube antiresonant fiber structure exhibits excellent symmetry, but has high uniformity requirements and certain gap size constraints (for example, a gap of <7μm for 1550nm light guidance), making it challenging to draw. This structure uses nested tubes to construct the cladding structure of the antiresonant hollow-core fiber. The recently reported loss of a double-nested-tube structure has reached 0.174dB / km. Future structural optimization may lead to even lower loss, but increasing the number of layers will be challenging.

[0070] (2) Conjoined tube-type antiresonant optical fiber

[0071] As shown in Figures 3 and 4, this structure uses the principle of anti-resonant planar waveguide to guide light and adopts a multi-layer structure with a simple structure. However, this optical fiber belongs to a cladding tube with a node structure, which causes the transmission spectrum of the optical fiber to be oscillatory and not smooth.

[0072] This structure is difficult to implement and currently can only achieve an ultra-low transmission loss of 2dB / km. New designs are expected to reduce the loss but have not yet been realized. The loss may be even lower in the future.

[0073] Because the fiber design proposed for this conjoined tube-type antiresonant fiber features nodes in its cladding microstructure not only at the connection with the outer tube but also within the internal structure, the quartz mode loss in the fiber is significantly reduced and its interaction with the core air mode is significantly enhanced, resulting in oscillations in the simulated loss spectrum. Furthermore, precisely because of this significant enhancement in the interaction between the air mode and the quartz wall mode, this type of structure cannot achieve broadband ultra-low-loss optical transmission.

[0074] (3) Bragg fiber

[0075] Bragg fiber (as shown in Figure 5) is a circularly symmetric optical waveguide structure with a large refractive index difference. The cladding is a periodic structure of high and low refractive index media with different thicknesses. A high refractive index layer and a low refractive index layer form a period, and light is transmitted in the low refractive index medium layer.

[0076] Bragg fiber uses two materials with different refractive indices as its cladding, requiring high cladding thickness and making it difficult to draw. This structure can only be drawn from soft glass, and its optimal light-guiding window is in the mid-infrared band. The drawing process involves rolling the film onto a glass mandrel and then etching away the mandrel. This creates a sudden change at the film's contact point, significantly increasing the loss. The lowest achievable loss is currently 1 dB / m.

[0077] (4) Polarization-Maintaining Antiresonant Hollow-Core Fiber

[0078] The polarization-maintaining antiresonant hollow-core fiber (structure shown in Figures 6 to 8) has an inner layer comprising a first thin wall, a second thin wall, and a third thin wall. High birefringence is introduced by the difference in wall thickness between the first and second thin walls, and the birefringence effect brought about by the thickness difference is effectively amplified by the quasi-multiple symmetric structure of the first and second thin walls. Furthermore, the inner layer, especially the third thin wall, reduces ultra-low transmission loss and inhibits light leakage, thereby enabling the hollow-core fiber of this technology to maintain polarization while minimizing loss.

[0079] This invention proposes a four-fold rotationally symmetrical structure, but it is only used to achieve the polarization-maintaining performance of the optical fiber. The inconsistent wall thickness greatly increases the transmission loss, and no technical exploration has been conducted on whether it can achieve wide-band light guidance.

[0080] In light of this, the present invention aims to address the current problems of hollow-core optical fibers (HCFs) with their single ultra-low-loss structure, lack of polarization-maintaining performance, and significant manufacturing difficulty. The present invention aims to design an antiresonant hollow-core optical fiber with comparable or even lower loss than current mainstream optical fiber designs, wide light transmission bandwidth, and polarization-maintaining performance.

[0081] This invention achieves a crescent-shaped core structure by placing the optical fiber core between two tangential or interlocking tubular structures. This crescent-shaped core divides the cladding microstructure into an inner and outer layer, both composed of multiple layers of tubular structures with adjustable air spaces between them. While achieving ultra-low loss and a wide light transmission band, this invention effectively addresses the difficulty of achieving polarization maintenance in existing hollow-core optical fibers.

[0082] Among them, since the existing optical fiber polarization-maintaining technologies include photonic bandgap hollow-core polarization-maintaining fiber, which mainly introduces high birefringence by reducing the multiple symmetries of the optical fiber core structure, and polarization-maintaining antiresonant hollow-core fiber, the method of achieving polarization maintenance is to introduce high birefringence by changing the wall thickness difference in the orthogonal direction of the core or to introduce high birefringence by constructing nested tubes and anti-cross coupling with the core mode, etc., both of which have certain difficulties in the actual manufacturing process.

[0083] The crescent-shaped hollow-core fiber of the present invention is suitable for use as an antiresonant hollow-core fiber for various applications and across a wide range of optical wavelengths, demonstrating its versatility. Furthermore, the crescent-shaped hollow-core fiber design proposed in the present invention ensures uniform curvature and thickness at all locations on the glass wall of the cladding, a structure achievable using fiber drawing methods based on fluid mechanics and thermodynamics. Therefore, the fiber design of the present invention is practically feasible.

[0084] As shown in FIG9 , the present invention provides a crescent-shaped hollow-core optical fiber, which is advantageous for achieving ultra-low loss when the core is large, and advantageous for achieving high birefringence and strong polarization maintenance when the core is small.

[0085] The crescent-core hollow-core optical fiber of the present invention comprises an air core 1 and a cladding microstructure region 2. The air core 1 is a crescent-shaped core located between an inner layer 21 and an outer layer 22 of the cladding microstructure region 2, forming a crescent-shaped structure. Both the air core 1 and the cladding microstructure region 2 are located within the lumen of an outer tubular element (not labeled), which serves as a cladding member. The lumen is defined by the inner cladding surface of the outer tubular element. In particular, the cladding microstructure region 2 contacts the inner cladding surface of the outer tubular element.

[0086] The air core 1 is a crescent-shaped air core, the crescent shape of which is formed by a convex region extending outward along the inner layer of the cladding microstructure region 2 and a concave region extending inward along the outer layer. Thus, the cladding microstructure 2 may include a concave region microstructure in the outer layer 22 and a convex region microstructure in the inner layer 21, wherein the concave region microstructure is located on the side of the optical fiber facing the convex shape of the crescent core, while the convex region microstructure is located on the side of the optical fiber facing the concave shape of the crescent core. The convex region microstructure and the concave region microstructure may each constitute an antiresonant layer, and the crescent core is confined between the convex region microstructure and the concave region microstructure.

[0087] The cladding microstructure region 2 adopts a multi-tubular structure, and the tubular structure can be a full-circular tube, a quasi-circular tube, or a semi-circular tube. The inner layer 21 of the cladding microstructure region 2 is composed of multiple air layers 23 and multiple tubular structures. The outer layer 22 of the cladding microstructure region 2 is composed of multiple air layers 23 and multiple tubular structures. The inner layer 21 and the outer layer 22 are tangentially or interlockingly connected. The air core 1 is placed between the two layers of tubular structures 24 of the inner layer 21 and the outer layer 22. The air layer 23 with adjustable degrees of freedom is located between the multiple tubular structures 24 of the inner layer 21 and the outer layer 22.

[0088] In some embodiments, the convex region microstructure includes a convex region outermost wall element closest to the concave shape of the crescent-shaped fiber core, and the concave region microstructure includes a concave region outermost wall element closest to the convex shape of the crescent-shaped fiber core. In some embodiments, the convex region microstructure may further include at least two convex region nested elements nested within the convex region outermost wall element, such as a first convex region nested element and a second convex region nested element, wherein the second convex region nested element is nested within the first convex region nested element. Typically, the at least two convex region nested elements may include two to six convex region nested elements nested within each other, so that the convex region microstructure achieves a better anti-resonance effect. Preferably, the at least two convex region nested elements may include three convex region nested elements nested within each other. Three convex region nested elements provide the best anti-resonance effect, thereby achieving lower fundamental mode loss and a better crescent-shaped fiber core shape. In particular, all elements in the protruding region microstructure may be arranged to be tangent to each other at the same point on the surface of the inner cladding. In addition, a crescent-shaped air layer, for example, may be defined between any two adjacent elements in the protruding region microstructure.

[0089] In some embodiments, the recessed region microstructure may further comprise at least two recessed region nested elements nested between the outermost wall element of the recessed region and the inner cladding surface of the outer tubular element of the optical fiber, such as a first recessed region nested element and a second recessed region nested element, wherein the second recessed region nested element is nested between the first recessed region nested element and the inner cladding surface. Typically, the at least two recessed region nested elements may comprise 2 to 8 recessed region nested elements in a nested relationship, so that the recessed region microstructure achieves a good antiresonance effect. Preferably, the at least two recessed region nested elements may comprise 3 recessed region nested elements in a nested relationship.

[0090] In particular, all elements in the recessed region microstructure may be arranged to be tangent to each other at the same point on the surface of the inner cladding. In addition, a crescent-shaped air layer, for example, may be defined between any two adjacent elements in the recessed region microstructure.

[0091] In yet other embodiments, the at least one recessed area nested element may include multiple groups of sub-recessed area nested elements, each of which is spaced apart from the other and each in contact with the inner cladding surface. Typically, the multiple groups of sub-recessed area nested elements include two to six groups of sub-recessed area nested elements, wherein each group of sub-recessed area nested elements includes the sub-recessed area outermost wall element that is most adjacent to the recessed area outermost wall element. Furthermore, in some embodiments, each group of sub-recessed area nested elements also includes multiple sub-recessed area nested elements nested within the corresponding sub-recessed area outermost wall element.

[0092] In an embodiment of the present disclosure, the elements in the aforementioned recessed area microstructure and the aforementioned protruding area microstructure are selected from full tubes, arc-shaped structures, and straight walls.

[0093] In some embodiments, adjacent elements in the above-mentioned recessed area microstructure define a plurality of first air layers on the side of the optical fiber facing the convex shape, and adjacent elements in the protruding area microstructure define a plurality of second air layers on the side of the optical fiber facing the concave shape, and the cross-sectional area of ​​each of the first air layers and the second air layers is less than 0.8 times the cross-sectional area of ​​the crescent-shaped core.

[0094] It should be understood that, compared with the plurality of first air layers and the plurality of second air cavities, the light transmitted in the crescent-shaped core has the least loss. In some embodiments, the wall thickness of the elements in the concave region microstructure and the convex region microstructure is between 0.1um and 4um.

[0095] As an example, in the present invention, the optical fiber cladding of the cladding microstructure region 2 is made of quartz, soft glass or plastic high refractive index thin-walled material. The inner layer 21 and outer layer 22 of the cladding microstructure region 2 have 1-10 thin-walled quartz layers.

[0096] The present invention features a crescent-shaped hollow-core optical fiber with ultra-low transmission loss and a wide light-guiding passband. It utilizes a crescent-shaped air core design and a multi-tubular cladding. The present invention employs a crescent-shaped air core (1) and a multi-tubular cladding. The inner layer (21) of the cladding microstructure region (2) is composed of multiple air layers (23) and multiple tubular structures. The outer layer (22) of the cladding microstructure region (2) also consists of multiple air layers (23) and multiple tubular structures.

[0097] For example, as shown in FIG9 , the crescent-shaped hollow-core optical fiber of the present invention includes an anti-resonance layer of greater than or equal to 2 and less than or equal to 6 layers from the core inward, and an anti-resonance layer of greater than or equal to 2 and less than or equal to 8 layers outward, wherein an odd number is a quartz layer and an even number is an air layer 23. If a first-order anti-resonance band is used to guide light in the near-infrared, the thickness of the quartz layer should be between 300-600nm. If a second-order anti-resonance band is used to guide light in the near-infrared, the wall thickness of the quartz layer should be around 1μm and as consistent as possible. The air layer 23 has a large degree of adjustment freedom, which can significantly reduce the difficulty of drawing. The crescent-shaped core is located in the part enclosed by the two-layer tubular structure. The outer layer 22 can also be a non-tubular structure, a straight wall or any other structure.

[0098] The following will clearly and completely describe the technical solutions in the exemplary embodiments of the present invention in conjunction with the accompanying drawings of the exemplary embodiments of the present invention. Obviously, the exemplary embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0099] Example 1

[0100] As shown in Figures 10 to 12, an embodiment of the present invention provides a crescent-shaped core hollow optical fiber, including an air core 1 and a cladding microstructure region 2; the air core 1 is a crescent-shaped core, located between the inner layer 21 and the outer layer 22 of the cladding microstructure region 2, forming a crescent-shaped structure.

[0101] In this embodiment, the cladding microstructure region 2 is composed of four inner quartz layers 21 and five outer quartz layers 22. The wall thickness can be adjusted according to the antiresonance conditions met in the operating band. As shown in Figure 10, the optical fiber core has a major axis diameter of 44 μm and a minor axis diameter of 20 μm. The wall thickness of all quartz cladding tubes is 0.53 μm. The thicknesses of the inner air layer 21 (2 / 4 / 6) are 11.8 / 11.1 / 9.2 μm, and the thicknesses of the outer air layer 22 (2 / 4 / 6 / 8) are 10.8 / 9.4 / 10.2 / 5.6 μm. The optical fiber has a loss of 0.026 dB / km at 1550 nm and a birefringence of 2.256e-5 at 1550 nm.

[0102] Example 2

[0103] As shown in Figures 13 to 15, an embodiment of the present invention provides a crescent-shaped core hollow optical fiber, including an air core 1 and a cladding microstructure region 2; the air core 1 is a crescent-shaped core, located between the inner layer 21 and the outer layer 22 of the cladding microstructure region 2, forming a crescent-shaped structure.

[0104] In this embodiment, the cladding microstructure region 2 is composed of four inner quartz layers 21 and five outer quartz layers 22. The wall thickness can be adjusted based on the antiresonance conditions in the operating band. As shown in Figure 13, the optical fiber core has a major axis diameter of 25.8 μm and a minor axis diameter of 12 μm. The wall thickness of all quartz cladding tubes is 0.53 μm. The thicknesses of the inner air layer 21 (2 / 4 / 6) are 7.05 / 6.64 / 5.53 μm, and the thicknesses of the outer air layer 22 (2 / 4 / 6 / 8 / 10) are 6.46 / 5.73 / 6.19 / 6.63 / 5.53 μm. The optical fiber has a loss of 0.388 dB / km at 1550 nm and a birefringence of 1.025e-4 at 1550 nm.

[0105] Example 3

[0106] As shown in Figures 16 to 18, an embodiment of the present invention provides a crescent-shaped core hollow optical fiber, including an air core 1 and a cladding microstructure region 2; the air core 1 is a crescent-shaped core, located between the inner layer 21 and the outer layer 22 of the cladding microstructure region 2, forming a crescent-shaped structure.

[0107] In this embodiment, as shown in Figure 16, the cladding microstructure region 2 is composed of four inner quartz layers 21 and five outer quartz layers 22. The wall thickness can be adjusted according to the antiresonance conditions met in the operating band. As shown in Figures 17 and 18, the large core of the crescent-shaped optical fiber of the present invention is conducive to achieving ultra-low loss. For example, when the core minor axis diameter is 20μm, the optical fiber achieves an ultra-low loss of 8.28e-4dB / km at 1550nm. A small core is conducive to achieving high birefringence and strong polarization-maintaining performance. For example, when the core minor axis diameter is 12μm, the optical fiber achieves a high birefringence of 1.025e-4 at 1550nm.

[0108] Example 4

[0109] As shown in Figures 19 and 20, an embodiment of the present invention provides a crescent-shaped core hollow optical fiber, including an air core 1 and a cladding microstructure region 2; the air core 1 is a crescent-shaped core, located between the inner layer 21 and the outer layer 22 of the cladding microstructure region 2, forming a crescent-shaped structure.

[0110] In this embodiment, the crescent-shaped hollow-core fiber consists of three layers: an inner layer 21 and an outer layer 22. The inner layer 21 comprises a three-layer tubular structure, while the outer layer 22 comprises a non-tubular structure, a tubular structure, and a straight wall. The fiber core has a major axis diameter of 44 μm and a minor axis diameter of 20 μm. The thickness of all thin quartz walls can be adjusted to meet the antiresonance conditions within the operating band, with a thickness difference within 10%. The thickness of the air layer 23 can be adjusted with considerable freedom.

[0111] Example 5

[0112] As shown in Figures 21 and 22, an embodiment of the present invention provides a crescent-shaped core hollow optical fiber, including an air core 1 and a cladding microstructure region 2; the air core 1 is a crescent-shaped core, located between the inner layer 21 and the outer layer 22 of the cladding microstructure region 2, forming a crescent-shaped structure.

[0113] In this embodiment, the crescent-shaped hollow-core fiber consists of three layers: an inner layer 21 and an outer layer 22. The inner layer 21 comprises a three-layer tubular structure, while the outer layer 22 comprises a non-tubular structure, a tubular structure, and a straight wall. The fiber core has a major axis diameter of 44 μm and a minor axis diameter of 20 μm. The thickness of all thin quartz walls can be adjusted to meet the antiresonance conditions within the operating band, with a thickness difference within 10%. The thickness of the air layer 23 can be adjusted with considerable freedom.

[0114] In addition to the above embodiments, the present invention also provides other possible embodiments, including an antiresonant hollow-core optical fiber (FIG. 23) in which the inner fiber layer 21 is a three-layer tubular structure and the outer fiber layer 22 is a three-layer non-tubular structure. Its light-guiding properties are comparable to those of Example 3. Alternatively, the present invention also provides an antiresonant hollow-core optical fiber in which the inner fiber layer 21 is a three-layer tubular structure, as shown in FIG. 24 , and the outer fiber layer 22 includes both tubular and non-tubular structures. Its light-guiding properties are comparable to those of Example 5.

[0115] The novel anti-resonant hollow-core fiber proposed in the present invention can be applied to optical fiber communication systems. In traditional optical fiber communication systems, ordinary single-mode optical fibers (e.g., Corning SMF-28 optical fibers) are mainly used for communication. The typical system components include single-mode transmitting devices, single-mode communication optical fibers, single-mode optical amplifiers, and single-mode optical receiving devices to respectively realize the excitation, transmission, amplification, and demodulation and reception of optical signals. Wavelength division multiplexing technology is used to transmit multiple wavelength channels in a single optical fiber to respectively carry different user information. In a communication system based on hollow-core optical fibers, the novel hollow-core optical fibers can be used to replace traditional single-mode optical fibers to achieve lower transmission delay, lower transmission signal damage (such as dispersion / nonlinear damage), wider optical signal transmission spectrum, and potentially lower transmission loss. In addition, since hollow-core optical fibers have good compatibility with other single-mode devices, low-loss connection between hollow-core optical fibers and single-mode wavelength division transceiver devices, single-mode optical amplifiers, etc. can be directly achieved through methods such as pigtail fusion splicing and docking, thereby bringing the above-mentioned performance improvements to traditional communication systems while minimizing the system's additional insertion loss and reducing the development and introduction of various adapter devices.

[0116] The novel antiresonant hollow-core fiber proposed in this invention can also be used, for example, in resonant fiber gyros (FOGs) for angle Ω sensing. In these FOGs, rotation rate is measured by determining the resonant frequency shift between clockwise (CW) and counterclockwise (CCW) light propagation in a multi-turn passive fiber ring resonator. Furthermore, the application of hollow-core fiber in FOGs can avoid or significantly reduce Rayleigh backscattering, temperature effects, Faraday effects, and optical Kerr effects.

[0117] In summary, the present invention discloses a crescent-shaped hollow-core optical fiber, which utilizes a crescent-shaped core and has a more complex concave-convex shape than a traditional circular core. This crescent-shaped core design provides improved light transmission control and polarization-maintaining performance. The optical fiber core is placed between two tubular structures 24, an inner layer 21 and an outer layer 22, forming a multi-layer tubular structure 24. This design allows for greater freedom in adjusting the air layer 23 between the multiple tubular structures 24 of the optical fiber, effectively reducing the difficulty of drawing the optical fiber. The cladding microstructure region 2 utilizes a multi-tubular structure, with the tubular structures being fully circular, quasi-circular, or semi-circular. This structure provides improved light transmission performance and polarization-maintaining effects, while reducing transmission loss. The crescent-shaped hollow-core optical fiber has a wide light transmission passband and can transmit a wider spectrum of optical signals. Through the crescent-shaped core design, the optical fiber can achieve polarization-maintaining performance, effectively maintaining the polarization state of the optical signal and reducing distortion and interference of the optical signal. The multi-layer tubular structure 24 design reduces the transmission loss of the optical fiber and provides higher signal quality and distance.

[0118] The crescent-shaped hollow-core optical fiber of the present invention has broad application prospects in the fields of optical communication and optical sensing. It can provide excellent performance characteristics such as low loss, high polarization maintenance and wide light-guiding passband, bringing new possibilities for the development of optical fiber communication systems and optical sensors.

[0119] It should be noted that for the aforementioned embodiments, for simplicity of description, they are all expressed as a series of action combinations. However, those skilled in the art should be aware that the present invention is not limited by the order of the actions described, because according to the present invention, certain steps may be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in this specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present invention.

[0120] In the several embodiments provided in this application, it should be understood that the disclosed devices can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the above-mentioned units is only a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or communication connection shown or discussed can be through some interfaces, and the indirect coupling or communication connection between devices or units can be in the form of telecommunications or other forms.

[0121] The units described above as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0122] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the scope of protection of the invention. Obviously, the embodiments described are only some embodiments of the present invention, rather than all embodiments. Based on these embodiments, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in this field can still combine, add, delete or make other adjustments to the features in the various embodiments of the present invention according to the circumstances without conflict, without making creative work, so as to obtain different other technical solutions that do not deviate from the concept of the present invention in essence, and these technical solutions also fall within the scope of protection of the present invention.

[0123] Based on the above description, it can be understood that the present application may relate to embodiments according to the following clauses or combinations thereof:

[0124] Item 1. A crescent-shaped core hollow optical fiber, characterized in that the optical fiber includes an air core and a cladding microstructure region; the air core is a crescent-shaped core, located between the outer side of the inner tube and the inner side of the outer tube of the cladding microstructure region, forming a crescent-shaped structure.

[0125] Clause 2. The crescent-shaped core hollow-core optical fiber according to Clause 1 is characterized in that the cladding microstructure region adopts a multi-tubular structure, and the tubular structure is a full circular tube, a quasi-circular tube, or a semi-circular tube.

[0126] Item 3. The crescent-shaped hollow-core optical fiber according to Item 2 is characterized in that the crescent shape of the optical fiber core is composed of an outward protruding area along the inner layer of the cladding microstructure area and an inward concave area along the outer layer.

[0127] Item 4. The crescent-shaped hollow-core optical fiber according to Item 3, wherein the inner layer of the cladding microstructure region is composed of multiple air layers and multiple tubular structures.

[0128] Item 5. The crescent-shaped core hollow optical fiber according to Item 4 is characterized in that the outer layer of the cladding microstructure region is composed of multiple air layers and multiple tubular structures.

[0129] Item 6. The crescent-shaped hollow-core optical fiber according to Item 5, characterized in that the optical fiber core is placed between two layers of tubular structures, the inner layer and the outer layer, and an air layer with adjustable freedom is formed between the inner and outer multi-tubes.

[0130] Item 7. The crescent-shaped hollow-core optical fiber according to Item 6, wherein the optical fiber cladding in the cladding microstructure region is made of a high-refractive-index thin-walled material such as quartz, soft glass, or plastic.

[0131] Item 8. The crescent-shaped hollow-core optical fiber according to Item 7, wherein the inner and outer layers of the cladding microstructure region have 1 to 10 thin-walled silica layers.

[0132] Item 9. The crescent-shaped hollow-core optical fiber according to Item 8, wherein the thickness of the quartz wall of the optical fiber is between 0.1 μm and 4 μm.

[0133] Clause 10. The crescent-shaped hollow-core optical fiber according to Clause 9, wherein the area of ​​the air layer in the cladding of the optical fiber is 0.8 times or less of the core area.

[0134] Clause 11. An antiresonant hollow core optical fiber, comprising: an air core and a cladding microstructure;

[0135] The air core is a crescent-shaped core, one side of the crescent-shaped core is concave and the other side is convex;

[0136] The cladding microstructure includes a convex region microstructure and a concave region microstructure, the convex region microstructure and the concave region microstructure constitute an anti-resonance layer, and the crescent-shaped fiber core is formed between the convex region microstructure and the concave region microstructure.

[0137] Clause 12. The antiresonant hollow-core optical fiber according to Clause 11 is characterized in that the protruding region microstructure is located on the side of the concave shape facing the crescent-shaped core within the optical fiber, and the concave region microstructure is located on the side of the convex shape facing the crescent-shaped core within the optical fiber.

[0138] Clause 13. The antiresonant hollow-core optical fiber according to Clause 11 is characterized in that the protruding region microstructure includes the outermost tube wall element of the protruding region that is closest to the inward concave shape of the crescent-shaped core, and the concave region microstructure includes the outermost tube wall element of the concave region that is closest to the outward convex shape of the crescent-shaped core.

[0139] Clause 14. The antiresonant hollow-core optical fiber according to Clause 13 is characterized in that it also includes: at least two protrusion area nested elements nested in the outermost tube wall element of the protrusion area, the at least two protrusion area nested elements including a first protrusion area nested element and a second protrusion area nested element, and the second protrusion area nested element is nested in the first protrusion area nested element.

[0140] Clause 15. The antiresonant hollow-core optical fiber according to Clause 14, wherein the at least two protrusion region nested elements comprise 2 to 6 protrusion region nested elements in a nested relationship with each other.

[0141] Clause 16. The antiresonant hollow-core optical fiber according to Clause 14, wherein the at least two protrusion region nested elements include three protrusion region nested elements in a nested relationship with each other.

[0142] Item 17. The antiresonant hollow-core optical fiber according to Item 11, characterized in that all elements in the protruding region microstructure are arranged to be tangent at the same point on the inner cladding surface of the outer tubular element of the optical fiber as the cladding element.

[0143] Clause 18. The antiresonant hollow-core optical fiber according to any one of clauses 11 to 17, wherein an air layer is defined between any two adjacent elements in the protruding region microstructure.

[0144] Clause 19. The antiresonant hollow-core optical fiber according to Clause 13 is characterized in that it also includes at least two recessed area nested elements nested between the outermost tube wall element of the recessed area and the inner cladding surface of the outer tubular element of the optical fiber serving as the cladding element, wherein the at least two recessed area nested elements include a first recessed area nested element and a second recessed area nested element.

[0145] Clause 20. The antiresonant hollow-core optical fiber according to Clause 19, wherein the at least two recessed region nested elements comprise 2 to 8 recessed region nested elements in a nested relationship with each other.

[0146] Clause 21. The antiresonant hollow-core optical fiber according to Clause 19, wherein the at least two recessed region nested elements include three recessed region nested elements that are in a nested relationship with each other.

[0147] Item 22. The antiresonant hollow-core optical fiber according to Item 19, wherein all elements in the depressed region microstructure are arranged to be tangent at the same point on the inner cladding surface of the outer tubular element of the optical fiber serving as the cladding element.

[0148] Clause 23. The antiresonant hollow-core optical fiber according to Clause 19, wherein an air layer is defined between any two adjacent elements in the recessed region microstructure.

[0149] Item 24. The antiresonant hollow-core optical fiber according to Item 19, characterized in that the at least one recessed area nested element includes multiple groups of sub-recessed area nested elements, which are spaced apart from each other and each contacts the inner cladding surface of the outer tubular element of the optical fiber serving as a cladding element.

[0150] Clause 25. The antiresonant hollow-core optical fiber according to Clause 24 is characterized in that the multiple groups of sub-recessed area nested elements include 2 to 6 groups of sub-recessed area nested elements, wherein each group of sub-recessed area nested elements includes the sub-recessed area outermost tube wall element that is most adjacent to the outermost tube wall element of the recessed area.

[0151] Clause 26. The antiresonant hollow-core optical fiber according to Clause 25, wherein each group of sub-recessed region nested elements further comprises a plurality of sub-recessed region nested elements nested within the outermost tube wall element of the corresponding sub-recessed region.

[0152] Clause 27. The antiresonant hollow-core optical fiber according to any one of clauses 11 to 26, wherein the elements in the recessed region microstructure and the protruding region microstructure are selected from full tubes, arc-shaped structures, and straight walls.

[0153] Clause 28. An antiresonant hollow-core optical fiber according to any one of clauses 11 to 26, characterized in that adjacent elements in the recessed region microstructure define a plurality of first air layers on the side of the optical fiber facing the convex shape, and adjacent elements in the protruding region microstructure define a plurality of second air layers on the side of the optical fiber facing the concave shape, and the cross-sectional area of ​​each of the first air layers and the second air layers is less than 0.8 times the cross-sectional area of ​​the crescent-shaped core.

[0154] Item 29. The antiresonant hollow-core optical fiber according to Item 28, wherein the loss of light transmitted within the crescent-shaped core is minimized compared to the plurality of first air layers and the plurality of second air layers.

[0155] Clause 30. The antiresonant hollow-core optical fiber according to any one of clauses 11 to 29, wherein the wall thickness of the elements in the recessed region microstructure and the protruding region microstructure is between 0.1 μm and 4 μm.

Claims

1. A crescent-shaped hollow core optical fiber, characterized in that: The optical fiber comprises an air core and a cladding microstructure region; the air core is a crescent-shaped core, which is located between the outer side of the inner tube and the inner side of the outer tube in the cladding microstructure region to form a crescent-shaped structure.

2. The crescent-shaped hollow-core optical fiber according to claim 1, characterized in that: The cladding microstructure region adopts a multi-tubular structure, and the tubular structure is a full-circular tube, a quasi-circular tube, or a semi-circular tube.

3. The crescent-shaped hollow-core optical fiber according to claim 2, characterized in that: The crescent shape of the optical fiber core is composed of an outwardly protruding area along the inner layer of the cladding microstructure area and an inwardly concave area along the outer layer.

4. The crescent-shaped hollow-core optical fiber according to claim 3, characterized in that: The inner layer of the cladding microstructure region is composed of multiple air layers and multiple tubular structures.

5. The crescent-shaped hollow-core optical fiber according to claim 4, characterized in that: The outer layer of the cladding microstructure region is composed of multiple air layers and multiple tubular structures.

6. The crescent-shaped hollow-core optical fiber according to claim 5, characterized in that: The optical fiber core is placed between two layers of tubular structures, the inner layer and the outer layer, and an air layer with adjustable freedom is formed between the inner layer and the outer layer of multiple tubes.

7. The crescent-shaped hollow-core optical fiber according to claim 6, characterized in that: The optical fiber cladding in the cladding microstructure region is made of quartz, soft glass or plastic high refractive index thin-wall material.

8. The crescent-shaped hollow-core optical fiber according to claim 7, characterized in that: The inner and outer quartz thin walls of the cladding microstructure region are 1 to 10 layers.

9. The crescent-shaped hollow-core optical fiber according to claim 8, characterized in that: The thickness of the quartz wall of the optical fiber is between 0.1um and 4um.

10. The crescent-shaped hollow-core optical fiber according to claim 9, characterized in that: The area of ​​the air layer in the cladding of the optical fiber is 0.8 times or less of the core area.

11. An antiresonant hollow core optical fiber, characterized in that , including: air core and cladding microstructure; The air core is a crescent-shaped core, one side of the crescent-shaped core is concave, and the other side is convex; The cladding microstructure includes a convex region microstructure and a concave region microstructure, the convex region microstructure and the concave region microstructure constitute an anti-resonance layer, and the crescent-shaped core is formed between the convex region microstructure and the concave region microstructure.

12. The antiresonant hollow core optical fiber according to claim 11, characterized in that The protruding area microstructure is located on the side of the concave shape facing the crescent-shaped core in the optical fiber, and the concave area microstructure is located on the side of the convex shape facing the crescent-shaped core in the optical fiber.

13. The antiresonant hollow core optical fiber according to claim 11, characterized in that The convex area microstructure includes the outermost tube wall element that is closest to the concave shape of the crescent-shaped fiber core, and the concave area microstructure includes the outermost tube wall element of the concave area that is closest to the convex shape of the crescent-shaped fiber core.

14. The antiresonant hollow core optical fiber according to claim 13, characterized in that , also includes: at least two protruding area nested elements nested in the outermost tube wall element of the protruding area, the at least two protruding area nested elements include a first protruding area nested element and a second protruding area nested element, the second protruding area nested element is nested in the first protruding area nested element.

15. The antiresonant hollow core optical fiber according to claim 14, characterized in that , the at least two protruding area nested elements include 2 to 6 protruding area nested elements that are in a nested relationship with each other.

16. The antiresonant hollow core optical fiber according to claim 14, characterized in that , the at least two protruding area nested elements include three protruding area nested elements that are in a nested relationship with each other.

17. The antiresonant hollow core optical fiber according to claim 11, characterized in that , all elements in the protruding region microstructure are arranged to be tangent at the same point on the inner cladding surface of the outer tubular element of the optical fiber as the cladding element.

18. The antiresonant hollow core optical fiber according to any one of claims 11 to 17, characterized in that , an air layer is defined between any two adjacent elements in the protruding area microstructure.

19. The antiresonant hollow core optical fiber according to claim 13, characterized in that , also includes at least two recessed area nested elements nested between the outermost tube wall element of the recessed area and the inner cladding surface of the outer tubular element of the optical fiber serving as a cladding element, the at least two recessed area nested elements include a first recessed area nested element and a second recessed area nested element, the second recessed area nested element is nested between the first recessed area nested element and the inner cladding surface.

20. The antiresonant hollow core optical fiber according to claim 19, characterized in that , the at least two recessed area nested elements include 2 to 8 recessed area nested elements that are in a nested relationship with each other.

21. The antiresonant hollow core optical fiber according to claim 19, characterized in that , the at least two recessed area nested elements include three recessed area nested elements that are in a nested relationship with each other.

22. The antiresonant hollow core optical fiber according to claim 19, characterized in that , all elements in the recessed region microstructure are arranged to be tangent at the same point on the inner cladding surface of the outer tubular element of the optical fiber as the cladding element.

23. The antiresonant hollow core optical fiber according to claim 19, characterized in that , an air layer is defined between any two adjacent elements in the recessed area microstructure.

24. The antiresonant hollow core optical fiber according to claim 19, characterized in that , the at least one recessed area nested element includes a plurality of groups of sub-recessed area nested elements, the plurality of groups of sub-recessed area nested elements are spaced apart from each other and each of them contacts the inner cladding surface of the outer tubular element of the optical fiber as a cladding element.

25. The antiresonant hollow core optical fiber according to claim 24, characterized in that The multiple groups of sub-recessed area nested elements include 2 to 6 groups of sub-recessed area nested elements, wherein each group of sub-recessed area nested elements includes the sub-recessed area outermost tube wall element that is most adjacent to the outermost tube wall element of the recessed area.

26. The antiresonant hollow core optical fiber according to claim 25, characterized in that ,Each group of sub-recessed area nested elements also includes a plurality of sub-recessed area nested elements nested in the outermost tube wall elements of the corresponding sub-recessed areas.

27. The antiresonant hollow core optical fiber according to any one of claims 11 to 26, characterized in that , the elements in the recessed area microstructure and the protruding area microstructure are selected from full tubes, arc-shaped structures, and straight walls.

28. The antiresonant hollow core optical fiber according to any one of claims 11 to 26, characterized in that Adjacent elements in the recessed area microstructure define a plurality of first air layers on the side of the optical fiber facing the convex shape, and adjacent elements in the convex area microstructure define a plurality of second air layers on the side of the optical fiber facing the concave shape, and the cross-sectional area of ​​each of the first air layer and the second air layer is less than 0.8 times the cross-sectional area of ​​the crescent-shaped core.

29. The antiresonant hollow core optical fiber according to claim 28, characterized in that Compared with the multiple first air layers and the multiple second air layers, the loss of light transmitted in the crescent-shaped core is minimal.

30. The antiresonant hollow core optical fiber according to any one of claims 11 to 29, characterized in that , the wall thickness of the elements in the recessed area microstructure and the protruding area microstructure is between 0.1um and 4um.

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