Hollow-core fiber and optical transmission system

Abstract

A hollow-core fiber and an optical transmission system. The hollow-core fiber comprises: a cladding layer having an annular structure, and a microstructure located in a space formed by the inner wall of the cladding layer. The microstructure comprises m tubular units, wherein the m tubular units are nested from inside to outside; among two adjacent tubular units, an inner tubular unit abuts against the inner wall of an outer tubular unit; the outermost tubular unit abuts against the inner wall of the cladding layer; the cladding layer and the m tubular units form m abutting points; two consecutive abutting points among the m abutting points and the center of a common tubular unit where the two consecutive abutting points are located form a central angle the apex of which is the center of the common tubular unit; and the m abutting points form m-1 central angles, with the angular difference between two consecutively formed central angles being greater than or equal to 0 degrees, less than or equal to 180 degrees, and not equal to 90 degrees.

Description

Hollow-core optical fiber and optical transmission system

[0001] This disclosure claims priority to Chinese Patent Application No. 202510378068.1, filed on March 26, 2025, entitled "Hollow-core optical fiber and optical transmission system", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to the field of optical communication technology, and in particular to a hollow optical fiber and an optical transmission system. Background Technology

[0003] With the increasing demands for high transmission capacity and high transmission rates in optical communication, traditional optical fibers face significant limitations in their further applications due to a series of problems, such as nonlinear effects and optical transmission delay. Compared to traditional solid-core fibers, hollow-core fibers offer advantages such as low latency, high laser damage threshold, weak nonlinearity, low dispersion, and ultra-low loss. Therefore, hollow-core fibers hold significant application potential in optical fiber communication, optical fiber sensing, and high-power laser transmission.

[0004] Hollow-core optical fiber consists of a hollow core, microstructures, and cladding. The medium in the core is generally air, while the cladding is made of transparent materials such as silicon dioxide, similar to the cladding of traditional solid-core optical fiber. The microstructures are arranged between the core and the cladding and are the key structure of hollow-core optical fiber, responsible for effectively confining the optical signal within the core for transmission.

[0005] Therefore, the performance of hollow fiber mainly depends on the design of the microstructure between the core and cladding. So how to design hollow fiber with ultra-low loss performance is a hot research topic for those skilled in the art. Summary of the Invention

[0006] This disclosure provides a hollow-core optical fiber and an optical transmission system with low transmission loss and good macrobending characteristics.

[0007] In a first aspect, this disclosure provides a hollow optical fiber, the hollow optical fiber comprising a ring-shaped cladding and a microstructure located in the space enclosed by the inner wall of the cladding, the microstructure comprising m tubular units, where m is an integer greater than or equal to 3;

[0008] The m tubular units are arranged in a ring from the inside to the outside. In two adjacent tubular units, the inner tubular unit abuts against the inner wall of the outer tubular unit, and the outermost tubular unit abuts against the inner wall of the cladding. The cladding and the m tubular units form m contact points.

[0009] Among the m contact points, two consecutive contact points and the center of the common tubular unit where the two consecutive contact points are located form a central angle with the center of the common tubular unit as the vertex. The m contact points form m-1 central angles. The angle difference between two consecutive central angles is greater than or equal to 0 degrees and less than or equal to 180 degrees and not equal to 90 degrees.

[0010] In the scheme disclosed herein, a microstructure is arranged at the center of the cladding of the hollow fiber. The microstructure is formed by multiple tubular units ringed together. This hollow fiber confines light whose wavelength does not meet the resonance condition to propagate within the fiber core. Simulation verification shows that the transmission loss is less than 0.1 dB / km in the ultra-wideband wavelength range of 450 nm (1.2 μm to 1.65 μm), which can realize ultra-wideband low-loss transmission. At the same time, it also has good macro-bending characteristics. For example, the macro-bending characteristics of the hollow fiber provided in this embodiment are comparable to those of G.652D fiber.

[0011] In one possible implementation, the angles of the m-1 central angles are all equal and not 0 degrees.

[0012] In the scheme shown in this disclosure, for example, the first contact point, the second contact point, and the center of the common tubular unit where the first and second contact points are located form a central angle with the center as its vertex. Since m tubular units and the inner wall of the cladding can form m contact points, and since two contact points form a central angle, m contact points can form m-1 central angles. All m-1 central angles are equal, that is, any two central angles among the m-1 central angles are equal.

[0013] Having any two central angles equal is beneficial for improving the rotational symmetry of hollow optical fibers. Once hollow optical fibers have good rotational symmetry, the macro-bending loss generated when the hollow optical fibers are bent will also be relatively low, thus possessing good macro-bending characteristics.

[0014] In one possible implementation, the angles of the m-1 central angles are all equal and are (360 / m) degrees.

[0015] Where m can be an integer divisible by 360. Of course, m can also be an integer not divisible by 360. In the case where m is not divisible by 360, the central angle value can be rounded to two or three decimal places. The relative difference between the central angle value and the theoretical value is considered equal within the allowable error range. For example, if the relative difference between the central angle and the theoretical value is within ±10%, the central angle is considered equal to the theoretical angle.

[0016] In the scheme shown in this disclosure, the central angle formed by two consecutive mating points is (360 / m) degrees, which is beneficial to make the center of the innermost tubular unit coincide with the center of the cladding. The hollow space enclosed by the innermost tubular unit is the core of the hollow fiber, so that the core can be located in the central region of the cladding.

[0017] In one possible implementation, among the m contact points, each contact point other than the first contact point deviates from the previous contact point in the same direction of rotation.

[0018] In the scheme disclosed herein, for example, the second contact point is offset by an angle relative to the first contact point in a clockwise rotation direction; this angle is the central angle formed by the first and second contact points. The third contact point is also offset by an angle relative to the second contact point in a clockwise rotation direction; this angle is the central angle formed by the second and third contact points. Each contact point being offset in the same rotation direction relative to the previous contact point facilitates locating the center of the innermost tubular unit at the center of the cladding, and placing the fiber core in the central region of the cladding.

[0019] In one possible implementation, an air layer is formed between the two tubular units of the ring, and the maximum thickness Hmax of the different air layers is equal.

[0020] In the scheme shown in this disclosure, for example, an air layer is formed between the first tubular unit and the second tubular unit, and the maximum thickness of the air layer is Hmax. An air layer is also formed between the second tubular unit and the third tubular unit, and the maximum thickness of the air layer is also Hmax.

[0021] In one possible implementation, the center of the innermost tubular unit coincides with the center of the cladding.

[0022] In the scheme shown in this disclosure, in the scheme with one microstructure, the hollow region enclosed by the innermost tubular unit is the core of the hollow fiber. The center of the innermost tubular unit coincides with the center of the cladding, indicating that the core of the hollow fiber is located in the central region of the cladding, which is beneficial to improving the macro-bending characteristics of the hollow fiber.

[0023] In one possible implementation, the two tubular units of the ring are tangent to each other, and the point of tangency serves as the abutment point between the two tubular units of the ring.

[0024] In one possible implementation, the outermost tubular unit is tangent to the inner wall of the cladding, and the tangent point serves as the contact point between the outermost tubular unit and the inner wall of the cladding.

[0025] In one possible implementation, the two tubular units of the ring abut against each other by an arc of equal curvature, with the abutment point between the two tubular units of the ring located on the arc.

[0026] In the scheme shown in this disclosure, the two tubular units of the ring have arcs of the same curvature and abut against each other at the position of the arc, so that the two tubular units of the ring are in surface contact, which enhances the support effect and makes the inner tubular unit stably supported on the inner wall of the outer tubular unit.

[0027] In one possible implementation, the outermost tubular unit abuts against the inner wall of the cladding via an arc of equal curvature, with the abutment point between the outermost tubular unit and the inner wall of the cladding located on the arc.

[0028] In the scheme shown in this disclosure, the outermost tubular unit is supported on the inner wall of the cladding. The two have arcs with equal curvature and are in contact at the arcs. Therefore, the outermost tubular unit and the cladding are in surface contact, so that the outermost tubular unit is stably supported on the inner wall of the cladding.

[0029] In one possible implementation, the value of m is in the range of 3 ≤ m ≤ 6.

[0030] In the scheme shown in this disclosure, m is the number of tubular units included in a single microstructure. The more tubular units there are, the lower the transmission loss of the hollow fiber. However, if there are too many tubular units, the effect on further reducing the transmission loss is limited, and the processing and manufacturing difficulty of the hollow fiber is further increased. Therefore, m is greater than or equal to 3 and less than or equal to 6, which can balance the transmission loss of the hollow fiber and the processing and manufacturing difficulty.

[0031] In one possible implementation, the ratio k between the maximum thickness Hmax of the air layer formed between the two tubular units of the ring and the radius R of the core of the hollow optical fiber ranges from 0.2 to k to 2.

[0032] The fiber core is a hollow region located at the center of the cladding. For example, in a scheme where the number of microstructures is one, the hollow region enclosed by the inner wall of the innermost tubular unit is the fiber core. In a scheme where the number of microstructures is multiple, the hollow region enclosed by multiple microstructures in the central region of the cladding is the fiber core.

[0033] In one possible implementation, the wall thickness d of the tubular unit is in the range of 0.05um ≤ d ≤ 3um.

[0034] In the scheme disclosed herein, the optical signal transmitted within the fiber core is enhanced through reflection and interference effects. For example, when light within the fiber core is incident on the wall of the tubular unit, interference occurs between the light reflected from the inner surface of the tube wall and the light reflected from the outer surface of the tube wall. By adjusting the wall thickness, constructive interference can occur, thus enhancing the transmitted signal. The wall thickness d of the tubular unit ranges from 0.05µm to 3µm, allowing for the transmission of a wider wavelength band of light within the fiber core.

[0035] In one possible implementation, the number of microstructures is one, and the hollow region enclosed by the innermost tubular unit serves as the core of the hollow optical fiber.

[0036] In the scheme shown in this disclosure, there is one microstructure. The hollow region enclosed by the inner wall of the innermost tubular unit serves as the core of the hollow fiber. In this scheme, the center of the innermost tubular unit coincides with the center of the cladding. The center of the outer ring of the cladding can be considered as the center of the cladding.

[0037] In one possible implementation, the number of microstructures is multiple and greater than or equal to 3. The multiple microstructures are distributed around the center of the cladding in a circumferential direction. The outermost tubular units of the multiple microstructures are all supported on the inner wall of the cladding, and the hollow region enclosed by the multiple microstructures serves as the core of the hollow optical fiber.

[0038] Among them, multiple microstructures can be microstructures with the same arrangement of tubular units, or microstructures with different arrangement of tubular units.

[0039] In the scheme shown in this disclosure, multiple microstructures are evenly distributed around the center of the cladding in the circumferential direction. The outermost tubular unit of each microstructure abuts against the inner wall of the cladding. The outermost tubular units of two adjacent microstructures in the circumferential direction do not contact each other, which helps to reduce transmission loss.

[0040] In one possible implementation, any two of the plurality of microstructures are rotationally symmetrical about the center of the fiber core.

[0041] In the scheme shown in this disclosure, the two microstructures are rotationally symmetrical, which is beneficial to improving the rotational symmetry of the hollow fiber, so that the hollow fiber has good macro bending characteristics.

[0042] In a second aspect, an optical transmission system is provided, the optical transmission system comprising an optical transmitter, an optical receiver, and a hollow optical fiber as described in the first aspect or any one of the first aspects, wherein the optical transmitter and the optical receiver are connected via the hollow optical fiber. Attached Figure Description

[0043] Figure 1 is a schematic cross-sectional view of a hollow optical fiber provided in an exemplary embodiment of this disclosure;

[0044] Figure 2 is a loss spectrum of the hollow fiber shown in Figure 1 after simulation testing.

[0045] Figure 3 is a schematic cross-sectional view of a hollow optical fiber provided in another exemplary embodiment of this disclosure;

[0046] Figure 4 is the loss spectrum of the hollow fiber shown in Figure 3 after simulation test.

[0047] Figure 5 is a schematic cross-sectional view of a hollow optical fiber provided in another exemplary embodiment of this disclosure;

[0048] Figure 6 is a loss spectrum of the hollow fiber shown in Figure 5 after simulation testing.

[0049] Figure 7 is a schematic cross-sectional view of a hollow optical fiber provided in another exemplary embodiment of this disclosure;

[0050] Figure 8 is a loss spectrum of the hollow fiber shown in Figure 7 after simulation testing.

[0051] Figure 9 shows the loss profile of the hollow fiber shown in Figure 7 after simulation testing at the other wall thickness of the tubular unit.

[0052] Figure 10 is a schematic cross-sectional view of a hollow optical fiber provided in another exemplary embodiment of this disclosure;

[0053] Figure 11 is the loss spectrum of the hollow fiber shown in Figure 10 after simulation test.

[0054] Figure 12 is a schematic cross-sectional view of a hollow optical fiber provided in another exemplary embodiment of this disclosure;

[0055] Figure 13 is the loss spectrum of the hollow fiber shown in Figure 12 after simulation test.

[0056] Figure 14 is a schematic cross-sectional view of a hollow optical fiber provided in another exemplary embodiment of this disclosure;

[0057] Figure 15 is the loss spectrum of the hollow fiber shown in Figure 14 after simulation test.

[0058] Figures 16 to 20 are schematic cross-sectional views of a hollow optical fiber provided in another exemplary embodiment of this disclosure. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of this disclosure clearer, the embodiments of this disclosure will be described in further detail below with reference to the accompanying drawings.

[0060] This embodiment relates to a hollow-core optical fiber. Hollow-core anti-resonant optical fiber has attracted widespread attention from researchers due to its lower transmission loss and higher laser damage threshold.

[0061] Hollow-core optical fiber consists of a cladding, a core located at the center of the cladding, and microstructures. The cladding is a transparent material such as silica, and is ring-shaped. The medium within the ring is air, an inert gas, or a vacuum. The microstructures, located within the ring region of the cladding, are the key structure of the hollow-core optical fiber, responsible for effectively confining the optical signal within the core for transmission. Therefore, the performance of hollow-core optical fiber mainly depends on the design and manufacturing of its microstructures.

[0062] Based on their different microstructures, hollow optical fibers are mainly divided into two categories: photonic bandgap fibers and anti-resonant fibers. Among them, the microstructure of photonic bandgap fibers is usually composed of transversely periodically arranged dielectric materials. Photonic bandgap fibers use the photonic bandgap effect to confine optical signals to the hollow core for transmission, forming a "bandgap" range, which prevents optical signals of a specific wavelength from propagating radially and can only be transmitted in the air core surrounded by periodically arranged dielectric materials.

[0063] The microstructure of antiresonant optical fiber is composed of regularly arranged tubular units. When light in the fiber core is incident on the tubular units, the light rays that meet the resonance condition resonate within the tubular unit wall, while the light rays that do not meet the resonance condition are reflected back into the fiber core by the tubular unit wall, thus achieving stable transmission.

[0064] Among them, tubular units are also called tubular structures, and because their walls are relatively thin, they are called capillaries.

[0065] This embodiment provides a hollow-core optical fiber, specifically an anti-resonant hollow-core optical fiber. This hollow-core optical fiber has low transmission loss and low macro-bending loss. Macro-bending loss is the optical signal loss generated by the hollow-core optical fiber at large curvature radii. For example, when light propagates in a bent hollow-core optical fiber, due to the change in the propagation speed and direction of light in the fiber core, some light rays will scatter and escape at the bend, thereby causing optical signal loss.

[0066] Macrobending loss is generally characterized by the following parameters: loss in various directions of the 1550nm band when bent 100 times with a bending radius of 30nm. The lower the macrobending loss, the better the macrobending characteristics of the hollow fiber.

[0067] Figure 1 shows a schematic cross-section of a hollow-core optical fiber. Referring to Figure 1, the hollow-core optical fiber includes a cladding with a ring-shaped structure consisting of an inner ring and an outer ring. The medium within the area enclosed by the inner ring is air, an inert gas, or a vacuum, typically air; for ease of explanation, air is used as an example in this text. The medium between the inner and outer rings is the cladding medium, generally a transparent material such as silicon dioxide. It should be noted that the hollow-core optical fiber also includes a coating layer (not shown in the figure). This coating layer surrounds the cladding and primarily serves to protect and enhance the flexibility of the hollow-core optical fiber.

[0068] Referring again to Figure 1, the hollow-core optical fiber also includes microstructures supported on the inner wall of the cladding. There can be one or more microstructures; as shown in Figure 1, there is only one microstructure, and as shown in Figure 20, there are multiple microstructures. The characteristics of a single microstructure will be described first, followed by the characteristics of multiple microstructures.

[0069] For a single microstructure, referring to Figure 1, the microstructure comprises m tubular units, where m is an integer greater than or equal to 3. For example, as shown in Figure 3, m is 4, and as shown in Figure 1, m is 6. A larger value of m makes the fabrication process of hollow-core optical fiber more difficult, while a smaller value of m may still result in relatively high transmission loss and macrobending loss. Therefore, this embodiment uses m=4 and m=6 as examples.

[0070] In one example, the m tubular units are arranged in a ring from the inside out, and in the two ringed tubular units, the diameter of the outer tubular unit is larger than the diameter of the inner tubular unit. This nested design, by nesting small-diameter tubular units within large-diameter tubular units, can further reduce the transmission loss of hollow-core optical fibers.

[0071] Since the tubular units cannot be suspended in the air, m tubular units are nested in sequence. The outermost tubular unit abuts against the inner wall of the cladding. In two adjacent layers of tubular units, the inner tubular unit abuts against the inner wall of the outer tubular unit. The hollow area enclosed by the innermost tubular unit serves as the fiber core.

[0072] In this embodiment, the m tubular units can be counted from the inside out, with the innermost tubular unit being designated as the first tubular unit and the outermost tubular unit as the m-th tubular unit, which is also the last tubular unit. Alternatively, the m tubular units can be counted from the outside in, with the outermost tubular unit being designated as the first tubular unit and the innermost tubular unit as the m-th tubular unit, which is also the last tubular unit. This embodiment does not limit the choice of tubular unit and will use the method of counting from the inside out, with the innermost tubular unit being designated as the first tubular unit.

[0073] So, from the inside out, the first tubular unit is located inside the second tubular unit and abuts against the second tubular unit. The second tubular unit is located inside the third tubular unit and abuts against the inner wall of the third tubular unit. And so on, the i-th tubular unit is located inside the (i+1)-th tubular unit and abuts against the inner wall of the (i+1)-th tubular unit. i takes a value between 1 and m-1. The m-th tubular unit is also the outermost tubular unit, located in the inner ring of the cladding and abuts against the inner wall of the cladding (i.e., the inner ring wall).

[0074] For example, referring to Figure 3, if there are 4 tubular units, then the first tubular unit is located inside the second tubular unit and abuts against the inner wall of the second tubular unit, the second tubular unit is located inside the third tubular unit and abuts against the inner wall of the third tubular unit, the third tubular unit is located inside the fourth tubular unit and abuts against the inner wall of the fourth tubular unit, the fourth tubular unit is located inside the fifth tubular unit and abuts against the inner wall of the fifth tubular unit, and the fifth tubular unit is located in the inner ring of the cladding and abuts against the inner wall of the cladding.

[0075] For example, referring to Figure 1, if there are 6 tubular units, the arrangement of the first 4 tubular units can be as described above. The 5th tubular unit no longer abuts against the inner wall of the cladding, but is located inside the 6th tubular unit and abuts against the inner wall of the 6th tubular unit. The 6th tubular unit is located in the inner ring of the cladding and abuts against the inner wall of the cladding.

[0076] Therefore, as shown in Figures 1 and 3, the inner tubular unit of the m tubular units abuts against the inner wall of the outer tubular unit, and the outermost tubular unit abuts against the inner wall of the cladding, thus forming m abutment points.

[0077] In this context, the abutment point can be a point (such as a tangent point) in the cross-sectional view of the hollow fiber, or a line on the axis of the hollow fiber. In other examples, referring to Figure 19, the abutment point can also be any point on an arc (such as the midpoint or end point of the arc). This approach will be introduced later. Below, we will first illustrate the abutment point as the tangent point of the inner tubular unit inscribed within the inner wall of the outer tubular unit.

[0078] The m landing points can be counted from the inside out, with the innermost landing point designated as the 1st landing point and the outermost landing point designated as the mth landing point. Alternatively, the m landing points can be counted from the outside in, with the innermost landing point designated as the mth landing point (the final landing point) and the outermost landing point designated as the 1st landing point. For ease of explanation, the innermost landing point will be designated as the 1st landing point.

[0079] The first tubular unit is supported on the inner wall of the second tubular unit, forming the first abutment point. The second tubular unit is supported on the inner wall of the third tubular unit, forming the second abutment point. And so on, the i-th tubular unit is supported on the inner wall of the (i+1)-th tubular unit, forming the i-th abutment point. The m-th tubular unit is supported on the inner wall of the cladding, forming the m-th abutment point.

[0080] It can be seen that the first contact point is on both the first and second tubular units, the second contact point is on both the second and third tubular units, and so on. The i-th contact point is on both the i-th and (i+1)-th tubular units, and the m-th contact point is on both the m-th tubular unit and the inner wall of the cladding.

[0081] Furthermore, two consecutive contact points, which lie on the same tubular cell, are referred to as the common tubular cell of these two contact points. The two consecutive contact points are the i-th contact point and the (i+1)-th contact point. For example, the common tubular cell belonging to the 1st and 2nd contact points is the 2nd tubular cell, and the common tubular cell belonging to the 2nd and 3rd contact points is the 3rd tubular cell. And so on, the common tubular cell belonging to the i-th and (i+1)-th contact points is the (i+1)-th tubular cell.

[0082] Among m contact points, the i-th contact point, the (i+1)-th contact point, and the center of their respective common tubular unit form a central angle with the center of the common tubular unit as its vertex. That is, two consecutive contact points and the center of their respective common tubular units form a central angle with the center of the common tubular unit as its vertex. Therefore, m contact points can form m-1 central angles.

[0083] For example, referring to Figure 7, the first and second contact points, together with the center of the second tubular unit, can form the first central angle α1 with the center of the second tubular unit as the vertex. The second and third contact points, together with the center of the third tubular unit, can form the second central angle α2 with the center of the third tubular unit as the vertex. And so on, the (m-1)th and the mth contact points, together with the center of the inner ring of the cladding, can form the (m-1)th central angle with the center of the inner ring of the cladding as the vertex.

[0084] It should be noted that, referring to Figure 7, two points on a circle and the center of the circle can form two central angles with the center as the vertex. The sum of these two central angles is 360 degrees. For ease of explanation, the central angles referred to in this embodiment are all central angles less than or equal to 180 degrees, that is, the central angles corresponding to the shorter arc segment, not the central angles corresponding to the longer arc segment. Therefore, the central angles formed by two consecutive contact points and the center of the common tubular unit are all less than or equal to 180 degrees.

[0085] In one example, the central angle formed by two consecutive contact points and the center of the common tubular unit can be greater than or equal to 0 degrees and less than or equal to 180 degrees. Specifically, the central angle formed by two consecutive contact points is 0 degrees, and the specifications state that the positions of the two consecutive contact points coincide.

[0086] In one example, among the m-1 central angles formed by the m contact points of a single microstructure, all central angles can be equal, and all are greater than 0 degrees and less than or equal to 180 degrees. The reason the central angles are greater than 0 in all cases is to avoid all contact points being in the same location. The dispersed locations of the m contact points help to distribute the thickness of the air layer, preventing concentration in areas with thinner air layers and in areas with thicker air layers. The air layer refers to the air region between two nested tubular units.

[0087] In one example, in a hollow-core optical fiber comprising a single microstructure, in order for the center of the innermost tubular unit to coincide with the center of the cladding (i.e., the center of the outer ring of the cladding, which is also the center of the cladding), all the central angles can be equal and all be (360 / m) degrees.

[0088] It should be noted that two central angles being equal means that the relative difference between the two central angles is within the allowable range of error. For example, if the relative difference between the two central angles is within ±10%, the two central angles are considered to be equal.

[0089] In addition, in the scheme where the central angle is (360 / m) degrees, m can be a factor of 360 that is greater than or equal to 3. A factor of 360 is an integer that is divisible by 360. For example, referring to Figure 5, if m is 4, the central angle is 90 degrees. Alternatively, if m is 6, the central angle is 60 degrees. Of course, m can also be an integer that is not a whole number of 360, such as m being 7 or 11. In this case, the central angle can be rounded to two or three decimal places. The relative differences between these central angles and the theoretical angle are all within the allowable error range, so these central angles are also considered equal.

[0090] In the scheme where all central angles are (360 / m) degrees, among the m contact points, in order to make the center of the innermost tubular unit coincide with the center of the cladding, it is also necessary to satisfy that: any contact point other than the first contact point deviates from the previous contact point by (360 / m) degrees in the same rotation direction.

[0091] In all schemes where the central angle is (360 / m) degrees, among the m contact points, in order to ensure that the center of the innermost tubular unit coincides with the center of the cladding, it is also necessary to satisfy that the maximum thickness Hmax of the air layer formed between the two tubular units of the ring is equal.

[0092] Of course, in all schemes where the central angles are equal, the value of the central angle can also be independent of the number of tubular units. For example, referring to Figures 1 and 3, all central angles are 180 degrees. In this scheme, any contact point other than the first contact point can deviate from the previous contact point by a specific angle in the same direction of rotation; this specific angle is the central angle formed by the two contact points. In this scheme, the maximum thickness Hmax of the air layer formed between the two nested tubular units can also be equal.

[0093] In another example, among the m-1 central angles formed by the m contact points of a single microstructure, not all central angles may be equal. In this scheme, the central angles can be greater than or equal to 0 degrees and less than or equal to 180 degrees. For example, among the m-1 central angles, there are central angles with equal angles and there are also central angles with unequal angles. For example, referring to Figure 7, the first central angle α1 is 60 degrees, the second central angle α2 is 60 degrees, the third central angle α3 is 120 degrees, the fourth central angle α4 is 60 degrees, and the fifth central angle α5 is 120 degrees.

[0094] In another example, among the m-1 central angles formed by the m contact points of a single microstructure, all central angles can be unequal. In this scheme, the central angles can be greater than or equal to 0 degrees and less than or equal to 180 degrees. For example, one central angle may be 0 degrees, while the other central angles are not 0 degrees.

[0095] It should be noted that among the m-1 central angles formed by the m contact points of a single microstructure, all the central angles are equal. Compared with all unequal or not all unequal, this is beneficial to simplifying the processing and manufacturing of hollow optical fibers.

[0096] In one example, regardless of the angular relationship between the m-1 central angles, the angular difference between any two consecutive central angles (i.e., the i-th central angle and the (i+1)-th central angle) is not equal to 90 degrees. For example, the angular difference between the first central angle α1 and the second central angle α2 is not equal to 90 degrees, and the angular difference between the (m-2)-th central angle and the (m-1)-th central angle is not equal to 90 degrees.

[0097] It should be noted that the angle difference between two consecutive central angles is the absolute value of the angle difference between the two central angles, which can also be understood as the larger central angle minus the angle difference of the smaller central angle.

[0098] As mentioned above, among the m-1 central angles formed by the m contact points of a single microstructure, all central angles can be equal. Therefore, in this scheme, the angle difference between two consecutive central angles is 0 degrees.

[0099] In the m-1 central angles formed by the m contact points of a single microstructure, all central angles can be unequal. Therefore, one of two consecutive central angles can be 0 degrees and the other can be 180 degrees. Thus, the angle difference between two consecutive central angles can be less than or equal to 180 degrees.

[0100] Therefore, the angle difference between two consecutive central angles is greater than or equal to 0 degrees and less than or equal to 180 degrees, but not equal to 90 degrees. That is, the angle difference between two consecutive central angles can be greater than or equal to 0 degrees and less than 90 degrees, or greater than 90 degrees and less than or equal to 180 degrees.

[0101] In one example, where the central angle formed by two consecutive contact points is 0 degrees to 180 degrees, then, referring to Figures 1 and 3, the straight line connecting the two consecutive contact points passes through the center of the hollow fiber (that is, the center of the fiber core). In other words, the center of the hollow fiber lies on the straight line connecting the two consecutive contact points.

[0102] In another example, where the central angle formed by two consecutive contact points is not 0 and is not 180 degrees, as shown in Figure 5, the line connecting the two consecutive contact points does not pass through the center of the hollow fiber; that is, the center of the hollow fiber is outside the line connecting the two consecutive contact points.

[0103] The following is an example where all central angles are equal.

[0104] As shown in Figure 1, there are six tubular units arranged in a left-right-right pattern relative to the center of the cladding. For example, the center of the first tubular unit coincides with the center of the cladding. Using the center of the first tubular unit as the origin and the first contact point between the first and second tubular units as a point on the x-axis, a Cartesian coordinate system is established for the cross-section of the hollow fiber. Referring to Figure 1, all six contact points are located on the x-axis, with the first contact point on the negative x-axis, the second on the positive x-axis, the third on the negative x-axis, the fourth on the positive x-axis, the fifth on the negative x-axis, and the sixth on the positive x-axis. Therefore, these six tubular units are arranged in a left-right-right pattern relative to the origin within the cladding.

[0105] Therefore, the central angle formed by two consecutive contact points and the center of the common tubular unit is 180 degrees, and the angle difference between two consecutive central angles is 0 degrees.

[0106] For example, referring to Figure 1, the first central angle α1 between the first and second contact points and the center of the common tubular unit (i.e., the second tubular unit) is 180 degrees. The second central angle α2 between the second and third contact points and the center of the common tubular unit (i.e., the third tubular unit) is 180 degrees. The third central angle α3 between the third and fourth contact points and the center of the common tubular unit (i.e., the fourth tubular unit) is 180 degrees. The fourth central angle α4 between the fourth and fifth contact points and the center of the common tubular unit (i.e., the fifth tubular unit) is 180 degrees. The fifth central angle α5 between the fifth and sixth contact points and the center of the common tubular unit (i.e., the sixth tubular unit) is 180 degrees.

[0107] In one example, when the maximum thickness Hmax of the air layer between two adjacent tubular units is a constant, that is, when the maximum thickness Hmax of any two air layers is equal, the centers of the first, third, and fifth tubular units coincide, and their cross-sections are concentric circles; the centers of the second, fourth, and sixth tubular units coincide, and their cross-sections are concentric circles.

[0108] For the hollow-core optical fiber shown in Figure 1, the core diameter (i.e., the diameter of the innermost tubular unit) is assigned a value of 35 μm, the wall thickness of each tubular unit is equal and assigned a value of 0.5 μm, and the maximum thickness Hmax of any two air layers is equal and assigned a value of 7.4 μm. Simulations are performed, resulting in the loss spectrum of the transmitted optical signal shown in Figure 2, where the horizontal axis represents the wavelength of the transmitted optical signal, and the vertical axis represents the loss value. Referring to Figure 2, the loss at 1550 nm is 3e. -4 dB / km, because the loss is less than 0.1dB in the 1.2um to 1.65um band.

[0109] Regarding the macro-bending loss of hollow-core fiber with these parameters, after 100 bends with a bending radius of 30 nm, the macro-bending losses at 1550 nm in the four directions shown in Figure 1 are as follows: 2.41 dB in the positive x-axis direction, 0.0028 dB in the negative x-axis direction, 0.007 dB in the positive y-axis direction, and 0.007 dB in the negative y-axis direction. The excessive macro-bending loss is due to the hollow-core fiber being symmetrical about the x-axis but not about the y-axis, resulting in poor rotational symmetry and hindering the confinement of the fiber mode field during bending.

[0110] Therefore, the hollow-core fiber shown in Figure 1 can achieve a loss of less than 0.1 dB / km in the ultra-wideband wavelength range of 450 nm (1.2 μm to 1.65 μm). Referring to Figure 2, a step in loss appears in the 1.3 μm to 1.45 μm band, which may be due to the presence of more contact points in the hollow-core fiber, introducing resonant loss in this band.

[0111] As shown in Figure 3, there are four tubular units. Compared with the hollow-core fiber shown in Figure 3, the arrangement of the tubular units is the same, but the number of tubular units is reduced by two. The distribution characteristics of these four tubular units within the cladding can be referred to the above description and will not be repeated here.

[0112] For the hollow-core optical fiber shown in Figure 3, the core diameter (i.e., the diameter of the innermost tubular unit) is assigned a value of 35 μm, the wall thickness of each tubular unit is equal and assigned a value of 0.5 μm, and the maximum thickness Hmax of any two air layers is equal and assigned a value of 5.8 μm. Simulation is performed, and the loss spectrum of the transmitted optical signal is shown in Figure 4. Referring to Figure 4, the loss at 1550 nm is 0.19 dB / km.

[0113] Regarding the macro-bending loss of hollow-core fiber with these parameters, after 100 bends with a bending radius of 30 nm, the macro-bending losses at 1550 nm in the four directions shown in Figure 3 are as follows: 0.18 dB in the positive x-axis direction, 8.9 dB in the negative x-axis direction, 0.57 dB in the positive y-axis direction, and 0.57 dB in the negative y-axis direction. The excessive macro-bending loss is due to the hollow-core fiber being symmetrical about the x-axis but not about the y-axis, resulting in poor rotational symmetry and hindering the confinement of the fiber mode field during bending.

[0114] Therefore, as shown in Figure 3, the hollow-core fiber can achieve a loss of less than 0.5 dB / km in the ultra-wideband wavelength range of 450 nm (1.2 μm to 1.65 μm). Referring to Figure 4, a step in loss occurs in the 1.3 μm to 1.45 μm band, which may be due to the presence of many contact points in the hollow-core fiber, introducing resonant loss in this band.

[0115] As shown in Figure 5, there are four tubular units. Using the center of the cladding as the origin and the first contact point as the point on the x-axis, a Cartesian coordinate system xoy is established. Referring to Figure 5, the central angle formed by any two consecutive contact points and the center of the common tubular unit is 90 degrees, and the angle difference between any two consecutive central angles is 0 degrees.

[0116] For example, referring to Figure 5, the first central angle α1 formed by the first contact point, the second contact point, and the center of the common tubular unit (i.e., the second tubular unit) where they are located is 90 degrees. The second central angle α2 between the second contact point, the third contact point, and the center of the common tubular unit (i.e., the third tubular unit) where they are located is 90 degrees. The third central angle α3 between the third contact point, the fourth contact point, and the center of the common tubular unit (i.e., the fourth tubular unit) where they are located is 90 degrees.

[0117] Referring to Figure 5, the four contact points are arranged radially outward in a clockwise direction from the inside out. Alternatively, they can also be arranged radially outward in a counter-clockwise direction. For example, if they are arranged radially in a clockwise direction, the second contact point is 90 degrees off-center from the first, the third, and the fourth are all 90 degrees off-center. Referring to Figure 5, in a scheme where the maximum thickness of the air layer between two tubular units is equal, the center of the inner ring wall of the cladding can coincide with the center of the innermost tubular unit. Thus, the area enclosed by the innermost tubular unit serves as the fiber core, located in the central region of the cladding.

[0118] It can be seen that the number of tubular units is a multiple of 4, the maximum thickness of different air layers is equal, and each of the multiple contact points is offset by 90 degrees relative to the previous contact point in the same rotation direction. This is beneficial to make the center of the innermost tubular unit coincide with the center of the inner ring of the cladding, so that the fiber core in the innermost tubular unit is located in the central region of the cladding.

[0119] Referring again to Figure 5, the center of the innermost tubular unit (i.e., the first tubular unit) lies outside the line connecting two consecutive contact points; that is, the line connecting two consecutive contact points does not pass through the center of the innermost tubular unit. For example, the line connecting the i-th contact point and the (i+1)-th contact point does not pass through the center of the innermost tubular unit. In the scheme shown in Figure 5, the center of the innermost tubular unit is the center of the fiber core, and the hollow region inside the innermost tubular unit serves as the fiber core.

[0120] For the hollow-core optical fiber shown in Figure 5, the core diameter (i.e., the diameter of the innermost tubular unit) is assigned a value of 35 μm, the wall thickness of each tubular unit is equal and assigned a value of 0.53 μm, and the maximum thickness Hmax of any two air layers is equal and assigned a value of 5.8 μm. Simulation is performed, and the loss spectrum of the transmitted optical signal is shown in Figure 6. Referring to Figure 6, the loss at 1550 nm is 0.13 dB / km.

[0121] Regarding the macrobending loss of hollow-core fiber with these parameters, when bent 100 times with a bending radius of 30 nm, the macrobending loss at 1550 nm in the four directions shown in Figure 5 is as follows: 0.01 dB in the positive x-axis direction, 0.1 dB in the negative x-axis direction, 0.01 dB in the positive y-axis direction, and 0.07 dB in the negative y-axis direction.

[0122] Therefore, the hollow-core fiber shown in Figure 5 can achieve a loss of less than 0.2 dB / km in the S+C+L wavelength range, where S represents the S-band (short-wavelength), C represents the C-band (conventional), and L represents the L-band (long-wavelength). Referring to Figure 6, the loss spectrum in the 1.3µm to 1.5µm range becomes flatter, possibly because the deviation between two consecutive splice points makes the hollow-core fiber structure more uniform, so that the resonance introduced by the splice point is not in this wavelength range. This hollow-core fiber can significantly reduce the macro-bending loss of the fiber, making its performance comparable to that of G.652D fiber.

[0123] The above describes an example where all central angles are equal and the angle difference between two consecutive central angles is 0 degrees. Below is an example where not all central angles are equal and the angle difference between two consecutive central angles is greater than or equal to 0 degrees, but not equal to 90 degrees.

[0124] As shown in Figure 7, there are 6 tubular units. The plane rectangular coordinate system xoy is established with the center of the cladding as the origin and the first contact point as the point on the x-axis. Referring to Figure 7, among these 6 contact points, the first central angle α1 formed by the first contact point, the second contact point, and the center of the common tubular unit (i.e., the second tubular unit) is 60 degrees; the second central angle α2 formed by the second contact point, the third contact point, and the center of the common tubular unit (i.e., the third tubular unit) is 60 degrees; the third central angle α3 formed by the third contact point, the fourth contact point, and the center of the common tubular unit (i.e., the fourth tubular unit) is 120 degrees; the fourth central angle α4 formed by the fourth contact point, the fifth contact point, and the center of the common tubular unit (i.e., the fifth tubular unit) is 60 degrees; and the fifth central angle α5 formed by the fifth contact point, the sixth contact point, and the center of the common tubular unit (i.e., the sixth tubular unit) is 120 degrees.

[0125] It can be seen that the angle difference between the first central angle α1 and the second central angle α2 is 0 degrees, the angle difference between the second central angle α2 and the third central angle α3 is 60 degrees, the angle difference between the third central angle α3 and the fourth central angle α4 is 60 degrees, and the angle difference between the fourth central angle α4 and the fifth central angle α5 is 60 degrees.

[0126] Referring again to Figure 7, the second contact point deviates by 60 degrees clockwise from the first contact point; the third contact point deviates by 60 degrees clockwise from the second contact point; the fourth contact point deviates by 120 degrees clockwise from the third contact point; the fifth contact point deviates by 60 degrees clockwise from the fourth contact point; and the sixth contact point deviates by 120 degrees counterclockwise from the fifth contact point (also referred to as a 240-degree clockwise rotation; in this embodiment, the central angle is less than or equal to 180 degrees). Therefore, it can be seen that multiple contact points can also split radially outwards from the inside out, not necessarily in the same direction of rotation.

[0127] Referring to Figure 7, the line connecting two consecutive contact points may not pass through the center of the innermost tubular unit; that is, the center of the innermost tubular unit is outside the line connecting the two consecutive contact points. For example, the line connecting the i-th contact point and the (i+1)-th contact point does not pass through the center of the innermost tubular unit. In the scheme shown in Figure 7, the center of the innermost tubular unit is the center of the fiber core, and the hollow region inside the innermost tubular unit serves as the fiber core.

[0128] For the hollow-core optical fiber shown in Figure 7, the core diameter (i.e., the diameter of the innermost tubular unit) is assigned a value of 35 μm, the wall thickness of each tubular unit is equal and assigned a value of 0.53 μm, and the maximum thickness Hmax of any two air layers is equal and assigned a value of 5.8 μm. Simulations are performed, and the loss spectrum of the transmitted optical signal is shown in Figure 8. Referring to Figure 8, the loss at 1550 nm is 1.8e. -3 dB / km.

[0129] Regarding the macrobending loss of hollow-core fiber with these parameters, after 100 bends with a bending radius of 30 nm, the macrobending losses at 1550 nm in the four directions shown in Figure 7 are as follows: 0.003 dB in the positive x-axis direction, 0.012 dB in the negative x-axis direction, 0.12 dB in the positive y-axis direction, and 0.00014 dB in the negative y-axis direction. It can be seen that the hollow-core fiber shown in Figure 7, due to its good rotational symmetry, can significantly reduce macrobending loss, and its performance is comparable to that of G.652D fiber.

[0130] Therefore, as shown in Figure 7, hollow-core fiber can achieve a loss of less than 0.1 dB / km in the ultra-wide wavelength range of 450 nm (1.2 μm to 1.65 μm). Referring to Figure 8, the loss spectrum in the range of 1.3 μm to 1.5 μm becomes flatter. Because the two consecutive mating points do not coincide, the structure is more uniform, and the resonance introduced by the mating points is not in this wavelength range. At the same time, it can significantly reduce the macrobending loss of the fiber. The level of hollow-core fiber is comparable to that of G.652D fiber.

[0131] In one example, still targeting the hollow-core fiber shown in Figure 7, the core diameter is still assigned a value of 35 μm, but the wall thickness of the tubular unit is assigned a value of 1.3 μm, and the maximum thickness of the air layer Hmax is still assigned a value of 5.8 μm. Under these parameter settings, the loss spectrum of the transmitted optical signal is obtained as shown in Figure 9. Referring to Figure 12, the loss at 1550 nm is 1.2 e -3 dB / km. This hollow-core fiber can achieve a loss of less than 0.1 dB / km in the S+C+L wavelength range.

[0132] As shown in Figure 10, there are 6 tubular units. The plane rectangular coordinate system xoy is established with the center of the cladding as the origin and the first contact point as the point on the x-axis. Referring to Figure 9, among these 6 contact points, the first central angle α1 formed by the first contact point, the second contact point, and the center of the common tubular unit (i.e., the second tubular unit) is 50 degrees; the second central angle α2 formed by the second contact point, the third contact point, and the center of the common tubular unit (i.e., the third tubular unit) is 60 degrees; the third central angle α3 formed by the third contact point, the fourth contact point, and the center of the common tubular unit (i.e., the fourth tubular unit) is 130 degrees; the fourth central angle α4 formed by the fourth contact point, the fifth contact point, and the center of the common tubular unit (i.e., the fifth tubular unit) is 60 degrees; and the fifth central angle α5 formed by the fifth contact point, the sixth contact point, and the center of the common tubular unit (i.e., the sixth tubular unit) is 120 degrees.

[0133] It can be seen that the angle difference between the first central angle α1 and the second central angle α2 is 10 degrees, the angle difference between the second central angle α2 and the third central angle α3 is 70 degrees, the angle difference between the third central angle α3 and the fourth central angle α4 is 70 degrees, and the angle difference between the fourth central angle α4 and the fifth central angle α5 is 60 degrees.

[0134] Referring to Figure 10, the second contact point is 50 degrees off from the first contact point in a clockwise direction; the third contact point is 60 degrees off from the second contact point in a clockwise direction; the fourth contact point is 130 degrees off from the third contact point in a clockwise direction; the fifth contact point is 60 degrees off from the fourth contact point in a clockwise direction; and the sixth contact point is 120 degrees off from the fifth contact point in a counterclockwise direction.

[0135] Referring to Figure 10, the line connecting two consecutive contact points may not pass through the center of the innermost tubular unit; that is, the center of the innermost tubular unit is outside the line connecting the two consecutive contact points. For example, the line connecting the i-th contact point and the (i+1)-th contact point does not pass through the center of the innermost tubular unit. In the scheme shown in Figure 10, the center of the innermost tubular unit is the center of the fiber core, and the hollow region inside the innermost tubular unit serves as the fiber core.

[0136] For the hollow-core optical fiber shown in Figure 10, the core diameter (i.e., the diameter of the innermost tubular unit) is assigned a value of 35 μm, the wall thickness of each tubular unit is equal and assigned a value of 0.53 μm, and the maximum thickness Hmax of any two air layers is equal and assigned a value of 5.8 μm. Simulations are performed, and the loss spectrum of the transmitted optical signal is shown in Figure 11. Referring to Figure 11, the loss at 1550 nm is 2e... -4 dB / km. This hollow-core fiber can achieve a loss of less than 0.1 dB / km in the S+C+L wavelength range.

[0137] Regarding the macrobending loss of this type of hollow-core fiber, after 100 bends with a bending radius of 30 nm, the macrobending losses at 1550 nm in the four directions shown in Figure 10 are as follows: 0.027 dB in the positive x-axis direction, 0.009 dB in the negative x-axis direction, 0.05 dB in the positive y-axis direction, and 0.001 dB in the negative y-axis direction. It can be seen that the hollow-core fiber shown in Figure 10, due to its better rotational symmetry and lower macrobending loss in all directions, outperforms the G.652D fiber.

[0138] As shown in Figure 12, there are 6 tubular units. Using the center of the cladding as the origin, a Cartesian coordinate system xoy is established with the first contact point as the x-axis. Referring to Figure 12, among these 6 contact points, the first central angle α1 formed by the center of the first contact point, the second contact point, and the center of the common tubular unit (i.e., the second tubular unit) is 50 degrees; the second central angle α2 formed by the center of the second contact point, the third contact point, and the center of the common tubular unit (i.e., the third tubular unit) is 150 degrees; and the third contact point, the fourth contact point, and the center of the common tubular unit... The third central angle α3 formed by the center of the tubular unit (i.e., the 4th tubular unit) is 40 degrees; the fourth central angle α4 formed by the center of the 4th and 5th contact points and the center of the common tubular unit (i.e., the 5th tubular unit) is 100 degrees; and the fifth central angle α5 formed by the center of the 5th and 6th contact points and the center of the common tubular unit (i.e., the 6th tubular unit) is 120 degrees.

[0139] It can be seen that the angle difference between the first central angle α1 and the second central angle α2 is 100 degrees, the angle difference between the second central angle α2 and the third central angle α3 is 110 degrees, the angle difference between the third central angle α3 and the fourth central angle α4 is 60 degrees, and the angle difference between the fourth central angle α4 and the fifth central angle α5 is 20 degrees.

[0140] Referring to Figure 12, the second contact point is 50 degrees off from the first contact point in a clockwise direction; the third contact point is 150 degrees off from the second contact point in a clockwise direction; the fourth contact point is 40 degrees off from the third contact point in a clockwise direction; the fifth contact point is 100 degrees off from the fourth contact point in a clockwise direction; and the sixth contact point is 120 degrees off from the fifth contact point in a clockwise direction.

[0141] Referring to Figure 12, the line connecting two consecutive contact points may not pass through the center of the innermost tubular unit; that is, the center of the innermost tubular unit is outside the line connecting the two consecutive contact points. For example, the line connecting the i-th contact point and the (i+1)-th contact point does not pass through the center of the innermost tubular unit. In the scheme shown in Figure 12, the center of the innermost tubular unit is the center of the fiber core, and the hollow region inside the innermost tubular unit serves as the fiber core.

[0142] For the hollow-core optical fiber shown in Figure 12, the core diameter (i.e., the diameter of the innermost tubular unit) is assigned a value of 35 μm, the wall thickness of each tubular unit is equal and assigned a value of 1.3 μm, and the maximum thickness Hmax of any two air layers is equal and assigned a value of 5.8 μm. Simulations are performed, yielding the loss spectrum of the transmitted optical signal shown in Figure 13. Referring to Figure 14, the loss at 1550 nm is 1e. -3 dB / km. This hollow-core fiber can achieve a loss of less than 0.1 dB / km in the S+C+L wavelength range.

[0143] Regarding the macrobending loss of this type of hollow-core fiber, after 100 bends with a bending radius of 30 nm, the macrobending losses at 1550 nm in the four directions shown in Figure 12 are as follows: 0.05 dB in the positive x-axis direction, 0.01 dB in the negative x-axis direction, 0.02 dB in the positive y-axis direction, and 0.0005 dB in the negative y-axis direction. It can be seen that the hollow-core fiber shown in Figure 12, due to its better rotational symmetry and lower macrobending loss in all directions, outperforms the G.652D fiber.

[0144] As shown in Figure 14, there are 6 tubular units. Using the center of the cladding as the origin and the first contact point as the point on the x-axis, a Cartesian coordinate system xoy is established. Referring to Figure 14, among these 6 contact points, the first central angle α1 formed by the center of the first contact point, the second contact point, and the center of the common tubular unit (i.e., the second tubular unit) is 50 degrees; the second central angle α2 formed by the center of the second contact point, the third contact point, and the center of the common tubular unit (i.e., the third tubular unit) is 90 degrees; and the third contact point, the fourth contact point, and the center of the common tubular unit... The third central angle α3 formed by the center of the fourth tubular unit (i.e., the fourth tubular unit) is 100 degrees. The fourth central angle α4 formed by the fourth and fifth contact points and the center of the common tubular unit (i.e., the fifth tubular unit) is 60 degrees. The fifth central angle α5 formed by the fifth and sixth contact points and the center of the common tubular unit (i.e., the sixth tubular unit) is 120 degrees.

[0145] It can be seen that the angle difference between the first central angle α1 and the second central angle α2 is 40 degrees, the angle difference between the second central angle α2 and the third central angle α3 is 10 degrees, the angle difference between the third central angle α3 and the fourth central angle α4 is 40 degrees, and the angle difference between the fourth central angle α4 and the fifth central angle α5 is 60 degrees.

[0146] Referring again to Figure 14, the second contact point deviates by 50 degrees clockwise from the first contact point; the third contact point deviates by 90 degrees clockwise from the second; the fourth contact point deviates by 100 degrees clockwise from the third; the fifth contact point deviates by 60 degrees clockwise from the fourth; and the sixth contact point deviates by 120 degrees counterclockwise from the fifth. This demonstrates that multiple contact points can also split radially outwards from the inside out, not necessarily in the same direction of rotation.

[0147] Referring to Figure 14, the line connecting two consecutive contact points may not pass through the center of the innermost tubular unit; that is, the center of the innermost tubular unit is outside the line connecting the two consecutive contact points. For example, the line connecting the i-th contact point and the (i+1)-th contact point does not pass through the center of the innermost tubular unit. In the scheme shown in Figure 14, the center of the innermost tubular unit is the center of the fiber core, and the hollow region inside the innermost tubular unit serves as the fiber core.

[0148] For the hollow-core optical fiber shown in Figure 14, the core diameter (i.e., the diameter of the innermost tubular unit) is assigned a value of 35 μm, the wall thickness of each tubular unit is equal and assigned a value of 0.53 μm, and the maximum thickness Hmax of any two air layers is equal and assigned a value of 5.8 μm. Simulation is performed, and the loss spectrum of the transmitted optical signal is shown in Figure 15. Referring to Figure 15, the loss at 1550 nm is 1.6 e -4 dB / km.

[0149] Regarding the macrobending loss of hollow-core fiber with these parameters, when bent 100 times with a bending radius of 30 nm, the macrobending loss at 1550 nm in the four directions shown in Figure 14 is as follows: 0.007 dB in the positive x-axis direction, 0.024 dB in the negative x-axis direction, 0.04 dB in the positive y-axis direction, and 0.0002 dB in the negative y-axis direction.

[0150] As can be seen, the hollow-core fiber shown in Figure 14 can achieve a loss of less than 0.1 dB / km in the S+C+L wavelength range. Due to the good rotational symmetry of the hollow-core fiber and its low macro-bending loss in all directions, the performance of this hollow-core fiber is superior to that of G.652D fiber.

[0151] As can be seen from the above, the angle difference between two consecutive central angles can be a constant value, such as 0 degrees or 60 degrees, or other angle values ​​other than 90 degrees. The angle difference between two consecutive central angles can also be non-constant.

[0152] As can be seen from the above, the wall thickness d of multiple tubular units in the microstructure is usually equal, and its value is related to the wavelength of the optical signal transmitted by the hollow optical fiber. For example, in order to realize the transmission of optical signals in the S+C+L band, the wall thickness d of multiple tubular units in the microstructure can be in the range of 0.05um≤d≤3um.

[0153] As described above, the maximum thickness Hmax of the air layer between two adjacent tubular units can be equal. In another example, the maximum thickness Hmax of the air layer between two adjacent tubular units may also be unequal. However, regardless of whether they are equal, the value of Hmax is related to the radius of the fiber core; for example, the ratio k between Hmax and the radius of the fiber core can be in the range of 0.2 ≤ k ≤ 2.

[0154] In one example, the maximum thickness Hmax of the air layer between two adjacent tubular units may not be equal. For example, as shown in Figure 16, in a scheme where there are 4 tubular units and the central angle formed by two consecutive contact points and the center of the common tubular unit is 90 degrees, the maximum thickness of the air layer between the 1st and 2nd tubular units is H1max, the maximum thickness of the air layer between the 2nd and 3rd tubular units is H2max, the maximum thickness of the air layer between the 3rd and 4th tubular units is H1max, and the maximum thickness of the air layer between the 4th tubular unit and the inner wall of the cladding is H2max. Here, H1max and H2max are not equal, for example, H2max = 1.5 × H1max. This can also be understood as the maximum thickness of multiple air layers from the inside out being H1max, H2max, H1max, H2max. That is, the maximum thickness of the odd-numbered air layer is H1max, and the maximum thickness of the even-numbered air layer is H2max. However, H1max and H2max are not equal.

[0155] For example, as shown in Figure 17, taking four tubular units as an example, in a scheme where the central angle formed by two consecutive contact points and the center of the common tubular unit is 180 degrees, the maximum thickness of the air layer between the first and second tubular units is H1max, the maximum thickness of the air layer between the second and third tubular units is H1max, the maximum thickness of the air layer between the third and fourth tubular units is H2max, and the maximum thickness of the air layer between the fourth tubular unit and the inner wall of the cladding is H2max. H1max and H2max are not equal. This can also be understood as the maximum thickness of the air layer on the same side of the first tubular unit being unequal, but the maximum thickness of the air layer on the left and right sides of the first tubular unit being equal.

[0156] For example, as shown in Figure 18, taking four tubular units as an example, in a scheme where the central angle formed by two consecutive contact points and the center of the common tubular unit is 180 degrees, the maximum thickness of the air layer between the first and second tubular units is H1max, the maximum thickness of the air layer between the second and third tubular units is H1max, the maximum thickness of the air layer between the third and fourth tubular units is H2max, and the maximum thickness of the air layer between the fourth tubular unit and the inner wall of the cladding is H1max. Among these, H1max and H2max are not equal.

[0157] It should be noted that whether the maximum thicknesses of different air layers are equal, and the relationship between the maximum thicknesses of different air layers, are all related to the macrobending loss, transmission loss, and broader loss spectrum of hollow-core optical fibers. Furthermore, air layers with different maximum thicknesses can adjust the effective refractive index of the cladding within the air layer, making it difficult for the refractive indices of higher-order modes in the cladding to match those in the fiber core. This enhances higher-order mode suppression coupling, reduces the transmission loss of higher-order modes, and thus enables the transmission of multiple sets of higher-order modes within the fiber core.

[0158] In one example, to make the inner tubular unit more firmly abut against the inner wall of the outer tubular unit, as shown in Figure 19, among the m tubular units, the i-th tubular unit and the (i+1)-th tubular unit have an arc with the same curvature, and the abutment point between the i-th tubular unit and the (i+1)-th tubular unit is located on the arc with the same curvature, and / or, the outermost tubular unit and the cladding have an arc with the same curvature, and the abutment point between the outermost tubular unit and the cladding is located on the arc with the same curvature.

[0159] For example, the first and second tubular units share a circular arc with the same curvature. The first tubular unit abuts against the inner wall of the second tubular unit via this arc. In this case, the first and second tubular units are in surface contact, not line contact (tangency is a form of line contact). Referring to Figure 19, the curvature of the circular arc with the same curvature in the first and second tubular units is the same as the curvature of the second tubular unit.

[0160] Similarly, the second and third tubular units share an arc with the same curvature. The second tubular unit abuts against the inner wall of the third tubular unit via this arc. In this case, the second and third tubular units are in surface contact, not line contact. Referring to Figure 19, the curvature of the arc segment with the same curvature in the second and third tubular units is the same as the curvature of the third tubular unit.

[0161] Similarly, the inner tubular units and the outer tubular units share a circular arc with the same curvature, which is the same as the curvature of the outer tubular units.

[0162] The outermost tubular unit and the inner wall of the cladding share a circular arc with the same curvature. The outermost tubular unit abuts against the inner wall of the third tubular unit via this arc. In this case, the outermost tubular unit and the inner wall of the cladding are in surface contact, not line contact. Referring to Figure 19, the curvature of the circular arc with the same curvature as the inner wall of the cladding is the same as the curvature of the inner wall of the cladding.

[0163] Of course, it can also be the other way around: the curvature of a segment of an arc in the inner tubular unit that has the same curvature as the outer tubular unit is equal to the curvature of the inner tubular unit; and the curvature of a segment of an arc in the outermost tubular unit that has the same curvature as the inner ring wall of the cladding is equal to the curvature of the outermost tubular unit.

[0164] The inner tubular unit is in surface contact with the outer tubular unit, which makes the microstructure inside the hollow fiber more stable in the cladding. This structure makes it easier to achieve a stable connection between the cladding and the tubular unit during the drawing process of the hollow fiber, thereby reducing the requirements for the manufacturing process of the hollow fiber.

[0165] It should be noted that in the scheme in Figure 19 where the inner tubular unit and the outer tubular unit have a segment of arc with equal curvature, the midpoint of the arc with equal curvature can be used as the contact point to determine the central angle mentioned above, or the endpoint of the arc with equal curvature can be used as the contact point to determine the central angle mentioned above.

[0166] In one example, the above figures illustrate a scheme where a microstructure is arranged within the cladding, as shown in Figure 20. Multiple microstructures can be arranged within the cladding, with the number of microstructures being greater than or equal to three. Figure 20 shows four microstructures as an example. Referring to Figure 20, the outermost tubular units of the multiple microstructures are all supported on the inner wall of the cladding, and these multiple microstructures are distributed (e.g., uniformly distributed) around the center (i.e., the center of the circle) of the cladding in the circumferential direction. The hollow region enclosed by these multiple microstructures is the core of the hollow-core optical fiber. Referring to Figure 20, the radius R of the core is the radius of the circle tangent to the outermost tubular unit of the multiple microstructures. The coordinate system in Figure 20 uses the line connecting the first contact point of the first microstructure 10 and the center of the innermost tubular unit as the x-axis.

[0167] In one example, the outermost tubular units of two adjacent microstructures typically do not contact each other; for example, referring to Figure 20, there is a gap between the outermost tubular units of the two microstructures. This reduces the transmission loss of the hollow-core fiber.

[0168] In one example, four microstructures are arranged in the cladding, as shown in Figure 20, and are respectively labeled as the first microstructure 10, the second microstructure 20, the third microstructure 30, and the fourth microstructure 40. The second microstructure 20 is rotated 90 degrees clockwise relative to the first microstructure 10, the third microstructure 30 is rotated 90 degrees clockwise relative to the second microstructure 20, and the fourth microstructure 40 is rotated 90 degrees clockwise relative to the third microstructure 30.

[0169] In this arrangement, any two microstructures are rotationally symmetrical about the center of the fiber core, with a rotation angle of (360 / n) degrees, where n is the number of microstructures. This arrangement enhances the rotational symmetry of the hollow fiber, thereby reducing macrobending loss.

[0170] It should be noted that multiple microstructures within the cladding can be the same microstructure. For example, the four microstructures in Figure 20 are the same microstructure, all of which are the microstructures shown in Figure 5. In other examples, the multiple microstructures of the cladding can be different microstructures. For example, they can be completely different or partially the same. The microstructure can be any of the microstructures described above.

[0171] In this embodiment, a microstructure is arranged at the center of the cladding of the hollow fiber. The microstructure is formed by multiple tubular units ringed together. This hollow fiber confines light whose wavelength does not meet the resonance condition to the core for transmission. Simulation verification shows that the transmission loss is less than 0.1 dB / km in the ultra-wideband wavelength range of 450 nm (1.2 μm to 1.65 μm), which can realize ultra-wideband low-loss transmission. At the same time, it also has good macro-bending characteristics. For example, the macro-bending characteristics of the hollow fiber provided in this embodiment are comparable to those of G.652D fiber.

[0172] This embodiment also provides an optical transmission system, which includes an optical transmitter, an optical receiver, and the hollow optical fiber described above. The optical transmitter and the optical receiver are connected by at least one section of hollow optical fiber.

[0173] In one example, hollow-core optical fiber, with its advantages of lower latency, lower transmission loss, and support for more optical bands, can be applied in fields such as optical communication, sensors, and high-power laser transmission. For instance, hollow-core optical fiber can be used in data center optical interconnects, where the optical transmitter and receiver can be network devices (such as switches or routers) deployed in the data center. Another example is the real-time online monitoring of hydrogen sulfide (H2S) in natural gas pipelines. Yet another example is its application in laser cutting or welding, medical laser surgery, and research-grade ultrafast lasers (femtosecond pulses).

[0174] The terminology used in the embodiments of this disclosure is for illustrative purposes only and is not intended to limit the disclosure. Unless otherwise defined, the technical or scientific terms used in the embodiments of this disclosure should be understood in their ordinary sense by one of ordinary skill in the art to which this disclosure pertains. The terms "first," "second," and similar terms used in this specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, "a" or "an," and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms "comprising," "including," and similar terms mean that the elements or objects preceding "comprising" or "including" encompass the elements or objects listed following "comprising" or "including" and their equivalents, but do not exclude other elements or objects. "Upper," "lower," "left," "right," etc., are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly. "A plurality" refers to two or more, unless otherwise expressly defined.

[0175] The above description is merely an optional embodiment of this disclosure and is not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A hollow-core optical fiber, characterized in that, The hollow optical fiber includes a ring-shaped cladding and a microstructure located in the space enclosed by the inner wall of the cladding. The microstructure includes m tubular units, where m is an integer greater than or equal to 3. The m tubular units are arranged in a ring from the inside to the outside. In two adjacent tubular units, the inner tubular unit abuts against the inner wall of the outer tubular unit, and the outermost tubular unit abuts against the inner wall of the cladding. The cladding and the m tubular units form m contact points. Among the m contact points, two consecutive contact points and the center of the common tubular unit where the two consecutive contact points are located form a central angle with the center of the common tubular unit as the vertex. The m contact points form m-1 central angles. The angle difference between two consecutive central angles is greater than or equal to 0 degrees and less than or equal to 180 degrees and not equal to 90 degrees.

2. The hollow-core optical fiber according to claim 1, characterized in that, The angles of the m-1 central angles are all equal and not 0 degrees.

3. The hollow-core optical fiber according to claim 1 or 2, characterized in that, The angles of the m-1 central angles are all equal and are (360 / m) degrees.

4. The hollow-core optical fiber according to any one of claims 1 to 3, characterized in that, Of the m contact points, each contact point except the first contact point deviates from the previous contact point in the same direction of rotation.

5. The hollow-core optical fiber according to any one of claims 1 to 4, characterized in that, The center of the hollow optical fiber is located outside the straight line connecting two consecutive mating points.

6. The hollow-core optical fiber according to any one of claims 1 to 5, characterized in that, The center of the innermost tubular unit coincides with the center of the cladding.

7. The hollow-core optical fiber according to any one of claims 1 to 6, characterized in that, The two tubular units of the ring are tangent to each other, and the point of tangency serves as the abutment point between the two tubular units of the ring.

8. The hollow-core optical fiber according to any one of claims 1 to 7, characterized in that, The outermost tubular unit is tangent to the inner wall of the cladding, and the point of tangency serves as the contact point between the outermost tubular unit and the inner wall of the cladding.

9. The hollow-core optical fiber according to any one of claims 1 to 6 or 8, characterized in that, The two tubular units of the ring abut against each other by an arc of equal curvature, and the abutment point between the two tubular units of the ring is located on the arc.

10. The hollow-core optical fiber according to any one of claims 1 to 7 or 9, characterized in that, The outermost tubular unit abuts against the inner wall of the cladding through an arc of equal curvature, and the abutment point between the outermost tubular unit and the inner wall of the cladding is located on the arc.

11. The hollow-core optical fiber according to any one of claims 1 to 10, characterized in that, The value of m is in the range of 3 ≤ m ≤ 6.

12. The hollow-core optical fiber according to any one of claims 1 to 11, characterized in that, The wall thickness d of the tubular unit ranges from 0.05um to 3um.

13. The hollow-core optical fiber according to any one of claims 1 to 12, characterized in that, The number of microstructures is one, and the hollow region enclosed by the innermost tubular unit serves as the core of the hollow optical fiber.

14. The hollow-core optical fiber according to any one of claims 1 to 12, characterized in that, The number of microstructures is multiple and greater than or equal to 3. The multiple microstructures are distributed around the center of the cladding in a circumferential direction. The outermost tubular units of the multiple microstructures are all supported on the inner wall of the cladding, and the hollow region enclosed by the multiple microstructures serves as the core of the hollow optical fiber.

15. The hollow-core optical fiber according to claim 13 or 14, characterized in that, For a single microstructure, the ratio k between the maximum thickness Hmax of the air layer formed between the two tubular units of the ring and the radius R of the fiber core ranges from 0.2 to 2.

16. The hollow-core optical fiber according to claim 15, characterized in that, Any two of the multiple microstructures are rotationally symmetrical about the center of the fiber core.

17. An optical transmission system, characterized in that, The optical transmission system includes an optical transmitter, an optical receiver, and a hollow optical fiber as described in any one of claims 1 to 16, wherein the optical transmitter and the optical receiver are connected via the hollow optical fiber.

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