Hollow-core anti-resonance optical fiber for transmission in ultraviolet-visible-short wave middle-infrared band

Abstract

The invention relates to an ultraviolet-visible-short wave mid-infrared transmission hollow-core anti-resonance optical fiber, which comprises an outer cladding region (7), an inner cladding region and an air fiber core region (1), and is characterized in that the inner cladding region comprises a cladding wall, an arc-shaped supporting tube (5) and a circular cladding tube (6); the cladding wall comprises a first cladding tube (2), a second nested cladding tube (3) and a supporting tube (4); the air fiber core area (1) is an air hole enclosed by a resonant tube cladding. A contact type and multi-wall-thickness combined design is provided to construct an efficient hollow-core anti-resonance structure, low-loss transmission of a fundamental mode and multiple high-order modes is supported, light leakage is restrained, and few-mode high-power low-loss stable transmission of three wavebands of ultraviolet light, visible light and short-wave near-infrared light can be achieved. The method has important application in the fields of laser transmission, medical treatment, processing, remote sensing and the like.

Description

A hollow anti-resonant optical fiber for transmission in the ultraviolet-visible-shortwave-mid-infrared band Technical Field

[0001] This invention relates to the field of optical fibers, and in particular to a hollow-core anti-resonant optical fiber for transmission in the ultraviolet-visible-shortwave-mid-infrared band. Background Technology

[0002] With the rapid development of fiber optic technology, hollow-core antiresonant fiber has gradually become a research hotspot in the field of fiber optics due to its unique structure and excellent performance. Hollow-core antiresonant fiber confines light within the air medium of the fiber core through the antiresonant reflection waveguide effect, achieving light transmission within the air core and greatly reducing the overlap between the mode field and the cladding material. This characteristic of hollow-core antiresonant fiber significantly reduces the interaction between light and the surrounding materials, resulting in advantages such as low loss, low dispersion, low nonlinearity, and a high damage threshold. Furthermore, the characteristics of hollow-core antiresonant fiber allow for optimized design, enabling energy transmission from the ultraviolet to the mid-infrared band.

[0003] In the ultraviolet (UV) band, material absorption is the main factor limiting traditional optical fiber transmission. Due to intrinsic defects in fiber materials, there is significant Rayleigh scattering and photodarkening, leading to increased transmission loss and irreversible damage. In contrast, hollow-core antiresonant fiber, by suppressing coupling, confines light within an air core, avoiding material absorption and damage problems, and providing a practical and efficient method for UV light transmission. However, there are currently relatively few hollow-core antiresonant fibers designed specifically for the UV band. The short wavelength of the UV band limits the theoretically suitable wall thickness, restricting the flexibility of fiber design and increasing the difficulty of the drawing process.

[0004] Existing fiber drawing technology makes it difficult to achieve theoretically thin-walled structures in the ultraviolet band. Furthermore, thin cladding tubes are prone to instability and deformation of the cladding structure, which in turn affects fiber performance and limits the application of hollow anti-resonant fibers in the ultraviolet band. Summary of the Invention

[0005] In view of this, it is of great significance to propose a hollow anti-resonant optical fiber that can achieve low-loss, high-power transmission in the ultraviolet band, and at the same time optimize its structure to make it have a simpler industrial drawing process and more reliable long-term stability.

[0006] To achieve the above objectives, this invention proposes a hollow-core anti-resonant optical fiber for high-energy transmission in the ultraviolet-visible-shortwave and mid-infrared ranges, comprising: an outer cladding region, an inner cladding region, and an air core region. The inner cladding region includes a cladding wall, an arc-shaped support tube, and a circular cladding tube. The cladding wall includes a first cladding tube, a second nested cladding tube, and a support tube. The air core region consists of air holes formed by the cladding of the resonant tubes, filled with gas or a vacuum.

[0007] Preferably, the arc-shaped support tube is located in the gap of the cladding wall and is used to support the outermost tube of the cladding wall.

[0008] Preferably, the size range of the first cladding tube and the circular cladding tube is 0.4 to 1 µm, and the wall thickness range of the second nested cladding tube and the support tube is 1.2 to 1.8 µm.

[0009] Preferably, the materials of the first cladding tube, the second nested cladding tube, the support tube, and the outer cladding region are quartz glass, fluoride glass, sulfide glass, or silicate glass.

[0010] Preferably, the refractive indices of the first cladding tube (2), the second nested cladding tube (3), and the support tube (4) are all equal, with a refractive index range of 1.4878 to 1.5853.

[0011] Preferably, the first cladding tube, the second nested cladding tube, and the support tube are tangent at a point on the inner glass wall of the outer cladding region.

[0012] Preferably, the diameter of the air core region is in the range of 20 to 50 μm; the diameter of the first cladding tube is in the range of 16 to 25 μm; the diameter of the second nested cladding tube is in the range of 10 to 15 μm; and the diameter of the arc-shaped support tube is in the range of 7 to 12 μm.

[0013] Preferably, the arc-shaped support tube is tangent to the adjacent first cladding tube at a point and also contacts the outer cladding region, and the circular cladding tube is nested inside the arc-shaped support tube and tangent to the outer cladding region at a point.

[0014] Preferably, the operating wavelength is in the ultraviolet, visible, and short-wave near-infrared range.

[0015] Preferably, the formula for the anti-resonant reflective waveguide effect is:

[0016]

[0017] Where λ is the wavelength, k is the anti-resonance order, nglass is the refractive index of the material used, and nair is the refractive index of air.

[0018] Preferably, t1 and t2 are multiples of each other, half of the resonant wavelength of t2 overlaps with the resonant wavelength of t1, and the resonant order of t2 is twice the adjacent resonant order of t1, resulting in a narrow resonant region. The other half overlaps with the anti-resonant wavelength.

[0019] Compared with the prior art, the advantages of the present invention are as follows: the supporting semi-circle of the present invention makes the outermost thin-walled large nested circular structure more stable and enhances the overall mechanical strength of the optical fiber.

[0020] The small holes within the supporting semi-circle of the present invention help to further reduce higher-order mode losses.

[0021] The multi-wall thickness combination of the present invention can reduce the difficulty of drawing thin-walled ultraviolet anti-resonant optical fibers, while the nested circles with different wall thicknesses widen the guide band of the optical fiber. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 is a schematic diagram of a hollow-core anti-resonant optical fiber for ultraviolet-visible-shortwave mid-infrared transmission provided by the present invention; Figure 2(a) is a diagram showing the confinement loss (CL) of the anti-resonant hollow-core optical fiber applied to the ultraviolet band (180-370nm) as a function of wavelength (fundamental mode and LP11, LP31, and LP32 higher-order modes) provided in the embodiment of this application; Figure 2(b) is a transverse field diagram of the fundamental mode and higher-order modes of the anti-resonant hollow-core optical fiber applied to the ultraviolet band (355nm) provided in the embodiment of this application; Figure 3(a) is a diagram showing the confinement loss (CL) of the anti-resonant hollow-core optical fiber applied to the visible light band (385nm-480nm) as a function of wavelength (fundamental mode and LP11, LP31, and LP32 higher-order modes) provided in the embodiment of this application; Figure 3(b) is a diagram showing the transverse field diagram of the fundamental mode and higher-order modes of the anti-resonant hollow-core optical fiber applied to the visible light band (50nm-480nm) provided in the embodiment of this application; Figure 3(c) shows the confinement loss (CL) of an antiresonant hollow fiber (5nm–570nm) as a function of wavelength (fundamental mode and higher-order modes LP11, LP31, and LP32); Figure 4(a) shows the confinement loss (CL) of an antiresonant hollow fiber (600nm–670nm) as a function of wavelength (fundamental mode and higher-order modes LP11, LP31, and LP32) as a function of wavelength (fundamental mode and higher-order modes LP11, LP31, and LP32) as a function of wavelength (5nm–570nm); Figure 4(b) shows the transverse field plots of the fundamental and higher-order modes of an antiresonant hollow fiber (821nm) as a function of wavelength (5nm–570nm); Detailed Implementation

[0024] To better understand the technical solution of the present invention, the following will provide a detailed and clear explanation of the technical solution with reference to the accompanying drawings. It should be noted that the described examples represent only some, not all, embodiments of the present invention. All other embodiments that can be derived by those skilled in the art based on these embodiments of the present invention without creative work are within the scope of protection of the present invention. Next, the present invention will be described in more detail with reference to the accompanying drawings.

[0025] As shown in Figure 1, a hollow-core antiresonant optical fiber comprises an elliptical core and a cladding region. The core is filled with air, and the outer cladding consists of five cladding walls of the same type, resulting in a circular core. Furthermore, five smaller supporting semi-circles are introduced into the gaps between each set of antiresonant cladding walls. These five semi-circles not only act as antiresonant layers, reflecting light leaking into the gaps back, but also significantly reduce light leakage. The inner cladding region includes cladding walls, arc-shaped support tubes, and a circular cladding tube. The cladding walls include a first cladding tube, a second nested cladding tube, and a support tube. The hollow-core antiresonant optical fiber exhibits a symmetrical relationship with respect to the core center.

[0026] The multi-cladding structure design of this invention is not limited to 5 groups; it can be flexibly adjusted to different configurations such as 4, 6, 7, and 8 groups according to actual needs. This flexibility provides a wider range of application scenarios for optical fiber structure design. However, as the number of anti-resonant cladding tubes changes, the core size and the number of contact sleeves also need to be adjusted accordingly to ensure optimized optical fiber performance. When the number of anti-resonant cladding tubes is even, the optical fiber exhibits a centrosymmetric structure; while when the number is odd, it forms a structure symmetrical with a fixed rotation angle. For example, when using 6 cladding groups, the optical fiber structure consists of two large tubes in 6 directions, forming a sixfold symmetry. This high degree of symmetry not only affects the two modes of the fundamental mode but also influences the characteristics of higher-order modes. Regardless of the number of symmetry designs, the size and wall thickness of each cladding group remain consistent and uniform to ensure the stability and consistency of optical fiber performance. This flexible structural design strategy, combined with symmetry and size optimization, provides a foundation for designing high-performance hollow-core anti-resonant optical fibers.

[0027] The external anti-resonance layer provided by the present invention has a dielectric thickness t2 of 500-1000 nm for the quartz resonator tubes; the dielectric material is SiO2; the spacing angle between adjacent quartz resonator tubes is θ = 72°; the spacing angle between the support tube layers is also θ = 72°. The use of the support half-tubes and the internal small nested tubes can further reduce the high-order mode confinement loss CL of the present invention.

[0028] In some embodiments, the wall thickness and other parameters of the cladding tubes in the five nested anti-resonance layer structures of the optical fiber need to satisfy the anti-resonance condition. When the anti-resonance condition is satisfied, the glass wall reflects the most light and transmits the least, allowing most of the light to be reflected back into the fiber core, thus forming an optical waveguide. The thickness t of each type of cladding tube is the same and satisfies: Where t represents the thickness of the cladding tube, n represents the operating wavelength, n1 and n0 are the refractive indices of the cladding tube material and air, respectively, and m is a positive integer. In some embodiments, m can be selected as 1st, 2nd, 3rd, or 4th order.

[0029] This invention uses the finite element simulation software COMSOL Multiphysics to simulate and test this embodiment, employing the finite element method combined with the perfectly matched layer boundary absorption condition for theoretical calculations. The calculations yielded the mode field distribution diagram, confinement loss, and higher-order mode loss as a function of wavelength.

[0030] In some embodiments, the materials of the multi-layer nested cladding tube and the outermost sleeve are quartz materials, and alternatively, they may be materials such as fluoride glass, sulfide glass or silicate glass.

[0031] The operating wavelength ranges from ultraviolet to visible light and from short-wave to near-infrared.

[0032] Formula for the anti-resonant reflection waveguide effect:

[0033]

[0034] Where λ is the wavelength, k is the anti-resonance order, nglass is the refractive index of the material used, and nair is the refractive index of air.

[0035] t1 and t2 are multiples of each other. Half of the resonant wavelength of t2 overlaps with the resonant wavelength of t1. At the same time, the resonant order of t2 is twice the resonant order of the adjacent resonant order of t1, and the resonant region is relatively narrow. The other half overlaps with the anti-resonant wavelength.

[0036] Figure 2(b) shows the fundamental mode field distribution of the example at a wavelength of 355 nm. As shown in Figure 2(b), the hollow fiber of the example can concentrate the energy of the light wave in the fiber core region when transmitting light, indicating that the present invention can effectively confine the light in the air fiber core region.

[0037] As shown in Figure 1, the hollow-core antiresonant fiber has a diameter of 85.9µm, an outer cladding thickness of 5µm, and a core diameter of D1. The thickness of each cladding wall layer and the width of each air layer in the cladding region are equal. The hollow-core antiresonant fiber can also have a perfectly matched layer outside the outermost sheath for ease of simulation, or it can be integrated with the outermost sheath. Understandably, due to the requirements of antiresonance, parameters such as the diameter of the cladding tube, the diameter of the nested tube's thin walls, the thickness of each wall, and the core diameter can be adjusted according to the needs of antiresonance. Furthermore, to achieve different low-loss, high-power transmission performance, other parameters can be further adjusted.

[0038] Traditional total internal reflection mechanisms face significant challenges in long-distance transmission of ultraviolet (UV) light, failing to meet the demands for high-efficiency transmission. In contrast, hollow-core optical fibers, with their unique structural advantages, exhibit outstanding transmission performance in both the UV and visible light bands, achieving efficient and stable transmission of both broadband optical signals and ultrashort pulse laser energy at UV wavelengths.

[0039] In low-loss ultraviolet fiber design, the stability of the cladding structure of negative curvature hollow-core fiber is crucial for drawing a uniform cladding tube. Its negative curvature resonator unit requires a precise air-medium combination. Specifically, the hollow-core anti-resonator unit should be configured with a more stable geometric support to ensure a larger air gap and a more sparser dielectric distribution. This design strategy can significantly improve the drawing success rate, and uniform size and wall thickness will also reduce loss during transmission, thereby improving the overall transmission performance of the fiber.

[0040] This invention overcomes the limitations of traditional designs on node loss by innovatively designing a circular cladding tube and cleverly utilizing the uncontacted half-cladding tube within the gap to achieve contact. In the field of high-power laser transmission, this strategy is not only effective but also exhibits significant advantages. Theoretical calculations show that by adding the half-cladding tube and the internal nested small circles, the leakage of optical energy through the gap can be significantly reduced, thereby lowering node loss. Specifically, the circular nested tube and semi-circular sleeve structure used in this invention form a tightly connected negative curvature resonant unit. The first layer of glass medium restricts light transmission through negative curvature, while the second layer of air medium provides secondary restriction to the unrestricted light. Further increasing the nesting combination can effectively reduce unnecessary optical energy loss. Furthermore, the combination of the support tube and the nested internal small circles can return some of the light reflected and leaking into the gap to the fiber core, further reducing optical energy loss. This structural design cleverly achieves low-loss transmission of optical fiber, and the special air cladding combination of the contact half-tube and the inner small nested small circles enables support for high-order mode transmission, especially in the ultraviolet band, where the loss can be as low as 10. -2 ~10 -4 The dB / km level provides an efficient solution for high-power ultraviolet light transmission.

[0041] This invention significantly improves the fabrication feasibility of hollow-core antiresonant optical fibers in the ultraviolet band by innovatively designing the wall thickness parameters of the circular cladding tube. Specifically, the circular cladding tube employs a dual-wall-thickness combination structure, where t1 is 0.7 μm and t2 is 1.4 μm. This design effectively enhances the mechanical stability and drawing process tolerance of the structure while ensuring good optical performance in the ultraviolet band. Furthermore, this scheme is also applicable to other optimized wall-thickness parameter combinations, further expanding the application potential of ultraviolet hollow-core antiresonant optical fibers in terms of process adaptability and fabrication stability.

[0042] This invention solves the problem of strong ultraviolet absorption in the ultraviolet range of traditional optical materials by employing anti-resonant hollow-core fiber to "suppress coupling." It reduces losses caused by unnecessary multi-level resonant points and energy losses due to mode field coupling through an effective combination of air-medium-air-medium structures. This results in a nested hollow-core fiber with a negative curvature contact support tube for ultraviolet transmission in the 190nm-360nm wavelength range. This fiber achieves a low loss of 0.00421dB / km at 255nm and possesses a light-guiding band with a loss level below 1dB / km and a bandwidth of approximately 170nm within the 190nm-360nm wavelength range; it can provide a medium for low-loss ultraviolet laser transmission. Furthermore, the structural design of the hollow-core anti-resonant fiber reduces the impact of mode coupling of higher-order modes and anti-resonance effects, minimizing the influence of cladding mode coupling on the fiber core fundamental mode. It is compatible with existing quartz core fibers and related devices and can be applied to low-loss, high-power ultraviolet transmission.

[0043] As shown in Figure 1, the optical fiber structure of this invention is simple and reasonable, with high process feasibility. It can meet the requirements of high-energy, low-mode, low-loss transmission applications in the ultraviolet, visible, and short-wave near-infrared bands. Within the range of 190nm to 360nm, the fundamental mode-limited loss fluctuates between 0.775 and 0.0003dB / km, as shown in the loss versus wavelength curve in Figure 2(a). This optical fiber structure can support low-loss high-order mode transmission of various purities. It exhibits good mode characteristics. The loss at 355nm is 10... -4 On the order of dB / km.

[0044] The innovations of this invention are as follows: First, in terms of structure, a unique arc-shaped negative curvature support sleeve contact is used; second, it achieves lower loss transmission of ultraviolet light (0.000137dB / km); third, the specific hollow fiber structure allows for good transmission of multiple high-order modes, ensuring that the transmission of high peak power lasers will not damage the fiber itself, thus resulting in long lifespan and low cost.

[0045] It should be noted that the introduction of different transmission bands and different anti-resonance wavelengths by changing different cladding wall thicknesses, as well as the use of contact sleeves of different shapes, should not be construed as limiting the present invention.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Those skilled in the art can modify the technical solutions described in the present invention, or make equivalent substitutions for some of the technical features, and these modifications or substitutions do not cause the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A hollow-core anti-resonant optical fiber for ultraviolet-visible-shortwave mid-infrared transmission, comprising an outer cladding region (7), an inner cladding region, and an air core region (1), characterized in that, The inner cladding region includes a cladding wall, an arc-shaped support tube (5), and a circular cladding tube (6); the cladding wall includes a first cladding tube (2), a second nested cladding tube (3), and a support tube (4); the air core region (1) is an air hole formed by the cladding wall, which is filled with gas or vacuum.

2. The hollow-core anti-resonant optical fiber for ultraviolet-visible-shortwave mid-infrared transmission according to claim 1, characterized in that, The arc-shaped support tube (5) is located in the gap of the cladding wall and is used to support the outermost tube of the cladding wall.

3. The hollow-core anti-resonant optical fiber for ultraviolet-visible-shortwave mid-infrared transmission according to claim 1, characterized in that, The wall thickness of the first cladding tube (2) and the circular cladding tube (6) is t1, and the size range of t1 is 0.4 to 1µm. The wall thickness of the second nested cladding tube (3) and the support tube (4) is t2, and the size range of t2 is 1.2 to 1.8µm.

4. The hollow-core anti-resonant optical fiber for ultraviolet-visible-shortwave mid-infrared transmission according to claim 1, characterized in that, The materials of the first cladding tube (2), the second nested cladding tube (3), the support tube (4) and the outer cladding region (7) are quartz glass, fluoride glass, sulfide glass or silicate glass.

5. The hollow-core anti-resonant optical fiber for ultraviolet-visible-shortwave mid-infrared transmission according to claim 1, characterized in that, The refractive indices of the first cladding tube (2), the second nested cladding tube (3), and the support tube (4) are all equal, with a refractive index range of 1.4878 ~ 1.5853.

6. The hollow-core anti-resonant optical fiber for ultraviolet-visible-shortwave mid-infrared transmission according to claim 1, characterized in that, The first cladding tube (2), the second nested cladding tube (3), and the support tube (4) are tangent at a point on the inner glass wall of the outer cladding region (7).

7. The hollow-core anti-resonant optical fiber for ultraviolet-visible-shortwave mid-infrared transmission according to claim 1, characterized in that, The diameter of the air core region (1) is 20-50 μm; the diameter of the first cladding tube (2) is 16-25 μm; the diameter of the second nested cladding tube (3) is 10-15 μm; and the diameter of the arc-shaped support tube (5) is 7-12 μm.

8. The hollow-core anti-resonant optical fiber for ultraviolet-visible-shortwave mid-infrared transmission according to claim 1, characterized in that, The arc-shaped support tube (5) is tangent to the adjacent first cladding tube (2) at a point and also contacts the outer cladding region (7). The circular cladding tube (6) is nested inside the arc-shaped support tube (5) and is tangent to the outer cladding region (7) at a point.

9. A hollow-core anti-resonant optical fiber for ultraviolet-visible-shortwave mid-infrared transmission according to claim 3, characterized in that, Formula for the anti-resonant reflection waveguide effect: Where λ is the wavelength, k is the anti-resonance order, nglass is the refractive index of the glass used, and nair is the refractive index of air.

10. A hollow-core anti-resonant optical fiber for ultraviolet-visible-shortwave mid-infrared transmission according to claim 9, characterized in that, t1 and t2 are multiples of each other. Half of the resonant wavelength of t2 overlaps with the resonant wavelength of t1. At the same time, the resonant order of t2 is twice the resonant order of the adjacent resonant order of t1, and the resonant region is relatively narrow. The other half overlaps with the anti-resonant wavelength.

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