A near-zero dispersion composite hollow-core optical fiber in the 3~5µm mid-infrared band

Abstract

The present invention discloses a composite hollow-core optical fiber in the near-zero dispersion 3-5µm mid-infrared band, comprising a photonic crystal bandgap region, an antiresonance region and an air core region arranged in sequence from the outside to the inside; the photonic crystal bandgap region is composed of a series of air holes at equal intervals; the antiresonance region is composed of a plurality of antiresonance units; the antiresonance unit is a nested cladding tube structure, which includes a first-type elliptical dielectric tube, and a second-type elliptical dielectric tube and a circular dielectric tube arranged inside the tube; the intangent point of the first-type elliptical dielectric tube and the second-type elliptical dielectric tube is in contact with and coincides with the inner wall surface of the photonic crystal bandgap region; the second-type elliptical dielectric tube and the circular dielectric tube are externally tangent and fused. The present invention has a working band in the 3-5µm mid-infrared band, and has the characteristics of low restrictive loss, large mode field area and low dispersion (near zero dispersion) within the working band, so that the light in this band can achieve high-power and high-quality transmission.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber technology, and more specifically, to a composite hollow-core optical fiber in the near-zero dispersion 3-5µm mid-infrared band. Background Art

[0002] Optical fiber has been developed for more than half a century, and optical fiber technology has been applied to various fields, such as optical fiber communication, optical fiber sensing and medical treatment. With the rapid development of society and the further improvement of people's pursuit of production and life, there is an urgent need for optical fibers with longer transmission distances, higher transmission power and larger capacity. However, the various performances of traditional quartz optical fibers (such as loss, nonlinearity and dispersion, etc.) are now approaching their limits and are difficult to meet the needs of modern life. Therefore, it is urgent to further design and study traditional quartz optical fibers in terms of structure or materials.

[0003] In order to solve the limitation of traditional quartz fiber intrinsic materials, scientists proposed the concept of hollow core fiber and the world's first hollow core fiber was launched in 1999. Unlike traditional solid core quartz fiber, hollow core fiber uses air hole structure to confine light into the hollow core through photonic band gap, mode coupling suppression and antiresonance effects, thereby realizing light transmission. At present, hollow core fiber mainly consists of two types: hollow core photonic band gap fiber and hollow core antiresonant fiber. Hollow core photonic band gap fiber, due to its equally spaced and periodically arranged air hole structure, allows light in a specific wavelength range to be transmitted in the hollow core. Therefore, hollow core photonic band gap fiber has the characteristics of low confinement loss and insensitivity to bending loss. Hollow core antiresonant fiber is surrounded by several negative curvature air tube claddings, and uses the reflection of incident light when it encounters the thin wall of the cladding to confine the light in the hollow core. Therefore, hollow core antiresonant fiber can achieve the characteristics of larger mode field area and wider working band.

[0004] Since SiO 2 In the mid-infrared band (3~5µm), multi-phonon absorption will occur, increasing the transmission loss of light in the optical fiber, which greatly limits the application of traditional quartz optical fiber in the mid-infrared band. At the same time, the 3~5µm band has a wide range of applications in environmental monitoring, biomedicine, surveying and measurement, national defense security and other fields, and there is an urgent need for research on new optical fiber structures and new materials. At this stage, the research on hollow-core optical fibers is mainly concentrated in the C-band (communication band), and has a very mature development. However, the research on hollow-core optical fibers in the mid-infrared band of 2~8µm is still extremely scarce. This is because the restrictive loss of hollow-core optical fibers will increase with the increase of the transmission wavelength. In recent years, the restrictive loss of hollow-core optical fibers in the mid-infrared band has been as low as 10 -2 dB / km and the main working band is in the 2~4µm band. As the input wavelength increases, the overall structure and limiting loss of the optical fiber will increase accordingly. Summary of the invention

[0005] Purpose of the invention: In view of the shortcomings of existing optical fiber technology research in the mid-infrared band, the present invention proposes a near-zero dispersion 3~5µm mid-infrared band composite hollow-core optical fiber, which can achieve light wave transmission with the characteristics of low loss, large mode field area and low dispersion (near-zero dispersion) in the 3~5µm wavelength range.

[0006] Technical solution: To achieve the purpose of the present invention, the following technical solution is adopted:

[0007] A near-zero dispersion composite hollow-core optical fiber in the 3-5µm mid-infrared band, the optical fiber comprising: a photonic crystal bandgap region, an anti-resonance region and an air core region arranged in sequence from the outside to the inside;

[0008] The photonic crystal band gap region is composed of a series of air holes with equal spacing, and is in the shape of a regular polygon as a whole;

[0009] The anti-resonance region is composed of a plurality of anti-resonance units; the anti-resonance unit is a nested cladding tube structure, and the nested cladding tube is a double-layer structure, including a first type of elliptical dielectric tube and a second type of elliptical dielectric tube and a circular dielectric tube arranged inside the first type of elliptical dielectric tube and the second type of elliptical dielectric tube are inscribed and contact and overlap with the inner wall of the photonic crystal band gap region; the second type of elliptical dielectric tube and the circular dielectric tube are externally inscribed and fused; the anti-resonance unit is symmetrical about the long axis of the first type of elliptical dielectric tube, the size of the air core region is determined by the first type of elliptical dielectric tube, and the circular dielectric tube does not contact the first type of elliptical dielectric tube;

[0010] The air core region is composed of a plurality of anti-resonance units uniformly distributed in the anti-resonance region, and is the main light guiding region of the hollow core optical fiber.

[0011] Preferably, the number of the anti-resonance units is 4 to 8.

[0012] Preferably, the base material of the photonic crystal band gap region and the various dielectric tube materials of the anti-resonance unit in the anti-resonance region are fluoride, sulfide, diamond or indium selenide.

[0013] Preferably, the diameter of the air holes in the band gap region of the photonic crystal is 10-20 μm, and the distance between the air holes is 35-45 μm.

[0014] Preferably, the photonic crystal band gap region is in the shape of a regular hexagon as a whole.

[0015] Preferably, the thicknesses of various types of dielectric tubes of the anti-resonance units in the anti-resonance region are all the same.

[0016] Preferably, the ratio of the major semiaxis to the minor semiaxis of the first type of elliptical dielectric tube in the anti-resonance unit is 1~2; the ratio of the major semiaxis to the minor semiaxis of the second type of elliptical dielectric tube is 1~4; the ratio of the major semiaxis of the second type of elliptical dielectric tube to the major semiaxis of the first type of elliptical dielectric tube is 0.2~0.4; the ratio of the radius of the circular dielectric tube to the major semiaxis of the second type of elliptical dielectric tube is 0.8~1.2.

[0017] Preferably, the major semi-axis of the first type of elliptical medium tube is 70-100 µm, and the minor semi-axis is 30-60 µm; the major semi-axis of the second type of elliptical medium tube is 20-40 µm, and the minor semi-axis is 5-25 µm; the radius of the circular medium tube is 20-40 µm.

[0018] Preferably, the air core is essentially an air hole surrounded by a plurality of anti-resonance units; the radius of the air core is 20-40µm.

[0019] Preferably, the air hole region in the photonic crystal band gap region, between the first type elliptical dielectric tube and the second type dielectric tube, between the second type dielectric tube and the circular dielectric tube in the antiresonance region, the air core region and other internal spaces are all filled with gas with a refractive index of 1.

[0020] Beneficial effects: Compared with the existing common hollow-core optical fibers, the present invention uses a composite optical fiber to better combine the advantages of the two types of optical fibers, and uses a multi-layer structure to make it have good structural adjustability. In terms of the design of the composite hollow-core optical fiber, the present invention is designed for the 3~5µm band as the transmission band of the optical fiber. The anti-resonance region is reasonably nested and designed with a composite structure of the photonic band gap to allow light to propagate in the core as much as possible, so that the designed optical fiber is about an order of magnitude lower than the minimum loss of the existing mid-infrared band optical fiber in theoretical calculations, and the band is extended to the 5µm range. At the same time, the composite cladding structure can not only adjust the size and hole spacing of the air holes in the photonic crystal band gap region, but also adjust the size of various dielectric tubes in the anti-resonance region, thereby adjusting the size of the air core. Through a reasonable cladding region design, the optical fiber can be effectively customized for a specific wavelength range. Experiments have shown that lower restrictive losses (as low as 10) can be obtained through the above-mentioned adjustment or optimization methods. -3 dB / km), larger mode area (1593µm 2 above) and near-zero flat dispersion over a wider wavelength range (stable at -6.31×10 -7 ~1.28×10 -6 ps / (nm·km)). The present invention only uses the common circular and elliptical nested double-layer structure in design, and the optical fiber structure is simple and easy to produce and prepare. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The figure is a schematic diagram of the overall structure of a near-zero dispersion composite hollow-core optical fiber in the 3-5µm mid-infrared band according to the present invention.

[0022] Figure 2 It is an enlarged view of the local details of the anti-resonance region of the present invention.

[0023] Figure 3 A diagram showing the mode field distribution and height expression of the fundamental mode at 4µm provided in an embodiment of the present invention.

[0024] Figure 4 FIG. 4 is a graph showing the relationship between the limiting loss of the fundamental mode and the wavelength according to an embodiment of the present invention.

[0025] Figure 5 FIG. 4 is a graph showing the relationship between the effective mode field area of ​​the fundamental mode and the wavelength according to an embodiment of the present invention.

[0026] Figure 6 FIG. 4 is a graph showing the relationship between the dispersion of the fundamental mode and the wavelength according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] refer to Figure 1 and Figure 2 As shown, a near-zero dispersion composite hollow-core optical fiber in the 3-5µm mid-infrared band, wherein the optical fiber is sequentially arranged from the outside to the inside as a photonic crystal band gap region, an antiresonance region, and an air core region; and from the inside to the outside, the optical fiber is sequentially arranged as an air core region (air core 1), an antiresonance region (mainly composed of a first type of elliptical dielectric tube 2, a second type of elliptical dielectric tube 3, and a circular dielectric tube 4), a photonic crystal band gap region (equally spaced air holes 5), and an optical fiber outer cladding 6.

[0029] The air core 1 is an air region, which is composed of a plurality of anti-resonance units uniformly distributed in the anti-resonance region and is the main light-guiding region of the hollow-core optical fiber.

[0030] The air core 1 is essentially an air hole surrounded by a plurality of anti-resonance units; the radius (R) of the air core is 20-40µm.

[0031] The photonic crystal band gap region is composed of a series of equally spaced air holes 5, which are in the shape of a regular polygon as a whole. In order to ensure the adaptability of the overall structure of the internal anti-resonance region and the air core region, the external photonic crystal band gap region is first designed as a whole, and then the required anti-resonance region and air core region are cut out in the middle.

[0032] The anti-resonance region is composed of a plurality of anti-resonance units; the anti-resonance unit is a nested cladding tube structure (reference Figure 2 ), the nested cladding tube structure is a double-layer structure, including an elliptical dielectric tube with a larger aperture (first type elliptical dielectric tube 2) and an elliptical dielectric tube with a smaller aperture (second type elliptical dielectric tube 3) and a circular dielectric tube 4 arranged inside it; wherein the first type elliptical dielectric tube 2 and the second type elliptical dielectric tube 3 are inscribed and contact and overlap with the inner wall of the photonic crystal band gap region; the second type elliptical dielectric tube 3 and the circular dielectric tube 4 are externally cut and fused; the first type elliptical dielectric tube 2 roughly determines the area size of the air core 1; the second type elliptical dielectric tube 3 is an embedded dielectric tube of the first type elliptical dielectric tube 2, mainly used to reflect the light in the first type elliptical dielectric tube 2 into the core; in order to ensure that the remaining transmission light in the first type elliptical dielectric tube 2 is completely reflected into the core area, the circular dielectric tube 4 is set so that the circular dielectric tube 4 and the first type elliptical dielectric tube 2 cannot contact each other, and a certain distance should be maintained. Because contact will increase the nodes between the dielectric tubes, which will increase the leakage of the light in the core, resulting in an increase in the restrictive loss of the core. When designing, it is required that all dielectric tubes in the anti-resonance unit are left-right symmetrical about the long axis of the first type elliptical dielectric tube.

[0033] The wall thickness and other parameters of the hollow-core antiresonant optical fiber need to meet the antiresonance conditions. As long as the antiresonance conditions are met, the glass wall reflection is maximum and the transmission is minimum, and most of the light is reflected back into the core to form an optical waveguide. According to the principle of antiresonance reflection, the nested structure can further effectively reduce the leakage loss of the optical fiber by adding additional antiresonance glass wall layers. The thickness of each type of dielectric tube (including: the first type of elliptical dielectric tube 2, the second type of elliptical dielectric tube 3 and the circular dielectric tube 4) of the antiresonance unit is the same and meets the following requirements:

[0034] ;

[0035] in, T 2 Indicates the thickness of the medium tube, represents the designed operating wavelength, n 1 and n 0 are the refractive index of the dielectric tube material and the refractive index of air, respectively. m is an integer.

[0036] In some embodiments, the number of the anti-resonance units is 4 to 8.

[0037] In some embodiments, the ratio of the major semi-axis to the minor semi-axis (a 1 / b 1 ) is 1~2; the ratio between the major semi-axis and the minor semi-axis of the second type of elliptical medium tube 3 (a 2 / b 2 ) is 1 to 4; the ratio of the major semi-axis of the second type elliptical medium tube 3 and the first type elliptical medium tube 2 (a 2 / a 1 ) is 0.2~0.4; the ratio between the radius of the circular medium tube 4 and the long semi-axis of the second type elliptical medium tube 3 (r 2 / a 2 ) is 0.8~1.2.

[0038] In some embodiments, the size can be optimized within the following range: the major semi-axis (a 1 ) is 70~100µm, the short semi-axis (b 1 ) is 30~60µm; the long semi-axis (a 2 ) is 20~40µm, the short semi-axis (b 2 ) is 5~25µm; the radius of the circular medium tube 4 (r 2 ) is 20~40µm.

[0039] In some embodiments, the photonic crystal band gap region is composed of a series of equally spaced air holes 5 , which are hexagonal in shape as a whole.

[0040] In some embodiments, the diameter of the air hole in the photonic crystal band gap region (r 1 ) is 10~20μm, the air hole spacing (T 1 ) is 35~45μm.

[0041] In some embodiments, the cladding 6 is a cylinder with a radius of 200-600 µm.

[0042] In some embodiments, the base material of the photonic crystal band gap region and the various dielectric tube materials of the anti-resonance unit in the anti-resonance region are fluoride, sulfide, diamond or indium selenide.

[0043] In some embodiments, the air hole region in the photonic crystal band gap region, between the first type elliptical dielectric tube and the second type dielectric tube in the antiresonance region, between the second type dielectric tube and the circular dielectric tube, the air core region and other internal spaces are all filled with gas with a refractive index of 1.

[0044] The design advantages of the present invention are described below through the following embodiments.

[0045] Example: Figure 1 The figure shows the overall structure of a composite hollow-core optical fiber in the near-zero dispersion 3~5µm mid-infrared band, which includes the air core 1, the first type of elliptical dielectric tube 2, the second type of elliptical dielectric tube 3, the circular dielectric tube 4, the air hole 5 and the cladding 6. The cladding 6 is a cylinder made of fluoride (ZBLAN) glass with a radius of 400µm; the radius (R) of the air core 1 is 30µm, and it is a "negative curvature" core structure; the radius (r) of the air hole 5 is 20µm, and the radius (R) of the air core 1 is 10µm, and the radius (r) of the air hole 5 is 10µm, and the radius (r) of the air core 1 is 10µm, and the radius (r) of the air hole 5 is 2 ...20µm, and the radius (r) of the air hole 5 is 20µm, and the radius (r) of the air core 1 is 20µm, and the radius (r) of the air hole 5 is 20µm, and the radius (r) of the air hole 5 is 20µm, and the radius (r) of the air core 1 is 20µm, and the radius (r) of the air hole 5 is 20µm, and the radius (r) of the air hole 5 is 20µm, 1 ) is 15 μm; the distance between two air holes (T 1 ) is 40μm.

[0046] Figure 2 The figure shows an enlarged view of the local details of the anti-resonance region, which is composed of 6 anti-resonance units. The anti-resonance unit is composed of a first type of elliptical dielectric tube 2, a second type of elliptical dielectric tube 3 and a circular dielectric tube 4, which are nested with each other. The first type of elliptical dielectric tube 2 and the second type of elliptical dielectric tube 3 are inscribed and contact and overlap with the inner wall of the photonic crystal band gap layer; the second type of elliptical dielectric tube 3 and the circular dielectric tube 4 are inscribed and fused. The thickness of each type of dielectric tube is T 2 are the same; the long semi-axis (a 1 ) is 85µm, the minor semi-axis (b 1 ) is 43µm; the long semi-axis (a 2 ) is 30µm, the short semi-axis (b 2 ) is 16µm; the radius of the circular medium tube 4 (r 2 ) is 30µm.

[0047] The base material of the photonic crystal band gap region and the materials of various dielectric tubes of the antiresonance unit in the antiresonance region are all selected as ZBLAN glass with a refractive index of 1.4619~1.4817. Other materials such as sulfide, diamond, indium selenide, etc. can be used as base materials. The air hole region in the photonic crystal band gap region, between the first type of elliptical dielectric tube and the second type of dielectric tube in the antiresonance region, between the second type of dielectric tube and the circular dielectric tube, the air core region and other internal spaces are filled with air. Other materials such as H 2 , CO 2 、N 2 The gas can be filled with any of the above gases.

[0048] The present invention uses finite element simulation software COMSOL Multiphysics to simulate and test the present embodiment, and uses the finite element method and combines the perfect matching layer boundary absorption condition to perform theoretical calculations. The mode field distribution diagram, limiting loss, effective mode field area, and dispersion versus wavelength curves of the present invention are obtained through calculation.

[0049] Figure 3 The diagram shows the mode field distribution and height expression of the fundamental mode at 4µm. It can be seen from the figure that the energy of the hollow core antiresonant photonic crystal composite fiber prepared in the embodiment is concentrated in the core region during light wave transmission, indicating that the light is well confined in the core region.

[0050] Figure 4 The relationship between the limiting loss of the fundamental mode of the embodiment and the wavelength is shown in the figure. It can be seen from the figure that the limiting loss of the embodiment is at a low level under the condition of an incident wavelength of 3~5µm, and the limiting loss is approximately stable at 2.7×10 -6 ~1.72×10 -3 dB / m. It can be seen that the present invention has a relatively low limiting loss in the mid-infrared band of 3~5µm.

[0051] Figure 5 The diagram is a graph showing the relationship between the effective mode field area of ​​the fundamental mode of the embodiment and the change in wavelength. From the diagram, it can be seen that the change trend of the mode field area of ​​the optical fiber is a slowly increasing trend with the change in wavelength, and the mode field area reaches 1593µm when the wavelength of light is 3~5µm. 2 The mode field area of ​​the invention has reached 10 3 μm 2 It can transmit high-power and high-energy lasers and improve conversion efficiency.

[0052] Figure 6 The figure shows the relationship between the dispersion of the fundamental mode of the embodiment and the wavelength. From the figure, we can see the dispersion of the optical fiber at the corresponding wavelength. In the wide band of 3~5µm, the value of the group velocity dispersion is still stable at -6.31×10 -7 ~1.28×10 -6 ps / (nm·km). According to the fiber dispersion, when the optical signal is transmitted in the optical fiber, the light wave will cause the pulse to expand due to the different propagation speeds, which will affect the quality of the optical fiber transmission data. Therefore, the closer the dispersion is to zero, the higher the optical fiber transmission quality.

[0053] In summary, the composite hollow-core optical fiber in the mid-infrared band of 3~5μm with near-zero dispersion described in the present invention has both low restrictive loss and wide mid-infrared transmission bandwidth, and has good near-zero dispersion characteristics in terms of dispersion, and can achieve low-loss and high-quality mid-infrared light transmission. The specific transmission wavelength is within the wide mid-infrared transmission wavelength range of 3~5μm, and the minimum transmission wavelength can reach 1×10 -6 dB / m-level restrictive loss; at the same time, the composite hollow-core optical fiber described in the present invention also has a large effective mode field area, low dispersion (near zero dispersion) and low restrictive loss, and can perform high-power, high-quality mid-infrared laser transmission. Therefore, the composite hollow-core optical fiber with near-zero dispersion in the mid-infrared band (3~5µm) proposed in the present invention, on the one hand, solves the dilemma that most of the current hollow-core optical fibers are concentrated in the 1~2µm near-infrared band, while the research in the mid-infrared band is extremely scarce (especially in the 5µm range); on the other hand, by combining the advantages of the two types of hollow-core optical fibers, it has the characteristics of a wider working band, lower restrictive loss and a larger mode field area, which greatly enhances the application prospects of the invention. At the same time, it provides a new idea for broadening the working band of hollow-core optical fibers.

[0054] The basic principle, main features and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed for protection.

Claims

1. A near-zero dispersion composite hollow-core optical fiber in the 3-5µm mid-infrared band, characterized by: It includes the photonic crystal band gap region, anti-resonance region and air core region from the outside to the inside; The photonic crystal band gap region is composed of a series of air holes with equal spacing, and is in the shape of a regular polygon as a whole; The anti-resonance region is composed of a plurality of anti-resonance units; the anti-resonance unit is a nested cladding tube structure, and the nested cladding tube is a double-layer structure, including a first type of elliptical dielectric tube and a second type of elliptical dielectric tube and a circular dielectric tube arranged inside the first type of elliptical dielectric tube and the second type of elliptical dielectric tube are inscribed and contact and overlap with the inner wall of the photonic crystal band gap region; the second type of elliptical dielectric tube and the circular dielectric tube are externally inscribed and fused; the anti-resonance unit is symmetrical about the long axis of the first type of elliptical dielectric tube, the size of the air core region is determined by the first type of elliptical dielectric tube, and the circular dielectric tube does not contact the first type of elliptical dielectric tube; The air core region is composed of a plurality of anti-resonance units uniformly distributed in the anti-resonance region, and is the main light guiding region of the hollow core optical fiber.

2. The near-zero dispersion composite hollow-core optical fiber in the 3-5µm mid-infrared band according to claim 1, characterized in that: The number of the anti-resonance units is 4 to 8.

3. The near-zero dispersion composite hollow-core optical fiber in the 3-5µm mid-infrared band according to claim 1, characterized in that: The base material of the photonic crystal band gap region and the various dielectric tube materials of the anti-resonance unit in the anti-resonance region are fluoride, sulfide, diamond or indium selenide.

4. The near-zero dispersion composite hollow-core optical fiber in the 3-5µm mid-infrared band according to claim 1, characterized in that: The diameter of the air holes in the band gap region of the photonic crystal is 10-20 μm, and the distance between the air holes is 35-45 μm.

5. The near-zero dispersion composite hollow-core optical fiber in the 3-5µm mid-infrared band according to claim 1, characterized in that: The photonic crystal band gap region is in the shape of a regular hexagon as a whole.

6. The near-zero dispersion composite hollow-core optical fiber in the 3-5µm mid-infrared band according to claim 1, characterized in that: The thicknesses of various dielectric tubes of the anti-resonance units in the anti-resonance region are all the same.

7. The near-zero dispersion composite hollow-core optical fiber in the 3-5µm mid-infrared band according to claim 1, characterized in that: The ratio of the major semi-axis to the minor semi-axis of the first type of elliptical dielectric tube in the anti-resonance unit is 1-2; the ratio of the major semi-axis to the minor semi-axis of the second type of elliptical dielectric tube is 1-4; the ratio of the major semi-axis of the second type of elliptical dielectric tube to that of the first type of elliptical dielectric tube is 0.2-0.4; the ratio of the radius of the circular dielectric tube to the major semi-axis of the second type of elliptical dielectric tube is 0.8-1.

2.

8. The near-zero dispersion composite hollow-core optical fiber in the 3-5µm mid-infrared band according to claim 7, characterized in that: The major semi-axis of the first type of elliptical medium tube is 70~100µm, and the minor semi-axis is 30~60µm; the major semi-axis of the second type of elliptical medium tube is 20~40µm, and the minor semi-axis is 5~25µm; the radius of the circular medium tube is 20~40µm.

9. The near-zero dispersion composite hollow-core optical fiber in the 3-5µm mid-infrared band according to claim 1, characterized in that: The air core region is an air hole surrounded by several anti-resonance units; the radius of the air core region is 20~40µm.

10. The near-zero dispersion composite hollow-core optical fiber in the 3-5µm mid-infrared band according to claim 1, characterized in that: The air hole region in the photonic crystal band gap region, between the first type elliptical dielectric tube and the second type elliptical dielectric tube in the antiresonance region, between the second type elliptical dielectric tube and the circular dielectric tube, and the air core region are all filled with gas with a refractive index of 1.

Images