Hollow-core optical fiber connection method based on 3D printing

Abstract

The invention relates to a hollow-core optical fiber connection method based on 3D printing, and the method comprises the steps: enabling a hollow-core optical fiber and a solid-core optical fiber to be inserted into a capillary glass tube which is dripped with photoresist in advance, carrying out the device processing and optical fiber fixation through the dripped photoresist, and achieving the effect of simplifying the packaging process flow. The air gap in the capillary glass tube can be automatically filled with the dropped photoresist, and air in the tube is extruded out of the tube, so that full-closed treatment of the connector is realized, and the situation that water vapor in the environment enters the tube to pollute the connector is avoided. The hollow-core optical fiber does not need to be heated or ground for sealing, and the condition that the air hole in the hollow-core optical fiber collapses can be avoided; the mode field converter between the hollow-core optical fiber and the solid-core optical fiber is processed by using the femtosecond direct-writing laser processing technology, so that the interconnection requirements between the hollow-core optical fibers and the solid-core optical fibers with various different mode field sizes can be met.

Description

Technical Field

[0001] The present invention relates to the technical field of optical communications, and more specifically, to a hollow-core optical fiber connection method based on 3D printing. Background Art

[0002] In recent years, data traffic in fiber optic communications has grown rapidly due to growing capacity demands (e.g., high-resolution video applications, massive data flows in mobile phone applications, etc.). Traffic inside data centers (typically short distances ranging from a few meters to 10 kilometers) accounts for more than 80% of global traffic because they often require ultra-high-speed interconnections. Hollow-core optical fibers are suitable media for data transmission due to their low signal latency, low nonlinearity, and wide bandwidth. For fiber optic communications, link power budget is critical, so low-loss hollow-core optical fibers and solid-core optical fibers have received great attention for interconnection. There are two main challenges in achieving low-loss interconnection. The first challenge is the need to accommodate the large mode field diameter (MFD) mismatch between the fundamental mode of the low-loss hollow-core optical fiber and the fundamental mode of the solid-core optical fiber. The second challenge is the Fresnel back reflection at the interface between the solid-core optical fiber and the hollow-core optical fiber. In addition, since the core of the hollow-core optical fiber is an air hole, water vapor or other impurities in the surrounding environment will enter the air hole during the active connection, causing the hollow-core optical fiber to degrade. Due to the particularity of the hollow-core optical fiber structure, it is difficult to avoid the collapse of the air holes in the hollow-core optical fiber due to arc discharge when it is fused with a single-mode optical fiber, thereby increasing the loss. In addition, there is usually a mode field mismatch problem between the hollow-core optical fiber and the solid-core optical fiber, which increases the loss of the direct interconnection between the two optical fibers. Summary of the invention

[0003] The purpose of the present invention is to overcome the disadvantage of high connection loss between hollow-core optical fiber and solid-core optical fiber in the prior art, and to provide a hollow-core optical fiber connection method based on 3D printing, which effectively reduces the connection loss between hollow-core optical fiber and solid-core optical fiber and improves transmission performance.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] A hollow-core optical fiber connection method based on 3D printing is provided, comprising the following steps:

[0006] Covering the light-transmitting film on the end face of the hollow-core optical fiber;

[0007] Dropping photoresist into the inside of the capillary glass tube;

[0008] Insert the hollow core optical fiber and the solid core optical fiber into the two ends of the capillary glass tube respectively;

[0009] Using femtosecond laser to 3D print mode field converter on photoresist between solid core fiber and hollow core fiber;

[0010] After the processing is completed, ultraviolet curing is performed to fix the hollow-core optical fiber and the solid-core optical fiber structure to obtain a hollow-core optical fiber connector.

[0011] A hollow-core optical fiber connection method based on 3D printing of the present invention inserts the hollow-core optical fiber and the solid-core optical fiber into a capillary glass tube dripped with photoresist in advance, and uses the dripped photoresist to process the device and fix the optical fiber, which has the effect of simplifying the packaging process flow. At the same time, the dripped photoresist will automatically fill the air gap in the capillary glass tube, squeeze the air in the tube out of the tube, and realize the fully enclosed treatment of the connector, avoiding the situation that the water vapor in the environment enters the tube and pollutes the connector. Utilizing the sealing property of the connector, the present invention does not need to heat or grind the hollow-core optical fiber to seal, and can avoid the situation that the air hole in the hollow-core optical fiber collapses; the present invention utilizes the femtosecond direct writing laser processing technology to process the mode field converter between the hollow-core optical fiber and the solid-core optical fiber, which can meet the interconnection requirements between the hollow-core optical fiber and the solid-core optical fiber of various different mode field sizes, and can realize the low-loss connection between the single-core optical fiber and the hollow-core optical fiber according to the type of the printing device, and can also be applied to the low-loss connection between the hollow-core optical fiber and the multi-core optical fiber, so relative to the existing scheme, the present invention expands the application scene.

[0012] Furthermore, the dripped photoresist fills up the air gap between the hollow-core optical fiber and the solid-core optical fiber, as well as the air gap between the hollow-core optical fiber and the solid-core optical fiber and the capillary glass tube, and squeezes the air in the capillary glass tube out of the tube, so as to achieve a fully enclosed treatment of the connector. The dripped photoresist automatically fills up the air gap between the hollow-core optical fiber and the solid-core optical fiber, as well as the air gap between the hollow-core optical fiber and the solid-core optical fiber and the capillary glass tube, and squeezes the air in the tube out of the tube, so as to achieve a fully enclosed treatment of the connector, and avoid the situation where water vapor in the environment enters the tube and contaminates the connector.

[0013] Furthermore, photoresist is dripped into the capillary glass tube from one end, and then the hollow-core optical fiber and the solid-core optical fiber are inserted into the capillary glass tube. Based on the light transmittance of the capillary glass tube, the insertion operation of the hollow-core optical fiber and the solid-core optical fiber is observed from the outside of the capillary glass tube, and the distance between the end face of the solid-core optical fiber and the end face of the hollow-core optical fiber is controlled so that the distance between the two reaches a preset distance; the photoresist dripped in advance now fills the air gap between the solid-core optical fiber and the hollow-core optical fiber, and squeezes the air in the tube out of the tube, thereby achieving a fully sealed treatment of the connector. Preferably, the preset distance is about 200um.

[0014] Furthermore, the size of the mode field on both sides is determined by the end face structure and refractive index distribution of the hollow core fiber and the solid core fiber, the structural parameters of the mode field converter in the middle are calculated by simulation, and the required mode field converter structure is prepared by 3D printing using femtosecond laser direct writing. The mode fields of the inserted solid core fiber and the hollow core fiber do not need to be consistent, and the mode field converter structure is printed between the solid core fiber and the hollow core fiber using femtosecond laser for mode field matching. The type of solid core fiber can be single mode fiber, multimode fiber or lens fiber, etc.

[0015] Furthermore, after the femtosecond laser direct writing process is completed, the connector is irradiated with an ultraviolet lamp, and the photoresist in the capillary glass tube is cured by the ultraviolet lamp, and the hollow core optical fiber, the solid core optical fiber and the printed mode field conversion device are self-encapsulated and fixed. No additional development process is required to wash away the dripped photoresist.

[0016] Furthermore, a femtosecond laser is used to print a mode field converter structure between the solid core optical fiber and the hollow core optical fiber to perform mode field matching, wherein the mode field converter includes a tapered waveguide with gradually varying size, a free-form surface lens, or a one-way M-splitter.

[0017] Preferably, a femtosecond laser with a wavelength of about 780 nm is used to focus in the photoresist between the solid core optical fiber and the hollow core optical fiber to perform mode field conversion device processing.

[0018] Furthermore, the end face of the hollow core optical fiber is cut at 2° to reduce backscattering of light between the film and the air.

[0019] Furthermore, the refractive index of the film is 1.4 to 1.6, and the light transmittance of the film is greater than 99%. Silicon dioxide is coated on both sides of the film as an anti-reflection film. The light reflection at the interface between the film and the hollow-core optical fiber can be reduced, and the coated film is fixedly inserted into the capillary glass tube close to the end face of the hollow-core optical fiber. The capillary glass tube is light-transmitting and has a high strength, which is not lower than that of the hollow-core optical fiber and the solid-core optical fiber, and is suitable for grinding and coating. The material of the capillary glass tube can be high borosilicate or silicon dioxide. The film can be a polyethylene film or glass.

[0020] Furthermore, the refractive index of the photoresist material is 1.3-1.8, the refractive index difference between the photoresist under multi-photon absorption processed by femtosecond laser and single-photon absorption cured by ultraviolet lamp is less than 1%, and the refractive index of multi-photon absorption polymerization is greater than that of single-photon absorption polymerization.

[0021] The present invention also provides a hollow-core optical fiber connector, which is connected using the method described above; it comprises a hollow-core optical fiber, a solid-core optical fiber, a mode field converter and a wool glass tube; the wool glass tube is filled with photoresist, the hollow-core optical fiber and the solid-core optical fiber are respectively inserted into the two ends of the wool glass tube, and the solid-core optical fiber is connected to the hollow-core optical fiber via the mode field converter; the mode field converter is prepared by 3D printing the photoresist between the solid-core optical fiber and the hollow-core optical fiber by femtosecond laser.

[0022] In the present invention, if one end is not connected to a solid core optical fiber, it can be applied to a high-power laser output scenario based on a hollow core optical fiber, so that high-power laser can be directly output from the hollow core optical fiber into the air without worrying about the external environment polluting the hollow core optical fiber and causing the performance of the hollow core optical fiber to degrade.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. A hollow-core optical fiber connection method of the present invention inserts the hollow-core optical fiber and the solid-core optical fiber into a capillary glass tube dripped with glue in advance, and uses the dripped photoresist to process the device and fix the optical fiber, which has the effect of simplifying the packaging process flow. At the same time, the dripped photoresist will automatically fill the air gap between the hollow-core optical fiber and the solid-core optical fiber and the air gap between the hollow-core optical fiber and the solid-core optical fiber and the capillary glass tube, squeeze the air in the tube out of the tube, and achieve a fully enclosed treatment of the connector, avoiding the situation where water vapor in the environment enters the tube and contaminates the connector. Utilizing the sealing property of the connector, the present invention does not need to heat or grind the hollow-core optical fiber to seal, and can avoid the situation where the air hole in the hollow-core optical fiber collapses.

[0025] 2. A hollow-core optical fiber connection method of the present invention uses femtosecond direct writing laser processing technology to process the mode field conversion device between the hollow-core optical fiber and the solid-core optical fiber, which can meet the interconnection requirements between hollow-core optical fibers and solid-core optical fibers of various mode field sizes. According to the type of printing device, it can not only realize the low-loss connection between single-core optical fiber and hollow-core optical fiber, but also be applied to the low-loss connection between hollow-core optical fiber and multi-core optical fiber. Therefore, compared with the existing solutions, the present invention expands the application scenarios. The present invention uses 3D printing to realize flexible mode field conversion function, which can meet the needs of hollow-core optical fiber mode field connection of various structures and realize low-loss connection.

[0026] 3. A hollow-core optical fiber connection method of the present invention does not require the addition of additional optical elements, and uses a femtosecond laser to perform one-time molding processing on the mode conversion device, which has the characteristics of low preparation cost and high preparation efficiency. The present invention does not require post-dispensing treatment of the capillary glass tube, and uses processed photoresist to self-assemble and fix the connector, which simplifies the process flow and has strong anti-pollution ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of a hollow core optical fiber connection method;

[0028] Figure 2 A schematic diagram of femtosecond laser processing for a hollow-core optical fiber connection method;

[0029] Figure 3 It is a schematic structural diagram of the mode field converter in the first embodiment when it is a tapered waveguide;

[0030] Figure 4 Schematic diagram of the structure when the mode field converter in the first embodiment is a free-form surface lens;

[0031] Figure 5 It is a structural schematic diagram of the mode field converter in the second embodiment when it is a one-to-M splitter;

[0032] Figure 6 It is a schematic diagram of the structure of a one-to-M optical splitter in the second embodiment.

[0033] In the attached figure: 1. capillary glass tube; 2. hollow core optical fiber; 3. solid core optical fiber; 4. photoresist; 5. mode field converter; 6. multi-core optical fiber; 7. femtosecond laser. DETAILED DESCRIPTION

[0034] The present invention is further described below in conjunction with specific implementation methods. The accompanying drawings are only used for exemplary descriptions and are only schematic diagrams, not actual drawings, and cannot be understood as limiting this patent; in order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the accompanying drawings may be omitted.

[0035] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right" and the like indicate directions or positional relationships based on the directions or positional relationships shown in the drawings, it is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limitations on this patent. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0036] Embodiment 1

[0037] This embodiment is a first embodiment of a hollow core optical fiber connection method based on 3D printing, comprising the following steps:

[0038] Covering the end face of the hollow core optical fiber 2 with a thin film coated with an anti-reflection film;

[0039] Dropping photoresist 4 into the capillary glass tube 1;

[0040] Insert the hollow core optical fiber 2 and the solid core optical fiber 3 into the two ends of the capillary glass tube 1 respectively;

[0041] A femtosecond laser 7 is used to perform a 3D printing mode field converter 5 on the photoresist 4 between the solid core optical fiber 3 and the hollow core optical fiber;

[0042] After the processing is completed, ultraviolet curing is performed to fix the structure of the hollow-core optical fiber 2 and the solid-core optical fiber 3 to obtain a hollow-core optical fiber 2 connector.

[0043] The dripped photoresist 4 fills the air gap between the hollow-core optical fiber 2 and the solid-core optical fiber 3, as well as the air gap between the hollow-core optical fiber 2, the solid-core optical fiber 3 and the capillary glass tube 1, and squeezes the air in the capillary glass tube 1 out of the tube to achieve fully enclosed processing of the connector, thereby preventing water vapor in the environment from entering the tube and contaminating the connector.

[0044] In this embodiment, the size of the mode field on both sides is determined by the end face structure and refractive index distribution of the hollow core fiber 2 and the solid core fiber 3, the structural parameters of the mode field converter 5 in the middle are calculated by simulation, and the required mode field converter 5 structure is prepared by 3D printing using femtosecond laser 7 direct writing. The inserted solid core fiber 3 does not need to have the same mode field as the hollow core fiber, and the femtosecond laser 7 is used to print the mode field converter 5 structure between the solid core fiber 3 and the hollow core fiber for mode field matching. The type of the solid core fiber 3 can be single mode fiber, multimode fiber or lens fiber, etc.

[0045] In this embodiment, the photoresist 4 is dripped into the capillary glass tube 1 from one end, and then the hollow-core optical fiber 2 and the solid-core optical fiber 3 are inserted into the capillary glass tube 1. Based on the light transmittance of the capillary glass tube 1, the insertion operation of the hollow-core optical fiber 2 and the solid-core optical fiber 3 is observed from the outside of the capillary glass tube 1, and the distance between the end face of the solid-core optical fiber 3 and the end face of the hollow-core optical fiber 2 is controlled so that the distance between the two reaches a preset distance; the photoresist 4 dripped in advance fills the air gap between the solid-core optical fiber 3 and the hollow-core optical fiber 2 at this time, and squeezes the air in the tube out of the tube, thereby achieving a fully enclosed treatment of the connector. The preset distance is about 200um.

[0046] In this embodiment, after the femtosecond laser 7 is directly written, the connector is irradiated with an ultraviolet lamp, and the photoresist 4 in the capillary glass tube 1 is cured by the ultraviolet lamp, and the hollow core optical fiber 2, the solid core optical fiber 3 and the printed mode field converter 5 are self-encapsulated and fixed. No additional development process is required to wash away the dripped photoresist 4.

[0047] In this embodiment, the end face of the hollow core optical fiber 2 is cut by 2° to reduce the backscattering of light between the film and the air. The refractive index of the film is 1.4-1.6, and the transmittance of the film is greater than 99%; silicon dioxide is coated on both sides of the film as an anti-reflection film. The light reflection at the interface between the film and the hollow core optical fiber 2 can be reduced, and the coated film is fixedly inserted into the capillary glass tube 1 close to the end face of the hollow core optical fiber. The refractive index of the photoresist 4 material is 1.3-1.8, and the refractive index difference between the photoresist 4 under multi-photon absorption processed by femtosecond laser 7 and single-photon absorption cured by ultraviolet lamp is about 5×10-3, and the refractive index of multi-photon absorption polymerization is greater than the refractive index of single-photon absorption polymerization.

[0048] In this embodiment, a femtosecond laser 7 with a wavelength of about 780 nm is focused in the photoresist 4 between the solid core optical fiber 3 and the hollow core optical fiber 2 to process the mode field converter 5. The type of the mode field converter 5 is a tapered waveguide or a free-form surface lens with a gradually varying size, see Figures 2 to 4 According to the type of printing device, not only can the low-loss connection between the single-core optical fiber and the hollow-core optical fiber 2 be realized, but also the low-loss connection between the hollow-core optical fiber 2 and the multi-core optical fiber 6 can be realized. Therefore, compared with the existing solutions, the present invention expands the application scenarios.

[0049] join Figure 2 , the nonlinear shape function of the tapered waveguide with gradient size can be determined by the formula D(z)=D2+(D1-D2)×(1-z / L)m, where L is the waveguide length, m is the nonlinear coefficient, and D1 and D2 are the diameters of the input and output surfaces of the tapered waveguide. For the hollow core fiber 2 with an output mode field of approximately 22um and the standard single-mode fiber, the input waveguide diameter and output waveguide diameter of the mode field matched tapered waveguide are approximately 25um and 13.2um, and the length of the tapered waveguide is 60um. The microlens on the end face is composed of a printed cylindrical structure plus a free-form surface, which performs the functions of chromatic aberration correction and mode field conversion. In addition, by controlling the exposure dose of the femtosecond laser 7 point by point during the processing of the femtosecond laser 7, the refractive index gradient function of the printed structure can be realized, thereby printing the effect of a Green lens on the end face.

[0050] A hollow-core optical fiber connection method based on 3D printing of the present invention inserts a hollow-core optical fiber 2 and a solid-core optical fiber 3 into a capillary glass tube 1 dripped with photoresist 4 in advance, and uses the dripped photoresist 4 to perform device processing and optical fiber fixation, which has the effect of simplifying the packaging process flow. At the same time, the dripped photoresist 4 will automatically fill the air gap in the capillary glass tube 1, squeeze the air in the tube out of the tube, and achieve a fully enclosed treatment of the connector, avoiding the situation where water vapor in the environment enters the tube and contaminates the connector. Utilizing the sealing of the connector, the present invention does not need to heat or grind the hollow-core optical fiber to seal, and can avoid the situation where the air hole in the hollow-core optical fiber 2 collapses; the present invention utilizes femtosecond direct writing laser processing technology to process the mode field converter 5 between the hollow-core optical fiber 2 and the solid-core optical fiber 3, which can meet the interconnection requirements between the hollow-core optical fiber 2 and the solid-core optical fiber 3 of various different mode field sizes, and can not only achieve a low-loss connection between a single-core optical fiber and a hollow-core optical fiber 2 according to the type of the printed device, but also can be applied to a low-loss connection between a hollow-core optical fiber 2 and a multi-core optical fiber 6, so relative to the existing scheme, the present invention expands the application scene.

[0051] Embodiment 2

[0052] This embodiment is the second embodiment of the hollow-core optical fiber connection method based on 3D printing. This embodiment is similar to the first embodiment, except that, in this embodiment, the mode field converter 5 structure processed by direct writing with a femtosecond laser 7 is a one-to-M splitter.

[0053] In the traditional solid core optical fiber 3, the power handling capacity is limited by the material damage threshold, nonlinear effects and thermally induced modal degradation. In the hollow core optical fiber 2, the interaction between light and the glass material in the optical fiber cladding can be ignored, making the hollow core optical fiber 2 an ideal transmission medium for high-power laser transmission. However, at the receiving end, in order to avoid the high pulse laser transmitted in the hollow core optical fiber 2 from damaging the solid core optical fiber 3, it is necessary to reasonably divert and receive the energy in the hollow core optical fiber 2. This embodiment uses 3D printing to achieve the interconnection between the hollow core optical fiber 2 and the multi-core optical fiber 6. In the multi-core optical fiber 6 transmission system, the optical amplifier is a key component; and to achieve independent core area pumping to guide the pump light directly into a specific core, a single pump source is required to have very high energy. Through the connection method of the hollow core optical fiber 2 and the multi-core optical fiber 6 proposed in this embodiment, the high pump energy in the hollow core optical fiber 2 can be connected to each core in the multi-core optical fiber 6, and the independent amplification of each core channel signal can be achieved.

[0054] Embodiment 3

[0055] This embodiment is a first embodiment of a hollow-core optical fiber 2 connector. The hollow-core optical fiber 2 connector provided in this embodiment is connected using the connection method of the first embodiment.

[0056] It includes a hollow-core optical fiber 2, a solid-core optical fiber 3, a mode field converter 5 and a woolen glass tube; the woolen glass tube is filled with photoresist 4, the hollow-core optical fiber 2 and the solid-core optical fiber 3 are respectively inserted into the two ends of the woolen glass tube, and the solid-core optical fiber 3 is connected to the hollow-core optical fiber 2 through the mode field converter 5; the mode field converter 5 is prepared by 3D printing on the photoresist 4 between the solid-core optical fiber 3 and the hollow-core optical fiber 2 by a femtosecond laser 7.

[0057] Embodiment 4

[0058] This embodiment is a second embodiment of a hollow-core optical fiber 2 connector. This embodiment is similar to the third embodiment, except that, in this embodiment, one end of the connector is not connected to the solid-core optical fiber 3. The connector provided in this embodiment can be applied to high-power laser output scenarios based on hollow-core optical fiber 2, so as to achieve high-power laser output from the hollow-core optical fiber 2 directly into the air without having to worry about the external environment polluting the hollow-core optical fiber 2 and causing the performance degradation of the hollow-core optical fiber 2.

[0059] In the specific contents of the above-mentioned specific implementation methods, the various technical features can be combined in any non-contradictory manner. In order to make the description concise, not all possible combinations of the above-mentioned technical features are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0060] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A hollow-core optical fiber connection method based on 3D printing, characterized in that: The following steps are involved: Covering the end face of the hollow core optical fiber (2) with a light-transmitting film; Dropping a photoresist (4) into the interior of the capillary glass tube (1); Inserting a hollow core optical fiber (2) and a solid core optical fiber (3) into two ends of a capillary glass tube (1) respectively; Using a femtosecond laser (7) to perform 3D printing of a mode field converter (5) on a photoresist (4) between a solid core optical fiber (3) and a hollow core optical fiber; After the processing is completed, ultraviolet curing is performed to fix the structure of the hollow-core optical fiber (2) and the solid-core optical fiber (3) to obtain a hollow-core optical fiber (2) connector.

2. The hollow-core optical fiber connection method based on 3D printing according to claim 1, characterized in that: The dripped photoresist (4) fills the air gap between the hollow-core optical fiber (2) and the solid-core optical fiber (3) as well as the air gap between the hollow-core optical fiber (2), the solid-core optical fiber (3) and the capillary glass tube (1), and squeezes the air in the capillary glass tube (1) out of the tube, so as to achieve a fully sealed treatment of the connector.

3. The hollow-core optical fiber connection method based on 3D printing according to claim 2, characterized in that: A photoresist (4) is dripped into the capillary glass tube (1) from one end thereof, and then a hollow-core optical fiber (2) and a solid-core optical fiber (3) are inserted into the capillary glass tube (1). Based on the light transmittance of the capillary glass tube (1), the insertion operation of the hollow-core optical fiber (2) and the solid-core optical fiber (3) is observed from the outside of the capillary glass tube (1), and the distance between the end face of the solid-core optical fiber (3) and the end face of the hollow-core optical fiber (2) is controlled so that the distance between the two reaches a preset distance; The photoresist (4) dripped in advance now fills the air gap between the solid core optical fiber (3) and the hollow core optical fiber (2).

4. The hollow-core optical fiber connection method based on 3D printing according to claim 1, characterized in that: The size of the mode fields on both sides is determined by the end face structures and refractive index distributions of the hollow core optical fiber (2) and the solid core optical fiber (3), the structural parameters of the mode field converter (5) are calculated by simulation, and the desired mode field converter (5) structure is prepared by 3D printing using femtosecond laser (7) direct writing.

5. The hollow-core optical fiber connection method based on 3D printing according to claim 1, characterized in that: After the femtosecond laser (7) direct writing process is completed, the connector is irradiated with an ultraviolet lamp, and the photoresist (4) in the capillary glass tube (1) is cured by the ultraviolet lamp, so that the hollow core optical fiber (2), the solid core optical fiber (3) and the printed mode field converter (5) are self-encapsulated and fixed.

6. The hollow core optical fiber connection method based on 3D printing according to claim 4, characterized in that: A femtosecond laser (7) is used to print a mode field converter (5) structure between a solid core optical fiber (3) and a hollow core optical fiber to perform mode field matching. The mode field converter (5) comprises a tapered waveguide with a gradually varying size, a free-form surface lens or a one-point M-splitter.

7. The hollow core optical fiber connection method based on 3D printing according to any one of claims 1 to 6, characterized in that: The end face of the hollow core optical fiber (2) is cut at 2° to reduce the backscattering of light between the film and the air.

8. The hollow core optical fiber connection method based on 3D printing according to any one of claims 1 to 6, characterized in that: The refractive index of the film is 1.4-1.6, and the light transmittance of the film is greater than 99%. Silicon dioxide is plated on both sides of the film as an anti-reflection film.

9. The hollow core optical fiber connection method based on 3D printing according to claim 8, characterized in that: The refractive index of the photoresist (4) material is 1.3-1.8, the refractive index difference between the photoresist (4) under multi-photon absorption processed by a femtosecond laser (7) and under single-photon absorption cured by an ultraviolet lamp is less than 1%, and the refractive index of multi-photon absorption polymerization is greater than the refractive index of single-photon absorption polymerization.

10. A hollow-core optical fiber (2) connector connected using the hollow-core optical fiber connection method according to any one of claims 1 to 9, characterized in that: The invention comprises a hollow-core optical fiber (2), a solid-core optical fiber (3), a mode field converter (5) and a wool glass tube; the wool glass tube is filled with photoresist (4); the hollow-core optical fiber (2) and the solid-core optical fiber (3) are respectively inserted into two ends of the wool glass tube; the solid-core optical fiber (3) and the hollow-core optical fiber (2) are connected via the mode field converter (5); the mode field converter (5) is prepared by 3D printing on the photoresist (4) between the solid-core optical fiber (3) and the hollow-core optical fiber (2) using a femtosecond laser (7).

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