A 3D printing based hollow core fiber connection method

Abstract

The application relates to a kind of hollow core optical fiber connection methods based on 3D printing, the application inserts hollow core optical fiber and solid core optical fiber into capillary glass tube in advance with photoresist, and utilizes the photoresist of drop to carry out device processing and optical fiber fixing, with the effect of simplifying packaging process flow.The photoresist of drop will automatically fill the air gap in capillary glass tube, and the air in the tube is extruded out of the tube, realizing the full sealing treatment of the connector, avoiding the situation that the water vapor in the environment enters the tube and pollutes the connector.The application does not need to heat or grind the hollow core optical fiber, and can avoid the air hole collapse in the hollow core optical fiber;The application utilizes femtosecond direct writing laser processing technology to process the mode field converter between hollow core optical fiber and solid core optical fiber, and can meet the interconnection demand between hollow core optical fiber and solid core optical fiber with various different mode field sizes.

Description

Technical Field

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

[0002] In recent years, due to the continuously growing capacity demand (such as high-resolution video applications, massive data streams in mobile phone applications, etc.), the data traffic in optical fiber communication has grown rapidly. The internal traffic in data centers (typical short distances range from a few meters to 10 kilometers) accounts for more than 80% of the global traffic because they usually require ultra-high-speed interconnections. Hollow-core optical fibers have become a suitable medium for data transmission due to their low signal delay, low nonlinearity, and wide bandwidth. For optical fiber communication, the link power budget is crucial, so the interconnection of low-loss hollow-core optical fibers and solid-core optical fibers has received great attention. Achieving low-loss interconnection faces two main challenges. The first challenge is the need to adapt to 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 existence of 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 process of active connection, resulting in the degradation of the hollow-core optical fiber. Due to the special structure of the hollow-core optical fiber, when it is fused with a single-mode optical fiber, the air holes of the hollow-core optical fiber are prone to collapse due to arc discharge during the fusion process, resulting in an increase in loss. In addition, there is usually a problem of mode field mismatch between the hollow-core optical fiber and the solid-core optical fiber, which increases the loss of direct interconnection of the two optical fibers. Summary of the Invention

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

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

[0005] Provide a method for connecting hollow-core optical fibers based on 3D printing, including the following steps:

[0006] Cover the end face of the hollow-core optical fiber with a light-transmitting thin film;

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

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

[0009] Use femtosecond laser to perform 3D printing of mode field converter processing on the photoresist between the solid-core optical fiber and the hollow-core optical fiber;

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

[0011] The 3D printing-based hollow core optical fiber connecting method of the application inserts the hollow core optical fiber and the solid core optical fiber into the capillary glass tube with the photoresist dropped in advance, and uses the dropped photoresist for device processing and fiber fixing, which has the effect of simplifying the packaging process flow. At the same time, the dropped photoresist will automatically fill the air gap in the capillary glass tube, expelling the air in the tube out of the tube, realizing the full sealing treatment of the connector, and avoiding the case that the water vapor in the environment enters the tube to pollute the connector. By using the sealing property of the connector, the application does not need to heat or grind the hollow core optical fiber, which can avoid the collapse of the air hole in the hollow core optical fiber; the application uses 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 with various different mode field sizes. According to the type of the printed device, not only the low-loss connection between the single-core optical fiber and the hollow core optical fiber can be realized, but also the low-loss connection between the hollow core optical fiber and the multi-core optical fiber can be applied, so the application expands the application scenarios compared with the existing solutions.

[0012] Further, the dropped photoresist fills the air gap between the hollow core optical fiber and the solid core optical fiber and the air gap in the capillary glass tube, expelling the air in the capillary glass tube out of the tube, to realize the full sealing treatment of the connector. The dropped photoresist will automatically fill the air gap between the hollow core optical fiber and the solid core optical fiber and the air gap in the capillary glass tube, expelling the air in the tube out of the tube, to realize the full sealing treatment of the connector, avoiding the case that the water vapor in the environment enters the tube to pollute the connector.

[0013] Further, the photoresist is dropped from one end of the capillary glass tube, and then the hollow core optical fiber and the solid core optical fiber are inserted into the capillary glass tube. Based on the light transmission property 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, the distance between the end face of the solid core optical fiber and the end face of the hollow core optical fiber is controlled, and the distance between the two is controlled to reach a preset distance. The photoresist dropped in advance fills the air gap between the solid core optical fiber and the hollow core optical fiber, expelling the air in the tube out of the tube, to realize the full sealing treatment of the connector. As a preferred, the preset distance is about 200um.

[0014] Further, the mode field size of the two sides is determined by the end face structure and the refractive index distribution of the hollow core fiber and the solid core fiber, the structure parameters of the middle mode field converter are calculated by simulation, and the required mode field converter structure is prepared by 3D printing using femtosecond laser direct writing. The mode field of the inserted solid core fiber and the hollow core fiber does not need to be consistent, and the mode field matching is performed by printing the mode field converter structure between the solid core fiber and the hollow core fiber using femtosecond laser. The type of the solid core fiber can be single mode fiber, multi-mode fiber or lens fiber, etc.

[0015] Further, after the femtosecond laser direct writing processing is completed, the connector is irradiated by using an ultraviolet lamp, the photoresist in the capillary glass tube is cured by ultraviolet irradiation, and the hollow core fiber, the solid core fiber and the printed mode field converter are self-packaged and fixed. There is no need for additional developing process to wash away the dropped photoresist.

[0016] Further, the mode field converter structure is printed between the solid core fiber and the hollow core fiber using femtosecond laser to perform mode field matching, and the mode field converter includes a tapered waveguide with gradually changing size, a free-form surface lens or a 1-to-M optical splitter.

[0017] As preferred, femtosecond laser with a wavelength of about 780 nm is focused in the photoresist between the solid core fiber and the hollow core fiber to process the mode field converter.

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

[0019] Further, the refractive index of the film is 1.4-1.6, and the light transmittance of the film is greater than 99%; the two sides of the film are coated with silicon dioxide as an anti-reflection film. The light reflection at the interface between the film and the hollow core fiber can be reduced, and the film after coating is fixed in the capillary glass tube by tightly contacting the end face of the hollow core fiber. The capillary glass tube has light transmittance and high strength, and the strength is not less than that of the hollow core fiber and the solid core fiber, which is suitable for grinding and coating. The material of the capillary glass tube can be high borosilicon or silicon dioxide. The film can be a polyethylene film or glass.

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

[0021] The application also provides an air-core optical fiber connector connected by the method; the air-core optical fiber connector comprises an air-core optical fiber, a solid-core optical fiber, a mode field converter and a capillary glass tube, the capillary glass tube is filled with photoresist, the air-core optical fiber and the solid-core optical fiber are respectively inserted into two ends of the capillary glass tube, and the solid-core optical fiber and the air-core optical fiber are connected through the mode field converter; the mode field converter is prepared by 3D printing on the photoresist between the solid-core optical fiber and the air-core optical fiber through femtosecond laser.

[0022] In the application, if one end is not connected with the solid-core optical fiber, the application can be applied to a high-power laser output scene based on the air-core optical fiber, and high-power laser can be directly output from the air-core optical fiber to the air without worrying about the performance degradation of the air-core optical fiber caused by the pollution of the external environment to the air-core optical fiber.

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

[0024] 1. The air-core optical fiber connecting method inserts the air-core optical fiber and the solid-core optical fiber into the capillary glass tube in which the photoresist is dripped in advance, and uses the dripped photoresist for device processing and optical fiber fixing, thereby simplifying the packaging process flow. Meanwhile, the dripped photoresist can automatically fill the air gap between the air-core optical fiber and the solid-core optical fiber and the air gap between the air-core optical fiber and the solid-core optical fiber and the capillary glass tube, and can squeeze the air in the tube out of the tube, thereby realizing the full sealing treatment of the connector and avoiding the pollution of the connector caused by the water vapor in the environment. By using the sealing property of the connector, the application does not need to heat or grind the air-core optical fiber, and can avoid the collapse of the air hole in the air-core optical fiber.

[0025] 2. The air-core optical fiber connecting method uses the femtosecond direct writing laser processing technology to process the mode field conversion device between the air-core optical fiber and the solid-core optical fiber, can meet the interconnection requirements between the air-core optical fiber and the solid-core optical fiber with various different mode field sizes, and can realize the low-loss connection between the single-core optical fiber and the air-core optical fiber according to the type of the printed device, and can also be applied to the low-loss connection between the air-core optical fiber and the multi-core optical fiber. Therefore, compared with the prior art, the application expands the application scenarios. The application uses 3D printing to realize the flexible mode field conversion function, can meet the requirements of the air-core optical fiber mode field connection with various different structures, and realizes the low-loss connection.

[0026] 3. The air-core optical fiber connecting method does not need to add additional optical elements, uses the femtosecond laser to process the mode conversion device once, has the characteristics of low preparation cost and high preparation efficiency. The application does not need to perform post-gluing treatment on the capillary glass tube, uses the processed photoresist to fix the self-assembly of the connector, simplifies the process flow, and has strong anti-pollution ability. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 A flowchart of a hollow-core fiber connection method;

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

[0029] Figure 3 A structure schematic diagram when the mode field converter in embodiment one is a tapered waveguide;

[0030] Figure 4 A structure schematic diagram when the mode field converter in embodiment one is a free-form surface lens;

[0031] Figure 5 A structure schematic diagram when the mode field converter in embodiment two is a 1-to-M optical splitter;

[0032] Figure 6 A structure schematic diagram of a 1-to-M optical splitter in embodiment two.

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

[0034] The application will be further described below in conjunction with specific embodiments. In the drawings, only for exemplary illustration, the representation is only a schematic diagram, not a physical diagram, and cannot be understood as a limitation on the patent; in order to better illustrate the embodiments of the application, some components in the 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 in the drawings and their descriptions may be omitted.

[0035] The same or similar reference numerals in the drawings of the embodiments of the application correspond to the same or similar components; in the description of the application, it should be understood that if the terms "upper", "lower", "left", "right" and the like indicate the orientation or positional relationship shown in the drawings, only for the convenience of describing the application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the positional relationship described in the drawings is only for exemplary illustration, and cannot be understood as a limitation on the patent, for those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0036] Embodiment one

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

[0038] A thin film coated with an anti-reflection film is covered on the end face of the hollow optical fiber 2;

[0039] The photoresist 4 is dropped into the capillary glass tube 1;

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

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

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

[0043] The dropped photoresist 4 fills the air gap between the hollow optical fiber 2 and the solid optical fiber 3 and the air gap between the hollow optical fiber 2 and the solid optical fiber 3 and the capillary glass tube 1, and the air in the capillary glass tube 1 is squeezed out of the tube to realize the full sealing treatment of the connector, avoiding the water vapor in the environment from entering the tube to pollute the connector.

[0044] In the embodiment, the mode field size of the two sides is determined by the end face structure and the refractive index distribution of the hollow optical fiber 2 and the solid optical fiber 3, the structure parameters of the middle mode field converter 5 are calculated by simulation, and the required mode field converter 5 structure is prepared by using the femtosecond laser 7 direct writing for 3D printing. The mode field of the inserted solid optical fiber 3 and the hollow optical fiber does not need to be consistent, and the femtosecond laser 7 is used to print the mode field converter 5 structure between the solid optical fiber 3 and the hollow optical fiber to match the mode field. The type of the solid optical fiber 3 can be a single-mode optical fiber, a multi-mode optical fiber or a lens optical fiber.

[0045] In the embodiment, the photoresist 4 is dropped into the capillary glass tube 1 from one end of the capillary glass tube 1, and then the hollow optical fiber 2 and the solid optical fiber 3 are inserted into the capillary glass tube 1. Based on the light transmission of the capillary glass tube 1, the insertion operation of the hollow optical fiber 2 and the solid optical fiber 3 is observed from the outside of the capillary glass tube 1, the distance between the end face of the solid optical fiber 3 and the end face of the hollow optical fiber 2 is controlled, and the distance between the two is reached to a preset distance; The photoresist 4 dropped in advance fills the air gap between the solid optical fiber 3 and the hollow optical fiber 2, and the air in the tube is squeezed out of the tube to realize the full sealing treatment of the connector. The preset distance is about 200um.

[0046] In the embodiment, after the direct writing processing of the femtosecond laser 7 is completed, the connector is irradiated by using the ultraviolet lamp, the photoresist 4 in the capillary glass tube 1 is cured by the ultraviolet lamp irradiation, and the hollow optical fiber 2, the solid optical fiber 3 and the printed mode field converter 5 are self-packaged and fixed. The dropped photoresist 4 does not need to be washed away by an additional developing process.

[0047] In the embodiment, the end face of the hollow core fiber 2 is cut by 2° to reduce the back scattering of light between the film and air. The refractive index of the film is 1.4-1.6, and the light transmittance of the film is greater than 99%; the two sides of the film are coated with silica as an anti-reflection film. The light reflection at the interface between the film and the hollow core fiber 2 can be reduced, and the film after coating is fixed and inserted into the capillary glass tube 1 tightly against the end face of the hollow core fiber. The refractive index of the photoresist 4 material is 1.3-1.8, and the difference between the refractive index of the photoresist 4 under the multi-photon absorption of the femtosecond laser 7 processing and the refractive index under the single-photon absorption of the ultraviolet lamp curing is about 5x10-3, and the refractive index of the multi-photon absorption polymerization is greater than that of the single-photon absorption polymerization.

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

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

[0050] The application discloses a 3D printing-based hollow core fiber connecting method, which inserts a hollow core fiber 2 and a solid core fiber 3 into a capillary glass tube 1 with photoresist 4 dropped in advance, and uses the dropped photoresist 4 for device processing and fiber fixing, and has the effect of simplifying the packaging process flow. Meanwhile, the dropped photoresist 4 can automatically fill the air gap in the capillary glass tube 1, and the air in the tube is squeezed out of the tube, so that the connector is fully sealed, and the water vapor in the environment is prevented from entering the tube to pollute the connector. By using the sealing property of the connector, the hollow core fiber does not need to be heated or ground to seal, so that the air hole in the hollow core fiber 2 can be prevented from collapsing; the femtosecond direct writing laser processing technology is used to process the mode field converter 5 between the hollow core fiber 2 and the solid core fiber 3, so that the interconnection requirement between the hollow core fiber 2 and the solid core fiber 3 with various different mode field sizes can be met. According to the type of the printed device, not only the low-loss connection between the single-core fiber and the hollow core fiber 2 can be realized, but also the low-loss connection between the hollow core fiber 2 and the multi-core fiber 6 can be applied, so that the application scene is expanded compared with the prior art.

[0051] Embodiment two

[0052] The application discloses a 3D printing-based hollow core fiber connecting method, which inserts a hollow core fiber 2 and a solid core fiber 3 into a capillary glass tube 1 with photoresist 4 dropped in advance, and uses the dropped photoresist 4 for device processing and fiber fixing, and has the effect of simplifying the packaging process flow. Meanwhile, the dropped photoresist 4 can automatically fill the air gap in the capillary glass tube 1, and the air in the tube is squeezed out of the tube, so that the connector is fully sealed, and the water vapor in the environment is prevented from entering the tube to pollute the connector. By using the sealing property of the connector, the hollow core fiber does not need to be heated or ground to seal, so that the air hole in the hollow core fiber 2 can be prevented from collapsing; the femtosecond direct writing laser processing technology is used to process the mode field converter 5 between the hollow core fiber 2 and the solid core fiber 3, so that the interconnection requirement between the hollow core fiber 2 and the solid core fiber 3 with various different mode field sizes can be met. According to the type of the printed device, not only the low-loss connection between the single-core fiber and the hollow core fiber 2 can be realized, but also the low-loss connection between the hollow core fiber 2 and the multi-core fiber 6 can be applied, so that the application scene is expanded compared with the prior art.

[0053] In the traditional solid core fiber 3, the power handling capability is limited by the material damage threshold, nonlinear effect and thermal-induced mode degeneration. In the hollow core fiber 2, the interaction between light and glass material in the fiber cladding can be ignored, so that the hollow core fiber 2 becomes an ideal transmission medium for high-power laser transmission. However, at the receiving end, in order to avoid the damage of high-pulse laser transmitted in the hollow core fiber 2 to the solid core fiber 3, the energy in the hollow core fiber 2 needs to be reasonably distributed and received. The embodiment uses 3D printing to realize the interconnection between the hollow core fiber 2 and the multi-core fiber 6. In the multi-core fiber 6 transmission system, the optical amplifier is a key element. In order to realize independent core pumping and directly guide the pumping light into a specific fiber core, a single pumping source needs to have very high energy. By using the connecting method of the hollow core fiber 2 and the multi-core fiber 6 provided in the embodiment, the high pumping energy in the hollow core fiber 2 can be connected to each fiber core in the multi-core fiber 6, so that the independent amplification of the signal in each fiber core channel can be realized.

[0054] Embodiment three

[0055] The application discloses a 3D printing-based hollow core fiber connecting method, which inserts a hollow core fiber 2 and a solid core fiber 3 into a capillary glass tube 1 with photoresist 4 dropped in advance, and uses the dropped photoresist 4 for device processing and fiber fixing, and has the effect of simplifying the packaging process flow. Meanwhile, the dropped photoresist 4 can automatically fill the air gap in the capillary glass tube 1, and the air in the tube is squeezed out of the tube, so that the connector is fully sealed, and the water vapor in the environment is prevented from entering the tube to pollute the connector. By using the sealing property of the connector, the hollow core fiber does not need to be heated or ground to seal, so that the air hole in the hollow core fiber 2 can be prevented from collapsing; the femtosecond direct writing laser processing technology is used to process the mode field converter 5 between the hollow core fiber 2 and the solid core fiber 3, so that the interconnection requirement between the hollow core fiber 2 and the solid core fiber 3 with various different mode field sizes can be met. According to the type of the printed device, not only the low-loss connection between the single-core fiber and the hollow core fiber 2 can be realized, but also the low-loss connection between the hollow core fiber 2 and the multi-core fiber 6 can be applied, so that the application scene is expanded compared with the prior art.

[0056] The hollow core fiber 2, the solid core fiber 3, the mode field converter 5 and the wool glass tube are included; the photoresist 4 is filled in the wool glass tube, the hollow core fiber 2 and the solid core fiber 3 are respectively inserted into two ends of the wool glass tube, the solid core fiber 3 and the hollow core fiber 2 are connected through the mode field converter 5; the mode field converter 5 is prepared by 3D printing on the photoresist 4 between the solid core fiber 3 and the hollow core fiber 2 through femtosecond laser 7.

[0057] Embodiment four

[0058] The second embodiment of the hollow core fiber 2 connector is provided in the embodiment, which is similar to the third embodiment, and the difference is that, in the embodiment, one end of the connector is not connected with the solid core fiber 3, the connector provided in the embodiment can be applied to the high-power laser output scene based on the hollow core fiber 2, and high-power laser can be directly output from the hollow core fiber 2 to the air without worrying about the pollution of the external environment to the hollow core fiber 2 causing the performance degradation of the hollow core fiber 2.

[0059] In the specific contents of the above specific embodiments, each technical feature can be combined arbitrarily without contradiction, and in order to make the description simple, all possible combinations of the above technical features are not described, however, as long as the combination of the technical features does not exist contradiction, it should be considered as the scope of the present application.

[0060] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the implementation modes of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, all the implementation modes do not need to be exhausted. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the claims of the present application.

Claims

1. A method for connecting hollow optical fibers based on 3D printing, characterized in that, Includes the following steps: A light-transmitting film is placed over the end face of the hollow fiber (2); The photoresist (4) is dropped into the inside of the capillary glass tube (1); Hollow-core optical fiber (2) and solid-core optical fiber (3) are inserted into the two ends of capillary glass tube (1), respectively; A 3D-printed mode field converter (5) is fabricated on the photoresist (4) between a solid fiber (3) and a hollow fiber using a femtosecond laser (7); After processing, UV curing is performed to fix the hollow fiber (2) and solid fiber (3) structure, resulting in a hollow fiber (2) connector.

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

3. The hollow optical fiber connection method based on 3D printing according to claim 2, characterized in that, Photoresist (4) is dripped into the capillary glass tube (1) from one end. Then, hollow fiber (2) and solid 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 fiber (2) and solid fiber (3) is observed from the outside of the capillary glass tube (1). The distance between the end face of the solid fiber (3) and the end face of the hollow fiber (2) is controlled so that the distance between the two reaches the preset distance. The photoresist (4) that has been pre-dropped now fills the air gap between the solid fiber (3) and the hollow fiber (2).

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

5. The hollow 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 ultraviolet light, and the photoresist (4) in the capillary glass tube (1) is cured by ultraviolet light, so as to self-encapsulate and fix the hollow fiber (2), solid fiber (3) and the printed mode field converter (5).

6. The hollow optical fiber connection method based on 3D printing according to claim 4, characterized in that, A mode field converter (5) structure is printed between a solid fiber (3) and a hollow fiber using a femtosecond laser (7) for mode field matching. The mode field converter (5) includes a tapered waveguide with gradually varying dimensions, a freeform lens, or a one-to-M beam splitter.

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

8. The method for connecting hollow optical fibers 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 to 1.6, and the light transmittance of the film is greater than 99%; silicon dioxide is deposited on both sides of the film as an anti-reflective film.

9. The hollow 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 to 1.

8. The difference in refractive index between the photoresist (4) under multiphoton absorption processed by femtosecond laser (7) and under single-photon absorption cured by ultraviolet lamp is less than 1%. The refractive index of multiphoton absorption polymerization is greater than that of single-photon absorption polymerization.

10. A hollow fiber (2) connector connected using the hollow fiber connection method according to any one of claims 1 to 9, characterized in that, The device includes a hollow fiber (2), a solid fiber (3), a mode field converter (5), and a capillary glass tube. The capillary glass tube is filled with photoresist (4). The hollow fiber (2) and the solid fiber (3) are respectively inserted into the two ends of the capillary glass tube. The solid fiber (3) and the hollow fiber (2) are connected by the mode field converter (5). The mode field converter (5) is 3D printed on the photoresist (4) between the solid fiber (3) and the hollow fiber (2) by a femtosecond laser (7).

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