A connection method for a multi-core optical fiber

Abstract

The present application provides a connection method for multi-core optical fibers. The two optical fibers to be connected are the main optical fiber and the slave optical fiber. The interface between the two optical fibers is connected through a connection area. The main optical fiber is a multi-core optical fiber, and the slave optical fiber includes: a single-core optical fiber or a multi-core optical fiber. The method includes: immersing one end of the main optical fiber and the slave optical fiber located at the interface in photoresist, drying the photoresist on the areas of the main optical fiber and the slave optical fiber located at the interface, planning the path and shape of the connection area at the interface of the main optical fiber and the slave optical fiber, using a photolithography exposure process to sequentially expose from the core position of the interface of the main optical fiber to the core position of the interface of the slave optical fiber along the set connection area path according to the connection area shape, curing the photoresist in the exposed area to realize the connection between the main optical fiber and the slave optical fiber, and removing the residual photoresist in the unexposed area through a developing process. This connection method can achieve connection adaptation between different types of optical fibers, including reliable low-loss connection between ordinary optical fibers and special optical fibers.

Description

Technical Field

[0001] This application belongs to the technical field of optical fiber communication. Specifically, it relates to a method for connecting optical fibers. Background Art

[0002] With the rapid development of passive optical networks, low-cost and high-density optical cables are necessary for building future optical access network systems. Therefore, optical fibers have been widely studied in the field of optical communication. Optical fiber transmission has the characteristics of low loss, wide transmission bandwidth, and large communication capacity. In addition, optical fibers and cables have a small diameter, light weight, and are not affected by electromagnetic interference. However, optical fibers will experience loss during transmission, which restricts the signal transmission distance and the distance between relay stations. Therefore, in practical engineering, reducing the fusion loss of optical fibers and improving the fusion quality of optical fibers have a great impact on information transmission.

[0003] Currently, the common direct connection and adaptation method between optical fibers is to use an optical fiber fusion splicer for fusion splicing. When splicing two sections of optical fibers, first, the outer coating of the optical fiber needs to be removed to ensure the cleanliness of the optical fiber. Then, an optical fiber cutting machine is used to process the end face of the optical fiber to make the end face of the optical fiber neat. Finally, the two sections of optical fibers are placed into the optical fiber fusion splicer, and the two sections of optical fibers are fused through discharging. Although the technology of fusing optical fibers by an optical fiber fusion splicer is the most mature, in actual use, if different types of optical fibers need to be fused, such as single-core optical fibers, multi-mode optical fibers, dispersion compensation optical fibers, polarization-maintaining optical fibers, etc., the fusion parameters of the optical fiber fusion splicer, such as the discharge amount and discharge time, need to be adjusted, or even different models of optical fiber fusion splicers need to be purchased. Since this fusion method requires removing the coating of the optical fiber, the mechanical strength of the optical fiber structure will become weaker. Therefore, in practical applications, a protective sleeve needs to be added to protect the fusion point part to enhance its mechanical strength. Therefore, in engineering applications, in order to achieve simple, fast, and low-loss connection between optical fibers, a variety of mechanical optical fiber connectors have been proposed. In addition, the Chinese utility model patent with the publication number CN201673283U discloses an optical fiber connector composed of structures such as a coupling sleeve, a tail sleeve, and a metal support tube, which fixes and couples the optical fiber mechanically. However, this type of connector is only suitable for connecting the same type of optical fibers and is not suitable for connecting and adapting two different types of optical fibers.

[0004] However, with the continuous expansion of communication capacity in optical fiber communication systems, especially the demand for transmission capacities in the Tbps range, multi-core optical fibers are considered to be the most advantageous implementation for solving ultra-high-capacity optical fiber communication. However, the main challenges faced by multi-core optical fibers during transmission are: (1) the adaptation and connection problems between multi-core optical fibers and single-core optical fibers; (2) the connection and adaptation problems between multi-core optical fibers. For the first problem, there are currently two main solutions. One is that in 2010, B. Zhu, T. F. Taunay et al. proposed a tapered seven-core optical fiber adapter (connector) with ultra-low crosstalk and loss. By tapering a fiber bundle with seven single-core optical fibers, a structure is formed with one end being a seven-core optical fiber (for docking with a commercial seven-core optical fiber) and the other end being seven single-core optical fibers (for docking with single-core optical fibers), achieving the adaptation and connection between the seven-core optical fiber and the single-core optical fiber [Zhu, B., et al. “Seven-Core Multicore Fiber Transmissions for Passive Optical Network.” Optics Express, vol. 18, no. 11, 2010, pp. 11117–11122.]. However, since this structure requires bundling seven single-core optical fibers together for tapering, during the tapering process, the diameter reduction ratio of each single-core optical fiber is not uniform with the tapering process, resulting in inconsistent losses corresponding to the cores of each optical fiber after tapering, causing a relatively large overall loss of the adapter and non-uniform loss values for each core. The other method is to output the light corresponding to each core of the multi-core optical fiber at different angles through a beam splitter prism, and then couple each path of light into a single-core optical fiber respectively to achieve the coupling between the multi-core optical fiber and the single-core optical fiber. This method is extremely difficult to implement because it requires discrete components such as beam splitter prisms and coupling prisms. In addition, due to the use of discrete devices, the loss of the device increases, and at the same time, when the number of cores of the multi-core optical fiber is too large, it cannot be realized due to the complexity of the system structure. For the second problem, Chinese invention patent CN 112255740A discloses a multi-core optical fiber connector and its manufacturing method. By inserting multiple cut multi-core optical fibers into a porous ferrule and protruding a certain distance from the end face of the porous ferrule. Then, the multi-core optical fibers are rotated and aligned. After rotating the core closest to the marking unit in each multi-core optical fiber to a preset position in the porous ferrule, fixed grinding is performed to form a multi-core optical fiber connector. Although this connector can achieve the connection between multi-core optical fibers, it is only applicable to multi-core optical fibers of the same type, the same number of cores, and the same structure. When the number of cores or the structure of the multi-core optical fibers to be connected is different, this method cannot be implemented. Summary of the Invention

[0005] To solve the problem that the connection of various types of optical fibers is not universal due to the complex existing optical fiber connection process, a connection method for multi-core optical fibers is proposed. As a universal optical fiber connection method, this connection method can realize the connection between multi-core optical fibers and single-core optical fibers, between multi-core optical fibers and multi-core optical fibers, and even between different special optical fibers, such as between multi-mode and single-mode optical fibers, between photonic crystal optical fibers and ordinary single-mode optical fibers, etc. It can be used as a universal optical fiber connection method and can meet the connection adaptation problems between various optical fibers.

[0006] To achieve the above object, the present application adopts the following technical solutions:

[0007] A connection method for multi-core optical fibers, where the two optical fibers to be connected are the main optical fiber and the slave optical fiber. The interface between the main optical fiber and the slave optical fiber is connected through a connection area. The main optical fiber is a multi-core optical fiber, and the slave optical fiber includes a single-core optical fiber and a multi-core optical fiber. The method is characterized in that one end of the main optical fiber and the slave optical fiber located at the interface is immersed in photoresist, the photoresist on the areas of the main optical fiber and the slave optical fiber located at the interface is dried, the path and shape of the connection area at the interface of the main optical fiber and the slave optical fiber are planned, and the photolithography exposure process is used to expose the core positions at the interface of the main optical fiber to the core positions at the interface of the slave optical fiber in sequence along the set connection area path according to the connection area shape. The exposed area of the photoresist is cured to realize the connection between the main optical fiber and the slave optical fiber, and the unexposed area is removed of the residual photoresist through the developing process.

[0008] The principle of the above solution is as follows: First, immerse the interface areas of the main optical fiber and the slave optical fiber in photoresist to form a photoresist wrap in the connection area. Dry the photoresist. During the drying process, the photoresist changes from a liquid state to a solid state, thereby realizing the fixation of the main optical fiber and the slave optical fiber. At this time, the fixation is not firm, and it is only a temporary support fixation of the main optical fiber and the slave optical fiber after the photoresist changes from a liquid state to a solid state. Use photolithography technology to perform photolithography along the connection area path according to the connection area shape. After the photoresist is exposed, the exposed photoresist is cured, thereby forming a connection area formed by the cured photoresist exposed between the main optical fiber and the slave optical fiber. The unexposed area is removed of its residual photoresist through the developing process. Therefore, the connection of the optical fiber is realized through this technical solution.

[0009] The preferred solution further includes: a surface cleaning treatment step for the interfaces of the main optical fiber and the slave optical fiber, that is, using an organic solvent to treat the surfaces of the interfaces of the main optical fiber and the slave optical fiber to be connected, and using a heating device to dry the surfaces of the interfaces.

[0010] The thickness of the photoresist layer at the interface on the main optical fiber and the secondary optical fiber ranges from 30 to 4000 μm. The thickness of the photoresist layer is at least greater than the outer diameters of the main optical fiber and the secondary optical fiber to be connected, so as to ensure the formation of a connection area composed of photoresist between the main optical fiber and the secondary optical fiber. The thickness ranging from 30 to 4000 μm basically covers the diameter ranges of common main optical fibers and secondary optical fibers.

[0011] The drying process of the photoresist in the area at the interface on the main optical fiber and the secondary optical fiber is carried out in two steps. First, use a heating device to pre-dry the photoresist in the area at the interface on the main optical fiber and the secondary optical fiber for 20 min - 30 min, and then dry and cure it in a photoresist oven for 30 min - 60 min.

[0012] The described photolithography exposure process is to use a two-photon lithography system to expose the photoresist. The connection area path and connection area shape at the interface of the main optical fiber and the secondary optical fiber are converted into three-dimensional space coordinate axes and input into the two-photon lithography system, and the two-photon lithography system completes the exposure in sequence according to the input three-dimensional space coordinates.

[0013] The shape of the connection area is conical.

[0014] The photoresist used is a liquid negative photoresist.

[0015] The described developing process includes: first rinsing in isopropyl alcohol to obtain the planned connection area shape; then using propylene glycol monomethyl ether acetate as a developer to further remove the residual photoresist.

[0016] Beneficial effects

[0017] The implementation mode of this application has universality and can be used for the connection between single-core optical fibers, between multi-core optical fibers, and can also achieve the connection between single-core optical fibers and multi-core optical fibers; moreover, the shape of the connection area can be conveniently controlled according to design requirements. It can achieve reliable low-loss connections between different types of optical fibers (including: special optical fibers), and simplifies the connection process. Brief description of the drawings

[0018] Figure 1 Schematic diagram of the connection between single-core optical fibers in an embodiment of this application.

[0019] Figure 2 Conical connection area structure formed by photolithography of four-core optical fibers in an embodiment of this application.

[0020] Figure 3 Conical connection area structure formed by photolithography of multi-mode optical fibers and multi-mode optical fibers in an embodiment of this application.

[0021] Figure 4 Cross-sectional view of the seven-core optical fiber used in an embodiment of this application.

[0022] Figure 5 Schematic diagram of adapter connection for an embodiment of the present application.

[0023] Figure 6 Conical connection area structure formed by lithography for an embodiment of the present application.

[0024] Figure 7 Schematic diagram of optical network transmission experiment for an embodiment of the present application. Detailed implementation manners

[0025] The above solution will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are used to illustrate the present application and are not limited to restricting the scope of the present application. The implementation conditions adopted in the embodiments can be further adjusted according to the conditions of specific manufacturers, and the implementation conditions not specified are usually the conditions in conventional experiments.

[0026] The present application discloses a connection method for multi-core optical fibers. Taking the example of using a two-photon lithography system to lead out each core of the main optical fiber (seven-core optical fiber) and connect and adapt it to the slave optical fiber (single-core optical fiber), the system is equipped with a 50x microscope objective lens (numerical aperture 1.6, field number 28mm, writing field diameter > 550μm) and a galvanometer mirror for quickly moving the beam laterally. The lithography light source uses femtosecond laser with a pulse length of 100 fs and a repetition frequency of 90 MHz.

[0027] First step: Clean the surface at the interface of the main optical fiber and the slave optical fiber using isopropyl alcohol or ethanol.

[0028] Second step: Drying treatment, heating at 150 - 200 °C on a hot plate for 2 - 3 minutes to remove the water vapor on the surface at the interface of the main optical fiber and the slave optical fiber, thereby improving the adhesion to the photoresist.

[0029] Third step: Immerse the surface at the interface of the main optical fiber and the slave optical fiber in the photoresist solution so that the surface at the interface is coated with photoresist. The thickness of the photoresist layer is about 30 - 200 μm. The best coating conditions are a temperature of 20 - 25 °C, a relative air humidity of 43%, and a temperature stability of ±1 °C (optimal 21 °C).

[0030] Fourth step: Pre-bake the photoresist film on the surface at the interface of the main optical fiber and the slave optical fiber on a hot plate for about 20 min - 30 min. This process volatilizes the organic solvent in the photoresist through temperature, improves the adhesion of the photoresist to the optical fiber surface, and can also reduce the occurrence of dark corrosion during the development process.

[0031] Fifth step: Further dry the photoresist film in an oven for 30 min - 60 min, take it out and wait for the photoresist to cool. So that it can pass through the exposure mask and the exposure system.

[0032] Step 6: Adjust the parameters of the two-photon lithography system. The two-photon lithography system is equipped with supporting control software. Set the marking points at the cross-sections of the main optical fiber and the slave optical fiber interfaces by adjusting the coordinates of the X, Y, and Z axes, and determine the connection area path and connection area shape at each core of the main optical fiber.

[0033] Step 7: Convert the connection area path and connection area shape at the interfaces of the main optical fiber and the slave optical fiber into three-dimensional space coordinate axes and input them into the two-photon lithography system.

[0034] Step 8: Start lithography. Connect the first core of the main optical fiber to the core of the single-core optical fiber. Use the imaging system of the lithography software to accurately position the coupling interface. Through the confocal imaging unit equipped in the system, use the lithography laser and its beam deflector to obtain 3D images during lithography, and monitor in real time whether the structures manufactured by lithography are completely aligned.

[0035] Step 9: Use propylene glycol methyl ether acetate as the developer, and remove the unexposed photoresist through two-step development. The temperature range is 21 - 23°C with an error of ±0.5°.

[0036] Step 10: Rinse the lithographed structure in isopropyl alcohol. After rinsing is completed, the required connection area between the main optical fiber and the slave optical fiber can be obtained.

[0037] Step 11: Adjust the focusing position of the two-photon lithography system on the main optical fiber, transfer the focusing position to the position of the next core to be taken out, and repeat the above steps until all the cores of the main optical fiber are taken out and connected to the single-core optical fiber.

[0038] This method solves the problems in the prior art that the direct connection of optical fiber fusion splicers has weak mechanical strength, is not suitable for engineering applications, and it is difficult to achieve low-loss connection between different types of optical fibers. Mechanical structure optical fiber connectors can achieve fast and low-loss connection between the same type of optical fibers, but are not suitable for the connection and adaptation between two different types of optical fibers. The preparation process of special optical fiber connectors (taking multi-core optical fibers as an example) is complex and expensive. The experimental results show that the connection and adaptation method proposed in this application enables the connection between cores to be close to 0 loss. And it greatly reduces the crosstalk between cores. At 1550 nm, the inter-core crosstalk can be reduced to an average of 0.2 dB. In addition, by adjusting the lithography software to increase the length of the lithography cone area during the connection process, the crosstalk between the central core and its external cores of the multi-core optical fiber can be further reduced.

[0039] During the photolithography process, bubbles may occur during and after exposure, for example, due to excessive exposure dose or excessive exposure intensity. The exposure dose can be optimized through multiple exposures or intermittent exposures. The exposure time is mainly determined by the stabilization time (105 ms) of the piezoelectric actuator used for the axial movement of the objective lens between the exposure layers and the exposure speed. In the experiments conducted, the manufacturing time required for each fiber core to be led out and connected to a single-core fiber is approximately 3 - 6 minutes.

[0040] Next, in combination with specific implementation manners, the fiber connection method proposed in this application will be verified.

[0041] Example 1, connection between single-core fibers:

[0042] As Figure 1 shown is the schematic diagram of two-photon lithography connection between single-core fibers. In the figure, 1 is a single-core fiber (Corning SMF-28) with a mode field diameter of (10.3 ± 0.4) μm, and 2 is the two-photon lithography tapered connection region.

[0043] After the core of the single-core fiber is tapered and led out through two-photon lithography technology and then connected to another single-core fiber, the loss is reduced. During the lithography process, after the core is led out, it is covered with a photoresist layer, and the anti-interference ability between the cores is further improved. After testing, the single-core fibers connected by this adapter have no loss.

[0044] Example 2, connection between multi-core fiber and single-core fiber:

[0045] As Figure 2 shown is the schematic diagram of two-photon lithography connection between a four-core fiber and a single-core fiber. In the figure, 1 is a single-core fiber, 2 is the two-photon lithography tapered connection region, and 3 is a four-core fiber.

[0046] After the cores of the multi-mode fiber are tapered and led out through two-photon lithography technology and then respectively connected to a single-core fiber, the cores are separated, thereby reducing crosstalk between the cores. During the lithography process, after the cores are led out, they are covered with a photoresist layer, and the anti-interference ability between the cores is further improved, approximately by 4 dB. The experimental results show that the connection loss between each core of the four-core fiber and the single-core fiber by this adapter is only about 0.05 dB. Similarly, it can be applied to other multi-core fibers.

[0047] Example 3, connection between multi-mode fiber and single-core fiber

[0048] As Figure 3 shown is the schematic diagram of two-photon lithography connection between a single-core fiber and a multi-mode fiber. In the figure, 1 is a single-core fiber, 2 is the two-photon lithography tapered connection region, and 4 is a multi-mode fiber.

[0049] The core of the multimode fiber is tapered out by two - photon lithography technology and then connected to a single - core fiber, reducing the loss. During the lithography process, after the core is tapered out, it is covered with a photoresist layer, and the anti - interference ability between cores is further improved. After testing, the loss between the multimode fibers connected by this adapter is 0.05 dB.

[0050] Example 4, Connection between a seven - core fiber and a single - core fiber

[0051] Figure 4 is the cross - sectional view of the seven - core fiber. Figure 5 is the schematic connection diagram based on the adapter. Its cladding diameter is 150 μm, the core diameter is 8 μm, and the core pitch is 42 μm. Among them, 5 is the core of the seven - core fiber. Each core of the seven - core fiber is tapered out and respectively connected to the single - core fiber. In the figure, 1 is the single - core fiber, 2 is the two - photon lithography connection structure, and 6 is the seven - core fiber. By using two - photon lithography technology to taper out each core of the seven - core fiber and then connect them to the single - core fiber respectively, the cores are separated, thus reducing the crosstalk between cores. Figure 6 is the two - photon lithography diagram. Among them, 1 is the single - core fiber, 2 is the two - photon lithography tapered connection area, 6 is the seven - core fiber, 7 is the central trajectory of the connection area path (see the upper half of Figure 6 ), 8 is the lithography contour line of the connection area shape, 9 is the laser beam, 10 is the lithography line pattern, and 11 is the lithography cone area. Schematic diagram of one core of the seven - core fiber connected to the single - core fiber 1 Figure 6 shown in the lower part.

[0052] During the lithography process, after the core is tapered out, it is covered with a photoresist layer, and the anti - interference ability between cores is further improved. The ability of the two - photon lithography system to accurately position the coupling interface and have high shape fidelity also makes the insertion loss of the adapter extremely small. The results show that the connection loss between each core of the seven - core fiber and the single - core fiber by this adapter is only about 0.1 dB. And it greatly reduces the crosstalk between cores. At 1550 nm, the crosstalk between cores can be reduced to an average of 2 dB. In addition, by adjusting the lithography software to increase the length of the lithography cone area during the connection process, the crosstalk between the central core and its outer cores of the seven - core fiber can be further reduced.

[0053] Example 5, Connection between multimode fibers

[0054] The core of the multimode fiber is tapered out by two - photon lithography technology and then connected to another multimode fiber, reducing the loss. During the lithography process, after the core is tapered out, it is covered with a photoresist layer, and the anti - interference ability between cores is further improved. After testing, there is no loss for the multimode fibers connected by this adapter. Similar to Figure 1 except that the core diameter of the single - core fiber is 8 μm and the core diameter of the multimode fiber is 62.5 μm.

[0055] Example 6, Connection between Multi-Core Fiber and Multi-Mode Fiber:

[0056] After the core of the multi-mode fiber is tapered and led out by two-photon lithography technology, it is connected to the multi-mode fiber to separate the cores, thus reducing the crosstalk between cores. During the lithography process, the led-out cores are covered with a photoresist layer, further improving the anti-interference ability between cores. The experimental results show that the connection loss between each core of the four-core fiber and the multi-mode fiber of this adapter is only about 0.12 dB. Similarly, it can be used for other multi-core fibers. The figure is similar to Figure 2 except that the core diameter of the single-core fiber is 8 μm and the core diameter of the multi-mode fiber is 62.5 μm.

[0057] Example 7, Connection between Seven-Core Fiber and Multi-Mode Fiber

[0058] After the cores of the seven-core fiber are tapered and led out by two-photon lithography technology, they are respectively connected to the multi-mode fiber, separating each core, thus reducing the crosstalk between cores. During the lithography process, the led-out cores are covered with a photoresist layer, further improving the anti-interference ability between cores. The ability of the two-photon lithography system to accurately position the coupling interface and have high shape fidelity also makes the insertion loss of the adapter extremely small. The results show that the connection loss between each core of the seven-core fiber and the single-core fiber of this adapter is only about 0.2 dB. And the crosstalk between each core is greatly reduced. In addition, by adjusting the lithography software to increase the length of the lithography cone area during the connection process, the crosstalk between the central core and its external cores of the seven-core fiber can be further reduced. The figure is similar to Figure 5 except that the core diameter of the single-core fiber is 8 μm and the core diameter of the multi-mode fiber is 62.5 μm.

[0059] Example 8 Transmission Experiment of Optical Network of Seven-Core Fiber Adapter Connected by Two-Photon Exposure

[0060] Figure 7Schematic diagram of optical network transmission experiment. In the figure, 1 is a single-core optical fiber, 2 is a two-photon lithography tapered connection area, 12 is a 10-km seven-core optical fiber coil, 13 is a 1310 nm / 1550 nm stable light source, 14 is an optical receiver. After testing, the attenuation of each core of the seven-core optical fiber at 1310 nm and 1550 nm is 0.36 dB / km and 0.22 dB / km respectively, which is similar to the loss of the standard single-core optical fiber. In addition, the optical crosstalk between adjacent cores is an important issue. In the experiment, 10 km of seven-core optical fiber was wound on a reel with a diameter of 20 cm, and each of its cores was connected to a 1-m standard single-core optical fiber. Then, signals of 1310 nm and 1550 nm were transmitted, and the optical crosstalk of each core of the seven-core optical fiber was measured by scanning the optical power intensity distribution at the output end face of the standard single-core optical fiber. Through bit definition, Table 1 shows the maximum crosstalk between the central core and the surrounding cores of the seven-core optical fiber at different wavelengths and the connection loss of each core. In addition, the experimental results show that the crosstalk between each outer core and the central core is related to the length of the lithography cone area. When the cone area length is increased (i.e., the taper during lithography is reduced), the crosstalk between the two decreases.

[0061] Table 1 Crosstalk characteristics

[0062]

[0063] Table 1

[0064] The above embodiments are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those who are familiar with this technology to understand the content of the present application and implement it accordingly, and it should not be used to limit the protection scope of the present application. Any equivalent transformation or modification made in accordance with the spirit of the present application should be covered within the protection scope of the present application.

Claims

1. A connection method for multi-core optical fibers. The two optical fibers to be connected are the main optical fiber and the slave optical fiber. The interface between the main optical fiber and the slave optical fiber is connected through a connection area, where, The main optical fiber is a multi-core optical fiber, and the slave optical fiber includes: a single-core optical fiber or a multi-core optical fiber. It is characterized in that the connection method includes: Dip one end of the main optical fiber and the slave optical fiber at the interface into photoresist. Dry the photoresist in the area of the main optical fiber and the slave optical fiber at the interface. Plan the connection area path and the connection area shape at the interface of the main optical fiber and the slave optical fiber. Use the photolithography exposure process to expose the core positions at the interface of the main optical fiber to the core positions at the interface of the slave optical fiber in sequence along the set connection area path according to the connection area shape. The exposed area of the photoresist is cured to realize the connection between the main optical fiber and the slave optical fiber, and the residual photoresist in the unexposed area is removed through the developing process. The photoresist used is a liquid negative photoresist. The said use of the photolithography exposure process is to use a two-photon lithography system to expose the photoresist. Input the connection area path and the connection area shape at the interface of the main optical fiber and the slave optical fiber into the two-photon lithography system, and the two-photon lithography system completes the exposure in sequence according to the input three-dimensional space coordinates. The connection area shape is conical. After the cores of the main optical fiber are led out conically by two-photon lithography, they are respectively connected to the slave optical fiber, and the cores of the main optical fiber are separated.

2. The connection method of a multi-core optical fiber according to claim 1, characterized in that, It also includes: The surface cleaning treatment step at the interface of the main optical fiber and the slave optical fiber, that is, use an organic solvent to treat the surface at the interface of the main optical fiber and the slave optical fiber to be connected, and use a heating device to dry the surface at the interface.

3. A connection method for multi-core optical fibers as described in claim 1, characterized in that The thickness of the photoresist layer at the interface of the main optical fiber and the slave optical fiber is between 30 - 4000 μm.

4. A connection method for multi-core optical fibers as described in claim 1, characterized in that The drying treatment of the photoresist in the area of the main optical fiber and the slave optical fiber at the interface is carried out in two steps. First, use a heating device to pre-dry the photoresist in the area of the main optical fiber and the slave optical fiber at the interface for 20 min - 30 min. Then, dry and cure in a photoresist oven for 30 min - 60 min.

5. The connection method of a multi-core optical fiber according to claim 1, characterized in that, The said developing process includes: First, rinse in isopropyl alcohol to obtain the planned connection area shape. Then, use propylene glycol monomethyl ether acetate as a developer to further remove the residual photoresist.

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