A connecting structure and a connecting method of a photonic crystal fiber and a single-mode fiber

Abstract

The application provides a photonic crystal fiber and single-mode fiber connecting structure and connecting method, which comprises a single-mode fiber, a photonic crystal fiber and a rigid connecting tube, the connecting tube has oppositely arranged first and second ends; the single-mode fiber has a first core body with a coating layer stripped off at one end, the first core body is inserted into the connecting tube along the first end of the connecting tube, and a first adhesive is arranged between the first end of the connecting tube and the single-mode fiber; the photonic crystal fiber has a second core body with a coating layer stripped off at one end, the second core body is inserted into the connecting tube along the second end of the connecting tube, so that the end face of the first core body and the end face of the second core body are connected, and a second adhesive is arranged between the second end of the connecting tube and the photonic crystal fiber; the photonic crystal fiber and the single-mode fiber are connected by cold connection, the operation process is simple, the problem of air hole collapse of the photonic crystal fiber caused by fusion connection can be effectively avoided, and the loss during the connection of the photonic crystal fiber and the single-mode fiber can be greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of optical fiber technology, and in particular to a connection structure and method for connecting photonic crystal fiber and single-mode fiber. Background Technology

[0002] Photonic crystal fibers, with their unique structural design and light guiding mechanism, possess many advantages that ordinary optical fibers lack, and have been successfully applied in many new optical fiber fields. Their unique performance has attracted widespread attention from scholars both domestically and internationally. Many optical instruments use single-mode fiber for their input and output interfaces; therefore, for photonic crystal fibers to become practical, the connection problem between photonic crystal fibers and single-mode fibers must be solved.

[0003] Currently, the common method for fiber optic connections is direct splicing using a fiber optic fusion splicer. While splicing ordinary single-mode fiber using a fusion splicer results in extremely low loss, splicing photonic crystal fiber (PCF) and single-mode fiber using the same splicer can lead to significant collapse of air holes near the PCF end face and the potential generation of impurities such as bubbles, resulting in increased splice loss and even rendering the fiber unusable. Numerous researchers both domestically and internationally have conducted extensive research on splicing PCF and single-mode fiber. For example, patent CN106019482B discloses a splicing method for PCF and single-mode fiber that reduces splice loss by filling air holes or adjusting splicing parameters to minimize air hole collapse. However, these methods are cumbersome, and improper selection of splicing parameters can easily cause complete air hole collapse, leading to even greater splice loss and limiting their applicability. Summary of the Invention

[0004] In view of this, the present invention proposes a connection structure and method for connecting photonic crystal fiber and single-mode fiber to solve the problem that the existing technology of fusion splicing causes the air hole collapse of photonic crystal fiber and the large fusion loss when connecting photonic crystal fiber and single-mode fiber.

[0005] The technical solution of this invention is implemented as follows:

[0006] On the one hand, the present invention provides a connection structure between a photonic crystal fiber and a single-mode fiber, the connection structure comprising a single-mode fiber and a photonic crystal fiber;

[0007] It also includes a rigid connecting pipe having a first end and a second end disposed opposite to each other;

[0008] The single-mode optical fiber has a first core with the coating removed at one end. The first core is inserted into the connecting tube along the first end of the connecting tube. A first adhesive is provided between the first end of the connecting tube and the single-mode optical fiber. The first adhesive is used to bond and fix the single-mode optical fiber to the connecting tube.

[0009] The photonic crystal fiber has a second core with the coating removed at one end. The second core is inserted into the connecting tube along the second end of the connecting tube, so that the end faces of the first core and the second core are aligned. A second adhesive is provided between the second end of the connecting tube and the photonic crystal fiber. The second adhesive is used to bond and fix the photonic crystal fiber to the connecting tube.

[0010] Based on the above technical solution, preferably, the first adhesive is located between the first end face of the connecting tube and the coating end face of its corresponding single-mode optical fiber, and the second adhesive is located between the second end face of the connecting tube and the coating end face of its corresponding photonic crystal optical fiber, and the first adhesive and the second adhesive are instant adhesives.

[0011] Furthermore, preferably, the distance between the first end face of the connector tube and the coating end face on the corresponding single-mode optical fiber is 0.5mm to 2mm, and the distance between the second end face of the connector tube and the coating end face on the corresponding photonic crystal optical fiber is 0.5mm to 2mm.

[0012] Based on the above technical solution, preferably, the first core and the second core have the same diameter.

[0013] Furthermore, preferably, the gap between the inner wall of the connecting tube and the outer walls of the first core and the second core is 0.2um-0.5um.

[0014] Based on the above technical solution, preferably, the connection structure further includes an optical fiber heat shrink tube, which is sleeved on the connecting tube. One end of the optical fiber heat shrink tube is sleeved on the outer peripheral wall of the coating layer on the single-mode optical fiber and is thermally fused to fix it to the single-mode optical fiber. The other end of the optical fiber heat shrink tube is sleeved on the outer peripheral wall of the coating layer on the photonic crystal optical fiber and is thermally fused to fix it to the photonic crystal optical fiber.

[0015] Furthermore, preferably, the outer diameter of the connecting tube is the same as the diameter of the coating layer on the single-mode optical fiber and the diameter of the coating layer on the photonic crystal optical fiber.

[0016] Preferably, the connecting pipe is a glass pipe, a ceramic pipe, or a metal pipe.

[0017] On the other hand, the present invention also discloses a method for connecting a photonic crystal fiber and a single-mode fiber, which adopts the aforementioned connection structure of the photonic crystal fiber and the single-mode fiber, and includes the following steps:

[0018] S1. Strip the coating layer from one end of the single-mode fiber to expose the first core, and cut the end face of the first core flat.

[0019] S2. Insert the first core into the predetermined position in the connecting tube from the first end of the connecting tube;

[0020] S3. A first adhesive is provided between the first end of the connector tube and the single-mode optical fiber to bond and fix the single-mode optical fiber to the connector tube.

[0021] S4. Strip the coating layer from one end of the photonic crystal fiber to expose the second core, insert the second core into the connecting tube from the second end of the connecting tube, and make the end face of the second core coincide with the end face of the first core.

[0022] S5. Slightly adjust the overlap between the end face of the second core and the end face of the first core. When the connection loss between the single-mode fiber and the photonic crystal fiber is the lowest, a second adhesive is placed between the second end of the connecting tube and the photonic crystal fiber to bond and fix the photonic crystal to the connecting tube.

[0023] S6. Insert the fiber heat shrink tubing into the connection position between the single-mode fiber and the photonic crystal fiber, heat the fiber heat shrink tubing to shrink it, and complete the connection between the photonic crystal fiber and the single-mode fiber.

[0024] Based on the above technical solution, preferably, the heating temperature of the optical fiber heat shrink tubing is lower than the melting point temperature of the first adhesive and the second adhesive.

[0025] The present invention has the following advantages over the prior art:

[0026] (1) The connection structure disclosed in this invention involves setting a connecting tube, inserting the first core of a single-mode fiber with its coating removed along one end of the connecting tube, and bonding and fixing the single-mode fiber to one end of the connecting tube with a first adhesive. Then, inserting the second core of a photonic crystal fiber with its coating removed along the other end of the connecting tube, so that the end face of the second core is aligned with the end face of the first core. This achieves a good connection between the photonic crystal fiber and the single-mode fiber, while bonding and fixing the single-mode fiber to the other end of the connecting tube with a second adhesive. The photonic crystal fiber and the single-mode fiber are connected by a cold connection, which is simple to operate and can effectively avoid the problem of air hole collapse in the photonic crystal fiber caused by fusion splicing. This can greatly reduce the loss when connecting the photonic crystal fiber and the single-mode fiber.

[0027] (2) By making the diameters of the first core and the second core the same, and making the inner diameter of the connecting tube slightly larger than the diameters of the first core and the second core, the optical fiber can be well collimated, fixed and protected.

[0028] (3) By using the first adhesive and the second adhesive to apply instant adhesive, the single-mode fiber, photonic crystal fiber and capillary connector can be bonded and fixed instantly. The operation is simple, the bonding is firm and reliable, and it will not affect the single-mode fiber and photonic crystal fiber.

[0029] (4) By setting up the fiber thermoplastic tube, the cold splice position of photonic crystal fiber and single-mode fiber can be protected and collimated, making the connection position safer and more stable.

[0030] (5) By making the outer diameter of the connecting tube the same as the diameter of the coating layer on the single-mode fiber and the diameter of the coating layer on the photonic crystal fiber, and by combining it with the fiber thermoplastic tube, the overall connection structure of the photonic crystal fiber and the single-mode fiber can be made more compact. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the planar structure of the connection structure between the photonic crystal fiber and the single-mode fiber disclosed in this invention.

[0033] Figure 2 This is a schematic diagram of the connection method between photonic crystal fiber and single-mode fiber disclosed in this invention;

[0034] Figure label:

[0035] 1. Single-mode optical fiber; 2. Photonic crystal optical fiber; 3. Connecting tube; 11. First core; 4. First adhesive; 21. Second core; 5. Second adhesive; 6. Optical fiber heat shrink tubing. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] like Figure 1 As shown in the figure, an embodiment of the present invention discloses a connection structure between a photonic crystal fiber and a single-mode fiber, the connection structure including a single-mode fiber 1 and a photonic crystal fiber 2.

[0038] In existing technologies, fiber optic fusion splicers are typically used to splice photonic crystal fiber 2 and single-mode fiber 1. However, this splicing method can cause a large number of air holes near the end face of photonic crystal fiber 2 to collapse and may generate impurities such as bubbles, leading to increased splicing loss and affecting the transmission of fiber optic signals.

[0039] To address the aforementioned problems, this embodiment proposes the following solution.

[0040] Specifically, the connection structure in this embodiment also includes a rigid connecting tube 3, which is a straight tube open at both ends and has a first end and a second end arranged opposite to each other. By choosing a rigid material for the connecting tube 3, a collimated and fixed environment can be provided for the single-mode fiber 1 and the photonic crystal fiber 2 during the connection process.

[0041] The single-mode fiber 1 needs to be spliced ​​at one end with a first core 11 with the coating layer stripped off. It can be understood that the first core 11 consists of a fiber core and a cladding, with the cladding wrapped around the outer peripheral wall of the fiber core.

[0042] The first core 11 is inserted into the connecting tube 3 along its first end. A first adhesive 4 is disposed between the first end of the connecting tube 3 and the single-mode optical fiber 1. The first adhesive 4 is used to bond and fix the single-mode optical fiber 1 to the connecting tube 3. In this embodiment, the first adhesive 4 is an adhesive glue. After the first core 11 is inserted into the connecting tube 3 at a predetermined position, the first adhesive 4 is applied between the connecting tube 3 and the single-mode optical fiber 1 to bond and fix the first core 11 to the connecting tube 3, thereby fixing the position of the single-mode optical fiber 1 at one end of the connecting tube 3.

[0043] The end of the photonic crystal fiber 2 that needs to be spliced ​​has a second core 21 with the coating stripped off. Understandably, the second core 21 consists only of a fiber core with multiple pores.

[0044] The second core 21 is inserted into the connecting tube 3 along its second end, with the end faces of the first core 11 and the second core 21 aligned. By adjusting the position of the photonic crystal fiber 2 along the axial direction of the connecting tube 3, the degree of overlap between the second core 21 and the first core 11 can be achieved. When the connection loss between the single-mode fiber 1 and the photonic crystal fiber 2 is minimized, a second adhesive 5 is applied between the second end of the connecting tube 3 and the photonic crystal fiber 2 to bond and fix the photonic crystal fiber 2 to the other end of the connecting tube 3. This achieves a cold connection between the single-mode fiber 1 and the photonic crystal fiber 2 in the connecting tube 3.

[0045] The photonic crystal fiber 2 and single-mode fiber 1 disclosed in this invention are connected by a connecting tube 3, and the two ends of the connecting tube 3 are bonded and fixed to the photonic crystal fiber 2 and the single-mode fiber 1 respectively by adhesive, so that the photonic crystal fiber 2 and the single-mode fiber 1 are cold connected in the connecting tube 3. The entire connection structure is simple and the operation process is simple. It can effectively avoid the problem of air hole collapse of photonic crystal fiber 2 caused by fusion splicing, and can greatly reduce the loss when connecting photonic crystal fiber 2 and single-mode fiber 1.

[0046] In order to facilitate the bonding and fixing of the first end of the connecting tube 3 and the single-mode fiber 1 by the first adhesive 4, and the bonding and fixing of the second end of the connecting tube 3 and the photonic crystal fiber 2 by the second adhesive 5, in this embodiment, the first adhesive 4 can be applied to the outer peripheral wall of the connection between the connecting tube 3 and the single-mode fiber 1, and correspondingly, the second adhesive 5 can be applied to the outer peripheral wall of the connection between the connecting tube 3 and the photonic crystal fiber 2.

[0047] The above method can achieve fixed bonding between the connecting tube 3, the single-mode fiber 1, and the photonic crystal fiber 2.

[0048] However, this method results in insufficient bonding strength between the connecting tube 3 and the single-mode fiber 1 and photonic crystal fiber 2. This is because the adhesive is only applied to the connection point of the connecting tube 3 and the single-mode fiber 1 and photonic crystal fiber 2, resulting in a small bonding area that cannot guarantee effective bonding and fixation between the connecting tube 3 and the single-mode fiber 1 and photonic crystal fiber 2.

[0049] Therefore, in this embodiment, the first adhesive 4 is applied between the first end face of the connecting tube 3 and the coating end face of its corresponding single-mode fiber 1. Correspondingly, the second adhesive 5 is applied between the second end face of the connecting tube 3 and the coating end face of its corresponding photonic crystal fiber 2. In this way, the bonding area between the end face of the connecting tube 3 and the coating end face of the single-mode fiber 1 can be increased by the application of the first adhesive 4, thereby improving the bonding strength between the connecting tube 3 and the single-mode fiber 1.

[0050] When the first core 11 and the second core 21 are connected in the connecting tube 3, even a small amount of movement will cause high connection loss between the first core 11 and the second core 21.

[0051] Therefore, in this embodiment, both the first adhesive 4 and the second adhesive 5 are instant adhesives. That is, after the first core 11 is inserted into the connecting tube 3, the connecting tube 3 and the single-mode fiber 1 are instantly bonded and fixed by the first adhesive 4. When the second core 21 is inserted into the connecting tube 3, the overlap between the end face of the second core 21 and the end face of the first core 11 is slightly adjusted. When the connection loss between the single-mode fiber 1 and the photonic crystal fiber 2 is at its lowest, the second adhesive 5 is placed between the second end of the connecting tube 3 and the photonic crystal fiber 2, which can instantly bond and fix the photonic crystal to the connecting tube 3, ensuring that after the first core 11 and the second core 21 are connected at low loss, the connecting tube 3, the single-mode fiber 1, and the photonic crystal fiber 2 are quickly bonded and fixed.

[0052] Using instant adhesive in the first adhesive 4 and the second adhesive component, the single-mode fiber 1 and photonic crystal fiber 2 can be instantly bonded and fixed to the capillary connector 3. The operation is simple, the bonding is firm and reliable, and it will not affect the single-mode fiber 1 and photonic crystal fiber 2.

[0053] In the above embodiments, a first adhesive 4 is applied between the first end face of the connecting tube 3 and the coating end face of its corresponding single-mode fiber 1, and a second adhesive 5 is applied between the second end face of the connecting tube 3 and the coating end face of its corresponding photonic crystal fiber 2. The gap between the connecting tube 3 and the first core 11 and the second core 21 can also be sealed to prevent weak airflow from entering between the connecting tube 3 and the first core 11 and the second core 21, causing slight displacement changes in the first core 11 and the second core 21, thereby reducing the connection loss between the single-mode fiber 1 and the photonic crystal fiber 2.

[0054] In this embodiment, the connecting tube 3 is a glass tube, a ceramic tube, or a metal tube. By using a rigid material, the connecting tube 3 can provide alignment and protection during the docking process of the first core 11 and the second core 21 within the connecting tube 3.

[0055] As some preferred embodiments, the connecting tube 3 is preferably a glass tube. Since the inner wall surface of the glass tube is relatively smooth, when the first core 11 and the second core 21 are inserted into the connecting tube, the friction damage between the first core 11 and the second core 21 and the inner wall of the glass tube can be reduced.

[0056] In some embodiments, the distance between the first end face of the connector tube 3 and the coating end face on the corresponding single-mode fiber 1 is 0.5mm to 2mm, and the distance between the second end face of the connector tube 3 and the coating end face on the corresponding photonic crystal fiber 2 is 0.5mm to 2mm. By setting appropriate distances between the two ends of the connector tube 3 and the coating end faces on the single-mode fiber 1 and the photonic crystal fiber 2 respectively, the adhesive application operation can be facilitated.

[0057] In some preferred embodiments, in order to facilitate the accurate positioning and docking of the first core 11 and the second core 21 in the connecting tube 3, and to facilitate the application of the first adhesive 4 and the second adhesive 5.

[0058] In this embodiment, the length of the first core 11 is set to be 0.5mm to 2mm longer than half the length of the connecting tube 3, and the length of the second core 21 is also set to be 0.5mm to 2mm longer than half the length of the connecting tube 3. Therefore, when the first core 11 is inserted into the connecting tube 3, the gap between the first end of the connecting tube 3 and the coating end face on the single-mode fiber 1 is controlled within the range of 0.5mm to 2mm, facilitating the application of the first adhesive 4. Then, when the second core 21 is inserted from the other end of the connecting tube 3, the end face of the second core 21 aligns with the end face of the first core 11. At this point, the distance between the second end of the connecting tube 3 and the coating end face of the photonic crystal fiber 2 is exactly within the range of 0.5mm to 2mm, facilitating the application of the second adhesive 5.

[0059] To ensure collimation and alignment of the first core 11 and the second core 21 within the connecting tube 3, and to improve the end-face overlap of the first core 11 and the second core 21, in this embodiment, the diameters of the first core 11 and the second core 21 are set to be the same. It is worth noting that, according to fiber optic standards, single-mode fiber 1 satisfies a coating diameter of 250±5 μm and a first core 11 diameter of 125±0.7 μm; the diameter of the first core 11 is also the diameter of the cladding. Photonic crystal fiber 2 satisfies a coating diameter of 250±5 μm and a second core 21 diameter of 125±0.7 μm, which is also the diameter of the core with pores.

[0060] The first core 11 and the second core 21 have the same diameter, which can keep the end faces of the first core 11 and the second core 21 connected and maintain coaxiality to the greatest extent, avoiding misalignment after cold connection of the first core 11 and the second core 21, thus increasing connection loss.

[0061] Furthermore, in order to ensure that the first core 11 and the second core 21 are aligned and coaxial within the connecting tube 3, this embodiment sets the gap between the inner wall of the connecting tube 3 and the outer walls of the first core 11 and the second core 21 to 0.2µm-0.5µm. This minimizes the gap between the inner wall of the connecting tube 3 and the first and second cores 11 and 21, reducing misalignment during the connection process and thus minimizing connection loss during cold bonding.

[0062] Although the first core 11 and the second core 21 are inserted into the connecting tube 3 and the connecting tube 3 is bonded and fixed to the single-mode fiber 1 and the photonic crystal fiber 2 by adhesive, the first core 11 and the second core 21 are relatively fragile. Although the first adhesive 4 is bonded between the first end face of the connecting tube 3 and the coating end face of the single-mode fiber 1, the connection between the connecting tube 3 and the single-mode fiber 1 is axial. The first core 11 is very easy to break at the first adhesive 4, and correspondingly, the second core 21 is very easy to break at the second adhesive 5.

[0063] Therefore, the connection structure in this embodiment also includes an optical fiber heat shrink tubing 6. The optical fiber heat shrink tubing 6 is sleeved on the connecting tube 3. One end of the optical fiber heat shrink tubing 6 is sleeved on the outer peripheral wall of the coating layer on the single-mode optical fiber 1 and is heat-fused and fixedly connected to the single-mode optical fiber 1. The other end of the optical fiber heat shrink tubing 6 is sleeved on the outer peripheral wall of the coating layer on the photonic crystal optical fiber 2 and is heat-fused and fixedly connected to the photonic crystal optical fiber 2. By setting the optical fiber heat shrink tubing, the connection points between the connecting tube 3 and the single-mode optical fiber 1 and the photonic crystal optical fiber 2 can be constrained and fixed in the circumferential direction. This can protect and align the cold-splitting positions of the photonic crystal optical fiber 2 and the single-mode optical fiber 1, making the connection position safer and more stable.

[0064] As some preferred embodiments, by making the outer diameter of the connecting tube 3 the same as the diameter of the coating layer on the single-mode fiber 1 and the diameter of the coating layer on the photonic crystal fiber 2, and by using a fiber thermoplastic tube, the overall connection structure between the photonic crystal fiber 2 and the single-mode fiber 1 can be made more compact.

[0065] This invention also discloses a method for connecting a photonic crystal fiber and a single-mode fiber, as shown in the appendix. Figure 2 As shown, it includes the following steps:

[0066] S1. Strip the coating layer from one end of the single-mode fiber 1 to expose the first core 11, and cut the end face of the first core 11 flat. In step S1, preferably, the length of the first core 11 is 0.5mm to 2mm longer than half the length of the connecting tube 3.

[0067] S2. Insert the first core 11 into the connector tube 3 from the first end of the connector tube 3 to a predetermined position; specifically, when inserting the first core 11 into the connector tube 3, control the gap between the first end of the connector tube 3 and the coating end face on the single-mode fiber 1 within the range of 0.5mm to 2mm.

[0068] S3. A first adhesive 4 is provided between the first end of the connecting tube 3 and the single-mode optical fiber 1 to bond and fix the single-mode optical fiber 1 to the connecting tube 3; preferably, the first adhesive 4 is ethyl cyanoacrylate instant adhesive.

[0069] S4. Strip the coating layer from one end of the photonic crystal fiber 2 to expose the second core 21, and set the length of the second core 21 to be 0.5mm to 2mm longer than half the length of the connecting tube 3. Insert the second core 21 into the connecting tube 3 from the second end of the connecting tube 3, and make the end face of the second core 21 coincide with the end face of the first core 11.

[0070] S5. Slightly adjust the overlap between the end face of the second core 21 and the end face of the first core 11. When the connection loss between the single-mode fiber 1 and the photonic crystal fiber 2 is the lowest, a second adhesive 5 is placed between the second end of the connecting tube 3 and the photonic crystal fiber 2 to bond and fix the photonic crystal to the connecting tube 3. The second adhesive 5 is also selected as ethyl cyanoacrylate instant adhesive.

[0071] S6. Insert the fiber heat shrink tube 6 into the connection position between the single-mode fiber 1 and the photonic crystal fiber 2, heat the fiber heat shrink tube 6 to shrink it, and complete the connection between the photonic crystal fiber 2 and the single-mode fiber 1.

[0072] In step S6, it is worth noting that the heating temperature of the fiber optic heat shrink tubing 6 is lower than the melting point temperatures of the first adhesive 4 and the second adhesive 5. This is to prevent the first adhesive 4 and the second adhesive 5 from melting due to excessively high temperatures when the fiber optic fusion splicer heats the fiber optic heat shrink tubing 6.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A connecting structure of a photonic crystal fiber and a single-mode fiber, the connecting structure comprising a single-mode fiber (1) and a photonic crystal fiber (2); characterized in that a rigid connecting tube (3) having a first end and a second end arranged oppositely; the single-mode fiber (1) has a first core (11) with stripped coating at one end, the first core (11) is inserted into the connecting tube (3) along the first end of the connecting tube (3), a first adhesive (4) is arranged between the first end of the connecting tube (3) and the single-mode fiber (1), and the first adhesive (4) is used to adhere and fix the single-mode fiber (1) and the connecting tube (3); the photonic crystal fiber (2) has a second core (21) with stripped coating at one end, the second core (21) is inserted into the connecting tube (3) along the second end of the connecting tube (3), so that the end face of the first core (11) and the end face of the second core (21) are oppositely connected, a second adhesive (5) is arranged between the second end of the connecting tube (3) and the photonic crystal fiber (2), and the second adhesive (5) is used to adhere and fix the photonic crystal fiber (2) and the connecting tube (3); the first adhesive (4) is located between the end face of the first end of the connecting tube (3) and the end face of the coating on the single-mode fiber (1), the second adhesive (5) is located between the end face of the second end of the connecting tube (3) and the end face of the coating on the photonic crystal fiber (2), and the first adhesive (4) and the second adhesive (5) are instant adhesives; the distance between the end face of the first end of the connecting tube (3) and the end face of the coating on the single-mode fiber (1) is 0.5mm-2mm, and the distance between the end face of the second end of the connecting tube (3) and the end face of the coating on the photonic crystal fiber (2) is 0.5mm-2mm.

2. The structure for connecting a photonic crystal fiber and a single-mode fiber according to claim 1, wherein: the diameters of the first core (11) and the second core (21) are the same.

3. The structure of connecting photonic crystal fiber and single mode fiber according to claim 2, wherein: the gap between the inner wall of the connecting tube (3) and the outer wall of the first core (11) and the second core (21) is 0.2um-0.5um.

4. The structure of connecting a photonic crystal fiber and a single mode fiber according to claim 1, wherein: the connecting structure further comprises a fiber heat shrink tube (6), the fiber heat shrink tube (6) is sleeved on the connecting tube (3), one end of the fiber heat shrink tube (6) is sleeved on the outer peripheral wall of the coating on the single-mode fiber (1) and is fixedly connected with the single-mode fiber (1) by heat melting, and the other end of the fiber heat shrink tube (6) is sleeved on the outer peripheral wall of the coating on the photonic crystal fiber (2) and is fixedly connected with the photonic crystal fiber (2) by heat melting.

5. The structure of connecting photonic crystal fiber and single mode fiber according to claim 4, wherein: the outer diameter of the connecting tube (3) is the same as the diameters of the coatings on the single-mode fiber (1) and the photonic crystal fiber (2).

6. The structure of connecting a photonic crystal fiber and a single mode fiber according to claim 1, wherein: the connecting tube (3) is a glass tube, a ceramic tube or a metal tube.

7. A method for connecting a photonic crystal fiber and a single mode fiber using the structure for connecting a photonic crystal fiber and a single mode fiber according to claim 4, characterized by, the connecting structure further comprises the following steps: S1, stripping the coating at one end of the single-mode fiber (1) to expose the first core (11), and cutting the end face of the first core (11) to be flat; S2, inserting the first core (11) into the connecting tube (3) from the first end of the connecting tube (3) to a predetermined position in the connecting tube (3). S3, a first adhesive (4) is arranged between the first end of the connecting tube (3) and the single-mode optical fiber (1) to adhere and fix the single-mode optical fiber (1) and the connecting tube (3); S4, the coating layer at one end of the photonic crystal optical fiber (2) is stripped to expose the second core (21), the second core (21) is inserted into the connecting tube (3) from the second end of the connecting tube (3), and the end face of the second core (21) is coincided with the end face of the first core (11); S5, the coincidence degree of the end face of the second core (21) and the end face of the first core (11) is slightly adjusted, the second adhesive (5) is arranged between the second end of the connecting tube (3) and the photonic crystal optical fiber (2) when the connection loss of the single-mode optical fiber (1) and the photonic crystal optical fiber (2) is the lowest, and the photonic crystal and the connecting tube (3) are adhered and fixed; S6, the optical fiber heat shrink tube (6) is inserted into the connection position of the single-mode optical fiber (1) and the photonic crystal optical fiber (2), the optical fiber heat shrink tube (6) is heated to shrink, and the connection of the photonic crystal optical fiber (2) and the single-mode optical fiber (1) is completed.

8. The method of splicing a photonic crystal fiber to a single mode fiber of claim 7, wherein: The heating temperature of the optical fiber heat shrink tube (6) is less than the melting point temperature of the first adhesive (4) and the second adhesive (5).

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