Optical fiber connection structure and connection method

Abstract

The invention relates to the technical field of optical fiber connection, and provides an optical fiber connection structure and method, and the structure comprises a first to-be-connected optical fiber (1), a second to-be-connected optical fiber (2), and a hollow connecting pipe (3). The connecting end of the first optical fiber (1) to be connected extends into the hollow part of the hollow connecting pipe (3) from the first end of the hollow connecting pipe (3), and the connecting end of the second optical fiber (2) to be connected extends into the hollow part of the hollow connecting pipe (3) from the second end of the hollow connecting pipe (3); wherein if the light beam output by the connection end of the first to-be-connected optical fiber (1) is matched with the mode field of the connection end of the second to-be-connected optical fiber (2), the connection end of the first to-be-connected optical fiber (1) is in contact with the connection end of the second to-be-connected optical fiber (2); otherwise, an air gap with the length being the preset distance # imgabs0 # exists between the connection end of the first optical fiber to be connected (1) and the connection end of the second optical fiber to be connected (2), and the spot size of the emergent light of the first optical fiber to be connected is matched with the mode field of the second optical fiber to be connected after passing through the air gap with the preset distance # imgabs1 #; by adopting the connection structure and the connection method, the back reflection can be reduced while the coupling loss is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of optical fiber splicing, and in particular to an optical fiber splicing structure and a splicing method. Background Art

[0002] Hollow-core fiber uses air as its transmission medium. It transmits light by confining the air core through the optical guidance principle of antiresonance or the photonic bandgap effect. It boasts advantages such as low latency, low dispersion, low nonlinearity, and a high laser damage threshold. These advantages have led to applications in fiber-optic communications, fiber-optic sensing, high-power lasers, and nonlinear effect research. Traditional single-mode fiber has been widely used after years of development. For hollow-core fiber to be widely used, it must be used in conjunction with traditional single-mode fiber.

[0003] However, there is a large mode field mismatch between hollow-core fiber and single-mode fiber, and direct connection will result in large coupling loss; the second problem occurs at the connection end of the solid-core fiber and the hollow-core fiber. Due to the difference in refractive index, a large Fresnel backreflection will be generated, causing the reflected light to enter the hollow-core fiber, affecting the transmission efficiency of the optical signal.

[0004] Research teams at home and abroad have conducted extensive research on how to address these two issues. For mode field mismatch, the mainstream approach involves thermal core expansion, reverse tapering, or splicing a section of graded-index fiber to achieve mode field matching. For backreflection, the mainstream approach involves bevel cleaving. While bevel cleaving reduces backreflection intensity, it also increases coupling loss between the single-mode fiber and the hollow-core fiber. Summary of the Invention

[0005] The present invention provides an optical fiber splicing structure and a splicing method to overcome the defect in the prior art that it is impossible to reduce back reflection while reducing coupling loss when splicing a solid core optical fiber and a hollow core optical fiber.

[0006] In order to solve the above technical problems, the technical solutions of the present invention are as follows: An optical fiber splicing structure, comprising a first optical fiber to be spliced 1, a second optical fiber to be spliced 2, and a hollow connecting tube 3; The connecting end of the first optical fiber 1 to be connected extends from the first end of the hollow connecting tube 3 into the hollow part of the hollow connecting tube 3, and the connecting end of the second optical fiber 2 to be connected extends from the second end of the hollow connecting tube 3 into the hollow part of the hollow connecting tube 3; Among them, if the light beam output from the connecting end of the first optical fiber 1 to be connected matches the mode field of the connecting end of the second optical fiber 2 to be connected, the connecting end of the first optical fiber 1 to be connected touches the connecting end of the second optical fiber 2 to be connected; otherwise, there is an air gap between the connecting end of the first optical fiber 1 to be connected and the connecting end of the second optical fiber 2 to be connected.

[0007] The present invention also provides a splicing method based on the optical fiber splicing structure, comprising the following steps: The connecting end of the first optical fiber 1 to be connected is extended from the first end of the hollow connecting tube 3 into the hollow of the hollow connecting tube 3, and the distance between the connecting end of the first optical fiber 1 to be connected and the first end of the hollow connecting tube 3 is a preset distance. Then, the first optical fiber to be connected 1 is connected to the hollow connecting tube 3 to obtain a first optical fiber to be connected-hollow connecting tube structure; The connecting end of the second optical fiber 2 to be connected is extended from the second end of the hollow connecting tube 3 of the first optical fiber-hollow connecting tube structure into the hollow of the hollow connecting tube 3, and the distance between the connecting end of the first optical fiber 1 to be connected and the connecting end of the second optical fiber 2 to be connected is a preset distance. Then, the second optical fiber to be connected 2 is connected to the hollow connecting tube 3 to obtain a structure of first optical fiber to be connected-hollow connecting tube-second optical fiber to be connected.

[0008] Compared with the prior art, the beneficial effects of the technical solution of the present invention are: The hollow connecting tube 3 is used as a connecting device, which can be applicable to hollow-core optical fibers and solid-core optical fibers of various cladding sizes, and the structure accepts connection methods such as gluing and hot melting, with greater flexibility and compatibility; and when the light beam output from the connecting end of the first optical fiber 1 to be connected does not match the mode field of the connecting end of the second optical fiber 2 to be connected, the mode field matching is achieved by introducing an air gap, which can reduce the coupling loss and the back reflection at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a schematic diagram of the first structural embodiment of the optical fiber splicing structure proposed in Example 1; Figure 2 This is a schematic diagram of the second structure of the optical fiber splicing structure proposed in Example 3; Figure 3 This is a schematic diagram of the structure of the single-mode spliced optical fiber proposed in Example 3; Figure 4 This is a schematic structural diagram of the hollow connecting tube proposed in Example 3; Figure 5 Schematic diagram of the relationship between the connection loss between a single-mode fiber and a hollow-core fiber and the air cavity length at different gradient-index fiber lengths proposed in Example 3. DETAILED DESCRIPTION

[0010] The accompanying drawings are for illustrative purposes only and are not to be construed as limiting this patent; In order to better illustrate this embodiment, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product size; It is understandable to those skilled in the art that some well-known structures and descriptions thereof may be omitted in the drawings.

[0011] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0012] Example 1 This embodiment proposes an optical fiber splicing structure. Figure 1 This is a schematic diagram of the first structure of the optical fiber splicing structure proposed in this embodiment.

[0013] like Figure 1 As shown, the optical fiber splicing structure of this embodiment includes: a first optical fiber to be spliced 1, a second optical fiber to be spliced 2 and a hollow connecting tube 3; The connecting end of the first optical fiber 1 to be connected extends from the first end of the hollow connecting tube 3 into the hollow part of the hollow connecting tube 3, and the connecting end of the second optical fiber 2 to be connected extends from the second end of the hollow connecting tube 3 into the hollow part of the hollow connecting tube 3; Among them, if the light beam output from the connecting end of the first optical fiber 1 to be connected matches the mode field of the connecting end of the second optical fiber 2 to be connected, the connecting end of the first optical fiber 1 to be connected touches the connecting end of the second optical fiber 2 to be connected, otherwise there is a preset distance between the connecting end of the first optical fiber 1 to be connected and the connecting end of the second optical fiber 2 to be connected. The air gap of the first optical fiber to be connected has a spot size of 100 nm. After the air gap, it matches the mode field of the second optical fiber to be connected.

[0014] In the specific implementation process, a hollow connecting tube 3 is used as a connecting device, which can be applicable to hollow-core optical fibers and solid-core optical fibers of various cladding sizes, and the structure accepts connection methods such as gluing and hot melting, and has greater flexibility and compatibility; and when the light beam output from the connecting end of the first optical fiber 1 to be connected does not match the mode field of the connecting end of the second optical fiber 2 to be connected, the mode field matching is achieved by introducing an air gap, which can reduce the coupling loss while reducing the back reflection.

[0015] In an optional embodiment, the hollow connecting tube 3 is a hollow glass capillary tube, and the minimum inner diameter of the hollow region of the first end of the hollow connecting tube 3 is greater than the cladding diameter of the first optical fiber 1 to be connected, and the difference between the minimum inner diameter and the cladding diameter of the first optical fiber 1 to be connected does not exceed a first preset value; The minimum inner diameter of the hollow area at the second end of the hollow connecting tube 3 is larger than the cladding diameter of the second optical fiber 2 to be connected, and the difference between the minimum inner diameter and the cladding diameter of the second optical fiber 2 to be connected does not exceed a second preset value.

[0016] In an optional embodiment, the end of the first optical fiber 1 to be connected extending into the hollow connecting tube 3 is beveled or coated with an anti-reflection coating, or is beveled with an anti-reflection coating.

[0017] In an optional embodiment, the first optical fiber 1 to be connected is a single-mode optical fiber or a single-mode connecting optical fiber, and the single-mode connecting optical fiber is formed by connecting a single-mode optical fiber and a bridging optical fiber 4, and the end of the bridging optical fiber 4 that is not connected to the single-mode optical fiber extends into the hollow part of the hollow connecting tube 3.

[0018] In an optional embodiment, the bridge optical fiber 4 is a graded-index optical fiber, and the length of the bridge optical fiber is , ,in, represents a non-negative integer, represents the multiplication operation, Represents the self-focusing period length of the graded-index fiber.

[0019] Example 2 This embodiment is based on the optical fiber splicing structure proposed in Example 1 and proposes a splicing method based on the optical fiber splicing structure.

[0020] The splicing method based on the optical fiber splicing structure comprises the following steps: The connecting end of the first optical fiber 1 to be connected is extended from the first end of the hollow connecting tube 3 into the hollow of the hollow connecting tube 3, and the distance between the connecting end of the first optical fiber 1 to be connected and the first end of the hollow connecting tube 3 is a preset distance. Then, the first optical fiber to be connected 1 is connected to the hollow connecting tube 3 to obtain a first optical fiber to be connected-hollow connecting tube structure; The connecting end of the second optical fiber 2 to be connected is extended from the second end of the hollow connecting tube 3 of the first optical fiber-hollow connecting tube structure into the hollow of the hollow connecting tube 3, and the distance between the connecting end of the first optical fiber 1 to be connected and the connecting end of the second optical fiber 2 to be connected is a preset distance. Then, the second optical fiber to be connected 2 is connected to the hollow connecting tube 3 to obtain a structure of first optical fiber to be connected-hollow connecting tube-second optical fiber to be connected.

[0021] In an optional embodiment, the method of connecting the first optical fiber 1 to be connected to the hollow connecting tube 3 and the method of connecting the second optical fiber 2 to be connected to the hollow connecting tube 3 includes a gluing method or a hot-melt method; When using the gluing method, glue is used to fill the gap between the connecting end of the first optical fiber 1 to be connected and the first end of the hollow connecting tube 3, and glue is used to fill the gap between the connecting end of the second optical fiber 2 to be connected and the second end of the hollow connecting tube 3; When using the hot melt method, a long-distance heating hot melt method is used; When the first optical fiber 1 to be connected is connected to the hollow connecting tube 3, the long-distance heating hot-melt method is to maintain a preset distance. While the first end of the hollow connecting tube 3 is heated by the fusion splicer, the driving motor of the fusion splicer is adjusted to uniformly change the heating position from the first end of the hollow connecting tube 3 to a position close to the connecting end of the first optical fiber 1 to be connected. After the heat shrinking operation is completed, the heating is stopped and the changing of the heating position is stopped. When the second optical fiber 2 to be connected is connected to the hollow connecting tube 3, the long-distance heating hot-melt method is to maintain the preset distance. While keeping the temperature unchanged, the second end of the hollow connecting tube 3 is heated by the fusion splicer, and the driving motor of the fusion splicer is adjusted to uniformly change the heating position from the first end port position of the hollow connecting tube 3 to the position close to the connecting end of the second optical fiber 2 to be connected, until the heat shrinking operation is completed, then stop heating and stop changing the heating position.

[0022] In an optional embodiment, the first optical fiber 1 to be spliced is a single-mode optical fiber; The preset distance The value is based on simulation method or obtained by calculation, and the preset distance is calculated. The steps for finding the value include: If the second optical fiber 2 to be connected is a solid core optical fiber, the preset distance The value of is set to 0; If the second optical fiber 2 to be connected is a hollow core optical fiber, the light beam output by the first optical fiber 1 to be connected is recorded as the first output light beam, and the spot size of the first output light beam after propagation through the air is calculated as follows: ,in, Indicates the distance the first output beam travels in the air, and sets the preset distance Set the value of Matches the mode field of the second optical fiber 2 to be connected The value of The spot size The expressions include:

[0023] Where, represents the waist radius of the light beam output by the first optical fiber 1 to be connected during the air propagation process; It represents the Rayleigh length of the first output beam during its propagation in the air.

[0024] In an optional embodiment, the first optical fiber 1 to be connected is a single-mode connecting optical fiber, which is formed by connecting a single-mode optical fiber and a bridge optical fiber 4, and the bridge optical fiber 4 has a length equal to a preset length. Graded refractive index optical fiber; the preset distance The value is based on the preset length The value is designed, and the preset distance is designed to optimize the connection effect. With preset length The difference between The second optical fiber 2 to be connected is a hollow core optical fiber; The preset length and preset distance The value is based on simulation or calculation, and the preset length is calculated. and preset distance The steps for finding the value include: Calculate the spot size of the beam output from bridge fiber 4 ,in, represents the length of the bridge optical fiber 4; If In the range of Matching the mode field of the second optical fiber (2) to be connected , then set the value to the preset length , and the preset distance The value of is set to 0; Otherwise, in Within the range, calculate the spot size The difference between the mode field radius of the second optical fiber 2 to be connected is less than or equal to the preset threshold, and Greater than the mode field radius of the second optical fiber 2 to be connected Set the value to the preset length ; and calculate the spot size when the first output beam is transmitted to the second optical fiber 2 to be connected Propagation distance matching the mode field of the second optical fiber 2 to be connected Set the value to the preset distance The value of The spot size The expressions include:

[0025]

[0026] Where, represents the mode field radius of the single-mode fiber that inputs the light beam into the graded-index fiber, Indicates the maximum refractive index value of the graded-index fiber core, represents the mode propagation constant, It represents the Rayleigh length of the incident light beam in the graded-index fiber; represents the refractive index difference of the graded-index fiber, represents the radius of the graded-index fiber; The spot size The expressions include:

[0027] , ,

[0028] Where, represents the equivalent beam waist radius, represents the equivalent waist position, represents the wavelength of the first output beam, represents the wavefront curvature, Represents the refractive index of air.

[0029] In an optional embodiment, before the formal optical fiber splicing is carried out, in order to reduce the splicing loss, the preset distance is Make fine adjustments; For preset distance The steps for fine-tuning include: The connecting end of the first optical fiber 1 to be connected is extended from the first end of the hollow connecting tube 3 into the hollow of the hollow connecting tube 3, and the distance between the connecting end of the first optical fiber 1 to be connected and the first end of the hollow connecting tube 3 is a preset distance. ; The connecting end of the second optical fiber 2 to be connected is extended from the second end of the hollow connecting tube 3 of the first optical fiber-hollow connecting tube structure into the hollow of the hollow connecting tube 3, and the distance between the connecting end of the first optical fiber 1 to be connected and the connecting end of the second optical fiber 2 to be connected is a preset distance. ; Measure at preset distance and preset distance If the coupling loss is less than or equal to the preset loss threshold, the preset distance and preset distance Carry out formal fiber optic splicing; Otherwise, fine-tune the preset distance The value of the coupling loss is less than or equal to the preset loss threshold. When the formal connection is made, the preset distance is used. and the preset distance after fine-tuning Carry out formal fiber optic splicing.

[0030] It can be understood that the splicing method based on the optical fiber splicing structure of this embodiment is implemented based on the structure of Example 1. The optional items in the above-mentioned Example 1 are also applicable to this embodiment, so they will not be repeated here.

[0031] Example 3 This embodiment provides a specific implementation example based on the optical fiber splicing structure of embodiment 1 and the splicing method based on the optical fiber splicing structure proposed in embodiment 2.

[0032] Figure 2 This is a schematic diagram of the second structure of the optical fiber splicing structure proposed in this embodiment; Figure 3 This is a schematic diagram of the structure of the single-mode spliced optical fiber proposed in this embodiment. Figure 4 This is a schematic structural diagram of the hollow connecting pipe proposed in this embodiment. Figure 5 This is a schematic diagram of the relationship between the connection loss between the single-mode fiber and the hollow-core fiber and the air cavity length under different gradient-index fiber lengths proposed in this embodiment. Figure 2 The numbers in the figure correspond to the following meanings: 1-first optical fiber to be connected, 11-single-mode optical fiber cladding, 12-single-mode optical fiber core; 2-second optical fiber to be connected, 21-second optical fiber cladding, 22-second optical fiber core to be connected; 3-hollow connecting tube, 31-outer ring of hollow connecting tube, 32-inner ring of hollow connecting tube; 4-graded-index optical fiber, 41-graded-index optical fiber cladding, 42-graded-index optical fiber core.

[0033] like Figures 1 to 5 As shown, in a specific implementation, preferably, the second optical fiber to be spliced is a hollow-core optical fiber. Light is transmitted within the air core. The second optical fiber to be spliced includes a second optical fiber cladding and a second optical fiber core. The diameter of the second optical fiber cladding ranges from 125 to 300 microns, and the diameter of the second optical fiber core ranges from 20 to 90 microns.

[0034] Preferably, the bridge optical fiber is a graded-index optical fiber, and the length of the graded-index optical fiber is , because it has self-focusing function, it meets the mode field matching condition.

[0035] Preferably, the single-mode optical fiber includes a single-mode optical fiber cladding and a single-mode optical fiber core, the diameter of the single-mode optical fiber cladding ranges from 60 to 300 microns, and the diameter of the single-mode optical fiber core ranges from 5 to 40 microns.

[0036] Preferably, the graded-index optical fiber comprises a graded-index optical fiber cladding and a graded-index optical fiber core; the diameter of the graded-index optical fiber cladding ranges from 125 to 330 microns, and the diameter of the graded-index optical fiber core ranges from 50 to 300 microns.

[0037] Preferably, the end where the graded-index optical fiber is located is the end coated with an anti-reflection coating.

[0038] Preferably, the hollow connecting tube is a hollow glass capillary tube, which is divided into a first end and a second end in relative positions, and is divided into an outer layer and an inner layer.

[0039] The outer diameter of the first end of the hollow connecting tube is in the range of 200-450 microns, and the inner diameter is in the range of 128-335 microns; the outer diameter of the second end of the hollow connecting tube is in the range of 200-430 microns, and the inner diameter is in the range of 128-305 microns.

[0040] Preferably, the hollow connecting tube can be formed by tapering. After cutting the tapered area of the hollow quartz tube, a hollow quartz tube connection structure with an inner diameter close to the cladding diameter of the optical fiber to be melted can be obtained. This structure can be adjusted to different optical fiber sizes to be melted, providing wide compatibility.

[0041] When the cladding diameters of the first optical fiber to be connected and the second optical fiber to be connected are similar, they can be directly connected using a hollow quartz tube with an inner diameter slightly larger than the cladding diameter by 3-5 microns.

[0042] Preferably, the offset distance between the anti-reflection coating and the fusion hot zone is adjusted so that the anti-reflection coating coupling end of the first optical fiber 1 to be connected is away from the fusion hot zone. The preferred range is 500 to 1200 microns.

[0043] Preferably, to achieve the best coupling effect, it is necessary to determine whether to use air gap If the light is of length If the mode field diameter of the second fiber to be connected is reached after the output of the graded refractive index fiber, there is no need to quote the air gap. Equal to 0; if the light is If the mode field diameter of the second fiber to be connected is not reached after the output of the graded refractive index fiber, an air gap is required. The purpose is to realize that the light output from the first optical fiber to be connected passes through a length of The graded-index fiber with a length of After being transmitted through air, the mode field diameter of the optical beam matches the mode field diameter of the second optical fiber to be connected.

[0044] Wherein, the air gap is the distance between the second end face of the graded-index optical fiber and the first end face of the second optical fiber to be connected.

[0045] The present invention provides a specific implementation example of a method for splicing a hollow-core optical fiber and a solid-core optical fiber. The first optical fiber to be spliced is a single-mode optical fiber fused with a graded-index optical fiber as an example, including the following steps: Step 1: Splice the single-mode fiber and the graded-index fiber together, and cut the graded-index fiber to the desired length. , and plate an anti-reflection coating on the end face of the graded refractive index optical fiber, and finally form a first optical fiber structure to be connected; The length of the graded-index fiber depends on the mode field diameter of the first fiber to be connected and the second fiber to be connected. In order to achieve mode field matching coupling, the present invention needs to determine the length of the graded-index fiber. , the air gap distance between the graded refractive index fiber and the second fiber to be connected The purpose is to realize that the light output from the first optical fiber to be connected passes through a length of The graded-index fiber with a length of After being transmitted through air, the mode field diameter of the optical beam matches the mode field diameter of the second optical fiber to be connected.

[0046] In order to achieve matching of mode field diameter, it is necessary to perform theoretical analysis and calculation of graded-index optical fiber. The following is the length of graded-index optical fiber: The air spacing distance between the graded refractive index fiber and the second fiber to be connected Related formulas.

[0047] The propagation state of light when it is emitted from a single-mode fiber and coupled into a hollow-core fiber can be divided into two parts: one is propagation in a graded-index fiber; the other is propagation from a length of After the output from the graded refractive index fiber end face, the propagates in the air cavity.

[0048]

[0049] First, when propagating in a graded-index fiber, the expression for its mode field radius is:

[0050] in is the mode field radius of the single-mode fiber of the input graded-index fiber, is the propagation distance, is the maximum refractive index value of the graded-index fiber core, is the mode propagation constant, and its expression is

[0051] in, is the refractive index difference, is the radius of the graded-index fiber.

[0052] is the Rayleigh length of the incident light beam in the graded-index fiber, which is expressed as

[0053] when in When the output beam is in the convergent state, the mode field radius at the end of the graded-index fiber is After entering the air cavity, the convergent beam will experience free space propagation. Considering that the beam is in a convergent state at this time, the beam wavefront curvature parameter is introduced. , whose expression is

[0054] The output from the graded-index fiber is considered as a mode field with a radius of , the wavefront curvature is A Gaussian beam enters the air cavity, and any point in the air The expression of the mode field radius (relative to the output end of the graded-index fiber) is: (1) in, is the equivalent waist position, and its expression is

[0055] is the equivalent beam waist radius, and its expression is

[0056] Substituting the mode field diameter of the target hollow-core fiber into the above formula (1), the length of the air cavity can be obtained: , thus obtaining a low-loss connection between single-mode fiber and hollow-core fiber.

[0057] Step 2: by adjusting the driving motor of the fusion splicer, insert the first optical fiber to be spliced into the first end of the hollow connecting tube, and move the anti-reflection coating coupling end of the first optical fiber to be spliced away from the fusion hot zone. , then heating the first end of the hollow connecting tube over a long distance to form a first optical fiber to be connected-hollow connecting tube structure; Among them, the long-distance heating is that during the heating process of the fusion splicer, the anti-reflection coating coupling end of the first optical fiber to be connected always maintains the same distance from the first end of the hollow connecting tube, and the relative position does not change. Then, while the fusion splicer is heating, the left and right drive motors synchronously and uniformly move toward the first optical fiber to be connected, so that the heating range of the hollow connecting tube 3 by the fusion splicer is further expanded. The ordinary fusion splicing method is to melt the end face of the optical fiber and slightly advance the optical fiber in the molten state to achieve the optical fiber fusion splicing operation. However, the first optical fiber to be connected and the second optical fiber to be connected are not connected by melting the end face of the optical fiber, but are connected by the heat shrinkage effect of the hollow connecting tube. Compared with the single-point heating method, the long-distance heating method has high heating uniformity, achieves uniform heat distribution on the hollow connecting tube, has greater connection strength, and provides strength guarantee for the connection structure of the first optical fiber to be connected and the second optical fiber to be connected.

[0058] Step 3: cutting the hollow connecting tube in the first optical fiber to be connected-hollow connecting tube structure obtained in step 2.

[0059] As an example, the first end of the hollow connector tube is cut during cleaving. Because the physical dimensions of the first and second connecting optical fibers are different, the hollow glass tube is tapered to adjust its dimensions to accommodate the different dimensions of the connecting optical fibers. After the first end is tapered, the first end is cleaved.

[0060] Step 4: insert the second optical fiber to be connected into the first optical fiber-first graded refractive index optical fiber-hollow connecting tube structure processed in step 3, and adjust the driving motor of the fusion splicer so that the distance between the second end face of the first optical fiber to be connected and the first end face of the second optical fiber to be connected is , and finally perform hot melt connection.

[0061] This splicing method is also applicable when the first optical fiber to be spliced is a thermally expanded core single-mode optical fiber or a reverse tapered single-mode optical fiber.

[0062] The first optical fiber to be connected and the first end of the hollow connecting tube are hot-fused, and the second end of the hollow connecting tube and the second optical fiber to be connected are hot-fused. The first optical fiber to be connected and the hollow connecting tube, and the second end of the hollow connecting tube and the second optical fiber to be connected can also be connected and fixed by gluing.

[0063] Compared with the prior art, the present invention has the following beneficial effects: First, although the angled cutting of the solid-core fiber and the hollow-core fiber can reduce the back-reflection intensity, it will cause damage to the end face of the hollow-core fiber and further increase the coupling loss between the solid-core fiber and the hollow-core fiber. The present invention uses an anti-reflection coating to avoid the coupling loss caused by angled cutting and simplifies the process difficulty. Second, the present invention adjusts the offset distance between the anti-reflection coating and the fusion hot zone to avoid the problem of damage to the anti-reflection coating due to heat, thereby reducing the back-reflection intensity between the hollow-core fiber and the solid-core fiber. Third, the use of a hollow glass capillary as a connecting device can be applicable to hollow-core fibers and solid-core fibers with a variety of cladding sizes, and the structure accepts connection methods such as gluing and hot melting, which has greater flexibility and compatibility. Fourth, the solid-core fiber of the present invention is a single-mode fiber, and can also be a thermally expanded single-mode fiber, a reverse tapered single-mode fiber, or a single-mode fiber fusion bridge fiber. For hollow-core fibers with different core and cladding sizes, a simple solid-core fiber can be selected to achieve mode field adaptation.

[0064] As an example, the first optical fiber 1 to be connected is a single-mode optical fiber fusion spliced to a length of The gradient refractive index fiber 4 has a length greater than or equal to the self-focusing length of the gradient refractive index fiber 4, which can be to In this example, about 280 microns is taken. Then, an anti-reflection coating operation is performed on one end of the graded-index optical fiber 4 to form a complete single-mode optical fiber-graded-index optical fiber structure, such as Figure 3 The end of the graded-refractive-index optical fiber is hot-fused to the first end of the hollow connecting tube 3 .

[0065] As a preferred technical solution, in this embodiment, the first optical fiber 1 to be spliced and the second optical fiber 2 to be spliced are single-mode optical fibers and hollow-core optical fibers, respectively. In this case, the first mode field diameter of the first optical fiber 1 to be spliced is smaller than the second mode field diameter of the second optical fiber 2 to be spliced.

[0066] The single-mode optical fiber includes a single-mode optical fiber cladding 11 and a single-mode optical fiber core 12 . The diameter of the single-mode optical fiber cladding 11 is 250 microns, and the diameter of the single-mode optical fiber core 12 is 8.5 microns.

[0067] The second optical fiber 2 to be connected is a hollow-core optical fiber and includes a second optical fiber cladding 21 and a second optical fiber core 22. The diameter of the second optical fiber cladding 21 is 250 microns, and the diameter of the second optical fiber core 22 is 30 microns.

[0068] The graded-index optical fiber 4 includes a graded-index optical fiber cladding 41 and a graded-index optical fiber core 42 . The diameter of the graded-index optical fiber cladding 41 is in the range of 250 microns, and the diameter of the graded-index optical fiber core 42 is in the range of 50 microns.

[0069] The hollow connecting tube 3 is a hollow glass capillary tube, which is divided into a first end and a second end in relative positions, and is divided into an outer layer 31 and an inner layer 32 .

[0070] The outer diameter 31 of the first end of the hollow connecting tube is in the range of 200 microns, and the inner diameter 32 is in the range of 130 microns; the outer diameter 31 of the second end of the hollow connecting tube is in the range of 400 microns, and the inner diameter 32 is in the range of 260 microns.

[0071] The hollow connecting tube 3 can be made by taper drawing, such as Figure 4 As shown, after cutting the tapered hollow quartz tube, a hollow quartz tube connection structure with an inner diameter close to the cladding diameter of the optical fiber to be melted is obtained. When the cladding diameters of the first and second optical fibers to be spliced are similar, the connection can be made directly using a hollow quartz tube with an inner diameter slightly larger than the fiber cladding diameter by 3-10 microns.

[0072] Preferably, the offset distance between the anti-reflection coating and the fusion hot zone is adjusted so that the anti-reflection coating coupling end of the first optical fiber 1 to be connected is away from the fusion hot zone. The preferred range is 500 to 1200 microns.

[0073] To achieve the best coupling effect, it is necessary to determine whether to use air gap If the light is of length If the mode field diameter of the second fiber to be connected is reached after the output of the graded refractive index fiber, there is no need to quote the air gap. Equal to 0; if the light is If the mode field diameter of the second fiber to be connected is not reached after the output of the graded refractive index fiber, an air gap is required. The purpose is to realize that the light output from the first optical fiber to be connected passes through a length of The graded-index fiber with a length of After the air transmission, the mode field diameter of the light beam matches the mode field diameter of the second optical fiber to be connected. is the distance between the second end face of the graded-index optical fiber and the first end face of the second optical fiber to be connected.

[0074] The present invention provides a method for splicing a hollow-core fiber and a solid-core fiber, which is applicable to any of the above-mentioned hollow-core fiber and solid-core fiber splicing structures. The first optical fiber 1 to be spliced is a single-mode optical fiber fused with a graded-index optical fiber 4 as an example, and includes the following steps: Step 1: The single-mode optical fiber and the graded-index optical fiber 4 are fused and fixed, and the graded-index optical fiber 4 is cut to a fixed length by cutting. =280 μm, and an anti-reflection coating is plated on the end face of the graded-index optical fiber 4, finally forming a first optical fiber structure to be connected; Step 2: by adjusting the driving motor of the fusion splicer, insert the first optical fiber to be spliced into the first end of the hollow connecting tube 3, and move the anti-reflection coating coupling end of the first optical fiber to be spliced away from the fusion hot zone. =500 μm to 1200 μm, 600 μm is used in this example. Then, the first end of the hollow connecting tube 3 is heated over a long distance to form a first optical fiber to be connected-hollow connecting tube structure; Among them, the long-distance heating is to achieve heating (fusion power is 400bit to 700bit) while synchronously and uniformly moving the relative positions of the first optical fiber to be connected and the hollow connecting tube 3 during the heating process of the fusion splicer, so that the heating range of the hollow connecting tube 3 by the fusion splicer is further expanded.

[0075] Step 3: Cut the hollow connecting tube in the first optical fiber-hollow connecting tube structure obtained in step 2. Step 4: insert the second optical fiber 2 to be connected into the first optical fiber-first graded refractive index optical fiber-hollow connecting tube structure processed in step 3, and adjust the driving motor of the fusion splicer so that the distance between the second end face of the first optical fiber 1 to be connected and the first end face of the second optical fiber 2 to be connected is = 100 microns to 200 microns, and finally hot melt connection (fusion power is 400bit to 700bit).

[0076] In this embodiment, the heat melting and welding methods are achieved by a welding machine, and the heat source of the welding machine is arc discharge or carbon dioxide laser.

[0077] Previously, without the aforementioned hollow-core fiber and solid-core fiber connection structure and method, the single-point connection loss between hollow-core fiber and single-mode fiber was as high as 3.2dB, and the backreflection intensity was approximately -17dB. However, with the aforementioned hollow-core fiber and solid-core fiber connection structure and method, the single-point connection loss between hollow-core fiber and single-mode fiber can be reduced to 0.5dB, and the backreflection intensity is approximately -45dB. This method not only improves the coupling efficiency between hollow-core fiber and single-mode fiber, but also reduces the backreflection intensity caused by the refractive index difference between the hollow-core fiber and solid-core fiber, thereby improving the transmission efficiency of the system.

[0078] This splicing method is also applicable when the first optical fiber to be spliced is a thermally expanded core single-mode optical fiber or a reverse tapered single-mode optical fiber.

[0079] In a preferred embodiment of the present application, the graded-index optical fiber 4 is a graded-index optical fiber or a combination of multiple graded-index optical fibers, wherein the combination of multiple graded-index optical fibers refers to a front-to-back combination of multiple graded-index optical fibers.

[0080] The present invention utilizes the periodic adjustment characteristics of the mode field diameter of the graded-index optical fiber 4 and accurately controls the length of the air core in the graded-index optical fiber 4 and the hollow connecting tube 3 in the connection area, so that the light beam emitted from the first optical fiber to be connected passes through the graded-index optical fiber 4 and a specific length of air medium. After transmission, its mode field diameter can achieve mode field matching coupling with the second optical fiber 2 to be connected, thereby significantly reducing the loss and back reflection at the connection between the single-mode optical fiber and the hollow-core optical fiber.

[0081] As an example, the tools needed to make the optical fiber connection structure include an optical fiber fusion splicer and an optical fiber cutter; the optical fiber fusion splicer is used to perform optical fiber fusion splicing; and the optical fiber cutter is used to cut the optical fiber end face, the fixed-length gradient refractive index optical fiber 4, and the hollow connecting tube 3.

[0082] like Figure 4 As shown, the hollow connecting tube 3 is a hollow quartz tube, which can be obtained by taper-drawing. Figure 4 As shown in the structural diagram, after cutting the cone area of the hollow quartz tube after taper drawing, a hollow quartz tube connection structure with an inner ring diameter close to the diameter of the optical fiber cladding to be melted can be obtained.

[0083] like Figure 3 As shown, the first optical fiber to be connected is a single-mode optical fiber, the second optical fiber 2 to be connected is a hollow-core optical fiber, the cladding diameter of the first optical fiber to be connected is 125 microns, and the core diameter of the first optical fiber to be connected is 8.5 microns; the cladding diameter 21 of the second optical fiber to be connected is 250 microns, and the core diameter 22 of the second optical fiber to be connected is 30 microns; the cladding diameter 41 of the graded refractive index optical fiber is 125 microns, and the core diameter 42 is 50 microns; the inner diameter 32 of the first end of the hollow connecting tube is 130 microns, and the outer diameter 31 is 200 microns, and the inner diameter 32 of the second end is 260 microns, and the outer diameter 31 is 400 microns; The first optical fiber 1 to be connected and the graded-index optical fiber 4 are cut with a cleaver respectively, and then fused together by a fusion splicer. Then, the graded-index optical fiber is cut to a fixed length by a cleaver cutting method or a grinding method, so that its length is The self-focusing period of the graded-index fiber is 1120 microns, so the length of the graded-index fiber cut in this example is approximately 280-300 microns. The single-mode fiber-graded-index fiber is then anti-reflection coated to form a single-mode fiber-graded-index fiber structure.

[0084] The anti-reflection coating mentioned in the patent is composed of two or more materials with different refractive indices, such as magnesium fluoride and titanium dioxide, deposited alternately. By depositing one or more layers of thin films on the end face of the optical fiber, surface reflection is reduced and transmittance is maximized.

[0085] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. An optical fiber splicing structure, characterized in that: include: A first optical fiber to be spliced (1), a second optical fiber to be spliced (2), and a hollow connecting tube (3); The connecting end of the first optical fiber (1) to be connected extends from the first end of the hollow connecting tube (3) into the hollow of the hollow connecting tube (3), and the connecting end of the second optical fiber (2) to be connected extends from the second end of the hollow connecting tube (3) into the hollow of the hollow connecting tube (3); Wherein, if the light beam outputted from the connecting end of the first optical fiber to be connected (1) matches the mode field of the connecting end of the second optical fiber to be connected (2), the connecting end of the first optical fiber to be connected (1) and the connecting end of the second optical fiber to be connected (2) touch each other; otherwise, a distance equal to a preset distance exists between the connecting end of the first optical fiber to be connected (1) and the connecting end of the second optical fiber to be connected (2). The air gap of the first optical fiber to be connected has a spot size of 100 nm. After the air gap, it matches the mode field of the second optical fiber to be connected.

2. The optical fiber splicing structure according to claim 1, characterized in that: The hollow connecting tube (3) is a hollow glass capillary tube, the minimum inner diameter of the hollow region of the first end of the hollow connecting tube (3) is greater than the cladding diameter of the first optical fiber (1) to be connected, and the difference between the minimum inner diameter and the cladding diameter of the first optical fiber (1) to be connected does not exceed a first preset value; The minimum inner diameter of the hollow area at the second end of the hollow connecting tube (3) is greater than the cladding diameter of the second optical fiber (2) to be connected, and the difference between the minimum inner diameter and the cladding diameter of the second optical fiber (2) to be connected does not exceed a second preset value.

3. The optical fiber splicing structure according to claim 1, characterized in that: One end of the first optical fiber to be connected (1) extending into the hollow connecting tube (3) is beveled or coated with an anti-reflection coating, or is beveled with an anti-reflection coating.

4. The optical fiber splicing structure according to any one of claims 1 to 3, characterized in that: The first optical fiber to be connected (1) is a single-mode optical fiber or a single-mode connecting optical fiber. The single-mode connecting optical fiber is formed by connecting a single-mode optical fiber and a bridge optical fiber (4). The end of the bridge optical fiber (4) not connected to the single-mode optical fiber extends into the hollow part of the hollow connecting tube (3).

5. The optical fiber splicing structure according to claim 4, characterized in that: The bridge optical fiber (4) is a graded refractive index optical fiber, and the length of the bridge optical fiber is , ,in, represents a non-negative integer, represents the multiplication operation, Represents the self-focusing period length of the graded-index fiber.

6. A splicing method based on an optical fiber splicing structure, characterized in that: The following steps are involved: The connecting end of the first optical fiber (1) to be connected is extended from the first end of the hollow connecting tube (3) into the hollow of the hollow connecting tube (3), and the distance between the connecting end of the first optical fiber (1) to be connected and the first end of the hollow connecting tube (3) is a preset distance. Then, the first optical fiber to be connected (1) is connected to the hollow connecting tube (3) to obtain a first optical fiber to be connected-hollow connecting tube structure; The connecting end of the second optical fiber to be connected (2) is extended from the second end of the hollow connecting tube (3) of the first optical fiber to be connected-hollow connecting tube structure into the hollow of the hollow connecting tube (3), and the distance between the connecting end of the first optical fiber to be connected (1) and the connecting end of the second optical fiber to be connected (2) is a preset distance. Then, the second optical fiber to be connected (2) is connected to the hollow connecting tube (3) to obtain a first optical fiber to be connected-hollow connecting tube-second optical fiber to be connected structure.

7. The optical fiber splicing method according to claim 6, wherein: The method for connecting the first optical fiber to be connected (1) to the hollow connecting tube (3), and the method for connecting the second optical fiber to be connected (2) to the hollow connecting tube (3) include a gluing method or a hot-melt method; When using the gluing method, the gap between the connecting end of the first optical fiber to be connected (1) and the first end of the hollow connecting tube (3) is filled with glue, and the gap between the connecting end of the second optical fiber to be connected (2) and the second end of the hollow connecting tube (3) is filled with glue; When using the hot melt method, a long-distance heating hot melt method is used; When the first optical fiber to be connected (1) is connected to the hollow connecting tube (3), the long-distance heating hot-melt method is to maintain a preset distance Under the condition that the heat source remains unchanged, while heating the first end of the hollow connecting tube (3) by using the fusion splicer, the driving motor of the fusion splicer is adjusted so that the heating position is uniformly changed from the first end port position of the hollow connecting tube (3) to the position close to the connecting end of the first optical fiber (1) to be connected, until the heat shrinking operation is completed, and then the heating is stopped and the change of the heating position is stopped; When the second optical fiber (2) to be connected is connected to the hollow connecting tube (3), the long-distance heating hot melting method is to maintain a preset distance Under the condition that the temperature remains unchanged, the second end of the hollow connecting tube (3) is heated by the fusion splicer while the driving motor of the fusion splicer is adjusted so that the heating position is uniformly changed from the first end port position of the hollow connecting tube (3) to the position close to the connecting end of the second optical fiber (2) to be connected until the heat shrinking operation is completed, and then the heating is stopped and the change of the heating position is stopped.

8. The optical fiber splicing method according to claim 6, wherein: The first optical fiber to be connected (1) is a single-mode optical fiber; The preset distance The value is based on simulation method or obtained by calculation, and the preset distance is calculated. The steps for finding the value include: If the second optical fiber (2) to be connected is a solid core optical fiber, the preset distance The value of is set to 0; If the second optical fiber (2) to be connected is a hollow core optical fiber, the light beam output by the first optical fiber (1) to be connected is recorded as the first output light beam, and the spot size of the first output light beam after propagation through the air is calculated. ,in, Indicates the distance the first output beam travels in the air, and sets the preset distance Set the value of Matching the mode field of the second optical fiber (2) to be connected The value of The spot size The expressions include: Where, represents the waist radius of the light beam output by the first optical fiber (1) to be connected during the propagation in the air; It represents the Rayleigh length of the first output beam during its propagation in the air.

9. The optical fiber splicing method according to claim 6, wherein: The first optical fiber to be connected (1) is a single-mode connecting optical fiber, which is formed by connecting a single-mode optical fiber and a bridge optical fiber (4), and the bridge optical fiber (4) has a length equal to a preset length. Graded refractive index optical fiber; the preset distance The value is based on the preset length The value is designed, and the preset distance is designed to optimize the connection effect. With preset length The difference between The second optical fiber to be connected (2) is a hollow core optical fiber; The preset length and preset distance The value is based on simulation or calculation, and the preset length is calculated. and preset distance The steps for finding the value include: Calculate the spot size of the beam output from the bridge fiber (4) ,in, represents the length of the bridge fiber (4); If In the range of Matching the mode field of the second optical fiber (2) to be connected , then set the value to the preset length , and the preset distance The value of is set to 0; Otherwise, in Within the range, calculate the spot size The difference in mode field radius between the first optical fiber (2) to be connected and the second optical fiber (2) to be connected is less than or equal to a preset threshold, and Greater than the mode field radius of the second optical fiber (2) to be connected Set the value to the preset length ; and calculate the spot size when the first output light beam is transmitted to the second optical fiber (2) to be connected Propagation distance matching the mode field of the second optical fiber (2) to be connected Set the value to the preset distance The value of The spot size The expressions include: Where, represents the mode field radius of the single-mode fiber that inputs the light beam into the graded-index fiber, Indicates the maximum refractive index value of the graded-index fiber core, represents the mode propagation constant, It represents the Rayleigh length of the incident light beam in the graded-index fiber; represents the refractive index difference of the graded-index fiber, represents the radius of the graded-index fiber; The spot size The expressions include: ， ， Where, represents the equivalent beam waist radius, represents the equivalent waist position, represents the wavelength of the first output beam, represents the wavefront curvature, Represents the refractive index of air.

10. The optical fiber splicing method based on the optical fiber splicing structure according to any one of claims 6 to 9, characterized in that: Before the formal fiber optic splicing, in order to reduce the splicing loss, the preset distance Make fine adjustments; For preset distance The steps for fine-tuning include: The connecting end of the first optical fiber (1) to be connected is extended from the first end of the hollow connecting tube (3) into the hollow of the hollow connecting tube (3), and the distance between the connecting end of the first optical fiber (1) to be connected and the first end of the hollow connecting tube (3) is set to a preset distance. ; The connecting end of the second optical fiber to be connected (2) is extended from the second end of the hollow connecting tube (3) of the first optical fiber to be connected-hollow connecting tube structure into the hollow of the hollow connecting tube (3), and the distance between the connecting end of the first optical fiber to be connected (1) and the connecting end of the second optical fiber to be connected (2) is set to a preset distance. ; Measure at preset distance and preset distance If the coupling loss is less than or equal to the preset loss threshold, the preset distance and preset distance Carry out formal fiber optic splicing; Otherwise, fine-tune the preset distance The value of the coupling loss is less than or equal to the preset loss threshold. When the formal connection is made, the preset distance is used. and the preset distance after fine-tuning Carry out formal fiber optic splicing.

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