Method and structure for connecting single-mode optical fiber and anti-resonance hollow-core optical fiber

Abstract

The invention relates to the technical field of optical communication, in particular to a connection method and structure of a single-mode optical fiber and an anti-resonance hollow-core optical fiber. The beam expanding waveguide is arranged on the end face of the single-mode optical fiber, the size of the beam expanding waveguide is accurately designed, the size of the fundamental mode field of the single-mode optical fiber is amplified to be accurately matched with the fundamental mode field of the anti-resonance hollow-core optical fiber, bidirectional low-loss coupling of the single-mode optical fiber and the anti-resonance hollow-core optical fiber is achieved, the theoretical bidirectional coupling efficiency exceeds 97.4%, and the coupling efficiency of the single-mode optical fiber and the anti-resonance hollow-core optical fiber is greatly improved. The insertion loss is lower than 0.114 dB, and is obviously superior to the loss of a traditional direct welding or splicing gradient refractive index multimode fiber scheme; and on the other hand, the single-mode optical fiber and the anti-resonance hollow-core optical fiber can be fixed without discharge welding, so that the problem of collapse of a nested tube structure in the anti-resonance hollow-core optical fiber caused by traditional discharge welding is avoided, and the integrity of the anti-resonance hollow-core optical fiber is protected.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical communication technology, in particular to a splicing method and structure of a single-mode optical fiber and a reverse resonance hollow-core optical fiber. BACKGROUND

[0002] Optical fiber is an important basic hardware material in the current information society, and its parameter index directly determines the performance of various optical systems based on optical fiber. Traditional solid-core optical fiber relies on the refractive index difference of the material to confine the light wave in the core for transmission, while reverse resonance hollow-core optical fiber confines the light wave in the air core for transmission through the reverse resonance effect, so it can achieve extremely low dispersion, nonlinearity and high damage threshold, and has been widely concerned and researched in the field of optical fiber communication and optical fiber laser in recent years.

[0003] Since the single-mode optical fiber still dominates in the existing optical fiber system, in order to realize the large-scale application of the reverse resonance hollow-core optical fiber, the low-loss splicing problem between the single-mode optical fiber and the reverse resonance hollow-core optical fiber needs to be solved. The existing technology introduces large optical loss after the butt joint of the single-mode optical fiber and the reverse resonance hollow-core optical fiber, which cannot meet the actual demand.

[0004] Therefore, overcoming the defects of the prior art is an urgent problem to be solved in the technical field. SUMMARY

[0005] The technical problem to be solved by the present application is how to reduce the optical loss after the butt joint of the single-mode optical fiber and the reverse resonance hollow-core optical fiber.

[0006] The present application adopts the following technical solutions: In a first aspect, a splicing method of a single-mode optical fiber and a reverse resonance hollow-core optical fiber is provided, comprising: forming an expanded beam waveguide on the end face of the single-mode optical fiber; inserting the expanded beam waveguide into the central air core of the reverse resonance hollow-core optical fiber, and fixing the end face of the single-mode optical fiber and the end face of the reverse resonance hollow-core optical fiber to complete the splicing of the single-mode optical fiber and the reverse resonance hollow-core optical fiber.

[0007] Preferably, the forming of the expanded beam waveguide on the end face of the single-mode optical fiber specifically comprises: putting the end face of the single-mode optical fiber after pretreatment upwards, and dropping photoresist on the end face of the single-mode optical fiber; printing the expanded beam waveguide in the photoresist by laser printing technology.

[0008] Preferably, the printing of the expanded beam waveguide in the photoresist by laser printing technology specifically comprises: fixing the single-mode optical fiber on an optical fiber clamp, and fixing the optical fiber clamp on a displacement platform; Raising the displacement platform until the photoresist contacts the objective lens of the laser light emitting surface; Adjusting the height of the displacement platform so that the focal point of the objective lens is on the end face of the single-mode optical fiber; Emitting a laser signal through the laser and focusing the laser signal through the objective lens, and the photoresist at the focal point of the objective lens is cross-linked after absorbing photons, thereby forming a solid polymer; Controlling the position of the focal point of the objective lens and the height of the displacement platform to form the solid polymer layer by layer to obtain the expanded beam waveguide.

[0009] Preferably, the method further comprises: After obtaining the expanded beam waveguide, cleaning the excess photoresist on the end face of the single-mode optical fiber with a first compound; Cleaning the residual first compound on the end face of the single-mode optical fiber with a second compound.

[0010] Preferably, the method further comprises: Fixing the single-mode optical fiber printed with the expanded beam waveguide and the anti-resonant hollow core optical fiber at both ends of the optical fiber fusion splicer; Using the automatic alignment program in the optical fiber fusion splicer to preliminarily align and approach the single-mode optical fiber and the anti-resonant hollow core optical fiber, and inserting the expanded beam waveguide into the central air core of the anti-resonant hollow core optical fiber through the displacement module in the optical fiber fusion splicer until the end face of the single-mode optical fiber contacts the end face of the anti-resonant hollow core optical fiber.

[0011] Preferably, the method further comprises: Wrapping the connection between the single-mode optical fiber and the anti-resonant hollow core optical fiber with ultraviolet curing glue; Irradiating the ultraviolet curing glue with ultraviolet light to fix the ultraviolet curing glue to fix the end face of the single-mode optical fiber and the end face of the anti-resonant hollow core optical fiber.

[0012] Preferably, the expanded beam waveguide is inverted conical, and the coupling surface between the expanded beam waveguide and the central air core of the anti-resonant hollow core optical fiber is a beveled surface with a preset angle.

[0013] Preferably, the length of the expanded beam waveguide ranges from 120μm to 345μm.

[0014] Preferably, the method further comprises: After the single-mode optical fiber and the anti-resonant hollow-core optical fiber are spliced, the base mode field distribution of the single-mode optical fiber and the anti-resonant hollow-core optical fiber is respectively calculated by the finite element method, and the base mode field distribution is taken as the input light field in the respective transmission direction; The evolution of each input light field in the beam expansion waveguide is simulated by the beam propagation method, and the coupling efficiency of the single-mode optical fiber to the anti-resonant hollow-core optical fiber and the coupling efficiency of the anti-resonant hollow-core optical fiber to the single-mode optical fiber are respectively obtained by overlapping integration with the base mode field distribution of the target end optical fiber.

[0015] In a second aspect, a splicing structure of a single-mode optical fiber and an anti-resonant hollow-core optical fiber is provided, and the splicing structure is used to implement the splicing method of the single-mode optical fiber and the anti-resonant hollow-core optical fiber as described in the first aspect.

[0016] Compared with the prior art, the present application has the following beneficial effects: The present application realizes the bidirectional low-loss coupling of the single-mode optical fiber and the anti-resonant hollow-core optical fiber by setting the beam expansion waveguide at the end face of the single-mode optical fiber and accurately designing the size of the beam expansion waveguide to amplify the base mode field size of the single-mode optical fiber to accurately match the base mode field of the anti-resonant hollow-core optical fiber. The theoretical bidirectional coupling efficiency is more than 97.4%, and the insertion loss is less than 0.114 dB, which is significantly better than the loss of the traditional direct fusion or spliced graded-index multimode fiber scheme.

[0017] On the other hand, the single-mode optical fiber and the anti-resonant hollow-core optical fiber can be fixed without discharge fusion, which avoids the collapse of the nested tube structure in the anti-resonant hollow-core optical fiber caused by traditional discharge fusion, and protects the integrity of the anti-resonant hollow-core optical fiber. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0019] Figure 1 is a flowchart of a single-mode optical fiber and an anti-resonant hollow-core optical fiber splicing method provided by an embodiment of the present application; Figure 2 is a flowchart of a single-mode optical fiber and an anti-resonant hollow-core optical fiber splicing method provided by an embodiment of the present application; Figure 3 is a structural schematic diagram of a cross section of an anti-resonant hollow-core optical fiber provided by an embodiment of the present application; Figure 4 is a flowchart of a printing method of a beam expansion waveguide provided by an embodiment of the present application; Figure 5 is a specific flow structure schematic diagram of a printing method of an expansion beam waveguide provided by an embodiment of the present application; Figure 6 is a size schematic diagram of an expansion beam waveguide provided by an embodiment of the present application; Figure 7 is a relationship schematic diagram of a lower bottom surface circle radius and transmissivity of an expansion beam waveguide provided by an embodiment of the present application; Figure 8 is a relationship schematic diagram of an upper end surface circle radius and length and light energy of an expansion beam waveguide provided by an embodiment of the present application; Figure 9 is a structure schematic diagram of an expansion beam waveguide provided by an embodiment of the present application; Figure 10 is a relationship schematic diagram of a length of an expansion beam waveguide in a single mode fiber to anti-resonant hollow core fiber direction and coupling efficiency provided by an embodiment of the present application; Figure 11 is a relationship schematic diagram of a length of an expansion beam waveguide in an anti-resonant hollow core fiber to single mode fiber direction and coupling efficiency provided by an embodiment of the present application. DETAILED DESCRIPTION

[0020] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0021] Unless otherwise required by context, the term "comprises" in the specification and claims is to be construed as open-ended, i.e. as "comprises but not limited to". In the description of the specification, the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example" or "some examples" are intended to mean that the specific feature, structure, material or characteristic associated with that embodiment or example is included in at least one embodiment or example of the present disclosure. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example. In addition, the specific features, structures, materials or characteristics described can be included in any one or more embodiments or examples in any appropriate manner, i.e. although they are carried in the embodiments or examples of the above terms due to the order of appearance and location, they are not limited to being carried by one embodiment or example in a combined manner.

[0022] In the description of the present application, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the embodiments of the present disclosure, unless otherwise stated, the meaning of "a plurality of" is two or more. In addition, for example, in the description, the same type of nouns may also be described as two independent individuals by adding "A", "B" at the end, in which case the features defined with "A", "B" are only used for the purpose of distinguishing the same type of individual description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated.

[0023] In describing some embodiments, "coupled", "coupling" and "connected" and their derivatives may be used. For example, the term "connected" may be used in describing some embodiments to indicate that two or more components have direct physical or electrical contact with each other. For another example, the term "coupling" may be used in describing some embodiments to indicate that two or more components have direct physical or electrical contact. However, the term "connected" or "coupled" can also refer to two or more components that do not have direct contact with each other, but still cooperate or interact with each other, such as "optical coupling", "wireless connection", etc. The embodiments disclosed herein are not necessarily limited to the content of the present application.

[0024] In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as there is no conflict between them.

[0025] Embodiment 1: The splicing loss of single-mode fiber and anti-resonant hollow fiber mainly comes from three aspects: mode field mismatch, microstructure collapse caused by discharge fusion, and Fresnel reflection of fiber-air contact surface.

[0026] In order to solve these problems, in recent years, various splicing schemes have been proposed, including optimizing the discharge power of the fusion machine to reduce the microstructure collapse of the end face of the anti-resonant hollow fiber; tapering the single-mode fiber or fusing a section of graded-index multimode fiber at the end of the single-mode fiber to match the mode field of the anti-resonant hollow fiber. However, these schemes are difficult to simultaneously solve the three problems of introducing splicing loss, and realize low-loss coupling of single-mode fiber→anti-resonant hollow fiber and anti-resonant hollow fiber→single-mode fiber in both directions.

[0027] In order to solve the above problems, the present embodiment proposes a splicing method of single-mode fiber and anti-resonant hollow fiber. In one embodiment, as shown in Figure 1 and Figure 2 The splicing method comprises: Step 101: forming an expansion waveguide on the end face of the single-mode optical fiber.

[0028] The expansion waveguide is used to optimize the output light field of the single-mode optical fiber to match the anti-resonant hollow core optical fiber.

[0029] In one embodiment, the geometric size of the expansion waveguide is optimized by using the beam propagation method under the premise of ensuring that the anti-resonant hollow core optical fiber can be inserted into the central air core. The specific structure of the expansion waveguide and the preparation method will be described below.

[0030] Step 102: inserting the expansion waveguide into the central air core of the anti-resonant hollow core optical fiber, and fixing the end face of the single-mode optical fiber and the end face of the anti-resonant hollow core optical fiber to complete the splicing of the single-mode optical fiber and the anti-resonant hollow core optical fiber.

[0031] In one embodiment, as shown in Figure 3 The cross-sectional view of the anti-resonant hollow core optical fiber with a five-nested tube structure is shown, where each group of nested tubes is independently connected to the inner edge of the cladding, and the cavity formed between the two groups of anti-resonant nested tubes suppresses high-order modes to ensure the transmission of the fundamental mode in the core. L1 is the diameter of the central air core. The anti-resonant hollow core optical fiber used in this embodiment can be an anti-resonant hollow core optical fiber with any number of nested tube layers and tube numbers.

[0032] How to insert the expansion waveguide into the central air core of the anti-resonant hollow core optical fiber and how to fix the end face of the single-mode optical fiber and the end face of the anti-resonant hollow core optical fiber will be described in detail below.

[0033] By setting an expansion waveguide on the end face of the single-mode optical fiber and accurately designing the size of the expansion waveguide, the present application realizes the amplification of the single-mode optical fiber fundamental mode field size to accurately match the anti-resonant hollow core optical fiber fundamental mode field, and realizes the bidirectional low-loss coupling of the single-mode optical fiber and the anti-resonant hollow core optical fiber. The theoretical bidirectional coupling efficiency is more than 97.4%, and the insertion loss is less than 0.114dB, which is significantly better than the loss of the traditional direct fusion or splicing graded-index multimode fiber scheme.

[0034] On the other hand, the single-mode optical fiber and the anti-resonant hollow core optical fiber can be fixed without discharge fusion, which avoids the collapse of the nested tube structure in the anti-resonant hollow core optical fiber caused by traditional discharge fusion, and protects the integrity of the anti-resonant hollow core optical fiber.

[0035] Next, the preparation method of the expansion waveguide will be described in detail. In one embodiment, as shown in Figure 4 The expansion waveguide formed on the end face of the single-mode optical fiber specifically includes: Step 1011: The end face of the pre-processed single-mode optical fiber is upward, and photoresist is dropped on the end face of the single-mode optical fiber.

[0036] First, the end face of the single-mode optical fiber needs to be pre-processed. The specific process of pre-processing includes: ensuring that the end face of the single-mode optical fiber is flat, the end face of the single-mode optical fiber can be cut flat using a fiber cutting knife, and ensuring that the end face is clean and undamaged. Then, the pre-processed single-mode optical fiber is fixed in the fiber clamp, ensuring that the end face is upward.

[0037] Then, photoresist (which can be negative photoresist) is dropped on the end face of the single-mode optical fiber, ensuring that the end face of the single-mode optical fiber is completely immersed in photoresist.

[0038] Step 1012: The expanded beam waveguide is printed in the photoresist by laser printing technology.

[0039] In one embodiment, the step 102 specifically includes: The single-mode optical fiber is fixed on the fiber clamp, and the fiber clamp is fixed on the displacement platform; the displacement platform is raised until the photoresist contacts the objective lens of the laser light emitting surface; by adjusting the height of the displacement platform, the focal point of the objective lens is located on the end face of the single-mode optical fiber; the laser signal is emitted by the laser, and the laser signal is focused by the objective lens, the photoresist at the focal point of the objective lens is cross-linked after absorbing photons, thereby forming a solid polymer; by controlling the position of the focal point of the objective lens and the height of the displacement platform, the solid polymer is formed layer by layer to obtain the expanded beam waveguide.

[0040] The laser can be a femtosecond laser, the wavelength can be set to 515 nm, the repetition frequency can be set to 80 MHz, and the 100 times objective lens and high-precision displacement platform can be used to complete the printing of the expanded beam waveguide.

[0041] In one embodiment, as Figure 5As shown, first, the end face of the single-mode fiber is ensured to be flat, and the single-mode fiber is fixed with the end face facing upward using a fiber clamp. Then a small amount of negative photoresist is added to the end face of the single-mode fiber to ensure that the end face of the fiber is completely immersed. Subsequently, the fiber clamp is fixed on a high-precision displacement platform, the end face of the fiber is aligned with a 100x oil immersion objective lens (i.e., an objective lens), and the displacement platform is slowly raised until the objective lens is in contact with the photoresist. By means of the surface tension of the liquid, the photoresist rapidly fills the space between the objective lens and the end face of the single-mode fiber. The height of the displacement platform is continuously adjusted to ensure that the focal point of the objective lens is located at the end face of the single-mode fiber. The femtosecond laser used emits femtosecond laser light (i.e., a laser signal) with a wavelength of 515 nm and a repetition frequency of 80 MHz. After focusing through the 100x objective lens, the negative photoresist at the focal point will undergo a multi-photon absorption effect and cross-link to form a solid-state polymer, while the negative photoresist at other positions remains liquid. Therefore, by precisely controlling the position of the focal point and the height of the high-precision displacement platform, layer-by-layer printing of the solid-state polymer can be achieved to obtain the final expanded waveguide.

[0042] In one embodiment, the method for splicing a single-mode fiber and an anti-resonant hollow fiber further comprises: after obtaining the expanded waveguide, cleaning the excess photoresist on the end face of the single-mode fiber by a first compound; and cleaning the residual first compound on the end face of the single-mode fiber by a second compound.

[0043] In one embodiment, the first compound can be used to clean the photoresist, and the second compound can be used to clean the first compound. In one embodiment, the first compound can be propylene glycol methyl ether acetate, and the second compound can be isopropyl alcohol.

[0044] In one embodiment, the excess photoresist on the end face of the single-mode fiber is first cleaned using propylene glycol methyl ether acetate, and then the residual propylene glycol methyl ether acetate is cleaned using isopropyl alcohol, thereby obtaining the printed expanded waveguide. Since the fundamental mode field diameter of the single-mode fiber used in this embodiment is about 9.8 μm, and the fundamental mode field diameter of the anti-resonant hollow fiber used is about 19 μm, the printing of the inverted taper expanded waveguide on the end face of the single-mode fiber in this embodiment expands the mode field to match the mode field of the anti-resonant hollow fiber. The inverted taper expanded waveguide has a circular cross-section, and the lower base circle radius, the upper end face circle radius, and the total length of the waveguide all directly affect the degree of mode field matching and the insertion loss. Therefore, under the premise of being able to be inserted into the central air core of the anti-resonant hollow fiber, the beam propagation method is used to optimize the geometric dimensions of the expanded waveguide.

[0045] In one embodiment, the beam expansion waveguide can be in an inverted tapered shape. Based on the parameters of the single-mode fiber and the antiresonant hollow-core fiber used, the geometric parameters of the inverted tapered beam expansion waveguide were designed and optimized to reduce coupling loss. Ultimately, the beam expansion waveguide's bottom circular diameter was designed to be 16 μm, its top circular diameter was 28 μm, and its total length was set to 345 μm.

[0046] Next, we will introduce how to obtain the dimensions of the beam expansion waveguide, which include the length, the bottom surface circular diameter, and the top surface circular diameter. Figure 6 As shown, the cross section of the beam expansion waveguide is circular. The three parameters that need to be optimized are the bottom radius Rc1, the top radius Rc2 and the length Lc of the beam expansion waveguide. The bottom radius Rc1 is optimized first. In one embodiment, Figure 7 The figure shows the energy transmittance at the interface when light with energy 1 is incident from the fiber end face to waveguides with different bottom surface circular radii. When the radius is greater than 8, that is, the diameter is greater than 16, the transmittance is already higher than 99.5%, and further increase in size will not significantly improve it. Therefore, the bottom surface circular diameter of the beam expanding waveguide is set to 16. Then, under the premise of the bottom surface circular diameter of 16, the energy of light with energy 1 after passing through beam expanding waveguides with different upper end surface circular diameters and different lengths is calculated. In one embodiment, as shown in FIG. Figure 8 As shown, the maximum value occurs at an upper end diameter of 28 μm and a total length of 345 μm. Therefore, the optimal parameters for the beam expansion waveguide are a lower base diameter of 16 μm, an upper end diameter of 28 μm, and a total length of 345 μm. These dimensions are smaller than the air hole in the center of the antiresonant hollow-core fiber, allowing insertion.

[0047] Next, we will introduce how to insert the beam expanding waveguide into the central air core of the hollow-core optical fiber. In one embodiment, the inserting of the beam expanding waveguide into the central air core of the antiresonant hollow-core optical fiber specifically includes: fixing the single-mode optical fiber printed with the beam expanding waveguide and the antiresonant hollow-core optical fiber at both ends of the optical fiber fusion splicer respectively; using the automatic alignment program in the optical fiber fusion splicer to preliminarily align and approach the single-mode optical fiber and the antiresonant hollow-core optical fiber, and inserting the beam expanding waveguide into the central air core of the antiresonant hollow-core optical fiber through the displacement module in the optical fiber fusion splicer until the end face of the single-mode optical fiber contacts the end face of the antiresonant hollow-core optical fiber.

[0048] A single-mode optical fiber (with a beam expansion waveguide laser-processed on its end face) is fixed to a fixture at one end of the fiber fusion splicer. An antiresonant hollow-core optical fiber is fixed to a fixture at the other end of the fiber fusion splicer.

[0049] Start the auto-alignment program built-in the fiber fusion splicer. The auto-alignment program automatically drives the displacement mechanism on both sides of the fiber fusion splicer through the camera and image processing system inside the fiber fusion splicer to adjust the position of the two optical fibers (single-mode fiber and anti-resonant hollow core fiber) in the horizontal direction (X-axis and Y-axis) and the rotational direction (Z-axis). The center axis of the single-mode fiber and the center axis of the anti-resonant hollow core fiber are aligned as accurately as possible, and the expanded beam waveguide is ensured to be directly opposite the central air core opening of the anti-resonant hollow core fiber.

[0050] After the initial alignment is completed, the auto-alignment program controls the clamps on both sides of the fiber fusion splicer to slowly drive the two optical fibers to move closer to each other in the axial direction (Z-axis). When the end faces of the two optical fibers are close enough (usually in the range of several microns to tens of microns), the operator or the program enables the displacement module of the fiber fusion splicer (usually a precise Z-axis moving mechanism that controls the clamp on the single-mode fiber side or the anti-resonant hollow core fiber side). By fine control of the displacement module, the single-mode fiber is slowly and accurately pushed to continue moving in the axial direction (Z-axis) towards the anti-resonant hollow core fiber. So that the expanded beam waveguide on the end face of the single-mode fiber is inserted into the central air core of the anti-resonant hollow core fiber.

[0051] This process requires very high positional accuracy (usually in the sub-micron level). The operation is usually monitored in real time under a high-power microscope or the camera of the fiber fusion splicer, to ensure that the expanded beam waveguide accurately enters the central air core without touching the anti-resonant tube wall or other microstructures inside the anti-resonant hollow core fiber. The end of the expanded beam waveguide is located in a position that is beneficial for light field coupling inside the central air core.

[0052] Continue to push the single-mode fiber forward until the end face of the single-mode fiber (i.e. the plane where the expanded beam waveguide root is located) physically contacts the end face of the anti-resonant hollow core fiber. The end faces of the two optical fibers are closely together, ready for the next step of fixing and bonding, to ensure that the relative position does not shift in subsequent operations.

[0053] The specific fixing method will be introduced next. The prior art fixes the single-mode fiber and the anti-resonant hollow core fiber by electric discharge welding, which can cause the microstructure of the anti-resonant hollow core fiber to collapse. In order to solve the above problem, in one embodiment, the fixing of the end face of the single-mode fiber and the end face of the anti-resonant hollow core fiber specifically includes: wrapping the connection between the single-mode fiber and the anti-resonant hollow core fiber with ultraviolet curing glue; and irradiating the ultraviolet curing glue with ultraviolet light to fix the ultraviolet curing glue, thereby fixing the end face of the single-mode fiber and the end face of the anti-resonant hollow core fiber.

[0054] In one embodiment, the ultraviolet curing adhesive is used for curing and packaging without discharge welding, which completely avoids the collapse of the nested tube structure of the anti-resonant hollow core fiber caused by the traditional discharge welding, and protects the integrity of the anti-resonant hollow core fiber. In one embodiment, since the diameter of the single-mode fiber is larger than the diameter of the central air core part of the anti-resonant hollow core fiber, the ultraviolet curing adhesive can be effectively prevented from penetrating into the nested tube or the central air core during the packaging process.

[0055] In order to avoid the increase of coupling loss caused by Fresnel reflection at the air-waveguide contact surface, in one embodiment, as shown in Figure 9 , the coupling surface of the expanded beam waveguide and the central air core of the anti-resonant hollow core fiber is a beveled surface with a preset angle.

[0056] In one embodiment, the coupling surface of the expanded beam waveguide and the central air core of the anti-resonant hollow core fiber is the top surface of the expanded beam waveguide and the contact surface of the central air core of the hollow core fiber. Specifically, the preset angle is in the range of 0°-60°, which can be preset according to actual needs. Through the aforementioned precise laser printing technology, the precise preparation of the inclined end of the expanded beam waveguide can be realized, and by flexibly controlling the preset angle, the strong Fresnel reflection at the air-waveguide interface can be effectively reduced.

[0057] The scheme proposed in this embodiment has high tolerance to waveguide length changes, as shown in Figure 10 and Figure 11 , wherein, as shown in Figure 10 , taking the transmission direction of the single-mode fiber to the anti-resonant hollow core fiber as an example, although the optimal length of the expanded beam waveguide is 345 μm, the coupling efficiency is higher than 97% in the range of 270 μm-345 μm, and the coupling efficiency is higher than 90% in the range of 120 μm-345 μm, which greatly improves the preparation efficiency and repeatability. That is, the length of the expanded beam waveguide can be in the range of 120 μm-345 μm, which means that the length of the expanded beam waveguide can be 120 μm, 345 μm, or any value between 120 μm and 345 μm, all of which can satisfy the coupling efficiency higher than 90%.

[0058] After the single-mode fiber and the anti-resonant hollow core fiber are fixed, a commercial single-mode fiber-anti-resonant hollow core fiber coupling device with a known loss is used, a 1550 nm laser is input, and the input and output optical powers and losses are measured by a power meter. The loss of the coupling device proposed in this embodiment can be obtained by subtracting the loss of the commercial device.

[0059] In order to obtain the coupling efficiency after the single-mode fiber and the anti-resonant hollow core fiber are spliced, in one embodiment, as shown in Figure 10 and Figure 11 , the splicing method of the single-mode fiber and the anti-resonant hollow core fiber further comprises: After the single-mode fiber and the anti-resonant hollow-core fiber are spliced, the base mode field distribution of the single-mode fiber and the base mode field distribution of the anti-resonant hollow-core fiber are calculated respectively by using the finite element method, and the base mode field distribution is taken as the input light field in the transmission direction of each; the evolution of each input light field in the expanding waveguide is simulated by using the beam propagation method, and the base mode field distribution of the target fiber is overlapped and integrated to obtain the coupling efficiency of the single-mode fiber to the anti-resonant hollow-core fiber and the coupling efficiency of the anti-resonant hollow-core fiber to the single-mode fiber respectively.

[0060] Wherein, the base mode field distribution of the single-mode fiber at its working wavelength and the base mode field distribution of the anti-resonant hollow-core fiber at its working wavelength are calculated respectively by using the finite element method.

[0061] In the transmission direction of the single-mode fiber to the anti-resonant hollow-core fiber, the base mode field distribution of the single-mode fiber is set as the input light field of the expanding waveguide close to the single-mode fiber, and the whole process of the input light field propagating and evolving in the expanding waveguide structure towards the anti-resonant hollow-core fiber is simulated by using the beam propagation method to obtain the light field distribution at the output end of the expanding waveguide structure in this direction.

[0062] In the transmission direction of the anti-resonant hollow-core fiber to the single-mode fiber, the base mode field distribution of the anti-resonant hollow-core fiber is set as the input light field of the expanding waveguide close to the anti-resonant hollow-core fiber, and the whole process of the input light field propagating and evolving in the expanding waveguide structure towards the single-mode fiber is simulated by using the beam propagation method to obtain the light field distribution at the output end of the expanding waveguide structure in this direction.

[0063] The overlapping integral value between the light field distribution at the output end of the expanding waveguide and the base mode field distribution of the anti-resonant hollow-core fiber is calculated, and the size of this integral value represents the efficiency of the light coupling from the single-mode fiber to the anti-resonant hollow-core fiber through the expanding waveguide structure.

[0064] The overlapping integral value between the light field distribution at the output end of the expanding waveguide and the base mode field distribution of the single-mode fiber is calculated, and the size of this integral value represents the efficiency of the light coupling from the anti-resonant hollow-core fiber to the single-mode fiber through the expanding waveguide structure. Finally, the light coupling efficiency in the transmission direction of the single-mode fiber to the anti-resonant hollow-core fiber and the light coupling efficiency in the transmission direction of the anti-resonant hollow-core fiber to the single-mode fiber are obtained.

[0065] Embodiment 2: This embodiment proposes an example to further illustrate the splicing method of the single-mode fiber and the anti-resonant hollow-core fiber proposed in embodiment 1. In one embodiment, the splicing method of the single-mode fiber and the anti-resonant hollow-core fiber comprises: 1. Device composition and materials.

[0066] (1) Standard single-mode fiber.

[0067] (2) Anti-resonant hollow core fiber.

[0068] (3) Negative photoresist, used for two-photon polymerization under femtosecond laser induction to form an expanded beam waveguide.

[0069] (4) Ultraviolet curing glue, used for packaging the connection between the single-mode fiber and the anti-resonant hollow core fiber.

[0070] 2. Preparation steps (1) Single-mode fiber end face pretreatment: use a fiber cutter to cut the single-mode fiber end face flat, ensure the end face is clean and undamaged, then fix it in a fiber clamp with the end face facing up.

[0071] (2) Photoresist coating: drop negative photoresist on the single-mode fiber end face, ensuring that the end face of the single-mode fiber is completely immersed in the photoresist.

[0072] (3) Femtosecond laser 3D printing waveguide: use a femtosecond laser (wavelength 515 nm, repetition frequency 80 MHz) with a 100x objective lens and a high-precision displacement platform to complete the expanded beam waveguide printing. The specific printing process is as follows: adjust the displacement platform so that the objective lens focal point is aligned with the end face of the single-mode fiber; print the inverted tapered expanded beam waveguide by layer-by-layer scanning, and optimize the laser power and scanning speed according to the characteristics of the photoresist; after printing is completed, clean the residual photoresist with propylene glycol methyl ether acetate and isopropyl alcohol in turn.

[0073] (4) Expanded beam waveguide insertion and alignment: fix the single-mode fiber printed with the expanded beam waveguide and the anti-resonant hollow core fiber on the two ends of the fiber fusion splicer clamp. Preliminary alignment is performed through the automatic alignment program of the fiber fusion splicer, switch to manual mode, slowly insert the expanded beam waveguide into the central air core of the anti-resonant hollow core fiber until the two end fiber end faces are in contact.

[0074] (5) Ultraviolet curing packaging: apply ultraviolet curing glue at the connection to ensure that the glue does not penetrate the air portion of the anti-resonant hollow core fiber. Then use a UV lamp to irradiate and cure the glue, completing the packaging.

[0075] 3. Key process parameters (1) Laser printing parameters: adjust the structure of the model to be printed (expanded beam waveguide) flexibly according to the characteristics of the photoresist.

[0076] (2) Expanded beam waveguide geometry: determine the optimal size by beam propagation method simulation.

[0077] 4. Verification and testing (1) Coupling efficiency test: couple a commercial single-mode fiber-anti-resonant hollow core fiber coupling device with known loss, input 1550 nm laser, measure the input and output optical power and loss with a power meter, and subtract the loss of the commercial device to obtain the loss of the coupling device proposed in this embodiment.

[0078] (2) Structure characterization: The morphology of the printed extended waveguide was observed by scanning electron microscope, and no cracks or deformation was confirmed.

[0079] Example 3: In this embodiment, a single-mode fiber and an anti-resonant hollow fiber splicing structure is proposed, which is used to realize the single-mode fiber and anti-resonant hollow fiber splicing method as described in embodiment 1.

[0080] For specific steps of the single-mode fiber and anti-resonant hollow fiber splicing method, see embodiment 1, which will not be repeated here.

[0081] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for splicing a single-mode optical fiber and an antiresonant hollow-core optical fiber, characterized in that: include: forming a beam-expanding waveguide on the end face of a single-mode optical fiber; The beam expansion waveguide is inserted into the central air core of the antiresonant hollow core fiber, and the end face of the single-mode fiber and the end face of the antiresonant hollow core fiber are fixed to complete the connection between the single-mode fiber and the antiresonant hollow core fiber.

2. The method for splicing a single-mode optical fiber and an antiresonant hollow-core optical fiber according to claim 1, wherein: The forming of a beam expansion waveguide on the end face of the single-mode optical fiber specifically includes: Place the end face of the pre-treated single-mode optical fiber upwards and drop photoresist on the end face of the single-mode optical fiber; The beam expansion waveguide is printed in the photoresist by laser printing technology.

3. The method for splicing a single-mode optical fiber and an antiresonant hollow-core optical fiber according to claim 2, wherein: Printing the beam expansion waveguide in the photoresist by laser printing technology specifically includes: Fixing the single-mode optical fiber on an optical fiber clamp, and fixing the optical fiber clamp on a displacement platform; Raising the displacement platform until the photoresist contacts the objective lens on the light-emitting surface of the laser; By adjusting the height of the displacement platform, the focus of the objective lens is located on the end face of the single-mode optical fiber; A laser signal is emitted by a laser and focused by the objective lens, and the photoresist at the focus of the objective lens absorbs photons and then cross-links, thereby forming a solid polymer; The solid polymer is formed layer by layer by controlling the position of the focus of the objective lens and the height of the displacement platform to obtain the beam expansion waveguide.

4. The method for splicing a single-mode optical fiber and an antiresonant hollow-core optical fiber according to claim 2, wherein: The method further comprises: After obtaining the beam expansion waveguide, cleaning excess photoresist on the end face of the single-mode optical fiber with a first compound; The residual first compound on the end face of the single-mode optical fiber is cleaned by the second compound.

5. The method for splicing a single-mode optical fiber and an antiresonant hollow-core optical fiber according to claim 1, wherein: Inserting the beam expansion waveguide into the central air core of the antiresonant hollow core optical fiber specifically comprises: Fixing the single-mode optical fiber printed with the beam expansion waveguide and the anti-resonant hollow-core optical fiber at two ends of the optical fiber fusion splicer respectively; The single-mode optical fiber and the antiresonant hollow-core optical fiber are preliminarily aligned and brought close together using an automatic alignment program in the optical fiber fusion splicer, and the beam expansion waveguide is inserted into the central air core of the antiresonant hollow-core optical fiber through a displacement module in the optical fiber fusion splicer until the end face of the single-mode optical fiber contacts the end face of the antiresonant hollow-core optical fiber.

6. The method for splicing a single-mode optical fiber and an antiresonant hollow-core optical fiber according to claim 1, wherein: The step of fixing the end face of the single-mode optical fiber and the end face of the antiresonant hollow-core optical fiber specifically includes: Wrapping the connection between the single-mode optical fiber and the antiresonant hollow-core optical fiber with ultraviolet curing glue; The ultraviolet curing adhesive is irradiated with ultraviolet rays to fix the ultraviolet curing adhesive, thereby fixing the end face of the single-mode optical fiber and the end face of the antiresonant hollow-core optical fiber.

7. The method for splicing a single-mode optical fiber and an antiresonant hollow-core optical fiber according to claim 1, wherein: The beam expansion waveguide is in an inverted cone shape, and the coupling surface between the beam expansion waveguide and the central air core of the antiresonant hollow core optical fiber is an oblique cut surface with a preset angle.

8. The method for splicing a single-mode optical fiber and an antiresonant hollow-core optical fiber according to claim 1, wherein: The length of the beam expansion waveguide ranges from 120 μm to 345 μm.

9. The method for splicing a single-mode optical fiber and an antiresonant hollow-core optical fiber according to claim 1, wherein: The method further comprises: After the single-mode fiber and the anti-resonant hollow-core fiber are connected, the fundamental mode field distributions of the single-mode fiber and the anti-resonant hollow-core fiber are calculated by the finite element method, and the fundamental mode field distributions are used as the input light fields in their respective transmission directions; The evolution of each input light field in the beam expansion waveguide is simulated by the beam propagation method, and the coupling efficiency from single-mode fiber to antiresonant hollow-core fiber and from antiresonant hollow-core fiber to single-mode fiber is obtained by overlapping integral with the fundamental mode field distribution of the target end fiber.

10. A splicing structure of a single-mode optical fiber and an anti-resonant hollow-core optical fiber, characterized in that: The splicing structure is used to implement the splicing method of a single-mode optical fiber and an antiresonant hollow-core optical fiber as described in any one of claims 1 to 9.

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