Intermediate infrared optical fiber beam combiner with multi-section conical structure and preparation method of intermediate infrared optical fiber beam combiner

Abstract

The invention discloses a mid-infrared optical fiber combiner with a multi-section conical structure and a preparation method thereof.The mid-infrared optical fiber combiner comprises an input optical fiber, a glass sleeve and an output optical fiber, the numerical aperture of the output optical fiber is larger than or equal to that of the input optical fiber, and the input optical fiber is a conical optical fiber bundle formed by combining a plurality of conical optical fibers; the conical optical fibers are arranged on the cross section of the optical fiber bundle in a symmetrical polygon mode, each conical optical fiber is of a conical structure with the diameter gradually reduced in the light path direction, the optical fiber bundle is sleeved with the glass sleeve, the output optical fiber comprises a front conical area, a non-tapering area and a rear conical area, and the input end of the front conical area is in butt joint with the output end of the optical fiber bundle. The front conical area is of a conical structure with the diameter gradually increasing in the light path direction, the non-tapering area is of a cylindrical structure with the constant diameter, and the rear conical area is of a conical structure with the diameter gradually decreasing in the light path direction. The mid-infrared optical fiber combiner is high in combining efficiency, excellent in light beam quality and high in thermal stability, and has high engineering practicability and good popularization prospects.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of fiber optics, and particularly relates to a multi-section tapered structure mid-infrared fiber combiner and a preparation method thereof. BACKGROUND

[0002] With the rapid development of mid-infrared laser technology and optical devices, high-power mid-infrared fiber lasers are gradually applied in multiple high-tech fields, such as infrared laser transmission, mid-infrared optical communication, environmental remote sensing, infrared imaging, and medical surgery, etc. Laser in the mid-infrared band (2~5 μm) has extremely important application value in optical detection, gas sensing and infrared transmission, especially in high-sensitivity gas detection and high-power optical transmission. Fiber lasers become an important choice in this field due to their superior thermal management performance and high beam quality. However, with the increasing demand for higher power and higher integration, the existing mid-infrared fiber combiner technology still faces many challenges, especially in terms of mode field matching, power transmission efficiency and device stability, etc.

[0003] At present, most of the traditional mid-infrared fiber combiners rely on single-section tapered fiber combiner structure and use simple spatial coupling method. Although these methods are simple in process, they have significant limitations in high-power applications. First, due to the mode field mismatch between fibers, the coupling efficiency is low, which leads to power loss and system efficiency decline. Second, the mode field mismatch of the fiber will cause the phenomenon of beam quality degradation at the output end of the combiner, which is a key problem in applications requiring high beam quality. In addition, the single-section tapered structure also has some shortcomings in improving the power density and its uniformity, and cannot effectively cope with the problem of heat accumulation in the process of high-power laser transmission.

[0004] With the increasing demand, a new design of mid-infrared fiber combiner is needed to improve the overall performance of the device. In order to overcome the shortcomings of the existing technology, the present application proposes a multi-section tapered structure mid-infrared fiber combiner design. SUMMARY

[0005] In view of the problems of mode field mismatch and uneven power density in the process of high-power transmission of the existing mid-infrared fiber combiner, the present application proposes a multi-section tapered structure mid-infrared fiber combiner and a preparation method thereof. By using a multi-section tapered structure design, the problems of uneven beam, increased transmission loss and heat accumulation caused by the single structure of the traditional fiber combiner are solved, thereby significantly improving the stability and power transmission efficiency of the fiber combiner.

[0006] The technical scheme adopted by the present application to solve the above technical problems is: a multi-section conical structure mid-infrared fiber combiner, comprising an input fiber, a glass sleeve and an output fiber, the numerical aperture (NA) of the output fiber is greater than or equal to the numerical aperture of the input fiber, the input fiber is a conical fiber bundle formed by bundling a plurality of conical fibers, the plurality of conical fibers are arranged in a symmetrical polygon on the cross section of the conical fiber bundle, each of the conical fibers is a conical structure with a diameter gradually decreasing along the optical path direction, the glass sleeve is sleeved outside the conical fiber bundle, and the output fiber is a taper fiber with a three-section structure, the output fiber comprises a front taper zone, an untapered zone and a rear taper zone connected in sequence, the input end of the front taper zone is butted with the output end of the conical fiber bundle, the front taper zone is a conical structure with a diameter gradually increasing along the optical path direction, the untapered zone is a cylindrical structure with a constant diameter, and the rear taper zone is a conical structure with a diameter gradually decreasing along the optical path direction.

[0007] The mid-infrared fiber combiner in the present application solves the problems of uneven light beam, increased transmission loss and heat accumulation of the traditional fiber combiner due to the single structure, thereby significantly improving the stability and power transmission efficiency of the fiber combiner. Specifically, the present application adopts a conical fiber bundle formed by bundling a plurality of conical fibers as the input fiber, and the output fiber adopts a three-section structure with a gradually expanding diameter of the front taper zone, a constant diameter of the untapered zone and a gradually decreasing diameter of the rear taper zone. Among them, the output fiber adopts the conical structure with a gradually expanding diameter of the front taper zone, which can optimize the mode transition of the light beam, reduce the unevenness of the light beam at the butt joint between the front taper zone and the output end of the conical fiber bundle, reduce the divergence angle and improve the light beam coupling efficiency; and the output fiber adopts the conical structure with a gradually decreasing diameter of the rear taper zone, so that the power density of the light beam gradually increases in the rear taper zone, thereby enhancing the focusing property of the light beam and improving the light beam quality. Although the power density of the rear taper zone of the output fiber increases, the overall power density distribution of the fiber combiner is relatively uniform, which can still avoid local heat accumulation and improve the heat management performance of the fiber combiner, thereby further improving the stability and durability of the fiber combiner.

[0008] Preferably, each of the conical fibers is a single-clad soft glass fiber, and the initial fiber of each of the conical fibers before tapering has a core diameter of 28-32 μm and a cladding diameter of 120-130 μm; the output fiber is a single-clad soft glass fiber, the taper zone length of the output fiber is 18-22 mm, and the initial fiber of the output fiber before tapering has a core diameter of 110-120 μm and a cladding diameter of 390-410 μm.

[0009] Preferably, the glass sleeve has an inner diameter of 290-310 μm and an outer diameter of 510-530 μm, and the material composition of the glass sleeve is the same as that of the cladding of each of the conical fibers.

[0010] Preferably, the waist region core diameter of the front taper region is 100-110 μm, and the cladding diameter is 370-380 μm; the waist region core diameter of the rear taper region is 70-80 μm, and the cladding diameter is 250-270 μm; the waist region diameter of the taper fiber bundle is 320-340 μm.

[0011] A method for preparing the above-mentioned mid-infrared fiber combiner with a multi-section taper structure, comprising the following steps: S1. Using a plurality of soft glass fibers as initial fibers of the plurality of taper fibers, and inserting the plurality of soft glass fibers into a glass sleeve in a symmetrical polygon arrangement to form an initial fiber bundle; S2. Melting and tapering the initial fiber bundle to form the taper fiber bundle; S3. Cutting and polishing the waist region end face of the taper fiber bundle; S4. Using a soft glass fiber as an initial fiber of the output fiber, and using the middle part of the soft glass fiber as an untapered region, melting and tapering both ends of the untapered region to form a front taper region and a rear taper region at both ends of the untapered region, respectively, and then cutting and polishing the waist region end face of the front taper region and the rear taper region, respectively, to obtain the output fiber; S5. Butting the input end of the front taper region of the output fiber with the output end of the taper fiber bundle through ultraviolet curing glue.

[0012] Preferably, in step S2, the melting and tapering to form the taper fiber bundle is performed in a protective gas atmosphere, the melting and tapering uses a graphite fire head for heating, the tapering power is 20-25 W, and the length of the taper region obtained after the melting and tapering is 15-25 mm, and the length of the waist region is 10-20 mm.

[0013] Preferably, in step S4, the melting and tapering to form the front taper region is performed in a protective gas atmosphere, the melting and tapering uses a graphite fire head for heating, the tapering power is 18-24 W, and the parameters of the fiber obtained after the melting and tapering are as follows: the waist region core diameter is 100-110 μm, the cladding diameter is 370-380 μm, the length of the taper region is 10-20 mm, and the length of the waist region is 5-10 mm; the melting and tapering to form the rear taper region is performed in a protective gas atmosphere, the melting and tapering uses a graphite fire head for heating, the tapering power is 20-28 W, and the parameters of the fiber obtained after the melting and tapering are as follows: the waist region core diameter is 70-80 μm, the cladding diameter is 250-270 μm, the length of the taper region is 15-30 mm, and the length of the waist region is 5-10 mm.

[0014] As preferred, the protective gas is argon with purity of 5N or above, the oxygen content in the protective gas is less than or equal to 0.5 ppm, and the water content in the protective gas is less than or equal to 1 ppm.

[0015] As preferred, in steps S2 and S4, the fusion tapering speed is 0.4-0.8 mm / s, and the flow rate of the protective gas is 400-500 mL / min.

[0016] As preferred, the soft glass optical fiber in steps S1 and S4 is a tellurite glass optical fiber, a fluoride glass optical fiber or a chalcogenide glass optical fiber.

[0017] Compared with the prior art, the present application has the following advantages: the infrared fiber combiner in the present application adopts a multi-section tapered structure design, optimizes the mode transition of the light beam, significantly improves the coupling efficiency and light beam quality of the fiber combiner, and further improves the focusing and uniformity of the output light beam by reducing the high-order modes generated in the high-power laser transmission process. In addition, the overall power density distribution of the infrared fiber combiner in the present application is relatively uniform, which can effectively avoid local heat accumulation, improve the thermal management performance of the fiber combiner, and further improve the stability and durability of the fiber combiner, thereby facilitating the improvement of the adaptability and output quality of the mid-infrared high-power laser system. The infrared fiber combiner in the present application realizes efficient laser transmission in the mid-infrared waveband, has the characteristics of high synthesis efficiency, excellent light beam quality and strong thermal stability, has strong engineering practicability and good popularization prospect, and can meet the demand of the mid-infrared laser system for high-power and high-integration output devices. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 FIG. 1 is a schematic diagram of the overall structure of the multi-section tapered structure of the mid-infrared fiber combiner of Example 1; Figure 2 FIG. 2 is a schematic diagram of the effect of inserting three tellurite optical fibers in a triangular arrangement into a glass sleeve in Example 1; Figure 3 FIG. 3 is a cross-sectional view of a single tellurite optical fiber before fusion tapering in Example 1; Figure 4 FIG. 4 is a cross-sectional view of a glass sleeve before fusion tapering in Example 1; Figure 5 FIG. 5 is an end face view of the waist region of the tapered fiber bundle prepared in Example 1; Figure 6 FIG. 6 is a simulation diagram of the light field distribution of the front tapered region cross-section of the output optical fiber of the multi-section tapered structure of the mid-infrared fiber combiner of Example 1; Figure 7 FIG. 7 is a simulation diagram of the light field distribution of the non-tapered region cross-section of the output optical fiber of the multi-section tapered structure of the mid-infrared fiber combiner of Example 1; Figure 8The simulation diagram of the light field distribution of the rear taper section cross section of the output fiber of the multi-taper structure mid-infrared fiber combiner of embodiment 1; Figure 9 The simulation curve of the relative maximum light intensity density at different end faces of the multi-taper structure mid-infrared fiber combiner of embodiment 1. DETAILED DESCRIPTION

[0019] In order to make the technical personnel in the art more clearly understand the technical solutions of the present application, the following will combine the preferred embodiments of the present application and the drawings to clearly and completely describe the mid-infrared fiber combiner and the preparation method thereof. It should be understood that these embodiments are only used to better illustrate the technical content of the present application, and should not be regarded as a limitation on the protection scope of the present application. Any equivalent replacement, modification or improvement made to the present application without departing from the spirit and essence of the present application shall fall within the protection scope of the present application.

[0020] It should be noted that although tellurite optical fibers are used in embodiment 1, the multi-taper structure design and preparation method of the present application is also applicable to other types of soft glass optical fibers, such as fluoride optical fibers and chalcogenide optical fibers, etc. The equipment, components or structures not specified in the present application use conventional technical means in the art.

[0021] The protective gas used in the following embodiment 1 is argon with a purity of ≥5N, the oxygen content in the protective gas is ≤0.5 ppm, and the water content is ≤1 ppm.

[0022] The multi-taper structure mid-infrared fiber combiner of embodiment 1, as shown in Figure 1 The mid-infrared fiber combiner includes an input optical fiber 1, a glass sleeve 2 and an output optical fiber 3, the numerical aperture of the output optical fiber 3 is greater than or equal to that of the input optical fiber 1, the input optical fiber 1 is a tapered fiber bundle formed by bundling 3 tapered optical fibers 11, the 3 tapered optical fibers 11 are arranged in a regular triangle on the cross section of the tapered fiber bundle, each tapered optical fiber 11 is a tapered structure with a diameter gradually decreasing along the optical path direction, the glass sleeve 2 is sleeved outside the tapered fiber bundle, and the output optical fiber 3 is a tapered fiber with a three-section structure, the output optical fiber 3 includes a front taper section 31, an untapered section 32 and a rear taper section 33 connected in sequence, the input end of the front taper section 31 is butted with the output end of the tapered fiber bundle, the front taper section 31 is a tapered structure with a diameter gradually increasing along the optical path direction, the untapered section 32 is a cylindrical structure with a constant diameter, and the rear taper section 33 is a tapered structure with a diameter gradually decreasing along the optical path direction.

[0023] The preparation method of the multi-taper structure mid-infrared fiber combiner of embodiment 1 includes the following steps: S1. Use three single-clad tellurite fibers with a core diameter of 30 μm, a cladding diameter of 125 μm, and a length of 30 cm as the starting fibers for the three tapered fibers. Insert the three tellurite fibers into a glass sleeve made of tellurite glass in an equilateral triangle arrangement, as shown in the following example: Figure 2 As shown in FIG, the inner diameter of the glass sleeve is 300 μm and the outer diameter is 520 μm, ensuring that the three tellurite optical fibers are stably arranged to form an initial optical fiber bundle with a diameter of 520 μm. All tellurite optical fibers and the glass sleeve surface are wiped with dust-free paper soaked in anhydrous alcohol to ensure that there is no dust or contaminants. The cross-sections of a single tellurite optical fiber and the glass sleeve before tapering are shown in FIG. Figure 3 and Figure 4 As shown; S2. Place two U-shaped fiber optic clamps with a clamping size of 550 μm in the clamp slots of the displacement stage. Place the initial fiber bundle in the clamps and clamp them. Start the fiber taper machine's tapering program, which alternates left and right tapers in the same direction. Melt-taper the initial fiber bundle in a protective gas atmosphere to form a tapered fiber bundle. The melt taper is heated using a graphite torch, with a taper power of 22-25 W and a taper speed of 0.7 mm / s. The protective gas flow rate is 400-500 mL / min. After melt tapering, a tapered fiber bundle with a waist diameter of 330 μm, a taper length of 20 mm, and a waist length of 10 mm is obtained. After melt tapering, measure the diameter curve of the tapered fiber bundle to ensure that the taper portion is linear and the actual waist diameter meets the requirements. S3. Cut and polish the waist end face of the tapered fiber bundle to ensure that the fiber end face is smooth. The waist end face of the tapered fiber bundle after cutting should be as follows: Figure 5 As shown; S4. Two U-shaped fiber clamps with a clamping size of 500 μm are placed in the clamp slots of the displacement platform. A single-clad tellurite fiber with a core diameter of 120 μm and a cladding diameter of 400 μm is used as the initial fiber for the output fiber. The middle portion of the soft glass fiber is used as the untapered region. The initial fiber is placed in the clamp and clamped. The fiber taper machine's tapering program, alternating left and right single-sided tapering, is started. In a protective gas atmosphere, both ends of the untapered region are melt-tapered to form a front taper region and a back taper region, respectively, at each end of the untapered region. The transmission characteristics of the beam are improved through step-by-step mode field transition and power density optimization. After tapering, the waist end faces of the front taper region and the back taper region are cut and polished to ensure smooth fiber end faces, thereby obtaining the output fiber. The fused taper adopts a graphite fire head to heat, the fused taper parameters of the front taper zone are: the fused taper power is 22-23 W, the fused taper speed is 0.7 mm / s, the flow of the protective gas is 400-500 mL / min, after the fused taper, the front taper zone with a waist zone core diameter of 110 μm, a cladding diameter of 370 μm, a taper zone length of 20 mm and a waist zone length of 5 mm is obtained, after the fused taper, the diameter curve of the front taper zone is measured to ensure that the taper zone part is linear and the actual diameter of the waist zone meets the requirements; the fused taper parameters of the rear taper zone are: the fused taper power is 22-24 W, the fused taper speed is 0.7 mm / s, the flow of the protective gas is 400-500 mL / min, after the fused taper, the rear taper zone with a waist zone core diameter of 80 μm, a cladding diameter of 270 μm, a taper zone length of 20 mm and a waist zone length of 5 mm is obtained, after the fused taper, the diameter curve of the rear taper zone is measured to ensure that the taper zone part is linear and the actual diameter of the waist zone meets the requirements; S5. The tapered fiber bundle and the output fiber are placed in the fiber clamp on the microscopic platform, the output end of the tapered fiber bundle and the front taper zone of the output fiber are precisely butt-jointed by adjusting the clamp, the stability and low loss of the fiber connection are ensured by curing treatment through ultraviolet curing glue, after butt-jointing, the multi-section tapered structure mid-infrared fiber combiner is obtained, and the overall structure is as shown in Figure 1 .

[0024] The multi-section tapered structure mid-infrared fiber combiner of embodiment 1 is subjected to overall performance test. The test result shows that there is no crosstalk between each tapered fiber of the input fiber, and there is also no crosstalk influence on the combination of different waveband lasers, and the overall transmission efficiency of 85% is realized at 2 μm wavelength. In addition, the comprehensive simulation test is carried out on the light field distribution in the working spectrum (2~5 μm) range, the simulation diagram of the output fiber light field distribution of the combiner is as shown in Figures 6-8 , and the simulation curve diagram of the relative maximum light intensity density is as shown in Figure 9 , which verifies that it meets the design requirements.

[0025] As shown in Figures 6-8 , the abscissa X and the ordinate Y represent the spatial coordinates on the fiber cross section, and the right color bar represents the relative intensity distribution of the light field (normalized processing, the intensity shown is a relative value).

[0026] As shown in Figures 6-8The light field distribution simulation diagram of the optical fiber combiner shows that the taper ratio of the optical fiber bundle of the optical fiber combiner is set to 1.6, the taper ratio of the front taper of the output optical fiber is 1.1, the taper ratio of the rear taper of the output optical fiber is 1.5, the core diameter and the cladding diameter of the three tapered optical fibers of the input optical fiber before tapering are 30 μm and 125 μm respectively. The core region diameter of the three-core optical fiber obtained after tapering is about 105 μm, the core diameter of the front taper region of the butt-jointed output optical fiber is about 110 μm (slightly larger than the core diameter of the three-core optical fiber), and the cladding diameter is about 363 μm; the core diameter of the rear taper region is about 80 μm, and the cladding diameter is about 266 μm. The theoretical simulation result shows that under the structure of the combiner, the beam quality (BPP value) of the front taper region of the output optical fiber is about 8.08 mm·mrad, the beam quality (BPP value) of the non-tapered region of the output optical fiber is about 8.15 mm·mrad, and the beam quality (BPP value) of the rear taper region of the output optical fiber is about 6.46 mm·mrad, which meets the design requirements.

[0027] Figure 9 The relative maximum light intensity density simulation curve of the optical fiber combiner shows that the abscissa represents the position Z along the transmission direction of the optical fiber, and the ordinate represents the normalized maximum light intensity density I, wherein the maximum light intensity density of the input laser is 1; L1 is the maximum light intensity density under different lengths of the input optical fiber, L2 is the front taper region of the output optical fiber, L3 is the non-tapered region of the output optical fiber, and L4 is the rear taper region of the output optical fiber. It can be known from Figure 9 that the light intensity density fluctuation of the front taper region of the output optical fiber is reduced, the transmission stability is improved; the light intensity density fluctuation of the non-tapered region of the output optical fiber is large; the light intensity density of the rear taper region of the output optical fiber is significantly improved, the power density is enhanced, and the design requirements are met.

Claims

1. A mid-infrared fiber combiner with a multi-segment tapered structure, characterized in that: It includes an input optical fiber, a glass sleeve and an output optical fiber, the numerical aperture of the output optical fiber is greater than or equal to the numerical aperture of the input optical fiber, the input optical fiber is a tapered optical fiber bundle formed by bundling multiple tapered optical fibers, the multiple tapered optical fibers are arranged in a symmetrical polygon on the cross section of the tapered optical fiber bundle, each of the tapered optical fibers is a tapered structure with a diameter gradually decreasing along the optical path, the glass sleeve is sleeved on the outside of the tapered optical fiber bundle, the output optical fiber is a tapered optical fiber with a three-section structure, the output optical fiber includes a front tapered region, an untapered region and a rear tapered region connected in sequence, the input end of the front tapered region is connected to the output end of the tapered optical fiber bundle, the front tapered region is a tapered structure with a diameter gradually increasing along the optical path, the untapered region is a cylindrical structure with a constant diameter, and the rear tapered region is a tapered structure with a diameter gradually decreasing along the optical path.

2. The mid-infrared fiber combiner with a multi-segment tapered structure according to claim 1, characterized in that: Each of the tapered optical fibers is a single-clad soft glass optical fiber, and the core diameter of each of the tapered optical fibers before being tapered is 28-32 μm, and the cladding diameter is 120-130 μm; the output optical fiber is a single-clad soft glass optical fiber, the tapered region length of the output optical fiber is 18-22 mm, and the core diameter of the initial optical fiber before being tapered is 110-120 μm, and the cladding diameter is 390-410 μm.

3. The mid-infrared fiber combiner with a multi-segment tapered structure according to claim 2, characterized in that: The inner diameter of the glass sleeve is 290-310 μm and the outer diameter is 510-530 μm. The material composition of the glass sleeve is the same as the material composition of the cladding of each tapered optical fiber.

4. The mid-infrared fiber combiner with a multi-segment tapered structure according to claim 2, characterized in that: The waist core diameter of the front cone region is 100-110 μm, and the cladding diameter is 370-380 μm; the waist core diameter of the rear cone region is 70-80 μm, and the cladding diameter is 250-270 μm; the waist diameter of the tapered optical fiber bundle is 320-340 μm.

5. A method for preparing a mid-infrared fiber combiner with a multi-segment tapered structure according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. A plurality of soft glass optical fibers as the initial optical fiber of the plurality of tapered optical fibers are inserted into the glass sleeve in a symmetrical polygonal arrangement to form an initial optical fiber bundle; S2 is melt-tapering the initial optical fiber bundle to form the tapered optical fiber bundle; S3 cutting and polishing the waist end face of the tapered fiber bundle; S4. Using a soft glass fiber as the starting fiber for the output optical fiber, with the middle portion of the soft glass fiber as the untapered region, melt-tapering the ends of the untapered region to form a front taper region and a back taper region at each end of the untapered region, respectively. The waist end faces of the front taper region and the back taper region are then cut and polished to obtain the output optical fiber; S5. Connecting the input end of the front cone region of the output optical fiber to the output end of the tapered optical fiber bundle using UV-curable adhesive.

6. The method for preparing the mid-infrared fiber combiner with a multi-segment tapered structure according to claim 5, characterized in that: In step S2, the fusion taper for forming the tapered optical fiber bundle is carried out in a protective gas atmosphere. The fusion taper is heated by a graphite torch with a taper power of 20-25 W. The length of the cone region obtained after the fusion taper is 15-25 mm and the length of the waist region is 10-20 mm.

7. The method for preparing the mid-infrared fiber combiner with a multi-segment tapered structure according to claim 5, characterized in that: In step S4, the melt-drawing of the front cone region is carried out in a protective gas atmosphere, the melt-drawing is heated by a graphite torch, and the taper pulling power is 18-24 W. The parameters of the optical fiber obtained after the melt-drawing are as follows: the waist core diameter is 100-110 μm, the cladding diameter is 370-380 μm, the taper region length is 10-20 mm, and the waist region length is 5-10 mm. The melt-drawing of the rear cone region is carried out in a protective gas atmosphere, the melt-drawing is heated by a graphite torch, and the taper pulling power is 20-28 W. The parameters of the optical fiber obtained after the melt-drawing are as follows: the waist core diameter is 70-80 μm, the cladding diameter is 250-270 μm, the taper region length is 15-30 mm, and the waist region length is 5-10 mm.

8. The method for preparing the mid-infrared fiber combiner with a multi-segment tapered structure according to claim 6 or 7, characterized in that: The protective gas is argon with a purity of ≥5N, and the oxygen content in the protective gas is ≤0.5 ppm and the water content is ≤1 ppm.

9. The method for preparing the mid-infrared fiber combiner with a multi-segment tapered structure according to claim 6 or 7, characterized in that: In steps S2 and S4, the taper pulling speed of the fused taper is 0.4-0.8 mm / s, and the flow rate of the shielding gas is 400-500 mL / min.

10. The method for preparing the mid-infrared fiber combiner with a multi-segment tapered structure according to claim 5, characterized in that: The soft glass optical fibers in steps S1 and S4 are respectively tellurite glass optical fibers, fluoride glass optical fibers or chalcogenide glass optical fibers.

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